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Dinuclear dinitrogen and mononuclear paramagnetic complexes of zirconium Mylvaganam, Murugesapillai 1994

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DINUCLEAR DINITROGEN AND MONONUCLEAR PARAMAGNETIC COMPLEXES OF ZIRCONIUM by MURUGESAPILLAI MYLVAGANAM B.Sc. (Hons.), University of Jaffna, Sri Lanka, 1985 M. Sc., University of British Columbia, 1989  A THESIS SUB MITfED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Chemistry)  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA June 1994 © M. Mylvaganam, 1994  In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department  or  by  his  or  her  representatives.  It  is  understood  that  copying  or  publication of this thesis for financial gain shall not be allowed without my written permission.  (Signature)  Department of  CYt  RI? S  7  The University of British Columbia Vancouver, Canada Date  DE-6 (2/88)  Ii  ABSTRACT The basic focus of this work is the use of the tridentate, mixed donor ligand, [N(SiM C P 1 2 ) R H e abbreviated as PNP, to generate zirconium compounds that contain dinitrogen ligands in unusual bonding modes, or to allow the stabilization of the very rare zirconium(III) oxidation state. The approach that is used is to combine synthetic methods in organometallic chemistry with semi-empirical molecular orbital calculations as a means of designing new complexes and to rationalize bonding. Reduction of [ZrCp 2 N(SiMe2CH2PPr2)2] Cl 2.6, or ZrCl2(OAr*)[N(SiMe2CH2 ] (Ar* ) 2 PPr  =  2 M 3 H 6 (C 2,6)) e 2.11, under a dinitrogen atmosphere gave complexes  )2N] ZrCp } 2(J.t-N2) 2.9, and ([(PPr2CH 2 S iMe2)2N] Zr(OAr*) } 2(I.t-N2) 2 { [(PPrCHS iMe 2.12, respectively. The X-ray structure determination of these complexes confirmed the presence of an end-on bridging (‘-i 1 -N clinitrogen ligand in 2.9 whereas, 2.12 has a 1 ) :2 side-on bridging : 2 (.t-fl N2) 1 dinitrogen ligand. The observed nitrogen-nitrogen bond distances in 2.9 was 1.301 (3)  A and in 2.12, it was  1.528 (7)  A.  The resonance Raman spectra of the solid and the solution state samples of 2.9 and 2.2 showed isotope sensitive peaks around 1200 and 730 cm 1 respectively, assigned to the nitrogen-nitrogen stretching of these complexes. Also, the fact that these resonance Raman features are the same in the solid and in the solution states strongly suggest that the mode of bonding of the dinitrogen ligand are same for the respective complexes. The semi-empirical molecular orbital studies performed on the end-on derivative 2.9 and on the side-on derivatives 2.2 and 2.12 show that the lu-acceptor interactions involving the  7t*orbitals of the dinitrogen ligand are significantly different. In the end-on case these interactions give rise to two it-MOs, whereas the side-on cases give rise to one ö-MO and one lu-MO where the lu-MO was found to be much lower in energy than the ö-MO. Mulliken population and Wiberg indices were calculated to show that in the side-on mode there is greater electron donation into the dinitrogen ligand than in the end-on cases and also the side-on bound  m 2 ligand has a very weak nitrogen-nitrogen bond, which is corroborated by the bond length N parameters and the resonance Raman data. An analysis of the frontier orbitals of the fragment 2 P 3 [(H N )ZrXI, )2(H where X  =  Cl, Cp or OH, shows that the metal-ligand d-p interactions  influence the mode of dinitrogen coordination, i.e., end-on vs. side-on.  The paramagnetic zirconium(ffl) complex, Zr(1 2 ) H 5 C P ] ) Cl[N(SiMe C Pr H 4.1, and the corresponding hafnium(III) derivative, ) Hf( ) H 5 C P ] 2 Cl[N(S C Pr H ri 4.1, iMe were synthesized by the reduction of the respective dichioro precursors H M(’fl ) 5 C12C [N(SiMe2-CH2PPr)2j, where M  =  Zr or Hf. The results of this study show that complex 4.1  is a viable precursor to the synthesis of a variety of derivatives such as the first stable examples of alkyl, aryl and borohydride complexes of zirconium(ffl). X-ray structure elucidation has been carried out for an alkyl 4.8, phenyl 4.4 and borohydride complex, 4.17. Spectroscopic studies (JR and ESR) indicate that in the case of the alkyl derivatives a weak agostic type interaction may be present between one of the x-hydrogens and the metal. Hydrogenolysis of certain alkyl complexes shows a clean conversion to the mononuclear zirconium(Ill) hydride complex 4.14. This hydride complex has been shown to undergo an insertion reaction with ethylene. The hydride complex also undergoes hydrogen exchange reactions with H—C(sp ) and H—C(sp 2 ) bonds, presumably by way of s-bond 3 metathesis. Complexes 4.1 and the zirconium(III) borohydride complex undergo reversible disproportionation reactions under a CO atmosphere to give zirconium(JV) and zirconium(ll) derivatives. It was also shown that 3 CH C N reacts in a similar fashion with 4.1, however the reversibility of this reaction was not established. In the case of the borohydride complex the reaction with CO proceeds further to give a complex containing a “formyl-ylid” type ligand.  iv  TABLE OF CONTENTS ABSTRACT  .  TABLE OF CONTENTS LIST  OF  .  TABLES  LIST OF FIGURES LIST OF ABBREVIATIONS  ii iv iv  xii xvii  ACKNOWLEDGEMENTS  xx  DEDICATION  xxi  Chapter 1 Introduction to Transition Metal Dinitrogen Chemistry 1.1 General  1  1.2 Biological Nitrogen Fixation  2  1.3 Other Methods of Nitrogen Fixation  4  1.4 Thermodynamic and Kinetic Factors  6  1.5 Dinitrogen Complexes  8  1.5.1 Mononuclear End-On Complexes  9  1.5.2 Dinuclear End-On complexes  10  1.5.3 Protonation of Terminally Bonded Dinitrogen Complexes  11  1.5.4 Polynuclear Dinitrogen Complexes  14  1.5.6 Mononuclear Side-On Complexes  15  1.5.7 Dinuclear Side-On Complexes  16  1.6 Summary  17  1.7 References  18  V  Chapter 2 Dinitrogen Complexes of Zirconium 2.1 General  22  2.2 Synthesis of a Dinitrogen Complex Containing PNP and Cp Ligands  24  2.2.1 Synthesis of Precursors of the Type ZrCpX2[N(SiMe2CH2PR ] ) 2  25  2.2.2 Synthesis of Precursors of the Type ZrCpX2[N(SiMe2CH2PR ] ) 2  28  2.3 Attempted Synthesis of a Dinitrogen Complex Containing PNP and Allyl ligands  33  2.4 Synthesis of a dinitrogen Complex Containing PNP and Aryl Oxide Ligands  35  ] ) 2 2.4.1 Synthesis of Zr(OAr*)C12[N(SiMe2CH2PPri  35  Zr(OAr*)Cl2 C ] ) H2PPri [N(SiMe 2.4.2 Reduction of 2  36  2.5 Synthesis of N {[(PrP S : ) 2 iMe2)2N]Zr( rI CH OBut))2(JIfl  45  2.6 Spectroscopy as a Diagnostic Tool for End-On and Side-On Dinitrogen Complexes  46  2.6.1 15 N NMR Spectroscopy  47  2.6.2 Resonance Raman Spectroscopy  51  2.7 Bonding Considerations  57  2.7.1 General  57  2.7.2 Bonding in ( 2 {[(Pr2PCH2S ) H 5 I-N2 C } iMe2)2N]Zr( ) rI  59  2.7.3 Bonding in Side-On Complexes  63  2.7.4 Bonding in ) {[(Pr2PCH2S N 2 ]ZrCl}2(.t-N iMe  64  2.7.5 Bonding in  { [(Pr2PCH2SiMe2)2N] Zr(OAr*) } (p.-N)  69  2.7.6 Factors Influencing the Side-On Mode of Coordination  77  2.7.7 Bonding in the Samarium and Lithium Dinitrogen Complexes  82  2.8 Reactions  84  2.8.1 Conversion of the Side-On Complex to the End-On Complex  84  2.8.2 Reaction of Side-On Complexes With LiBEt 4  86  2.8.3 Protonation Reactions  90  2.8.4 Reactions With Halo Alkanes  93  v 2.8.4a Reactions of the End-On Complex With BzBr and CH I 3  93  2.8.4b Reactivity With Dihaloalkanes  96  2.9 Conclusions  100  2.10 Experimental  102  2.lOa  General Procedures  102  2.lOb Synthesis of Precursors  105  2.lOb.1 3 ZrBr { N(SiMe2CH2PPr2)2], 2.4  105  2.lOb.2 ) Zr ) H 5 [ C P ] 2 N(SiM Cl C Pr H , ( e 2.6  105  2.lOb.3 Zr(11 2 ) H 5 [ C P ] ) N(SiM Br C Pr H , e 2.7  106  2lOb.4 Zr(11 2 ) H 5 [ C P 1 ) N(SiM C1 Me C H , e 2.8  106  2.lOb.5 ) Zr( ) 5 H 3 [ C P ] 2 N(SiM Cl C Pr H , ri e 2.10  106  2. lOb.6 Zr(OAr*)C12[N(SiMe2CH2PPrj2)2], 2.11  107  Zr(OBut)C1 [ N(S ) 2. lOb.7 2 2 iMe2CH2PP 2],r 2.11  108  Zr(OB [ C P 1 2 N(SiM Me H , ut)C1 e 2.13 2.lOb.8 )  108  2. lOb .9 [ )N(S 2 Zr(OCHPh C1 2 C iMe P j ) Pr , 2.16 H  108  2.lOb.10 ) Zr(NP ) [ C P ] 2 N(SiM Cl Pr H , h e 2.17  109  2.lOb.11 ) Zr(C S ) 3 [ C P j 2 N(SiM Cl iMe Pr H , H e 2.18  109  2.lOc Synthesis of Dinitrogen Complexes  110  2.lOc.1 { ) P]ZrCl [(Pr S N 2 iMe CH } 2 : 2(1.t-TI N2), T 2.2  110  2.lOc.2  110  P]ZrCl [(Pr S N ) iMe CH } 5 (p.-i : ) 2 N ri ’ , 2.2 {2  2.lOc.3 { H P [(Pr S N 2 ) 5 1 :i 2 ]Zr(11 iMe CH -N 1 ) C ) .t , 2.6 2.lOc.4  [(Pr2PCH2S N 2 ) CsH ]Zr(rI iMe {5  15 1 ) 2 , 2.6 .trI’ :r N  110 111  2.lOc.5 { ) PiMe [(Pr S N 2 CH ] Zr(OAr*) ) 2 (ji-i1 : ) r1 N , 2.12  111  ([(Pr P S N 2 ]Zr(OAr*) iMe CH i}2.lOc.6 ) ), 2.12 2 N :11 15 2 2(.t-11  113  P [(Pri S N 2 ]Zr(OBut) iMe CH } 2.lOc.7 { ) : 2 2(.L-T N2), rI 2.14  113  2.lOc.8 ) P ([(Pr S N 2 ]ZrBr iMe CH } ) (i.-rI : 2 TI N , 2.19  113  2.lOc.9 ) P ([(Pr S N 2 JZrBr} iMe CH N 5 ( : ) 2 .t-T1 1 ’ , 2.19  114  VII  2.lOc.10 ([(P P S ) C : 2 N2) 2NJ lBr(.LiMe CH 1 r 1 , 2.20. 114 2.lOc.11  2.20  114  2.lOd Reactions Involving Dinitrogen Complexes  115  2.lOd.1 {[(P P N ) : 2 ]ZrCl}2(.L-r CH2Si N2) fl Me r and NaCp.DME  115  2.lOd.2 Protonation Reactions  115  {[(P P S N ( : ) 2 j.if ]ZrX iMe CH r ri l } where X 2.lOd.3 N  =  Cl, Br or  OAr*, and LiBEt 4  2.lOd.4 2 {[(P P N ) ]ZrX}2(J.t-N CH2SiMe r 2) Where X  116 =  Cp, Cl or OAr*, and  Alkyl Halides  2.lOe Molecular Orbital Calculations 2.11 References  117 117 119  Chapter 3 Introduction to Zirconium(HI) Chemistry 3.1 General  124  3.2 Coordination Complexes of zirconium(III)  125  3.3 Organometallic Complexes of zirconium(1II)  126  3.3.1 Dinuclear organometallic complexes of zirconium(ffl)  126  3.3.2 Mononuclear organometallic complexes of zirconium(III)  129  3.4 Summary  133  3.5  133  References  Chapter 4 Zirconium(III) Complexes: Synthesis and Reactivity 41 General  136  4.2 Synthesis of Zirconium(llI) and Hafnium(llI) Complexes  136  4.3 Synthesis of Zirconium(llI) Hydrocarbyl Complexes  139  vifi 4.4 Oxidation of Zirconium(ffl) Complexes  .  4.5 Hydride Complexes of Zirconium(III)  151 153  4.5.1 General  153  4.5.3 Reactions of 2 Zr( ) H 5 C P ] ) H[N(SiMe C Pr H  161  4.5.4 Synthesis of Zirconium(ffl) Borohydride Complex  163  4.6 Disproportionation Reactions of Mononuclear Zirconium(I1T) Complexes  169  4.7 Further Reaction with CO: Formation of Zirconium Formyl Complex  177  4.8 Conclusions  185  4.9 Experimental Procedures  186  4.9a General  186  4.9b Synthesis of Complexes  187  4.9b.1 ] Zr(rI ) H 5 C P 2 Cl[N(SiMe Pr2) C H , 4.1  187  4.9b.2 ) Hf(1 ) H 5 [ C P ] 2 N(SiM Cl C Pr H , e 4.2  188  4.9b.3 Hf(11 2 . ) H 5 C P ] ) Cl[N(SiMe C Pr H , 4.3  188  4.9b.4 ) Zr(q ) [ 5 H 6 C P J 2 N(SiM C Pr H , e 4.4  188  4.9b.5 ) Zr(1 ) H 5 C P ] 2 Me[N(SiMe C Pr H , 4.5  189  4.9b.6 Zr(rt t ) H 5 [ 3 C P j ) 2 N(SiM CH C Pr H , e 4.6  189  4.9b.7 D Zr( ) H 5 C 2 CH C H2 1 PPr [N(SiMe2CH ] ) , 4.6-d  190  4.9b.8 Zr(rI  190  )[N(SiMe H 5 C H C P ] 2 ) CD Pr D H , 4.6-cLi  4.9b.9 ) 5 Zr( ) H 5 [ 3 C P 1 2 N(SiM CD Pri C D H , ri e 4.6-d  190  4.9b.1O ) Zr( ) H 5 P C P ] 2 hN(SiMe CH C Pr H , 4.7  191  4.9b.11 ) P ZrC1(CH [ C P ] 2 N(SiM Pr h) H , e 4.9  191  4.9b.12 ) Zr( ) H 5 S [ 3 C P J 2 N(SiM CH iMe C Pr H , 1 e 4.8  191  4.9b.13 ) Zr(1 ) H 5 C P ] 2 OPh[N(SiMe C Pr H , 4.10  192  4.9b.14 Zr(rj ) ) H 5 [ C P ] 2 N(SiM NPh C Pr H , e 4.11  192  4.9b.15 Zr(ri 2 ) H 5 [ C P ] ) N(SiMe PPh C Pr H , 4.12  192  4.9b.16 Zr(i 2 ) H 5 C P ] ) H[N(SiMe C Pr H , 4.14  192  ix  Cpr[N(MeSi C P ) Pr1 H dH [ZrHCp[N(S C P ) 2 Pr J H iMe { 2 4.9b.17 1 C (SiMe P ) 2 , ]}(i.t-H Pr’ H ) 4.15  193  4.9b.18 Zr(T 2 ) H 5 [ 4 C P ] N(SiM BH Pr) C H , e 4.17  194  4.9b.19 Zr(T 2 ) H 5 C (CCPh)[N(S H2PPr C iMe 2)2]  194  4.9b.20 Zr(11 2 ) H 5 P ] ) (CCPh)C1[N C Pr (SiMe2CH , 4.16  195  4.9b.21 Hf(rl 2 ) H 5 ) 4 C P ] ) [N(S C1(B C Pr H , iMe H 4.21  195  4.9c Disproportination Reactions  195  4.9c.1 -Zr( 5 CSH5)(CO)2[N(SiMe2CH r1 2PPr’2)21, 4.18  196  4.9c.2 Zr(T 2 ) H 5 [ 4 C P ] ) N(Si (BH C Pr H , Me 4.19  196  4.9c.3 Hf(TI 2 ) H 5 [ C j ) N(Si (CO H2P C , Me Pr ) 4.20  196  4.9c.4 ) Zr ) H 5 C 2 (CH3CN)[N( 21 H2P C (fl SiMe , 4.22 Pr  196  4.9c.5 ) Cp ) 4 C 3 P ) C P P 2 HO)[N (Si Zr .B Pr ] (BH r’ (SiMe H Me (’ H , ’ 4.23. 4.9d  Oxidation Reactions  197 197  4.9d.1 ) Zr ) H 5 C P ] 2 C1(SPh)[N(S C Pr H (rI iMe 4.13 ,  198  4.9d.2 Zr(T H )5 C1Et[[N(SiM C e2CH2PPr2)2]  198  4.9d.3 Zr(rI 2 ) H 5 P C1(CH C h) [N(S 2 C iMe P ] ) Pr H  198  4.9d.4 5 Zr(fl C5H5) 2 (CH2S ) 3 P 2 1 ] (SPh){N(SiM Pr iMe e2CH )  198  4.9d.5 Zr(i 5 -C (CH2CH ) H )(SPh) 2 3 PPr2) [N(SiMe2CH 1  198  4.10 Refferences  199  Chapter 5 On-Going and Future Prospects Appendix  202  210  x  List of Tables Table 2.1  Selected bond distances of complex 2.7  27  Table 2.2  Selected bond angles of complex 2.7  27  Table 2.3  Selected bond distances of complex 2.9  30  Table 2.4  Selected bond angles of the complex 2.9  31  Table 2.5  Selected bond distances of complex 2.12a  39  Table 2.6  Compilation of nitrogen-nitrogen bond lengths for some selected compounds  39  Table 2.7  Selected bond angles of complex 2.12a  41  Table 2.8  Compilation of 31 P{ ‘H} NMR chemical shifts for some zirconium precursors and the dinitrogen complexes derived from them. In all these  Table 2.9  complexes PNP corresponds to ) P 2 [N(SiMe2CH 2] Pr  46  Compilation of some 15 N chemical shifts for some selected compounds  48  Table 2.10 Compilation of some nitrogen-nitrogen bond lengths and stretching frequencies associated with them  57  Table 2.11 Some orbital parameters of le and 2e MOs of model complex A  61  Table 2.12 Bond indices and population analysis of model complex A  62  Table 2.13 Some orbital parameters oft and ö MOs of complex A  63  Table 2.14 Bond indices and population analysis of model complex F  69  Table 2.15 SCF energy values and the energies of some MOs of models H, J, K, L, MandF  71  Table 2.16 Some orbital parameters of model H  72  Table 2.17 Wiberg bond indices and Mulliken orbital populations of model H  73  Table 2.18 A comparison of the energies of the lone pair electrons of Cl, NH 2 and OH ions.  74  Table 2.19 A compilation of chemical shifts of NH protons associated with hydrazido ligands  91  Table 2.20 1 H ( P} 3 1 NMR data for complexes 2.12 and 2.12a  112  xi Table 2.21 Moles of hydrazine measured from the reaction of 2 PiMe ([(Pr S ) CH -C5H5)} 5 NJZr(r ( 2 t-r ‘:ri’-N) complex in toluene with anhydrous HC1 gas.  Expected concentration was calculated by taking into account the amount of pentane present in the complex. *  Table 2.22 Mole percent gas evolved during the reaction of 2 PiMe ([(Pr S ) CH -C5H5)) 5 N]Zr(fl ( 2 t-T 1 -N) complex with H20 and HC1 solution. * : Percent gas evolutions were calculated by taking into account the amount of pentane present in the complex. ** The data in parenthesis was obtained after 30 minutes Table 3.1  115  116  Selected zirconium-zirconium distances. (C OH8 refers to the fulvalene 1 ligand  128  Table 4.1  Elemental composition found for some hafnium(ffl) derivatives  139  Table 4.2  Micro-analytical data for the hydrocarbyl derivatives of 5 Zr(i ) H C1C  Table 4.3 Table 4.4 Table 4.5  1 C [N(SiMe ] ) 2 H2PPr  141  Selected bond lengths of complexes 2 Zr(r1 H 5 S)Ph[N(SiM C e2CH ] 4.4, and 2 ) 2 Pi Zr( ) H 5 S [ 3 ) N(SiMe2CH CH 2], iMe C 2PPr 4.8 1  143  Selected bond angles of complexes 2 Zr(fl H 5 5)Ph[N(SiM C e2CH ] 4.4, and 2 2 PPr’) Zr( ) H 5 S [ 3 P ) N(SiM CH 2], iMe C Pr e2CH rI 4.8  144  Hyperfine coupling constants (G) for the chioro and the hydrocarbyl derivatives of 2 Zr( H 5 C ) s)R[N(SiMe PPr 2]. C H 1 All the values were obtained from simulations  Table 4.6 Table 4.7  Table 4.8 Table 4.9  147  Selected bond lengths of complex 2 Zr( ) 5 BH4)[N(SiM C5H (rj T e2CH2PPr’2)21, 4.17  167  Selected bond angles of complex 2 Zr(r1 ) H 5 BH4)[N(SiM (1 C e2CH2], 4.17 ) 2 PPr  167  Selected bond lengths of complex Zr(r1 ) H 5 2 ) 4 CHO)BH (11 (1 C CH2PPr 3 (N(SiMe ) 2 (Pr’2PBH 2 [SiMe2CH ) 1), 4.23  183  Selected bond angles of complex 2 Zr( ) H 5 ) 4 CHO)BH (rj C (r CH2PPr2) 3 2 ( 2 [SiMe2CH 2 1 ) P•BH Pr J }, 4.23 { N(SiMe  183  x  List of Figures  Figure 1.1  Figure 1.2  Schematic representation of the MoFe nitrogenase and the structures of the MoFe cofactor and the P cluster.  3  (a) A proposed energy diagram for the reaction of dinitrogen and dihydrogen in gas phase (top), in biological systems (middle) and in the Haber process (bottom). Nad and Had represent these atoms adsorbed on a catalytic surface. (b) An example of a diazine ligand involved in intramolecular hydrogen bonding. 8  Figure 1.3  Figure 1.4  Dinitrogen bonding modes. M, M’ and M ’ can be different metals or t same metals with different ligand environments.  9  The proposed mechanism for the protonation of end-on bound dinitrogen in molybdenum(O) and tungsten(O) complexes by HC1 in THF. The chelating phosphine ligand in this case is 2 PCH Ph C P . Ph H The intermediates I and J are proposed for the protonation of bridging complex H. 12  Figure 1.5  Figure 2.1  Figure 2.2  The proposed cycle for the catalytic reduction of hydrazine by complex -C5Me5)WMe3(NNH2), K. 5 (fl I ORTEP view showing the complete atom labeling scheme of the complex 2 ZrCpB [ C P ] ) N(SiMe Pr H , r 2.7. II A Chem 3D® view showing the pseudo octahedral geometry at the zirconium.  13  26  I ORTEP view showing the complete atom labeling scheme of complex -C } 2(t-11’ : ‘-N2), 2.9. II A Chem ) H SiMe2)2NjZr(rI 5 2 { [(Pr2PCH 3D® view of the arrangement of atoms around the zirconium centre. U A Chem 3D® view showing the arrangement of the PNP ligand and the Zr2N2 core. 29  Figure 2.3  I ORTEP view showing the complete atom labeling scheme of complex :rI {[(Prj2PCH2SiMe2)2N1Zr(OAr*))2(i1 ) N 2 , 2.12a. II A Chem 3D® view showing the arrangement of the PNP ligand and the Zr N 2 3D® core. III A Chem view of the arrangement of atoms around the zirconium centre. 38  xiii  Figure 2.4  Figure 2.5  Variable temperature 121 MHz 31 P{ ‘HI NMR spectra of 2.12a recorded in C . 8 D 7 (right) 31 P{ 1 H} NMR spectrum of the sample obtained from the reaction described in Scheme 2.8. (left) 15 N NMR spectrum of the same sample (1:1 ratio of THF:C ). 8 D 7  Figure 2.6  Figure 2.7  43  The resonance Raman spectra of complex 2.9 recorded at approximately 90 K. A and B correspond to the (.i) and (j.L-’ 2 N 14 N2) complexes 5 respectively. The top two traces were recorded in the solid state and the bottom two were recorded in the solution (THF) state. Each trace is a sum of 5 scans, each recorded at 2 cm/s using 40 mW of 514. 5 nm laser 1 excitation (Appendix A.1).  50  52  The resonance Raman spectra of complex 2.2 recorded at approximately 90 K. A and B correspond to the (.t-’ N2) complexes 15 N2) and (j.L4 respectively. The top two traces were recorded in the solid state (sum of 9 scans) and the bottom two were recorded in the solution (THF) state (sum of 5 scans). Each scan was recorded at 1 cm /s using 20 mW of 647.1 1 nm laser excitation (Appendix A.1).  Figure 2.8  Figure 2.9  Depiction of the in-plane normal vibrational modes of the side-on peroxide bridged copper dimer. 68 Broken lines increase in length as solid lines decrease in length. Bonds which do not change in length during a given vibration are not shown. Thicker lines indicate the dominant motion in the two Ag modes. 68 The Bi deformation mode is not shown.  54  The solid state resonance Raman spectra of 2.2, (A) and 2.19, (C) and of the sample (B) obtained from the reaction shown in Scheme 2.6. All of the samples contain a 2 ) ligand. Spectral conditions are 2 N :1 15 (L-rI similar to Figure 2.8.  56  Figure 2.10 Qualitative bonding description for mononuclear complexes (top) and end on bridging dinuclear complexes (bottom).  58  Figure 2.11 Bonding scheme for the model A.  60  Figure 2.12 Bonding scheme (in the box) describes the edge-on bridging dinitrogen complexes of Co and Ni.  64  xiv  Figure 2.13  Bonding scheme illustrating the types of overlap leading to the formation of the it-MO and the 6-MO.  66  • Figure 2.14 Plot showing the change of energy in the model complex F with the rotation of the dinitrogen ligand.  67  Figure 2.15  Splitting of the it-MO in complex H.  72  Figure 2.16 The angular overlap for the side-on bonded dinitrogen with a bent Zr N 2 core.  75  Figure 2.17 The orbital interactions for a bent Zr N core of complex 2.12 where the 2 bend angles are greater than 1500.  76  Figure 2.18 The change in SCF energy with respect to the bending of the Zr N core 2 of model M. The core was bent along the nitrogen-nitrogen axis.  77  Figure 2.19 Bonding scheme illustrating the symmetry based orbital requirements for the dinitrogen binding in bridging side-on and end-on modes involving 4 fragments. ML  78  Figure 2.20 Important it-type interactions that determine the type of dinitrogen bonding in model complexes F and H.  80  Figure 2.21 The frontier orbitals of the fragments G and N arranged in increasing order of their energy.  81  Figure 2.22 I The parent ion peaks of the ‘ N2 analogue of 2.9. II Parent ion peaks 5 of 2.9 formed from the reaction of 15 N2 analogue of 2.2 with NaCp’DME under an atmosphere of 14 . 2 N Figure 2.23 The 500 MHz 31 Hf NMR; B 121.4 MHz 31 1 P} H) NMR; C 30.406 1 P{ MHz 15 N NMR and 96.2 MHz 11 B{1 H} NMR spectra of the crude reaction mixture obtained from the reaction of 2.2 and LiBEt 4 in C . 8 D 7 Figure 2.24  A Variable temperature 1 H NMR spectra (300 MHz) of complex 2.26 recorded in C P{ 1 H) NMR (121 MHz) spectra of D8. B and C are 31 7 2.26 and of the crude reaction mixture obtained from the reaction of 2.9 and PhCH Br. 2  85  88  94  xv  Figure 2.25 The models used to generate the intermediate structures for the bending P, and rotation 0, of side-on bound dinitrogen complexes. The phantom atom “A” is placed in the middle of the N—N bond. The line X—Y in model P refers to the axis of the hinge about which the Zr N2 plane was 2 bent. 118 Figure 4.1  An overlapping room temperature ESR spectra of a solution (toluene) sample of 2 HfCpCl[N(S C P ] ) Pr H iMe 4.3, and 2 ZrCpC1[N(SiMe P 2 CH ) 2], Pr 4.1.  Figure 4.2  138  I and III are ORTEP views showing the complete atom labeling scheme for complexes 2 ZrCpPh[N(S C ] ) 2 H2PPr iMe 4.4, and ZrCp(CH SiM ) 3 C P ] 2 ) [N(SiM Pr H e e 4.8, respectively. II and IV are Chem 3D® views showing the arrangements of ligands around the zirconium in complexes ZrCpPh [N(SiMe2CH PPr2)2] 4.4, and 3 2 ZrCp(CH2Si ) Me CH2PPr2) 4.8, respectively. [N(SiMe ] 2 142  Figure 4.3  The ESR spectra of the ailcyl complexes A 4.6, B 4.6-d , C 4.5 and D 1 4.8. For each case the observed spectrum is shown on the top and the simulated spectrum is shown below.  146  Figure 4.4  The solution infrared spectra of complexes 4.6, 4.6-d 1 and 4.6-d . 5  149  Figure 4.5  The room temperature solution (toluene) ESR spectrum of the phosphide ZrCpPPh[N( P Pri)j, SiMeCH 4.12. complex 2  151  Figure 4.6  The X-band room temperature solution (toluene) ESR spectrum of, (A) Zr( 5 ) H H[N(S C2 iMe2CH2PP ) -C5H ) D [N 2]r 4.14, and(B) Zr(1 5 . 1 2 (SiMe2CH2P j , Pr2) 4.14-d  Figure 4.7  156  A 500 MHz 31 H{ NMR spectrum of 4.15 showing the resonances 1 P} associated with the PNP ligand. B 500 MHz 1 H NMR spectrum of 4.15 showing the resonances associated with the Cp ligand. C 500 MHz 31 H 1 P} { NMR spectrum of the deuteride analogue 4.15-do showing the resonances associated with the SiMe2 groups. D 76.77 MHz 2 H NMR spectrum of 4.15-dn showing the resonances associated with the PNP ligand. E 121.4 MHz 31 P{ 1 H} NMR spectrum of 4.15. 158  xvi  Figure 4.8  Figure 4.9  (A) Solution (toluene) ESR spectrum of 4.17 recorded in at room temperature. (B) The simulated spectrum of 4.17. I ORTEP view showing the complete atom labeling scheme of complex ZrCp(BH4)[N(SiMe2CH2PPr2)2], 4.17. II A Chem 3D® view showing the arrangement of the PNP and borohydride ligand around the zirconium center.  Figure 4.10 The Chem 3D® view of the equatorial planes of complexes 4.4, 4.8 and 4.17. All numerical values given correspond to the nearest bond angle. The Chem Draw® drawing inside the box is the proposed structure for the alkyl complexes in solution. Figure 4.11  164  166  168  (top) H 1 (300 MHz, C Dg) spectrum of the diamagnetic species obtained 7 from the reaction of 4.17 and CO. (bottom) 1 H NMR (300 MHz, C ) 8 D 7 spectrum of the diamagnetic species obtained from the reaction of 4.1 and CO.  170  Figure 4.12 UV-Vis spectroscopic monitoring of the reaction of 4.17 (top right) and 4.1 (bottom right) with CO (1 atmosphere). (left) Infrared spectrum (solution in toluene) of the reaction of 4.17 with CO. Figure 4.13 A, B Low temperature 1 H (300 MHz) and 31 H} (121 MHz) NMR 1 P{ spectra (C ) of the diamagnetic species obtained from the reaction of 8 D 7 4.1 and CH CN. 3  171  174  Figure 4.14 A H 1 NMR (300 MHz) spectrum of 4.23. B, C 1 H (300 MHz) and gated decoupled 13 C (75.4 MHz) resonances associated with the formyl ligand of 4.23 labelled with ‘ C. U H{ 11 3 B} NMR (500 MHz) spectrum showing the BH 3 unit and E 11 H} NMR (96.2 MHz) B(1 spectrun of 4.23 (C D8). 7 180 Figure 4.15 I ORTEP view showing the complete atom labeling scheme of complex Zr(T H 5 C 2 BH4)( HO) 5)(fl C T{2 PPr2)[SiMe N(SiMe2CH C H2P.BH 2 (Pri ) 3 }, 4.23. II and III are Chem 3D® views of complex 4.23.  182  xvii  LIST OF ABBREVIATIONS The following abbreviations, most of which are commonly found in the literature, are used in this thesis.  A  m) 10 angstrom(10  Anal.  analysis  atm  atmosphere  avg  average  hr  broad  Bu  n-butyl group, 3 -CH C 2 H  Bu  iso-butyl group, 3 CH(CH -CH 2 )  ButO  tertiary butoxy group, -OC(CH ) 3  11 H 1 B{ }  observe boron while decoupling proton degrees Celsius  C{ 1 13 H}  observe carbon while decoupling proton  Calcd  calculated  Chem 3D®  molecular modelling program for the Macintosch  1 cm  wave number  Cp  cyclopentadienyl group, [C ] H 5  Cp*  pentamethylcyclopentadienyl group, ) 3 ( (C 5 CH }  -  Cp’  substituted Cp ligand, e.g., 5 [C M 4 H e]  x.y-d  Complex x.y has n number of 1 H atoms replaced by 2 H atoms  d  doublet  d sept  doublet of septets  d of d  doublet of doublets  deg (or 0)  degrees  xviii  A  heat  G  gauss  AG  free energy of activation  AH°  enthalpy of reaction  El  electron ionization  equiv  equivalent(s)  ESR  electron spin resonance  eV  electron Volt  H{ 1 1 B}  observe proton while decoupling boron  31 H 1 P} {  observe proton while decoupling phosphorus deuterium  rn-Ph  rneta-hydrogen or rneta-carbon  o-Ph  ortho-hydrogen or ortho-carbon  p-Ph  para-hydrogen orpara-carbon  h  Planck’s constant (or hour)  HOMO  highest occupied molecular orbital  Hz  Hertz, seconds1  INDO  intermediate neglect differential overlap  JR  infrared  JA—B  n-bond scalar coupling constant between A and B nuclei  K  Kelvin  kcal  kilocalories  Keq  equilibrium constant  LUMO  lowest occupied molecular orbital  M  central metal atom (or “molar”, when refening to concentration)  m  multiplet (or “medium”, for infrared data)  M+  parent ion  xix  MS  mass spectrometry  Me  methyl group, -CH 3  mg  milligram(s)  MHz  megaHertz  mL  millilitre  mm  millimetre  mmol  millimole(s)  MO  molecular orbital  mol  mole  NMR  nuclear magnetic resonance  ORTEP  Oakridge Thermal Ellipsoid Plotting Program  OTf  triflate group, 3 CF 2 -OSO  P{ 1 31 H}  observe phosphorus while decoupling proton  Ph  phenyl group, -C 5 H 6  ppm  parts per million  Pr  isopropyl group, -CH(CH 2 ) 3  ppm  parts per million  RT  room temperature  s  singlet (or “strong”, for infrared data)  sept  septet  T  temperature  t  triplet  THF  tetrahydrofuran  TMS  tetramethylsilane  THT  tetrahydrothiophine  TMS  tetramethylsilane  VT  variable temperature  xx  ACKNOWLEDGMENTS I would like to thank my supervisor, Professor Mike Fryzuk, for sharing his inspired mind and for his meticulous guidance and patience (i.e., whenever I failed to make him famous) throughout this project. I enjoyed working with past and present members of Fryzuk’s team; Dave, Guy, Patric, Lisa, Pauline, Tim, D. Berg, Kiran, Cam, Neil, Chas, Randy, Jesse, Craig, Cindy, Brian, Bobbi, Warren, Graham, Jonker, Danny, Garth, Laleh, Martin, Paul and Gao; I am thankful to all of them. I extend my thanks to Professor Zaworotko, Department of Chemistry, St. Mary’s University, for solving the zirconium(III) structures which were vital to this thesis; also, Dr. Steve Rettig for solving the dinitrogen structures. I greatly appreciate Mr. Jonathan Cohen and Professor Tom Loehr, Department of Chemistry, Oregon Graduate Institute of Science and Technology, for their contribution towards the resonance Raman studies. Dr. Peter Wassell is greatly appreciated for allowing (tolerating) me to use the JR and UV-Vis spectrometers; also, it is a pleasure working with Peter. Many thanks go to Richard Schutte, Ken MacFarlane, Veranja Karunaratne, Danny Leznoff, Garth Giesbrecht and Guy Clentsmith, for proof reading my thesis, hopefully I will spell planer correctly in future. I would also like to acknowledge the assistance provided by the support staff of the chemistry department. I greatly appreciate Yoga’s family for their support during the course of my writing; if not for their help I would have been writing Chapter 2 forever. I still admire and appreciate the professors and other support staff from the University of Jaffna for providing an excellent curriculum amidst the turbulent atmosphere.  xxi  TO MY PARENTS with love and respect  Chapter 1 Introduction to Transition Metal Dinitrogen Chemistry Li General In the primitive atmosphere of the earth, the gaseous ammonia and dinitrogen molecules played a crucial role in the formation of more complex nitrogen containing derivatives, such as amino acids and other nitrogen-containing bases.’3 Formation of such biomonomers led to the chemical evolution of complex polymers such as proteins and nucleic acids, which eventually led to the origin of life on our planet. 4 After a few billion years of complex evolution, all living organisms rely on these essential building blocks for their survival.  Presently, mankind  consumes an enormous amount of nitrogen-containing fertilizers, which indirectly supplies their nutritional needs. In this respect, the synthesis of ammonia from dinitrogen and dihydrogen, the Haber process, could be ranked as one of the most important discoveries. This event led to the cheaper manufacture of fertilizers and thereby has helped to sustain the population explosion of this century and to some extent social and political stability. Towards the end of nineteenth century, there was serious concern that the world’s nitrate reserves would be exhausted due to the increased consumption by the explosives industry. This issue was certainly appreciated by the scientific community of the time. In 1898 William Crookes, in his presidential address to the British association for the advancement of science, said, “it is through the laboratory that starvation may ultimately be turned into plenty”, and added that, “the fixation of atmospheric nitrogen is one of the great discoveries awaiting the ingenuity of chemists”. 5 Rayleigh and Crookes developed a method to fix atmospheric dinitrogen by electric discharge of hot air to give nitrous and nitric acids. This so-called arc process consumed such an enormous amount of energy that it was only feasible in countries where cheap hydroelectric power was available. In 1895 Frank and Caro discovered that the reaction of calcium carbide, CaC2, with atmospheric nitrogen at very high temperatures gave calcium cyanamide CaCN2.  references on page 18  Chapterl  2  This led to the development of cyanamide process in which the cyanamide produced was then hydrolyzed to give ammonia. 6 In 1905 Fritz Haber 7 studied the equilibrium reaction of dinitrogen with dihydrogen over an iron catalyst, and determined the thermodynamic data associated with this reaction. Although his findings were disputed by Nernst, Haber within a few years not only confirmed his experimental data but also developed a reactor which utilized the heat evolved during the exothermic reaction to heat the reaction gas. 8 This convincing demonstration attracted the interest of the mighty, ambitious BASF company. An engineer from BASF, Carl Bosch, developed the high pressure technology, leading to the opening of a commercial plant in 1911.6 At present, most Haber processes operate at pressures between 100 and 350 bar and at temperatures around 530 °C using a 0 2 3 Fe-A120 K catalyst. Dihydrogen used in the process is obtained by steam reforming or by partial oxidation of hydrocarbons and dinitrogen from air. 6  1.2 Biological Nitrogen Fixation Photosynthesis and nitrogen fixation are the two basic life processes that enable the survival of the plant and animal kingdoms. Unlike photosynthesis, nitrogen fixation is only carried out by some primitive prokaryotic micro-organisms. Bortels, in 1930, discovered that the trace element molybdenum is essential for dinitrogen metabolism. 9 It is now known that nitrogen fixation is carried out by enzymes known as nitrogenases which contain different combinations of transition metal elements: Fe-Mo, Fe-V and Fe-Fe.’ 0 The enzymatic reduction of one mole of dinitrogen requires the break-down of 16 MgATPs, equivalent to the loss of 488kJ, and suggests that the process is energy intensive (equation 1.1).” 2 N  +  8H  +  8e  +  16 MgATP 2 ase N  1.1  -  2 NH 3  +  2 H  +  16 MgADP  +  3 4 16 P0  -  The nitrogenase enzyme consists of two proteins, the Fe protein and the MoFe protein. The Fe protein is a dimer of two identical subunits bridged by a Fe S cluster which has a 4 references on page  Chapter I  3  cubane type geometry with alike atoms occupying the opposite corners of the cube. The MoFe protein has four subunits and contains two MoFe cofactors and two P clusters as illustrated in Figure 1.1.12,13 The Fe protein pumps the electrons into the cofactor consuming two moles of MgATP per electron. The reduction of the nitrogen proceeds in the cofactor. For a long time molybdenum was thought to be directly involved in the binding and the reduction of dinitrogen. On the basis of spectroscopic and modeling studies many structural models have been proposed for the cofactor. 14-16 Recently Rees et al. unveiled a crystallographic structure of MoFe protein from Azotobacter vinelandil at 2.7  A resolution.  The structure of the cofactor consists of two  cuboidal units bridged by two sulfur atoms and another unidentified atom “Y”.’ 749  The  coordination geometry around the iron atoms is approximately trigonal planar. The location and the coordinative saturation of molybdenum seems to diminish the role played by molybdenum in the cofactor. Low-Potential reductant e  / 2NH 2 6H+N 3  }  [e]  i  MgATP NMgADP÷Pi 2H  Fe Protein  H  MoFe Protein  -  -  /FeFe2S\  /  Cys S—Fe  “I.. S Fe  .X  Fq 5—  / \Mo—O  FLS/  MoFe cofactors  S Cys  N His  P clusters  Cys  Figure 1.1 Schematic representation of the MoFe nitrogenase and the structures of the MoFe cofactor and the P cluster. references on page .i  Chapter I  4  In the newly described cofactor, imaginative ideas have been presented regarding the mode of dinitrogen binding. At the observed separation, the two iron atoms bound to “Y”, may be privileged to accommodate a side-on bound dinitrogen molecule. 12 Theoretical studies done on the Mo-Fe cofactor also suggests that a dinitrogen ligand bound in a side-on fashion will be activated to a greater extent than the end-on case. 20 The most prevalently known end-on mode of binding is also possible at the same site, but accessed only by the expansion of the MoFe cage. The role of molybdenum is still alive. The molybdenum centre which is at the +4 oxidation level during the resting state of the cofactor could possibly be reduced to the +2 oxidation level during its active state. This could lead to the dissociation of certain ligands attached to the molybdenum centre and thereby create a vacant site for the coordination of 13 dinitrogen.  1.3 Other Methods of Nitrogen Fixation Lithium and some alkaline earth metals react with dinitrogen at ambient conditions to give metal nitrides, a process referred to as nitriding.” Vol’pin et at. showed that at elevated temperatures and pressures, nitriding of some main group metals could be catalyzed by transition metal salts in aprotic media. The nitrides thus formed are then hydrolyzed to form ammonia. A highly active system in this respect is formed by a mixture of TiC1 , AlCl 4 3 and metallic aluminum, where greater than 200 moles of ammonia (after hydrolysis) per mole of titanium were produced. Circumstantial evidence suggests that reduced species of titanium formed during the reaction, form Lewis type adducts with A1C1 . A species formulated as 3 3 • H 6 C . 2 2A1C1 TiC1 has been isolated in benzene, which is a catalyst for nitriding of aluminum, and also reacts with dinitrogen in the absence of aluminum to give a nitride complex. 22 ’ 21 The aprotic system described in Scheme 1.1 fixes dinitrogen at ambient conditions, where the operation is carried out in cycles. It is presumed that the low valent titanium species generated by the reaction of Ti(OR) 4 and sodium naphthalide reduces dinitrogen to some unknown nitride species. Operation of the cyclic process depends on the sequence involving references on page .i  Chapter 1  5  judicious addition of proton source (isopropyl alcohol); the addition of electron source (sodium metal) and removal of ammonia at the appropriate stages of the reaction 21 sequence. 2 ’ 3 Systems similar to the ones described above also facilitate in the incorporation of nitrogen from dinitrogen into organic molecules as amine and nitrile 21 functionalities. ’  2 Ti(OR)  4 Ti(OR)  +2Na  +  123  2 RONa  I/1  N2  +  r  I4RONa  I”-  6ROH  11  [nitride] 4 Na Np Scheme 1.1  Shilov et a!. demonstrated that dinitrogen could be reduced in protic media. Two potent examples are the gels formed by the combination of salts, Mo 5 or 3 / 4 /V MgCl2 Ti /KOH in an aqueous alcoholic medium. 25 These systems are catalytic with respect to molybdenum and vanadium ions and fix dinitrogen only in the presence of these ions. Mechanistic investigations suggest that the dinitrogen is probably activated within a preorganized bimetallic centre where the active metal centres are held by a complex arrangement of titanium and magnesium ions (Scheme 1.2).26  IIIMo---NN--- Molli I I •  IVM0—HN—NH—M0IV  I I  I  OH  HO  —Tilil  NITI—  I  Mg  0  0  II  II  —TiIV  IVTi—  H20 HN—NH  Mg  Scheme 1.2  Schrauzer et a!. have suggested a different mechanism for the reduction of dinitrogen in aqueous gel matrices. The mechanism involve a side-on bound dinitrogen complex as the references on page  Chapter 1  6  intermediate, which is then reduced to give diazine*, HN=NH.  The condition of the gel  determines whether diazine undergoes disproportionation to give hydrazine , N—NH and 2 H dinitrogen or will decompose to give dihydrogen and dinitrogen. (Scheme 1.3).27.28 Other than the methods described above, ’ 29 electrochemi 7 3 cal and photochemic 30 al studies have also been carried out.  Recently, concerns have been raised regarding the reproducibility of the  photochemical reduction of dinitrogen. ’ 3  -  H •  HO%  HO IV%  N  iiv%%j1  iI)  HO _VO  ‘N  :  N2H4 2 N  I  + IH0IHOINHO.N.N+H I  Scheme 1.3  1.4 Thermodynamic and Kinetic Factors On the basis of the discussion presented above, one can gauge the difficulties in fixing** dinitrogen. The extraordinary stability of dinitrogen reflects the relatively high ionization potential (15.6 eV)*** making it difficult to 32 oxidize. 3 ’ 3 A comparison of the dissociation energies of dinitrogen, 946 kJ mol, diazine, 414 kJ mo1 1 , and hydrazine, 159 Id mo1 1 , 1 suggests that the cleavage of the first nitroge-nitrogen bond consumes most of the energy ( 532 kJ mol34 1 ). Although the reduction of dinitrogen to ammonia is exothermic the calculated heat of formation of diazine is highly endothermic by 205 kJ 1 mo1 Therefore a reaction path . involving a diazine intermediate will require an activation energy not less than 205 Id mold. Such  a  high  activation  energy  will  correspond  to  a  negligible  *Dii is also refered to as diimide. **The term fixation will refer to the partial or complete dissociation of the dinitrogen triple bond to give products such as hydrazine and ammonia. Activation will refer to the lengthening of the dinitrogen triple bond compared to its gaseous state. Degree of activation can be observed directly in structurally known complexes or indirectly by other spectroscopic methods, e.g., infrared spectroscopy. ***Comparable to the ionization energy of argon (15.75 eV) references on page  Chapterl  7  rate of reaction between gaseous dinitrogen and dihydrogen. 26 Biological and industrial means of surmounting this kinetic barrier are by the use of metal catalysts.  2 N  +  H  H 2 N  AH =88 U mo1 1  1.2  2 N  ÷  1H 2  H 2 N  AH  1.3  2 N  +  2H 2  NH  AH° =92 U mol t  2 N  +  2 3H  3 2 NH  AH°  =  =  205 U mo1 1  -92 U mo1 1  1.4 1.5  Comparison of the heats of formation of diazine and hydrazine indicates that a simultaneous reduction of two of the three bonds of dinitrogen seems more favorable than a stepwise reduction (equations 1.3 and 1.4). This analysis has been extended to rationalize the activation of dinitrogen coordinated between two metal centres, M—NN---*M, where it is likely to undergo a four electron reduction to give a hydrazine type complex, M=N—N=M. Still, these metals would require such high reduction potentials that such reactions could not occur in protic media. 26 Interestingly, in some diazine complexes the hydrogen atoms of the diazine ligand were found to be involved in hydrogen bonding with sulfur atoms of the ancillary ligand (Figure In biological systems such multiple hydrogen bonds have been shown to exhibit bond energies up to 70 U mo1 . Under such circumstances the formation of diazine intermediate 1 would possibly become exotherniic. Also for systems that operate in aqueous media, the heat of hydration* will aid in the stabilization of the 26 intermediates. In the Haber process, the first step is the dissociative adsorption of dinitrogen and hydrogen to give surface bound nitrogen and hydrogen atoms. Under the conditions of Haber process the dissociative adsorption of dinitrogen is the rate-limiting step. The energy associated  *\}f ) 3 (NH  =  0) of N 2 (H 4 = 34 U mo1--; t\H298K(H3O) of N H 2 4 H 2 mo1 IH29gK 3 ; -161 U 1 (H O ) of (NH ) = -168 U mo1. 3  =  -7.5 U  ; zH298Kin (H 1 mo1 0) of 2 references on page j  Chapter I  8  with the formation of surface-atom bonds over the catalyst compensates for the relevant dissociation energy, making the overall adsorption reaction exothermic.**  The adsorbed  nitrogen atoms are then hydrogenated in a stepwise manner to give NH, NH 2 and NH 3 respectively. Although these steps are thermodynamically “uphill” they are easily overcome at the operating temperatures of the Haber process. 6  H 2 N 200 100  (a) -  (g-i-H 2 N ( g)  H 2 N N  ii +H 2 N ” +M  M-N H 2 M  M-N 2 M  100  .  .  -—..  --  Biological M-N -M 4 H 2 systems  -  Haberrocess  -  -  2ad+Had -  200  NH  3ad  ad + 2 Had / 1  -  Nad + 3 Had  Reaction Coordinate Figure 1.2 (a) A proposed energy diagram for the reaction of dinitrogen and dihydrogen; in gas phase (top), in biological systems (middle) and in the Haber process (bottom). Nad and Had represent these atoms adsorbed on a catalytic surface. (b) An example of a diazine ligand involved in intramolecular hydrogen bonding.  1.5 Dinitrogen Complexes In 1965 Allen and Senoff isolated the first dinitrogen complex, ) 3 {Ru(N 3 . ] 2 N 5 6 H Since then a wide variety of dinitrogen complexes have been prepared encompassing nearly all the transition metals. In most cases the coordinated dinitrogen ligand was derived from gaseous dinitrogen and in some cases was derived from hydrazine, azides, nitrous oxide 37 etc. 3 ’ 8 A convenient way to present an overview of dinitrogen complexes is to group them on the basis of  **FOr the adsorption  of one nitrogen and three hydrogen atoms the reaction is exothermic by 259 kJ mo1 . 1 references on page i  Chapter I  9  bonding of dinitrogen ligand as shown in Figure 1.3. This figure will form the basis for discussion in the following section. M—NN I  M-—NN---M’ or M-—NN--’M  MN  NM’ or  4  M=N  N=M fiB  M  MEIM ,N.  M—NN: M  M”  III  M—NN—M’ M  M’  Iv V  M—WHM  M—HI N  MM  N N  VI  VII  VIII  Figure 1.3 Dinitrogen bonding modes. M, M’ and M” can be different metals or same metals with different ligand environments.  1.5.1 Mononuclear End-On Complexes Mononuclear complexes with end-on bonded dinitrogen ligands, I (Figure 1.3), are overwhelmingly represented. The bond distances of the nitrogen-nitrogen bond in these complexes range from 1.0  A to  1.15  A, and have a M—NN bond angle greater than  175°. This  mode of coordination is scarcely known for Group 3, Group 4 and Group 5 metals. Recently an anionic vanadium complex with two terminally bound dinitrogen ligands has been structurally characterized, [Na(THF)j 2 [V( ( P C P 1 ) Ph CH Ph H N 72  Monodentate and chelating  phosphine ligands are the common ancillary ligands in mononuclear complexes. Complexes with porphyrin ligands have also been reported. ° Some dinitrogen 4 ’ 39 complexes of iron, ruthenium and cobalt have been prepared by the addition of dinitrogen to references on page  Chapter 1  10  metal hydride complexes (equation 1.6).41 It has been proposed that in nitrogenase, hydrogen is evolved during the coordination of dinitrogen, which is comparable to the aforementioned reaction. Another pertinent reaction is the mutual exchange of hydride and dinitrogen ligands, where the metals involved are also present in nitrogenase (equation 1.7).42  (PPh 4 [RuH ] 3 )  ( [RuH ) 2 ] 3 ) (PPh N  +  2] )(dmpe) 2 [FeH(H  +  2 H  1.6  2 ( 4 [M0H J dppe)  1.7  +  (dppe) ) 2 [Mo(N J 2J )(dmpe) 2 [FeH(N  +  1.5.2 Dinuclear End-On complexes + rJ,NH 3 3 H H y Ha] N—Fu—N—N—Ru—NH 3 H N 3 3 H NH  (15)A 1.1  1.124  3 NH  1.165 (14)A 1.2  In the linearly bridged end-on binding mode, II, the dinitrogen ligand shows a wide range of activation. The observed nitrogen-nitrogen bond lengths range from 1.0 and have a M—NN angle greater than 170°. Case ha (examples 1.1 and 1.4)  A to  1.3  A,  may be  regarded as a Lewis acid-Lewis base type interactions where the nitrogen-nitrogen bond lengths are close to that of free dinitrogen (1.098  A).  In case hib (examples 1.3 and 1.7),4546 the  bonded dinitrogen ligand is envisaged as a hydrazido type ligand, (N2) 4 where the nitrogennitrogen bond lengths are approximately 1.3A. These two cases can be considered as the two limiting resonance forms for the bridging end-on case II. The intermediate cases (example 1.2 and  can be understood on the basis of different contributions from the two forms Ha  references on page .2  Chapterl  11  and JIb. Although the two limiting cases can be reasonably depicted, for the intermediate cases  different authors seem to adopt different representations. Interestingly, a close resemblance exists between complex 1.3 and the proposed intermediates in the systems which fix dinitrogen in protic media (Scheme 1.2). In both cases the metal ions, sodium or magnesium, seem to aid in the stabilization of the bimetallic centre. A rare example of case II having porphyrin as the ancillary ligand (example 1.6) is also known. These complexes are viewed as possible electrode catalysts for the reduction of dinitrogen. 48 F 3 Ph  2 ?Et  2 CI I Me P 2 he JPhMe  Ph P 3 2 —C o—N——N—U•••••’OEt F 3 Ph  PMe P 2 h  CI—R e—N—N—M o—N—N—R e—CI Me2PhF”pphM>\j\I  l.19(4)A 1.4  P 2 PhMe  F 2 2 PhMe ‘\Me P h  1.28 (5)A  1.5  Porphyrin ligand 1.6  1.7  1.5.3 Protonation of Terminally Bonded Dinitrogen Complexes  M—NN—M M—NN  Proton source M(O)(d) +  Solvent  3 and/or N NH 4 H 2 2 and/or N  1.8  Protonation reactions of ligated dinitrogen can be summarized as in equation 1.8. Ratios of dinitrogen, ammonia and hydrazine produced vary widely, depending on the metal, proton source and solvent. The reaction of ] S0 in methanol gave 1.86 2 H 4 [W(N2)2(PM e2Ph) with 4 moles of ammonia per mole of complex, which indicates almost a quantitative use of metal  references on page j  Chapter I  12  electrons. The same complex reacted with HC1 in dimethoxyethane gave 0.5 moles of ammonia and 0.3 moles of hydrazine per mole of complex. 49 H\  H  P-I—p  \  HCI./ M  2 -N  -H  / I \P _/ 1 P  N  CIII  D  N  N  N  [j  j  I —“  /ri\ 1  III  AN  HC1  // p  N  IjiH  N  ‘  III  : :  N  N  N  M  M  M  H  I  I  I  +  —i  2+  ici1  M  jj  Lowacid Concentration  \P  M P 1 CI  /F  E  M  PIP  —Cl  HC1  ÷  i’i — /M\.I-cI BN  \  rvi CI  CIH  IHC1 Highacid Concentration  H\/H  II  NH  I  J  \H”H’ ’ri 1  MC1 Dihydride H 2 Complex -  2 N  , Hydrazine 4 H 2 N  G N  Figure 1.4 The proposed mechanism for the protonation of end-on bound dinitrogen in molybdenum(0) and tungsten(0) complexes by HC1 in TEIF. The chelating phosphine ligand in this case is 2 PCH Ph C P . Ph H The intermediates I and J are  proposed for the protonation of bridging complex H.  Some high oxidation state, dinuclear complexes of tantalum(V), niobium(V) and tungsten(VI), where the dinitrogen ligand is formulated as a hydrazido ligand (N , give 4 ) 2 quantitative yields of hydrazine upon 50 protonation. Conversely, complexes similar to 1.7 5 ’ (example ) [(rj M ) 5 ( 2 ] 3 MM i-N C , e e M  =  Mo or W) also formulated as tungsten(VI) and  dinitrogen as hydrazido ligand (N2) , react with acid to give only 0.3 moles of ammonia per 4 mole of complex. The yields of ammonia in these complexes were increased to 1.86 equivalents references on page  Chapterl  13  when protonation was carried out under reducing conditions. 52 It is important to point out that a survey of numerous protonation reactions suggests no correlation between the degree of activation of the dinitrogen ligand and the observed fixation during protonation reactions. 53 The protonation reactions of complexes 2 M(N2) L n where M 4 or L ) 2 (PPhMe  =  =  W or Mo and L  =  PCH (Ph C P 2 ) Ph H have been extensively 5 34 ’ 37 investigated. 8 Figure 1.4  depicts the intermediates involved during the first two proton transfers to the coordinated dinitrogen. Intermediates B, C, D and E are invoked on the basis of kinetic and spectroscopic studies. Diazenido (NNH) 1 intermediates, similar to D or E are yet to be authenticated, but a Lewis acid adduct ) 3 (N—HN---B -’, Ph has been structurally characterized 49. The hydrazido intermediate F has been substantiated by NMR spectroscopy and X-ray  ) 2 (NNH  crystallographic analysis. An interesting feature in some structurally known examples of intermediate F (e.g., { H 5 [W(N ) P 2 ( 3 N 4 Br( Me-3)] C h) PM NH (Br) e }) is the presence of hydrogen bonding between the hydrogens of the hydrazido ligand and the halide ions. 37 Different mechanistic pathways have been proposed for the formation of ammonia and/or hydrazine from intermediate F. 2 M (C ) 5 ( 3 ) WM NNH e e Kj H/e 3 NH •-y!<— w MeJNH 2 Me Me  Q  4 H 2 N  Me’.w..’Me Me’NH NHj  Me’.w”Me Me’’NH 2 2 NH  L  e  M  H Me7NH 2 MeMe  Me C 4 NH MeMe  p  3 NH  Me’4”NH 2 2 NH  0  N  Figure 1.5 The proposed cycle for the catalytic reduction of hydrazine by complex 3 (r 5 ( C5MeS)WM NNH2 i e K. ), references on page j.  Chapter 1  14  Schrock et a!. have invoked similar hydrazido (NNH - intermediates during the ) 2 protonation of dinuclear complexes, for example ) (r1 M ) 5 ( 2 J 3 MM J.tC , e N e M  =  Mo or W  (Figure 1.5). The hydrazido (NNH ) intermediate formed in this case 2 3 ((r1 M ) 5 MMe C e ) M 2 (NNH  Mo or W) is formally in a higher oxidation state (+6) compared to the  intermediates (e.g., F, Figure 1.4) formed from mononuclear complexes. Therefore for the further reduction of the hydrazido ligand in K an external electron source is needed. The suggested mechanism for the protonation of ) 2 (r M C ) 5 ( 3 WM NNH , e i e under reducing conditions is shown in Figure 1.5.  In the absence of a suitable electron source some  intermediates undergo disproportionation reactions to give ammonia and 54 dinitrogen. 5 ’ 5 Also, intermediates K and M have been shown to catalytically reduce hydrazine (up to 10 equivalents of hydrazine). It is also noteworthy that some sulfur ligated molybdenum(IV) complexes (e.g. [( C ( 4 ) N ) N 3 H 5 ] 2 ) (j.t (2 H-3 -3M t -2S -S -SiM SiM SC l C o e .THF) have shown to be e effective in the catalytic disproportionation of hydrazine to ammonia and dinitrogen. However, in the presence of a reductant the conversion of hydrazine to ammonia occurs catalytically (up to 1200 cycles). 56  1.5.4 Polynuclear Dinitrogen Complexes In principle, the interaction of dinitrogen with three or more metal centres could generate numerous modes of bonding (eg. III, IV and V in Figure 1.3). So far only a few different modes are known, each uniquely exemplified by 1.8, 1.9, 1.10 and 1.11. In most of these cases the dinitrogen ligand is bound terminally as well as side-on. These complexes usually show a higher degree of activation of dinitrogen, with nitrogen-nitrogen bond lengths greater than 1.3  A.  A few examples of case III (Figure 1.3) are  known, where M is tungsten or cobalt and M’ is either lithium, aluminum or magnesium (e. g. 1.8).5758 Complex 1.9 exemplifies case IV. Treatment of the complex 1.9 with acid gave four equivalents of dihydrogen and one equivalent of dinitrogen, whereas with water, a mixture of hydrazine and ammonia was obtained (greater than 90% fixation). 59 Until recently complex 1.10, an example of case V, exhibited the longest nitrogen-nitrogen bond length of 1.36(2) A.60 references on page i  Chapter 1  15  Although this complex showed a high degree of dinitrogen activation, reaction with ethylene smoothly displaced the dinitrogen ligand. 61 The alkali-metal-cobalt complexes 1.4 and 1.11 are closely related, and in fact exhibit similar nitrogen-nitrogen bond lengths. However, the solid state structures of these two derivatives differ drastically. In 1.11 the dinitrogen interacts with the alkali metal both in an end-on and a side-on fashion. 62 Interestingly this type of coordination of dinitrogen closely resembles the environment of the isoelectronic carbide ion in the alkaline earth salts 2 (C2 ; , etc). Calcium carbide has a tetragonally distorted NaC1 structure where 2 CaC2, MgC2, BaC each carbide ion is coordinated to six calcium ions. Four of these calcium ions interact side-on with the carbide ion and the other two end-on. 63 CI CI Me P 2 hP  2 PPhMe  I  ‘  AL  CI—W-—N—N  I 2 PhMe  N—N—W—CI  I\ Py  NAI PPhMe CI J  1.46  PMe P 2 h  Py  1.9  PMe P 2 h  l.301(12)A  (4)A Cl  and 1.25  (3)A 1.8 ) 3 Co(PMe  O( —  ) 3 ,Co(PMe  Li\LIJ  Ni  Ni  ,K-F+---,1I  I  OLI’X) 1.36(2)  1.10  A  /  N  1.16A 1.11  :  K---- 3 —‘-N—Co(PMe ) Po (Me C 3 )  3 P) (Me Co 3  1.5.6 Mononuclear Side-On Complexes On the basis of spectroscopic evidence only one example of a mononuclear side-on bound dinitrogen complex has been reported. The temperature invariant ESR spectrum of this zirconium(Ill) complex, ) C Z j ) 3 2 r[CH(S (r N p , iMe shows coupling due to two equivalent references on page  Chapterl  16  nitrogen atoms.  Upon protonation, this complex gave hydrazine and dinitrogen (25%  65 fixation).M. In some cases side-on complexes have been implicated as intermediates. In the case of complex ) 4 (r1 M ) 1 N 5 Re(CO)2(1 —N’ C ’ , e the dinitrogen ligand was found to undergo end-toend rotation in an intramolecular fashion. Inevitably the proposed mechanism involves a sideon bound intermediate (Scheme 1.4).66 Mononuclear dihapto dinitrogen complexes have been spectroscopically detected with many metals in low temperature matrices. 67  [Re]  N 14 [Re]—  N 15 N— 14  N 14 N— 15 [Re]—  N 15 [Re]  =  4 (1 M ) ( 2 N 5 ) Re(CO --N’ C ’ e ) Scheme 1.4  1.5.7 Dinuclear Side-On Complexes In the past five years, two examples of case VII and one example of case VIII have been structurally characterized. Case VII examples are complexes of samarium (example 1.12) and lithium (example 1.13). Although the complexes 1.12 and 1.13 are formed by different types of metals (lanthanide vs. alkali metal) the properties of the dinitrogen ligand are almost identical. The nitrogen-nitrogen bond lengths of these two complexes are identical to that of free dinitrogen and have a planar 2 M—N — M core. Under vacuum the clinitrogen ligand can be stripped from the metals coordination 68 sphere. 6 ’ 9 Reversible binding of dinitrogen in solid and in solution states have been demonstrated for complex 1.12.69  Stephan et al. have proposed that for  complex 1.13, the zirconium-phosphinidene dianion fortuitously favors the 2 —N dication Li rather than a fully solvated lithium counter ions. 68  Unfortunately, the mode of dinitrogen  bonding in solution has not been verified for examples 1.12 and 1.13. The anionic complex 1.14 (example of case VIII), described by Gambarotta et al. has a pseudo octahedral Ti(t-N2)2Ti core with the clinitrogen ligands defining the opposite edges of  references on page j  Chapter I  17  an equatorial plane. ° This anion is a mixed oxidation state complex where the titanium centres 7 can be formulated as either titanium(I) and titanium(ll) or as titanium(III) and titanium(IV) corresponding to neutral N 2 and (N - ligands respectively. Although the formalism predicts ) 2 activation only to the extent of (N - the observed nitrogen’-nitrogen bond length of (1.38(2) ) 2  A)  in 1.14, is much longer than a nitrogen-nitrogen double bound; by comparison PhN=NPh has a bond distance of 1.255 A.71 The nitrogen-nitrogen distance in 1.14 seems to correlate more closely to dinitrogen complexes where the dinitrogen is formulated as hydrazido ligand, 2 (N 4 ) . The discussion presented so far on dinuclear side-on dinitrogen complexes seems to suggest that the degree of activation of dinitrogen as measured by bond lengths falls in two extreme ends. For the samarium and lithium cases dinitrogen is barely activated whereas in the titanium case the observed dinitrogen bond distances are much greater than what would be expected.  1.38 (2)A 1.14  1.12 2-  2+  1  a 1.06 (l)A  1.6 Summary Terminally bound dinitrogen complexes have been synthesized with most transition metal complexes with varying degrees of activation. Although the motive for this type of research was eventually to develop complexes that could catalytically reduce dinitrogen, so far  references on page  .  Chapter 1  mononuclear and dinuclear end-on complexes have been extensively investigated.  18 Yet,  compared to the mechanistic understanding of reactions involving other small molecules such as carbonmonoxide, dihydrogen etc., the protonation reactions of dinitrogen are limited. In the past five years, few side-on bound dinitrogen complexes have been structurally characterized. Another important milestone is the structural elucidation of the cofactor of the enzyme nitrogenase. Ironically, a few researchers have proposed that the dinitrogen might interact in a side-on fashion during its activation in the cofactor. Structural and theoretical studies seem to suggest that a side-on mode of bonding leads to a greater degree of activation of dinitrogen. In the following chapter new side-on bound dinitrogen complexes of zirconium will be discussed. Aspects of the bonding both in solution and in the solid state, and some aspects of the reactivity of the coordinated dinitrogen will be considered.  1.7 References (1)  Miller, S. L. J. Am. Chem. Soc. 1955, 77, 2351.  (2)  Lemmon, R. M. Chem. Rev. 1970, 70, 95.  (3)  Ponnamperuma, C. Quart. Rev. Biophys. 1971,4, 77.  (4)  Price, C. C. Synthesis of Life; Dowden, Hutchingon & Ross, Inc.: Stroudsburg, Pennsylvania, 1974; Vol. 1.  (5)  Crookes, W. In The Report of the 68th meeting of the British Associationfor the  (6)  Advancement of Science; John Murray, London: Bristol, 1898; p 3. Jennings, I. R. Catalytic Ammonia Synthesis: Fundamentals and Practice; Plenum Press: New York and London, 1991; Vol. 1.  (7)  Feldman, M. R.; Tarver, M. L. .1. Chem. Ed. 1983, 60, 463.  (8)  Haber, F.; vonOordt, G. Z. Anorg. Chem. 1905,44, 341.  (9)  Bortels, H. Arch. Mikrobiol. 1930, 1, 333.  (10)  Dilworth, M. J.; Glenn, A. R. Biology and Biochemistry ofNitrogen Fixation.; Elsevier: New York, 1991, pp Chapter 4.  (11)  Chatt, J.; Leigh, G. 3. Chem. Soc. Rev. 1972, 1, 121.  (12)  Orme-Johnson, W. H. Science 1992,257, 1639.  (13)  Sellmann, D. Angew. Chem., mt. Ed. Engi. 1993,32, 64.  Chapter I  (14)  Ciuril, S.; Hoim, R. H. Inorg. Chem. 1989,28, 1685.  (15)  Coucouvanis, D. Acc. Chem. Res. 1991,24, 1.  (16)  Burgess, B. K. Chem. Rev. 1990, 90, 1377.  (17)  Georgiadis, M. M.; Komiya, H.; Chakrabati, P.; Doo, D.; Komuc, 3. J.; Rees, D. C.  19  Science 1992, 257, 1653. (18)  Kim, J.; Rees, D. C. Nature 1992, 360, 553.  (19)  Kim, J.; Rees, D. C. Science 1992, 257, 1677.  (20)  Deng, H.; Hoffmann, R. Angew. Chem., mt. Ed. Engi. 1993,32, 1062.  (21)  vanTamelen, E. E. Acc. Chem. Res. 1970,3, 361.  (22)  Volpin, M. E.; flatovskaya, M. A.; Kosyakova, L. V.; Shur, V. B. J. Chem. Soc., Chem. Commun. 1968, 1074.  (23)  vanTamelen, E. E.; Fechter, R. B.; Schneller, S. W.; Boche, G.; Greeley, R. H.; Akermark, B. J. Am. Chem. Soc. 1969, 91, 1551.  (24)  vanTamelen, E. E.; Rudler, H. J. Am. Chem. Soc. 1970, 92, 5253.  (25)  Shilov, A.; Denisov, N.; Efimov, 0.; Shuvalov, N.; Shuvalova, N.; Shilova, A. Nature 1971,231, 460.  (26)  Shilov, A. E. Russ. Chem. Rev. 1974,43, 378.  (27)  Zones, S. I.; Palmer, M. R.; Palmer, J. G.; Doemeny, 3. M.; Schrauzer, G. N. J. Am. Chem. Soc. 1978, 100, 2113.  (28)  Liu, N. 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J.; Kruger, C.; Roberts, P. J.; Tsay, Y. H. J. Am. Chem. Soc. 1976, 98, 74.  (61)  Jonas, K. Angew. Chem., mt. Ed. Engi. 1973, 12, 997.  (62)  Hanimer, R.; Klein, H. F.; Friedrich, P.; Huttner, G. Angew. Chem., mt. Ed. EngI. 1977, 16,485.  (63)  Greenwood, N. N.; Earnshaw, A. Chemistry of The Elements; 1st edition ed.; Pergamon Press: Oxford, 1986, pp 318.  (64)  Jerrery, 3.; Lappert, M. F.; Riley, P. I. J. Organomet. Chem. 1979, 181, 25.  (65)  Gyane, M. J. S.; Jeffery, J.; Lappert, M. F. J. Chem. Soc., Chem. Commun. 1978, 34.  (66)  Dengel, A. C.; Griffith, W. P.; O’Mahoney, C. A.; Williams, D. 3. J. Chem. Soc., Chem. Commun. 1989, 1720.  (67)  Ozin, G. A.; Voet, A. V. Can. J. Chem. 1973,51, 637.  (68)  Ho, 3.; Drake, R. J.; Stephan, D. W. J. Am. Chem. Soc. 1993, 115, 3792.  (69)  Evans, W. 3.; Ulibarri, T. A.; Ziller, 3. W. J. Am. Chem. Soc. 1988, 110, 6877.  (70)  Duchateau, R.; Gambarotta, S.; Bensimon, C. J. Am. Chem. Soc. 1991, 113, 8986.  (71)  Allen, F. H.; Kennard, 0.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 1987,11, Si.  (72)  Rehder, D.; Woitha, C; Priebsch, W; Gailus, H. J. Chem. Soc., Chem. Commun. 1992, 365.  (73)  Pickett, C. J; Ryder, K. S; Talarmin, J. J. Chem. Soc., Dalton Trans. 1986, 1453.  22_  Chapter 2 Dinitrogen Complexes of Zirconium 2.1 General One of the on going research interests of our group involves the synthesis of transition metal complexes containing the tridentate ligand ) CR [N(SiMe P , 1 ] 2 H abbreviated as PNP. This hybrid ligand was designed with a central amide unit flanked by two identical arms containing phosphine donors. 5 The incorporation of mismatched donor groups, i.e., the hard 1 amide and the soft phosphine donors, has enabled the successful coordination of this ligand to hard, early and soft, late transition metals. 7 The formation of two fused five-membered chelate ’ 6 rings has also been shown to favour the complexation of this ligand. As a formal six electron donor the PNP ligand is somewhat comparable to the isoelectronic Cp ligand. However, in certain instances, due 2 Me  F  P 2 R  2 Me  M  -  to the availability of lone pair electrons on the nitrogen, PNP  1  PNP R  Me, Ph, Pr , But 1 M = metal ion  =  2 PR  could donate a maximum of eight electrons, which would be manifested by shorter than usual metal-amide bond 8 Also, in some late transition metal complexes distances. the nitrogen lone pair has played an important role as an intramolecular Lewis base (e.g., Ir(2-propenyl)(A1Me2)-  C [N(SiMe P ] 2 ) Ph ) and as a proton acceptor (e.g., C H 2 IrHMeBr[NH PPh H ] ) 2 ” ). ° (SiMe 9 The tridentate ligand usually exhibits meridional coordination, but occasionally facial coordination has been observed in the solid (e.g., ] [N(SiMe2CH 3 ZrCl P 2 Me2) )’ and in the solution (e.g., ” kH( ) 5 H C P 1 ) 2 3 [N(SiM C Ph )’ H 1 e states. Also, the ligand could influence the reactivity at the metal center by changing the coordination from tridentate to bidentate, or even monodentate, a process that could be compared to the ring slippage of the Cp ligand from 5 to r1  3 i  to q P{ 1 H} NMR spectra of PNP derivatives are useful in assigning structures . The 31 1  of these molecules and to monitor the reaction progress. The steric bulk of PNP can be readily altered by changing the size of the substituents on the phosphine donors, for example, the Me, Ph Pr 1 and But derivatives are all available. references on page j9.  Chapter II  23  Investigations involving PNP as an ancillary ligand on zirconium led to the discovery of carbon-carbon bond formation between butadiene and allylic fragments.’ 4 Also some zirconium complexes have shown fluxional behavior (e.g., ] Zr ) 6 H 4 P 2 Cl[N(SiMe2C Pr’) C ) (r H and intriguing coordination geometries such as a bicapped tetrahedron (e.g., C 2 [ 3 ZrMe N(SiMe H215 ] ) 2 PMe 1 ’ ). 6  Pr 2 1 P  \  Me S 2 i  2 Na/Hg  %CI %s.  2 (4atm) N  Zr__Cl  Me Si” C  P.  (—2NaC1) 2.1  t N—N  =  Zr—N(1)  1.548 (7) =  A  2.175 (3)  Zr—P  A  N 2 Zr  Zr—N =  =  2.77A  2.024 (4)  A  2.2  Planar Scheme 2.1  N  Investigations  on  the  reduction  of  [N(SiM 3 ZrCl C P J 2 ) Pr H e 2.1, under a dinitrogen •Zr—N—N—  atmosphere gave rise to a deep blue complex. Structural analysis of the blue complex 2.2, revealed  N  2.3  it to be a dinuclear derivative containing a bridging  T1nlN Z 2 1.l2A  side-on bound dinitrogen ligand (Scheme 2.1).8 The observed nitrogen-nitrogen bond distance of 1.548(7)  A in 2.2 was significantly longer than that observed for a nitrogen-nitrogen single bond; for example in hydrazine the nitrogen-nitrogen bond length is 1.46  Prior to this work there  was only one other structurally characterized zirconium dinitrogen complex [(ri 5 references  on page 1.2.  Chapter II  24  C5Me5)2ZrN212-(p.-fl’:fl’-N2) 2.3.18-21 The dinuclear complex 2.3 has three dinitrogen ligands, two terminal and one bridging, and the bridging dinitrogen ligand has a nitrogen-nitrogen bond length of 1.182  A, considerably shorter than that found in 2.2.  To elaborate on the chemistry of side-on dinitrogen complexes similar to 2.2 we investigated the synthesis of other dinitrogen complexes of zirconium incorporating the PNP ligand. We were particularly interested in substituting the chloride ligand of 2.2 with other substituents such as Cp, alkoxide, etc. This chapter describes the synthesis of a series of dinitrogen complexes and aspects of their bonding. The mode of dinitrogen bonding in the solid versus the solution states was of interest along with some aspects of reactivity.  2.2 Synthesis of a Dinitrogen Complex Containing PNP and Cp Ligands  Me S 2 I\  NaCp•DME  :j—  / Si 2 Me  Toluene  2.1 R=Pr’,X=Cl 2.4 R=Pr ,X=Br 1 2.5 R = Me, X = Cl  Na/Hg Toluene  R=PX=Y  2.6 R=,X=Cl 2.7 R=Pr ,X=Br 1 2.8 R = Me, X = Cl  (i—N)  2 2 Pr’  2.9 Scheme 2.2 Initial attempts to metathesize the zirconium-chloride bonds of the side-on dinitrogen complex 2.2 with alkyl lithium or sodium aryl oxides resulted in decomposition to unidentified products. Also the synthesis of 2.2 involves a tedious workup procedure, where optimum references on page 2.22  Chapter II  25  conditions give only 40% yields. Therefore a two step reaction sequence starting with complex 2.1 was developed as shown in Scheme 2.2. Selective metathesis of a single zirconium halide bond of the trihalo precursor and subsequent reduction did enable the synthesis of a new dinitrogen complex.  2.2.1 Synthesis of Precursors of the Type ) ZrCpX2[N(S C P ] 2 H R 1Me Synthesis of ZrCpC12[N(SiMe2CH2PPr’)2] 2.6, was readily achieved by reacting one equivalent of solid NaCp•DME with a toluene solution of P 2 [ 3 ZrCl N(SiMe2CH Pr)2], 2.1. After recrystallization, pure hexagonal shaped crystalline material was obtained in excellent yields (> 75%).  The related complexes 2.7 and 2.8 were also synthesized via a similar  reactions. A single resonance for the SiMe2 moieties in the H 1 NMR spectrum and a single resonance in the 31 P{ 1 H} NMR spectrum suggest a symmetric structure for the complex 2.6 in solution.* The protons of the  Cp ligand appear as a triplet, due to the coupling of two equivalent  phosphines. These spectroscopic data are consistent with a C2v structure for complex 2.6 in solution, i.e., assuming free rotation of the Cp ligand about the 119 axis defined by the zirconium and the centroid of the Cp (Scheme 2.2). The principal C2 axis coincides with the axis defined by the centroid of the Cp, the zirconium and the nitrogen, and the zirconium lies in a pseudo-octahedral environment. No evidence of fluxionality was observed in the 1 H NMR spectrum when a sample of 2.6 was cooled to -90 °C. This could imply that the Cp ligand is coordinated in an fl 5 fashion in solution. The solution spectroscopic data obtained for the analogous complexes 2.7 and 2.8 also suggest geometries similar to complex 2.6. Figure 2.1 shows the X-ray structure of complex ] 2 ZrCpBr2{N( , SiMe2CH2P Pr’) 2.7. The Cp ligand is found to be trans to the amide linkage, and the nitrogen, zirconium and the centroid of the Cp are arranged almost linearly (Table 2.1). The two phosphorus atoms and the two bromide atoms are slightly bent away from the Cp ligand. Assuming that in solution the Cp *  In the 1 H NMR spectrum of complexes containing PM the resonances due to Si(CH 2 group appear between ) 3 0.00 ppm and 0.75 ppm. The number of resonances observed for the Si(CH )2 moieties, in conjunction with the 3 P( 1 31 H) NMR spectrum enable us to predict the geometry of the molecule with reasonable accuracy. references on page  Chapter II  26  ligand is undergoing rapid rotation about the zirconium centroid axis the overall geometry of the molecule in solid state agrees with the geometry inferred from solution spectroscopic data. The structure also shows the T coordination of the Cp ligand.  czz N CZ3 C19  I  Br  II  Figure 2.1 I ORTEP view showing the complete atom labeling scheme of the complex ZrCpBr2[N(S C P ] 2 ) Pr H , iMe 2.7. II A Chem 3D® view showing the pseudo octahedral geometry at the zirconium.  The bond lengths (Table 2.1) and bond angle (Table 2.2) parameters associated with the “Zr[N( C P ] 2 ) Pr ” H SiMe unit are similar to other structurally known complexes of zirconium(IV) with the PNP ligand.” The distance from zirconium to the centroid of the Cp, 2.286(2)  A is comparable to the distances observed for the bis(cyclopentadienyl) derivatives (e.  g Cp2ZrI2, 2.20 A)22 and the monocyclopentadienyl derivatives (e.g. [CpZrCl3], 2.196 A) 24 . 23  references on page  Chapter II  27  Table 2.1 Selected bond distances of complex 2.7  ZrCpB [ C 2 ] N(SiM H2PPr . r e ) atom  atom  Zr  Cp  Zr  distance  (A)  (A)  atom  atom  2.286(2)  Zr  Br(1)  2.6871(7)  P(1)  2.817(1)  Zr  Br(2)  2.6842 (7)  Zr  P(2)  2.821(1)  Zr  C(average)  2.57  Zr  N  2.227(2)  N  Si(average)  1.736  distance  Table 2.2 Selected bond angles of complex 2.7 ZrCpB [ C 2 } N(SiM H2PPr . r e ) atom  atom  atom  angle  P(1)  Zr  P(2)  Cp  Zr  Br(1)  (0)  atom  atom  atom  152.82(4)  P(1)  Zr  Cp  103.02(7)  N  179.2(1)  P(2)  Zr  Cp  104.16(7)  Zr  Br(2)  162.95(2)  P(1)  Zr  N  76.18(9)  P(1)  Zr  Br(1)  90.31(3)  P(2)  Zr  N  76.65(9)  P(1)  Zr  Br(2)  86.00(3)  Cp  Zr  Br(1)  99.02(7)  P(2)  Zr  Br(1)  85.08(3)  Cp  Zr  Br(2)  98.03(6)  P(2)  Zr  Br(2)  90.62(3)  N  Zr  Br(1)  81.50(8)  angle  (0)  Much of what is known about the reactivity of organometallic complexes of zirconium arises from the work done on dihalo zirconocene derivatives, 2 Cp’ Z rX2 (Cp’  =  any ligand  containing a cyclopentadienyl unit, X = halide). 2536 Because complexes 2.6, 2.7 and 2.8 can be considered as isoelectronic to Cp’2ZrX2 useful comparisons are possible.  An important  difference in their physical properties is that the PNP derivatives are soluble in aliphatic references on page 112  Chapter II  28  hydrocarbon solvents, whereas the zirconocene derivatives are usually soluble only in polar solvents. Preliminary studies involving PNP derivatives and aluminoxanes have shown catalytic activity towards the polymerization of ethylene. 37 It is well established that zirconocene derivatives also function as excellent catalysts under similar conditions.  Stereo-regular  polymerization involving chiral zirconocene 38 derivatives 3 ’ 9 could also be extended to the PNP systems by incorporating chiral cyclopentadienyl ligands or by using chiral phosphine donors. 40 Reactions mediated by Cp’2ZrX2 complexes take place at adjacent sites, i.e., the sites occupied by the halide atoms. From a mechanistic viewpoint, the availability of adjacent reactive sites has been conducive to the successful utilization of these complexes (e.g., reductive elimination, a-H abstraction), particularly in their applications to organic synthesis. 36 In the case of PNP derivatives, the reactive sites, i.e., the sites occupied by the halides, are trans related. Therefore, for these sites to become involved in a mutual manner they have to be brought closer, either by the rearrangement of the PNP to a facial type coordination or by the dissociation of one of the phosphine donors.  2.2.2 Reduction of Complexes of the Type ) ZrCpX2[N(S C P ] 2 H R 1Me A toluene solution of complex J ZrCpC [ C P 2 N(SiM Pr’) H l 2.6, was reduced with e Na/Hg under 4 atmospheres of dinitrogen. The yellow color of the reaction mixture rapidly disappears to give a deep green solution which turns deep brown within a few days. The intermediate responsible for the green colour was also formed in the absence of dinitrogen (under an argon atmosphere) implying that it does not contain a dinitrogen ligand. A deep brown crystalline material was isolated from the brown solution which was formulated as a dinuclear dinitrogen complex (Scheme 2.2) on the basis of spectroscopic and micro analytical data.  references on page 112  Chapter II  29  P  P  N P  Si  P  Si  III  Si N Si II I Figure 2.2 I ORTEP view showing the complete atom labeling scheme of complex ([(Pr S ) ) H 5 ( 2 ) JI-11’: 2N]Z iM C 1 , PCH r’-N r(1 e 2.9. II A Chem 3D® view of the arrangement of atoms around the zirconium centre. II A Chem 3D® view showing the arrangement of the PNP ligand and the Zr2N2 core.  references on page Q  Chapter II  30  The X-ray structure of the dinitrogen complex {[(P P S N ) 2 ) H 5 ]Zr(ri iMe CH C } r -N 2.9, is depicted in Figure 2.2. The solid state structure unequivocally shows that 1 ) (.t-11 ‘:rl 2 the dinitrogen ligand is bound in an end-on fashion bridging two zirconium centres. The observed nitrogen-nitrogen bond distance of 1.30 1(3) comparison to the similar distance of 1.548(7) (by 0.1  A  A in the  (Table 2.3) is significantly shorter in  side-on derivative 2.2, but longer than  A) the end-on derivative 2.3, which is the only other zirconium complex with an end-on  bound dinitrogen ligand that has been structurally characterized. When a comparison is made with end-on complexes in general where the nitrogen-nitrogen bond lengths range from 1.1 1.3  A,  A to  the nitrogen-nitrogen distance in 2.9 falls in the upper limit (Chapter 1, section 1.5.2).  Also, in complex 2.9 the zirconium-nitrogen distances associated with the dinitrogen ligand are approximately 0.1  A shorter as compared to the side-on complex 2.2 or to the similar distance in  complex 2.3*.21 The dinitrogen ligand in 2.9 is slightly offset from the zirconium-zirconium axis, having a Zr—N—N angle of 170°.  Table 2.3 Selected bond distances of complex 2.9 [(Pr’PCH2Si ) H C Me2)2N]Zr(11 } 2(L11 1 :r ‘-N2). {5 atom  atom  Zr(1)  Cp(1)  Zr(1)  distance  (A)  (A)  atom  atom  distance  2.294 (2)  Zr(2)  Cp(2)  2.286 (2)  P(1)  2.8 16 (1)  Zr(2)  P(3)  2.778 (1)  Zr(1)  P(2)  2.776 (1)  Zr(2)  P(4)  2.828 (1)  Zr(1)  N(1)  2.306 (3)  Zr(2)  N(2)  2.303 (3)  Zr(1)  N(3)  1.920 (3)  Zr(2)  N(4)  1.923 (3)  N(3)  N(4)  1.301 (3)  Zr  C(average)  2.58  *  In complex 2.3 the zirconium-nitrogen bond distances for the bridging dinitrogen ligand are 2.087 (3) A and 2.075 (3) A, and for the terminal dinitrogen ligands is 2.188 (4) A. references on page  Chapter II  31  Table 2.4 Selected bond angles of the complex 2.9 [(PrPCH2SiM H C 5) e2)2N]Zr(rI } 2(.LT1’ :r ‘-N2) {5  atom  atom  atom  angle (°)  atom  atom  atom  angle (°)  P(l)  Zr(1)  P(2)  145.87 (4)  P(3)  Zr(2)  P(4)  145.65 (3)  N(1)  Zr(1)  N(3)  115.1 (1)  N(2)  Zr(2)  N(4)  115.3 (1)  N(l)  Zr(l)  Cp(l)  127.61 (9)  N(2)  Zr(2)  Cp(2)  127.49 (9)  N(3)  Zr(1)  Cp(1)  117.2 (1)  N(4)  Zr(2)  Cp(2)  117.1(1)  P(l)  Zr(1)  N(1)  71.74 (8)  P(3)  Zr(2)  N(2)  75.37 (7)  P(l)  Zr(1)  N(3)  98.92 (8)  P(3)  Zr(2)  N(4)  86.10 (8)  P(1)  Zr(1)  Cp(l)  102.89 (6)  P(3)  Zr(2)  Cp(2)  104.84 (6)  P(2)  Zr(1)  N(l)  75.66 (8)  P(4)  Zr(2)  N(2)  71.53 (8)  P(2)  Zr(l)  N(3)  85.76 (8)  P(4)  Zr(2)  N(4)  99.76 (8)  P(2)  Zr(1)  Cp(1)  104.84 (6)  P(4)  Zr(2)  Cp(2)  102.41 (6)  Zr(1)  N(3)  N(4)  170.6 (2)  Zr(2)  N(4)  N(3)  170.1 (2)  A comparison of the arrangement of the PNP ligand in complexes 2.2 and 2.9 shows that in the end-on case it is significantly twisted where as in the side-on case it is almost planar, reflecting the increased steric crowding around each metal centre in the end-on derivative. Also, the bond distances associated with the zirconium-amide bonds are approximately 0.1  A longer  than those observed in complex 2.2. In fact, the zirconium-amide bond distances in 2.9 are the longest of any zirconium-nitrogen distances that have been measured for PNP coordinated to zirconium, 1 ’ 8 1 and are just slightly shorter than the distances of 2.443(1)  A  and 2.412(2)  A  found in neutral amine type adducts of 41 zirconium(IV 4 ’ 2 ). The zirconium-Cp bond distances of complexes 2.6 and 2.9 are identical. Analysis of the bond angles (Table 2.4) around each  references on page i;i  Chapter II  32  zirconium of 2.9 suggests an approximate trigonal bipyramidal geometry, with the phosphines occupying the apical positions, slightly bent away from the Cp ligand. The 1 H NMR spectrum of 2.9 has only one resonance associated with the Cp ligand and two resonances associated with the SiMe2 moieties; the 31 H} NMR spectrum consists of a 1 P{ single resonance at room temperature. These spectroscopic data suggest that complex 2.9 adopts a more symmetric structure (C2v) in solution than that observed in the solid state 2 (C ) . Variable temperature NMR spectroscopic studies with complex 2.9 show fluxionality. The variable temperature 31 F1 } NMR spectra show broadening and decoalescing of the singlet p{ 1 resonance which below -40 C separates into an AB quartet ( Jp..p 2  =  80 Hz). In the 1 H NMR  spectra the two resonances associated with the SiMe2 groups give rise to four peaks at low temperature.  These low temperature spectroscopic data are consistent with the structure  observed in the solid state. The 1 H and 31 P{ 1 H} NMR spectra were virtually unchanged through the temperature range from -40 C to -90 C, suggesting that phosphine dissociation is not involved in this particular fluctional process. Imagining a fluctional process involving synchronized pivoting of the zirconium-amide bonds with respect to the Zr2N 2 core would render the two phosphines equivalent (Scheme 2.3).  P e i 2 2 Si../ Pr 2 Me  Me S 2 i 2 Pr’  2 SiMe  pr  Scheme 2.3  references on page 112  Chapter II  33  The replacement of a chloride ligand of the side-on dinitrogen complex 2.2 by a Cp would dramatically increase the steric interactions between the two zirconium centres. By this rationale, substituting the chloride ligands of 2.2 with Cp ligands would favor the formation of the end-on complex over the side-on complex. In the side-on complex 2.2 the two metal atoms are separated by 3.7 A which is significantly closer than the comparable distance of 5.1  A in the  end-on complex 2.9. The important difference in the electronic properties of the two complexes is that the Cp ligand in 2.9 is bonded to the metal by a a and two it-bonds whereas in 2.2 the Cl ligand is mainly bonded via a a-bond. These interactions will significantly alter the type of orbitals available for dinitrogen bonding. Considering electron donor properties, the Cp ligand is likely to make the metal more electron rich. Although this would increase metal to dinitrogen backbonding interactions it is difficult to predict how this would influence the mode of dinitrogen bonding.  2.3 Attempted Synthesis of a Dinitrogen Complex Containing PNP and Allyl ligands Considering the discussion presented in Section 2.2, replacing the chloride ligand of the dinitrogen complex 2.2 with an allyl ligand would be a suitable extension of our investigation. Sterically, an allyl ligand is less bulky than a Cp ligand. Electronically, it donates less electrons to the metal than a Cp ligand and is bonded to the metal via one a and one it-bond. Synthesis of the monoallyl derivative was achieved by a metathesis reaction involving 1 equivalent of C3H5MgC1 and 2.1 (Scheme 2.4). However, initial attempts to synthesize the allyl derivative using 5 C3H M gBr and 2.1, gave a mixture of products. Spectroscopic and elemental analysis suggests that the mixture consists of two products, the desired complex 2 Zr(i ) 5 H 3 C1 C C [N(SiMe P 2 j Pr) H } 2.10, and 2 Zr( ) 5 H 3 C P ] ) ClBr[N(SiM C Pr H , r e 2.lOa. In the 1 H NIVIR spectrum of 2.10 the SiMe2 moieties gives rise to two resonances and the P( 31 H 1 } NMR spectrum consists of a single peak. The syn, anti and central protons of the allylic group appear as three separate resonances in the 1 H NMR spectrum suggesting that the allyl group is rigid within the observed time scale.  The 31 P{ 1 H} NMR spectrum of a references on page  Chapter II  34  recrystallized sample from the reaction of C MgBr and 2.1 consists of a singlet and a set of 5 H 3 AB quartets 2 J( p..p = 7.9 Hz) corresponding to 2.10 and 2.lOa, respectively. Assuming that 2.10 and 2.lOa are isostructural in solution the 31 P{ 1 H) NMR data can be explained only if the PNP ligand adopts a facial geometry. The suggested geometry for 2.10, shown in Scheme 2.4 has C symmetry, which intuitively suggests that 2.lOa will be asymmetric. The 1 H NMR data suggests that in 2.10 the symmetry plane containing the central proton of the allylic ligand and bisects the molecule into two chemically equivalent halves.  Me Sr”\  \:N r 1  2  C M 5 H 3 gX  \  S 2 Me  Me S 2  X = Cl, Y = Cl, 2.10 X = Br, Y = Br, 2.lOa and Cl, 2.10  2.1  Scheme 2.4  NOEDIFF experiments involving the irradiation of the syn or the anti protons of the allylic ligand resulted in the spin saturation of both the syn and the anti protons and showed enhancement of the resonance due to central proton. frradiating the central proton resulted in the enhancement of the resonances due to syn and anti protons. This seems to suggest that the allyl ligand undergoes syn anti exchange with a time scale comparable to the duration of radiation during the NOEDIFF experiment. When a toluene solution of complex 2.10 was reduced with Na/Hg or with Mg under 4 atmospheres of dinitrogen the yellow colour of the reactant rapidly changed to give a green solution. Upon further reaction the green colour slowly changed to give a deep brown solution. Attempts to isolate solid materials from these solutions only resulted in impure oils.  references on page fl  Chapter II  35  2.4 Synthesis of a Dinitrogen Complex Containing PNP and Aryl Oxide Ligands After exploring the effects of substituting the Cl ligand of 2.2 with It-type ligands such as Cp and allyl, attention was focused on investigating the preparation of the following monodentate ligands: amide (NPh ), ailcyl 3 2 SiMe 2 (CH ) , alkoxides (OCHPh 2 and OBut) and aryl oxides (OPh and OAr* where Ar*  =  Me2-2,6). Of these, OAr* was the most 3 H 6 (C  successful in leading to the synthesis of a dinitrogen complex, hence the chemistry associated with OAr* ligand will be discussed in detail.  [N(SiMe Zr(OAr*)C1 C P ] ) Pri H 2.4.1 Synthesis of 2  2 PP1j  Si 2 Me  ci  \:N—zr—ci /1 e21\  NaOAr  *  Toluene  /  2.1  Toluene  2 Pr  2.12 Scheme 2.5  Addition of solid NaOAr* to a toluene solution of the trichloro starting material 2.1 led [N(SiMe Zr(OAr*)C1 C P ] Pr1) H , 2.11 in good yields (Scheme 2.5). It is to the synthesis of 2 important that toluene be used as the solvent to obtain high yields of the monoaryloxide complex. During test runs in THF it was found that the reaction yielded a mixture of mono and  references on page  Chapter II  36  bis OAr* substituted products in approximately a 3:1 ratio, respectively. When the reaction was carried out in an NMR tube containing a solvent mixture of THF/C D 6 D (THF:C 6  =  4:1), the  P{ 1 31 H} NMR spectrum showed two resonances: one corresponds to unreacted 2.1 and the other to the uncoordinated phosphine of PNP. A sample prepared in C D after stripping the 6 THF solvent did not show any resonances due to uncoordinated phosphines. This spectroscopic  evidence seems to suggest that soon after the formation of mono OAr* the phosphines become labile in THF solution (Scheme 2.6). The substitution of bulky phosphine donors by THF ligands is likely to decrease the steric crowding around the metal center, allowing further metathesis reactions. When the reaction was carried out in toluene, after the formation of the mono OAr* derivative the phosphine donors remained coordinated. This makes the metal centre sterically more crowded and therefore the metathesis of the second zirconium-chloride bond is significantly slower.  P 2 R  Me S 2 i\Ci  S 2 Me  :Nzr___oAr* *  / Si 2 Me  /1 CI  /  —  •NZf—QAr  Me S 2 i” CI”  P 2 PIA  I  > ()  Scheme 2.6  The 1 H and 31 P{ ‘H} NMR spectra of the monoaryloxide 2.11 show that the complex essentially has the same symmetry (C2) as complexes 2.1 or 2.6. As depicted in Scheme 2.5 the molecule adopts an approximately octahedral geometry having trans geometry.  [N(S1M Zr(OAr*)C1 C P ] ) Pri H e 2.4.2 Reduction of 2 During the reduction of 2.11 with Na/Hg under a dinitrogen atmosphere, depending on the purity of the dinitrogen gas, two types of materials were isolated. When the reaction was references on page  Chapter II  37  carried out under normal dinitrogen (refer to experimental for the purification of dinitrogen) the crude material contained many impurities. The crude material was washed with hexanes and then recrystallized from a toluene solution to give pure material directly. When the reduction was carried out under 5 ‘ N 2 gas the crude product had fewer impurities, and washing with hexanes afforded pure material. The spectroscopic analysis ( P( 3 11 H) NMR spectroscopy) of the pure material obtained with normal dinitrogen showed the presence of one compound, whereas the product obtained from the 15 2 reduction showed the presence of two compounds N in approximately 2:1 ratio. In the latter case the chemical shift of the major peak was identical to that obtained under normal dinitrogen. The elemental analysis of both materials gave {[(P P S N ( N2) ]Zr(OA iMe2 CH identical results, and was consistent with the formula 2 ri r*)} , ) 2.12. The above experimental details show that the reduction of 2.11 under dinitrogen gives rise to two isomers of complex 2.12. The major isomer, 2.12a has slightly better solubility properties than complex 2.2 whereas the minor isomer 2.12b dissolves readily in hexanes and toluene. Therefore when reductions were carried out under normal dinitrogen, during workup most of the minor isomer was removed along with the hexane washings. Single crystals suitable for X-ray analysis were obtained for the major isomer 2.12a. The solid state structure unequivocally shows that the dinitrogen is bound in a side-on fashion bridging the two zirconium centers (Figure 2.3). The observed nitrogen-nitrogen bond length of 1.528(7)  A (Table 2.5) is identical to the other side-on derivative 2.2, and is significantly longer  than the bridging end-on complexes where, as already mentioned, the nitrogen-nitrogen bond lengths range from 1.12  A to  1.3  A.  A compilation of nitrogen-nitrogen bond lengths, presented  in Table 2.6, provides a comparison with other dinitrogen complexes and also to selected other molecules of interest. The dinitrogen bond lengths in complexes 2.2 and 2.12a are not only longer than that of free hydrazine but also longer than that found for coordinated hydrazine ligand 2 (N ) 4 H , or hydrazido ligand (NHNH) 2 (Table 2.6).  references on page 112  Chapter II  38  P  P  Si Si Ill I Figure 2.3 I ORTEP view showing the complete atom labeling scheme of complex ([(PrPCH2Sifl : ) 2 N Me2)2N]Zr(O , Ar*)}2(IIfl 2.12a. II A Chem 3D® view showing the arrangement of the PNP ligand and the Zr2N2 core. III A Chem 3D® view of the arrangement of atoms around the zirconium centre. references on page 212  Chapter II  39  Table 2.5 Selected bond distances of complex 2.12a, : }2(JI-’q N2). fl { [(PrPCH2SiMe2)2N]Zr(OAr*) 2  atom  atom  Zr(1)  0(1)  Zr(1)  distance  (A)  (A)  atom  atom  2.020(3)  Zr(1)  N(1)  2.211 (3)  P(1)  2.818 (1)  Zr(1)  N(2)  2.034 (4)  Zr(1)  P(2)  2.846 (1)  Zr(1)  N(2)’  2.082 (4)  N(2)  N(2)’  1.528 (7)  N(1)  Si(1)  1.718 (4)  distance  Table 2.6 Compilation of nitrogen-nitrogen bond lengths for some selected compounds.  Compound  Bond Length  (A)  ref.  2 N  1.0975 (2)  Ph—N=N—Ph  1.255  2 ON—NO  2.08  69  N—NO O 2  1.75  69  N—NH H 2  1.46  17  S [(PrPCH N ) ]Zr(OAr*) iMe } {2  2.12a  1.528 (7)  this work  {[(PrPCH2S N ( : 2 ) ,I-1 ]ZrCl} rI N iMe 2.2  1.548 (7)  8,45  S [Cp* ( : ) 2 N I11 11 mj 1.12  1.088 (12)  W(NPh)Me ( 2 ] 3 J.I-1’ :11 2 N ‘NH ) : N HNH) (1 1 H NI{ 2 1H1’NH  46 47  1.434 (14) 1.391 (15)  [(PrPCH2SiM N ) H 5 ( ) i-N JZr(11 C } e {2  2.9  1.301 (3)  this work  {[(PriPCH2S N Q 2 ) ]TiCl} IN iMe  1.275 (7)  48  PCH2SiMe {{(Pr N ( 2 ) .L-N ]VC1}  1.257 (8)  48  P (Me ( C ) 2 Ta=CHCMe Me CH ) 12 (.t-N ) {3  1.298 (12)  references on page 212  Chapter II  40  The very long nitrogen-nitrogen bond distances of complexes 2.2 and 2.12a vindicates the discussion presented for the titanium complex with a : 2 “Ti2(I-T1 N2)2” ’ri core, 1.14 (Chapter 1, Section 1.5.7). In complexes 2.2 and 2.12a the dinitrogen ligand can have a maximum formal charge of 4-, 4 (N2) . However, comparison with end-on complexes where the dinitrogen ligand can be formulated as a (N - ligand, for example, as found in complexes with 4 ) 2 nitrogen-nitrogen bond distances closer to 1.3  A,  the side-on complexes of zirconium exhibit  extravagant nitrogen-nitrogen bond lengths, in fact they are longer than that found in hydrazine. A conspicuous difference between the side-on complexes 2.2 and 2.12a is that the Zr N 2 core in 2.12a is hinged along the nitrogen-nitrogen axis, whereas in the chloro derivative 2.2 it is planar. In complex 2.12a the triangular planes defined by each zirconium and the nitrogens of the Zr2N2 core form an angle of 156.2, and the orientation of the PNP ligands with respect to the Zr2N2 core can be described as syn. Considering the structure of 2.12a as a whole, the bending of the core perhaps eases any steric interactions that might arise if the core was planar, since with a bent core, PNP ligands are moved away from each other. zirconium-zirconium separation of 3.7  The calculated  A in 2.12a is identical to that of 2.2.  The bond distances associated with the phosphine donors and zirconium are comparable to other PNP complexes of ’ 10 8 zirconium. 5 1 The bond lengths from the zirconium to each of the bridging nitrogens Zr-N(2), are 2.034(4) and 2.082(4) amide bond length, Zr-N(1), 2.211(3) same bond parameters of 2.2.  A, and this is shorter than the zirconium  A of the ancillary ligand, PNP; and are comparable to the  Also the zirconium-amide bond, Zr-N(1), 2.211(3)  A,  is  significantly shorter than the comparable bond length of the cyclopentadienyl dinitrogen complex 2.9, which is 2.306 range from 1.826(4) 2.443(1)  A  (3)A.  Other zirconium-nitrogen bond distances in the literature  Cp Z r=NBut(THF)S’ to for a zirconium-nitrogen double bond in 2  A in Schiff base chelate derivatives. 52  The zirconium-oxygen bond separation, Zr-O(1) is 2.020(3)  A  and the bond angle  defined by the atoms Zr, 0(1) and C(19) is 161.5(4)° (Table 2.7). These two interrelated structural features are indicators of metal-oxygen d-p interactions where larger bond angles and shorter bond lengths are correlated with iu-electron donation from the oxygen. 53 By  references on page j  Chapter II  41  comparison,  parameters  associated  with  the  zirconium-oxygen  bond  for  [(Bu C . 3 5 } ) Li(OE 0]2ZrC Z(OC [Cp ) B 3 H 6 2 2 r(NMe 3 ,6)] t) t ut l are 1.859 A and 169°; for 24 {2 they are 2.056(1) A and 142.7(7)° and for 54 ZrMe)201 1.945 A and 174.1° are found. In 2 [(Cp , the solid state structure of 2.12a the OAr* ligand is oriented such that the methyl substituents are directed away from the isopropyl substituents of the phosphine donors. Table 2.7 Selected bond angles of complex 2.12a, ([(PPrj2CH2SiMe2)2N]Zr(OAr*) 2 : 12(.t-fl N2). rI atom  atom  atom  angle  atom  atom  atom  angle  P(1)  Zr(1)  P(2)  145.54 (4)  P(1)  Zr(1)  N(2)  128.10 (10)  N(1)  Zr(1)  2 N  114.9*  P(2)  Zr(1)  N(2)  82.89 (10)  N(1)  Zr(1)  0(1)  123.0 (1)  P(1)  Zr(1)  1 N(2)  85.10 (10)  0(1)  Zr(1)  2 N  122.3*  P(2)  Zr(1)  N(2)’  126.19 (10)  0(1)  Zr(1)  N(2)  119.8(1)  P(1)  Zr(1)  0(1)  87.6(1)  0(1)  Zr(1)  N(2)’  119.1 (1)  P(2)  Zr(1)  0(1)  88.1 (1)  N(1)  Zr(1)  N(2)  111.4(1)  P(1)  Zr(1)  N(1)  79.4(1)  N(1)  Zr(1)  N(2)’  114.7 (1)  P(2)  Zr(1)  N(1)  74.5 (1)  N(2)  Zr(1)  N(2)’  43.6 (2)  Zr(1)  N2  Zr(1)’  156.2*  P  Zr(1)  2 N  106.4*  Zr(1)  N(2)  N(2)  69.9 (2)  P  Zr(1)  2 N  104.8*  Zr(1)  N(2)  Zr(1)’  130.7 (2)  Zr(1)  0(1)  C(19)  161.5 (4)  *  These data were measured from a molecule constructed by using the structural data of 2.12a in a CAChe work station.  The room temperature 1 H NMR spectrum of the major isomer shows two resonances for the SiMe 2 moieties and a singlet for the protons of the two ortho methyl groups of OAr*; the P{ 1 31 H) NMR spectrum consists of a singlet. An averaged solution structure depicted in 2.12a references on page 212  Chapter II  42  having C2 symmetry accounts for both 1 P{ ‘H) NMR spectral features. H and 31  The  spectroscopic analysis of the sample containing a mixture of both isomers suggests that the minor isomer adopts a less symmetric structure, where the SiMe2 protons give rise to four overlapping signals and the phosphines give rise to two singlet resonances in the 1 H and 31 H 1 P{ ) NIvIR spectra, respectively. On the basis of the assumption that the minor isomer has the same type of 2 (.t-rI Zr : ) 11 N core as the major isomer the structure depicted as 2.12b is proposed, having C symmetry. By having the bent 2 Zr core, the ends of the molecule are N now different, consistent with the solution spectral data. Considering the arrangement of the ligands with respect to the Zr N core, the two isomers can be envisaged as the syn 2.12a and 2 the anti 2.12b isomers.  2.12a  2.12b  A variable temperature 31 P( 1 H} NMR analysis of 2.12a showed an unsymmetrical broadening of the singlet resonance at 8.69 ppm.  At temperatures below -70 °C a new  resonance began to appear around 4.0 ppm which increased in intensity as the temperature was lowered to -90 °C. Upon cooling, it was expected that the singlet resonance would decoalesce in a symmetric manner to give an AB quartet or two singlets which could be related to the solid state structure of 2.12a.  However, none of the low temperature 31 H} NMR features P{ 1  correspond to the solid state structure of 2.12a (Figure 2.4). Considering the room temperature H NMR spectrum of 2.12a, the appearance of a singlet due to the methyl protons of OAr* 1 references on page Q  Chapter II  43  group can result from rotation about the oxygen-carbon bond; but the appearance of only two peaks for the SiMe 2 units, instead of four as predicted by the solid state structure, would require the rotation of the OAr* group about the zirconium-oxygen bond, averaging the inequivalent phosphine environments.  -55 °C  95  V  -80 °C  room temperature  I  I  12  10  I  8  I  6  I  4  I  2PPIb4  14  12  10  8  6  4PP2  Figure 2.4 Variable temperature 121 MHz 31 H} NMR spectra of 2.12a recorded in C 1 P{ . 8 D 7  Studies associated with zirconium aryloxide complexes (e.g., H 6 [C Z ) 2 3 (0C r(NM 2, p e 6But ) 2 ]) suggest restricted rotation about the zirconium-oxygen bond, where the calculated AGI values were around 73 kJ 1 mol It is possible that in complex 2.12a rotation about the . zirconium-oxygen bond could be sterically hindered.  The complex probably undergoes references on page  Chapter II  44  reversible dissociation of one of the phosphine arms of PNP during which the OAr* group swings from one end of PNP to the other end. The intermediate observed in the variable temperature 31 P{ 1 H} NMR spectrum may be due to the rapid equilibrium between the two intermediates which have one phosphine arm dissociated (Scheme 2.7).  0 9c  0  ‘Si  2 Me  I  ‘I PrZrP  2 Pr’  O’  2 Me  N— ,  ,N.Sj’NI 2 Me  Scheme 2.7  Replacing the chloride of 2.1 with OAr* ligand has not altered the mode of dinitrogen bonding nor the degree of activation. The structural parameters associated with the zirconiumoxygen bond indicate that there is t-bonding between the two atoms, which would make the metal centers of 2.12 more electron rich than the metal centers in the side-on derivative with the chloride ligand 2.2. The increased steric crowding caused by the replacement of the chloride ligand of 2.2 with OAr* is overcome by the bending of the Zr N core. A favorable physical 2  references on page fl  Chapter II  45  property attained by the substitution of the chloride ligand with OAr* is the increased solubility of the minor isomer 2.12b in hydrocarbon solvents.  2.5 Synthesis of { 2 ) 2 [(P P S N ) Q ]Zr(OB iM .irI2 CH ri ut)} e 2..N :1 Selective metathesis of only one chloride of 2.1 with one tert-butoxide (OBut) group to Zr(OB [ C P ] N(SiM Pr1 H yield the precursor 2 ut)Cl e 2.13, was partially successful. Reactions ) carried out under different conditions gave oily mixtures of mono and bis substituted complexes which were difficult to separate. The reduction of the crude precursor (containing approx. 80% of the monosubstituted derivative 2.13) with Na/Hg gave a deep purple solution. The 31 P{ 1 H} NMR spectrum of the reduced material has a broad peak at 8.16 ppm, which is comparable to other side-on bound dinitrogen complexes 2.2 and 2.12. Unfortunately the complex 2.14 was extremely soluble in hydrocarbon solvents (pentane) and remains as an impure oil even at -78 °C. This could be partly attributed to the build up of impurities, since the precursor also could not be purified. The 1 H NMR features were similar to the side-on dinitrogen complexes 2.12 having two resonances for the 2 SiMe group and a singlet for the OBut group. A compilation of 31 P{ ‘H} NMR chemical shifts for some zirconium precursors and the dinitrogen complexes derived from them is given in Table 2.8. The data suggest that the phosphorus-3 1 chemical shifts for a given precursor will shift to high-field upon formation of a side-on dinitrogen complex and shift to low-field upon the formation of an end-on dinitrogen complex. The zirconium tert-butoxy precursor, having a 31 P chemical shift of 11.6 ppm, shifts to a lower field upon its reduction under dinitrogen atmosphere. Therefore, it is presumed that the product is a side-on dinitrogen complex and is formulated as 2 {[(PrP S N ) ](OBu iMe CH t) :rI Zr}2(.t-rI 2 ) N , 2.14. In the absence of other corroborating evidence, however, this proposal is speculative. Zr(OB [ C P ] ) N(SiM Me H The methyl-PNP derivative 2 ut)C1 e 2.15, can be synthesized and isolated as a pure material. The reduction of this complex under dinitrogen atmosphere was slow and prolonged reaction times afforded many products as detected by P H} NMR 31 ( 1 spectroscopy. Also, the final reaction mixture was only faintly colored, whereas the reduction references on page fl  Chapter II  46  of other precursors that yielded dinitrogen complexes always gave deeply colored solutions. A different alkoxide precursor 2 )Zr(O C12[N(SiMe 2CH2PPr’)2] CHP h 2.16, upon reduction (Na/Hg or Mg) gave uncoordinated PNP ligand. The mono amide precursor ) 2 Zr(N Cl2[N(SiMe2 Ph PPr) 2.17, and the mono alkyl precursor ) 2 CH ] 3 Zr(C Cl2[N(SiMe2 H2S CH2PPr)2] iMe 2.18, gave intractable materials upon reduction.  Table 2.8 Compilation of H} NMR chemical shifts for some zirconium precursors and 1 P{ 31 the dinitrogen complexes derived from them. In all these complexes PNP corresponds to  2 [N(SiM C H2PPr’2)2]. e Precursors  Chemical  Dinitrogen Complexes  Shift (ppm)  Chemical Shift (ppm)  3 (PNP)ZrC1  15.4  [(PNP)ZrC1] 2 : 2(I-rI N2) fl  10.0  3 (PNP)ZrBr  16.5  [(PNP) ( : 2 ) ji-1 N r ZrBr]  10.0  15.0  [(PNP)Zr(OA : 2 N 11 2) r*)12(p.11  8.7, 8.9 &1 1.3  2 (PNP)Zr(OB ut)C1  11.6  [(PNP)Zr(OB : 2 N fl 2) ut)]2(.t11  8.2  2l (PNP)ZrCpC  16.1  1 ( 2 [(PNP)ZrCp1 : .t’2 -N 1 )  20.3  3 (PNP)TiC1  -1.9  -N 1 ) [(PNP)TiC1]2(I.L-’il’ :T 2  21.2  (PNP)Ta(=CHBut) Cl 2  37.5  2 [(PNP)Ta(=C ( I.trl HBut)] l : ‘-N2)  48.8  2 (PNP)Ta(=C HPh)C1  40.1  [(PNP)Ta(=CHPh)] 2(.t-TI’ :fl -N)  51.1  2.6 Spectroscopy as a Diagnostic Tool for End-On and Side-On Dinitrogen Complexes Although X-ray structure determination of dinitrogen complexes will unequivocally show the mode of dinitrogen binding in the solid state, it does not necessarily relate to the mode of dinitrogen binding in the solution state. Also, X-ray analysis inevitably requires the isolation of single crystals which ultimately relies on serendipity. Therefore, any spectroscopic technique that could differentiate between these two modes of bonding would not only help in the assignment of dinitrogen bonding in complexes that are difficult to crystallize but would also references on page  Chapter II  47  enable one to ascertain the mode of dinitrogen bonding both in the solid and the solution states. We were particularly interested in discerning the mode of dinitrogen bonding in the side-on complex 2.2 in the solution state.  2.6.1 15 N NMR Spectroscopy The nitrogen-15 analogues of complexes 2.2, 2.9 and 2.12 were prepared by introducing gas during the reductions of the corresponding precursors. Originally, we had hoped that the measurement of the nitrogen-15 chemical shifts 55 would provide a diagnostic handle on the mode of binding in these derivatives, that is, side-on bridging versus end-on bridging. However, as is evident from the chemical shifts compiled in Table 2.9, there is no obvious correlation between the two modes of coordination. For example, the chemical shift of the sideon complex 2.2, whether in the solid or in the solution state, is in the range of 345 to 351 ppm while the end-on derivative 2.9 is at 354 ppm. In fact, the only correlation seems to be related to which metal the dinitrogen ligand is attached, since the zirconium complexes resonate around 350 ppm, with the exception of the bridging dinitrogen ligand of  The  dinuclear tantalum complexes also seems to display very similar chemical shifts irrespective of the ancillary ligands. [Cp*WMe J 3 2Q.LN2),  But, also notable is that the formally tungsten(VI) derivative, and  the  mononuclear  molybdenum(0)  complex,  tra n s  (PMePh show similar chemical shifts to the tantalum diniirogen complexes. The 2 Mo(N2) , 4 ) chemical shift of the bridging dinitrogen ligand in the diamagnetic titanium dinitrogen complex having PNP as the ancillary ligand appears around 375 ppm. Dinuclear titanium dinitrogen complexes reported in the literature are paramagnetic complexes. 5658 None of the dinitrogen complexes containing PNP as the ancillary ligand showed any observable coupling to the phosphine donors in their 15 N NMR spectra. ° 6 ’ 59  references on page flQ  Chapter II  48  Table 2.9 Compilation of some 15 N chemical shiftsa for some selected compounds.  Compound : 2 ([(2PCH2SiMe2)2N]ZrCl}2Q1-n N2) r1  Chemical Shift (ppm)  350.9 (solution)  Reference this work  345.0 (solid) SiMe2)2N]ZrBr}2(.t-rI [(PrPCH : N2) 11 {2  345.8  this work  :fl 2 {[(PrPCH2SiMe2)2NJZr(OAr*)}2(J.trI N 2)  342.9 and 339.1  this work  SiMe2)2N]Zr( 2 [(PrPCH CSHS) 1 } 201-1 1:1 --N2) {5  354.0  this work  SiMe2)2NjTiCl}2(J.t-fl’:1 ‘-N2) 2 { [(PrPCH  3755  48  [Cp*2Zr(1 2 1 ) 12(t-r N :rI ‘-N2)  452.01 (bridging)  61  354.Ob (terminal) S [(PrPCH N ) iMe I 20.1-ri’ :r 1 JTa=CHBut -N2) {2  301.2  62  -N 1 ) P)2C1Ta=CHCMe }2(t-n’ : 2 (Me {3  296.2c  63  (,.Lr:riuN 2 ] 3 [Cp*WMe )  310.9c  64  4 ) 2 trans-Mo(1’-N2)2(PMePh  d 4 • 298.3 & 305  60  Afl chemical shifts are referenced to external neat formamide set at 0.0 ppm. boflginally referenced to nitric acid. COriginally referenced to liquid ammonia. doriginally referenced to nitromethane.  A different approach to probe the binding of the dinitrogen ligand in the binuclear side-on zirconium complexes is to synthesize closely related complexes where the two zirconium centers are chemically different. For example, substituting one of the chloride ligands of complex 2.2 with a different ligand (e.g., Br or OAr*) will render the two zirconium centers chemically different, and also change the symmetry of 2.2 from C2h to C. Assuming that the ancillary ligand arrangements are similar in the solid and in the solution states, the solution 15 N NMR spectrum of the complex corresponding to C symmetry should give a singlet resonance, if the dinitrogen ligand is bound in a side-on manner in solution. Conversely, if the  references on page Q  Chapter II  49  dinitrogen is bound in an end-on fashion the 15 N NMR spectrum may consist of two singlets or a doublet-of-doublets corresponding to an AB type spin system. Since attempts to selectively metathesize the zirconium-chloride bonds of 2.2 were futile, 6 ’ 65 6 mixtures containing a 1:1 ratio of two different precursors were reduced under 15 2 N atmosphere. When an equimolar mixture of 2.1 and 2.11 was reduced under dinitrogen it gave mainly complex 2.2 and none of the desired dinitrogen complex containing one chloride and one OAr* ligand. Conversely, when a similar reduction was carried out with complex 2.1 and the bromide analogue ] [N(SiM 3 ZrBr C P 2 Pr) H e 2.4, it gave a mixture of three dinitrogen complexes. The 31 P( 1 H} NMR spectrum of the mixture had four singlet resonances, which were very close in their chemical shifts. Two of these resonances were assigned to complex 2.2 and to the dibromo analogue 2.19, and the other two resonances were assigned to the mixed halogen derivative, 2.20 where each signal is associated with one type of zirconium centre (Figure 2.5). The 1 H NMR spectrum of the mixture shows the presence of eight equal intensity resonances (some overlapping) in the SiMe 2 region. This spectroscopic analyses shows that the above reaction produces a mixture of three complexes, 2.2, 2.20 and 2.19 in approximately a 1:2:1 ratio (Scheme 2.8). 32 ZrC1 C [N(SiMe P j ) ’Pr H 2.1 2 Me Pr’ SL  2 Si  +  N2  [1  32 ZrBr CH [N(SiMe P 1 P ] ) r Na/Hg Toluene  2.4 2 Me  Pr’  2  <c-? 2 Me  PP2 Si-” 2 Me  2.2  2 Me Ie 2  2.20  2.19  Scheme 2.8  references on page 112  Chapter II  50  N C,,  C) C C)  C,,  0 1’,  1  35C  355  1111  350  I  I  I  II  345  III  I  340 PPM  T I 1 I IiI i l i j  iO.5  iO.O  9.5 PP9.O  Figure 2.5 (right) 31 P{ 1 H} NMR spectrum of the sample obtained from the reaction described in Scheme 2.8. (left) 15 N NMR spectrum of the same sample  The solution 15 N NMR spectrum of the sample containing the three dinitrogen complexes has three singlet resonances in approximately 1:2:1 ratio, of which the two low intensity peaks were assigned to complexes 2.2 and 2.19 (Figure 2.5). The high intensity peak was assigned to the mixed halogen derivative, 2.20 which, being a singlet resonance suggests that the dinitrogen ligand is bound in a side-on fashion in solution. It is theoretically possible that the observed singlet resonance of 2.20 is a time averaged signal resulting from a rapid  references on page ii  Chapter II  51  fluxional process that involves intermediates containing end-on and side-on bound dinitrogen ligand. However, the dinitrogen ligand is highly activated in these complexes, and therefore the metal-nitrogen interactions are likely to be strong, which in turn would imply that the rotation of the dinitrogen ligand may have a high activation barrier. To confirm that the bromide ligand also favors the formation of a side-on dinitrogen complex the pure dibromo derivative 2.20 was synthesized from 2.19. A preliminary X-ray analysis of this complex showed that in the solid state the Zr2N2 core is identical to that of complex 2.2.  2.6.2 Resonance Raman Spectroscopy Further evidence for the mode of dinitrogen coordination in the zirconium complexes has been obtained from resonance Raman spectroscopic analysis. 67 Resonance Raman spectra of both isotopomers, nitrogen-15 and nitrogen-14, were obtained for solid samples and for solution samples made up in THF. The most prominent feature in the solid state resonance Raman spectrum of the end-on complex 2.9 is the peak at 1211 cm, which shifts to 1172 cm-’ 1 upon substitution of the 14 N2 ligand with 15 N2 (Figure 2.6, page 52). The magnitude of this isotope shift, 39 cm , is essentially equal to the calculated value of 41 cm. The solution 1 spectra of the two isotopomers are very similar to the solid state spectra, except for the presence of some solvent peaks. These spectral data imply that the dinitrogen ligand in 2.9 is bound in an end-on manner both in the solid and in the solution states. The solid state resonance Raman spectrum of the side-on derivative 2.2 has two intense peaks at 317 cm’ and 731 cm1 and a few low intensity peaks. Substituting the dinitrogen ligand with nitrogen-15 isotopomer the peaks at 731 cm , 991 cm and 1046 cm 1 1 shift to 709 , 968 1 and 1024 cnr 1 cm 1 respectively (Figure 2.7, page 53). The isotopic shift of 22 cm 1 observed for the peak at 731 cm 1 is within 2 cm 1 of the calculated value, suggesting almost pure nitrogen-nitrogen bond stretching character.  references on page i2  Chapter II  52  (N  (‘4  A  C’ Lft4  S  500  —  1000  1500  cm-i  2000  Figure 2.6 The resonance Raman spectra of complex 2.9 recorded at approximately 90 K. A and B correspond to the (p.) and (i2 N 14 ) complexes respectively. The top 2 N 15 two traces were recorded in the solid state and the bottom two were recorded in the solution (THF) state. Each trace is a sum of 5 scans, each recorded at 2 cm /s using 1 40 mW of 514. 5 nm laser excitation (Appendix A.1).  The resonance Raman studies done on the oxyhemocyanin model complex {Cu[HB(3,53 p 2 Ph ] z) } ( ) :ri 11 2 0 were used as the basis for the interpretation of the resonance Raman features of complex 2.2.68 It is important to note that both complexes have planar M X (where 2 M  =  Zr and X  =  N or M  =  Cu and X  =  0) type cores with the X 2 moiety bound in an identical  side-on fashion. references on page j  Chapter II  53  C.’  1 cm-  500  A  1400  1000 THF  —  Co  cqo  V)  -  I  I  5O0  8O0  I  cm-i  Figure 2.7 The resonance Raman spectra of complex 2.2 recorded at approximately 90 K. A and B correspond to the (p,N2) and (J.t-’ 14 N2) complexes respectively. The top 5 two traces were recorded in the solid state (sum of 9 scans) and the bottom two were recorded in the solution (THF) state (sum of 5 scans). Each scan was recorded at 1 cm’/s using 20 mW of 647.1 nm laser excitation (Appendix A.1).  The vibrational modes derived from normal coordinate analysis of the Cu 0 core are 2 depicted in Figure 2.8. The peak observed at 731 cm 1 for the complex 2.2 has been assigned to the symmetric mode Ag where the dominant stretch involves the nitrogen-nitrogen bond references on page fl  Chapter II  54  (Figure-2.8). By comparison, the similar stretching mode in the copper peroxide complex gives a value of 763 cm1 for the 1602 complex which shifts to 723 cm-’ upon 1802 substitution.  Cu,,,_,Cu  Ag  Cu C 1 u  Ag  Cu_.Cu  CuCu  2 B  3 B  C U.  Big  Figure 2.8 Depiction of the in-plane normal vibrational modes of the side-on peroxide bridged copper dimer. 68 Broken lines increase in length as solid lines decrease in length. Bonds which do not change in length during a given vibration are not shown. Thicker lines indicate the dominant motion in the two Ag modes. 68 The 114 B, deformation mode is not shown.  The other two isotope sensitive peaks of the side-on derivative 2.2, 991 cm1 and 1046 4 shift by 23 cm cm 1 and 22 cm1 respectively, upon substitution with the 15 N isotope. These two peaks are assigned as combination bands where the former is due to the peaks at 258 cm’ and 731 cm-’ and the latter is due to the peaks at 317 cm1 and 731  . 1 cnT  Since the peaks at 258  1 and 317 cm cm 1 are not isotope sensitive, the shifts in the combination bands can be attributed to the isotope sensitive band at 731 cm . Overall the spectrum consists of a few 1 fundamental bands and the rest of the peaks are a result of overtones or combination bands. The solution resonance Raman spectrum of 2.2 was different in some aspects. The peak due to the nitrogen-nitrogen stretching at 731 cm1 in the solid state was split into two resonances at 745 cm 1 and 733 cm. These two peaks shift to 719 cur’ and 709 cm 1 respectively, upon substitution with nitrogen-15 dinitrogen ligand. The magnitude of the shifts (26 cm1 and 24 cm-’) are similar to the shifts observed in the solid state spectra. Also the feature at 317 cm1 of the solid state spectrum was split into two resonances at 331 cm 4 and 321 . The fact that the peaks corresponding to the nitrogen-nitrogen stretching are very close in 1 cur the solid and in the solution state spectra strongly suggests that the mode of dinitrogen binding is very similar in the solid and in the solution states.  references on page Q  Chapter II  55  It is possible that the appearance of two peaks associated with the nitrogen-nitrogen stretching of the side-on complex 2.2 in the solution (THF) state is due to some solvent effects. However, recording the spectra in a relatively non-coordinating solvent like pentane also showed two peaks. Therefore it is believed that the molecule is undergoing some fluxional process, for example, a process that involves the bending of the planar Zr N core along the 2 nitrogen-nitrogen axis (Equation 2.1). An isomer with a bent core is comparable to the OAr* derivative, 2.12.  zrNz r zrNIIh1zr  Planar Core  2.1  Bent Core  Curiously, the solution spectrum of the 15 N isotopomer of the side-on complex 2.2 had a peak at 1028 cm1 which was comparable to the dinitrogen stretching of the end-on complex 2.9. To ascertain the origin of this peak, polarization studies were carried out on the nitrogen-15 isotopomer in solution. It was found that the peaks at 719 cnr 1 (p, 0.32), 709 cm 1 (p, 0.32), 327-i (p, 0.40), 318 cm 1 (p, 0.40) and 260 cm 1 (p. 0.35) were polarized and the peak at 1028 1 (p. 0.76) was depolarized. The lower polarization associated with the peaks at 700 cm cm 1 and the peak at 260 cm 1 suggest that they are due to the Ag modes, where the former peak corresponds to the nitrogen nitrogen stretching mode and the latter to the breathing mode of the 2 core (Figure 2.8). The peaks around 300 cm’ also share some Ag character. Also the Zr2N depolarized peak at 1028 cm 1 is not associated with any totally symmetric mode and is probably due to solvent (THF). The resonance Raman spectra of the sample containing a mixture of three complexes 2.2, 2.21 and 2.20 gives only a single peak at 709 cm 1 (Figure 2.9). The absence of a center of symmetry in the mixed halogen complex 2.18 does not seem to affect the Ag stretching mode associated with the dinitrogen ligand. This is in agreement with our previous suggestion that the peaks around 700 wave numbers are almost purely of dinitrogen stretch in character. The  references on page  Chapter II  56  resonance Raman spectra of the aryloxy derivative 2.12 also gives a strong Raman feature at . 1 730cm-  -I  S  0  %0 0 C’ 00  C’  A  B  500  1000  cm-i  1400  Figure 2.9 The solid state resonance Raman spectra of 2.2, (A) and 2.19, (C) and of the sample (B) obtained from the reaction shown in Scheme 2.6. All of the samples contain a 5 : (.i-1 ) 2 N 1i ’ ligand. Spectral conditions are similar to Figure 2.8.  A compilation of various bond lengths and stretching frequencies associated with a nitrogen-nitrogen bond are shown in Table 2.10. The stretching frequencies associated with the dinitrogen ligand in the side-on complexes are significantly lower than what has been observed for hydrazine, whereas the comparable feature of the end-on derivative, 2.9 is higher; i.e., in these zirconium complexes the stretching frequencies seems to corroborate well with the observed nitrogen-nitrogen bond distances. Also these data suggest that the end-on zirconium derivative has a bond order higher than that of hydrazine whereas the side-on derivatives have a bond order of less than one. references on page i;i  Chapter II  57  Table 2.10 Compilation of some nitrogen-nitrogen bond lengths and stretching frequencies associated with them. Compound  Bond length  NN  A  1 V cm-  references  1.0975(2)  2331  115  Me—N=N—Me  l.247°  71  Ph—N=N—Ph  1.255  1576 1442  71  N—NH 2 H  1.46  1111  71  600, 588  71  2050-2 100  72  1211  this work  this work  N—NF 2 F -N 1 ) 2 ] {Ru2(NH ) 3 lo(.t-1’ :‘q 4  1.124(15)  [(PrPC S N 2 ) H ]Zr(r iMe C H I I 2(P-fl {5 1 :T -N) 1.301(3) : (.t-r N2) T ( [(PrPCH2SiMe2)2N]Zr(X) } 2 X=Cl  1.548(7)  731  XOAr  1.51(1)  732  2.7 Bonding Considerations 2.7.1 General The Dewar-Chatt-Duncanson bonding model developed for the qualitative understanding of metal-olefin interactions has been extended to explain the bonding of transition metal dinitrogen 73 complexes. 7 ’ 4 This synergic bonding formalism involves electron donation from a filled hg and orbital into a vacant metal orbital, and concomitant back donation of electrons from a filled metal orbital into a vacant ligand orbital. In mononuclear end-on complexes, the lone-pair orbitals of the end-on bound dinitrogen ligand act as the donor orbitals and the vacant 7t*orbitals act as the acceptor orbitals. 75 The bonding in mononuclear side-on dinitrogen complexes can be rationalized by invoking the filled it-orbitals as the donor orbitals and the vacant t*orbitals as the acceptor orbitals. 76 To explain the bonding in dinuclear metal complexes having an end-on bridging dinitrogen unit, M—NN—M, Chatt et a!. proposed the qualitative molecular orbital (MO) analysis depicted in Figure 2.10.77,78 For this four-center M—N—N—M interaction, the atomic references on page U.Q  Chapter II  58  orbitals (AO) of each center (i.e., of both the metals and the two nitrogens) contribute equally towards each MO.  NJ  Donor-Acceptor interactions for the mononuclear end-on mode  ‘3’’9  Donor-Acceptor interactions for the mononuclear side-on mode  4e  8;i8 j.  i8!3.Ij  1 3jj 2e  ie A qualitative MO bonding scheme for the end-on bridging mode  A more realistic representation for the case described on the left  Figure 2.10 Qualitative bonding description for mononuclear complexes (top) and end-on bridging dinuclear complexes (bottom).  Molecular orbital calculations performed on structurally known complexes give a slightly different picture. 79 Fenske-Hall type calculations performed on the end-on dinuclear complexes,  )(CH (PH 2 (CH ) )S]2(i-N } 4, { [Nb 3 3 [Ru(NH ) Z r N2)2)2]2(.L-N2) } and (Cp* 2 3 {2  (p.-N2), 2.3, suggest that the MOs labelled 3e for all of the :N2 1 .I-1 fl complexes are either non-bonding or weakly bonding in character so that their occupation cannot affect the nitrogen nitrogen bond length. 79 Thus, the character of the 2e MOs must control the strength of the references on page  Chapter II  59  metal-nitrogen and nitrogen-nitrogen bonds.  The AO composition of the 2e MOs vary  considerably for different complexes. It was found that the participation of the dinitrogen *bital in the 2e MOs was greater for the zirconium and niobium cases and was less for the ruthenium case, which also corroborates with the longer nitrogen-nitrogen bond distances observed in the zirconium and niobium complexes. For the niobium and zirconium complexes,  { [Nb(CH2)(CH3)(PH3)2]2(p-N2) } and (Cp*2ZrN2)2(.LN2), a push-pull type of bonding mechanism has been postulated that parallels the synergic bonding in mononuclear complexes. 7 ’ 21 9 In these examples, of the two d-orbitals (one from each metal) that contribute towards the 2e MOs, only one is filled and the other is vacant. As a result, metal to dinitrogen , and dinitrogen to metal N 2 M—*N —*M, electron flow can occur without significant charge 2 build up on the dinitrogen 21 ligand. 7 ’ 9  2.7.2 Bonding in ) P {[(Pr’ S 2 2N] iMe CH 2 -J.t-N Zr(1 ) 5 ( ) C5H } INDO/l-MO calculations were performed on the idealized metal complex 45 The P 3 [(II ( N 5 Q 2 ) CsHs) .t-ri’:ri’-N , symmetry. 2 )Zr(r H ) ] A, which was restricted to C fragment MO analysis was carried out on the idealized fragment 5 P 3 [(H CSHS)] )2(H2N)Zr(T 1 B with an imposed C symmetry. In these models, the relative spatial arrangement of the atoms directly bonded to zirconium was kept very close to that of the X-ray structure. 45 In order to minimize the total number of AOs associated with the model the isopropyl groups on the phosphine donors were replaced with hydrogen atoms. The isopropyl substituents are important in view of their steric contribution but in a semi-empirical level of calculations they are unlikely to have a significant influence in the electronic properties associated with the metal.  I  H3 r ZNN—Z” 3  H  P 3 H  P 3 H  A  A  H ....Zr piø’ 4  H H  H  B references on page fl  Chapter II  60  x  y :  ..4%  o  88á,::  , 4 S 4 4%  ,2 LiX  4% 4% 44 4% 4% 4% 4  2 y  4%  2N P 3 (H ( 2 )CpZr H )  88 4 S S  e  N — 2 it  8 8w” Figure 2.11 Bonding scheme for the model A.  From the dinitrogen ligand the lone-pair orbital G 3 g, the bonding tu-orbita1s and the antibonding 1t*orbitals are available for bonding. MO analysis of the fragment B indicated that there are two metal-based orbitals a’ and a” which are available for bonding with dinitrogen. These frontier orbitals a’ and a” mainly consist of d 2 (52%) and dx y (68%) respectively 2 (Table 2.11).* The d 2 lies along the axis containing the metal and the centroid of the Cp ligand, and is therefore higher in energy than the d , 2 2 which lies between the phosphine and the amide ligands.** The  and dyz orbitals are involved in bonding with the Cp ligand and the  dxy-orbital is directed towards the ancillary ligand atoms. This formalism is consistent with the *  The total d-orbital contribution towards the frontier orbital a’ (-0.674 eV) is 63% and a” (1.556 eV) is 85%. Orbital a’ has a significant zirconium p-orbital (Pz %) contribution as well. 47 ** If the symmetry of the major d-orbital contributing towards a frontier orbital agrees with the adopted coordinate system then that frontier orbital will be referred to by the symmetry symbol of the d-orbital. references on page 112  Chapter II  61  3 M [(C ) 5 WMe *SO e where the two isolobal a’ isoelectronic and qualitatively isolobal fragment ] and a” orbitals mainly consist of d 2 and  orbitals.M,Sl  Table 2.11 Some orbital parameters of le and 2e MOs of model complex A. Energy (eV)  Zr d-orbital contribution per metal  N2 p-orbital contri bution per nitrogen  HOMO (2e)  -5.824  10%  23% (Py = 18%)  HOMO-1 (2e)  -6.594  24%  21% (P  HOMO-9 (le)  -11.065  8%  26% (Pz  HOMO-li (le)  -12.363  9%  24% (Py= 19%)  Molecular orbital  =  14%) 17%)  The bonding scheme for model A is shown in Figure 2.11. The symmetric combination of the . 2 d orbita1 . with one of the ic-orbitals of dinitrogen gives rise to HOMO-9 and the symmetric combination of the d -orbitals with the second ic-orbital of dinitrogen gives rise to 2 HOMO-il. These two MOs correspond to the le MOs depicted in Figure 2.11 and consist mainly of ic-N 2 in character.* In a similar fashion the anti-symmetric combinations of the d 2 and  orbitals can interact with the it*orbitals of dinitrogen to give the 2e MOs, which  correspond to HOMO and HOMO-1 respectively.  The relative energies and orbital  contributions (for one Zr and one nitrogen atom of the dinitrogen ligand) of le and 2e MOs are given in Table 2.11. With regard to the AO contributions towards the 2e MOs, the HOMO has a significantly greater dinitrogen p-orbital character than the d-orbital character of zirconium, which in turn suggests that the occupation of the HOMO would lead to a charge build up on the dinitrogen ligand. The le and 2e MOs are occupied by eight electrons, four of which are from the dinitrogen and the remainder from the metal orbitals where each metal formally contributes  *  it *  The 2 (NH fragment deviates from being ideally isolobal to the (C5Me5)2WMe 3 CpZr(PH ) 3 fragment due to the interactions of the amide lone pair with the metal d-orbital. Both fragments belong to point group. Since these two MOs have different energy they are not strictly le MOs. They are comparable to le MOs only on  the basis of the number of nodes and the type of interactions between the metal and N . Similar reasoning is 2 adopted for the 2e, 3e and 4e MOs. references on page 212  Chapter II  62  two electrons. The unoccupied 3e MOs (LUMO+2, 0.602 eV and LUMO+4, 1.392 eV) are mainly metal d-orbital in character, i.e., these MOs can be considered as virtual non-bonding orbitals. In principle therefore, addition of electrons into the 3e MOs (i.e., further reduction of 2.9, e.g., electrochemical reduction) is unlikely to lead to any significant activation of dinitrogen. The values for the Wiberg 82 indices 8 4 (Table 2.12) clearly show a weak nitrogennitrogen bond in A; by comparison, the calculated bond indices of diazenido (N2) - and 2 hydrazido (N - ligands give rise to bond orders of 2 and 1, respectively. 4 ) 2 86 Therefore the ’ 85 calculated bond order of 1.15 for the nitrogen-nitrogen bond in A, agrees well with the formalism of the dinitrogen ligand as a hydrazido (N2) 4 ligand and is also in line with the resonance Raman data where the observed nitrogen-nitrogen stretch for the end-on derivative 2.9 was approximately 100 cm 1 higher than that of hydrazine. Also the calculated bond order of 2.18 for the zirconium-nitrogen bond of the Zr2N2 core supports the formulation of the Zr2N2 core as a Zr=N—N=Zr unit. The population analysis shows a net donation of 0.22 electrons from the dinitrogen lone pairs (on the basis of a decrease of electron density of the nitrogen s  and Px orbitals). It also shows a net gain of 0.61 electrons into the 1*orbitals The calculated total charge on the dinitrogen ligand is -0.76 (-0.38x2).  Table 2.12 Bond indices and population analysis of model complex A. Wiberg Bond Index Bond  Index  Mullilcen Orbital Populations of N 2 per nitrogen Orbital  2 complex N  free N 2  (N—N  =  l.096A)  Zr—N (N ) 2  2.18  s  1.684  1.906  Zr—N (arnide)  1.00  Px  1.086  1.096  N—N  1.15  P,,  1.276  1.000  Zr—P  0.63  P  1.333  1.000  references on page 2i  Chapter II  63  2.7.3 Bonding in Side-On Complexes Due to the lack of experimental evidence for side-on bound dinitrogen complexes, only a few publications have addressed the issue of bonding in these complexes. Theoretical studies on some mononuclear dinitrogen complexes have shown that the nitrogen-nitrogen bond is weakened (i.e., on the basis of longer nitrogen-nitrogen distances) to a greater extent in the side-on mode of coordination as compared to the end-on 76 mode. 8 ’ 7 For example, the simple interaction of a CH 2 fragment with dinitrogen in an end-on (diazomethane) fashion versus the corresponding side-on form (diazirine) showed a greater weakening of the dinitrogen bond in the latter case. 87  Also, calculations done on model complexes [Ru(NH 2 ( 5 ) 3 N2)] and  2 ( ) 3 [CoH(PH ) N ] indicate that the metal nitrogen bond strengths are stronger for side-on cases, whereas the nitrogen-nitrogen bond strengths (i.e., calculated bond energies) were greater for the end-on cases. It has been suggested 87 that the paucity of side-on complexes may be attributed to the overwhelming destabilization of the nitrogen-nitrogen bond upon complexation which in turn is not stabilized adequately by the formation of the metal-nitrogen bond. In the case of the model complex ) (N 2 ) 3 [Ni(PH ] the SCF binding energies are calculated to be -15.1 kcal mol 1 and -12.6 kcal mo1 1 for side-on and end-on cases respectively, favoring the side-on mode. It was also shown that the nitrogen-nitrogen bond was more elongated in the side-on case and also the negative charge on the nitrogens of the dinitrogen ligand was greater (0.30 electrons for side-on versus 0.02 electrons for end-on), implying increased ic-backdonation for the former. 76 Conversely, calculations done on a different nickel complex, 2 [Ni(02)(N ) J showed that the end on mode of coordination is favored. 88 Hoffmann et a!. have performed MO calculations on dinuclear complexes containing side-on bound dinitrogen unit where the 2 M—N -M core adopts a bent geometry (Figure 2.12). They considered the cobalt complex C as a possibility and the nickel complex D as a model for example 1.10 (Chapter 1).89  The two important It-acceptor interactions of the bridging  dinitrogen are shown in Figure 2.12. The in-phase and out-of-phase combinations of the fragment orbitals overlap with the two 7t*orbita1s to give two It MOs, bi and a. Also, the references on page fl  Chapter II  64  EH-MO calculations on C and D gave a substantial energy separation (3 eV) between the HOMO and LUMO for the side-on mode, whereas similar energy separation for the parallel end-on case E was only 0.02 eV. These energy values clearly indicate higher thermodynamic and kinetic stability for the side-on modes. 89  it-MO b 1  Ni.  C  it-MO a 2  D  H  OC ,N=N\ /CO .Co Co.,  V”co  oc”J OC  E  CO  Figure 2.12 Bonding scheme (in the box) describes the edge-on bridging dinitrogen complexes of Co and Ni.  2.7.4 Bonding in ) P {[(Pr’ S N ( 2 }ZrCI} ii-N 1Me CH  P 3 H  F  I f  H P— Zr—R H H’ GH  H  Using the INDO 1/MO level, semi-empirical calculations were performed on this side-on complex using the idealized form ) P 3 {(H ( N ( 2 .t-N )ZrCl1 H , ) F, with an imposed C2h symmetry. 6 ’ 45 2 The fragment MO analysis was carried out on the species N P 3 [(H ( 2 )ZrC1], H ) G, with an imposed C symmetry. 62 In these models, the relative spatial arrangement of the ’ 45 atoms directly bonded to zirconium was kept very close to what was observed in the X-ray references on page fl  Chapter II  65  8 The isopropyl substituents are important in view of their steric contribution but in a structure. semi-empirical level of calculations they are unlikely to have a significant influence in the electronic properties associated with the metal. The SiMe 2 groups associated with the amide were also replaced with hydrogens, and a comparison of the theoretical electronic data for F and the silyl substituted analogue, ) P {(H [ S 3 N ( 2 j.t-N )]ZrC1} (H i) ) gave identical results. The fragment orbitals la” and 2a” of G have the appropriate symmetry to form a it-MO and a s-MO, respectively. The frontier orbital la’ has 84% d-character (55%, d 22 ; 23%, d 2 and 6%, d) and 2a” has 80% d-character (38%, d,,; 25%,  and 16%, d). In the case of G,  due to the extensive mixing of the d-orbitals the frontier orbitals la” and 2a” will be referred to as virtual-d, and virtual-d orbitals* respectively (Table 2.13).  Table 2.13 Some orbital parameters of it and Molecular orbital HOMO  ()  Energy (eV)  -6.937  MOs of complex F.  Zr d-orbital contribution per metal  p-orbital contribution N2  12%  34%  per nitrogen  (Px HOMO-9  (it)  -10.329  20%  12 % 4 . ;pz= 15%) 27%  21 % 7 . 5 (Pz= %) ;Py  From a symmetry point of view the acceptor interactions of the dinitrogen 7c*orbitals with the metal in the side-on case F differ considerably from that of the end-on model A. In F the 7c*orbitals in the plane of Zr N core overlap with a virtual d-orbita1, which is also 2 contained in the same plane to give a ic-MO (Figure 2.13). This MO has 27% zirconium-d and 20% dinitrogen-p character, which is similar to the orbital contributions calculated for the HOMO-1 of the model complex A (Table 2.13). But, an important difference is that the it-MO of F is much lower in energy than the it-MOs of A. This is probably due to the fact that the dinitrogen it*orbitals overlap better with the metal d-orbitals in the side-on mode than in the *  These frontier orbitals are referred to as virtual orbitals because they are assigned according to the adopted coordinate system and not on the basis of which atomic orbital contributes the most. references on page  Chapter II  66  end-on mode. By comparison, the overlap values calculated for the t-type interaction between the 7t*orbital of dinitrogen and titanium d-orbitals give a value of 0.227 for the side-on bonding  and 0.155 for the end-on bonding. ° 9 The out of plane 1t*orbitals of the dinitrogen in F overlap with a virtual d-orbital, which is contained in a parallel plane to form a 6-MO (Figure 2.13). This MO has 12% zirconium-d and 34% nitrogen-p character and suggests that there is considerable ionic character with electron density mainly located on the nitrogens of the dinitrogen ligand. A survey of the low lying LUMOs of F (up to LUMO+5) showed that they are mainly non-bonding metal-based orbitals.  Figure 2.13 Bonding scheme illustrating the types of overlap leading to the formation of the  it-MO and the 6-MO.  references on page ii2  Chapter II  67  The large energy gap (6.4 eV) between the HOMO and LUMO is consistent with the observed stability of this complex. When the hypothetica:1 end-on complex* having identical ligand arrangements around the zirconium core, as that of F, was subjected to INDO/1-MO analysis the HOMO-LUMO gap (6.3 eV) was found to be very close to the gap for F. Therefore, an analysis on the basis of HOMO-LUMO gap does not favor the side-on mode over 89 However, the SCF energy value does favor the side-on case F, by greater than the end-on. 1 eV.  -103.15  -103.35  -103.55  -103.75  -103.95  -104.15  -104.35  0  20  40  60  80  Angle of rotation (°) Figure 2.14 Plot showing the change of energy in the model complex F with the rotation of the  dinitrogen ligand.  To evaluate the barrier for the conversion of the side-on complex to the end-on complex, the dinitrogen ligand was rotated in a stepwise manner on the plane of the Zr N core 2 until the dinitrogen ligand became coordinated end-on. The angle of rotation 9 is depicted in *  The Zr N core of F was changed to a linear end-on mode, Zr—N—N—Zr; Zr—N = 1.92 A, N—N = 1 .30A. Bond 2 length parameters of the ligands were kept identical to F. references on page  68  Chapter II  Figure 2.14 where it was increased from 0° to 90°. During rotation the closest distances between a zirconium center and a nitrogen of the dinitrogen ligand were kept constant. The curve obtained from the plot of e vs. energy (at the SCF level) suggests that the barrier for the rotation from an end-on to side-on coordination is greater than 1 eV.  More importantly, from a  thermodynamic viewpoint the shape of the curve suggests that this particular end-on complex should spontaneously convert to the side-on complex. It is of interest to point out that ab initio calculations done on naked dinuclear side-on dinitrogen complexes of the type 2 : M2(t-i1 N2), fl where M  =  Ti, Zr and Y, suggested that zirconium and yttrium favor a side-on bound dinitrogen  ligand. The calculated nitrogen-nitrogen bond distances for the ligand-free zirconium case (Zr2N2) was 1.48  A, which was only 0.07 A  shorter than the experimental value 1.55  A found  for complex 2.2. 1 In the model F, the calculated value of 0.85 (Table 2.14) for the nitrogen-nitrogen bond order, is less than the value of 1.15 found for the end-on case A, and this corroborates well with the resonance Raman data of complex 2.2, where the observed nitrogen-nitrogen stretching frequency was approximately 300 cm 4 lower than that of hydrazine. But, comparison with the observed differences in the nitrogen-nitrogen bond lengths of end-on and side-on complexes (e.g., 2.2 versus 2.9) the differences in bond indices are not significant. By the definition of bond order, i.e., the net bonding electrons are equal to twice the value of bond order, in going from models A to F the number of bonding electrons associated with the dinitrogen ligand have decreased by 0.6. This would imply greater backbonding in the side-on complexes and is consistent with other theoretical studies done on side-on complexes. The overall bond order between the dinitrogen and zirconium in the side-on case was found to be 2.38 (2x1.19), and suggests stronger metal dinitrogen interactions than in the end-on case. The calculated bond order between the amide nitrogen and zirconium was found to be greater than 1, implying significant  t  interactions. The significance of this interaction will be discussed later.  references on page 212  Chapter II  69  Table 2.14 Bond indices and population analysis of model complex F. Wiberg Bond Index Bond  Mulliken Orbital Populations of N 2 per nitrogen  Index  Orbital  N2 complex  free N 2 (N-N  =  1.548  Zr—N (N ) 2  1.19  s  1.845  1.937  Zr—N (amide)  1.13  Px  1.152  1.063  N—N  0.85  P,,  1.284  1.000  Zr—P  0.61  Pz  1.260  1.000  A)  Population analysis of F shows only a small decrease in the s-orbital population of dinitrogen, but the populations of all the p-orbitals have been increased. The calculated formal charge of -1.08 on the dinitrogen ligand is significantly higher than what was found for the end-on species A (-0.76). It is possible that the increased coulombic repulsion (due to the higher charge) between the two nitrogens of the dinitrogen ligand and weak bonding interactions (on the basis of Wiberg indices) are important factors contributing to the long nitrogen-nitrogen distances observed in the side-on complex 2.2. With regard to this coulombic repulsion, the changes in nitrogen-nitrogen bond lengths in neutral hydrazine and its protonated derivatives are important. The observed nitrogen-nitrogen bond length decreases consistently upon successive protonation of hydrazine, i.e., the nitrogen-nitrogen bond lengths for H4N2, 5 (H N 2)Br, and 4 ) 2 N 6 (H S0 are 1.47  A,  1.45  A and  1.40  A respectively.  This decrease in bond length has been  attributed to the removal of the highly repulsive lone-pair interactions by protonation. 69  [(Pr P S N ( ) ]Zr(OAr*)} LN iMe CH i 2.7.5 Bonding in { 2 Using the INDO 1/MO level, semi-empirical calculations were performed on this side-on complex using the idealized form N P 3 ((H ( 2 )Zr(OH) H ) }2(.t-N2), H, with an imposed C 2 symmetry. The relative positions of the ligands around each zirconium are within actual parameters found in the solid state structure.  10  of the  When model H was subjected to  INDO/l-MO analysis, the MOs changed considerably from those found for F.  Most  references on page fl  Chapter II  70  importantly, the it-MO associated with the dinitrogen ligand was split into two separate MOs, which also showed some d-p type interactions with the lone-pairs of the oxygen. To evaluate the cause of this change the model J was constructed as follows: the bent core of model H was made planar and one zirconium was rotated by 1800 with respect to the other and then the OH groups were replaced by chloride (Zr—Cl  =  2.5A). Model J now mimics model F and they differ  only in their angle parameters associated with the zirconium and the ancillary ligands. H H H  2.5A  H  \  3 PH  \  Step 1  PHa 3 /..PH Zr__NZr  Replacement of ClwithOH  P 3 H  J  H  I-I Bending of the N core 2 Step 4  H  H \ H  P 3 H 3 PH  H  / 0  -  K  N/ P 3 H  \ H  Step 2 Adjustment of Zr—O bond to 2.02A  0  3 P 0 H  o’  N..., H  H H  3 PH \:  H  Step 3  N H  /  N..,  3 PH  H  Rotation of one Zrcenterby 180°  M  N.., H  L Scheme 2.9  Then model J was changed to model H in a stepwise manner, as described in Scheme 2.9; in each case the MOs were compared to the previous case. The results of this step-wise analysis are shown in Table 2.15. The SCF-energy values of the models J and K were within  references  on page 222  Chapter II  71  0.02 eV, and the bonding interactions associated with the dinitrogen ligand, i.e., the it and the MOs were similar to F.  Table 2.15 SCF energy values and the energies of some MOs of models H, J, K, L, M and F. Model  Energy (SCF)  s-MO  it-MO  J  -104.070 eV  -6.830 eV (HOMO)  -10.229 eV (HOMO-9)  K  -104.046 eV  -6.640 eV (HOMO)  -10.049 eV (HOMO-7)  L  -104.597 eV  -5.924  eV (HOMO)  -9.213 eV (HOMO-3) -11.070 eV (HOMO-8)  M  -104.597 eV  -5.930 eV (HOMO)  -9.190 eV (HOMO-3) -11.001 eV (HOMO-9)  H  -104.616 eV  -6.093 eV (HOMO)  -9.019 eV (HOMO-3) -11.041 eV (HOMO-9)  F  -104.306 eV  -6.937 eV (HOMO)  -10.329 eV (HOMO-9)  The shortening of the zirconium-oxygen bond of K gave model L, which was stabilized by 0.6 eV than models J and K. Analyzing the contours of the MOs corresponding to L shows that the zirconium-dinitrogen bonding had significantly changed. The it-MO has been split into two separate MOs and their contours suggest a d-p type interaction between the zirconium orbitals and the oxygen lone-pair orbitals. These interactions are depicted in Figure 2.15, which also qualitatively explain the relative contributions of different AOs to each MOs (also see Table 2.16). The lower energy it-MO was largely oxygen p-orbital in character with a bonding interaction with the metal orbital. The higher energy it-MO was mainly a metal dinitrogen bonding interaction with antibonding character between the metal and oxygen orbitals. Further modifications from L to H do not seem to cause any major changes in the type of overlaps or in the total energies of the models. references on page  Chapter II  72  N 2 H  P 3 H  P 3 H  HOMO-3 P 3 H  P 3 H  P 3 H  P 3 H  Oxygen 2p-orbital HOMO-8 H N 2 ,  P 3 H  Figure 2.15 Splitting of the it-MO in complex H.  Table 2.16 Some orbital parameters of model H. Molecular  Energy (eV)  orbital  HOMO (6)  -6.098  Zr d-orbital  2 p-orbital N  0 p-orbital  contribution per metal  contribution per  contribution per  nitrogen  oxygen  9%  36% (Px  =  21%;  <  1%  Py= 14%) HOMO-3  (it)  -9.018  17%  HOMO-9  (it)  -11.041  5%  22% (Py  =  3%  18%)  4% 31% (Pz = 23%; Px % 8 )  references on page  Chapter II  73  The metal and dinitrogen orbital contributions of HOMO and HOMO-3 are similar  to  that in model F (Table 2.17). Comparison of bond orders associated with similar bonds of models F and H show that the zirconium-amide bond and the zirconium-phosphine bonds are slightly weaker in H than in F.* A bond order of 1.16 between the zirconium-oxygen bond, comparable to the bond orders between the zirconium and nitrogens of the dinitrogen ligand, confirms the presence of p-d bonding, which was previously suggested on the basis of structural features. The bond indices associated with the 2 Zr N 2 core are also comparable to model F. For H, the indices indicate a weakening of the zirconium-aniide bond compared to the same indices of model F. This could probably be due to the increased  it  interactions of the  oxygen lone pairs since the bond order between the zirconium and oxygen was greater than one.  Table 2.17  Wiberg bond indices and Mullilcen orbital populations of model H.  Wiberg Bond Index  Bond  Index  Mulliken Orbital Populations of N2 per nitrogen  Orbital  N2 Complex  free N2  (N-N  =  1.548  Zr—N(N2)  1.17  s  1.85  1.937  Zr—N (NH ) 2  1.07  Px  1.25  1.063  N—N  0.87  Py  1.22  1.000  Zi—P  0.55  Pz  1.23  1.000  Zr—O  1.16  A)  Alkaline salts of chloride and hydroxide ions were analyzed to estimate the relative energies of the lone-pair electrons of the anions. It was assumed that in these alkaline salts there would be  no it-type interactions,  and therefore this enables the estimation of the energies of the  lone-pairs. Calculations suggest that the oxygen lone-pairs are relatively lower in energy than those on the chloride. Comparison of these energies with the it-MO of F shows that the oxygen  *  The ZINDO output files gives the values of Mulliken populations and Wiberg bond indices to six significant figures. references on page fl  Chapter II  74  lone pairs are the closest in energy (Table 18). The calculated it overlap values for F were also greater for oxygen p-orbitals than those of the chloride porbitals*  .  These factors are likely to  contribute towards the mixing of the it-MO with the oxygen lone pair resulting in the formation of two it-MOs. When the hydroxyl ligand of model L was replaced with a chloride ligand without altering the zirconium-chloride distance (2.02  A), analysis gave almost identical results  to those obtained for L. This could be explained on the basis of the lowering of the energy of the chloride lone pair (with the shortening of distances) and also increasing the overlap with the d-orbitals.  Table 2.18 A comparison of the energies of the lone pair electrons of Cl, 2 NH and OH ions. Salt  Distance  Lone pair  Salt  Distance  Energy (eV)  Lone pair Energy (eV)  2 LiNH  2.20 A  -7.789  LiC1  2.50  A  -8.548  LiOH  2.02 A  -9.344  NaCl  2.50  A  -8.793  LiC1  2.02 A  -9.002  NaOH  2.02  A  -9.391  The angular overlap model 92 suggests that the frontier orbital requirements for a side-on bound dinitrogen ligand with a bent core can be different from those of a planar core. With reference to the planar case depicted in Figure 2.16, the frontier orbitals shown can only overlap with one 7t*orbital of the dinitrogen, which is also contained on the same plane, whereas the other 7c*orbital of dinitrogen is perpendicular to the plane and will require a different metal based orbital for bonding, for example see the bonding scheme for the planar side-on model F depicted in Figure 2.13. It is also important to note in Figure 2.13, that each set of frontier orbitals (i.e., the set corresponding to the it-MO and the set corresponding to the ö-MO), can have a symmetric and an anti-symmetric combination, of which only the anti-symmetric combination is involved in bonding. In the absence of bonding, i.e., in the absence of a *  Calculated overlap integerals for Zr—Cl, 2.50 A; Zr—Cl, 2.02 A and Zr—OH, 2.02 A are 0.087,0.192 and 0.110  respectivly.  referenced on page  Chapter II  75  dinitrogen ligand in between the two metal centers, these two combinations corresponding to each set will be degenerate (i.e., in Figure 2.13). In fact, during the MO analysis of models F and M the symmetric combinations were found to be non-bonding, because they do not have a suitable dinitrogen based orbital for bonding.  Anti-symmetric combination of the frontier orbitals N 2 H  Symmetric combination of the frontier orbitals  Planar core  NH  Bonding interactions with N 2  Non-bonding interactions with N 2  Bending Anti-symmetric combination of the frontier orbitals  core N 2 of,ll,Zr  Symmetric combination of the frontier orbitals  i 2 H N 2 H H P 3 ’  > 4 N  2 NH  H3Pfl.:...11PH3  H P 3 ’  Bonding interactions with N 2  Open three centre bond  Bonding interactions with N 2  I  L  I  j  Figure 2.16 The angular overlap for the side-on bonded dinitrogen with a bent Zr N core. 2  references on page 112  Chapter II  76  Figure 2.16 illustrates the bonding of a side-on bound dinitrogen ligand where the Zr2N2 core is bent. It can be seen that the bonding in this case can be rationalized by using only one set of frontier orbitals, where both, the symmetric and anti symmetric combinations are used in bonding with the dinitrogen ligand. 89 The interaction of the anti-symmetric combination (i.e., in the bent mode shown on the right) with the dinitrogen *orbita.l is comparable to an open three-center bond whereas the interaction of the symmetric combination is comparable to a closed three-center bond. To evaluate this hypothesis the model M was bent in a step-wise manner using the nitrogen-nitrogen bond as a hinge. To perform this calculation, a phantom atom X was placed in the middle of nitrogen-nitrogen bond and the bend angle was measured by taking the Zr—X— Zr angle,  e.  Calculations were done for different models which were constructed by decreasing  the Zr—X—Zr angles by approximately 5° from that of the planar case M (i.e., decreased from 180°), and for each case the SCF energy and the contours of 13 HOMOs (from HOMO to HOMO-12) were analyzed. The contours of the models with values of 0 greater than 150° show the involvement of two different frontier orbitals (i.e., similar to the bonding described for model H) with the 7u*orbitals of dinitrogen. These interactions are shown in Figure 2.17. It is important to note that the &-interaction is weakened above the Zr2N 2 core and is strengthen below the core. For smaller values 0, i.e., less than 120°, the contours seem to suggest the involvement of only one frontier orbital (i.e., from each metal) as described in Figure 2.16. Because of extensive mixing of atomic orbitals during the ZINDO/1-MO analysis a more definite evaluation was not possible. N 2 H 3 PH  HO  HO  OH  Figure 2.17 The orbital interactions for a bent Zr2N2 core of complex 2.12 where the bend angles are greater than 150°,  references on page  Chapter II  77  The change in the SCF energy values of the models with different values of 8 is shown in Figure 2.18. The curve suggests that the bending of the planar Zr2N2 core, even by a small angle (5°) increases the energy of the model by approximately 0.1 eV, but upon further bending the energies of the model decreases. The energies become comparable to the planar model H when the core is bent by about 135°. In fact, the shape of the curve suggests that continued bending produces even more stable geometries, although presumably steric factors will become dominant as the angle decreases.  -104.65  5:’  I -104.75  -104.85  •  115  135  Bending Angle  155  175  9 (°)  Figure 2.18 The change in SCF energy with respect to the bending of the Zr N core of model 2 M. The core was bent along the nitrogen-nitrogen axis.  2.7.6 Factors Influencing the Side-On Mode of Coordination On the basis of the discussion presented on dinuclear dinitrogen complexes in Chapter 1 it is clear that the precedence for the formation of end-on bonded complexes is overwhelming. references on page 112  Chapter II  78  The bonding description that has been presented so far has been mainly concerned with the analysis of the MOs of complexes 2.2, 2.9 and 2.12 and how they relate to their structural features. So far no attempts have been made to address the question that why complexes 2.2  and 2.12 did not form the end-on complexes, despite the overwhelming experimental evidence for their formation.  3e :.  lt*  •  lt*  LM L M 4  d  \  2 N END-ON  •.,  :  d, d  N 2 SIDE-ON  1ti  7tp  :.  /  •  2t  ‘flif  o It  2 d  Figure 2.19 Bonding scheme illustrating the symmetry based orbital requirements for the  dinitrogen binding in bridging side-on and end-on modes involving ML 4 fragments.  In an attempt to evaluate the electronic factors which favored the formation of side-on complex 2.2 a simple, back of the envelope type MO analysis was considered (Figure 2.19). During analysis two ML 4 fragments having C4v symmetry, were arranged to satisfy an overall references on page hf  Chapter II  79  D4h symmetry, with ligands pointing away from the center of metal-metal axis (Figure 2.19). The metal-centers were separated by sufficient distance, such that a dinitrogen ligand could be inserted in an end-on or side-on manner. The d - and d 2 2 orbitals which point toward the ligands are used for a-bonding with ligands L of ML 4 and also with the clinitrogen. The remaining three d-orbitals, the  and  pointing in between the ligands, are available for bonding. ° Since it is already established 8 that the  it  acceptor interactions of dinitrogen are the most crucial, only the bonding of  it*orbitals of dinitrogen with the metal d-orbitals are 79 considered. 9 ’ 0 Simple analysis shows that the end-on mode results in the formation of two degenerate it-MOs which correspond to the 2e MOs described previously (Figure 2.10). In the side-on mode the dinitrogen 1t*orbital in the plane of 2 M—N — M will form a it-MO; however, the it*orbital perpendicular to the plane will form the S-MO, with the it-MO is placed lower in energy. 90 Although this relative positioning of the MOs agree with the conventional wisdom that it-orbitals are more stable than 5-orbitals, a comparison of the it-MOs of the end-on case, A and the side-on case, F show that the it-MO of side-on is much lower in energy. A rationale for the formation of lower energy it-MOs in the side-on case is that the respective overlaps of the AOs leading to the formation of the it-MO is greater for the side-on mode than that of the end-on mode. By comparison, the overlap values calculated for the interaction of naked titanium metal with dinitrogen ligand are 0.227 and 0.155 for side-on and end-on cases respectively. 90 In the two analyses described in Figure 2.19 only two of the three available d-orbitals are used in bonding. In the end-on case the two dy-orbitals and in the side-on case the two d,-orbitals are non-bonding. Therefore, any it-type interactions with one of these three metal d-orbitals with an appropriate ligand orbital (excluding the dinitrogen hg and) will leave only two d-orbitals available for bonding with the 1t*orbital of dinitrogen. In the case where the orbital is not available then only the end-on complex can be formed. If the  or  orbital is  not available then the result would be the formation of a side-on complex. When the HOMOs of F were carefully analyzed at the INDO 1/MO level, the orbital HOMO-8 (Figure 2.20) was intriguing in that one of the d-orbitals on the metal was involved in references  on page fl  Chapter II  80  it-bonding with the aniide lone pair and a-bonding with the chloride ligand. Principally, this is one of the non-bonding d-orbitals described in Figure 2.19, which according to the symmetry based analysis can only form a it-MO. Therefore, due to the formation of HOMO-8 the remaining d-orbitals can only form one it-MO and one s-MO resulting in the formation of the side-on complex. In the model complex H the d-orbital that is required for the second it-MO was it-bonded to oxygen and a-bonded to the amide.  0 3 PH  P 3 H  3 PH  H P 3 g:i N $:d PH 3  HsPNJ  Y  HH  H  HOMO-8 in F  3 PH 4’H H  HOMO-12 in H  Figure 2.20 Important it-type interactions that determine the type of dinitrogen bonding in model complexes F and H.  To vindicate this claim the MOs of the fragment G and those of the fragment N, obtained by rotating the plane of the amide by 90°, were analyzed. In Figure 2.21 the fragment MOs corresponding to G (on the left) and those of N (on the right) are arranged such that their energies decrease in going from top to bottom. For both cases the set of orbitals la” and 2a” will favor the side-on mode and the set la” and la’ will favor the end-on mode of bonding. The calculated energy for the Ia’ orbital of G was found to be much higher (37 kJ moll) than the nearest orbital 2a”. The la orbital of G is raised in energy partly due to the amide d-p interactions and also due to the  interactions with the chloride ligand. Therefore, on the basis  of symmetry the available orbitals that will lead to the side-on complex are la” and 2a”. When the plane of the amide in model G was rotated by 90°, the model N was obtained. Calculations on model N show that, due to the removal of the d-p interactions, the orbital la’ was lowered in energy. Also, due to the newly imposed d-p interactions, the frontier orbital 2a” is raised in energy. It was found that orbitals la’ and 2a” were only separated by 0.5 kJ references on page fl  Chapter II  81  . Therefore la’ can form two sets of orbitals (i.e., la and la” or la’ and 2att) which are 1 mo1 energetically similar, where each set will lead to different mode of bonding. The case leading to the end-on mode will generate two it-MOs, while the other will generate a t-MO and a 6-MO, where the formation of two t-MOs will be energetically more favorable. Therefore in theory the fragment N should lead to an end-on complex.  H  H  cv4 H  G  N  1 a’  2 NH  1 a’  2 a” 1 a” NH  Ci P  fr 2 a” 1 a”  ci—1Y  2 NH  P  Figure 2.21 The frontier orbitals of the fragments G and N arranged in increasing order of their energy  Support for this analysis can be found in two recent X-ray structures of related isoelectronic dinuclear titanium dinitrogen complexes, shown in 2.27 and 2.28, both of which display the bridging end-on 57 mode. 5 ’ 8 In 2.27, having cis disposed neutral amine donors rather than trans disposed phosphine ligands, the major difference is that the bis(trimethylsilyl)amide ancillary ligand is arranged perpendicular to the plane defined by the donor atoms; this is also found in 2.28 but now the neutral pyridine donors are trans disposed. Both of these complexes are similar to that proposed in model conformer N and their structures are a reasonable consequence of the fact that both 2.27 and 2.28 have no conformational restrictions to force the  references on page fl  82  Chapter II  amide ligand to bond in a manner as is found in the chelating amido-diphosphine ligand of the side-on derivative 2.2. 3 SiMe Me S 3 i/  CI I’py  Me S 3 i../  N :-=-  N 2 Me  2 /NMe 11NN11 3 \N—SiMe N’’7 2 Me Si 3 Me 2 NMe  2.27  N  CI  N....SiM Me S 3 i 2.28  This rationale could be also extended to explain the formation of the end-on complex 2.9. The replacement of the chloride ligand of 2.2 by a cyclopentadienyl group has altered the available d-orbitals for dinitrogen bonding. Analysis of the molecular orbitals of the fragment B shows that the d-orbital that would be used to generate the 6-molecular orbital for a side-on dinitrogen fragment overlaps with the ic-orbitals of the cyclopentadienyl ligand. Also an important structural feature that correlates well with the electronic description is the zirconium amide bond distances. Since the fragment orbital that has the correct symmetry to overlap with the amide p-orbital is involved in it-bonding with the dinitrogen ligand, one would expect a long zirconium amide bond length (see section 2.2.2). It is noteworthy that in the solid-state structure, the NSi2 plane in the tridentate ligand is twisted with respect to the plane of the three donors (NP ) and this would be expected to further minimize overlap between the lone pair on 2 the amide and the d orbital. references on page fl  Chapter II  83  2.7.7 Bonding in the Samarium and Lithium Dinitrogen Complexes The dinuclear samarium and lithium dinitrogen complexes discussed in Chapter 1 have a very weak, side-on bound dinitrogen 93 ligand. 9 ’ 4 This is in stark contrast to the side-on dinitrogen complexes of zirconium where the dinitrogen ligand is highly activated and is strongly bound to the metal. For comparative reasons some suggestions can be made with regard to the weak bonding interactions of the samarium complex, 1.12, and the lithium derivative, 1.13. To understand the origin of molecular interactions in electron donor-acceptor complexes N—*BH 3 H (e.g., ) , the total interaction energy of these complexes can be decomposed into five components; electrostatic (ES), polarization (PL), exchange repulsion (EX), charge transfer (CT) and coupling (MIX). 95 This ab initio SCF method has been extended to the donoracceptor interactions of a dinitrogen ligand with a transition metal, for example, in the complex 2 ( 5 ) 3 [Ru(NH N2)] having the dinitrogen end-on, the calculated energy for the metal dinitrogen interaction was -15.52 eV of which -0.68 eV has been attributed to the ES interaction, whereas for the side-on mode of bonding, the calculated energy for the metal dinitrogen bond was -18.64 eV of which -1.15 eV has been atthbuted to the ES 87 interaction. 8 ’ 8 It is therefore possible that in the samarium and lithium complexes 1.12 and 1.13 the primary interaction between the dinitrogen and the metals is wealdy electrostatic in nature. On the basis of this assumption, the bonding in these complexes can be compared to the bonding in dilithioacetylide, Li C where the interactions between the lithium and the acetylide are ionic in 2 nature. X-ray structure analysis and theoretical studies done on dilithioacetylide have shown that the favored mode of coordination is side-on: ’ 29 : Li2(J.t-T 2 ° 3 C2). 1 Therefore, in complexes 1.12 and 1.13 if the metal dinitrogen interactions are mainly ionic in nature the favored mode of dinitrogen coordination could be side-on. However, it is important to note that the mode of dinitrogen coordination in the solution state has not been determined for these complexes. Also, in the case of the lithium complex it has been suggested that the solid state structure could be attributed to solid state effects. 94  references on page fl  Chapter II  84  2.8 Reactions 2.8.1 Conversion of the Side-On Complex to the End-On Complex When the side-on complex 2.2 was reacted with NaCp•DME in THF the deep blue colour of the solution changed to give a deep brown solution over a period of 1 week. The 1 H and 31 P{ 1 H} NMR spectra of the final product showed only the presence of the end-on derivative 2.9 (Equation 2.2). Monitoring the reaction shown in Equation 22 by NMR spectroscopy showed only the depletion of the side-on complex 2.2, and concomitant formation of the end-on derivative, 2.9.  This seems to suggest that the mono cyclopentadienyl  intermediate formed by the metathesis of only one zirconium-chloride bond of 2.2 is rapidly converted to the bis cyclopentadienyl derivative 2.9.  NaCp’DME 2.2  2.9  2.2 NaCpDME (PNP)CpZr  15  15  15  N— N= ZrCp(PNP)  15  (PNP)CpZr= N— N  ZrC1(PNP)  2.22a  2.9  II  Rapid Isomerization  I 1:  NaCp•DME (PNP)C1ZrjZrCl(PNP) 2.22  2.2  “(PNP)CpZr”  *  “ZrC1(PNP)(N ) 2 ”  Scheme 2.10  references on page 112  Chapter II  85  One possible mechanistic proposal for the reaction shown in Equation 2.2 is given in Scheme 2.10. The elusive mono cyclopentadienyl intermediate, { [(Pr2PCH2SiMe2)2N] Zr} 2) 2.22, could dissociate into mononuclear zirconium species and then recombine to 2 ClCp(i-N form complexes 2.2 and 2.9  In accordance with this postulate, before or during the  recombination of the monomers the coordinated dinitrogen may be exchanged with free dinitrogen from the surroundings.  Control reaction under Ar  Reaction under 4 ‘ N 2 1E83  1126  1075  1125  I  1126  1175  1110  1125  II  Figure 2.22 I The parent ion peaks of the 15 N2 analogue of 2.9. II Parent ion peaks of 2.9 formed from the reaction of 15 2 analogue of 2.2 with NaCp•DME under an N atmosphere of 4 ‘ N 2.  Aforementioned hypothesis was tested by performing the reaction with the nitrogen-15 labelled material of 2.2, under an atmosphere of normal dinitrogen 4 (‘ N 2). When the product of this reaction was analyzed by mass spectroscopy, the relative intensities of the peaks associated with the parent ions were virtually identical to the parent ion peaks found for an authentic sample of the 15 2 analogue of complex 2.9 (Figure 2.22). This experiment suggests that there N references on page fl  Chapter II  86  is no exchange between the coordinated dinitrogen and the dinitrogen from the surroundings. Therefore, it is possible that the side-on bound dinitrogen ligand in the intermediate 2.22 rotates in an intramolecular fashion to give an end-on intermediate 2.22a (Scheme 2.10). Also, the endon isomer 2.22a is sterically less hindered than the side-on isomer, 2.22, and therefore kinetically more favored to react with the second equivalent of NaCp•DME to give complex 2.9.  2.8.2 Reaction of Side-On Complexes With LiBEt4 Earlier work in our laboratory has shown that in the case of the dinuclear palladium complex 2.23 the 2 (j.i-H) core interacts with a 4 Pd LiBEt unit, where the lithium ion is found sandwiched between the borate moiety and the Pd2(1.L-H)2 96 core. It is postulated that the interaction between the 2 Pd ( -H)2 core and the lithium cation is a Lewis acid, Lewis base type. By comparison, complex 2.2 has a planar Zr2N2 core, with considerable negative charge on the nitrogen atoms. Therefore reacting complex 2.2 and LiBEt 4 may lead to the synthesis of a complex that would resemble 2.23, for example a complex having a core similar to T. Furthermore, an X-ray structure elucidation of such an adduct of LiBEt4 could provide some experimental evidence for the suggestion that the very long nitrogen-nitrogen bond length of 2.2 is partly attributed to the higher charge densities on the nitrogens of the dinitrogen ligand.  [Li] It II  S  I I ‘  [Zr]  [Zr]  2 J 1 p  T  2 Pr  2.23  [Li] = LiEt B 4 [Zr] = 2 “ZrX[N(SiM C P ] ) Pr’ H e where X = Cl or OAr  Reacting the side-on derivative, 2.2 with LiBEt 4 in toluene over a period of 7 days gave a yellow solution. The 31 P{ 1 H} NMR spectrum of the yellow material had a spectral pattern references on page fl  Chapter II  87  which is consistent with an ABMX spin system (Figure 2.23). The P} 31 H 1 ( NMR spectrum  consists of 8* resonances in the SiMe 2 region, which implies that the complex is an unsymmetrical dimeric species. The resonance at 4.81 ppm is attributed to a hydride ligand. The multiplet at 0.03 ppm is probably an overlapping doublet of quartets with small coupling to phosphorus nuclei. This suggest that the peak at 0.03 ppm probably corresponds to one of the methylene protons of an ethyl ligand, and the other methylene proton is probably beneath the 2 resonances. The 15 SiMe N NMR spectrum has two doublets centered at 250.5 ppm and 185.9 ppm, with 2 JNN  =  12 Hz. The llB{ lH} NMR spectrum has a broad resonance** centered  around -41.6 ppm. On the basis of the aforementioned spectroscopic evidence the complex can be formulated as  P [(Pri S N ) ]ZrH} iMe CH { 2 P [(Pr S N ) ]ZrEt} iMe CH } (.t-N.BEt), {f 2  2.24. The reaction of LiBEt 4 with other side-on derivatives, 2.12, 2.20 and 2.21 also gave a yellow material which had identical spectral features to that of 2.24. This seems to suggest that during the reaction the zirconium-X bond, where X  =  Cl, Br or OAr*, undergoes a metathesis  reaction to give a diethyl intermediate, ) P]ZrEt}2(p.-N “{[(Pr N ) 2 CH2SiMe ” where one of the ethyl group undergoes a 3-hydride elimination reaction. Monitoring the reaction (inside a sealed NMR tube) by 1 H and 31 P{ 1 H} NMR spectroscopy failed to provide any useful information; however, the 1 H NMR spectrum showed the formation of ethylene. Also, the presence of free Et B in the 11 3 B{1 H } NMR suggests that only one of the BEt 3 is associated with the complex 2.24.  *  One of the methyl group of a SiMe2 seems to have shifted into the region where the isopropyl methyl resonances appear. By comparison with the 1 H and 31 H( NMR spectra the resonance at 0.95 ppm was assigned to one 1 P) methyl group of a SiMe 2 moiety. ** The broad resonances due to the glass of the NMR tube also appears from -20 to -140 ppm. The peak at -41.6 was found by subtracting the spectra due to the glass. references on page fl  Chapter II  88  96.2 MHz B{ 11 H 1 } NMR D  /  30.406 MHz 15 N NMR C  J II  do  ao  20  20  B  III  0  do  121.4 MHz P{ 31 H 1 } NMR  —  0  —40  —60  IiI —0 PP.+1Q0  111111 20  i0  III 15  IIj  I  10  liii!  PPM  0  500 MHz P} 31 H 1 { NMR A  2 ) 3 Si(CH iV  2 ) 3 Si(CH  [ZrJ_Jj  •  -I,  I  I  •iii  I  I  5  UI  111111  4  ] 2 ) 3 P[CH(CH  2  N  2.5 ppm  2.0  is  0.5  0.0  Figure 2.23 AThe500MHz P} 31 H 1 ( NMR;B 121.4 31 MHz H 1 P{ } NMR; C30.406 MHz N NMR and D 96.2 MHz 11 15 B(1 H} NMR spectra of the crude reaction mixture obtained from the reaction of 2.2 and LiBEt 4 in C . 8 D 7 references on page 1i  Chapter II  89  The 15 N NMR chemical shifts of the nitrogens of the dinitrogen ligand are centered around 250.5 and 185.9 ppm, which by comparison with the side-on complexes are shifted by more than a 100 ppm. Also, comparison of the chemical shifts of the two nitrogens, which are separated by 65 ppm, suggests that the BEt 3 is probably interacting with one of the nitrogens of the dinitrogen ligand. In the 31 P( 1 H} NMR spectrum the two high field singlet resonances are probably due to a PNP ligand that is facially coordinated*, whereas the two low field doublets are due to a meridionally coordinated PNP ligand where the observed coupling constant 2 A-B  =  72 Hz is comparable to other zirconium complexes containing a meridional PNP ligand.’ 5 The structure depicted as 2.24 seems to fit most of the NIVIR spectroscopic data. A structure involving an 2 -dinitrogen ligand, 2.24a with one of the nitrogens interacting with BEt 3 is also possible. The coordination around the dinitrogen ligand in 2.24a is comparable to the tetranuclear titanium dinitrogen complex 1.9. Although the complex 2.24 gave good crystals at -40 C, upon warming to room temperature they melted, which hampered attempts to obtain an X-ray structure. 2 Ph  2 Me  1 /—...p p N.... Se2  1  Me S 2 i  /c  Me S 2 iZ  2 Phi  L__ p”  \  SiM e 2 N_z  NH\ 2 SiMe  /  B 3 Et 2.24  2 pJ  2.24a  *  The chemical shift for uncoordinated phosphine is usually between -4.5 and -4.8 ppm. It is believed that facial coordination of the PNP ligand with isopropyl substituents is not sterically favored. However, it could approach facial coordination by lengthening the zirconium-phosphorus bond which would enable the bulky isopropyl substituents to be further away. Therefore, the P(1 31 H1 NIvIR chemical shifts of such phosphines are also likely to shift towards that of the uncoordinated phosphines. references on page ii  Chapter H  90  2.8.3 Protonation Reactions When a toluene solution of 2.9 was reacted with anhydrous HC1 gas 1 equivalent of hydrazine was produced. By comparison, the side-on derivative 2.2 also gave 1 equivalent of hydrazine under similar conditions. However, when the end-on derivative 2.9 was reacted with 1M 1 HC ( aq) or with water, approximately 0.8 equivalents of gas was produced, and a qualitative test of the aqueous solutions after the reaction showed the presence of hydrazine. Also, when 2.9 was decomposed with D 0 inside a NMR tube, the 1 2 H NMR spectrum showed the  formation of only a small amount of cyclopentadine (<2%), suggesting that the hydrolysis of the zirconium-Cp bonds is minimal during protonation in aqueous media.* The gaseous mixture probably consists mainly of dinitrogen and dihydrogen in approximately a 1:1 ratio. When complex 2.9 is decomposed to give dinitrogen it would also generate a zirconium(ll) species which, under aqueous conditions, is likely to reduce hydrogen ions to dihydrogen (Scheme 2.11). Therefore depending on the strength of the acid, complex 2.9 could either give only hydrazine, or a mixture of hydrazine, dinitrogen and dihydrogen.  [R2 NllZr=-N=[Zr][R2 N]  Reduced to Hydrazine 2 N] 2 N][Zrj=N—N=[Zr][R [R  O 3 H 2 N][Zr]=N—N=[Zr][R [R 2 N]  >  [R N][Zr]=N—N=[Zr][R 2 N] H  1 Dinitrogen  Dihydrogen + Zr(IV) Species <  Zr(ll) Species  Scheme 2.11  *  This reaction was done to show that the amount of gas measured did not contain any volatile cyclopentadiene. references on page  Chapter II  91  Under anhydrous conditions and in a non-polar solvents like toluene, HC1 acts as a weak 97 and therefore is likely to react at the most basic site of the molecule which is probably acid,* the reduced dinitrogen ligand, (N2) . The reaction in toluene can also be envisaged as an 4 addition of HC1 across the zirconium-dinitrogen bonds (Scheme 2.11). Under aqueous conditions the strength of HC1 is many orders of magnitude greater than its strength in toluene and therefore protonation at different sites of the complex becomes possible. When a C 8 D 7 solution of 2.9 was reacted with pyridinium hydrochloride inside a sealed NMR tube, the P( 1 31 H} NMR spectrum showed a clean conversion of 2.9 to the uncoordinated amine of PNP, and no signals were found around 4 ppm that would correspond to hydrazine. This observation  suggests that the protonation probably takes place at the nitrogen of the amide ligand which in turn could result in the decomposition of the complex.  Table 2.19 A compilation of chemical shifts of NH protons associated with hydrazido ligands. Compound  ö (NH) ppm  references  2 W 3 Cp*Me =NNH  4.48  98  W=NNH(SiMe 3 Cp*Me )  5.12  98  [Cp*Me W 3 =NNHLi]x  6.10  98  W=NNH] 3 [Cp*Me Z 2 rCp  7.81  98  2 W 3 Cp*Me M =NNH(ZrCp e)  8.03  98  2 M 5 [W(C B 4 ) 3 ( ut)(CCMe J.trl Clj e :‘q 1 N}TJJ}i)  10.7  99,100  N 1 ) N : N (p,-r HNH) rj H W(NPh)Me j 3 2(-1’ :i 2  47  L-fl’:r’NB N 2 H2  4.26  : 2 1 N HN}I 1  5.70  When the side-on complex 2.2 was reacted with pyridinium hydrochloride in C 8 the D 7 P{ 1 31 H} NMR spectrum showed the presence of one intermediate, 2.25 (amounts to approx. *  The Ka for the dissociation of HBr in 3 CH C N solvent was found to be 3.16x10 . 6  HBr + CH CN = CH 3 CNH + Br. 3 references on page 212  Chapter II  92  30%) along with the trichioro complex 2.1 (20%) and the uncoordinated amine of the ligand PNP, [(Pr2PCH2SiMe2)2N}1] (40%). Repeating the reaction with the 5 ‘ N 2 analogue of 2.2 the H NMR spectra showed that the resonance at 4.99 ppm was split into a doublet 2 1 J( N-H  59.7  Hz), suggesting that the intermediate has a hydrazido type ligand, 2 (N H )-. Comparison of the chemical shifts (Table 2.19) of different types of hydrazido ligands suggest that the peak at 4.99 ppm probably corresponds to a hydrazido ligand of the type, (NNH -. ) 2 The mononuclear structures, for example 2.25a are excluded on the basis of the integration of (NNH - protons with respect to the SiMe2 resonances. The structure depicted in ) 2 2.25 (Scheme 2.12) is proposed for the intermediate which has a bridging hydrazido (N2H2) 2 ligand. Although the structure is drawn with an overall C2 symmetry, a fluxional process that would enable the chloro ligands trans to the amide nitrogen to exchange positions would give a time averaged C2v symmetry to the molecule. This would be consistent with a broad 31 P( 1 H} NMR signal and two singlets for the SiMe2 groups in the 1 H NMR spectra. 2 Me  e  Ci— Zr—.  2.2 j  \,  i’L  Me S 2 I\  \  C5HN•HCl  CI  Me S 2 i\  .  :N—zr Me S 2 i  I  :N—Zr I.-..-.  I’ IN  /  \ci  ‘  2 NH  Me S 2 i  /  \%___.  /  2 SiMe  zr—N:  \  N  I 2 NH  2 Pr’ 2.25a  /  2 SIMe  2 J 1 p  2.25  Scheme 2.12  references on page fl  Chapter II  93  2.8.4 Reactions With Halo Alkanes Although the chemistry associated with dinitrogen is mainly directed towards the protonation of the coordinated dinitrogen ligand, occasionally attention has been focused towards incorporating nitrogen from dinitrogen into organic molecules. Reactions involving N2 complexes and ailcyl or aryl halides have led to the synthesis of alkyl or aryl 101 amines. 0 ” 2 Recently, molecular nitrogen has been incorporated into N-heterocycles by using titanium and palladium as catalysts.’° 3 In some instances, the reactivity of the coordinated dinitrogen has been helpful in understanding the nature of metal-dinitrogen interactions, e.g., some tantalum dinitrogen complexes react with ketones to form hydrazones, where the (formulated) Ta=N—N=Ta unit has been transformed into 2 C=N—N=CR R 4 . 9  2.8.4a Reactions of the End-On Complex With BzBr and CH3I When the reactivity of 2.9 was investigated with CH3I or B 2 C 5 C6H H r (BzBr), even under carefully controlled conditions, a complex mixture of products was obtained. On the basis of 31 P{1 H} NMR spectral analysis the only identifiable product was the dihalide derivative of 2 ZrCp [ C P ] N(SiM Pr’) H e (X X  =  Br or I), which corresponds to a resonance  around 15 ppm. Fortunately, when the reaction of 2.9 with approximately 1 equivalent of BzBr was monitored by variable temperature 31 P{ 1 H} NMR spectroscopy from -78 °C to room temperature, the formation of two products was observed. The crude material from the reaction of 2.9 with BzBr consisted of three compounds: j ZrCp [ P 2 N(SiM Pr) e2CH Br 2.7, the intermediate 2.26, along with some unreacted 2.9 (Figure 2.24). Persistent attempts, by repeated fractional crystallization, eventually led to the isolation of the intermediate 2.26 as pale yellow crystals. Elemental analysis of this intermediate was consistent with a product formed by the addition of one equivalent of BzBr to the dimer 2.9.  It was found that in solution the  intermediate 2.26 slowly reacts to give the end-on complex 2.9 and other unidentified products.  references on page  Chapter II  94  *  I III 1 I III  I I I I 1111 II II  III  I  I 111111111  8  III 4  I lIlt I I I 111111  I  III I 1 I I 11111111 III III 11111 lii  3  2  1.  I OPPM  2.7 [ 2 ZrC N(SiMe2CH2 pBr PPr)2J 2.9 *  [(PrP M e2Si)2NjZrC CH p } (p-N) {2 2.26  f (PNP)H Figure 2.24 A Variable temperature 1 H NMR spectra (300 MHz) of complex 2.26 recorded in  . B and C are 31 8 D 7 C P( 1 H} NMR (121 MHz) spectra of 2.26 and of the crude reaction mixture obtained from the reaction of 2.9 and 2 PhCH B r.  references on page ii  Chapter II  95  The complexity of the variable temperature 1 H and 31 P{ 1 H} NMR spectra of 2.26 is consistent with the presence of more than one isomer in solution, and also that these isomers interconvert with one another. The SiMe2 resonances in the 1 H NMR spectrum were too broad to be interpreted.  However, some of the resonances associated with the Cp ligand were  informative. The appearance of two broad doublets at 6.05 and 4.65 ppm were assigned to the olefinic protons of an r 1 -Cp ligand. The variable temperature 1 H NMR spectra show that the resonances associated with the r 1 -Cp ligand decrease in intensity with a concomitant increase of the peak at 5.22 ppm. This spectral feature could be due to the Cp ring-slip between a TI 5 1 and T coordination, where the latter corresponds to the resonance at 5.22 ppm. Comparison of the 1 H NMR chemical shifts of the Cp ligand in zirconium(IV) PNP derivatives, which appear around 6 ppm, the peak at 5.22 ppm is significantly shifted to higher field. In fact, in the zirconium(II) Zr(1 ) H 5 [ C P ] 2 N(Si (CO dicarbonyl complex, ) Pr H 1SC , Me ) the resonances due to Cp appear i at 4.7 ppm. The fluxional process shown in Scheme 2.13 can rationalize some of the spectral features of intermediate 2.26. The species 2.26a is generated by the addition of one BzBr unit across one of the zirconium-nitrogen bonds of the Zr N core, which probably undergoes rapid 2 isomerization to give other species. The species depicted as 2.26b, 2.26c and 2.26d are generated by incorporating a zirconium(ll) fragment, ) “ZrCp[N(SiM C P ] 2 Pr ” H e into a benzyldiazinide 2 (PhCH N =N) ligand of a zirconium(IV) monomer, P 2 “ZrCpBr(N= h)NCH [N(SiM C P 1 2 ) Pr ”. H e All of the structural types associated with the benzyldiazinide ligand have precedence in the 104 literature. 1 ’ 05 The intermediates 2.26a and 2.26b are formulated as Zr(IV)-Zr(IV) complexes whereas 2.26c and 2.26d are formulated as Zr(ll)-Zr(IV) complexes. In 2.26b one of the zirconium centers has a Cp ligand bound in an r 1 fashion and also interacts with the diazinide ligand in an 112 fashion. 106 Of the two Zr(II)-Zr(IV) complexes 2.26d is sterically more congested than 2.26c and could dissociate into Zr(II), “ZrCp[N(SiMe2PPr) 2 CH J ” and zirconium(IV), P 2 “ZrCpBr(N= h) NCH 2 [N(SiM C P J Pr’) H ” e monomers. The former, in the presence of dinitrogen, may proceed to form the end-on dinitrogen complex 2.9 whereas the latter is probably unstable and undergoes decomposition. It is important to note references on page 2.12  Chapter H  96  that in Scheme 2.13 all of the intermediates are drawn with phosphine donors coordinated, but each case can involve reversible dissociation of the phosphine donors. Such a process would explain the broad resonances observed in the 31 P{ ‘HI NMR spectrum. Complex 2.6 2 Pr’ 2 Si Me  2 Pt  2 Pr’  Me S 2 i  2.26a 2.26b  UI  2 prj  2 Pr’  2 Pr’ 2 Me  2 Si Me 2 \SIMe  I 2.26c  2.26d  SIMe  Scheme 2.13  2.8.4b Reactivity With Dihaloalkanes Initial investigations involved the reaction of the simplest dihalo alkane dibromomethane, CH Br and complexes 2.2 and 2.9. It was envisaged that the reaction of 0.5 2 equivalents of CH2Br2 with 2.2 or 2.9 would lead to the formation of an isodiazomethane or a diazomethane complex respectively (Scheme 2.14). It is also known that reactions involving references on page 112  Chapter II  97  diazomethane and low valent metal complexes (e.g., ) 3 [Ru(NO)(PP C 2 ll) h lead to the formation of methylidene intermediates which then proceed to form ethylene complexes.’ 07 2 Pr’ Me2\  Br 2 CH  : N—Zr  Me S 2 1  /  /  N  2 Pr  2.9  N 2 CH  2 Pr’  Br 2 CH  \  MeSi  0  :N—Zr” %S44  Me S 2 i S[ Me 2  2 pPr’ ‘Si Me 2  /  N’L_N  \-CH2 2.2  Scheme 2.14  Reacting the end-on complex 2.9 with approximately 0.5 equivalent of 2 Br inside a CH sealed NMR tube and monitoring by P( 31 H 1 } NMR spectroscopy showed a clean conversion of the dinitrogen complex 2.9 to the zirconium(IV) derivative C ZrCp [ 2 N(Si H2PPrMe Br 2.7. ’)2], The only peak unaccounted for in the 1 H NMR spectrum was at 5.2 ppm, which is identical to the chemical shift of ethylene. Also, at the end of the reaction (i.e., when all the CH Br was 2 consumed) approximately 0.5 equivalent of the dinitrogen complex 2.9 was left unreacted and no NMR features that would correspond to an oxidative addition product (e.g., ZrCpBr(CH B 2 r) 2 [N(SiM C P ] Pr) ) H e were observed. The above results seems to suggest that the proposed diazomethane intermediate, ZrCp ) C P ] 2 ) [N(S Pr H (N 2.27, was formed during the course of the reaction. Low iMe temperature NMR studies did not show any features that would correspond to free diazomethane , or . N 2 CH NNCH Scheme 2.15 shows a possible mechanistic pathway to generate 2 CH references on page  Chapter II  98  ethylene from the proposed diazo intermediate. The diazomethane intermediate probably undergoes a bimolecular decomposition pathway to yield ethylene and 0.5 equivalent of dinitrogen complex. However, the literature precedence seems to suggest that the diazomethane ZrCp(CH)[N C ] 2 HPP (SiMe ri which then complex could form a methylidene intermediate, ) proceeds to yield ethylene and the dinitrogen complex 2.9.1,b07 2 [Zr]Br [ZrN—N[Zr]  2 [ZrN—N=CH  -  r  N 2 1  4 H 2 C  [Zr](II) Species  [Zr]  [Zr]CH  -  =  “ZrCp 1 C [N(S1Me P ] ) 2 Pr ” H  Scheme 2.15  H  Me  MeH  H  NOC1  Me  2.3  [MeH] N0  MeH  Br [Zr]N—N=[Zrj  [Zr]N—N  4  )[Zr] Br  N2 4 H 2 C  2 [Zr]Br  [Zr](II) Species  d-’:  [Zr]N—N  [Zr]  =  “ZrCp[N(SiM C P ] 2 ) P? ” H e Scheme 2.16  references on page 212  Chapter H  99  The reaction involving 0.5 equivalents of 1,2-dibromoethane and the end-on derivative 2.9  also  gave  exclusively  2 ZrCpBr2[N(S C H2PPr’2)2]. iMe  ethylene  and  the  zirconium(IV)  complex,  In this case a three-membered azacyclic intermediate,  ZrCp[NN(CH2)2][N(SiMe2CH2PPr)2] is probably formed during the reaction (Scheme 2.16). The elimination of ethylene from this intermediate may be comparable to the reaction of some N-nitrosyl aziridine derivatives which decompose to give olefins and N20 (Equation 2.3).b08  Br 2 CH  I  [Zr] [Zr]  -  N [Zr]  I  Br  Br  Br  I  [Zr]...[Zr]  Br [Zr]  N C H2  [Zr](  +  Br  2 [Zr](I)CH  Ethrlene  N  4  Br  Br [Zr][Zr]  -j  .  CH 2 BrCH B r [Zr]  =  [ZrkN[Zr]  N  1 “ZrX[N C P ] ) 2 Pr ” H (SiMe Scheme 2.17  The reactions involving side-on complexes 2.2 or 2.12 and CH2Br2 or BrCH2CH2Br also gave ethylene and the zirconium(IV) trihalo derivative 2 1 ZrBr2C C P ] ) Pr H . l[N(SiM e Due to the poor solubility of the side-on dinitrogen complexes the solutions always contained an excess of the dihalo alkane and therefore hampered the NMR experiments to detect the intermediates involved in the reaction. The possible intermediates involved during the reactions with CH Br could be either an 2 2 -r diazirine complex or a bridging t-r 1 -diazomethane complex (Scheme 2.17). For the reaction of the side-on derivatives with BrCH2CH2Br the intermediate  references on page 1.12  Chapter II  100  {(P P S N [ j 2 ) j.LNN ]ZrX iM CH (CH , Br} ri e where X  =  Cl or OAr*, with a bridging  - ligand is possible, which is similar to the proposed intermediate for the end-on ] 2 [NN(CH) case (Scheme 2.17).  2.9 Conclusions The synthesis of dinitrogen complexes similar to ) {[(P P S N 2 ]ZrC1} iMe CH r 2: 2 (i.-11 N2) 1 2.2 was successful in two cases where the chloride ligand was replaced with the Cp or with an aryloxy ligand, ) 2 3 ((0C6H 2,6-Me ’, OAr*). The complex with Cp ligands, PZrCp [(Pri S N ) iMe CH } 2(I.t-11 -N 2.9 has a bridging end-on bound dinitrogen ligand 1 ) {2 1:2 ([(P P S N ) : 2 ]ZrOA iM CH 1 whereas the complex with OAr’ ligands N 2) r*}2(i. rj e rI 2.12 has a side-on bound dinitrogen ligand with a bent Zr2N2 core. However, attempts to incorporate allyl, alkyl or amide ligands or the incorporation of the less bulky tridentate ligand “Zr[N(SiMe2CH2PMe2)21” were not successful. The solid state X-ray structures of the two complexes show that in the end-on case 2.9, the nitrogen-nitrogen bond distance of the dinitrogen ligand was 1.301(3) 1.528(7)  A  A  whereas in the side-on case 2.12, the bond distance was  which was identical to the chloride analogue 2.2 (1.548(7)  A).  The tert-butoxy  {[(P P S N ) ( 2 ]ZrOB p,N iMe CH analog of complex the 2.12, ) , ut) 2.14, shows certain NMR ri spectroscopic features which tend to suggest that it is similar to other side-on derivatives, although the lack of suitable crystals hampered full charecterization. Solid and solution state resonance Raman spectroscopic studies on the side-on 2.2 and on the end-on 2.9 derivatives show that the mode of clinitrogen coordination observed in the solid state X-ray structures of these complexes is also preserved in the solution state. The observed nitrogen-nitrogen stretching frequencies for the end-on and side-on derivatives were 1211 cm1 and 731 cm1 respectively, which correlate well with the observed bond distances associated with the same atoms. The 15 N NMR spectroscopic evidence also shows that the side-on derivative has the same mode of dinitrogen coordination in both the solid and the solution states. The mixed halogen derivative  gives rise  to a singlet in the 15 N NMR spectrum showing that nitrogens of the dlinitrogen ligand are references on page 212  Chapter II  101  chemically equivalent and therefore, it is inferred that the bonding mode of the 2 N ligand in the solution state is side-on, : 2 (.t-r N2). rI The ML 4 fragment (C ) has three available orbitals 4 that are suitable for dinitrogen bonding  1  Cl, Cp or OAr* the it-interactions leads to two cases  In the case of 2 P 3 [(H ( N )ZrX], H )X  =  , it-interactions on the plane defined by the ligands  it-interactions perpendicular to the plane defined by the ligands  L  / L  11  The remaining two metal based orbitals are  Of the remaining two metal based orbitals  perpendicular to the plane and can form only two it-type bonds with the dinitrogen it*orbitals  ii  one is perpendicular to the plane and the other is on the plane and can form one it-type and one ö-type bond respectively with the dinitrogen 1t*orbitals  Ji  End-On Complex  Side-On Complex Scheme 2.18  The semi-empirical molecular orbital studies performed on the end-on derivative 2.9 and on the side-on derivatives 2.2 and 2.12 show that the it-acceptor interactions involving the it orbitals of the dinitrogen ligand are significantly different. In the end-on case these interactions give rise to two it-MOs (HOMO and HOMO-l) whereas, the side-on cases gives rise to one ö-MO (HOMO) and one it-MO (HOMO-9 for 2.2 and HOMO-3 for 2.12), which were found to be much lower in energy than the ö-MO. The Mulliken population analysis shows greater electron donation into the dinitrogen ligand in the side-on cases than in the end-on case, which references on page 112  Chapter II  102  in turn is reflected in the formal charge on the dinitrogen ligand which was greater for the former than in the latter. The Wiberg indices suggest a weaker nitrogen-nitrogen bond for the side-on mode than the end-on mode, which is consistent with the observed nitrogen-nitrogen bond distances of these complexes. An analysis of the fragment orbitals of the metal unit, [(H P)2(H2N)ZrX], where X 3  =  Cl,  Cp or OH, show that the metal-ligand 1 d, p interactions influence the mode of dinitrogen coordination, i.e., end-on vs side-on.  Scheme 2.18 summarizes how the metal-ligand  it-  interactions influence the mode of dinitrogen bonding. An intramolecular rotation of the dinitrogen ligand within a dinuclear center was demonstrated by the conversion of the side-on complex 2.2 to the end-on complex 2.9 by the reaction of NaCp.DME. The reaction of the side-on derivative 2.2 and 2.12 with LiBEt 4 forms an unusual complex, ) P ([(Pr S N 2 ]ZrH} iMe CH { ) P [(Pr S N 2 ]ZrEt} iMe CH 3 .BEt 2 Qi-N ) where the dinitrogen ligand seems to be bonded to a BEt 3 unit. Reactions of the dinitrogen complex 2.9 with alkyl halides were very complex, but in the case of benzyl bromide it was found that the reaction proceeds through an intermediate containing a benzyl diazenido, , ligand. The side-on and end-on derivatives react with methylene dibromide or with 1 (NNBz)1,2-dibromoethane to give ethylene.  2.10 Experimental 2.lOa General Procedures All manipulations were performed under prepurified nitrogen in a Vacuum Atmospheres HE-553-2 work station equipped with a MO-40-2H purification system or in Schienk-type glassware. 0 Pentane, diethyl ether and hexanes were dried and ” 109 deoxygenated by distillation from sodium-benzophenone ketyl under argon. Toluene was predried by refluxing over CaH2 and then distilled from sodium under argon. Tetrahydrofuran and hexanes were predried by refluxing over CaH2 and then distilled from sodium benzophenone ketyl under argon. Deuterated benzene (C , 99.6 atom % D) and deuterated D 6 toluene 7 (C 99.6 atom %D), purchased from MSD Isotopes, were dried over activated , 8 D  4A  molecular sieves, vacuum transferred and freeze-pump-thawed three times before use. references on page j2  Chapter II  103  Dinitrogen gas was purified by purging through a column containing manganese oxide, MnO, and activated  4A  molecular sieves. The 99% 15 2 was obtained from Cambridge N  Isotopes Ltd., and was used as supplied. H, 31 The 1 P and 13 C NMR spectra were recorded on a Varian XL-300, a Bruker AC 200, a Bruker WH-400 or a Bruker AM 500 spectrometer. Proton spectra were referenced using the partially deuterated solvent peak as the internal reference, C H at 7.15 ppm and 5 D 6 2 C 5 D 6 C H D at 2.09 ppm relative to Me4Si. The P{ 31 ‘H) NMR spectra were referenced to external P(OMe)3 set at +141.00 ppm relative to 85% . 4 P 3 H H} NMR spectra were 0 The ‘3C{ 1 referenced to the 6 5 signal at 20.4 ppm. Solution D 6 C 3 C D 6 signal at 128.0 ppm or to the CD N{ 1 15 H} NMR spectra were recorded on the Varian XL-300, referenced to external formamide set at 0.00 ppm. Solid-state 15 N NMR spectra were run on a Bruker MSL-400, referenced to solid NH4C1 set at -73.39 ppm with respect to neat formamide at 0.00 ppm. 11 B{IH} NMR spectra were recorded in C 8 on the Varian XL-300 referenced to external Et D 7 B set at 0.00 3 ppm. The final 11 B (‘H) NMR spectra were obtained by subtracting the spectra of glass obtained using identical acquisition parameters as those of the sample spectra. 1 P) NIVIR H { 31 spectra were recorded on the Bruker AM 500 spectrometer. Resonance Raman* spectra were recorded on a modified Jarrel-Ash model 25-300 Raman spectrometer. Excitation radiation was supplied by Spectra Physics LAJ+ and Kr+ laser soperating at 514.5 nm and 647.1 nm respectively. Scattered radiation was collected by a back scattering geometry. Multiple scans were collected and calibrated against indene, toluene and THF as external standards for peak positions. All wave number assignments were estimated to be accurate within 2 cm . Spectra for polarization studies of solution samples were collected in 1 a 90° scattering geometry at 278 K on a Dilor Z-24 Raman spectrophotometer. Typical slitwidth settings were between 5 cm1 and 9 cm-’. All samples were sealed under N2 in 1.5  -  1.8x90 mm Kimax glass capillary tubes.  *  The resonance Raman spectra were recorded at the Department of Chemistry, Biochemistry and Molecular Thomas M. Loehr and Jonathan D. Cohen. Biology of the Oregon Graduate Institute of Science and Technology by Prof.  references on page fl  Chapter II  104  UV-Vis spectra were recorded on a Perkin Elmer 5523 UV/Vis spectrophotometer stabilized at 20CC. Mass spectral studies were carried out on a Kratos MS 50 using an El source. JR spectra were recorded on a Bomem MB-l00 spectrometer. Solution samples were recorded in a 0.1mm KBr cell and solid samples were recorded as KBr pellets. Carbon, hydrogen and nitrogen analyses were performed by the microanalyst of this department. The complexes [ZrC 3 N(SiMe2CH2PR2)2] 1 where R  =  Pr and Me, were prepared  according to the published procedures. ’ NaCp•DME, 1 1 ” where DME  =  l,2-dimethoxyethane,  was prepared by the reaction of sodium metal with freshly cracked cyclopentadiene in dry DME and crystallized directly from the reaction mixture. Mercury was purchased from BDH and purified as foilows: 2 in a separatory funnel mercury (500g) was washed with 2M HC1 (2x25 mL) acid then with distilled water (2x50 mL) and finally rinsed a few times with Et20 (25 mL) until no further gray colour was present in the ether washings. During washings a slag was formed on the surface of the Hg which was separated from the shiny Hg. Pure Hg was dried under vacuum for 12 hours. Amalgam was made under a nitrogen atmosphere and washed with toluene (2x25 mL) until the washings showed no gray coloration. Sodium ailcoxide, NaOR’, where R’  =  2 and aryloxides, NaOAr where Ar CHPh  =  Ph or  C M 3 H 6 e2-2,6 were prepared by reacting (3 hours at room temperature and then refluxed for 3 hours) a toluene solution of the alcohol with sodium. The resulting white solid was filtered, extracted with THF (to remove finely dispersed sodium) and stripping off THF under vacuum gave alcohol free NaOAr. Prior to the reaction the alcohol was dissolved in toluene and stirred with Mg turnings (0.1 equivalent) for 12h and then filtered. The above procedure is likely to minimize the presence of NaOH or unreacted alcohol in the final product.  KOBut was  purchased from Aldrich and was sublimed prior to use. The sodium amide, NaNPh2 was prepared by reacting the amine, HNPh2 with NaN(SiMe3)2 in toluene. The NaNPh2 precipitates out of toluene, which was then collected on a frit and washed with hexanes to obtain pure material.  references on page  Chapter II  105  Br C2H4Br2 and 6 CH , CH I 3 ,2 C C 5 H H2Br were purchased from Aldrich and were dried over activated  4A  molecular sieves for 24h. ZrBr4 was purchased from Strem and used as  supplied.  2.lOb Synthesis of Precursors 2.lOb.1 P [N(SiMe 3 ZrBr C 2 Pr2)2J, H 2.4. To a suspension of ZrBr4 (2.03 g, 4.94 mmol) in toluene (50 mL) was added a solution of P 2 Li[N(SiMe2C Pr2)2j, H (1.00 g, 2.50 mmol) in toluene (10 mL) at room temperature. The reaction mixture was stirred for 16 hours and then the salt (LiCl) was removed by filtering the solution through Celite.  The filtrate was  concentrated to 15 mL and hexanes was added until the solution turned turbid; cooling at -30 °C gave a colorless crystalline product (1.12 g, 73%). 1 H NMR (6, 200. 123 MHz, C6D6): 0.41 (s, 12H, 3 Si(CH ) 2 ) ; 1.11 (m, 28H, 3 P); 2.07 (sept of triplets, 4H, 2 P[CH(CH ) 2]2, SiCH ,2 J 2 ) 3 P[CH(CH JH-P  =  2.7 Hz, 3 JHH  =  7.2 Hz). P{ 31 H 1 ) NMR (6, 81.015 MHz, C ): 16.52 D 6  (s). C{ 13 H 1 } NMR (6, 50.323 MHz, 6 C ) D : 4.50 (s, Si(CH ); 11.93 (s, SiCH 2 ) 3 P); 18.85 (s, 2 P[CH(CH ) j 2 ) 3 ; 19.12 (s, 3 P[CH(CH ) J 2 ) ; 25.14 (t, P[CH(CH ,2 ] 2 ) 3 Jc.p  =  6.8 Hz). Anal.  Calcd for Cl HBr3NP2Si2Zr: C, 29.88; H, 6.13; N, 1.94. Found: C, 30.00; H, 6.30; N, 1.99. 8 2.lOb.2 2 [N(SiMe 3 ZrCl C 1 Zr( ) H 5 [ C P ] ) H N(S1M C1 C Pr H , i e 2.6. To a solution of 2 PPr)2] 2.1, (4.040 g, 6.84 mmol) in toluene (150 mL) was added solid NaCp.DME (1.340 g,  7.52 mmol) at room temperature. The reaction mixture was stirred for 16 hours and then the salt (NaCl) was removed by filtering through Celite. The filtrate was concentrated to 15 mL and hexanes was added until the solution turned turbid; cooling at -30 °C gave yellow hexagonal shaped crystals (3.16 g, 75%). 1 H NMR (6, 300 MHz, 6 ); 1.00 (m, 2 C6D ) : 0.64 (s, 12H, Si(CH3) 28H, P[CH(CH3)2]2, SiCH P); 2.12 (m, 4H, 3 2 P[CH(CH ) j 2 ) ; 6.15 (t, -5H, C ,3 H 5 Jp  1.4  Hz). P{ 31 H 1 } NMR (6, 121.421 MHz, 6 C ) D : 16.11 (s). C{ 13 H 1 } NMR (8, 50.323 MHz, C ) D 6 : 7.82 (s, Si(CH ); 8.71 (s, SiCH2P); 18.74 (s, P[CH(CH 2 ) 3 ); 18.96 (s, J 2 ) 3 P[CH(CH ) ] 2 ) 3 ; 24.72 (t, 3 J..p P[CH(CH ) 2]2, 2  =  4.5 Hz); 116.00 (s, 5 C ) H . Anal. Calcd for  49 H 3 C2 N C1 S 2 Z r: P i C, 44.56; H, 7.97; N, 2.26. Found: C, 44.72; H, 8.20; N, 2.32.  references on page  Chapter II  106  2.lOb.3 2 1 Z ) H 5 [ C P J ) N(Si B C Pr r( H Me , r 2.7. This complex was synthesized by a procedure similar to the one described above in section 2.2b.2, using 2 ZrB [ 3 C P ] ) N(SiM R H e r  (0.180 g, 0.270 mmol) and NaCp.DME (0.053 g, 0.300 mmol). 1 H NMR spectrum of the crude reaction mixture showed the presence of 2.7 in greater than 90% yield. 1 H NMR (ö, 300 MHz, C ) D 6 : 0.69 (s, 1211, 3 Si(CH ) 2 ) ; 0.98 (m, 24H, 3 P[CH(CH ) ] 2 ) ; 1.06 (t, 4H, 2 SiCH P , J 3 pH 5.4 Hz); 2.13 (sept, 4H, P[CH(CH ,3 ] 2 ) 3 JH-H  =  =  7.2 Hz); 6.62 (br, 511, 5 C ) H . P{ 31 H 1 } NMR  (, 121.421 MHz, C6D6): 16.57 (s). Anal. Calcd for C23H4 Br2NP2Si2Zr: C, 38.97; H, 6.97; N, 9 1.98. Found: C, 39.00; H, 7.08; N, 1.98. 2.lOb.4 ) Zr ) H 5 [ C P ] 2 N(Si C M C (ri H , Me 1 e 2.8. To a solution of [N(SiM 3 ZrC1 C 2 H e PMe2)21 (1.45 g, 3.03 mmol) in toluene (150 mL) was added solid NaCp.DME (0.541 g, 3.04 mmol) in two portions at 1 hour interval at room temperature. The reaction mixture was stirred for 16 hours and then the salt (NaC1) was removed by filtering through Celite. The filtrate was concentrated to 20 mL and hexanes was added until the solution turned turbid; cooling at -30 °C gave a yellow crystalline material (1.08 g, 70%). 1 H NMR  D6): 0.58 (s, 12H, 6 (, 300 MHz, C  Si(CH3)2); 0.92 (br, 411, 2 SiCH P ); 0.95 (t, 1211, P(CH3)2, 2 3H-P 3 3 H-P  1.5Hz). 31 P{ 1 H} NMR  =  3.6Hz); 6.33 (t, 5H, C , H 5  H} NMR (, 50.323 C( 1 3 D6): -21.73 (s). ‘ 6 (, 121.421 MHz, C  MHz, 6 C ) D : 7.24 (s, 3 , 2 ) 3 Si(CH ) 2); 14.96 (t, P(CH  31 c..p = 7.8Hz); 20.64 (s, 2 SiCH P ); 115.50  (s, 5 CH ) . Anal. Calcd for Z 13 C 3 H N C1 S 2 5 r: P i C, 35.49; H, 6.55; N, 2.76; Cl, 13.98. Found: C, 35.53; H, 6.38; N, 2.76; Cl, 14.20. 2.lOb.5 ) Zr ) 5 H 3 [ C P ] 2 N(Si C Pr C (ri H , Me 1 ’ 2.10. To a cooled solution (-78 °C) of ZrC1 3 2 [N(SiMe2CH j 2PPr’) (2.50 g, 4.24 mmol) in THF (70 mL) was added a THF solution of C3H5MgC1 (23.3 mL of 0.2 M solution, 4.66 mmol) and stirred at -78 °C for 10 minutes. After allowing the reaction mixture to warm to room temperature, dioxane (4.5 mL, 50 mmol) was added and stirred for 3 hours. A copious white precipitate of MgC12’xTHF was removed by filtering through Celite. Solvent was stripped under vacuum and redissolved the crude product in hexanes and cooled to -30 °C to give a bright yellow crystalline product. (1.62 g, 64%). H 1 )*: 0.58 (s, 6H, Si(CH D 6 NMR (6, 300 MHz, C ); 0.59 (s, 6H, Si(CH 2 ) 3 ); 0.96 (m, 4H, 2 ) 3 *  , Ha and H 0 H  refer to central, anti and syn protons of the allylic ligand respectivly. references on page  Chapter II  107  SiCH P 2 );1.08 (m, 24H, 3 P[CH(CH ) ] 2 ) ; 2.18 (sept, 2H, ) 2 ) 3 P[CH(CH 2j ; 2.25 (sept, 2H, P[CH(CH ) ] 2 ) 3 ; 3.32 (d of triplets, H ,3 3 H 5 2 a, C JHa-Hc triplets, 2H ,C 5 , ’3 3 H 5 Hs-Hc Hz, J3 Hc-Hs  =  =  8.8 Hz, J3 Hs-p  =  =  15.2 Hz, 3 JHa-P  =  3.4 Hz); 4.46 (d of  4.4 Hz); 6.08 (t of t, lH, C , 3 3 H 5 Jj-ja  =  15.2  31 H 1 8.8 Hz). P( } NIVIR (6, 121.421 MHz, 6 C ) D : 21.13 (s). C{ 13 H 1 } NMR (6,  50.323 MHz, 6 C ) D : 78.20 (s, 2 CHCH CH ) . NOEDIFF Experiments CH C HCH2); 139.25 (s, 2 (6, 400 MHz, 6 C ) D : Irradiating the resonance at 6.08 ppm resulted in the enhancement of peaks at 3.32 and 4.46 ppm. Attempts to radiate peaks at 3.32 or 4.46 ppm resulted in spin saturation of both resonances and enhanced the peak at 6.08 ppm. Anal. Calcd for Z 29 C 4 H N C1 S 2 r: 1 P i C, 42.33; H, 8.29; N, 2.35. Found: C, 42.67; H, 8.47; N, 2.34. The 31 P( 1 H) NMR (6, 8 1.015 MHz, C6D ) data for 6 Zr( ) 5 H 3 C 2 C1Br[N(S1M C H 1 e ] 2.lOa, an AB quartet, 21.08 (1P, 2 ) 2 PPr Jp..p  =  7.9 Hz) and 21.65 (1P, J2 p.p  =  7.9 Hz). Anal.  Calcd for 2 29 C 4 H CIBrN S Z r: 1 i P C, 39.39; H, 7.71; N, 2.19. Found: C, 38.90; H, 7.58; N, 2.10. Zr(OA [ C P ] 2 N(SIM Pri H , r*)C1 e 2.11. To a solution of ZrCl 2. lOb.6 ) 32 CH [N(SiMe PPr’)2] 2.1, (4.00 g, 5.08 mmol) in toluene (150 mL) was added solid Na(OAr*) (1.03 g, 6.35 mmol) in three portions at 1 hour intervals at room temperature. The reaction mixture was stirred for 16 hours and then the salt (NaC1) was removed by filtering through Celite. The  filtrate was concentrated to 25 mL, an equal volume of hexanes added, and the mixture allowed to stand at room temperature for 24 hours. A colorless crystalline product slowly separated from the solution (2.41 g, 70%). 1 H NMR (6, 300 MHz, 6 C ) D : 0.48 (s, 12H, 3 Si(CH ) 2); 0.96 (d of d, 16H, 12H of P[CH(CH3) 12 and 4H of SiCH2P, 3 2 3 H.H (d of d, 12H, 3 P[CH(CH J3 , ] 2 ) wH ]3 2 ) 3 P[CH(CH 3H-H 3 3 H-H  =  =  6.1 Hz, J 2 pH  =  =  6.1 Hz, 3 Jp..H  =  =  6.1 Hz, J3 P-H  =  14.0 Hz); 1.06  14.0 Hz); 2.00 (sept, of t, 4H,  2.0 Hz); 2.80 (s, 6H, 2, 6-Me2Ph); 6.82 (t, 1H, p-Ph,  7.4 Hz); 7.05 (d, 2H, rn-Ph, J 3 wH  =  7.4 Hz). 31 P{ ‘H) NMR (ö 121.421 MHz, C ): D 6  14.98 (s). 3 H} NMR (6, 50.323 MHz, 6 ‘ C {1 C ) D : 5.41 (s, 3 P); 19.07 2 Si(CH ) 2); 10.70 (s, SiCH (s, 3 P[CH(CH ) 1 2 ) ; 19.15 (s, 3 P[CH(CH ) 1 2 ) ; 19.86 (s, 2, 6-Me2-Ph); 24.09 (t, P[CH(CH , J 2 ) 3 =  6.2 Hz); 120.94 (s, p-Ph); 128.79 (s, rn-Ph). Anal. Calcd for 2 2 C 5 H N C1 S Z OP r: 6 3 i C,  46.20; H, 7.90; N, 2.07. Found: C, 46.07; H, 8.10; N, 2.03.  references on page 112  Chapter II  108  Zr(OB [ C P ] 2 N(S1 Pr ut)C1 H , Me i 2.11. 2.lOb.7 )  To a  solution of [N(SiM 3 ZrC1 C 2 H e  j (1.50 g, 2.54 mmol) in Et 2 PPri) 0 (60 mL) was added a solution of KOBut (285 mg, 2.54 2 mmol) in Et 0 (10 mL) at room temperature and stirred for 3 hours. The solvent was stripped 2 under vacuum and the residues were extracted with pentane (40 mL) and then filtered through a layer of Celite. Stripping off the solvent gave a colorless oil containing >80% (by 1 H NMR spectroscopy) of the desired product. 1 H NMR (6, 300 MHz, 6 C ) D : 0.45 (s, 12H, 3 Si(CH ) 2 ) ; 1.05 (d, 4H, SiCH P2 2 Jp..H 2.9 Hz, 3 H-H  =  5.7 Hz); 1.32 and 1.35 (each d of d, 24H, 3 P[CH(CH P , J 2 ) 3 H  =  7.6 Hz); 1.50 (s, 9H, 3 OC(CH ) ) ; 2.04 (t of sept, 4H, 3 P[CH(CH J2 , j 2 ) p..H  =  =  1.9 Hz, J3 H) NMR (6, 81.015 MHz, C 1 P{ ): 11.60 (s). D 6 H..H =7.6Hz). 31 Zr(OB [ C P ] 2 N(Si M ut)C1 H , Me e 2.13. The complex was prepared by a procedure 2.lOb.8 ) similar to the one described above in section 2.lOb.7, using ) ZrC [ 3 C P J 2 N(SiM Me H e (440 1 mg, 0.92 mmol) and KOBut (114 mg, 1.01 mmol). The product was crystallized from a solvent mixture containing Et 0 and pentane (0.38 g, 7 1%). LH NMR (6, 300 MHz, 6 2 C ) D : 0.26 (s, 12H, 3 Si(CH ) 2 ) ; 0.87 (d, 4H, 2 SiCH P ,2 Jp..H  =  9.6 Hz); 1.01 (d, 12H, P(CH , 2 ) 3  =  6.3 Hz);  1.50 (s, 9H, 3 OC(CH ) 3). P{ 31 H 1 } NMR (6, 121.421 MHz, 6 H} NMR 1 C( C D 6): -32.33 (s). 13 (6, 50.323 MHz, 6 C ) D : 5.92 (s, Si(CH ); 12.53 (d, P(CH 2 ) 3 J..p , 1 2 > 3  =  10.6 Hz); 17.48 (s,  SiCH P 2 ); 32.14 (s, 3 OC(CH ) ) . Anal. Calcd for Z 1 C 3 H N C1 S 2 OP 4 7 r: i C, 32.61; H, 7.23; N, 2.72. Found: C, 32.72; H, 7.13; N, 2.80. 2.lOb.9 2 1 Zr(O ) [ C P ] ) N(Si C Pr CHP H Me , 1 h 2.16.  The complex was prepared by a  procedure similar to the one described above in section 2.lOb.6, using [N(SiM 3 ZrC1 C 2 H e j (1.25 g, 2.12 mmol) and 2 2 PPr) Ph C HONaTHF (589 mg, 2.12 mmol). The product was crystallized from a solvent mixture containing Et 0 and pentane (1.23 g, 7 8%). 1 2 H NMR (6, 200.132 MHz, 6 C ) D : 0.50 (s, 12H, 3 Si(CH ) 2 ) ; 0.94 (m, 28H, SiCH P and P[CH(CH 2 ); 1.73 ] 2 ) 3 (sept, 4H, P[CH(CH , 3 ] 2 ) 3 JH-H Hz); 7.16 (4H, t, rn-Ph, J3 H..H  =  =  6.8 Hz); 6.82 (s, 1H, CHPh); 7.00 (211, t, p-Ph, 3 JH-H  7.6 Hz); 7.71 (4H, d, o-Ph, J3 H..H  =  =  7.6  7.6 Hz). 31 P{ 1 H} NMR (6,  81.015 MHz, 6 C ) D : 13.53 (s). Anal. Calcd for Z 3 C 5 H O C1 S 2 NP 1 5 r: i C, 50.45; H, 7.51; N, 1.90. Found: C, 51.25; H, 7.67; N, 1.76.  references on page 2i  Chapter II  109  2.lOb.1O 2 1 Zr(NP ) [ C P ] ) N(SiMe C1 Pr H , h 2.17. To a solution of [N(SiMe 3 ZrC1 C 2 H 1 (1.25 g, 2.12 mmol) in THF (60 mL) was added a solution of NaNPh 2 PPr’) 2 (199 mg, 2.12 mmol) in THF (20 mL), at room temperature and stirred for 2 hours. The solvent was stripped undervacuum and the residues were extracted with toluene (20 mL) and then filtered through a layer of Celite. The product was crystallized from a solvent mixture containing toluene and hexanes (1.15 g, 75%). 1 H NMR (6, 400 MHz, 6 C ) D : 0.47 (s, 12H, Si(CH ); 1.16 and 1.10 2 ) 3 (m, 28H, SiCH P and 3 2 P[CH(CH ) ] 2 ) ; 2.12 (sept, 4H, P[CH(CH , 3 ] 2 ) 3 HH (2H, t, p-Ph, 3 JH-H  =  8.0 Hz); 7.23 (4H, t, rn-Ph, 3 JH.H  =  =  4.0 Hz); 6.96  8.0 Hz); 7.30 (4H, d, o-Ph, 3 JH..H  =  8.0  Hz). 31 P{ 1 H} NMR (6, 81.015 MHz, 6 C ) D : 15.58 (s); in a solvent mixture containing THF and C : 2.70 (br.); -1.20 (br.). C( D 6 13 H 1 } NMR (6, 50.323 MHz, 6 C ) D : 5.04 (s, SiCMe ); 2 Si); 18.85 and 19.59 (s, CH(CH 2 9.69 (s, CH ); 24.28 (t, CH(CH 2 ) 3 , 1 2 ) 3 Jp..  =  5.6 Hz); 123.41  (s, Ph); 126.98 (s, Ph); 128.26 (s, Ph). Anal. Calcd for 2 34 C 5 H S P N C1 Z 0 r: i C, 49.83; H, 7.53; N, 3.88. Found: C, 50.09; H, 7.56; N, 4.00. 2.lOb.11 2 1 S Zr(CH ) 3 [ C P ] ) N(S1M C1 1Me Pr H , e 2.18. To a cooled (-78 °C) solution of [N(SiMe 3 ZrCl C P J 2 ) Pr H , (1.25 g, 2.12 mmol) in THF (60 mL) was added a solution of 3 S 2 LiCH iMe (199 mg, 2.10 mmol) in toluene (15 mL) over a period of 30 minutes. The resulting yellow colored reaction mixture was stirred at -78 °C for lh, warmed to room temperature and stirred for another 1 hour. The solvent was stripped off under vacuum and extracted with pentane (20 mL) and then filtered through a layer of Celite. It is important to remove THF as completely as possible to ensure complete precipitation of LiC1. Gradual stripping of pentane (5 mL at a time) and cooling at -30 °C gave yellow solid (960 mg, 7 1%). H NMR (6, 300 MHz, 6 1 C ) D : 0.33 (s, 12H, ) 3 S CH ) 2 i(CH ; 0.52 (s, 9H, 3 Si(CH3) ) ; 0.97 (d, 2H, 2 SiCH P ,J 2 pH  =  9.2 Hz); 1.10 (d of d, 12H, 3 P[CH(CH J3 , ] 2 ) p.H  Hz); 1.18 (d of d, 12H, 3 P[CH(CH J3 , J 2 ) p-H  =  13.4 Hz, 3 JH..H  3 S CH ) 2 ) i(CH ; 2.01 (d of sept, 4H, 3 P[CH(CH J2 , ] 2 ) p.H  =  =  =  13.0 Hz, 3 JHH  =  7.3  7.3 Hz); 1.35 (hr s, 2H,  4.1 Hz, 3 JH-H  =  H} 1 P{ 7.3 Hz). 31  NMR (6, 121.421 MHz, 6 C ) D : 8.48 (s).  references on page 2i  Chapter II  110  2.lOc Synthesis of Dinitrogen Complexes 2.lOc.1 2 N {[( P S N ) ( : 1 ) 1Zr tiM CH ii Pr 4 , ri CI} e ’ 2.2. This complex was made according to the published procedure. 8 Resonance Raman 1 (cm) : Solid, 258, 317, 393, 518, 579, 636, 731, 991,1046; Solution (THF), 262,321,331,585,733,745, 1030. MS (El) m/z: 1066 (Mj, 1023, 981, 935, 803, 350, 262. 2.lOc.2 2 N {[ P S N ) : 1 ]ZrC1} iM CH 1 (P 2) 5 2(J.-rl e r , 2.2. The nitrogen-15 analogue of 2.2 was prepared by introducing 15 2 gas into the flask containing the degassed reaction mixture. N Workup was carried out under normal N . 15 2 N{ 1 H} NMR (8, 30.406 MHz, 7 C ) 8 D : 350.92 (s). N MAS NMR (6, 40.60 MHz): 345 (s). Resonance Raman 1 15 (cm) : Solid, 258, 317, 339, 518, 579, 636, 709, 968, 1024; Solution (THF), 260, 318, 327, 710, 718, 1028. MS (El) m/z: 1068 (M), 1025, 983, 937, 805, 350, 262. 2.lOc.3 ) {[ P 1 S N ) ) H 5 ( 2 .LrI ]Zr iM C } (P l:1L (1S , H e C r 2.9. A solution of Zr(r N -C5H5)5 [N(SiM 2 C1 C H2PPr)2] e (0.980 g, 1.58 mmol) in toluene (60 mL) was transferred into a thickwalled reaction flask (300 mL) containing Na/Hg (85 g of 0.33% amalgam, 12.17 mmol of Na). The flask was then cooled to —196 °C, filled with 1 atmosphere of N2, sealed, and allowed to warm slowly to room temperature with stirring. Upon warming up to room temperature the reaction mixture quickly turned green (1 hour) and then slowly turned deep brown. After the disappearance of the green colour (3 days) the solution was decanted from the amalgam and filtered through a layer of Celite. The amalgam was extracted with 15 mL portions of toluene (total of 60 mL), until the extracts showed no brown colour. The filtrate and the extracts were combined and stripping off the solvent gave a dark brown powder (0.860 g, 96%) in high purity (>95% by NMR spectroscopy). The product was crystallized from a 1:1 mixture of toluene and pentane. 1 H NMR (6, 300 MHz, C13D6): 0.28 (s, 12H, 3 ); 1.18 2 ) 3 Si(CH ) 2); 0.33 (s, 12H, Si(CH (m, 48H, 3 P[CH(CH ) J 2 ) ; 1.54 (broad, 8H, 2 SiCH P ); 1.88 (m, 4H, 3 P[C[I(CH ) 212); 2.54 (m, 4H, 3 P[CH(CH ) 2]2); 6.11 (broad, —10H, 5 C ) H . P{ 31 H 1 } NMR (6, 121.421 MHz, 7 C ) 8 D : at 20 °C 20.26 (s); at -40 °C, AB quartet at 19.95 (d, 2 Jp..p  =  80.7Hz) and 20.57 (d, 2 Jp.p  80.7Hz).  C{H} NMR (6, 50.323 MHz, 6 13 C ) D : 6.46 (s, 3 Si(CH ) 2 ) ; 6.71 (s, 3 Si(CH ) 2 ) ; 11.63 (s, P[CH(CH ) ] 2 ) ; 20.94 (s, P[CH(CH SiCH2P); 18.40 (s, 3 ); 21.35 (s, 3 J 2 ) 3 P[CH(CH ) ] 2 ) ; 101,37 references on page  Chapter II  111  ). Anal. Calcd for 5 H 5 (s, C 9 6 C4 S 4 N4P 2 1 H i4Zr2•0.5C 8 : C, 50.13; H, 9.02; N, 4.82. Found: C, 50.11; H, 8.94; N, 4.90. Resonance Raman 1 (cm) : Solid, 226, 277, 295, 325, 1126, 1211; Solution (toluene), 225, 290, 320, 1125, 1201. MS (El) m/z: 1124 (Mj, 1081, 993, 949, 732, 688, 562, 519, 497, 475, 445, 431, 350, 262. 2lOc.4 { 2 [(P 2 1 S H 5 ( iMe2)2N1Zr PCH p-f C s)} (fl N), r l 15 2.9. The nitrogen- 15 analogue 1 : was prepared by a procedure similar to the one described in section 2.lOc.3, by introducing 15 2 N gas into the flask containing the degassed reaction mixture. Workup was carried out under unlabelled N2. 15 H} NMR (8, 30.406 MHz, C N{ 1 ): 353.95 (s). Resonance Raman 4 8 D 7 (cm ) : Solid, 228, 277, 294, 323, 1125, 1172; Solution (toluene), 227, 290, 319, 1124, 1165. MS (El) m/z:  1126 (M), 1083, 995, 951, 734, 690, 563, 520, 498, 476, 446, 432, 350, 262.  {[(P P S N ) ( ) 2 N irIl: ]Zr(OA iM CH , ri rll r*)} e 2.12. A solution of Zr(OAr*)C12 2.lOc.5 4 C [N(SiMe P 2 ] Pr) H (1.05 g, 1.48 mmol) in toluene (100 mL) was transferred into a thickwalled reaction flask (300 mL) containing Na/Hg (80 g of 0.17% amalgam, 5.74 mmol of Na). The flask was then cooled to —196 C, filled with 1 atmosphere of N2, sealed, and allowed to warm slowly to room temperature with stirring. The colorless solution slowly takes on the deep blue colour of the product. The reaction mixture was stirred for 5 days the solution was decanted from the amalgam and then filtered through a layer of Celite.  The amalgam-  containing residue was extracted with several 50 mL portions (approx. 400 mL) of toluene, until the extracts showed no blue colour. The filtrate and the extracts were combined and stripping off the solvent gave a deep blue solid which was washed with hexanes (2x25 mL). Pure product was obtained by slow evaporation of a toluene solution of the crude product at room temperature (0.36 g, 40%). 31 H{ NMR (8, 500 MHz, C 1 P) ): See Table 2.20 8 D 7 P( 1 31 H} NMR (6, 121.421 MHz, 7 C D 8): at 20 °C, major isomer 8.69 (s); minor isomer 8.85 (s) and 11.26 (s). NOEDIFF experiments (6, 400 MHz, 7 C ) 8 D : radiating the resonances at 7.00 or 6.98 ppm showed enhancements at 2.34 and 2.32. Variable temperature 31 P( 1 H} NMR (6, 121.42 MHz, 7 C ) 8 D : upon cooling a sample of pure major isomer, the resonance at 8.69 ppm broadens and below -40  begins to show shoulders at 7.60 ppm and 9.10 ppm. Below -78 °C  a broad peak begins to appear at 4.00 ppm which increases in intensity with decreasing references on page j  Chapter H  112  temperature (up to -93 °C). Anal. Calcd for a sample containing only the major isomer, C26H53ON2P2Si Z 2 r: C, 50.44; H, 8.63; N, 4.53. Found: C, 50.70; H, 8.87; N, 4.33. Anal. Calcd for a sample containing a mixture of major isomer and minor isomer (major:minor = 2:1), 53 H 6 C2 S 2 ON2P Z i C, 50.44; H, 8.63; N, 4.53. Found: C, 50.24; H, 8.71; N, 4.29. Resonance r: Raman 1 (cm) : Solid, 258, 278, 314, 350, 595, 732, 751, 1046. MS (El) m/z: 1236, 1193, 1107, 1063, 1007, 975, 695, 350, 262.  Table 2.20 1 H P} 31 NMR data for complexes 2.12 and 2.12a. ( Groups  Major isomer (8)  Minor isomer(8)  2 ) 3 Si(CH  0.37 (s, 12H)  0.29 (s, 6H), 0.32 (s. 6H)  0.41 (s, 12H)  0.32 (s, 6H), 0.35 (s, 6H)  1.30 (d, 4H, 2 JHH = 1.6 Hz)  obscured  P 2 SiCH  1.32 (d, 4H, J2 H-H = 1.6 Hz) ] 2 ) 3 P[CH(CH  ] 2 ) 3 P[CH(CH  1.04 (d, 12H, 3 JH..H  =  6.7 Hz)  1.13 (d, 6H), 1.26 (d, 6H)  1.05 (d, 12H, 3 HH  =  6.7 Hz)  1.34 (d, 6H), 1.44 (d, 6H)  1.17 (d, 12H, 3 JH.H  =  7.3 Hz)  rest of the resonances were  1.23 (d, 12H, 3 H-H  =  7.3 Hz)  obscured  2.03 (sept. 4H, 3 JH-H = 7.3 Hz)  2.04 (sept. 2H, JH.H = 7.4 Hz)  2.39 (sept. 4H, 3 JH..H  2.20 (sept. 2H, 3 JH..H  =  6.7 Hz)  =  7.4 Hz)  2.48 (sept. 2H, 3 JH-H = 7.4 Hz) 2.53 (sept. 2H, 3 JH-H = 7.4 Hz) 2, 6-Me Ph 2  2.34 (s, 12H)  only assignable resonance was a broad peak at 2.32  p-Ph  6.66 (t, 2H, 3 JH..H  =  7.1 Hz)  6.62 (t, 2H, 3 JH.H  =  6.9 Hz)  rn-Ph  7.00 (t, 4H, 3 JH..H  =  7.1 Hz)  6.98 (t, 4H, 3 JH-H  =  6.9 Hz)  references on page  Chapter II  113  Zr(OA ( : J ) SN rI 1 , r*} 2.12. The nitrogen- 15 analogue 2.lOc.6 ) {[(P P 1 S N 2 iMe CH ] r2 was prepared by a procedure similar to the one described in section 2.lOc.5, but by introducing ‘ N 5 2 gas into the flask containing the degassed reaction mixture. Workup was carried out under unlabelled N2. 15 H} NMR (6, 30.406 MHz, 7 N{ 1 C D 8): minor isomer, 342.91 (s); major isomer, 339.06 (s). Resonance Raman 1 (cm) : Solid, 278, 310, 350, 577, 595, 725, 751, 1046. MS (El) m/z: 1238, 1195, 1111,977,696,350,262.  {[( P S N ) ( ) 2 J.Ii1 ]Zr(OB 2.lOc.7 N iM CH Pri Z:11 , ut)} e 2.12. A solution of crude Zr(OBut) Cl2[N(SiMe2CH2PPr)2] (approx. 1.05 g, 1.48 mmol) from the reaction described in section 2.lOb.7 was dissolved in toluene (100 mL) and transferred into a thickwalled reaction flask (300 mL) containing Na/Hg (80 g of 0.30% amalgam, 10.4 mmol of Na). The flask was then cooled to —196 °C, filled with 1 atmosphere of N2, sealed, and allowed to warm slowly to room temperature with stirring. The colorless solution slowly takes on a deep purple colour of the product. The reaction mixture was stirred for 5 days and the solution was decanted and filtered through a layer of Celite. Stripping off the solvent from the filtrate gave a dark purple oil. Attempts to crystallize the product were not successful. 1 H NMR (6, 300 MHz, 6 C ) D : 0.46 and 0.42 (s, 12H, 3 Si(CH ) 2 ) ; 1.24 (br m, 28H, SiCH P and 3 2 P[CH(CH ) j 2 ) ; 1.42 (s, 9H, OC(CH ) ) 3 ; 1.97 (br sept. 2H, P[CH(CH , 1 2 ) 3 ,3 ] 2 ) 3 P[CH(CH JH-H  =  3 J H-H  =  7.2 Hz); 2.25 (br sept. 2H,  6.6 Hz). P{ 31 H 1 ) NIVIR (6, 81.015 MHz, 6 C ) D : 8.16 (s). 15 N{’H}  NIVIR (6, 30.406 MHz, 7 C ) 8 D : 346.41 (s); 334.35 (s); 319.64 (s); 254.87 (s); 248.86 (s). 2.lOc.8  [(P P 1 S N ) ( : 1 ) 2 ]ZrB iM iCH ii {N 4 , r} i r e  2. 19.  A  solution  of  [2 3 ZrBr } N(SiMe2CH2-PPr’) (0.628 g, 0.943 mmol) in toluene (80 mL) was transferred into a thick-walled reaction flask (300 mL) containing 0.35% Na/Hg (24 g, 3.59 mmol). The flask was then cooled to —196 °C, filled with 1 atmosphere of N , sealed, and allowed to warm slowly 2 to room temperature with stirring. The colorless solution slowly takes on the deep blue colour of the product. The reaction mixture was stirred for 7 days and the solution was decanted and filtered through a layer of Celite. The amalgam-containing residue was extracted with 80 mL portions (approx. 1L) of toluene, until the extracts showed no blue colour. Stripping off the solvent from the combined filtrate and extracts gives a dark blue crystalline material (0.23g references on page Z;L  Chapter II  114  42%). 1 H NMR (6, 300 MHz, 7 C ) 8 D : 0.30 (s, 12H, 3 Si(CH ) 2 ) ; 0.34 (s, 12H, 3 Si(CH ) 2 ) ; 1.02 (m, 8H, SiCH2P); 1.44 (d of d, 12H, P[CH(CH ,3 ] 2 ) 3 JH..H  =  7.3 Hz, J 2 ..p  36H, 3 P[CH(CH ) ] 2 ) ; 2.18 (d of sept, 4H, P[CH(CH , J3 ] 2 ) 3 H.H (d of sept, 4H, 3 P[CH(CH J3 , ] 2 ) H.H  =  7.6 Hz, 2 JH-P  =  =  13.7 Hz); 1.24 (m,  7.5 Hz, J2 H-P = 4.2 Hz); 2.42  3.9 Hz). 31 P{ 1 H} NMR (6, 121.4 MHz,  C ) 8 D 7 : 9.96 (s). Anal. Calcd for C H44BrN2P2S 1 8 i2Zr: C, 37.42; H, 7.68; N, 4.85. Found: C, 37.84; H, 7.84; N, 3.89. According to the microanalysts comments, the complex shows lower nitrogen content than expected due to the formation of nitrides during the combustion. 2.lOc.9 N 5 {[( P 1 S N ) ( : ) 2 p.]ZrB 1M CH i ’ , Pr r} ri e 2.19. The nitrogen-15 analogue was prepared by a procedure similar to the one described in section 2.lOc.8, but by introducing 5 ‘ N 2 gas into the flask containing the degassed reaction mixture. Workup was carried out under unlabelled N2. ‘ H} NMR (6, 30.406 MHz, THF / C6D N( 1 5 ): 345.75 (s). Resonance Raman 6 (cm) 1 : Solid, 295, 589, 709, 880, 1009, 1167, 1293. MS (El) mlz: 1158, 1113, 1025, 941, 895, 350, 262. 2.lOc.10 ) {[( P S N ) C : 2 1Br( iM CH ]Zr N r , Pr .t-i e } 2.20. A solution containing a mixture of 2 [N(SiMe2CH2PPr’) (0.160 g, 0.221 mmol) and ZrCl3[N(SiMe2CH2PPr’)2J (0.131g, 3 ZrBr ] 0.222 mmol) was treated with 0.34% Na amalgam (12.2 g, 1.79 mmol) as described in the synthesis of ) ([(Pr2PCH2S ) : 2 2N]ZrBr}2($ H P} 31 NMR (6, 500 MHz, 7 ( N fl iMe .t-1 1 . C ) 8 D : 0.28 (s, 3 Si(CH ) 2 ) ; 0.29 (s, Si(CH ); 0.31 (s, Si(CH 2 ) 3 ); 0.32 (s, 3 2 ) 3 Si(CH ) 2 ) ;  0.33 (s,  Si(CH ) 2 ) 3 ; 0.34 (s, 3 Si(CH ) 2 ) ; 0.65 (m, 2 SiCH P ); 1.00 (m, 2 SiCH P ); 1.28 (m, 3 P[CH(CH ] 2 ) 2); 1.41 (m, 3 P[CH(CH ) 1 2 ) P[CH(CH ) J 2 ) ; 2.40 (m, 3 . P 1 {1 H} NMR (3, 121.4 MHz, 7 C ) 8 D : 10.30 (s); 10.06 (s); 9.96 (s); 9.89 (s). MS (El) mlz: 1111, 1067, 1023, 979, 262. 2.lOc.11 ) {[(P P 1 S N 2 1Me CH ] rN C1Br(.i-rI Zr} : 1 ) 2 1 5 2.20. The nitrogen- 15 analogue was prepared by a procedure similar to the one described in 2.lOc.10, but by introducing 15 N2 gas into the flask containing the degassed reaction mixture. Workup was carried out under unlabelled N2. 15 H} NMR (6, 30.406 MHz, C N{ 1 0 / C 8 H 4 ): 352.50 (s, approx. iN); D 6 349.26 (s, approx. 2N); 345.75 (s, approx. iN). Resonance Raman (cm): Solid, 264, 300, 313, 579, 709, 884, 976, 1021. MS (El) m/z: 1113, 1069, 1025, 981, 895, 849, 350, 262.  references on page 112  Chapter II  115  2.lOd Reactions Involving Dinitrogen Complexes 2.lOd.1 2 N {[(P P 1 S N ( : 1 ) j.t-ii ]ZrCI} iMe CH ii 5 r and NaCp.DME. To a solution of 5 P ([(P S N ( : ) 2 N jZrC1) t-r iMe CH 1 ’ (30 mg, 0.028 mmol) in THF (4 mL) was added a solution of NaCp.DME (11 mg, 0.062 mmol) dissolved in TFIF (2 mL), under an atmosphere of unlabelled dinitrogen. A control experiment was set up under an atmosphere of argon. Both reactions were stirred at room temperature until they turned brown (6 days). The solvent was removed in vacuo, and extraction of the crude product with pentane and striping off the solvent gave a brown powder.  The brown powder was shown to be  { [(Pr2PCH2SiMe2)N]Zr-  -C 1 (.i.-N) by NMR. A similar reaction carried out in an NMR tube showed clean (r1 ) 5 H conversion of the side-on complex to the end-on complex. MS (El) mlz: 1126 M, 1083, 995, 951,734, 690. 2.lOd.2 Protonation Reactions. The zirconium dinitrogen complex { ) SiMe [(PrPCH N 2 ]Zr-.t-1’:T’-N 5 (ri ( 2 ) C5H5)} , 2.9 was protonated by the addition of excess dry HC1 gas to a toluene solution of the complex. Extraction of the organic phase with distilled water and calorimetric analysis to determine the amount of hydrazine produced by the method of Watt and 3 gave the following results: Chrisp”  Table 2.21 Moles of hydrazine measured from the reaction of { ) PiMe [(Pr S N 2 CH ]Zr2 5 (fl ( i-rI’:r’-N) CsHs)} complex in toluene with anhydrous HC1 gas.  *  Expected  concentration was calculated by taking into account the amount of pentane present in the complex.  Sample Weight  *Expected Concentration Measured Concentration Ratio of 2 —NH NH of NTI2—NH2 Measured/Expected  0.023 g  5.09 10-6 M  5.43. 10-6 M  1.07  0.037g  M 6 6.33•10  M 6 7.08•10  1.12  references on page  Chapter II  116  The reactions with 1M HC1 solution and with water were carried out with a gas uptake apparatus. An appropriate amount of sample was weighed into the glass bucket and was covered with KBr. The proton source 1 (HC ( aq) or water) was syringed into the flask and allowed to equilibrate at a known pressure of dinitrogen. Then the bucket was dropped and the flask was vigorously shaken and the pressure change was measured after 15 minutes. A qualitative test with the colour developer used in the Watt and Chrisp method showed the presence of hydrazine.  Table 2.22  Mole percent gas evolved during the reaction of  0 and HC1 solution. 2 -C5H5) 5 (1 ( 2 : 1 N) TI -r complex with H  *  PiMe [(Pr S N ) CH ]Zr{2  Percent gas evolutions were  calculated by taking into account the amount of pentane present in the complex.  **  The data in  parenthesis was obtained after 30 minutes.  Sample Weight  Proton Source  Measured Pressure  % Gas evolution*  0.066 g  1 M HC1  351 mniHg  90%  0.037 g  0 2 H  349 mmHg  81% (114%)**  Protonation reactions with pyridinium hydrochloride were carried out inside a NMR tube. Complex 2.6 or 2.2 (approx. 30 mg) was dissolved in 7 C D 8 (1 mL) and added an excess of C N•HC1 (5 mg) and shaken occasionally until the colour of the N2 complex dissappeared. H 5 H NMR data for complex 2.25: 0.40 and 0.55 (s, Si(CH 1 ), 1.48 and 2.35 (m, 3 2 ) 3 P[CH(CJzT ] 2 ) ), 4.99 (s, NNH2). 31 P( ‘H) NMR has a broad peak centered at 14 ppm. 2.lOd.3 {[(Pr2PCH2S : 2 N2) 11 iMe2)2N]ZrX}2(J.t-fl where X  =  Cl, Br or OAr*, and L1BEt . 4  The side-on dinitrogen complexes were reacted with LiBEt 4 in an approximately 1:2 mole ratio in toluene. The deep blue colour of the reaction mixture slowly decreased in intensity to give a yellow solution over a period of 7 days. Stripping off the toluene and extracting the residue with pentane and subsequent stripping off pentane gave a yellow oily substance which seemed to consist of a single complex. Monitoring the reaction by NMR spectroscopy suggested an references on page 112  Chapter II  117  almost quantitative conversion of the N 2 complex to the product. The following spectroscopic data is for a reaction carried out in a sealed NMR tube. H ( 1 P} 3 1 NMR (6, 500 MHz, C ): 0.05 (d of quartet, 1H, 2 8 D 7 JH.H  =  10.2 Hz, 3 3H-H  =  7.1 Hz);  4.81 (s, 1H); 0.19, 0.31, 0.33, 0.44, 0.48, 0.52, 0.54 and 0.95 (s, each 3H, Si(CH ); 1.62, 1.70, 2 ) 3 1.78, 1.82, 1.85, 1.95, 2.15 and 2.25 (sept, P[CH(CH3)212, each 1H, 3 3H..H  7.0 Hz); 1.51, 1.37  and 1.31 (t, 3 CH 3 2 B(CH , ) ); 0.9 to 1.3 2 JHH = 8.3 Hz); 0.6 to 0.85 (overlapping singlets, SiCH CH 2 B(CH ) ) P{ 1 . 31 H} NMR (6, 121.4 MHz, 7 (P[CH(CH ) 3 2]2 and 3 C ) 8 D : Spectrum consisted of an ABMX spin system; 22.28 (d, 1P, 2 Jp..p  71.7 Hz); 18. 56 (d, 1P, 2 Jp.p  =  71.7 Hz); 12.56  (s, 1P); 0.06 (s, 1P). 15 N{ 1 H} NMR (6, 30.406 MHz, 7 C ) 8 D : 250.5 (d, approx. iN, J2 NN Hz); 185.9 (d, approx. iN, 2 1N-N  =  =  12  12Hz). “B(’H) NMR (6, 96.2 MHz 7 C ) 8 D : 0.00 (s, free  BEt ) 3 ; -41.6 (br., coordinated BEt ); -104.1 (s, unreacted LiBEt4). 3 2.lOd.4 ) {[(P P 1 S N ( 2 j.t-N JZrX} iMe CH r Where X  =  Cp, Cl or OAr*, and Alkyl  Halides. A typical reaction involved a toluene solution of the dinitrogen complex and varying equivalents of the alkyl halides. Appropriate equivalents of the volatile alkyl halides Mel, CH2Br2 and 2 BrCH2CH B r were transfered into the reaction flask by using a constant volume gas bulb. The constant volume bulbs were filled with the vapor of the alkyl halide at room temperature at the vapor pressure of the pure alkyl halide and then condensed into the reaction flask. Benzyl bromide was made up into a standard toluene solution and then an appropriate volume of the solution was used. The isolation of H {[(Pr2PCH2SiMe2)2N]ZrC B 7 r, p}2(N2).C 2.26.  Anal. Calcd for  C53H B 5 O 1 rN4P4Si4Zr2: C, 49.08; H, 8.16; N, 4.32. Found: C, 49.44; H, 8.19; N, 4.21.  2.lOe Molecular Orbital Calculations. All molecular orbital calculations were performed on the CAChe Worksystem, a product developed by Tektronix. The parameters used in the INDO/i and Extended Huckel semi-empirical molecular orbital calculations were used as provided by the CAChe Work system, which in turn were taken from the 9 ’ 45 literature. 3 The 4 structural parameters for the model ( [(H3P) ) : 2 ZrC112(I-1 N2), NH fl F were taken from the 8 The structural parameters for the models ) literature. P 3 [(H ( ) ( 2 : 1 ZrCpJ NH j.tN i , ) A and references on page  Chapter II  118  H were obtained from the X-ray crystal structure analysis of complexes  C5H5) } 2(JI11l :i 2 5 -N 1 ) , { [(Pri2PCH2SiMe2)2N]Zr(r1  2.9  and  ([(Pri2PCH21 : 2 N 2), Si)21Zr(OAr *)}2(.ifl 2.12a. The symmetry of the models H and A were restricted to C2v and C2 respectively. The hydrogen atoms were aligned to satisfy the overall symmetry of the model. For all the models the following standard bond lengths were used: P—H  =  1.38  A,  C—H  =  1.09  A, N—H =  1.07  A.  The fragment model ( 2 P 3 (H NH2)ZrCl, )G  was obtained from the literature, 45 and the model (H3P)2(NH )ZrCp, B was constructed from 2 the model A. The model 0 was used to obtain the intermediate cases for the rotation of the side-on bound dinitrogen to the end-on bonding mode. The dinitrogen ligand was rotated in the plane defined by the Zr2N 2 core (which also contains the phosphine ligands) without altering the relative positions of the ligands on the metal centers. A phantom atom “A” was placed in the centre of the dinitrogen ligand and the rotation angle was measured as showed in Figure 2.16. The shortest zirconium-nitrogen bond distance between the zirconium and dinitrogen was kept identical to that in model F.  —  S  — — —  H3P  P 3 H  3 PH  P 3 H  H PH 3  H  P  0  Figure 2.25 The models used to generate the intermediate structures for the bending P, and rotation 0, of side-on bound dinitrogen complexes. The phantom atom “A” is placed in the middle of the N—N bond. The line X—Y in model P refers to the axis of the hinge about which the Zr2N 2 plane was bent.  references on page flQ  Chapter II  119  The model P was used to obtain the intermediate cases for the bending of the side-on bound dinitrogen complex. The bending was carried out by moving the clinitrogen ligand on a plane perpendicular to the zirconium-zirconium axis while having the zirconium-”A” distance constant. Also the dihedral angle H—N—Zr—O, where the hydrogen and nitrogen corresponds to the amide, was set to  900.  The angle  e  was measured by taking Zr—”A”--Zr bond angles. The  bond angle parameters associated with “A”—Zr—Z, where Z  P, N or Cl were maintained  constant. The process can be imagined as bending of the Zr N core using the nitrogen2 nitrogen axis as a hinge.  2.11 References. (1)  Fryzuk, M. D. Can. J. Chem. 1992, 70, 2849.  (2)  Fryzuk, M. D.; MacNeil, P. A. .1. Am. Chem. Soc. 1981, 103, 3592.  (3)  Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. 3.; Secco, A. 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A. 1929, 15, 431.  Lq  Chapter 3 Introduction to Zirconium(III) Chemistry 3.1 General It is well established in transition metal chemistry that the first row elements show some deviations from their second and third row counterparts. 2 For example, if one considers formal ’ 1 oxidation states, then for complexes of the group 4 elements, titanium exhibits +3 and +4 formal oxidation states predominant 2 ly, which is in stark contrast to the heavier members of the group, namely zirconium and hafnium, for which the +4 formal oxidation state dominates. 3 In fact, organometallic and coordination compounds of zirconium(III) and hafnium(llI) are very poorly documented in the literature and still remain a scarcity. 3 The rarity of the +3 formal oxidation state in zirconium is partly attributed to the relatively low potential at which it is reduced from the +4 to the +3 state. Reduction potentials for various zirconocene derivatives range from B 0  =  -1.6 V to E 0  =  -2.1  4 ’ 3 v.  In comparison to  their titanium counterparts, for example the first reduction potential for CpTiC12 is E 0  =  -0.75  V, zirconium derivatives are reduced approximately 1 V more negative. 4 This large difference ’ 3 in reduction potential is in part due to the coordinative solvation (by THF) of the zirconium 4 Electrochemical studies involving complexes containing bulky ligands, for example ’ 3 center. complexes of the type ) 3 C M ( 4 H 6 2 CHSiM l,21 [C p e gave E , 0 values of -1.46, -2.02 and -2.26 V for M  =  titanium, zirconium and hafnium respectively, where the differences between the  reduction potentials of titanium and zirconium are only 0.56 V. 6 , 5 A comparison of the ionic radius of titanium (for 4, 5, 6 and 8 coordination numbers the effective ionic radii are 56, 65, 74.5 and 88 ppm respectivly) 7 and zirconium (for 4, 5, 6, 7, 8 and 9 coordination numbers the effective ionic radii are 73, 80, 86, 92, 98 and 103 ppm 7 in their +4 formal oxidation state suggests that for complexes with same respectivly) coordination number and identical ligands, a titanium center in +3 formal oxidation state will be more effectively shielded than the a zirconium(llI) center. Therefore, it has been suggested that the zirconium(ffl) centers could be kinetically activated to undergo further reactions. 4 ’ 3  references on pace 133  Chapter III  125  3.2 Coordination Complexes of Zirconium(Ill) A number of adducts of ZrX3 (X  Cl, Br and I) with nitrogen containing donor ligands  such as ammonia, pyridine, acetonitrile, bipyridyl and phenanthroline have been prepared. Although these can be considered as zirconium(ffl) derivatives the evidence is circumstantial. These compounds are highly colored and have unusual stoichiometries; for example, the metal to-ligand ratio is 1:2 for ZrCI3(py)2, 1:1.5 for Zr2C1 3 ( 6 bipy) and 1:2.5 for ” 8 Zr2C16(MeC N)5. The magnetic properties of these complexes are lower than what would be expected for a complex, and suggest dinuclear or oligonuclear structures with some magnetic exchange between neighboring zirconium atoms. Due to the low solubility of these complexes molecular weight measurements were not possible and therefore any structural proposals are necessarily speculative.  4 + ZrC1  toluene  3 2PR  3 C 2 [Zr ( 6 ] 4 ) PR 1  Na/Hg 3 PR  =  3.1  , PPr 3 , PEt 3 PMe , PBu 3 3 T1  3.2  3 C 2 [Zr ( 6 ] 4 ) PR 1  C 2 [Zr ( 6 ] 3 ) PR 1  +  3 PR  3 +PR 3 C 2 [Zr ( 6 ] 4 PR 0.5 ) 1  —  (PR [ZrC1 1 3 )  (PR 3 [ZrC1 ] 2 )  3.3  3 -PR  The class of complexes [ZrC12(p,-Cl)(PR3)2]2, (R  Me, Et, Pr or Bus) prepared by the  reduction of ZrC1 4 in the presence of an alkyl phosphine was the first well characterized coordination complexes of zirconium(Ill), with complex ) 3 [ZrC ( ] 2 p-Cl)(PBu l 3.1, being structurally ’ 12 characterized 1 3. The solid state structure of ) 3 [ZrC ( , ] 2 .t-Cl)(PBu’ l 3.1, is centrosymmetric with the zirconium atoms positioned in a pseudo octahedral environment. The short zirconium-zirconium separation of 3.182(1) and is close to that of zirconium metal, 3.1789  A in 3.1 is attributed to a metal-metal bond  A.  The NMR spectroscopic studies with the  complexes analogous to 3.1, ([ZrC 2 L-C1)(PR3)21 ]2, indicate that they undergo reversible references on pace 133  Chapter III  126  phosphine dissociation (Equation 3.2). Also the ESR spectra of a toluene solution of these complexes show a weak signal which becomes more intense when excess phosphine is added, implying the break-down of the dimer into monomers (Equation 3.3). Recently, complexes analogous to 3.1 have been synthesized; addition of 4-tert-butyl[Zr ( N 4 H 5 , 2 .tCl) But4 pyridine to complex 3.1 gave j Cl (C ) which upon reaction with ButCN gave a dinuclear complex containing a bridging ButCN ligand where the bonding of the nitrile ligand could be described as (L.112:11 1), 3.2.’  CI  3 CMe (Bu) P 3 ss,.\  .ssCL,,  / P 0 y PY0/CI’”  (Bun)aP/%ScV  \cI  CI  3.3 Organometallic Complexes of Zirconium(Ill) 3.3.1 Dinuclear Organometallic Complexes of Zirconium(Ill)  Most of the attempted syntheses of organometallic zirconium(III) derivatives have resulted in the formation of dinuclear and diamagnetic 3 complexes.’ 2 ’ 6 One class of dinuclear zirconium(ffl) complexes that contain fulvalene type ligands were synthesized by the reduction of dihalozirconocene 17 derivatives 2 ’ 0 or by disproportionation reactions involving Zr(II) and zirconium(IV) precursors (Scheme 3.1). During the course of the reaction, coupling of two Cp ligands leads to the formation of the fulvalene ligand which bridges the two metal centers. The second class of complexes are of the type ) Z (Cp’ Q 2 .t-X r) , where Cp’  =  H or 5 5 C C M 4 H e and  the bridging ligands are either halide groups’ 9 or dialkyl phosphide 21 groups. The bridging halide derivatives are prepared by the photochemical reaction of the monoalkyl derivatives, Cp’ Z 2 rXBui (Cp’ = 5 C M 4 H e) and the corresponding phosphide derivatives were prepared by the  references on pane 133  Chapter III  127  reduction of Cp2ZrC12 (Cp’  =  C5H5) in the presence of Me2P—PMe2. The hafnium derivatives  of the latter case (i.e., with bridging phosphides) have also been synthesized. Na/Hg ZrC1 Cp 2 ZrC1 2 Cp  + ) 3 Z Cp 2 r(PMe 3.3 hv  2 (ri M 4 H 5 Z rX(Bu C e) )  istene r  X  -C (fl M 2 ) H 5 C1  +  =  Cl, Br and I, 3.5  P—PMe 2 Me  M  =  Zr, 3.6 or Hf  Scheme 3.1  Considerable attention has been focused on the metal-metal separations in the dinuclear zirconium(III) derivatives and their relationship to the possible existence of metal-metal 29 In fact, the incorporation of a fulvalene dianion as a bridging ligand allows one to bonding. constrain the two metal centers within short distances i.e., in the range of zirconium-zirconium 29 bonds.  The compilation of metal-metal separations given in Table 3.1 shows that the  zirconium-zirconium separations range from 3.099  A to 4.171 A.  Of all the known dimers, only  the complexes of the type ) ( 3 H 5 [C -l,3]2Zr(i-X) SiMe ]2 where X  =  Cl, 3.7 (Scheme 3.4), Br  and I, show paramagnetic behavior. 26 The diamagnetic behaviour of the complexes with metalmetal separations less than 3.4  A is  attributed to metal-metal bonding, whereas for the cases  with metal-metal separations greater than 3.4  A  ligand mediated superexchange is invoked.  However, ab initio calculations done with zirconium dimers having metal-metal separation ranging from 3.6  A to 4.0 A, for example, [(C Hs)2Zr(t-PMe2)j2, 3.6, have shown that there is 5 references on pace 133  Chapter III  128  significant d-orbital interactions between the two zirconium centers of the zirconocene fragments (i.e., up to 4  A separation between “Cp2Zr”),  suggesting the existence of the “super  long” metal-metal bonds. 30  Table 3.1 Selected zirconium-zirconium distances. (C 8 refers to the fulvalene ligand). H 10  Complex  metal-metal separation  reference  f-Zr  3.1789 A  3 13-ZrCl  3.07  A  28  3 ZrBr  3.16 A  28  3 Zn  3.32 A  28  )(dppe)] 2 [Zr(.t-Cl)(Cl  3.099(2)  t ( [Zr(.t-Cl)Cl , ] 2 ) 3 ’ PBu 3.1  3.182 A  ) 8 10 [(C Z ) H 5 ( 2 , t-Cl) (C r 3.3  3.233(1)  A  23  2 ) 8 [(ClOH ) H 5 ( .L-I)2, 2Zr (C 3.4  3.472(1)  A  19  2 [(C5H4Me)2 , Zr(p.-I)] 3.5  3.649 (1)  A  19  H 5 [(C Z ) 2 , r(.L-PMe ] 3.6 5) )- 1 ,312Zr(p.-X)12 3 [C5H3(SiMe  3.653 (2)  A  21  X  Cl, 3.7 X=Br X= I =  27  A  16 13  3.90 A 4.101(1)A 4.171(2)A  26  Most of the chemistry associated with the dinuclear zirconium(ffl) complexes has been restricted to their synthesis and X-ray structure elucidation. The oxidation of the fulvalene derivatives (e.g., complex 3.3 in Scheme 3.1) gives Zr(IV)-Zr(IV) dimers having cis (i.e., both zirconium centers on the some side of the fulvalene ligand) or trans geometries. 29 It was expected that during the oxidation of the fulvalene bridged Zr(III)-Zr(III) dimers to Zr(IV)-Zr(IV) dimers the cis geometry would be retained, however, experimental evidence  references on page 133  Chapter III  129  shows that the cis geometry is retained only when good bridging ligands (e.g., S 2 or 02) are present, whereas trans geometry was found for poorly bridging ligands (e.g., methyl group). The thermal or photochemical disproportionation reactions of the complexes of the type Zr(p-X)] where X 2 [Cp ,  =  Cl, Br and I, giving zirconium(IV), ) ZrX and Zr(ll), 2 2 (Cp (“Cp Z r”)  species is probably the only reactivity know for bimetallic zirconium(llI) complexes.’ 9 Studies show that the complexes with bridging chloride ligands were the most susceptible towards disproportionation whereas the iodide and bromide analogues were significantly slower. An important feature of these reactions is that their disproportionation was accelerated in the presence of coordinating solvents and in the presence of ligands such as CO and butadiene. For example, reacting [Cp2Zr(I.L-I 2 )] with CO gives an equimolar ratio of Cp2ZrI2 and 9 Z Cp . 2 r(CO) ’  3.3.2 Mononuclear Organometallic Complexes of Zirconium(Ill) In most instances mononuclear zirconium(ffl) species were generated in situ under photochemical or reducing conditions; typically a common synthetic procedure involved performing reactions inside the cavity of an ESR spectrometer 3. 1-42 Photochemical reactions of zirconium(IV) zirconocene derivatives leads to the homolysis of a zirconium-carbon bond, forming the corresponding organic radical and the zirconium(III) species. The photolysis of ZrC1 led to the formation of CpZrCl 2 Cp 2 and a Cp radical, whereas the photolysis of Cp Z 2 rMeC1 gave 2 Cp Z rC1 and a Me radical. ’ When the dialkyl or diaryl derivatives, Cp 4 ZrR 2 (where R  =  alkyl or Ph) were irradiated, the ESR spectral features consisted of a doublet which  has been attributed to the formation of a mononuclear hydride species. 38 The reduction of dialkyl zirconocene derivatives with sodium dihydronaphthylide have shown the formation of an anionic zirconium(llI) species, some of which were stable up to 12 hours at room temperature.  The anionic species, formed by the reduction of  3 Z Cp S , 2 ) r(CH iMe gave a binomial quintet, coupling due to the methylene protons of the two alkyl groups, suggesting that it is a mononuclear species formulated as 3 Zr(CH [Cp S 1 2 ) iMe 4 By comparison, the ESR spectrum of a similar titanium species, for example, [Na(THF)x].  references on page 133  Chapter III  130  T 2 [Cp J [Na(THF),J, iCl shows coupling due to the interaction of the d 1 metal center with a solvated sodium ion ( Na, 2 3 I  =  3/2,  The absence of such features in the ESR  spectrum of the zirconium species is attributed to the steric bulk of the alkyl groups which probably hinders the formation of ion pairs. Mononuclear neutral zirconium(III) intermediates have been synthesized by the reduction of the corresponding monoalkyl zirconocene derivatives, Cp2ZrC1R, with sodium amalgam.  Among these neutral zirconium(III) derivatives, complexes containing a  diphenyiphosphinomethyl group, , PPh are particularly interesting because of their ability 2 CH to form a three membered chelate ring upon formation of the zirconium(III) species (Scheme 3.2).374045 The complex 3.7 was formed by reducing the precursor, ) ZCl, Cp P 2 r(CH Ph with Na/Hg whereas, complexes 3.8 and 3.9 were formed by electrochemical reduction (Scheme 3.2).3740.46  Na/Hg THF  R  Electrochemical  R = Cl PPh CH 2  =  R= R = PPh CH 2  Electrochemical reduction  R=R = PPh 2 0c0CH  -Cp  0  3.7  3.8 Scheme  3.9 3.2  It was found that a toluene solution of 2 Zr(CH Cp P ) Ph 3.7 slowly decomposes to give a diamagnetic dinuclear species, the formation of which is accelerated in THF solvent. On the basis of NMR spectroscopy, the mechanistic pathway shown in Scheme 3.3 is proposed for the references on pane 133  Chapter III  131  decomposition of 3•7•42,47 This study is important because it shows that the instability of the zirconium(II1) complexes is at least partly due to their ability to undergo bimolecular disproportionation reactions which in turn sets off a series of other reactions.  ‘ 2 PPh Zr(II)—Zr(IV) Zr(llI), Zr(llI)  /  2 Ppph  Zr(IV)—Zr(IV) -PPh M 2 e  2 PPh  Zr(ll)—Zr(IV)  Zr(Ill)—ZrWI)  (1) 2 -PPh M e (2) +2 2 PPh M e  P 2 PPh  Zx(IV)—Zr(IV)  Zr(TII)—Zr(Ill)  Scheme 3.3  The first step involves a bimolecular disproportionation of 3.7 to form a Zr(II)—Zr(IV) dimeric intermediate, where the zirconium(II) center oxidatively adds a C-H bond of a Cp ligand to give a Zr(IV)—Zr(TV) intermediate with one bridging (it-ri 5 :fl Cp ligand. 1 ) 3 This ’ 22 Zr(IV)—Zr(IV) intermediate reductively eliminates one MePPh2 unit to form a Zr(III)—Zr(III) species which in turn disproportionates to give another Zr(H)—Zr(IV) intermediate. The Zr(II) references on pace 133  Chapter III  132  center of this intermediate can C—H activate a second Cp ring and eventually lead to the formation of a second Zr(IV)—Zr(IV) dimer with two bridging ) 5 : 1 (t-fl 11 Cp ligands. The reductive elimination of the second mole of MePPh2 gives the final product which is a Zr(llI)-Zr(Ill) dimer.  ] 4 [N(n-Bu) Si  3.7  3.12  f 4 [N(n-Bu)  Scheme 3.4  ri  ‘S  3.10  3.11  I  To our knowledge there are only four mononuclear zirconium(III) complexes that have been well characterized (i.e., including elemental analysis): 8 48 (1 M ) 5 H Zr( C 8), e r 3.10, 2 B 3 H C 5 (rI ut 1 49 ZrC1, 3. 1 1, 2 ,3)  [B u4N]{ { 3 ZrC1 ,2 6 3• 12, ] (ri ( H 5 2 ) SiM C e 1,3) 2  and  3 Zr ) H 5 2 ) 3 N2)[C 2( 2] C H(SiM 6 (1 r1 ; e of these, only three, 3.10, 3.11 and 3.12, have been characterized by X-ray crystallography. The anionic complex 3.12 was prepared by reacting the dinuclear Zr(III)—Zr(llI) dimer 3.7, with a tetraalkyl ammonium salt (Scheme 3.4), whereas the other three were made by the reduction of the corresponding zirconium(IV) halide precursor. references on pace 133  Chapter III  133  These examples illustrate that with sufficiently sterically demanding ligands, the tendency of the zirconium(III) state to dimerize and possibly disproportion 42 ate can be avoided. However, the chemistry of these complexes has not been explored. In fact, there are no examples of simple, well characterized hydrocarbyl or hydride complexes of zirconium(ffl) known.  3.4 Summary The chemistry of zirconium(III) complexes is rather poorly developed, with most of the attention being focused on the synthesis of such complexes. The dinuclear Zr(III)—Zr(III) complexes seem to be favored over the corresponding mononuclear counterparts. It appears that the disproportionation of zirconium(llI) complexes to give Zr(II) and zirconium(IV) species is thermodynamically favored, which in part can be attributed to the stability of the zirconium(IV) complexes. The incorporation of bulky ligands around zirconium(III) centers can provide kinetic stability, which in turn has led to the isolation of some mononuclear zirconium(llI) complexes. In the following chapter the preparation of a series of mononuclear zirconium(III) complexes which also incorporate hydrocarbyl and hydride ligands will be discussed. These paramagnetic zirconium(Ill) derivatives provide the first opportunity to examine the reactivity of Zr—C and Zr—H bonds in d 1 complexes.  3.5 References (1)  Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry; Third Edition ed.; Wiley Interscience: New York, 1972.  (2)  Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Pergamon Press: Oxford, 1984; Vol. p. 1116.  (3)  Cardin, D. J.; Lappert, M. F.; Raston, C. L. Chemistry of Organo-Zirconium and Hafnium Compounds; 1 ed.; Ellis Horwood Limited: Toronto, 1986.  (4)  Lappert, M. F.; Pickett, C. J.; Riley, P. I.; Yarrow, P. I. W. J. Chem. Soc., Dalton Trans.  1981, 805. (5)  Dumond, D. S.; Richmond, M. G. .1. Am. Chem. Soc. 1988, 110, 7547.  Chapter III  134  (6)  Gladysz, 3. A.; Tam, W. J. Am. Chem. Soc. 1978, 100, 2545.  (7)  Shannon, R. D. Acta Crystallogr. 1976, A32, 751.  (8)  Fowles, G. W. A.; Russ, B. 3.; Willy, G. R. Chem. Commun. 1967, 646.  (9)  Fowles, G. W. A.; Willey, G. R. J. Chem. Soc. (A) 1968, 1435.  (10)  Larsen, E. N.; Hehzler, T. E. Inorg. Chem. 1974, 13, 581.  (11)  Nicholls, D.; Ryan, T. A. Inorg. Chim. Acta 1977,21, L17.  (12)  Wengrovius, J. H.; Schrock, R. R. J. Organomet. Chem., 1981,205, 319.  (13)  Wengrovius, J. H.; Schrock, R. R.; Day, C. S. Inorg. Chem. 1981,20, 1844.  (14)  Hoffman, D. M.; Lee, S. Inorg. Chem. 1992,31, 2675.  (15)  Ho, 3.; Drake, R. J.; Stephan, D. W. J. Am. Chem. Soc. 1993, 115, 3792.  (16)  Cotton, F. A.; Diebold, M. P.; Kibala, P. A. Inorg. Chem. 1988,27, 799.  (17)  Ashworth, T. V.; Agreda, T. C.; Herdtweck, E.; Herrmann, W. A. Angew. Chem.., mt. Ed. Engi. 1986,25, 289.  (18)  Wielstra, Y.; Gambarotta, S.; Meetsma, A.; Boer, 3. L. d. Organometallics 1989, 8, 250.  (19)  Wielstra, Y.; Gambarotta, S.; Meetsma, A. Organometallics 1989, 8, 2948.  (20)  Cuenca, T.; Herrmann, W. A.; Ashworth, T. V. Organometallics 1986,5, 2514.  (21)  Chiang, M. Y.; Gambarotta, S.; Boihuis, F. v. Organometallics 1988, 7, 1864.  (22)  Gell, K. I.; Harris, T. V.; Schwartz, 3. Inorg. Chem. 1981,20, 481.  (23)  Gambarotta, S.; Chiang, M. Y. Organometallics 1987, 6, 897.  (24)  Gambarotta, S.; Wielsira, Y.; Spek, A. L.; Smeets, W. J. 3. Organometallics 1990, 9, 2142.  (25)  Edwards, P. G.; Howard, J. A. K.; Perry, 3. S.; Al-Soudani, A. R. J. Chem. Soc., Chem. Commun. 1991, 1385.  (26)  Hitchcock, P. B.; Lappert, M. F.; Lawless, G. A.; Olivier, H.; Rayn, E. 3. .1. Chem. Soc. Chem. Commun. 1992,474.  (27)  Pearson, W. B. Handbook ofLattice Spacing Structures ofMetals and Alloys; Pergomon: New York, 1976; Vol. 2, p 90.  (28)  Dahi, L. F.; Chiang, T.; Seabaugh, P. W.; Larsen, E. M. Inorg. Chem. 1964,3, 1236.  (29)  Wielstra, Y.; Gambarotta, S.; Spek, A. L.; Smeets, W. J. 3. Organometallics 1990, 9, 2142.  (30)  Benard, M.; Rohmer, M. M. J. Am. Chem. Soc. 1992, 114, 4785.  Chapter III  135  (31)  Choukroun, R.; Gervais, D. J. Chem. Soc., Chem. Commun. 1985, 224.  (32)  Choukroun, R.; Basso-Bert, M.; Gervais, D. J. Chem. Soc., Chem. Commun. 1986, 1317.  (33)  Choukroun, R.; Dahan, F.; Larsonneur, A. M.; Samuel, E.; Peterson, J.; Meunier, P.; Somay, C. Organometallics 1991, 10, 374.  (34)  Jones, C. B.; Petersen, 3. F. J. Am. Chem. Soc. 1983, 105, 5503.  (35)  Jones, C. B.; Petersen, J. F. Inorg. Chem. 1981, 20, 2889.  (36)  Samuel, E. Inorg. Chem. 1983,22, 2967.  (37)  Schore, N. E.; Hope, H. J. Am. Chem. Soc. 1980, 102, 4251.  (38)  Hudson, A.; Lappert, M. F.; Pichon, R. J. Chem. Soc., Chem. Commun. 1983, 374.  (39)  Gynane, M. J. S.; Jeffery, J.; Lappert, M. F. J. Chem. Soc., Chem. Commun. 1978, 34.  (40)  Etienne, M.; Choukroun, R.; Gervais, D. J. Chem. Soc., Dalton Trans. 1984, 915.  (41)  Atkinson, J. M.; Brindiley, P. B.; Davis, A. G.; Hawaii, I. A. A. J. Organomet. Chem. 1984,264, 253.  (42)  Blandy, C.; Locke, S. A.; Young, S. J.; Schore, N. E. .1. Am. Chem. Soc. 1988, 110, 7540.  (43)  Kenworthy, 3. G.; Myatt, J.; Todd, P. F. Chem. Commun. 1969, 263.  (44)  Olive, H.; Olive, S. Angew. Chem., mt. Ed. Engi. 1968, 7, 386.  (45)  Manzer, L. E. J. Am. Chem. Soc. 1978, 100, 8068.  (46)  Raoult, Y.; Choukroun, R.; blandy, C. Organometallics 1992, 11, 2443-2446.  (47)  Schore, N. B.; Young, S. 3.; Olmstead, M. M. Organometallics 1983,2, 1769.  (48)  Rogers, R. D.; Teuben, 3. H. J. Organomet. Chem. 1989,359, 41.  (49)  Urazowski, I. F.; Ponomaryev, V. I.; Nifantev, I. E.; Lemenovskii, D. A. J. Organomet. Chem. 1989,368, 287.  13  Chapter 4 Zirconium(llI) Complexes: Synthesis and Reactivity 4.1 General A survey of the literature on zirconium(III) complexes in Chapter 3 has shown that almost all of the stable mononuclear organometallic derivatives contain bulky ligands such as - 1,3]-1, ) 2 ) 3 -C (CMe 5 [1 3 H -C 2 ] H [r1 ( 3 H 5 2 SiMe C 1,31 1 or cyclooctatetraenyl ligand, [TI 8 (Chapter 3). By comparison the tridentate ligand , 1 C [N(SiMe P j ) 2 H PNP is somewhat R isoelectronic to the Cp ligand and, in addition, the steric bulk of PNP can be considerably altered by changing the substituents on the phosphorus, for example R  =  Me, Ph, Pr or But.  Therefore by incorporating bulky PNP ligand systems that are comparable to the bulky Cp based ligands such as ) [T1 ( 3 H 5 2 1,31-’, CMe C it should be possible to stabilize mononuclear zirconium(III) complexes.  It is also important to note that the syntheses of dinitrogen  complexes (e.g., 2.2, 2.9, 2.12 etc.) were only successful with the isopropyl version of the PNP ligand, 2 [N(SiMe2CH P Pr)2]’ whereas reactions involving complexes containing the less bulky PNP ligand , 1 C [N(SiMe P ] ) 2 Me H - gave intractable material (Chapter 2). This last result seems to suggest that incorporating the isopropyl substituents on PNP could provide adequate kinetic stability for stabilizing reactive intermediates.  4.2 Synthesis of Zirconium(Ill) and Hafnium(llI) Complexes It has been previously shown (Section 2.2.2) that the reduction of the zirconium(IV) complex 2 1 Zr(r1 ) H 5 [ C ] ) N(SiM H2PPr C1 C , e 2.6 with excess Na/Hg under dinitrogen leads to the formation of the dinuclear dinitrogen complex { 5 [(PP C S N 2 ) H ]Zr(T iMe C H r } 2(-N ) 2 , 2.9. During this process there is a color change from yellow to deep green which persists for hours followed by a slow change to deep brown, the color of the dinuclear dinitrogen derivative. By control of reaction times, the intermediate was intercepted in high yield (88%) as dark green crystals having the formula ) Zr( ) H 5 C P ] 2 Cl[N(SiMe C Pr H , ri 4.1 (Scheme 4.1). This highly colored (?max  324 nm, Emax  2600 ) cm zirconium(III) 1 M  references on page  Chapter IV  137  chioro derivative, in contrast to other unstable (see Chapter 3) zirconium(III) derivatives, exhibits high thermal stability. 2 ’ 1  2 Pr’ Me S 2 i  Na/Hg toluene  \  M=Zr,2.6 M=Hf,4.2  M=Zr,4.1 M=Hf,4.3 Scheme 4.1  H NMR spectrum of 4.1 is consistent with it being a paramagnetic system since The 1 only a broad resonance is observed and no signals were observed in the 31 P{ 1 H} NMR spectrum. Moreover, the solution (in toluene) ESR spectrum recorded at room temperature shows a binomial triplet at g  =  1.955 with coupling to two phosphorus-31 nuclei and satellites  due to one magnetically dilute zirconium nucleus (a( Zr) 91  =  37.2 G, 91 Zr, 11.23%, I  =  5/2),  which is consistent with a mononuclear species in solution. The ESR spectrum of 4.1 was simulated using the following parameters: a( P) 31 G, 5H; linewidth  =  =  21.1 G, 2P; a( N) 14  =  2.9 G, iN; 1 a( H )  =  1.8  2.3 G. The solution magnetic measurements of 4.1 gave a value of ff  =  1.57 B. M.*  The reduction of the hafnium(IV) precursor H Hf( 5 5)Cl2[N(SiM C q] 4.2, e2CH2PPr’)2 with Na/Hg gave a brown material, from which deep brown crystalline cubes were isolated by recrystallization. The ESR spectrum of the recrystallized material consisted of a triplet and a broad singlet, where the triplet resonance was identical to the resonance of the zirconium(III) complex 4.1 (Figure 4.1).  The broad signal is assigned to the hafnium(III) species  Hf( ) H 5 C P ] 2 ) C1[N(SiMe C Pr H , ri 4.3. An intriguing feature of the spectrum shown in *  This value is lower than the spin only value of 1.73 B. M. The lower magnetic moment could be atthbuted to magnetic exchange, i.e., some degree of association between mononuclear species; or to spin-orbit coupling. The calculated spin-orbit coupling constant of Zr , 500 cm 3 , should give a magnetic moment of about 1.2 B.M. 4 74 references on page  Chapter IV  138  Figure 4.1 is that the signals due to the zirconium(III) and the hafnium(III) species have approximately equal intensity. However, it will be shown later that the sample consists mainly of hafnium(ffl) complex in approximately 10:1 ratio. This suggests that the ESR sensitivity of the zirconium(Ill) complex is approximately ten times greater than that of hafnium(III). 21.1 G  1 C HfCpC1[N(SiMe P 1 ) 2 Pr H , 4.3  C ‘,ZrCpCl[N(SiMe P ] 2 ) Pr’ , 4.1 H Figure 4.1 Overlapping room temperature ESR spectra of a solution (toluene) sample of C ZrCpCl[N(SiMe P ] Pri) H , 4.1. C HfCpCl[N(SiMe P 2 ] Pr’) H 4.3, and 2  Commercially available hafnium precursors (e.g., HfCl ) contain zirconium impurities in 4 the range of 1 to 4%. Therefore, most organometallic complexes of hafnium are likely to have a very small percentage of the zirconium analogue as an impurity. During the reduction of the hafnium(IV) derivatives the hafnium intermediates possibly undergo decomposition at a higher rate than the zirconium counterparts, which would eventually lead to the enrichment of zirconium analogue in the product. The presence of zirconium impurities would also hamper the isolation of analytically pure hafnium(III) samples (Table 4.1). To our knowledge the  references on page  Chapter IV  139  hafnium(HI) complex 4.3 is the only complex that has been characterized by satisfactory microanalysis.  Table 4.1 Elemental composition found for some hafnium(Ill) derivatives. Complex  H  C  Other  HfCpCl[N(SiMe2CH2PPr’)J, 4.3  references  N  Calculated  41.13  7.35  2.09  Found  41.49  7.49  1.96  (dippe) 3 [HfC1 2 ]  this work  Cl  Calculated  30.7  5.89  19.4  Found  31.7  6.05  18.3  -C5Me5)(r 5 Hf(fl ) 7 H C  4  Hf  Calculated  50.43  5.48  44.09  Found  51.86  5.63  44.55  3  4.3 Synthesis of Zirconium(ffl) Hydrocarbyl Complexes  RM Toluene  RM = MeMgC1, EtLi, PhLi, K, 2 2 PhCH SiCH 3 Me L i  4.1  2 J 1 p  R=Me4.5, Et4.6, Ph 4.4, Ph 4.7, 3 2 CH SiMe 4.8 2 CH Scheme 4.2  The metathesis reaction of Zr(T1 2 ) H 5 C P ] ) C1[N(SiMe C Pri H , 4.1 with PhLi at -78 C in toluene gives an instantaneous color change from a green to a deep red solution. Recrystallization from the crude product gave diamond shaped crystals; these were shown to be references on page  Chapter IV  140  Zr(1 ) H 5 ] 2 ) Ph[N(SiMe2CH2PPr C , 4.4. The solution (in toluene) ESR spectrum of complex 4.4 recorded at room temperature shows a broad binomial triplet at g coupling to two phosphorus-31 (a( P) 31  =  =  1.981 indicating  20.3 G) nuclei, however no satellites due to the  coupling of the zirconium-91 nucleus were observed. The zirconium(llI) alkyl complexes 1 Zr(fl ) H 5 C 2 R[N(SiMe H2PPr) C where R  =  Me,  4.5; Et, 4.6; PhCH2, 4.7 and 2 SiCH 4.8, were synthesized using different alkyl transfer 3 Me , reagents (Scheme 4.2). A typical reaction was carried out with a toluene solution of the chioro derivative 4.1 and an alkyl transfer reagent, usually at room temperature. Unlike the phenyl derivative, all of the ailcyl derivatives are deep green in colour. Isolation of micro-analytically pure samples of the complexes with small alkyl groups, for example methyl, 4.5 and ethyl, 4.6 was hampered by the incorporation of LiCl or MgC12 in the samples. Table 4.2 gives the elemental compositions found for the hydrocarbyl derivatives of 4.1 and it can be noted that the values for complexes 4.5 and 4.6 are lower than expected. For the ethyl derivative, 4.6 the analytical data for the crystals from the first recrystallization and from the second recrystallization seem to fit for 0.6 and 0.2 equivalents of LiCl respectively. Also, for the methyl derivative 4.5 the crystals from the first recrystallization seem to contain 0.2 equivalents of MgC12, which is further corroborated by the determination of the chloride content of the sample. It has been established that some zirconium(IV) complexes form adducts with LiC1, 5 a phenomenon that could be attributed to the Lewis acidity and to the coordinative unsaturation of the zirconium(IV) center. Similar factors may be responsible for the incorporation of LiC1 and MgC12 into the zirconium(III) complexes 4.6 and 4.5 respectively.  However, in these  zirconium(llI) derivatives, the interactions between the zirconium and the halide ion of the salts (i.e., LiCl or MgC12) are probably weaker and become insignificant as the steric bulk of the alkyl group is increased. The room temperature solution ESR spectra of the samples formulated as 4.6•(LiCl) 06 and 4.6•(LiC1) 2 were virtually identical. It is noteworthy that the ESR . 0 spectrum of the anionic zirconium species 3 [Cp2Zr(CH2SiMe ] 2 ) iNa(THF)J did not show  references on page  Chapter IV  141  hyperfine interaction due to sodium; 2 in contrast, the phosphide derivative ) Zr(PEt [Cp ] 2 [Na(THF)x]+ shows hyperfine features due to the coupling of one sodium nucleus. 6  Table 4.2 Micro-analytical data for the hydrocarbyl derivatives of ) H 5 C P ] Cl[N(S Pr’ C H . iMe Zr(r1 2 ) Complex  C  H  N  Calculated for 4.5  51.11  9.29  2.48  Calculated for 22 )o. 2 4.5.(MgC1 Found  49.28 48.90  8.96 9.08  2.39 2.39  Calculated for 4.6  51.95  2.42  Calculated for 4.6•(LiCl) 06 1St found for recrystallization Calculated for 4.6•(LiC1) 02 found for 2nd recrystallization ) H 5 C P ] ) Ph[N(S C Pr H , iMe 4.4 Zr(1 2  49.76 49.81  9.42 9.02 9.14  2.32 2.30  51.20 51.21  9.28  2.39  9.27  2.40  Calculated Found  55.63 55.51  8.69 8.68  2.24 2.35  Cl  Zr(rj 2 ) H 5 C Me[N( H2PPr C SiMe )2], .4.5 2.67 2.52  ) H 5 C P ] ) Et[N(S C Pr H , Zr(1 2 iMe 4.6  H 5 P ] 5)CH2Ph[N( Zr(rI 2 Pr’ C SiMe2CH , ) 4.7 Calculated Found  56.29  8.82  2.19  56.58  8.86  2.25  H 5 S [ 3 C P ] N(Si 5)C iM Pr C Zr(11 2 H Me , H ) 4.8 e Calculated  50.97  9.51  Found  50.68  9.46  2.20 2.21  Figure 4.2 shows the X-ray structures of the phenyl derivative Zr(rj 2 ) H 5 Ph[N(SiMe C PPr) 4.4, and the alkyl derivative ] 2 CH ] Zr H 5 [ 3 C 2 N(S 5)CH2 H2P C SiMe (1 , iMe Pr) 4.8. These two examples are the first structurally characterized, mononuclear hydrocarbyl derivatives of zirconium(III).  references on page i  Chapter IV  142  Si Si N  II  Iv  Si  c3  Cl 4  I  Ill  Figure 4.2 I and III are ORTEP views showing the complete atom labeling scheme for complexes 2 Zr( ) H 5 C ] Ph[N(S H2PPr C r iMe ) 4.4, and 5 Zr(fl ) H CH2SiMe3C [N(SiMe2CH2PPr)2] 4.8, respectively. II and IV are Chem 3D® views showing the arrangements of ligands around the zirconium in complexes 5 Zr(rj ) H PhC {N(SiMe2CH2PPr)21 4.4, and Zr(1 2 ) H 5 S [ 3 C P ] N(Si CH iMe Pr) C H Me 4.8, respectively.  references on page  Chapter IV  143  Table 4.3 Selected bond lengths of complexes 2 Zr( ) 5 C J Ph[N(SiMe C5H H2PPr T ’) 4.4, and 2 Zr( ) H 5 [ 3 C P ] CH2Si N(SiM Pr’) C H , Me e 4.8. fl ) H 5 C P ] Ph[N(SiMe Pr’) C H Zr(11 2  Zr(i 2 ) H 5 [ 3 C P ] ) CH2Si N(SiM C Pr H Me e  4.4  4.8  Atom  Atom  Zr  P(l)  Zr  P(2)  Zr  (A)  Distance  (A)  Atom  Atom  2.7819 (14)  Zr  P(l)  2.7923 (16)  2.7843 (16)  Zr  P(2)  2.8563 (17)  N  2.231 (3)  Zr  N  2.216 (4)  Zr  C(31)  2.272 (4)  Zr  C(31)  2.337 (5)  Zr  Cp  2.225  Zr  Cp  2.2162 (5)  Distance  The structural parameters (Table 4.3 and 4.4) associated with the PNP ligand in both complexes are similar to other zirconium(IV) derivatives. 79 A comparison of bond angles around the zirconium centers suggests that the coordination environment can be envisaged as a distorted trigonal bipyramid with the phosphine donors of the meridionally coordinated PNP ligand occupying the axial positions. The distances from the zirconium to the centroid of the Cp ligand in the phenyl, 4.4 (2.225  A)  and the alkyl, 4.8 (2.2162 (5)  shorter (the difference is greater than 0.05 derivatives 2.7 (2.286  A)  derivatives are slightly  A) than the distances observed for the zirconium(IV)  A) and 2.9 (2.286 and 2.294 A).  Shorter zirconium—Cp distances reflect  the decreased steric constrains around the zirconium(III) centers of 4.4 and 4.8 than the zirconium centers of 2.7 and 2.9. The zirconium-carbon bond distances associated with the phenyl, 4.4 (2.272 (3) and the alkyl, 4.8 (2.337 (5)  A)  A)  derivatives are within the observed range for zirconium  complexes containing bulky alkyl groups, for example in ) 3 Cp2ZrPh[CH ] 2 (SiMe the 0 zirconium-C p and zirconium-C(alkyl) distances are 2.324 (7) and 2.329 (6)  A respectively. 10  For zirconocene derivatives the ) 3 zirconium-C (sp bond distances range from 2.25 1 (6) 2.388 (12)  A where the longer distances  A  to  are associated with larger alkyl groups. ”°’ In the 2  PNP derivative ) Zr( ) 6 H 4 C P ] 2 Ph[N(SiMe C Pr H , r the zirconium-C 0 jp distance of 2.3 17 (7)  A is slightly longer than what was observed in the zirconium(Ill) phenyl derivative, 4.4. references on page  122.  144  Chapter IV  Table 4.4 Selected bond angles of complexes 5 C 4.4, Zr(rl ) H Ph[N(SiMe2CH2PPr)2) and 3 iMe CH C [N(SiMe2CH2PPr)2], 4.8. Zr(11 ) H 5 S 2  CH C [N(SiMe2CH2PPr)2] ) H 5 S 2 iMe Zr(1 3 4.8  Zr( 5 C )H Ph[N(SiMe2CH2PPr)2] 4.4  Atom  Atom  Atom  Angle (°)  150.09 (4)  P(1)  Zr  P(2)  151.17 (5)  N  79.47 (9)  P(l)  Zr  N  77.83 (11)  Zr  N  75.01 (10)  P(2)  Zr  N  74.37 (11)  P(1)  Zr  C(31)  87.04 (11)  P(l)  Zr  C(31)  85.13 (13)  P(2)  Zr  C(31)  88.57(11)  P(2)  Zr  C(31)  93.47 (13)  P(1)  Zr  Cp  104.27  P(1)  Zr  Cp  103.95 (4)  P(2)  Zr  Cp  104.82  P(2)  Zr  Cp  102.08 (4)  N  Zr  C(3l)  112.60 (13)  N  Zr  C(31)  102.47 (16)  N  Zr  Cp  135.57  N  Zr  Cp  139.47 (10)  C(31)  Zr  Cp  111.81  C(31)  Zr  Cp  118.05 (13)  Zr  C(31)  C(36)  132.5 (5)  Zr  C(31)  Si(3)  134.0 (3)  Zr  C(31)  C(32)  114.9 (3)  Si(3)  C(31)  C(33)  114.9 (3)  Si(1)  N  Si(2)  119.15 (17)  Si(1)  N  Si(2)  120.18 (23)  Atom  Atom  Atom  P(l)  Zr  P(2)  P(l)  Zr  P(2)  Angle  ()  Cp refers to the centroid of the Cp ligand. All structural parameters associated with the Cp ligand for the complex 4.4 were taken from the Chem 3D® structure.  The bond angles between the zirconium, ipso-carbon and the ortho-carbons in H are 121.1° (6) and 125.3° (6)’; however, the comparable C Pr Zr( ) 6 H 4 C P ] 2 ) Ph[N(SiMe angles in the zirconium(III) phenyl complex 4.4, Zr—C(31)—C(36) and Zr—C(31)—C(32) are 132.5° (5) and 114.9° (3)  A respectively.  These angle parameters seems to suggest that in 4.4  the phenyl ligand is twisted about the ipso-carbon towards the nitrogen of the PNP. The phenyl group in complex 4.4 is coplanar with the equatorial plane and therefore is expected to  references on page jQ  Chapter IV  145  experience significant steric interactions with the Cp ligand, where the centroid of the Cp ligand also lies on the equatorial plane. It is noteworthy that attempts to metathesize the zirconium-chloride bond of 4.1 with the Grignard reagent BzMgC1 gave a diamagnetic compound (in approximately 20% isolated yield) as one of the products. Spectroscopic and elemental analysis of this compound are consistent with the formula ] Cl[N(SiMe ZrBz C 2 H2PPr , ) 4.9. It seems that the reaction of 4.1 with BzMgC1 or BzK involves more than one reaction pathway, one of which being the exchange of the Cp ligand of 4.1 with the benzyl group. This exchange reaction is less significant when BzK was used, where the zirconium(III) benzyl derivative was the main product. It is noteworthy that the 31 H} NMR spectrum of the mother liquor of the aforementioned reactions shows P{ 1 that one of the diamagnetic impurities is the end-on dinitrogen complex 2.9. This observation seems to suggest the formation of a zirconium(TI) species (which subsequently binds dinitrogen) during the reaction of 4.1 with benzyl transfer reagents. A possible mechanism to rationalize the formation of the zirconium(IV) dibenzyl derivative 4.9 could involve the formation of the zirconium(III) benzyl intermediate ZrBzCl[N(Si C P 2 ] Pr) H Me by the exchange of the Cp ligand of 4.1 rather than the replacement of the chloride ligand.  This intermediate, by comparison with the stable  zirconium(ffl) complex ZrCpCl[N(SiMe2CH2PPr)2j 4.1, is sterically less crowded. Therefore, 2 ZrBzCl[N(Si P Pr)2] Me2CH is likely to be kinetically labile towards disproportionation to give the zirconium(IV) complex 4.9 and some unknown zirconium(II) species. Solution magnetic studies (Evans Method) on the 2 CH S iMe3 derivative gave a value of .teff.  =  1.73 B.M., which is close to the calculated spin only value of a d 1 zirconium(llI) center.  The room temperature solution ESR spectra of the alkyl derivatives are more complicated than the spectrum of the phenyl derivative 4.4. With the exception of the benzyl derivative, the hyperfine interaction of the unpaired electron with the two phosphorus nuclei are in the range of 20 to 21 G. In the case of the Et and the Bz derivatives, the satellites due to zirconium-91 nuclei were not observed.  references on page j  Chapter IV  146  [Zr]-C C 2 D H H 2 [Zr].C C H3 H Observed A 2OG  B  Simulated  3 [Zr]-C S 2 1Me H  3 [Zr]-CH Observed  D  2OG  C  Simulated  [Zr]  =  “Z rCp 2 [N(SiM C P ] ) Pr’ ” H e  Figure 4.3 The ESR spectra of the alkyl complexes A 4.6, B 4.6-d , C 4.5 and D 4.8. For each 1 case the observed spectrum is shown on the top and the simulated spectrum is shown below.  references on page 122  Chapter IV  147  Table 4.5 Hyperfine coupling constants (G) for the chloro and the hydrocarbyl derivatives of  2 ZrCpR[N(SiM j . e2CH2PPr) All the values were obtained from simulations.  *  R  g  Zr) 91 a(  P) 31 a(  N) 14 a(  Cl  1.955  37.2  21.1  2.9  1.8  5 C6H  1.981  20.7  20.3  1.8  1.1  3 CH  1.963  28.0  21.1  2.1  3 C 2 CH H  1.962  20.9  2.6  * 5 H 6 C 2 CH  1.956  18.6  3.4  Si(CH 2 CH 3 )  1.973  21.4  2.0  30.5  a( H 1 ) a(’Hcp)  a(’Ha)  6.6 9.3  3.2  1.8  3.2 9.3  1.2 6.2  The hyperfine values given for the benzyl derivative are only an approximate value. Simulation studies of the room temperature solution (toluene) ESR spectrum of the  methyl derivative 4.5 suggest that the three cc-hydrogens of the methyl group attached to zirconium are isotropic. It is important to note that the minor features of the simulated ESR spectrum of the methyl complex 4.5 (Figure 4.3) using the values given in Table 4.5 are slightly different from that of the actual spectrum. It is believed that this could be a result of the unsophisticated ESR simulation program, where only one overall line broadening value could be used. It is possible that a more accurate spectral simulation could be obtained using different values of line broadening for each type of spin system, for example, a different line broadening value for the two phosphorus nuclei and a different value for the three ct-hydrogens. An intriguing feature in the ESR spectra of the ethyl and CH2SiMe 3 derivatives is that the cc-hydrogens have different hyperfine coupling constants. This difference in hyperfine interaction could be due to restricted rotation about the zirconium-carbon bond associated with the alkyl substitution. If the rotation is slow on the ESR time scale, some rotational isomers references on page  Chapter IV  148  would have a longer lifetimes that the others. 15 Scheme 4.3 shows the two types of ’ 14 conformational isomers for the ethyl and the 3 SiMe derivatives, where type A has 2 CH diastereotopic cc-hydrogens, and type B has enantiotopic cc-hydrogens. The diastereotopic a-hydrogens of conformer A will have different hyperfine coupling 14 constants. 1 ’ 5  2 Pr’  Pr’ 2  0 S 2 Me (’\  0 S 2 Me (’\  Sç,/ 2 Me  / 1 S 2 Me  2 Pr  A  Pr’ 2  R  2 Pr’  B  C  R=Me, SiMe 3 Scheme 4.3 An alternate explanation for the different coupling constants for the c-hydrogens would be that, in solution, one of the a-hydrogens weakly interacts with the metal center, C (Scheme 4.3). Infrared spectroscopic experiments were carried out to elucidate the presence of agostic C—H bond interactions. Any such bonding interactions of the c-hydrogens should be reflected in the stretching frequencies associated with the carbon-hydrogen bonds of the a-hydrogens. The carbon-hydrogen stretching frequencies associated with the PNP ligand give rise to a very complicated pattern from 3000 to 2700 cm . Therefore the solution infrared spectra of 1 deuteride derivatives of the ethyl complex, ] )CH2CH2D[N(SiMe2CH H C 5 Zr(rI P 2 Pr) , 1 and ) 4.6-d 5 were analyzed. The infrared Zr(1 ) H 5 [ 3 C P ] 2 N(SiMe CD Pr C , 4.6-d D H spectra of the monodeuterio derivative 4.6-d 1 enabled the assignment the stretching frequencies associated with the -deuterides of the ethyl group and then comparison with the infrared spectra of the perdeuterio ethyl derivative 4.6-d 5 enabled to assign the stretching bands associated with the a-deuterides.  references on page  Chapter IV  149  2 [Zr]-CH  3 C 2 [Zr]-CD D  [Zr]  3200  2960  =  C “ZrCp[N(SiMe p ] 2 ) pri ” H  2720.  2480  2240.  2000.  Figure 4.4 The solution infrared spectra of complexes 4.6, 4.6-d 1 and 4.6-d . 5  A comparison of the infrared spectra of complexes 4.6-d 5 show that the latter 1 and 4.6-d has an absorption band at 2043 cm-’ which can be assigned as an x-deuterium stretch. Also, this band is 85 cm 1 lower than the next nearest carbon-deuterium stretching band, suggesting some weakening of the C—D bond associated with the band at 2043 cm. The carbon 1 deuterium stretching band at 2043 cm-’ will correspond to a carbon-hydrogen stretching band around 2783 cm . For comparison, the agostic carbon-hydrogen stretching frequencies of 4 various transition metal complexes range between 2700 cm 1 and 2350 8 ’ 1 . 1 cm 6 However, in some rarer occasions higher C—H stretches have been reported for agostic C-H bonds. For example in the cationic complex ) 3 ( [frH L 2 PPh ], where L  =  8-methylquinoline, an agostic  bond is formed between the iridium and the one of the C—H bonds of the methyl group, and an references on page  i2  Chapter IV  150  infrared band at 2848 cm1 has been assign to the agostic C—H stretch. 19 Therefore it is possible that one of the cc-hydrogen of the ethyl derivative could be weakly interacting with the metal center which in turn could be attributed to different coupling constants observed for the cc hydrogens in the ESR spectra of the alkyl derivatives. The solution ESR spectrum of the benzyl zirconium(III) derivative 4.7, does not have a center of symmetry, suggests that more than one species exist in solution. It is possible that the benzyl ligand is coordinated in an 12 fashion, with a geometry similar to C shown in Scheme 4.3. Such a geometry would make the two benzylic protons enantiotopic, and this proposal is consistent with the hyperfine values obtained (by simulation) for the cc-hydrogens.  LiPPh NaNPh , 2 2 or PhONa  4.1  Y  =  OPh 4.10, NPh 2 4.11 or 2 PPh 4.12  Scheme 4.4 Metathesis reactions with the zirconium(Ill) chloride complex 4.1 with one equivalent of NaOPh, NaNPh2 or LiPPh 2 led to the synthesis of P 2 Zr( ) H 5 OPh[N(SiMe Pr)2 C 1 2CH ] 4.10, Zr(1 2 ) H 5 P ) NPh2[N(SiM C Pr ) H 5 C [ C P ] ) N(SiM PPh e2CH 1 4.11, and Zr(1 Pr H e 5 2 -  4.12, respectively (Scheme 4.4). The phenoxy derivative was deep green in colour whereas the amido and the phosphido derivatives gave dark brown solutions. These complexes were extremely soluble in hydrocarbon solvents and only the phenoxy derivative was isolated in a solid form amenable to elemental analysis. However, the ESR spectra of the crude samples were symmetric, and the 1 H NMR spectra showed only broad peaks, suggesting that the synthesis of these complexes proceeds in virtually quantitative yields. The room temperature solution ESR spectra of the amido derivative, 4.11 (g phenoxy derivative, 4.10 (g  =  1.955, a( P) 31  =  =  1.953, a( P) 31  =  11.2 G), and the  18.7 G), consist of a broad binomial triplet references on page  Chapter 1V  151  indicating coupling of two equivalent phosphorus nuclei. The phosphido derivative, 4.12 displays of a doublet of triplets (g  =  1.965; a( P) 31  =  29.8 G, 1P; a( P) 31  =  18.6 G, 2P) which is  consistent with a mononuclear zirconium species (Figure 4.5). It is important to note that other phosphido derivatives of zirconium(III) cited in the literature are reported to be binuclear and diamagnetic containing bridging phosphido ligands (e.g., 3.6).  Figure 4.5 The room temperature solution (toluene) ESR spectrum of the phosphide complex Zr(rj 5 H 5)PPh2[N(Si C Me2CH2PPr)2j, 4.12.  4.4 Oxidation of Zirconium(Ill) Complexes Treating a solution of zirconium(llI) chioro derivative 4.1 with solid TiC1 3 or PbC1 2 led to the oxidation of the zirconium complex to give the dichloro zirconium(IV) complex 2.6 in almost quantitative yield. Also, 0.5 equivalents of Ph S react with complex 4.1 to give the 2 zirconium(IV) thiolate derivative, ] Zr( ) H 5 C P 2 (SPh)Cl[N(S C Pr) H , iMe r 4 13 in .  quantitative yields (Scheme 4.5). These reactions have been useful in quantifying the purity of some zirconium(Ill) derivatives. For example, during the synthesis of the alkyl complex Zr H 5 S [ 3 C 2 ] N(SiM H2PPr S)CH iMe C , e ( ) 4.8 an aliquot of the crude reaction mixture was titrated against a solution of Ph , where a color change occurs from deep green to yellow. S 2 The resulting solution is then analyzed by 31 P{ 1 H} NMR spectroscopy. Such analyses have references on page i2  Chapter IV  152  shown that the metathesis reactions involving 4.1 and alkyl transfer reagents proceed in almost quantitative (>95%) yields. Oxidation of a crude sample of the hafnium(ffl) chioro derivative, 4.3 with TiC1 3 showed the presence of hafnium(IV) and zirconium(IV) species in approximately 10:1 ratio. This result is consistent with the previous suggestion that during the reduction of the hafnium(IV) precursor the ratio of the zirconium impurity increases.  Me S 2 i  2 3 or Phd TiC1 Toluene  Me S 2 i  4.1  2.6  Me S 2 i  Me S 2 i\  S 2 Ph Toluene Me S 2 i  Me S 2 I  R=Cl 4.1, Me 4.5, Et 4.6, 3 SiMe 4.8 2 CH Ph  RPh [Zr]Q[Zr]  .  R  [Zr][Zr] R  Ph  Slow Dimerization For R = Me, Et, 3 SiMe 2 CH [Zr] = 2 C ZrCp[N(SiMe P Pr’J H Scheme 4.5  references on page  ChapterlV  153  It is noteworthy that the oxidized monoallcyl derivatives, i. e., allcykhiolate and the alkylchloro complexes, -Zr( 5 C5H5)XR[N(SiMe2CH2P 1 Pr2)2], where X or CH2SiMe3 or X  =  Cl and R  =  SPh and R  Me, Et  =  Me, Et or Bz, show broad resonances in their NMR spectra,  suggesting the molecules are fluxional. The alkylchloro derivatives could be isolated as solid materials and were found to be thermally labile. The alkyithiolate derivatives are oils at room temperature and undergo further reaction to give a material which has complex 1 H NMR spectra. Also, the 31p ( H 1 } NMR spectra of this materials were virtually identical for all three derivatives, consisting of two low field and two high field singlets around 19 and -.2 ppm respectively. The NMR spectral features are possibly a result of an unsymmetrical dimeric species, containing bridging sulfido ligands (Scheme 4.5).20  However, more investigation is  required to comfirm the nature of this diamagnetic complex.  4.5 Hydride Complexes of Zirconium(llI) 4.5.1 General Hydride derivatives of zirconocene dihalides; for example Schwartz’s reagent, Cp2ZrHC1, are among the transition metal hydrides that have been found useful in stoichiometric and catalytic reactions. 21  Although there are a number of reports of  zirconium(llI) hydride derivatives, they are all poorly characterized (only by ESR) and all of these hydride complexes have been generated in situ by different reduction methods (Scheme 4.5)2228  Also, there are no unambiguously understood reactions of zirconium(III) hydrides,  even the migratory insertion of the hydride into an unsaturated organic functionality such as olefm is not well established.’ 28 ’ 26 [(1 2 C 4 H 5 Z ) 3 rH(p.-H)] C Me NaorK  -C [01 C 4 H 5 Z 2 ) 3 ] rH Me Electrochemical Reduction  -  H) = 8.4 G, triplet 1 g = 1.996, a( Zr)=16.2G 91 a(  H 1 C 8 0 g = 1.992, a( H) = 8.3 G, triplet 1 Na) = 10.1 G or a( 23 a( K) = 2.0 G 39 Zr) = 10.4 G 91 a(  Scheme 4.6 continued references on page i2  Chapter IV  154  hv  -rH(t-H)] 5 [(11 M 4 Z 2 CsH e)  2 (T M 4 H 5 Z rH C e) + H . 2  orA  H)=6.8G 1 g= 1.9854 A(  /CPh  \PPh3  2 (11 M 4 H 5 Z rD C e) 2 (1 M 4 H 5 Z rH. C e) (PhCCPh) 3 (rL M 4 H 5 Z 2 rHPPh C e)  H) = 5.6 G, 1 g = 1.9931, A( Zr) 91 A(  (rj Z ) H 5 P 2 rCH C Ph  =  26.0 G  Mg  24.3 G, Zr) = 11.3 G 91 A( No evidence for hydride =  2 H  “(it C ZrH” 2 ) H 5 -  g = 1.985, a( P) = 19.5 G 31  1 (ri Z 2 ) H 5 C rC1  P) 31 g = 1.9977, A(  g  PhCCPh -rH” “(T1 Z 2 ) 5 H C or Styrene  =  1.987, a(’H)  =  8G  Insertion Products  Scheme 4.6  The hydride species Z 2 (r1 M 4 H 5 rH, C e) generated by thermolysis or photolysis of  {(n M 4 H 5 Z ( 2 , s.t-H) C rHI e) is suggested to form an adduct with diphenyl acetylene; however, there is no evidence for the insertion of the triple bond into the zirconium-hydrogen 22 bond. 2 ’ 6 However, the zirconocene monohydride, Cp2ZrH, generated either by magnesium reduction 28 of 24 Cp2ZrC12 or by the hydrogenoly sis of , ZrCH2PPh is suggested to insert carbon-carbon 2 Cp triple and double bonds into the zirconium-hydrogen bond. In an experiment monitored by ESR spectroscopy, Cp2ZrH was generated in situ by magnesium reduction and then, upon addition of styrene or diphenyl acetylene, there was a disappearance of the doublet resonance due to the hydride species and the formation of a singlet resonance, which has been attributed to the formation of the insertion product. 28 Also, hydrolysis of the reaction mixture shows the presence of hydrogenated products. 28 However, it is important to note that ESR spectra of the adduct formed from the reaction of Z 3 consists only of a doublet, 2 (r1 M 4 H 5 rH C e) and PPh  references on page  i2  Chapter IV  155  coupling that has been atthbuted to one phosphorus-31 nucleus; no coupling was observed due to the hydride ligand. 26 Hydrogenolysis of Cp2ZrCH2PPh2 in the presence of a substrate shows catalytic hydrogenation of the substrate. For example, 1-hexene was hydrogenated to hexane at 80 °C and 40 bar hydrogen pressure in THF using a catalyst/substrate/solvent ratio of 1:300:1000 where 100% conversion was observed in 20 minutes. However, when the reaction mixture was analyzed by ESR spectroscopy only two doublets were observed, one of which corresponded to Cp2ZrCH2PPh2 and the other to the hydride species Cp2ZrH; no evidence for the zirconium(llI) alkyl intermediate was found. 24  4.5.2 Synthesis of 2 Zr(1 ) H 5 C P ] ) H[N(SiMe C Pr H  2 Pr  2 H 1 atm (-RH) 2 Pr’  R=3 SiMe 4.8 2 CH , ,4.S 3 R=CH  4.14  Scheme 4.7  The reaction of the zirconium(Ill) alkyl complexes such as the methyl 4.5 or the 3 S 2 CH iMe 4.8 derivatives with one atmosphere of dihydrogen at room temperature proceeds smoothly over a period of 10 to 12 hours to generate the mononuclear zirconium(III) hydride complex H Zr(T ) 5 H[N(SiMe2C C H2PPr)21, 4.14 (Scheme 4.7). The ESR spectrum of the hydride complex consists of a 1:1:2:2:1:1 doublet of triplets centred at g coupling to two phosphorus-31 nuclei (a( P) 31  =  =  1.988, due to the  21.7 G) and one hydride 1 (a( H )  =  8.7 0) ligand.  The same reaction with molecular deuterium gas produces the corresponding deuteride ; the triplet observed in the ESR spectrum of this 1 Zr(1 H 5 C 2 P S)D[N(SiMe Pr)2], C H 4.14-d references on page Q  Chapter IV  156  material is consistent with the expected deuterium hyperfine interaction of approximately one seventh of 1 a( H ) (Figure 4.6). For comparison, ESR data reported for other d’ hydride complexes are as follows: (g, a( H)); 2 1 Cp N 29 J TiH 2 [Cp bH2, (2.0097, 11.7 G); , (1.992, 7 G 30 (approximate 3 2 )); 3 TaC12 ( , 2 ) PMe 33 H (1.960, 6 to7 G (estimated)).  21.7G  21.7 G  8.7G  1 ZrCpH[(NSi C P J ) 2 r P H Me A  ZrCpD[(NSi C P ] 2 ) P’r H Me  B  Figure 4.6 The X-band room temperature solution (toluene) ESR spectrum of, (A) Zr(rI 2 ) H 5 C P ] H[N(S Pr) C H iMe 4.14, and (B) Zr(Ti 2 H 5 P . 1 S)D[N(SiMe Pr)2 C 2CH ], 4.14-d  Monitoring the hydrogenolysis reaction of the CH 3 S 2 iMe derivative 4.8 by ESR and H NMR spectroscopy shows a clean conversion to the hydride complex with concomitant 1 formation of tetramethyl silane. Also, the reaction of the methyl derivative 4.5 with molecular deuterium shows the formation of 3 CH D . However, we have not been able to isolate the hydride complex as a solid due to its high solubility in hydrocarbon solvents. In the absence of dihydrogen, complex 4.14 is thermally stable for 48 hours at RT as evidenced by monitoring a toluene solution of 4.14 by ESR spectroscopy. The hydrogenolysis of the benzyl derivative, references on page  Chapter IV  157  4.12 was very slow at room temperature whereas the phenyl derivative was inert under dihydrogen. An attempted one-pot synthesis of the zirconium(Ill) hydride by reacting the zirconium chloro derivative 4.1 with LiCH2SiMe 3 and then, without removing the LiCl, stirring under an atmosphere of dihydrogen resulted in the formation of a diamagnetic zirconium species 4.15. This reaction reaches completion in approximately 5 hours. However, when a pure sample of the alkyl derivative was sealed under 4 atmospheres of dihydrogen and monitored by 1 H and P{ 1 31 H} NMR spectroscopy, there was observed a slow formation (approximately 5 days) of a diamagnetic species, 4.15.  Also, the reduction of the zirconium(IV) dichloro derivative  ) H 5 C Cl2[N(SiMe H2PPr)2] Zr(1 2 C 2.6, under dihydrogen gave the identical diamagnetic species, 4.15. The micro-analytical data of this compound was consistent with the formula Zr( 2 H 5 [ C P 1 N(SiMe s)H C Pr) H . The NMR and infrared spectroscopic data strongly suggest that this diamagnetic hydride complex is not a mononuclear species. The solid state infrared spectra of 4.15 show a broad band at 1435 cm 4 which shifts to 1160 cm 4 upon substitution of the hydrides with deuterium,  4.15cL1.* Although, this infrared spectral feature could be assigned to a Zr—H bond stretch, by comparison with other known zirconium hydride complexes it is difficult to assign whether it is due to a terminal or a bridging hydride ligand. For example, in 2 Z (Cp’ ( .t-H) rH) the terminal and the bridging hydrides give rise to absorptions at 1565 and 1330 cm’ respectively. 34 The 1 H { 31 P } and 31 H } NMR (Figure 4.7) data suggest that the complex is an P{ 1 unsymmetrical dinuclear species and in solution it exists in two isomeric forms in approximately a 9:1 ratio. The 1 H NMR spectrum shows 7 separate resonances for the SiMe2 protons of the major isomer and two resonances, 6.15 (triplet) and 6.57 (singlet) ppm corresponding to the Cp ligand. Occasionally, when the hydride complex was precipitated from a Et20 solution it gave only the major isomer, which within a few hours isomerized to give the mixture of isomers.  *  It will be more appropriate to designate the deuteride as 4.15-d.  references on page 122  Chapter IV  158  Facial-PNP Meridional-PNP H} NMR 1 P{ 121 MHz 31  100  0  76.77 MHz 2 H NMR  B ppm  I 0  I  20  10  500 MHz H 1 NMR ‘SI  SiMe2 region of 4.15..d Cp C  B LI  14  I.3  60  0•5  Si(CH3)2 ] 2 ) 3 P[CH(CH  [Zr]— ‘ I.); ,N—Si Me A  2.5  ppm  2:0  1.5  0.5  Figure 4.7 A 500 MHz 31 H{ NMR spectrum of 4.15 showing the resonances associated 1 P} with the PNP ligand. B 500 MHz 1 H NMR spectrum of 4.15 showing the resonances associated with the Cp ligand. C 500 MHz 31 H{ NMR spectrum of 1 P} the deuteride analogue 4.15-d 11 showing the resonances associated with the SiMe2 groups. D 76.77 MHz 2 H NMR spectrum of 4.15-do showing the resonances associated with the PNPligand. E 121.4 MHz 31 H} NMR spectrum of 4.15. 1 P{ references on page 122  Chapter IV  159  The 1 P} NMR spectrum of the major isomer seems to suggest that the hydride 3 H {1 resonances are probably obscured by the resonances due to the ligand. Also, the two doublets 3H-H 2 (  =  10.7 Hz) around 1.48 and 2.18 ppm may correspond to a cyclometalated CH 2 unit of  the missing methyl of the SiMe2 unit. The P{ 31 ‘HI NMR spectrum consist of an ABMX spin system where the AB spins appear at lower field and the MX spins appear at higher fields. In fact the 31 P( ‘HI NMR spectral pattern of complex 4.15 was very similar to the product 2.24, obtained from the reaction of the side-on dinitrogen complexes with LiBEt . It is possible that 4 the low field phosphorus resonances, that is the AB spins, correspond to the meridionally bound PNP ligand of one zirconium center and the high field resonances, that is the MX spins, correspond to a facially bound PNP ligand of the second zirconium center. Selective 31 P decoupled 1 H NMR spectra show that the triplet resonance of the Cp ligand at 6.15 ppm is due to the coupling of the two low field 31p nuclei. To locate the resonances due to the hydride ligands, the deuteride analogue 4.15-d 4 was synthesized by reducing the zirconium(IV) precursor 2.6 under molecular deuterium. However, the 1 H NMR spectrum of this material was more complicated than the spectrum of the hydride analogue; in particular, the SiMe 2 region showed numerous broad peaks. Also, the H 2 NMR spectrum showed overlapping resonances between 0.0 and 0.7 ppm, which clearly indicate that some of the protons of the SiMe 2 moieties are replaced by deuterium. The 2 H NMR showed no evidence for the incorporation of deuterium into the isopropyl groups of PNP.  4.15  4.15a references on page i  Chapter IV  160  On the basis of the available NMR spectroscopic data the structures depicted as 4.15 and 4.15a have been proposed for the diamagnetic dinuclear hydride complex. Because the major and the minor isomers show similar spectroscopic features they are likely to have closely related structures; for example 4.15a could be the minor isomer. C 2 [(PP’r S iMeNjCpZr H —H Zr(ffl) LiCI  1k  ‘-CI  zH]  C [(PPLr S N 2 ) iMe ]CpZr H  C r 1 [(PP S N 2 ) iMe H 1 CpZr  Zr(IV)  Binuclear disproportionation  Na/Hg  CI  Toluene  LiC1 “ZrCp[N(SiM C P j 2 ) P’r ” H e 2 H  Zr(IV)  H  C 2 [(PP’r S iMeN]HCpZ H r( H  Zr(II)  )  ZrCpH[N(S1 C P J 2 ) P’r H Me  4 2 -i-H  C r 1 [(PP S N 2 ) ]HCpZr iMe H  2 -H  ZrCp { 2 )CH N[(SiMeCH P I%] 2 C [SiMe P j Pr H} H  Scheme 4.8  With regard to the mechanism of formation of the diamagnetic hydride complex, the reduction of the zirconium(IV) complex 2.6 could possibly generate the zirconium(ll) species, “Zr( ) H 5 C P 2 J [N(SiM Pr) C ” H 1 e which then oxidatively adds dihydrogen and forms the dihydride intermediate, Zr(1 2 ) H 5 [ C P j ) N(SiM H C Pr H e (Scheme 4.8). Dimerization of references on page  Chapter IV  161  this intermediate and a a-bond metathesis reaction with one of the carbon-hydrogen bonds of the SiMe2 unit would lead to the formation of complex 4.15. In the presence of dihydrogen the zirconium-carbon bond of the metallacycle could undergo reversible hydrogenolysis and a-bond metathesis; such a process, under molecular deuterium would lead to the exchange of hydrogens of the SiMe2 unit with deuterium. As mentioned before the formation of the diamagnetic hydride 4.15 from the zirconium(III) hydride 4.14 under dihydrogen is influenced by the presence of LiC1. On the basis of the discussion presented for the ailcyl derivatives, particularly the methyl and ethyl derivatives, it is reasonable to presume that the hydride derivative could also interact with LiCl (Scheme 4.8). In the presence of LiC1 the neutral hydride complex 4.14 may establish an equilibrium with an anionic zirconium(Ill) hydride species. This anionic species could interact with a neutral zirconium(III) hydride species, for example formation of a dimeric species having bridging hydride ligands.  Such a species could undergo disproportionation to give a  zirconium(II) and a zirconium(IV) dihydride species (Scheme 4.8). It is possible that even a pure sample of the zirconium(llI) ailcyl precursor 4.8, may contain small amounts of LiCl which could be catalyzing the formation of the zirconium(IV) hydride, 4.15 during hydrogenolysis.  4.5.3 Reactions of Zr(1 1 ) H 5 C P ] ) 2 H[N(SiMe C Pr H The paramagnetic hydride 4.14 reacts almost instantaneously with 1 atmosphere of ethylene at room temperature.  The ESR spectrum of the product was identical to the  zirconium(III) ethyl derivative 4.6, generated by the metathesis reaction of EtLi and 4.1. Reacting the hydride complex with ethylene-d4 gave -C5H5)CD2C 5 Zr(T H C 2 [N(SiMe H D PPr’)2] 4.6-cLi, and similarly the deuteride complexes -C5HS)CH2C 5 Zr(r1 D C 2 [N(SiMe H H ] 4.6-d 2 PPr) , and Zr(rI 2 1 H 5 [ 3 C P ] ) 5 were synthesized by N(SiM S)CD2CD C Pr H e 4.6-d  reacting 4.14-d 1 with ethylene and ethylene-d4, respectively. The comparison of the hyperfine coupling information obtained form the three deuterio ethyl derivatives and the non-deuterlo ethyl derivative correlates well with the transfer of the hydride or the deuteride ligand to the position of the ethyl group.  J3-  Solution monitoring by ESR spectroscopy of the deuteride references on page  Chapter IV  162  derivatives 4.6-d 1 and 4.6-d4 shows that over a period of 72 hours there is no scrambling of the 13-deuterium or the 3-hydride into the ce-position, consistent with no 3-hydride elimination for these zirconium(III) ailcyl derivatives. In this respect, these zirconium(Ill) alkyls mirror related zirconocene alkyl derivatives for which f3-elimination is a slow process for unhindered alkyl 35 derivatives. 2 Pr’  2 or C D D or 6 6 C 1 D 2  Me S 2 Pr  H or C 6 10 H 5 112 or C  A900CI  A90°C 6 CH  2 H  2 Pr’  Me S 2 i(\\O  D  D 6 C  Pr’ 2 Me S 2 I\  \  2 Pr’ /P Me S 2 I\  N— ZC Me S 2 i 2 Pr’ = C ,C 5 H 6 , 5 D 6 , 1 H 6 C 1C 9 H 5 Proposed transition state for hydride exchange  Me S 2 i))c%/ ‘)H H 2 Pr  Me S 2 1  /H  2 Pr  [Cl  Proposed transition states for the exchange of hydride with phenyl Scheme 4.9  references on page i2  Chapter IV  163  The hydride ligand of complex 4.14 was found to undergo exchange reactions with deuterium from molecular deuterium gas or from the carbon-deuterium bonds of both aromatic and aliphatic compounds (Scheme 4.9). Also, when the hydride complex 4.14 is heated in benzene at 90 C the deep green color due to the hydride complex slowly changes to give a red solution. The ESR and UV-Vis. spectrum of this red solution indicates the formation of the phenyl derivative 4.4. It is presumed that these reaction involve a four centered transition state similar to the one proposed for a-bond metathesis reactions in d 0 metal complexes. 36 According to the depictions shown in Scheme 2.8, and considering only the steric factors, the exchange of hydrogen atoms between a metal-hydride bond and a carbon-hydrogen bond should be favored. The proposed mechanism is consistent with the experimental observation that the conversion of the zirconium(III) hydride to the phenyl derivative only takes place at elevated temperatures and with longer reaction times. The reaction of the zirconium(III) hydride complex with a tenninal acetylene did not show any evidence for the formation of the insertion product. For example, reacting Ph—CC--H with complex 4.14 and oxidizing the product with PbC1 2 gave a product which did not show any characteristic olefinic signals in the 1 H NMR spectrum. However, this crude sample contained mainly of one complex (>80 %) and the 1 P[’H} NMR features were consistent with the H and 31 formula ) 5 Zr(1 C1(CCPh) C5H 2 C [N(SiMe P Pr)2J, H 4.16. This result suggests that the zirconium-hydride bond probably undergoes a rapid a-bond metathesis with the terminal carbon—hydrogen bond of the acetylene to give the zirconium(III) acetylide derivative ) H (CECPh) C [N(SiMe2CH2PPr’) Zr(rj 5 j. 2  4.5.4 Synthesis of Zirconium(llI) Borohydride Complex A variety of tetrahydroborate derivatives of early and late transition metals have been 37 These complexes are potentially important as precursors to solid metal borides, synthesized. 38 to metal 39 hydrides, 4 ’ 0 to metal alkyls ’ and they may also function as olefin polymerization 4 42 From a structural point of view, they are intriguing due to the versatility displayed catalysts. references on page  Chapter IV  164  by the tetrahydroborate group in the mode of its coordination to the metal center, which may involve triple, double and single hydrogen bridges; 37 all of these ligation modes are known for group 4 transition metals. 2 Pr’  2 Pr’ 4 LiBH  4.1  Toluene  4.1  The reaction of the chioro derivative 4.1 with LiBH 4 in toluene slowly changed color from deep green to give a dark brown solution (Equation 4.1). Recrystallization of the crude material from an Et20 solution gave a pure crystalline material in greater than 80% yield with an elemental composition that was consistent with the formula 2 Zr(r1 ) H 5 ) 4 [N(SiMe (BH C CH2PPr) ] 2 , 4.17. This zirconium(III) borohydride complex exhibits good thermal stability. For example, heating a toluene solution of the complex at 90 °C for 12 hours shows no decomposition by ESR spectroscopic analysis.  20 G  Observed A  Simulated B  Figure 4.8 (A) Solution (toluene) ESR spectrum of 4.17 recorded at room temperature. (B) The simulated spectrum of 4.17. references on page  Chapter IV  165  The solution ESR spectrum of 4.17 consists of a broad binomial triplet due to coupling to two equivalent phosphorus nuclei; no satellites due to the magnetically dilute zirconium-91 nuclei were observed (Figure 4.8). The ESR spectrum of 4.17 was simulated using the following parameters: g  =  1.958; a P) 31 (  =  20.7 G, 2P; a( N) 14  =  2.0 0, iN and 1 a( H )  =  2.8 g,  4H; this last hyperfine coupling parameter suggests that all four hydrogens of the borohydride ligand have similar interactions with the metal center.  The borohydride ligand may be  undergoing some fluctional process that exchanges the positions of the terminal and bridging hydrides (Scheme 4.1O). The solid state infrared spectrum of the complex consists of bands at 2401 and 2374 cm 1  and strong absorptions at 2126 and 1460 cm, consistent with a BH4 ligand bound in a 1  bidentate fashion. The bands at 2401 and 2392 cm1 were assigned to the terminal B—H bond stretches and the absorption at 2124 cm-’ was assigned to the bridging B—H bond stretch. The solution (toluene) infrared spectrum of complex 4.17 was identical in the region associated with the B—H stretches, however the feature at 1460 cm-’ observed in the solid state was absent. 2 H 4 ’ 1 H ...  2 H  /‘ —  1 H H 1 • ’ 2 ... 4  —Bç”H 1 Zr—.’H  /‘  -  2 H  ,  H . , 1 .  /  2 H  2 H  2 H  1 -  ZrHB_H2  , ’ 2 H 1 ..  /  2 H  /  2 H 2 H  2 H  H ’ 1 ....• B 1 Zr....,,,,  .  Zr H2  1 H  H ’ 1 ...  I  .  Zr....,,,,  -‘  2 H 1 H  H . 2 ,..  / B\  1 H  1 H 2 H  Scheme 4.10  A fluctional process that would exchange the terminal and bridging hydrogens could involve a monodentate or a tridentate or an agostic type intermediate (Scheme 4.9). On the basis of the solution infrared spectra the tridentate intermediate seems unlikely since this would references on page  Chapter IV  166  significantly alter the B—Ht stretching region. In the literature it has been stated that the infrared spectra of monodentate and bidentate borohydride derivatives are likely to give similar features, particularly for the B—H stretches. 43 It is possible that the fluctional process could involve an agostic type intermediate. Such agostic type* bonding of the BH4 ligand is known for the complex ) 4 T 2 (PMe 3 i(BH where two of the BH 4 ligands are bound in an agostic fashion, involving the B—H bond. C15 C13 C14  C3  Si  I  C2  Cl  Cl 2  H  Si  C8 I  II  Figure 4.9 I ORTEP view showing the complete atom labeling scheme of complex Zr( ) H 5 ) 4 C P J 2 ) [NSiM BH (l1 C Pr H , 1 e 4.17. II A Chem 3D® view showing the arrangement of the PNP and borohydride ligands around the zirconium center.  The X-ray structure of the borohydride derivative 4.17, is depicted in Figure 4.9. The structure clearly shows the complex to be mononuclear with the borohydride ligand bound in a bidentate fashion. All of the hydrogen atoms associated with borohydride ligand were located during the refinement of the X-ray structure. By comparison with the structures of the phenyl *  These interactions are also refered to as side-on bound borohydride ligand references on page  Chapter IV  167  4.4 and the 3 SiMe 4.8 derivatives the borohydride complex 4.17 is somewhat isostructural. 2 CH Analysis of the bond angles around the zirconium center suggests a pseudo trigonal bipyramidal geometry with the phosphine donors occupying the axial positions. The centroid of the Cp ligand, the nitrogen and the two bridging hydrogens of the BH4 ligand, all lie in the equatorial plane.  Table 4.6 Selected bond lengths of complex 2 Zr( ) H 5 ) 4 ] [N(SiMe2CH BH (T C , 2PPr) 1 4.17  Atom  Atom  Zr  P(1)  Zr  Distance  (A)  (A)  Atom  Atom  2.7933 (15)  Zr  P(2)  N  2.224 (4)  Zr  B  2.617 (7)  Zr  Cp  2.204 (3)  Zr  HB(1)  2.19(5)  N  Si(1)  1.714 (4)  Zr  HB(2)  2.09(4)  N  Si(2)  1.726 (4)  B  HB(1)  1.12(5)  Distance  2.7849 (15)  Table 4.7 Selected bond angles of complex 2 Zr( ) H 5 ) 4 C P } [N(SiM BH (ri C Pr) H ri , e 4.17  Atom  Atom  Atom  Angle  P(1)  Zr  P(2)  P(1)  Zr  P(2)  (0)  Atom  Atom  Atom  147.66(5)  P(1)  Zr  N  78.80(10)  Cp  105.55  P(2)  Zr  N  74.00 (10)  Zr  Cp  104.74  P(l)  Zr  B  84.04  Cp  Zr  N  127.21  P(2)  Zr  B  90.29  Cp  Zr  B  120.48  N  Zr  B  112.32  HB(l)  Zr  1113(2)  47.0 (20)  Zr  1113(1)  B  99 (3)  Cp  Zr  HB(2)  98.2  Cp  Zr  1113(1)  145.1  Angle  ()  Cp refers to the centroid of the Cp ligand. All structural parameters associated with the centroid of Cp and B for the complex 4.17 were taken from the Chem 3D® structure.  references on page  222  Chapter IV  168  A comparison of the X-ray structures of the phenyl 4.4, CH2SiMe 3 4.8, and the borohydride 4.17, show that the centroid of the Cp ligand the nitrogen of PNP and the ligating atoms of the third group, that is the phenyl or the CH 3 S 2 iMe or the BH4, lie in the pseudo equatorial plane. Also, the plane of the phenyl ring and the chelating ring of the BET 4 ligand lie on the equatorial plane. A Chem 3D® illustration of the equatorial planes of the three molecules are shown in Figure 4.10.  98.22° 127.2°  Zr  120.5° 139.  H  18.05° Zr  N  H 2 Pr /P  135.6° Zr N  Me S 2 ç  :N  4 H—L’-j S 2 Me 2 Pr’  3 R=H,Me,SiM e  Figure 4.10 The Chem 3D® view of the equatorial planes of complexes 4.4, 4.8 and 4.17. All numerical values given correspond to the nearest bond angle. The Chem Draw® drawing inside the box is the proposed structure for the ailcyl complexes in solution.  It seems that in the borohydride complex the site occupied by the hydrogen atom trans to the Cp ligand is probably the vacant site in the phenyl and the alkyl complexes. The unusual bond angles around the ipso-carbon of the phenyl group may be due to a weak interaction of the references on page  Chapter IV  169  ortho-hydrogen of the phenyl group with the metal centre. Also, for the alkyl derivatives the solution structure could be depicted as shown inside the box in Figure 4.10, where one of the x hydrogen is involved in a weak agostic type interaction in the equatorial plane. The zirconium-Cp bond distance of 2.209  A in the borohydride complex is comparable  to the phenyl, 4.4 and the alkyl, 4.8 complexes and is shorter than the distances observed in complexes 2.7 and 2.9. The zirconium-hydride distances, 2.19 (5) and 2.09 (4) and the zirconium-boron distance was 2.617 (7)  A are identical  A, all of which is consistent with the bidentate  coordination of the BH 4 ligand. The calculated zirconium-boron distance for the tridentate and bidentate modes are 2.35 and 2.60  A respectively. 45  The metal-BH4 interactions in complex  4.17 are similar to those in ) (PMe 3 H Zr ( 5 4 2 BH and ’ . 4 Zr(BHt) 3 4 9 6 7  4.6 Disproportionation Reactions of Mononuclear Zirconium(Ill) Complexes Treating a solution of the zirconium(ffl) chloro derivative 4.1 with an atmosphere of CO resulted in a rapid color change from deep green to dark brown. Monitoring the reaction by 1 H and 31 P{ 1 H} NMR spectroscopy showed the formation of diamagnetic species; the ESR spectrum of the same sample showed only a very weak signal.* However, upon removing CO from the aforementioned reaction, the color changed from dark brown to deep green and the ESR and NMR spectra of the resulting product were identical to the paramagnetic chioro derivative, 4.1. This result clearly suggests a reversible reaction of complex 4.1 with CO. Upon monitoring the reaction by UV-Vis spectroscopy, a band at 450 nm was observed which disappears upon the removal of CO from the reaction mixture. The solution infrared spectrum of a CO saturated toluene solution of 4.1 shows a weak and a strong band at 1965 and 1871 , respectively. A similar reaction involving the borohydride complex 4.17 with CO also 1 cmgave diamagnetic species, for which some of the spectroscopic features (JR. UV-Vis and NMR) were identical to those observed for the diamagnetic species generated by the reaction of CO and 4.1. As mentioned above, the reaction could be reversed by the removal of CO to give the paramagnetic borohydride derivative, 4.17. *  The signal could be observed only at very high gain. references on page j  Chapter IV  170  ZrCp ) 4 C p 2 2 ) [N(SjM pri fJ 1 (BH e  o  +  8 D 7 C  P[CH(CH ) 3 ]  ZrCpCJ{N(S C p ] 2 ) pr’ H iMe  CO  +  a  78)  P[CH(C113)2]  11111  11111 6  II!! liii 1111111 I  5  III 4  I I  11111111!!  3  1111111  III 111111  2  IPPM  111111 0  Figure 4.11 (top) 1 H (300 MHz, 7 C D g) spectrum of the diamagnetic species obtained from the reaction of 4.17 and CO. (bottom) 1 H NMR (300 MHz, 7 C D 8) spectrum of the diamagnetic species obtained from the reaction of 4.1 and CO. references on page 222  Chapter IV  171  AbsorbanCe (ZH)[N(SiMezCHzPPzj  +  CO) toluene  (U  B-Ht B—Hb (ZrCpC1[N(S C P ] 2 > Pr1 H 1Me + CO) toluene  —  ZOO.  ‘  ‘  ‘  I  2000.cml  2 JZrCp ) 4 [N(SiM (BH e PPr] + Co 2 lCH toluene  1 J  icm  Wave length (nm) Figure 4.12 UV-Vis spectroscopic monitoring of the reaction of 4.17 (top right) and 4.1 (bottom right) with CO (1 atmosphere). (left) Infrared spectrum (solution in toluene) of the reaction of 4.17 with CO.  These results indicate that complexes 4.1 and 4.17 react with CO to give two complexes, with one of the products common for both reactions. On the basis of the spectroscopic features, the common species is formulated as the zirconium(II) dicarbonyl derivative, H -C Zr(r1 ) 5 (CO [ C P 2 ] N(SiM Pr) H , e 4.18. The 1 ) H NMR spectrum of 4.18 has only a single resonance for the SiMe2 groups and a triplet for the Cp ligand due to coupling to two equivalent phosphorus-31 nuclei. The singlet resonance at 37.91 ppm in the P{ 31 H 1 ) NMR spectrum, which was common for both reactions, was assigned to the dicarbonyl complex 4.18. The  references on page  i2  Chapter IV  172  complex could be envisaged as having a pseudooctahedral geometry with a meridionally bound PNP ligand and trans disposed CO ligands.  After assigning the NMR resonances associated with the dicarbonyl complex 4.18 the remaining spectroscopic features from the reaction of 4.1 with CO shows it to be the zirconium(IV) dichloro derivative ] Zr( ) 5 C 2 Cl2[N C5H H2P r1 , (SiMe Pr) 2.6. Therefore, it is presumed that the second diamagnetic species obtained from the reaction of the borohydride complex 4.17 is the zirconium(IV) bis(borohydride) derivative, Zr(1 5 -C5H5)(BH4)2[N(SiMe2CH2PPr)2j, 4.19. The hafnium(Ill) chioro complex 4.3 also reacts with CO to give the hafnium(IV) dichloro complex P 2 Hf ) H 5 Cl2[N(SiMe2 Pr)2 C (fl CH ] 4.2, and the hafnium(II) dicarbonyl derivative j Hf ) H 5 [ C 2 N(Si (CO H2P C (rI , Me Pr) ) 4.20. Therefore, these disproportionation reactions could be given in a general form as shown in Scheme 4.11.  2 Me  MeSj  2 , 2 Me  M(ffl) M=Zr;X=Cl, 4.1;X=BH ,4.17 4 M = Hf; X Cl, 4.3  M(ll) M=Zr,4.18 M Hf, 4.20  M(IV) 4 M=Zr;X=Cl, , 4.19 2.6;BH M = Hf; X = Cl, 4.2  Scheme 4.11  The solution infrared spectrum of the bis(borohydride) complex 4.19 shows strong absorptions due to the terminal boron-hydrogen stretches at 2429 and 2381 cm1 and a band at 2134 cm1 corresponding to the bridging boron-hydrogen stretch. These boron-hydrogen stretching frequencies are comparable to that observed for the zirconium(Ill) borohydride complex, 4.17. Therefore it is presumed that the BH 4 ligands in complex 4.17 are also bound in a bidentate fashion.  references on page  Chapter IV  173  The NMR spectroscopic features of the bis(borohydride) derivative 4.19 suggest that it is isostructural with the dichioro derivative 2.6 with trans disposed BIT 4 ligands. Also, the 1 H and P{ 1 31 H} NMR spectra of 4.19 recorded at room temperature and at -85 °C were virtually identical; the resonances due to the 4 BIT ligands were not located in the 1 H NMR spectrum. Although the disproportionation of the zirconium(III) borohydride complex 4.17 proceeds quantitatively to give the bis(borohydride) complex 4.19, attempts to synthesize it by other routes were unsuccessful. For example, reacting the dichioro complex 2.6 with 4 LiBH or attempts to oxidize complex 4.17 with PbCl 2 to make 2 -C5H5)(BH4)Cl[N(SiMe2CH 5 Zr(fl PPr)21 4.17, only produced intractable materials. Also, the reaction of the hafnium dichioro  complex ) Hf(1 ) H 5 [ C P 1 2 N(SiM Cl C Pr H e  4.2,  with  4 LiBH  gave  only  the  monoborohydride complex J Hf(f 5 C P 2 C5H5)(BH4) Pr) H , l 4.21.* Cl[N(SiMe  2 4.2  Zr(llI) 4.1  Zr(IV) 2.6  Zr(ll) 4.22 CN 3 L=CH  The room temperature reaction of the zirconium(III) chloro derivative 4.1 with CH3CN gave a deep red solution; the 1 H and 31 P{ hH} NMR spectral analysis showed the presence of zirconium(IV) dichioro complex 2.6 and some unidentified products, and no paramagnetic species were found by ESR spectroscopy.  Monitoring the reaction by 31 P{ 1 H} NMR  spectroscopy at low temperatures showed the formation of a second product, 4.22 which correlated to a resonance at 19.78 ppm. By comparison with the reaction of CO with 4.1, the complex 4.22 could possibly be an acetonitrile adduct of a zirconium(ll) species. Spectroscopic monitoring also showed that the zirconium(II) complex is only stable at lower temperatures and *  The solid state infrared spectrum of the complex 4.21 shows that the BH4 ligand is bound in a bidentate fashion references on page  Chapter IV  174  rapidly decomposes at room temperature. Although the low temperature experiments show that the zirconium(ffl) chloro derivative 4.1 does undergo disproportionation reaction in the presence of acetonitrile, due to the instability of the zirconium(II) species it was difficult to establish whether the reaction is a reversible process. *  decomposition products  4.22  *  21  20  19  18  17  16  15  14  8 D 7 C  ZrCpCI 1 C [N(SiMe P ] ) 2 Pr H  +  CH C 3 N  -10 C  Cp  z c)  Cp  III III) IlillIlil  6  liii II II)IIIII1IIII I III IIIIII  4  liii  11111111111)11  iPPM  0  Figure 4.13 A, B Low temperature H 1 (300 MHz) and 31 P{ 1 H} (121 MHz) NMR spectra ) of the diamagnetic species obtained from the reaction of 4.1 and 3 8 D 7 (C CH C N.  On the basis of the 1 H NMR spectrum of the zirconium(II) acetonitrile adduct 4.22, the molecule appears to be less symmetric than the zirconium(ll) dicarbonyl species, 4.18. The 1 H NMR spectrum of 4.22 has two resonance in the SiMe2 region and integration values suggest that the molecule has only one acetonitrile ligand. Considering that the complex gives only a references on page  Chapter IV  175  singlet in the 31 P( 1 H} NMR spectrum, the geometry around the zirconium center in 4.22 could be described as a pseudo trigonal bipyramidal, with the phosphine donors occupying the apical positions (Equation 4.2). Some dinuclear zirconium(III) complexes (Chapter 3) undergo thermally or photochemically induced disproportionation to give zirconium(IV) and zirconium(II) species where the zirconium(ll) species can be trapped with ligands such as CO* and butadiene (top of Scheme 4.12, also see Chapter 3).48 It was also shown that these dinuclear zirconium(III) complexes are stable in noncoordinating solvents like toluene and, in polar solvents like THF, they undergo decomposition. However, the mononuclear zirconium(Ill) complexes 4.1 or 4.17 do not shown any sign of such a disproportionation even at elevated temperatures or in the presence of ligands such as THF, ethylene or PMe . 3 The dicarbonyl titanium(II) complex , Ti(CO) reacts with the titanium(IV) complex 2 Cp Cp T 2 iX2, where X  =  Cl or SPh, to give the dinuclear titanium(III) species . T [Cp ( 2 4 .t-X) iCl] 9  A similar reaction has also been reported between Cp Zr(CO) and , 2 ZrX where X 2 Cp  =  Cl or  ° These reactions are somewhat comparable to the reverse reactions shown in Scheme 5 SPh. 4.11. The proposed mechanism for the reaction for the chloro complex 4.1 with CO is shown in Scheme 4.12. It is believed that the initial step involves the formation of an adduct with CO, intermediate A, where, as shown in Scheme 4.11, the CO could adopt a linear or a bent structure.  Intermediates having bent CO ligands have been proposed for the hydrogen  abstraction reactions by 19-electron metal carbonyl complexes, for example the reaction of ] with HSnBu 6 [Cr(CO) 3 (bottom of Scheme 4.12).51 It could be argued that the formation of a bent CO ligand in 19-electron complexes enables the metal center to attain an 18-electron configuration. However, intermediate A is a 17-electron complex and therefore bending the CO ligand would give the metal center a 16-electron configuration. For electropositive metals like zirconium, a bent CO could also donate electrons from the oxygen. The intermediate A could disproportionate via a dimeric intermediate as shown in Scheme 4.12. *  j  is important to note that the disproportionation reactions in these dinuclear complexes are not initiated by CO. references on page  Chapter IV  176  ZN  [Zr] [Zr] . 7  Zr(ffl)  ___  Zr(ffl) x  7 + “[Zr]” [Zr]  L __  Zr(ll)  Zr(IV)  11 [Zr]L Zr(ll)  L = CO, butadiene  Cl, Br,  Me2Sj  \ A Disproportionation Dinitrogen Complex 2.9  Zr(II) [Zr]CO +CO  Zr(IV) 2 + [Zr] Cl 2.6  :::::  [Zl [Zr]  cz 0  -CO 1•  [Zr] (CO) 2 4.18  c  ci  Dimeric intermediate [Zr]  =  1 C “ZrCp[N(SiMe P ] ) 2 r ” H P  3 HSnBu f 6 [Cr(CO)  -  (CHO)F 5 [Cr(CO)  —  0  0..t##  Scheme 4.12  It is noteworthy that a solution of the dicarbonyl complex under a dinitrogen atmosphere slowly converts to give the dinitrogen complex 2.9. This suggests that the CO ligands of the dicarbonyl complex are labile, a process that is important for the reverse disproportionation reaction to occur. Removal of CO from the reaction could accelerate the dissociation of CO from 4.18 and lead to the formation of complex 4.1. Acetonitrile and CO being similar ligands, references on page  Chapter IV  177  the disproportionation reactions involving acetonitrile may also proceed via an intermediate similar to A. Outer sphere electron transfer type process might also be important; however, it is difficult to rationalize the exchange of ligands that must occur to generate the product.  4.7 Further Reaction with CO: Formation of Zirconium Formyl Complex The Fischer-Tropsch process involves the reaction of CO with dihydrogen over a heterogeneous metal catalyst to form a mixture of hydrocarbons and oxygenated products. Considerable efforts have been made to model different intermediates that are involved during the Fischer-Tropsch process. It is believed that the CO is reduced in a stepwise manner, where at the initial stages an intermediate containing a formyl type ligand has been invoked. 53 ’ 52 (1) K[HB(OP’r) f 3 4 F 3 P(OPh) e(CO)  4 [P(OPh F 3 N e(CO)(CHO) ) f(Et ) (2) 4 (Et N Br  4 [CpRe(NO)( ) 3 ) (CO)](BF PPh  ‘H NMR, 14.82 ppm (pH = 44.4 Hz)  Li[Et B 3 H1  -  3 CpRe(NO)(P ) (CHO) Ph  —-  or NaBH 4 ‘H NMR, 16.48 ppm (JP-H = 44.4 Hz) C NMR, 251.3 ppm (Jp- = 11 Hz) 3 ‘ 3 PPh  3 Ph  oc (PPh 2 Os(CO) 3 )  0  O 2 CH  Solid %%%%  75°C 0/H2 3P Ph  ‘H NMR, 7.44 ppm  (P-H  II  3 Ph =  ,H 0  4.0 Hz)  Scheme 4.13 Most of the known transition metal formyl complexes are synthesized by the addition of 3 . 4 M58, l Only a few cases are a hydride ligand to a coordinated carbonyl ligand (Scheme ) known where the formyl ligand is formed by the reaction of a metal hydride complex with CO, where the reaction is presumed to take place by the insertion of CO into the metal-hydride bond (Scheme 4.14).59.60 However it is important to note that for 0 -d metal complexes, the formyl references on page  Chapter IV  178  ligand is only observed at low temperatures or was found to be involved in some type of secondary interaction (Scheme 4.14).60.61  Rh(OEP)H + Co 2 [Rh(OEP)]  OEP  =  Rh(OEP)(CHO)  2 ++ H  2 CO  2Rh(OEP)(CHO)  Octaethylporphyrin ‘H NMR, 2.90 ppm (ic-H = 200 Hz) C NMR, 194.4 ppm 13  CO  Observed at -80 °C ‘H NMR, 15.2 ppm (ic-H = 114 Hz) CNMR,372ppm 3 ‘  OR 4.26 M 5 (C E 4 T C 2 H t) 1 a e  CO 7 Cl  4.24  3 PMe  ‘H NMR, 6.08 ppm (ic-H = 168 Hz) c NMR, 168 ppm 3 ‘ H NMR, 1.8 ppm 1 C NMR, 94 ppm ( 3 ‘ c- = 44 Hz) 3 Scheme 4.14  The bis(borohydride) complex 4.19 formed from the disproportionation reaction reacts slowly with CO to give a complex which has an elemental composition that is consistent with references on page  Chapter IV  179  the formula C 2 Zr( H 5 5)(BH4)2(CO H2PPr C )[N(SiMe 1 4.23. The solid state infrared )2], spectrum of this complex did not show any characteristic peak that would correspond to a terminal carbonyl stretch and also the boron-hydrogen stretching region clearly suggested that each BH 4 ligand is bound in a different fashion. The terminal B—H bond stretches at 2423 and 2378 cm-’ and the only bridging B—H band stretch at 2146 cm t suggests that one of the BH 4 ligands is bound in a bidentate fashion to zirconium. H NMR spectrum (Figure 4.14) of this complex shows four resonances for the The 1 P{ 1 H} NMR spectrum consists of a sharp peak at 39.72 ppm and a SiMe2 protons and the 31 broad peak at 31.20 ppm, which are consistent with an unsymmetrical mononuclear complex. The mukiplet underneath the SiMe 2 protons (around 0.25 ppm) and the broad resonance around 1.2 ppm could be attributed to the boron hydrides. The intriguing feature in the 1 H NMR spectrum is the doublet at 3.02 ppm which corresponds to one proton. Selective 31 P decoupled H NMR experiments suggest that the resonance at 3.02 ppm is coupled to the 31 1 P resonance at 39.72 ppm with a coupling constant of Jp..H  =  27.4 Hz. The B { 1 H} NMR spectrum of this  complex has a singlet at -101.3 ppm and a doublet at -127.2 ppm, the latter is probably due to the coupling with one phosphorus-31 nucleus  (JB-P  =  47.4 Hz).  The carbon-13 analogue of complex 4.23 was synthesized using 13 C0 and shows that the resonance at 3.02 ppm in the 1 H NMR spectrum has an unusually large coupling constant to carbon, JCH  161.8 Hz; in addition, the 31 P{ 1 H} resonance at 39.72 ppm was now split into a  doublet with Jp.  =  55 Hz. In the 13 H} NMR spectrum the signal due to the enriched C{1  carbon was found to be a doublet at 60.73 ppm, Jp.c =55 Hz. One possibility, suggested by the spectroscopic data, is that the complex 4.23 has a formyl type ligand; a proposed structure is depicted in Scheme 4.15. However, the main problem with this proposed structure is that the C and 1 13 H NMR chemical shifts associated with the formyl ligand in complex 4.23 are significantly shifted to higher field than the usual shifts observed for a formyl ligand (Scheme 4.13 and 4.14). Fortunately, we were able to grow single crystals of complex 4.23 and subject them to X-ray analysis.  references on page  Chapter IV  180  H} NMR 1 B{ 96.2 MHz 11  C  °UUUL  E  1111111111! 111111111111111111 III If II —100 —110 —120 PPM-130  1I11 I 1 I 1 1 I111 I1I1I l1I1 II1J l111 1II1 1111 l1II II11 1Il IlII IIII III 1 64 63 62 61 59 PPM 60  500 MHz B} 11 H 1 { NMR [1  D 1.5 ppm B III  1111111111 3.2  1 1)1111 lIuII 3.0  1111111)1  C.)  2.8 PPM Zr1 —0  Cl)  /  Cp  r°’H  i rTrrFi I  6.5 6.0  tIII I 5.5 5.0  [[  1111111111111 4.5 4.0 3.5 M  ] 2 ) 3 P[CH(CH  11111111 Jil till liii IL lU  2.0  1.8  ill 11111111111 11111  1.6  1.4  JIl 11111 Iij 11111111111111111111 1111111111111111! lijI 1111111 lj 11111  1.2  1.0  0.8  0.6  0.4  0.2 PF1.0  Figure 4.14 A H H (300 MHz) and gated 1 NMR (300 MHz) spectrum of 4.23. B, C 1 decoupled 13C (75.4 MHz) resonances associated with the formyl ligand of 4.23 labelled with 13 B) NMR (500 MHz) spectrum showing the BH3 unit H( 1 C. D 1 ). 8 D 7 and E B(’H} NMR (96.2 MHz) spectrun of 4.23 (C references on page 122  Chapter IV  181  2 Pr’  2 Pr’  2 Si’’ Me 2  \BH4  Me2Si  :N—  +  :N_zr_(C1I -b 1” B 4 S1 H 2 Me  2C0  /  I  Me2SI  2 P  P  / P.  BH .4  V  Me2SI +  Me S 2 1  “  :N—zr / /1  2 Pr’  Co  4.17  \ p0 2 Pr’  4.18  4.19 Slow  H NMR, 3.02 ppm, 3 1 C-H  HH  P-H 3  =  27.4  =  161.8 Hz  HZ  C NMR = 161.8 ppm 13 3 ‘Pr2pBH  H/H  4.23  Scheme 4.15  The X-ray structure (Figure 4.15) of the complex 4.23 agrees with most but not all of the features determined from the spectroscopic analysis. However, the original proposal has one of the phosphine donors of the PNP ligand coordinated to the zirconium whereas, in the X-ray structure, this phosphine ligand is bound to the carbon atom of the formyl ligand. Such a phosphine interaction would probably explain the relatively high field proton and carbon-13 NMR signals observed for the formyl ligand. In fact the coordination around the formyl carbon  atom is somewhat comparable to the proposed structure of the tantalum formyl complex 4.24 (Scheme 4.14) where a second tantalum atom is interacting in a similar fashion to the phosphine in 4.23. Also, the NMR spectroscopic features associated with the formyl ligand of both complexes are comparable. 61 The structure also shows that the the second phosphine donor of the PNP ligand is coordinated to a BH3 unit.  references on page  Chapter IV  182  H  H  0 H  H  ifi  II ‘P  C15  C19  do CP4 CP3  C8 C3  C4  HB1D  Cl  C7  Bi HB1C  C6 I Figure 4.14 I ORTEP view showing the complete atom labeling scheme of complex -CHO) { 3 2 Zr(’rI 4 ) H C 5 2 ) BH (1 (q N(Si P ( P 2 ) Pr)[SiM •B P Me2 ] e2CH H r CH }, 4.23. II and III are Chem 3D® views of complex 4.23. references on page  Chapter IV  183 Table 4.8 Selected bond lengths of complex  -C 2 ) H C N(SiMe P Pr) H3 Zr(1 5 (1 ) 4 CHO) BH (r1 { 2 (PrP•BH 2 [SiMe2CH ) ] }, 4.23 Atom  Atom  Zr  N  Zr  0  Zr  HB1A  P(1)  Distance  (A)  (A)  Atom  Atom  2.135 (3)  Zr  Cp  2.2855 (9)  1.987 (3)  Zr  C(1)  2.254 (4)  2.09(4)  Zr  HB1B  2.31 (4)  C(8)  1.795 (4)  Zr  B(1)  2.594 (6)  P(1)  C(1)  1.765 (4)  P(2)  B(2)  1.927 (7)  C(1)  0  1.429 (5)  Si(1)  N  1.731 (4)  Distance  Table 4.9 Selected bond angles of complex Zr( 2 C N(SiMe P Pr) H3 ) H 5 ) 4 CHO) BH (i1 (T C{2 C [SiMe ( 2 ) Pr2P•B j), H H 4.23 Atom  Atom  Atom  0  Zr  N  0  Zr  N  Angle  ()  Atom  Atom  Atom  104.63 (13)  C(1)  Zr  N  95.70 (14)  Cp  105.68 (9)  C(1)  Zr  Cp  141.84(12)  Zr  Cp  110.30 (9)  0  Zr  C(1)  38.73 (14)  Zr  0  C(1)  80.78 (21)  0  C(1)  Zr  60.49 (19)  P(1)  C(1)  0  116.1 (3)  P(1)  C(1)  Zr  129.48 (22)  C(1)  P(1)  C(8)  114.15 (20)  P(1)  C(8)  Si(1)  120.78 (23)  N  Si(1)  C(8)  110.55 (18)  Zr  N  Si(1)  115.11 (17)  Si(1)  N  Si(2)  122.11 (20)  Zr  N  Si(2)  122.76 (18)  Angle  (0)  In Scheme 4.16 the bonding parameters associated with the formyl ligand in complex 4.23 and a molybdenum complex containing an analogous phosphine stabilized acyl ligand 4.25 are shown. 62 The phosphorus-carbon bond distance of 1.831(5)  A in  4.25 is very similar to a  single bond. By comparison, in the zirconium complex the distance was 1.765(4)  A  and is  significantly shorter. In fact it is comparable to a related tantalum formyl complex 4.24,61 references on page i  Chapter IV  1.750(18)  184  A,  and to the dinuclear iron complex, ) 1 ( Fe [ E 6 C 2 C(CHO)P(Ph CO) ], L 1.748(6) A.63  In these complexes the bonding between the phosphorus and the carbon of the “R P—C” moiety 3 is regarded as an ylid. The carbon-oxygen bond distance, 1.429(5)  A of the metallaoxirane ring  of the zirconium complex, 4.23 is longer than the molybdenum complex, 1.367(6)  A;  this is  consistent with greater electron donation from oxygen to zirconium (Chapter 2, Section 2.5.2).  A is within the range of 2.25 1(6) to 2.3 88(12) A.  The zirconium-carbon distance of 2.254(4)  80.78(21)’  4.23  “a  74.96(25)’  ‘—-—flip  I  bo  P  P P 3 Me  4.25 Scheme 4.16  H  H  I  /  C  Zr”O  Zr’O  H  R P 3 .  / •  Zr—O  H  >  H  R3PCI  R F 3 ,’  \  \  Zr  0  Zr  0  I  >  R3PC/ Zr”  \  Scheme 4.17 references on page  Chapter IV  185  The bonding of the formyl ligand can be described in terms of two limiting resonance forms as shown on the top of Scheme 4.17, where one is an 2 -formyl and the other is an 112  structure. In the case of d 65 ,M, oxycarbene canonical 61 0 transition metal complexes, the  oxycarbene canonical form has a significant contribution towards the nature of the bonding of the formyl ligand. For example, the synthesis of complex 4.26 from the thorium formyl complex could be envisaged as a coupling of two thorium oxycarbene units (Scheme 4.14). A similar rational could be extended to describe the derivation of the “formyl-ylid” ligand in complex 4.23 (Scheme 4.17).  4.8 Conclusions The reduction of the zirconium(IV) or the hafnium(IV) complex 2 M(1 ) H 5 Cl C CH2PPr) 2 [N(SiMe ] , where M  =  Zr or Hf, has enabled the synthesis of the zirconium(Ill) and  the hafnium(III) complexes.  The zirconium(III) complex, -2 5 Zr(11 CSH5)Cl[N(SiMe2CH  PPr2) ] 2 , 4.1 was obtained in excellent yields, and was used as a precursor to synthesize zirconium(III) alkyl, aryl and borohydride complexes via simple metathesis reactions. Most intriguingly, all of the zirconium(III) hydrocarbyl complexes, Zr( 5 2 )R[N(SiMe H 5 C PPr) 2 CH ] , where R  =  Ph, Me, Et, Bz and , 3 S 2 CH iMe show very good thermal stability. The  X-ray structure determination of the aryl (Ph), ailcyl (CH2SiMe ) and the borohydride (BH 3 ) 4 derivatives showed that all of the complexes are mononuclear and have closely related structures. These examples constitute the first well characterized zirconium(III) complexes containing hydrocarbyl and borohydride ligands. The ESR spectroscopic studies indicate that the x-hydrogens of the alkyl ligands show different hyperfine coupling constants. Although this could be explained on the basis of restricted rotation about the zirconium-carbon bond, infrared studies and some structural features seem to suggest a weak agostic type interaction may be present between one of the oc-hydrogens and the metal. Hydrogenolysis of certain alkyl complexes shows a clean conversion to the mononuclear zirconium(Ill) hydride complex. This hydride complex undergoes an insertion reaction with references on page  Chapter IV  186  ethylene. By means of labeling studies with the ethyl zirconium(Tll) complex it was shown that no scrambling of the 13-hydrogens occurred which mirrored the behavior of unhindered zirconium(IV) alkyls. The hydride complex also undergoes hydrogen exchange reactions with ) and H—C(sp 2 H—C(sp ) bonds, presumably by way of a-bond metathesis. Reactions with 3 terminal acetylene predominantly gave the acetylide complex and no definitive evidence was found for the formation of the insertion product. Complexes H Zr( ) 5 Cl[N(SiMe2C C H2PPr)2], 1 4.1 and H Zr(r1 ) 5 (BH21) C [N(SiMe2CH2PPr1)2j, 4.17 undergo a reversible disproportionation reactions under a CO atmosphere to give zirconium(IV) and zirconium(ll) derivatives. It was also shown that 3 CH C N reacts in a similar fashion with 4.1; however the reversibility of this reaction was not established. In the case of the borohydride complex the reaction with CO proceeds further to give a complex containing a “formyl-ylid” type ligand. Finally it could be stated that the isopropyl version of the PNP ligand “[N(SiMe C 2 H2PPr’)2j” was very effective in stabilizing the zirconium(ffl) complexes. Also, these complexes have shown many different types of reactivity, which is in stark contrast to the bulky Cp ligand based zirconium(III) complexes where no reactivity has been reported.  4.9 Experimental Procedures 4.9a General Unless otherwise stated all procedures were as described in section 2.9a. Hydrogen gas, purchased from Matheson, was purified by passage through a column of activated 4A molecular sieves and MnO supported on vermiculite. Deuterium (99.5 atom %D) gas and ethylene-d4 (99.5 atom %D) were obtained from MSD Isotopes. Ethylene and CO were purchased from Matheson and were used as supplied. Phenyllithium 66, 67 ethyllithium, benzylpotass 68 ium, ° and ’ 7 LiCH2SIMe 6 , 3 7 dibenzyl-mag 9 NaCp•DME nesium were prepared according to literature procedures.  Methylmagnesiumbromide (1.4 M solution in 75% toluene and 25% THF),  benzylmagnesiumchloride (1 M solution in 2 Et 0 ), 3 CH C N, TiCl , 2 3 Ph and 2 S PbCl were purchased from Aldrich and LiBH 4 was purchased from BDH.  Diphenyldisuiphide was references on page j  Chapter IV  187  purified by sublimation, acetonitrile was dried over 4A activated molecular sieves for 12 hours and then vacuum transferred and degassed by three freeze-pump-thaw cycles.  Lead(II)  dichioride and LiBH 4 were pumped under vacuum for 24 hours prior to use. The ESR spectra were recorded on Varian E-3 spectrometer calibrated with a sample of VO(acac)2, g  =  1.965.72 ESR simulations were done on a Macintosh lix using ESR II from  Calleo Scientific Software. The values of line broadening and coupling constants were obtained from the simulated spectra (see appendix Bi). NMR, UV/Vis, JR and MS spectra were recorded on the instruments described in section 2.9a. The complex ] -C5H5)C12[N(SiMe2CH 5 Zr(fl P 2 Pr’) , 2.6 was prepared according to the procedure described in section 2.9b.2. HfCl3[N(SiMe2CH2PPr) j was synthesized according 2 to the published procedure. 73  4.9b Synthesis of Complexes 4.9b.1 ) Zr(1 ) H 5 C P ] 2 C1[N(SiMe Pr’ C H , 4.1. A solution of 2 Zr(1 ) H 5 C12[N(SiMe C PPr) 2.6, (1.50 g, 2.42 mmol) in toluene (80 mL) was transferred into a thick-walled CH ] 2 reaction flask containing Na/Hg (100 g of 0.3% amalgam, 13.0 mmol). The flask was then evacuated under vacuum (3 minutes) and sealed. Upon stirring the reaction mixture turns deep green. After 48 hours the reaction mixture was decanted from the amalgam and filtered through a layer of Celite®. The amalgam was extracted with 20 mL portions of hexanes (total of 60 mL) until the washings showed no green color. Upon removal of the solvent from the combined filtrate and extracts a dark green solid was obtained (95%). ESR spectrum of this green solid shows only the presence of 4.1 and 1 H NMR shows <5% (estimated relative to the amount of H present in C6D 5 D 6 C ) diamagnetic impurities. 6  Recrystallization from hexanes gave  analytically pure material (1.25 g, 88%). ESR (toluene): g P) 31 a(  =  21.1 G, 2P; a( N) 14  G. .teff (Evans method) =  2600 1 cm Lmo1 ;  =  =  2.9 G, iN; a( H) 1  =  =  1.955; a( Zr) 91  =  37.2 G, lZr;  1.8 G, 5H; linewidth used for simulation, 2.3  1.57 B. M. UV-Vis (toluene, 1 cm quartz cell): 2 max  360 nm, e  =  =  324 nm, 6 max  2500 Lmol cm. Anal. Calcd for Z 1 49 H 3 C2 S 2 C1NP i r:  C, 47.27; H, 8.45; N, 2.40. Found: C, 46.99; H, 8.99; N, 2.20. references on page i2  Chapter IV  188  4.9b.2 ) Hf ) H 5 [ C P ] 2 N(S1M C1 Pr’ C H , (i e 4.2. To a solution of 2 [ 3 HfC1 N(SiMe2CH PPr’)2] (6.00 g, 8.89 mmol) in toluene (150 mL) was added solid NaCp•DME (1.736 g, 9.74 mmol) at room temperature. The NaCp•DME was added in three portions at 1 hour intervals and the resulting mixture was stirred for 12 hour. The salt (NaC1) was removed by filtering through Celite®, the filtrate concentrated to 15 mL, hexanes was added until the solution turned turbid and cooling at -30 C gave a pale white crystalline material (5.52 g, 88%). 1 H NMR (6, 300 MHz, C6D6): 0.60 (s, 12H, Si(CH3) ); 1.6 to 0.96 (m, 28H, P[CH(CH 2 ,2 ] 2 ) 3 SiCH P ); 2.17 (sept, 4H, P[CH(CH ,J ] 2 ) 3 3 wH  =  8.9 Hz); 6.46 (br s —5H, 5 C ) H . P{ 31 H 1 ) NMR (6, 121.421  MHz, 6 C ) D : 20.04 (s). Anal. Calcd for H 29 C 4 H S P 2 NC1 3 f: i C, 39.07; H, 6.98; N, 1.98. Found: C, 39.36; H, 7.16; N, 1.87. 4.9b.3 ) Hf ) H 5 C P ] 2 C1[N(SiMe C Pr H , ( 4.3. A solution of 2 Hf(r ) H 5 [ N(SiMe C1 C i PPr) (2.00 g, 2.83 mmol) in toluene (80 mL) was transferred into a thick-walled reaction 2 CH J flask containing Na/Hg (100 g of 0.33% amalgam, 14.1 mmol). The flask was then evacuated under vacuum (3 minutes) and sealed. Upon stirring the reaction mixture turns deep greenish brown. After 48 hours, the reaction mixture was decanted from the amalgam and filtered through a layer of Celite®. The amalgam was extracted with 20 mL portions of hexanes (total of 60 mL), until the extracts show no color. Upon stripping off solvent from the combined filtrate and extracts a dark brown solid was obtained.  Pure material was obtained by  recrystallization from a pentane solution (0.8 g, 47%). ESR spectrum of this brown solid shows the presence of 4.1 and 4.3. ESR (toluene): g  =  1.9 16. Anal. Calcd for S 2 2 C N 9 H4 i2Hf: C1P 3 C,  41.13; H, 7.35; N, 2.09. Found: C, 41.49; H, 7.49; N, 1.96. 4.9b.4 ) Zr( ) [ 5 H 6 C P ] 2 N(SIM C Pr’ H , e 4.4. To a solution of 4.1 (240 mg, 0.41 i mmol) in toluene (5 mL) was added PhLi (1.6 mL of 0.25 M solution in Et20, 0.40 mmol) at -78 °C and stirred for 5 minutes. After stirring the reaction at room temperature for 3 hours the solvent was removed under vacuum. The deep brown residue was extracted with pentane (20 mL) and the extract was filtered through Celite®. The filtrate was concentrated (2 mL) and then cooled at -40 °C to give hexagonally shaped crystals (190 mg, 74%). ESR (toluene): g Zr) 91 a(  =  20.7 G, lZr a( P) 31  =  20.3 G, 2P; a( N) 14  =  1.8 G, lN; a( H) 1  =  =  1.981;  1.1 G, 5H; linewidth references on page  Chapter IV  189  used for simulation, 2.8 G. UV-Vis (toluene, 1 cm quartz cell):  =  342 nm;  =  478 nm.  Anal. Calcd for 9 C2 4 5 H NSi2P2Zr: C, 55.63; H, 8.69; N, 2.24. Found: C, 55.51; H, 8.68; N; 2.35. 4.9b.5 ) Zr(T 5 C P ] 2 CSHS)Me[N Pr’ H , (SiMe 1 4.5. To a solution of 4.1 (825 mg, 1.46 mmol) in toluene (25 mL) was added a solution of MeMgX (X mmol; X  =  =  Br, 1.1 mL of 1.4 M solution, 1.54  Cl, 0.55 mL of 3.OM solution in THF, 1.6 mmol) at room temperature. The reaction  mixture was stirred for 4 hours and then the solvent was stripped off under vacuum. The resulting solid was extracted with pentane (10 mL) and the extract was filtered through a layer of Celite®. The filtrate was concentrated  (-- 3 mL) and then cooled at -40 °C to give a deep  green crystalline product (480 mg, 58%). ESR (toluene): g P) 31 a(  =  21.1 G, 2P; a( H) 1  =  6.6 G, 3H; a( N) 14  =  =  1.963; a( Zr) 91  =  28.0 G, lZr;  2.1 G, iN; linewidth used for simulation, 3.0  G. Anal. Calcd for : 22 2 C 2 5 H S Z ) 2 r(MgC1 NP o. 4 i C, 49.28; H, 8.96; N, 2.39; Cl 2.67. Found: C, 48.90; H, 9.08; N, 2.39; Cl, 2.52. 4.9b.6 ) Zr ) H 5 [ 3 C P 1 2 N(S1M CH Pr’ C H (i , e 4.6. Method 1: To a solution of 4.1 (1.00 g, 1.71 mmol) in toluene (25 mL) was added a solution of 2 CH3CH L i (70 mg, 1.94 mmol) in toluene (10 mL) at -78 ‘C. The reaction mixture was allowed to warm to room temperature and stirred for 8 h. The solvent was stripped off under vacuum, the residue was extracted with pentane (10 mL) and the extract was filtered through a layer of Celite®. The filtrate was concentrated (3 mL) and then cooled to -40 ‘C to give a deep green crystalline product (560 mg, 56%). ESR (toluene): g a(’Hp)  =  1.962; a( P) 31  1.8 G, 3H; a( N) 14  =  =  20.9 G, 2P; a(’Ha)  =  9.3 G, 1H; a(’Ha)  =  3.2 G, 1H;  2.6 G, iN; linewidth used for simulation, 2.2 G. Anal. Calcd for  54 H 5 C2 S 2 NP Z r: i C, 51.95; H, 9.42; N, 2.42. Found: (a) C, 49.76; H, 9.02; N, 2.32; (b) C, 51.20; H 9.28; N 2.39. Case (a) was obtained from the first recrystallization and case (b) was obtained from the second recrystallization and the data seems to fit for 0.6 equivalents and 0.2 equivalents of LiCl respectively. Method 2: To a solution 4.1 (300 mg, 0.51 mmol) was added a solution of MeMgBr (0.4 mL of 1.4 M solution) and this was stirred at room temperature for 4 hours. The solvent was then stripped off under vacuum and the resulting solid was extracted with pentane. Stripping off the references on page  Chapter IV  190  pentane gave a green solid containing 4.5. The solid was dissolved in toluene (15 mL) and transferred into a thick walled reaction flask (150 mL). The solution was freeze-pump-thawed twice and stirred under 1 atmosphere of H 2 for 12 hours at room temperature to give 4.14. The 2 was removed under vacuum and ethylene was introduced into the reaction flask and stirred H for 0.5 hours. After removing the ethylene under vacuum, dlioxane (1.0 mL) was added and stirred for lh. The solvent was stripped under vacuum and the resulting solid was extracted with pentane. ESR spectrum of the pentane shows only the presence of 4.6. 4.9b.7 ) . A solution of 4.14-d 1 Zr(T 5 D C P ] 2 CsHs) 1 [N(SiM Pr H , I CH e 4.6-d  (— 0.5  mmol) was prepared as described in the synthesis of 4.14 using D 2 gas. After removing the deuterium gas and stirring the solution under ethylene for 0.5 hours gave 4.6-d . ESR (toluene): 1 g  =  1.962; a( P) 31  a( H 2 )  =  =  20.9 G, 2P; a(’Ha)  N) 14 0.3 G, 1D; a(  =  =  9.3 G, 1H; a(’Ha)  =  3.2 G, 1H; 1 a( H )  =  1.8 G, 2H;  2.6 G, iN; linewidth used for simulation, 1.7 G. JR (cm, 1  toluene): 2169 (w, f3C-D of Et ligand); 2143 (m, 13C-D of Et ligand); 2109 (s, j3C-D of Et ligand). 4.9b.8 2 1 5 Zr( C H C ] ) CsHs) HPPr [N(SiM D , CD e 4.6-d4. A solution of 4.14 (-0.5mmol) was prepared as described in the synthesis of 4.14. After removing the hydrogen gas and stirring the solution under ethylene-d4 for 0.5 hours gave 4.6-d4. ESR (toluene): g P) 31 a(  =  20.9 G, 2P; 2 a( H a)  G, 1H; a( N) 14  =  =  1.5 G, 1D; agH)  =  0.5 G, 1D; 2 a( H )  =  =  1.962;  H) 1 0.3 G, 2D; a(  =  1.8  2.6 G, iN; linewidth used for simulation, 2.2 G.  4.9b.9 2 1 Zr( ) H 5 [ 3 C P ] ) . A solution of 4.14- d 5 N(SIM CD C Pr D H , i 1 (‘—0.5 e 4.6-d mmol) was prepared as described in the synthesis of 4.14 using D 2 gas. After removing the deuterium gas and stirring the solution under ethylene-cL for 0.5 hours gave 4.6-d5. ESR (toluene): g  =  1.962; a( Zr) 91  0.5 G, 1D; a( H) 2  =  =  28.4 G lZr; a( P) 31  0.3 G, 3D; a( N) 14  =  =  20.9 G, 2P; 2 a( H a)  =  1.5 G, 1D; 2 a( H a)  =  2.6 G, iN; linewidth used for simulation, 2.2 G. JR  , toluene): 2192 (m, f3C-D and possibly an ctC-D of Et ligand); 2164 (m, C-D of Et 1 (cm ligand); 2128 (m, C-D of Et ligand); 2043 (s, ctC-D of Et ligand). 4.9b.1O 2 1 Zr( ) H 5 P C P ] ) h[N(SiMe CH C Pr H , ’ 4.7. To a solution of 4.1 (315 mg, 0.57 mmol) in THF (20 mL) was added a solution of PhCH K (70 mg, 0.54 mmol) in THF (5 mL) at 2 references on page  i2.  Chapter IV  191  -40 DC. The reaction was warmed to room temperature and stirred for 5 hours. The solvent was stripped off under vacuum, and the resulting solid was extracted with hexanes (10 mL). The extract was filtered through a layer of Celite®, concentrated  (— 3 mL) and cooled at -40 DC to  give a dark green crystalline product (275 mg, 75%). ESR (toluene): g G, 2P; 1 a( H a)  =  3.2 G, 2H; a( N) 14  =  3.4 G, iN; 1 a( H )  =  =  1.956; a( P) 31  =  18.6  1.2 G, 5H linewidth used for  simulation, 1.6 G. Anal. Calcd for Z OH56NP 3 C S 2 r: i C, 56.29; H, 8.82; N, 2.19. Found: C, 56.58; H, 8.86; N, 2.25. 4.9b.11 ] ZrC1(C P [ P 2 N(SiM Pr2 h) , e2CH H ) 4.9. To a solution of 4.1 (350 mg, 0.6 mmol) in toluene (30 mL) was added a solution of PhCH MgC1 (0.6 mL of 1 M solution in 2 2 Et 0 , 0.6 mmol) at room temperature and stirred for 6 hours. The solvent was stripped off under vacuum, the resulting solid was extracted with toluene (10 mL) and filtered through a layer of Celite®. The filtrate was concentrated (1 mL), and added hexanes (10 mL) and cooling at -40 °C gave a pale yellow material (63 mg, 15%). Upon further recrystallization the zirconium-(Ill) benzyl derivative 4.7 was isolated. 1 H NMR  ): 0.18 (s, 6H, Si(CH D 6 ); 0.45 (s, 6H, 2 ) 3 (, 300 MHz, C  Si(CH ) 2 ) 3 ; 0.6 (m, 4H, 2 SiCH P ); 0.8 to 1.0 (m, 24H, 3 P[CH(CH ) ] 2 ) ; 1.60 (sept, 2H, P[CH(CH ) 3 2]2,  3 3 H-H  6.3 Hz); 1.70 (sept, 2H, P[CH(CH , 1 2 ) 3  =  CH P 2 h); 2.02 (s, 2H, CH Ph); 6.87 2 4H, o-Ph, J3 H..H  =  (t,  2H, p-Ph, J3 H..H  =  3 J H-H  =  7.5 Hz); 1.98 (s, 2H,  6.6 Hz); 7.23 (m, 4H, rn-Ph); 7.37 (d,  6.6 Hz). P( 31 H 1 } NMR (8, 121.421 MHz, 6 C ) D : -11.87 (s). Anal. Calcd  for 2 C1NSi 3 C 5 H Z P r: C, 54.78; H, 8.33; N, 2.00. Found: C, 55.08; H, 8.56; N; 1.89. 2 8 4.9b.12 ) Zr ) H 5 S [ 3 C P ] 2 N(Si CH iM Pr C H (i , Me e ’ 4.8. To a solution of 4.1 (250 mg, 0.43 mmol) in toluene (10 mL) was added a solution of L 2 S 3 Me iCH i (42 mg, 0.45 mmol) in toluene (3 mL) at room temperature. After stirring for 12 hours the solvent was stripped off under vacuum, and the resulting solid was extracted with pentane (10 mL). The filtrate was filtered through a layer of Celite® and concentrated  (‘-  3 mL) and then cooling this solution at  -40 °C gave a dark green crystalline product (165 mg, 60%). ESR (toluene): g =  30.5 G, lZr; a( P) 31  =  21.4 G, 2P; a(’Ha)  =  9.3 G, 1H; a(’Ha)  =  =  1 cm quartz cell): m 2 ax  430 nm, C  334 nm, Emax  =  2700 Lmol cm; ? 1  =  1.973; a( Zr) 91  6.2 G, 1H; a( N) 14  iN; linewidth used for simulation, 2.6 G. ji (Evans method) =  =  2.0 G,  1.71 B. M. UV-Vis (toluene, =  1700 Lmolcm. references on page  Chapter IV  192  Anal. Calcd for Z 3 2 C 6 H S 2 NP 7 0 r: i C, 50.97; H, 9.51; N, 2.20. Found: C, 50.68; H, 9.46; N, 2.21. 4.9b.13 P Zr( 5 C 2 CSHS)OPh[N Pr’2 H ’fl (SiMe 4.10. To a solution of 4.1 (200 mg, 0.34 )2], mmol) in THF (10 mL) was added a solution of PhONa (40 mg, 0.34 mmol) in THF (5 mL) at -10 C and stirred for 10 minutes. The reaction was then warmed to room temperature and stirred for 12 hours to give a deep green solution. The solvent was stripped off under vacuum, and the resulting solid was extracted with hexanes (10 mL). The extract was filtered through a  layer of Celite®, concentrated  (- 3 mL) and cooled at -40 °C to give a dark green crystalline  product (130 mg, 60%). ESR (toluene): g  =  1.955; a( P) 31  =  18.7 G, 2P. Anal. Calcd for  24 C 5 H S 2 NOP Z r: 9 i C, 54.25; H, 8.48; N, 2.18. Found: C, 54.04; H, 8.50; N, 2.13. 4.9b.14 ) Zr ) H 5 [ C P ] 2 N(Si NP C Pr H , (i Me h 4.11. To a solution of 4.1 (200 mg, 0.34 mmol) in THF (10 mL) was added a solution of NaNPh2 (66 mg, 0.34 mmol) in THF (5 mL) at -10 C and stirred for 10 minutes. The reaction was then warmed to room temperature and stirred for 12 hours to give a deep brown solution. The solvent was stripped off under vacuum, and the resulting solid was extracted with hexanes (10 mL). The extract was filtered through a layer of Celite® and stripping off the solvent gave an oil. ESR (toluene): g  =  1.953; a( P) 31  =  11.2 G, 2P. 4.9.15 ) Zr ) H 5 [ C P ] 2 N(Si PP C Pr H , (i Me h 4.12. To a solution of 4.1 (200 mg, 0.34 mmol) in THF (10 mL) was added a solution of LiPPh 2 (66 mg, 0.34 mmol) in THF (5 mL) at -10 °C and stirred for 10 minutes. The reaction was then warmed to room temperature and stirred for 12 hours to give a deep brown solution. The solvent was stripped off under vacuum, and the resulting solid was extracted with hexanes (10 mL). The extract was filtered through a  layer of Celite® and stripping off the solvent gave an oil. ESR (toluene): g 18.6 G, 2P; a( P) 31  =  1.965; a( P) 31  =  29.8 G.  4.9b.16 ) Zr ) H 5 C P ] 2 H[N(S Pr’ C H , (i 1Me 4.14. A solution of 4.5 or 4.8  (- 0.1  mmol) in  toluene (5 mL) was degassed by freeze-pump-thaw cycles and then stirred under 1 atm of H 2 for 10 to 12 hours at room temperature. Spectroscopic (ESR, NMR) analysis of the resulting solution shows clean formation of the hydride complex. A solution of 3 (0.05 mmol, 0.6 mL of references on page  Chapter IV  193  ) in a sealable NMR tube was treated with H 8 D 7 C 2 as described above, and its 1 H NMR spectrum shows only the formation of Me4Si and the ESR spectrum of the same sample shows only 7. Treatment of 4.5 in a similar fashion with D 2 shows the formation of CH D (0.17 ppm, 3 1:1:1 triplet, 2 3H-D Zr) 91 a(  =  =  1.9 Hz) and the formation of the deuteride 4.14. ESR (toluene): g = 1.988;  25.1 G, lZr; a( P) 31  21.7 G, 2P; a( H) 1  =  8.7 G, 1H or 2 a( H )  =  1.4 G, 1D; a( N) 14  =  1.4 G, iN; linewidth used for simulation, 1.6 G. 4.9b.17 [ZrHCp 2 [N ) ) C P ) ]{CiZr (S ]} (Si P [N(Me iM H Me r’ SkH e , 4.15. 2 -(jt-H) Method 1: A solution of Zr(1 5 )H Cl2[N(SiMe2 C CH2PPr)2] 2.6, (300 mg, 0.48 mrnol) in toluene (40 mL) was transferred into a thick-walled reaction flask (300 mL) containing Na/Hg (56 mg of 0.1% amalgam, 2.4 mmol of Na). The dinitrogen in the flask was removed under vacuum (approximately 5 mL of solvent was removed) and then the reaction mixture was degassed once by a freeze-pump-thaw cycle. The flask was then cooled to —196 °C, filled with 1 atmosphere of dihydrogen, sealed, and allowed to warm slowly to room temperature with stirring. Upon warming up to room temperature the reaction mixture quickly turned green (1 hour) and slowly the intensity of the green color decreased. After the disappearance of the green colour (7 days) the solution was decanted from the amalgam and filtered through a layer of Celite®. The amalgam was extracted with 15 mL portions of toluene (total of 60 mL), until the extracts showed no yellow colour. The filtrate and the extracts were combined and stripping off the solvent gave a yellow powder (0.20 g, 76%). The product was crystallized from a 1:1 mixture of toluene and Et 0. 2 Method  2:  Approximately  30  mg  of  Zr( ) H 5 P 2 ] R[N(SiMe2C Pr) C , H where R r  =  the  zirconium(III)  alkyl  derivative  Me, CH 3 S 2 iMe or C 2 C 5 H 6 H was dissolved in  0.5 mL of C6D 6 inside a NMR tube and the resulting solution was degassed by three freeze pump-thaw cycles. Then the NMR tube was cooled to -196 C, filled with 1 atmosphere of dihydrogen and sealed.  Monitoring the reaction by NMR spectroscopy shows only the  formation of the diamagnetic hydride complex.  references on page  Chapter IV  194  Major isomer: 1 31 NMR (6, 500 MHz, 7 { H P} C ) 8 D : 0.17, 0.25, 0.29, 0.39, 0.46, 0.50 and 0.68 (s, each 3H, 3 P); 1.0 to 1.30 (m, 3 2 Si(CH ) 2); 0.84 to 0.92 (m, SiCH (P[CH(CH ) J 2 ) ; 1.48 (d, 1H, SiCH2Zr, 2 JH-H  =  11.2 Hz); 1.6 to 1.9 (overlapping sept, 7H, P[CH(CH , 3 1 2 ) 3 JH-H  2.16 (d, 1H, SiCH2Zr, 2 3H-H (t, —5H,  C H 5 5, 11 Jp.. 3  =  =  11.2 Hz); 2.45 (sept, 1H, 2 P[CH(CH3) 3 , ] 3 H-H  =  =  7.0 Hz);  7.0 Hz); 6.15  1.4 Hz); 6.56 (s, —5H, C ). P( H 5 31 H 1 } NMR (6, 121.4 MHz, 7 C D 8):  Spectrum consisted of an ABMX spin system; 22.31 (d, 1P, 2 Jp..p = 64.7 Hz); 17.45 (d, 1P, 2 Jpp 64.7 Hz); 0.48 (s, 1P); -1.90 (s, 1P). C{ 13 H 1 } N?vIR (6, 50.324 MHz, 7 C ) 8 D : 111.67 (s, Cp); 104.94 (s, Cp). Minor isomer: 1 H{ P} 3 1 NMR (6, 500 MHz, 7 C ) 8 D : 6.12 (t, —5H, 5 C J3 , H p..H 1.3 Hz); 6.39 (s, —5H, ) 11 5 C P{ 1 . 31 H} NMR (6, 121.4 MHz, C ): Spectrum consisted of 8 D 7 an ABMX spin system; 22.00 (d, 1P, 2 Jp.p  =  65.1 Hz); 18.38 (d, 1P, 2 Jp.p  =  1P); -1.34 (s, 1P). JR (cm , KBr): 1435 (br s, Zr—Ht), 1159 (Zr—Dt). 1  65.1 Hz); 0.90 (s, Anal. Calcd for  51 H 3 C2 S 2 NP Z r: i C, 50.13; H, 9.33; N, 2.54. Found: C, 50.35; H, 9.15; N; 2.33. 4.9b.18 ) Zr( ) 5 [ 4 C P ] 2 N(Si Cs BH Pr H , rI Me H 4.17. To a solution of 4.1 (800 mg, 1.37 mmol) in toluene (40 mL) was added solid LiBH 4 (150 mg, 6.84 mmol) and was stirred at room temperature. After stirring for 12 hours the reaction mixture was filtered through a layer of Celite® and the filtrate was concentrated to give a black oil. The oil was dissolved in Et 0 (5 2 mL) and cooled at -40 C to give black rectangular crystals (650 mg, 84%). ESR (toluene): g 1.958; a( P) 31  =  20.7 G, 2P; a( N) 14  =  2.0 G, iN; a( H) 1  simulation, 2.8 G. UV-Vis (toluene, 1 cm quartz cell): 2 ’max  =  =  2.8 G, 4H; linewidth used for  =  332 nm; Em  2800 Lmol cm 1  1 JR (cm, KBr): 2953, 2871, 2401 (s, B-1I), 2379 (s, B-Ht), 2126 (s, B-Hb), 1457 (m, Zr-H), 1  1373, 1244, 1124. Anal. Calcd for P 2 H 3 C2 S3NESi 2Zr: C, 49.00; H, 9.47; N, 2.48. Found: C, 48.82; H, 9.46; N; 2.48. 4.9b.19 ) Zr ) H 5 C P ] 2 (CCPh C Pr H (1 )[N(Si . Me A solution of 4.14 (—0.5 mmol) was prepared as described in the synthesis of 4.14. The hydrogen gas was removed under vacuum, the solution cooled to -78 C and then a solution (toluene) of PhCCH (1 equivalent) was added. Instantly the color changed from deep green to purple. approximatly close to the observed spectrum: ESR (hexanes): g  The simulated spectrum was =  P) 31 9.8; a(  =  15 G, 2P; a( N) 14  =3.5G, 1 JN;a( H )=1G,5H. references on page  Chapter IV  195  4.9b.20 ) Z ) H 5 C P ] 2 (C—=CPh)C C Pr H r( 1[N(SiMe 4.16. ,  Complex Zr( 5. C )H 5  2 (CCPh)[N(S C H2PPr’)2] iMe was oxidized with PbC12. 1 H NMR (6 300 MHz, C ): 0.55 8 D 7 (br s, 6H, 3 Si(CH ) P); 0.98 to 1.1 (m, 24H, 2 2); 0.60 (br s, 6H, 3 Si(CH ) 2); 0.86 (br s, 4H, SiCH P[CH(CH ) ] 2 ) 3 ; 2.13 (brm, 4H, 3 P[CH(CH ) ] 2 ) ; 6.53 (s, Cp, 5H); 6.95 (br, 1H,p-Ph); 7.08 (m, 2H, rn-Ph); 7.35 (br, 2H, o-Ph). 31 P{ 1 H} NMR (6, 121.421 MHz, 6 C ) D : 16.32 (s). 4.9b.21 ) Hf ) H 5 ) 4 C P ] 2 [N(S C1(B Pr C H , (i 1Me H ’ 4.21. To a solution of 4.2 (250 mg, 0.35 mmol) in toluene (25 mL) was added solid LiBH 4 (60 mg, 2.74 mmol) and was stirred at room temperature. After stirring for 3 days the reaction mixture was filtered through a layer of Celite® and the filtrate was concentrated to give an oil. The oil was dissolved in hexanes and cooled at -40 C to give a white crystalline material (170 mg, 7 1%). 1 H NMR (6, 300 MHz, ); 0.59 (s, 6H, 2 2 ) 3 C6D ) 6 : 0.56 (s, 6H, Si(CH Si(CH3) ) ; 0.8 to 1.1 (m, 28H, P[CH(CH , ] 2 ) 3 SiCH P 2 ); 1.96 (sept, 2H, P[CH(CH ,3 J 2 ) 3 3H-H =  =  6.8 Hz); 2.24 (sept, 2H, 3 P[CH(CH J3 , ] 2 ) HH  6.8 Hz); 6.25 (br s —5H, C ). 31 H 5 P{ 1 H} NMR (6, 121.421 MHz, 6 C ) D : 14.07 (s). 13 H} C{ 1  NMR (6, 50.323 MHz, 6 C ) D : 110.05 (s, C ). JR (cm H 5 , KBr): 2488 (s, B-Hi), 2414 (s, B 1  Ht), 2143 (s, B-Hb), 1456 (m, Zr-H). Anal. Calcd for 2 2 C 5 H NBC1 P 2Hf: 3 7 Si C, 40.24; H, 7.78; N, 2.04. Found: C, 40.02; H, 7.79; N; 1.98. 4.9c Disproportionation Reactions A solution of ZrCp(BH4)[N(SiMe2CH2PPr)2] 4.17, (30 mg, 0.05 mmol) in C 8 (0.5 mL) was D 7 transferred into an NMR tube and degassed three times by freeze-pump-thaw cycles. The NMR tube was then filled with 1 atmosphere of CO and sealed. The NMR spectroscopic analysis (within  15  minutes)  shows  the  formation  of two  diamagnetic  complexes,  2 ZrCp(B ) 4 P 2[N(SiMe2C Pr)2 H 4.19, and ] H J ZrCp(CO)2[N P 2 Pr) (SiMe2CH 4.18 in 1:1 ratio. Upon standing (3 days) the peak associated with 4.19 decreases in intensity and two new peaks appear which correspond to the fomiyl complex, 4.23. The reactions with CO and the zirconium(III) chloro derivative 4.1, or with the hafnium(ffl) chioro derivative 4.3, were carried out as described for the borohydride complex 4.17. The reaction of the zirconium-(Ill) chioro derivative, 4.1 with 3 CH C N was carried out at low temperature. A solution of 4.1 (30 mg in 0.5 mL of C ) was transferred into a NMR 8 D 7 references on page  Chapter IV  196  tube, degassed three times by freeze-pump-thaw cycles, and using a constant volume gas apparatus 2 equivalents of CH CN vapor was condensed at -196 °C, and sealed. The sample 3 was transferred into a -60 C bath and allowing to stand for 1 hour gave a deep red solution. The  NMR  spectroscopic  analysis  shows  the  presence  of two  complexes,  [N(SiMe ZrCpC1 C P ] 2 ) Pri H 2.6, and ZrCp(CH CN) [N(SiMe2CH2PPr’)2], 4.22. Warming 3 the sample to room temperature shows a rapid decrease in the intensity of the resonances associated with complex 4.22. 4.9c.1 ) [N(SiMe ZrCp(CO) C P ] 2 Pr H , 4.18. 1 H NMR (8, 300 MHz, 6 C ) D : 0.31 (s, 12H, Si(CH ) 2 ) 3 ; 0.68 (m, 4H, SiCH P); 0.85 to 1.0 (m, 24H, 3 2 P[CH(CH ) j 2 ) ; 1.70 (br sept, 4H, , .. ] 2 ) 3 P[CH(CH 11 J 3 11  =  7.4 Hz); 4.75 (t —5H, 5 C3 , H 3 p-H = 1.5 Hz). Gated decouplled C  NMR (6, 75.4 MHz, C ): 92.12 (s, Cp, 31 8 D 7 H} NMR (6, 1 P( C..H = 171.5 Hz); 249.0 (s, CO). 31 121.421 MHz, 6 C ) D : 37.91 (s). JR (cm , toluene): 1965 (w, CO); 1871 (s, CO); 1845 4 (shoulder, CO). Anal. Calcd for 2 29 C 4 H S P O NC1 Z 5 i C, 49.63; H, 8.16; N, 2.32. Found: C, r: 49.72; H, 8.35; N, 2.27. 4.9c.2 2 1 [ 4 ZrCp(BH C P ] ) N(S1Me Pr H , 4.19. 1 H NMR (6, 300 MHz, 6 C ) D : 0.44 (s, 12H, Si(CH ) 2 ) 3 ; 0.89 (br m, 4H, SiCH P); 1.0 to 1.1 (m, 24H, 3 2 P[CH(CH ) ] 2 ) ; 2.00 (br sept, 4H, ,3 1 2 ) 3 P[CH(CH ,3 H 5 C NMR (6, 75.4 MHz, 3 3H.H = 7.4 Hz); 6.28 (t —5H, C 3p..H = 1.5 Hz). ‘ C ) D 6 : 109.53 (s, Cp). 31 H} NMR (6, 121.421 MHz, 6 1 P{ C ) D : 5.80 (s). 11 H} NMR(6, 1 B( 96.2 MHz, 7 C ) 8 D : -92.00 (s, BH ). JR (cm4 , solution): 2427 (s, B-He), 2381 (s, B-Ht), 2130 (s, 1 B-Hb). 4.9c.3 ) [N(SiMe HfCp(CO) C P ] 2 Pr H , 4.20. 1 H NMR (6, 300 MHz, 6 C ) D : 0.30 (s, 12H, Si(CH ) 2 ) 3 ; 0.75 (m, 4H, SiCH P); 0.55 to 1.1 (m, 24H, 3 2 P[CH(CH ) ] 2 ) ; 1.70 (br sept, 4H, , .. ] 2 ) 3 P[CH(CH 11 = 8.0 Hz); 4.68 (t, 5H, C5H5, 3 J 3 11 P{ H} NMR (6, 121.421 3 p.H = 1.5 Hz). 31 MHz, 6 C ) D : 32.92 (s). 4.9c.4 2 1 C 3 ZrCp(CH C P ] ) N)[N(SIMe Pr H , 4.22. 1 H NMR (6, 300 MHz, 6 C ) D : at 10 °C, 0.02 (s, 6H, 3 Si(CH ) 2 ) ; 0.15 (s, 6H, 3 Si(CH ) 2 ) ; 1.12 to 1.26 (m, 24H, 3 P[CH(CH ) ] 2 ) ; 2.00 (hr sept, 2H, P[CH(CH ,3 ] 2 ) 3 J-p = 6.5 Hz); 2.36 (hr sept, 2H, 3 P[CH(CH J , ] 2 ) 3 wH = 6.5 Hz);  references on page  Chapter IV  197  2.78 (s, 3H, 3 CH C N); 5.66 (s, 5H, C ). 31 H 5 H} NMR (6, 121.421 MHz, 6 1 P( C ) D : at -18 °C, 32.92 (s).  4.9c.5 13 )Zr( 4 Cp(BH CH0 [N( P ) C P P 2 ) (S1 )3 •B Pr ], SiM r’ H Me H ’ e 4.23. H NMR (6, 500 MHz, 7 1 C ) 8 D : 0.23, 0.35, 0.61, 0.69 (s, each 3H, 3 Si(CH ) 2 ) ; 0.60 (overlapping d of d, 6H, 3 (P[CH(CH ) ] 2 ) ,3 JH-H (P[CH(CH ) j 2 ) 3 ,3 3H-H  =  =  7.6 Hz, 3 JP-H  =  15.3 Hz); 0.94 (overlapping d of d, 6H,  7.1 Hz, 3 P); 0.98 2 JpH = 15.3 Hz); 1.03 (two overlapping d, 2H, SiCH  to 1.11 (m, 14H, (P[CH(CH ] and 2 2 ) 3 SiCH P ); 1.54 (sept, 1H, P[CH(CH ,3 ] 2 ) 3 JwH = 7.1 Hz); 1.77 (sept, 1H, 3 P[CH(CH J3 , ] 2 ) ,3 ] 2 ) 3 H.H = 7.1 Hz); 1.80 (sept, 2H, P[CH(CH 3H-H = 7.6 Hz); 3.10 (d of d, 1H, CHO, J ). 31 H 5 H} NMR 1 P{ 2 pH = 27.4 Hz, J 1 CH = 161.9 Hz); 6.41 (s, 5H, C (8, 121.4 MHz, 7 C ) 8 D : 31.20 (br, 1P); 39.72 (d, 1P, 2 Jp..c NMR (8, 75.4 MHz, 7 C ) 8 D : 60.73 (d of d, CHO, 2 Jp.. , J1 H 5 C C-H  =  =  =  55.1 Hz). Gated decoupled ‘ C 3  55.7 Hz, UC-H  =  162.2); 113.5 (d,  170.8 Hz). B{ 11 H 1 } NMR (8, 96.2 MHz, 7 ); -127.23 4 C D 8): -101.33 (br s, BH  (hr d, ) ).P[CH(CH 1 3 (BH , j 2 3P-B  =  47.4 Hz). B} 11 H 1 ( NMR (6, 500 MHz, 7 C ) 8 D : 1.22 (s,  3H, probably ) )•P[CH(CH 3 (BH ) j 2 ; also showed some changes in the minor resonances located around 0.2 to 0.4 ppm (probably, 4 BH ) . JR (cm , KBr): 2423 (s, B-Ha, 2378 (s, B-Ht), 4 2355 (s, B-Ht); 2345 (s, B-Ht); 2146 (s, B-Hb), 1460 (m, Zr-H).  Anal.  Calcd for  2 C 5 H N B S 2 Z OP 4 7 r: i C, 47.52; H, 9.47; N, 2.31. Found: C, 47.93; H, 9.45; N, 2.64. 4.9e Oxidation Reactions  Oxidation reactions with TiC13 or PbC1 2 was carried out by adding an excess of solid oxidant (approximately 10 equivalents) to a cooled (approximately -10 °C) toluene solution of the zirconium(III) complex. The resulting yellow or orange solution was then decanted, toluene was striped off, and the residue was extracted with pentane and filtered through a layer of Celite®. Oxidation with Ph S was carried out by adding a toluene solution of the oxidant (0.5 2 equivalents) to a solution of the zirconium(III) complex at -78 °C.  Analytically pure  chlorothiolate complex, 4.13 was obtained (75%) by recrystallization from 2 Et O . The alkylthiolate complexes gave only an oily material.  references on page  Chapter IV  198  4.9e.1 ) ZrCpC1(SPh C P ] 2 Pr H , )[N(SiMe 4.13. 1 H NMR (6, 300 MHz, 6 C ) D : 0.71 (s, 6H, Si(CH ) 2 ) 3 ; 0.74 (s, 6H, 3 Si(CH ) 2 ) ; 0.93 to 1.15 (m, 24H, 3 P[CH(CH ) j 2 ) ; 1.15 to 1.26 (m, 4H, SiCH P 2 ); 2.28 (m, 4H, P[CH(CH ); 6.33 (s, 5H, Cp); 7.05 (t, 1H, p-Ph, 3 J 2 ) 3 JH-H 7.24 (m, 2H, in-Ph); 7.47 (d, 2H, o-Ph, J3 wH  =  7.4 Hz);  7.4 Hz). P( 31 H 1 } NMR (6, 121.421 MHz,  =  C ) D 6 : 13.74 (s). 13 H} NMR (6, 50.324 MHz, 6 1 C( C ) D : 113.34 (s, Cp). Anal. Calcd for 2 4 5 H 9 C2 S NC1Si2P Zr: C, 50.22; H, 7.85; N, 2.02. Found: C, 50.14; H, 7.87; N; 1.93. 4.9e.2 2 1 ZrCpC1Et[N C P ] ) Pr H . (SIMe Complex 4.6 was oxidized with PbC12. 1 H NMR (6, 300 MHz, ) ]) 6 C : 0.40 (br s, 6H, 3 Si(CH ) 2, Avia  =  40 Hz); 0.55 (s, 6H, 3 Si(CH ) 2, Avia = 40  Hz); 0.75 to 0.90 (br, 6H, SiCH P and ) 2 3 C 2 CH ; 0.95 to 1.10 (m, 24H, 3 H P[CH(CH ) ] 2 > ; 1.78 (br m, 4H, P[CH(CH3)2j2); 1.78 (t, 3H, , 3 C 2 CH H J3 wH NIvIR (6, 121.421 MHz, 6 C ) D : -0.5 (br s, iXvl/2  =  =  7.6 Hz); 6.33 (s, Cp, 5H). 31 P( 1 H}  370 Hz); 8.0 (br s,  tWl/2  =  370 Hz). Anal.  Calcd for C2 HC1NSi2P2SZr: C, 48.94; H, 8.87; N, 2.28. Found: C, 48.30; H, 8.64; N; 2.20. 5 4.9e.3 2 1 ZrCpC P C P ] ) h)[N(S Pr H 1(CH . IMe Complex 4.7 was oxidized with TiC1 . 1 3 H NMR (6, 300 MHz, 6 C ) D : 0.40 (br s, 6H, Si(CH3)2); 0.50 (s, 6H, Si(CH ); 0.70 (br, 4H, 2 ) 3  SiCH P 2 ); 0.90 to 1.0 (m, 24H, P[CH(CH3)2j2); 1.70 (br m, 4H, P[CH(CH ); 2.68 (d, 1H, 1 2 ) 3 CH P 2 h, J2 H..H  =  11 Hz); 2.98 (d, 1H, 2 CH P h, 32 H..H  (6, 121.421 MHz, 6 1 C D 6): -0.5 (br s, AV  =  =  11 Hz); 6.20 (s, Cp, 5H). 31 H} NMR 1 P(  370 Hz); 8.0 (br s, 1XV 112 = 370 Hz).  4.9e.4 ) ZrCp S ) 3 C P ] 2 (SPh)[ iM Pr H N(SiM (CH . e e Spectra were recorded within 2 hours after the reaction. 1 H NIvIR (6, 300 MHz, 6 C ) D : 0.32 (s, 9H, ) Si(CH 2 CH ) 3 ; 0.42 (s, 6H, Si(CH ) 2 ) 3 ; 0.52 (s, 6H, 3 Si(CH ) 2 ) ; 0.87 (m, 4H, 2 SiCH P ); 0.98 to 1.12 (m, 26H, 3 P[CH(CH ) 2]2 and ) Si(CH 2 CH ) 3 ; 1.80 (m, 4H, 3 P[CH(CH ) ] 2 ) ; 6.40 (s, 5H, Cp); 6.98 (t, 1H, p-Ph, 3 3H-H 7.3 Hz); 7.18 (m, 2H, rn-Ph); 7.83 (d, 2H, o-Ph, 3 JHH  =  =  7.4 Hz). 31 P(’H} NMR (6, 121.421  MHz, 6 C D 6): 2.50 (br s). Complicated spectra were obtained after 7 days. 1 H NMR (6, 300 MHz, 6 C ) D : 6.08 (s, 5H, Cp); 6.28 (s, 5H, Cp). P{ 31 H 1 ) NMR (6, 121.421 MHz, 6 C D 6): -1.9 (s), -2.2 (s), 18.6 (s), 18.8 (s).  4.9e.5 ) ZrCp ) 3 C P J 2 (SPh)[ Pr H N(SiM (CH . e Spectra were recorded within 2 hours after the reaction. 1 H NMR (6, 300 MHz, 6 C ) D : 0.45 (br s, 6H, 3 112 Si(CH ) 2, Av  =  35 Hz); 0.68  references on page Q  Chapter IV  (br s, 6H, Si(CH , Avia 2 ) 3  199 =  35 Hz); 0.85 to 0.90 (br m, 6H, SiCH P and ) 2 3 C 2 CH ; 0.95 to 1.15 H  (m, 24H, 3 P[CH(CH ) ] 2 ) ; 1.75 (m, 4H, 3 P[CH(CH ) 1 2 ) ; 1.81 (t, 3H, , 3 C 2 CH H3 3 H-H 6.13 (s, 5H, Cp); 7.00 (t, 1H,p-Ph, 3 JH..H H  =  =  =  6.7 Hz);  7.0 Hz); 7.18 (m, 2H, rn-Ph); 7.70 (d, 2H,o-Ph, 3 JH..  H) NMR (8, 121.421 MHz, 6 1 P{ 7.0 Hz). 31 C ) D : -1.0 (br s, Av 112  Avl/2  =  =  250 Hz); 11.0 (br s,  250 Hz).  Complex spectra were obtained after 7 days. 1 H NMR (6, 300 MHz, C ): 6.05 (s, 5H, Cp); D 6 6.24 (s, 5H, Cp). 31 H} NN’IR (6, 121.421 MHz, 6 1 P{ C ) D : -1.8 (s), -2.1 (s), 18.6 (s), 18.8 (s).  4.10 Refferences (1) (2)  Ashworth, T. V.; Agreda, T. C.; Herdtweck, E.; Herrmann, W. A. Angew. Chem.,Jnt. Ed. Engi. 1986,25, 289 Lappert, M. F.; Pickett, C. 3.; Riley, P. I.; Yarrow, P. I. W. J. Chem. Soc., Dalton Trans. 1981, 805.  (3) (4)  Blenkers, 3.; Bruin, P.; Teuben, 3. H. J. Organomet. Chem. 1985,297, 61. Morse, P. M.; Wilson, S. R.; Girolami, G. S. Inorg. Chem. 1990,29, 3200.  (5)  Lubben, T. V.; Wolczanski, P. T.; vanDuyne, G. D. Organometallics 1984,3,977. Baker, R. T.; Whitney, J. F.; Wreford, S. S. Organometallics 1983,2, 1049.  (6) (7) (8) (9) (10) (11) (12) (13) (14) (15)  (16) (17) (18) (19) (20)  Fryzuk, M. D.; Haddad, T. S.; Berg, D. 3. Coord. Chem. Rev. 1990, 99, 137. Fryzuk, M. D.; Montgomery, C. D. Coord. Chem. Rev. 1989, 95, 1. Fryzuk, M. D. Can. J. Chem. 1992, 70, 2849. 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Organometallics 1990, 9, 2142.  Chapter IV  (21) (22) (23) (24) (25)  200  Cardin, D. J.; Lappert, M. F.; Raston, C. L. Chemistry of Organo-Zirconium and Hafnium Compounds; 1 ed.; Ellis Horwood Limited: Toronto, 1986. Bajgur, C. S.; Jones, C. B.; Petersen, J. F. Organometallics 1985,4, 1929. Choukroun, R.; Gervais, D. J. Chem. Soc., Chem. Commun. 1985, 224. Choukroun, R.; Basso-Bert, M.; Gervais, D. .1. Chem. Soc., Chem. Commun. 1986, 1317. Choukroun, R.; Dahan, F.; Larsonneur, A. M.; Samuel, E.; Peterson, J.; Meunier, P.;  (30) (31) (32)  Sornay, C. Organometallics 1991, 10, 374. Jones, C. B.; Petersen, J. F. J. Am. Chem. Soc. 1983, 105, 5503. Raoult, Y.; Choukroun, R.; blandy, C. Organometallics 1992, 11, 2443. Samuel, E. Inorg. Chem. 1983,22,2967. Elson, I. H.; Kochi, J. K.; Kiabunde, U.; Manzer, L. E.; Parshall, G. W.; Tebbe, F. N. J. Am. Chem. Soc. 1974,96, 7374. Bercaw, J.; Brintzinger, H. J. Am. Chem. Soc. 1969,91, 7301. Brintzinger, H. J. Am. Chem. Soc. 1967,89, 6871. Kenworthy, 3. G.; Myatt, J.; Todd, P. F. J. Chem. Soc. (B) 1970, 791.  (33) (34)  Luetkens, M. L.; Huffman, J. C.; Sattelberger, A. P. .1. Am. Chem. Soc. 1983, 105, 4474. Jones, C. B.; Petersen, 3. F. Inorg. Chem. 1981,20, 2889.  (35)  Schwartz, J.; Libinger, 3. A. Angew. Chem., mt. Ed. Engi. 1976, 15, 333. Coilman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotranstion Metal Chemistry; second edition ed.; University Science Books: Mill Valley, CA., 1987. Marks, T. 3.; Kolb, 3. R. Chem. Rev. 1977, 77, 263. Jensen, J. A.; Gozum, J. E.; Pollina, D. M.; Girolami, G. S. J. Am. Chem. Soc. 1988, 110,  (26) (27) (28) (29)  (36)  (37) (38) (39) (40) (41) (42) (43) (44) (45) (46) (47) (48) (49)  1643. Fryzuk, M. D.; Rettig, S. 3.; Westerhaus, A.; Williams, H. G. Inorg. Chem. 1985,24, 4316. Luetkens, M. L.; Huffman, J. C.; Sattelberger, A. P. .1. Am. Chem. Soc. 1985, 107, 3361. Jensen, J. A.; Wilson, S. R.; Schultz, A. J.; Girolami, G. S. J. Am. Chem. Soc. 1987, 109, 8094. Raum, A. L. 3.; Frazer, D. A. British Patent. 1958, 801401. Marks, T. J.; Kennelly, W. 3.; Koib, J. R.; Shimp, L. A. Inorg. Chem. 1972, 11, 2540. Jensen, 3. A.; Girolami, G. S. J. Chem. Soc., Chem. Commun. 1986, 1160. Edelstein, N. Inorg. Chem. 1981,20, 297. Gozum, 3. E.; Girolan,i, G. S. J. Am. Chem. Soc. 1991, 113, 3829. Plato, V.; Hedberg, K. Inorg. Chem. 1971, 10, 590. Wielsira, Y.; Gambarotta, S.; Meetsma, A. Organometallics 1989, 8, 2948. Floriani, C.; Fachinetti, G. J. Chem. Soc., Dalton Trans. 1973, 1954.  Chapter IV  (50) (51) (52) (53) (54) (55) (56) (57)  Fochi, G.; Guidi, G.; Floriani, C. J. Chem. Soc., Dalton Trans. 1984, 1253. Tyler, D. R. Prog. Inorg. Chem. 1988,36, 125. Masters, C. Adv. Organomet. Chem. 1979, 17, 61. Herrmann, W. A. Angew. Chem., mt. Ed. Engl. 1982,21, 117. Dumond, D. S.; Richmond, M. G. J. Am. Chem. Soc. 1988, 110, 7547. Gladysz, 3. A.; Tam, W. J. Am. Chem. Soc. 1978, 100, 2545. Casey, C. P.; Neumann, S. M. J. Am. Chem. Soc. 1978, 100, 2544. Casey, C. P.; Andrews, M. A.; McAlister, D. R.; Rinz, 3. E. J. Am. Chem. Soc. 1980, 102, 1925.  (58)  Tam, W.; Lin, G. Y.; Wong, W. K.; Kiel, W. A.; Wong, V. K.; Gladysz, 3. A. J. Am. Chem. Soc. 1982, 104, 141.  (59) (60) (61)  Wayland, B. B.; Woods, B. A.; Pierce, R. .1. Am. Chem. Soc. 1982, 104, 302. Fagan, P. 3.; Moloy, K. G.; Marks, T. 3. .1. Am. Chem. Soc. 1981, 103, 6959.  (62) (63) (64) (65)  Belmonte, P.; Schrock, R. R.; Churchill, M. R.; Youngs, W. 3. J. Am. Chem. Soc. 1980, 102, 2858. Bonnesen, P. V.; Yau, P. K. L.; Hersh, W. H. Organometallics 1987,6, 1587. Churchill, M. R.; Rotella, F. 3. Inorg. Chem. 1978, 17, 2614. Wolczanski, P. T.; Bercaw, 3. E. Acc. Chem. Res. 1980, 13, 121.  (73)  Wolczanski, P. T.; Threlkel, R. S.; Bercaw, J. E. J. Am. Chem. Soc. 1979, 101, 218. Schlosser, M.; Ladenberger, V. J. Organomet. Chem. 1967, 8, 193. Bryce-Smith, D.; Turnrt, E. E. J. Chem. Soc. 1953, 861. Schiosser, M.; Hartmann, J. Angew. Chem., mt. Ed. Engi. 1973, 12, 508. Schrock, R. R.; Fellmann, 3. D. J. Am. Chem. Soc. 1978, 100, 3359. Smart, 3. C.; Curtis, C. 3. Inorg. Chem. 1977, 16, 1788. Schrock, R. R. J. Organomet. Chem. 1976, 122, 209. Stewart, C. P.; Porte, L. A. J. Chem. Soc., Dalton Trans. 1972, 15, 1661. Fryzuk, M. D.; Carter, A.; Westerhaus, A. Inorg. Chem. 1985,24, 642.  (74)  Figgis, B. N.; Lewis, 3.; Prog. Inorg. Chem. 1964,6, 37.  (66) (67) (68) (69) (70) (71) (72)  201  Chapter 5 On-Going and Future Prospects Dinitrogen Chemistry Synthesis The synthesis of side-on dinitrogen complexes having favorable solubility properties in hydrocarbon solvents is very important in order to investigate their stoichiometric reactions. The following possibilities could be considered: (a) to investigate the synthesis of side-on dinitrogen complexes analogous to 2.12 by incorporating aryloxy ligands having substituents on the para positions; (b) to reduce ditriflate precursors of the type 2 ZrR(O ) 3 2[N(SiMe2C SO2CF H PPr)2J, where R  =  alkyl or aryl ligands (Scheme 5.1). In comparison with the reduction of the  dichioro precursors, for example reduction of ZrC12(OAr*)[N(SiMe2CH2PPIr2)2 1 4.11, the second possibility may give better yields of the dinitrogen complex.  2 Me Reduction  -CI 2 Me  Dinitrogen Complex  X=Y=Me X = Me, Y = But  2.1 (1)NaOTf (2) RLi  2 Me  sç,  \  ph  Reduction  :N—zr—R 2 s(’ TfO”/ Me  [Zn  [Zn  =  I  Hydrogenolysis [Zr]  1 C Zr[N(SiMe P ] ) 2 Pr H  Scheme 5.1 Electrochemical studies with concomitant ESR measurements on the side-on dinitrogen complexes could provide valuable information. ESR spectra of the oxidized species could yield  Chapter V  203  some information about the 6-MO (HOMO) which in turn can be compared with the results of the MO analysis.  Reactivity Studies Reactions that would lead to the formation of Lewis-acid Lewis-base type “adducts” will provide useful information regarding the nature of the dinitrogen ligand, particularly in the side-on dinitrogen complexes. The usefulness of such investigation will depend on the X-ray structure determination of the final product. The reactions shown in Scheme 5.2 are similar to the reaction of LiBEt 4 with the side-on dinitrogen complexes discussed in chapter 2. [(C B 3 ) 5 F 6 EtrLi..  :  +  (2,61 H 6 [C 2 ) 3 B CF ) {4 [Zr]  =  Product similar to 2.24  C Zr[N(SiMe P ] 2 ) Pr’ H  H  (2,6] H 6 [C 2 ) 3 B CF } {4  -  Scheme 5.2  Some reactions with ailcyl halides that could be investigated are shown in Scheme 5.3. The motive for such reactions would be to incorporate the activated dinitrogen ligand into organic molecules. Such reactions could also be useful for incorporating nitrogen- 15 into organic molecules. It is important to note that the end-on complex 2.6 is synthesized in greater than 90% yields and therefore is an ideal candidate to explore its reactivity with alkyl halides. The suggestions given in Scheme 5.3 take into consideration what has been discussed under the section on reactivity of dinitrogen complexes in Chapter 2. Preliminary reactivity studies with Br(CH B 3 ) 2 r and 2 Cl(CH C 4 ) l and dinitrogen complexes show a clean reaction, but the organic products are not yet identified.  On-Going and Future Prospects  Chapter V  204  Controlled reaction of the end-on dinitrogen complex with two equivalents of ketone could provide a route to synthesize a zirconium oxo complex (Scheme 5.3). In the case of the side-on dinitrogen complexes the dinitrogen ligand forms a three membered ring with each zirconium. The possibility of expanding these three membered metallacycles by the insertion of other unsaturated functionalities may be investigated (Scheme 5.3). R Cp[Zr]=C R I  X[Zr]()C R 2 CR 2 Br 2  X[Zr] /[zrlx N  R Cp[Z r]N—NC R  CR 2 Br [Dinitroen Complexes 1  Side-On  End-On and Side-On_J  -  Or  End-ON  /0R2 X[Zr]N—N=C 2 CR CR 2 BrCR B r  -  I  - -  CR 2 BrCR B r R C 2 ZNC R 2 Br(CH B 3 ) 2 r C1 4 ) 2 CI(CH  End-ON and Side-On  C) 2 (H C 2 )N—(CH ) Or (H 2  (CH  n  =  1 or 2  R C 2 =O Cp[Zr]N—N=[Zr]Cp  Cp[Zr]0  +  CN—N=CR 2 R  x  ;O M 2 e  I—  [Zr] F C 2 CF 2  CO M 2 e  CCO e 2 MeO M  x [Zr]  =  C Zr[N(SiMe P ] 2 ) Pr’ H  Scheme 5.3  The mechanism for the formation of the end-on dinitrogen complex could be envisaged ZrCpC [ C P , 2 N(SiM Pri H la e as follows: during the reduction of the zirconium(IV) complex )  On-Going and Future Prospects  Chapter V  205  zirconium(II) species of the type ] 2 “ZrCp[N(SiM ” e2CH2PPr) is probably formed which reacts further with dinitrogen to yield the end-on dinitrogen complex 2.9. This suggested mechanism could be corroborated by the fact that stable zirconium(II) complexes, for example ZrCp [ 2 P N(SiM Pr’) e2CH (CO 2], ) have been isolated.  However, the reduction of  ZrC [ 3 C P 2 ] N(Si Pr) H Me l 2.1, may involve a different pathway. Attempts to isolate any zirconium(H) species formed during the reduction of 2.1, for example reductions carried out in the presence of PMe , gave a brown material which contained mainly one product. Although it 3 was important to reduce 2.1 in the presence of PMe 3 the 1 H and 31 P{ 1 H} NMR spectra of this brown product did not show any resonances that could be attributed to a PMe 3 ligand. This product is formulated as a dimeric species , {ZrCl[ C P 2 Pr)2 H N(SiM ]) e which did not show any reactivity with dinitrogen at room temperature. ZrC [ 3 C P 1 2 ) N(SiM Pr’ H e I L  fl  N  Reduction L  =  2 N [Zr]  1 ZrClL C P ] ) 2 Pr H (SiMe R  [Zr]  ci”  bi  [Zrr( S  ci”  L=THF’J  L=PMe j 3 J,  brown {ZrCI[N(SiM C P ] ) 2 Pr H e 12  Red solution probably decomposition by ring opening of  N [Zr  [Zr]  =  N Zr[N(S C P ] 2 Pr’) H iMe  [Zr]  x  Scheme 5.4  It is noteworthy that the reduction of 2 ZrC [ 3 C ] N(Si H2PPr Me 2) l 2.1 in toluene under vacuum gave uncoordinated PNP ligand whereas, repeating the same reduction in THF (Haddad, T. S.; UBC, unpublished work) gave a deep red solution. These results suggest that during the reduction of 2.1 an intermediate of the type ] “ZrClL[N(Si P 2 Pr ”, Me2CH ) R, where n<3 and L  =  dinitrogen, PMe 3 or THF is produced. A speculative but intriguing  mechanism for the formation of the side-on complex is shown in Scheme 5.4. Tn the case of the On-Going and Future Prospects  Chapter V  intennediate S if the metal-metal bond has  206 It  symmetry then the insertion of the 7t*orbital (that  is contained in a plane parallel to the it-orbital associated with the metal-metal bond) of the “N2” unit should be symmetry allowed. It is important to point out that when model F (Section  2.7.4) was modified by removing the dinitrogen ligand and then subjecting to INDO 1/MO analysis showed the presence of one a and one  it  bond between the two zirconium centers.  Investigating the reduction of ZrC1 32 [N(SiM C ] H2-PPr) e with different substrates (e.g., butadiene or R—CC—R) may provide some useful information about the reduced zirconium species formed during the reduction of 2.1.  Zirconium(III) Chemistry Synthesis and Characterization Since complexes of the type “ZrCp[N(SiMe2CH2PPr)2]” gave stable zirconium(IlI) complexes electrochemical measurements on these systems would be valuable information. The choice of the supporting electrolyte during electrochemical measurements is critical; for example, attempts to use 6 [NBu4J[PF ] - resulted in rapid decomposition of the zirconium complex, presumably due to the attack by fluoride ions on the PNP ligand. The zirconium complexes may be stable in the presence of electrolytes like 4 [NBu ] [BPh4]-. Low temperature solution and frozen glass ESR spectra with better resolution may be obtained for the alkyl and the borohydride derivatives. Disproportionation reactions could be extended to other ligands comparable to CO, for example benzonitrile and tert-butylisocyanide. Monitoring the disproportionation reactions of the zirconium(ffl) chloro and the borohydride derivatives by UV-Vis spectroscopy shows the presence of two isobestic points. By monitoring the band associated with the dicarbonyl complex useful kinetic data could be obtained. The hydrogenolysis of the zirconium(III) ailcyls also warrants kinetic measurements. Importantly, measurement of the kinetic isotope effect for the hydrogenolysis would show whether the reaction proceeds by a-bond metathesis. Attempts to investigate such studies using NMR techniques did show that the hydrogenolysis obeys  On-Going and Future Prospects  Chapter V  207  overall second order kinetics. However, more accurate (and reliable) measurements could be obtained by performing the experiments in a gas uptake apparatus. Excessive solubility of the zirconium(Ill) hydride complex has hindered the isolation of this complex as a solid material. Incorporating the phenyl version of PNP may lower the solubility of the hydride complex and thereby enable the isolation of the complex as a pure solid material. It important to note that previous attempts in our laboratory has shown that reacting Li[N(S C P ] 2 ) H h iMe with ZrC14 results in the formation of the bis ligand complex ZrC { C P . ] 2 ) N(SiM Ph H 1 e However, using a different zirconium precursor may lead to the desired product; for example, reaction involving C .(DME) 3 2 Li[N(S H2Ph2)2] iMe and CpZrC1 could yield complex P ZrCp [ 2 N(SiM h2)2 e2CH Cl ] (Scheme 5.5). It is known that the reaction of • 3 CpZrC (DME1 ) with the less bulky PN ligand P Li[N(P ) 2 (SiMe2 Ph2) hCH CH j forms the mono PN derivative of zirconium, ) ZrC [ ) C 2 N(Ph (SiM H2P J. pCl CH Ph e  Me S 2 i  CpZrC1 • 3 (DME)  JL C Li[N(SiMe P ] 2 ) Ph H  (1) Reduction  :N— Zr— Me S 2 i” CI \___p  (2) 2 SiCH 3 Me L i  2 Ph  2 (3) H  3 CpZrC • (DME) l Li[N(C P C P 2 ) h)(SiM Ph ] H H e  Scheme 5.5  Reactivity Reactions involving some zirconium(Ill) complexes (e.g., 4.1) and B(C 3 gave a ) 5 F 6 deep blue solution which is stable for approximately 10 minutes at room temperature. The formation of the blue color seems to suggest the formation of the radical anion, 6 [B(C ] 3 ) 5 F . On-Going and Future Prospects  Chapter V  208  For comparison the radical anion } (2,6] H 6 {B[C 2 ) 3 CF is stable at room temperature and has an intense blue color in solution.  Therefore reactions with 3 (2,6j H 6 B[C 2 ) CF and  zirconium(III) complexes could be investigated.  Cationic Complexes  1 ) t Li[N(Bu C P ) 2 (SiMe Pr H ]  2 Pi  CpZrC1 • 3 (DME)  (  Zr /\CI  Me2Si—.N  CI  (1) Alkylation (2) AgBPh 4 or B (C ) 5 F 6 Cationic Species  1 ) t Li[N(Bu C P ) 2 (SiMe Pr H ] LIDME  2 . 4 ZrCl (THT) CI  -.-‘i) Alkylation  Monocatiomc Species  (2) 4 AgBPh or  (1) Alkylation (2) B(C ) 5 F 6 (3) 3 (CF H 6 H{B[C 4 j 2 ) Dicationic Species  Scheme 5.6  Species generated by treating j ZrCpCl2[N(S C P 2 Pr) H iMe and alumoxanes have been shown to be catalytically active towards ethylene polymerization (see Section 2.2.1, page 28). Many of the precursors that have been synthesized during the investigation of the dinitrogen chemistry are potential candidates for generating cationic complexes. Spectroscopic evidence On-Going and Future Prospects  Chapter V  209  P{ 1 1 H and 3 1 ( H} NMR) suggests that the methyl derivative ] ZrCpM [ C P 2 N(SiM Pr) H e  reacts with AgBPh 4 in THF to yield two isomeric cationic species.  Also, the dibenzyl  Zr(OAr*)(Ph [ C P ] 2 N(SiM Pri H CH e reacts with B(C derivative ) 3 to generate species ) 5 F 6 Zr(OA ) . ) 3 ) 5 F 6 C P ] ][N( (B( [Ph Pr H r*)(Ph SiM . CH C ) CH e which could be formulated as 2 Oue efforts in ligand design have so far concentrated on the tridentate PNP systems. Very recently, we have developed an isopropyl version of the PN ligand, C 2 Li[N(SiMe P Pr)(But)] H that has been incorporated on to zirconium (Scheme 5.6). Some suggested reactions that could lead to the synthesis of mono and dicationic species are shown in Scheme 5.6.  On-Going and Future Prospects  Appendix  A.1 UV-Vis Spectra of Complexes 2.2 and 2.9  304nm  1.9000  {[(PPr C S N 2 ) 1ZrC1}2(N2 iMe 11 i ) 2.2  4’ 1. 5200  646 nm, excitation wave length during resonance Raman experiment.  1.1400  •‘  0.76000  576 nm 4..  402 nm 4.  0.38000  646 nm 4.  0.0000 300  400  0.95000  0.76000  I  356nm  500 L)VELNTH  600  700  5 {[(PPr C S N ) 2 C 5H5)}2(P’2) iMe Zr(fl H i 2.9  ‘I,  514 nm, excitation wave length during resonance Raman experiment.  0.57000.  0.38000.  0.19000  300  400  500  600  WRVELEHGTH  Appendix  Appendix  211  B..1 ESR Simulations The solution ESR spectra of the zirconium(III) complexes, i.e., complexes incorporating PNP ligand, consist mainly of a triplet due to the coupling of two equivalent phosphorus nuclei of the PNP ligand. Therefore the a( P) values used for the simulations were measured directly 31 from the actual solution spectra. The coupling constants due to other nuclei were obtained by iteration and the values reported gave the best possible fit between the observed and simulated spectra. Simulations were carried out in such a manner that a lowest possible value is obtained for line broadening. When the coupling constants were lower than the value obtained for line broadening it could be considered as the upper or the lower limit for the given nucleus where the limits are within 0.5 G. For example, in 4.17 the a( N) value is the upper limit of the 14 estimated coupling constant due to nitrogen of the PNP. It is important to note that in the case of the ethyl derivative the values obtained from simulation correlate well with the deuterio derivatives, i.e., a( H) 1/6 a( 2 H). 1 (II) different from I is = 4.5 MHz,1N. N) 14 a( (I) line broadening = 2.8 G; a( H) = 8.0 MHz, 4H; 1 N) = 5.5 MHz, iN; a( 14 a( P) = 58.0 MHz, 2P. 31 (Ill) thfferer!t from I is rest of the parameters were identical for hne broadening = 2.5 G. simulations 1,11 and III.  (I)  2’  (II)  (Ill)  Appendix  AppendiX  212  Appendix C.1 The Cartesian Coordinates for the Model Complexes Used in INIJO/1-MO Analysis C.1.1 The Atom Numbering Scheme and the Cartesian Coordinates for the Model Complex A H25 C35  C9  1128  c8  Hi  H43  H19  1141  H21  N34  1120  Ni2  1136  H13 H35  1114  Atom  X  Y  Z  Atom  X  Y  Z  Zr(1)  2.832  -0.227  0.138  P(38)  -2.440  -0.722  -2.597  C(7)  3.879  1.743  1.435  H(39)  -1.204  -1.426  3.251  C(8)  2.612  2.182  1.035  H(40)  -3.233  -2.285  2.778  C(9)  2.614  2.295  -0.360  H(41)  -3.056  -0.180  3.562  C(10)  3.881  1.924  -0.822  H(42)  -1.175  -0.931  -3.110  C(11)  4.664  1.583  0.287  H(43)  -3.025  0.350  -3.240  N(12)  4.096  -2.141  -0.021  H(44)  -3.208  -1.851  -2.793  P(15)  3.024  -0.746  -2.606  N(45)  0.934  -0.498  0.116  P(16)  3.000  -1.214  2.753  N(46)  -0.366  -0.486  0.118  H(17)  1.760  -0.926  -3.130  H(2)  4.261  1.739  2.487  H(18)  3.772  -1.888  -2.807  H(3)  1.826  2.595  1.716 Appendix  Appendix  213  H(19)  3.634  0.320  -3.235  H(4)  1.800  2.811  -0.929  H(20)  1.731  -1.481  3.226  H(5)  4.269  2.098  -1.857  H(21)  3.603  -0.273  3.562  H(6)  5.772  1.432  0.274  H(22)  3.747  -2.374  2.760  H(13)  4.390  -2.510  -0.981  Zr(23)  -2.258  -0.180  0.144  H(14)  4.391  -2.663  0.866  C(29)  -3.267  1.994  -0.8 10  H(24)  -3.648  2.170  -1.848  C(30)  -1.993  2.338  -0.346  H(25)  -1.198  2.843  -0.951  C(31)  -1.995  2.221  1.049  H(26)  -1.173  2.622  1.694  C(32)  -3.270  1.802  1.446  H(27)  -3.655  1.811  2.496  C(33)  -4.056  1.662  0.297  H(28)  -5.168  1.531  0.287  N(34)  -3.557  -2.072  -0.012  H(35)  -3.859  -2.588  0.875  P(37)  -2.464  -1.140  2.766  H(36)  -3.860  -2.436  -0.972  C.1..2 The Atom Numbering Scheme and the Cartesian Coordinates for the Model Complex B H6 C7  H22 H20  H15 H21  N13  H14 H18  Appendix  Appendix  214  Atom  X  Y  Z  Atom  X  Y  Z  Zr(1)  -0.031  -0.734  -0.065  H(20)  3.408  -0.100  0.236  C(7)  -1.127  1.553  -0.536  H(21)  -3.252  -2.126  -0.138  C(8)  -0.757  1.044  -1.786  H(22)  -3.408  0.023  0.521  C(9)  0.641  1.010  -1.842  H(23)  -2.757  -1.561  1.986  C(10)  1.135  1.496  -0.627  H(2)  -2.147  1.706  -0.182  C(11)  0.042  1.832  0.181  H(3)  -1.438  0.730  -2.577  N(13)  0.047  -1.404  2.134  H(4)  1.240  0.665  -2.685  P(16)  2.674  -1.249  0.444  H(5)  2.186  1.595  -0.356  P(17)  -2.700  -1.153  0.669  H(6)  0.093  2.240  1.191  H(18)  3.121  -2.240  -0.406  H(14)  0.990  -1.582  2.606  H(19)  2.826  -1.661  1.752  H(15)  -0.861  -1.537  2.685  C.1.3 The Atom Numbering Scheme and the Cartesian Coordinates for the Model Complex H Si  H19  1111  H14  H15  H13 114’  H38  Appendix  Appendix  215  Atom  X  Y  Z  Atom  X  Y  Z  Zr(1)  1.900  0.018  -0.632  P(37)  -3.290  0.107  -1.556  P(2)  1.634  0.176  -3.468  0(40)  -2.190  1.834  1.168  P(3)  3.664  -0.492  1.507  N(41)  -2.884  -1.820  0.921  0(6)  2.605  1.911  -0.666  N(42)  0.414  -0.495  0.700  N(7)  3.063  -1.725  -1.344  H(61)  -2.607  2.792  1.068  N(8)  -0.132  -0.307  -0.737  H(4)  2.584  -2.348  -2.070  H(9)  0.324  -0.074  -3.821  H(5)  4.059  -1.952  -1.027  H(10)  2.457  -0.760  -4.061  H(15)  -0.167  -1.009  3.803  H(11)  1.992  1.439  -3.894  H(16)  -1.741  0.555  4.198  H(12)  2.948  -0.945  2.596  H(17)  -2.347  -1.580  3.809  H(13)  4.582  -1.451  1.129  H(18)  -2.553  -0.108  -2.703  H(14)  4.327  0.671  1.844  H(19)  -3.874  1.356  -1.613  H(27)  3.075  2.794  -0.349  H(20)  -4.273  -0.856  -1.454  Zr(35)  -1.595  -0.037  0.692  H(38)  -2.473  -2.631  1.485  P(36)  -1.443  -0.589  3.486  H(39)  -3.877  -1.896  0.530  C.1.4 The Atom Numbering Scheme and the Cartesian Coordinates for the Model Complex M H61  h27 Hil  N42  H4  H5  1113  H38  Appendix  Appendix  216  Atom  X  Y  Z  Atom  X  Y  Z  Zr(1)  1.815  -0.023  -0.502  P(37)  -3.263  0.262  -2.011  P(2)  1.820  0.400  -3.323  0(40)  -2.869  1.494  1.142  P(3)  3.238  -1.084  1.688  N(41)  -2.862  -2.079  0.081  0(6)  2.930  1.651  -0.322  N(42)  0.148  -0.272  0.685  N(7)  2.605  -1.932  -1.294  H(61)  -3.432  2.380  1.159  N(8)  -0.224  0.143  -0.761  H(4)  2.057  -2.371  -2.102  H(9)  0.520  0.489  -3.777  H(5)  3.495  -2.406  -0.938  H(10)  2.455  -0.655  -3.946  H(15)  -0.752  -1.530  3.486  H(11)  2.488  1.573  -3.611  H(16)  -2.617  -0.335  3.900  H(12)  2.352  -1.437  2.685  H(17)  -2.776  -2.398  3.010  H(13)  3.942  -2.200  1.282  H(18)  -2.350  0.411  -3.034  H(14)  4.117  -0.135  2.168  H(19)  -4.046  1.395  -1.924  H(27)  3.560  2.376  0.102  H(20)  -4.064  -0.833  -2.264  Zr(35)  -1.892  -0.121  0.423  H(38)  -2.395  -2.925  0.541  P(36)  -2.027  -1.240  3.043  H(39)  -3.763  -2.212  -0.480  Appendix  I  —  V 3133.9  6.0° 6.0 mm horizontal  Take—off Angle  Detector Aperture  6.0 mm vertical  21°C  0.71069 A)  Temperature  —  Rigaku AFC6S  Intensity Measurements  MOKa (X  B.  30.S9 cm 4  1448  Radiation  Diffractometer  ‘(MoKa)  000 F  3 1.502 g/cm  3 (9)A  18.306 (3)A 100.59 (l)°  4  —  5  10.678 (2)A  I value  —  c  37.6)  0.300  16.310 (2)A  —  /a (*14) 1 P2  —  b  28.5  Space Group  —  a  0.41  Omega Scan Peak Width at Half—height  Lattice Parameters:  25 (  No. Reflections Used for Unit Cell DeterminatiOn (20 range)  monoclinic  Crystal System  x  yellow, hexagonal  Crystal Color, Habit 0.080 X 0.300  708.79  Formula Weight  Crystal Dimensions (mm)  29 C 4 H N Br S 2 Z 3 i r P  Crystal Data  Empirical Formula  A.  —  .045)  All non—hydrogen atoms Anomalous Dispersion  0.37  Maximum Peak in Final Diff. Map Minimum Peak in Final Diff. Map  3 eiA —0.41 e/A 3  0.01 Max Shift/Error in Final Cycle  0.031; 0.030 1.27  R; R Goodness of Fit Indicator  Residuals:  3645 281 12.97  0.02 p—factor  No. Observations (I>3.OOq(I)) No. Variables Reflection/Parameter Ratio  / 4Fo ( 2 ) Fo o  Least—squares Weights  FcI £ w (  Function Minimized  —  Full—matrix least—squares  Refinement  Fol  Patterson Method  Structure Solution and Refinement  Structure Solution  C.  —  Lorentz—polarization Absorption 0.54 1.00) (trans. factors: Decay ( —3.10% decline) Secondary Extinction 0.30238E—06) (coefficient:  0.35 tano)°  Corrections  +  Total: 7845 Unique: 7582 (Ri t 0  SS.0  (1.05  16.0/min (in omega) (8 rescans)  —29  285 mm  No. of Reflections Measured  max 20  Scan Width  Scan Rate  Scan Type  Crystal to Detector Distance  D.1.1 X-ray Crystallographic Analysis of 2 Zr(1 ) H 5 [ C P ] ) N(S1Me Br Pr’ C H , 2.7  D.1 X-ray Crystallographic Analysis Data  0.6570(4)  0.45539(8)  0.3629(2)  Si(2)  N(1)  0.4598(5)  0.3758(6) 0.5018(6)  0.3721(4)  0.3693(3)  0.1737(4)  0.0931(3)  0.3118(3)  0.3940(3)  0.2345(3)  C(S)  C(6)  C(7)  C(8)  C(9)  C(l0)  C(l1)  0.7997(4) 0.7913(5)  0.4367(4)  0.2702(3)  0.4098(3)  C(14)  C(15)  C(16)  0.2063(6)  0.1140(5)  0.3606(4)  0.4445(3)  C(12)  C(13)  0.1985(4)  0.4465(5)  0.4956(6)  0.5150(6)  0.6174(6)  0.3798(6)  0.5045(5)  0.3600(3)  0.1738(3)  C(3)  0.4274(4)  0.5683(1)  0.6925(1)  0.3501(1)  0.4991(1)  0.50463(5)  C(4)  0.2S03(3)  0.32572(8)  Si(l)  0.4684(3)  0.36988(7)  P(2)  C(l)  0.26513(7)  P(l)  C(2)  0.5532(3)  0.17026(3)  Br(2)  0.37118(4) 0.30222(5)  0.44783(3)  Br(l)  Y  0.29705(2)  x  Zr(l)  atom  0.3330(3)  0.2028(3)  0.0143(3)  0.1406(3)  —0.0106(3)  0.0068(3)  0.0811(3)  0.0453(3)  0.3687(4)  0.4964(4)  0.5029(3)  0.4930(3)  0.4203(3)  0.4501(3)  0.1531(2)  0.3415(2)  0.2469(2)  0.21340(7)  0.27709(7)  0.12231(6)  0.37654(7)  0.17361(3)  0.32472(3)  0.25013(2)  * 2 A  4.8(3)  4.6(2)  6.8(3)  5.2(3)  5.7(3)  5.2(3)  3.8(2)  3.8(2)  6.1(3)  6.7(3)  5.7(3)  5.5(3)  4.4(2)  3.9(2)  3.2(2)  3.2(2)  2.3(1)  3.05(5)  3.00(5)  2.79(5)  2.84(5)  3.86(2)  3.71(2)  2.25(2)  Final atomic coordinates (fractional) and Beg  *Be q —  C(23)  C(22)  C(21)  C(20)  C(19)  C(18)  C(17)  atom  Table  0.1812(3)  0.1720(3)  0.2398(4)  0.2910(3)  0.2555(3)  0.4565(3)  0.5541(3)  x  0.2127(5)  0.2407(5)  0.1941(5)  0.1344(5)  0.1477(4)  0.7092(5)  0.5806(5)  Y  0.1998(3)  0.2708(4)  0.3197(3)  0.2774(4)  0.2039(3)  0.1517(3)  0.2841(3)  z  4.3(2)  4.8(3)  5.1(3)  5.1(3)  4.2(2)  4.9(3)  4.6(2)  Beg  Final atomic coordinates (fractional) and Beq (2)* (cont.)  (8/3) 2 £tVjjaj*a*(ai.aj)  .  Zr H 5 [ C P N(S Pr2 C s)B D.1.1 X-ray Crystallographic Analysis of 2 (rj H iMe )2], r 2.7 continued  00  98.03(6) 152.82(4)  Cp(1)  P(2)  Cp(1)  r1(1)  Cp(1)  Cp(1)  Zr(l)  Zr(l)  Zr(l)  Zr(1)  Zr(1)  Zr(1)  Zr(1)  Zr(1)  Zr(1)  Zr(l)  Zr(1)  Zr(1)  Zr(1)  Zr(1)  Br(l)  Br(l)  Br(l)  Br(2)  Br(2)  Br(2)  Br(2)  P(1)  p(l)  P(1)  P(2)  P(2)  N(1)  C(3)  C(4)  P(l)  P(l)  P(1)  Zr(1)  C(1)  C(1)  C(1)  C(9)  P(2)  P(2)  P(2)  P(2)  Zr(l)  Zr(1)  C(2).  C(2)  C(10)  C(9)  C(lO)  101.0(1)  106.4(2)  106.5(2)  124.0(2)  110.6(2)  108.7(2)  C(4)  C(2)  P(1)  P(2)  Zr(1)  107.3(2)  105.6(2)  121.8(2)  110.8(2)  101.2(1)  179.2(1)  104.16(7)  76.65(9)  103.02(7)  76.18(9)  81.46(8)  90.62(3)  86.00(3)  99.02(7)  81.50(8)  85.08(3)  90.31(3)  C(S)  C(4)  C(3)  P(1)  P(1)  Zr(l)  Zr(1)  N(1)  N(1)  P(2)  P(l)  Cp(l)  N(l)  P(2)  P(l)  162.95(2)  Br(l)  Br(2)  Zr(1)  angle  Br(l)  atom  P(2)  P(2)  C(7)  P(i)  P(l)  C(S)  P(1)  P(1)  P(2)  P(l)  Si(l)  Zr(l)  Zr(1)  C(17)  C(2)  C(2)  (1)  N(1)  N(l)  C(15)  C(1)  C(1)  N(l)  N(l)  N(l)  C(9)  atom  C(9)  C(S)  C(4)  C(4)  C(4)  C(3)  C(3)  C(3)  C(2)  C(1)  14(1)  N(1)  N(1)  Si(2)  Si(2)  Si(2)  Si(2)  Si(2)  Si(2)  Si(l)  Si(1)  Si(1)  Si(1)  Si(l)  Si(l)  P(2)  atom  C(12)  C(11)  C(8)  C(8)  C(7)  C(6)  C(6)  C(S)  Si(2)  Si(1)  Si(2)  Si(2)  Si(l)  c(18)  C(18)  C(17)  C(18)  C(17)  C(2)  C(16)  C(16)  C(15)  C(16)  C(15)  C(l)  C(l0)  atom  117.9(4)  109.8(4)  109.0(4)  110.3(4)  116.4(4)  111.6(4)  117.0(4)  110.8(4)  110.9(2)  110.4(2)  114.2(2)  123.0(2)  122.8(2)  104.9(2)  105.6(2)  106.4(2)  113.0(2)  117.0(2)  109.2(2)  105.0(2)  105.5(2)  106.9(2)  113.1(2)  116.2(2)  109.4(2)  106.9(2)  angle  Bond angles (deg) with estimated standard deviations.  atom  .  atom  Table  *  C(1)  14(1)  C(10)  C(9)  C(2)  C(4)  C(3)  C(1)  Cp(1)  C(23)  C(22)  C(21)  C(20)  C(19)  t4(1)  P(2)  P(l)  Br(2)  Br(l)  1.893(5)  1.734(3)  1.859(5)  1.858(5)  1.802(4)  1.863(5)  1.856(5)  1.804(4)  2.286(2)  2.578(5)  2.555(5)  2.551(5)  2.583(5)  2.581(5)  2.227(3)  2.821(1)  2.817(1)  2.6842(7)  2.6871(7)  distance  C(22)  C(21)  C(20)  C(19)  C(19)  C(10)  C(10)  C(9)  C(S)  C(4)  C(4)  C(3)  C(3)  Si(2)  Si(2)  Si(2)  Si(2)  Si(l)  Si(l)  atom  C(23)  C(22)  C(21)  C(23)  C(20)  C(14)  C(13)  C(12)  C(ll)  C(8)  C(7)  C(6)  C(5)  C(18)  C(17)  C(2)  N(l)  C(16)  C(15)  atom  1.369(7)  1.382(8)  1.393(8)  1.386(7)  1.371(7)  1.517(7)  1.532(7)  1.526(7)  1.527(7)  1.522(8)  1.514(8)  1.535(7)  1.541(7)  1.884(5)  1.876(5)  1.900(5)  1.738(3)  1.877(5)  1.879(5)  distance  Bond lengths (A) with estimated standard deviations.*  atom  .  of the C(19—23) cyclopentadienyl ring.  Here and elsewhere, Cp(1) refers to the unweighted centroid  Si(1)  si(1)  P(2)  P(2)  P(2)  P(1)  PCi)  P(1)  Zr(1)  Zr(1)  Zr(1)  Zr(1)  Zr(1)  Zr(1)  Zc(l)  Zr(l)  Zr(l)  Zr(l)  zr(l)  atom  Table  D.1.1 X-ray Crystallographic Analysis of 2 Z ) H 5 [ C P ] ) N( B P C r( Si H , M r’ 1 r e 2.7 continued  Appendix  220  z In In In  5  Appendix  monoclinic  25 ( 29.2  0.36  Crystal System  No. RefleCtionS Used for Unit Cell Determination (28 range)  Omega Scan Peak Width at Half—height  6.0°  6.0 mm horizontal 6.0 mm vertical  Detector Aperture  0.71069 A)  Take—off Angle  —  21°C  MOKa (X  Rigaku AFC6S  Intensity Measurements  5.34  4968  Temperature  Radiation  Diffractometer  000 F  B.  8  Z value 1.236 9/cm 3  C2/c (#15)  Dcalc  (9)°  (4)A (7)A (4)A  12539 (9)A 3  48.755 10.226 25.987 104.582  Space Group  V  6—  a— b— c—  0.120 x 0.250 X 0.450  Crystal Dimensions (mm)  Lattice Parameters:  red—brown, prism  Crystal Color, Habit  33.8°)  1167.06  Formula Weight  —  i r 03 9 2 4 C 1 H S P N Z 4  Crystal Data  Empirical Formula  A.  EXPERIMENTAL DETAILS  I w (IFOL— Fo a / 4Fo ( 2 )  0.02  Function Minimized Least—squares Weights p—factor  7287 S73 12.72 0.034; 0.035  No. Observations (I>3.OOq(I)) No. Variables Reflection/Parameter Ratio Residuals:  0.21 0.37 e/A 3  Max Shift/Error in Final Cycle Maximum Peak in Final Diff. Map Minimum Peak in Final Diff. Map  —0.27 e/A 3  1.40  Goodness of Fit Indicator  R;  All non—hydrogen atoms  Anomalous Dispersion  2 Fc()  Full—matrix least—squares  Refinement  Structure Solution and Refinement  —  1.00)  .025)  Patterson Method  C.  15389 15197 (Rit Lorentz—polarization Absorption (trans. factors: 0.97  Total: Unique:  55.0  (0.91 + 0.35 tan9)  32.0°/mm (in omega) (8 rescans)  285 mm  Structure Solution  Corrections  No. of Reflections Measured  max 28  Scan Width  Scan Rate  Scan Type  Crystal to Detector Distance  , 2.9 continued H } ]Zr(r C iMe j.i-N C 1 {{[(PPr S N ) ) H 5 ( ) D.1.2 X-ray Crystallographic Analysis of 2  0.2757(1)  0.0731(1) 0.2988(1) 0.2905(1) 0.3162(1)  0.14629(2) 0.06178(2) 0.20307(2) 0.11478(2) 0.08718(2) 0.05801(2)  P(l) P(2) P(3) ?(4) Si(l) Si(2)  0.565 0.435  5.7(2) 5.7(2) 6.7(3) 6.5(3) 7.9(3) 7.9(6) 7.9(8)  0.0516(2) 0.1470(2) 0.2368(2) 0.2188(2) 0.1086(2) 0.0781(5) 0.0548(5) 0.2986(1)  0.1769(5) 0.2428(5) —0.0340(5) —0.1851(5> 0.0208(6) —0.144(1) —0.051(2) 0.2406(4) 0.3229(4) —0.0219(4)  0.1909(1)  0.20304(9)  0.0346(1)  0.0723(1)  0.0011(1)  0.0324(2)  0.0331(3)  0.20888(8)  0.13492(8)  0.2051(1)  0.2346(1)  0.11695(8)  C(13)  C(14)  C(15)  C(16  C(17)  C(18)  C(18A)  C(l9)  C(20)  C(21)  C(22)  c(23)  C(24)  0.4617(5) 0.3373(5) 0.4827(4)  0.0685(1) 0.0750(1) 0.0223(1) 0.0674(1)  C(7) C(8> C(9) C(10)  0.510 0.490  6.5(3) 7.8(3) 8.1(7) 8.1(7)  0.2604(2) 0.2381(2) 0.3648(2)  —0.1658(5) —0.0088(5) 0.0808(5)  0.1977(1)  0.2326(1)  0.2630(1)  C(28)  C(29)  C(30)  C(31)  0.4622(4)  0.2789(2)  0.1058(1)  0.1792(5)  0.0305(1) C(6)  5.6(2)  0.4555(2)  0.5119(5)  0.1837(1)  C(33)  —0.0207(6)  0.0621(1) C(5)  6.0(2)  0.4961(2)  0.2362(5)  0.1937(1)  C(27)  0.4002(6)  0.2707(4) —0.0427(4)  0.18427(8) C(4)  4.9(2)  0.3149(2)  0.5132(4)  0.1900(1)  C(26)  0.4203(4)  0.4433(4)  0.14174(8) C(3)  5.6(2)  0.3984(2)  0.4001(5)  0.23721(9)  c(25)  0.013(2)  0.2081(4)  0.05336(8) C(2)  —0.092(1)  0.2856(4)  0.12611(8) C(l)  4.2(2)  0.3714(2)  0.2869(4)  0.07689(8)  0.2326(3)  0.1382(3)  0.13675(6)  N(4)  3.6(2)  0.3389(1)  0.4624(4)  .0.2336(3)  0.1315(3)  0.12671(6)  N(3)  7.3(3)  0.3700(2)  0.0304(6)  c(32A)  0.2841(3)  0.17794(6)  4.6(2)  c(32)  0.2446(3)  0.08336(6)  N(1) N(2)  3.8(2)  0.4371(1) 0.2564(2)  5.4(2)  6.8(3)  0.3367(1)  Si(4)  0.3570(1)  0.20215(2) 0.17371(2)  Si(3)  3.7(2)  0.0400(1)  0.11657(3)  0.150099(7)  Zr(2)  4.6(2)  0.0885(2)  0.5547(4)  0.1522(1)  C(12)  x 0.09216(3)  atom 0.113703(7)  0CC.  Zr(l)  Beg  0.1380(2)  0.0602(2)  0.0007(2)  —0.0327(2)  0.1030(2)  0.2175(2)  0.0920(1)  0.1175(1)  0.1654(2)  0.0241(1)  0.2587(1)  0.2074(1)  0.3784(1)  0.0834(1)  0.43869(4)  0.35039(4)  0.10898(4)  0.02207(4)  0.36856(4)  0.31595(4)  0.15426(4)  0.09337(4)  0.33438(1)  0.13299(1)  z  4.8(2)  6.0(2)  5.6(2)  5.8(2>  7.5(3)  4.8(2)  3.7(2)  3.4(2)  3.9(2)  3.7(2)  2.6(1)  2.7(1)  3.0(1)  3.2(1)  3.75(5)  3.49(5)  3.71(5>  3.79(5)  3.12(4)  3.52(4)  3.71(5)  3.12(4)  2.77(1)  2.83(1)  Beg  Final atomic coordinates (fractional) and Beg (2)*  5.5(2)  z  .  0.1775(2)  Y  Table  0.4564(4)  x  )* (cont.) 2 Final atomic coordinates (fractional) and Beg (A  0.1526(1)  .  C(ll)  atom  Table  -N2), 2.9 continued H iMe IZr(11 CSHS)}20.L C 1 {{[(PPr S N ) 2 D.1.2 X-ray Crystallographic Analysis of 5  0cc.  t’J t.J  4.9(2) 4.9(2) 4.8(2) 5.0(2) 5.0(2) 5.3(2) 5.7(2) 5.7(2) 5.4(2) 5.1(2) 15.4(3) 21.3(8) 23(1) 22.7(6)  0.1142(2) 0.1494(2) 0.1232(2) 0.0706(2) 0.0656(2) 0.4008(2) 0.4090(2) 0.3630(2) 0.3262(2) 0.3491(2) 0.1510(4) 1/4 0.216(2) 0.1934(7)  —0.1573(4) —0.1375(4) —0.0698(4) —0.0498(4) —0.1025(4) —0.0177(4) —0.0620(5) —0.1245(4) —0.1200(4) —0.0518(4) 0.107(1) 0.055(3) 0.115(3) 0.035(2)  0.1081(1)  0.1343(1)  0.1514(1)  0.1357(1)  0.1089(1)  0.1297(1)  0.1572(1)  0.1596(1)  0.1336(1)  0.1148(1)  0.4857(2)  1/2  0.4873(7)  0.4944(3)  C(37)  C(38)  C(39)  C(40)  C(41)  C(42)  C(43)  C(44)  C(45)  C(46)  C(47)  C(48)  C(49)  C(50)  eq  0.500  7.0(3)  0.3183(2)  0.2439(6)  0.0579(1)  C(36)  E 2 (8/3)n * 1 a a*(aj.aj) U  0.500  6.8(3)  0.4160(2)  0.2046(5)  0.0718(1)  oCC•  C(35)  Beg 5.0(2)  Z  0.3644(2)  Y  (coot.)  0.5753(4)  X  2)* Final atomic coordinates (fractional) and Beq  0.1049(1)  .  C(34)  atom  Table  C(4)  P(1) C(3)  103.7(2)  105.9(2)  101.7(2)  130.1(1)  111.4(1)  100.6(1)  117.1(1)  127.49(9)  115.3(1)  102.41(6)  99.76(8)  71.53(8)  104.84(6)  86.10(8)  75.37(7)  145.65(3)  117.2(1)  127.61(9)  115.1(1)  104.84(6)  85.76(8)  75.66(8)  102.89(6)  98.92(8)  71.74(8)  145.87(4)  angle  N(1)  N(1)  C(7)  C(1)  C(1)  N(1)  N(1)  N(1)  c(23)  C(20)  C(20)  1r2)  Zr(2)  Zr(2)  c21  C(19)  C(19)  Zr(2)  zr(2)  Zr(2)  C(S)  C(2)  C(2)  Zr(1)  Zr(1)  zr(l)  atom  si(2)  Si(2)  Si(1)  Si(1)  Si(1)  Si(1)  Si(1)  Si(1)  P(4)  P(4)  P(4)  P(4)  P(4)  P(4)  P(3)  P(3)  P(3)  P(3)  P(3)  P(3)  P(2)  P(2)  P(2)  P(2)  P(2)  P(2)  atom  C(9)  C(2)  C(8)  C(8)  C(7)  C(8)  C(7)  C(1)  c(24)  C(24)  C(23)  C(24)  c(23)  C(20)  c(22)  C(22)  C(21)  C(22)  c(21)  C(19)  C(6)  C(6)  C(5)  115.0(2)  106.9(2)  106.5(2)  105.8(2)  107.4(2)  115.3(2)  113.2(2)  108.1(2)  103.6(2)  105.4(2)  102.2(2)  130.9(1)  111.1(1)  100.1(1)  107.5(2)  105.0(2)  104.1(2)  122.4(2)  118.4(1)  95.9(1)  107.9(3)  104.7(2)  104.1(2)  123.1(2)  c(5) C(6)  96.0(1) 117.5(1)  angle c(2)  atom  Angles are in degrees. Estimated standard deviations in the least significant figure are given in parentheses.  C(3) C(4)  P(1) p(1)  C(1) C(l)  C(4)  C(3)  PCI) Zr(l)  P(1)  C(1)  P(1) Zr(1)  Zr(1)  Cp(2)  Cp(2)  N(4)  Cp(2)  N(4)  N(2)  Cp(2)  N(4)  N(2)  P(4)  Cp(1)  Cp(1)  N(3)  Cp(1)  N(3)  N(l)  Cp(l)  Zr(2)  lr(2)  zr(2)  Zr(2)  Zr(2)  Zr(2)  Zr(2)  Zr(2)  Zr(2)  Zr(2)  Zr(l)  Zr(1)  Zr(1)  Zr(1)  Zr(l)  Zr(l)  Zr(1)  N(3)  N(4)  N(2)  N(2)  P(4)  p4  P(4)  p(3)  P(3)  P(3)  P(3)  N(3)  N(l)  N(l)  P(2)  P(2)  P(2)  P(1)  Zr(l)  Zr(l)  PCI.)  P(2) N(1)  Zr(l)  atom  PU)  atom  P(l)  atom  Intramolecular Bond Angles  {[(PPr S N ) 2 C5H5)}2(.t-N 1Zr(T1 iMe iZCH 2), 2.9 continued D.1.2 X-ray Crystallographic Analysis of 5  t’-)  115.0(7)  119.1(6) 112.5(3)  115.7(3)  C(32) C(32A) C(33) C(34)  C(22) C(22) C(22) C(23) C(23)  9(3)  C(31) C(31) P(4) 9(4)  120.5(2) 170.6(2) 170.1(2) 108.5(2) 110.8(2)  Si(4)  N(4)  N(3)  31(1)  Sj(2)  N(2)  N(3)  N(4)  C(l)  •C(2)  Zr(2)  Si(3)  Zr(1)  Zr(2)  9(1)  9(2)  P.ngles are in degrees. Estimated standard deviations in the least significant figure are given in parentheses.  121.3(6) 117.8(6)  C(32) C(32A)  C(22)  9(3)  119.7(1)  Si(4)  N(2)  Zr(2)  81(2)  N(1)  Zr(l)  117.0(4)  110.1(4)  C(30)  C(21)  9(3)  119.8(1)  31(1)  N(1)  Zr(1)  C(31)  116.5(3)  C(30)  C(21)  120.0(1)  C(28)  Si(4)  C(27)  C(22)  112.7(3)  Si(4) C(29)  c(20)  9(4) 9(3)  106.6(2)  C(28)  Si(4)  C(20)  C(21)  108.8(2)  31(3)  9(3)  106.0(2)  Si(4)  C(20)  9(3)  110.6(2)  C(l8A)  C(6) C(19)  C(17)  107.2(2)  C(27)  Si(4)  N(2)  C(29)  117.7(8)  C(6)  C(17)  115.3(2)  119.9(1)  117.0(6)  C(18)  C(6)  9(2)  113.4(2)  C(27)  C(28)  Si(4)  N(2)  120.2(2)  119.9(7)  C(l8A)  107.8(2)  C(20)  si(4)  N(2)  Si(3)  118.9(6)  C(l8)  C(6)  9(2)  104.3(2)  C(26)  Si(3)  C(25)  Si(2)  117.1(4)  C(17)  C(6)  9(2)  C(26)  Si(3)  C(19)  N(1)  110.4(4)  C(16)  C(5)  C(15)  106.1(2)  C(25)  Si(3J  C(19)  N(2)  112.6(3)  C(16)  C(5)  9(2)  N(2)  Si(l)  116.6(3)  C(l5)  C(5)  P(2)  114.7(2) 109.0(2)  C(26)  Si(3)  N(2)  110.5(4)  C(4)  C(13)  115.3(2)  C(14)  C(4)  P(1)  107.0(2)  110.7(3)  C(14)  104.9(2)  C(l0)  Si(2)  C(9)  C(25)  114.7(3)  C(13)  C(4)  P(1)  106.5(2)  C(10)  Si(2)  C(2)  C(19)  111.5(3)  C(12)  C(3)  C(11)  Si(2)  C(2)  Si(3)  116.1(3)  C(12)  C(3)  9(1)  108.4(2)  C(9)  Si(2)  N(1)  Si(3)  112.8(3)  C(ll)  C(3)  9(1)  114.8(2)  C(10)  N(2)  angle  atom  atom  atom  angle  atom  atom  atom  Intramolecular Bond Angles  (cont.)  C(6)  C(S)  C(2)  C(4)  C(3)  C(1)  Cp(2)  C(46)  C(45)  C(44)  C(43)  C(42)  N(4)  N(2)  P(4)  9(3)  Cp(1)  C(41)  C(40)  C(39)  C(38)  C(37)  N(3)  N(l)  9(2)  P(l)  atom  1.860(5)  1.845(4)  1.808(4)  1.862(4)  1.857(4)  1.825(4)  2.286(2)  2.529(4)  2.541(4)  2.583(4)  2.622(4)  2.591(4)  1.923(3)  2.303(3)  2.828(1)  2.778(1)  2.294(2)  2.624(4)  2.600(4)  2.536(4)  2.547(4)  2.599(4)  1.920(3)  2.306(3)  2.776(1)  2.816(1)  distance  C(4)  C(3)  C(3)  N(3)  Si(4)  Si(4)  Si(4)  si(4)  Si(3)  Si(3)  si(3)  Si(3)  si(2)  si(2)  Si(2)  si(2)  si(1)  si(1)  Si(1)  Si(1)  P(4)  9(4)  9(4)  p(3)  9(3)  9(3)  atom  C(13)  C(12)  C(11)  N(4)  C(28)  C(27)  C(20)  N(2)  C(26)  C(25)  C(19)  N(2)  C(10)  C(9)  C(2)  N(l)  C(8)  C(7)  C(l)  N(1)  c(24)  C(23)  C(20)  C(22)  C(21)  C(19)  atom  1.515(5)  1.523(5)  1.520(5)  1.301(3)  1.879(5)  1.870(4)  1.886(4)  1.718(3)  1.865(4)  1.897(4)  1.887(4)  1.706(3)  1.872(4)  1.890(4)  1.895(4)  1.709(3)  1.887(5)  1.870(4)  1.887(4)  1.716(3)  1.871(4)  1.857(4)  1.821(4)  1.854(5)  1.852(4)  1.812(4)  djtance  Estimated standard deviations in Distances are in angstroms. the least significant figure are given in parentheses.  9(2)  P(2)  9(2)  9(1)  9(1)  9(1)  Zr(2)  Zr(2)  Zr(2)  Zr(2)  Zr(2)  Zr(2)  zr(2)  zr(2)  zr(2)  Zr(2)  Zr(l)  Zr(l)  Zr(1)  Zr(1)  Zr(1)  zr(l)  zr(l)  zr(1)  Zr(l)  zr(1)  atom  Intramolecular Distances  D.1.2 X-ray Crystallographic Analysis of ) SiMe 2.9 continued Hs)} CH2 .N &Cs Pr’2 p ]Zr(1 {[(P N ( 2  0.15 X 0.25 X 0.25 mm orthorhombic Primitive  Crystal System Lattice Type  45.53 cm  o(CuKo)  Rigaku AFC6S CuKo (A = 1.54178 A) graphite monochromated  6.0  Diffractometer Rediation  Take-off Angle  B. lnten8ity Measurements  2632  000 F  1.239 g/cm 3  4  6638.8(7) A  14.384(1) A 17.754(1) A 25.997(1) A  Z value  =  = =  =  Pbcn (#60)  V  b  a  0.38  25 ( 46.4 72.7  Space Group  Lattice Parameters  Omega Scan Peak Width at Half-height  -  dark, prism  Crystal Dimensions  No. of Reflections Used for Unit Cell Determination (20 range)  1238.11  Formula Weight  S P N 6 o 1 H Cs O 4 2 Zr i  A. Crystal Data  EXPERIMENTAL DETAILS  Crystal Color, Habit  Empirical Formula  D.1.3 X-ray Crystallographic Analysis of 2 S {[(PPri2CH N ) ( ) ]Zr(OAr*} iN iMe , 2.12a  t..J cM  I.  4.5(1) 4.3(1) 6.7(2) 6.0(2)  5.9(2) 5.2(2)  10.3(3) 10.4(3) 6.9(2) 5.1(1) 5.4(2) 8.9(2) 7.0(2)  0.1066(2) 0.1441(2) 0.0843(2) 0.0201(2) 0.1825(2) 0.0695(2) 0.2157(2) 0.1871(3) 0.2172(2) 0.2096(3) 0.2137(3) 0.1366(3) 0.0568(2) 0.1481(2) 0.0323(2) 0.0282(2)  0.3145(3) 0.3659(3) 0.4750(3) 0.3477(3) 0.4923(3) 0.4746(3) 0.3375(3) 0.1859(4) 0.4113(3) 0.3496(5) 0.1423(4) 0.1886(4) 0.2706(3) 0.2174(3) 0.1954(4) 0.3072(4)  0.2335(4) .0.1621(3) 0.1714(4) 0.1029(4) -0.0394(4) -0.0739(4) 0.2788(4) 0.2961(4) 0.2276(4) 0.3822(5) 0.2974(6) 0.3853(4) -0.1389(4) -0.2518(4) -0.1117(5) -0.2208(5)  CCI)  C(2)  C(3)  C(4)  C(5)  C(6)  C(7)  C(8)  C(9)  cOo)  C(11)  C(12)  C(13)  C(14)  C(15)  C(16)  6.1(2)  6.4(2)  6.0(2)  3.49(9)  0.2426(1)  0.2812(2)  .0.0514(2)  N(2)  3.38(9)  0.1289(1)  0.3585(2)  0.0391(3)  N(1)  437(9)  0.1539(1)  0.1522(2)  0.0407(2)  0(1)  3.92(3)  0.13069(5)  0.42082(8)  .0.0524(1)  Si(2)  4.34(4)  0.08792(6)  0.37463(9)  0.1306(1)  Si(1)  4.01(3)  0.12761(5)  0.26760(8)  .0.14513(9)  P(2)  3.85(3)  0.22304(9)  P(1)  0.17013(5)  2.990(7)  0.27162(8)  0.02851(3)  Zr(1)  0.17979(1)  Y 0.25905(2)  atom  Table IT. Atomic coordinates and Bq  Max Shift/Error in Final Cycle  Goodness of Fit Indicator  Iesiduals: R; Rw  Reflection/Parameter Ratio  No. Variables  No. Observations (1>3.OOcT(I))  Anomalous Dispersion  p-factor  Least Squares Weights  Function Minimized  Refinement  Structure Solution  Corrections  No. of Reflections Measured  2Omar  Scao Width  Scan Rate  Scan Type  Temperature  Crystal to Detector Distance  Detector Aperture  —  2 IFcD  0.0003  1.54  0.037 0.034  11.18  308  3444  All non-hydrogen atoms  0.000  ;‘ p 1 -y =  Ew(IFoI  Full-matrix least-squares  Patterson Methods (DIRDIFO2 PATI’Y)  C. Structure Solution and Refinement  Lrentz-polarization Absorption (trans. factors: 0.78- 1.00) Decay (2.01% decline) Secondary Extinction (coefficient: 9.2(5) x _5)  Total: 6948  155.5  (0.84 + 020 tan 9)5  16.0 / 5 min (in u) (up to 9 scans)  w-29  21 .0CC  285 mm  6.0 mm horizontal 6.0 mm vertical  {[( C S N ) ( ) ]Zr(O p. iM PP H , N Ar*} ri e 2.12a continued D.1.3 X-ray Crystallographic Analysis of 2  0  =  0.2091(2) 0.0594(2)  0.0387(3) -0.0318(4) -0.0571(4) -0.0118(4) 0.0599(3) 0.0653(4) 0.1096(3)  -0.0447(4) -0.0655(5) .0.0240(6) 0.0371(5) 0.0593(4) -0.0951(5) 0.1240(4)  C(20)  C(21)  C(22)  C(23)  C(24)  C(25)  COG)  0.0895(2)  0.0705(2)  0.0964(3)  0.1412(3) 7.1(2)  6.2(2)  6.9(2)  4.4(1)  6.2(2)  7.8(2)  PU) P0) PU)  1.824(5) 1.8510) 1.844(5) 1.718(4)  C(S)  C(8)  C(13)  NO)  CU)  PU)  PU)  P0)  Si(1)  SI(S)  Si(S)  COO)  COO)  00)  C(19)  N(S)  00)  1.528(7)  C(6) N(S)’  Si(S)  1.861(6) 1.331(6)  C(5)  Si(S)  C(14)  1.881(5)  C(S)  Si(2)  1.720(4)  N(S)  PU)  1.887(5)  C(4)  Si(S)  1.878(6)  110.5(5) 119.8(5)  CU8) C(24)  C(S4) COO)  CU7) 00)  116.7(4) 120.1(5)  1.870(6)  1.890(5)  C(S)  1.813(5)  C(S)  Si(S)  1.848(6)  C(7)  1.852(6)  2.082(4)  2.211(3)  NO)’  NO)  2.8460)  distance  CU4)  C(18)  Zr(S)  2.034(4)  14(2)  ZrU)  Zr(S)  2.020(3)  0(5)  Zr(1)  P0)  Zr(S)  2.8180)  PU)  Zr(S)  atom  atom  atom  atom  distance  ,r2(Ui ( 5 aa)2 + (.122(06’)’ + U,s(cc’)’ + 2U aa’cc coefl + 2Umbbce’ roan) 5 ,aa’bb’ cony + 2Uj 1  Table 111. Bond Lengths(A)  B,  0.1354(2)  0.0845(3)  0.0193(4)  C(19) 5.1(2)  4.3(1)  0.1430(3)  0.2603(4)  -0.3433(4)  C(18)  0.1614(2)  6.4(2)  0.1246(3)  0.1400(4)  -0.2603(5)  C(17)  7.7(2)  z  y  x  atom  Table 11. Atomic coordinates and B, (continued)  Zr(S) Zr(S) Zr(S) Zr(S) Zr(S) P(l) PU) PU)  P(2) P(2) 0(1) N(l) 14(2) Zr(1) CU) C(7)  CU)  Zr(1)  SI(S)  Zr(l)  C(S)  C(2)  N(S)  CU)  14(2)  14(1)  N(S)  Si(S)  SI(S)  14(2)’  Si(S)  Si(S)  C(S)  C(S)  C(5)  Si(l) Si(2)  CU) C(4)  Si(l)  69.9(2)  119.7(2)  123.9(2)  106.4(3)  107.7(2)  112.4(2)  105.1(3)  107.7(3)  115.4(2) CU)  Si(1)  NU)  109.9(3)  C(14)  115.8(2)  107.6(3)  106.3(3)  115.1(2)  43.6(2)  111.4(1)  PU)  CU3)  126.19(10) 119.8(1)  102.3(2)  C(t3)  C(8)  C(7)  C(7)  14(2)’  N(2)  14(2)  14(2)’  74.5(1)  85.10(10)  79.4(1)  145.54(4)  angle  CU3)  PU)  C(S)  PU)  N(2)’  Zr(1)  PU)  ZrO)  NO)  Z(1)  PU)  N(S)  P(2)  Z(1)  PU)  atom  atom  atom  Table IV. Road Augles()  Zr(S)’  Zr(S)  Zr(1)  Zr(S)  CU)  NO)  NO)  CU)  N(S)  14(1)  C(S)  Zr(S)  Zr(1)  CU)  Zr(l)  Zr(S)  14(1)  0(1)  0(1)  P(2)  P(2)  PU)  PU)  atom  D.1.3 X-ray Crystallographic Analysis of 2 {[(PPr N ) ]Zr(O i2CH2 Ar*} SiMe2 , Z(tN ) 2.12a continued  14(2)  14(2)  N(S)  0(1)  Si(S)  Si(2)  Si(S)  SU)  SiU)  SIU)  P(2)  PU)  PU)  PU)  P(i)  P(1)  Zr(S)  ZrU)  Zr(l)  Zr(S)  Zr(1)  Zt(1)  Zr(l)  atom atom  NO)’  Zr(l)’  Si(S)  C(19)  C(6)  C(S)  C(S)  C(4)  C(4)  CU)  CU4)  C(14)  CU)  C(8)  C(8)  C(1)  N(2)’  N(S)’  N(S)  14(2)  0(1)  14(2)  0(1)  angle  86.5(2)  130.7(2)  116.4(2)  161.5(4)  106.3(2)  115.4(2)  108.2(2)  105.4(2)  112.3(2)  110.3(2)  106.5(3)  124.4(2)  93.3(2)  104.9(3)  120.1(2)  101.3(2)  114.7(1)  119.5(1)  123.0(1)  82.89(10)  88.1(1)  128.50(10)  87.6(1)  I.  C14  C9  Cl 5  P2  C31  Cl 3  C21  C22  C8  07  Zr N  C17  C32  P1  010  016  C6  S12  C5  Cl  cli  012  018  Sil  02 04  C3  29 N P 2 ZrSi 5 H C 4  =  Z =  1.202Mg.m—3, mu  626.08  : 2  X X =  0.50  660  mm  lambda 0.70930A,  F(000)  0.40  0.49mm—i,  0.30  2Theta(max)  In the last D—map, the deepest hole was and the highest peak . 3 0.240e/A  , 3 —0.280e/A  —  The residuals are as follows :—— For significant reflections, RF 0.036, Rw 0.038 G0F 2.67 For all reflections, RF 0.036, Rw 0.038. where RF = Sum(Fo—Fc)/Sum(Fo, Rw = Sqrt[Sum(w(Fo-Fc) )/Sum(wFo )] and 2 Sqrt[Sum(w( ) /(No G0F = 2 Fo—Fc) . of ref ins No. of params.)] The maximum shift/sigma ratio was 0.008.  The last least squares cycle was calculated with 89 atoms, 316 parameters and 3361 out of 4512 reflections. Weights based on counting—statistics were used. The weight modifier K in KF0 2 is 0.000050  The intensity data were collected on a Nonius diffractometer, using the omega scan mode. The h,k,1 ranges are :—— —9 9, ii, 0 —20 20 No. of reflections measured 7929 No. of unique reflections 4512 No. of reflections with met > 3.Osigma(Inet) 3361 Absorption corrections were made. The minimum and maximum transmission factors are 0.831 and 1.00.  Dcalc  FW  Crystal dimensions  —  44.9  Cell dimensions were obtained from 24 reflections with 2Theta angle in the range 28.00 36.00 degrees.  Empirical formula :  Space Group and Cell Dimensions Triclinic, P -l 9.0970(10) a 10.512(3) b c 19.079(5) alpha 90.90(3) beta 95.890(10) gamma 107.390(20) Volume 3 1729.8(7)A  D.1.4 X-ray Crystallographic Analysis of 5 -Zr( CSHS)Ph[N(SiMe2CH2P r) Pr’2)2], 4.4  t-) 00  1.  0.92623( 5) 1.15726(14) 0.78042(13) 1.12160(14) 0.79039(15) 0.9521 ( 3) 1.2555 ( 5) 1.2305 ( 5) 1.0972 ( 6) 0.8312 ( 6) 0.6687 ( 6) 0.6673 ( 5) 1.3134 ( 6) 1.4275 ( 6) 1.2491 ( 7) 1.0984 ( 6) 0.9545 ( 7) 1.2291 ( 8) 0.6458 ( 7) 0.7095 ( 6) 0.4989 ( 7) 0.9058 ( 6) 0.9991 ( 6) 0.8272 ( 7) 0.8565 ( 6) 0.8293 ( 6) 0.7098 ( 6) 0.6606 ( 5) 0.7543 ( 5) 1.1072 ( 4) 1.2228 ( 5) 1.3475 ( 5) 1.3640 ( 5) 1.2556 ( 6) 1.1309 ( 5)  0.33970( 4) 0.35823(12) 0.23576(11) 0.10076(11) 0.00660(12) 0.1357 ( 3) 0.2491 ( 4) 0.0727 ( 4) —0.0516 ( 5) —0.1360 ( 4) —0.0675 ( 5) 0.0731 ( 4) 0.5149 ( 5) 0.5681 ( 5) 0.6189 ( 6) 0.2909 ( 5) 0.1719 ( 5) 0.2657 ( 8) 0.3020 ( 5) 0.4480 ( 5) 0.2321 ( 6) 0.1930 ( 5) 0.3133 ( 5) 0.0788 ( 5) 0.5348 ( 4) 0.4390 ( 5) 0.3301 ( 5) 0.3568 ( 5) 0.4861 ( 5) 0.4931 ( 4) 0.4462 ( 4) 0.5248 ( 5) 0.6560 ( 5) 0.7081 ( 4) 0.6299 ( 4)  y 0.26186( 3) 0.37245-( 7) 0.12882( 7) 0.28202( 8) 0.22164( 8) 0.25364(18) 0.3364 ( 3) 0.2077 ( 3) 0.3352 ( 3) 0.1759 ( 3) 0.2911 ( 3) 0.1552 ( 3) 0.4041 ( 3) 0.3529 ( 3) 0.4319 ( 4) 0.4587 ( 3) 0.4509 ( 3) 0.5079 ( 4) 0.0723 ( 4) 0.0582 ( 3) 0.0474 ( 4) 0.0669 ( 3) 0.0288 ( 3) 0.0136 ( 3) 0.3143 ( 3) 0.3639 ( 3) 0.3366 ( 3) 0.2681 ( 3) 0.2539 ( 3) 0.20838(22) 0.18375(25) 0.1532 ( 3) 0.1454 ( 3) 0.1664 ( 3) 0.1972 ( 3)  z 3.716(20) 4.38 ( 6) 4.45 ( 6) 4.29 ( 7) 4.78 ( 7) 3.75 (18) 4.8 ( 3) 5.6 ( 3) 6.8 ( 3) 7.2 ( 3) 7.6 ( 3) 4.8 ( 3) 6.2 ( 3) 7.3 ( 3) 10.1 ( 4) 6.4 ( 3) 7.6 ( 3) 11.9 ( 5) 10.7 ( 4) 6.4 ( 3) 10.1 ( 4) 5.7 ( 3) 7.3 ( 3) 8.4 ( 4) 5.8 ( 3) 6.7 ( 3) 7.7 ( 4) 6.8 ( 3) 6.0 ( 3) 3.63 (21) 4.62 (25) 5.6 ( 3) 6.4 ( 3) 6.4 ( 3) 5.3 ( 3)  0 B  B is the Mean of the Principal axes of the Thermal Ellipsoid  Zr P1 P2 Sil Si2 N Cl C2 C3 C4 C5 C6 C7 C8 C9 ClO Cli C12 C13 C14 C15 C16 C17 C18 C21 C22 C23 C24 C25 C31 C32 C33 C34 C35 C36  x  Atomic Parameters x,y,z and B 0  -  .nqle5  ()  9(2)—Zr—N P(2)—Zr—C(24) P(2)—Zr—C(25) P(2)—Zr—C(31) N—Zr—C(24) N—Zr—C(25) N—Zr—C(31) Zr—P(1)—C(1) Zr—P(1)—C(7) Zr—P(1)—C(10) C(1)—P(1)—C(7) C(1)—P(1)—c(10) C(7)—P(1)—C(10) Zr—P(2)—C(6) Zr—P(2)—C(13) Zr—P(2)—C(16) C(6)—P(2)—C(13) C(6)—P(2)—C(16) C(13)—P(2)—C(16) N—Si(1)—C(1) N—Si(1)—C(2) N—Si(1)—C(3) C(1)—Sj(1)—C(2) C(1)—Si(1)—C(3) C(2)—Si(1)—C(3) N—Si(2)—C(4) N—Sj(2)—C(5) N—Si(2)—C(6) C(4)—Si(2)—C(5)  P(1)—Zr—C(31)  P(1)—Zr—P(2) P(1)—Zr—N  75.01(10) 78.50(13) 85.80(12) 88.57(11) 117.57(14) 149.07(14) 112.60(13) 99.87(16) 124.83(17) 118.31(17) 105.65(22) 106.44(22) 100. 10(23) 97.73(16) 125.97(24) 115.96(16) 106.77(22) 103.08(21) 104.4(3) 108.72(17) 113.18(20) 115.19(20) 105.86(21) 108.66(23) 104.75(23) 115.13(20) 112.86(22) 108.72(17) 105.7(3)  87.04(11)  150.09(4) 79.47(9)  2.7819(14) 2.7843(16) 2.231(3) 2.540(4) 2.549(5) 2.526(5) 2.491(4) 2.497(4) 2.272(4) 1.817(5) 1.868(5) 1.868(5) 1.821(4) 1.846(5) 1.861(5) 1.726(3) 1.883(5) 1.878(5) 1.878(5) 1.725(3) 1.871(5)  (A) 1.846(6)  Zr—N—Si(2) Si(1)—N—Si(2) P(1)—C(1)—Si(1) P(2)—C(6)—Si(2) P(1)—C(7)—C(8) P(1)—C(1)—C(9) C(8)—C(7)—C(9) P(1)—C(10)—C(11) P(1)—C(10)—C(12) C(11)—C(10)—C(12) P(2)—C(13)—C(14) P(2)’—C(13)—C(15) C(14)—C(13)—C(15) P(2)—C(16)—C(17) P(2)—C(16)—C(18) c(17)—C(16)—C(18) C(22)—C(21)—C(25) C(21)—C(22)—C(23) C(22)—C(23)—C(24) C(23)—C(24)—C(25) C(21)—C(25)—C(24) Zr—C(31)—C(32) Zr—C(31)—C(36) C(32)—c(31)—C(36) C(31)—C(32)—C(33) C(32)—C(33)—C(34) C(33)—C(34)—C(35) C(34)—C(35)—C(36) C(31)—C(36)—C(35)  Zr—N—Si(1)  C(4)—Sj(2)—C(6) C(5)—Si(2)—C(6)  Si(2)—C(6) 1.885(5) C(7)—C(8) 1.490(8) 1.498(8) C(7)—C(9) C(10)—C(11) 1.508(7) C(10)—C(12) 1.527(8) C(13)—C(14) 1.509(7) C(13)—C(15) 1.350(8) C(16)—C(17) 1.537(7) C(16)—C(18) 1.512(7) C(21)—C(22) 1.378(7) C(21)—C(25) 1.390(7) C(22)—C(23) 1.373(8) C(23)—C(24) 1.397(9) C(24)—C(25) 1.420(7) C(31)—C(32) 1.405(6) C(31)—C(36) 1.412(6) C(32)—C(33) 1.378(6) C(33)—C(34) 1.355(7) C(34)—C(35) 1.352(8) C(35)—C(36) 1.380(7)  Si(2)—C(5)  Int.ratoidc Distanc.s and ng1.e  Zr—P(1) Zr—P(2) Zr—N Zr—C(21) Zr—C(22) Zr—C(23) Zr—C(24) Zr—C(25) • Zr—C(31) P(1)—C(1) P(1)—C(7) P(1)—C(10) P(2)—C(6) P(2)—C(13) P(2)—C(16) Si(1)—N Si(1)—C(1) Si(1)—C(2) Si(1)—C(3) Si(2)—N Sj(2)—C(4)  Diatanc.a  D.1.4 X-ray Crystallographic Analysis of 2 Zr(1 ) H 5 C P ] ) Ph[N(S1Me PrI C H , 4.4 continued  117.54(16) 119.15(17) 113.90(22) 109.65(22) 114.5(4) 112.0(4) 112.6(4) 113.1(4) 114.3(4) 112.0(4) 114.4(4) 125.0(4) 120.5(5) 113.7(3) 116.1(4) 109.3(4) 108.7(4) 109.1(5) 108.0(5) 107.5(4) 106.7(5) 114.9(3) 132.5(3) 112.5(4) 124. 1(4) 120.0(4) 119.5(4) 120.7(4) 123.2(4)  123.21(16)  106.63(23) 107.32(23)  C23  C24(  C14  C15  C21  P2  C32  S3  C22  C25  C13  j  C31  Zr  C34  P1  C7  C8A  C18  C16  C17  C12  C6  N  )  -Th  SM  C5  Ci  S12  Cli  C4  C2  C88  C3  Zr Si 3 P 2 N C H  —  Monoclinic, 20.414(4)  P 2 /c 1  Cell dimensions were obtained from 24 reflections with 2Theta angle in the range 37.00 — 44.00 degrees. Crystal dimensions : 0.40 0.60 X 0.90 mm X FW = 636.21 4 F(000) = 1364 Z = D 0.50mm—i, X 0.70930A, 2Theta(max) 45.0 i.l7Mg.m—3, mu The intensity data were collected on a Nonius CAD-4 diffractometer, using the omega scan mode. The h,k,i ranges used during structure solution and refinement are :—— llnin,max Lmin,nax 0 21 -10 10; Kmin,max 0 19; No. of reflections measured 4831 4686 No. of unique reflections No. of reflections with I > 3.0sigma(I) 3647 Merging R—value on intensities 0.026 Absorption corrections were made. The minimum and maximum transmission factors are 0.887 and 0.999. The last least squares cycle was calculated with 88 atoms, 319 parameters and 3647 out of 4686 reflections. Weights based on counting—statistics were used. The weight modifier K in KF0 2 is 0.000006 The residuals are as follows 4.37 For significant reflections, RF 0.039, Rw 0.043 G0F For all reflections, RF 0.039, Rw 0.043. where RF = Sum(Fo-Fc)/Sum(Fo, )) and 2 Rw Sqrt[Sum(w(Fo-Fc) )/Sum(wFo No. of params.)] G0F = Sqrt[Sum(w(Fo—Fc) )/(No. of ref ins 2 The maximum shift/sigma ratio was 0.000. , 3 -0.330e/A In the last D-map, the deepest hole was and the highest peak . 3 0.400e/A  Empirical formula  Space Group and Cell Dimensions a 10.0813(19) b 17.7883(18) C beta 100.243(22) Volume 3 3602.5(10)A  D.1.5 X-ray Crystallographic Analysis of 2 H C 5 Zr(rI S [ 3 C P ] ) N(SiMe s)CH iMe Pri H , 4.8  C  0.10188( 5) —0.05298(14) 0.30818(15) 0.14827(17) 0.15093(18) 0.31782(17) 0.1386 ( 4) 0.0631 ( 5) 0.3286 ( 7) 0.0751 ( 8) 0.2493 ( 6) —0.0214 ( 6) 0.2265 ( 6) —0.2113 ( 9) —0.2234 (23) —0.2560 (10) —0.324]. (23) —0.0813 ( 8) —0.1079 ( 8) —0.1504 ( 9) 0.3682 ( 9) 0.4163 (11) 0.3390 (13) 0.4630 ( 6) 0.5365 ( 8) 0.5526 ( 7) —0.1028 ( 7) —0.1120 ( 7) —0.0059 ( 7) 0.0705 ( 6) 0.0108 ( 8) 0.2534 ( 5) 0.1950 ( 7) 0.3617 ( 8) 0.4712 ( 7)  0.78205 0.71414 0.77622 0.62939 0.59864 0.89647 0.66093 0.6390 0.5826 0.5041 0.5413 0.6121 0.7061 0.6666 0.6417 0.5977 0.7018 0.7629 0.7163 0.8325 0.8488 0.9197 0.8486 0.7252 0.6820 0.7767 0.8296 0.8626 0.9115 0.9094 0.8591 0.8088 0.9403 0.9709 0.8801  y 3) 9) 9) 9) 9) 10) 21) 3) 4) 3) 3) 3) 3) 7) 15) 7) 12) 4) 4) 5) 5) 5) 6) 5) 5) 6) 4) 4) 3) 3) 4) 3) 4) 4) 4)  0.16239 3) 0.05109 7) 0.27798 8) 0.26445 8) 0.12111 9) 0.06021 9) 0.18376 20) 0.0391 3) 0.1106 3) 0.1301 3) 0.2865 3) 0.2851 3) 0.3227 3) 0.0598 6) 0.1234 9) 0.0130 5) 0.0710 20) —0.0318 3) —0.0930 3) —0.0358 4) 0.3424 4) 0.3189 5) 0.4024 5) 0.2631 4) 0.3200 5) 0.2327 4) 0.2031 5) 0.1410 4) 0.1426 4) 0.2061 4) 0.2444 3) 0.0912 3) —0.0077 4) 4) 0.1235 0.0223 4)  z 2.987 22) 7) 4.02 7) 4.48 4.27 8) 4.45 9) 8) 4.87 21) 3.35 3) 3.9 4) 7.3 5) 7.9 5.9 3) 3) 5.8 4.8 3) 10.1 6) 15) 15.6 10) 20.4 19.7 24) 8.2 4) 5) 8.8 5) 10.0 5) 9.3 7) 14.0 9) 16.3 7.4 4) 6) 11.1 6) 11.3 5) 6.8 4) 6.2 4) 5.4 4) 5.4 5.8 4) 3) 3.9 7.6 4) 5) 9.1 5) 9.7  3, is theMean of the Principal Axes of the Thermal Ellipsoid  Zr P1 P2 Sil Si2 Sj3 N Cl C2 C3 C4 CS C6 C7 C8A CBB C8C ClO Cli C12 Ci) C14 C15 C16 Cl7 C18 C21 C22 C23 C24 C25 C3l C32 C33 C34  x  Atomic Parameters x,y,z and B  2.7923(16) 2.8563(17) 2.216(4) 2.505(6) 2.561(6) 2.549(5) 2.475(5) 2.463(6) 2.337(5) 1.821(5) 1.842(8) 1.877(7) 1.826(5) 1.866(7) 1.876(7) 1.726(4) 1.879(6) 1.858(6) 1.889(6) 1.713(4) 1.890(5)  151.17(5) 77.83(11) 92.39(22) 126.89(17) 124.85(19) 85.13(13) 74.37(11) 105.06(24) 81.75(17) 76.33(17) 93.47(13) 112.41(20) 147.80(22) 118.45(20) 102.47(16) 53.55(22) 32.7(3) 143.69(23) 32.8(3) 100.21(21) P1—Zr—Cent 103.95(4) P2—Zr—Cent 102.08(4)  P1—Zr—P2 P1—Zr—N P1—Zr—C2l P1—Zr—C24 Pl—Zr—C25 Pl—Zr—C3l P2—Zr—N P2—Zr—C2l P2—Zr—C24 P2—Zr—C25 P2—Zr—C31 N—Zr—C21 N—Zr—C24 N—Zr—C25 N—Zr—C3]. C21—Zr—C24 C21—Zr—C25 C21—Zr—C31 C24—Zr—C25 C24—Zr—C3l  Angles  Zr—Cent 2.2162(5)  Zr—Pl Zr—P2 Zr—N Zr—C2]. Zr—C22 Zr—C23 Zr—C24 Zr—C25 Zr—C31 P1—Cl P1—C7 P1—dO P2—C6 P2—C13 P2—C16 Sil—N Sil—C4 Sil—C5 Sil—C6 Si2—N Si2—C1  Distances  (A) ()  N—Zr—Cent 139.47(10) C31—Zr—Cent 118.05(13)  107.0(3) 107.0(3) 112.5(3) 114.9(3) 112.2(3) 105.4(4) 104.3(3) 106.7(4) 118.88(21) 120.90(21) 120.18(23) 111.8(3) 110.7(3) 117.1(9) 117.3(6) 124.9(11) 104.7(12) 77.0(23) 107.8(12) 50.4(14)  1.864(7) 1.870(6) 1.843(5) 1.858(7) 1.848(7) 1.871(7) 1.396(22) 1.571(13) 1.353(23) 1.71(5) 1.483(10) 1.416(10) 1.463(11) 1.308(13) 1.477(11) 1.497(11) 1.385(13) 1.398(12) 1.375(12) 1.385(11) 1.393(11)  and Angles  Cl—Si2—C3 C2—Si2—C3 C31—Si3—C32 C31—Si3—C33 C3l—Sj3—C34 C32—Si3—C33 C32—Si3—C34 C33—Si3—C34 Zr—N—Sil Zr—N—Si2 Sil—N—Sj2 P1—C1—Si2 P2—C6—Sil P1—C7—C8A Pl—C7—C8B P1—C7—CBC C8A—C7—C8B C8A—C7—C8C C8B—C7—C8C C7—C8A—C8C  Si2—C2 Si2—C3 Si3—C31 Si3—C32 Si3—C33 Si3—C34 C7—C8A C7—C8B C7—C8C C8A—C8C ClO—Cil C10—C12 C13—C14 C13—C15 C16—C17 C16—C18 C21—C22 C21—C25 C22—C23 C23—C24 C24—C25  Interatomic Distances PCH,SiMe Pr N 2 ) )Cp 3 SiMe Zr 2 (CH )  Zr(i ) H 5 S [ 3 C P ] ) N(S1Me CH 1Me Pr’ C , 4.8 continued H D.1.5 X-ray Crystallographic Analysis of 2  I  C3  C2  C17  09  Cl  C8  Cl 3  C22  C12  Cl 5  C21  S ZrP N 2 53 CH i  Monoclinic, 33.754(4) I 2/a  Z  1.168Mg.m—3, mu  553.02 8  X  X  F(000)  0.30  0.80  2366  mm  0.53mm—l, lambda 0.70930A, 2rheta(max)  0.20  47.9  , 3 —0.460e/A Hydrogen atoms were treated as follows: 4 BH Located and refined with isotropic thermal parameters: Located and fixed with isotropic thermal parameters: CH groups 1.08A) and fixed with isotropic thermal parameters: CH , CH 2 Calculated (DCK groups.  In the last D—map, the deepest hole was . 3 0.470e/A and the highest peak  The residuals are as follows :—— RF 0.041, Rw 0.045 GoF 2.00 For significant reflections, RF 0.041, Rw 0.045. For all reflections, where RF Sum(Fo—Fc)/Sum(Fo, )] and 2 Sgrt[Sum(w(Fo—Fc) )/Sum(wFo Rw G0F = Sqrt(Sum(w(Fo_Fc)Z)/(No. of ref lns — No. of params.)) The maximum shift/sigma ratio was 0.001.  The last least squares cycle was calculated with 83 atoms, 287 parameters and 3370 out of 4903 reflections. Weights based on counting—statistics were used. 2 is 0.000100 The weight modifier K in KF0  The intensity data were collected on a Siemens P3/PC diffractometer, using the omega scan mode. The h,k,l ranges are :—— —19 19, 0 12, 0 38 5096 No. of reflections measured 4903 No. of unique reflections 3370 No. of reflections with met > 3.Osigma(Inet) An empirical absorption correction was made  Dcalc  FW  Crystal dimensions :  Cell dimensions were obtained from 25 reflections with 2Theta angle in the range 30.00 — 40.00 degrees.  Empirical formula :  Space Group and Cell Dimensions C b 10.8752(14) a 17.1426(19) beta 90.804(9) Volume 6292.1(l3)A 3  D.1.6 X-ray Crystallographic Analysis of 2 Zr(i ) H 5 ) 4 C P ] ) [N(SiMe BH (1i Pr’ C H , 4.17  Appendix  233  D.1.6 X-ray Crystallographic Analysis of 2 Zr(1 ) H 5 ) 4 C P ] ) [N(SiMe BH (r1 Pr’ C H , 4.17 continued  Atomic  10 Parameters x,y,z and B x  Zr P1 P2 Sil Si2 N Cl C2 C3 C4 C5 C6 C7 C8 C9 dO Cli C12 C13 C14 C15 C16 C17 C18 C21 C22 C23 C24 C25 B HB1 HB2 HB3 HB4  0.61108( 3) O.55982( 9) 0.63355( 8) 0.58831( 9) 0.72058( 8) 0.64155(21) 0.5213 ( 3) 0.6489 ( 4) 0.5216 ( 3) 0.8147 ( 3) 0.7164 ( 4) 0.7254 ( 3) 0.4839 ( 4) 0.4825 ( 5) 0.4064 ( 4) 0.6388 ( 4) 0.6146 ( 5) 0.6717 ( 5) 0.6524 ( 5) 0.5872 ( 4) 0.6991 ( 4) 0.5645 ( 3) 0.5930 ( 4) 0.4843 ( 4) 0.7285 ( 4) 0.6684 ( 4) 0.6403 ( 4) 0.6799 ( 4) 0.7365 ( 3) 0.4627 ( 4) 0.491 ( 3) 0.508 ( 3) 0.434 ( 3) 0.420 ( 3)  y 0.31118( 4 0.2l150(14 0.52057(l4 0.48788(15 0.55335(15 0.4612 ( 4) 0.3529 ( 5) 0.5102 ( 7) 0.6245 ( 6) 0.4838 ( 7) 0.7129 C 6) 0.5741 ( 5) 0.0908 ( 7) —0.0037 ( 8) 0.1322 ( 8) 0.1675 ( 6) 0.1785 ( 8) 0.0368 ( 8) 0.5156 ( 7) 0.4572 ( 7) 0.6005 ( 8) 0.6473 ( 5) 0.7775 ( 6) 0.6311 ( 6) 0.1789 ( 6) 0.0957 ( 6) 0.1179 ( 6) 0.2159 ( 6) 0.2544 ( 6) 0.3106 ( 8) 0.382 ( 5) 0.252 ( 4) 0.354 ( 5) 0.246 ( 6)  z 0.152689(14) 0.08063 ( 4) 0.19895 ( 4) 0.06837 ( 4) 0.12248 ( 4) 0.11086 (11) 0.05972 (15) 0.02310 (17) 0.07138 (19) 0.10542 (19) 0.10101 (20) 0.17823 (15) 0.07280 (23) 0.10478 (25) 0.0618 ( 3) 0.04443 (17) 0.00115 (22) 0.05227 (21) 0.25340 (18) 0.27576 (18) 0.27316 (18) 0.18681 (18) 0.19446 (23) 0.2042 ( 3) 0.14958 (19) 0.15739 (19) 0.19428 (20) 0.21001 (17) 0.18292 (23) 0.16984 (23) 0.1515 (14) 0.1788 (13) 0.1927 (15) 0.1494 (17)  0 B 3.402(19) 4.70 ( 7) 4.24 ( 6) 4.44 ( 7) 4.61 ( 7) 3.61 (17) 4.8 ( 3) 7.5 ( 4) 6.4 ( 3) 6.9 ( 4) 7.6 ( 4) 4.64 (25) 8.3 ( 4) 10.3 ( 5) 11.3 ( 6) 6.6 ( 3) 9.7 ( 5) 9.4 ( 5) 8.7 ( 4) 7.6 ( 4) 8.2 ( 4) 5.6 ( 3) 7.5 ( 4) 9.1 ( 5) 5.9 ( 3) 5.9 ( 3) 6.0 ( 3) 6.2 ( 3) 6.1 ( 3) 5.0 ( 3) 5.8 (13) 4.8 (12) 6.5 (15) 8.2 (15)  0 is the Mean of the Principal Axes of the Thermal Ellipsoid B  Appendix  1.  Zr—P(1) Zr—P(2) Zr—N Zr—C(21) Zr—C(22) Zr—C(23) Zr—C(24) Zr—C(25) Zr—B Zr—HB(1) Zr—HB(2) P(1)C(1) P(1)C(7) P(1)C(10) P(2)—C(6) P(2)—C(13) p(2)C(16) Si(1)N Si(1)—C(1) Si(1)—C(2) si(1)c(3) Si(2)—N Si(2)C(4) Si(2)—C(5) Si(2)C(6) Si(2)H(4C) C(1)14(1A) C(1)—H(1B) C(2)—14(2A) C(2)—H(2B) C(2)—H(2C) C(3)H(3A) c(3)N(3B) C(3)—H(3C) C(4)—H(4A) C(4)H(48) C(4)B(4C) c(5)H(5A) C(5)—N(5B) C(5)—fl(SC) C(6)H(6A) C(6)—H(6B) C(7)—C(8) C(7)—C(9) C(7)H(7) C(7)H(9B) C(8)H(8A) C(8)—H(8B) C(8)—H(BC)  Distances  2.7933(15) 2.7849(15) 2.224(4) 2.477(5) 2.545(6) 2.573(6) .2.479(5) 2.446(5) 2.617(7) 2.19(5) 2.09(4) 1.813(6) 1.866(7) 1.898(6) 1.826(5) 1.862(6) 1.859(6) 1.714(4) 1.884(6) 1.876(6) 1.878(6) 1.726(4) 1.879(6) 1.882(7) 1.896(5) 2.2679(15) 1.009(5) 1.021(5) 0.940(7) 1.017(7) 1.066(6) 1.010(6) 1.136(7) 0.986(6) 0.969(7) 1.076(6) 0.969(6) 0.879(6) 1.028(7) 1.140(7) 1.007(5) 1.023(5) 1.491(12) 1.446(11) 1.017(8) 1.853(8) 1.001(7) 1.059(8) 1.161(10) C(12)—H(12B) C(12)—H(12C) C(13)—C(14) C(13)—C(15) C(13)—H(13) C(14)—N(14A) C(14)—H(14B) C(14)—H(14C) C(15)H(13) C(15)—H(15A) C(15)—H(15B) C(15)H(15C) C(16)C(17) C(16)—C(18) C(16)M(16) C(17)—H(17A) C(17)H(178) c(17)H(17c) C(18)—H(18A) C(18)—H(18B) C(18)H(18C) C(21)—C(22) C(21)C(25) C(21)—H(21) C(22)C(23) c(22)H(22) C(23)C(24) C(23)—H(23) C(24)—C(25) C(24)—H(24) C(25)—H(25) BHB(1) BMB(2) B—HB(3) B—HB(4) HB(1)—HB(2) H(1A)R(1B) H(2A)H(25) H(2A)—H(2C) H(2B)—H(2C) H(3A)N(3B) N(3A)—H(3C) 14(4A)—N(4B) H(4B)—H(4C) H(5A)H(5B) H(6A)H(6B) H(8A)H(8B) H(8A)—H(SC) H(8B)—H(8C) 1.117(9) 1.110(7) 1.499(9) 1.386(10) 1.042(9) 0.986(6) 0.974(7) 1.147(8) 1.848(8) 1.032(7) 1.040(6) 1.134(8) 1.519(8) 1.513(9) 1.019(6) 1.122(8) 0.970(7) 0.755(7) 1.119(8) 0.865(7) 1.184(8) 1.399(10) 1.399(10) 1.014(6) 1.363(10) 1.036(6) 1.367(10) 1.046(7) 1.406(11) 1.038(6) 1.031(6) 1.12(5) 1.04(5) 1.04(5) 1.22(6) 1.71(7) 1.63295(18) 1.36590(17) 1.62532(15) 1.66291(16) 1.64914(19) 1.59300(14) 1.55129(18) 1.56897(17) 1.47341(15) 1.63295(18) 1.46359(12) 1.63738(16) 1.68244(18) 147.66(5) 78.80(10) 89.06(17) 131.14(15) 121.96(18) 80.7(12) 89.5(13) 74.00(10) 113.10(18) 81.00(16) 81.86(17) 81.0(13) 97.2(13) 101.58(18) 133.50(22) 103.71(20) 87.6(14) 134.5(14) 54.00(21) 33.00(24) 164.8(14) 122.2(14) 33.2(3) 126.6(13) 86.5(14) 156.0(12) 119.4(14) 47.0(20) 96.79(17) 127.37(25) 116.08(20) 107.0(3) 102.8(3) 103.6(3) 99.15(17) 123.4(3) 113.58(19) 104.4(3) 103.2(3) 109.9(3)  1.126(8) 1.100(10) 1.099(9) 1.518(10) 1.551(10) 1.011(7) 1.782(7) 0.999(8) 1.158(8) 1.100(9) 0.936(7)  P(1)—Zr—P(2) p(1)..zrN P(1)—Zr—C(21) p(1)Zrc(24) P(1)ZrC(25) P(1)—Zr—HB(1) P(1)—zr—HB(2) P(2)—Zr—N P(2)—Zr—C(21) P(2)—Zr—C(24) P(2)—Zr—C(25) p(2)jr.NB(1) P(2)—Zr—HB(2) N—Zr—C(21) N—Zr—C(24) N—Zr—C(25) N—Zr—14B(1) N—Zr—HB(2) c(21)—zr—c(24) c(21)—zr—c(25) C(21)—Zr—HB(1). c(21)—zr—BB(2) C(24)—Zr—C(25) C(24)—Zr—HB(1) C(24)—zr—HB(2) C(25)—Zr—HB(1) C(25)—Zr—HB(2) HB(1)—Zr—HB(2) Zr—P(1)—C(1) Zr—P(1)—C(7) Zr—P(1)—C(10) C(1)—P(1)—c(7) C(1)—P(1)—C(10) C(7)—P(1)—C(10) Zr—P(2)—C(6) zr-P(2)—c(13) Zr—P(2)—C(16) C(6)—P(2)—C(13) C(6)—P(2)—C(16) C(13)—P(2)—C(16)  Angles  C(9)—H(9A) C(9)—H(9B) C(9)—H(9C) C(10)—C(11) c(lo)—c(12) C(10)—U(10) C(10)—H(12B) C(11)—H(11A) c(11)—N(11B) C(11)—H(11C) c(12)—H(12A)  114.5(7) 113.5(7) 114.3(5) 112.4(5) 106.0(4) 109.3(5) 106.9(6) 107.5(6) 105.2(6) 98.0(6) 109.2(7) 112.7(8) 115.8(8) 113.9(6) 108.0(7) 82.1(5) 105.5(6) 132.8(8) 113.3(8) 107.5(6) 112.9(5) 123.1(5) 99.0(4) 118.0(5) 97.3(6) 98.1(7) 129.4(6) 129.8(6) 89.2(5) 100.4(5) 87.5(5) 86.8(6) 114.8(6) 110.9(6) 97.4(6) 126.9(6) 99.9(6) 99.5(6) 116.8(4) 114.1(4)  1.71165(19) 1.50581(15) 1.47993(13) 1.46254(18) 1.66048(17) 1.66109(14) 1.70590(17) 1.58234(18) 1.37468(14) 1.70246(17) 1.64798(15)  H(9A)—c(9)—M(9c) H(9B)—C(9)—1(9C) P(1)—C(j0)—C(j1) P(1)—C(10)—C(12) P(1)—C(10)—H(10) C(11)—C(l0)—C(12) C(11)—C(10)—H(10) c(12)—C(10)—H(10) C(10)—C(11)—R(11A) c(lo)—c(11)—H(11B) C(10)—C(11)—H(11C) fl(11A)—C(11)—H(11E) N(11A)—c(11)—14(11c) H(11B)—C(11)—H(11C) C(10)—C(12)—H(12A) C(10)—C(12)—H(12B) C(10)—C(12)—H(12C) H(12A)—C(12)—H(128) H(12A)—C(12)—H(12C) H(128)—C(12)—H(12C) P(2)—C(13)—C(14) P(2)—C(13)—C(15) P(2)—C(13)—H(13) c(14)—c(13)—c(15) c(14)—c(13)—H(13) C(15)—C(13)—H(13) C(13)—C(14)—H(14A) C(13)—C(14)—H(14B) C(13)—C(14)—H(14c) H(14A)—C(14)—H(14B) B(14A)—C(14)—H(14C) H(14B)—C(14)—H(14C) C(13)—C(15)—H(15A) C(13)—C(15)—H(158) C(13)—C(15)—H(15C) N(15A)—C(15)—N(15B) H(15A)—C(15)—fl(15C) H(158)—C(15)—H(15C) P(2)—C(16)—C(17) P(2)—C(16)—C(18)  H(12A)—N(12C) H(14A)—H(14B) N(14A)—H(14C) H(14B)—H(14C) H(15A)—H(15C) H(15B).-H(15C) H(17A)’-H(178) H(17A)—H(17c) li(17B)—H(17C) H(18A)—H(1SB) H(18B)—H(18C)  Z 1 ) H 5 ) 4 C P ] ) [N(S B (1 Pr C r( H 1Me , H ’ 4.17 continued D.1.6 X-ray Crystallographic Analysis of 2  4.  -)  c  :1  Zr 2  2 H 2 0 N C, B Si  P 21/c  =  1.l8Mg.m-3, p  606.67 =  4  X  0.4lmni—l,  Z  0.40  X  0.60 1296  mm  .0.70930A, 20(max)  F(000)  0.50  45.0’  —0.430e/A’,  C4  C3  C8.  010  C15  After anisotropic refinement of all non—hydrogen atoms, methyl, formyl, and borane hydrogen atoms were located and fixed via inspection of a difference Fourier map, temperature factors being based upon the atom to which they are bonded. Borate hydrogen atoms were located and refined. Methylene and sp 2 hydrogen atoms were fixed in calculated positions (d =l.O8) 41 with temperature factors being based upon the carbon to which they are bonded. All crystallographic calculations were conducted with the PC version of the NRCVAX program package locally implemented on an IBM compatible 80486 computer.  In the last 0—map, the deepest hole was . 3 0.420e/A and the highest peak  —  The residuals are as follows :—— For significant reflections, RF 0.038, Rw 0.042 G0F 4.53 For all reflections, RF 0.038, Rw 0.042. where RF = Sum(Fo_Fc)/Sum(Fo) Rw = Sqrt[Sum(w(Fo—Fc) )/Sum(wFo )] and 2 )/(No. of ref lns 2 GoF = SqrtSum(w(Fo—Fc) No. of params.) The maximum shift/sigma ratio was 0.005.  The last least squares cycle was calculated with 90 atoms, 314 parameters and 3626 out of 4447 reflections. Weights based on counting—statistics were used. The weight modifier K in KFo 2 is 0.000004  The intensity data were collected on a Nonius CAD—4 diffractometer, using the omega scan mode. The h,k,l ranges used during structure solution and refinement are Hmin,max —14 13; Kmin,max 0 10; Lmin,max 0 29 No. of reflections measured 4680 No. of unique reflections 4447 No. of reflections with I, > 3.Osigma(I,,,) 3626 Merging R—value on intensities 0.018 Absorption corrections were made. The minimum and maximum transmission factors are 0.843 and 0.992.  D  FW  Crystal dimensions :  Cell dimensions were obtained from 24 reflections with 20 angle in the range 36.00 — 40.00 degrees.  Empirical formula  Space Group and Cell Dimensions Monoclinic, a 13.303(3) c 27.518(7) b 9.5813(7) beta 103.42(5) Volume 3411.8(12)A 3  3 C [S1Me ( P 2 1 ) •BH J), Pr H 4.23  C6  C7  Cl  D.1.7 X-ray Crystallographic Analysis of 2 Zr(1 ) H 5 ) 4 CHO){[N(SiMe2CH2PPr’2)BH (1 C (r  HB1C  HB1D  B  CP3  CP4  019  Bi  C18  Ui  •1  x  0.59612( 4) 0.68673( 9) 0.86911(10) 0.69846(10) 0.80563(11) 0.52305(22) 0.7087 ( 3) 0.4318 ( 5) 0.4185 ( 4) 0.4837 ( 7) 0.5338 ( 5) 0.5037 ( 6) 0.6127 ( 3) 0.6108 ( 4) 0.5224 ( 4) 0.6778 ( 4) 0.7936 ( 4) 0.7575 ( 5) 0.8637 ( 4) 0.7387 ( 3) 0.5652 ( 4) 0.7844 ( 4) 0.8093 ( 4) 0.9364 ( 4) 0.7767 ( 4) 0.9470 ( 5) 0.8917 ( 6) 1.0457 ( 7) 0.7898 ( 4) 0.8558 ( 6) 0.7094 ( 5) 0.6696 ( 5) 0.9545 ( 6)  y 0.85878( 5) 1.11441(11) 0.92905(15) 1.16080(13) 0.91100(14) 0.9919 ( 3) 0.9827 C 3) 0.8835 ( 6) 0.7701 ( 8) 0.6694 ( 6) 0.7264 ( 9) 0.8542 ( 9) 0.9665 ( 4) 1.2365 ( 4) 1.2977 ( 5) 1.3520 ( 5) 1.0547 ( 5) 0.9896 ( 7) 0.9551 ( 6) 1.2072 ( 4) 1.2287 ( 5) 1.2739 ( 5) 0.7158 ( 5) 0.9669 ( 6) 0.9597 ( 5) 1.0882 ( 7) 1.2176 ( 7) 1.0849 (11) 0.9284 ( 7) 0.9172 ( 8) 0.8175 ( 8) 0.6441 ( 6) 0.7647 ( 8)  z  (  0.3621 3)  (24)  0.10097  0.138626(16) 0.06067 ( 4) 0.35646 ( 5) 0.17736 ( 4) 0.23448 ( 5) 0.08702 (11) 0.18801 (12) 0.1695 ( 3) 0.14117 (22) 0.1645 ( 3) 0.2075 ( 3) 0.21052 (23) 0.06808 (15) 0.01540 (15) 0.03501 (18) —0.00019 (19) 0.03513 (18) —0.01698 (20) 0.07098 (22) 0.11764 (16) 0.17330 (18) 0.22539 (18) 0.23357 (20) 0.22802 (19) 0.29700 (16) 0.3665 ( 3) 0.3771 C 3) 0.3820 ( 5) 0.40251 (19) 0.45659 (21) 0.3927 ( 3) 19.5 6.3 9•3 10.0 5.5 7.0  10.0  9.6  4.39  3.66 3.94 3.19 8.6 7.9 12.0 12.2 11.3 321 3.49 4.43 5.1 4.07 6.7 6.0 3.32 4.7 5.6 5.9 5.4  3.33  x  1.006  0.903  1.001  H82A  NB2C  0.703 0.678  0.718 0.577  1B2S  HB1D  HB1A RB1B 881C  ( 4> ( 3)  ( 3) ( 3)  (13) (17) (19)  (14)  0.1207  0.770  0.332  0.354  0.666  0.0734  0.0846  0.1292  0.401  ( 4)  ( 5) ( 5) ( 4)  0.749  0.671 0.646 0.540  0.731  Sydrogen Parameters x,y,a and  7.9 79 7.9  5.3  3.9 7.0 9.2  (11)  ( 9> (13) (16>  3) 3)  ( (  ( ( ( ( ( 4)  4)  5) 5)  3)  9)  5)  5)  3) 3) 3) (25)  ( ( (  (21) 3)  ( (  2.594(6) 1.765(4) 1.832(4) P1—C5 1.818(5) P1—C8 1.795(4) P2—C13 1.828(5) P2—C14 1.828(7)  112.7(3) 111.3(3) 111.2(4) 120.78(23) 122.3(3) 115.5(5) 122.0(7) 117.7(7) 112.2(4) 112.5(5) 110.4(5)  111.5(4)  80.78(21) 115.11(17) 122.76(18) 122.11(20) 107.3(6) 108.8(6) 105.2(6) 110.2(6) 108.5(7) 129.48(22) 60.49(19) 116.1(3) 110.8(3) 112.6(3)  11818—Zr—Cent 94.1(11) Zr—Cl—Ni 115.2(3) P1—Cl—Hi 110.0(3) 0—Cl—Ni 116.6(4)  P1—C5—C6 Pl—C5—C7 C6—C5—C7 P1—C8—Si1 P2—C13—Si2 P2—C14—C15 P2—C14—C16 C15—C14—C16 P2—C17—C18 P2—C17—C19 C18—C17—Cl9 105.68(9) 110.30(9> 141.84(12) 121.6(10)  C3-C2-C4  111.4(3) 110.55(18) 112.93(20) 116.00(20) 108.77(21) 103.08(22) 104.81(24) 113.80(21) 111.47(21) 107.30(19) 104.9(3) 105.55(24) 113.78(23)  C17-P2B2 N—Sjl—C8 N—Sj1—C9 N—Sil—C10 C8—Sil—C9 C8—Sil—C10 C9—Sil—C10 N—Si2—C11 N—Si2—C12 N—Si2—C13 C11—Si2—C12 C11—Sj2—C13 C12—Si2—C13 0—Zr—Cent N—Zr—Cent Cl—Zr—Cent H81h—Zr—Cent  Zr—0—C1 Zr—N—Sil Zr—N—Sj2 Sii—N—Si2 Cp2—Cp1—Cp5 Cpl—Cp2—Cp3 Cp2—Cp3—C94 Cp3—Cp4—Cp5 Cpi—CpS—C94 Zr—C1—P1 Zr—Ci—0 P1—C1—0 P1—C2—C3 P1—C2—C4  104.63(13) 38.73(14) 95.70(14) 110.90(21) 107.41(21) 114.15(20) 107.18(21) 108.51(20) 108.43(22) 103.9(3) 104.17(23) 117.7(3) 107.2(3) 111.5(3)  0—Zr—N 0—Zr—Cl N—Zr—Cl Cl—P1—C2 C1P1C5 C1P1C8 c2—P1—C5 C2—P1C8 C5—P1—C8 C13—P2—C14 C13—P2—C17 C13—P2—82 C14—P2—C17 C14—P2—B2  angles  Zr—Cent 2.2855(9) Zr—HB1A 2.09(4)  S11—C8 1.896(4) Sil—C9 1.868(5)  P1-Cl P1C2  Zr—HB1B 2.31(4)  C14—C16 1.283(11) C17—C18 1.546(8) C17—C19 1.487(9)  (24)  ( 3) (24)  C14—C15 1.504(10)  1.927(7) 1.731(4)  P2—82  0—Cl 1.429(5) Cpl—Cp2 1.325(10) Cpl—Cp5 1.330(11) Cp2—cp3 1.355(11) Cp3—Cp4 1.332(13) Cp4—Cp5 1.297(13) C2—C3 1.520(7) C2—C4 1.543(7) C5—C6 1.535(7) C5—C7 1.525(7)  2.573(6) 2.560(6) 2.254(4)  P2—Cl? 1.827(5)  Sil—ClO Si2—N sil—c11 Si2—C12 Si2—C13  1.878(5) 1.733(4) 1.871(5) 1.868(5) 1.906(5)  (A) and Angl.s ()  1.987(3) 2.135(3) 2.534(6) 2.527(5) 2.555(6)  Interatomic Distance.  SL1N  6) 6)  Zr—0 Zr—N Zr—Cpl Zr—Cp2 Zr—Cp3 Zr—Cp4 Zr—CpS Zr—Cl Zr—B1  Distances  (15) (18) ( 5) ( 4) ( 6) ( 6) ( 5) (21) (22)  ( (  3.334(20) 2.98 ( 5) 3.90 ( 6)  B is the Mean of the Principal Axes of the Thermal Ellipsoid  C14 C15 C16 C17 C18 C19 B1 82  C12 C13  Zr P1 P2 Sil Si2 0 N CP1 CP2 CP3 CP4 CP5 Cl C2 C3 C4 C5 C6 C7 Ca C9 ClO Cli  Atomic Parameters x,y,z and B  3 C [SiMe ( P 2 ) PrI J}, .BH H 4.23 continued  X-ray Crystallographic Analysis of 2 Zr 5 C P ) CHO){ C5H BH4 Pr H (T [N(SiM 5)(1 )(r1 i e  C’  

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