Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Group 4 complexes of an arene-bridged diamidophosphine ligand for nitrogen activation Maclachlan, Erin Alisa 2006

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-ubc_2006-317211.PDF [ 6.65MB ]
Metadata
JSON: 831-1.0062195.json
JSON-LD: 831-1.0062195-ld.json
RDF/XML (Pretty): 831-1.0062195-rdf.xml
RDF/JSON: 831-1.0062195-rdf.json
Turtle: 831-1.0062195-turtle.txt
N-Triples: 831-1.0062195-rdf-ntriples.txt
Original Record: 831-1.0062195-source.json
Full Text
831-1.0062195-fulltext.txt
Citation
831-1.0062195.ris

Full Text

Group 4 Complexes of an Arene-Bridged DiamidophosphineLigand for Nitrogen ActivationbyERIN ALISA MACLACHLANB. Sc., University of Toronto, 1999M. Sc., Massachusetts Institute of Technology, 2001A thesis submitted in partial fulfillment ofthe requirements for the degree ofDOCTOR OF PHILOSOPHYinTHE FACULTY OF GRADUATE STUDIES(CHEMISTRY)THE UNIVERSITY OF BRITISH COLUMBIASeptember 2006© Erin Alisa MacLachian, 2006AbstractMolecular nitrogen comprises about 80% of the earth’s atmosphere, but is only usedas a starling material in one industri2l rection: NH3 synthesis from N2 and H2 by the HaberBosch process. Dinitrogen is generally unreactive, however, N2 complexes of most transitionmetals and lanthanides are known,. and the challenge remains to discover metal dinitrogencomplexes that can functionalize N2. This thesis describes a new ligand, [NPN]*, itscoordination to Zr and Hf, and the use of [NPNJ*Zr complexes to transform N2.Arene-bridged diamidophosphine ligand [NPN]*Li2 ([NPNJ* = [{N-(2,4,6-Me3C6H2)(2-N-5-Me-C}PPhJ is synthesized from simple organic compounds and’PhPC12 in high yield. Zr and Hf complexes, [NPN]*MC12 (M = Zr, Hf), are prepared viaprotonolysis from [NPN]*H2,M(NMe2)4,and Me3SiC1. OrganometaDic [NPN]*MR2 (R =Me, CH2Ph, CH2SiMe3)are prepared from [NPN]*MC12 and Grignard or organ9lithiumreagents. [NPN]*ZrR2(R = CH2Ph, CH2SilVIe3)are light- and heat-sensitive, and’decomposeto cyclometalated [NPNCJ *ZrR ([NPNCJ * = [(2-MesN-5-MeC6H3)P(Ph)(2-(NC6H- ,4-CH3-6-CH2)-5-MeCH]and RH via an intramolecular a-bond metathesis mechanism;A Zr-N2 complex, {[NPN]*Zr(THF)}2(I12:rI2N),is synthesized in high yield from[NPNI*ZrC1 and 2.2 equiv. of KC8 in THF under 4 atm of N2. By single crystal X-rayanalysis, N2 has been reduced to N2 and is side-on bound to two Zr atoms. Excess Py andPMe2R (R = Me, Ph) reacts with the Zr-N2 complex to furnishN2), and { [NPN] *Zr(PMe2R)} (II-rI2:r-N2) {Zr[NPN] * }, respectively. The PMe2R adductsreact with H2 to provide with ,a newN—H bond. A new N—Si bond forms upon addition of PhSiH3 to the Py adduct to give{[NPN]*Zr(Py)}QIH)OI1]1:1]2NNSiHPh){Zr[NPN]}* in high yield. The reaction of 4,4’-dimethylbenzophenone with the THF adduct providesNNC(4-MeC6H4)2)with a new N=C bond, and benzophenone imine reacts with the Pyadduct to generate {[NPN]*Zr(NCPh2)}2(I.I11:rIH2)with two new N—H bonds.The dilithium complex of (Ar = 4-’PrC6H)is prepared in two steps fromcommercially available reagents. PhAr[NPN]Lj2(S) (S = THF, dioxane) is similar to[p]*(5) in solution and in the solid state, and is converted toPh4r[NPN]Zr(NMe2)2viaprotonolysis. Future directions for research are also suggested.11‘I able of ContentsAbstract.iiTable of Contents iiiList of Tables viiList of Figures ixGlossary of Terms xvAcknowledgements xixDedication xxiChapter 1: Synthesis and Reactivity of Side-on Bound Dinitrogen1.1 Introduction 11.2 Side-on Coordination of N2 Prior to 1988 31.3 Side-on Coordination of N2 Since 1988 51.4 Side-on N2 Complexes of the Lanthanides 61.5 Side-on N2 Complexes of the Actinides 111.6 Side-on N2 Complexes of the Transition Metals 121.7 Reactivity of Side-on Dinitrogen Complexes 171.8 Conclusions and Scope of Thesis 251.9 References 28Chapter 2: Zirconium and Hafnium Complexes of an Arene-BridgedDiamidophosphine Ligand2.1 Introduction 332.2 Results and Discussion 392.2.1 Synthesis of a phenyl-bridged diamidophosphine [NPN]’ 392.2.2 Metathesis approach to [NPNI* 432.2.3 Synthesis of group 4 complexes of [NPN]* 472.2.4 Adducts of [NPN]*ZrCl2 532.2.5 Synthesis and structure of [NPN]*HfC12 562.2.6 Synthesis and structure of {NPN]*Hfl2 601112.3 Conclusions .622.4 Experimental 632.4.1 General experimental 632.4.2 Starting materials and reagents 642.5 References 79Chapter 3: Zirconium and Hafnium Organometallic Complexes3.1 Introduction 843.2 Results and Discussion 883.2.1 Synthesis of [NPN]*MMe2(M = Zr, Hf) 883.2.2 Synthesis and reactivity of {NPN]*M(CH2Ph) 923.2.3 Kinetics of [NPNJ*Zr(CH2Ph)zdecomposition 1003.2.4 Synthesis and reactivity of [NPN]*M(CH2SiMe3) 1043.2.5 Attempted hydrogenolysis of [NPN]*MMe2 1083.3 Conclusions 1103.4 Experimental Ill3.4.1 General experimental Ill3.4.2 Starting materials and reagents 1113.5 References 120Chapter 4: Synthesis and Structure of Zirconium Dinitrogen Complexes4.1 Introduction 1274.2 Results and Discussion 1314.2.1 Synthesis and structure of {{NPN]*Zr(THF)}2(j112:112N) 1314.2.2 Synthesis and structure of 1414.2.3 Phosphine adducts of {[NPN]*Zr}2Q.112:12N) 1474.2.4 UV-visible spectroscopy of zirconium dinitrogen complexes 1544.2.5 Attempted synthesis of a hafnium dinitrogen complex 1574.3 Conclusions 1594.4 Experimental 1604.4.1 General experimental 160iv4.4.2 Starting materials and reagents .1614.5 References 169Chapter 5: Reactivity of Zirconium Dinitrogen Complexes5.1 Introduction 1735.2 Results and Discussion 1775.2.1 Reactions of N2 complexes with H2 1775.2.2 Reaction of N2 complexes with phenylsilane 1855.2.3 Reaction of 4.1 with 4,4’-dimethylbenzophenone 1915.2.4 Reaction of 4.1 or 4.2 with (CH3)C (=O)H 1995.2.5 Reaction of 4.1 or 4.2 with benzophenone 1mm 2015.2.6 Reaction of N2 complexes with CO 2065.2.7 Reaction of N2 complexes with ethylene 2115.2.8 Reaction of 4.1 with Ph3=O 2125.3 Conclusions 2145.4 Experimental 2155.4.1 General experimental 2155.4.2 Starting materials and reagents 2165.5 References 230Chapter 6: Thesis Overview and Future Work6.1 Thesis overview 2366.2 Ongoing and Future Projects 2406.2.1 Synthesis and characterization of Ph,Mes [NPN]’ 2406.2.2 Synthesis and characterization of Ph.Arp] (Ar = 4-1PrC6H) 2476.2.3 Other reactions of ZrN2 complexes 2576.3 Conclusions 2586.4 Experimental 2595.4.1 General experimental 2595.4.2 Starting materials and reagents 2596.5 References 266VAppendix One: X-ray Crystal Structure Data 268Appendix Two: Spectroscopic Supporting Information 280viList ofTablesCaption PageTable 1.1. General bonding modes of N2 in mononuclear and dinuclear 2metal complexes.Table 1.2 A selection of side-on N2 complexes and related species for whichN-N bond lengths are known; also included are 5N NMR chemical 26shifts along with JR and Raman data, if available.Table 4.1 UV-visible absorption maxima of some Group 4 N2 complexesin toluene. 157Table A1.1. Crystal Data and Structure Refinement for [NPN]*Li2(THF)(2.72THF), [NPN]*ZrCl2(2.10) and [NPN]*ZrCl2( y) (2.13). 268Table A1.2. Crystal Data and Structure Refmement for [NPNI*Hf(NMe2)(2.14), [NPN]*HfCl2(2.15), [NPNJ*Hfl2(2.17). 269Table A1.3. Crystal Data and Structure Refinement for [NPN]*HfMe2(3.2),[NPNCJ*Zr(r2HCo s) (3.4). 270Table A1.4. Crystal Data and Structure Refinement for [NPNj*Hf(rI1CH2C6H5)(3.5), [NPNC]*Zr(CH2SiMe3)(3.7). 271Table A1.5. Crystal Data and Structure Refmement for{ [NPN]*ZrHF)}2(1i:-N (4.1), { [NPN]*Zr(Py)}2(ji-i:r-N(4.2), and { [NPN]*Zr(PMePh)}2(ii-1:r-N){Zr[NPNj * } (4.4). 272viiTable A1.6. Crystal Data and Structure Refinement for{ [NPN] *Zr(PMe3)} (ji-H)(JI-12:T-NNH) {Zr{NPN] * } (5.1),{ [NPN] *Zr(Py) } Qi-H)(i-i1:r-NNSiHPh){Zr[NPN] * } (5.3). 273Table A1.7. Crystal Data and Structure Refinement for{ [NPN] *Zr} 2Q--O) {p-r1:ri2-NNC(4-MeC6H4}(5.4),{ [NPN] *Zr(NCPh2)}(,t-ri:ri-N(5.5),{[NPN]*Zr}2(JIO) (5.6). 274Table A1.8. Crystal Data and Structure Refinement for PhMesjpN]Lj2(p.djoxane)(6.2),PhMes[NpN]H (6.3). 275Table A1.9. Crystal Data and Structure Refinement for PhAr[NpN]Lj2(pdjoxane)(Ar = 4-1PrC6H)(6.5), PhAr[NpN1Zr(NMe2(6.6). 276Table A1.1O. Crystallographic Data Collection and Structure Solution Information. 278viiiList of FiguresCaption PageFigure 2.1. Dinitrogen complexes prepared in the Fryzuk group with [PNP],[P2N] and [NPN] ancillary ligands. 35Figure 2.2. Comparison of two diarnidophospbine ligands:attributes of the —CH2SiMe bridged and arene-bridgeddiamidophospbine ligands [NPN]Li2and [NPN]*Li2. 38Figure 2.3. Arene-bridged [NP]H and {PNP]H ligands. 42Figure 2.4. 31P{1H} and7Li{1H} NMR spectra of2.7p-C4H8O)in C6D. 45Figure 2.5. ORTEP drawing of the solid-state molecular structure of[NPN]*Li2.2THF, 2.72THF. 46Figure 2.6. 300 MHz 1H NMR spectrum of 2.9 in C6D. 49Figure 2.7. 300 MHz 1H NMR spectrum of 2.10 in C6D. 51Figure 2.8. ORTEP drawing of the solid-state molecular structure of[NPN]*ZrC12,2.10. 52Figure 2.9. ORTEP drawing of the solid-state molecular structure of[NPN]*ZrC12( y), 213. 56Figure 2.10. ORTEP drawing of the solid-state molecular structure of[NPN]*Hf(NMe2),2.14. 58ixFigure 2.11. ORTEP drawing of the solid-state molecular structure of{NPN]*HfC12,2.15. 59Figure 2.12. ORTEP drawing of the solid-state molecular structure of[NPN]*Hfl 217 61Figure 3.1. 300 MHz ‘H NMR spectrum of 3.1 in C6D. 89Figure 3.2. ORTEP drawing of the solid-state molecular structure of[NPN]*HfMe2,3.2. 91Figure 3.3. 400 MHz ‘H NMR spectrum of 3.4 in C6D. 94Figure 3.4. ORTEP drawing of the solid-state molecular structure of[NPNC]*Zr(12CH2Ph),3.4. 95Figure 3.5. 500 MHz ‘H NMR spectrum of 3.5 in C6D. 97Figure 3.6. ORTEP drawing of the solid-state molecular structure of[NPN]*Hf(qhCH2Ph),3.5. 98Figure 3.7. Eyring plot for the thermal decomposition of[NPN]*Zr(CH2Ph),3.3. 101Figure 3.8. ORTEP drawing of the solid-state molecular structure of[NPNC]*Zr(CH2SiMe),3.7. 107Figure 4.1. Zirconium dinitrogen complexes. 128Figure 4.2. Reactions of low-valent early transition-metal complexes with N2. 129xFigure 4.3. 500 MHz ‘H NMR spectrum of 4.1 in THF-d8. 133Figure 4.4. 40 MHz 15N{’H} NMR spectrum of4.1-ThN2in THF-d8. 136Figure 4.5. ORTEP drawing of the solid-state molecular structure of{[P\fJ*ZrHF)} 01 12:192 N2) 4.1. 138Figure 4.6. Two views of the stereochemistry around Zr in 4.1. 139Figure 4.7. Structure of {[PNP]Zr(O-2,6-Me2C6H3)}(i-i:i- . 140Figure 4.8. 500 MHz ‘H NMR spectrum of 4.2 in C6D. 142Figure 4.9. ORTEP drawing of the solid-state molecular structure of4.2. 144Figure 4.10. Two views of the stereochemistry around Zr in 4.2. 145Figure 4.11. 162 MHz 31P{’H} NMR spectrum of 4.3 in C6D. 149Figure 4.12. 162 MHz 31P{’H} NMR spectrum of 4.4 in C6D. 151Figure 4.13. ORTEP drawing of the solid-state molecular structure of{ [NPN]*Zr(PMe2Ph)}(ji-r2:r-N2){Zr[NPN] * }, 4.4. 153Figure 4.14. Two views of the stereochemistry around Zr in 4.4. 154Figure 4.15. UV-visible absorption spectrum of 4.1 in toluene. 156Figure 4.16. UV-visible absorption spectrum of 4.2 in toluene. 156xiFigure 4.17. UV-visible absorption spectrum of 4.4 in toluene. 157Figure 5.1. Formation of new N—E bonds from([P2NZr)t-:rI-N). 176Figure 5.2. 202 MHz 31P{1H} NMR spectrum of 5.1 in toluene-d8at 273 K 179Figure 5.3. ZrHZr and NNH resonances in the 500 MHz 1H NMR spectrumof 5.1 in toluene-d8at 298 K. 179Figure 5.4. Ball-and-stick model of the solid-state molecular structure of{ [NPN] *Zr(PMe3)} (ji-H) (ji-NNH) (Zr[NPN] *), 5.1. 180Figure 5.5. Projection of 5.1 down the Zr2---Zrl axis. 181Figure 5.6. 400 MHz 1H NMR spectrum of 5.3-dinC6D. 187Figure 5.7. ORTEP drawing of the solid-state molecular structure of{ [NPN] *Zr(Py) } (pt-H) (ji-NNSiH2Ph){Zr[NPN] * }, 5.3. 189Figure 5.8. Two views of the N, P, Si, and Zr atoms in 5.3. 190Figure 5.9. ORTEP drawing of the solid-state molecular structureof { [NPN] *Zr} 2(-0)(i-r1:r-NNC(4-MeC6H4),5.4. 194Figure 5.10. Two hydrazonato complexes: [(ri5-MeCH4)2Zr]Qi-ri1:ri2-NNCHPh)-(j..t-r1-NNCHPh) andCp*2U(T1MeN_NzCPh(OTf). 195Figure 5.11. Proposed mechanism for the formation of 5.4 from 4.1. 196Figure 5.12. 162 MHz 31P{1H} NMR spectrum of the yellow product (inC6D) obtained from the reaction of(CH3)C (0)H and 4.2. 200xiiFigure 5.13. ORTEP drawing of the solid-state molecular structure ofr2-NH),5.5. 204Figure 5.14. Two views of N, P, and Zr atoms in 5.5. 205Figure 5.15. 500 MHz ‘H NMR spectrum of 5.6 in C6D. 207Figure 5.16. Ball-and-stick representation of the solid-state molecular structureof {{NPN]*Zr}QiO) 5.6. 210Figure 5.17. Two views of the stereochemistry around Zr in 5.6. 211Figure 5.18. 162 MHz 31P{’H} NMR spectrum taken one hour after addition oftriphenylphosphine oxide to 4.1 in 213Figure 6.1 ORTEP drawing of the solid-state molecular structure ofPh,Mes [NPN] Li2 (p-dioxane), 6.2(p-C4H80. 243Figure 6.2 ORTEP drawing of the solid-state molecular structure ofPhMCS[-NPNIH 6.3. 245Figure 6.3 ORTEP representation of crystal packing in 6.3. 246Figure 6.4 31P{’H} and7Li{1H} NMR spectra of 6.52THF in C6D. 248Figure 6.5 ORTEP drawing of the solid-state molecular structure ofPhAr[NpN]‘-2 (p-C4H80),6.5 (b-C4H302). 250Figure 6.6 500 MHz ‘H NMR spectrum of Ph.AC{NPN]H2in C6D. 251xliiFigure 6.7 500 MHz 1H NMR spectrum of 6.6 in C6D. 252Figure 6.8 ORTEP drawing of the solid-state molecular structure ofPhAr[NPN]ZrNMe2)6.6. 254Figure 6.9 [NPN]’ ligands with 2,6-1PrC6H3[3,5-(2,6-1Pr2CH)H],and 1Pr substituents on N. 256Figure 6.10 Variations on [NPN]’ with CyP, 1PrP, and (4-CF3C6H)Nsubstituents. 256Figure 6.11 Diamidophosphine ligands with alternative bridging groups. 257Figure A2.1. 1H NMR spectra of [NPN]*H2(2.8) in toluene-d8from 300 Kto 370 K in 10 K increments. 282Figure A2.2. Plot of ln[3.3] vs. tat 338 K. 283xivGlossary of TermsA Angstrom (1O° mAnal. analysisAr aryl group (unless context indicates argon)atm atmosphereb broadBn benzyl group (-CH26H5)Bu normal butyl group (-CHC393u tertiary butyl group (-C(CH3)°C degrees Celsiuscarbon-13Calcd. calculatedcm’ reciprocal centimetres (wavenumbers)COSY correlated spectroscopyCp cyclopentadienyl group ([C5H])Cp* pentamethylcyclopentadienyl group ([C5Me])cryst crystald doubletD or deuterium2D two-dimensional6 deltaheatdd doublet of doubletsddd doublet of doublets of doubletsdeg (°) degreesdens or p densityDFT density functional theory1Gt free energy of activationenthalpy of activationxvDME dimethoxyethane (MeOCH2CHOMe)n-deuteratedentropy of activationdt doublet of tripletse or e electron(s)E elementE energyB entgegen or transEl electron impactESI electrospray ionizationESR or EPR electron spin resonance or electron paramagnetic resonanceEt ethyl group (-CH2C3)EtO ethoxide group (-OCH2CH3)Et20 diethyl etherEtOAc ethyl acetatefw formula weightg gram(s)gof goodness of fith hour(s)1H proton{1H} proton decoupledhapticity of order nHMDSO hexamethyldisioxane [(CH3)SiJ2OHMQC heteronuclear multiple quantum coherenceHMSC heteronuclear single quantum coherenceHOMO highest occupied molecular orbitalHz Hertz, seconds1I nuclear angular momentum quantum number (spin)I intensityJR infraredJAB I coupling constant between nuclei A and B over n bondsK Kelvinxvikcal kilocalorieskE Boltzmann constantkJ kilojoules7Li lithium-7LUMO lowest unoccupied molecular orbitalm mukipletmeta- position of aryl ringM metalM parent ionbridging, absorption coefficient, or microMe methyl group, (-CH3)Mes mesityl group, (-2,4,6-C6CHmg milligram(s)MHz megaHertzmm. minute(s)mL millilitre(s)mm millimetre(s)mmol millimole(s)MO molecukr orbitalmol mole(s)MS mass spectrometry(m/ mass-to-charge ratio15N nitrogen-15v stretchnm nanometre(s)NMR nuclear magnetic resonanceNOE nuclear overhauser effectNOESY nuclear overhauser enhancement spectroscopy[NPNI [PhP(CH2SiMeN h)[NPN] * [{N-(2,4,6-Me3C6H)(2-N-5-MeC63}2PPh]ortho- position of aryl ringORTEP Oakridge Thermal Ellipsoid Plotting Programxviipara- position of aryl ringphosphorus-31Ph phenyl group (-C6H5)[PNP] [(R2PCHSiMe)N] R = Me, 1Pr[P2Nd {PhP(CHSiMeNSiMPPh]ppm parts per million1Pr isopropyl group (-CH(CH3)2Pr normal propyl group (-CHCPy Pyridine (C5HN)R alkyl or aryl grouprefi reflectionsRf retention factorRR resonance Ramanrt room temperatures singlets second(s)29Si silicon-29syst systemt timet tripletT temperatureTHF tetrahydrofuranTLC thin layer chromatographytmeda tetramethylethylenediamine (IVIe2NCHCHM)TMS tetramethylsilane ((CH3)4Si)Tol tolyl group (-C6H4CH3)UV-Vis ultraviolet-visibleV VoltV Volume (of unit cell)VT variable temperaturexs excessZ number of formuk units in the unit cellxviiiAcknowledgementsI would like to thank Mike Fryzuk for being an excellent supervisor. His research ideasand patient support were invaluable for the past five years.I am greatly indebted to past and present members of the Fryzuk group for creating asupportive and fun lab environment, and for all of their help showing me techniques andsharing in the group jobs. I would especially like to thank Howie Jong and Ham Spencer formany productive discussions about chemistry and crystallography, and for making the lab agreat place to be. I am very grateful to have worked alongside Lara Morello, a great labmateand friend. Thanks are due to Mike Petrella, Bruce MacKay, Scott Winston, Thorsten vonFehren, and Mike Shaver for many hours showing me the ropes. I have also had the goodfortune to supervise many talented undergraduates including Shiva Shoai, SharonnaGreenberg, Nelly Ousatiouk, and Malte Wohifart. Thanks for all of the hard work,enthusiasm, patience and new ideas.Many thanks are due to the excellent support staff at the Chemistry Department atU.B.C.: Dr. Brian Patrick, our very talented departmental crystallographer, for his patientinstruction, Minaz Lakha and Marshall Lapawa and all of the staff at the massspectrometry/microanalysis facility for their patience and skill with my finicky air-sensitivesamples. Thank you to Zorana Danilovic, Maria Ezhova, Marietta Austria, Liane Darge, andNick Burlirison for their incredible knowledge and assistance with NMR spectroscopy.Thanks very much to the excellent support staff in the mechanical and electronic/computingshop, glassblowing shop, chemistry stores, and in the front office. I am especially indebtedto Ken Love for many hours of tireless detective work in front of the Fryzuk lab’s glovebox.Thanks are due to Peter Legzdins for reading my thesis, and for support through theyears. I would also like to acknowledge Peter Wassell for allowing me to teach in theinorganic undergraduate lab — it’s been a fun five years! Thanks are also due to DougStephan at the University of Windsor for help with one of the crystal structures, and generalsupportiveness. I am very grateful to Sharonna Greenberg for editing this entire thesis, andxixfor her friendship. Thank you to Britta Boden, Tracey Stott, Amanda Gallant, MeghanDureen, and Carolyn Moorlag for friendship and support. I’m going to miss all of the goodcooking!Thank you to my parents and my brother for being such good role models, and foryour generosity, love, and support.Thank you to Mark for being such a fun and kind husband, and for curing my allergies!xxTo my parents and Mark...Chapter OneSynthesis and Reactivity of Side-on Bound Dinitrogen1.1 Introduction.tTransition-metal complexes that incorporate dinitrogen as a ligand have enjoyed a specialstatus in inorganic coordination chemistry. In contrast to isoelectronic carbon monoxide, which isreactive and binds strongly to many transition-metal ions, N2 is remarkably stable and a poor ligand.1Although more is known about CO as a ligand,2 since the first N2 complex, [Ru(NH3)5N2]wasdiscovered in 1965, a great deal has been learned about how N2 binds to a metal, and the reactivityof coordinated N2.3 Early investigations into the reactivity of coordinated N2 focused on protonationin an effort to mimic the conversion of N2 to ammonia by the enzyme nitrogenase.4’5Anotherreaction of interest is the addition of organic and inorganic electrophiles, such as acyl halides ormain group halides, to dinitrogen complexes. The displacement of N2 by better donor ligands is alsoa well known, albeit unproductive reaction of coordinated dinitrogen. Until relatively recently,research on dinitrogen coordination chemistry has focused on these three types of reactions.6In the past decade, the chemistry of coordinated clinitrogen has been reinvigorated by thediscovery of new reactions, including N—N bond cleavage, and functionalization of coordinatedN2.1’7What has also emerged as significant is the binding mode of the N2 unit to one or more metals,and the extent of activation of coordinated N2 (Table 1.1). While the end-on bonding mode is themost common for coordinated N2, in 1988, the first planar side-on bound N2 complex (Cp*2Sm)QIwas communicated.8The N2 unit is only weakly activated in this dinuclear compound, and* A version of this chapter has been published: MacLachian, E. A.; Fryzuk, M. D. O,ganometaluics 2006, 25,1530.1its reactivity is limited by the fact that N2 dissociates from the complex in solution and in the solidstate. Since 1988, however, many other side-on bound dinitrogen complexes have been discoveredand their reactivity is beginning to be investigated. What is apparent so far is that side-on N2complexes show enhanced reactivity compared to end-on N2 complexes. This chapter will focus onthe side-on bound N2 unit in metal complexes, with some discussion of the side-on—end-on bondingmode of N2 (E in Table 1.1).Table 1.1. General bonding modes of N2 in mononuclear and dinuclear metal complexes. Onlyconnectivity is indicated, along with extremes in N—N bond activation from weak activation (N—Ntriple bond) to strong activation (N—N double and single bonds).Weak Activation Strong ActivationM N N End-onMononuclearM N N M M N N M End-onDinuclearSide-onDinuclearA B C DNN\ / . Side-on End-onDinuclearM M E21.2 Side-On Coordination of N2 Prior to 1988.Orgel was the first to propose the side-on bonding mode of N2 in 1960, many years beforeany such complexes existed.9 In 1970, the side-on bonding mode was invoked when[(H3N)5Ru(14’)]Br2and [(H3N)5Ru(154)]Br2were observed to interconvert over a few hoursat room temperature by JR spectroscopy.1°Because isomerization is faster than the dissociation ofN2 from (NH3)5Ru2,the isomerization reaction is intramolecular and proceeds via a mononucleartransition state with N2 bound side-on to Ru. In 1973, the isolation of triatomic Co(ri2-N)in amatrix containing Co atoms and N2 at 10 K was reported.11 A single peak is observed in the JRspectrum when‘4N15 gas is used, indicating that a symmetric species with N2 bound side-on to Cois present. In 1978, a mononuclear side-on N2 complex was reported on the basis of evidenceobtained by EPR spectroscopy.’2Cp2ZrR(N) (R = CH(SiMe3)2is prepared from Cp2ZrR(Cl) andNa/Hg amalgam in THF under N2. There is a quintet in the EPR spectrum of the Zr(III) complexdue to coupling to two equivalent ‘4N nuclei (I = 1). Cp2ZrR(’5Nis prepared analogously and atriplet is observed in its EPR spectrum due to coupling to two equivalent 15N nuclei (I = 1/2).Unfortunately, the solid-state molecular structure of the complex has not been reported, so thisresult has not been widely acknowledged.The first crystallographically characterized side-on N2 complex, [{(C6H5Li)3N }2(OEt)]1,was reported in 1973; 1 is synthesized from a//-trans-1,5,9-cyclododecatrienenickel, [(CDT)Ni], andPhLi in Et20 under N2.13 N2 is bound side-on to a Ni—Ni bond, and end-on to four Li atoms, andthe N—N bond is elongated to 1.35 A. Similarly, {(C6H)[Na(OEt)]2i]a-Li6(OEt)4t2)},2, is prepared from PhLi, PhNa, and [(CDT)Ni] under N2.’4 The N—N bondlength is 1.359(18) A, and N2 is bound side-on to a Ni—Ni bond, and associated with Na and Liatoms (see D in Table 1.1).The numbering scheme for compounds in chapter one differs from that used in the remaining chapters.38) A(only selected core atoms are indicated for clarity)An intriguing example of N2 bound to multiple metals, a component of which has N2 boundside-on—end-on (E in Table 1.1), was reported in 1982. Upon exposure of solutions of [i-(11’:r15C5H4)](r15-CH)3Ti2 to N2 a tetranuclear compound, (,i3-r ‘:rl‘:ri2-N)[(‘q5:r5-C10H8)(ii][(11’:1-) 1,3, forms.15 N2 is coordinated side-on to one Ti, and end-on totwo Ti atoms, with an N—N bond length of 1.301 (12) A.16In an early theoretical investigation, side-on bonding of N2 was predicted to be favourable forgroup 4 complexes.17 If two group 4 transition-metal ions (e.g., Zr(H)) donate two electrons each tobridging N2, one it bond, and either a ö bond (if N2 is coordinated side-on) or a second it bond (ifN2 is coordinated end-on) will form. If more than two electrons are available from each metal, theformation of it-bonding interactions will stabilize the complex to a greater extent than the formationI 234of a bond. The authors challenged synthetic chemists to focus theii: attention on early transitionmetals in the quest for side-on complexes of N2.In the examples described above, side-on bonding of N2 is just a part of the larger picture.The side-on bound N2 may be in a larger multinuclear complex, or in some cases the complex couldnot be isolated and characterized in the solid state. In 1988, a simple unequivocal example of a side-on bound N2 complex was reported. For this reason, this date stands as a milestone in dinitrogencoordination chemistry.1.3 Side-On Coordination of N2 Since 1988.In 1988, the ftrst discrete dinuclear N2 complex in which the N—N bond is perpendicular to,and coplanar with, the M---M axis was reported. (Cp*2Sm)Q112:T12N),4, forms when toluenesolutions of Cp*2Sm are exposed to N2; 4 loses N2 under vacuum. In the solid-state molecularstructure of 4, the N—N bond length is 1.088(12) A, not elongated over free N2 (1 .0975(2) A) (see Ain Table 1.1). The Cp*2Sm units are perpendicular to each other, and the N2 unit is canted: theSm2N plane is at an angle of 62.9° to the Smi Cp* (centroid)2 plane. Although N2 appears to beneutral in this structure, the Sm—C bond lengths are typical for a Sm3 species, as are the chemicalshifts observed by 13C NMR spectroscopy. To maintain charge neutrality, N2 with an elongated N—N bond would have to be present. The discrepancy between the expected and observed N—N bondlengths has not been fully rationalized.1.088(12) A5In 1990, the second discrete dinuclear complex with side-on bound N2 was reported.18 Darkblue ({PNP]ZrCl)2ii-r: i-)({PNPJ = [(Pr2PCHSiMe2)N]), 5, is prepared from {PNP]ZrC13andNa/Hg amalgam in toluene under 4 atm of N2. The N—N bond length is 1.548(7) A, longer than theN—N single bond in hydrazine, and the longest measured to date for an N2 complex (C in Table 1.1).Since 4 and 5 were reported, many other lanthanide, actinide, and transition-metal complexes thatcontain side-on bound N2 have been discovered. In some cases, side-on N2 complexes displayinteresting new reactions for coordinated dinitrogen.Me251.4 Side-On N2 Complexes of the Lanthanides.Since the report of 4 in 1988, many other lanthanide dinitrogen compounds have beendiscovered. Tm12 reacts with two equivalents of KCp* in Et20 under N2 to giveN2), 6, in 55% yield.19 The low-resolution solid-state molecular structure of 6 shows N2 bound side-on to two Tm centres in a planar Tm2N core. Side-on N2 complexes have been synthesized with[C5H3(SiMe)2] and [C5H4(SiMe3)] ancillary ligands; N2 is moderately activated in{[C(SiMeTm}i-i:-N2) (N—N bond: 1.259(4) A), 7, and {[C5H4(SiMe3)JTm(THF)}-T12:r-N2) (N—N bond: 1.236(8) A), 8.19 N2 may be more strongly activated in these complexesbecause Tm(ll) is more reducing (—2.3 V) than Sm(II) (—1.5 V). N2 is also side-on bound in{[C5H3(SiMe)2JDy}QI-1:r)-N2),9, prepared from Dy12 and K[C5H3(SiMe)2]under N2.°Me26JMS7 (TMS = SiMe3) 8The synthesis of a neodymium N2 complex required the use of harder ligands than Cp, i.e.,[(Me3Si)2N] and (O2,6tBuC6H3),and these ligands also support Tm and Dy dinitrogen complexes.Two equivalents of NaN(SiMe3)2react with Tm12(IEHF)3 or Dy12 in THF under N2 to give{[(Me3Si)2N]Ln(THF)}(Ji-1i:1-N)Ln = Tm, 10, and Dy, 11).21 The two complexes haveanalogous solid-state structures with N—N bond lengths of 1.264(7) A and 1.305(6) A, respectively.The first example of a Nd-N2 complex, blue-green [(ArO)2Nd1HF 2(-ri:r)-N) (Ar = 2,6-tBu2C6H3),12, is prepared from Nd12 and two equivalents of KOAr in THF under N2 (N—N bond:1.242(7) A).21 The use of Tm2,Dy2, and Nd2 was significant since these species are extremelyreducing and their molecular chemistry had been relatively unexplored. A versatile route to Ln-N2complexes is via reduction of Ln[N(SiMe3)21with one equivalent of KC8 in THF under N2 to give{[(Me3Si)2N]Ln(THF)}(ji-r: i-N),13, (Ln = Tm, Dy, Nd, Gd, Ho, Th, Y, Er, Lu, La) (Equation1.1).23 The N—N bond lengths range from 1.258(3) A for Ln = Nd, to 1.305(6) A for Ln = Dy (11).1.236(8) AN(SIMe3)210 Ln = Tm 1.264(7) A11 Ln=Dy 1.305(6)A127(M N(SiMe3)2N22 Ln[N(SiMe3)}+ 2 KC8 (1.1)THF / “N(SiMe3)2(Me3Si)2NLn = Tm, Dy, Nd, Gd, Ho, Tb, Y, Er, LuAlthough KG8 reduction of Ln[N(SiMe3)21has provided many new Ln-N2 complexes, singlecrystals of {[(Me3Si)2NjLa(THF)}Q -r:r1-N),an attractive diamagnetic target, could not beobtained by this route. Crystalline La-N2 complexes could be prepared, however, with a differentancillary ligand.24 {(C5Me4H)2La(THF) } Qi-r:rj-N2), 14, and {Cp*2La(THF)}2(I1-11:T-N, 15, areobtained by KG8 reduction ofLa(C5Me4H)3and [Cp*2La][(IPh)BP],respectively. The N—N bondin 15 is 1.233(5) A, corresponding to reduction to N2, and there is a singlet at 3 569 in the ‘5NNMR spectrum. The discovery of these dinuclear side-on Ln-N2 complexes has been recentlyrecounted.25The synthesis and reduction ofLu(C5Me4H)3to give{(C5Me4H)LuHF)}(ji-ri:-N)was recently reported.261.233(5) A15The second Ln-N2 compound was reported in 1994. In one pot, [HF)2Li{{EtC(cc-C4H2N)]}Sm1(NLi),16, is prepared from {[Et2C(c-C4HN)]}Li(THF),SmC13(THF),Li metal,and N2. In the solid state, N2 is encapsulated in an Sm2Li4octahedron and the N—N bond length of1.525(4) A indicates that N2, or hydrazide, is present.27138Et EtLLi)N/L.•2 Li(THF)\/Li16 EtEtWhen [{(CH)5C(cL-C4H2N)}]is the ancillary ligand, a labile Sm2N complex, [{[(CH)5CQx-N)1}Sm[Li(THF)1301-C1)1Q ii:i-N)(THF,17, with weakly activated N2 (N—N bond:1.08(3) A) forms from the Sm(II) reduction product, [{[(CH2)5C c-C4H2N)]}Sm(THF)] [Li(THF)]2F)Qi3-C1), 18.28 Solutions of 17 readily lose N2 to regenerate18, and concentrating solutions of 18 under N2 yields the Sm3N2 complex, [{[(CH2)5C(cIL-N)JSm3Li](j.t-NLi(THF)](THF), 19. N2 is bound side-on to three Sm centres and end-onto two Li centres with an N—N bond length of 1.502(5) A.29•CILi3(THF)When dipyrrolide ancillary ligands are used, N2 is once again strongly activated by Sm(II).K2[PhC(cL-C4H3N)]reacts with SmI2HF) under N2 to give {[Ph2C(c-C4H3N)]Sm}(iN)(THF)2,20, in high yield. Diriltrogen is bound side-on to two Sm atoms and end-on to two Smatoms in an Sm4N2 coplanar array, and the N—N bond is 1.412(17) A.3° A similar Sm4N2 complex,{[(CH2)5C(c-C4H3N)]Sm}4CrHF)2Qi-N)[Na(THF)]2(TH (N—N bond: 1.371(19) A), 21, isprepared in two steps from 1,1 -dlipyrrolylcyclohexane, KR, SmCl3(I’HF) and Na/naphthalene.179Complex 21 can also be prepared by Na reduction of{[(CH)5C c-C4H3N)2]Sm}(THF5Qi-N)(N—N bond: 1.392(16) A), 22, which is prepared from [(I\4e3Si)2N]m(THF) and 1,1-dipyrrolylcyclohexane.3’[(Me3N)Si]m(THF) has proven to be a versatile Sm(II) starting material.The reaction of [Et2C(cL-C4HNH)]with [(IVIe3N)2Si]m(THF) under N2 gives [{[Et2C(c-C4H3N)]Sm}(THF)2]Qi-N)(T,23. N2 is bound side-on to two Sm atoms and end-on to twoSm atoms with an N—N bond length of 1.415(3) A.32I. 2THFPr and Nd tetrapyrrolide complexes also activate N2. Reduction of [{[Et2C(c-C4H2N)]}M(THF)] [Na(THF)2 (M = Pr, Nd) with Na/naphthalene under N2 gives the side-on N2complexes 25 (M = Pr) and 26 (M = Nd) upon crystallization. In the solid state, the complexescontain rI’:15-bound pyrrole ligands, planar M2N cores, and moderately activated N2 (N—N bonds:1.254(7) A (25), 1.234(8) A (26)).Et Et[Na(DME)3]2=2 Na(DME)Et Et1.371 (1 9) A2510Since 1988, side-on binding of N2 has been found to be ubiquitous for lanthanide complexes.The coordinated N2 unit varies from unactivated to highly activated, and there will likely be manymore reports of N2 coordination by lanthanides. Research into other aspects of lanthanidedinitrogen chemistry also continues. For example, side-on coordination of N2 to lanthanides has alsobeen observed by JR spectroscopy using matrix isolation techniques.341.5 Side-On N2 Complexes of the Actinides.The first actinide dinitrogen complex was reported in 1998. Reduction of [N3NIUC1 ([N3N]= [N(CH2CHNSi93uMe)3]with K in pentane produces [N3N]U(III), 27, upon sublimation.Under I atm of N2,{[jU}Qt-1i:rI-N),28, forms (Equation 1.2). N2 binding is reversible, and27 is regenerated under vacuum. At 1.109(7) A, the N—N bond is essentially unactivated in 28 andUV/visible spectroscopy and magnetic susceptibility measurements show that the complex containsU(III).RN22 N—U —-U’ IIIUN (1.2)1.1O9(7)A\NIL)27 28 R = tBuMeSiAlthough it may seem that the it bond of N2 is a a donor to U in 28, calculations suggest thatit back-bonding from U to N2 is the most important U—N bonding interaction.36 By DFT, the itbond of N2 is too low in energy to interact with U in the model compound, [(NH2)3(UJQi-q2:r-N), 29. The bulky [N3N] ligand may hinder U f and N2 itK orbital overlap and prevent strong11activation of N2; compared to 28, complex 29 is predicted to have a long N—N bond and short U—Nbonds.37Moderate activation of N2 by an actinide was reported in 2002.38 The N—N bond is 1.232(10)A in {Cp*U(C8H4(Si2Pri))}Q112: I2N),30, although N2 binding is reversible: starting complexCp*U(C(Si1Pr32is regenerated under vacuum. DFT calculations on the model complex [(r15-Cp)(r8-CH6)U](JI-:TNindicate that U(5f)—*N2(7t) t back-bonding is substantial.39Pr3Si’I...In contrast to Ln—N2 complexes, which generally feature N2 coordinated in the bridging sideon mode, actinide dinitrogen chemistry is diverse. Since the first report of N2 fixation by anorganouranium complex,4° a heterodinuclear U-N2 compound,41 a mononuclear end-on U-N2compound,42and N2 cleavage by U43 and Th compounds have been reported.1.6 Side-On N2 Complexes of the Transition Metals.Since the discovery18 of ({PNPJZrCl)2Ji-r:rl- ), 5, many transition-metal complexes withside-on N2 have been reported. Since the early 1990s, there has been speculation on the bindingmode of N2 in nitrogenase. Some have suggested that N2 binds side-on to Fe in the FeMo cofactor.45In 1991, an intriguing pair of N2 complexes showed how capricious N2 bonding could be.46{[(Me3Si)N]TiC1(tmeda)}(j.i-r:i-N)(tmeda =Me2NCHCHMe)(N—N bond: 1.289(9) A), 31,with end-on bound N2 forms from mixtures of (tmeda)2TiC1 and one equivalent of (Me3Si)2NLi3012under N2. When (trneda)2TiC1 reacts with 2.5 equivalents of (Me3Si)2NL1 and excess tmeda underN2, purple [Li(t eda)][{[(Me3SiN]T }Q -i:ri-N ,32, forms (anion shown below). To date, 32is unique because two molecules of N2 are bound side-on to two metals. The N—N bonds are1.379(21) A.1.379(21)A eSiMe3 N SiMe3NI IMe3SVN ‘SiMe3‘ 1”N”Me3SI-......N” \j/ \_.SIMe3I N ISMe3 SIMe332Since 1990, other [PNP]Zr-N2complexes have been discovered.47When [PNP]ZrCl2(15-CH)is reduced with Na/Hg amalgam under N2, ([PNP]ZrCp)jt-1:r-),33, forms, wherein N2 iscoordinated end-on to two Zr centres and the N—N bond length is 1.301(3) A.48 N2 may adopt theend-on bonding mode in 33 because the Cp ligand interacts with the d orbitals required for 6bonding to N2; in addition, steric factors may be important. In contrast, Na/Hg reduction of[PNP]Zr(O-2,6-MeC6H3)C1 under N2 gives { [PNP]Zr(O-2,6-Me2C6H3)}2(ji-r:T-N), 34. In thesolid state, N2 is bound side-on to two Zr atoms with a 1.528(7) A N—N bond. In contrast to 5, theZr2N core in 34 is not planar, but has a butterfly distortion (D in Table 1.1); the angle between thetwo ZrN2 planes is 156°. A peak at 751 cm’ in the KR spectrum of 34 is assigned to the symmetricv(N—N) mode, consistent with the presence of a long N—N bond. KG8 reduction of [P2N]ZrC]([P2N] = [PhP(CHSiMeNSiMeCHh]under N2 generates dark-blue([P2N]Zr),i-i:-N),35. In the solid state, one macrocycic [P2N] coordinates to each Zr atom, and N2 is bound side-onin a planar Zr2N core (N—N bond: 1.43(1) A).4913(Mes on Siomitted)Side-on N2 complexes have been implicated as intermediates in N2 cleavage by a Nbcalixarene. The end-on Nb-N2 complex, [{ptBu-caliX[4]Q4]Nb}2(J..t-1] :rl-N)][ a(diglyme) 36,reacts with Na to give{b-Bu-calix[4J-O4]Nb}(I-N)[Na(DME ],with two bridging nitrides.5°Theside-on Nb-N2 complex, [{Lb-tBu-calix[41-0]Nb}2(p.-r:r-N)][Na(DME)]4(DME), 37, a possibleintermediate in the N—N cleavage reaction, is prepared from 36 and Na.5’ In the solid-state, N2 isperpendicular to a Nb—Nb bond, and the N—N bond length is 1.403(8) A. Because the N—N bondlength is similar in 36 and 37, Na has reduced Nb(V) to Nb(IV), and the formation of a Nb—Nbbond has forced N2 to become side-on bound.1.403(8) A36 3714The side-on—end-on bonding mode of N2 is known for [NPNITa complexes ([NPN] ={PhP(CH2SiMeN h)]).52[NPNITaMe3reacts with H2 to provide ([NPN]Ta)2Qi-H)4,which reactswith N2 to give ([NPN]Ta)ji-H)Q i’:r-),38 (Equation 1.3). In 38, N2 is bound side-on to oneTa and end-on to the other Ta, and N2 is moderately activated (N—N bond: 1.319(6) A). Thisreaction is remarkable for two reasons. First, H2 is the relatively mild reducing agent that generatesthe strongly reducing tetrahyciride dimer. Thus, the use of alkali metal reductants (e.g., KG8 Na) orstrongly reducing metal starting materials (e.g., Sm(II)) is avoided. Second, this is a rare example53 ofan early transition-metal hydride complex that coordinates N2 via displacement of H2, although thisreaction is known for late transition metals.54 The JR and RR spectra of 38 confirm that N2 isstrongly activated in this complex.55PPhPI>N * / )SIMe2 N2MeS(/\/HY’ ( H2) Me2(1.3)In 2001, another early transition-metal hydride was observed to coordinate N2.56 The side-onZr-N2 complex, (rac-BpZr)2Qi-r1:r1-N)(rac-Bp = 39, issynthesized from rac-BpZrH2and N2, and rac-BpZrH2is prepared from rac-BpZrMe2and H2. TheZr2N core is planar, and the N—N bond length is 1.241(3) A.1.241(3) AMe2SiMe3Si3915An intermediate in the formation of a Zr-N2 complex was discovered in 2OO3. Twoequivalents oftBuLi add to Cp”2ZrC1 (Cp” = [1,3-(MeSi)-ri5CH])to yield [Cp”2Zr](ji-r:rì-N),40, (N—N bond: 1.47(3) A). Low temperature NMR spectroscopy shows that cyclometalated (Cp”)[l(Me3Si)-i5-CH3--SiMe2CH]Zr , 41, is an intermediate in the formation of 40. Relatedcyclometalated zirconocenes, such as (Cp*) [1 -(Me3Si)-i5-CH33-i-SiMe2CH]ZrH, do not react withN2.1.47(3)A 1.377(3)AMe3Sir1IN NSiMe340 42In 1974, the reduction of Cp*2ZrC1 to give was reported.58Witha slight modification to the ancillary ligand, from pentamethyl to tetramethyl Cp, a complex in whichN2 coordinates side-on to two Zr atoms is isolated. Thus, the reduction of(‘ri5-CMe4H)2ZrC1 withNa/Hg amalgam under N2 gives[(r5-CMe4H)Zr](i-i:rN), The N—N bond length in theplanar Zr2N array is 1.377(3) A. With one additional methyl group per zirconocene, the end-ondinitrogen complex is obtained; Cp*(r5CsMe4H)ZrI2reduction gives [Cp*(T15CsMe4H)Zr(T11N2)}(ji-i’:ri1-N,4360 The hafnium analogue of 42,[(1-CMeH)f]QI- ]:rIN ,was recentlyprepared.61 Complex 43 is the first Hf-N2 complex characterized in the solid state; 43 is prepared bythe same route used to prepare 42 and N2 is strongly activated (N—N bond: 1.423(1 1) A).Whereas most side-on N2 complexes are multinuclear, there is evidence for a metastablemononuclear side-on N2 complex of Os(II). Photolysis of single crystals of[(H3N)50s(rl’-N2)]{PF6causes partial formation of [(H3N)5Os(r2-N)]{PF6]2.2 Analysis by X-ray crystallography and JR16spectroscopy confirms the presence of side-on N2. Although the change in the N—N bond length iswithin error for the structure, the Os—N1bond lengths are 0.263(1 7) A longer than Os—N(X in thestarting material, and the N—N stretching frequency is decreased by 187 cm’. 15N NMRspectroscopy has also been used to observe transient side-on N2; intramolecular isomerization ofCp’Re(CO)(L)(15N’4(for Cp’ = Cp, L = CO; for Cp’ = Cp*, L = GO, PMe3 P(OMe)3)occurs viaan12-N intermediate,63similar to isomerization of [Ru(NH3)5N2]observed by JR spectroscopy.1°Side-on [NPN]Zr-N2complexes were recently reported;64 KG8 reduction of [NPN]ZrC12inTHF under N2 gives purple {[NPN]Zr(THF)}2(.t-r1:rl- ), 44. N2 is bound side-on to two Zratoms and N2 is strongly activated; the N—N bond length is 1.503(3) A.1.7 Reactivity of Side-On Dinitrogen Complexes.Prior to 1997, few reactions were known for side-on N2 complexes, and most involved theaddition of acid to a complex to yield hydrazine. To date, no reactions have been reported for N2bound side-on to a lanthanide or actinide; reactivity of side-on N2 has only been observed intransition-metal complexes. In 1997, the first functionalization reactions of side-on N2 were reported(Scheme 1.1). Under H2,([PN]Zr)ji-11:Tl-N)(35) transforms to(2NZr)-H)Qt-11:r),45•49 Neutron diffraction analysis confirms that new N—H and Zr—H bonds form, and that the N—Nbond length in side-on bound hydrazide (NNH) is 1.39(2) A.65 In a similar fashion, a new N—Si4417bond is produced upon addition of BuSiH3 to 35. 46,features side-on bound NNSiH2Buwith a 1.530(4) A N—N bond.49Scheme 1.1.35\\3SiBu(Mes on Si omitted)The hydrogenation and hydrosilylation of 35 represent new transformations for coordinateddinitrogen that transcend the reaction of end-on N2 complexes with electrophiles. The formation ofan N—H bond in 45 was the first report of this kind of reaction; typically, H2 displaces N2 in adinitrogen complex. DFT calculations on the addition of H2 and SiH4 to model complex([p2JZr)i-ii:t-N)([p2n] = [(PH3)2H] show that the reactions proceed via a-bondmetathesis.66 The addition of a second equivalent of H2 to give([p2n]ZrQi-i:-NH)(j. -H) ispredicted to be spontaneous, although this has not been observed experimentally.67H/45 4618Another new reaction for coordinated N2, N—C bond formation, is observed upon addition oftwo equivalents of ArC ECH (Ar = Ph, p-MeC6H4p-tBuC6H4),to 35 to give ([P2N]Zr)Qi-CCR)(ji-i2:ri-NCH=CHAr), 47, with bridging acetylide and p-Me-styryl-hydrazide (N—N bond = 1.457(4)A) groups (Equation I .4).68 The proposed mechanism involves [2 + 2] cycloaddition of ArCCHacross Zr—N to give a zirconaazacyclobutene intermediate, followed by protonolysis of the Zr—Cbond with the second ArCCH; the arylacetylide anion bridges the Zr atoms.2 H-CC-Ar(1.4)(Me’s on Si omitted)(Ar = Ph, p-MeC6H4pButC6H4)Recently, the functionalization of N2 side-on bound to a zu:conocene complex has beenobserved.59 When[(i5-CMe4H)2Zr](t-ri:rN),42, is exposed to H2,[(i5-CMe4)Zr H)](j..t-r12:-NH), 48, is produced with side-on bound hydrazide (N—N bond = 1.475(3) A) and twoterminal zirconium hydrides (Scheme 1.2). Heating 48 under H2 yields a small amount of ammonia,whereas heating 48 in the absence of H2 generates[(ri5-CMeH)Z ](,i-N)(,i-NH) 49, in which theN—N bond has been cleaved. This discovery illustrates how a small change to an ancillary ligand canimpact not only the extent of activation of coordinated N2, but also the reactivity of the N2 complex.Whereas the addition of H2 to liberates N2,58 the hydrogenation of{(rj5-CMe4H)2Zr}(,i-i:N)enables new N—H bonds to form. Predictably, [Cp*(l5eH)Zr(i’-N]Q-r’:rt’-N,43, reacts with H2 to liberate N2.6° The effect of Cp substituentson N2 activation was recounted recently.6935 4719Scheme 1.2.1 377 3 A1.475(3) A2H2Zki2Z -}\ N/T—ZrAn investigation into the mechanism of H2 addition to[(r5-CMe4H)(113Z ]2(J.I-12:T1-N), 50, shows the reaction is first order in both H2 and 50 with a large negative entropy ofactivation.70 The primary kinetic isotope effect indicates that H—H bond breaking is the rate-determining step. Together these observations are consistent with 1,2-addition of H2 across Zr—Nvia an ordered transition state with simultaneous Zr—H and N—H bond formation. New N—H bondsalso form during the reaction of [(15-CMe4H)2fj(j.t-T1:TN with H2 to give [(iiC5Me4H)2fH](ji-r:r-N)61In addition to the hydrogenation of 42, its reactivity with terminal alkynes, amines, ethanol,and water has been explored.71 When two equivalents of a terminal acetylene, R’CCH (R’ = Ph, tBu,‘Bu) are added to 42, the hydrazide complex,[(i5-CMeH)Zr( CR’)](.L-11:N),51, forms.The production of N—H bonds from a dinitrogen complex and an alkyne is a new reaction, and itstands in contrast to the N—C bond formation observed upon addition of alkynes to 3568 The solidstate molecular structure of 51 (R’ = tBu) shows that hydrazide is side-on bound with an N—N bondlength of 1.454(2) A, and one1-acetylide coordinates to each Zr.7’20Water adds to 42 to give hydrazine and(rl5-CMe4H)2Zr(OH).7’In contrast, the addition ofH20 to end-on bound produces N2 and [Cp*2ZrH1(J.tO).72 Theaddition of excess EtOH to 42 gives hydrazine and(q5-CMe4H)2Zr(OEt).71When dimethylamineor 1,1-dimethythydrazine is added to 42, the end-on hydrazide complex {(iC5Me4H)2Zr(NR”}(Ji-ii:ii’ N)(NR”2 = NMe2,NHNMe2),52, forms (Scheme 1.3), which alsoyields hydrazine upon treatment with EtOH. In these reactions, N2 in 42 acts as a strong base.Scheme 1.3.1 377 3 A 1.475(3) A)Z12HNR \.R=Ph,Bu,Bu52 HNR”2 = HNMe2,H2NNMeThe side-on_end-on dinitrogen complex, ({NPN]Ta)I-H)QI-1’:r-)(38), is remarkable inits breadth of reactivity. Some reactions involve only the bridging hydrides; for example, the reactionwith propene results in migratory insertion and the formation of a propyl complex with end-on N2,53•73 N2 in 38 is displaced by phenylacetylene, and ([NPN]Ta)2Qi-H)2(i-ri’:i’-HCCPh), 54, with a bridging bis(i-a1kylidene) is generated.74 Coordinated N2 in 38 canalso act as a nucleophile: benzyl bromide reacts with 38 to give the N-benzyl derivative21{ [NPN]Ta(Br) } Qt-H)2 1’2NN(CH26H5)} Ja[NPN]), 55,73 (N—N bond: 1.353(4) A). Thesereactions are summarized in Scheme 1.4.Scheme 1.4Ph/CHS2 HC=CHThe reactions of 38 with boranes,75 silanes,76 and alanes77 provide even more dramatictransformations. Hydride reagents with the general formula B-H (B-H = 9-BBN (HBR2), DIBAL(HAIR2), and H3SiBunl) add to 38 to give the intermediate ([NPN]TaH)(ji-F2ji-r’:rjN2E)(Ta[NPN]), 56 (Equation 1.5). The solid-state molecular structure of 56 (E = BR2 or Sil-l2Bu”)confirms the solution spectroscopic data; for E = AIBu’2,56 has only been characterized in solution.Thus, E-H addition across N2 in 38 is another new transformation of coordinated dinitrogen andrepresents a starting point for further chemistry.(—N2)Nhh-CH2BrP5522(1.5)E-HMSolutions of intermediate 56 yield different products depending on the identity of E. Uponhydroboration of 38 (E = BC8H14), the {NPN] ligand degrades and [(PhNSiMe2CHP(Ph)CHSiMe-ji-N)Ta(=NBC8H14)](j.i-N)(Ta[ PN]), 58, eventually forms;75 one equivalent of benzene, from N-Phof [NPN] and B—H, and one equivalent of H2 from the bridging hydrides are also produced. In thistransformation, N2 is cleaved and functionalized. Hydroalumination (E = A11Bu2) also results in N—N bond cleavage and functionalization, and ([NPN]TaH)Qi-H)2t ri’:ii2-NA1(ji-H)13u) a[NPN]),59 is produced;77 although [NPNJ does not degrade, one amide donor migrates from Ta to Al, andone equivalent of isobutene is eliminated. Hydrosilylation (E = H2SiBu”) produces the verysymmetrical disilylinilde species ([NPNJTa)2ji-NSiHBu’),60.76 In this case N2 has been cleavedand functionalized, and the ancillary ligand remains intact. The addition of E—H to 38 is summarizedin Scheme 1.5./E 5623Scheme 1.5.Ph BuH2S1P[Ph\N ru f\.SiMe2Me2Si’T/ Ta’ N.S1Me2eSi/ PhPh iH2BUPh60N—N bond cleavage appears to be triggered by H2 elimination from intermediate 57. DFTcalculations for E = SiH3 suggest that the transition state along the path to 57 is a species with a Ta—Ta bond, such as 61.78 Thus, the Ta—Ta bond contains the electrons required for N—N cleavage.(— H)PhSiH3Bu58Me2S1,I’h59241.8 Conclusions and Scope of Thesis.The side-on bonding mode of N2 is no longer rare, and there are approximately fiftycomplexes where the side-on mode has been confirmed using X-ray crystallography (see Table 1.2).In terms of the extent of activation of N2, there are no obvious trends. Lanthanide and transition-metal side-on N2 complexes show wide variation in the extent of activation as measured by N—Nbond distances, although in general, more transition-metal N2 complexes than lanthanide N2complexes contain long N—N bonds. What is evident is that more investigations into the reactivityof side-on N2 are warranted. In the cases described above, it is clear that new reactions have beendiscovered that seem to correlate with the bonding mode. Whether these reactions can be harnessedto produce useful organonitrogen products catalytically remains to be seen.In this thesis, a new dinitrogen complex with N2 coordinated in the side-on mode will bedescribed. In chapter two, the synthesis and characterization of a new diamidophosphine ligand ispresented. [NPN]* ([p]* = [{N-(2,4,6-Me3C6H2)(2-N-5-MeC}PPh]is an arene-bridgedanalogue of [NPN] previously reported by the Fryzuk group. Complexes of this ligand are expectedto be more robust than those of [NPN] because they lack the reactive N—Si bond and the flexible —CH2SiMe— backbone. In chapter two, the synthesis and characterization of Zr(IV) and Hf(IV)complexes of [NPN]* are described. In particular, [NPN]*ZrCl2is a useful starting material in thesynthesis of organometallic and dinitrogen complexes. In chapter three, the synthesis,characterization, and reactivity of [NPNI*Hf and [NPN]*Zr organometallic complexes is discussed.In chapter four, the synthesis of {[NPN]*Zr(THF)}2QIr12: 12N)from [NPN]*ZrCl2and KC8 inTHF is introduced. The synthesis of Py and PMe2R (R = Me, Ph) adducts of the Zr-N2 complex isalso presented. In chapter five, the reactivity of the side-on bound N2 complexes with H2, PhSiH3,4,4’-dimethylbenzophenone, (CH3)CC(0)H, benzophenone imine, and Ph3 0 is discussed.25Table 1.2. A selection of side-on N2 complexes and related species for which N-N bond lengths areknown; also included are ‘5N NMR chemical shifts along with JR and Raman data if available.N2Trans-PhN=NPhH2NNH[{(C65Li)3N }2N(OEt](1)(C6H5)[Na(OEt](Ci]NaLio(OEt)4(OE2}(2)(,13-T ’ :11‘:2—Nz) [i5:5-C10H8)(Ti5—CH)2i][(ri ‘:rl 5—C5H4)(r5-CH)3Ti](3)(4){ [PNP]ZrC1}2(i-ii:1- (5){(SilvIeTm}J.t_r1:112_N (7){[C5H4(SiMe3)]Tm}2(i-fl:11-N)(8){[( ei)2N]Tm(rHF)] }(j.i-t2:-N) (10){[(MeSi)]Dy(THF)] }Qt-r:r-N) (11){[O2,6tBuCoHNd(T F)}(-t-tii2-N) (12){[(Me3Si)2]LuçrHF)] } (jt-i:r-N) (13-Lu){[(Mei)N]Y(THF)]2(J.i-fl:ri-N (13-Y){[(Me3Si)2N]La(THF)J } (13-La){[( ei)]Nd(THF)]2(JLr2:r12N (13-Nd){[(IVIeSi)]Gd(THF)J}(j.t-i:i-N) (13-Gd){[(Me3Si)2NITb(THF)]}2(Ji-Ti:Ti-N2) (13-Tb){[( ei)]Ho(THF)] }(.L-T:-N) (13-Ho){[QvIeSi)N]Er(rHF)]}20i-Ti:fl-N2) (13-Er){[(Me3i)2]Tm(THF)] } (13-Tm)[(C5Me4J-I)2LaCI’HF)]2(J.I-Ti: i-N2)(14)[(CSMe4H)2Lu(THF)1J.t- i:Ti)(14-Lu)(15)[(THF)Li {[EtC(ct-CN)1}Sm]2(NLi4(16)[{[(CH2)sC(c-C4-1N)]4})çrHf) (17)[{[(CH5C(ct-CN)]2Sm3Li](ji-N2)[Li(THF)2J(THF) (19){[jI-Ph2C(cL-C4-13N)]Sm}4(J.-11 2:112-N)(THF)2 (20){[(CH5C(a-C4)Sm}(THF)2L-N2)[NaHF)](T ) (21){[(CHC(cL-CH3)]Sm}4(THF).5ji-N (22)[{ RtQx-C)] m}çr F)(j.i-)QrHF (23)1.301(12) 1282(’5N: 15, 161240) (IR)1.088(12)1.548(7)1.259(4)1.236(8)1.264(7)1.305(6)1.242(7)1.268(3)1.258(3)1.278(4)1.271 (4)1.264(4)1.276(5)1.261 (4)1.285(4)1.233(5)1.525(4)1.08(3)1.502(5) 29Compound 15N NMR Bond length vNN (cm-i) Reference( (A) R = Ramanvs. IR = InfraredI .0975(2)1.255g1.47”1.351.359(18)2331e1441 (p,)h1111 (P)k1314731 (R)MeNO2)a293.4b,c129.0689.7619.9i557.0513.3;= 7 Hz516495.0521569.1818202021212123232323232323232324262427291.412(17)1.371(19)1.392(1 6)1.415(3)3031313226{(OEPG)Pr}2(i-11:1i-N)[Na(DME)3]2(25) 1.254(7) 33{(OEPG)Nd}ji-:ri- 1.234(8) 33[Na(dioxane)]i xane)](26){[N3N]U}2(j.i-ri-)(28) 1.109(7) 35{Cp*U(CSH4(SijPr}(jt-r:’r-N) (30) 1.232(10) 38[Li(tmeda)2][{[(Me3i)2]T }(ii-11:1-)z (32) 1.379(21) 46([PNP]Zr(O-2,6-Me-CsH)L-1i:fl(34) 608.1 1.528(7) 751 (15N2: 48725) (R)([P2]Zr)j.i-ri:1i-N(35) 1.43(1) 775 (15N2: 49753) (R)[{ [p.tBucalix[4]04]Nb}2(.I-T1:11- -30.6 1.403(8) 51N2)][Na(DME)](DM (37)([NPN]Ta)Qi-H),.i-rl1:r- (38) -20.4, 1.319(6) 1165 (R) 52163.6 QJNN= 21.5 Hz)(rac-BpZr)2j.i-ii:r-N)(39) 1.241(3) 56[Cp”Zr](.i-:- (40) 1.47(3) 57(i5-CsMe4H)rQi-Ti (42) 621.1 1.377(3) 59[(1Mef](J.i-1i:1N 590.5 1.423(11) 61{ [NPN] Zr(THF) }2Qt-fl:1l-N2) (44) 1.503(3) 64a Liquid MeNO2is 6 361 relative to aqueous NH4 (5 M NH4O3/2M HNO3). See Mason, J. Chem.Rev. 1981, 81, 205, for more information on Nitrogen NMR.Originally 6—67.6 as referenced to N03 in a 5 M solution ofNH4O3in 2 M HNO3.Bradley, C. H.; Hawkes, G. E.; Randall, E. W.; Roberts, J. D. J. Am. Chem. Soc. 1975, 97, 1958.d Sutton, L. E. Tables ofInteratomic Distances and Configurations in Molecules and Ions Chemical Sociefy SpecialPub/ication.r, The Chemical Society: London, 1958, Vol. 11.eMecjina F. D.; Daniels, W. B.J. Chem. P,ys. 1973, 59, 6175.Ly&a, A. Collect. Czech. Chem. Commun. 1982, 47, 1112.g Allen, F. H.; Kennard, 0.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J. Chem. Soc.,Perkin Trans. 21987, 51.h Schroetter, H. W. Naturwissenschaften 1967, 54, 513.Originally referenced to NO;. Lichter, R. L.; Roberts, J. D. J. Am. Chem. Soc. 1972, 94, 4904.k Dung, J. R.; Bush, S. F.; Mercer, E. E. J. Chem. Piys. 1966, 44, 4238.‘Originally measured as 6 350.9 referenced to formaniide at 0 ppm.271.9 References.A) MacKay, B. A.; Fryzuk, M. D. Chem. Rev. 2004, 104, 385. B) Gambarotta, S.; Scott, J. Angew.Chem. mt. Ed. 2004, 43, 5298.2 Miessler, G. L.; Tart, D. A. Inorganic Chemistry, 3 ed.; Pearson Prentice Hall: New Jersey, 2004, p.467.A) Allen, A. D.; Senoff, C. V. Chem Commun. 1965, 621. B) Leigh, G. J. Can. J. Chem. 2005, 83, 277.Einsle, 0.; Tezcan, F. A.; Andrade, S. L. A.; Schnild, B.; Yoshida, M.; Howard, J. B.; Rees, D. C.Science, 2002, 297, 1696. B) Lee, S. C.; Holm, R. H. Proc. Nati. Acad. Sd. USA 2003, 100, 3595.Chatt, J.; Dilworth, J. R.; Richards, R. L. Chem. Rev. 1978, 78, 589.6 Leigh, G. J. Acc. Chem. Res. 1992, 25, 177. B) Hidai, M.; Mizobe, Y. Chem. Rev. 1995, 95, 1115.A) Shaver, M. P.; Fryzuk, M. D. Adv. Sjnth. Catal. 2003, 345, 1061. B) Fryzuk, M. D.; Johnson, S.A. Coord. Chem. Rev. 2000, 200-202, 379.8 Evans, W. J.; Ulibarri, T. A.; Ziller, J. W. J. Am. Chem. Soc. 1988, 110, 6877.Orgel, L. E. An Introduction to Transition Metal Chemistry; Methuen: London, 1960, p. 137.10 Armor, J. N.; Taube, H. J. Am. Chem. Soc. 1970, 92, 2560.11 Ozin, G. A.; Vander Voet, A. Can. J. Chem. 1973, 51, 637.12A) Gynane, M. J. S.; Jeffery, J.; Lappert, M. F. J. Chem. Soc., Chem. Commun. 1978, 34. B) Jeffery, J.;Lappert, M. F.; Riley, P. I. J. Organomet. Chem. 1979, 181, 25.13 A) Jonas, K. Angew. Chem. mt. Ed. 1973, 12, 997. B) Kruger, C.; Tsay, Y.-H. Angew. Chem. mt. Ed.1973, 12, 998.14JOnaS K.; Brauer, D. J.; Kruger, C.; Roberts, P. J.; Tsay, Y.-H. J. Am. Chem. Soc. 1976, 98, 74.15 A) Pez, G. P. J. Am. Chem. Soc. 1976, 98, 8072. B) Pez, G. P.; Kwan, S. C. J. Am. Chem. Soc. 1976,98, 8079.28Pez, G. P.; Apgar, P.; Crissey, R. K. J. Am. Chem. Soc. 1982, 104, 482.17 Lauher, J. W.; Hoffmann, R. J. Am. Chem. Soc. 1976, 98, 1729.18 Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J. J. Am. Chem. Soc. 1990, 112, 8185.19 Evans, W. J.; Allen, N. T.; Ziller, J. W. J. Am. Chem. Soc. 2001, 123, 7927.20 Evans, W. J.; Allen, N. T.; Ziller, J. W. Angew. Chem. mt. Ed. 2002, 41, 359.21 Evans, W. J.; Zuccbi, G.; Ziiler, J. W. J. Am. Chem. Soc. 2003, 125, 10.A) Bochkarev, M. N.; Fedushkin, I. L.; Fagin, A. A.; Petrovskaya, T. V.; Ziller, J. W.; BroomhallDillard, R. M. R.; Evans, W. J. Angew. Chem., mt. Ed. Eng1. 1997, 36, 133. B) Evans, W. J.; Allen, N.T.; Ziller, J. W. J. Am. Chem. Soc. 2000, 122, 11749. C) Bochkarev, M. N.; Fedushkin, I. L.; Dechert,S.; Fagin, A. A.; Schumann, H. Angew. Chem. mt. Ed. 2001, 40, 3176.23 Evans, W. J.; Lee, D. S.; Rego, D. B.; Perotti, J. M.; Kozimor, S. A.; Moore, E. K; Ziller, J. W.J. Am. Chem. Soc. 2004, 126, 14574. B) Evans, W. J.; Lee, D S.; Ziller, J. W. J. Am. Chem. Soc. 2004,126, 454.24 Evans, W. J.; Lee, D. S.; Lie, C.; Ziller, J. W. Angew. Chem. mt. Ed. 2004, 43, 5517.25 Evans, W. J.; Lee, D. S. Can. J. Chem. 2005, 83, 375.26 Evans, W. J.; Lee, D. S.; Johnston, M. A.; Zifler, J. W. Otganometallics 2005, 24, 6393.27Jubb J.; Gambarotta, S. J. Am. Chem. Soc. 1994, 116, 4477.28 Dubé, T.; Gambarotta, S.; Yap, G. P. A. Organometallics 2000, 19, 121.29 Guan, J.; Dubé, T.; Gambarotta, S.; Yap, G. P. A. Organometallics 2000, 19, 4820.30 Dubé, T.; Conoci, S.; Gambarotta, S.; Yap, G. P. A.; Vasapollo, G. Angew. Chem. mt. Ed. 1999, 38,3657.31 Dubé, T.; Ganesan, M.; Conoci, S.; Gambarotta, S.; Yap, G. P. A.; Organometallics 2000, 19, 3716.32 Bérubé, C. D.; Yazdanbakhsh, M.; Gambarotta, S.; Yap, G. P. A. Organometallics 2003, 22, 3742.29Campazzi, E.; Solari, E.; Floriani, C.; Scopeffiti, R. Chem. Commun. 1998, 2603.Green, D. W.; Reedy, G. T. J. Mol. Spec. 1979, 74, 423. B) Wilson, S. P.; Andrews, L. J. Phys.Chem. A. 1999, 103, 1311. C) Wilson, S. P.; Andrews, L.J. Phjs. Chem. A 1998, 102, 10238.A) Roussel, P.; Scott, P. j. Am. Chem. Soc. 1998, 120, 1070. B) Roussel, P.; Tinker, N. D.; Scott, P.J. A/Jo3 Compd. 1998, 271-273, 150.36 Kaitsoyannis, N.; Scott, P. Chem. Commun. 1998, 1665.Roussel, P.; Errington, W.; Kaitsoyannis, N.; Scott, P. J. O,ganomet. Chem. 2001, 635, 69.38 Cloke, F. G. N.; Hitchcock, P. B. J. Am. Chem. Soc. 2002, 124, 9352.A) Cloke, F. G. N.; Green, J. C.; Kaltsoyannis, N. O,ganometallics 2004, 23, 832. B) Kaltsoyannis, N.Chem. Soc. Rev. 2003, 32, 9.° Arnaudet, L.; Brunet-Billiau, F.; Foicher, G.; Saito, E. C. R. Acad. Sc. II B-Mec 1983, 296, 431.41 Odom, A. L.; Arnold, P. L.; Cummins, C. C. J. Am. Chem. Soc. 1998, 120, 5836.Evans, W. J.; Kozimor, S. A.; Ziller, J. W. J. Am. Chem. Soc. 2003, 125, 14264.‘ Korobkov, I.; Gambarotta, S.; Yap, G. P. A. Angew. Chem. mt. Ed. 2002, 41, 3433.Korobkov, I.; Gambarotta, S.; Yap, G. P. A. An&ew. Chem. mt. Ed. 2003, 42, 4958.“ A) Deng, I-I.; Hoffmann, R. Angew. (‘hem. ml. Ed. 1993, 32, 1062. B) Sellmann, D.; Utz, J.; Blum,N.; Heinemann, F. W. Coord. Chem. Rev. 1999, 190-192, 607. C) Cao, Z.; Zhou, Z.; Wan, H.; Zhang,Q.; Thiel, W. Inorg. Chem. 2003, 42, 6986. D) Orme-Johnson, W. H. Science 1992, 257, 1639.46 Duchateau, R.; Gambarotta, S.; Beydoun, N.; Bensimon, C. J. Am. Chem. Soc. 1991, 113, 8986.Cohen, J. D.; Fryzuk, M. D.; Loehr, T. M.; Mylvaganam, M.; Rettig, S. J. Inorg. Chem. 1998, 37, 112.48 Fryzuk, M. D.; Haddad, T. S.; Mylvaganam, M.; McConville, D. H.; Rettig, S. J. J. Am. Chem. Soc.1993, 115, 2782.Fryzuk, M. D.; Love, J. B.; Rettig, S. J.; Young, V. G. Science 1997, 275, 1445.3050 Zanotti-Gerosa, A.; Solari, E.; Giannini, L.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J. Am. Chem.Soc. 1998, 120, 437.Caselli, A.; Solari, E.; Scopelliti, R.; Floriani, C.; Re, N.; Rizzoli, C.; Chiesi-Villa, A. J. Am. Chem.Soc. 2000, 122, 3652.52 Fryzuk, M. D.;Johnson, S. A.; Rettig, S. J. J. Am. Chem. Soc. 1998, 120, 11024.de Wolf J. M.; Blaauw, R.; Meetsma, A.; Teuben, J. H.; Gyepes, R.; Varga, V.; Mach, K; Veldman,N.; Spek, AL. Organometallics 1996, 15, 4977.Bianchini, C.; Meli, A.; Perruzzini, M.; Vizza, F.; Zanobini, F. Organometallics 1989, 8, 2080. B)Chaudret, B.; Devillers, J.; Poilbianc, R. Organometallics 1985, 4, 1727.Studt, F.; MacKay, B. A.; Fi-yzuk, M. D.; Tuczek, F. J. Am. Chem. Soc. 2004, 126, 280.56 Chink, P. J.; Henling, L. M.; Bercaw, J. E. Organometallics 2001, 20, 534.57Pool, J. A.; Lobkovsky, E.; Chink, P. J. J. Am. Chem. Soc. 2003, 125, 2241.58 A) Manriquez, J. M.; Bercaw, J. E. J. Am. Chem. Soc. 1974, 96, 6229. B) Manriquez, J. M.; Sanner, R.D.; Marsh, R. E.; Bercaw, J. E. J. Am. Chem. Soc. 1976, 98, 3042.Pool, J. A.; Lobkovsky, E.; Chink, P. J. Nature 2004, 527.60Pool J. A.; Bernskoetter, W. H.; Chink, P. J. J. Am. Chem. Soc. 2004, 126, 14326.61 Bernskoetter, W. H.; Olmos, A. V.; Lobkovsky, E.; Chink, P. J. Organometallics 2006, 125, 1021.62 Fomitchev, D. V.; Bagley, K. A.; Coppens, P. J. Am. Chem. Soc. 2000, 122, 532.63 Cusaneffi, A.; Sutton, D. Organometallics 1996, 15, 1457.64Morello, L.; Yu, P.; Carmichael, C. D.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc. 2005, 127,12796.65 Basch, H.; Musaev, D. G.; Morokuma, K.; Fryzuk, M. D.; Love, J. B.; Seidel, W. W. Albinati, A.;Koetzle, T. F.; Klooster, W. T.; Mason, S. A.; Eckert, J. J. Am. Chem. Soc. 1999, 121, 523.31Basch, H.; Musaev, D. G.; Morokuma, K. J. Am. Chem. Soc. 1999, 121, 5754.67 Basch, H.; Musaev, D. G.; Morokuma, K. Oiganometallics 2000, 19, 3393.68 Morello, L.; Love, J. B.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc. 2004, 126, 9480.Pool, J. A.; Chink, P. J. Can. J. Chem. 2005, 83, 286.70 Bernskoetter, W. H.; Lobkovsky, E.; Chink, P. J. J. Am. Chem. Soc. 2005, 127, 14051.71 Bernskoetter, W. H.; Pool, J. A.; Lobkovsky, E.; Chink, P. J. J. Am. Chem. Soc. 2005, 127, 7901.72 Hillhouse, G. L.; Bercaw, J. E. J. Am. Chem. Soc. 1984, 106, 5472.Fryzuk, M. D.; Johnson, S. A.; Patrick, B. 0.; Albinati, A.; Mason, S. A.; Koetzle, T. F. J. Am.Chem. Soc. 2001, 123, 3960.Shaver, M. P.; Johnson, S. A.; Fryzuk, M. D. Can. J. Chem. 2005, 83, 65275A) MacKay, B. A.; Johnson, S. A.; Patrick, B. 0.; Fryzuk, M. D. Can.J. Chem. 2005, 83, 315. B)Fryzuk, M. D.; MacKay, B. A.;Johnson, S. A.; Patrick, B. 0. An<gew. Chem. mt. Ed. 2002,41, 3709.76 Fryzuk, M. D.; MacKay, B. A.; Patrick, B. 0. J. Am. Chem. Soc. 2003, 125, 3234.MacKay, B. A.; Patrick, B. 0.; Fryzuk, M. D. Organometallics 2005, 24, 3836.78 Studt, F.; MacKay, B. A.; Fryzuk, M. D.; Tuczek, F. Dalton Trans. 2006, 1137.32Chapter IWIOZirconium and Hafnium Complexes of an Arene-BridgedDiamidophosphine Ligand2.1 Introduction.At the core of inorganic chemistry is the idea that the structure and reactivity of ametal complex may be controlled by the ancillary ligand. With the appropriate ligand,chemists prepare metal complexes that catalyze organic transformations,1readily changeoxidation state,2 impart chiral environments for asymmetric synthesis,3 attain unusualelectronic states,4 and absorb light for energy transfer.5 Although it is not yet possible topredict reactivity based on the choice of ancillary ligand, research into ligand designcontinues guided by ideas of geometry control, donor atom properties, and substituenteffects. The importance of ligand choice was dramatically illustrated in 2004 when Chink etal. reported that the reduction of(r)5-CMe4H2Z C1 under N2 yields [(r15-CMeH)Z ]0i-12:1-N2) in which N2 bridges two Zr atoms side-on. The activated N2 in this complex reactswith H2 to yield [(r15-CMe4H)Zr(H)](ji-r,: iNwith two new N-H bonds.6 Aboutthree decades earlier, the reduction of(15-CMe)2ZrC1 was reported to yield the end-ondinuclear complex, [(i5-CMe)2Zr(ri1-N2)](ii-i:11 ‘-N2), which releases N2 when it isexposed to H2.7 The difference of one methyl group in the ancillary ligand changed theextent of activation of N2, its coordination mode to Zr, and its reactivity, thus exemplifyingA portion of this chapter has been published: MacLachian, E. A.; Fryzuk, M. D.Organometallics 2005, 24, 1112.33the challenges chemists face in trying to design ancillary ligands to change a complex in apredictable way.Research in the Fryzuk group has focused on creating multidentate ligands thatincorporate amide and phosphine donors. Chelating amidophosphine ligands allowsimultaneous coordination by amide donors, which stabilize high-valent, electron-poor metalcomplexes, and phosphine donors, which stabilize low-valent, electron-rich metalcomplexes, to a single metal centre. These ligands can facilitate nitrogen activation by earlytransition metals because they stabilize the metal complex in the presence of strong reducingagents.8 As described in chapter one, the tridentate anionic [PNP] ligand ([PNP] =[N(SilV1e2CHPR2)] R = lPr)O stabilizes one of the earliest examples of a side-on N2complex: ({PNP]ZrCl)ji-i1r- (Figure 2.1) contains the longest intact N—N bond in ametal complex (1.548(7) A).10 A side-on Zr2N complex also forms when macrocycic [P2N]([P2N] = PhP(CHSiMeNSil\4eCHh]11is the ancifiary ligand: ([P2N]Zr)Qi-r-N2) has a 1.43(1) A N—N bond, consistent with the presence of an N—N single bond, or anN2 unit, in the complex (Figure 2.1).12 In 1997, ([P2N]Zr)ji-i:-N2 became the firsttransition-metal N2 complex to react with H2 to yield new N—H bonds. Previously, theaddition of H2 to an N2 complex had only been observed to liberate N2 gas and produce ametal hydride complex.’3This [P2N] stabilized complex also reacts with silanes and terminalacetylenes to yield new N—Si and N—C bonds.1434Me2([PNP]ZrCI)2t-:r-)Figure 2.1. Dinitrogen complexes prepared in the Fryzuk group with {PNP], [P2N] and[NPN] ancillary ligands. In [P2N], the silyl methyls have been omitted for clarity.The Fryzuk group reported the synthesis of a tridentate dianionic ligand [NPNI([NPN] = [PhP(CH2SiMeN h))and its Ta complexes in 1998.15 The reaction of[NPN]TaMe3 with dihydrogen provides the Ta(IV) hydride ([NPN]Ta)2ii-H)4.Thetetrahydride reacts with N2 to yield ([NPN]Ta)2QL-H)t-111:rI-),the first dinuclearcomplex with N2 coordinated in the side-on—end-on bonding mode (see Figure 2.1). Theaddition of boranes, alanes, and silanes to this complex results in the formation of a new N—E (where E = B, Si, or Al) bond and cleavage of the N2 unit.16 Zr-N2 complexes of the[NPN] ligand have also been reported.17Although N2 coordinated to an early transition-metal amidophosphine complexundergoes a variety of transformations, ancillary ligand decomposition often accompaniesthese reactions. For example, the addition of 9-BBN to ([NPNjTa)2ji-H)-1:r-)(9-BBN = 9-borabicyclo[3.3.l]nonane) leads to N—N bond cleavage and the formation of anew B—N bond.18 However, [NPN] is degraded in the course of the reaction; benzene isMe2([P2N]Zr)Qi-1:-N) ([NPN]Ta)2i.t-H). ii1:12-N35elin-iinated from one of the two phenylamido substituents and the amido N bridges the twoTa centres as a nitride ligand (Scheme 2.1).Scheme 2.1.PhiMe29-BBNMe2SV .. SiMe2eS/Tciac4PhhPhIt should be noted here that the Fryzuk group has also explored the chemistry of —CH2SiMe— bridged [NPN] ligands with non-phenyl substituents on N and P, such asmesitylamide (MesN) and cyclohexyiphosphine (CyP), and that decomposition reactions ofthese ligands are also observed. For brevity, when there are one or two non-phenylsubstituents on [NPNJ, they are specified before the square brackets as superscripts in thefollowing order: P substituent, N substituent. In other words, the —CH2SiMe bridged[NPN] ligand with CyP and MesN substituents is abbreviated: CYMes[pMe-C6H,-H2iMe236Other undesirable reactions observed for the [NPN] ligand include the formation of aphosphinimide ([NP(=N)Nj) complex from a Ti-N2 complex,17 the migration of the Ndonor of [NPN] from Ta to Al when DIBAL-H is added to the Ta2N complex,19 theformation of cYMeS[NPN1V_NMeS and a cyclic CY.MCS[PN] compound (Me[PN] =CyP(CH2SiMe)NMes) when (cYM[NPNJV)2ICl) is reduced with KC8,2° CYPh[p](cYPh[PN1= CyP(CH2SiMeN h) elimination and cY.Ph[NpN]Nb(Cl)(=Nph) formationwhen CY.Ph[NpNINbC12is reduced with KG8,2’ as well as several other uncharacterizeddecomposition reactions of [NPN] metal complexes. Similarly, side-reactions of [PNP] and[P2N] have also been reported.22 Decomposition of these complexes may result from thereactivity of the N—Si bond and the flexibility of the —CH2SiMe backbone. [PNP], [P2N],and [NPNI ligands all contain N—Si bonds to facilitate ligand synthesis, and to reduce thebasicity of the amido nitrogen donor.Ancillary ligand decomposition is a major barrier to the development of a catalyticcycle based on N2 functionalization, and for this reason the synthesis of a more robusttridentate diamidophosphine ligand was initiated. This new ligand should mimic theelectronic and steric properties of [NPN], but lack the reactive and extremely moisture-sensitive N—Si bond. An early analogue of [NPNI contained a —CH2CH-- linker,[(PhNCH2CH)PPh].3Although Ta complexes can be prepared with this ligand, attemptsto hydrogenate or reduce these complexes give mixtures of products. The seemingly minorsubstitution of one CH2 group for SiMe2 in the backbone of [NPNJ has a dramatic impacton the reactivity of the corresponding metal complexes. One possible explanation is that thereduction of [NPNITa complexes is facilitated by the slightly electron-withdrawingsilylamide substituents, whereas the reduction of [(PhNCH2CH)P ]Ta complexes ishindered by the presence of the more electron-donating alkylamide substituents. Secondary37alkylamines are generally stronger bases than secondary silyl-substituted amines. The PI<a ofdiisopropylaniine is 36,24 whereas the P’a of bis(trimethylsilyl)amine is 26.25 An arenebridged diamidophospbine ligand may be electronically similar to [NPN], and the amidodonors are expected to have similar basicity. The pKa of diphenylarnine is 25.26 In addition,an arene-bridged diamidophosphine would lack the reactive N—Si bond of [NPN], andshould not be readily decomposed by nucleophiles or H20. An arene-bridgeddiamidophosphine ligand may also be less flexible than [NPNI, which may hinder themigration of N and P donors that is observed under some conditions. A comparison of —CH2SiMe—bridged {NPN] and an arene-bridged diamidophosphine ligand is given in Figure2.2. This chapter describes the synthesis of an arene-bridged diamidophosphine ligand andits Zr(IV) and Hf(W) complexes.Increased steric bulk at NN-Si bond is reactive andextremely moisture sensitiveN-Si & arene backbones areslightly electron withdrawingArene backbone is rigidP substituents are tunableFigure 2.2. Comparison of two diamidophosphine ligands: Attributes of the —CH2SiMebridged and arene-bridged diamidophosphine ligands [NPN]Li2and [NPN]*Li2.[N PN]L12 [NPN]*L12382.2 Results and Discussion.2.2.1 Synthesis of a phenyl-bridged diamidophosphine [NPN]’.The phenyl-bridged diamidophosphine ligand [NPN]’, ([NPN]’ = {[N-(4-MeC6H4)(2-NC6H4)J2PhP} can be prepared in three steps from (2-NHC6H4)PhP.7 The 2,2’-diaminotriphenyiphosphine starting material is synthesized by a Pd-catalyzed P—C couplingreaction from phenyiphosphine (PhPH2)and 2-iodoaniline in the presence of Pd(PPh3)4andthe water-soluble triaryiphosphine GUAP-3 (GUAP-3 = [(3-GuanN(H)C6H4)P]3HC1,Guan = C(H)(NH2)(NMe.7The N-arylation of (2-NHC6H4)PhPwith aryliodides via Cu-or Pd-catalyzed C—N coupling is unsuccessful, possibly because the chelatingdiarninophosphine substrates and products coordinate to the metal catalyst. To decrease thelikelihood of catalyst poisoning, (2-NHC6H4)PhPwas first oxidized by H20 to provide (2-NH2C6H4)PhP=O as a beige solid in high yield. The phosphine oxide reacts with 2.2equivalents of 4-iodotoluene and catalytic CuI(Phen)(PPh3)to give [N-(4-MeC6H4)(2-N(H)C6H4)]2PhP=O, 2.1, as a beige powder in high yield (Scheme 2.2).There is a singlet at 6 42.4 in the 31P{’H} NMR spectrum of 2.1, which is in the rangeexpected for a triarylphosphine oxide. The ‘H NMR spectrum of 2.1 shows a singlet at 62.26 that is assigned to two equivalent p-CH3 groups on the NTol substituents, a broadsinglet at 6 8.52 assigned to the NH groups, as well as resonances in the aromatic region thatare consistent with the proposed C symmetric compound. Overall, this two-step procedureprovides the N-arylated diaminophosphine oxide in 85% yield.• The abbreviations [NPN], [NPN]’, and [NPN]* are used to distinguish three differentdiamidophosphine ligands. PN] = [(PhNSiMe2CH)PPh] [NPNj’ = {[N-(4-MeCH4)(2-NC6H4)]2PPh},and [NPN]= { [N-(2,4,6-Me3CH(2-N-5-MeC3)]PPh}.39Scheme 2.2.2.2NH2 NH2 4 K2C03H202 cat C:I(phen)(PPh3) +3 NEt3Nl&\zE /1:;-” 2.2THF, hexanes2.4There are several drawbacks to the Cu-catalyzed route to 2.1 described above. Thereaction must be heated at a high temperature for several days before it goes to completion.Moreover, a by-product forms when the reaction is conducted on scales larger than 5 g. Theby-product, [N,N-(4-MeC6H4)2(2 NC][N-(4-MeC6H4)(2-N(H)C6H4)]PhP=0, 2.2, resultsfrom the reaction of three equivalents of p-CH3C6H4Iwith (2-NH64PhP=O.Compound 2.2 is isolated as a white microcrystalline solid after it is separated from 2.1 bysilica gel chromatography and recrystallized. It was characterized by multinuclear NMRspectroscopy, EI-MS, and microanalysis. The formation of the by-product, and thechromatography required to separate it from 2.1 decrease the yield of the desired diarylatedcompound to 55% when the reaction is carried out on a 5 g scale.2.1 2.22.340Compound 2.1 is reduced to [NPN]’H2,2.3, using standard phosphine oxide reductionconditions (see Scheme 2.2).29 The reaction is quenched with degassed H20, and 2.3 isobtained as a translucent white residue in high yield upon work-up. The singlet in the31P{’H} NMR spectrum is at 6 —30.9 for 2.3, typical for a triarylphosphine.3°In the 1H NMRspectrum, resonances diagnostic of NH (6 6.36) and ArCH3 (6 2.06) groups are present, aswell as the expected ArH resonances. Finally, addition of two equivalents of BuLi to 2.3 in amixture of hexanes and THF provides [NPN]’Li2(THF) 2.4, in 53% yield as small yellowcrystals (see Scheme 2.2). The 31P{1H} NMR spectrum of 2.4 is similar to that of[NPN]Li2(THF);15a quartet is observed at 6 —33.0 (I(7Li) = 3/2, JPLi = 41 Hz). As expected,there are a doublet and a singlet in the 7Li{’H} NMR spectrum of [NPNI’Li2CFHF),indicating that one Li ion is bound to P (6—0.35) and the other is not (6—1.72). By 1H NMRspectroscopy, two equivalents of THF are coordinated to 2.4.In addition to the problems noted above for the Cu-catalyzed arylation, there areseveral other drawbacks to the synthesis of {NPN]’ outlined above. First, the reactionrequires four steps from phenylphospbine, which is odious to prepare. The purification of2.1 is labour intensive and any impurities that remain are difficult to remove after subsequentsteps. Also, the presence of small amounts of H20 and NEt3 remaining after the work-up of2.3, which are difficult to eliminate completely from the oily residue, are incompatible withthe lithiation reaction to give 2.4. Despite many attempts to modify the conditions, multi-gram quantities of pure 2.4 could not be obtained. It was clear that a new route to arenebridged diamidophosphines was needed.In 2003, Liang and co-workers described the synthesis of arene-bridged [PNP] and[NP] ligand precursors by the reaction of an alkali metal phosphide with an aryl fluoride.41This reaction is sometimes referred to as nucleophilic phosphanylation. Steizer and coworkers prepared a series of substituted triaryiphosphines in an earlier example ofnucleophilic phosphanylation.31 The aminophosphine [NP]H ([NP]H = (2-Ph2C6H4)NH(2,6-RC3;R = Me, Pr) is synthesized by heating (2-FC64)NH(2,6-R2C6H3) and KPPh2 in dimethoxyethane (DME) to reflux for several days.32 Theaminodiphosphine [PNP]H ([PNP]H = (2-RPC64)NH, R = Ph, Pr, 1Bu, Cy) is preparedin a similar manner from (2-FC6H4)NH and two equivalents of MPR2 (M = Li, K) (FigureFollowing this report, the synthesis of an arene-bridged diaminophosphine bynucleophilic phosphanylation was attempted in the Fryzuk group. Thus, two equivalents of(2-FC6H4)NH(Ph) in DME are added to a clear red solution formed from the addition oftwo equivalents of K to PhPH2in DME, and the solution is heated to reflux for several days.In the 31P{1H} NMR spectra of aliquots taken from the reaction mixture, the peak due tostarting material disappears, and several new peaks grow in. To date, attempts to separate theproducts of this reaction for further characterization have been unsuccessful.NH‘PPh2[NP]H [PNP]HFigure 2.3. Arene-bridged [NPJH and [PNP]H.In 2004, a second route to arene-bridged aminophosphines was reported. [PNP]H([PNP]H = (2-PrP-4-MeC63)NH) is prepared in two steps. First, (4-MeC6H)2NH isbrominated to yield (2-Br-4-MeC63)NH. Addition of three equivalents of BuLi and two42equivalents of IPr2PC1 to the bis(bromoaryl)amine, followed by treatment with deoxygenatedwater yields [PNP]H (Scheme The synthesis of these proligands and theit Li andtransition-metal complexes was recently reviewed.35Scheme 2.3.Br21) 3 BuLi, 2 ‘PrPCI— AcOH 2)H0 /<[PNP]H2.2.2 Metathesis approach to [NPNJ .As an alternative to the Cu-catalyzed route described above, the synthesis of adiamidophosphine ligand by a metathesis pathway, similar to that used to prepare [PNP]H(see Scheme 2.3) was undertaken. The brominated diarylamine, (2,4,6-Me3C6H)(2-Br-4-MeC6H3)NH, 2.5, can be readily prepared from (Mes)ol)NH36and N-bromosuccinimide(NBS) in acetonitrile.37 To determine if 2.5 undergoes complete NH deprotonation andLi/Br exchange in the presence of ‘BuLi, 2.1 equivalents of t1BuLi are added to a solution of2.5 and 2.1 equivalents of tmeda (tmeda = MeNCHCHMe)in Et20 at —35 °C. Theproduct of this reaction, light yellow (2,4,6-Me36H)(2-Li-4 eCNLi(tmeda), 2.6, hasbeen characterized by ‘H and 13C {‘H} NMR spectroscopy.To form the diamidophosphine ligand [NPNI* ([p]* = {[N-(2,4,6-Me3C6H2)(2-N-5-MeC6H3)]2PPh},or a ligand bridged with a 5-MeC6H3group), 2.5 is lithiated in Et20solution (no tmeda is used) and reacted in situ with 0.48 equivalents of PhPC12 (Scheme 2.4).Upon work-up, [NPN]*Li2.(pC4HsO),2.7p-C4H8O),is obtained in 85% yield as a yellow43powder that is somewhat soluble in toluene and freely soluble in THF. Compound 2.7p-C4H802)is thermally unstable and can decompose to a brown powder over a few days in anN2-filled glovebox. Single crystals suitable for X-ray analysis of the THF adduct, 2.72THF,were grown from a concentrated solution of 2.7(p-C4H80)in benzene with a few drops ofTHF added.Scheme 2.4.1. 2 BuLI, Et20,NBS -35°C;rt,3hCH3N 2. 0.5 PhPCI2,Et20,0°C -35°C;rt,24hS = THF or dioxaneAlthough the formation of 2.7.(p-C4H80)proceeds in one pot from an easilysynthesized organic starting material and a commercially available phosphine, PhPC12 thereaction is quite sensitive to changes in certain reaction conditions. For example, a change insolvent from Et20 to THF or hexanes gives a mixture of products that does not contain aresonance attributable to 2.7 in its 31P{1H} NMR spectrum. When more than twoequivalents of “BuLi are added, 2.7 cannot be separated from a brown hexanes-solubleimpurity. Thus, determining the exact concentration of BuLi in hexanes by titration isessential. It is also important to add slightly less than 0.5 equivalents of PhPC12 dropwise,very slowly, to the solution of lithiated 2.5 at —35 ± 5 °C. Regardless of the scale of thereaction, if the PhPC12 addition is carried out over less than 2 h, a low yield of 2.7 isobtained. As yet, it is unclear why the synthesis of 2.7 is so sensitive to the conditions used,or by what mechanism the reaction proceeds.JH2.52.744Similar to other [NPN] lithium derivatives,15’20the 31P{1H} NMR spectrum of 2.7(p-C4H802)shows a quartet at 6 —35.2 (‘JPL = 40 Hz), and the7Li{1H} NMR spectrum shows adoublet at 6 —0.07 and a singlet at 6 —1.97 (Figure 2.4). The 1H NMR spectrum of 2.7(p-C4H802)in C6D (with a drop of THF added to increase solubility) is notable because foursinglets are observed in the ArCH3 region (6 2.0). The two ontho-Me groups of each MesNsubstituent are inequivalent to each other because of restricted rotation about the N—C0bond on the NMR timescale at 298 K. In addition, two singlets are observed for theinequivalent meta C—H groups on each MesN. The other resonances in the aromatic regionof the 1H NMR spectrum are consistent with the proposed C symmetric compound.6 2 -2 -6 -10(ppm) (ppm)Figure 2.4. 31P{1H} and7Li{’H} NMR spectra of 2.7(p-C4H80)in C6D.The solid-state molecular structure of 2.72THF (Figure 2.5) as determined by single-crystal X-ray diffraction shows two distinct Li environments: Lii is coordinated to Ni, N2,and P1 of [NPNj’, and 01 of THF, whereas Li2 is coordinated to Ni and N2, and 02 ofthe second coordinated THF. The P—Lu bond is 2.510(3) A, the Ui—N bonds (2.08 A) are-30 -32 -34 -36 -38 -4045the same within error, and the Lil—Ol bond is 1.908(3) A. The Li2—N bonds (2.05 A) arethe same within error, and the Li2—02 bond is 1.932(3) A. The Lil---Li2 separation is2.518(4) A. The stereochemistry at Lii is best described as distorted tetrahedral and thestereochemistry at Li2 is distorted trigonal. The remaining bond lengths and angles in the[NPN]* ligand are unremarkable. Crystallographic supporting information is in appendixone. Although spectroscopic and X-ray diffraction techniques confirmed the identity of2.72THF, several attempts to characterize this compound by microanalysis have shown it tobe low in carbon. This may be due incomplete combustion, or to the extreme air- andmoisture-sensitivity of this material.Figure 2.5. ORTEP drawing of the solid-state molecular structure of [NPN]*Li2.2THF,2.72THF (ellipsoids drawn at the 50% probability level). All hydrogen atoms, and thecarbon atoms of THF have been omitted for clarity. Selected bond lengths (A) and angles(°): P1—Lu 2.510(3), NI—Lu 2.0783), N1—Li2 2.046(4), Lil---Li2 2.518(4), 01—Lu 1.908(3),02—Li2 1.932(3), N2—Li2 2.051(3), N2—Lil 2.076(3), P1—Lil--Li2 77.01(11), N1—Li2—N2105.76(15), O1—Lil—Li2 144.07(18).46The solid-state and solution data indicate that the structures of 2.7 and[NPN]Li2THF are remarkably similar.’5 A diamond-shaped Li2N core in the solid state,and a quartet due to Li-P coupling in the 31P{1H} NMR spectrum have also been observedfor lithium diamidophospbines with other substituents at N and P.2° For example,CYMeS[NPN]LiCfHF) is structurally analogous to 2.7 with similar bond lengths and angles(N—Lu bonds average to 2.12 A, N—Li2 bonds average to 1.95 A). However, there is onlyone equivalent of THF coordinated to Li in the complex, and Li-P coupling is not detectedat ambient temperature in C6D by NMR spectroscopy for this compound.PhMeS[NPN]Li2.2(C4HSO)Ph.Me[p]2.(t’-C4H802),°and CYPh[NPN]Li2.2THF3Ball displayquartets between —30 and —38 in their 31P{’H} NMR spectra (1JPL = 18.9, 26.6, and 40.1Hz, respectively). The solid-state molecular structure of CYPh[NP]]Li2rHF) is similar tothat of 2.7.382.2.3 Synthesis of group 4 complexes of [NPN] .Dichiorozirconium complexes of [NPNI* are prepared in a three-step route from2.7(p-C4H8O). First, the lithiated ligand is protonated; then the proligand reacts withZr(NMe2)4via elimination of Me2NH to give the bis(dimethylamido)zirconium complex.Excess Me3SiC1 is added to this Zr complex to obtain [NPN]*ZrC12.To prepare theproligand [NPN]*H2,2.8, excess Me3NHC1 was stirred with 2.7(p-C4H8Oin THF (Scheme2.5). Taking the reaction mixture to dryness and extracting the product with toluene easilyremoves LiCl and Me2NH from 2.8, which is obtained as an air-stable white powder in highyield. There is a singlet at 6 —31.4 in the 31P{’H}NMR spectrum of 2.8 in C6D. The ‘HNMR spectrum acquired at 298 K shows broad singlets attributable to the oilho-Me and meta47CR groups of MesN, as well as resonances for the other ArCH3 and ArH groups, and adoublet at 6 5.88 (4J = 5 Hz) assigned to NH in the C symmetric compound. The broadsinglets seen for the MesN substituents indicate that rotation about the N—C0 bond toMesN is hindered. In the variable-temperature ‘H NMR (VT-NMR) experiment, coalescenceof the broad Me singlets is observed at 320 K. Thus, AGTO is 15.5 ± 0.3 kcal mo]*’.39 Astacked-plot of the VT-NMR spectra for 2.8 and the calculation of z\G0 are included inappendix two.[NPN]*Zr(NMe2),2.9, is synthesized by adding toluene to a 1:1 mixture of 2.8 andZr(NMe2)4.Upon work-up, 2.9 is obtained as a toluene-soluble yellow powder in high yield(Scheme 2.5). The 31P{1H} NMR spectrum of 2.9 in C6D shows a singlet at 8—11.5, and the‘H NMR spectrum (Figure 2.6) shows four singlets for the [NPN]* ArCH3groups, indicatingthat rotation about N—C50 of MesN does not occur at 298 K on the NMR timescale. Thereare two NMe2 resonances at 6 3.06 and 2.31, corresponding to two different amidomethylenvironments. Complex 2.9 appears to be a C symmetric trigonal-bipyramidal complex insolution, with one NMe2 apical and the other equatorial. Addition of THF, Py or PMe3 to2.9 in benzene produces no color change or shift in the peak in the3’P{1H} NMR spectrum,which suggests that a sixth neutral donor ligand cannot coordinate to Zr. The ‘H and31P{’H} NMR spectra of 2.9 are similar to those reported for[PhP(CH2CHNSiMe)Zr(NMe2).4°48bg4Figure 2.6. 300 MHz ‘H NMR spectrum of 2.9 in C6D.a[NPN]*ZrC12,2.10, is synthesized from 2.9 and excess Me3SiC1 in toluene and isisolated in 89% yield as a bright yellow powder (Scheme 2.5). No attempt has been made toobserve the expected by-product of the reaction, Me3SiNMe2which is likely eliminated fromthe reaction mixture upon removal of the volatiles under vacuum. A singlet at ö —2.8 isobserved in the 31P{’H} NMR spectrum of 2.10 in C6D. By 1H NMR spectroscopy (Figure2.7), 2.10 has the expected characteristics of a C, symmetric monomer, although theformulation of this complex as a C2 symmetric dimer in solution, ([NPN]*ZrCl)2IC1)cannot be ruled out based on the available evidence. In the ‘H NMR spectrum of 2.10, therebgddlbCa CCfd d eI I I I I I I I I I I I I I 1 I I I78 7O 6.07 6 5 3 249are signals due to four distinct ArCH3 groups, similar to 2.7 and 2.9, as well as the expectedArH resonances.Scheme 2.5.3 MeNHCITHF10 Me3SiCItolueneZr(NMe2)4toluene2.7S = THF or dioxaneZrCI4(THF)2toluene2.10 2.950aaaas:o7.5o6.o:o4oJo2.ol.5(ppm)Figure 2.7. 300 MHz 1H NMR spectrum of 2.10 in C6D.The ORTEP representation of the solid-state molecular structure of 2.10 is shown inFigure 2.8. The stereochemistry around Zr is distorted trigonal bipyramidal with C12 and P1apical, and NI, N2, and Cli equatorial. [NPN]” coordinates to Zr facially, and the twochlorides are cis to each other. Facial coordination of [NPN]* is not unexpected because thephosphine donor should prevent the ligand from coordinating in a meridional fashion. TheP—Zr—NI, P—Zr---N2 angles are noticeably smaller than 90° with the two amido donorsappearing to be hinged out of the equatorial plane by the arene bridge of [NPNI*. The Zr—N(average 2.07 A), Zr—Cl (average to 2.42 A), Zr—P (2.7229(8) A), and other bond lengths in2.10 are typical.41 In addition, angles about NI and N2 add to 359.25 and 359.97°,respectively, indicating that the amide N atoms are planar and sp2 hybridized.afCCbbbC fed75 7.0 6.5 6051Figure 2.8. ORTEP thawing of the solid-state molecular structure of [NPN]*ZrC12,2.10(ellipsoids at 50% probability). All hydrogen atoms and the proximal Mes substituent (exceptC have been omitted for clarity. Selected bond lengths (A) and angles (°): Zn—Ni2.060(2), Zrl—N2 2.072(2), Znl—P1 2.7229(8), Zn—Cu 2.4279(8), Znl—C12 2.4099(8), NI—Zrl—N2 113.96(9), Cl1—Zri—C12 96.23(3), N1—Zrl—Pi 72.73(7), N2—Zni—P1 70.38(7), Ni—Zrl—Cll 106.25(7), P1—Znl—Cll 178.63(3), P1—Zrl—C12 85.02(3).The synthesis of 2.10 from proligand 2.8 is an example of a protonolysis reaction.Although group 4 complexes are often prepared by a metathesis reaction between the Li,Na, or K salt of the ligand and a metal halide complex, such as ZrC14(THF)2,this reaction issometimes unselective; the desired complex may form in low yield, or be present in amixture of products from which it cannot be readily separated. Protonolysis, or the reactionof a proligand with a metal amide or alkyl compound to yield a new metal complex, and avolatile amine or alkane by-product, is used to prepare Zr complexes when the metathesiscli,c3o52route is unsuccessful.42 For example, ansa-zirconocene dichloride catalyst precursors forolefm polymerization are synthesized from substituted cyclopentadiene ligands, Zr(NMe2)4and Me3SiC1.43 When a simple metathesis reaction between 2.7(p-C4H8O)and ZrCl4HF)2is carried out, the product mixture is dark brown with several peaks in its 31P{1H} NMRspectrum. Despite extensive effort, the products of this reaction could not be separated.2.2.4 Adducts of [NPN] *ZrCI2.When one or two drops of THF are added to 20 mg of 2.10 in C6D in an NMR tube,an instant yellow to red colour change occurs. The red product, [NPN]*ZrCl(THF), 2.11,was only characterized by solution NMR spectroscopy because the compound could not beisolated. Attempts to concentrate solutions of 2.11, or to precipitate 2.11 from THF withpentane, for example, result in the precipitation of 2.10. The singlet in the 31P {‘H} NMRspectrum of 2.11 in C6D is at ö 2.7, shifted downfield relative to the starting material. In the1H NMR spectrum, there are two sharp resonances that can be assigned to free THF. Aswell, there are only four singlets in the ArCH3 region of the spectrum, and not the eightsinglets that would be predicted if 2.11 is a C1 symmetric complex. Thus, coordinated THFappears to exchange rapidly with excess THF in solution on the NMR timescale, and thisfluxionality is responsible for the apparent plane of symmetry in the product.The addition of a slight excess of PMe3 to 20 mg of 2.10 in C6D in an NMR tube alsoproduces an instant yellow to red colour change. As for 2.11, the adduct is not isolable, and[NPN]*ZrC12( Me3),2.12, could only be characterized via solution NMR spectroscopy. Thesinglet due to [NPN]* in the 31P{’H} NMR spectrum is shifted downfield from 8 —2.8 to 3.4upon addition of PMe3, and there is a broad singlet that integrates as 2P at 6 —50. The53bound and free PMe3 average to give the broad singlet at 8 —50 that shifts to 8 —59 uponaddition of another drop of PMe3 to the sample tube, closer to the value expected for freePMe3 (8 —62). The 1H NMR spectrum displays four singlets in the ArCH3 region, and thereis no resonance diagnostic of coordinated PMe3.These observations suggest that bound andfree PMe3 are exchanging rapidly on the NMR timescale in samples of 2.12.The addition of Py to a toluene solution of 2.10 produces a yellow to red-orangecolour change. Upon taking the reaction mixture to dryness, [NPN]*ZrC12( y), 2.13, isisolated. As for 2.11 and 2.12, the singlet in the 31P{1H} NMR spectrum (8 2.7) is shifteddownfield relative to the starting material 2.10. There are four ArCH3 singlets in the ‘HNMR spectrum, indicative of a plane of symmetry in the six-coordinate complex. If Pycoordinates to Zr in the equatorial plane of trigonal-bipyraniidal 2.10, then 2.13 is expectedto be a racenric mixture of C, symmetric complexes. The loss of the plane of symmetrywould give eight inequivalent ArCH3 groups that should be observable as eight singlets inthe ArCH3 region of the 1H and 13C{1H} NMR spectra. The presence of only four ArCH3singlets indicates that either a C symmetric product is present in solution, in other words Pycoordinates axially and the two chlorides are equatorial, or that 2.13 appears C5 symmetricbecause it is fluxional on the NMR timescale at 298 K. The reactions of 2.10 with THF, Pyand PMe3 are summarized in Scheme 2.6.54Scheme 2.6.PMe3vacuumThe ORTEP representation of the solid-state molecular structure of 2.13 is shown inFigure 2.9. Two nearly identical molecules of C1 symmetry are located in the asymmetric unit(only one is presented here), related by a centre of inversion to two complexes of oppositeconfiguration in the unit cell. The geometry around Zr is distorted octahedral with faciallycoordinated {NPN]*, and the chlorides are cis disposed, with one trans to P and the othercis. As was observed for 2.10, the P—Zr—Ni and P—Zr—N2 angles are less than 90°, at70.00(4) and 73.45(4)°, respectively. The Zr—N bonds (to [NPN]*) in 2.13 average to 2.14 A,slightly longer than the Zr—N bonds in 2.10 (average to 2.07 A). Similarly, the Zr—Cl bondsare longer in 2.13 (average to 2.48 A) than in 2.10 (average to 2.42 A). As expected, the Zr—N3 bond (2.3889(i6) A) to Py is longer thanthe Zr—NdO bonds.2.11 2.10Pytoluene2.122.1355Figure 2.9. ORTEP cfrawing of the solid-state molecular structure of [NPNI*ZrC12( y), 2.13(ellipsoids drawn at the 50% probability level). Hydrogen atoms and carbon atoms of theproximal Mes substituent (except C have been omitted for clarity. Selected bond lengths(A) and angles (°): Zrl—Pl 2.7131(5), Zn—NI 2.1081(15), Zrl—N2 2.1693(16), ZrI—N32.3889(16), Zn—Cu 2.4418(5), Zrl—Cl2 2.5257(5), NI—Cl 1.455(2), PI—ZrI—Nl 70.00(4),Pl—ZrI---N2 73.45(4), PI—ZrI—Cll 176.657(18), PI—Zrl—Cl2 82.142(17), Nl—ZnI---N297.87(6), Cl1—Zrl—C12 99.062(19), CI—NI—ClO 117.42(15), CI5—P1—C17 109.59(9).2.2.5 Synthesis and structure of [NPN] *HfCHafnium complexes of [NPN]* are prepared by the same protonolysis route used tosynthesize [NPN]*Zr complexes. [NPNJ*Hf(NMe2) 2.14, is synthesized from 2.8 andHf(NMe2)4in toluene solution, and is isolated as a pale yellow toluene-soluble powder inhigh yield (Scheme 2.7). The NMR spectra of 2.14 are similar to those of its Zr analogue,2.9. There is a singlet at ö —4.5 in the 31P{1H} NMR spectrum of 2.14 in C6D.The 1H NMRcli56spectrum features four singlets that are assigned to {NPN]* ArCH3 groups. Two inequivalentNMe2 groups are assigned to two singlets in the ‘H NMR spectrum in the ö 2 — 3 range.Overall, the ‘H and 13C {‘H} NMR spectra show the expected resonances for a C, symmetriccomplex.Scheme 2.7.Me21Hf(NMe2)4 3 MeS1CI2.8toluene tolueneThe ORTEP representation of the solid-state molecular structure of 2.14 is shown inFigure 2.10. The geometry about Hf is distorted trigonal bipyramidal with [NPN]*coordinated facially to Hf. Unsurprisingly, the P—Hf—Ni and P—Hf—N2 angles of 72.89(4)°and 70.71 (4)°, respectively, deviate from 900 because of strain imposed by the arene bridge.Two inequivalent NMe2 groups are apparent in the solid state: one NMe2 is apical and transto P, and the other is equatorial. The Hf—P and Hf—N bond lengths are unremarkable.2.14 2.1557Figure 2.10. ORTEP drawing of the solid-state molecular structure of [NPNJ*Hf(NMe)2,2.14 (effipsoids drawn at the 50% probability level). All hydrogen atoms have been omittedfor clarity. Selected bond lengths (A) and angles (°): Hf—P1 2.7721(5), Hf—NI 2.1366(17),Hf—N2 2.1585(16), Hf—N3 2.0632(18), Hf—N4 2.0173(17), Ni—Cl 1.449(3), P1—Hf—NI72.89(4), P1—Hf—N2 70.71(4), P1—Hf—N3 163.60(6), Pl—Hf—N4 95.11(5), Ni—Hf—N2120.91(6), N3—Hf—N4 100.92(8), CI—Ni—ClO 117.05(16), C15—P1—C17 107.82(9).[NPN]*HfC1 2.15, is isolated as a pale yellow powder in quantitative yield from thereaction of 2.14 and excess chlorotrimethylsilane in toluene (see Scheme 2.7). The NMRspectra of 2.15 in C6D are analogous to those observed for its Zr congener, 2.10: there is asinglet at 0.1 in the 31P{1H} NMR spectrum, and four singlets attributable to the ArCH3substituents in the 1H NMR spectrum. The ORTEP drawing of the solid-state molecularstructure of 2.15 is shown in Figure 2.11. The geometry around Hf is distorted trigonal58bipyramidal, with two chlorides cis-disposed; one is apical and trans to P. The structureresembles that of 2.10 with small differences in bond lengths and angles.Figure 2.11. ORTEP drawing of the solid-state molecular structure of [NPN]*HfCl2,2.15(ellipsoids drawn at the 50% probability level). All hydrogen atoms have been omitted forclarity. Selected bond lengths (A) and angles (°): Hf—PI 2.7059(9), Hf—NI 2.072(3), Hf—N22.076(3), Hf—Cu 2.3903(10), Hf—N4 2.4003(9), Ni—Cl 1.450(4), P1—Hf—Ni 73.75(8), P1—Hf—N2 71.81(9), Pl—Hf—ClI 86.14(3), Pl—Hf—C12 176.49(3), N1—Hf—N2 115.05(11), Cli—Hf—C12 97.36(4), Cl—Ni—dO 115.0(3), C15—Pi—C17 108.5(2).Similar to 2.10, compound 2.15 coordinates a sixth donor ligand (Equation 2.1).2.16, is prepared from 2.15 and Py in toluene solution, and is isolated asan orange powder in high yield. There is a singlet at ö 3.2 in the 31P{1H} NMR spectrum of2.16 in C6D.As for 2.11, 2.12, and 2.13, the P resonance of 2.16 is shifted downfield fromthat of the [NPN]*MCI2starting material. Although there are only three resonances in thecliC1259ArCH3 region of the 1H NMR spectrum, one is broad and integrates to 12H, indicating thattwo of the ArCH3 signals are coincident.Py(2.1)tolueneWhen a toluene-d8 solution of 2.16 is cooled to 220 K, a loss of symmetry in thecomplex is apparent in the 1H NMR spectrum. The presence of eight singlets in the ArCH3region is diagnostic of a C1 symmetric complex, and the ArH region also shows the expectedresonances for a C1 symmetric structure. At 360 K, there are three ArCH3 resonances (againtwo singlets appear to overlap), and the ArH resonances are consistent with a C symmetricsolution structure for 2.16. The apparent plane of symmetry in 2.16 at 298 K in solution isconsistent with either intra- or intermolecular exchange of Py.2.2.6 Synthesis and structure of [NPNI*Hfl2.[NPN]*Hfl2,2.17, is prepared from 2.15 and excess iodotrimethylsilane in toluenesolution and is isolated in quantitative yield as a yellow powder (Equation 2.2). In C6Dsolution, the 31P{1H} and 1H NMR spectra closely resemble those of 2.10 and 2.15, and areconsistent with a C symmetric trigonal-bipyramidal structure for 2.17. The ORTEPrepresentation of the solid-state molecular structure of 2.17 is shown in Figure 2.12. Thegeometry at Hf is distorted trigonal bipyramidal, and the bond lengths and angles are2.15 2.1660Figure 2.12. ORTEP drawing of the solid-state molecular structure of [NPN]*Hf12,2.17(ellipsoids drawn at the 50% probability level). All hydrogen atoms have been omitted forclarity. Selected bond lengths (A) and angles (°): Hfl—P1 2.6994(13), Hfl—N1 2.061 (4), Hfl—N2 2.068(4), Hfl—I1 2.7924(5), Hfl—12 2.7573(4), P1—Hfl—N1 70.94(12), P1—Hfl—N273.56(12), P1—Hfl—I1 177.36(3), P1—Hfl—12 86.03(3), N1—Hfl—N2 112.94(16), I1—Hfl—1296.605(14).unremarkable. In particular, at about 2.77 A, the Hf—I bond lengths agree well with othersreported in the literature.4510 Me3SiI(2.2)toluene2.15 2.17612.3 Conclusions.In this chapter, two new routes to diamidophosphine ligands are reported. Although itwas possible to prepare small quantities of [NPNj’Li2HF) using Cu-catalyzed C—Ncoupling to obtain an N,N-diarylated diaminotriphenyiphosphine ligand precursor, thepurity and overall yield provided by this route were disappointing. In contrast, the metathesismethod provides a good overall yield of [NPN]*Li2(pC4H8O)from (Mes)(2-Br-4-MeC6H3)NH, BuLi, and PhPC12 in three simple steps. This reaction has been reproducedseveral times on a large scale (up to 25 g). [NPNI*Li2has been characterized in solution andin the solid state.The metathesis route is used extensively in the Fryzuk group to make early transition-metal complexes by the reaction of [PNP]Li, [P2N]Li or [NPN]Li2 with MCl(THF).Zirconium complexes of [NPN]* cannot be prepared by salt metathesis because multiplemetal-containing products form; however, Zr and Hf complexes are prepared in high yieldby protonolysis. The proligand [NPN]*H2 is synthesized in high yield from [NPN]*LibC4H802)and NMe3HC1. Zr and Hf complexes of [NPN]* are prepared from [NPNI*H2andM(NMe2)4(M = Zr, Hf). The reaction of [NPNI*M(NMe2)with excess Me3SiC1 furnishesthe dichloride complexes, [NPN]*MC12.Overall, this three-step route provides [NPN]*ZrC12and [NPNI*HfC12 in 78% and 85% yield, respectively, from [NPNj*Li2(pC4H8O).Bothmetal dichloride complexes, as well as the hafnium bis(dimethylaniide) complex, have beencharacterized in the solid state by single-crystal X-ray diffraction. [NPN]*Hf12can also beprepared in high yield from [NPN]*HfCl2and excess TMSI.The trigonal-bipyramidal complexes, [NPN]*MC12 coordinate small neutral donorligands such as Py to give racernic mixtures of C1 symmetric six-coordinate complexes.62[NPN]*ZrC12( y) has been characterized crystallographically, and the solid-state molecularstructure is consistent with the low temperature 1H NMR data obtained for[NPN]*HfC12( y). In chapter three, [NPNI*ZrC]Q and [NPNI*HfC12 are used as startingmaterials for the preparation of organometallic complexes [NPN]*MR2 (M = Zr, Hf; R =Me, CH2Ph, and CH2SiMe3).The attempted synthesis of Zr and Hf hydride complexes from[NPN]*MMe2is also described. In chapter four, the preparation of an N2 complex from[NPNI*ZrC12,and the attempted preparation of an N2 complex from {NPNJ*Hf12 isdescribed.2.4 Experimental.2.4.1 General experimental.Unless otherwise stated, all manipulations were performed under an atmosphere ofdry, oxygen-free N2 or Ar by means of standard Schlenk or glovebox techniques (Vacuumatmospheres HE-553-2 glovebox equipped with an MO-40-2H purification system and a —35 °C freezer). Ar and N2 were dried and deoxygenated by passing the gases through acolumn containing molecular sieves and MnO. Hexanes, toluene, tetrahydrofuran, pentane,benzene, and diethyl ether were purchased anhydrous from Aldrich, sparged with N2, andpassed through columns containing activated alumina and Ridox catalyst. Dioxane was driedover sodium-benzophenone ketyl and distilled. THF-d8,C7D8, and C6D were dried overNa/K alloy under partial pressure, trap-to-trap distilled, and freeze-pump-thaw degassedthree times. ‘H, 31P{’H}, and 13C{’H} NMR spectra were recorded on a Bruker AV-300,Bruker AV-400, or Bruker AMX-500 spectrometer, operating at 300.1, 400.0, and 500.1MHz for ‘H spectra, respectively.7Li{1H} NMR spectra were recorded on the AV-400 or63AMX-500. Unless otherwise noted, all spectra were recorded at room temperature. 1H NMRspectra were referenced to residual protons in the deuterated solvent: C6D (6 7.16), CDC13(6 7.24), C7D8 (6 2.09), or THF-d8 (6 3.58). 31P{’H} NMR spectra were referenced toexternal P(OMe)3 (6 141.0 with respect to 85% H3P04 at 6 0.0). 13C{H} NMR spectra arereferenced to residual solvent: C6D (6 128.0), CDC13 (6 77.23), or THF-d8 (6 67.4).7Li{1H}NMR spectra were referenced to external LiC1 in D20/H at 6 0.0. Chemical shifts (6)listed are in ppm, and absolute values of the coupling constants are in Hz. Massspectrometry (EI-MS) and microanalyses (C, H, N) were performed at the Department ofChemistry at the University of British Columbia. Microanalysis of compound 2.17 wasperformed at CHEMISAR laboratories in Guelph, Ontario.2.4.2 Starting materials and reagents.Me3SiCl, Me3SiI, C13SiH, and PhPC12 (Aldrich) were distilled prior to use. Pyridine,triethylamine and tetramethylethylenediamine (tmeda) were dried over CaH2 and distilledprior to use. Me3NHC1 was suspended in benzene and heated to reflux in a Dean-Starkapparatus to remove water. (2-NHC6H4)PPh,3’ Hf(NMe2)4 and Zr(NMe2)43CuI(Phen)(PPh3)(Phen = ortho-phenanthroline), and (Mes)(Tol)NH36 were prepared byliterature methods. BuLi Q—1.6 M in hexanes) was titrated against benzoic acid in THF witho-phenanthroline as an indicator. All other compounds were purchased from commercialsuppliers and were used as received.[N-(4-MeC6H4)(2-N(H)]PhPO (2.1). In air, (2-NHC6H4)PPh (1.00 g, 3.42rnmol) was dissolved in hexanes (30 mL) and acetone (5 mL). H20 (30% w/v, 0.5 mL, 4.464mmol) was added dropwise to the stirred solution. The beige reaction mixture was taken todryness, and the pale brown residue so obtained was dissolved in CH21 and washed withwater (3 x 50 ml). The organic layer was separated, dried over Na2SO4, filtered, andconcentrated under vacuum to obtain (2-NHC6H4)PhP=O as a beige solid (1.03 g, 3.34mmol, 98%). (2-NHC6H4PhP=O can be recrystallized from acetone/EtOAc.‘H NMR (CDC13,200 MHz): ö 7.6 — 7.3 (m, 7H), 7.23 (t, 2H, 7 Hz), and 6.8 — 6.5 (m, 4H)(ArH), 4.51 (bs, 4H, NH).31P{’H} NMR (CDC13,81 MHz): ö = 40.8 (s).Anal. Calcd. forC18H,7N20P: C, 70.12; H, 5.56; N, 9.09; Found: C, 69.98; H, 5.62; N, 9.24.In air, (2-NHC6H4)PhPO (1.03 g, 3.34 mmol) was dissolved in xylenes (30 mL) andTHF (10 mL), and to this solution was added K2C03 (2.00 g, 14.5 mmol), 4-iodotoluene(1.64 g, 7.52 mmol), and CuI(Phen)(PPh3)(0.220 g, 0.35 mmol). The reaction mixture wasstirred and heated to reflux for 4 d at 120 °C and appeared as white and orange solidssuspended in a brown solution over the course of the reaction. Because no visible changesoccurred, the reaction was followed by TLC in 9:1 petroleum ether:EtOAc (R1 = 0.8). Thereaction mixture was cooled to rt and taken to dryness to obtain a beige residue that waspurified by silica gel chromatography (9:1 petroleum ether:EtOAc). Compound 2.1 wasisolated as a beige powder (1.42 g, 2.91 mmol, 85% relative to (2-NHC6H4)PhP).‘H NMR (CDC13,300 MHz): ö = 8.52 (bs, 2H, NH), 7.67 (dd, 2H,J = 8 Hz,JH,, = 7 Hz),7.51 (t, IH, 7 Hz), 7.44 (m, 2H), 7.29 (m, 4H), 7.03 (d, 4H, 8 Hz), 6.97 (d, 4H, 8 Hz), 6.86(dd, 2H, JHH = 8 Hz, JHP = 7 Hz) and 6.68 (t, 2H, 7 Hz) (ArH), 2.26 (s, 6H, ArCH3).31P{1H} NMR (CDC13,121 MHz): = 42.4 (s).6513C{’H} NMR (CDC13, 75 MHz): 6 = 150.9 (d, 5 Hz), 139.0, 133.8, 133.7, 133.6 (d, 2 Hz),132.4, 132.3, 132.2, 129.9, 128.7 (d, 23 Hz), 121.7, 118.0 (d, 13 Hz), 115.2 (d, 8 Hz), and113.6 (ArC), 20.9 (ArCH3).El-MS (m/): 488 (100, [M]j, 305 (50, [M — (Tol)(Ph)NH]’), 183 (40, [(Tol)(Ph)NHf).[N,N-(4-MeC6H4)2(2 NC][N-(4-MeC6H4)(2-N(H)]PhP=0 (2.2). Compound2.2 was obtained as an impurity when the synthesis of 2.1 was repeated with >5 g of (2-NH2C6H4)PPh. The off-white product was purified by silica gel chromatography (4:1petroleum ether/EtOAc, Rf = 0.8), followed by recrystallization from EtOH/H20to yieldwhite crystals.1H NMR (CDCI3,300 MHz): 6 = 7.41 (m, 4H), 7.31-7.07 (m, 9H), 7.03 (d, 2H, 8 Hz), 6.94(d, 2H, 8 Hz), and 6.71 (bd, 8H) (ArH), 6.54 (t, 1H, 7 Hz, NH), 2.27 (s, 3H) and 2.12 (s, 6H)(ArCH3).31P{’H} NMR (CDC13,121 MHz): 6 = 34.1 (s).‘3C{1H} NMR (CDC13,75 MHz): 6 = 152.2 (d, 3 Hz), 149.8 (d, 4 Hz), 145.8, 139.3, 135.4 (d,11 Hz), 133.5 (d, 2 Hz), 133.2 (d, 11 Hz), 132.6 (d, 3 Hz), 132.5, 132.4 (d, 2Hz), 132.0 (d, 10Hz), 131.4, 131.2 (d, 6 Hz), 131.1 (a, 3 Hz), 130.9, 129.7, 129.2, 128.1 (d, 12 Hz), 124.7 (d,13 Hz), 123.8, 120.4, 117.4 (d, 7 Hz), 116.4 and 115.0 (ArC), 20.9 and 20.8 (ArCH3).El-MS (m/3: 578 (100, [Mfl.Anal. Calcd. forC39H5N20P: C, 80.95; H, 6.10; N, 4.84; Found: C, 80.63; H, 6.22; N, 5.24.[N-(4-MeC6Hj(2-N(H)4)]PhP,[NPN]’H2 (2.3). Toluene (30 niL), trichiorosilane(1.2 g, 8.9 mmol), and triethylamine (0.62 g, 6.1 mmol) were added to 2.1 (1.00 g, 2.04 mrnol)66under N2 in a long Schienk tube. The translucent light brown mixture was heated to refluxovernight, whereupon an off-white suspension formed. The reaction mixture was cooled,degassed H20 (3 mL) was added, and the mixture was taken to dryness to obtain a beigeresidue. The residue was triturated with toluene (25 mL), and the solution was filteredthrough Celite. The colourless solution was taken to dryness to obtain a translucent whiteresidue (0.890 g, 1.88 mmol, 92%).‘H NMR (C6D, 300 MHz): ö = 7.48 (bd, 2H), 7.29 (m, 4H), 7.04 (m, 5H), 6.82 (d, 4H, 8Hz), 6.76 (d, 4H, 8 Hz), and 6.72 (m, 2H) (ArH), 6.36 (bs, 2H, NH), 2.06 (s, 6H, ArCH3).31P{1H} NMR (C6D,121 MHz): ö = —30.9 (s).13C{’H} NMR (C6D, 75 MHz): ö = 148.5 (bs), 140.4, 135.2 (bs), 134.6, 134.3 (bs), 131.5,130.8, 130.1, 129.2, 129.1, 122.5, 121.2, 120.5, and 116.6 (ArC), 20.7 (ArCH3).[N-(4-MeC6H4)(2-N(Li)C6H4)]2PhP2THF, [NPNJ‘Li2THF (2.4). “BuLi (1.6 M inhexanes, 1.10 mL, 1.75 mmol) was added dropwise to a solution of 2.3 (0.37 g, 0.78 mmol)in hexanes (10 mL) and THF (1 mL) at —35 °C. The yellow clear solution was shakenthoroughly to mix, and was stored overnight at —35 °C. A yellow precipitate formedovernight that was collected on a fit, washed with pentane (3 X I mL), and dried.Compound 2.4 was recrystallized from THF/toluene layered with pentane. Small yellowcrystals were collected on a frit and dried (0.26 g, 0.41 mmol, 53%).1H NMR (C6D,500 MHz): ö = 7.81 (bt, 2H, 6 Hz), 7.74 (t, 2H, 7 Hz), 7.66 (t, 2H, 7 Hz),7.38 (d, 4H, 8 Hz), 7.13 (m, 8H), 7.02 (t, 1H, 7 Hz), and 6.67 (t, 2H, 7 Hz) (ArH), 2.96 (bs,8H, THF), 2.27 (s, 6H, ArCH3), 0.87 (bs, 8H, THF).31P{’H} NMR (C6D,202 MHz): = —33.0 (q,J = 41 Hz).677Li{1H} NMR (C6D,194 MHz): 6 = —0.35 (d, iLi, fLIP = 41 Hz), —1.72 (s, iLi).(2,4,6-Me3C6)(2-Br-4 eCNH(2.5). In a flask shielded from the light and open tothe air, N-bromosuccinirnide (3.00 g, 16.9 mmol) was added portion-wise to a stirred paleyellow solution of (Mes)To1)NH (3.80 g, 16.9 mmol) in CH3N (100 mL) at 0 °C over 30mm. The brown suspension was allowed to warm to rt, and a saturated solution of NaHSO3(5 mL) was added. The beige reaction mixture was taken to dryness to obtain a beige solidthat was dissolved in a minimum amount of petroleum ether and filtered through silicapowder about 5 cm deep in a 60-rnL glass frit. The silica was rinsed with petroleum etheruntil the washings were colourless. Beige crystals were obtained when the filtrate was takento dryness. The crystals were isolated, washed with petroleum ether (2 X 5 mL), and dried(4.94 g, 16.2 mniol, 96%).1H NMR (CDC13,300 MHz): 6 = 7.33 (s, IH), 6.96 (s, 2H), 6.83 (d, 1H, 8 Hz), and 6.07 (d,IH, 8 Hz) (ArH), 5.51 (bs, IH, NH), 2.33 (s, 3H), 2.23 (s, 3H), 2.17 (s, 6H) (ArCH3).‘3c{1H} NMR (CDC13,75 MHz): 6 = 141.5, 136.5, 136.0, 135.5, 132.9, 129.4, 129.1, 128.1,112.6, and 109.4 (ArC), 21.1,20.2, and 18.3 (ArCH).El-MS (m/: 303 (100, [M]).Anal. Calcd. forC16H8NBr: C, 63.17; H, 5.96; N, 4.60; Found: C, 62.81; H, 5.99; N, 4.72.(2,4,6-Me36H)(2-Li-4-Me-CN itmeda (2.6). A stirred solution of 2.5 (0.790 g,2.59 mmol) and tmeda (0.80 mL, 0.62 g, 5.3 mniol) in Et20 (5 mL) was cooled to —35 °C,and rBuLi (3.4 mL, 1.6 M in hexanes, 5.4 mmol) was added dropwise. A light yellow68precipitate formed immediately that was collected on a frit, washed with hexanes (5 rnL), anddried (0.680 g, 1.92 mmol, 74%).1H NMR (THF-d8,300 MHz): 6 6.93 (d, 1H, 2 Hz), 6.74 (s, 2H), 6.38 (dd, 1H, 8 Hz, 2Hz), and 5.54 (d, IH, 8 Hz) (ArH), 2.31 (s, 4H, tmeda), 2.17 (s, 3H, CH3), 2.15 (s, 12H,tmeda), 2.02 (s, 3H), and 2.00 (s, 6H) (ArCH3).‘3C{’H} NMR (I’HF-d8,75 MHz): 6 = 153.8, 152.1, 133.5, 132.2, 129.4, 129.3, 128.4, 116.4,113.3, and 111.5 (ArC), 58.8 and 46.2 (tmeda), 21.0, 20.0, and 18.9 (ArCH3).Satisfactory elemental analysis could not be obtained; samples darkened instantly in themodifiedN2-filled glovebox used in the microanalytical facility of the UBC Chemistry Dept.[NPNj*Li2(pC4H8O)(2.7p-C4H80).To a stirred solution of 2.5 (4.84 g, 15.9 mmol) inEt20 (100 mL) at —35 °C was added BuLi (1.55 M in hexanes, 20.5 mL, 31.8 mmol)dropwise over 15 mm. The clear yellow solution was allowed to warm to rt and stirred for 3h. The solution was chilled (—35 °(Z), and PhPC12 (1.40 g, 7.82 mmol) in EtO (10 mL) wasadded dropwise over 2— 3 h at this temperature. The yellow solution became dark orangethroughout the addition. The reaction mixture was warmed slowly to rt and stirred for 24 hto obtain a pale orange suspension that was taken to dryness to obtain an orange foam.Hexanes (30 mL) were added to the foam to obtain a translucent orange solution. 1,4-Dioxane (5 mL) was added to the solution to obtain a yellow precipitate that was collectedon Celite —3 cm deep in a frit. The precipitate was washed with hexanes and the dark orangefiltrate was concentrated and chilled to induce the formation of yellow crystals. The solidtrapped on Celite in the frit was eluted through the Celite with a mixture of toluene (50 mL)and THF (0.1 mL) to obtain a yellow filtrate that was taken to dryness. The yellow powder69so obtained can be recrystallized from toluene (with a drop of THF to dissolve) layered withhexanes. The combined powder and crystals (4.37 g, 6.65 mmol, 85% isolated yield based onPhPC12) were stored at —35 °C because thermal decomposition has been observed. NMRspectroscopy was facilitated by the addition of a drop of THF to the suspension of 2.7(p-C4H802) in C6D. Resonances for free (not coordinated to Li) p-C4H802,and free andcoordinated THF were observed in the ‘H NMR spectrum. Signals due to coordinated THFappear as shoulders on the peaks for free THF in the 1H NMR spectrum and cannot beintegrated accurately. Elemental analyses of 2.7 (b-C4H802)were hampered by its sensitivityto moist air; the yellow powder darkened instantly upon opening sample vials in themodified glovebox used for microanalysis at U.B.C. Despite many attempts, results that werelow in carbon were found. X-ray quality crystals of 2.72THF were obtained by slowevaporation of a benzene solution of 2.7 (p-C4H802)with a small amount of THF added.‘H NMR (C6D,300 MHz): 6 = 7.81 (t, 2H, 7 Hz), 7.72 (bd, 2H, 3 Hz), 7.19 (t, 2H, 7 Hz),7.02 (t, 1H, 8 Hz), 6.97 (s, 2H), 6.87 (s, 2H), 6.85 (d, 2H, 8 Hz), and 6.52 (dd, 2H, J = 6Hz,JHH = 8 Hz) (ArH), 2.35 (s, 6H), 2.33 (s, 6H), 2.28 (s, 6H), and 2.16 (s, 6H) (ArCH3).31P{1H} NMR (C6D,121 MHz): 6 = —35.2 (q,J1 = 40 Hz).7Li{’H} NMR (C6D,155 MHz): 6 = —0.07 (d, lLi,JLIP = 40 Hz), —1.97 (s, ILi).“C{’H} NMR (C6D, 75 MHz): 6 = 162.1 (d, 28 Hz), 152.0, 140.2, 134.9 (d, 3 Hz), 133.8,132.3 (d, 14 Hz), 132.2, 132.1, 131.8, 130.8, 129.0, 128.8, 126.8, 122.9, 120.9 (d, 12 Hz), and117.9 (d, 5 Hz) (ArC), 20.9, 20.7, 20.4, and 20.2 (ArCH3).The data for one representative attempt at microanalysis is reported below.Anal. Calcd. forC46H55N2LiOP:C, 77.51; H, 7.78; N, 3.93; Found: C, 74.75; H, 7.59; N,4.02.70LNPNI*HZ (2.8). Trimethylammonium chloride (0.319 g, 3.34 mmol) was added all at onceto a stirred yellow solution of 2.7(p-C4H8O)(1.06 g, 1.61 mrnol) in THF (15 mL). After 15mm., the reaction mixture was a white suspension. After I h, the reaction mixture was takento dryness to obtain a white solid that was extracted with warm toluene (20 mL). Thetoluene suspension was filtered through Celite, the Celite was washed with additional warmtoluene (10 mL), and the filtrate was taken to dryness to obtain a white solid. The solid waswashed with pentane and dried to yield a white powder (0.872 g, 1.57 mmol, 97%).Compound 2.8 is air-stable as a solid for weeks and in solution for days, although in ourlaboratory it is stored in the glovebox to keep it water-free.‘H NMR (C6D,300 MHz, 300 K): ö = 7.68 (dd, 2H, J = 7 Hz, JHH = 7 Hz), 7.29 (d, 2H,JHP = 7 Hz), 7.12 (d, 2H, 6 Hz), 7.02 (t, IH, 8 Hz), 6.88 (d, 2H, 7 Hz), 6.78 (bs, 2H), 6.74 (bs,2H), and 6.38 (ad, 2H,JHP = 5 Hz,JHH = 9 Hz) (ArH), 5.98 (d, 2H,J = 5 Hz, NH), 2.12 (s,6H), 2.04 (bs, 6H), 1.98 (s, 6H), and 1.90 (bs, 6H) (ArCH3).1H NMR (C7D8,500 MHz, 273 K): = 7.63 (t, 2H, 7 Hz), 7.26 (d, 2H, 7 Hz), 7.10 (m, 3H),6.84 (d, 2H, 7 Hz), 6.75 (s, 2H), 6.69 (s, 2H), and 6.35 (ad, 2H, JHP = 5 Hz, J = 9 Hz)(ArH), 5.91 (d, 2H, 5 Hz, NH), 2.16 (s, 6H), 2.08 (s, 6H), 2.01 (s, 6H), and 1.93 (s, 6H)(ArCH3).‘H NMR (C7D8,300 MHz, 370 K): 6 = 7.59 (t, 2H, 8 Hz), 7.12 (m, 4H), 6.95 (m, IH), 6.82(d, 2H, 8 Hz), 6.73 (s, 4H), and 6.23 (dd, 2H, JHP = 5 Hz, JHH = 9 Hz) (ArH), 5.88 (bd, 2H,JHP = 5 Hz, NH), 2.12 (s, 6H), 2.01 (s, 6H), and 1.98 (s, 12H) (ArCH3).31P{’H} NMR (C6D,121 MHz): 6 = —31.4 (s).7113C{’H} NMR (C6D, 75 MHz): ö = 147.7 (d, 16 Hz), 136.5, 135.7 (bs), 135.5 (bs), 135.1,135.0, 134.8, 134.7, 134.5, 131.8, 129.6, 129.1, 129.0, 128.9, 117.9 (d, 7 Hz), and 112.5 (d, 3Hz) (ArC), 20.6, 20.1, 18.0 (bs), and 17.7 (bs) (ArCH3).JR (KBr): 3360 (m), 3012 (m), 2917 (m), 2854 (m), 1601 (m), 1491 (s), 1389 (m), 1310 (s),1293 (s), 1268 (m), and 1028 (m) cm1.El-MS (m/J: 556 (20, [IVl]), 541 (100, [M — Me]).Anal. Calcd. forC38H41N2P:C, 81.98; H, 7.42; N, 5.03; Found: C, 82.04; H, 7.46; N, 4.87.[NPNI*Zr(NMe2)z(2.9). Zr(NMe24(0.580 g, 2.17 mmol) and 2.8 (1.21 g, 2.17 mmol) weremixed together, and toluene (15 mL) was added to obtain a lemon yellow solution that wasstirred for 2 h. The reaction mixture was taken to dryness to obtain a yellow residue. Uponaddition of pentane (5 mL), a light yellow precipitate formed that was collected on a fit anddried (1.43 g, 1.95 mmol, 90%).1H NMR (C6D,300 MHz): 8 = 7.60 (t, 2H, 8 Hz, o-PPh), 7.52 (d, 2H, 7 Hz, m-Tol), 7.11 (m,3H, 7 Hz, m-, p-PPh), 7.02 (s, 2H, m-Mes), 6.97 (s, 2H, m-Mes), 6.93 (d, 2H, 9 Hz, o-Tol),6.19 (dd, 2H, 8 Hz, m-Tol), 3.06 (s, 6H, N(CH3), 2.42 (s, 6H), and 2.32 (s, 6H) (ArCH3),2.31 (s, 6H, N(CH3)2,2.25 (s, 6H), and 2.08 (s, 6H) (ArCH3).31P{1H} NMR (C6D,121 MHz): 6 = —11.5 (s).‘3C{1H} NMR (CD6, 75 MHz): 6 = 161.5 (d, 31 Hz), 145.2, 144.6, 137.2, 136.4, 135.0,134.7, 134.3, 133.3, 133.1, 130.3, 130.2, 118.0, 117.6, 115.1, and 115.0 (ArC), 43.6 and 43.5(N(CH3)2,21.0, 20.4, 19.3, and 19.2 (ArCH3).El-MS (m/3: 732 (1, [M]), 688 (30, [M — NMe2]), 556 (30, [2.8]), 541 (100, [2.8 — Me]).Anal. Calcd. forC42H5NPZr: C, 68.72; H, 7.00; N, 7.63; Found: C, 68.42; H, 6.99; N, 7.38.72[NPN]*ZrC12 (2.10). To a stirred yellow toluene solution (40 mL) of 2.9 (1.20 g, 1.63mmol) was added chlorotrimethylsilane (1.77 g, 16.3 mmol) dropwise. The clear yellowsolution was stirred overnight, whereupon a yellow precipitate formed. The reaction mixturewas taken to dryness to obtain a yellow powder that was collected on a frit, washed withpentane (3 X 5 mL), and dried (1.04 g, 1.45 mmol, 89%). X-ray quality crystals of 2.10 weregrown by slow evaporation of a benzene solution of the compound.1H NMR (C6D,400 MHz): 6 = 7.60 (dd, 2H, JHH = 7 Hz, JHP = 7 Hz), 7.45 (d, 2H, 8 Hz),7.05 (m, 3H), 6.91 (s, 2H), 6.84 (d, 2H, 8 Hz), 6.80 (s, 2H), and 6.05 (dd, 2H,JHH = 7 Hz,J1,= 7 Hz) (ArH), 2.46 (s, 6H), 2.34 (s, 6H), 2.09 (s, 6H), and 1.94 (s, 6H) (ArCH3).31P{1H} NMR (C6D,121 MHz): 6 = —2.8 (s).13C{H} NMR (C6D, 75 MHz): 6 = 159.9 (d, 32 Hz), 138.5, 138.3, 137.0, 135.3, 134.6,132.3, 132.2, 131.1, 130.8, 129.6, 125.6, 121.1, 120.6, 114.9, and 114.8 (ArC), 21.1, 20.3, and19.1 (ArCH3).El-MS (m/: 714 (3, [Mf’), 541 (100, [2.8 — Me]).Anal. Calcd. forC38H9N21PZr: C, 63.67; H, 5.48; N, 3.91; Found: C, 63.65; H, 5.80; N,3.98.[NPNJ*ZrC12(THF) (2.11). THF (1-2 drops) was added to an NMR tube with 2.10 (20 mg,28 imol) in C6D (0.8 niL) to produce a bright red-orange solution. Attempts to isolate 2.11by precipitation (from toluene/THF solutions layered with pentane at —35 °C) or byconcentrating solutions under vacuum gave 2.10. Two sharp resonances due to free THFwere observed by ‘H NMR spectroscopy, but signals due to coordinated THF could not bedistinguished.731H NMR (C6D,300 MHz): ö = 7.75 (t, 2H, 8 Hz), 7.38 (d, 2H, 8 Hz), 7.07 (m, 3H), 6.91 (s,2H), 6.83 (s, 2H), 6.82 (d, 2H, 8 Hz), and 6.04 (dd, 2H, JHH = 7 Hz,J = 6 Hz) (ArH), 2.46(s, 6H), 2.30 (s, 6H), 2.12 (s, 6H), and 1.95 (s, 6H) (ArCH,).‘1P{’H} NMR (C6D,121 MHz): ö = 2.7 (s).[NPN]*ZrC12( Me3)(2.12). PMe, (1-2 drops) was added to an NMR tube with 2.10 (20mg, 28 imol) in C6D (0.8 niL) to produce a bright red solution. Attempts to isolate 2.12 byprecipitation (from toluene/PMe3 solutions layered with pentane at —35 °C) or byconcentrating solutions under vacuum gave 2.10. A broad singlet due to free PMe3 wasobserved by ‘H and “P{’H} NMR spectroscopy, but a separate peak due to coordinatedPMe, could not be distinguished.‘H NMR (C6D,500 MHz): ö = 7.78 (t, 2H, 8 Hz), 7.35 (d, 2H, 8 Hz), 7.12 (m, 3H), 6.88 (s,2H), 6.84 (s, 2H), 6.78 (d, 2H, 8 Hz), and 5.97 (dd, 2H, JHH = 8 Hz, JHP = 5 Hz) (ArH), 2.42(s, 6H), 2.19 (s, 6H), 2.16 (s, 6H), and 1.99 (s, 6H) (ArCH,).‘1P{’H} NMR (C6D,202 MHz): ö = 3.4 (s).[NPN]*ZrC12( y) (2.13). Pyridine (0.49 g, 0.50 mL, 6.2 mmol) was added dropwise to astirred yellow solution of 2.10 (0.400 g, 0.558 mmol) in toluene (5 mL). The solution turnedred-orange instantly and was stirred for 30 mm. The reaction mixture was taken to drynessto obtain a red-orange powder that was collected on a fit, rinsed with hexanes (5 niL), anddried (0.434 g, 0.545 mmol, 98%). Red single crystals of 2.13 suitable for X-ray diffractionwere grown by slow evaporation of a benzene solution of the compound.741H NMR (C6D,400 MHz): 6 = 8.38 (d, 2H, 4 Hz,C5HN), 7.96 (t, 2H, 8 Hz), 7.34 (d, 2H, 8Hz), 7.13 (m, 3H), 6.95 (s, 2H), 6.78 (d, 2H, 7 Hz), 6.73 (s, 2H), 6.60 (t, IH, 7 Hz,p-C5N),6.18 (t, 2H, 7 Hz, C5HN), and 6.04 (dd, 2H, JHH = 8 Hz, J, = 6 Hz) (AtH), 2.30 (s, 6H),2.18 (s, 6H), 2.05 (bs, 6H), and 1.95 (s, 6H) (ArCH3).31P{H} NMR (C6D,162 MHz): 6 = 2.7 (s).13C{H} NMR (C6D, 101 MHz): 6 = 151.6, 140.9, 139.2, 139.0, 137.7, 136.3, 134.1, 133.4,132.9, 132.8, 130.6, 130.5, 130.0, 129.9, 129.7, 129.6, 125.6, 123.2, and 115.7 (d, 9 Hz) (ArC),21.0, 20.5, 20.1, and 19.6 (ArCH3).El-MS (m/,: 716 (40, [M — Pyf’), 556 (10, [2.8f’), 541 (50, [2.8 — Mefl, 225 (100,[(I’ol) (Mes)NH])Anal. Calcd. forC43HN3l2PZr: C, 64.89; H, 5.57; N, 5.28; Found: C, 65.20; H, 5.89; N,5.35.[NPN]*Hf(NMe2)z(2.14). Hf(NMe24(2.85 g, 8.03 rnmol) and 2.8 (4.48 g, 8.05 nmiol)were mixed together and toluene (50 mL) was added. The lemon yellow solution was stirredfor 2 h, and the reaction mixture was taken to dryness. The pale yellow residue so obtainedwas dissolved in pentane (25 mL), and after about 30 s a pale yellow precipitate formed thatwas collected on a frit, washed with pentane (5 mL), and dried under vacuum (5.81 g, 7.07mmol, 88%). X-ray quality crystals of 2.14 were grown by slow evaporation of a benzenesolution of the compound.1H NMR (C6D,500 MHz): 6 = 7.50 (t, 2H, 8 Hz), 7.44 (d, 2H, 8 Hz), 7.06 (m, 2H), 7.01 (m,1H), 6.96 (s, 2H), 6.92 (s, 2H), 6.88 (d, 2H, 8 Hz), and 6.15 (dd, 2H,JHH = 8 Hz,JfW = 6 Hz)75(ArH), 3.02 (s, 6H), 2.38 (s, 6H), 2.33 (s, 6H), 2.28 (s, 6H), 2.18 (s, 6H), and 2.00 (s, 6H)(N(CH3)2and ArCH3).31P{1H} NMR (C6D,202 MHz): 6 = —4.5 (s).13C{’H} NMR (C6D, 75 MHz): 6 = 162.4 (d, 30 Hz), 144.7, 136.6, 135.9, 134.7, 134.5,134.1, 133.8, 132.9, 132.8, 129.9, 129.8, 129.0, 128.6 (d, 8 Hz), 117.4 (d, 32Hz), and 115.9 (d,9 Hz) (ArC), 43.2, and 43.0 (NCH3), 20.9, 20.2, 19.2, and 19.1 (ArCH3).El-MS (m/r: 777 (100, [M — NMe2]), 733 (40, [M — 2(NMe)]j.Anal. Calcd. forC42H5NPHf: C, 61.42; H, 6.26; N, 6.82; Found: C, 61.64; H, 6.15; N, 6.57.[NPN]*HfC12(2.15). To a stirred toluene solution (50 mL) of 2.14 (5.10 g, 6.94 mmol) wasadded chlorotrimethylsilane (2.55 g, 23.5 mmol) dropwise. The clear yellow solution wasstirred overnight, whereupon a pale yellow precipitate formed. The reaction mixture wastaken to dryness and the pale yellow solid so obtained was suspended in pentane (25 mL).The solid was collected on a fit, washed with pentane (3 X 5 mL), and dried under vacuumto obtain a pale yellow powder (4.97 g, 6.87 mmol, 99%). X-ray quality crystals were grownby slow evaporation of a benzene solution of 2.15.‘H NMR (C6D,, 300 MHz): 6 = 7.59 (dd, 2H,J = 8 Hz, JHH = 10 Hz), 7.42 (d, 2H, 8 Hz),7.03 (m, 3H), 6.92 (s, 2H), 6.86 (d, 2H, 8 Hz), 6.82 (s, 2H), and 6.10 (dd, 2H,JHH = 8 Hz,J= 6 Hz) (ArH), 2.48 (s, 6H), 2.41 (s, 6H), 2.10 (s, 6H), and 1.96 (s, 6H) (ArCH3).31P{1H} NMR (C6D,121 MHz): 6 = 0.1 (s).‘3C{’H} NMR (C6D, 75 MHz): 6 = 160.9 (d, 30 Hz), 139.0 (d, 5 Hz), 138.3, 137.4, 136.5,135.5, 134.6, 132.3 (d, 12 Hz), 131.0 (d, 5 Hz), 130.9, 130.8, 130.4 (d, 2 Hz), 129.2 (d, 10Hz), 120.1, 119.5, and 116.2 (d, 10 Hz) (ArC), 21.1, 20.2, 19.14, and 19.12 (ArCH3).76El-MS (m/): 804 (100, [M]j, 541 (40, [2.8 — MeJ).Anal. Calcd. forC38H9N21PHf: C, 56.76; H, 4.89; N, 3.48; Found: C, 57.10; H, 5.00; N,3.68.[NPN]*HfCI2( y) (2.16). Pyridine (0.49 g, 0.50 mL, 6.2 mmol) was added dropwise to astirred solution of 2.15 (0.400 g, 0.498 mmol) in toluene (10 mL). The light yellow solutionturned yellow-orange instantly and was stirred for 30 mm. at rt. The reaction mixture wastaken to dryness to obtain a pale orange powder that was collected on a frit, rinsed withhexanes, and dried (0.420 g, 0.476 mmol, 95%).‘H NMR (C6D,400 MHz, 300 K): 8 = 8.31 (d, 2H, 5 Hz), 7.97 (m, 2H), 7.32 (dd, 2H, 8 Hz,1 Hz), 7.14 (m, 3H), 6.96 (s, 2H), 6.82 (d, 2H, 8 Hz), 6.73 (bs, 2H), 6.60 (t, 1H, 7 Hz), 6.15(t, 2H, 7 Hz), and 6.10 (dd, 2H,JHH = 8 Hz,J = 6 Hz) (ArH), 2.31 (bs, 12H), 2.20 (s, 6H),and 1.97 (s, 6H) (ArCH3).‘H NMR (C7D8,400 MHz, 220 K): 6 = 8.47 (bs, 2H), 7.89 (bs, 2H), 7.38 (d, IH, 8 Hz), 7.32(d, 1H, 8 Hz), 7.14 (s, 3H), 7.03 (s, 1H), 6.95 (s, IH), 6.92 (s, 1H), 6.77 (d, 1H, 8 Hz), 6.74 (d,1H, 8 Hz), 6.50 (bt, IH, 7 Hz), 6.36 (s, 1H), 6.12 (bs, 2H), and 6.01 (bs, 2H) (AtH), 3.15 (s,3H), 2.62 (s, 3H), 2.26 (s, 3H), 2.17 (s, 3H), 2.08 (s, 3H), 2.02 (s, 3H), 1.88 (s, 3H), and 0.84(s, 3H) (ArCH3).‘H NMR (C7D8,400 MHz, 360 K): 8 = 8.46 (bs, 2H), 7.73 (dd, 2H,JHH = 8 Hz,JHP = 8 Hz),7.29 (d, 2H, 8 Hz), 7.14 (m, 3H), 6.91 (bs, IH), 6.88 (s, 2H), 6.79 (d, 2H, 8 Hz), 6.68 (s, 2H),6.53 (bs, 2H), and 5.97 (dd, 2H,JHH = 8 Hz,J = 6Hz) (ArH), 2.22 (s, 6H), 2.14 (s, 12H),2.00 (s, 6H) (ArCH3).31P{’H} NMR (C6D,162 MHz): 6 = 3.2 (s).77‘3C{’H} NMR (C6D, 101 MHz): ö = 151.5, 139.0, 138.1, 135.4, 134.3, 133.3 (bs), 133.0,132.9, 130.4, 130.3, 129.7, 129.5, 129.4, 129.3, 129.1, 128.5, 125.6, 123.4, and 116.9 (bd, 5Hz) (ArC), 21.4, 21.0, 20.4, and 19.5 (ArCH3).Anal. Calcd. forC43H4N312PHf: C, 58.48; H, 5.02; N, 4.76; Found: C, 58.87; H, 5.40; N,4.66.[NPN]*Hfl2(2.17). To a stirred toluene solution (15 mL) of 2.15 (1.75 g, 2.18 mniol) wasadded iodotrimethylsilane (3.0 rnL, 2.6 g, 24 mmol) dropwise. The cleat yellow solution wasstirred overnight, whereupon a bright yellow precipitate formed. The reaction mixture wastaken to dryness to obtain a yellow solid that was suspended in pentane (25 mL), collectedon a frit, washed with pentane (3 X 5 mL), and dried under vacuum to obtain a yellowpowder (2.13 g, 2.15 rnmol, 99%). Single crystals of 2.17 were grown by slow evaporation ofa benzene solution of the compound.‘H NMR (C6D,500 MHz): 8 = 7.55 (dd, 2H,JHH = 8 Hz,JPH = 10 Hz), 7.36 (d, 2H, 8Hz),7.11 (t, 2H, 8 Hz), 7.05 (t, IH, 8 Hz), 6.89 (s, 2H), 6.84 (d, 2H, 7 Hz), 6.84 (s, 2H), and 6.09(dd, 2H, JHH = 8 Hz, J = 6 Hz) (ArH), 2.56 (s, 6H), 2.30 (s, 6H), 2.10 (s, 6H), and 1.92 (s,6H) (ArCH3).31P{1H} NMR (C6D,202 MHz): 6 = 3.9 (s).‘3C{’H} NMR (C6D, 126 MHz): 8 = 160.3 (d, 29 Hz), 138.6, 138.3, 137.8, 135.8, 135.4,134.6, 133.0 (d, 11 Hz), 131.4, 131.2, 131.1, 130.5, 129.0 (d, 10 Hz), 121.3, 121.0, and 116.3(d, 10 Hz) (ArC), 21.4, 20.7, 20.2, and 20.1 (ArCH3).El-MS (m/: 988 (100, {M]j, 861 (100, [M —78Anal. Calcd. forC38H9N2IPHf: C, 46.24; H, 3.98; N, 2.84; Found: C, 46.58; H, 4.23; N,2.81.2.5 References.1 A) Beletskaya, I. P.; Cheprakov, A. V. Chem. Rev. 2000, 100, 3009. B) Chen, Y.; Yekta, S.;Yudin, A. K. Chem. Rev. 2003, 103, 3155. C) Leadbeater, N. E.; Marco, M. Chem. Rev. 2002,102, 3217.2A) Matyjaszewski, K.;Xia,J. Chem. Rev. 2001, 101, 2921. B) Gultneh, Y.; Tesema, Y. T.;Yisgedu, T. B.; Butcher, R. J.; Wang, G.; Yee, G. T. Inorg. Chem. 2006, 45, 3023. C) Salem, H.;Ben-David, Y.; Sbimon, L. J. W.; Milstein, D. Organometallics 2006, 25, 2292.3A) Whitesell, J. K. Chem. Rev. 1989, 89, 1581. B) Burk, M. J. Acc. Chem. Res. 2000, 33, 363.C) Ihori, Y.; Yamashita, Y.; Ishitani, H.; Kobayashi, S. J. Am. Chem. Soc. 2005, 127, 15528. D)Garcia, C.; Walsh, P. J. Org. Lett. 2003, 5, 3641.4A) Lentz, M. R.; Fanwick, P. E.; Rothwell, I. P. Organometallics 2003, 22, 2259. B) Schrock,R. R. Acc. Chem. Res. 1986, 19, 342. C) Diaconescu, P. L.; Odom, A. L.; Agapie, T.; Cumrnins,C. C. Organometallics 2001, 20, 4993. D) MacBeth, C. E.; Thomas, C. J.; Betley, T. A.; Peters, J.C. Inorg. Chem. 2004, 43, 4645. E) Brown, S. D.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc.2003, 125, 322.A) Chang, C. J.; Loh, Z.-H.; Deng, Y.; Nocera, D. G. Inorg. Chem. 2003, 42, 8262. B)Pistorio, B. J.; Chang, C. J.; Nocera, D. G. J. Am. Chem. Soc. 2002, 124, 7884. C) Meyer, T. J.Acc. Chem. Res. 1989, 22, 163. D) Campagna, S.; Di Pietro, C.; Loiseau, F.; Maubert, B.;McClenaghan, N.; Passalacqua, R.; Puntoriero, F.; Ricevuto, V.; Serroni, S. Coord. Chem. Rev.792002, 229, 67. H) Faiz, J. A.; Williams, R. M.; Silva, M. J. J. P.; De Cola, L.; Pikramenou, Z. J.Am. Chem. Soc. 2006, 128, 4520.6 Pool, J. A.; Lobkovsky, E.; Chink, P. J. Nat.ure 2004, 427, 527.Manriquez, J. M.; Sanner, R. D.; Marsh, R. E.; Bercaw, J. E. J. Am. Chem. Soc. 1976, 98,3042.8 Fryzuk, M. D. Chem. Rec. 2003, 3, 2.Fryzuk, M. D.; MacNeil, P. A. J. Am. Chem. Soc. 1981, 103, 3592.10 Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J. J. Am. Chem. Soc. 1990, 112, 8185.Fryzuk, M. D.; Love, J. B.; Rettig, S. J. Chem. Commun. 1996, 2783.12A) Fryzuk, M. D.; Love, J. B.; Rettig, S. J.; Young, V. G. Science 1997, 275, 1445. B) Basch,H.; Musaev, D. G.; Morokuma, K.; Fryzuk, M. D.; Love, J. B.; Seidel, W. W.; Albinati, A.;Koetzle, T. F.; Klooster, W. T.; Mason, S. A.; Eckert, J. J. Am. Chem. Soc. 1999, 121, 523.13 A) Manriquez, J. M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J. E. J. Am. Chem. Soc. 1978,100, 2716. B) Hidai, M.; Tominari, K.; Uchida, Y. J. Am. Chem. Soc. 1972, 94, 110. C) George,T. A.; Tisdale, R. C. Inorg. Chem. 1988, 27, 2909.‘4Morello, L.; Love, J. B.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc. 2004, 126, 9480.15 A) Fryzuk, M. D.; Johnson, S. A.; Rettig, S. J. J. Am. Chem. Soc. 1998, 120, 11024. B)Fryzuk, M. D.; Johnson, S. A.; Patrick, B. 0.; Albinati, A.; Mason, S. A.; Koetzle, T. F. J.Am. Chem. Soc. 2001, 123, 3960.16A) MacKay, B. A.; Munha, R. F.; Fryzuk, M. D. J. Am. Chem. Soc. 2006, ASAP. B) MacKay,B. A.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc. 2003, 125, 3234. C) MacKay, B. A.;Johnson, S. A.; Patrick, B. 0.; Fryzuk, M. D. CanJ. Chem. 2005, 83, 315.8017 Morello, L.; Yu, P.; Carmichael, C. D.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc.2005, 127, 12796.18 Fryzuk, M. D.; MacKay, B. A.; Johnson, S. A.; Patrick, B. 0. Angew. Chem. mt. Ed. 2002,41, 3709.19 MacKay, B. A.; Patrick, B. 0.; Fryzuk, M. D. O,ganometallics 2005, 24, 3836.20 Shaver, M. P.; Thompson, R. K.; Patrick, B. 0.; Fryzuk, M. D. Can. J. Chem. 2003, 81,1431.21 Fryzuk, M. D.; Shaver, M. P.; Patrick, B. 0. Ino,g. Chim. Acta 2003, 350, 293.A) Fryzuk, M. D.; MacNeil, P. A. J. Am. Chem. Soc. 1984, 106, 6993. B) Fryzuk, M. D.;Haddad, T. S.; Rettig, S. J.; Secco, A. S.; Trotter, J. Oganometallics 1991, 10, 2026. C) Ozerov,0. V.; Gerard, H. F.; Watson, L. A.; Huffman, J. C.; Cauton, K. G. Inorg. Chem. 2002, 41,5615.23 Corkin, J. R.; Fryzuk, M. D. unpublished results.24 Evans pKa table: http://daecrl.harvard.edu/pdf/evans pKa table.pdf accessed on March30, 2006.25 Fraser, R. R.; Mansour, T. S.; Savard, S. J. Org. Chem. 1985, 50, 3232.26 Bordwell, F. G. Acc. Chem. Res. 1988, 21, 456.27 A) Hessler, A.; Kottsieper, K. W.; Schenk, S.; Tepper, M.; Stelzer, 0. Z. Natuforsch. 2001,56b, 347. B) Herd, 0.; Hessler, A.; Hingst, M.; Machnitzki, P.; Tepper, M.; Steizer, 0.Cata/ysis Todqy 1998, 42, 413. C) Hessler, A.; Steizer, 0.; Dibowski, H.; Worm, K.;Schmidtchen, F. P. J. Ot. Chem. 1997, 62, 2362. D) Herd, 0.; Hessler, A.; Hingst, M.;Tepper, M.; Stel2er, 0. J. Otganomet. Chem. 1996, 522, 69.Gujadhur, R. K.; Bates, C. G.; Venkataraman, D. Oig. Lett. 2001, 3, 4315.8129 Quin, L. D. A Guide to Organopho.phorus Chemistry; Wiley: New York, 2000.30Tolman, C. A. Chem. Rev. 1977, 77, 313.31 Hingst, M.; Tepper, M.; Steizer, 0. Eur. J. Inorg. Chem. 1998, 37, 73.32 Liang, L.-C.; Lee, W.-Y.; Hung, C.-H. Inoig. Chem. 2003, 42, 5471. B) Lang, L.-C.;Huang, M.-H.; Hung, C.-H. Inorg. Chem. 2004, 43, 2166. C) Lang, L.-C.; Lee, W.-Y.; Yin, C.C. Otganometallics 2004, 23, 3538.Lang, L.-C.; Lin, J.-M.; Hung, C.-H. Oiganometallics 2003, 22, 3007. B) Liang, L.-C.;Chien, P.-S.; Lin, J.-M.; Huang, M.-H.; Huang, Y. L.; Liao, J.-H. Organometallics 2006, 25,1399. C) Harkins, S. B.; Peters,J. C.J.Am. Chem. Soc. 2005, 127, 2030.Fan, L.; Foxman, B. M.; Ozerov, 0. V. Organometallics 2004, 23, 326.Liang, L. C. Coord. Chem. Rev. 2006, 250, 1152.36Antilla, J. C.; Buchwald, S. L. Org. Lett. 2001, 3, 2077.A) Buu-HoI, N. P. Ann. 1944, 556, 1. B) Djerassi, C. Chem. Rev. 1948, 43, 271. C) Kellogg,R. M.; Schaap, A. P.; Harper, E. T.; Wynberg, H. J. Org. Chem. 1968, 33, 2902.Shaver, M. P. Small Molecule Activation hy Diamidophoiphine Complexes of Vanadium, Niobium,and Tantalum. Ph.D. thesis; University of British Columbia: Vancouver, B.C., 2005.Friebolin, H. Basic One-and Two-DimensionalNMR Spectroscopy, 3fl ed.; Wiley-VCH:Weinheim, 1998, p. 307.Schrock, R. R.; Seidel, S. W.; Schrodi, Y.; Davis, W. M. Organometallics 1999, 18, 428.41 A) Skinner, M. E. G.; Li, Y.; Mountford, P. Inorg. Chem. 2002, 41, 1110. B) Chien, P.-S.;Liang, L.-C. Inorg. Chem. 2005, 44, 5147. C) Scott, M. J.; Lippard, S. J. Inorg. Chem. Acta 1997,263, 287. D) Zhang, X.; Zhu, Q.; Guzei, I. A.; Jordan, R. F. J. Am. Chem. Soc. 2000, 122,8093.8242A) Chandra, G.; Lappert, M. F. J. Chem. Soc. A 1968, 1940. B) Lappert, M. F.; Power, P. P.;Sanger, A. R.; Srivastava, R. C. Metal and MetalloidAmides; Ellis Horwood: Chichester, WestSussex, U.K., 1980. C) Bradley, D. C. Ady. Inorg. Chem. Radiochem. 1972, 15, 259.Diamond, G. M.; Jordan, R. F.; Petersen, J. L. Otganometallics 1996, 15, 4045. B)Diamond, G. M.; Jordan, R. F.; Petersen, J. L. J. Am. Chem. Soc. 1996, 118, 8024.44Airoldi, C.; Bradley, D. C.; Chudzynska, H.; Hursthouse, M. B.; Malik, K. M. A.; Raithby,P. R.J. Chem. Soc., Dalton Trans. 1980, 2010.Troyanov, S. I.; Meetsma, A.; Teuben, J. Ino,g. Chim. Acta 1998, 271, 180.Diamond, G. M.; Rodewald, S.; Jordan, R. F. Oganometallics 1995, 14, 5.83Chapter ThreeZirconium and Hafnium Organometaffic Complexes3.1 Introduction.Since Ziegler and Natta discovered that mixtures of Ti or Zr halides andorganoaluminum reagents catalyze olefin polymerization,1interest in group 4 chemistry hascontinued unabated.2A major development in the organometallic chemistry of group 4 hasbeen the creation of homogeneous olefin polymerization catalysts based on titano- andzirconocenes,’ which have been found to be highly active in the presence of co-catalystssuch as boranes or methylaluminoxane (MAO).4Metallocene catalysts have not only allowedchemists to probe the mechanism of olefin polymerization,5but they have also been tailoredto yield polymers with narrow molecular weight distributions,6 to polymerize prochiralolefins stereospecifically,7and to give polyolefin products with new structures for advancedapplications.8 In addition, non-metallocene group 4 complexes are being investigated forolefin polymerization.9In 1995, Ziegler-Natta catalysis was estimated to provide over 35million tonnes of polyolefins per year.’° Recent estimates include the production of over 80million tonnes of polyethylene and 65 million tonnes of polypropylene per year.”In addition to olefin polymerization, metallocene and non-metallocene organotitanium, -zirconium, and -hafnium complexes have been investigated as hydrogenation,’2hydroamination,’3 C—C cross-coupling,’4 silane dehydropolymerization,’5enantioselectiveorganic synthesis,16 and hydrosilylation17 catalysts. Small molecule activation,18 C—F bondactivation,19 C—H bond activation20 and migratory insertion reactions2’to yield new organiccompounds are other areas of interest to early transition-metal chemists.84A new reaction for early transition-metal alkyl complexes emerged in the late I 990swhen a group 4 organometallic complex was reacted with H2 gas, followed by N2 gas; adinitrogen complex, methane, and hydrogen are the major products of this reaction. Thesynthesis of N2 complexes by the hydrogenolysis of early transition-metal alkyl complexes isattractive because H2 is the only reagent besides N2 that is added to the reaction. There aremany examples of early transition-metal complexes that bind and activate N2 followingreduction by an alkali metal reagent, such as potassium graphite (KC8) or sodium amalgam.The use of strong reductants to activate N2 is one of the major barriers to the developmentof homogeneous catalytic or industrial processes for nitrogen fixation. Among otherproblems, reducing agents such as KC8 or Na/Hg amalgam are difficult to work withbecause they are pyrophoric, are generally incompatible with other reagents required tofunctionalize N2 (such as electrophiles), and are difficult to introduce into a catalytic or large-scale reaction.The reaction of (r15-CMe4H)2TiR (R = Me, Ph) with H2 gives the red-brown Ti(III)hydride,(15-CMe4H)2TiH,2that instantly forms a blue Ti-N2 complex, [(r15-CMe4H)2Ti]Q1-upon exposure to N2 (Scheme 3.1).23 Dinitrogen is weakly activated in this end-ondinuclear complex: the N—N bond length is 1.170(4) A. Overall, this reaction represents theformation of an N2 complex from an organometallic complex, H2, and N2.Scheme 3.1.H2E_2 2 Ti—H Ti—N—N--—-Ti- CH4 H285A Zr-N2 complex is also prepared by hydrogenolysis of an alkylzirconium complex.24When solutions of (rac-Bp)ZrMe2(rac-Bp = are exposedto H2 gas, (rac-Bp)ZrH2forms. Exposure of the dihydride to N2 gas yields [(rac-Bp)Zr]2i-112:i-N) with loss of H2 (Scheme 3.2). Again, a group 4 organometallic complex hasactivated N2 without the use of harsh reductants. The N—N bond length of 1.241(3) Asuggests a diazenide, or N2, unit is present in the complex.Scheme 3.2.H22 Me Si Zr 2 Me2Si Zr2 \Me-CH4R = R’ = TMSMe2SiHydrogenolysis of an alkyltantalum complex provides a dinuclear Ta-N2 compound inwhich N2 is coordinated in the side-on—end-on bonding mode.25 The reaction of[NPN]TaMe3 ([NPNJ = [(PhNSiMe2CH)PPh] with H2 gives the Ta(IV) tetrahydride,([NPN]Ta)2ji-H)4,which reacts with N2 to give ([NPN]Ta)QL-H)i-111:ri-).Althoughthis side-on—end-on N2 complex reacts with boranes, alanes and silanes to generate newnitrogen-element (N—E) bonds, ligand decomposition has stymied efforts to fix nitrogencatalytically with this system.26The preceding examples illustrate a rare, but appealing method of synthesizing earlytransition-metal N2 complexes: the addition of N2 to a metal hydride. The reverse reaction,R86however, is well known; some early transition-metal complexes react with H2 to liberate N2,even if the N—N bond is activated in the starting complex. The addition of H2 to [Cp*2Zr(111N2)]Q1-11:r1-Ngives Cp*2ZrH,which cannot be induced to coordinate N2.7 It should benoted that there are many reports of late transition-metal N2 complexes synthesized by theelimination of H2 from a metal hydride, but N2 is only weakly activated in the products.28The use of H2 in the synthesis of N2 complexes has two main advantages: it can bereadily added to a reaction mixture under a variety of conditions, and it is compatible with arange of reagents that functionalize coordinated N2, such as silanes, boranes, alanes, andsome organic electrophiles. The use of hydrogen as a reductant may someday facilitate thedevelopment of catalytic N—E bond-forming reactions. The incompatibility of reductantsand electrophiles has been overcome recently in a different manner under carefully designedexperimental conditions.29 Eight equivalents of ammonia are obtained from N2 in thepresence of a bulky Mo catalyst, a weak organic acid ([2,6-MeC5HNHJ[(3,5-(CF)2C6H4B],and a relatively mild reducing agent (Cp*2Cr). In this system, the electrophile and reducingagent do not react with each other to give H2. The choice of electrophile, reductant, andsolvent (heptane), and the use of an automated syringe pump proved crucial in this regard.To determine if group 4 organometallic complexes with the [NPN]* ancillary ligandreact with H2 to give metal hydride complexes, the M(IV) dialkyl complexes, [NPN]*MR2(M= Zr, Hf R = Me, CH2Ph,CH2SiMe3),have been prepared and characterized. The reactivityof [NPN]*MMe2with H2 gas, as well as the thermal decomposition of the Zr complexes aredescribed in this chapter.873.2 Results and Discussion.3.2.1 Synthesis of [NPN]*MMe2(M = Zr, Hf).[NPN]tZrMe2,3.1, can be prepared as a light- and heat-sensitive hexanes-solubleyellow powder in high yield from {NPN]*ZrC12 (2.10) and 2.2 equivalents of MeMgC1 inEt20 (Equation 3.1). There is a singlet at 8 —14.1 in the 31P{’H} NMR spectrum of 3.1 inC6D.By ‘H and 13C {‘H} NMR spectroscopy, there are four distinct ArCH3groups, which issuggestive of a C symmetric complex, and the peaks in the aromatic regions of both spectraare also consistent with the proposed structure. In the 1H NMR spectrum (Figure 3.1), thedoublet at 6 0.93 (3JHP = 5 Hz) is assigned to one Zr—CH3group (Met), and the singlet at 8 —0.11 is assigned to the second Zr—CH3 group (Me5). MeA and MeB do not interconvert onthe NMR timescale. By HMQC spectroscopy, MeA is assigned to a doublet at 8 45.1 (2J 6Hz), and Me5 is assigned to a doublet at 6 41.8 (2J = 29 Hz) in the ‘3C{’H} NMRspectrum. Unfortunately, NOE difference spectroscopy could not distinguish whether MeAor MeB is trans to P.2.2 MeMgCIEt20 (3.1)M = Zr, Hf88ArCH3(ppm)Figure 3.1. 300 MHz 1H NMR spectrum of 3.1 in C6D.The NMR spectra of 3.1 resemble those of methyizirconium complexes of anotherdiamidophosphine ligand.3° In the 1H NMR spectrum of [Ar2NPN]ZrMe ([Ar2NPNJ =[(2,6-MeC6H3NSilVIH)PPh]j there are two doublets due to the Zr—CH3 groups at 60.88 (3J = 6.6 Hz) and 6 —0.24 (3JHP = 1.5 Hz). The 13C{’H} NMR spectrum also has twodoublets for the Zr—CH3groups at 6 46.4 (2J = 30.1 Hz) and 45.0 (2J = 6.2 Hz). The Zr—CR3 groups in [Ar2NPNjZrMe were assigned as cis (1H: 6 0.88,J, = 6.6 Hz; 13C: 6 45.0,J= 6.2 Hz) and trans (1H: 6 —0.24, J = 1.5 Hz; ‘3C: 6 46.4, = 30.1) to phosphorus.Schrock et al. illuminated the solution- and solid-state structures of alkylzirconium complexesfurther by preparing monosubstituted [Ar2NPN]ZrMe(Cl). The solid-state molecularstructure shows that the Me group is equatorial (cis to P), whereas the Cl substituent is apicaland trans to P. The Zr—CH3group gives rise to a doublet at 6 0.54 (3JHP = 8.8 Hz) in the 1HArHZrCH3ZrCH389NMR spectrum of the complex. Although at first glance the apparent mismatch in themagnitude of andJ for two methyl substituents coordinated to Zr on [Ar2NPN]ZrMemay seem unusual, it is not inconsistent with the Karplus relationship.31 In particular, thesign and magnitude of heteronuclear coupling constants in some organometaDic complexeshave been rationalized in terms of torsion angles and stereochemistry at the metal centre.32Complex 3.1 decomposes in C6D solution over several days to give a red-brownsolution that shows several peaks in its 31P {‘H} NMR spectrum. If a solution of 3.1 is storedat 298 K in a sealed J. Young NMR tube, a singlet attributable to methane is observed by ‘HNMR spectroscopy.33Although small crystals of 3.1 grow in pentane in the dark at —35 °C,rapid desolvation and decomposition prevent them from being analyzed by X-raydiffraction. Since Hf alkyl complexes are often less thermally sensitive than their Zrcongeners,34the preparation of [NPN] *HfMe2has been undertaken.[NPN]*HfMe2,3.2, can be prepared as a pale yellow powder in high yield from 2.15and 2.2 equivalents of MeMgCl in EtO (see Equation 3.1). The 31P{’H}, 1H and 13C{’H}NMR spectra are very similar to those observed for 3.1, and are consistent with a complexthat is a C symmetric monomer in solution with two inequivalent Hf—CH3 groups that donot interconvert on the NMR timescale. The ‘H NMR spectrum of 3.2 in C6D displays twoHf—CH3 resonances: a doublet at ö 0.67 (3JHP = 5 Hz) (Met), and a singlet at ö —0.21 (Me5).By‘3C{1H} NMR and HMQC spectroscopy, 3.2 has two doublets: MeA is at ö 55.1 (2J = 8Hz), and MeB is at 54.8 (2J = 24 Hz). Again NOE difference spectroscopy is unable toestablish whether MeA is cis or trans to P. Although it is likely that MeA is cis to P, and MeBis trans to P in 3.1 and 3.2,30 it may be necessary to characterize 3.1 and 3.2 further, or toprepare complexes such as [NPN]*MMe(Cl), to obtain additional support for thisassignment.90The ORTEP representation of the solid-state molecular structure of 3.2 is shown inFigure 3.2. The five-coordinate complex is distorted trigonal bipyramidal at Hf, and the Megroups are axial and equatorial. The Hf—C (C39, C40) bond lengths to methyl groups cis andtrans to P are the same, within error, at —2.22 A. Again, the [NPN]* ligand appears to hingethe anude donors out of the equatorial plane with P—Hf—Ni and P—Hf—N2 angles of70.10(12) and 72.09(13)°, respectively. The Hf—N, Hf—P, Hf—C bond lengths are similar toothers reported in the literature.35Figure 3.2. ORTEP drawing of the solid-state molecular structure of [NPN]*HfMe2,3.2(effipsoids drawn at the 50% probability level). All hydrogen atoms have been omitted forclarity. Selected bond lengths (A) and angles (°): Hfl—Pl 2.7861(14), Hfl—N1 2.092(4), Hfl—N2 2.075(4), Hfi—C39 2.211(6), Hfl—C40 2.232(6), P1—Hfl—N1 70.10(12), P1—Hfi--N272.09(13), P1—Hfl—C39 86.79(19), P1—Hfi—C40 i78.Oi(18), N1—Hfl—N2 ii6.35(i7), C39—Hfi—C40 95.2(3).III913.2.2 Synthesis and reactivity of LNPNI*M(CHZPh)2.[NPN]*Zr(CHCH) 3.3, can be prepared from [NPN]*ZrCl2 (2.10) and 2.2equivalents ofC6H5H2MgC1 in Et20, and is isolated as a heat- and light-sensitive yellowpowder in high yield (Scheme 3.3). When [NPN]*H2 (2.8) and Zr(CH2Ph)436 are mixedtogether in C6D solution, no new signals appear in the 31P{1H} NMR spectrum. Thus, thisroute to benzylzirconium complexes cannot be used as an alternative to the Grignardreaction described above.37Scheme 3.3.2.2 BnMgCI[NPN]*ZrCI2Et202.10The 31P{’H} NMR spectrum of 3.3 in C6D shows a singlet at —7.2. The 1H NMRspectrum is consistent with the assignment of 3.3 as a five-coordinate C symmetric complexin solution. Once again, restricted rotation about N—C0 gives rise to four inequivalentArCH3 groups, but singlets due to two of the four ArCH3 groups overlap. There are twodifferent benzyl groups that do not exchange on the NMR timescale. The benzylic protonsappear as a doublet (ö 2.92, 3J, = 9 Hz), assigned to CH2(A), and a singlet (ö 1.81), assignedto CH2), in the ‘H NMR spectrum. By HMQC spectroscopy, CH2@) appears as a singlet (ö74.6) and CH2(A) appears as a doublet (ö 73.0, 2J = 22 Hz) in the ‘3C {‘H} NMR spectrum.3.392Although 3.3 has not been characterized in the solid state, crystals of a derivative ofthis complex suitable for X-ray diffraction were obtained from C6D solutions of 3.3 at roomtemperature over one week. This derivative can also be prepared on a preparative scale whena toluene solution of 3.3 is stirred in the dark at ambient temperature for two days (seeScheme 3.3). The red-orange product, 3.4, displays a singlet at 3 —5.2 in the 31P {‘H} NMRspectrum acquired in C6D.The absence of C symmetry in the product is apparent in its ‘HNMR spectrum.The ‘H and ‘3C {‘H} NMR spectra of 3.4 in C6D are consistent with the formulationof the complex as a C, symmetric monomer with one CH2Ph ligand and a cyclometalated[p]*There are two doublets, each integrating to IH, at 3 2.28 (1JHH = 7 Hz) and 1.75(‘JHH = 7 Hz) in the 1H NMR spectrum (Figure 3.3). These resonances are assigned todliastereotopic benzylic protons. The doublet at 3 2.28 overlaps with two ArCH3 singlets andcan be located using ‘H-’H COSY. A second set of diastereotopic benzylic resonances isobserved: a doublet of doublets integrating to 1H at 3 2.70 (1JHH = 9 Hz, 3J, = 1 Hz) and abroad doublet integrating to IH at 8 1.85 (‘JHH = 9 Hz). These signals are assigned to theZr(-2-CH2-4,6-MeC6HN) protons of the onho-methy1 metalated [NPNI* ligand. Theobservation of seven ArCH3 singlets in the ‘H and‘3C{’H} NMR spectra, and two benzylicCH2 resonances in the ‘3C {‘H} NMR spectrum supports the proposed structure for 3.4. Theorlho-methyl metalated [NPN]* ligand will be denoted [NPNC]* because it coordinates to N,P, N, and C atoms on [NPN]* ([NPNCI* = [(2-MesN-5-MeC6H3)P(Ph)(2-(N-- ,4-CH6-CH)-5-MeC3)]. The proposed structure of 3.4, [NPNC]*Zr(CH2Ph), has beenconfirmed by single-crystal X-ray diffraction analysis.93— ArCH3JJJjI6.0Figure 3.3. 400 MHz ‘H NMR spectrum of 3.4 in C6D.The ORTEP representation of the solid-state molecular structure of 3.4 is shown inFigure 3.4. Complex 3.4 features one ri2-CHPh substituent bound to Zr with a Zr—C39—C40 angle of 85.74(1 1)°. This compares well to otherT2-benzy1 Zr complexes that have Zr—C—C angles in the range of 85 to 1000.38 The Zr—C bond lengths and interatomic distancesare also typical: the Zr—C39 bond length is 2.3027(19) A, and there is a distance of2.6346(17) A between Zr and C40. The C39—C40 bond is 1.462(3) A. In addition, the Zr—C0, distances (Zr—C41 and Zr—C45), at 2.96 and 3.48 A, respectively, are too long to beconsidered bonding interactions. The two Zr—C bond lengths differ because the benzylligand is tilted to one side of the complex; the non-cyclometalated MesN substituent of[NPN]* is effectively blocking the other side of 3.4. The C40—C41 and C40—C45 bondlengths (1.410(3), 1.424(3) A) that are slightly longer than the remaining four C—C bondlengths in the phenyl ring, and the similarity of these four remaining C—C bond lengths toArHZrCH2Ph\ZrCH2Mes7.0ZrCH2MesZrCH2Ph15.0 2.094each other, are all consistent withri2-coordination of the benzyl ligand to Zr.39 One (2-CH4,6-Me2CH)N group is coordinated through N2 and C38 to Zr with bond lengths of2.1230(14) and 2.2807(19) A, respectively. The Zr—C38—C35 angle is 93.34(11)°. Thegeometry at Zr is best described as distorted square pyramidal with C39 apical and P1, Ni,N2, and C38 basal. It appears that complex 3.3 has lost one equivalent of toluene to yield3.4. The mechanism of toluene elimination is discussed in the following section.Figure 3.4. ORTEP drawing of the solid-state molecular structure of [NPNC]*Zr(12CH2Ph) (3.4) (effipsoids drawn at the 50% probability level). Hydrogen atoms and carbonatoms of the distal Mes substituent (except C0) have been omitted for clarity. Selected bondlengths (A) and angles (°): Zrl—P1 2.7646(5), Zn—Ni 2.1132(14), Zrl—N2 2.1230(14), Zn—C38 2.2807(19), Zrl—C39 2.3027(19), Zrl---C40 2.6346(17), C39—C40 1.462(3), P1—Zn—NI71.65(4), P1—Znl—N2 70.21(4), Pi—Zrl—C39 133.09(5), Zri—C39—C40 85.74(11), Zni—C38—C35 93.34(1 1), Ni—Zri—N2 127.13(5).‘C3895To characterize dibenzyl complexes of group 4 in the solid state, the Hf analogue of3.3 has been prepared. As with 3.1 and 3.2, the Hf dibenzyl complex is more heat- and light-stable than 3.3, and could be characterized crystallographically. [NPNI*Hf(CH2CSHS),3.5, isprepared from 2.15 and 2.2 equivalents ofC6H5H2MgC1 in Et20, and is isolated as a paleyellow powder in quantitative yield (Equation 3.2). In C6D solution, the benzylic resonancesappear as doublets at 2.59 (3J = 7.6 Hz) and 1.59 (3J = 2 Hz) (Figure 3.5) in the 1HNMR spectrum. In the 13C{H} NMR spectrum, the two CH2P1I resonances appear asdoublets at ö 72.3 (2J = 6 Hz) and 66.0 (2J = 20 Hz). Thus, the structure of 3.5 insolution is proposed to be five-coordinate and C symmetric with two distinct CH2Phsubstituents, one trans and one cis to P.2.2 BnMgCI[NPNJ*HfCI2 (3 2)Et202.1596ArCH3ArHHtCH Ph Hf CH Ph5155O2 2Figure 3.5. 500 MHz 1H NMR spectrum of 3.5 in C6D.The ORTEP representation of the solid-state molecular structure of 3.5 is shown inFigure 3.6. The complex is distorted trigonal bipyramidal at Hf, and has typical Hf—P andHf—N bond lengths.35 In the equatorial plane, the Hf—C39 bond length is 2.263(3) A, and theHf—C39—C40 bond angle is 120.32(18)°. For the axial benzyl ligand trans to P, the Hf—C46bond is 2.298(3) A, slightly longer than for Hf—C39, and the Hfl—C46—C47 angle is118.74(1 8)°. The solid-state molecular structure is consistent with the solution data in that itshows two distinct r’-CH2Ph groups coordinated to Hf.97Figure 3.6. ORTEP thawing of the solid-state molecular structure of [NPN]*Hf(tI1CH2Ph), 3.5 (effipsoids drawn at the 50% probability level). Hydrogen atoms and carbonatoms of the proximal Mes (except C have been omitted for clarity. Selected bond lengths(A) and angles (°): Hfl—Pl 2.8228(7), Hfl—N1 2.079(2), Hfl—N2 2.1250(19), Hfl—C392.263(3), HfI—C46 2.298(3), C39—C40 1.495(4), C46—C47 1.514(4), NI—Cl 1.462(3), P1—HfI—Nl 69.96(6), Pl—HfI-.-N2 71.12(5), Pl—Hfl—C39 87.78(7), Pl—Hfl—C46 175.67(8),Nl—Hfl—N2 115.36(8), C39—Hfl—C46 96.49(10), Hfl—C39—C40 120.32(18)°, Hfl—C46—C47118.74(1 8)°.Benzyl ligands are known to coordinate to metals in the ri’-, 2 orr13-bonding mode.The1-bonding mode is sp3 hybridized at the benzylic C, and the M—C(l—C0angle is closeto the 109.5° predicted for tetrahedral C. A good example of the r’-bonding mode of benzylis Sn(CH2Ph)4.The Sn—C—C0angles in tetxabenzyl tin are all nearly 1110 (110, 110, 11298and 114°), and the bonding is analogous to a simple organic compound without any unusualintra- or intermolecular interactions.40 If there is an interaction between M and C0 ofCH2Ph, then ther2-coordination mode may be present. For theri2-bonding mode, M—C—C0 angles of about 900, and a shortened M—C,0 distance are typically observed, although arange of bond lengths and angles has been reported.41 For example, the solid-state molecularstructure of[N2P]Zr(CH3)(CHh)([N2P] = [(Me3SiNCH2CH)PPh] determined by X-raycrystallography indicates that anr2-CHPh group is present with a Zr—C—C50 angle of95.4(2)° and a Zr—C0distance of 2.835(4) A.3° In comparison, Hf(CH2Ph)4has at least threer2-benzyl groups, and the Hf—C—C50angles are 88, 92, 93, and 101o4OA Thus, there is somevariety in the degree of2-bonding observed for the benzyl ligand. Although other bondingmodes have been proposed for transition-metal bound benzyl ligands,42’3 they are notusually cited in discussions of group 4 benzyl complexes.In 3.5, the Hf—Ca—C angles (120.32(18)° and 118.74(18)°) are larger than thoseobserved for Hf(CH2Ph)4in the solid state. The Hf—C(x—C30 angles are also larger thanwould be predicted for an sp3 hybridized C of ‘q’-benzyl, although a range of angles has alsobeen reported for the ‘q1-bonding mode.’ For example, in [Cp*Cr(CH2Ph)(jLC1)] (M—C(x—C0 121.4(3)°), and in Cp*Cr(CH2Ph)(Py (M—C(x—C0124.0(6)°, M—C--C0119.5(5)°), thelarge M—Ca—Cxo angles may be explained by the steric influence of the bulky Cp* ligand.One benzyl ligand in the complex [O2NN’M9Zr(CHPh) ([O2NN’Me] = [(2-5H4N)CH2(-2-O-3,5-C6Me]also features a large M—Ca—C angle (1 18.9(2)°).Although the bis(aminophenolate) ligand is not very bulky, the coordination sphere of theoctahechal complex is quite crowded.lTh Thus, the Hf—C(x—C50 angles observed in 3.5 arewithin the range of literature values for i’-benzyl complexes, and may be slightly larger than991110 (found for Sn(CH2Ph)4)because of the steric influence of the bulky mesitylamidosubstituents on [NPN]* or because of crystal packing.3.2.3 Kinetics of [NPN]*Zr(CH2Ph)zdecomposition.The formation of red-orange [NPNC}*Zr(q2CH2Ph) (3.4) and one equivalent oftoluene from yellow [NPNI*Zr(CH2Ph) (3.3) in C6D solution occurs over about two dayswith no detectable intermediates (see Scheme 3.3). The reverse of this reaction, formation of3.3 from 3.4 in the presence of excess toluene is not observed. By monitoring thedecomposition of three samples with different concentrations (25.9, 41.4, and 56.9 ± 2 mM)at 298 K over two days by NMR spectroscopy, the reaction was determined to be first orderin 3.3. The decomposition of five 43.1 ± 0.8 mM concentration samples in toluene-d8hasbeen followed by 1H NMR spectroscopy at 328 K., 338 K, 348 K or 358 K in a pre-heatedNMR probe, or at 298 K by periodically acquiring a 1H NMR spectrum. The combination ofintegrals used to calculate the fraction of 3.3 is outlined in appendix two, as is a sample plotof ln[3.3] vs. time (at 338 K) used to determine kQb, and a discussion of the estimation oferrors. The Eyring plot of ln(k/1) vs. 1 /T is shown in Figure 3.7. From the Eyring plot, theactivation parameters for the reaction are = 20.8 ± 0.4 kcal mo11,and = —10.3 ± 1.3cal K mol’.45 The negative value for the entropy of activation is consistent with theformation of an ordered transition state for the intramolecular reaction.461003.4Figure 3.7. Eyring plot for the thermal decomposition of [NPN]*Zr(CH2Ph),3.3.Two possible mechanisms for the decomposition of 3.3 are illustrated in Scheme 3•447In Path A, direct a-bond metathesis via a four-centre—four-electron transition state allowsconcerted bond forming (C—H of toluene, and Zr—C to [NPNC]*) and breaking (C—H ofNMes, and Zr—C of CH2Ph) to yield 3.4. The second benzyl ligand is not directly involved inPath A. In Path B, toluene is lost via intramolecular ce-H abstraction from one Zr—CH2Phgroup to give [NPN]*ZrCHPh, a benzylidene intermediate. [NPNI*ZrCHPh accepts aproton from the ortho-CH3group on NMes to give cyclometalated 3.4.-10—11-12-13-14-15-16-172.7 2.8 2.9 3.0 3.1 3.2 3.3lIT (x103 K’)101Scheme 3.4. NPN* abbreviated with —CH2CH linker in the intermediates, for clarity.Path A Path B - CH36H5[o:”There are several examples of transition-metal benzyl complexes that formcyclometalated products with loss of toluene. The decomposition may go through abenzylidene intermediate,48 whereas in other cases a a-bond metathesis mechanism isinvoked.47’9 Sigma-bond metathesis is usually accompanied by a negative entropy ofactivation (zS = —10 to —24 cal mo1 K1), since the ancillary ligand and benzyl ligand haveto adopt an ordered geometry in the transition state for bond making and breaking to-CH36H5\102occur.46 Of course, ]igand cyclometalation reactions are also known for complexes withoutbenzyl substituents.5°If C—H activation occurs via a benzylidene or alkylidene intermediate,the entropy of activation is usually near zero, typical for cx-hydrogen abstraction processes.51It should be noted, however, that there are many exceptions to this pattern.47’52 For example,[PNP]Y(CH2h) ([PNP] = [N(SiMe2CHPMe]) produces cyclometalated [PNP]’Y ([PNP]’= [MePCHSiMNSiMe(CH-)PMe and toluene via a-bond metathesis since theformation of an alkylidene to C in the backbone of [PNP] is unlikely.53 The 1St for thereaction is —3 ± 3 cal mol’ 1K’, which is atypically close to zero for a reaction that proceedsvia a-bond metathesis. The authors speculate that dissociation of a phosphine donor of[PNP] from the metal centre in the transition state might offset the negative entropy ofactivation expected for this process.53The negative entropy of activation for the decomposition of 3.3 is consistent with thereaction occurring via a-bond metathesis (Path A). To test this proposed mechanism, anisotopic labelling experiment has been performed. Complex 3.3 with perdeuterated benzylgroups can be prepared by the reaction of 2.2 equivalents of KCD2C6D5and 2.10 in Et20.When [NPNJ*Zr(CD2C6D5),3.3-d is dissolved in C6D, transferred to an NMR tube, andheated at 55 °C for 3 h, a clear red-orange solution is observed. Toluene-d7(C6D5CD2H)gives rise to a quintet at 6 2.09 in the ‘H NMR spectrum, which is consistent with thedecomposition of 3.3-d,4 occurring by Path A, since the ‘H is transferred directly fromNMes to the leaving toluene. In addition, there is no evidence for [NPNC]*Zr(r2CHD(C6DS)), or 3.4-d6, in the ‘H NMR spectrum of the product. Thus, the presence of aperdeuteratedr2-benzy1 on 3.4-d7is confirmed. If decomposition of 3.3-c44occurs by PathB, then 3.4-d6 would be the expected product because of ‘H transfer from MesN to103Zr=C(D)Ph. A fraction of the reaction mixture can be separated from the solvent by GC,and the highest molecular weight peak of this fraction is at m/Z = 99 in the mass spectrum.Thus, the results of GC-MS are consistent with the presence of toluene-d7. Thedecomposition of 3.3-d14 to 3.4-d7 and toluene-d7 lends further support to the a-bondmetathesis mechanism proposed for this reaction.3.2.4 Synthesis and reactivity of [NPN]*M(CH2SiMe3).The decomposition of [NPN]*ZrMe2 yields a mixture of products that includesmethane, as determined by ‘H NMR spectroscopy. Similarly, the evolution of toluene isobserved by ‘H NMR spectroscopy when 3.3 decomposes in C6D solution. To determine ifthe cyclometalated [NPNCI* ligand can form via e]irriination of other alkanes from[NPNI*ZrR2,pale yellow [NPN]*Zr(CH2SiMe3),3.6, has been prepared and characterized.Complex 3.6 can be prepared in high yield from 2.10 and 2.2 equivalents of LiCH2S Me3inEt20 (Scheme 3.5). The ‘H NMR spectrum of C symmetric 3.6 in C6D features resonancesassigned to two distinct CH2SiMe3groups: a doublet at ö 1.39 ([, = 7 Hz) and a singlet at 60.04, and singlets due to two Si(CH3)groups at 6 0.10 and —0.08, as well as the expectedArH and ArCH3 resonances. The 31P{’H} NMR spectrum of 3.6 shows a singlet at 6 —15.3.The ‘H NMR spectrum compares well to other Zr—CH2SiMe3complexes.54104Scheme 3.5.2.2 LiCHSIMe3 M[NPN]*ZrCI2Et202.10Upon stirring a toluene solution of 3.6 at ambient temperature in the dark for threedays, a yellow to red-orange colour change occurs. Red-orange 3.7 is obtained in high yield(see Scheme 3.5). The singlet observed in the 31P{’H} NMR spectrum of 3.6 shifts to ö —8.5for 3.7, and the ‘H NMR spectrum is indicative of a loss of C, symmetry in the complex. Inparticular, the ‘H NMR spectrum features seven ArCH3 singlets and one singlet integratingto 9H at —0.32 attributable to Si(CH3). Four diastereotopic CH2 resonances are alsoobserved. By analogy with the assignment of 3.4, 3.7 contains the cyclometalated [NPNCI*ligand. Assigned to the Mes—CH2—Zr group are a doublet at ö 2.36 (1JHH = 11.8 Hz) and adoublet of doublets at 1.56 (‘J,,11 = 11.8 Hz, JHP = 4 Hz), each integrating to IH. Assignedto the Me3Si—CH2—Zr group are two doublets at ö 0.56 and —0.13, each integrating to IHwith JHH = 11.4 Hz. In the‘3C{’H} NMR spectrum, the two CH2 groups appear as a singletat ö 65.6 and a doublet at 8 64.1 (2J = 8 Hz). In addition to the expected ArC and ArCH3resonances, a singlet at 8 2.38 due to Si(CH3)is observed in the ‘3C {‘H} NMR spectrum.The ORTEP representation of the solid-state molecular structure of 3.7 is shown inFigure 3.8, and it bears a strong resemblance to [NPNC]*Zr(rI2CH2Ph) (3.4). The C,symmetric structure of 3.7 features the cyclometalated [NPNCI* ligand and one CH2SiMe3ligand bound to Zr. The geometry about Zr is distorted square pyramidal. The Zr—N, Zr—P,3.6105and Zr—C bond lengths are similar to those in 3.4, although the Zr—C39 (2.218(2) A) bond isslightly shorter in 3.7 (Zr—C39 is about 2.30 A in 3.4). The Zr—C39—Si angle is 124.79(1 1)°.The Zr—C bond and the Zr—C—Si angle are similar to those observed for other group 4trimethylsilylmethyl complexes.54The P—Zr—N angles are also both acute at about 700, as isobserved for the other [NPN]*Zr complexes reported here.As expected, tetramethylsilane forms in C6D solutions of 3.6 over several days atroom temperature. Also, the formation of 3.7 from 3.6 appears to proceed withoutintermediates by 31P{’H} NMR spectroscopy. The decomposition of [NPNJ*ZrR2 to[NPNC]*ZrR may be a general mode of decomposition for these complexes, provided Rdoes not contain [-hydrogens.55An investigation into the mechanism of formation of 3.6has not been performed.106Figure 3.8. ORTEP thawing of the solid-state molecular structure of[NPNC]*Zr(CH2SiMe3),3.7, (ellipsoids drawn at the 50% probability level). Hydrogen atomshave been omitted for clarity. Selected bond lengths (A) and angles (°): Zrl—P1 2.7349(5),Zn—Ni 2.1237(15), Zrl—N2 2.1022(15), Zrl—C36 2.270(2), Znl—C39 2.218(2), C39—Sil1.864(2), C35—C36 1.487(3), P1—Zrl-.--N1 71.77(4), P1—Znl—N2 69.19(4), P1—Znl—C39118.37(6), P1—Zrl—C36 127.41(6), N1—Zrl—N2 131.71(6), Znl—C39—Sil 124.79(11), Zn—C36—C35 92.05(13).[NPNJ*Hf(CH2SiMe3),3.8, can be prepared from 2.15 and 2.2 equivalents ofLiCH2S Me3in Et20, in the same fashion as 3.6 (Equation 3.3). H NMR spectroscopy of3.8 in C6D indicates that the pale yellow complex has two Hf—CH2SiMe3environments: adoublet at 6 0.80 ([HP = 6 Hz), and a singlet at 6 —0.30 are assigned to the Hf-CH2TMSprotons, and two singlets are assigned to two distinct Si(CH3)groups at 6 0.10 and —0.10.The 31P{’H} and 13C{H} NMR spectra are also consistent with 3.8 being a five-coordinateC symmetric complex with inequivalent CH2SiMe3 groups that do not exchange on the107NMR timescale. Although El-MS was helpful in assigning the structure of 3.4, only peaksdue to [NPNI*H2are seen in the mass spectra of 3.6, 3.7 and 3.8.[NPN]*HfCI2 (3.3)2.153.2.5 Attempted hydrogenolysis of [NPN]*MMe2.When C6D solutions of 3.2 are stored under 1 atm of H2 in a sealed J. Young NMRtube for one month, there is no change in the colour of the solution, and no new signalsappear in the 31P{1H} or 1H NMR spectra of the sample. When a toluene solution of 3.1 or3.2 is stirred under 4 atm of H2, the reaction mixture becomes brown immediately. However,the solution reverts to yellow after about 5 mm., and no further colour changes are observed.There is also no reaction by 31P{1H} or 1H NMR spectroscopy, since the yellow productobtained upon work-up contains only peaks that can be attributed to starting material in itsNMR spectra. The brown species has not been isolated or identified.The reaction of an organometa]lic complex with hydrogen gas to liberate an alkane andyield a metal hydride is also called hydrogenolysis.56The hydrogenolysis of late transition-metal alkyl complexes is exothermic since the bond dissociation enthalpy of M—H is greaterthan for M—C.57 The reaction of early transition-metal alkyl complexes with H2 to yield metalhydrides is typically less exothermic, but can be spontaneous.24 In addition, thehydrogenolysis of late transition-metal alkyl complexes often occurs by oxidative addition, aroute that is not invoked for Zr([V) or Hf(IV) complexes. Instead, for early transition-metalMe3SiEt203.8108alkyl complexes, a a-bond metathesis mechanism in which H2 adds across the M—C bond viaa four-centred transition state may be invoked. This is a preferable explanation for thereactivity of a Zr(IV) alkyl complex because it requires a vacant orbital on the metal centre,but does not requite d electrons.58 If a Zr(IV) alkyl complex does not react with H2, it maybe because there is no readily accessible orbital for H2 to interact with the metal.5’Theinaccessibility itself may be due to electronic or steric factors, or a combination of the two.For example, the presence of t-donating ligands, or bulky ancillary ligands, may prevent H2from approaching the M—C bond.6°The reaction of 3.2 with 4 atm of H2 gas does not yield a metal hydride complex. In arelated system, the hydrogenolysis of [P2N]HfMe ([P2N] =[PhP(CH2SiMeNSiMeCH)h]yields ([P2N]Hf)i-H4,while a zirconium hydride isnot obtained from the reaction of[P2N]ZrMe with H2.6’ However, since Hf-N2 complexesare rare, and have only been prepared from Hf diiodides in the presence of strong reducingagents, 61,62 it is unlikely that one would be obtained from the reaction of a Hf hydride withN2 gas. The formation of hydride complexes from 3.1 or 3.2 may be possible by a two-steproute: the synthesis of complexes of the type {[NPN]*M(CH)}+ (M = Zr, Hf), followed byreaction with H2 in the absence of coordinating solvents or counterions.63 Although thereactions of 3.3, 3.5, 3.6 or 3.8 with H2 have not been attempted, the presence of benzyl ortrimethylsilymethyl ligands is not likely to increase the reactivity of the complex since thesteric crowding at the metal centre should be even greater.Although a Zr or Hf hydride complex has not been prepared by hydrogenolysis of 3.1or 3.2, there are many other routes to early transition-metal hydrides that have not beenattempted. Since the synthesis of metal-hydride precursors for N2 activation from H2 undermild conditions is a major goal outlined in this chapter, the use of metal hydride reagents109such as lithium aluminum hydride, or other strong reducing agents64 to obtain Zr or Hfhydrides holds limited appeal.3.3 Conclusions.Zr and Hf alkyl complexes with the [NPN]* ancillary ligand are synthesized as yellowpowders in high yield from [NPN]*MC12(M = Zr, Hf). By NMR spectroscopy, [NPN]*MR2complexes (M = Zr, Hf R = Me, CH2Ph, CH2SiMe3)are monomeric C symmetric 5-coordinate species with two distinct alkyl groups that do not interconvert on the NMRtimescale. In addition, the solid-state molecular structures of [NPN]*HfMe2 and[NPN]*Hf(CH2Ph)confirm the solution structures.Whereas the Hf alkyl complexes are thermally stable and can be analyzed by X-raydiffraction, [NPN]*ZrR2complexes decompose over several hours to give either a mixtureof products (R = Me), or cyclometalated [NPNC]*ZrR (R = CH2Ph, or CH2SiMe3)by C—Hactivation of the ancillary ligand. The two [NPNC]*ZrR complexes have been characterizedin solution and in the solid state as C1 symmetric five-coordinate complexes. Thedecomposition of {NPN]*Zr(CH2Ph) to give [NPNC]*Zr(r12CH2Ph) and toluene is firstorder in [NPN]*Zr(CH2Ph),and occurs with AHt = 20.8 ± 0.4 kcal mol’, and AS = —10.3± 1.3 cal K1 mol1. The negative value for the entropy of activation, and the fact thatdecomposition of [NPNI*Zr(CD2C6D5)yields toluene-d7 and [NPNC]*Zr(CD2C6D5)indicate that the reaction proceeds via a-bond metathesis.Hydrogenolysis of [NPNJ*MMe2(M = Zr, Hf) does not yield hydride complexes underthe conditions employed here. In the absence of a hydrogenolysis route to Zr-N2 complexes,a more direct route to dinitrogen complexes from [NPN]*ZrCl2 (2.10) and alkali metal110reducing agents is described in chapter four. The synthesis, characterization, and reactivity ofa Zr-N2 complex are presented in chapters four and five.3.4 Experimental.3.4.1 General experimental.Except where noted, experimental procedures follow those outlined in chapter two.GC-MS spectra were recorded on an Agilent series 6890 GC system with a 5973 massselective detector.3.4.2 Starting materials and reagents.Hydrogen gas was purchased from Praxair and used as received. LiCH2S Me3waspurchased from Aldrich as a IM solution in pentane that was taken to dryness, andrecrystallized from pentane prior to use. Deuterated benzyl potassium was prepared fromtoluene-d8, freshly sublimed KOtBu, and BuLi in hexanes solution according to theliterature.65All other compounds were purchased from commercial sources and were used asreceived.[NPN]*ZrMe2(3.1). To a stirred suspension of 2.10 (0.300 g, 0.419 mmol) in Et20 (10 mL)at —35 °C in the dark was added methylmagnesium chloride (3.0 M in THF, 0.31 mL, 0.92mmol) dropwise. The yellow suspension became translucent pale yellow as it warmed to rt,whereupon 1,4-dioxane (0.1 mL) was added. The reaction mixture was taken to dryness, andhexanes (10 mL) and toluene (5 mL) were added to the yellow solid. The yellow suspensionwas filtered through Ceite, and the filtrate was taken to dryness to obtain a pale yellow111powder. The pale yellow powder was collected on a frit, washed with pentane (5 mL), driedunder vacuum, and stored in the dark at —35 °C (0.225 g, 0.332 mmol, 80%).1H NMR (C6D,500 MHz): ö = 7.54 (m, 4H), 7.07 (m, 2H), 7.02 (m, 1H), 6.93 (s, 2H), 6.90(d, 2H, 2 Hz), 6.88 (s, 2H), and 6.12 (t, 2H, J- = JHH = 7 Hz) (ArH), 2.51 (s, 6H), 2.14 (s,6H), 2.09 (s, 6H), and 2.00 (s, 6H) (ArCH3), 0.93 (d, 3H, J = 5 Hz), and —0.11 (s, 3H)(ZrCH3).31P{’H} NMR (C6D,202 MHz): = —14.1 (s).‘3C{’H} NMR (C6D, 126 MHz): ö = 159.4 (d, 33 Hz), 139.4, 138.6, 137.5, 135.3 (d, 5 Hz),135.1 (d, 3 Hz), 134.4, 132.1 (d, 13 Hz), 130.9, 130.4, 129.2 (d, 4 Hz), 129.1, 129.0, 128.3,121.1 (d, 25 Hz), and 114.3 (d, 9 Hz) (ArC), 45.1 (d, 6 Hz), and 41.8 (d, 29 Hz) (ZrCH3),21.1, 20.3, 19.1, and 18.9 (ArCH3).Anal. Calcd. for CH45N2PZr: C, 71.07; H, 6.71; N, 4.14; Found: C, 71.35; H, 7.06; N, 4.08.[NPN]*HfMe2(3.2). In the dark at —35 °C, MeMgC1 (3.0 M in THF, 0.78 mL, 2.34 mmol)was added to a stfrred suspension of 2.15 (0.840 g, 1.04 mmol) in Et20 (10 mL). The mixturewas translucent pale yellow after 30 mm. at rt. 1 ,4-Dioxane (0.5 mL) was added to thereaction mixture and it was taken to dryness to obtain yellow solids that were extracted withhexanes (30 mL), followed by toluene (10 mL). The extracts were filtered through Celite, andthe filtrate was taken to dryness to obtain a pale yellow powder (0.770 g, 1.01 rnmol, 96%).‘H NMR (C6D,500 MHz): ö = 7.53 (m, 4H), 7.06 (m, 2H), 7.00 (t, 1H, 7 Hz), 6.93 (s, 2H),6.91 (d, 2H, 7 Hz), 6.90 (s, 2H), and 6.15 (dd, 2H, J = 6 Hz, JHH = 8 Hz) (ArH), 2.52 (s,6H), 2.19 (s. 6H), 2.14 (s, 6H), and 2.00 (s, 6H) (ArCH3),0.67 (d, 3H, JHP = 5 Hz), and —0.21(s, 3H) (HfCH3).11231P{1H} NMR (C6D,202 MHz): 6 = —8.9 (s).13C{’H} NMR (C6D, 126 MHz): 6 = 161.1 (d, 32 Hz), 139.1, 137.6, 137.0 (d, 5 Hz), 136.7,135.1, 134.8, 132.0 (d, 13 Hz), 130.8, 130.4, 129.1, 129.0, 128.3, 120.1, 119.9, and 115.4 (d,10 Hz) (ArC), 55.1 (d, 8 Hz), and 54.8 (d, 24 Hz) (HfCH3), 21.1, 20.2, 19.0, and 18.9(ArCH3).El-MS (m/: 749 (1, [M — Me]j, 733 (2, [M — 2MeJ), 556 (40, [2.8]j, 541 (100, [2.8 —Me]j.Anal. Calcd. for CH45N2PHf: C, 62.94; H, 5.94; N, 3.67; Found: C, 62.83; H, 6.26; N, 4.00.[NPNI*Zr(CH2Ph)(3.3). To a stirred suspension of 2.10 (0.770 g, 1.07 mmol) in Et20 (15mL) at —35 °C in the dark was added benzylmagnesium chloride (1.0 M in Et20, 2.40 mL,2.40 mmol) dropwise. The yellow suspension became translucent pale yellow as it warmed tort, whereupon 1,4-dioxane (0.1 niL) was added. The reaction mixture was taken to dryness toobtain a yellow solid that was extracted with hexanes (10 mL) and toluene (5 mL). Theextracts were filtered through Celite, and the filtrate was taken to dryness to obtain a yellowpowder that was collected on a flit, washed with pentane (5 mL), dried under vacuum, andstored in the dark at —35 °C (0.795 g, 0.960 mmol, 89%).1H NMR (C6D,300 MHz): 6 = 7.60 (t, 2H, 8 Hz), 7.53 (d, 2H, 7 Hz), 7.07 (m, 5H), 6.95 (m,4H), 6.80 (m, 6H), 6.36 (d, 2H, 7 Hz), 6.33 (d, 2H, 7 Hz), and 6.02 (dd, 2H, J = 5 Hz, JHH= 8 Hz) (ArH), 2.92 (d, 2H,JHP = 9 Hz, ZrCH2), 2.17 (s, 12H), 2.03 (s, 6H), and 1.96 (s, 6H)(ArCH3), 1.81 (s, 2H, ZrCH2).31P{1H} NMR (C6D,121 MHz): 6 = —7.2 (s).113‘3C{’H} NMR (C6D,75 MHz): = 159.1 (d, 31 Hz), 150.4, 146.0, 139.5, 138.9, 138.0, 136.2(d, 4 Hz), 134.5, 134.3, 132.7, 132.6, 131.3, 131.1, 130.8, 130.4, 129.9 (d, 4 Hz), 129.3, 128.2,127.2, 126.1, 122.0 (a, 5 Hz), 121.6, 120.6, and 114.3 (d, 9 Hz) (ArC), 74.6, and 73.0 (d, 22Hz) (ZrCH2),21.1, 20.3, 19.0, and 18.5 (ArCH3).Anal. Calcd. forC52H3N2PZr: C, 75.41; H, 6.45; N, 3.38; Found: C, 75.06; H, 6.65; N, 3.68.[NPN]*Zr(11CD2C6Ds)(3.3—d14).KCD2C6D5(62 mg, 0.45 mmol) suspended in Et20 (3mL) was added dropwise to a stirred suspension of 2.10 (0.145 g, 0.202 mmol) in Et20 (5mL) at —35 °C in the dark. The red-orange mixture was stirred at rt for 30 mm., and 1,4-dioxane (0.1 mL) was added. The mixture was taken to dryness to obtain a yellow powder.The yellow powder was extracted with C6D (1.0 mL), and the yellow extracts were filteredthrough Celite into an NMR tube.‘H NMR (C6D,400 MHz): ö = 7.60 (t, 2H, 8 Hz), 7.53 (d, 2H, 7 Hz), 7.10 (m, IH), 7.08 (d,2H, 7 Hz), 6.96 (s, 2H), 6.82 (d, 2H, 8 Hz), 6.80 (s, 2H), and 6.02 (dd, 2H,JHP = 5 Hz,JHH =8 Hz) (ArH), 2.17 (s, 12H), 2.03 (s, 6H), and 1.96 (s, 6H) (ArCH3).31P{’H} NMR (C6D,162 MHz): ö = —6.8 (s).[NPNC]*Zr(12CH2Ph) (3.4). Compound 3.3 (0.450 g, 0.540 mmol) was dissolved intoluene (15 mL) and stirred in the dark at rt for 2 d to obtain a clear, red-orange solution.The reaction mixture was taken to dryness to obtain a red solid that was collected on a frit,rinsed with pentane (5 mL), and dried under vacuum (0.390 g, 0.530 mmol, 98%). Crystals of3.4 suitable for X-ray analysis were grown by slow evaporation of a benzene solution of 3.3.114cti‘pp)OLZ‘(Hv)(zil9=f‘ZH8=HHf‘HI‘PP)86c‘(HI‘m)9‘(ilL‘m)w9-c69‘(ilt’‘m)00L-cvL‘(zH8‘HI‘p)cL‘(zH8‘HI‘p)19L=9:(zpçooi7‘9u3)aJAINH1sJT-DDAqsiujysspnoio‘ppu‘!PDnonpp.jysuojsudsnsppp(iwro)HOJ’Ipu‘irpudosi’qm1NN‘p‘Ado3sonDdsIJ’INAqjduns‘puizAjwrJvuorinosuro-partjuqrnqooitjççvqmJJAINu’wpiqsoqipdds“p-ççjouopnlos99;°i’woTur!xoddVp-vc)(a9aD- 1L.L)Jz[DNJN]t’017‘NO9‘HcIL‘3:punojI8‘N9V9‘HIL‘3:JZdN t’HDJOJpDp3JV(÷[uq]‘001)16‘(+[w—8z1‘oi)1179‘([u—J’\I]‘)179‘(+[JAII‘)17’L:/)HDv)£61Pt‘L61‘V0‘cot‘to‘V1‘911‘(vHDz)(zil8‘p)wc9TJ1‘ç99‘(3w)(zH6‘p)LiIIpu‘(zH01‘P)ocii‘t8II‘çiI‘L17i1‘8ti1‘V8i1‘98i1‘98i1‘68i1‘V0I‘t’•OI‘cici‘iCI‘Vi1‘0I‘I‘LcI‘(ZJ-{c‘p)O17I‘(ZHi‘P)1c171‘Lt’C1‘(zH‘p)c17I‘917I‘99c1‘0•9cI‘i9I‘9’9I‘OLI‘(zH1‘P)WLI‘86I‘(ZHLi‘p)oLcI‘(zHi‘p)9091=9:(zj-jj,j101‘9u3)IJ’\IN{Hj 1(s)ç_=9:(zjj,ji91‘9U3)I1’IN{R1}a‘ZHL‘HI‘P)9LI‘(sJH tR3Z‘ZH6‘HI‘pci)c8I‘(HDv)(Hc‘s)ç6pu‘(-jç‘s)‘(j-ç‘s)1,7O‘(ps‘s)I.Z‘(Hg‘s)9‘(jjç‘s)Lii‘zHL‘HI‘p)8ii‘(i-w‘s)6i1‘(sp”HH3JZ‘ZHI=cIH[ZH6=HH.[HI‘pp)OLi‘Q-iw)(zH8‘Hi‘p)86’9pu‘(zH9=dHf‘ZH8=HHf‘HI‘pp)%9‘(ZH9=dHf‘ZH8=HH[‘Hi‘pp)ii•9‘(zH8‘Hi‘)8179‘(zH8‘HI‘p)IW9‘(He‘s)069‘(ZR8‘HI‘p)169‘(i-it’‘w)00L‘(i-u‘w)9VL‘(zn1‘ZR8‘HI‘pp)617L‘(ZR1‘ZR8‘HI‘pp)19L=9(ZJ-{JAJ0017‘EID)>IJAINH1IH, 9 Hz, 1 Hz, ZrCHaHbMes), 2.29 (s, 3H), 2.27 (s, 3H), 2.26 (s, 3H), 2.21 (s, 3H), 2.04 (s,3H), 2.02 (s, 3H), and 1.96 (s, 3H) (ArCH3), 1.85 (bd, 1H, 9 Hz, ZrCHaHbMes).31P{1H} NMR (C6D,162 MHz): = —5.3 (s).GC-MS: 3.48 — 3.59 mm. (m/,’): 99 (15, [C7DH]).[NPN] *Hf(cHPh) (3.5). In the dark at —35 °C, benzylmagnesium chloride (1.0 M inEt20, 2.0 mL, 2.0 mmol) was added to a stirred suspension of 2.15 (0.721 g, 0.900 mmol) inEt20 (10 mL). The solution was translucent pale yellow after 30 mm. at rt, whereupon 1,4-dioxane (0.5 mL) was added. The pale yellow suspension was taken to dryness to obtain ayellow solid that was extracted with hexanes (20 mL), followed by toluene (10 mL). Theyellow extracts were filtered through Celite, and the filtrate was taken to dryness to obtain apale yellow powder (0.805 g, 0.880 nimol, 98%). X-ray quality crystals were grown by slowevaporation of a benzene solution of the compound.1H NMR (C6D,500 MHz): 3 = 7.52 (m, 2H, 8 Hz), 7.13 (t, IH, 7 Hz), 7.07 (m, 4H, 8 Hz),7.02 (t, 2H, 7 Hz), 6.97 (s, 2H), 6.94 (t, 2H, 8 Hz), 6.85 (d, 2H, 7 Hz), 6.82 (s, 2H), 6.76 (t,1H, 7 Hz), 6.73 (t, 1H, 7 Hz), 6.49 (d, 2H, 7 Hz), 6.28 (d, 2H, 7 Hz), and 6.06 (dd, 2H,J =8 Hz,JHH = 8 Hz) (ArH), 2.59 (d, 2H,JHP = 7.6 Hz, CH2Ph), 2.19 (s, 6H), 2.17 (s, 6H), 2.13(s, 6H), and 1.96 (s, 6H) (ArCH3),and 1.59 (d, 2H,JHp = 2 Hz, CH2Ph).31P{1H} NMR (C6D,121 MHz): 3 = —5.8 (s).13C{H} NMR (C6D, 75 MHz): 3 = 160.3 (d, 31 Hz), 150.2, 146.4, 138.9, 138.7, 137.4,134.7, 134.6, 133.8, 133.6, 132.6 (d, 12 Hz), 131.1, 130.8, 129.7 (d, 4 Hz), 129.4, 129.1, 129.0,128.5, 127.3, 126.9, 122.1, 121.0, 120.8, and 115.6 (d, 10 Hz) (ArC), 83.2 (d, 6 Hz), and 81.5(d, 21 Hz) (HfCH2),21.1, 20.2, 19.1, and 18.5 (ArCH3).Anal. Calcd. forC52H3N2PHf: C, 68.22; H, 5.84; N, 3.06; Found: C, 67.98; H, 5.93; N, 3.44.116[NPN]*Zr(CH2SiMe3)(3.6). To a stirred suspension of 2.10 (0.750 g, 1.05 rnmol) in Et20(5 mL) at —35 °C in the dark was added LiCH2S Me3(0.217 g, 2.30 mrnol) in Et20 (2 mL)dropwise. The solution became clear pale yellow instantly and was stirred at rt for 30 mm.1,4-Dioxane (0.5 niL) was added to obtain a pale yellow suspension that was taken todryness. Toluene (10 niL) was added to the yellow solid, and the suspension was filteredthrough Celite. The yellow filtrate was taken to dryness to obtain a pale yellow powder. Thepowder was collected on a fit, washed with pentane (5 mL), and dried under vacuum (0.815g, 0.994 mmol, 95%).‘H NMR (C6D, 500 MHz): 6 = 7.60 (t, 2H, 8 Hz), 7.53 (d, 2H, 7 Hz), 7.10 (t, 2H, 7 Hz),7.03 (t, 1H, 7 Hz), 6.97 (s, 2H), 6.85 (s, 2H), 6.84 (d, 2H, 7 Hz), and 6.06 (dd, 2H,JHH = 8Hz,JHP = 6 Hz) (ArH), 2.57 (s, 6H), 2.17 (s, 6H), 2.11 (s, 6H), and 1.96 (s, 6H) (ArCH3), 1.39(d, 2H, JHP = 7 Hz, CH2SiMe3),0.10 (s, 9H, Si(CH3),0.04 (s, 2H, CH2SiMe3),and —0.08 (s,9H, Si(CH3).31P{’H} NMR (C6D,202 MHz): 6 = —15.3 (s).[NPNC]*Zr(CH2S1Me3)(3.7). A yellow solution of 3.6 (0.350 g, 0.427 mmol) in toluene(10 niL) was stirred for 3 d at rt until the reaction mixture was clear, bright red-orange. Thereaction mixture was taken to dryness to obtain an orange powder that was recrystallizedfrom benzene. The red-orange crystals were collected on a frit, rinsed with pentane (5 niL),and dried under vacuum (0.273 g, 0.373 mniol, 87%). Red single crystals of 3.7 were grownby slow evaporation of a benzene solution of the compound.‘H NMR (C6D,500 MHz): 6 = 7.59 (d, 1H, 8 Hz), 7.56 (d, IH, 8 Hz), 7.49 (dd, 2H, 11 Hz,7 Hz), 7.05 (m, 3H), 7.02 (d, 1H, 8 Hz), 7.01 (s, 1H), 6.98 (bs, 1H), 6.96 (s, 1H), 6.94 (d, 1H,1178 Hz), 6.88 (s, 1H), 6.44 (dd, 1H,JHH = 8 Hz,JHP = 6 Hz), and 6.28 (dd, IH,JHH = 8 Hz,JHP= 6 Hz) (ArH), 2.53 (s, 3H), 2.51 (s, 3H), 2.36 (d, 1H, 11.8 Hz, ZrCHaHbAr), 2.25 (s, 3H),2.21 (s, 3H), 2.18 (s, 3H), 2.04 (s, 3H), and 1.99 (s, 3H) (ArCH3), 1.56 (bdd, 1H, J = 11.8Hz, J = 4 Hz, ZtCHaHbAt), 0.56 (d, 1H, 11.4 Hz, ZrCHCHdTMS), —0.13 (d, 1H, 11.4 Hz,ZrCHCHdTMS), —0.32 (s, 9H, Si(CH3).31P{’H} NMR (C6D,202 MHz): 6 = —8.5 (s).‘3C{’H} NMR (C6D, 126 MHz): 6 = 160.9 (d, 32 Hz), 157.0 (d, 27 Hz), 140.3, 138.3, 137.8,137.7, 136.6, 136.1, 135.8, 135.2, 135.0, 134.7, 133.8, 133.5, 131.8, 131.7, 130.5, 130.4, 130.2,129.6, 129.2, 127.7, 116.5, 116.2, 115.5, 115.2, 114.4 (d, 10 Hz), and 113.4 (d, 10 Hz) (Arc),65.6, and 64.1 (d, 8 Hz) (ZrCH2R), 21.3, 21.1, 20.4, 20.3, 20.0, 19.6, and 18.7 (ArCH3), 2.38(Si(CH3).Anal. Calcd. for 3.71.5(C6H):51H8N2PSiZr: C, 72.12; H, 6.88; N, 3.30; Found: C, 72.38;H, 6.84; N, 3.51.[NPN]*Hf(CH2SiMe3)z(3.8). To a stirred suspension of 2.15 (0.385 g, 0.479 mmol) inEt20 (5 mL) at —35 °C in the dark was added LiCH2S Me3(0.099 g, 1.05 mmol) in Et20 (2rnL) dropwise. The reaction mixture became clear yellow instantly and was stirred at rt for 30miii. 1,4-Dioxane (0.5 mL) was added, and the reaction mixture was taken to dryness toobtain a yellow solid that was suspended in toluene (10 rnL). The suspension was filteredthrough Celite, and the filtrate was taken to dryness to obtain a light yellow powder (0.370 g,0.408 mmol, 86%).‘H NMR (C6D,500 MHz): 6 = 7.58 (t, 2H, 8 Hz), 7.51 (d, 2H, 7 Hz), 7.09 (m, 2H), 7.01 (t,IH, 7 Hz), 6.97 (s, 2H), 6.87 (bs, 4H), and 6.10 (dd, 2H,JHII = 8 Hz,J11 = 6 Hz) (ArH), 2.58118(s, 6H), 2.19 (s, 6H), 2.17 (s, 6H), and 1.97 (s, 6H) (ArCH3), 0.80 (d, 2H, J = 6 Hz,CH2SiMe3),0.10 (s, 9H, Si(CH3),—0.10 (s, 9H, Si(CH3),—0.30 (s, 2H, CH2SiMe3).31P{1H} NMR (C6D,202 MHz): = —7.5 (s).13C{’H} NMR (C6D, 126 MHz): ö = 160.7 (d, 31 Hz), 140.1, 138.2, 137.4, 136.6, 134.6,133.1, 133.0, 130.8, 129.3, 129.1, 128.9, 128.8, 120.4, 120.2, and 115.6 (d, 10 Hz) (ArC), 72.3(d, 6 Hz), and 66.0 (d, 20 Hz) (CH2SiMe3,20.9, 20.2, 19.9, and 19.3 (ArCH), 3.74, and 2.86(Si(CH3).Anal. Calcd. forC46H61N2PSif: C, 60.87; H, 6.77; N, 3.09; Found: C, 61.00; H, 6.81; N,3.10.Thermal Decomposition Studies. The rt decomposition of 3.3 was monitored by NMRspectroscopy to determine the order of the reaction. Complex 3.3 (15.0, 24.0 or 33.0 mg)was weighed into a 3-mL vial and 0.70 mL of C6D was transferred to the vial by syringe.The yellow solution was transferred to an NMR tube and the sample was analyzedperiodically over 2 d by 1H NMR spectroscopy. To determine the rate constant for thereaction at each of five different temperatures, 3.3 (25.0 mg) was weighed into a 3-mL vialand dissolved in 0.70 mL toluene-d8.The solution was transferred to an NMR tube andimmediately frozen at —10 °C until it could be analyzed. Each sample was placed in the NMRprobe heated to 328, 338, 348, or 358 K, and the reaction was followed by 1H NMRspectroscopy. The first 1H NMR spectrum was measured two mm. after the sample wasinserted into the probe. From the plot of ln[3.3] vs. time, no further time appeared necessaryfor the sample to reach thermal equilibrium before the first 1H NMR spectrum wascollected. One sample was stored at rt, and monitored periodically over 2 d.119Reaction of [NPN]*MMC2with 4 atm H2 (M = Zr or Hf). In a typical experiment, yellow3.1 (0.300 g, 0.444 mmol) was dissolved in toluene (10 mL) in a 200-mL Teflon-sealed thick-walled bomb. The solution was degassed by three freeze-pump-thaw cycles and filled withH2 at 77 K. The flask was warmed to rt (4 atm H2) behind a blast shield. The solutionbecame pale brown after the solvent thawed, but after about 5 mm. the reaction mixture wasclear yellow again. The yellow solution was stirred in the dark for 4 h. (For 3.2, the reactionmixture was stirred for 3 d since starting material decomposition was not a concern.) Afterventing the pressure of H2, an aliquot of the yellow reaction mixture was analyzed by31P{1H} NMR spectroscopy, and a second aliquot was concentrated under vacuum to obtaina yellow powder that was analyzed by NMR spectroscopy. Visually, and by NMRspectroscopy, only starting material was present.Reaction of [NPN]*HfMe with 1 atm H2. Pale yellow 3.2 (50 mg, 66 iimol) wasdissolved in CD6 (- 1 mL), filtered, and transferred to a J. Young NMR tube. The solutionwas degassed by three freeze-pump-thaw cycles (frozen at —10 °C, thawed under flow of H2gas) and sealed (1 atm H2) at rt. The solution was monitored over 4 weeks. There was nocolour change and no new peaks were observed in the 31P{1H} or 1H NMR spectra.3.5 References.‘A) Ziegler, K. Belgium Patent 553, 362, 1953. B) Natta, G.; Pino, P.; Corradini, P.;Danusso, F.; Mantica, E.; Mazzanti, G.; Moraglio, G. J. Am. Chem. Soc. 1955, 77, 1708.C) Ziegler, K.; Holzkamp, E.; Breil, H.; Martin, H. Angew. Chem. 1955, 67, 541.1202A) Alt, H. G.; Koppl, A. Chem. Rev. 2000, 100, 1205. B) McKnight, A. L.; Waymouth, R. M.Chem. Rev. 1998, 98, 2587.A) Ziegler, K.; Koster, R.; Breil, H.; Martin, H.; Holzkamp, E. German Patent 1016023,19570919, 1957. B) Breslow, D. S.; Newburg, N. R. J. Am. Chem. Soc. 1957, 79, 5072. C)Brintzinger, H. H.; Fischer, D.; Mülhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem., mt.Ed. EngI. 1995, 34, 1143.Chen, E. Y.-X.; Marks, T. Chem. Rev. 2000, 100, 1391.Clawson, L.; Soto, J.; Buchwald, S. L.; Steigerwald, M. L.; Grubbs, R. H. J. Am. Chem.Soc. 1985, 107, 3377. B) Marks, T. J. Acc. Chem. Res. 1992, 25, 57.6 Coates, G. W.; Hustad, P. D.; Reinartz, S. Angew. Chem. mt. Ed. 2002, 41, 2236.A) Ewen, J. A.; Jones, R. L.; Razavi, A.; Ferrara, J. D. J. Am. Chem. Soc. 1988, 110, 6255. B)Lee, I.-M.; Gautbier, W. J.; Ball, J. M.; Iyengar, B.; Collins, S. Oganometallics 1992, 11, 2115.8 Coates, G. W. Chem. Rev. 2000, 100, 1223.Coates, G. W. J. Chem. Soc., Dalton Trans. 2002, 467. B) Mehrkhodavandi, P.; Schrock, R.R.; Pryor, L. L. Oiganometallics 2003, 22, 4569. C) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev.2003, 103, 283.10Thayer, A. M. Chem. Eng. News 1995, 73, 15.‘ A) http: / /www.sriconsulting.com/SRIC/Public/NewsEventsArt/2005APICIntille.pdfaccessed on March 21, 2006.B) http: / /www.epsem.ucsb.edu/surnmer programs /epsemsi/projects /projects2005 /pdfs /green bazan.pdf accessed on March 21, 2006.l2Troutman, M. V.; Appella, D. H.; Buchwald, S. L. J. Am. Chem. Soc. 1999, 121, 4916.121A) Esteruelas, M. A.; Lopez, A. M.; Mateo, A. C.; Oñate, E. Otganometallics 2005, 24, 5084.B) Li, Y.; Shi, Y.; Odom, A. L. J. Am. Chem. Soc. 2004, 126, 1794.14 Guo, H.; Kong, F.; Kanno, K.-I.; He, J.; Nakajima, K.; Takahashi, T. O,ganometa11ics 2006,25, 2045.15 Tilley, T. D. Acc. Chem. Res. 1993, 26, 22.16 Collins, S.; Kuntz, B. A.; Hong, Y. J. Org. Chem. 1989, 54, 4154. B) Grossman, R. B.;Davis, W. M.; Buchwald, S. L. J. Am. Chem. Soc. 1991, 113, 2321.17 Molander, G. A.; Dowdy, E. D.; Noll, B. C. Organometallics 1998, 17, 3754.18 Gately, D. A.; Norton, J. R.; Goodson, P. A. J. Am. Chem. Soc. 1995, 117, 986.19 Turculet, L.; Tilley, T. D. Organometallics 2002, 21, 3961.20 Bennett, C. R.; Bradley, D. C. J. Chem. Soc., Chem. Commun. 1974, 29. B) Simpson, S. J.;Anderson, R. A. Inorg. Chem. 1981, 20, 3627.21 Lee, H.; Jordan, R. F. J. Am. Chem. Soc. 2005, 127, 9384.Bercaw, J. E.; Marvich, R. H.; Bell, L. G.; Brintzinger, H. H. J. Am. Chem. Soc. 1972, 94,1219.23 de Wo1f J. M.; Blaauw, R.; Meetsma, A.; Teuben, J. H.; Gyepes, R.; Varga, V.; Mach, K.;Veldman, N.; Spek, A. L. Organometallics 1996, 15, 4977.24 Chink, P. J.; Henling, L. M.; Bercaw, J. E. Or.ganometallics 2001, 20, 534.25 Fryzuk, M. D.; Johnson, S. A.; Rettig, S. J. J. Am. Chem. Soc. 1998, 120, 11024.26A) Fryzuk, M. D.; MacKay, B. A.; Johnson, S. A.; Patrick, B. 0. A,gew. Chem. mt. Ed. 2002,41, 3709. B) MacKay, B A.; Patrick, B. 0.; Fryzuk, M. D. Organometallics 2005, 24, 3836. C)Fryzuk, M. D.; MacKay, B. A.; Patrick, B. 0. J. Am. Chem. Soc. 2003, 125, 3234.12227 Manriquez, J. M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J. E. J. Am. Chem. Soc. 1978,100, 2716.28 A) Bianchirii, C.; Meli, A.; Perruzzini, M.; Vizza, F.; Zanobini, F. Organometallics 1989, 8,2080. B) Vigalok, A.; Ben-David, Y.; Milstein, D. Organometallics 1996, 15, 1839. C) Morris, R.H. Inorg. Chem. 1992, 31, 1471.29Yandov D. V.; Schrock, R. R. Science 2003, 301, 76.30 Schrock, R. R.; Seidel, S. W.; Schrodi, Y.; Davis, W. M. Organometallics 1999, 18, 428.31 Karplus, M. J. Am. Chem. Soc. 1963, 85, 2870.32 A) Partridge, M. G.; Messerle, B. A.; Field, L. D. O,ganometallics 1995, 14, 3527. B)Kuhiman, R.; Streib, W. E.; Huffman, J. C.; Caulton, K. G. J. Am. Chem. Soc. 1996, 118, 6934.Emsley, J.; Feeney, J.; Sutdiffe, L. H. High Resolution NMR Spectroscopy, Vol. 2; PergamonPress: Oxford, 1996, Appendix B.Negishi, E. Acc. Chem. Res. 1994, 27, 124. B) Guo, Z.; Swenson, D. C.; Jordan, R. F.Otganometallics 1994, 13, 1424. C) Erker, G; Schiund, R.; Krueger, C. Organometallics 1989, 8,2349.A) Fryzuk, M. D.; Carter, A.; Rettig, S. J. Organometallics 1992, 11, 469. B) Mehrkhodavandi,P.; Schrock, R. R.; Bonitatebus, P. J., Jr. Organometallics 2002, 21, 5785. C) Liang, L.-C.,Schrock, R. R.; Davis, W. M. Organometallics 2000, 19, 2526.1 Zucchini, U.; Giannini, U.; Albizzati, E.; D’Angelo, R. Chem. Comm. 1969, 1174.A) Zucchini, U.; Albizzati, E.; Giannini, U. J. Organomei Chem. 1971, 26, 357. B) Toupance,T.; Dubberley, S. R.; Rees, R. H.; Tyrrell, B. R.; Mountford, P. Organometallics 2002, 21, 1367.38 A) Jordan, R. F.; LaPointe, R. E.; Baenziger, N.; Hinch, G. D. Organometallics 1990, 9, 1539.B) Jordan, R. F.; LaPointe, R. E.; Bajgur, C. S.; Echols, S. F.; Willett, R. J. Am. Chem. Soc.1231987, 109, 4111. C) Latesky, S. L.; McMullen, A. K.; Niccolai, G. P.; Rothwell, I. P.Organometallics 1985, 4, 902.Dryden, N. H.; Legzdins, P.; Phillips, E. C.; Trotter, J.; Yee, V. C. Organometallics 1990, 9,882.40 A) Davies, G. R.; Jarvis, J. A. J.; Ki1bourn, B. T. Chem. Comm. 1971, 1511. B) Davies, G. R.;Jarvis, J. A. J.; Kilbourn, B. T.; Pioli, A. J. P. Chem. Comm. 1971, 677.41 A) Horton, A. D.; de With, J.; van der Linden, A. J.; van de Weg, H. Organometallics 1996,15, 2672. B) Novak, A.; Blake, A. J.; Wilson, C.; Love, J. B. Chem. Comm. 2002, 2796.42 Cotton, F. A.; Marks, T. J. J. Am. Chem. Soc. 1969, 91, 1339.Burch, R. R.; Muetterties, E. L.; Day, V. W. Organometallics 1982, 1, 188.A) Bhandari, G.; Kim, Y.; McFarland, J. M.; Rheingold, A. L.; Theopold, K. H.Organometallics 1995, 14, 738. B) Girolami, G. S.; Wilkinson, G.; Thomton-Pett, M.;Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1984, 2789. C) Pellecchia, C.; Immirzi, A.;Grassi, A.; Zambelli, A. Organometallics 1993, 12, 4473. D) Morgan, A. R.; Kloskowski, M.;Kalischewski, M.; Kalischewski, F.; Philips, A. H.; Petersen, J. L. Organometallics 2005, 24,5383.Friebolin, H. Basic One-and Two-Dimensional NMR Spectroscopy, 3’’ ed.; Wiley-VCH:Weinheim, 1998, p. 309.A) Rothwell, I. P. Po/yhedron 1985, 4, 177. B) Smith, G. M.; Carpenter, J. D.; Marks, T. J. J.Am. Chem. Soc. 1986, 108, 6805. C) Bruno, J. W.; Smith, G. M.; Marks, T. J.; Fair, C. K.;Schultz, A. J.; Williams, J. M. J. Am. Chem. Soc. 1986, 108, 40.‘ Shao, P.; Gendron, R. A. L.; Berg, D. J.; Bushnell, G. W. Organometallics 2000, 19, 509.48 Bulls, A. R.; Schaefer, W. P.; Serfas, M.; Bercaw,J. E. Organometallics 1987, 6, 1219.12449A) Latesky, S. L.; McMullen, A. K.; Rothwell, I. P.; Huffman, J. C. J. Am. Chem. Soc. 1985,107, 5981. B) Watson, P. L.J. Am. Chem. Soc. 1983, 105, 6491. C) Chamberlain, L. R.;Rothwell, I. P.; Huffman, J. C. J. Am. Chem. Soc. 1986, 108, 1502. D) Smith, G. M.;Carpenter, J. D.; Marks, T. J. J. Am. Chem. Soc. 1986, 108, 6805.5° A) Stella, S.; Chiang, M.; Floriani, C. J. Chem. Soc., Chem. Commun. 1987, 161. B) Schrock,R. R.; Bonitatebus, P. J., Jr.; Schrodi, Y. Organometallics 2001, 20, 1056. C) Schrodi, Y.;Schrock, R. R.; Bonitatebus, P. J., Jr. Organometallics 2001, 20, 3560.51 McDade, C.; Green, J. C.; Bercaw, J. E. O,ganometa1Iics 1982, 1, 1629.52 Cheon, J.; Rogers, D. W.; Girolami, G. J. Am. Chem. Soc. 1997, 119, 6804. B) Li, L.;Hung, M.; Xue, Z. J. Am. Chem. Soc. 1995, 117, 12746. C) van der Heijden, H.; Hessen, B. J.Chem. Soc., Chem. Commun. 1995, 145.Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J. Organometallics 1991, 10, 2026.54A) McAlexander, L. H.; Hung, M.; Li, L.; Diniinnie, J. B.; Xue, Z.; Yap, G. P. A.;Rheingold, A. L. Organometallics 1996, 15, 5231. B) Amor, F.; Butt, A.; du Plooy, K. E.;Spaniol, T. P.; Okuda, J. Organometallics 1998, 17, 5836. C) Spencer, L. P.; Winston, S.;Fryzuk, M. D. Organometallics 2004, 23, 3372.A) Schrock, R. R.; Parshall, G. W. Chem. Rev. 1978, 78, 243. B) Spessard, G. 0.; Miessler,G. L. Organometallic Chemistry; Prentice-Hall, Inc.: Upper Saddle River, New Jersey, 1997, p.118.56 A) Lee, H.; Desrosiers, P. J.; Guzei, I.; Rheingold, A. L.; Parkin, G. J. Am. Chem. Soc. 1998,120, 3255. B) Gell, K. I.; Schwartz, J. J. Am. Chem. Soc. 1978, 100, 3246.‘ Labinger, J.; Bercaw, J. E. Oiganometallics 1988, 7, 926.58 Gell, K. I.; Posin, B.; Schwartz, J.; Williams, G. M. J. Am. Chem. Soc. 1982, 104, 1846.12559Lauher, J. W.; Hoffman, R. J. Am. Chem. Soc. 1976, 98, 1729.60 Evans, W. J.; Bloom, I.; Hunter, W. E.; Atwood, J. L. J. Am. Chem. Soc. 1983, 105, 1401.61 Fryzuk, M.D.; Corkin,J. R.; Patrick, B. 0. Can.J. Chem. 2003, 81, 1376.62 Bernskoetter, W. H.; Olmos, A. V.; Lobkovsky, E.; Chink, P. J. Organometallics 2006, 25,1021.63Jordan, R. F.; Bajgur, C. S.; Dasher, W. E.; Rheingold, A. L. Organometallics 1987, 6, 1041.64 Roddick, D. M.; Fryzuk, M. D.; Seidler, P. F.; Hilihouse, G. L.; Bercaw, J. E. Organometallics1985, 4, 97.Kneifel, H.; Bayer, E. Angew. Chem. mt. Ed. 1973, 12, 508.126Chapter FourSynthesis and Structure of Zirconium Dinitrogen Complexes4.1 Introduction.Molecular nitrogen is unreactive, in part because it has a strong triple bond (945 kJmol’), a large HOMO-LUMO gap, and it lacks a dipole.1 In 1965, however, the firstdinitrogen complex, {Ru(NH3)5(i1-N]2was reported.2 Initially prepared serendipitouslyfromN2H40and RuCl3xH2O, the complex was later intentionally synthesized from N2gas, Ru(NH3)5C1 and Zn.3 Today, N2 complexes of most of the transition elements and thelanthanides are known.4 Diriitrogen coordinated to a transition metal from groups 7 to 10gate transition metals for the purpose of this discussion) is usually unactivated or onlyweakly activated, with an N—N bond length similar to that of N2 gas (1.0975 A).5 Transitionmetals from groups 4 to 6 (termed early transition metals here) can activate N2 stronglybecause they are more reducing. The N—N bond in ([PNP]ZrC1)2j.i-ri:-)is 1.548(7) A,longer than the N—N single bond in hydrazine (1.47 A).6Most late transition-metal dinitrogen complexes are electronically saturated speciesprepared without strong reducing agents or harsh conditions. For example, [Re(PMe3)5(11-N)]Cl forms when Re(PMe3)5C1 is dissolved in EtOH in the presence of N2.7 In contrast,early transition-metal dinitrogen complexes are usually synthesized by reducing a metalhalide complex with a strong alkali metal reducing agent. Reduction of [PNP]ZrC13withNa/Hg amalgam provides ([PNP]ZrCl)2Qt-:1-),6whereas potassium graphite (KC8)reduction of [P2N]ZrC1 provides ([PN]Zr)ji-ii:-N(N—N bond: 1.43(1) A) (Figure1274.1).8 Recently, the reduction of [NPN]ZrC12HF) with KC8 to give {[NPNjZr(THF)}2(i-q2:r-N) (N—N bond: 1.503(3) A) has been reported.9CI Cl2Ls/iKC8N2Me2Si,i N—SiMe2Pr2 / )Cl—Zr-P/\ PiN.Pr’2 \,“ClMe2SiN\_.., 2Me2Early transition-metal N2 complexes can be synthesized directly from low-valent metalcomplexes and N2. The Nb(III) complex, [P2NJNbCH3reacts with N2 to give diamagnetic{[P2NJNb(CH3)}Qi-i1:- ,with an N—N bond length of 1.280(7) A (Figure 4.2).’°Complete cleavage of the N—N triple bond is also achieved from the direct reaction of N2Cl2Na/HgN22Me2S1Me2SiKC8N2Figure 4.1. Zirconium dinitrogen complexes (silyl methyl substituents of [P2N]omitted).128RR R NN.. / N2 R (II R2 )‘N— Mo—N 2 R”N......ArAr” Ar, \Ar ArAr = 3,5-Me2C6HR = C(CH)( DFigure 4.2. Reactions of low-valent early transition-metal complexes with N2 (silyl methylsubstituents of {P2N]omitted).with a reduced metal complex; two equivalents of [Ar(R)N]3Mo(III) (Ar = 3,5-Me2C6HR =C(CD3)2H reduce N2 by six electrons to yield two equivalents of [Ar(R)NJ3MoE (Figure4.2).h1 Early transition-metal hydrides can also activate N2. (Cp”Zr)jt-:’q-N)(Cp” = 1,3-(SiMe3)2- i5-CH3)forms when two equivalents of 93uLi are allowed to react with Cp”2ZrC1(Scheme 4.1).12 The initial product of the reaction,Cp”2Zr(H)(CHH(C),decomposesto give a cyclometalated Zr hydride, Cp”(1-SiMe3-3- SiM2_)5H)ZrH,that activatesN2.MeI N22 Ph. _—- Nb-LJ-S,129Scheme 4.1.NMe3Sie3Me3Although many N2 complexes are known, predicting the conditions that will lead totheir formation is a challenge. Ancillary ligand, metal, solvent, and N2 pressure are importantfactors in determining whether N2 activation occurs rather than activation of the solvent,13 orthe ancillary ligand,’4 formation of a reduced product that does not contain N2,15 orformation of a mixture of products. Chelating it-acceptor ligands can facilitate synthesis ofearly transition-metal N2 complexes because they stabilize reduced species.It is an exciting time in N2 research since ancillary ligand design is at the core of severalrecent major breakthroughs.16 In 1974, the synthesis of [Cp*2Zr(rl‘-N2)](ii-ri’:rI ‘-N2) fromCp*2ZrC1 and Na/Hg amalgam was reported.17 The bridging end-on bound N2 is slightlyactivated (N—N bond: 1.182(5) A), and hydrazine is produced in high yield upon addition ofHC1 to the complex. The addition of H2 to the complex provides Cp*2ZrH and free N2.18 In2004, the synthesis of[(1]5-CMe4H)2Zr(Ji-11:rN)from (r15-CMe4H)2Z Cl and Na/Hgamalgam was reported.’9N2 in this complex is strongly activated (N—N bond: 1.377(3) A),and it reacts with H2 to yield[(r5-CMe4H)Zr H)](ji- l:1iN)with two new N—HMe3Si4 ‘BuLlMe3SI________2 M’CI. 2S1Me3SiMe2•ZcH2Me3Si ZrMe3S1 \S1Me3Me3Si130bonds. Thus, the use of tetramethylcyclopentadiene rather than pentamethylcyclopentadienechanged the coordination mode, bond length and reactivity of N2.In this chapter, the synthesis of a dinuclear Zr-N2 complex by KC8 reduction of[NPN]*ZrC12is described. N2 is coordinated side-on to the two Zr atoms, as revealed bysingle crystal X-ray analysis. Coordinated THF can be replaced with Py, PMe3 and PMe2h,and these adducts are characterized in the solid state (Py and PMe2h) and in solution. Anattempt to synthesize a Hf-N2 complex is also presented.4.2 Results and Discussion.4.2.1 Synthesis and structure of {[NPN]*Zr(THF)}2(t12:12N).Deep blue-green {[NPN}*Zr(THF)}(Ir12:112N), 4.1, can be prepared from[NPN]*ZrCl2(2.10) and 2.2 equivalents of KC8 in THF under 4 atm of N2 (Equation 4.1).Black crystals of 4.1 are obtained upon work-up in 79% yield. Initially, a Zr-N2 complexcould not be isolated using this method, although there were signs that an N2 complexformed: the reaction mixture turned bright green and a peak attributable to a dimeric[NPN]*Zr species was apparent in the mass spectrum. There is also evidence that a Zr-N2complex forms under other conditions (i.e., 2.2 equivalents KC8, THF, 1 atm N2, or fiveequivalents Na/Hg, THF, 4 atm N2), but in all cases, the green reaction mixture transformsto a beige powder during work-up.1314.4 KC, N22 (4.1)THFThe isolation of a Zr-N2 complex is possible if the THF used for the reaction isrigorously H20- and 02-free, if the reaction mixture warms slowly to room temperature(EtOH/liquid-N2bath: —116 °C), and if the mixture is vigorously stirred and the flaskperiodically inverted over the course of the reaction. If a deep purple or blue-green colour isobserved during the fiist hour after the flask is charged with N2, then a high yield of 4.1 isgenerally obtained. It is unclear why 4.1 can be isolated under these conditions, whereasdecomposition is observed otherwise. It is known that Zr-N2 complexes are extremely airand moisture sensitive, and that vigorous stirring will increase the concentration of N2 in thereaction mixture.Another factor that may have complicated the isolation of 4.1 is its apparentdecomposition in the absence of THF. Crystalline samples are dried under vacuum briefly(- 15 mm.) prior to analysis because 4.1 becomes an off-white powder when it is storedunder vacuum for prolonged periods. The powder contains a benzene-soluble fraction, and afraction that is insoluble in benzene, water, THF or DMSO. The benzene-soluble fraction is[NPNI*H2 (2.8), as determined by 1H and 31P{’H} NMR spectroscopy, El-MS andmicroanalysis. The insoluble white fraction has not been characterized. The mechanism ofthe decomposition of 4.1 under vacuum remains a mystery.2.104.1132There is a singlet at 6 5.0 in the 31P{’H} NMR spectrum of 4.1 in THF-d3. Bothphosphines in the proposed dimeric structure are equivalent. The ‘H NMR spectrum (Figure4.3) shows four singlets between 6 2.2 and 1.7 due to four distinct ArCH3 groups in the C2hsymmetric complex, as well as the expected ArH resonances. Singlets due to coordinatedTHF appear at 6 3.54 and 1.69, and partially overlap with resonances due to free THF in the‘H NMR spectrum. In the‘3C{’H} NMR spectrum, the expected arylmethyl and aromaticcarbon signals, as well as resonances attributable to free and coordinated THF, are observed.There are two equivalents of THF in the crystal lattice of 4.1 as revealed by ‘H NMRspectroscopy of 4.1 in C6D.The results of combustion analysis are also consistent with theformulation 4.12THF. Crystalline samples of 4.F2THF are stable, and can be stored formonths at —35 °C. Prior to use, crystalline samples can be dissolved in THF and dried (withcareful monitoring) to obtain a green powder that does not contain solvent of crystallization,which is convenient for determining stoichiometry. In the mass spectrum of 4.1, there is apeak at = 1320 that is assigned to [M — 2THF]ArCH3TH FArH THE• • • • • • • . • • . • • . • • • . . • • • • • •••7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5(ppm)Figure 4.3. 500 MHz ‘H NMR spectrum of 4.1 in THF-d8.133Little is known about the mechanism of formation of early transition-metal dinitrogencomplexes, although some relevant information can be gleaned from the literature.Potassium graphite (KG8) has a reduction potential sini1ar to potassium metal, although itspower decreases as electrons are transferred to the substrate.2°Like elemental potassium,reduction by KC8 occurs via one-electron transfer steps. KG8 has become a widely usedreducing agent for metal complexes because it is easy to work with on a multi-gram scale,and graphite is the only by-product, in addition to KCI, for example, if metal chlorides arereduced. Cyclic voltarnmetry of(i5-CH4R)2ZrC1 (R = Me, Et, SiMe3 H) shows that areversible one-electron reduction at E172 —1.7 V occurs to yield the Zr(III) species [(reG5H4R)2ZrCl]’ Chemical reduction of Gp2TiC1 produces the Ti(III) species,[Na(THF)J[CpTiC1],which is observed by ESR spectroscopy. Although some Zr(III) andHf(III) complexes are stable and have been structurally characterized, othersdisproportionate to give a mixture of M(H) and M([V) species.24 A Ti(H) dinitrogencomplex, (i5-GH4(SiMe2Ph))T (i1-N8), has been characterized crystallographically,25whereas discrete mononuclear Zr(TI) N2 complexes are unknown, likely due to the strongerreduction potential of Zr compared to Ti.One proposed route to 4.1 involves the one-electron reduction of [NPN]*ZrCl2 toproduce a species like [K(THF),L]([NPN]*ZrG12).Disproportionation of this Zr(III) anion isexpected to give [NPN]*ZrGl2, and a solvated [NPNI*Zr(II) intermediate, such as[NPN]*Zr(THF)2,along with two equivalents of KC1. Although N2 is a weaker donor thanmost solvents or Lewis bases, the formation of strong hard-hard bonding interactionsbetween Zr and N2 is a thermodynamic driving force for Zr-N2 complex formation. Sincethe first step in the reduction of N2 (i.e., N2 to N2) occurs at a higher potential than the134subsequent reduction steps (e.g., N2 to N2j,4 the formation of a formally Zr4N2jZdimer may be facile compared to the initial formation of a Zr2(N)species. This is onepossible explanation for the prevalence of dinuclear N2 complexes of the early transitionmetals. In addition, a species such as Zr(N2) is expected to be much more Lewis basicthan N2, which may allow the formation of a dinuclear complex. The mechanism ofdinitrogen activation by reduced Zr species is still unclear, probably because the conditionsrequired for the synthesis of most Zr-N2 complexes are somewhat incompatible withcharacterizing intermediates spectroscopically, or monitoring reactions over time.When 2.10 is reduced with 2.2 equivalents of KC8 under identical conditions used toobtain 4.1, but in the absence of N2, blue-green 4.1 does not form. Instead, the reactionmixture turns brown. When an aliquot of the reaction mixture is analyzed by 31P{1H} NMRspectroscopy, singlets at ö —14.6 and —15.4 are observed due to the major diamagnetic Pcontaining products, along with minor products such as 2.8, and other unidentified species.No peaks at m/> 556 (2.8) are observed by El-MS. The major products could not beseparated from each other for further characterization.Reduction of early transition-metal halide complexes in the absence of N2 can lead tosolvent activation, ancillary ligand activation, or formation of a reduced complex that doesnot contain N2. Solvent activation by reduced species is exemplified by C—O cleavage ofTHF,26 or C—H activation of toluene to give an i’-benzy1 complex,27whereas ancillary ligandactivation is exemplified by the formation of dimericri6-phenyl-bridged ([P2NJZr)2 from[P2N]ZrC’. The reduction of ZrC14/PEt3 mixtures with sodium amalgam gives[ZrC13(PEt)]2as a forest green Zr(III) compound with bridging chlorides.15 Likewise,sodium amalgam reduction of [PCP]ZrC13 ({PCP] = [1,3-(Pr2PCHSilVIe)-15H3)under135Ar yields {PCP] ZrC12.8 There is insufficient evidence to determine if any of these reactionshas occurred for the reduction of 2.10.When 2.10 is reduced under ‘5N2, blue-green 4.1ThN2 is obtained. It should be notedthat‘5N2-labelled 4.1 cannot be isolated if a glass bulb of 15N2 gas is used, possibly because apressure of 4 atm of N2 is not attained in the flask at room temperature. When 15N2 from asmall lecture bottle is used, 4.1-15N2is isolated in high yield as a black crystalline solid. Thereis a doublet (2JPN = 6.7 Hz) at 6 5.0 in the 31P{’H} NMR spectrum of 4.1-’5N2,where asinglet was observed for 4.1. There is also a doublet at 6 116.6 (relative to MeNO2at 6 0) inthe‘5N{’H} NMR spectrum (Figure 4.4). The 31P{1H} and 15N{H} NMR spectra indicatethat an AA’XX’ spin system is present in 4.1ThN2 although ‘5N can only be observed tocouple to one 31P nucleus (2JPN 0). Since the two 15N and 31P nuclei are magneticallyinequivalent, N2 evidently does not rotate about the Zr---Zr axis in 4.1.122 120 118 11.6 114 112 110(ppm)Figure 4.4. 40 MHz 15N{H} NMR spectrum of 4.1-’5N2in THF-d8.The presence of a signal in the ‘5N {‘H} NMR spectrum of 4.1-’5N2confirms that thesource of N2 in the complex is 15N2 gas. At this time, it is difficult to correlate the 15Nchemical shift in dinitrogen complexes with the coordination mode or extent of N2136activation. A wide range of such chemical shifts is known for N2 complexes.29The majorityof side-on N2 complexes listed in Table 1.2 have 15N chemical shifts between 6 495 and 621,and the chemical shift of hydrazine is 6 690. The 15N chemical shifts of ([NPN]Ta)2jt-H)Q.t-ri’:r12-N) are 6 —20.4 and 163.6. The 6.7 Hz P-N coupling is similar to other JNP valuesobserved for 15N2 complexes with phosphine ligands,3°although the reported values of 2JNPcover a wide range,31 and in many cases P-N coupling in 15N2 complexes is unreported orunobserved.The ORTEP representation of the solid-state molecular structure of 4.1 is shown inFigure 4.5, and the arrangement of P, N, and 0 about Zr is illustrated in Figure 4.6. Thedinuclear complex features one THF molecule, and one facially coordinated [NPN per Zr.N2 is bound side-on to both zirconium centres with a slight butterfly or hinge distortion; theangle between the two ZrN2 planes is 166°. The two halves of the molecule are related by atwo-fold rotation axis that bisects the N—N bond; 4.1 is C2 symmetric in the solid state. TheN—N bond length is 1.503(6) A, which corresponds to reduction to N24, or hydrazide. TheZr—N bond lengths to N2 are slightly different: Zri—N3 is 2.023(3) A, and Zrl—N3’ is2.089(3) A. The Zr—Ni and Zr—N2 bonds are 2.184(3) A and 2.224(3) A, respectively. TheZr—Pi bond is 2.6777(10) A, and the Zr—0 bond is 2.371(2) A. The geometry around Zr isbest described as distorted trigonal bipyramidal with 0 and P donors apical and Ni, N2 andthe dinitrogen fragment equatorial. As with other complexes of [NPNI*, the P—Zr—NI andP—Zr—N2 angles are acute at 71.84(8), and 73.42(8)°, respectively.137Figure 4.5. ORTEP drawing of the solid-state molecular structure of{{NPNj*ZrCFHF)}2(I112:112N),4.1 (ellipsoids drawn at the 50% probability level). Carbonatoms of the proximal Mes substituents (except for C) and all hydrogen atoms have beenomitted for clarity. Selected bond lengths (A) and angles (°): Zrl—P1 2.6777(10), Zn—NI2.184(3), Znl—N2 2.224(3), Zrl—O1 2.371(2), Znl—N3 2.023(3), Zrl—N3’ 2.089(3), N3--N3’1.503(6), P1—Zn—Ni 71.84(8), P1—Znl—N2 73.42(8), N3--Znl—N3’ 42.85(15), Zri—N3’—Zri’135.02(15), Oi—Zrl—Pi 154.14(7), Pi—Zr—N3 82.00(8).138N2’ N2 P1N2N2’Ni01NiFigure 4.6. Two views of the stereochemistry around Zr in 4.1.Complex 4.1 is C2 symmetric in the solid state, but C2h symmetric in solution. Themirror plane of symmetry in the solution structure encompasses the Zr2N core that isbutterfly-distorted in the solid state. Thus, if Zr2N is butterfly-distorted in solution, afluxional process that flips N2 from one side of the Zr---Zr axis to the other may beresponsible for the apparent mirror plane on the NMR timescale. DFT calculations on amodel compound of ([P2N]Zr),i-i:r1-N)show that a butterfly-distorted structure(147.8° between ZrN2 planes) is 11.2 kcal mol’ more stable than the planar structure foundin the solid state,32 and Raman spectroscopy provides evidence that a butterfly-distortedconformation of the compound exists in solution. Like 4.1, {[PNP]Zr(O-2,6-Me2C6H3)}Q.iii2:r-N) ([PNP] = [ePr2PCHSiMe)N1) is butterfly-distorted (152.6° between ZrN2planes) (Figure 4.7), with two halves of the dinuclear complex equivalent, and N2 bonds toZr with two different Zr—N bond lengths (2.034(4) and 2.082(4) A).33 Also, a singlet isapparent in the 31P{’H} NMR spectrum of the complex, implying that if the butterflyP101’01’N3Ni’Ni’P1’01139distortion exists in solution, a fluxional process lets N2 experience both sides of the Zr---Zraxis.Figure 4.7. Structure of {[PNP]Zr(O-2,6-Me2C6H3)}(p-1i: i- .Complex 4.1 resembles {[NPN]Zr(THF)}2(t-ri:ri-),reported by the Fryzuk groupin 2005. This dark purple complex forms in high yield from the reaction of 2.2 equivalentsof KC8 with [NPN]ZrCl(THF) under I or 4 atm of N2. Like 4.1, there is a singlet in the31P{’H} NMR spectrum (ö —5.6) and the complex appears to have C2h symmetry in solution.In the solid state, one [NPN] and one THF ligand coordinate to each Zr, and N2 is boundside-on to two Zr centres. The N—N bond is 1.503(3) A, identical to that of 4.1, and theother bond lengths and angles are similar between the two structures. The Zr-N2-Zr core isplanar, not butterfly-distorted, in { [NPN] ZrCHF) }2(j..t-r:r-N.Compared to other side-on bound Zr-N2 complexes, 4.1 and {[NPN]ZrCfHF)}2(ii-112:ri-N) have long N—N bonds, although neither are as long as the N—N bond in{[PNP]ZrCl}Q-Ti:ii- (1.548(7) A), which contains the longest intact N—N bondobserved for a metal complex.34 (Cp”2Zr)ji-:-N(Cp” = 1,3-(SiMe)2-T15CHhas asimilar N—N bond length to 4.1, within error, at 1.47(3) A.12 Other side-on bound Zr-N2140complexes contain somewhat shorter N—N bonds: ({[P2N]Zr}p-i1-N)(1.43(1) A)8[0i5-CMe4H)2Zr]01-r1:r1N)(1.377(3) A)19 and (rac-BpZr)ji-i:r-N(1.241(3) A)35 andare discussed in detail in chapter one.4.2.2 Synthesis and structure of { [NPN]*Zr(py)}2(JJ..:..N)The pyridine adduct of the Zr2N complex, {[NPN]*Zr(Py)}Qtr12:r12N),4.2, can beprepared from 4.1 and excess Py in C6H solution (Equation 4.2). The dark evergreencomplex appears to form instantly, and is isolated in high yield as a dark green powder uponwork-up. In contrast to 4.1, complex 4.2 can be stored under vacuum for several hourswithout any noticeable decomposition, possibly because Py is bound more tightly to Zr thanTHF is. The results of combustion analysis of 4.2 are consistent with the formula given, anda peak corresponding to [M — Py] is apparent in the mass spectrum.(4.2)There is a singlet in the 31P{’H} NMR spectrum of 4.2 in C6D at ö 6.0, and the ‘Hand ‘3C {‘H} NMR spectra are also consistent with the C symmetric structure proposed. Inthe 1H NMR spectrum (Figure 4.8), there are three singlets at ö 2.0 assigned to ArCH3groups; although four singlets should appear based on the symmetry of the complex, thesinglet at ö 2.03 integrates to 24H, indicating that two of the ArCH3 groups have accidental4.2141magnetic equivalence. In the 13C{H} NMR spectrum, the expected four distinct ArCH3resonances are apparent. The aromatic regions of the 1H and 13C{H} NMR spectra containthe expected peaks for Py and [NPN]*.(ppm)Figure 4.8. 500 MHz 1H NMR spectrum of 4.2 in C6D.ArCH34.2-d10, can be prepared from 4.1 and Py-d5 by thesame method used to prepare 4.2. The singlet in the 31P{1H} NMR spectrum is at 6 6.0, notshifted from that of 4.2. The 1H NMR spectrum of 4.2-d10 in C6D is nearly identical to thatof 4.2, except that the mukiplet at 6 7.12 and the triplet at 6 6.55 are absent, and themultiplet at 6 6.01 integrates to only 4H. Thus, these resonances are assigned to coordinatedPy in 4.2. There is a peak assigned to [M — Py-d5] in the mass spectrum.‘5N-labelled4.2-’5N2, can be prepared from 4.1-15N2 and Py in C6HArH and PyH7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0142solution. There is a 1:3:1 triplet at 6 6.0 in the 31P{1H} NMR spectrum of 4.2-N thatcorresponds to an AXX’ (each 31P nucleus couples to two magnetically inequivalent 15Nnuclei) spin system with 2JPN = 7 Hz, and 2JpN’ = 3 Hz. A multiplet appears at 6 118.2 in the15N{1H} NMR spectrum that corresponds to an AA’XX’ spin system with 2JNP = 7 Hz, 2JNP’= 3 Hz, and 1JNN’ = 2 Hz. As for 4.1, the magnetic inequivalence of the two 31P and two 15Nnuclei indicates that N2 does not freely rotate about the Zr---Zr axis in 4.2.The ORTEP representation of the solid-state molecular structure of 4.2 is shown inFigure 4.9, along with selected bond lengths and angles. Two views of the arrangement of Nand P donors around Zr are shown in Figure 4.10. The dinuclear structure is similar to thatobserved for 4.1. The N—N bond length is 1.481(5) A, about the same as the N—N bondlength observed for 4.1, within error. Similar to 4.1, there are two sets of similar length Zr—Nbonds: the Zrl—N5 and Zr2—N6 bond lengths average to 2.00 A, and the Zrl—N6 and Zr2—N5 bond lengths average to 2.09 A. Thus, the N2 unit is slightly canted: the N—N bond isnot exactly perpendicular to the Zr---Zr axis. One Py is coordinated to each Zr, and theZrl—N7 and Zr2—N8 bonds to Py are the same within error at about 2.44 A. These arewithin the expected range, but are slightly longer than the Zr—N bond to Py in[NPN]*ZrC12( y) 2.13, which is 2.3889(1 6) A, and may be due to the trans influence of the pdonor in 4.2. The bond lengths and angles between [NPN]* and Zr are similar to those in 4.1and the other [NPN}*Zr complexes reported here. There is a butterfly distortion in theZr2N core: the two ZrN2 planes meet at a 168° angle.143Figure 4.9. ORTEP drawing of the solid-state molecular structure ofti2:r-N), 4.2 (ellipsoids drawn at the 50% probability level). Carbon atoms of the proximalMes substituents (except C) and all hydrogen atoms have been omitted for clarity. Selectedbond lengths (A) and angles (°): Zrl—P1 2.6699(12), Zn—Ni 2.203(4), Znl—N2 2.166(4),Zrl—N5 2.002(4), Zrl—N6 2.092(4), Znl—N7 2.448(4), Zr2—P2 2.6725(12), Zn2—N3 2.172(4),Zr2—N4 2.218(4), Zr2—N5 2.097(4), Zr2—N6 2.011(4), Zr2—N8 2.441(4), N5—N6 1.481(5),N5—Zrl—N6 42.33(14), N6—Zn2—N5 42.19(14), P1—Znl—N7 156.80(9), N1—Znl—N2109.51(14), N7—Znl—N5 119.68(13).144N7Figure 4.10. Two views of the stereochemistry around Zr in 4.2.Complex 4.2 resembles {[NPNZr(Py)}2(jt-:-),previously prepared in theFryzuk group.36 This dark green complex is synthesized from the bright purple THF adduct{[NPN]Zr(THF)}2(l.i-ri:1-),and appears C2h symmetric in solution and in the solid state.The solid-state molecular structure of the complex confrms that one Py is coordinated toeach Zr and that N2 is coordinated side-on to two Zr atoms, as is observed for the THFadduct. The two Py molecules adopt a trans configuration about the Zr---Zr axis. The N—Nbond length is 1.503(2) A, and the N2 unit is also canted with respect to the Zr---Zr axis:Each Zr atom has a 2.0453(14) A and a 2.0819(1 3) A bond to N of coordinated N2. As withthe THF adduct of this complex, the Zr2N core is planar. The other bond lengths aresimilar to those of 4.2.Py is a stronger Lewis base than THF,37 so it is likely to displace THF from 4.1 in C6Hsolution spontaneously. Although both 4.1 and 4.2 are intensely coloured green compounds,an instant blue-green to dark evergreen colour change is apparent when excess Py is addedN3 N2N8P2P2N4N6N4N3N7NiN2P1NO145to a benzene solution of 4.1. In addition to the donor strength of Py, the synthesis of 4.2 isfacilitated by the low volatility of Py: upon work-up, THF and even the solvent will beremoved before Py. No evidence for an asymmetric complex such as {[NPNJ*Zr(Py)}(JIrj2:r1-N){Zr[NPNI * UHF) } is observed, although [NPN] -supported { [NPN] Zr(Py) } (ji-){Zr[NPN](fHF)} is known.36 This asymmetric adduct forms along with the bis-Pyand bis-THF adducts upon dissolving the bis-Py adduct in THF.Complex 4.2 and {[NPNZr(Py)}(Ji-r: l-)have another thing in common: theycan be readily prepared by the addition of Py to an N2 complex. In contrast,{ {PNP] Zr(OAr) }2(i-r:ri-N and ([PNP]ZrCp)2Q-r1:11 ‘-Ni’) cannot be prepared directlyfrom ([PNP]ZrC1)2J1-ri:i-).33Instead, these complexes must be prepared by the alkalimetal reduction of separately prepared precursors, such as [PNP]ZrCl2(OAr). Thus, the[NPN] and [NPN]* ligated Zr-N2 complexes can be tuned electronically and sterically by thesimple addition of a donor molecule to a solution of {[NPN]ZrCfHF)}2Q- 1:T-)and 4.1,respectively. In addition, {[PN]Zr(PhCN)}2(,i-r:rI- ) has been prepared andcharacterized in solution,36 and other adducts of the [NPN]-supported N2 complex, as wellas many other adducts of the [NPN]*supported N2 complex are waiting to be synthesized.If tuning the {[NPNj*Zr}2Qir12:r12N)core of 4.1 by replacing THF with other donorligands is a major goal of this chapter, it should be determined what effect, if any, Py has onthe structure of the Zr-N2 complex. In addition to comparing 4.1 to 4.2,{[NPN]ZrrHF)}2(i-r:ri-)(A) will be compared to {[NPN]Zr(Py)}2(.t-r:- ) (B).The singlets observed in the 31P{1H} NMR spectra of 4.1 and A shift upfield by 1 ppm forPy adducts 4.2 and B. The N—N bond lengths for all four compounds are the same, withinerror. The Zr—P and Zr—N (to N2) bonds are slightly shorter (‘—O.O2 A) in A than in B,146whereas these bonds are essentially the same for 4.1 and 4.2. So far, no major differencesexist among these four complexes, except for the identity of the donor itself. Thus, acomparison between 4.1 and 4.2 will not be complete until vibrational analysis andsupporting DFT calculations are performed. The UV-Visible absorption spectra of 4.1 and4.2 are provided in section 4.2.4.4.2.3 Phosphine adducts of {[NPN]*Zr)z(.L12:12Nz).In addition to THF and Py adducts of phosphine adductsof the Zr2N complex can be readily prepared. {Zr[NPN]*},4.3, can be prepared from 4.1 and excess PMe3 in Et20 solution (Equation 4.3). Uponaddition of excess PMe3 to a solution of 4.1 in Et20, a colour change from deep blue-greento bright emerald green is observed. Complex 4.3 is isolated as a hexanes-soluble greenpowder in quantitative yield upon taking the reaction mixture to dryness. As occurs with 4.1,complex 4.3 decomposes under prolonged exposure to vacuum to a beige powder thatcontains 2.8 and a white insoluble solid. In contrast to 4.1, 4.3 is also unstable in the solidstate and can decompose spontaneously at ambient temperature or at —35 °C. Samples of 4.3are synthesized immediately before use, or are stored for a few days in hexanes solutionswith a small amount of added PMe3 at —35 °C. Small crystals of 4.3 can be obtained fromtoluene/HMDSO in the presence of PMe3 at —35 °C overnight. Unfortunately, singlecrystals suitable for X-ray analysis could not be obtained, due in part to the solubility of thecomplex in non-polar solvents, and to its tendency to decompose.147xs PMe3(4.3)Et20Complexes 4.1 and 4.2 are C2h symmetric in solution and each Zr atom is coordinatedto one [NPNI* and one THF or Py molecule. In contrast, complex 4.3 appears to beasymmetric in C6D by 31P{’H} NMR spectroscopy. Two doublets at 6 5.1 and —33.1 (2J =44 Hz) and a singlet at 6 2.5, each integrating to 1P, are apparent (Figure 4.11). Thedownfield signals are due to coordinated [NPN]* and the signal at —33.1 is due tocoordinated PMe3. The 44 Hz coupling is consistent with two-bond P-P coupling of transdisposed phosphines on an early transition-metal complex.38 Thus, the 31P{1H} NMRspectrum suggests that one Zr is coordinated to [NPN]*, and the other Zr is coordinated to[NPNI* and PMe3. In the 1H NMR spectrum, there are eight singlets due to ArCH3groups, adoublet at 6 0.27 (2JPH = 6 Hz, 9H) attributable to coordinated PMe3, and ArH resonancesconsistent with 4.3 being a C, symmetric dimer. The absence of resonances for free orcoordinated THF in the 1H and 13C {‘H} NMR spectra also supports the proposed structure.4.1 4.3148Figure 4.11. 162 MHz 31P{’H} NMR spectrum of 4.3 in C6D.As with Py adduct 4.2, complex 4.3 appears to form instantly in Et20 solution becausethere is a blue-green to emerald green colour change upon addition of the phosphine. Thechoice of solvent for this reaction is critical because PMe3 is volatile. If the reaction is carriedout in toluene, 4.1 is isolated upon work-up.Isotopically labelled 4.3-15N2can be readily prepared from 4.1-15N2and PMe3 in Et20by the method used to prepare 4.3. At room temperature, the 31P{’H} and 1H NMR spectraof 4.3-’5N2in C6D are identical to those of 4.3, whereas the 15N{H} NMR spectrum showstwo broad singlets at 119.3 and 117.9. Since attempts to grow single crystals of 4.3 werehindered by its high solubility and its tendency to decompose, a different phosphine waschosen to prepare an asymmetric adduct of {[NPN]*Zr}2(). Benzene-soluble{{NPN1*Zr(1)Me2Ph)}Ot 12:112N {Zr[NPNI*}, 4.4, can be prepared from 4.1 and excessPMe2h in toluene solution (Equation 4.4). The complex is obtained as an emerald green10 6 2 -2 -6 -10 -14 -18 -22 -26 -30 44 4(ppm)149powder in 82% yield upon work-up. Complex 4.4 can be placed under vacuum for severalhours without decomposition, which is necessary for the complete removal of excessPMe2h.(4.4)Similar to 4.3, there are two doublets at 6 7.3 and —22.5 (2J = 46 Hz), and a singlet ato 1.9 in the 31P{1H} NMR spectrum of 4.4 in C6D (Figure 4.12). Again, the doublet at 0 —22.5 is assigned to PMe2h coordinated to Zr, and the downfield resonances are due tocoordinated [NPNJ’. In the ‘H NMR spectrum there are eight ArCH3 singlets, a doublet at 60.80 (J = 6 Hz) due to coordinated P(CH3)2h, and peaks in the ArH region consistentwith the C, symmetric structure proposed for 4.4.4.1 4.4150I-I12 8 4 0 -4 -8 -12 -16 -20 -24 -28(ppm)Figure 4.12. 162 MHz 31P{1H} NMR spectrum of 4.4 in C6]).Isotopically labelled 4.4-15N2can be prepared from 4.1-15N2and PMe2h by the samemethod used to prepare 4.4. The 31P{1H} NMR spectrum of 4.4-’5N2in C6D is similar tothat of 4.4, but with additional P—N coupling apparent at 253 K in toluene-d3.There is adoublet of doublets of doublets at 6 7.3 (2J = 46 Hz, 2JPN = 4 Hz, 2JPN = 7 Hz), a singlet at6 —1.9, and a doublet of doublets at 6 —22.5 (2J = 46 Hz, 2JPN = 7 Hz). It is unclear why thesinglet at 6 —1.9 is not split by 15N. There are two AA’XX’ multiplets (2JNN = 8 Hz, 2JPN = 4Hz, JPN = 7 Hz) in the 15N{’I-l} NMR spectrum in toluene-d8at 253 K at 6 119.0 and 118.0,each integrating to iN.The ORTEP representation of the solid-state molecular structure of 4.4 is shown inFigure 4.13, along with selected bond lengths and angles. Two views of the arrangement ofN and P donors around Zr are shown in Figure 4.14. As expected from the NMR spectra ofthe complex, 4.4 is asymmetric; there is one [NPNI* coordinated to each Zr, but Zr2 also151has a coordinated PMe2h. The N—N bond length is 1.488(2) A, the same as that in 4.1,within error. The Zr—P bond lengths to [NPNI* (Zrl—P1 2.6967(6), Zr2—P2 2.6445(6) A) aresimilar to those of 4.1 and 4.2, but the Zr2—P3 bond length to PMe2h is much longer at2.9139(6) A. The Zr2—P3 bond length is similar to other long Zr—P bonds to tertiaryphosphines reported in the literature.39Unlike in 4.1 and 4.2, three of the Zr—N bond lengthsto N2 are similar (Zrl—N3, Zrl—N4, and Zr2—N3 average to ‘—2.04 A) and the Zr2—N4 bondis longer (2.1153(17) A), possibly due to the steric influence of PMe2h. As with 4.1 and 4.2,there is a butterfly distortion between the two ZrN2 planes of 165° in the C1 symmetricsolid-state structure. P1 and P2 are staggered across the Zr---Zr axis (P1_Zrl—Zr2—P2torsion angle is 179.9°), whereas P1 and P3 are nearly eclipsed (P1—Zrl—Zr2—P3 torsionangle is 7.8°). Since 4.4 is C symmetric in solution, the Zr2N core is either planar, or there isa fluxional process that allows N2 to sample both sides of the Zr---Zr axis on the NMRtimescale.152Figure 4.13. ORTEP drawing of the solid-state molecular structure of{ [NPN]*Zr(PMe2Ph)}(i-i:i2-N){ [NPN] *Zr} 4.4 (effipsoids drawn at the 50% probabilitylevel). Carbon atoms of the proximal Mes substituents (except C0) and all hydrogen atomshave been omitted for clarity. Selected bond lengths (A) and angles (°): Zrl—P1 2.6967(6),Zr2—P2 2.6445(6), Zn—NI 2.1370(18), Znl—N2 2.1689(18), Zr2—N5 2.1818(18), Zr2—N62.1747(17), Znl—N3 2.0450(17), Znl—N4 2.0315(17), Zr2--N3 2.0371(18), Zr2—N42.1153(17), Zr2—P3 2.9139(6), N3—N4 1.488(2), N3—Zrl—N4 42.83(7), Znl—N3—Zr2137.18(9), P2—Zr2—P3 166.605(19), P1—Znl—N4 94.18(5), P1—Znl—N3 136.91(5), P1—Zn—Ni 71.28(5), P1—Znl—N2 75.25(5), N1—Zrl—N3 118.84(7), N1—Znl—N4 115.84(7).153P2N5The solid-state molecular structure of 4.4 provides some clue as to why only onephosphine donor is coordinated in 4.3 and 4.4. From Figure 4.14, it appears as though thecoordination of PMe2h to Zr2 pushes the [NPN]* ligand on Zn away. The new position ofthe NMes substituents of .[NPN]* on Zn, and the PPh substituent of [NPN]* on Zr2effectively block a second equivalent of PMe2h from coordinating to Zn. Complex 4.4appears to be the first dinuclear Zr-N2 complex characterized in the solid state with differentcoordination environments at each Zr.4.2.4 UV-Visible spectroscopy of zirconium dinitrogen complexes.Complexes 4.1, 4.2, and 4.4 are intensely green coloured compounds in solution and inthe solid state. The UV-visible absorption spectrum of blue-green 4.1 in toluene is shown inFigure 4.15. There is one peak at 652 nm ( = 6.1 X IO L mol’ cm1) and a second peak at358 nm (e = 1.0 X i04 L mol’ cmj. It should be noted that 8 values are approximate forN2P1P3N4N6N3NiNiN6Figure 4.14. Two views of the stereochemistry around Zr in 4.4.154these complexes because the dilute solutions become less intensely coloured over severalhours under N2 in Teflon-sealed cuvettes as they react with trace °2 and H20 in the solvent.By analogy with the UV-visible absorption spectrum of([P2N]ZrQi-ri:-N),32the peak at652 nm is tentatively assigned to a charge-transfer (CT) transition from the MO of N24 toa d orbital of Zr(IV), and the peak at 358 nm is assigned to a CT from the 7t’ MO of N2 toa higher energy d orbital of Zr(W). Similarly, absorption maxima in the UV-visibleabsorption spectrum of evergreen-coloured 4.2 in toluene solution (Figure 4.16) at 736 nm(6 = 6.1 X iO L mol1 cmj and 366 nm (6 = 1.0 X i04 L mol1 cm’) are assigned to N2 it—. Zr(IV) d CT transitions. There is also a shoulder on the high energy CT band at 401 nm(6 = 6.6 X i03 L mol’ cm’), as well as a smaller peak at 504 nm (6 = 2.2 X iO L mol’ cm’)that have not been assigned, but are similar to features observed in the spectrum of([2NZr)Oi- i: i-N).There are two peaks in the UV-visible absorption spectrum of green4.4 in toluene solution (Figure 4.17) at 699 nm (c = 9.7 X i03 L mol’ cm1), and 363 nm (6 =1.1 x I 0 L mot’ cm’) also tentatively assigned to N2 —+ Zr CT transitions. The UV-visibleabsorption spectra of 4.1, 4.2, and 4.4 are similar to other group 4 dinitrogen complexes(Table 4.1).1550.90.60.70.60.50.40.30.20.1430 530 630 730ci)C.)CCu-o0U)-o0330Xmax (nm)Figure 4.15. UV-visible absorption spectrum of 4.1 in toluene.CCu-oI0Co-o4:Figure 4.16. UV-visible absorption spectrum of 4.2 in toluene.330 380 430 480 530 580 630 680 730 780Xmax (nm)1560.90.80.7CI) 0.60C- 0.5I—00.40.30.20.10330 380 430 480 530 580 630max(nrn)Figure 4.17. UV-visible absorption spectrum of 4.4 in toluene.N2 complexmax (nm) 6 (X iO L mo11 cm’)4.1 652, 358 6.1, 104.2 736, 401, 366 6.1, 6.6, 104.4 699, 363 9.7, 11670, 455, 390 c[(rac-Bp)Zr]2t_q:r-N 612, 392 c648, 351 c, 3.7[(T5-CMe4H)f](J1- 1: 1 886, 553 6.5, 0.38-a: Ref. 31; b: (rac-Bp =Me2Si(-2-Me3i-4-tBu C5H]jRef. 34; C: not reported; d:Ref. 19; e: Ref. 16B.4.2.5 Attempted synthesis of a hafnium dinitrogen complex.When the conditions used to prepare 4.1 are replicated in an attempt to prepare ahafnium-dinitrogen compound from [NPN]*Hfl2 (2.15) and KC8, the formation of atoluene-soluble brown solid is observed. The brown solid has not been characterized, as it680 730 780Table 4.1. UV-visible absorption maxima of some Group 4 N2 complexes in toluene.157could not be separated from [NPNJ*H2 (2.8). Only peaks due to 2.8 are apparent by NMRspectroscopy and El-MS. The brown product may be paramagnetic, and higher molecularweight peaks may not be apparent by El-MS because any Hf complexes that are present arethermally sensitive, or not volatile enough for this technique. When 2.15 is stirred withNa/Hg amalgam in toluene solution under I atm of N2 at ambient temperature, a deep red-brown colour forms over four weeks. After one week, signals attributable to multipleproducts can be seen in the 31P{’H} NMR spectrum, including a small peak at ö 3.5. Afterfour weeks, the peak at 8 3.5 and a peak due to 2.8 represent the major products of thereaction. Unfortunately, 2.8 could not be removed completely from the red-brown solids.If 2.15 is stirred over Na/Hg amalgam in THF under 4 atm of N2, a slow colourchange from orange to yellow-green is observed over three weeks. According to 31P{1H}NMR spectroscopy, the major product is characterized by a singlet at 6 —10.6 (62%). Thereare also minor products at 6 —3.1 (16%), —6.9 (10%), and —10.5 (12%). Attempts to purifythe major product are currently ongoing, however, there is no evidence that the mixturecontains a Hf-N2 complex.While there are quite a few examples of Zr-N2 complexes, the synthesis of Hf-N2complexes remains a challenge. In 1985, the first Hf dinitrogen complex, [Cp*2Hf(N.)]QINi), was prepared from Cp*2HfI and Na/K alloy in 20% yield.4°Unfortunately, the producthas not been crystallographically characterized. Although the reduction of [P2N]Hf1 withKG8 yields {[P2N]Hf}(N)by EI-MS, and hydrazine is obtained upon addition of HC1 tothe product, the complex could not be purified or characterized in the solid state.41 Thereduction of (ri5-CMe4H)2fIwith Na/Hg amalgam yields {(ri5-CsMe4H)2f}ii-i:N ,in which N2 is bound side-on to two Hf centres with an N—N bond length of 1.423(1 1) A.165158This complex reacts with H2 to give { (r5-CMe4H)2f(H)}2(j.i-r:r-NH,as was observedfor the Zr congener. Hafnium cliiodides have been used as starting materials for Hf-N2complexes because the analogous hafnium dichioride complexes contain strong Hf—Clbonds that are unreactive in the presence of strong reducing agents. Hf—I and Zr—I bondshave similar bond dissociation enthalpies,42but Zr(IV) complexes are easier to reduce thancorresponding Hf(IV) complexes.434.3 Conclusions.In this chapter, the synthesis of a new arene-bridged zirconium dinitrogen complex,is reported. The deep blue-green compound has beencharacterized in solution and in the solid state. By 31P{1H}, 1H, and 13C{H} NMRspectroscopies, the dinuclear complex is C2h symmetric with one THF and one FNPN]*coordinated to each Zr. The solid-state molecular structure of the complex shows that N2 iscoordinated side-on to two Zr atoms with an N—N bond length of 1.503(6) A. N2 is formallyN24, or hydrazide, in the complex.Adducts of the Zr-N2 complex can be prepared easily by adding Py, PMe3 or PMe2hto a solution of {{NPN]*ZrFHF)}(J1 1:rj).The addition of excess Py to this complexprovides {[NPN]*Zr(Py)}2(:r)in high yield as a dark green powder. The complex isC2h symmetric in solution by 31P{1H}, 1H and 13C{H} NMR spectroscopies. The solid-statemolecular structure shows that N2 is coordinated side-on to two Zr atoms, as expected. Infact, the only major difference between the structure of the THF adduct and that of the Pyadduct is the identity of the donor. The N—N bond lengths are the same within error, andboth structures show a similar butterfly distortion between the ZrN2 planes.159The addition of excess PMe3 or PMe2h to {[NPNj*Zr(THF)}2QI11:1)provides{{NPN}*Zr(PMe2R) (irI:r2){Zr[NPN]*} (R = Me, Ph) as a bright green powder inhigh yield. In solution, the PMe2R adducts are C symmetric with one Zr atom coordinatedto N2, [NPN]* and PMe2h, and the other coordinated to N2 and [NPN]t.The solid-statemolecular structure of the PMe2h adduct confirms that only one PMe2h is coordinated tothe dimeric species, and that N2 is side-on bound to two Zr atoms. As with the THF and Pyadducts, the N—N bond length indicates that an N—N single bond is present, and the N2 unitis butterfly-distorted relative to the Zr---Zr axis. The synthesis of {[NPN]*Zr(Py)}2(JI-T1:1-N2) and { [NPN] *Z (PM Ph)(ji-r2:r-N2) {Zr[NPN] * } from { [NPN] *Z (J’HF)}2(i-ri:ri-N2) represents a simple, high-yield route to side-on N2 complexes with new donor groups.4.4 Experimental.4.4.1 General experimental.General experimental conditions are as given in chapter two. Flasks sealed under N2gas at liquid-nitrogen temperature reach a pressure of 4 atm at ft. Only thick-walled Teflon-sealed Kontes glassware should be used for these procedures. Reaction mixtures should bethawed completely behind a blast shield and handled with great care whenever the flask mustbe removed from behind the shield. Warming solutions slowly to rt in a liquid-N2/EtOHslurry may minimize shock to the flask upon thawing. 15N{’H} NMR spectra were recordedon a Bruker AV-400 direct detect spectrometer operating at 400.1 MHz for 1H NMR spectraand were referenced externally to MeNO2 at ö 0. 15N-labelled complexes were isolated andhandled under unlabelled N2. UV-visible spectra were recorded on a Varian/Cary 5000 livVis spectrometer using a 1 cm cuvette. For UV-vis spectra, the compound was dissolved in160toluene (dried according to the procedu.re outlined in chapter two, then stirred over sodiumsand for one hour in anN2-filled glovebox, and filtered through Celite), and the solution wastransferred to a Teflon-sealed Kontes UV-Vis cuvette.4.4.2 Starting materials and reagents.Tetrahydrofuran was purified as usual, stored over purple sodium benzophenone ketylindicator and degassed by three freeze-pump-thaw cycles prior to use. Pyridine was driedover CaH2 and distilled under N2 prior to use. Potassium graphite (KG8) was preparedaccording to literature methods. Trimethylphosphine and dimethylphenylphosphine werepurchased from Strem Chemical Ltd. and used without further purification. ‘5N2 gas(isotopic purity 98+%, 1 or 2 litres) was purchased from Cambridge Isotopes Ltd. in a smallcarbon steel lecture bottle and used as received. Mercury was purified according to literaturemethods.45 Sodium amalgam was prepared immediately before use in a nitrogen atmosphere,and was washed with toluene until the washings were clear and colourless.{[NPN]*Zr(THF)}2O.tT12:T)2N)(4.1). Compound 2.10 (1.00 g, 1.40 mmol) and KC8(0.414 g, 3.07 mmol) were added to a 400-mL thick-walled bomb and shaken to mixthoroughly. THF (10 mL) was vacuum-transferred to the mixture at 77 K. The flask wasfilled with N2 gas at 77 K, sealed, and warmed slowly to rt in a liquid-N2/EtOH slurrybehind a blast shield. As soon as the mixture had melted, it was stirred vigorously. The flaskwas periodically inverted to coat the walls of the flask with the concentrated reactionmixture. The solution turned purple after 2 h, and bright blue-green after 5 h, and was stirredovernight. The suspension was diluted with THF (10 mL), and filtered through Celite. TheGeite was washed with additional THF (--‘10 —20 mL). The filtrate was concentrated under161vacuum to about 5 — 10 mL The deep blue-green solution was layered with pentane (50 mL)and chilled to —35 °C. The black crystals that formed were collected on a frit, washed withpentane (5 mL), and dried under vacuum for 15 mm. (0.802 g, 0.548 rnmol, 79%). Storingcrystals of 4.1 under vacuum overnight gave a white powder that contained benzene-solubleand -insoluble fractions. Crystals of 4.1 suitable for X-ray analysis were grown in a largeTeflon-sealed bomb by vapour diffusion of hexanes into a concentrated benzene/THFsolution of the compound in an NMR tube over 3 weeks.1H NMR cTHF-d8,500 MHz): 3 = 7.42 (t, 4H, 7.5 Hz), 7.22 (m, 6H), 7.08 (d, 4H, 7.5 Hz),6.82 (s, 4H), 6.73 (s, 4H), 6.64 (d, 4H, 8.5 Hz), and 5.43 (dd, 4H, JHH = 8 Hz, J, = 6 Hz)(ArH), 3.54 (bs, THF), 2.18 (s, 12H), 2.07 (s, 12H), 1.94 (s, 12H), and 1.74 (s, 12H) (ArCH3),1.69 (bs, THF).31P{1H} NMR (THF-d, 202 MHz): 6 = 5.0 (s).13C{’H} NMR (THF-d3,126 MHz): 6 = 163.1 (d, 11 Hz), 144.7, 137.9, 136.7, 136.4, 134.9,134.1, 133.8, 130.0, 129.9, 128.9, 128.8, 125.1, 118.2, 117.9, and 113.7 (d, 10 Hz) (ArC), 68.2,and 26.4 (THF), 20.9, 20.4, 20.3, and 19.2 (ArCH3).El-MS (m/: 1432 (1, [M— Nr), 1320 (2, [M — 2THFJt), 541 (100, [2.8 — MelD.Anal. Calcd. for 4.F2THF:C921106O4P2ZrC, 68.71; H, 6.89; N, 5.23; Found: C, 68.34;H, 7.24; N, 4.90.UV-Vis (toluene)‘umax () = 358 (1.0 X 10k), 652 (6.1 X 10) nm (L mol1 cmj.Reduction of [NPN]*ZrC12in the absence of N2. Using the procedure outlined for thesynthesis of 4.1, THF (10 mL) was transferred to a mixture of [NPN]*ZrC12(0.350 g, 0.488mniol) and KC8 (0.145 g, 1.07 mmol) at 77 K, and the flask was evacuated and sealed. The162reaction mixture was a brown suspension while warming to rt. The mixture was stirredovernight, the pressure was vented, and an aliquot of the reaction mixture was analyzed by‘1P{H} NMR spectroscopy. The reaction mixture was filtered, and the filtrate wasconcentrated and layered with pentane, but no crystals were obtained. After 2 d, the brownsolution was taken to dryness to obtain a brown powder. 31P{’H} NMR spectroscopyindicated the reaction mixture and solid obtained upon work-up had the same composition.‘1P{’H} NMR (C6D,202 MHz): 6 = 20.3 (s, 5%), 17.9 (s, ‘-‘5%), —14.6 (s, 30%), —15.4(s, 40%), —31.4 (s, ‘-20%).(4.1-’5N2). Complex 4.1-15N2 (0.254 g, 0.173 mmol,83%) was prepared from 2.10 (0.321 g, 0.448 mmol) and KC8 (0.133 g, 0.985 mmol) in a200-nil. Teflon-sealed bomb by the same general method used to prepare 4.1. After vacuum-transferring THF (5 mL) to the flask at 77 K, the sealed, frozen flask was connected to alecture bottle of 15N2 gas (1 L, 1 — 2 atm pressure) via a small transfer bridge. The apparatuswas evacuated and backfilled three times, the flask containing the frozen solution wasopened, and the entire apparatus was evacuated and then closed to the Schlenk line. Thelecture bottle was slowly opened in the closed system. The flask was warmed to rt in a liquidN2/EtOH slurry (4 atm N2) behind a blast shield with vigorous stirring. The ‘H NMRspectrum was the same as for 4.1.31P{1H} NMR (THF-d8,162 MHz): 6 = 5.0 (d, 2JpN = 6.7 Hz).15N{H} NMR (THF-d8,40MHz): 6 = 116.6 (d, 2JpN = 6.7 Hz).El-MS (m/: 1432 (8, [M — N2]), 1322 (6, [M — 2THF]j, 541 (100, [2.8 — Me]j.163(4.2). To a stirred blue-green suspension of 4.1 (0.815 g,0.557 mniol) in C6H (15 mL) was added Py (0.98 g, 1.0 rnL, 12 mmol) dropwise. Thesolution turned dark evergreen instantly. After 15 mm. the reaction mixture was taken todryness to obtain a dark green powder that was suspended in hexanes, collected on a frit,rinsed with hexanes (5 mL), and dried (0.723 g, 0.489 mmol, 88%). Large black crystalssuitable for X-ray analysis were grown by slow evaporation of a benzene solution of thecompound in an NMR tube.‘H NMR (C6D,500 MHz): ö = 7.55 (bm, 4H), 7.45 (d, 4H, 6 Hz), 7.12 (m, 4H, Py), 6.84 (d,4H, 8 Hz), 6.77 (s, 4H), 6.65 (bs, 6H), 6.55 (t, 2H, 8 Hz, Py), and 6.47 (s, 4H) (ArH), 6.00(m, 8H, ArH and Py), 2.23 (s, 12H), 2.11 (s, 12H), and 2.03 (s, 24H) (ArCH3).31P{’H} NMR (C6D,202 MHz): ö = 6.0 (s).‘3C{’H} NMR (C6D, 126 MHz): ö = 162.7 (d, 33 Hz), 149.9, 143.9, 137.3, 136.8, 136.0,134.6, 133.7, 133.2, 133.0, 129.6, 129.5, 128.3, 127.6 (d, 8 Hz), 127.5, 125.6, 125.1, 121.9, and114.0 (d, 10 Hz) (ArC), 20.8, 20.4, 20.1, and 19.3 (ArCH).El-MS (m/): 1399 (30, [M — Py]j, 1320 (30, [M — 2Py]), 541 (100, [2.8 — Me]j.Anal. Calcd. forC86H8NP2Zr:C, 69.88; H, 6.00; N, 7.58; Found: C, 70.20; H, 6.31; N, 7.20.UV-Vis (toluene)‘m (E) = 366 (1.0 x 10), 401 (6.6 x 10), 504 (2.2 x 10), 736 (6.1 x 10)nm (L mol’ cm1).{[NPN]*Zr(Pydg)}z(.LrI2:112N2)(4.2-drn). Complex 4.2-cl10 was prepared in the samemanner as 4.2 from 4.1 (0.290 g, 0.198 mmol) and Py-d5 (0.53 g, 0.50 mL, 6.3 mmol) in C6H(5 mL), and was isolated as a moss green powder (0.270 g, 0.181 mmol, 91%). The 31P{’H}and‘3C{1H} NMR spectra are the same as those of 4.2.1641H NMR (C6D,500 MHz): ö = 7.55 (m, 4H), 7.45 (d, 4H, 7 Hz), 6.84 (d, 4H, 8 Hz), 6.77 (s,4H), 6.65 (bs, 6H), 6.46 (s, 4H), and 6.01 (dd, 4H, JHP = 6 Hz, JHH = 8 Hz) (ArH), 2.23 (s,12H), 2.11 (s, 12H), and 2.03 (s, 24H) (ArCH3).El-MS (m/,J: 1404 (10, [M — (Py-d5)]j, 1320 (15, [M — 2(Py-d5)]), 541 (100, [2.8 — Me]).{[NPN]*Zr(Py)}2O.L12:11215N)(4.2-’N2). Complex 4.2-15N2 was prepared in the samemanner as 4.2 from 4.1-’5N2 (0.150 g, 0.102 mmol) and Py (0.24 g, 0.25 mL, 3.0 mrnol) inC6H (3 mL), and was isolated as a dark green powder (0.129 g, 0.087 mmol, 85%). The 1HNMR spectrum was the same as that of 4.2.31P{’H} NMR (C6D,161 MHz): ö = 6.0 (AXX’ triplet 2JPN = 6 Hz, 2JpN’ = 3 Hz).15N{H} NMR (C6D,40 MHz): = 118.2 (AA’XX’ multiplet, 2JNP = 7 Hz, 2JNp’ = 3 Hz, 1JNN’= 2 Hz).El-MS (m/): 1322 (10, [M — 2Py]j, 541 (100, [2.8 — Me]).{[NPN]*Zr(PMe)}O.L12:112NZ){Zr[NPN]*} (4.3). Et20 (5 mL) and 4.1 (0.320 g, 0.221mmol) were mixed and chilled to —35 °C. To the stirred solution was added PMe3 (0.52 g,0.60 mL, 6.9 mmol) in Et20 (3 mL), and the mixture turned clear bright green instantly.After 30 miii. the reaction mixture was taken to dryness to obtain a green powder (0.306 g,0.219 mmol, 99%). A sample of 4.3 for microanalysis was recrystallized from toluene, with afew drops of PMe3 added, layered with (Me3Si)20(HMDSO) at —35 °C. The supernatantliquid was decanted, and the micràcrystaflune solid was rinsed with pentane and dried undervacuum for 5 miii.165‘H NMR (C6D,400 MHz): 6 = 7.82 (m, 4H), 7.56 (d, 2H, 8 Hz), 7.37 (d, 2H, 8 Hz), 7.27 (t,2H, 8 Hz), 7.18 (t, IH, 7 Hz), 7.13 (t, IH, 7 Hz), 7.01 (t, 2H, 7 Hz), 6.94 (t, 2H, 7 Hz), 6.78(d, 4H, 7Hz), 6.77 (s, 2H), 6.74 (s, 2H), 6.66 (s, 2H), 6.13 (dd, 2H,JHH = 8 Hz,JHP = 6 Hz),and 5.78 (dd, 2H, JHH = 8 Hz, JHP = 6 Hz) (ArH), 2.31 (s, 6H), 2.23 (s, 6H), 2.17 (s, 6H), 2.11(s, 6H), 2.00 (s, 6H), 1.92 (s, 6H), 1.68 (s, 6H), and 1.43 (s, 6H) (ArCH3), 0.27 (d, 9H,J, = 6Hz, PMe3).31P{1H} NMR (C6D,162 MHz): 6 = 5.1 (d, IP, 2J = 44 Hz), 2.5 (s, IP), —33.1 (d, IP, 2J, =44 Hz, PMe3).13C{’H} NMR (C6D, 101 MHz): 6 = 162.8 (d, 29 Hz), 159.6 (d, 25 Hz), 143.0, 141.8, 137.7,137.1, 135.8, 134.9, 134.3, 134.1, 133.9, 133.6, 133.2, 130.7, 130.0, 129.7, 129.6, 129.3, 129.0,128.8, 128.7, 128.6, 128.5, 128.1, 127.9, 127.0, 125.7 (d, 5 Hz), 125.6, 118.0, 117.6, 114.7 (d, 9Hz), and 113.5 (d, 11 Hz) (ArC), 21.0, 20.9, 20.5, 20.3, 19.8, 19.7, 17.7, and 16.0 (ArCH3),15.4 (d, 13 Hz, PMe3).Anal. Calcd. for 4.3(HMDSO)067:C83H99N6P3Zr2Si,067:C, 66.27; H, 6.63; N, 5.59;Found: C, 66.38; H, 6.90; N, 5.22.{ [NPN] *Zr(PMe3)}(,.L-112:1-15N){Zr[NPNJ *} (4.3-’5N2). Compound 4.3-’5N2was madeby the same route used to prepare 4.3, from 4.1-N2 (0.120 g, 82 tmol) and PMe3 (0.26 g,0.30 mL, 3.5 mmol) in Et20 (5 mL). The bright green solution was taken to dryness toobtain a bright green powder (0.114 g, 82 imo1, 99%). The 31P{1H} and ‘H NMR spectrawere the same as those observed for 4.3.15N{’H} NMR (C6D,40 MHz): 6 = 119.3 (bs, iN), 117.9 (bs, iN).166(4.4). To a stirred blue-green suspensionof 4.1 (0.410 g, 0.280 mmol) in toluene (10 mL) was added PMe2h (0.250 g, 1.81 mmol).The suspension turned bright green, and was stirred at rt for 30 mm. to obtain a clear,emerald green solution. The reaction mixture was taken to dryness to obtain a green residuethat was triturated and taken to dryness, first with toluene (5 mL), then with hexanes (3 X 5mL). The deep green solids obtained were suspended in pentane (5 mL), and the mixturewas chilled to —35 °C overnight. The solids were collected on a frit, rinsed with hexanes (5mL), and dried for 1 h to obtain a bright green powder (0.335 g, 0.229 mmol, 82%). Smallcrystals of 4.4 suitable for microanalysis were grown by slow evaporation of abenzene/HMDSO solution of the complex. Crystals of 4.4 suitable for X-ray analysis weregrown by slow evaporation of a concentrated hexanes solution of the compound.1H NMR (C6D,400 MHz): ö = 7.79 (t, 2H, 9 Hz), 7.74 (t, 2H, 9 Hz), 7.51 (d, 2H, 7 Hz),7.38 (d, 2H, 8 Hz), 7.25-7.15 (m, 3H), 6.98 (m, 2H), 6.91 (t, 2H, 7 Hz), 6.79-6.65 (m, 16H),6.12 (dd, 2H,JHH 8 Hz,JHP = 6.5 Hz), and 5.77 (dd, 2H,JHH = 8 Hz,JHP = 6.5 Hz) (ArH),2.28 (s, 6H), 2.19 (s, 6H), 2.16 (s, 6H), 1.98 (s, 12H), 1.92 (s, 6H), 1.67 (s, 6H), and 1.48 (s,6H) (ArCH3),0.80 (d, 6H, JHP = 6 Hz).31P{1H} NMR (C6D, 162 MHz): ö = 7.3 (d, 1P, 2J, = 46 Hz), 1.9 (s, IP), —22.5 (d, IP, 2J, =46 Hz, PMe2h).‘3C{’H} NMR (C6D, 101 MHz): ö = 162.9 (d, 31 Hz), 159.4 (d, 26 Hz), 141.4, 137.8, 137.5(d, 4 Hz), 136.1, 135.4, 135.0, 134.7, 134.3, 134.2, 133.9, 133.7, 133.6, 133.5, 133.4, 133.3,131.7, 131.4, 131.3, 130.8 (d, 8 Hz), 129.7 (d, Hz), 129.2, 129.0, 128.7 (d, 3 Hz), 128.6 (d, 3Hz), 127.9, 127.4 (d, 7.5 Hz), 127.1 (d, 5 Hz), 125.8 (d, 5 Hz), 118.1, 117.8, 117.6, 117.2,114.5 (d, 9 Hz), and 113.6 (d, 11 Hz) (ArC), 21.1, 21.0, 20.5, 20.3, 19.5, 19.1, 17.9, and 16.1(ArCH3), 15.6 (d, 13 Hz, PPh(CH3)2.167El-MS (m/J: 1320 (8, [M — PMe2h}j, 541 (100, [2.8 — Me}).Anal. Calcd. for4.4(C6H)(HMDSO):C99NO,5SiZrC, 66.81; H, 6.91; N, 4.72;Found: C, 67.21; H, 6.86; N, 4.35.UV-Vis (toluene) max (6) = 363 (1.1 x 10k), 699 (9.7 x 10) nm tL mo11 cm1).{ [NPN] *Zr(PPJ1e )}(.t-q2:r-15N{Zr[NPN] *} (4.4-15N2) Complex 4.4-N2 (74 mg, 51imol, 97%) was prepared in an analogous fashion to 4.4 from 4.1-’N2 (77 mg, 53 jimol) intoluene (1 mL) and PMe2h (73 mg, 53 jimol). The ‘H NMR spectrum was identical to thatobserved for 4.4.31P{1H} NMR (toluene-d3,162 MHz, 253 K): ö = 7.3 (ddd, IP, = 46 Hz, 2JpN = 4 Hz,JPN = 7 Hz), —1.9 (s, 1P), —22.5 (dd, IP, 2J,,,, = 46 Hz, 2JPN = 7 Hz).‘5N{’H} NMR (toluene-d8,40 MHz, 253 K): ö = 119.0 (AA’XX’ multiplet, iN, 1JNN = 8 Hz,JNP = 7 Hz, 2JNP = 4 Hz), 118.0 (AA’XX’ multiplet, IN, ‘JNN = 8 Hz, 2JNp = 7 Hz, 2JNP = 4Hz).El-MS (m/: 1322 (15, [M — PMe2hfl, 541 (100, [2.8 — Me]j.Reduction of LNPN]*Hf12under N2. Complex 2.15 (1.33 g, 1.35 mmol) was transferred toa Teflon-sealed bomb, and THF (10 mL) was vacuum-transferred into the flask at 77 K.Upon warming to rt, the flask containing the bright orange solution was returned to theglovebox and Na/Hg amalgam (25 g, 0.7%, 7.39 mmol) was added. The flask was evacuatedand filled with N2 at 77 K. The reaction mixture was allowed to warm slowly to rt in a liquidN2/EtOH slurry behind a blast shield. When the solvent had thawed, the solution wasstirred vigorously. A gradual colour change from bright orange to green was observed over 4168weeks of stirring at rt. The pressure was vented, and the THF solution was decanted fromthe mercury and filtered through Celite. The filtrate was concentrated under vacuum to 5mL, hexanes (15 mL) were added, and the clear solution was heated to Ca. 40 °C to obtain awhite precipitate. The slurry was filtered through Celite to eliminate the white precipitate andthe clear yellow-green solution was taken to dryness to obtain a dark yellow residue (0.83 g).Attempts to separate the products based on solubility differences in toluene/hexanessolutions at —35 °C, or by slow evaporation of a benzene/HMDSO solution of the mixturefailed.31P{1H} NMR (C6D, 162 MHz): = —3.1 (s, 16%), —6.9 (s, 10%), —10.5 (s, 12%), —10.6 (s,62%).4.5 References.1 Shaver, M. P.; Fryzuk, M. D. Adv. Sjnth. Cat. 2003, 345, 1061.2Allen A. D.; Senoff, C. V. Chem. Commun. 1965, 621.Harrison, D. E.; Taube, H. J. Am. Chem. Soc. 1967, 89, 5706.‘ Fryzuk, M. D.;Johnson, S. A. Coord. Chem. Rev. 2000, 200-202, 379.Fryzuk, M. D. Chem. Rec. 2003, 3, 2.6 Fryzuk, M. D.; Haddad, T. S.; Mylvaganam, M.; McConville, D. H.; Rettig, S. J. J. Am.Chem. Soc. 1993, 115, 2782.Cbiu, K. W.; Howard, C. G.; Rzepa, H. S.; Sheppard, R. N.; Wilkinson, G.; Galas, A. M. R.;Hursthouse, M. B. Po/yhedron 1982, 1, 441.8 Fryzuk, M. D.; Love, J. B.; Rettig, S. J.; Young, V. G. Science 1997, 275, 1445.Morello, L.; Yu, P.; Carmichael, C. D.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc. 2005,127, 12796.16910 Fryzuk, M. D.; Kozak, C. M.; Patrick, B. 0. Inorg. Chim. Acta 2003, 345, 53.Laplaza, C. E.; Curniriins, C. C. Science 1995, 268, 861.12 Pool, J. A.; Lobkovsky, E.; Chink, P. J. J. Am. Chem. Soc. 2003, 125, 2241.13Love, J. B.; Fryzuk, M. D. Unpublished results.14 Fryzuk, M. D.; Kozak, C. M.; Mehrkhodavandi, P.; Morello, L.; Patrick, B. 0.; Rettig, S. J.J. Am. Chem. Soc. 2002, 124, 516.Wengrovius, J. H.; Schrock, R. R.; Day, C. S. Inorg. Chem. 1981, 20, 1844.16A) Yandulov, D.V.; Schrock, R. R. Science 2003, 301, 76. B) Bernskoetter, W. H.; Olmos, A.V.; Lobkovsky, E.; Chink, P. J. Organometallics 2006, 25, 1021. C) Evans, W. J.; Lee, D. S.;Johnston, M. A.; Ziller, J. W. Organometallics 2005, 24, 6393.17 A) Manniquez, J. M.; Sanner, R. D.; Marsh, R. E.; Bercaw, J. E. J. Am. Chem. Soc. 1976, 98,3042. B) Manriquez, J. M.; Bercaw, J. E. J. Am. Chem. Soc. 1974, 96, 6229.18 Manriquez, J. M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J. E. J. Am. Chem. Soc. 1978,100, 2716.Pool, J. A.; Lobkovsky, E.; Chink, P. J. Nature 2004, 427, 527.20Weitr A.; Rabinovitz, M. Sjnth. Met. 1995, 74, 201.21 Lappert, M. F.; Pickett, C. J.; Riley, P. I.; Yarrow, P. I. W. J. Chem. Soc., Dalton Trans. 1981,805.Kenworthy, J. G.; Myatt, J.; Todd, P. F. Chem. Commun. 1969, 263.A) Fryzuk, M. D.; Mylvaganam, M.; Zaworotko, M. J.; MacGillivray, L. R. Po/yhedron 1996,15, 689. B) Ho, J.; Drake, R. J.; Stephan, D. W. J. Am. Chem. Soc. 1993, 115, 3792. C) Bajgur,C. S.; Tikkanen, W. R.; Petersen, J. L. Inorg. Chem. 1985, 24, 2539.17024A) Blandy, C.; Locke, S. A.; Young, S. J.; Schore, N. E. J. Am. Chem. Soc. 1988, 110, 7540.B) Wielstra, Y.; Gambarotta, S.; Meetsma, A.; de Boer, J. L. Organometallics 1989, 8, 250. C)Wielstra, Y.; Gambarotta, S.; Meetsma, A.; Spek, A. L. Organometallics 1989, 8, 2948.25 Hanna, T. E.; Lobkovsky, E.; Chink, P. J. J. Am. Chem. Soc. 2004, 126, 14688. B) Hanna,T. E.; Lobkovsky, E.; Chink, P. J. J. Am. Chem. Soc. 2006, 128, 6018.26 Grobelny, Z. Ear. J. Org. Chem. 2004, 2973.27 Bartmann, E. J. Organomet. Chem. 1985, 284, 149. B) Evans, W. J.; Chamberlain, L. R.;Ulibarri, T. A.; Zifler, J. W. J. Am. Chem. Soc. 1988, 110, 6423.28 Fryzuk, M. D.; Jafarpour, L.; Rettig, S. J. Organometallics 1999, 18, 4050.29 Mason, J. Chem. Rev. 1981, 81, 205. B) Donovan-Mtunzi, S.; Richards, R. L.; Mason, J. J.Chem. Soc., Dalton Trans. 1984, 2429.° A) Thom, D. L.; Tulip, T. H.; Ibers, J. A. J. Chem. Soc., Dalton Trans. 1979, 2002. B) Klahn,A. H.; Sutton, D. Organometallics 1989, 8, 198. C) Field, L. D.; Hazari, N.; Li, H. L.; Luck, I. J.Magn. Reson. Chem. 2003, 41, 709.31 Bemers-Pnice, S. J.; Morden, K.; Opella, S. J.; Sadler, P. J. Magn. Reson. Chem. 1986, 24, 734.32 Studt, F.; Morello, L.; Lehnert, N.; Fryzuk, M. D.; Tuczek, F. Chem. Ear. J. 2003, 9, 520.Cohen, J.; Fryzuk, M. D.; Loehr, T. M.; Mylvaganam, M.; Rettig, S. J. Inorg. Chem. 1998, 37,112.Fryzuk, M. D.; Haddad, T. S.; Rettig, S.J.J. Am. Chem. Soc. 1990, 112,8185.Chink, P. J.; Henling, L. M.; Bercaw, J. E. Otganometallics 2001, 20, 534.36 Morello, L. Amidophoiphine Complexes ofZirconium and Titaniumfor Dinitrogen Activation. Ph.D.Thesis; University of British Columbia: Vancouver, 2005.Henrickson, C. H.; Duffy, D.; Eyman, D. P. Inorg. Chem. 1968, 7, 1047.171Morello, L.; Love, J. B.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc. 2004, 126, 9480.A) Schrock, R. R.; Seidel, S. W.; Schrodi, Y.; Davis, W. M. Organometallics 1999, 18, 428. B)Fryzuk, M. D.; Duval, P. B.; Mao, S. S. H.; Zaworotko, M. J.; MacGillivray, L. R. J. Am.Chem. Soc. 1999, 121, 2478. C) Fryzuk, M. D.; Mao, S. S. H.; Zaworotko, M. J.; MacGillivray,L. R. J. Am. Chem. Soc. 1993, 115, 5336. D) Cayias, J. Z.; Babaian, E. A.; Hrncir, D. C.; Bott,S. G.; Atwood, J. L. J. Chem. Soc., Dalton Trans. 1986, 2743.° Roddick, D. M.; Fryzuk, M. D.; Seidler, P. F.; Hilihouse, G. L.; Bercaw, J. E. Oganometa/lics1985, 4, 97.‘ Fryzuk, M.D.; Corkin,J. R.; Patrick, B. 0. Can.J. Chem. 2003, 81, 1376.42 Schock, L. E.; Marks, T. J. J. Am. Chem. Soc. 1988, 110, 7701.Cardin, D. J.; Lappert, M. F.; Raston, C. L. Chemistry of Oigano-zjrconium and HafniumCompound.r, Ellis Hoiwood Ltd.: West Sussex, 1986, p. 21.44A) Lalancette, J. M.; Rollin, G.; Dumas, P. Can. J. Chem. 1972, 50, 3058. B) Bergbreiter, D.E.; Killough, J. M. J. Am. Chem. Soc. 1978, 100, 2126.45Perrin, D. D.; Armarego, W. L. F. Purification ofL2boratoy Chemicals, 3?1 ed.; ButterworthHeinemann Ltd.: Oxford, 1988.172Chapter FiveReactivity of Zirconium Dinitrogen Complexes5.1 Introduction.The economically and biologically important reaction to convert elemental nitrogen toammonia is achieved in one of two ways: by nitrogen-fixing bacteria or by the Haber-Boschprocess. Biological nitrogen fixation occurs in bacteria such as Aotobacter vinelandii at theactive site of the nitrogenase enzyme, which contains an Fe, FeMo, or FeV cofactor.1 Thisreaction proceeds at ambient pressure and temperature, but it requires energy in the form of16 equivalents of MgATP, the cell’s energy carrier.2 The mechanism of this reaction isunknown, and investigations into the structure and function of nitrogenase are ongoing.3 Itis estimated that nitrogen-fixing bacteria produce 108 million tonnes of NH3 worldwide peryear.4 In industry, the Haber-Bosch process yields NH3 from the reaction of nitrogen andhydrogen gases in the presence of an Fe or Ru catalyst at high temperature (400 °C) andpressure (200 atm). Today, the Haber-Bosch reaction also supplies the world with about 108tonnes of ammonia per year.5 There is no indication that this process, first implementedindustrially in 1913, will be replaced by another method for ammonia synthesis in the nearfuture.After the first N2 complexes were synthesized under mild conditions, chemists soughtto develop a homogeneous transition-metal-catalyzed route to ammonia from N2 at ambienttemperature and pressure. Stoichiometric nitrogen gas, hydrazine, or ammonia may beproduced if acid is added to an N2 complex. Alternatively, a hydrazido complex (MN—NH2) may be obtained. While it can be difficult to predict what products will form during173protonation reactions, the extent of activation of N2 in the complex, and the experimentalconditions used (e.g., temperature, acid, solvent) can be important. Protonation of cisW(N2)(PMePh)4]yields nearly two equivalents of ammonia,6whereas protonation of trans{M(N2)(dppe)] (M = Mo, W; dppe Ph2CHCPh)with HC1 gives trans[M=NNH(Cl)(dppe)]Cl (Equation 5.1). In 2003, Schrock and co-workers reported thatabout eight equivalents of ammonia are produced catalytically from N2, a weak organic acid,a reducing agent, and a bulky triamidoamine Mo(HI) catalyst under carefully designedexperimental conditions8HN/HPh2 N Ph2 Ph2 N Ph22 HCI CI (5.1)Ph2 N Ph2 Ph2 CI Ph2NM=Mo,WTransition-metal dinitrogen complexes are also known to react with electrophilicorganic compounds. N—C bonds form when ailcyl and acyl halides react with [MN2)(dppe)](M = Mo, W) to produce [MX(NN(H)R)(dppe)2] or [MX(NN(H)C(=O)R)(dppe)2] (X =Cl, Br; R = Me, Et, “Pr, 93u, Ph) upon work-up with HCI(aq)•9Until recently, the majority ofreactions for coordinated N2 required two steps: protonation of a dinitrogen complex togenerate a nucleophilic hydrazido complex, followed by reaction with an electrophile.Aldehydes and ketones react with coordinated [NNH2] by a condensation reaction to givehydrazonato complexes with new N—C bonds (Equation 5.2).b0 Metal-bound pyrroles,pyrazoles, pyridines, and indoles can also be synthesized stoichiometrically from hydrazidocomplexes and C0 containing electrophiles.1’In some cases, the heterocycle is released174from the complex upon addition of a reductant and a proton source to the reactionmixture.12HN/HPh2 N Ph2 7ll Ph2R Rci (5.2)Ph2 CI Ph2 L Ph2 Ph2M = Mo w R = alkyl, arylR’=:H,alkylAs is discussed in chapter one, new transformations for coordinated dinitrogen havebeen discovered relatively recently, and many of these involve side-on bound N2. New N—Hand N—Si bonds form when H2 and “BuSil-13 add to N2 in ([P]Zr)i.t-T1:1-N)to yield([P2N]Zr)2(i-H)(II-r12:r1-NNH) and ([P2N]Zr)2(ji-H)(ji-:r-NNS ’Bu), respectively(Figure 5.1) H also adds to [(C5Me4H)2Zr](,i-ri:11-Nto provide [(C5Me4H)2Zr(H)](II-12:1-NHz).4Boranes, silanes, and alanes add to ([NPN]Ta)2Qi-H)ji-r:- to produceN—B, N—Si, and N—Al bonds, in some cases with concomitant N—N bond cleavage.15 Theformation of N—C bonds is observed upon addition of arylacetylenes (ArCCH) to([P2N]Zr)O.-iin-N)to yield ({ (Ar = Ph, PMeC6H4,p-tBuC6H4)(Figure 5. 1).16175(Ar = Ph, p-MeC6H4pButC6H4)Figure 5.1. Formation of new N—E bonds from (F2N]Zr)(j.i-1i:ri-N)(E = H, Si, C) (silylmethyl groups of [P2NJomitted for clarity).In most cases, when coordinated dinitrogen or hydrazide is functionalized, the new N—E component is not readily released from the transition metal. This is one barrier to thedevelopment of catalytic N—E bond-forming processes based on transition-metal dinitrogencomplexes. Catalytic N—Si bond formation provides a low yield of (Me3Si)Nwhen TMSC1,Na, and N2 are mixed in the presence ts-[Mo(N2)(P ePh)4J.17Anilines can be preparedfrom aryl chlorides, Ti(OtPr)4Li, TMSC1 and N2 under Pd-catalyzed C—N cross-couplingconditions.18 Thus far, few catalytic processes are known for molecular nitrogen, and mostare poorly understood.2 H-CCAr176In this chapter, the reactivity of the Zr-N2 complexes described in chapter four withH—H, Si—H, C0, C=N, and P0 containing compounds is presented. H2 reacts with(R = Me, Ph) to yield a new N—H bond. Anew N—Si bond is obtained upon addition of PhSiH3 to {[NPNj*Zr(Py)}2(tr)2:112N).Thereaction of 4,4’-dimethylbenzophenone with {[NPN1*Zr(THF)}(L12:r12N provides ahydrazonato complex with a new N=C bond, and the reaction ofN2) with benzophenone imine yields new N—H bonds.5.2 Results and Discussion.5.2.1 Reactions of N2 complexes with H2.When a toluene solution of 4.3 is stirred under H2, the bright green solution becomesyellow over two to three weeks, and an orange precipitate forms after five weeks. Theyellow-orange toluene-soluble product, { [NPN] *Zr(PMe3)} (ji-H) (i-NNH) {Zr[NPNI* }, 5.1,can be prepared in high yield from 4.3 and PMe3 in toluene solution under H2 (1 atm)(Equation 5.3). Complex 5.1 can also be synthesized from 4.3 and H2 without added PMe3,but an unidentified brown by-product forms in about 10% yield by this method. Samples of5.1 are stable in solution and in the solid state for months under N2 at —35 °C.H2 (5.3)toluene4.3 5.1177NMR spectra of 5.1 were acquired in toluene-d8solution. At 298 K, the 31P{1H} NMRspectrum of 5.1 shows three broad peaks at 6 13, —2.5, and —36, which decoalesce at 273K to two doublets at 6 13.8 and —34.5 (2J = 56.7 Hz), and a singlet at 8 —2.2 (Figure 5.2).Because the spectrum is reminiscent of that of starting material 4.3, a dinuclear structure inwhich one Zr atom is coordinated to [NPN]* (6 —2.2), and the other Zr atom is coordinatedto [NPN]* (6 13.8), and PMe3 (6 —34.5) is proposed for 5.1. The 56.7 Hz P-P couplingconstant is typical for a two-bond coupling between trans-disposed phosphines in an earlytransition-metal complex.19In the 1H NMR spectrum at 298 K, some of the peaks in the ArH and ArCH3 regionare broad; however, a triplet and a broad singlet that each integrate to I H are apparent at 64.83 (2J = ii Hz) and 4.78, respectively. These are assigned to a hydride bridging the twoZr atoms (ZrHZr), and the hydrogen atom of bridging NNH (Figure 5.3). At 253 K, thepeaks in the 1H NMR spectrum are sharper, and 13 singlets are observed at 6 2.0 that areassigned to ArCH3 groups. Sixteen singlets are expected based on the C1 symmetry of theproduct, but six of these singlets overlap and integrate to 6H each. A broad singlet at 8 0.09due to coordinated PMe3, and an overlapping triplet at 8 4.84 (ZrHZr), and broad singlet at6 4.82 (NNH) are also apparent in the spectrum at this temperature.In the1H{31P} NMR spectrum at 253 K, the resonances assigned to ZrHZr and NNHappear as two singlets at 6 4.84 and 4.82. Thus, the bridging hydride is a triplet in the 1HNMR spectrum because it couples to two inequivalent 31P nuclei. One possible explanationis that ZrHZr couples to 31P nuclei of two [NPN]* ligands, and that the weak Zr—P bond toPMe3 and/or the H—Zr—PMe3torsion angle causes the coupling between ZrHZr and PMe3to be unobservable.178- I20 15 10 5 0 -5 -10 -15 -20 -25 -30 -35 -40(ppm)Figure 5.2. 202 MHz 31P{1H} NMR spectrum of 5.1 in toluene-d8at 273 K.4.88 4.80 4.72Figure 5.3. ZrHZr and NNH resonances in the 500 MHz 1H NMR spectrum of 5.1 intoluene-d8at 298 K.The solid-state molecular structure of 5.1 is illustrated in Figure 5.4. Unfortunately, thedata are of poor quality, and only the connectivity of the non-hydrogen atoms has beenestablished. The position of the bridging hydride and the hydrogen atom of bridging NNHI I I I I I I(ppm)179cannot be determined. Zn is coordinated to [NPN]* and N2, and Zr2 is coordinated to[NPN] ‘, PMe3 and N2. It is apparent that P2 and P3 are nearly trans-disposed (‘- 1610), andthat P1 is bent away from the Zr---Zr axis compared to P2 (Zr---Zn--P angles of 120° and89°, respectively). Also, there is a much greater butterfly distortion (‘ 109°) between the twoZr-N2 planes than is observed for 4.1, 4.2, and 4.4 that is consistent with the presence of abridging hydride between the two Zr atoms. The Zr---Zr distance (‘—‘3.2 A) is similar to thatobserved in other hydride-bridged dinuclear Zr(IV) complexes,2°and it is slightly shorterthan in others.21 A projection of the N, P, and Zr atoms is shown in Figure 5.5.Figure 5.4. Ball-and-stick model of the solid-state molecular structure of{[NPN]*Zr(PMe3)}QIH)(,.INNH)(Zr[NPN]*), 5.1. Carbon atoms of the proximal Messubsfltuents (except C) have been omitted for clarity.180Ni P3N5N6Figure 5.5. Projection of 5.1 down the Zr2--.-Zrl axis (only Zr, P, and N atoms included).Over one to two weeks at 298 K under N2, yellow C6D solutions of 5.1 turn green. Inthe 31P{’H} NMR spectrum, peaks due to 5.1 are absent, and singlets at 6 —5.0 (62%), —7.6(13%), and —31.4 (19%) appear. There are no signals in the spectrum that can be attributedto free or coordinated PMe3.The major product at 6 —5.0 has not been identified, but it maycorrespond to a PMe3-fre complex such as {[NPN]*Zr}2QIH)QINNH), or to{[NPN]*Zr}2O1N),if H2 has been eliminated. The peak at 6 —31.4 is due to [NPNJ*H2(2.8). Fortunately, in the presence of excess PMe3, solutions of 5.1 remain yellow for weeksat room temperature and no decomposition is detected by 31P{1H} NMR spectroscopy.Thus, as with 4.3, decomposition appears to involve loss of PMe3.To confirm that the resonances at 6 4.84 and 4.82 originate from H2 gas, toluene-d8solutions of 4.3 have been stored under H2 or D2 gas in sealed J. Young NMR tubes andmonitored for several weeks. Whereas the reaction of 4.3 with H2 is complete in six weeks,the reaction with D2 takes about three months, and a mixture of {[NPN1*Zr(PMe3)}(JID)(JINND){Zr[NPNJ*}, 5.1-d and 5.1 is produced. In the 1H NMR spectrum at 253 K,the triplet and singlet resonances at 6 4.84 and 4.82 integrate to about 0.02H each relative toP1P2181one of the ArCH3 resonances (set to 3H). Thus, the bridging hydride and NNH protons in5.1 originate with H2 gas. The resonances at 6 4.84 and 4.82 appear in spectra of 5.1-d2because there are trace HD impurities (O.4%) in the D2. Since 4.3 reacts with H2 faster thanit reacts with D2, the formation of 5.1 in this reaction cannot be prevented. Complex 5.1-d2can also be prepared as an orange solid on a larger scale (300 mg) from 4.3, PMe3 and D2 (4atm). By integration of the resonances at 6 4.84 and 4.82 in the 1H NMR spectrum intoluene-d8acquired at 253 K, 5.1-d2and 5.1 are present in a 10:1 ratio. A signal attributableto the parent ion, [5.1-d2J, appears in the mass spectrum of the compound.To determine if the hydrogenation of 4.3 can be extended to the PMe2h congener, atoluene solution of 4.4 and PMe2h has been stirred under I atm of H2 gas. The greensolution turns yellow after three weeks at room temperature, and a yellow precipitate formsafter six weeks. Upon work-up, { [NPN]*Zr(PMe2Ph)} (ji-H) (-NNH) {Zr[NPNj * }, 5.2, isisolated as a yellow solid in good yield (Equation 5.4).(5.4)Similar to 5.1, the 31P{’H} NMR spectrum of 5.2 in toluene-d8at 298 K shows threebroad singlets at 8 15, —2 and 25. At 253 K, the broad resonances decoalesce and a doubletat 6 14.6 (2J = 57.4 Hz), a broad singlet at 6 —24.6, and a singlet at 6 —2.3 are observed.These signals correspond to [NPN]* and PMe2h coordinated to one Zr, and [NPN]*coordinated to the other Zr, respectively. In the 1H NMR spectrum at 233 K, the expected4.4 5.2182signals due to ArH, ArCH3 and PMe2h groups in the C1 symmetric dimer are apparent. Inaddition, a singlet at 6 4.94, and a broad singlet at 6 4.88 are attributable to NNH andZrHZr protons, respectively.The formation of a new N—H bond upon hydrogenation of 4.4 has been confirmed byan isotopic labelling experiment. { [NPN]*Zr(pMe2Ph)} Q.t-H)(-15NH){Zr[NPNJ * }, 5.2-can be prepared from 4.4-15N2,PMe2h and H2 (1 atm) in toluene solution. At 273 K,the 31P{’H} NMR spectrum of 5.2-’N2shows the same peaks as that of 5.2, but the broadsinglet at 6 —24.6 is split into a broad doublet. In the 1H NMR spectrum acquired at 233 K,the ArH, ArCH3 and PMe2h resonances are analogous to those of 5.2, but the peak at6 4.94 is a doublet (1JHN = 72 Hz), and the peak at 6 4.88 is a broad triplet (2J = 9.7 Hz). Inthe1H{31P} NMR spectrum, the doublet at 6 4.94 is apparent, but the resonance at 6 4.88 isa singlet. The 72 Hz ‘5N-1H coupling constant is typical for one-bond coupling, and issimilar to that observed for([P2JZr)ji-H)(ji-15N ).3’2The 15N{’H} NMR spectrumat 273 K shows a singlet at 6 143.9 and a doublet at 6 29.8 (2JNP = 10 Hz). In the massspectrum, a peak due to [M — PMe2h] is apparent.H2 may add to 4.3 or 4.4 by a a-bond metathesis mechanism across the Zr—N bondvia a four-centred transition state: N of dinitrogen acts as a nucleophile and Zr acts as anelectrophile in this reaction, which is an example of heterolytic H—H activation. A similarmechanism has been invoked for the addition of H2 to([PN]ZrQi-i:ri-N).13Whereas H2 adds to 4.3 and 4.4, H2 does not react with THF adduct 4.1. When a blue-green toluene solution of 4.1 is stirred under 4 atm of H2 gas for six weeks at roomtemperature, there is no colour change, and no new peaks appear in any NMR spectra.When a toluene solution of 4.2 is stirred under 4 atm of H2 for eight weeks, there is a183gradual colour change from green to yellow-brown. By 31P{’H} NMR spectroscopy, there isa mixture of products, including 2.8 ({NPN]*H2). In the ‘H NMR spectrum, no peaksdiagnostic of bridging hydride or NNH protons are observed, and the major products couldnot be separated from each other.As introduced in chapter one, in 1997, the Fryzuk group reported the first reaction ofan N2 complex with H2 to yield a new N—H bond. Yellow ([P2NJZr)Ji-H)(i-NNH) isprepared from blue ([PN]Zr)-ii:rI-N)under 1 or 4 atm of H2.13 A broad singlet at 65.53 and a multiplet at 6 2.07 observed in the ‘H NMR spectrum are due to EI-NNH and tH groups, respectively. When the reaction is conducted under D2 gas, these resonancesdisappear, and when H2 reacts with ([P2N]Zr)Q-15),the NH resonance is split into adoublet (1JHN = 71.3 Hz). The ZrHZr resonances for 5.1 and 5.2 are about 3 ppm downfieldcompared to the hydride observed for ({P2N]Zr)i-H)(j.iNNH), but are within the rangeof known chemical shifts for hydrides bridging two Zr atoms. The solid-state structure of([P2N]Zr)0.i-H)O1-NNH) determined by neutron diffraction shows that the N—N and N—Hbonds in the bridging hydrazide (NNH) are 1.39(2) and 0.93(6) A, respecdvely.20In contrast to (E2JZr)Ji-11:r-N), ([PNP]ZrCl)II-r:T1- and{[NPN]Zr(THF)}2(ji-i:-)do not react with H2 gas.24 Prior to 1997, attempts togenerate N—H bonds by the reaction of a dinitrogen complex with hydrogen had beenunsuccessful, but in some cases H2 had been observed to react with a dinitrogen complex toproduce a metal hydride complex and liberate N2 gas.25 As discussed in chapter one, two newN—H bonds also form when H2 adds to [(1-CMe4H)Zr]Qi-ri:1N)to provide [(ri5-C5Me4)2Zr(H)](I1-r1:-N).’Heating this complex under H2 yields NH3, whereasheating it under vacuum yields[(5-CMe42Zr]2(j-N)(jt-NH in which the N—N bond is184cleaved. [(i5-CMe4H)2f]i-ri:riN)also reacts with H2, and [(q5-CMe4H)2f(H 1(JI-ri2:r1-NH)is produced.26Thus, 4.3 and 4.4 join a relatively small number of N2 complexesthat react with H2 to provide new N—H bonds.5.2.2 Reaction of N2 complexes with phenylsilane.Upon addition of 1.1 equivalents of PhSiH3 to a toluene solution of 4.2, a colourchange from deep blue-green to yellow-brown occurs.NNSiH2Ph){Zr[NPN]*}, 5.3, is isolated as an orange-brown toluene-soluble powder in highyield upon work-up (Equation 5.5). In the mass spectrum of 5.3, the highest molecularweight peak can be assigned to [M — PyJ. The results of microanalysis are consistent withthe proposed formula plus co-crystallized solvent, as has been observed in ‘H NMR spectraof crystals of 5.3 dissolved in toluene-d8._______(5.5)The 31P{’H} NMR spectrum of 5.3 in C6D shows two singlets at 14.9 and —4.3. The‘H NMR spectrum shows 13 singlets at 2.0 assigned to ArCH3 groups (six of theexpected 16 peaks are accidentally coincident), and peaks in the aromatic region consistentwith the proposed C, symmetric structure. Two doublets at 6 5.17 and 3.94 (2JHH = 9.5 Hz)integrate to IH each and are assigned to two diastereotopic SiH protons. Small satellites arePhS1H3toluene4.2 5.3185present that flank the SiH peaks (1JHs = 208 Hz, isotopic abundance 29Si = 4.7%). There isalso a doublet of doublets at 6 8.25 (2J = 15 Hz, 2JHP = 2 Hz) assigned to a bridginghydride (ZrHZr) that couples strongly to one phosphine (31P at 6 —4.3 according to 1H-31PHSQC) and weakly to the second phosphine. There are only a few examples of nonmetallocene group 4 complexes with bridging hydrides. Most hydrides bridging dinuclear Zrcomplexes have chemical shifts between 6 2.0 and 6.0.20 The downfield chemical shift seenfor the bridging hydride in 5.3, however, is not unprecedented among group 4 hydridecomplexes.27 Signals due to bridging hydrides are also often observed downfield of 6 5.0 innon-metallocene Ta complexes, such as ([NPNjTa)2i-H)4(6 10.62), and ([NPN]Ta)2Qi-H)(-i1:ri2-N)(6 10.85).28In the‘3C{1H} NMR spectrum of 5.3 in C6D, 16 ArCH3 singlets and 63 peaks in thearomatic region are observed, consistent with the C, symmetric structure proposed. By29Si{’H} NMR spectroscopy, a doublet at 6 —34.4 is apparent; the doublet is due to a three-bond coupling to phosphorus-31 (3J = 10 Hz). The chemical shift and coupling observedby 29Si{’H} NMR spectroscopy are similar to those of other complexes prepared in ourgroup. For example, the addition of one equivalent of PhSiI-13 to ([NPN]Ta)2II-H)01-rl’:r1N2) induces a series of reactions. The final product, {[NPNITa(H)}(Ji-NSiHPh) J.i-N) {Ta[NPN] }, and an intermediate in the reaction, { [NPN]Ta(H) } (j.i-H)(j.i-r’ :r12-NNSiH2Ph){Ta{NPN]}, have peaks at 6 —39 and —9, respectively, in their 29Si NMRspectra.29To simplify the aromatic region of the ‘H NMR spectrum of 5.3, the Py-d, adduct hasbeen prepared and characterized. { [NPN] *Zr(Pydr) } (j.t-H) (j.i-ri‘:2NNSiHPh){Zr[NPN] * }5.3-d, can be prepared from 4.2-cl10 and 1.1 equivalents of PhSiH3.The 1H NMR spectrum186of 5.3-c1 in C6D is analogous to that of 5.3, except that the multiplets at 6 6.73 and 5.84integrate to only I H and 2H each, respectively, rather than 3H and 5H (Figure 5.6).ArCH3ZrHZr(ppm)Figure 5.6. 400 MHz 1H NMR spectrum of 5.3-dinC6D.By the same route used to prepare 5.3, 5.3-’N2is obtained from 4.2-N and PhSiI-13.In the 31P{1H} NMR spectrum of the 15N-Jabelled compound in C6D there is a singlet at 614.9 and a doublet of doublets at 6 —4.2 (2JPN = 10 Hz, 3JPN = 3 Hz). The 1H NMR spectrumis similar to that of 5.3, but the doublet (2JHH = 9.7 Hz) observed for 5.3 appears to be abroad multiplet at 6 3.94. In the 1H{31P} NMR spectrum additional coupling to the 15Nnuclei is observed for the peak at 6 3.94 (J = 10 Hz, JHN = 5 Hz, 3JHN = 3 Hz). In the‘5N{1H} NMR spectrum there are two doublets of doublets at 6 —9.7 and —105.6. The twoinequivalent 15N nuclei of the rj’:r2-5N15SiHPhgroup are coupled to each other (‘JNN =15 Hz), and each is coupled to 31P (3JNP = 3 Hz, 2JNP = 10 Hz). In the 29Si{1H} NMRspectrum, an AMXX’ multiplet (1JsN = 7 Hz, 2J = 6 Hz, 3J = 3 Hz) is observed for 5.3-7.58.5 8.0ArH7.0 6.5 6.0SIHI I I 11111111111 I I I I I8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.018715N2, due to coupling to two different nitrogen-15 nuclei, and to one phosphorus-31nucleus.30 As for 5.3, the highest molecular weight peak in the mass spectrum of 5.3-N2corresponds to [M — Py].The ORTEP representation of the solid-state molecular structure of 5.3 is shown inFigure 5.7. Zn in the dinuclear C, symmetric complex is coordinated to [NPN]*, Py and N5of the side-on—end-on bound NNSiH2Ph unit, whereas Zr2 is coordinated to [NPNJ*, andN5 and N6 of ji-’:i12-NNSiHPh. The bridging hydride, HI, can be located from theelectron density map and refmes normally. The Zr—P and Zr—N bond lengths to [NPNI* aresimilar to others reported in this thesis, and are typical for Zr(IV) arnide and phosphinecomplexes.3’The Zrl—N7 bond (2.408(3) A) is not unusual for Py coordinated to Zr,32 andis slightly shorter than the Zr—N bonds to Py in starting material 4.2, which average to 2.44A. The ZnI—N5 bond is short (1.958(3) A) relative to the Zr2—N5 (2.142(3) A) and Zr2—N6(2.064(3) A) bonds, reflecting the end-on vs. side-on bonding modes to Zn and Zr2,respectively. At 1.407(4) A, the N5—N6 bond is shorter than in the starting material, but canstill be considered as a single bond. Also, the N5—N6 bond length is similar to other N—Nbonds observed in the Fryzuk group for ri’:i2-coordinated dinitrogen and functionalizeddinitrogen units.’5’28 The N6—Sil bond is 1.737(3) A, typical of a N—Si single bond. Theangles around N6 add to ‘—357°, indicating that N6 is nearly planar. Two views of the N, P,Si, and Zr atoms are shown in Figure 5.8.188Figure 5.7. ORTEP drawing of the solid-state molecular structure of {[NPN]*Zr(Py)}(jiH)(INNSiH2Ph {Zr[NPNj*}, 5.3, (ellipsoids drawn at the 50% probability level). Carbonatoms of the Mes substituents (except C) and all hydrogen atoms (except bridging hydrideHI and HI Si, H2Si) have been omitted for clarity. Selected bond lengths (A) and angles (°):ZrI—PI 2.6853(11), Zr2—P2 2.7311(11), Zn—Ni 2.288(3), Zrl—N2 2.172(3), ZnI—N72.408(3), Zr2—N3 2.175(3), Zr2—N4 2.146(3), Zrl—N5 1.958(3), Zr2—N5 2.142(3), Zr2—N62.064(3), N5—N6 1.407(4), N6—Sil 1.737(3), Sii—C82 1.867(4), Znl---Zr2 3.2256(6), Ni—ZrI—PI 69.12(8), N2—Znl—P1 74.71(9), N3—Zr2—P2 70.60(8), N4—Zr2—P2 74.01(9), Zn—N5—Zr2 103.68(13), Znl—N5--N6 170.7(2), Zr2—N6—SiI 160.9(2), N6—SiI—C82 113.60(17),Ni—ZnI—N7 100.73(12), N5—N6—Sii 122.3(2).189SilAs mentioned in chapter one, ([P2N]Zr)ji-H)(ji-NNSiHBu is synthesi2ed from([P2N]Zr)0i-11:n-N)and BuSiH3,and is an example of the formation of an N—Si bondby functionalization of coordinated dinitrogen (see Figure 5.1).13 The ‘H NMR spectrum of([PN]Zr)i-H)(i-ii:i-NNSiHBu) shows broad singlets at 6 5.07 and 4.80 due toinequivalent SiFT groups, and a broad quintet at 6 1.53 assigned to the bridging hydride.Whereas product 5.3 has a shorter N—N bond than is observed for starting material 4.2, theN—N bond in([P2N]Zr)i-H)(j.i-NNSiH’Bu is 1.530(4) A, significantly longer than theN—N bond in starting material ([P2N]Zr)p-i1:r1-N)(1.43(1) A). That the N—N bond in5.3 is shorter than the N—N bond in starting material 4.2, and in ([P2]Zr)t-H)(ji-NNSiH2’Bu) is not surprising; shorter N—N bonds are typically observed when the N2 orNNR groups are coordinated in the side-on—end-on mode rather than in the side-on mode.Thus far, it is unclear why NNSiH2Rcoordinates side-on—end-on to the two Zr atoms in 5.3.N2P2P1Figure 5.8. Two views of the N, P, Si, and Zr atoms in 5.3.190The presence of one molecule of Py, however, means that both of the Zr atoms are six-coordinate.Another reaction between Si—H and coordinated N2 introduced in chapter one is theaddition of silanes to The N—N bond is cleaved, and anew N—Si bond is formed in this reaction. Two equivalents of ‘BuSil-I3 react with([NPN]Ta)2t-H)QI-1’:ii-)to yield the bis(silylimide) complex, ([NPN]Ta)2Qi-NSiH2But).SC PhSiH3 adds to the Ta-N2 complex to produce {[NPNTa(H)}Qi-H)2(j.t‘r11: i-NNS l-lPh){Ta[NPNI}, with a new N—Si bond.29 This complex spontaneouslydecomposes to give { [NPN]Ta(H) } Qi-N) (ji-NSiH2Ph){Ta[NPN] }, in which the N—N bondis cleaved.It has been proposed that the reaction of RSiH3 with the Ta-N2 complex proceeds viaSi—H addition across one of the Ta—N bonds to yield a new N—Si bond and a terminaltantalum hydride. Complex 5.3 may form by a similar mechanism: Si—H addition across aZr—N bond in 4.2. Dinitrogen complexes 4.1 and 4.4 also react with PhSil-13 to produce N—Si containing complexes, { [NPN] *Zr(THF) } Qi-H) (t-ii‘:rj2-NNSiHPh){Zr[NPN] * } and{ [NPN]*Zr(PMe2Ph)} (ji-H)Qi-i’:rj2-NNSiHPh){Zr[NPN]* }, respectively.5.2.3 Reaction of 4.1 with 4,4’-dimethylbenzophenone.The addition of one equivalent of 4,4’-dimethylbenzophenone to a toluene solution of4.1 initiates a blue-green to red-brown to orange colour change over 15 nun, at roomtemperature. Upon work-up, { {NPN] *Zr} 2(!-O) (u-ril:ri2NNZC(4MeCoH4 5.4, isisolated as a yellow-orange toluene-soluble powder in high yield (Equation 5.6). Althoughthere are no peaks with m/ > 556 ([NPN]*Hz) in the mass spectrum, the results of191elemental analysis are consistent with the proposed formula plus co-crystallized benzene as isobserved in ‘H NMR spectra of crystals of 5.4 dissolved in THF-d8.(5.6)10.4. In the ‘H NMR spectrum there are eight singlets at ö 2.0, each integrating to 6H, dueto ArCH3 groups of [NPN]K, two singlets at ö 2.2 integrating to 3H each due to (pCH36H4)2=N groups, and ArH resonances consistent with the proposed C symmetricstructure. Similarly, the predicted 10 ArCH3 singlets at ö 20, and 41 peaks attributable toArC and CN groups appear in the ‘3C{’H} NMR spectrum. There are no resonancescharacteristic of free or coordinated THF in the ‘H or ‘3C{1H} NMR spectra. Althoughstrong peaks are apparent in the JR spectrum of 5.4 at about 1500 cm’ that can be attributedto a C=N stretch, several peaks are typically observed in this region for [NPN]*complexes such as 4.1, and no single peak could be attributed to this ftmnctional groupdefinitively.The ORTEP representation of the solid-state molecular structure of 5.4 is shown inFigure 5.9. Each Zr atom in the dinuclear structure is coordinated to one [NPN]* ligand, andan oxo group, and the NNC(p-MeC6H4)2fragment bridge the two Zr atoms. The N5—N6bond length is 1.357(10) A, which is intermediate between a single and double N—N bond,4.1 5.4In the 31P{1H} NMR spectrum of 5.4 in C6D there are two singlets at ö —7.7 and —192and shorter than in the starting material 4.1 (1.503(6) A). The N—N bond is slightly shorterthan that observed for side-on—end-on bound NNSiH2Ph in 5.3 at 1.407(4) A, and is withinthe range of N—N bond lengths observed for side-on—end-on dinitrogen complexes. As wasmentioned in chapter one, the N—N bond length in ([NPN1Ta)2ji-H).L-r1:r-)is1.319(6) A. The N6—C77 bond length is 1.347(12) A, consistent with a C—N double bond,and the N5—N6—C77 angle is 120.6(8)°. The hydrazonato group coordinates to the two Zratoms in an rI1:bonding mode. The Zrl—N5 bond length is 2.016(7) A, whereas the Zr2—N5 and Zr2—N6 bonds are much longer at 2.241(9) and 2.351(9) A, respectively. The Zn—N5—Zr2 angle is 93.0(3)°, and the Znl—N5—N6 angle is 155.0(6)°. The other bond lengthsand angles within the bridging hydrazonato group are unremarkable. The Znl—O1 and Zr2—01 bonds are the same, within error, and average to - 1.97 A. The Zrl—P1 bond (2.711(2)A) is slightly longer than the Zr2—P2 bond (2.687(3) A), whereas the Zn—NI, Znl—N2, Zr2—N3, and Zr2—N4 bonds are essentially the same length (-2.16 A, on average). The otherbond lengths and angles are similar to those of the other [NPN]*Zr([V) complexes reportedhere.Overall, this structure is reminiscent of [(‘q5-MeCH4)2Zr](jt-r1:q2-NNCHPh)(pt-riNNCHPh), which contains one equivalent of ,I-r11:n2 hydrazonate and is prepared from(ri5-MeCH4)2Z Cl,H2NNCHPh, and BuLi (Figure 5.10). An example of a mononuclearcomplex with a side-on bound hydrazonate is Cp*U(r(N,N)MeN_NCPh)(OTf),which is synthesized from Ph2CNN and Cp*2U(OTf)(Me). This actinide complex has aC=N double bond (1.32(3) A) and an N—N single bond (1.41(3) A) (Figure 5.10). Whilethese complexes are not examples of N2 activation or functionalization, they provide a usefulstructural comparison to 5.4.193Figure 5.9. ORTEP drawing of the solid-state molecular structure of {[NPN]tZr}2(i-O)(i-‘nt:12-NNC(4-MeC6H4),5.4, (ellipsoids drawn at the 50% probability level). Carbon atomsof the proximal Mes substituents (except CJ and all hydrogen atoms have been omitted forclarity. Selected bond lengths (A) and angles (°): Zrl—P1 2.711(2), Zr2—P2 2.687(3), Zn—NI2.166(8), Zrl—N2 2.145(7), Zr2-.-N3 2.189(9), Zr2—N4 2.160(7), Zrl—O1 1.962(6), Zr2—O11.982(6), Zrl—N5 2.016(7), Zr2—N5 2.241(9), Zr2—N6 2.351(9), N5—N6 1.357(10), N6—C771.347(12), C77—C78 1.460(14), C77—C85 1.475(13), Zn ---Zr2 3.0932(12), Znl—O1--Zr2103.3(3), Zrl—N5—Zr2 93.0(3), N5—Zr2—N6 34.3(3), N5—Zr2—N6 34.3(3), N5—N6—C77120.6(8), C77—N5—Zr2 161.7(8), Znl—N5—N6 155.0(6), N5—Znl--P1 161.8(2), N5—Zr2—P2149.4(2), N6—Zr2—P2 166.0(2), O1—Zr2—N6 111.2(3).194Figure 5.10. Two hydrazonato complexes: [(ri5-MeCH4)2Z ](Ji-111:r12-NNCHPh)(u-u ‘NNCHPh) andCp*2U(r1MeN_N=CPh(OTf).The reaction of 4.1 with 4,4’-dimethylbenzophenone in toluene-d8can be followed atlow temperature by 31P {‘H} NMR spectroscopy. After mixing the two reagents at 253 K, thesinglet at 8 5.0 due to starting material 4.1 decreases in intensity and two singlets integratingto 1P each at 8 —5.9 and —8.4 increase in intensity over 25 mm. at this temperature. About 10mm. after warming the sample to 273 K, two singlets appear at 6 —7.7 and —10.4 thatintegrate to 1P each and are assigned to 5.4. The peaks due to 5.4 continue to increase inintensity over 20 miii. at 273 K, and over 15 miii. at 300 K, but the peaks at 6 5.0, —5.9 and —8.4 do not disappear. After 24 h at 300 K, the peaks at 6 —5.9 and —8.4 have disappeared,and peaks attributable to 5.4, 4.1, and minor impurities are observed in the 31P{1H} NMRspectrum.From this evidence it appears that the peaks at 6 —5.9 and —8.4 are due to anintermediate in the formation of 5.4, which may be a dunuclear complex with twoinequivalent phosphines. One proposed formulation is {[NPN]*Zr}(u195N){[NPNj*Zr[O=C(pMeC6H42}},the ketone adduct of the dinitrogen complex, with oneequivalent of 4,4’-dimethylbenzophenone coordinated. By analogy with the synthesis ofPMe2h adduct 4.4, one equivalent of the bulky donor ligand replaces two equivalents ofcoordinated THF in the starting complex. A mechanism for the formation of 5.4 isproposed in Figure 5.11.Figure 5.11. Proposed mechanism for the formation of 5.4 from 4.1.196Thus far, the only evidence for the mechanism outlined in Figure 5.11 is theobservation of an intermediate with two inequivalent P atoms by 31P{’H} NMRspectroscopy at low temperature. It may be possible to obtain further mechanistic insight byfollowing the reaction by JR spectroscopy, or by UV-visible absorption spectroscopy. Itshould also be noted that impurities that also appear to be dinuclear Zr complexes withinequivalent phosphines (two equal intensity singlets in the 31P{’H} NMR spectrum) formduring this reaction if two or three equivalents of the ketone are added to 4.1, or if THF isused as the solvent.A new N=C bond forms when 4,4’-dimethylbenzophenone reacts with the hyckazido(N2) fragment in 4.1 to produce the hydrazonato complex 5.4. In organic chemistry,hycfrazones are prepared by the condensation reaction of hydrazine with an aldehyde orketone.’6The direct formation of N=C bonds from dinitrogen complexes and aldehydes orketones is unusual. One example includes the addition of two equivalents of benzaldehyde toa Nb-N2 complex, [Na(diglyme)2]{ [(calix- [4] -O)Nb]2(j.i-i1;‘-N2)}, to generate PhHCN—N=CHPh with two new N=C bonds, and two equivalents of the Nb oxo complex,[Na(T’HF)4][(cahx-[4]-O)Nb0].37Another example involves the addition of acetone to[T’aCl,(PEt)2(ji-N2) to give Me2CN—NCMe.’8The authors also report the reverse ofthis reaction: PhHC=NN=CHPh reacts with M(CHCMe3)(T F)2C1 (M = Nb, Ta) togenerate {MC1,(T’HF)2}(,..t-ii1:11 ‘-N2).As mentioned in the introduction, another way to prepare N=C bonds fromdinitrogen complexes is by a two-step process. First, a hydrazido complex is prepared byprotonation of an N2 complex; next, the condensation reaction between the hydrazidocomplex and an aldehyde or ketone furnishes the hydrazonato complex. For example, trans[MF(NNCRR’)(dppe)2][BF4] (M = Mo, W; R = Et, Ph, Me; R’ = H, Me) forms upon197addition of RR’C=O to trans-[MF(NNH2)(dppe)][BF4.10’39 Similarly, trans{MBr(NNH2)(depe),]Br (M = Mo, W; depe =Et2PCHCE ) reacts with acetaldehyde togive trans-[MBr(NN=CHMe)(depe)] r, which can be reduced by LiAIH4 to yield trans[MBr(NNEt)(depe)]Br.4°The addition of FcC(0)H or FcC(0)Me (1k =(i5-CH4)Fe(qC5H)) to cis,mer-[WC12(NNH(PMe2Ph)3]in the presence of catalytic HC1(aq) yields cis,mer[WCI(NN=C(Fc)(R))(PMePh3](R = H, Me).41 In the presence of the acidic hydrideHFeCo3(CO)12, acetone adds to trans-[W(OH)(NNH2)(dppe)]PF6to produce trans[W(OH)(NNCMe)(dppe)]PF6.42Mo and W hydrazido complexes are transformed into awide range of complexes with coordinated hydrazones. Efforts directed at releasing theseorganic moieties from the metal complex have mostly been unfruitful. A high yield ofMe2CN-NCMe can be obtained, however, from t-is-[W(N2)(PMePh)4]and acetone inthe presence of an unusual proton source, [{[(PhPCHC]Fe}Qi-S )3]BF.43The synthesis of new N=C bonds from group 6 hydrazido complexes and aldehydesor ketones proceeds via elimination of one equivalent of water. In contrast, group 4 or 5transition-metal dinitrogen complexes react with aldehydes or ketones to produce stablemetal-oxo complexes. The formation of 5.4 from N2 complex 4.1 is likely driven by thenucleophilicity of coordinated dinitrogen and the oxophilicity of Zr. Although it may bepossible to release an organic compound such asH2N-NC(4-MeC64)from 5.4 by addingacid or water to the complex, strong Zr—O bonds are expected to form, and it is difficult toenvision a catalytic N=C bond forming reaction based on this process.1985.2.4 Reaction of 4.1 or 4.2 with (CH3)C (O)H.The addition of one or two equivalents of (CH3)C (=O)H to benzene or toluenesolutions of 4.1 or 4.2 produces an instant blue-green to yellow colour change (Scheme 5.1).Upon work-up, a hexanes-soluble yellow powder is obtained that contains multiple productsby NMR spectroscopy. For the product formed from 4.2 and (CH3)C (=O)H, the 31P{’H}NMR spectrum of the mixture dissolved in C6D shows several peaks upfleld of ö 0 that canbe assigned to a mixture of at least four complexes with two inequivalent phosphines each(Figure 5.12). When the yellow powder is recrystallized from hexanes, a small amount of ayellow crystalline solid is obtained. Although the crystals still contain a mixture ofcompounds, there is one major product with peaks at ö —10.7 and —14.9 in the 31P{’H}NMR spectrum of the crystals dissolved in C6D.The ‘H NMR spectrum shows singlets at ö4.71 and 0.80 that integrate in a 1:9 ratio, consistent with the presence of an NCHC(CH3)unit. There are 13 large peaks at 2.0, a feature consistent with the major product being aC, symmetric dimer. If a complex such as {[NPN]*Zr}QIO)(J.i-NNC(H)C(CH3is themajor product, two diastereomers with different orientations of the H and tBu groupsrelative to the C=N bond may be present in the mixture (Scheme 5.1).It may be possible to obtain one product selectively from the reaction of an aldehydewith coordinated dinitrogen by modifying the reaction conditions used, or by choosing adifferent aldehyde. As with ketones, the condensation of an aldehyde with a hydrazidocomplex is well known. For example, [WF(NNH)(dppe)2][BF4] reacts with salicylaldehydeto give [WF(NNCHC6H4-2-OH)(dppe)[BF4].199(ppm)Figure 5.12. 162 MHz 31P{1H} NMR spectrum of the yellow product (in C6D) obtainedfrom the reaction of(CH3)C (0)H and 4.2.Scheme 5.1.C6D+ 24 0 -4 -8 -12 -16 -20 -24 -284.12005.2.5 Reaction of 4.1 or 4.2 with benzophenone imine.Coordinated diriitrogen in 4.1 reacts with 4,4’-dimethylbenzophenone to yield ahydrazonato complex with a bridging oxo group. In an attempt to find new reactions for{NPN]*ZrN2with electrophilic organic compounds, the addition of benzophenone imine to4.1 and 4.2 was studied. The addition of 2.1 equivalents of benzophenone imine to a toluenesolution of 4.1 or 4.2 induces a blue-green to brown colour change. After about 15 mm., thereaction mixture becomes clear red, and a bright red, toluene-soluble powder,{[NPN]*Zr(NCPh)}2(II112:rI2N),5.5, is isolated in high yield upon work-up (Equation5.7). The same product forms regardless of whether 4.1 or 4.2 is used as the startingmaterial.2PhC=NH (5.7)tolueneIn the 31P{1H} NMR spectrum of 5.5 in C6D, two singlets of equal intensity appear at6 1.2 and —9.2. By analogy with 5.3 and 5.4, the red product is a dimeric complex with twodifferent 31P environments. In the 1H NMR spectrum acquired at 298 K, the peaks are broadand overlapping. At 273 K the 1H NMR spectrum of 5.5 in toluene-d8shows 14 peaks at 62.0, attributable to 16 inequivalent ArCH3 groups (there are two sets of overlapping peaks),and two doublets (3JHH = 13.7 Hz) at 6 4.45 and 3.51 that each integrate to 1H andcorrespond to two inequivalent NH groups. There are also ArH resonances consistent with4.2 5.5201the proposed C1 symmetric structure, although this region is complicated by the presence ofmany inequivalent protons on the two [NPNI* and two Ph2C=N ligands. In the 13C{’H}NMR spectrum acquired at 248 K there are 16 peaks that can be assigned to ArCH3 groups,and 72 peaks in the aromatic region, as expected for the C1 symmetric complex. In addition,two doublets at 175.4 (3J, = 7 Hz) and 170.5 (3J = 8 Hz) can be assigned to inequivalentN=CPh2nuclei in the complex.In the mass spectrum of 5.5, the highest molecular weight peak corresponds to =[{[NPNI*Zr}2(NH)(NCPh)J+({M — (N + HN=CPh2)]), and the results of microanalysisare consistent with the proposed formula, plus co-crystallized solvent. By JR spectroscopy,two peaks at 3390 and 3250 cm4 are observed that can be assigned to v(N-H), and twopeaks at 1623 and 1615 cm4 are observed that can be assigned to v(C=N).45 It should benoted that the structure of 5.5 could not be determined with confidence until the results ofX-ray analysis were obtained.The ORTEP representation of the solid-state molecular structure of the red product,{[NPNj*Zr(NCPh2)}(I1]2:ri2-NH), 5.5 is shown in Figure 5.13. Each Zr atom iscoordinated to [NPN]*, a ketimido group (Ph2CN), and a side-on N2H unit bridges thetwo Zr atoms in the dimer. Two peaks consistent with hydrogen atoms bound to N5 and N6are apparent in the electron density map of the compound, but are not amenable torefinement. The kethnido fragments contain N=C double bonds (N7—C77 1.273(5) A, N8—C90 1.279(5) A), and coordinate to Zr with bond lengths that are shorter than Zr—N bondsto [NPN]* (Zrl—N7 2.015(3) A, Zr2—N8 2.007(4) A). The orientation of [pj* on Znmakes one of the ketimido fragments nearly trans to P (P1—Zrl—N7 167°), whereas theketimido on Zr2 is cis to P of [NPN]* (P2—Zr2—N8 78°). The angles around C77 and C90202add to ,3600 and 362°, respectively, suggesting that both C atoms are planar and sp2hybridized. At 1.507(4) A, the N5—N6 bond is slightly longer than is observed for startingmaterial 4.2 (1.481(5) A), consistent with the presence of an N—N single bond. The N2Hunit is not coplanar with the Zr atoms: the two ZrN2 planes meet at a 138° angle. Thisrepresents a larger butterfly distortion than is observed for the N2 complexes 4.1, 4.2, and4.4, but a smaller butterfly distortion relative to the hydride-bridged dimer, 5.1. The Zr—Nbond lengths to the N2 unit are essentially the same, at about 2.22 A, and are longer than theZr—N bonds to N2 in 4.1, 4.2, and 4.4 (average to 2.05 A). This is not unexpected since abridging [N2H] unit is present in 5.5, rather than an N2 unit. The other bond lengths andangles in the complex are unremarkable. Two views of the N, P, and Zr atoms in 5.5 areshown in Figure 5.14. The two phospbines are staggered (P1—Zrl---Zr2—P2 167°) across theZr---Zr axis, whereas the amides of [NPNI* on each Zr atom are nearly eclipsed (NI—Zn--Zr2—N3 22°, N2—Zrl---Zr2—N4 3°). The two ketiniido N atoms are also nearly eclipsed(N7—Znl ---Zr2—N8 23°).203Figure 5.13. ORTEP drawing of the solid-state molecular structure of{[NPN]*Zr(NCPh2)}U.t1]2:rI2-NH), 5.5, (ellipsoids drawn at the 50% probability level).Carbon atoms of the Mes substituents (except C30) and all hydrogen atoms have beenomitted for clarity. Selected bond lengths (A) and angles (°): Zrl—P1 2.7718(11), Zr2—P22.7222(12), Zn—NI 2.172(3), Zrl—N2 2.179(3), Zrl—N5 2.229(3), Znl—N6 2.224(3), Zrl—N72.015(3), Zr2—N3 2.179(3), Zr2--N4 2.203(3), Zr2—N5 2.205(3), Zr2—N6 2.239(3), Zr2—N82.007(4), N5—N6 1.507(4), N7—C77 1.273(5), N8—C90 1.279(5), N1—Zrl—N7 112.99(13),N7—Zrl—N2 94.97(12), N7—Znl—N6 98.82(12), N7—Zrl—N5 113.78(12), N7—Zrl--P1166.52(9), N5—Zrl—P1 78.43(9), N6—Zrl—P1 87.15(9), N8—Zr2—N5 101.49(13), N5—Zr2—P2160.63(8), N8—Zn2—N4 121.64(13), Zr2—N5—Zrl 123.53(14), Znl—N6—Zr2 122.16(13), C77—N7—Zrl 165.1(3), C90—N8—Zn2 173.1(3).204N6Overall, the reaction of benzophenone imine with 4.2 protonates coordinated N2 toyield a dinuclear hydrazido complex with two Zr-coordinated ketimido (Ph2C=N) ligands.The mechanism of formation of 5.5 from 4.2 has not been explored, however, it mayproceed by initial coordination of Ph2C=NH to Zr, followed by proton transfer to thenucleophilic coordinated dinitrogen. Another example of a ketimido complex isCp2Ti(NCPh)(NHCHP, which also contains cyclopentadienyl and alkylamidoligands.45A This complex is prepared fromCp2Ti(Me3SiCECSiMe)and two equivalents ofbenzophenone imine, but the protons are transferred to one of the ketirnido ligands to giveTi-NHCHPI-I2.Although this complex is not an example of N2 activation, it provides a usefulstructural comparison.Coordinated N2 in 4.2 acts as a base in the reaction with benzophenone imine. Asdescribed in chapter one, side-on bound N2 acts as a base in the reaction of HNR2 (NR2 =NMe2, N(H)NMe) with[(5-CMe4H)2Zr](ji-:TN to yield[(15-CMe4H)2Zr(NR)J(-1:ii-N2H.46New N—H bonds also form upon addition of alkynes, RCECH (R = Ph, tBu,to this Zr-N2 complex to yield[(1-CMeH)Zr(CECR)1Q1- 1:N).46N2N5 P2N3N3Figure 5.14. Two views of N, P, and Zr atoms in 5.5.P12055.2.6 Reaction of N2 complexes with Co.When toluene solutions of 4.1 or 4.4 are stirred under I atm of CO a colour changefrom deep green to dark yellow is observed. A yellow powder, {[NPN]*Zr}2QIO) 5.6, isisolated upon work-up in good yield (Equation 5.8). The 31P{’H} NMR spectrum of 5.6 inC6D shows one singlet at —19.2. With four ArCH3 singlets, and eight resonances in thearomatic region, the 1H NMR spectrum of 5.6 (Figure 5.15) is consistent with the proposedC2h symmetric complex. The 13C {‘H} NMR spectrum also shows the expected four ArCH3singlets, and 16 aromatic resonances. The molecular ion for 5.6 was detected by EI-MS, andthe microanalytical data are consistent with the formula proposed.(5.8)4.4 5.6206ArCH3The formation of 5.6 under the conditions described above is reproducible. Todetermine if any carbon-containing products form, the reaction described above wasrepeated in C6D solution. Complex 5.6 can be separated from the yellow-brown supematantliquid by filtration. The 31P{’H} NMR spectrum of the supernatant liquid shows peaks dueto two major products: a singlet due to free PMe2h, and two doublets present in a 1:1 ratioat —4.6 (7.5 Hz) and —9.4 (7.5 Hz). The chemical shifts of these resonances are typical forphosphines of [NPNI* coordinated to Zr, and are tentatively assigned to a dinuclear complexwith inequivalent phosphorus-31 nuclei that couple to each other. Such a complex with the[NPN]* ligand is not known to us: all of the dimeric species with inequivalent phospbines,e.g., 5.4, do not show coupling P-P coupling between [NPNI* ligands. For steric reasons, it isunlikely that {[NPN]*}zZr can form. Instead, a complex with a Zr—Zr bond may be present.(ppm)Figure 5.15. 500 MHz 1H NMR spectrum of 5.6 in C6D.ArHO 5’’.O’6.58.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0207It has proved difficult to isolate such a complex, or to obtain meaningful information on thisproduct and others that may be present in the supernatant liquid by GC-MS, EI-MS, ESIMS or NMR spectroscopy.When a C6D solution of 4.4 is stirred under I atm of 13C0 gas, a blue-green to yellow-brown colour change is observed over three hours. After two days, an aliquot of the clearyellow-brown solution shows a singlet due to free PMe2h (50% by integration), and the twodoublets at 6 —4.6 and —9.4 (2J = 7.4 Hz, 30% by integration) as is observed when thereaction is conducted under unlabelled CO. Two singlets at 6—7.1(14%) and —7.7 (20%) dueto two unidentified products, and two singlets that can be assigned to 5.6 (2%) and[NPNI*H2 (2.8) (1%) also appear in the 31P{1H} NMR spectrum. It is unclear why such ahigh yield of 5.6 is obtained when regular CO gas, rather than ‘3C0 gas is used in thisreaction. The formation of 5.6 from°2 or H20 impurities in the CO cannot be ruled out atthis point, but decomposition reactions have not been observed when other air- andmoisture-sensitive Zr complexes are treated with CO from the same cylinders used for thisreaction. In addition, only a small volume of CO gas is used in these reactions; it would haveto contain a large percentage of 02 to produce the amount of 5.6 observed.In the 13C{H} NMR spectrum of the reaction mixture two large doublets areobserved at 6 177.5 (5.3 Hz) and 124.5 (8.4 Hz). These peaks do not resonate at chemicalshifts expected for zirconium carbonyl compounds.47The reaction of 4.4 with higher purityCO gas, and attempts to characterize the products by mass spectrometry, IR spectroscopy,and other techniques is currently ongoing. The formation of N—C bonds by the reaction ofCO with dinitrogen complexes is as yet unknown.The ball-and-stick representation of the solid-state molecular structure of 5.6 is shownin Figure 5.16. It is apparent that 5.6 is a dinuclear C2 symmetric compound with two208bridging oxo groups. Two views of the stereochemistry of N, P, and 0 donors around Znand Z2 are shown in Figure 5.17. The Zr—P (2.7390(9) A) and Zr—N (2.13 A on average)bond lengths are typical for Zr(IV) amidophosphine complexes,32 and for the other[NPN]*Zr(IV) complexes reported herein. The Zr—O bond lengths average to about 1.98 A,which is similar to Zr—O bond lengths reported for other dinuclear Zr(TV) compounds withbridging oxygen ligands. Examples of such complexes include [ZrCl2Q-OH)(bdmpza)](bdmpza = bis(3,5-dimethylpyrazol-1 -yl)acetate) (Zr_O: 2.09 A),48 {Zr[OB(IVIes)]3(ii-OH)} 2’(Zr—O: 1.96 A),49 and (Cp2ZrCl)t-O (Zr—O: 1.945 A).5oThe Zr---Zr separation in 5.6 is 3.0116(8) A, which is consistent with the presence oftwo Zr(TV) centres bridged by 2 ions. If the bridging groups were 0H rather than 2, Zrin 5.6 would be in the 3+ oxidation state. Since 5.6 is neutral and diamagnetic, a Zr—Zr bondwould be present, and a smaller Zr—-Zr separation would be expected. Examples of Zr—Zrbonded species with bridging ligands appear to be absent from the literature, however,Zr—Zr bonded species with bridging C1, Bi, and f ligands are well known. The Zr—Zr bondis typically between 3.1 and 3.2 A for chloride-bridged dinners, although the presence of Zr--Zr bonds has also been inferred for complexes with longer Zr---Zr distances in the solidstate. Thus far, the 3.0 A Zr-—Zr separation observed for 5.6 is typical for an oxo-bridgedZr(IV) dimer. In contrast to the N2 complexes described in chapter four, there is only aslight butterfly distortion between the Zr02 planes: the two Zr02 planes are —178 ° disposedto one another.209Figure 5.16. Ball-and-stick representation of the solid-state molecular structure of{[NPN1*Zr}2(tO),5.6, (ellipsoids drawn at the 50% probability level). Carbon atoms ofthe Mes substituents (except C0) and all hydrogen atoms have been omitted for clarity.Selected bond lengths (A) and angles (°): Zrl—P1 2.7390(9), Zrl—O1 1.9800(19), Zrl—O1’1.9819(19), Zn—NI 2.144(2), Znl—N2 2.111(2), Zr---Zr 3.0116(8), Znl—O1—Znl’ 98.95(9),OI—Znl—O1’ 80.58(9), P1—Znl—O1 164.13(6), PI—ZnI—OI’ 90.64(6), N1—Zrl—P1 70.01(6),N2—Zrl—P1 74.64(7), N2—Znl—N1 111.67(10), 01—Zn—Ni 103.81(8), 01 ‘—Zn—Ni123.29(8), 01—Zrl—N2 120.96(9), 01 ‘—Zrl—N2 113.32(9).210N2’P1’N2’N2Figure 5.17. Two views of the stereochemistry around Zr in 5.6.5.2.7 Reactivity of 4.1 with ethylene.When a blue-green toluene solution of 4.1 is stirred under I atm of ethylene gas atroom temperature for four weeks, the reaction mixture does not appear to change. Theabsence of any new peaks in the 31P{1H} and 1H NMR spectra indicates that no reaction hasoccurred. In contrast to the lack of reactivity observed for 4.1, C6D solutions of{ [NPN] Zr(THF) }2(i-i:i-N react with ethylene to give a white precipitate. By 31P{1H}NMR spectroscopy, the purple supernatant liquid only contains the dinitrogen complex, andthe white precipitate, although it has not been characterized, may be polyethylene. Thereaction of ethylene with a dinitrogen complex to generate an N—C bond is intriguing, albeitunknown. Olefin polymerization catalyzed by dinitrogen complexes, however, is notunprecedented. For example, a heterobimetallic Ti-N2 complex,N2)(W(depe)Cl) is a highly active catalyst for ethylene/i -hexene copolymerization in thepresence of modified methylaluminoxane.51Ni0101’NiP1N2 NI’012115.2.8 Reaction of 4.1 with triphenyiphosphine oxide.The addition of one equivalent of triphenyiphosphine oxide to a toluene solution of4.1 produces an instant blue-green to bright blue colour change. Small teal blue crystals,{ [.NJpN}*Zr(0pph) }(-:r2-N){Zr[NPNJ * }, 5.7, are obtained upon work-up (Equation5.9). The 31P{1H} NMR spectrum of 5.7 in C6D shows three singlets at 6 40.4, 4.7, and 0.1,integrating to IP each (Figure 5.18). The two singlets at 6 4.7 and 0.1 are characteristic of adinuclear complex with two different [NPN]* coordination environments, whereas the peakat 6 40.4 is at a chemical shift expected for coordinated triphenylphosphine oxide.52 Eightsinglets due to ArCH3 groups in the C5 symmetric complex are apparent in the ‘H NMRspectrum, and resonances in the aryl region are consistent with [NPN]* and Ph3O protons.There are no signals that can be assigned to free or coordinated THF. Similarly, the ‘3C {‘H}NMR spectrum indicates that the complex is C symmetric, since there are eight ArCH3singlets and 40 peaks in the aromatic region.(5.9)5.7212____r-Et(ppm)Figure 5.18. 162 MHz 31P{1H} NMR spectrum taken one hour after addition oftriphenyiphosphine oxide to 4.1 in C6D.Unfortunately, crystals of 5.7 suitable for X-ray analysis could not be obtained fromhexanes solutions of the blue compound. Upon dissolution of 5.7 in benzene or toluene, theblue solution turns green over 24 h, concomitant with the formation of a mixture ofproducts indicated by 31P {H} NMR spectroscopy. By analogy with the formation of{ [NPN]*Zr}2(JLO)(p-ii’:r2-NNC(4-CHC64), { [NPN]*Zr}2OtO)(J.tl:2NNZPPh3)may be present in the green mixture, along with 5.7 and other compounds. After severaldays at room temperature, there are still many peaks in the 31P{’H} NMR spectrum of thegreen solution. The oxophilicity of Zr and the nucleophilicity of coordinated N2 may drivethe formation of a dimer with bridging oxo and phosphininiide groups, and it may benecessary to change the reaction conditions, or the phosphine oxide to obtain aphosphinimide complex selectively. Coordinated N2 in a Ti-N2 complex acts as a nucleopbileby attacking the phosphine donor of [NPN] to yield {[NP(N)N]Ti}2([NP(N)N] =213[hNSiMe2CH)P(=N)Ph]3)with coordinated phosphinimide.53Another interesting facetof the reaction ofPh3O with 4.1 is the fact that Ph3O does not react with Py adduct 4.2 atroom temperature in C6D over two weeks. The strength of Py donation and steric factorsmay block this reaction.5.3. Conclusions.In this chapter, the formation of N—H, N—Si, and N=C bonds from dinitrogencomplexes is described. The reaction of H2 and {Zr[NPN]*}provides in high yield, with new N—Hand Zr—H bonds. The product was characterized by solution NMR spectroscopy, isotopiclabelling experiments, and by a low-resolution solid-state molecular structure. Similarly,{ [NPNJ*Zr(PMe2Ph)} (ji-H)(ii-1i2:1-NNH) {Zr[NPNI * } can be prepared from{Zr[NPN]*} and H2 in toluene.A new N—Si bond forms when PhSiH3 reacts with intoluene to give in high yield. The C1symmetric complex has been characterized in solution by multinuclear NMR spectroscopy,and in the solid state by X-ray analysis. The NNSiH2Ph fragment is coordinated side-on—end-on to two Zr atoms, and the N—N bond length is 1.372(14) A. Synthesis andcharacterization of labelled { [NPN]*(p)} (.i-H) (u-il1I2.NNSiHPh){Zr[NPN] * } andalso support the proposedstructure.The addition of 4,4’-dimethylbenzophenone to { [NPNj *ZrCrHF) }2(,L-ii:i-N1provides { [NPN] *Zr} 2Q-O) (u-’i‘:T12-NNC(4-CH3C6Hin high yield. The solid-state214molecular structure indicates that the dimeric compound is C symmetric with bridging oxoand side-on—end-on hydrazonato ([(p-MeC6H4)2C=N—Nj groups coordinated. The N—Nbond is 1.357(10) A, intermediate between a single and double bond, and the C=N bond is1.347(12) A, typical for a CN double bond. Benzophenone imine reacts with{ [NPN] *Zr(Py) }2Ot-q:11-N to yield { [NPN]*ZtQ=CPh2)}2Qi-ri:ri-NH), in whichcoordinated dinitrogen is protonated. The addition of Ph3=O to {[NPN]*Zr(THF)}(JIi2:r1-N)initially provides a blue complex, {Zr[NPN]*},that continues to react in benzene solution to yield a green mixture of products.The dinitrogen complexes described in chapter four react with a variety of compoundsincluding H2, PhSiH3, and 4,4’-dimethylbenzophenone to generate new N—H, N—Si, andN=C bonds. Preliminary results indicate that the reactions of 4.1 with (CH3)C (0)H orPh3O may be worth pursuing. In addition, when other aldehydes, ketones, phosphineoxides, or silanes react with the N2 complexes, new and interesting transformations may beobserved. Clearly, it is worth exploring the reactivity of the N2 complexes with othersubstrates. In particular, the reactivity of the N2 complexes with arylacetylenes, boranes,alanes, CS2, C02, or organometallic compounds such as Cp2ZrH may be profitable, sincethese compounds have been observed to react with other N2 complexes.29’545.4. Experimental.5.4.1. General experimental.General experimental procedures follow those of chapter two. 15N{H} NMR spectrawere recorded on a Bruker AV-400 direct detect spectrometer operating at 400.1 MHz for‘H NMR spectra and were referenced externally to MeNO2 at 6 0. 29Si{1H} NMR spectra215were collected on a Bruker AV-400 instrument operating at 400.0 MHz for 1H NMR spectraand were referenced externally to TMS (6 0).5.4.2. Starting materials and reagents.Hydrogen, carbon monoxide and ethylene gases were obtained from Praxair.Deuterium gas (RD 0.4%) and ‘3C0 gas (<2% ‘2C0) were purchased from CambridgeIsotopes Ltd. Toluene, benzene, and Et20 used as reaction solvents were purified accordingto the procedure outlined in chapter two, then stirred over sodium sand, and filtered throughCelite prior to use. PhSiH3was degassed by three freeze-pump-thaw cycles. (CH3)C (=O)Hand benzophenone mime were stored over activated Linde 4A molecular sieves anddegassed by three freeze-pump-thaw cycles. All other reagents were obtained fromcommercial sources and used without further purification.{[NPN]*Zr(PMe3)}(pH)(JJNNH){Zr[NPN]*} (5.1). Complex 4.3 (0.400 g, 0.287mmol) was dissolved in toluene (10 mL), and PMe3 (0.010 g, 0.132 rnmol) was added. Thesolution was transferred to a Teflon-sealed bomb and degassed by three freeze-pump-thawcycles. At rt, the flask was filled with I atm of H2 gas and sealed, and the contents of theflask were stirred vigorously for 6 weeks. Over 2 — 3 weeks, the bright green solutionbecame light yellow-green, and after 5 — 6 weeks an orange precipitate formed. In theglovebox, the precipitate was collected on a flit, rinsed with pentane (10 mL), and driedunder vacuum for 10 mlii. to obtain a yellow-orange powder (0.224 g, 0.160 nimol, 56%).The filtrate was stored under H2 (1 atm) in a Teflon-sealed bomb for one week to obtainyellow crystals that were collected on a frit and dried under vacuum (0.105 g, 0.075 nimol,26%). Samples of 5.1 can be stored in solution or in the solid state at —35 °C for months216without decomposition. At rt, toluene solutions of 5.1 with added PMe3 (10 mg per 1 mLtoluene) can be stored for weeks without decomposition. Small yellow-orange crystals weregrown from toluene/HMDSO at —35 °C. The amount of co-crystallized HMDSO wasconsistent with the results of 1H NMR spectroscopy performed on crystalline samplesdissolved in C6D. Orange single crystals suitable for X-ray analysis were grown in an NMRtube under H2 by vapour diffusion of pentane into a C6H solution of the compound with10 mg PMe3 added per I mL of benzene.1H NMR (C6D,400 MHz, 298 K): 6 = 7.98 (bt, 4H, 5 Hz), 7.45-7.25 (m, 4H), 7.14-7.00 (m,4H), 6.91-6.68 (m, 12H), 6.07 (dd, IH,JHH = 8 Hz,J = 6 Hz), 6.01 (dd, 1H,JHH = 8 Hz,JHP= 6 Hz), 5.86 (bs, 11-I), 5.83 (s, 1H), 5.71 (bs, 1H), and 5.47 (bs, 11-I) (ArH), 4.83 (t, 1H, JHP= 11 Hz, ZrHZr), 4.78 (bs, IH, NNH), 2.41 (s, 3H), 2.39 (s, 3H), 2.26 (s, 3H), 2.25 (s, 3H),2.16 (s, 3H), 2.13 (s, 6H), 1.99 (s, 6H), 1.97 (s, 6H), 1.94 (s, 3H), 1.93 (s, 3H), 1.90 (s, 3H),1.88 (s, 3H), and 1.59 (s, 3H) (ArCH3),0.19 (d, 9H,Jm = 5 Hz, P(CH3).1H NMR (toluene-d8,500 MHz, 253 K): 6 = 8.14 (dd, 2H, JHH = 8 Hz,J11, = 8 Hz), 7.62 (d,1H, 7 Hz), 7.48 (d, 1H, 8 Hz), 7.45 (d, IH, 8 Hz), 7.34 (d, 1H, 9 Hz), 7.18 (m, 4H), 7.06 (m,2H), 6.99 (m, 4H), 6.86 (d, IH, 8.5 Hz), 6.80 (d, 1H, 8.5 Hz), 6.76 (bs, 3H), 6.72 (s, 1H), 6.67(s, 2H), 6.57 (d, 2H, 8 Hz), 6.16 (dd, 1H,J = 8 Hz,JHP = 6 Hz), 5.94 (dd, 1H,J = 8 Hz,= 6 Hz), 5.79 (dd, IH, JHH = 8 Hz, J, = 6 Hz), and 5.70 (dd, 1H, JHH = 8 Hz, JHP = 6Hz) (AtH), 4.84 (t, IH, 2JHp = 11 Hz, ZrHZr), 4.82 (bs, 1H, NNH), 2.65 (s, 3H), 2.27 (s,3H), 2.25 (s, 3H), 2.19 (s, 3H), 2.14 (s, 6H), 2.08 (s, 6H), 2.01 (s, 3H), 1.99 (s, 6H), 1.95 (s,31-I’), 1.94 (s, 3H), 1.80 (s, 3H), 1.69 (s, 3H), and 1.64 (s, 3H) (ArCH3), 0.09 (bs, 9H, P(CH3).31P{1H} NMR (toluene-d8,202 MHz, 273 K): 6 = 13.8 (d, IP, = 56.7 Hz), —2.2 (s, IP), —34.5 (d, 1P, 2j = 56.7 Hz).El-MS (m/: 1338 (4, [{[NPN]*Zr}2( + H20f’), 541 (100, [2.8 — Me]).217Anal. Calcd. for 5.1.(HMDSO)067:C83H101N6P3067Si33Zr2:C, 66.19; H, 6.76; N, 5.58; Anal.Found C, 65.98; H, 6.60; N, 5.50.Decomposition of 5.1. A yellow solution of 5.1 (30 mg) in toluene-d8(0.7 mL) was stored atrt for two weeks under N2 and gradually became light green. The major peaks in the 31P{1H}NMR spectrum and the approximate percentages based on integration are listed below.31P{1H} NMR (toluene-d8,202 MHz): ö = —5.0 (62%), —7.6 (13%), and —31.4 (19%).{ [NPN] *Zr(PMe3)}(-D)(ji.-NND) {Zr[NPN] *) (5.1-d2). Complex 4.3 (0.300 g, 0.215mmol) was dissolved in toluene (5 mL) and PMe3 (0.010 g, 0.132 mmol) was added. Thesolution was transferred to a Teflon-sealed bomb, and was degassed by three freeze-pump-thaw cycles. D2 gas was added to the flask at rt. The solution was stirred vigorously for fourweeks to obtain a deep green solution with a small amount of a yellow-green precipitate. Theflask was then refilled with D2 at 77 K and allowed to warm to rt (4 atm D2 pressure) behinda blast shield. After the solution had been stirred vigorously for four weeks, the reactionmixture was a dark-orange suspension. The pressure was vented, and the reaction mixturewas taken to dryness to obtain a dark orange solid. The solid was triturated with hexanes toobtain an orange powder that was collected on a flit, washed with pentane (3 X 5 mL), anddried under vacuum (0.185 g, 0.132 mmol, 61%). A 10:1 mixture of 5.1-d2 and 5.1 wasobtained. The 31P {‘H} NMR spectrum was identical to that of 5.1.‘H NMR (toluene-4, 400 MHz, 253 K): 6 = same as for 5.1 except the resonances at 6 4.84and 4.82 integrate to 0.IH each rather than 1H relative to one of the ArCH3 resonances.El-MS (m/: 1396 (1, [M]), 541 (100, [2.8 — Me]).218{ [NPN] lcZr(pMe2ph)}(ji-H)(i.-NNH) {Zr[NPNI *} (5.2). Complex 4.4 (0.380 g, 0.261mniol) and PMe2h (0.010 g, 0.073 mmol) were dissolved in toluene (7 mL). The brightgreen solution was transferred to a Teflon-sealed bomb and degassed by three freeze-pump-thaw cycles. At rt the flask was filled with I atm of H2 gas, the bomb was sealed, and thereaction mixture was stirred vigorously for 6 weeks. Over several weeks, the bright greensolution gradually became light yellow-green and an orange precipitate formed. In theglovebox, the reaction mixture was taken to dryness, and pentane (10 mL) was added toobtain a yellow suspension that was chilled to —35 °C. The yellow solid was collected on afrit and dried (0.275 g, 0.188 mmol, 72%). Small yellow crystals were grown fromtoluene/HMDSO at —35 °C, and the amount of co-crystallized HMDSO was confirmed by1H NMR spectroscopy of samples of the crystals dissolved in C6D.‘H NMR (toluene-d8,400 MHz, 233 K): ö = 7.99 (t, 2H, 8 Hz), 7.80 (t, IH, 8 Hz), 7.49 (d,1H, 7.5 Hz), 7.41 (d, 1H, 7.5 Hz), 7.32 (d, 1H, 7.5 Hz), 7.27 (d, 1H, 7.5 Hz), 7.09 (m, 2H),7.05 (s, IH), 6.97 (s, 2H), 6.89 (s, 2H), 6.81 (s, IH), 6.64 (m, IOH), 6.54 (s, 1H), 6.49 (s, 1H),6.36 (bm, 2H), 6.07 (dd, 2H,JHH = 8 Hz,JHP = 6 Hz), 5.89 (m, 2H), 5.70 (t, IH, 7 Hz), 5.48(t, IH, 7 Hz) (ArH), 4.94 (s, 1H, NNH), 4.88 (bs, IH, ZrHZr), 2.64 (s, 3H), 2.25 (s, 3H),2.02 (s, 6H), 2.00 (s, 9H), 1.95 (s, 3H), 1.92 (s, 3H), 1.89 (s, 3H), 1.87 (s, 3H), 1.84 (s, 6H),1.79 (s, 3H), 1.59 (s, 3H), 1.55 (s, 31-I) (ArCH3),0.53 (bs, 3H), and 0:33 (bs, 3H) (P(CH32Ph).31P{1H} NMR (toluene-d8,162 MHz, 253 K): 8 = 14.6 (d, 2J, = 57.4 Hz, IP), —2.3 (s, IP), —24.6 (bs, IP).El-MS (m/: 1318 (5, [M — PMe2h]), (100, [2.8 — Mef).Anal. Calcd. for 5.2(HMDSO)033:C86H97N6033Si7Zr:C, 68.22; H, 6.46; N, 5.55; Anal.Found C, 68.48; H, 6.62; N, 5.90.219{ [NPN] *Zr(pMe2ph)}(p-H)(p-N15NH){Zr[NPN] *} (5.2-’N2). Complex 5.2-15N2(0.163 g, 0.112 mmol, 82%) was prepared in an analogous manner to 5.2 from 4.4-15N2(0.200 g, 0.137 mmol), PMe2h (0.010 g, 0.073 mmol) and H2 in toluene (5 mL).‘H NMR spectrum (toluene-d8, 400 MHz, 233 K) is the same as that of 5.2, but theresonance at 8 4.94 is a doublet (IH, 1JHN = 72 Hz), and the resonance at 8 4.88 is a broadtriplet (IH, JHP = 9.8 Hz).‘H{’1P} NMR (toluene-d8,400 MHz, 233 K): 8 = 7.99 (d, 2H, 7 Hz), 7.80 (d, IH, 7.5 Hz),7.49 (s, 1H), 7.41 (s, IH), 7.32 (s, IH), 7.27 (s, IH), 7.09 (m, 2H), 7.05 (s, 1H), 6.97 (s, 2H),6.89 (s, 2H), 6.81 (s, IH), 6.64 (m, IOH), 6.54 (s, IH), 6.49 (s, 1H), 6.36 (bm, 2H), 6.06 (d,2H, 8 Hz), 5.89 (d, 2H, 8 Hz), 5.70 (d, 1H, 7 Hz), and 5.48 (d, 1H, 7 Hz) (ArH), 4.94 (d, 1H,JHN = 72 Hz, NNH), 4.88 (bs, 1H, ZrHZr), 2.64 (s, 3H), 2.25 (s, 3H), 2.02 (s, 6H), 2.00 (s,9H), 1.95 (s, 3H), 1.92 (s, 3H), 1.89 (s, 3H), 1.87 (s, 3H), 1.84 (s, 6H), 1.79 (s, 3H), 1.59 (s,3H), and 1.55 (s, 3H) (ArCH3),0.53 (bs, 3H, P(CH3)2h), 0.33 (bs, 3H, P(CH3)2h).31P{’H} NMR (toluene-d8,162 MHz, 253 K): 8 = 14.6 (d, IP, 2J, = 57.4 Hz), —2.3 (s, 1P), —24.6 (bd, 1P, 2J = 51.5 Hz).‘5N{’H} NMR (toluene-d8,40 MHz, 298 K): 8 = 143.9 (s), 29.8 (d, 2JNP = 10 Hz).El-MS (m/: 1320 (12, {M — PMe2h]’), 541 (100, [2.8 — Me]j.Reaction of 4.1 with H2. A solution of 4.1 (0.365 g, 0.249 mmol) in toluene (10 mL) in athick-walled Teflon-sealed bomb was degassed by three freeze-pump-thaw cycles. At 77 Kthe flask was filled with H2. The solution was warmed slowly to rt behind a blast shield. Thedeep green solution was stirred for 6 weeks. No change was observed visually or detected by31P{’H} NMR spectroscopy.220Reaction of 4.2 with H2. A solution of 4.2 (0.430 g, 0.291 mmol) in toluene (15 mL) wastransferred to a thick-walled Teflon-sealed bomb and degassed by three freeze-pump-thawcycles. At 77 K, the flask was filled with H2 gas, and allowed to warm slowly to rt behind ablast shield. The solution was stirred vigorously for 8 weeks, and a gradual green to yellowcolour change was observed. The pressure was vented, and the yellow reaction mixture wastaken to dryness to obtain a yellow hexanes-soluble solid.31P{’H} NMR (C6D,121 MHz): ö = —7.6 (s), —8.0 (s), —21.3 (s), —31.4 (s).{ [NPN] *Zr(Py)} (jt-H)(j.i.-1:q2-NNSiHPh){Zr[NPN] *} (5.3). To a stirred solution of4.2 (0.430 g, 0.291 mmol) in toluene (5 mL) at —35 °C was added dropwise a solution ofphenylsilane (35 mg, 0.32 mmol) in toluene (2 mL). The reaction mixture was warmed slowlyto rt, and it turned orange-brown after 5 mm. After 1 h, the clear orange-brown solution wastaken to dryness to obtain a brown residue. Hexanes (5 mL) were added to precipitate abrown solid that was collected on a frit, washed with pentane (2 X 5 mL), and dried undervacuum to obtain a light brown powder (0.378 g, 0.248 mmol, 85%). Small crystals of 5.3suitable for elemental analysis were grown by slow evaporation of a benzene/HMDSOsolution of the compound. Samples obtained in this manner contain approximately 1equivalent of HMDSO and I — 2 equivalents of benzene of solvation, as determined by ‘HNMR spectroscopy of the crystals dissolved in toluene-d8.Larger single crystals of 5.3 weregrown by slow evaporation of a benzene solution of the compound.‘H NMR (C6D,400 MHz): 6 = 8.25 (dd, IH, =15 Hz, 2JH = 2 Hz, ZrHZr), 7.92 (bs,1H), 7.86 (t, 2H, 8 Hz), 7.60 (bd, 1H, 7 Hz), 7.44 (bd, IH, 8 Hz), 7.29 (bd, 2H, 7 Hz), 7.15-7.02 (m, 7H), 7.00 (s, IH), 6.92 (m, 5H), 6.86-6.77 (m, 6H), 6.73 (d, 3H, 7 Hz), 6.64 (s, 2H),2216.58 (s, IH), 6.09 (dd, 1H,JHH = 8 Hz,JHP = 6 Hz), 5.84 (m, 5H), 5.82 (s, 1H), and 5.72 (dd,IH, J = 8 Hz, JHP = 6 Hz) (ArH), 5.17 (d, 1H, 9.5 Hz), and 3.94 (d, 1H, 9.5 Hz) (SiH2),2.57 (s, 3H), 2.47 (s, 3H), 2.22 (s, 3H), 2.16 (s, 91-1), 2.07 (s, 3H), 1.98 (s, 3H), 1.97 (s, 6H),1.92 (s, 3H), 1.89 (s, 3H), 1.69 (s, 3H), 1.68 (s, 3H), 1.53 (s, 3H), and 1.24 (s, 3H) (ArCH3).31P{1H} NMR (C6D,162 MHz): = 14.9 (s, IP), —4.3 (s, IP).29Si{1H} NMR (C6D,80 MHz): ö = —34.4 (d, 3J = 10 Hz).13C{’H} NMR (C6D, 101 MHz): ö = 162.7 (d, 27 Hz), 161.8 (a, 29 Hz), 160.6 (d, 31 Hz),159.6 (d, 23 Hz), 152.6, 147.7, 147.5, 146.9, 146.7, 143.4, 139.6, 138.5, 137.8, 137.6, 137.5,136.9, 136.6, 136.4, 136.1, 135.8, 135.1, 134.9, 134.7, 134.6, 134.5, 134.4, 134.0, 133.9, 133.8,133.5, 133.4 (d, 3 Hz), 133.2, 133.0, 132.8, 132.5, 132.0, 131.9, 131.8, 131.6, 131.5, 130.3,130.1, 129.9, 129.6, 129.5, 129.3, 129.2, 128.8 (d, 3 Hz), 127.3, 126.9 (d, 4 Hz), 125.6, 123.9(d, 6 Hz), 123.2, 122.8 (d, 31 Hz), 121.9 (d, 32 Hz), 119.9 (d, 40 Hz), 118.9 (d, 26 Hz), 118.1(d, 7 Hz), 116.5 (d, 8 Hz), 115.2 (d, 11 Hz), 113.7 (d, 20 Hz), 113.6, and 112.7 (d, 19 Hz)(ArC), 21.1, 21.0, 20.94, 20.91, 20.8, 20.6, 20.47, 20.45, 20.37, 20.30, 20.08, 19.81, 18.83,18.61, 18.54, and 17.98 (ArCH3).El-MS (m/: 1424 (10, [M — Py}), 541 (80, [2.8 — Me]j.Anal. Calcd. for 5.3(HMDSO)(C6)15102H18ON7PZrSi3:C, 68.57; H, 6.66; N, 5.49;Anal. Found C, 68.59; H, 6.40; N, 5.60.{ [NPN] *zf(Py d5)} (j.i.-H) (.i-11‘:i2-NNS HPh){Zr[NPNJ *} (5.3-d5). Complex 5.3-d5was prepared by the method used to prepare 5.3 from 4.2-d10 (0.120 g, 0.081 nimol), andPhSiH3 (10 mg, 0.089 mmol) in toluene (5 mL).2221H NMR (C6D,400 MHz): 6 = 8.25 (dd, IH, 2J 15 Hz, 2JHp = 2 Hz, ZrHZr), 7.92 (bs,IH), 7.86 (t, 2H, 8 Hz), 7.60 (bd, IH, 7 Hz), 7.44 (bd, 1H, 8 Hz), 7.29 (bd, 2H, 7 Hz), 7.15-7.06 (m, 7H), 7.00 (s, 1H), 6.92 (m, 5H), 6.86-6.77 (m, 6H), 6.73 (a, 1H, 7 Hz), 6.64 (s, 2H),6.58 (s, 1H), 6.09 (dd, IH,JHH = 8 Hz,J = 6 Hz), 5.88 (dd, 1H,J = 8 Hz,J = 6 Hz),5.84 (dd, IH,JHH = 8 Hz,J = 6 Hz), 5.82 (s, IR), and 5.72 (dd, IH,JHH = 8 Hz,J = 6Hz) (ArH), 5.17 (d, IH, 9.5 Hz), and 3.94 (a, IH, 9.5 Hz) (SiH2), 2.57 (s, 3H), 2.47 (s, 3H),2.22 (s, 3H), 2.16 (s, 9H), 2.07 (s, 3H), 1.98 (s, 3H), 1.97 (s, 6H), 1.92 (s, 3H), 1.89 (s, 3H),1.69 (s, 3H), 1.68 (s, 3H), 1.53 (s, 3H), and 1.24 (s, 3H) (ArCH3).{ [NPNJ *Zr(Py)} (-F{) (-‘it:1215N’5S1HPh){Zr[NPN] *} (5.3-N2).Complex 5.3-N2was prepared by the same route used to prepare 5.3, from 4.2-15N2(40 mg, 27 jimol) andphenylsilane (4 mg, 37 jimol) in toluene solution.1H NMR (C6D,400 MHz): same as for 5.3, but resonance at 6 3.94 is a broad multiplet.1H{31P} (C6D,400 MHz): 6 = 8.25 (s, IH, ZrHZr), 7.92 (bs, IH), 7.86 (d, 2H, 8 Hz), 7.60(s, IH), 7.44 (s, IH), 7.29 (s, 2H), 7.13-6.77 (m, 19H), 6.73 (d, 3H, 7 Hz), 6.64 (s, 2H), 6.58(s, 1H), 6.09 (d, IH, 8 Hz), 5.86 (m, 6H), and 5.72 (d, IH, 8 Hz) (ArH), 5.17 (d, IH, 9.5 Hz),and 3.94 (bm, IH, JHH = 10 Hz, JHN = 5 Hz, 3JHN = 3 Hz) (SiH2), 2.57 (s, 3H), 2.47 (s, 3H),2.22 (s, 3H), 2.15 (s, 3Ff), 2.14 (s, 3H), 2.12 (s, 3H), 2.05 (s, 3H), 2.00 (s, 3H), 1.98 (s, 3H),1.97 (s, 6H), 1.92 (s, 3H), 1.89 (s, 3H), 1.69 (s, 31-1), 1.68 (s, 3H), and 1.53 (s, 3H) (ArCH3).31P{1H} NMR (C6D,162 MHz): 6 =14.9 (s, IP), —4.2 (dd, IP, 2JPN = 10 Hz, 3JPN = 3 Hz).29Si{1H} NMR (C6D,80 MHz): 6 = —34.4 (ddd, 1Js = 5.5 Hz, 2J = 9.5 Hz, 3J = 10 Hz).15N{H} NMR (C6D,40 MHz): 6 = —9.7 (dd, 1JNN = 15 Hz, 2JNp = 3 Hz) —105.6 (dd, IJNN =15 Hz, JNP = 10 Hz).223El-MS (m/: 1426 (30, [M — Py]j, 541 (40, [2.8 — Me]), 78 (100, [C6H]).(5.4). A solution of 4.1 (0.380 g, 0.260mmol) in toluene (5 mL) was chilled to —35 °C. To this stirred solution was added 4,4’-dimethylbenzophenone (57 mg, 0.27 mrnol) in toluene (2 mL) dropwise. The reactionmixture was allowed to warm to rt, whereupon it became brown after 10 mm. After 30 mm.,the reaction mixture was a clear orange solution. After 4 h, the solution was taken to drynessto obtain a dark orange solid. Upon addition of pentane (15 mL), a yellow-orange solidremained, which was isolated on a fit, washed with pentane (2 X 5 mL), and dried to give abright yellow-orange powder (0.330 g, 0.216 mmol, 83%). Compound 5.4 was recrystaffizedfrom benzene, and orange single crystals of 5.4 suitable for X-ray analysis were grown byslow evaporation of a benzene solution of the compound. The ratio of 5.4 to benzene in thecrystals was consistent with that observed by 1H NMR spectroscopy of crystals of 5.4dissolved in THF-d8,and by X-ray analysis before solvent suppression.1H NMR (C6D,400 MHz): ö = 7.79 (t, 2H, 8 Hz), 7.71 (t, 2H, 8 Hz), 7.40 (d, 2H, 8 Hz),7.36 (d, 2H, 7 Hz), 7.08 (m, 5H), 6.93 (d, 2H, 8 Hz), 6.88 (d, 2H, 8 Hz), 6.83-6.74 (m, 1IH),6.70 (s, 2H), 6.62 (d, 2H, 8 Hz), 6.55 (s, 2H), 5.84 (dd, 2H,JHH = 8 Hz,J, = 6 Hz), and 5.81(dd, 2H,JHH = 8 Hz,J = 6 Hz) (ArH), 2.22 (s, 3H), and 2.20 (s, 3H) (N—CC64CH,2.13(s, 6H), 2.09 (s, 6H), 2.04 (s, 6H), 1.99 (s, 6H), 1.94 (s, 6H), 1.92 (s, 6H), 1.83 (bs, 6H), and1.68 (s, 6H) (ArCH3).31P{’H} NMR (C6D,162 MHz): ö = —7.7 (s, 1P), —10.4 (s, IP).‘3C{1H} NMR (C6D, 101 MHz): 6 = 162.1 (d, 30 Hz), 161.0 (d, 25 Hz), 151.7, 143.2, 142.9(d, 3 Hz), 138.6, 137.9, 137.3, 137.2, 136.84, 136.81, 136.5, 135.9 (d, 14 Hz), 134.6, 134.34,134.28, 134.04, 133.95, 133.8, 133.6, 133.5, 133.4, 133.3, 132.6 (d, 8 Hz), 132.3, 130.75,224130.71, 130.5, 130.4, 130.1, 129.7, 129.3, 129.0, 128.9, 128.5, 128.3, 128.1, 127.9, 127.6, 119.5(d, 33 Hz), and 115.0 (d, 10 Hz) (ArC and CN), 21.5, 21.4, 21.2, 21.0, 20.3, 20.2, 19.4, 19.19,19.16, and 19.08 (ArCH3).Anal. Calcd. for 5.42.5C6H:1067N6P2ZrO:C, 73.79; H, 6.25; N, 4.87; Anal. Found C,73.52; H, 6.61; N, 4.49.JR (KBr): 3005 (w), 2952 (w), 2918 (m), 2855 (w), 2723 (w), 2030 (w), 1601 (s), 1509 (s),1494 (s), 1468 (s), 1436 (m), 1390 (m), 1271 (s), 1242 (s), 1191 (m), 1155 (m), 1087 (m), and1057 (m) cm1.Low temperature reaction of 4.1 with 4,4’-dimethylbenzophenone. In a 3-mL vial, 4.1(10 mg, 6.8 prnol) was dissolved in toluene-d8 (0.8 mL), and the blue-green solution wastransferred to an NMR tube. In a separate 3-mL vial, 4,4’-dimethylbenzophenone (3 mg, 14jimol) was dissolved in toluene-d8 (0.1 mL) and transferred very carefully to a melting pointcapillary tube via syringe. One edge of the open end of the capillary tube was chipped away,and the tube was transferred open-end-up to the NMR tube. The NMR sample was cooledto 253 K in the spectrometer probe, and a 31P{1H} NMR spectrum was acquired. The NMRtube was then removed from the spectrometer, shaken vigorously to mix for 30 s, andreturned to the cooled probe. 31P{1H} NMR spectra were acquired every 5 mm. at 253 K for30 nun., then every 5 mm. at 273 K for 30 mm., then every 5 mm. at 300 K for 15 mm. Afinal 31P{1H} NMR spectrum was acquired after the sample was stored in an N2-filledglovebox at rt for 24 h.Reaction of 4.2 with (CH3)C (0)H. To a stirred solution of 4.2 (0.489 g, 0.33 1 mmol)in toluene (7 mL) at —35 °C was added dropwise a solution of(CH3)C (0)H (61 mg, 0.71225mmol) in toluene (2 mL). The reaction mixture turned brown, then red, then yellowthroughout the addition. After 24 h, the yellow solution was taken to dryness to obtain ayellow residue. The residue was triturated with hexanes (15 mL), and the yellow extractswere filtered through Ceite, and taken to dryness to obtain a yellow powder (0.230 g).“P{1H} NMR (C6D,162 MHz): 6 = —6.5 (s), —6.6 (s), —9.3 (s), —10.7 (s), —13.7 (s), —14.9 (s).Yellow crystals (60 mg) grew from a hexanes solution of the yellow powder at rt.31P{’H} NMR (C6D,162 MHz): 6 = —6.6 (s, 1P), —10.7 (s, 7P), —13.7 (s, 1P), —14.9 (s, 7P).Peaks that appear consistent with the major product are noted below:‘H NMR (C6D,400 MHz): 6 = 7.67 (t, 2H, 7 Hz), 7.49 (d, IH, 7 Hz), 7.29 (d, IH, 7 Hz),7.18-6.97 (m, 8H), 6.89-6.73 (m, 12H), 6.66 (s, 2H), 6.24 (dd, 1H,J = 8 Hz,J, = 6Hz),6.13 (t, 2H, 7 Hz), and 5.43 (dd, 1H,JHH = 8 Hz,JHP = 6 Hz) (ArH), 4.71 (s, IH) (N=CHR),2.53 (s, 3H), 2.46 (s, 3H), 2.30 (s, 3H), 2.25 (s, 3H), 2.20 (s, 3H), 2.15 (s, 6H), 2.13 (s, 3Ff),2.10 (s, 3H), 2.09 (s, 6H), 2.06 (s, 6H), 1.95 (s, 3H), 1.88 (s, 3H), and 1.68 (s, 3H) (ArCH3),0.80 (s, 9H) (C(CH3.{[NPN]*Zr(NCPh2)}z(J.Lr)2:T)2NHz (5.5). To a stirred solution of 4.2 (0.360 g, 0.244mmol) in toluene (5 mL) was added clropwise a solution of benzophenone imine (93 mg,0.51 mmol) in toluene (2 mL). The reaction mixture turned brown through the addition, andit was bright red after 5 mm. The reaction mixture was stirred for 24 h, and the clear redsolution was taken to dryness to obtain a red solid that was suspended in pentane (2 X 5mL), collected on a fit, rinsed with hexanes (5 mL), and dried (0.390 g, 0.232 mmol, 95%).Small crystals of 5.5 were grown by layer diffusion of HMDSO into a solution of thecompound in benzene. The amount of co-crystallized solvent observed by microanalysis isconsistent with that observed by ‘H NMR spectroscopy of samples dissolved in toluene-d8.226Single crystals of 5.5 suitable for X-ray analysis were grown by slow evaporation of abenzene solution of the compound.‘H NMR (toluene-d8,400 MHz, 273 K): 6 = 7.25 (m, 14H), 7.11 (m, 6H), 6.93 (m, IOH),6.84 (s, 2H), 6.77 (d, 2H, 7.5 Hz), 6.67 (m, 2H), 6.53 (m, 3H), 6.42 (t, 2H, JHP = 6 Hz), 6.26(bt, 2H), 6.13 (s, 1H), 6.04 (bs, 1H), 5.97 (bs, 4H), and 5.65 (bt, IH) (ArH), 4.45 (d, IH, 13.7Hz), and 3.51 (d, 1H, 13.7 Hz) (NH), 2.53 (s, 3H), 2.45 (s, 6H), 2.42 (s, 3H), 2.32 (s, 3H),2.17 (s, 3H), 2.12 (s, 3H), 2.01 (s, 3H), 1.95 (s, 3H), 1.92 (s, 3H), 1.86 (s, 3H), 1.82 (s, 3H),1.75 (s, 6H), 1.42 (s, 3H), and 1.14 (s, 31-I) (ArCH3).31P{1H} NMR (C6D,162 MHz, 300 K): 6 =1.2 (s, IP), —9.2 (s, IP).13C{’H} NMR (THF-d8,101 MHz, 248 K): 6 = 175.4 (d, 7 Hz), and 170.5 (d, 8 Hz) (C=N),165.2 (d, 30 Hz), 165.1 (d, 29 Hz), 162.1 (d, 26 Hz), 161.6 (d, 29 Hz), 149.8, 147.8, 146.8,146.7, 141.7, 140.3, 140.2, 139.7, 139.3, 138.9, 137.5, 137.2, 136.9, 136.3, 136.0, 135.9, 135.6,135.4, 135.3, 135.2, 134.8, 134.6, 134.4, 133.8, 133.7, 133.3, 133.0, 132.9, 132.7, 132.1, 132.0,131.9, 131.5, 131.4, 131.2, 130.7, 130.6, 130.5, 130.3, 130.2, 130.1, 130.0, 129.9, 129.6, 129.4,129.1, 128.9, 128.7, 128.6, 128.2, 128.1 (d, 2 Hz), 127.8, 127.4, 126.9, 126.7 (d, 4 Hz), 126.5(d, 4 Hz), 121.1, 120.8, 120.7, 120.4, 118.4 (d, 8 Hz), 118.2 (d, 8 Hz), 117.8 (d, 2 Hz), 116.4(d, 7 Hz), 115.4 (d, 8 Hz), 114.6 (d, 9 Hz), 114.4 (d, 9 Hz), and 112.7 (ArC), 21.9, 21.7, 21.6,21.4, 21.3, 21.2, 20.8, 207, 20.5, 20.3, 19.3, 19.2, 19.1, 18.7, 18.5, and 18.4 (ArCH3).El-MS (m/J: 1484 (20, [{[NPN]*Zr}(NH)(NCPh)]+),1318 (80, [{[NPNI*Zr}2()]j,541 (100, [2.8 — Me]).Anal. Calcd. for 5.5(HMDSO)05:C105H,09N8P2SiO5Zr:C, 71.51; H, 6.23; N, 6.35; Anal.Found C, 71.54; H, 6.33; N, 6.48.227JR (KBr): 3390 (w), 3250 (w), 3051 (m), 3003 (m), 2918 (m), 2854 (m), 1623 (s), 1615 (s),1574 (s), 1519 (m), 1514 (w), 1504 (m), 1494 (m), 1469 (s), 1393 (m), 1302 (w), 1269 (m),1241 (s), 1190 (m), 1154 (m), 864 (s), 813 (m), and 696 (s) cm1.{[NPN]*Zr}(iO) (5.6). A solution of 4.4 (0.150 g, 0.103 mrnol) in C6D (2 mL) in a 40-mL Teflon-sealed bomb was degassed with three freeze-pump-thaw cycles. At rt, the flaskwas filled with CO gas. The reaction mixture turned yellow after 30 s of shaking. Thesolution was stirred overnight to obtain a yellow-brown suspension. The solution was thenstirred under a flow of N2 for I h. In the glovebox, the yellow precipitate was collected on afit, washed with hexanes (2 x 5 mL), and dried (0.106 g, 0.080 mmol, 78%). Single crystalsof 5.6 were grown by slow evaporation of a benzene solution of the compound in an NMRtube.‘H NMR (C6D,500 MHz): 6 = 7.93 (t, 4H, 8.5 Hz), 7.41 (d, 4H, 6 Hz), 7.15 (m, 4H), 7.03(t, 2H, 8 Hz), 6.78 (s, 4H), 6.77 (d, 4H, 8.5 Hz), 6.67 (s, 4H), and 5.98 (dd, 4H, 8 Hz, 6 Hz)(ArH), 2.30 (s, 12H), 2.23 (s, 12H), 1.97 (s, 12H), and 1.92 (s, 12H) (ArCH3).31P{1H} NMR (C6D,202 MHz): 6 = —19.2 (s).‘3C{1H} NMR (C6D, 126 MHz): 6 = 159.7 (d, Hz), 140.4, 137.6, 136.7, 134.6, 134.4, 134.0,133.6 (d, Hz), 130.7, 129.8, 129.5, 129.2 (d, Hz), 128.5, 125.6, 119.6 (d, Hz), and 115.0 (ArC),21.2, 20.8, 19.6, and 18.5 (ArCH3).El-MS (m/: 1322 (60, [IV1]), 541 (100, [2.8— Me]).Anal. Calcd. for 5.6:C76H8N4OPZrC, 68.95, H, 5.94; N, 4.23; Anal. Found C, 68.60; H,5.90; N, 4.63.228Reaction of 4.4 with‘3C0. A solution of 4.4 (0.150 g, 0.103 mmol) in C6D (2 mL) in a 40-mL Teflon-sealed bomb was degassed by three freeze-pump-thaw cycles, and refilled with‘3C0 gas at rt (1 atm). The reaction mixture was stirred vigorously and turned yellow-brownafter 3 h. After 2 d, the flask was stirred under a flow of N2 for 1 h. In the glovebox, aportion of the yellow brown solution was transferred to an NMR tube.31P{1H} NMR (C6D, 162 MHz): ö = —4.6 (d, 17%, 7.4 Hz), —7.1 (s, 14%), —7.7 (bs, 20%), —9.5 (d, 17%, 7.4 Hz), —19.2 (s, 2.5%, 5.6), —31.4 (s, 0.8%, 2.8), —46.5 (s, 50%, PMe2h).‘3C{1H} NMR (C6D, 162 MHz): = 177.5 (d, 5.3 Hz), 124.5 (d, 8.4 Hz).Reaction of 4.1 with ethylene. A solution of 4.1 (0.350 g, 0.239 niniol) in toluene (7 niL) ina 100-niL Teflon-sealed bomb was degassed by three freeze-pump-thaw cycles and filledwith C2H4 at rt (1 atm). The deep green solution was stirred for I month. No change wasobserved visually or detected by 31P{1H} NMR spectroscopy.Reaction of 4.1 with triphenylphosphine oxide. To a stirred solution of 4.1 (85 mg, 0.058mmol) in toluene (3 niL) at —35 °C was added a solution of triphenyiphosphine oxide (18mg, 0.065 mmol) in toluene (1 niL) dropwise over 5 miii. The reaction mixture turned brightblue throughout the addition, and was stirred for 30 miii. at rt. The bright blue solution wastaken to dryness, and the blue-green solid was triturated with hexanes (10 niL). The blueextracts were filtered through Celite, and the filtrate was allowed to concentrate overnight atrt to obtain small teal blue crystals. The pale blue-green supematant liquid was decanted, andthe crystals were dried under vacuum for 30 miii. (39 mg, 0.024 nimol, 42%).1H NMR (C6D,400 MHz): = 7.86 (t, 2H, 8 Hz), 7.53 (d, 2H, 8 Hz), 7.46 (d, 2H, 7.5 Hz),7.43 (d, 2H, 7.5 Hz), 7.28 (m, 3H), 7.22 (t, 1H, 7.5 Hz), 7.11 (m, 4H), 6.87 (s, 2H), 6.80 (m,22916H), 6.53 (s, 2H), 6.58 (t, IH, 7 Hz), 6.37 (t, 2H, 7 Hz), 6.33 (s, 2H), 6.14 (dd, 2H,JHH = 8Hz,JHP = 6 Hz), and 5.82 (dd, 2H,JHH = 8 Hz,JHP = 6 Hz) (ArH), 2.40 (s, 6H), 2.23 (s, 6H),1.99 (s, 6H), 1.96 (s, 6H), 1.93 (s, 12H), 1.70 (s, 6H), and 1.62 (s, 6H) (ArCH3).31P{1H} NMR (C6D,162 MHz): 8 = 40.4 (s, IP), 4.7 (s, IP), 0.1 (s, 1P).13C{H} NMR (C6D, 101 MHz): 8 = 163.2 (d, 32 Hz), 159.4 (d, 25 Hz), 145.5 (d, 4 Hz),143.3, 139.3 (d, 28 Hz), 137.2, 136.6, 135.6, 135.1, 134.8, 134.4, 134.3, 134.2, 134.1, 133.8,133.7, 133.6, 133.5, 133.4, 133.3, 133.1, 132.9, 132.8, 132.7, 132.4, 132.2, 131.5 (d, 3 Hz),130.2, 129.7, 129.3, 128.9, 128.7, 128.4, 127.8, 125.6, 125.5, 118.3 (d, 34 Hz), 117.5 (d, 29Hz), 114.3 (d, 8 Hz), and 113.4 (d, 11 Hz) (ArC), 21.1, 20.9, 20.5, 20.3, 19.8, 19.1, 18.5, and15.7 (ArCH3).The blue crystals were dissolved in C6D and the blue solution became green over 24 h at rt.After 24 h at rt, the green solution was analyzed by 31P{1H} NMR spectroscopy.31P{1H} NMR (C6D, 162 MHz): 8 = 43.2 (s), 42.4 (s), 40.4 (s), 6.2 (s), 4.7 (s), 0.1 (s), —3.8(s), —8.9 (s), —12.8 (s), —17.4 (s), —18.1 (s).5.5 References.Shah, V. K.; Brill, W. Proc. Nati. Acad. Sci. U.S.A. 1977, 74, 3249.2 Eady, R. R. Chem. Rev. 1996, 96, 3013.Einsle, 0.; Schmid, B.; Tezcan, F. A.; Andrade, S. L. A.; Yosbida, M.; Howard, J. B.;Rees, D. C. Science 2002, 297, 1696. B) Yang, T.-C.; Maeser, N. K.; Laryukhin, M.; Lee, H.-I.;Dean, D. R.; Seefeldt, L. C.; Hoffman, B. M. J. Am. Chem. Soc. 2005, 127, 12804.4Leigh, G. J. The World’s Greatest F&-, Oxford University Press: New York, 2004, p. 17.Smil, V. Nature 1999, 400, 415.2306 A) Chatt, J.; Pearman, A. J.; Richards, R. L. Nature 1975, 253, 39. B) Chatt, J.; Pearman, A.J.; Richards, R. L. J. Chem. Soc., Dalton Trans. 1977, 1852.Chatt, J.; Heath, G. A.; Richards, R. L.; Sanders, J. R. J. Chem. Soc., Chem. Commun. 1972,1010.8 Yandulov, D. V.; Schrock, R. R. Science 2003, 76, 301. B) Ritleng, V.; Yandulov, D. V.;Weare, W. W.; Schrock, R. R.; Hock, A. S.; Davis, W. M. J. Am. Chem. Soc. 2004, 126, 6150.A) Chatt, J.; Diamantis, A. A.; Heath, G A.; Hooper, N. A.; Leigh, G. J. J. Chem. Soc., DaltonTrans. 1977, 688. B) Chatt, J.; Heath, G. A.; Leigh, G. J. J. Chem. Soc., Chem. Commun. 1972,444.10A) Hidai, M.; Mizobe, Y.; Sato, M.; Kodama, T.; Uchida, Y. J. Am. Chem. Soc. 1978, 100,5740. B) Bevan, P. C.; Chatt, J.; Hidai, M.; Leigh, G. J. J. Oiganomet. Chem. 1978, 160, 165. C)Mizobe, Y.; Ono, R.; Uchida, Y.; Hidai, M.; Tezuke, M.; Moue, S.; Tsuchiya, A. J. Oiganomet.Chem. 1981, 204, 377.Hidai, M.; Mizobe, Y. Chem. Rev. 1995, 95, 1115.12 Seino, H.; Ishii, Y.; Hidai, M. J. Am. Chem. Soc. 1994, 116, 7433.Fryzuk, M. D.; Love, J. B.; Rettig, S. J.; Young, V. G. Science 1997, 275, 1445.14 Pool, J. A.; Lobkovsky, E.; Chink, P. J. Nature 2004, 427, 527.15A) Fryzuk, M. D.; MacKay, B. A.; Johnson, S. A.; Patrick, B. 0. Angew. Chem. mt. Ed. 2002,41, 3709. B) MacKay, B. A.; Patrick, B. 0.; Fryzuk, M. D. Organometallics 2005, 24, 3836. C)Fryzuk, M. D.; MacKay, B. A.; Patrick, B. 0. J. Am. Chem. Soc. 2003, 125, 3234.16 Morello, L.; Love, J. B.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc. 2004, 126, 9480.17 Komori, K.; Oshita, H.; Mizobe, Y.; Hjdai, M. J. Am. Chem. Soc. 1989, 111, 1939.18 Hoti, K.; Mori, M. J. Am. Chem. Soc. 1998, 120, 7651.23119A) Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J. O,ganometallics 1989, 8, 1723. B) Fryzuk, M.D.; Haddad, T. S.; Rettig, S. J. Otganometallics 1988, 7, 1224.20 Basch, H.; Musaev, D. G.; Morokuma, K.; Fryzuk, M. D.; Love, J. B.; Seidel, W. W.;Albinati, A.; Koetzle, T. F.; Kkoster, W. T.; Mason, S. A.; Eckert, J. J. Am. Chem. Soc. 1999,121, 523. B) Gozum, J. E.; Wilson, S. R.; Girolanil, G. S. J. Am. Chem. Soc. 1992, 114, 9483.C) Màtsuo, T.; Kawaguchi, H. J. Am. Chem. Soc. 2005, 127, 17198.21 A) Luinstra, G. A.; Rief U.; Prosenc, M. H. O,ganometallics 1995, 14, 1551. B) Larsonneur,A.-M.; Choukroun, R.; Jaud, J. Oiganometallics 1993, 12, 3216. C) Choukroun, R.; Dahan, F.;Larsonneur, A.-M.; Samuel, E.; Petersen, J.; Meunier, P.; Sornay, C. O,ganometallics 1991, 10,374. D) Jones, S. B.; Petersen, J. L. Inog. Chem. 1981, 20, 2889. E) Chink, P. J.; Henhing, L.M.; Bercaw, J. E. O,ganometallics 2001, 20, 534.Binsch, G.; Lambert, J. B.; Roberts, B. W.; Roberts, J. D. J. Am. Chem. Soc. 1964, 86, 5565.23A) van den Hende, J. R.; Hessen, B.; Meetsma, A.; Teuben, J. H. Organometallics 1990, 9,537. B) Weigold, H.; Bell, A. P.; Willing, R. I. J. Oiganomet. Chem. 1974, 73, C23.24A) Mylvaganam, M. Dinitrogen and Paramagnetic Complexes ofZirconium. Ph.D. Thesis;University of British Columbia: Vancouver, 1994. B) Morello, L. Amidophosphine Complexes ofZirconium and Titaniumfor Dinitrogen Activation. Ph. D. Thesi.r, University of British Columbia:Vancouver, 2005.25 Manriquez, J. M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J. E. J. Am. Chem. Soc. 1978,100, 2716.26 Bernskoetter, W. H.; Ohnos, A. V.; Lobkovsky, E.; Chink, P. J. Oiganometallics 2006, 25,1021.27 Gozum, J. E.; Girolami, G. S. J. Am. Chem. Soc. 1991, 113, 3829.23228A) Fryzuk, M. D.; Johnson, S. A.; Patrick, B. 0.; Albinafi, A.; Mason, S. A.; Koetzle, T. F.J. Am. Chem. Soc. 2001, 123, 3960. B) Johnson, S. A. Lgand Design and the Sjnthesis ofReactiveOiganometallic Complexes ofTantalumfor Dinitrogen Activation. Ph. D. Thesis; University of BritishColumbia: Vancouver, 2000.29 MacKay, B. A. A New Reactionfor Coordinated Dinitrogen. Ph.D. thesir, University of BritishColumbia: Vancouver, 2003.30 Some coupling constants have been determined by simulation of NMR spectra using theprogram MestRe-C available at: www.mestrec.com.31 A) Airoldi, C.; Bradley, D. C.; Chudzynska, H.; Hursthouse, M. B.; Malik, K. M. A.;Raithby, P. R. J. Chem. Soc., Dalton Trans. 1980, 2010. B) Schrock, R. R.; Seidel, S. W.; Schrodi,Y.; Davis, W. M. Organometallics 1999, 18, 428.32A) Howard, W. A.; Waters, M.; Parkin, G. J. Am. Chem. Soc. 1993, 115, 4917. B) Chen, L.;Cotton, F. A. Inorg. Chem. 1996, 35, 7364.33MacKay, B. A.; Munha, R. F.; Fryzuk, M. D. J. Am. Chem. Soc. 2006, ASAP.34Arvanitis, G. M.; Smegal, J.; Meier, I.; Wong, A. C. C.; Schwartz, J.; Van Engen, D.Organometallics 1989, 8,2717.Kiplinger, J. L.; John, K. D.; Morris, D. E.; Scott, B. L.; Burns, C. J. Organometallics 2002,21, 4306.36 Szmant, H. H.; McGinnis, C. J. Am. Chem. Soc. 1950, 72, 2890.Zanotti-Gerosa, A.; Solari, E.; Giannini, L.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J. Am.Chem. Soc. 1998, 120, 437.38 Rocklage, S. M.; Schrock, R. R. J. Am. Chem. Soc. 1982, 104, 3077.Hidai, M.; Mizobe, Y.; Ucbida, Y. J. Am. Chem. Soc. 1976, 98, 7824.233° Hussain, W.; Leigh, G. J.; Ali, H. M.; Picket, C. J. J. Chem. Soc., Dalton Trans. 1988, 553.41 Harada, Y.; Mizobe, Y.; Hidai, M. Inotg. Chim. Acta 1999, 285, 336.42 Imaeda, I.; Nishihara, H.; Nakano, K.; Ichida, H.; Kobayashi, A.; Saito, T.; Sasaki, Y. Inotg.Chem. 1985, 24, 1246.Nishibayashi, Y.; Iwai, S.; Hidai, M. J. Am. Chem. Soc. 1998, 120, 10559.Bossard, G. E.; George, T. A.; Lester, R. K.; Tisdale, R. C.; Turcotte, R. L. Inorg. Chem.1985, 24, 1129.45A) Lefeber, C.; Arndt, P.; Tillack, A.; Baumann, W.; Kempe, R.; Burkalov, V. V.;Rosenthal, U. Organometallics 1995, 14, 3090. B) Zippel, T.; Arndt, P.; Ohff A.; Spannenberg,A.; Kempe, R.; Rosenthal, U. Or&anometallics 1998, 17, 4429. C) Collier, M. R.; Lappert, M. F.;McMeeking, J. Inotg. NucI. Chem. Lett. 1971, 7, 6898.46 Bemskoetter, W.; Pool, J. A.; Lobkovsky, E.; Chink, P. J. J. Am. Chem. Soc. 2005, 127,7901.A) Basta, R.; Harvey, B. G.; Arif A. M.; Ernst, R. D. Inorg. Chim. Acta 2004, 357, 3883. B)Beatty, R. P.; Datta, S.; Wreford, S. S. Inorg. Chem. 1979, 18, 3139. C) Wielstra, Y.;Gambarotta, S.; Roedelof, J. B.; Chiang, M. Y. Organometallics 1988, 7, 2177. D) Guram, A. S.;Swenson, D. C.; Jordan, R. F. J. Am. Chem. Soc. 1992, 114, 8991.48 Otero, A.; Fernandez-Baeza, J.; Antiñolo, A.; Tejeda. J.; Lana-Sanchez, A.; Sanchez-Barba,L.; Fernandez-Lopez, M.; Lopez-Solera, I. Inorg. Chem. 2004, 43, 1350.4° Cole, S. C.; Coles, M. P.; Hitchcock, P. B. Organometallics 2005, 24, 3279.° Clarke, J. F.; Drew, M. G. B. Acta Cystallogr. 1974, B30, 2267.51 Ishino, H.; Takemoto, S.; Hirata, K.; Kanaizuka, Y.; Hidai, M.; Nabika, M.; Seki, Y.;Miyatake, T.; Suzuki, N. Organometallics 2004, 23, 4544.23452A) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. Oranometallics 1993, 12, 3705. B) Cross, R.J.; Farrugia, L. J.; Newman, P. D.; Peacock, R. D.; Stirling, D. J. Chem. Soc., Dalton Trans.1996, 4449.Morello, L.; Yu, P.; Carmichael, C. D.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc.2005, 127, 12797.54A) Spencer, L. P.; MacKay, B. M.; Patrick, B. 0.; Fryzuk, M. D. Proc. NatI. Acad. SUSA 2006, in press. B) van Rijt, S.; MacKay, B. M.; Patrick, B. 0.; Fryzuk, M. D.unpublished results.235Chapter SixThesis Overview and Future Work6.1 Thesis overview.This thesis describes a new arene-bridged diamidophosphine ligand, [NPN]*Li2(S) (S =p-C4H802,THF), its coordination to Zr(IV) and Hf(IV), and the application of [NPNJ”Zrcomplexes to the activation and functionalization of N2. At the outset, [NPN]* was designedto mintic the steric and electronic properties of the —SiMe2CH bridged [NPN] ligand, butwith the reactive and moisture-sensitive N—Si bond replaced by an N—C bond. Remarkably,the solution and solid-state structures of [NPN]*Li2and [NPN]Li2are nearly identical.1Bothcompounds feature a P—Li bond and a diamond-shaped Li2N core. One major differencebetween the two ligands is that [NPNI*Li2is prepared from air-stable organic compounds,and PhPC12, whereas [NPN]Li2 is prepared from air- and moisture-sensitivePhN(H)SiMeC1, and pyrophoric PhPH2. In terms of structure and reactivity, there arealso many similarities between analogous [NPN]*Zr and [NPNIZr complexes.Another compelling similarity between [NPNJ and [NPN]* is that both ligandssupport Zr-N2 complexes. { [NPN] Zr(THF)}20i-1:r1-N and { [NPNj *Zr(THF) } 2O’-11-N2) are prepared by KC8 reduction of dichiorozirconium complexes in THF under N2. Thesolution and solid-state structures of these two complexes, as well as those of thecorresponding Py adducts, { [NPN] Zr(Py) }2(ii-i1:-N2) and { [NPN] *Zf (Py) }2Qi-ii:r-N2),are essentially the same in terms of connectivity and stereochemistry.3Phosphine adductscould not be prepared from {[NPNZr(THF)}2(i-ri:ri- 2); however, the addition of236PMe2R (R = Me, Ph) to {[NPN]*ZrHF)}2(,IrI2:12N gives {[NPN1*Zr(PMe2R)} iri2:r-N){Zr[NPN]*} in high yield. This type of dinitrogen complex is unique because thetwo Zr atoms have different coordination environments. From the solid-state molecularstructure of the PMe2h complex, it appears that [NPN]* blocks the coordination of asecond equivalent of PMe2R to these derivatives. The [NPN]Zr and [NPN]*Zr dinitrogencomplexes are the first early transition-metal dinitrogen complexes for which thecoordination environment at the metal can be altered simply by adding a donor molecule toa dinitrogen complex. In contrast, ([PNP]ZrCl)2jt-i1:-)and its congeners, ([PNP]Zr(O2,6-MeCH3))(ji i1:r-N and ([PNP]ZrCp)2Q-q1:11-N2), are prepared by reducingseparately prepared metal precursors under N2.4The reactivity of the Zr-N2 complexes of [NPNJ and [NPNJ* can also be compared.When solutions of {[NPN]*ZrHF)}OI12:r12N)or {[NPN]ZrHF)}2(ji- i:i- areexposed to H2 gas, no reaction takes place.3 For both and{[NPN]Zr(Py)}2(ji-t:-),the reactions with H2 provide a mixture of products that couldnot be separated. Finally, the addition of H2 to {[NPN]*Zr(PMeR)}(12:T12N2){Zr[NPN] * } generates { [NPNj } (ji-H)(ji-ri2: i-NNH) {Zr[NPN] * } with anew N—H bond. This reaction offers no direct comparison with the [NPN]Zr-N2complexesbecause no PR3 adduct could be synthesized from {[NPN]ZrCfHF)}0t-ri:ri- 2).However, it may only be possible to synthesize {[NPN]*Zr(PMe2R)}QI12:12N2) {Zr[NPN]*} because of the unique properties of the [NPN]* ligand. What is clear is thatthe hydrogenation of side-on bound N2 is not observed when [NPN] is the ancillary ligand,but it is observed in one case when {NPN]* is the ancillary ligand. As is described in chapterone, the formation of new N—H bonds from H2 and a dinitrogen complex has been237observed three other times: ([P2N]Zr)2(i-ii:r-NH)forms from ([P2N]Zr)2(,.i-ri:ri-N),5and [(i5-CMe4H)2(H)](jt-r1N)forms from [(ri5-CMe4H)2](.t-1i:iiN),for M= Zr and Hf.6 Thus, the hydrogenation of the PMe2R adducts is the fourth example of anN—H bond forming from side-on bound dinitrogen.The addition of PhSiH3 to the [NPN]*ZrN2and [NPN]Zr-N2 complexes providesanother opportunity to compare the reactivities of these two systems. {[NPN1*Zr(Py)}2(JLi2:r1-N) reacts with PhSiH3 to yield { [NPN] *Zr(Py) } (pt-H) (ji-T’ :T12NNSiHPh){Zr[NPN]*} with a new N—Si bond. In contrast, the reaction of{[NPNjZr(THF)}2(t-ri:ri- with PhSiH3 provides an intractable mixture of products.3Inchapters one and five, some other examples of the functionalization of coordinateddinitrogen with silanes are described.The reaction of the [NPN]*ZrN2and [NPN]Zr-N2complexes with ethylene gas offersthe final comparison for the two systems. {{NPN]*Zr(IHF)}QL1 2:12N)does not reactwith ethylene gas. In contrast, stirring a benzene solution of {[NPN]ZrHF)}Qi-ii:-)under 1 atm of ethylene results in the formation of a white precipitate that may bepolyethylene.3The other reactions that have been carried out using the [NPN]*ZrN2or[NPN]-ZrN2complexes cannot be compared since different reagents have been used. When{[NPN]ZrcfHF)}Qt-ii:r-)is reacted with p-tolylacetylene, allene, BH3THF, CH3N,or ‘BuSiH3,mixtures of products are obtained.3 It is unclear whether any of these productsform as a result of [NPNJ decomposition.Several reactions of the [NPN]*ZrN2complexes proceed selectively. For example,{ [NPN] *Zr(THF) }20i-11:1-N reacts with 4,4’-dimethylbenzophenone to givein high yield. Also, only one product forms238from the reaction of the THF or Py adducts of {[NPN]*Zr}2(ir12:rI2NZ) withbenzophenone imine. A red complex, {[NPN]*Zr(N=CPh)}2(IIrI2:i12N),is obtained inhigh yield. The addition of Ph3=O to initially generatesone product selectively, bright blue {[NPN]*Zr(O=PPh)}(i12:12N{Zr[NPNJ*}.At this point the following question remains unanswered: is the [NPNI* ligandsuperior to [NPN] in terms of supporting new chemistry for coordinated dinitrogen andminimizing non-productive side reactions? So far, no ligand decomposition reactions orunusual donor atom migrations have been observed for complexes of [NPN]*. Furtherinvestigations may reveal whether side reactions have been minimized by eliminating thereactive N—Si bond from the backbone of [NPN], or by decreasing the flexibility of thisdiamidophosphine. The results reported in chapter five represent all of the reactions thathave been attempted for the {NPN]*ZrN2 complexes. Based on the numeroustransformations observed so far, it seems likely that other new and interesting reactions canbe achieved starting from {[NPN]*Zr(HF)}2QI12:rI2N).In this chapter, the synthesis of a phenyl-bridged diamidophosphine ligand with MesNand ArN (Ar = 4-’PrC6H)substituents (denoted PhMesJpJ and PhArpNJ) is presented.This ligand only differs from [NPN]’ reported in chapter two (section 2.2.1) in thesubstituents at N, but it is prepared in two steps from commercially available reagents. First,the bromodiarylamine ligand precursor is prepared in one pot from a substituted aniline and1,2-dibromobenzene by a Pd-catalyzed cross-coupling reaction. Second, as with {NPN]’, thelithiated ligands,PhMeS[NPN1Lj2.Q,C4HSOZ) and Ph.ArpN]Li2(5) (S = THF,p-C4H802),areobtained from the bromodiarylamine, two equivalents of BuLi and O.5 equivalents of239PhPC12. PhAr[NPN1Zr(NMe2)is prepared in two steps from PhAr[PN]Li2(rHf) by theprotonolysis method used to prepared [NPNI*Zr(NMe2).6.2 Ongoing and Future Projects.From commercially available compounds, the synthesis of [NPN]*Lij(pC4H8O2)canbe accomplished in three or four steps, depending on whether p-tolylboronic acid used toprepare (Mes)(Tol)NH is purchased, or prepared by a Grignard reaction.7 An alternativeapproach to an arene-bridged diamidophosphine ligand is via (Ar)(2-BrC6H4)NH, which canbe prepared in one pot from commercially available anilines and l,2-dibromobenzene by Pd-catalyzed cross-coupling. Although very few reports of C—N coupling reactions from 1,2-dibromobenzene are available,8it seemed unlikely that disubstituted 1,2-(ArNH)C6H4wouldform in high yield due to steric congestion, at least for Ar = Mes. Ph4t[p]j issynthesized from (Ar)(2-BrC6H4)NH, BuLi, and PhPC12.As was outlined in chapter two,phenyl-bridged diamidophosphine ligands are denoted [NPNJ’, and changes to P or Nsubstituents are indicated by superscripts before the square brackets (e.g., with PhP and ArNsubstituents, a phenyl-bridged ligand is denoted PhAr[NPN]Li2).6.2.1 Synthesis and characterization of Ph,Mes(2,4,6-Me3CH)(2-BrCNH, 6.1, can be prepared in one pot from 2,4,6-trimethylaniline and 1,2-dibromobenzene, in the presence of 2 mol % (DPPF)PdC12(DPPF= 1,l’-bis(diphenylphosphino)ferrocene), 4 mol % DPPF, and K093u in 1,4-dioxane uponheating at 80 °C for three days (Equation 6.1). It is isolated as a white crystalline solid in fairyield (53%) upon work-up. Thus far, attempts to improve the yield of this reaction byincreasing the amount of catalyst or trimethylaniline, heating the reaction for seven days, or240by using a different catalyst and ligand (Pd2dba)3 and rac-BINAP) have failed.9 Excessdibromobenzene and trimethylaniline can be removed from 6.1 by flash columnchromatography, but filtering the reaction mixture through silica, followed byrecrystallization, is also an effective method of purification. Compound 6.1 has beencharacterized by ‘H and ‘3C {‘H} NMR spectroscopy, GC-MS, and combustion analysis.(DPPF)PdCI2DPPF, KOtBu+ I 1 (6.1)1 ,4-dioxaneiX, 3dPhMes[p‘-2 (b-C4H80)([N-(2,4,6-Me36H2)(2-N(Li)C6H4)]PhP(p-C4H802)),6.2 (pC4H802),can be prepared from 6.1, two equivalents of “BuLi and 0.48 equivalents of PhPC12in Et20by the same method used to prepare 2.7(p-C4H8O)(Equation 6.2). Toluene-soluble6.2.(b-C4H8O)is isolated as a yellow solid in high yield. It has been characterized in C6Dsolution by ‘H, 31P{’H},‘3C{’H}, and7Li{’H} NMR spectroscopy, and in the solid-state bysingle crystal X-ray diffraction.1. 4 BuLi, Et20,-35 °C; rt, 3 h2. PhPCI2,Et20,-35 °C; rt, 24 hS = (CH8O5There is a quartet in the 31P{’H} NMR spectrum of 6.2(p-C4H80)at 6 —35.2 (‘JPLI =41 Hz), and a doublet (6 0.05) and singlet (6 —1.89) appear in the7Li{’H} NMR spectrum. Inthe ‘H NMR spectrum there are three singlets at 6 2.3 assigned to ArCH3 groups. As for1H2JH6.126.1(6.2)6.22412.7(p-C4H8O),the ortho-methyl groups on MesN are inequivalent due to restricted rotationabout N—C0.Resonances attributable to ArH protons in the C symmetric compound andone equivalent of coordinated dioxane are also evident. The peaks in the 13C{1H} NMRspectrum are also consistent with the proposed structure.The solid-state molecular structure of 6.2(p-C4H80)is shown in Figure 6.1. Thecompound forms chains of 6.2 linked by clioxane molecules, and one half of each dioxanecoordinated to 6.2 is shown in Figure 6.1. As with 2.72THF, there are two Li environments.Li2 is coordinated to NI, N2 and P1 of [NPN]’, and 01 of dioxane, whereas Lii iscoordinated to NI and N2, and 02 of another molecule of dioxane. The stereochemistryaround Lii is distorted tetrahedral, and the stereochemistry around Li2 is distorted trigonal.The bond lengths are essentially the same as those in 2.72THF, within error. The P—Uibond length is 2.484(8) A, the Ui—N bond lengths average to about 2.06 A, and the Li2—Nbond lengths average to about 2.02 A. The Lil---Li2 separation is 2.474(12) A. The bondlengths and angles are similar to those of —SiMe2CH bridged CYMeS[PLiçHF)CYPh[PNJLiHF) and PhPh[NPN]LiCIHF)IAIO242Figure 6.1. ORTEP drawing of the solid-state molecular structure of PhMes[NPyLi2.(t)dioxane), 6.2(p-C4H80(effipsoids drawn at the 50% probability level). Half of eachmolecule of dioxane coordinated to 6.2 in the 1-D network is shown. All hydrogen atomshave been omitted for clarity. Selected bond lengths (A) and angles (°): P01—LiOl 2.484(8),NOl—LiOl 2.065(9), N01—Li02 2.014(10), LiOl---Li02 2.474(12), O01—Li02 1.910(9), 02—LiOl 1.892(9), N02—Li02 2.022(9), N02—LiOl 2.056(9), P01—LiOl—Li02 77.4(3), NOl—LiOl—N02 103.7(4), LiOl—N01—Li02 74.7(4), O01—Li02—N01 126.3(5), O01—Li02—N02 122.7(5),002—LiOl—NOl 123.8(5), 002—LiOl—N02 118.8(4).The proligand, [NPNJ’H26.3, can be prepared from 6.2t-C4H8O)and Me3NHC1 inTHF (Equation 6.3), and is isolated as a white solid in quantitative yield. In C6D solution,6.3 is similar to [NPN]*H2(2.8). There is a singlet in the 31P{1H} NMR spectrum at ö —34.3.In the ‘H NMR spectrum, there is a sharp singlet at 2.14, due topara-methyl on MesN, andtwo broad singlets at 2.06 and 1.92, due to two on’ho-methyl groups on MesN. There are243also two broad singlets at ö 6.77 and 6.72 assigned to meta C—H groups. As with 2.8,hindered rotation about N—C50 broadens resonances on MesN. In the 13C{H} NMRspectrum of 6.3, peaks due to ortho-methyl ( 18.2 and 18.0) and meta carbons ( 135.9 and135.8) are also broad. The other resonances observed in the 1H and 13C{H} NMR spectracan all be assigned to groups in the proposed C symmetric diaminophosphine.(6.3)S = dioxaneThe solid-state molecular structure of 6.3 is shown in Figure 6.2. The P—C bondlengths are the same within error, at 1.83 A, and the C—P—C angles are 103°, with C16—P1—C22 slightly shorter at 102.24(10)°, possibly due to crystal packing effects. The bondlengths and angles are similar to those of N(2,6lPrCoH)(2_NC6H4PPh.h There is adistance of 3.66 A between C19 on the (C6H5)P group of 6.3 in the asymmetric unit and C20of the other molecule of 6.3 in the unit cell (Figure 6.3), which is consistent with thepresence of weak intermolecular it-It interactions in the solid state.12THF6.2 6.3244Figure 6.2. ORTEP drawing of the solid-state molecular structure of PhMeS[NPN]H2 6.3(ellipsoids drawn at the 50% probability level). All hydrogen atoms except HIN and H2N(located from the electron density map) have been omitted for clarity. Selected bond lengths(A) and angles (°): NI—Cl 1.436(3), Nl—CI0 1.390(3), Pl—C15 1.835(2), Pl—C16 1.833(2),PI—C22 1.830(2), N2—C27 1.400(3), C15—P—C16 103.11(10), C15—Pl—C22 102.83(9), C16—PI—C22 102.24(10), ClO—NI—CI 121.10(18), Nl—Cl—C2 119.30(19), C27—N2—C28123.99(18).245Figure 6.3. ORTEP representation of crystal packing in 6.3. it-stacking interactions may beresponsible for close contact of (C6H5)P substituents (3.66 A) at the centre of the unit cell.Phenyl-bridged 6.2 and 6.3 are similar to [NPN]*Li2pC4Hsoa) (2.7) and [NPN]*H2(2.8) by all the methods used to characterize the compounds thus far. The electronic andsteric effects of replacing one Me group on the arene backbone with hydrogen are probablyminimal, and the synthesis of group 4 complexes of PhMes[NpN] by a protonolysis route isongoing. Although 6.2 and 2.7 are similar, other modifications to the arene-bridgeddiamidophosphines may have a greater impact on the structure and reactivity of the ligandand its complexes. It is likely that aniidophospbine ligands could be synthesized withdifferent P or N substituents, and the nature of the backbone could also be altered.2466.2.2 Synthesis and characterization of PI1ArLNPN18 (Ar = 4-PrC6H).The synthesis of bromo(diarylamine) ligand precursors from 1,2-dibromobenzene is aconvenient new route to diamidophosphine ligands with different amide substituents. Forexample,(4-1PrC6H)(2-BrCNH, 6.4, can be prepared in moderate yield as a colourlessoil by refluxing 4-1PrC6HNH2,1,2-dibromobenzene, and NaOtBu in the presence ofPd2(dba)3 (1 mol %) and rac-BINAP (2 mol %) in toluene (Equation 6.4). Since 6.4 is a liquidat room temperature, it cannot be purified easily by recrystallization. Instead, 6.4 must beseparated from unreacted 1,2-dibromobenzene by column chromatography. As with 6.1, theoptimization of the synthesis of 6.4 is ongoing.8The compound has been characterized by1H and 13C{H} NMR spectroscopies, EI-MS, and combustion analysis.Pd2(dba)3+rac-BINAP,NaOtBu (6.4)NH26.4Ph.Ar[NPN1Li2.cy,C4H8O)6.5(p-C4H8O2),can be prepared from 6.4, two equivalentsof BuLi, and 0.48 equivalents of PhPC12 in Et20 (Equation 6.5). The product is isolated inhigh yield as a yellow solid that is freely soluble in toluene, and somewhat soluble in hexanes.The major peaks in the 1H NMR spectrum can be assigned to protons in the C symmetriccomplex, and minor peaks are consistent with the presence of about 5% of (4-’PrC6H)(2-LiC6H4)NLi. When 6.5(b-C4H8O2)is recrystallized from hexanes/THF at —35 °C, 6.52THFis obtained. In the 1H NMR spectrum, signals due to coordinated THF appear and there isno peak due to dioxane. In addition, only peaks attributable to the major product arepresent. The isolated yield of 6.5, however, is decreased upon recrystallization. There is a247quartet (‘JPL = 42 Hz) at 6 —34.8 in the 31P{1H} NMR spectrum, and a doublet (8 —0.36) andsinglet (6—1.70) appear in the7Li{1H} NMR spectrum of 6.52THF in C6D (Figure 6.4). Inthe ‘H NMR spectrum, a heptet at 6 2.83 and two doublets at 6 1.26 and 1.25 are assigned toCH(CH3)2and two inequivalent CH(CH3)2groups, respectively. Resonances in the aromaticregion can be assigned to protons in C symmetric 6.5, and there are two resonancesconsistent with the presence of two equivalents of coordinated THF. In the 13C {‘H} NMRspectrum, the expected resonances for ArC, CH(CH3)2CH(CH3)2,and coordinated THFappear. Ongoing efforts to optimi2e this reaction indicate that 6.5(p-C4H8O2)forms inhigher yield and purity by adding exactly 0.50 equivalents of PhPC12 slowly to the Et2Osolution of the proposed intermediate, (4-1PrC6H)(2-LiCN i, slowly warming thereaction mixture to room temperature, and fmally, heating the reaction mixture to refluxovernight.’3-30 -32 -34 -36 -38 6 2 -2 -6 -10(ppm) (ppm)Figure 6.4. 31P{’H} and7Li{1H} NMR spectra of 6.52THF in C6D.2481. 4 BuLI, Et20,I -35°C;rt3hNH2 I2. PhPCI2,Et20,[LJ -35°C;rt,24h6.4S = THF or dioxaneThe ORTEP representation of the solid-state molecular structure of 6.5(p-C4H802)isshown in Figure 6.5. The compound forms a one-dimensional chain of PhAr[p] unitsbridged by 1,4-dioxane. The P1—Li2 bond length is 2.477(7) A. The N—Lu bond lengths aresimilar and average to 1.98 A, and the N—Li2 bond lengths are similar, but average to —2.06A. The 0—Li bond lengths are identical, within error, at about 1.87 A, and the Lil---Li2separation is 2.418(10) A. The bond lengths are very similar to those of 6.2(p-C4H80)andare slightly shorter than thosç of 2.72THF.(6.5)6.5249Figure 6.5. ORTEP drawing of the solid-state molecular structure of PhArNPLi2.Q,C4H802),6.5(p-C4H8O2)(ellipsoids drawn at the 50% probability level). All hydrogen atomsand the carbon atoms of dioxane have been omitted for clarity. Selected bond lengths (A)and angles (°): P1—Li2 2.477(7), Ni—Lu 1.974(9), N1—Li2 2.050(9), N2—Li2 2.079(8), N2—Lii 1.978(9), 01—Lu 1.867(8), 02—Li2 1.868(8), Lil---Li2 2.418(10), P1—Lii—Li2 80.9(3),N1—Li2—N2 102.8(3), Lii—Ni—Li2 73.8(3), Lii—N2—Li2 73.1(3), 01—Lu—Ni 123.4(5), 01—Lii—N2 126.7(5), 02—Li2—N1 131.3(4), 02—Li2—N2 120.0(4).PhAr[NPN1Zr(NMez)26.6, can be prepared in two steps from 6.52THF by the sameroute used to prepare [NPN]*Zr(NMe2(2.9) (Scheme 6.1). First, excess Me3NHCl is addedto a THF solution of the lithiated ligand. The yellow suspension turns white instantly, andPh.Ar[NPN]H2is isolated in quantitative yield as a white translucent residue upon work-up.There is a singlet at 6 —32.4 in the 31P{1H} NMR spectrum of’[NPNj’H2in C6]).The 1HNMR spectrum (Figure 6.6) features a doublet (J = 6 Hz) at 6 6.39 assigned to NH, aheptet at 6 2.66 assigned to CH(CH3)2,and a doublet at 6 1.12 assigned to CH(CH3)2,as well250as the expected aromatic protons. The peaks in the ‘3C{1H} NMR spectrum are alsoconsistent with the proposed structure for the proligand.CH (CH3)2—ArH—(ppm)Figure 6.6. 500 MHz 1H NMR spectrum ofPh4rpN1H2in C6D.In the second step, PhAr[NPNJH2 is mixed with equimolar Zr(NMe2)4in toluene.PhAr[NpN1Zr(NMe2)(6.6) is obtained in high yield as a toluene-soluble yellow powder (seeScheme 6.1). A singlet is observed at 6 —10.0 in the 31P{1H} NMR spectrum of 6.6 in C6D.In the 1H NMR spectrum (Figure 6.7), there are singlets due to two inequivalent N(CH3)2groups at 6 2.84 and 2.51, and a heptet (6 2.76) and doublet (61.19) due to CH(CH3)2andCH(CH3)2groups of the para-isopropyl substituents, as well as the expected ArH peaks forthe C, symmetric complex. Although two doublets are expected for the two inequivalentCH(CH3)2groups (6 1.2), these resonances overlap. Two singlets are observed for theinequivalent CH(CH3)2groups at 6 24.3 and 24.2 in the ‘3C{1H} NMR spectrum. Theexpected CH(CH3)2(6 34.0), N(CH32(6 41.5, and 40.7), and ArC peaks also appear.251Scheme 6.1.6.5S THF, dioxane—ArHxs Me3NHCI Zr(NMe2)4THF tolueneN(CH3)2CH(CH3)25.5 4.5CH(CH3)21J3.5 .5(ppm)Figure 6.7. 500 MHz 1H NMR spectrum of 6.6 in C6D.The ORTEP representation of the solid-state molecular structure of 6.6 is shown inFigure 6.8. Tridentate [NPN]’ coordinates to Zr facially, and the P1—Zn—Ni (72.06(5)°),and P1—Znl—N2 (70.70(5)°) angles are less than 900, as was observed for [NPN]” complexesof Zr and Hf. The geometry at Zr can best be described as intermediate between trigonal6.6252bipyranildal and square pyramidaL14 The bond lengths and angles are as expected: the P1—Zn bond length is 2.7353(6) A. The N—Zr bonds to [NPN]’ are the same within error, atabout 2.16 A. The N3—Zr bond to N(CH3)2approximately trans to P (2.053(2) A) is slightlylonger than the N4—Zr bond (2.0253(19) A). The solid-state molecular structure of complex6.6 can be compared to that of [NPNJ*Hf(NMe)(2.14). The two structures have similarM—P and M—N bond lengths, and these fall within the range of expected values.’5 In 2.14,the P1—Hf—Ni and P1—Hf—N2 angles (72.89(4), and 70.71(4)°) are similar to those in 6.6.The P1—Zr—N3 angle (155.11 (6)°) is slightly mote acute than the P1—Hf—N3 angle(163.60(6)°). The N1—Zr—N2 (125.14(7)°) and N3—Zr—N4 angles (104.44(8)°) are slightlymote obtuse than N1—Hf—N2 (120.91(6)°) and N3—Hf—N4 (100.92(8)°). It will be necessaryto prepare other group 4 [NPN]’ complexes to determine if 6.6 differs from 2.14 because thedianiidophosphine ligand is less bulky, or because of other factors (e.g., identity of the metal,crystal packing).253Figure 6.8. ORTEP drawing of the solid-state molecular structure of PhAr[NPN]Zt(NMC2),6.6 (effipsoids drawn at the 50% probability level). All hydrogen atoms have been omittedfor clarity. Selected bond lengths (A) and angles (°): P1—ZrOl 2.7353(6), N1—ZrOl2.1563(19), N2—ZrOl 2.159(2), N3—ZrOl 2.053(2), N4—ZrOl 2.0253(19), P1—ZrOl—N172.06(5), P1—ZrOl—N2 70.70(5), N3—ZrOl—N4 104.44(8), N1—ZrOl—N2 125.14(7), P1—ZrOl—N3 155.11(6), P1—ZrOl—N4 100.37(6), N1—ZrOl—N4 115.42(8), N2—ZrOl—N398.62(8).The preparation of PhAr{PNlZrC and its application to nitrogen activation areongoing projects in the Fryzuk group. The PhArpJ ligand may support very differentchemistry than [NPN]t.For example, the intramolecular cyclometalation reaction that occursspontaneously for [NPN]*Zr(CH2Ph) and [NPN]*Zr(CH2SiMe3)cannot occur for theproposed complex PhAr[NpZt(CHph) because it lacks on’ho-methyl substituents. If254alkyizirconium complexes of [NPN]’ can be prepared, their reactivity with H2 should beexplored; zirconium hydrides are attractive starting materials for Zr-N2 complexes. Since[NPNJ and [NPN]* ligands support dinuclear side-on Zr-N2 complexes, it is likely that asimilar N2 complex can be prepared with [NPN]’. It will be interesting to determine theeffect the [NPN]’ ligand has on the structure and reactivity of a Zr-N2 complex.PhArpN] is expected to mimic [NPN] more closely than [NPN]* does because bothcontain ArN substituents without bulky ortho- or meta-substituents. [NPN]TaMe, reacts withH2 to yield ([NPN]Ta)2j.i-H)4,which reacts with N2 to give {[NPN]Ta}20.i-H)(ii-ri’:iN2).16 This unusual reaction has proven difficult to replicate when other N substituents on[NPNJ are present. For example, when PhAr[NPN]TaMe3(Ar = 2,6-MeCH3)is stirred underH2, (PhAr[NpN]Ta)OIH)4does not form.’7 Only one other [NPN] ligand, CyPhp]supports a Ta(V) trimethyl complex that yields a Ta(IV) tetrahydride upon reaction withH2.18 The sensitivity of this reaction to the amide substituent of [NPN] is a compeDingreason to prepare a complex such as PhAr[NPN]TaMe, and characterize its reactivity with H2.[NPN]* has bulky MesN substituents compared to PhAr[NpNl. There are, however,other aniide substituents that would provide even greater steric bulk. For example, it may bepossible to synthesize bulky PhArpN]Li2(s) (Ar = 2,6-tPrC6H3S = p-C4H802,THF)(Figure 6.9) by a similar route used to prepare 6.5(p-C4H802) from 2,6-’PrCH3and 1,2-dibromobenzene. If a super-bulky diamidophosphine ligand, such as PhAr[JpN]jj(5) (Ar =3,5-(2,6-1Pr2C6H)(Figure 6.9) can be prepared, it may support new reactivity forcoordinated N2. Extremely bulky triamidoamine ligands were recently used to carry out thefirst catalytic formation of NH3 from N2.’9 A simpler diamidophosphine ligand,Ph1PrpN]U2(5) (Figure 6.9) is less bulky than [NPN]*, but the ailcyl substituents will255increase the basicity of the amides. Thus, the PrN-substituted ligand may not be ideal for thesynthesis of dinitrogen complexes, but the ligand may be suited to other applications.Some other variations of {NPNI’ are illustrated in Figure 6.10. The synthesis of ligandssuch as CYMes[NPN]Li(S) and Me5[NPN]Lj2(S) should be possible if commerciallyavailable CyPC12 and ‘PrPC12 are used instead of PhPC12 in the metathesis reaction with 6.1.The use of substituted anilines should allow the electronic properties of the ligand to betuned. For example, (4-CF3C6H)N donors will make PhAr[NpN]J.i2(S) less basic, whereas(4-MeOC6H)Ndonors will make the amide donor more basic.2°Figure 6.10. Variations on [NPN]’ with GyP, ‘PrP, and (4-CF3C6H)Nsubstituents.Figure 6.9. [NPN]’ ligands with 2,6-1PrC6H3[3,5-(2,6-’Pr2CH)] and ‘Pr substituentson N (S = THF or dioxane).256In addition to varying the N and P substituents of a diamidophosphine ligand, thebackbone itself may be altered. Although the use of Si—N bonds in the backbone should beavoided, other C—N bridged ligands could be explored. A 2,3-substituted naphthalene-linkeddiamidophosphine ligand may be a starting point in the design of hemilabile ligands for latetransition metals with applications to photochemistry (Figure 6.1 1).21 It should be possible totune the ligand electronics by adding electron-donating or -withdrawing groups to the linker.For example, it may be possible to prepare ([N-(MesN)-2-N(Li)-5-CF3CH)2PPh2(S))(Figure 6.11) by the same route used to prepare [NPNj’, from 4-CF3C6HNH2and pMeC6H4B(OH)2.It may be possible to synthesize chiral diamidophosphine ligands with alkyllinkers (Figure 6.11) for applications to chiral synthesis.6.2.3 Other reactions of zirconium dinitrogen complexes.The reactions of H2, PIISiH3, CO. ethylene, 4,4’-dimethylbenzophenone,benzophenone imine, Ph3O, and Me3CC(0)H with Zr-N2 complexes are explored tosome extent in this thesis. The addition of other silanes, ketones, phosphine oxides, andaldehydes to the Zr-N2 complexes may help to shed light on the factors governing thesereactions. In addition, the reactions of 4.4 with H2, 4.1 with 4,4’-dimethylbenzophenone orPh3O, or 4.2 with benzophenone iniine may be good candidates for mechanistic studyFigure 6.11. Diamidophosphine ligands with alternative bridging groups.257because of the time required for the reaction, the colour changes observed, and the potentialto use UV-vis, JR or NMR spectroscopy to follow the formation of products orintermediates. Other reactions that may yield new N-element bonds include the addition ofboranes, alanes, or transition metal hydrides (e.g., Cp2ZrH) to the Zr-N2 complexes. Thereaction of alkynes with Zr-N2 complexes should be attempted because new N—C bondsform from the addition of ArCECH to([P2N]Zr)i-i:-N).The addition of aldehydesor ketones that contain additional functional groups, such as olefins, may yield interestingnew products. For example, the addition of dibenzy]ideneacetone (dba) to 4.1 may generate anew C=N bond, followed by reaction of Zr with an olefm group. There are many potentiallyinteresting reactions between the Zr-N2 complexes described in chapter four and organic orinorganic reagents that have not yet been explored.6.3 Conclusions.In this chapter, an onho-phenylene-bridged diamidophosphine ligand,PhMes[NpN1Li2.(p.C4H8O)is described. The bromodiarylamine precursor to this ligand issynthesized from l,2-dibromobenzene and 2,4,6-Me3C6HNHin one pot by a Pd-catalyzedC—N coupling reaction. By a similar procedure, the bromodiarylamine ligand precursor, (4-1PrC6H4)NH(2-BrC, is prepared in one pot from 4-1PrC6HNH2 and 1,2-dibromobenzene. From this compound, the less bulky diamidophosphine ligand,PhAT[NPNILi.Q,CHO2)(Ar = 4-1PrC6H), is synthesized. A Zr(IV) complex,PhArpN1Zr(NMe.)is prepared from the lithiated ligand by a two-step protonolysis route.The Pd-catalyzed C—N coupling route to bromodiarylamine ligand precursorsdescribed in this chapter allows arene-bridged diamidophosphine ligands with differentsubstituents at N to be prepared. Thus far, this synthetic strategy has provided two ligands:258one with a bulky MesN substituent, and one with a4-1PrC6HNsubstituent. The synthesis ofgroup 4 complexes of these ligands, and the application of these complexes to the activationand functionalization of molecular nitrogen are ongoing projects in the Fryzuk group.6.4 Experimental.6.4.1 General experimental.General experimental conditions are as given in chapter two. GC-MS spectra wererecorded on an Agilent series 6890 GC system with a 5973 Mass selective detector.6.4.2 Starting materials and reagents.Zr(NMe2)4,4Pd2(dba)3,5 DPPF,26 and (DPPF)PdC12,7 were prepared according toliterature methods. Dichlorophenylphosphine, and 2,4,6-trimethylaniline were distilled priorto use. Trimethylamine hydrochloride was suspended in benzene and heated to refluxovernight in a Dean-Stark apparatus to remove water. 1,2-Dibromobenzene was stored overactivated Linde 4 A molecular sieves and sparged with N2 prior to use. BuLi (—l.6 M inhexanes) was titrated against benzoic acid in THF with o-phenanthroline as an indicator. Allother compounds were purchased from commercial suppliers and used as received.(2,4,6-Me3C6H)(2-BrCNH (6.1). (DPPF)PdC12 (0.620 g, 0.848 mmol) and DPPF(0.939 g, 1.69 mmol) were added to 1,4-dioxane (100 mL). To this mixture was addedK093u (6.2 g, 55.4 mmol), 1,2-dibromobenzene (10 g, 42.4 mmol), and 2,4,6-trimethylaniline (7.4 g, 54.8 rnmol). The orange-brown mixture was heated to reflux for 3 d,cooled, and taken to dryness to obtain a brown residue. The residue was suspended inEtOAc (100 mL) and the suspension was filtered through a plug (—5 cm deep) of silica in a259120-mL glass frit. The dark yellow filtrate was taken to dryness to obtain a light brownresidue. The residue was dissolved in petroleum ether (50 mL), and the solution wastransferred by 5-mL aliquots onto a plug (5 cm deep) of silica in a 120-mL glass fit. Thesilica was then rinsed with 5-mL aliquots of petroleum ether until the yellow product waseluted from the silica. A brown by-product remained on the top layer of silica. The ifitratewas taken to dryness to obtain a yellow residue that was dissolved in EtOH. Dilutehydrochloric acid (0.01 M) was added dropwise to the yellow EtOH solution until themixture became cloudy. The mixture was heated until it became clear yellow, and was cooledslowly to obtain white flaky crystals. The crystals were collected on a frit, rinsed withpetroleum ether (2 X 5 mL), and dried (6.5 g, 22.5 mmol, 53%). To ensure that 6.1 was dryand acid-free before use, the white crystals were dissolved in EtO and extracted with asaturated aqueous solution ofK2C03.The organic layer was separated, dried over Na2SO4,ifitered, and taken to dryness to yield white crystals.‘H NMR (CDC13,300 MHz): ö = 7.40 (d, 1H, 8 Hz), 6.79 (t, IH, 8 Hz), 6.77 (s, 2H), 6.37 (t,IH, 8 Hz), and 6.19 (d, 1H, 7 Hz) (ArH), 5.49 (bs, IH, NI-I), 2.15 (s, 3H), and 2.00 (s, 6H)(ArCH3).‘3C{’H} NMR (C6D, 75 MHz): 3 = 143.5, 136.0, 132.2, 129.0, 127.6, 127.4, 127.1, 118.2,112.1, and 109.0 (ArC), 20.4, and 17.4 (ArCH3).GC-MS: 17.6 mm (m/: 291 (100, [M + I-1]).Anal. Calcd. forC,5H6NBr: C, 62.08; H, 5.56; N, 4.83. Found: C, 62.41; H, 5.47; N, 4.72.PhMes[NpN]Lj.(CHO) (6.2(p-C4H8)). To a stirred solution of 6.1 (8.7 g, 30.0mmol) in Et20 (250 mL) at —35 °C was added BuLi (1.6 M, 37.5 mL, 60 mmol) dropwiseover 15 mm. The clear yellow solution was warmed to ft and stirred for 3 h. The solution260was chilled (—.35 °C), and PhPCI2 (2.58 g, 14.4 mmol) in Et20 (20 mL) was added dropwiseover 2 h at this temperature. The reaction mixture turned dark orange throughout theaddition. The orange solution was warmed slowly to rt and stirred for 24 h to obtain anorange-yellow suspension. The suspension was taken to dryness under vacuum to obtain anorange foam. Hexanes (100 mL) was added to the foam to obtain a translucent pale orangesolution. Upon addition of I ,4-dioxane (5 mL) a yellow precipitate formed. The yellowsuspension was frltered through Celite in a fit, and the yellow solids and Celite were rinsedwith hexanes (3 x 10 mL). The yellow solids were then transferred to an Erlenmeyer flaskalong with some of the Celite. The yellow filtrate was allowed to concentrate overnight inthe glovebox atmosphere to obtain small yellow crystals that were collected on a fnt anddried. Meanwhile, the yellow solids mixed with Celite were suspended in toluene (150 mL)with THF added (2 niL), and the suspension was filtered through Celite (—3 cm deep in aglass fit). The yellow filtrate was taken to dryness to obtain a yellow powder. The combinedsolids (6.60 g, 10.5 mmol, 73%) were stored at —35 °C. Single crystals of 6.2p-C4H8O)weregrown by slow evaporation of a concentrated benzene solution of the compound.1H{31P} NMR (C6D,300 MHz): 7.81 (m, 4H), 7.05 - 6.99 (m, 5H), 6.97 (s, 2H), 6.89 (s,2H), 6.60 (d, 2H, 8 Hz), and 6.58 (d, 2H, 8 Hz) (ArH), 3.35 (bs, 4H, dioxane), 2.34 (s, 6H),2.32 (s, 6H), and 2.29 (s, 6H) (ArCH3), 1.25 (bs, 4H, dioxane).31P{1H} (C6D,121 MHz): 6 = —35.2 (q, JPb = 41 Hz).7Li{1H} (156 MHz, C6D): 6 = 0.05 (d, lii, = 41 Hz), —1.89 (s, iLi).Ph,Mes [NPN] ‘H2 (6.3). Trimethylammonium chloride (0.836 g, 8.75 mmol) was added all atonce to a stirred solution of 6.2(p-C4H80)(1.10 g, 1.75 mniol) in THF (15 mL). The yellowsuspension immediately became colourless. After 1 h, the white suspension was taken to261dryness to obtain white solids. The solids were extracted with hot toluene (20 mL, 50 °C)and the extracts were filtered through Celite in a glass frit. The colourless filtrate was takento dryness to obtain a white powder that was collected on a fit, washed with cold pentane (3mL, —35 °C), and dried (0.88 g, 1.7 mmol, 95%). Compound 6.3 is air-stable as a solid forweeks and in solution for days, although in our laboratory it is stored in the glovebox tokeep it water-free. Single crystals of 6.3 suitable for X-ray analysis were grown by slowevaporation of a benzene solution of the compound.1H{31P} NMR (C6D, 300 MHz): 3 = 7.59 (t, 2H, 7 Hz), 7.35 (d, 2H), 7.16-6.98 (m, 5H),6.77 (bs, 2H), 6.72 (bs, 2H), 6.65 (t, 2H, 7 Hz), and 6.37 (d, 2H, 8 Hz) (ArH), 6.11 (s, 2H,NH), 2.14 (s, 6H), 2.06 (bs, 6H), and 1.92 (bs, 6H) (ArCH3).31P{1H} NMR (C6D,121 MHz): 6 = —34.3 (s).‘3C{1H} NMR (C6D, 300 MHz): 6 = 149.9 (d, 18 Hz), 136.0, 135.9 (bs), 135.8 (bs), 135.3,134.9 (4 Hz), 134.6, 134.4, 134.1 (5 Hz), 131.2, 129.6, 129.1, 129.0 (7 Hz), 118.8, 117.8 (d, 6Hz), and 112.3 (ArC), 21.4, 18.2 (bs), and 18.0 (bs) (ArCH3).(4-PrC6H)(2-BrNH (6.4). In an N2 glovebox, rac-BINAP (1.74 g, 2.8 mmol) andPd2(dba)3 (1.28 g, 1.4 mn-iol) were suspended in toluene (200 mL) in a 500-mL Teflon-sealedbomb and stirred for 10 mm. 1,2-Dibromobenzene (35.4 g, 17.9 mL, 0.15 mol) and NaOtBu(20.2 g, 0.21 mol) were added to the solution, and the flask removed to the Schlenk line.Under N2, 4-isopropylaniline (22.4 g, 23.4 mL, 0.17 mol) was added to the reaction. Thepuce suspension was stirred and heated at 80 °C for 5 d under N2. The brown reactionmixture was cooled, and extracted with H20 (3 X 200 mL). The organic phase wasseparated, dried with Na2504, filtered, and concentrated under vacuum to obtain a dark262purple residue. The residue was purified by flash column chromatography on silica gel (petether, Rf = 0.6) to obtain 6.4 as a colourless liquid (27.1 g, 62%).‘H NMR (C6D, 500 MHz): ö = 7.37 (d, 1H, 8 Hz), 7.07 (d, 1H, 8 Hz), 6.97 (d, 2H, 8 Hz),6.85 (d, 2H, 8 Hz), 6.84 (t, 1H, 8 Hz), and 6.43 (t, IH, 8 Hz) (ArH), 5.94 (bs, IH, NH), 2.70(m, IH, 7 Hz, CR), 1.15 (d, 6H, 7 Hz, CH3).13C{’H} NMR (CDC13,75 MHz): ö = 143.7, 142.0, 139.0, 132.8, 128.0, 127.3, 121.1, 120.2,115.1, and 111.5 (ArC), 33.5 (CR), 24.1 (CR3).Anal. Calcd. forC,5H16NBr: C, 62.08; H, 5.56; N, 4.83; Found: C, 62.35; H, 5.66; N, 4.70.El-MS (m/: 289 (40, [Mj4), 274 (100, [M — Me] ‘), 195 (40, [M — (Me + Br)]).Ph.Ar[NpN]Lj.(,,..CHO) (6.5(p-C4H802)(Ar = 4-’PrC6H).To a stirred solution of (4-1PrC6H4)NH(2-BrC (10.4 g, 35.8 mmol) in EtO (300 mL) at —35 °C was added BuLi(1.55 M in hexanes, 46 mL, 71.7 mmol), dropwise over 30 mm. The clear yellow solutionwas warmed to room temperature and stirred for 3 h. The solution was chilled (—35 °C) andPhPC12 (3.20 g, 17.9 mmol) in Et20 (50 mL) was added dropwise over 2 h to obtain anorange suspension. The reaction mixture was warmed slowly to room temperature andstirred for 24 h to obtain a yellow suspension. The reaction mixture was taken to drynessunder vacuum to obtain a pale yellow foam. Hexanes (75 mL) was added to the foam toobtain a translucent yellow solution. Upon addition of 1,4-dioxane (5 mL) a yellowprecipitate formed. The yellow suspension was filtered through Celite (3 cm deep) in aglass frit, and the solids and Celite were washed with hexanes (20 mL). The yellow filtratewas transferred to a second Erlenmeyer flask, and was concentrated and chilled to obtain ayellow crystaffine solid that was collected on a frit. Meanwhile, the yellow solids trapped onCelite in the frit were eluted with toluene (50 mL) into the Erlenmeyer flask. The yellow263toluene filtrate was taken to dryness to obtain a yellow powder. This powder was combinedwith the crystals from the hexanes filtrate and the solids were dried under vacuum (7.4 g,11.8 mmol, 66% yield based on PhPC12). A portion (4 g) of the powder was recrystallizedfrom THF/hexanes at —35 °C (1.50 g, 38 %). Single crystals of 6.5 (p-C4H802)were grownby slow evaporation of a benzene solution of the compound.NMR data for yellow crystals of 6.52THF grown from THF/hexanes:1H NMR (C6D, 500 MHz): 6 = 7.79 (t, 2H, 8 Hz), 7.72 (t, 2H, 7 Hz), 7.65 (t, 2H, 7 Hz),7.41 (d, 4H, 8 Hz), 7.17 (d, 4H, 8 Hz), 7.12 (t, 4H), 7.02 (t, 1H, 7 Hz) and 6.67 (t, 2H, 7 Hz)(ArH), 3.10 (m, 8H, THF), 2.83 (m, 2H, 7 Hz, CR), 1.26 (d, 6H, 7 Hz, CR3), 1.25 (d, 6H, 7Hz, CR3), 1.06 (m, 8H, THF).31P{’H} NMR (C6D,202 MHz): 6 = —34.8 (q, 1JpL = 42 Hz).7Li{’H} NMR (C6D,194 MHz): 6 = —0.36 (d, iLi, ‘J = 42 Hz), —1.70 (s, ILi).13C{H} NMR (C6D, 126 MHz): 6 = 161.6 (d, 28 Hz), 154.7, 138.8, 137.2, 135.4, 132.6 (d,14 Hz), 130.3, 128.2, 127.6, 126.8, 126.0, 120.6, 119.3 (d, 5 Hz), and 117.0 (ArC), 67.9C1’HF), 33.8 (CR), 25.2 (THF), 24.66, and 24.69 (CR3).Ph4f[NPN]Zr(NMe2)(6.6). Trimethylammonium chloride (0.518 g, 5.42 mmol) wasadded all at once to a stirred solution of 6.5p-C4H802(1.06 g, 1.69 mmol) in THF (30 mL).The reaction mixture became an off-white suspension after 15 mm. After 1 h, the reactionmixture was taken to dryness to obtain white solids. The solids were extracted with hottoluene (20 mL, 50 °C), and the extracts were filtered through Celite in a glass frit. Thefiltrate was taken to dryness to obtain a translucent white residue (0.85 g, 1.61 mrnol, 95%).264‘H NMR (C6D,500 MHz): ö = 7.50 (t, 2H, 7 Hz), 7.29 (m, 4H), 7.05 (m, 5H), 6.91 (d, 4H, 7Hz), 6.82 (d, 4H, 7 Hz), and 6.72 (t, 2H, 7 Hz) (ArH), 6.39 (d, 2H,J, = 6 Hz, NH), 2.66 (m,2H, 7 Hz, CH), 1.13 (d, 12H, 7 Hz), and 1.12 (d, 12H, 7 Hz) (CH331P{1H} NMR (C6D,202 MHz): ö = —32.4 (s).‘3c{’H} NMR (C6D, 126 MHz): ö = 160.0, 148.4 (d, 18 Hz), 142.7, 140.8, 135.0, 134.2 (d,19 Hz), 130.7, 129.2, 129.1 (d, 8 Hz), 127.4, 122.5 (d, 6 Hz), 121.2, 120.5, and 116.7 (ArC),33.8 (CH), 24.2 (CH3).Zr(NMe2)4(0.430 g, 1.61 nimol) and PhAr[NpN]H2(0.85 g, 1.61 mmol) were mixedtogether, and toluene (15 mL) was added. The lemon yellow solution was stirred for 2 h, andthe solvent was removed to obtain a yellow residue. The addition of pentane (5 mL) to theresidue provided a clear yellow solution. After about 30 s a light yellow precipitate formedthat was collected on a frit and dried (1.07 g, 1.52 mmol, 94%). Single crystals of 6.6 suitablefor X-ray analysis were grown by slow evaporation of a benzene solution of the compound.‘H NMR (C6D,500 MHz): = 7.48 (t, 2H, 7 Hz), 7.44 (t, 2H, 8 Hz), 7.17 (m, 7H), 7.07 (m,4H), 7.00 (dd, 2H,J11 = 6 Hz, JHH = 8 Hz), 6.75 (dd, 2H, JHH = 8 Hz, JHP = 6 Hz), and 6.65(t, 2H, 7 Hz) (ArH), 2.84 (s, 6H, N(CH3)2,2.76 (m, 2H, 7 Hz, CH), 2.51 (s, 6H, N(CH3),1.19 (d, 12H, 7 Hz, CH3).31P{’H} NMR (C6D,202 MHz): 8 = —10.0 (s).‘3C{1H} NMR (C6D, 126 MHz): 6 = 163.7 (d, 29 Hz), 149.2, 143.2, 134.9, 133.2, 133.0 (d,25 Hz), 132.2 (d, 13 Hz), 129.3, 129.0, 127.6, 126.1, 119.3 (d, 5 Hz), 117.7 (d, 8 Hz), and116.4 (d, 34 Hz) (ArC), 41.5, and 40.7 (N(CH3)2, 34.0 (CH(CH3)2, 24.3, and 24.2(CR((H3)2.2656.5. References.A) Fryzuk, M. D.;Johnson, S. A.; Patrick, B. 0.; Albinati, A.; Mason, S. A.; Koetzle, T. F.J.Am. Chem. Soc. 2001, 123, 3960. B) Shaver, M. P. Small Molecule Activation bj DiamidophosphineComplexes of Vanadium, Niobium, and Tantalum. Ph.D. thesis; University of British Columbia:Vancouver, 2005.2Morello L.; Yu, P.; Carmichael, C. D.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc. 2005,127, 12796.Morello, L. Amidophoiphine Complexes ofZirconium and Titaniumfor Dinitrogen Activation, Ph.D.Thesis; University of British Columbia: Vancouver, 2005.4A) Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J. J. Am. Chem. Soc. 1990, 112, 8185. B) Cohen, J.D.; Fryzuk, M. D.; Loehr, T. M.; Mylvaganam, M.; Rettig, S. J. Ino,g. Chem. 1998, 37, 112.Fryzuk, M. D.; Love,J. B.; Rettig, S. J.; Young, V. G. Science 1997, 275, 1445.6 Pool, J. A.; Lobkovsky, E.; Chink, P. J. Nature 2004, 527. B) Bernskoetter, W. H.;Olmos, A. V.; Lobkovsky, E.; Chink, P. J. Or&anometallics 2006, 125, 1021.Norrild,J. C.; Eggert, H.J. Am. Chem. Soc. 1995, 117, 1479.8 A) Tietze, M.; Iglesias, A.; Mensor, E.; Conrad, J.; Klaiber, I.; Beifuss, U. Og. Lett. 2005, 7,1549. B) Ferreira, I. C. F. R.; Queiroz, M.j. R. P.; Kirsch, G. Tetrahedron 2003, 59, 3737.9Wohlfart, M.; MacLachlan, E. A. unpublished results.10 Shaver, M. P.; Thomson, R. K.; Patrick, B. 0.; Fryzuk, M. D. Can. J. Chem. 2003, 81, 1431.Liang, L.-C.; Huang, M.-H.; Hung, C.-H. Ino,. Chem. 2004, 43, 2166.12 A) Hunter, C. A. Chem. Soc. Rev. 1994, 101. B) Hunter, C. A.; Sanders, J. K. M. J. Am. Chem.Soc. 1990, 112, 5525.13 Fiona Hess, personal communication.26614Addjson A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C. J. Chem. Soc., DaltonTrans. 1984, 1349.Airoldi, C.; Bradley, D. C.; Chudzynska, H.; Hursthouse, M. B.; Malik, K. M. A.;Raithby, P. R. J. Chem. Soc., Dalton Trans. 1980, 2010. B) Schrock, R. R.; Seidel, S. W.; Schrodi,Y.; Davis, W. M. Organometallics 1999, 18, 428.Fryzuk, M. D.;Johnson, S. A.; Rettig, S. J. J. Am. Chem. Soc. 1998, 120,11024.MacKay, B. A.; Munha, R. unpublished work.18 Shaver, M. P.; Fryzuk, M. D. Organometallics 2005, 24, 1419.Yandulov, D.V.; Schrock, R. R. Science 2003, 301, 76.WA) Sykes, A. C.; White, P.; Brookhart, M. Organometallics 2006, 25, 1664. B) Gross, K. C.;Seybold, P. G.; Peralta-Inga, Z.; Murray, J. S.; Politzer, P. J. Org. Chem. 2001, 66, 6919.21 Matkovich, K. M.; Thorne, L. M.; Wolf M. 0.; Pace, T. C. S.; Bohne, C.; Patrick, B. 0.Inorg. Chem. 2006, 45, 4610.22 Ghebreyessus, K.Y.; Gui, N.; Nelson, J. H. Organometallics 2003, 22, 2977.23 Morello, L.; Love, J. B.; Patrick, B. 0.; Fryzuk, M. D. J. Am. Chem. Soc. 2004, 126, 9480.24 Diamond, G. M.; Rodewald, S.;Jordan, R. F. Organometallics 1995, 14, 5.25 Fairlamb, I. J. S.; Kapdi, A. R.; Lee, A. F. Org. Lett. 2004, 6, 4435.26 Bishop, J. J.; Davison, A.; Katcher, M. L.; Lichtenberg, D. W.; Merril, R. E.; Smart, J. C. J.Organomet. Chem. 1971, 27, 241.27 Hayashi, T.; Konishi, M.; Kobori, Y.; Kumada, M.; Higuchi, T.; Hirotsu, K. J. Am. Chem.Soc. 1984, 106, 158.267OneX-ray Ci ystal Structure DataTable A1.1. Crystal Data and Structure Refinement for [NPN]*Li2(THF) (2.72THF),[NPNI*ZrCl2(2.10) and [NPN]*ZrC12( y) (2.13).compound 2.72THF 2.102.5C6H 2.130.33C6Hformula C46H55LiNOP C531NPZr C445H45C12NPZrfw 712.77 911.06 815.43colour, habit colourless, tablet yellow, needle red, tabletcryst size, mm 0.30 X 0.25 X 0.10 0.35 X 0.35 X 0.20 0.25 X 0.12 X 0.08cryst syst monoclinic monoclinic tnchnicspace group P21/n C2/c P-Ia,A 12.0195(11) 44.638(2) 13.0128(3)b, A 24.292(2) 10.8958(5) 18.6267(4)c,A 14.2557(11) 19.4505(9) 19.0488(4)cçdeg 90 90 112.4990(10)1, deg 102.308(4) 94.334(2) 100.0810(10)‘y,deg 90 90 92.1610(10)v,A3 4066.7(6) 9433.0(8) 4171.96(16)Z 4 8 4T,°C 173 173 173p, g/cm3 1.164 1.283 1.298F(000) 1528 3792 1690radiation Mo Mo Mojt, cm’ 0.106 0.417 0.464transmission factors 0.9688 — 0.9894 0.716-0.920 0.8406 — 0.963620m,deg 47.748 55.96 56.34total no. of reflns 54955 95472 119902no. ofuniquerefins 9577 11331 19756Rtnerge 0.049 0.083 0.061no. with I nO(I) 6409 8972 14529no. of parameters 486 541 944R 0.0510 0.0505 0.03580.1411 0.1379 0.1007gof 1.044 1.163 1.106residual dens, e/A3 0.720, -0.472 0.920, -0.661 0.833, -0.456R1 (F2, I>2a(I)) = Fj -I F fl /I F01 ; R (all data) = QDwd F021 _I FI )2/wI F021 2)1/2268Table A1.2. Crystal Data and Structure Refinement for [NPN]*Hf(NMC2)(2.14),[NPNJ*HfC1 (2.15), [NPN]*Hf12(2.17).compound 2.14 2.152.5C6H 2.17 1 .5C6Hformula C42H5NfP C5341NPHf C47H8INPHffw 821.33 999.34 736.09colour, habit pale yellow, needle pale yellow, plate yellow, prismcryst size, mm 0.35 X 0.15 X 0.07 0.30 X 0.13 X 0.07 0.35 X 0.15 X 0.10cryst syst monoclinic monochnic monoclinicspace group P21/c C2/c P21/na,A 11.5176(2) 44.7205(16) 10.5510(6)b,A 19.3137(4) 11.0406(4) 17.2009(9)c,A 17.9531(4) 19.4718(5) 24.6184(13)ct, deg 90 90 903,deg 105.0270(10) 94.1910(10) 95.214(5)y, deg 90 90 90v, A 3857.05(14) 9588.3(5) 4449.4(4)Z 4 8 6T,°C 173 173 173p, g/cm3 1.414 1.385 1.648F(000) 1672 4056 2148radiation Mo Mo Moji, cm 2.78 2.357 3.801Trans. factors 0.5382 — 0.8529 0.4060 — 0.68382Omax, deg 55.416 45.392 54.77total no. of reflns 80641 72405 16781no.ofuniquereflns 9136 10472 9455Rrnerge 0.07 0.103 0.153no. with I > nO(J) 7398 7378 6559no. of parameters 445 541 486R 0.0296 0.0357 0.0367R 0.049 0.0753 0.0774gof 1.059 1.018 0.907residual dens, e/A3 1.172, -0.699 1.110, -1.004 1.685, -2.085R1 (F2 I>2CT(1)) = Fj -I F /I Fj ; R (all data) = (wd F021 _I FI )2/wI F021 2)1/2269Table A1.3. Crystal Data and Structure Refinement for [NPNJ*HfMe2(3.2), [NPNC]*Zr(11CH26H5) (3.4).compound 3.2C6H 3.4formula CH51NHfP C45HN2PZrfw 841.35 736.02colour, habit pale yellow, needle orange, irregularcryst size, mm 0.50 X 0.35 X 0.05 0.25 X 0.15 X 0.10cryst syst trichmc triclinicspace group P-i P-ia,A 11.6308(11) 11.2260(3)b,A 12.7965(10) 15.3120(4)c,A 13.6170(11) 15.5773(4)cL, deg 84.039(7) 64.7420(10)3,deg 80.881(7) 70.8540(10)y, deg 87.582(8) 70.5370(10)v,A3 1989.5(3) 2228.39(10)Z 2 2T,°C 173 173p, g/cm3 1.404 1.097F(000) 856 768radiation Mo Mo2.695 0.311transmission factors 0.3305-0.8739 0.8774-0.969429,deg 54.15 55.64total no. of reflns 12008 46139no. ofuniquereflns 6580 102151merge 0.137 0.058no. withlZnO(I) 5611 7857no. of parameters 461 465R 0.0367 0.03460.0908 0.0892gof 1.014 1.026residual dens, e/A3 1.568, -1.653 0.481, -0.314R1 (F2, I>2a(I)) = Eli Fj -I F /I Fj ; R (all data) = (w(I F021 -I F1 )2/EwI F021 2)1/2Residual electron density consistent with disordered solvent was evident, however, noreasonable model could be established. Instead, the program SQUEEZE was used togenerate a data set that corrects for the scattering contribution from this disordered solvent.270Table A1.4. Crystal Data and Structure Refmement for [NPN]*Hf(r11CH2C6HS) (3.5),[NPNC] Zr(CH2SiMe3)(3.7).compound 3.5C6H 3.7formula C589N2PHf C42H9N2PSiZrfw 993.53 732.11colour, habit pale yellow, chip red, platecryst size, mm 0.35 X 0.12 X 0.05 0.50 X 0.40 X 0.08cryst syst trichnic triclinicspace group P-I P-ia,A 11.268(2) 9.22160(10)b,A 12.550(2) 11.5343(2)c,A 17.847(3) 19.5329(3)x,deg 93.0410(10) 86.9080(10)13,deg 93.5840(10) 78.1770(10)‘,deg 103.1290(10) 76.0500(10)v,A3 2447.1(7) 1973.54(5)Z 2 2T,°C 173 173p, g/cm3 1.348 1.232F(000) 1016 768radiation Mo Moi, cm1 2.203 0.379transmission factors 0.590-0.896 0.8609-0.97012Om,deg 46.75 51.932totalno.ofreflns 87588 43622no. ofuniquereflns 11461 9436Rmetge 0.087 0.06no.withln8(I) 9139 7340no. of parameters 567 434R 0.0284 0.0349R 0.0599 0.0973gof 1.013 1.109residual dens, e/A3 0.985, -0.519 0.495, -0.313R1 (F2, I>2oI)) = II F01 -I F /I Fj ; R (all data) = (Zw(l F021 - F2I )2/wI F021 1,12271Table A1.5. Crystal Data and Structure Refinement for {[NPNj*Zr(rHF)}2(,Iii2:112N)(4.1), { [NPN]tZr(Py)}2(ii-i:-N(4.2), and { [NPN]*Zr(PMePh)} O-ri.riN2){Zr[NPN]*} (44)compound 4.F(Sol) 4.2 4.4formula C98H120N6O3P2Zr C86H8NPZr C84H8N6P3Zr2fw 1674.38 1478 1456.95colour, habit black, prism black, prism black, rectangularcryst size, mm 0.30 X 0.15 X 0.10 0.50 X 0.40 X 0.30 0.30 X 0.10 X 0.10cryst syst trigonal monoclinic monoclinicspace group R-3c P21/n P21/ca,A 27.3381(7) 19.6395(7) 23.7417(8)b, A 27.3381 19.7497(8) 15.2378(5)c,A 59.1867(16) 27.0757(12) 23.7851(8)ct, deg 90.00 90.00 90.003, deg 90.00 91 .7900(1 0) 98.896(2)y, deg 120.00 90.00 90.00v,A3 38308.2(14) 10496.8(7) 8501.3(5)Z 18 6 5T,°C 173 173 173p, g/cm3 1.306 0.935 1.138F(000) 15912 3080 3036radiation Mo Mo Mop., cm1 0.337 0.265 0.344transmission factors 0.839-0.967 0.8580-0.9241 0.812-0.9662Omax, deg 40.48 44.892 53.038totalno.ofreflns 210263 35075 88103no. of unique reflns 7426 13279 20097Rmerge 0.080 0.088 0.063no. with I? nO(I) 5613 9468 14389no. of parameters 467 899 873R 0.0481 0.0561 0.0396R. 0.1429 0.1630 0.1045gof 1.043 1.020 1.017residual dens, e/A3 1.174, -0.522 0.971, -0.548 0.779, -0.282R1 (F2, I>2a(I)) = Fj-I F fl /I F01 ; R.N (all data) = (wd F021 _I F1 )2/EwI F021 2)1/2Sol =(C6H+THF+0.67(C14))See note on Squeeze (fable Al .3)272Table A1.6. Crystal Data and Struture Refinement for {[NPN]*Zr(PMe3)}(JIH)(I.i12:112NNH) {Zr[NPNJ* } (5.1), { [NPN]*Zr(Py) } (jt-H) (ji-NNSiH2Ph){Zr[NPN]* }1 (53)compound 5.1 5.3C6Hformula C79H8N6P3Zr2 C936N7P2SiZrfw 1397.91 1585.32colour, habit yellow, rod red, platecryst size, mm 0.5 X 0.1 X 0.1 0.5 x 0.3 X 0.1cryst syst triclinic triclinicspace group P-I P-ia,A 13.418 12.8123(4)b,A 19.268 13.1606(5)c,A 20.788 25.1766(11)cc deg 67.54 85.4180(10)3, deg 75.49 84.5970(1 0)‘, deg 86.02 74.8280(1 0)v,A3 4806.3 4072.3(3)Z 2 2T,°C 173 173p, g/cm3 0.966 1.292F(000) 1460 1654radiation Mo Moji, cm1 0.302 0.360transmission factors 0.390-0.980 0.773-0.9822O,deg 45.537 44.91total no. of reflns 51485 43112no. of unique reflris 12606 10446Rmerge 0.324 0.065no. with I > nO(1) 7222 7593no. of parameters 811 959R 0.1663 0.0413R 0.4129 0.1020gof 1.633 1.002residual dens, e/A3 6.601, -2.132 0.470, -0.344R1 (F2, I>2a(I)) F01 -I F /I Fj ; R (all data) = (w( F021 F1 )2/wI F021 2)1/2See note on Squeeze (Table Ai.3)Hi (bridging hydride) and HISi, H2Si were located from the electron density map andrefined normally.273Table A1.7. Crystal Data and Structure Refinement forNNC(4MeC6H4)2}t(5.4), { [NPN*Zr(NCPh2)}2Qi-T1:ri-NH)(5.5), and{[NPN]*Zr}(,IO)z (5.6).compound 5.4 5.52C6H 5.6C6Hformula C91H2N6OP2Zr C11413N8PZr 824N4P2ZrOfw 1530.09 1839.48 1401.91colour, habit orange, platelet red, platelet yellow, plateletcryst size, mm 0.3 X 0.1 X 0.1 0.35 x 0.20 x 0.05 0.21 x 0.17 x 0.15cryst syst monoclinic monoclinic monochrucspace group P21 P21 C2/ca, A 13.875(2) 13.3465(3) 22.298(5)b, A 14.394(3) 23.3359(6) 14.064(3)c,A 23.553(4) 16.1975(4) 23.800(5)c, deg 90.00 90.00 90.00f3, deg 104.983(10) 107.4220(10) 93.884(4)‘y, deg 90.00 90.00 90.00v,A3 4544.0(14) 4813.3(2) 7446(3)Z 2 3 4T,°C 173 173 296Pcaic, g/cm3 1.118 1.267 1.250F(000) 1596 1920 2920radiation Mo Mo Moji, cm’ 0.309 0.303 0.371transmission factors 0.793-0.970 0.856-0.985 0.881-0.9452O,deg 46.61 44.632 46.52total no. of reflns 30481 29776 29927no.ofuniquereflns 13553 6478 5350Rmerge 0.107 0.046 0.049no.withlnO(I) 9195 6359 4612no. of parameters 937 1149 415R 0.0712 0.0341 0.03350.1902 0.0762 0.1125gof 1.004 1.035 0.748residual dens, e/A3 0.561, -0.503, 0.477, -0.227, 0.294, -0.227,R1 2 I>2o(I)) = II Fj -I F /I F01 ; R.. (all data) = (w(I F021 Fi )2/wI F021 2)1/2See note on Squeeze (fable Al .3)274Table A1.8. Crystal Data and Structure Refinement for PhMes[NpN1U2çpdioxane) (6.2),PhMes[pJ‘2 (6.3).compound 6.22CH 6.3formula C525LiNOP C36H7N2Pfw 784.83 528.65colour, habit yellow, prism colourless, prismcryst size, mm 0.50 X 0.30 X 0.20 0.50 X 0.30 X 0.20cryst syst monoclinic triclinicspace group P21/c P-ia, A 17.0576(1 3) 7.9830(8)b, A 25.018(2) 13.3300(13)c,A 11.3813(9) 14.4770(14)cc deg 90.00 97.374(5)3,deg 71.743(5) 105.276(5)y, deg 90.00 91.745(5)v,A3 4612.5(6) 1470.5(3)Z 5 2T,°C 173 173p,g/cm3 1.130 1.194F(000) 1672 564radiation Mo Mo0.100 0.121transmission factors 0.837-0.970 0.854-0.9762O,deg 53.12 59.32totalno.ofreflns 10317 11151no. ofuniquereflns 9059 7659Rmetge 0.071 0.060no. with I nO(I) 5871 5370no. of parameters 537 360R 0.0808 0.0541R. 0.2087 0.1607gof 1.098 1.031residual dens, e/A3 0.461, -0.339 0.511, -0.451R1 (F2, I>2a(I)) = Fj -I F /I F01 ; R (all data) = (Ewd F021 F1 )2/EwI F021 2)1/2275Table A1.9. Crystal Data and Structure Refinement forPh4r[NPN]U2(pdjoxane) (Ar = 4-1PrC6H4)(6.5), PhAr[p] Zr(NMe2)(6.6).compound 6.51.5CH 6.6formula C4952Li2NOP CH47NPZrfw 745.78 706.01colour, habit pale, plate yellow, irregularcryst size, mm 0.35 X 0.15 X 0.05 0.50 X 0.20 X 0.15cryst syst tricliruc monoclinicspace group P-I P21/ca,A 11.5372(7) 19.7201(5)b,A 13.4014(8) 11.5343(2)c,A 16.1799(9) 17.3982(5)ct,deg 107.995(2) 90.0013, deg 109.297(2) 66.3300(10)y, deg 97.418(2) 90.00v,A3 2169.8(2) 3687.69(17)Z 2 4T,°C 173 173p,g/cm3 1.141 1.272F(000) 794 1480radiation Mo Mo, cm’ 0.103 0.374transmission factors 0.837-0.995 0.816-0.9452Om,j,deg 43.012 45.752total no. of reflns 17773 60432no. of unique reflns 5573 8808Rmg 0.047 0.072no.withIn9(I) 2965 6212no. of parameters 509 423R 0.0716 0.0392R. 0.1817 0.1260gof 1.036 1.052residual dens, e/A3 0.315, -0.212 1.109, -0.294R1 F2 I>2a(I)) = E Fj -I F ff /,I Fj ; R., (all data) = (w(j F021 FI )2/w F021 2)1/2X-ray Crystal Structure AnalysisSelected crystals were coated in oil, mounted on a glass fiber, and placed under an N2stream. Measurements for compounds were made on a Bruker X8 Apex diffractometer or aRigaku AFC-7 diffractometer, both with graphite-monochromated Mo Kct. radiation (?0.7 1073 A). The data were collected at a temperature of —100 ± I °C. Data were collected276and integrated using the Bruker SAINT software package.1 Data were corrected forabsorption effects using the multiscan technique (SADABS)2 and for Lorentz andpolarization effects. Neutral atom scattering factors were taken from Cromer and Waber.3Anomalous dispersion effects were included in the values for Af” and I\f” were thoseof Creagh and McAuley.5 The values for the mass attenuation coefficients are those ofCreagh and Hubbell.6All refinements were performed using the SHELXTL crystallographicsoftware package of Bruker-AXS. The structure was solved by direct methods. All non-hydrogen atoms were refined anisotropically using SHELXL-97. Except where noted,hydrogen atoms were included in fixed positions. Structures were solved and refined usingthe WinGX software package version 1.64.05.Crystals for structure 5.6 were sent to the University of Windsor. Data collection andrefinement were performed by Greg Welch and Prof. Douglas Stephan in the Department ofChemistry.277Table A1.10. Crystallographic Data Collection and Structure Solution Information.Corn- Code Solvent in Diffrac- Data Structure Specialpound mf# asym. unit tometer Collection solution details2.72THF 592 - BX8 BP BP, EM2.10 590 2.5C6H BX8 BP BP, EM2.13 599 0.5C6H BX8 BP EM2.14 612 - BX8 BP EM2.15 608 2.5C6H BX8 BP EM2.17 648 1.5CH6 RAFC7 HJ EM3.2 649 C6H RAFC7 HJ EM3.4 602 - BX8 BP BP, EM 5, H3.5 607 C6H BX8 BP EM3.7 643 - BX8 BP EM H4.1 636 C6H+THF BX8 BP EM, BP 5, M+0.67(C14)4.2 657 - BX8 HJ EM, BP S4.4 666 - BX8 HJ HJ, EM S5.1 665 - BX8 HJ HJ,EM S,LR5.3 671 C6H BX8 BP EM H, M5.4 652 - RAFC7 HJ EM S5.5 670 2C6H BX8 BP EM5.6 MF3 C6H SSS GW GW, DS6.2 646 2C6H RAFC7 HJ MW, EM6.3 661 - RAFC7 HJ MW, EM H6.5 629 - BX8 BP EM6.6 627 1.5C6H BX8 BP EMBX8 = Bruker Apex X8 Diffractometer, RAFC7 = Rigaku AFC-7 Diffractometer, SSS =Siemens SMART System CCD Diffractometer; BP = Dr. Brian Patrick, HJ = Howard Jong,GW = Greg Welch, DS = Prof. Doug Stephan, MW = Malte Wohlfahrt; S = Squeeze, H =Hydrogen atoms of interest located from electron density and stable to refinement, LR =low resolution structure, M = solvent modeled.‘SAINT. Version 6.02. Bruker AXS Inc., Madison, Wisconsin, USA. (1999).2 SADABS. Bruker Nonius area detector scaling and absorption correction - V2.05, BrukerAXS Inc., Madison, Wisconsin, USA.‘ Cromer, D. T.; Waber, J. T. International Tablesfor X-rqy Cystaiographj, Vol. 1T4 The KynochPress: Birmingham, England, 1974, Table 2.2 A.278Ibers, J. A.; Hamilton, W. C. Acta Cystaiogr., 1964, 17, 781.Creagh, D. C.; McAuley, W.J. International Tablesfor Cystallgraphj, Vol C; Wilson, A. J. C.,ed., Kiuwer Academic Publishers: Boston, 1992, Table 4.2.6.8, pp. 219-222.6 Creagh, D. C.; Hubbell, J.H. International Tablesfor Cystallographji, Vol C; Wilson, A.J.C, ed.,Kiuwer Academic Publishers: Boston, 1992, Table 4.2.4.3, pp. 200-206.279Appendix TwoSpectroscopic Supporting InformationA2.2 Variable-temperature NMR investigation of [NPN]*H2(2.8).A stacked plot of the 1H NMR spectra of 2.8 in toluene-d8at 300 MHz acquired every10K from 300 to 370 K is shown in Figure A2.1. At 300 K, the two ortho-methylresonances on MesN are broad singlets. 1H NMR spectra were acquired at 5 Kincrements between 300 K and 340 K, and at 10 K increments between 240K and 300K, and between 340 K and 370 K. Coalescence is observed at 320 K, and the two orthomethyl resonances are separated by 75 Hz at 273 K. The exchange of the two orthomethyl groups on each MesN substituent of 2.8 due to rotation about the N—C0 isdepicted in Equation A2.1.(A2.1)A2.2):k =—=2.22AvcJ(A2.2)k is the rate constant at the coalescence temperature, T, and iv is the separationbetween the two peaks at a temperature well below the coalescence temperature. In thiscase, zv did not increase below 273 K (spectra acquired to 240 K).1 In this experiment,k = 166.5 ± 2 s_i.Me8The rate constant for the exchange reaction at the coalescence temperature is (Equation280L\G:rot is calculated from the Eyring equation (Equation A2.3):AG = —RT ln(kh / kBTC)(A2.3)R is the gas constant, T is the coalescence temperatuxe, k is the rate constant, h isPlanck’s constant, and kB is the Boltzmann constant.Equation A2.3 can be restated (Equation A2.4):= 4.58T0[10.32 + iog[jJ cal(A2.4)The main sources of error in this experiment are those associated with measuring thecoalescence temperature; this error will be much greater than the error in determiningthe peak separation at low temperature. For T, a value of 320 ± 5 K has been used todetermine In this experiment, AGIO is 15.5 ± 0.3 kcal mo11281Figure A2.1. ‘H NMR spectra of [NPNJ*H2 (2.8) in toluene-d8from 300 K (bottom) to 370K (top) in 10 K increments.A2.2. Kinetics of Decomposition of [NPN]*Zr(CH2Ph)(3.3).At room temperature, the decomposition of [NPNI*Zr(CH2Ph)(3.3) occurs over 2d to yield [NPNC]*Zr(r2CH2Ph) (3.4) as a red-orange complex. The decompositionreaction was followed by ‘H NMR spectroscopy. The decrease in the concentration of 3.3was taken as the integral measured for ZrCH2Ph in 3.3 (6 2.92), divided by the sum of thatintegral plus two times the integral for CHaHbMes in 3.4 (6 2.70), according to EquationA2.5, where int. is the integral value. Thus, the fraction of 3.3 relative to an initial value of1.0 was used, rather than the molar concentration. These resonances were chosen becausethey did not overlap with any other resonances in the spectrum. The values obtained weresimilar to those from other related combinations of integrals taken from other parts of thespectrum, and their values were standardized to a peak of unchanging concentration.370 K360 K350 K340 K330 K320 K310 K7 6 5 4 3 ppm300 K282— d[3.3]_________________________________—kObS[3.]=— kObS[intCH2Ph(3.3)]dt [(mtCH2Ph(3.3))+ 2(int CHaHbMes(3.4))1(A2.5)The thermal decomposition reaction was determined to be first order in 3.3 (spectra notshown) by determining the rate of decomposition for three solutions of differentconcentration at room temperature. The rate constants (kObS) at five different temperatures(298, 328, 338, 348, and 358 K) were then determined from the plots of ln[3.3] vs. time, forwhich a representative plot is shown in Figure A2.2 (338 K).In[3.3] vs. time at 328 K0.0-0.2-0.4-0.6-0.8c, -1.0C-1.2-1.4-1.6-1.8-2.00 200 400 600 800Time (s)1000 1200 1400Figure A2.2. Plot of ln[3.3J vs. tat 338 K. From the slope of the line, k338 = 1.403 X iO ±1.0 x i0 s.283Thus, the values of kOb, at 5 different temperatures were obtained:k298 = 1.80 x I 0 ± 6 X 1 o s1k223 = 4.33 x iO ± 1 x i0 s1k238 = 1.40 x iO ± 1 X iO5 s’k248 = 3.44 x iO ± 2 x iO s1k258 = 7.35 x i03 ± 5 x iO s’The free energy of activation (AG’) is related to the enthalpy of activation (AH) and entropyof activation (AS’) (Equation A2.6).AG = AH - TAS(A2.6)By inserting equation A2.6 into the Eyring equation (A2.3), Equation A2.7 is obtained:(kh AH AStmi ° 1=—kBTc) RT R(A2.7)This expression can be simplified to (Equation A2.8):k ARt ASlog—=1O.32— +T 19.14T 19.14(A2.8)284From the Eyring plot of ln(kOb/I) vs. I /T (Figure 3.7), the enthalpy (AR’) and entropy (AS’)of activation were determined according to Equation A2.8 from the y-intercept and theslope of the line. Thus:AH = 20.8 ± 0.4 kcal mol’, and ASt = —10.3 ± 1.3 cal K’ mol’The two main sources of error in this experiment are due to temperature measurement andintegration of resonances in the ‘H NMR spectrum. The error in temperature is estimated tobe ± 1K, and the error is estimated to be ± 5% for the fractions of 3.3 and 3.4 in solutionbased on integration of the 1H NMR spectrum. The error in kOb was determined statistically.‘Friebolin, H. Basic One-and Two-Dimensional NMR Spectroscopy, 3 ed.; Wiley-VCH: Weinheim,1998, pp. 307-10.285

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0062195/manifest

Comment

Related Items