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Cyclopentadienyldiphosphine complexes of zirconium and hafnium Duval, Paul Bernard 1998

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Cyclopentadienyldiphosphine Complexes Zirconium and Hafnium by Paul Bernard Duval  B.Sc. (Hons.), Dalhousie University, 1993  A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in THE F A C U L T Y OF G R A D U A T E STUDIES (Department of Chemistry)  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH C O L U M B I A August 1998 © Paul Bernard Duval, 1998  In  presenting this  degree at the  thesis in partial  fulfilment  of  the  requirements  for  an advanced  University of British Columbia, I agree that the Library shall make it  freely available for reference and study, i further agree that permission for extensive copying of  this thesis for  department  or  by  his  or  scholarly purposes may be granted by the head of her  representatives.  It  is  understood  that  copying  my or  publication of this thesis for financial gain shall not be allowed without my written permission.  Department of  CjVy^^; ^"^"^  The University of British Columbia Vancouver, Canada Date  DE-6 (2/88)  H  ABSTRACT The  preparation of zirconium and hafnium complexes coordinated by a  cyclopentadienyldiphosphine ligand are reported. Metal chloride complexes [P2Cp]MCl3 (P2Cp =  Ti -C5H3-l,3-(SiMe2CH2PPr 2)2, M = Zr, Hf) are six-coordinate with an apical 5  i  cyclopentadienyl donor tethered by two pendant chelating phosphines. Alkylating reactions give [P2Cp]MCl R . (R = Me, CH Ph, CH CMe3, C H S i M e , x = 0, 2). The monoalkyl derivatives x  3 x  2  2  2  3  exhibit fluxional coordination of the side-arm phosphines, which generates an equilibrium mixture of isomers.  A similar solution behaviour is noted for the trimethyl species  [P2Cp]M(CH3)3. In comparison, in the bulkier trialkyl complexes the side-arms remain dangling with no observation of phosphine coordination. The dialkyl complexes [P2Cp]MClR2 are not isolable, but instead yield a thermally sensitive equilibrium mixture of alkyl complexes, which upon thermolysis generates in high yield the first structurally characterized alkylidene complexes [P2Cp]M=CH(R)Cl (R = CH Ph, CH2CMe3, CH2SiMe ). Kinetic studies indicate a composite 2  3  reaction mechanism of a-abstraction from the dialkyl complex. Reaction of [P Cp]Zr=CH(R)Cl with ethylene yields an ethylene adduct [P2Cp]Zr(r| 2  2  CH2=CH2)C1.  Kinetic studies show this reaction to be first order in both alkylidene and  ethylene. Insertion reactions of alkylidenes with carbon monoxide generates ketene complexes [P2Cp]M(r) -C(0))=CH(R)Cl, while a reaction with tert-butyl isocyanide produces an analogous 2  ketenimine. Reaction of the ketene complexes with ethylene gives metallacyclic complexes resulting from insertion of one ethylene unit. These species in turn react with carbon monoxide to produce acyl-ylide zwitterionic complexes. Methyl substituted  phosphines  give the zirconium chloride  ( M e [ p c ] M C l 3 = r| -C5H3-l,3-(SiMe2CH PMe2)2)5  2  Me  p  [P2Cp]ZrCl(CH2Ph)2-  2  Alkylation  Me  [P2Cp]MCi3  reactions  yield  Thermolysis of this complex produces a toluyne complex  ii  Me  [P2Cp]ZrCl(ri -C6H3Me) instead of the anticipated alkylidene complex. Photolysis of the 2  dibenzyl species generates a metal complex resulting from activation of a benzyl ligand. The ethylene complexes [ri5-C H3-l,3-(SiMe2CH2PR2)2]Zr(r|2-CH2=CH2)Br (R = Me, 5  PrO can be prepared from the reaction of the starting trichloride with two equivalents of EtMgBr. Both of these ethylene derivatives react with carbon monoxide to give carbonyl complexes, and with dihydrogen to produce asymmetric dinuclear hydride complexes. Reaction of ethylene complexes with 1,2-diphenylacetylene eliminates the ethylene ligand to give an alkyne complex. Alkylating reagents permit the formation of the alkyl-ethylene complexes [r) -C5H3-l,35  (SiMe CH PPr )2]Zr(ri2-CH2=CH2)(R) (R = Me, Cp). i  2  2  iii  TABLE OF CONTENTS  ABSTRACT  ii  T A B L E OF CONTENTS  iv  LIST OF FIGURES  x  LIST OF TABLES  xiv  GLOSSARY O F T E R M S  xvii  ACKNOWLEDGMENTS  xxi  Chapter  INTRODUCTION T O CYCLOPENTADIENYL COMPLEXES O F  1:  ZIRCONIUM AND HAFNIUM  1  1.1 Introduction  1  1.2 Cyclopentadienyl Complexes  2  1.3 Group 4 Bent Metallocene Complexes  5  1.4 Mono(cyclopentadienyl) Complexes of Zr and H f  7  1.5 Mono (cyclopentadienyl) Complexes with Pendant Donors  10  1.6 Phosphine Complexes of the Zirconium and Hafnium  12  1.7 Cyclopentadienylphosphine Complexes of Zirconium and Hafnium  14  1.8 Scope of this Thesis  15  1.9 References  17  Chapter  2:  HALIDE AND  ALKYL  COMPLEXES  OF ZIRCONIUM  AND  HAFNIUM STABILIZED B Y T H E ANCnXARY P2Cp LIGAND... 24 2.1 Introduction  24  2.2 Synthesis of [ P C p ] L i (R = Me, Pt*, But) R  2  25  2.3.1  Synthesis and Structure of P r ^ C p l M C l s (M= Zr, Hf)  26  2.3.2  Solution Behaviour of [ P C p ] M C l (M = Zr, Hf)  30  P r  2  3  iv  2.3.3 General Reactivity of [ P C p ] M C l (M = Zr, Hf)  39  P r  2  3  2.4.1 Synthesis of Pr[P Cp]MR ( M = Zr, Hf; R = C H P h , C H C M e , C H S i M e )  .39  2.4.2. Synthesis and Fluxional Behaviour of [P Cp]Zr(CH3)3  42  2.4.3 Reactivity of P ^ C p l M R s  48  2  3  2  2  3  2  Pr  2  2.5.1 Synthesis of P ^ C p ^ r C ^ R (R = C H C M e , C H S i M e , Me, Et, OBu )  .49  2.5.2 Synthesis of [ P C p ] M C l ( C H P h ) (M = Zr, Hf)  51  2.5.3 Reactivity of P q P ^ p J Z r C ^ R  54  1  2  3  2  3  Pr  2  2  2  2.5.4 Synthesis of ^P Cp]ZrCl (r|2-C(0)CH Ph) (12)  54  2.6 Conclusions  61  2.7 Experimental  62  p  2  2  2  2.7.1 General Considerations  62  2.7.2 Materials  63  2.7.3 Synthesis  64  2.7.3.1 Ligand Synthesis  64  2.7.3.2 [ P C p ] H f C l (2)  66  Pr  2  3  2.7.3.3 [ P C p ] Z r ( C H P h ) (3)  67  2.7.3.4 [ P C p ] H f ( C H P h ) (4)  68  2.7.3.5 [ P C p ] Z r ( C H C M e ) (5a)  68  2.7.3.6 [ P C p ] Z r ( C H S i M e ) (5b)  69  2.7.3.7 [ P C p ] Z r ( C H ) (6)  69  Pr  2  2  3  Pr  2  2  3  Pr  2  2  3  3  Pr  2  2  3  3  Pr  2  3  3  2.7.3.8 [ P C p ] Z r C l ( C H C M e ) (7a)  .70  2.7.3.9 [ P C p ] Z r C l ( C H S i M e ) (7b)  70  2.7.3.10 [ P C p ] Z r C l ( C H ) (8)  .71  2.7.3.11 [ P C p ] Z r C l ( C H C H ) (9)  71  2.7.3.12 r[P Cp]ZrCl (OBut) (10)  .72  2.7.3.13 r[P Cp]ZrCl (CH Ph) (11)  73  2.7.3.14 [ P C p ] H f C l ( C H P h ) (12)  73  Pr  2  2  2  3  3  Pr  2  2  2  3  3  Pr  2  2  3  3  Pr  2  2  2  3  p  2  2  p  2  2  2  Pr  2  v  2  2  2.7.3.15 [P Cp]ZrCl (r| -C(0)CH2Ph) (13) Pr  2.8  .74  2  2  2  References  Chapter  75  3: Z I R C O N I U M  AND  HAFNIUM  ALKYLIDENE  COMPLEXES  MECHANISM OF FORMATION AND REACTIVITY  78  3.1 Introduction  78  3.2.1  N M R spectroscopic identification of [P2Cp]ZrCl(CH Ph)  3.2.2  Equilibrium between [ P C p ] Z r C l ( C H P h ) (11),  79  Pr  2  Pr  2  and  frtPlCpJZrtCH^rOs  2  Pr  2  2  [P Cp]ZrCl(CH Ph) 2  2  2  (14),  (3)  83  3.3.1  Synthesis and structure [P Cp]M=CHPh(Cl) ( M = Zr, Hf)  87  3.3.2  Mechanistic studies of the formation of P ^ C p l Z ^ C H P h t C l ) (16)  91  3.3.3  Other alkylidene analogues P r ^ C p F ^ C H E M e ^ C l ) (E = C, Si)  96  3.3.4  Pr  2  Mechanistic studies of the formation of P r i T ^ C p j Z ^ C H E M e ^ C l ) (E = C, Si)  3.3.5 Crossover experiments  103  3.4 Reactivity of [P Cp]Zr=CHR(Cl) (R = Ph, SiMe )  104  Pr  2  3.4.1  3  Reactivity of ^P2Cp]Zr=CHR(Cl) with alkenes (R=Ph, SiMe )  105  Kinetic study into the formation of 20  109  3  3.4.2  99  3.4.3 Reactivity of [P Cp]Zr=CHR(Cl) with larger substrates Pr  2  112  3.4.4 Preparation of ketene and ketenimine complexes Pr  [P Cp]Zr(ri -C(X)=CHR (X = O, NBu ) 2  113  1  2  3.4.5  Insertion reactivity of ketene [P Cp]Zr(ri -C(0)=CHRCl  122  3.4.6  Formation of acyl-ylide complexes  125  Pr  2  2  3.5 Conclusions  127  3.6 Experimental Section  130  3.6.1  Procedures and materials  130  3.6.2  Syntheses  130  vi  3.6.2.1 [P Cp]ZrCl(CH2Ph) (14)  130  3.6.2.2 [P Cp]Hf=CHPh(Cl) (17)  131  3.6.2.3. [P Cp]Zr=CHCMe (Cl) (18a)  132  3.6.2.4 [P Cp]Zr=CHSiMe (Cl) (18b)  132  3.6.2.5 [ P C p ] Z r C l ( C H C M e ) (19a)  133  3.6.2.6 [ P C p ] Z r C l ( C H S i M e ) (19b)  134  3.6.2.7 r[P Cp]Zr(r)2-CH =CH )C1(20)  134  3.6.2.8 [P Cp]ZrC(0)=CHPh(Cl)  135  Pr  2  Pr  2  Pr  2  3  Pr  2  3  Pr  2  2  3  2  Pr  2  2  3  2  p  2  2  2  Pr  2  (21a)  3.6.2.9 [P Cp]ZrC(0)=CHSiMe (Cl) (21b)  136  3.6.2.10 [P Cp]Zi€(N Bu)=CHPh(Cl) (22)  136  3.6.2.11 [P Cp]ZrCH CH C(0)=CHPh(Cl) (23a)  137  3.6.2.12 [ P C p ] Z r C H C H C ( 0 ) = C H S i M e ( C l ) (23b)  137  3.6.2.13 [P Cp]ZrC(0)CH CH C(0)=CHPh(Cl) (24a)  138  Pr  2  3  Pr  t  2  Pr  2  2  2  Pr  2  2  2  3  Pf  2  2  2  3.6.2.14 [ P C p ] Z i C ( 0 ) C H C H C ( 0 ) = C H S i M e ( C l ) Pr  2  2  2  3  (24b)  138  3.6.3 N M R study of the equilibrium between 3,12, and 14  139  3.6.4 Kinetic studies of the formation of alkylidene 16 and 18b  139  3.7 References  Chapter 4:  141  E F F E C T S O F LIGAND MODIFICATION O N S T R U C T U R E AND REACTIVITY  145  4.1 Introduction  145  4.2. Preparation of [ P C p ] Z r C l  146  M e  2  3  4.3.1 Preparation of [ P C p ] Z r C l ( C H P h )  147  4.3.2 Isolation of [ P C p ] Z r C l ( C H P h )  147  Me  2  2  2  Me  2  2  2  4.3.3 Formation of toluyne [P Cp]Zr(r) -C6H Me)Cl from thermolysis of Me  2  2  Me  [P Cp]ZiCl(CH Ph) 2  2  3  150  2  vii  4.3.4 Photolysis of [P2Cp]ZrCl(CH Ph)  156  Me  2  4.3.5 Preparation of [ P C p ] Z r ( C H P h )  2  159  Me  2  2  3  4.4 Synthesis and reactivity of the ethylene complexes [ P C p ] Z r ( r | - C H = C H ) B r R  2  2  2  2  (R=Me,Pr )  163  i  4.4.1 Preparation of [P Cp]Zr(n2-CH =CFf )Br ( R = Me, Pr )  163  4.4.2 Reaction of R[P Cp]Zr(n2-CH =CH )Br (R = Me, Pr>)  167  4.4.3 Preparation of [P Cp]Zr(ri2-PhCCPh)Br  171  R  1  2  2  2  2  2  2  Pr  2  4.4.4 Preparation of asymmetric dinuclear hydrides { [ P C p ] Z r B r H } (R = Me, Pr ) R  175  1  2  2  2  4.4.5 Preparation of Pr[P Cp]Zr(n2-CH =CH )R' (R' = Me, C5H5) 2  2  182  2  4.4.5 Reactivity of [P Cp]Zr(n2-CH2=CH )(ri2-C5H5) with C O , H ...183 Pr  2  2  2  4.5 Future Work  186 4.5.1 Modification to a [P Cp'] ligand set  187  4.5.2 P C p complexes of Th(IV)  192  2  2  4.6 Concluding remarks  193  4.7. Experimental Section  194  4.7.1 Procedures and Materials  194  4.7.2 Synthesis  194  4.7.2.1 e [ P C p ] Z r C l (23)  194  M  2  3  4.7.2.2 M e [ p c ] Z r C l ( C H P h ) (26)  194  4.7.2.3 M p c ] Z i € l ( C H P h ) (27)  195  4.7.2.4 Me[p c ]Zr(n2-C H Me)Cl (28)  196  4.7.2.5 Me[p c ]Zr(n2-C H =CH )Cl (29)  196  4.7.2.6 e[P Cp]Zr(CH Ph) (30)  197  4.7.2.7 Pr[P Cp]Zr(r|2-CH =CH )Br (31)  197  4.7.2.8 e[P Cp]Zr(r]2-CH =CH )Br (32)  198  4.7.2.9 Pr[P Cp]Zr(CO) Br (33)  198  2  2  e [  p  2  p  2  2  2  2  p  2  6  p  3  6  4  2  M  2  2  3  2  2  2  M  2  2  2  viii  2  2  4.7.2.10 Me[p c ]Zr(CO)2Br (34)  199  4.7.2.11 Pr[P Cp]Zr(T| -PhCCPh)Br (35)  199  2  p  2  2  4.7.2.12 {Pr[P Cp]ZrBrH}(n-H)3{BrZr[P Cp]} ( 36)  200  4.7.2.13 {Me[p c ]ZrBr} (u-H) (37)  201  4.7.2.14 Pr[P Cp]Zr(ri2-CH =CH )Me (38)  201  2  2  2  p  2  4  2  2  2  4.7.2.15 Pr[P Cp]Zr(ri2-CH2=CH ) (TI5-C H ) (39)  202  4.7.2.16 Pr[P Cp]Zr(r|5-C5H5) (CO) (40)  203  4.7.2.17 Pr[P Cp]Zr(ri5-C H ) H (41)  203  4.7.2.18 Ligand synthesis: P ^ C p ' l L i  204  4.7.2.19 Isolation of P r ^ C p l Z r C h (42)  206  2  2  5  5  2  2  5  5  2  4.7.2.20 Stepwise reduction to [ P C p ] Z r C l (43) and Pr  2  2  {Pr[P Cp]ZrCl} (u-N ) (44)  207  4.7.2.21 {Me[p c ]ZrCl} (p:-Cl) (45)  207  4.7.2.22 Pr^CpJThBrs (46)  208  2  2  2  p  2  2  2  4.8 References  208  APPENDIX 1: X-ray Crystal Structure Data  212  ix  List of Figures  Figure  Caption  Page  Figure 1.1  Schematic diagram of the bonding of ethylene to a transition  2  metal. Figure 1.2  The molecular orbital scheme for the cyclopentadienyl anion.  3  Figure 2.1  Molecular structure of Pr[P Cp]HfCl3 (2); 33% probability 2  29  thermal ellipsoids are shown. Hydrogen atoms and dissorder not shown for clarity. Figure 2.2  Ambient termperature *H NMR spectrum of [P2Cp]ZrCl3 (1).  Figure 2.3  Variable Temperature 31p{ lH} NMR spectra of [P Cp]HfCl  31  Pr  Pr  2  3  33  (2) Figure2.4  A van't Hoff plot of the P{ H} NMR spectral data for the 31  1  36  equilibrium shown in equation 2.2. Figure 2.5  Variable Temperature P{  NMR spectra of the two species  31  in solution for  Pr  [P2Cp]Zr(CH3)3  44  (6) . A minor impurity is  shown with an asterisk. Figure 2.6  A van't Hoff plot of the P{ H} NMR spectral data for the 31  1  47  equilibrium shown in equation 2.10. Figure 2.7  Eyring Pr  plot of ln(k/T) versus  1/T for the complex  53  [P2Cp]ZrCl2(CH Ph) (11) using the equation k = (k T/h)exp(2  B  AG*/RT) = (k T/h)exp((TAS*-AH*)/RT); the rate constants and B  termperatures are taken directly from Table 2.6. Figure 2.8  Proposed transition state for the intercoversion of the phosphine site in fr[P Cp]ZrCl2(CH Ph) (11). 2  2  x  53  Figure 2.9  Molecular structure of [P Cp]ZrCl2(ri -C(0)CH2Ph) (13); 33% Pr  2  2  57  probability thermal ellipsoids are shown. Hydrogen atoms not shown for clarity. Figure 2.10  Region in H N M R spectrum of [P Cp]ZrCl2(Tl -C(0)CH2Ph) l  Pr  2  2  59  (13) showing one of the diastereotopic protons (two isomers present). Figure 3.1  31p{ lH} N M R spectrum of the reaction mixture from equation  81  3.1 in C D at 30 °C. 7  Figure 3.2  8  Variable Pr  Temperature  NMR  spectrum  for  82  33%  89  [ P C p ] Z r C l ( C H P h ) (14) from 2-3 ppm in C D . 2  Figure 3.3  H  l  2  2  7  Molecular structure of  Pr  8  [ P C p ] H f = C H P h ( C l ) (17); 2  probability thermal ellipsoids are shown. A l l hydrogen atoms other than the a-agostic hydrogen atom are omitted for clarity. Figure 3.4  Non-linear  of  94  Eyering lot of the first-order portion of the decomposition of  95  p  p  the  first-order  decomposition  2  r[P Cp]ZrCl(CH Ph)2 (14). 2  Figure 3.6  to  r[P Cp]ZrCl(CH Ph)2 (14). 2  Figure 3.5  fit  2  A Chem 3D® view of the molecular structure of 18b.  All  98  hydrogen atoms other than the a-agostic hydrogen atom are omitted for clarity. Figure 3.7  Eyering plot of the first-order decomposition of 19b.  Figure 3.8  A Chem 3D® view of the molecular structure of [P2Cp]Zr(ri Pr  101 2  108  CH2=CH2)C1 (20). Hydrogen atoms are omitted for clarity. Figure 3.9  Pseudo first-order kinetics in the reaction 16 with ethylene to give 20.  xi  110  Figure 3.10  Molecular structure of [P Cp]Zr(ri -C(0)=CHPh)(Cl) (21a); Pr  2  2  117  33% probability thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity. Figure 3.11  Molecular structure of [P Cp]Zr(ri2-CH2CH2C(0)=CHR)(Cl) Pr  2  123  (23b); 33% probability thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity. Figure 4.1  Molecular structure of  Me  [ P C p ] Z r C l ( C H P h ) 2 (27); 33% 2  2  148  probability thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity. Figure 4.2  Molecular structure of [P2Cp]Zr(ri2-C H Me)Cl (28); 33% Me  6  3  152  probability thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity. Figure 4.3  Molecular structure of  M e  [P Cp]Zr(CH Ph) 2  2  3  (30); 33%  160  probability thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity. Figure 4.4  Molecular structure of e[p Cp]Zr(r|2-CH2=CH2)Br (32); 33% M  2  165  probability thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity. Figure 4.5  Variable  temperature  of  169  in  170  Molecular structure of [P Cp]Zr(ri2-PhCCPh)Br (35); 33%  173  1 3  C{ H} A  N M R spectra  Pr[P Cp]Zr(CO) Br (33). 2  Figure 4.6  Eyring plot  2  for the C O lignd exchange  process  Pr[P Cp]Zr(CO) Br (33). 2  Figure 4.7  2  Pr  2  probability thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity.  xii  Figure 4.8  Molecular structure of { [P2Cp]ZrBrh(H-H)4-(37); Me  33%  177  probability thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity. Figure 4.9  Hydride  region  of  the  {Merp c ]ZrBr}2(fi-H)4.(37). 2  p  *H  NMR  spectrum  for  179  The bottom trace shows the  corresponding i H j ? } N M R spectrum. 3 1  Figure 4.10  Molecular structure of [P Cp']ZrCl2 (42); 33% probability Pr  2  189  thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity. Figure 4.11  Molecular structure of { [P2Cp]ZrCl}2(^-Cl)2 (37); Me  33%  probability thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity.  xiii  191  List of Tables  Table Table 2.1  Title  Page  Selected Bond Lengths (A) and Bond Angles (deg) for [P Cp]UC\3  (1: M = Z r , 2: M = Hf). The numbering scheme  Pr  2  29  2  l  is identical for each. Table 2.2  Equilibrium constant (K) as a function of termperature fo the  35  two H f trichloride species in equation 2.2 obtained from the 31  Table 2.3  P { H} N M R spectra shown in Figure 2.6. A  Equilibrium data for the two trimethyl complexes. The data were  46  taken from the P { H } N M R spectra shown in Figure 2.9. 3 1  Table 2.4  1  Rate constants of phosphine exchange for [P2Cp]ZrCl2(CH2Ph) Pr  52  (11) as obtained from line shape analysis using D N M R - 5 . Table 2.5  Selected Bond Lengths (A) and Bond Angles (deg)  for  56  Pr[P Cp]ZrCl (Tl2-C(0)CH2Ph) (13). 2  2  Table 2.6  Coupling constants (Hz) for the benzylic(CZ/2Ph) protons in 13.  59  Table 3.1  Equilibrium concentrations of  84  Pr  [P2Cp]ZrCl(CH Ph)2(14) and 2  Pr  [P Cp]ZrCl2(CH Ph) (11), 2  Pr  2  [P2Cp]Zr(CH Ph) 2  3  (3)  from  mixed solutions at 295 K , and the equilibrium constant (K) calculated according to equation 3.3. Table 3.2  Lengths (A) and  Selected Bond Pr  Bond  Angles  (°) for  89  [P Cp]M=CHPh(Cl) (16: M = Zr, 17: M = Hf). The numbering 2  scheme is identical for each. Table 3.3  Estimated rate constants for the first-order a-abstraction of  95  Pr[P Cp]ZrCl(CH Ph)2 (14). 2  Table 3.4  Selected Bond Pr  2  Lengths (A) and  [P Cp]Zr=CHSiMe (Cl) (18b). 2  3  xiv  Bond  Angles  (°) for  98  Table 3.5  Rate constants for the first-order portion of the decomposition of Pr  [P2Cp]ZrCl(CH SiMe )2 (19b). 2  Table 3.6  101  3  Selected Bond Lengths ( A ) and Bond Angles  (°) for  109  (°) for  118  (") for  124  (°) for  149  Selected Bond Lengths and Bond Angles (°) for [P Cp]Zr(r)2-  153  Pr[P Cp]Zr(n2_CH =CH )Cl (20). 2  Table 3.7  2  2  Selected Bond Lengths (A) and Bond Angles Me  [P Cp]Zr(n2-C(0)=CHPh)Cl (21a). 2  Table 3.8  Selected Bond Lengths Pr  [P Cp]Zr(ri2_CH CH C(0)=CHR)Cl (23b). 2  Table 4.1  (A) and Bond Angles  2  2  Selected Bond Lengths  ( A ) and Bond Angles  Me[P Cp]ZrCl(CH Ph) (27). 2  Table 4.2  2  2  Me  2  C H M e ) C l (28). 6  Table 4.3  3  Assignments for the H N M R spectrum of 29 between 2.8 and 1  157  6.0 ppm. . Table 4.4  Selected Bond Lengths ( A ) and Bond Angles  (°) for  161  (°) for  166  (°) for  174  ( A ) and Bond Angles  (°) for  178  Selected Bond Lengths ( A ) and Bond Angles  (°) for  190  (") for  192  Me[p Cp]ZrCl(CH Ph) (30). 2  Table 4.5  2  Selected Bond Lengths M  2  2  Selected Bond Lengths Pr  ( A ) and Bond Angles  e[P Cp]Zr(n2-CH =CH )Br (32) 2  Table 4.6  3  ( A ) and Bond Angles  [P Cp]Zr(n2-PhCCPh)Br (35). 2  Table 4.7  Selected Bond Lengths {Me[p Cp]ZrBr} (Ll-H)4.(37). 2  Table 4.8  2  Me[P Cp']ZrCl (42) 2  Table 4.9  2  Selected Bond Lengths ( A ) and Bond Angles {Me c ]ZrCl(p:-Cl)} .(45). [P2  p  2  xv  Table A l . l Crystallographic Data, Fractional Atomic Coordinates and B to A1.16  ( A ) for reported crystal structures (fifteen sets) 2  xvi  e q  212 to 242  GLOSSARY OF TERMS The following abbreviations, most of which are commonly found in the literature, used in this thesis.  A  angstrom (10" m)  Anal.  analysis  atm  atmosphere  Bq  equivalent isotropic thermal parameter  br  broad  10  e  Bu  tertiary butyl group, -C(CFf3)3  l  Bz 13  benzyl group, -CH^Ph  C{ U) l  observe carbon-13 while decoupling proton  °C  degrees Celcius  cal  calories  calc  calculated  Chem 3D  molecular modelling program for the Macintosh computer  cm  wave number  -1  COSY  Correlated SpectroscopY  Cp  cyclopentadienyl group, {C5H5}-  Cp*  pentamethylcyclopentadienyl group, {CsCCH^}"  d  doublet  D  deuterium  dd  doublet of doublets  d  n deuterated  n  d of sept  doublet of septets  deg  degrees  DME  1,2-dimethoxyethane  xvii  E  a  activation energy  equiv  equivalent(s)  ESR  Electron Spin Resonance  Et  ethyl group, -CH2CH3  g  gram  AG"  Gibb's standard free energy of reaction  AG*  Gibb's energy of activation  GC-MS  Gas Chromatography/Mass Spectrometry  h  hour  *H  proton  APT  enthalpy of reaction  AH*  enthalpy of activation  HOMO  Highest Occupied Molecular Orbital  Hz  Hertz, second"  I  spin  IR  infrared  /A-B  n-bond scalar coupling constant between nuclei A and B  K  degrees Kelvin, or equilibrium constant  lq  forward rate constant  k_i  reverse rate constant  k  observed rate constant  n  orjs  1  kcal  kilocalories  kHz  kiloHertz  6  Li{ ! H }  observe lithium-6 while decoupling proton  7  L i { lH}  observe lithium-7 while decoupling proton  In  natural log  Ln  n number of ligands  xviii  LUMO  Lowest Unoccupied Molecular Orbital  m  multiplet, or medium for infrared data  m  meta  M  molar, or central metal atom  Me  methyl group, -CH3  mg  milligram  MHz  megaHertz  mL  millilitre  mmol  millimole  MO  Molecular Orbital  mol  ^  mole  ms  millisecond  MS  Mass Spectrometry  NOESY  Nuclear Overhauser Enhancement SpectroscopY  NMR  Nuclear Magnetic Resonance  o  ortho  3 1  P{ H} 1  observe phosphorus-31 while decoupling proton  p  para  Ph  phenyl group, -C6H5  ppm  parts per million  n-Pr  propyl group, - C H 2 C H 2 C H 3  Pr*  isopropyl group,  q  quartet  R  hydrocarbyl substituent  r  correlation  s  singlet, or seconds, or strong for infrared data  AS"  entropy of reaction  xix  -CH(CH3)2  AS*  entropy of activation  sext  sextet  SN2  substitution, nucleophilic, 2nd order  t  triplet  T  temperature  THF  tetrahydrofuran  THT  tetrahydrothiophene  VT  Variable Temperature  X  chloride or alkyl group  CL  on a carbon that is directly bonded to a metal  P  on a carbon that is two bonds away from a metal  8  chemical shift  A  heat  A1/2  peak width at half height  T|  n-hapto  (l-X  X-bridging ligand  V -x  vibrational band for bond x-x  n  x  xx  ACKNOWLEDGEMENTS  I would like to express my thanks to Mike Fryzuk for his expert supervision, patience and good humour throughout the course of my studies. I would also like to thank all the past and present members of the fryzuk group, for providing a stimulating environment in which to work and play. I am indebted to the top-notch crystallographers for solving the crystal structures presented in this thesis.  Steve rettig (UBC), Mike Zaworotko (St. Mary's), Glenn Yap  (University of Windsor), and Victor Young (University of Minnesota) all contributed to illuminate much of this chemistry. I am most appreciative of the advice and assistance received from the N M R staff, especially Nick Burlinson, Liane Darge, Marietta Austria, and Orson Chan, who were most helpful with suggestions regarding my N M R experiments. I would also like to mention the expert microanalyses work performed here at U B C by M r . Peter Borda. Special mention must also be made of Elizabeth Varty for all her help with many of the illustrations in this thesis.  xxi  To Vasiliky who made this all possible  xxii  Chapter 1  Introduction to Cyclopentadienyl Complexes of Zirconium and Hafnium  1.1  Introduction The chemistry of transition metal organometallic complexes is a field of study that has  grown immensely in recent years, and currently is a focal point for both industrial applications and fundamental research.  1  The versatility of this chemistry originates from the degree of  covalency in the metal-carbon bond that typically defines an organometallic complex. This feature is generally lacking in classical Werner complexes, which have significant ionic character in the bonding owing to the coordination of metal ions by either hard anionic ligands (i.e. Cl", NO3", OH"), or by neutral donors (i.e. H2O, NH3) in dative interactions. The covalent nature of the bonding in organometallic complexes is demonstrated by the pronounced stability of derivatives that obey the "18-electron rule", an accounting system of electrons for transition metal organometallic species that is an expanded version of the octet rule for covalent compounds of the p-block elements. The bridge between inorganic and organic chemistry is also exemplified by the coordination of organic molecules such as ethylene to a transition metal. The donation of electrons from the ligand to the metal in the formation of a CT-bond is often complemented by jr-backbonding from the metal (Figure 1.1).  This synergistic bonding  potentially modifies the reactivity of both the metal centre and the bound ligand, a synthetically useful feature that is generally absent in classical inorganic coordination compounds. Thus,  1  references begin on page 17  Chapter 1: Introduction to Cyclopentadienyl Complexes...  much of the rich chemistry available to transition metal organometallic complexes can be traced to these two main facets: 1) the reactivity of the polar M - C bond, and 2) the synergistic bonding between the metal and organic fragment. Indeed, the combination of both of these properties adds a new dimension that has been extended to a number of catalytic organic transformations that are mediated at the coordination sphere of a metal centre.  H Figure 1.1  1.2  Schematic diagram of the bonding of ethylene to a transition metal  Cyclopentadienyl Complexes The explosive growth in the field of organometallic chemistry since the early 1950's is  largely rooted in the discovery of ferrocene, Fe(C5H5)2, in 1951.  2,3  The elucidation of the  structure and bonding of this sandwich complex introduced inorganic chemists to the potential 4  of the ancillary cyclopentadienyl (Cp) ligand, which has since spawned a wealth of  2  references begin on page 17  Chapter 1: Introduction to Cyclopentadienyl Complexes...  organometallic compounds.  An examination of the molecular orbital scheme for the  cyclopentadienyl anion illustrates how this planar aromatic five-membered ring coordinates to a metal as a ligand. The diagram is shown below in Figure 1.2; each ring carbon contributes a p 5  orbital to give five molecular orbitals.  Figure 1.2  The molecular orbital scheme for the cyclopentadienyl anion.  3  references begin on page 17  Chapter 1: Introduction to Cyclopentadienyl Complexes..,  These are built up in increasing energy, beginning with the low energy symmetric ai orbital, followed by two sets of doubly degenerate orbitals, with one (ei) and two (e2) nodal planes, respectively.  These molecular orbitals may then interact with metal valence orbitals of  appropriate symmetry; the filled symmetric ai orbital overlaps with a metal s orbital to form a abond, while the occupied ei orbitals act as rc-donors into the metal d interaction of one of the degenerate ei orbitals with the metal d  y z  x z  and d  y z  orbitals. The  orbital is illustrated as an  example in Figure 1.2. The empty e orbitals are of appropriate symmetry to interact with a 2  filled metal d y orbital, but the 8-oveiiap is negligible for bonding. X  Based on the molecular orbital depiction shown above, the cyclopentadienyl anion can be characterized as a good a - and Tt-donor and a poor rc-acceptor, a combination that stabilizes a metal by increasing its electron density, that is especially useful for early metals in high oxidation states. Coordination simultaneously confers resistance to the Cp ligand with respect to both electrophilic and nucleophilic attack. These combined qualities are ideal for a spectator or ancillary ligand, which is specified to moderate the chemistry elsewhere in the coordination sphere of the metal while not participating directly in any of the reactions. A n added benefit is the steric and electronic saturation provided by the r| -hapticity of the planar ring, thereby 5  offering stereochemical control to the reactivity at the metal centre.  Perhaps the most  advantageous feature of this ligand is that these steric and electronic factors can be modified by introducing alkyl substituents to the ring. A simple example is the permethylated analogue CsMes (Cp*), which is bulkier, more electron releasing as a donor, and forms complexes that are generally more soluble in organic solvents and more crystalline than the analogous Cp derivatives. Such ligand "tuning" is a fundamental aspect of Cp-ligated complexes, some of which will be encountered in the next section.  4  references begin on page 17  Chapter 1: Introduction to Cyclopentadienyl Complexes...  1.3  Group 4 Bent Metallocene Complexes A limiting factor to the use of the cyclopentadienyl unit as an ancillary ligand is its high  electron count. A formally six-electron donor as an anion, it is well suited to stabilize electron deficient early metals, but less compatible with electron-rich late members of the series. For example ferrocene is an electronically saturated 18-electron complex, which explains its remarkable stability but also restricts potential reactivity at the metal centre. To accommodate reactive ligands into a Cp2M framework one must move to the left of the transition metal series. As shown below for Nb, the addition of ligands breaks the D5h symmetry of the sandwich geometry observed in ferrocene (A), inducing a distortion to a bent metallocene configuration (B) with up to three additional ligands occupying the equatorial wedge between the two Cp rings.  6  A  B  The bent metallocenes constitute a dominant fraction of the research conducted on Cpligated systems.  7  Foremost among these are the Group 4 derivatives CP2MCI2 ( M = T i , Zr, Hf),  which exhibit a rich metathesis chemistry to generate a multitude of Cp2MR(X) (R = H , alkyl; X = halide, alkoxide, etc.) and CP2MR2 complexes.  8  The use of Cp* and other substituted Cp  ligands has provided for additional bent metallocene derivatives.  1  The stability of these  complexes in comparison to homoleptic Group 4 alkyl species (MR4) is testimony to the ancillary ligand set, and control of the stereochemistry to the equatorial wedge permits well-  5  references begin on page 17  Chapter I: Introduction to Cyclopentadienyl Complexes..  defined reactivity.  Examples include the synthetically useful hydrozirconation reagent  Cp2Zr(H)Cl for alkene and alkyne insertion products,  9  ring-opening olefin metathesis  polymerization (ROMP) mediated by T i alkylidene intermediates, '  10 11  cycloaddition reactions at  a Zr phosphinidene Cp Zr(=PR) complex, and a variety of C - C coupling reactions which are 12  2  either mediated by Cp Zr(benzyne) complexes, 2  13  or conducted on the intermediate "Cp2Zr"  synthon obtained from the Negishi reagent ( C p Z r C l / 2 B u L i ) . n  2  1 4  2  Since the early 1980's the focus in Group 4 metallocene chemistry has centered on cationic alkyl species [Cp ZrR] , which have proven to be very active homogeneous catalysts for +  2  the Ziegler-Natta polymerization of alkenes.  15,16  Substantial efforts into the steric and electronic  modification of Cp-based metallocene ligands have coincided with these developments. The impetus started with the discovery by Kaminsky in 1980 that C p Z r C l polymerizes propylene 17  2  2  in the presence of excess methylalumoxane ((MeA10) ) to generate high molecular weight n  polypropylene. These results prompted an interest to develop chiral metallocene catalysts to induce stereoregularity into the polymers obtained from prochiral a-olefins such as propylene. This was soon accomplished with the C -symmetric ansa-metallocenes (C), in which the indenyl 2  rings are linked by an interannular bridge to give a rigid chiral structure.  C  D  6  references begin on page 17  Chapter 1: Introduction to Cyclopentadienyl Complexes..  These catalysts were found to be effective in producing isotactic polypropylene, ' and neutral 18 19  complexes employing this ligand set have been utilized in a number of other asymmetric transformations as well. For example, Buchwald has used T i derivatives for the hydrogenation of highly substituted alkenes,  20  and in the Pauson-Khand cyclization reaction involving the 21  intramolecular coupling of an alkene, an alkyne and C O .  2 2  Further modification of the  metallocene ligand to a fluorenyl-Cp linkage to give a polymerization catalyst with C symmetry s  (D) has permitted the formation of mainly syndiotactic propylene.  23  Such ligand tuning for  stereospecific cx-olefin polymerization has continued steadily with the synthetic preparation of a variety of elegant ligand architectures. " 24  1.4  27  Mono(cyclopentadienyl) Complexes of Z r and H f In comparison to the exhaustive reports on the chemistry of the Group 4 metallocenes,  there has been considerably less study into the mono(cyclopentadienyl) analogues (e.g., CpMCl3). Some of this disparity stems from the synthetic difficulties encountered in accessing the latter derivatives, although adducts (i.e., CpMCl3(DME)) can be readily prepared. There 28  29  are significant differences in reactivity and structure between bis(cyclopentadienyl) Group 4 complexes and their mono(cyclopentadienyl) analogues. In comparison to the bent metallocene structure of monomeric Cp2ZrCl2, CpZrCl3 exists as an insoluble polymer that resembles the structure of Z1CI4. ZrCL} is a one-dimensional polymeric network with zigzag chains of edgeshared, chloride-bridged Z1CI6 octahedra ( E ) dimensional polymer (F),  31  3 0  CpZrCl3 is similarly a chloride-bridged one-  but the octahedral geometry at the Zr centre is distorted by the  presence of the bulky cyclopentadienyl group, such that all equatorial Z r - C l bonds are bent away from the Cp ring. The Cp ring also induces bond lengthening in both the terminal and bridging Zr-Cl bonds in comparison to Z r C U , presumably due to both steric and electronic factors. 7  references begin on page 17  C h a p t e r I: I n t r o d u c t i o n to C y c l o p e n t a d i e n y l C o m p l e x e s . . .  Increasing the steric bulk of the Cp unit can break up the polymeric network. For example, the structure of Cp*ZrCl3 is that of a chloride-bridged dimer, in which the Z r - C l bonds are again 32  bent away from the ring to give a four-legged piano-stool structure.  With even bulkier  substituents the isolation of monomeric Cp'ZrCl3 derivatives that exhibit a three-legged pianostool geometry has been achieved.  33  8  r e f e r e n c e s b e g i n o n p a g e 17  C h a p t e r 1: I n t r o d u c t i o n to C y c l o p e n t a d i e n y l C o m p l e x e s . . .  Compared to 16-electron Cp2ZrCl2 metallocenes, the CpZrCi3 unit is formally a 12-electron species that can accommodate up to two additional two-electron donors upon break up of the polymer structure. However, the hard Lewis acidity of CpZrCl3 is demonstrated by the inability to form adducts with phosphines, as opposed to harder donors such as ethers and amines. The addition of a single neutral donor gives a chloride-bridged dimer [CpZrCl3(L)]2 (i.e., L = butanone, tethered ether donor ), while the addition of two molecules generates monomeric 34  35  bis(adduct) complexes of the general formula CpZrCi3(L)2 (i.e., L = T H F , Hf derivatives have also been isolated.  29  3 6  H2O ). Analogous 37  A l l of the structurally characterized examples share the  same distorted quasi-octahedral geometry (G), with the cyclopentadienyl donor represented as occupying a single coordination site. The distortion is evident in the equatorial bond angles, which are directed away from the Cp unit as noted above for (CpZrCl3) and (Cp*ZrCl3)2- The n  arrangement of ligands is also consistent for each example; one neutral donor occupies an equatorial site cis to the Cp ring, while the axial site trans to the Cp group is coordinated either by the bridging chloride of the dimer, or by the second neutral donor. This axial ligand is typically labile, as evidenced by reversible dissociation of either the bridging ligand or the 43  terminal donor.  36  G Cp'ZrCl3 complexes are strong Lewis acids that have been used as catalysts for the epoxidation of alkenes, in Diels-Alder reactions, and in asymmetric aldol reactions using 38  chiral catalysts  4 0  The bulky Cp*  36  39  group has enabled the tri-alkyl complexes Cp*ZrR3 (R = Me,  9  r e f e r e n c e s b e g i n o n p a g e 17  C h a p t e r 1: I n t r o d u c t i o n to C y c l o p e n t a d i e n y l C o m p l e x e s . .  CH2Ph, Ph, C H 2 C M e 3 )  41,42  to be isolated. These species show thermal stabilities intermediate  between those of the analogous metallocenes and the homoleptic M R 4 alkyls mono(cyclopentadienyl) derivatives [Cp'MR^]" " of T i , " 1  4 4  4 6  4 3  Cationic  and to a lesser extent Z r ,  have  4 4  shown some capacity as polymerization catalysts, albeit with substantially lower activities in comparison to their metallocene counterparts.  The cationic [Cp*ZrR2] species are highly +  electrophilic and decompose readily in either CH2CI2 or T H F .  4 7  The electronic and coordinative  unsaturation of the [Cp*MR2] moiety is further illustrated by the ability to coordinate toluene as +  found in [Cp*H17vIe2(r| -PhMe)][BMe(C6F5)3], a rare example of an r|6-arene complex of a d° 6  48  metal.  1.5  Mono(cyclopentadienyl) Complexes with Pendant Donors Appending an anionic amide donor on a silyl link to a Cp ligand has yielded "constrained  geometry" complexes (H)  49  polymerization of a-olefins.  that compare favourably with ansa-metailocene catalysts for the One of the Cp donors of the metallocene ligand set has been  replaced by a smaller amide, which combined with the short silyl bridge gives less steric and electronic saturation at the metal centre. The enhanced Lewis acidity of these amido-linked systems is indicated by their being highly active in the catalytic copolymerization of a-olefins (including styrene) with ethylene. ' 50  51  As with the metallocenes, the success of this system has  encouraged ligand modifications. Chiral examples have been made by incorporating a chiral substituent on the amido group, ring.  53  52  or by introducing planar chirality to the cyclopentadienyl  Other modifications of this system have included the use of a linked fluorenyl-amido  ligand, and a few examples have been noted where the side-arm is extended further (I) to allow 54  coordination of an additional neutral donor L , which may be either an amine or an ether. 55  56  The  latter example has been used to stabilize rare Zr complexes that possess two higher alkyl ligands that are resistant to P-hydrogen elimination. There is also a similar analogue of I in which the equatorial donor is a neutral ether instead of an amide, with an amine as the basal donor. 10  references  b e g i n o n p a g e 17  57  As a  C h a p t e r 1: I n t r o d u c t i o n to C y c l o p e n t a d i e n y l C o m p l e x e s . .  mono-anionic ancillary ligand this is coordinated to a ZrCl3 fragment to give an octahedral complex similar to that depicted in G . A different strategy for adding another donor is the use of a second side-arm from the Cp ring (J), for which a Sc derivative has been reported.  58  A related class of pendant donor cyclopentadienyl ligands with a less constrained twocarbon backbone (K) has been extensively used for a variety of metals.  59  There are also a few  examples in which the chelating donors are separated by a three-carbon backbone.  Group 4  60  derivatives that incorporate pendant side-arms have included donors such as amides, amines, ' ' 59  62  63  pyridines, phosphines, 64  alkenes,  65  66  phenolates,  67  and ethers.  35,68  61  Chiral  complexes have been prepared in which the chirality is applied either within the bridge or as a 61  substituent on the pendant donor atom.  68  Some metallocene species have been designed  whereby two appended-donor Cp ligands are bound to the same metal, with intramolecular coordination of both side-arms to give a complex with helical chirality. ' 69  11  references  70  b e g i n o n p a g e 17  C h a p t e r 1: I n t r o d u c t i o n to C y c l o p e n t a d i e n y l C o m p l e x e s . .  Complexes with cyclopentadienyl ligands having appended side-arms can be compared to the constrained geometry polymerization catalysts. The strategy with a weak neutral side-arm donor is to enable reversible coordination, whereby a reactive cationic intermediate can be stabilized by intramolecular chelation, yet be sufficiently labile to provide an open site for reactivity. ' 54  73  Intramolecularly stabilized cations have been isolated that are similar to  analogous cationic metallocene alkyl species that have been trapped by the formation of an adduct, as in [Cp2ZrR(L)] (L = T H F , +  71  PMe3  7 2 , 7 3  ) . However, with one exception there have 74  not been any reports on catalytic activity, which is not surprising in view of the dampening effect the presence of donor molecules (especially phosphines) have on the catalytic activity of cationic metallocene systems.  1.6  Phosphine Complexes of Zirconium and Hafnium Phosphine ligands (PR3) comprise one of the most important classes of ligands in  inorganic chemistry and are utilized in numerous catalytic cycles.  75  The diversity of phosphine  derivatives is impressive, including a variety of chelating multidentate ligands and chiral examples for asymmetric synthesis.  76  However, in contrast to the later metals of the transition metal series, for which phosphine complexes are common, there are correspondingly fewer examples for the early metals.  77  This is  primarily due to the mismatch between metal and donor; phosphines are generally soft polarizable ligands, whereas early metals are typically in a high oxidation state and therefore favour hard N - and O-atom donors. A useful example was alluded to earlier in which C p * Z r C l  3  forms stable adducts with ethers and amines but not with phosphines. For early metals in lower oxidation states (i.e., Zr(II)) the occurrence of phosphine ligands becomes more prevalent, especially with bidentate chelating or macrocyclic phosphines. " 78  80  The presence of Cp ligands  can assist in stabilizing these low-valent species, as electron density provided by rc-donation from  12  r e f e r e n c e s b e g i n o n p a g e 17  C h a p t e r 1: I n t r o d u c t i o n to C y c l o p e n t a d i e n y l C o m p l e x e s . . .  the Cp ligand can be transferred to ^-acceptor ligands that are usually present in these complexes.  81  Despite the relative scarcity of phosphine coordination to high-valent early metals, representative examples illustrate the importance of this group of complexes. One of the major roles of phosphines in the chemistry of the early metals is to trap a reactive intermediate as an isolable species. Examples of this have been seen above with the isolation of cationic alkyl derivatives. ' '  72 73 82  Other examples include the addition of phosphines to trap Zr benzyne and 13  Ti alkylidene complexes. The general strategy is to supply steric and electronic saturation to 83  the metal to stabilize a highly reactive species, potentially capturing a snapshot of an otherwise undetected intermediate. A particularly useful aspect of phosphine ligands in organometallic complexes is the application of P NMR 3 1  spectroscopy. The phosphorus-31 nucleus (I = 1/2) is 100% abundant  and possesses reasonable sensitivity (6.6% that of H ) for spectroscopic study. 1  84  Chemical shift  values span a wide range (> 1200 ppm) and thus provide general information regarding the coordination of a phosphine to a metal centre.  Spin-coupling to other nuclei can be very  sensitive to the stereochemistry of a complex and may supply a more detailed analysis of the coordination sphere. One  feature that makes phosphine ligands extremely versatile is that they comprise a  select group of ligands in which the steric and electronic properties can be modified by varying the substituents. Electron-releasing substituents such as alkyl groups increase the donor ability of the phosphine, while the steric bulk of a phosphine can be measured by the Tolman cone angle.  85  This combination of electronic and steric modification is the basis for "fine-tuning" a  ligand to moderate the reactivity at the metal centre, which has been encountered previously with the Cp group. Therefore, combining a phosphine donor with a Cp unit in the same ligand set offers a wealth of flexibility to experiment with the chemistry of a particular system.  13  r e f e r e n c e s b e g i n o n p a g e 17  C h a p t e r 1: I n t r o d u c t i o n to C y c l o p e n t a d i e n y l  1.7  Complexes...  Cyclopentadienylphosphine Complexes of Zirconium and Hafnium In spite of the potential mentioned above for the combination of a Cp donor with a  phosphine, cyclopentadienyl ligands with pendant phosphine donors have received less attention in comparison to other members of this series. Complexes of these ligand with late metals and 86  main group elements have shown intramolecular coordination of the side-arm donor. There are 87  also examples of dinuclear structures where the side-arm phosphine bridges across to coordinate to another metal.  88  A notable utilization of this bridging feature is the incorporation of pendant  phosphines on the Cp rings of ferrocene, which generates a new chelating ligand for coordination to a second metal centre.  Chiral derivatives of this ligand have been successfully used in  asymmetric synthesis,  and one strategy has taken advantage of the redox behaviour of  89  ferrocene to give a redox-switchable hemilabile ligand for Rh complexes.  90  Complexes of cyclopentadienylphosphine ligands with Group 4 metals are relatively few. Except for a T i example in which the ligand coordinates the phosphine in a chelating fashion, and a zirconocene cation with chelating donors appended from the Cp rings,  70  65  the side-arm  generally remains dangling and in some instances, as noted above, this free donor can bridge to a later metal (i.e., Fe(CO)4) to give a heterobimetallic complex.  91  However, these examples are  all metallocene derivatives that are electronically and coordinatively unsaturated. To allow the phosphine to bind it is preferable that only one Cp ligand be present within the coordination sphere.  1.8 The Scope of this Thesis  14  r e f e r e n c e s b e g i n o n p a g e 17  C h a p t e r 1: I n t r o d u c t i o n to C y c l o p e n t a d i e n y l C o m p l e x e s . .  Previous work in the Fryzuk laboratory has focused on the tridentate chelating amidodiphosphine ligand, N(SiMe2CH2PR2)2 [ P N P ] .  92  The strategy of combining the hard  amide donor with two soft donor phosphines within the same ligand framework was designed to effect new reactivity patterns with potential application for a variety of metals. For Zr and H f the amide anchors the ancillary ligand to the metal while phosphine coordination is enhanced by chelation.  93  Fluxional coordination of the side-arm donors allows open sites to be temporarily  available for controlled reactivity.  R [P2Cp]  [PNP]  In view of the interest in cyclopentadienyl complexes of the Group 4 metals, and the scarcity of complexes with pendant phosphine donors, it was a logical extension to substitute the amide donor in [PNP] with a Cp group to give the analogous hybrid-donor ligand I3-C5H3(SiMe2CH2PR2)2 [P2Cp]. This is a rare example of a Cp ligand with two pendant phosphine donors,  94,95  which resembles the dianionic ligand depicted in J. Employing this ancillary ligand  with Zr and H f allows comparisons with other Cp complexes, in addition to a parallel comparison with results obtained with the [PNP] ligand set.  One of the main differences  between the two ligands arises from the steric bulk of the substituted Cp ring in [P2Cp] compared to the amide in [PNP], which extends the side-arms and introduces a different distortion in the metal-phosphine bond angles. Additionally, the steric hulk and higher electron count of the Cp donor increases saturation at the metal centre. Substituting the Cp group for the more basic  15  r e f e r e n c e s b e g i n o n p a g e 17  C h a p t e r 1: I n t r o d u c t i o n to C y c l o p e n t a d i e n y l C o m p l e x e s . . .  amide and removing the reactive silyl-amide linkage also adds greater hydrolytic stability to the ancillary ligand, while a further advantage is the option to modify the Cp group in addition to the phosphine substituents to change the ligand environment. Early work with the P2Cp ligand has enabled the isolation of the first structurally characterized zirconium alkylidene complex.  96  However, the mechanism of this reaction was not  determined. A n investigation into these mechanistic details may furnish insight into the role of the ancillary ligand in the formation and stabilization of this alkylidene species, in view of the relative scarcity of Group 4 alkylidenes derivatives in comparison to the number of examples from Group 5. Information obtained from this study can be applied towards the chemistry of other complexes coordinated by the P C p ancillary ligand. This thesis is therefore organized into 2  three experimental chapters, with the mechanism of formation and reactivity of the alkylidene complex serving as a central theme. Chapter 2 introduces zirconium(IV) and hafnium(IV) halide and alkyl complexes stabilized by the isopropyl-substituted phosphine version of the ancillary ligand. Surprising differences between the Zr and H f chloride complexes are examined. The structure of the alkyl complexes are discussed, with an emphasis on the effects of the size and number of the alkyl ligands on the fluxional coordination of the side-arm phosphines. Conspicuously absent in the discussion of alkyl complexes in Chapter 2 are the dialkyl derivatives. In Chapter 3 it is shown that attempts to synthesize these complexes leads to an equilibrium with the mono- and tri-substituted species. Kinetic details of the subsequent thermal reaction of this mixture to give Zr and H f alkylidene complexes are investigated. Sequential insertion reactions starting from these alkylidene species are described, along with a discussion concerning the influence of the ancillary ligand in the observed reactivity. In view of the important role of the bulky isopropyl phosphines in the solution behaviour and reactivity of the complexes described in the preceding chapters, Chapter 4 examines the  16  references  b e g i n on p a g e 17  C h a p t e r 1: I n t r o d u c t i o n to C y c l o p e n t a d i e n y l C o m p l e x e s . . .  effect of steric modification with considerably smaller methyl groups. Changes in structure, solution dynamics and reactivity are observed for the alkyl complexes with these less bulky derivatives. The reactivity of a series of Zr(II) ethylene complexes is also studied as a contrast to the insertion reactions observed in Chapter 3. Concluding remarks will summarize the results of this thesis and delineate extensions for future work to other metals and alternate strategies for ligand modification.  1.9  References  (1)  Comprehensive Organometallic Chemistry II; Wilkinson, G.; Stone, F. G . A.; Abel, E.  W., Ed.; Pergamon Press: Oxford, 1995. (2)  Kealy, T. J.; Pauson, P. L . Nature 1951,168, 1039.  (3)  Miller, S. A.; Tebboth, J. A.; Tremaine, J. F. J. Chem. Soc. 1952, 632.  (4)  Wilkinson, G.; Rosenblum, M . ; Whiting, M . C ; Woodward, R. B . J. Am. Chem. Soc.  1952, (5)  74, 2125. Greenwood, N . N.; Earnshaw, A . Chemistry of the Elements; Pergamon Press: Oxford,  England, 1993. (6)  Lauher, J. W.; Hoffman, R. J. Am. Chem, Soc. 1976, 98, 1729.  (7)  Comprehensive Organometallic Chemistry; Wilkinson, G.; Stone, F. G . A.; Abel, E. W.,  Ed.; Pergamon Press: Oxford, 1982. (8)  Cardin, D. J.; Lappert, M . F.; Raston, C . L . 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J.; Maitra, K.; Nelson, J. H . OrganometalUcs 1996,15,  3924. (96)  Fryzuk, M . D.; Mao, S. S. H.; Zaworotko, M . J.; MacGillivray, L . R. J. Am. Chem. Soc  1993,115, 5336.  23  references  b e g i n o n p a g e 17  Chapter 2  Halide and Alkyl Complexes of Zirconium and Hafnium Stabilized by the Ancillary P2Cp Ligand  2.1  Introduction In this chapter the preparation of a new type of ancillary ligand is presented, and the  coordination chemistry of the isopropyl variant of this ligand is examined with zirconium (TV) and hafnium (IV), to form a series of halide and alkyl complexes. The stability conferred by the ancillary ligand to these species, and in particular the role of the side-arm phosphines, will be investigated. The sensitivity of the coordination of these pendant donors to the number and size of the alkyl substituents on the metal centre will be evaluated, and the reactivity of these complexes will also be briefly discussed. The dialkyl complexes [P2Cp]MClR2 are omitted in Pr  the discussion of alkyl complexes in this chapter. The inability to isolate these species is the initial focus for Chapter 3, as these complexes disproportionate to give an equilibrium mixture of alkyl-substituted derivatives [P2Cp]MCl R3- (x = 0-2), which undergoes a thermal reaction to x  x  yield an alkylidene complex in a composite mechanism.  24  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  2.2  Synthesis of [ P C p ] L i (R = Me, Pr , Bu*) R  j  2  Shown below in Scheme 2.1 is the sequence of reactions in the synthesis of the ancillary ligand P C p to be employed in the course of this study. 2  CISiMe CH CI 2  2  NaCp  SiMe CH CI  NaCI  2  2  1) Na[N(SiMe ) ] 3  NaCI  2  2) C I S i M e C H C I 2  2  SiMe CH CI 2  2  ,SiMe CH CI 2  2  SiMe CH CI 2  2  SiMe CH CI 2  2 LiCI HPR  3 LiPR  2  2  2  R = Me, Pr', B u  1  <[P Cp]Li 2  Scheme 2.1  The  Reaction scheme for the synthesis of the ancillary ligand [ P C p ] L i . R  2  preparation of this ligand involves the stepwise attachment of the two side-arms to a  cyclopentadienyl anion. Each of these steps begins with deprotonation of an acidic ring proton, followed by attack of the Cp anion at the more electrophilic sibyl-chloride bond. A silatropic 25  references  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  shift gives rise to isomeric forms as shown above, but in the last step only the 1,3-disubstituted isomer possesses an acidic proton, which yields directly to a high yield of the desired lithium salt of the ancillary ligand. The steric bulk of the ligand can be adjusted by the choice of phosphide utilized in this last synthetic step. The advantage of the silatropic shift is evident in comparison to synthetic difficulties encountered with the analogous bis(side-arm) ligand system J illustrated in Chapter l .  Attachment of the two-carbon backbone in this latter system generates a mixture  1  of 1,2- and 1,3-isomers in the final product, which both lowers the yield and introduces the synthetic complication of separating products. The  Pr and B u ligand salts are both obtained as white solids while the Me derivative is 1  l  isolated as a viscous reddish oil. supplied by the P { H } NMR 3 1  l/up  1  Evidence for the coordination of both pendant donors to L i is spectrum, which shows a distinct 1:1:1:1 quartet (for example,  = 48Hz for the B u complex) for equivalent phosphines coupled to a L i centre (I = 3/2). l  7  Additional coupling to L i (I = 1, 7.4 % natural abundance) is also observed in the same 6  spectrum (^LiP  2.3.1  = 48Hz).  Synthesis and Structure of [ P C p ] M C I ( M = Z r , Hf) P r  2  3  A stoichoimetric reaction of MCl4(THT)2 (M = Zr, Hf; THT  = tetrahydrothiophene) with  the ligand [P2Cp]Li in toluene produces the complex [P2Cp]MCl3 (1: M = Z r , 2: M = Hf) in Pr  Pr  2  high yield as pale yellow (1) or white (2), air- and moisture-sensitive crystals (equation 2.1). The comparative inertness of Hf relative to Zr is apparent in the conditions used in these reactions. The  formation of 1 is complete within 12 h under ambient conditions, while the H f derivative 2  requires 24 h at 65 "C.  26  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  MCI (THT) + [ P C p ] L i rr  4  2  2  LiCI 2THT  (2.1)  M = Zr M = Hf  A non-coordinating solvent such as toluene is utilized in the preparation of 1, since the same reaction conducted in THF gives an oily mixture consisting of 1, unreacted [P2Cp]Li, and an additional species characterized as the bis(ligand) complex [P2Cp]2ZrCl2. The formation Pr  2  of [P Cp]2ZrCl2 is obtained from the reaction of 1 with another equivalent of ^ ^ C p J L i in Pr  2  THF.  This new species, a side-aim substituted analogue of zirconocene dichloride, is tentatively  identified by assigned resonances for the ancillary ligand in the *H NMR, and a singlet in the 3 1  P { H } NMR spectrum for equivalent dangling phosphines. The formation of this species 1  involves initial metathesis of the chloride in ZrCl4(THT)2 by [P2Cp]Li to give Pr  Pr  [P2Cp]ZrCl3(THT)2 having both phosphine arms dangling. In toluene, the THT ligands of this  intermediate are replaced by the intramolecular phosphine donors to generate 1 before a further reaction can occur with [P2Cp]Li. In THF, rapid ligand exchange with the solvent yields the Pr  solvated species [P2Cp]ZiCl3(THF)2, which preventis the phosphines from coordinating. As Pr  this species is more soluble than MCl4(THT) it can effectively compete for a second equivalent 2  of [P2Cp]Li to generate the bis(ligand) complex [P2Cp]2ZrCl2. This synthetic complication of Pr  forming an intermediate in a coordinating solvent that is more soluble and kinetically prone to 27  references  b e g i n on p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s  of...  further reactivity, before the reaction of the starting material ZrCl4(THF)2 can proceed to completion, has been noted in other instances." The  trichloride derivatives 1 and 2 are isostructural, as determined by X-ray  crystallography.  This is not surprising, given the close similarity in size and electronic  configuration between the two congeners Zr and Hf. The Hf derivative 2 is depicted in Figure 4  2.1,  and selected bond length and bond angles are presented for both 1 and 2 in Table 2.1 for  comparison. Note that corresponding metal-ligand bond distances are slightly shorter for 2, a feature that reflects a general trend in Hf complexes versus Zr analogues. 5 The overall geometry of 2 can be described as a quasi-octahedral structure of C symmetry, with the cyclopentadienyl s  ring of the ancillary ligand occupying an apical coordination site and the two pendant phosphine donors in mutually trans equatorial positions. A pair of trans chloro ligands are located in the same equatorial plane as the two phosphines, with a third chloride trans to the cyclopentadienyl ring. This monomeric, octahedral structure has been similarly observed in other structurally characterized adducts of the general formula CpMCl3(L)2, ' including examples in which one or both of the donor atoms is appended to the cyclopentadienyl ring via a side-arm tether. 9  However, in all of these structures the thee chlorides are in equatorial positions, with one of the neutral donors adopting the labile axial site trans to the cyclopentadienyl ring. Spectroscopic 7 10  studies have commonly observed fluxional coordination of the donor molecule at this site. ' By comparison, it is readily apparent in 2 that the constrained geometry imposed by the two chelating side-arms induces a unique orientation of the ligands within this octahedral framework, as neither phosphine can reach the axial site trans to the Cp ring, and the 1,3-configuration of the side-arms further restricts these pendant donors to mutually trans positions within the equatorial plane.  28  references  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  Figure 2.1  Molecular structure of [P2Cp]HfCl3 (2); 33% probability thermal Pr  ellipsoids are shown. Hydrogen atoms and disorder not shown for clarity. Table 2.1  Selected Bond Length (A) and Bond Angles (deg) for P r  [ P C p ] M C l (1: M = Z r , 2: M = Hf). The numbering scheme is identical for 2  2  3  each.  1  2  1  2  M-Cl(l)  2.489(1)  2.466(3)  C1(1)-M-C1(2)  160.61(5)  160.6(1)  M-C1(2)  2.490(1)  2.476(3)  C1(1)-M-C1(3)  80.79(3)  80.7(1)  M-C1(3)  2.529(1)  2.514(3)  C1(2)-M-C1(3)  81.19(5)  81.1(1)  M-P(l)  2.897(1)  2.876(4)  P(l)-M-P(2)  159.53(4)  159.3(1)  M-P(2)  2.871(1)  2.847(4)  Cl(3)-M-P(l)  78.32(4)  78.1(1)  M-Cp'  2.260(5)  2.25  Cl(3)-M-P(2)  81.43(4)  81.4(1)  Cp'-M-Cl(3)  177.50  177.4  29  references  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  For  both 1 and 2, the steric bulk of the Cp ring induces the equatorial M - C l  and M - P  bonds to bend away from this group towards the axial chloride. The P(l)-M(l)-P(l) and Cl(l)M(1)-C1(2) angles are therefore distorted from ideal octahedral geometry by approximately 20°, while the axial Cp(centroid)-M-Cl(3) angle remains unaffected. As mentioned in the previous chapter this structural mode is prevalent for mono(cyclopentadienyl) complexes.  11  The  substituted Cp ring in 1 is also responsible for a lengthened M(l)-Cp(centroid) distance that is generally found with bulky Cp derivatives, particularly those which have pendant side-arm donors.  In comparison, for complexes coordinated by unsubstituted cyclopentadienyl rings,  such as polymeric C p Z r C l 3  13  and monomeric Cp2ZrCl2,  2.196 A and 2.20 A , respectively. The M - P and M-Cl  14  the Zr-Cp(centroid) distances are  bond distances in 1 are within the normal  range for Zr(IV) and Hf(IV) species; of note, however, is the lengthened axial M(1)-C1(3) bond relative to the two equatorial M-Cl  bond distances due to its position trans to the strong Cp  donor.  2.3.2  Solution Behaviour of [P Cp]lVICl3 ( M = Z r , Hf) Pr  2  It is interesting to note that although the trichloride complexes 1 and 2 possess essentially identical molecular structures in the solid state, the solution behavior of these species as measured by multinuclear NMR NMR  spectroscopy differ markedly. The P { H } , ^ C p H } , and H 3 1  1  X  spectra of the Zr derivative 1 are consistent with the solid state structure and remain  unchanged over a wide temperature range, whereas the corresponding spectra for the H f analogue 2 exhibit complicated temperature-dependent fluxionality. The spectral data of 1 are straightforward and will be addressed first, to provide a foundation from which the fluxional processes associated with the complicated NMR The  3 1  spectra of 2 can be more easily interpreted.  P { H } N M R spectrum of 1 shows a singlet at 10.7 ppm for two equivalent 1  phosphines in a chemical shift region that is indicative of coordination to the metal centre. In the *H NMR  spectrum there are two cyclopentadienyl proton resonances in a 2:1 ratio due to the C  s  symmetry of the complex, along with two peaks for the silylmethyl (Si(C//3)2), two for the 30  references  b e g i n on p a g e 75  Chapter  methylene  2: H a l i d e and Alkyl  Complexes  of...  (PCH2S1), and four for the isopropyl (PC7/(C7/?)2) protons of the ligand backbon  (Figure 2.2). The isopropyl and methylene protons exhibit additional coupling to the phosphorus nuclei. These combined features are all in agreement with the structure of 1 depicted in Figure 2.1,  and as mentioned above, these spectra remain invariant with changes in temperature,  implying that any exchange process involving the side-arm phosphines is undetectable on the NMR  time scale. This solution behaviour contrasts with the adduct CpZrCl3(THF)2,  a  schematic structure of which is shown as G in Chapter 1, which undergoes rapid exchange of the THF  ligand trans to the Cp ring with bulk solvent molecules, presumably via a dissociative  process involving a CpZrCl3(THF) intermediate. The absence of similar fluxional behavior in 1 attests to the stability of the chelating phosphine donors.  T—i—[—i—i—i—i—|—i—i—i—r—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—r 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 PPM  Figure 2.2  Ambient temperature *H NMR 31  spectrum of [P2Cp]ZrCl3 (1) in C6D6Pr  references  begin  on p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  A curious aspect of the *H NMR  spectrum of 1 is the observation that the resonance of  the unique proton of the cyclopentadienyl ring (attached to C(2) in Figure 2.1) shifts from 6.0 ppm  in [ P 2 C p ] L i to 7.3 ppm in 1, while the resonance due to the remaining two protons, Pr  attached to C(4) and C(5), remain at the same position of 6.4 ppm. This may be due to a weak interaction between that single proton and Cl(2). The distance between these two atoms as measured from the X-ray crystal structure is 2.7 A , which is closer than the van der Waals H---C1 distance of 3.0 A. "* 1  The sensitivity of the chemical shifts of these cyclopentadienyl protons to  the chemical environment of the rest of the complex is a characteristic feature with this ancillary ligand and will be encountered further in a number of other examples. In contrast to the routine solution behavior observed for 1, the N M R spectroscopic features of the structurally similar H f derivative 2 are surprising. For example, the ambient temperature 14.9,  3 1  P { H } N M R spectrum of 2 shows thee exchange-broadened resonances at -4.9, 1  and 24.9 ppm, in an approximate 1:2:1 ratio, respectively, in comparison to the sharp  singlet seen for 1. The two equal intensity peaks at -4.9 and 24.9 ppm also share a resemblance in line shape, while the remaining peak at 14.9 ppm is somewhat narrower. Meanwhile, the H A  NMR  spectrum of 2 at this temperature also exhibits extremely broad resonances from which  little information can be gleaned. Variable temperature (VT)  31  P { H.) and *H NMR l  spectroscopies were utilized to monitor  the exchange process that is operative at room temperature, and the results are shown in Figure 2.3.  As the temperature is lowered below ambient temperature the peaks in the  3 1  P NMR  spectrum gradually sharpen, and the two resonances at -4.9 ppm and 24.9 ppm decrease in intensity relative to the other peak at 14.9 ppm. This trend continues until only the sharp singlet at 14.9 ppm remains below -65 °C. At this temperature the * H N M R spectrum is also straightforward, with well defined peaks for the ancillary ligand that bear a striking resemblance to the ambient temperature spectrum of 1. Indeed, the similarity extends to the cyclopentadienyl resonances, where the same 2:1 integration ratio is observed with the peak for the unique Cp proton again located downfield. 32  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  i i 111 r i | ri 11 [ 1111| 1111 r 11111 n 11 [ 1111 [ i i i 20  Figure 2.3  10  0  PPM  Variable Temperature  3 L  ii|iiii|iiii|iiii|iiii|iiiniiii|iui|in 20  -10  P { H} L  10  0  PPM  -10  NMR spectra of P ^ C p l H f C l s (2) in  C D . 7  8  If the singlet at 14.9 ppm in the P NMR spectrum is identified with the octahedral 3 1  structure shown in Figure 2.1, then the two other peaks at -4.9 and 24.9 ppm appear to belong to a single separate isomer, as they are related by equivalent line shapes and integration in each spectrum that is obtained. The structures of this second species is hinted at by the spectral data: the downfield peak at 24.9 ppm suggests a strongly coordinating phosphine donor, while the 33  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  other peak at -4.9 ppm is indicative of an unbound phosphine. A five coordinate structure as shown below (2') is consistent with this data.  The *H N M R spectrum also supports this  proposed structure. Above -65 °C the emergence of new resonances can be discerned that are separate from those assigned to the octahedral isomer 2. These new peaks are indicative of the low  symmetry presented by lb'. For example, separate singlets are observed for the four  inequivalent silylmethyl groups, and the thee cyclopentadienyl protons are also inequivalant. Assignment of the remaining resonances for 2' in the H NMR A  spectrum is complicated by the  coexistence of 2, which results in an overlap of resonances for the methylene and isopropyl groups. Analysis of the spectrum is hampered further as the temperature is raised, since the exchange-broadening increases as coalescence is approached at 20 °C.  2' It is evident from the V T spectral data that the two isomers 2 and 2' are in equilibrium (equation 2.2). The former is exclusively favoured at low temperatures, while the latter becomes increasingly abundant as temperature is raised. To evaluate this equilibrium, the relative concentration of each species was measured at separate temperatures in the range between -65 °C and 20 °C, for which reliable measurements could be made from integration of the  3 l  P  NMR  spectra. Equilibrium constants were calculated according to the equation K = [2']/[2] and plotted as a function of temperature. The data are listed in Table 2.2 and the resulting van't Hoff plot shown in Figure 2.4, from which the thermodynamic parameters AH" = 4.9(5) kcal m o H and AS" = 17(1) cal m o H K " were obtained. The errors were estimated from separate experimental runs 1  and indicate reproducibility. The positive entropy term is in accord with a less-ordered structure  34  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  for 2', represented by the dangling pendant side-arm and the overall lower symmetry of this molecule.  (2.2)  Table 2.2  Equilibrium constant (K) as a function of temperature for the two Hf trichloride species in equation 2.2, obtained from the P { H} NMR 31  X  spectra  shown in Figure 2.6.  T(°C)  -67.1  -48.0  -28.3  2.1  24.0  36.6  K  0.04  0.08  0.19  0.60  1.22  1.54  35  references  b e g i n on p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  1  -i  -H InK -2H  -3H  -4 0.003  0.0035  0.004  0.0045  0.005  \n (K-i) Figure 2.4  A van't Hoff plot of the P {  N M R spectral data for the equilibrium shown in  3 1  equation 2.2.  The resonances in the ^^Pf^H} and H N M R spectra for this system are broadened J  because the fluxional process that interconverts the equilibrium species occurs at a rate comparable to the N M R time scale. The value of the equilibrium constant has a significant effect on line broadening.  16  The increase in line width (Av) due to chemical exchange is dependent on  the average lifetime (l) that a nuclear spin-state is populated, which is directly proportional to the rate at which that spin-state is exchanged (equation 2.3). AVA =  where T A = 1/kA  (2.3)  For sites that are unequally populated (i.e., K * 1) the exchange rates will also differ (K = ki/k.i), so that the resulting line-broadening will be greater for the less abundant species. This is 36  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of.  observed in the present system where the lower concentration of 2' results in proportionally wider peaks at lower temperatures relative to 2.  The peaks for 2' show additional line  broadening as the two phosphine environments within this molecule are also under exchange (Scheme 2.2).  2 Scheme 2.2  Exchange process in the equilibrium of [P2Cp]HfCl3 (2). Pr  In the low temperature spectrum this process is frozen out at the slow exchange limit, and distinct peaks with narrow line width can be identified for each isomer. A rise in temperature increases the rate of exchange and produces greater line broadening until coalescence (T ) is c  reached. This point occurs at a higher temperature in the P { ^ H } N M R 31  comparison to the *H NMR  spectrum (50 °C) in  spectrum (20 "C), for spectra obtained from the same 300 M H z  instrument, because of the wider peak separation (in Hz) between the resonances under exchange (equation 2.4).  17  37  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  at T , kex = 2.22A8 c  AS = peak separation (Hz) in the slow exchange limit  (2.4)  A similar effect of raising the coalescence temperature is observed upon measuring the same NMR  spectrum at higher field (i.e. T = 65 "C at 202.33 c  Above the coalescence temperature the  3 1  P NMR  3 1  P  MHz). spectrum displays a single broad signal  near 15 ppm that narrows in line width as the temperature is raised. The re-emerging peaks in the *H N M R spectrum above coalescence also become increasingly sharper until assignable resonances are observable for an average chemical environment near 50 °C.  This corresponds to  an averaging of the chemical environments of the two species in solution in the fast exchange limit. The  different solution behavior between 1 and 2 is puzzling, as the two species are  isostructural in the solid state as indicated earlier. Since the ligand coordination sphere is identical in 1 and 2, these complexes therefore offer a unique example of the subtle electronic differences that occasionally surface between these otherwise near-identical congeners. One can speculate why 2 should display fluxional phosphine coordination in solution to generate two species in equilibrium. The metal-ligand bond distances are shorter in the H f derivative, suggesting that stronger Hf bonding may allow the metal centre to competitively attain a stable electronic configuration with a smaller coordination number and a correspondingly lower formal electron count (as in 2'). In addition, this more open geometry may relieve steric pressures arising from closer Hf-ligand contacts in the octahedral geometry. A similar example where a Hf analogue adopts a coordination geometry in which the electron count is lower relative to the corresponding Zr species, is observed for the tetracyclopentadienyl derivatives C p M (M = Zr, 4  H f ) . In this instance, only two of the Cp ligands are bound facially in an r| -fashion for the H f 19  5  structure (compared to three for the Zr complex). Again, this modification is probably an attempt to relieve a similarly crowded coordination sphere.  38  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  2.3.3  General Reactivity of [ P C p ] M C l 3 (M=Zr, Hf) P r  2  The  air and moisture sensitivity of trichloride 1 is dramatically reduced in comparison to 1 O  O A  the strong Lewis acids C p Z r C V  and Cp*ZrCl3.  1 is also essentially inactive as a co-catalyst  for the polymerization of ethylene in the presence of M A O .  The side-arm phosphine donors  provide electronic and coordinative saturation, the latter significantly enhanced by the steric bulk of the substituted cyclopentadienyl ring and the isopropyl groups on the phosphines. This protection also helps to control the reactivity which is outlined below.  2.4.1  Synthesis of [ P C p ] M R ( M = Z r , Hf; R = C H P h , C H C M e , C H S i M e ) 2  3  2  2  3  2  3  Addition of either 3 equivalents of K ( C H P h ) in T H F or 1.5 equivalents of 2  Mg(CH Ph)2(THF)2 2  Pr  in toluene  to  Pl  ' [ P C p ] M C l 3 generates the tribenzyl derivatives 2  [P2Cp]M(CH Ph) (3: M = Zr, 4: M = Hf) as shown below (equation 2.5). 2  3  3KCH Ph • - 3 KCI 2  Pr  [P Cp]MCl3 2  Pr  [P Cp]Zr(CH Ph) , „ _ 3 M = Zr 2  2  3 ( 2 , 5 )  4 M = Hf These compounds can be isolated cleanly as yellowish air- and moisture-sensitive, thermally21  stable oils, that remain highly soluble in hydrocarbon solvents. In comparison to Zr(CH Ph)4 2  ;  which decomposes rapidly in solution above 0 "C, the robust thermal stability of 2 is more in line 22  with another tribenzyl derivative Cp*Zr(CH Ph)3, 2  exemplifying the stabilizing influence  provided by coordination of a bulky cyclopentadienyl donor. The  1  H,  13  C{ H}, and P { H} NMR l  31  l  spectroscopic data for 3 and 4 are very similar and  are both consistent with the presence of thee benzyl groups and one P2Cp moiety. At ambient 39  references  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  temperatures, a singlet in the P { H} NMR 3 1  l  spectrum is observed for each species at -5.2 ppm  (3) and -5.9 ppm (4), respectively, which as described previously is in the chemical shift range for uncoordinated phosphine donors. Further evidence that the phosphine arms of the ligand are dangling in these complexes is furnished by the absence of P coupling for both the protons and 3 1  the carbons of the benzylic C H 2 groups, which appear as singlets in the respective *H and 13  C { ! r I } NMR  spectra. The structure of 2 can therefore be described as a thee-legged piano  stool as depicted below, with phosphine coordination to the metal prevented by the presence of thee relatively bulky alkyl ligands. In addition, all three benzyl groups are equivalent in both the H  l  and ^ C f ^ H } NMR  spectra, as only one set of resonances is observed for each of the ortho,  meta, para, and benzyl groups. The benzyl ligands are therefore undergoing rapid exchange, facilitated by a lack of interference from the dangling side-arms.  Multinuclear N M R  spectroscopic studies showed that this behavior persists even at low temperatures.  There is a tendency for benzyl ligands bound to early transition metals to depart from the conventional T| ^coordination mode of a normal a-bond to improve electron donation. ' 10  23  This  24  is accomplished either though an a-agostic  interaction or by increasing the hapticity to access  the 7i-system in the phenyl ring. Both of these distortions induce shifts in the NMR  and the  1 3  C  spectroscopic features. A weakening of the agostic C-H bond decreases the V C H coupling  (< 120 Hz) for this group, while an r| -benzyl ligand displays upfield chemical shifts for both the 2  methylene and ortho protons, and a corresponding upfield shift in the methylene and ipso carbon 40  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  atoms. A n T| structure is also typified by relatively large V C H coupling (> 140 Hz) for the N  methylenes as a result of partial rehybridization to an sp electronic configuration. 2  There is spectroscopic evidence that the benzyl ligands in 2 may be coordinated in an r) 2  interaction, which would not be unexpected given that the pendant phosphines are unable to bind in this unsaturated 14-electron complex. The H NMR  spectrum shows upfield resonances for  X  the methylene and ortho protons near 1.9 and 6.6 ppm, respectively. The ipso and ortho carbon atoms are both located within an intermediate chemical shift range (near 125 ppm) in the NMR  1 3  C  spectrum as are the methylene carbons at 70 ppm. The ^JCH value of 125 Hz for the  methylene group in the coupled spectrum is within the normal range. Overall, in the absence of an X-ray structure the NMR  data are inconclusive regarding the possible binding mode of these  ligands, although fluxional behaviour may be responsible for averaging the values of these parameters. The  preparation of similar bulky trialkyl derivations, [P2Cp]Zr(CH2EMe3)3 (5a: E = C, Pr  5b: E = Si), could be achieved from l a with the appropriate alkylating reagent (equation 2.6).  3 LiCH EMe ^ 2  Pr  [P Cp]ZrCI 2  j  3  3 Pr  [P Cp]Zr(CH EMe ) 2  2  - 3 LiCI  5a: E = C  1  5b:  3  3  ( 2  -  6 )  E = Si  The tri-neopentyl (CH2CMe3) and tri-neosilyl (CH2SiMe3) complexes 5a and 5b, respectively, were both isolated cleanly as air- and moisture-sensitive, hydrocarbon-soluble oils. These species exhibit thermal stability similar to that observed for 2 and with the analogous trisubstituted derivative Cp*ZrR3 (R= CH CMe3, CH SiMe ). 23  2  2  3  The *H NMR spectra for 3 and 4 show resonances for the methyl and methylene groups of the respective neopentyl and neosilyl ligands that integrate correctly for the stoichiometry 41  references  b e g i n on p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  indicated. In the  3 1  P N M R spectrum a singlet is observed at -5.5 ppm for 5a and similarly at -5.9  ppm for 5b. These resonances remain unchanged at lower temperatures and are indicative of dangling phosphines, indicating a similar thee-legged piano stool geometry as found for 3. It is evident that the ability of thee bulky alkyl ligands to sterically saturate the coordination sphere is a general feature with this ancillary ligand system.  2.4.2  Synthesis and Fluxional Behavior of [ P C p ] Z r ( C H ) P r  2  3  3  To examine the phosphine behaviour in a trialkyl species in which steric factors are minimized, the starting Zr chloride complex 1 was methylated; addition of three equivalents (or a slight excess) of MeMgBr in toluene generates the trimethyl derivative [P2Cp]Zr(CH3)3 (6) (equation 2.7). The trimethyl derivative 6 can also be synthesized using M e L i , although this reaction is quite sensitive to reaction stoichiometry and solvent conditions. The addition of a slight excess of M e L i in ether results in decomposition of the entire reaction mixture; one of the reaction products detected in the resultant mixture is [P2Cp]Li. Similarly, adding 0.1 equiv. of Pr  M e L i to 6 induces the same decomposition process. Pr  One by-product of this reaction is  [P2Cp]Li, so it is conceivable that the unstable tetramethyl species Zr(CH3)4 is formed, which  acts as a catalyst for the decomposition of [P2Cp]Zr(CH ) . Pr  3  Pr  [P Cp]ZrCI 2  1a  3  3 MeMgBr • - 3 MgCIBr  Pr  3  [P Cp]Zr(CH )3 2  3  (-) 2  6  7  Trimethyl 6 is isolated as a yellowish air- and moisture-sensitive, slightly impure oil. This compound decomposes upon exposure to visible light within hours but has remarkable thermal stability in the dark at 100 "C, in marked contrast to the reported thermal lability of the 22  related complex Cp*Zr(CH3)3.  The latter gradually decomposes under ambient conditions, 42  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  although the addition of external phosphine donors yields adducts (i.e., Cp*Zr(CH3)3(PMe3)2 and Cp*Zr(CH3)3(dmpe)) which can be isolated as thermally stable solids. It is worth noting that these adduct species comprise the same general ligand set that is present in 6. The  ambient temperature NMR  spectroscopic parameters for this trimethyl derivative are  simple. A singlet at 2.3 ppm in P { H } NMR 3 1  1  spectrum is observed, indicative of equivalent  phosphine donors, while the methyl groups attached to zirconium appear as one triplet in the ! H NMR  spectrum and one triplet at 42.7 ppm in the C{ ^H} NMR 13  spectrum, indicating that these  resonances are coupled to both phosphines. In addition, the ligand backbone resonances are also suggestive of high symmetry, giving rise to only one singlet for the silyl methyl groups and a doublet for the methylene hydrogens. The peaks due to the cyclopentadienyl protons appear in the familiar 1:2 ratio as a triplet at 6.42 ppm for the unique proton and a doublet at 6.71 ppm for the two equivalent protons. Variable temperature experiments show that as the temperature is lowered, these simple NMR the  3 1  spectra broaden and become more complicated (Figure 2.4). For instance, the singlet in P NMR  spectrum gets increasingly broader down to -33 "C, and below this temperature  two very broad resonances grow out of the baseline near -37 "C. These new resonances, near -10 and 10 ppm, respectively, display similarly broad line shapes and peak intensities. A further decrease in temperature reveals an equivalent amount of narrowing in the line width of these peaks, while the other signal at 1.6 ppm shinks in relative intensity until it disappears into the baseline near -67 C. The H and ^ C f ! ! } NMR l  1  spectra also show the corresponding changes,  although less clearly.  43  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  so  10  Figure 2.5  o  - i o PPM  -a  go  ib  o  -10 PPM -20  Variable temperature P { NMR spectra of the two species in solution for [P2Cp]Zr(CH3)3 (6). A minor unknown impurity is shown with an asterisk. 31  Pr  Aspects of this curious variable temperature behaviour parallel the complicated phenomena described earlier for the Hf trichloride 2. Between -70 "C and -38 °C the  3 l  P  NMR  spectrum reveals the co-existence of two sets of resonances: one pair of related peaks for a single complex consisting of one coordinated and one uncoordinated phosphine (6'), and a separate singlet between these resonances belonging to a second species having equivalent phosphine donors (6). As with 2 the relative concentration of these species again varies according to a temperature-dependent equilibrium (equation 2.8), generating exchange broadening in the line width.  Note that there is a significant difference with this equilibrium compared to the 44  r e f e r e n c e s b e g i n on p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  equilibrium observed for 2, however, in that the species favoured at lower temperatures is the asymmetric complex 6'. At -80 "C this is the only detectable species, and additional support for the asymmetric structure is provided by the H NMR A  spectrum obtained at this temperature,  where three inequivalent protons are represented in the Cp region. At this temperature there are also thee distinct methyl carbon resonances at 41.0, 44.0 and 44.2 ppm, respectively. At higher temperatures the exchange rate between 6 and 6' increases until coalescence near -33 °C, above which a broad singlet is observed in the fast exchange limit in the  3 1  P NMR  spectrum, which  sharpens further with rising temperature. Likewise, the highly symmetric ambient temperature i H NMR  spectrum is also suggestive of an averaged chemical environment, as are the single  resonances for three equivalent methyl groups in both the  1 3  C and *H NMR  spectra.  (2.8)  45  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  Integration of the variable temperature  3 1  P { H } NMR  spectra between -68°C and -43°C  1  permitted equilibrium constants to be calculated as a function of temperature from the concentration measurements for each species. The results are presented in Table 2.3, and a van't Hoff plot using these data is shown in Figure 2.5, from which values for the thermodynamic parameters AH" = 6.1(1.0) kcal mol"  1  and AS° = -25(5) cal K  _ 1  mol" were determined. It should 1  be noted that there are relatively large error bars in the thermodynamic parameters due to the difficulty in accurately measuring the integration from the P { H } NMR 3 l  1  spectra, especially in  the higher temperature region where line broadening is more pronounced. The errors were estimated from different runs and indicate reproducibility.  Table 2.3  Equilibrium data for the two trimethyl complexes. The data were taken from the P { H } NMR 31  1  spectra shown in Figure 2.9.  T(°C)  -67.6  -62.7  -57.7  -52.8  -47.8  -42.8  K  12.8  8.1  5.7  5.0  3.3  2.4  46  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  3-i  InK  0.0043  0.0044  0.0045  0.0046  1/T  Figure 2.6  l  0.0048  0.0049  (K-l)  A van't Hoff plot of the P{ H} NMR 31  0.0047  spectral data for the equilibrium shown in  equation 2.10.  An unexpected result from the van't Hoff plot shown above is the negative entropy term for the equilibrium in equation 2.8, suggesting that 6' is the more ordered of the two complexes. It is also surprising that phosphine dissociation as observed in 6' would be favoured at lower temperatures. One possible reconciliation of the data is that 6' actually exists as a dimer with bridging methyl groups. The equilibrium would then be modified to the equation K = [6']/[6] , 2  which yields AH°  = 11.2(1.0) kcal mol"  1  and AS" = -40(5) cal K"  1  mol" when the concentration 1  data are replotted. In this instance the negative entropy term would be consistent with favouring the break-up of a dimer at higher temperatures. Analogous dinuclear species with this ancillary ligand system are proposed as intermediates for intermolecular ligand exchange processes which will be encountered later. 47  references begin on page 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  2.4.3  Reactivity of [ P C p ] M R 3 P r  2  All of the trialkyl complexes mentioned above react within hours to an atmosphere of H2, generating putative hydride resonances in the H NMR  spectrum, and in the reaction of H with  X  6 a doublet of doublets is observed in the  3 1  P NMR  2  spectrum for a pair of mutually coupled  inequivalent phosphines. However, a mixture of products is obtained in these reactions from which identifiable species could not be isolated. It was anticipated that hydrogenation of the alkyl groups might yield a ( [P2Cp]ZrH3) hydride species that could be trapped by the side-arm Pr  n  phosphines. However, these observations are in line with similar unsuccessful attempts to trap stable products from the hydrogenation of C p * Z r R complexes in the presence of external 3  phosphines.  In both cases the observation of multiple products may be due to a propensity of  the resulting hydrides to oligomerize. Similarly, the reaction of [P2Cp]ZrR species with an 3  excess of CO leads to decomposition of the whole reaction mixture. Presumably, with thee alkyl ligands to potentially undergo C O insertion there are a number of reaction pathways which could eventually lead to homolytic or heterolytic bond cleavage. These results can be contrasted with  48  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  the analogous reaction of CO with [P2Cp]ZrCl2(CH2Ph) (13) (see later in section 2.5.4), which Pr  offers fewer options for decomposition.  2.5.1  Synthesis of [ P C p ] Z r C l R ( C H C M e , C H S i M e , Me, Et, OBu*) P r  2  In  2  2  3  2  3  light of the complex solution behaviour noted above for 6, a series of  mono(substituted) complexes were prepared in order to assess the electronic effects with the presence of a single alkyl ligand. Substituents of varying size were selected, ranging from the relatively bulky neopentyl and neosilyl groups to the much smaller methyl and ethyl derivatives. A large electron-withdrawing alkoxide (OBu ) was also employed to obtain a bulky complex 1  with similar electronic properties to 1. However, it was anticipated that steric effects in these mono(substituted) species would be minor in comparison to the bulky trialkyl species. The  mono-alkyl complexes [P2Cp]ZrCl2(CH2EMe3) (7a: E = C, 7 b : E = Si) were Pr  prepared from reactions of 1 with the appropriate stoichiometry of LiCH2EMe3 in toluene (equation 2.9).  LiCH EMe 2  Pr  [P Cp]ZrCI 2  3  i  3  [P Cp]ZrCI (CH EMe ) 2  2  2  3  -LiCI 1  The  7a  E=C  7b  E = Si  methyl and ethyl analogues [P Cp]ZrCl2R (8: R = Me, 9: R = Et) were more readily made Pr  2  from the corresponding Grignard (equation 2.10) as opposed to the alkyl lithium reagent.  49  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  RMgBr Pr  [P Cp]ZrCI 2  •  3  Pr  [P Cp]ZrCI R 2  MgCIBr  0  2  „  % t  8  R = Me  9  R = Et  (2.10)  The mono(alkoxide) species [P2Cp]ZiCl2(OBu ) (10) was synthesized from the reaction of the Pr  alkoxide with 1 in THF  Pr Pr  t  (equation 2.11).  K  [P Cp]ZrCI 2  1  3  0  B  L  - KCI  j  t  •  t  Pr  ^[PaCplZrClg^Bu )  » '  1  ( 2  10  i n 1 1 }  A l l of these reactions were conducted using high dilution to ensure that only one equivalent of reagent was added to each metal centre. Mono(alkyl) 7a,7b and 8 were each obtained as yellow oils, 9 as a reddish oil, and 10 as a pale cream-coloured oil. compounds could be isolated free of impurities (typically 5-10% by NMR  None of these  spectroscopy), and all  species slowly disproportionate to regenerate 1 and a number of unidentified decomposition products. A dinuclear species analogous to that proposed for 6' is a possible intermediate in this disproportionation reaction. The analogous monoalkyl Cp*ZrCl2Me complex is also suspected to undergo oligomerization and/or halide exchange, and slowly decomposes in solution.  In  contrast, H f mono(alkyl) complexes Cp*HfCl2R (R = Me, Ph) are generally more thermally stable.  26  The N M R spectra of these mono(alkyl) complexes show complicated exchanged broadened resonances that suggest a similar equilibrium process is operative as noted for 2 and 6. For  example, in 7a, 7b, 8 and 10 there are two small peaks near 10 and -5 ppm in the ambient  temperature  3 1  P N M R spectrum associated with the five-coordinate species, and a separate  resonance in the vicinity of 0 ppm for the symmetric six-coordinate complex, which is the major 50  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  isomer (> 75%) in solution. The corresponding ambient temperature spectrum of 9 is near coalescence. The equilibria for these systems are suggested by consistent changes in peak broadening and intensity as a function of temperature, although these processes could not be satisfactorily studied by V T NMR  spectroscopy due to the inherent impurities present in the  samples.  2.5.2  Synthesis of [ P C p ] M C l ( C H P h ) ( M = Z r , Hf) P r  2  2  2  Addition of one equivalent of K C H P h to trichloride 1 generates the monobenzyl 2  derivative [P Cp]MCl2(CH Ph) (11: M = Zr, 12: M = Hf), which is obtained either as a red Pr  2  2  solid (11) or an orange-yellow oil (12) (equation 2.12).  KCH Ph 2  Pr  [P Cp]MCI 2  [P Cp]ZrCI (CH Ph) 2  3  2  2  (2.12)  -KCI 1  11: M = Zr 12: M = Hf  Integration of the *H NMR ambient temperature  3 1  P NMR  spectrum shows only one benzyl group per P C p unit. The 2  spectrum for 11 shows two broad resonances which coalesce into  a broad singlet near 5.8 ppm that sharpens at higher temperatures.  Below room temperature  these broad peaks gradually sharpen to a pair of singlets at 14.2 and -6.9 ppm, again corresponding to a five-coordinate geometry in the slow exchange limit.  The variable  temperature spectroscopic data show the familiar line-broadening effects as the temperature is raised to the fast exchange limit where the two phosphine sites are averaged. This averaged chemical environment is also reflected in the benzylic carbon (CH2)  1 3  C NMR  spectrum, which shows a triplet for the  due to coupling to both phosphorus nuclei. No coupling was observed to  phosphorus for the benzylic protons in the *H NMR  51  spectrum.  references  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  In contrast to the other fluxional complexes described previously, however, the dynamic solution behaviour of 11a is unique in that the intermediate six-coordinate species that mediates phosphine exchange is not directly observed. Rather, instead of being present as an equilibrium species, this intermediate is inferred as an undetected transition state structure. To support this analysis, simulation of the temperature dependent P { H } NMR 3 1  spectra by NMR  1  line shape  analysis (DNMR-5) enabled rate constants to be calculated (Table 2.4). From the resulting Eyring plot (Figure 2.6) the following activation parameters were obtained: AH* = 8.8 kcal mol" AS* = -13.1 cal m o H K " . The negative entropy of activation for this process is consistent 1  with a six-coordinate structure for the transition state (Figure 2.7), implying that phosphine exchange in 11 occurs via the same associative pathway as found for the other fluxional systems, except that in this instance the lifetime of the six-coordinate intermediate is too fleeting to be directly observed.  Table 2.4 Rate constants of phosphine exchange for [P2Cp]ZrCl2(CH2Ph) (11) as obtained Pr  from line shape analysis using DNMR-5.  T(°C) k  -18.4  -8.4  1.9  12.1  22.4  30.5  40.5  50.5  60.5  70.4  200  400  800  1500  2500  4000  6500  11000  16000  24000  52  references  b e g i n on p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  5 -i  In (k/T)  "i  0.0028  0.003  0.0032  r  0.0034  0.0036  0.0038  0.004  1/T(K-1)  Figure 2.7  Eyring plot of ln(kJT) versus 1/T for the complex [P2Cp]ZrCl2(CH2Ph) (11) Pr  using the equation k = (k T/h)exp(-AG*/RT) = (k T/h)exp((TAS*-AH*)/RT); the B  B  rate constants and temperatures are taken directly from Table 2.6.  7{ Figure 2.8  c/l  CH Ph 2  Proposed transition state structure for the interconversion of the phosphine sites in Pr  [P2Cp]Zi€l (CH Ph) (11). 2  2  53  references  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  2.5.3  Reactivity of [ P C p ] Z r C l R P r  2  Due  2  to the inability to purify most of the alkyl derivatives described above, reactions  involving these species generally did not lead to clean products. For example, attempts to alkylate alkoxide 10 (prepared in situ) with K C H P h does yield two main products as observed 2  in the  3 1  P NMR  spectrum at -3.5 and -5.5 ppm, but a number of organic byproducts are also  formed, hampering efforts to isolate or identify these compounds. Analogous reactions to form mixed alkyl species for a series of cross-over experiments will be discussed in the next chapter. In comparison, monobenzyl 11 can be obtained as a pure compound suitable for reactivity studies. However, except for the C O insertion reaction outlined below, the reaction of 11 with reagents such as H and C 0 led to decomposition products. 2  2.5.4  2  Synthesis of [ P C p ] Z r C l ( n 2 - C ( 0 ) C H P h ) (13) Pr  2  2  2  Exposure of a toluene solution of mono(benzyl) 11 to an atmosphere of C O under ambient conditions for 6 h affords the acyl-ylide complex [P Cp]ZrCl (r|2-C(0)CH Ph) (13) Pr  2  2  2  as pale yellow, air- and moisture-sensitive crystals (equation 2 13). The open site for initial coordination of a C O molecule prior to migratory insertion into the Zr-benzyl cr-bond is made available by fluxional phosphine dissociation in the exchange process described above for 11. Despite the electrophilic nature of the acyl carbon in early metal acyl complexes, similar reports of adduct formation to give an ylide species are relatively rare.  A Ta silaacyl complex,  Cp*TaCl3(ri2-C(0)SiMe3), forms adducts with pyridine, P(OMe)3, and PEt3, and there is an 27  example similar to 13 of a Zr formyl-ylide complex that is stabilized by intramolecular 28  coordination of a pendant donor of a chelating amidodiphosphine (PNP)  54  ligand.  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  Pri  [P Cp]ZrCI (CH Ph) 2  2  2  11  C  o  (2.13)  Me •Si  SiMeg  2  13 PhH C 2  The X-ray crystal structure of 13 is shown in Figure 2.8, with selected bond length and bond angles listed in Table 2.5. The unusual arrangement of the ancillary ligand has one pendant phosphine attached to the acyl carbon to generate a zwitterionic ylide moiety and a chiral carbon centre, while the other side-arm is directed well away from the coordination sphere and remains dangling. The main structural features of interest in 13 are associated with the acyl-ylide unit. Although the ri -binding mode in 13 is typical for oxophilic early metal acyl complexes (I), the 2  29  increased electron density supplied to the electrophilic acyl carbon from intramolecular phosphine coordination results in modest changes in the bond length and bond angles. For example, relative to other Zr acyl complexes (i.e., Cp2ZrMe(r) -C(0)Me)), ° in 13 the Zr(l)2  C(24)  3  and C(24)-0(l) bond distances are comparatively longer, the Zr(l)-0(1) distance is  shorter, and the Zr(l)-C(24)-0(1) angle is smaller. These effects indicate an increase in the Z r - 0 bonding interaction as the bonding contribution to the metal from the phosphine-stabilized acyl carbon is lessened, and point to a significant oxycarbene character in this moiety (II). The reduced C - 0 bond order is also reflected in the lack of an obvious carbonyl stretch in the IR spectrum. The strength of the P(l)-C(24) bond is suggested by the fact that the other P-C single  55  references  b e g i n on p a g e 75  Chapter 2: Halide and Alkyl Complexes of...  bonds associated with this phosphonium centre are actually slightly longer in comparison. The Zr-Cl bond distances are comparable to the equatorial Zr-Cl bonds in 1.  •O M  JO.  C>  I Table 2.5  II  Selected Bond Length (A) and Bond Angles (deg) for Pr[P Cp]ZrCl (ri2-C(0)CH2Ph) (13) 2  2  Zr(l)-Cl(l)  2.463(2)  Zr(l)-Cl(2)  2.470(2)  Zr(l)-0(1)  2.037(5)  Zr(l)-C(24)  2.284(9)  Zr(l)-Cp'(l)  2.21  P(l)-C(6)  1.809(7)  Pd)-C(lO)  1.811(8)  P(l)-C(13)  1.815(8)  P(l)-C(24)  1.779(8)  0(1)-C(24)  1.476(9)  C(24)-C(25)  1.54(1)  56  Cl(l)-Zr(l)-Cl(2)  94.77(8)  Cl(l)-Zr(l)-0(1)  92.0(1)  Cl(l)-Zr(l)-C(24)  113.1(2)  Cl(l)-Zr(l)-Cp'  117.4  Cl(2)-Zr(l)-0(1)  129.7(2)  Cl(2)-Zr(l)-C(24)  93.4(2)  Zr(l)-C(24)-0(1)  61.3(4)  Zr(l)-C(24)-P(l)  132.8(4)  0(1)-C(24)-C(25)  111.0(6)  P(l)-C(24)-0(1)  111.2(5)  P(l)-C(24)-C(25)  116.8(6)  references begin on page 75  C h a p t e r 2: H a l i d e a n i l A l k y l C o m p l e x e s  of...  C(30)  Figure 2.9  Molecular structure of [P2Cp]ZrCl2(ri -C(0)CH2Ph) (13); 33% probability Pr  2  thermal ellipsoids are shown. Hydrogen atoms not shown for clarity.  Two  isomers are observed in solution for 13 with a slight excess of one species relative to  the other. Each isomer displays a separate singlet near 47 ppm in the P{!H} NMR 31  spectrum  for the ylide phosphorus nucleus, and a second peak near -5 ppm for the dangling phosphine. The  ylide resonance is located downfield relative to the normal chemical shift range (0-20 ppm)  for  a metal-bound phosphine with this ligand system, and is consistent with the chemical  environment of a phosphonium centre. A doublet ( Jpc = 57Hz) for the acyl carbon is observed l  near 79 ppm in the C{ !H} NMR 13  spectrum for each C-labeled isotopomer. In comparison to 13  other Zr acyl complexes (5 > 200 ppm), this peak resonates considerably further upfield in the region for a typical sp -hybridized carbon atom with a C-0 single bond, in agreement with the 3  31  molecular structure. The ^Jpc coupling is similar to that found in the analogous intramolecular Zr formyl-ylide complex (^Jpc = 55Hz). Contrasting with the reported coupling for a Ta adduct 57  references  b e g i n on p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  (1/pC = 8Hz), in which the ylide results from attack by an intermolecular phosphine, the larger values for the two Zr examples may be due to steric effects associated with the chelating sidearms. The iff N M R spectrum of 13 is complicated by the asymmetry of the molecule and by the presence of two diastereomers. The effect of the chiral centre is particularly evident in the resonances of the diastereotopic geminal protons of the benzyl group, which have a chemical shift separation of nearly 1 ppm. This generates an A M X splitting pattern for each unique benzyl proton originating from i3  x  JHH  and  3  JPH  coupling, and additional  3  JPH  coupling is observed to the  C-labeled acyl carbon (Figure 2.9). These values re listed in Table 2.6; note the significant  differences between H A and H M in their respective coupling to the phosphorus and carbon nuclei. The low C i symmetry of this complex is also evident in the cyclopentadienyl region where thee separate peaks are seen in the *H N M R spectrum for each isomer. These resonances could be individually assigned from cross-peaks in the 2D-COSY N M R spectrum.  The  resonances associated with the dangling side-arm exhibit are isochronous, due to the remoteness of these groups from the chiral centre.  58  r e f e r e n c e s b e g i n on p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  3.80  3.85  3.75  3.70  3.65  ppm  Region in H NMR spectrum of [P2Cp]ZrCl2(ri -C(0)CH2Ph) (13) showing  Figure 2.10  Pr  L  2  one of the diastereotopic protons (two isomers present). Coupling constants (Hz) for the benzylic (C//2Ph) protons in 13.  Table 2.6  H  ^HH JCH  2  3  JPH 59  A  H  M  16.5  16.5  < 1  5.7  2.0  36.2 r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  The two diastereomers seen for 13 likely differ in the relative orientation of the coordinated acyl unit.  A similar feature has been observed in other early metal r| -acyl 2  complexes. For example, the kinetic product from the insertion reaction of CO with Cp2ZrMe2 is oriented as shown in A , which isomerizes upon heating at 50 "C to give the thermodynamically favoured product B, where steric interactions between the two methyl groups are eliminated (equation 2.14).  Theoretical calculations suggest that this transformation may proceed via an  rj -intermediate with subsequent rotation about the M - 0 bond axis. 1  33  (2.14)  Me A  B  In the case of 13, it is not obvious that one isomer should be energetically preferred over the other; hence, it is reasonable that both species should co-exist in nearly equal proportions in solution (equation 2.15).  (2.15)  2.6  Summary and conclusions  60  references  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s  A  of..  potentially chelating hybrid-donor ligand system consisting of a central  cyclopentadienyl ring with two pendant side-arm phosphines has been developed. The steric properties of the ligand can be varied depending on the alkyl substituents (Me, Pr , 1  phosphines.  Bu ) on the l  The variant of the ligand with isopropyl groups on the phosphines has been  employed to examine its coordination chemistry with zirconium(IV) and hafnium (IV). The trichloride complexes [P2Cp]MCl3 (1: M = Zr, 2: M = Hf) have been prepared; these derivatives serve as versatile starting materials for the synthesis of a series of alkyl complexes. What emerges from this study is that coordination of the pendant phosphine arms becomes less favorable as the electron density at the metal increases. For example, the electron-withdrawing ligands in trichloride 1 and alkoxide 10 encourage the coordination of both phosphine donors. The  introduction of a single electron-releasing alkyl ligand at zirconium is sufficient to increase  the tendency for phosphine dissociation such that the low temperature limiting structure for 8 is five-coordinate with a dangling side-arm. A further consequence of this reduced tendency for phosphine binding is that fluxional processes become prevalent for these mono-substituted alkyl complexes. Indeed, the subtle electronic balance that influences the coordination mode of the pendant phosphines is perhaps best illustrated by a comparison of the trichloride derivatives 1 and 2. A similar mononuclear solid state structure is observed for both 1 and 2 with two pendant phosphine donors coordinated to the metal centre. However, while the solution behavior of 1 remains consistent with the solid state structure at all temperatures studied, NMR  spectroscopic  studies reveal fluxional processes for 2 involving the side-arm phosphines. The divergent solution behavior of these otherwise identical species is perhaps attributed to the capacity for Hf to form comparatively stronger bonds, thus enabling the metal to be competitively saturated electronically with a lower coordination number. The  coordination mode of the side-arms in the trialkyl derivatives is dependent on the  size of the alkyl groups. Sterically bulky ligands (i.e., CH2Ph, CH2CMe3, CH2SiMe3) crowd the metal centre and prevent the phosphines from binding, resulting in a thee-legged piano stool geometry. With three small methyl groups in 5 (i.e., comparable in size to the chloride ligands in  61  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  1), there is ample space for the phosphines to access the metal; therefore, electronic factors dominate and an equilibrium mixture of species ensues, as observed for 2 and a few of the mono(alkyl) derivatives. These systems all undergo similar exchange processes for the phosphines that reflect the subtle electronic factors mentioned above. There is a difference in the thermal stability of the mono- versus tri-alkyl complexes. Except for mono(benzyl) 11 there is a tendency for the mono-substituted derivatives (including alkoxide 10) to disproportionate over time to give trichloride 1 and a number of unidentified decomposition products. The mechanism for the disproportionation of these species may involve ligand exchange via a binuclear intermediate. The trialkyl complexes are considerably more robust, and the resistance of these species to thermal decomposition will be addressed again in the next chapter.  2.7  Experimental  2.7.1  General Considerations Unless otherwise stated all manipulations were performed under an atmosphere of pre-  purified dinitrogen in a Vacuum Atmospheres HE-553-2 glove box equipped with a MO-40-2H purification system, or in standard Schlenk-type glassware on a dual vacuum/dinitrogen line. The  glove box was also equipped with a -40 "C freezer. Reactions involving gaseous reagents  were conducted in Pyrex vessels (bombs) designed to withtand pressures up to and including 4 atm.  IH NMR  200.1 MHz,  spectroscopy was performed on either a Bruker AC-200 instrument operating at or a Bruker AM-500 instrument operating at 500.33 MHz,  complexity of the particular spectrum. *H NMR (7.15 ppm) or C6D5CD2// (2.09 ppm).  1 3  C NMR  Bruker AC-200 instrument operating at 50.3 MHz, 75.4 MHz.  1 3  C NMR  depending on the  spectra were referenced to internal C^O^H spectroscopy was performed on either a or a Varian XL-300 instrument operating at  spectra were referenced to internal Q D (128.0 ppm) or C6D CD3 (137.5 6  62  5  references  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  ppm).  3 1  P { H } N M R spectroscopy was performed on either a Bruker AC-200 instrument X  operating at 81.0 MHz, 500  a Varian XL-300 instrument operating at 121.4 MHz,  instrument operating at 202.3 MHz.  3 1  P { l H } NMR  or a Bruker  AM-  spectra were referenced to external  P(OMe)3 (141.0 ppm). Variable temperature experiments were performed on either the Varian XL-300 or the Bruker AM-500 instrument. All chemical shifts are reported in ppm and all coupling constants are reported in Hz.  Microanalyses (C, H, N) were performed by Mr. P. Borda  within this department.  2.7.2 Materials Pr  [P2Cp]ZrCl3 was prepared according to published procedures. HfCl4(THT)2 was 2  prepared according to the analogous published procedure for HfCl4(THF)2, substituting 34  for THF.  NaCp(THF),  35  KCH Ph, 2  3 6  LiCH CMe , 2  3  3 7  LiCH SiMe , 2  3  3 8  THT  were prepared according  to published procedures. MeMgBr (1.4 M solution in toluene/THF), EtMgBr (3.0 M solution in ether), and M e L i (1.4 M solution in ether) were purchased from Aldrich and used as received. K O B u was purchased from Aldrich and sublimed before use. 1  Hexanes, tetrahydrofuran (THF), ether, and toluene were pre-dried over CaH2 followed by distillation under argon from either sodium metal or sodium-benzophenone ketyl. Pentane and  hexamethyldisiloxane were distilled from sodium-benzophenone ketyl. The deuterated  solvents C6D6 and C6D5CD3 were dried over molten sodium metal, vacuum transferred to a bomb, and degassed by thee freeze-pump-thaw cycles before use.  Ethylene and carbon  monoxide were obtained as lecture bottles from Matheson and dried over P2O5 before use. Labeled  1 3  C O (Cambridge Isotopes) was used as received. Hydrogen was purchased from  Matheson and purified by passage though a column of activated 4 A molecular sieves and M n O supported on vermiculite.  63  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  2.7.3  Synthesis  2.7.3.1  Ligand synthesis C5H5SiMe2CH Cl 2  A 0.85 M T H F solution of NaCp prepared in situ (200 mL, 170 mmol) maintained at -30 °C was added dropwise via cannula over a period of 30 minutes to a cooled (-78 °C) stirring solution of C l S i M e C H C l (25.0 g, 174 mmol) dissolved in 300 mL of THF. 2  The solution  2  gradually turned viscous and pale cream in colour. The mixture was allowed to slowly warm to room temperature and stirred for 1 h. The solvent was removed under vacuum and 100 mL water added to the flask, and extracted with four aliquots (25 mL) of diethyl ether. The ether layer was dried over MgSO-4 and filtered, and the solvent subsequently removed to give a yellow oil. Vacuum distillation yielded a clear liquid (bp 30-35 "C, 1 0 isomer (> 85 % by ! H NMR  -2  Torr) consisting mainly of one  spectroscopy). Yield: (21.7 g, 74 %). *H NMR  (20 °C, CDCI3): 8  0.0 (s, 6H, Si(C#3)2), 2.59 (s, 2H, S i C / / C l ) , 3.41 (very br, I H , Cp-//Si), 6.7 (overlapping br, 2  4H, Cp-fl).  C H4(SiMe CH Cl)2 5  2  2  A solution of NaN(SiMe3) (22.3 g, 122 mmol) in 150 mL of THF 2  was added dropwise  over a period of 15 minutes to a cooled (-90 "C) stirring solution of C 5 H 5 S i M e C H C l (21.0 g, 2  122 mmol) dissolved in 150 mL of THF.  2  The temperature of the ethanol/liquid N cooling bath 2  was maintained below -85 °C during this addition. The mixture was stirred at -90 °C for another 30 minutes after the addition was complete, and then added dropwise over a period of 20 minutes to a cooled (-78 " Q stirring solution of C l S i M e C H C l (18.0 g, 126 mmol) in 300 mL of 2  2  THF.  The reaction mixture became viscous during the course of the addition. The solution was slowly warmed to room temperature and stirred for 2 h, the solvent was then removed under vacuum and 80 mL water added to the flask, and extracted with four aliquots (25 mL) of diethyl ether. The ether layer was dried over MgSO-4 and filtered, and the solvent subsequently removed to  64  references  b e g i n on p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  give a clear yellow oil.  Vacuum distillation yielded some of the starting C 5 H 5 S i M e C H C l (bp 2  2  34-41 °C, l O Torr) and a viscous pale yellow oil (bp 95-100 "C, 10" Torr) consisting primarily 2  2  (> 90 % by H NMR l  spectroscopy) of the 1,1-substituted isomer. Yield: (19.8 g, 58 %). Anal.  Calcd. for C i i H 2 o S i C l : C, 47.29; H , 7.22. Found: C, 46.96; H , 7.25. U N M R (20 °C, l  2  2  C D C 1 ) : 8 0.0 (s, 12H, Si(C//j) ), 2.38 (s, 4 H , S i C / / C l ) , 6.20 and 6.59 (m, 4 H , Cp-//). 3  1 3  2  2  C { ! H } N M R (20 "C, CDCI3): -3.7 (Si(CH ) ), 30.2 (SiCFf Cl), 100.5 ( C ( S i ( C H ) C H ) ) , 3  2  2  3  2  2  2  132.2 (Cp), 134.5 (Cp).  M e  [P Cp]Li 2  A solution of C 5 H 4 ( S i M e C H C l ) (4.88 g, 17.4 mmol) dissolved in a mixture of 10 raL 2  2  2  of toluene and 60 mL of T H F was added dropwise to a heated (50 °C) stirring solution of L i P M e (3.56 g, 52.4 mmol) dissolved in 60 mL of THF. 2  The green colour of the phosphide  solution was immediately discharged upon addition of the last drops, and shortly afterward turned pink. The reaction mixture was immediately removed from the heating bath, cooled to room temperature, and the solvent removed under vacuum. The red oily residue was extracted with hexanes and filtered, and the solvent removed to yield a viscous pink gel. Yield: (5.50 g, 94 %).  l H NMR  (20 °C, C D ) : 8 0.42 (s, 12H, Si(CH ) ), 6  S i C / / P ) , 0.73 (s, 12H, 2  H). 31p NMR  6  3  P(CH ) ), 6.46 (t, 1H, 4 / 3  2  H H  2  0.51 and 1.02 (d, 2H, 7 H = 8Hz, 2  H  = 1Hz, Cp-//), 6.53 (d, 2H, 4 /  H H  = 1Hz, Cp-  (20 "C, C D ) : 8 -54.0 (s). 6  6  Pr[P Cp]Li 2  The procedure followed was as above, adding C 5 H 4 ( S i M e C H C l ) (5.00 g, 17.8 mmol) 2  to a heated (65 °C) solution of L i P P r  J 2  2  2  (6.66 g, 53.6 mmol). A white solid was obtained from a  cold (-40 "C) saturated hexanes solution.  Yield: (6.78 g, 84 %).  Anal. Calcd. for  C 3 H L i P S i : C, 61.57; H , 10.56. Found: C, 61.54; H , 10.77. U N M R  (20 °C, C D ) : 8  l  2  4 7  2  2  65  references  6  b e g i n o n p a g e 75  6  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  0.49 (d, 2H, 2 /  = 4Hz, SiC# P), 0.52 (s, 12H, Si(C#j) ), 0.91 (m, 24H, C H ( C / / j ) ) , 1.60  PH  2  2  (sept, 4H, 7 H = 7Hz, C / / ( C H ) ) , 6.51 (t, I H , / H 3  4  H  Cp-//)-  3 1  3  P NMR  2  H  (20 °C, C D ) : 8 0.2 (quartet, l / 6  6  L i P  2  = 1Hz, Cp-H), 6.56 (d, 2H, 7 H = 1Hz, 4  H  = 55Hz).  1 3  C { U} NMR  (20 °C, C D ) : 8  l  6  6  -0.6 (Si(CH ) ), 8.1 (SiCH P), 19.7 and 23.8 (CH(CH ) ), 114.5 (CH(CH ) ), 115.8 and 117.8 3  Cp),  2  2  3  2  3  2  137.4 (CpSi).  B u  [P Cp]Li 2  The procedure followed was again as above, adding C 5 r L t ( S i M e C H C l ) (3.31 g, 11.8 2  2  2  mmol) to a heated (65 °C) solution of L i P B u ^ (5.40 g, 35.5 mmol). A white crystalline solid was obtained from a cold (-40 "C) saturated hexanes solution. Yield: (4.60 g, 77 %). Anal. Calcd. for C H L i P S i : C, 64.24; H , 10.98. Found: C, 64.33; H , 11.03. U N M R (20 °C, l  2 7  5 5  2  2  C D ) : 8 0.38 (s, 12H, Si(C//j) ), 0.86 and 0.91 (d, 18H, V 6  4  6  2  7 H = 1Hz, Cp-H), 6.44 (d, 2H, H  4  7 H = 1Hz, Cp-H). H  3 1  P NMR  P  = 8Hz, C ( C / / ) ) , 6.41 (t, I H ,  H  5  3  (20 "C, C D ) : 8 24.4 (quartet, 6  6  i/LiP = 48Hz).  2.7.3.2  P r  [ P C p ] H f C I (2). 2  3  100 mL of toluene was added to an intimate mixture of [P Cp]Li (1.82 g, 4.06 mmol) and 2  HfCl4-(THT) (2.02 g, 4.08 mmol) at 0 "C. 2  The mixture was heated to 65 °C and stirred at that  temperature for 24 h, during which the yellowish colour of the ligand gradually diminished to give a pale buff yellow solution. The solution was filtered and the solvent reduced to with 10 mL,  from which pale yellow crystals were obtained at -78 "C. The crystals were washed with  cold hexanes and dried. Yield: (1.99 g, 67 %). Anal. Calcd. for C H C l H f P S i : C, 38.02; 2 3  4 7  3  2  2  H, 6.52. Found: C, 38.40; H , 6.70. In solution, 2 exists as an equilibrium mixture consisting of two complexes of the same formula.  66  references  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  isomer 2: H N M R (-40 °C, C D ) : 5 0.12 and 0.38 (s, 6H, Si(C//j) ), 0.84 (dd, l  7  8  2  4H, 7 H = 6Hz, 7 p = 4Hz, SiC// P), 0.99 and 1.34 (m, 12H, CH(C//j)2), 2.15 and 2.77 (sept., 2  2  H  H  2H, 3 j 3 1  2  = 7Hz, C//(CH ) ), 6.51 (d, 2H, 7 H = 1Hz, Cp-//), 7.18 (t, 1H, 7 H = 1Hz, Cp-H). 4  H H  3  4  2  H  H  P N M R (-40 °C, C D ) : 8 14.9 (s). 7  8  isomer 2': H N M R (-40 °C, C D ) : 8 0.08, 0.30, 0.68 and 0.71 (s, 3H, l  7  8  Si(C// ) ), 1.08 and 1.17 (m, 12H, CHfCZ/jk), 1.52 and 1.84 (m, 2H, C Z / f C H ^ ) , 6.62, 6.66 and 5  2  7.12 (m, 1H, Cp-//).  2.7.3.3  P r  3 1  P N M R (-40 "C, C D ) : 8 -4.9 and 24.9 (br s). 7  [P Cp]Zr(CH Ph) 2  2  8  (3).  3  A solution of M g ( C H P h ) ( T H F ) (82 mg, 0.23 mmol) in 10 mL of toluene was added 2  2  2  dropwise over a period of 15 minutes to a cooled (-78 °C) stirring solution of 1 (100 mg, 0.16 mmol) dissolved in 60 mL of toluene. The colour of the solution immediately changed from pale yellow to orange. The solution was allowed to slowly warm to room temperature, the volatiles were then removed under vacuum and the residue extracted with hexanes and filtered. Removal of the solvent under vacuum yielded a hydrocarbon soluble yellowish oil. *H N M R (20 °C, C D ): 6  8  6  0.36 (s, 12H, Si(C7/j)2), 0.58 (d, 4H,  2  1.53 (d of sept, 4H, 4  J  H  2  J  H  H  = 7Hz,  = 2Hz, Cp-H), 6.68 (d, 6H,  H  (t, 1H,  3  J  H  3  2  J  P  J H H  P  = 4Hz, SiC// P), 0.96 (m, 24H, CH(C//j) ), 2  H  = 3Hz, CH(CHjh),  H  2  1.91 (s, 6H, C / / P h ) , 6.40 (d, 2H, 2  = 7Hz, o - C H ) , 6.93 (t, 3H, 6  = 2Hz, Cp-H), 7.11 (t, 6H,  H  J  3  J H H  3  5  = 7Hz, m - C H ) . 6  5  3 1  J  H  H  = 7Hz, p - C H ) , 6.96 6  5  P { H } N M R (20 °C, C D ) : 1  6  6  8  -5.2 (s). " C l ' H } N M R (20 "C, C D ) : 8 -0.2 and -0.1 (s, S i ( C H ) ) , 7.7 (d, U P C = 40Hz, 6  6  3  2  SiCH P), 18.7, 19.1, 19.6 and 20.0 (s, C H ( C H ) ) , 24.9 and 25.2 (d, ijpc = 17Hz, C^(CH3>2), 2  3  2  69.2 (s, CH Ph), 123.4 (s, Cp), 123.6 (s, Cp), 128.9 (s, o - C H ) , 129.8 (s, m - C H ) , 144.9 (s, p2  6  5  6  5  C H ). 6  5  67  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  P«-[P Cp]Hf(CH Ph)3 (4)  2.7.3.4  2  2  A solution of KCH2Ph (19 mg, 0.24 mmol) in 30 mL of toluene was added dropwise over a period of 20 minutes to a cooled (-78 °C) stirring solution of 2 (156 mg, 0.24 mmol) dissolved in 60 mL of toluene. The solution was allowed to slowly warm to room temperature and stirred for 12 h, during which the colourless H f solution gradually turned bright yellow. The volatiles were then removed under vacuum and the residue extracted with hexanes and filtered. Removal of the solvent under vacuum yielded a hydrocarbon soluble yellowish oil. * H N M R (20 °C, C D ) : 8 0.34 (s, 12H, Si(C//j) ), 0.56 (d, 4H, J 2  6  6  2  P H  = 5Hz, S i C / / P ) , 0.95 (m, 24H, Ck\{CH ) ), 2  3  1.50 (sept, 4H, J H = 7Hz, C / / ( C H ) ) , 1.90 (s, 6H, Ctf Ph), 6.28 (d, 2H, J 2  4  H  6.69 (t, I H , 3 j  H H  3  2  = 2Hz, Cp-H), 6.78 (d, 6H, 3 j  C H ) , 7.17 (t, 6H, 3 j 6  2  5  H H  H H  H H  = 2Hz, Cp-H),  = 7Hz, o - C H ) , 6.87 (t, 3H, 3 j 6  2  5  H H  = 7Hz, p-  = 7Hz, m - C H ) . 31p{lH} N M R (20 "C, C D ) : 5 -5.6 (s). " C p H } 6  5  6  6  N M R (20 °C, C D ) : 8 -0.2 and 0.2 (s, Si(CH ) ), 8.1 (d, 'Jpc = 35Hz, SiCH P), 16.5, 17.2, 17.4 6  6  3  2  2  and 18.0 (s, C H ( C H ) ) , 26.0 and 26.4 (d, 'Jpc = 15Hz, C # ( C H ) ) , 70.1 (s, CH Ph), 121.6 (s, 3  2  3  2  2  Cp), 130.1 (s, o - C H ) , 131.7 (s, m - C H ) , 140.9 (s, p - C H ) . 6  2.7.3.5  P r  5  6  5  6  5  [ P C p ] Z r ( C H C M e ) 3 (5a) 2  3  2  A solution of L i C H C M e (56 mg, 0.72 mmol) in 30 mL of toluene was added dropwise 2  3  to a cooled (-78 "C) stirring solution of 1 (154 mg, 0.24 mmol) dissolved in 60 mL of toluene. The colour of the solution immediately turned bright yellow upon addition. The mixture was warmed to room temperature, and stirring was continued for 30 minutes. The solvent was then removed in vacuo, and the oily residue extracted with hexanes and filtered. The filtrate was reduced under vacuum to give 5a as a bright yellow oil which remained soluble in pentane even at -40 °C, precluding the isolation of crystalline material. Yield: (130 mg, 72 %). H N M R (20 l  °C, C D ) : 8 0.48 and 0.49 (s, 6H, Si(CH ) ), 6  6  3  2  68  0.70 (dd, 4H, 7 H = 6Hz, 7 2  2  H  references  P H  = 4Hz, SiCtf P),  b e g i n on p a g e 75  2  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  0.99 (m, 24H, CH(CH ) ),  1.21 (s, 6H, C / / C ( C H ) ) , 1.22 (s, 27H, C H C ( C / 7 ) ) , 1.55 (m, 4H,  3 2  2  3  3  2  5  3  CH(CU )2), 6.68 (d, 2H, 7 H = 1Hz, Cp-H), 6.94 (t, 1Hz, 7 H = 1H, Cp-H). 3lp N M R (20 °C, 4  4  3  H  H  C D ):5-5.5(s). 6  6  2.7.3.6  Pr  [ P C p ] Z r ( C H S i M e 3 ) 3 (5b) 2  2  A solution of L i C H S i M e (82 mg, 0.87 mmol) in 30 mL of toluene was added dropwise 2  3  to a cooled (-78 °C) stirring solution of 1 (185 mg, 0.29 mmol) dissolved in 60 mL of toluene. The mixture was warmed to room temperature and left to stir for 2 h, during which the colour of the solution slowly turned pale yellow. The solvent was then removed in vacuo, and the oily residue extracted with hexanes and filtered. The filtrate was reduced under vacuum to give a pale yellow, hydrocarbon-soluble oil. Yield: (176 mg, 76 %). K N M R (20 °C, C D ) : 8 0.28 (s, l  6  6  27H, C H S i ( C # 3 ) ) , 0.29 and 0.45 (s, 6H, Si(C77 ) ), 0.32 and 0.63 (d, 2H, 7 H = 6Hz, 2  2  3  5  2  H  SiC77 P), 0.68 (s, 6H, C/7 Si(CH ) ), 1.00 (m, 24H, CH(C//j) ), 1.59 (m, 4H, C # ( C H ) ) , 6.74 2  2  3  3  2  (d, 2H, 7 H = 2Hz, Cp-H), 6.91 (t, 1H, 7 H = 2Hz, CpH)4  4  H  2.7.3.7  H  Pr  [  P  2  C  p  ]  Z  r  (  C  H  3  )  3  (  6  3 1  3  2  P N M R (20 °C, C D ) : 8 -5.9 (s). 6  6  )  A solution of 1.4 M MeMgBr (3.91 mL, 5.47 mmol) was diluted in 310 mL of toluene and added dropwise to a cooled (-78 °C) stirring solution of 1 (1.00 g, 1.56 mmol) dissolved in 50 mL of toluene. The pale yellow solution gradually turned pale yellow over the course of the addition. The solution was warmed to room temperature, covered with metal foil, and stirred for 12 h, after which the solvent was removed under vacuum and the residue extracted with hexanes and filtered. Removal of the solvent under vacuum yielded approximately 0.6 g of trimethyl 5 as a slightly impure (impurities total less than 5% by  3 1  P N M R spectroscopy) yellowish oil . H A  N M R (20 "C, C D ) : 8 0.37 (s, 12H, Si(C#?) ), 0.54 (t, 9H, 7 3  6  6  2  P H  = 2Hz, ZrCZ/j), 0.70 (d, 4H,  2/PH = 7Hz, SiC/7 P), 1.00 (m, 24H, C H ( C / / ) ) , 1.62 (d of sept, 4H, 7 3  2  5  69  2  = 7Hz, 7 2  H H  P H  = 3Hz,  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  C//(CH )2), 6.42 (t, I H , 7 H = 2Hz, Cp-//), 6.71 (d, 2H, 7 4  3  4  H  (20 °C, C D ) : 8 -0.6 (d, 7  = 5Hz, Si(CH ) ), -0.2 (d, 7  3  6  6  3  P C  3  24Hz, S i C H P ) , 19.2 and 19.6 (d, 7 42.7 (t, 7  P C  = 2Hz, Cp-//). ^ C ^ H } N M R  = 4Hz, Si(CH ) ), 10.3 (d, 1 / 3  = 8Hz, C H ( C H ) ) , 25.7 (d, J  2  2  2  H H  l  P C  3  2  PC  = 3Hz, ZrCH ), 121.5 (Cp), 121.9 (d, Cp), 125.35 (d, 7  2  3  P C  =  P C  = 8Hz, C H ( C H ) ) , 3  = 4Hz, Cp).  3  P C  2  3 1  2  P{ H} 1  N M R (20 °C, C D ) : 8 2.3 (s). 6  2.7.3.8  P r  6  [ P C p ] Z r C l ( C H C M e ) (7a) 2  2  2  3  A solution of L i C H C M e (19 mg, 0.24 mmol) in 30 mL of toluene was added dropwise 2  3  over a period of 20 minutes to a cooled (-78 °C) stirring solution of 1 (156 mg, 0.24 mmol) dissolved in 50 mL of toluene. The colour of the solution gradually changed from pale to bright yellow. The solution was stirred at -78"C to 0°C for another 30 minutes, and then allowed to warm slowly to room temperature. The solvent was then removed in vacuo, and the oily residue extracted with hexanes and filtered. The filtrate was reduced to yield 0.87 g of a slightly impure (by *H and  3 1  P N M R spectroscopy) yellow oil consisting of 7a as the main (>90%) product. ! H  N M R (20 °C, C D ) : 8 0.26 and 0.36 (s, 6H, Si(C//j) ), 0.70 (dd, 4H, 7 H = 6Hz, 7 2  6  6  2  2  S i C / / P ) , 1.00 (m, 24H, C H ( C / / ) ) , 1.20 (d, 2H, 7  H  3  2  5  2  P H  P H  = 7Hz,  = 7Hz, C / / C ( C H ) ) , 1.47 (s, 9H, 2  3  3  C H C ( C / / j ) ) , 1.52 (m, 4H, C/7(CH ) ), 1.68 (s, 2H, C / / C ( C H ) ) , 6.54 (t, I H , 7 H = 1Hz, 4  2  3  3  2  2  3  3  H  Cp-//), 6.98 (d, 2H, 7 H = 1Hz, Cp-H). *P N M R (20 "C, C D ) : 8 0.7 (very br) (isomer 1 4  3  H  6  6  75%); -6.8 and 8.7 (br s) (isomer 2 - 25%).  2.7.3.9  P r  [ P C p ] Z r C l ( C H S i M e ) (7b) 2  2  2  3  A solution of L i C H S i M e (27 mg, 0.29 mmol) in 30 mL of toluene was added dropwise 2  3  over a period of 20 minutes to a cooled (-78 °C) stirring solution of 1 (185 mg, 0.29 mmol) dissolved in 50 mL of toluene. The solution was allowed to warm slowly to room temperature and stirred for another 2 h, during which the pale yellow solution brightened somewhat. The 70  references  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  solvent was then removed in vacuo, and the oily residue extracted with hexanes and filtered. The solvent was removed under vacuum to yield 0.90 g of a slightly impure (by *H and  P NMR  3 l  spectroscopy) yellow oil consisting of 7b as the main (>85%) product. *H N M R (20 °C,  CQDG):  5 0.31 (s, 9H, CH Si(C//3) ), 0.38 and 0.50 (s, 6H, Si(C//j) ), 0.69 (s, 2H, C7/ Si(CH )3), 0.71 2  (dd, 4 H , 2 /  H H  3  = 6Hz, 2 /  CH(CH )2), 6.50 (t, IH, 4 / 3  2  P H  2  3  = 7Hz, SiC7/ P), 1.05 (m, 24H, C H ( C / / j ) ) , 1.61 (m, 4 H , 2  2  = 1Hz, Cp-H), 7.05 (d, 2H, 7 H H = 1Hz, Cp-H). 3 1 p N M R (20 °C, 4  H H  C D ) : 8 1.5 (very br) (isomer 1 - 85%); -6.5 and 9.0 (br s) (isomer 2 - 15%). 6  6  2.7.3.10  P r  [ P C p ] Z r C l ( C H ) (8) 2  2  3  A solution of 1.4 M M e L i (0.54 mL, 0.76 mmol) was diluted in 10 mL of ether and added dropwise to a cooled (-78 "C) stirring solution of 1 (481 mg, 0.75 mmol) dissolved in 40 mL of toluene. The solution turned yellow during the course of the addition. The reaction mixture was then warmed to room temperature, covered with metal foil, and stirred for 2 h. The solvent was subsequently removed in vacuo, the oily residue extracted with a toluene/hexanes mixture, and filtered. The filtrate was reduced under vacuum to yield 0.39 g of a slightly impure (by *H and 31p N M R spectroscopy) yellow oil consisting of 8 as the main (>85%) product. This material slowly decomposed over a period of weeks at (-78 "C) to give the starting trichloride 1 and a variety of unidentified products. Si(Cffj)2), 0 -  5 6  and 0.62 (dd, 2H, 2 /  !  H N M R (20 "C, C6D6): 5 0.21 and 0.26 (s, 6H,  = 3Hz, 7 2  H H  P H  = 6Hz, SiCtf P), 0.91 (m, 24H, CH(C//j) ), 2  2  1.01 (br, 3H, ZrCT/j), 1.50 (m, 4H, C / / ( C H ) ) , 1.51 (6.71 (d, 2H, 3 7 3  I H , 7 H = 2Hz, Cp-H). 4  H  3 1  2  H H  = 1Hz, Cp-H), 6.75 (t,  P N M R (20 "C, C D ) : 5 1.3 (very br) (isomer 1 - 90%); -7.4 and 8.6 6  6  (br s) (isomer 2 - 10%).  2.7.3.11  P r  [ P C p ] Z r C I ( C H C H ) (9) 2  2  2  3  71  r e f e r e n c e s b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  A solution of 3.0 M EtMgBr (0.12 mL, 0.36 mmol) was diluted in 10 mL of toluene and added dropwise over a period of 15 min to a cooled (-78 °C) stirring solution of 1 (225 mg, 0.35 mmol) dissolved in 50 mL of toluene. The solution turned bright yellow during the course of the addition. The reaction mixture was stirred at this temperature for 30 min, then warmed to room temperature and stirred for 6 h. The colour of the solution changed gradually from bright yellow to a dull reddish-brown. The solvent was removed in vacuo and the oily residue extracted with hexanes and filtered. The filtrate was reduced under vacuum to yield 0.17 g of a slightly impure (by H and A  3 1  P NMR  spectroscopy) dark red oil consisting of 9 as the main (>90%) product.  This material slowly decomposed over a period of weeks at (-78 °C) to give the starting trichloride 1 and a variety of unidentified products. near coalescence at room temperature. 2  H and P { H } NMR 3 1  H N M R (60 "C, C6D6): 5 0.3 and 0.4 (br, 6H,  2  3 2  1.8 (br, 4H, C7/(CH ) ), 1.9 ( br quartet, 3  3H, C H C / / ) , 6.8 (br, 1H, Cp-H), 6.9 (br, 2H, Cp-H). 3lp{lpi} NMR 2  spectra of this are  1  l  Si(C7/ ) ), 0.9 (br, SiC# P), 1.1 (br, 24H, CH(CH ) ), 5  X  2  (20 °C, C D ) : 8 -5 and  3  6  6  11 (very br - near coalescence).  2.7.3.12  P q P i C p J Z r C ^ O B u * ) (10)  A solution of K O B u (39 mg, 0.35 mmol) in 10 mL of T H F was added dropwise with f  stirring to a cooled (-78 "C) solution of 1 (221 mg, 0.35 mmol) dissolved in 30 mL of THF.  The  pale yellow colour of the chloro complex gradually dissipated after the addition was complete. The solution was slowly warmed to room temperature and stirred for another 24 hours. The solvent was then removed in vacuo, and the residue extracted with hexanes and filtered to give a hydrocarbon-soluble yellowish-white oil, which slowly decomposed at (-78 °C) to give the starting trichloride 1 and a variety of unidentified products.  j  H NMR  5 0.28 and 0.39 (s, 6H, Si(C//. ) ), 0.62 and 0.72 (dd, 2H, / H 2  ?  2  H  (20 "C, 400 MHz,  = 7Hz, 7 2  P H  C6E»6)  = 6Hz, SiC7/ P),  0.98 (m, 24H, C H C C / ^ ) , 1.26 (s, 9H, OC(C//j) ), 1.61 (m, 4H, C7/(CH ) ), 6.71 (d, 2H, 3  72  3  references  :  2  b e g i n on p a g e 75  2  3  / H H  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  = 1Hz, Cp-H), 6.75 (t, I H , 7 H = 2Hz, Cp-H). 4  3 1  H  P N M R (20 "C, C D ) : 5 0.6 (br s) (isomer 1 6  6  95%); -7.8 and 8. (br s) (isomer 2 - 5%).  2.7.3.13  Pr[P Cp]ZrCI (CH Ph) (11) 2  2  2  A solution of KCH2Ph (115 mg, 0.8 mmol) in 30 mL of T H F was added dropwise to a cooled (-78 °C) stirring solution of 1 (156 mg, 0.24 mmol) dissolved in 60 mL of THF. The colourless solution immediately turned yellowish-orange. The mixture was allowed to warm to room temperature and then stirred for 2 h, during which the colour of the solution gradually turned red. The volatiles were then removed under vacuum and the residue extracted with hexanes and filtered.  Red crystals were obtained from slow evaporation of a concentrated  hexamethyldisiloxane solution. Anal. Calcd. for C2 H4 Cl2P2Si Zr: C, 56.43; H , 6.53. Found: 3  7  2  C, 55.45; H , 6.72. *H N M R (20 "C, C D ) : 5 0.22 (s, 12H, Si(C#j) ), 0.41 and 0.61 (d, 2H, 6  2  6  2  / p H = 4Hz, SiCZfeP), 0.98 (m, 24H, CH(C//j) ), 1.63 (m, 4H, CHQCHjk), 2.90 (s, 2H, C# Ph), 2  2  6.54 (d, 2H, / H H = 2Hz, Cp-H), 6.92 (t, I H , 3 / 4  Cp-H), 7.32 (t, 2H, 3 7  H H  = 7Hz, P-C5H5), 6.95 (t, I H , 7 H = 2Hz, 4  H H  H  = 7Hz, m-C H ), 7.55 (d, I H , 3 7 H = 7Hz, o - C H ) . 31p{lH} N M R (6  5  H  20 "C, C D ) : 6 -6.9 (s), 14.2 (s); (20 "C, C D ) : 5 5.8 (s). 7  8  7  (d, 7 p = 4Hz, Si(CH ) ), -0.3 (d, 3 7 3  C  3  2  PC  8  6  1 3  5  c { l H } N M R (20 "C, C D ) : 8 -1.2 7  8  = 6Hz, Si(CH )2), 9.8 (br, SiCH P), 18.4, 19.1, 19.3 and 3  2  19.5 ( C H ( C H ) ) , 25.5 (d, ^ P C = 7Hz,CH(CH ) ), 25.9 (d, ^ P C = 5Hz, C H ( C H ) ) , 75.7 (t, 3  2  7  2  3  2  3  2  = 9Hz, CH Ph), 121.6 (s, Cp), 123.5 (s, Cp), 126.1 (s, Cp), 127.9 (s, o - C H ) , 130.3 (s, m-  P C  2  6  5  C H ) , 146.8 (s, p - C H ) . 6  5  6  2.7.3.14  Pr  5  [ P C p ] H f C l ( C H P h ) (12) 2  2  2  A solution of KCH2PI1 (115 mg, 0.8 mmol) in 30 mL of T H F was added dropwise to a cooled (-78 °C) stirring solution of 2 (156 mg, 0.24 mmol) dissolved in 60 mL of THF. The colourless H f solution gradually turned yellowish-orange. The mixture was allowed to warm to 73  references  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of..  room temperature and then stirred for 12 h. The volatiles were then removed under vacuum and the residue extracted with hexanes and filtered. Removal of the solvent under vacuum yielded a yellowish oil, soluble in pentane. 0.60 (d, 2H, 2 /  P H  6  2  3  = 2Hz, Cp-H), 6.74 (t, 1H, J  = 1Hz, Cp-H),  4  H  H  = 7Hz, P-C6H5), 7.23 (t, 2H, / 3  H  H  H  H  = 7Hz, m - C H ) , 7.42 (d, 1H, 3 j 6  0.24 and  2  1.55 (m, 4H, C t f f C H ^ ) , 2.42 (s,  3 2  4  2  31P{1H}  6  = 5Hz, S i C / / P ) , 0.91 (m, 24H, CU(CH ) ),  2H, C # P h ) , 6.38 (d, 1H, y 3/HH  H N M R (20 "C, C D ) : 8 0.02 (s, 12H, Si(CH ) ),  J  5  6.79 (t, 1H,  = 7Hz, o-QHs).  H H  N M R (-20 °C, C D ) : 8 0 and 19 (very br). 7  2.7.3.15  Pr  8  [ P C p ] Z r C l ( r i - C ( 0 ) C H P h ) (13) 2  2  2  2  A solution of 11 (170 mg, 0.24 mmol) in 30 mL of toluene was placed in a 200 mL bomb and affixed to a dual vacuum/nitrogen line. A small portion of solvent was removed under vacuum, and an atmosphere of carbon monoxide introduced at -30 °C. The reaction mixture was warmed to room temperature and left to stir for 2 h, during which the red colour of the solution gradually changed to a pale orange-yellow. The solvent was reduced to 3 mL, and from this saturated solution pale yellow prisms were obtained.  The crystals were washed with cold  hexanes and dried. Yield 138 mg (78 %). Anal. Calcd. for C i H 4 C l 2 0 P S i 2 Z r : C, 51.50; H , 3  5  2  7.53. Found: C, 51.53; H , 7.55. isomer 1 (55%): YL N M R (20 "C, 400 MHz, C D ) : 8 0.13 and 0.36 (s, 6H, SKCtfjfe), l  6  0.84 (dd, 4H, 2 /  = 6Hz, 7  = 4Hz, SiCff P). 1-03 (m, 24H, CH(CH ) ),  2  HH  P H  2  2H, Ctf(CH ) ), 3.02 (dd, 1H, 2y 3  2  HH  = 16Hz, 3 /  3/PH = 35Hz, CtfflHPh), 6.63 (dd, 1H, 3 / (dd, 1H, 3 /  6  1.60 and 1.81 (m,  3 2  PH  = 3Hz, CH UPh), A  3.82 (dd, 1H, 27  = 16Hz,  = 2Hz, Cp-H), 6.87 (t, 1 H , 7 H = 2Hz, Cp-H), 7.46 4  H H  H  = 2Hz, Cp-H), 7.10 and 7.56 (m, 5H, overlapping phenyl resonances).  H H  HH  3 1  P NMR  (20 °C, C D ) : 8 -5.1 (s), 44.4 (s). 6  6  isomer 2 (45%): *H N M R (20 "C, 400 MHz, C D ) : 8 0.09 and 0.23 (s, 6H, SiiCHfo), 6  0.52 (dd, 4H, 7 2  = 6Hz, / 2  H H  P  H  6  = l()Hz, S i C / / P ) , 1.03 (m, 24H, CH(CH ) ), 2  74  3 2  references  1.50 (m, 4H,  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  C//(CH )2), 2.95 (dd, I H , 7 H = 16Hz, 7 2  3  3  7  3  H  P H  = 2Hz, CH B?h), A  3.89 (dd, I H , 7 H = 16Hz, 2  H  = 35Hz, C / / H P h ) , 6.63 (dd, IH, 7 H = 2Hz, Cp-H), 6.74 (t, IH, 7 H = 2Hz, Cp-H), 7.26 3  P H  5  4  H  H  (dd, I H , 7 H H = 2Hz, Cp-H), 7.10 and 7.56 (m, 5H, overlapping phenyl resonances). 3  3 1  P NMR  (20 "C, C D ) : 8 -5.4 (s), 45.9 (s). 6  6  2.8  References  (1)  M u , Y . ; Piers, W . E . ; MacQuarrie, D . C ; Zaworotko, M . J.; V G Young, J.  Organometallics 1996,15, 2720. (2)  Fryzuk, M . D.; Mao, S. S. H.; Duval, P. B.; Rettig, S. J. Polyhedron 1995,14, 11.  (3)  Plooy, K . E . ; M o l l , U . ; Wocadlo, S.; Massa, W.; Okuda, J. Organometallics  1995,14,  3129. (4)  Cotton, F. A . ; Wilkinson, G . Advanced Inorganic Chemistry; 5th ed.; John Wiley &  Sons: Toronto, 1988. (5)  Comprehensive Organometallic Chemistry II; Wilkinson, G.; Stone, F. G . A . ; Abel, E .  W., Ed.; Pergamon Press: Oxford, 1995. (6)  Lund, E. C ; Livinghouse, T. Organometallics 1990, 9, 2426.  (7)  Erker, G.; Sarter, C ; Albrecht, M . ; Dehnicke, S.; Kriiger, C ; Raabe, E.; Schlund, R.;  Benn, R ; Rufinska, A . ; Mynott, R. 7. Organomet. Chem, 1990, 382, 89. (8)  Zeijden, A . A . H . v. d.; Mattheis, C ; Frohlich, R.; Zippel, F. Inorg. Chem. 1997, 36,  4444. (9)  Mu, Y . ; Piers, W . E.; MacGillivray, L . R.; Zaworotko, M . J. Polyhedron 1995,14, 1.  75  references  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  (10)  Crowther, D. J.; Jordan, R. F.; Baenziger, N . C ; Verma, A . Organometallics 1990, 9,  2574. (11)  Winter, C. H.; Zhou, X . - X . ; Dobbs, D. A.; Heeg, M . J. Organometallics 1991,10, 210.  (12)  Jutzi, P.; Kleimeier, J. J. Organomet. Chem, 1995, 486, 287.  (13)  Engelhardt, L . M . ; Papasergio, R. I.; Raston, C. L.; White, A . H . Organometallics 1984,  3, 18. (14)  Prout, K.; Cameron, T. S.; Forder, R. A.; Critchley, S. R.; Denton, B.; Rees, G . V . Acta  Crystallogr. 1974, B30, 2290. (15)  Bondi, A. J. Phys. Chem, 1964, 68, 441.  (16)  Hore, P. J. Nuclear Magnetic Resonance; Oxford University Press: Oxford, 1995.  (17)  Sanders, J. K . M . ; Hunter, B. K. Modem NMR Spectroscopy; 2nd ed.; Oxford University  Press: Oxford, 1993. (18)  Rogers, R. D.; Bynum, R. V.; Atwood, J. L. J. Am, Chem. Soc. 1978,100, 5238.  (19)  Rogers, R. D.; Bynum, R. V.; Atwood, J. L. J. Am. Chem. Soc. 1981,103, 692.  (20)  Martin, A.; Mena, M . ; Palacios, F. J:Organomet. Chem. 1994, 480, C10.  (21)  Berthold, H. J.; Groh, G. Angew. Chem,, Int. Ed. Engl, 1966, 5, 516.  (22)  Wolczanski, P. T.; Bercaw, J. E. Organometallics 1982,1, 793.  (23)  Legzdins, P.; Jones, R . H . ; Phillips, E . C . ; Yee, V.C.;  Trotter, J.; Einstein, F.W.B.  Organometallics 1991,10, 986. (24)  Brookhart, M . ; Green, M . L. H.; Wong, L. L . Prog. Inorg. Chem, 1988, 36, 1.  76  references  b e g i n o n p a g e 75  C h a p t e r 2: H a l i d e a n d A l k y l C o m p l e x e s of...  (25)  Wengrovius, J. H.; Schock, R. R. J. Organomet. Chem. 1981, 205, 319.  (26)  Roddick, D . M . ; Santarsiero, B. D.; Bercaw, J. E. J. Am. Chem. Soc. 1985, 707,4670.  (27)  Arnold, J.; Tilley, T. D.; Rheingold, A . L . ; Geib, S. J.; Arif, A . M . J. Am. Chem, Soc.  1989,777,149. (28)  Fryzuk, M . D . ; Mylvaganum, M . ; Zaworotko, M . J.; MacGillivray, L . R.  Organometallics 1996, 75, 1134. (29)  Crab tree, R. H . The Organometallic Chemistry of the Transition Metals; 2nd ed.; John  Wiley & Sons: USA, (30)  1994, pp 487.  Fachinetti, G . ; Floriani, C.; Marchetti, F.; Merlino, S. J. Chem, Soc, Chem. Commun.  1976, 552. (31)  Williams, D. H . ; Fleming, I. Spectroscopic Methods in Organic Chemistry; 4th ed.;  McGraw-Hill: London, 1989. (32)  Erker, G. Acc Chem, Res. 1984, 77, 103.  (33)  Tatsumi, K.; Nakumura, A.; Hofmann, P.; Stauffert, P.; Hoffmann, R. J. Am. Chem. Soc.  1985, 707, 4440. (34)  Manzer, L . E. Inorg. Synth, 1982, 27, 137.  (35)  King, R. B . ; Stone, F. G. A . Inorg. Synth. 1963, 7, 99.  (36)  Schlosser, M . ; Hartmann, J. Angew. Chem,, Int. Ed. Engl, 1973, 72, 508.  (37)  Schrock, R. R.; Fellman, J. D. J. Am, Chem, Soc 1978,100, 3359.  (38)  Schrock, R. R. J. Organomet. Chem, 1976, 722, 209.  77  r e f e r e n c e s b e g i n o n p a g e 75  Chapter 3  Zirconium and Hafnium Alkylidene Complexes: Mechanism of Formation and Reactivity  3.1  Introduction The previous chapter surveyed the synthesis and solution structure of a series of mono-  and tri-substituted alkyl complexes of Zr and Hf coordinated by the ancillary P2Cp ligand. The trialkyl derivatives were found to possess considerable thermal stability in comparison to the monoalkyl species, which were prone to disproportionate over time. Fluxional coordination of the side-arm phosphine was seen to be a prevalent trait in several of these complexes. In this chapter the focus shifts to the solution dynamics and thermal reactivity of the dialkyl complexes. The conversion of these species to rare Zr and Hf alkylidene merits special attention, so the composite mechanism involved in this high yield reaction will be investigated, with an emphasis towards evaluating the role of the ancillary ligand. The extension of this mechanism to the formation of other alkylidene derivatives will also be tested. The reactivity of the resulting alkylidene complexes will also be explored. If the sidearm phosphines are an integral factor in the stability of these complexes, they nevertheless allow controlled reactivity at the metal centre by virtue of their labile coordination, which provides an open site for substrate activation to occur. However, it is evident that slower reaction rates are  78  references begin on page 141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m  Alkylidene...  observed in comparison to other alkylidene derivatives, and the steric bulk of the ligand also limits the size of reactants that can access the metal.  3.2.1  NMR  spectroscopic identification of  P r  [P2Cp]  ZrCI(CH Ph) 2  2  In the previous chapter the preparation of benzyl derivatives [P Cp]M(CH Ph)3 (3: M = 2  2  Zr, 4: M = Hf) and [P Cp]MCl2(CH Ph) (11: M = Zr, 12: M = Hf) were described. In contrast Pr  2  2  to these results, treating the starting trichloride complex 1 or 2 with 2 equivalents of K C H P h in 2  THF  (or 1 equiv of M g ( C H P h ) ( T H F ) in toluene) does not give the anticipated dibenzyl 2  2  2  complex [ P C p ] M C l ( C H P h ) (14: M = Zr, 15: M = Hf) as the sole product, but instead yields Pr  2  2  2  a thermally and photochemically labile greenish-orange oil consisting of a mixture of mono-, di-, and tri-benzyl species, which occur in a 5 : 4 : 5 ratio, respectively, at room temperature (equation 3.1):  p ._ ,.. [P Cp]MCI  2 KCHpPh -—  K rr  2  3  -2 KCI  1 M=Zr  2 M = Hf (3.1) Pr  [P Cp]MCI (CH Ph) 2  2  2  +  Pr  [P Cp]MCI(CH Ph) 2  2  2  +  Pr  [P Cp]M(CH Ph) 2  2  11 M= Zr  14 M= Zr  3 M= Zr  12 M = Hf  15 M = Hf  4 M = Hf  3  These are all observed together as products of this reaction as long as the stoichiometry of K C H P h reacted with 1 is greater than 1 equivalent and less than 3 equivalents, the relative 2  proportion of tribenzyl present in the mixture increasing with the amount of benzyl reagent used. Attempts to separate individual species from this mixture have repeatedly proved unsuccessful.  79  references  b e g i n on p a g e 141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . . .  The subsequent thermal and photochemical decomposition of this ensemble to produce the benzylidene complex ^[PaCplM^HPhCCl) (16: M = Zr, 17: M = Hf) will be discussed later. The following discussion will centre on the Zr system as it has been more extensively studied. Familiarity with the *H and P { H } N M R spectroscopic features of tribenzyl 3 and 3 1  1  monobenzyl 11 assists in the interpretion of the N M R spectra of the reaction mixture obtained in equation 3.1. The coexistence of all three species in solution generates a complicated *H N M R spectrum with some peaks overlapping, even when conducted on the 500 M H z instrument. This renders some of the resonances unassignable, although separating those peaks attributed to known 3 and 11 permits the identification of 14 from the remaining diagnostic resonances. Integration of the benzyl protons relative to those of the ancillary ligand supports the stoichiometry of 14 as the dibenzyl complex. In the complicated ^ C f ^ H ) N M R spectrum the benzylic carbon resonance for 14 can be identified at 71 ppm. A cursory examination of the ambient temperature P { * H } N M R spectrum of the 3 l  reaction mixture (Figure 3.1) suggests that only two species are present in solution, in approximately equal proportions. However, there is an additional pair of resonances that are almost completely broadened into the baseline, associated with 11 and resulting from the previously described fluxional process for this complex in Chapter 2, which is near coalescence at this temperature.  The reappearance of diagnostic peaks upon raising or lowering the  temperature from the coalescence point is in agreement with the V T behavior identified with this species. Therefore, of the two distinct singlets seen in the P { H} N M R spectrum in Figure 3.1, 31  l  one at -5.6 ppm is attributed to 3, leaving the other at 0.5 ppm assigned to 14. The singlet for 14 in the ambient temperature P { H } N M R spectrum at 0.5 ppm sharpens as the temperature is 3 1  1  elevated to 95 °C. Below room temperature, this peak gradually broadens as the temperature is lowered until it disappears into the baseline near -70 °C, beyond which a reappearance of new peaks is not observed down to the experimental temperature limit in C-jDg at -95 °C. These observations are consistent with fluxional coordination of the side-arm phosphines to the metal  80  r e f e r e n c e s b e g i n on p a g e 1 4 1  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . . .  centre, as previously noted with 11. However, the inability to detect resonances at any temperature below coalescence precluded a kinetic study of this process by line shape analysis.  (  S is  Figure 3.1  31  P{  16  NMR  14  12  10  benzylic (CHjPh)  -I—•—r—  ~i—•—ra a PPM  -6  -a  spectrum of the reaction mixture from  equation 3.1 in C 7 D 8 at 30 °C.  The  J  Arrows refer to presence of 11 in the spectrum.  protons of 14 also exhibit fluxional behavior in the *H  NMR  spectrum. This region of the spectrum is relatively unobscured, thus permitting a variable temperature study which is summarized below (Figure 3.2).  81  r e f e r e n c e s b e g i n on p a g e  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . . .  I  Figure 3.2  |  3  I  I  I  I  |  I  I  I  I  ppm  Variable temperature H NMR l  |  2  spectrum for [ P C p ] Z r C l ( C H P h ) (14) Pr  2  2  2  from 2-3 ppm in C7DR. At -40 °C the benzylic protons appear as a pair of unresolved multiplets centered near 2.45 ppm. As the temperature is raised to -10 °C these multiplets evolve into a doublet of doublets, which  82  r e f e r e n c e s b e g i n on p a g e  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .,  gradually converges to two broad singlets at 30 °C. Eventually these peaks coalesce as the temperature approaches 40 °C, and a further temperature increase gradually sharpens this singlet further. To account for these observations, it is apparent that in any structural configuration of 14 the benzyl ligands are chemically inequivalent, although these groups could exchange via a fluxional process involving dissociation of the pendant phosphine donors, as hinted at by the variable temperature NMR  3 1  P NMR  spectra mentioned above. Therefore, the low temperature *H  spectrum corresponding to the slow exchange limit shows two multiplets, one for each  benzyl group. As the temperature is raised the rate of ligand exchange gradually increases until it coincides with the NMR  time scale at coalescence, and eventually in the fast exchange limit of  this process a singlet is observed as an average of two chemical environments.  3.2.2  Equilibrium between [P Cp]ZrCl (CH Ph) (11), [P Cp]ZrCl(CH Ph) (14), and 2  2  2  2  2  2  [P Cp]Zr(CH Ph) (3) 2  2  3  Given that monobenzyl 11 and tribenzyl 3 are each isolable in high yield from reactions conducted under the appropriate stoichiometric conditions, it is interesting to note that dibenzyl 14 cannot be isolated. A possible explanation for the coexistence of all three alkyl derivatives from the reaction in equation 3.1 is that 14 could undergo some degree of ligand redistribution to form 3 and 11 (equation 3.2):  2  rr  [P Cp]ZrCI(CH Ph) 2  2  2  14  (3.2)  Pr, [P Cp]ZrCI (CH Ph) + [ P C p ] Z r ( C H P h ) rr  2  2  11  83  2  2  2  3  3  r e f e r e n c e s b e g i n on p a g e  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . ,  That the initial ratio of products remains constant indefinitely (i.e., the disproportionation of 14 does not continue to completion) suggests the reverse reaction of equation 3.2 must also occur, indicating that an equilibrium is established between these species in solution. In support of this hypothesis, combining solutions of tribenzyl 3 and monobenzyl 11 immediately shows the formation of dibenzyl 14, irrespective of the order of addition, to regenerate a mixture of all three compounds. Again, the ratio of species observed depends on the relative amounts of 3 and 11 initially added. Table 3.1 shows the equilibrium concentrations obtained from separate prepared solutions in which the initial proportions of 3 and 11 added together were varied. From the data below it is evident that these species are indeed in equilibrium (equation 3.3) with an equilibrium constant (K = [14] /[3][11]) equal to 0.7(1) at 25 °C. The estimated uncertainty in K is a 2  function of the imprecision in the integration measurements of the H N M R  spectra, as evaluated  A  from repetitive experiments.  Table 3.1  Equilibrium concentrations of [P2Cp]ZrCl2(CH Ph) (11), [ P C p ] Z r C l Pr  Pr  2  2  ( C H P h ) (14) and [P2Cp]Zr(CH Ph) (3) from mixed solutions at 295 K , Pr  2  2  2  3  and the equilibrium constant (K) calculated according to equation 3.3.  [11] (M)  [14] (M)  [3] (M)  K  0.55  0.12  0.04  0.7  0.23  0.10  0.07  0.6  0.15  0.11  0.17  0.7  0.04  0.07  0.17  0.7  84  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . . .  Pr, [P  Cp]ZrCI (CH Ph) + [P Cp]Zr(CH Ph) rr  2  2  2  2  2  3  3  2  rr  (3.3)  k!  k-i  [P Cp]ZrCI(CH Ph) 2  2  2  14  VT N M R experiments were conducted on sample mixtures to obtain thermodynamic information from the temperature-dependence of the equilibrium constant pertaining to equation 3.3. Precise integration measurements of the spectra obtained were hampered, however, by a combination of the fluxional behaviour of various species and by the temperature-induced migration of some resonances, leading to broadened and/or overlapping peaks at various temperatures. As a result, the van't Hoff plots obtained were subject to considerable uncertainty in the linear fits. Therefore, reproducible values for the thermodynamic parameters AH°, AS°, and AG° could not be calculated. However, the measurements are sufficiently reliable to be able to discern a small increase in the concentration of dibenzyl 14 relative to 3 and 11 as the temperature is increased over a wide (-65 "C to 60 °C) range. Therefore, a qualitative assessment of the thermodynamics in this reaction can be offered. The minimal temperature-dependence of the equilibrium constant apparent from the results suggests that the magnitude of AH° is fairly small, a positive value being inferred from the observed increase in K with temperature. Also, since the species on either side of equation 3.3 are equal in number and approximately similar in structure, one could argue that AS° is also relatively small. Overall, this would give a low value for AG° in this reaction, although admittedly there is a degree of uncertainty associated with the assumptions made in this analysis. A similar generalization can be made regarding the rates k i and k_i of this reversible reaction, as the peaks in the N M R spectra do not show appreciable line  85  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  broadening, even in the high temperature regime, indicating that the slow exchange limit is still maintained (i.e., rate constants are relatively small) Pr  [P Cp]ZrCI (CH Ph) + [P Cp]Zr(CH Ph) Pr  2  2  2  Pr  2  2  [P Cp]ZrCI(CH Ph) 2  2  2  3  2  14 Scheme 3.1  Proposed intermediate in the ligand exchange mechanism for the  equilibrium in equation 3.3.  The mechanism that interconverts monobenzyl 11 and tribenzyl 3 to 2 equivalents of dibenzyl 14 involves a mutual exchange of benzyl and chloro ligands. An intermediate is not  86  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  observed in this reaction, but a plausible candidate could be the binuclear adduct A shown in Scheme 3.1. There are two options for dissociation of the bridging ligands in complex A : path (a) regenerates 3 and 11, while path (b) leads to the formation of two equivalents of 14; both pathways are consistent with the reaction in equation 3.3. Since the equilibrium concentrations are established relatively quickly (within minutes), this places a lower limit on the exchange rates (k > 0.001 s" ), suggesting that the energy barrier to transition state A is fairly low in this system. 1  It should be stated at this point that both monomeric 14 and binuclear adduct A possess an identical stoichiometry of two benzyl ligands for each P C p group. The distinction that 2  identifies 14 as the observed equilibrium species in the N M R spectra instead of A , thereby designating the latter as an undetected intermediate, is made from the relative equilibrium concentrations shown in Table 3.1. This set of data is not in accord with a process involving binuclear A in direct equilibrium with tribenzyl 3 and monobenzyl 11 (i.e., in which path b in Scheme 3.1 is omitted).  The equilibrium constant calculated using this relationship (K =  [A]/[3][ll]), where the value for [A] determined by integration of the N M R spectra would equal one-half the value listed for 14 in Table 3.1, shows poor correlation between the separate sample mixtures. Further, if this equilibrium were in effect then high dilution of the reaction mixture should induce further disproportionation of A to restore the equilibrium, a feature that is not observed.  3.3.1  Synthesis and Structure of [P2Cp]M=CHPh(Cl) ( M = Z r , Hf) Pr  As briefly mentioned in section 3.3.2, thermolysis of a toluene solution of the equilibrium mixture consisting of tribenzyl 3, dibenzyl 14 and monobenzyl 11 produces the alkylidene  1  complex P i - ^ C p l M ^ H P h f C l ) (16: M = Zr, 17: M = Hf) in high yield (equation 3.5). The 2  conditions differ dramatically for each derivative: the reaction that forms 16 is complete within  87  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e ...  12 hours at 65 "C, while the Hf analogue 17 requires 6 days at 95 °C. Both species are thermally stable and can be isolated as moderately air- and moisture-sensitive crystals. 0.5 [ P C p ] M ( C H P h ) C I + 0.5 [ P C p ] M ( C H P h ) Pr  P r  2  2  2  2  2  3  11 k-i  Pr  [P Cp]M(CH Ph) CI 2  2  2  14  (3.4)  - PhMe  Pr,  16: M = Zr [P Cp]M=CHPh(CI) 2  17: M = Hf  These are the first examples of Zr and H f alkylidene complexes to be structurally characterized by X-ray diffraction. As with trichlorides 1 and 2, the molecular structures of 16 3  and 17 are nearly identical; the Hf example is depicted below (Figure 3.3), with bond distances and bond angles listed for both derivatives in Table 3.2 for comparison.  88  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . ,  C(I7)  C(IO)  Figure 3.3  Molecular structure of PTF^CpJHf^CHPKCl) (17); 33% probability thermal ellipsoids are shown. A l l hydrogen atoms other than the a-agostic hydrogen atom are omitted for clarity.  Table 3.2  Selected Bond Lengths (A) and Bond Angles (") for [P Cp]M=CHPh(Cl) Pr  2  (16: M = Zr, 17: M = Hf). The numbering scheme is identical for each. 16  17  16  17  M-Cl(l)  2.5418(13)  2.5068(11)  Cl(l)-M-P(l)  77.23(4)  75.90(4)  M-P(l)  2.8299(16)  2.8038(14)  Cl(l)-M-P(2)  76.35(4)  76.79(4)  M-P(2)  2.8425(17)  2.7986(13)  P(l)-M-P(2)  153.58(4)  152.68(4)  M-C(24)  2.024(4)  1.994(4)  Cl(l)-M-C(24)  110.11(11)  108.87(13)  C(24)-C(25)  1.456(5)  1.481(5)  M-C(24)-C(25) 169.2(3)  167.8(4)  M-Cp'  2.234  2.22  M-C(24)-H(48) 79.8(23)  71.6(17)  M-H(48)  2.07(4)  1.93(3)  89  r e f e r e n c e s b e g i n on p a g e 1 4 1  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  Once again, as in the trichloride derivatives, the bond lengths are slightly shorter for the corresponding Hf complex. The alkylidene unit in 17 is indicated by the very short Hf(l)-C(24) bond distance of 1.994(4) A .  For comparison, a typical H f - C single bond averages  approximately 2.3 A . The analogous Zr=C bond distance of 2.024(4) A is also considerably 4  short for that metal. A characteristic feature of unsaturated metal alkylidene complexes is an ocagostic C - H interaction to the metal; in 16 and 17, this interaction orients the alkylidene unit 5  such that the phenyl ring points toward the cyclopentadienyl portion of the ancillary ligand. For both alkylidene derivatives the position of the a-hydrogen atom was located and refined (for 17, this atom was refined with restraints). The short M---H  contact is indicative of an oc-agostic  bond, which is reflected in an open M - C - C p bond angle of nearly 170° for each complex. The a  phenyl ring is aligned perpendicular to the Cp ring, both to minimize steric interactions with the bulky isopropyl groups on the phosphines, and to maximize orbital overlap with the metal. The structure also has the alkylidene group pointed syn to the unique carbon atom of the cyclopentadienyl ring. The absence of an axial ligand in these alkylidenes (compensated somewhat by the agostic interaction in the direction of this open site) results in a modified geometry approaching that of a typical piano stool. Therefore the angular distortion of the equatorial bonds away from the Cp ring is increased in 17 relative to trichloride 2, and is particularly evident with the trans chloride and alkylidene ligands, where the C l - M - C bond angle is near 110". The decrease in the coordination number also is responsible for shorter bond lengths in comparison to 2. The NMR  spectroscopic data for the alkylidene complexes are consistent with the solid  state structure. A singlet is seen in the P { 'H} NMR 3 l  spectrum (18.8 ppm for 16, 23.4 ppm for  17) for a pair of equivalent metal-bound phosphines. Diagnostic of the alkylidene unit are the downfield resonances for both the oc-carbon atom (229.4 ppm in 16, 210 ppm in 17) and a hydrogen atom (8.08 ppm in 16, 7.33 ppm in 17) in the respective  1 3  C and *H N M R  spectra.  The small ^ C H value of 87 Hz determined for the Zr complex indicates a weakening of this C-H  90  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  bond as a result of the agostic interaction. In a NOEDIFF U NMR l  experiment, irradiation of the  unique Cp proton was observed to enhance the signal of the ortho protons of the phenyl ring in the H N M R 1  spectrum, but did not affect the alkylidene proton resonance.  In comparison,  irradiation of the signal corresponding to the two equivalent Cp protons yielded no change (enhancement) in any of the peaks associated with the alkylidene group. These results signify both that the stereochemical preference observed in the solid state is maintained in solution, and that the agostic interaction is also unbroken, with no sign of rotation about the Zr=C bond axis.  3.3.2  Mechanistic studies of the formation of [ P C p ] Z r = C H P h ( C l ) (16) Pr  2  The  unusual transformation of this mixture of benzyl species to produce alkylidene 16  prompted an investigation of the reaction mechanism employed, especially given the stark contrast between the paucity of Group 4 alkylidene complexes in comparison to the number of 6  examples known for Group 5.  5  This difference has been attributed to the mechanism by which  these complexes are formed, whereby a sterically congested precursor decomposes via a thermally induced a-abstraction reaction involving two presumably cis alkyl ligands (Scheme 3.2). For Group 5 this arrangement can be satisfactorily met either with bulky homoleptic alkyl 7  complexes like Ta(CH2CMe3)5  1  or similar derivatives such as Cp*TaCl2(CH2CMe )2.  8  3  Conversely, the analogous group 4 complexes contain at least one less alkyl ligand and hence are at a considerable disadvantage to achieve a similarly crowded coordination sphere.  9  Therefore,  all group 4 alkylidene complexes reported thus far have required the addition of either inter- or intramolecular phosphine donors, and of these examples, only a handful of Ti derivatives have 10  been isolated as thermally stable compounds. ' n  two  1 2  It is reasonable to suggest that the presence of  intramolecular phosphine donors appended to a bulky Cp ligand is a major factor in the  formation and thermal stability of both 16 and 17.  91  r e f e r e n c e s b e g i n on p a g e  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  C H CMe  Np Ta  2  3  Ta(CH CMe ) 2  3  t 3  5  Me C—C  H  3  H  - CMe  A  4  Ta=CHCMe (CH CMe ) 3  Scheme 3.2  2  3  3  Mechanism of oc-hydrogen abstraction to yield an alkylidene complex.  The results of the mechanistic study into the Zr system that forms 16 are outlined here. Of importance, neither tribenzyl 3 nor monobenzyl 11 are independently reactive under the conditions that generate alkylidene 16. The dibenzyl complex 14 is therefore a likely precursor to undergo oc-abstraction and give 16 and one equivalent of toluene, as shown in Scheme 3.3. Accordingly, the continued depletion of 14 in forming 16 would perturb the pre-equilibrium, thus prompting the conversion of additional tribenzyl 3 and monobenzyl 11 to replenish 14, eventually resulting in the observed high yield production of 16. Added support that 14 is the reactive species is provided by heating reaction mixtures prepared from unequal proportions of 3 and 11. In each case the formation of 16 ceases when the precursor 14 can no longer be replenished, which occurs once the limiting component (either 3 or 11) as a source for 14 has been consumed.  92  references begin on page 141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  0.5 [PrP C p ] Z r ( C H P h )  0.5 [ P C p ] Z r C I ( C H P h ) + Pr  2  2  r r  2  r  2  2  3  11  Pr [P Cp]ZrCI 2  2 KCH Ph 2  Pr,  [P Cp]ZrCI(CH Ph) 2  3  2  2  14  1 k  A  2  fast  PhMe  -Zr-  "77  p P  Pr  h  H  ?  -p:  ,CH Ph 2  V\  [P Cp]Zr=CHPh(CI) 2  16 Scheme 3.3  Proposed reaction scheme for the formation of 16 from the mixture of  benzyl species 3,11 and 14.  A kinetic analysis of the thermal decomposition of this reaction mixture was conducted by monitoring the 31p{lH} NMR  spectra for separate reactions performed at 70, 80, 85 and 95  °C, respectively. A similar study was also conducted at 70 °C on the perdeuterated analogue [P2Cp]ZrCl(CD2C6D5)2 (14-d7) to examine a possible kinetic isotope effect. In all instances the decline in [14] followed a pattern as shown in Figure 3.4. The non-linear fit of the plot of ln[14] versus time illustrates a departure from first-order kinetics. The pre-equilibrium in this composite mechanism is likely responsible for these complicated results. The steep initial  93  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  decrease in the concentration of 14 corresponds more closely to the actual first-order ocabstraction reaction rate, but curvature in the In plot in Figure 3.4 arises due to a steady decrease in the observed rate (k bs) as the continued lowering in the concentrations of the equilibrium G  species makes it more difficult to replenish 14 from bimolecular collisions of 3 and 11. To evaluate the complicating factor of the pre-equilibrium, the results were simulated (Chemical Kinetics Simulator®) from input of the initial concentrations and the kinetic parameters k i , k . i and k_2-  Knowledge of the approximate equilibrium constant K gives the ratio  k i / k - i , with limits for these values set (1 < k < 10" s" ) by the spectroscopic data as outlined in 3  1  the discussion of this equilibrium in the previous section. A more precise estimate of these parameters, as well as the rate constant k for the irreversible a-abstraction step, could be made 2  by iteration of the simulation results to give the best agreement with the experimentally determined changes in [3], [14] and [16] as a function of time. The simulations show that including the pre-equilibrium in the analysis reproduces the experimental results depicted in Figure 3.4.  -2.5-1  In [14]  time (min)  Figure 3.4  Non-linear fit to the first-order decomposition of [P2Cp]ZrCl(CH2Ph)2 Pr  (14).  94  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . .  Table 3.3  Estimated rate constants for the first-order a-abstraction of Pr[P Cp]ZiCl(CH Ph)2 (14). 2  2  T(K)  k x l O ' (s" ) 5  1  2  343(1)  3.7(3)  353(1)  4.8(3)  363(1)  7.7(4)  373(1)  9.7(5)  -13-1  In (k/T)  0.0027  0.00275  0.0028  0.00285  0.0029  0.00295  in ( K / ) 1  Figure 3.5  Eyring plot of the first-order portion of the decomposition of Pr  [ P C p ] Z i € l ( C H P h ) (14). 2  2  2  The rate constants (k ) obtained for each temperature from the simulated data are shown 2  in Table 3.3; a kinetic isotope effect of 3.0(0.5) was observed at 70 °C for the perdeuterated  95  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . .  species, in support of rate-determining C-H  bond activation in a concerted four-centred 7  transition state as shown in Scheme 3.2. From the Eyring plot in Figure 3.5 the activation parameters AH* AHt and  = 19(1)  kcal mol"  and AS* = -22(5) cal mol"  1  1  K were obtained. The _ 1  value for  is in accord with kinetic studies conducted on other systems involving alkylidene formation related C-H  mol . _i  activation processes. " 13  15  In those studies AH^  ranges between 20 to 30 kcal  However, the experimentally determined value of AS^  for 14 is rather large in  comparison to these other systems (typically between 0 and -10 cal mol K" ), -1  1  although the  decomposition of Ti(CH2CMe3)4 via an alkylidene intermediate has a similar large negative AS* = -16 cal mol K" . -1  1 9  An in-depth analysis of the kinetic results for 14 will be given in  conjunction with the analogous results for the cc-abstraction of [P2Cp]ZiCl(CH2SiMe3)2 (19b) Pr  to give alkylidene [P2Cp]Zr=CHSiMe (Cl) (18b). Pr  3  3.3.3  Other alkylidene analogues [ P C p ] Z r = C H E M e ( C l ) (E = C, Pr  2  3  Si)  In view of the success in synthesizing and isolating both a Zr and a Hf example of a benzylidene complex, we were interested in testing both the generality of this reaction mechanism and the versatility of the P2Cp ligand in stabilizing other Zr alkylidene complexes. Two  examples of bulky alkyl groups with oc-hydrogens that have been commonly chosen for the  synthesis of early transition-metal alkylidene complexes are the neopentyl (CH2CMe3) and 5  neosilyl (CH2SiMe3) ligands.  7  Treating 1 with 2 equivalents of LiCH2EMe3 (E = C , Si) in  toluene at -78 °C yields a bright yellow oil after workup. Thermolysis of this material in toluene at 95 °C generates the corresponding alkylidene complex [P2Cp]Zr=CHEMe (Cl) (18a: E = C, Pr  3  18b: E = Si) (equation 3.5). The formation of 18a requires 6 days at 95°C, while the analogous reaction to produce 18b is complete within 3 days under the same conditions.  96  r e f e r e n c e s b e g i n on p a g e  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e ..  2 LiCH EMe 2  Pr  3  [P Cp]ZrCI 2  bright yellow oil  3  2 LiCI EMe, (3.5)  Pr  [P Cp]Zr=CHEMe (CI) 2  3  18a E = C 18b E = Si  A green oil is obtained for 18a, which is accompanied by inseparable side-products (approximately 20% by N M R spectroscopy) accumulated over the prolonged duration of the thermolysis. This complex is identified by assignable resonances in the H , l ^ C ^ H } , and 1  3 1  P { H } N M R spectra; of note are a singlet observed at 8.56 ppm in the *H N M R spectrum and 1  a triplet at 209 ppm in the C { H } N M R spectrum, for the alkylidene proton (Zr=C77CMe3) and 13  ]  carbon, respectively. In contrast, 18b can be isolated as thermally stable, air- and moisturesensitive yellow crystals in very good yield from cold hexanes.  Spectroscopic data for 18b  reveal a singlet in the H N M R spectrum at 8.99 ppm for the alkylidene proton (Zr=C/7SiMe ) A  3  and a triplet at 225 ppm in the  1 3  C { l H } N M R spectrum for the alkylidene carbon  (Zr=CHSiMe3), arising from / p c coupling to two equivalent phosphines. 2  An X-ray structure determination of 18b was undertaken, and the molecular structure is shown in Figure 3.6, with selected bond lengths and bond angles given in Table 3.4. The very short Zr-C bond distance of 2.015(9) A is similar to that of 2.024(4) A for Zr benzylidene 16. As also observed for 16, the alkylidene fragment in 18b is oriented syn  to the unique  cyclopentadienyl carbon, with the a-hydrogen atom directed below the metal centre to form the same type of agostic C - H interaction. This hydrogen was located and refined, and the Zr—H  97  references begin on page 141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e ...  distance of 2.28(8) A , together with the distorted Zr-C-Si angle of 164.3(6)°, is characteristic of an a-agostic C - H bond.  A l l other bond lengths and angles are similar to those in the  corresponding alkylidene 16.  Figure 3.6  A Chem 3D®  view of the molecular structure of 18b. All hydrogen atoms except  the a-agostic hydrogen are omitted for clarity.  Table 3.4  Selected Bond Lengths (A) and Bond Angles (") for P r f P i C p l Z r ^ H S i M e s t C l )  (18b).  Zr-Cl  2.508(3)  P(l)-Zr-P(2)  154.91(8)  Zr-P(l)  2.838(3)  Cl-Zr-C(19)  108.0(3)  Zr-P(2)  2.820(3)  Cl-Zr-P(l)  76.48(8)  Zr-C(19)  2.015(9)  Cl-Zr-P(2)  76.44(9)  Zr-Cp'  2.2557(13)  Zr-C(19)-Si(3)  164.3(6)  Zr-H(19)  2.28(8)  Zr-C(19)-H(19)  89(5)  Si(3)-C(19)  1.848(9)  Cp'-Zr-Cl  141.23(8)  C(19)-H(19)  1.10(8)  98  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e ...  3.3.4  Mechanistic studies of the formation of [ P C p ] Z r = C H E M e ( C l ) (E = C , Si) Pr  2  3  An examination of the yellow oil obtained from the reaction of 1 with 2 equivalents of LiCH.2EMe3 prior to the thermolysis reveals the presence of trialkyl [P2Cp]Zr(CH2EMe3)3 Pr  (5a: E = C, 5b: E = Si), monoalkyl Pr[P Cp]ZrCl2(CH EMe3) (7a: E = C, 7b: E = Si), and 2  2  another species which is observed as a singlet in the P NMR spectrum and identified from the 3 1  integration of peaks in the *H NMR spectrum as the dialkyl derivative [P Cp]ZrCl(CH2EMe3)2 2  (19a: E = C, 19b: E = Si). It seems that a similar equilibrium (equation 3.6) is established between all three alkyl species for both the neopentyl and neosilyl systems as has been observed for the benzyl derivative, since combining together separate samples of the trialkyl and monoalkyl species again generates the dialkyl complex to produce a similar mixture of all three alkyl species.  Pr  [P Cp]ZrCI (CH EMe ) + 2  2  2  Pr  3  [P Cp]Zr(CH EMe ) 2  2  3  7a E = C  5a E = C  7b E = Si  5b E = Si  3  (3.6)  Pr,  [P Cp]ZrCI(CH EMe ); 2  2  3  19a E = C 1 9 b E = Si  Detailed analyses of these equilibria were precluded by the overlap of peaks in the *H and 3 1  P { H } N M R spectra for various species at separate temperatures. However, it could be 1  99  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  ascertained that below the temperature at which one observes alkylidene formation, the equilibrium increasingly favours ligand distribution of the dialkyl species 19 as the temperature is raised (i.e., the value of K decreases with an increase in temperature), in contrast to the observations for 14 in the equilibrium of equation 3.3. It is evident that the mechanistic details for the formation of the neopentyl and neosilyl alkylidene complexes 18 are similar to those previously outlined for benzylidene 13.  For  example, heating either the trialkyl 5 or monoalkyl 7 derivatives independently does not generate an alkylidene complex, and the production of alkylidene from the thermolysis of the equilibrium mixture in equation 3.5 ceases when the supply of dialkyl precursor 19 has been exhausted. Once again this points to a mechanism analogous to that in Scheme 3.2, where the dialkyl complex 19 is the thermally labile species that leads directly to the alkylidene product in a first order mechanism. Experimental complications associated with the long reaction time and the formation of interfering impurities precluded a kinetic study of the neopentyl system. However, an analysis of the reaction kinetics for the thermal decomposition of neosilyl 19b was conducted by P 3 l  NMR  spectroscopy, for reactions performed at 80, 95, 110 and 125 "C. In all instances the same pattern for the decrease in [19b] over time was observed as has been noted for benzyl 14 in Figure 3.4. Therefore, the results for 19b were simulated by the same iterative procedure followed for 14, from which the first-order rate constant (k ) was obtained for each temperature 2  (Table 3.5). The corresponding Eyring plot is shown in Figure 3.7, from which the activation parameters AH* = 6.2 kcal mol" and AS* = -60 cal m o H K " were obtained;these values are 1  1  significantly different to the parameters obtained for 14.  100  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . . .  Table 3.5  Rate constants for the first-order portion of the decomposition of [P2Cp]ZrCl(CH SiMe )2 (19b) 2  3  T(K)  k  2  x lO"  5  353(1)  3.7(3)  368(1)  4.8(3)  383(1)  7.7(4)  398(1)  9.7(5)  (s- ) 1  In (k/T)  0.0025  0.0026  0.0027  0.0028  0.0029  l/T ( K / ) 1  Figure 3.7  The  Eyring plot of the first-order decomposition of 19b.  trend reported in the literature for the relative rates of alkylidene complex formation  follows the order neopentyl > neosilyl > benzyl, which reflects faster rate-determining ocabstraction for complexes bound by alkyl ligands that can provide greater steric congestion at the  101  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  metal centre. For example, for the first-order decomposition of Ta(CH2R)5 (R = Ph, SiMe3, CMe3), the rate constants follow the order k = 4.3 x 10" (at 313 K ) < 3.5 x l O (311 K) < too 5  4  fast to monitor, for R = P h , SiMe3, and CMe3, respectively. Our results indicate a reversal of 16  7  7  this trend for the complexes studied here. The neopentyl system that produces alkylidene 18a was found to be too slow to study, and a comparison of the first order rate constants in Table 3.3 and Table 3.4 for the dialkyl species studied reveals the slower thermal reactivity of neosilyl 19b versus benzyl 14. This surprising observation may be partially related to the unusual preequilibrium step associated with the postulated mechanism (Scheme 3.2), where ligand distribution of the dialkyl species is favoured at higher temperatures for the bulkier derivatives, in competition with the irreversible step leading to alkylidene formation. However, the effect of the pre-equilibrium is evidently secondary in comparison to the activation parameters, particularly AS*,  associated with the rate determining cc-abstraction step. As mentioned above,  both near-zero and negative values (0 to -10 cal m o l K ) have been typically observed for the -1  majority of C-H  _ 1  bond activation processes that have been studied. The results from this work  show considerable departure from these values, especially with the large negative AS$ of -62 cal mol  -1  K  _ 1  for 19b, which has been rarely seen for a first-order process. To account for this  remarkable difference it is useful to examine the proposed transition state structure ($) in this reaction as shown below:  Me2  Meg -Si  .Si-  <  >  102  r e f e r e n c e s b e g i n on p a g e  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . .  There are two features that indicate a significantly more ordered structure in the transition state in comparison to the ground state structure of the dialkyl derivatives, which could generate a large negative AS*  term. The first is the coordination of both bulky side-arm phosphines,  considered to help lower the activation energy by increasing steric saturation at the metal centre to induce cx-abstraction as a means of relieving the steric pressure. The second feature is the necessity for the two alkyl ligands to attain a cis configuration in order to permit the concerted abstraction step to proceed via the four-centred transition state. However, if the phosphines are coordinated then a mutually trans arrangement of the bulky alkyl ligands is perhaps sterically favoured, as supported by structural evidence from  Me  [P2Cp]Cl(CH2Ph)2 (27), a dibenzyl  derivative with methyl groups attached to the phosphines, which is discussed separately in the next chapter. The steric difficulties that must be surmounted to reach the transition state are more pronounced for the bulkier dialkyl species 19b. For example, the singlet in the P { ! H } 31  NMR  spectrum for 19b at -4.5 ppm is indicative of phosphine donors that are at best only weakly  interacting with the metal. Overall, these factors could account for a much larger negative value of AS* for the bulkier alkyl derivatives and hence the observed reversal of the reactivity trend, which arises from entropic factors. These factors also help to explain the otherwise contradictory observation that the bulky trialkyl derivatives are thermally unreactive, as these complexes are paradoxically less sterically hindered in comparison to the dialkyl analogues because the bulky phosphines are unable to coordinate in the trialkyl species.  3.3.7  Crossover experiments Crossover experiments were conducted as a further test for the general mechanism  proposed for the alkylidene reaction, and as an attempt to compare competitive cx-abstraction rates for various alkyl groups. Accordingly, solutions of monobenzyl 11 and tris(neosilyl) 7b were combined as shown in Scheme 3.3 in an attempt to generate the mixed alkyl species (B).  103  r e f e r e n c e s b e g i n on p a g e  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e ...  Pr,  [P Cp]ZrCI(CH Ph)(CH2SiMe ) + [P Cp]ZrCI ( C H S i M e ) Kr  2  - SiMe  2  3  2  2  B  4  3  2  19b - SiMe  4  t Pn  [P Cp]Zr=CHPh(CI) 2  Pr,  16  Scheme 3.3  [P Cp]Zr=CHSiMe (CI) 2  3  - PhMe  18b  Alkylidene products arising from crossover experiments.  Additional recombination products were also formed in small amounts. Thermolysis of such a mixture offers two competing a-abstraction pathways for B , offering a route to two different alkylidene products. Indeed, both products were observed, providing additional support for the ligand redistribution mechanism in the pre-equilibrium step detailed above in Scheme 3.2.  3.4.  Reactivity of [ P C p ] Z r = C H R ( C l ) (R = Ph, S i M e ) Pr  2  3  Early metal alkylidene complexes continue to attract considerable attention by virtue of the diverse reactivity arising from the metal-carbon multiple bond.  4  These species have been  utilized as catalysts in a number of transformations involving alkenes " and alkynes, and in 17  20  21  stoichiometric Wittig-like olefination reactions with organic carbonyl functionalities. " 22  24  Probably the most notable catalytic reaction is the olefin metathesis process for which the ring 10  104  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . ,  opening version has had a huge impact in polymer chemistry, while the ring closing version is 5  an exciting new synthetic method in organic synthesis.  26  As the alkylidene complexes discussed  in the previous sections are to our knowledge the only stable zirconium and hafnium derivatives, an investigation of the their reactivity patterns provides a unique opportunity to examine the results in comparison to the reactivity trends that have been noted for Group 5 and 6 alkylidene complexes. Again, the role of the hemilabile phosphines in moderating the reactivity of these complexes is shown in their capacity to provide an open coordination site for reactivity to occur. Importantly, this hemilabile coordination of the phosphines moderates and controls the reactivity (i.e., controlled reactivity).  3.4.1  Reactivity of [ P C p ] Z r = C H R ( C I ) with alkenes (R = Ph, S i M e ) Pr  2  3  An orange toluene solution of '[P2Cp]Zr=CHR(Cl) (16: R = Ph, 18b: R = SiMe3) reacts Pl  slowly (12 h for 16, 8 h for 18b) with ethylene under ambient conditions to generate a dark red solution consisting of a 9:1 ratio of the two isomers of the ethylene complex [P2Cp]Zr(ri2Pr  C H = C H ) C 1 (20) (equation 3.7). Each isomer of 20 displays a singlet in the P { ! H } N M R 3 1  2  2  spectrum and corresponding resonances in the  NMR  spectrum, consistent with a structure in  which the orientation of the ethylene unit is directed either syn or anti with respect to the unique Cp carbon of the ancillary ligand. The organic by-products that accompany the formation of 20 were detected by H N M R l  spectroscopy and identified by G C - M S . For example, from benzylidene 16 the major product (approx. 70 %) is the terminal alkene PhCH2CH=CH2, while the cis and trans isomers of the internal alkene PhCH=CHCH3 are obtained in approximately equal quantity. Similar results for 18b are observed.  105  r e f e r e n c e s b e g i n o n p a g e 141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .,  Me2 Si  R = Ph 18b R = S i M e 16  3  H2C—CH2  (3.7)  , _ Z r -  HC  C  /  I  CH  2  2  +  V \  syn-20  anti-20  H CH  3  H RCH  :CH,  /  In the ^ C f ! - ! } N M R spectrum of 2 0 (only peaks due to the major syn isomer are 1  observed), the ethylene carbon resonances are located upfield at 35 ppm with a V C H value of 142 Hz, consistent with hybridization intermediate between sp and s p . 2  3  27  The ethylene protons  give rise to a complex multiplet centred near 1.0 ppm in the *H N M R spectrum, originating from an A A ' B B ' X X ' spin system due to additional 7 P H coupling from the side-arm phosphines. This 3  106  references begin o n page 141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m  Alkylidene...  coupling pattern remains unchanged even at higher temperatures, indicating that the ethylene unit is firmly bound with no evidence for rotation about the metal-ethylene bond axis on the  NMR  time scale. A C=C stretch in the IR spectrum for the coordinated ethylene unit was also not observed. complexes  These spectroscopic data are similar to those of other early-metal ethylene 13,28  "  31  and are consistent with a formulation of 20 as a Zr(IV) zirconacyclopropane  complex rather than as a Zr(II) adduct. However, aspects of the solid state structure and the reactivity of this species, to be outlined later, suggest a fair degree of Zr(II) character still extant in this molecule. Attempts to determine the major isomer in solution by *H N M R spectroscopy by irradiating the Cp proton resonances to examine a possible nuclear Overhauser enhancement (nOe) on the protons of the coordinated ethylene fragment were inconclusive. However, as will be discussed in the following chapter, an analogous ethylene complex can be prepared by an independent route, [P2Cp]Zr(r| -CH2=CH2)Br (32), in which the isopropyl substituents on the Me  2  phosphines are replaced by methyl groups. Only the syn isomer is observed in this species, and by extrapolating the *H N M R spectrum of this derivative to 20, especially with excellent correlation seen in the sensitive Cp region, it is evident that the major isomer in solution corresponds to sy/?-20. Further insight into the Zr-ethylene bonding interaction was furnished by a crystal structure determination of ,sy«-20. The molecular structure is shown in Figure 3.9, with relevant bond distances and bond angles given in Table 3.6. The C(19)-C(20) bond distance of 1.433(17) A is lengthened relative to free ethylene (1.337 A )  3 2  and is comparable (albeit somewhat shorter)  to that of the only other monomeric Zr(II) ethylene complex that has been structurally characterized, Cp2Zr(T| -CH2=CH2)(PMe3), 2  33  which has a corresponding C - C bond length of  1.486(8) A for the ethylene unit. This distance range is indicative of significant back-bonding from the metal and supports the metallacyclopropane bonding depiction for 20. Also consistent with this formalism are the Zr-C bond lengths (average 2.319(11) A ) in 20, which are  107  r e f e r e n c e s b e g i n on p a g e  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m  Alkylidene.  considerably shorter than the Zr-C distance of 2.68(2) in a cationic Zr(IV) olefin complex in which d-7i* back-bonding is necessarily absent.  34  The orientation of the ethylene unit parallel to  the Cp ring not only reduces steric interactions with the Cp ring, but also situates the rc*-orbital to overlap favourably with the metal d  x y  orbital. Investigations into bonding interactions in  electron-rich complexes with piano-stool geometries, of which this formally Zr(II) species is a suitable example, suggest that it is the metal d acceptor l i g a n d . ' 35  36  x y  orbital that offers the best donation to a rt-  These studies also indicate that rc-donor ligands (such as a chloride) are  better located further away from the Cp group, which is supported by the wider Cp'-Zr-Cl angle in 20 (152°) as found in alkylidene 18b (141°).  Figure 3.8  A Chem 3 D ® view of the molecular structure of [ P 2 C p ] Z r ( r i -  CH2=CFf2)Cl  Pr  2  (20). Hydrogen atoms are omitted for clarity.  108  references  b e g i n on p a g e 1 4 1  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  Table 3.6  Selected Bond Lengths (A) and Bond Angles (°) for [P2Cp]Zr(ri Pr  2  CH =CH )C1 (20). 2  3.4.2  2  Zr-Cl  2.500(4)  P(l)-Zr-P(2)  153.45(11)  Zr-P(l)  2.872(4)  Cl-Zr-P(l)  77.85(12)  Zr-P(2)  2.850(4)  Cl-Zr-P(2)  77.42(12)  Zr-C(19)  2.326(11)  Cl-Zr-C(19)  98.8(3)  Zr-C(20)  2.318(11)  Cl-Zr-C(20)  100.6(3)  Zr-Cp'  2.2361(16)  Cp'-Zr-Cl  152.23(10)  C(19)-C(20)  1.433(17)  Kinetic study into the formation of 20 Kinetic experiments were conducted to investigate the mechanism of the formation of the  ethylene complex 20 from alkylidene 16. Figure 3.9 illustrates a plot of ln[16] vs. time for reactions carried out to between two and three half-lives for a number of different ethylene concentrations. In all instances the ethylene concentration remained unchanged during the course of the reaction, so that the results shown in Figure 3.9 exhibit pseudo first-order behaviour consistent with overall second order kinetics, where the observed rate = k [16][C2H4]. 0  Although intermediates in the transformation of alkylidenes 16 or 18b to ethylene 20 were not observed, the second-order kinetics, together with the organic by-products from reaction 3.7, are consistent with the reaction mechanism depicted in Scheme 3.5. The initial coordination of ethylene to the alkylidene is likely assisted by dissociation of either the agostic interaction or one of the potentially labile side-arm phosphines. Subsequent cycloaddition of the coordinated ethylene with the alkylidene moiety gives a four-membered metallacycle ( M ) , an intermediate that has been trapped and isolated ' ' in analogous reactions between alkylidene 11  109  17  37  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m  Alkylidene.  complexes and certain alkenes. P-hydride elimination of zirconacyclobutane M can occur via two pathways; in Scheme 3.5, only the pathway that generates the terminal alkene RCH2CH=CH2,  the product of the more kinetically favored route, is shown. In the presence of  excess ethylene, the zirconium centre is trapped by a second equivalent of ethylene, to generate the final product 20. It is noteworthy that products resulting from alkene metathesis (RCH=CH2) were not detected, an indication of the presumed rapid rate for the P-elimination process. This particular mechanism has been generally observed in the reaction of alkylidene complexes with ethylene, ' '  11 12 38  although further coupling from an additional equivalent of ethylene to give a  metallacyclopentane ' complex has also been noted. However, this feature is not observed for 28 39  20, which does not react further with additional ethylene.  In [16]  0.00E+00  5.00E+04  1.00E+05  1.50E+05  2.00E+05  time (s)  Figure 3.9  Pseudo first-order kinetics in the reaction of 16 with ethylene to give 20.  HO  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m  Scheme 3.5  Alkylidene.,  Proposed mechanistic steps in the formation of 20. Ill  r e f e r e n c e s b e g i n on p a g e  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m  3.4.3  Alkylidene...  Reactivity of [ P C p ] Z r = C H R ( C I ) with larger substrates Pr  2  In comparison with some group 5 alkylidene systems,  39  the slow reaction with ethylene  that produces 20 indicates the steric and electronic saturation at the Zr centre in alkylidenes 16 and 18b. When the slightly larger and more weakly binding olefin propylene is employed the reaction is considerably slower, eventually yielding unidentified paramagnetic products after more than one week.  However, the organic by-product observed in this reaction is almost  exclusively the terminal alkene R C H 2 C ( M e ) = C H 2 , which again is consistent with (3-H elimination from an analogous zirconacyclobutane intermediate. The predominant elimination of only one alkene from this reaction signifies two points. First, the propylene addition with either 16 or 18b is highly regioselective, with the substituted portion of the double bond adding to the alkylidene carbon. Second, the kinetic preference noted earlier for the elimination of a terminal alkene rather than an internal alkene is magnified in the propylene reaction. The significantly longer duration needed for the this reaction, together with the apparent instability of the resulting propylene adduct, points to steric factors. It is evident that steric crowding from the ancillary ligand restricts the size of molecules that can access the metal centre, even with the advent of side-arm phosphine dissociation. This property is accentuated by the equally slow reaction of these alkylidenes with the relatively small cumulene allene, and the total inability to react with larger activated substrates like norbornene, butadiene, and internal alkynes. Another reaction that is characteristic of early metal alkylidene complexes is a parallel of the Wittig reaction,  23  and an example is shown below in the reaction of either 16 or 18b with  acetone (equation 3.8). The alkene RCH=C(CH3)2 was isolated and identified by G C - M S , but unfortunately, a Zr containing species could not be isolated from this reaction. The P { ! H } 31  N M R spectrum of this reaction mixture shows a variety of unidentified species, presumably due to decomposition of the putative oxo species [P2Cp]ZrO(Cl). Pr  112  r e f e r e n c e s b e g i n on p a g e  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m  Me2  —T~S\.  Me  Alkylidene.,  2  (3.8)  t  ? 3.4.4  Preparation of ketene and ketenimine complexes [ P 2 C p ] Z r ( r | - C ( X ) = C H R Pr  2  (X = O, NBu*) In comparison to the extensive chemistry of alkylidene complexes with alkenes and organic carbonyls, much less attention has been directed towards their reactivity with carbon  113  r e f e r e n c e s b e g i n on p a g e  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e ...  monoxide and isonitriles. This is somewhat surprising, given that these reactions have been noted to yield unusual ketene and ketenimine complexes, ' ' 11  40  species that have demonstrated  41  their synthetic utility in a variety of organic transformations.  42-44  Of the ketene complexes  obtained by the insertion reaction of metal alkylidenes and C O , structural analysis of the products detailing the mode of insertion have not been reported. A toluene solution of the alkylidene complex 16 or 18b reacts with C O under ambient conditions over a period of 24 hours to yield the thermally stable ketene complex [P2Cp]Zr(r| Pr  2  C(0)=CHR(C1) (21a: R = Ph, 21b: R = SiMe3) in moderate yield (equation 3.9).  Orange  crystals of 21a can be isolated from cold hexanes whereas 21b is obtained as an orange oil which remains soluble in hydrocarbon solvents.  Me Si  — r S \ Me ^a=s^—-Si 1  2  2  (3.9)  114  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m  Alkylidene.,  Similar to the solution behaviour noted previously for 20, both 21a and 21b exhibit two stereoisomers each, either in a 4:1 (21a) or 2:1 (21b) ratio at room temperature. These species are identified by separate singlets in the resonances in the *H NMR  /pC  P { H } N M R spectrum and by corresponding 1  spectrum. Additionally, for each isomer there is a triplet located  downfield in the ^ C ^ H } NMR 2  3 1  spectrum for the ketene carbon, the observed splitting due to  coupling to two equivalent phosphines. For 21a these resonances are at 192 ppm (minor  isomer) and 205 ppm (major isomer), while 21b exhibits triplets at 203 ppm (major isomer) and 216 ppm (minor isomer), respectively. 21a also shows a strong peak in the IR spectrum for the ketene moiety at 1495 c m . Again, as with 20 these stereoisomers are likely the structures syn-1  21 and anti-21, which differ in the relative orientation of the ketene unit with respect to the ancillary ligand. It is evident that both species are in equilibrium, as variable temperature  NMR  spectroscopy reveals a smooth temperature dependent variation in the relative concentrations (the major isomer is present in lesser amounts at higher temperature), and an increase in line broadening in the  3 1  P { H } NMR 1  spectrum is observed as the temperature is raised, due to a  faster exchange rate between the two structures.  However, it could not be unambiguously  determined which species is the syn isomer as the spectroscopic data are unable to distinguish between the two structures in solution. It is not possible to examine a nuclear Overhauser enhancement (nOe) between the Cp ring protons and protons within the ketene unit as these nuclei are too far apart. Attempts to introduce an NMR  active nucleus closer to the Cp ring  protons by substituting the chloride of 21 with either a fluoride or an alkyl group were unsuccessful, and a heteronuclear nOe experiment conducted on a sample of 21b containing a 13  C-labeled ketene carbon was also inconclusive. Regarding the method of interconversion of  the syn and and isomers of 21 (and presumably of 20 as well), it is likely that dissociation of both phosphines is followed by a 180° rotation of the ancillary ligand around the Zr-Cp axis occurs (Scheme 3.6).  115  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m  Scheme 3.6  Alkylidene.,  Proposed mechanism for the interconversion of stereoisomers in 20.  Crystals suitable for X-ray structure determination were obtained for benzylidene ketene 21a, and the molecular structure is shown in Figure 3.10. Selected bond distances and bond angles are given in Table 3.7. The mononuclear structure arises from the steric bulk of the ancillary ligand, a feature in common with analogous early metal ketene complexes where bulky  116  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m  substituents are required to prevent dimerization. " 45  49  Alkylidene...  The r| - C , 0 coordination of the ketene 2  fragment is also a typical binding mode to oxophilic metals, ' ' ' 47  48  50  51  and is exhibited here by the  short Zr-C(24) and Z r - 0 distances of 2.172(3) A and 2.027(2) A , respectively, and a correspondingly long C - 0 distance of 1.374(3) A . These parameters are similar to the analogous bond distances in another monomeric Zr ketene complex, Cp*2Zr(py)(r| -C(0)=CH2) 2  4 7  which  are 2.181(2) A , 2.126(1) A , and 1.338(2) A , respectively. The C(24)-C(25) distance of 1.349(4) is indicative of a double bond, and the coplanarity of the ketene moiety is illustrated by the dihedral angle of 2° between O(l), C(24), C(25), and C(26). Additionally, the phenyl ring is also nearly coplanar with the ketene fragment with a tilt angle of 8°, an alignment that presumably optimizes derealization of electron density over the organic fragment and reduces steric interactions with the ancillary ligand.  Figure 3.10  Molecular structure of [P Cp]Zr(ri -C(0)=CHPh)(Cl) (21a); 33% Pr  2  2  probability thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity.  117  references begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e ...  Table 3.7  Selected Bond Lengths (A) and Bond Angles (°) for Pr[P Cp]Zr(r|2-C(0)=CHPh)(Cl) (21a). 2  Zr(l)-Cl(l)  2.4976(8)  Cl(l)-Zr(l)-P(l)  87.66(3)  Zr(l)-P(l)  2.8261(8)  Cl(l)-Zr(l)-P(2)  86.54(3)  Zr(l)-P(2)  2.8517(8)  Cl(l)-Zr(l)-0(1)  141.42(6)  Zr(l)-0(1)  2.027(2)  Cl(l)-Zr(l)-C(24)  103.43(8)  Zr(l)-C(24)  2.172(3)  Cl(l)—Zr(l)—Cp  107.1  Zr(l)-Cp  2.25  P(l)-Zr(l)-P(2)  156.25(2)  C(24)-C(25)  1.349(4)  Zr(l)-C(24)-0(1)  65.3(1)  0(1)-C(24)  1.374(3)  0(1)-Zr(l)-C(24)  37.99(8)  Zr(l)-C(24)-C(25)  169.5(2)  Two  points can be made regarding the solid state structure of 21a in comparison to that of  the precursor benzylidene 16 (see Figure 3.3 for the isostructural H f analogue 16). First, the observed molecular structure of the ketene complex corresponds to the anti stereoisomer of 21, a reversal of the orientation noted for 16. Presumably, anti-21 is the least soluble isomer of the two  ketene species in equilibrium. The second point is that the a-hydrogen involved in the  agostic interaction in 16 is still oriented below the zirconium in 21a, resulting in an E-geometry for the ketene unit. In other words, insertion of CO proceeds with retention of stereochemistry about the zirconium-carbon double bond. This geometry arises from the lack of rotation previously noted in the Zr=C bond of the precursor alkylidene.  Furthermore, no E / Z  isomerization is observed for the ketene complexes 21, and this contrasts some other early metal ketene complexes that have been studied.  50,51  Without this isomerization process, an exo  orientation of the ketene unit relative to the Cp ring is adopted to minimize steric interactions between the phenyl group and the ancillary ligand.  118  r e f e r e n c e s b e g i n o n p a g e 141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  6  Z rK -0  Cl'  H  Cl'  Zr-  \  H  o  /  / endo  exo  As an extension of the insertion reaction that produces 21, a toluene solution of tert-butyl isocyanide reacts with 16 to give the analogous ketenimine " 52  55  complex [P2Cp]Zr(n -C,NPr  2  C(NBu )=CHPh)Cl (22) as dark red crystals (equation 3.10). To our knowledge this is the first t  example of a ketenimine complex obtained from the insertion of an isocyanide into an earlymetal alkylidene complex.  Bu —N=C l  t  16  (3.10)  ^••/ Birv. / N P  \  C N H  119  anti-22  R e f e r e n c e s b e g i n on p a g e  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  The stoichiometry of this reaction is important as an excess of the isonitrile reacts further with 22. The spectroscopic parameters for ketenimine 21 are similar to those of the analogous ketene complex; for example, the ketenimine moiety shows a peak in the IR spectrum at 1504 cm  -1  and the ketenimine carbon displays a downfield resonance in the l^C^H} NMR  at 204 ppm.  spectrum  In contrast to 21a, however, only a single isomer is observed for 22 in solution (i.e.,  a single resonance is present in the P{lH} NMR spectrum), presumably because the 31  isomerization mechanism mediated by Cp rotation (Scheme 3.6) is impeded by the tert-butyl group. A *H NOEDIFF NMR  experiment conducted on 22 established that the isomer obtained  is anti-22, since irradiating the methyl resonance of the tert-butyl group leads to an enhancement of the peak assigned to the two equivalent Cp protons, but no effect is observed for the resonance ascribed to the unique Cp proton. However, if neither the precursor alkylidene 16 nor the product ketenimine 22 undergo synlanti isomerization, then the transformation from syn-16 to anti-22 must occur during the migratory insertion of the isocyanide into the Zr-C bond (Scheme 3.7).  alkylidene  In this instance the bulky tert-butyl group is directed away from the  ancillary ligand until the final step when the nitrogen atom binds to give the T| (C, N)2  coordinated ketenimine complex. The same mechanism is likely involved in the formation of ketene 21, although as mentioned previously this complex is capable of isomerizing after the product is formed. The  steric effects of the large Bu group are also apparently manifested in a pronounced l  broadening of peaks in the H NMR A  spectrum in 22 for the ortho protons on the phenyl ring (and  to a lesser extent the meta protons as well), and the resonances of the portion of the ancillary ligand that is syn to the ketenimine unit. However, all of these peaks are narrow in the low temperature spectrum (-25 "C), suggesting that some dynamic process is frozen out at low temperature, perhaps rotation of the phenyl ring restricted by steric interaction with the tert-butyl group, and begins exchanging chemical environments as the molecule is heated.  120  References begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  Scheme 3.7  Proposed mechanism for the formation of anti-22 from syn-16.  121  R e f e r e n c e s b e g i n o n p a g e 141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . . .  3.4.5  Insertion reactivity of ketene [P Cp]Zr(ri -C(0)=CHR)Cl Pr  2  2  A toluene solution of 21 reacts with ethylene under ambient conditions over a period of two days to give the insertion product [P2Cp]Zr(r| -CH2CH2C(0)=CHR)Cl (23a: R = Ph, 23b: Pr  2  R = SiMe3; equation 3.11).  (3.11)  23b R = S i M e  H  The  i H and P { iff} NMR 3 1  3  spectra reveal that both 23a and 23b exist as a single species  in solution, despite the fact that the precursor 21 consists of an equilibrium mixture of two stereoisomers. This suggests either that one isomer of 21 is kinetically more reactive, or that  122  References begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . . .  both possible stereoisomers of 23 are initially formed, followed by complete conversion of the less stable isomer to the thermodynamically-favored observed product. We were able to isolate crystals of 23b suitable for X-ray structure determination, and the molecular structure is shown in Figure 3.11. The X-ray data of selected bond distances and bond angles are given in Table 3.8.  C(ll)  Figure 3.11  C(23)  C(28)  Molecular structure of [ P C p ] Z r ( r i - C H 2 C H 2 C ( 0 ) = C H R ) C l (23b); 33% 2  Pr  2  probability thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity.  Figure 3.11 shows that one ethylene molecule has inserted into the Zr-C bond of the ketene unit, which is now bound to Zr solely via the oxygen atom as an enolate fragment, to give a fivemembered metallacycle. The short C(26)-C(27) distance of 1.329(5) A is a relic of the Zr=C 123  References begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . . .  bond from the original alkylidene 18b. The overall configuration of 23b is retained from the precursor ketene complex and resembles the isomer pertaining to anti-21. Therefore if the observed stereoselectivity is due to a kinetic factor then this implies that anti-21 is the more reactive of the two ketene isomers with respect to ethylene insertion. The stereochemical preference for one orientation over the other is a recurring theme for many of the complexes involving the P C p ligand, as noted previously with the alkylidene complexes and with 22, and is 2  somewhat puzzling, given that the apparent differences between the two sides of the ligand are unremarkable.  The steric differences are almost negligible, so it seems likely that subtle  electronic factors are involved in favoring a particular configuration.  Table 3.8  Selected Bond Lengths (A) and Bond Angles (") for Pr  [P Cp]Zr(ri2.CH2CH2C(0)=CHR)Cl (23b). 2  Zr(l)—Cl(l)  2.5234(10)  Cl(l)-Zr(l)-P(l)  81.39(3)  Zr(l)-P(l)  2.9527(11)  Cl(l)-Zr(l)-P(2)  86.31(3)  Zr(l)-P(2)  2.9007(11)  Cl(l)-Zr(l)-0(1)  156.64(6)  Zr(l)-0(1)  2.036(2)  Cl(l)-Zr(l)-C(24)  82.83(9)  Zr(l)-C(24)  2.172(3)  Cl(l)—Zr(l)—Cp  107.1  Zr(l)-Cp  2.30  P(l)-Zr(l)-P(2)  159.21(3)  C(26)-C(27)  1.329(5)  0(1)-Zr(l)-C(24)  74.10(10)  0(1)-C(24)  1.374(3)  Zr(l)-0(1)-C(26)  128.4(2)  C(24)-C(25)  1.519(5)  Zr(l)-C(24)-C(25)  110.4(2)  Monomeric ketene complexes are generally more reactive to substrates such as alkenes, '  23 43  alkynes, and H 2 56  47  than are the corresponding dimeric derivatives.  56  However,  except for the reaction noted above with ethylene, the monomeric ketene complex 20 is comparatively inert, showing no reactivity with either internal alkynes, butadiene, alkylating reagents, or H . 2  Again, the bulk of the ancillary ligand may contribute to this lack of reactivity. 124  References begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . . .  In line with this idea, the even more sterically encumbered ketenimine complex 22 undergoes a considerably slower reaction with ethylene (approximately 5 days), and a clean product could not be isolated. 3.4.6  Formation of acyl-ylide complexes Metallacycle 23 reacts with carbon monoxide to yield an ri -acyl-ylide complex 2  57  (24a:  R = Ph, 24b: R = SiMe3) in which the metallacycle has expanded to a six-membered ring to accommodate the insertion of CO (equation 3.12):  23b R = S i M e  H C  3  O  (3.12)  H H  2  24a R = Ph 24b R = S i M e  125  3  R e f e r e n c e s b e g i n on p a g e 1 4 1  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . .  A single isomer is observed in solution for 24a, while two species are evident in a 9:1 ratio for 24b. The r| -coordination mode of the acyl unit resembles that found in ketene 21, except the 2  carbonyl carbon of the latter is saturated electronically by the double bond to C(22), a feature that is absent in 24.  To compensate for this discrepancy, one of the side-arm phosphines  coordinates not to the metal but instead stabilizes the electrophilic acyl carbon. The other pendant side-arm remains dangling, so that two singlets are observed in the  31  P{!H} NMR  spectrum, one located downfield near 46 ppm for the ylide phosphine, and an upfield peak near 7 ppm  corresponding to a free phosphine. The H NMR A  spectrum reveals a complicated second  order splitting pattern for the diastereotopic protons of the ethylene portion of the metallacycle. For  the two protons a to the chiral acyl carbon this pattern is further complicated by  3  /PH  coupling, which could be identified by decoupling the phosphorus resonance near 46 ppm. The low  C i symmetry of this complex is also evident in the cyclopentadienyl region where three  separate resonances are seen in the *H N M R spectrum. However, the dangling side-arm is further removed from the chiral carbon centre and these protons belie a more symmetric environment in the *H NMR  spectrum.  The unusual acyl-ylide structure of 24 recalls the structurally characterized acyl-ylide 13 encountered in the previous chapter, obtained from the analogous insertion reaction of C O into the monobenzyl species 11. The NMR  spectroscopic features of 13 and 24 are quite similar.  The resemblance between the two structures originates from the similarity between the precursors, where the general ligand set for each comprises C p L M X 2 R , if the vinyl alkoxide 2  fragment in 23 is regarded as a pseudo-halide. Therefore, it is not surprising that the products obtained from the insertion of CO into either 11 or 23 have the same generic structure. The only difference between the two is the cyclic unit in 24, which is inherited from the precursor metallacycle. The sequence of insertion reactions beginning with the alkylidene complexes ceases with the acyl-ylide 24, which does not react with ethylene. The preceding insertion reactions required 126  R e f e r e n c e s b e g i n on p a g e  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . . .  in each case the predissociation of a pendant phosphine to create an available coordination site for  the incoming substrate prior to insertion. For alkylidene 16 and 18b, ketene 21, and  metallacycle 23 this process was possible, but in 24 one phosphine is firmly bound to the acyl carbon while the other is already uncoordinated, thereby leaving the metal centre without a labile ligand.  3.5  Summary and conclusions The ancillary ligand P C p has been utilized in the synthesis of the first reported examples 2  of stable zirconium and hafnium alkylidene complexes, which are isolated in high yield as crystalline solids. The structural parameters are similar for each and the solid state structure is maintained in solution. Both complexes are monomeric with C symmetry, and the alkylidene s  units are oriented in the same configuration with respect to the ancillary ligand. A n agostic interaction between the alkylidene C - H moiety and the metal centre is also present in both compounds, a common feature for unsaturated alkylidene complexes. The alkylidene complexes 16,17 and 18 are formed via the thermal decomposition of the corresponding bis(alkyl) precursors 14,15 and 19, respectively. The reaction mechanism is complicated by a pre-equilibrium route in which the dialkyl species undergo reversible disproportionation, presumably via a bridging binuclear adduct, to give the corresponding monoand tri-alkyl species (Scheme 3.2). Kinetic studies show that the decomposition of 14 and 18b follow first order kinetics, indicating that the rates associated with the equilibrium are rapid and do not interfere with the irreversible thermal reaction. The activation parameters obtained from the reaction are consistent with an intramolecular a-abstraction process, as is the kinetic isotope effect of 3.0 (0.5) obtained for the benzyl derivative. However, in the systems studied here the reaction rates follow the order benzyl > neosilyl > neopentyl, exactly opposite to that found previously in other systems. We believe that our results reflect a subtle balance between the 127  References  begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . . .  steric crowding imposed by the alkyl ligands and the side-arm phosphines of the ancillary ligand. The  bulkier neopentyl ligands crowd the metal centre to a greater extent than do the benzyl  groups, thus providing less opportunity for the bulky phosphines to coordinate. As alkylidene formation is hastened by phosphine coordination, this may account for the faster rates observed for  the less bulky benzyl derivative, in addition to the otherwise surprising lack of thermal  reactivity of the trialkyl species, where phosphine coordination remains absent under all conditions. The  rarity of alkylidene complexes found in Group 4 is striking in comparison to the  number of examples known for the group 5 metals . These differences are largely based on the added coordinative saturation available to the precursor complexes of the group 5 congeners, due to the presence of an extra alkyl ligand. A l l Group 4 derivatives reported thus far have required the additional steric saturation of a phosphine donor. Clearly this steric requirement is adequately met with the P Cp ligand, by employing bulky chelating bis(phosphines) appended to 2  a substituted cyclopentadienyl ring, to stabilize alkylidenes 16,17 and 18.  The  alkylidene complexes undergoes cycloaddition and insertion reactions with a variety  of unsaturated substrates. The reactivity at the Zr=C bond is moderated by the bulky ancillary ligand, which induces slow reaction rates and imposes a limit on the size of substrates that can access the metal. Although unreactive with larger olefins and internal alkynes, a reaction of alkylidene 16 with ethylene follows first-order kinetics in both alkylidene and ethylene to yield the ethylene complex 20 . 16 also inserts molecules such as C O and CNtJSu to yield T | 2  coordinated ketene and ketenimine complexes, 21 and 22, respectively. Ketene 21 in turn reacts with ethylene to give metallacycle 23, which undergoes a final insertion of C O to give the zwitterionic n -acyl-ylide species 24. 2  All of the reactions noted above involve an insertion into a Zr-C  bond, and a monomeric  structure is observed for each product due to the large isopropyl substituents on the pendant phosphines of the ancillary ligand.  The labile phosphines also play an important role in 128  References  begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . . .  providing an open coordination site for these insertion reactions to occur, which accounts for the absence of further insertion chemistry with 24, where phosphine dissociation to create a reactive site at the metal is not available . A characteristic feature of all of these complexes is associated with the C symmetry of s  the P C p ligand. As depicted in the schematic of the ligand backbone below, there are two 2  possible configurations with this ligand set, syn or anti with respect to the unique Cp carbon, which seem to present very similar steric and electronic environments for a given R group. Indeed, some of the complexes reported here (20, 21) exhibit both configurations in equilibrium with each other, apparently isomerizing in solution by the mechanism in Scheme 3.6. Alternately, other complexes ( 1 6 , 2 2 , 2 3 ) exclusively favor one configuration over the other. Furthermore, while 1 6 adopts the syn structure, the chosen structure for 2 3 corresponds to the anti derivative. The factors responsible for a given configuration are evidently more subtle than the simplified diagram below suggests.  129  References begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  3.6 Experimental Section  3.6.1 Procedures and materials Unless otherwise stated, general procedures were performed according to Section 2.7.1. K C D 2 C 6 D 5 was prepared according to the same procedure followed for KCH2Ph in Chapter 2. Tert-butyl isonitrile (Aldrich) was prepared as a toluene solution (0.88 M). The procedures for the preparation of [P2Cp]Zr=CHPh(Cl) (15) has been described elsewhere. Pr  2  3.6.2 Syntheses 3.6.2.1 Pr[P Cp]ZrCl(CH Ph) (14) 2  (a) From  2  Pr  [ P C p ] Z r C l (1) and K C H P h : A solution of KCFf Ph (0.100 mg, 2  3  2  2  0.43mmol) in 10 mL of THF was added with stirring to a cooled (-78 "C) solution of 1 (65 mg, 0.23 mmol) dissolved in 30 mL of THF. The dark red colour of the K C H P h solution was 2  discharged upon addition and the colour of the reaction mixture became greenish-orange. The mixture was allowed to slowly warm to room temperature, whereupon all the volatiles were then removed under vacuum and the residue extracted with hexanes and filtered. The filtrate was reduced under vacuum to give a thermally and photochemically labile sensitive orange oil. N M R spectra of this oil indicate the presence of 14, in addition to both tribenzyl 3 and monobenzyl 12. (b)  From Pr[P Cp]ZrCl (CH Ph) (1 ) and 2  2  2  2  Pr  [P Cp]Zr(CH Ph) 2  2  3  (3).  Mixing  together stoichiometric benzene-c/g solutions of 3 and 12 produced a mixed solution with the same spectroscopic results as observed for procedure (a) above. The assignment of peaks in the * H , c { ! H } and 13  3 1  P { ! H } N M R spectra for 14 is  provided by eliminating the known resonances for 3 and 12. Note that some peaks for 14 are 130  R e f e r e n c e s b e g i n on p a g e 1 4 1  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . .  obscured by overlapping resonances arising from the coexistence of all three benzyl species. *H NMR  (20 °C, C D ) : 8 0.33 and 0.44 (s, 6H, S i ( C / / ) ) , 0.89 (m, 4H, SiC# P), 1-23 (m, 24H, 6  6  ?  CH(Cfl3)2), 2.34 (m, 4H, CH Ph), 6.49 (d, 2H,  4  2  C H ) , 6.87 (t, I H , 7 5  H H  p - C H ) . 3 1 p { l H } NMR  7Hz,  6  5  3.6.2.2  Pr  2  7 H = 1Hz, Cp-H), 6.65 (d, 4H, 7 H = 7Hz, o4  H  H  = 1Hz, Cp-H), 7.03 (t, 4H, - V  4  6  2  = 7Hz, m - C H ) , 7.22 (t, 2H, 3 / H = 6  H H  5  H  (20 °C, C D ) : 8 0.1 (s). 6  6  [ P C p ] H f = C H P h ( C l ) (17) 2  A solution of K C H P h (68 mg, 0.55 mmol) in 20 mL of T H F was added dropwise with 2  stirring to a cooled (-78 °C) solution of 2 (400 mg, 0.55 mmol) dissolved in 20 mL of THF.  The  colour of the solution slowly changed to bright yellow. The solution was warmed to room temperature and then stirred for another 3 hours. The solvent was then removed in vacuo, and the residue extracted with hexanes and filtered. The filtrate was reduced under vacuum to give a yellow oil which was redissolved in 30 mL of toluene. This solution was placed in a 95 °C oilbath for 6 days, after which no further reaction could be detected by NMR corresponding NMR  spectroscopy (for a  scale reaction). The solvent was removed, and the oil extracted with hexane  to give a bright yellow solid, which yielded crystals suitable for X-ray diffraction from a toluene/hexanes solution mixture at -40 "C.  Yield: (307 mg, 75 %). H NMR  0.12 and 0.31 (s, 6H, Si(Ctfj)2), 0.42 and 0.49 (dd, 4H, 7 H = 5Hz, 7 2  H H  = 7Hz, 3 /  6  = 7Hz, S i C / / P ) ,  P H  2  = 6Hz, C H ( C / / ) ) , 1.73 and 2.43 (m, 2H,  P H  5  CH(C#3>2), 6.11 (t, I H , 7 H = 1Hz, Cp-H), 6.67 (t, I H , 3 / 4  H  4  6  2  H  0.79, 0.96, 1.33 and 1.14 (dd, 6H, 3 /  (20 °C, C D ) : 8  ]  H H  2  = 7Hz, p - C H ) , 7.09 (d, 2H, 6  5  7 H = 1Hz, Cp-H), 7.16 (t, 2H, 7 H = 7Hz, m - C H ) , 7.33 (s, I H , CTTPh), 7.45 (d, 2H, 7 H = 3  4  H  H  7Hz,  o-C H 6  5  3 1 p N M R (20 " C , C D ) : 8  ).  5  6  6  6  H  23.4  (s).  Anal.  Calcd.  C3 H53ClHfP Si (C H )o.5 : C, 50.81; H , 7.25 Found: C, 50.86; H , 7.51. 0  2  2  7  8  131  R e f e r e n c e s b e g i n o n p a g e 141  for  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  3.6.2.3  Pr  [ P C p ] Z r = C H C M e ( C l ) (18a) 2  3  A solution of LiCH2CMe3 (51 mg, 0.65 mmol) in 20 mL of toluene was added dropwise with stirring to a cooled (-78 °C) solution of 1 (210 mg, 0.33 mmol) dissolved in 60 mL of toluene. The colour of the solution immediately changed to bright yellow. The solution was stirred at -78 "C to 0 "C for another 30 minutes, and then for another 3 hours at room temperature. The solvent was then removed in vacuo, and the residue extracted with hexanes and filtered. The filtrate was reduced under vacuum to give a green oil which was redissolved in 30 mL of toluene. This solution was placed in a 95 "C oilbath for 6 days, after which no further reaction could be detected by N M R spectroscopy.  The solvent was removed, and the oil  extracted with pentane to give a green oil, containing 18a and other unidentified products. Repeated attempts to obtain crystals from cold pentane were unsuccessful. Estimated yield: (65% by  3 1  P NMR  spectroscopy). iff NMR  0.80 (dd, 4H, / H H = 6Hz, 7 2  2  P H  (20 °C, C D ) : 8 0.38 and 0.40 (s, 6H, 6  2  3  1Hz, C$H), 8.20 (s, 1H, CHC(CH ) ).  3 1  3 3  Pr  Si(CH ) ), 3  2  = 7Hz, SiC7/ P), 1-10 and 1.30 (m, 12H, CH(C//j) ), 1-50 (s, 2  9H, CHC(C#i)3), 2.10 (m, 4H, C / / ( C H ) ) , 6.60 (d, 2H,  3.6.2.4  6  2  P NMR  4  / H = 1Hz, H  C H), 7.41 (t, 1H, / H 4  5  H  =  (20 "C, C D ) : 8 14.0 (s). 6  6  [ P C p ] Z r = C H S i M e ( C l ) (18b) 2  3  A solution of LiCH2SiMe3 (155 mg, 1.64 mmol) in 30 mL of toluene was added dropwise with stirring to a cooled (-78 "C) solution of 1 (525 mg, 0.82 mmol) dissolved in 90 mL of toluene. The colour of the solution immediately changed from pale yellow to bright yellowish green. The solution was stirred at -78 "C to 0 °C for another 30 minutes, and then for another 2 hours at room temperature. The solvent was then removed, and the residue extracted with hexanes and filtered. The filtrate was reduced under vacuum to give a greenish yellow oil which was redissolved in 60 mL toluene. This solution was placed in a 95 "C oilbath for 3 days, after which the volume was reduced under vacuum to 1 mL and 5 mL hexanes added. Bright yellow 132  References  begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . .  crystals were slowly obtained from this concentrated solution at -40 "C. The supernatant solution was filtered away, and the crystals washed twice with cold hexanes and dried under vacuum. More crystalline material could be obtained from the mother liquor. Yield: (440 mg, 82 %). H l  N M R (20 "C, C D ) : 8 0.21 and 0.53 (s, 6H, Si(C//j) ), 0.32 (s, 9H, CHSi(C7/j) ), 0.68 and 0.72 6  (dd, 4H, /  6  2  H = 6Hz, 7  2  = 7Hz, SiC# P), 1.04 and 1.48 (m, 12H, CH(CH ) ),  2  H  3  P H  2  2.11 and 2.29  3 2  (m, 2H, C/7(CH ) ), 6.07 (d, 2H, 7 H = 1Hz, C H), 7.30 (t, 1H, 7 H = 1Hz, C /7), 8.99 (s, , 4  3  4  2  H  5  C / / S i ( C / / ) ) . 31p N M R (20 °C, C D ) : 5  3  6  H  8 16.2 (s).  6  1 3  5  C N M R (20 °C, C D ) : 8 5.9 and 11.1 6  6  (Si(CH ) ), 7.9 ( C H ( C H ) ) , 16.5 (SiCH P), 25.6 and 30.9 ( C H ( C H ) ) , 26.6 (CHSi(CH ) ), 3  2  3  2  2  3  2  3  35.4 and 35.5 ( C H ( C H ) ) , 119.0 (Cp), 121.9 (Cp), 129.5 (Cp), 213.8 (t, 7  = 12Hz,  2  3  2  3  P C  C H S i ( C H ) ) . Anal. Calcd. for C H C l P S i Z r : C, 49.54; H , 8.78; C l , 5.42. Found: C, 3  3  2 7  5 7  2  3  49.58; H , 8.71; C l , 5.65.  3.6.2.5  P r  [ P 2 C p ] Z r C l ( C H C M e ) 2 (19a) 2  A solution of L i C H C M e 2  3  3  (1.09 mg, 0.24 mmol) in 60 m L of toluene was added  dropwise to a cooled (-78 "C) stirring solution of 1 (350 mg, 0.58 mmol) dissolved in 60 mL of toluene. The colour of the solution immediately changed in intensity from pale to bright yellow. The solution was allowed to warm slowly to room temperature and stirred for another 2 hours. The solvent was then removed in vacuo, and the residue extracted with hexanes and filtered. The filtrate was reduced to give a bright yellow oil consisting of 19a, in addition to trialkyl 5a and monoalkyl 7a. The assignment of resonances for 19a is based on the known resonances for 5a and 7a obtained by independent syntheses. U N M R (20 °C, l  C6D6):  8 0.45 and 0.47 (s, 6H,  Si(C/7j) ), 0.63 (d, 4H, 7 R H = 6Hz, SiC/7 P), 0.89 (m, 24H, C H C O / j ^ ) , 1.23 (s, 18H, 2  2  2  C H C ( C # 3 ) ) , 1.31 and 1.78 (d, 2H, 7 2  2  3  H H  = 8Hz, C/7 C(CH ) ), 1.55 (m, 4H, C/7(CH )2), 6.82 2  (d, 2H, 7 H = 1Hz, Cp-H), 7.03 (t, 1H, 7 R H = 1Hz, Cp-H). 4  4  H  3  3  3 1  3  P N M R (20 "C, C D ) : 8 -5.9 6  6  (s).  133  References begin o npage 141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  3.6.2.6  P [ P C p ] Z r C l ( C H S i M e ) (19b) r  2  2  3  2  The procedure followed is analogous to that for 19a above, using LiCH2SiMe3 (117 mg, 1.24 mmol) and 1 (398 mg, 0.62 mmol). The resulting greenish oil consists of 19b, trialkyl 5b, and monoalkyl 7b. Again, the assignment for 7b is based on integration of the l H N M R spectrum.  N M R (20 "C, C D ) : 8 0.32 (s, 18H, C H S i ( C / / i ) ) , 0.41 and 0.43 (s, 6H, 6  Si(CH ) ), 3  0.63 (d, 4 H , 7 H 2  2  H  6  2  = 6Hz, S i C / / P ) , 0.70 and 1.14 (d, 2 H , 7 H  3  3  3 2  Cp-H), 6.86 (d, 2H, 7 H = 1Hz, Cp-H)4  3 1  H  3.6.2.7  Pr  = 12Hz,  2  2  C / / S i ( C H ) ) , 0.99 (m, 24H, CU(CH ) ), 2  3  H  1.57 (m, 4H, C / / ( C H ) ) , 6.81 (t, I H , 7 H = 1Hz, 4  3  2  H  P N M R (20 "C, C D ) : 8 -4.5 (s). 6  6  [ P C p ] Z r ( r ) - C H = C H ) C l (20) 2  2  2  2  A solution of Zr alkylidene 16 (1.932 g, 2.93 mmol) in 60 mL of toluene was placed in a 200 mL reactor equipped with a needle valve and affixed to a dual vacuum/nitrogen line. A small portion of solvent was removed under vacuum, and an atmosphere of ethylene introduced at -78 °C. The reaction mixture was warmed to room temperature and left to stir for 12 h, during which time the colour of the solution gradually changed from bright yellowish-orange to dark red. The solvent was then removed in vacuo, and the oily residue extracted with pentane and filtered. Reducing the solution to 7 mL and cooling to -40 "C produced dark red crystals. Yield 1.61 g (92 %). Method 2. The procedure was identical to that for 16 above, reacting Zr alkylidene 18b with ethylene. A reaction conducted on the same scale as above was complete within 8 h. IH N M R (20"C, C D ) : 8 0.22 and 0.23 (s, 6H, Si(C7/j) ), 0.78 and 0.83 (d, 2H, 7 2  6  6  2  5Hz, S i C / / P ) , 0.99 and 1.04 (m, 2H, ZrCH =CH ), 2  2  2  1.08, 1.17, 1.22 and 1.29 (dd, 6H, 3 /  9Hz, 7 H = 7Hz, CH(C/7?) ), 2.19 (m, 4H, 7 H = 7Hz, 7 2  2  H  2  2  H  134  P H  P H  =  P H  =  = 7Hz, C / / ( C H ) ) , 4.32 (t, I H , 3  2  References begin o npage 141  C h a p t e r 3: Z i r c o n i u m a n i l H a f n i u m A l k y l i d e n e .  7 H H = 1Hz,  4  C{ U}  li  Cp-H), 6.29 (d, 2H,  / H H = 1Hz, Cp-H). 3 1 p { lH} NMR  (20°C, C D ) : 8 19.5 (s). 6  6  (20"C, C D ) : 8 -2.0 and 1.6 (Si(CH 3 )2), 9.3 (SiCH P), 9.3, 13.5, 22.7 and 25.4  NMR  l  4  6  6  2  ( C H ( C H 3 ) 2 ) , 31.4 (ZrCH ), 31.5 (CH(CH ) ), 106.8 (Cp-CH), 125.9 (Cp-CH). 2  3  Anal. Calcd.  2  f o r C H i C l P S i Z r : C, 50.34; H , 8.62. Found: C, 50.35; H , 8.51. 2 5  5  2  3.6.2.8  2  Pr  [ P C p ] Z r C ( 0 ) = C H P h ( C l ) (21a) 2  A solution of 16 (1.390 g, 2.11 mmol) in 60 mL of toluene was placed in a 200 mL bomb and affixed to a dual vacuum/nitrogen line. A small portion of solvent was removed under vacuum, and an atmosphere of carbon monoxide introduced. The reaction mixture was left to stir at room temperature for 48 hrs, during which the colour of the solution gradually changed from bright yellowish-orange to reddish-orange. The solution was then filtered, and the filtrate reduced to 3 mL and layered with hexanes . Orange crystals were obtained from this solution at -40 °C. Yield 1.26 g (87 %). H NMR  (20 "C, C D ) : 8 0.20 and 0.46 (s, 6H, Si(CH ) ),  !  (dd, 4H, 2 2  /  H  H  = 6Hz, 2  /  P  3  1Hz, 3/ 1 3  C  H  2  Cp-H), 7.09 (t, I H , 3 H  2  NMR  j  3  2  P  H  = 9Hz, 4  y  = 7Hz, P-Q3H5), 7.14 (t, I H , 7 H = 1Hz, Cp-H), 7.39 (t, 2H, 4  H  H  5  j  H  H  = 7Hz, 0-C6H5).  31p  H  NMR  (20 "C, C D ) : 8 9.5 (s). 6  6  (20 "C, C D ) : 8-1.4 and 0.7 (Si(CH ) ), 9.9 (SiCH P), 17.5, 19.9, 26.2 and 30.9 6  (CH(CH3h),  6  3  2  2  102.3 (CHPh), 117.1 (CpSi), 122.3 (Cp-CH2), 125.1 ( p - C H ) , 126.3 (Cp-CH), 6  129.2 ( m - C H ) , 142.0 ( o - C H ) , 205.1 (t, 6  5  6  5  JCP  2  =  14Hz, C(0)=C).  5  Anal.  Calcd. for  C i H C 1 0 P S i Z r : C, 54.23; H , 7.78. Found: C, 54.35; H , 7.85. 3  5 3  0.70  2.10 (m, 4H, C ^ C H ^ ) , 5.96 (s, I H , CtfPh), 6.60 (d, 2H, 7 H H =  = 7Hz, m - C H ) , 8.09 (d, 2H, 3 6  6  = 7Hz, S i C / / P ) , 0.67, 0.95, 1.20, and 1.36 (dd, 6H, 3  H  7 H H = 7Hz, CH(CH ) ),  6  2  2  135  References begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e ...  3.6.2.9  Pr  [ P C p ] Z r C ( 0 ) = C H S i M e 3 ( C l ) (21b) 2  The procedure followed was similar to that for 21a, by reacting 18b (0.98 g, 1.50 mmol) in an atmosphere of CO.  The reaction mixture was left to stir at room temperature for 48 hrs,  during which no colour change in the solution was noted. The solvent was then removed in vacuo, and the oily residue extracted with hexanes and filtered, yielding a hydrocarbon-soluble orange oil from which crystals could not be obtained. Yield 0.87 g (85%); spectroscopic data for the major isomer:  N M R (20 "C, C D ) : 8 0.18 and 0.41 (s, 6H, S i ( C # ) ) , 0.48 (s, 9H, 6  CHSi(C/7 ) ), 0.82 (dd, 4H, / H  = 5Hz,  2  5  (m,  3  H  2  6  7  5  P H  = 7Hz,  2  S i O / P ) , 1.12 (m, 24H, CH(C#j) ), 2.38 2  2  4H, C # ( C H ) ) , 4.39 (s, 1H, C / / S i ( C H ) ) , 6.18 (t, 1H, 7 H = 1Hz, Cp-H), 6.43 (d, 2H, 4  3  4/ H  = 1Hz,  H  2  3  Cp-H). 31p NMR  3.6.2.10  Pr  3  H  (20 "C, C D ) : 8 11.9 (s). 6  6  [ P C p ] Z r C ( N B u ) = C H P h ( C I ) (22) t  2  A toluene solution of 0.088 M tert-butyl-isocyanide (6.4 mL, 0.56 mmol) was added dropwise with stirring to a cooled (0 °C) solution of 16 (366 mg, 0.56 mmol) dissolved in 60 mL of toluene. The reaction mixture was stirred at 0 "C for another 30 minutes, and then slowly warmed to room temperature, during which colour of the solution gradually changed from bright orange to dark red. The solution was stirred at room temperature for another 12 hours, the solvent then removed in vacuo,  and the residue extracted with hexanes and filtered. The solution  was reduced to 5 mL, from which dark red crystalline needles were obtained at -40 °C. Yield 320 mg (77%). H N M R (20 "C, C D ) : 8 0.20 (br s, 6H, SKCffjfc), 0.40 (s, 6H, Si(C7/j) ), l  6  6  2  0.69 (m, 4 H , S i C t f P ) , 1.03 (m, 24H, C F K C / ^ h ) , 1.57 (s, 9H, N(CH ) ), 2  3  1.82 (m, 2H,  3  CHQCHjh), 2.49. (br m, 2H, C / / ( C H ) ) , 6.55 (s, 1H, CtfPh), 6.80 (d, 2H, 7 H = 1Hz, C H), 4  3  2  H  5  6.89 (t, 1H, 7 H = 1Hz, C H), 7.02 (t, 1H, 7 H = 7Hz, p - C H ) , 7.37 (t, 2H, / H 4  3  H  5  C H ) , 8.20 (br m, 2 H , o - C H ) . 6  5  3  H  6  5  3  6  5  l p N M R (20 °C, C D ) : 8 11.8 (s). 6  6  H  = 7Hz, m-  Anal. Calcd. for  C H C l N P S i Z r : C, 56.68; H , 8.43; N , 1.89. Found: C, 56.85; H , 8.49; N 1.91. 3 5  6 2  2  2  136  References begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  3.6.2.11  [P Cp]ZrCH CH2C(0)=CHPh(CI) (23a) 2  2  A solution of 21a (1.09 g, 1.59 mmol) in 60 mL of toluene was placed in a bomb and affixed to a dual vacuum line. The head space was partially evacuated, and an atmosphere of ethylene introduced. The solution was left to stir at room temperature for 48 hrs, during which the orange colour of the solution slowly turned red. The solvent was then removed in vacuo, and the oily residue extracted with hexanes and filtered. The solution was reduced to 5 mL, from which orange crystals were obtained at -40 "C. Yield 0.87 g (77%). H N M R (20 °C, C D ) : 8 l  6  0.24 and 0.49 (s, 6H, Si(C//j) ), 0.72 (dd, 4H, 2 / (m, 12H, CH(CH )2), 3  3/ H =  7 H z  H  4  = 6Hz, J  H  H  P H  2  1.50 (m, 2H, Z r C / / C H ) , 2.09 and 2.21 (m, 2H, CJ/(CH )2), 3.41 (t, 2H, 2  2  3  > Z r C H C t f ) , 5.43 (s, I H , C//Ph), 6.79 (d, 2H, / 4  2  2  7 H = 1Hz, Cp-H), 7.06 (t, I H , 3 / H  (d, 2H, 3 /  = 7Hz, SiC/f P), 0.97 and 1.17  2  2  H H  6  = 7Hz,  0-C6H5).  H H  H  H = 2Hz, Cp-H), 7.01 (t, I H ,  = 7Hz, p-QH^), 7.42 (t, 2H, 3 /  = 7Hz, m - C H ) , 8.05  H H  6  3 l p N M R (20 "C, C D ) : 8 7.8 (s). 6  Anal.  6  5  Calcd. for  C 3 3 H C 1 0 P S i Z r : C, 55.47; H , 8.04. Found: C, 55.67; H , 8.19. 57  2  3.6.2.12  2  Pr  [ P C p ] Z r C H C H C ( 0 ) = C H S i M e ( C l ) (23b) 2  2  2  3  The procedure followed was analogous to that for 23a above, reacting 21b (0.80 g, 1.17 mmol) with an atmosphere of ethylene. The reaction mixture was left to stir at room temperature for 36 hrs, during which there was no colour change to the orange solution. The solution was concentrated to 2 mL and layered with hexanes, from which orange crystals were obtained at -40 °C from a solution consisting of toluene/hexanes in a 1:1 mixture. Yield 0.66 g (79 %). *H N M R (20 °C, C D ) : 8 0.28 and 0.48 (s, 6H, Si(C//j) ), 0.47 (s, 18H, CHSi(C//j)3), 0.91 (d, 4H, 6  2  6  2  / H H = 6Hz, SiCtf P), 1.11 (m, 24H, CU(CH ) ), 2  CHiCHih),  3.34 (t, 2H, 3 /  3  2  1.39 (m, 2H, Z r C / / C H ) , 2.21 (m, 4H, 2  2  = 7Hz, Z r C H C / / ) , 4.22 (s, I H , C / / S i ( C H ) ) , 6.59 (d, 2H, 7 H 4  H H  2  137  2  3  3  References begin on page 141  H  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . ,  = 1Hz,  Cp-H), 6.90 (t, 1H, 7 4  H  H = 1Hz,  Cp-H)-  3 1  P N M R (20 °C, C D ) : 8 8.2 (s). 6  6  An  Calcd. for C3oH iC10P Si3Zr: C, 50.70; H , 8.65. Found: C, 50.60; H , 8.57. 6  3.6.2.13  Pr  2  [P Cp]ZrC(0)CH CH C(0)=CHPh(CI) (24a) 2  2  2  A solution of 23a (0.64 g, 0.90 mmol) in 30 mL of toluene was placed in a bomb and affixed to a dual vacuum line. An atmosphere of carbon monoxide was introduced at -78 °C, and the reaction mixture was warmed to room temperature and stirred for 24 hrs, during which the reddish solution gradually faded to an orange-yellow colour. The solvent was then reduced to 5 mL and layered with hexanes, from which yellow crystals were obtained at -40 °C. Yield 0.54 g (80%). *H N M R (20 C, C D ) : 8 0.01 and 0.28 (s, 6H, S i ( C / / ) ) , 0.61 (dd, 2H, / H = 6Hz, 2  6  2  7p  6  5  = 6Hz, SiC7/ P), 0.71 (dd, 2H, / H = 6Hz, / 2  H  2  2  H  P  H  2  H  = 6Hz, SiC// P), 0.91 (m, 24H, 2  CH(CUi) ), 2.19 (m, 2H, C=CCH ), 2.75 (m, 2H, Z r C C / / ) , 5.06 (s, 1H, CHPh), 6.72 (dd, 1H, Cp-H), 6.83 (dd, 1H, Cp-H), 7.02 (t, 1H, 3 / = 7Hz, p-Q (dd, 1H, Cp-H), 7.30 (t, 2H, - V = 7Hz, m - C H ) , 7.94 (d, 2H, 3 / = 7Hz, o-QHs), . 31p  CH(C/7j0 ), 1.62 (m, 4H,  2  2  2  2  H H  H H  6  5  H H  N M R (20 "C, C D ) : 8 46.8 (s),-5.1 (s). Anal. Calcd. for C34H57C10 P Si3Zr(C H )o.5: C , 6  6  2  2  7  8  57.11; H , 7.80. Found: C, 57.30; H , 7.80.  3.6.2.14  PqP Cp]ZrC(0)CH CH C(0)=CHSiMe (Cl) (24b) 2  2  2  3  The procedure followed was similar to that for 24a, by reacting 23b (0.50 g, 0.70 mmol) with an atmosphere of CO. There was no obvious colour change to the orange solution after stirring at room temperature for 48 hrs. The solvent was then removed and the residue extracted with hexanes and filtered.  A yellow-orange crystalline solid was isolated from a cold,  concentrated hexanes solution. Yield: (0.39 mg, 76 %). H N M R (20 "C, C D ) : 8 0.02, 0.19, !  6  6  0.32 and 0.49 (s, 3H, Si(C//?) ), 0.48 (s, 9H, CHSi(C//i) ), 0.60 (dd, 4H, 7 H = 7Hz, / 2  2  3  138  2  H  References  begin on p a g e 141  P  H  =  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e .  7Hz,  S i C / / P ) , 0.85 and 1.09 (m, 12H, C H ( C / / j ) ) , 1.62 (m, I H , C = C C / / ) , 1.67 (m, 4H, 2  CHiCHih),  2  2  2.04 (dd, I H , C = C C / / ) , 2.21 (dd, I H , Z r C C / / ) , 2.74 (dd, I H , Z r C C / / ) , 4.04 (s, 2  2  2  IH, C / / S i ( C H ) ) , 6.71 (dd, I H , Cp-//), 6.83 (dd, I H , Cp-//), 7.10 (dd, I H , Cp-//). 31p 5  (20 °C, C D ) : 8 46.2 (s), -5.9 (s). 6  NMR  3  6  Anal. Calcd. for C i H i C 1 0 P S i 3 Z r : C, 50.40; H , 8.32. 3  6  2  2  Found: C, 50.42; H, 8.35.  3.6.3  NMR  study of the equilibrium between 3,12, and 14  Separate stock solutions of [3] and [12] were prepared in benzene-^/g, the concentrations of which were determined by comparing the integrated intensity of the C / / P h signals relative to 2  external ferrocene. Incrementally varied proportions of these initial solutions were combined together to generate mixed solutions consisting of 3, 12 and 14. calculated from the integration of the C / / P h signals in the H NMR l  2  The concentrations were spectra with respect to that  of the ferrocene standard.  3.6.4  Kinetic studies of the formation of alkylidene 16 and 18b A sample of the equilibrium mixture consisting of monobenzyl 12, dibenzyl 14 and  tribenzyl 3 was dissolved in toluene-dg and used as a stock solution for kinetic study. The initial concentrations in this solution were calculated from the integration of the 31p N M R  signals of a  representative sample with respect to that of the internal standard P P h . The disappearance of 14 3  and  3 (and the concomitant appearance of 16) as recorded by 3ip{lH} NMR  spectroscopy was  monitored for a period of at least three half-lives; samples with an internal P P h reference were 3  employed to calibrate the measurements. Separate kinetic runs were conducted on the Varian 300-XL instrument at temperatures set to 70, 80, 85 and 90 "C. The uncertainty in the temperature settings was estimated to be +/- 1 "C. Similar experiments with the CD C6D5 2  139  References begin on page  141  C h a p t e r 3: Z i r c o n i u m a n i l H a f n i u m A l k y l i d e n e ...  labeled complexes were performed at 70 "Cto examine kinetic isotope effects (KIE) with the proposed mechanism.  associated  Each experiment was repeated at least once to indicate  reproducibility. For the duration of the kinetic experiments, all sample tubes were protected from light sources where possible using metal foil wrap to minimize the competitive photochemical transformation of 14 to 16. A similar procedure was followed for the study into the formation of neosilyl 18b, except the P { H } N M R 3 1  1  spectra were conducted at 20 °C, as the resonances due to dialkyl 19b and  trialkyl 7b merge together at higher temperatures. For a typical run, a 0.5 mL sample of the toluene solution was placed in a 5mm NMR  tube, the solution frozen and degassed, and the tube  then flame sealed and placed in a constant temperature oil bath (uncertainty in the temperature measurements estimated to be 1 "C).  The tube was removed from the bath after a period of 1.5  hours and immersed in an ice bath to quench the reaction. A P { 1 H } N M R 31  recorded at 20 "C on the Bruker-AMX 500 MHz  spectrum was  instrument, and the tube returned to the oil bath.  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Soc. 1986,108, 3318.  143  References  begin on page  141  C h a p t e r 3: Z i r c o n i u m a n d H a f n i u m A l k y l i d e n e . . .  (46)  Bristow, G . S.; Hitchcock, P. B.; Lappert, M . F. J. Chem. Soc, Chem. Commun. 1982,  462. (47)  Moore, E. J.; Straus, D. A.; Armantrout, J.; Santarsiero, B. D.; Grubbs, R. H.; Bercaw, J.  E. J. Am. Chem. Soc 1983,105, 2068. (48)  Fachinetti, G.; Biran, C.; Floriani, C. J. Am, Chem, Soc. 1978,100, 1921.  (49)  Scott, M . J.; Lippard, S. J. J. Am, Chem, Soc 1997,119, 3411.  (50)  Fermin, M . C.; Hneihen, A. S.; Maas, J. L.; Bruno, J. W. OrganometalUcs 1993,12,  1845. (51)  Antinolo, A.; Otero, A.; Fajardo, M . ; Lopez-Mardomingo, C.; Lucas, D.; Mugnier, Y.;  Lanfranchi, M . ; Pellinghelli, M . J. Organomet, Chem. 1992, 435, 55. (52)  Antinolo, A.; Fajardo, M.; Lopez-Mardomingo, C.; Otero, A.; Mourad, Y.; Mugnier, Y.;  Aparicio, J.; Fonseca, I.; Florencio, F. OrganometalUcs 1990, 9, 2919. (53)  Antinolo, A.; Fajardo, M.; Gil-Sanz, R.; Lopez-Mardomingo, C.; Martin-Villa, P.; Otero,  A.; Kubicki, M . ; Mugnier, Y.; Krami, S.; Mourad, Y. OrganometalUcs 1993,12, 381. (54)  Antinolo, A.; Fajardo, M.; Gil-Sanz, R.; Lopez-Mardomingo, C.; Otero, A.; Atmani, A.;  Kubicki, M . ; Krami, S.; Mugnier, Y.; Mourad, Y. OrganometalUcs 1994,13, 1200. (55)  Fandos, R.; Lanfranchi, M . ; Otero, A.; Pellinghelli, M . ; Ruiz, M . ; Teuben, J.  OrganometalUcs 1997,16, 5283. (56)  Straus, D. A.; Grubbs, R. H . J. Am, Chem. Soc 1982,104, 5499.  (57)  Fryzuk, M . D.; Mylvaganum, M . ; Zaworotko, M . J.; MacGillivray, L . R.  OrganometalUcs 1996,15, 1134.  144  References begin on page  141  Chapter 4  Effects of Ligand Modification on Structure and Reactivity  4.1  Introduction In the previous two chapters the solution behaviour and reactivity of zirconium and  hafnium complexes stabilized by the [P2Cp] ancillary ligand were detailed. This final chapter Pr  will cover preliminary efforts to examine the effects on structure and reactivity resulting from modifications of this general system. There are two areas where alterations of the ligand can be made. The first strategy involves replacement of the isopropyl substituents with smaller methyl groups. The steric bulk of the isopropyl group has been demonstrated to be advantageous in the stabilization of alkylidene and ketene complexes, but at the expense of imposed limitations in the reactivity of these complexes. The sterically hindered phosphines exhibit complicated fluxional coordination in several of the alkyl species, which is a factor in the inability to isolate dialkyl derivatives. The increased aliphatic content of the isopropyl groups also contributes to increased solubility in organic solvents and introduces complications in separation and characterization. Employing methyl substituents is anticipated to improve the ability of the phosphines to coordinate, thus reducing the tendency for fluxional solution behaviour and introducing different steric and electronic influences on the reactivity. One  of the topics for future work will address a second direction for ligand modification,  which entails placing a bulky substituent on the Cp ring to force the side-arms away from the 1,3-configuration to adjacent 1,2-positions on the ring. Preliminary results assess whether this  145  references begin on page  208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n .  change induces the phosphines to switch from trans to syn positions in the coordination sphere, and will lead to a brief structural comparison of a few Zr(III) derivatives. Another approach to changing the system is to extend the coordination chemistry of this ancillary ligand with other metals. The ligand framework is such that the appendment of two side-arms to a central Cp donor creates a wide chelate that is a potentially compatible fit with a larger metal ion such as Th(IV).  4.2  Preparation of [ P C p ] Z r C b M e  2  A toluene solution of the ancillary ligand [ P 2 C p ] L i reacts with ZrCl4(THT)2 to give Me  the trichloride complex [P2Cp]ZrCl3 (25) as colourless crystals (equation 4.1). The P { H } Me  NMR  1  spectrum shows a singlet at -21.0 ppm for two equivalent coordinated phosphines, while  the H NMR 1  3 1  spectrum resembles that found in the Pr derivative 1, with a nearly identical pattern J  for the Cp resonances in the downfield region of the spectrum. The structure of 25 is thus considered to have the same C -symmetric quasi-octahedral geometry as determined previously s  for 1.  ZrCI (THT) + 4  2  Me  [P Cp]Li 2  -LiCI -2THT t  (4.1)  Cl 25  146  references begin on p a g e  208  C h a p t e r 4: Effects  of L i g a n d Modification...  This compound has considerably lower solubility in toluene in comparison to 1; therefore the reactions outlined below are all conducted in THF  4.3.1  solvent.  Preparation of [ P C p ] Z r C l ( C H P h ) M e  2  The  2  2  addition of 1 equivalent of K C H P h to a THF 2  solution of trichloride 25 generates the  monobenzyl complex [ P C p ] Z r C l ( C H P h ) (26) as a red solid (equation 4.2). The *H  NMR  Me  2  2  2  spectrum is consistent with the stoichiometry of one benzyl group per P C p unit. As with the 2  Pr  [ P C p ] analogue 12, the methylene protons of the benzyl ligand show a downfield broadened 2  singlet near 3.25 ppm. The ambient temperature 3 1 p { lH} NMR  spectrum for 26 shows a singlet  at -19.0 ppm for two equivalent phosphine donors, which remains unchanged down to -40 °C. This observation contrasts with the fluxional phosphine dissociation seen for the 12, and is indicative of a greater inclination for the methyl substituted phosphines to coordinate.  Me  [P Cp]ZrCI 2  3  25  4.3.2  ^  1 - KCI  Isolation of [ P C p ] Z r C l ( C H P h )  Me  [P Cp]ZrCI (CH Ph) 2  2  2  ( 4  26  -  2 )  M e  2  2  2  A conspicuous theme of the previous chapter was the lack of success in isolating dialkyl complexes with the [ P C p ] ancillary ligand, where disproportionation of the intended product Pr  2  yielded an equilibrium mixture of alkyl species. By contrast, adding 2 equivalents of K C H P h to 2  a THF  solution of trichloride 25 produces the dibenzyl complex [ P C p ] Z r C l ( C H P h ) (27), an Me  2  2  2  exceedingly air- and moisture-sensitive species, that can be isolated in moderate yield as red crystals (equation 4.3).  147  references begin on page  208  C h a p t e r 4: Effects  of L i g a n d Modification.  2 K C H Ph Me  [P Cp]ZrCI 2  3  —  Me  [P Cp]ZrCI(CH Ph) 2  - 2 KCI  2  (4.3)  2  27  25  An X-ray crystal structure determination was performed on 27, and the molecular structure is shown in Figure 4.1, with selected bond lengths and bond angles given in Table 4.1.  C(28) C(19)  CI11)  Figure 4.1  Molecular structure of [P2Cp]ZrCl(CH2Ph)2 (27); 33% probability thermal Me  ellipsoids are shown. Hydrogen atoms are omitted for clarity.  The six-coordinate geometry shows distortion of the equatorial ligands away from the Cp donor, in common with trichloride 1 and metallacycle 23. The benzyl ligands are coordinated trans to each other, presumably to minimize steric interactions within this crowded geometry.  148  references begin on page  208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n .  Each benzyl ligand is bound in an V-mode; the Zr(l)-C(16)-C(17) and Zr(l)-C(23)-C(24) bond angles of 114.15(14)° and 106.47(13)", respectively, are both consistent with the geometry of a normal sp -hybridized carbon centre, in contrast to the angular distortion observed in n -benzyl 3  2  complexes like Zr(CFJ.2Ph)4 (average corresponding M-CorCip  SO  bond angle of 92°). TheZr(l)1  C(16)  and Zr(l)-C(23) bond lengths of 2.404(2) A and 2.407(2) A, respectively, are  approximately 0.06 A longer than the corresponding distance in analogous ri -benzyl 2  complexes.  Unlike most Zr benzyl species, the coordination of two phosphines in 27 helps to  saturate the metal so that it is unnecessary for the benzyl ligands to increase hapticity in order to improve their electron donor ability. In 27 the steric congestion is reflected in the two Zr-P bond distances differing by approximately 0.7 A, which may result from the phenyl rings of both benzyl ligand being directed towards the same phosphine, which in turn forces this donor further away from the metal. Table 4.1  Selected Bond Lengths (A) and Bond Angles (") for [ P C p ] Z r C l ( C H P h ) 2 (27). Me  2  2  Zr(l)-Cl(l)  2.5379(5)  Cl(l)-Zr(l)-P(l)  86.41(2)  Zr(l)-P(l)  2.8079(6)  Cl(l)-Zr(l)-P(2)  78.75(2)  Zr(l)-P(2)  2.8757(6)  P(l)-Zr(l)-P(2)  164.79(2)  Zr(l)-C(16)  2.407(2)  Cl(l)-Zr(l)-C(16)  78.86(5)  Zr(l)-C(23)  2.404(2)  Cl(l)-Zr(l)-C(23)  80.52(5)  C(16)-Zr(l)-C(23)  140.21(8)  Zr(l)-C(16)-C(17)  114.15(14)  Zr(l)-C(23)-C(24)  106.47(13)  The P { H } NMR 3 1  1  spectrum of 27 displays a singlet at -18.5 ppm for a pair of equivalent  coordinated phosphines, in the same chemical shift region as found for trichloride 25 and for monobenzyl 26. This spectrum remains unchanged at low temperature (-60 °C), indicating that any fluxional process involving the side-arm phosphines is undetected in the NMR  149  references begin on page  time scale.  208  C h a p t e r 4: Effects  The  X  of L i g a n d Modification.  H N M R spectrum is consistent with the approximate C symmetry of the solid state s  structure. However, the two benzyl groups in 27 are chemically inequivalent in Figure 4.1 (or in any geometry in which the two phosphines are bound). Therefore, the prominent broad peak near 2.8 ppm for the methylene protons of the benzyl group indicates chemical exchange occurring at a rate that is comparable to the NMR  time scale. This process likely involves  dissociation of one or both side-arms, although as noted above this is not detected in the P { H } 31  NMR  spectra. At -20 °C the benzylic region of the ' H N M R  1  spectrum shows two separate  multiplets, one for each set of methylene protons, indicating that the fluxional process is at the slow exchange limit at this temperature. The downfield chemical shifts of the methylene (2.83 ppm) and ortho (7.66 ppm) protons of the benzyl ligands are consistent with the r^-coordination of these groups being maintained in solution. This contrasts with the upfield location of these resonances for the tribenzyl species 3, where as discussed in section 2.4.1 the benzyl ligands in this complex are suspected of coordinating in an T) -fashion to compensate for the absence of 2  phosphine coordination.  4.3.3  Formation of toluyne [P Cp]Zr(r| -C6H3Me)Cl from thermolysis of Me  2  2  Me  [P2Cp]ZrCI(CH Ph) 2  The  2  ability to isolate dibenzyl 27 in the absence of a complicating equilibrium is in sharp  contrast with the disproportionation behaviour of 14, which stems from the tendency for phosphine dissociation in the latter species. That the phosphines are more strongly bound in 27 also accounts for the absence of fluxional isomerization that is seen in several of the alkyl complexes encountered in Chapter 2.  The smaller methyl substituents likely encourage  phosphine coordination in 27 as a result of reduced steric conflict with the other ligands, despite the presence of two bulky benzyl groups. As will be noted in the next section there is probably also an electronic component to the superior coordination of the  150  M e  [P2Cp]  ligand.  references begin on p a g e  208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n . . .  Given the thermal reaction of dibenzyl 14 to generate alkylidene 16, we were interested in determining whether the same result would obtain for the less bulky analogue 27. The results in the previous chapter hinted that the cc-abstraction mechanism for alkylidene formation is promoted by phosphine coordination. Dibenzyl 27 clearly meets these criteria and provides a unique opportunity to directly test this hypothesis. Further, a kinetic study should be facilitated since the suspected precursor is a isolable crystalline solid, as opposed to one component in an inseparable equilibrium mixture, as is the case with 14. Thermolysis of a toluene solution of 27 for 12 hours at 70 "C eliminates one equivalent of toluene to form.a new complex, but instead of the anticipated benzylidene species the new product is a toluyne complex  M e  [ P 2 C p ] Z r ( r | - C 6 H 3 M e ) C l (28), which is obtained in two 2  isomeric forms in a 2:1 ratio as shown below (equation 4.4). The major isomer can be separated as pale yellow crystals, which when redissolved regenerates the same single product in solution, indicating that although both isomers of 28 are formed together during the thermal decomposition of dibenzyl 27, these species are not in equilibrium.  (4.4)  minor  151  r e f e r e n c e s b e g i n on p a g e 2 0 8  C h a p t e r 4: Effects  An  X-ray crystal structure analysis was obtained for the major isomer of 28. The  molecular structure is depicted in Figure 4.2, in Table 4.2.  of L i g a n d M o d i f i c a t i o n .  with selected bond lengths and bond angles given  The structure in Figure 4.3 shows the methyl group of the toluyne fragment in the  sterically favoured position furthest from the metal. The  planar phenyl ring is oriented parallel to  the Cp ring to minimize steric congestion, as similarly observed for the ethylene complex 20. The  bonding parameters are consistent with the depiction of the toluyne ligand as an ortho-  phenylene unit as shown in equation 4.4.  The C(17)-C(18) bond length is similar to the other C-  C bonds in the phenyl ring, and the short Zr(l)-C(17) and Zr(l)-C(18) bond distances of 2.222(2) A and 2.213(2) A , respectively, are indicative of Zr-C  a-bonds. These distances are similar to  the parameters of analogous Zr benzyne complexes. For example, in Cp2Zr(r| -C6H4)(PMe3)^ 2  the Zr-C  bond lengths to the benzyne ligand average 2.25 A .  C<22) Figure 4.2  Molecular structure of  Me  [P2Cp]Zr(r] -C6H3Me)Cl (28); 2  33%  probability  thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity.  152  references begin on page  208  C h a p t e r 4: Effects  of L i g a n d Modification...  Selected Bond Lengths (A) and Bond Angles (°) for Me[p c ]Zr(r| -C6H3Me)Cl  Table 4.2  2  2  p  (28).  Zr(l)-Cl(l)  2.5385(8)  Cl(l)-Zr(l)-P(l)  77.41(3)  Zr(l)-P(l)  2.7192(7)  Cl(l)-Zr(l)-P(2)  77.50(3)  Zr(l)-P(2)  2.7194(8)  P(l)-Zr(l)-P(2)  154.03(3)  Zr(l)-C(17)  2.222(2)  Cl(l)-Zr(l)-C(17)  116.70(7)  Zr(l)-C(18)  2.213(2)  Cl(l)-Zr(l)-C(18)  117.12(7)  C(17)-C(18)  1.366(3)  C(17)-Zr(l)-C(18)  35.87(9)  C(18)-C(19)  1.410(4)  C(16)-C(17)-C(18)  120.3(2)  C(19)-C(20)  1.375(4)  C(16)-C(21)-C(22)  123.6(3)  NMR  spectroscopic data for the two isomers of 28 are straightforward. A singlet is seen  in the P { H) NMR 31  l  spectrum for both the major (-7.0 ppm) and minor species (-7.3 ppm). The  methyl group on the toluyne fragment is prominent for each isomer in the  NMR  spectrum at  2.43 ppm (major) and 2.67 ppm (minor), respectively. The position of this methyl substituent on the phenyl ring with respect to the coordinated toluyne ligand gives rise to a distinctive pattern in the downfield region. For the major isomer there is a singlet at 7.82 ppm for the sole ring proton adjacent to both the methyl group and the metal-bound carbon atom, and a doublet for each of the other two ring protons. In comparison, the minor isomer shows a triplet and two doublets in the same downfield region of the N M R spectrum for the three aryl protons of the toluyne fragment. Benzyne complexes are reactive species that have found synthetic utility with insertion reactions involving alkenes, alkynes, and other unsaturated substrates. " In contrast however, 4  6  toluyne 28 is surprisingly unreactive with ethylene even at 90 "C.  153  r e f e r e n c e s b e g i n on p a g e  208  C h a p t e r 4: Effects  of L i g a n d Modification...  The unexpected result that yields toluyne 28 from dibenzyl 27 prompted consideration of the reaction mechanism. Zr benzyne complexes are conveniently generated from a thermally 7 8  induced abstraction of an aryl C - H bond by on adjacent alkyl or aryl ligand (equation 4.5). ' The product is isolated with the addition of a trapping phosphine.  (4.5)  The pendant phosphines of the P C p ancillary ligand are well suited to stabilize the 2  toluyne product 28. A n appropriate intermediate that resembles the precursor indicated in equation 4.5 could be derived from the expected alkylidene complex, as shown in Scheme 4.1. Since the thermolysis was conducted in toluene the intermediate alkylidene species could possibly activate a solvent molecule to generate the aryl-alkyl species C , which leads directly to the toluyne complex (in Scheme 4.1 a benzyne complex should be formed). However, the same toluyne complex 28, not the benzyne species shown in Scheme 4.1, is obtained when the reaction is conducted in benzene, indicating that the reaction mechanism does Q 19  not proceed via intermolecular activation of the solvent by an alkylidene species. an alternate intramolecular process, most likely route to toluyne 28.  Therefore,  perhaps still involving an intermediate alkylidene, is the A n examination of the photochemical decomposition of  dibenzyl 27 detailed below may shed light on the thermal reaction.  154  references begin on p a g e  208  C h a p t e r 4: Effects  Scheme 4.1  of L i g a n d M o d i f i c a t i o n .  Possible mechanistic route to a benzyne complex via C-H activation of a solvent molecule by an intermediate alkylidene complex.  155  references begin on p a g e  208  C h a p t e r 4: Effects  4.3.4  Photolysis of [ P C p ] Z r C I ( C H P h )  of L i g a n d M o d i f i c a t i o n .  M e  2  Red  2  2  dibenzyl 27 is stable upon prolonged exposure to visible light. The U V - V I S  spectrum of this complex shows a strong X ,  m a x  near 310 nm, however, and irradiation of 27  including this wavelength generates a new species in a clean reaction within 6 hours (equation 4.6).  Unfortunately, this product is thermally sensitive and could not be isolated under the  reaction conditions employed.  (4.6)  H The  *H NMR  spectrum shows that one equivalent of toluene is also produced in this  reaction. A n A B doublet of doublets for 29 in the P { H } NMR 3 1  1  spectrum ( /pp = 76 Hz) at 2  -18.6 and -18.9 ppm is indicative of two inequivalent, mutually coupled phosphine donors coordinated to the metal centre, suggesting an asymmetric molecular structure. This observation is supported by the corresponding *H NMR  spectrum, which shows four resonances for the  silylmethyl protons and another four peaks for the methyl groups attached to the phosphines, in addition to three separate peaks for the Cp protons. There are also six additional resonances  156  references begin on page  208  C h a p t e r 4: Effects  of L i g a n d Modification.  ranging between 2.8 and 6.0 ppm, each corresponding to a single proton and exhibiting a secondorder splitting pattern. The combination of a 2D C O S Y H NMR 1  NMR  spectrum and the i H f ? } 3 1  spectrum enabled the following assignments to be made in Table 4.3, consistent with the  structure shown in equation 4.6.  Table 4.3  Assignments for the H NMR X  proton H  A  H  B  H  C  H  D  chemical shift (8)  spectrum of 29 between 2.8 and 6.0 ppm. coupled to  splitting pattern dd  2.78  H ,H  3.08  H , H  3.17  H ,H ,P  m  3.52  H , H , P  m  B  A  B  C  E  d  C  F  dd  H  E  5.04  H B , Hp  dd  H  F  5.99  H , H  dd  D  E  A common result from the irradiation of photochemically sensitive organometallic complexes is M-C  bond homolysis. In the case of Zr(CH2Ph)4 the benzyl radical generated is 14  not observed to react with the toluene solvent (i.e., bibenzyl PhCH2CH2Ph is not formed), but instead remains within the coordination sphere in a radical cage mechanism.  15  A similar  mechanism may be operative in the formation of 29 (Scheme 4.2). The benzyl radical that is generated is resonance-stabilized, and one of these resonance forms could recombine with the Zr(III) intermediate to give a suitable precursor D. Abstraction of an aryl C - H bond by the remaining benzyl ligand would produce the observed equivalent of toluene and the final product  157  r e f e r e n c e s b e g i n on p a g e  208  C h a p t e r 4: Effects  29.  16  of L i g a n d M o d i f i c a t i o n .  This intramolecular process may be reflected in a similar mechanism for the thermal  reaction that forms 28.  hv  PhMe  •CH; C!  XPhH c^ 2  L  Scheme  4.2  ; V^  y  /  S  PhH C  *CH  2  v  "  2  \  H  D  Proposed mechanism for the photochemical decomposition of Me  [ P C p ] Z r C l ( C H P h ) (27). 2  2  158  2  references begin on p a g e 2 0 8  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n .  The photochemical product 29 is thermally sensitive and decomposes within hours under ambient conditions.  A minor decomposition product is the Zr(III) chloride-bridged dimer  ( [ P 2 C p ] Z r C l ( | i - C l ) } 2 (45). The structure of this diamagnetic species will be discussed further Me  in comparison to analogous Zr(III) derivatives in section 4.3.2, but the formation of this compound implies that a naked Zr(II) " ( [ P C p ] Z r C l ) " intermediate is generated in the Me  2  decomposition process arising from loss of the organic ligand from 29.  Subsequent  disproportionation of this intermediate could produce the observed Zr(III) chloride 45. A n organic compound, 4-benzyltoluene, identified by L C - M S and H N M R spectroscopy, is also a l  byproduct in this decomposition, and is observed in small amounts from the thermal reaction that yields toluene 28. This molecule can be broken down into a benzylic and a p-tolyl fragment, implying that its formation could arise from reductive elimination from intermediate C in Scheme 4.1, in competition with the production of 28, or from an analogous coupling reaction of the benzyl ligands in the formation of 29.  4-benzyltoluene  4.3.5  Preparation of  M e  [P Cp]Zr(CH Ph) 2  2  3  The tribenzyl complex [P2Cp]Zr(CH2Ph)3 (30) can be prepared as a red crystalline Me  solid from the reaction of trichloride 25 with 3 equivalents of K C H P h in T H F (equation 4.7). 2  159  r e f e r e n c e s b e g i n on p a g e 2 0 8  C h a p t e r 4: Effects  Mo M e  _  [P Cp]ZrCI 2  25  3 KCHoPh  ,. M e  3  - 3 KCI  of L i g a n d M o d i f i c a t i o n .  [P Cp]Zr(CH Ph) 2  2  3  ( 4  30  -  7 )  A crystal structure determination was obtained for tribenzyl 30, and the molecular structure is shown in Figure 4.3, with selected bond lengths and bond angles listed in Table 4.4.  Figure 4.3  Molecular structure of [P2Cp]Zr(CH2Ph)3 (30); 33% probability thermal Me  ellipsoids are shown. Hydrogen atoms are omitted for clarity.  160  references begin on p a g e  208  C h a p t e r 4: Effects  Table 4.4  of L i g a n d M o d i f i c a t i o n . . .  Selected Bond Lengths (A) and Bond Angles (") for [P Cp]Zr(CH Ph)3 (30). Me  2  2  Zr(l)-P(l)  2.9005(7)  P(l)-Zr(l)-P(2)  162.85(2)  Zr(l)-P(2)  2.9093(6)  P(l)-Zr(l)-C(16)  74.02(6)  Zr(l)-C(16)  2.416(3)  P(l)-Zr(l)-C(23)  106.80(6)  Zr(l)-C(23)  2.413(3)  P(l)-Zr(l)-C(30)  102.13(6)  Zr(l)-C(30)  2.391(3)  P(2)-Zr(l)-C(16)  89.15(6)  Zr(l)-Cp'  2.30  C(16)-Zr(l)-C(23)  80.93(9)  C(23)-Zr(l)-C(30)  141.30(9)  Zr(l)-C(23)-C(24)  111.6(2)  The  structure shows that both phosphines are coordinated to the metal, in direct contrast  to the solution structure of the ^ [ P ^ p ] tribenzyl analogue 3. The crowded quasi-octahedral arrangement of three bulky ligands in 30 evidently induces bond lengthening. The Zr-P bond distances (average 2.9 A) are longer than in dibenzyl 27 and considerably longer (by 0.2 A ) than the corresponding Zr-P bond lengths in toluyne 28. The Zr-Cp' bond distance of 2.30 A is also approximately 0.07 A longer than in comparatively uncrowded complexes with this ancillary ligand set. The saturated six-coordinate geometry results in undistorted r\ -coordination of all 1  three benzyl ligands, as demonstrated by the normal Zr(l)-C(23)-C(24) bond angle of 111.6(2)°. The  *H and P { *H} NMR 3 1  spectrum of 30 are consistent with the solid state structure. A  broadened singlet at -23.8 ppm in the P { H } NMR 3 1  J  spectrum is indicative of two equivalent  coordinated phosphines, while the downfield chemical shifts for the methylene (2.60 ppm) and ortho (7.50 ppm) protons of the benzyl groups are consistent with the hl-hapticity of these ligands observed in the solid state. The triplet for the methylene protons ( / P H 3  = 6 Hz) arises  due to coupling to the bound phosphines. That all three inequivalent benzyl groups display one  161  references begin on p a g e  208  C h a p t e r 4: Effects  of L i g a n d Modification...  averaged chemical environment indicates that these ligands undergo a similar exchange process as seen for dibenzyl 27. The distinct structural differences between the two tribenzyl complexes 3 and 30 attests to the ability of the small methyl substituents to permit the side-arm donors access to the metal within the same array of alkyl ligands. However, there must be an electronic component to the better donor ability of the [P2Cp] ligand in addition to the obvious steric factors, since the Me  coordination sphere in [P2Cp]ZrCl2(CH3) (9) must surely be less congested than that found in Pr  30, yet the former is still observed to undergo fluxional isomerization involving the side-arm donors. As mentioned previously, tribenzyl 3 is thermally unreactive, presumably because the pendant phosphines remain dangling and hence are unable to assist in a mechanism that may require phosphine complexation. However, preliminary studies indicate that the [P2Cp] Me  analogue 30 does in fact undergo a thermal reaction, in further support of the concept that the phosphines are an integral component in promoting this reactivity. As yet the product of this reaction has remained unidentified.  ,CH Ph 2  •Zr-  /  ""7  PhH C  27  CH Ph  2  2  PhCH ^ 2  V"" 2 CH  Ph  CH Ph 2  162  references begin on p a g e  208  C h a p t e r 4: Effects  4.4  of L i g a n d M o d i f i c a t i o n . . .  Synthesis and reactivity of the ethylene complexes [P2Cp]Zr(r| -CH2=CH2)Br (R R  2  = Me, Pr ) !  In the previous chapter the isolation of ethylene complex 20 from the reaction of either alkylidene 16 or 18b with excess ethylene was reported. A n interest to study the reactivity of this complex, as a probe into the nature of the metal-alkene bonding in this formally Zr(II) species, prompted a more direct synthetic route from the starting chloride 1. One advantage of this alternate preparation is the versatility to obtain the corresponding  Me  [ P 2 C p ] ethylene  complex from 25. Examples were noted in the previous sections, most notably with dibenzyl 27, where the structure and reactivity of analogous complexes differed depending on the phosphine substituents. These ethylene derivatives thus provide an opportunity to compare further the effects of the two ligand systems on the chemical properties of analogous complexes.  4.4.1  Preparation of [P Cp]Zr(r| -CH2=CH2)Br (R = Pr , Me) R  2  1  2  A toluene solution of 1 or 25 reacts with 2 equivalents of EtMgBr at -78 °C to give a bright yellow solution, which upon warming to room temperature generates the ethylene complex [P2Cp]Zr(r) -CH2=CH2)Br (31: R = Pr', 32: R = Me) in excellent yield, either as dark R  2  purple (31) or dark red (32) crystals (equation 4.8). The yellow precursor is presumed to be the diethyl species [P2Cp]ZrBr(CH2CH3)2, an intermediate which undergoes a P-H abstraction R  reaction with the elimination of ethane to form the final product. A quantitative halide exchange incorporates a bromide ligand in the final product, based on chemical analyses data and an X-ray structural determination for 32 (see below).  163  references begin on p a g e  208  C h a p t e r 4: Effects  2 EtMgBr  Cl Zr-  R  P.  - MgCI - MgBrCI 2  Y'R  cr  R  Cl  of L i g a n d Modification...  1 R = Pr' 25 R = Me  ZrR  CH CH 3  P-.  Y"R 2  CH CH 2  Br  R  (4.8)  Zr'-  R  3  CH3CH3  H C-—CH  R  2  R  2  31 R = Pr  1  32 R = Me The H and P { H } N M R spectra of purple 31 are nearly identical to that of the red l  3 1  1  chloro derivative [P2Cp]Zr(r| -CH2=CH2)Cl (20), showing two species in equilibrium in the Pr  2  same 9:1 ratio of syn (major) and anti (minor) isomers. One minor difference is evident in the chemical shifts of the respective methine protons of the ancillary ligand. In comparison, a single species is seen in solution for 32, indicating that stronger phosphine coordination discourages an exchange process in this complex. The distinctive pattern of the Cp protons for 32 in the *H N M R spectrum with a triplet for the unique proton at 4.15 ppm and a doublet for the two equivalent protons at 6.02 ppm recalls a very similar pattern for the major isomers of 20 and 31. The molecular structure of the [P2Cp] derivative 32, determined by an X-ray crystal Me  determination, is shown in Figure 4.4. Selected bond distances and bond angles are presented in  164  references begin o n p a g e 2 0 8  C h a p t e r 4: Effects  of L i g a n d Modification.  Table 4.5. The structure reveals the ethylene unit coordinated parallel to the Cp ring and oriented syn to the unique Cp carbon atom, precisely as found for 20. As only one isomer is seen for 32 in solution it is assumed that it corresponds to this structure, from which it is inferred that the major isomers for 20 and 31 are also the syn isomer, based on the resemblances in the respective *H N M R spectra mentioned above. The C(16)-C(17) bond distance of 1.431(6) A in 32 is similar to the corresponding value of 1.433(17) A for 20, suggesting that the degree of backbonding from the metal is not significantly altered upon substituting either the halide (Br for Cl) or the groups attached to the phosphines (methyl for isopropyl). However, the phosphines are bound considerably closer to the metal in 32, with Zr-P bond distances averaging 2.72 A in comparison to 2.86 A for 20.  C<7) C(10}  165  references begin on p a g e  208  C h a p t e r 4: Effects  Table 4.5  of L i g a n d Modification...  Selected Bond Lengths (A) and Bond Angles (°) for [P2Cp]Zr(r] Me  2  C H = C H ) B r (2b). 2  2  Zr(l)-Br(l)  2.6744(6)  Br(l)-Zr(l)-P(l)  78.28(3)  Zr(l)-P(l)  2.730(1)  Br(l)-Zr(l)-P(2)  76.94(3)  Zr(l)-P(2)  2.703(1)  Br(l)-Zr(l)-C(16)  109.7(1)  Zr(l)-C(16)  2.293(5)  Br(l)-Zr(l)-C(17)  109.7(1)  Zr(l).-C(17)  2.312(5)  P(l)-Zr(l)-P(2)  155.17(4)  Zr(l)-Cp'  2.23  P(l)-Zr(l)-C(16)  75.6(1)  C(16)-C(17)  1.431(6)  P(l)-Zr(l)-C(17)  111.0(1)  C(16)-Zr(l)-C(17)  36.2(2)  The  formation of the ethylene complexes 31 and 32 directly from the respective starti  trichlorides offers a facile alternative to the multistep approach to 2c via an alkylidene complex. TI general synthetic route has been employed elsewhere to obtain a number of early metal alke 17 18  complexes. '  Unfortunately, this procedure could not be extended to other Zr alkene complexes w:  this system. For example, propylene complexes could not be isolated by using Grignard reagents su as P r M g B r or Pr'MgCl, nor was B u L i helpful in obtaining a coordinated butene species. All of the n  n  attempts resulted in complete decomposition of the reaction mixture, which recalls the instability of t resulting propylene complex presumably generated from the metallacyclic intermediate in the reaction either alkylidene 16 or 18b with propylene. It is apparent from these results that the stability of alke complexes with this ligand system is restricted to the ethylene derivatives.  166  references begin on p a g e  208  C h a p t e r 4: Effects  4.4.2  of L i g a n d M o d i f i c a t i o n .  Reaction of [ P C p ] Z r ( r | 2 - C H = C H ) B r with C O to give [ P C p ] Z r ( C O ) B r (R R  R  2  2  2  2  2  = Me, Pr') A purple toluene solution of ethylene 31 reacts instantly under an atmosphere of CO to generate a dark greenish-orange solution that shows a single resonance in the P { H } 3 1  spectrum at 29.1 ppm. In the  NMR  1  NMR  spectrum the only resonances observed are attributed to  the ancillary ligand, and a sealed N M R tube reaction reveals a singlet at 5.25 ppm for the evolution of free ethylene. A similar result is obtained in the reaction with 32. Therefore, it is apparent in both instances that the coordinated ethylene unit has been replaced by C O in a ligand substitution reaction to give a carbonyl complex (equation 4.9).  (4.9)  O 33 R = Pr" 34 R = Me  167  references begin on page  208  C h a p t e r 4: Effects  For  the reaction of 31 with  1 3  of L i g a n d M o d i f i c a t i o n .  C O the downfield region of the C { ! H } NMR 13  spectrum  displays two carbonyl peaks at 241 and 249 ppm for 33 in addition to a third resonance at 184 ppm  for excess free C O ,  indicating that an 18-electron dicarbonyl species has been formed. In  13  34 the corresponding carbonyl resonances are located at 240 and 245 ppm, respectively. These complexes have a ligand arrangement that is similar to known derivatives such as CpZr(CO)2(dmpe)Cl.  19  The presence of a carbonyl ligand is supported by absorptions in the IR  spectra at 1890 and 1898 c m for 33 and 34, respectively, which shift to 1865 and 1855 c m for - 1  the  1 3  -1  C labeled isotopomers. The low Vco values of the coordinated carbonyl ligands in  comparison to free C O (vco  = 2143 cm ) is due to strong back-bonding from the electron-rich -1  Zr(II) centre to the 7t* orbital of the C O ligand and is consistent with the stretching frequency in analogous Zr(II) carbonyls (i.e., CpZr(CO)2(dmpe)Cl, vco  = 1940 c m ) . Unfortunately, -1  although both carbonyl complexes 33 and 34 are stable indefinitely in solution in the presence of excess CO,  attempts to isolate these species in the absence of CO led to decomposition. This  trait of instability outside of a protective C O atmosphere has been noted with other Zr carbonyl derivatives, demonstrating the labile nature of these ligands with early metals. 19  An interesting feature of the ambient temperature C{ 13  !H}  NMR  spectrum of 33 is that  the peak for free C O at 184 ppm is broadened, as is the carbonyl peak at 241 ppm. This curious observation suggests that this C O ligand is undergoing an exchange process with free C O in solution; the remaining ligand either is not involved in this process, or is at the slow exchange limit at this temperature, since the peak for this ligand at 249 ppm is quite sharp in comparison. This exchange process was monitored by variable temperature C{ H} NMR 13  l  spectroscopy; the  VT spectra, shown in Figure 4.5, demonstrate an increase in line broadening as the temperature is raised, in agreement with an increase in the exchange rate between free C O and the exchanging carbonyl ligand. The NMR  spectra were simulated (DNMR-5) to obtain rate constants at each  temperature, which were used in the resulting Eyring plot shown in Figure 4.6. The kinetic parameters A H * = 9.2(5) kcal m o H and AS* = -17(2) cal mol" K 1  168  _ 1  were calculated from this  references begin on p a g e  208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n . . .  plot. The negative entropy term is unexpected, as ligand exchange from this saturated 18electron species is anticipated to proceed in a dissociative mechanism that should produce a positive entropy term for a less ordered transition state. A concerted mechanism involving dissociation of a pendant phosphine may be a factor in this exchange. A n associative process has also been suggested from a separate kinetic study into similar C O ligand exchange in other 18electron Zr carbonyl species. '  60 °C  A 40 °C  1  LA 20 °C  rr[in![!!ll[in![l!I[!!!!l[IIII|IIII|!l!!|!l!l(!lll|ll!IJI!!!|IIII|III!| 250  Figure 4.5  240  230  220  Variable temperature C { H } NMR 13  169  l  210  200  190  PRM0  spectra of [P Cp]Zr(CO)2Br (33). Pr  2  r e f e r e n c e s b e g i n on p a g e  208  C h a p t e r 4: Effects  of L i g a n d Modification.  2-,  0.0029 0.003  0.0031 0.0032 0.0033 0.0034 0.0035  1/T (K" ) 1  Figure 4.6  Eyring plot for the CO ligand exchange process in [P2Cp]Zr(CO)2Br (33). Pr  Ligand exchange is not uncommon for early metal carbonyl complexes.  In  21  Cp*Hf(CO) (dmpe)Cl) 2  with excess  1 3  zl  both C O ligands are observed to rapidly and quantitatively exchange  C O . One can speculate why only one carbonyl ligand in 33 undergoes this  exchange. As mentioned in chapter 1 and seen for trichloride 1, the ligand trans to the Cp group in a six-coordinate mono(cyclopentadienyl)complex is typically weakly bound, with a tendency for fluxional coordination in some instances. In 33 it is probable that one of the carbonyl ligands is located at this labile site trans to the Cp ring, while the other is trans to the bromide. There are two reasons why the former is more weakly bound in this geometry. First, the strong labilizing trans effect of the Cp donor contrasts with the weak trans effect of the electron withdrawing 170  references begin on p a g e  208  C h a p t e r 4: Effects  bromide.  of L i g a n d Modification...  Second, and as noted for ethylene 20, backbonding from the metal in  monocyclopentadienyl complexes is optimized by the d  2 z  and dxy orbitals (the z-axis passes  through the Cp-centroid in this geometry), which are well suited to stabilize the carbonyl trans to the bromide but have a negligible effect on the other carbonyl ligand trans to the Cp group. Therefore, the combination of these factors may account for the observation that there is only one labile carbonyl ligand in 33 undergoing observable exchange with free  CO.  The insertion reactions discussed in the previous chapter require dissociation of a labile phosphine to provide a vacant coordination site, and hence are relatively sluggish. In comparison to the slow insertion of C O into alkylidene 16 or 18b to give ketene 21, the immediate reaction of C O with ethylene 31 or 32 indicates an associative mechanism involving nucleophilic attack by a C O molecule without the need for prior phosphine dissociation. The ligand substitution reactions that produce these carbonyl derivatives also differ from the insertion chemistry outlined previously. The displacement of a coordinated ethylene unit by C O is a rare occurrence in early 22  metal complexes.  The strong backbonding in Zr ethylene complexes should confer a degree of  Zr(IV) metallacycle character in the metal-ethylene bonding; however, it is apparent that considerable Zr(II) character is still present in these ethylene derivatives.  4.4.3  Preparation of [ P C p ] Z r ( r | 2 - P h C C P h ) B r Pr  2  Given the facile ligand substitution reaction observed for the ethylene derivatives 31 and 32 with CO, and the tendency for early metal alkene complexes to be substituted by alkynes, we were interested to test whether a bulky alkyne would give a similar result in these systems. In this context, none of the complexes described in the previous chapter were observed to react with internal alkynes. A toluene solution of ethylene 31 reacts with 1 equivalent of diphenylacetylene (PhCCPh) under ambient conditions to displace the ethylene ligand and generate the alkyne complex [P2Cp]Zr(r| -PhCCPh)Br (35), which can be isolated as pale yellow crystals (equation Pr  2  171  references begin on page  208  C h a p t e r 4: Effects  of L i g a n d Modification...  4.10). In contrast to the immediate displacement of ethylene by C O to give carbonyl 33, the corresponding ligand substitution reaction of 31 with diphenylacetylene is slower, requiring 24 hours for completion. This observation is consistent with a slower rate for the bulky alkyne in comparison to the small linear C O molecule, and points to a probable requirement that a phosphine must dissociate to allow room for the incoming alkyne.  (4.10)  syn-35  anti-35  The molecular structure of alkyne 35, shown in Figure 4.7, was determined by an X-ray crystal structure analysis. Selected bond lengths and bond angles are listed in Table 4.6.  172  references begin on p a g e  208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n . . .  C(23) Figure 4.7  Molecular structure of [P2Cp]Zr(ri -PhCCPh)Br (35); 33% probability Pr  2  thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity.  The solid state structure corresponds to the syn isomer, with the alkyne coordinated in a similar orientation parallel to the Cp ring as found in the structurally ethylene complexes 20 and 32, and also as found in toluyne 27. However, in 35 the alkyne unit is tilted from this parallel orientation by 9°. The short Zr(l)-C(24) and Zr(l)-C(25) bond lengths of 2.20 A and 2.18 A , respectively, are indicative of strong backbonding from the metal. This is also reflected in the C(25)-C(24)C(26)  bond angle of 127", which illustrates the degree to which the phenyl rings are pulled back  from the metal as a result of back-donation. Typical of metal alkyne complexes, this gives a 14  geometry of the coordinated alkyne resembling that of a metallacyclopropene (E), not unlike the  173  references begin on page  208  C h a p t e r 4: Effects  of L i g a n d Modification...  ortho-phenylene depiction for toluyne 28. The double bond character is indicated by the C(24)C(25)  bond length of 1.32 A .  M  A  /  C  Pl-i  C  \  Ph  E Table 4.6  Selected Bond Lengths (A) and Bond Angles (") for [P Cp]Zr(r) -PhCCPh)Br Pr  2  2  (35).  Zr(l)-Br(l)  2.6771(5)  Br(l)-Zr(l)-P(l)  78.61(2)  Zr(l)-P(l)  2.8367(8)  Br(l)-Zr(l)-P(2)  76.35(2)  Zr(l)-P(2)  2.8129(8)  Br(l)-Zr(l)-C(24)  102.85(8)  Zr(l)-C(24)  2.197(3)  Br(l)-Zr(l)-C(25)  116.88(8)  Zr(l)-C(25)  2.182(2)  P(l)-Zr(l)-P(2)  154.87(4)  Zr(l)-Cp'  2.264  P(l)-Zr(l)-C(24)  77.57(7)  C(24)-C(25)  1.322(6)  Zr(l)-C(24)-C(26)  111.0(1)  C(24)-C(26)  1.471(4)  C(25)-C(24)-C(26)  126.8(2)  A comparison of the bonding in 35 with that of the ethylene complexes 20 and 32 shows in all cases that backbonding from the metal induces a lengthening of the C-C  bond. However,  the alkyne has a second 7i-orbital that can overlap with a metal d orbital of suitable symmetry such that this ligand can potentially be represented as a 4-electron donor. In 35 this interaction is in competition with one of the 7t-donor orbitals from the Cp ring, which diminishes the ability of the alkyne to donate electron density from its second rc-bond. But the observation that alkyne 35 is unreactive in the presence of CO, 174  in direct contrast to the rapid reaction seen for ethylene 31,  references begin on p a g e  208  C h a p t e r 4: Effects  of L i g a n d Modification...  suggests that the former complex is a fully saturated 18-electron species, implying that there is at least some component present to this rc-bond from the alkyne to the metal centre. In solution alkyne 35 exists as two isomers in a 3:2 ratio, based on the H and P { H } 1  NMR  spectra. There are two singlets in the P { ! H } NMR  31  1  spectrum for the major (8.53 ppm)  3l  and minor isomer (11.6 ppm), respectively, and a corresponding set of resonances in the *H NMR  spectrum for each species. As with analogous examples encountered in the previous  chapter, these species are likely the syn and anti stereoisomers.  A ! H NOEDIFF N M R  experiment determined that the anti isomer is the major species in solution. Irradiation of the resonance assigned to the two equivalent protons in the Cp ring of the major isomer showed an enhancement of the signals for the ortho protons of the phenyl ring; no effect was detected when the resonance of the unique Cp proton was irradiated. The V T P { !H} NMR 3 1  spectra show that  these isomers interconvert, with increased line broadening evident in both peaks as the temperature is raised. Curiously, a change in the equilibrium ratio of these species was not detected from this study.  4.4.4  Preparation of asymmetric dinuclear hydrides { [ P 2 C p ] Z r B r H 2 h (R = Me, Pr') R  The  ethylene complexes 31 and 32 each react slowly under an atmosphere of H2 to give  dinuclear bridging hydride species of the general formula { [P2Cp]ZrBrH2}2 (36: R = Pr"- 37: R R  = Me) (equation 4.11).  Pi  { [P Cp]ZrBrH }  [P Cp]Zr(Ti -CH =CH )Br  R  2  2  2  2  2  2  2  - CH3CH3  31 R = Pr'  36 R = Pr'  32 R = Me  37 R = Me  175  references begin on page  (4.11)  208  C h a p t e r 4: Effects  The  of L i g a n d Modification.  and P { H } N M R spectra indicate that both of these derivatives possess an 3 l  1  asymmetric structure, and that this asymmetry is represented in a different manner for each. A n X-ray crystal structure determination obtained for the [ P 2 C p ] derivative 37, depicted in Figure Me  4.8,  serves to evaluate the structural differences between the two complexes. Selected bond  lengths and bond angles for 37 are listed in Table 4.8. A skeletal representation of the molecular structure shown below, with all the substituents removed from the silyl and phosphine groups, simplifies the important aspects of the asymmetric geometry.  The structure above exhibits an asymmetric dinuclear framework bridged by four hydride ligands. Two of the bridging hydrides (H(l) and H(2)) were refined isotropically; the other two hydrides were placed in difference map or geometrically reasonable positions but were not refined. The two sides of this asymmetric structure can be assessed separately. The geometry  176  r e f e r e n c e s b e g i n on p a g e  208  C h a p t e r 4: Effects  of L i g a n d Modification.  around Zr(l) approaches that of a normal piano-stool geometry. The two phosphine donors are coordinated trans to each other, while the bromide is located .syn to both phosphines and trans to a general coordination site occupied by the bridging hydrides. In contrast, only one of the phosphines is coordinated to Zr(2), while the remaining side-arm is left dangling. A reduction in the number of ligands bound to Zr(2) is compensated for by a Zr-P bond distance that is 0.1 A shorter than the corresponding Zr(l)-P bond lengths.  A twist in the ancillary ligand of  approximately 90 " around the Zr(2)-Cp'(2) axis orients the dangling side-arm towards the other half of the molecule, and also gives rise to an eclipsed geometry between P(2) and Br(2), and between Br(l) and P(3).  Figure 4.8  Molecular structure of { [P2Cp]ZrBr}2(H-H) (37); 33% probability Me  4  thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity.  177  r e f e r e n c e s b e g i n on p a g e  208  C h a p t e r 4: Effects  Table 4.7  of L i g a n d Modification...  Selected Bond Lengths (A) and Bond Angles (") for { [P Cp]ZrBr} (|i-H)4 Me  2  2  (37).  Zr(l)-Zr(2)  3.1418(10)  Br(l)-Zr(l)-P(l)  74.43(5)  Zr(l)-Br(l)  2.7234(10)  Br(l)-Zr(l)-P(2)  74.41(5)  Zr(2)-Br(2)  2.7212(10)  P(l)-Zr(l)-P(2)  148.22(6)  Zr(l)-P(l)  2.8367(8)  Br(2)-Zr(2)-P(3)  79.84(5)  Zr(l)-P(2)  2.8129(8)  Br(l)-Zr(l)-Cp'(D  112.7  Zr(2)-P(3)  2.711(2)  Br(2)-Zr(2)-Cp'(2)  105.5  Zr(l)-H(l)  1.86(5)  P(l)-Zr(l)-H(l)  127.2(15)  Zr(l)-H(2)  2.12(6)  P(l)-Zr(l)-H(2)  75.0(15)  Zr(2)-H(l)  2.03(5)  P(3)-Zr(2)-H(l)  136.5(15)  Zr(2)-H(2)  2.06(6)  P(3)-Zr(2)-H(2)  135.6(15)  The  Z r - Z r contact of 3.142 is relatively short in comparison to some bridging hydride  species, but similar to other analogues that also have phosphine coordination present. Bridging of the small hydrides brings the two Zr centres in close proximity to one another, which in turn induces significant steric interactions between the two ancillary ligands of each monomer. It is this steric pressure that forces one of the phosphines out of the coordination sphere. The  3 1  P { H } N M R spectrum of 37 shows a singlet at -55 ppm for the dangling 1  phosphine, another at -15 ppm for the lone phosphine coordinated to Zr(2), and an AB doublet of doublets ( /pp = 58 Hz) at -15 ppm and -17 ppm for the two phosphines coordinated to the other 2  metal centre. This spectrum is in agreement with the chemical environment of the phosphines in the solid state structure. The complicated ! H NMR  spectrum of 37 is also consistent with the C i  symmetry shown in Figure 4.8, with separate resonances for each group in the ancillary ligands. For  example, there are eight singlets for the silylmethyl groups, another eight peaks for the  methyl substituents of the isopropyl groups, and six peaks in the Cp region. The hydride region  178  references begin on p a g e  208  C h a p t e r 4: Effects  of the i H f ? } NMR 3 1  and  of L i g a n d Modification...  spectrum (Figure 4.9) shows two broad, equal intensity peaks at 3.74 ppm  3.89 ppm that each integrate to two protons. These resonances are not observed when  ethylene 32 is reacted with D . The narrower peak at 3.74 ppm is split into two resonances in the 2  corresponding H NMR l  spectrum ( 7PH = 80 Hz) (Figure 4.8). 2  —i—i i i i i—i—.—i—i—i—i—i—i—i—i—i—•—i—i—i—•—i—i—i—i—p—i—i—<—i—•—i—'—i—i—i—•—i—i—i—•—i—> 4.0H  Figure 4.9  4.04  400  3.96  3.92  3.HH  3X4  Hydride region of the U NMR l  The  3.M0  3.71,  3.72  3.6M  3.60  3.}«  spectrum for { [P2Cp]ZrBr}2(^i-H)4 (37). Me  bottom trace shows the corresponding ! H { P } NMR 3l  179  i • i • i i i—•—i——• 3.64  spectrum.  references begin on p a g e  208  ' 3.32  C h a p t e r 4: Effects  of L i g a n d Modification.  These observations indicate that there are two averaged chemical environments for the hydrides, with an exchange process suggested by the broadened line widths. The chemical shifts are in the normal range for bridging ligands in Zr hydride complexes, but the rather large Jpu coupling 2?  2  for two of the hydrides is more suggestive of terminal ligands. The latter possibility is consistent with the vacant site on Zr(2) that is evident in the solid state structure, which could easily accommodate two terminal hydrides. As mentioned earlier, the positions of two of the metal hydrides were not refined. This arrangement could also account for the observed coupling of these protons to only one phosphorus nucleus. However, the chemical shift for a terminal hydride in a Zr complex is generally located further downfield in comparison to the resonances observed for 37. In contrast to crystalline 37, the [P2Cp] derivative 36 was isolated as a hydrocarbonPr  soluble greenish oil.  There are two singlets in the P { U) NMR 3 1  l  spectrum for 36, at -5.6 ppm  for an uncoordinated phosphine environment, and at 39.2 ppm for a bound phosphine. The H X  NMR  spectrum reveals the presence of two different ancillary ligand environments, each  corresponding to C symmetry. For example, there are four silylmethyl resonances observed s  (two for each ligand), while the Cp region of the spectrum shows a separate doublet and triplet for each ligand. The remainder of the spectrum exhibits a similar duplication of peaks for two ancillary ligands. The hydride resonances are identified by those peaks that disappear in the *H NMR  spectrum obtained from a sample of ethylene 31 that is treated with D . There is one 2  broad hydride peak near 2.3 ppm, which integrates for three protons, that does not change appreciably in the i H j ? } NMR 3 1  one hydride in the H NMR !  spectrum. In contrast, a triplet at 5.23 ppm (2/PH = 74 Hz) for  spectrum becomes a singlet in the corresponding ^ { ^ P }  spectrum.  180  references begin on p a g e  208  NMR  Chapter 4: Effects of Ligand Modification.  Based on the spectroscopic data the structure depicted above is proposed for 36. This structure is consistent with two different ancillary ligand environments, each possessing C  s  symmetry. The coordinated phosphines on one metal centre are equivalent, as are the two dangling phosphines on the other ligand, which overall give rise to two singlets in the  31  P{ H} 1  N M R spectrum as observed. The broad peak at 2.3 ppm is in an appropriate range for three bridging hydrides, while the downfield chemical shift and the large Jpu value for the triplet at 2  5.23 ppm is consistent with a terminal hydride coupled to two equivalent phosphines. Unfortunately, an identifiable peak could not be detected in the solution IR spectrum of 36 for either an M - H or M - D bond stretch. Although the asymmetric structures depicted above for hydrides 36 and 37 are unusual, there is precedent with other asymmetric dinuclear Group 4 hydride species, analogous example, Zr2H4(BH4)4(dmpe)2,  24  including an  that contains a similar arrangement of one terminal  and three bridging hydride ligands to that proposed for 36. In comparing the structures of the two hydride complexes reported here, there is one less phosphine able to coordinate to the metal in the bulkier [P2Cp] derivative 36 than in 37. This observation is consistent with the different Pr  181  references begin on page 208  Chapter 4: Effects of Ligand Modification...  manner in which the two ancillary ligands adjust to the crowded geometry imposed by the bridging hydride structure.  4.4.5  Preparation of [ P 2 C p ] Z r ( r l - C H 2 = C H 2 ) R (R' = Me, P r  2  ,  C5H5)  In contrast to the alkylidene and ketene complexes discussed in the previous chapter, which are resistant to alkylating agents, the bromide ligand in ethylene 31 can be substituted as shown below (equation 4.12) to yield new Zr ethylene derivatives.  MR' Pr  [P Cp]Zr(Ti -CH =CH )Br  •  2  2  2  2  ^CpJZr^-Cr^CH^R'  - MBr  .  -  ( 4  1 2 )  38 R' = Me  3 1  39 R' = C5H5  The characteristic spectroscopic feature of the methyl derivative 38 is the triplet ( /pH = 3  10 Hz) at -0.67 ppm in the *H N M R spectrum for the methyl group attached to Zr. The distinctive Cp region of this spectrum is nearly identical to that of the major syn isomer of 31, suggesting that the solution structure of 38 (only one species seen) is exclusively the syn isomer. The Cp derivative 39 could be isolated as reddish-orange crystals. There are two equal intensity singlets in the P { H } N M R spectrum for 39 at -5.3 and 42.3 ppm, corresponding to 3 1  X  one coordinated and one dangling phosphine, respectively. The H N M R spectrum shows a X  doublet ( 7PH = 2 Hz) at 5.20 ppm for the five protons of the C5H5 ring; the downfield chemical 3  shift suggests that this ligand is coordinated in an r|5-mode, although rapid ring whizzing of an ri -ligand could also account for the averaged chemical environment. As the ligand array in this 1  complex is similar to that in the structurally characterized metallocene derivative Cp2Zr(r| 2  CH2=CH2)(PMe3),  it is reasonable to consider an analogous structure for 39 as shown below.  182  references begin on page 208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n . . .  The asymmetric geometry renders all four ethylene protons inequivalent, thus generating a complicated second order splitting pattern in the iff NMR  spectrum for each (with additional  coupling to the coordinated phosphine). This asymmetry is also evident in three separate resonances for the Cp ring of the ancillary ligand. The presence of only one coordinated phosphine in 39 supports the view of the C5H5 ligand as r)5-bound; the steric and electronic saturation provided by this coordination mode yields an 18-electron species which would force one side arm to remain dangling, as observed. The ethylene unit and the coordinated phosphine thus can be considered to be occupying the metallocene wedge, with the other side-arm left out of the coordination sphere.  4.4.6  Reactivity of ^ P C p ] Z r ( n 2 - C H = C H ) ( n 5 - C H ) with CO, H p  2  2  2  5  5  2  The reactivity of the 18-electron ethylene complex 39 was briefly examined to compare with the results observed for the 16-electron ethylene analogue 31. As opposed to 31, which coordinates C O almost instantly, the reaction of 39 with C O is considerably slower, requiring more than two weeks for completion under the same reaction conditions (equation 4.13). This remarkable difference in reaction times can be traced to the electronic saturation in 39, adding  183  references begin on page  208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n . . .  further evidence that the C5H5 donor in this complex is T|- -coordinated. As a result, either a s  ligand in 39 must dissociate or alternatively the Cp ring must undergo ri^-rj ring slippage, prior 3  to the coordination of a C O molecule. The similar lack of reactivity of alkyne 35 with C O presumably originates from the same electronic saturation of that species.  Pr  [P Cp]Zr(Ti -CH =CH )(Ti -C5H5) _ J Z _ ^ 2  2  2  2  5  P r  - C H 2  [P Cp]Zr(T 2  5 1  -C5H )(CO) 5  ( 4 4  39  4  '  1 3 )  0  The eventual product from the above reaction is the carbonyl species [P2Cp]Zr(n 5  Pr  C5H5XCO) (40), which is accompanied by the evolution of free ethylene as observed with the analogous reaction that forms carbonyl 33. The P { H } NMR 3 1  1  spectrum of 40 is similar to that  of the precursor 39, with one singlet at 58.7 ppm and another at -4.8 ppm. The presence of the carbonyl ligand is indicated by a single downfield resonance at 308 ppm ( /pc = 2 Hz) in the 2  reaction with C O . 13  In contrast to 33, the line width of this carbonyl peak is very narrow, with  no evidence for exchange with the peak for excess  1 3  C O at 184 ppm. This difference in the  lability of the respective carbonyl ligands in 33 and 39 may originate from the presence of one less C O ligand in 39, which is not in competition for backbonding and hence is less labile. As an analogue of the metallocene carbonyl species Cp Zr(CO)(PMe3), 2  the proposed structure of 40  is depicted as shown below.  184  references begin on p a g e  208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n .  Exposure of a toluene solution of ethylene 39 to 4 atmospheres of H2 over a period of one week yields very cleanly a new metal complex as a yellow oil that is proposed to be the hydride derivative [P2Cp]Zr(ri5-C H5)H2 (41) (equation 4.14). Pr  5  H Pr  [P Cp]Zr(ri -CH =CH )(Ti -C5H5) 2  2  5  2  2  2  • [P2Cp]Zr(Ti -C H )H P r  5  5  - CH3CH3  4  5  2  (  4  U  )  1  39 Unfortunately, the hydride resonances in 41 could not be located in the *H N M R spectrum between -10 and 20 ppm, although in a related hydride species, (Cp*CpZrH2)2, the hydride resonances were similarly noted to be undetected. In the latter example this negative observation was ascribed to exchange processes involving the hydride ligands. The formulation of yellow 41 as a Zr(IV) hydride species is based on the absence of resonances in the *H N M R spectrum for either an intact ethylene ligand or an alkyl ligand resulting from an insertion reaction with H2. The  31  P { i H } N M R spectrum shows two new resonances for 41 at -5.6 and 43.9 ppm, indicating  a structure that is similar to that of the precursor 39.  This complex is depicted here as a  saturated, 18-electron metallocene analogue and hence a monomelic species, although examples of monomeric Zr and Hf hydrides are extremely scarce, as dimers are typically observed unless considerably bulky ligands are employed. Two notable examples are the metallocene derivative Cp* ZrH2 2  and the related anionic species [Cp*2ZrH3]\  The 16-electron complex Cp*2HfH2  does coordinate donor molecules at the central site of the equatorial wedge, but stable adducts -in  have been restricted to using donors such as C O and PF3.  In contrast, 41 may have an  advantage in that the phosphine is an intramolecular donor already in place within the coordination sphere, to give a structure as proposed below.  185  r e f e r e n c e s b e g i n on p a g e 2 0 8  C h a p t e r 4: Effects  4.5  of L i g a n d Modification.  Future Work In this chapter the steric and electronic effects of substituting methyl groups for isopropyl  groups on the pendant phosphines were examined. This modification of the ancillary ligand resulted in a greater tendency for the less sterically hindered phosphines to coordinate, as illustrated by the structures of dibenzyl 27 and tribenzyl 30. In 27 the improved phosphine binding eliminates the complicated equilibrium seen in the [P2Cp] analogue 14, while the Pr  presence of two coordinated phosphines in 30 is in sharp contrast to the dangling side-arms evident in the other tribenzyl species 3. The modified ligand can also affect the observed reactivity, as seen for the two dibenzyl complexes. The thermal reaction of one derivative leads to an alkylidene complex, while the other dibenzyl species yields a toluyne complex as a final product. With the ethylene derivatives 31 and 32 the effects of the different ligands are more subtle. The structures of these complexes are evidently similar, and the observed reactivity with CO and H2 yields similar products. However, although asymmetric dinuclear hydride species are  186  r e f e r e n c e s b e g i n on p a g e  208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n . . .  obtained in the latter reaction for each derivative, the different steric requirements of each ligand are manifested in a distinct structure for each hydride complex. As mentioned in the introduction to this chapter, several aspects of the chemistry outlined here are preliminary results, which may be pursued further.  For example, mechanistic  information regarding the intramolecular thermal reaction that generates a toluyne complex 28 from dibenzyl 27 may be obtained from selective labeling studies. The thermal reactivity of analogous dialkyl species (i.e., the neosilyl or neopentyl derivatives) could also be compared to the results seen for the [P2Cp] analogues. Pr  In addition, the reactivity of several of the  complexes described in this thesis has either not been tested or only briefly examined. Examples within this category include the hydride and carbonyl complexes. Another direction for future work is outlined below in two alternate strategies to modify the steric or electronic properties of complexes coordinated by these hybrid ancillary ligands. The first is a modification of the cyclopentadienyl ring, while the second is an extension of P C p 2  chemistry with other metals.  4.5.1  Modification to a [P2Cp'] ligand set The strategy for a new ligand design, P2Cp' (' denotes substitution at the Cp ring), is  shown below in Scheme 4.3. The attachment of a bulky te/t-butyl substituent to the Cp ring is anticipated to direct the two side-arms into adjacent 1,2 positions, in a manner similar to that observed in a related chiral metallocene-based ligand."  Otherwise, the synthetic steps shown  below are analogous to those utilized in the preparation of the underivatized ancillary ligand outlined in Chapter 2.  187  references begin on p a g e  208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n .  MeLi  Dimethylfulvene CISiMe CH CI  -LiCI  1) N a N ( S i M e ) 3  2  2  2  2) C I S i M e C H C I 2  2  HN(SiMe ) 3  2  NaCI CICH SiMe 2  3 LiPR  2  2  CICH SiMe 2  CICH SiMe 2  R  [P Cp']Li 2  --P  R— j R Scheme  4.3  p  S^-R R  Reaction scheme for the synthesis of the ancillary ligand [P2Cp']Li. R  188  references begin on p a g e  208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n .  The reactions leading up to the disubstituted side-arm precursor are very clean. However, initial attempts to obtain the lithiated salt of the ligand shown above have met with mixed results. The desired product is formed, but the yield is lowered by a complicating coupling reaction that generates R^P-PR^- This result is consistently observed in a variety of reaction conditions. One surreptitious result has yielded a structurally characterized Zr(HI) chloride complex, Pr  [P2Cp']ZrCl2, the structure of which is shown below in Figure 4.10. Selected bond lengths and  bond angles are listed in Table 4.8.  Figure 4.10  Molecular structure of "[P2Cp']ZrCl2 (42); 33% probability thermal ellipsoids Pl  are shown. Hydrogen atoms are omitted for clarity.  189  references begin on p a g e  208  C h a p t e r 4: Effects  Table 4.8  of L i g a n d M o d i f i c a t i o n .  Selected Bond Lengths (A) and Bond Angles (") for [P2Cp']ZrCl2 (32). Pr  Zr(l)-Cl(l)  2.4869(8)  Cl(l)-Zr(l)-Cl(2)  109.09(3)  Zr(l)-Cl(2)  2.5091(8)  Cl(l)-Zr(l)-P(l)  92.44(3)  Zr(l)-P(l)  2.8569(9)  Cl(l)-Zr(l)-P(2)  91.51(3)  Zr(l)-P(2)  2.8571(9)  P(l)-Zr(l)-P(2)  157.29(3)  Zr(l)-C(l)  2.622(3)  C(3)-Si(l)-C(12)  107.87(13)  Zr(l)-C(2)  2.502(3)  C(4)-Si(2)-C(21)  102.61(13)  Zr(l)-C(3)  2.406(3)  P(l)-C(12)-Si(l)  112.7(2)  Zr(l)-C(4)  2.390(3)  P(2)-C(21)-Si(2)  114.1(2)  Zr(l)-C(5)  2.500(3)  A n examination of the structure of this compound leads to a comparison with other Zr(III) derivatives as discussed below. The structure shown above for 42 depicts a monomeric Zr(III) species in a four-legged piano-stool geometry, with the phosphines located in mutually trans coordination sites. The steric impact of the bulky tert-butyl group is evident in the long Z r ( l ) - C ( l ) bond distance of 2.62 A in comparison to the other Zr-Cp bond lengths.  The  monomeric structure is presumably due to the large isopropyl phosphine substituents preventing dimerization. A similar result is observed for the analogous [ P 2 C p ] Z r C l 2 derivative (43), an Pr  isolable intermediate in the preparation of the bridging dinitrogen complex { [P Cp]ZrCl}2(|J-Pr  2  N2) (44).  As with the [P Cp'] derivative 42, 43 is also a green paramagnetic species (an ESR 2  triplet is observed due to coupling to two equivalent phosphines), which is consistent with a monomeric structure. Contrasting with these structures is that of the [ P 2 C p ] derivative (45), a Me  minor product in the thermal decomposition of 29 as mentioned earlier. The solid state structure of 45 is depicted in Figure 4.11. Selected bond lengths and bond angles are given in Table 4.9. The structure of 45 reveals a chloride-bridged dimer as a result of a less crowded geometry afforded by the methyl groups on the phosphines. Each metal centre is also coordinated by a  190  references begin on p a g e 2 0 8  C h a p t e r 4: Effects  of L i g a n d Modification...  terminal chloride ligand that is bound trans to the Cp donor. The diamagnetic behaviour of this species in solution is consistent with the solid state structure.  Figure 4.11  Molecular structure of { [ P 2 C p ] Z r C l hOi-Clte (45); 3 3 % probability Me  thermal ellipsoids are shown. Hydrogen atoms are omitted for clarity.  191  r e f e r e n c e s b e g i n on p a g e 2 0 8  C h a p t e r 4: Effects  Table 4.9  of L i g a n d Modification...  Selected Bond Lengths (A) and Bond Angles (") for { [ P 2 C p ] Z r C l } 2 ( u - C l ) Me  2  (45). Zr(l)-Cl(l)  2.6712(15)  Cl(l)-Zr(l)-Cl(l*)  80.27(4)  Zr(l)-Cl(l*)  2.6673(14)  Cl(l)-Zr(l)-Cl(2)  82.75(5)  Zr(l)-Cl(2)  2.6014(15)  Cl(l)-Zr(l)-P(l)  84.92(5)  Zr(l)-P(l)  2.763(2)  Cl(l)-Zr(l)-P(2)  155.01(5)  Zr(l)-P(2)  2.750(2)  Cl(l)-Zr(l)-Cp  103.8  Zr(2)-Cl(l)  2.6492(14)  P(l)-Zr(l)-P(2)  96.48(5)  Zr(2)-Cl(l*)  2.6742(15)  Zr(l)-Cl(l)-Zr(2)  99.86(5)  Zr(2)-Cl(3)  2.6197(15)  Zr(l)-Cl(l*)-Zr(2)  99.32(5)  Zr(2)-P(3)  2.752(2)  Cl(l)-Zr(2)-Cl(l*)  80.54(4)  Zr(2)-P(4)  2.743(2)  P(3)-Zr(2)-P(4)  97.70(5)  4.5.2  P C p complexes of Th(IV) 2  In considering other metals that might show interesting chemistry with the ancillary ligand utilized for Zr and Hf in this thesis, one appealing choice is Th(IV). This tetravalent actinide exhibits reactivity analogous to the heavier Group 4 analogues, including applications in metallocene-based catalysis."  Another potential advantage is the large size (ionic radius = 0.90  A compared to 0.75 A for Zr(IV),"" which provides ample room for the extended chelate size of this particular ligand. A suitable soluble precursor is the adduct ThBi 4(THF)4, which reacts with -  one equivalent of [ P 2 C p ] L i in toluene to give [P2Cp]ThBr3 (46) in good yield as colourless P r  Pr  crystals. The N M R spectroscopic features for this complex are very similar to the N M R spectrum seen for the Zr derivative 1. Therefore, it is not unreasonable to assume that a similar six-coordinate geometry is present for 46. Unfortunately, this complex exhibits poor solubility in organic solvents, and preliminary reactivity studies suggest a more inert behaviour in comparison to the chemistry that has been observed for Zr.  192  references begin on page 2 0 8  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n .  ThBr (THF) + [P Cp]Li rr  4  4  2  -LiBr - 4 THF  Me ^^  Me  2  2  (4.15)  X  %  (  46 The large size and high electron count of this ancillary ligand restricts its use to metals with a large ionic radius and/or a low coordination number. For example, current work in laboratory is examining the chemistry of this ligand with Nb(III), Y(III) and Yb(II).  4.6  Concluding remarks This thesis has investigated the structure, solution behaviour, and reactivity of a series of  alkyl complexes of Zr and Hf coordinated by a cyclopentadienyldiphosphine ligand (P2Cp). What emerges from this study is a common theme of subtle steric and electronic influences that becomes evident from the disparate solution dynamics of the two isostructural trichloride complexes to the appropriate balance of steric crowding and electronic stabilization that produces the alkylidene complexes.  193  r e f e r e n c e s b e g i n on p a g e  208  C h a p t e r 4: Effects  4.7  Experimental Section  4.7.1  Procedures and Materials  of L i g a n d M o d i f i c a t i o n .  Unless otherwise stated, general procedures were performed according to Section 2.7.1. ThBr4(THF)4 was synthesized according to literature preparations. 34  4.7.2  Syntheses  4.7.2.1  M e  [ P C p ] Z r C l (25) 2  3  A solution of [ P 2 C p ] L i (3.56 g, 10.56 mmol) in 60 mL of toluene was added dropwise Me  with stirring to a toluene slurry (60 mL) of ZrCl4(THT)2 (4.325 g, 10.56 mmol) at room temperature. The red colour of solution containing the lithiated ligand was discharged upon addition, and the slurry gradually turned yellow. The reaction mixture was left to stir for 48 h after which the solution was filtered, and the volume reduced to 30 mL and layered with hexanes. Pale yellow crystals were deposited from slow evaporation of this solution, and the procedure repeated by sequentially layering the mother liquor with hexanes. The isolated crystals were washed with cold hexanes and dried. Yield 4.73 g (85 %). *H NMR  (20 "C, C D ) : 5 0.01 and 6  6  0.25 (s, 6H, Si(Cfl»2), 0.60 and 0.72 (dt, 2H, 7 H = 14Hz, J \-i = 6Hz, S i C / / P ) , 1.14 and 1.25 2  2  H  (t, 6H, 7 2  P H  = 5Hz, P(Cff j) ), 6.48 (d, 2H, 4 / 2  H H  P  2  = 2Hz, Cp-H), 7.24 (t, I H , 4 /  HH  = 2Hz, Cp-H)-  31p{lH} N M R (20 "C, C D ) : 8 -21.0 (s). Anal. Calcd. for C i . s H ^ C b P ^ Z r : C, 34.18; H , 6  6  5.93. Found: C, 35.80; H , 5.98.  4.7.2.2  Me p [  2 C p  ]  Z r C l 2  (  C H 2  p ) (26) h  A solution of K C H P h (74 mg, 0.57 mmol) in 20 mL of THF  was added with stirring to a  cooled (-78 °C) slurry of 25 (298 mg, 0.57 mmol) in 30 mL of THF.  The dark red colour of the  2  KCH2PI1 solution was discharged upon addition and the reaction mixture gradually turned  194  references  begin on page  208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n .  reddish after the addition was complete. The mixture was allowed to slowly warm to room temperature and left to stir for 12 h The solvent was then removed under vacuum and the red oily residue extracted with toluene and filtered. A bright red solid was obtained from a cold (-40 °C) toluene/hexanes mixture. Yield: (270 mg, 82 %). iff NMR (s, 6H, Si(C//. ) ), 0.58 and 1.10 (dd, 2H, 7 H = 7Hz, 7 2  ?  6H,  7  2  H  = 5Hz, P(C//-?)2), 3.27 (br t, 2H, 7 2  P H  H), 6.72 (t, 1H,  7 H  4  H  = 1Hz,  m - C H ) , 7.42 (d, 2H, 3 / 6  5  4.7.2.3  H H  6  6  = 8Hz, S i C / / P ) , 0.93 and 1.51 (d,  2  2  (20 °C, C D ) : 5 0.01 and 0.28  P H  2  = 4Hz, CH Ph), 5.97 (d, 2H, 7 H = 1Hz, Cp4  P H  2  Cp-H), 6.80 (t, 1H, 3 7 = 7Hz, 0 - Q H 5 ) . 31p{ lR}  H H  H  = 7Hz, p - C H ) , 7.09 (t, 2H, 3 7 6  NMR  5  H H  = 7Hz,  (20 "C, C D ) : 8 -19.0 (s). 6  6  M [ P 2 C p ] Z r C l ( C H P h ) (27) e  2  2  A solution of K C H P h (530 mg, 4.07 mmol) in 60 mL of THF  was added with stirring to  2  a cooled (-78 °C) slurry of 25 (1.070 g, 2.03 mmol) in 60 mL of THF.  The dark red colour of the  K C H P h solution was discharged upon addition and the reaction mixture gradually changed from 2  a cream coloured slurry to a cloudy brown solution. The mixture was allowed to slowly warm to room temperature and left to stir for 3 h, during which the colour turned more reddish. The solvent was then removed under vacuum and the red oily residue extracted with 30 mL of toluene and filtered. The filtrate was reduced to 10 mL, from which red crystals were obtained at -40 °C. A second crop of was obtained from the mother liquor, and the combined crystalline material was washed with cold hexanes. Yield: (820 mg, 60 %). H NMR l  and 0.23 (s, 6H, Si(C/7j) ), 0.19 and 0.84 (dd, 2H, 7 H = 6 H z , 7 2  2  1.19 (d, 6H, 7 2  (t, 2H, 3 7  H H  P H  = 5Hz,  = 7Hz,  6  ?(CH ) ), 2.83 (br s, 4H, 3  P-G5H5),  C H ) , 7.66 (d, 4H, 3 7 5  2  H  H H  2  H  6  6  = 7Hz, SiCtf P), 0.42 and 2  CH Ph), 6.35 (d, 2H,  6.81 (t, 1H, 7 H = 1Hz, 4  P H  (20 "C, C D ) : 5 0.00  2  4  7 H = 1Hz, H  Cp-H), 7.14 (t, 4H, 3 7  H H  = 7Hz, 0-Q5H5). 31p{lH} N M R (20 "C, Q D e ) : 5 -18.5 (s).  Calcd. for C 9 H C l P S i Z r : C, 54.56; H , 7.10. Found: C, 54.90; H , 7.19. 2  45  2  2  195  references  b e g i n on p a g e  208  CpH), 6 = 7Hz, m-  Anal.  C h a p t e r 4: Effects  4.7.2.4  Me  of L i g a n d M o d i f i c a t i o n .  [P Cp]Zr(ri -C6H3Me)Cl (28) 2  2  A solution of 27 (520 mg, 0.81 mmol) in 20 of toluene was heated at 70 "C for 12 h. The bright red colour darkened slightly to a reddish brown. The solution was filtered and the volume reduced to 3 mL, from which pale yellow crystals were obtained at -40 °C. A second crop crystals was grown from the mother liquor, and the combined crystalline material was washed with cold hexanes. Yield: (263 mg, 59 %). *H N M R (20 "C, C D ) : 8 -0.02 and 0.19 (s, 6H, 6  Si(CH ) ),  0.90 and 1.01 (dd, I H , 7 H = 10Hz, 7 2  3 2  2  7  P H  = 3Hz, P(CH )2),  3  P H  = 6Hz, S i C / / P ) , 1.29 and 1.31 (d, 6H, 2  1.76 and 1.79 (dd, I H , 7 H = 6 H z , 7 2  3  C H CH ), 6  2  H  6  2  H  P H  = 5Hz, SiCtf P), 2.43 (s, 3H, 2  4.78 (t, I H , 7 H = 1Hz, Cp-H), 6.41 (d, 2H, 7 H = 1Hz, CpH), 7.36 (d, I H , 3 7 H 4  3  4  H  H  = 7Hz, C6H ), 7.82 (s, I H , 3 / H 3  H  =  7  H  Z  *  c  H  6#3)> 7.91 (d, I H , 3 7  H H  = 7Hz, CeH ). 31p{lH} N M R 3  (20 °C, C D ) : 8 -7.0 (s). Anal. Calcd. for C H C l P S i Z r : C, 48.37; H , 6.83. Found: C, 6  6  2 2  3 7  2  2  48.68; H , 6.75.  4.7.2.5  Me  [P Cp]Zr(r| -C6H4=CH2)Cl (29) 2  2  A C6D6 N M R sample of 27 was immersed in a cooled bath (0 "C), and exposed to U V radiation ranging to 300 nm for a duration of 8 h. The bright red colour darkened slightly to a reddish brown. The I H N M R spectrum obtained at intervals during this reaction showed the emergence of new resonances assigned to 29. After 8 h the spectrum showed the persistence of residual 27, and the emergence of additional peaks corresponding to the decomposition of 29. Increasing the scale yielded a thermally sensitive reddish oil after workup in toluene. * H N M R (20 °C, C D ) : 8 0.21, 0.25, 0.30 and 0.42 (s, 3H, Si(CH ) ), 0.90 and 1.78 (dd, 2H, 7 H = 8Hz, 2  6  2  7  3  H  = 7Hz, S i C / / P ) , 0.72, 0.98, 1.12 and 1.21 (d, 3H, 7  P H  = 5Hz, P(CH ) ),  = 7Hz, 7  H H  = 1Hz, / £ ) , 3.17 (dd, IH, 7  2  4  H H  = 2Hz, 7 4  P H  H H  = 2Hz, H ), 3.08 (dd, I H , 3 7 A  = 6Hz, H ), 3.52 (m, I H , - V C  = 7Hz, 7 4  H H  4  H  2  2.78 (dd, I H , 4  = 7Hz, 7 H = 4Hz, 7 4  H H  3  P H  H H  = 7Hz, H ), 5.04 (dd, I H , D  7 H = 7Hz, 7 H = 1Hz, HE), 5.26, 5.59 and 6.47 (m, I H , Cp-H), 5.99 (dd, 1 H , 3 7 H = 7Hz, 4  H  4  2  2  P H  37  3  6  H  H  7 R H = 4Hz, H ). 3 1 p { lH} N M R (20 "C, C D ) : 8 -13.8 and -13.9 (dd, 7 2  F  6  196  6  P P  = 76Hz).  r e f e r e n c e s b e g i n o n p a g e 208  C h a p t e r 4: Effects  4.7.2.6  Me  of L i g a n d M o d i f i c a t i o n .  [P2Cp]Zr(CH Ph)3 (30) 2  A solution of K C H P h (212 mg, 1.62 mmol) in 20 mL of THF 2  a cooled (-78 "C) slurry of 25 (266 mg, 0.54 mmol) in 30 mL of THF.  was added with stirring to The dark red colour of the  KCH2Ph solution was discharged upon addition and the reaction mixture gradually changed from a cream coloured slurry to a dark red solution. The mixture was allowed to slowly warm to room temperature and left to stir for 2 h. The solvent was then removed under vacuum and the red oily residue extracted with 20 mL of toluene and filtered. The filtrate was reduced to 3 mL and combined with hexamethyldisiloxane, from which red crystals were obtained at -40 °C. Yield: (820 mg, 75 %). *H N M R (20 "C, C D ) : 8 0.04 and 0.25 (s, 6H, Si(C#?)2), 0.11 and 0.39 (dd, 6  2H, 2/HH 2  = 5Hz, 2/PH  6  = 7Hz, SiC/7 P), 0.36 and 0.78 (t, 6H, 7  = 5Hz, P(C//?) ), 2.60 (t, 6H,  2  2  P H  2  /pH = 4Hz, C H P h ) , 6.21 (d, 2H, 7 H = 1Hz, Cp-H), 6.71 (t, 1H, 7 H = 1Hz, Cp-H), 6.82 (t, 4  2  3H,  3  4  H  H  7 H = 7Hz, P-C5H5), 7.01 (t, 6H, 7 H = 7Hz, m - C H ) , 7.60 (d, 6H, 7 H = 7Hz, o3  H  C H ) . lP{*H} NMR 3  6  3  H  5  4.7.2.7  1>r  6  5  H  (20 "C, C D ) : 8 -23.8 (s). 6  6  [P Cp]Zr(r|2-CH2=CH )Br (31) 2  2  A solution of 3.0 M EtMgBr (2.15 mL, 6.45 mmol) was diluted in 20 mL of toluene and added dropwise with stirring to a cooled (-78 "C) solution of 1 (2.06 g, 3.23 mmol) dissolved in 100 mL of toluene. The pale yellow colour of the solution turned to bright yellow upon addition. The mixture was stirred at -78"C for 1 hr and allowed to slowly warm to room temperature, whereupon the colour of the solution gradually changed to a dark reddish purple. The volatiles were then removed under vacuum and the residue extracted with pentane and filtered. Dark purple crystals of 31 were obtained from a cold (-40 °C) concentrated pentane solution. Yield 1.86 g (90 %). *H NMR 2  7  (20 "C, C D ) : 8 0.21 and 0.23 (s, 6H, Si(CH ) ), 6  6  3 2  = 8Hz, SiC/7 P), 0.98 and 1.01 (m, 2H, 7 3  P H  2  (dd, 6H, 7 H = 7Hz, 7 2  2  H  P H  = 7Hz, CH =CH ), 2  2  0.82 and 0.85 (d, 2H,  1.08, 1.15, 1.26 and 1.31  = 7Hz, CH(C/7 ) ), 2.23 and 2.35 (sept, 2H, 7 H = 7Hz, 3  P H  ?  197  2  H  references begin on p a g e  208  C h a p t e r 4: Effects  Ctf(CH )2), 4.37 (t, I H , 4 /  = 1Hz, Cp-H), 6.31 (d, 2H, / H = 2Hz, Cp-H). 31p{lH} N M R 4  3  H H  (20 °C, C D ) : 8 19.5 (s). 6  of L i g a n d Modification.  H  Anal. Calcd. for C 5 H B r P S i 2 Z r : C, 46.85; H , 8.02. Found: C,  6  2  51  2  46.89; H , 8.06.  4.7.2.8  Merp c ]Zr(r|2-CH2=CH2)Br (32) 2  p  A solution of 3.0 M EtMgBr (1.50 mL, 4.50 mmol) was diluted in 20 mL of toluene and added dropwise with stirring to a cooled (-78 "C) solution of 25 (1.19 g, 2.26 mmol) dissolved in 60 mL of toluene. The reaction mixture was allowed to warm to room temperature and stirred for 3 h, during which a dark reddish brown colour was generated. The solvent was removed and the residue extracted with hexanes and filtered. Reducing this solution to 5 mL permitted the isolation of dark red crystals at -40 "C, which were washed with cold pentane and dried. Yield 0.93 g (79 %). ! H NMR  (20 "C, C D ) : 8 0.09 and 0.16 (s, 6H, Si(C//j) ), 0.84 and 1.15 (d, 2H, 6  6  2  2/ H  = 12Hz, SiCH V), 0.88 and 1.33 (d, 2H, 3 /  Jp  = 7Hz, ?(CH ) ),  H  2  H  2  3  31p{lH} NMR  2  P H  = 9Hz, CH =CH ), 2  1.24 and 1.27 (d, 6H,  2  4.15 (t, I H , 7 H = 1Hz, Cp-H), 6.02 (d, 2H, / H 4  4  H  H  = 1Hz, Cp-H).  (20 "C, C D ) : 8 0.0 (s). Anal. Calcd. for Ci7H35BrP Si Zr: C, 38.62; H , 6.67. 6  6  2  2  Found: C, 38.54; H , 6.74.  4.7.2.9  P r  [ P C p ] Z r ( C O ) B r (33) 2  2  A benzene-d solution of 31 was placed in a sealable N M R tube and affixed to a dual 6  vacuum/nitrogen line.  A small portion of solvent was removed under vacuum, and an  atmosphere of carbon monoxide introduced at -78 "C. The colour of the solution instantly changed from dark purple to dark green. *H N M R spectroscopy revealed the evolution of free ethylene and the formation of one clean product with resonances associated solely with the ancillary ligand, while the 31p{lH} N M R spectrum showed a single new resonance. Repeating  198  references begin on p a g e  208  C h a p t e r 4: Effects  of L i g a n d Modification.  the reaction in a sealed tube with the addition of C O yielded diagnostic peaks for the carbonyl 1 3  ligands in the  1 3  C N M R spectrum.  Conducting the reaction on a larger scale in toluene  generated the same colour change in solution as noted before upon addition of C O , although removal of the volatiles induced a subtle degradation of the green colour to this solution. A hydrocarbon-soluble, thermally labile dark orange-green oil was obtained after workup in hexanes. U N M R (20 "C, C D ) : 8 0.12 and 0.28 (s, 6H, S\(CH ) ),  0.51 and 0.82 (dd, 2H,  l  6  6  3 2  Jim = 15Hz, 2/PH = 9Hz, SiC// P), 0.97, 1.22, 1.29 and 1.32 (dd, 6H,  2  2  CH(C#5)2),  1.95 and 2.48 (sept, 2H,  5.19 (t, 1H, 4 y  3  7 H H  3  7 H = 7Hz, 7 3  H  = 7Hz,  = 7Hz, 0 / ( C H ) ) , 5.16 (d, 2H, 7 H = 1Hz, Cp-H), 4  3  2  H  = 1Hz, Cp-H). P { l H } N M R (20 "C, Q D g ) : 8 29.1 (s). 3 1  H H  P H  13  C { ! H } N M R (20  °C, C D ) : 8 241.1 (br s, Zr(CO)), 249.1 (s, Zr(CO)). IR ( C D ) v o 1890, 1865 ( C O ) cm-1. 13  6  6  6  4.7.2.10  M e  6  C  [ P C p ] Z r ( C O ) B r (34) 2  2  The procedure followed was similar to that for 33, reacting ethylene 32 in an atmosphere of CO.  The colour of the solution gradually changed?from dark red to a dull purplish red after  the addition of CO.  Once again, a scaled up version of this reaction permitted only the isolation  of a thermally labile oil. 1.03 (d, 2H, 7 2  4  E NMR  6  6  3 2  = 7Hz, SiC/7 P), 1.41 and 1.50 (t, 6H, 7 2  P H  2  7 H = 1Hz, Cp-H), 5.08 (t, 1H, H  UC{ H}  (20 "C, C D ) : 8 0.09 and 0.18 (s, 6H, Si(CH ) ),  l  4  7  = 5Hz, P(CH ) ),  4.82 (d, 2H,  3 2  = 1Hz, CpH). l p { Iff} NMR 3  H H  P H  0.57 and  (20 °C, C D ) : 8 -12.0 (s). 6  6  N M R (20 "C, C D ) : 8 240.5 and 245.1 (s, Zr(CO)). IR ( C D ) v o 1898, 1855  l  6  6  6  6  C  ( C O ) cm- . 13  1  4.7.2.11  Prrp Cp]Zr(ri2-PhCCPh)Br (35) 2  A solution of diphenylacetylene (106 mg, 0.59 mmol) was diluted in 30 mL of toluene and added dropwise with stirring to a cooled (-78 "C) solution of 31 (410 mg, 0.59 mmol)  199  references  b e g i n on p a g e  208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n .  dissolved in 50 mL of toluene. The mixture was slowly warmed to room temperature and stirred for another 24 h The colour of the solution gradually changed from a deep purple to a dark brown. The volatiles were then removed under vacuum and the residue extracted with hexanes and filtered. Pale yellow crystals were obtained from slow evaporation of a concentrated hexamethyldisiloxane/hexanes mixture. The crystals were washed with two aliquots of cold hexamethyldisiloxane and dried. Yield 313 mg (67 %). Anal. Calcd. for C37H57P2Si2Zr: C, 56.18; H , 7.26. Found: C, 56.15; H, 7.31. major isomer (60 %). H N M R (20 "C, C D ) : 8 0.27 and 0.46 (s, 6H, Si(Cffj)2), 0.84 l  6  and 1.28 (dd, 2H, 2 /  = 15Hz, 7 2  H H  7Hz, 3/PH = 7Hz, CH(CH ) ),  = 4Hz, S i C / / P ) , 0.80, 0.98, 1.04 and 1.13 (dd, 6H, 3 / 2  1.74 and 2.53 (sept, 2H, 3 j  3 2  7 H H = 1Hz, Cp-H), 6.86 (t, IH, 4 /  4  P H  6  H H  =  H H  = 7Hz, C#(CH )2), 6.75 (d, 2H, 3  = 1Hz, Cp-H), 7.00 (t, 2H, p - C H ) , 7.24 (t, 4H, m - C H ) ,  H H  6  5  6  5  7.45 (d, 4H, o - C H ) . 3lp{lH} N M R (20 "C, C D ) : 8 9.3 (s). 6  5  6  6  minor isomer (40 %). H N M R (20 °C, C D ) : 8 0.21 and 0.33 (s, 6H,  Si(CH ) ),  J  6  0.67and 1.14 (dd, 2H, 2 /  = 14Hz, 7 2  H H  JUH = 7Hz, 3 7 = 7Hz, CH(CH ) ), 3 2  3  2  = 5Hz, SiCtf P), 0.75, 1.19, 1.29 and 1.35 (dd, 6H, 2  2.10 and 2.15 (sept, 2H, 3 /  3  PH  P H  6  H H  = 7Hz, Ctf(CH ) ), 6.46 (t, 3  2  IH, 7 H H = 1Hz, Cp-H), 6.80 (d, 2H, / H = 1Hz, Cp-H), 6.94 (t, 2H, p - C H ) , 7.18 (t, 4H, m4  4  6  H  5  C H ) , 7.35 (d, 4H, o - C H ) . 31p{lH} N M R (20 "C, C D ) : 8 6.9 (s). 6  5  6  4.7.2.12  5  6  6  {P«-[P Cp]ZrBrH}(n-H)3{BrZr[P Cp]} (36) 2  2  A solution of 31 (1.390 g, 2.11 mmol) in 60 mL of toluene was placed in a 200 mL bomb and affixed to a dual vacuum/nitrogen line. The contents were frozen and the head space evacuated, and an atmosphere of hydrogen introduced at -196 "C. The bomb was sealed and the solution allowed to slowly warm to room temperature, resulting in a reaction vessel containing H2 at a pressure of 4 atm. The colour of the solution slowly faded from dark purple to dark green. I H N M R (20 "C, C D ) : 8 0.01, 0.38, 0.51 and 0.62 (s, 6H, Si(CH ) ), 0.75 and 0.84 (m, 6  6  3  200  2  references begin on page 2 0 8  C h a p t e r 4: Effects  4H, S i C / / P ) , 1.04 (m, 24H, CU(CH ) ), 2  CH(CH )2), 3  3  2  1.25 (dd, 12H, 7 H = 7Hz, 7 3  1.18 and 1.37 (dd, 6H, 7 H = 7Hz, 7 3  3  H  3  H  of L i g a n d M o d i f i c a t i o n . . .  P H  = 7Hz,  = 7Hz, C H ( C / / ) ) , 1.59 and 1.62 (sept, 2H, 7 H 3  P H  5  2  H  = 7Hz, C / / ( C H ) ) , 1.73 and 2.72 (m, 2H, C / / ( C H ) ) , 2.30 (br, 3H, Zr//), 5.23 (t, 1H, 7 2  3  2  3  2  P H  = 74  Hz, Zr/7), 5.72 and 7.21 (t, 1H, 7 H = 1Hz, Cp-H), 6.69 and 7.08 (d, 2H, 7 H = 1Hz, Cp-H). 4  4  H  3  H  l P { l H } N M R (20 "C, C D ) : 8 -5.6 (s, 2P), 39.2 (s, 2P). 6  4.7.2.13  6  { [P Cp]ZrBr}2(n-H) (37) Me  2  4  A solution of 32 (300 mg, 0.58 mmol) in 20 mL of toluene was placed in a 100 mL bomb and affixed to a dual vacuum/nitrogen line. The contents were frozen and the head space evacuated, and an atmosphere of hydrogen introduced at -196 "C. The bomb was sealed and the solution allowed to slowly warm to room temperature, resulting in a reaction vessel containing H  2  at a pressure of approximately 4 atm. The solution was left to stir for 24 h, during which the  colour slowly faded from dark red to pale yellow. The solvent was removed and the residue extracted with hexanes.  Colourless needles were obtained from a cold, concentrated  hexamethyldisiloxane solution (-40 "C). Yield 170 mg (60 %). *H N M R (20 °C, C D ) : 8 0.18, 6  6  0.20, 0.21, 0.28, 0.33, 0.42, 0.81 and 0.86 (s, 3H, Si(C//?) ), 0.74, 0.79, 1.14 and 1.43 (d, 2H, 2  2  7  = 7Hz, S i C / / P ) , 1.06, 1.17, 1.36, 1.39, 1.46, 1.63, 1.81 and 1.88 (d, 3H, 7 2  p H  2  P(C7/j?) ), 3.74 (br d, 2H, 7 2  2  P H  P H  = 6Hz,  = 80 Hz, Zr//), 3.89 (br, 2H, Zr//), 6.19, 6.35, 6.39, 6.42, 6.45  and 6.46 (br, 1H, Cp-H). l p { lH} N M R (20 "C, Q D g ) : 8 -54.9 (s), -17.6 and -14.7 (d, IP, 7 3  2  P P  = 58Hz), -13.0 (s).  4.7.2.14  Pr  [ P C p ] Z r ( n 2 . C H 2 = C H ) M e (38) 2  2  A solution of 1.4 M MeMgBr (0.75 mL, 1.05 mmol) was diluted in 10 mL of toluene and added dropwise with stirring to a cooled (-78 "C) solution of 31 (620 mg, 0.97 mmol) dissolved in 60 mL of toluene. The mixture was allowed to slowly warm to room temperature, during  201  references  begin on page 2 0 8  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n .  which the colour of the solution gradually changed from a deep purple to a dark reddish orange. The reaction mixture was stirred for another 24 h, the volatiles then removed under vacuum and the residue extracted with hexanes and filtered. A pale pink, thermally sensitive solid was obtained by slow evaporation of the filtrate, washed with cold pentane and dried. Yield 425 mg (76 %). ! H N M R (20 "C, C D ) : 8 -0.67 (t, 3H, 3 / 6  Si(CH ) ), 3  2  0.86 (m, 4H, 7 2  (m, 24H, CH(CH ) ), 3  6.32 (d, 2H, 4 /  4.7.2.15  2  P H  6  = 8Hz, S i C / / P ) , 1.05 (m, 2H, 3 / 2  2.09 (sept, 4H, 3 /  = 7Hz, CHiCHjk),  H H  = 2Hz, Cp-H). 3lp{lH} NMR  H H  = l()Hz, ZrCi/j), 0.24 and 0.26 (s, 6H,  P H  p H  = 8Hz, Zr(CH =CH )), 2  1.10  2  4.61 (t, I H , 7 H = 2Hz, Cp-H), 4  H  (20 C, C D ) : 8 20.1 (s). 6  6  Pr[P2Cp]Zr(r)2-CH2=CH )(ri5-C5H5) (39) 2  A solution of NaCp.DME (106 mg, 0.59 mmol) was diluted in 30 mL of toluene and added dropwise with stirring to a cooled (-78 "C) solution of 31 (410 mg, 0.59 mmol) dissolved in 50 mL of toluene. The mixture was stirred at -78 "C for 2 h, then allowed to slowly warm to room temperature and stirred for another 24 h The colour of the solution gradually changed from a deep purple to a orange-red. The volatiles were then removed under vacuum and the residue extracted with hexanes and filtered.  Orange crystals were obtained from a cold (-40 °C)  concentrated hexamethyldisiloxane/hexanes  mixture.  The crystals were washed with cold  hexamethyldisiloxane and dried. Yield 310 mg (84 %). *H N M R (20 "C, C D ) : 8 0.08, 0.13, 6  0.52 and 0.58 (s, 3H, Si(CH ) ), 3  0.42,0.75, and 0.85 (ddt, IH, 7  = 6Hz, CH77=CH ), 0.74 and 0.81 (dd, 2H, 7 H = 15Hz, 7 2  2  2  H  1.03, 1.04, 1.05, 1.05 and 1.13 (dd, 3H, 7 3  (sept, I H , 3 /  NMR  P H  = 7Hz, 3 y  PH  = 7Hz, C / / ( C H ) ) , 1.74 (d of sept, IH, 7 3  1.98 (d of sept, I H , 3 y (s, 5H, 3 /  H H  P H  = 7Hz, 7 2  H H  = 1Hz, C H ), 5  2  5  = 4Hz, SiC/7 P), 0.94, 1.00, 1.02, 2  = 7Hz, 7 2  H H  P H  = 3Hz, O f (CH )2), 3  = 7Hz, C / / ( C H ) ) , 5.21 (t, I H , 7 H = 2Hz, Cp-H), 5.35, 3  5.61 and 5.62 (dd, I H , 3 y  6  P  4  P H  (20 "C, C D ) : 8 -5.3 (s), 42.3 (s). 6  3  H H  = 7Hz, CH(C#j)2), 1.59 and 1.60  3  H H  = 10Hz(cw and trans), / H  3  2  6  2  H  = 6 H z , 7 H = 2Hz, Cp-H). 31p{lH} 4  H H  H  Anal. Calcd. for C H5 P2Si2Zr: C, 57.55; H , 9.01. 30  6  Found: C, 57.25; H , 9.15. 202  references begin on p a g e  208  C h a p t e r 4: Effects  4.7.2.16  Pr  of L i g a n d M o d i f i c a t i o n . . .  [ P C p ] Z r ( r | - C 5 H 5 ) ( C O ) (40) 5  2  A benzene-d solution of 39 was placed in a sealable NMR  tube and affixed to a dual  6  vacuum/nitrogen line.  A small portion of solvent was removed under vacuum, and an  atmosphere of carbon monoxide introduced at -78 "C. The contents within the sample were continually mixed under ambient temperature by a constant inversion of the sample by mechanical method. The reaction was monitored by  and ^ P f ! ! } NMR  spectroscopy until  1  the reaction was complete (approximately two weeks). There was no obvious colour change associated with this reaction. 40 was observed to be the major product (90 %) based on the NMR  spectra. Repeating the procedure in a sealed tube with the addition of  strong diagnostic peak at 308 ppm for the carbonyl ligand in the  1 3  1 3  C O yielded a  C N M R spectrum.  Conducting the reaction on a larger scale in toluene generated a thermally sensitive hydrocarbonsoluble orange oil after workup that gradually decomposed at -40 "C.  *H NMR  (20 °C, C6D6): 8  0.13, 0.24, 0.35 and 0.47 (s, 3H, Si(CH ) ), 0.42 and 0.63 (dd, 1H, 7 H = HHz,  2  S i C / / P ) , 0.69 (d, 2H, 7  3  2  3  3  7  H  P H  2  3  2  3 2  C#(CH )2), 1.59 (sept, 2H, 7 H = 7Hz,  3  4  3 1  H  C{  !  H } NMR  4.7.2.17  6  2  P H  = 1Hz, C H ), 5.08, 5.55 5  5  ]  6  2  Pr  H  P { H } N M R (20 C, C D ) : 8 -4.8 and 58.7 (s).  (20 "C, C D ) : 8 308.0 (d, 7 6  3  3  H  and 5.62 (dd, 1H, 7 H = 1Hz, Cp-H). 13  = 9Hz,  1.29 and 1.55 (sept, 1H, 7 H = 7Hz,  C#(CH ) ), 4.95 (s, 5H, 7  3  3  P H  H  = 7Hz, CH(C/7 ) ), 1.05 (m, 12H, CH(CH ) ),  p H  7  = 7Hz, SiC/7 P), 0.75, 0.78, 0.90 and 0.91 (dd, 3H, 7 H = 7Hz,  2  2  2  P C  6  = 3Hz, Zr(CO)).  [ P C p ] Z r ( T | 5 . C 5 H 5 ) H (41) 2  2  A benzene-d solution of 39 was placed in a sealable NMR 6  vacuum/nitrogen line.  tube and affixed to a dual  The contents were frozen and the head space evacuated, and an  atmosphere of hydrogen introduced at -196 "C. The N M R tube was sealed and the sample allowed to slowly warm to room temperature, resulting in a reaction vessel containing H at a 2  pressure of 4 atm. The orange colour of the sample slowly faded to a pale buff over the course of  203  references begin on p a g e  208  C h a p t e r 4: Effects  four days until the reaction was complete as monitored by  of L i g a n d M o d i f i c a t i o n .  and ^ P ^ H } NMR  A new complex was obtained quantitatively (> 99 %) based on the NMR  spectroscopy.'  spectra. Conducting  the reaction on a larger scale in toluene generated a yellow hydrocarbon-soluble oil after workup. ! H NMR 2/  H H  (20 "C, C D ) : 5 0.16, 0.40, 0.43 and 0.55 (s, 3H, Si(C//?)2), 0.69 and 0.85 (dd, 1H, 6  = 10Hz,  2  7  6  = 12Hz, SiC/7 P), 0.74 and 0.75 (dd, 1H, 7 R H = 2Hz, 2  P H  0.93, 0.98, 1.01, 1.02, 1.03, 1.04, 1.06, and 1.17 (dd, 3H, 7 3  1.30 (sept, 2H, 7 3  H H  = 7Hz,  4.7.2.18  = 7Hz,  3  7  P H  P H  = 2Hz,  2  H  4  7 H = 1Hz, H  Cp-H),  SiC# P), 2  = 7Hz, CHCCZ/jh),  3  3  2  31p{lH} NMR  H H  7  C#(CH ) ), 1.35 and 1.56 (d of sept, 1H, 7 H = 7Hz,  C/7(CH ) ), 5.21, 6.42 and 6.46 (dd, 1H, 3  2  2  5.52 (s, 5H, 7 3  P H  2  7  P H  = 1Hz,  = 2Hz, C5//5).  (20 "C, C D ) : 8 -5.6 (s), 43.9 (s). 6  6  Ligand synthesis:  P r  [P Cp']Li 2  C5H4SiMe CH2Cl-3-CMe3 2  A 500 mL 3-necked round-bottomed flask was equipped with a magnetic stir bar, a 100 mL dropping funnel, a rubber septum cap, and a ground glass stopper. The flask was charged with dimethylfulvene (12.0 mL, 99.6 mmol) and diethyl ether (150 mL) under a nitrogen purge, and the contents cooled in an ice bath (0 "C).  A solution of 1.4 M M e L i (70.0 mL, 98.0 mmol)  was added dropwise from the dropping funnel over a period of 20 min, during which the orange colour of the dimethylfulvene solution turned to a pale yellow slurry. The reaction mixture was left to stir at 0 "C for 90 min. This mixture was then added dropwise via cannula to a 1 L 3necked round-bottomed flask charged with C l S i M e C H C l (13.5 mL, 102 mmol) and THF 2  mL),  cooled at -78 "C.  2  (250  The reaction mixture became viscous and pale yellowish-green in colour  during the course of the addition. The solution was slowly warmed to room temperature and stirred for 12 h. The solvent was then removed in vacuo and 100 mL water added to the flask, and extracted with four aliquots (25 mL) of diethyl ether. The ether layer was dried over MgS04 and filtered, and the solvent subsequently removed to give a clear yellow oil. Vacuum  204  r e f e r e n c e s b e g i n on p a g e  208  C h a p t e r 4: Effects  of L i g a n d M o d i f i c a t i o n .  distillation yielded a clear yellow liquid (bp 74-78 "C, 10" Torr) consisting mainly of the 1,32  isomer (> 85 % by U NMR  spectroscopy). Yield: (15.88 g, d = 0.97 g mol" , 73 %). H  l  1  (20 °C, C D ) : 8 -0.02 (s, 6H, Si(C/7-?) ), 1.09 (s, 9H, C(CH ) ), 6  6  2  3 3  NMR  l  2.68 (s, 2H, SiC/7 Cl), 3.40 (br 2  s, I H , Cp-/7Si(CH ) ), 6.02, 6.41 and 6.64 (br s, IH, Cp-H)3  2  C5H3-l,l-SiMe2CH2Cl2-3-CMe3 A 250 mL 3-necked round-bottomed flask was equipped with a magnetic stir bar, a 100 mL  dropping funnel, a rubber septum cap, and a ground glass stopper. The flask was charged  with C5H4SiMe2CH2Cl-3-CMe3 (5.2 mL, 21.8 mmol) and THF  (60 mL) under a nitrogen purge,  and the contents cooled in an ice bath (0 " Q . A solution of N a N ( S i M e ) (4.00 g, 21.8 mmol) in 3  50 mL of THF  2  was added dropwise from the dropping funnel over a period of 25 min, during  which the yellow solution became slightly viscous. The reaction mixture was left to stir at 0 °C for 30 min, after which the solution became darker (orange) and more viscous. This mixture was then added dropwise via cannula to a 500 mL 3-necked round-bottomed flask charged with C l S i M e 2 C H C l (3.0 mL, 23 mmol) and T H F (600 mL),  cooled at -78 °C. The reaction mixture  2  turned ochre-yellow and translucent in appearance during the course of the addition. The solution was slowly warmed to room temperature and stirred for 2 h, after which the colour was a paler yellow. The solvent was then removed in vacuo and 80 mL water added to the flask, and extracted with four aliquots (25 mL) of diethyl ether. The ether layer was dried over MgS04 and filtered, and the solvent subsequently removed to give a clear yellow oil.  Vacuum distillation  yielded a viscous yellow oil (bp 118-121 "C, 1()" Torr) consisting solely of the 1,1-side-arm 2  disubstituted species. Yield: (4.30 g, 60 %). *H NMR  (20 "C, C D ) : 8 0.02 and 0.03 (s, 6H, 6  6  Si(C/7 ) ), 1.04 (s, 9H, C(C#j) ), 2.36 (s, 4H, SiC/7 Cl), 5.98 (dd, I H , 7 H = 4Hz, 7 H = 4  5  2  3  2  4  H  H  3Hz,  Cp-77), 6.35 (dd, I H , 7 R H = 4Hz, 7 H = 8Hz, Cp-H), 6.63 (dd, I H , 7 H = 3Hz, 7 H =  8Hz,  Cp-H).  4  4  3  H  205  4  H  r e f e r e n c e s b e g i n on p a g e  H  208  C h a p t e r 4: Effects  of L i g a n d Modification.  Pr[P Cp']Li 2  A mixed solvent solution of 34 (2.05 g, 6.15 mmol) in 60 mL of T H F and 10 mL of toluene was added dropwise with stirring to a heated (50 "C) solution of LiPPri2 (2.25 g, 18.3 mmol) dissolved in 90 mL of THF.  Upon addition of the last drops of 34 the bright yellow  phosphide solution dimmed rapidly to give a pale greyish-yellow colour. The reaction mixture was immediately removed from the oil bath and allowed to cool to room temperature. The solvent was removed under vacuum and the viscous gray residue extracted with hexanes and filtered. A small yield of colourless crystals was obtained form a cold (-40 °C), concentrated hexanes solution. X-ray diffraction data revealed that this compound consisted of a 1:1 mixture of  P r  [P2Cp']Li  with one of the phosphines  bridged to a unit of (r|5-C5H -l,22  SiMe CH CH SiMe2-3-CMe3). Yield 1.40 g (54 %). *H NMR 2  2  0.53 and 0.67 (s, 6H, Si(CH ) ), 3  2  H  S i C / / C / / S i ) , 1.14 (t, 4H, 7 H = 7Hz, THF), 3  H  (sept, 2H, C / / ( C H ) ) , 3.12 (t, 7 3  3  2  (20 "C, C D ) : 5 0.0 (q, J l  6  ^PLi  6  PU  2  H  3  2  6  0.72 and 0.78 (dd, 2H, / H = 14Hz, 7  2  0.93, 0.95, 0.96 and 1.01 (dd, 6H, 7 H = 8Hz, - V 2  (20 "C, C D ) : 5 0.33, 0.46,  2  H H  = 7Hz, THF),  P H  P H  6  = 5Hz, S i C / / P ) , 2  = 7Hz, CHCCT^h), 1.06 (m, 4H,  1.46 and 1.46 (s, 9H, C(CH3)3), 1.53 and 1.67 6.47 and 6.50 (s, 1H, Cp-//). 3 P{ H}  = 33Hz). ^ L i f l H } NMR  1  1  NMR  (20 "C, C D ) : 5 -11.7 (br s), -10.9 (t, 6  6  = 33Hz). Anal. Calcd. for Q H9oLi OP2Si4: C, 65.20; H , 10.70. Found: C, 64.80; H , 6  2  10.20.  4.7.2.19  Isolation of [ P C p ' ] Z r C l (42) p,  2  2  This product was obtained inminute quantities as dark green crystals, with poor solubility in organic solvents, in n unsuccesful attempt to alkylate the trichloride derivative [P Cp']ZrCl3. 2  Anal. Calcd. for C27H55Cl P2Si2Zr: C, 49.14; H, 8.40. Found: C, 48.93; H, 8.47. 2  206  references begin on page  208  C h a p t e r 4: Effects  4.7.2.20  of L i g a n d M o d i f i c a t i o n .  Stepwise reduction to [ P C p ] Z r C l (43) and { [ P C p ] Z r C l } ( j i - N ) (44) P r  Pr  2  2  2  An intimate mixture of 1 (640 mg, 1.00 mmol) and KC8  2  2  (474 mg, 3.50 mmol) was placed  in a 200 mL bomb and 50 mL of toluene added. The mixture immediately turned to a dark blue slurry. The mixture was stirred at room temperature for 3 days, at which time the colour of the solution was dark green. Two possibilities follow at this stage. Isolation of the intermediate Zr(II) species could be obtained by filtration, followed by reducing the volume of the solvent to 3 mL.  Dark green crystals of [P2Cp]ZrCl2 were obtained at -40 "C from toluene. Anal. Calcd. for  C23H47Cl2P2Si2Zr: C, 45.75; H , 7.84. Found: C, 45.41; H , 7.83. ESR (toluene): g = 1.96; a( P) = 18.00G, 2P. 31  If the above reduction is conducted with heating at 40 "C for one week the solution gradually turns brown. Filtration of the graphite, followed by removal of the solvent, yields a red oil that is soluble in hexanes. Dark reddish crystals were obtained from cold hexanes (-40 °C). Yield 425 mg (76 %). Anal. Calcd. for C 6H9 Cl2N P4Si4Zr2: C, 47.43 H , 8.13 N , 2.40. 4  Found: C, 48.03; H , 8.40 N, 2.20. H NMR  4  2  (20 °C, C D ) : 8 0.28, 0.29, 0.32 and 0.35 (s, 6H,  }  6  6  Si(C7/j)2), 0.80 (m, 8H, S i C / / P ) , 1.19 (m, 48H, Ct\{CH ) ), 2  7Hz,  C / / ( C H ) ) , 6.30 and 6.52 (d, 2H, 3  2  Cp-//). - ^ P ^ H } NMR  4.7.2.21  2.38 and 2.41 (sept, 4H, 3 /  3 2  4  7  H H  = 2Hz, Cp-//), 6.73 and 7.00 (t, IH,  4  / H  H H  =  = 2Hz,  H  (20 "C, C D ) : 8 16.4 (s). 6  6  {Merp c ]ZrCI} (|t-Cl)2 (45) 2  p  2  This compound was isolated as dark red crystals as a minor product (< 5 %) from the thermal decomposition of the photolysis product 29. H NMR  (20 "C, C6D ): 8 0.12, 0.19, 0.30  ]  and 0.42 (s, 6H, Si(C// ) ), 0.8, 1.22, 1.39 and 1.41 (d, 2H, ?  2  (d, 2H, 7 H = 1Hz, Cp//), 6.23 and 6.40 (t, 2H, / H 4  4  H  H  C D ) : 8 -18.0 and -17.4 (dd, 2H, 6  6  4  7  207  P P  2  6  /  P H  = 6Ffz, S i C / / P ) , 6.15 and 6.26 2  = 1Hz, Cp//). P { ! H } N M R 31  (20 °C,  = 3Hz).  references  begin on page  208  C h a p t e r 4: Effects  4.7.2.22  P r  of L i g a n d M o d i f i c a t i o n . . .  [ P C p ] T h B r (46) 2  3  A solution of [P2Cp]Li (1.12 g, 2.50 mmol) in 30 mL of toluene was added dropwise Pr  with stirring to ThBi'4(THF)4 (2.10 g, 2.50 mmol) dissolved in 30 mL of toluene at room temperature. The solution gradually became turbid during the course of the addition but remained colourless. The reaction mixture was left to stir for 48 h after which the solution was filtered, and the volume reduced to 3 mL. Colourless crystals were deposited from slow evaporation of this concentrated solution. The isolated crystals were washed with cold hexanes and dried. Yield 1.67 g (73 %). *H NMR (dd, 4H, 2 y 3y  = 6Hz, 7 2  H H  P H  (20 "C, C D ) : 8 0.18 and 0.56 (s, 6H, Si(C//j>2), 1.05 6  6  = 7Hz, S i C / / P ) , 1.34 (m, 24H, CH(C/7j) ), 2.08 and 2.37 (sept, 2H, 2  2  = 7Hz, C/7(CH ) ), 6.97 (d, 2H, 7 H = 1Hz, Cp-H), 7.68 (t, 1H, 7 H = 1Hz, Cp-H). 4  H H  NMR  3  2  4  H  H  3 1  P  (20 C , C D ) : 8 33.2 (s). Anal. Calcd. for C 2 H 4 B r P S i T h : C, 30.24; H , 5.19. 6  6  3  7  3  2  2  Found: C, 29.68; H , 5.14.  4.8  References  (1)  Davies, G. R.; Jarvis, J. A . J.; Kilboum, B . T.; Pioli, A . J. P. Chem.Commun.  1971, 677. (2)  Jordan, R. F.; LaPointe, R. E.; Baenziger, N.; Hinch, G. D. OrganometalUcs 1990,  9, 1539. (3)  Buchwald, S. L.; Watson, B . T.; Huffman, J. C. 7. Am. Chem. Soc. 1986,108,  (4)  Rosa, P.; Floch, P. L.; Ricard, L.; Mathey, F. 7. Am. Chem, Soc. 1997,119, 9417.  (5)  Dupuis, L.; Pirio, N.; Meunnier, P.; Igau, A.; Donnadieu, B.; Majoral, J.-P.  7411.  Angew. Chem,, Int. Ed. 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Am, Chem, Soc 1992,114, 9483.  (26)  Alt, H. G.; Denner, C. E.; Thewalt, U.; Rausch, M . D. J. Organomet. Chem. 1988,  356, C83. (27)  Demerseman, B.; Bouquet, G.; Bigome, M . J. Organomet. Chem, 1977,132, 223.  (28)  Manriquez, J. M . ; McAlister, D. R.; Sanner, R. D.; Bercaw, J. E. J. Am. Chem,  Soc. 1978,700, 2716. (29)  Etkin, N.; Hoskin, A. J.; Stephan, D. W. J. Am, Chem, Soc 1997,119, 11420.  (30)  Roddick, D. M . ; Fryzuk, M . D.; Seidler, P. F.; Hillhouse, G. L.; Bercaw, J. E.  OrganometalUcs 1985, 4, 97. (31)  Mitchell, J. P.; Hajela, S.; Brookhart, S. K.; Ffardcastle, K . I.; Henling, L. M . ;  Bercaw, J. E. J. Am, Chem, Soc 1996,118, 1045. (32)  He, M . - Y . ; Xiong, G.; Toscano, P.; Burwell, R. L.; Marks, T. J. J. Am, Chem. Soc.  1985,707,641.  210  references  begin on page  208  C h a p t e r 4: Effects  (33)  of L i g a n d Modification...  Cotton, F. A . ; Wilkinson, G. Advanced Inorganic Chemistry; 5th ed.; Wiley: New  York, 1988; (34)  Clark, D. L.; Frankom, T. M . ; Miller, M . M.; Watkin, J. G. Inorg. Chem. 1992,  31, 1628.  211  references begin on p a g e  208  Appendix One: X-ray Crystal Structure Data  Table A l . l  Crystallographic data. '  Compound  3  2 [P Cp]inCl Pr  2  b  13 [P Cp]ZrCl2  17 [P Cp]Hf=CH  Pr  3  Pr  2  2  (Tl -C(Q)CH Ph)  18b ^[P^pJZ^CH  Ph(Cl)  2  2  SiMe3(Cl)  Empirical Formula  C 3H47Cl3HrP Si2  C iH54Cl20P2Si Zr C 3.5oH57ClHiP Si2 C27H 7ClZrP Si3  fw  726.57  723.01  791.88  654.62  Color, habit  yellow, block  yellow, plate  yellow, irregular  yellow, block  Crystal system  monoclinic  monoclinic  triclinic  monoclinic  Space group  Pldn  Plilc  PI  P2 /n  a, A  17.0071(1)  15.248(6)  11.7554(11)  12.982(5)  b, A  11.7419(2)  16.192(5))  12.488(2)  16.679(6)  c,k  17.1842(1)  15.524(2))  13.9584(10)  16.710(5)  a, deg  90  90  98.3839(7)  -  P,deg  116.509(1)  100.007(2)  95.0101(9)  98.99  y, deg  90  90  111.100(3)  -  V,A3  3070.82(6)  3774(2)  1869.5(3)  3573.7(22)  Z  4  4  2  4  1.572  1.272  1.407  1.22  F(000)  1464  1520.00  810.00  1392  Radiation  Mo  Mo  Mo  Mo  u, cm"  3.851  6.02  30.26  5.1  Crystal size, mm  0.32x0.18x0.12  0.15x0.40x0.45  0.45x0.35x0.15  0.30 x 0.40 x 0.50  Transmission factors 0.775-1.000  0.7066-1.0226  0.92-1.00  0.823 to 0.999  Scan type  co-29  co-29  ea-29  co-29  Scan range, Q)°  1.00+0.35 tan 0  -  1.00+0.35 tan 9  -  Peak- g  / c m 3  1  2  2  3  2  212  3  2  5  2  x  Appendix l:X-ray  Crystal Structure  Data  16 (up to 8 scans)  Scan speed, °min-l  4.2 (1 rescan)  29  45  63.8  60.1  45  Total reflections  15681  31051  15781  4817  Unique reflections  5391  7757  8376  4640  R,  0.0260  0.0933  0.043  0.040  Number w/ / > 3o(/) 1832  2529  6427  Variables  334  352  374  334  R  0.064  0.219  0.069  0.056  0.037  0.168  0.072  0.055  1.87  0.733  1.82  3.16  Max A/a (final cycle) 0.004  0.0002  0.0006  Residual density e/A --1.052 to 0.588  -2.88 to 2.67  -2.97 to 2.47  20 [P2C ]Zr  21a [P2Cp]Zr  23b [P2Cp]ZrCH2 27 [P2Cp]ZrCl  ( T I - C H = C H )C1  C(0)=CHPh(Cl)  inax  , deg  Crystal, decay, %  merge  gof  3  Compound  Pr  P  2  2  2  Pr  -0.610 to 0.880  Me  Pr  (CH Ph)  CH2C(0)=CH  2  2  SiMe3(Cl) Formula  C .sH ClZrP2Si2  C3iH5 C10P Si2Zr  C H6lClOP2Si3Zr  C29H ClP2Si Zr  fw  596.47  686.55  710.69  638.44  Color, habit  red, block  orange, irregular  yellow, prism  red-brown, block  Crystal system  triclinic  inonoclinic  monoclinic  triclinic  Space group  PI  Fide  Fide  PI  a, A  115.432(3)  8.666(1)  12.6352(12)  11.6130(2)  b, A  20.483(3)  24.244(1))  16.520(2)  12.0201(1)  c, A  20.995(7)  17.543(1)  18.5436(4)  12.9477(2)  a, deg  76.50(3)  90  90  75.805(1)  Meg  83.12(7)  100.936(8)  92.4321(4)  70.011(1)  2  51  3  213  2  30  45  2  Appendix l:X-ray Crystal Structure Data  Y, deg  88.52(4)  90  90  75.118(1)  v,A  6407(3)  3618.9(6)  3867.1(4)  1616.66(4)  8  4  4  2  1.24  1.26  1.221  1.312  F(000)  2528  1448  1512.00  668  Radiation  Mo  Mo  Mo  Mo  u, cm"  6.0  5.53  5.49  6.12  Crystal size, mm  0.30 x 0.40 x 0.45  0.25 x 0.30 x 0.45  0.20x0.45x0.45  0.40x0.30x0.25  Transmission factors 0.903-1.00  0.956-1.000  0.5744-1.0291  0.844-1.000  Scan type  eo-29  oo  oo-29  co-20  Scan range, co°  1.05+0.35 tan 0  0.79+0.35 tan 9  1.56+0.35 tan 0  1.25+0.20 tan 0  Scan speed, °min"l  16 (up to 8 scans)  16 (up to 9 scans)  3-30 (up to 8 scans)  16 (up to 9 scans)  26^, deg  40.0  60  60  3  z Peak' 8  / c m 3  1  Crystal, decay, %  1.95  Total reflections  11928  11425  36109  5433  Unique reflections  11917  10783  9656  5433  D  0.023  0.034  0.046  Number w/ / > 3a(/) 7589  5598  5373  merge  Variables  396  344  343  R  0.055  0.034  0.064  R  0.060  0.031  0.045  gof  3.71  1.49  1.83  Max A/a (final cycle) 0.02  0.003  0.007  Residual density e/A -0.550 to 0.640  -0.35 to 0.31  -2.19 to 1.77  w  3  Compound  28  Me  [P Cp]Zr 2  3»  Me  (r) -C6H3Me)Cl  [P C ]Zr 2  P  (CH Ph)3  2  2  214  32  Me  369  1.021  -0.383 to 0.333  35 [P Cp]Zr  [P Cp]Zr  Pr  2  2  (r| -CH =CH )Br 2  2  2  (n -PhCCPh)Br 2  A p p e n d i x 1.-X-ray  Crystal Structure Data  Formula  C 9H47ClP Si2Zr  C H P Si Zr  Ci H CBrP Si Zr  C3 H BrP Si Zr  fw  640.46  1256.07  528.71  791.10  Color, habit  -  red, irregular  red-brown, prism  yellow, plate  Crystal system  monoclinic  monoclinic  monoclinic  monoclinic  Space group  Pldn  Pldc  Pldc  Pl la  a, A  15.1458(8)  8.9145(5)  12.352(1)  18.8932(11)  ft, A  9.9410(5)  35.292(2)  15.333(1)  23.2223(14)  c, A  23.252(1)  20.6605(3)  13.567(1)  20.5753(2)  90  90  90  -  Meg  105.135(1)0)  93.3670(3)  108.352(6)  118.1110(2)  Y, deg  90  90  90  -  V, A  3379.5(3)  6488.9(4)  2438.7(3)  7962.4(5)  4  4  4  8  1.259  1.286  1.440  1.320  F(000)  1344  2640.00  1080.00  3296.00  Radiation  Mo  Mo  Mo  Mo  u, cm"  5.86  4.88  78.93  14.47  Crystal size, mm  0.10x0.10x0.10  0.15x0.35x0.45  0.20 x 0.30 x 0.45  0.30x0.30x0.10  Transmission factors 0.95-1.00  0.8201-0.9972  0.736- 1.000  0.6288 - 1.0000  Scan type  co-28  00-20  co-20  co-20  Scan range, co°  1.10+0.35 tan 0  1.15+0.35 tan 8  1.00+0.20 tan 0  1.37+0.20 tan 0  32 (up to 8 scans)  16 (up to 8 rescans)  16 (up to 9 scans)  16 (up to 8 scans)  55  60.2  155  60.1  Crystal, decay, %  -1.66  -  -  -  Total reflections  19827  61655  5395  74849  Unique reflections  7924  16262  5163  20481  a,  2  deg  3  Z Pcalc S  / C m 3  1  Scan speed, °min 29  max'  de  _1  8  2  36  215  52  2  2  7  35  2  2  7  57  2  2  x  Appendix l:X-ray Crystal Structure Data  p  0.027  merge  0.0777  0.044  Number w//>3c(/) 3617  10192  3408  11170  Variables  366  722  225  775  R  0.038  0.031  0.035  R  w  0.039  0.040  0.033  0.030  gof  1.95  1.17  1.78  1.26  Max A/a (final cycle) 0.01  0.04  0.0004  0.002  Residual density e/A -0.687 to 0.471  -4.38 t 6.03  -0.49 to 0.42  -1.99 to 1.64  3  Compound  37 { [P2Cp]ZrBr)2 43 [P Cp']ZrCl Me  2  44 { [P Cp]ZrCl} Me  Pr  2  2  (H-H)4  (M--CQ2  Formula  C3oH66Br P Si Zr2  C27H55Cl P Si Zr  C33.50H66C  fw  1005.34  659.95  1029.38  Color, habit  colorless, needle  dark green, block  red, prism  Crystal system  monoclinic  monoclinic  monoclinic  Space group  Plylc  P2\lc  P2dc  a, A  13.576(2)  16.2492(3)  12.7313(7)  b,k  10.3435(7)  11.2733(2)  35.0096(5)  c, A  32.0759(10)  19.1230(3)  22.0768(13)  a, deg  90  90  90  P, deg  92.2027(9)  96.478  90.1059(4)  Y, deg  90  90  90  v,A3  4500.9(5)  3480.63(10)  9840.0(6)  z  4  4  8  1.483  1.259  1.390  F(000)  2048.00  1396  4248.00  Radiation  Mo  Mo  Mo  Pcalc S  / c m 3  2  4  4  2  216  2  2  2  Appendix l:X-ray Crystal Structure D a t a  u, cm"  25.12  6.45  8.90  Crystal size, mm  0.04 x 0.08 x 0.50  0.30x0.18x0.16  0.15x0.25x0.30  Transmission factors 0.5022 - 1.0005  0.838- 1.000  0.8270-1.0100  Scan type  co-20  co-20  1  co-20  Scan range, co°  0.94+0.20 tan 0 16 (up to 9 scans)  Scan speed, "min"  1  max> S  2e  56.7  60  de  Crystal, decay, % Total reflections  41794  17147  74078  Unique reflections  10785  6049  20251  Number w/ / > 3a(7) 4787  4824  11200  Variables  387  377  837  R  0.063  0.0735  0.133  K  0.061  0.01274  0.150  gof  1.92  1.021  2.59  merge  0.09  Max A/a (final cycle) -0.327 to 0.332  Residual density e/A -0.53 to 1.51 3  -1.71 to 2.82  Complex 2,13, 21a, 23b, 32: Temperature 294 K, Rigaku AFC6S diffractometer, Mo K (k = 0.71069 A) radiation; by Dr. S. J. Rettig at UBC. Complex 17, 30, 35, 37, 44: Temperature 294 K, Rigaku AFC6S diffractometer, Cu K (k = 1.54178 A) radiation; by Dr. S. J. Rettig at UBC. Complex 18b, 20: Temperature 294 K, Nonius CAD-4 diffractometer, Mo K (k = 0.70930 A) radiation; by Dr. M. J. Zaworotko at Dalhousie Univ. Complex 27, 43: Temperature 173 K, Siemens SMART Platform CCD diffractometer, Mo K (k = 0.71073 A) radiation; by Dr. V. G. Young at Univ. of Minnesota. Complex 28: Temperature 294 K, Siemens SMART Platform CCD diffractometer, Mo K (k = 0.71073 A) radiation; by Dr. G. P. Yap at Univ. of Windsor. a  a  a  a  a  a  b  For Rigaku structures, function minimized £w(IF l-IF l) wherew = 4 F / a ( F ) , R = aiF l-IF l!/IIF l, R = 2  0  2  c  2  2  0  0  0  c  w  0  (Zw(IF l-IF l) <EvvlF l ) , and gof = [Zw(IF l-IF l) /(m-«)] (where m = number of observations, n = number of variables). Values given for R, R , and gof are based on those reflections with /> 3a(/). For Siemens structures, function minimized Xw(IF l-IF l) where v^ = a (F ) + 0.0010F , R = EIF -IF I/ZIF I, R = ZI(w (F 2  0  c  2 1/2  2  0  0  1/2  c  w  2  0  1  c  2  2  t)  217  o  1/2  0  C  0  w  0  Appendix l:X-ray Crystal Structure D a t a  and gof = reflections with / > 4o(/). F )\ni{w) F \, m  c  0  Table A1.2  [Lw(\F \-\F \) /(m-n)] 2  0  Values given for  1 / 2  c  R, R  w  and gof are based on those  Fractional Atomic Coordinates and U q (A xl0 ) for 2  3  e  Pr[P Cp]HfCl (2)2  3  atom  X  y  z  Ueq  Hf(l)  0.54890  0.94400  0.81040  15(1)  Cl(l)  0.61660  0.80960  0.74540  26(1)  Cl(2)  0.42990  0.95370  0.65710  25(1)  Cl(3)  0.44030  1.06710  0.82960  27(1)  P(l)  0.44770  0.75140  0.80600  17(1)  C(l)  0.38250  0.77400  0.86790  24(1)  C(2)  0.29730  0.83710  0.81350  33(1)  C(3)  0.36600  0.66800  0.91100  36(1)  C(4)  0.37030  0.69340  0.69790  25(1)  C(5)  0.31260  0.59320  0.70040  34(1)  C(6)  0.41900  0.65770  0.64520  34(1)  C(7)  0.52480  0.63730  0.86170  21(1)  Si(l)  0.62160  0.68480  0.96480  22(1)  C(8)  0.60240  0.66720  1.06260  37(1)  C(9)  0.71860  0.60210  0.97420  41(1)  C(10)  0.70220  0.88980  0.92930  20(1)  C(ll)  0.63980  0.84090  0.95320  19(1)  C(12)  0.59840  0.93510  0.97270  20(1)  C(13)  0.63400  1.03710  0.95920  20(1)  C(14)  0.69880  1.01160  0.93120  20(1)  218  Appendix 1:X-ray Crystal Structure D a t a  Si(2)  0.77270  1.11370  0.91070  20(1  C(15)  0.88620  1.05430  0.95150  32(1  C(16)  0.77810  1.25050  0.96780  30(1  C(17)  0.72410  1.12780  0.78920  23(1  P(2)  0.60430  1.12270  0.73850  19(1  C(18)  0.56760  1.26150  0.76400  26(1  C(19)  0.46990  1.28220  0.70440  38(1  C(20)  0.62290  1.36790  0.76740  38(1  0.56980  1.12020  0.61990  25(1  C(22)  0.59650  1.22690  0.58540  38(1  C(23)  0.60320  1.01310  0.59300  33(1  C(21)  Table A1.3  ,  Fractional Atomic Coordinates and B  ( A ) for 2  e q  Pr[P Cp]Zi€l (Ti -C(0)CH2Ph) (13). 2  2  2  atom  X  y  z  Beq  Zr(l)  0.21456  0.19237  0.19888  3.03  Cl(l)  0.2076  0.0538  0.1327  3.71  Cl(2)  0.2610  0.1425  0.3503  3.96  P(l)  0.0355  0.3384  0.2351  2.76  P(2)  0.5281  0.2603  -0.0117  4.37  Si(D  0.1676  0.4066  0.1044  3.43  Si(2)  0.4370  0.1415  0.1082  3.61  0(1)  0.0908  0.2216  0.1334  2.8  C(l)  0.2541  0.3279  0.1398  3.0  C(2)  0.2912  0.2651  0.0911  3.0  C(3)  0.3610  0.2207  0.1450  2.9  219  Appendix l:X-ray  0.3705  0.2562  0.2304  0.3071  0.3211  0.2274  0.1030  0.4187  0.1986  0.5393  0.1986  0.0896  0.0977  0.3781  -0.0030  0.2260  0.5083  0.0965  0.0362  0.3631  0.3490  0.1288  0.3413  0.4075  -0.0392  0.3269  0.3938  -0.0789  0.3515  0.1802  -0.0964  0.3244  0.0853  -0.1165  0.4378  0.1895  0.3822  0.0930  0.0023  0.4673  0.0649  0.1973  0.63315  0.2290  -0.0539  0.6199  0.1430  -0.0912  0.6545  0.2902  -0.1238  0.5543  0.3653  0.0308  0.6390  0.3763  0.0953  0.4749  0.4022  0.0667  0.0797  0.2380  0.2244  0.0325  0.1658  0.2612  -0.0554  0.1360  0.2089  -0.0572  0.0947  0.1300  -0.1382  0.0673  0.0830  -0.2176  0.0811  0.1160  -0.2143  0.1188  0.1911  220  Crystal Structure D a t a  Appendix l:X-ray Crystal Structure Data  C(31)  Table A 1.4  atom  0.2412  0.1459  -0.1351  Fractional Atomic Coordinates and B  ( A ) for [P Cp]Hf=CHPh(Cl) (17). 2  e q  3.4  Pr  2  Beq  X  y  z  Hf(l)  0.41538  0.22299  0.270757  1.34  Cl(l)  0.55695  0.12692  0.32591  2.50  P(l)  0.65229  0.39149  0.27821  1.88  P(2)  0.25280  0.00248  0.29033  1.59  Si(l)  0.49836  0.54651  0.26367  1.68  Si(2)  0.06801  0.12857  0.27850  1.72  C(l)  0.3922  04179  0.3064  1.60  C(2)  0.2761  0.3390  0.2575  1.48  C(3)  0.2200  0.2532  0.3138  1.53  C(4)  0.3064  0.2822  0.4020  1.49  C(5)  0.4091  0.3812  0.3973  1.58  C(6)  0.6551  0.5417  0.2921  2.16  C(7)  0.0991  -0.0021  0.3097  1.91  C(8)  0.4947  0.6834  0.3351  2.55  C(9)  0.4497  0.5386  0.1321  2.35  C(10)  -0.04105  0.1569  0.3576  3.05  C(ll)  0.0097  0.1134  0.1462  2.46  C(12)  0.7309  0.3763  0.1698  2.80  C(13)  0.7434  0.2601  0.1506  3.55  C(14)  0.6652  0.3971  0.0771  2.63  C(15)  0.7735  0.4046  0.3790  2.88  221  Appendix I:X-ray Crystal Structure Data  C(16  0.7307  0.4165  0.4785  2.88  C(17  0.8973  0.5030  0.3798  6.4  C(18  0.21770  -0.1200  0.1844  2.22  C(19  0.3346  -0.1369  0.1598  3.04  C(20  0.1472  -0.1016  0.0943  2.46  C(21  0.3006  -0.0575  0.3939  2.38  C(22  0.3335  0.0312  0.4907  3.23  C(23  0.2081  -0.1769  0.4048  3.43  C(24  0.3796  0.1868  01248  1.74  C(25  0.3381  0.1762  0.0193  1.60  C(26  0.3707  0.1078  -0.0558  2.11  C(27  0.3309  0.0981  -0.1532  2.71  C(28  0.2575  0.1561  -0.1813  2.40  C(29  0.2225  0.2227  -0.1117  2.26  C(30;  0.2634  0.2336  -0.0124  1.89  C(31  0.0784  0.4768  0.1238  8.0  C(32  0.0363  0.5226  0.0708  7.1  C(33  -0.0105  0.5853  0.0694  7.4  C(34;  0.0584  0.4202  0.0208  7.5  C(35  0.139  0.543  0.2076  8.3  Table A1.5  Fractional Atomic Coordinates and B\ Pr  ( A ) for 2  s0  [P Cp]Zr=CHSiMe (Cl) (18b). 2  3  atom  X  y  z  Biso  Zr(l)  .77343  .31361  .01264  2.99  222  Appendix l:X-ray  .61477  .37854  -.06587  .63425  .32524  .1273  .83602  .33571  -.14002  .84008  .2985  .24829  1.04766  .2873  -.04109  .7844  .085  -.00407  .8899  .323  .1515  .8848  .402  .1167  .9342  .3999  .0477  .9725  .3201  .0388  .9461  .2768  .1034  .7028  .3192  .2313  .8754  .1958  .2791  .9079  .3648  .3324  1.1143  .1899  -.013  1.1495  .3615  -.0548  .9529  .276  -.1373  .5575  .4191  .1263  .6243  .4914  .1222  .49  .4258  .1915  .5292  .25  .1215  .5868  .1657  .1397  .4619  .2429  .0479  .8859  .4386  -.1595  .8072  .5042  -.1461  .9245  .4503  -.2404  .7572  .3038  -.2358  223  Crystal Structure D a t a  Appendix l:X-ray Crystal Structure Data  C(17)  .7156  .2204  -.2312  10.7  C(18)  .6693  .3597  -.2642  9.4  C(19)  .7595  .1941  -.0032  4.2  C(20)  .6621  .0274  -.0219  8.4  C(21)  .8623  .0492  .0901  10.1  C(22)  .8618  .0524  -.0847  8.5  Table A1.6  Fractional Atomic Coordinates and B q ( A ) for 2  e  Pr  [P Cp]Zr(Ti -CH2=CH2 )C1 (20). 2  2  atom  X  y  z  Biso  Zr  .86636  .26553  .28801  3.40  Cl  .85694  .26009  .40883  5.44  PI  .91701  .12938  .33997  4.02  P2  .78304  .38902  .29842  4.17  Sil  .917  .12195  .19602  4.95  Si2  .7864  .40293  .14769  4.50  CP1  .8566  .2013  .1979  3.9  CP2  .8749  .2681  .1628  3.5  CP3  .8063  .3111  .1777  3.6  CP4  .7431  .2694  .2218  3.6  CP5  .7723  .2038  .2341  3.5  Cl  .8994  .0753  .2848  4.2  C2  1.034  .1367  .1626  6.3  C3  .8663  .0751  .1443  6.3  224  Appendix 1:X-ray Crystal Structure D a t a  C4  .8863  .4504  .1081  5.8  C5  .7031  .4151  .0879  6.4  C6  .7313  .4269  .2249  4.6  C7  .8534  .0885  .4200  5.1  C8  .8752  .0138  .4493  6.0  C9  .7544  .0989  .4132  5.1  CIO  1.036  .1151  .3537  4.8  Cll  1.0754  .0446  .3541  5.9  C12  1.0539  .1418  .4152  5.2  C13  .8524  .4587  .3105  8.7  C14  .8656  .5176  .2701  16.9  C15  .8894  .4394  .3762  7.6  C16  .6886  .3808  .3676  6.0  C17  .6307  .4455  .3632  9.7  C18  .6350  .3190  .3710  6.6  C19  1.0174  .2713  .2630  4.4  C20  .9835  .3383  .2486  4.1  Table A 1.7  Fractional Atomic Coordinates and B Pr  ( A ) for 2  e q  [P Cp]ZiC(0)=CHPh(Cl) (21a). 2  atom  X  y  z  Beq  Zr(l)  .49748  .879344  .24186  2.212  Cl(l)  .26683  .91947  .28863  3.81  P(D  .6855  .91379  .38361  2.63  P(2)  .27696  .81154  .14252  2.72  Si(l)  .70857  1.02012  .28962  3.51  225  Appendix l:X-ray  .25922  .9149  .0413  .6383  .81142  .25361  .6265  .97033  .2110  .7021  .92597  .1782  .593  .90196  .11807  .4463  .92938  .11054  .4702  .97229  .16799  .6792  .98916  .38507  .9185  1.03352  .2861  .5948  1.08518  .2743  .0939  .94666  .0759  .2738  .93882  -.0581  .2377  .83775  .04211  .6327  .89021  .47677  .4621  .90084  .4765  .7347  .91335  .5503  .8948  .89533  .38838  1.0185  .93066  .4405  .9228  .8342  .4081  .0850  .80967  .1740  -.0628  .79701  .1146  .0959  .7736  .2456  .3416  .73903  .1328  .4945  .73736  .1021  .2166  .70271  .0832  .5354  .8007  .30274  .5353  .75526  .34689  226  Crystal Structure Data  Appendix J:X-ray Crystal Structure Data  C(26)  .6373  .70661  .35237  3.13  C(27)  .6266  .66575  .4075  4.73  C(28)  .7165  .61876  .4133  6.3  C(29)  .8226  .61095  .3658  6.0  C(30)  .8354  .65052  .3107  5.31  C(31)  .7444  .69627  .3037  4.22  Table A1.8  Fractional Atomic Coordinates and B q ( A ) for 2  e  Pr  [ P C p ] Z i C H C H C ( 0 ) = C H S i M e ( C l ) (23b). 2  2  2  3  atom  X  y  z  Beq  Zr(l)  .15920  .01898  .28411  2.550  Cl(l)  .08992  -.11699  .24182  3.93  P(D  .35087  -.07855  .31755  3.89  P(2)  -.06068  .06954  .28351  2.93  SKD  .37138  -.05512  .15225  4.47  Si(2)  -.01419  .1417  .13575  3.31  Si(3)  .28006  .26496  .44148  4.26  0(1)  .2074  .10509  .35682  2.80  CQ)  .2728  .0238  .1706  3.26  C(2)  .1668  .0286  .1429  3.18  C(3)  .1176  .1018  .1648  2.90  C(4)  .1986  .1435  .2067  3.04  C(5)  .2899  .0974  .2100  3.41  C(6)  .4400  -.0744  .2424  7.5  C(7)  -.0869  .1538  .2216  3.22  227  Appendix l:X-ray Crystal Structure Data  C(8)  .3080  -.1447  .1117  12.1  C(9)  .4755  -.0127  .0974  11.2  c(io:  -.0796  .0718  .0699  5.64  c(ii:  .0002  .2423  .0940  25.32  C(i2;  .3238  -.1852  .3399  5.98  c(i3;  .3990  -.2488  .3096  9.7  C(i4;  .3140  -.1968  .4220  9.9  C(15]  .4455  -.0413  .3933  6.38  C(16]  .4660  .0457  .3887  7.7  C(n;  .5491  -.0912  .4000  9.3  C(i8;  -.1502  -.0137  .2510  3.99  C(19]  -.1620  -.0770  .3097  5.61  c(2o;  -.2572  .0111  .2162  5.57  C(2i;  -.1125  .1057  .3701  4.04  C(22;  -.0506  .1805  .3944  5.48  C(23;  -.2302  .1221  .3706  5.81  C(24;  .1160  -.0305  .3969  3.34  C(25;  .1668  .0212  .4566  4.38  C(26;  .2051  .1026  .4297  2.93  C(27;  .2335  .1656  .4706  3.28  C(28;  .1685  .3282  .4061  11.5  C(29;  .3763  .2609  .3704  8.2  c(3o;  .3433  .3167  .5210  10.2  Table A1.9  Fractional Atomic Coordinates and U q (A xl0 ) for 2  e  Me[p Cp]ZrCl(CH Ph)2 (27) 2  2  228  3  Appendix l:X-ray Crystal Structure Data  X  y  z  Zr(l)  .3668  .3038  .3265  18(1)  Cl(l)  .2081  .491  .3593  31(1)  C(l)  .5855  .1795  .2448  22(1)  C(2)  .5006  .1460  .2064  21(1)  C(3)  .4128  .0898  .2966  21(1)  C(4)  .4426  .0899  .3948  20(1)  C(5)  .5486  .1426  .3626  22(1)  Si(D  .7232  .2485  .1537  26(1)  C(6)  .8567  .1811  .2125  42(1)  C(7)  .7648  .2209  .0080  42(1)  C(8)  .6762  .4111  .1522  28(1)  P(D  .5497  .4380  .2797  26(1)  C(9)  .6421  .4127  .3767  37(1)  C(10)  .4954  .5958  .2656  41(1)  Si(l)  .2958  .0158  .2828  23(1)  C(ll)  .2797  -.1191  .3912  34(1)  C(12)  .3520  -.0290  .1427  42(1)  C(13)  .1451  .1268  .3008  26(1)  P(2)  .1362  .2204  .3964  24(1)  C(14)  .1009  .1233  .5322  32(1)  C(15)  -.0125  .3232  .4085  37(1)  C(16)  .3785  .3280  .5015  28(1)  C(17)  .2844  .2783  .6008  26(1)  C(18)  .3158  .1695  .6654  28(1)  C(19)  .2302  .1228  .7609  34(1)  atom  229  U  e a  A p p e n d i x /.-X-ray C r y s t a l S t r u c t u r e D a t a  C(20)  .1085  .1846  .7951  38(1)  C(21)  .0746  .2913  .7334  40(1 J  C(22)  .1598  .3382  .6379  32(1)  C(23)  .3977  .4037  .1368  27(1)  C(24)  .3041  .3758  .0967  27(1)  C(25)  .1773  .4307  .1280  34(1)  C(26)  .0914  .4084  .0863  43(1)  C(27)  .1278  .3317  .0124  47(i;  C(28)  .2522  .2753  -.0197  42(i;  C(29)  .3375  .2972  .0222  34(1]  Table A L I O Fractional Atomic Coordinates (xlO ) and U 4  Me  (A xl0 ) for 2  e q  3  [P2Cp]Zr(Ti -C H3Me)Cl (28). 2  6  atom  X  y  z  Uq  Zr  19600  8543  1344  38(1)  Cl  19555  11012  1059  68(1)  P(l)  21369  9053  1357  48(1)  P(2)  17863  9262  1333  58(1)  Si(D  21360  6142  964  55(1)  Si(2)  17535  6257  1106  62(1)  C(l)  21978  10197  1939  70(1)  C(2)  21641  9807  702  75(1)  C(3)  22008  7487  1475  55(1)  C(4)  21677  6144  239  87(1)  C(5)  21574  4457  1328  94(1)  C(6)  20117  6551  817  43(1)  230  e  Appendix l:X-ray Crystal Structure Data  C(7)  19484  6043  1114  44(1)  C(8)  18606  6599  874  45(1)  C(9)  18696  7446  395  45(1)  C(10)  19606  7419  364  44(1)  C(ll)  16589  5911  426  115(2)  C(12)  17736  4785  1614  116(2)  C(13)  17257  7787  1502  67(1)  C(14)  17092  9942  650  91(1)  C(15)  17764  10544  1873  82(1)  C(16)  19226  7901  2789  55(1)  C(17)  19487  8073  2256  45(1)  C(18)  20388  8004  2257  44(1)  C(19)  21064  7757  2791  55(1)  C(20)  20806  7628  3313  60(1)  C(21)  19890  7702  3317  58(1)  C(22)  19687  7583  3917  74(2)  Table A l . l l  Fractional Atomic Coordinates and J3 q ( A ) for 2  e  Me[P Cp]Zr(CH Ph) (30). 2  2  3  atom  X  y  z  Beq  Zr(l)  0.25509  0.68132  0.567653  1.134  Zr(2)  0.21393  0.520815  0.178298  1.454  P(l)  0.12261  0.73646  0.65136  1.94  P(2)  0.30709  0.61363  0.4918  1.87  P(3)  0.37504  0.45597  0.22494  1.54  Si(l)  0.28697  0.79351  0.57253  1.92  231  Appendix l:X-ray  0.50372  0.6685  0.41585  0.1376  0.41534  0.13735  0.3741  0.74717  0.55086  0.3671  0.7299  0.48881  0.4644  0.69828  0.48762  0.5353  0.69611  0.55151  0.4797  0.72508  0.58951  0.109  0.78271  0.61287  0.4235  0.81952  0.6283  0.2417  0.82111  0.4974  -0.0607  0.72981  0.6853  0.2362  0.74706  0.7252  0.4745  0.61901  0.4475  0.6996  0.6719  0.3921  0.3800  0.6813  0.3447  0.1695  0.5976  0.4291  0.3473  0.56701  0.5318  0.0504  0.64912  0.61611  0.0041  0.60964  0.60217  -0.1104  0.60151  0.5545  -0.151  0.56468  0.5381  -0.0811  0.53427  0.5692  0.0278  0.54132  0.6186  0.0688  0.57807  0.63478  0.3987  0.63807  0.63731  0.4323  0.65438  0.70232  0.5672  0.67371  0.71882  232  Crystal Structure Data  Appendix 1:X-ray  0.5969  0.68992  0.7792  0.4935  0.68711  0.82709  0.3621  0.66706  0.81283  0.3318  0.65128  0.75235  0.0836  0.68211  0.47424  -0.0036  0.7175  0.46208  -0.1193  0.72853  0.5012  -0.204  0.76112  0.4884  -0.1746  0.78359  0.4367  -0.0631  0.77342  0.3963  0.0211  0.74095  0.40874  0.0543  0.46359  0.14651  -0.0098  0.4794  0.20201  -0.0688  0.51528  0.1861  -0.0425  0.52259  0.1211  0.0313  0.49106  0.09645  0.3402  0.41824  0.16522  0.1158  0.40257  0.05  0.0355  0.38106  0.1871  0.5791  0.45691  0.23816  0.3166  0.43389  0.29932  0.1981  0.58515  0.15047  0.0832  0.61069  0.1757  -0.0506  0.61914  0.1398  -0.1598  0.64174  0.164  -0.1415  0.65752  0.2244  -0.0102  0.65055  0.2607  233  Crystal Structure D a t a  Appendix l:X-ray Crystal Structure Data  C(53  0.1012  0.62765  0.23669  2.67  C(54  0.4096  0.51303  0.11004  2.41  C(55  0.4119  0.53971  0.05448  2.22  C(56;  0.4964  0.57279  0.0578  3.38  C(57  0.4897  0.59878  0.0063  4.74  C(58  0.3962  0.59139  -0.0483  5.21  C(59  0.3162  0.55877  -0.0527  4.55  C(60  0.3241  0.53319  -0.0029  3.20  C(61  0.2413  0.53501  0.28729  2.00  C(62  0.4002  0.54068  0.31038  2.00  C(63  0.4952  0.56533  0.27872  2.61  C(64  0.6454  0.56943  0.2984  3.38  C(65  0.7074  0.54905  0.3508  3.64  C(66  0.6154  0.52505  0.3833  3.04  C(67  0.4658  0.52098  0.36405  2.44  Table A1.12  Fractional Atomic Coordinates and B q ( A ) for 2  e  Me  [P Cp']Zr(ri -CH2=CH2)Br (32). 2  2  atom  X  y  z  Beq  Zr(l)  .25164  .1281  .33516  3.362  Br(l)  .35572  -.00551  .27573  6.50  P(l)  .46524  .1938  .36653  4.30  P(l)  .0879  .00401  .2835  5.31  SiQ)  .34727  .36592  .38574  4.35  Si(2)  -.07305  .15529  .279  5.54  234  Appendix 1:X-ray Crystal Structure D a t a  C(l)  .2259  .2931  .3168  3.50  C(2)  .1351  .2626  .3499  3.63  C(3)  .0606  .2089  .2743  3.87  C(4)  .1077  .2053  .1904  4.01  C(5)  .2071  .2558  .2164  3.75  C(6)  .4805  .298  .4352  4.9  C(7)  -.038  .0381  .315  6.7  C(8)  .367  .4493  .2928  5.7  C(9)  .3152  .4193  .4967  6.4  C(10)  -.1843  .1623  .1492  7.7  C(ll)  -.1225  .2094  .3788  8.6  C(12)  .514  .2197  .2556  6.2  C(13)  .5851  .1292  .4456  6.4  C(14)  .0328  -.0275  .1472  8.5  C(15)  .1217  -.102  .3459  7.2  C(16)  .3246  .1459  .5116  4.4  C(17)  .2225  .0953  .4913  4.6  Table A1.13 Fractional Atomic Coordinates and B Pr  ( A ) for 2  e q  [P Cp]Zr(ri -PhCCPh)Br (35). 2  2  atom  X  y  z  Beq  Zr(l)  .28571  .309908  .058288  1.044  .445  .29557  .13184  3.388  P(l)  .33788  .42261  .11315  1.34  P(2)  .30709  .19366  .03323  1.50  Br(l)  235  Appendix 1:X-ray  .15584  .43208  .05443  .14133  .17982  .03065  .1764  .35487  .07848  .1398  .30666  .03161  .1715  .25376  .06818  .2277  .26965  .14178  .2312  .32884  .1484  .2482  .46571  .05758  .2086  .15821  -.00931  .0691  .43701  -.04002  .1292  .46833  .1204  .0358  .17975  -.0444  .146  .1306  .1041  .4198  .45139  .09624  .3586  .44453  .2078  .344  .18637  -.0368  .3763  .14716  .1105  .5038  .44505  .1628  .4073  .5133  .0661  .4199  .4052  .26873  .378  .50796  .2281  .4342  .1847  -.0034  .307  .1376  -.0922  .3718  .15892  .1824  .3688  .08307  .094  .2684  .35673  -.04091  .2298  .30713  -.06174  236  Crystal Structure D a t a  Appendix l:X-ray Crystal Structure Data  C(26)  .2724  .40192  -.08918  1.57  C(27)  .3437  .41371  -.0898  2.43  C(28)  .3478  .4532  -.1384  3.42  C(29)  .2804  .4829  -.1864  3.62  C(30)  .2097  .47259  -.1872  3.28  C(31)  .2045  .43248  -.13904  2.44  C(32)  .1841  .28379  -.13729  1.68  C(33)  .1045  .26789  -.1661  2.20  C(34)  .0613  .24793  -.2384  3.23  C(35)  .0982  .243  -.2821  3.71  C(36)  .1779  .2585  -.2551  3.82  C(37)  .2204  .27953  -.1828  2.71  Table A1.14  Fractional Atomic Coordinates and B i o ( A x 10 ) for 2  3  S  {Me Cp]ZrBr} (M.-H)4. (37). [P2  2  atom  X  y  z  Biso  Zr(l)  .11172  .33924  .36729  1.628  Zr(2)  .3355  .28637  .35236  1.96  Br(l)  -.03218  .2136  .32178  3.57  Br(2)  .36614  .43295  .28361  3.59  P(l)  .08343  .1071  .40832  2.19  P(2)  .07645  .4888  .29694  2.13  P(3)  .3709  .0982  .29605  2.78  P(4)  .3128  .7492  .47929  3.96  Si(l)  .0942  .2744  .48542  2.28  237  Appendix l:X-ray  -.1015  .5719  .34791  .5788  .1235  .33423  .4391  .5995  .41284  .0677  .3905  .4422  -.0200  .4076  .4168  -.0105  .5129  .3876  .0886  .5621  .3963  .1337  .4866  .4293  .1367  .1203  .4612  -.0520  .5360  .2947  .1922  .3398  .5205  -.0185  .2509  .5145  .1325  -.0402  .3867  -.0442  .0622  .4168  -.1173  .7483  .3548  -.2179  .4874  .3556  .1413  .6419  .2920  .0981  .4151  .2472  .5155  .2380  .3703  .5088  .3730  .3682  .4527  .4236  .3994  .4209  .3158  .4239  .4591  .2016  .4057  .4807  .0071  .3141  .3931  .6114  .4677  .6788  .0313  .3626  .6334  .2197  .2913  238  Crystal Structure D a t a  A p p e n d i x 1.-X-ray  Crystal Structure D a t a  C(25)  .2756  -.0268  .2897  3.8  C(26)  .3962  .1351  .2413  4.0  C(27)  .5648  .6725  .4113  4.5  C(28)  .3574  .6889  .3752  3.2  C(29)  .4034  .8786  .4818  6.1  C(30)  .2988  .7256  .5355  4.5  H  .2310  .4240  .3600  1.0  H  .2450  .3060  .4020  2.9  H  .2073  .2321  .3565  2.1  H  .2100  .3100  .3200  2.1  Table A1.15  Fractional Atomic Coordinates and U q ( A x 10 ) for 2  3  e  P [ P C p ] Z r C l (43) r  2  2  atom  X  y  z  Ueq  Zr(l)  0.2554  0.9313  0.7911  21(1)  Cl(l)  0.3597  0.893  0.7081  39(1)  Cl(2)  0.1302  0.8049  0.757  36(1)  C(l)  0.346  1.0882  0.866  26(1)  C(2)  0.3292  0.9906  0.9078  25(1)  C(3)  0.2414  0.9791  0.9118  22(1)  C(4)  0.2018  1.0726  0.8674  23(1)  C(5)  0.2687  1.1366  0.8404  25(1)  C(6)  0.4311  1.1392  0.8561  38(1)  C(7)  0.4295  1.2078  0.7871  59(1)  C(8)  0.4545  1.2248  0.9181  60(1)  239  Appendix l:X-ray Crystal Structure Data  C(9)  0.4971  1.0413  0.8582  Si(l)  0.2055  0.8614  0.9705  C(10)  0.0982  0.8866  0.9931  C(ll)  0.2775  0.8614  1.0539  C(12)  0.2117  0.714  0.9245  P(l)  0.2911  0.7121  0.8632  C(13)  0.2777  0.5681  0.8142  C(14)  0.2045  0.4978  0.8256  C(15)  0.2997  0.5762  0.7421  C(16)  0.3891  0.6861  0.9219  C(17)  0.3876  0.58  0.9727  C(18)  0.4628  0.681  0.8794  Si(2)  0.0942  1.1275  0.8384  C(19)  0.0058  1.0214  0.8334  C(20)  0.0698  1.2534  0.8964  C(21)  0.1038  1.1866  0.7473  P(2)  0.1675  1.093  0.6948  C(22)  0.0899  1.0185  0.631  C(23)  0.0239  1.0929  0.5888  C(24)  0.1316  0.9343  0.5829  C(25)  0.2254  1.2059  0.6476  C(26)  0.1737  1.3067  0.6106  C(27)  0.2829  1.1523  0.5984  Table A1.16 Fractional Atomic Coordinates and B q (A ) for 2  e  {Pr[P Cp]ZrCl} ai-Cl)2 (44). 2  2  240  Appendix l:X-ray Crystal Structure Data  X  y  z  Zr(3)  0.63287  0.29429  0.45373  1.488  Zr(4)  0.41796  0.21022  0.42391  1.402  Cl(5)  0.48835  0.25379  0.51331  1.73  Cl(6)  0.56025  0.25125  0.36318  1.79  Cl(7)  0.47163  0.33645  0.42583  2.38  Cl(8)  0.58100  0.16805  0.45183  2.13  P(5)  0.60932  0.34647  0.54611  2.36  P(6)  0.70260  0.34567  0.36770  2.21  P(7)  0.35398  0.16101  , 0.51380  2.18  P(8)  0.44236  0.15714  0.33363  2.43  Si(5)  0.75679  0.29219  0.61088  2.5.1  Si(6)  0.87867  0.28915  0.35572  2.08  Si(7)  0.16786  0.21408  0.52016  2.24  Si(8)  0.29442  0.21011  0.26617  2.23  C(31)  0.76898  0.27776  0.53107  1.90  C(32)  0.81758  0.29803  0.48311  2.04  C(33)  0.81730  0.27521  0.42835  1.80  C(34)  0.76595  0.24052  0.44417  1.78  C(35)  0.73821  0.24107  0.50418  2.06  C(36)  0.71014  0.34332  0.60489  3.22  C(37)  0.84131  0.34128  0.34921  2.25  C(38)  0.88793  0.29074  0.64893  3.76  C(39)  0.66130  0.26132  0.65181  2.90  C(40)  1.02348  0.28258  0.35903  3.40  C(41)  0.82396  0.26054  0.29250  2.91  atom  241  Appendix l:X-ray  0.48848  0.33967  0.58958  0.68626  0.39733  0.37855  0.63807  0.33931  0.29552  0.23026  0.22789  0.44806  0.23399  0.20518  0.39380  0.28301  0.22612  0.34575  0.31215  0.26237  0.37168  0.27962  0.26303  0.43182  0.21535  0.16414  0.53233  0.34442  0.15965  0.27338  0.02110  0.21445  0.51492  0.20914  0.24696  0.58105  0.16089  0.20914  0.23051  0.38585  0.24139  0.22298  0.41951  0.17108  0.58564  0.37376  0.10980  0.50695  0.56511  0.16284  0.29093  0.44728  0.10636  0.35057  242  Crystal Structure Data  

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