Highly electron deficient scandocene derivatives of the types (η^5-C_5Me_5)_2ScR, {(η^5-C_5Me_4)_2SiMe_2}ScR and {(η^5-C_5H_3CMe_3)_2SiMe_2}ScR catalyze the polymerization of ethylene, the head-to-tail dimerization of α olefins, the cyclization of α,ω dienes to methylene cycloalkanes, and the branching of 1,4 pentadienes to isoprenes. The mechanisms of the individual steps have been studied. Key steps involve sequential and reversible olefin insertion/β H elimination/β alkyl elimination, the last of which is particularly facile in these systems. [((η^5-C_5Me_4)Me_2Si(η^1-NCMe_3)(PMe_3)Sc(µ-H)]_2, catalyzes the polymerization of α olefins. Evidence is presented in support of a well defined, one component catalyst system with all scandium centers functioning alike

Bercaw, John E.

Caltech Authors - Main

fure&App/.  Chem.,Vol. 62, No. 6, pp. 1151-1154,1990. 
Printed in Great Britain. 
@ 1990 IUPAC 
Carbon-hydrogen and carbon-carbon bond 
activation with highly electrophilic transition metal 
complexes 
John E. Bercaw 
Contribution Number 7964 from the Division of Chemistry and Chemical Engineering, 
California Institute of Technology, Pasadena, California 91 125 
Abstract - Highly electron deficient scandocene derivatives of the types (q5-CsMe&ScR, 
{(q5-CsMe4)2SiMe2}ScR and {(q5-C5H3CMe3)2SiMe2}ScR catalyze the polymerization of 
ethylene, the head-to-tail dimerization of a olefins, the cyclization of a,w dienes to meth lene 
cycloalkanes, and the branching of 1,4 pentadienes to isoprenes. The mechanisms oythe 
individual steps have been studied. Key steps involve sequential and reversible olefin 
insertionlb H eliminationlb alkyl elimination, the last of which is particularly facile in these 
sys!ems. [((q5-C5Me4)Me2Si(qi-NCMe3)(PMe3)Sc(p-H)]2, catalyzes the polymerization of a 
olefins. Evidence is presented in support of a well defined, one component catalyst system 
with all scandium centers functioning alike. 
INTRODUCTION 
Organometallic compounds of scandium resemble those of aluminum, particularly in their tendency to 
form dimeric or oligomeric structures with bridging alkyl or hydride groups. Recently our research 
group has reported the synthesis and some features of the reactivity of alkyl and hydride derivatives 
of bis(pentamethylcyclopentadienyl)scandium, Cp*2ScR (Cp* = (q5-C5Mes)) (ref.1). The bulky 
(q5-CsMe5) ligands prevent dimerization and restrict the types of ligands which can coordinate to the 
formally 14 electron, do scandium center. We have suggested the name "sigma bond metathesis" for 
a dominant reaction type for these highly electrophilic compounds: 
Cp*2Sc-R + R'-H CP*~SC-R' + R-H (1) 
(R, R' = hydride, alkyl, alkenyl, aryl, alkynyl) 
More recently we have turned our attention to the reactivity of these compounds with olefins. Early 
indications were that they readily polymerize ethylene without coordinating bases or co-catalysts, 
common complications for Ziegler-Natta polymerizations using group 4 transition metal catalysts. We 
have therefore undertaken a study of this model system (ref. 2). 
Cp*2Sc-R + n CH2=CH2 - C P * ~ S C ( C H ~ C H ~ ) ~ R  (2) 
Due to unfavorable steric interactions with the (q5-C5Me5) ligands, a olefins do not undergo insertion 
into the scandium-carbon bonds of Cp*2ScR; rather, they react by sigma bond metathesis (eq. 1). 
Less crowded scandocene derivatives were prepared, and, indeed, these proved to be very efficient a 
olefin dimerization catalysts. Moreover, with 1,4-pentadienes, skeletal rearrangement to isoprenes are 
observed. A related system with linked cyclopentadienyl and amide ligands 
{(q5-C5Me4)SiMe2(q1-NCMe3)}ScR catalyzes the polymerization of a olefins in a quasi-living manner. 
ETHYLENE INSERTION AND PH ELIMINATION FOR 
PERMETHYLSCANDOCENE ALKYLS 
The rates of ethylene insertion into the Sc-C bond for Cp*2ScR (R = H, CH3, CH2CH3, CH2CH2CH3) 
have been examined at -80% by I3C NMR spectroscopy. 
k l  CH2=CH2 
Cp*2Sc-R +CH2=CH2 - Cp"2ScCH2CH2R -etc. (3) 
The following second order rate constants (kl; M-lsec-i, -8OOC) have been measured: R = H 
R = CH3,(8.1(2)x The fast rate for 
the hydride derivative is expected, and almost certainly is due to the greater overlap, hence better 
bonding in the transition state for H (nondirectional Is orbital) vs. alkyl (more directional sp3 orbital). 
On the other hand, the greater insertion rate for the scandium propyl relative to the scandium methyl is 
likely due to ground state differences. Equilibrium measurements indicate that the relative ordering of 
Sc-R bond dissociation ener ies (BDEs) mirrors that for the corresponding H-R BDEs (ref 3); hence, 
complex is slowest to insert ethylene cannot be rationalized by these types of metal-carbon bond 
R = CH2CH3 (4.4(2) x R = CH2CH2CH3 (6.1 (2) x 
BDE(Sc-CH3) - BDE(Sc-CH2 e H2CH3) t ca. 6 kcal.mol-I. The observation that the scandium ethyl 
1151 
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1152 J. E. BERCAW 
strength considerations or by transition state differences. Spectroscopic data and an X-ray diffraction 
study indicate a f l  agostic interaction for the stable form of Cp*zScCH2CH3. A similar f l  agostic 
interaction is, of course, possible for C ~ * ~ S C C H ~ C H ~ C H ~ .  Whereas such a structure (A) is 
electronically favored, it is sterically less favorable than the conventional structure (B), due to adverse 
interactions of the methyl group with a (v5-C5Me5) ligand. 
A B 
Presumably this j3 agostic interaction for Cp*2ScCH2CH3 must be broken prior to ethylene insertion, 
thus increasing the barrier relative to the other alkyls. Cp*2ScCH3 undergoes a single insertion with 
2-butyne with a moderate enthalpy of activation (AH# = 9.7(3) kcal.mol-1) and a large, negative entropy 
of activation (AS* = -36(20) eu), indicating highly ordered transition states for these insertion reactions. 
The distributions of molecular weights for ethylene oligomers (CH3(CH2),CH3, n = 11-47) produced 
from known amounts of ethylene and C ~ * ~ S C C H ~ C H ~ C H ~  at -78OC satisfactorily fit a Poisson 
distribution, indicative of a "living" Zie ler-Natta polymerization system. From the measured, slower 
initiation rates of insertion for Cp*2Sc8H3 and Cp*2ScCH&H3 and propagation rates equal to that for 
CP*~SCCH~CH~CH~,  the molecular weight distributions of ethylene oligomers are also predicted. 
The rates for f l  hydrogen elimination for members of the series of permethylscandocene alkyl 
have been obtained by rapidly trapping Cp*2Sc-H with 2-butyne (eqs 4 and 5). 
complexes CP*~SCCH~CH~R (R = H, CH3, CH2CH3, C&, CsHd-p-CH3, C6H4-P-CF3, C6H4-p-NMe2) 
Cp*2Sc-H + CH3CmCCH3 - E-C~*~SC-C(CH~)=CH(CH~) (5) 
For the phenylethyl series k l  linearly correlates with up (R = 0.9967) with a slope ( p )  of -1.87(11). A 
transition state for the f l  hydrogen elimination is indicated with partial charge on the f l  carbon. 
Hydrogen is thus transferred to the scandium center as hydride in the f l  H elimination process. 
OLEFIN DIMERIZATION, DlOLEFlN CYCLIZATION A N D  SKELETAL 
HYDRIDES 
REARRANGEMENT WITH DIMETHYLSILYL-BRIDGED SCANDOCENE 
Whereas Cp*nScH ultimately generates (via u bond metathesis) permethylscandocene alkenyl 
complexes, Cp*2Sc-CH=CHR, with a olefins CH2=CHR, less sterically encumbered scandocene 
hydrides {(v5-C5Me4 2SiMez)ScH (OpScH) and [{(v5-C5H3CMe3)2SiMe2}ScH]2 ([DpScHIz) promote 
R [OpSc-HI 
rapid, remarkably se I ective, head-to-tail dimerization of a olefins. 
2 J  
+OpSc-H 1 J R 
-R 
OpSc-H = Me,Si 
R 
- OpSc-H 1, \ 
fast 
R )-L 
slow (only for high 
[olefin], IOWT) 
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C-H and C-C bond activation with transition metal complexes 1153 
Moreover, Q,O dienes are clean1 cyclized to the corresponding methylene cycloalkane. Cyclization of 
1,4-pentadiene is endothermic; Lence, catalytic opening of methylene c clobutane to 1,4-pentadiene 
At 1 4OoC catalytic conversion of 1 ,Gpentadienes to the corresponding isoprenes is observed, albeit 
with only a moderate number of turnovers (ref 4). 
is observed. Unexpectedly, under more forcing conditions, 1 ,Pdimethy Y allyl scandocene is obtained. 
\ 
25OC, 95-99+%* - 
(n = 2,3,4,5,6) , ca. 100 turnovers 
[ DPSC-H] 
* 
1 4OoC; 5 turnovers 
58% selectivity 
[DpSc-HI 
8OoC; 8 turnovers 
87% selectivity I 
DpSc-H 
The (reversible) cyclization and branching of 1 ,4-dienes is proposed to occur via addition of Sc-H, 
followed by intramolecular olefin insertion to afford the (methylcyclopropylmethyl)scandium 
intermediate. The methyl branch is introduced by /I alkyl elimination in the alternate sense. /I H 
elimination yields isoprene, which may readd to DpScH to yield the stable branched allyl derivative. 
-3 ~ DPSC-H + 
DpscJ = ""'0 - 
I t  
QUASI-LIVING (Y OLEFIN POLYMERIZATION WITH A DIMETHYLSILYL- 
LINKED CYCLOPENTADIENYL-AMIDE LIGAND SYSTEM 
Using the hydride derivative of scandium with the dimethylsilyl-linked cyclopentadienyl-amide ligand, 
[{(v5-CgMe4)Me2Si(v1-NCMe3)(PMe3)Sc(p-H)]2 (((Cp*SiNR)(PMe3)ScH}z), propene, 1 -butene and 
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1154 J. E. BERCAW 
1 -pentene are cleanly, albeit slowly, polymerized with >99% head-to-tail coupling to produce atactic 
polymers with Mn = 3,000-4,000 and polydispersity indices of 1.7-2.1 (ref 5). Chain transfer is relatively 
slow. The molecular weight distributions for oligomers obtained at relatively low conversion of 
propene are adequately described by a Poisson function based on the amount of monomer 
consumed, assuming all scandium centers are participating, as a "living" system. 
(Cp'SiNR)( PMe3)Sc &R, 
- PMe, 1 I+ PMe, 
R' 
* (Cp*SiNR)Sc& R' 
[(Cp*SiNR)(PMe,)ScH], 
25OC; - PMe,? (n+2)  J 
\ 'n 
I Me$ 
Acknowledgements The author wishes to thank those members of his research group, past 
and present, whose names are indicated in the references for their enthusiastic and 
insightful contributions to this work. Support from the USDOE Office of Basic Energy 
Sciences (Grant No. DE-FG03-85ER13431) and Shell Companies Foundation is gratefully 
acknowledged. 
REFERENCES 
1. (a) Thompson, M. E.; Bercaw, J. E. Pure andAppl. Chem. 56, 1 (1984). (b) Parkin, G.; Bunel, E.; 
Burger, 8. J.; Trimmer, M. S.; van Asselt, A.; Bercaw, J. E. J. Molecular. Catal. 47, 21 (1987). (c) 
Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, 8. J.; Nolan, M. C.; Santarsiero, B. D.; 
Schaefer, W. P.; Bercaw, J. E. J .  Am. Chem. SOC. 709, 203 (1987). 
Burger, B. J.; Thompson, M. E.; Cotter, W. D.; Bercaw, J. E. J .  Am. Chem. SOC., submitted for 
publication. 
Bulls, A. R.; Manriquez, J. M.; Thompson, M. E.; Bercaw, J. E. Polyhedron 7, 1409 (1988). 
Bunel, E.; Burger, B. J.; Bercaw, J. E. J .  Am. Chem. SOC. 770, 976 (1988). 
Shapiro, P. J.; Bunel, E.; Schaefer, W. P.; Bercaw, J. E. J .  Am. Chem. SOC., submitted for 
publication. 
2. 
3. 
4. 
5. 
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Carbon-hydrogen and carbon-carbon bond activation with highly electrophilic transition metal complexes

Abstract -Highly electron deficient scandocene derivatives of the types (q5-CsMe&amp;ScR, {(q5-CsMe4)2SiMe2}ScR and {(q5-C5H3CMe3)2SiMe2}ScR catalyze the polymerization of ethylene, the head-to-tail dimerization of a olefins, the cyclization of a,w dienes to meth lene cycloalkanes, and the branching of 1,4 pentadienes to isoprenes. The mechanisms oythe individual steps have been studied. Key steps involve sequential and reversible olefin insertionlb H eliminationlb alkyl elimination, the last of which is particularly facile in these sys!ems. [((q5-C5Me4)Me2Si(qi-NCMe3)(PMe3)Sc(p-H)]2, catalyzes the polymerization of a olefins. Evidence is presented in support of a well defined, one component catalyst system with all scandium centers functioning alike

John E Bercaw

CiteSeerX

fure&App/.  Chem.,Vol. 62, No. 6, pp. 1151-1154,1990. 
Printed in Great Britain. 
@ 1990 IUPAC 
Carbon-hydrogen and carbon-carbon bond 
activation with highly electrophilic transition metal 
complexes 
John E. Bercaw 
Contribution Number 7964 from the Division of Chemistry and Chemical Engineering, 
California Institute of Technology, Pasadena, California 91 125 
Abstract - Highly electron deficient scandocene derivatives of the types (q5-CsMe&ScR, 
{(q5-CsMe4)2SiMe2}ScR and {(q5-C5H3CMe3)2SiMe2}ScR catalyze the polymerization of 
ethylene, the head-to-tail dimerization of a olefins, the cyclization of a,w dienes to meth lene 
cycloalkanes, and the branching of 1,4 pentadienes to isoprenes. The mechanisms oythe 
individual steps have been studied. Key steps involve sequential and reversible olefin 
insertionlb H eliminationlb alkyl elimination, the last of which is particularly facile in these 
sys!ems. [((q5-C5Me4)Me2Si(qi-NCMe3)(PMe3)Sc(p-H)]2, catalyzes the polymerization of a 
olefins. Evidence is presented in support of a well defined, one component catalyst system 
with all scandium centers functioning alike. 
INTRODUCTION 
Organometallic compounds of scandium resemble those of aluminum, particularly in their tendency to 
form dimeric or oligomeric structures with bridging alkyl or hydride groups. Recently our research 
group has reported the synthesis and some features of the reactivity of alkyl and hydride derivatives 
of bis(pentamethylcyclopentadienyl)scandium, Cp*2ScR (Cp* = (q5-C5Mes)) (ref.1). The bulky 
(q5-CsMe5) ligands prevent dimerization and restrict the types of ligands which can coordinate to the 
formally 14 electron, do scandium center. We have suggested the name "sigma bond metathesis" for 
a dominant reaction type for these highly electrophilic compounds: 
Cp*2Sc-R + R'-H CP*~SC-R' + R-H (1) 
(R, R' = hydride, alkyl, alkenyl, aryl, alkynyl) 
More recently we have turned our attention to the reactivity of these compounds with olefins. Early 
indications were that they readily polymerize ethylene without coordinating bases or co-catalysts, 
common complications for Ziegler-Natta polymerizations using group 4 transition metal catalysts. We 
have therefore undertaken a study of this model system (ref. 2). 
Cp*2Sc-R + n CH2=CH2 - C P * ~ S C ( C H ~ C H ~ ) ~ R  (2) 
Due to unfavorable steric interactions with the (q5-C5Me5) ligands, a olefins do not undergo insertion 
into the scandium-carbon bonds of Cp*2ScR; rather, they react by sigma bond metathesis (eq. 1). 
Less crowded scandocene derivatives were prepared, and, indeed, these proved to be very efficient a 
olefin dimerization catalysts. Moreover, with 1,4-pentadienes, skeletal rearrangement to isoprenes are 
observed. A related system with linked cyclopentadienyl and amide ligands 
{(q5-C5Me4)SiMe2(q1-NCMe3)}ScR catalyzes the polymerization of a olefins in a quasi-living manner. 
ETHYLENE INSERTION AND PH ELIMINATION FOR 
PERMETHYLSCANDOCENE ALKYLS 
The rates of ethylene insertion into the Sc-C bond for Cp*2ScR (R = H, CH3, CH2CH3, CH2CH2CH3) 
have been examined at -80% by I3C NMR spectroscopy. 
k l  CH2=CH2 
Cp*2Sc-R +CH2=CH2 - Cp"2ScCH2CH2R -etc. (3) 
The following second order rate constants (kl; M-lsec-i, -8OOC) have been measured: R = H 
R = CH3,(8.1(2)x The fast rate for 
the hydride derivative is expected, and almost certainly is due to the greater overlap, hence better 
bonding in the transition state for H (nondirectional Is orbital) vs. alkyl (more directional sp3 orbital). 
On the other hand, the greater insertion rate for the scandium propyl relative to the scandium methyl is 
likely due to ground state differences. Equilibrium measurements indicate that the relative ordering of 
Sc-R bond dissociation ener ies (BDEs) mirrors that for the corresponding H-R BDEs (ref 3); hence, 
complex is slowest to insert ethylene cannot be rationalized by these types of metal-carbon bond 
R = CH2CH3 (4.4(2) x R = CH2CH2CH3 (6.1 (2) x 
BDE(Sc-CH3) - BDE(Sc-CH2 e H2CH3) t ca. 6 kcal.mol-I. The observation that the scandium ethyl 
1151 
1152 J. E. BERCAW 
strength considerations or by transition state differences. Spectroscopic data and an X-ray diffraction 
study indicate a f l  agostic interaction for the stable form of Cp*zScCH2CH3. A similar f l  agostic 
interaction is, of course, possible for C ~ * ~ S C C H ~ C H ~ C H ~ .  Whereas such a structure (A) is 
electronically favored, it is sterically less favorable than the conventional structure (B), due to adverse 
interactions of the methyl group with a (v5-C5Me5) ligand. 
A B 
Presumably this j3 agostic interaction for Cp*2ScCH2CH3 must be broken prior to ethylene insertion, 
thus increasing the barrier relative to the other alkyls. Cp*2ScCH3 undergoes a single insertion with 
2-butyne with a moderate enthalpy of activation (AH# = 9.7(3) kcal.mol-1) and a large, negative entropy 
of activation (AS* = -36(20) eu), indicating highly ordered transition states for these insertion reactions. 
The distributions of molecular weights for ethylene oligomers (CH3(CH2),CH3, n = 11-47) produced 
from known amounts of ethylene and C ~ * ~ S C C H ~ C H ~ C H ~  at -78OC satisfactorily fit a Poisson 
distribution, indicative of a "living" Zie ler-Natta polymerization system. From the measured, slower 
initiation rates of insertion for Cp*2Sc8H3 and Cp*2ScCH&H3 and propagation rates equal to that for 
CP*~SCCH~CH~CH~,  the molecular weight distributions of ethylene oligomers are also predicted. 
The rates for f l  hydrogen elimination for members of the series of permethylscandocene alkyl 
have been obtained by rapidly trapping Cp*2Sc-H with 2-butyne (eqs 4 and 5). 
complexes CP*~SCCH~CH~R (R = H, CH3, CH2CH3, C&, CsHd-p-CH3, C6H4-P-CF3, C6H4-p-NMe2) 
Cp*2Sc-H + CH3CmCCH3 - E-C~*~SC-C(CH~)=CH(CH~) (5) 
For the phenylethyl series k l  linearly correlates with up (R = 0.9967) with a slope ( p )  of -1.87(11). A 
transition state for the f l  hydrogen elimination is indicated with partial charge on the f l  carbon. 
Hydrogen is thus transferred to the scandium center as hydride in the f l  H elimination process. 
OLEFIN DIMERIZATION, DlOLEFlN CYCLIZATION A N D  SKELETAL 
HYDRIDES 
REARRANGEMENT WITH DIMETHYLSILYL-BRIDGED SCANDOCENE 
Whereas Cp*nScH ultimately generates (via u bond metathesis) permethylscandocene alkenyl 
complexes, Cp*2Sc-CH=CHR, with a olefins CH2=CHR, less sterically encumbered scandocene 
hydrides {(v5-C5Me4 2SiMez)ScH (OpScH) and [{(v5-C5H3CMe3)2SiMe2}ScH]2 ([DpScHIz) promote 
R [OpSc-HI 
rapid, remarkably se I ective, head-to-tail dimerization of a olefins. 
2 J  
+OpSc-H 1 J R 
-R 
OpSc-H = Me,Si 
R 
- OpSc-H 1, \ 
fast 
R )-L 
slow (only for high 
[olefin], IOWT) 
C-H and C-C bond activation with transition metal complexes 1153 
Moreover, Q,O dienes are clean1 cyclized to the corresponding methylene cycloalkane. Cyclization of 
1,4-pentadiene is endothermic; Lence, catalytic opening of methylene c clobutane to 1,4-pentadiene 
At 1 4OoC catalytic conversion of 1 ,Gpentadienes to the corresponding isoprenes is observed, albeit 
with only a moderate number of turnovers (ref 4). 
is observed. Unexpectedly, under more forcing conditions, 1 ,Pdimethy Y allyl scandocene is obtained. 
\ 
25OC, 95-99+%* - 
(n = 2,3,4,5,6) , ca. 100 turnovers 
[ DPSC-H] 
* 
1 4OoC; 5 turnovers 
58% selectivity 
[DpSc-HI 
8OoC; 8 turnovers 
87% selectivity I 
DpSc-H 
The (reversible) cyclization and branching of 1 ,4-dienes is proposed to occur via addition of Sc-H, 
followed by intramolecular olefin insertion to afford the (methylcyclopropylmethyl)scandium 
intermediate. The methyl branch is introduced by /I alkyl elimination in the alternate sense. /I H 
elimination yields isoprene, which may readd to DpScH to yield the stable branched allyl derivative. 
-3 ~ DPSC-H + 
DpscJ = ""'0 - 
I t  
QUASI-LIVING (Y OLEFIN POLYMERIZATION WITH A DIMETHYLSILYL- 
LINKED CYCLOPENTADIENYL-AMIDE LIGAND SYSTEM 
Using the hydride derivative of scandium with the dimethylsilyl-linked cyclopentadienyl-amide ligand, 
[{(v5-CgMe4)Me2Si(v1-NCMe3)(PMe3)Sc(p-H)]2 (((Cp*SiNR)(PMe3)ScH}z), propene, 1 -butene and 
1154 J. E. BERCAW 
1 -pentene are cleanly, albeit slowly, polymerized with >99% head-to-tail coupling to produce atactic 
polymers with Mn = 3,000-4,000 and polydispersity indices of 1.7-2.1 (ref 5). Chain transfer is relatively 
slow. The molecular weight distributions for oligomers obtained at relatively low conversion of 
propene are adequately described by a Poisson function based on the amount of monomer 
consumed, assuming all scandium centers are participating, as a "living" system. 
(Cp'SiNR)( PMe3)Sc &R, 
- PMe, 1 I+ PMe, 
R' 
* (Cp*SiNR)Sc& R' 
[(Cp*SiNR)(PMe,)ScH], 
25OC; - PMe,? (n+2)  J 
\ 'n 
I Me$ 
Acknowledgements The author wishes to thank those members of his research group, past 
and present, whose names are indicated in the references for their enthusiastic and 
insightful contributions to this work. Support from the USDOE Office of Basic Energy 
Sciences (Grant No. DE-FG03-85ER13431) and Shell Companies Foundation is gratefully 
acknowledged. 
REFERENCES 
1. (a) Thompson, M. E.; Bercaw, J. E. Pure andAppl. Chem. 56, 1 (1984). (b) Parkin, G.; Bunel, E.; 
Burger, 8. J.; Trimmer, M. S.; van Asselt, A.; Bercaw, J. E. J. Molecular. Catal. 47, 21 (1987). (c) 
Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, 8. J.; Nolan, M. C.; Santarsiero, B. D.; 
Schaefer, W. P.; Bercaw, J. E. J .  Am. Chem. SOC. 709, 203 (1987). 
Burger, B. J.; Thompson, M. E.; Cotter, W. D.; Bercaw, J. E. J .  Am. Chem. SOC., submitted for 
publication. 
Bulls, A. R.; Manriquez, J. M.; Thompson, M. E.; Bercaw, J. E. Polyhedron 7, 1409 (1988). 
Bunel, E.; Burger, B. J.; Bercaw, J. E. J .  Am. Chem. SOC. 770, 976 (1988). 
Shapiro, P. J.; Bunel, E.; Schaefer, W. P.; Bercaw, J. E. J .  Am. Chem. SOC., submitted for 
publication. 
2. 
3. 
4. 
5. 


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Carbon-hydrogen and carbon-carbon bond activation with highly electrophilic transition metal complexes

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