Showing papers by "Maurice Brookhart published in 1991"

Enantioselective cyclopropane syntheses using the chiral carbene complexes (SFe)- and (RFe)-C5H5(CO)(PR3)Fe:CHCH3+. A mechanistic analysis of the carbene transfer reaction

Abstract: The enantiomerically pure acyl complexes were converted to the corresponding enantiomerically pure carbene complexes (S Fe )- and (R Fe )-C 5 H 5 (CO)(PR 3 )Fe=CHCH 3 + by using standard techniques. Enantioselective ethylidene transfer from these complexes to styrene, vinyl acetate, and isopropenyl acetate gave methylcyclopropanes in high optical yields. A mechanistic analysis of the transfer reaction is presented by using the stereochemical results obtained coupled with deuterium labeling and relative reactivity studies. It is concluded that the most likely mechanism for carbene transfer involves reaction of the olefin with the minor but more reactive synclinal isomer of C 5 H 5 (CO)(PR 3 )Fe=CHCH 3 + followed by backside attack of the developing electrophilic center at Cγ on the Fe-Cα bond. A rationale is offered for the differing diastereoselectivities of ethylidene transfer from C 5 H 5 (CO)(PR 3 )Fe=CHCH 3 + versus C 5 H 5 (CO) 2 Fe=CHCH 3 + to various olefins

Late transition metal catalysts for olefin polymerization

Abstract: A polymerization catalyst and a method of polymerizing ethylene, other olefins, and alkynes with such catalyst are provided by the present invention. In particular, the polymerization catalyst comprises an active cationic portion of the formula LM-R⁺ wherein M is a Group VIII metal, L is a ligand or ligands which stabilize the Group VIII metal, and R is H, a hydrocarbyl radical or a substituted hydrocarbyl radical; and a stabilizing anionic portion of the formula wherein X is F, Cl, a hydrocarbyl radical, a substituted hydrocarbyl radical, or combinations thereof, and n is an integer from 1 to 5. Polymerization is accomplished by contacting a monomer of ethylene, other olefin or alkyne with the catalyst.

Investigation of the stereochemistry of iron-carbon.alpha. bond cleavage when phenylcyclopropane is generated by .gamma.-ionization of stereospecifically deuterated C5H5(CO)2FeCHDCHDCH(OCH3)C6H5 complexes. A transition-state model for transfer of the carbene ligand from C5H5(CO)2Fe:CHR+ to alkenes

Abstract: C 5 H 5 (CO) 2 FeCH 2 CH 2 CH(OCH 3 )C 6 H 5 , 4, and stereospecifically deuterium labeled threo-d 2 -C 5 H 5 -(CO) 2 FeCHDCHDCH(OCH 3 )C 6 H 5 , 7a,b and erythro-d 2 -C 5 H 5 (CO) 2 FeCHDCHDCH(OCH 3 )C 6 H 5 , 8a,b were synthesized. Treatment of compound 4 with trimethylsilyl triflate results in ionization of the γ-methoxy group and formation of phenylcyclopropane in good yields. Ionization of 7a,b gives a 1:1 mixture of cis-2, cis-3-dideuterio- and trans-2, trans-3-dideuterio-r-1-phenylcyclopropane, while ionization of 8a, b gives cis-2, trans-3-dideuterio-r-1-phenylcyclopropane. These results established that the cyclopropane ring is formed by backside attack of electrophilic Cγ on Cα with net inversion of stereochemistry at Cα. These reactions serve as models for the reactions of carbene complexes C 5 H 5 (CO) 2 Fe=CHR + with alkenes to give cyclopropanes and suggest that in the transfer reactions Fe-cα is cleaved with inversion

Rhodium-catalyzed olefin dimerization

Abstract: A process is disclosed for preparing functionalized linear olefins by dimerizing terminal olefins in the presence of a cationic rhodium compound. Novel rhodium compounds useful in this process are also disclosed.

Carbon Electrophiles with Dienes and Polyenes Promoted by Transition Metals

Abstract: Numerous synthetically useful carbon-carbon bond-forming reactions are based on the fact that unsaturated hydrocarbon ligands bound to electrophilic transition metal moieties are activated toward addition of nucleophiles. Normally the metal moiety in such complexes is a neutral or cationic metal carbonyl group. Prominent and well-studied examples include [Cr(arene)(CO)3] complexes (covered in Chapter 2.4, this volume),1 [Fe(dienyl)(CO)3]+ complexes (covered in Chapter 3.4, this volume),2[FeCp(CO)2(alkene)]+ complexes3 and [M(CO)n(diene)] complexes.4