No abstract

The a-ether complexes Cp(CO)(L)FeCH(OCH,)R (L = CO, P(C6H5),; R = CH3, CH2CH3, CH(CH3)2) have been prepared in good yields from readily available acetyl complexes, Cp(CO)(L)FeCOR, by 0-methylation followed by reduction with borohydride. These ether complexes are rapidly converted to the corresponding cationic carbene complexes, Cp-(CO)(L)Fe=CHR+, via ionization with trimethylsilyl triflate at -78 OC. The triphenylphosphine-substituted species, Cp-(C0)(P(C6HS),)Fe=CHR+, have been characterized in solution with 'H and I3C NMR spectroscopy. The CP(CO)~F~=CHR+ species are too unstable to observe directly; however, decomposition products have been characterized. For R = CH, an unusual cationic binuclear complex 6 is formed, while for R = CH2CH3 and CH(CH3)2 intramolecular hydride migration occurs to give the alkene complexes Cp(C0)2Fe(CH3CH=CH2)+ and Cp(C0)2Fe((CH3)2C=CH2)+. When Cp(C0)2Fe=CHCH3+ is generated in situ at -78 OC in the presence of a variety of alkenes, ethylidene transfer occurs to give methylcyclopropanes in good yields. Very high to moderate cis stereoselectivity is generally observed for polysubstituted alkenes. The ease of preparation and handling of Cp(CO),FeCH(OCH,)CH, and mild reaction conditions make this ethylidene transfer procedure attractive for synthesis of methyl-substituted cyclopropanes.Although numerous electrophilic transition-metal carbene complexes stabilized by a-heteroatoms or a-aryl substituents are known,' few simple complexes possessing only a-hydrogens or a-alkyl substituents have been characterized. The latter complexes can be rapidly enumerated: Cp(NO)(P(C6H5)3)Re=CH2+;2 Cp(di~hos)Fe=CH,+;~ Cp(C0)2M=C(CH3)2, (M = Mn, Re);4 Cp(NO)(P(C6Hs)3)Re=CHR+, (R = CH3, CHzCH3);5 Cp(di-~~o s ) F~= C H C ( C H , ) , + ;~ 101, 6473-6475.

No abstract