STEREOCHEMISTRY AND MECHANISM OF CYCLOPROPANE FORMATION FROM IONIZATION OF C5H5(CO)2FE(CH2)3X

Cyclopropane was produced efficiently both in the Ag+-assisted dissociation of bromide from C5H5(CO)2Fe(CH2)3Br (1) and in the dissociation of phenyl methyl sulfide from C5H5(CO)2Fe(CH2)3S(CH3)C6H5+CF3SO3- (8). Clean inversion of stereochemistry at the carbon bound to ion was seen in the formation of cis-1,2-dideuteriocyclopropane from the threo sulfonium salt C5H5(CO)2FeCHDCHDCH2S(CH3)C6H5+CF3SO3- (threo-8-d2). This stereochemical result is consistent with a W-shaped transition state for cyclopropane formation and rules out a mechanism involving a metallacyclobutane intermediate. A new explanation for the selective formation of cis cyclopropanes from the reaction of alkenes with (CO)5W = CHC6H5 is proposed in light of the results reported here.