The structures of some derivatives of dicarbonylcyclopentadienyliron dimer [{Fe(π-C5H5)(CO)2}2] obtained from the reaction of pentacarbonyliron with fulvenes

Abstract

Pentacarbonyliron and fulvenes, C₅H₄CR¹R²(R¹,R²= Me, Et, or Ph) react in diglyme under reflux to give [{Fe(π-R¹R²CH·C₅H₄)(CO)₂}₂] these compounds exist as their trans-bridged isomers in the solid state, but primarily as a mixture of these with their cis-counterparts in solution. The relative proportions of these species depends upon the solvent, and upon R¹ and R². The complex obtained from 6-dimethylaminofulvene is a ‘linked’ dimer, [Fe₂(π-C₅H₄·CHNMe₂·CHNMe₂·C₅H₄)(CO)₄] with a cis-conformation. Its i.r. spectrum is independent of solvent and shows that although [{Fe(π-C₅H₅)(CO)₂}₂] does not exist solely as its cis-isomer in, for example, heptane solution, this is the principal tautomer present in acetonitrile and related solvents.