Mechanism of Endo−Exo Interconversion in η³-Allyl Cp Complexes: A Longstanding Unresolved Issue

Abstract

Density functional theory studies of the d6 allyl complexes CpM(CO)(η3-C3H5) (M = Fe, Ru) and the d4 allyl complex CpMo(CO)2(η3-C3H5) show that the interconversion for CpMo(CO)2(η3-C3H5) through the η3 → η3 → η3 pathway is intrinsically more favorable than the η3 → η1 → η3 pathway. However, the η3 transition states for CpM(CO)(η3-C3H5) (M = Fe, Ru) are inaccessible, because one pair of the six metal d electrons has to occupy a d orbital having significant metal−Cp antibonding character in the transition structure.