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-C 3H5) 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.