Nature of the cycloheptatrienyl-transition metal bond.

Abstract

The photoelectron spectra of [Ti(η-C7H7)(η-C5H5)], [Nb(η-C7H7)(η-C5H5)], [Nb(η-C7H7)(η-C5H5)], [Ta(η-C7H7) (η-C5H4Me)], and [Mo(η-C7H7)(η-C5H5)] have been acquired with synchrotron radiation in the incident photon energy range 20-95 eV. Relative partial photoionization cross sections have been derived for the valence bands. The la1 highest occupied molecular orbital (in [Nb(η-C7H7)(η-C5H5)], [Ta(η-C7H7)(η-C5H4Me)], and [Mo(η-C7H7)(η-C5H5)]) is confirmed as almost wholly metal-localized. The principal source of metal-cycloheptatrienyl ring covalent bonding is found to be the 1e2 molecular orbitals. The mixed metal/ligand character of the le2 orbitals, estimated as around 60-80% metal character, indicates that neither the +1 nor the -3 formalism for the charge on the cycloheptatrienyl ring is an accurate description of the metal-ring bonding in these complexes. It is considered that three metal valence electrons are required to form the metal-cycloheptatrienyl bond.