SYNTHESIS AND ELECTRONIC AND MOLECULAR-STRUCTURES OF ETA-CYCLOHEPTATRIENYL ETA-CYCLOPENTADIENYL DERIVATIVES OF VANADIUM, NIOBIUM, AND TANTALUM - PHOTOELECTRON SPECTROSCOPIC, ELECTROCHEMICAL, AND X-RAY CRYSTALLOGRAPHIC STUDY

The new compounds [Ta(eta-C7H7)(eta-C5H4Me)] (3), [Nb(eta-C7H7)(eta-C5H4R)(thf)[PF6] (R = H (4), Me (4a)), [Nb(eta-C7H7)(eta-C5H4Me)(PMe3)][PF6] (5), [Nb(eta-C7H7)(eta-C5H4Me)(CO)][PF6] (6), [K(19-crown-6)][Nb-(eta-C7H7(eta-C5H5)] (7), and [Nb(eta-C7H7)(eta-C5H4Me)Me] (8) have been prepared, and an improved route to [Nb(eta-C7H7)(eta-C5H4R)] (R = H (2), Me (2a)) is reported. The X-ray crystal structures of 4a and 7 have been determined. The He I and He II photoelectron spectra of [M(eta-C7H7)(eta-C5H5)] (M = V, Nb) and 3 have been obtained and the bonding is discussed. It is considered that (eta-C7H7)-M bonding requires a contribution of three valence electrons from the metal.