Dibismuth as a four-electron donor ligand. Synthesis and molecular and electronic structure of [M2(CO)4(η-C5H4Me)2(µ-η2-Bi2)](M = Mo or W)

Abstract

The compounds [M2(CO)4(η-C5H4R)2(µ-η2-Bi2)](M = Mo or W, R = H or Me) have been prepared by the solid-state thermolysis or solution-state photolysis of [Bi{M(CO)3(η-C5H4R)}3]. The structures of the methylcyclopentadienyl derivatives were determined by X-ray crystallography and show a M2(CO)4(η-C5H4Me)2 unit in which the M–M vector is transversely bridged by a Bi2 ligand so as to give a tetrahedral M2Bi2 core. The Bi2 ligand acts as a four-electron donor. The electronic structure of [Mo2(CO)4(η-C5H5)2(µ-η2-Bi2)] has been examined by extended-Hückel molecular orbital calculations and compared with the related diphosphorus complex [Mo2(CO)4(η-C5H5)2(µ-η2-P2)]. Substantial differences are found in the nature of those frontier orbitals which are localised primarily on the P2 and Bi2 units. These are consistent with the observed differences in the chemistry of P2vs. Bi2 ligands in general. The chromium complexes [BiCl{Cr(CO)3(η-C5H5)}2] and [Bi{Cr(CO)3(η-C5H5)}3] are also described.