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.