A dimolybdenum complex with an alkyneligand parallel to the metal–metal bond: synthesis, structure and cluster formation reactions of [Mo2(μ-η1,η1-C2Ph2)(μ-S)(μ-SPri)2Cp2]

Abstract

The dimolybdenum alkyne complex [Mo₂(μ-C₂Ph₂)(CO)₄Cp₂] 1 (Cp = η-C₅H₅), in which the alkyne ligand is perpendicular to the Mo–Mo bond, reacts with PrⁱSH to afford two separable isomers of [Mo₂(μ-η¹,η¹-C₂Ph₂)(μ-S)(μ-SPrⁱ)₂Cp₂] 2 in which the alkyne lies parallel to the Mo–Mo bond. In crystallographically characterised 2a the Prⁱ substituents are both directed away from the alkyne ligand in a syn arrangement, creating a plane of symmetry, whereas in unsymmetrical 2b they are presumed to occupy an anti arrangement. Extended-Hückel molecular orbital calculations show that the alkyne orientation in 2 results in better overlap between the alkyne and metal orbitals, as well as reduced repulsive interactions with the bridging thiolate ligands. Both isomers of 2 react with [Ru₃(CO)₁₂] to afford the same two products: the tetrahedral cluster [Mo₂Ru₂(μ₃-C₂Ph₂)(μ₃-S)(μ-SPrⁱ)₂(CO)₄Cp₂] 7 in which the alkyne ligand remains parallel to the Mo–Mo edge, and trinuclear [Mo₂Ru(μ-C₂Ph₂)(μ₃-S)₂(CO)₃Cp₂] 8 in which the alkyne has resumed its original perpendicular orientation; the crystal structures of both clusters are reported.