Metal–metal bond fission and the formation of triosmium–alkene complexes via the reaction of [Os3(µ-H){µ3-η2-CF3CC(H)CF3}(CO)10] with nucleophiles; a complete model for the catalytic reduction of an alkyne to an alkene by a cluster

Abstract

The reaction of [Os₃H₂(CO)₁₀] with hexafluorobut-2-yne gives the complex [Os₃(µ-H){µ₃-η²-CF₃CC(H)CF₃}(CO)₁₀] in 88% yield. The reactions of this complex with a variety of nucleophiles have been investigated and have led to the preparation of a series of stable fluoro-alkene complexes [Os₃{CF₃(H)CC(H)CF₃}(CO)₁₀Y](Y = PEt₃, CO, Cl^–, Br^–, I^–, or H^–). For Y = PEt₃ and CO both the cis- and trans-fluoro-alkene complexes are formed in approximately equimolar proportions, but the other nucleophiles give only a single fluoro-alkene complex which, for Y = Br^–, is the trans product. The major product of the reaction with Y = PEt₃ results from metal–metal bond cleavage to give the complex [Os₃H{µ-η²-CF₃CC(H)CF₃}(CO)₁₀(PEt₃)] which contains a bent chain of Os atoms and a terminal Os–H ligand. The reactions of [Os₃(µ-H){µ₃-η²-CF₃CC(H)CF₃}(CO)₁₀] with nucleophiles are compared with those of the unsubstituted vinyl complex [Os₃(µ-H)(µ-η²-CHCH₂)-(CO)₁₀], and a model is proposed for the catalytic reduction of an alkyne to an alkene by a trinuclear osmium cluster.