Intramolecular nucleophilic attack at the α-carbon atom of a µ3-alkynyl ligand in a triosmium cluster

Abstract

The cluster [Os₃(CO)₁₂] reacts with but-3-yn-1-ol, HCCCH₂CH₂OH, in hydrocarbon solvent at 130 °C to give the 2,3-dihydrofuran-4,5-diyl complex [Os₃H₂(CO)₉(µ₃-[graphic omitted])](3)(yield 48%). The probable route to this compound is indicated by the formation of the simple alkyne compound [Os₃(CO)₁₀(µ₃-HCCCH₂CH₂OH)](1) from [Os₃(CO)₁₀(MeCN)₂] and the alkynol at room temperature which at higher temperatures converts to compound (3) probably via its isomer [Os₃H(CO)₉(µ₃-CCCH₂CH₂OH)](2). This isomerisation occurs because α-carbon atoms of µ₃-alkynyl ligands are susceptible to nucleophilic attack which in this case occurs intramolecularly with cyclisation. The dynamic behaviour of clusters (1) and (3) is described; in both cases inversion of the chiral Os₃(alkyne) group is observed.