Metallation of 2-ethenylpyridine at triosmium clusters: X-ray crystal structures of the open trinuclear clusters [Os3H(CO)9L(NC5H4CHCH)](L = CO or PMe2Ph)

The compounds [Os3H2(CO)10] and [Os3(CO)10(MeCN)2] each react with 2-ethenylpyridine (NC5H4CHCH2) with C–H bond cleavage at the terminal carbon atom to give [Os3H(CO)10-(NC5H4CHCH)], (1). An analogous compound [Os3H(CO)9(PMe2Ph)(NC5H4CHCH)], (2), is formed similarly from [Os3H2(CO)9(PMe2Ph)]. Single-crystal X-ray structures of compounds (1) and (2) are reported. In these clusters the metal triangles have opened out with Os–Os–Os angles of 160.0(1) and 160.4(1)° in (1) and (2) respectively. Each of the compounds contains a terminal hydride ligand replaceable by Cl in carbon tetrachloride and has a five-electron donor NC5H4CHCH ligand chelating at a terminal Os atom of the Os3 chain with a η2-alkene co-ordination at the central Os atom. 2-Ethynylpyridine (NC5H4CCH) reacts with [Os3H2(CO)10] to give compound (1) and an isomer in which the alkene is trans rather than cis and in which the 2-pyridyl group is non-co-ordinated.