Reactions of H2Os3(CO)10 with triallylboranes: formation of novel triosmium boron-containing olefin clusters

H2Os3(CO)10 (1) reacts with triallylborane B(CH2CHCH2)3 at 25 °C to form the cluster [Os3(CO)10(μ-η2:η2-trans-MeHCCH)2BC3H7] (2). Reaction of 1 with a mixture of triallylborane–trimethallylborane (1 : 3) gives a mixture of clusters 2, [Os3(CO)10(μ-η2:η2-Me2CCH)2BC3H7] (3) and {Os3(CO)10[μ-η2:η2-(trans-MeCHCH)(Me2CCH)]BC3H7} (4). The reaction results in the B–C bond cleavage and the isomerization of two allyl fragments into substituted vinyl groups coordinated to the osmium atoms in an η2-fashion, and reduction of the third fragment to a propyl group. The mechanism of the reaction is discussed based on isotope labelling and influence of the boron substituent ligand on the reaction path and product identity. Clusters 2, 3, 4 are characterized by spectroscopic means as well as by X-ray studies.