Metal-induced BH activation. Addition of phenylacetylene to Cp*Rh-, Cp*Ir-, (p-cymene)Ru- and (p-cymene)Os halfsandwich complexes containing a chelating 1,2-dicarba-closo-dodecaborane-1,2-dichalcogenolate ligand

The addition reactions of the 16e halfsandwich complexes Cp*M[S2C2(B10H10)] (1S M=Rh, 2S M=Ir) and η6-(4-isopropyltoluene)M[S2C2(B10H10)] (3S M=Ru and 4S M=Os) with phenylacetylene lead selectively to the 18e complexes 5S–8S, in which a metalboron bond is present and the phenylacetylene is regio- and stereoselectively inserted into one of the MS bonds, with one hydrogen atom transferred from the carborane cage to the terminal carbon of the alkyne, corresponding to ortho-metalation of the carborane cage. In all cases, the S-η2-(Ph)CC and the C(1)B units are linked to the metal in cisoid positions. The analogous reaction of Cp*Ir[Se2C2(B10H10)] 2Se with phenylacetylene gives 6Se. Complex 5S undergoes an intramolecular rearrangement in solution to the isomer 9S, where the RhB bond is cleaved, the B-atom now bearing the organic substituent, and a metalcarbon σ bond being formed together with a coordinative S→Rh bond. In contrast, the p-cymene complexes 7S and 8S rearrange into isomers 10S and 11S, in which the S-η2-(Ph)CC and the C(1)B(M) moieties occupy transoid positions, preventing further intramolecular rearrangements. The proposed structures in solution were deduced from NMR data (1H-, 11B-, 13C-, 77Se-, and 103Rh-NMR) and X-ray structural analyses were carried out for 5S, 6Se, 9S and 10S.