A dimolybdenum complex with an alkyne ligand parallel to the metal-metal bond: synthesis, structure and cluster formation reactions of [Mo-2(mu-eta(1),eta(1)-C2Ph2)(mu-S)(mu-SPri)(2)Cp-2]

The dimolybdenum alkyne complex [Mo-2(muC(2)Ph(2))(CO)(4)CP2] 1 (Cp = eta - C5H5), in which the alkyne ligand is perpendicular to the Mo-Mo bond, react s with (PrSH)-S-i to afford two separable isomers of [Mo-2(mu-eta (1), eta (1)-C2Ph3)(mu -S)- (mu -SPri)(2)Cp-2] 2 in which the alkyne lies parallel t o the Mo-Mo bond. In crystallographically characterised 2a the Pr-i substit uents are both directed away from the alkyne ligand in a syn arrangement, c reating a plane of symmetry, whereas in unsymmetrical 2b they are presumed to occupy an anti arrangement. Extended-Huckel molecular orbital calculatio ns show that the alkyne orientation in 2 results in better overlap between the alkyne and metal orbitals, as well as reduced repulsive interactions wi th the bridging thiolate ligands. Both isomers of 2 react with [Ru-3(CO)(12 )] to afford the same two products: the tetrahedral cluster [Mo2Ru2(mu (3)- C2Ph2)(mu (3)-S)(mu -SPri)(2)(CO)(4)Cp-2] 7 in which the alkyne ligand rema ins parallel to the Mo-Mo edge, and trinuclear [Mo2Ru(mu -C2Ph2)(mu (3)-S)( 2)(CO)(3)Cp-2] 8 in which the alkyne has resumed its original perpendicular orientation; the crystal structures of both clusters are reported.