Syntheses and structures of dimethylamino-bridged bis(silylene)ruthenium and -osmium complexes

Treatment of Os(SiMe2Cl)Cl(CO)(PPh3)2 with an excess of the amino-substituted silane, HSiMe2NMe2, produces a mixture of two products, the relative proportions of which depend upon the reaction conditions. These are, iMe2)Cl(CO)(PPh3)2 (1) and iMe2)H(CO)(PPh3)2 (2). Similar treatment of Ru(SiMe2Cl)Cl(CO)(PPh3)2 with HSiMe2NMe2 produces the ruthenium analogues of 1 and 2, iMe2)Cl(CO)(PPh3)2 (3), and iMe2)H(CO)(PPh3)2 (4), together with a third compound, the novel dimethylsilylene-bridged diruthenium complex, [iMe2)(CO)(μ-{SiMe2})2(μ-Cl)RuH2(CO)(PPh3)] (5). A ligand exchange reaction occurs when 3 is treated with 1,2-bis(diphenylphosphino)ethane (dppe) yielding iMe2)Cl(CO)(dppe) (6), in which the bis(silylene) ligand is retained. Crystal structures of 1, 2, 4, and 6 reveal that the i and i rings of the bis(silylene) ligand system are folded at the Si atoms and the RuSi and OsSi distances are short, while SiN distances are long. These structural data suggest some multiple bond character in the metal–silicon bonds and this is further supported by the down-field chemical shifts observed in the 29Si-NMR spectra of these compounds. A crystal structure has also been determined for the diruthenium complex 5 and this reveals a RuRu distance of 2.7557(2) Å, and two unsymmetrically bridging dimethylsilylene ligands each with a close approach to one of the ruthenium hydride ligands (SiH, 1.56(2) and 1.67(2) Å).