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, Os(SiMe2NMe2SiMe2)-Cl(CO)(PPh3)(2) (1) and Os(SiMe2NMe2SiMe2)H(CO)(PPh3)(2) (2). Similar treatment of Ru(SiMe2Cl)Cl(CO)(PPh3)(2) with HSiMe2NMe2 produces the ruthenium analogues of 1 and 2, Ru(SiMe2NMe2SiMe2)Cl(CO)(PPh3)(2) (3), and Ru(SiMe2NMe2SiMe2)H(CO)(PPh3)(2) (4). together with a third compound, the novel dimethylsilylene-bridged diruthenium complex, [Ru(SiMe2NMe2SiMe2)(CO)(mu-{SiMe2}(2)(mu-Cl)RuH2(CO)(PPh3)] (5). A ligand exchange reaction occurs when 3 is treated with 1,2-bis(diphenylphosphino)ethane (dppe) yielding Ru(SiMe2NMe2SiMe2)Cl(CO)(dppe) (6), in which the bis(silylene) ligand is retained. Crystal structures of 1, 2, 4, and 6 reveal that the RuSiNSi and OsSiNSi 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 Si-29-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) Angstrom, 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) Angstrom). (C) 2002 Elsevier Science B.V. All rights reserved.