E-H bond activation reactions (E = H, C, Si, Ge) at ruthenium: Terminal phosphides, silylenes, and germylenes

Abstract

The placement of a strongly trans-influencing ligand on a ruthenium center opposite an anchoring silyl group of the tetradentate tripodal tris(phosphino)silyl ligand, [SiP ph1 3] - ([SiP ph3] -= tris(2-(diphenylphosphino)phenyl) silyl), has been explored. Installation of alkyl or terminal phosphide ligands trans to the anchoring silyl group affords the complexes [SiP ph3]RuR (R = Me (2), CH 2Ph(4), PPh 2 (5), P iPr 2 (6)). Complexes 2,4, and 5 are thermally unstable. Complexes 2 and 4 decay to the cyclometalated complex [SiP ph2P' ph1]Ru (3), whereas complex 5 decays to the cyclometalated phosphine adduct [SiP pl:2P'Ph]Ru(PHPh 2) (7). Complex 3 is found to effect E-H (E = H, C, Si, Ge) bond activation of substrates such as secondary silanes and germanes to yield the structurally unusual silylene complexes [SiPph3]Ru(H) (SiRR) (R = R' = Ph (10a), R = Ph R = Me (10b)) and the germylene complex [SiP ph3]Ru(H)(GeR2) (R = Ph) (11) via double E-H activation transformations. Both theory and experiments suggest electrophilic character at the silylene moiety. Reaction of 3 with catecholborane, in contrast to silanes and germanes, results in insertion of the B-H unit into the M-C bond of the cyclometalated species to yield the borate complex [SiP ph2P ph1-B(cat)]Ru(μ-H) (14). Complex 3 also reacts with bis(catecholato) diboron to yield a similar complex, [SiP ph2P C6H3B(cat)-B(cat)]Ru(μ-H) (15), with selective borylation of an ortho C-H bond. © 2009 American Chemical Society.