959981-12-5Relevant articles and documents
Reactions of H2 and R3SiH with electrophilic cobalt(III) alkyl complexes: Spectroscopic characterization, dynamics, and chemistry of [Cp*Co(L)(H)(η2-H2)][B(Ar F)4] and [Cp*Co(L)(H)η2-HSiR 3][B(ArF)4]
Doherty, Mark D.,Grant, Brian,White, Peter S.,Brookhart, Maurice
, p. 5950 - 5960 (2008/10/09)
Co(III) agostic alkyl complexes [Cp*Co(L)(CH2CH 2-μ-H)][B(ArF)4] (Cp* = C 5(CH3)5, L = P(OCH3)3, 1a, or P(CH3)3, 1b; ArF = 3,5-(CF 3)2C6H3) react with H2 to yield ethane and trihydride complexes characterized as η2- dihydrogen hydride species [Cp*Co(L)(H)(η2-H 2)][B(ArF)], 2a and 2b, in which there is rapid scrambling between the η2-H2 ligand and the terminal Co-H. Complexes 2a and 2b react with a variety of neutral donor ligands (L′ = RCN, PMe3, P(OMe)3, H2O, CH3OH) to yield [Cp*Co(L)(L′)(H)][B(ArF)4] complexes. Reaction of silanes with either 1a,b in the presence of traces of water or 2a,b yields η2-silane hydrides, [Cp*Co(L)(H)(η2- HSiR3)][B(ArF)4]. Analysis of the dynamics of these species by NMR spectroscopy provides evidence for an extremely rapid process involving silyl migration between hydrogens and a slower process in which a cobalt-silyl η2-H2 complex is formed as an intermediate and results in hydrogen scrambling between the two diastereomers of [Cp*Co(L)(H)(η2-H-SiHMePh)][B(ArF) 4]. The structures and dynamics of 2a,b and the η2- silane complexes imply that cleavage of the cobalt alkyl bonds of la,b in hydrogenation and hydrosilation catalytic cycles occurs by the σ-CAM (σ-complexassisted metathesis) process.
