Synthesis and catalytic application of [PPP]-pincer iron, nickel and cobalt complexes for the hydrosilylation of aldehydes and ketones

A new synthetic strategy for the novel diphosphine-phosphine oxide ligand (1) (Ph2P-(C6H4))(2)P(O)H was designed. A series of [PPP]-pincer Fe, Ni, and Co complexes were prepared. All of them were formed by chelate-assisted P-H activation. Two metal hydrides [(Ph2P-(C6H4))(2)P(O)]Fe(H)(PMe3)(2) (2) and [(Ph2P-(C6H4))(2)P(O)]Ni(H)(PMe3) (3) were obtained at room temperature. The combination of ligand 1 with Co(PMe3)(4)Me or Co(PMe3)(4) afforded the same Co(i) complex [(Ph2P-(C6H4))(2)P(O)]Co(PMe3)(2) (4) via P-H bond activation. The catalytic performance of the Fe, Ni, and Co complexes for the hydrosilylation of aldehydes and ketones was explored. At a catalyst loading of 2 mol%, complex 2 displayed the best catalytic activity for the hydrosilylation by using (EtO)(3)SiH as the hydrogen source under mild conditions. Complexes 2, 3, and 4 were characterized by spectroscopic methods and X-ray diffraction analysis.