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

Abstract

A new synthetic strategy for the novel diphosphine-phosphine oxide ligand (1) (Ph₂P-(C₆H₄))₂P(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))₂P(O)]Fe(H)(PMe₃)₂ (2) and [(Ph₂P-(C₆H₄))₂P(O)]Ni(H)(PMe₃) (3) were obtained at room temperature. The combination of ligand 1 with Co(PMe₃)₄Me or Co(PMe₃)₄ afforded the same Co(I) complex [(Ph₂P-(C₆H₄))₂P(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)₃SiH as the hydrogen source under mild conditions. Complexes 2, 3, and 4 were characterized by spectroscopic methods and X-ray diffraction analysis.