Synthesis of a Silyl Cobalt Hydride and Its Catalytic Performance in Kumada Coupling Reactions.

Four silyl [P,Si]-chelate cobalt complexes ( 2- 5) have been synthesized through the chelate-assisted Si−H activation of bidentate preligand ortho-HSi(Me)₂(PPh₂)C₆H₄ ( 1) with CoMe(PMe₃)₄ and CoCl(PMe₃)₃. The silyl Co^I complex, Co(PMe₃)₃(1-Si(Me)₂-2-(PPh₂)C₆H₄) ( 2), was synthesized by Si−H activation of 1 with CoMe(PMe₃)₄ or by combining complex 5 with MeLi and PMe₃. Complex 2 was treated with CH₃I or EtBr, generating the silyl Co^II products CoI(PMe₃)₂(1-Si(Me)₂-2-(PPh₂)C₆H₄) ( 3) and CoBr(PMe₃)₂(1-Si(Me)₂-2-(PPh₂)C₆H₄) ( 4). The silyl Co^III hydride, CoHCl(PMe₃)₂(1-Si(Me)₂-2-(PPh₂)C₆H₄) ( 5), was obtained by the reaction of complex 1 with CoCl(PMe₃)₃. The catalytic performance of complex 5 was explored for Kumada coupling reactions, showing good to excellent catalytic efficiency with 2 mol % catalyst loading for the reactions of aryl chlorides or aryl bromides with Grignard reagents. It is noteworthy that the synthesis of 5 as a chelate complex is easier than that of previously reported [PSiP]-pincer cobalt hydride. With similar catalytic efficiency for Kumada reactions, the catalyst loading (2 %) of 5 was lower than that (5 %) of [PSiP]-pincer cobalt hydride. [ABSTRACT FROM AUTHOR]