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 CoI 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 CoII 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 CoIII 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.