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

Abstract

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 )C6 H4 (1) with CoMe(PMe3 )4 and CoCl(PMe3 )3 . The silyl CoI complex, Co(PMe3 )3 (1-Si(Me)2 -2-(PPh2 )C6 H4 ) (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 CH3 I or EtBr, generating the silyl CoII products CoI(PMe3 )2 (1-Si(Me)2 -2-(PPh2 )C6 H4 ) (3) and CoBr(PMe3 )2 (1-Si(Me)2 -2-(PPh2 )C6 H4 ) (4). The silyl CoIII hydride, CoHCl(PMe3 )2 (1-Si(Me)2 -2-(PPh2 )C6 H4 ) (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.