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Synthesis of a Silyl Cobalt Hydride and Its Catalytic Performance in Kumada Coupling Reactions
Shilu Xu1, Peng Zhang1, Xiaoyan Li1
1School of Chemistry and Chemical Engineering, Key Laboratory of Special Functional Aggregated Materials, Ministry of Education, Shandong University, Shanda Nanlu 27, 250199, Jinan, People's Republic of China.
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.