Synthesis and Reactivity of N-Heterocyclic PSiP Pincer Iron and Cobalt Complexes and Catalytic Application of Cobalt Hydride in Kumada Coupling Reactions

Abstract

The new N-heterocyclic σ-silyl pincer ligand HSiMe(NCH2PPh2)2C6H4 (1) was designed. A series of tridentate silyl pincer Fe and Co complexes were prepared. Most of them were formed by chelate-assisted Si–H activation. The typical iron hydrido complex FeH(PMe3)2(SiMe(NCH2PPh2)2C6H4) (2) was obtained by Si–H activation of compound 1 with Fe(PMe3)4. The combination of compound 1 with CoMe(PMe3)4 afforded the Co(I) complex Co(PMe3)2(SiMe(NCH2PPh2)2C6H4) (3). The Co(III) complex CoHCl(PMe3)(SiMe(NCH2PPh2)2C6H4) (5) was generated by the reaction of complex 1 with CoCl(PMe3)3 or the combination of complex 3 with HCl. However, when complex 3 was treated with MeI, the Co(II) complex CoI(PMe3)(SiMe(NCH2PPh2)2C6H4) (4), rather than the Co(III) complex, was isolated. The catalytic performance of complex 5 for Kumada coupling reactions was explored. With a catalyst loading of 5 mol %, complex 5 displayed efficient catalytic activity for Kumada cross-coupling reactions of aryl chlorides and aryl bromides with Grignard r...