Synthesis and Reactivity of a Hydrido CNC Pincer Cobalt(III) Complex and Its Application in Hydrosilylation of Aldehydes and Ketones

Abstract

Reaction of the N-benzylidene-1-naphthylamine with CoMe(PMe3)4 afforded the hydrido CNC pincer cobalt complex CoH(PMe3)2[(C6H4)CH═N(C10H6)] (1) via double C–H bond activation. In the 1H NMR spectrum, a triplet at −18.98 ppm is the typical signal of the hydrido ligand (Co–H). Complex 1 reacted with haloalkane (CH3I and EtBr) to deliver CoX(PMe3)2((C6H4)CH═N(C10H6)) (X = I (2); Br (3)). However, the reactions of complex 1 with HCl and trifluoroacetic acid (TFA) delivered HCoCl(PMe3)2((C6H4)CH═N(C10H7)) (4) and HCo(OCOCF3)(PMe3)2((C6H4)CH═N(C10H7)) (5) with the cleavage of the Co–C(naphthyl) bond. In the 1H NMR spectra, the signals of the hydrido ligands were found at −21.31 (4) and −18.71 (5) ppm. A reaction of complex 1 with DCl was carried out to prove that the hydrogen atom eliminated to the naphthyl carbon comes from HCl. Complex 1 reacted with acetylacetone, resulting in the formation of Co(acac)(PMe3)2((C6H5)CHNH(C10H6)) (7). Complex 1 was found to be an efficient catalyst for hydrosilylation of aldehydes and ketones. The molecular structures of complex 1, 2, 4, and 7 were determined by X-ray single-crystal diffraction.