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

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.