Cobalt Nanoparticles Formed upon Reaction of Cp*Co(III) Metallacycles with Na[BHEt3] Show Catalytic Activity in the Hydrosilylation of Aryl Ketones,Aldehydes and Nitriles

The reactivity of the 2-phenylpyridine-derived Cp*CoI(phpy-κ^C,N)] metallacycle towards Et₃SiH and hydrides was evaluated. The treatment of the same Co(III) complex with NaBHEt₃] resulted in its decomposition into cobalt nanoparticles. The hydride-promoted decomposition of the metallacycle involves the transient formation of an elusive hydrido-cobalt(III) intermediate, the traces of which were detected by ¹H NMR spectroscopy at sub-ambient temperature. The Co nanoparticles produced from a 5 mol% and 10 mol% load of cobaltacycle and NaBHEt₃] respectively contain Co(0) that is responsible for the hydrosilylation by Et₃SiH of arylketones into silylalkyl ethers. To minimize the residual side reduction of carbonyls by NaBHEt₃], a mixture of 5 mol% of the latter with 5 mol% of BEt₃ was found to produce optimal hydrosilylation yields at 40 °C in 2 h. Under similar conditions, several arylnitriles were mono-hydrosilylated into N-silyl-imines in yields ranging from 68 to 100 %.