Hydrocyanation and hydrogenation of acetylenes catalysed by cyanocobaltates

Abstract

Acetylenes are regioselectively hydrocyanated by cyanocobaltate prepared at CN : Co < 5 : 1 to give saturated secondary nitriles via unsaturated nitriles without the use of hydrogen cyanide, and partly hydrogenated to olefins or saturated hydrocarbons. In the presence of 2,2′-bipyridyl, hydrogenation of acetylene predominates, reflecting the formation of a highly active hydride complex [Co(CN)₃(bipy)H]^–. The preliminary formation of a [π-acetylene–Co(CN)₄]^3– complex is assumed to explain the fact that the complex is active only at CN : Co < 5 : 1. Hydrocyanation is explained by the reductive coupling of the vinyl and cyano ligands of [σ-vinyl–Co(CN)₅]^3– which is formed by the reaction of the π-acetylene complex, rather than acetylene itself, with [Co(CN)₅H]^3–.