Mechanism of ruthenium-catalyzed linear dimerization of acrylonitrile: a kinetic study

Abstract

A detailed kinetic study of the RuCl 2(AN) 3-catalyzed linear dimerization of acrylonitrile reveals that the reaction is first order in Ru and H 2, and zero order in acrylonitrile. A reaction model is proposed which is consistent with the observed kinetic behavior and product distribution data, including our previous deuterium-labelling study [4]. It is visualized that two equivalents of base are first utilized to facilitate the generation of the active catalyst, a zero-valent Ru complex. The Ru(0) complex interacts reversibly with H 2 to give a ruthenium dihydride, which then enters into the dimer-forming catalytic cycle. Two subsequent acrylonitrile insertions, the first into one of the Ru—H bonds followed by another into the Ru—C bond formed in the first insertion, and a β-hydride elimination produce the observed linear dimer. The major side product, propionitrile, is formed by a competing reductive elimination from the hydrido(α- or β-cyanoethyl)ruthenium intermediate. Detailed product distribution analysis reveals the presence of one base ligand in the coordination sphere of the Ru. The coordination of base favors the production of saturated dimer vs. unsaturated dimer, but has no effect on the propionitrile: linear dimer ratio.