Theoretical Analysis of the Hydrogen-Transfer Reaction to C═N, C═C, and C≡C Bonds Catalyzed by Shvo’s Ruthenium Complex

Abstract

The Shvo catalyst {[Ph4(η5-C4CO)]2H}Ru2(CO)4H belongs to the so-called bifunctional catalysts, containing one hydride (bonded to Ru) and one proton (bonded to a ligand), which are easily transferred. The mechanism of hydrogenation of polar double bonds by Shvo’s catalyst has been extensively studied; however, imine hydrogenation is still a controversial topic. The outer-sphere mechanism (without substrate coordination) and the inner-sphere mechanism (with substrate coordination) are the two main proposals. Several experimental observations account for each proposed mechanism, besides a theoretical analysis of their respective suggested mechanism. In the present work inner- and outer-sphere mechanisms for hydrogenation of C═N, C═C, and C≡C bonds are analyzed and compared by means of theoretical calculations, complementing our previous work in C═O hydrogenation. The obtained energy profiles support an outer-sphere mechanism in all the cases.