Recent advances in homogeneous base-metal-catalyzed transfer hydrogenation reactions

Abstract

Owing to availability of various hydrogen sources, operational simplicity, and mild reaction conditions, catalytic transfer hydrogenation (TH) has emerged as an appealing alternative for the direct hydrogenation reactions with H2 gas. Conventional TH catalysts are based on noble metals, such as Ru, Rh, and Ir, which are toxic and expensive due to their limited availability. Current research in this area is oriented towards the development of more sustainable catalysts utilizing abundant 1st row transition metals with readily accessible ligand platforms. During the past few decades, many novel examples of such systems appeared in the literature, expanding not only the number of catalyst surrogates but also the scope of unsaturated substrates, opening new venues for TH in organic synthesis. This review aims to provide an update on recent advances in homogeneous TH reactions catalyzed by base-metal (Mn, Fe, Co and Ni) complexes. Special attention is paid to selectivity and the mechanisms of such transformations.