Additive-Free Cobalt-Catalyzed Hydrogenation of Esters to Alcohols

Here, we report an additive-free catalytic system for hydrogenation of carboxylic acid esters to alcohols with a well-defined cobalt pincer catalyst precursor. Various substrates, including methyl, ethyl, and benzyl esters, have been evaluated under hydrogenation conditions; however, methyl esters have low reactivity compared to those of the corresponding ethyl and benzyl esters. The biomass-derived γ-valerolactone successfully formed 1,4-pentanediol with a turnover number of 3890 with this system. Metal–ligand cooperativity is probed with the related [PN­(Me)­P] derivative of the cobalt catalyst, and the results suggest a nonbifunctional hydrogenation mechanism.