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.