A Highly Active and Easily Accessible Cobalt Catalyst for Selective Hydrogenation of CO Bonds

The
substitution of high-price noble metals such as Ir, Ru, Rh,
Pd, and Pt by earth-abundant, inexpensive metals like Co is an attractive
goal in (homogeneous) catalysis. Only two examples of Co catalysts,
showing efficient CO bond hydrogenation rates, are described.
Here, we report on a novel, easy-to-synthesize Co catalyst family.
Catalyst activation takes place via addition of 2 equiv of a metal
base to the cobalt dichlorido precatalysts. Aldehydes and ketones
of different types (dialkyl, aryl-alkyl, diaryl) are hydrogenated
quantitatively under mild conditions partially with catalyst loadings
as low as 0.25 mol%. A comparison of the most active Co catalyst with
an Ir catalyst stabilized by the same ligand indicates the superiority
of Co. Unique selectivity toward CO bonds in the presence
of CC bonds has been observed. This selectivity is opposite
to that of existing Co catalysts and surprising because of the directing
influence of a hydroxyl group in CC bond hydrogenation.