Low-Pressure Hydrogenation of Enoates and Carbonyl Compounds with a Bifunctional Copper(I)/NHC Catalyst

Reductive transformations with copper(I) hydride complexes driven by dihydrogen (H2) as the stoichiometric reducing agent typically suffer from limited scope and practicability due to the strongly basic conditions and high H2 pressure that are required. In this work, we show that catalytic hydrogenations of α,β-unsaturated esters and carbonyl compounds are realized by a copper(I) complex constructed from a bifunctional N-heterocyclic carbene complex bearing a 2-iminopyridine subunit. The highly active catalyst allows for practical catalytic hydrogenations at low H2 pressure, in standard laboratory glassware, reaching balloon pressure. The protocol displays high chemoselectivity as functional groups such as halides, nitro groups, amides, and heterocycles are tolerated. Mechanistic experiments, including isotope labeling studies, are consistent with a proximity-induced proton transfer step facilitated by the bifunctional catalyst.