Employing a bifunctional catalyst based on a copper­(I)/NHC complex and a guanidine organocatalyst, catalytic ester reductions to alcohols with H2 as terminal reducing agent are facilitated. The approach taken here enables the simultaneous activation of esters through hydrogen bonding and formation of nucleophilic copper­(I) hydrides from H2, resulting in a catalytic hydride transfer to esters. The reduction step is further facilitated by a proton shuttle mediated by the guanidinium subunit. This bifunctional approach to ester reductions for the first time shifts the reactivity of generally considered “soft” copper­(I) hydrides to previously unreactive “hard” ester electrophiles and paves the way for a replacement of stoichiometric reducing agents by a catalyst and H2.

Copper(i)/N-heterocyclic carbene complexes enable a catalytic transfer semihydrogenation of alkynes employing simple and readily available alcohols such as isopropanol.

A simple and air-stable copper(i)/N-heterocyclic carbene complex enables the catalytic hydrogenation of enoates and enamides, hitherto unreactive substrates employing homogeneous copper catalysis and H2 as a terminal reducing agent.

A protocol for the mechanochemical synthesis of copper(I)/N-heterocyclic carbene complexes using cheap and readily available K3PO4 as base has been developed. This method employing a ball mill is amenable to typical simple copper(I)/NHC complexes but also to a sophisticated copper(I)/N-heterocyclic carbene complex bearing a guanidine moiety. In this way, the present approach circumvents commonly employed silver(I) complexes which are associated with significant and undesired waste formation and the excessive use of solvents. The resulting bifunctional catalyst has been shown to be active in a variety of reduction/hydrogenation transformations employing dihydrogen as terminal reducing agent.

Employing a bifunctional catalyst based on a copper(I)/NHC complex and a guanidine organocatalyst, catalytic ester reductions to alcohols with H₂ as terminal reducing agent are facilitated. The approach taken here enables the simul-taneous activation of esters through hydrogen bonding and formation of nucleophilic copper(I) hydrides from H₂, resulting in a catalytic hydride transfer to esters. The reduction step is further facilitated by a proton shuttle mediated by the guani-dinium subunit. This bifunctional approach to ester reductions for the first time shifts the reactivity of generally considered “soft” copper(I) hydrides to previously unreactive “hard” ester electrophiles and paves the way for a replacement of stoichi-ometric reducing agents by a catalyst and H₂.<br>