Medium Effects in the Homogeneous Catalytic Activation of Molecular Hydrogen by Metal Salts. II. Anion and Solvent Effects for Cupric and Cuprous Salts1

A Bifunctional Copper Catalyst Enables Ester Reduction with H2: Expanding the Reactivity Space of Nucleophilic Copper Hydrides

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.

Asymmetric hydrogenation catalyzed by first-row transition metal complexes

This review focuses on asymmetric direct and transfer hydrogenation with first-row transition metal complexes. The reaction mechanisms and the models of enantiomeric induction were summarized and emphasized.

Catalytic Generation and Chemoselective Transfer of Nucleophilic Hydrides from Dihydrogen

Copper(I)-N-heterocyclic-carbene (NHC) complexes enabled the catalytic generation of nucleophilic hydrides from dihydrogen (H₂ ) and their subsequent transfer to allylic chlorides. The highly chemoselective catalyst displayed no concomitant hydrogenation reactivity; in fact, the terminal double bond formed in the hydride transfer remained intact. Switching to deuterium gas (D₂ ) allowed for regioselective monodeuteration with excellent isotope incorporation.

Catalytic hydrogenation of α,β-unsaturated carboxylic acid derivatives using copper(i)/N-heterocyclic carbene complexes

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.