Molecular Electrocatalytic Hydrogenation of Carbonyls and Dehydrogenation of Alcohols

Abstract

The development of safe and energy efficient redox processes is key for a future sustainable organic chemistry and energy storage/vector applications. Molecular electrocatalysts have demonstrated their potential in the realm of CO 2 reduction, however, successful implementations for the reduction of other carbonyl groups remain sporadic. Building on the reversibility of hydrogenation and dehydrogenation of carbonyls and alcohols, an overview of current molecular electrocatalytic systems is presented. Key mechanistic concepts are emphasized to facilitate the link with more mature schemes in transfer hydrogenation, proton-and CO 2 -reduction. Thus, this work contributes to future catalyst generation development bridging fundamental aspects of electrochemical bond activation with molecular catalytic concepts in the context of societal challenges of today.

Determining overpotentials for the oxidation of alcohols by molecular electrocatalysts in non-aqueous solvents

“…Molecular catalysts for electrochemical alcohol oxidation have been reviewed recently. [17][18][19] Here, we focus on a subset of catalysts for which electrochemical two-electron oxidation of alcohols was performed in THF or MeCN using bases with known pK a values, which allows the determination of overpotentials (Figure 5 and Table 2). As discussed in the previous section, catalyst performance should be evaluated under buffered conditions.…”

Electrocatalysis with Molecular Transition-Metal Complexes for Reductive Organic Synthesis

“…Another important challenge is here to reduce the carbonyl to the alcohol in a chemoselective way, avoiding the ketyl radical coupling and the hydrogenation of other unsaturations (e.g., C=C) when present ( Figure 5 b). 48 , 49 To drive carbonyl hydrogenation to the desired selectivity, molecular electrocatalysts have been investigated, 50 , 51 mostly based on Ni, 52 , 53 Fe, 52 , 53 Ru, 54 and Rh 55 − 57 metal complexes, with a body of work using homogeneous and immobilized Rh bipyridine type complexes. 55 − 57 …”

Electroreduction of Carbonyl Compounds Catalyzed by a Manganese Complex

“…The selective electrochemical reduction of polar CO moieties catalyzed by transition metal complexes is still largely underexplored . In radical-type reductions that proceed via 1H + /1e – steps, the initially formed XH bond is very weak, which necessitates the use of catalysts with a low bond dissociation free energy (BDFE).…”