ChemInform Abstract: Catalytic Reduction of CO2by Renewable Organohydrides

Dihydropyridines are renewable organohydride reducing agents for the catalytic reduction of CO2 to MeOH. Here we discuss various aspects of this important reduction. A centerpiece, which illustrates various general principles, is our theoretical catalytic mechanism for CO2 reduction by successive hydride transfers (HTs) and proton transfers (PTs) from the dihydropyridine PyH2 obtained by 1H+/1e–/1H+/1e– reductions of pyridine. The Py/PyH2 redox couple is analogous to NADP+/NADPH in that both are driven to effect HTs by rearomatization. High-energy radical intermediates and their associated high barriers/overpotentials are avoided because HT involves a 2e– reduction. A HT–PT sequence dictates that the reduced intermediates be protonated prior to further reduction for ultimate MeOH formation; these protonations are aided by biased cathodes that significantly lower the local pH. In contrast, cathodes that efficiently reduce H+ such as Pt and Pd produce H2 and create a high interfacial pH, both obstructing di...