Understanding the Interplay of the Brønsted Acidity of Catalyst Ancillary Groups and the Solution Components in Iron-porphyrin-Mediated Carbon Dioxide Reduction.

The rapid and efficient conversion of carbon dioxide (CO) to carbon monoxide (CO) is an ongoing challenge. Catalysts based on iron-porphyrin cores have emerged as excellent electrochemical mediators of the two proton + two electron reduction of CO to CO, and many of the design features that promote function are known. Of those design features, the incorporation of Brønsted acids in the second coordination sphere of the iron ion has a significant impact on catalyst turnover kinetics.

Further Understanding the Roles of Solvent, Brønsted Acids, and Hydrogen Bonding in Iron Porphyrin-Mediated Carbon Dioxide Reduction.

Improving our understanding of how molecules and materials mediate the electrochemical reduction of carbon dioxide (CO) to upgraded products is of great interest as a means to address climate change. A leading class of molecules that can facilitate the electrochemical conversion of CO to carbon monoxide (CO) is iron porphyrins. These molecules can have high rate constants for CO-to-CO conversion; they are robust, and they rely on abundant and inexpensive synthetic building blocks.

Heterogeneous aqueous CO reduction by rhenium(i) tricarbonyl diimine complexes with a non-chelating pendant pyridyl group.

Electrocatalytic CO2 reduction in water using a series of chlorotricarbonylrhenium(i) diimine complexes deposited on pyrolytic graphite electrodes is described. Two known CO2 reduction catalysts (with diimine = 4,4'-di-tert-butyl-2,2'-bipyridine or 2-(2'-quinolyl)benzimidazole), that are highly active in organic solvent, proved to be only weakly active in water. In contrast, Cl(CO)3Re(L) complexes with tridentate nitrogen-containing ligands (L = 4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine or 2,6-bis(2-benzimidazolyl)pyridine) were better CO2 reduction catalysts.

Heterogeneous Aqueous CO Reduction Using a Pyrene-Modified Rhenium(I) Diimine Complex.

The development of molecular catalysts and materials that can convert carbon dioxide (CO) into a value-added product is a great chemical challenge. Molecular catalysts set benchmarks in catalyst investigation and design, but their incorporation into solid-state materials, and optimization of the electrochemical operating conditions, is still needed. For example, rhenium(I) diimine catalysts show almost quantitative selectivity for the conversion of CO to carbon monoxide (CO) in acetonitrile (MeCN), but the modification of diimine backbones can be challenging if the goal is to incorporate such molecules into materials.