Light-driven CO2 reduction with substituted imidazole-pyridine Re catalysts favoring formic acid production

TL;DR

Scientists developed new light-driven catalysts that efficiently convert CO2 into formic acid, a useful chemical product, under specific conditions.

Contribution

The study introduces substituted imidazole-pyridine Re catalysts that show high selectivity and turnover for formic acid production.

Findings

The A-π complex RC4 achieved a turnover number of 844 with 86% carbon selectivity for formic acid.

RC4 outperformed other catalyst types in formic acid production under photocatalytic conditions.

The benchmark catalyst Re(bpy)(CO)3Br produced no formic acid under the same conditions.

Abstract

Removing carbon dioxide from the atmosphere is an attractive way to mitigate the greenhouse gas effect that contributes to climate change. A series of donor-pi (D-π), acceptor-pi (A-π), and π Re(i) pyridyl imidazole complexes have been synthesized and examined under photocatalytic conditions for the photocatalytic reduction of CO2. The catalytic activity of the complexes was further supported by cyclic voltammetry through the presence of a catalytic current under CO2 atmosphere. The D-π, π, and A-π complexes were studied to elucidate the effects of incorporating conjugated electron donating vs. withdrawing groups on the catalytic rates and product selectivity. The synthesized complexes were compared with Re(bpy)(CO)3Br (where bpy is 2,2′-bipyridine), the benchmark catalyst for this transformation. Remarkably, the complex with A-π pendant (RC4) outperformed the π (RC2–3) and D-π (RC5) complexes for the production of formic acid (HCO2H) in the presence of photosensitizer [Ru(bpy)3]2+ and sacrificial electron donor BIH (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]-imidazoline). Among the investigated catalysts, RC4 with the A-π pendant showed the highest turnover number (TON) value of 844 for HCO2H production with 86% carbon selectivity. In stark contrast to the imidazole-pyridine based catalysts reported here that favor formic acid as a product, Re(bpy)(CO)3Br generated no formic acid under the same conditions. The imidazole-pyridine complexes also function as catalysts for CO2 reduction without an added photosensitizer, however, the TON values under self-sensitized conditions are poor.

Novel imidazole-pyridine photocatalysts favoring selectivity for formic acid production.

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