Earth-abundant metal complexes are of great interest to chemists as photocatalysts reduce carbon dioxide to more valuable molecules (e.g. carbon monoxide). Using these photo-driven systems for the reduction of CO2 promotes promising advancements for effective strategies to decrease carbon footprint. These proposed systems strive to replicate natural photoreduction by directly reducing CO2. To successfully artificialize photosynthesis, a sacrificial electron donor (eD), photosensitizer (PS), and catalyst (CAT) are needed to drive the reduction reaction. Metal complexes are often used as photosensitizers and CO2 reduction catalysts due to their photophysical and photochemical properties, high selectivity, and flexible molecular design. Previous advancements in the group have reported heteroleptic CuI complexes as photosensitizers. Their unique structures adopt a diimine and diphosphine ligand that demonstrates strong oxidation properties in the excited state, which is ideal to avoid photodegradation. In this report, a library of 4, heteroleptic, diamine-diphosphine CuI complexes were synthesized and utilized as efficient photosensitizers. In addition, 11 new catalysts derived from porphyrins, 1,4,8,11-tetraazacyclotetradecane, and pyridine complexes were prepared using Fe, Cu, Mn, and Co metal centers. The efficacy of the photosensitizers and novel catalysts were assessed using existing photocatalytic systems at the visible light range (λ=420nm) and measuring the amount of CO2 reduced to CO. Complexes made from iron-tetraphenylporphyrins were shown to catalytically reduce CO2 with a greater turnover number than other known published photocatalytic systems using the same photosensitizers.

Photocatalytic CO2 reduction using complexes based on earth-abundant metals

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