The cooperative effect of imidazolium based ionic liquids on CO₂ photoreduction was investigated using [Ru(bpy)₃](PF₆)₂ and [Re(bpy)(CO)₃]Cl. Ionic liquids were employed as low-level additives (<10 % (w/v)), investigating counterion effects. The impact of different counterions could be correlated with counterion basicity, by a up to a 20-fold increase of CO formation.

Abstract

Efficiently generating C₁ building blocks from environmentally friendly carbon sources, such as through photocatalytic CO₂ reduction, is essential for fostering a sustainable circular economy. The pursuit of mild catalytic activation methods has yielded powerful catalysts that can be synergistically employed alongside various reaction media to enhance overall performance. Herein, we elucidate the influence of diverse imidazolium-based ionic liquids as additives for visible-light-driven CO₂ reduction with ruthenium(II)- and rhenium(I)-bipyridine complexes. Our investigation reveals that incorporating ionic liquids into traditional solvents at concentrations below 10 % can markedly boost CO production while suppressing H₂ generation. The best results were obtained for the highly basic ionic liquid [C₂mim][OAc], resulting in a substantial rise in CO formation from 0.3 μmol/h to 5.4 μmol/h and an increase in turnover number from 3 to 59. This study underscores the cooperative influence of imidazolium-based ionic liquids on CO₂ photoreduction while circumventing their use as primary solvents, thus offering a promising avenue for sustainable chemical synthesis.