Substantial improvement in the efficiency and durability of a photocatalyst for carbon dioxide reduction using a benzoimidazole derivative as an electron donor

•1,3-Dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) was used as reductant.•The photocatalytic activity Ru–Re for CO2 reduction was drastically improved.•ΦCO=0.45, TONCO=3029, TOFCO=35.7min−1.•These are the best photocatalysis results using supramolecular complexes. We found a very suitable sacrificial electron donor, 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH), to demonstrate the proper ability of a Ru(II)–Re(I) supramolecular photocatalyst for CO2 reduction. The efficiency, durability, and rate of the photocatalytic reaction were drastically improved (ΦCO=0.45, TONCO=3029, TOFCO=35.7min−1) using BIH as an electron donor compared to that using 1-benzyl-1,4-dihydronicotinamide as an electron donor (ΦCO=0.15, TONCO=207, TOFCO=4.7min−1). The reasons for the improvement were clarified based on the detailed mechanistic investigations.