We present two as-synthesized Fe(II)-based molecular catalysts with 1,10-phenanthroline (phen) ligands; Fe(phen)₃Cl₂ (1) and [Fe(phen)₂(CH₃CH₂OH)Cl]Cl (2), and their robust catalytic properties for the conversion of CO₂ to CO in DMF/TEOA (DMF = N,N’-dimethylformamide; TEOA = triethanolamine) solution containing Ru(bpy)₃²⁺ and BIH (1,3-dimethyl-2-phenyl-2,3- dihydro-1H-benzo-[d]-imidazole). High turnover numbers (TONs) of 19,376 were achieved with turnover frequencies (TOFs) of 3.07 s⁻¹ for complex 1 (1.5 × 10⁻⁷ M). A quantum efficiency of 0.38% was observed after 5 h irradiated by 450 nm monochromatic light. The generation rate of CO₂ and H₂ were tuned by optimizing the experimental conditions, resulting in a high CO selectivity of 90%. The remarkable contribution of the photosensitizer to the total TON_CO was found being 19.2% (as shown by tests under similar conditions without catalysts) when BIH was employed as a sacrificial electron donor. The product selectivity in complex 2 reached 95%, and the corresponding TON_CO and TOF_CO were 33,167 and 4.61 s⁻¹ in the same concentration with complex 1 used as catalyst; respectively. This work provides guidance for future designs of simple, highly efficient and selective molecular catalytic systems that facilitate carbon-neutral solar-to-fuel conversion processes

To study the effects of substituent electron - donor on the efficiency of manganese - based photocatalyst, four different Mn(II) complexes have been used as catalysts, the ligands including phenanthroline with methyl and phenanthroline without methyl, bipyridine with methyl and bipyridine without methyl. [Ru(bpy)3]2+ ([Ru]) has been used as a photosensitizer with triethanolamine (TEOA) in CH3CN solution for the photochemical reduction of CO2 to CO under visible light irradiation. The turnover numbers of the four catalysts are found to be 99, 717, 167, and 1038, respectively. The experiments have revealed that the catalytic effects of phenanthroline-type complexes are superior to the dipyridyl-type complexes, which has no methyl groups on their ligand. For both phenanthroline-type and dipyridyl-type complexes, the catalysts with a methyl group on the ligand shows good performance than those without a methyl group. The phenanthroline-type complexes with methyl groups has displayed the best catalytic activity among these four catalysts.