Underevaluated Solvent Effects in Electrocatalytic CO2 Reduction by FeIII Chloride Tetrakis(pentafluorophenyl)porphyrin

Fe-III chloride tetrakis(pentafluorophenyl)porphyrin (1) is known to have poor electrocatalytic activity for the CO2-to-CO conversion in dimethylformamide. In this work, we re-examined Fe porphyrin 1 as a CO2 reduction catalyst in various solvents. Our results show that 1 displays fairly high electrocatalytic CO2-to-CO activity in acetonitrile with a turnover frequency (TOF) up to 4.2x10(4) s(-1). On the other hand, 1 shows a modest activity in propylene carbonate, and is inefficient to catalyze CO2 reduction in benzonitrile, dimethylformamide, and tetrahydrofuran. Several solvent effects were considered, but none of these effects alone can explain the observed large activity difference of 1 for CO2 reduction in these solvents. Based on the results, it is suggested that more care should be paid when comparing different CO2 reduction catalysts because solvent effects are significant and are underevaluated.