The Importance of Temperature Control for the Synthesis of Fluorinated Phenanthroline-Extended Porphyrins and the Evaluation of Their Photocatalytic CO2Reduction Ability

Abstract

The synthesis and characterization of new fluorinated meso-aryl-substituted phenanthroline-extended porphyrin complexes is reported. The synthesis of the ligand(s) is challenging as it includes the handling of a temperature sensitive amino-substituted porphyrin intermediate. Thus, this is the first report on a high-yielding synthesis of π-extended porphyrinic systems involving fluorinated substituents. In addition, preliminary studies on the light-induced catalytic CO2 reduction have been performed in DMF solution. Former studies have shown that at least a double reduced species of the complexes has to be formed before the catalytic reaction takes place. Electrochemical investigations have been performed and confirm more positive reduction potentials for the fluorinated compounds compared to non-fluorinated systems. The more positive reduction potentials should be advantageous to generate quickly the catalytically active species for CO2 reduction, which theoretically can also lead to higher turnover numbers. Catalytic investigations on the light-driven CO2 reduction, using in particular cobalt complexes, reveals, in fact, a lower catalytic activity compared to the non-fluorinated systems. Presumably, the stability of the catalytically active reduced species is also influenced by introduction of fluorinated substituents that allows different side reactions to occur.