Calculation of the properties of molecules in the pyridine catalyst system for the photochemical conversion of CO2 to methanol

Bocarsly and coworkers have recently developed a catalytic system based on pyridine, C5NH5, for the photochemical conversion of CO2 to methanol and other value-added products. Other N-containing molecules such as the pyrrolide anion C 4 NH 4 - and TBD, C7N3H13, have been found to absorb CO2 but do not show reductive photochemistry. We have calculated structures, energetics, visible–UV spectra and reduction free energies for several of the species within these systems to identify those properties which are required for photochemical activity. We find it to be necessary for the species involved to form a reasonably stable complex with CO2, for this complex to have a more negative reduction free energy than free CO2 itself, for the complex to show absorption in the visible region and for light absorption by the complex to lead to N–C bond weakening.