Methane Formation Induced via Face-to-Face Orientation of Cyclic Fe Porphyrin Dimer in Photocatalytic CO Reduction.

Iron porphyrins are known to provide CH as an eight-electron reduction product of CO in a photochemical reaction. However, there are still some aspects of the reaction mechanism that remain unclear. In this study, we synthesized iron porphyrin dimers and carried out the photochemical CO reduction reactions in -dimethylacetamide (DMA) containing a photosensitizer in the presence of 1,3-dimethyl-2-phenyl-2,3-dihydro-1-benzo[d]imidazole (BIH) as an electron donor. We found that, despite a low catalytic turnover number, CH was produced only when these porphyrins were facing each other. The close proximity of the cyclic dimers, distinguishing them from a linear Fe porphyrin dimer and monomers, induced multi-electron CO reduction, emphasizing the unique role of their structural arrangement in CH formation.