Selective H2 and CO production with rhenium(I) biscarbonyl complexes as photocatalyst

Rhenium(I) biscarbonyl complexes with two phosphine ligands photocatalyzed not only CO2 reduction under CO2 atmosphere but also H-2 evolution under Ar. The reductant 1-benzyl-1,4-dihydronicotinamide (BNAH) worked only as a one-electron donor, and it was quantitatively converted to its corresponding oxidized dimer (BNA(2)). The photocatalytic reactions required addition of a base such as triethanolamine, because deprotonation from the oxidized BNAH (BNAH(aEuro cent+)) is essential for the suppression of the back electron transfer from the reduced rhenium(I) complex to BNAH(aEuro cent+). H-1, C-13, and P-31 NMR studies under vacuum or (CO2)-C-13 atmosphere indicated that the rhenium(I) complex is relatively stable under the CO2 reduction conditions, but it is converted to some other complexes under the H-2 evolution conditions.