Selective H_2 and CO production with rhenium(I) biscarbonyl complexes as photocatalyst

摘要

Rhenium(I) biscarbonyl complexes with two phosphine ligands photocatalyzed not only CO_2 reduction under CO_2 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~(?+)) is essential for the suppression of the back electron transfer from the reduced rhenium(I) complex to BNAH~(?+). ~1H, ~(13)C, and ~(31)P NMR studies under vacuum or ~(13)CO_2 atmosphere indicated that the rhenium(I) complex is relatively stable under the CO_2 reduction conditions, but it is converted to some other complexes under the H_2 evolution conditions.