Architecture of supramolecular metal complexes for photocatalytic CO2 reduction: III: Effects of length of alkyl chain connecting photosensitizer to catalyst

New Ru(II)–Re(I) binuclear complexes [{Ru(dmb)2}-LL-{Re(CO)3Cl}]2+(dmb = 4,4′-dimethyl-2,2′-bipyridine) with 1,2-bis(4′-methyl-[2,2′]bipyridinyl-4-yl)-ethane (MebpyC2H4Mebpy), 1,4-bis(4′-methyl-[2,2′]bipyridinyl-4-yl)-butane (MebpyC4H8Mebpy), and 1,6-bis(4′-methyl-[2,2′]bipyridinyl-4-yl)-hexane (MebpyC6H12Mebpy) as bridge ligands (LL) have been synthesized, and their photocatalytic activity for CO2 reduction has been investigated. The most efficient photocatalyst had MebpyC2H4Mebpy as the bridge ligand, but no difference in photocatalysis was observed between the diads with MebpyC4H8Mebpy and MebpyC6H12Mebpy. Weak interaction between the Ru and Re sites was observed only through the MebpyC2H4Mebpy ligand but not through the other bridge ligands. This interaction induces a higher reductive quenching efficiency of the 3MLCT excited state of the diad with MebpyC2H4Mebpy by the reductant, BNAH, and consequently the quantum yield of CO2 reduction is higher.