Highly Efficient Supramolecular Photocatalysts for CO₂ Reduction with Eight Carbon-Carbon Bonds between a Ru(II) Photosensitizer and a Re(I) Catalyst Unit

Supramolecular photocatalysts, wherein redox photosensitizer(PS)and catalyst (CAT) molecules are connected to each other, have beenextensively studied because of their high photocatalytic activityin both homogeneous and heterogeneous environments compared with thecorresponding mixed systems of separated PS and CAT. A supramolecularphotocatalyst RuC2PhC2Re, wherein [Ru(diimine)(3)](2+) redox PS and fac-[Re(diimine)(CO)(3){OC(O)OCH2CH2N(CH2CH2OH)(2)}] CAT units were spatially separated by abridging ligand p(-C2H4)(2)Ph consisting of 8 C-C bonds including a p-phenylene ring, was developed. Although the rate of intramolecularelectron transfer of RuC2PhC2Re from one-electron-reducedRu unit to the Re unit, which is a critical process of photocatalysisproceeding through the bond mechanism, was slower than that of RuC2Re having shorter bridging ligand with an ethylene chain,it could reduce CO2 to CO with higher durability (TON =3880) than RuC2Re (TON = 2800). These results clearlysuggest that the PS and CAT units can be separated further withoutlowering photocatalysis of supramolecular photocatalysts because therate of intramolecular electron transfer is much faster, even in RuC2PhC2Re, than that of the subsequent processes in photocatalyticCO(2) reduction.