Photocatalyses of Ru(II)-Re(I) binuclear complexes connected through two ethylene chains for CO2 reduction

We synthesized two novel supramolecular photocatalysts for CO2 reduction [Ru(BL1)Re(CO)(3)Cl](2+) (1(2+)) and [Ru(BL1)Re(CO)(2){P(P-F-C6H4)(3))(2)](3+) (3(3+)), where BL1 is two 2,2'-bipyridine moieties connected through two ethylene chains. Compared to the corresponding supramolecular photocatalysts (2(2+), 4(3+)) with only one ethylene chain in the bridging ligand (BL2), these complexes had stronger electronic interactions between the Ru and Re units through the two ethylene chains, which strengthened the oxidation power of the excited Ru unit. Although BL1 compounds functioned as photocatalysts for CO2 reduction by selectively providing CO2 their photocatalyses were very different, especially, when compared with BL2 compounds. In the case of 1(2+), the quantum yield of CO formation (Phi(CO)) was larger than that of the corresponding BL2 compound. Conversely, Phi(CO) of the system using 3(3+) was approximately 40% less than the corresponding BL2 compound. The reasons for these differences were successfully clarified through mechanistic studies of these photocatalytic CO2 reductions. (C) 2016 Elsevier Inc. All rights reserved.