Binuclear rhenium(I) complexes for the photocatalytic reduction of CO2

Binuclear rhenium(I) complexes with 1,2-bis(4,4'-methyl-[2,2'] bipyridyl)-ethane and 1,2-bis(4,4'-methyl-[ 2,2'] bipyridyl)-dodecane as bridging ligands and their mononuclear analogues have been synthesized and characterized by their spectroscopic and electrochemical properties. First reduction potentials and luminescence properties as well as the reductive quenching of the emissive state with TEOA were not affected by the alkyl linker. By means of a detailed comparison of the photocatalytic CO2 reductions of the monometallic and the bimetallic complexes a great beneficial effect on the activity depending on the proximity of the centres was found. In high dilution the overall kinetics in the CO2 photoreduction of mononuclear complexes are clearly monometallic. If the proximity of the centres is adjusted according to the lifetime of the OER (one electron reduced species) the photocatalytic activity is greatly improved showing a clear bimetallic mechanism. In the binuclear rhenium complexes, both the facile generation of a free coordination site and binuclear interactions for effective two electron transfer can be realized.