Photochemistry of [Re(bipy)(CO)(3)(PPh(3))](+) (bipy equals 2,2'-bipyridine) in the presence of triethanolamine associated with photoreductive fixation of carbon dioxide: Participation of a chain reaction mechanism

The complex fac-[Re(bipy)(CO)(3)(PPh(3))](+) 1(+) (bipy = 2,2'-bipyridine) was converted into a formate complex fac[Re(bipy)(CO)(3)(OC(O)H)}] 2 in a 52.2% yield by irradiation in the presence of triethanolamine (teoa) and CO2. This photochemical fixation of CO2 proceeds via a unique reaction mechanism: (i) irradiation of 1(+) in teoadimethylformamide (dmf) resulted in the efficient formation of fac-[Re(bipy)(CO)(3)(teoa)](+) 3(+)-and fac-; [Re(bipy)(CO)3(dmf)](+) 4(+) in a quantum yield of 16.9; (ii) the ligand substitution was explained in terms of a chain mechanism involving an initial electron transfer from teoa to excited 1(+), followed by substitution of the PPh, ligand of 1 with teoa and dmf to give 3 and 4; subsequent electron exchange of 3 and 4 with 1(+) leads to the formation of 3(+) and 4(+) accompanied by the regeneration of 1; (iii) the formate complex 2 was formed in a quantum yield of 1.1 x 10(-3) upon excitation of 3(+) and 4(+) in the presence of CO2; (iv) further irradiation after the formation of 2 resulted in the photocatalytic reduction of CO2 to CO in a quantum yield of 0.05.