PHOTOCHEMISTRY OF [RE(BIPY)(CO)(3)(PPH(3))](-BIPYRIDINE) IN THE PRESENCE OF TRIETHANOLAMINE ASSOCIATED WITH PHOTOREDUCTIVE FIXATION OF CARBON-DIOXIDE - PARTICIPATION OF A CHAIN-REACTION MECHANISM() (BIPY EQUALS 2,2')

The complex fac-[Re(bipy)(CO)(3)(PPh(3))](+) 1(+) (bipy = 2,2'-bipyrid ine) 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 uni que reaction mechanism: (i) irradiation of 1(+) in teoadimethylformami de (dmf) resulted in the efficient formation of fac-[Re(bipy)(CO)(3)(t eoa)](+) 3(+)-and fac-; [Re(bipy)(CO)3(dmf)](+) 4(+) in a quantum yiel d of 16.9; (ii) the ligand substitution was explained in terms of a ch ain mechanism involving an initial electron transfer from teoa to exci ted 1(+), followed by substitution of the PPh, ligand of 1 with teoa a nd 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 regener ation 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 CO 2; (iv) further irradiation after the formation of 2 resulted in the p hotocatalytic reduction of CO2 to CO in a quantum yield of 0.05.