T. Ogata et al., PHENAZINE-PHOTOSENSITIZED REDUCTION OF CO2 MEDIATED BY A COBALT-CYCLAM COMPLEX THROUGH ELECTRON AND HYDROGEN-TRANSFER, Journal of physical chemistry, 99(31), 1995, pp. 11916-11922
Photoreduction of carbon dioxide (CO2) to formate (HCO2-) can be achie
ved by UV-irradiation of the system involving phenazine (Phen) as a ph
otosensitizer, a cobalt complex of cyclam (Co(III)L, L = cyclam = 1,4,
8, 11-tetraazacyclotetradecane) as an electron mediator, and triethyla
mine (TEA) as an electron donor. Reduction products from the system ar
e HCO2- and a small quantity of CO and H-2. The quantum yield is 0.07
for the formation of HCO2- at lambda = 313 nn. Preferential electron t
ransfer from the photoformed radical anion of phenazine (Phen(.-)) to
Co(III)L is confirmed by EPR analysis and the reaction between Phen(.-
) and Co(III)L with a second-order rate constant, k = 4.3 x 10(9) M(-1
) s(-1). The resulting Co(II)L reacts with phenazinyl radical,1 giving
[CoL(H)](2+) by hydrogen transfer from phenazinyl radical. The effect
ive insertion of a CO2 molecule into [CoL(H)](2+) yields HCO2- selecti
vely.