KEY PROCESS OF THE PHOTOCATALYTIC REDUCTION OF CO2 USING [RE(4,4'-X-2-BIPYRIDINE)(CO)(3)PR3](- PR3 = PHOSPHORUS LIGANDS) - DARK REACTION OFTHE ONE-ELECTRON-REDUCED COMPLEXES WITH CO2() (X = CH3, H, CF3 )

Reduction of CO2 to CO was efficiently photocatalyzed by [Re(4,4'-X(2) bpy)(CO)(3)PR3](+) (X = H, Me; PR3 = P(OEt)(3), P(O-i-Pr)(3)) in quant um yields of 0.16-0.20. Complexes with CF3 as X or trialkylphosphine a s PR3 have much lower photocatalytic ability. One-electron-reduced spe cies of the complexes, which were produced by the photoinduced electro n-transfer reaction with triethanolamine, reacted with CO2 in the dark with rate constants of 3.5 x 10(-4)-1.9 x 10(-2) M-1 s(-1). The faste r the rate of this process, the higher the quantum yield of CO formati on. The calculated amount of CO formation, based on the assumption tha t the process gives CO quantitatively, was similar to the actually obs erved amount under various conditions. This is consistent with the the rmal process being one of the rate-limiting steps in the photocatalyze d reduction of CO2 by the rhenium complexes.