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A mechanistic study of the photoinduced reduction of carbon dioxide to carbon monoxide in the triethanolamine /dimethylformamide/ReBr(CO)3(bpy) (bpy is 2,2'-bipyridine) system is described. Continuous photolysis at 436 nm results in the highly specific formation of CO with a quantum yield, that reaches 0.15. The value of €0 decreases with increasing triethanolamine concentration in the range 0.75-3.8 M; addition of 10% water to the solvent medium also lowers 0co-Luminescence measurements reveal that triethanolamine reductively quenches the Re-to-bpy charge-transfer excited state of ReBr(CO)3(bpy) with a rate constant of 6 X 107 M"1 2s'1, whereas C02 undergoes no discernible interaction with the photoexcited complex. Formation and decay of the initial reduction product [ReBr(CO)3(bpy)]~h ave been observed in flash photolysis experiments. The amount of [ReBr(CO)3(bpy)]' produced correlates with the value of 0CO, thereby implicating this 19e complex in the mechanism of C02 reduction. Evidence that [ReBr-(CO)3(bpy)]' reacts directly with C02 has been obtained, although the identity of the resulting product is unknown at present.

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