Reported are mechanistic studies of the photoinduced reduction of carbon dioxide to carbon monoxide mediated by ReBr(CO),(bpy) (bpy is 2,2'-bipyridine). Water, ethanol, and perchlorate ion enhance the intensity of luminescence from the Re-to-bpy charge-transfer excited state, whereas bromide ion and triethylamine (TEA) quench this emission. In the case of the amine, the quenching process leads to prompt formation of [ReBr(CO),(bpy)]-. Additional, slower production of this 19e species by reduction of the parent complex by a TEA-derived radical is unimportant. Water and ethanol lower the quantum efficiency of CO formation, whereas Br-has little effect. Reduction of bicarbonate ion to CO can be excluded as an important pathway in the system. Patirradiation spectral changes occur over several hours, but the chemistry responsible for this behavior is unrelated to CO formation.
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