Selectivity control of CO versus HCOO− production in the visible-light-driven catalytic reduction of CO2 with two cooperative metal sites

It is highly desirable to discover molecular catalysts with controlled selectivity for visible-light-driven CO2 reduction to fuels. In the design of catalysts employing earth-abundant metals, progress has been made for CO production, but formate generation has been observed more rarely. Here, we report a binuclear Co complex bearing a bi-quaterpyridine ligand that can selectively reduce CO2 to HCOO− or CO under visible light irradiation. Selective formate production (maximum of 97%) was obtained with a turnover number of up to 821 in basic acetonitrile solution. Conversely, in the presence of a weak acid, CO2 reduction affords CO with high selectivity (maximum of 99%) and a maximum turnover number of 829. The catalytic process is controlled by the two Co atoms acting synergistically, and the selectivity can be steered towards the desired product by simply changing the acid co-substrate. Performing photocatalytic CO2 reduction in a selective fashion with molecular catalysts represents a considerable challenge. Here, a binuclear cobalt complex featuring a bi-quaterpyridine ligand is developed that can selectively afford either carbon monoxide or formate by selection of the reaction medium acidity.