Electronic effects promoted the catalytic activities of binuclear Co(II) complexes for visible-light-driven CO 2 reduction in a water-containing system.

Under the action of a catalyst, the photoinduced reduction of CO 2 to chemicals and fuels is one of the greenest and environment-friendly approaches for decreasing atmospheric CO 2 emissions. Since the environment was affected by the greenhouse effect, scientists have never stopped exploring efficient photoinduced CO 2 reduction systems, particularly the highly desired non-noble metal complexes. Most of the currently reported complexes based on non-noble metals exhibit low catalytic activity, selectivity, and stability in aqueous systems under the irradiation of visible light. Herein, we report a new binuclear cobalt complex [Co 2 (L 1 )(OAc) 2 ](OAc) (Co2L1, HL 1 = 2,6-bis((bis(pyridin-2-ylmethyl)amino)methyl)-4-methoxyphenol), which accelerates the visible-light-driven conversion of CO 2 to CO in acetonitrile/water (4/1, v / v ) nearly 40% more than that for the previously reported [Co 2 (L 2 )(OAc) 2 ](OAc) (Co2L2, HL 2 = 2, 6-bis((bis(pyridin-2-ylmethyl)amino)methyl)-4-( tert -butyl)phenol) by our research group. It has an excellent CO selectivity of 98%, and the TON CO is as high as 5920. Experimental results and DFT calculations showed that the enhanced catalytic performance of Co2L1 is due to the electron-donating effect of a methoxy group (-OCH 3 ) in Co2L1 compared to a tertiary butyl group (-C(CH 3 ) 3 ) in Co2L2, which reduces the energy barrier of the rate-limiting CO 2 coordination step in the visible-light-driven CO 2 reduction process.