Photocatalytic reduction of CO2 to CO by a dinuclear carbonyl polypyridyl rhenium(I) complex

The new dinuclear Re(I) complex, [ReCl(CO)3(μ-tptzH)Re(CO)3], where tptzH− is 2,4,6-tri(pyridine-2-yl)-2H-1,3,5-triazine-1-ide has been synthesized and characterized by spectroscopic methods and X-ray crystallography. During the preparation of the dinuclear complex, a carbon atom of the triazine ring in the tptz bridging ligand is saturated by two consecutive redox reactions. It is worthy to mention that this partial saturation of tptz to tptzH− is the first example of the saturation of a triazine ring without a nucleophilic attack. The photocatalytic activity of the dinuclear complex for the photochemical reduction of CO2 to CO has been also investigated. The photocatalytic reduction of CO2 was carried out in three different conditions and the turnover number for the CO formation in the TEOA/DMF/NEt4Cl mixture reached a maximum of 15.8, which was 1.17 and 1.71 times the turnover numbers for the TEA/DMF and TEOA/DMF mixtures, respectively. The theoretical calculations show that the metal moiety containing the chloro ligand (ReCl(CO)3) is the most likely active site for the photocatalytic reduction of CO2. Finally, a photocatalytic cycle was proposed for the reduction of CO2 on the metal moiety containing the chloro ligand.

Graphical abstractThe dinuclear Re(I) complex, [ReCl(CO)3(μ-tptzH)Re(CO)3], where tptzH− is 2,4,6-tri(pyridine-2-yl)-2H-1,3,5-triazine-1-ide has been synthesized and characterized by spectroscopic methods and X-ray crystallography. During the preparation of the dinuclear complex, a carbon atom of the triazine ring in the tptz bridging ligand is saturated by two consecutive redox reactions. This partial saturation is the first example of the saturation of a triazine ring without a nucleophilic attack.Figure optionsDownload full-size imageDownload as PowerPoint slide