Electrocatalytic Reduction of CO2 and H2O with Zn(II) Complexes Through Metal-Ligand Cooperation.

Air and water-stable zinc (II) complexes of neutral pincer bis(diphenylphosphino)-2,6-di(amino)pyridine ("PN3P") ligands are reported. These compounds, [Zn(κ2-2,6-{Ph2PNR}2(NC5H3))Br2] (R=Me, 1; R=H, 2), were shown to be capable of electrocatalytic reduction of CO2 at -2.3 V vs. Fc+/0 to selectively yield CO in mixed water/acetonitrile solutions. These complexes also electrocatalytically generate H2 from water in acetonitrile solutions, at the same potential, with Faradaic efficiencies of up to 90 %. DFT computations support a proposed mechanism involving the first reduction of 1 or 2 occurring at the PN3P ligand. Furthermore, computational analysis suggested a mechanism involving metal-ligand cooperation of a Lewis acidic Zn(II) and a basic ligand.

Electrocatalytic reduction of CO2 to CO and HCO2- with Zn(II) complexes displaying cooperative ligand reduction.

Air-stable zinc(II) pyridyl phosphine complexes, [Zn(κ2-2,6-{Ph2PNMe}2(NC5H3))Br2] (1) and [Zn(κ2-2-{Ph2PNMe}(NC5H3))Br2] (2) are reported and 1 was capable of electrocatalytic reduction of CO2 at -2.3 V vs. Fc+/0 to yield CO/HCO2H in mixed water/acetonitrile solutions. DFT computations support a proposed mechanism involving electron transfer reactions from a species with the anionic PN3P ligand ("L-/Zn(II)").

An integrated Re(i) photocatalyst/sensitizer that activates the formation of formic acid from reduction of CO2.

The complex cis-[Re(bpy)2(CO)2]+OTf- (1+OTf-) is an integrated photosensitizer/catalyst for the selective visible light promoted photocatalytic reduction of CO2. The formation of formic acid is unique among this class of Re catalysts, which yield CO as the selective product. A supplemental photosensitizer, Ru(bpy)32+, considerably enhanced the performance of this catalyst.