First-Row Transition Metal Complexes for Photocatalytic and Electrocatalytic CO2 Reduction

Abstract

Converting CO2 into value-added compounds is an important approach for mitigating greenhouse gas emissions. This research investigates CO2 reduction using photochemical and electrochemical approaches. The photochemical study focuses on electron-transfer limitations arising from diffusion and collision in a typical three-component system consisting of a photosensitizer, a catalyst, and a sacrificial electron donor. To address these constraints, a single-molecule photocatalyst integrating photosensitizing and catalytic functions was developed. To realize such a system, a light-harvesting pyrene unit was incorporated into the well-studied Iminobpy framework. This ligand was then coordinated to Fe to construct a single-molecule photocatalyst system. The photocatalytic activity was discussed with respect to operation under photochemical conditions without an external photosensitizer. In the electrochemical study, heterogeneous Cu is known to stabilize key intermediates (*CO, *CHO, and *OCCO), enabling the formation of C2+ products. On this basis, it was hypothesized that extending these intrinsic properties of Cu to homogeneous systems could yield high reactivity toward CO2. Indeed, under homogeneous conditions a dinuclear Cu(I) complex has been reported to produce C2 and C3 products, supporting this view. Accordingly, Cu(I) with a d10 electron configuration was selected as the central metal, and a strongly σ-donating BpyNHC ligand was coordinated to Cu(I) to enhance metal-ligand binding, and the CO2 activation capability was discussed.