A nickel complex, bearing a sulfur-containing macrocyclic ligand, achieved a high selectivity of 89 % towards CO and a remarkable turnover number (TON) of ca. 8000 during 8 h of visible light irradiation under CO₂ in the presence of phenol as a co-substrate, highlighting the ability of properly designed bioinspired molecular photocatalysts to efficiently activate carbon dioxide.

Abstract

Inspired by natural enzymes, this study presents a nickel-based molecular catalyst, [Ni^‖(N₂S₂)]Cl₂ (NiN₂S₂ , N₂S₂=2,11-dithia[3,3](2,6)pyridinophane), for the photochemical catalytic reduction of CO₂ under visible light. The catalyst was synthesized and characterized using various techniques, including liquid chromatography-high resolution mass spectrometry (LC-HRMS), UV-Visible spectroscopy, and X-ray crystallography. The crystallographic analysis revealed a slightly distorted octahedral coordination geometry with a mononuclear Ni²⁺ cation, two nitrogen atoms and two sulfur atoms. Photocatalytic CO₂ reduction experiments were performed in homogeneous conditions using the catalyst in combination with [Ru(bpy)₃]Cl₂ (bpy=2,2’-bipyridine) as a photosensitizer and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as a sacrificial electron donor. The catalyst achieved a high selectivity of 89 % towards CO and a remarkable turnover number (TON) of 7991 during 8 h of visible light irradiation under CO₂ in the presence of phenol as a co-substrate. The turnover frequency (TOF) in the initial 6 h was 1079 h⁻¹, with an apparent quantum yield (AQY) of 1.08 %. Controlled experiments confirmed the dependency on the catalyst, light, and sacrificial electron donor for the CO₂ reduction process. These findings demonstrate this bioinspired nickel molecular catalyst could be effective for fast and efficient photochemical catalytic reduction of CO₂ to CO.