Photocatalytic CO2 reduction reaction on [TM(tpy)(ppy)]0 (TM = Re and Rh) species with a square pyramidal nitrogen-coordinated structure: a computational study.

The photocatalytic performance of d-block metal complexes with unsaturated coordination circumstances after one dative-bond cleavage has become an emerging domain. Especially, the photocatalytic CO₂ reduction reaction (CO₂RR) on the active center of d-block metals in tridentate/bidentate ligands with square pyramidal nitrogen-coordinated atoms has been reported. In this study, the photocatalytic CO₂RR performance of six metals in [TM(tpy)(ppy)]⁰ as possible active candidates (TM = Fe, Co, Ru, Rh, Re, and Ir) for CO production was evaluated in detail using DFT computations. The theoretical data demonstrate that the screened-out [Re(tpy)(ppy)]⁰ exhibits superior photocatalytic CO₂RR activity to other identical species due to the only downhill process for CO₂ activation and the second one-electron photoreduction step as its lowest rate-limiting step of 38.41 kcal mol^-1. Besides, [Rh(tpy)(ppy)]⁰ also possesses comparable CO₂RR activity theoretically with the reported [Ir(tpy)(ppy)]⁰. In addition, our calculations reveal that the electron-transfer processes along the CO₂RR pathway on [TM(tpy)(ppy)]⁰ are mainly sourced from the tpy ligand. Therefore, our study paves the way for exploring the active species of metal complexes as photocatalysts for the CO₂RR before executing the targeted experimental exploration on their precursor complexes to discover other qualified ones.