Mechanistic Insights Into Iron(II) Bis(pyridyl)amine‐Bipyridine Skeleton for Selective CO2 Photoreduction

• Published in: Angewandte Chemie International Edition Vol. 60; no. 50; pp. 26072 - 26079
• Main Authors: Wang, Xu‐Zhe, Meng, Shu‐Lin, Chen, Jia‐Yi, Wang, Hai‐Xu, Wang, Yang, Zhou, Shuai, Li, Xu‐Bing, Liao, Rong‐Zhen, Tung, Chen‐Ho, Wu, Li‐Zhu
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 06.12.2021
• Edition: International ed. in English
• Subjects: Carbon dioxide; Carbon dioxide concentration; carbon dioxide reduction; Carbon monoxide; Catalysts; Electron density; Electron transfer; Hydrogen evolution; Iron; mechanism; Photocatalysis; Photoreduction; polypyridine metal complex; Protons; Reduction; Selectivity; Synthesis gas
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202107386

A bis(pyridyl)amine‐bipyridine‐iron(II) framework (Fe(BPAbipy)) of complexes 1–3 is reported to shed light on the multistep nature of CO2 reduction. Herein, photocatalytic conversion of CO2 to CO even at low CO2 concentration (1 %), together with detailed mechanistic study and DFT calculations, reveal that 1 first undergoes two sequential one‐electron transfer affording an intermediate with electron density on both Fe and ligand for CO2 binding over proton. The following 2 H+‐assisted Fe‐CO formation is rate‐determining for selective CO2‐to‐CO reduction. A pendant, proton‐shuttling α‐OH group (2) initiates PCET for predominant H2 evolution, while an α‐OMe group (3) cancels the selectivity control for either CO or H2. The near‐unity selectivity of 1 and 2 enables self‐sorting syngas production at flexible CO/H2 ratios. The unprecedented results from one kind of molecular catalyst skeleton encourage insight into the beauty of advanced multi‐electron and multi‐proton transfer processes for robust CO2RR by photocatalysis. A polypyridine Fe‐based skeleton is reported for selective CO2‐to‐CO photoreduction even under 1 % CO2. Mechanistic insights reveal two sequential one‐electron transfer affording an intermediate with delocalized electron density on both Fe and ligand for CO2 addition. Proton‐assisted CO formation is crucial for CO2 reduction. A pendant, proton‐shuttling α‐OH group switches the transformation to H2 exclusively, which enables self‐sorting syngas formation at flexible CO/H2 ratios.