Dissection of Light‐Induced Charge Accumulation at a Highly Active Iron Porphyrin: Insights in the Photocatalytic CO2 Reduction

• Published in: Angewandte Chemie International Edition 2022-03, Vol.61 (14), p.e202117530-n/a
• Main Authors: Pugliese, Eva, Gotico, Philipp, Wehrung, Iris, Boitrel, Bernard, Quaranta, Annamaria, Ha‐Thi, Minh‐Huong, Pino, Thomas, Sircoglou, Marie, Leibl, Winfried, Halime, Zakaria, Aukauloo, Ally
• Format: Article
• Language: English
• Subjects: Carbon Dioxide; Catalysts; Catalytic activity; Chemical reduction; Hydrogen bonding; Iron; Mechanism; Photo-Reduction; Photocatalysis; Porphyrins; Redox properties; Substrates; Urea; Ureas
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202117530

Iron porphyrins are among the best molecular catalysts for the electrocatalytic CO2 reduction reaction. Powering these catalysts with the help of photosensitizers comes along with a couple of unsolved challenges that need to be addressed with much vigor. We have designed an iron porphyrin catalyst decorated with urea functions (UrFe) acting as a multipoint hydrogen bonding scaffold towards the CO2 substrate. We found a spectacular photocatalytic activity reaching unreported TONs and TOFs as high as 7270 and 3720 h−1, respectively. While the Fe0 redox state has been widely accepted as the catalytically active species, we show here that the FeI species is already involved in the CO2 activation, which represents the rate‐determining step in the photocatalytic cycle. The urea functions help to dock the CO2 upon photocatalysis. DFT calculations bring support to our experimental findings that constitute a new paradigm in the catalytic reduction of CO2. The exceptionally high performance for CO2‐to‐CO photocatalytic reduction displayed by an iron–porphyrin bearing urea groups in the second coordination sphere is the result of the interaction of CO2 with the catalyst prior to the occurrence of the second electron uptake in the catalytic cycle.