Pendant Catechol\nGroup Improves the Performance of\nIron Porphyrin CO<sub>2</sub> Reduction Catalysts

In this work, we prepared chloroiron 5-(2,3-dihydroxyphenyl)-10,15,20-triphenyl\nporphyrin (Fe(Cat)TPP) and investigated its properties for CO<sub>2</sub> reduction. Iron porphyrins make up a class of compounds that\nare known to efficiently convert CO<sub>2</sub> to carbon monoxide\n(CO). There exist many different porphyrin derivatives that reduce\nCO<sub>2</sub> with some leading examples, including structures that\nplace hydrogen bond donors and/or proton donors near the iron ion\nactive site. Here, the presence of an internal H-bond in the 2,3-dihydroxyphenyl\ngroup in Fe(Cat)TPP increases the observed CO<sub>2</sub> reduction\nrate constants by a factor of 10 with respect to the parent chloroiron-5,10,15,20-tetraphenyl\nporphyrin and a factor of 3 with respect to a porphyrin with only\none hydroxyphenyl (i.e., chloroiron 5-(2-hydroxyphenyl)-10,15,20-triphenyl\nporphyrin). The presence of the internal H-bond is proposed to facilitate\nthe proton-coupled electron transfer process of carbon–oxygen\nbond breaking, which has been established as the rate-limiting step\nin CO<sub>2</sub>-to-CO conversion. The Fe(Cat)TPP molecule, and those\nlike it, are important to improving designs of molecular electrocatalysts.\nThe ongoing development of platforms that can rapidly and selectively\nmediate the electrochemical transformation of carbon dioxide (CO<sub>2</sub>) to valorized products is a great technical challenge.