A macrocyclic iron complex bearing a redox-active pentadentate N5 ligand (2,13-dimethyl-3,6,9,12,18-pentaazabicyclo- [12.3.1]octadeca-1(18),2,12,14,16-pentaene; FeN5) has been reported to catalyze CO2 reduction to CO in a photochemical system with minimal competition from hydrogen evolution. Here, this complex is investigated by cyclic voltammetry to better understand its lack of activity for hydrogen evolution. Upon acid titration, a prewave which is prominent at low acid concentrations and saturates as acid concentration is increased as well as a current enhancement around the Fe(II/I) couple are observed. A prewave in a catalytic voltammogram can be suggestive of total catalysis (Zone KT2) which leads to an S-shaped curve at high acid concentrations. The persistence of the peak-shaped voltammograms at high acid concentrations and the total electrons passed in the prewave here suggest hydrogenation and/or decomposition of initial molecular species to electrodeposited species. These observations are in parallel with the loss in reversibility of the Fe(III/II) couple and the appearance of new oxidative feature. Although initial rinse tests do not point towards strongly-adsorbed species, more definitive answers to complex modification and mechanism will be sought via Infrared spectroelectrochemistry (IR-SEC) and electron microscopy studies.

Electrochemical modification of a macrocyclic iron catalyst

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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