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An Iron Porphyrin Complex with Pendant Pyridine Substituents Facilitates Electrocatalytic CO 2 Reduction via Second Coordination Sphere Effects
Author(s) -
Ramuglia Anthony R.,
Budhija Vishal,
Ly Khoa H.,
Marquardt Michael,
Schwalbe Matthias,
Weidinger Inez M.
Publication year - 2021
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.202100625
Subject(s) - chemistry , porphyrin , catalysis , pyridine , lewis acids and bases , coordination sphere , reaction rate constant , ligand (biochemistry) , resonance raman spectroscopy , coordination complex , photochemistry , medicinal chemistry , metal , kinetics , organic chemistry , raman spectroscopy , biochemistry , physics , receptor , optics , quantum mechanics
Abstract A bispyridylamine‐based hanging unit within the ligand framework of a newly synthesized iron porphyrin complex ( Py 2 XPFe ) can act, on the one hand, as a hydrogen bonding site to facilitate proton transfer in catalysis and, on the other hand, as coordination site for a second Lewis acidic metal center. The bispyridylamine group in close proximity of the iron porphyrin center is able to mediate electrocatalytic CO 2 reduction in anhydrous MeCN. The hydrogen bonding interactions within the hanging group affect the kinetics of catalysis likely through stabilization of the [Fe I (CO 2 H)] − intermediate, increasing the overall rate of catalysis when compared to the non‐functionalized analog, TMPFe (TMP=tetramesitylporphyrin). The rate constants ( k app ) of the reduction reaction were calculated using the FOWA method which resulted in a higher TOF max for the complex Py 2 XPFe compared with TMPFe in neat MeCN (1.7×10 2 vs. 1.1×10 1 s −1 ). The addition of weak Brønsted acids to the reaction mixture (TFE or PhOH) shows an increase in the rate of catalysis for both complexes, yet the Py 2 XPFe analog displays higher TOF max at each relative acid concentration, suggesting the hanging group beneficially impacts the rate of catalysis in the presence of these proton sources. The addition of Lewis acidic Sc 3+ to Py 2 XPFe also results in an increase in current density of the CO 2 reduction reaction. Resonance Raman as well as 1 H‐NMR spectroscopy indicates coordination to the pyridine substituents.