Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 60, Issue 23, Pages 12742-12746Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202102523
Keywords
atropisomers; molecular electrocatalysis; oxygen reduction; selectivity control; steric effect
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Funding
- National Natural Science Foundation of China [21773146]
- Fok Ying-Tong Education Foundation for Outstanding Young Teachers in University
- Fraunhofer Internal Programs [Attract 097-602175]
- Deutsche Forschungsgemeinschaft [AP242/2-1, EXC 2033-390677874 - RESOLV]
- Fundamental Research Funds for the Central Universities
- Shaanxi Normal University
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This study demonstrates the control of ORR selectivity of Co porphyrins by tuning steric effects, with αβαβ isomer catalyzing 2 e(-) ORR and αααα isomer improving 4 e(-) ORR selectivity. This finding expands the pathway for modulating molecular selectivity in catalytic performance.
Achieving a selective 2 e(-) or 4 e(-) oxygen reduction reaction (ORR) is critical but challenging. Herein, we report controlling ORR selectivity of Co porphyrins by tuning only steric effects. We designed Co porphyrin 1 with meso-phenyls each bearing a bulky ortho-amido group. Due to the resulted steric hinderance, 1 has four atropisomers with similar electronic structures but dissimilar steric effects. Isomers alpha beta alpha beta and alpha alpha alpha alpha catalyze ORR with n=2.10 and 3.75 (n is the electron number transferred per O-2), respectively, but alpha alpha beta beta and alpha alpha alpha beta show poor selectivity with n=2.89-3.10. Isomer alpha beta alpha beta catalyzes 2 e(-) ORR by preventing a bimolecular O-2 activation path, while alpha alpha alpha alpha improves 4 e(-) ORR selectivity by improving O-2 binding at its pocket, a feature confirmed by spectroscopy methods, including O K-edge near-edge X-ray absorption fine structure. This work represents an unparalleled example to improve 2 e(-) and 4 e(-) ORR by tuning only steric effects without changing molecular and electronic structures.
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