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Ligand Controls the Activity of Light‐Driven Water Oxidation Catalyzed by Nickel(II) Porphyrin Complexes in Neutral Homogeneous Aqueous Solutions
Author(s) -
Liu Chengyu,
Bos Daan,
Hartog Barthold,
Meij Dennis,
Ramakrishnan Ashok,
Bonnet Sylvestre
Publication year - 2021
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202103157
Subject(s) - porphyrin , photocatalysis , catalysis , photosensitizer , aqueous solution , chemistry , electron acceptor , photochemistry , nickel , turnover number , electron donor , electron transfer , ligand (biochemistry) , inorganic chemistry , organic chemistry , biochemistry , receptor
Finding photostable, first‐row transition metal‐based molecular systems for photocatalytic water oxidation is a step towards sustainable solar fuel production. Herein, we discovered that nickel(II) hydrophilic porphyrins are molecular catalysts for photocatalytic water oxidation in neutral to acidic aqueous solutions using [Ru(bpy) 3 ] 2+ as photosensitizer and [S 2 O 8 ] 2− as sacrificial electron acceptor. Electron‐poorer Ni‐porphyrins bearing 8 fluorine or 4 methylpyridinium substituents as electron‐poorer porphyrins afforded 6‐fold higher turnover frequencies (TOFs; ca. 0.65 min −1 ) than electron‐richer analogues. However, the electron‐poorest Ni‐porphyrin bearing 16 fluorine substituents was photocatalytically inactive under such conditions, because the potential at which catalytic O 2 evolution starts was too high (+1.23 V vs. NHE) to be driven by the photochemically generated [Ru(bpy) 3 ] 3+ . Critically, these Ni‐porphyrin catalysts showed excellent stability in photocatalytic conditions, as a second photocatalytic run replenished with a new dose of photosensitizer, afforded only 1–3 % less O 2 than during the first photocatalytic run.