Water-Nucleophilic Attack Mechanism for the Cu^II(pyalk)₂ Water-Oxidation Catalyst

Abstract

We investigate the mechanism of water oxidation catalyzed by the CuII(pyalk)2 complex, combining density functional theory with experimental measurements of turnover frequencies, UV–visible spectra, H/D kinetic isotope effects (KIEs), electrochemical analysis, and synthesis of a derivative complex. We find that only in the cis form does CuII(pyalk)2 convert water to dioxygen. In a series of alternating chemical and electrochemical steps, the catalyst is activated to form a metal oxyl radical species that undergoes a water-nucleophilic attack defining the rate-limiting step of the reaction. The experimental H/D KIE (3.4) is in agreement with the calculated value (3.7), shown to be determined by deprotonation of the substrate nucleophile upon O–O bond formation. The reported mechanistic findings are particularly valuable for rational design of complexes inspired by CuII(pyalk)2.

Efficient Homogeneous Electrocatalytic Water Oxidation by a Manganese Cluster with an Overpotential of Only 74 mV

“…[24] Among these,t he "water nucleophilic attack" pathway is one of the most common mechanisms proposed. [4,8,25] Accordingly,aninitial Mn +3 -OH 2 ! Mn +4 =Oo xidation step should take place by ap rotoncoupled electron-transfer reaction, and this should further lead to oxygen production from water.…”

Copper Containing Molecular Systems in Electrocatalytic Water Oxidation—Trends and Perspectives

“…catalytic water oxidation potentials can be shifted significantly by applying molecular metal catalysts bearing an ionizable imidazole ligand. The fully characterized copper complex, 9, of a tetradentate ligand based on bpy, 2,2'-[(2,2'bipyridine)-6,6'-diyl]bis(propan-2-ol) (bpydipyalkH2) has been tested in water oxidation very recently [46] in context with the corresponding complex cis-Cu(pyalk)2 (10a, the catalytically active isomer of 10b) [47] utilizing 2-pyridyl-2-propanol (pyalkH), a ligand known to be very robust from molecular WOC systems involving other metals [48,49]. Both complexes contain two alkoxide and two pyridyl groups coordinated to copper, but the rigid, tetradentate ligand structure of bpydipyalk 2− in 9 impedes flexibility for the pyridines.…”

“…The related copper(II)-bis-picolinate ( Figure 8, 11) was also tested in WOC, but the observed activity at pH 12.5 could be clearly assigned to in situ forming Cu(OH)2 underlining again the unique robustness of pyalkH. Steps of the water nucleophilic attack mechanism for 10 by density functional theory (DFT) and the behavior of the closely related 9 and 11 [47]. Steps of the water nucleophilic attack mechanism for 10 by density functional theory (DFT) and the behavior of the closely related 9 and 11 [47].…”

Two Trinuclear CuII Complexes: Effect of Phosphonate Ligand on the Magnetic Property and Electrocatalytic Reactivity for Water Oxidation

“…[12][13][14][15] Among these non-precious metal complexes, owing to the multiplex coordination geometries and redox or electron transfer reactions of Cu II ion, someC u II complexes have been provedt oh aveh igh activity in electrocatalytic water oxidation. [16,17] However,m any of thesereported mononuclear Cu II water oxidation catalysts (WOC)n eed to get high oxidation state for the four electrons transfer catalytic process, which lead to low stability or high overpotentials of these catalysts. [18] Thus, to avoid this shortcoming, exploringm ultinuclear complexesi sagreat strategy,f or the accumulated charges could be spread to different metal ionsa st he OEC Mn 4 O 4 Ca cluster in nature.…”