Electrochemical Water Oxidation Catalyzed by N₄‐Coordinate Copper Complexes with Different Backbones: Insight into the Structure‐Activity Relationship of Copper Catalysts

Abstract

Copper complexes with a general formula of [(L)Cu(OH2)](BF4)2 (1, L1=N,N′‐dimethyl‐N,N′‐bis(pyridin‐2‐ylmethyl)‐1,2‐diaminoethane; 2, L2=N,N′‐bis(pyridin‐2‐ylmethyl)piperazine); 3, L3=N,N′‐bis(pyridin‐2‐ylmethyl)diazepane) were prepared as molecular catalysts for oxygen evolution reaction. These catalysts have the same first coordination environment but different backbones of diamine‐dipyridine N4‐ligands. Single crystal X‐ray diffraction studies on the molecular structures of 1–3 revealed that the backbone rigidity of the N4‐ligand has apparent influence on the Npy−Cu−N′py open angle of copper complexes. Comparative studies manifested that the subtle structural change caused by the backbone rigidity of N4‐ligands has an important influence on the catalytic performance and reaction pathway of copper catalysts for electrochemical water splitting.

Electrocatalytic water oxidation by copper(ii) complexes with a pentadentate amine-pyridine ligand

“…The formation of the O–O bond by the reaction of Cu( iv )O species with the water molecule is widely regarded as the rate-limiting step for oxygen evolution via a mononuclear catalytic mechanism. 10,13,14,22 Electrochemical measurements reveal that the N–H structure of the amine containing ligand of complex 2 is favourable for the generation of [Cu IV O(L)] 2+ species. Additionally, the electron-withdrawing group on the ligand results in higher reactivity of some MO intermediates (M is the transition metal) in the water oxidation catalytic cycle mediated by the metal complex while the electron-donating group on the ligand is exactly the opposite.…”

“…9 Moreover, research on the influence of the first- and second-coordination spheres on metal complexes for catalytic water oxidation can provide guidelines for the design of efficient catalysts for other catalytic systems, such as artificial photosynthesis. 10,11…”

“…Also, factors such as structure flexibility, electronic properties and the steric effect have a determining influence in terms of the reaction mechanism. 10,27–29 However, the associated effect of coordinating –NH groups on Cu-based homogeneous WOCs receives much less attention. 22,30…”

Homogeneous Water Oxidation Catalyzed by First‐Row Transition Metal Complexes: Unveiling the Relationship between Turnover Frequency and Reaction Overpotential

“…[190] Shen et al also reported a Cu complex with a diamine-dipyridine ligand (Cu-24) that promoted the electrochemical oxygen evolution reaction. [191] Meyer and co-workers explored the electrochemical properties of a single-site Cu complex (Cu-25) with a rugged ligand. [192]…”

Ligand Radical Mediated Water Oxidation by a Family of Copper o-Phenylene Bis-oxamidate Complexes

“…[28][29][30][31][32][33][34] Recently, copper complexes have joined the short list of molecular catalysts for the WOR. [35][36][37][38][39][40][41][42][43] Reasons behind this stem from the copper oxygenase functions where O 2 activation leads to the cleavage of the O-O bond leading to highly oxidized copper species. 44 Hence reversing the activation steps from H 2 O to form O-O bond is an attractive perspective.…”