Further Investigation of a Nickel‐Based Homogeneous Water Oxidation Catalyst with Two cis Labile Sites

The reaction of N , N′ ‐dimethyl‐ N , N′ ‐bis(pyridin‐2‐ylmethyl)‐1,2‐diaminoethane ligand (L) with Ni(ClO 4 ) 2 ⋅6 H 2 O generated a complex of [NiL(H 2 O) 2 ](ClO 4 ) 2 ( 1 ) with two cis labile sites occupied by two coordinated H 2 O molecules, which can homogeneously electrocatalyze water oxidation in pH 6.5 acetate (OAc − ) buffer at room temperature. The catalytic mechanism was studied by electrochemical experiments and density functional theory calculations to elucidate the following steps: (a) one of two water molecules in 1 is exchanged by OAc − to generate [NiL(H 2 O)(OAc)] + when dissolved in OAc − buffer, (b) Ni II is directly oxidized to Ni IV and OAc − is replaced with OH − to form [Ni IV L(OH) 2 ] 2+ , and (c) a peroxide intermediate is formed through the intramolecular O−O coupling in the presence of OAc − , which undergoes further oxidation to release O 2 .