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(ClO4)(2)6H(2)O generated a complex of [NiL(H2O)(2)](ClO4)(2) (1) with two cis labile sites occupied by two coordinated H2O molecules, which can homogeneously electrocatalyze water oxidation in pH6.5 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(H2O)(OAc)](+) when dissolved in OAc- buffer, (b)Ni-II is directly oxidized to Ni-IV and OAc- is replaced with OH- to form [(NiL)-L-IV(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.