New polypyridine Ru(II) dinuclear complex capable of catalyzing the water oxidation reaction

Abstract

In natural and artificial photosynthesis, the water oxidation reaction is the bottleneck for the conversion of solar energy into chemical energy. In this work, we report the syntheses and physicochemical characterization of two new dinuclear Ru(II) complexes, with molecular formula [{Ru(tpy)Cl}2(μ-dpp)](PF6)2 (1) and [{Ru(tpy)(H2O)}2(μ-dpp)](PF6)4 (2) (with tpy=2,2’ : 6’,2”-terpyridine and dpp=2,3-bis(2-pyridyl)pyrazine). Chloro-complex (1) was used as a precursor for the aquo-complex (2) which can act as an active water oxidation reaction catalyst using Ce(IV) in CF3COOH 0.1 M as sacrificial oxidant. The mechanism and rate constants were explored by combining conventional mixing and stopped-flow experiments with spectrophotometric monitoring in the UV-visible region. DFT and TD-DFT calculations were done to support the assignments of the experimental data. From the kinetic and theoretical data obtained, we propose- that (2) catalyses water oxidation via a nucleophillic water attack mechanism (WNA). Besides, catalytic activity for (2) was evaluated from reported values of turnover frequency (TOF) and turnover number (TON) values at pH=1.