Influence of chloro substituent on photoisomerization, redox reactions and water oxidation catalysis of mononuclear ruthenium complexes

distal-[Ru(Cl-tpy)(pynp)Cl](+) (d-2Cl) (Cl-tpy = 4'-chloro-2,2';6',2-terpyridine, pynp =2-(2-pyridy1)-1,8-naphthyridine), and distal- and proximal-[Ru(Cl-tpy)(pynp)OH2](2+) (d- and p-2H(2)O) complexes are newly synthesized and characterized to compare structures and physicochemical properties with a 2,2';6',2 ''-terpyridine (tpy) ligand derivatives of distal-[Ru(tpy)(pynp)Cl](+) (d-1Cl), distal- and proximal-[Ru(tpy) (PYnP)OH2](2+) (d- and p-1H(2)O). The equilibrium turned out to be involved in the aquation reaction of d-2Cl to d-2H(2)O in contrast to observed irreversible aquation reaction of d-1Cl under the same conditions. The kinetic analysis showed that the aquation reaction of d-2Cl is slightly slower than that of d-1Cl. The stoichiometric photoisomerization of d-2H(2)O to p-2H(2)O occurs by visible light irradiation as it is for d-1H(2)O, and (2.1%) at 520 nm for photoisomerization of d-2H(2)O was higher than that (1.5%) observed for d-1H(2)O. d-2H(2)O undergoes the two-step reaction involving the successive one-proton-coupled oneelectron reactions of the Ru-II-OH2/Ru-III-OH and Ru-III-OH/Ru-IV=O redox couples, whereas p-2H(2)O undergoes the one-step reaction involving the two-proton-coupled two-electron reaction of the RuII-OH2/Ru-IV=O redox couple. These redox potentials of d- and p-2H(2)O are higher than those for d- and p-1H(2)O at pH 7.0 by 10 similar to 50 my due to the electron-withdrawing chloro substitution. The turnover frequency (k(o2) = 6.3 x 10(-3) s(-1)) of d-2H(2)O for water oxidation was higher than that (3.9 x 10(-4) s(-1)) of p-2H(2)O by a factor of 16. k(o2) for d-2H(2)O was also 1.6 times higher than that (3.8 x 10(-3) s(-1)) for d-1H(2)O, whereas k(o2) for p-2H(2)O was 1.2 times lower than that (4.8 x 10(-4) s(-1)) for p-1H(2)O. (C) 2015 Elsevier B.V. All rights reserved.