Effect of Quinoline Substitution on Water Oxidation by [Ru(Ql–tpy)(bpy)(OH 2 )](PF 6 ) 2

The new ligand Ql‐tpy (8‐(2,6‐di(pyridin‐2‐yl)pyridin‐4‐yl)quinoline) and the corresponding aqua complex [Ru(Ql‐tpy)(bpy)(OH 2 )](PF 6 ) 2 ( 1 ) have been synthesized and characterized by the different spectroscopic methods. This complex shows two pK a values, pK a 1 due to the deprotonation from the protonated N atom located on the quinoline moiety at 3.0 and another pK a 2 at 10.5 due to the deprotonation from aqua ligand. The catalytic activity of the complex 1 towards water oxidation was studied in CF 3 SO 3 H solution (pH ≈ 1) using Ce IV as an oxidant. The free N atom of the substituted quinoline moiety of the complex gets protonated at pH ≈ 1 and acts as an electron withdrawing group instead of electron donating group. Due to the electron withdrawing effect it shows a lower catalytic activity towards chemical water oxidation having turnover number (TON) of 18 (out of 25) and initial turnover frequency (TOF) 0.003 s −1 as compared to the previously reported [Ru II (QCl‐tpy)(bpy)(H 2 O)] 2+ complex.