Unexpected Promotional Effects of Alkyl‐Tailed Ligands and Anions on the Electrochemical Generation of Ruthenium(IV)‐Oxo Complexes

Electro‐generation of RuIV=O species from the RuII‐aqua complex is a crucial step to excel the electrocatalytic water oxidation performance of ruthenium oxo complexes. We report herein the synthesis and X‐ray crystal structural characterizations of new RuII‐aqua complexes containing N‐substituted 2,2′‐dipyridylamine ligands (L) tagged with an alkyl chain of various lengths, [Ru(tpy)(L)(OH2)]2+. Cyclic voltammetric analyses show that the length of the alkyl chain exerts great influence on the electro‐generation of RuIV=O species. The L with a longer alkyl chain in an acidic aqueous medium promotes the conversion of RuIII−OH to RuIV=O efficiently. Surprisingly, this conversion can be further enhanced by the presence of perchlorate anions. Chronocoulometric data reveal that the alkyl chain on L promotes the adsorption of the ruthenium complex on the electrode surface. Bulk electrolysis results indicate that the [Ru(tpy)(dppa)(OH2)]2+ (dppa=(2,2′‐dipyridyl)‐n‐propylamine) gives the most active electrocatalytic water oxidation activity among the ruthenium‐aqua complexes investigated in this study. The electro‐generation of RuIV=O species from the corresponding RuII‐aqua complex is significantly promoted by an N‐substituted 2,2′‐dipyridylamine ligand with an alkyl chain as the coordinating ligand in the presence of perchlorate anions. Electrochemical results demonstrate the importance of both ligand and anion effects in facilitating the in situ formation of RuIV=O species, which enhance the electrochemical water‐oxidation activity.