Electrochemical and Resonance Raman Spectroscopic Studies of Water-Oxidizing Ruthenium-Terpyridyl-Bipyridyl Complexes

Abstract

The irreversible conversion of single-site water oxidation catalysts (WOC) into the more rugged catalysts structurally related to [(trpy)(5,5&rsquo;-X2-bpy)RuIV(&mu;-O)RuIV(trpy)(O)(H2O)]4+ (X = H, 1-dn4+; X = F, 2-dn4+) represents a critical issue in developing active and durable WOC. In this work, the electrochemical and acid-base properties of 1-dn4+ and 2-dn4+ were evaluated. In-situ resonance Raman spectroscopy was employed to characterize species formed upon stoichiometric oxidation of single-site catalysts demonstrating the formation of high oxidation states mononuclear Ru=O and RuO-O complexes. Under turnover conditions, the dinuclear intermediates, 1-dn4+ and 2-dn4+, as well as the previously proposed [RuVI(trpy)(O)2(H2O)]2+ complex (32+) are formed. 32+ is a pivotal intermediate that provides access to the formation of dinuclear species. Single crystal X-ray diffraction analysis of the isolated complex [RuIV(O)(trpy)(5,5&rsquo;-F2-bpy)]2+ reveals a clear elongation of the Ru-N bond located in the trans position to the oxo group, documenting the weakness of this bond which promotes the release of the bpy ligand and the subsequent formation of 32+. &nbsp;</p