“Covalent Hydration” Reactions in Model Monomeric Ru 2,2'-Bipyridine Complexes: Thermodynamic Favorability as a Function of Metal Oxidation and Overall Spin States

Density functional theory (DFT) has been used to investigate the plausibility of water addition to the simple mononuclear ruthenium complexes, [(NH3)3(bpy)Ru═O]2+/3+ and [(NH3)3(bpy)RuOH]3+, in which the OH fragment adds to the 2,2′-bipyridine (bpy) ligand. Activation of bpy toward water addition has frequently been postulated within the literature, although there exists little definitive experimental evidence for this type of “covalent hydration”. In this study, we examine the energetic dependence of the reaction upon metal oxidation state, overall spin state of the complex, as well as selectivity for various positions on the bipyridine ring. The thermodynamic favorability is found to be highly dependent upon all three parameters, with free energies of reaction that span favorable and unfavorable regimes. Aqueous addition to [(NH3)3(bpy)Ru═O]3+ was found to be highly favorable for the S = 1/2 state, while reduction of the formal oxidation state on the metal center makes the reaction highly unfavorable. E...