O–H and C–H Bond Activations of Water and Methane by RuO²⁺ and (NH₃)RuO²⁺: Ground and Excited States

Investigation of the ground and excited states of RuO²⁺ is carried out using multireference quantum chemical methodologies. The electronic structure is explored in detail, and accurate spectroscopic constants for 12 states are reported. Although ruthenium belongs to the same group as iron, the ground state of RuO²⁺ is ¹Σ⁺ with a strong oxo character as opposed to the ³Δ of FeO²⁺ with primarily oxyl character. To see the effect of the different electronic structure of RuO²⁺ on the O–H and C–H bond activation processes, we studied its reaction with one water or methane molecule. Reaction energies and activation barriers are given for six low-lying electronic states of singlet, triplet, and quintet spin multiplicities. It is found that the higher-energy quintet state (⁵Σ⁺) provides the lowest activation energies and is the same state responsible for the C–H activation for FeO²⁺ complexes. The reason is attributed to its weaker metal–oxygen bond (longer bond length), which is “prepared” to be activated at the same time with the O–H and C–H bonds. The effect of an ammonia ligand in the chemical activity is also discussed.