Computational study of the C - H bond activation in ethylene on a binuclear ruthenium complex

The reaction is substantially exothermic - the calculated total reaction enthalpy ΔH^o₂₉₈ between 1 + 6C₂H ₄ and 26 + 3C₂H₆ is about -90 kcal·mol^-1. The reaction occurs through a number of stages, each including ethylene coordination, at least two hydride migrations, and ethane elimination. The rate-determining step of the mechanism is the initial coordination of the first ethylene molecule to the reactant 1 to give the ethylene π complex (H)₂CpRu(μ-H)₂RuCp(η ²-C₂H₄) (2). The free energy barrier is about 27 kcal·mol^-1 according to the static DFT calculations. Metadynamic simulations of the coordination process yield a ΔG ₂₉₈ barrier of about 20 kcal ·mol^-1. Another high-barrier step is the ethylene coordination to CpRu(η²: η¹-CH=CH₂)₂RuCp (25) to give the final product 26. In total, the tide reaction is a sophisticated multistep reaction with a large number of possible pathways. The mechanism of the reaction is largely determined by the flexibility of hydride ligands and by cooperation between both Ru centers.