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 Delta H degrees(298) between 1 + 6C(2)H(4) and 26 + 3C(2)H(6) is about -90 kcal center dot 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 I to give the ethylene T complex (H)(2)CpRu(mu-H)2RuCp(eta(2)-C2H4) (2). The free energy barrier is about 27 kcal center dot mol(-1) according to the static DFT calculations. Metadynamic simulations of the coordination process yield a Delta G(298) barrier of about 20 kcal center dot mol(-1). Another high-barrier step is the ethylene coordination to CpRu(eta(2):eta(1)-CH=CH2)(2)RuCp (25) to give the final product 26. In total, the title 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.