The reaction is substantially exothermic - the calculated total reaction enthalpy ΔHo298 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.