Computational Study of the C−H Bond Activation in Ethylene on a Binuclear Ruthenium Complex

Abstract

The reaction is substantially exothermic—the calculated total reaction enthalpy ΔH298° between 1 + 6C2H4 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(η2-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 ΔG298 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 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.