Computational study of C-C coupling on diruthenium bis(μ-vinyl) ethylene π-complex

We have performed a computational study of the C-C coupling reaction between coordinated ethylene and two vinyl ligands in the binuclear bis(vinyl)-ethylene complex CpRu(η²-C₂H ₄)(μ-η¹:η²-CHCH₂) ₂RuCp (1) to yield the ruthenacyclopentadiene complex CpRu(η²-C₂H₄)(CMe=CH-CH=CMe)RuCp (28), described by Suzuki et al. This reaction is a sophisticated multistep process with a large number of possible pathways. Agostic interactions and the cooperativity of both Ru centers play a crucial role in the mechanism of the reaction. Our calculations provide support for Suzuki et al.'s proposal that the conversion of the reactant 1 to the final product 28 proceeds through the intermediate Cp(H)Ru(w-H)(CMe=CH-CH=CMe)RuCp (20). However, the pathway originally proposed by Suzuki et al. leading to the intermediate 20 is unfavorable (Δ‡G°₂₉₈ = 33 kcal·mol ^-1). We found a new, more favorable pathway with a Δ‡G°₂₉₈ of 20 kcal·;mol^-1. The rate-determining step of the mechanism is ethylene coordination to the intermediate CpRu(W-H)(CHMe=CH-CH=CMe)RuCp (22). The free energy barrier is about 29 and 24 kcal·mol^-1 at the BP86 and MPWLYP1M level, correspondingly.