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.