The Mechanism of Ethylene Dimerization with the Ti(OR′)4/AlR3 Catalytic System: DFT Studies Comparing Metallacycle and Cossee Proposals

The mechanism of ethylene dimerization to 1-butene, as promoted by the Ti(OR′) 4 /AlR 3 catalyst system, has been explored with the aid of density functional theory (DFT) to determine which mechanistic proposal, metallacycle or Cossee–Arlman, is most likely. The theoretical studies predict that the Cossee mechanism has the lowest rate-determining reaction barrier and also that this mechanism is more likely to lead to selective dimerization. In contrast, for the metallacycle mechanism, a higher likelihood of 1-hexene formation is predicted. The possibility of isomerization or codimerization of 1-butene has also been studied according to a Cossee mechanism, with the results obtained in good agreement with previous experiments. As a result of this study and recent experimental results, a Cossee mechanism of dimerization with this catalyst, proceeding via a titanium-hydride intermediate, is considered the most probable route.