DFT calculations have been used to determine the thermodynamic and kinetic preference for ruthena-cyclobutanes resulting from the experimentally proposed interconversion pathways (olefin and alkylidene rotations) through the investigation of cross-metathesis reaction mechanism for neutral Grubbs catalyst, RuCl2 (=CHEt) NHC (A), with ethylene and 1-butene as the substrates. Our results show that although the proposed interconversions are feasible due to the predicted low energy barriers (2-6 kcal/mol), the formation of ruthenacyclobutane is kinetically favored over the competitive reactions involving alkylidene rotations. In comparison with catalyst A, the reaction energy profile for cationic Piers catalyst [RuCl2 (=CHPCy3)NHC+] (B) is more endothermic in nature with both ethylene and 1-butene substrates.
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