Molecular Modeling of Ruthenium Alkylidene Mediated Olefin Metathesis Reactions. DFT Study of Reaction Pathways

Three possible reaction pathways have been studied for the Cl 2 (PMe 3 ) 2 Ru CH 2 and Cl 2 (PCy 3 ) 2 Ru CH 2 (Cy = cyclohexyl) mediated metathesis reaction of propylene by quantum-mechanical DFT calculations. It was found that in all cases the metathesis reaction proceeds via dissociative substitution of a phosphine ligand with propylene, giving a monophosphine complex. This tendency increases with ligand volume, and in the case of smaller PMe 3 groups it is the entropy contribution to the reaction energetics that causes the monophosphine complex to participate in the metathesis reaction, according to the modeling data.