Olefin Metathesis with Ru-Based Catalysts Exchanging the Typical N-Heterocyclic Carbenes by a Phosphine–Phosphonium Ylide

摘要

Density functional theory (DFT) calculations have been used to describe the first turnoverof an olefin metathesis reaction calling for a new in silico family of homogenous Ru-based catalystsbearing a phosphine–phosphonium ylide ligand, with ethylene as a substrate. Equal to conventionalRu-based catalysts bearing an N-heterocyclic carbene (NHC) ligand, the activation of these congenersoccurs through a dissociative mechanism, with a more exothermic first phosphine dissociation step.In spite of a stronger electron-donating ability of a phosphonium ylide C-ligand with respect to adiaminocarbene analogue, upper energy barriers were calculated to be on average ca. 5 kcal/molhigher than those of Ru–NHC standards. Overall, the study also highlights advantages of bidentateligands over classical monodentate NHC and phosphine ligands, with a particular preference forthe cis attack of the olefin. The new generation of catalysts is constituted by cationic complexespotentially soluble in water, to be compared with the typical neutral Ru–NHC ones