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

Abstract

Density functional theory (DFT) calculations have been used to describe the first turnover of an olefin metathesis reaction calling for a new in silico family of homogenous Ru-based catalysts bearing a phosphine-phosphonium ylide ligand, with ethylene as a substrate. Equal to conventional Ru-based catalysts bearing an N-heterocyclic carbene (NHC) ligand, the activation of these congeners occurs 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 a diaminocarbene analogue, upper energy barriers were calculated to be on average ca. 5 kcal/mol higher than those of Ru-NHC standards. Overall, the study also highlights advantages of bidentate ligands over classical monodentate NHC and phosphine ligands, with a particular preference for the cis attack of the olefin. The new generation of catalysts is constituted by cationic complexes potentially soluble in water, to be compared with the typical neutral Ru-NHC ones.

The activity of indenylidene derivatives in olefin metathesis catalysts

“…Although most of the olefin metathesis catalysts are based on ruthenium [ 21 – 22 ], because these are more stable to oxygen and moisture [ 23 ] than their molybdenum counterparts, they display sensitivity to decomposition while in solution [ 24 – 25 ]. Understanding and/or the elimination of potential pathways that leads to catalyst decomposition is extremely important [ 26 – 28 ], since any knowledge obtained in this area can guide the catalyst design efforts [ 29 – 31 ].…”

Role of Electronic and Steric Effects on Ruthenium Catalysts with Bulky NHC Ligands and Relationship with the Z-Selectivity in Olefin Metathesis

“…The application of topographic steric maps has been extremely useful in the design of transition metal complexes [25,38,49,50]. The computational tool developed by Carvallo et al [41] provides a picture of the interaction surface between the catalyst and the substrates that are formed by the ligands in the complex.…”

Regio, stereo and chemoselectivity of 2nd generation Grubbs ruthenium-catalyzed olefin metathesis

“…[97] This is intended to support related predictive catalysis in future, [98,99,100]even though much more efforts must still be undergone in the future to further understand the Z/E isomer selectivity, as well as to expand the scope of the metathesis reactions, by means of other ligands and/or metals. [101,102,103,104,105]  COMPUTATIONAL DETAILS DFT calculations were performed at the generalized gradient approximation (GGA) level with the Gaussian09 package, [106] using the M06 functional of Truhlar, [107]whose exchange functional is built based on the hybrid-meta generalized gradient approximation (HMA).…”