Ruthenium-Catalyzed Olefin Metathesis:  A Quantum Molecular Dynamics Study

Abstract

Chemical reactions are usually performed in solvents. The course of the reaction varies with solvent, temperature, etc. Solvent molecules are usually not taken into account in quantum simulations due to the rising computational effort. However, their ability to transfer heat (kinetic energy) to and from the reacting species can be incorporated in the simulations. We demonstrate that different chemistry follows by varying absolute simulation temperature and the range for temperature fluctuations in Car−Parrinello dynamics simulations applied to ruthenium catalyzed metathesis reactions. The bisphosphine Cl2(PH3)2RuCH2 complex and its monophosphine equivalent were taken as model compounds for the Grubbs catalyst. Depending on temperature conditions set in the molecular dynamics simulations, the interaction of these ruthenium−phosphine catalysts with ethylene revealed insertion, the formation of a metallacyclobutane, or a pure metathesis reaction. It was found that selective bond vibrational activation is required to induce metathesis activity. A comparison with recent experimental results from Grubbs et al. (J. Am. Chem. Soc. 1997, 119, 3887) shows that the results of our simulations reveal and lend support to the mechanism proposed by Grubbs. These include, in the order of appearance in the reaction scheme, the relative easiness of Cl−Ru−Cl cis−trans configurational exchange, carbene rotation and the loss of one phosphine, formation of a metallacyclobutane intermediate, and finally completion of the metathesis reaction. The presence of a small fraction of the monophosphine complex (the reaction proposed in Scheme , which was adopted from Grubbs et al.) is confirmed by the present simulations. Starting from the observation that selective bond excitation is necessary to exhibit reactivity, the higher activity of the monophosphine system compared to bisphosphine complexes reported by Grubbs et al. can be understood. We stress that we have also found that the bisphosphine is active, which also agrees with the experimental data. Finally, the fact that ruthenium−carbene complexes based on sterically crowded phosphines give higher metathesis activity, can be rationalized by their intrinsically more labile Ru−P bonds as indicated by longer Ru−P bond lengths.

The First Grubbs-Type Metathesis Catalyst withcis Stereochemistry: Synthesis of [(η2-dtbpm)Cl2Ru=CH−CH=CMe2] from a Novel, Coordinatively Unsaturated Dinuclear Ruthenium Dihydride

“…The dissociative pathway was derived experimentally from kinetic data by Grubbs et al [13a] It is supported by a recently isolated ruthenium chelate carbene ± olefin complex, [15] in which an olefin side arm of the carbene moiety is intramolecularly coordinated to the Ru center and replaces one monodentate phosphane in the trans position. The only theoretical study available, a quantum molecular dynamics calculation by Meier et al [14] also seems to support the mechanistic proposals of Grubbs et al…”

“…To date, there are only two detailed experimental studies [13] and one recent theoretical paper [14] on the reaction mechanism and catalyst activity in typical Grubbs systems. Two competing processes were postulated for Ru-catalyzed olefin metathesis: an associative pathway with direct olefin attack and metallacycle formation at the five-coordinate trans- ].…”

“…Apart from the above-mentioned mechanistic quantum MD study by Meier et al, [14] there are only two other quantum chemical studies of Grubbs-type complexes in the literature. One of them employed restricted Hartree ± Fock (HF) calculations with imposition of C 2v symmetry, [18] and the other reports a density functional theory (DFT) calculation on trans-[(PH 3 ) 2 Cl 2 RuCHCH 3 ] at the B3LYP level.…”

Comparing Intrinsic Reactivities of the First‐ and Second‐Generation Ruthenium Metathesis Catalysts in the Gas Phase

“…Meier and coworkers [19] reported a molecular-dynamics study of the first-generation catalysts. A DFT treatment of model complexes accompanied the experimental study by Chen and Scheme 5 co-workers [12].…”

Ring‐Closing Olefin Metathesis on Ruthenium Carbene Complexes: Model DFT Study of Stereochemistry

“…There were early computational studies on titanium- [24] and later on molybdenumcatalyzed [25][26][27] metathesis. Metathesis reactions on model ruthenium-carbene complexes [(PH 3 ) 2 Cl 2 Ru=CH 2 ] were examined by using Car-Parrinello molecular dynamics, [28] but without addressing mechanistic details. Two extensive studies on Grubbs-type catalysts have been published recently, [29,30] which are complementary in essence.…”