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The Right Computational Recipe for Olefin Metathesis with Ru-Based Catalysts: The Whole Mechanism of Ring-Closing Olefin Metathesis.

The initiation mechanism of ruthenium methylidene complexes was studied detailing mechanistic insights of all involved reaction steps within a classical olefin metathesis pathway. Computational studies reached a good agreement with the rarely available experimental data and even enabled to complement them. As a result, a highly accurate computational and rather cheap recipe is presented; M06/TZVP//BP86/SVP (PCM, P = 1354 atm).

Chelating Ruthenium Phenolate Complexes: Synthesis, General Catalytic Activity, and Applications in Olefin Metathesis Polymerization

Cyclic Ru-phenolates were synthesized, and these compounds were used as olefin metathesis catalysts. Investigation of their catalytic activity pointed out that, after activation with chemical agents, these catalysts promote ring-closing metathesis (RCM), enyne and cross-metathesis (CM) reactions, including butenolysis, with good results. Importantly, these latent catalysts are soluble in neat dicyclopentadiene (DCPD) and show good applicability in ring-opening metathesis polymeriyation (ROMP) of this monomer.

A theoretical view on the thermodynamic cis–trans equilibrium of dihalo ruthenium olefin metathesis (pre-)catalysts

This work was conducted to provide an overview on the position of the thermodynamic cis–trans equilibrium of 85 conventional and X-chelated alkylidene-ruthenium complexes (X=O, S, Se, N, P, Cl, I, Br). The reported energies (ΔE) were obtained through single-point calculations with M06 functional and TZVP basis set from BP86/SVP-optimized cis- and trans-dichloro geometries and using the polarizable continuum model to simulate the influence of the solvent. Dichloromethane and toluene were selected as examples for solvents with high and low dielectric constants. The obtained relative stabilities of the cis- and trans-dihalo derivatives of the respective alkylidene complexes will serve for a better explanation of their catalytic activity as has been disclosed herein with selected examples.Graphical abstract

On the chloride lability in electron-rich second-generation ruthenium benzylidene complexes

A series of electron-rich second-generation cis-dichloro ruthenium aldehyde-chelating benzylidene complexes was prepared, characterized, and tested in typical ring-opening metathesis polymerization (ROMP) experiments. The benzylidene precursors were prepared via etherification of the hydroxyl group and vinylation at position 2 of 2-bromo-5-hydroxy-4-methoxybenzaldehyde. The corresponding ruthenium complexes were obtained from a carbene exchange reaction and were characterized by a cis-dichloro arrangement. A pronounced lability of the chloride ligand trans to the N-heterocyclic carbene ligand in methanol was observed and it was shown that this feature is responsible for a particularly slow ROMP in this solvent.Graphical abstract

Consequences of the electronic tuning of latent ruthenium-based olefin metathesis catalysts on their reactivity

Summary Two ruthenium olefin metathesis initiators featuring electronically modified quinoline-based chelating carbene ligands are introduced. Their reactivity in RCM and ROMP reactions was tested and the results were compared to those obtained with the parent unsubstituted compound. The studied complexes are very stable at high temperatures up to 140 °C. The placement of an electron-withdrawing functionality translates into an enhanced activity in RCM. While electronically modified precatalysts, which exist predominantly in the trans-dichloro configuration, gave mostly the RCM and a minor amount of the cycloisomerization product, the unmodified congener, which preferentially exists as its cis-dichloro isomer, shows a switched reactivity. The position of the equilibrium between the cis- and the trans-dichloro species was found to be the crucial factor governing the reactivity of the complexes.

cis/trans Coordination in Olefin Metathesis by Static and Molecular Dynamic DFT Calculations

In regard to [(N-heterocyclic carbene)Ru]-based catalysts, it is still a matter of debate if the substrate binding is preferentially cis or trans to the N-heterocyclic carbene ligand. By means of static and molecular dynamic DFT calculations, a simple olefin, like ethylene, is shown to be prone to the trans binding. Bearing in mind the higher reactivity of trans isomers in olefin metathesis, this insight helps to construct small alkene substrates with increased reactivity.

Exploiting the interactions between the ruthenium Hoveyda–Grubbs catalyst and Al-modified mesoporous silica: the case of SBA15 vs. KCC-1

2nd generation Hoveyda–Grubbs catalyst immobilized onto well-ordered 2D hexagonal (SBA15) and 3D fibrous (KCC-1) mesostructured silica displaying tetra-coordinated Al–H via Surface Organometallic Chemistry (SOMC).