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

Structural analogues of Hoveyda–Grubbs catalysts bearing the 1-benzofuran moiety or isopropoxy-1-benzofuran derivatives as olefin metathesis catalysts

We have used the DFT/M06-D3 computational method to study structures and activation free energies for a series of Hoveyda–Grubbs-like catalysts with the isopropoxybenzene part replaced by 1-benzofuran and ten derivatives of isopropoxy-1-benzofuran.

Theoretical characterization of first and second generation Grubbs catalysts in styrene cross-metathesis reactions: insights from conceptual DFT

Reorganization energy and DFT-based reactivity descriptors revealed important issues regarding the performance of Grubbs catalysts.

Computational study of productive and non-productive cycles in fluoroalkene metathesis

A detailed DFT study of the mechanism of metathesis of fluoroethene, 1-fluoroethene, 1,1-difluoroethene, cis- and trans-1,2-difluoroethene, tetrafluoroethene and chlorotrifluoroethene catalysed with the Hoveyda-Grubbs 2(nd) generation catalyst was performed. It revealed that a successful metathesis of hydrofluoroethenes is hampered by a high preference for a non-productive catalytic cycle proceeding through a ruthenacyclobutane intermediate bearing fluorines in positions 2 and 4. Moreover, the calculations showed that the cross-metathesis of perfluoro- or perhaloalkenes should be a feasible process and that the metathesis is not very sensitive to stereochemical issues.

A comprehensive study of olefin metathesis catalyzed by Ru-based catalysts

During a Ru-catalyzed reaction of an olefin with an alkylidene moiety that leads to a metallacycle intermediate, the cis insertion of the olefin can occur from two different directions, namely side and bottom with respect to the phosphine or N-heterocyclic ligand (NHC), depending on the first or second generation Grubbs catalyst. Here, DFT calculations unravel to which extent the bottom coordination of olefins with respect is favored over the side coordination through screening a wide range of catalysts, including first and second generation Grubbs catalysts as well as the subsequent Hoveyda derivatives. The equilibrium between bottom and side coordination is influenced by sterics, electronics, and polarity of the solvent. The side attack is favored for sterically less demanding NHC and/or alkylidene ligands. Moreover the generation of a 14-electron species is also discussed, with either pyridine or phosphine ligands to dissociate.

Mechanism of Oxidation of Ethane to Ethanol at Iron(IV)-Oxo Sites in Magnesium-Diluted Fe2(dobdc)

The catalytic properties of the metal-organic framework Fe2(dobdc), containing open Fe(II) sites, include hydroxylation of phenol by pure Fe2(dobdc) and hydroxylation of ethane by its magnesium-diluted analogue, Fe0.1Mg1.9(dobdc). In earlier work, the latter reaction was proposed to occur through a redox mechanism involving the generation of an iron(IV)-oxo species, which is an intermediate that is also observed or postulated (depending on the case) in some heme and nonheme enzymes and their model complexes. In the present work, we present a detailed mechanism by which the catalytic material, Fe0.1Mg1.9(dobdc), activates the strong C-H bonds of ethane. Kohn-Sham density functional and multireference wave function calculations have been performed to characterize the electronic structure of key species. We show that the catalytic nonheme-Fe hydroxylation of the strong C-H bond of ethane proceeds by a quintet single-state σ-attack pathway after the formation of highly reactive iron-oxo intermediate. The mechanistic pathway involves three key transition states, with the highest activation barrier for the transfer of oxygen from N2O to the Fe(II) center. The uncatalyzed reaction, where nitrous oxide directly oxidizes ethane to ethanol is found to have an activation barrier of 280 kJ/mol, in contrast to 82 kJ/mol for the slowest step in the iron(IV)-oxo catalytic mechanism. The energetics of the C-H bond activation steps of ethane and methane are also compared. Dehydrogenation and dissociation pathways that can compete with the formation of ethanol were shown to involve higher barriers than the hydroxylation pathway.

Mechanistic insight into water-modulated cycloisomerization of enynyl esters using an Au(i) catalyst

The Au(i)-catalyzed cycloisomerization reactions of 1,6-enylnyl ester are theoretically investigated to rationalize the observed product divergences by modulating H₂O participation.

Hypercoordinate β-carbon in Grubbs and Schrock olefin metathesis metallacycles

From the analysis of structural, bond order, electron density and ¹³C NMR data of a large variety of ruthenacyclobutanes and tungstenacyclobutanes, we show that the C_β of the metallacycle is pentacoordinate.

Full kinetic analysis of a rhodium-catalyzed hydroformylation: beyond the rate-limiting step picture

A complete dynamic kinetic analysis beyond the steady state approximation of the rhodium-catalyzed hydroformylation with the 6-DPPon ligand is presented. The results show that not one single step but several transition states and intermediates control the selectivity and activity of the catalysis.