What is the initiation step of the Grubbs-Hoveyda olefinmetathesiscatalyst?

Ashworth, Ian W.; Hillier, Ian H.; Nelson, David J.; Percy, Jonathan M.; Vincent, Mark A.

doi:10.1039/c1cc11230a

Cited by 88 publications

(132 citation statements)

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“…The interchange mechanism supported by our computational work 17 and also by Plenio's experimental data, 18 is earlier with respect to the Ru⋯O extension, and includes the approach of an alkene molecule towards the Ru centre (EVE in the case of initiation) and some sharing of alkene electron density with the Ru centre. The three types of transition states have different shapes, volumes and polarities so it is not surprising that there is no simple relationship between dielectric constant or E T (30) for either pre-catalyst, and that multi-parameter approaches are required.…”

Section: Dalton Transactions Communicationmentioning

confidence: 52%

Solvent effects on Grubbs’ pre-catalyst initiation rates

2013

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Initiation rates for Grubbs and Grubbs-Hoveyda second generation pre-catalysts have been measured accurately in a range of solvents. Solvatochromic fitting reveals different dependencies on key solvent parameters for the two pre-catalysts, consistent with different mechanisms by which the Grubbs and Grubbs-Hoveyda pre-catalysts initiate.The alkene metathesis reaction is now a standard transformation in academic laboratories, and has been applied to the synthesis of a wide range of natural 1,2 and unnatural products, 3 fine chemicals, 4,5 and polymers. 6 The availability of robust and commercially available pre-catalysts such as 1 and 2 has enabled the rapid growth of alkene metathesis in the synthetic repertoire. Although transition metal catalysts have enabled many efficient large scale processes to be carried out in industry, 5,7 the application of alkene metathesis to industrial processes has been more limited. 7,8For industrial-scale syntheses, the implications of the reaction solvent must be considered carefully; these include costs of purchase, purification, drying, recycling and/or disposal, and the health and safety implications of transport, transfer, storage and use. There are also sustainability issues raised by projected uncertainty of supply and by legislative changes. 9These considerations have led major pharmaceutical companies to encourage their discovery chemists to anticipate scaleup in their laboratory practice and reaction design, 9 replacing solvents which are problematic for scale-up, wherever practicable, and at the earliest stage possible.The classical set of solvents for RCM is dichloromethane (DCM), 1,2-dichloroethane (DCE), benzene and toluene; of these, toluene raises the fewest issues while the other three are problematic. It has been reported that other solvents, including acetic acid, 10 methyl tert-butyl ether (MTBE), 11 dimethyl carbonate 12 and hexafluorobenzene (HFB) 13,14 are particularly effective for RCM, mostly on the basis of reaction yields or qualitative comparisons of kinetic profiles, so the precise locus of any solvent effect is not clear. If solvent effects on reaction chemistry could be revealed in detail, solvents could be selected for scale-up on the basis of both chemical efficacy and sustainability, and from a strong experimental starting point. We therefore sought to reveal the effects of solvent on the initiation rates of 1 and 2, which are currently the most popular metathesis pre-catalysts.Initiation rates were measured for 1 and 2 by reaction of the pre-catalyst with ethyl vinyl ether 15 in a number of solvents.Initiation rates for 1 were obtained following the method of Sanford et al.; 16 the rate-determining step in this reaction is known to be dissociation of the phosphane ligand. The integral versus time data was processed using a simple first order treatment (eqn (1)).For solvents where deuterated analogues were unavailable commercially, 10% v/v chloroform-d was added to enable a deuterium lock.Initiation rates for pre-catalyst 1 cover only a ca. fou...

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Section: Dalton Transactions Communicationmentioning

confidence: 52%

Solvent effects on Grubbs’ pre-catalyst initiation rates

2013

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“…Notice also that in our previous work [21], the enthalpy for nitrogen interaction with Na-ETS-10 calculated with the same cluster model and DFT approach compared well with the available experimental result while a noticeable underestimation (~7 kJ·mol -1 with the M06-L/6-31++G** approach and ~3 kJ·mol -1 with the M06-L/6-31G** approach) was found in the case of carbon dioxide. Note however that the experimental result for carbon dioxide was determined by the same authors reporting the largest value (-49.7 kJ·mol -1 ) for ethene interaction with Na-ETS-10 [36]. This suggests that the much more negative isosteric heats reported by Shi et al [36] may be due to the presence of other cations than Na + in the Na-ETS-10 sample, which interact strongerthan Na cations with CO 2 and with the double bond in ethene.…”

Section: Adsorption Of C 2 H X and C 3 H X Hydrocarbons In Ets-10mentioning

confidence: 93%

“…Note however that the experimental result for carbon dioxide was determined by the same authors reporting the largest value (-49.7 kJ·mol -1 ) for ethene interaction with Na-ETS-10 [36]. This suggests that the much more negative isosteric heats reported by Shi et al [36] may be due to the presence of other cations than Na + in the Na-ETS-10 sample, which interact strongerthan Na cations with CO 2 and with the double bond in ethene. The verification of this hypothesis needs further experimental work and we hope that the present and previous [21] studies on the interaction of gaseous molecules with Na-ETS-10 can trigger such experiments.…”

Section: Adsorption Of C 2 H X and C 3 H X Hydrocarbons In Ets-10mentioning

confidence: 93%

“…The M06-L functional is used in this work since in a recent comparative study on the performance of nine different DFT functionals to calculate the interaction enthalpy of methane with a cluster model of Na-ETS-10, the M06-L approach was found to provide the best results [21].Besides,the M06-L approach together with a cluster model was found to provide very accurate energetic, vibrational and structural information for some other difficult systems such as i) adsorption of CO on MgO(001) [30], ii) the adsorption of CO and NO on Ni-doped MgO(001) [31], and iii) the interaction of water with open metal sites of CuBTC [32]. Very encouragingly, recent works concerning the interaction of CO with the (111) surfaces of Rh, Pt, Cu, Ag and Pd [33] or the interaction of benzene, pyridine, thymine and cytosine with Au(111) [34]showed that the M06-L method is suitable for treating dispersion dominated interactionsof adsorbateswith metallic surfaces [35].The M06-L approach was also effectively employed to predict reaction energies in organometallic systems [36][37][38] and the benchmark study on the interaction of hydrocarbons and smaller gases with several zeolite clusters byZhao and Truhlar [39]shows that the M06 family of functionals is well suited to study this kind of systems.Additionally, in our very recent work on the interaction of five atmospheric gases with Na-ETS-10 [21], calculated enthalpic data for methane, nitrogen and, at some extent, carbon dioxide, and calculated vibrational data for methane, nitrogen, hydrogen, carbon dioxide and water were found to be in very satisfactory agreement with experimental isosteric heats [40,41] and infrared results [42][43][44][45], respectively. The same 2Ti cluster model used in Ref.…”

Section: Computational Detailsmentioning

confidence: 99%

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A density functional theory study on the interaction of paraffins, olefins, and acetylenes with Na-ETS-10

2015

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High demand for economically viable separation processes like adsorptive separation for mixtures of hydrocarbons drives the need for understanding the interaction of hydrocarbons with titanosilicate adsorbents, to replace the energy intensive cryogenic hydrocarbon separation.Density functional theory (DFT) was used to optimize the geometries and calculate the enthalpies for the interactions between paraffins (C 2 H 6 , C 3 H 8 ), olefins (C 2 H 4 , C 3 H 6 ) and acetylenes (C 2 H 2 , C 3 H 4 ) with a cluster model of the Engelhard titanosilicatehaving sodium extra framework cations (Na-ETS-10). The DFT calculations were performed with theM06-L exchange correlation functional and were corrected for the basis set superposition error with the counterpoise method. The calculated enthalpies for the interaction of hydrocarbons with Na-ETS-10 decrease with the decrease in the number of carbon atoms, in the order acetylenes >olefins >paraffins,and compare well with experimental data available in the literature. The enthalpies calculated at the M06-L/6-31++G** level of theory for the two extreme cases, i.e., strongest and weakest interactions, are -62.8 kJ·mol -1 (C 3 H 4 ) and -26.9 kJ·mol -1 (C 2 H 6 ).Additionally, the calculated vibrational frequencies are in good agreement with the characteristic vibrational modes of ETS-10 and of the interactions of hydrocarbons with Na + in the 12-membered channel in ETS-10.

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“…Understanding this part of the mechanism is very important because it is central to understanding the entire catalytic cycle. Despite many theoretical efforts on Grubbs catalysts, to our knowledge, only three works have described the metathesis with Hoveyda-Grubbs catalyst: two of them use a dissociative mechanism [18,19] and the other uses an interchange-associative mechanism [20]. We found that the mechanism of catalysis depends on the size of both the olefin and the Hoveyda ligand.…”

Section: Introductionmentioning

confidence: 94%