Limits...
Toward a simulation approach for alkene ring-closing metathesis: scope and limitations of a model for RCM.

Nelson DJ, Carboni D, Ashworth IW, Percy JM - J. Org. Chem. (2011)

Bottom Line: A published model for revealing solvent effects on the ring-closing metathesis (RCM) reaction of diethyl diallylmalonate 7 has been evaluated over a wider range of conditions, to assess its suitability for new applications.Unfortunately, the model is too flexible and the published rate constants do not agree with experimental studies in the literature.However, by fixing the values of important rate constants and restricting the concentration ranges studied, useful conclusions can be drawn about the relative rates of RCM of different substrates, precatalyst concentration can be simulated accurately and the effect of precatalyst loading can be anticipated.

View Article: PubMed Central - PubMed

Affiliation: WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, United Kingdom.

ABSTRACT
A published model for revealing solvent effects on the ring-closing metathesis (RCM) reaction of diethyl diallylmalonate 7 has been evaluated over a wider range of conditions, to assess its suitability for new applications. Unfortunately, the model is too flexible and the published rate constants do not agree with experimental studies in the literature. However, by fixing the values of important rate constants and restricting the concentration ranges studied, useful conclusions can be drawn about the relative rates of RCM of different substrates, precatalyst concentration can be simulated accurately and the effect of precatalyst loading can be anticipated. Progress has also been made toward applying the model to precatalyst evaluation, but further modifications to the model are necessary to achieve much broader aims.

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Experimental concentration/time data and simulations thereof obtained using the Adjiman and Taylor model and rate constants for the RCM of 7 in dry DCM-d2 (red ●, red line) and wet DCM-d2 (●, black line) at 298 K. Diene and cycloalkene concentration were both fitted, but only cycloalkene concentration is shown for clarity.
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fig1: Experimental concentration/time data and simulations thereof obtained using the Adjiman and Taylor model and rate constants for the RCM of 7 in dry DCM-d2 (red ●, red line) and wet DCM-d2 (●, black line) at 298 K. Diene and cycloalkene concentration were both fitted, but only cycloalkene concentration is shown for clarity.

Mentions: Unfortunately, the concentration/time profile recorded indicated a faster reaction than the one published (Figure 1). A slower reaction took place in DCM-d2 from a freshly opened ampule, although this did not match the literature concentration/time profile either. Karl Fischer titration showed that the drying procedure had been effective, with a water content of ca. 30 ppm before drying (untreated chloroform-d and DCM-d2) but less than 10 ppm afterward. It is clear that commercial NMR solvents from ampules must be treated with some caution if relatively significant amounts of water are not to be introduced. Straightforward drying of solvents using molecular sieves reduced the water content of the deuterated solvents to a level similar to that found in DCM obtained from widely used solvent purification systems; for example, DCM from the Innovative Technologies PureSolv system used in-house contains water at no more than 5 ppm. Although the kinetic data were not consistent with the published literature profile, we fitted the data set; diene and cycloalkene concentration were both fitted, but only cycloalkene concentration is shown for clarity. An excellent fit was obtained for both species. However, quite different values for all rate constants were required (Table 1), prompting further investigation with this data set.


Toward a simulation approach for alkene ring-closing metathesis: scope and limitations of a model for RCM.

Nelson DJ, Carboni D, Ashworth IW, Percy JM - J. Org. Chem. (2011)

Experimental concentration/time data and simulations thereof obtained using the Adjiman and Taylor model and rate constants for the RCM of 7 in dry DCM-d2 (red ●, red line) and wet DCM-d2 (●, black line) at 298 K. Diene and cycloalkene concentration were both fitted, but only cycloalkene concentration is shown for clarity.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3675522&req=5

fig1: Experimental concentration/time data and simulations thereof obtained using the Adjiman and Taylor model and rate constants for the RCM of 7 in dry DCM-d2 (red ●, red line) and wet DCM-d2 (●, black line) at 298 K. Diene and cycloalkene concentration were both fitted, but only cycloalkene concentration is shown for clarity.
Mentions: Unfortunately, the concentration/time profile recorded indicated a faster reaction than the one published (Figure 1). A slower reaction took place in DCM-d2 from a freshly opened ampule, although this did not match the literature concentration/time profile either. Karl Fischer titration showed that the drying procedure had been effective, with a water content of ca. 30 ppm before drying (untreated chloroform-d and DCM-d2) but less than 10 ppm afterward. It is clear that commercial NMR solvents from ampules must be treated with some caution if relatively significant amounts of water are not to be introduced. Straightforward drying of solvents using molecular sieves reduced the water content of the deuterated solvents to a level similar to that found in DCM obtained from widely used solvent purification systems; for example, DCM from the Innovative Technologies PureSolv system used in-house contains water at no more than 5 ppm. Although the kinetic data were not consistent with the published literature profile, we fitted the data set; diene and cycloalkene concentration were both fitted, but only cycloalkene concentration is shown for clarity. An excellent fit was obtained for both species. However, quite different values for all rate constants were required (Table 1), prompting further investigation with this data set.

Bottom Line: A published model for revealing solvent effects on the ring-closing metathesis (RCM) reaction of diethyl diallylmalonate 7 has been evaluated over a wider range of conditions, to assess its suitability for new applications.Unfortunately, the model is too flexible and the published rate constants do not agree with experimental studies in the literature.However, by fixing the values of important rate constants and restricting the concentration ranges studied, useful conclusions can be drawn about the relative rates of RCM of different substrates, precatalyst concentration can be simulated accurately and the effect of precatalyst loading can be anticipated.

View Article: PubMed Central - PubMed

Affiliation: WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, United Kingdom.

ABSTRACT
A published model for revealing solvent effects on the ring-closing metathesis (RCM) reaction of diethyl diallylmalonate 7 has been evaluated over a wider range of conditions, to assess its suitability for new applications. Unfortunately, the model is too flexible and the published rate constants do not agree with experimental studies in the literature. However, by fixing the values of important rate constants and restricting the concentration ranges studied, useful conclusions can be drawn about the relative rates of RCM of different substrates, precatalyst concentration can be simulated accurately and the effect of precatalyst loading can be anticipated. Progress has also been made toward applying the model to precatalyst evaluation, but further modifications to the model are necessary to achieve much broader aims.

Show MeSH