Cleaving bonds in CH3OSO2CF3 with [1,2,4-(Me3C)3C5H2]2CeH; an experimental and computational study
Résumé
The reaction at 20 °C of the metallocenelanthanide hydride, [1,2,4-(Me3C)3C5H2]2CeH, , and excess methyltrifluoromethanesulfonate, CH3OSO2CF3, results in formation of , , and the bimetallic complex . The metallocenes , , and react with excess CH3OSO2CF3 to form , CH3OCH3, CH3F, and (CH3O)2SO, respectively, at 20 °C. Thus, the net reaction is but the pathway is not a direct methyl transfer. Comparison of the reactivity of CH3OSO2CF3 and CH3OSO2CH3 (Werkema et al., Organometallics, 2012, 31, 870) is revealing since both form a similar set of products but the rates of reaction of CH3OSO2CF3 are faster. The bimetallic complex, in which the SO32− anion bridges two fragments, is unique in organometallic chemistry. The 1H NMR spectrum is fluxional at 20 °C and the low temperature spectrum is consistent with the geometry observed in the solid state. Density Functional Theory (DFT) calculations of the Gibbs energy profiles for the reaction of CH3OSO2CF3 with show that the CH-bond activation and direct CH3 group transfer have similar activation energy barriers. This contrasts with what is observed in the reaction of with CH3OSO2CH3, where CH-bond activation at the SCH3 group is preferred. Remarkably, the activation energy barriers for C-O-bond cleavage are similar in CH3OSO2CH3 and CH3OSO2CF3, which is traced to the calculated small exoergicity of −1.7 kcal mol−1 for the reaction of . This contrasts, perhaps, with conventional wisdom that overemphasizes the effect of the electron-withdrawing ability of the CF3 group on the chemical and physical properties of sulfonate esters.