| Abstract
| - Oxidation of N,N-benzylmethylamine,N,N-benzylisopropylamine, andN,N-benzyl-tert-butylamineby both anionic and neutral Mo(VI) and W(VI) oxodiperoxo complexesyields the correspondingnitrones quantitatively. The oxidation reactions employing anionicoxidants were performed inCHCl3 and follow second-order kinetics, first order withrespect to the amine and to the oxidant.The data were rationalized on the basis of a rate-determiningnucleophilic attack of the amineonto the peroxide oxygen of the oxidant, with a transition state inwhich N−O bond formation andO−O bond cleavage occur in a concerted way (electrophilic oxygentransfer mechanism). This attackyields the corresponding hydroxylamine, which then is furtherlyoxidized to nitrone in a fast step.On the other hand, in the case of neutral oxidants1H-NMR data as well as kinetic data indicatethat amine coordinates the metal center replacing the original ligandHMPA and yields a newperoxo complex. ForN,N-benzyl-tert-butylamine such acomplex was isolated and characterized.These new peroxo complexes can themselves behave as electrophilicoxidants, transferring oxygento external amine molecules through the same pathway followed byanionic oxidants, or can yieldthe reaction product by intramolecular oxidation of the coordinateamine. Measurements of addedHMPA effects on oxidation rate would seem more consistent with theelectrophilic oxygen transfermechanism.
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