Ammonium-carbenium dications

Ammonium-carbenium dications and related species are also generated readily from olefinic precursors.77 For example, the tetrahydropyridine (226) leads to the 1,3-dication (227) and vinyl-substituted /V-heteroaromatics can give dications (i.e., 228) in superacid, both of which show high electrophilic reactivities (eqs 70-71). 

Initial ionization gives an ammonium-carboxonium dication, which then produces the ammonium-carbenium dication (230). A variety of dicationic electrophiles like 230 have been proposed. 

Examination of the dication pairs 122/123 and 125/126 may also suggest a further useful definition of the distonic superelectrophiles the distonic superelectrophiles may be distinguished from onium dications that are without superelectrophilic activation (i.e., two isolated cationic centers) by comparison of the energies, reactivities, or structural/electronic criteria, of two closely related species. For example, it is expected that ammonium-carbenium dications 127 and 128 should vary considerably in terms of energy, due to the proximity of the charges. 

Related ammonium-carbenium distonic superelectrophiles (1,4-dications, 103-104) have been shown to possess strong electrophilic reach vies, undergoing arylation with benzene and dichlorobenzene (eqs 40-41).38... 

The protonation of the methyleneiminium cation gives rise to the superelectrophilic methyleniminium dication, 19, which is a gitonic 1,2-dicationic species (carbenium ammonium species). Such a carbodication has been observed by charge stripping mass spectrometry by Schwarz and coworkers.Olah and coworkers have shown by theoretical calculations that the carbenium ammonium species, 19a, is 27.6 kcal/mol more stable than the three-center two-electron (3c-2e) bonded structure, 19b. ... 

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