Tetraphenylethylene dication

Typical studies, in which the RDE has been used, include the dimerization of the triphenylamine radical cation [257] and the cyclization of the tetraphenylethylene dication [258]. 

That disproportionation can be an alternative is shown by the case of tetraphenylethylene, the cyclization of which presumably occurs via the dication according to eqn (80) (Svanholm et al., 1974a). This is a somewhat disconcerting conclusion, since it will now be necessary to work through a fair number of systems in order to find out the structural factors favouring either type of process. 

Tetraphenylethylene is coupled to 9,10-diphenylphenanthrene (Table 7, number 3). The corresponding coupling with tri- and diphenylethylene was unsuccessful. It was proposed that the initially formed cation radical disproportionates to a dication that couples to the observed product [138]. 

The oxidation of substituted tetraphenylethylenes (IV) to dications depends on the solvent and substituents, and is either separated and sequential (two one-electron waves observed, E > E ), concerted (single two-electron wave, E < E ) or sequential with AE = 0. 

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