The Consequences of an Electrostatic 'Forced Marriage' between Two Electron-Rich Particles: Strained Ion Pairs

摘要

Two translationally independent electron-rich particles would principally repel each other, unless they had opposing electrical charge and would thus form an ion pair in a suitable solvent. Under these conditions, a novel interionic strain could buildup. which would result from the interionic orbital repulsion and should express itself in the increased reactivity of both ionic components towards other reagents. In order to confirm this, salts would have to be synthesized in which electron-rich cations are combined with electron-rich anions. Cations are generally, however, electron-deficient systems; the notable exception to this rule are the tris(dialkylamino)-substituted cyclopropenylium ions, which according to Gerson et al. can be considered aselectron-excess systems. These electronic properties are the cause of their unusual behavior in comparison to other carbenium ions: For example, the tris(dimethylamino)cyclopropenylium ion (TDA cation) functions as the donor component in deeply colored charge transfer (CT) salts with tetracyanoethylene (TCNE) or 2.3-dichloro-5.6-dicyano-rha-benzoquinone (DDQ). The TDA cation also behaves as a donor with respect to electron-deficient anions of the type EICV (E1 = Sb. Nb. Ta); in these reactions deeply coloured "inverse CT salts" with one-dimensionally stacked structures result. TDA salts can be readily oxidized to give stable isolable radical dicationic salts.