Stable carbocations. Part 275. The dodecahedryl cation and 1,16-dodecahedryl dication. Proton and carbon-13 NMR spectroscopic studies and theoretical investigations

Abstract

Ionization of dodecahedryl derivatives (4, X = Cl, OH) as well as of the parent hydrocarbon 1 itself under superacidic conditions (SbF{sub 5}/SO{sub 2}ClF) gave the dodecahedryl cation, 2, which was found to be a static ion with no tendency to undergo degenerate hydrogen scrambling (on the NMR time scale) up to 0{degree}C. The unique ion 2 was characterized by {sup 1}H and {sup 13}C NMR spectroscopy. Upon prolonged exposure to the superacidic medium, the dodecahedryl cation was irreversibly transformed into the 1,16-dodecahedryl dication, 3, which opens up the possibility for regioselective difunctionalization of the dodecahedrane sphere. According to semiempirical SCF-MO calculations, the dodecahedrane skeleton is incapable of accommodating a planar cation geometry. This situation is still more acute in dictation 3, which is considered to constitute the first true sp{sup 3}-hybridized carbocation. Likewise, the static nature of these cations is shown to be due to unfavorable bending in the transition state for intramolecular 1,2-hydride shifts on the convex surface of the cage. 36 refs., 8 figs., 2 tabs.