Dicarboxonium ions

Dodecahedryl dication 242 Diamantane-4,9-diyl dication 243 3,3 -(l,l -Biadamantyl) dication 243 Cubyl-l,4-dicarboxonium ion 244... 

The dicarboxonium ions would be useful intermediates for the diacylation of aromatics. The 1,2-dicarboxonium ion (oxalyl dication, 17) has yet to be experimentally obtained. The ionization of the oxalyl fluoride in SbFs presumably forms the donor-acceptor complex, 18, which spontaneously decomposes to CO and COF2. The expected oxalyl dication (OCCO), 17, was not observed although theoretical calculations at MP2/6-31G level indicate 17 to be a minimum on the potential energy surface. 

Several 1,4-disubstituted derivatives of the dication, 63, were successfully prepared. The 1,4-diphenyl, 1,4-dimethyl, 1,4-dicyclopropyl-substituted derivatives of carbodication 63 (65, 66, and 67) are exceptionally stable. The 1,4-dimethyl-1,4-cyclohexyl dication, devoid of the adjacent cyclopropyl groups, could not be prepared. The carbocationic center in all these dications are somewhat shielded as compared to their monocations. The C NMR chemical shifts of the carbocationic centers for the dications 65, 66, and 67 are 235.4, 293.4, and 260.8 ppm, respectively. The diprotonated ann -tricyclo(5.1.0.0 )octa-2,6-dione, 68, may be treated as a dicarboxonium ion, instead of dihydroxy dicarbenium ion, since the cabronyl carbon is shielded by only 25.2 ppm, much smaller than that observed for the protonated cyclohexanedione (34 ppm). The para carbons of the phenyl substituents in carbodication 65 are relatively shielded by about 5 ppm from that of the parent l,4-diphenylcyclohexane-l,4-diyl dication showing relatively less delocalization of the charge into the aromatic rings. 

The dissolution of the adamanantane-2,6-dione in 1 4 SbFs FSO3H/SO2 gave the 2,6-dihydroxy-2,6-adamantanediyl dication (99). This dicarboxonium ion has more oxonium character than the carbenium character as shown by the much shielded absorption for the carbonyl carbon (8 C 247.7), relative to the monocarboxonium ion, 100(8 C 267.1). ... 

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