CUBYL ONIUM IONS - CUBYLCARBOXONIUM, CUBYLACYLIUM, AND DIMETHYL CUBYL-1,4-DIHALONIUM IONS

The first onium ions of cubane: cubylcarboxonium, cubylacylium, and cubylhalonium ions were prepared and characterized by C-13 NMR spectroscopy. Treatment of mono-, di-, or tetracubanecarboxylic acids (or esters) with FSO3H in either SO2CIF or SO2 gave the respective cubylcarboxonium ions. Reaction of mono- or dicubanecarbonyl chlorides with SbF5 gave rise to the corresponding mono- and diacylium ions. These ions were also subjected to theoretical investigation at the DFT B3LYP/6-31G* and IGLO II' levels. The NMR experimental data were well reproduced by the IGLO calculations with similar accuracy seen in earlier onium ion studies. The calculated charge density distributions indicate that the cubyl system by virtue of its strained C-C bonds is able to engage in hyperconjugative stabilization of the adjacent charge to a greater extent than unstrained systems such as adamantyl. Treatment of 1,4-dihalocubanes with CH3F-SbF5 complex in SO2 afforded the first stable bridgehead halonium ions, namely the dimethyl cubyl-1,4-dihalonium ions. These halonium ions were found to possess typical halonium ion structures in most respects although hyperconjugative delocalization of the positive charge also appears to be important for these species. The corresponding cubylmonohalonium ions could not be prepared as stable species.