Perfluoroaryltetrahedranes: tetrahedranes with extended sigma-pi conjugation.

The first stable aryl-substituted tetrahedrane derivatives 4-6 were synthesized by the reaction of tris(trimethylsilyl)tetrahedranyllithium with hexafluorobenzene or [(pentafluorophenyl)ethynyl]benzene in THF. Tetrahedranes having the fluoroaryl groups as electron-withdrawing substituents were found to be thermally stable up to 170 degrees C. X-ray analyses of 4 and 6 and UV-vis absorption spectra of 4-6 suggest sigma-pi conjugation between the strained tetrahedrane core and the benzene ring, which causes a considerable bathochromic shift.