Syntheses and properties of the mesoionic analogues of sesquifulvalene possessing a 1,3-diphenyltetrazolium ring

Abstract

The mesoionic analogue of sesquifulvalene, 1,3-diphenyltetrazol-5-yliocyclopentadienide (1), and the benzannelated indenide (2), fluorenide (3), and cyclopenta[def]phenanthrenide derivatives (4), have been synthesized from the 5-ethoxy-1,3-diphenyltetrazolium salt and the corresponding carbanion. The electronic structures of the synthesized fulvalenes are discussed on the basis of their spectroscopic evidence and it is shown that the polarized structures make a significant contribution to the ground state of these π-electron systems. The influence of benzannelation on the structure of the mesoionic fulvalene system is also described.