The doubly oxidized, antiaromatic tetraphenylporphyrin complex [Li(TPP)][BF4].

[reaction: see text] Oxidation of dilithium tetraphenylporphyrin, Li(2)(TPP), yields the doubly oxidized porphyrin complex [Li(TPP)][BF(4)]. Free TPP appears to be unstable. The crystal structure of [Li(TPP)][BF(4)] reveals that the 16-atom C-N inner ring of the porphyrin consists of alternating single and double bonds. NMR spectroscopy and nucleus-independent chemical shift (NICS) calculations, in addition to the distortion from planarity observed in the crystal structure, indicate that the 16 pi-electron inner C-N ring of the porphyrin is antiaromatic.