An Antiaromatic Porphyrin Complex:  Tetraphenylporphyrinato(silicon)(L)2 (L = THF or Pyridine)

Treatment of Si(TPP)Cl2 (TPP = tetraphenylporphyrinato) with 2 equiv of Na/Hg in THF yields the reduced porphyrin complex, Si(TPP)(THF)2, in which the porphyrin ring system has an oxidation state of 4- and the complex is antiaromatic. Single-crystal X-ray diffraction reveals that Si(TPP)(THF)2 is highly ruffled and exhibits a unique C-C bond length alternation around its periphery. In addition, experimental 1H and 29Si NMR chemical shifts and NICS (nucleus-independent chemical shift) calculations on a model compound indicate a strong paratropic ring current in Si(TPP).