Aluminum Tetraphenylporphyrin and Aluminum Phthalocyanine Neutral Radicals

Treatment of tetraphenylporphyrinato(aluminum) chloride, Al(TPP)Cl, with Na/Hg in THF yields the stable radical Al(TPP)(THF)2.
Similarly, treatment of aluminum phthalocyanine chloride, Al(Pc)Cl, with Na/Hg in THF yields the stable radical Al(Pc)(THF)2.
Solution-phase magnetic susceptibility measurements show that
both are monomeric radicals in solution, and ESR spectroscopy
and density functional theory (DFT) calculations indicate that in
both molecules the unpaired electron is delocalized throughout
the ring system. While DFT calculations indicate that both
molecules should undergo a Jahn−Teller distortion, only the
porphyrin complex exhibits the predicted C−C bond length
alternation in its X-ray crystal structure. That distortion of the ring
system has precedent only in the similar reduced porphyrin complex
Si(TPP)(THF)2.