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.