A Direct Synthesis of Carbaporphyrinoid Systems

Joseph Szymanski
Illinois State University

Benziporphyrins, carbaporphyrins in which one of the pyrrolic units have been replaced by a benzene ring, have previously been synthesized via multistep routes. These systems are part of a group of porphyriniods that exhibit interesting chemistry. A two-step synthesis of dimethoxytetraarylbenziporphyrins has been achieved; exploitation of this direct route has allowed convenient exploration of this system’s properties and reactivity. Although these porphyrin analogues are cross-conjugated, the diprotonated species possess a significant diamagnetic ring current. Also, reaction with either nickel(II) acetate or palladium(II) acetate affords the corresponding organometallic derivatives, both of which have borderline aromatic characteristics. In addition, reaction with silver(I) acetate results in oxidation of the internal benzene carbon to introduce an acetate group that is oriented into the center of the macrocycle. Surprisingly, although it is predicted that this acetate group considerably distorts the planarity of the macrocycle, this species also shows significant aromatic character upon diprotonation.