Expansion of a Pyrrole in meso-Tetraphenylporphyrin to a Pyrazine Imide Moiety Using a Beckmann Rearrangement

The group 10 metal complexes of ,-dioxoporphyrin monooxime 10M (M = NiII, PdII, PtII) are susceptible to a Beckmann rearrangement to produce the corresponding ring-expanded metallopyrazinoporphyrin imides 11M in good yields. These chromophores possess metallochlorin-like optical properties. Demetalation of the NiII complex furnishes the free-base porphyrinoid 11, which possesses a porphyrin-like optical spectrum. The monooximes are ultimately derived from meso-tetraphenylporphyrin, and the formal replacement of the porphyrin ,-double bond by an imide functionality is thus demonstrated. The imide functionality serves as a synthetic handle for further modification of the chromophore.