New insights into the synthesis of porphyrin-corrole and biscorrole systems

As in the case of porphyrins, the relatively easier synthesis of meso-substituted corroles compared to that of beta-pyrrole substituted ones greatly limits the use of these latter derivatives. Here we show, for the synthesis of beta-substituted biscorrole and porphyrin-corrole dyads, that a simple replacement of sodium hydrogen carbonate by sodium acetate in the final cyclisation step of the a,c-biladiene to the corrole ring, increases the yield by at least a factor of 3. This reaction can be extended to the synthesis of beta-substituted monocorroles. Moreover, when cobalt acetate is added instead of the reoxidation step, a 34 to 63% yield in porphyrin-spacer-Co(III) corrole is obtained, thus avoiding isolation of the free-base and further metalation of this latter derivative. This "cyclisation-oxidation-metalation" reaction is of particular interest in the preparation of heterobimetallic species in porphyrin-corrole series. Indeed, it leads to the formation of the monocobalt derivative with the cobalt atom inside the cor-role moiety allowing for the further insertion of a large variety of metals into the porphyrin macrocycle. Crystals of the monocobalt complex of a biphenylene bridged porphyrin-corrole derivative were obtained in the presence of pyridine and the structure was determined by Xray diffraction analysis. The structure shows that only one pyridine molecule is bound to the cobalt centre in an exo position, thus indicating a strong steric hindrance from the porphyrin counterpart. Copyright (C) 2003 Society of Porphyrins & Phthalocyanines.