One-Step Template-Directed Synthesis of a Macrocyclic Tetraarylporphyrin Hexamer Based on Supramolecular Interactions with a C3-Symmetric Tetraarylporphyrin Trimer

Taking into consideration the model geometry of the macrocyclic hexaporphyrin 1 as a host molecule, the structure of a benzene-centered porphyrin trimer bearing pyridine rings at the apical positions has been designed with the aim to use the latter as a template for the synthesis of its own host. Indeed, in the presence of the porphyrin trimer 5, the yield of the cyclization of a linear porphyrin hexamer, as a precursor of 1, could be improved from 8 to 30% (variable yield) to 50% (reproducible yield). Even the condensation of equimolecular amounts of porphyrin monomers 20b and 21b in the presence of 5 ledprobably through a loose preorganized complex between the latter and the Zn(II) chelate 20bto the formation of 1 in only five steps from 19, as compared with 13 steps of the synthesis via linear porphyrin hexamer in the absence of template. As evidenced by 1H NMR spectroscopic analysis of the supramolecular complex between 5 and an analogue of 1b in which all H-atoms at the pyrrole rings have been replac...