Design, synthesis, structural analysis and atropoisomerisation studies of polynucleating ligands based on porphyrins bearing catechol units

New polynucleating ligands based on a combination of a meso-tetrakis( phenyl) porphyrin core and four catecholamido units connected at the ortho positions of the phenyl moieties have been prepared. All four atropoisomers of the methoxy-protected meso-tetrakis(o-catecholamidophenyl) porphyrin 2 were obtained in high yields, however, the separation of isomers, although achievable, was found to be extremely tedious and did not allow he preparation of large quantities of the different atropoisomers. This difficulty was overcome by first separating he atropoisomers of the precursor meso-tetrakis(o-aminophenyl) porphyrin 3 and then by a quantitative condensation reaction of he separated isomers with the acyl chloride derivative of methyl-protected catechol 6. All four atropoisomers were subsequently deprotected in quantitative yields using BBr3. Although following this route he protected 2(alpha4) and 2(alpha3beta) atropoisomers were obtained on the gram scale, for he other two 2(alphabetaalphabeta) and 2(alpha2beta2) isomers, due to separation difficulties, only low quantities could be synthesised. After a systematic kinetic study of the atropoisomerisation process, the 2(alphabetaalphabeta) isomer was obtained in large quantities by thermal isomerisation of he random mixture of isomers of 2 in toluene a 110degreesC in he presence of a large excess of trifluoroacetic acid, whereas the 2(alpha2beta2) isomer was isolated under he same conditions but in the absence of acid. All four atropoisomers were characterised by classical 1- and 2-D NMR spectroscopy. Furthermore, the 1(alphabetaalphabeta), 1(alpha4), 2(alphabetaalphabeta), 2(alpha4) and 3(alphabeta)alphabeta atropoisomers were also characterised in the solid state by X-ray diffraction on single crystals.