Highly brominated porphyrins: synthesis, structure and their properties

This article reports the first perbromination of beta-pyrrole and meso-phenyl groups of the 5,10,15,20-tetrakis(3',5'-dimethoxyphenyl)porphinato copper(II) to generate highly brominated porphyrin, 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(2',6'-dibromo-3',5'dimethoxyphenyl)-porphinato copper(II), CuT(3',5'-DMP)PBr16 complex. Its crystal structure exhibited unusual five-coordination geometry with saddle shaped conformation of the porphyrin core. H2T(3',5'-DMP)PBr16 and its metal complexes exhibited large anodic shift of oxidation potentials with marginal changes in reduction potentials relative to their corresponding octabromotetraphenylporphyri n, MTPPBr8 derivatives. The enhanced electron deficiency of the ZnT(3',5'-DMP)PBr16 complex was probed by axial ligation of various Lewis bases with differing pK(a) values. The ZnT(3',5'-DMP)PBr16 complex exhibited decrease in equilibrium constants for the ligation of bases relative to sterically unhindered ZnTPPBr8. This has been ascribed to the sterics induced by the bulky ortho-bromo phenyl substituents that prevents the facile binding of Lewis bases to the Zn(Il)-center. Copyright (C) 2003 Society of Porphyrins & Phthalocyanines.