Synthesis and Acid–Base Properties of β-Octabromo-Substituted Unsymmetrical Nitrophenylporphyrins

The bromination of [5-(4-nitrophenyl)-10,15,20-triphenylporphyrinato]cobalt(II) and [5,10,15-tris-(4-nitrophenyl)-20-phenylporphyrinato]cobalt(II) with N-bromosuccinimide in a mixture of chloroform and dimethylformamide gave [2,3,7,8,12,13,17,18-octabromo-5-(4-nitrophenyl)-10,15,20-triphenylporphyrinato]-cobalt(II) and [2,3,7,8,12,13,17,18-octabromo-5,10,15-tris(4-nitrophenyl)-20-phenylporphyrinato]cobalt(II). Treatment of the cobalt complexes with a mixture of perchloric and sulfuric acids afforded the corresponding metal-free porphyrins. Electron absorption, 1H NMR, and mass spectra of the synthesized compounds were studied, and acidity and basicity constants of the porphyrin ligands in acetonitrile were determined.