Synthesis and Characterization of beta-Trifluoromethyl-meso-tetraphenylporphyrins
Terazono, Y. and David Dolphin
J. Org. Chem.
β-Trifluoromethyl-meso-tetraphenylporphyrins were synthesized to investigate the electronic and steric effects of the trifluoromethyl groups on the macrocycle. Preparation of these novel porphyrins was carried out by copper-assisted trifluoromethylation of β-tetrabromo-meso-tetraphenylporphyrin metal complexes and in situ generated CF3Cu. For comparison, the β-methyl analogues were also prepared. Analysis of β-trifluoro-methylporphyrins by UV-vis, NMR, and cyclic voltammetry (CV) showed that the electron-withdrawing effects of the trifluoromethyl groups on the antipodal pyrroles required the macrocycle to take a fixed 18π-electron pathway. UV-vis, CV, and molecular modeling studies suggest that the novel porphyrins are distorted following introduction of trifluoromethyl groups onto the pyrrolic β-position of meso-tetraphenylporphyrin. The pKa difference of β-tetrakis(trifluoromethyl)-meso-tetraphenylporphyrin from that of DBU in CH2Cl2, obtained by spectrophotometric titration, affirms that it is one of the most electron-deficient porphyrins so far prepared