Interaction of Porphyrins and Porphyrin Analogs with Coordinating Organic Solvents

Abstract

Chemical interaction “porphyrin-solvent” between the reaction center of basic solvent and weakly acidic macrocyclic NH group is analyzed for different types of porphyrin ligands (H2P). Planar and distorted ligands, common H2P and porphyrin analogs are considered using spectrophotometric titration, kinetic measurements, 1H NMR and fluorescent spectroscopy as well as quantum-chemical calculations. Reaction is usually reversible for non-planar compounds and proceeds in kinetic regime in the case of H2P with more rigid aromatic structure like porphyrazines. Deepening of the saddle non-planar conformation favors formation of H-associates as compared to other distorted types of porphyrins (ruffle, wave, stepped, etc.) due to polarization of saddle structure. In dependence on the class of H2P analogs they either, like corroles, repeat behavior of saddle non-planar common porphyrins, or undergo some kind of specific transformations like tautomerism of inverted H2P analogs. Addition of a stronger base like diethylamine or piperidine to solution of H-associate in polar donating solvent usually results in formation of porphyrin monoanion.