5-(2-Pyridyl)tetrabenzoporphyrin and Its Complexes with Zinc, Cobalt, Copper, and Iron. Synthesis, Spectral, Electrochemical, and Electrocatalytic Properties

Abstract 3-(Pyridin-2-ylmethylene)isoindolin-1-one was synthesized by the reaction of phthalimide with 2-picoline in the presence of zinc oxide. Heating its mixture with an excess of phthalimide and zinc acetate leads to the formation of zinc 5-(2-pyridyl)tetrabenzoporphyrinate, which, upon treatment with acid, is converted to 5-(2-pyridyl)tetrabenzoporphyrin. The latter, when reacting with cobalt(II), copper(II), and iron(III) chlorides in DMF, forms the corresponding metal complexes. The composition and structure of the obtained compounds were confirmed by mass spectrometry, vibrational, 1H NMR, and electron spectroscopy. The results of quantum-chemical calculations of complexes by the DFT method are presented. It is found that the energy gap between the frontier orbitals correlates with the positions of the first bands in the electronic absorption spectra. All the synthesized tetrabenzoporphyrins exhibit catalytic activity in the electroreduction of oxygen, cobalt and copper complexes being the most active.