Structural modification and kinetic stability of octaethylporphyne complexes with palladium (II)

The influence of gradual meso-phenyl substitution in 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyne (H2OEP) on the stability of its complexes with Pd(II) in comparison to the meso-tetraphenylporphyne complex with unsubstituted C-beta atoms is investigated by means of the chemical kinetics and physicochemical analysis. Using the spectral methods, the states and reactions of complexes in the AcOH-H2SO4 mixures is studied for the wide range of compositions. It is found that, the coordination centers are stable in mixtures with compositions of up to 100% of H2SO4. Whether in the molecular state or in association with a proton (PdOEP and its mono-meso-phenyl derivative), the complexes undergo transformations that are investigated by chemical kinetics. It is shown that instead of the usual dissociation of the coordination center, single-electron oxidation in the macrocycle of complexes takes place. A multistage mechanism is revealed that involves the kinetically significant equilibrium between the formation of H-associated complex and irreversible coordination of molecular oxygen, followed by the acid-assisted transfer of an electron from the aromatic system to this oxygen. The oxidation stability of complexes is determined, and the relation between the structure of macrocyclic ligand and the electronic structure of coordination center is discussed.