Transformations of meso‐Iminofunctionalized Pd(II) and Ni(II)‐Complexes of β‐Alkylsubstituted Porphyrins

The meso‐imino derivatives of the palladium (II) and nickel (II) complexes of coproporphyrins I and II and β‐octaethylporphyrin were obtained by the Vilsmeier formylation followed by interaction with amines. The metal complexes of the azomethines obtained were transformed to the corresponding complexes of cyclopentane and cyclopentane‐pyrrolidone fused porphyrin derivatives by thermolysis. The plausible mechanism of such transformations was suggested and substantiated with quantum chemical calculations. Meso‐cyano‐, meso‐hydroxy‐, and meso‐aminocarbonyl derivatives of β‐octaethylporphyrin were obtained by treatment of the corresponding meso‐imino derivatives with bases. Demetalation of the nickel complex of the meso‐ hydroxy‐β‐octaethylporphyrin led to formation of the free base derivative. The structures of new types of the porphyrin derivatives were determined via X‐ray powder diffraction analysis. The obtained types of porphyrins are promising candidates to use as photosensitizers in medicine applications due to their longer wave absorption combined with high stability. New types of meso‐functionalization of porpyrins through formylation, Schiff base formation followed by thermal annulation or base treatment leading to cyclopentane‐condensed or meso‐cyano‐, meso‐amido‐, and meso‐hydroxy‐porphyrins.