Study of acid-base interactions of mono- and diazaporphyrin indium complexes with acetic and trifluoroacetic acids by 1H NMR and electronic spectroscopy

Abstract

Indium complex of 13,17-dibutyl-2,3,7,8,12,18-hexamethyl-5-azaporphyrin (Cl)InMAP was synthesized, and acid-base interactions of the meso-nitrogen atoms in (Cl)InMAP and its diaza analog (Cl)InDAP with acetic and trifluoroacetic acids were studied by 1H NMR and electronic spectroscopy. Depending on the medium, the complexes and proton-donor species HA give rise to acid solvates >N⋅⋅⋅(HA)n which are converted to final acid-base interaction products, H-complexes >N⋅⋅⋅H+⋅⋅⋅A−(HA)m or ionic associates >NH+⋅⋅⋅A−(HA)l , as the acidity of the medium rises. In acetic acid solution, the acid solvates derived from more basic (Cl)InMAP exist in equilibrium with the H-associates (pK a1 = 4.45±0.03). From (Cl)InDAP, the corresponding H-associates are formed only in the presence of H2SO4 (pK a1 = 2.10±0.03). In more polar media (solutions of trifluoroacetic acid in methylene chloride), ionic associates are formed, which involve one [(Cl)InMAP, pK 1 = 2.46±0.02] or two meso-nitrogen atoms [(Cl)InDAP, pK 1 = 2.11±0.03, pK 2 = 0.41±0.04).