Dicationic salt of β-alkyl substituted sapphyrin-type porphyrinoid: Acid-basic properties, thermal stability and quantum-chemical calculations

The UV-Vis spectra of the dicationic salt of 2,3,7,13,17,18,18,22,23-octamethyl-8,12-diethylsapphyrin {H 5 β-Me 8 Et 2 Sap[Formula: see text](Cl[Formula: see text]} in solutions with different polarity and acid-basic properties have been investigated. The tautomeric and acid-base equilibria of H 5 β-Me 8 Et 2 Sap[Formula: see text](Cl[Formula: see text] in the presence of organic bases have been examined by spectrophotometric titration. It was demonstrated that an addition of small amounts of 1,8-diazabicyclo[5.4.0]undecene (DBU) and tetramethylammonium hydroxide (Me 4 NOH) dissolved in methylene chloride (DCM) and MeOH, respectively results in a stepwise detachment of two protons from the basic nitrogen atoms of the macrocycle, with no anionic forms of sapphyrin being registered. The results obtained were supported using quantum-chemical calculations (DFT, B3LYP, cc-pVDZ including NBO analysis). The interactions of 2,3,7,13,17,18,18,22,23-octamethyl-8,12-diethylsapphyrin (H 3 β-Me 8 Et 2 Sap) with a series of compounds of different acidity and basicity were studied and the formation of very weak hydrogen bond of H 3 β-Me 8 Et 2 Sap as NH-acid with N,N-dimethylformamide (DMF) molecule with the value of the interaction energy (E[Formula: see text] equal -16.40 kJ/mol was revealed. The low acidity of bonds NH in the sapphyrin molecule was confirmed on the base of thermogravimetric data obtained for the solid samples of H 5 β-Me 8 Et 2 Sap[Formula: see text](Cl[Formula: see text] evaporated from DMF and DCM concentrated solutions.