Rhodium(III) and Iridium(III) Complexes with Octaphenyltetraazaporphine: Synthesis and Study of Their Acid Forms in Proton-Donor Media

Abstract

The Rh(III) and Ir(III) complexes with octaphenyltetraazaporphine (X)MOPTAP (M = Rh, X = HSO4, OH; M = Ir, X = HSO4) are synthesized and their specific acid–base interactions in the CF3COOH–CH2Cl2 and H2SO4–CH3COOH systems are studied. The quantitative characteristics of equilibria between the acid and basic forms are obtained. The stability constants рK 1 of the first acid forms, in which one of the meso-N atom is protonated, for hydrosulfate (HSO4)MOPTAP complexes in the H2SO4–CH3COOH mixture are equal to –0.54 (Rh) and 0.0057 (Ir). The Ir complexes have more basic meso-N atoms due to more strong π-backbonding effect of coordination and, therefore, the second protonation stage (рK 2 = –4.25) could be also observed. In the CF3COOH–CH2Cl2 mixture, the basic properties of the meso-N atoms are levelled out. For (HSO4)RhOPTAP рK 1 = 1.35, while for (HSO4)IrOPTAP рK 1 = 1.24 and рK 2 = 0.45.