Indium(III) complexes of octaphenylporphyrazine: Effect of halide coordination on the basic properties and stability in acid media

Abstract

Influence of halide ion coordination on the basic properties and stability of indium(III) octaphenylporphyrazine complexes in acid medium have been studied. Five-coordinated halide complexes [(Hal)InPAPh8] (Hal = F, Cl, Br) are stable in dichloromethane or chloroform solutions acidified with trifluoroacetic acid up to 100%. One of four meso-nitrogen atoms is protonated in 0.1 M solution; their basicity depending of the ionic character of In–Hal bond is decreased in the order F > Cl > Br . Addition of an excess of fluoride, chloride or bromide anions leads to formation of anionic cis-dihalide complexes cis [(Hal)2InPAPh8] - which undergo very facile demetalation with formation of the free-base H2PAPh8 even in a slightly acidified solutions (0.001 M of acid). Such catalytic effect of halide anions seems to be general for demetalation reactions of indium(III) complexes with tetrapyrrolic macrocycles and was also observed for the phthalocyanine complex [(Cl)InPc] . Coordination of iodide leads to reduction of porphyrazine macrocycle assisted by meso-protonation with formation of π-anionic species, which upon demetalation and subsequent deprotonation give a mixture of free-base porphyrazine H2PAPh8 and tetraazachlorin derivatives.