Hydrolytic Cleavage and Deborylation of Boron(III) Subphthalocyanines─A Synthetic Approach to Fused Diazatripyrrins

Abstract

Boron(III) subphthalocyanine analogues with enhanced electron affinity in the presence of water undergo hydrolytic cleavage of the macrocycle and deborylation, resulting in formation of noncyclic aza-bridged tris-isoindoles, which are fused derivatives of 5,10-diazatripyrrines (DATRIPY). Spectral data, kinetic studies, and DFT results allow us to suggest a plausible mechanism of DATRIPY formation, which includes nucleophilic addition of water to one of the C_αN_meso bonds and its rupture as a key stage. This reaction is possible for perhalogenated or/and azasubstituted boron(III) subphthalocyanine analogues and occurs especially easily for hexachlorinated tripyrazinosubporphyrazinatoboron(III) chloride, affording the corresponding 14-amino-5,10-diazatripyrrin-1-one [DATRIPY1a] bearing fused dichloropyrazine fragments in each pyrrole unit. An X-ray diffraction study revealed that DATRIPY1a has an S-like conformation, which is stabilized by two intramolecular hydrogen bonds between pyrrolic NH groups and pyrrolenine and pyrazine nitrogens. DATRIPY1a reacts with BF₃, forming a noncyclic tripyrrolic bis-boron(III) complex [BODATRIPY] in which two BF₂ fragments are bonded by pyrrole-pyrrolenine and pyrrole-pyrazine coordination sites. Due to rearrangement of intramolecular H-bonds occurring in aprotic and proton donor solvents, DATRIPY1a exhibits strong solvatochromism and can also be used as a colorimetric sensor for the presence of hard anions (fluoride, hydroxide, cyanide, and cyanate).