Different phenylboronic acid azaester formation modes in a substituted zinc phthalocyanine and its precursor

With the aim of preparing a novel Zn phthalocyanine bearing four phenylboronic azaester substituents at peripheral positions, 4(2-(bis(2-hydroxyethypamino)ethoxy]phthalonitrile (2) was synthesized by the aromatic nucleophilic substitution reaction of 4-nitrophthalonitrile with triethanolamine. 2,9(10),16(17),23(24)-Tetrakis-[2-(bis( hydroxyethyl)amino)ethoxy]-phthalocyaninatozinc (II) (4) was prepared from the cyclotetramerization of dinitrile 2 in the presence of anhydrous zinc(II) acetate by microwave irradiation. Alternatively, treatment of 2 with phenylboronic acid yielded the phenylboronic azaester (3), namely 4-(2-(2-phenyl-1,3,6,2-dioxazaborocan-6-ypethoxy)phthalonitrile. Treatment of phthalocyanine 4 with phenylboronic acid in a mixture of DMSO/toluene (20/1, v/v) afforded the desired phthalocyanine 5. The novel compounds were characterized by elemental analyses, IR, UV-Vis, H-1, C-13 and B-11 NMR spectra. The B-11 NMR data indicated that the boron atom of phthalonitrile 3 is in the tetra-coordinated state with the formation of a coordinative N-B bond (closed form), while in the case of phthalocyanine 5, the open conformer possessing a tricoordinated B atom is favoured. (C) 2012 Elsevier Ltd. All rights reserved.