Synthesis of hydrophilic copper(II) complexes of 5,10,15,20-tetraaryl-5,15-diazaporphyrins substituted with carboxy or (2,3-dihydroxypropyl)carbamoyl groups

Abstract

Porphyrins containing hydrophilic auxiliaries have received considerable attention. Herein we report the first examples of strongly hydrophilic copper(II) complexes of 5,10,15,20-tetraaryl-5,15-diazaporphyrins (TADAPs) substituted with carboxy or (2,3-dihydroxypropyl)carbamoyl groups. Metal-templated cyclization reactions of a common dipyrrin precursor with nickel(II) or copper(II) acetate afforded the corresponding metal(II) complexes of 5,10,15,20-tetrakis(4-alkoxycarbonylphenyl)-5,15-diazaporphyrin (M-TADAP-COOR; M = Ni, Cu) as air-stable 19[Formula: see text] radical cations, which were reversibly interconvertible with 20[Formula: see text]- and 18[Formula: see text]-electron states by redox reactions. NMR spectroscopy of 20[Formula: see text] and 18[Formula: see text] Ni-TADAP-COORs revealed antiaromatic and aromatic characteristics, respectively. Alkaline hydrolysis of the 19[Formula: see text] Cu-TADAP-COOR afforded a carboxylic acid, Cu-TADAP-COOH, which was freely soluble in water under basic conditions, but poorly soluble under neutral or acidic conditions. Dehydrative condensation of Cu-TADAP-COOH with 2,3-bis((tert-butyldimethylsilyl)oxy)propan-1-amine followed by deprotection of the silyl groups afforded an amide, Cu-TADAP-CONHR, with four (2,3-dihydroxypropyl)carbamoyl groups. Although the 20[Formula: see text] Cu-TADAP-CONHR was poorly soluble in water, oxidation of its DAP ring notably changed the solubility, and the resulting 18[Formula: see text] dication was homogeneously dispersed in neutral water. Cyclic voltammetry of the present TADAP derivatives showed the 21[Formula: see text]/20[Formula: see text], 20[Formula: see text]/19[Formula: see text] and 19[Formula: see text]/18[Formula: see text] redox couples in the range of −1.8 to +0.2 V vs. Fc/Fc[Formula: see text]. Furthermore, Cu-TADAP-CONHR exhibited reversible redox processes in neutral water. This study shows that TADAP could be a potential platform for the development of hydrophilic DAP-based materials.