Synthesis and redox reactions of amphiphilic metal(II) complexes of 5,10,15,20-tetraaryl-5,15-diazaporphyrinoids containing triethylene glycol or tetraethylene glycol units

Abstract

In this paper, we report the first examples of amphiphilic metal(II) complexes of 5,10,15,20-tetraaryl-5,15-diazaporphyrinoids (M-TADAPs) containing triethylene glycol (TriEG) or tetraethylene glycol (TetEG) auxiliaries. A common dipyrrin precursor substituted with TriEG or TetEG groups underwent metal-templated cyclization with zinc(II), nickel(II), or copper(II) acetate to afford the corresponding TriEG- or TetEG-appended M-TADAPs (M = Zn, Ni, Cu) as air-stable 19[Formula: see text]-electron radical cations. These 19[Formula: see text]-electron M-TADAPs were reversibly interconvertible with 20[Formula: see text]-electron antiaromatic M-TADAPs and 18[Formula: see text]-electron aromatic M-TADAP dications by redox reactions. The newly prepared M-TADAPs were basically amphiphilic, but their water solubilities varied considerably depending on the charge of the diazaporphyrin (DAP) ring and the number of ethylene glycol units. The neutral 20[Formula: see text]-electron M-TADAPs were poorly soluble in water, whereas the 18[Formula: see text]-electron M-TADAP dications were soluble in water. Cyclic voltammetry of all M-TADAP derivatives revealed 20[Formula: see text]/19[Formula: see text]-electron and 19[Formula: see text]/18[Formula: see text]-electron redox couples in both CH2Cl2 and H2O with appropriate electrolytes. The addition of M[Formula: see text]X (M[Formula: see text] = Li, Na; X = Cl, OH) or HCl to aqueous solutions of the M-TADAPs highlighted their reactivities with anions and changes in pH. When treated with M[Formula: see text]X in H2O, the 19[Formula: see text]-electron M-TADAP radical cations underwent anion exchange but the 18[Formula: see text]-electron Zn-TADAP dications were reduced to the corresponding 19[Formula: see text]-electron species. Upon treatment with HCl in H2O, the 19[Formula: see text]-electron M-TADAP radical cations underwent one-electron oxidation of the DAP ring, and the resulting 18[Formula: see text]/19[Formula: see text]-electron abundance ratio increased with decreasing solution pH.