Redox switchable 19π and 18π 5,10,20-triaryl-5,15-diazaporphyrinoid–nickel(II) complexes

Abstract

The synthesis and optical, electrochemical, and magnetic properties of nickel(II) complexes of 5,10,20-triaryl-5,15-diazaporphyrin (TriADAP) are reported. Metal-templated cyclization of unsymmetrically substituted nickel(II)–bis(1-amino-9-chloro-5-mesityldipyrrin; mesityl = 2,4,6-trimethylphenyl) complexes afforded the corresponding TriADAPs or 5-aryl-15-benzyl-10,20-dimesityl-5,15-diazaporphyrin, depending on the combination of base and solvent. The latter macrocycle was converted to TriADAP by deprotection of the [Formula: see text]-benzyl group through Pd/C-promoted hydrogenation. TriADAPs were isolated in both 18[Formula: see text] (cation) and 19[Formula: see text] (neutral) forms. The interconversion between these two oxidation states resulted in a distinct change in the optical properties of the DAP [Formula: see text]-system. NMR spectroscopy of the 18[Formula: see text] TriADAP cations showed that they had aromatic character, whereas EPR spectroscopy of the 19[Formula: see text] TriADAP showed a highly delocalized electron spin of the [Formula: see text]-radical. The para substituents of the [Formula: see text]-aryl groups of TriADAPs had a small but distinct impact on their HOMO and LUMO energies. The change in the net charge of one electron was directly reflected in the redox properties of the DAP ring; TriADAP was more easily reduced and less easily oxidized than DAP. The difference in the net charge was also reflected by the shielding of the pyrrolic [Formula: see text]-protons observed in the [Formula: see text]H NMR spectra. The present results confirm that TriADAP is a highly promising framework for constructing a new class of azaporphyrin-based materials with 18[Formula: see text]–19[Formula: see text] redox-switchable optical and magnetic properties.