Synthesis and optical, magnetic, and electrochemical properties of 5,10,15,20-tetraaryl-5,15-diazaporphyrin — tertiary amine conjugates

Abstract

We report on the synthesis and optical, magnetic, and electrochemical properties of nickel(II) and copper(II) complexes of 5,10,15,20-tetraaryl-5,15-diazaporphyrin–tertiary amine (TADAP–TA) conjugates. Metal-templated cyclization reactions of 9-(4-(dimethylamino)phenyl)amino-1-chloro-5-mesityldipyrrin and 9-(4-(diphenylamino)phenyl)amino-1-chloro-5-mesityldipyrrin (mesityl = 2,4,6-trimethylphenyl) with nickel(II) or copper(II) acetate afforded the corresponding metal(II) complexes of TADAP–TA. The 20[Formula: see text], 19[Formula: see text], and 18[Formula: see text] oxidation states of the DAP ring in the TADAP – TAs were reversibly interconvertible by redox reactions. NMR spectroscopy of the 20[Formula: see text] and 18[Formula: see text] Ni-TADAP – TAs revealed their antiaromatic and aromatic characters, respectively, whereas electron paramagnetic resonance spectroscopy of the 19[Formula: see text] Ni-TADAP–TAs showed effective delocalization of an unshared electron spin in the DAP ring. The interconversion between the three oxidation states of TADAP – TAs also caused a distinct change in the optical properties of the DAP [Formula: see text]-electron system. Notably, all the 18[Formula: see text] dications exhibited weak and broad absorption bands in the near infrared region owing to the charge-transfer from the peripheral tertiary amine units (donor) to the cationic DAP center (acceptor). Cyclic voltammetry of TADAP – TAs exhibited the reversible 20[Formula: see text]/19[Formula: see text] and 19[Formula: see text]/18[Formula: see text] redox couples and the irreversible amine oxidation at the periphery. The electrochemical oxidation of the Ni-TADAP–triphenylamine conjugate generated reactive ammoniumyl radicals, which underwent intermolecular coupling to form a polymer of TADAP–TA on the electrode surface.