Benzoylation and Properties of 14-π Nickel(II)-Tetraazaannulene Complexes with Substituents on the Phenyl Ring

The benzoylated asymmetrical nickel(II) complexes, 2,4,9,11-tetramethyl-3,10-dibenzoyl-1,5,8,12-([14]-Xbenzo)tetraazacyclotetradecinato(2-)nickel(II) ( A_1-4) and 2,4,10,12-tetramethyl-3,11-dibenzoyl-1,5,9,13-([15]-Xbenzo)tetraazacyclotetradecinato(2-)nickel(II) (B_1-4), wherein X = CH₃(A₁ and B₁), H ( A₂ and B₂), Cl (A₃ and B₃) and NO₂(A₄ and B₄), have been synthesized and characterized by analysis, IR, electronic, ¹H- and ¹³C-NMR spectra. An intense IR band due to C=O stretching is present in the range 1630-1650 cm^-1 upon benzoylation. Electronic spectra show bands at 375-390 nm with k_max = 10000-26000 M^-1cm^-1 due to π→π* transitions of macrocycles and at 500-550 nm with k_max = 1000-5000 M^-1cm^-1 attributable to LMCT for each of the complexes. The proton peaks of methine sites in the NMR spectra disappear on benzoylation. Results of the carbon-13 NMR spectra are compatible with those of the proton NMR. Cyclic voltammograms of the complexes in acetonitrile exhibit two successive and reversible (irreversible in DMSO) oxidation peaks for the macrocycle (Mc M Mc ^{” +} and Mc ^{” +} M Mc ²⁺) in the ranges +0.31 - +0.51 and +0.60 - +0.84 V, respectively. In the reduction area, a reversible wave is followed by reduction of metal {Ni(II) M Ni(I) at around m 2.32 V}. Unlike analogous complexes without the benzoyl group, those compounds are not electropolymerized by cyclic voltammetry.

Keywords:

• Asymmetric 14-π Nickel(II)-tetraazaannulene
• Benzoylation
• Substituent Effect
• Electrochemistry