Synthesis and characterization of nickel(II) complexes of di- N-alkylated 14-membered tetraaza macrocycles containing cyclohexane rings via regioselective alkylation reaction

Abstract

Square-planar nickel(II) complexes of new di- N-alkylated 14-membered tetraaza macrocycles 6,17-dimethyl (L 5),6,17-diethyl (L 6), and 6,17-bis(n-propyl) (L 7) derivatives of 3,14-dimethy1-2,6,13,17-tetraazatricyclo-[16,4,0 1.18O, 7.12]docosane (L 1) have been prepared by one-step, regioselective reaction of [NiL 1] 2+ with RI (R  Me, Et, or n-Pc) in basic Me 2SO solution. The nickel(II) complexes were characterized by 1H and 13C NMR spectroscopy and/or by single crystal X-ray crystallography. Crystal structures of [NiL 1] (ClO 4) 2 and the di- N-propyl derivative [NiL 7] (ClO 4) 2 show that the two complexes have normal square-planar coordination geometries with the nickel atoms lying on the N 4 planes; however, the NiN bond distances of the latter are about 0.03 Å longer than those of the former. The electronic spectra, redox potentials and/or structures of the nickel(II) complexes are strongly affected by the presence of N- and C-substituents, but little affected by the nature of the N-alkyl groups.