Oxidative dehydrogenation of a saturated tetraaza macrocyclic nickel(II) complex: selective formation of nickel(II) complexes containing one or two imino groups

Abstract

The reaction of the saturated polyaza macrocyclic nickel(II) complex [NiL¹][ClO₄]₂(L¹= C-meso-3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.0^7.12] docosane) with concentrated HNO₃ in water–methanol (1 : 1) solution yielded the low-spin nickel(III) complex [NiL¹(NO₃)₂]ClO₄. The latter is further oxidized in the presence of the acid to produce the diimine complex [NiL²]²⁺(L²= 3,14-dimethyl-2,6,13,17-tetraazatricyclo-[16.4.0.0^7.12]docosa-2,13-diene). The monoimine complex [NiL³][ClO₄]₂(L³= C-meso-3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.0^7.12] docos-5-ene) can also be prepared by the oxidative dehydrogenation reaction of [NiL¹]²⁺ with HNO₃ in water–acetonitrile (1 : 1) solution. The square-planar nickel(II) complexes of L² and L³ were characterized. The crystal structure of [NiL³][ClO₄]₂ shows that the complex has a somewhat distorted square-planar geometry.