Synthesis and Characterization of New Hexaaza Macrotricyclic Copper(II) Complexes with a 5-6-6-6 Chelate Ring Sequence

Abstract

The design and synthesis of new polyaza macrocyclic complexes have received much attention, since their chemical properties are strongly influenced by the structural characteristics of the ligands. Metal-directed condensation reactions of coordinated amines with formaldehyde are useful for the preparation of polyaza macrocyclic complexes containing N-CH2-N linkages. 4-13 For instance, the squareplanar complexes [ML] and [ML] (M = Cu(II) or Ni(II)) with a 5-6-5-6 chelate ring sequence have been prepared by the one-pot reaction of Eq. (1) or (2). Although numbers of polyaza macrocyclic complexes containing N-CH2-N linkages have been prepared and investigated, most of them contain 14-membered hexaaza macrocycles and have squareplanar coordination polyhedron with a 5-6-5-6 chelate ring sequence. Some 15-membered hexaaza macrocyclic complexes with a 5-6-5-5-4 chelate ring sequence, such as [NiL] (Eq. (3)), have been also investigated. As far as we know, however, the preparation of 15-membered hexaaza macrocyclic copper(II) or nickel(II) complexes with a 5-6-66 chelate ring sequence is not reported to date. Herein, we report new copper(II) complexes [CuL] and [CuL] with a 5-6-6-6 chelate ring sequence. They were prepared by the metal-directed reactions (Eqs. (4) and (5)) of appropriate amines with formaldehyde. Interestingly, [CuL] is considerably inert against decomposition even in concentrated acid solution, unlike [CuL] and other polyaza macrocyclic copper(II) complexes with a 5-6-6-6 chelate ring sequence. Synthesis and chemical properties of the copper(II) complexes are described.