Template synthesis of N-aminoethylated hexaaza macrobicyclic nickel(II) complexes containing one four-membered chelate ring

New nickel(II) complexes of the hexadentate macrobicycles 6-(2-aminoethyl)- 1,3,6,9,11,14-hexaazabicyclo[12.3.1]octadecane (1), 6-(2-aminoethyl)-1,3,6, 9,11,14-hexaazabicyclo[12.2.1]heptadecane (2), and 6-(2-aminoethyl)-1,3,6,9 ,11,15-hexaazabicyclo[13.3.1]- nonadecane (3) have been prepared selectivel y by the metal template condensation of formaldehyde with tris(2-aminoethyl )amine and a triamine (1,4,8-triazaoctane, 1,4,7-triazaheptane, or 1,5,9-tr iazanonane). The complexes [Ni(L)](2+)(L = 1, 2, or 3), in which one 2-amin oethyl pendant arm is coordinated to the metal ion, have distorted octahedr al coordination geometry with a rarely observed four-membered chelate ring. They are extremely stable in neutral or basic aqueous solutions but are re adily decomposed in acidic conditions. The decomposition rate of the comple xes in HCIO4 solutions is not affected significantly by the ring size of th e macrobicyclic ligands. Synthesis and characterization of the nickel(II) c omplexes are reported, together with the crystal structure of [Ni(1)][ZnCl4 ]. (C) 2001 Elsevier Science B.V. All rights reserved.