Synthesis and characterization of new adjacent-bridged tetraaza macrocyclic compounds with C-alkyl groups: crystal structure and spectral properties of a copper(II) complex

Abstract

New structurally constrained tetraaza macrocycles 2,3-dimethyl-1,5,12,16-tetraazapentacyclo[14.6.3.3(5.12).0(6.11).0(17.22)]octacosane (L-6) and 2,2,4,10,12,18,20-octamethyl-1,5,9,13-tetraazatricyclo[11.3.2. 2(5.9)]eicosane (L-7) have been prepared in high yield by direct reaction of 1,3-dibromopropane with 3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.0(7.12)]docosane (L-3) or 2,5,5,7,9,12,12,14-octamethyl- 1,4,8,11-tetraazacyclodecane (L-5). The macrocycle L-6 readily reacts with anhydrous copper(II) ion to yield [CuL6](2+) in dry methanol but does not react with nickel(II) ion, showing a high copper(II) ion selectivity. On the other hand, neither of the metal ions is inserted into the cavity of L-7 in similar conditions. The copper(II) complex [CuL6] (ClO4)(2) has a severely distorted square-planar coordination polyhedron with a rarely observed trans-IV type N-conformation. The visible absorption spectrum of [CuL6](2+) shows the d-d transition band at 490 nm (epsilon = 690 M-1 cm(-1)); the wavelength is quite similar to that of [CuL3](2+), but the molar absorption coefficient is extraordinarily larger than those of [CuL3](2+) and other related tetraaza macrocyclic copper(II) complexes. (C) 2004 Elsevier B.V. All rights reserved.