N-methylation of diamino-substituted macrocyclic complexes: intramolecular cyclisation

Abstract

Two new macropolycyclic hexaamines L² and L⁴ as their copper(II) complexes have been isolated as products from the condensation of the diamino-substituted macrocyclic complex trans-(6,13-dimethyl-1,4,8,11-tetraazacyclo-tetradecane-6,13-diamine)copper(II)[CuL¹]²⁺ with aqueous formaldehyde. Both of the complexes exhibit methylene bridges between the pendant amine and the adjacent co-ordinated macrocyclic N-donors. Their crystal structures have been determined: [CuL²(NCS)][SCN], triclinic, space group P, a= 7.133(2), b= 9.813(2), c= 16.745(3)Å, α= 101.05(2), β= 99.36(2), γ= 99.77(2)°, Z= 2; [CuL⁴Cl][ClO₄]·H₂O, triclinic, space group P, a= 9.3327(8), b= 10.8989(6), c= 12.672(1)Å, α= 68.591(6), β= 78.899(6), γ= 87.384(6)°, Z= 2. The complexes exhibit square-pyramidal geometries, and significantly lower-energy electronic maxima relative to their parent complex [CuL¹]²⁺. Electrochemistry of [CuL²]²⁺ revealed a reversible Cu^II-Cu^I redox couple, by contrast to those of macromonocyclic analogues.