Synthesis and Characterization of Various Di-N-Functionalized Tetraaza Macrocyclic Copper(II) Complexes

Abstract

Two copper(II) complexes, [CuL 3 ](ClO 4 ) 2 bearing one N-CH 2 CH 2 CONH 2 group as well as one N-CH 2 CH 2 CN group and [CuL 4 ](ClO 4 ) 2 bearing two N-CH 2 CH 2 CONH 2 groups, have been prepared by the selective hydrolysis of [CuL 2 ](ClO 4 ) 2 (L 2 = C-meso-1,8-bis(cyanoethyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane). The complex [CuL 5 ](ClO 4 ) 2 bearing one N-CH 2 CH 2 C(=NH)OCH 3 and one N-CH 2 CH 2 CN groups has been prepared as the major product from the reaction of [CuL 2 ](ClO 4 ) 2 with methanol in the presence of triethylamine. In acidic aqueous solution, the N-CH 2 CH 2 C(=NH)OCH 3 group of [CuL 5 ](ClO 4 ) 2 undergoes hydrolysis to yield [CuL 6 ](ClO 4 ) 2 bearing both N-CH 2 CH 2 COOCH 3 and N-CH 2 CH 2 CN groups. The crystal structure of [CuL 5 ](ClO 4 ) 2 shows that the complex has a slightly distorted square-pyramidal coordination polyhedron with an apical Cu-N (N-CH 2 CH 2 C(=NH)OCH 3 group) bond. The apical Cu-N bond distance (2.269(3) A) is ca. 0.06 A longer than the apical Cu-O (N-CH 2 CH 2 CONH 2 group) bond of [CuL 4 ](ClO 4 ) 2 . The pendant amide group of [CuL 3 ](ClO 4 ) 2 is involved in coordination. The carboxylic ester group of [CuL 6 ](ClO 4 ) 2 is also coordinated to the metal ion in various solvents but is removed from the coordination sphere in the solid state.