Synthesis of C-meso and/or C-racemic isomers of tetraaza macrocyclic copper(II) and nickel(II) complexes bearing one or two N-CH2OCH3 pendant arms

Two configurational isomers of 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazatricyclo[9.3.1.14.8]hexadecane, C-meso-L5 and C-racemic-L5, react with methanol in the presence of copper(II) ion to yield [Cu(C-meso-L2)](ClO4)2 (1) or [Cu(C-racemic-L2)](ClO4)2 (2) (L2 = 1,8-bis(methoxymethyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclodecane) bearing two N-CH2OCH3 pendant arms. The reaction of C-meso-L5 with methanol in the presence of nickel(II) ion produces [Ni(C-meso-L3)](ClO4)2·H2O (3) (L3 = 1-methoxymethyl-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclodecane) bearing one N-CH2OCH3 pendant arm. The C-meso isomer 1 exhibits trans-III-type N-configuration and has trans-octahedral coordination geometry with two axial Cu–O (N-CH2OCH3 group) bonds (2.457(3) Å), whereas 2 exhibits trans-I-type N-configuration and has severely distorted square-pyramidal coordination geometry with a relatively weak apical Cu–O (N-CH2OCH3 group) bond (2.499(3) Å). In the case of 3, the N-CH2OCH3 group is not directly involved in coordination in the solid state and in nitromethane. Effects of the C-configuration and the metal ion upon the coordination behaviors of the complexes are described.

New complexes [Cu(C-meso-L2)]2+, [Cu(C-racemic-L2)]2+, and [Ni(C-meso-L3)]2+ bearing one or two N-CH2OCH3 pendant arms can be prepared by the reaction of methanol with C-meso-L5 or C-racemic-L5 containing two N–CH2–N linkages in the presence of the corresponding metal ion. Their coordination geometries as well as the reactivity of L5 are influenced by the C-configuration of the macrocycles.Figure optionsDownload as PowerPoint slideHighlights
► Preparation of new macrocyclic copper(II) and nickel(II) complexes bearing N-CH2OCH3 pendant arm(s).
► Metal induced reactions of methanol with a macrocycle containing N–CH2–N linkages.
► Coordination geometry and chemical properties of a macrocyclic complex are influenced by the C-configuration of the ligand.