An Unusual Cleavage and Macrocyclization in the Zinc-Aqueous Acid Reduction of [2-Methyl-2-Nitro-N,N'-Bis(Pyridin-2-Ylmethyl)-Propane-1,3-Diamine]Coppe R(II) Cation - Crystal-Structure of the (6,13-Dimethyl-1,4,8,11-Tetraazacyclotetradecane-6,13-Diamine)Copper(II) Perchlorate Product

Abstract

Reduction of [2-methyl-2-nitro-N,N?-bis(pyridin-2-ylmethyl)propane- 1,3-diamine]copper(II) with zinc in aqueous hydrochloric acid and subsequent recomplexation yields the macromonocyclic complex (6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine)copper(II) perchlorate as the major product, apparently by cleavage of both pyridine rings from the precursor ligand and direct recombination of two saturated residues. Catalytic reduction of the nitro group in the precursor compound can be achieved cleanly over palladium-carbon with hydrogen. The macrocyclic complex crystallized in the space group P2₁/c, a 8.031(4), b 17.45(1), c 8.436(5) Ǻ, β 117.87(4)°, Z 2; for a single-crystal X-ray structure determination R was 0.078 for 1378 'observed' reflections. The complex is centrosymmetric, the macrocycle having pendant amines on opposite sides of the macrocyclic plane, while perchlorate oxygen atoms occupy the axial sites with Cu-O at 2.59 Ǻ. Observed Cu-N distances of 2.022(6) and 1.996(7) Ǻ are longer than usual for copper(II) amines. Electron spin resonance and electronic spectroscopy define an essentially square-planar geometry in solution, with only weak axial interactions.