Synthesis and X-ray Crystal Structure Determination of the First Copper(II) Complexes of Tetraazamacrocycle−Glyoxal Condensates

Novel Cu<sup>II</sup> complexes CuLCl<sub>2</sub> (L = <b>1</b><b>−</b><b>4</b>) have been synthesized containing the metal bound to a well-known type of tetracyclic bisaminal formed from the condensation of glyoxal and tetraazamacrocycles (<b>1</b> = cyclam−glyoxal condensate, <b>2</b> = [13]aneN4−glyoxal condensate, <b>3</b> = cyclen−glyoxal condensate, <b>4</b> = isocyclam−glyoxal condensate). The four-coordinate complexes were characterized by X-ray crystallography, electronic spectroscopy, solid-state magnetic moments, and electron spin resonance spectroscopy. The tetracyclic bisaminals, although having four potential donor atoms, are bound in a <i>cis</i>-bidentate fashion to Cu<sup>II</sup> with two additional <i>cis</i>-chloride donors. The ligands take up folded conformations, and with the exception of ligand <b>4</b>, only nonadjacent nitrogen atoms coordinate. As expected, ligand <b>2</b> in Cu(<b>2</b>)Cl<sub>2</sub> has a folded structure similar to those of the previously characterized <b>1</b> and <b>3</b>. The conformation of <b>4</b> in the complex Cu(<b>4</b>)Cl<sub>2</sub> differs from <b>1</b><b>−</b><b>3</b> in that three nitrogens direct their lone pairs to one side of the folded tetracycle, with adjacent nitrogen atoms coordinated to Cu<sup>II</sup>. This difference is probably caused by the presence of the more flexible seven-membered ring rather than the five- to six-membered rings in <b>1</b><b>−</b><b>3</b>. Air oxidation of Cu<sup>I</sup> in the presence of <b>1</b> or <b>3</b> results in bis(μ-hydroxo) dimers as characterized by X-ray crystal structures, suggesting dioxygen binding, followed by O−O bond splitting to give the Cu<sub>2</sub>O<sub>2</sub> diamond core.