Preparation and dioxygen binding properties of a new cobalt(II) complex and the crystal structure of the corresponding copper(II) adduct

The synthesis and characterization of a new cobalt(II) complex [Co(Me2H2Me2malox)(py)2][Me2H2Me2malox = 4,4′-oxalyldinitrilodi(pent-2-en-2-olato)(2–), py = pyridine], based on a chelating ligand containing no saturated chelate rings, is described together with the corresponding cobalt(III) complex. The cobalt(II) complex binds dioxygen in a reversible manner in pyridine solution at temperatures near –20 °C. The corresponding copper(II) complex [Cu(Me2H2Me2Me2malox)] crystallizes in the monoclinic system P21/c with a= 8.866(1), b= 16.029(1), c= 9.106(1)A, β= 97.57(2)° and Z= 4. Structural refinement resulted in R= 0.0423 and R′= 0.0436 for 2153 observed reflections. Studies of [Cu(Me2H2Me2malox)] using X-ray crystallography and IR spectroscopy guided the development of the synthetic procedure used in the isolation of the cobalt(II) adduct. A six-co-ordinate cobalt(III) complex is reported as a model for the cobalt–dioxygen adduct. Proton exchange with solvent has been observed using NMR spectroscopy and implications for the rational design of dioxygen carriers is discussed.