Monomeric di-oxygen adducts of high spin cobalt(II) complexes

The complexes Co(s-R 2 en) 2 X 2 where R is Me, Et, and X is Cl, Br, I, NCS, or NO 3 , are shown to reversibly bind di-oxygen in polar solvents. Electron spin resonance and spectrophotometric measurements reveal the formation of 1:1 adducts which are fairly stable towards further reaction. Thermodynamic binding constants are determined and are found to be larger than hitherto reported for such Co(II)-O 2 systems. This is ascribed to the high basicity of the amines employed. Conductivity measurements reveal extensive hydrogen bonding for these adducts in butyronitrile.