Bridged (alkoxo)CoIII(salen) complexes: synthesis and structure

The preparation and oxygenation of CoII(salen) complexes 2a–d whose ethanediyl moieties carry an ω-hydroxyalkyl pendant arm is reported. Air oxidation of 2a gives bridged (alkoxo)CoIII(salen) complex 1a with a planar salen ligand. Upon aeration of 2b in MeOH, monomeric bridged complex 1b with a planar salen ligand precipitates, whereas in CH2Cl2 a dimeric bridged complex 1b′ with twisted-salen ligands is obtained and characterized by X-ray crystallography. Formation of a bridged (alkoxo)CoIII(salen) complex upon aeration of 2c is probably followed by β-elimination. The tert-butyl substituted oxidation product of 2d is paramagnetic in non-coordinating and diamagnetic in coordinating solvents, supporting the concept that the salen moiety of (alkoxo)CoIII(salen) complexes can have either a planar or a twisted geometry depending on the solvent and the solid state properties.