Dinuclear CoIIMII (M = Pb or Co) complexes having a “Co(salen)” entity in a macrocyclic framework: ligand modulation effect and neighboring metal(II) effect upon oxygenation at the “Co(salen)” center

Abstract

Dinuclear Co^IIPb^II and Co^IICo^II complexes, [CoPb(L)(CH₃OH)][ClO₄]₂ (L²⁻ = (L¹)²⁻1 or (L²)²⁻2) and [Co₂(L)(CH₃CN)₂][ClO₄]₂ (L²⁻ = (L¹)²⁻3 or (L²)²⁻4), have been obtained where (L¹)²⁻ is a dinucleating macrocyclic ligand derived from the [2∶1∶1] condensation of 2,6-diformyl-4-methylphenol, ethylenediamine, and diethylenetriamine and (L²)²⁻ is an analogous ligand comprised of 1,1,2,2-tetramethylethylenediamine instead of ethylenediamine. The macrocycles have a “salen”-like N₂O₂ metal-binding site and a “saldien”-like N₃O₂ site sharing two phenolic oxygens. Crystal structures of the complexes 1–4 have been determined by X-ray crystallography. Complex 1 reacted reversibly with dioxygen in acetonitrile at 0 °C to form a peroxo complex [{CoPb(L¹)(CH₃CN)}₂(O₂)][BPh₄]₂[ClO₄]₂·4CH₃CN·5.5H₂O (peroxo-1), whose structure was determined by X-ray crystallography. The peroxo group assumes a rare μ₃-1κO,2κO,3κO′ binding mode, where one peroxo oxygen bridges the Co and Pb in one {CoPb(L¹)(CH₃CN)} unit whereas the other oxygen is unidentate to the Co in another unit. Complex 3 is very sensitive to dioxygen so as to be irreversibly oxidized even at −30 °C. A Co^IIICo^II complex, [Co₂(L¹)(AcO)][ClO₄]₂·dmf·H₂O (oxi-3), was isolated by adding sodium acetate to the oxidized solution. Complexes 2 and 4 are inert toward dioxygen.