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Deprotonation of Oxime Complexes: Dimethylglyoxime-Cobalt(III) Complexes

1969; Oxford University Press; Volume: 42; Issue: 8 Linguagem: Inglês

10.1246/bcsj.42.2296

1348-0634

Isao Masuda, Mitsuhiro Sakano, Koichiro Shinra,

Metal-Catalyzed Oxygenation Mechanisms

Abstract Dimethylglyoxime-Co(III) complexes with the formula [Co(dmgH)2A2]n (I), where dmgH is dimethylglyoximato mono-anion, A is an axial ligand such as aniline, p-anisidine, pyridine, γ-picoline, imidazole, NH3, CN−, and NO2−, and n is −1, 0, or +1, were found to change their electronic absorption spectra reversibly depending on the pH of the solution. These changes have been attributed to the dissociation of the proton from the intramolecular hydrogen bridges of the complex; the changes are accompanied by the formation of the complex [Co(dmgH)(dmg)A2]n−1, where dmg represents the dimethylglyoximato di-anion. The proton dissociation constants (pKa) obtained by the spectrophotometric method indicated that the complex I is generally a weak acid of pKa=7.7–12.6. With the exception of the pyridine and the γ-picoline ligand, axial ligands do not appreciably affect the pKa values. However, axial pyridine and the γ-picoline ligand increase the tendency of the hydrogen bridges to dissociate the proton.