Mononuclear cobalt(II) carboxylate complexes: Synthesis, molecular structure and selective oxygenation study

Some cobalt carboxylate (both mononuclear as well as binuclear) complexes have been prepared by using hindered hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (TpiPr2) as supporting ligand. The reaction of [TpiPr2Co(NO3)] (2) with sodium benzoate resulted in the formation of acetonitrile coordinated complex [TpiPr2Co(OBz)(CH3CN)] (3) whereas the reaction of 2 with sodium fluorobenzoate gave coordinately unsaturated five coordinate complex of the type [TpiPr2Co(F-OBz)] (4). The oxidation of compound 4 in the presence of 3,5-diisopropylpyrazole 3,5-Pr2ipzH resulted in the formation of a unique compound [Co(F-OBz){HB(3-OCMe2-5-Pripz)(3,5-Pr2ipz)2}(3,5-Pr2ipzH)] (5) where only one methine carbon of isopropyl group on pyrazole ring of hydrotris(3,5-diisopropyl-1-pyrazolyl)borate oxidized and coordinated with cobalt center. In compound 5, the binding behavior of fluorobenzoate also changes from bidentate to monodentate and the nonbonded oxygen atom formed intramolecular hydrogen bond with the hydrogen atom of the NH fragment of the coordinated 3,5-Pr2ipzH. X-ray crystallography and IR studies confirmed the existence of hydrogen bonding in complex 5. The pyrazolato bridged binuclear cobalt(II) complex [(3,5-Pr2ipzH)2Co2(μ-3,5-Pr2ipz)2(NO2-OBz)2] (6) was prepared by the reaction of hydrated cobalt(II) nitrate, 3,5-diisopropylpyrazole and sodium nitrobenzoate where, each cobalt is four coordinate. The X-ray structure of 6 showed that the NH fragment of terminally coordinated 3,5-Pr2ipzH formed intramolecular hydrogen bonding with nonbonded oxygen atom of monodentately coordinated nitrobenzoate.

Cobalt carboxylate complexes having hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (TpiPr2) have been prepared. The reaction of [TpiPr2Co(NO3)] with sodium fluorobenzoate gave five coordinate [TpiPr2Co(F-OBz)] which undergoes oxidation in the presence of 3,5-Pr2ipzH and gave a unique compound where only one methine carbon of isopropyl group of TpiPr2 ligand oxidized and coordinated with cobalt. The nonbonded oxygen atom of fluorobenzoate forms intramolecular hydrogen bond with the hydrogen atom of 3,5-Pr2ipzH. In pyrazolato bridged binuclear cobalt(II) complex, each cobalt is four coordinate and NH fragment of terminally coordinated 3,5-Pr2ipzH forms intramolecular hydrogen bonding with nonbonded oxygen atom of nitrobenzoate.Figure optionsDownload as PowerPoint slide