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

Abstract

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 - Pr2i pzH resulted in the formation of a unique compound [Co (F-OBz) {HB (3 - OCMe2 - 5 - Pri pz) (3, 5 - Pr2i pz)2} (3, 5 - Pr2i pzH)] (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 - Pr2i pzH. X-ray crystallography and IR studies confirmed the existence of hydrogen bonding in complex 5. The pyrazolato bridged binuclear cobalt(II) complex [(3, 5 - Pr2i pzH)2 Co2 (μ - 3, 5 - Pr2i pz)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 - Pr2i pzH formed intramolecular hydrogen bonding with nonbonded oxygen atom of monodentately coordinated nitrobenzoate. © 2007 Elsevier B.V. All rights reserved.