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 (Tp iPr2 ) as supporting ligand. The reaction of [Tp iPr2 Co(NO 3)] ( 2) with sodium benzoate resulted in the formation of acetonitrile coordinated complex [Tp iPr2 Co(OBz)(CH 3CN)] ( 3) whereas the reaction of 2 with sodium fluorobenzoate gave coordinately unsaturated five coordinate complex of the type [Tp iPr2 Co(F-OBz)] ( 4). The oxidation of compound 4 in the presence of 3,5-diisopropylpyrazole 3 , 5 - Pr 2 i pzH resulted in the formation of a unique compound [ Co ( F-OBz ) { HB ( 3 - OCMe 2 - 5 - Pr i pz ) ( 3 , 5 - Pr 2 i pz ) 2 } ( 3 , 5 - Pr 2 i 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 - Pr 2 i 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 - Pr 2 i pzH ) 2 Co 2 ( μ - 3 , 5 - Pr 2 i pz ) 2 ( NO 2 -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 - Pr 2 i pzH formed intramolecular hydrogen bonding with nonbonded oxygen atom of monodentately coordinated nitrobenzoate.