Cobalt complexes bridge with a (μ-X)(μ-carboxylato) unit (X = OH, N3): synthesis and structural studies

By using the hindered tris(pyrazolyl)borate ligand TpiPr2 (hydrotris(3,5-diisopropyl-1-pyrazolyl))borate, both mono- and binuclear complexes of cobalt [TpiPr2Co](X) (X = NO3 and OBz) and [TpiPr2Co]2(μ-X)(μ-OBz) (X = OH, N3) were synthesized. The nitrato complex, [TpiPr2Co](NO3) (1), which could be converted to (2), was prepared by reaction of KTpiPr2 with hydrated Co(NO3)2 and its molecular structure was determined by X-ray crystallography. The dinuclear di(μ-hydroxo) complex, [TpiPr2Co]2(μ-OH)2 (2), which was obtained by treatment of 1 with aqueous NaOH, reacted with one equivalent of benzoic acid to give the (μ-benzoato)(μ-hydroxo) complex, [TpiPr2Co]2(μ-OH)(μ-OBz) (3). X-ray crystallography shows the presence of both hydroxy and carboxylate group as bridging ligands and both cobalt metals are in five coordination environment in 3. The μ-azido complex, [TpiPr2Co]2(μ-N3)(μ-OBz) (5), was prepared by reaction of 3 with one equivalent of aqueous sodium azide. The spectroscopic studies suggested μ-1,1-bridging nature of View the MathML sourceN3- group in this complex. The reaction of 2 with excess amount of benzoic acid resulted in the destruction of the bimetallic core to give the mononuclear carboxylato complex, [TpiPr2 Co](OBz) (4), which was characterized by X-ray crystallography.