Potassium hydrotris borate, reaction

Potassium hydrotris(l-pyrazolyl)borate is a white crystalline solid. As prepared, m.p. 185-190°C., it is suitable for the synthesis of transition-metal chelates. Its melting point may be raised to 188-189°C. by recrystallization from anisole but this entails large solubility losses. Its infrared spectrum has a sharp BH peak at 2500 cm.-1. This salt is very soluble in water, alcohols, and polar organic solvents. It is stored best as a solid, and its reactions should be carried out on freshly prepared solutions. 

The reaction is carried out in a Schlenk tube, Fig. 1. Acetone (10 mL) is cooled in an ice bath and saturated with carbon monoxide by passing in a brisk stream of the gas for 10 minutes. Potassium hydrotris(pyrazolato)borate (252 mg, 1.0 mmole) and copper(I) chloride (99 mg, 1 mmole) are added to the acetone, and the mixture is stirred for 30 minutes while continuing to pass a slow stream of carbon monoxide. At the end of this period, the white suspension is filtered, using the Schlenk-type apparatus illustrated, Fig. 2, keeping the whole under an atmosphere of CO. The clear colorless filtrate is evaporated to dryness, and the cream-colored residue is extracted with 10 mL light petroleum (boiling range 40-60°, saturated with CO) and filtered. Evaporation of the solvent from the filtrate affords a white powder of Cu(CO)[(pz)3BH] (156 mg, 51%). 

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