Potassium Hydrotris l-pyrazolyl borate

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. 

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Potassium hydrotris(l-pyrazolyl)borate, 25.2 g. (0.1 mole), of the solid, as prepared in Sec. B, is stirred in 300 ml. of distilled water, and any insolubles are removed by filtration. To this solution is added, with stirring, 100 ml. of 0.5 M cobalt(II) acetate [or any other Co (II) salt] solution. A yellowish precipitate forms promptly. The mixture is stirred at room temperature for 10 minutes and is filtered after washing with copious amounts of water and then with methanol, the solid is air-dried. It is obtained in 22-23-g. (91-95%) yield and may be purified either by recrystallization from toluene or by chromatography (on acid-washed aluminum oxide packing and eluting with dichloromethane). 

B. POTASSIUM HYDROTRIS(1 -PYRAZOLYL)BORATE— ALKALI METAL POLY(l-PYRAZOLYL)BORATES... 

BFtKNsCi5H2i, Borate(l-), tris(3,5-dimethyl-pyrazolyl)hydn>, potassium, 33 220 BFtKNsS3Ci2Hi5, Borate(l-), hydrotris(methi-mazolyl)-, potassium, 33 200 BF1N703WC26H41, Tungstate(O), tricarbonyl [tris(3,5-dimethylpyrazolyl)hydroborato]-, tetraethylammonium, 33 221 BM0N10O3C62H56, Molybdenium(V), 5- 2,3-catecholato[hydrotris(3,5-dimethyl-l-pyra-zolyl)borato]oxo- -, 10,15,20-tri-p-tolyl-porphyrin, 33 45... 

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