Potassium Dihydrobis l-pyrazolyl borate

Syntheses of the potassium salts of the parent bidentate and the tridentate ligands are described. Other alkali metal salts can be prepared in similar fashion. Quaternary ammonium salts are made by neutralization of the free acids.2 C- and B-substituted ligands have been prepared by similar procedures.8 

Potassium dihydrobis(l-pyrazolyl)borate, m.p. 171-172°C., is a white crystalline solid, highly soluble in water and polar solvents. It may be recrystallized from anisole, but with large solubility losses. The infrared spectrum has a complicated BH2 stretch multiplet in the 2200-2500-cm.-1 range. It is very soluble in water and alcohols, but the ligand undergoes slow solvolysis, and solutions should be made up just before use. 

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

The reaction is started as in Sec. A. When about 35 1. of hydrogen has been evolved, the oil bath is replaced with a heating mantle, and the temperature is raised gradually to about 190°C. until a total of 751. (3 moles) of hydrogen has been evolved. The melt is cooled to about 150°C. and is then poured into 600 ml. of stirred toluene the resulting mixture is stirred for 5 minutes and then filtered hot. The product is washed with hot toluene and then with hexane as in Sec. A. After air-drying it is obtained in about 190-g. (80%) yield, f 

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Potassium dihydrobis(l-pyrazolyl)borate (18.6 g., 0.1 mole) of the solid as prepared in Sec. A is stirred in 300 ml. of distilled water, and any insolubles are removed by filtration. To the resulting clear solution is added, with stirring, 100 ml. of 0.5 M solution of nickel(II) acetate [or any other Ni(II) salt]. A yellowish precipitate forms immediately. The mixture is stirred at room temperature for 10 minutes and is then filtered. The solid is washed with copious amounts of water, then with... 

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