High-Yield Syntheses of Sodium,Potassium, and Thallium Hydrotris[3,5-bis(trifluoromethyl)pyrazolyl]borates and the X-ray crystal structure of {hydrotris[3,5-bis(trifluoromethyl)pyrazolyl]borato} thallium(I)

An improved synthesis of 3,5-bis(trifluoromethyl)pyrazole ( 1 ) is described. This compound was used for the high-yield syntheses of the tris(pyrazoly1)borates NdHB(3,5-(CF₃),-pz)₃] ( 2a ) and the corresponding potassium salt, 2b , starting from 1 and NaBH₄ and KBH₄, respectively. A convenient route to the corresponding thallium(I) salt, 2c , using thallium(I) acetate and either 2a or 2b in CHCI₃, is also described. The sodium ( 3a ), potassium ( 3b ), and thallium ( 3c ) salts of bis(pyrazolyl)borate H₂B(3,5-(CF₃)₂-pz)₂]^? were also prepared. The above pyrazolylborates were characterized by ¹H-, ¹³C-, ¹⁹F-, and ¹¹B-NMR spectroscopy. The X-ray crystal structure of the thallium derivative 2c was determined. The compound crystallizes in the monoclinic space group P2₁/m with a = 8.248(9) Å, b = 15.034(12) Å c = 9.243(8) Å, β = 100.10(7)°, Z = 2. The Tl-atom adopts a pyramidal geometry with respect to the three N-atoms. However, two TI–N distances (2.725(7) Å) are longer than the third (2.675(10) Å).