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 Nd [HB(3,,-pz),1 (2a) and the corresponding potassium salt, 2b, starting from 1 and NaBH, and KBH,, respectively. A convenient route to the corresponding thallium(1) salt, 2c, using thallium(1) acetate and either 2a or 2b in CHCI,, is also described. The sodium (3a), potasium (3b), and thallium (3c) salts of bis(pyrazoly1)borate [H,B(3,,-pz),]-were also prepared. The above pyrazolylborates were characterized by 'H-, I3C-, I9F-, and "B-NMR spectroscopy. The X-ray crystal structure of the thallium derivative 2c was determined. The compound crystallizes in the monoclinic space group P2,/rn with a = 8.248(9) A, b = 15.034( 12)& c = 9.243(8)A,p = 100.10(7)O,Z = 2. TheTI-atomadoptsapyramidalgeometry with respect to the three N-atoms. However, two TI-N distances (2.725(7) A) are longer than the third (2.675(10) A).
Introduction. -The poly(pyrazoly1)borates are the most studied among the pyrazolederived chelating agents. In particular, the donor properties of pyrazolylborate anions [H,_,B(pz),]-(pz = pyrazole, n = 2-4), have been extensively investigated, as their steric and electronic properties can easily be modified by changing the number of pyrazolyl rings and the substituents thereon or at the B-center [l].
The tris(pyrazolyl)borates, Tp" [la], are the most widely used ligands of this family, as they form a wide range of complexes with metal ions throughout the Periodic Table [l]. Substituent changes on the C-centers of the pyrazolyl groups have strong effects on the nuclearity, geometry, spectroscopic properties, and reactivity of complexes containing those ligands. H