Synthesis, structure, and properties of group 4 and 5 metal pyrazolato chloride complexes

Treatment of titanium tetrachloride with 3,5-di-tert-butylpyrazole (2 equiv ) and triethylamine (2 equiv) in toluene afforded dichlorobis(3,5-di-tert-b utylpyrazolato)titanium(IV) (93%). A similar reaction with 3 equiv of 3,5-d i-tert-butylpyrazole and triethylamine gave chlorotris(3,5-di-tert-bulylpyr azolato)titanium(IV) (91%). Trichloro(3,5-di-tert-butylpyrazolato)titanium( IV) was prepared in 93% yield through reaction of titanium tetrachloride wi th 1-trimethylsilyl-3,5-di-tert-butylpyrazole (1 equiv) in toluene. Treatme nt of zirconium and hafnium tetrachlorides with 3,5-di-tert-butylpyrazolato potassium (4 equiv) in toluene afforded the homoleptic pyrazolato complexes tetrakis(3,5-di-tert-butylpyrazolato)zirconium(IV) (90%) and tetrakis(3,5- di-tert-butylpyrazolato)hafnium- (IV) (68%). Analogous reaction of 3,5-di-t ert-butylpyrazolatopotassium (greater than or equal to 3 equiv) with niobiu m and tantalum pentachlorides gave dichlorotris(3,5-di-tert-butylpyrazolato (98%) and dichlorotris(3,5-di-tert-butylpyrazolato)tantalum(V) (83%). Reac tion of the complexes tetrakis(3,5-di-tert-butylpyrazolato)met (metal = Zr, Hf) and dichlorotris(3,5-di-tert-butylpyrazolato)metal (V) (metal = Nb, Ta ) with the metal tetrachlorides and metal pentachlorides, respectively, in dichloromethane afforded the complexes chlorotris(3,5-di-tert-butylpyrazola to)metal(IV) (metal = Zr, 89%; Hf, 97%) and trichlorobis(3,5-di-tert-butylp yrazolato (metal = Nb, 90%; Ta, 84%). Crystal structures of trichloro(3,5-d i-tert-butylpyrazolato)titanium(IV), chlorotris(3,5-di-tert-butylpyrazolato )hafnium(IV), and dichlorotris(3,5 -di-tert-butylpyrazolato)niobium(V) were determined. Trichloro(3,5-di-tert-butylpyrazolato)titanium(IV) crystallize s in the space group C2/c with a = 22.6542(8) Angstrom, b = 9.5147(3) Angst rom, c = 16.5329(6) Angstrom, beta = 113.5780(10)degrees, and Z = 8. Chloro tris(3,5-di-tert-butylpyrazolato)hafnium(IV) crystallizes in the space grou p P2(1)/c with a = 10.4529(7) Angstrom, b = 10.1437(6) Angstrom, c = 36.986 (3) Angstrom, beta = 93.3080(10)degrees, and Z = 4. Dichlorotris(3,5-di-ter t-butylpyrazolato)niobium(V) crystallizes in the space group P2(1)/c with a = 10.2051(3) Angstrom, b = 38.3650(12) Angstrom, c = 9.7585(3) Angstrom, b eta = 93.3280(10)degrees, and Z = 4. Kinetic analysis of a dynamic process observed for dichlorotris(3,5-di-tert-butylpyrazolato is described. The res ults of this study suggest that eta(2)-pyrazolato donors may be useful anci llary ligands in the development of new reactive early transition metal com plexes.