SYNTHESIS AND CHARACTERIZATION OF (ETA(5)-C(5)ME(5))(2)TACL(THF), A USEFUL SYNTHETIC PRECURSOR FOR THE PREPARATION OF OXO, IMIDO AND METHYLIDENE DERIVATIVES OF PERMETHYLTANTALOCENE

The synthesis and characterization of Cp*Ta-2(=O)Cl (Cp*=(eta(5)-C(5)Me(5))), Cp*Ta-2(=NPh)Cl, Cp*Ta-2(=O)H, Cp*Ta-2(=NR)H (R=Ph, CMe(3)), Cp*Ta-2(=CH2)H, Cp*Ta-2(=CH2)Cl, Cp*Ta-2(H2C=CH2)H, and the unusual cyclometallated product Cp*(eta(6)-C(5)Me(4)CH(2))TaH2 from Cp*2TaCl(THF) (THF = tetrahydrofuran) is described. Cp*2TaCl(THF) is prepared by the Na/Hg reduction of Cp*2TaCl2 in THF and used in situ. These synthetic routes are more convenient than those previously described and in most cases give much higher yields and purer products. All attempts to isolate Cp*2TaCl(THF) as a pure crystalline solid have led instead to less reactive [Cp*2TaCl](n), whose structure is uncertain. Although Cp*2TaCl(THF) is only moderately stable in THF at room temperature, it has been characterized in solution by H-1 NMR spectroscopy. Both [Cp*2TaCl](n) and Cp*2TaCl(THF) react with CO to afford Cp*2TaCl(CO), An X-ray crystal structure determination for Cp*Ta-2(=NPh)Cl (triclinic space group P (1) over bar (number 2) with Z = 2; a = 8.627(2); b = 9.538(5), c = 16.890(5) Angstrom alpha= 74.81(3)degrees, beta = 87.12(2)degrees, gamma = 63.79(3)degrees, with V = 1200.0(8) Angstrom(3)) reveals a linear Ta-N-C group, as had been found previously for the closely related complex Cp*Ta-2(=NPh)H.