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 CpTa-2(=O)Cl (Cp*=(eta(5)-C(5)M e(5))), CpTa-2(=NPh)Cl, Cp*Ta-2(=O)H, Cp*Ta-2(=NR)H (R=Ph, CMe(3)), C pTa-2(=CH2)H, Cp*Ta-2(=CH2)Cl, Cp*Ta-2(H2C=CH2)H, and the unusual cyc lometallated product Cp(eta(6)-C(5)Me(4)CH(2))TaH2 from Cp*2TaCl(THF) (THF = tetrahydrofuran) is described. Cp2TaCl(THF) is prepared by th e Na/Hg reduction of Cp2TaCl2 in THF and used in situ. These syntheti c routes are more convenient than those previously described and in mo st cases give much higher yields and purer products. All attempts to i solate Cp2TaCl(THF) as a pure crystalline solid have led instead to l ess reactive [Cp2TaCl](n), whose structure is uncertain. Although Cp* 2TaCl(THF) is only moderately stable in THF at room temperature, it ha s been characterized in solution by H-1 NMR spectroscopy. Both [Cp2Ta Cl](n) and Cp2TaCl(THF) react with CO to afford Cp*2TaCl(CO), An X-ra y crystal structure determination for CpTa-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)degre es, 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 rel ated complex CpTa-2(=NPh)H.