STEREOSELECTIVITY IN THE SYNTHESIS OF TETRAMETHYLETHANO-BRIDGED 3,3'-DI-TERT-BUTYLTITANOCENE DICHLORIDE

Racemic and meso ansa-(2,3-dimethyl-2,3-butano)-3,3'-bis(1,1'-dimethylethyl)cyclopenta-1,3-dien-5-yl)titanium dichloride (5 and 4) were prepared in a 1:4 to 1:2 ratio by the addition of TiCl3.3THF to 2,3-bis[3-(1,1-dimethylethyl)-1,3-cyclopentadien-5-yl]-2,3-dimethylbutanedilithium (3) in THF with subsequent oxidation by HCl in a 44% yield. A 30% yield of the 1:1 racemic:meso ratio resulted when 3 was treated with titanocene dichloride in THF followed by carbon tetrachloride oxidation. In the attempts to synthesize the desired anti isomer, 3 was treated with in-situ generated racemic dichloro-1,1'-bi-2-naphtholatetitanium(IV) to give ansa-(2,3-dimethyl-2,3-butano)-anti-3,3'-bis(1,1-dimethylethyl)cyclopenta-1,3-dien-5-yl)titanium 1,1'-bi-2-naphtholate (6) in a 10-15% yield. 6 crystallized in a monoclinic space group P2(1)/c with a = 10.084(2) angstrom, b = 29.312(7) angstrom, c = 12.190(2) angstrom, beta = 99.37(2)degrees, V = 3555(2) angstrom3, and Z = 4. Refinement of 425 least squares variables converged to R = 0.044 and R(w) = 0.046 for 4153 observed reflections with I > 2-sigma(I). The molecule contains an approximate C2 axis of symmetry with the t-butyl groups anti to each other. The C(Cp)-C(t-butyl) bonds are displaced from the plane defined by the cyclopentadienyls by about 10-degrees.