EFFICIENT SYNTHESIS OF CHIRAL ANSA-METALLOCENES BY AMINE ELIMINATION - SYNTHESIS, STRUCTURE, AND REACTIVITY OF RAC-(EBI)ZR(NME(2))(2)

The amine elimination reaction of Zr(NMe(2))(4) (2) and (EBI)H-2 (1,2- bis(3-indenyl)ethane, 3) in toluene at 100 degrees C affords pure rac- (EBI)Zr(NMe(2))(2) (rac-4, EBI=ethylene-1,2-bis(1-indenyl)) in 68% iso lated yield. This reaction proceeds via the rapidly formed mono-indeny l intermediate (eta(5)-C9H6CH2CH2C9H7)Zr(NMe(2))(3) (6) which undergoe s reversible intermolecular amine elimination with a second equivalent of 2 to give the binuclear species (mu-eta(5),eta(5)-EBI){Zr(NMe(2))( 3)}(2) (5, rac and meso isomers) or reversible intramolecular amine el imination to give either rac-4 or meso-4. The kinetic metallocene prod uct is a 1/1 mixture of rac-4 and meso-4, the thermodynamic product is rac-4, and the meso-4 to rac-4 isomerization is catalyzed by the NMe( 2)H co-product. The rac-4/meso-4 product ratio can be controlled by ad justing the rate of NMe(2)H removal from the reaction vessel and the s teady state concentration of amine in the reaction mixture. The molecu lar structure of me-4 has been determined by X-ray crystallography. ra c-4 is converted to rac-(EBI)ZrCl2 (rac-1) in high yield by reaction w ith NMe(2)H . HCl (92% isolated) or Me(3)SiCl (quantitative). The synt heses of 2, rac-4, and rac-1 can be combined in a ''one pot'' synthesi s of rac-1 from ZrCl4 in 68% overall yield. Alkylation of rac-4 with A lMe(3) affords rac-(EBI)ZrMe(2) (rac-7) in 90%, isolated yield. rac-4 can be used directly as a catalyst precursor for the isospecific polym erization of propylene.