Chelate-controlled synthesis of racemic ansa-zirconocenes.

The reaction of Zr[PhN(CH(2))(3)NPh]Cl(2)(THF)(2) (5) with lithium ansa-bis-indenyl reagents Li(2)[XBI](Et(2)O) (XBI = (1-indenyl)(2)SiMe(2) (SBI, 7a), (2-methyl-1-indenyl)(2)SiMe(2) (MSBI, 7b), (2-methyl-4,5-benz-1-indenyl)(2)SiMe(2) (MBSBI, 7c), (2-methyl-4-phenyl-1-indenyl)(2)SiMe(2) (MPSBI, 7d), and 1,2-(1-indenyl)(2)ethane (EBI, 7e)) affords rac-(XBI)Zr[PhN(CH(2))(3)NPh] (8a-e) in high yield. The meso isomers were not detected by (1)H NMR. X-ray crystallographic studies show that the Zr[PhN(CH(2))(3)NPh] rings in 5, 8a, 8c, and (C(5)H(5))(2)Zr[PhN(CH(2))(3)NPh] (10) adopt twist conformations that position the N-Ph groups on opposite sides of the N-Zr-N plane.

Enantioselective synthesis of ansa-zirconocenes.

The reaction of the chiral chelated bis-amide complex Zr{(2R,4R)-PhNCHMeCH2CHMeNPh}Cl2(THF)2 (R,R-7) with lithium ansa-bis-indenyl reagents Li2[SBI](Et2O) (8a, SBI = (1-indenyl)2SiMe2) or Li2[EBI](Et2O) (8b, EBI = 1,2-(1-indenyl)2ethane) in THF affords the corresponding ansa-zirconocenes S,S-(SBI)Zr{(2R,4R)-PhNCHMeCH2CHMeNPh} (S,S,R,R-9a) or S,S-(EBI)Zr{(2R,4R)-PhNCHMeCH2CHMeNPh} (S,S,R,R-9b) in >95% isolated yield and >99% enantiomeric excess. Compound 9b was converted to the corresponding enantiomerically pure dichloride S,S-(EBI)ZrCl2 (S,S-10b) in 91% isolated yield by reaction with HCl in Et2O. The chiral diamine (2R,4R)-HPhNCHMeCH2CHMeNHPh (R,R-5) was recovered from this reaction.