Synthesis and characterization of planarly chiral nonbridged bis(1-R-indenyl) zirconium dichloride complexes and X-ray structure of rac-[(η5-C9H6-1-C(CH3)2o-C6H4OCH3)2ZrCl2]·THF

Reactions of the lithium salts of 3-substituted indenes 1, 2 with ZrCl4(THF)2 gave two series of nonbridged bis(1-substituted)indenyl zirconocene dichloride complexes. Fractional recrystallization from THF–petroleum ether furnished the pure racemic and mesomeric isomers of [(η5-C9H6-1-C(R1)(R2)o-C6H4OCH3)2ZrCl2]·nTHF (R1=R2=CH3, n=1, rac-1a and meso-1b; R1=CH3, R2=C2H5; n=0.5 or 0, rac-2a and meso-2b), respectively. Complex 1a was further characterized by X-ray diffraction to have a C2 symmetrically racemic structure, where the six-member rings of the indenyl parts are oriented laterally and two o-CH3OC6H4C(CH3)2 substituents are oriented to the open side of the metallocene (Ind: bis-lateral, anti; Substituent: bis-central, syn). The four zirconocene complexes are highly symmetrical in solution as characterized by room temperature 1H-NMR, however 1H–1H NOESY of meso-1b shows that some of the NOE interactions arise from the two separated indenyl parts of the same molecule, which can only be well explained by taking into account the torsion isomers in solution.