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Chiral Epoxides as Building Blocks for Ethylene‐Bridged ansa ‐Metallocene Complexes – Synthesis of C 1 ‐Symmetrical Zirconocene Dichlorides with Two Different Cyclopentadienyl Units
Author(s) -
Rieger Bernhard,
Steimann Manfred,
Fawzi Riad
Publication year - 1992
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19921251108
Subject(s) - cyclopentadienyl complex , chemistry , metallocene , trifluoromethanesulfonate , ethylene , yield (engineering) , ring (chemistry) , sandwich compound , medicinal chemistry , stereochemistry , ligand (biochemistry) , crystallography , catalysis , organic chemistry , x ray crystallography , polymerization , diffraction , biochemistry , materials science , physics , receptor , optics , metallurgy , polymer
Epoxystyrene undergoes ring opening on treatment with tetraphenylcyclopentadienyl‐ and fluorenyllithium to give the corresponding chiral alcohols 3 and 4 in high yield. Their trifluoromethanesulfonate derivatives 5 react with one equivalent of cyclopentadienylsodium to form the ligand precursors 1‐cyclopentadienyl‐1‐phenyl‐2‐(tetraphenylcyclopentadienyl)ethane (L 1 H 2 ) and 1‐cyclopentadienyl‐2‐(9‐fluorenyl)‐1‐phenylethane (L 2 H 2 ). The zirconocenes L 1 ZrCl 2 ( 7a ) and L 2 ZrCl 2 ( 7b ) are prepared from the dilithio salts L 1 Li 2 and L 2 Li 2 , respectively. A low‐temperature X‐ray structure investigation of complex 7a demonstrates the chiral arrangement of the four phenyl substituents of the tetraphenylcyclopentadienyl (C 5 Ph 4 ) unit. A 1 H‐NMR study shows that the phenyl groups rotate rapidly on the NMR time scale at room temperature. The dependence of phenyl rotation on temperature is discussed.