On the structural features of the chiral organometallic Lewis-acid catalyst “(dibornacyclopentadienyl)zirconiumtrichloride”
1993; Elsevier BV; Volume: 459; Issue: 1-2 Linguagem: Inglês
10.1016/0022-328x(93)86061-l
ISSN1872-8561
AutoresGerhard Erker, J. Schamberger, A. A. H. VAN DER ZEIJDEN, Stefan Dehnicke, Carl Krüger, Richard Goddard, M. Chester Nolte,
Tópico(s)Asymmetric Hydrogenation and Catalysis
Resumo2-Bornenyllithium (3) was prepared from camphor by a variant of the Shapiro reaction and then reacted with 0.5 molar equivalents of ethylformate to give the dibornenylcarbinol 4. Subsequent acid-catalyzed cyclization of 4 yielded "dibornacyclopentadiene" as a mixture of two diastereoisomers; their deprotonation with n-butyllithium produced a single "dibornacyclopentadienyllithium" reagent (6). Reaction of 6 with MCl4 (M Zr, Hf, Ti) gave the chiral organometallic Lewis-acids "(diborna-Cp)MCl3". "(+)-(Dibornacyclopentadienyl)zirconiumtrichloride" (7a) was characterized by X-ray diffraction. The molecular structure of 7a provides a basis for discussing the stereochemical characteristics of the enantioselective arene hydroxyalkylation process catalysed by the optically active organometallic Lewis-acid "(dibornacyclopentadienyl)zirconiumtrichloride".
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