Enantiomerically pure organolanthanides for asymmetric catalysis. Synthesis, structures, and catalytic properties of complexes having pseudo-meso-Me2Si(η5-C5H 3R)(η5-C5H3R*) ancillary ligation

Peter W. Roesky, Uwe Denninger, Charlotte L. Stern, Tobin J Marks

Research output: Contribution to journalArticle

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Abstract

As established by NMR, circular dichroism, and X-ray diffraction, organolanthanides of the new chelating ligand Me2Si(tBuCp)[(+)-neo-Men-Cp]2- (Men = menthyl; Cp = η5-C5H3) preferentially adopt a single chiral configuration of the asymmetric metal-ligand template. Metallocene dichloro complexes (R,S)-Me2Si(tBuCp)[(+)-neo-Men-Cp]Ln(μ-Cl 2)Li(OEt2)2 (Ln = Y, Lu) are synthesized by alkylation of the corresponding lanthanide trichlorides with the ligand dilithium salt and are isolated isomerically pure by crystallization from diethyl ether. Alkylation of the (R,S)-epimers with MCH(SiMe3)2 (M = Li, K) proceeds with retention of configuration at the lanthanide center, affording chiral hydrocarbyl complexes in high yield. Reaction of the Lu-hydrocarbyl with hydrogen affords diastereomerically pure {(R,S)-Me2Si(tBuCp)[(+)-neo-Men-Cp]LuH}2, an active catalyst for asymmetric olefin hydrogenation. X-ray diffraction reveals a pseudo-C2-symmetric dimer with a pseudo-meso Cp ring substituent arrangement. The two Me2Si(tBu-Cp)[(+)-raeo-Men-Cp]LuH fragments are slightly twisted with respect to each other. These hydrocarbyls are effective precatalysts for asymmetric hydrogenation of unfunctionalized olefins. The ee values obtained for deuteration of 1-pentene (up to 63%) are the highest reported to date for this reaction, and in all reactions, the (R)-product enantiomer is favored. These results together with those obtained using other chiral organolanthanides provide better insight into lanthanocene stereochemical preferences and chirality transfer mechanisms.

Original languageEnglish
Pages (from-to)4486-4492
Number of pages7
JournalOrganometallics
Volume16
Issue number20
Publication statusPublished - Sep 30 1997

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Catalysis
catalysis
Lanthanoid Series Elements
Alkylation
Alkenes
Ligands
Hydrogenation
synthesis
alkylation
X ray diffraction
Enantiomers
Chirality
ligands
alkenes
hydrogenation
Chelation
Crystallization
Dimers
Ether
Hydrogen

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Organic Chemistry

Cite this

Enantiomerically pure organolanthanides for asymmetric catalysis. Synthesis, structures, and catalytic properties of complexes having pseudo-meso-Me2Si(η5-C5H 3R)(η5-C5H3R*) ancillary ligation. / Roesky, Peter W.; Denninger, Uwe; Stern, Charlotte L.; Marks, Tobin J.

In: Organometallics, Vol. 16, No. 20, 30.09.1997, p. 4486-4492.

Research output: Contribution to journalArticle

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abstract = "As established by NMR, circular dichroism, and X-ray diffraction, organolanthanides of the new chelating ligand Me2Si(tBuCp)[(+)-neo-Men-Cp]2- (Men = menthyl; Cp = η5-C5H3) preferentially adopt a single chiral configuration of the asymmetric metal-ligand template. Metallocene dichloro complexes (R,S)-Me2Si(tBuCp)[(+)-neo-Men-Cp]Ln(μ-Cl 2)Li(OEt2)2 (Ln = Y, Lu) are synthesized by alkylation of the corresponding lanthanide trichlorides with the ligand dilithium salt and are isolated isomerically pure by crystallization from diethyl ether. Alkylation of the (R,S)-epimers with MCH(SiMe3)2 (M = Li, K) proceeds with retention of configuration at the lanthanide center, affording chiral hydrocarbyl complexes in high yield. Reaction of the Lu-hydrocarbyl with hydrogen affords diastereomerically pure {(R,S)-Me2Si(tBuCp)[(+)-neo-Men-Cp]LuH}2, an active catalyst for asymmetric olefin hydrogenation. X-ray diffraction reveals a pseudo-C2-symmetric dimer with a pseudo-meso Cp ring substituent arrangement. The two Me2Si(tBu-Cp)[(+)-raeo-Men-Cp]LuH fragments are slightly twisted with respect to each other. These hydrocarbyls are effective precatalysts for asymmetric hydrogenation of unfunctionalized olefins. The ee values obtained for deuteration of 1-pentene (up to 63{\%}) are the highest reported to date for this reaction, and in all reactions, the (R)-product enantiomer is favored. These results together with those obtained using other chiral organolanthanides provide better insight into lanthanocene stereochemical preferences and chirality transfer mechanisms.",
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