ENANTIOMERICALLY PURE ORGANOLANTHANIDES FOR ASYMMETRIC CATALYSIS - SYNTHESIS, STRUCTURES, AND CATALYTIC PROPERTIES OF COMPLEXES HAVING PSEUDO-MESO-ME2SI(ETA(5)-C5H(3)R) (ETA(5)-C5H3R-ASTERISK) ANCILLARY LIGATION

As established by NMR, circular dichroism, and X-ray diffraction, orga nolanthanides of the new chelating ligand Me2Si((BuCp)-Bu-t)[(+)-neo-M en-Cp](2-)(Men = menthyl; Cp = eta(5)-C5H3) preferentially adopt a sin gle chiral configuration of the asymmetric metal-ligand template. Meta llocene dichloro complexes (BuCp)-Bu-t)[(+)-neo-Men-Cp]Ln(mu-Cl-2)Li(O Et2)(2) (Ln = Y, Lu) are synthesized by alkylation of the correspondin g lanthanide trichlorides with the ligand dilithium salt and are isola ted isomerically pure by crystallization from diethyl ether. Alkylatio n of the (R,S)-epimers with MCH(SiMe3)(2) (M = Li, K) proceeds with re tention of configuration at the lanthanide center, affording chiral hy drocarbyl complexes in high yield. Reaction of the Lu-hydrocarboyl wit h hydrogen affords diastereomerically pure {(R,S)-Me2Si((BuCp)-Bu-t)[( +)-neo-Men-Cp]LuH}(2), an active catalyst for asymmetric olefin hydrog enation. X-ray diffraction reveals a pseudo-C-2-symmetric dimer with a pseudo-meso Cp ring substituent arrangement. The two Me2Si(Bu-t-Cp)[( +)-neo-Men-Cp]LuH fragments are slightly twisted with respect to each other. These hydrocarbyls are effective precatalysts for asymmetric hy drogenation of unfunctionalized olefins. The ee values obtained for de uteration of 1-pentene (up to 63%) are the highest reported to date fo r this reaction, and in all reactions, the (R)-product enantiomer is f avored. These results together with those obtained using other chiral organolanthanides provide better insight into lanthanocene stereochemi cal preferences and chirality transfer mechanisms.