Enantiomerically Pure Organolanthanides for Asymmetric Catalysis. Synthesis, Structures, and Catalytic Properties of Complexes Having Pseudo-meso-Me2Si(η5-C5H3R)(η5-C5H3R*) Ancillary Ligation

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-Cl2)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)[(+)-neo-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.