Coordinative Unsaturation in Chiral Organolanthanides. Synthetic and Asymmetric Catalytic Mechanistic Study of Organoyttrium and -lutetium Complexes Having Pseudo-mesoMe2Si(η5-RC5H3)(η5-R*C5H3) Ancillary Ligation1

Abstract

As established by NMR, circular dichroism, and X-ray diffraction, organolanthanide complexes of the new chelating ligand Me2Si(3-Me3SiCp)[3-(−)-menthylCp]2- (Cp = η5-C5H3) preferentially adopt a single planar chiral configuration of the asymmetric metal−ligand template. Chloro complexes (S,R)-Me2Si(Me3SiCp)[(−)-menthylCp]Ln(μ-Cl)2Li(OEt2)2 (Ln = Y, Lu) were isolated diastereomerically pure by crystallization from diethyl ether. The unusual pseudo-meso configuration leads to a gross distortion from ideal C2v symmetry, evidenced by a significant deviation of ∠Sibridge−Lu−Li from linearity (158°). At least two additional epimers are detected in THF solution. Alkylation of the (S,R) epimers with LiCH(SiMe3)2 proceeds with retention of configuration, affording chiral hydrocarbyl complexes in quantitative yield. In solution, the hydrocarbyls exhibit temperature-dependent conformational exchange processes in the NMR ascribable to restricted rotation about the Ln−CH(SiMe3)2 bond. These complexes are effective pre...