Novel chiral Lewis acids based on a new asymmetric cyclopentadienyl ligand

The chiral N-functionalized cyclopentadiene ligand CpEH (CpEC5H4CH(Ph)CH(Me)NMe2) was used for the preparation of a series of (transition) metal complexes. Metallation of CpEH is accomplished by reaction with nBuLi, K or TlOEt. Reaction of CpELi with Me3SiCl and AlCl3 yields CpESiMe3 and CpEAlCl2 respectively. In the aluminium compound a bidentate coordination of the Cp unit and the nitrogen side-arm is observed. Reaction of CpESiMe3 with MCl4 (MTi,Zr) affords CpEMCl3 in moderate yield. In CpETiCl3 the nitrogen side-arm is only weakly coordinated, whereas in CpEZrCl3 it is firmly coordinated to the metal centre. Moreover, CpEZrCl3 behaves as a moderate Lewis acid, and hitherto catalyzes the Diels-Alder reaction between methacroleine and cyclopentadiene, albeit with no measurable enantiomeric excess.