Enantiomerically Pure Constrained Geometry Complexes of the Rare-Earth Metals featuring a Dianionic N-Donor Functionalised Pentadienyl Ligand - Synthesis and Characterisation.

We report the preparation of enantiomerically pure constrained geometry complexes ( cgc ) of the rare-earth metals bearing a pentadienyl moiety (pdl) derived from the natural product (1 R )-(-)-myrtenal. The potassium salt 1 , [Kpdl*], was treated with ClSiMe 2 NH t Bu, and the resulting pentadiene 2 was deprotonated with the Schlosser -type base KO t Pen/ n -BuLi ( t Pen = CMe 2 (CH 2 Me)) to yield the dipotassium salt [K 2 (pdl*SiMe 2 N t Bu)] ( 3 ). However, 3 rearranges in THF solution to its isomer 3' by a 1,3-H shift, which elongates the bridge between the pdl and SiMe 2 N t Bu moieties by one CH 2 unit. This is crucial for the successful formation of various monomeric C 1 - or dimeric C 2 -symmetric rare-earth cgc complexes with additional halide, tetraborohydride, amido and alkyl functionalities. All compounds have been extensively characterised by solid-state X-ray diffraction analysis, solution NMR spectroscopy and elemental analyses.