Synthesis and molecular structure of enantiomerically pure pentadienyl complexes of the rare-earth metals

The enantiomerically pure pentadienyl (Pdl*) ligand derived from the natural product (1R)-(-)-myrtenal forms with MCl3 (M = La, Ce, Pr, and Nd) the corresponding homoleptic [(eta(5)-U-Pdl*)(3)M compounds (1-M). These complexes were fully characterised by H-1 NMR spectroscopy, elemental analyses and X-ray diffraction. They exhibit in solution and solid state idealized C-3 symmetry, and their molecular structures also reveal that the Pdl* ligand adopts a U-conformation and coordinates exclusively with its less sterically encumbered face to the rare-earth metal atom. For the paramagnetic representatives an assignment of the H-1 NMR resonances based on a simple dipolar model gave satisfactory results.