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Selected 1 H NMR chemical shifts (C6D6 or THF-d8, T = 298 K) for dipotassium salts 3 and 3' and the diamagnetic lanthanide compounds.
Source publication
![General formula of a constrained geometry complex (cgc).[2a]](publication/343356337/figure/fig1/AS:11431281246240445@1716337176947/General-formula-of-a-constrained-geometry-complex-cgc2a_Q320.jpg)
![¹H NMR spectrum (500 MHz, [D8]THF) for the ligand rearrangement...](publication/343356337/figure/fig3/AS:11431281246240450@1716337177381/HNMR-spectrum-500MHz-D8THF-for-the-ligand-rearrangement-reaction-at-55C_Q320.jpg)
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 (1R)‐(−)‐myrtenal. The potassium salt 1, [Kpdl*], was treated with ClSiMe2NHtBu, and the resulting pentadiene 2 was deprotonated with the Schlosser‐type base KOtPen/nBuL...
Contexts in source publication
Context 1
... spectroscopic studies. The diamagnetic compounds 6-Sc, 4-Y and 5-La were analysed by solution NMR spectroscopy (C6D6, T = 298 K; Table 4). The NMR data are consistent with C2-or C1-symmetric structures, as determined in the solid state. 1 H, 1 H NOESY experiments confirmed the U-conformation of the pdl ligand in solution by through-space coupling between the H atoms endo-H1 and H5. ...Context 2
... NMR spectroscopic studies. In addition, the diamagnetic compounds 7-La and 7-Y were fully characterised by NMR spectroscopic studies using 2D NMR techniques (see Table 4 and SI). The resonances match the molecular C1-symmetry observed in the solid state. ...Context 3
... spectroscopic studies. Solution NMR spectroscopy was conducted for both complexes (see Table 4 and SI). For the diamagnetic compound 8-La, the observed resonances are consistent with the solid-state molecular structure. ...Similar publications
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Citations
The alkyl-functionalised scandium complex [(pdl*SiMe2NtBu)Sc(thf)(CH2SiMe3)] (2) was synthesised in enantiomerically pure form and characterised by NMR spectroscopy and X-ray diffraction analysis. Complex 2 features a chiral constrained geometry ligand derived from the natural compound (1R)-(-)-myrtenal, in which the pentadienyl (pdl*) fragment coordinates in η3:η2-allyl-en fashion to the scandium atom. Compound 2 catalyses the polymerisation of rac-lactide at 30 °C and 50 °C yielding amorphous poly(lactide) with slightly heterotactic enchainment (Pm = 0.36 and 0.37). In agreement with the data obtained from GPC and DSC measurements, a chain-end control mechanism is proposed with fast chain propagation relative to the initiation, which leads to broad molecular weight distributions (Đ ≈ 1.80) and higher than expected molecular weights. Furthermore, chain transfer processes are observed, but only small amounts of transesterification and racemisation occur. Kinetic studies reveal a second-order dependence in rac-lactide (monomer) concentration and a first-order dependence in the concentration of catalyst 2.
Recent developments in closely related rare-earth-metal diene and metallacyclic chemistry revealed interesting structural features and reactivities of special significance for polymer science and small molecule activation. This article covers the syntheses of metalla(carbo)cycles, cyclobutadienyl and pentadienyl complexes but also refers to their role as reagents, catalysts or single-molecule magnets. In particular, the ability to act as catalyst precursors for 1,3-diene polymerization catalysis has been a major driving force for studying pentadienyl complexes. More detailed investigations into the properties of such group 3 and lanthanide complexes might trigger novel organic and inorganic transformations and the isolation of complexes with the rare-earth metal in non-classical low oxidation states.
