Synthesis Of Rare Earth Metal Bis(amide) Complexes Containing Ln–N σ-bonds And Their Catalytic Performances

A series of guanidinate-or pyridine founctionalized indenyl-ligated rare earth metalbis（amide） complexes were synthesized and well-characterized. These complexes could act asgood catalysts/initiators in the ring-opening polymerization of lactides and guanilation.1. One-pot salt metathesis reaction of anhydrous LnCl₃with one equivalent ofguanidinate lithium [（SiMe₃）₂NC（NCy）2]Li （Cy=cyclohexyl）, following the introduction oftwo equivalents of NaN（SiMe₃）₂or LiN（SiHMe₂）2in THF at room temperature, afforded afamily of mono（guanidinate） rare earth metal bis（amide） complexes[（SiMe₃）₂NC（NCy）₂]Ln[N（SiRMe₂）₂]₂（THF）n（R=Me, n=0, Ln=Nd （1）, Lu （2）, Y （3）; R=H, n=1, Ln=Y （4）） in62–79%isolated yields. These complexes were characterized byelemental analysis, NMR spectroscopy (except for1for its strong paramagnetic property ofNd³⁺), FT-IR spectroscopy, and X-ray single crystal diffraction. Single crystal structuraldetermination revealed that the central metals in1–3are four-coordinated with a distortedtetrahedral geometry, while that in4is five-coordinated with a distorted trigonal bipyramidalgeometry.2. Treatment of rare earth tris（amide） complexes Ln[N（SiHMe2）2]3（THF）n（n=2, Ln=La, Nd, Sm, Er, Lu, Y; n=1, Ln=Sc） with1equivalent of pyridyl-functionalized indeneC₉H₇CMe₂CH₂C₅H₄N-α via amine elimination afforded a series of neutral rare earth metalbis（amide） complexes （C₉H₆CMe₂CH₂C₅H₄N-α）Ln[N（SiHMe₂）₂]₂（Ln=La （5）, Nd （6）, Sm（7）, Er （8）, Lu （9）, Y （10）, Sc （11）） in70–87%isolated yields. These complexes werecharacterized by elemental analysis, FT-IR and NMR (except for8for its strong paramagneticproperty of Er³⁺). X-ray single crystal structural diffraction showed that5–11are THF-freeisostructural species with the center metal adopting a distorted tetrahedral geometry. Themonoanionic pyridyl-functionalized indenyl ligand bonds to the central metal in5/1 constrained geometry configuration （CGC） mode.3. Complex1–4could serve as highly active initiators for L-lactide polymerization intoluene at50C. They also showed high activity towards rac-lactide polymerization in THFat room temperature, and afforded a moderate level of heterotactic polymers （Pr>0.70）.Employing4as an initiator, a controllable polymerization fashion was observed both inL-lactide polymerization and rac-lactide polymerization under certain conditions. Thepolymerization proceeded via a coordination-insertion mechanism verified experimentally byend group analysis of the oligomer.4. Complex5–10were highly active for the polymerization of lactides. In the presence oftwo equivalents of benzyl alcohol, both5and6could initiate the ring-opening polymerizationof L-lactide, as well as rac-lactide, in a controlled manner. Kinetics studies showed thepolymerization procesded in first-order with5/2BnOH and zero-order with6/2BnOH. Theend group analysis of the oligomer indicated the polymerization proceeded via acoordination-insertion mechanism.5. Complex5–10were found to be efficient catalysts for guanilation between aniline andN,N′-diisopropylcarbodiimide under mild condition. The ionic radius of central metalsaffected significantly on the catalytic activity with a trend of Y> Er> Lu> La> Nd> Sm>Sc. Detailed addition reactions of aromatic amines with carbodiimides were investigated withcomplex10as a catalyst.