Synthesis And Catalytic Activity Of Enol Functionalized N-heterocyclic Carbene Complexes With Rare Earth Metals

A series of rare earth metal amide complexes supported by enol functionalized N-heterocyclic carbene ligands were successfully synthesized. All complexes were structurally were characterized by X-ray diffraction. Complexes1-4were found to be the catalyzer for addition of amines to carbodiimides, while their activity variation was in-depth studied. Complexe1showed a wide scope of substrates and a wide scope of amines including primary and secondary cyclic amines.1-4could also serve as initiators for the ring-opening polymerization of□-caprolactone.1. Reaction of LnCl3(Ln=Yb, Nd, Sm and Y) with enol-functionalized imidazolium salt H2L1Br (L=4-OMe-C6H4COCH{C(NCHCHN’Pr)}) and NaN(TMS)2at a molar ratio of1:4:1in THF at room temperature afforded the corresponding novel bis-(enol-functionalized N-heterocyclic carbine) lanthanide amides L2LnN(TMS)2(Ln=Y (1), Nd (2), Sm (3), Yb (4)). Complexes1-4were characterized by elemental analysis, infrared spectroscopy and1H NMR and13C NMR for complexes4. Molecular structures of1-4were determined by X-ray structure analysis.2. To assess the chemistry behavior of complexes1-4, catalytic addition of aniline to N N’-diisopropylcarbodiimide (’PrN=C=N’Pr) by1-4was conducted under various conditions. Complex1showed high activity for the addition reaction of various amines including primary and secondary amines to carbodiimides at60℃under solvent free condition.3. Under mild conditions,1-4can serve as initiators for ring-opening polymerization reaction of□-Caprolactone. The influence of the temperature and solvent on the polymerization of□-Caprolactone was observed. The polymerization by complex2showed the first order kinetic plots of Ln([M]0/[M]) versus time at60℃.4. Rare earth metal amide complexes bearing various ligands were also synthesized including L22YbN(TMS)2(6)(L2 4-OCH3-C6H4COCH2{CH-(NCHCHNMe)}Br), L32YbN(TMS)2(7)(L3=4-OCH3-C6H4COCH2{CH-(NCHCHNCH2Ph)}Br) and L62YbN(TMS)2(8)(L6=F-C6H4COCH2{CH-(NCHCHNCH3)}Br). Their molecular structures were determined by X-ray diffraction respectively.5. An attempt to synthesized the momo-chloride carbene complexe supported by enol-functionalized N-heterocyclic carbene ligand by reaction of H2L1Br, n-BuLi and NdCl3was failed. It’s unexpected that a complex9was isolated instead.