Synthesis And Characterization Of NHC Rare Earth Complexes And Their Applications In Polymerization

A serial of o-aryloxide-substituted N-heterocyclic carbene(NHC)proligands were prepared successfully,and they were fully characterized by NMR spectrum and elemental analysis.Four kinds of heterobimetallic organolanthnide complexes bearing aryloxide-N-heterocyclic carbene ligands were synthesized and characterized by single-crystal X-ray diffraction analysis,NMR spectrum and elemental analysis.These rare earth complexes could be applied in the ring-opening polymerization ofε-caprolactone.The NHC rare earth complexes la and lb were synthesized by the reaction of 3-((2-hydroxynaphthalenyl)methyl)-1-mesityl-3,4,5,6-tetrahydropyrimidiniumc H2L1 and Ln[N(SiMe3)2]3 and KN(SiMe3)2 in toluene at room temperature.Complexes 2a and 2b were prepared successfully in the same method,using 3-(2-hydroxybenzyl)-1-mesityl-3,4,5,6-tetrahydropyrimidinium chloride H2L2 as a reactant.All these complexes were characterized by single-crystal X-ray diffraction analysis.The single-crystal X-ray diffraction analyses revealed monomeric structures with the Ln[N(SiMe3)2]3(Ln=Y,Nd)coordinated to the aryloxide oxygen of K-LNHC structures.The potassium cation,in these structures,bonded to the carbene carbon in the ligand,the coordination sphere of rare earth metal center adapts a distorted tetrahedral geometry connected with the phenol oxygen and three amino groups.What’s more,the K-NHC structures in complexes la and 2a was confirmed by NMR spectra.In order to provide an assessment of the binding of the aryloxide-N-heterocyclic carbene ligands to the alkali metal and the rare earth metals within these unusual heterobimetallic compounds,we have undertaken density functional theory(DFT)calculations upon the single-crystal structures la and 2a.The proposed mechanism in the formation of complexes la and lb was developed through in-situ NMR analysis.These heterobimetallic organolanthnide complexes la-2b were applied in the ring-opening polymerization of ε-caprolactone,obtained s-PCLs with high-molecular weight.Otherwise,polymerization of ε-caprolactone could be catalyzed by complexes la-2b in the addition of iPrOH.The catalytic activity was changed with the different content of iPrOH.The catalyst system with 10 equiv.of iPrOH reached the best catalytic activity in the ring-opening polymerization of ε-caprolactone.