Rare-earth metal derivatives supported by aminophenoxy ligand: Synthesis,characterization and catalytic performance in lactide polymerization |
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| Authors: | Min Li Jie Zhang Jue Chen Yingming Yao Yunjie Luo |
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| Institution: | 1. School of Biological and Chemical Engineering, Ningbo Institute of Technology, Zhejiang University, Ningbo, 315100 China;2. College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, 215123 China;3. School of Material Science and Chemical Engineering, Ningbo University, Ningbo, 315211 China |
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| Abstract: | A library of rare-earth metal derivatives supported by an aminophenoxy ligand was prepared and their catalytic performance in lactide polymerization was investigated. It was found that the synthetic strategy had a profound effect on the formation of aminophenoxy rare-earth metal complexes. Amine elimination between LnN(SiMe3)2]3(μ-Cl)Li(THF)3 (Ln = Yb, Y) and 1 equiv. of the aminophenol HONH] (HONH] = ο-OCH3-C6H4NHCH2(3,5-tBu2-C6H2-2-OH)) in toluene gave the unexpected heterobimetallic bis(aminophenoxy) rare-earth metal complexes ON]2LnLi(THF)2 (Ln = Yb ( 1 ), Y ( 2 )). When the reactions were carried out in THF and TMEDA, amine elimination produced the aminophenoxy rare-earth metal amide complexes {ON]LnN(SiMe3)2}2 (Ln = Yb ( 5 ), Y ( 6 )) in ca 85% isolated yields. Complexes 5 and 6 could also be obtained from salt metathesis reaction of {ON]LnCl(THF)}2 (Ln = Yb ( 3 ), Y ( 4 )) with NaN(SiMe3)2 in a 1:2 molar ratio. In addition, treatment of complexes 3 and 4 with NaOAr (Ar = &bond;C6H4-4-tBu) and (SiMe3)2NC(NPri)2Na in 1:4 and 1:2 molar ratios provided the corresponding aminophenoxy rare-earth metal derivatives {ON](μ-OAr)Ln(μ-OAr)Na(THF)2}2 (Ln = Yb ( 7 ), Y ( 8 )) and {ON]Ln(iPrN)2CN(SiMe3)2]}2 (Ln = Yb ( 9 ), Y ( 10 )), respectively. These complexes were fully characterized, and their molecular structures were determined using single-crystal X-ray diffraction. Polymerization experiments showed that complexes 1 , 2 , 5 , 6 , 9 and 10 were highly active for the ring-opening polymerization of l -lactide in toluene, and complex 1 promoted l -lactide polymerization in a controlled fashion. The polymerization of rac-lactide initiated by the neutral aminophenoxy rare-earth metal complexes 5 , 6 , 9 and 10 in THF afforded heterotactic polymers. |
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| Keywords: | rare-earth metal complex aminophenolate ligand polymerization lactide |
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