Bis(guanidinate) alkoxide complexes of lanthanides: synthesis, structures and use in immortal and stereoselective ring-opening polymerization of cyclic esters |
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Authors: | Ajellal Noureddine Lyubov Dmitrii M Sinenkov Mikhail A Fukin Georgii K Cherkasov Anton V Thomas Christophe M Carpentier Jean-François Trifonov Alexander A |
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Institution: | Organometallics and Catalysis, UMR CNRS 6226, Sciences Chimiques de Rennes, University of Rennes 1, 35042 Rennes Cedex, France. |
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Abstract: | A series of new bis(guanidinate) alkoxide Group 3 metal complexes Ln((Me3Si)2NC(NiPr)2)2(OR)] (R=OtBu, Ln=Y, Nd, Sm, Lu; R=OiPr, Ln=Y, Nd, Lu) has been synthesized. X-ray structural determinations revealed that bis(guanidinate) tert-butoxides are monomeric complexes. The isopropoxide complex Y((Me3Si)2NC(NiPr)2)2(OiPr)] undergoes slow decomposition in solution, to afford the unusual dimeric amido complex (Y((Me3Si)2NC(NiPr)2)2(mu-N(iPr)C triple chemical bond N))2]. Complexes Ln((Me3Si)2NC(NiPr)2)2(OR)] (R=OtBu, Ln=Y, Nd, Sm, Lu; R=OiPr, Ln=Y, Nd, Lu) are active catalysts/initiators for the ROP of rac-lactide and rac-beta-butyrolactone under mild conditions. Most of those polymerizations proceed with a significant degree of control. Bis(guanidinate) alkoxides appear to be well suited for achieving immortal polymerization of lactide, through the introduction of large amounts of isopropanol as a chain-transfer agent. The synthesized complexes are able to promote the stereoselective ROP of rac-beta-butyrolactone to afford syndiotactic poly(hydrobutyrate) through a chain-end control mechanism, while they are surprisingly non-stereoselective for the ROP of lactide under strictly similar conditions. |
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Keywords: | guanidinate ligands lactides lanthanides polymerization ring‐opening polymerization |
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