title: Bis(guanidinate) alkoxide complexes of lanthanides: synthesis, structures and use in immortal and stereoselective ring-opening polymerization of cyclic esters.
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.
authors.affiliation: Organometallics and Catalysis, UMR CNRS 6226, Sciences Chimiques de Rennes, University of Rennes 1, 35042 Rennes Cedex, France.
authors.forename: Noureddine
authors.initials: N
authors.lastname: Ajellal
authors.forename: Dmitrii M
authors.initials: DM
authors.lastname: Lyubov
authors.forename: Mikhail A
authors.initials: MA
authors.lastname: Sinenkov
authors.forename: Georgii K
authors.initials: GK
authors.lastname: Fukin
authors.forename: Anton V
authors.initials: AV
authors.lastname: Cherkasov
authors.forename: Christophe M
authors.initials: CM
authors.lastname: Thomas
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Carpentier
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Trifonov