title: Group 3 metal initiators with an [OSSO]-type bis(phenolate) ligand for the stereoselective polymerization of lactide monomers.
abstract: A series of 1,ω-dithiaalkanediyl-bridged bis(phenols) of the general type [OSSO]H(2) with variable steric properties and various bridges were prepared. The stoichiometric reaction of the bis(phenols) 1,3-dithiapropanediyl-2,2'-bis(4,6-di-tert-butylphenol), 1,3-dithiapropanediyl-2,2'-bis[4,6-di(2-phenyl-2-propyl)phenol], rac-2,3-trans-propanediyl-1,4-dithiabutanediyl-2,2'-bis[4,6-di(2-phenyl-2-propyl)phenol], rac-2,3-trans-butanediyl-1,4-dithiabutane diyl-2,2'-bis[4,6-di(2-phenyl-2-propyl)phenol], rac-2,3-trans-hexanediyl-1,4-dithiabutanediyl-2,2'-bis[4,6-di(2-phenyl-2-propyl)phenol], 1,3-dithiapropanediyl-2,2'-bis[6-(1-methylcyclohexyl)-4-methylphenol] (C(1), R=1-methylcyclohexyl), and 1,4-dithiabutanediyl-2,2'-bis[6-(1-methylcyclohexyl)-4-methylphenol] with rare-earth metal silylamido precursors [Ln{N(SiHMe(2))(2)(3)(thf)(x)] (Ln=Sc, x=1 or Ln=Y, x=2; thf=tetrahydrofuran) afforded the corresponding scandium and yttrium bis(phenolate) silylamido complexes [Ln(OSSO){N(SiHMe(2))(2)}(thf)] in moderate to good yields. The monomeric nature of these complexes was shown by an X-ray diffraction study of one of the yttrium complexes. The complexes efficiently initiated the ring-opening polymerization of rac- and meso-lactide to give heterotactic-biased poly(rac-lactides) and highly syndiotactic poly(meso-lactides). Variation of the ligand backbone and the steric properties of the ortho substituents affected the level of tacticity in the polylactides.
authors.affiliation: Institute of Inorganic Chemistry, RWTH Aachen, Landoltweg 1, 52056 Aachen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kapelski
authors.forename: Jean-Charles
authors.initials: JC
authors.lastname: Buffet
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Spaniol
authors.forename: Jun
authors.initials: J
authors.lastname: Okuda
mesh_terms: D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004146:Dioxanes / Q000737:chemistry*; D062385:Hydroxybenzoates / Q000737:chemistry*; D008024:Ligands; D008674:Metals, Rare Earth / Q000737:chemistry*; D008968:Molecular Conformation; D011091:Polyesters / Q000138:chemical synthesis / Q000737:chemistry; D058105:Polymerization; D013237:Stereoisomerism
chemical_list: D056831:Coordination Complexes; D004146:Dioxanes; D062385:Hydroxybenzoates; D008024:Ligands; D008674:Metals, Rare Earth; D011091:Polyesters; C033616:poly(lactide); C091880:dilactide; C017616:phenolic acid