title: Scandium versus yttrium{amino-alkoxy-bis(phenolate)} complexes for the stereoselective ring-opening polymerization of racemic lactide and β-butyrolactone.
abstract: Scandium and yttrium amide complexes Ln{ONXO(R1,R2)}(N(SiHMe2)2)(THF)n (Ln = Sc, n = 0 or Y, n = 1; X = NMe2 or OMe; R(1) = Cumyl or p-Cl-Cumyl; R(2) = Me or Cumyl) were prepared by aminolysis of Ln[N(SiHMe2)2]3(THF) with the corresponding tetradentate diamino- or alkoxy-amino-bis(phenol) pro-ligands {ONXO(R1,R2)}H2. In the solid state and in toluene solution, the scandium complexes are monomeric and 5-coordinated, while the analogous yttrium complexes all bear an extra THF-coordinated molecule and are 6-coordinated. Sc{ONXO(R1,R2)}(N(SiHMe2)2) complexes are single-site initiators for the ring-opening polymerization (ROP) of racemic lactide but are less active than their yttrium analogues Y{ONXO(R1,R2)}(N(SiHMe2)2)(THF); also, in contrast to the latter ones, they are inactive in the ROP of the more demanding racemic β-butyrolactone. On the other hand, the scandium amide complexes feature a significantly improved control over the ROP of lactide, yielding PLAs with much narrower molecular weight distributions (Đ(M) < 1.1 for Sc vs. 1.5-2.0 for Y). The yttrium complex with the very bulky o,p-dicumyl-substituted ligand is more heteroselective than its scandium analogue (P(r) = 0.88 vs. 0.83), while the opposite is observed with complexes based on p-methyl-substituted ligands (P(r) = 0.50 in toluene or 0.72-0.75 in THF for Y vs. P(r) = 0.75-0.83 for Sc in toluene). These reactivity and selectivity trends are rationalized by a much more sterically crowded coordination sphere in scandium than in yttrium complexes.
authors.affiliation: Institut des Sciences Chimiques de Rennes, Organometallics: Materials and Catalysis Laboratories, UMR 6226 CNRS-Université de Rennes 1, F-35042 Rennes Cedex, France. evgueni.kirillov@univ-rennes1.fr jean-francois.carpentier@univ-rennes1.fr.
authors.forename: Yulia
authors.initials: Y
authors.lastname: Chapurina
authors.forename: Joice
authors.initials: J
authors.lastname: Klitzke
authors.forename: Osvaldo de L
authors.initials: Ode L
authors.lastname: Casagrande
authors.forename: Mouhamad
authors.initials: M
authors.lastname: Awada
authors.forename: Vincent
authors.initials: V
authors.lastname: Dorcet
authors.forename: Evgueni
authors.initials: E
authors.lastname: Kirillov
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Carpentier
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000737:chemistry; D000438:Alcohols / Q000737:chemistry; D000588:Amines / Q000737:chemistry; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004146:Dioxanes / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D010636:Phenols / Q000737:chemistry*; D058105:Polymerization; D012538:Scandium / Q000737:chemistry*; D013237:Stereoisomerism; D015019:Yttrium / Q000737:chemistry*
chemical_list: D000438:Alcohols; D000588:Amines; D056831:Coordination Complexes; D004146:Dioxanes; D008024:Ligands; D010636:Phenols; C059688:alkoxyl radical; C013426:beta-butyrolactone; D015019:Yttrium; C091880:dilactide; D015107:4-Butyrolactone; D012538:Scandium