title: Alkali aminoether-phenolate complexes: synthesis, structural characterization and evidence for an activated monomer ROP mechanism.
abstract: Several monometallic {LO(i)}M complexes of lithium (M = Li; i = 1 (1), 2 (2), 3 (3)) or potassium (M = K, i = 3 (4)) and the heteroleptic bimetallic lithium complex {LO(3)}Li·LiN(SiMe2H)2 (5), all supported by monoanionic aminoether-phenolate {LO(i)}(-) (i = 1-3) ligands, have been synthesized and structurally characterized. A large range of coordination motifs is represented in the solid state, depending on the chelating ability of the ligand, the size of the metal and the number of metallic centres found in the complex. Pulse-gradient spin-echo NMR showed that 1-4 are monomeric in solution, irrespective of their (mono- or di)nuclearity in the solid-state. VT (7)Li and DOSY NMR measurements conducted for 5 indicated that the two Li atoms in the complex do not exchange positions even at 80 °C. Upon addition of 1-10 equiv. of BnOH, the electron-rich and sterically congested {LO(3)}Li complex (3) promotes the controlled living and immortal ring-opening polymerisation of L-lactide. The combination of polymer end-group analyses and stoichiometric model reactions unambiguously provided evidence that ROP reactions catalyzed by these two-component {LO(i)}Li/BnOH catalyst systems operate according to an activated monomer mechanism, and not via the coordination-insertion scenario frequently assumed for similar alkali phenolate-alcohol systems.
authors: Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes 1, Campus de Beaulieu, 263 avenue du Général Leclerc, 35042 Cedex, Rennes, France.
authors: Sorin-Claudiu
authors: SC
authors: Roşca
authors: Dragoş-Adrian
authors: DA
authors: Roşca
authors: Vincent
authors: V
authors: Dorcet
authors: Christopher M
authors: CM
authors: Kozak
authors: Francesca M
authors: FM
authors: Kerton
authors: Jean-François
authors: JF
authors: Carpentier
authors: Yann
authors: Y
authors: Sarazin
mesh_terms: D004146:Dioxanes / Q000737:chemistry*; D004987:Ethers / Q000737:chemistry*; D008672:Metals, Alkali / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*; D058105:Polymerization
chemical_list: D004146:Dioxanes; D004987:Ethers; D008672:Metals, Alkali; D009942:Organometallic Compounds; D010636:Phenols; C091880:dilactide