title: Ring-opening polymerization of rac-lactide mediated by tetrametallic lithium and sodium diamino-bis(phenolate) complexes.
abstract: Lithium and sodium compounds supported by tetradentate amino-bis(phenolato) ligands, [Li2(N2O2(BuBuPip))] (1), [Na2(N2O2(BuBuPip))] (2) (where [N2O2(BuBuPip)] = 2,2'-N,N'-homopiperazinyl-bis(2-methylene-4,6-tert-butylphenol), and [Li2(N2O2(BuMePip))] (3), [Na2(N2O2(BuMePip))] (4) (where [N2O2(BuMePip)] = 2,2'-N,N'-homopiperazinyl-bis(2-methylene-4-methyl-6-tert-butylphenol) were synthesized and characterized by NMR spectroscopy and MALDI-TOF mass spectrometry. Variable temperature NMR experiments were performed to understand solution-phase dynamics. The solid-state structures of 1 and 4 were determined by X-ray diffraction and reveal tetrametallic species. PGSE NMR spectroscopic data suggests that 1 maintains its aggregated structure in CD2Cl2. The complexes exhibit good activity for controlled ring-opening polymerization of rac-lactide (LA) both solvent free and in solution to yield PLA with low dispersities. Stoichiometric reactions suggest that the formation of PLA may proceed by the typical coordination-insertion mechanism. For example, (7)Li NMR experiments show growth of a new resonance when 1 is mixed with 1 equiv. LA and (1)H NMR data suggests formation of a Li-alkoxide species upon reaction of 1 with BnOH.
authors.affiliation: Department of Chemistry, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X7. fkerton@mun.ca.
authors.forename: Dalal
authors.initials: D
authors.lastname: Alhashmialameer
authors.affiliation: Department of Chemistry, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X7. fkerton@mun.ca.
authors.forename: Nduka
authors.initials: N
authors.lastname: Ikpo
authors.affiliation: C-CART X-ray Diffraction Laboratory, Memorial University of Newfoundland, St. John's, Newfoundland, Canada.
authors.forename: Julie
authors.initials: J
authors.lastname: Collins
authors.affiliation: Department of Chemistry, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X7. fkerton@mun.ca and C-CART X-ray Diffraction Laboratory, Memorial University of Newfoundland, St. John's, Newfoundland, Canada.
authors.forename: Louise N
authors.initials: LN
authors.lastname: Dawe
authors.affiliation: Department of Chemistry, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X7. fkerton@mun.ca.
authors.forename: Karen
authors.initials: K
authors.lastname: Hattenhauer
authors.affiliation: Department of Chemistry, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X7. fkerton@mun.ca.
authors.forename: Francesca M
authors.initials: FM
authors.lastname: Kerton