title: Ring-opening polymerization of cyclic esters by phenoxy-thioether complexes derived from biocompatible metals.
abstract: A series of novel Mg(II) and Zn(II) complexes of the form LMX or L2M, supported by phenoxy-thioether ligands bearing different substituents at the ortho position of the thiophenol rings [L(-) = 4,6-tBu2-OC6H2-2-CH2S(2-R-C6H4)(-)] [M = Zn, R = H, X = N(SiMe3)2 (1) and X = Et (2); M = Mg, X = n-Bu, R = H (3), R = CH3 (4), R = Br (5); M = Mg, R = H (6)], were synthesized and characterized. Reaction of the proper zinc precursor (Zn[N(SiHMe2)2]2 or ZnEt2) with one equivalent of the phenoxy-thioether proligand produced the corresponding amido (1) and ethyl (2) zinc complexes in high yields. The monoalkylmagnesium complexes (3-5) were all obtained by butane elimination reaction of the dialkylmagnesium reagent, Mg(n-Bu)2, with one equivalent of the proligand in good yields. The homoleptic complex 6 was obtained by reaction of 0.5 equivalent of Mg(n-Bu)2 and the proper proligand. Variable temperature (1)H NMR studies performed on 2 and 3 demonstrated that the named complexes are involved in fluxional processes concerning a fast conformational change of the six-membered metallacycle. DOSY (Diffusion Ordered SpectroscopY) (1)H experiments and ligand scrambling strongly suggested that complexes 1-6 exist as dimeric species in solution. All complexes were active as catalysts in the ring-opening polymerization of cyclic esters. In particular, magnesium complexes showed superior ε-caprolactone and lactide ROP behavior in terms of activity, control of molecular weights and molecular weight distributions.
authors.affiliation: Department of Chemistry and Biology, University of Salerno, I-84084, via Ponte don Melillo, Fisciano, Salerno, Italy. mlamberti@unisa.it mmazzeo@unisa.it.
authors.forename: Alessia
authors.initials: A
authors.lastname: Pilone
authors.forename: Marina
authors.initials: M
authors.lastname: Lamberti
authors.forename: Mina
authors.initials: M
authors.lastname: Mazzeo
authors.forename: Stefano
authors.initials: S
authors.lastname: Milione
authors.forename: Claudio
authors.initials: C
authors.lastname: Pellecchia
mesh_terms: D040761:Biomimetic Materials / Q000138:chemical synthesis / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D004952:Esters / Q000737:chemistry*; D007700:Kinetics; D017616:Magnesium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D058105:Polymerization; D013440:Sulfides / Q000138:chemical synthesis / Q000737:chemistry*; D013816:Thermodynamics; D017967:Zinc Compounds / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D004952:Esters; D017616:Magnesium Compounds; D013440:Sulfides; D017967:Zinc Compounds