Stereorigid OSSO-Type Group 4 Metal Complexes in the Ring-Opening Polymerization of rac-Lactide
| Autor: | Carmine Capacchione, Assunta De Nisi, Alfonso Grassi, Stefano Milione, Rosita Lapenta, Magda Monari, Antonio Buonerba |
|---|---|
| Přispěvatelé: | Lapenta, Rosita, Buonerba, Antonio, De Nisi, Assunta, Monari, Magda, Grassi, Alfonso, Milione, Stefano, Capacchione, Carmine |
| Jazyk: | angličtina |
| Rok vydání: | 2017 |
| Předmět: |
Lactide
010405 organic chemistry Inorganic chemistry Nuclear magnetic resonance spectroscopy 010402 general chemistry 01 natural sciences Ring-opening polymerization Medicinal chemistry 0104 chemical sciences Metal Inorganic Chemistry chemistry.chemical_compound chemistry visual_art visual_art.visual_art_medium Salt metathesis reaction Physical and Theoretical Chemistry Phenol Methylene Homoleptic |
| Popis: | The synthesis and characterization of a series of group 4 metal complexes of general formula OSSOXM(OR)2 (X = R =tBu, M = Zr (1); X = cumyl, M = Zr, R =tBu (2); X = cumyl, M = Ti, R =iPr (4); X = cumyl, M = Hf, R =tBu (5)) and OSSOX2Zr (X = Cl (3)) supported by o-phenylene-bridged bis(phenolato) ligands (OSSOtBu-H = 6,6′-((1,2-phenylenebis(sulfanediyl))bis(methylene))bis(2,4-di-tert-butyphenol); OSSOCum-H = 6,6′-((1,2-phenylenebis(sulfanediyl))bis(methylene))bis(2,4-bis(2-phenylpropan-2-yl)phenol); OSSOCl-H = 6,6′-((1,2-phenylenebis(sulfanediyl))bis(methylene))bis(2,4-dichlorophenol)) are described herein. Complexes 1-5 were readily obtained by σ-bond metathesis reactions between the proligand and the appropriate homoleptic metal precursor. The reaction with OSSOCl yielded the bis-ligand complexOSSOCl2Zr (3) regardless of the OSSOCl-H/Zr(OtBu)4 molar ratio or experimental conditions. All complexes were characterized in solution using NMR spectroscopy and, in the case of 2, by single-crystal X-ray diffraction experiments. These complexes show a fac-fac ligand wrapping and a cis relationship between the other two monodentate ligands; zirconium and hafnium complexes 1-3 and 5 are configurationally stable, whereas titanium complex 4 is fluxional in solution at room temperature. The complexes tested in the ring-opening polymerization (ROP) of racemic-lactide showed, except in the case of 3, moderate rates and good levels of polymerization control. Upon addition of an exogenous alcohol (isopropyl alcohol or tert-butyl alcohol) efficient binary catalytic systems were achieved. Polymerizations were well-controlled, as testified by the linear growth of the molecular weight as polymerization proceeded, narrow polydispersity indices, and molecular weights close to those expected on the basis of added alcohol amounts. Experimental and theoretical evidence is provided that ROP reactions operate according to an activated monomer mechanism. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|