Abstract
The syntheses of a library of new chiral aminophenolate bidentate O,N-type ligands HOC6H4(2-R- 4-R′)CH2N(Me)CH(Me)C6H5 [R = R′ = But, 1; R = R′ = Pent, 2; R = But, R′ = Me, 3; R = Me, R′ = But, 4; R = R′ = Me, 5] and tridentate O,N,O-type ligands HOC6H4(2,4-But)CH = NCH(R′′)C6H5 [R′′ = Me, 6; R′′ = CH2OMe, 7] are reported. These ligands were characterized by elemental analysis, nuclear magnetic resonance spectroscopy (1H & 13C), and single crystal X-ray diffraction. These ligands serve as chiral auxiliaries for inorganic chemists to design chiral metal-based complexes for asymmetric catalysis and stereoselective polymerization reactions. Three new heteroleptic zinc complexes based on these ligands have been synthesized in moderate yields via a ligand-exchange transamination reaction between homoleptic [Zn(N(SiMe3)2)2] and one equivalent of corresponding ligands to afford [L3ZnN- (SiMe3)2] (3a), [L4ZnN(SiMe3)2] (4a), and [L7ZnN(SiMe3)2] (7a). Solvent-free polymerization of raclactide at 130°C using these zinc compounds yielded atactic polylactides with Mw 10,000 g/mol and narrow polydispersity of 1.3.
Highlights
Due to the problems associated with conventional olefinic polymeric materials, the production of biodegradableHow to cite this paper: Binda, P., Rivers, K. and Padgett, C. (2016) Zinc Complexes of New Chiral Aminophenolate Ligands: Synthesis, Characterization and Reactivity toward Lactide
Metal-based initiators of aluminum, magnesium, zinc, tin, iron, titanium, zirconium, yttrium, and lanthanide metals have been employed with reactivity increasing with metal size due to increase in electropositivity, while polymerization control decreases in the same order
As the reactivity and selectivity of a metal catalyst are largely determined by the auxiliary ligands [71]-[74], ligand design has been a central focus in ring-opening polymerization (ROP) of cyclic esters, with aminophenolate ligands receiving great attention due to the potential to fine tune the steric and electronic properties by varying the substituent groups and pendant side-arms to afford different donor atoms, as well as their inexpensive synthetic strategies [67]-[70], [75]-[80]
Summary
Due to the problems associated with conventional olefinic polymeric materials, the production of biodegradableHow to cite this paper: Binda, P., Rivers, K. and Padgett, C. (2016) Zinc Complexes of New Chiral Aminophenolate Ligands: Synthesis, Characterization and Reactivity toward Lactide. As the reactivity and selectivity of a metal catalyst are largely determined by the auxiliary ligands [71]-[74], ligand design has been a central focus in ROP of cyclic esters, with aminophenolate ligands receiving great attention due to the potential to fine tune the steric and electronic properties by varying the substituent groups and pendant side-arms to afford different donor atoms, as well as their inexpensive synthetic strategies [67]-[70], [75]-[80]. Given their widespread application, it is somewhat surprising that the chiral variants of aminophenolate ligands are relatively lacking in the literature. Controlling the microstructure of PLA produced from rac-LA has received great attention [6], [81]-[87] and chiral catalysts can provide a better stereo-control
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