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Issue 17, 2014
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Lactide polymerization catalyzed by Mg and Zn diketiminate complexes with flexible ligand frameworks

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Abstract

Diketimine ligands bearing N-benzyl, N-9-anthrylmethyl and N-mesitylmethyl substituents (nacnacBnH, nacnacAnH, and nacnacMesH) were prepared from condensation of the amine with either acetyl acetone or its ethylene glycol monoketal. Chlorination with N-chlorosuccinimide in the 3-position yielded ClnacnacBnH and ClnacnacAnH. The ligands were reacted with Zn(TMSA)2 (TMSA = N(SiMe3)2) to yield nacnacAnZn(TMSA) and ClnacnacBnZn(TMSA). Protonation with isopropanol afforded nacnacAnZnOiPr and ClnacnacBnZnOiPr. Reaction of the diketimines with Mg(TMSA)2 afforded nacnacAnMg(TMSA), nacnacMesMg(TMSA), ClnacnacBnMg(TMSA) and ClnacnacAnMg(TMSA). Subsequent protonation with tert-butanol produced nacnacMesMgOtBu and ClnacnacBnMgOtBu, but only decomposition was observed with N-anthrylmethyl substituents. Most complexes were characterized by X-ray diffraction studies. TMSA complexes were monomeric and alkoxide complexes dimeric in the solid state. All alkoxide complexes, as well as nacnacAnMg(TMSA)/BnOH and ClnacnacAnMg(TMSA)/BnOH were moderately to highly active in rac-lactide polymerization (90% conversion in 30 s to 3 h). nacnacAnZnOiPr produced highly heterotactic polymers (Pr = 0.90), ClnacnacBnMgOtBu/BnOH produced slightly isotactic polymers at −30 °C (Pr = 0.43), and all other catalysts produced atactic polymers with a slight heterotactic bias.

Graphical abstract: Lactide polymerization catalyzed by Mg and Zn diketiminate complexes with flexible ligand frameworks

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Publication details

The article was received on 29 Jan 2013, accepted on 02 Feb 2014 and first published on 03 Feb 2014


Article type: Paper
DOI: 10.1039/C3DT53278J
Citation: Dalton Trans., 2014,43, 6339-6352
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    Lactide polymerization catalyzed by Mg and Zn diketiminate complexes with flexible ligand frameworks

    T. J. J. Whitehorne, B. Vabre and F. Schaper, Dalton Trans., 2014, 43, 6339
    DOI: 10.1039/C3DT53278J

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