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Magnesium and zinc complexes bearing NNO-tridentate ketiminate ligands: synthesis, structures and catalysis in ring-opening polymerization of lactides

Abstract

A series of magnesium and zinc complexes [(L1-3)2M2(μ-OBn)2] (M = Mg (1-3), Zn (4-6)), have been synthesized by the reaction of NNO-tridentate ketiminate ligands (L1-3-H) and a stoichiometric amount of MgnBu2 (or ZnEt2) and BnOH. In addition, the reaction of these ketiminate ligands (L1-4-H) with half equiv of MgnBu2 (or ZnEt2) in toluene provides [M(L1-4)2] (M = Mg (7-10), Zn (11-14)) in good yields. All of these complexes have been fully characterized by NMR spectroscopy and elemental analysis, and the molecular structures of [(L1)2Mg2(µ-OBn)2] (1), [(L3)2Mg2(µ-OBn)2] (3), [(L1)2Zn2(µ-OBn)2] (4), [Mg(L1)2] (7), [Zn(L1)2] (11) and [Zn(L4)2] (14) have been further confirmed by X-ray crystallographic studies. X-ray diffraction studies revealed that complexes 1, 3 and 4 were dimeric in the solid state, bridging through the benzyloxy groups, while the solid-state structures of 7, 11 and 14 revealed a mononuclear species, six-coordinated by N, N, O atoms of two ketiminate ligands, forming a distorted octahedron around the metal centre. Complexes 1-6 acted as efficient initiators for the ring-opening polymerization of lactides, producing PLAs with controlled molecular weight and narrow molecular weight distribution. Complex 6 [(L3)2Zn2(μ-OBn)2] exhibited highest activity towards ROP of lactides. And complexes 1-6 initiated rac-lactide polymerization to afford heterotactic enriched polymers (Pr up to 0.82). In addition, complexes 7-14 were also shown to efficiently catalyze the ring-opening polymerization of lactides in the presence of BnOH.

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Publication details

The article was received on 08 Mar 2018, accepted on 07 May 2018 and first published on 08 May 2018


Article type: Paper
DOI: 10.1039/C8DT00888D
Citation: Dalton Trans., 2018, Accepted Manuscript
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    Magnesium and zinc complexes bearing NNO-tridentate ketiminate ligands: synthesis, structures and catalysis in ring-opening polymerization of lactides

    Y. Huang, X. Kou, Y. Duan, F. Ding, Y. Yin, W. Wang and Y. Yang, Dalton Trans., 2018, Accepted Manuscript , DOI: 10.1039/C8DT00888D

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