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Issue 38, 2017
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Mononuclear salen-gallium complexes for iso-selective ring-opening polymerization (ROP) of rac-lactide

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Abstract

A series of mononuclear salen-supported gallium amido/alkoxide derivatives were prepared and structurally characterized and subsequently used as initiators in rac-lactide ring-opening polymerisation (ROP). The reaction of variously substituted salen ligands (1a–1f) with 0.5 equiv. of Ga2(NMe2)6 allowed the isolation of the corresponding (salen)Ga-NMe2 chelates (2b–2d, 2f) via an amine elimination route, as poorly soluble compounds in common solvents. The (salen)Ga-OBn derivatives (3a–3e) may be readily accessed by an amine-elimination/alcoholysis sequence and the molecular structures of 3a, 3d and 3e were confirmed through X-ray crystallography diffraction analysis. The present (salen)Ga-X species may effectively mediate the iso-selective ROP of rac-LA in a controlled manner (Pm up to 0.77 using a 1/1 2f/BnOH mixture as ROP initiator), with a ROP activity greatly dependent upon steric hindrance and geometrical constraints imposed by the variously substituted salen ligands. Based on the present study, salen ligands with limited steric hindrance and a certain degree of flexibility appear best suited for iso-selective ROP by (salen)Ga chelates. The salen-gallium complex 3a is also effective for the controlled ROP of ε-caprolactone (CL) and the production of PCL-b-PLA copolymers.

Graphical abstract: Mononuclear salen-gallium complexes for iso-selective ring-opening polymerization (ROP) of rac-lactide

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Publication details

The article was received on 26 Jul 2017, accepted on 07 Sep 2017 and first published on 08 Sep 2017


Article type: Paper
DOI: 10.1039/C7DT02730C
Citation: Dalton Trans., 2017,46, 12824-12834
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    Mononuclear salen-gallium complexes for iso-selective ring-opening polymerization (ROP) of rac-lactide

    D. Specklin, C. Fliedel, F. Hild, S. Mameri, L. Karmazin, C. Bailly and S. Dagorne, Dalton Trans., 2017, 46, 12824
    DOI: 10.1039/C7DT02730C

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