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Tracking the Structure-Reactivity Relationship of Zinc Guanidine-Pyridine Hybrid Complexes Initiating Lactide Polymerisation

Authors

  • Janna Börner,

    1. Department Chemie, Anorganische Chemie, Universität Paderborn, Warburger Straße 100, 33098 Paderborn, Germany
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  • Ulrich Flörke,

    1. Department Chemie, Anorganische Chemie, Universität Paderborn, Warburger Straße 100, 33098 Paderborn, Germany
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  • Artjom Döring,

    1. Department Chemie, Organische Chemie, Universität Paderborn, Warburger Straße 100, 33098 Paderborn, Germany
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  • Dirk Kuckling,

    1. Department Chemie, Organische Chemie, Universität Paderborn, Warburger Straße 100, 33098 Paderborn, Germany
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  • Sonja Herres-Pawlis

    Corresponding author
    1. Department Chemie, Anorganische Chemie, Universität Paderborn, Warburger Straße 100, 33098 Paderborn, Germany
    2. Fakultät Chemie, Anorganische Chemie, Technische Universität Dortmund, 44221 Dortmund, Germany
    • Department Chemie, Anorganische Chemie, Universität Paderborn, Warburger Straße 100, 33098 Paderborn, Germany Fax: +49-5251-603423.
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Abstract

Summary: Three zinc guanidine-pyridine hybrid complexes [Zn(TMGqu)2(CH3SO3)][CH3SO3] (1), [Zn(DMEGqu)(CH3SO3)2] (2) and [Zn(DMEGqu)2(CH3SO3)][CH3SO3] (3) were synthesised, completely characterised and investigated on their activity in the solvent-free ring-opening polymerisation of D,L-lactide. It was proven that the bis-chelate trigonal-bipyramidally coordinated compounds 1 and 3 are able to act as initiators for lactide polymerisation, and polylactides with molecular weights (Mw) of around 28000 g/mol could be obtained with relatively narrow polydispersities. The tetrahedral complex 2 does not initiate lactide polymerisation. In an integrated approach of structural studies and DFT calculations, the active complexes 1 and 3 were analysed towards their structural and electronical pre-requisites in comparison to their more active triflate analogues 1OTf and 3OTf. The influence of coordination strength of the anionic component on the charge distribution within the complex and on the substrate accessibility to the zinc centre is highlighted as crucial factor for the polymerisation initiation. As result, it is shown that the mesylate complexes 1 and 3 have less positive charge on the zinc centre and the mesylate is stronger bound than the corresponding triflate in the triflate complexes 1OTf and 3OTf. Consequently, the reactivity of the complexes is directly correlated to the coordinational behaviour of the anionic component.

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