Combining alkali metals and zinc to harness heterometallic cooperativity in cyclic ester ring-opening polymerisation |
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| Authors: | Weronika Gruszka Anna Lykkeberg Gary S. Nichol Michael P. Shaver Antoine Buchard Jennifer A. Garden |
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| Affiliation: | EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh EH9 3FJ UK.; School of Natural Sciences, Department of Materials, Henry Royce Institute, University of Manchester, Manchester M13 9PL UK ; Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY UK |
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| Abstract: | Heterometallic cooperativity is an emerging strategy to elevate polymerisation catalyst performance. Here, we report the first heterotrimetallic Na/Zn2 and K/Zn2 complexes supported by a ProPhenol ligand, which deliver “best of both” in cyclic ester ring-opening polymerisation, combining the outstanding activity (Na/K) and good control (Zn2) of homometallic analogues. Detailed NMR studies and density-functional theory calculations suggest that the Na/Zn2 and K/Zn2 complexes retain their heterometallic structures in the solution-state. To the best of our knowledge, the K/Zn2 analogue is the most active heterometallic catalyst reported for rac-lactide polymerisation (kobs = 1.7 × 10−2 s−1), giving activities five times faster than the Na/Zn2 complex. These versatile catalysts also display outstanding performance in ε-caprolatone and δ-valerolactone ring-opening polymerisation. These studies provide underpinning methodologies for future heterometallic polymerisation catalyst design, both in cyclic ester polymerisation and other ring-opening (co)polymerisation reactions.Cooperative heterotrimetallic Na/Zn2 and K/Zn2 complexes combine the excellent activities and control of the homometallic analogues, giving “best of both” in cyclic ester ring-opening polymerisation. |
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