Discrete Cationic Zinc and Magnesium Complexes for Dual Organic/Organometallic‐Catalyzed Ring‐Opening Polymerization of Trimethylene Carbonate |
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| Authors: | Dr Pierre Brignou Dr Sophie M Guillaume Dr Thierry Roisnel Dr Didier Bourissou Prof Jean‐François Carpentier |
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| Institution: | 1. Laboratoire Organométalliques: Matériaux et Catalyse, Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS and Université de Rennes 1, Campus de Beaulieu, 35042 Rennes (France);2. Centre de Diffractometrie X, Sciences Chimiques de Rennes, UMR 6226 CNRS and Université de Rennes 1, Campus de Beaulieu, 35042 Rennes (France);3. LHFA, UMR 5069 CNRS, and Université de Toulouse, UPS, 118 route de Narbonne, 31062 Toulouse (France) |
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| Abstract: | We describe herein an original approach for the efficient immortal ring‐opening polymerization (iROP) of trimethylene carbonate (TMC) under mild conditions using dual‐catalyst systems combining a discrete cationic metal complex with a tertiary amine. A series of new zinc and magnesium cationic complexes of the type {NNO}M]+anion]? ({NNO}?=2,4‐di‐tert‐butyl‐6‐{(2′‐dimethylaminoethyl)methylamino]methyl}phenolate; M=Zn, anion]?=B(C6F5)4]? ( 2 ), H2N‐ {B(C6F5)3}2]? ( 3 ), and EtB(C6F5)3]? ( 4 ); M=Mg, anion]?=H2N{B(C6F5)3}2]? ( 7 )) have been prepared from the corresponding neutral compounds {NNO}ZnEt] ( 1 ) and {NNO}‐ Mg(nBu)] ( 6 ). Compounds 2 – 4 and 7 exist as free ion pairs, as revealed by 1H, 13C, 19F, and 11B NMR spectroscopy in THF solution, and an X‐ray crystallographic analysis of the bis(THF) adduct of compound 7 , 7? (THF)2. The neutral complexes 1 and 6 , in combination with one equivalent or an excess of benzyl alcohol (BnOH), initiate the rapid iROP of TMC, in bulk or in toluene solution, at 45–60 °C (turnover frequency, TOF, up to 25–30 000 mol(TMC)?mol(Zn)?h?1 for 1 and 220–240 000 mol(TMC)?mol(Mg)?h?1 for 6 ), to afford H‐PTMC‐OBn with controlled macromolecular features. ROP reactions mediated by the cationic systems 2 /BnOH and 7 /BnOH proceeded much more slowly (TOF up to 500 and 3 000 mol(TMC)?mol(Zn or Mg)?h?1 at 110 °C) than those based on the parent neutral compounds 1 /BnOH and 6 /BnOH, respectively. Use of original dual organic/organometallic catalyst systems, obtained by adding 0.2–5 equiv of a tertiary amine such as NEt3 to zinc cationic complexes {NNO}Zn]+anion]? ( 2 – 4 ), promoted high activities (TOF up to 18 300 mol(TMC)?mol(Zn)?h?1 at 45 °C) giving H‐PTMC‐OBn with good control over the Mn and Mw/Mn values. Variation of the nature of the anion in 2 – 4 did not significantly affect the performance of these catalyst systems. On the other hand, the dual magnesium‐based catalyst system 7 /NEt3 proved to be poorly effective. |
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| Keywords: | cationic complexes dual catalyst magnesium ring‐opening polymerization zinc |
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