Ring‐opening polymerization of lactides catalyzed by magnesium complexes coordinated with NNO‐tridentate pyrazolonate ligands

Abstract

A series of magnesium benzylalkoxide complexes, [LnMg(μ‐OBn)]2 (1–14) supported by NNO‐tridentate pyrazolonate ligands with various electron withdrawing‐donating subsituents have been synthesized and characterized. X‐ray crystal structural studies revealed that Complexes 1–3, 5, 7, 9, and 10 are dinuclear bridging through benzylalkoxy oxygen atoms with penta‐coordinated metal centers. All of these complexes acted as efficient initiators for the ring‐opening polymerization of L‐lactide and rac‐lactide. Based on kinetic studies, the activity of these metal complexes is significantly influenced by the electronic effect of the ancillary ligands with the electron‐donating substituents at the phenyl rings enhancing the polymerization rate. In addition, the “living” and “immortal” character of 6 has paved a way to synthesize as much as 40‐fold polymer chains of polylactides with a very narrow polydispersity index in the presence of a small amount of initiator. Among all of magnesium complexes, Complex 6 exhibits the highest stereoselectivity toward ring‐opening polymerization of rac‐lactide with Pr up to 88% in THF at 0 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Controlled ring‐opening polymerization of trimethylene carbonate and access to PTMC‐PLA block copolymers mediated by well‐defined N‐heterocyclic carbene zinc alkoxides

“…The use of ROP initiators incorporating a cheap, non‐toxic and biocompatible metal center such as Ca, Mg or Zn is an important objective considering the biomedical applications of the derived materials. Zn(II)‐based initiators for the ROP of cyclic esters may be divided into two families: (i) neutral complexes of the type [(L n X)ZnR] (R = alkyl, amine, alkoxide), in which L n X represents a monoanionic chelating ancillary ligand, and (ii) cationic complexes of general formula [(L n )ZnR] + [X] − (R = alkyl, amine, alkoxide; X = non‐coordinating anion) supported by neutral polydentate L n ligands.…”

“…Zn(II)‐based initiators for the ROP of cyclic esters may be divided into two families: (i) neutral complexes of the type [(L n X)ZnR] (R = alkyl, amine, alkoxide), in which L n X represents a monoanionic chelating ancillary ligand, and (ii) cationic complexes of general formula [(L n )ZnR] + [X] − (R = alkyl, amine, alkoxide; X = non‐coordinating anion) supported by neutral polydentate L n ligands. The first class of complexes has been by far the most studied and monoanionic chelating L n X ligands are typically β‐diiminate, phenoxy‐amine phenoxy‐imine [11] or other N , O / O , O ‐type ligands (Scheme , A and B ). Lewis acidic Zn(II) cations have also been used as cyclic esters ROP initiators (Scheme , C and D ) …”

Synthesis, characterization and catalytic activity of zinc complex for ring‐opening polymerization of lactide

“…On the basis of the ‘immortal’ property of lactide polymerization demonstrated by several zinc complexes and the evidence of in situ formation of metal alkoxide in the presence of alcohol, the complex Zn‐HMBED was expected to behave as a catalyst towards the ROP of lactide in the presence of benzyl alcohol. The zinc complex Zn‐HMBED in the presence of benzyl alcohol initiates the ROP of l ‐lactide in dichloromethane at 30 o C (Scheme ).…”

“…Thus, use of environmentally benign metals that are part of the mammalian anatomy is essential, so that there will be no damage for living beings . Different metal initiators or catalysts have been used in the formation of PLA, such as compounds of aluminium, lithium, magnesium, iron, tin, titanium and zinc . Recently, initiators or catalysts based on metals such as Ca, Mg, Fe and Zn has received great interest because of their metabolized activity in the body .…”

Synthesis and Application of Bimetallic Zinc(II) Phenoxy-Imine Complexes as Initiators for Production of Lactide Polymers

“…[5][6][7] Although different coordination compounds could be used as catalysts for LA polymerization, little is known about the influence of their structures and electronic properties on PLA production. 8,9 In this respect, we have been interested in the synthesis of phenoxy-imine ligands capable of simultaneously coordinating two metal atoms. This kind of ligand can furnish bimetallic Zn-based initiators containing two metal centers close to each other, which can act in a synergic fashion during the polymerization reaction.…”