Single-site bismuth alkoxide catalysts for the ring-opening polymerization of lactide

Dalton Trans. 2013 Aug 21;42(31):11234-41. doi: 10.1039/c3dt50629k.

Abstract

Salen bismuth alkoxides, where the salen ligand contains 2,4-di-tert-butylphenoxy groups and one of ethylene, cyclohexane or ortho-phenyl as a backbone have been prepared from reactions involving Bi[N(SiMe₃)₂]₃ and the free salen ligand followed by alcoholysis (ButOH, PriOH and 2,6-But₂C₆H₃OH). The molecular structures of the salen ligand with the cyclohexyl back-bone have been determined for the complexes salenBiCl and salenBiOC₆H₃-2,6-But₂. The chloro compound is a dimer with chloride bridges while the phenoxide is monomeric with an unusually distorted five-coordinate geometry. The phenoxide and tert-butoxide complexes have been employed in the ring-opening polymerization of lactides (L- and rac-) to give polylactides, PLAs. With rac-LA heterotactic PLA is formed preferentially, Pr = ~0.9, in dichloromethane or toluene at room temperature. The reaction is first order in [Bi] and is notably faster than most aluminum and zinc initiators as well as tin(II) octanoate. These results are discussed in terms of a recent report on the polymerization of LA by Peptobismol® and bismuth subsalicylate.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bismuth / chemistry*
  • Catalysis
  • Coordination Complexes / chemical synthesis
  • Coordination Complexes / chemistry
  • Crystallography, X-Ray
  • Dioxanes / chemistry*
  • Ethylenediamines / chemistry
  • Kinetics
  • Molecular Conformation
  • Organometallic Compounds / chemistry*
  • Polyesters / chemical synthesis
  • Polyesters / chemistry*
  • Salicylates / chemistry*

Substances

  • Coordination Complexes
  • Dioxanes
  • Ethylenediamines
  • Organometallic Compounds
  • Polyesters
  • Salicylates
  • poly(lactide)
  • bismuth subsalicylate
  • disalicylaldehyde ethylenediamine
  • dilactide
  • Bismuth