Multisite catalysis: A mechanistic study of β-lactone synthesis from epoxides and CO - Insights into a difficult case of homogeneous catalysis

Ferenc Molnar, Gerrit A. Luinstra, Markus Allmendinger, Bernhard Rieger

Research output: Contribution to journalArticlepeer-review

51 Scopus citations

Abstract

Carbonylation of epoxides with a combination of Lewis acids and cobalt carbonyls was studied by both theoretical and experimental methods. Only multisite catalysis opens a low-energy pathway for trans opening of oxirane rings. This ring-opening reaction is not easily achieved with a single-site metal catalyst due to structural and thermodynamic constraints. The overall reaction pathway includes epoxide ring opening, which requires both a Lewis acid and a tetracarbonylcobaltate nucleophile, yielding a cobalt alkyl - alkoxy-Lewis acid moiety. After CO insertion into the Co-Calkyl bond, lactone formation results from a nucleophilic attack of the alkoxy Lewis acid entity on the acylium carbon atom. A theoretical study indicates a marked influence of the Lewis acid on both ring-opening and lactone-formation steps, but not on carbonylation. Strong Lewis acids induce fast ring opening, but slow lactone formation, and visa versa: a good balance of Lewis acidity would give the fastest catalytic cycle as all steps have low barriers. Experimentally, carbonylation of propylene oxide to β-butyrolactone was monitored by online ATR-IR techniques with a mixture of tetracarbonylcobaltate and Lewis acids, namely BF3, Me3Al, Et2Al+ · diglyme, and a combination of Me3Al/dicobaltoctacarbonyl. We found that the last two mixtures are extremely active in lactone formation.

Original languageEnglish
Pages (from-to)1273-1280
Number of pages8
JournalChemistry - A European Journal
Volume9
Issue number6
DOIs
StatePublished - 17 Mar 2003
Externally publishedYes

Keywords

  • Carbonylation
  • Homogeneous catalysis
  • Multisite catalysis
  • Polymerization
  • Reaction mechanisms

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