Tripodal titanium silsesquioxane complexes immobilized in polydimethylsiloxane (PDMS) membrane: Selective catalysts for epoxidation of cyclohexene and 1-octene with aqueous hydrogen peroxide

Emad H. Aish, Mark Crocker, Folami T. Ladipo

Research output: Contribution to journalArticlepeer-review

23 Scopus citations

Abstract

We investigated the activity, epoxide selectivity, H2O 2 efficiency, and recyclability of heterogeneous alkene epoxidation catalysts prepared by encapsulation of tripodal Ti silsesquioxane complexes in polydimethylsiloxane (PDMS) membrane. We found that [Ti(NMe2){(c- C6H11)7Si7O12}]/PDMS (3) and [Ti(NMe2){(i-C4H9)7Si 7O12}]/PDMS (4) displayed high activity, epoxide selectivity (≥97%), and H2O2 efficiency (≥97%) in cyclohexene-and 1-octene epoxidation with aqueous H2O2. Moreover, these catalysts were highly recyclable. The high H2O 2 efficiency can be attributed to the uniformly non-polar environment provided about the Ti silsesquioxane complex in 3 and 4 by the PDMS membrane, which presumably results in low local water concentrations and higher [alkene]:[H2O2] ratios at the Ti center than in the bulk reaction medium; both of these effects favor the epoxide selectivity and minimal leaching of titanium. Our study of the effect of solvent on catalyst activity revealed that acetonitrile is to be preferred as solvent, since methanol inhibits the epoxidation at long reaction times.

Original languageEnglish
Pages (from-to)66-72
Number of pages7
JournalJournal of Catalysis
Volume273
Issue number1
DOIs
StatePublished - Jul 7 2010

Bibliographical note

Funding Information:
Thanks are expressed to the Chemistry Department and the University of Kentucky (Office of the Vice President for Research) for support of this work. Thanks are also expressed to the Egyptian Government (Ministry of Education) for the award of a fellowship to E.A. NMR instruments utilized in this research were funded in part by the CRIF program of the US National Science Foundation (Grant No. CHE-9974810 ). Finally, we thank Mr. John Layton for his assistance with NMR spectroscopy experiments.

Keywords

  • 1-Octene
  • Cyclohexene
  • Encapsulated catalyst
  • Epoxidation
  • Ti-silsesquioxane

ASJC Scopus subject areas

  • Catalysis
  • Physical and Theoretical Chemistry

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