Methyl-ligated tin silsesquioxane catalyzed reactions of glucose

Stephen K. Brand, Tyler R. Josephson, Jay A. Labinger, Stavros Caratzoulas, Dionisios G. Vlachos, Mark E. Davis

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

Tin-containing zeolite Beta (Sn-Beta) has been investigated as a catalyst for isomerizing aldohexoses into ketohexoses through a Lewis acid mediated hydride shift. Recent studies on the reactivities of Lewis base-doped and alkali-exchanged Sn-Beta samples have conclusively demonstrated that the “open” tin site performs the glucose isomerization reaction. With Lewis base doped Sn-Beta, glucose conversion is almost completely eliminated and product selectivity is shifted predominantly to mannose. These data suggest that glucose reactions may occur through pathways that do not involve the “open” site in Sn-Beta; albeit at significantly lower rates. To examine this possibility, reactions of glucose catalyzed by a homogeneous model of Sn-Beta that does not contain “open” sites, methyl-ligated tin silsesquioxane 1a, is experimentally and theoretically examined. 1a is an active glucose conversion catalyst selectively producing mannose, although the rates of reaction are far below those obtained from Sn-Beta. A hybrid quantum mechanical/molecular mechanics model is constructed, and the complete catalytic cycle is computationally examined, considering ring-opening, three distinct pathways for each hydride- and carbon-shift reaction, and ring-closing. The combined experimental and computational results suggest that there could be reaction pathways that involve Si–O–Sn cleavage that give much slower reaction rates than the open tin site in Sn-Beta.

Original languageEnglish (US)
Pages (from-to)62-71
Number of pages10
JournalJournal of Catalysis
Volume341
DOIs
StatePublished - Sep 1 2016

Bibliographical note

Publisher Copyright:
© 2016 Elsevier Inc.

Keywords

  • Epimerization
  • Glucose conversion
  • Isomerization
  • Lewis acid
  • Tin silsesquioxanes

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