1,2-H- versus 1,2-C-Shift on Sn-Silsesquioxanes

Tyler R. Josephson, Stephen K. Brand, Stavros Caratzoulas, Dionisios G. Vlachos

Research output: Contribution to journalArticle

  • 1 Citations

Abstract

Lewis acidic zeolites such as Sn-Beta catalyze glucose isomerization to fructose via an intramolecular 1,2-H-shift reaction, a key step for converting lignocellulosic biomass into renewable chemicals. Na-exchange of Sn-Beta titrates the neighboring SiOH group in the open Sn site and shifts catalyst selectivity to mannose formed by a 1,2-C-shift reaction. To probe structure/activity relationships in the zeolite, tin-containing silsesquioxanes with (1a) and without (1b) a neighboring SiOH group were recently synthesized and tested. These molecular catalysts are active for glucose conversion, and the presence (absence) of the SiOH favors fructose (mannose) selectivity by intramolecular H(C)-shift reactions. Using density functional theory, we investigated numerous H/C-shift pathways on these tin-silsesquioxane catalysts. On both 1a and 1b, the H-shift reaction occurs through a bidentate binding mode without participation of the SiOH, while the bidentate binding mode is not favored for the C-shift due to steric hindrance. Instead, the C-shift reaction occurs through different concerted reaction pathways, in which an acetylacetonate (acac) ligand interacts with the substrate in the transition state complexes. Favorable H-shift pathways without SiOH participation and acac ligand promotion of the C-shift pathway explain why 1a produces mannose from C-shift reactions instead of exclusively catalyzing H-shift reactions, as the Sn-Beta open site does.

Original languageEnglish (US)
Pages (from-to)25-33
Number of pages9
JournalACS Catalysis
Volume7
Issue number1
DOIs
StatePublished - Jan 6 2017
Externally publishedYes

Fingerprint

Fructose
Tin
Glucose
Ligands
Catalysts
Afferent Loop Syndrome
Catalyst selectivity
Isomerization
Zeolites
Density functional theory
Biomass
Substrates
Alcuronium
Cosmic Radiation
Panthera
Mandibular Condyle

Keywords

  • Bader
  • Bilik reaction
  • hydride transfer
  • Lewis acids
  • silsesquioxanes
  • zeolites

ASJC Scopus subject areas

  • Catalysis

Cite this

Josephson, T. R., Brand, S. K., Caratzoulas, S., & Vlachos, D. G. (2017). 1,2-H- versus 1,2-C-Shift on Sn-Silsesquioxanes. ACS Catalysis, 7(1), 25-33. DOI: 10.1021/acscatal.6b03128

1,2-H- versus 1,2-C-Shift on Sn-Silsesquioxanes. / Josephson, Tyler R.; Brand, Stephen K.; Caratzoulas, Stavros; Vlachos, Dionisios G.

In: ACS Catalysis, Vol. 7, No. 1, 06.01.2017, p. 25-33.

Research output: Contribution to journalArticle

Josephson, TR, Brand, SK, Caratzoulas, S & Vlachos, DG 2017, '1,2-H- versus 1,2-C-Shift on Sn-Silsesquioxanes' ACS Catalysis, vol 7, no. 1, pp. 25-33. DOI: 10.1021/acscatal.6b03128
Josephson TR, Brand SK, Caratzoulas S, Vlachos DG. 1,2-H- versus 1,2-C-Shift on Sn-Silsesquioxanes. ACS Catalysis. 2017 Jan 6;7(1):25-33. Available from, DOI: 10.1021/acscatal.6b03128

Josephson, Tyler R.; Brand, Stephen K.; Caratzoulas, Stavros; Vlachos, Dionisios G. / 1,2-H- versus 1,2-C-Shift on Sn-Silsesquioxanes.

In: ACS Catalysis, Vol. 7, No. 1, 06.01.2017, p. 25-33.

Research output: Contribution to journalArticle

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AB - Lewis acidic zeolites such as Sn-Beta catalyze glucose isomerization to fructose via an intramolecular 1,2-H-shift reaction, a key step for converting lignocellulosic biomass into renewable chemicals. Na-exchange of Sn-Beta titrates the neighboring SiOH group in the open Sn site and shifts catalyst selectivity to mannose formed by a 1,2-C-shift reaction. To probe structure/activity relationships in the zeolite, tin-containing silsesquioxanes with (1a) and without (1b) a neighboring SiOH group were recently synthesized and tested. These molecular catalysts are active for glucose conversion, and the presence (absence) of the SiOH favors fructose (mannose) selectivity by intramolecular H(C)-shift reactions. Using density functional theory, we investigated numerous H/C-shift pathways on these tin-silsesquioxane catalysts. On both 1a and 1b, the H-shift reaction occurs through a bidentate binding mode without participation of the SiOH, while the bidentate binding mode is not favored for the C-shift due to steric hindrance. Instead, the C-shift reaction occurs through different concerted reaction pathways, in which an acetylacetonate (acac) ligand interacts with the substrate in the transition state complexes. Favorable H-shift pathways without SiOH participation and acac ligand promotion of the C-shift pathway explain why 1a produces mannose from C-shift reactions instead of exclusively catalyzing H-shift reactions, as the Sn-Beta open site does.

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