Operando XAFS Studies on Rh(CAAC)-Catalyzed Arene Hydrogenation

Ba L. Tran, John L. Fulton, John C. Linehan, Mahalingam Balasubramanian, Johannes A. Lercher, R. Morris Bullock

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Rh K-edge X-ray absorption fine structure (XAFS) spectroscopy was used to examine the Rh-catalyzed arene hydrogenation of diphenyl ether by a combination of stoichiometric reactions of [(CAAC Cy,Dipp )Rh(COD)Cl] (Rh-Cl) (CAAC Cy,Dipp = cyclic alkyl amino carbene) and operando XAFS kinetics studies. Our results unequivocally show that Rh nanoparticles, generated from the single-site Rh complex Rh-Cl, catalyze the arene hydrogenation. Operando XAFS studies illuminate the role of silver cation on the precatalyst reactivity, the effect of increasing H 2 pressure on increasing the catalytic efficiency, the stabilizing influence of Ph 2 O on the relative rate of formation of active Rh nanoparticles, and the absence of soluble single-site Rh species that might leach from bulk heterogeneous Rh nanoparticles. We gained insights into the divergent deactivation pathways mediated by substoichiometric benzothiophene and excess KO t Bu toward H 2 activation, which is a key step en route to Rh nanoparticles for arene hydrogenation. Excess KO t Bu leads to the formation of a Rh-O t Bu complex that interferes with H 2 activation, precluding the formation of Rh nanoparticles. Benzothiophene does not interfere with the activation of H 2 at Rh in the CAAC Cy,Dipp complex while Rh nanoparticles are formed. Once Rh nanoparticles are formed, however, benzothiophene binds irreversibly to the Rh nanoparticles, preventing the adsorption of H 2 and diphenyl ether for arene hydrogenation.

Original languageEnglish
Pages (from-to)4106-4114
Number of pages9
JournalACS Catalysis
Volume9
Issue number5
DOIs
Publication statusPublished - May 3 2019

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Keywords

  • Rh(CAAC)
  • arene hydrogenation
  • benzothiophene poisoning
  • cationic rhodium
  • operando XAFS
  • rhodium nanoparticles

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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