Poison or Promoter? Investigating the Dual-Role of Carbon Monoxide in Pincer-Iridium-Based Alkane Dehydrogenation Systems via Operando Diffuse Reflectance Infrared Fourier Transform Spectroscopy

Boris Sheludko, Cristina F. Castro, Alan S. Goldman, Fuat E. Celik

Research output: Contribution to journalArticlepeer-review

Abstract

Pincer-ligated iridium complexes of the form [(R4PCP)IrL] (R4PCP = κ3-C6H3-2,6-(XPR2)2; X = CH2, O; R = tBu, iPr) have previously been shown competent for acceptorless alkane dehydrogenation when supported on silica. It was observed by postcatalysis solid-state NMR that silica-tethered [(SiO-tBu4POCOP)Ir(C2H4)] (3-C2H4) was converted fully to [(SiO-tBu4POCOP)Ir(CO)] (3-CO) at 300 °C. In this work, the characterization of species under dehydrogenation reaction conditions far from equilibrium between butane and butenes (approach to equilibrium Q/Keq= 0.3 at 300 °C) is performed with operando Diffuse Reflectance Infrared Fourier-Transform Spectroscopy (DRIFTS) to show the kinetics of species conversion from 3-C2H4to 3-CO. It is further found that [(SiO-tBu4POCOP)IrHCl] (3-HCl), a species considered to be a precatalyst for alkane dehydrogenation, is also fully converted to 3-CO. A mechanism of decomposition is proposed that implicates surface silanol groups, while carbon monoxide acts as a "stabilizer" for the catalyst by promoting their reductive elimination and maintaining the complex in the I oxidation state.

Original languageEnglish
Pages (from-to)12425-12436
Number of pages12
JournalACS Catalysis
Volume10
Issue number21
DOIs
Publication statusPublished - Nov 6 2020

Keywords

  • alkane dehydrogenation
  • DRIFTS
  • FT-IR
  • iridium
  • pincer ligand
  • supported molecular catalyst

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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