ChemRxiv
These are preliminary reports that have not been peer-reviewed. They should not be regarded as conclusive, guide clinical practice/health-related behavior, or be reported in news media as established information. For more information, please see our FAQs.
1/1
0/0

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

preprint
revised on 02.06.2020 and posted on 03.06.2020 by Boris Sheludko, Cristina Castro, Alan Goldman, Fuat E. Celik

Pincer-ligated iridium complexes of the form [Ir(R4PCP)L] (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 post-catalysis solid-state NMR that silica-tethered [Ir(C2H4)(≡SiO-tBu4POCOP)] (3-C2H4) was converted fully to [Ir(CO)(≡SiO-tBu4POCOP)] (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-C2H4 to 3-CO. It is further found that [IrClH(≡SiO-tBu4POCOP)] (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.

Funding

NSF CHE-1205189

History

Email Address of Submitting Author

fuat.celik@rutgers.edu

Institution

Rutgers, The State University of New Jersey

Country

USA

ORCID For Submitting Author

0000-0002-5891-6375

Declaration of Conflict of Interest

no conflict of interest

Exports

Logo branding

Exports