Heterolytic Scission of Hydrogen Within a Crystalline Frustrated Lewis Pair

Mark Bowden, Bojana Ginovska, Martin Jones, Abhijeet Karkamkar, Anibal Ramirez-Cuesta, Luke Daemen, Gregory Schenter, Seth Miller, Timo Repo, Konstantin Chernichenko, Noemi Leick, Madison Martinez, Tom Autrey

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7 Scopus Citations


We report the heterolysis of molecular hydrogen under ambient conditions by the crystalline frustrated Lewis pair (FLP) 1-{2-[bis(pentafluorophenyl)boryl]phenyl}-2,2,6,6-tetramethylpiperidine (KCAT). The gas-solid reaction provides an approach to prepare the solvent-free, polycrystalline ion pair KCATH2 through a single crystal to single crystal transformation. The crystal lattice of KCATH2 increases in size relative to the parent KCAT by approximately 2%. Microscopy was used to follow the transformation of the highly colored red/orange KCAT to the colorless KCATH2 over a period of 2 h at 300 K under a flow of H2 gas. There is no evidence of crystal decrepitation during hydrogen uptake. Inelastic neutron scattering employed over a temperature range from 4-200 K did not provide evidence for the formation of polarized H2 in a precursor complex within the crystal at low temperatures and high pressures. However, at 300 K, the INS spectrum of KCAT transformed to the INS spectrum of KCATH2. Calculations suggest that the driving force is more favorable in the solid state compared to the solution or gas phase, but the addition of H2 into the KCAT crystal is unfavorable. Ab Initio methods were used to calculate the INS spectra of KCAT, KCATH2, and a possible precursor complex of H2 in the pocket between the B and N of crystalline KCAT. Ex-situ NMR showed that the transformation from KCAT to KCATH2 is quantitative and our results suggest that the hydrogen heterolysis process occurs via H2 diffusion into the FLP crystal with a rate-limiting movement of H2 from inactive positions to reactive sites.

Original languageAmerican English
Pages (from-to)15295-15301
Number of pages7
JournalInorganic Chemistry
Issue number20
StatePublished - 19 Oct 2020

Bibliographical note

Publisher Copyright:
© 2020 American Chemical Society.

NREL Publication Number

  • NREL/JA-5900-77173


  • frustrated Lewis acid pairs
  • hydrogen storage
  • KCAT


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