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Unlocking Frustrated Lewis Pairs: Neutron & X-ray Insights

Explore the relationship between Frustrated Lewis Pairs (FLPs), ionic liquids, neutron scattering, and NEXAFS spectroscopy. Learn about steric hindrance, encounter complexes, and small molecule complexation. Neutron diffraction and NEXAFS techniques are highlighted for understanding FLPs in various solvents. Future work includes analysis and upcoming research plans. Acknowledgements to the project team members and institutions.

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Unlocking Frustrated Lewis Pairs: Neutron & X-ray Insights

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  1. FLPs, Neutrons and Photons Anne McGrogan Supervised by: GosiaSwadźba-Kwaśny and John Holbrey 19th September 2019

  2. Presentation Overview • What are Frustrated Lewis Pairs (FLPs)? • What is the connection between FLPs and ionic liquids? • How can we use neutron scattering and NEXAFS Spectroscopy to understand FLPs?

  3. Sterically hindered systems Unquenched Lewis acid and Lewis base species Small molecule complexation Frustrated Lewis pairs (FLPs) G. C. Welch and D. W. Stephan, J. Am. Chem. Soc., 2007, 129, 1880–1881.

  4. Encounter complexes L. Rocchigianiet al., J. Am. Chem. Soc., 2014, 136, 112–115; S. Grimme et al. , Angew. Chem, 2010, 49, 8 , 1402–1405

  5. ISIS neutron and muon source • Harwell site in Oxfordshire • Opened in 1985 • The Small Angle Neutron Diffractometer for Amorphous and Liquid Samples (SANDALS) • Disordered materials

  6. Neutron diffraction • Interacts with nucleus of atom – not electron cloud • Intensity of diffraction is not dependent on atomic number (Z) • Distinguishes between isotopes • Very sensitive to small atoms – such as hydrogen M. J. Schrappet al., Journal of Applied Physics, 2014, 116, 163104–8.

  7. Hydrogen in neutron diffraction • Large difference in H and D cross sections • H and D scattering lengths have opposite signs • Use H/D exchange to provide neutron scattering contrast • Hydrogen scattering has a large inelastic component 1H 2D

  8. FLP in benzene – neutron scattering About 5% of FLP components form encounter complex in benzene Brown, Hogg, Gilmore, Moura, Imberti, Gärtner, Gunaratne, O’Donnell, Artioli, Holbrey and Swadźba-Kwaśny, Chem. Commun., 2018, 54, 8689.

  9. FLP in [C10mim][NTf2] – NMR spectroscopy BCF in benzene BCF in [C10mim][NTf2] FLP in benzene -150 -135 -165 𝛿 (19F)/ppm About 20% of FLP components form encounter complex in [C10mim][NTf2] FLP in [C10mim][NTf2] -150 -165 -135 -165 -150 -135 𝛿 (19F)/ppm 𝛿 (19F)/ppm -150 -165 -135 Brown, Hogg, Gilmore, Moura, Imberti, Gärtner, Gunaratne, O’Donnell, Artioli, Holbrey and Swadźba-Kwaśny, Chem. Commun., 2018, 54, 8689. 𝛿 (19F)/ppm

  10. FLP in [C2mim][NTf2] H = protonated D = deuterated P = P(tBu)3 Highlighted green = completed samples Samples prepared for ISIS  Neutron scattering with isotopic substitution  Second trip to ISIS in October P(tBu)3

  11. Diamond Light Source • UK's national synchrotron light source  • Harwell site in Oxfordshire • Opened in 2007 • Near Edge X-ray Absorption Fine Structure (NEXAFS)

  12. NEXAFS Spectroscopy • Absorption of an x-ray photon • NEXAFS and XANES - measurements in the vicinity of the absorption edge • Element specific • EXAFS - oscillatory data extending hundreds of volts above the edge NEXAFS = Near Edge X-ray Absorption Fine Structure XANES = X-ray Absorption Near Edge Structure EXAFS = Extended X-ray Absorption Fine Structure

  13. [NTf2]- [OTf]- Bcat P(tBu)3OTf Trimesityl phosphine BcatCl P(tBu)3 Bcat P888 P(tBu)3 NTf2 [OTf]- BcatCl P888 P66614Cl BcatCl P888O Bcat P888OTf [NTf2]- [NTf2]- [C10mim] [NTf2] P(tBu)3 BCF [C2mim] [NTf2]

  14. Summary • Neutron scattering at ISIS; investigating the enhanced stability of FLP encounter complexes in ILs • NEXAFS at Diamond; investigatingthe nature of the interaction between the FLP components in various solvents Future work: • Second trip to ISIS planned for October • Analysis of results from ISIS and Diamond • Bessy II, Berlin, LiquidJet XPS

  15. Acknowledgements With thanks to: Dr Malgorzata (Gosia) Swadźba-Kwaśny Prof John Holbrey Miss Lucy Brown Dr Kevin Lovelock Mr Jake Seymour Dr GiannantonioCibin (Diamond) • DrSabrina Gaertner (ISIS) • Dr Sarah Youngs (ISIS) • Dr James Tellam (ISIS) • Dr Leila Moura • Mr Richard Murphy Thank you for listening

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