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Generation and Structure of Unique Boriranyl Radicals
John C Walton1, Timothy R McFadden2, Dennis P Curran2
1EaStCHEM School of Chemistry, University of St. Andrews , St. Andrews, Fife KY16 9ST, United Kingdom.
Journal of the American Chemical Society
|November 4, 2017
Summary
Boriranyl radicals, derived from three-member ring boracyclopropanes, were detected for the first time using EPR spectroscopy. Their planar π-character and reactivity were characterized, providing insights into boron-hydrogen bond dissociation energies.
Area of Science:
- Organoboron Chemistry
- Radical Chemistry
- Spectroscopy
Background:
- Three-member ring boracyclopropanes (boriranes) are novel compounds synthesized via a recently developed method.
- N-heterocyclic carbene (NHC) substituents are incorporated into these borirane structures.
- Understanding the reactivity and properties of transient radical species is crucial in chemical synthesis.
Purpose of the Study:
- To prepare and characterize boriranes with NHC substituents.
- To detect and study boriranyl radicals for the first time.
- To investigate the H atom abstraction kinetics and B-H bond dissociation energy (BDE) in these systems.
Main Methods:
- Synthesis of NHC-substituted boriranes using a new synthetic route.
- Selective hydrogen atom abstraction from boron atoms using t-butoxyl radicals.
- Detection and characterization of boriranyl radicals via Electron Paramagnetic Resonance (EPR) spectroscopy.
- Competition experiments to determine rate constants for H atom abstraction.
Main Results:
- Boriranyl radicals were successfully generated and detected by EPR spectroscopy.
- EPR parameters indicated that the boriranyl radicals possess planar π-character.
- The rate constant for H atom abstraction from NHC-boriranes is approximately two orders of magnitude lower than that for NHC-boranes.
- The B-H bond dissociation energy (BDE) of an NHC-borirane was estimated to be around 95 kcal mol⁻¹.
Conclusions:
- This study reports the first successful detection and characterization of boriranyl radicals.
- The findings provide valuable information on the electronic structure and reactivity of these novel boron-containing radicals.
- The estimated B-H BDE offers insights into the stability and potential applications of NHC-boriranes in chemical reactions.
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