A new mode of chemical reactivity for metal-free hydrogen activation by Lewis acidic boranes

Elliot Bennett, Elliot Lawrence, Robin Blagg, Anna Mullen, Fraser Macmillan, Andreas Ehlers, Daniel Scott, Joshua Sapsford, Andrew Ashley, Gregory Wildgoose, Chris Slootweg

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We herein explore whether tris(aryl)borane Lewis acids are capable of cleaving H2 outside of the usual Lewis acid/base chemistry described by the concept of “frustrated Lewis pairs” (FLPs). Instead of a Lewis base we use a chemical reductant to generate stable radical anions of two highly‐hindered boranes: tris(3,5‐dinitromesityl)borane and tris(mesityl)borane. NMR spectroscopic characterization reveals that the corresponding borane radical anions activate (cleave) dihydrogen, whilst EPR spectroscopic characterization, supported by computational analysis, reveals the intermediates along the hydrogen activation pathway for the first time. This radical–based, redox pathway involves homolytic cleavage of H2, in contrast to conventional models of FLP chemistry which invoke a heterolytic cleavage pathway. This represents a new mode of chemical reactivity for hydrogen activation by borane Lewis acids.
Original languageEnglish
Pages (from-to)8362-8366
Number of pages5
JournalAngewandte Chemie-International Edition
Issue number25
Early online date9 Apr 2019
Publication statusPublished - 17 Jun 2019

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