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A New Mode of Chemical Reactivity for Metal‐Free Hydrogen Activation by Lewis Acidic Boranes
Author(s) -
Bennett Elliot L.,
Lawrence Elliot J.,
Blagg Robin J.,
Mullen Anna S.,
MacMillan Fraser,
Ehlers Andreas W.,
Scott Daniel J.,
Sapsford Joshua S.,
Ashley Andrew E.,
Wildgoose Gregory G.,
Slootweg J. Chris
Publication year - 2019
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201900861
Subject(s) - boranes , borane , heterolysis , chemistry , lewis acids and bases , frustrated lewis pair , homolysis , reactivity (psychology) , ammonia borane , tris , photochemistry , radical , medicinal chemistry , polymer chemistry , hydrogen , organic chemistry , catalysis , hydrogen storage , boron , medicine , alternative medicine , pathology , biochemistry
We herein explore whether tris(aryl)borane Lewis acids are capable of cleaving H 2 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. This radical‐based, redox pathway involves the homolytic cleavage of H 2 , 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.