|Title:||A family of N-heterocyclic carbene-stabilized borenium ions for metal-free imine hydrogenation catalysis||Authors:||Farrell, Jeffrey M.
Posaratnanathan, Roy T.
Stephan, Douglas W.
JEFFREY M. FARRELL
|Issue Date:||2015||Journal Volume:||6||Journal Issue:||3||Start page/Pages:||2010-2015||Source:||CHEMICAL SCIENCE||Abstract:||
This manuscript probes the steric and electronic attributes that lead to "frustrated Lewis pair" (FLP)-type catalysis of imine hydrogenation by borenium ions. Hydride abstraction from (ItBu)HB(C6F5)2 2 prompts intramolecular C-H bond activation to give (CHN)2(tBu) (CMe2CH2)CB(C6F5)2 3, defining an upper limit of Lewis acidity for FLP hydrogenation catalysis. A series of seven N-heterocyclic carbene-borane (NHC-borane) adducts ((R′CNR)2C)(HBC8H14) (R′ = H, R = dipp 4a, Mes 5a, Me 8a; R = Me R′ = Me 9a, Cl, 10a) and ((HC)2(NMe)(NR)C)(HBC8H14) (R = tBu, 6a, Ph 7a) are prepared and converted to corresponding borenium salts. These species are evaluated as catalysts for metal-free imine hydrogenation at room temperature. Systematic tuning of the carbene donor for the hydrogenation of archetypal substrate N-benzylidene-tert-butylamine achieves the highest reported turn-over frequencies for FLP-catalyzed hydrogenation at amongst the lowest reported catalyst loadings. The most active NHC-borenium catalyst of this series, derived from 10a, is readily isolable, crystallographically characterized and shown to be effective in the hydrogenation catalysis of functional group-containing imines and N-heterocycles. ? The Royal Society of Chemistry 2015.
|DOI:||10.1039/c4sc03675a||metadata.dc.subject.other:||Catalysis; Catalysts; Nitrogen compounds; Organic compounds; Catalyst loadings; CH-bond activation; Frustrated lewis pairs; Hydride abstraction; Hydrogenation catalysis; N-heterocyclic carbenes; Room temperature; Turnover frequency; Hydrogenation|
|Appears in Collections:||化學系|
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