N-Heterocyclic Carbene Boryl Radicals: A New Class of Boron-Centered Radical
Citations Over TimeTop 1% of 2009 papers
Abstract
Reduction of xanthates by N-heterocyclic carbene boranes (NHC-boranes) has been suggested to occur by a radical chain mechanism involving heretofore unknown NHC-boryl radicals. In support of this suggestion, both the expected borane dithiocarbonate product and an unexpected borane xanthate product have now been isolated. These are the first NHC-boranes with boron-sulfur bonds, and their structures have been secured by spectroscopic and crystallographic means. The first rate constants for H-atom transfer from an NHC borane complex were determined by using the ring opening of a substituted cyclobutylcarbinyl radical as a clock reaction. The rate constant for reaction of the NHC-borane with a secondary alkyl radical at ambient temperature is 4 x 10(4) M(-1) s(-1), and the Arrhenius function displayed an entropic term (log A term) that was typical for a bimolecular reaction. The B-H bond dissociation energy of an NHC-borane complex has been estimated at 88 kcal/mol. The putative NHC-boryl radical in these transformations has been detected by EPR spectroscopy. Spectral analysis suggests that it is a pi-radical, analogous to the benzyl radical.
Related Papers
- → Preparation of NHC Borane Complexes by Lewis Base Exchange with Amine− and Phosphine−Boranes(2010)66 cited
- → Unusual Cationic Tris(Dimethylsulfide)-Substituted closo-Boranes: Preparation and Characterization of [1,7,9-(Me2S)3-B12H9] BF4 and [1,2,10-(Me2S)3-B10H7] BF4(2012)15 cited
- → A topological pattern for understanding the structures of boranes and borane analog compounds(2014)6 cited
- → ChemInform Abstract: BORON COMPOUNDS, XXXVII. (Z E)‐ISOMERS OF DIETHYL(VINYLOXY)BORANES SUBSTITUTED AT THE VINYL GROUP FROM TRIETHYLBORANE AND VINYLCARBONYL COMPOUNDS(1976)
- → ChemInform Abstract: BORON COMPOUNDS. L. DIETHYL(SUBSTITUTED VINYLAMINO)BORANES FROM TRIETHYLBORANE AND N‐ALKYLKETIMINES(1981)