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N-heterocyclic carbene boryl radicals: A new class of boron-centered radical

Ueng, SH and Solovyev, A and Yuan, X and Geib, SJ and Fensterbank, L and Lacôte, E and Malacria, M and Newcomb, M and Walton, JC and Curran, DP (2009) N-heterocyclic carbene boryl radicals: A new class of boron-centered radical. Journal of the American Chemical Society, 131 (31). 11256 - 11262. ISSN 0002-7863

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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 × 104 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 π-radical, analogous to the benzyl radical. © 2009 American Chemical Society.


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Details

Item Type: Article
Status: Published
Creators/Authors:
CreatorsEmailPitt UsernameORCID
Ueng, SH
Solovyev, A
Yuan, X
Geib, SJgeib@pitt.eduGEIB0000-0002-9160-7857
Fensterbank, L
Lacôte, E
Malacria, M
Newcomb, M
Walton, JC
Curran, DPcurran@pitt.eduCURRAN
Date: 12 August 2009
Date Type: Publication
Journal or Publication Title: Journal of the American Chemical Society
Volume: 131
Number: 31
Page Range: 11256 - 11262
DOI or Unique Handle: 10.1021/ja904103x
Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
Refereed: Yes
ISSN: 0002-7863
PubMed ID: 19606860
Date Deposited: 21 Feb 2013 22:53
Last Modified: 02 Feb 2019 19:55
URI: http://d-scholarship.pitt.edu/id/eprint/17350

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