eprintid: 16322 rev_number: 22 userid: 1418 dir: disk0/00/01/63/22 datestamp: 2012-11-15 21:09:26 lastmod: 2021-06-13 01:55:32 status_changed: 2012-11-15 21:09:26 type: article metadata_visibility: show item_issues_count: 0 eprint_status: archive creators_name: Walton, JC creators_name: Brahmi, MM creators_name: Monot, J creators_name: Fensterbank, L creators_name: Malacria, M creators_name: Curran, DP creators_name: Lacǒte, E creators_email: creators_email: creators_email: creators_email: creators_email: creators_email: curran@pitt.edu creators_email: creators_id: creators_id: creators_id: creators_id: creators_id: creators_id: CURRAN creators_id: title: Electron paramagnetic resonance and computational studies of radicals derived from boron-substituted N-heterocyclic carbene boranes ispublished: pub divisions: sch_as_chemistry full_text_status: public abstract: Fifteen second-generation NHC-ligated boranes with aryl and alkyl substituents on boron were prepared, and their radical chemistry was explored by electron paramagnetic resonance (EPR) spectroscopy and calculations. Hydrogen atom abstraction from NHC - BH2Ar groups produced boryl radicals akin to diphenylmethyl with spin extensively delocalized across the NHC, BH, and aryl units. All of the NHC - B·HAr radicals studied abstracted Br-atoms from alkyl bromides. Radicals with bulky N,N′-dipp substituents underwent dimerization about 2 orders of magnitude more slowly than first-generation NHC-ligated trihydroborates. The evidence favored head-to-head coupling yielding ligated diboranes. The first ligated diboranyl radical, with a structure intermediate between that of ligated diboranes and diborenes, was spectroscopically characterized during photolysis of di-t-butyl peroxide with N,N′-di-t-butyl-imidazol-2-ylidene phenylborane. The reactive site of B-alkyl-substituted NHC - boranes switched from the boron center to the alkyl substituent for both linear and branched alkyl groups. The β-borylalkyl radicals obtained from N,N′-dipp-substituted boranes underwent exothermic β-scissions with production of dipp-Imd - BH2· radicals and alkenes. The reverse additions of NHC - boryl radicals to alkenes are probably endothermic for alkyl-substituted alkenes, but exothermic for conjugated alkenes (addition of an NHC - boryl radical to 1,1-diphenylethene was observed). A cyclopropylboryl radical was observed, but, unlike other α-cyclopropyl-substituted radicals, this showed no propensity for ring-opening. © 2011 American Chemical Society. date: 2011-07-06 date_type: published publication: Journal of the American Chemical Society volume: 133 number: 26 pagerange: 10312 - 10321 refereed: TRUE issn: 0002-7863 id_number: 10.1021/ja2038485 pmid: 21619055 citation: Walton, JC and Brahmi, MM and Monot, J and Fensterbank, L and Malacria, M and Curran, DP and Lacǒte, E (2011) Electron paramagnetic resonance and computational studies of radicals derived from boron-substituted N-heterocyclic carbene boranes. Journal of the American Chemical Society, 133 (26). 10312 - 10321. ISSN 0002-7863 document_url: http://d-scholarship-dev.library.pitt.edu/16322/1/licence.txt