Polarity Reversal Catalysis in Radical Reductions of Halides by N-Heterocyclic Carbene Boranes PanXiangcheng LacôteEmmanuel LalevéeJacques CurranDennis P. 2012 Otherwise sluggish or completely ineffective radical reductions of alkyl and aryl halides by N-heterocyclic carbene boranes (NHC-boranes) are catalyzed by thiols. Reductions and reductive cyclizations with readily available 1,3-dimethylimidazol-2-ylidene borane and a water-soluble triazole relative are catalyzed by thiophenol and <i>tert</i>-dodecanethiol [C<sub>9</sub>H<sub>19</sub>C­(CH<sub>3</sub>)<sub>2</sub>SH]. Rate constants for reaction of the phenylthiyl (PhS•) radical with two NHC-boranes have been measured to be ∼10<sup>8</sup> M<sup>–1</sup> s<sup>–1</sup> by laser flash photolysis experiments. An analysis of the available evidence suggests the operation of polarity reversal catalysis.