Synthesis and Reactivity of (C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>B−<i>N</i>-Heterocycle Complexes. 1. Generation of Highly Acidic sp<sup>3</sup> Carbons in Pyrroles and Indoles GuidottiSimona CamuratiIsabella FocanteFrancesca AngelliniLuca MoscardiGilberto ResconiLuigi LeardiniRino NanniDaniele MercandelliPierluigi SironiAngelo BeringhelliTiziana MaggioniDaniela 2003 The reaction of pyrroles and indoles with B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> and BCl<sub>3</sub> produces 1:1 B−N complexes containing highly acidic sp<sup>3</sup> carbons, for example, <i>N</i>-[tris(pentafluorophenyl)borane]−5<i>H</i>-pyrrole (<b>1</b>) and <i>N</i>-[tris(pentafluorophenyl)borane]−3<i>H</i>-indole (<b>2</b>), that are formed by a new formal N-to-C hydrogen shift, the mechanism of which is discussed. With some derivatives, restricted rotation around the B−N bond and/or the B−C bonds was observed by NMR techniques, and some rotational barriers were calculated from experimental data. The acidity of the sp<sup>3</sup> carbons in these complexes is shown by their ability to protonate NEt<sub>3</sub>, with formation of pyrrolyl- and indolyl-borate ammonium salts. The driving force for this reaction is given by the restoration of the aromaticity of the heterocycle.