Metal-Free Borylation of Heteroarenes Using Ambiphilic Aminoboranes: On the Importance of Sterics in Frustrated Lewis Pair C–H Bond Activation Julien Légaré Lavergne Arumugam Jayaraman Luis C. Misal Castro Étienne Rochette Frédéric-Georges Fontaine 10.1021/jacs.7b08143.s001 https://acs.figshare.com/articles/journal_contribution/Metal-Free_Borylation_of_Heteroarenes_Using_Ambiphilic_Aminoboranes_On_the_Importance_of_Sterics_in_Frustrated_Lewis_Pair_C_H_Bond_Activation/5475136 Two novel frustrated Lewis pair (FLP) aminoboranes, (1-Pip-2-BH<sub>2</sub>-C<sub>6</sub>H<sub>4</sub>)<sub>2</sub> (<b>2</b>; Pip = piperidyl) and (1-NEt<sub>2</sub>-2-BH<sub>2</sub>-C<sub>6</sub>H<sub>4</sub>)<sub>2</sub> (<b>3</b>; NEt<sub>2</sub> = diethylamino), were synthesized, and their structural features were elucidated both in solution and in the solid state. The reactivity of these species for the borylation of heteroarenes was investigated and compared to previously reported (1-TMP-2-BH<sub>2</sub>-C<sub>6</sub>H<sub>4</sub>)<sub>2</sub> (<b>1</b>; TMP = tetramethylpiperidyl) and (1-NMe<sub>2</sub>-2-BH<sub>2</sub>-C<sub>6</sub>H<sub>4</sub>)<sub>2</sub> (<b>4</b>; NMe<sub>2</sub> = dimethylamino). It was shown that <b>2</b> and <b>3</b> are more active catalysts for the borylation of heteroarenes than the bulkier analogue <b>1</b>. Kinetic studies and density functional theory calculations were performed with <b>1</b> and <b>2</b> to ascertain the influence of the amino group of this FLP-catalyzed transformation. The C–H activation step was found to be more facile with smaller amines at the expense of a more difficult dissociation of the dimeric species. The bench-stable fluoroborate salts of all catalysts (<b>1F</b>–<b>4F</b>) have been synthesized and tested for the borylation reaction. The new precatalysts <b>2F</b> and <b>3F</b> are showing higher reaction rates and yields for multigram-scale syntheses. 2017-09-13 00:00:00 FLP-catalyzed transformation BH NEt 2 reaction rates heteroarene Pip multigram-scale syntheses C 6 H 4 precatalysts 2 F theory calculations Lewis pair -2- Kinetic studies TMP -2-BH borylation reaction Metal-Free Borylation Ambiphilic Aminoboranes dimeric species 3 F NMe 2 bulkier analogue 1 bench-stable fluoroborate salts