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