Nitro-Assisted
Brønsted Acid Catalysis: Application
to a Challenging Catalytic Azidation
- Publication date
- Publisher
Abstract
A cocatalytic effect of nitro compounds
is described for the B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>·H<sub>2</sub>O catalyzed azidation
of tertiary aliphatic alcohols, enabling catalyst turnover for the
first time and with a broad range of substrates. Kinetic investigations
into this surprising effect reveal that nitro compounds induce a switch
from first order concentration dependence in Brønsted acid to
second order concentration dependence in Brønsted acid and second
order dependence in the nitro compounds. Kinetic, electronic, and
spectroscopic evidence suggests that higher order hydrogen-bonded
aggregates of nitro compounds and acids are the kinetically competent
Brønsted acid catalysts. Specific weak H-bond accepting additives
may offer a new general approach to accelerating Brønsted acid
catalysis in solution
