10.1021/jacs.7b11334.s003
William Cullen
William
Cullen
Alexander J. Metherell
Alexander J.
Metherell
Ashley B. Wragg
Ashley B.
Wragg
Christopher G. P. Taylor
Christopher G. P.
Taylor
Nicholas H. Williams
Nicholas H.
Williams
Michael D. Ward
Michael D.
Ward
Catalysis
in a Cationic Coordination Cage Using a
Cavity-Bound Guest and Surface-Bound Anions: Inhibition, Activation,
and Autocatalysis
American Chemical Society
2018
Cationic Coordination Cage
Kemp elimination
anion
hydroxide
cage surface
product 2- cyanophenolate
cavity-bound guest
2- cyanophenolate
M 8 L 12 coordination cage
cationic cage surface
sigmoidal reaction profile
autocatalytic pathway
default reaction pathway
2018-02-07 00:00:00
Dataset
https://acs.figshare.com/articles/dataset/Catalysis_in_a_Cationic_Coordination_Cage_Using_a_Cavity-Bound_Guest_and_Surface-Bound_Anions_Inhibition_Activation_and_Autocatalysis/5891998
The
Kemp elimination (reaction of benzisoxazole with
base to give 2-cyanophenolate) is catalyzed in the cavity of a cubic
M<sub>8</sub>L<sub>12</sub> coordination cage because of a combination
of (i) benzisoxazole binding in the cage cavity driven
by the hydrophobic effect, and (ii) accumulation of hydroxide ions
around the 16+ cage surface driven by ion-pairing. Here we show how
reaction of the cavity-bound guest is modified by the presence of
other anions which can also accumulate around the cage surface and
displace hydroxide, inhibiting catalysis of the cage-based reaction.
Addition of chloride or fluoride inhibits the reaction with hydroxide
to the extent that a new autocatalytic pathway becomes apparent, resulting
in a sigmoidal reaction profile. In this pathway the product 2-cyanophenolate
itself accumulates around the cationic cage surface, acting as the
base for the next reaction cycle. The affinity of different anions
for the cage surface is therefore 2-cyanophenolate (generating autocatalysis)
> chloride > fluoride (which both inhibit the reaction with
hydroxide
but cannot deprotonate the benzisoxazole guest) > hydroxide
(default reaction pathway). The presence of this autocatalytic pathway
demonstrates that a reaction of a cavity-bound guest can be induced
with different anions around the cage surface in a controllable way;
this was confirmed by adding different phenolates to the reaction,
which accelerate the Kemp elimination to different extents depending
on their basicity. This represents a significant step toward the goal
of using the cage as a catalyst for bimolecular reactions between
a cavity-bound guest and anions accumulated around the surface.