72332-14-0Relevant academic research and scientific papers
Catalysis in a Cationic Coordination Cage Using a Cavity-Bound Guest and Surface-Bound Anions: Inhibition, Activation, and Autocatalysis
Cullen, William,Metherell, Alexander J.,Wragg, Ashley B.,Taylor, Christopher G. P.,Williams, Nicholas H.,Ward, Michael D.
, p. 2821 - 2828 (2018)
The Kemp elimination (reaction of benzisoxazole with base to give 2-cyanophenolate) is catalyzed in the cavity of a cubic M8L12 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.
Kemp elimination: A probe reaction to study ionic liquids properties
D'Anna, Francesca,La Marca, Sandra,Noto, Renato
, p. 3397 - 3403 (2008)
(Chemical Equation Presented) The amino induced elimination of benzisoxazole into the relevant o-cyanophenolate ion (Kemp elimination) has been studied in [bmim] [BF4] solution at 298 K. To have information about the interactions between reactants and ionic liquid, the reaction has been carried out at different temperatures (293-313 K). Several primary, secondary, and tertiary amines have been used to study the effect of amine structure on the reaction rate. The collected data show that the amine structure seems to have a crucial role in determining the reaction rate. Furthermore, as different cation or anion structures of an ionic liquid can significantly affect its properties, the title reaction has been performed in four different ionic liquids ([bmim][PF6], [bmim][NTf2], [bm2im][NTf 2], and [bmpyrr][NTf2]), using pyrrolidine and piperidine as model amines. An H-donor negative solvent (MeOH and [bmim][NTf2]) effect on reaction rate was detected. Finally, a narrow range of activation parameters was calculated both for the reaction induced by different amines and for pyrrolidine and piperidine, in the presence of different ILs. This fact suggests the occurrence of an early transition state.
Highly Sterically hindered Carbon Acids: The Intrinsic Reactivity of 5,5',5''-Trimethyl- and 3,3',3'',5,5',5''-Hexamethyl-2,2',2'',4,4',4''-Hexanitrotriphenylmethanes
Terrier, Francois,Xiao, Lan,Farrell, Patrick G.,Moskowitz, Danielle
, p. 1259 - 1263 (2007/10/02)
Rate constants (kpB,kpBH) for the reversible deprotonation of 5,5',5''-trimethyl- and 3,3',3'',5,5',5''-hexamethyl-2,2',2'',4,4',4''-hexanitrotriphenylmethanes (2 and 3) by primary aliphatic amines, piperidine and morpholine as well as by phenoxide anions and hydroxide anion have been measured in H2O-Me2SO (20:80) at 25 deg C.Comparison of the results obtained with those for 2,2',2'',4,4',4''-hexanitrotriphenylmethane (1a) shows that the introduction of methyl groups in positions adjacent to the nitro groups decreases markedly the thermodynamic acidity of theexocyclic CH group: ΔpK2a1a = 1.68; ΔpK3a1a = 6.48.It is suggested that these decreases are very likely the reflection of a twisting of the nitro groups out of their attached aromatic planes and therefore of a reduced resonance stabilization of the conjugated carbanions C-2 and C-3.Other important steric effects are operating in the ionization of 2 and 3.These arise from the accumulation of ortho-nitro groups in the triphenylmethane system which makes the approach of the base reagents from the exocyclic carbon of 2 and 3 very difficult.The finding of extremely low intrinsic reactivities for 2 and 3 and the observation of a much greater catalytic efficiency of primary amines than of secondary amines in assisting the proton transfers are the two most striking manifestations of these F-strain effects.
