Confinement induced catalytic activity in a Diels-Alder reaction: comparison among various CB[n], n = 6–8, cavitands
The impact of the size of the confining regime on the thermodynamic and kinetic outcome of a representative Diels-Alder reaction between ethylene and 1,3 butadiene has been investigated in silico. To this end, two organic hosts namely cucurbituril (CB) and cucurbituril (CB) have been considered in order to impose confinement on the reactants/transition state/product of the concerned reaction. The obtained results have been compared with the recently reported (Chakraborty et al. ChemPhysChem 18:2162–2170, 2017) corresponding case of the same reaction happening inside cucurbituril (CB). Results indicate that as compared to the reaction of ethylene and 1,3 butadiene inside CB, both CB and CB cavitands slow down the same reaction at 298.15 K and 1 atm. It appears that the size of the cavitand plays a crucial role in affecting the kinetic outcome of the considered reaction. While CB can enforce productive alignment of the reactants inside its cavity thereby facilitating the reaction, neither CB nor CB can perform the same task as effectively. This situation bears qualitative resemblance with the cases of enzyme catalyzed reactions.
KeywordsConfinement Kinetic facilitation Cucurbit[n]uril Host-guest complex Partial covalent bond
P.K.C. would like to thank DST, New Delhi for a J. C. Bose National Fellowship. MG thanks CSIR, New Delhi for his senior research fellowship.
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