Catalysis by Cucurbituril. The Significance of Bound-Substrate Destabilization for Induced Triazole Formation

Article abstract of DOI:10.1021/jo00283a024

A mechanistic investigation is described for the cycloaddition induced between RNH2⁺CH2C<*>CH and RNH2⁺CH2CH2N3 (R = H, t-Bu) consequent to encapsulationby the polycyclic molecular receptor cucrbituril (C36H36N24O12).The reaction is shown to be substantially accelerated (ca. 10⁵-fold), and the kinetic characteristics of catalytic saturation behavior, substrate inhibition, and slow product release are documented.For substrates with R = t-Bu a rotaxane product results, and inhibition kinetics with NH3⁺CH2CH2C(CH3)3 are also examined.A rate enhancementattributed to bound-substrate destabilization is detected.The significance of this effect and its connection with the phenomenon of nonproductive binding in catalytic systems are discussed.