Conditional Copper‐Catalyzed Azide–Alkyne Cycloaddition by Catalyst Encapsulation

Cooperative Effects in Switchable Catalysis: Enhancing Double-Click Reaction Yield of Symmetrical Rotaxanes

Reversible switching between the closed cyclic dimeric assembly [Cu₂(1)₂]²⁺ (OFF state) and the extended dimeric homoleptic complex [FeCu₂(1)₂]⁴⁺ (ON State) by addition/removal of Fe²⁺ triggered catalysis of a double‐click reaction and high yield preparation of [2]rotaxanes. Mechanistic and computational studies provide valuable general insight for double‐click strategies by revealing cooperative effects in the second cycloaddition step due to a distance‐tolerant preorganization of the first‐click product by the two copper(I)‐loaded phenanthroline subunits of [FeCu₂(1)₂]⁴⁺.

Tuneable Control of Organocatalytic Activity through Host-Guest Chemistry

Dynamic regulation of chemical reactivity is important in many complex chemical reaction networks, such as cascade reactions and signal transduction processes. Signal responsive catalysts could play a crucial role in regulating these reaction pathways. Recently, supramolecular encapsulation was reported to regulate the activities of artificial catalysts. We present a host-guest chemistry strategy to modulate the activity of commercially available synthetic organocatalysts. The molecular container cucurbit[7]uril was successfully applied to change the activity of four different organocatalysts and one initiator, enabling up- or down-regulation of the reaction rates of four different classes of chemical reactions. In most cases CB[7] encapsulation results in catalyst inhibition, however in one case catalyst activation by binding to CB[7] was observed. The mechanism behind this unexpected behavior was explored by NMR binding studies and pKa measurements. The catalytic activity can be instantaneously switched during operation, by addition of either supramolecular host or competitive binding molecules, and the reaction rate can be predicted with a kinetic model. Overall, this signal responsive system proves a promising tool to control catalytic activity.