Interlocking increases the persistence of N-heterocyclic carbenes in solution

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry

Background:

• N-heterocyclic carbenes (NHCs) are crucial in catalysis but often unstable.
• Previous attempts to stabilize NHCs have faced challenges with persistence in solution.

Purpose of the Study:

• To synthesize and stabilize N-heterocyclic carbene centers using a supramolecular approach.
• To investigate the persistence of these stabilized NHCs in solution.

Main Methods:

• Deprotonation of imidazolium and imidazolinium precursors within [2]rotaxane architectures.
• Utilizing macrocyclic components to shield the reactive carbene centers.
• Monitoring the stability of the resulting interlocked molecules in solution at 253 K.

Main Results:

• Successfully generated interlocked molecules featuring stabilized N-heterocyclic carbene centers.
• The macrocyclic components of the [2]rotaxanes significantly enhanced carbene persistence.
• Stabilized imidazolidin-2-ylidenes remained intact in solution for over a week at 253 K, in the absence of air.

Conclusions:

• Supramolecular encapsulation within [2]rotaxanes provides an effective strategy for stabilizing otherwise transient N-heterocyclic carbenes.
• This method offers a pathway to utilize reactive carbene species in solution-based applications.