Electrochemical Generation of N-Heterocyclic Carbenes on an Imidazolium-Based Covalent Organic Framework

The electrochemical generation of N-heterocyclic carbenes (NHCs) by cathodic reduction of azolium cations represents a particularly attractive approach to access species that are widely used both as organocatalysts and organometallic ligands. In parallel, the development of covalent organic frameworks (COFs) made them emerge as highly valuable porous materials for a wide range of applications, owing to their high surface areas and ordered architectures. The integration of active sites within COFs offers a powerful platform to design robust heterogeneous catalytic systems, with ease of recovery and reuse. We herein report the evidence of what represents, based on available literature data, the first electrochemical generation of NHCs deriving from the reduction of azolium functionalities incorporated in a COF. The study involved voltammetric analyses of a triazine-based, imidazolium-rich COF, and tests of the involvement of the species generated upon potentiostatic electrolysis in NHC-catalysed reaction pathways in the presence of p-anisaldehyde, when the COF is employed as electrode modifier. GC-MS analyses confirmed the formation of a 1,2-diketone product compatible with a NHC-catalysed condensation and subsequent oxidation. Combining the electrochemical reactivity of azolium cations with operational advantages of COFs opens new promising avenues in sustainable organic electrosynthesis.