N-Heterocyclic Carbene Chemistry and Catalysis

N-Heterocyclic carbenes (NHCs) are a class of persistent singlet carbenes featuring a divalent carbon atom flanked by nitrogen heteroatoms. Their remarkable combination of strong σ-donor and tunable π-acceptor properties has transformed organometallic chemistry and catalytic science over the past two decades. Advances in ligand design, including variation of the heterocycle backbone and wingtip substituents, have enabled precise control of steric and electronic parameters, facilitating fine-tuning of metal–ligand cooperativity. NHCs have been exploited in bond activation, cross-coupling, and organocatalysis, with applications spanning small-molecule synthesis, polymerisation and surface functionalisation. Their bench stability and adaptability under ambient conditions underpin widespread adoption in industrial processes and emerging fields such as sustainable catalysis, biosensing and materials science.

Research from Nature Portfolio

Recent studies have demonstrated the use of NHCs as robust σ-donor ligands for stabilising low-valent main-group cations. In particular, bis(silylene)-stabilised antimony(I) and bismuth(I) cations have been isolated and characterised, revealing dual lone-pair coordination at the pnictogen centre. These species serve as donors to group 6 metal carbonyls, illustrating the versatility of NHC frameworks in constructing unusual metal-ligand architectures and expanding the scope of main-group catalysis.

Foundational work on self-assembled NHC monolayers has shown that bench-stable benzimidazolium hydrogen carbonate precursors enable vapour-phase and solution deposition of films on gold surfaces. Detailed surface science analyses have yielded the first direct measurement of NHC desorption energies and confirmed upright coordination geometries. These monolayers exhibit enhanced stability compared with thiolate films and have been deployed in surface plasmon resonance biosensing, demonstrating practical applications of NHC-based interfaces.

N-Heterocyclic Carbene Chemistry and Catalysis publication trend

The graph below shows the total number of articles in n-heterocyclic carbene chemistry and catalysis across all publications each year (not limited to Nature Index journals).

Technical terms

N-heterocyclic carbene (NHC): A stable carbene featuring a divalent carbon centre within a nitrogen-containing heterocycle that acts as a strong ligand in organometallic complexes.

σ-donor ligand: A ligand that donates electron density to a metal centre through a sigma-bond orbital, increasing electron density at the metal.

π-acceptor ligand: A ligand possessing vacant π* orbitals that can accept electron density from a metal centre, stabilising low-oxidation states.

%Vbur (percent buried volume): A steric descriptor quantifying the fraction of space around a metal centre occupied by a ligand, used to compare spatial demands of different ligands.

Self-assembled monolayer: An organised, single-molecule-thick film formed spontaneously by adsorption of amphiphilic molecules onto a substrate, imparting functional surface properties.

References

1. Isolation and characterization of bis(silylene)-stabilized antimony(I) and bismuth(I) cations. Nature Communications (2023).
2. Simple direct formation of self-assembled N-heterocyclic carbene monolayers on gold and their application in biosensing. Nature Communications (2016).
3. % V Bur index and steric maps: from predictive catalysis to machine learning. Chemical Society Reviews (2024).
4. What can NMR spectroscopy of selenoureas and phosphinidenes teach us about the π-accepting abilities of N -heterocyclic carbenes?. Chemical Science (2015).
5. Recent Developments in the Medicinal Applications of Silver-NHC Complexes and Imidazolium Salts. Molecules (2017).