N-Heterocyclic carbenes at supported metal sites: binding modes and electronic effects through the lens of NMR spectroscopy

N-Heterocyclic carbenes (NHCs) have become ubiquitous ligands for stabilizing metal centers across molecular, colloidal, and heterogeneous catalysts, yet their binding modes and electronic effects remain challenging to decipher on surfaces. This review highlights how solid-state NMR spectroscopy provides direct, site-specific insight into NHC-metal interactions on supports ranging from hybrid organic–inorganic materials and single-site catalysts to supported metal nanoparticles. By integrating experimental NMR signatures with computational analysis, we show how carbene 13 C chemical shifts and related parameters serve as sensitive probes of local coordination environments, electronic structures, ligand identity, surface acidity, and metal-support interactions. Having established how solid-state NMR parameters sensitively reflect NHC-metal bonding across diverse supported environments, we turn to coinage-metal systems, where a shared bonding motif allows systematic comparison. Within this series, only Au exhibits a pronounced balance of paramagnetic (σ para ) and spin-orbit (σ SO ) contributions: relativistic effects uniquely intensify these contributions in NHC-Au(I)-X complexes, leading to chemical-shift responses far more sensitive to trans X-ligand identity than those observed for Cu or Ag. These same principles extend from mononuclear complexes to well-defined Au clusters where diverse surface geometries modulate the trans influence and relativistic effects experienced by NHC-bound metal atoms. Together, these advances demonstrate that solid-state NMR spectroscopy offers unparalleled molecular-level resolution for decoding the structure and electronic properties of NHC-metal sites across heterogeneous catalytic architectures.