Comparing the 1 H-NMR spectra of P1-prepared AuNP-1 recorded in D2O with 1', NHC backbone signals (C 4/5 H) of AuNP-1s are high field shifted by 0.18 ppm (see Figure ). Both backbone signals show cross peaks with the NHC C 2 signal in 1 H/ C heteronuclear multiple bond correlation ( 1 H/ 13 C-HMBC), clearly identifying the key components of the imidazole ring of NHC anchored to AuNPs. In contrast, 1 H-NMR of AuNP-2s prepared via P2 shows a mixture of ligands on the surface. One set of backbone signals observed in the 1 H-NMR corresponds to the NHC structure, like previously shown for P1 and the second set in the lower field corresponds to an IMZ species (for 1 H-NMR see Figure ). The absence of the IMZ proton (C 2 H) suggests the presence of masked NHC from 1' as precursor undergoing insufficient NHC activation. Conversely, the ratio of observed surface species (1 NHC /1'-HCO3/1'-CO2, 6:3:1; Figure ) indicated that the NHC-CO2 adduct is the major reactive component of the precursor 1' under ambient conditions as previously suggested by He and co-workers. Based on the observed incomplete activation of 1' while employed in P2, obtained AuNP-2 were redispersed in THF and heated to 40 °C for 62 h. Heating AuNP-2 (procedure P2∆) leads to the activation of remaining loosely coordinated species including IMZ•HCO3 and NHC-CO2 species and converts them into the desired NHC species firmly attached to the AuNP surface. 1 H-NMR of the heated sample shows full conversion of IMZ•HCO3 species (IMZ related backbone signals; see Figure ) into the desired NHC bond to the surface. Subsequently, an alternative exchange route was tested whereby the masked NHC 1' was mixed with OAm@AuNPs and heated to 40 °C for 62 h (procedure P3), yielding upon purification stable AuNP-3 covered in the desired PEG-NHC 1 NHC . To further simplify the ligand exchange procedure, the ion metathesis to generate 1' was combined with the ligand exchange in a 'one-pot' approach. The developed procedure P4, uses the imidazolium bromide 1 and KHCO3 in OAm@AuNP dispersed in THF, in situ generating masked NHC and which is concomitantly activated at 40 °C to generate AuNP-3 stabilized by 1 NHC . NMR, FT-IR, and XPS spectroscopic evidence show that procedures P2 (followed by P2∆), P3, and P4 all lead to full conversion of 1' into Au surface-bound NHCs. However, the different procedures yield particles with significantly different colloidal quality. While AuNP-3 obtained by P2 and P4 have lower colloidal stability and broader dispersity, AuNP-3 obtained by procedure P3 stand out with higher colloidal stability and minimal decomposition of AuNPs during the exchange procedure. Finally, procedures P3 and P4 were tested under aerobic conditions using non-anhydrous THF. All attempts failed and no stable AuNP-3 were isolated. Obtained AuNPs decomposed during the transfer in aq. conditions or during dialysis, suggesting incomplete ligand exchange or only loosely-bound IMZ species on the AuNP surface. We attribute this to the H2O content of used THF, which drives the equilibrium of the masked NHC 1' towards the less active IMZ•HCO3 species. Simultaneously, H2O also promotes the rapid protonation of free 1 NHC generated.