A Benchtop Method for Appending Protic Functional Groups to N‐Heterocyclic Carbene Protected Gold Nanoparticles

• Published in: Angewandte Chemie International Edition 2020-05, Vol.59 (19), p.7585-7590
• Main Authors: DeJesus, Joseph F., Sherman, Lindy M., Yohannan, Darius J., Becca, Jeffrey C., Strausser, Shelby L., Karger, Leonhard F. P., Jensen, Lasse, Jenkins, David M., Camden, Jon P.
• Format: Article
• Language: English
• Subjects: Alcohols; Amines; Carbon dioxide; Carboxylic acids; Functional groups; Gold; Metal surfaces; N-heterocyclic carbenes; Nanoparticles; Noble metals; Reagents; Resilience; SERS; surface modification
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202001440

The remarkable resilience of N‐heterocyclic carbene (NHC) gold bonds has quickly made NHCs the ligand of choice when functionalizing gold surfaces. Despite rapid progress using deposition from free or CO2‐protected NHCs, synthetic challenges hinder the functionalization of NHC surfaces with protic functional groups, such as alcohols and amines, particularly on larger nanoparticles. Here, we synthesize NHC‐functionalized gold surfaces from gold(I) NHC complexes and aqueous nanoparticles without the need for additional reagents, enabling otherwise difficult functional groups to be appended to the carbene. The resilience of the NHC−Au bond allows for multi‐step post‐synthetic modification. Beginning with the nitro‐NHC, we form an amine‐NHC terminated surface, which further undergoes amide coupling with carboxylic acids. The simplicity of this approach, its compatibility with aqueous nanoparticle solutions, and its ability to yield protic functionality, greatly expands the potential of NHC‐functionalized noble metal surfaces. A straightforward and robust method to functionalize SERS‐active gold nanoparticles with bifunctional N‐heterocyclic carbenes is presented. The method gives access to amine‐functionalized surfaces and enables the amide coupling to be monitored by SERS.