Sieving for Gold─An Efficient Method for Generating N-Heterocyclic Carbene Self-Assembled Monolayers on Nanostructured Gold Surfaces.

N-Heterocyclic carbene self-assembled monolayers (NHC-SAMs) are an emerging class of ligands for metal surfaces with impressive chemical stability, proving vastly superior in specific applications compared to their thiol counterparts. Yet, unlike the latter, methods of forming such monolayers have poor functional group tolerability and require harsh or expensive reagents. Using a surface-enhanced Raman spectroscopy (SERS)-led optimization, we have developed a solution deposition methodology that relies on low-cost and easily accessible starting reagents. The addition of an external bicarbonate source greatly expanded the functional group tolerability, circumventing the need for the isolation of the benzimidazolium hydrogen carbonate. Additionally, inclusion of scavengers during the deposition, namely, molecular sieves (5 Å), improved monolayer formation and long-range ordering via the sequestration of CO2, a key side-product in the equilibrium between benzimidazolium salts with the hydrogen carbonate anion and their corresponding carbene. The methodology is operationally accessible, has broad functional group tolerability, and enables access to a wide substrate scope of NHCs using commonly available reagents.