Electrochemical deposition of N-heterocyclic carbene monolayers on metal surfaces

Einav Amit,Elad Gross,Tamar Stein,Helen Eisenberg,Shahar Dery,Suhong Kim,Vitaly Gutkin,Linoy Dery,Anirban Roy,Qichi Hu,Daniel Mandler,F Dean Toste

doi:10.1038/s41467-020-19500-7

Abstract

N-heterocyclic carbenes (NHCs) have been widely utilized for the formation of self-assembled monolayers (SAMs) on various surfaces. The main methodologies for preparation of NHCs-based SAMs either requires inert atmosphere and strong base for deprotonation of imidazolium precursors or the use of specifically-synthesized precursors such as NHC(H)[HCO3] salts or NHC–CO2 adducts. Herein, we demonstrate an electrochemical approach for surface-anchoring of NHCs which overcomes the need for dry environment, addition of exogenous strong base or restricting synthetic steps. In the electrochemical deposition, water reduction reaction is used to generate high concentration of hydroxide ions in proximity to a metal electrode. Imidazolium cations were deprotonated by hydroxide ions, leading to carbenes formation that self-assembled on the electrode’s surface. SAMs of NO2-functionalized NHCs and dimethyl-benzimidazole were electrochemically deposited on Au films. SAMs of NHCs were also electrochemically deposited on Pt, Pd and Ag films, demonstrating the wide metal scope of this deposition technique.

Highlights

N-heterocyclic carbenes (NHCs) have been widely utilized for the formation of selfassembled monolayers (SAMs) on various surfaces
NHC-based self-assembled monolayers (SAMs) have been mostly prepared on metallic surfaces, and on Au surfaces, by two approaches: (i) base-induced deprotonation of imidazolium salt precursors[5,7,17,26,34] and (ii) annealing of NHC(H)[HCO3] salts[10,13,15,21] or NHC–CO2 adducts[5,11,14,15] under vacuum conditions (Fig. 1)
Under an anhydrous environment with a strong base, such as potassium tert-butoxide (KOtBu), for deprotonation and carbene formation[5,7,17,26]. This deposition approach has been widely utilized for the preparation of NHC-based SAMs, it has a number of inherent drawbacks: First, an anhydrous environment is required since residual water can quench the active carbene

Summary

Introduction

N-heterocyclic carbenes (NHCs) have been widely utilized for the formation of selfassembled monolayers (SAMs) on various surfaces. We demonstrate an electrochemical approach for the preparation of NHC-based SAMs, in which deprotonation of the imidazolium salt is electrochemically induced (Fig. 1).

Results

Conclusion