N-Heterocyclic Carbene Monolayers on Nickel, Iron, and Steel by a Radical-to-Carbene Strategy.

Gutheil C; Petti A; Gemen J; Rendel NH; Amirjalayer S; Feld H; Braunschweig B; Glorius F

Abstract

N-Heterocyclic carbenes (NHCs) have recently emerged as the next-generation surface ligands with improved stability and molecular flexibility. Despite these premises, research on NHC-enriched flat surfaces is mainly limited to noble metals, while formation of free NHCs often requires the use of vacuum, bases, or strictly air- and moisture-free conditions. We hereby report an unprecedented radical-to-carbene-based approach for fabricating NHC monolayers on earth-abundant and naturally oxidized metal surfaces of nickel, iron, and stainless steel. Following an open-cell electrografting approach, 2-azolyl radicals are firstly formed and immobilized on the metal to then rearrange into NHC monolayers apparently composed of flat-lying NHCs, as corroborated by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), sum-frequency generation (SFG), and cyclic voltammetry (CV) measurements. Density functional theory (DFT) calculations highlighted the role of metal adatoms in facilitating the radical-to-carbene transition. A surface stability test was conducted to assess the tolerance of the NHC-enriched surfaces toward physical, chemical, and electrochemical stress. Ultimately, this work expands the application field of carbenes-on-surfaces to cost-effective and widely used materials, while offering an agile and, until now, mechanistically unknown approach to their generation.