Elucidating the Influence of Anchoring Geometry on the Reactivity of NO2-Functionalized N-Heterocyclic Carbene Monolayers

The development of chemically addressable N-heterocyclic carbene (NHC) based self-assembled monolayers (SAMs) requires in-depth understanding of the influence of NHC’s anchoring geometry on its chemical functionality. Herein, it is demonstrated that the chemical reactivity of surface-anchored NO2-functionalized NHCs (NO2–NHCs) can be tuned by modifying the distance between the functional group and the reactive surface, which is governed by the deposition technique. Liquid deposition of NO2–NHCs on Pt(111) induced a SAM in which the NO2-aryl groups were flat-lying on the surface. The high proximity between the NO2 groups and the Pt surface led to high reactivity, and 85% of the NO2 groups were reduced at room temperature. Lower reactivity was obtained with vapor-deposited NO2–NHCs that assumed a preferred upright geometry. The separation between the NO2 groups in the vapor-deposited NO2–NHCs and the reactive surface circumvented their surface-induced reduction, which was facilitated only after exposure to ...