The development of chemically-addressable N-heterocyclic carbene (NHC) based self-assembled monolayers (SAMs) requires in-depth understanding of the influence of NHCs anchoring geometry on its chemical functionality. Herein, it is demonstrated that the chemical reactivity of surface anchored NO 2 -functionalized NHCs (NO 2 -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 NO 2 -NHCs on Pt (111) induced a SAM in which the NO 2 -aryl groups were flat-lying on the surface. The high proximity between the NO 2 groups and the Pt surface led to high reactivity and 85% of the NO 2 groups were reduced at room temperature. Lower reactivity was obtained with vapor-deposited NO 2 -NHCs that assumed a preferred upright geometry. The separation between the NO 2 groups in the vapor-deposited NO 2 -NHCs and the reactive surface circumvented their surface-induced reduction, which was facilitated only after exposure to harsher reducing conditions. KEYWORDS Self-assembled monolayers; N-Heterocyclic Carbene; NEXAFS; Anchoring geometry;The high chemical tunability and metal-affinity of N-heterocyclic carbene molecules (NHCs) have enabled to form robust NHCs-based self-assembled monolayers (SAMs) with exceptional stability and functionality. [1][2][3][4][5][6][7][8][9][10] Chemically-functionalized NHCs have been utilized for the formation of SAMs with varied applications range, including molecular patterning, biosensing and catalysis. [11][12][13][14][15][16] Two main approaches have been developed for surface-anchoring of NHCs: 1. Liquiddeposition; in which deprotonation is facilitated by a strong base, such as potassium tert-butoxide (KO t Bu), for the formation of an active carbene that can be anchored on metallic surfaces (Scheme 1a). 12, 17 2. Vapor-deposition; in this approach hydrogen carbonates counteranion serves as a base for deprotonation of the imidazolium cation, enabling active carbene formation and its surface-anchoring under ultra-high vacuum (UHV) conditions (Scheme 1b). 11 Scheme 1. Schematic illustration of liquid-(a) and vapor-deposition (b) of NO 2 -functionalized NHCs.

Nanoporous gold (np-Au) is a catalytically highly active material, prepared by selectively dealloying silver from a gold–silver alloy. It can promote aerobic CO oxidation and a range of other oxidation reactions. It has been debated whether the remarkable catalytic properties of np-Au are mainly due to its structural features or whether the residual Ag remaining in the material after dealloying is decisive for the activity, especially for the activation of O2. Recent theoretical studies provided evidence that Ag impurities can facilitate the adsorption and dissociation of O2 on np-Au. However, these studies predicted quite a high activation barrier for O2 dissociation on Au–Ag alloy catalysts, whereas experimentally reported activation energies are much lower. In this work we use the stepped Au(321) surface with Ag impurities, which is arguably a realistic model for np-Au material as well as for Au–Ag catalysts in general. We present alternative routes for O2 activation via its direct reaction with adsorbed CO or H2O. In all of the reactions considered, surface atomic O is generated via a sequence of elementary steps with calculated low activation energies of <0.4 eV with respect to coadsorbed reactants. Ag impurities are shown to increase the adsorption energy of O2 and hence the probability of a surface-mediated reaction versus desorption. We considered four possible mechanisms of CO oxidation in dry and humid environments in a microkinetic modeling study. We show that via the proposed mechanisms water indeed promotes O2 dissociation; nevertheless, the “dry” mechanism, in which CO directly reacts with O2, is by far the fastest route of CO2 formation on pure Au and on Au with Ag impurities. Ag impurities lead to significantly higher turnover rates; thus, calculations point to the key role of Ag in promoting the catalytic activity of Au–Ag alloy systems.

The formation of flexible self‐assembled monolayers (SAMs) in which an external trigger modifies the geometry of surface‐anchored molecules is essential for the development of functional materials with tunable properties. In this work, it is demonstrated that NO2‐functionalized N‐heterocyclic carbene molecules (NHCs), which were anchored on Au (111) surface, change their orientation from tilted into flat‐lying position following trigger‐induced reduction of their nitro groups. DFT calculations identified that the energetic driving force for reorientation was the lower steric hindrance and stronger interactions between the chemically reduced NHCs and the Au surface. The trigger‐induced changes in the NHCs′ anchoring geometry and chemical functionality modified the work function and the hydrophobicity of the NHC‐decorated Au surface, demonstrating the impact of a chemically tunable NHC‐based SAM on the properties of the metal surface.

Abstract:The reactions of the group 4 metallocene alkyne complexes Cp* 2 M(η 2 -Me 3 SiC 2 SiMe 3 ) (M = Ti, Zr) with different cyanopyridines were investigated. For the zirconium compound, the unstable products Cp* 2 Zr(η 2 -Me 3 SiC 2 SiMe 3 )(N≡C-py) were first formed by the end-on coordination of the substrate. Subsequent reaction with a second equivalent resulted in the elimination of the alkyne and in the formation of 1-zircona-2,5-diazacyclopenta-2,4-dienes. By applying (2-bromo)-5-cyanopyr-