N‐Heterocyclic Carbene Self‐assembled Monolayers on Copper and Gold: Dramatic Effect of Wingtip Groups on Binding, Orientation and Assembly

Abstract

Self‐assembled monolayers of N‐heterocyclic carbenes (NHCs) on copper are reported. The monolayer structure is highly dependent on the N,N‐substituents on the NHC. On both Cu(111) and Au(111), bulky isopropyl substituents force the NHC to bind perpendicular to the metal surface while methyl‐ or ethyl‐substituted NHCs lie flat. Temperature‐programmed desorption studies show that the NHC binds to Cu(111) with a desorption energy of E des=152±10 kJ mol−1. NHCs that bind upright desorb cleanly, while flat‐lying NHCs decompose leaving adsorbed organic residues. Scanning tunneling microscopy of methylated NHCs reveals arrays of covalently linked dimers which transform into adsorbed (NHC)2Cu species by extraction of a copper atom from the surface after annealing.

Flexible NO2‐Functionalized N‐Heterocyclic Carbene Monolayers on Au (111) Surface

“…NHCs with small side groups, such as methyl (marked by yellow disks in Scheme ), which do not lead to strong lateral interactions, form planar bis‐carbene metal complexes on metal surfaces . NHCs with larger dimethyl substituents formed films with mixtures of flat and upright orientations, whereas surface‐anchored NHCs with larger diisopropyl and diisopropylphenyl groups (marked by blue spheres in Scheme ) were detected only in an upright position . Density functional theory (DFT) calculations also support the hypothesis that the orientation of surface‐anchored NHCs is directed by the steric properties of their side groups .…”

Identifying site-dependent reactivity in oxidation reactions on single Pt particles

“… 32 – 35 The structure and stability of surface anchored NHCs were studied by several surface-sensitive techniques. 36 – 38 However, in depth analysis of the chemical and structural properties of chemically-active NHCs, which were recently utilized as indicators for surface induced reactivity, 23 , 25 remains rare.…”

N-heterocyclic carbene-functionalized magic-number gold nanoclusters

“…[11][12][13][14][15][16][17] N-heterocyclic carbenes (NHCs) are phosphine analogues that have attracted considerable attention in organometallic chemistry, and recently in surface science. [18][19][20][21][22][23][24][25][26][27][28][29][30] In organometallics, these ligands are known for their ability to form strong, substitutionally inert bonds to various metals. 31,32 Recently they have been shown to form highly robust selfassembled monolayers (SAMs) on Au(111) surfaces and nanoparticles, 20 however their use as stabilizing ligands in magic number nanoclusters has not been previously described.…”