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1. The Search for Molecular Corks Beyond Carbon Monoxide: A Quantum Mechanical Study of N-Heterocyclic Carbene Adsorption on Pd/Cu(111) and Pt/Cu(111)

   Simpson, Scott (March 2022, ACS Spring 2022)

   Periodic Density Functional Theory calculations reveal the potential application of 10 imidazole based N-heterocyclic carbenes (NHCs) to behave as “molecular corks” for hydrogen storage on single atom alloys, comprised of Pd/Cu(111) or Pt/Cu(111). Calculations show that functionalizing the NHC with different electron withdrawing/donating functional groups results in different binding energies of the NHC with the alloy surfaces. The results are compared to DFT calculations of carbon monoxide bound to these alloys. The Huynh electronic parameter (HEP) is calculated for several simple imidazole NHCs to gauge σ-donor ability, while Se-NMR and P-NMR calculations of selenourea derivatives and carbene-phosphinidene adducts, respectively, have been utilized to gauge π-acidity of the NHCs. It is demonstrated that consideration of both σ and π donating/accepting ability must be considered when predicting the surface-adsorbate binding energy. It was found that electron withdrawing groups tend to weaken the NHC-surface interaction while electron donating substituents tend to strengthen the interaction. 

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2. Molecular Modeling Insights of N-Heterocyclic Carbenes Adsorbed to Single Atom Alloys

   Simpson, S (December 2025, 2025 International Chemical Congress of Pacific Basin Societies)

   We utilize non-local density functional theory (DFT) to investigate the potential of N-heterocyclic carbenes (NHCs) to be utilized as “molecular corks” on single atom alloys (SAAs) of Pd/Cu(111) and Pt/Cu(111). We discuss an intriguing chemical phenomenon called the "molecular corking effect," which may prove useful as a hydrogen gas storage mechanism. Given the modular σ-donating/π-accepting abilities, and large synthetic library of NHCs, this class of compounds are investigated. We utilize a molecular orbital (MO) approach to understand/explain the NHC-SAA interface to fundamentally understand how these molecules anchor themselves to metal surfaces. 

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3. Binding Interactions in Copper, Silver and Gold π‐Complexes

   https://doi.org/10.1002/chem.202103984  

   Mehara, Jaya; Watson, Brandon_T; Noonikara‐Poyil, Anurag; Zacharias, Adway_O; Roithová, Jana; Rasika_Dias, H_V (February 2022, Chemistry – A European Journal)

   Abstract The copper(I), silver(I), and gold(I) metals bind π‐ligands by σ‐bonding and π‐back bonding interactions. These interactions were investigated using bidentate ancillary ligands with electron donating and withdrawing substituents. The π‐ligands span from ethylene to larger terminal and internal alkenes and alkynes. Results of X‐ray crystallography, NMR, and IR spectroscopy and gas phase experiments show that the binding energies increase in the order Ag 

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4. Illuminating the Performance of Electron Withdrawing Groups in Halogen Bonding

   https://doi.org/10.1002/cphc.202400607  

   Devore, Daniel_P; Ellington, Thomas_L; Shuford, Kevin_L (November 2024, ChemPhysChem)

   Abstract Throughout the halogen bonding literature, electron withdrawing groups are relied upon heavily for tuning the interaction strength between the halogen bond donor and acceptor; however, the interplay of electronic effects associated with various substituents is less of a focus. This work utilizes computational techniques to study the degree ofσ‐ andπ‐electron donating/accepting character of electron withdrawing groups in a prescribed set of halo‐alkyne, halo‐benzene, and halo‐ethynyl benzene halogen bond donors. We examine how these factors affect theσ‐hole magnitude of the donors as well as the binding strength of the corresponding complexes with an ammonia acceptor. Statistical analyses aid the interpretation of how these substituents influence the properties of the halogen bond donors and complexes, and show that the electron withdrawing groups that are bothσ‐ andπ‐electron accepting form the strongest halogen bond complexes. 

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5. Ad aurum: tunable transfer of N-heterocyclic carbene complexes to gold surfaces

   https://doi.org/10.1039/d2qi01941h  

   Dominique, Nathaniel L.; Chen, Ran; Santos, Alyssa V.; Strausser, Shelby L.; Rauch, Theodore; Kotseos, Chandler Q.; Boggess, William C.; Jensen, Lasse; Jenkins, David M.; Camden, Jon P. (November 2022, Inorganic Chemistry Frontiers)

   The exceptional stability of N-heterocyclic carbene (NHC) monolayers on gold surfaces and nanoparticles (AuNPs) is enabling new and diverse applications from catalysis to biomedicine. Our understanding of NHC reactivity at surfaces; however, is quite nascent when compared to the long and rich history of NHC ligands in organometallic chemistry. In this work, well-established transmetalation reactions, previously developed for NHC transfer in homogeneous organometallic systems, are explored to determine how they can be used to create carbene functionalized gold surfaces. Two classes of NHCs, based on imidazole and benzimidazole scaffolds, were tested. The resulting AuNP surfaces were analyzed using X-ray photoelectron spectroscopy (XPS), laser desorption ionization mass spectrometry (LDI-MS), and surface-enhanced Raman spectroscopy (SERS). Reaction of either a Au( i ) or Ag( i ) isopropyl benzimidazole NHC complex with citrate-capped AuNPs yields, in both cases, a chemisorbed NHC that is bound through a Au adatom. Theoretical calculations additionally illustrate that binding through the Au adatom is favored by more than 10 kcal mol −1 , in good agreement with experiments. Surprisingly, reaction of Au( i ), Ag( i ), and Cu( i ) diisopropylphenyl imidazole NHCs do not follow the same pattern. The Cu complex undergoes transmetalation with very little deposition of Cu; whereas, unexpectedly, the Ag complex foregoes transmetalation and instead adducts to the AuNP with retention of the Ag–C bond. Theoretical calculations illustrate that the imidazole ligand affords significant dispersion interactions with the gold surface, which may stabilize binding through the Ag adatom motif, despite its less favorable bonding energies. Taken together these results suggest a unique ability to tune the reactivity by changing the carbene structure and raise critical questions about how established transmetalation reactions in organometallic chemistry can be applied to form NHC functionalized surfaces. 

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