Interplay between Gold(I)-Ligand Bond Components and Hydrogen Bonding: A Combined Experimental/Computational Study

Area of Science:

• Organometallic Chemistry
• Supramolecular Chemistry
• Computational Chemistry

Background:

• N-heterocyclic carbenes (NHCs) are versatile ligands in organometallic chemistry.
• Selenourea (SeU) complexes with gold exhibit interesting electronic properties.
• Weak interactions, such as hydrogen bonding, can significantly influence metal-ligand bonding.

Purpose of the Study:

• To investigate the influence of weak interactions on donation/back-donation bond components in [(NHC)Au(SeU)]+ complexes.
• To characterize the hydrogen bond (HB) between SeU and anions (PF6-, ClO4-).
• To quantify the Dewar-Chatt-Duncanson (DCD) components of Au-C and Au-Se bonds.

Main Methods:

• Experimental techniques: NMR 1H, pulsed-field gradient spin-echo titrations, 77Se NMR spectroscopy.
• Theoretical techniques: Natural orbital for the chemical valence (NOCV) framework, charge displacement analysis.
• Decomposition of Au-Se and Au-C orbital interactions.

Main Results:

• Hydrogen bonding between SeU and anions (PF6-, ClO4-) was characterized.
• Anions exhibit dual mode action: modifying cation conformation via ion pairing and inducing polarization effects.
• Perchlorate enhances Se → Au σ donation and Au → C back-donation, while depressing C → Au σ donation.
• Hexafluorophosphate depresses both Se → Au and C → Au σ donations.

Conclusions:

• Anion interactions play a crucial role in modulating the electronic structure of [(NHC)Au(SeU)]+ complexes.
• The relative orientation of the anion and cation influences the extent of polarization and bond component changes.
• Understanding these weak interactions is key to designing and controlling the properties of gold complexes.