Ligand Effect on Bonding in Gold(III) Carbonyl Complexes

Area of Science:

• Organometallic Chemistry
• Computational Chemistry
• Chemical Bonding Theory

Background:

• Gold(III) complexes are crucial in catalysis and materials science.
• Understanding the electronic structure of gold-carbonyl bonds is key to predicting reactivity.
• Previous studies on gold(I) carbonyls provide a basis for comparison.

Purpose of the Study:

• To quantitatively analyze the Dewar-Chatt-Duncanson (DCD) components of the gold(III)-CO bond.
• To investigate charge density polarization within the CO ligand in gold(III) complexes.
• To correlate bonding parameters with reactivity in a model water-gas shift reaction.

Main Methods:

• Charge-displacement (CD) analysis was employed.
• A series of neutral, cationic, and dicationic bis- and monocyclometalated gold(III) complexes were studied.
• Comparative analysis with a platinum(II) complex in a model water-gas shift (WGS) reaction was performed.

Main Results:

• A small, stable net electron charge flux from CO to the gold(III) fragment was observed, independent of complex charge and gold oxidation state.
• Significant Au(III) ← CO σ donation (0.19–0.31 e) and Au(III) → CO π back-donation (-0.09–-0.22 e) were quantified.
• π back-donation strongly correlated with CO bond distance and stretching frequencies, similar to gold(I) complexes.
• An unexpected lack of anisotropy in π back-donation was found for gold(III) complexes, contrasting with prior findings for a specific gold(III) complex.

Conclusions:

• Gold(III)-CO bonding is characterized by robust σ donation and variable π back-donation.
• The electronic structure of the Au(III)-CO bond influences CO bond properties and vibrational frequencies.
• The study provides a foundation for understanding the bonding and reactivity relationships in gold(III) carbonyl complexes, with implications for catalysis.