Studies on gold(I) and gold(III) alcohol functionalised NHC complexes

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• N-heterocyclic carbene (NHC) ligands are crucial in organometallic chemistry.
• Gold complexes are increasingly utilized as catalysts in organic transformations.
• Chiral ligands are essential for asymmetric synthesis.

Purpose of the Study:

• To synthesize and characterize novel chiral alcohol-functionalized gold(I) and gold(III) NHC complexes.
• To evaluate the catalytic activity of these new gold complexes in 1,6-enyne alkoxycyclization.
• To compare the catalytic performance of gold(I) and gold(III) NHC complexes with varying ligand properties.

Main Methods:

• Synthesis of chiral imidazolium preligands via oxalamides, reduction, and orthoformate condensation.
• Preparation of gold(I) NHC complexes using an improved method (up to 92% yield).
• Oxidation of gold(I) complexes to gold(III) NHC complexes (up to 99% yield).
• Characterization using NMR, IR, HRMS, and single crystal X-ray diffraction.
• Catalytic testing in 1,6-enyne alkoxycyclization reactions.

Main Results:

• Successful synthesis and characterization of five pairs of novel chiral gold(I) and gold(III) NHC complexes.
• Demonstrated significantly higher catalytic activity of the new gold NHC complexes compared to previously reported gold catalysts.
• Identified ligand flexibility and bulkiness as key factors influencing catalytic ability.
• Achieved excellent yields (92-99%) for the alkoxycyclization product using bulky NHC ligands.

Conclusions:

• Novel chiral alcohol-functionalized gold NHC complexes represent a promising class of catalysts.
• The developed synthetic routes provide efficient access to gold(I) and gold(III) NHC complexes.
• Ligand design, specifically bulkiness and flexibility, is critical for optimizing catalytic performance in alkoxycyclization reactions.