Diastereoselective Synthesis of Sulfoxide-Functionalized N-Heterocyclic Carbene Ruthenium Complexes: An Experimental...

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Development of novel ligands is crucial for advancing catalytic applications.
• Ruthenium complexes are versatile catalysts in organic transformations.
• Sulfoxide-functionalized ligands offer unique coordination properties.

Purpose of the Study:

• To synthesize novel sulfoxide-functionalized N-heterocyclic carbene (NHC-SO) ligand precursors.
• To prepare and characterize cationic ruthenium(II) complexes featuring these NHC-SO ligands.
• To investigate the catalytic activity of these complexes in the beta-alkylation of alcohols.

Main Methods:

• Mild oxidation of thioether precursors to sulfoxide-functionalized NHC ligand salts.
• Synthesis of cationic [Ru(II)(η⁶-p-cymene)(NHC-SO)Cl]⁺ complexes via Ag₂O transmetallation.
• Structural characterization using NMR spectroscopy and X-ray diffractometry.
• Computational studies (DFT) to understand diastereomer formation and inversion barriers.
• Catalytic evaluation in the beta-alkylation of secondary alcohols.

Main Results:

• Successful synthesis of sulfoxide-functionalized NHC ligand precursors with high selectivity.
• Preparation of ruthenium(II) complexes in excellent yields, confirming bidentate (κ²,C,S) coordination.
• Observation of a single diastereomer (as an enantiomeric pair) due to thermodynamic control.
• Demonstrated catalytic activity in the beta-alkylation of secondary alcohols.
• Complex 4dPF6 exhibited high reactivity and selectivity with various alcohol substrates.

Conclusions:

• Novel sulfoxide-functionalized NHC ligands and their ruthenium complexes were successfully synthesized and characterized.
• The complexes exhibit a preferred bidentate coordination mode and form a single diastereomer.
• These ruthenium complexes are effective catalysts for the beta-alkylation of secondary alcohols, showing promising reactivity and selectivity.