Electron-poor hemilabile dicationic palladium NHC complexes - synthesis, structure and catalytic activity

Area of Science:

• Organometallic Chemistry
• Catalysis
• Coordination Chemistry

Background:

• N-heterocyclic carbenes (NHCs) are versatile ligands in organometallic chemistry.
• Palladium complexes are widely used as catalysts in organic synthesis.
• Dicationic palladium NHC complexes offer unique electronic and steric properties.

Purpose of the Study:

• To synthesize and characterize a new class of dicationic palladium NHC complexes.
• To investigate the coordination behavior of these complexes in solution.
• To evaluate their catalytic activity in the hydroarylation of alkynes.

Main Methods:

• Synthesis of dicationic palladium NHC complexes via silver transmetalation or direct deprotonation.
• Solid-state structure determination using X-ray diffraction.
• Solution behavior analysis using NMR spectroscopy and Density Functional Theory (DFT) calculations.
• Catalytic testing for alkyne hydroarylation.

Main Results:

• Successfully synthesized and characterized novel dicationic palladium NHC complexes with varying aryl substituents and a hemilabile pyrimidyl group.
• Determined solid-state structures for four representative complexes.
• Observed dynamic interchange between chelating and non-chelating coordination modes in solution, influenced by ligand sterics.
• Demonstrated catalytic activity in the hydroarylation of alkynes.

Conclusions:

• The synthesized dicationic palladium NHC complexes represent a new class of catalysts.
• Ligand sterics play a crucial role in dictating the coordination modes and catalytic performance.
• These complexes show promise for applications in alkyne functionalization reactions.