Catalytic Activity of Ruthenium Complexes Containing Hydrotris(pyrazolyl)methane or Cyclopentadienyl Ligands in the...

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Ruthenium(II) complexes are versatile catalysts for various organic transformations.
• The azide-alkyne cycloaddition, or
• click
• reaction, is a powerful tool for constructing triazole rings.
• Hydrotris(pyrazolyl)methane (Tpm) is a tridentate ligand known to stabilize metal complexes.

Purpose of the Study:

• To evaluate the catalytic activity of novel Ru(II)-Tpm complexes in the azide/alkyne cycloaddition reaction.
• To compare the performance of Tpm-based catalysts with traditional piano-stool Ru(II) complexes.
• To investigate the influence of reaction parameters (solvent, temperature, concentration) on catalytic efficiency and regioselectivity.

Main Methods:

• Synthesis and characterization of six Ru(II)-Tpm complexes.
• Evaluation of catalytic activity in azide/alkyne cycloaddition under varying conditions.
• Comparative studies with four piano-stool Ru(II) complexes.
• Mechanistic investigations using DFT calculations, NMR, and TOF-MS.

Main Results:

• Ru(II)-Tpm complexes, particularly complexes 3 and 4, demonstrated high catalytic activity and regioselectivity for the 1,5-disubstituted triazole in solvents like DMF and aqueous mixtures.
• Complex 3 achieved a turnover number (TON) of 75 and a turnover frequency (TOF) of 12.5 h^-1 for the cycloaddition of benzyl azide to diphenylacetylene.
• Reaction conditions significantly influenced conversion rates and product distribution, with polar solvents favoring the desired 1,5-isomer.

Conclusions:

• Ru(II)-Tpm complexes represent a promising class of catalysts for efficient and regioselective "click" reactions.
• The Tpm ligand plays a crucial role in enhancing catalyst performance.
• Optimized conditions, especially solvent choice, are key to maximizing catalytic efficiency and selectivity.