Borane-functionalized heteroscorpionate copper complexes as catalysts for azide-alkyne cycloaddition.

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Copper(I) complexes are widely used as catalysts in organic synthesis.
• Bis(3,5-dimethylpyrazolyl)methane ligands offer versatile coordination environments for metal centers.
• Functionalization of ligands can tune catalyst activity and selectivity.

Purpose of the Study:

• To synthesize and characterize novel copper(I) complexes with borane-functionalized bis(3,5-dimethylpyrazolyl)methane ligands.
• To evaluate the catalytic performance of these new complexes in the cycloaddition of phenylacetylene and azides.
• To investigate the role of the borane functionality in enhancing catalytic activity.

Main Methods:

• Synthesis of copper(I) complexes with allylated and borane-functionalized ligands.
• Characterization using NMR, FTIR, elemental analysis, cyclic voltammetry, and X-ray diffraction.
• Catalytic testing for the cycloaddition reaction with various azides.

Main Results:

• Successfully synthesized and characterized four new copper(I) complexes: [(La)CuCl] (1a), [(La)Cu(NCMe)]2(BF4)2 (2a2), [(Lb)CuCl] (1b), and [(Lb)Cu(NCMe)2]BF4 (2b).
• Complexes 1a, 1b, 2a2, and 2b effectively catalyzed the cycloaddition of phenylacetylene and benzyl azide to form 1,2,3-triazoles.
• Borane-functionalized complexes 1b and 2b exhibited approximately four times higher activity than their allylated counterparts.
• Complex 2b achieved a maximum yield of 97% and a turnover frequency (TOF) of 800 h⁻¹, and catalyzed reactions with seven different azides in 87%-99% yields.

Conclusions:

• Borane-functionalized copper(I) complexes are highly effective catalysts for the synthesis of 1,2,3-triazoles.
• The borane moiety plays a crucial role in enhancing catalytic activity, likely through a substrate-directing effect.
• These findings open new avenues for designing advanced organometallic catalysts for click chemistry applications.