Catalytically Relevant Organocopper(III) Complexes Formed through Aryl-Radical-Enabled Oxidative Addition.

Area of Science:

• Organometallic Chemistry
• Catalysis
• Reaction Mechanisms

Background:

• Stepwise oxidative addition via single electron transfer (SET) is a proposed mechanism in copper catalysis.
• Direct observation of copper(III) intermediates is challenging due to slow reaction rates and instability.

Purpose of the Study:

• To report a novel aryl-radical-enabled pathway for forming well-defined alkyl-copper(III) species from copper(I) complexes.
• To provide a general strategy for investigating elusive formal copper(III) complexes in catalysis.

Main Methods:

• Utilized single electron transfer (SET) from Cu(I) to an aryl diazonium salt to generate aryl radicals.
• Employed aryl radicals for iodine abstraction from alkyl iodides, forming alkyl radicals.
• Characterized resulting alkyl-Cu(III) complexes using NMR spectroscopy and X-ray crystallography.
• Identified Cu(II) intermediates via electronic paramagnetic resonance (EPR) studies.

Main Results:

• Successfully formed and characterized novel alkyl-Cu(III) complexes, [(bpy)Cu(III)(CF3)2(alkyl)].
• Demonstrated that the rate of oxidative addition correlates with iodine abstraction rates by carbon-centered radicals.
• Identified a four-coordinate Cu(II) intermediate, [Cu(II)(CH3CN)2(CF3)2].
• Showcased catalytic relevance through C-C bond-forming reductive elimination of Cu(III) complexes.
• Localized orbital bonding analysis revealed inverted ligand fields in Cu-CH2 bonds.

Conclusions:

• Established a stepwise oxidative addition pathway for copper catalysis mediated by aryl radicals.
• Provided a viable strategy for the synthesis and study of transient copper(III) species.
• Offered insights into the electronic structure of formal Cu(III) complexes.