C(sp³)-H Fluorination with a Copper(II)/(III) Redox Couple

Area of Science:

• Organometallic Chemistry
• Organic Synthesis
• Fluorination Chemistry

Background:

• Direct C(sp³)-H fluorination remains a significant challenge in organic synthesis.
• Existing methods often lack efficiency or require harsh conditions.

Purpose of the Study:

• To develop a new method for direct C(sp³)-H fluorination using a copper complex.
• To investigate the mechanism of C-H fluorination involving copper(III) fluoride.

Main Methods:

• Synthesis and characterization of copper(III) halide complexes (LCuF, LCuCl, LCuBr).
• Experimental studies including single-crystal X-ray diffraction, X-ray absorption spectroscopy, UV-vis spectroscopy, and NMR spectroscopy.
• Quantum chemical calculations to understand electronic structure and reaction mechanisms.
• Kinetic studies using 9,10-dihydroanthracene and mechanistic studies with triphenylmethyl radical.

Main Results:

• Copper(III) halide complexes were synthesized and characterized, showing significant halide radical character.
• LCuF demonstrated a 2-orders-of-magnitude higher hydrogen atom abstraction rate compared to LCuCl and LCuBr.
• All complexes efficiently captured carbon radicals to form C(sp³)-halogen bonds.
• LCuF utilizes a concerted mechanism for radical capture, while LCuCl and LCuBr use a stepwise pathway.

Conclusions:

• The developed copper(III) fluoride complex enables efficient direct C(sp³)-H fluorination at room temperature.
• The complex's ability to perform both hydrogen atom abstraction and radical capture is key to its reactivity.
• This work provides a new tool for synthesizing fluorinated organic compounds with potential applications in various fields.