C(sp³)-H cyanation by a formal copper(iii) cyanide complex

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• High-valent metal oxo complexes are key intermediates for alkyl C-H bond activation and hydroxylation.
• Functionalizing C-H bonds beyond C-O formation requires alternative ligands and reactivity.
• Few complexes, besides metal oxo species, activate and functionalize C-H bonds.

Purpose of the Study:

• To report the first isolated copper(III) cyanide complex and investigate its C-H cyanation reactivity.
• To elucidate the mechanism of C-H functionalization, focusing on the role of substrate redox potential and C-H bond dissociation energy.
• To demonstrate selective C-H functionalization of amines using mechanistic insights.

Main Methods:

• Synthesis and isolation of a novel copper(III) cyanide complex (LCu^IIICN).
• Investigation of C-H cyanation reactivity with various substrates.
• Analysis of reaction kinetics and mechanistic pathways, including proton-coupled electron transfer (PCET).

Main Results:

• LCu^IIICN exhibits C-H cyanation reactivity, representing a new class of C-H functionalization agents.
• Substrate redox potential, not C-H bond dissociation energy, is the primary determinant of the proton-coupled electron transfer (PCET) rate.
• LCu^IIICN demonstrates high selectivity for the cyanation of amines, attributed to an asynchronous or stepwise H+/e- transfer mechanism.

Conclusions:

• The asynchronous effect in PCET is a critical factor for controlling selectivity in C-H functionalization reactions.
• Copper(III) cyanide complexes offer a new platform for selective C-H bond functionalization.
• This work expands the scope of C-H functionalization beyond traditional metal oxo pathways.