A Hydrogen Evolution Catalyst [Co₂O₂] Metallacycle Enables Regioselective Allene C(sp²)-H Functionalization

Area of Science:

• Organic Chemistry
• Catalysis
• Electrochemistry

Background:

• Selective functionalization of allenic C(sp²)-H bonds is crucial for synthesizing valuable allene derivatives.
• Challenges include inert reactivity and poor selectivity in existing methods.
• Activating weakly acidic C-H bonds requires innovative strategies.

Purpose of the Study:

• To develop a novel strategy for selective C-H functionalization of allenes.
• To leverage a catalytic hydrogen evolution reaction (HER) for reductive activation of allenic C(sp²)-H bonds.
• To achieve regioselective electrochemical functionalization of allenes with alcoholic C(sp³)-H bonds.

Main Methods:

• Development of [Co₂O₂] metallacycle complexes as HER catalysts, synthesized from amino acids.
• Application of a catalytic HER strategy to selectively activate allenic C(sp²)-H bonds.
• Regioselective electrochemical coupling of allenes with alcoholic C(sp³)-H bonds.
• Mechanistic studies including experimental investigations and Density Functional Theory (DFT) calculations.

Main Results:

• Successfully devised robust [Co₂O₂] metallacycle complexes acting as HER catalysts.
• Achieved unprecedented regioselective electrochemical functionalization of allenic C(sp²)-H with alcoholic α C(sp³)-H.
• Demonstrated excellent regioselectivity, unconventional chemoselectivity, and good functional-group tolerance across 62 examples under mild conditions.
• Identified a reactive hydroxy-coordinated cobalt(II) species and rationalized regioselectivity via DFT calculations.

Conclusions:

• The developed HER strategy offers an efficient and selective method for allene functionalization.
• This approach overcomes previous limitations in reactivity and selectivity for allenic C-H activation.
• The findings provide a new pathway for synthesizing complex allene structures with broad applicability.