Superbasic Anionic Calcium Alkyl Complexes: Templated Twofold Deprotonation of Benzene

Area of Science:

• Organometallic Chemistry
• Calcium Chemistry

Background:

• Anionic calcium hydrides are known reducing agents.
• Calcium complexes are increasingly explored for catalytic applications.

Purpose of the Study:

• To synthesize and characterize novel anionic calcium alkyl complexes.
• To investigate the reactivity and catalytic potential of these complexes.

Main Methods:

• Synthesis of anionic calcium alkyl complexes via ethylene reduction.
• Reactivity studies involving deprotonation of ethers and metalation of benzene.
• Mechanistic investigations using co-complexation with organometallic reagents.

Main Results:

• Successful synthesis of anionic calcium alkyl complexes.
• Demonstration of superbasic properties, enabling rapid ether deprotonation and C─O bond cleavage below room temperature.
• Observation of selective 1,4-metalation of benzene, forming an inverse-crown areneide complex.
• Elucidation of a stepwise mechanism for benzene metalation, enhanced by co-complexation.

Conclusions:

• Anionic calcium alkyl complexes are potent superbase catalysts.
• These complexes facilitate challenging C─O bond cleavage and benzene functionalization reactions.
• The observed benzene metalation represents a novel transformation for calcium chemistry.