Synthesis and characterization of Craig-type antiaromatic species with [4n + 2] π electrons

Significance Antiaromaticity is associated with extra thermodynamic instability and makes the synthesis and isolation of antiaromatic molecules particularly challenging. Craig-type (anti)aromaticity, with a reversal to Hückel rule, describes a planar molecule with π-conjugated systems involving pπ–dπ interaction. To synthesize Craig antiaromatic compound is challengeable as it contains a set of properties that initially seems mutually incompatible: 1) antiaromaticity destabilization; 2) a planar structure with [4n + 2] π electrons; and 3) pπ–dπ interaction with phase shift in d orbital. In this work, we report the first synthesis of the Craig-type antiaromatic compounds via the deprotonation-induced reduction process and the Craig antiaromaticity along with the driving force of realization of Craig-type antiaromatic compounds was evidenced both experimentally and theoretically.

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