Stepwise Reduction of Azapentabenzocorannulene.

Mono- and dianions of 2-tert-butyl-3a ² -azapentabenzo[bc,ef,hi,kl,no]corannulene (1 a) were synthesized by chemical reduction with sodium and cesium metals, and crystallized as the corresponding salts in the presence of 18-crown-6 ether. X-ray diffraction analysis of the sodium salt, [{Na ⁺ (18-crown-6)(THF) ₂ } ₃ {Na ⁺ (18-crown-6)(THF)}(1 a ^2- ) ₂ ], revealed the presence of a naked dianion. In contrast, controlled reaction of 1 a with Cs allowed the isolation of singly and doubly reduced forms of 1 a, both forming π-complexes with cesium ions in the solid state. In [{Cs ⁺ (18-crown-6)}(1 a ^- )]⋅THF, asymmetric binding of the Cs ⁺ ion to the concave surface of 1 a ^- is observed, whereas in [{Cs ⁺ (18-crown-6)} ₂ (1 a ^2- )], two Cs ⁺ ions bind to both the concave and convex surfaces of the dianion. The present study provides the first successful isolation and characterization of the reduced products of heteroatom-containing buckybowl molecules.
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