Reduction-Induced C─C Cleavage and Site-Specific Hydrogenation of a Highly Strained Bilayer Spironanographene.

The chemical reduction of a bilayer spironanographene, spiro-NG (CH), with Na and K metals in the presence of [2.2.2]cryptand to yield Na(2.2.2-cryptand) (1) and K(2.2.2-cryptand) (2), respectively, is reported. X-ray crystallography reveals the formation of a new "naked" anion (spiro-NG ), in which spirocyclic ring cleavage and subsequent hydrogenation have occurred. Density Functional Theory (DFT) calculations suggest that the generation of the radical anion of the parent nanographene (spiro-NG ), upon electron acceptance from Na and K metals, induces the cleavage of the strained spirobifluorene core. The resulting spin density localizes on a particular carbon atom, previously attached to the spiranic sp carbon atom, facilitating a site-specific hydrogenation to afford (spiro-NG ). The electrostatic potential map of this anion reveals electron density concentrated at the five-membered ring of the readily formed indenyl fragment, thus enhancing the aromaticity of the system. Furthermore, nuclear magnetic resonance (NMR) and UV-vis absorption spectroscopy experiments allowed to follow the in situ reduction and hydrogenation processes in detail.