I have recently come across a statement which states:
The relative stability of the 1,3-dehydro-5,7-adamantanediyl dication is ascribed to its three-dimensional aromaticity. [1]
My understanding of aromatic nature is, that the molecule must be cyclic and planar, every atom in the ring must be $\ce{sp^2}$-hybridized and the molecule must have [4n+2] $\pi$ electrons, where $n\in\mathbb{N}$ (Hückel’s rule). The molecular orbitals also have to have the correct orientation and phase for aromaticity (2).
In my understanding 1,3-dehydro-5,7-adamantanediyl dication does not follow these rules for Y-aromaticity (3).
So my question is: What is three-dimensional aromaticity and how does it stabilise the 1,3-dehydro-5,7-adamantanediyl dication?
References
Firme, C. L.; Antunes, O. A. C.; Esteves, P. M. Electronic nature of the aromatic adamantanediyl ions and its analogues. J. Braz. Chem. Soc. 2008, 19 (1), 140–149. DOI: 10.1590/S0103-50532008000100020.
- What is Y-aromaticity? Is the trinitromethanide anion aromatic?