o-C2B10H12 isomerizes to m-C2B10H12 upon heating at 400 °C. Deboronation in o-C2B10H12 is a relatively easy process, whereas it is more difficult in m-C2B10H12. These two experimental facts indicate that m-C2B10H12 is thermodynamically more stable than o-C2B10H12. On the other hand, it is widely accepted that closo-boranes and -carboranes are aromatic compounds. In this work, we relate the difficulty in the deboronation of the carboranes with their stability and aromaticity. We do this by combining lab work and DFT calculations. Computationally, our results show that the higher thermodynamic stability of m-C2B10H12 is not related to aromaticity differences but to the location of the C atoms in the carborane structure. It is also demonstrated that the aromaticity observed in closo-boranes and -carboranes is also present in their nido counterparts, and consequently, we conclude that aromaticity in boron clusters survives radical structural changes. This observation is the first unique evidence that proves experimentally the existence of diatropic currents, and hence aromaticity, in clusters and is comparable to the existence of diatropic currents in planar aromatic compounds. This research accounts very well for the “paradigm for the electron requirements of clusters”, in which a closo-cluster that is aromatic upon addition of 2e– becomes also an aromatic nido-species, and explains the informative schemes by Rudolph and Williams.<sup>1-4</sup>

From closo to nido carboranes: Aromaticity in boron clusters survives radical structural changes

ACS Spring 2022

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