Single─Not Double─3D-Aromaticity in an Oxidized <i>Closo</i> Icosahedral Dodecaiodo-Dodecaborate Cluster
Jordi Poater, Sílvia Escayola, Albert Poater, Francesç Teixidor, Henrik Ottosson, Clara Viñas, Miquel Solà
Abstract
High Resolution Image Download MS PowerPoint Slide 3D-aromatic molecules with (distorted) tetrahedral, octahedral, or spherical structures are much less common than typical 2D-aromatic species or even 2D-aromatic-in-3D systems. Closo boranes, [B n H n ] 2– (5 ≤ n ≤ 14) and carboranes are examples of compounds that are singly 3D-aromatic, and we now explore if there are species that are doubly 3D-aromatic. The most widely known example of a species with double 2D-aromaticity is the hexaiodobenzene dication, [C 6 I 6 ] 2+ . This species shows π-aromaticity in the benzene ring and σ-aromaticity in the outer ring formed by the iodine substituents. Inspired by the hexaiodobenzene dication example, in this work, we explore the potential for double 3D-aromaticity in [B 12 I 12 ] 0/2+ . Our results based on magnetic and electronic descriptors of aromaticity together with 11 B{ 1 H} NMR experimental spectra of boron-iodinated o -carboranes suggest that these two oxidized forms of a closo icosahedral dodecaiodo-dodecaborate cluster, [B 12 I 12 ] and [B 12 I 12 ] 2+, behave as doubly 3D-aromatic compounds. However, an evaluation of the energetic contribution of the potential double 3D-aromaticity through homodesmotic reactions shows that delocalization in the I 12 shell, in contrast to the 10σ-electron I 6 2+ ring in the hexaiodobenzene dication, does not contribute to any stabilization of the system. Therefore, the [B 12 I 12 ] 0/2+ species cannot be considered as doubly 3D-aromatic.