Metal-centered monocyclic carbon wheel clusters with record coordination numbers in planar species

The highest coordination number identified to date in planar species is CN = 10 in metal-centered monocyclic boron wheel clusters D(10h) M©B(10)(−) (M = Ta and Nb) (Galeev et. al., Angew. Chem. Int. Ed., 2012, 51, 2101). Extensive global minimum searches and first-principles theory calculations performed herein indicate that the experimentally observed LaC(13)(+) and LaC(14)(+) possess the well-defined global minima of perfect metal-centered monocyclic carbon wheel D(13h) La©C(13)(+) (1) [Image: see text] and slightly off-centered C(2v) La©C(14)(+) (4) ((1)A(1)) with record coordination numbers of CN = 13 and 11 in planar structures, respectively, further pushing the boundary of our understanding of chemical structures and bonding. Detailed molecular orbital, nucleus-independent chemical shift, and ring current analyses indicate that D(13h) La©C(13)(+) (1) is σ + π dually aromatic in nature, with 14 totally delocalized in-plane σ electrons and 14 totally delocalized out-of-plane π electrons each matching the 4N + 2 aromatic rule (N(σ) = N(π) = 3). Similar σ + π dually aromatic metal-centered monocyclic wheel clusters D(13h) Ca©C(13) (2), C(13v) Ac©C(13)(+) (3), C(2v) Y©B(6)C(6)(+) (5), and C(2v) Sc©B(5)C(6) (6) have also been obtained with CN = 13, 13, 12, and 11, respectively. The results obtained in this work effectively enrich the chemical structures and bonding patterns of planar hypercoordinated complexes.