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) 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 4 N + 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.