Lewis Superacidic Divalent Bis(m-terphenyl)element Cations [(2,6-Mes2C6H3)2E]+ of Group 13 Revisited and Extended (E=B, Al, Ga, In, Tl)

In a combined experimental and computational study, the molecular and electronic structures of the divalent bis(m-terphenyl)element cations [(2,6-Mes(2)C(6)H(3))(2)E](+) of group 13 (1, E=B; 2, E=Al; 3, E=Ga; 4, E=In; 5, E=Tl) were investigated. The preparation and characterization of 2, 3 and 5 were previously reported by Wehmschulte's (Organometallics 2004, 23, 1965-1967; J. Am. Chem. Soc. 2003, 125, 1470-1471) and our groups (Organometallics 2009, 28, 6893-6901). The indinium ion 4 was prepared and fully characterized for the first time. Attempts to prepare the borinium ion 1 by fluoride or hydride abstraction were unsuccessful. The electronic structures of 1-5 and the stabilization by the bulky m-terphenyl substituents were analyzed using quantum chemical calculations and compared to the divalent bis(m-terphenyl)pnictogenium ions [(2,6-Mes(2)C(6)H(3))(2)E](+) of group 15 (6, E=P; 7, E=As; 8, E=Sb; 9, E=Bi) previously investigated by our group (Angew. Chem. Int. Ed. 2018, 57, 10080-10084). The calculated fluoride ion affinities (FIA) of 1-9 are higher than that of SbF5, which classifies them as Lewis superacids.

Automated summary

In this study, the molecular and electronic structures of five divalent bis(m-terphenyl)element cations were investigated using experimental and computational methods. The preparation and characterization of some of these cations have been previously reported, while one was prepared and characterized for the first time. Quantum chemical calculations were used to analyze their electronic structures and compare them to a similar group of compounds previously studied. The results showed that these compounds have high fluoride ion affinities, classifying them as Lewis superacids.