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.