Isolable Silicon‐Based Polycations with Lewis Superacidity

Molecular silicon polycations of the types R(2)Si(2+) and RSi(3+) (R=H, organic groups) are elusive Lewis superacids and currently unknown in the condensed phase. Here, we report the synthesis of a series of isolable terpyridine‐stabilized R(2)Si(2+) and RSi(3+) complexes, [R(2)Si(terpy)](2+) (R=Ph 1 (2+); R(2)=C(12)H(8) 2 (2+), (CH(2))(3) 3 (2+)) and [RSi(terpy)](3+) (R=Ph 4 (3+), cyclohexyl 5 (3+), m‐xylyl 6 (3+)), in form of their triflate salts. The stabilization of the latter is achieved through higher coordination and to the expense of reduced fluoride‐ion affinities, but a significant level of Lewis superacidity is nonetheless retained as verified by theory and experiment. The complexes activate C(sp(3))−F bonds, as showcased by stoichiometric fluoride abstraction from 1‐fluoroadamantane (AdF) and the catalytic hydrodefluorination of AdF. The formation of the crystalline adducts [2(F)](+) and [5(H)](2+) documents in particular the high reactivity towards fluoride and hydride donors.