Isolable Silicon-Based Polycations with Lewis Superacidity

Molecular silicon polycations of the types R(2)Si(2+)and RSi3+(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, [R2Si(terpy)](2+)(R=Ph1(2+); R-2=C(12)H(8)2(2+), (CH2)(3)3(2+)) and [RSi(terpy)](3+)(R=Ph4(3+), cyclohexyl5(3+), m-xylyl6(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.