Isolable Silicon-Based Polycations with Lewis Superacidity

Molecular silicon polycations of the types R Si and RSi (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 Si and RSi complexes, [R Si(terpy)] (R=Ph 1 ; R =C H 2 , (CH ) 3 ) and [RSi(terpy)] (R=Ph 4 , cyclohexyl 5 , m-xylyl 6 ), 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 )-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)] documents in particular the high reactivity towards fluoride and hydride donors.