Taming Super Lewis Acids for Catalysis: The Family of Ferrocene-Stabilized Silicon Cations

Tricoordinate silicon cations are exceptionally strong electron pair acceptors, so strong that they react with almost any σ and π basic molecule. In order to use such reactive intermediates in synthetic chemistry, Lewis acid catalysis in particular, we have designed intramolecularly stabilized silylium ions whose electron deficiency is attenuated by an adjacent, electron-rich ferrocenyl fragment. Here we wish to present the synthesis and structural characterization of these unique transition metal-stabilized silicon cations which reveal an unprecedented bonding situation different from its isoelectronic analogues. The potential of this motif is further highlighted in challenging Diels–Alder reactions, which are catalyzed at low temperatures with exceptional reaction rates and selectivities.