Silicon Tetrakis(trifluoromethanesulfonate): A Simple Neutral Silane Acting as a Soft and Hard Lewis Superacid.

A facile synthesis and isolation of pristine silicon tetrakis(trifluoromethanesulfonate), Si(OTf) , is reported, acting as the first neutral silicon-based Lewis superacid suitable towards soft and hard Lewis bases. Its OTf groups have a dual function: they are excellent leaving groups and modulate the degree of reactivity towards soft and hard Lewis bases. Exposed to soft Lewis donors, Si(OTf) leads to [L Si(OTf) ] complexes (L=isocyanide, thioether and carbonyl compounds) with retention of all Si-OTf bonds. In contrast, it can cleave C-X bonds (X=F, Cl) of hard organic Lewis bases with a high tendency to form SiX (X=F, Cl) after halide/triflate exchange. Most notable, Si(OTf) allows a gentle oxydefluorination of mono- and bis(trifluoromethyl)benzenes, resulting in the formation of the corresponding benzoylium species, which are stabilized by the weakly coordinating [Si(OTf) ] dianion.