Chapter 5 - Silicon-Centered Cations

Abstract

Silylium ions are the silicon analogs of carbenium ions, and as such they play a pivotal role in organosilicon chemistry, like carbenium ions in organic chemistry. However, unlike the latter species, silylium ions are remarkably more difficult to stabilize because of the lower electronegativity of a silicon atom, its greater polarizability, and larger size, which overall results in exceptionally high electrophilicity/Lewis acidity of silylium ions. These peculiarities of silylium ions require very different approaches for their generation, isolation, and structural elucidation on the one hand, and opens unprecedented perspectives for their use as extraordinarily potent Lewis acids in a number of catalytic organic transformations on the other hand. In this contribution, we discuss the latest developments in the field of isolable silylium ion derivatives, with the particular emphasis given to the general synthetic approaches for their generation, their structural studies both in solution and in the solid state, most remarkable recent examples of the stable silylium ions, and finally, use of silylium ions in synthetic organic chemistry.