Tricoordinate Silicon Ion Prepared in Solution

Abstract

A long-sought organic intermediate—the silylenium ion (R 3 Si + )—has been prepared in solution for the first time by Northwestern University chemistry professor Joseph B. Lambert and graduate student William J. Schulz Jr. [ J. Am. Chem. Soc. , 105 , 1671 (1983)]. Evidence has been presented for the existence of the silylenium ion in the gas phase, Lambert says, but numerous efforts to prepare it in solution have failed. He points out that the analogous carbenium ion (R 3 C + ) also is less stable than the common tetracoordinate form; however, carbenium ions can be stabilized by 2p-3p resonance. In contrast, the silylenium ion is more weakly stabilized by 2p-3p overlap, over longer bond distances. The chemists' strategy was to stabilize the silylenium ion by the use of alkylthio substituents. They turned to sulfur because of its high polarizability, its low electronegativity, and the possibility that the 3p-3p overlap would be more effective than 2p-3p overlap. Lambert notes that the leaving group proble...