Closely Approaching the Silylium Ion (R 3 Si + )

• DOI: 10.1126/science.262.5132.402
• Publication Date: 2006-10-05T23:05:09Z
• Authors: Christopher A. Reed; Zuowei Xie; Robert Bau; Alan Benesi
• Keywords: Isopropyl; Planarity testing

The crystal structure of the tri-isopropyl silyl species, i-Pr(3)Si(Br(6)-CB(11)H(6)), where brominated carborane Br(6)-CB(11) H(6)(-) is perhaps least nucleophilic anion presently known, has revealed highest degree silylium cation character (R(3)Si(+)) yet observed. average C-Si-C angle 117 degrees , only 3 short planarity expected a pure ion(120 ). This value compares to 114 recently reported for toluene-solvated cation, [Et(3)Si(toluene)](+) by Lambert and co-workers. greater ion i-Pr(3)Si(Br(6)-CB(11)H(6)) versus [i-Pr(3)Si(toluene)](+) also reflected in larger downfield shift silicon-29 nuclear magnetic resonance, 109.8 </=94.0 parts per million. unusual bonding toluene R(3)Si(+) Lambert's compound reinterpreted as significant covalent pi interaction.