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Science 15 October 1993:
Vol. 262. no. 5132, pp. 402 - 404
DOI: 10.1126/science.262.5132.402
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Articles

Closely Approaching the Silylium Ion (R3Si+)

Christopher A. Reed 1, Zuowei Xie 1, Robert Bau 1, and Alan Benesi 2

1 Department of Chemistry, University of Southern California, Los Angeles, CA 90089-0744
2 Department of Chemistry, Pennsylvania State University, University Park, PA 18602

The crystal structure of the tri-isopropyl silyl species, i-Pr3Si(Br6-CB11H6), where the brominated carborane Br6-CB11 H6– is perhaps the least nucleophilic anion presently known, has revealed the highest degree of silylium cation character (R3Si+) yet observed. The average C—Si—C angle is 117°, only 3° short of the planarity expected of a pure silylium ion(120°). This value compares to 114° recently reported for a toluene-solvated silyl cation, [Et3Si(toluene)]+ by Lambert and co-workers. The greater silylium ion character of i-Pr3Si(Br6-CB11H6) versus [i-Pr3Si(toluene)]+ is also reflected in the larger downfield shift of the silicon-29 nuclear magnetic resonance, 109.8 versus le94.0 parts per million. The unusual bonding of toluene to R3Si+ in Lambert's compound is reinterpreted as a significant covalent pgr interaction.

Submitted on July 22, 1993
Accepted on September 3, 1993


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Response.
J. B. Lambert and S. Zhang (1994)
Science 263, 984-985
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Science. ISSN 0036-8075 (print), 1095-9203 (online)