Onium ions of group 15 elements

Synthesis and Characterization of Bissilylated Onium Ions of Group 15 Elements... 

The cations are prepared from 2,5-disilaheptanes, 3, by hydride transfer reactions. The transient silylium ion 4 undergoes an intramolecular reaction to the more stable cyclic onium ion 2. The precursor silanes, 3, are synthesized by salt metathesis reaction from compounds of the type Ph2ELi, where E is the relevant Group 15 element, and the silylchloride 5. The salts 2 [B(C6Fs)4]" are isolated after washing with pentane as white to yellow microcrystalline powders in nearly quantitative yield. Solutions of the cations 2a-c in aromatic solvents are stable at room temperature. The stibonium ion 2d decomposes in solution slowly, yielding unidentified products. 

Cyclic bissilylated onium ions of the group 15 elements 2a-d were synthesized and characterized by NMR spectroscopy supported by quantum mechanical calculations. All onium ions with the exception of the stibonium ion, 2d, are stable in solution at room temperature. Experiments to test the potential of these cations in Lewis acid-catalyzed organic transformations are under way in our laboratories. 

At room temperature bismuthine rapidly decomposes into its elements. The rate of decomposition increases markedly at higher temperatures (8). Bismuthine decomposes when bubbled through silver nitrate or alkafl solutions but is unaffected by light, hydrogen sulfide, or 4 sulfuric acid solution. There is no evidence for the formation of BiH, though the phenyl derivative, (C H BU, is known. The existence of BiH would not be anticipated on the basis of the trend found with other Group 15 (V) "onium" ions. 

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