Intramolecular Halo Stabilization of Silyl Cations-Silylated Halonium- and Bis-Halo-Substituted Siliconium Borates

The stabilizing neighboring effect of halo substituents on silyl cations was tested for a series of peri-halo substituted acenaphthyl-based silyl cations 3. The chloro- (3b), bromo- (3c), and iodo- (3d) stabilized cations were synthesized by the Corey protocol. Structural and NMR spectroscopic investigations for cations 3b-d supported by the results of density functional calculations, which indicate their halonium ion nature. According to the fluorobenzonitrile (FBN) method, the silyl Lewis acidity decreases along the series of halonium ions 3, the fluoronium ion 3a being a very strong and the iodonium ion 3d a moderate Lewis acid. Halonium ions 3b and 3c react with starting silanes in a substituent redistribution reaction and form siliconium ions 4b and 4c. The structure of siliconium borate 4c(2)[B12Br12] reveals the trigonal bipyramidal coordination environment of the silicon atom with the two bromo substituents in the apical positions.

Automated summary

The stabilizing neighboring effect of halo substituents on silyl cations was tested for a series of peri-halo substituted acenaphthyl-based silyl cations. Different halonium ions show varying levels of Lewis acidity, with fluoronium ion being very strong and iodonium ion being moderate. Additionally, halonium ions can undergo substituent redistribution reactions to form siliconium ions.