Preparation, X-ray Structure, and Reactivity of Triisopropylsilyl-Substituted Aryliodonium Salts

(4-Triisopropylsilylphenyl)phenyliodonium tosylate, an aryliodonium salt bearing an extremely bulky, electron-donating triisopropylsilyl (TIPS) substituent in the phenyl ring, was prepared by the reaction of (4-tributyltinphenyl)triisopropylsilane with [hydroxy(tosyloxy)iodo]benzene (Koser's reagent). The TIPS-substituted aryliodonium tosylate was further converted into (4-triisopropylsilylphenyl)phenyliodonium bromide, the structure of which was established by single-crystal X-ray diffraction. Reactions of the TIPS-substituted arylodonium tosylate with bromide, azide, and thiocyanate anions predominantly afforded products of nucleophilic substitution in the electron-rich aromatic ring bearing the TIPS substituent. This unusual result is explained by the steric effect of the extraordinary bulky para-TIPS substituent on the configuration of the reaction intermediate.