Fluorination/Dearomatization of C 6 F 5 Groups: An FLP Route to an Electrophilic Borane and Non-Coordinating Anions.

B(C ₆ F ₅ ) ₃ and the corresponding anion [B(C ₆ F ₅ ) ₄ ] ^- are ubiquitous in main group and transition metal chemistry. Known derivatives are generally limited to the incorporation of electron donating substituents. Herein we describe electrophilic fluorination and dearomatization of such species using XeF ₂ in the presence of BF ₃ or Lewis acidic cations. In this fashion the anions [HB(C ₆ F ₅ ) ₃ ] ^- , [B(C ₆ F ₅ ) ₄ ] ^- and [(C ₆ F ₅ ) ₃ BC≡NB(C ₆ F ₅ ) ₃ ] ^- , are converted to [FB(C ₆ F ₇ ) ₃ ] ^- , [B(C ₆ F ₇ ) ₄ ] ^- , and [(C ₆ F ₇ ) ₃ BC≡NB(C ₆ F ₇ ) ₃ ] ^- , respectively. Similarly, the borane adducts (L)B(C ₆ F ₇ ) ₃ (L=MeCN, OPEt ₃ ) are produced. These rare examples of electrophilic attack of electron deficient rings proceed as [XeF][BF ₄ ] acts as a frustrated Lewis pair effecting fluorination and dearomatization of C ₆ F ₅ rings.
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