Syntheses, Solution Multi-NMR Characterization, and Reactivities of [C6F5Xe]~+ Salts of Weakly Coordinating Borate Anions, [BY4]~- (Y = CF3, C6F5, CN, or OTeF5)

摘要

New examples of [C6F5Xe]~+ salts of the weakly coordinating anions [B(CF3)4]~-, [B(C6F5)4]~-, [B(CN)4]~-, and [B(OTeF5)4]~- have been synthesized by metathesis reactions of [C6F5Xe][BF4] with the corresponding M~I[BY4] salts (M~I = K or Cs; Y = CF3, C6F5, CN, or OTeF5). The salts were characterized in solution by multi-NMR spectroscopy. Their stabilities in prototypic solvents (CH3CN and CH2Cl2) and decomposition products are reported. The influence of the coordinating nature of [BY4]~- on the decomposition rate of [C6F5Xe]~+ as well as the presence of the weakly nucleophilic [BF4]~- ion has been studied. The electrophilic pentafluorophenylation of C6H5F by [C6F5Xe][BY4] in solvents of different coordinating abilities (CH3CN and CH2Cl2) and the effects of stronger nucleophiles (fluoride and water) on the pentafluorophenylation process have been investigated. Simulations of the ~(19)F and ~(129)Xe NMR spectra of [C6F5Xe]~+ have provided the complete set of aryl ~(19)F-~(19)F and ~(129)Xe-~(19)F coupling constants and their relative signs. The ~(19)F NMR parameters of the [C6F5Xe]~+ cation in the present series of salts are shown to reflect the relative degrees of cation-solvent interactions.