Bis(trifluoromethyl)disulfide and the EtP₄ Phosphazene Base-Formation of a Bench-Stable [EtP₄SCF₃]⁺[SCF₃]^- Salt

The reaction of the {(Et₂N)₃P═N}₃P═N^tBu phosphazene base (EtP₄) with bis(trifluoromethyl)disulfide, (F₃CS)₂, selectively affords [EtP₄SCF₃][SCF₃], which arises from formal heterolytic S─S bond cleavage. The phosphazenium salt represents the first structurally characterized SCF₃ substituted iminium derivative. Subsequent reaction with methyl halides MeX (X = Br, I) leads to selective substitution of the anionic SCF₃ moiety and facilitates isolation of the corresponding [EtP₄SCF₃]X (X = Br, I) salts. Treatment of [EtP₄SCF₃][SCF₃] with trimethylsilyl halides Me₃SiX (X = Cl, Br) affords halogenophosphonium halide salts [({Et₂N}₃P═N)₃PX]X (X = Cl, Br), via removal of the iminium unit at the phosphazene center. All compounds were characterized by multinuclear NMR spectroscopy, single-crystal X-ray diffraction experiments, and elemental analyses. Both SCF₃ units are chemically addressable and can be employed in further functionalization. In contrast, no reaction of (F₃CS)₂ is observed when the iminophosphorane (C₄H₈N)₃P═N^tBu is employed under comparable conditions, whereas the phosphanes PMe₃ and P(NEt₂)₃ undergo conversion to the corresponding difluorophosphoranes. These observations underline the exceptional ability of the EtP₄ phosphazene base to promote bond activation and to stabilize the resulting reactive SCF₃.