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

The reaction of the (Et2N) 3P═N3P═NtBu phosphazene base (EtP4) with bis (trifluoromethyl) disulfide, (F3CS) 2, selectively affords EtP4SCF3SCF3, 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 EtP4SCF3X (X = Br, I) salts. Treatment of EtP4SCF3SCF3 with trimethylsilyl halides Me3SiX (X = Cl, Br) affords halogenophosphonium halide salts (Et2N3P═N) 3PXX (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═NtBu 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.