Alkali metals have been used to degrade SF ₆ in liquid ammonia. The products include metal fluorides. In this study, we reacted K ⁻ and Ag ⁻ with SF ₆ in a triple quadrupole mass spectrometer. The atomic metal anions were formed by in-source collision-induced dissociation (CID) of their respective oxalate salts as previously described by our group. The only two reaction products observed were SF ₆ ⁻ and SF ₅ ⁻. At low collision energy, the latter was deduced to be formed via an abstraction by the metal of F from SF ₆ ⁻ formed by electron transfer in the encounter complex between the metal anion and neutral SF ₆. As the collision energy was increased, there was evidence of a CID contribution to SF ₅ ⁻ directly from SF ₆ ⁻.