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Improved synthetic conditions allow preparation of TMSCCl₃ in good yield (70 %) and excellent purity. Compounds of the type NBu₄X [X=Ph₃SiF₂ (TBAT), F (tetrabutylammonium fluoride, TBAF), OAc, Cl and Br] act as catalytic promoters for 1,4‐additions to a range of cyclic and acyclic nitroalkenes, in THF at 0–25 °C, typically in moderate to excellent yields (37–95 %). TBAT is the most effective promoter and bromide the least effective. Multinuclear NMR studies (¹H, ¹⁹F, ¹³C and ²⁹Si) under anaerobic conditions indicate that addition of TMSCCl₃ to TBAT (both 0.13 M) at −20 °C, in the absence of nitroalkene, leads immediately to mixtures of Me₃SiF, Ph₃SiF and NBu₄CCl₃. The latter is stable to at least 0 °C and does not add nitroalkene from −20 to 0 °C, even after extended periods. Nitroalkene, in the presence of TMSCCl₃ (both 0.13 M at −20 °C), when treated with TBAT, leads to immediate formation …