In nucleophilic trifluoromethylation the active species is the CF anion. It was, however, widely believed that the trifluoromethyl anion is a transient species and thus cannot be isolated or observed in the condensed phase.  Contrary to the popular belief, the CF anion, with [K(18-crown-6)] as a countercation, was produced and characterized by Prakash and coworkers. The challenges associated with observation of CF anion are alluded to its strong basic nature and its tendency to form pentacoordinated silicon species, such as [MeSi(CF)] or [MeSi(F)(CF)].
The reactivity of fluoroform in combination with a strong base such as t-BuOK with carbonyl compounds in DMF is an example. Here CF and DMF form an hemiaminolate adduct ([MeNCH(O)CF]K).