Trifluoromethanesulfonate
Trifluoromethanesulfonate, also known by the trivial name triflate, is a functional group with the formula CF3SO3−. The triflate group is often represented by −OTf, as opposed to −Tf (triflyl). For example, n-butyl triflate can be written as CH3CH2CH2CH2OTf.
The corresponding triflate anion, CF
3SO−
3, is an extremely stable polyatomic ion, being the conjugate base of triflic acid (CF3SO3H), one of the strongest acids known. It is defined as a superacid, because it is more acidic than pure sulfuric acid.
A triflate group is an excellent leaving group used in certain organic reactions such as nucleophilic substitution, Suzuki couplings and Heck reactions. Since alkyl triflates are extremely reactive in SN2 reactions, they must be stored in conditions free of nucleophiles (such as water). The anion owes its stability to resonance stabilization which causes the negative charge to be spread over the three oxygen atoms and the sulfur atom. An additional stabilization is achieved by the trifluoromethyl group as a strong electron-withdrawing group.
...
Wikipedia