Lanthanide trifluoromethanesulfonates

Lanthanide triflates are triflate salts of the lanthanide family with many uses in organic chemistry as Lewis acid catalysts. The catalysts act similarly to aluminium chloride or ferric chloride, but are stable in water, which makes it possible to use water as a solvent instead of organic solvents.

Molecular structure

Lanthanide triflates consist of a lanthanide metal ion and three triflate ions. The lanthanides, or rare earth metals, are the elements from Lanthanum to Lutetium in the periodic table. Triflate is a contraction of trifluoromethanesulfonate; its molecular formula is CF₃SO₃, and is commonly designated ‘OTf’. Triflic acid is a ‘superacid’ so its conjugate base ions are very stable. The metal triflate complex is strongly electrophilic, thus acts as a strong Lewis acid.

Lewis acid catalysis

Lewis acids are used to catalyse a wide variety of reactions. The mechanism steps are:

1. Lewis acid forms a polar coordinate with a basic site on the reactant (such as an O or N)
2. Its electrons are drawn towards the catalyst, thus activating the reactant
3. The reactant is then able to be transformed by a substitution reaction or addition reaction
4. The product dissociates and catalyst is regenerated

Common Lewis acids include aluminium chloride, ferric chloride and boron trifluoride. These reactions are usually carried out in organic solvents; AlCl₃, for example, reacts violently with water. Typical...
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