Lanthanide triflates as water-tolerant Lewis

As mentioned earlier (Section 1.5) another example of novel catalysis in an aqueous medium is the use of lanthanide triflates as water-tolerant Lewis acid catalysts for a variety of organic transformations in water [39]. 

To improve the yields and therefore the scope of this aqueous aldolization, the use of lanthanide triflates as water-tolerant Lewis acids was recommended [9, 60]. After completion of the reaction nearly 100% of the catalyst is recovered from the aqueous layer and can be re-used quite easily. Other water-tolerant Lewis acids, including indium chloride [61] and tris(pentafluorophenyl) boron [62], were proposed as catalysts in the aqueous aldol reaction. 

Kobayashi, S. and Hachiya L, Lanthanide triflates as water-tolerant Lewis acids. Activation of commercial formaldehyde solution and use in the aldol reaction of silyl enol ethers with aldehydes in aqueous media, /. Org Chem., 1994, 59, 3590-3596. 

---