Triflate catalysts, molecular metal reactions

Alkylations are Friedel-Crafts-type electrophilic reactions requiring the participation of a strong Lewis catalyst. Obviously they were carried out in the presence of hazardous Lewis acid catalysts as metal halides. Switching from these molecular compounds to solid embedded triflates led to catalysts on which such reactions occurred with turnover frequency (TOFs) having at least one order of magnitude higher than on classic acid solid catalysts as zeolites [100,101]. Examples of such reactions are alkylations of phenols or naphthols occurring on immobilized La, Ag, or r rr-butyldimethylsilyl-trifluoromethane-sulfonate catalysts. 

Diels-Alder reactions constitute one of the most important methodologies for the constructuction of a cyclic molecular framework. Lanthanide Lewis acid catalyzed Diels-Alder reaction was pioneered by Danishefsky et al., who revealed that NMR shift reagent Eu(hfc)3 served as chiral catalyst in hetero Diels-Alder reaction of silyloxydiene and aldehydes [32]. Later, although Yb(OTf)3 was first introduced for Diels-Alder reactions as an effective catalyst among lanthanide triflates, scandium triflates (Sc(OTf)3), classified as rare earth metal triflate, has gained popularity as a superior catalyst for Diels-Alder reactions [11, 33]. This section highlights several examples of the reactions where lanthanide triflates displayed preferable performance over scandium triflates. 

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