Metal Triflates as Catalysts in Organic Synthesis: Determination of Their Lewis Acidity by Mass Spectrometry.

Metal triflates have shown a large variety of possibilities as catalysts in organic reactions. Some selected examples of their catalytic activity, in particular in C-O and C-C bond formation are presented. A better understanding of the mode of interaction between these Lewis acids and organic functional groups as ligands should allow for an easier choice of a tailored metal cation for a given reaction. Electrospray ionization mass spectrometry enables the characterization and the quantification of the donor/acceptor interactions involved in the catalytic processes. Both gas-phase and solution-phase interactions between various metal triflates and organic functionalities were studied. Based on an original probabilistic model, ligand displacement experiments lead us to establish quantitative affinity scales of ligands toward the metal centers. The main structural effects governing the ranking are identified and discussed.