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Quantitative Ligand Affinity Scales for Metal Triflate Salts : Application to Isomer Differentiation

Dr. Claudio Iacobucci, Nédra Jouini, Dr. Lionel Massi, Dr. Sandra Olivero, Prof. Francesco De Angelis, Dr. Elisabet Duñach, Prof. Jean-François Gal

Owing to the importance of metal triflates in catalysis, the affinity of the cationic center for a selection of organic ligands was explored for InIII and ZnII triflates. The organic Lewis bases include a variety of carbonyls (amides, unsaturated ketones, a lactone) and cyclic 1,2-diols. The relative affinity of the ligands for the cationic center in triflates was quantitatively determined on the basis of relative ion concentrations determined by electrospray-ionization mass spectrometry. The affinity scales were discussed with reference to gas-phase proton basicity and Lewis basicity scales. Structural isomers and stereoisomers display significant affinity differences in several cases. In the case of isomer mixtures, a model describing the relative peak intensities in the mass spectra was developed. On this basis, an isomer titration method was set up. Remarkably, this MS-based method overcame the blindness of mass spectrometry to isomers without the need for isotope labeling or MS/MS experiments. This model may prove to have applications in analytical chemistry and catalysis.

affinity ; isomer recognition ; Lewis acids ; mass spectrometry ; metal triflates

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