Intramolecular C-F Activation in Schiff-Base Alkali Metal Complexes

A series of alkali metal complexes (Li, Na, K) with different fluorinated phenoxo-imine ligands [M{(O-2-(RN=CH)-C6H4}] [R = C6F5; 2,4,6-F3C6H2F3; 2,6-C6H3F2; 2,3-C6H3F2; 2-C6H4F; 2-CF3C6H4CH2; CF3CH2] have been synthesized and fully characterized. By using THF as solvent, suitable crystals for X-ray diffraction analysis were obtained, and the solid state structure of some of the prepared compounds has been determined. This analysis reveals the formation of a C-F bond activation product for the potassium compound with the five-fluorinated ligand. In stronger donor solvents, such as dimethylsulfoxide, this process occurs immediately, independently of the metal used. This C-F activation takes place in a smooth process at room temperature. The nature of this reaction is studied by H-1-DOSY NMR experiments with stoichiometric amounts of DMSO, monitoring the disaggregation process from the initial solution structure to the final activation product. The variation of the number of fluorine atoms and their location in the iminic ring is also studied, showing their influence in this intramolecular C-F bond activation process.