Alumina-supported fluoride reagents for organic synthesis: optimisation of reagent preparation and elucidation of the active species

Reagent loading and drying conditions have been compared for alkali metal fluride (MF)–alumina supported reagents, by reaction studies and a series of analytical techniques. The reaction studies indicate that whereas a combination of low MF loadings and highly efficient drying procedures give the best reagents for catalytic reactions, somewhat higher loadings and more moderate drying conditions give the best reagents for non-catalytic reactions. The analytical studies enable some rationalisation of the reaction results as well as providing important clues concerning the nature of the active-basic species. The formation of OH– on the reagent surface cannot be entirely responsible for the high basicity of the reagents and it seems that co-ordinately unsaturated F– ions on the reagent surface play an important role in the behaviour of the reagents. High MF loadings and high drying temperatures result in significant structural damage to the reagents with resulting loss in activity.