NbF5, NbCl5 and WCl6 are commercial non expensive compounds, which have found large application as catalytic precursors in synthetic organic chemistry. However, the direct interactions of such transition metal halides with stoichiometric amounts of organic reactants has been limitedly explored. Our recent, systematic investigation on the chemistry of NbF5, NbCl5 and WCl6 with oxygen donors has provided evidences of unusual features: 1) such halides are capable of directing mild conditions transformations, which are not commonly achieved by means of other transition metal compounds; 2) NbX6- (X = F, Cl) and WOCl5 are easily obtained and may allow the isolation of unstable organic cations. Examples will be provided with particular reference to natural -aminoacids, such as L-proline
