Polydentate phosphinoamine ligands: a class of efficient chelating agents for the stabilization of various technetium(V) and rhenium(V) cores

A review of all the X-ray structurally characterized Tc-complexes shows that nitrogen and phosphorus are among the most frequent donor atoms(1). For this reason we have recently undertaken a systematic in- vestigation on the reactivity of polydentate phosphino- amines towards the group 7 metals (Tc and Re) relevant to nuclear medicine(2). This class of ligands incorporate `soft' phosphine phosphorus and `hard' amine nitrogen atoms in the chelate(3), whose simultaneous presence on the metal ion ensures both reduction of the permetallate salts (P) and coordination (P and N), thus allowing stabilization of Tc and Re in intermediate oxidation states. For example, bis-substituted monooxo-MV and nitrido-MV complexes (M = Tc, Re) are readily pre- pared from [MO4]) or suitable pre-reduced precursors using the bidentate o-(diphenylphosphino)aniline ligand (PNH2) shown in (1).