Synthesis and characterization of novel phosphinimine ligand systems for potential applications in radiopharmaceuticals

Multidentate phosphinimine ligands, C25H49N2P2Si2,(2) C34H38N2P2Si2(3), and C50H66N3P3Si3(4), were synthesized in near quantitative yields by Staudinger reaction using appropriate phosphines. Coordination chemistry of 2 and 3 with Re was performed and the X-ray crystallographic study of the Re ion-pair complex of ligand 2 is reported. Radiolabeling of ligands 2, 3 and 4 with Tc was performed. Simple mixing of ligand solutions with aqueous TcO4 in saline solution produced ion-pairs with more than 95% yields. All three ion-pairs produced are stable for more than 24 h in organic media and in alcohols. The ion-pair produced with ligand 3 ([(NH2PPh2CH2PPh2NH or O) (TcO4)] ), upon heating has resulted in the neutral complex [(NH2PPh2CH2PPh2NH or O) (TcO3)]. Upon heating the ion-pair ([(NH2PPh2CH2PPh2NH) (ReO4)] in the presence of Verkade’s superbase led to the rearrangement of the ligand via cleavage of the P-C-P bridge to produce P-N-P bridged compound.