Synthesis and characterization of novel phosphinimine ligand systems for potential applications in radiopharmaceuticals
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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 ⁹⁹[superscript]mTc was performed. Simple mixing of ligand solutions with aqueous ⁹⁹[superscript]mTcO₄⁻ 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)⁺ (⁹⁹[superscript]mTcO₄)⁻] ), upon heating has resulted in the neutral complex [(NH₂PPh₂CH₂PPh₂NH or O)⁺ (⁹⁹[superscript]mTcO3)]. 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.