Synthesis and characterization of rhenium (III and V) Schiff base complexes for nuclear medicine.

摘要

This dissertation investigates the synthesis and characterization of several rhenium Schiff base complexes as potential radiopharmaceuticals for imaging and therapeutic purposes. A series of acetylacetone derived tetradentate N₂O₂ Schiff base ligands (i.e., acac₂en, acac₂pn, acac₂dmpn) were reacted with a rhenium (V) starting material (i.e., n-Bu₄N[ReOCl₄], ReOCl ₃(PPh₃)₂) to yield a series of compounds. In most cases, reaction's involving [n-Bu₄N][ReOCl₄] with two equivalents of ligand in ethanol yielded monomer complexes of the form trans-[ReO(Ligand)X]. The type of axial substituent, X = Cl −, H₂O, ReO₄−, MeO −, found trans to the rhenium oxo group can be adjusted by altering the reaction conditions. A similar reaction utilizing ReOCl₃(PPh₃)₂, one equivalent of the ligand, and triethylamine yielded μ-oxo dimer complexes, trans-[Re ₂O₃(Ligand)₂]. The conversion of rhenium (V) Schiff base monomer complexes into μ-oxo dimer complexes was investigated to gain a better understanding of conditions that yield monomer compounds. Experiments reacting trans-[ReO(acac₂pn)Cl] with various solution conditions led to the proposal of a dimer formation mechanism that involves two pathways: (1) addition of base(OH−) and (2) addition of water to generate a trans aquo species and additional water molecules to deprotonate the coordinated water molecule.; The rhenium (V) monomer complexes, trans-[ReO(acac ₂en)OH₂]Cl and trans-[ReO(acac₂pn)Cl], were also reacted with phosphine ligands to potentially generate a bis-phosphine(Schiff base)rhenium(III) cationic complexes, trans-[Re(Ligand)(PR₃)₂]+. The trans-[ReO(acac₂en)H₂O]Cl complex yielded the Re (III) complex when reacted with phosphines, while the Schiff base ligand of the [trans-ReO(acac₂pn)]Cl complex underwent an intramolecular rearrangement to yield an asymmetric complex, [ cis-ReO(acac₂pn)PR₃]X. A mechanism is proposed for the rearrangement of the Schiff base ligand in the complex upon treatment with phosphine ligands. Further experiments with other soft monodentate ligands (i.e., thiocyanate, cyanide) yielded neutral asymmetric complexes.; A series of experiments investigated the removal radioactive Tc-99 from solution through precipitation. The study focused on precipitating agents that could be added to a simulated waste stream at a uranium reprocessing plant to remove Tc-99 as a pertechnetate ion pair or a reduced Tc (IV) complex.