Synthesis and structural characterization of new oxorhenium and oxotechnetium complexes with XN2S-tetradentate semi-rigid ligands (X = O, S, N)

Abstract

Twelve novel oxo-technetium and oxo-rhenium complexes based on N₂S₂-, N₂SO- or N₃S-tetradentate semi-rigid ligands have been synthesised and studied herein. By reacting the ligands with a slight excess of suitable [MO]³⁺ precursor (ReOCl₃(PPh₃)₂ or [NBu₄][^99gTcOCl₄]), the monoanionic complexes of general formula [MO(Ph–XN₂S)]⁻ could be easily produced in high yield. The complexes have been characterized by means of IR, electrospray mass spectrometry, elemental analysis, NMR and conductimetry. The crystal structures of [PPh₄][ReO(Ph–ON₂S)] 1b and [NBu₄][^99gTcO(Ph–ON₂S)] 1c have been established. The [MO]³⁺ moiety was coordinated via the two deprotonated amide nitrogens, the oxygen and the terminal sulfur atoms in 1b and 1c. In both compounds, the ON₂S coordination set is in the equatorial plane, and the complexes adopted a distorted square-pyramidal geometry with an axial oxo-group. The chemical and structural identity of the different prototypic complexes (rhenium, ^99gTc complexes and their corresponding ^99mTc radiocomplexes) have been also established by a comparative HPLC study.