Synthesis and Characterization of [MIII(PS)2(L)] mixed-ligand compounds (M = Re, 99Tc; PS= phosphino-thiolate; L= dithiocarbamate) as a model for the Development of New Agents for SPECT Imaging and Radiotherapy

The synthesis and the characterization of a new series of neutral, six-coordinated mixed ligand [MIII(PS)2(L)] compounds (M= Re; Tc), where PS a is bis-aryl-alkyl or tris-alkyl-phosphino-thiolate and L is a dithiocarbamate are reported. Stable [MIII(PS)2(L)] complexes were easily synthesized, in good yield, starting from precursors where the metal was in different oxidation states (III, V and VII), involving ligand exchange and/or redox-substitution reactions. The compounds were characterized by elemental analysis, ESI(+)-MS, multinuclear NMR, cyclic voltammetry and X-ray diffraction analysis. All complexes are constituted by the presence of the [MIII(PS)2]+ moiety where two phosphino-thiolate ligand are tightly bond to the metal while the remaining two position were saturated by a dithiocarbamate chelate, also carrying bulky bioactive molecule (3-6; M=Re). X-ray analyses were performed on crystalline specimens of the 1, 2, 7 (M= Re) and 9 (M= Tc) compounds. Complex 1 is isostructural and isomorphic with 9; all complexes share a distorted trigonal prismatic geometry, with a P2S4 coordination donor set. The possibility to easily prepare these [MIII(PS)2(L)] complexes, starting from the corresponding permetalate anions, in mild reactions conditions and in high yield, lays the first stone to the preparation of a new series of M(III)-based (M=99mTc/188Re) compounds useful in theragnostic applications.