Tc(IV)Cl4(PPh3)2 and Tc(III)Cl3(CH3CN)(PPh3)2 as precursors of trans dioxo technetium(V) complexes with chelating amines and tetraazamacrocycles

The trans dioxo complexes [TcO2(L)]+ (L = 1,4,8,11-tetraazacyclotetradecane (cyclam), 1,4,8,11-tetraazacyclotetradecane-5-one, 1,4,8,11-tetraazacyclotetradecane-5,7-dione) have been prepared through a new alternative route involving the reaction of excess of the appropriate ligand with the complexes [TcCl4(PPh3)2] and [TcCl3(CH3CN)(PPh3)2] in CH3CN solution, at room temperature. The yields of formation of the final products obtained through this new synthetic method (30-55%) are significantly higher than that found in the synthesis of the complex [TcO2(cyclam)]+ (7%) obtained through a previously reported procedure involving pertechnetate reduction by Na2S2O3 in alkaline solution and in the presence of the ligand or by substitution reaction onto the mono-oxo complex [TcOCl4]-. The new synthetic method was also efficiently applied to the synthesis of the trans dioxo complexes [TcO2(L?)2]+ (L = enthylenediamine, 1,3-propanediamine) and [Tc2(tad)]+ (tad = 1,5,8,12-tetraazadodecane), containing bidentate and tetradentate chelating amines, giving final yields similar to those obtained using [TcOCl4]- as starting substrate. These results indicate that the complex [TcCl4(PPh3)2] and [TcCl3(CH3CN)(PPh3)2] are superior precursors for the synthesis, at macroscopic level, of trans dioxo Tc(V) complexes with tetraazamacrocylic ligands as compared to [TcO4]- and [TcOCl4]-. All the complexes have been characterized by elemental analysis, FTIR and mass spectra, and magnetic susceptibility measurements in solution.