Tc(IV)Cl 4(PPh 3) 2 and Tc(III)Cl 3(CH 3CN)(PPh 3) 2 as precursors of trans dioxo technetium(V) complexes with chelating amines and tetraazamacrocycles

Abstract

The trans dioxo complexes [TcO 2(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 [TcCl 4(PPh 3) 2] and [TcCl 3(CH 3CN)(PPh 3) 2] in CH 3CN 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 [TcO 2(cyclam)] + (7%) obtained through a previously reported procedure involving pertechnetate reduction by Na 2S 2O 3 in alkaline solution and in the presence of the ligand or by substitution reaction onto the mono-oxo complex [TcOCl 4] −. The new synthetic method was also efficiently applied to the synthesis of the trans dioxo complexes [TcO 2(L′) 2] + (L = enthylenediamine, 1,3-propanediamine) and [Tc 2(tad)] + (tad = 1,5,8,12-tetraazadodecane), containing bidentate and tetradentate chelating amines, giving final yields similar to those obtained using [TcOCl 4] − as starting substrate. These results indicate that the complex [TcCl 4(PPh 3) 2] and [TcCl 3(CH 3CN)(PPh 3) 2] are superior precursors for the synthesis, at macroscopic level, of trans dioxo Tc(V) complexes with tetraazamacrocylic ligands as compared to [TcO 4] − and [TcOCl 4] −. All the complexes have been characterized by elemental analysis, FTIR and mass spectra, and magnetic susceptibility measurements in solution.