Synthesis and characterization of nitrido Tc(V) and Re(V) complexes with ferrocenedithiocarboxylate {FcCS(2)=[Fe(C5H4CS2)(C5H5)](-)}

The first mixed technetium-iron complexes [99gTc(N)(FcCS2)2] {FcCS2 = [FeII(C5H5)(C5H4CS 2)]-} (1) and [99gTc(N)(FcCS2)(FcCS*2)]+ {FcCS2 = [FeII(C5H5)(C5H4CS 2)]-; FcCS*2 = FeIII(C5H5)(C5H4CS 2)} (2) have been prepared and characterized. Complex 1 was obtained by reaction of the precursor complex [99gTc(N)Cl2(PPh3)2] with the piperidinium salt of the ligand FcCS2. The resulting biferrocene complex is formed by two FcCS2 ligands bound to the Tc atom through the four sulfur atoms of the two CS2- groups and bridged by a Tc≡N multiple bond. The mixed-valence Fe2+-Fe3+, monocationic complex 2 was isolated as secondary product of the reaction of the precursor complex [99gTc(N)Cl4]- with the ligand FcCS2. It has the same composition as 1 except for the fact that the Fe(II) center of one FcCS2 ligand has been oxidized to Fe(III). The electrochemical properties of 1 and 2 are consistent with their formulations. Cyclic voltammetric studies and controlled potential electrolyses showed that complex 1 undergoes a quasi-reversible, two-electron exchange at 0.320 V (vs ferrocene/ ferrocenium couple) attributed to the oxidation of the two Fe(II) ions, while complex 2 undergoes a quasi-reversible, one-electron exchange at nearly the same potential (0.344 V) assigned to the oxidation of the residual Fe(II) ion. These results indicate that in complex 1 the two Fe(II) atoms behave as independent redox centers. The synthesis, characterization, and electrochemical behavior of the analogous, six-coordinated rhenium(V) complex [Re(N)(FcCS2)2(PPh3)] are also reported.