The synthesis and characterization of [M(C 8H 5N 2N=NH) 3](BPh 4), where M = Tc or Re. Tris-diazene chelate complexes of technetium( I) and rhenium( I)

Abstract

The reaction of ammonium pertechnetate or tetrabutylammonium perrhenate with the chelating organohydrazine hydralazine hydrochloride gives the Tc( I) (or Re( I)) cationic tris-chelate complex [M(C 8H 5N 2N=NH) 3] +, which is isolated as the tetraphenylborate salt. These dark green complexes are freely soluble in ethanol but decompose in solution in the absence of excess ligand. The infrared spectra of these complexes show no peaks associated with ν(M=O), nor associated with ν(C=N) or ν(N=N), indicative of exclusively chelated organodiazene ligation. A weak absorption near 3250 cm −1 is associated with ν(N-H) from the organodiazene ligands. The FAB(+) mass spectra of the complexes show the free parent ions for both metals. For the technetium complex M + = 573 m/z and for the rhenium complex M + =661 m/z. The technetium complex's mass spectrum also shows a peak of 417 m/z associated with a fragment from the loss of one of the three chelated diazene ligands. The 99Tc NMR spectroscopy shows the technetium complexes resonance occurring in the established Tc(V) region, at ∼1620 ppm. This downfield shift is attributed to a paramagnetic shielding effect. These complexes are electrochemically active, with each complex exhibiting a pair of reversible oxidations. One of the two observed processes is likely ligand based, since it occurs at very similar E 1/2 values for both the rhenium and technetium complexes.