Neutral and asymmetrical hydrazido(3-)rhenium(V) heterocomplexes of the type [Re(eta(2) -L-4)(L-n)(PPh3)] (eta(2)-L-4 = NNC(SCH3)S; H2L1 = S-methyl beta-N-((2-hydroxyphenyl)ethylidene)dithiocarbazate, 1, H2L2 = S-methyl beta-N-((2-hydroxyphenyl)methylidene)dithiocarbazate, 2) are prepared via ligand-exchange reactions in ethanolic solutions starting from [Re-V(O)Cl-4](-) in the presence of PPh3 or from [Re-V(O)Cl-3(PPh3)(2)]. The distorted octahedral coordination sphere of these compounds is saturated by a chelated hydrazido group, a facially ligated ONS Schiff base, and PPh3. Reduction-substitution reactions starting from [NH4][(ReO4)-O-VII] in acidic ethanolic mixtures containing PPh3 and H2Ln (or its dithiocarbazic acid precursor H3L4) produce another example of chelated hydrazido(3-) rhenium(V) derivative, namely [Re(eta(2) -L-4)Cl-2(PPh3)(2)], 3. On the contrary, the N-methyl-substituted dithiocarbazic acid H2L3 reacts with perrhenate to give the known nitrido complex [Re(N)Cl-2(PPh3)(2)]. Rhenium(V) complexes incorporating the robust eta(2)-hydrazido moiety represent key intermediates helpful for the comprehension of the reaction pathway which generates nitridorhenium(V) species starting from oxo precursors. An essential requirement for the stabilization of such chelated hydrazido-Re(V) units is the triple deprotonation at the hydrazine nitrogens, thereby providing efficient pi-electron circulation in the resulting five-membered ring. The thermal stability of these units is affected by the nature of the anchoring donor, thione sulfur ensuring stronger chelation than nitrogen and oxygen. The eta(2)-hydrazido complexes are characterized by conventional physicochemical techniques, including the X-ray crystal structure determination of 1 and 3.