Chelated hydrazido(3-)rhenium(V) complexes: On the way to the nitridoM(V) Core (M = Tc, Re)

Neutral and asymmetrical hydrazido(3-)rhenium(V) heterocomplexes of the type [Re(ƒØ2-L4)(Ln)(PPh3)] (ƒØ2-L4 = NNC(SCH3)S; H2L1 = S-methyl-ƒÒ-N-(2- hydroxyphenylethylidene)dithiocarbazate, 1, H2L2 = S-methyl-ƒÒ-N-(2- hydroxyphenylmethylidene) dithiocarbazate, 2) are prepared via ligand- exchange reactions in ethanolic solutions starting from [ReV(O)Cl4]- in the presence of PPh3, or from [ReV(O)Cl3(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][ReVIIO4] 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 [ReƒnƒvƒØ2-L4)Cl2(PPh3)2] 3. On the contrary, the N- methyl substituted dithiocarbazic acid H2L3 reacts with perrhenate to give the known nitrido complex [Re(N)Cl2(PPh3)2]. Rhenium(V) complexes incorporating the robust ƒØ2-hydrazido moiety represent key intermediates helpful for the comprehension of the reaction pathway which generates nitrido-rhenium(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 ƒà-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 ƒØ2-hydrazido complexes are characterized by conventional physicochemical techniques, including the X-ray crystal structure determination of 1 and 3.