Chelated Hydrazido(3−)rhenium(V) Complexes:  On the Way to the Nitrido−M(V) Core (M = Tc, Re)

Abstract

Neutral and asymmetrical hydrazido(3-)rhenium(V) heterocomplexes of the type [Re(eta(2)-L(4))(L(n))(PPh(3))] (eta(2)-L(4) = NNC(SCH(3))S; H(2)L(1) = S-methyl beta-N-((2-hydroxyphenyl)ethylidene)dithiocarbazate, 1, H(2)L(2) = 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 PPh(3) or from [Re(V)(O)Cl(3)(PPh(3))(2)]. The distorted octahedral coordination sphere of these compounds is saturated by a chelated hydrazido group, a facially ligated ONS Schiff base, and PPh(3). Reduction-substitution reactions starting from [NH(4)][Re(VII)O(4)] in acidic ethanolic mixtures containing PPh(3) and H(2)L(n) (or its dithiocarbazic acid precursor H(3)L(4)) produce another example of chelated hydrazido(3-) rhenium(V) derivative, namely [Re(eta(2)-L(4))Cl(2)(PPh(3))(2)], 3. On the contrary, the N-methyl-substituted dithiocarbazic acid H(2)L(3) reacts with perrhenate to give the known nitrido complex [Re(N)Cl(2)(PPh(3))(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.

Synthesis of 17-α-Substituted Estradiol-Pyridin-2-yl Hydrazine Conjugates as Effective Ligands for Labeling with Alberto's Complex fac-[Re(OH2)3(CO)3]+ in Water

“…The remarkable synthesis of Alberto's fac -[ 99m Tc(OH 2 ) 3 (CO) 3 ] + complex directly from [ 99m TcO 4 ] - in water under mild conditions has made this an important precursor for radiopharmaceutical labeling with a variety of chelators. − A highly stable complex with 2-hydrazinopyridine formed rapidly and quantitatively under dilute (μM) concentrations, which indicates the potential of this ligand class for producing radiopharmaceuticals with high specific activity . Hydrazine ligands are also known to form stable complexes with Tc/Re in higher oxidation states. − Hydrazinonicotinamide derivatives have become important bifunctional ligands that can be conjugated to substrates possessing an available amino group. − …”

“…47 Hydrazine ligands are also known to form stable complexes with Tc/Re in higher oxidation states. [52][53][54][55][56][57][58] Hydrazinonicotinamide derivatives have become important bifunctional ligands that can be conjugated to substrates possessing an available amino group. 59 Our interest has focused on the synthesis of pyridin-2-yl hydrazine derivatives of estradiol 1 and 2 as potential ligands for labeling with Alberto's complex.…”

A thiolate-bridged ruthenium–molybdenum complex featuring terminal nitrido and bridging amido ligands derived from the N–H and N–N bond cleavage of hydrazine

“…These shifts are in good agreement with reduced-mass induced isotope shift estimation. 38 Although nitrides derived from substituted hydrazine have been reported, 21,39–42 to the best of our knowledge, complex 4 represents one of the rare examples where nitride is generated directly from the cleavage of parent hydrazine. 43…”

“…These shifts are in good agreement with reduced-mass induced isotope shift estimation. 38 Although nitrides derived from substituted hydrazine have been reported, 21,[39][40][41][42] to the best of our knowledge, complex 4 represents one of the rare examples where nitride is generated directly from the cleavage of parent hydrazine. 43 To probe the other potential activation mode of hydrazine in this system, we also attempted to synthesize independently a bis(amido) complex derived from the N-N bond cleavage of hydrazine without hydrogen abstraction.…”