Coordination Chemistry of Potentially S,N,Npy-Tridentate Thiosemicarbazones with the {Re(CO)3}+ Fragment and Formation of Hemiaminal Derivatives

Nine potentially S,N,N_py-tridentate thiosemicarbazones (HL) derived from pyridine-2-carbaldehyde or 1-(2-pyridyl)ethanone have been prepared and fully characterized. The X-ray crystal structures of six of them and two hydrochlorides were determined and analyzed. The reaction of the [ReX(CH₃CN)₂(CO)₃]/[ReX(CO)₅] (X = Cl and Br) precursors with these ligands yielded different kinds of compounds: the adducts [ReX(HL)(CO)₃], in which the ligands were S,N-bidentate; the trinuclear species [Re₃Cl₂(L²³)(HL²³)(CO)₉]; and the thiosemicarbazonate compounds [Re(L)(CO)₃], where the ligand is S,N,N_py-tridentate. Besides, the reaction in methanol or ethanol of the thiosemicarbazones derived from aldehydes yielded S,N,N_py-tridentate hemiaminal cationic [Re(HL^OR)(CO)₃]X and neutral [Re(L^OMe)(CO)₃] complexes after the coordinated ligand underwent addition of the alcohol group to the imine bond. The reactivity of the complex [ReX(HL)(CO)₃] in MeOH and NEt₃ led to the formation of dinuclear [Re₂(L)₂(CO)₆], where the thiosemicarbazonate is again S,N-bidentate. The influence that the substituents on the thiosemicarbazone ligands have on the stability of the complexes and the effect of the reaction medium on the resulting compounds have been analyzed.