Synthesis, characterization, reactivity and computational studies of new rhenium(I) complexes with thiosemicarbazone ligands derived from 4-(methylthio)benzaldehyde

N-thioamide thiosemicarbazone derived from 4-(methylthio)benzaldehyde (R = H, HL1; R = Me, HL2 and R = Ph, HL3) have been prepared and their reaction with fac-[ReX(CO)3(CH3CN)2] (X = Br, Cl) in methanol gave the adducts [ReX(CO)3(HLn)] (1a X = Cl, n = 1; 1a′ X = Br, n = 1; 1b X = Cl, n = 2; 1b′ X = Br, n = 2; 1c X = Cl, n = 3; 1c′ X = Br, n = 3) in good yield.All the compounds have been characterized by elemental analysis, mass spectrometry (ESI), IR and 1H NMR spectroscopic methods. Moreover, the structures of HL2, HL3, HL3·(CH3)2SO and 1b′·H2O were also elucidated by X-ray diffraction. In 1b′, the rhenium atom is coordinated by the sulphur and the azomethine nitrogen atoms (κS,N3) forming a five-membered chelate ring, as well as three carbonyl and bromide ligands. The resulting coordination polyhedron can be described as a distorted octahedron.The structure of the dimers is based on rhenium(I) thiosemicarbazonates [Re2(L1)2(CO)6] (2a), [Re2(L2)2(CO)6] (2b) and [Re2(L3)2(CO)6] (2c) as determined by X-ray studies. Methods of synthesis were optimized to obtain amounts of these thiosemicarbazonate complexes. In these compounds the dimer structures are achieved by Re–S–Re bridges, where S is the thiolate sulphur from a κS,N3-bidentate thiosemicarbazonate ligand.Some single crystals isolated in the synthesis of 2b contain [Re(L4)(L2)(CO)3] (3b) where L4 (=2-methylamine-5-(para-methylsulfanephenyl)-1,3,4-thiadiazole) is originated in a cyclization process of the thiosemicarbazone. Furthermore, the rhenium atom is coordinate by the sulphur and the thioamidic nitrogen of the thiosemicarbazonate (κS,N2) affording a four-membered chelate ring.

Thiosemicarbazone (1) and thiosemicarbazonate (2) complexes have been isolated and characterized. In both kind of complexes the rhenium atom is coordinated by the sulphur and the azomethine nitrogen atoms (κS,N3). Single crystals of 3b are originated by cyclization of a thiosemicarbazone molecule and κS,N2-coordination of other one.Figure optionsDownload as PowerPoint slideHighlights
► Rhenium(I) tricarbonyl adducts of thiosemicarbazone derived from 4-(methylthio)benzaldehyde and their thiosemicarbazonate complexes.
► Spectroscopic and X-ray methods confirm the κS,N3-coordination of the thiosemicarbazone thiosemicarbazone and the formation of the five-membered chelate ring.
► Thiosemicarbazonate complexes are dimers by Re–S–Re bridges.
► Formation of a thiadiazole ring and κS,N2-thiosemicarbazonate has been confirmed by X-ray diffraction.