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

Abstract

N-thioamide thiosemicarbazone derived from 4-(methylthio)benzaldehyde (R = H, HL2; 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; 1a0 X = Br, n = 1; 1b X = Cl, n = 2; 1b0 X = Br, n = 2; 1c X = Cl, n = 3; 1c0 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 HL 2, HL3, HL3.(CH3)2SO and 1b0-H2O were also elucidated by X-ray diffraction. In 1b', the rhenium atom is coordinated by the sulphur and the azomethine nitrogen atoms (jS,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 [Re 2(L1)2(CO)6] (2a), [Re2(L 2)2(CO)6] (2b) and [Re2(L 3)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 jS,N3-bidentate thiosemicarbazonate ligand. Some single crystals isolated in the synthesis of 2b contain [Re(L4)(L2)(CO)2] (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 (jS,N2) affording a four-membered chelate ring. © 2011 Elsevier Ltd.