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, HL 1; R = Me, HL 2 and R = Ph, HL 3 ) have been prepared and their reaction with fac-[ReX(CO) 3(CH 3CN) 2] (X = Br, Cl) in methanol gave the adducts [ReX(CO) 3(HL n)] ( 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 HL 2 , HL 3 , HL 3 ·( CH 3) 2SO and 1b′·H 2O were also elucidated by X-ray diffraction. In 1b′, the rhenium atom is coordinated by the sulphur and the azomethine nitrogen atoms (κ S,N 3 ) 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(L 1) 2(CO) 6] ( 2a), [Re 2(L 2) 2(CO) 6] ( 2b) and [Re 2(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 κ S,N 3 -bidentate thiosemicarbazonate ligand. Some single crystals isolated in the synthesis of 2b contain [Re(L 4)(L 2)(CO) 3] ( 3b) where L 4 (=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 (κ S,N 2 ) affording a four-membered chelate ring.