Metal‐Catalysed Oxidation Processes in Thiosemicarbazones: New Complexes with the Ligand N‐{2‐([4‐N‐Ethylthiosemicarbazone]methyl)phenyl}‐p‐toluenesulfonamide

Abstract

The coordination behaviour of a new thiosemicarbazone Schiff-base building block, N-{2-([4-N-ethylthiosemicarbazone]methyl)phenyl}-p-toluenesulfonamide, H2L1 (1), incorporating a bulky tosyl group, towards Mn II, Fe II, Co II, Ni II, Cu II, Zn II, Cd II, Ag I, Sn II, and Pb II has been investigated by means of an electrochemical preparative procedure. Most metal complexes of L1 have the general formula [M(L1)]2.nX (M=Mn, Fe, Co, Ni, Cu, Cd, Pb; n=0-4, X=H2O or CH3CN), as confirmed by the structure of [Pb(L1)]2 (15), in which the lone pair on lead is stereochemically active. This lead(II) complex shows an intense fluorescence emission with a quantum yield of 0.13. In the case of silver, the complex formed was found to possess a stoichiometry of [Ag2(L1)]2.3H2O. During reactions with manganese and copper metals, interesting catalysed processes have been found to take place, with remarkable consequences regarding the ligand skeleton structure. In synthesising the manganese complex, we obtained an unexpected dithiolate thiosemicarbazone tosyl ligand, H2L2, as a side-product, which has been fully characterised, including by X-ray diffraction analysis. In the case of copper, the solid complex has the formula [CuL1]2, but the crystallised product shows the copper atoms coordinated to a new cyclised thiosemicarbazone ligand, H2L3, as in the structures of the complexes [Cu(L3)]2.CH3CN (8) and [Cu(L3)(H2O)]2.CH3CN.H2O (9). The zinc complex [Zn(L1)]4 (12) displays a particular tetranuclear zeolite-type structure capable of hosting small molecules or ions, presumably through hydrogen bonding.

The use of sacrificial anodes for the electrochemical synthesis of metallic complexes

“…was reported [146]; both of these groups were deprotonated due to the electrolysis of an The structure of the [Zn 4 (L51) 4 ] (Fig. 4, left) is quite similar to those reported for zeolites [147].…”

“…The structure of [Pb 2 (L51) 2 ] shows the ligands acting in a dianionic tetradentate coordination mode with nitrogen atoms acting as µ 2 -bridges between the two lead centers [146].…”

“…12, right) and [Cu(L105)(H 2 O)] 2 ·CH 3 CN·H 2 O are dinuclear species with two dianionic tetradentate bridging ligands [146]. In this case, the formation of a triazole ring in the new ligand was proposed to start with a nucleophilic attack of a thioamide nitrogen to the imine carbon, followed by the addition of an acetamide moiety (possibly the result of the copper catalyzed hydrolysis of acetonitrile) [335] and the formation of a new N-S bond which is attributable to the coordination of the metal followed by a reductive elimination [336].…”

“…The expected Ga(III) was not obtained but the corresponding disulfide (L84a-L84a) [342]. A compound with a disulfide group was also obtained as a byproduct of the electrolysis of an acetonitrile solution of H 2 L51 (Scheme 8) with a manganese anode [146]. The structure can be described as a dimer of the initial proligand involving the two sulfur atoms from the thiosemicarbazone moieties.…”

Exoplasmic cysteine Cys384 of the HDL receptor SR-BI is critical for its sensitivity to a small-molecule inhibitor and normal lipid transport activity

“…1) might interact with Cys384's free thiol (34) include (i) thiol nucleophilic attack on the thiocarbonyl as proposed for thiosemicarbazone inhibition of cysteine proteases (39), (ii) transition metal mediated interaction (40,41), and (iii) disulfide bond formation between the thiosemicarbazone's sulfur and Cys384's free thiol (42,43). These mechanisms could contribute to BLT-1's high potency.…”