Benzaldehyde Thiosemicarbazone Research Articles

Rhodium Assisted C−H Activation of Benzaldehyde Thiosemicarbazones and Their Oxidation via Activation of Molecular Oxygen

The benzaldehyde thiosemicarbazones are found to undergo oxidation at the sulfur center upon reaction with [Rh(PPh3)3Cl] in refluxing ethanol in the presence of a base (NEt3). A group of organorhodium complexes are obtained from such reactions, in which the oxidized thiosemicarbazones are coordinated to rhodium as tridentate CNS donors, along with two triphenylphosphines and a hydride. From the reaction with para-nitrobenzaldehyde thiosemicarbazone, a second organometallic complex is obtained, in which the thiosemicarbazone is coordinated to rhodium as a tridentate CNS donor, along with two triphenylphosphines and a hydride. Reaction of the benzaldehyde thiosemicarbazones with [Rh(PPh3)3Cl] in refluxing ethanol in the absence of NEt3 affords another group of organorhodium complexes, in which the thiosemicarbazones are coordinated to rhodium as tridentate CNS donors, along with two triphenylphosphines and a chloride. Structures of representative complexes of each type of complexes have been determined by X-ray crystallography. In all of the complexes, the two PPh3 ligands are trans. All of the complexes show intense MLCT transitions in the visible region. Cyclic voltammetry on these complexes shows a Rh(III)-Rh(IV) oxidation on the positive side of SCE. Redox responses of the coordinated thiosemicarbazones are also displayed by all of the complexes.

Crystal structures of organomercury(II) derivatives of cyclohexanone and benzaldehyde thiosemicarbazones

The crystal and molecular structures of the organomercury(II) complexes [Hg(C6H5)(chtsc)], 1, and [Hg(C6H5C5H4N)(btsc)], 2, obtained from the reaction of phenylmercury(II) acetate with cyclohexanone thiosemicarbazone (Hchtsc) and that of [2-(pyridin-2′-yl)]phenyl]mercury(II) acetate with benzaldehyde thiosemicarbazone (Hbtsc), respectively, are described. Both 1 and 2 are monoclinic, space group C2/c. Complex 1 has a distorted T-shaped geometry {C-Hg-S, 161.91(10)°} and 2 can be considered to have a distorted seesaw geometry {C-Hg-S, 171.2(10)°}. In both complexes the ligands act as bidentate chelating anions bonding through azomethine N1 and thiolato S atoms.

Thiosemicarbazone complexes of the platinum metals. A story of variable coordination modes

Salicylaldehyde thiosemicarbazone (H2saltsc) reacts with [M(PPh3)3X2] (M = Ru, Os; X = Cl, Br) to afford complexes of type [M(PPh3)2(Hsaltsc)2], in which the salicylaldehyde thiosemicarbazone ligand is coordinated to the metal as a bidentate N,S-donor forming a four-membered chelate ring. Reaction of benzaldehyde thiosemicarbazones (Hbztsc-R) with [M(PPh3)3X2] also affords complexes of similar type, viz. [M(PPh3)2(bztsc-R)2], in which the benzaldehyde thiosemicarbazones have also been found to coordinate the metal as a bidentate N,S-donor forming a four-membered chelate ring as before. Reaction of the Hbztsc-R ligands has also been carried out with [M(bpy)2X2] (M = Ru, Os; X = Cl, Br), which has afforded complexes of type [M(bpy)2(bztsc-R)]+, which have been isolated as perchlorate salts. Coordination mode of bztsc-R has been found to be the same as before. Structure of the Hbztsc-OMe ligand has been determined and some molecular modelling studies have been carried out determine the reason for the observed mode of coordination. Reaction of acetone thiosemicarbazone (Hactsc) has then been carried out with [M(bpy)2X2] to afford the [M(bpy)2(actsc)]ClO4 complexes, in which the actsc ligand coordinates the metal as a bidentate N,S-donorformingafive-membered chelate ring. Reaction of H2saltsc has been carried out with [Ru(bpy)2Cl2] to prepare the [Ru(bpy)2(Hsaltsc)]ClO4 complex, which has then been reacted with one equivalent of nickel perchlorate to afford an octanuclear complex of type [Ru(bpy)2(saltsc-H)4Ni4](ClO4)4.

Transition Metal Complexes with Thiosemicarbazide-Based Ligands. Part 37.* Synthesis and Study of the first Thiosemi-Carbazide-Derived Copper(I) Complexes: Crystal Structure of [2-(Diphenylphosphino)Benzaldehyde Thiosemicarbazonato(−1)] Copper(I)-Nitrate-Methanol Solvate

The preparation and physical characterization of two copper(I) complexes Cu(HL)NO3 and [Cu(HL)2]NO3·MeOh formed with a newly synthesized tridentate [S,N,P] HL = 2-(diphenylphosphino)benzaldehyde thiosemicarbazone ligand and the crystal structure analysis of the latter have been carried out. An X-ray study of [Cu(HL)2]NO3·MeOH revealed a copper(I) ion coordinated tetrahedrally to S,N,P,P atoms donated by two HL ligands. One is tridentate [S,N,P], whereas the second HL ligand is monodentate, ligating only its phosphorus atom to the copper. The geometry around the four-coordinate Cu(I) is comparable with Cu{N,S,P,X} tetrahedra (X = N, P, or S) retrieved from the Cambridge Structural Database. In addition, with a restriction to Cu{N,P,X,X} (X = C,N,P) tetrahedra ‐ S is excluded ‐ ca. 60 structures against

Unusual coordination mode of thiosemicarbazone ligands. A search for the origin.

Twelve mixed-ligand thiosemicarbazone complexes of ruthenium and osmium, ten of general formula [M(bpy)2(bztsc-R)]ClO4, (M = Ru, Os; bpy = 2,2'-bipyridine, Hbztsc-R = benzaldehyde thiosemicacbazone) and two of type [M(bpy)2(actsc)]ClO4 (Hactsc = acetonethiosemicarbazone), have been synthesized and characterized. All the complexes are diamagnetic (low-spin d6, S = 0) and in acetonitrile solution show several intense metal-to-ligand charge-transfer (MLCT) transitions in the visible region. Structures of Hbztsc-OMe, [Ru(bpy)2(bztsc-NO2)]ClO4 and [Ru(bpy)2(actsc)]ClO4 have been determined by X-ray crystallography. Benzaldehyde thiosemicarbazone exists in the thione form with the phenyl group trans to the hydrazinic nitrogen. The benzaldehyde thiosemicarbazone ligand coordinates to the metals through the hydrazinic nitrogen and sulfur with a bite angle of approximately 67 degrees, forming a four-membered chelate ring. However, the actsc ligand coordinates through the imine nitrogen and sulfur, forming a five-membered chelate ring with a bite angle of approximately 81 degrees. The difference in coordination modes of two types of thiosemicarbazone ligands, viz., bztsc-R and actsc, appears to result from the difference in steric bulk of the aryl and methyl group trans to the hydrazinic nitrogen. In acetronitrile solution they all show a reversible metal(II)-metal(III) oxidation in the range 0.18-0.58 V vs SCE followed by an irreversible oxidation in the range 1.11-1.60 V vs SCE. Two successive one-electron reductions of the coordinated bipyridine are also observed in the range -1.53 to -1.96 V vs SCE.

Photocyclization Reaction of some 2-Methyl-4-phenyl- Substituted Aldehyde Thiosemicarbazones. Mechanistic Aspects

Irradiation of 2-methyl-4-phenyl- substituted benzaldehyde thiosemicarbazones led with good yields to the corresponding Δ 2-1,2,4-triazoline-5-thione derivatives through the formation of stable 1,2,4-triazolidine-5-thione intermediates. The relative quantum yields of photocyclization at 313 nm were analysed by means of the Hammett equation and ρ values determined. We interpreted the results in terms of the mechanism of photocyclization of 2-methyl-4-phenyl-substituted benzaldehyde thiosemicarbazones.

A FACILE ONE STEP SYNTHESIS OF [3-(2-HYDRAZINO-4-THIAZOLYL) COUMARINO] DIMETHYL METHINES AND SOME 3-SUBSTITUTED-7H-6-(6/8,6,8-SUBSTITUTED-3-COUMARINO)-S-TRIAZOLO[3,4-b][1,3,4]THIADIAZINES

Some [3-(2-hydrazino-4-thiazolyl) coumarino]dimethyl methine derivatives (III) have been prepared by the condensation of 3-(2-bromoacetyl)-coumarin and thiosemicarbazide in acetone. These compounds formation was further confirmed by the condensation of acetone thiosemicarbazone (I) and p-N,N-dimethyl amino benzaldehyde thiosemicarbazone (II) with 3-(2-bromoacetyl)coumarin in anhydrous ethanol and dimethyl formamide in a two step process. 3-Substituted-7H-6-(6 or 8 or 6,8-disubstituted 3-coumarino)-s-triazolo[3,4-b] [1,3,4]thiadadiazines (V) have also been prepared from simple condensation of appropriate 4-amino-5-mercapto-1, 2,4-triazole with various 3-(2-bromoacetyl) coumarins in anhydrous ethanol and dimethyl formamide.

Synthesis and characterization of complexes of p-isopropyl benzaldehyde and methyl 2-pyridyl ketone thiosemicarbazones with Zn(II) and Cd(II) metallic centers. Cytotoxic activity and induction of apoptosis in Pam- ras cells

It is known that metallic complexes of methyl 2-pyridyl ketone thiosemicarbazone (HL 1) and p-isopropyl benzaldehyde thiosemicarbazone (HL 2) may have potential antitumor activity. We have prepared complexes of HL 1 and HL 2 with Zn(II) and Cd(II). The cytotoxic activity shown by these compounds against cell lines sensitive and resistant to cis-diamminedichloroplatinum(II) ( cis-DDP) indicates that coupling of HL 1 and HL 2 to Zn(II) and Cd(II) centers may result in metallic complexes with important biological properties since they display IC 50 values in a μM range similar to that of the antitumor drug cis-DDP. Moreover, it is interesting to note that the Zn/HL 2 complex exhibits specific cytotoxic activity against Pam- ras cells ( cis-DDP resistant cells which overexpress the H- ras oncogene) with an in vitro therapeutic index of 3.26 versus 0.78 for cis-DDP. Treatment of Pam- ras cells with the IC 50 value of the Zn/HL 2 compound induces a ‘DNA ladder’ (fragmentation of genomic DNA in nucleosome units) indicative of apoptosis in this ras-transformed cell line. In contrast, a ‘DNA smear' (non-specific fragmentation of genomic DNA) is observed in Pam 212 normal cells treated with the IC 50 of this compound. The analysis by circular dichroism (CD) spectroscopy of the interaction of the Zn/HL 2 compound with calf thymus DNA (CT DNA) indicates that it produces stronger alterations on the double helix conformation than cis-DDP. So, these results suggest that Zn/HL 2 may be considered a potential antitumor agent.

Unusual Coordination Mode of Thiosemicarbazone Ligand. Synthesis, Structure, and Redox Properties of Some Ruthenium and Osmium Complexes

Reaction of benzaldehyde thiosemicarbazone (HL-R, 1) with [M(PPh3)3X2] (M = Ru, Os; X = Cl, Br) in ethanol affords complexes of the type [M(PPh3)2(L-R)2] (2), where the L-R ligand is coordinated as...

Palladium(II) complexes containing a P, N chelating ligand Part II. Synthesis and characterisation of complexes with different hydrazinic ligands. Catalytic activity in the hydrogenation of double and triple C-C bonds

Abstract Palladium(II) complexes of the type Pd(PNO)Y (PNO = 2-(diphenylphosphino)benzaldehyde picolinhydrazone, nicotinhydrazone, isonicotinhydrazone; Y = CH3CO2, Cl, I) and Pd(PNS)Y (PNS = 2-(diphenylphosphino)benzaldehyde thiosemicarbazone; Y = CH3CO2, Cl, I) were synthesised and characterised by spectroscopic methods. The X-ray structure of an iodo complex was also determined. The catalytic activity of all the complexes in the homogeneous hydrogenation of terminal double and triple bonds was tested with particular regards to the chemoselectivity from triple to double bond. A correlation between the catalytic activity and the nature of the ligand and Y group was established. In the hydrogenation of phenylacetylene using acetato complexes as catalysts, stable phenylethynylpalladium(II) complexes were recovered and characterised by spectroscopic methods. A facile route of synthesis of alkynyl complexes was also determined.

Synthesis, Characterisation, Electrochemistry and Biological Activity of Ruthenium(III) Complexes Containing N.S Donor Ligands and Triphenylphosphine or Triphenylarsine

Several new hexa-coordinated low-spin d5 ruthenium(III) complexes of the type [RuX2(TSC)(EPh3)2] (where X = Cl or Br; H-TSC = benzaldehyde thiosemicarbazone, cinnamaldehyde thiosemicarbazone, thiophene-2-carboxaldehyde thiosemicarbazone and 2-furaldehyde thiosemicarbazone, E = P or As) have been synthesised by the reactions of [RuX3(EPh3)3] or [RuBr3(PPh3)2(MeOH)] with the various thiosemicarbazones. All the new complexes were characterised using various physico-chemical methods such as elemental analysis, spectral (IR, UV-VIS, EPR), magnetic moment and cyclic voltammetry data. In all these complexes, the thiosemicarbazones are bonded to the central ruthenium ion through the thiolato sulphur, after deprotonation, and the azomethine nitrogen. The antibacterial activity of some of the ligands and their complexes were also tested against two species of bacteria. Referee I: M. J. Clarke Referee II: M. B. Sponsler

The Crystal and Molecular Structure of Benzaldehyde Thiosemicarbazone

The Crystal and Molecular Structure of Benzaldehyde Thiosemicarbazone

TRANSITION METAL COMPLEXES WITH THIOSEMICARBAZIDE-BASED LIGANDS. PART 28. SYNTHESIS AND X-RAY CRYSTAL STRUCTURE OF THE FIRST PHOSPHORUS-BONDED THIOSEMICARBAZIDE COMPLEX: [2-(DIPHENYLPHOSPHINO) BENZALDEHYDE THIOSEMICARBAZONATO(1-)] PYRIDINENICKEL(II)-NITRATE

Abstract The synthesis and crystal structure analysis of the diamagnetic complex [Ni(L)Py]NO3 (L = the monoanion of the newly synthesized ligand 2-(diphenylphosphino)benzaldehyde thiosemicarbazone) are reported. The complex crystallizes in the space group P21/n (No. 14) with a = 8.533(1), b = 29.123(3), c = 10.627(a) A, β = 100.36(1)°, V = 2597.8(5) A3. As revealed by X-ray analysis, the 2-(diphenylphosphino)benzaldehyde thiosemicarbazone ligand deprotonated at N(3) acts as a monoanionic tridentate donor, coordinating through SNP. The core of the bulky {Ni[(C6H5)2P-(C6H4CH=N-N=CS-NH2)·]}+ cation is a slightly puckered quadrangle formed around Ni2+ by SNP accompanied by a pyridine nitrogen. The dihedral angle of the atomic triangles S/N(4)/N(41) and P(2)/N(4)/N(41) is 18.0(4)°. The NO3 − anions are well separated from the cations which may account for the observed disorder of the oxygen atoms.

5-Phenyl-1,3,4-thiadiazole and 5-phenyl-1,2,4-triazoline-3-thione as products of dehydrogenation of cyclic tautomeric forms of benzaldehyde thiosemicarbazone

5-Pkenyl-1,3,4-thiadiazole and 5-phenyl-1,4-triazoline-3-thione are produced from heterocyclic tautomeric forms of benzaldehyde thiosemicarbazone in the gas phase under conditions existing in a mass spectrometer, and also in the solid phase in the course of thermolysis.

Spectrophotometric Determination of Palladium(II) Using 4-(Dimethylamino)benzaldehyde Thiosemicarbazone

Abstract A simple, rapid, and selective spectrophotometric method is proposed for the determination of palladium(II), using 4-(dimethylamino)benzaldehyde thiosemicarbazone (DMABT) as a spectrophotometric reagent. The reagent forms a 1 : 2 complex (Pd : Reagent) with Pd(II) in the pH range 2.2—3.6. The complex is soluble in aqueous solution containing 20% acetone and 30% ethanol by volume. Beer’s law is valid upto 2.3 ppm of palladium. The molar absorptivity is 4.59 × 104 dm3 mol−1 cm−1 and Sandell’s sensitivity 2.33 × 10−3 μg cm−2. The method tolerates large number of cations and anions.

Kinetics and mechanisms of oxidation of thiosemicarbazide, its metal complex and hydrazones byN-chlorobenzamide in water methanol medium

The kinetics of oxidation of thiosemicarbazide (TSC) its zinc metal complex and hydrazones by N-chlorobenzamide (NCB) were investigated in water methanol (1 : 1, v/v) medium in the presence of perchloric acid. The hydrazones studied were benzaldehyde, propionaldehyde, acetone and acetophenone thiosemicarbazones. The reactions show first-order kinetics in [NCB], a fractional order dependence in [substrate] and an inverse fractional to inverse first order in [H+]. Addition of benzamide has no significant effect on the rates of oxidations. Variation in the ionic strength of the medium has little effect on the rates of reactions, but a decrease in the dielectric constant of the medium by increasing the methanol concentration in the solvent increases the rates. The rate-limiting steps were identified in all cases and the rate coefficients of these steps and the related activation parameters were also evaluated. The consistency of the deduced rate laws was checked by recalculating the rate constants as the substrate and H+ concentrations were varied.

Electrolytically generated manganese(III) sulphate as a redox titrant: potentiometric determination of thiosemicarbazide, its metal complexes and thiosemicarbazones

Conditions have been established for the electrogeneration of MnIII from MnII in a sulphuric acid medium. The MnIII formed was identified and characterized by ultraviolet spectra. The stability of standard solutions of manganese(III) sulphate at various concentrations of H+, MnII and acetic acid and in the presence of the complexing agents P2O74–, Cl– and F– was studied and conditions for the potentiometric determination of thiosemicarbazide (TSC), its metal complexes, M(TSC)2SO4, and its thiosemicarbazone derivatives, propanal thiosemicarbazone (PTSC) and benzaldehyde thiosemicarbazone (BTSC), have been investigated. Thiosemicarbazide in H2SO4 underwent a six-electron oxidation. The M(TSC)2SO4 complex participates in a 12-electron redox process, indicative of the number of TSC ligands present in the complex. The PTSC in an H2SO4–HOAc (20% v/v) medium underwent oxidation in two stages, namely, six-electron oxidation of TSC with the regeneration of propionaldehyde and two-electron oxidation of the aldehyde to the corresponding carboxylic acid. The benzaldehyde regenerated from BTSC did not undergo further oxidation. Above 40% HOAc, a reproducible four-electron stoichiometry was achieved thereby showing the selectivity of MnIII as an oxidizing agent. The formal redox potential of the MnIII–MnII couple with and without the complexing agents and at various concentrations of H+ was determined. Addition of complexing agents decreased the formal redox potential of the MnIII–MnII couple, thereby reducing the oxidation rate, but did not alter the over-all stoichiometry of the electron transfer process.

Mechanism of oxidations in partially aqueous media: Kinetics of oxidation of thiosemicarbazide and thiosemicarbazone by chloramine‐T and dichloramine‐T in aqueous methanol

AbstractKinetics of oxidation of thiosemicarbazide (TSC) and its hydrazone (Benzaldehyde thiosemicarbazone) by chloramine‐T (CAT) and dichloramine‐T (DCT) in aqueous methanol medium in the presence of perchloric acid has been studied. Oxidation of TSC by both the oxidants showed first order dependences in [oxidant], fractional order in [TSC] and nearly inverse first order in [H+]. The conversion of TSC into its benzaldehyde hydrazone changed the rate dependence in [CAT] from first to second order, while the dependence in [DCT] remained unchanged. The dependence in [TSC] changes from fractional order to zero order in both CAT and DCT oxidations. The rate followed inverse fractional order kinetics in [H+] in both the cases. Increase in ionic strength of the medium slightly decreased the rate, while the decrease in dielectric constant of the medium increased the rates of oxidations for both the oxidants. But the addition of reaction products, p‐toluenesulphonamide and chloride had no effect on the rate. Oxidation of TSC with both the oxidants has been shown to follow Michaelis‐Menten type mechanism. In hydrazone oxidations oxidants have been shown to disproportionate in slow steps to HOCl, which in turn attacks the substrate in fast steps to give the final products. [TSC] was varied at different temperatures and the constants of rate limiting steps were calculated at each temperature. Using the latter constants the activation parameters have been computed from the Arrhenius plots. The rate constants have been predicted from the rate law for the variation of [H+] at constant [TSC] and [oxidant]. The predicted values are in reasonable agreement with the experimental rate constants, providing additional support to the suggested mechanisms.

Crystal and molecular structure of 4-(N,N-dimethylamino) benzaldehyde thiosemicarbazone

4-(N,N-Dimethylamino)benzaldehyde thiosemicarbazone, C10H14N4S, has been prepared. The crystal structure has been determined from X-ray diffractometer data byMultan 78. The crystals are triclinic:P¯1,a=8.532(1),b=9.391(1),c=15.592(4) A,α=73.81(2),β=79.59(2), γ=82.85(2)°,Z=4, finalR=0.033 for 2198 observed reflections. Atomic charge densities have been calculated by the CNDO/2 method. The S and hydrazinic N atoms in both molecules in the asymmetric unit are in thetrans configuration. The crystal structure is stabilized by N-H⋯S hydrogen bonds. The net negative charge on the hydrazinic N atom, calculated by the CNDO/2 method, is decreased as compared to those in some 4-phenylthiosemicarbazide derivatives.

TELLURIUM(II)-THIOSEMICARBAZONE COMPLEXES‐A PARALLEL TO THE LIGATION OF THIOUREAS

Abstract The tellurium(II)-complexes of the type Te(XTSC)2Cl2 (I) and Te(XTSC)4Cl2 (II), where XTSC=benzaldehyde, acetophenone, salicylaldehyde or 2-hydroxyacetophenone thiosemicarbazone have been isolated. The IR, PMR and CMR spectra of the complexes in conjunction with their elemental analyses and conductance measurements, indicate the formation of a three centre-four electron bond between tellurium and two sulphur atoms of the thiosemicarbazones, trans to each other. These results exhibit for the first time that thiosemicarbazones may ligate with tellurium(II) in a manner parallel to that of thioureas. The square planar and octahedral arrangement of the ligands around tellurium are proposed for I and II type complexes respectively.