Thiol Tautomer Research Articles

Formation of thiophenethiols by flash vacuum pyrolysis of 1,6,6aλ4-trithiapentalenes

R. Flammang, M. Barbieux-Flammang, P. Gerbaux and C. Th. Pedersen, J. Chem. Soc., Perkin Trans. 2, 1997, 1261 DOI: 10.1039/A700502D

Crystal structures, spectroscopic and nonlinear optical properties of metal complexes of Schiff-base ligands containing nitrogen and sulfur donors

ML2 type CuII chelates with the Schiff base ligands R-C6H4CHNNHC(S)SCH2Ph (R=NMe2 or -OMe) have been prepared and characterized. Spectroscopic data suggest that the Schiff bases act as singly charged anionic bidentate ligands, forming stable neutral metal complexes. Magnetic and e.s.r. data support a square-planar coordination geometry for both complexes. Single crystal X-ray diffraction analysis of the complexes has established that the Schiff base ligand is deprotonated to give the thiol tautomer, coordinated via the thiolato sulfur and β-nitrogen. The geometry around the metal is square-planar with two equivalent Cu-N and Cu-S bonds; the two phenyl rings and the donor atoms are in one plane forming an extensive electronic delocalization system. Third-order optical nonlinearity measurements show that the complexes exhibit fairly large second-order hyperpolarizabilities.

Preparation and characterization of metal complexes containing a NS donor ligand derived from S-benzyldithiocarbazate and p-nitrobenzaldehyde. X-ray crystal structure of the nickel(II) chelate

A series of metal (Cu, Ni, Zn, Cd and Pd) complexes of a Schiff base ligand derived from S-benzyldithiocarbazate and p-nitrobenzaldehyde were prepared and characterized. The Schiff base acts as a single negatively-charged bidentate ligand forming stable neutral metal complexes. Magnetic and spectroscopic data suggest a square planar structure for the CuII, NiII and PdII chelates. Single X-ray diffraction analysis of the NiII chelate established that the Schiff base loses a proton from its tautomeric thiol form and coordinates to the metal via the thiolato sulfur and β-nitrogen. The geometry around NiII is square planar with two equivalent Ni-N and Ni-S bonds; the two nitrobenzyl rings and the coordination plane are almost isoplanar, giving a delocalized electronic system.

CRYSTAL STRUCTURE AND SPECTROSCOPIC STUDIES OF A NICKEL(II) COMPLEX OF A LIGAND CONTAINING NITROGEN-SULPHUR DONORS

Abstract A bis-ligand neutral Ni(II) complex of a Schiff base ligand derived from S-benzyldithiocarbazate and p-dimethylaminobenzyldehyde was prepared and characterized. Single crystal X-ray diffraction analysis of the nickel(II) chelate established that the Schiff base loses a proton from its tautomeric thiol form and coordinates to Ni(II) via the mercapto sulphur and β-nitrogen atoms. The geometry of the Ni(II) ion is square-planar with two equivalent Ni-N and Ni-S bonds; the two dimethylaminobenzyl rings and the coordinated plane are almost in one plane, forming an electronic delocalization system. When the complex crystallizes, benzene molecules are included in the crystal. However, there is no obvious interaction between the complex molecule and the benzene molecule. Magnetic and spectroscopic data support the square-planar structure found in the structure analysis. The complex crystallizes in the triclinic space group P1 with cell parameters a = 7.839(2), b = 10.528(4), c = 10.832(5) Å, α = 100.61(2), β = 92.39(2), γ = 93.99(2)° and Z = 1. The structure was refined by full-matrix least-squares to R = 0.050 and Rw = 0.064, with 2955 reflections having I>3[sgrave](I).

Thione-disulfide interchange of some heterocyclic tautomeric thiones and their symmetrical disulfides

The UV/Vis spectroscopic properties of some symmetrical disulfides derived from potentially tautomeric thiones are investigated. Reversed thione-disulfide transformation is observed, and the influence of several factors including the nature of solvent, concentration, and UV irradiation, is studied. Possible implication of the tautomeric thiol form and the importance of this thione-disulfide redox system in biological aspects is suggested. A general scheme including monomer-dimer equilibrium, thione-thiol tautomeric equilibrium, and reversible thiol-disulfide redox behaviour is proposed in order to explain the factors affecting the overall thione-disulfide transformation.

Photochemistry of the Nonspecific Hydroxyl Radical Generator,N-Hydroxypyridine-2(1H)-thione

The photochemistry of N-hydroxypyridine-2(1H)-thione (N-HPT) has been investigated in aqueous and organic solvents using laser flash photolysis (λexc = 308 or 355 nm). Independent of the environment, UV excitation of N-HPT causes homolytic N−O bond cleavage, which leads to formation of the 2-pyridylthiyl (PyS•) and hydroxyl (•OH) radicals. In aqueous media, this process occurs efficiently from both the anionic and neutral forms (ΦN-O ≈ 0.20−0.30). In addition to N−O bond scission, N-HPT undergoes other primary photoprocesses which are pH-dependent. At pH = 7, photoionization (Φe− = 0.09 (λexc = 308 nm) and 0.05 (λexc = 355 nm)) of the anionic form generates the hydrated electron as well as the semioxidized radical of N-HPT. Fast rearrangement of the latter species produces the N-oxy-2-pyridylthiyl radical. At pH = 2, where the uncharged structure predominates, formation of an excited triplet state (ET ≥ 59.5 kcal mol-1) is observed (ΦT ≥ 0.05 using λexc = 355 nm) but photoionization does not take place. The neutral form of N-HPT displays similar photochemical behavior in organic solvents, generating •OH, PyS•, and the triplet state (ΦN-O = 0.30−0.45 and ΦT = 0.03−0.05 using λexc = 355 nm). In nonpolar, aprotic media, the subsequent reaction of PyS• with the thiol tautomer of N-HPT leads to the formation of an unsymmetric disulfide radical. Reactivities of the different transient species toward potential scavengers have also been investigated. The results obtained show that the simultaneous generation of several highly reactive intermediates is a major drawback in the use of N-HPT as a clean and simple photolytic source of •OH.

The occurrence of both amide and thiolate forms of the benzoxazole-2-thionate anion (C7H4ONS–) in the same molecule: synthesis and crystal structure of C7H4ONSNa[µ-OP(NMe2)3]3NaC7H4ONS

The reaction of benzoxazole-2(1H)-thione (C7H5ONS) with either solid NaOH or NaH, in toluene solution, in the presence of hexamethylphosphoramide (hmpa), afforded the new complex C7H4ONSNa(µ-hmpa)3NaC7H4ONS 1 in good yield. In contrast to similar lithium and calcium complexes, 1 resists the incorporation of water into the metal co-ordination sphere. Characterisation by single-crystal X-ray diffraction revealed that, in the solid state, complex 1 is dimeric through three bridging hmpa ligands. This dimer is unsymmetrically co-ordinated by C7H4ONS– anions, one metal centre being co-ordinated by a N,S-chelated anion formally derived from the thiol tautomer, the other being co-ordinated only through N of an anion formally derived from the amine tautomer of benzoxazole-2(1H)-thione. In addition to these unusual structural features, the dimeric complex 1 is further associated by weak C–H ⋯ O and C–H ⋯ S hydrogen bonding interactions.

Ab initio SCRF study of the tautomeric equilibrium of 2-thiopyrimidine

Ab initio SCRF calculations have been carried out for the prototropic tautomerism of 2-thiopyrimidine (2TP) in gas phase and in solution. In the gas phase the thiol tautomer is the more stable species in keeping with the reported IR spectra in isolated matrices. In polar solvents the thione tautomer becomes more stabilized. The calculated tautomerism free energy changes for 2TP in the gas phase, cyclohexene dimethylsulfoxide and water are 8.165, 5.906, −5.513 and −5.829 kcal/mol, respectively.

A dihydrogen complex, [Os(η2-H2)(CO)(quS)(PPh3)2]+, in equilibrium with its coordinated thiol tautomer (quS = quinoline-8-thiolate)

The mixture of two isomers of the new complex Os(H)(CO)(quS)(PPh3)23 reacts with HBF4·Et2O at –80 °C to form the complexes [Os(η2-H2)(CO)(quS)(PPh3)2]+, with dihydrogen trans to sulfur 4a or nitrogen 4b along with tautomeric thiol complexes [Os(H)(CO)(quSH)(PPh3)2]+4c,d; the tautomeric equilibria shift with temperature.

Mise en Evidence des Tautomeres Enethioliques des Mercaptopyridines en Spectrometrie de Masse

AbstractEquimolar mixtures of HS‐Py (Py=pyridine) and DS‐Py show primary isotope effects upon metastable ions for the CS loss. This is valid for the 3‐ and 4‐ isomers and this observation implies that thiol forms exist in the gaz phase. This result is also confirmed by the analogy in isotope effects between molecular ions of H(D)S‐Py and the daughter ones, generated by a four centered elimination of C2H4 and C2D4 respectively from Py‐S‐C2H5 and Py‐S‐C2D5. The insensibility of the CS loss following deuteriation of the 2‐isomer does not exclude the presence of the thiol tautomer: this phenomenon is explained by and ortho effect exerted by the pyridinic nitrogen.

Polyhalogeno-aromatic compounds. Part XXXIII. Structures of polyhalogenopyridine-2(and 4)-thiols, polyhalogenopyridin-2(and 4)-ols, and their N- and S(or O)-methyl derivatives

Comparative u.v. studies of tetrachloropyridine-2-thiol and its N- and S-methyl derivatives in methanol show that the thiol exists predominantly as the thiol tautomer, while tetrachloropyridin-2-ol and 3,5-dichloro-2,4-difluoropyridin-6-ol exist predominantly in the enol form in methanol. U.v. data are given also for a number of polyhalogeno-pyridine-4-thiols and -pyridin-4-ols and their S- or O-methyl derivatives. Chemical shift values for the methyl protons in N- and S(or O)-methyl derivatives of polyhalogeno-pyridinethiols or -pyridinols allow them to be distinguished. Mass spectroscopic data are reported.

The dual reactivity of 3-aminorhodanine

3-Aminorhodanine in ethanol reacts in the hydrazine form with aromatic aldehydes to give 3′-arylidene derivatives, while in ammonia it reacts in the tautomeric thiol form to give 5-arylidene derivatives. 3′, 5-Diarylidene derivatives of 3-aminorhodanine can be obtained by reacting aromatic aldehydes with 3′ -aminorhodanine in glacial acetic acid, with 3-arylideneminorhodanines in ammonia solution, or with 5-aryliden-3-aminorhodanines in ethanol.

CONTRIBUTION TO THE INFRARED SPECTRA OF ORGANOSULPHUR COMPOUNDS

Infrared spectra of various types of organosulphur compounds have been examined and group frequencies arising from G—S, S—S, N—S, O—S, and C=S stretching vibrations have been assigned and discussed. The C—S bands of thioketals and S—S bands of tri- and tetra-sulphides show splittings due to vibrational coupling. The O—S and N—S stretching frequencies are found around 890 and 820 cm−1 respectively, values which are much higher than the C—S stretching frequencies. Potassium alkyl xanthates exhibit the asymmetric and symmetric stretching frequencies of the CS2− ion. The splitting of C—O and C=S stretching bands in dialkyl dixanthogens have been interpreted in terms of the Fermi interaction with the combination tone of C—S and S—S stretching vibrations and with the overtone of S—S stretching vibrations respectively. The relative intensity of the C=S stretching bands in a few derivatives show marked dependence on the electronegativities of the elements directly linked to the thiocarbonyl group. It is found that the earlier assignments of the "[Formula: see text] bands" due to mixed vibrations in thioamide type derivatives have been found to be well justified on the basis of the recent normal coordinate treatment. Another band tentatively designated as the "[Formula: see text] IV band" has been assigned for these derivatives in the region 850–680 cm−1. Examination of the spectra of a number of thioamide type derivatives has shown no evidence for the presence of thiol tautomers. All of them exist as thiones exhibiting characteristic N—H absorption and "[Formula: see text] bands".

THE PREPARATION OF SOME THIOSEMICARBAZONES AND THEIR COPPER COMPLEXES: PART III

Reactions of some diketones with thiosemicarbazide have been studied under various conditions. Monothiosemicarbazones, dithiosemicarbazones, and cyclization products can be obtained. It was found that dithiosemicarbazones form 1:1 complexes with Cu(II) but failed to react with Cu(I). Dithiosemicarbazones in which the N2-hydrogen atom has been replaced by Me do not form complexes, confirming our views about the importance of this hydrogen atom in the thione ↔ thiol tautomerism necessary for complex formation. 4,4-Dimethyldithiosemicarbazones behave like the unsubstituted parent compounds in forming 1:1 complexes with Cu(II). Infrared spectra provide evidence for the structure of a cyclization product, 5,6-diphenyl-3-thio-1,2,4-triazine, which had been erroneously described by various authors as the thiol tautomer, 5,6-diphenyl-3-mercapto-1,2,4-triazine.