Alkali-metal-intercalated transition metal disulfides: A thermodynamic model

In the lithium-intercalated disulfides, Li_xMS₂, where M = Ti, Ta, a nearly linear compositional variation of the lithium chemical potential is observed throughout the composition range 0 < x < 1.0. For most sodium-intercalated disulfides, chemical potential plateaus are observed between regions exhibiting linear variations of sodium chemical potential. Our thermodynamic model indicates that the two most important factors which determine the compositional variation of the alkali metal chemical potential are the interaction energy between intercalated alkali-metal atoms and the compositional variation of the electron chemical potential. Although these two factors determine the compositional variation of chemical potential in single-phase regions, the existence of two-phase regions in the concentration range x = 0?0.15 are influenced by the energy required to expand the interlayer gap and the configurational entropy.     

Group 4 metal initiators for the controlled stereoselective polymerization of lactide monomers

Group 4 metal initiators with a tetradentate bis(phenolato) ligand polymerized meso-lactide efficiently under ring-opening to give syndiotactic polylactide. L-Lactide was converted faster than rac-lactide and meso-lactide.     

2-(2-Hydroxy-4-methoxybenzoyl)benzoic acid derivatives of Group 4 metal alkoxides

Continued exploration of the coordination behavior of derivatives of 2-benzophenone-based ligands with metal alkoxides ([M(OR)₄]) was undertaken from the reaction of 2-(2-hydroxy-4-methoxybenzoyl)benzoic acid (H₂-OBzA) with a series of Group 4 precursors. The products of these reactions were identified as: [(OR)₂Ti(μ-(c,c-OBzA))]₂ (OR?=?OCHMe₂ (OPrⁱ; 1 ?2tol); OCMe₃ (OBu^t; 2 ?THF); OCH₂CMe₃ (ONep; 3)), [[(OPrⁱ)₃Ti(μ-OPrⁱ)Ti(OPrⁱ)₂]₂(μ-(μ_c,μ-OBzA))₂]₂ (4), [(ONep)₃Zr(μ-ONep)₂Zr(ONep)₂]₂(μ-(c,μ-OBzA)₂) (5 ?tol), [(py)(OBu^t)₃Zr]₂(μ-(c,c-OBzA)) (6), [(OBu^t)₂Hf(μ-OBu^t)]₂(μ-(c,η¹-OBzA)) (7) where ‘c’?=?chelating or η²; ‘μ’?=?bridging or η¹,η¹(O,O’); and μ_c?=?bridging chelating or η¹,η¹(O,O’); η^2?:?η¹. The metal centers for each of these compounds adopt a pseudo-octahedral geometry employing the OBzA ligand in numerous binding modes. The different functional oxygens (carboxylate, hydroxyl, and carbonyl) were employed in a variety of coordination modes for 1–7. The complexity of these OBzA-modified compounds is driven by a combination of the coordination behavior of the OBzA moieties, the size of the metal cation, and the pendant chain of the OR ligand. Solution NMR indicates a complex structure exists in solution that was considered to be consistent with the solid-state structure.     

Magnetic properties of ammonia intercalates of some IV B and V B transition metal disulfides

Intercalates 3RVS₂NH₃ and 3RTaS₂NH₃, isostructural with 3RTiS₂NH₃, are described for the first time. Magnetic properties of 3RTiS₂NH₃, 3RVS₂NH₃, and 2HTaS₂NH₃ respectively are interpreted in terms of a charge transfer (in agreement with an ionic model) from the intercalant to the lowest conduction band which consists mainly ofe_g, a_1g anda′₁ transition metald states.     

Phosphorescence of Group IVB metal complexes

Russian Chemical Bulletin -     

Well-defined single-site thiobis(phenolate) Group 4 metal catalysts for heterogeneous olefin polymerization

The tridentate (OSO-function) thiobis(phenolate) ligand derived from 2,2′-thiobis[4-(1,1,3,3-tetramethylbutyl)phenol] (tbopH₂) is an alternative to the cyclopentadienyl ancillary group for Group 4 heterogeneous olefin polymerization. The tbop ligand placed on titanium, zirconium and hafnium forms a wide family of homoleptic compounds as well as heteroleptic alkoxo- and aryloxo-bridged complexes modified with coligands like chlorides, imides, and monoaryloxides. Among these heteroleptic titanium complexes when activated with cocatalysts and supported on MgCl₂ are highly effective heterogeneous, well-defined, single-site ethene polymerization catalysts. The active centres of these catalysts consist of Ti(III) species with the alkyl group and the sulfur atom of the tbop ligand coordinated in axial positions. Titanium, zirconium and hafnium systems both heteroleptic and homoleptic show moderate activity in 1-hexene polymerization producing atactic poly(1-hexenes).     

Unsymmetrical fluorine-containing disulfides

Russian Chemical Bulletin -     

Isomerization of β-halo disulfides (alkyl 2-haloethyl disulfides)

The methyl ester, amide, dimethylamide, and anilide of -methylthioglycidic acid are readily cleaved by methane and acetylsulfenyl chlorides to give mixtures of the corresponding isomeric cleavage products — vicinal chlorodithio derivatives of isobutyric acid. It is shown that the ratio of isomers obtained depends both on the character of the substituent in the carboxyl group of the isobutyric acid and on the character of the substituent attached to the sulfur atom in the sulfenyl chloride (sulfomonochloride) used. It was found that -halo disulfides, like -halo sulfides, are capable of isomerization.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 8–12, January, 1973.     

Dithia-crown-annelated tetrathiafulvalene disulfides: synthesis, electrochemistry, self-assembled films, and metal ion recognition

The synthesis and electrochemistry of a series of tetrathiafulvalene (TTF) and dithia-crown-TTF derivatives attached with one or two disulfide group(s) 7a-f are reported. The self-assembled monolayers (SAMs) of these TTF disulfides on gold were prepared and characterized by reflection-absorption infrared spectroscopy. The SAMs are extremely stable under a wide variety of conditions and over extended periods of time and show remarkable electrochemical stability upon repeated potential scans. SAMs of the crown-TTF disulfides 7c,d,f can recognize alkali metal ions, and the process can be monitored following the electrochemical potential shift of the surface-confined TTF group.     

Synthesis and structural characterization of sulfonates, phosphinates and carboxylates of organometallic Group 4 metal fluorides

Reaction of [Cp^*TiF₃] (Cp^* = (ν⁵-C₅Me₅)) with Me₃SiOSO₂- p-C₆H₄CH₃, Me₃SiOPOPh₂ and 1,2-(Me₃SiOCO)₂C₆H₄ yields the dinuclear complexes [{Cp^*TiF(μ-F)(μ-OSO₂-p-C₆H₄CH₄)}₂] (1), [{Cp^*TiF(μ-F)(μ-OPOPh₂)}₂] (2) and [{Cp^*TiF(μ-F)(μ-OCO-o-C₆H₄CO₂SiMe₃)}₂] (3). The molecular structures of 1 and 2 have been determined by single-crystal X-ray analysis. In complexes 1-3, the two titanium atoms are connected by bridging fluorine atoms as well as bridging sulfonate, phosphinate and carboxylate groups respectively. Each titanium atom is also bonded to a terminal fluorine atom. Reaction of [Cp₂^*ZrF₂] with 1,2-(Me₃SiOCO)₂C₆H₄ leads to the mononuclear pentacoordinate 18-electron species [Cp₂^*ZrF(μ-OCO-o-C₆H₄CO₂SiMe₃)] (4) and its structure was determined by X-ray crystallographic methods.     

On the capabilities of the x-ray diffraction method in determining polytypes in nanostructured layered metal disulfides

By the example of multilayer MoS₂ nanotubes the capabilities of the X-ray diffraction method in determining possible polytypic forms of layered metal dichalcogenides, which may appear due to the nanostructuring of these compounds, are discussed. The conclusion about a low information value of the X-ray diffraction method is drawn, therefore the experimental analysis of the polytypic composition of nanostructures of metal dichalcogenides needs to attract electron microscopy and electronoй tomography methods.     

Group 4 metal silylidenes and germylidenes: towards the silicon and germanium variations of olefin metathesis

The current progress in the field of the stable Schrock-type silylidenes and germylidenes of the group 4 metals, along with their prospective use in the development of the silicon or germanium variations of olefin metathesis, is briefly overviewed in this focus article.     

Bond-selective photodissociation of aliphatic disulfides

The photochemistry of aliphatic disulfides is presented. The photolysis products are photoionized with coherent vacuum ultraviolet radiation and analyzed by time-of-flight mass spectrometry. With 248-nm excitation, the predominant dissociation pathway is S—S bond cleavage. With 193-nm excitation, S—S bond cleavage, C—S bond cleavage, and molecular rearrangements are all observed as primary processes. The branching ratio for S—S bond cleavage relative to C—S bond cleavage is typically 1–2 orders of magnitude greater at 248 run than 193 run. This wavelength dependence cannot be explained readily by photodissociation from the ground electronic state. The ground state S—S bond energy, ～ 280 kJ/mol, is much larger than the C—S bond energy, ～ 235 kJ/mol. If dissociation occurred from the ground state, higher wavelength radiation would be expected to favor the lower energy process, but the opposite effect is observed. Thus, excited state photochemistry is indicated. These results are discussed with respect to the differences between low and high energy collision-induced dissociation of peptides that contain disulfide linkages and to the possibility of achieving bond-selective photodissociation of such ions.     

Geminal conjugation in disulfides

Some aspects of the spatial and electronic structure of disulfides XSSX (X = H, Alk, Ph, Hal) are considered. It is shown that the growth of the geminal n_s-σ_SX* conjugation efficiency leads to a shortening of the SS bond that is more than three times as large as the simultaneous SX bond lengthening. The positive effective charge on the sulfur atom also increases as a result of this conjugation. These effects increase with the growth of - I and + M abilities of the substituents X. The SK_a line shifts and the HOMO bonding degree (Delta;n_S) have been measured by the X-ray fluorescence spectroscopy method for dialkyl disulfides (Alk = Me, Et, Pr, i-Pr, Bu, i-Bu, t-Bu, C₅H₁₁, C₈H₁₇, H₂NCH₂CH₂, CH₂CH  CH₂, CH₂Ph) and S₈. With the help of Δn_S values that are proportional to the n_S–σ_SC* conjugation efficiency, the sequence of the enhancement of the geminal conjugation efficiency has been established for the disulfides investigated. In the framework of the n_S–σ_SS* geminal conjugations, the shortening of the SS bonds in S₈ is explained. © John Wiley & Sons, Inc.     

Electrodeposition of ferrocenoyl peptide disulfides

Using electrodeposition of cyclic and acyclic Fc-peptide disulfides tightly-packed Fc-peptide monolayers were conveniently formed, which exhibit significant differences in their electron transfer kinetics.     

Catalytic conversions of dialkyl disulfides

The results of the studies of catalytic conversions of lower dialkyl disulfides performed at the Boreskov Institute of Catalysis (Siberian Branch, Russian Academy of Sciences) are summarized. The selective hydrogenolysis of dimethyl and diethyl disulfides with the formation of alkanethiols occurs in a hydrogen medium on transition metal sulfides. Dimethyl disulfide turns into dimethyl sulfide in an inert gas medium on oxide catalysts with acid and basic sites on their surface. Lower dialkyl disulfides are dehydrocyclized to thiophene under the action of sulfide catalysts. In an oxygen medium on the metal oxides and salts, diethyl disulfide and a lower disulfide concentrate are selectively oxidized to form alkanethiolsulfinates, alkanethiolsulfonates, and alkanesulfonic acids.