Hypervalent Tellurium Research Articles

Cationic Hypervalent Chalcogen Bond Catalysis on the Povarov Reaction: Reactivity and Stereoselectivity.

Chalcogen bond catalysis, particularly cationic hypervalent chalcogen bond catalysis, is considered to be an effective strategy for organocatalysis. In this work, the cationic hypervalent chalcogen bond catalysis for the Povarov reaction between N-benzylideneaniline and ethyl vinyl ether was investigated by density functional theory (DFT). The catalytic reaction involves the cycloaddition process and the proton transfer process, and the rate-determining step is the cycloaddition process. Cationic hypervalent tellurium derivatives bearing CF3 and F groups exhibit superior catalytic activity. For the rate-determining step, the Gibbs free energy barrier decreases as the positive electrostatic potential of the chalcogen bond catalysts increases. More importantly, the Gibbs free energy barrier has a strong linear correlation with the electrostatic energy of the chalcogen bond in the catalyst-substrate complex. Furthermore, the catalytic reactions include the endo pathway and exo pathway. The C-H⋅⋅⋅π interaction between the substituent of the ethyl vinyl ether and the aryl ring of the N-benzylideneaniline contributes to the endo-selectivity of the reaction. This research contributes to a deeper understanding of chalcogen bond catalysis, providing insights for designing chalcogen bond catalysts with high performance.

Anodic Carboxylation and Sulfonylation of Organotellurium Compounds. Electrochemical Synthesis of Hypervalent Tellurium Compounds Bearing Te–O Bonds

Anodic oxidation of PhTeR (R = CF3CH2, CF2H, Me, Ph) was carried out in methanol containing various supporting electrolytes (YO− M+) such as p-tosylate, benzenesulfonate, acetate, and benzoate salts using a divided cell to provide the corresponding hypervalent tellurium compounds such as monomeric PhRTe(OY)2 and dimeric PhR(OY)Te–O–TePhR(OY) predominantly in moderate to good yields.

Epoxidation of olefins using diaryltellurium dicarboxylates.

This paper reports an efficient method for the epoxidation of a variety of functionalized olefins using diaryltellurium dicarboxylates as hypervalent tellurium compounds. This method is able to efficiently convert olefins into epoxides using catalytic amounts of tellurium and urea hydrogen peroxide. Furthermore, we propose that this reaction proceeds via the formation of peroxides of phenol, carboxylic acid, and tellurium peroxide when diaryltellurium dicarboxylates and hydrogen peroxide react. This is the first example of an epoxidation reaction using hypervalent tellurium compounds.

Telluracarbaporphyrins and a Related Palladium(II) Complex: Evidence for Hypervalent Interactions.

The reaction of a carbatripyrrin with a tellurophene dicarbinol in the presence of BF3·Et2O, followed by oxidation with DDQ, afforded the first example of a telluracarbaporphyrin. Although this system exhibits strongly aromatic characteristics, it is prone to air oxidation, giving rise to a hydroxy derivative that was characterized by X-ray crystallography. The initial telluracarbaporphyrin reacted with palladium(II) acetate to give a stable organometallic complex, and X-ray crystallography showed that the palladium cation was coordinated to all four atoms in the CNTeN core. An oxacarbatripyrrin was also reacted with a tellurophene dialcohol to give an air-stable porphyrin analogue with a CNTeO core. Nonmetalated telluracarbaporphyrins showed relatively short Te-N separations that strongly implied the involvement of hypervalent tellurium interactions. Furthermore, despite the presence of a very large tellurium atom, the tellurophene subunit is not strongly pivoted away from the mean macrocyclic plane as would be expected in the absence of these interactions. The aromatic properties of heterocarbaporphyrins were assessed by proton NMR spectroscopy, NICS calculations, and AICD plots. In addition, the relative stability of hydroxytelluraporphyrins in comparison to their tellurophene oxide tautomers was investigated and the aromatic characteristics of these oxidized structures were evaluated.

Development of a methodology for reversible chemical modification of silicon surfaces with application in nanomechanical biosensors

Hypervalent tellurium compounds have a particular reactivity towards thiol compounds which are related to their biological properties. In this work, this property was assembled to tellurium-functionalized surfaces. These compounds were used as linkers in the immobilization process of thiolated biomolecules (such as DNA) on microcantilever surfaces. The telluride derivatives acted as reversible binding agents due to their redox properties, providing the regeneration of microcantilever surfaces and allowing their reuse for further biomolecules immobilizations, recycling the functional surface. Initially, we started from the synthesis of 4-((3-((4-methoxyphenyl) tellanyl) phenyl) amino)-4-oxobutanoic acid, a new compound, which was immobilized on a silicon surface. In nanomechanical systems, the detection involved a hybridization study of thiolated DNA sequences. Fluorescence microscopy technique was used to confirm the immobilization and removal of the telluride-DNA system and provided revealing results about the potentiality of applying redox properties to chalcogen derivatives at surfaces.

Diacetal Ditellurides as Highly Active and Selective Antiparasitic Agents toward Leishmania amazonensis.

Leishmaniasis is a neglected tropical disease and a public health concern in at least 98 countries, affecting mainly the poorest populations. Pharmaceuticals and chemotherapies available for leishmaniasis treatment have several limitations, which clearly justify the efforts to find new potential antileishmanial drugs. In this context, antiprotozoal activities toward different Leishmania species have been reported for hypervalent tellurium compounds, which motivated us to investigate, for the first time, the leishmanicidal properties of some nonhypervalent diaryl ditellurides. Thus, this work describes in vitro activity against Leishmania amazonensis and the cytotoxicities of diaryl ditellurides. Ditelluride LQ7 revealed a strong leishmanicidal activity on promastigotes and amastigotes at submicromolar levels (IC50 = 0.9 ± 0.1 and 0.5 ± 0.1 μmol L-1, respectively) and presented selectivity indexes greater than those of reference drug miltefosine. This preliminary study suggests that diaryl ditellurides may be promising scaffolds for the development of new agents for leishmaniasis treatment.

Isomorphic substitution in molecular crystals and geometry of hypervalent tellurium: comments inspired by a case study of RMeTeI2 and [RMe2Te]+I− (R = Ph, Fc)

Unusual isomorphic substitution in the crystals of [FcMe2Te]+I− with an admixture of Te–I ionized [FcMeTeI+]I− supports the 3c-4e as a general, seamless bonding model for the hypervalent tellurium in both the isolated molecules and crystals.

Synthesis and Characterization of Fluorinated Hypervalent Tellurium Derivatives

The synthesis of tellurium derivatives bearing fluorinated groups, similar in structure to their hypervalent iodine congeners, is reported. Thus, a series of CF3, CF2H, and C6F5 aryltellurium(II) species bearing various functional groups interacting with the Te atom was obtained. The installation of the various fluorinated groups relies on the use of the corresponding trimethylsilyl precursors. The hypervalent nature of the products is discussed on the basis of their NMR spectroscopic and X-ray crystallographic characterization.

Stability Study of Hypervalent Tellurium Compounds in Aqueous Solutions.

Hypervalent tellurium compounds (telluranes) are promising therapeutical agents with negligible toxicities for some diseases in animal models. The C–Te bond of organotellurium compounds is commonly considered unstable, disfavoring their applicability in biological studies. In this study, the stability of a set of telluranes composed of an inorganic derivative and noncharged and charged organic derivatives was monitored in aqueous media with 1H, 13C, and 125Te NMR spectroscopy and high-resolution mass spectrometry. Organic telluranes were found to be remarkably resistant and stable to hydrolysis, whereas the inorganic tellurane AS101 is totally converted to the hydrolysis product, trichlorooxytellurate, [TeOCl3]−, which was also observed in the hydrolysis of TeCl4. The noteworthy stability of organotelluranes in aqueous media makes them prone to further structure–activity relationship studies and to be considered for broad biological investigations.

Electrochemical Transformation of 2,5-Diphenyltellurophene

Tellurphene-containing materials are attracting great attention in a wide range of chemistry field. Due to the metalloid nature of tellurium, tellurophene shows unique reactivity. Previous report revealed that the 2,5-diphenyltellurophene (PT) reacted with halogen sources to give its dihalogen adducts PT-X2 (Seferos et al., Dalton Trans. 2015, 44, 2092.) (Figure, upper). In this reaction, the oxidation state of tellurium-center changed from Te(II) to Te(IV), in other word, tellurium transformed into the hypervalent state. Interestingly, dehalogenation also occurred by the irradiation of the lights to give an original Te(II)-centered tellurophene. In this study, we have investigated the electrochemical transformation of PT (Figure, lower). The spectroelectrochemistry measurements have successfully revealed that the oxidation of PT in the presence of halides (F-, Cl-, Br-) gave the corresponding hypervalent tellurium compound, PT-X2 . In addition, the electrochemical reduction of PT-X2 resulted in the recovery of PT. In the course of Te(II)/Te(IV) redox cycle, there were no trace of side reaction, evidenced by the existence of isobestic points in absorption spectra. The bulk electrolysis of PT was also succeeded to give PT-X2 in sufficient yield. Figure 1

Synthesis and structural characterization of a novel tellurane with four sulfur ligands

AbstractThe molecular structure of a novel hypervalent tellurium(IV) compound, 2,2′‐spirobi[4,7‐diisopropyl‐1,3,2‐benzodithiatellurole] (1), has been determined by a single crystal X‐ray diffraction study. The results represent the first crystal structural characterization of a hypervalent tellurium(IV), tellurane, with only four sulfur ligands. The tellurane has a distorted pseudo‐trigonal‐bipyramidal geometry with the axial sulfur atoms bending toward the equatorial ones. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:586–589, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20697

Irreversible inhibition of human cathepsins B, L, S and K by hypervalent tellurium compounds

The inhibition of human cysteine cathepsins B, L, S and K was evaluated by a set of hypervalent tellurium compounds (telluranes) comprising both organic and inorganic derivatives. All telluranes studied showed a time- and concentration-dependent irreversible inhibition of the cathepsins, and their second-order inactivation rate constants were determined. The organic derivatives were potent inhibitors of the cathepsins and clear specificities were detected, which were parallel to their known substrate specificities. In all cases, the activity of the tellurane-inhibited cathepsins was recovered by treatment of the inactivated enzymes with reducing agents. The maximum stoichiometry of the reaction between cysteine residues and telluranes were also determined. The presented data indicate that it is possible to design organic compounds with a tellurium(IV) moiety as a novel warhead that covalently modifies the catalytic cysteine, and which also form strong interactions with subsites of cathepsins B, L, S and K, resulting in more specific inhibition.

Hypervalent Tellurium Compounds Containing Te-N Interactions. Mononuclear and Polynuclear Derivatives

Various organotellurium derivatives containing the pendant arm (2-Me2NCH2)C6H4 group have been prepared and characterized. The structure of a hydrolysis by-product, [(Ph2TeCl)2O]2, was also established.

Synthesis and Characterization of a Hypervalent Tellurium Cation, Ph5Te+: A Stable Nonclassical Onium Compound

Synthesis and Characterization of a Hypervalent Tellurium Cation, Ph₅Te⁺: A Stable Nonclassical Onium Compound

New Aspects of Hypervalent Tellurium Compounds

New Aspects of Hypervalent Tellurium Compounds

Crystal Structures and ab Initio Calculations of New Dicationic Telluranes (λ4-Tellane), [10−Te−4(C2X2)]2+ (X = S, Se): Positively Charged Hypervalent Bonding Systems

The reactions of 2,6-bis[(phenylthio- or phenylseleno)methyl]phenyl phenyl telluride or the corresponding Te-oxide, with NOBF4 or trifluoromethanesulfonic anhydride afforded the new telluranes, [10−Te−4(C2X2)]2+·2Y- (λ4-tellane) (X = S or Se, Y = BF4 or CF3SO3). These compounds were characterized by elemental and spectroscopic (FABMS, 1H, 13C, and 125Te NMR) analyses. X-ray structure determinations revealed that the hypervalent tellurium atoms are at the center of a distorted trigonal bipyramid, with two apical sulfonio or selenonio ligands connected via transannular bonds. The Te−S distances are in the range 2.652−2.706 Å, the Te−Se distances in the range 2.759−2.807 Å, and the X−Te−X bond angles in the range 160.41−163.92 °. Ab initio calculations indicate that the positive charges in the dications are exclusively on the three chalcogen atoms that form three-center, four-electron bonds.

Synthesis of Tellurium Centered Novel Hypervalent Dications

The reactions of 2,6-bis[(phenylthio- or phenylseleno)methyl]phenyl phenyl telluride or the corresponding Te–oxide with NOBF4 or trifluoromethanesulfonic anhydride afforded the new telluranes, [10–Te–4(C2X2)]2+ 2Y- (λ4-tellane) (X = S or Se, Y = BF4 or CF3SO3). X-ray structure determinations revealed that the hypervalent tellurium atoms are at the center of a distorted trigonal bipyramid with two apical sulfonio or selenonio ligands connected via transannular bonds. Ab initio calculations indicate that the positive charges in the dications are exclusively on the three chalcogen atoms that form three-center, four-electron bonds.

New Aspects of Hypervalent Tellurium Compounds

Te(C6H4-4-CF3)6 1a was obtained by the unique one-pot reaction of LiC6H4-4-CF3 with TeCl4, where oxidation of Te(IV) to Te(VI) occurred. Compound 1a is extremely thermally stable and not light sensitive unlike tetraorganotellurium compounds. Thermolysis and some reactions of 1a are described. ClTe(C6H4-4-CF3)5, synthesized by chlorination of LiTe(C6H4-4-CF3)5, reacted with LiC6H4-4-CF3 to give 1a. Bond dissociation energies of Te(CH3)n (n = 2, 4, 6) were calculated in order to explain the stability of Te(VI) compounds.

ChemInform Abstract: The Electronic Structure of (Te15Br4)(MoOBr4)2 and Some General Aspects of Bonding in “Classical” and Hypervalent Tellurium Halides.

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The Electronic Structure of [Te15Br4][MoOBr4]2 and Some General Aspects of Bonding in “Classical” and Hypervalent Tellurium Halides

AbstractApproximate MO and band structure calculation are used to analyze the bonding in the recently synthesized paramagnetic, semiconducting phase [Te15Br4]2+. The [Te15Br4]2+ chains are very similar to those in the tellurium subhalide Te2Br. The electronic structure and bonding within these chains is analysed and the possibility of hypervalency in both [Te15Br4][MoOBr4]2 and Te2Br is discussed. The bonding in the classically hypervalent molecule TeBr42− and a model Te3Br24‐ is compared to that of the infinite system. Our calculations indicate that both [Te15Br4][MoOBr4]2 and Te2Br contain weakly hypervalent Te atoms and that the interesting electronic properties of [Te15Br4][MoOBr4]2 arise within the distinct sublattices, which do not interact significantly.