A well-defined dinuclear telluronic acid [RTe(μ-O)(OH)3]2

N-Coordinated tellurenium(II) and telluronium(IV) cations: synthesis, structure and hydrolysis

A set of N-coordinated tellurium(II) compounds containing either C,N-chelating ligands CNR (where CN = 2-(RNCH)C6H4, R = tBu or Dipp; Dipp = 2,6-iPr2C6H3) or N,C,N pincer ligands NCNR (where NCN = 2,6-(RNCH)2C6H4, R = tBu or Dipp) were synthesized. In the case of C,N-chelated compounds, the reaction of CNDippLi with Te(dtc)2 (where dtc = Et2NCS2) in a 1 : 1 molar ratio smoothly provided the carbamate CNDippTe(dtc) which upon treatment with 2 eq. of HCl provided the chloride CNDippTeCl. In contrast, the analogous conversion of NCNRLi with Te(dtc)2 surprisingly furnished ionic bromides [NCNRTe]Br as a result of the exchange of dtc by Br coming from nBuBr present in the reaction mixture. Furthermore, the reaction of CNDippTeCl or [NCNRTe]Br with silver salts AgX (X = OTf or SbF6) provided the expected tellurenium cations [CNDippTe]SbF6 and [NCNRTe]X. To further increase the Lewis acidity of the central atom, the oxidation of selected compounds with 1 eq. of SO2Cl2 was examined yielding stable compounds [CNtBuTeCl2]X and [NCNtBuTeCl2]X. The oxidation of the Dipp substituted compounds proved to be more challenging and an excess of SO2Cl2 was necessary to obtain the oxidized products [CNDippTeCl2]SbF6 and [NCNDippTeCl2]SbF6, which could solely be characterized in solution. Compounds [CNtBuTeCl2]OTf and [NCNtBuTeCl2]OTf were shown to undergo a controlled hydrolysis to the corresponding telluroxanes. All compounds were studied by multinuclear NMR spectroscopy in solution and for selected compounds solid state 125Te NMR spectroscopy and single-crystal X-ray diffraction analysis were performed. The Lewis acidity of the studied cations was examined by the Gutmann-Beckett method using Et3PO as the probing agent. The Te-N chalcogen bonding situation of selected compounds has also been examined computationally by a set of real-space bonding indicators.

A tellura-Baeyer-Villiger oxidation: one-step transformation of tellurophene into chiral tellurinate lactone

Baeyer-Villiger (BV) oxidation is a fundamental organic reaction, whereas the hetero-BV oxidation is uncharted. Herein, a tellura-BV oxidation is discovered. By oxidizing a tellurophene-embedded and electron-rich polycycle (1) with mCPBA or Oxone, an oxygen atom is inserted into the Te-C bond of the tellurophene to form tellurinate lactone mono-2. This reaction proceeds as follows: (i) 1 is oxidized to the tellurophene Te-oxide form (IM-1); (ii) IM-1 undergoes tellura-BV oxidation to give mono-2. Moreover, the hybrid trichalcogenasumanenes 7 and 8 are, respectively, converted to tellurinate lactones mono-9 and mono-10 under the same conditions, indicating that tellura-BV oxidation shows high chemoselectivity. Due to the strong secondary bonding interactions between the Te[double bond, length as m-dash]O groups on tellurinate lactones, mono-2, mono-9, and mono-10 are dimerized to form U-shaped polycycles 2, 9, and 10, respectively. Notably, mono-2, mono-9, mono-10, and their dimers show chirality. This work enables one-step transformation of tellurophene into tellurinate lactone and construction of intricate polycycles.

Oxidation behavior of intramolecularly coordinated unsymmetrical diorganotellurides: isolation of novel tetraorganoditelluronic acids, [RR'Te(μ-O)(OH)2]2

The oxidation reaction of unsymmetrical diorganotellurides, namely, bis[2-{(dimethylamino)methyl}aryl]tellurides [aryl = phenyl (6), 2-methylphenyl (7), 2,6-dimethylphenyl (8) and 2,6-diisopropylphenyl (9)] with meta-chloroperbenzoic acid afforded the first examples of tetraorganoditelluronic acids, [RR'Te(μ-O)(OH)₂]₂, where R = 2-NMe₂CH₂C₆H₄, R' = C₆H₅ (10), 2-MeC₆H₄ (11), 2,6-MeC₆H₃ (12) and 2,6-ⁱPrC₆H₃ (13). The structures of tetraorganoditelluronic acids 10-13 were authenticated by single crystal X-ray diffraction studies. From the molecular structures of 10-13, it was observed that the sp³ N-donor atoms, which were initially involved in intramolecular TeN bonding interactions in diorganotellurides 6-9, did not interact with the tellurium atoms in tetraorganoditelluronic acids 10-13. The ¹²⁵Te chemical shifts for 10-13 were considerably downfield shifted as compared with the values observed for the corresponding tellurides 6-9. The relative stabilities of the tetraorganoditelluronic acids 10-13 with respect to their lighter analogues (S and Se) have been assessed using DFT calculations.

Syntheses, characterization, DNA/BSA binding, and in vitro cytostatic activity of fluorobenzenetelluronic triorganotin(iv) esters

A new series of fluorobenzenetelluronic triorganotin(iv) esters (1–6) have been synthesized by the reaction of deprotonated fluorobenzenetelluronic acid ligands and the corresponding R₃SnCl (R = Me, Ph).

Conformational trimorphism of bis(2,6-dimesitylphenyl)ditelluride

Besides the previously known α-form (monoclinic, P21/c, Z=4) of bis(2,6-dimesitylphenyl)ditelluride, two new polymorphic modifications, namely the β-form (monoclinic, P21/c, Z=8) and the γ-form (triclinic, P1̅, Z=2), were obtained serendipitously during chemical reactions. In all three modifications, the individual molecules possess significantly different conformations and bond parameters, such as Te–Te bond lengths, C–Te–Te bond angles, C–Te–Te–C torsion angles and intramolecular Menshutkin interactions, which is also reflected in their non-covalent interactions with adjacent molecules in the crystal lattice via London dispersion and electrostatic forces. The interplay between intermolecular and intramolecular forces in these conformational polymorphs was investigated using quantum chemical calculations, which reveal that the β-form should be thermodynamically stable at absolute zero. In contrast, crystallization experiments and thermoanalytical investigations indicate that the α-form is stable at high temperatures and therefore, both forms might be related by enantiotropism.

A novel 4-fluorobenzenetelluronic trimethyltin ester: synthesis, characterization and in vitro cytotoxicity assessment

A novel 4-fluorobenzenetelluronic trimethyltin ester (Me₃Sn)₄[p-F-PhTe(μ-O)(OH)O₂]₂ (1) has been prepared and structurally characterized, and apoptotic cytotoxicity assessments for A549 cells are made.

Tellurium: a maverick among the chalcogens

This tutorial review elucidates the fundamental concepts necessary for an understanding of the unique structures and reactivities of tellurium compounds.

Reaction of L2Zn2 with Ph2E2 – synthesis of LZnEPh and reactions with oxygen and H-acidic substrates

L₂Zn₂ (L = HC[C(Me)N(2,4,6-Me₃C₆H₂)]₂) and Ph₂E₂ (E = Se, Te) react to form LZnSePh (1) and LZnTePh (2).