Formation of Diaryl Telluroxides and Tellurones by Photosensitized Oxygenation of Diaryl Tellurides

Exploring the fluorescence properties of tellurium-containing molecules and their advanced applications

This review article explores the fascinating realm of fluorescence using organochalcogen molecules, with a particular emphasis on tellurium (Te). The discussion encompasses the underlying mechanisms, structural motifs influencing fluorescence, and the applications of these intriguing phenomena. This review not only elucidates the current state of knowledge but also identifies avenues for future research, thereby serving as a valuable resource for researchers and enthusiasts in the field of fluorescence chemistry with a focus on Te-based molecules. By highlighting challenges and prospects, this review sparks a conversation on the transformative potential of Te-containing compounds across different fields, ranging from environmental solutions to healthcare and materials science applications. This review aims to provide a comprehensive understanding of the distinct fluorescence behaviors exhibited by Te-containing compounds, contributing valuable insights to the evolving landscape of chalcogen-based fluorescence research.

Affinity of Telluronium Chalcogen Bond Donors for Lewis Bases in Solution: A Critical Experimental-Theoretical Joint Study

Telluronium salts [Ar2 MeTe]X were synthesized, and their Lewis acidic properties towards a number of Lewis bases were addressed in solution by physical and theoretical means. Structural X-ray diffraction analysis of 21 different salts revealed the electrophilicity of the Te centers in their interactions with anions. Telluroniums' propensity to form Lewis pairs was investigated with OPPh3 . Diffusion-ordered NMR spectroscopy suggested that telluroniums can bind up to three OPPh3 molecules. Isotherm titration calorimetry showed that the related heats of association in 1,2-dichloroethane depend on the electronic properties of the substituents of the aryl moiety and on the nature of the counterion. The enthalpies of first association of OPPh3 span -0.5 to -5 kcal mol-1 . Study of the affinity of telluroniums for OPPh3 by state-of-the-art DFT and ab-initio methods revealed the dominant Coulombic and dispersion interactions as well as an entropic effect favoring association in solution. Intermolecular orbital interactions between [Ar2 MeTe]+ cations and OPPh3 are deemed insufficient on their own to ensure the cohesion of [Ar2 MeTe ⋅ Bn ]+ complexes in solution (B=Lewis base). Comparison of Grimme's and Tkatchenko's DFT-D4/MBD-vdW thermodynamics of formation of higher [Ar2 MeTe ⋅ Bn ]+ complexes revealed significant molecular size-dependent divergence of the two methodologies, with MBD yielding better agreement with experiment.

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.

Crystal structure of di([1,1′:3′,1″-terphenyl]-2′-yl)tellane, C36H26Te

C36H26Te, orthorhombic, Pca21 (no. 29), a = 13.5004(4) Å, b = 13.5677(3) Å, c = 14.2006(4) Å, V = 2601.12(12) Å3, Z = 4, Rgt (F) = 0.0247, wRref (F 2) = 0.0530, T = 93 K.

Tellurium-induced cyclization of olefinic compounds

In this article, we discuss about the importance of Tellurium (Te) in organic synthesis. Tellurium-induced cyclization of alkenyl compounds, as well as alkynyl compounds, are considered for the study. The developments in this area are incorporated in great detail. The mechanism of the reactions does not follow any straightforward process. This study opens up the possibility of stereocontrolled synthesis of complex natural products.

Transition-Metal-Free Synthesis of Unsymmetrical Diaryl Tellurides via SH2 Reaction of Aryl Radicals on Tellurium

Although diaryl tellurides are parent organotellurium compounds, their synthesis methods, especially for unsymmetrical ones, are limited. This may be due to the instability of diaryl tellurides and their synthesis intermediates under reaction conditions. Radical reactions are known to exhibit excellent functional group selectivity; therefore, we focused on a bimolecular homolytic substitution (S_H2) reaction between the aryl radical and diaryl ditelluride. Aryl radicals are generated from arylhydrazines in air and captured by diaryl ditellurides, resulting in a selective formation of unsymmetrical diaryl tellurides with high yields. The electronic effects of the substituents on both arylhydrazines and diaryl ditellurides on the S_H2 reaction of tellurium are also discussed in detail.

Bis(2,6-diisopropylphenyl) tellurone: a well-defined monomeric diorganotellurone without cocrystallized solvents and without stabilizing intramolecular contacts

Only two crystal structures of diorganotellurones have been reported to date, both of which contain cocrystallized solvents and one of which is stabilized by intramolecular Te—N secondary bonding interactions. This work describes the crystal structure of bis(2,6-diisopropylphenyl) tellurone, (C12H17)2TeO2 or C24H34O2Te, the first well-defined diorganotellurone without cocrystallized solvents and without stabilizing intramolecular contacts. The molecule has crystallographic twofold symmetry, with half the molecule as the asymmetric unit. The molecular structure is compared to previously reported tellurones and those computed at the density functional theory DFT/B3PW91 level. The molecules form two-dimensional layers as a result of a weak intermolecular hydrogen-bonding network. The layers are then stacked in an antiparallel manner to form the crystal packing structure. The Hirshfeld surface analysis was employed to visualize and quantify the intermolecular contacts in the molecular crystal structure, and the contribution of O...H and H...H interactions was found to be the dominating factor.

Bis(2-pyridyl)ditellane as a precursor to CoII, CuI and CuII complex formation: structural characterization and photocatalytic studies

Coordination compounds containing bis(2-pyridyl)ditellane as a precursor and transition metals are described. The cobalt-containing photocatalysts are active for H2 production.

Photo-oxidative cross-linking of thiol polydimethylsiloxane co-polymers via disulfide formation

Disulfide bonds are often employed as reductively cleavable sites in biomaterials and polymers. Here we demonstrate the aerobic photo-cross-linking of thiol-containing polymers through disulfide formation using a sensitizer and telluride catalyst.

Design of Azobenzene beyond Simple On-Off Behavior

Azobenzenes are without a doubt the most widely used light-induced switching units, and there is a plethora of application examples ranging from supramolecular chemistry to material science and biological chemistry. Here, we present a smart azobenzene, in which the photoswitching capability of the azobenzene moiety can be reversibly switched on and off using a second unit (redox switch). This second switching unit is based on the variation of the strength of a chalcogen bond between the azo group and a Te-Ph unit in ortho position to the azo group. This allows the selective switching of only one azobenzene unit in the presence of other azobenzene switches. The entire double-switch is a very simple, small system that can also be easily synthesized. As a result, this double-switch can be used as a smarter replacement for the established azobenzene system in the future. For example, in contrast to the latter this double-switch could be employed to store state information analogous to a flip-flop in digital electronic systems.

Transition-metal-free C-S, C-Se, and C-Te Bond Formation from Organoboron Compounds

The present review describes the successful application of organoboron compounds in transition-metal-free C-S, C-Se, and C-Te bond formations. We presented studies regarding these C-Chalcogen bond formations using organoboron reagents, such as boronic acids, boronic esters, borate anions, and several sources of chalcogen atoms/moieties. Moreover, a broad range of transition-metal-free approaches to synthesize sulfides, selenides, and tellurides were described using conventional heating methods, which are sometimes green since they use green solvents, safe reagents, among others. Furthermore, protocols using alternative energy sources, including ultrasound, microwave irradiation, photocatalysis, and electrolytic processes, were also shown to be suitable. These protocols were applied to prepare a broad scope of functionalized chalcogenides with high molecular diversity. These studies and their proposed mechanisms were also reported herein in addition to the reuse of reaction promoters.

Redox-controlled chalcogen-bonding at tellurium: impact on Lewis acidity and chloride anion transport properties

Our interests in the chemistry of atypical main group Lewis acids have led us to devise strategies that augment the affinity of chalcogen-bond donors for anionic guests. In this study, we describe the oxidative methylation of diaryltellurides as one such strategy along with its application to the synthesis of [Mes(C₆F₅)TeMe]⁺ and [(C₆F₅)₂TeMe]⁺ starting from Mes(C₆F₅)Te and (C₆F₅)₂Te, respectively. These new telluronium cations have been evaluated for their ability to complex and transport chloride anions across phospholipid bilayers. These studies show that, when compared to their neutral Te(ii) precursors, these Te(iv) cations display both higher Lewis acidity and transport activity. The positive attributes of these telluronium cations, which originate from a lowering of the tellurium-centered σ* orbitals and a deepening of the associated σ-holes, demonstrate that the redox state of the main group element provides a convenient handle over its chalcogen-bonding properties.

The oxidative alkylation of diorganotellurides enhances the chalcogen-bond donor properties of the tellurium center, an effect manifested in the enhanced chloride anion affinity and transport properties of the resulting telluronium cations.

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.

Organoselenium and organotellurium compounds containing chalcogen-oxygen bonds in organic synthesis or related processes

This chapter emphasizes aspects related to the role of organochalcogen (Se, Te) compounds with single E‒O and/or double E=O (E=Se, Te) bonds in organic synthesis, as reagents, intermediates, or catalysts, and it gives a larger extent mainly to data reported in the field during the last ten years. For each of these two heavier chalcogens the material is structured according to the oxidation state of the chalcogen and, for the same oxidation state, in sections dedicated to a particular type of compounds. Functionalization or cyclization reactions in which the organochalcogen compounds take part as nucleophiles, electrophiles or radicals, employed in various synthetic transformations, are discussed and, where available, the mechanistic aspects are outlined. New chiral species and new strategies were developed during last years in order to increase the yield, the reaction rate and the stereoselectivity in specific organic transformations, i.e. addition, oxidation, elimination, cyclization or rearrangement reactions. A notably attention was devoted to easily accessible and environmental friendly catalysts, re-usable and “green” solvents, as well as waste-free procedures.

Probing interactions through space using spin–spin coupling

A series of eight 5-(TeAr)-6-(SePh)acenaphthenes (Ar = aryl) were prepared and structurally characterised by X-ray crystallography, solution and solid-state NMR spectroscopy and DFT/B3LYP calculations.