Breathing some new life into an old topic: chalcogen-nitrogen π-heterocycles as electron acceptors

Solid-State Assembly by Chelating Chalcogen Bonding in Quinodimethane Tetraesters Fused with a Chalcogenadiazole

In contrast to p-quinodimethane tetraesters, which undergo facile polymerization due to their diradical character, newly synthesized 1 and 2 consisting of a chalcogenadiazole fused to a p-naphthoquinodimethane tetraester are thermodynamically stable due to butterfly-shaped deformation. Such a folded molecular structure is also favorable for chalcogen bond (ChB) formation through intermolecular close contacts between a chalcogen atom (E: Se or S) and the oxygen atoms of ester groups in a crystal. The less-explored chelating-ChB through a C=O⋅⋅⋅E⋅⋅⋅O=C contact [Se⋅⋅⋅O: 2.94-3.37 Å] is the key supramolecular synthon for the formation of a one-dimensional rod-like assembly in a crystal, which is commonly observed in selenadiazole-tetraesters (1) with OMe, OEt, and OiPr groups. The formation of inclusion cavities between the rods shows that 1 could serve as solid-state host molecules for clathrate formation, as found in a hexane-solvated crystal. In contrast, thiadiazole-tetraesters (2) are less suitable for the formation of a rod-like assembly since the ChB involving S is less effective, and thus is overwhelmed by weak hydrogen bonds through C-H⋅⋅⋅O contacts.

Acid-Base and Anion Binding Properties of Tetrafluorinated 1,3-Benzodiazole, 1,2,3-Benzotriazole and 2,1,3-Benzoselenadiazole

The influence of fluorination on the acid-base properties and the capacity of structurally related 6-5 bicyclic compounds - 1,3-benzodiazole 1, 1,2,3-benzotriazole 2 and 2,1,3-benzoselenadiazole 3 to σ-hole interactions, i. e. hydrogen (1 and 2) and chalcogen (3) bondings, is studied experimentally and computationally. The tetrafluorination increases the Brønsted acidity of the diazole and triazole scaffolds and the Lewis acidity of selenadiazole scaffold decreases the basicity. Increased Brønsted acidity facilitates anion binding via the formation of hydrogen bonds; particularly, tetrafluorinated derivative of 1 (compound 4) binds Cl^- . Increased Lewis acidity of tetrafluorinated derivative of 3 (compound 10), however, is not enough for binding with Cl^- and F^- via chalcogen bonds in contrast to previously studied Te analog of 10. It is suggested that the maximum positive values of molecular electrostatic potential at the σ-holes, V_S,max , can be a reasonable metric for design and synthesis of new anion receptors with selenadiazole-diazole/triazole hybrids as a special target. Related chlorinated compounds are also discussed.

Benzo[1,2,3]dithiazole Compounds: A History of Synthesis and Their Renewed Applicability in Materials and Synthetic Chemistry, Originating from the Herz Reaction

The benzo[1,2,3]dithiazole is a unique heteroaromatic functionality whose conjugated profile instils some fascinating electronic properties. This has been historically recognized in the design and manufacture of organic dyes early last century. Although, with the benefit of increased diagnostic techniques and improved understanding, these structures are attracting greater attention in additional research settings, including applications as organic radicals and semiconductors. In addition, the benzodithiazole functionality has been shown to be a valuable synthetic intermediate in the preparation of a variety of other privileged aromatic and heteroaromatic targets, many of which are important APIs. In this review, the authors aim to critically analyse the potential applicability of these compounds to the fields of not only small-scale laboratory synthetic and medicinal chemistry but also commercial-scale processes and increasingly materials chemistry.

A Sterically Hindered Derivative of 2,1,3-Benzotelluradiazole: A Way to the First Structurally Characterised Monomeric Tellurium-Nitrogen Radical Anion

Interaction of the tetradentate redox-active 6,6'-[1,2-phenylenebis(azanediyl)]bis(2,4-di-tert-butylphenol) (H₄ L) with TeCl₄ leads to neutral diamagnetic compound TeL (1) in high yield. The molecule of 1 has a nearly planar TeN₂ O₂ fragment, which suggests the formulation of 1 as Te^II L^2- , in agreement with the results of DFT calculations and QTAIM and NBO analyses. Reduction of 1 with one equivalent of [CoCp₂ ] leads to quantitative formation of the paramagnetic salt [CoCp₂ ]⁺ [1]^.- , which was characterised by single-crystal XRD. The solution EPR spectrum of [CoCp₂ ]⁺ [1]^.- at room temperature features a quintet due to splitting on two equivalent ¹⁴ N nuclei. Below 150 K it turns into a broad singlet line with two weak satellites due to the splitting on the ¹²⁵ Te nucleus. Two-component relativistic DFT calculations perfectly reproduce the a(¹⁴ N) HFI constants and A_∥ (¹²⁵ Te) value responsible for the low-temperature satellite splitting. Calculations predict that the additional electron in 1^.- is localised mainly on L, while the spin density is delocalised over the whole molecule with significant localisation on the Te atom (≥30 %). All these data suggest that 1^.- can be regarded as the first example of a structurally characterised monomeric tellurium-nitrogen radical anion.

Bis(2,1,3-benzotelluradiazolidyl)2,1,3-benzotelluradiazole: a pair of radical anions coupled by TeN chalcogen bonding

Reduction of 2,1,3-benzotelluradiazole (3) yielded a crystalline solid that features a trimeric dianion formally composed of two [3]˙- and one 3 bridged by unusually asymmetric TeN chalcogen bonds. The solid is diamagnetic due to strong antiferromagnetic coupling, as revealed by CASSCF/CASPT2 and BS-DFT.

5,5′-Thiobis(3-methoxy-4H-1,2,6-thiadiazin-4-one)

The reaction of 3-chloro-5-methoxy-4H-1,2,6-thiadiazin-4-one (9) with Na2S·9H2O (0.5 equiv) in tetrahydrofuran (THF) at ca. 20 °C for 20 h gives 5,5′-thiobis(3-methoxy-4H-1,2,6-thiadiazin-4-one) (10) in a 44% yield as yellow needles. The compound was fully characterized.

3,6-Dibromopyridazine-4,5-diamine

Dihalogenated derivatives of 1,2,5-chalcogenadiazoles fused with benzene or heterocyclic rings are of interest as starting compounds for photovoltaic materials. The 1,2,5-chalcogenadiazole ring in these heterocycles was most commonly prepared from the corresponding ortho-diamine moiety. In this communication, 3,6-dibromopyridazine-4,5-diamine was prepared via the reaction of 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine with sodium methoxide in THF by heating at reflux for four hours. The structure of the newly synthesized compound was established by means of high resolution mass-spectrometry, 1H, 13C-NMR and IR spectroscopy, and mass-spectrometry.

3-Chloro-5-(3-n-hexylthien-2-yl)-4H-1,2,6-thiadiazin-4-one

Stille coupling of 5-chloro-4-oxo-4H-1,2,6-thiadiazin-3-yl trifluoromethanesulfonate (7) with tributyl(3-n-hexylthien-2-yl)stannane and Pd(Ph3P)2Cl2 in PhMe at ca. 20 °C, for 24 h gave 3-chloro-5-(3-n-hexylthien-2-yl)-4H-1,2,6-thiadiazin-4-one (9) with a 60% yield. The latter is a potentially useful building block for the synthesis of oligomeric and polymeric donors for organic photovoltaics.

Design, synthesis and isolation of a new 1,2,5-selenadiazolidyl and structural and magnetic characterization of its alkali-metal salts

A new electron acceptor is synthesized and reduced into its radical-anion isolated in the form of two salts with different structures and magnetic properties.

Efficient green photoluminescence and electroluminescence of iridium complexes with high electron mobility

Aiming to balance the injection and transport of electrons and holes, nitrogen heterocycle and 1,3,4-oxadiazole derivatives were introduced in iridium(iii) complexes to obtain organic light-emitting diodes (OLEDs) with high performances. Thus, two novel Ir(iii) complexes (Ir(tfmphpm)2(pop) and Ir(tfmppm)2(pop)) with green emissions using 2-(3,5-bis(trifluoromethyl)phenyl)pyrimidine (tfmphpm) and 2-(2,6-bis(trifluoromethyl)pyridin-4-yl)pyrimidine (tfmppm) as cyclometalating ligands, and 2-(5-phenyl-1,3,4-oxadiazol-2-yl)phenol (pop) as an ancillary ligand were synthesized. Both emitters show high photoluminescence efficiencies up to 94% and good electron mobility. The devices using two emitters with the structure of ITO (indium-tin-oxide)/MoO3 (molybdenum oxide, 5 nm)/TAPC (di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane, 30 nm)/mCP (1,3-bis(9H-carbazol-9-yl)benzene, 5 nm)/Ir(iii) complexes (6 wt%) : PPO21 (3-(diphenylphosphoryl)-9-(4-(diphenylphosphoryl)phenyl)-9H-carbazole, 10 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl) benzene, 40 nm)/LiF (1 nm)/Al (100 nm) display good electroluminescence performances with a maximum luminance of 48 981 cd m-2, a maximum current efficiency of 92.79 cd A-1 and a maximum external quantum efficiency up to 31.8%, respectively, and the efficiency roll-off ratio is low, suggesting that they have potential application in OLEDs.

Donor-Acceptor Complexes between 1,2,5-Chalcogenadiazoles (Te, Se, S) and the Pseudohalides CN- and XCN- (X=O, S, Se, Te)

Donor-acceptor (D-A) complexes between 3,4-dicyano-1,2,5-chalcogenadiazoles [chalcogen=Te (1 a), Se (1 b), S (1 c)] and the pseudohalides CN^- and XCN^- (X=O, S, Se, Te) were studied experimentally and theoretically. For 1 a, they were isolated as [K(18-crown-6)][1 a-CN] (2), [K(18-crown-6)][1 a-NCO] (3), [K(18-crown-6)][1 a-SCN] (4), [K(18-crown-6)][1 a-SeCN] (5), and [K][1 a-NCSe] (6) and characterized by X-ray diffraction (XRD), UV/Vis and NMR spectroscopy, and DFT and QTAIM calculations. For 1 b and 1 c, the complexes were not isolated due to unfavorable thermodynamics. In all isolated complexes, the D-A bonds, stabilized by negative hyperconjugation, were longer than the sum of the covalent radii and shorter than the sum of the van der Waals radii of the bonded atoms. In mixtures of 1 a, F^- , and SeCN^- , the complex [1 a-F]^- was selectively formed in accordance with thermodynamics. The reaction of 1 a with SeCN^- and the cyclic trimeric perfluoro-ortho-phenylene mercury afforded the complex [K(18-crown-6)][SCN]⋅(o-C₆ F₄ Hg)₃ , which was characterized by XRD.

Efficient electroluminescence of bluish green iridium complexes with 2-(3,5-bis(trifluoromethyl)phenyl)pyrimidine and 2-(3,5-bis(trifluoromethyl)phenyl)-5-fluoropyrimidine as the main ligands

Four bluish green iridium complexes with high photoluminescence quantum efficiencies were applied in OLEDs, and they showed a maximum current efficiency of 74.70 cd A⁻¹ and a maximum external quantum efficiency of 35.0% with mild efficiency roll-off.

3D molecular network and magnetic ordering, formed by multi-dentate magnetic couplers, bis(benzene)chromium(i) and [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazolidyl

The bis(benzene)chromium(i) salt of [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazolyl radical-anion formed a 3D network structure and realized a magnetically ordered state below 8 K.

Efficient bluish green electroluminescence of iridium complexes with good electron mobility

Two efficient bluish green iridium complexes with good electron mobility were applied in efficient OLEDs, showing a maximum current efficiency of 71.18 cd A⁻¹ and a maximum external quantum efficiency of 27.7%.

The Many Facets of Chalcogen Bonding: Described by Vibrational Spectroscopy

A diverse set of 100 chalcogen-bonded complexes comprising neutral, cationic, anionic, divalent, and double bonded chalcogens has been investigated using ωB97X-D/aug-cc-pVTZ to determine geometries, binding energies, electron and energy density distributions, difference density distributions, vibrational frequencies, local stretching force constants, and associated bond strength orders. The accuracy of ωB97X-D was accessed by CCSD(T)/aug-cc-pVTZ calculations of a subset of 12 complexes and by the CCSD(T)/aug-cc-pVTZ //ωB97X-D binding energies of 95 complexes. Most of the weak chalcogen bonds can be rationalized on the basis of electrostatic contributions, but as the bond becomes stronger, covalent contributions can assume a primary role in the strength and geometry of the complexes. Covalency in chalcogen bonds involves the charge transfer from a lone pair orbital of a Lewis base into the σ* orbital of a divalent chalcogen or a π* orbital of a double bonded chalcogen. We describe for the first time a symmetric chalcogen-bonded homodimer stabilized by a charge transfer from a lone pair orbital into a π* orbital. New polymeric materials based on chalcogen bonds should take advantage of the extra stabilization granted by multiple chalcogen bonds, as is shown for 1,2,5-telluradiazole dimers.

Fused 1,2,3-Dithiazoles: Convenient Synthesis, Structural Characterization, and Electrochemical Properties

A new general protocol for synthesis of fused 1,2,3-dithiazoles by the reaction of cyclic oximes with S₂Cl₂ and pyridine in acetonitrile has been developed. The target 1,2,3-dithiazoles fused with various carbocycles, such as indene, naphthalenone, cyclohexadienone, cyclopentadiene, and benzoannulene, were selectively obtained in low to high yields. In most cases, the hetero ring-closure was accompanied by chlorination of the carbocyclic moieties. With naphthalenone derivatives, a novel dithiazole rearrangement (15→13) featuring unexpected movement of the dithiazole ring from α- to β-position, with respect to keto group, was discovered. Molecular structure of 4-chloro-5H-naphtho[1,2-d][1,2,3]dithiazol-5-one 13 was confirmed by single-crystal X-ray diffraction. Electrochemical properties of 13 were studied by cyclic voltammetry and a complex behavior was observed, most likely including hydrodechlorination at a low potential.

Novel luminescent β-ketoimine derivative of 2,1,3-benzothiadiazole: synthesis, complexation with Zn(ii) and photophysical properties in comparison with related compounds

2,1,3-Benzothiadiazoles and their Zn complexes show fluorescence in different wavelength regions, one of the complexes reveals white emission.

A Qualitative Comparison of the Reactivities of 3,4,4,5-Tetrachloro-4H-1,2,6-thiadiazine and 4,5-Dichloro-1,2,3-dithiazolium Chloride

The high yielding transformations of 3,4,4,5-tetrachloro-4H-1,2,6-thiadiazine into 3,5-dichloro-4H-1,2,6-thiadiazin-4-one (up to 85%) and 2-(3,5-dichloro-4H-1,2,6-thiadiazin-4-ylidene)malononitrile (up to 83%) have been investigated and compared to the analogous transformations of the closely-related 4,5-dichloro-1,2,3-dithiazolium chloride (Appel's salt) into 4-chloro-5H-1,2,3-dithiazol-5-one and 2-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)malononitrile. Furthermore, cyclocondensation of 3,4,4,5-tetrachloro-4H-1,2,6-thiadiazine with 2-aminophenol and 1,2-benzenediamines gave fused 4H-1,2,6-thiadiazines in 68%-85% yields.