Lewis Base Sequestered Chalcogen Dihalides: Synthetic Sources of ChX2(Ch=Se, Te; X=Cl, Br)

Flexible and hierarchical metal-organic framework composite as solid-phase media for facile affinity-tip fabrication to selectively enrich glycopeptides and phosphopeptides

Micro-tip-based solid-phase microextraction is considered as one of the green and powerful analytical sample preparation techniques, but its efficiency is severely hampered by some basic issues such as tedious fabrication, instability of sorbent bed, and blocking of the tip, especially for biological samples due to low permeability. These issues are tackled by introducing a flexible and hierarchical substrate in the microtip, having good mechanical strength and specific functionality to capture the desired biomolecules. Considering the well-ordered and flexible structure of melamine foam, it was used as a substrate and for hydrophilic interaction chromatography (HILIC). Metal-organic framework, due to its excellent characteristics, was grafted on its surface anchored by self-assembling polydopamine. The resulting material was characterized and packed in the tip by just pressing the material in the conical structure of the tip. This affinity tip established good and tunable permeability and was used to selectively enrich glycopeptides as well as phosphopeptides. The affinity tip demonstrated excellent performance to enrich glycopeptides and phosphopeptides with a low limit of detection up to 0.5 fmol μL^-1 from tryptic digests of horseradish peroxidase and β-Casein, respectively, and was stable up to 5 rounds of enrichment. Moreover, this affinity-tip also exhibited high selectivity up to up to 1:1000 (HRP digest to BSA digest) for glycopeptides and 1:200 (β-Casein digest to BSA digest) for phosphopeptides and demonstrated several other fascinating characteristics such as; excellent size exclusion effect for the omission of large-sized proteins, modest backpressure, reproducibility, reusability, smooth enrichment, and successfully applied to a human saliva sample.

Tellura(benzo)bithiophenes: Synthesis, Oligomerization, and Phosphorescence

A series of planar π-extended Te-containing heteroacenes, termed tellura(benzo)bithiophenes, were synthesized. This new structural class of heterocycle features a tellurophene ring fused to a benzobithiophene unit with aromatic side groups (either -C₆H₄ⁱPr or -C₆H₄OCH₃) positioned at the 2- and 5-positions of the tellurophene moiety. Although attempts to enhance molecular rigidity and extend ring-framework π-delocalization in a cumenyl (-C₆H₄ⁱPr)-capped tellura(benzo)bithiophene led to oxidation (and Te-C bond scission) to form a diene-one, the formation of an oligomeric tellura(benzo)bithiophene was possible via Kumada catalyst-transfer polycondensation (KCTP). Furthermore, one tellura(benzo)bithiophene derivative exhibits orange-red phosphorescence at room temperature in air when incorporated into a poly(methyl methacrylate) host; accompanying TD-DFT computations provided insight into a potential mechanism for the observed phosphorescence.

Metallacycle Transfer and its Link to Light-Emitting Materials and Conjugated Polymers

Major advances in optoelectronic technologies (e. g., solar cells, organic light-emitting diodes, etc…) are prefaced by the discovery of new synthetic methodologies. In this review, the key role of the Fagan-Nugent reaction in enabling our team (and others) to gain access to new building blocks for luminescent materials and conjugated polymers bearing p-block elements will be described. The Fagan-Nugent reaction is extremely powerful as a synthetic tool since the efficient zirconium-element atom exchange involved affords a wide range of unsaturated inorganic heterocycles of controllable composition and function.

A Modular Approach to Phosphorescent π-Extended Heteroacenes

A modular route to previously inaccessible classes of ring-fused π-extended heteroacenes bearing the heavy inorganic element tellurium (Te) is presented. These new materials can be viewed as n-doped analogs of molecular graphene subunits that exhibit color tunable visible light phosphorescence in the solid state and in the presence of air. The general mechanism of phosphorescence in these systems was probed experimentally and computationally via time-dependent density functional theory (TD-DFT). The incorporation of Te into π-extended oligoacene frameworks was achieved by an efficient Zr/Te transmetalation protocol; related zirconium-element exchange reactions have been used to prepare both electron-rich and electron-deficient heterocycles containing different elements from throughout the p-block. Therefore, the current study provides a clear path to incorporate inorganic elements into heteroacenes of greater complexity and side group selectivity compared to existing synthetic routes.

Using boryl-substitution and improved Suzuki-Miyaura cross-coupling to access new phosphorescent tellurophenes

A new di(isopropoxy)boryl -B(OⁱPr)₂ tellurophene precursor is described, from which several previously inaccessible phosphorescent borylated tellurophenes are formed via exchange of the -OⁱPr groups. One such tellurophene Mes(ⁱPrO)B-Te-6-B(OⁱPr)Mes, bearing a sterically encumbered mesityl (Mes) substituent at each boron center, exhibits bright yellow-orange phosphorescence in the solid state at room temperature and in the presence of the known quencher O₂. Furthermore, Suzuki-Miyaura cross-coupling between the newly prepared borylated tellurophenes and the test substrate 2-bromothiophene was examined with the pre-catalyst Cl(XPhos)Pd(aminobiphenyl). While more electron deficient boryl groups such as catecholatoboryl (-Bcat) yield significant protodeboronation in place of productive C-C bond formation, efficient formation of the desired thiophene-capped tellurophene thienyl-Te-6-thienyl was noted from tellurophenes bearing the readily accessible pinacolatoboryl (-Bpin) and 1,8-naphthalenediaminatoboryl (-Bdan) functional groups. These findings open the door for the efficient synthesis of aryl tellurophenes and polytellurophenes via the ubiquitous Suzuki-Miyaura coupling of borylated tellurophenes, which was previously hampered by protodeboronation.

Selenium– and tellurium–halogen reagents

Selenium and tellurium form binary halides in which the chalcogen can be in formal oxidation states (IV), (II) or (I). They are versatile reagents for the preparation of a wide range of inorganic and organic selenium and tellurium compounds taking advantage of the reactivity of the chalcogen–halogen bond. With the exception of the tetrafluorides, the tetrahalides are either commercially available or readily prepared. On the other hand, the low-valent species, EX2 (E = Se, Te; X = Cl, Br) and E2X2 (E = Se, Te; X = Cl, Br) are unstable with respect to disproportionation and must be used as in situ reagents. Organoselenium and tellurium halides are well-known in oxidation states (IV) and (II), as exemplified by REX3, R2EX2 and REX (R = alkyl, aryl; E = Se, Te; X = F, Cl, Br, I); mixed-valent (IV/II) compounds of the type RTeX2TeR are also known. This chapter surveys the availability and/or preparative methods for these widely used reagents followed by examples of their applications in synthetic inorganic and organic selenium and tellurium chemistry. For both the binary halides and their organic derivatives, the discussion is subdivided according to the formal oxidation state of the chalcogen.

Moving Beyond Boron-Based Substituents To Achieve Phosphorescence in Tellurophenes

Previous research in our group showed that tellurophenes with pinacolboronate (BPin) units at the 2- and/or 5-positions displayed efficient phosphorescence in the solid state, both in the presence of oxygen and water. In this current study, we show that luminescence from a tellurophene is possible when various aryl-based substituents are present, thus greatly expanding the family of known (and potentially accessible) Te-based phosphors. Moreover, for the green phosphorescent perborylated tellurium heterocycle, 2,3,4,5-TeC₄BPin₄ (4BTe), oxygen-mediated quenching of phosphorescence is an important contributor to the lack of emission in solution (when exposed to air); thus, this system displays aggregation-enhanced emission (AEE). These discoveries should facilitate the future design of color tunable tellurium-based luminogens.

Titanocene-Mediated Dinitrile Coupling: A Divergent Route to Nitrogen-Containing Polycyclic Aromatic Hydrocarbons

A general synthetic strategy for the construction of large, nitrogen-containing polycyclic aromatic hydrocarbons (PAHs) is reported. The strategy involves two key steps: (1) a titanocene-mediated reductive cyclization of an oligo(dinitrile) precursor to form a PAH appended with di(aza)titanacyclopentadiene functionality; (2) a divergent titanocene transfer reaction, which allows final-step installation of one or more o-quinone, diazole, or pyrazine units into the PAH framework. The new methodology enables rational, late-stage control of HOMO and LUMO energy levels and thus photophysical and electrochemical properties, as revealed by UV/vis and fluorescence spectroscopy, cyclic voltammetry, and DFT calculations. More generally, this contribution presents the first productive use of di(aza)metallacyclopentadiene intermediates in organic synthesis, including the first formal [2 + 2 + 2] reaction to form a pyrazine ring.

Insights into the formation of inorganic heterocycles via cyclocondensation of primary amines with group 15 and 16 halides

The cyclocondensation reaction of primary amines with pnictogen and chalcogen halides is a major preparative route for the generation of inorganic heterocycles involving a Group 15 or 16 element linked to nitrogen.

Transition metal mediated formation of dicationic diselenides stabilised by N-heterocyclic carbenes: designed synthesis

Designed syntheses of dicationic diselenides have been developed by (i) reduction of dihaloselones (routes A and B) and (ii) by oxidation of selone adducts of metal halides (route C).

A 2,2′-bipyridine coordination complex of [ICl2]+

A straightforward synthesis of a new type of iodine(iii) complex is presented – anN′Nchelated [ICl₂]⁺cation.

2,6-Dihalo-9-selenabicyclo[3.3.1]nonanes and their complexes with selenium dihalides: synthesis and structural characterisation

2,6-Dihalo-9-selenabicyclo[3.3.1]nonanes form the 2 : 1 complexes with SeCl₂and SeBr₂, which are the first representatives of coordination compounds with the Se⋯Se⋯Se bonds.

Phosphorescence within benzotellurophenes and color tunable tellurophenes under ambient conditions

The zirconium-mediated syntheses of pinacolboronate (BPin) appended benzo[b]tellurophenes and two phenyl/BPin substituted tellurophene isomers with different colors of emission have been achieved.

Experimental and theoretical investigations of selenium nuclear magnetic shielding tensors in Se–N heterocycles

A preliminary study involving solid-state 77Se NMR spectroscopy and first principles calculations of 77Se NMR parameters in Se–N heterocycles is reported. 77Se CP/MAS NMR spectra of the ring systems reveal expansive selenium chemical shift (CS) tensors, which are extremely sensitive to molecular geometry, symmetry, ligand substitution, and intermolecular contacts. For systems with known crystal structures, hybrid density functional theory (DFT) calculations of selenium nuclear magnetic shielding (NMS) tensors were carried out, and tensor orientations in the molecular frames examined. Additional DFT calculations of selenium NMS tensors are presented, along with a detailed analysis of pairs of occupied and virtual molecular orbitals that give rise to the Se NMS tensors. A new naturalized local molecular orbital (NLMO) analysis under the same DFT framework is also discussed. Collectively, the NMR data and first principles calculations provide understanding of the influences of electronic structure, bonding, and intermolecular interactions on the selenium NMS tensors, allowing for (i) prediction of unknown molecular structures and (ii) insight into the positions of the stereochemically active selenium lone pairs.