Selective access to either a doubly boron-doped tetrabenzopentacene or an oxadiborepin from the same precursor

Depending on the solvent, a brominated arylborane gave the multiple helicene B₂-TBPA (pyridine) or the oxadiborepin ODBE (THF) after intramolecular Yamamoto coupling.

The well-known red emitter tetrabenzo[de,hi,op,st]pentacene (TBPA) has been transformed into a bright blue emitter (B₂-TBPA; λ_em = 472 nm; c-hexane) via substitutional doping with two boron atoms. In contrast to the electron-rich TBPA, which forms endo-peroxides with O₂ under daylight, the benchtop-stable B₂-TBPA is a good electron acceptor and undergoes reversible reduction at a moderate half-wave potential of E_1/2 = –1.73 V (vs. FcH/FcH⁺; THF). Although the size of B₂-TBPA falls within the nanoscale, the helically twisted compound readily dissolves in c-hexane and does not require solubilizing substituents. The synthesis of B₂-TBPA is based on the nickel-mediated Yamamoto-type dehalogenation of tetrabrominated 9,10-di(naphth-1-yl)-9,10-dihydro-9,10-diboraanthracene. This intramolecular C–C heterocoupling reaction shows a remarkable solvent dependence: B₂-TBPA forms only in pyridine (79% yield), whereas an oxadiborepin is obtained from THF solutions (ODBE, 81%; the reaction mixture is quenched with air in both cases). Insight into the corresponding reaction mechanism was gained from the isolation of intermediates and an investigation of their chemical properties. ODBE is an interesting blue emitter in its own right. Furthermore, it can be ring-opened with excess BBr₃ at the B–O–B moiety to afford a dimeric borabenzo[de]anthracene.

Iodo(triphenyl)silane

The molecular structure of the title compound, C18H15ISi, which crystallizes in the space group C2/c, does not exhibit any unusual features. Two weak C—H...π interactions may help to consolidate the packing. The present structure is not isostructural with the known Ph3SiX (X = F, Cl or Br) compounds.

Aryl-aryl coupling in a polycyclic aromatic hydrocarbon with embedded tetracoordinate boron centre

The addition of 2 eq. of MesLi to the biphenylene-containing 9,10-dihydro-9,10-diboraanthracene (DBA) 2 results in the formation of the corresponding oxaboraphenanthrene 3 after column chromatography under ambient conditions. In the initial step, the anionic B-Mes monoadduct of 2 is generated, which eliminates a formal [Mes₂B:]^- ion with concomitant C-C-bond formation (room temperature, 18 h). The resulting biphenylene-containing borafluorene 4 is still sufficiently Lewis acidic to add the second equivalent of MesLi ([4Mes]^-). Using pristine 9-mesityl-9-borafluorene as a model system, we confirmed that both 4 and [4Mes]^- should be capable of inserting an oxygen atom to furnish the observed oxaboraphenanthrene scaffold. The biphenylene-containing oxaboraphenanthrene 3 is a yellow compound with an absorption maximum at λ_max = 450 nm. Similar to its DBA analogue 2, 3 shows no photoluminescence.

Polymorphism and pseudosymmetry of 10,10'-oxybis(9-thia-10-hydro-10-boraanthracene)

Two polymorphs of the title compound are reported. The first crystallizes in the non-centrosymmetric space group P2₁ with four mol­ecules, related by pseudosymmetry, in the asymmetric unit. The second crystallizes in the centrosymmetric space group P2₁/c with only two mol­ecules in the asymmetric unit.

We have encountered two polymorphs of the title compound, C₂₄H₁₆B₂OS₂, both of which display almost the same unit-cell parameters. Compound (I) crystallizes in the non-centrosymmetric space group P2₁ with four mol­ecules in the asymmetric unit. These mol­ecules are related by pseudosymmetry. As a result, the space group looks like P2₁/c, but the structure cannot be refined successfully in that space group. Compound (II) on the other hand crystallizes in the centrosymmetric space group P2₁/c with only two mol­ecules in the asymmetric unit. The crystals studied for (I) and (II) were both non-merohedral twins.

Simultaneous expansion of 9,10 boron-doped anthracene in longitudinal and lateral directions

Doubly boron-doped anthracenes and pentacenes have been longitudinally and laterally expanded through annulation of thiophene or benzene rings. The obtained series of closely related compounds allowed an assessment of key structure-property relationships with a focus on optoelectronic characteristics. Most of the products are benchtop-stable blue emitters and capable of accepting two electrons in a reversible manner. The syntheses involved late-stage modifications through photocyclization or stepwise oxidative C-C coupling (DDQ/BF₃·Et₂O) as well as cyclocondensation of ortho-disilylated or -diborylated aryl building blocks.

Challenging structure determination from powder diffraction data: two pharmaceutical salts and one cocrystal with Z′ = 2

Structure solution of molecular crystals from powder diffraction data by real-space methods becomes challenging when the total number of degrees of freedom (DoF) for molecular position, orientation and intramolecular torsions exceeds a value of 20. Here we describe the structure determination from powder diffraction data of three pharmaceutical salts or cocrystals, each with four molecules per asymmetric unit on general position: Lamivudine camphorsulfonate (1, P 21, Z=4, Z′=2; 31 DoF), Theophylline benzamide (2, P 41, Z=8, Z′=2; 23 DoF) and Aminoglutethimide camphorsulfonate hemihydrate [3, P 21, Z=4, Z′=2; 31 DoF (if the H2O molecule is ignored)]. In the salts 1 and 3 the cations and anions have two intramolecular DoF each. The molecules in the cocrystal 2 are rigid. The structures of 1 and 2 could be solved without major problems by DASH using simulated annealing. For compound 3, indexing, space group determination and Pawley fit proceeded without problems, but the structure could not be solved by the real-space method, despite extensive trials. By chance, a single crystal of 3 was obtained and the structure was determined by single-crystal X-ray diffraction. A post-analysis revealed that the failure of the real-space method could neither be explained by common sources of error such as incorrect indexing, wrong space group, phase impurities, preferred orientation, spottiness or wrong assumptions on the molecular geometry or other user errors, nor by the real-space method itself. Finally, is turned out that the structure solution failed because of problems in the extraction of the integrated reflection intensities in the Pawley fit. With suitable extracted reflection intensities the structure of 3 could be determined in a routine way.

C-Halogenated 9,10-Diboraanthracenes: How the Halogen Load and Distribution Influences Key Optoelectronic Properties

9,10-Dihydro-9,10-diboraanthracenes (DBAs) have low-energy LUMOs and narrow HOMO-LUMO gaps and are thus attractive electron-transporting and light-emitting materials in optoelectronic devices. A systematic series of ten C-halogenated 9,10-(Mes)₂ -DBAs was synthesized and studied by cyclic voltammetry, UV/Vis absorption and emission spectroscopy, and quantum-chemical calculations (Mes=mesityl). We probed the influence of the nature of the halogen atoms and the halogen substitution patterns on key optoelectronic properties of the DBAs. All 9,10-(Mes)₂ derivatives can be reversibly reduced at the DBA cores and at electrode potentials between E_1/2 ^Red1 =-1.84 and -1.26 V (vs. FcH/FcH⁺ ). The most bathochromic UV/Vis absorption and the fluorescence emission of each DBA correspond to an ICT transition between the Mes rings and the DBA core. Br substituents lower the DBA LUMO energy and narrow the energy gap to the highest degree along the series F<Cl<Br. Halogen atoms located at 1,4,5,8-positions are more influential than those at 2,3,6,7-positions. An increasing fluorine load continuously decreases the LUMO levels and HOMO-LUMO gaps. Colorless octafluoro- and tetrafluoro-DBAs form colored and fluorescent π-stacked hetero dimers with anthracene in C₆ H₆ solutions and in the solid state. The sterically congested 1,5-(ThMe)₂ -9,10-(Mes)₂ -DBA was prepared in 74 % yield from 1,5-(Br)₂ -9,10-(Mes)₂ -DBA and Me₃ Sn-ThMe through a Stille-type C-C coupling reaction (ThMe=5-Me-2-thienyl).

Bi(OTf)3-Catalyzed Diastereoselective One-Pot Synthesis of 1,3-Diamines with Three Continuous Stereogenic Centers

A highly modular, diastereoselective one-pot-synthesis of 1,3-diamines with three contiguous stereogenic centers is reported. Our method provides a fast and efficient access to 1,2- anti-2,3- anti-1,3-diamines from three readily available building blocks. This Bi(OTf)₃-catalyzed reaction is insensitive to air and moisture and can be performed on a multigram scale.

Crystal growth and magnetic characterization of HoIr2Si2 (I4/mmm)

Single crystals of HoIr₂Si₂ with the body-centered ThCr₂Si₂-type structure (I4/mmm) were grown by Bridgman method from indium flux. Single crystal structure determination yielded a Si-z position of 0.378(1) in the structure. We excluded the presence of the high temperature phase with the primitive CaBe₂Ge₂-type structure (P4/nmm) by powder x-ray diffraction. Magnetic measurements on the single crystals yield a Néel temperature of [Formula: see text] K. In the inverse magnetic susceptibility a strong anisotropy with Weiss temperatures [Formula: see text] K and [Formula: see text] K occurs above T _N. The effective magnetic moment [Formula: see text] and [Formula: see text] is close to the expected value for a free Ho³⁺ ion, [Formula: see text]. The field dependent magnetization shows a step-like behaviour due to crystalline electric field effects. The temperature and field dependence of the magnetization hint to the ordering of the magnetic moments along the c direction below T _N.

Syntheses and Crystal Structures of Phenyl-Lithium Derivatives

Although organolithium compounds have been studied and applied for ∼100 years, only few crystal structures of pure, unsolvated organolithium compounds have been reported so far. Therefore, several phenyl-lithium derivatives were synthesized by lithium-halogen exchange reactions, yielding fairly soluble polymers in the cases of 4- and 2-methylphenyl-lithium ( p-TolLi and o-TolLi). Their crystal structures have been determined by X-ray powder diffraction. Remarkably, o-TolLi crystallizes in the noncentrosymmetric space group P2₁2₁2₁ with two independent monomers, whereas the crystal structure of p-TolLi is described in spacegroup P2₁/ a. In contrast, no polymer of 5- m-XyLi (3,5-dimethyl-phenyl-lithium) could be observed, but single crystals of a [(5- m-XyLi)₃(MTBE)₃LiBr] adduct were isolated (MTBE = methyl- tert-butylether). This gives hints on the nature of lithium-halogen exchange reactions. Steric and electronic effects of the phenyl-lithium substitution are further discussed in conjunction with related compounds.