Linear and Hyperbranched Poly(arylene ether)s from a New Semifluorinated AB Monomer

A new trifluoromethyl-activated AB monomer has been successfully synthesized by Pd-initiated coupling of 4-bromo anisole with 4-fluoro-3-trifluoromethylphenylboronic acid followed by demethylation. The monomer leads to a semifluorinated poly(arylene ether) by nucleophilic displacement polymerization reaction. The AB monomer has been further copolymerized with a corresponding AB ₂ monomer to form the corresponding semifluorinated hyperbranched (hb) poly(arylene ether). The resulting linear and hb poly(arylene ether)s exhibited weight average molecular weight of 75700 and 144100 g/mol, respectively. The hb copolymer exhibited better solubility in different organic solvents compared to the linear poly(arylene ether). The polymers showed excellent thermal stability up to 522°C at 10% wt loss in air and glass transition temperatures as high as 187°C. The mechanical properties of the linear poly(arylene ether) film 1a exhibited tensile strength at break of 89 MPa, elongation at break of up to 3% and a Young’s modulus value of 2.66 GPa. The films of the polymers were hydrophobic in nature and showed water contact angle as high as 93.6°.     

2-Hydroxyphenylphosphinic Acid: P-Analogue of Salicylic Acid?

Abstract

Substitution of the carboxyl group -C(O)OH by -P(O)(OH)₂ and -P(O)R(OH) leads to compounds of interest to agriculture, technics and pharmacology. Under these aspects the P-analogon 1 of salicylic acid was prepared, because the monobasic -P(O)H(OH) group resembles more the carboxyl function than the dibasic moiety -P(O)(OH)₂.     

A small cavity with reactive internal shell atoms spanned by four {As(W/V)9}-type building blocks allows host-guest chemistry under confined conditions

The reaction of [H2As(III)W18O60]7- with VO2+ and SO4(2-) ions in aqueous solution leads to a V(IV)/V(V) mixed-valence cluster anion containing the {As4M40O140}-type cryptand which has a high formation tendency. An important result is that it exhibits a new type of reactive internal cavity shell. The correspondingly obtained compound Na(NH4)20[{(V(IV)O(H2O))(V(IV)O)2(SO4)2}{(As(III)W9O33)2(As(III)W7.5V(V)1.5O31)2(WO2)4}] x 40 H2O (1), which can also be synthesized from a precursor with the preorganized cryptand, was characterized by elemental and thermogravimetric analyses (determination of crystal water content), redox titrations (determination of the number of V(IV) centers), electronic absorption as well as vibrational spectra, single-crystal X-ray structure analysis (including bond valence sum calculations), and magnetic susceptibility measurements. The relatively small central cavity--formed by the linking of four {AsM9}-type lacunary units (M = W/V) by four WO6 octahedra--allows positioning of a variety of cationic as well as anionic "guests" under confined conditions according to a new approach: replacement of some of the W by V atoms leads to high reactivity of the internal cavity shell as a result of relatively weak VO bonds compared to the WO bonds. This allows an interesting "encapsulation chemistry" with new options. In the present case the cavity contains besides an arrangement of three V(IV) centers, two sulfate groups that replace O atoms of the {AsM9} units as well as an interesting hydrogen bond situation.     

Polypyrrole-Coated and Polysulfate-Modified CE Capillaries

Fused-silica capillaries covalently coated with polypyrrole offer some interesting properties for capillary electrophoresis. The polymeric, surface-bonded coating is chemically stable and reduces the adsorptive properties of the silica surface. At the same time, the weak positive surface charges offer the possibility of creating a strongly anionic surface when poly-sulfates are used as counter-ions. This affords an electroosmotic flow which is largely independent of pH. With sodium dodecyl sulfate in the background electrolyte, this effect is further enhanced. The potential of the approach is demonstrated with the separation of herbicides by micellar electrokinetic chromatography. Repeatability of electroosmotic mobility of less than 1% RSD is achieved.     

A simplified but intuitive analytical model for intermittent-contact-mode force microscopy based on Hertzian mechanics

The forces acting on the substrate in intermittent-contact-mode (IC mode, tapping mode) atomic force microscopy are not accessible to a direct measurement. For an estimation of these forces, a simple analytical model is developed by considering only the shift of the cantilever resonance frequency caused by Hertzian (contact) forces. Based on the relationship between frequency shift and tip–sample force for large-amplitude frequency-modulation atomic force microscopy, amplitude and phase versus distance curves are calculated for the intermittent contact mode, and the forces on the substrate are calculated. The results show a qualitative agreement with numerical calculations, yielding typical maximal forces of 50–150 nN. When working above the unperturbed resonance, forces are found to be significantly larger than below the resonance.     

Porous Capsules with a Large Number of Active Sites: Nucleation/Growth under Confined Conditions

This work deals with the generation of large numbers of active sites and with ensuing nucleation/ growth processes on the inside wall of the cavity of porous nanocapsules of the type (pentagon)₁₂(linker)₃₀≡{(Mo^VI)Mo^VI₅}₁₂{Mo^V₂(ligand)}₃₀. A first example refers to sulfur dioxide capture through displacement of acetate ligands, while the grafted sulfite ligands are able to trap {MoO₃H}⁺ units thereby forming unusual {(O₂SO)₃MoO₃H}^5? assemblies. A second example relates to the generation of open coordination sites through release of carbon dioxide upon mild acidification of a carbonate‐type capsule. When the reaction is performed in the presence of heptamolybdate ions, MoO₄^2? ions enter the cavity where they bind to the inside wall while forming new types of polyoxomolybdate architectures, thereby extending the molybdenum oxide skeleton of the capsule. Parallels can be drawn with Mo‐storage proteins and supported MoO₃ catalysts, making the results relevant to molybdenum biochemistry and to catalysis.     

Helical Bilayer Nonbenzenoid Nanographene Bearing a [10]Helicene with Two Embedded Heptagons

The precision synthesis of helical bilayer nanographenes (NGs) with new topology is of substantial interest because of their exotic physicochemical properties. However, helical bilayer NGs bearing non-hexagonal rings remain synthetically challenging. Here we present the efficient synthesis of the first helical bilayer nonbenzenoid nanographene ( HBNG1 ) from a tailor-made azulene-embedded precursor, which contains a novel [10]helicene backbone with two embedded heptagons. Single-crystal X-ray analysis reveals its highly twisted bilayer geometry with a record small interlayer distance of 3.2 Å among the reported helical bilayer NGs. Notably, the close interlayer distance between the two layers offers intramolecular through-space conjugation as revealed by in situ spectroelectrochemistry studies together with DFT simulations. Furthermore, the chiroptical properties of the P/M enantiomers of HBNG1 are also evaluated by circular dichroism and circularly polarized luminescence.     

Molecular Ln(III)−H−E(II) Linkages (Ln=Y,Lu; E=Ge,Sn, Pb)

Following the alkane-elimination route, the reaction between tetravalent aryl tintrihydride Ar*SnH₃ and trivalent rare-earth-metallocene alkyls [Cp*₂Ln(CH{SiMe₃}₂)] gave complexes [Cp*₂Ln(μ-H)₂SnAr*] implementing a low-valent tin hydride (Ln=Y, Lu; Ar*=2,6-Trip₂C₆H₃, Trip=2,4,6-triisopropylphenyl). The homologous complexes of germanium and lead, [Cp*₂Ln(μ-H)₂EAr*] (E = Ge, Pb), were accessed via addition of low-valent [(Ar*EH)₂] to the rare-earth-metal hydrides [(Cp*₂LnH)₂]. The lead compounds [Cp*₂Ln(μ-H)₂PbAr*] exhibit H/D exchange in reactions with deuterated solvents or dihydrogen.     

Hydridotetrylene [Ar*EH] (E = Ge,Sn, Pb) coordination at tantalum,tungsten, and zirconium

In a reaction of tantalocene trihydride with the low valent aryl tin cation [Ar*Sn(C₆H₆)][Al(OC{CF₃}₃)₄] (1a) the hydridostannylene complex [Cp₂TaH₂–Sn(H)Ar*][Al(OC{CF₃}₃)₄] (2) was synthesized. Hydride bridged adducts [Cp₂WH₂EAr*][Al(OC{CF₃}₃)₄] (E = Sn 3a, Pb 3b) were isolated as products of the reaction between Cp₂WH₂ and cations [Ar*E(C₆H₆)][Al(OC{CF₃}₃)₄] (E = Sn 1a, Pb 1b). The tin adduct 3a exhibits a proton migration to give the hydridostannylene complex [Cp₂W(H) Sn(H)Ar*][Al(OC{CF₃}₃)₄] 4a. The cationic complex 4a is deprotonated at the tin atom in reaction with base ^MeNHC at 80 °C to give a hydrido-tungstenostannylene [Cp₂W(H)SnAr*] 5a. Reprotonation of metallostannylene 5a with acid [H(Et₂O)₂][BAr^F] provides an alternative route to hydridotetrylene coordination. Complex 4a adds hydride to give the dihydrostannyl complex [Cp₂W(H)–SnH₂Ar*] (7). With styrene 4a shows formation of a hydrostannylation product [Cp₂W(H) Sn(CH₂CH₂Ph)Ar*][Al(OC{CF₃}₃)₄] (8). The lead adduct 3b was deprotonated with ^MeNHC to give plumbylene 5b [Cp₂W(H)PbAr*]. Protonation of 5b with [H(Et₂O)₂][Al(OC{CF₃}₃)₄] at −40 °C followed by low temperature NMR spectroscopy indicates a hydridoplumbylene intermediate [Cp₂W(H) Pb(H)Ar*]⁺ (4b). Hydrido-tungstenotetrylenes of elements Ge (5c), Sn (5a) and Pb (5b) were also synthesized reacting the salt [Cp₂W(H)Li]₄ with organotetrylene halides. The metallogermylene [Cp₂W(H)GeAr*] (5c) shows an isomerization via 1,2-H-migration to give the hydridogermylene [Cp₂W Ge(H)Ar*] (9), which is accelerated by addition of AIBN. 9 is at rt photochemically transferred back to 5c under light of a mercury vapor lamp. Zirconocene dihydride [Cp₂ZrH₂]₂ reacts with tin cation 1a to give the trinuclear hydridostannylene adduct 10 [({Cp₂Zr}₂{μ-H})(μ-H)₂μ-Sn(H)Ar*][Al(OC{CF₃}₃)₄]. Deprotonation of 10 was carried out using benzyl potassium to give neutral [({Cp₂Zr}₂{μ-H})(μ-H)μ-Sn(H)Ar*] (11). 11 was also obtained from the reaction of low valent tin hydride [Ar*SnH]₂ with two equivalents of [Cp₂ZrH₂]₂. The trihydride Ar*SnH₃ reacts with half of an equivalent of [Cp₂ZrH₂]₂ under evolution of hydrogen and formation of a dihydrostannyl complex 13 [Cp₂Zr(μ-H)SnH₂Ar*]₂ and with further equivalents of Ar*SnH₃ to give bis(hydridostannylene) complex [Cp₂Zr{Sn(H)Ar*}₂].

Low valent cations of tin and lead were used to form hydridotetrylene coordination compounds. The mobility of the hydrogen substituent was investigated in deprotonation equilibria as well as in 1,2-H-shift reactions.