Rudolf Pietschnig

Surface Modifications Using a Water-Stable Silanetriol in Neutral Aqueous Media

Surface modifications of glass slides employing the sterically hindered tert-butyl substituted silanetriol are described. To the best of our knowledge, this is the first time that a stable silanetriol has been directly used for this purpose. So far unprecedented, this process runs under neutral aqueous conditions and in the absence of organic solvents, which makes coating protocols accessible to acid-sensitive substrates. The layer thickness and surface topography are investigated by the Sarfus technique, by X-ray reflectivity, and by atomic force microscopy (AFM). These techniques yield values of 0.8±0.1 (XRR) and 0.6±0.2 nm (Sarfus) for layer thickness and 0.33 nm for root mean square roughness (AFM). The modified surfaces have hydrophobic and oleophilic character and contact angles (CA) between 60° (formamide, CH2I2) and 90° (water) are obtained. The thin coatings allow a structuring by UV/ozone treatment in order to get hydrophilic and hydrophobic compartments on the surfaces. For all coatings, surface free energies are calculated using different models. To determine the isoelectric points (IEP) of the modified surfaces, we performed zeta-potential measurements. Correlations between zeta potentials and hydrophilicity of the surfaces are shown.

Optimized synthesis of tetrafluoroterephthalic acid: a versatile linking ligand for the construction of new coordination polymers and metal-organic frameworks.

Pure 2,3,5,6-tetrafluoroterephthalic acid (H2tfBDC) is obtained in high yields (95%) by reacting 1,2,4,5-tetrafluorobenzene with a surplus (>2 equiv) of n-butyllithium in tetrahydrofuran (THF) and subsequent carbonation with CO2 without any extensive purification procedure. A single crystal X-ray structure analysis of H2tfBDC (1) confirms former data obtained for a deuterated sample (P1̅, Z = 1). Recrystallization from water/acetone leads to single crystals of H2tfBDC·2H2O (2, P21/c, Z = 2), where an extensive hydrogen bonding network is found. By reacting H2tfBDC with an aqueous ammonia solution, single crystals of (NH4)2tfBDC (3, C2/m, Z = 2) are obtained. 3 is thermally stable up to 250 °C and shows an enhanced solubility in water compared to H2tfBDC. Monosubstituted 2,3,5,6-tetrafluorobenzoic acid (H2tfBC, 4) is obtained by reacting 1,2,4,5-tetrafluorobenzene with stoichiometric amounts (1 equiv) of n-butyllithium in THF. Its crystal structure (Fdd2, Z = 16) shows dimeric units as characteristic structural feature.

Silanetriols as in vitro inhibitors for AChE

Graphical abstract

Diphospha[2]ferrocenophane (alias 1,4-dihydrotetraphosphaneoxide): stereoselective formation via hydrolytic P-P bond formation.

Phosphorus-rich compounds recently attracted great interest as primary products in the direct functionalization of elemental phosphorus. Linear oligo-/polyphosphanes (PnHn+2), which are particularly rich in phosphorus, are on the other hand unstable against disproportionation, unlike their carbon analogues, the alkanes (CnH2n+2). [10,11] In the past, linear tetraphosphanes have been stabilized to some extent by partial substitution—ideally with sterically demanding substituents. Also the embedding of H-terminated tetraphosphane units into bicyclic systems improves their thermal stability which allowed the first crystal structure determinations for such compounds. The rigid geometry in such bicyclic systems ensures that the phosphorus lone pairs of neighboring atoms adopt the more stable gauche conformation. Herein, we report synthesis, structure and stereochemical aspects of a stable ferrocenylene bridged H-terminated tetraphosphane oxide (1), which is only the second diphospha[2]ferrocenophane as well as the first monooxidized tetraphosphane reported so far. Ferrocenylene-bridged bisdiphosphene 2, which represents a unique organometallic chromophore, was used as a starting point in the preparation of 1. Earlier we found that a single diphosphene unit attached to ferrocene reacts with water under cleavage of the P P bond as common for diphosphenes. Similar behavior has also been reported for 2 where a second diphosphene unit is present in the molecule. Now we found that a contrary reaction occurs if 2 is reacted with small amounts of water. In this case no fission of the P P bonds occurs, but actually a new P P bond is formed. This reaction behavior can be rationalized as summarized in Scheme 1. After initial addition of H2O to a diphosphene unit the primarily resulting hydroxy phosphane 3 can be expected to tautomerize to its corresponding oxophosphorane 4. The latter could subsequently or concurrently undergo intramolecular 1,2-addition to the second diphosphene unit in the proximity (Scheme 1). It needs to be pointed out that this reaction proceeds quantitatively, but none of the intermediates postulated above have been observed spectroscopically. The difference in reactivity depending on the amount of water is unprecedented for diphosphenes but related to the first observation of 1-hydroxytriphosphane in complexed form published recently. Also the addition of secondary oxophosphoranes to double bonds is well established.

Synthesis and reactivity of P-ferrocenylalkylidenephosphanes and related iminophosphanes and diphosphenes

P-Ferrocenyl-substituted alkylidenephosphanes have been prepared and characterized spectroscopically. Their ready conversion to the corresponding acylphosphanes and 1,2-diacyldiphosphanes, as well as a new type of phosphirene synthesis are presented. The X-ray structure of the tetraferrocenyl-substituted diacyldiphosphane has been investigated. Furthermore, P-ferrocenyl iminophosphanes and their complexation behaviour are described. Diferrocenyldiphosphene, which is known to be unstable, has been stabilized by complexation; this has been confirmed by NMR-spectroscopy and X-ray structure analysis.

Silanetriols as Powerful Starting Materials for Selective Condensation to Bulky POSS Cages.

Controlled condensation reactions of tertiary silanetriols CH3(CH2)n(CH3)2CSi(OH)3 (1b–f; n = 1–5) in the presence of trifluoroacetic acid and the hydrolysis of CH3(CH2)6(CH3)2CSiCl3 (3) lead to the selective formation of the corresponding disiloxane tetrols [CH3(CH2)n(CH3)2CSi(OH)2]2O (2b–g; n = 1–6) in good yields. The TBAF-driven condensation reactions of the silanetriols CH3(CH2)n(CH3)2CSi(OH)3 (1a–c; n = 0–2) as well as of the disiloxane-1,1,3,3-tetrol 2d (n = 3) yield in the selective formation of the first T8 cages bearing tertiary carbon substituents, CH3(CH2)n(CH3)2C (4a–d; n = 0–3), which was not possible via the condensation of their alkoxysilane counterparts so far. The resulting compounds 2b–g and 4a–d have been characterized by multinuclear NMR, MS, and single-crystal X-ray diffraction.

Silanol-based surfactants: synthetic access and properties of an innovative class of environmentally benign detergents.

Herein, environmentally friendly surfactants based on new silanols as substitutes for the isoelectronic phosphonates were explored. Surface tensions of aqueous solutions are significantly reduced, particularly with those silanols that feature a high ratio of organic moiety to silanol. Besides their use as surfactants, their potential as coating agents for hydrophilic oxide surfaces was investigated for the example of glass substrates. In the solid-state sheet structures with silanol, double layers are present, in which the sheet spacing varies with the alkyl-chain length.

Phosphaalkenylidene bridged ferrocenes.

The lithiation of ferrocenylphosphane Fc-PH2 (Fc = –C5H4FeC5H5) has been reinvestigated and both Fc-PHLi and Fc-PLi2 have been identified by NMR-spectroscopy. The lithiated phosphanides have been converted to the corresponding mono and bis(silylated) species the latter of which gave synthetic access to an oligomer in which three ferrocene units are symmetrically connected by phosphaalkene units. The charge distribution within this oligomer and its isomers has been analyzed using DFT calculations which indicates that the iron atom of the central metallocene unit is slightly more positive than the terminal ones. These findings are supported experimentally by Mößbauer spectroscopy and cyclic voltammetry.

Exploring the Anion-Cation Interaction in m-Terphenyltetrafluorosilicates by Using Multinuclear NMR Spectroscopy, X-ray Diffraction, and ICR-FT-MS

The synthesis of a series of m-terphenyl-substituted tetrafluorosilicates with different cations (Na(+), K(+), Rb(+), Cs(+), Ag(+), Tl(+)) is described and the interactions between the anion and cation are investigated in the solid, solution, and gas states by using multinuclear NMR spectroscopy, X-ray diffraction, and ion cyclotron resonance Fourier-transform mass spectrometry (ICR-FT-MS). In solution, heteronuclear NMR spectroscopy parameters show only limited sensitivity to the nature of the cation, which furthermore can be affected by solvent effects. More pronounced effects are observed in the structural data obtained from X-ray diffraction studies, which are in good agreement with experimental gas-phase data from ESIMS. ESIMS also reveals the existence of dimeric species of the type [M(DmpSiF(4))(2)](-) (Dmp = 2,6-dimesitylphenyl), the stability of which was determined by normalized collision energy experiments.

Self-assembly of tert-butyl silanetriol in solution and aggregation with tetrahydrofuran

tert-Butyl silanetriol behaves like a surfactant and self-assembles in aqueous and tetrahydrofuran (THF) solutions. Micelle formation was studied with pulsed field gradient stimulated spin echo (PFG-SSE) NMR, while multilayer lamellar vesicles can be concluded from small/wide angle X-ray scattering measurements in concentrated solutions at elevated temperature. The significant interaction between tert-butyl silanetriol and THF is further highlighted by a crystal structure featuring a 3:1 adduct of silanetriol and THF.