Dendritic, nanosized building block for siloxane-based materials: a spherosilicate dendrimer

A spherosilicate dendrimer ( DMS‐1 ) with closely spaced reaction sites (Si? H groups) on the dendrimer surface has been synthesized by stepwise silylation of double‐four‐ring silicate with chlorotriethoxysilane (ClSi(OEt)₃) and subsequently with chlorodimethylsilane (ClSiHMe₂). DMS‐1 consists of a maximum of 40 Si atoms in the interior frameworks and 24 reactive Si? H groups on the surface. Because DMS‐1 is spherical and about 1.5 nm in diameter, it can be regarded as the smallest well‐defined silica‐based nanoparticle. DMS‐1 also forms molecular crystals and is soluble in typical organic solvents. A molecularly ordered silica‐based hybrid can be prepared by heating a cast film of DMS‐1 at 180 °C for 5 days. The surface of DMS‐1 can be modified by hydrosilylation with 1‐hexadecene, triethoxyvinylsilane, and allylic‐terminated tetraethylene glycol monomethyl ether. More than 20 Si? H groups out of 24 react with these reagents. The solubilities of the products depend on the modification. DMS‐1 is not only a building block for nanohybrids, but also the smallest and most precisely designed siloxane‐based nanoparticle.     

Application of Sulfonic Acid Functionalized SBA‐15 as a New Nanoporous Acid Catalyst in the Green One‐Pot Synthesis of Spirooxindole‐4H‐pyrans

Sulfonic acid functionalized SBA‐15 (SBA‐Pr‐SO₃H) as a new nanoporous solid acid catalyst was applied in the green one‐pot synthesis of spirooxindole‐4H‐pyrans via condensation of isatins, malononitrile or methyl cyanoacetate or ethyl cyanoacetate, and 4‐hydroxycoumarin in water solvent. SBA‐Pr‐SO₃H was proved to be an efficient heterogeneous nanoporous solid acid catalyst with a pore size of 6 nm that could be easily handled and removed from the reaction mixture by simple filtration and can be recovered and reused for several times without any loss of activity. The significant merits of present methodology are its simplicity, short reaction time, good yields, and environmentally benign mild reaction condition as water was used as a green solvent.     

Hydrido(hydrosilylene)tungsten Complexes: Dynamic Behavior and Reactivity Toward Acetone

Reaction of a labile tungsten nitrile complex, [(Cp*)W(CO)₂(NCMe)Me] (Cp*=η⁵‐C₅Me₅), with H₃SiC(SiMe₃)₃ gave the hydrido(hydrosilylene) complex [(Cp*)(CO)₂(H)W?Si(H){C(SiMe₃)₃}] ( 1a ). The hydrido(silylene) complex [(η⁵‐C₅Me₄Et)(CO)₂(H)W?SiMes₂] ( 2 ) (Mes=2,4,6‐Me‐C₆H₂) was synthesized by a similar reaction with H₂SiMes₂. There is a strong interligand interaction between the hydrido and silylene ligands of these complexes; this was confirmed by a neutron diffraction study of [D₂] 1b , that is, the deuterido and η⁵‐C₅Me₄Et derivative of 1a . The exchange between the W? H and the Si? D groups was observed in the deuterido complex [D] 1a . This H/D exchange proceeded slowly at room temperature, but very rapidly under UV irradiation. Variable‐temperature NMR spectroscopy measurements show the dynamic behavior of carbonyl ligands in 1a . Complex 1a reacted with acetone at room temperature to give mainly a hydrosilylation product, [(Cp*)(CO)₂(H)W?Si(OiPr){C(SiMe₃)₃}] ( 3a ), along with a siloxy complex, [(Cp*)(CO)₂WO(Si(H)iPr{C(SiMe₃)₃})] ( 4a ). At low temperature, a different reaction, namely, α‐H abstraction, proceeded to give an equilibrium mixture of 1a and a dihydrido(silyl) complex, [(Cp*)(CO)₂(H)₂W(Si(H){OC(?CH₂)Me}{C(SiMe₃)₃})] ( 5 ).     

Stabilization of a Silaaldehyde by its η2 Coordination to Tungsten

Treatment of pyridine‐stabilized silylene complexes [(η⁵‐C₅Me₄R)(CO)₂(H)W?SiH(py)(Tsi)] (R=Me, Et; py=pyridine; Tsi=C(SiMe₃)₃) with an N‐heterocyclic carbene ^MeIⁱPr (1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene) caused deprotonation to afford anionic silylene complexes [(η⁵‐C₅Me₄R)(CO)₂W?SiH(Tsi)][H^MeIⁱPr] (R=Me ( 1‐Me ); R=Et ( 1‐Et )). Subsequent oxidation of 1‐Me and 1‐Et with pyridine‐N‐oxide (1 equiv) gave anionic η²‐silaaldehydetungsten complexes [(η⁵‐C₅Me₄R)(CO)₂W{η²‐O?SiH(Tsi)}][H^MeIⁱPr] (R=Me ( 2‐Me ); R=Et ( 2‐Et )). The formation of an unprecedented W‐Si‐O three‐membered ring was confirmed by X‐ray crystal structure analysis.     

UV–visible spectroscopy for zirconocene activation by MAO in olefin polymerization: activity versus wavenumber

Activation of ansa‐zirconocenes of the type Rac [Zr{1‐Me₂Si(3‐R‐(η⁵‐C₉H₅))(3‐R′‐(η⁵‐C₉H₅))}Cl₂] [R = Et, R′ = H ( 1 ); R = Pr, R′ = H ( 2 ); and R = Et, R′ = Pr ( 3 ), R, R′ = Me ( 4 ) and R, R′ = Bu ( 5 )] by MAO has been studied by UV–visible spectroscopy. Compounds 1–3 have been tested in the polymerization of ethylene at different Al:Zr ratios. UV–vis spectroscopy was used to determine a correlation between the electronic structures of ( 1–5 ) and their polymerization activity. Copyright © 2009 John Wiley & Sons, Ltd.     

Efficient One‐Pot Synthesis of Bis(4‐hydroxycoumarin)methanes in the Presence of Sulfonic Acid Functionalized Nanoporous Silica (SBA‐Pr‐SO3H)

An efficient and simple method for the synthesis of bis(4‐hydroxycoumarin)methanes has been achieved through a one‐pot condensation of aryl aldehydes and 4‐hydroxycoumarin in the presence of nanoporous solid acid catalyst of SBA‐Pr‐SO₃H with pore size of 6 nm. Excellent yields, short reaction times, reusability of the catalyst and simple workup are advantages of this synthetic procedure.     

Cross-aldol Condensation of Cycloalkanones and Aromatic Aldehydes in the Presence of Nanoporous Silica-based Sulfonic Acid (SiO2-Pr-SO3H) under Solvent Free Conditions

The aromatic aldehydes underwent cross aldol condensation with cycloalkanones in the presence of a catalytic amount of nanoporous silica-based sulfonic acid (SiO2-Pr-SO3H) under solvent-free conditions to afford the corresponding α,α’-bis(substituted benzylidene)cycloalkanones in excellent yields with short reaction time without any side reactions. This method is very general, simple and environmentally friendly in contrast with other existing methods. SiO2-Pr-SO3H was proved to be an efficient heterogeneous solid acid catalyst, which could be easily handled and removed from the reaction mixture by simple filtration, and also recovered and reused without loss of reactivity.     

Assessment of DNA Binding to Human Rad51 Protein by using Quartz Crystal Microbalance and Atomic Force Microscopy: Effects of ADP and BRC4‐28 Peptide Inhibitor

The interaction of human Rad51 protein (HsRad51) with single‐stranded deoxyribonucleic acid (ssDNA) was investigated by using quartz crystal microbalance (QCM) monitoring and atomic force microscopy (AFM) visualization. Gold surfaces for QCM and AFM were modified by electrografting of the in situ generated aryldiazonium salt from the sulfanilic acid to obtain the organic layer Au–ArSO₃H. The Au–ArSO₃H layer was activated by using a solution of PCl₅ in CH₂Cl₂ to give a Au–ArSO₂Cl layer. The modified surface was then used to immobilize long ssDNA molecules. The results obtained showed that the presence of adenosine diphosphate promotes the protein autoassociation rather than nucleation around DNA. In addition, when the BRC4‐28 peptide inhibitor was used, both QCM and AFM confirmed the inhibitory effect of BRC4‐28 toward HsRad51 autoassociation. Altogether these results show the suitability of this modified surface to investigate the kinetics and structure of DNA–protein interactions and for the screening of inhibitors.     

Bright Solid‐State Emission of Disilane‐Bridged Donor–Acceptor–Donor and Acceptor–Donor–Acceptor Chromophores

The development of disilane‐bridged donor–acceptor–donor (D‐Si‐Si‐A‐Si‐Si‐D) and acceptor–donor–acceptor (A‐Si‐Si‐D‐Si‐Si‐A) compounds is described. Both types of compound showed strong emission (λ_em=ca. 500 and ca. 400 nm, respectively) in the solid state with high quantum yields (Φ: up to 0.85). Compound 4 exhibited aggregation‐induced emission enhancement in solution. X‐ray diffraction revealed that the crystal structures of 2 , 4 , and 12 had no intermolecular π–π interactions to suppress the nonradiative transition in the solid state.     

Efficient One‐Pot Solvent‐Free Synthesis of 1H‐Pyrazolo[1,2‐b]phthalazine‐5,10‐diones Catalyzed by Sulfonic Acid Functionalized Nanoporous Silica (SBA‐Pr‐SO3H)

A green protocol has been developed for the synthesis of 1H‐pyrazolo[1,2‐b]phthalazine‐5,10‐diones by one‐pot cyclocondensation reaction of phthalhydrazide, aromatic aldehydes, and malononitrile or ethyl cyanoacetate using sulfonic acid functionalized SBA‐15 (SBA‐Pr‐SO₃H) as a heterogeneous solid acid catalyst under solvent‐free conditions.     

29Si NMR Investigation of Si‐alkylsubstituted 1,3,5‐Trisilacyclohexanes

²⁹Si NMR spectra of 29 Si‐alkylsubstituted derivatives of 1,3,5‐trisilacyclohexanes have been recorded and analyzed. A systematic preparation of alkyl derivatives with mixed substituents made it possible to evaluate substituent‐induced chemical shift (SCS) values for the ring silicon atoms in α and γ position. It is found that the equatorial α‐effect increases in the order Me < Et < i‐Pr < t‐Bu. For the alkyl groups Me, Et, and i‐Pr the axial α‐effect is similar in magnitude to the α_e‐effect. Axial SCS values for the t‐Bu group are not accessible because chair conformations with an axial t‐Bu group are energetically unfavourable and escape into a twisted boat form. The observed γ‐effects exhibit the γ_gauche‐effect for axial substituents as known from compounds with a pure carbon framework.     

Designing Sub‐2 nm Organosilica Nanohybrids for Far‐Field Super‐Resolution Imaging

Stimulated emission depletion (STED) microscopy enables ultrastructural imaging of biological samples with high spatiotemporal resolution. STED nanoprobes based on fluorescent organosilica nanohybrids featuring sub‐2 nm size and near‐unity quantum yield are presented. The spin–orbit coupling (SOC) of heavy‐atom‐rich organic fluorophores is mitigated through a silane‐molecule‐mediated condensation/dehalogenation process, resulting in bright fluorescent organosilica nanohybrids with multiple emitters in one hybrid nanodot. When harnessed as STED nanoprobes, these fluorescent nanohybrids show intense photoluminescence, high biocompatibility, and long‐term photostability. Taking advantage of the low‐power excitation (0.5 μW), prolonged singlet‐state lifetime, and negligible depletion‐induced re‐excitation, these STED nanohybrids present high depletion efficiency (>96 %), extremely low saturation intensity (0.54 mW, ca. 0.188 MW cm^?2), and ultra‐high lateral resolution (ca. λ_em/28).     

New procedure for nucleophilic sulfonation of aromatic nitro compounds: Destructive oxidation of S-arylthioglycolic acids esters

A new reaction was discovered: oxidative destruction of sulfides of ArSCH₂CO₂Me type to sulfonic acids ArSO₃H effected by 70% HNO₃. This reaction was used to introduce an SO₃H group instead of aromatic nitro group activated only by meta-substituents: At treating with HSCH₂CO₂Me + K₂CO₃ the NO₂ group was substituted to form ArSCH₂CO₂Me with subsequent transformation into ArSO₃H. p-Fluoronitrobenzene behaved similarly (with replacement of the fluorine).     

Tunable Emissive Lanthanidomesogen Derived from a Room‐Temperature Liquid‐Crystalline Schiff‐Base Ligand

A novel photoluminescent room‐temperature liquid‐crystalline salicylaldimine Schiff base with a short alkoxy substituent and a series of lanthanide(III) complexes of the type [Ln(LH)₃(NO₃)₃] (Ln=La, Pr, Sm, Gd, Tb, Dy; LH=(E)‐5‐(hexyloxy)‐2‐ [{2‐(2‐hydroxyethylamino)ethylimino]methyl}phenol) have been synthesized and characterized by FTIR, ¹H and ¹³C NMR, UV/Vis, and FAB‐MS analyses. The ligand coordinates to the metal ions in its zwitterionic form. The thermal behavior of the compounds was investigated by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The ligand exhibits an enantiotropic hexagonal columnar (Col_h) mesophase at room temperature and the complexes show an enantiotropic lamellar columnar (Col_L) phase at around 120 °C with high thermal stability. Based on XRD results, different space‐filling models have been proposed for the ligand and complexes to account for the columnar mesomorphism. The ligand exhibits intense blue emission both in solution and in the condensed state. The most intense emissions were observed for the samarium and terbium complexes, with the samarium complex glowing with a bright‐orange light (ca. 560–644 nm) and the terbium complex emitting green light (ca. 490–622 nm) upon UV irradiation. DFT calculations performed by using the DMol3 program at the BLYP/DNP level of theory revealed a nine‐coordinate structure for the lanthanide complexes.     

High‐Yield Synthesis of Amido‐Functionalized Polyoctahedral Oligomeric Silsesquioxanes by Using Acyl Chlorides

Homosubstituted amido‐functionalized polyoctahedral oligomeric silsesquioxanes (POSS) have been synthesized by using acyl chlorides in high yields (ca. 95 %). The method proved to be superior over “conventional” syntheses applying carboxylic acids or acid anhydrides, which are much less efficient (ca. 60 % yield). A palette of aryl and alkyl groups has been used as side‐chains. The structures of the resulting amide‐POSS are supported by multinuclear ¹H, ¹³C, ²⁹Si NMR and FTIR spectroscopy and their full conversion into octasubstituted derivatives was confirmed using mass spectrometry. We also demonstrate that the functionalized silsesquioxanes with bulky organic side‐chains attached to cubic siloxane core form spherical‐like, well‐separated nanoparticles with a size of approximately 5 nm.     

Glucose‐ and Cellulose‐Derived Ni/C‐SO3H Catalysts for Liquid Phase Phenol Hydrodeoxygenation

Sulfonated carbons were explored as functionalized supports for Ni nanoparticles to hydrodeoxygenate (HDO) phenol. Both hexadecane and water were used as solvents. The dual‐functional Ni catalysts supported on sulfonated carbon (Ni/C‐SO₃H) showed high rates for phenol hydrodeoxygenation in liquid hexadecane, but not in water. Glucose and cellulose were precursors to the carbon supports. Changes in the carbons resulting from sulfonation of the carbons resulted in variations of carbon sheet structures, morphologies and the surface concentrations of acid sites. While the C‐SO₃H supports were active for cyclohexanol dehydration in hexadecane and water, Ni/C‐SO₃H only catalysed the reduction of phenol to cyclohexanol in water. The state of 3–5 nm grafted Ni particles was analysed by in situ X‐ray absorption spectroscopy. The results show that the metallic Ni was rapidly formed in situ without detectable leaching to the aqueous phase, suggesting that just the acid functions on Ni/C‐SO₃H are inhibited in the presence of water. Using in situ IR spectroscopy, it was shown that even in hexadecane, phenol HDO is limited by the dehydration step. Thus, phenol HDO catalysis was further improved by physically admixing C‐SO₃H with the Ni/C‐SO₃H catalyst to balance the two catalytic functions. The minimum addition of 7 wt % C‐SO₃H to the most active of the Ni/C‐SO₃H catalysts enabled nearly quantitative conversion of phenol and the highest selectivity (90 %) towards cyclohexane in 6 h, at temperatures as low as 473 K, suggesting that the proximity to Ni limits the acid properties of the support.     

Tridentate Lewis Acids Based on 1,3,5‐Trisilacyclohexane Backbones and an Example of Their Host–Guest Chemistry

Directed tridentate Lewis acids based on the 1,3,5‐trisilacyclohexane skeleton with three ethynyl groups [CH₂Si(Me)(C₂H)]₃ were synthesised and functionalised by hydroboration with HB(C₆F₅)₂, yielding the ethenylborane {CH₂Si(Me)[C₂H₂B(C₆F₅)₂]}₃, and by metalation with gallium and indium organyls affording {CH₂Si(Me)[C₂M(R)₂]}₃ (M=Ga, In, R=Me, Et). In the synthesis of the backbone the influence of substituents (MeO, EtO and iPrO groups at Si) on the orientation of the methyl group was studied with the aim to increase the abundance of the all‐cis isomer. New compounds were identified by elemental analyses, multi‐nuclear NMR spectroscopy and in some cases by IR spectroscopy. Crystal structures were obtained for cis‐trans‐[CH₂Si(Me)(Cl)]₃, all‐cis‐[CH₂Si(Me)(H)]₃, all‐cis‐[CH₂Si(Me)(C₂H)]₃, cis‐trans‐[CH₂Si(Me)(C₂H)]₃ and all‐cis‐[CH₂Si(Me)(C₂SiMe₃)]₃. A gas‐phase electron diffraction experiment for all‐cis‐[CH₂Si(Me)(C₂H)]₃ provides information on the relative stabilities of the all‐equatorial and all‐axial form; the first is preferred in both solid and gas phase. The gallium‐based Lewis acid {CH₂Si(Me)[C₂Ga(Et)₂]}₃ was reacted with a tridentate Lewis base (1,3,5‐trimethyl‐1,3,5‐triazacyclohexane) in an NMR titration experiment. The generated host–guest complexes involved in the equilibria during this reaction were identified by DOSY NMR spectroscopy by comparing measured diffusion coefficients with those of the suitable reference compounds of same size and shape.     

Synthesis and X‐ray Crystal Structures of Homotrimetallic Zinc Bisureate Complexes

Alkane elimination reactions of the tethered bis(urea) proligand 1,4‐(tBuNHCONH)₂‐C₄H₈ ( 1 ) with ZnR₂ (R = Me, Et, nPr) yielded trimetallic zinc complexes [RZn‐1,4‐(tBuNHCON)₂‐C₄H₈]₂Zn [R = Me ( 2 ), Et ( 3 ), and nPr ( 4 )]. 2 – 4 were characterized by heteronuclear NMR (¹H, ¹³C) and IR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction.     

Insertion Reactions of Carbon Disulfide into Mg‐C and Mg‐N Bonds: Syntheses and Structural Determinations of Mg(S2CY)2(THF)n(Y=NEt2, NiPr2, iPr,Ph) and BrMg(S2CZ)(THF)3(Z=Ph,iPr)

The insertion reaction of CS₂ with Mg(NR₂)₂ (R= Et, ⁱPr), MgR′₂ (R′= Et, Ph) and R″MgBr (R″= ⁱPr, Ph) respectively lead solid products, Mg(S₂CNR₂)₂(THF)_n ( 1 : R= Et, n=2; 2 : R= ⁱPr, n=1), Mg(S₂C′R)₂(THF)₂ ( 3 : ′R= Et, 4 : ′R= Ph), BrMg(S₂C″R) (THF)₃ ( 5 : ″R= ⁱPr, 6 : ″R= Ph) in which the inserted carbon disulfides act as terminal chelating ligands. These compounds were characterized with ¹H, ¹³C NMR, IR spectroscopy, mass spectrometry, elemental analyses, and X‐ray crystallography.     

15N NMR spectroscopy of 3‐substituted 5‐trichloromethyl‐1,2‐dimethyl‐1H‐pyrazolium chlorides

¹⁵N NMR data of a series of 3‐alkyl[aryl] substituted 5‐trichloromethyl‐1,2‐dimethyl‐1H‐pyrazolium chlorides (where the 3‐substituents are H, Me, Et, n‐Pr, n‐Bu, n‐Pe, n‐Hex, (CH₂)₅CO₂Et, CH₂Br, Ph and 4‐Br‐C₆H₄), are reported. The ¹⁵N substituent chemical shifts (SCS) parameters are determined and these data are compared with the ¹³C SCS values and data obtained by MO calculations. Copyright © 2002 John Wiley & Sons, Ltd.