Synthesis and characterization of macrocyclic polystyrene block-copolymers

The synthesis of macrocyclic polystyrene- block-poly(2-vinylpyridine) and macrocyclic polystyrene- block-poly(dimethylsiloxane) was carried out by initiation of 2-vinylpyridine (2VP) and hexamethyl-cyclotrisiloxane (D3) by difunctional living polystyryllithium followed by coupling with 1,4-bis(bromethyl)benzene (1,4-DBX) and dichloro-dimethylsilane (Cl₂SiMe₂), respectively. A small portion of the living ABA precursors were protonated to serve as isobaric linear precursors. The linear and macrocyclic block copolymers were characterized by size-exclusion chromatography (SEC). The ratios of apparent cyclic/linear SEC molecular-weight maxima versus degree of polymerization (DP) show increases with decreasing DP varying from 0.70 ± 0.03 at high DP ≤ 200 to 0.78 ± 0.044 at low DP (≥60) whereas that of the linear ABA block copolymers decreased. Increases in glass transition temperature (Tg) were also observed for the cyclic PS-b-PDMS copolymers with respect to the isobaric linear precursors. The macrocycles were characterized by ¹H and ¹³C NMR and in the case of macrocyclic PS-b-PDMS by ²⁹Si NMR as well. Broadening in the NMR absorptions of the macrocyclic block copolymers is general and is similar to that observed for the homopolymers. Differemtial scanning calorimetry (DSC) analysis of the PS-b-P2VP macrocycles shows increases in Tg at lower molecular weight as was observed for the PS and P2VP macrocycles.     

Hydrolysis behavior of a precursor for bridged polysilsesquioxane 1,4-bis(triethoxysilyl)benzene: a <Superscript>29</Superscript>Si NMR study

The hydrolysis behavior of 1,4-bis(triethoxysilyl)benzene (BTB), a precursor of bridged polysilsesquioxane, was investigated with high-resolution ²⁹Si nuclear magnetic resonance (²⁹Si NMR) spectroscopy at ambient temperature in a system with BTB:ethanol:water:HCl = 1:10:x:0.8 × 10⁻⁴ (x = 3, 6 or 9). Signals due to hydrolyzed triethoxysilyl groups as well as unhydrolyzed triethoxysilyl groups [−Si(OEt)₃, −Si(OEt)₂(OH), −Si(OEt)(OH)₂ and −Si(OH)₃ (OEt = OCH₂CH₃)] formed four sub-regions based on the number of hydroxyl groups bound to a silicon atom. In addition, one silicon environment influenced the other silicon environment by an intra-molecular interaction between two silicon atoms, and each sub-region for monomeric species thus contained four signals. Based on the development of signal intensity, it is revealed that one of the two triethoxysilyl groups in BTB is hydrolyzed preferentially. Thus, when a triethoxysilyl group is hydrolyzed, the −Si(OH) _x (OEt)_3−x (x = 1, 2) groups formed undergo further hydrolysis, which is opposite to the tendency expected from the hydrolysis behavior of organotrialkoxysilanes under acidic conditions.     

Sol–gel chemistry: evidence of redistributionat silicon atom induced by NaOH as catalystduring ageing

The influence of the ageing conditions on the properties of organic-inorganic hybrid solids obtained by sol–gel route using NaOH catalysis has been studied. The cases of 1,4-bis(trimethoxysilyl)benzene 1 (‘rigid’ precursor) and 1,4-bis(trimethoxysilylethyl)benzene 2 (‘more flexible’ one) have been investigated. The ²⁹Si CP MAS NMR spectra of the silsesquioxanes clearly reveal that Si–O–Si bond cleavage and redistribution reactions occur when the ageing time is increased or is performed at higher temperatures. This particular behaviour observed only with NaOH is of importance in the choice of the catalyst.     

Crystal Structure and Spectroscopic Characterization of Zinc(II) and Mercury(II) Complexes of N‐(Pyridin‐2‐ylmethylene)benzene‐1,4‐diamine

The behavior of N,N′‐bis(pyridin‐2‐ylmethylene)benzene‐1,4‐diamine (L) towards zinc(II), cadmium(II), and mercury(II) chlorides was studied in methanol solutions. In the presence of metal ions, the organic molecule was decomposed to N‐(pyridin‐2‐ylmethylene)benzene‐1,4‐diamine (L′), and complexes of general formula M(L′)Cl₂ were isolated from the mixture. The complexes were identified by elemental analysis, IR, ¹H NMR, and ¹³C NMR spectra, and their structures were further confirmed by single‐crystal X‐ray diffraction analysis of Zn(L′)Cl₂ and Hg(L′)Cl₂. In the solid state of both complexes, the molecules are stabilized by N–H ··· Cl hydrogen bonds and aromatic π–π stacking interactions.     

<Superscript>29</Superscript>Si NMR Spectroscopy Investigation of Alcoholic Phenyltrimethyl Ammonium Silicate Solutions

²⁹Si NMR spectroscopy is a powerful tool for studies of the silicate species existing in both aqueous and non-aqueous solutions. In this report ²⁹Si NMR spectroscopy was used to characterize species present in alkaline alcoholic silicate solutions. Phenyltrimethylammonium (PTMA) hydroxide was used as a base. The effects of polymerization/depolymerization of silicate anions in alcoholic alkaline solutions were investigated with different alcohols by ²⁹Si NMR spectroscopy. The esterification of monomeric silicate, Si(OH)₄, in the presence of different alcohols was also studied. Esterification depends on the alkyl chain as well as number of hydroxyl groups in the alcohol.     

Reaction of Hexamethyldisilazane with Borane in Tetrahydrofuran

Hexamethyldisilazane 1 reacts with borane in tetrahydrofuran (THF? BH₃, 2 ) first by formation of an adduct (Me₃Si)₂NH? BH₃ ( 3 ), and then either to the N,N-bis-(trimethylsilyl)-μ-aminodiborane 5 or to the mixture of 5 and N-trimethylsilyl-μ-aminodiborane(6) 6 , depending on the reaction conditions. The compounds 5 and 6 can be quantitatively converted to the N,N′,N″-tris(trimethylsilyl)borazine 4 . Three intermediates can be identified, namely N,N-bis(trimethylsilyl)borane 7 , N,N-bis(trimethylsilyl)amino(N′-trimethylsilylamino)borane 8 and N-trimethylsilylaminoborane-trimer. All products and intermediates were characterized by multinuclear NMR spectroscopy, and coupling constant ¹J(²⁹Si, ¹⁵N) were measured from ²⁹Si NMR spectra by using the Hahn-echo-extended (HEED) INEPT pulse sequence.     

Synthesis,electrochemistry and IR spectroelectrochemistry of bisferrocenyl bridged benzene derivates

Two novel biferrocenylcarboxylate benzene derivatives, namely, 1,4-bis(2-Ferrocenecarboxylate) benzene (Fc₂B) and 1,4-bis(2-Ferrocenecarboxylate)-2′-methylbenzene (Fc₂M), have been synthesized. The as-prepared complexes have been confirmed by IR, ¹H NMR and MS. The electron transfer mechanisms of the two compounds and the other three bisferrocenyl bridged benzene complexes, 1,4-disferrocenyl benzene (Fc₂P), 1,4-bis(2-ferrocenylvinyl) benzene (Fc₂E), and 1,4-bis(2-ferrocenylacetyleneyl) benzene (Fc₂Q), have been studied by cyclic voltammetry (CV), in situ difference FT-IR (SNFTIR), and rapid-scan time-resolved FT-IR spectroelectrochemistry (RS-TRS FT-IR). The CV results suggest that the redox formal potentials of the five bridged complexes are depended on their bridged groups and abilities of withdrawing electron. IR absorption peaks arisen from intermediate appearance and disappearance in the oxidation and reduction process of Fc₂B, Fc₂E, Fc₂P and Fc₂Q were clearly observed by the in situ rapid-scan or SNFTIR spectroelectrochemistry. The results indicated the redox process of the four bisferrocenyl bridged benzene complexes involved two consecutive one-electron steps. Although the intermediate peak of Fc₂M was not observed by in situ FT-IR spectroelectrochemistry, we still thought the redox process of Fc₂M could involve two consecutive one-electron steps.     

Improved pulse sequences for measurement of small long‐range couplings between heteronuclei (29Si?13C) at natural abundance

The gradient pulse sequences for measurement of small long‐range couplings between heteronuclei (²⁹Si? ¹³C) in natural abundance reported to date (INEPT‐(Si,C)gCOSY and INEPT‐(Si,C,Si)HMQC) suffer from significant signal loss when these nuclei (²⁹Si, ¹³C) are coupled through one‐bond couplings to protons. This negative effect can be completely eliminated by using non‐gradient versions (INEPT‐(Si,C)COSY) or by switching proton decoupling off during gradient pulses (modified INEPT‐(Si,C,Si)gHMQC pulse sequence). The beneficial effects of these two approaches on the quality of the spectra are demonstrated here. Copyright © 2009 John Wiley & Sons, Ltd.     

Ionic Dissociation of SiCl4: Formation of [SiL6]Cl4 with L=Dimethylphosphinic Acid

Reactions of SiCl₄ with R₂PO(OH) (R=Me, Cl) yield compounds with six-fold coordinated silicon atoms. Whereas R=Me afforded the hexacoordinated tetra-cationic silicon complex [Si(Me₂PO(OH))₆]⁴⁺ with chloride counter-ions, R=Cl caused release of HCl with formation of a cyclic dimeric silicon complex [Si(Cl₂PO(OH))(Cl₂PO₂)₃(μ-Cl₂PO₂)]₂ with bridging bidentate dichlorophosphates.     

Bridged Polysilsesquioxane Xerogels Functionalizated by Amine- and Thiol- Groups: Synthesis, Structure, Adsorption Properties

Bridged polysilsesquioxane xerogels containing amine (–NH₂; –NH(CH₂)₂NH₂; —NH) and thiol (–SH) groups were synthesized by hydrolytic polycondensation of 1,2-bis(triethoxysilyl)ethane, 1,4-bis(triethoxysilyl)benzene and appropriate trifunctionalized silanes in the presence of a fluoride-ion catalyst in an ethanol solution. ²⁹Si CP/MAS NMR give indication of the molecular framework of these materials formed by structural T¹, T² and T³ units. 3-aminopropyl or 3-mercaptopropyl groups accessible to proton or metal ions are fixed to the xerogel surface by the siloxane bonds. IR and ¹³C CP/MAS NMR data clearly show that 3-aminopropyl groups form hydrogen bonds. The same data testify that all xerogels contain non-condensed silanol groups and some fraction of non-hydrolyzed ethoxygroups. Functionalized polysilsesquioxane xerogels obtained by means of organic spacers have a porous structure (500–1000 m²/g) and a high content of functional groups (1.0–2.7 mmol/g). AFM data indicate that xerogels are formed by aggregating primary particles—the size of such aggregates is in the range 30–65 nm. It was established that the main factors influencing the structure and adsorption properties considered hybrid materials are: the nature and geometrical size of the functional groups, spacer flexibility and, in some cases, the ratio of the reacting alkoxysilanes and the ageing time of the gel.     

Zur Kenntnis des Natrium-tetrahydroxoaluminat-chlorids Na2[Al(OH)4]Cl

On the Sodium Tetrahydroxoaluminate Chloride Na₂[Al(OH)₄]Cl The hitherto unknown compound Na₂[Al(OH)₄]Cl was prepared by crystallisation from a NaCl containing sodium aluminate solution. According to the X-ray single crystal investigation (tetragonal, space group P4/nmm, a = 7.541 Å, c = 5.059 Å, Z = 2) the compound represents the first example of a crystalline hydroxoaluminate with monomeric [Al(OH)₄]^? anions. Cl^? shows a quadratic anti prismatic coordination to 4 Na⁺ and over hydrogen bonds to 4 O^2? while Na⁺ is octahedrally coordinated by 4 O^2? and 2 Cl^? (axial). The results of the crystal structure analysis are confirmed by ²⁷Al and ²³Na MAS NMR investigations. Na₂[Al(OH)₄]Cl decomposes at about 200°C without intermediates under formation of β-NaAlO₂ and NaCl.     

First cyclotrisiloxanes with three different R2Si-units of the general formula R2Si(OSiR2)(OSiR2)O (R2 = Me2Si(NSiMe3)2, R = Cl, Ot-Bu, R = Me)

The reaction of compound Me₂Si(NSiMe₃)₂Si(OH)Cl with Me₂SiCl₂ leads to the disiloxane Me₂Si(NSiMe₃)₂Si(Cl)OSi(Me₂)Cl (1). Hydrolysis of 1 in the presence of pyridine results in Me₂Si(NSiMe₃)₂Si(OH)OSi(Me₂)OH (2), which is allowed to react with SiCl₄ to give cyclotrisiloxane [Me₂Si(NSiMe₃)₂Si](OSiMe₂)(OSiCl₂)O (3). The treatment of 1 with (t-BuO)₂Si(OH)₂ forms cyclotrisiloxane [Me₂Si(NSiMe₃)₂Si](OSiMe₂)[OSi(Ot-Bu)₂]O (4). Compound 3 is obtained as a crystalline solid while 4 is an oily liquid. The ring size of these new types of cyclotrisiloxanes with three different R₂Si-units is confirmed by cryoscopy in benzene, ²⁹Si NMR chemical shifts and in case of 3, additionally by a single X-ray diffraction study. The different electronegativities of the substituents in the R₂Si-units lead to different bond lengths and bond angles within the Si₃O₃ cycle, which are discussed in detail in the molecular structure of 3.     

Regioselective double intramolecular bridging of p-tert-butylcalix[7]arene

The first examples of doubly bridged calix[7]arenes 2a-h have been obtained by base-promoted O-alkylation of p-tert-butylcalix[7]arene 1 or 1,4-tetramethylene-bridged calix[7]arene 3a with a variety of bis-electrophiles including BrCH₂Cl, oligoethylene glycol ditosylates, and 1,2-bis(bromomethyl)benzene. In the presence of Cs₂CO₃ as the base, in acetone, the syn-1,4:2,3-bis-bridged regioisomer was obtained in yields up to 76%. Assignment of bridging pattern was based on chemical shift of OH groups in conjunction with chemical correlations with known compounds. Stereochemical and conformational features were investigated with the aid of 2D and Dynamic NMR studies and MM3 calculations.     

Solid-state high-resolution 29Si NMR in zunyite

High-resolution ²⁹Si NMR spectra of zunyite Si₅Al₁₃O₂₀ (OH,F)₁₈Cl have been studied by magic-angle sample spinning in combination with high-power proton decouplina and polarization transfer. The isotropic ²⁹Si chemical shift depends mainly on the number of Si-O-Si bridges and the bond angles in these bridges connecting the different SiO₄ tetrahedra.     

New hyperbranched carbosiloxane–carbosilane polymers with aromatic units in the backbone

New hyperbranched polymers based on a carbosiloxane–carbosilane skeleton with aromatic units in the backbone have been prepared via one-pot hydrosilylation reaction using HSi(Me)₂–O–CH₂–C₆H₄–OSiMe–(CH₂)₄(C₃H₅)₂ as a novel AB₂ monomer. These polymers are easy to prepare, have narrow polydispersity values and present allyl groups on the surface which can be used as synthetic platforms for the introduction of different terminal groups like amine groups through hydrosilylation reactions, opening the door to functionalized polymers. The polymerization process was monitored using real-time ¹H NMR spectroscopy and the resulting hyperbranched polymers were characterized using ¹H NMR, ¹³C NMR, ²⁹Si NMR and SEC/MALLS. The degree of branching in these polymers was determined by quantitative ²⁹Si NMR spectroscopy and found to be very close to the theoretical value of 0.50 for AB₂ systems. The hydrolytic degradation of these polymers in protic solvents has been studied by ²⁹Si NMR.     

Cyclooctene epoxidation with H2O2 and single crystal X-ray determined crystal structures of new molybdenum and tungsten catalysts bearing the hydrophilic ligand hydroxymethyldiphenylphosphine oxide

The dioxo molybdenum and tungsten complexes MoO₂Cl₂(OPPh₂CH₂OH)₂ and WO₂Cl₂(OPPh₂CH₂OH)₂ have been synthesized and characterized by FT-IR, ¹H and ³¹P NMR. Their structures, as determined by single crystal X-ray diffraction analysis, reveal distorted octahedral geometries with cis terminal oxygen atoms, trans Cl ligands and that the hydroxymethyldiphenylphosphine oxide ligands coordinate through the oxygen atom bonded to the P atom. Both of the compounds are studied as catalysts for the epoxidation of cis-cyclooctene in the presence of hydrogen peroxide as a source of oxygen. Both complexes showed good activity and very high selectivity for the formation of cyclooctene oxide.     

Selective Construction of Trefoil knots and a Molecular Borromean Ring Induced by Steric Hindrance of Thioether Ligands

Two Cp*−Rh^III based trefoil knots were obtained in high yield under ambient conditions via the coordination-driven self-assembly of semi-rigid thioether dipyridyl ligand 1,4-bis[(pyridin-4-ylthio)methyl]benzene ( L₁ ), ligand chloranilic acid (H₂− CA ) and 6,11-dihydroxytetracene-5,12-dione (H₂- TtDo ) with Cp*Rh^III metal corner units, respectively. Furthermore, using the bulkier 4,4′-{[(2,5-dimethyl-1,4-phenylene)bis(methylene)]bis(sulfanediyl)}dipyridine ( L₂ ) in the place of ligand L₁ in the construction process resulted in the formation of a teranuclear metallacycle and a template-free Borromean ring in high yields thanks to significantly altered intermolecular forces between the constituent ligands induced by the sterically-hindering methyl groups of L₂ , as demonstrated via a detailed X-ray crystallographic analysis and NMR spectroscopy.     

Structural study of arylsilanes using 29Si NMR

²⁹Si NMR data (σ and ¹H, ²⁹Si coupling constants) of a series of arylsilanes were studied in relation to their molecular structure. It is shown that silicon chemical shift variation is too weak to allow empirical attribution. In contrast, ²⁹Si, ¹H coupling constants across the aromatic ring, especially the ³J, allow structural assignment. Generally, SPT experiments are sufficient to obtain these values. However, full attribution of polysilylated derivatives sometimes needs other experiments to identify all the silicons. A 2D J-resolved INEPT experiment is described and has proven to be an efficient method for ²⁹Si NMR signal identification. The usefulness of this approach is demonstrated by the complete analysis of all the ²⁹Si lines in a trisilyl derivative. An easy-to-use INEPT decoupled-type sequence is also proposed for a rapid characterization of polysilylated derivatives or mixture of isomers.     

Synthesis of aromatic polyethers by Scholl reaction. V. Synthesis and polymerization of 1,3-bis[4-(1-naphthoxy) benzoyl]benzene, 1,4-bis[4-(1-naphthoxy)benzoyl]benzene,bis[4-(1-naphthoxy)phenyl]methane, 1,3-bis[4-(1-naphthoxy) phenylmethyl]benzene,and 1,4-bis-[4-(1-naphthoxy)phenylmethyl]benzene

This article describes the synthesis and the cation-radical polymerization (Scholl reaction) of 1,3-bis[4-(1-naphthoxy) benzoyl] benzene ( 6 ) and 1,4-bis[4-(1-naphthoxy) benzoyl]- benzene ( 7 ) initiated by FeCI₃. This polymerization produced poly(ether ether ketone ketone)s (PEEKK) of number average molecular weight (M?_n) up to 5400 g/mol. The synthesis of bis[4-(1-naphthoxy) phenyl] methane ( 8 ), 1,3-bis[4-(1-napthoxy) phenylmethyl] benzene ( 9 ), and 1,4-bis[4-(1-naphthoxy) phenylmethyl] benzene ( 10 ) are also described. Polyethers of M?_n up to 15400 g/mol at a FeCl₃/monomer molar ratio of 2/1 were obtained. An increased polymerizability of the monomers 9 and 10 containing two CH₂ groups versus that of the corresponding monomers containing two carbonyl groups ( 6 and 7 ) was observed. This enhanced polymerizability was explained based on the increased nucleophilicity of monomers 9 and 10 .     

Poly-Diels-Alder Addition with a Bisoxazole as Bisdiene and a Bismaleinimide as Bisdienophile

Abstract

The poly-Diels-Alder addition between the new bisdiene 1,4-bis(5-methoxy-2-oxazolyl)benzene (4) and N,N′-hexamethylene-bis[2-(2,5-dihydro-2,5-dioxo-pyrrole-1-yl) acetamide] (7) is described. The structure of the resulting polyadduct 12 was proved by ¹H NMR spectroscopy with the aid of the low-molecular-weight model compounds 1,4-bis(1,3-dihydro-7-hydroxy-1,3-dioxo-2-phenyl-pyrrolo[3,4-c] pyridine-4-yl)benzene (9) and N,N'-hexamethylene-bis[2-(1, 3-dihydro-7-hydroxy-6-methyl-1,3-dioxo-4-phenyl-pyrrolo [3,4-c]pyridine-2-yl)acetamide] (11). The reaction proceeds via the aromatization of the primarily formed cycloadducts. Polyadduct 12 shows a number average degree of polymerization P_n of about 11 – 12 (M_n = 8500 ? 9200 g/mol), calculated from ¹H NMR endgroup signals.