The Preparation of the Carbosilane Dendrimers with Pentafluorophenyl Groups

Dendrimers as intriguing macromolecules possess potential in phase transfer catalysis, hosts-guest chemistry, controlled release drugs or might serve as recyclable extracting agents1,2,3. The fluorine-containing dendrimers can be used as low surface-energ…     

Synthesis of Novel Carbosilane Dendrimers Based on Pentaerythritol

Novel pentaerythritol-based carbosilane dendrimers centered at carbon have been synthesised. Starting from tetraallyl ether based upon pentaerythritol as the core molecule, a succession of alternate Pt-catalyzed hydrosilylation of allyl groups with HSiC13 and allylations of SiC1 groups thus introduced with CH2=CHCH2MgBr in THF provided a divergent synthesis of three generations of carbosilane dendrimers in which the Si atoms are linked by CH2CH2CH2 groups. The reaction conditions for hydrosilylation must be well controlled. After purification by chromatography on silica gel pure products for each generation were obtained. The IR, ^1H and ^13C NMR spectra and elemental analysis data are consistent with the proposed structures. The molecular weights of the resulting carbosilne dendrimers have been determined by vapor pressure osmometry.     

Ring‐Closing Metathesis on an Allyl‐Terminated Carbosilane Dendrimer

Grubbs' catalyst was used to prepare a series of carbosilane dendrimers with silacyclopentene peripheral groups, suitable for further elaboration to functional dendrimers. The efficiency of the ring closing metathesis reaction was found to be strongly dependent on the reaction temperature and the amount of catalyst used, as shown by ¹H NMR monitoring.     

碳硅烷树枝状化合物的功能化研究

本文根据碳硅烷树枝状化合物功能基的种类及反应特性,介绍了有关含硅树枝状化合物的功能化的方法,并对功能化含硅树枝状化合物的用途做了相应评述.     

Synthesis of anionic carbosilane dendrimers via “click chemistry” and their antiviral properties against HIV

The synthesis and characterization of four families of anionic carbosilane dendrimers bearing carboxylate, phosphonate, naphthylsulfonate, and sulfate terminal groups prepared by cycloaddition of azide–alkyne catalyzed by copper (CuAAC) are presented here. For the preparation of these anionic carbosilane dendrimers, two strategies starting from azide‐terminated carbosilane dendrimers were followed: (i) click coupling of neutral alkynes followed by derivatization into anionic moieties or (ii) click coupling of anionic alkynes. Both strategies require different reaction conditions in order to accommodate the different substrate polarities. These anionic dendrimers, in general, do not present cell toxicity in vitro until concentration up to 20 µM. Therefore, they can be used in inhibition experiments in concentrations below this limit. We have observed that dendrimers bearing phosphonate groups possess poor anti‐HIV capabilities in vitro in PBMCs, while carboxylate dendrimers can reduce HIV infection levels moderately. On the other hand, sulfate and naphthylsulfonate dendrimers are powerful anti‐HIV agents and their antiviral activity is generation and concentration dependent. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1099–1112     

"A posteriori" modification of carbosilane dendrimers and dendrons: their activation in core and branch positions

The introduction of phenyl groups at different points on carbosilane dendrimers allows their acidolytic conversion to highly reactive triflato groups which in turn are readily substituted by anionic nucleophiles. Core phenylated first-fourth generation dendrimers were synthesized from tri(allyl)phenylsilane by an alternating sequence of hydrosilylation and allylation steps. Similarly, carbosilane dendrimers containing phenyl-Si groups at the branching points and in the periphery were prepared from tetraallylsilane which was hydrosilylated with PhHSiCl2. Reaction of the phenylated dendrimers with triflic acid in toluene cleanly gave the silyl triflate derivatives, provided that the correct stoichiometry of the reagents was used. In the presence of a large excess of triflic acid the SiMe3-end groups are slowly converted to SiMe2(OTf)-units. The proof of concept was provided by the fixation of a {Ph2PCH2} group using the lithiated diphenylphosphinomethanide Ph2PCH2Li, obtained by cleavage of Ph3SnCH2PPh2 with PhLi, as well as a lithiated ether-alcohol functionalized triphos derivative to the core of a third generation carbosilane dendrimer.     

Dendritic polyols based on carbosilanes - lipophilic dendrimers with hydrophilic skin

Carbosilane dendrimers with up to 108 end groups were prepared by a divergent synthetic route via repeated alternating Grignard-reaction with allylmagnesium bromide and hydrosilylation. Quantitative hydroboration of the dendrimers was achieved with 9-BBN/H₂O₂,OH⁻. Employing this synthetic route, rather monodisperse dendritic polyols with lipophilic carbosilane core and hydrophilic shell were prepared. All dendrimers were characterized with MALDI-TOF, showing low polydispersities. The novel dendritic polyols constitute interesting molecular scaffolds for the preparation of unusual supermolecules. As an example, reaction with cholesteryl chloro-formiate was used to prepare a series of dendrimers with 12, 36 and 108 mesogenic cholesteryl end groups.     

Synthesis and comparative studies of carbosilane liquid crystalline dendrimers with chiral terminal mesogenic groups

A new series of carbosilane liquid crystalline (LC) dendrimers from the first to the third generations with 8, 16 and 32 chiral terminal mesogenic groups, respectively, has been synthesized. The molecular structures and purity of all new compounds were confirmed by ¹H NMR spectroscopy and GPC analysis. Data of polarization microscopy and SAX analysis demonstrated that all LC dendrimers synthesized form a chiral smectic SmC* phase at temperatures below 50 °C. It has been found that bistable electrooptical switching is observed for all dendrimers. The influence of chiral mesogenic fragment length on phase behavior and ferroelectric properties of carbosilane LC dendrimers is discussed.     

Pentaerythritol-based Carbosilane Dendrimers

A series of novel pentaerythritol-based carbosilane dendrimers have been synthesized. Using pentaerythritol-based tetraallyl ether as core molecule, the dendrimers have been prepared up to the third generation with I08 allyl groups on the periphery by alternate allylation-hydrosilylation approach.     

Synthesis,structure, and phase behavior of carbosilane LC dendrimers with terminal butoxyphenylbenzoate mesogenic groups

Two series of carbosilane LC dendrimers with terminal protonated and deuterated butoxyphenylbenzoate mesogenic groups linked to carbosilane dendritic matrices of the first to fifth generations via an undecylene spacer have been synthesized. The chemical structure of new dendrimers has been studied by ¹H NMR spectroscopy and gel-permeation chromatography. The dendrimers of first-fourth generations are characterized by formation of the smectic C mesophase in a wide temperature range, whereas much more complex columnar supramolecular structures are formed in dendrimers of the fifth generation. Structural studied of mesophases by X-ray diffraction and small-angle neutron scattering show that segregation takes place in mixtures of deuterated and protonated LC dendrimers; as a result, huge aggregates composed of hundreds of chemically unbound molecules develop and the sizes of these aggregates reversibly change with temperature.     

外围含对-硝基偶氮苯介晶基团的椭球型硅碳烷树状物

Novel carbosilane liquid crystalline dendrimers based on 1,6-hexanediol were prepared. Using the precursors Gn-C1 （n = 1-3） with Si-C1 bonds on the periphery as dendritic scaffolds and 4-[4-（6-hydroxyhexyloxy）phenylazo]- nitrobenzene as mesogenic group, a series of carbosilane liquid crystalline dendrimers from the first to the third generation were synthesized. These carbosilane liquid crystalline dendrimers showed smectic phase.     

Janus carbosilane/phosphorhydrazone dendrimers synthesized by the ‘click’ Staudinger reaction

The first association of carbosilane dendrons (having a phosphine at the focal point) with phosphorhydrazone dendrons (having a thiophosphoryl azide at the focal point) has been successfully carried out by ‘Staudinger click’ reaction. The corresponding Janus dendrimers possess the characteristics of both components; they are oily as the carbosilane dendrons, and they can be easily functionalized as the phosphorhydrazone dendrons.     

基于1,6-己二醇的哑铃型树状大分子

Novel carbosilane dendrimers based on 1,6-hexanediol were prepared by divergent approach. Using 1,6-hexanediol-based diallyl ether as the core molecule, the dendrimers were prepared to the third generation with 54 allyl groups on the periphery by alternate hydrosilylation-allylation reactions.     

Synthesis and physical behavior of amphiphilic dendrimers with layered organization of hydrophilic and hydrophobic blocks

Amphiphilic carbosilane dendrimers with novel architectural layout have been synthesized. These dendrimers contain peripheral groups consisting of covalently bound promesogenic fragments and hydrophilic (oligoethyleneglycolic) linkages which are connected to a carbosilane core in two distinct ways: as spacer or as tail arrangement. Such molecules have a block structure where the hydrophilic and hydrophobic blocks are distributed within the dendrimer forming layers of different polarity. The hydrophilic layer is either enclosed between two hydrophobic parts of the molecule or is situated on the periphery. The synthetic strategy for achieving these structures is described. The interfacial properties of the dendrimers were studied and the influence of the dendritic structure’s organization on the Langmuir film formation process is assessed.     

Rheology of carbosilane dendrimers with various types of end groups

The rheological properties of high-generation carbosilane dendrimers carrying different kinds of terminal groups are studied. It is shown that the nonlinear viscoelastic behavior of dendrimers and the high-temperature relaxation transition in dendrimers are interrelated and result from the reversible breakdown of the supramolecular structure formed by the system of contacts of exterior shells of dendrimers. The strength of the supramolecular structure is dependent on the specific interaction of terminal groups of dendrimers and their mobility. The dendrimers under study demonstrate the dualism of macromolecule-particle properties: They behave as both polymer melts and colloidal systems.     

Synthesis of ester-capped carbosilane dendrimers via a hybrid divergent–convergent method

A series of novel ester-capped carbosilane dendrimers（G0-COOCH3–G2-COOCH3） were designed and successfully synthesized via a hybrid divergent–convergent method through a facile hydrosilylation reaction. The structures of these dendrimers were confirmed by FTIR,1H NMR, and HRMS analyses.     

FTIR spectroscopy and DFT studies of carbosilane dendrimers

The FTIR spectra of G(3), G(4), and G(9) generations of polybutylcarbosilane dendrimers have been recorded and analyzed. The structural optimization and normal mode analysis were performed for G(1) generation on the basis of density functional theory (DFT). This calculation gave vibrational frequencies and infrared intensities for the t,t- and g,-g-conformers of the butyl terminal groups, attached to the same silicon atom. The g,-g-conformer is 5.83 kcal/mol less stable compared to t,t-conformer. Relying on DFT calculations a complete vibrational assignment is proposed for different parts of the studied dendrimers. The dependence of band full width at half height in the IR spectra on generation number is established. The IR spectra of carbosilane dendrimers at higher temperatures at the ambient air and isolated from atmosphere air were studied. At temperature 180 degrees C all studied carbosilane dendrimers are stable when contact with atmosphere is absent, in the air they oxidize and thus CO and SiO groups appear.     

Synthesis and properties of carbosilane dendrimers with perfluorohexyl groups in the outer layer of the molecular structure

Branched perfluorohydrosiloxane with CF₃CF₂CF₂C(CF₃)₂(CH₂)₃ groups at the silicon atom was synthesized by a sequence of chemical reactions. The resulting compound was used as a modifying agent for carbosilane dendrimers of the 3rd and 6th generations. Dendrimers with perfluorohexyl terminal groups in surface layer are characterized by a complex of physicochemical methods. It is demonstrated that due to the branching of perfluoroalkyl terminal groups, obtained carbosilane dendrimers are soluble in organic and inorganic media. Differences in the solubility of small and large dendrimers are caused by the formation of the outer fluoride shell of different densities.     

Synthesis of Novel Carbosilane Dendrimers with Myo—inositol Cores

The preparation of carbosilane dendrimers with cores of myo-inositol and the outmost periphery grougs of allyl groups has been reported.By using alternate hydrosilylation and alkenyiation reactions,the dendrimer have been carried up to the third generation with 48 allyl groups on the periphery.