P-substituted Styrenes Research Articles

Aziridination Reactivity of a Manganese(II) Complex with a Bulky Chelating Bis(Alkoxide) Ligand.

Treatment of Mn(N(SiMe3)2)2(THF)2 with bulky chelating bis(alkoxide) ligand [1,1′:4′,1′′-terphenyl]-2,2′′-diylbis(diphenylmethanol) (H2[O-terphenyl-O]Ph) formed a seesaw manganese(II) complex Mn[O-terphenyl-O]Ph(THF)2, characterized by structural, spectroscopic, magnetic, and analytical methods. The reactivity of Mn[O-terphenyl-O]Ph(THF)2 with various nitrene precursors was investigated. No reaction was observed between Mn[O-terphenyl-O]Ph(THF)2 and aryl azides. In contrast, the treatment of Mn[O-terphenyl-O]Ph(THF)2 with iminoiodinane PhINTs (Ts = p-toluenesulfonyl) was consistent with the formation of a metal-nitrene complex. In the presence of styrene, the reaction led to the formation of aziridine. Combining varying ratios of styrene and PhINTs in different solvents with 10 mol% of Mn[O-terphenyl-O]Ph(THF)2 at room temperature produced 2-phenylaziridine in up to a 79% yield. Exploration of the reactivity of Mn[O-terphenyl-O]Ph(THF)2 with various olefins revealed (1) moderate aziridination yields for p-substituted styrenes, irrespective of the electronic nature of the substituent; (2) moderate yield for 1,1′-disubstituted α-methylstyrene; (3) no aziridination for aliphatic α-olefins; (4) complex product mixtures for the β-substituted styrenes. DFT calculations suggest that iminoiodinane is oxidatively added upon binding to Mn, and the resulting formal imido intermediate has a high-spin Mn(III) center antiferromagnetically coupled to an imidyl radical. This imidyl radical reacts with styrene to form a sextet intermediate that readily reductively eliminates the formation of a sextet Mn(II) aziridine complex.

Design mitochondria-specific fluorescent turn-on probes targeting G-quadruplexes for live cell imaging and mitophagy monitoring study

A series of new mitochondrial-selective fluorescent probe was designed and synthesized based on the integration of two planar molecular scaffolds of benzo-indole/indole with a p-substituted styrene moiety. The small-sized probes are flexible and rotatable via an ethylene bridge. The restriction of free rotation upon interaction with targeting biomolecules of G-quadruplexes in mitochondria generates strong emission in visible range (575–615 nm). Cell imaging study showed that the ligands are targeting mitochondria but not nucleus. Competition experiments showed that the ligand BYM is highly selective towards mitochondrial G4-DNA structures against other non-G4 nucleic acid structures including single-/double-stranded DNA and hairpin. The equilibrium binding constant (Keq) of BYM interacting with mitochondrial G4-DNA (mt6363, Keq = 10.8 × 106 M−1) is almost 1000-fold higher than that of mitochondrial double-stranded DNA (Keq = 0.01 × 106 M−1). The probe also showed high sensitivity (LOD = 1.52 nM) and good linear relationship (R2 = 0.9983) with the mitochondrial G4-DNA. The delivery of BYM to mitochondria is not mitochondrial membrane potential dependent but mainly through the permeability transition pore on the mitochondrial inner membrane. In addition, BYM exhibits low cytotoxicity against a number of human cancer and noncancerous cells, indicating that BYM could be a good ligand for bioorthogonal study in live cells by targeting the mitochondrial G4-DNA structures. In the present study, BYM was demonstrated in monitoring the dynamic process of mitochondrial autophagy. The small-sized fluorescent probe possessing high photostability, selectivity and sensitivity targeting mitochondrial G-quadruplexes may able to provide a useful chemical tool for real-time study of mitochondrial functions in live cells.

Structure and Reactivity of a Manganese(VI) Nitrido Complex Bearing a Tetraamido Macrocyclic Ligand.

Manganese complexes in +6 oxidation state are rare. Although a number of Mn(VI) nitrido complexes have been generated in solution via one-electron oxidation of the corresponding Mn(V) nitrido species, they are too unstable to isolate. Herein we report the isolation and the X-ray structure of a Mn(VI) nitrido complex, [MnVI(N)(TAML)]- (2), which was obtained by one-electron oxidation of [MnV(N)(TAML)]2- (1). 2 undergoes N atom transfer to PPh3 and styrenes to give Ph3P═NH and aziridines, respectively. A Hammett study for various p-substituted styrenes gives a V-shaped plot; this is rationalized by the ability of 2 to function as either an electrophile or a nucleophile. 2 also undergoes hydride transfer reactions with NADH analogues, such as 10-methyl-9,10-dihydroacridine (AcrH2) and 1-benzyl-1,4-dihydronicotinamide (BNAH). A kinetic isotope effect of 7.3 was obtained when kinetic studies were carried out with AcrH2 and AcrD2. The reaction of 2 with NADH analogues results in the formation of [MnV(N)(TAML-H+)]- (3), which was characterized by ESI/MS, IR spectroscopy, and X-ray crystallography. These results indicate that this reaction occurs via an initial "separated CPET" (separated concerted proton-electron transfer) mechanism; that is, there is a concerted transfer of 1 e- + 1 H+ from AcrH2 (or BNAH) to 2, in which the electron is transferred to the MnVI center, while the proton is transferred to a carbonyl oxygen of TAML rather than to the nitrido ligand.

SYNTHESIS OF ETHYL ESTERS OF PHENYL- AND p-PHENYL SUBSTITUTED CYCLOPROPANECARBOXYLIC ACIDS AND THEIR CONVERSION

The reaction of carboethoxycarbene with styrene and p-substituted styrenes in the conditions of thermocatalytic decomposition of ethyl diazoacetate has been studied. It has been shown that the substituents in the investigated styrenes have an essential effect on the activity of the double bond with respect to carboethoxy¬¬carbene. It has been established as a result of the investigation that the substituents in the para- position of styrene influence essentially on the activity of the double bond with respect to carboethoxycarbene. It has been revealed that carboethoxycarbene is connected to the double bond of styrene and p-styrenes practically without formation of by products. As a result of the reaction, 2-phenyl and 2-p-substituted phenyl-1-ethoxycarbonyl cyclopropane (1–4) as a mixture of cis- and trans- isomers at a ratio of~ (30:70) with the predominant formation of a trans-isomer has been obtained. The composition and structure of the synthesized compounds have been established. It has been revealed that all synthesized cyclopropane-containing compounds show the various biologically active properties. In addition, the compounds 9–12 can be used as a modifier and diluent for epoxy resin ED-20

Amido Ca and Yb(II) Complexes Coordinated by Amidine-Amidopyridinate Ligands for Catalytic Intermolecular Olefin Hydrophosphination.

A series of amido Ca and Yb(II) complexes LM[N(SiMe3)2](THF) (1Yb, 1-4Ca) coordinated by amidine-amidopyridinate ligands L1-4 were synthesized via a transamination reaction between proligands L1-4H and bisamido complexes M[N(SiMe3)2]2(THF)2 (M = Yb, Ca). The reactions of Yb[N(SiMe3)2]2(THF)2 with proligands L2H-L4H containing CF3 and C6H4F fragments do not allow for preparing the target Yb(II) complexes, while the Ca analogues were synthesized in good yields. Complexes 1Yb and 1-4Ca were evaluated as precatalysts for hydrophosphination of styrene, p-substituted styrenes, α-Me-styrene, and 2,3-dimethylbutadiene with various primary and secondary phosphines (PhPH2, 2,4,6-Me3C6H2PH2, 2-C5NH4PH2, Ph2PH, Cy2PH). Complexes 1Yb, 1-4Ca performed high catalytic activities in styrene hydrophosphination with PhPH2 and Ph2PH and demonstrated high regioselectivity affording exclusively the anti-Markovnikov addition products. For primary PhPH2 the reactions (1:1 molar ratio of substrates) catalyzed by 1Yb, 1Ca, and 2Ca proved to be highly chemoselective affording the secondary phosphine Ph(PhCH2CH2)PH; however, complexes 3Ca and 4Ca led to the formation of both secondary and tertiary phosphines in 80:20 and 86:14 ratios. Styrene hydrophosphinations with 2,4,6-Me3C6H2PH2 and 2-pyridylphosphine for all complexes 1Yb and 1-4Ca proceeded much more slowly compared to PhPH2. Addition of 2-C5NH4PH2 to styrene catalyzed by complex 1Yb turned out to be non-regioselective and led to the formation of a mixture of Markovnikov and anti-Markovnikov addition products, while all Ca complexes enabled regioselective anti-Markovnikov addition. Complexes 1Ca and 1Yb containing catalytic centers featuring similar ionic radii performed different catalytic activity: the ytterbium analogue proved to be a more active catalyst for intermolecular hydrophosphination of styrene with Cy2PH, 2-C5NH4PH2, and PhPH2, but less active with sterically demanding 2,4,6-Me3C6H2PH2. Styrenes containing in p-position electron-donating groups (Me, tBu, OMe) performed with noticeably lower rates in the reactions with PhPH2 compared to styrene. Complexes 1Yb, 1Ca, 2Ca, 3Ca, and 4Ca enabled addition of PhPH2 toward the double C═C bond of α-Me-styrene, and the reaction rate for this substrate is noticeably lower; however quantitative conversions were reached in ∼40 h. Complexes 1Ca and 2Ca promoted 1,2-addition of PhPH2 to 2,3-dimethyl butadiene with excellent regio- and chemoselectivity to afford linear secondary phosphines. Hydrophosphination of inert 1-nonene with Ph2PH with 40% conversion becomes possible due to the application of complex 2Ca (40 h, 70 °C). The rate law for the hydrophosphination of styrene with Ph2PH catalyzed by 1Ca was found to agree with the idealized equation: v = k[styrene]1[1Ca]1.

Mechanistic insights into catalytic linear cross-dimerization between conjugated dienes and styrenes by a ruthenium(0) complex

The mechanistic studies for linear cross-dimerization between 2,3-dimethylbuta-1,3-diene and styrene by a Ru(0) complex, Ru(η6-naphthalene)(η4-1,5-COD) (1), are performed both by kinetic and computational studies. This reaction is basically zero-order to both of the diene and styrene concentrations and first-order to the catalyst concentration. The Hammett plot using p-substituted styrenes gives a linear relationship with a positive slope (ρ = +0.482). The deuterium isotope experiment clearly shows the present reaction being a formal 1,4-addition of a C–H bond in styrene to cisoid-1,3-diene. These kinetic studies show the reaction proceeding via oxidative coupling mechanism that is also supported by the DFT calculations.

Titanium salan catalysts for the asymmetric epoxidation of alkenes: steric and electronic factors governing the activity and enantioselectivity.

A new insight into the highly enantioselective (up to >99.5 % ee) epoxidation of olefins in the presence of chiral titanium(IV) salan complexes is reported. A series of 14 chiral ligands with varying steric and electronic properties have been designed, and it was found that electronic effects modulate the catalytic activity (without affecting the enantioselectivity), whereas the steric properties account for the enantioselectivity of the epoxidation. Competitive oxidations of p-substituted styrenes reveal the electrophilic nature of the oxygen-transferring active species, with a Hammett ρ value of -0.51; the enantioselectivity is unaffected by the electron-donating (or withdrawing) ability of the p-substituents. Mechanistic studies provide evidence in favor of a stepwise reaction mechanism: in the first (rate-determining) stage, olefin most probably coordinates to the active species, followed by intramolecular enantioselective oxygen transfer. The enantioselectivity increases with decreasing temperature. The modified Eyring plots for the epoxidation of styrene and (Z)-β-methylstyrene are linear, indicating a single, enthalpy-controlled mechanism of stereoselectivity, with ΔΔH(≠) =-6.6 kJ mol(-1) and -5.4 kJ mol(-1) , respectively.

A General Mechanism for the Copper- and Silver-Catalyzed Olefin Aziridination Reactions: Concomitant Involvement of the Singlet and Triplet Pathways

The olefin aziridination reactions catalyzed by copper and silver complexes bearing hydrotris(pyrazolyl)borate (Tp(x)) ligands have been investigated from a mechanistic point of view. Several mechanistic probe reactions were carried out, specifically competition experiments with p-substituted styrenes, stereospecificity of olefins, effects of the radical inhibitors, and use of a radical clock. Data from these experiments seem to be contradictory, as they do not fully support the previously reported concerted or stepwise mechanisms. But theoretical calculations have provided the reaction profiles for both the silver and copper systems with different olefins to satisfy all experimental data. A mechanistic proposal has been made on the basis of the information that we collected from experimental and theoretical studies. In all cases, the reaction starts with the formation of a metal-nitrene species that holds some radical character, and therefore the aziridination reaction proceeds through the radical mechanism. The silver-based systems however hold a minimum energy crossing point (MECP) between the triplet and closed-shell singlet surfaces, which induce the direct formation of the aziridines, and stereochemistry of the olefin is retained. In the case of copper, a radical intermediate is formed, and this intermediate constitutes the starting point for competition steps involving ring-closure (through a MECP between the open-shell singlet and triplet surfaces) or carbon-carbon bond rotation, and explains the loss of stereochemistry with a given substrate. Overall, all the initially contradictory experimental data fit in a mechanistic proposal that involves both the singlet and the triplet pathways.

Substituent-Induced Switch of the Role of Charge-Transfer Complexes in the Diels–Alder Reactions of o-Chloranil and Styrenes

Addition of p-substituted styrenes, XSty (X = H, Me, MeO, or Cl) to the solutions of o-chloranil, oCA, in dichloromethane resulted in the transient formation of the charge-transfer complexes, [XSty, oCA], followed by the Diels-Alder reaction. At low temperatures, these reactions led to formation of essentially pure endocycloadducts. As expected for the inverse-electron-demand Diels-Alder reaction, the rate constants of the cycloaddition rose with the increase of the donor strength. However, while facile cycloaddition took place in the neat mixtures of the o-chloranil with p-methyl, p-chloro-, or unsubstituted styrenes at low temperatures, a similar system involving the strongest MeOSty donor was surprisingly persistent. X-ray structural measurements and quantum-mechanical computations indicated that this anomaly is related to the fact that the diene/dienophile orientation in the charge-transfer [MeOSty, oCA] complex is opposite to that in the endocycloadduct and in the lowest-energy transition state leading to this isomer. Thus, the proceeding of the cycloaddition requires dissociation of the (dead-end) complex. For the systems involving the oCA diene and either the HSty, ClSty, or MeSty dienophile, the donor/acceptor arrangements in the charge-transfer complexes apparently are consistent with that in the corresponding products, and the formation of these complexes does not hinder the Diels-Alder reaction.

β-メチルスチレン類のカチオン重合

EtAlCl2/SnCl4 is an initiating system for the living cationic polymerization of various p-substituted styrenes in the presence of added bases, but neither cis- nor trans-β-methylstyrene (βMeSt) can be polymerized by it. In contrast, after adding p-methylstyrene, the random copolymerization of trans-βMeSt proceeded, producing copolymers with up to 30% of βMeSt content as confirmed by 1H and 13C NMR spectroscopy. In addition, long-lived cationic species were observed at −78°C, which could not be observed in the polymerization of the cis-isomer. The copolymer of the trans-isomer had a higher stereoregularity compared to that of the cis-isomer. Copolymerization of trans-anethole, a more reactive βMeSt derivative having a p-methoxy group, with pMeSt proceeded in an alternating fashion. Thus, the successful copolymerization of βMeSts, generally considered difficult to polymerize, was achieved by the judicious choice of the comonomer with appropriate reactivity and a suitable initiating system.

Molecules with Perfect Cubic Symmetry as Nanobuilding Blocks for 3-D Assemblies. Elaboration of Octavinylsilsesquioxane. Unusual Luminescence Shifts May Indicate Extended Conjugation Involving the Silsesquioxane Core

The objectives of this work are to demonstrate facile routes to 3-D star materials with octa- and hexadecafunctionality to provide new nanoconstruction tools for the synthesis of new types of stars, dendrimers, and hyperbranched molecules or for the assembly of novel nanocomposites. A further objective is to identify novel properties inherent in the resulting new compounds. Octavinylsilsesquioxane (OVS, [VinylSiO1.5]8) with perfect 3-D or cubic symmetry is elaborated through metathesis with substituted styrenes to produce a series of RStyrenylOS compounds. The p-BrStyrenylOS compound is then further reacted with other sets of p-substituted styrenes via Heck coupling to produce a set of R′VinylStilbeneOS compounds. The R′ = NH2 compound is then reacted with 3,5-dibromo or dinitrobenzoyl chloride to produce hexadecafunctional 3-D stars. These synthetic methods provide perfect single core and then core−shell 3-D stars including in the third generation branch points such that these molecules can be used for t...

Nickel-Catalyzed Addition of C−H Bonds of Terminal Alkynes to 1,3-Dienes and Styrenes

The C-H bond of a terminal alkyne adds to a carbon-carbon double bond of 1,3-dienes, styrenes, and norbornene at room temperature in the presence of a nickel catalyst in regio- and stereoselective manners. Reaction of triisopropylsilylacetylene with 1-substituted 1,3-butadiene derivatives afforded hydroalkynylation products via introduction of a hydrogen atom and a triisopropylsilylethynyl group to 4- and 3-positions of the dienes, respectively. Likewise, 1-triisopropylsiloxy-1,3-butadiene, 1,3-pentadiene, 1-cyclohexen-1-yl-1,3-butadiene, and 1,3-cyclohexadiene underwent the hydroalkynylation reaction, giving the corresponding 1,4-enyne derivatives in good yields at room temperature. Reaction of p-substituted styrene with triisopropylsilylacetylene also proceeded in the presence of the nickel catalyst, giving the branched hydroalkynylation products in good yields. Norbornene gave a exo-addition product in good yield under the same reaction conditions.

Olefin Epoxidation with Hydrogen Peroxide Catalyzed by Lacunary Polyoxometalate [γ‐SiW10O34(H2O)2] 4‐.

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Mechanism of [γ-H2SiV2W10O40]4--Catalyzed Epoxidation of Alkenes with Hydrogen Peroxide

The mechanism of [gamma-H2SiV2W10O40]4--catalyzed epoxidation of alkenes with hydrogen peroxide in acetonitrile/tert-butyl alcohol was investigated. The negative Hammett rho+ (-0.88) for the competitive oxidation of p-substituted styrenes and the low XSO (XSO = (nucleophilic oxidation)/(total oxidation)) value of <0.01 for the [gamma-H2SiV2W10O40]4--catalyzed oxidation of thianthrene-5-oxide reveal that the strong electrophilic oxidant species is formed on [gamma-H2SiV2W10O40]4- (I). The preferable formation of trans-epoxide for the epoxidation of 3-substituted cyclohexenes shows the steric constraints of the active oxidant on I. The 51V NMR, 183W NMR, and CSI-MS spectroscopy show that the reaction of I with hydrogen peroxide leads to the reversible formation of a hydroperoxo species [gamma-HSiV2W10O39OOH]4- (II). The successive dehydration of II forms III, which possibly has an active oxygen species of a mu-eta2:eta2-peroxo group. The kinetic and spectroscopic studies show that the present epoxidation proceeds via III. The energy diagram of the epoxidation with density functional theory (DFT) supports the idea.

Olefin Epoxidation with Hydrogen Peroxide Catalyzed by Lacunary Polyoxometalate [γ‐SiW10O34(H2O)2]4−

The tetra-n-butylammonium (TBA) salt of the divacant Keggin-type polyoxometalate [TBA](4)[gamma-SiW(10)O(34)(H(2)O)(2)] (I) catalyzes the oxygen-transfer reactions of olefins, allylic alcohols, and sulfides with 30 % aqueous hydrogen peroxide. The negative Hammett rho(+) (-0.99) for the competitive oxidation of p-substituted styrenes and the low value of (nucleophilic oxidation)/(total oxidation), X(SO)=0.04, for I-catalyzed oxidation of thianthrene 5-oxide (SSO) reveals that a strongly electrophilic oxidant species is formed on I. The preferential formation of trans-epoxide during epoxidation of 3-methyl-1-cyclohexene demonstrates the steric constraints of the active site of I. The I-catalyzed epoxidation proceeds with an induction period that disappears upon treatment of I with hydrogen peroxide. (29)Si and (183)W NMR spectroscopy and CSI mass spectrometry show that reaction of I with excess hydrogen peroxide leads to fast formation of a diperoxo species, [TBA](4)[gamma-SiW(10)O(32)(O(2))(2)] (II), with retention of a gamma-Keggin type structure. Whereas the isolated compound II is inactive for stoichiometric epoxidation of cyclooctene, epoxidation with II does proceed in the presence of hydrogen peroxide. The reaction of II with hydrogen peroxide would form a reactive species (III), and this step corresponds to the induction period observed in the catalytic epoxidation. The steric and electronic characters of III are the same as those for the catalytic epoxidation by I. Kinetic, spectroscopic, and mechanistic investigations show that the present epoxidation proceeds via III.

Alkenecis-Dihydroxylation by [(Me3tacn)(CF3CO2)RuVIO2]ClO4(Me3tacn = 1,4,7-Trimethyl-1,4,7-triazacyclononane): Structural Characterization of [3 + 2] Cycloadducts and Kinetic Studies

cis-Dioxoruthenium(VI) complex [(Me(3)tacn)(CF(3)CO(2))Ru(VI)O(2)]ClO(4) (1, Me(3)tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) reacted with alkenes in aqueous tert-butyl alcohol to afford cis-1,2-diols in excellent yields under ambient conditions. When the reactions of 1 with alkenes were conducted in acetonitrile, oxidative C=C cleavage reaction prevailed giving carbonyl products in >90% yields without any cis-diol formation. The alkene cis-dihydroxylation and C=C cleavage reactions proceed via the formation of a [3 + 2] cycloadduct between 1 and alkenes, analogous to the related reactions with alkynes [Che et al. J. Am. Chem. Soc. 2000, 122, 11380]. With cyclooctene and trans-beta-methylstyrene as substrates, the Ru(III) cycloadducts (4a) and (4b) [formula; see text] were isolated and structurally characterized by X-ray crystal analyses. The kinetics of the reactions of 1 with a series of p-substituted styrenes has been studied in acetonitrile by stopped-flow spectrophotometry. The second-order rate constants varied by 14-fold despite an overall span of 1.3 V for the one-electron oxidation potentials of alkenes. Secondary kinetic isotope effect (KIE) was observed for the oxidation of beta-d(2)-styrene (k(H)/k(D) = 0.83 +/- 0.04) and alpha-deuteriostyrene (k(H)/k(D) = 0.96 +/- 0.03), which, together with the stereoselectivity of cis-alkene oxidation by 1, is in favor of a concerted mechanism.

Radical copolymerization of maleic anhydride and substituted styrenes by reversible addition-fragmentation chain transfer (RAFT) polymerization

Reversible addition fragmentation transfer (RAFT) copolymerization with benzyl dithiobenzoate (BDTB) as chain transfer agent was used to copolymerize maleic anhydride (MA) with styrene (St) and with the substituted styrenes p-chlorostyrene ( pClSt), p-methoxystyrene ( pMeOSt) and p-methylstyrene ( pMeSt). Kinetic studies indicated that radical copolymerizations proceeded with apparent ‘living’ character, deduced from experiments demonstrating an increase in molar mass with monomer conversion, narrow molar mass distribution and chain extension to form block copolymer. All copolymers were alternating in chain structure as confirmed by determinations of monomer reactivity ratios. The degree of control in the RAFT mechanism and the establishment of the fragmentation equilibrium incorporating MA are discussed for styrene and for p-substituted styrenes, in relation to experimental copolymerizations producing molar masses somewhat higher than expected. For copolymerizations of MA with α-methylstyrene (αMeSt), conventional rather than controlled behaviour was observed, suggesting that the fragmentation equilibrium could be shifted towards the αMeSt propagating radical.

Synthesis of styrylcoumarins from coumarin diazonium salts and studies on their spectra characteristics

A facile synthesis of styrylcoumarins based on Palladium-catalyzed reaction of coumarin diazonium salts with substituted styrenes is described. The reactions produced a series of 7-styrylcoumarins in good yields under mild conditions. The absorption and emission spectra of different styrylcoumarins were compared and discussed. Although the λ a,max of the styrylcoumarins changed only slightly with a p-substituted styrene, the λ e,max produced a blue shift which increased with the electron-withdrawing ability of the p-substituted group. The p-CH 3 of styrylcoumarin caused a red shift of ca. 20 nm and also a higher fluorescence quantum yield. Styrylcoumarins with o, p-CN obtained well-resolved vibrational bands and the latter possessed higher fluorescence quantum yield. In addition, a coumarin extended at both the 3-positions with benzene and 7-position with p-chlorostyrene had better fluorescence properties.

Novel Organosilicon Starburst Compounds Based on Ruthenium-Catalyzed Silylative Coupling Reactions of 1,3,5-Tris(dimethylvinylsilyl)benzene

The highly stereo- and regioselective reaction of 1,3,5-tris(dimethylvinylsilyl)benzene (1) with p-substituted styrenes, p-XC 6 H 4 CH=CH 2 , where X = H (2), Cl (3), Br (4), vinyl (5), catalyzed by RuHCl(CO)(PCy 3 ) 2 (I) appeared to be an efficient basis for new starburst compounds involving silylene-vinylene-arylene sequences. Attempts were made to synthesize the first generation of dendrimer (12), based on 1 as a core, via two methods: direct silylative coupling of 1,3,5-tris[dimethyl(4-vinylstyryl)silyl]benzene (5) with 1, which gave a mixture of oligomers containing the SiCH=CHSi structure, and successfully via silylation of 5 with vinylsilyl-3,5-bis(isopropoxysilyl)benzene (10) followed by vinylation with Grignard reagent. Additionally, the double silylation of DVB with 10 followed by vinylation allowed the synthesis of an analogous starburst compound (14), which can be a new core for analogous dendritic compounds.

Fluorescence studies of associative behavior of cationic surfactant moieties covalently linked to poly(acrylamide) at the surfactant head or tail

Association properties of hydrophobically modified water-soluble polymers bearing the same (or similar) hydrophobic and charged groups at different relative positions (with respect to the polymer main chain) were compared. Two types of surfactant monomers (surfmers) were synthesized; a cationic surfactant was linked to the p-position of styrene at the surfactant charged head (dimethyldodecyl-4-vinylbenzylammonium chloride (St-QC 12)) or at the tail end (13-(4-vinylphenyl)tridecyltrimethylammonium bromide (St-C 13Q)). These surfmers were copolymerized with acrylamide (AAm), and the association behavior of the copolymers in water was characterized using different fluorescence techniques. The surfmer contents in the AAm/St-QC 12 and AAm/St-C 13Q copolymers were fixed to more or less 10 mol%. The surfmer units in the copolymers self-associate to form multipolymer aggregates. An apparent critical micelle concentration (cmc) (i.e. a polymer concentration for the onset of interpolymer association of the surfmer units) estimated from excitation spectra of pyrene probes for AAm/St-QC 12 (cmc=2.6×10 −4 g/l) was several times lower than that for AAm/St-C 13Q (cmc=1.3×10 −3 g/l), surfmer units in AAm/St-QC 12 showing a stronger tendency for interpolymer association than those in AAm/St-C 13Q. The presence of excimer emissions in steady-state fluorescence spectra for the p-substituted styrene residues (phenylene groups) in AAm/St-C 13Q indicated that the benzene rings are in close proximity to one another in the polymer aggregates. Steady-state fluorescence spectra and fluorescence quenching by thallium nitrate and 1-nitrohexane indicated that the phenylene groups in AAm/St-C 13Q were incorporated in hydrophobic microdomains formed from surfactant hydrocarbon chains, whereas the phenylene groups in AAm/St-QC 12 are located near the surface of polymer aggregates in a way that they are sufficiently apart from each other and hence no excimer is formed.