Electrochemically controlled self-assembly of an organometallic block copolymer

A new means of controlling the order-disorder transition of block copolymers is presented. By applying small electrical potentials (2 V/cm) to disordered solutions of an organometallic block copolymer, oriented ordered grains were obtained near the positive electrode. After reversing the electrical bias on the system, the ordered grains disappeared, and new, oriented, ordered regions were formed at the opposite electrode. Our work establishes the concept of electrochemical self-assembly for controlling order formation in block copolymers.     

A photochromic,electrochromic, thermochromic Ru complexed benzannulene: an organometallic example of the dimethyldihydropyrene-metacyclophanediene valence isomerization

The preparation of the first photochromic, organometallic derivative of the diarylethene class, the CpRu-complexed benzodimethyldihydropyrene 3, in which the organometallic is directly attached to the photochromic core, is described. The negative dark purple photochrome 3 readily bleaches to form the almost colorless cyclophanediene 3' on irradiation with visible light. The latter switches back to 3 either photochromically with UV light, electrochromically on reduction, or thermochromically on heating. Essentially quantitative conversion between the two states is possible. The open complex 3' thermally closes 2.6 times faster than the uncomplexed parent 2', but the closed form 3 opens with visible light at about 30% of the rate of uncomplexed 2. Both open forms, complexed 3' and uncomplexed 2' close equally fast with UV light.     

Homoallylic alcohol isomerization in water over an immobilized Ru(II) organometallic catalyst with mesoporous structure

PPh(2)-functionalized SBA-15 was synthesized by co-condensation of tetraethyl orthosilicate and 2-(diphenylphosphino)ethyltriethoxysilane through prehydrolysis. The as-prepared PPh(2)-SBA-15 was used as the support to immobilize the Ru(II) organometallic catalyst through the strong coordination between the Ru(II) and the PPh(2)-ligand (Ru-PPh(2)-SBA-15). During 1-phenyl-3-buten-1-ol isomerization carried out in water as an environmentally friendly medium, the Ru-PPh(2)-SBA-15 catalyst exhibited almost the same activity and selectivity as the corresponding RuCl(2)(PPh(3))(3) homogeneous catalyst and could be used repetitively nearly 7 times. On the basis of various characterizations, the correlation of the catalytic behaviors of the Ru-PPh(2)-SBA-15 to its structural characteristics was discussed briefly. Obviously, the high activity of the Ru-PPh(2)-SBA-15 could be attributed to both the high surface area of the support, which ensured the good dispersion of Ru(II) active sites, and the ordered mesoporous structure, which facilitated the diffusion of organic reactants.     

Photoinduced E to Z isomerization of tetraphenylethylene derivatives within organometallic supramolecular assemblies

Isolation of E-1,2-bis(4-bromophenyl)-1,2-diphenyl-ethylene from the E/Z isomer mixture obtained by a Mc Murry coupling reaction and reaction of this isomer with imidazole followed by N-alkylation with n Bu Br and anion exchange yielded the bisimidazolium tetraphenylethylene (TPE) derivative H_2-E-1(PF_6)_2.The reaction of H_2-E-1(PF_6)_2 with Ag_2O yielded the dinuclear metallarectangle[Ag_2(E-1)_2](PF_6)_2 where the two bis-NHC donors E-1 bridge two silver atoms.Irradiation of[Ag_2(E-1)_2](PF_6)_2 leads to E/Z isomerization of the di-NHC ligand and formation of Z-1 in the mononuclear complex[Ag(Z-1)]PF_6.Demetallation of the di-NHC ligand with NH_4Cl/NH_4PF_6 yielded bisimidazolium salt H_2-Z-1(PF_6)_2.The unique isomerization of the E-TPE derivative into its Z-isomer via metal complex formation/irradiation/demetallation cannot be achieved by irradiation of the individual imidazolium salt.The emissive properties of the TPE complexes[Ag_2(E-1)_2](PF_6)_2 and[Ag(Z-1)]PF_6 have been investigated.     

Kinetics of the geometric isomerization of aqueous cis-diamminedichloroplatinum(II)

The rate of the isomerization of cis-diamminedichloroplatinum(II) to the trans form has been determined in aqueous KCl solutions from 65°C to 100°C. At 37°C the half-life is 1.8 years. Pt, AgCl, Si, SiO₂, and graphite did not catalyse the isomerization while other chemical reactions occurred with Ag and Ketjenblack carbon.

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-(II) - KCl 65°C 100°C. 37°C 1,8 . Pt, AgCl, Si, SiO₂ , Ag Ketjenblack.

     

Light-induced geometric isomerization of 1,2-diphenylcyclopropanes included within Y zeolites: role of cation-guest binding

Through a systematic study of several diphenylcyclopropane derivatives, we have inferred that the cations present within a zeolite control the excited-state chemistry of these systems. In the parent 1,2-diphenylcylopropane, the cation binds to the two phenyl rings in a sandwich-type arrangement, and such a mode of binding prevents cis-to-trans isomerization. Once an ester or amide group is introduced into the system (derivatives of 2beta,3beta-diphenylcyclopropane-1alpha-carboxylic acid), the cation binds to the carbonyl group present in these chromophores and such a binding has no influence on the cis-trans isomerization process. Cation-reactant structures computed at density functional theory level have been very valuable in rationalizing the observed photochemical behavior of diphenylcyclopropane derivatives included in zeolites. While the parent system, 1,2-diphenylcylopropane, has been extensively investigated in the context of chiral induction in solution, owing to its failure to isomerize from cis to trans, the same could not be investigated in zeolites. However, esters of 2beta,3beta-diphenylcyclopropane-1alpha-carboxylic acid could be studied within zeolites in the context of chiral induction. Chiral induction as high 20% ee and 55% de has been obtained with selected systems. These numbers, although low, are much higher than what has been obtained in solution with the same system or with the parent system by other investigators (maximum approximately 10% ee).     

Separation techniques in speciation analysis for organometallic species

A comprehensive review of the state-of-the-art of the separation of various organically-bound metals and metalloids for speciation analysis is presented. Recent developments in chromatographic (gas, liquid and supercritical fluid), electrophoretic (free-flow and gel) and fractionation techniques are discussed, followed by a survey of pertinent applications to speciation analysis for organometals and metalloids. The required sample characteristics for a given separation technique are specified and appropriate derivatization procedures are characterized. Methods applicable to the speciation of organic species of a particular element in various matrices are critically evaluated.List of abbreviations APS ammonium pentanesulfonate - CCC counter current chromatography - CZE capillary zone electrophoresis - DBT dibutyltin - DCyT dicyclohexyltin - DDTC diethyldithicarbamate - DEAE diethylaminoethyl gel (anion exchanger) - DEL diethyllead - DET diethyltin - DMA dimethylarsinic acid - DMGe dimethylgermanium - DMHg dimethylmercury - DML dimethyllead - DMSb dimethylstibinic acid - DMT dimethyltin - DPhT diphenyltin - DPrT dipropyltin - EDTA ethylenediaminetetraacetate - FFF field flow fractionation - GC gas chromatography - HEPES 4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid - HPLC high performance liquid chromatography - ICP inductively coupled plasma - IEC ion exchange chromatography - IIC ion interaction chromatography - LC liquid chromatography - MBT monobutyltin - MCyT monocyclohexyltin - MEA monoethylarsinic acid - MEHg monoethylmercury - MEL monoethyllead - MET monoethyltin - MIP microwave induced plasma - MMA monomethylarsonic acid - MMGe monomethylgermanium - MMHg monomethylmercury - MML monomethyllead - MMSb monomethylstibonic acid - MMT monomethyltin - MPhHg monophenylmercury - MPhT monophenyltin - MPrT monopropyltin - MS mass spectrometry - NAA neutron activation analysis - NaBS sodium 1-butanesulfonate - NaDS sodium dodecylsulfonate - NaPS sodium pentanesulfonate - PAGE polyacrylamide gel electrophoresis - PAR 4-(2-pyridylazo)resorcinol - PIXE proton induced X-ray emission - QF quartz furnace - RPC reversed phase partition chromatography - SDS sodium dodecyl sulfate - SEC size exclusion chromatography - SFC supercritical fluid chromatography - TBAP tetrabutylammonium phosphate - TAL tetraalkyllead - TBT tributyltin - TCyT tricyclohexyltin - TeEL tetraethyllead - TEL triethyllead - TeML tetramethyllead - TET triethyltin - TGME thioglycolic methyl ester - THF tetrahydrofuran - TMA trimethylarsinic acid - TMAH tetramethylammonium hydroxide - TMGe trimethylgermanium - TML trimethyllead - TMT trimethyltin - TPhT triphenyltin - TPrT tripropyltin - Tris tris(hydroxymethyl)aminomethane     

Extraction and pre-concentration of organometallic species from environmental samples

Methods of extraction, clean-up and preconcentration normally reserved for organic trace analysis are considered with a view to applying such techniques to the developing field of organometallic speciation. The overview covers the main compartments of the natural environment; water, soil and sediment, plant and animal tissue.     

Optimization of an n-pentane isomerization reactor

The optimization of the operating variables in a pentane isomerization reactor was studied. The isomerization reaction was carried out on a commercial     

Self-assembly of an organometallic side-by-side double helix

The first polymeric organometallic double helix has been synthesized by self-assembly through hydrogen bonding by using a biomimetic strategy and a new side-by-side structural motif.     

Where organometallics and dendrimers merge: the incorporation of organometallic species into dendritic molecules

This review will describe the ongoing efforts being made to incorporate organometallic fragments into the framework of dendrimers. While purely dendritic organic molecules are well known and well studied, species incorporating organometallic moieties potentially offer many benefits that are not available to only organic containing dendrimers. For example, catalytic or redox active organometallic functions can be included in the dendritic framework and impart these characteristics onto the dendrimer. This report will give an overview of the latest developments in this field by highlighting selected examples that detail novel synthetic strategies or dendrimer construction methodologies, interesting practical applications or address specific problems associated with organometallic dendrimers.     

Osmium tetroxide-promoted catalytic oxidative cleavage of olefins: an organometallic ozonolysis

A mild, organometallic alternative to ozonolysis utilizing oxone and OsO(4) is presented. This is a direct oxidation of olefins via the carbon-carbon cleavage of an osmate ester by the action of oxone. Twenty-four different olefins were converted to their corresponding ketones or carboxylic acids in high yields (>80%). Free alcohols, acetate- and benzyl-protected alcohols, and 1,2-diols were stable under these conditions. This method should be applicable for traditional organic synthesis.     

Positional and geometric isomerization of diacetoxy derivatives of 1-phenyl-1(2)-octenes

Isomerization of 1,2-, 3,4-, and 1,4-diacetoxy derivatives of 1-phenyl-1(2)-octenes in the presence of Pd₃Sb/C and/or RhBi₄/C as catalysts was studied. The kinetic and thermodynamic characteristics of the reaction were evaluated.     

An organometallic derivative of a BAPTA ligand: towards electrochemically controlled cation release in biocompatible media

The combination of a ferrocenyl moiety with BAPTA provides a novel, water-soluble, redox-active chelator. This chelator behaving as a conformational sensor exhibits an unexpected electrochemical response with high affinity and selectivity for calcium.     

Trans-cis isomerization of an azoxybenzene liquid crystal

Trans-cis isomerization was investigated in a room temperature liquid crystal mixture of two azoxybenzene compounds. Experiments were performed on isolated molecules in dilute solutions and on the liquid crystal phase composed of the pure compounds. The absorption spectra of the trans and cis isomers were found to be similar to those of azobenzene compounds, as were the birefringence and order parameter of the nematic liquid crystal phase. The photo-optic properties were also similar in that irradiation by ultraviolet light caused the conversion from trans to cis isomers, while short wavelength visible light incident on these compounds resulted in the conversion from cis to trans isomers. The activation energy for thermal relaxation from the cis to trans isomer in the liquid crystal phase was determined to be (66±7) kJ/mole, which is less than for azobenzene in solution. While a photostationary state in a dilute solution with approximately equal numbers of trans and cis isomers was achieved, the nematic-isotropic transition of the mixture of the pure compounds decreased from 70°C to room temperature with a cis concentration of only about 12%. One unusual finding was that the photostationary concentration of trans and cis isomers due to irradiation with light of a specific visible wavelength depended on the starting concentrations of the two isomers, indicating that there may be a molecular conformation that is not photo-responsive and relaxes only thermally.     

Crystalline graphite from an organometallic solution-phase reaction

We report a chemical method by which graphitic carbon is prepared at reaction temperatures as low as 110 degrees C from readily available molecular reagents. This process requires no forcing conditions such as high pressures, intense light, or electrical discharge but is a simple, catalytic organometallic reaction. The carbon forms in a variety of morphologies including graphene sheets and nanotubes. The mild reaction conditions are similar to those routinely employed in homogeneous catalysis; therefore, they will allow the subtle manipulation of reaction variables to give desired morphologies selectively.     

Phthalocyanine-modulated isomerization behaviour of an azo-based photoswitch

A photoswitchable azobenzene-phthalocyanine-azobenzene triad has been synthesized and its electrochemical properties determined. Energy transfer among the subunits allows for modification of the E-Z ratio by selective excitation of the phthalocyanine moiety.     

Subnanosecond isomerization in an osmium-dimethyl sulfoxide complex

We report the structure, spectroscopy, and electrochemistry of cis-[Os(bpy)(2)(DMSO)(2)](OTf)(2), where bpy is 2,2'-bipyridine, DMSO is dimethyl sulfoxide, and OTf is trifluoromethanesulfonate. Electrochemical measurements are consistent with S-to-O isomerization following the oxidation of Os(2+) (1.8 V vs Ag/AgCl). Visible irradiation of the metal-to-ligand charge-transfer transition (355 nm) of [Os(bpy)(2)(DMSO)(2)](2+) in the solid state and solution yields an emissive S-bonded excited state and S-to-O excited-state isomerization on a subnanosecond time scale. These results and a comparison to the nonphotoactive [Os(bpy)(2)Cl(DMSO)](+) are discussed.