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Potassium and ammonium salts of the tungstoarsenate anion [(ReVO)3(AsW9O33)2]9– (1) have been isolated and characterized by elemental analysis, infrared and 183W NMR spectroscopy. The five-line NMR spectrum indicates a sandwich structure of C2v symmetry analogous to that found for [As2W21O69(H2O)]6–. Thermal treatment of both salts of 1 at temperatures to 900 °C leads to materials in which ~95% of the rhenium is retained, in contrast to the Keggin-derived K4PW11ReO40 which loses rhenium at ~500 °C. Based upon powder diffraction analysis, following quantitative loss of As2O3 at 420–430 °C, the following phases were identified in samples heated to 600 and 725 °C. From the potassium salt, a monoclinic K2W3O10-type bronze, and from the ammonium salt a mixture of hexagonal and tetragonal WO3 bronzes. Reflections corresponding to ReO2, ReO3, solid solutions of ReO3 in WO3, and Re2O7 were absent. The incorporation of rhenium into tungsten bronze phases suggests that technetium might behave similarly, opening a possible route to storage of 99Tc waste. To cite this article: A. Besserguenev, M.T. Pope, C. R. Chimie 8 (2005).

The synthesis and characterization of the previously unknown mixed-metal sandwich-type Wells–Dawson complexes, αββα-[(ZnIIOH2)2(FeIII)2(P2W15O56)2]14– (Zn2Fe2P4) and αββα-[(ZnIIOH2)2(FeIII)2(As2W15O56)2]14– (Zn2Fe2As4), are described. The complexes are prepared by the reaction of Zn(II) with the divacant lacunary species, αααα-[(NaOH2)2(FeIII)2(P2W15O56)2]16– and αααα-[(NaOH2)2(FeIII)2(As2W15O56)2]16–, respectively, and are characterized by X-ray crystallography, infrared and NMR spectroscopy, elemental and thermogravimetric analyses, differential scanning calorimetry, and cyclic voltammetry. Like their analogues, αββα-[(MnIIOH2)2(FeIII)2(P2W15O56)2]14– (Mn2Fe2P4) and αββα-[(MnIIOH2)2(FeIII)2(As2W15O56)2]14– (Mn2Fe2As4), the remarkable stability observed for these complexes from pH 0 to at least 6 has permitted a comprehensive evaluation of their electrocatalytic abilities toward the reduction of O2, H2O2, HNO2 and NO. A comparison of the properties of the mixed-metal Zn(II) and Mn(II) complexes is provided. To cite this article: I.M. Mbomekalle et al., C. R. Chimie 8 (2005).

Copolymers of ethene and longer chained 1-olefins such as 1-octene, 1-decene, 1-dodecene, 1-octadecene and 1-hexacosene with 8 to 28 carbon atoms were carried out using [Ph2C(2,7)-di tert BuFlu)(Cp)]ZrCl2/MAO as catalyst. Precisely designed microstructures and activities up to 168 000 kgcopoiymer/(mol zirconocene .h.mol/l monomer ) can be obtained. There is a remarkable polymerization activity left even after a time of 4 hours. The incorporation of the longer chained 1-olefins reaches 19 wt% and depends on the chain length and the concentration of the comonomer in the feed, the LLDPE materials prepared show melting points of 129 - 112 °C.

The transition metal-substituted heteropolyoxoanion, Cd4(H2O)2(As2W15O56)212− (As4W30Cd4), is one of the trivacant Dawson derivatives. Its redox electrochemistry has been studied in acid buffer solutions using cyclic voltammetry. It exhibited three steps of four-electron redox waves attributed to redox processes of the tungsten-oxo framework. Through layer-by-layer assembly, the compound was first successfully immobilized on a 4-aminobenzoic acid modified glassy carbon electrode surface by alternate deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)2Cl]2+/+ (denoted as QPVP-Os). Thus, prepared multilayer films have been characterized by cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and UV–vis spectroscopy (UV–vis). The electrocatalytic activities of the multilayer films containing As4W30Cd4 have been investigated on the reduction of three substrates of important analytical interests, NO2−, BrO3− and IO3−. And with the increase of the number of As4W30Cd4 layers, the catalytic current towards the reduction of BrO3− was enhanced and the catalytic potential shifted positively.

A number of novel C1-symmetric metallocenes based on substituted fluorenyl and indenyl ligands, [dimethylsilyl(2,7-di-tert-butyl-9-η5-fluorenyl)(1-η5-indenyl)]zirconium dichloride (3), [dimethylsilyl(1,1,4,4,7,7,10,10-octamethyl-1,2,3,4,7,8,9,10-octahydrodibenzo[b,h]-9-η5-fluorenyl)(1-η5-indenyl)]zirconium dichloride (5), and [dimethylsilyl(1,1,4,4,7,7,10,10-octamethyl-1,2,3,4,7,8,9,10-octahydrodibenzo[b,h]-9-η5-fluorenyl)(2-methyl-1- η5-indenyl)]zirconium dichloride, and the analogue complexes with a Ph2Si bridge (4, 6, and 8) have been synthesized and used for alternating ethene/propene copolymerizations and compared to the unsubstituted complexes 1 and 2. With growing sterical demand of the substituents, the activities of the catalysts at moderate temperatures decrease strongly, but a very high-temperature stability is achieved. Usage of catalyst species with a Ph2Si instead of a Me2Si bridge leads to higher activities and molar masses. The percentages of alternating triads are high for all catalysts a...

Copolymerization of propene with two α-olefins (1-hexene and 1-octadecene) using iso- and syndioselective metallocene catalysts (EtInd2ZrCl2, Et(2-MeInd)2ZrCl2, Me2SiInd2ZrCl2, Ph2CFluCpZrCl2 and Me2CFluCpZrCl2) activated with methylaluminoxane (MAO) is reported. The so-called comonomer effect was seen in the catalytic activity of the Me2SiInd2ZrCl2/MAO system. Incorporation of syndiotactic copolymers was greater than that of isotactic copolymers. The molecular weight of the isotactic copolymers was not affected significantly by the presence of the comonomer, but the molecular weights of the copolymers obtained with the syndioselective catalysts decreased with increasing comonomer concentration in the medium. Tensile properties were studied. Syndiotactic copolymers with incorporation of the order of 6 mol% of 1-octadecene presented elastomeric properties.

Temperature (T) effects on the microstructure of polypropylene made with metallocene catalysts have been investigated with the theoretical framework originally developed by Coleman and Fox and extended to the stereospecific polymerization of propylene with two-state ansa and fluxional metallocene catalysts. T effects on the polymer microstructure are mainly due to factors other than changes in the intrinsic stereoselectivity of the two states. The model has been applied to the stereosequence distributions of polypropylene prepared with the C 1 -symmetric Me 2 Si(Ind)(Flu)ZrCl 2 complex, activated with methyl aluminoxane, over a range of T and monomer concentration ([M]) values. The use of these two variables, in combination with the Coleman-Fox model (or a kinetic model), allows more reliable estimates of fundamental parameters, especially when the microstructure is a weak function of one of these variables at a constant value of T (e.g.,[M]).

A systematic study of the influence of the α-olefin size, the catalyst stereospecificity and the reaction temperature was done on the catalytic activity and tacticity of poly-α-olefins from 1-hexene to 1-octadecene. The metallocenes used were rac-Et[Ind2]ZrCl2 (1) and Me2C[Cp(9-Flu)]ZrCl2 (2) to obtain isotactic and syndiotactic polyolefins. Some catalysts giving atactic polymers were also used in order to study all the possible 13C NMR pentades. Catalytic activities increased and isotacticity and syndiotacticity decreased with temperature, but no real trend was found with the α-olefin size. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4744–4753, 2005

Eight Cs-symmetric complexes, R 1 R 2 C(Cp)(Flu)MCl 2 [R 1 = R 2 = CH 3 CH 2 CH 2 , M = Zr (1), Hf (2); R 1 = R 2 = p-CH 3 OC 6 H 4 , M = Zr (3), Hf (4); R 1 = p- t BuC 6 H 4 , R 2 = Ph, M = Zr (5), Hf (6); R 1 = R 2 = p- t BuC 6 H 4 ,M = Zr (7); R 1 = R 2 = PhCH 2 , M = Zr (8)] have been synthesized and characterized. Zirconocenes all showed the same high catalytic activities in ethylene polymerization as complex Ph 2 ClCp)(Flu)ZrCl 2 (9). However, in the propylene polymerization, the catalytic activities decreased in the order 5 9 > 7 > 8. Introduction of t Bu decreased the activities, probably due to the bulk steric hindrance. The polypropylene produced by 5 and 7 with t Bu substituent showed a higher molecular weight (Mη) than that produced by 9. The 1 3 C NMR spectrum revealed the polymers from 7 and 8 to have shorter average syndiotactic block length than polymer produced by 9. It was noted that [mm] stereodefect of polypropylene by 8 could not be observed from 1 3 C NMR, which showed that the benzyl on bridge carbon 8 prevented chain epimerization and enatiofacial misinsertion in polymerization.

The novel iron(I) sandwich compound [Cp*Fe(η4-C4Py4)] (1) was prepared and characterized by various methods, including X-ray crystallography. Coordination-driven self-assembly of a diruthenium acceptor with the tetrapyridyl metalloligand [Cp*Fe(I)(η4-C4Py4)] led to a D4-symmetric three-dimensional M4L2 tetragonal supramolecular cage. This cage was characterized by IR and high-resolution electrospray ionization mass spectrometry. Its solid-state structure was confirmed by X-ray crystallography, showing a novel D4 cage system.

Three alkali-metal-indium compounds K34In(92.30)Li(12.70) (I), K14Na20In(91.82)Li(13.18) (II), and K14Na20In(96.30) (III) (all Rm) have been synthesized and characterized by structural and physical property measurements and electronic structure calculations. Novel mixed In/Li anionic icosahedra and fused icosahedra form in I and II. All three contain In28 as the first triply fused In icosahedra, which are further linked into (In28)In(In28) sandwich adducts in compounds I and II and (In28)In2(In28) in III. Stabilization of these electron-poorer phases through electronic tuning occurs via two different structural (redox) perturbations, either by substitution of certain indium atoms in the clusters by electron-poorer lithium atoms or by the introduction of defects and disorder in the fused cluster (III). The preferential occurrence of either substitutions or defect formation in the clusters is consistent with extended Huckel band calculation results for both the ideal pure indium phase and the Li-substituted equivalent. Model (ideal) and experimental EF values (based on stoichiometries) fall around a pseudogap in DOS. All three compounds are metallic according to both EHTB band calculations and measured resistivities. The cations (A = K, Na) in all the three structures generate A136 clathrate-IotaIotatype networks with remarkably specific and transferable cation dispositions around the two types of anionic cluster units.

The copolymerization of ethylene and norbornene by catalytic systems composed of i-Pr[(3-R−Cp)(Flu)]ZrCl2 (R = Me or Pri) and methylaluminoxane was investigated. Isotactic, alternating ethylene−norbornene (E−N) copolymers with percentages of pentads NENEN up to 21% and norbornene incorporation up to 40% were obtained. NEENE sequences were observed in copolymers synthesized with both metallocenes. The microstructural analysis by 13C NMR of such alternating isotactic copolymers was completely obtained at pentad level by a methodology that exploits all the peak areas of the spectra and accounts for the stoichoimetric requirements of the copolymer chain. Such a methodology has allowed us to reconsider some controversial assignments of ethylene CH2 signals. The present understanding of E−N copolymer NMR spectra at the pentad level has allowed us to test the statistical model best describing E−N copolymerization with C1 symmetric catalysts and to study the influence of ligand substitution of these catalysts on ...

Ethylene was copolymerized with the non-conjugated diene 5,7-dimethylocta-1,6-diene by metallocene catalysts, homogenous and supported on MCM-41 mesoporous material activated by methylaluminoxane at room temperature. The employed metallocenes were (BzCp)2ZrCl2 (1), (C18H37Cp)2ZrCl2 (2), (CH3)2Si(Ind)2ZrCl2 (3) and ϕ2C(Cp,Flu)ZrCl2 (4). Diene incorporation and thermal characteristic of the polymers were determined by 13C-NMR and DSC. For the homogeneous systems, only the unbridged metallocene (1) showed a decrease in the activity as the diene content was increased. The ability for diene incorporation in the polymer chain followed the catalyst order (1)

1,2-Dihydro-2-phenyl-1,2-azaborine (6a) has been prepared by a multistep synthesis from the readily available 2,2-dibutyl-2,5-dihydro-1-trimethylsilyl-1H-1,2-azastannole (7). Deprotonation of 6a affords 1-phenyl-1,2-azaboratabenzene 1a, which on reaction with [Cp*RuCl]4 gives the sandwich compound 5. 5 has been shown to function as a nucleophilic catalyst for the acylation of benzyl alcohol by phenylethylketene.

The reaction of nickel atoms with tBuCP affords a mixture of the isomeric complexes [Ni(η3-PC2But2)(η5-P3C2tBu2)] and [Ni(η4-P2C2But2)2]. The former complex has been structurally characterised in the solid sate as its [W(CO)5] adduct, which in solution undergoes fluxional behaviour. To cite this article: F.G.N. Cloke et al., C. R. Chimie 7 (2004).

Combination of trimeric perfluoro-ortho-phenylene mercury (1) with TTF and TCNQ in a 1:1 mixture of CH2Cl2 and CS2 followed by slow evaporation of the solvent leads to the formation of orange needles of [(1)2·TTF] (2) and light yellow needles of [(1)2·TCNQ] (3), respectively. The structure of both complexes has been determined by X-ray analysis. The solid-state structure of 2 consists of centrosymmetrical supramolecules of [(1)2·TTF], in which the TTF molecule is sandwiched by two molecules of 1. This supramolecule is held by multiple Hg···S secondary interactions ranging from 3.467(5) A to 3.533(5) A. The solid state of 3 also consists of centrosymmetrical molecules of [(1)2·TCNQ]. In this case, however, the TCNQ molecule is approximately perpendicular to the neighboring molecules of 1 with which it interacts by coordination of two nitrile groups. Examination of the atomic connectivity indicates the simultaneous coordination of the coordinated nitrile nitrogen atoms to the three mercury centers of 1. The resulting Hg···N distances range from 3.102(11) to 3.134(11) A. To cite this article: M.R. Haneline et al., C. R. Chimie 7 (2004).

The kinetics of ethene polymerization with metallocene/[Me 2 PhNH] + [B(C 6 F 5 ) 4 ] - /Al i Bu 3 (ternay system) and metallocene/methylaluminoxan (MAO) systems respectively has been investigated at 100-140°C and 7 MPa. Overall, eight different unbridged and ansa-metallocenes were tested. The effect of ligand structure, cocatalyst and catalyst concentration on the thermostability and the activation energy of deactivation were studied. Deactivation with respect to the catalyst concentration followed a first order reaction. The half-life as well as the activation energy of the ternary systems depended strongly on ligand structure while the ligand structure of MAO-activated metallocenes merely influenced the half-life. The half-life associated with MAO activation is approximately twice as high as that in ternay activation. Based on these results, conclusions about the activation reactions have been drawn.

Propylene homopolymerizations were conducted by using three kinds of metallocenes: Cp 2 ZrCl 2 , En(Ind) 2 ZrCl 2 and i Pr(Cp)(Flu)ZrCl 2 , all of which were activated with methylaluminoxane. Detailed NMR analyses of the chain ends in the resulting polymers were carried out to discuss the chain end structures of the polypropylenes and the mechanism of polymerization. The characteristic of each metallocene for the mechanism of polymerization was also described.

Ethylene/propylene and ethylene/1-hexene copolymerizations were studied with a series of ansa-metallocenes characterized by a gauche orientation of the indenyl ligands: [1-(1-indenyl)-2-(2-indenyl)ethane]zirconium dichloride, Et(2-Ind)(1-Ind)ZrCl2 (1)/MMAO, [2-(2-indenyl)-1-(2-phenyl-1-indenyl)ethane]zirconium dichloride, Et(2-Ind)(2-Ph-1-Ind)ZrCl2 (2)/MMAO, and [(2-indenyl)(2-phenyl-1-indenyl)dimethylsilyl]zirconium dichloride, Me2Si(2-Ind)(2-Ph-1-Ind)ZrCl2 (3)/MMAO to determine the significance of 2-phenyl ligand substitution as well as bridge type and placement on a series of gauche-1,2‘-bridged metallocenes. Comparison between the 1,1‘-bridged metallocene anti-ethylenebis(1-indenyl)zirconium dichloride and gauche-1 showed that the different bridge placements gave similar copolymerization reactivity in contrast to the different reactivities observed for anti-1,1‘-bridged dimethylsilylbis(2-phenylindenyl)zirconium dichloride and gauche-1,2‘-dimethylsilyl-bridged 3 respectively. Similar to trends observ...

The synthesis of sulfone-containing monomers with pendent cationic cyclopentadienyliron (CpFe + ) moieties has been accomplished via nucleophilic aromatic substitution of dichloroarene complexes with a number aliphatic dithiols. These complexes were further oxidized using m-CPBA to give the sulfone-based monomers. Polymerization of the sulfone-based monomers with O-containing nucleophiles produced the sulfone-based polymers. Direct nucleophilic aromatic substitution of dichloroarene complexes with dinucleophiles allowed for the formation of organoiron sulfide-based polymers. Oxidation of these polymers led to the formation of sulfone polymers with the pendent iron moieties. The organometallic monomers and polymers were found to be more soluble in polar solvents in comparison to their organic analogues.

Organometallic polymers containing metallacycles in the main chain were prepared by the reactions of diynes with low-valent organometallic complexes such as CpCo(PPh 3 ) 2 , CP 2 Ti(CH 2 =CHC 2 H 5 ), and ( i PrO) 2 Ti(CH 2 =CHCH 3 ). Their polymer reactions involving the conversion of the main chain structures gave rise to polymers containing functional groups in their main chain repeating units. Design and synthesis of organometallic polymers that potentially serve as novel functional materials are also described.

Recent studies on two types of n-conjugated metallacylce polymers are reviewed. Reaction of CpCo(PPh 3 ) 2 with conjugated diacetylenes afford poly(arylene cobaltacyclopentadienylene) and that of CpRuBr(cod) does poly(arylene ruthenacyclopentrienylene)s in ambient conditions. Regioselectivity of the former metallacycling reacion is not perfect (at most 80% of the 2,5-diaryl selectivity) but that of the latter is satisfactory (∼100% of the 2,5-diaryl selectivity) for the formation of n-conjugated structure. Electrochemical oxidation of the cobaltacyclopentadiene polymer and reduction of the ruthenacycle polymer occur facilely and quasi-reversibly by the contribution of metal d-orbitals. Physical properties in undoped (neutral) and doped (charged) sates show the behavior of electronic band structure derived from the organic n-conjugated main chain strongly coupled with the metal d-orbitals. This affords, for example, photoconductivity in the neutral form of the cobaltacylopentadiene polymer and ferromagnetic interaction in the reduced form of the ruthenacyclopentatriene polymer.

The stereochemistry of propylene insertion/propagation reactions with a variety of C s and C 1 symmetric bridged cyclopentadienyl-fluorenyl ligand containing metallocene catalysts are investigated. It is shown that active species with a local C s symmetric and enantiotopic coordination positions, in the general contest of the chain migratory insertion, behave syndioselective. However, the bilateral symmetry rule, central dogma of syndioselectivity, is not a catholic prerequisite and may be ignored by the C s systems whenever symmetric excess in steric bulk is present. An asymmetric excess of steric forces, on the other hand, will perturb the migratoy insertion process completely and induce a full tactic inversion in resulting C 1 symmetric catalysts. The findings also reveal that C 2 symmetry and helicity of homotopic catalysts, conditions thought to be essential for high isoselectivity, can be lifted in light of recent developments in high performance centrally chiral, C 1 symmetric enantiotopic catalysts.

Stereoblock, isotactic-hemiisotactic poly(propylene) is produced with C 1 -symmetric Me 2 C(n 5 -3-(2-adamantyl)-C 5 H 3 )(n 5 -C 9 H 4 S 2 )ZrCl 2 (1). Ethylene/propyle copolymerization data with the C s -symmetric Me 2 C(n 5 -C 5 H 4 )(n 5 -C 9 H 4 S 2 )ZrCl 2 (2) metallocene reveals that it is highly propylene-specific and that it produces more random ethylene/propylene copolymers than its fluorenyl analog.

The possibility of coupling lacunary polyoxometalates through a cationic center present in the vacancy by negatively charged organic ligands is demonstrated for the first time by single-crystal X-ray diffraction. The structure of the dimeric K12[{Yb(α-SiW11O39)(H2O)}2(μ-CH3COO)2]·38H2O complex, where two acetato ligands connect the ytterbium centers in a (η2, μ-1,1) fashion, is reported. Using gadolinium instead of ytterbium, both the isostructural dimeric compound K12[{Gd(α-SiW11O39)(H2O)}2(μ-CH3COO)2]·38H2O and the mononuclear sandwich complex [Gd(SiW11O39)2]13− can be selectively isolated, depending on the synthetic conditions. The magnetic properties of the dimeric gadolinium complex are presented. The influence of the nature of the rare-earth metal on the final compound is further highlighted by the fact that when praseodymium is used as the rare-earth element, only the sandwich compound can be obtained. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

A molecular approach to information storage employs redox-active molecules tethered to an electroactive surface. Attachment of the molecules to electroactive surfaces requires control over the nature of the tether (linker and surface attachment group). We have synthesized a collection of redox-active molecules bearing different linkers and surface anchor groups in free or protected form (hydroxy, mercapto, S-acetylthio, and Se-acetylseleno) for attachment to surfaces such as silicon, germanium, and gold. The molecules exhibit a number of cationic oxidation states, including one (ferrocene), two [zinc(II)porphyrin], three [cobalt(II)porphyrin], or four (lanthanide triple-decker sandwich compound). Electrochemical studies of monolayers of a variety of the redox-active molecules attached to Si(100) electrodes indicate that molecules exhibit a regular mode of attachment (via a Si-X bond, X = O, S, or Se), relatively homogeneous surface organization, and robust reversible electrochemical behavior. The acetyl protecting group undergoes cleavage during the surface deposition process, enabling attachment to silicon via thio or seleno groups without handling free thiols or selenols.

To examine the effects of molecular structure on charge storage in self-assembled monolayers (SAMs), a family of redox-active molecules has been prepared wherein each molecule bears a tether composed of a tripodal linker with three protected thiol groups for surface attachment. The redox-active molecules include ferrocene, zinc porphyrin, ferrocene-zinc porphyrin, magnesium phthalocyanine, and triple-decker lanthanide sandwich coordination compounds. The tripodal tether is based on a tris[4-(S-acetylthiomethyl)phenyl]-derivatized methane. Each redox-active unit is linked to the methane vertex by a 4,4'-diphenylethyne unit. The electrochemical characteristics of each compound were examined in solution and in SAMs on Au. Redox-kinetic measurements were also performed on the SAMs (with the exception of the magnesium phthalocyanine) to probe (1) the rate of electron transfer in the presence of an applied potential and (2) the rate of charge dissipation after the applied potential is disconnected. The electrochemical studies of the SAMs indicate that the tripodal tether provides a more robust anchor to the Au surface than does a tether with a single site of attachment. However, the electron-transfer and charge-dissipation characteristics of the two tethers are generally similar. These results suggest that the tripodal tether offers superior stability characteristics without sacrificing electrochemical performance.

Redox properties of mono- and binuclear π-complexes of Cr with fluoranthene with the composition of (η6-C16H10)Cr(η6-C6H6), (η6-C16H10)Cr(CO)3 and (μ-η6,η6-C16H10)Cr2(η6-C6H6)(CO)3 are studied by cyclic voltammetry. Relations between half-wave potentials of redox processes and coordination sites of fragments Cr(η6-C6H6)- and Cr(CO)3 with the ligand and their nature are found.

ZnO thin films were deposited on silicon substrate by rf magnetron sputtering from metallic zinc target. The electrical properties of ZnO are currently being studied. In this work, measurements of the ac conductivity properties of ZnO sandwich structures with silver and platinum electrodes are reported. The frequency dependence of both the ac conductivity and dielectric constant of thin films of ZnO have been investigated in the frequency range 5 kHz–13 MHz. It is shown that the total ac conductivity σ ( ω ), obeys the equation σ ( ω )= Aω S where s is an index which increases with frequency and decreases with temperature. It appears that for ZnO films, the conduction mechanism is thermally activated and both the overlap large polaron tunnelling and the correlated barrier-hopping of charge carrier over localized states fit the experimental data. The dielectric constant, e r , lies in the range 8–9 at room temperature and is independent of the frequency in the dielectric thin films.

A series of 7 cerium double-decker complexes with various tetrapyrrole ligands including porphyrinates, phthalocyaninates, and 2,3-naphthalocyaninates have been prepared by previously described methodologies and characterized with elemental analysis and a range of spectroscopic methods. The molecular structures of two heteroleptic \[(na)phthalocyaninato](porphyrinato) complexes have also been determined by X-ray diffraction analysis which exhibit a slightly distorted square antiprismatic geometry with two domed ligands. Having a range of tetrapyrrole ligands with very different electronic properties, these compounds have been systematically investigated for the effects of ligands on the valence of the cerium center. On the basis of the spectroscopic (UV−vis, near-IR, IR, and Raman), electrochemical, and structural data of these compounds and compared with those of the other rare earth(III) counterparts reported earlier, it has been found that the cerium center adopts an intermediate valence in these complexes. It assumes a virtually trivalent state in cerium bis(tetra-tert-butylnaphthalocyaninate) as a result of the two electron rich naphthalocyaninato ligands, which facilitate the delocalization of electron from the ligands to the metal center. For the rest of the cerium double-deckers, the cerium center is predominantly tetravalent. The valences (3.59−3.68) have been quantified according to their LIII-edge X-ray absorption near-edge structure (XANES) profiles.

Ground-state electronic absorption and fluorescence spectra of sandwich-type bis(phthalocyaninato) europium(III) compound Eu(Pc) 2 are described. The emission spectra changed dramatically under different excitation wavelength. An energy level diagram is proposed to interpret the electron and energy transition and photophysical process of the strongly coupled rare earth sandwich compound.

Kinetic studies on the syndiospecific polymerizations of propylene with i Pr(Cp)(Flu)ZrCl 2 /methylaluminoxane (MAO) were performed at 20, 40 and 70 °C and at 5 atm with various Al/Zr molar ratios. The average polymerization activity for 60 min decreased, and the time to reach a maximum activity ( t max ) decreased as Al/Zr molar ratio increased. However, at Al/Zr molar ratio of 10,000, catalytic activity decreased rapidly and became the smallest among any other Al/Zr molar ratios after 20 min of polymerization. At higher Al/Zr molar ratio, methylation and cationization progress rapidly, but its polymerization rate decayed quickly due to strong interaction between MAO and metallocene, resulting in less active species. Regardless of change in polymerization temperature, t max was maintained around 15 min. Stereoregularity was strongly dependent on the polymerization temperature, and active site isomerization was dominant source for stereoirregularity, and it was strongly influenced by polymerization temperature.

The synthesis of linear and star-shaped oligomers containing cationic and neutral organoiron groups in their structures was achieved by reaction of cationic arene complexes of cyclopentadienyliron containing terminal hydroxyl groups with 1,1'-ferrocenedicarbonyl chloride or ferrocene carboxylic acid. The use of chloroarene complexes allowed for the formation of triiron complexes that were subsequently polymerized via nucleophilic aromatic substitution with various oxygen-and suite-based dinucleophiles. The corresponding polyethers and thioethers were isolated in good yields and these materials exhibited excellent solubilities in polar organic solvents. Cyclic voltammetric investigations revealed that the cationic iron centers pendent to the polymer backbones underwent reversible reduction steps, while the neutral iron centers within the polymer backbones underwent reversible oxidation steps. Photolysis of these polymers resulted in the removal of the cationic cyclopentadienyliron moieties pendent to the polymer backbones. Thermogravimetric analysis (TGA) revealed that the cationic iron complexes were cleaved from the polymers at approximately 210 °C. Differentials scanning calorimetry (DSC) revealed that the glass transition temperatures of the cationic polymers occurred at higher temperatures than their neutral analogs.

The reaction of [Ru(η3:η3-C10H16)Cl2]2 (1) with the Cp-linked phosphine ligands Ln (C5H5CH2CHRPR′2; R=H, R′=Ph, n=1; R=Ph, R′=Ph, n=2), in a 5:1 mixture of acetonitrile–ethanol and in the presence of Li2CO3 and KPF6 affords the cationic half-sandwich ruthenium(II) complexes [{η5-C5H4CH2CHRPR′2-κP}Ru(CH3CN)2]·[PF6] (4) and (5). Both complexes have been characterized in the solid state by an X-ray structure analysis. In contrast, the reaction between 1 and L3 (R=Ph, R′=o-xylyl) affords the cationic sandwich compound [{η5:η6-C5H4CH2CHPhPR′2}Ru]·[PF6] (7), in which one arene substituent of the phosphine is η6-coordinated to the metal and the phosphorus remains pendant. Treatment of 5 with tertiary phosphines (PR″3, R″=i-Pr, Ph, Cy) affords a mixture of the diastereomers [L2Ru(CH3CN)PR″3]+. The diastereoselectivity observed depends on the steric bulkiness of the phosphines and on the reaction conditions.

The catalyst [Me 2 C(Flu)(3-MeCp)ZrCl 2 ] (1) activated by MAO was used for the copolymerization of ethylene and 1,7-octadiene (OD) to form copolymers with pendent double bonds. The properties of the copolymers were strongly dependent on the purity of the comonomer. Formation of ethylene-rich sequences and increased levels of cross-linking were observed with highly purified 1,7-octadiene. Catalysts 1 and [Me 2 Si(Flu) 2 ZrCl 2 ] (2), activated by MAO, were used for the copolymerization of ethylene and 7-methyl-1,6-octadiene (MOD). In both cases, alternating copolymers were formed with unreacted pendent double bonds. The triad distributions were analyzed by Markovian first- and second-order statistics. Copolymers produced by catalyst 2 were significantly more alternating than copolymers produced by catalyst 1 despite the fact that catalyst 2 is highly symmetrical. Epoxidation of pendent double bonds was examined.

Because of the great economic interest in propylene-based polymers and the possibility of designing materials with desired properties with metallocene catalyst mixtures, we investigated the characteristics ofpolypropylenes produced by mixtures of SiMe 2 Ind 2 ZrCl 2 : dimethylsilane-bis(indenyl) zirconocene (1) and Et(Flu)(Cp)ZrCl 2 : ethylidene (fluorenyl cyclopentadienyl) zirconocene (2) in different proportions. The polymers were fractionated with solvents, and the fractions were characterized. We observed that the polymers produced by the different mixed systems showed lower weight-average molecular weights and only slightly broader molecular weight distributions than polypropylenes synthesized by the individual catalysts. We concluded that catalyst 1 acted independently of catalyst 2, producing polymers with the same isotacticity.

The electrochemical behaviour of the copper-substituted Keggin-type and sandwich-type polyoxotungstate anions of the compounds α-[(C4H9)4N]4H[PW11CuIIO39] and α-B-[(C4H9)4N]7H3[CuII4(H2O)2(PW9O34)2] was studied by cyclic voltammetry in acetonitrile. In both cases two copper 1-electron reduction waves were detected in the cathodic scan. The first one was due to the reduction of one CuII to CuI in the polyoxoanion and the second one to the consecutive reduction of the preformed CuI to Cu0, with the consequent deposition/adsorption of the ejected metal atom at the glassy carbon electrode surface. In the anodic scan, Cu0 was re-oxidised with regeneration of the initial copper(II) complexes, via a CuI intermediate. The observed two-step reduction of copper(II) to copper(0) and the formation of intermediate species containing copper(I) is here reported for the first time for copper substituted polyoxotungstates. The co-ordination of the acetonitrile molecules to the copper ions must play a role in the formation of the copper(I) species, which are not detected in aqueous solution. Keywords: Polyoxometalates, Keggin, Sandwich complexes, Copper, Electrochemistry, Cyclic voltammetry

The homo- and copolymerization behaviors of two C1-symmetric metallocenes Me2Si(Ind)(9-Flu)ZrCl2 (2) and Me2Si(1-(4,7-Me2Ind))(9-Flu)ZrCl2 (3) in the presence of methylaluminoxane (MAO) are compare...

Metallocenes are highly active catalysts for the production of precisely designed polyolefins and engineering plastics. Especially zirconocene/methylalumoxane (MAO) catalysts and half-sandwich titanium complexes have opened a frontier in the area of new polymer synthesis and processing. The materials obtained show different microstructures, tacticities and properties compared with conventional polymers. Alternating ethene/propene polymers show lower glass transition temperatures than random copolymers. Constrained geometry catalysts are useful for the synthesis of norbornene/ethene copolymers.

m- or p-phenylenediamine and m- or p-chlorophenyl-substituted azacrown ether derivatives were synthesized through sequential nucleophilic substitution of [(eta(5)-cyclopentadienyl)(eta(6)-(m- or p-dichlorobenzene))]iron hexafluorophosphate by azacrown ethers and cyclohexaamines. Monoarylation is the main reaction for diazacrown ethers. The overall yield from the starting complex is 50-96% for multiple steps.

Sandwich-type polyoxometalates (POMs), namely [WZnM2(ZnW9O34)2]q- [M = Mn(II), Ru(III), Fe(III), Pd(II), Pt(II), Zn(II); q = 10-12], are shown to catalyze selectively the epoxidation of chiral allylic alcohols with 30% hydrogen peroxide under mild conditions (ca. 20 degrees C) in an aqueous/organic biphasic system. The transition metals M in the central ring of polyoxometalate do not affect the reactivity, chemoselectivity, or stereoselectivity of the allylic alcohol epoxidation by hydrogen peroxide. Similar selectivities, albeit in significantly lower product yields, are observed for the lacunary Keggin POM [PW11O39]7-, in which a peroxotungstate complex has been shown to be the active oxidizing species. All these features support a tungsten peroxo complex rather than a high-valent transition-metal oxo species operates as the key intermediate in the sandwich-type POM-catalyzed epoxidations. On capping of the hydroxy functionality through acetylation or methylation, no reactivity of these hydroxy-protected substrates [1a(Ac) and 1a(Me)] is observed by these POMs. A template is proposed to account for the marked enhancement of reactivity and selectivity, in which the allylic alcohol is ligated through metal-alcoholate bonding, and the H2O2 oxygen source is activated in the form of a peroxotungsten complex. 1,3-Allylic strain promotes a high preference for the threo diastereomer and 1,2-allylic strain a high preference for the erythro diastereomer, whereas tungsten-alcoholate bonding furnishes high regioselectivity for the epoxidation of the allylic double bond. The estimated dihedral angle alpha of 50-70degrees for the metal-alcoholate-bonded template of the POM/H2O2 system provides the best compromise between 1,2A and 1,3A strain during the oxygen transfer. In contrast to acyclic allylic alcohols 1, the M-POM-catalyzed oxidation of the cyclic allylic alcohols 4 by H2O2 gives significant amounts of enone.

The previously reported product from the solid-state reaction of quinolin-8-ol (oxine) with salicylic acid has been characterized using single crystal X-ray diffraction methods and confirmed as the discrete dimeric proton-transfer sandwich compound [(C9H8NO+)2(C7H5O3–)2] (1). As with similar compounds of carboxylic acids and oxine, protonation of the quinoline nitrogen occurs. However, in the case of 1, the two salicylate anions provide unusual duplex carboxylato-(O,O′) hydrogen-bonding bridges [(oxine)-N+H⋯O,O′(salicylate)⋯H′–O′-(oxine)′] which stitch together the pairs of π–π-associated oxine cations. This structure determination may provide a possible explanation of the mechanism involved in the facile solid-state reaction of oxine with salicylic acid.

Both amido-(cyclopentadienyl)boranes and bis(cyclopentadienyl)boranes of the types R 2 NB(C x H y ) (NR') and R 2 NB(C x H y ) 2 (R = alkyl, trimethylsilyl; R' = Ph; C x H y = C 5 H 5 (cyclopentadienyl), C 9 H 7 (indenyl), C 13 H 9 (fluorenyl)) were recently shown to form corresponding boron-bridged Group 4 metallocenes that exhibit high activities in Ziegler-Natta-type catalysed olefin polymerization. Here, the same boranes were utilized in the formation of metallocenes of ytterbium and zirconium, where the ligands selectively bind in a non-chelate fashion. The resulting complexes [Yb{η 5 -(C 5 H 4 )B(N i Pr 2 )NH t Bu} 2 {N(SiMe 3 ) 2 }] (2) and [Zr{η 5 -(C 9 H 6 )B(N(SiMe 3 ) 2 )(C 9 H 7 )}Cl 2 ] (4) allow studies on these ligands in a metal-bonded, though unstrained, environment. Furthermore, these complexes might find use as precursors in the formation of organometallic polymers, since they exhibit a readily available moiety for the coordination of further transition metal centres. Both complexes were fully characterized by multinuclear magnetic resonance spectroscopy and X-ray structure determination.

The interactions between the non-bonded atoms on adjacent units were assumed to be one of the major factors that hinder the exploration and advancement of macropolyhedral borane chemistry. In sandwich complexes involving boron as the bridging atom, the interaction between non-bonded atoms tends to be antibonding, but a closer analysis of various condensed systems shows that this cannot be generalized. The overlap populations (OPs) calculated for structures optimized at the B3LYP/6-31g* level [B 21 H 18 1- (5), B 20 H 16 (6), [Al(C 2 B 4 H 6 ) 2 ] 1- (7), B 12 H 10 2- (8), B 10 H 8 2- (9 and 14), B 11 H 13 (10), B 10 H 14 (11), C 2 B 8 H 12 (13) and B 20 H 18 2- (15)] indicate bonding interactions between the caps, except for 7 and 13. This is substantiated by a detailed extended Huckel-based molecular orbital (MO) study using B 10 H 14 as a model system to represent macropolyhedral boranes with higher fusions. An isolobal equivalent structure, [C 8 H 6 (Ru(CO) 2 Me) 2 ] (17), studied at the B3LYP/LANL2DZ level has weak RuRu interactions. An analysis of the nature of the MOs in B 10 H 14 (11) shows that there is no direct head on overlap of the cap orbitals that are antibonding; this is in contradiction to sandwiched molecules (7), where there are two occupied MOs with antibonding interactions. The m + n + o electron pair count (m is the number of cages involved in condensation, n is the number of vertices and o is the number of single vertex condensations) of sandwich complexes requires the filling of these two MOs. The negative OP between the carbon atoms in 13 is attributed to the greater electronegativity of carbon and is substantiated by a fragment MO analysis.

Copolymerization of ethylene or propylene and norbornene (NB) was carried out with stereospecific zirconocene catalysts rac-ethylenebis(indenyl)zirconium dichloride, rac-dimethylsilylenebis(indenyl)zirconium dichloride (2), rac-dimethylsilylenebis(2-methylindenyl)zirconium dichloride, and diphenylmethylene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride combined with cocatalysts at 40 °C. Temperature-rising elution fractionation of the copolymers was carried out with cross-fractionation chromatography with o-dichlorobenzene as a solvent, and a broad distribution of the copolymer composition was detected. The fraction eluted at lower temperature contained higher NB. The effect of the polymerization time was examined in the ethylene–NB copolymerization with catalyst 2, and the higher-temperature elution fraction increased with increasing polymerization time. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 441–448, 2003

The 13 C NMR spectra of ethene/norbornene copolymers in which there are no norbornene microblocks are much simpler than those of copolymers in which norbornene microblocks are present, making it possible to completely assign all the 13 C resonances to the corresponding pentads in the copolymer chain. However, there is disagreement in the literature over several assignments of the ethene 13 C NMR signals. In this paper these discrepancies are summarized and discussed. This contribution also reports ethene/norbornene copolymerizations carried out at various temperatures using the homogeneous catalyst system Pr i [(3-Pr i -Cp)Flu]ZrCl 2. The 13 C NMR spectra of the copolymers were analyzed in the light of the discussion above and the triad distributions were used to determine the copolymerization parameters by Markov first- and second-order statistical models. On the basis of these results, the mechanism generating such an alternating microstructure in these copolymers is discussed and compared with the mechanism previously proposed in the literature.

Ethylene, propylene and α-olefins were homo- and copolymerized in the presence of a series of homogeneous catalytic systems consisting of methylaluminoxane (MAO) and group IV metallocenes such as Et(Ind) 2 ZrCl 2 (I), Me 2 Si(Ind) 2 ZrCl 2 (II), Et(2-Me-Ind) 2 ZrCl 2 (III), Ph 2 C(Flu)(Cp)ZrCl 2 (IV). It was found that the catalytic activity, the incorporation of comonomer in the case of copolymers, and the microstructure of the polymers depend on the catalyst's structure. For heterogeneous catalysts, several supports based on metal oxide compounds have been investigated, with special emphasis in those obtained by the sol-gel preparation technique. The homo- and copolymerization of the monomers in the homogeneous systems studied where also investigated using the same catalyst system, but in a heterogeneous medium. Comparative results from the homogeneous and heterogeneous systems are presented and discussed.

A general method for rapid construction of metallocene-based hosts is described. Treatment of polyether bridged bis(diphenylacetylenes) with a source of cyclopentadienyl cobalt at high temperature leads, via macrocyclization and capture of the intermediate cyclobutadiene, to macrocyclic systems tethered to an integral metallocene platform. Equal yields of the two possible structural isomers, the products of parallel or antiparallel cycloaddition of the precursor, are obtained. A combination of X-ray crystallography and NMR is employed to assign structures to the individual isomers and to assess the strength of lithium ion binding by the individual macrocycles.