Cyclopentadienyl Ring (cyclopentadienyl + ring)

Distribution by Scientific Domains


Selected Abstracts


Preparation of Chiral Homoannularly Bridged N,P-Ferrocenyl Ligands by Intramolecular Coupling of 1,5-Dilithioferrocenes and Their Application in Asymmetric Allylic Substitution Reactions,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 33 2007
Shin-ichi Fukuzawa
Abstract Homoannularly bridged ferrocene 6b was prepared by intramolecular coupling of 1,5-dilithioferrocene 5b mediated by Fe(acac)3. Dilithioferrocene 5b was prepared by lithium,halogen exchange of the corresponding diiodide, which was prepared by 1,5-dilithiation of the o -TMS-blocked ferrocene and followed by trapping with iodine and removal of the TMS group. Alternatively, 5b could be readily prepared by the reaction of o -bromophenylferrocene 8 with nBuLi (>2 equiv.). The benzene ring of 6b underwent ortho lithiation with tBuLi, and the resulting lithiated species was trapped with Ph2PCl to produce corresponding aminophosphane 7d. Aminophosphane 13, which has the phosphanyl group on the cyclopentadienyl ring, was prepared by intramolecular coupling of 1,5-dilithiated PhPPFA 11 mediated by Fe(acac)3. New N,P ligands 7d and 13 were used in the palladium-catalyzed allylic alkylation and amination of 1,3-diphenyl-2-propenyl acetate (14), and ligand 7d was found to give good yields with enantioselectivities as high as 96,% ee. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]


Syndiospecific polymerization of styrene with BzCpTiCl3 and methylaluminoxane as cocatalysts

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2001
Constantin Schwecke
Abstract Benzyl cyclopentadienyl titanium trichloride (BzCpTiCl3) was synthesized from benzyl bromide, cyclopentadienyl lithium, and titanium tetrachloride and used in combination with methylaluminoxane (MAO) for the syndiospecific polymerization of styrene. Kinetic measurements of the polymerization were carried out at different temperatures. The polymerization with BzCpTiCl3/MAO differs from the polymerization with cyclopentadienyl titanium trichloride in its behavior toward the Al/Ti ratio. In addition, high activities are observed at high Al/Ti ratios. By analyzing the polymerization runs and the physical properties of the polymers with differential scanning calorimetry, 13C NMR spectroscopy, wide-angle X-ray scattering measurements, and gel permeation chromatography, we found that the phenyl ring coordinates to the titanium atom during polymerization. Other known substitutions of the cyclopentadienyl ring (V. Scholz, Dissertation, University of Hamburg, 1998) in principle influence the polymerization activity. The physical properties of the polymers produced by the catalysts already known are nearly identical. BzCpTiCl3 is the first catalyst that leads to polystyrene obviously different from the polystyrene produced by other highly active catalysts. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2805,2812, 2001 [source]


Video Microscopy for the Investigation of Gas Phase Copolymerization

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2005
Daniela Ferrari
Abstract Summary: Video microscopy as a tool for investigating olefin gas phase copolymerization is presented for the first time in this paper. The central theme of this work is the study of the comonomer effect shown by an unbridged metallocene catalyst supported on silica. By using video microscopy, it is possible to observe the increase in catalytic activity in terms of particle growth as well as monomer consumption. The observation that a more pronounced induction period in the particle growth profile is shown with increasing propylene concentration led us to investigate the copolymers obtained at different polymerization times using 13C NMR analysis and single particle energy dispersive X-ray (EDX mapping). This allowed us to adapt the "polymer growth and particle expansion model" to the copolymerization. Besides physical causes for the comonomer effect, we wanted to determine whether the catalyst structure plays an important role in the comonomer effect. To this end we investigated two metallocenes bearing the same long bridging unit but differing in the ligand bound to the zirconium center. One metallocene bears a cyclopentadienyl ring, while the other bears an indenyl group. From a close analysis of the 13C NMR, it is clear that both catalysts insert ethylene more easily then propylene, probably due to the long bridging unit that results in a narrower aperture angle of the ligand. In addition to this, the indenyl ligand does not allow the formation of propylene blocks even at high propylene concentration. Snapshot of the polymer particles taken after 165 min of ethylene-1-butene copolymerization with catalyst 1. [source]


Muon Implantation of Metallocenes: Ferrocene

CHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2007
Upali
Abstract Muon Spin Relaxation and Avoided Level Crossing (ALC) measurements of ferrocene are reported. The main features observed are five high field resonances in the ALC spectrum at about 3.26, 2.44, 2.04, 1.19 and 1.17,T, for the low-temperature phase at 18,K. The high-temperature phase at 295,K shows that only the last feature shifted down to about 0.49,T and a muon spin relaxation peak at about 0.106,T which approaches zero field when reaching the phase transition temperature of 164,K. A model involving three muoniated radicals, two with muonium addition to the cyclopentadienyl ring and the other to the metal atom, is postulated to rationalise these observations. A theoretical treatment involving spin-orbit coupling is found to be required to understand the Fe,Mu adduct, where an interesting interplay between the ferrocene ring dynamics and the spin-orbit coupling of the unpaired electron is shown to be important. The limiting temperature above which the full effect of spin-orbit interaction is observable in the ,SR spectra of ferrocene was estimated to be 584,K. Correlation time for the ring rotation dynamics of the Fe,Mu radical at this temperature is 3.2,ps. Estimated electron g values and the changes in zero-field splittings for this temperature range are also reported. [source]


Photooxidation and Photoconductivity of Polyferrocenylsilane Thin Films

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 7 2003
Paul W. Cyr
Abstract Irradiation of thin films of poly(ferrocenylmethylphenylsilane) ([Fe(,5 -C5H4)2SiMePh]n) cast from chloroform solution with UV light leads to photooxidation of ferrocene centers in the polymer main chain. The extent of the polymer oxidation can be controlled in the range ca. 0,5% by the duration of the irradiation exposure and by the concentration of chloroform. The photooxidized polyferrocenylsilane material is conductive, with an increased conductivity of greater than three orders of magnitude relative to the unoxidized material. In addition, the photooxidized polymers have been found to be photoconductive. The photooxidation process can be reversed by means of chemical reduction using hydrazine or decamethylferrocene, leading to the regeneration of the neutral polymers. However, substantial molecular weight decline was detected during the photooxidation/reduction process, presumably as a result of chain cleavage reactions induced by the anionic or radical chlorinated photoproducts. Methylation of the cyclopentadienyl rings of the ferrocene moiety in the polymer was found to lead to materials which are significantly more stable. Time trace of the current at constant applied voltage of 100 V for a PFS film upon illumination. The ON and OFF states were created by using a mechanical shutter. [source]


Photoreactivity and Photopolymerization of Silicon-Bridged [1]Ferrocenophanes in the Presence of Terpyridine Initiators: Unprecedented Cleavage of Both Iron,Cyclopentadienyl Bonds in the Presence of Chlorosilanes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2007
Yan Chan
Abstract The photopolymerisation of sila[1]ferrocenophane [Fe(,-C5H4)2SiMe2] (3) with 4,4,,4,,-tri- tert -butyl-2,2,:6,,2,,-terpyridine (tBu3terpy) as initiator has been explored. High-molecular-weight polyferrocenylsilane (PFS) [{Fe(,-C5H4)2SiMe2}n] (5) was formed in high yield when a stoichiometric amount of tBu3terpy was used at 5,°C. Photopolymerisation of ferrocenophane 3 at higher temperatures gave PFS 5 in lower yield and with a reduced molecular weight as a result of a slower propagation rate. Remarkably, when Me3SiCl was added as a capping agent before photopolymerisation, subsequent photolysis of the reaction mixture resulted in the unprecedented cleavage of both iron,Cp bonds in ferrocenophane 3: iron(II) complex [Fe(tBu3terpy)2Cl2] (7Cl) was formed and the silane fragment (C5H4SiMe3)2SiMe2 (8) was released. The iron,Cp bond cleavage reaction also proceeded in ambient light, although longer reaction times were required. In addition, the unexpected cleavage chemistry in the presence of Me3SiCl was found to be applicable to other photoactive ferrocenes such as benzoylferrocene. For benzoylferrocene and ferrocenophane 3, the presence of metal-to-ligand charge transfer (MLCT) character in their low-energy transitions in the visible region probably facilitates photolytic iron,Cp bond cleavage, but this reactivity is suppressed when the strength of the iron,Cp bond is increased by the presence of electron-donating substituents on the cyclopentadienyl rings. [source]


Synthesis, characterization and catalytic applications of tridentate Schiff base derivatives of bis and mono(cyclopentadienyl)-lanthanocene complexes

CHINESE JOURNAL OF CHEMISTRY, Issue 5 2000
Muhammad Yousaf
Abstract Seven kinds of lanthanocene complexes were prepared by the reaction of tridentate Schiff base | N -(2-methoxyphenyl)salicylideneamine with tris(cyclopentadienyl) lanthanide tetrahydrofuranate or bis (cyclopentadienyl) lanthanide chloride tetrahydrofuranate in THF. All the complexes were characterized by MS, EA and IR respectively. The structure of |Cp2LnC14U13NO2) Ln = Sm, Dy, Y, Er| (1,4) was further confirmed by X-ray determination of Cp2Sm(C14H13NO2) (1) which indicates that the complex is monomeric in which central metal is coordinatively saturated by two cyclopentadienyl rings, two oxygens and one nitrogen of the ligand. The isomerization of 1,5-hexadiene explains that complexes (1,4) isomerize this monomer into a mixture of 1,4-hexadiene, 2,4-hexadiene, 1,3-hexadiene, methylenecyclopentane and methyl,cyclopentene. Similarity complexes |CpLn(a) C14 H13NO2) (THF) (Ln=Sm, Dy, Y, Er)| (5,7) polymerize methyl-methacrylate (MMA) to give polyMMA (PMMA) in 51.8% yield and high molecular weight (274 × 103), which shows narrow molecular weight distributions and partially syndiotactic. [source]