Polymerization and copolymerization of ethene initiated with disiloxane-bridged biscyclopentadienylzirconium complexes and methylaluminoxane

The disiloxane-bridged zirconocene complexes, tetramethyldisiloxanediylbis (cyclopentadienyl)zirconium dichloride and tetramethyldisiloxanediylbis(cyclopentadienyl) dimethylzirconium initiate the homopolymerization of ethene as well as the copolymerization of ethene and α-olefin with a modified methylaluminoxane as cocatalyst. The catalyst systems give resonable activity but the molecular weight of polyethene decreases drastically with increasing polymerization temperature.     

Syndiospecific polymerizations of styrene with siloxane-bridged dinuclear titanocenes and mao catalyst systems

The syndiotactic polymerizations of styrene are carried out with dinuclear titanocenes such as tetramethyldisiloxanediylbis(cyclopentadienyltitanium trichloride), Cl₃Ti-CpSi(CH₃)₂-O-Si(CH₃)₂Cp-TiCl₃ (1), hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride), Cl₃Ti-CpSi(CH₃)₂-O-Si-(CH₃)2-0-Si(CH₃)₂Cp-TiCl₃ (₂) and hexamethyl-trisiloxanediylbis(dicyclopentadienyltitanium dichloride), Cl₂CpTi-CpSi(CH₃)₂-O-Si-(CH₃)₂-O-Si(CH₃)₂Cp-TiCpCl₂ ( 3 ) in the presence of modified methylaluminoxane (MMAO). Although the catalyst activity of dinuclear titanocenes is lower than that of the corresponding mononuclear titanocenes CpTiCl₃ and Cp₂TiCl₂, the former produce polystyrene of higher weight-average molecular weight and higher syndiotactic index than the latter. Among the dinuclear titanocenes examined, 2 has the largest catalyst activity. In addition, the copolymerizations of styrene and ethylene are carried out with 2 .     

Syntheses of mono- and dinuclear diiodoboryl complexes of platinum

Treatment of [Pt(PCy(3))(2)] (Cy = cyclohexyl) with BI(3) afforded trans-[(Cy(3)P)(2)Pt(I)(BI(2))] by the oxidative addition of a B-I bond. The title compound represents the first diiodoboryl complex and was fully characterized by NMR spectroscopy and X-ray diffraction analysis. The latter revealed a very short Pt-B distance, thus indicating a pronounced pi contribution to this bond. By the addition of another 1 equiv of BI(3) to trans-[(Cy(3)P)(2)Pt(I)(BI(2))], a new Pt species [(Cy(3)P)(I(2)B)Pt(mu-I)](2) was formed with concomitant buildup of the phosphine borane adduct [Cy(3)P-BI(3)]. The former is obviously obtained by abstraction of PCy(3) from trans-[(Cy(3)P)(2)Pt(I)(BI(2))] and the subsequent dimerization of two remaining fragments. Interestingly, the dimerization is reversible, and the dinuclear compound can be converted to trans-[(Cy(3)P)(2)Pt(I)(BI(2))] upon the addition of PCy(3).     

Polymerization of olefins with a novel dinuclear ansa-zirconocene catalyst having a biphenyl bridge

Both the rac- and meso-dinuclear ansa-zirconocene catalysts (μ-C₁₂H₈{[SiPh(Ind)₂]ZrCl₂}₂) were prepared by a coupling reaction between 2 equiv of diindenylphenylchlorosilane (rac- and meso-isomers) and 1 equiv of p-dilithiobiphenyl in diethyl ether at −80°C, followed by a successive reaction with ZrCl₄ · 2THF in THF at −78°C. Polymerizations of ethene and propene were conducted in a 1 dm³ high-pressure glass reactor equipped with a mechanical stirrer at 60, 80, 100, 120, and 150°C using methylalumoxane (MAO) as cocatalyst and toluene or decahydronaphthalene as the solvent. Copolymerization of ethene and 1-octene was also checked in brief. For ethene polymerization, the meso-catalyst was found to be more active, which displayed an extremely high activity to give linear polyethene with a high molecular weight and a narrow molar mass distribution (MMD). The apparent activity increased monotonously with rising polymerization temperature from 60°C up to 150°C, indicating that the active species are stable even at a high temperature. On the other hand, both the rac- and meso-catalysts showed very poor activities for propene polymerization. However, copolymerization of ethene and 1-octene proceeded at a high speed. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2269–2274, 1998     

Formal DNA hydrolysis by mono- and dinuclear iron complexes

The complexes CpFe(CO)(2)Ph and [CpFe(CO)(2)](2) cleave DNA in the presence of H2O2 or organic peroxides to give products resulting from the formal hydrolysis of the phosphodiester groups.     

Polymerization of mono- and multilayer forming diacetylenes

Summary Heptadeca-2,4-diine-1-ol and Heptadeca-2,4-diine-1-acid were synthesized and their polymerization behaviour in the solid state was investigated. Both compounds polymerize thermally below the melting point and photochemically under the action of uv-light to form polymers via 1,4-addition to the conjugated triple bonds with a backbone of conjugated double-and triple-bonds. The photoresponse spectra resemble the absorption spectra exhibiting maxima of photoreactivity in the absorption band of the conjugated triple bonds of the monomers.Both compounds satisfy the general criteria of formation of monomeric monolayer films at the air-water-interface of a Langmuir-trough. The monolayers could be transfered onto quartz or metal substrates by the Langmuir-Blodgett-technique and multilayers of the monomers could be built up. These multilayers were polymerized by exposure to high energy-radiation and thus, multilayers of the crystalline, well ordered polymer were obtained. The polymer multilayers were studied by electron diffraction and ir-spectroscopy. The polymer has the same structure as the one obtained by solid-state polymerization of the crystals. A model of the structure of the monomeric and polymeric multilayers is proposed, which is based on the combined evidences from the known chemical structure, the diffraction and spectroscopic data and the formation of the layered structure.

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Zusammenfassung Heptadeca-2,4-diin-1-ol und Heptadeca-2,4-diin-1-säure wurden dargestellt und das Polymerisationsverhalten im festen Zustand untersucht. Beide Verbindungen polymerisieren thermisch und photochemisch bei Bestrahlung mit UV-Licht und bilden dabei über eine 1,4-Addition an die konjugierten Dreifachbindungen Polymere mit einer Hauptkette aus konjugierten Doppel- und Dreifachbindungen. Die Photoantwortspektren ähneln den Absorptionsspektren und Maxima der Photoreaktivität liegen in dem Bereich der Absorption der konjugierten Dreifachbindungen der Monomeren. Beide Verbindungen lassen sich an der Grenzfläche Gas-Wasser eines Langmuir-Troges spreiten. Die Monoschichten konnten nach der Langmuir-Blodgett-Technik auf Quarz- oder Metallunterlagen überführt und auf these Weise Multischichten der Monomeren erzeugt wurden. Diese Multischichten wurden durch Bestrahlung mit energiereicher Strahlung polymerisiert und dadurch Multischichten des kristallinen, geordneten Polymeren erhalten. Die Multischichten des Polymeren wurden mit Elektronenbeugung und IR-Spektroskopie untersucht. Die Polymeren hatten die gleiche chemische Struktur wie die aus den Kristallen der Monomeren erhaltenen. Auf der Grundlage der bekannten chemischen Struktur der Polymeren, der Beugungs- und spektroskopischen Daten und aus der Tatsache, daß sich Monoschichten erhalten lassen, wurde ein Modell für die Struktur der Multischichten der Monomeren und der Polymeren entwickelt.

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With 11 figures and 1 table     

Studies on mono- and dinuclear bisoxime copper complexes with different coordination geometries

Two new mono- and dinuclear Cu(II) complexes, namely [CuL¹]·0.5H₂O (1) and [(Cu₂(L²)₂)(DMF)]·0.5DMF (2) (H₂L¹ = 1,2-bis{[(Z)-(3-methyl-5-oxo-1-phenyl-1H-pyrazolidin-4(4H)-yl)(phenyl)]methylene-aminooxy}ethane; H₂L² = 1,3-bis{[(Z)-(3-methyl-5-oxo-1-phenyl-1H-pyrazolidin-4(4H)-yl)(phenyl)] methyleneaminooxy}propane), have been synthesized and characterized by X-ray crystallography. The unit cell of complex 1 contains two crystallographically independent but chemically identical [CuL¹] molecules and one crystalline water molecule, showing a slightly distorted square-planar coordination geometry and forming a wave-like pattern running along the a-axis via hydrogen bonding and π···π stacking interactions. Complex 2 has a dinuclear structure, comprising two Cu(II) atoms, two completely deprotonated phenolate bisoxime (L²)²⁻ moieties (in the form of enol), and both coordinated and hemi-crystalline DMF molecules. Complex 2 has square-planar and square-pyramidal geometries around the two copper centers, whose basic coordination planes are almost perpendicular and form an infinite three-dimensional supramolecular network structure involving intermolecular C–H···N, C–H···O, and C–H···π(Ph) hydrogen bonding and π···π stacking interactions of neighboring pyrazole rings.     

Structure and reactivity of mono- and dinuclear diiminate zinc alkyl complexes

The synthesis, structure and reactivity of several diiminate ligands are presented. The syntheses of five representative β-diiminate (BDI) zinc alkyl complexes and one β-oxo-δ-diiminate (BODDI) zinc alkyl are described. BDI ligands with varying backbone and N-aryl substituents display different solid state structures. [(BDI)ZnR] are synthesized by the reaction of (BDI)H with ZnR₂ in quantitative yield. Previously reported (BDI-1)ZnEt is a three-coordinate monomer in the solid state whereas [(BDI-3)ZnEt]_∞ [(BDI-3)=2-((2,6-diisopropylphenyl)amido)-3-cyano-4-((2,6-diisopropylphenyl)imino-2-pentene] and [(BDI-4)ZnEt]_∞ [(BDI-4)=2-((2,6-diethylphenyl)amido)-3-cyano-4-((2,6-diethylphenyl)imino-2-pentene] form one dimensional coordination polymers. The bimetallic complex [(BODDI-1)(ZnEt)₂] [(BODDI-1)=2,6-bis((2,6-diisopropylphenyl)amido)-2,5-heptadien-4-one] is prepared through the reaction of (BODDI-1)H₂ with two equivalents ZnEt₂. Both [(BDI)ZnEt] and [(BODDI)ZnEt] complexes react with acetic acid to give the acetate complexes in moderate to high yields, offering a superior synthetic route to these complexes. [(BDI)ZnR] [BDI=(BDI-3) or 1,1,1-trifluoro-2-((2,6-diisopropylphenyl)amido)-4-((2,6-diethylphenyl)imino-2-pentene), (BDI-5)] complexes react with MeOH to produce [{(BDI)Zn(μ-OMe)}₂Zn(μ-OMe)₂] in moderate yields. The molecular structures of [(BDI-3)ZnEt], [(BDI-4)ZnEt], [(BODDI-1)(ZnEt)₂], [(BODDI-1)Zn₂(μ-OAc)₂], [{(BDI-3)Zn(μ-OMe)}₂Zn(μ-OMe)₂] and [{(BDI-5)Zn(μ-OMe)}₂Zn(μ-OMe)₂] have been determined by X-ray diffraction.     

FTIR spectroscopic study of the Cl- and Br-atom initiated oxidation of ethene

The reaction mechanism of the halogen (Cl and Br)-atom initiated oxidation of C₂H₄ was studied using the long path FTIR spectroscopic method in 700 torr of air at 296 ± 2 K. Among the major halogen-containing products were X? CH₂CHO, X? CH₂CH₂OH, and X? CH₂CH₂OOH (X = Cl or Br) which were shown to be formed via the self-reaction of the X? CH₂CH₂OO radicals, i.e., 2X? CH₂CH₂OO → 2X? CH₂CH₂O + O₂; (a) 2X? CH₂CH₂OO → X? CH₂CHO + X? CH₂CH₂OH + O₂ and (b) followed by X? CH₂CH₂O + O₂ → X? CH₂CHO + HO₂ and X? CH₂CH₂OO + HO₂ → X? CH₂CH₂OOH + O₂. From the observed yields of X? CH₂CHO and X? CH₂CH₂OH the branching ratios for reactions (a) and (b) were determined to be k_a/k_b = 1.35 ± 0.07(2σ) for both X = Cl and Br. In addition, the O₂-dependence of the rate constant for the Br + C₂H₄ reaction was determined by the relative rate technique as a function of O₂ partial pressure from 140 to 700 torr at 700 torr total pressure of N₂/O₂ diluent. Rate constants for the reactions of Cl-atoms with Cl-CH₂CHO and Br-atoms with Br-CH₂CHO were also determined to be [4.3 ± 0.2(2sigma;)] × 10^?11 and less than or equal to [1.83 ± 0.11(2σ)] × 10^?13 cm³ molecule^?1 s^?1, respectively.     

Polymerization of cyclopentadiene initiated by methylaluminoxane

The polymerization of cyclopentadiene (CPD) was effectively initiated by methylaluminoxane (MAO) to generate poly(cyclopentadiene) (polyCPD). The effects on the polymerization of some reaction parameters such as the monomer concentration, the initiator concentration, and solvents were investigated. The conversion of CPD was monitored with gas chromatography to investigate the reaction kinetics. The polymerization rate was proportional to the concentrations of MAO in the first order and of the CPD monomer in the second order, and a reasonable cationic polymerization mechanism was suggested on the basis of the kinetic study. PolyCPD obtained at a low temperature could be dissolved in toluene or chloroform, and this indicated lower cross‐coupling during the polymerization reaction. ¹H NMR and IR analysis of the polymer indicated that there were almost equal amounts of 1,2‐enchainment and 1,4‐enchainment in the polymer chain. The measurement of polyCPD showed its unique properties as a potential candidate for stable wrappings or electronic packaging materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 264–272, 2006     

Asymmetric synthesis of mono- and dinuclear bis(dipyrrinato) complexes

The diastereoselective syntheses of Zn(II) bis(dipyrrinato) helicates is reported, involving ligands templated by the incorporation of homochiral binol within the linker joining the two dipyrrinato units. The most diastereoselective formation of dinuclear bis(dipyrrinato) helicates to date is reported. The formation of either mononuclear or dinuclear helicates can be tuned by varying the length of the linker between the dipyrrinato units and by varying the complexation procedure. The neutral dipyrrinato helicates were readily analyzed by HPLC to ascertain diastereoselectivity, and circular dichroism studies revealed the helical nature of the complexes. The molar ellipticities of the helicates produced by diastereoselective complexation are very large in the visible region and typically correspond to binol moieties in the UV region. Extensive X-ray crystallographic investigations further confirmed the helicity of the mononuclear Zn(II) helicates and identified significant interlayer displacement and bending within crystals.     

Phosphate diester hydrolysis by mono- and dinuclear lanthanum complexes with an unusual third-order dependence

A series of mono- and dinuclear lanthanum complexes of 15,31-dimethyl-3,11,19,27,33,35-hexaazapentacyclo[27.3.1.1.(5,9)1,(13,17). 1(21,25)]hexatriaconta-5,7,9(33),13,15,17(34),21,23,25(35),29,31, 1(36)-dodecaene-34,36-diol (24RBPyBC, L) have been defined in solution. Their ability to hydrolyze bis(4-nitrophenyl) phosphate, a phosphate diester, was studied. The various metal-coordinated hydroxide nucleophiles that form in solution attack the substrate in the hydrolysis reaction. The dihydroxo dilanthanum complex, L-2La-2(OH), is the most effective catalyst. Its rate constant is 75 times larger than the rate constant for the monohydroxo dilanthanum complex, L-2La-OH. The mononuclear complexes are not as successful as the dinuclear complexes because they have fewer metal ions per complex to act as Lewis acids. They also cannot generate hydroxide nucleophiles at low pH values like the dinuclear complexes can. The reaction has an unusual third-order dependence on the catalyst concentration which is valid for the dinuclear complexes as well as the mononuclear complexes. This implies a mechanism where a metal-coordinated hydroxide nucleophile attacks the phosphorus of the substrate on the side opposite the negatively charged oxygens.     

Antibiotic resistance: mono- and dinuclear zinc complexes as metallo-beta-lactamase mimics

Biomimetic systems containing one or two zinc(II) ions supported by phenolate ligands were developed as functional mimics of metallo-beta-lactamase. These complexes were shown to catalytically hydrolyze beta-lactam substrates, such as oxacillin and penicillin G. The dinuclear zinc complex 1, which has a coordinated water molecule, exhibits high beta-lactamase activity, whereas the dinuclear zinc complex 2, which has no water molecules, but labile chloride ligands, shows a much lower activity. The high beta-lactamase activity of complex 1 can be ascribed to the presence of a zinc-bound water molecule that is activated by being hydrogen bonded to acetate substituents. The kinetics of the hydrolysis of oxacillin by complex 1 and the effect of pH on the reaction rates are reported in detail. In addition, the kinetic parameters obtained for the synthetic analogues are compared with those of the natural metallo-beta-lactamase from Bacillus cereus (BcII). To understand the role of the second metal ion in hydrolysis, the syntheses and catalytic activities of two mononuclear complexes (3 and 4) that include coordinated water molecules are described. Interestingly, the mononuclear zinc complexes 3 and 4 also exhibit high activity, supporting the assumption that the second zinc ion is not crucial for the beta-lactamase activity.     

Polymerization of styrene initiated by acetylenic peroxides

The initiating activity of acetylenic peroxides in polymerization of styrene was studied. The kinetic parameters of the polymerization and its initiation were calculated. The effect exerted by the structure of radicals on the initiating activity of peroxides was evaluated.

     

Investigation of the polymerization behavior of polysiloxane-bridged dinuclear zirconocenes as model compounds for a heterogenized metallocene at the silica surface

The polymerization of ethylene was studied by using a series of polysiloxane-bridged dinuclear zirconocenes [(SiMe₂O)_nSiMe₂(C₅H₄)₂][(C₉H₇)ZrCl₂]₂ ( 7 , n = 1 ; 8 , n = 2; 9 , n = 3), the corresponding mononuclear zirconocene (C₅H₅)(C₉H₇)ZrCl₂, 10 , and the pentamethylene-bridged dinuclear zirconocene [(CH₂)₅(C₅H₄)₂][(C₉H₇)-ZrCl₂]₂, 13 . From the polymerization studies using these catalysts it was found that (i) activities of the polysiloxane dinuclear zirconocenes 7–9 wre lower than that of the corresponding mononuclear zirconocene 10 , (ii) molecular weights of polyethylenes produced by the dinuclear metallocenes are greater than that of polyethylene produced by the mononuclear metallocene, (iii) the complex 9 holding the longest bridging ligand exhibited the highest activity but produced a polymer having the smallest molecular weight among the polysiloxane-bridged dinuclear zirconocenes, and (iv) the pentamethylene-bridged dinuclear metallocene 13 showed higher activity than the complexes 7–9 and the mononuclear zirconocene 10 . The formation of the lowest molecular weight of polyethylene by 9 was attributed to the influence of electron withdrawal caused by the Lewis acid–base interaction between the acidic aluminum of the cocatalyst and the basic oxygen at the polysiloxane linkage as well as the lack of a steric problem. An increase in steric congestion around the metal center led to not only a decrease in catalytic activity due to preventing facile monomer access to the active site but also an increase in the molecular weight of polyethylenes due to supressing β-H elimination. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3717–3728, 1997     

Synthesis and characterisation of mono- and dinuclear diethyldithiocarbamatonickel(II) organochalcogenide complexes

The reaction of Ni(dtc)(PR₃)Cl (dtc=diethyldithiocarbamate, R=Ph or Bu) with HSC₆H₄Cl-4 or HSCH₂C₆H₄Cl-4 and Et₃N gave two types of complex. For PPh₃, the products were [Ni(dtc)(μ-SC₆H₄Cl-4)]₂ (1) and [Ni(dtc)(μ-SCH₂C₆H₄Cl-4)]₂ (2); whilst PBu₃ gave Ni(dtc)(PBu₃)(SC₆H₄Cl-4) (3). The structure of freshly prepared 3 was determined to be monomeric, as indicated by X-ray diffraction studies. However, at room temperature in solution, 3 was observed to slowly convert to 1. Structural identification of 1 and 2 and similar dimers, and structural identification of 3 and analogous monomers, were investigated by mass spectrometry. Electron impact mass spectrometry (EIMS) failed to confirm the proposed structures due to extensive decomposition in the mass spectrometer. In the electron impact (EI) mode, all complexes invariably decomposed to Ni(dtc)₂; on the other hand, fast atom bombardment (FAB) ionisation gave the expected molecular ions for all compounds.