Polymerization of ethene initiated with a mixture of siloxane-bridged mono- and dinuclear zirconocenes

In the polymerization of ethene cocatalyzed with modified methylaluminoxane, the catalyst activities of the siloxane-bridged dinuclear zirconocenes, tetramethyldisiloxanediylbis(cyclopentadienylindenylzirconium dichloride) ( 3 ) and hexamethyltrisiloxanediylbis(cyclopentadienylindenylzirconium dichloride) ( 4 ) were lower than that obtained with the siloxane-bridged mononuclear zirconocene, tetramethyldisiloxanediyldicyclopentadienyldimethylzirconium ( 1 ). On the other hand, weight-average molecular weight M̄_w and ratio of weight- to number-average molecular weights M̄_w/M̄_n of polyethene (PE) obtained with 3 or 4 were higher than those of PE obtained with 1. For a binary mixture of 1/3 or 1/4 , it was found that the obtained PE exhibits a bimodal molecular weight distribution for an appropriate composition of the mixed zirconocenes. M̄_w/M̄_n of PE could be adjusted by changing the relative concentrations of the two zirconocenes.     

Synthesis and reactivity of di(silylamido)cyclopentadienyl titanium and zirconium complexes

We present in this account the synthesis and recent developments of a new class of group 4 metal complexes with the tridentate di(silylamido)cyclopentadienyl ligand. These doubly silyl-bridged group 4 metal amido chelates are receiving increasing interest as they are efficient catalysts for ethene polymerization when activated with MAO despite generating 14-electron d⁰ cationic species free of the alkyl group required for the first insertion reaction in the polymerization process.     

Metallocene-catalyzed ethene/styrene co- and terpolymerization with olefinic termonomers

Ethene was co- and terpolymerized with 1-octene and styrene using the methylalumoxane (MAO) activated halfsandwich metallocene Me₂Si(Me₄Cp)(N-t.-butyl)TiCl₂(Cp = cyclopentadienyl, Me = methyl) as catalyst. At temperatures of 40 and 60°C styrene concentration was varied in order to investigate the influence of the comonomers. Despite decreasing the overall activity with respect to ethene/1-octene copolymerization, polymerization activity was found to exibit a relative maximum with increasing styrene concentration. An explanation is given taking two different comonomer effects into account. Low styrene concentration promoted higher 1-octene incorporation compared to ethene/1-octene copolymerization but significantly lowered the molecular weight of the terpolymers. With constant ethene and 1-octene concentration it was possible to produce ethene/1-octene/styrene terpolymers with styrene content varying from 0 to 25 mol % and 1-octene content varying from 8 to 21 mol %. All terpolymers were amorphous. With constant ethene content it was found possible to vary their glass transition temperature with 1-octene/styrene molar ratio incorporated in the terpolymer. ¹³C-NMR spectroscopic microstructure analysis showed that no styrene/1-octene sequences were found in the terpolymer backbone. Furthermore terpolymerizations were conducted successfully incorporating norbornene, 1,5-hexadiene and propene as monomers in terpolymertization with ethene and styrene. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2549–2560, 1997     

Syntheses and structures of sterically congested linear and branched cobalta[n]triangulanes

Treatment of {eta(5):eta(1)[2-(di-tert-butylphosphanyl-P)ethyl]cyclopentadienyl}cobalt(I) chloride (5) with methylenecyclopropane (3) or bicyclopropylidene (4), as well as with their spirocyclopropanated analogues methylenespiropentane (7), cyclopropylidenespiropentane (10), or 7,7'-bi(dispiro[2.0.2.1]heptylidene) (15) in the presence of sodium amalgam at -50 degrees C, furnished the stable cobalt complexes 6, 9, 8, 11, and 16, respectively, in 72, 83, 84, 86, and 54 % isolated yield, respectively. The complexes 14 and 16 were also obtained by ligand exchange of the ethene complex {eta(5):eta(1)[2-(di-tert-butylphosphanyl-P)ethyl]cyclopentadienyl}(eta(2)-ethene)cobalt(I) (12) with 13 and 15 in 79 and 52 % yield, respectively. The X-ray crystal-structure analyses of complexes 9, 14, and 16, as well as the NMR-spectroscopic data of all complexes, reveal that they can be regarded as linear and branched cobalta[n]triangulanes. The thermal stability of complexes 6, 8, and 9 up to 109, 145, and 160 degrees C was determined by differential thermal analysis-thermogravimetry (DTA-TG) analysis.     

A hydrogen-1 nuclear magnetic resonance,mass spectral and extended Hückel study of some olefin complexes of rhodium(I) and iridium(I) and the crystal and molecular structure of η4-2,4-dimethylpenta-1,4-diene(η5-formylcyclopentadienyl)rhodium(I)

A ¹H NMR study of monosubstituted η-cyclopentadienyl-rhodium(I) complexes of type LLRh(C₅H₄X) and -iridium(I) complexes of type L₂Ir(C₅H₄X) (L = ethene, LL = 1,3- or 1,5-diolefin; X = C(C₆H₅)₃, CHO, or COOCH₃) has been carried out. For complexes of both metals in which the neutral ligand is ethene or a non-conjugated diolefin the NMR spectra of the cyclopentadienyl protons are unusual in that H(2), H(5) resonate to high field either at room temperature or below.The corresponding NMR spectra for the cyclopentadienyl ring protons of complexes where the neutral ligand is a conjugated diene are, with one exception, normal.A single crystal X-ray structural analysis of (η⁴-2,4-dimethylpenta-1,4-diene)(η⁵-formylcyclopentadienyl)rhodium(I) (which exhibits an abnormal ¹H NMR spectrum) reveals substantial localisation of electron density in the C(3)C(4) Cp ring bond (1.283(33) Å) which may be consistent with a contribution from an ‘allyl-ene’ rotamer to the ring—metal bonding scheme. An extended Hückel calculation with self consistent charge iteration was performed on this complex.The results predict a greater Mulliken overlap population for the C(3)C(4) bond in the cyclopentadienyl ring and show that the localisation is dependent on both the Cp ring substituent and the nature of the diolefin. The mass spectral fragmentation patterns of some representative diene complexes of iridium(I) and rhodium(I) are presented.     

Copolymerization of vinylcyclohexane with ethene and propene using zirconocene catalysts

Vinylcyclohexane (VCH) was copolymerized with ethene and propene using methylaluminoxane‐activated metallocene catalysts. The catalyst precursor for the ethene copolymerization was rac‐ethylenebis(indenyl)ZrCl₂ ( 1 ). Propene copolymerizations were further studied with C_s‐symmetric isopropylidene(cyclopentadienyl)(fluorenyl)ZrCl₂ ( 2 ), C₁‐symmetric ethylene(1‐indenyl‐2‐phenyl‐2‐fluorenyl)ZrCl₂ ( 3 ), and “meso”‐dimethylsilyl[3‐benzylindenyl)(2‐methylbenz[e]indenyl)]ZrCl₂ ( 4 ). Catalyst 1 produced a random ethene–VCH copolymer with very high activity and moderate VCH incorporation. The highest comonomer content in the copolymer was 3.5 mol %. Catalysts 1 and 4 produced poly(propene‐co‐vinylcyclohexane) with moderate to good activities [up to 4900 and 15,400 kg of polymer/(mol of catalyst × h) for 1 and 4 , respectively] under similar reaction conditions but with fairly low comonomer contents (up to 1.0 and 2.0% for 1 and 4 , respectively). Catalysts 2 and 3 , both bearing a fluorenyl moiety, gave propene–VCH copolymers with only negligible amounts of the comonomer. The homopolymerization of VCH was performed with 1 as a reference, and low‐molar‐mass isotactic polyvinylcyclohexane with a low activity was obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6569–6574, 2006     

Well-defined single-site thiobis(phenolate) Group 4 metal catalysts for heterogeneous olefin polymerization

The tridentate (OSO-function) thiobis(phenolate) ligand derived from 2,2′-thiobis[4-(1,1,3,3-tetramethylbutyl)phenol] (tbopH₂) is an alternative to the cyclopentadienyl ancillary group for Group 4 heterogeneous olefin polymerization. The tbop ligand placed on titanium, zirconium and hafnium forms a wide family of homoleptic compounds as well as heteroleptic alkoxo- and aryloxo-bridged complexes modified with coligands like chlorides, imides, and monoaryloxides. Among these heteroleptic titanium complexes when activated with cocatalysts and supported on MgCl₂ are highly effective heterogeneous, well-defined, single-site ethene polymerization catalysts. The active centres of these catalysts consist of Ti(III) species with the alkyl group and the sulfur atom of the tbop ligand coordinated in axial positions. Titanium, zirconium and hafnium systems both heteroleptic and homoleptic show moderate activity in 1-hexene polymerization producing atactic poly(1-hexenes).     

Toward block copolymers from nonliving isospecific single‐site catalytic systems

Ethene/1‐olefin blocky copolymers were obtained through nonliving insertion copolymerizations promoted by an isospecific single site catalyst. Propene or 4‐methyl‐1‐pentene were copolymerized with ethene with metallocenes endowed with different stereospecificity in propene polymerization: (i) aspecific “constrained geometry” half‐sandwich complex, {η¹:η⁵‐([tert‐butyl‐amido)dimethylsilyl](2,3,4,5‐tetramethyl‐1‐cyclopentadienyl)}titanium dichloride [Me₂Si(Me₄Cp)(N‐^tBu)TiCl₂] ( CG ), (ii) moderately isospecific rac‐ethylenebis(indenyl)zirconium dichloride [rac‐(EBI)ZrCl₂] ( EBI ), (iii) slightly more isospecific hydrogenated homologue, rac‐ethylenebis(tetrahydroindenyl)zirconium dichloride [rac‐(EBTHI)ZrCl₂] ( EBTHI ), (iv) highly iso‐specific rac‐[methylenebis(3‐tert‐butyl‐1‐indenyl)]zirconium dichloride [rac‐H₂C‐(3‐^tBuInd)₂ZrCl₂] ( TBI ), (v) most isospecific rac‐[isopropylidene‐bis(3‐tert‐butyl‐cyclopentadienyl)]zirconium dichloride [rac‐Me₂C‐(3‐^tBuCp)₂ZrCl₂] ( TBC ). Copolymerizations were described by a 2^nd order Markovian copolymerization model and data are proposed to correlate the formation of 1‐olefin sequences with catalytic site isospecificity, made by the cooperation of organometallic complex and growing chain. Blocky copolymers were prepared over wide ranges of compositions: with any of the isospecific metallocenes when 4‐methyl‐1‐pentene was the 1‐olefin and only with the highly isospecific ones ( TBI , TBC ) when propene was the comonomer. A penultimate unit effect was observed with TBI as the metallocene, whereas a 1^st order Markov model described the ethene/propene copolymerization from TBC . A moderately isospecific metallocene, such as EBI , is shown to be able to prepare blocky ethene copolymers with 4‐methyl‐1‐pentene. These results pave the way for the synthesis of new ethene based materials. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2063–2075, 2010     

Role of cluster size in catalysis: spectroscopic investigation of gamma-Al2O3-supported Ir4 and Ir6 during ethene hydrogenation

gamma-Al(2)O(3)-supported Ir(4) and Ir(6) were prepared by decarbonylation of tetra- and hexanuclear iridium carbonyls, respectively, and compared as catalysts for ethene hydrogenation at atmospheric pressure and temperatures in the range 273-300 K. Rates of the reaction were determined along with extended X-ray absorption fine structure (EXAFS) and IR spectra characterizing the clusters in the working catalysts. EXAFS data show that the Ir(4) and Ir(6) cluster frames remained intact during catalysis. Di-sigma-bonded ethene and pi-bonded ethene on the clusters were identified by IR spectroscopy and found to compete as the principal reaction intermediates, with the former predominating at ethene partial pressures less than about 200 Torr and the latter at higher ethene partial pressures. Hydrogen on the clusters is inferred to form by dissociative adsorption of H(2); alternatively, it is provided by OH groups of the support. The rate of ethene hydrogenation on Ir(4) is typically several times greater than that on Ir(6).     

Photoinduced ethane formation from reaction of ethene with matrix-isolated Ti, V, or Nb atoms

The reactions of matrix-isolated Ti, V, or Nb atoms with ethene (C(2)H(4)) have been studied by FTIR absorption spectroscopy. Under conditions where the ethene dimer forms, metal atoms react with the ethene dimer to yield matrix-isolated ethane (C(2)H(6)) and methane. Under lower ethene concentration conditions ( approximately 1:70 ethene/Ar), hydridic intermediates of the types HMC(2)H(3) and H(2)MC(2)H(2) are also observed, and the relative yield of hydrocarbons is diminished. Reactions of these metals with perdeuterioethene, and equimolar mixtures of C(2)H(4) and C(2)D(4), yield products that are consistent with the production of ethane via a metal atom reaction involving at least two C(2)H(4) molecules. The absence of any other observed products suggests the mechanism also involves production of small, highly symmetric species such as molecular hydrogen and metal carbides. Evidence is presented suggesting that ethane production from the ethene dimer is a general photochemical process for the reaction of excited-state transition-metal atoms with ethene at high concentrations of ethene.     

Random ethene/propene copolymerization from a catalyst system based on a “constrained geometry” half‐sandwich complex

Ethene/propene copolymerizations were performed in solution with a single centre catalyst system composed of a “constrained geometry” half‐sandwich organometallic complex {η¹: η⁵‐[(tert‐butylamido)dimethylsilyl](2,3,4,5‐tetramethyl‐1‐cyclopentadienyl)}titanium dichloride, and methylaluminoxane. The statistical treatment of polymerization data allowed to determine the reactivity ratios for ethene and propene: r_E = 1.35 ± 0.09, r_P = 0.82 ± 0.05, r_Er_P = 1.10 ± 0.14. This catalyst system promotes an almost random distribution of ethene and propene and gives rise to values of r_P and r_E very similar to each other.     

Pseudohexagonal crystallinity and thermal and tensile properties of ethene–propene copolymers

Structural (X‐ray diffraction), melting (differential scanning calorimetry), as well as mechanical (tensile tests) characterizations on uncrosslinked ethene–propene copolymer samples, obtained using a metallocene‐based catalytic system and having an ethene content in the range 80–50% by mol, are reported. Samples with an ethene content in the range 80–60% by mol present a disordered pseudohexagonal crystalline phase, whose melting moves from ≈ 40°C down to ≈ −20°C as the ethene content is reduced. The dramatic influence of the crystalline phase on tensile properties of uncrosslinked ethene–propene copolymers is shown. In particular, highest elongation at break values are obtained for samples being essentially amorphous in the unstretched state and partially crystallizing under stretching. On the other hand, lowest tension set values (most elastic behavior) are observed for samples presenting, already in the unstretched state, microcrystalline domains acting as physical crosslinks in a prevailing amorphous phase. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1095–1103, 1999     

Direct synthesis of hyperbranched ethene oligomers and ethene-MA co-oligomers using iminopyridyl systems with weak neighboring group interactions

The synthesis of hyper-branched ethene oligomers through catalytic insertion reactions with late transition metal catalysts is unique in its synthetic and practical scope. In this study, a series of iminopyridyl Ni(II) and Pd(II) complexes with electron-rich distal aryl motifs were synthesized and characterized. These complexes were very efficient in ethene oligomerization and co-oligomerization with methyl acrylate (MA). Hyperbranched ethene oligomers with different microstructures were generated using different metal species in ethene oligomerization. More importantly, hyperbranched ethene-MA co-oligomers with varying incorporation ratios were generated via ethene and MA co-oligomerization using the Pd(II) complexes. Most notably, weak neighboring group interactions of distal aryl motifs in the nickel system are more effective in influencing the microstructure of ethene oligomers than the corresponding palladium system.     

Ab Initio Study of Structures,Metallotropic 1,2-Shifts and Prototropic 1,2-Shifts of Cyclopentadienyl(trimethyl)silane, -germane and -stannane

Molecular structures, metallotropic and prototropic shifts of cyclopentadienyl(trimethyl)silane ( 1 ), cyclopentadienyl(trimethyl)germane ( 2 ), and cyclopentadienyl(trimethyl)stannane ( 3 ) were investigated using ab initio molecular orbital and the Becke, Lee, Yang, and Parr density functional (B3LYP) methods. The results show that the most stable structure of compounds 1-3 has the (CH 3 ) 3 M fragment in the allylic position. The energy barrier of metallotropic shifts in compound 1 is higher than in 2 , and in compound 2 higher than in 3 , in good agreement with experimental data. The cyclopentadienyl rings in compounds 1-3 are found to be planar but this result contradicts the reported experimental data.     

酸性分子筛催化乙烯二聚反应

应用密度泛函理论(DFT), 采用5T簇模型来模拟分子筛催化剂的酸性位, 在B3LYP/6-311+G(3df, 2p)的条件下通过理论计算研究了乙烯在酸性分子筛上的二聚反应. 对反应各驻点进行了全局优化, 经过零点能校正后, 计算得出乙烯二聚反应的活化能. 研究表明, 乙烯在分子筛上的二聚反应分三步进行: 单个乙烯分子化学吸附→第二个乙烯分子的物理吸附→两乙烯分子二聚反应. 乙烯化学吸附生成的烷氧化合物与物理吸附的乙烯分子发生二聚反应生成新的C—C键同时生成新的烷氧化合物. 计算得到的乙烯化学吸附和二聚反应的反应能垒分别为108和149 kJ·mol-1. 反应的逆过程也就是1-丁烯在酸性分子筛表面的1-丁基烷氧化合物发生β分裂反应, 计算所得相应的1-丁烯β分裂反应的能垒为217 kJ·mol-1, 远高于相应的乙烯二聚反应能垒. 此外还进一步研究了所用基组对计算结果的影响.     

Observation of the pi...H hydrogen-bonded ternary complex, (C(2)H(4))(2)H(2)O, using matrix isolation infrared spectroscopy

FTIR absorption spectra of water-containing ethene:Ar matrices, with compositions of ethene up to 1:10 ethene:Ar, have been recorded. Systematically increasing the concentration of ethene reveals features in the spectra consistent with the known 1:1 ethene:water complex, which subsequently disappear on further increase in ethene concentration. At high concentrations of ethene, new features are observed at 3669 and 3585 cm(-1), which are red-shifted with respect to matrix-isolated nu(3) and nu(1) O-H stretching modes of water and the 1:1 ethene:water complex. These shifts are consistent with a pi...H interaction of a 2:1 ethene:water complex of the form (C(2)H(4)...H-O-H...C(2)H(4)). The analogous (C(2)D(4))(2)H(2)O complex shows little shifting from positions associated with (C(2)H(4))(2)H(2)O, while the (C(2)H(4))(2)D(2)O isotopomer shows large shifts to 2722.3 and 2617.2 cm(-1), having identical nu(3)(H(2)O)/nu(3)(D(2)O) and nu(1)(H(2)O)/nu(1)(D(2)O) values when compared with monomeric water isotopomers. Features at 3626.1 and 2666.2 cm(-1) are also observed and are attributed to (C(2)H(4))(2)HDO. DFT calculations at the B3LYP/6-311+G(d,p) level for each isotopomer are presented, and the predicted vibrational frequencies are directly compared with experimental values. The interaction energy for the formation of the 2:1 ethene:water complex from the 1:1 ethene:water complex is also presented.     

Computational study of ethene hydroarylation at [Ir(κ(2)-OAc)(PMe3)Cp]+

Density functional theory calculations have been employed to model ethene hydroarylation using an [Ir(κ(2)-OAc)(PMe(3))Cp](+) catalyst, 1. The reaction proceeds via: (i) an acetate-assisted C-H activation of benzene via an AMLA-6 transition state; (ii) rate-limiting insertion of ethene into the Ir-Ph bond; and (iii) protonolysis of the β-phenylethyl species by HOAc. A range of competing processes are assessed, the most important of which are the C-H activation of ethene at 1 and trapping of the β-phenylethyl intermediate with ethene. The former process gives rise to Ir-vinyl species which can then access further ethene insertion to give stable allyl by-products. A comparison with other ethene hydroarylation catalysts reported in the literature is presented.     

Amineborane dehydrogenation promoted by isolable zirconium sandwich, titanium sandwich and N(2) complexes

Catalytic dehydrogenation of R(2)NHBH(3) (R = Me, H) promoted by a family of bis(cyclopentadienyl)titanium and bis(indenyl)zirconium compounds is reported; structure-reactivity relationships as a function of cyclopentadienyl and indenyl substituents have been examined.     

Tetrakis(2-hydroxyphenyl)ethene and derivatives. A structurally preorganized tetradentate ligand system for polymetallic coordination chemistry and catalysis

A topologically unique, conformationally constrained tetradentate ligand system for polymetallic coordination chemistry has been developed: tetrakis(2-hydroxyphenyl)ethene (1a) and substituted derivatives. The design exploits the planarity of the tetraphenylethylene core to impart rigidity to the roughly square oxygen binding array, while maintaining a degree of conformational mobility associated with rotation about the aryl-ethylene carbon-carbon bonds. Tetrakis(2-hydroxyphenyl)ethene derivatives are designed to promote multiple metal bridging over chelating coordination modes. The ligand is synthesized from anisole or 4-tert-butylanisole in four steps via the 2,2'-dimethoxybenzophenone hydrazones 4a,b. The sterically hindered ortho-substituted tetraphenylethylene core is produced in high yield by acid-catalyzed decomposition of the corresponding diaryl diazomethane prepared in situ by oxidation of the hydrazone using nickel peroxide. Deprotection of the methyl ethers using boron tribromide gives tetrakis(2-hydroxyphenyl)ethene (1a), characterized by X-ray crystallography, and tetrakis(5-tert-butyl-2-hydroxyphenyl)ethene (1b). Sterically isolating substituents in the 3-position can be installed via Claisen rearrangement/hydrogenation, providing tetrakis(3-n-propyl-2-hydroxyphenyl)ethene (6) efficiently. To illustrate potential applications of this unprecedented ligand class, two coordination complexes are reported, including tetrakis(2-diethylaluminoxyphenyl)ethene (8), a structurally robust eight-membered-ring aluminum/oxygen crown complex characterized both in solution and in the solid state.     

Carbon incorporation in Pd(111) by adsorption and dehydrogenation of ethene

The decomposition of ethene on the Pd(111) surface was studied at effective pressures in the 10(-8) to 10(-7) mbar range and at sample temperatures between 300 and 700 K, using an effusive capillary array beam doser for directional adsorption, LEED, AES, temperature programmed reaction, and TDS. In the temperature range of 350-440 K increasingly stronger dehydrogenation of the ethene molecule is observed. Whereas at 350 K an ethylidyne adlayer is still present after adsorption, already at temperatures around 440 K complete coverage of the surface by carbon is attained, while the bulk still retains the properties of pure Pd. Beyond 440 K a steady-state surface C coverage is established, which decreases with temperature and is determined by detailed balancing between the ethene gas-phase adsorption rate and the migration rate of carbon into the Pd bulk. This process gives rise to the formation of a "partially carbon-covered Pd(x)C(y) surface". Above 540 K the surface-bulk diffusion of adsorbed carbon becomes fast, and in the UHV experiment the ethene adsorption rate becomes limited by the ethene gas-phase supply. The carbon bulk migration rate and the steady-state carbon surface coverage were determined as a function of the sample temperature and the ethene flux. An activation energy of 107 kJ mol(-1) for the process of C diffusion from surface adsorption sites into the subsurface region was derived in the temperature range of 400-650 K by modeling the C surface coverage as a function of temperature on the basis of steady-state reaction kinetics, assuming a first-order process for C surface-subsurface diffusion and a second-order process for C(ads) formation by dissociative C2H4 adsorption.