Type Of Cocatalyst Research Articles

Binary molybdenum-based catalyst for coordination polymerization of styrene

Coordination polymerization of styrene (St) using molybdenum pentachloride supported by phosphite ligand in the presence of metal organic compound was studied for the first time. The types of phosphite and co-catalysts significantly affected the catalytic activity of the molybdenum (V) (Mo(V)) active center and the number-average molecular weight ( Mn) of the resultant polymer. Among the examined catalysts, tri(nonylphenyl)phosphite (TNPP) ligand and AlOPhCH3( i-Bu)2 as co-catalyst provided the polymer with highest yield (up to 87.1%), metallocene as co-catalyst provided the polymer with highest Mn (up to 5.32 × 105). The effect of [P]/[Mo] molar ratio on catalyst activity of the polymerization was discussed and the structures of Mo·TNPP complexes were preliminarily studied by infrared (IR) and ultraviolet spectroscopies. Besides, the polystyrene (PS) samples synthesized through bulk polymerization and solution polymerization were characterized by gel permeation chromatography, IR, carbon 13 nuclear magnetic resonance, and differential scanning calorimetry, respectively, and the results indicated both of the PS had high molecular weight (approximately 105) and atactic structure. All these results demonstrated that Mo(V) catalyst system was very effective for St polymerization.

Synthesis and characterization of ether-imine-furfural [ONO] nickel(II) complexes and their application in oligomerization of ethylene

A series of new Ni(II) complexes of general formula {NiCl2(L)}2 [Ni1, L=5-methyl-2-(C4H3O-2-CHN)C2H4OPh; Ni2, L=5-Methyl-2-(C4H3O-2-CHN)Ph-2-OPh; Ni3, L=2-(C4H3O-2-CHN)Ph-2-OPh; Ni4, L=5-Methyl-2-(C4H3O-2-CHN)CH2Ph-2-OMe were prepared and characterized by IR spectroscopy, elemental analysis, high-resolution mass spectrometry (HRMS), and X-ray photoelectron spectroscopy (XPS). XPS data suggest no interaction of the pendant ether/furfural donor groups with the nickel metal center. Density functional theory studies indicate the formation of nickel dimeric species with ether-imine-furfural acting as a monodentate ligand. All nickel precatalysts, activated with polymethylaluminoxane-improved performance (PMAO-IP), exhibited moderate to good activities for ethylene oligomerization [TOF=14.7–57.3×103mol(ethylene)mol(Ni)−1h−1] with high selectivities for production of 1-butene (63.2–83.2wt.%). Activation of Ni2 using different types of cocatalysts (PMAO-IP, DMAO, MAO or EASC) led to formation of active oligomerization systems with a significant impact on the activity and selectivity. The use of MAO instead of PMAO-IP gave a slight improvement in the TOF [69.3×103mol(ethylene)mol(Ni)−1h−1] with lower selectivity for 1-butene. Higher activity was obtained using EASC as cocatalyst [206.1×103mol(ethylene)mol(Ni)−1h−1] along with a drastic reduction in the selectivity for 1-butene (10.4wt.%). Under optimized conditions [[Ni]=5μmol, 30°C, oligomerization time=20min, 20bar ethylene, MAO as cocatalyst (500 equiv)], precatalyst Ni2 led to TOF=63.2×103mol(C2H4)·(mol(Ni)−1h−1) and 75.2wt.% selectivity for 1-butene.

아미노-기능화된 실리카 위 후전이 금속 촉매 담지 및 이를 이용한 노보넨 중합

In this study, an amorphous silica was functionalized with aminosilane, N-((3-trimethoxysilyl)propyl)ethylenediamine (2NS) and the late transition metal catalysts including ((DME)NiBr2 and PdCl2(COD)) were subsequently immobilized on the func- tionalized amorphous silica for norbornene polymerization. Effects of the polymerization temperature, polymerization time, Al/Ni molar ratio, and type of co-catalyst on norbornene polymerization were investigated. Unsupported late transition metal catalysts did not show any activities for norbornene polymerization. However, the SiO2/2NS/Ni catayst with MAO system, with increasing polymerization temperature, increased the polymerization activity and decreased the molecular weight of the polynorbornene (PNB). Furthermore, the catalyst when increasing polymerization temperature caused the decrease in both the polymerization activity and molecular weight of PNB. This confirmed that the stability of SiO2/2NS/Ni at a high temperature was greater than that of SiO2/2NS/Pd. Also the longer polymerization time resulted in the higher conversion of norbornene for both catalysts. When the Al : Ni molar ratio was 1000 : 1, the highest activity (15.3 kg-PNB/ (µmol-Ni*hr)) but lowest molecular weight (Mn = 124,000 g/mol) of PNB were achieved. Also SiO2/2NS/Ni catalyst with borate/TEAL resulted in di- minishing the polymerization activity and molecular weight of PNB with increasing the polymerization temperature.

Synthesis and catalytic performance in ethylene and 1-octene polymerization of chlorotitanium(IV) silsesquioxane complexes. Effect of increasing ligand denticity and type of nonreactive organic substituents

The series of titanasilsesquioxanes that differ in a way of binding to the transition metal (via one, two or three oxygen atoms) and type of nonreactive substituents bonded to inorganic oxygen-silicon cage (i-Bu, Ph, c-C6H11) were prepared by reacting of TiCl4 with 1 eqv. of the silsesquioxane ligand. Upon treatment with an appropriate cocatalyst, all titanium precatalysts are active in ethylene and 1-octene polymerization and produce from low to high molecular weight polyethylenes and moderately ([mmmm]=44–74%) isotactic poly(1-octene)s. The influence of polymerization parameters, type of cocatalyst and the silsesquioxane structure on the catalytic behavior of the title titanium silsesquioxane complexes have been investigated.

Effect of electron density on the catalysts for copolymerization of propylene oxide and CO2

Copolymerization of propylene oxide and carbon dioxide (CO2) has been studied using different R-salophenCoOBzF5 (OBzF5 = pentaflorobenzoate, R = CH3, H, Cl, Cl2) based catalysts. The central moiety of the catalysts R-salophenCoOBzF5 has been kept the same and effect of the catalyst electron density on the copolymerization reaction has been studied. It has been observed that introduction of an electron withdrawing group (like Cl, Cl2) on the o-phenylenediamine backbone moiety of the catalyst makes it more selective for poly(propylene carbonate) synthesis. On the other hand, introduction of an electron donating group (like CH3) makes the catalyst selective for cyclic carbonate conversion. The effect of different type of co-catalysts has also been investigated using tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, [PPN]+Cl− ([PPN]+ = bis(triphenylphosphine)iminium), DMAP and tetrabutyl ammonium bromide.

ChemInform Abstract: Photocatalytic and Photoelectrocatalytic Reduction of CO2 Using Heterogeneous Catalysts with Controlled Nanostructures

AbstractReview: [130 refs.

Photocatalytic and photoelectrocatalytic reduction of CO2 using heterogeneous catalysts with controlled nanostructures.

The development of efficient artificial photocatalysts and photoelectrocatalysts for the reduction of CO2 with H2O to fuels and chemicals has attracted much attention in recent years. Although the state-of-the-art for the production of fuels or chemicals from CO2 using solar energy is still far from practical consideration, rich knowledge has been accumulated to understand the key factors that determine the catalytic performances. This Feature article highlights recent advances in the photocatalytic and photoelectrocatalytic reduction of CO2 with H2O using heterogeneous semiconductor-based catalysts. The effects of structural aspects of semiconductors, such as crystalline phases, particle sizes, morphologies, exposed facets and heterojunctions, on their catalytic behaviours are discussed. The roles of different types of cocatalysts and the impact of their nanostructures on surface CO2 chemisorption and reduction are also analysed. The present article aims to provide insights into the rational design of efficient heterogeneous catalysts with controlled nanostructures for the photocatalytic and photoelectrocatalytic reduction of CO2 with H2O.

Highly active and stereospecific polymerization of 1,3-butadiene catalyzed by bis{[2-(4,5-diphenylimidazolyl)phenylimino]phenolate}cobalt(II) complexes

A series of bis{[2-(4,5-diphenylimidazolyl)phenylimino]phenolate}cobalt(II) complexes (C1–C4) has been synthesized and characterized. Single-crystal X-ray analysis demonstrated that the cobalt center was coordinated by two [NNO–] ligands and adopted a slightly distorted octahedronal geometry. The type of cocatalyst had a remarkable influence on the catalytic properties and ethylaluminum sesquichloride (EASC) was proved to be more efficient for the polymerization of 1,3-butadiene to produce higher conversion of butadiene and cis-1,4 content of polybutadienes. On activation with EASC, all the cobalt complexes displayed high catalytic activity for the polymerization of 1,3-butadiene. The microstructure determined by FT-IR and NMR spectra demonstrated that high cis-1,4 contents in the resulting polymers were obtained. The conversion of butadiene, microstructure, molecular weight and molecular weight distribution of polybutadienes were influenced by the reaction parameters and ligand structure.

Nickel complexes incorporating pyrazole-based ligands for ethylene dimerization to 1-butylene

In this study we synthesized and characterized bis(3,5-dimethylpyrazolyl)dimethylsilane (L1) and bis(3,5-dimethylpyrazolyl)phenylphosphine (L2) and then prepared bidentate (NˆN) nickel complexes by reacting L1 or L2 with NiBr2(DME). In combination with methylaluminoxane, diethylchloroaluminum or ethyldichloroaluminum (EADC) as co-catalyst, L1/Ni and L2/Ni complexes exhibited moderate catalytic activities (240–1310 kg/molNi h) and high selectivities (up to 93.2%) for ethylene dimerization toward 1-butylene. The catalytic performance was substantially affected by the co-catalyst type and ligand environment, especially the bridge atom.

Observation on different reducing power of cocatalysts on the Ziegler–Natta catalyst containing alkoxide species for ethylene polymerization

ABSTRACTIn this work, the effects of three types of cocatalyst having different alkyl groups, such as triethylaluminium (TEA), triisobutylaluminum (TiBA), and trioctylaluminium (TnOA), and their concentrations on the catalytic activity and polymer properties were investigated for the Ziegler–Natta catalyst containing alkoxide species. The drastic escalation of catalytic activity was observed when the ratio of Al/Ti was increased only for TEA because of its good diffusivity as proven by the electron spin resonance technique. Moreover, it was found that the characteristic of the alkyl group in cocatalyst affected on the chain transfer ability. The chain transfer ability of TnOA was found to be equal to the TiBA in spite of its concentration was higher. By the way, the cocatalyst types and their concentrations did not affect on the variety of active sites as seen in molecular weight distribution of polymer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40884.

Olefin polymerization and copolymerization by complexes bearing [ONNO]-Type salan ligands: Effect of ligand structure and metal type (titanium, zirconium, and vanadium)

A series of novel titanium(IV) complexes bearing tetradentate [ONNO] salan type ligands: [Ti{2,2′-(OC6H3-5-t-Bu)2-NHRNH}Cl2] (Lig1TiCl2: R = C2H4; Lig2TiCl2: R = C4H8; Lig3TiCl2: R = C6H12) and [Ti{2,2′-(OC6H2-3,5-di-t-Bu)2-NHC6H12NH}Cl2] (Lig4TiCl2) were synthesized and used in the (co)polymerization of olefins. Vanadium and zirconium complexes: [M{2,2′-(OC6H3-3,5-di-t-Bu)2-NHC6H12NH}Cl2] (Lig4VCl2: M = V; Lig4ZrCl2: M = Zr) were also synthesized for comparative investigations. All the complexes turned out active in 1-octene polymerization after activation by MAO and/or Al(i-Bu)3/[Ph3C][B(C6F5)4]. The catalytic performance of titanium complexes was strictly dependent on their structures and it improves for the increasing length of the aliphatic linkage between nitrogen atoms (Lig1TiCl2 << Lig2TiCl2 < Lig3TiCl2) and declines after adding additional tert-Bu group on the aromatic rings (Lig3TiCl2 < Lig4TiCl2). The activity of all titanium complexes in ethylene polymerization was moderate and the properties of polyethylene was dependent on the ligand structure, cocatalyst type, and reaction conditions. The Et2AlCl-activated complexes gave polymers with lover molecular weights and bimodal distribution, whereas ultra-high molecular weight PE (up to 3588 kg mol−1) and narrow MWD was formed for MAO as a cocatalyst. Vanadium complex yielded PE with the highest productivity (1925.3 kg molv−1), with high molecular weight (1986 kg mol−1) and with very narrow molecular weight distribution (1.5). Copolymerization tests showed that titanium complexes yielded ethylene/1-octene copolymers, whereas vanadium catalysts produced product mixtures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2111–2123

Kinetic studies on the pyrrole–Cr-based Chevron-Phillips ethylene trimerization catalyst system

An extensive experimental kinetic study of ethylene trimerization was carried out over the Chevron-Phillips homogeneous catalyst system [Cr(2-ethylhexanoate)3 (Cr(2-EH)3)/2,5-dimethylpyrrole (DMP)/co-catalyst/halide] in terms of the effects from organic halide additives, type of co-catalysts, temperature, ethylene pressure, Cr concentration, and ligand/Cr molar ratio, etc. Ten kinds of organic halides and four kinds of organometallic co-catalysts were tested in this work. The 1,1,2,2-tetrachloroethane (TCE) and triethylaluminum (TEA) were found to be the best candidates for this catalyst system. The molar ratios of DMP/Cr, TCE/Cr and TEA/Cr showed a strong impact on the catalytic performance of ethylene trimerization. A detailed catalytic kinetic behavior and the kinetic simulation were also performed for the first time over this catalyst system. It could be extrapolated that the dependency of the trimerization reaction rate on ethylene concentration and catalyst concentration is second-order and first-order, respectively. The apparent activation energy of this reaction is 99.1kJ/mol at the temperature range from 65°C to 95°C. And the apparent reaction rate equation is achieved as follows:.R=5.23×1018exp−99.1RTCca1.12Ce1.95.

Study of the coordinative nature of alkylaluminum modified Phillips CrO x /SiO2 catalyst by multinucleai solid-state NMR

Solid-state nuclear magnetic resonance spectroscopy was used to investigate the coordinative states of surface Al species on various alkylaluminum-modified Phillips CrOx/SiO2 catalysts. The alkylaluminum-modified Phillips CrOx/SiO2 catalysts were examined via ethylene homopolymerization. 1H and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra clearly demonstrated that the existing states of surface Al species in alkylaluminum-modified catalysts strongly depended on the type of alkylaluminum cocatalyst, concentration of alkylaluminum and the calcination temperature. 1H MAS NMR spectra of alkylaluminum-modified Phillips CrOx/SiO2 catalysts, calcined at two different temperatures, exhibited similar trends in peak shift. 1H spectra showed that with an increase of Al/Cr ratio and calcination temperature, the main peak shifted to high field, indicating that the dominant surface proton species changed from hydroxyl to ethoxyl and ethyl groups. 27Al MAS NMR spectra showed the presence of three different coordination states (6-, 5-, and 4-coordinated Al species) in the alkylaluminum-modified Phillips catalysts. In comparison of different alkylaluminum cocatalysts, it was found that the reactivity of alkylaluminum modified Phillips catalyst decreased in the order of TEA>DEAH>DEAE. The amount of 4-coordinated Al species of Phillips catalysts modified by TEA, DEAE and DEAH also decreased in the order of TEA>DEAH>DEAE, indicating that the presence of 4-coordinated Al species is related to the polymerization activity.

Polymerization of 1,3-butadiene catalyzed by ion-pair cobalt complexes with (benzimidazolyl)pyridine alcohol ligands

A series of ion-pair cobalt complexes (C1–C6) supported by (benzimidazolyl)pyridine alcohol ligands ([NNO]) were synthesized and characterized. The single-crystal X-ray diffraction demonstrated that the ion-pair cobalt complexes formed, consisting of [CoL2]2+ and [CoCl4]2−, in which the cobalt center was surrounded by two [NNO] ligands and adopted distorted octahedronal geometry in the cationic moiety along with [CoCl4]2− as the counterion. The type of cocatalyst had a remarkable influence on the catalytic properties and ethylaluminum sesquichloride (EASC) was proved to be the most efficient cocatalyst for the polymerization of 1,3-butadiene to produce high conversion of butadiene and high cis-1,4 content in the resulting polymers. Upon activation with EASC, all the cobalt complexes (C1–C6) displayed high catalytic activity for the polymerization of 1,3-butadiene to yield cis-1,4-polybutadiene with high selectivity (>95%) under the Al/Cat molar ratio of 50 at 30°C. The conversion of butadiene, microstructure and properties of the resulting polymers were also affected by the reaction parameters and ligand structure.

Influence of the aluminum alkyl co-catalyst type in Ziegler-Natta ethene polymerization on the formation of active sites, polymerization rate, and molecular weight

The influence of the concentration of the co-catalysts triethylaluminium (TEAL), tri-iso-butylaluminium (TIBAL), tri-n-octylaluminium on the polymerization rate for standard Ziegler-Natta catalyst systems was studied. By comparing the influence of monomeric TIBAL with TEAL co-catalyst on the polymerization activity, the effect of TEAL dimerization was described. The use of the Eley-Ridealadsorption model instead of Langmuir-Hinselwood model is proposed for the absorption of monomeric aluminiumalkyl species and for the formation of active centers C*. It is further proposed that steric hindrance from different co-catalysts, which results in a higher molecular weight (MW) of polymers, is caused by active centers with reduced space for chain transfer reactions.

Stereospecific polymerization of 1,3-butadiene catalyzed by cobalt complexes bearing N-containing diphosphine PNP ligands

A series of cobalt complexes bearing N-containing diphosphine PNP ligands has been synthesized and characterized. The nature of the ligand structure affects the binding of the ligand to the cobalt center and determines the coordination geometry of the cobalt complexes. All the complexes have been employed to catalyze the polymerization of 1,3-butadiene, in combination with methylaluminoxane (MAO) or ethylaluminum sesquichloride (EASC) as the cocatalyst. Both the nature of the ligand and the type of cocatalyst had a remarkable influence on the polymerization activity, microstructure and molecular weight of the resulting polymers. The [Co]/MAO catalytic systems resulted in relatively lower conversions of butadiene and cis-1,4 contents in the polymers than the corresponding [Co]/EASC catalytic systems. Upon activation with EASC, the polymerization behaviors of the catalytic systems were also affected by the reaction parameters.

Semi-aromatic polyesters by alternating ring-opening copolymerisation of styrene oxide and anhydrides

Ring-opening copolymerisation of styrene oxide with alicyclic anhydrides containing different ring strains (succinic anhydride, maleic anhydride, citraconic anhydride, cyclopropane-1,2-dicarboxylic acid anhydride, cyclopentane-1,2-dicarboxylic acid anhydride and phthalic anhydride) was performed applying metal salen and tetraphenyl porphyrin complexes where for (salen)MX, M = Cr, X = Cl (1), M = Al, X = Cl (2), M = Mn, X = Cl (3), M = Co, X = OAc (4) and salen = N,N-bis(3,5-di-tert-butylsalicylidene)-diimine and for porphyrin complex, M = Cr, X = Cl (5), M = Mn, X = Cl (6), M = Co, X = OAc (7). The chromium catalysts performed best and therefore 1 was chosen as the selected catalyst for further studies. Investigation of the effect of different cocatalysts on the copolymerisation of styrene oxide and phthalic anhydride revealed that phosphines and onium salt showed quite similar activities whereas N-heterocyclic based amines showed somewhat lower activity. 1H NMR and MALDI-ToF-MS spectra of the copolymers formed confirmed the alternating microstructures. Increasing the monomer to catalyst ratio resulted in the isomerisation of styrene oxide to phenyl ethanal. The aldehyde functions as a chain transfer agent influencing the molecular weight of the polymers. Copolymerisation of styrene oxide with anhydrides bearing a double bond in their structure, such as maleic anhydride and citraconic anhydride, was shown to be highly dependent on temperature, time, type of cocatalyst and solvent used in the copolymerisation reaction.

A highly active Zn(salphen) catalyst for production of organic carbonates in a green CO2 medium

Zn(salphen), in combination with Bu4NI, was studied as a binary catalyst system for CO2-fixation in the context of organic carbonate formation. The catalytic potential of this binary catalyst system was considerably improved by working in a solvent-free, CO2-rich environment, thereby increasing the overall contact between the reagents and catalyst. Under these green conditions, excellent conversion and selectivity towards the cyclic carbonate product were obtained with epoxides that are generally less prone to undergo cycloaddition with carbon dioxide. The effect of the reaction conditions and the type of co-catalyst employed together with Zn(salphen) were systematically investigated and optimised.

Control of morphology in olefin polymerization catalyzed by nickel diimine complexes encapsulated into polybutadiene based support

A commercially available hydroxyl terminated low molecular cis-1,4-polybutadiene was modified by carboxylic functions and used as an effective support in single-site α-olefin polymerization. Dynamic light scattering analysis of support solution in heptane confirmed increased ability to self-assembly of modified polybutadienes in the presence of methylaluminoxane cocatalyst (MAO). α-Diimine nickel and bis(indenyl)zirconium dichloride catalysts activated by trimethylaluminium or MAO cocatalysts were encapsulated into polymer micellar aggregates and used for ethylene and octadec-1-ene polymerization. Furthermore, the effects of cocatalyst type and concentration on the micelle-formation process, activity and morphology of polyethylene (polyoctadec-1-ene) particles were investigated. In the presence of polybutadiene supports, formation of spherical micrometric PE beads was observed during MAO cocatalyzed ethylene polymerization, whereas the activity of polymerization was not decreased.

Polymerization of higher α-olefins with the catalytic system (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-bis(perfluorophenyldimethanolate) titanium(IV) dichloride-organoaluminum compound

The catalytic activity of the titanium(IV) dichloride complex with the (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-bis(perfluorophenyldimethanol) ligand in the presence of a cocatalyst (polymethylaluminoxane, triethylaluminum, or triisobutylaluminum) in the polymerization of higher α-olefins (1-hexene, 1-octene, 1-decene) is investigated. It is shown that, depending on the types of cocatalyst and monomer and the molar ratio of components of the catalytic system, high- or ultrahigh-molecular-mass poly(α-olefins) with Mw = (4 × 105)−(3 × 106) can be prepared. The chain microstructure of polyhexene is examined.