Al Cocatalyst Research Articles

Solution XAS Analysis for Reactions of Phenoxide-Modified (Arylimido)vanadium(V) Dichloride and (Oxo)vanadium(V) Complexes with Al Alkyls: Effect of Al Cocatalyst in Ethylene (Co)polymerization

V K-edge XANES (XANES = X-ray Absorption Near Edge Structure) spectra of the reaction solution of V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3) with halogenated Al alkyls (Me2AlCl, Et2AlCl, EtAlCl2, 50 equiv) in toluene showed low energy shifts (2.6–3.6 eV on the basis of inflection point in the photon energy) in the edge absorption accompanying slight shift to low photon energy in the pre-edge peak (λmax values); a similar spectrum was observed when the reaction of 1 with Me2AlCl was conducted in n-hexane. These results strongly suggest a formation of similar vanadium(III) species irrespective of kind of Al alkyls and solvent (toluene or n-hexane). Significant low-energy shifts in the edge absorption accompanied with diminishing the strong pre-edge absorption were also observed when VOCl3 or VO(OiPr)3 was treated with Me2AlCl (10 equiv) in toluene, clearly indicating a formation of low oxidation state vanadium species accompanied with certain structural changes (from tetrahedral to octahedral) in solution.

Biogas Reforming over Al-Co Catalyst Prepared by Solution Combustion Synthesis Method

The results of carbon dioxide reforming of CH4 (model biogas) on catalysts prepared by solution combustion synthesis (SCS) and impregnation of moisture capacity methods are presented. Investigation of the activity of catalysts synthesized from initial mixtures of Co(NO3)2-Al(NO3)3-urea of different compositions was carried out for the production of synthesis-gas, and SCS and traditional incipient wetness impregnation catalyst preparation methods were compared. The methane conversion reached 100%, and the conversion of CO2 increased to 86.2%, while the yield of H2 and CO was 99.2% and 85.4%, respectively, at 900 °C. It was found that CoAl2O4 spinel formation was due to substitution of Al3+ with Co2+ cations. Consequently, CoAl2O4 lattice parameters increased, since the ionic radius of Al3+ (0.51 Å) less than Cο2+ (0.72 Å). Advantages of SCS catalysts in comparison with catalysts prepared by the traditional incipient wetness impregnation method in dry reforming of methane were shown. The aim of this work is to develop a new catalyst for the conversion of model biogas into synthesis gas, which will contribute to the organization of a new environmentally friendly, energy-saving production in the future.

Highly 2,3-selective polymerization of phenylallene and its derivatives by vanadium complexes

Allene polymerizations by vanadium complexes using various Al co-catalysts were carried out. All the vanadium complexes show moderate activity for phenylallene and high 2,3-selectivity (>99%).

Solution X-Ray Absorption Spectroscopy (XAS) for Analysis of Catalytically Active Species in Reactions with Ethylene by Homogeneous (Imido)vanadium(V) Complexes—Al Cocatalyst Systems

Solution V K-edge XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) analysis of vanadium(V) complexes containing both imido ligands and anionic ancillary donor ligands (L) of type, V(NR)(L)X2 (R = Ar, Ad (1-adamantyl); Ar = 2,6-Me2C6H3; X = Cl, Me, L = 2-(ArNCH2)C5H4N, OAr, WCA-NHC, and 2-(2’-benzimidazolyl)pyridine; WCA-NHC = anionic NHCs containing weak coordinating B(C6F5)3), which catalyze ethylene dimerization and/or polymerization in the presence of Al cocatalysts, has been explored. Different catalytically actives species with different oxidation states were formed depending upon the Al cocatalyst (MAO, Me2AlCl, AliBu3, etc.) and the anionic ancillary donor ligand employed. The method is useful for obtainment of the direct information of the active species (oxidation state, basic framework around the centered metal) in solution, and for better understanding in catalysis mechanism and organometallic as well as coordination chemistry.

Synthesis of Ultrahigh Molecular Weight Polymers with Low PDIs by Polymerizations of 1-Decene, 1-Dodecene, and 1-Tetradecene by Cp*TiMe2(O-2,6-iPr2C6H3)⁻Borate Catalyst.

Polymerizations of 1-decene (DC), 1-dodecene (DD), and 1-tetradecene (TD) by Cp*TiMe2(O-2,6-iPr2C6H3) (1)–[Ph3C][B(C6F5)4] (borate) catalyst have been explored in the presence of Al cocatalyst. The polymerizations of DC and DD, in n-hexane containing a mixture of AliBu3 and Al(n-C8H17)3, proceeded with high catalytic activities in a quasi-living manner, affording high molecular weight polymers (activity 4120–5860 kg-poly(DC)/mol-Ti·h, Mn for poly(DC) = 7.04–7.82 × 105, after 20 min at −30 °C). The PDI (Mw/Mn) values in the resultant polymers decreased upon increasing the ratio of Al(n-C8H17)3/AliBu3 with decreasing the activities at −30 °C. The PDI values also became low when these polymerizations were conducted at low temperatures (−40 or −50 °C); high molecular weight poly(DD) with low PDI (Mn = 5.26 × 105, Mw/Mn = 1.16) was obtained at −50 °C. The TD polymerization using 1–borate–AliBu3 catalyst (conducted in n-hexane at −30 °C) afforded ultrahigh molecular weight poly(TD) (Mn = 1.02 × 106, Mw/Mn = 1.38), and the PDI values also decreased with increasing the Al(n-C8H17)3/AliBu3 ratio.

Effect of Al Cocatalyst in Ethylene and Ethylene/Norbornene (Co)polymerization by (Imido)vanadium Dichloride Complexes Containing Anionic <i>N</i>-Heterocyclic Carbenes Having Weakly Coordinating Borate Moiety

Effect of Al cocatalyst in ethylene polymerization using (imido)vanadium(V) complexes containing anionic N-heterocyclic carbenes with a weakly coordinating borate moiety in 4-position (WCA-NHC), [V(N-2,6-Me2C6H3)Cl2(WCA-NHC)] [1; NHC=1,3-bis(2,6-dimethylphenyl)-imidazolin-2-ylidene], have been explored. The activities by 1 upon presence of AliBu3 in ethylene polymerization and in the copolymerization with norbornene (NBE) were higher than those in the presence of MAO, and the resultant poly(ethylene-co-NBE)s prepared by 1-AliBu3 catalyst possessed uniform molecular weight distributions and compositions. Formation of vanadium(III) species could be assumed upon presence of AliBu3, especially on the basis of both NMR and ESR spectra (silent) and certain significant changes in the V K-edge XANES (pre-edge and edge region) spectrum, whereas no significant changes in the XANES spectrum were observed from the toluene solution containing 1 upon addition of MAO. It is thus suggested that a difference in the catalyst performances between in the presence of MAO and AliBu3 should be due to a formation of different catalytically active species with different oxidation states.

Theoretical investigation of the mechanism of ethylene polymerization with salicylaldiminato vanadium(III) complexes

The use of vanadium-based catalysts allows the preparation of high molecular mass polymers with uniform molecular mass distributions, polypropylene and ethylene/α-olefin copolymers with high α-olefin incorporation. However, the design of ligand systems with vanadium catalysts would face difficulties, because it is difficult to experimentally determine the structures of the active species of vanadium catalysts. In this paper, possible structural candidates for the active species in ethylene polymerization catalyzed by the salicylaldiminato vanadium complex combined with AlEt2Cl were investigated using density functional theory. By comparing theoretical simulation results with previous experimental investigations, especially regarding the crucial role of the diethyaluminum chloride (AlEt2Cl) cocatalyst, it was concluded that a neutral bimetallic species containing two Al–Cl–V bridging bonds is the most favorable structure model for the active vanadium species. A notable effect of Al co-catalysts was clarified in the theoretical investigation. During the formation of the active species, AlEt2Cl act as an assistant for the alkylation and alkyl abstract processes of precursors. More importantly, AlEt2Cl is necessary for the formation of the bis(chlorine-bridged) structure in the active species, which showed a notable effect on the structural stability of the active species and its catalytic activity. Additionally, we investigated the chain termination mechanism in this system.

Ethylene Polymerization Using (Imino)vanadium(V) Dichloride Complexes Containing (Anilido)methyl-pyridine, -quinoline Ligands–Halogenated Al Alkyls Catalyst Systems

The effect of ligand and Al cocatalysts in ethylene polymerization, using V(N-1-adamantyl)Cl2(L) [L = 2-(2,6-Me2C6H3)NCH2(C9H6N), 8-(2,6-Me2C6H3)NCH2(C9H6N)] and V(N-2-MeC6H3)Cl2[2-(2,6-R'2C6H3)NCH2(C5H4N)] (R' = Me, iPr), has been explored. The reaction products in the presence of Et2AlCl or Me2AlCl cocatalyst were polyethylene whereas the reaction product of the 2-methylphenylimido analogues in the presence of MAO cocatalyst was 1-butene with high selectivity, suggesting that the catalyst/cocatalyst nuclearity effect plays a role in this catalysis.

Effect of Cocatalyst in Ethylene/Styrene Copolymerization by Aryloxo‐Modified Half‐Titanocene–Cocatalyst Systems for Exclusive Synthesis of Copolymers at High Styrene Concentrations

AbstractFactors affecting the product distributions in ethylene/styrene copolymerizations catalyzed by Cp*TiCl2(O‐2,6‐iPr2C6H3) are explored in the presence of various cocatalysts at high styrene/ethylene feed ratios (at 40 and 55 °C). Ethylene/styrene copolymers were the sole product when the reactions were conducted in the presence of [PhN(H)Me2][B(C6F5)4] and AliBu3/Al(octyl)3 even at 55 and 70 °C, whereas syndiotactic polystyrene was by‐produced when the polymerizations were performed at >40 °C in the presence of MAO; the ratios of the copolymer/SPS were affected by the reaction temperature as well as Al cocatalyst employed.magnified image

(Imido)vanadium Complexes as Efficient Catalyst Precursors for Olefin Polymerization/Oligomerization

(Arylimido)vanadium(V) complexes containing anionic ancillary donor ligands of type, V(NAr)Cl2(L) (Ar = 2,6-Me2C6H3, L = aryloxo, ketimide phenoxyimine, etc.) exhibited high catalytic activities for ethylene polymerization in the presence of Al cocatalyst; V(NAr)Cl2(O-2,6-Me2C6H3) showed the exceptionally high activities in the presence of halogenated Al alkyls such as Et2AlCl, EtAlCl2, etc. (Arylimido)vanadium(V)-alkylidene complexes, V(CHSiMe3)(NAr)(L′) (L′ = N=C t Bu2, O-2,6- i Pr2C6H3) exhibited the remarkable catalytic activities for ring-opening metathesis polymerization of norbornene. (Imido)vanadium(V) complexes containing the (2-anilidomethyl)pyridine ligand, V(NR)Cl2[2-Ar′NCH2(C5H4N)] (R = 1-adamantyl, cyclohexyl, phenyl, Ar′ = 2,6-Me2C6H3, 2,6- i Pr2C6H3), exhibit the remarkable activities for ethylene dimerization in the presence of MAO, affording 1-butene exclusively (selectivity 90.4 to >99%). The steric bulk of the imido ligand plays an important role in the selectivity, and the electronic nature directly affects the activity.

Synthesis of (Arylimido)vanadium(V) Complexes Containing (2-Anilidomethyl)pyridine Ligands and Their Use as the Catalyst Precursors for Olefin Polymerization

A series of (arylimido)vanadium(V) dichloride complexes containing (2-anilidomethyl)pyridine ligands of the type V(NAr)Cl2[2-Ar′NCH2(C5H4N)] [Ar = 2,6-Me2C6H3; Ar′ = 2,6-Me2C6H3 (1a), 2,6-iPr2C6H3 (1b), 2,6-F2C6H3 (1c)] have been prepared from V(NAr)Cl3 by treating with Li[2-Ar′NCH2(C5H4N)], and the structures of 1b,c have been determined by X-ray crystallography. These complexes are effective catalyst precursors for ethylene polymerization in the presence of Al cocatalysts: 1b showed the highest catalytic activities in the presence of Et2AlCl (6000 kg PE/mol V·h), and the observed activities of 1a,b in the presence of Et2AlCl were much higher than those in the presence of MAO. V(NAr)(CH2SiMe3)2[2-Ar′NCH2(C5H4N)] (2a,b) have been prepared by treating 1a,b with 2.0 equiv of LiCH2SiMe3, and their structures have been determined by X-ray crystallography. The dialkyl complex 2b cleanly reacted with 2.0 equiv of (CF3)2CHOH in C6D6 at 25 °C to afford V(NAr)(CH2SiMe3)[OCH(CF3)2][2-Ar′NCH2(C5H4N)] (3), and the reaction with 3.0 equiv of (CF3)2CHOH eventually afforded V(NAr)[OCH(CF3)2]2[2-Ar′NCH2(C5H4N)] (4) from 3 after 3 days. The dialkyl complexes 2a,b showed catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene in benzene at 80 °C in the presence of PMe3. The ROMP did not occur in the absence of PMe3 under the same conditions, suggesting that an additional coordination of PMe3 may be required to induce the α-hydrogen elimination.

A comparative study of SiO2- and ZrO2-supported zirconocene/MAO catalysts on ethylene/1-olefin copolymerization

In this present study, the use of silica and zirconia as a support for zirconocene/MAO catalyst for copolymerization of ethylene/1-olefin (1-hexene, 1-octene, and 1-decene) was investigated. First, MAO as the cocatalyst was impregnated onto the support. Then, copolymerization of ethylene/1-olefin was performed. It was found that the use of zirconia support showed promising activities compared to those of the silica. Increased activities can be attributed to higher amount of [Al] MAO present on the zirconia support coupled with strong interaction between the O support –Al cocatalyst linkage. In addition, the use of zirconia also resulted in higher degree of 1-olefin insertion and decreased T m of copolymers produced.

Notable Effects of Aluminum Alkyls and Solvents for Highly Efficient Ethylene (Co)polymerizations Catalyzed by (Arylimido)- (aryloxo)vanadium Complexes

The effects of both Al cocatalyst and solvent on catalytic activity in the ethylene polymerization by the (arylmido)(aryloxo)vanadium(V) complex, VCl2(N-2,6-Me 2 C 6 H 3 )(O-2,6-Me 2 C 6 H 3 ) (1), have been explored in detail. The activity of 5.84 × 10 5 kgPE/molV-h (TOF 2.08 × 10 7 h -1 ) has been achieved by 1/EtAlCl 2 catalyst in CH 2 Cl 2 at 0°C, and the activity in toluene increased in the order: i-Bu 2 AlCl > EtAlCl 2 > Me 2 AlCl > Et 2 AlCl > Et 2 Al(OEt), AlEt 3 , AlMe 3 (negligible activities). Both aluminum alkyl cocatalyst and solvent also affected the catalytic activity and the norbornene (NBE) incorporation in the ethylene/NBE copolymerization using complex 1, whereas the NBE contents were not strongly affected by the kind of aryl oxide ligand in VCl2(N-2,6-Me 2 C 6 H 3 )(OAr) [OAr=O-2,6-Me 2 C 6 H 3 (1), O-2,6-i-Pr 2 C 6 H 3 (2), O-2,6-Ph 2 C 6 H 3 (3)].

Remarkable Effects of Aluminum Cocatalyst and Comonomer in Ethylene Copolymerizations Catalyzed by (Arylimido)(aryloxo)vanadium Complexes: Efficient Synthesis of High Molecular Weight Ethylene/Norbornene Copolymer

Copolymerizations of ethylene with norbornene (NBE), cyclopentene (CPE) and 1-hexene by (arylimido)(aryloxo)vanadium(V) complexes of the type VCl2(N-2,6-Me2C6H3)(OAr) [Ar = 2,6-Me2C6H3 (1), 2,6-iPr2C6H3 (2), 2,6-Ph2C6H3 (3)] with cocatalyst [methylaluminoxane (MAO) or Et2AlCl] catalyst systems have been explored. These complexes exhibited remarkable catalytic activities for ethylene polymerization in the presence of Et2AlCl cocatalyst; in particular, the resultant polyethylene prepared by 1 possessed narrow molecular weight distributions and the Mn value increased linearly upon increasing the polymer yields (TON values). Notable effects of Al cocatalyst have been observed in the copolymerization of ethylene with NBE: the catalytic activities, the NBE incorporation, dominant chain transfer reactions, and the Mn values for resultant copolymers were highly dependent upon the Al cocatalyst employed (MAO or Et2AlCl). The 1−Et2AlCl catalyst system exhibited remarkable catalytic activities, affording ultrahigh ...

Vanadium-Catalyzed Ethylene−Propylene Copolymerization: The Question of the Metal Oxidation State in Ziegler−Natta Polymerization Promoted by (β-diketonate)3V

Four different (β-diketonate)3V complexes [β-diketonate = 2,4-pentanedione (acac), 2-acetylcyclohexanone (Cy-acac), 2,2,6,6-tetramethyl-3,5-heptanedione (t-Bu-acac), and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (F-acac)] have been prepared and tested as catalysts for propylene−ethylene copolymerization with the aim of gaining insights into the structure of the active species. Data on polymer composition and catalyst activity indicate that one of the roles of the Al cocatalyst is to trigger a major ligand scrambling around the transition metal. Attempts to isolate the catalytically active species afforded a compound formulated as {[(β-diketonate)AlCl2][VCl2][(β-diketonate)2AlCl]}. This species, which displayed only a minor catalytic activity, arises from a parasite process (catalyst deactivation). The formulation was supported by chemical degradation experiments with THF, which afforded a mixture of [V2Cl3(THF)6][AlCl4] and [(acac)2Al(THF)2][Al Cl4] (5). Two unprecedented V(II) complexes (R-acac)2V(TMEDA) [...

Study on the enantioselective oligomerization of 1‐butene by chiral non‐racemic Ti complexes fixed on MgCl2

AbstractA number of chiral non‐racemic titanium complexes of the type (R*O)2TiCl2 (R* being an enantiomerically pure monosaccharide derivative) was incorporated in a MgCl2 matrix by coprecipitation from a non‐solvated n/iso‐Bu2Mg solution with CCl4. The precatalysts formed were activated with different organoaluminium cocatalysts and used for the oligomerization of 1‐butene. In dependence of the cocatalyst and the temperature various reaction pathways were observed. In most cases saturated oligomers were isolated. At −20°C with i‐Bu3Al2OBuCl2 as cocatalyst 55–65% olefinic oligomers with 50–70% enantiomeric excess (ee) are formed. If the growing chain is terminated by chain transfer to the Al cocatalyst, epimerization of the last inserted monomer occurs, possibly due to a rearrangement which might be favoured by an agostic interaction. The fixation of TiCl4 to a chiral modified MgCl2 support does not lead to enantiomerically enriched oligomers under the same reaction conditions.

Cationic metal alkyl olefin polymerization catalysts

This article reviews recent progress and current work in the area of isolation and characterization of Cp2Zr(R)+ complexes in the absence of Al co-catalysts.