Amount Of Cocatalyst Research Articles

Chemical CO2 fixation using a cyanido bridged heterometallic Zn(II)-Mn(II) 2D coordination polymer.

A new cyanido bridged Zn(II)-Mn(II) mixed-metal coordination polymer, {[Zn(μ-L)(μ-CN)2Mn0.5]·(CH3OH)}n (1), has been synthesized by the reaction of Zn(CN)2, Mn(II) salts and a hydrazone ligand (HL = (E)-N'-(phenyl(pyridin-2-yl)methylene)isonicotinohydrazide) in methanol. Compound 1 was characterized using various analytical methods (including elemental analysis, photoluminescence, FT-IR, XRD, SEM, and EDX analyses, and TGA), and its structure was determined by X-ray analysis. These analyses confirmed the formation of a mixed metal Zn(II)-Mn(II) coordination polymer containing both cyanide and hydrazone bridging ligands. This mixed metal coordination polymer exhibits interesting emission spectra by having several emissions via excitation at 230, 270, 375 and 385 nm. The catalytic activity of compound 1 in chemical CO2 fixation was investigated in the presence of epoxides, and the effects of various parameters on its catalytic performance were evaluated. The results of catalytic studies show that compound 1 can efficiently catalyze the chemical CO2 fixation reaction under mild conditions. The amount of co-catalyst, temperature of the reaction, nature of the solvent and also the substituent connected to the epoxide ring are some of the important parameters that have considerable effects on the catalytic activity of 1.

Deciphering charge transfer dynamics of a lead halide perovskite-nickel(ii) complex for visible light photoredox C-N coupling.

Photoredox catalysis involving perovskite quantum dots (QDs) has gained enormous attention because of their high efficiency and selectivity. In this study, we have demonstrated CsPbBr3 QDs as photocatalysts for the C-N bond formation reaction. The introduction of Ni(dmgH)2 (dmgH = dimethyl glyoximato) as a cocatalyst with CsPbBr3 QDs facilitates photocatalytic C-N coupling to form a wide variety of amides. The optimized interaction between the cocatalyst and photocatalyst enhances charge transfer and mitigates charge recombination, ultimately boosting photocatalytic performance. The photocatalytic activity is notably influenced by the variation in the amount of cocatalyst and 7 wt% Ni(dmgH)2 produces the best yield (92%) of amide. Femtosecond transient absorption spectroscopy reveals that the dynamics of the trap states of QDs are affected by cocatalyst. Further, Ni(dmgH)2 facilitates molecular oxygen activation to form superoxide radicals, which further initiates the radical pathway for the C-N coupling.

Single-atom Pt anchored thiophene ring doped carbon nitride nanosheets for enhanced visible-light photocatalytic H2 evolution and ciprofloxacin degradation

A small amount of cocatalysts often play a crucial role in polymerization semiconductor photocatalytic reactions, and precious metals, like Pt, remain irreplaceable as cocatalysts in most applications due to their excellent properties. Meanwhile, maximizing the atomic utilization of cocatalysts and enhancing the host-guest interactions are important routes to enhance photocatalytic efficiency. Single Pt atoms anchored thiophene ring-doped carbon nitride nanosheets (Ptx-CNA) by a facile incipient wetness impregnation were successfully synthesized in this work. Single-atom Pt are uniformly embedded in CNA nanosheets through Pt–N coordination bonds. Coordinated electron-rich thiophene ring-doping and single-atom Pt modifications promote wider visible light response, enhanced charge response, and fast transport capability in Pt-CNA materials. Pt1.0-CNA sample displays the most outstanding photocatalytic H2 evolution rate (360.0 μmol h−1), which is nearly 5 times that of Pt1.0-CN (70.5 μmol h−1). Excellent photocatalytic degradation performance of ciprofloxacin is also achieved and the degradation rate constant of Pt1.0-CNA is 1.8 times that of CNA. Molecular modifications and single-atom cocatalytic together significantly improve the photocatalytic efficiency of polymer semiconductors.

Implanting nitrogen-doped graphene quantum dots on porous ultrathin carbon nitride for efficient metal-free photocatalytic hydrogen evolution

Mimicking natural photosynthesis to make solar power into hydrogen energy is widely perceived as a promising and sustainable way to alleviate the energy crisis and environmental pollution. However, adding metallic cocatalysts and even noble metal cocatalysts into carbon nitride-based photocatalysts still seriously restrict the practical development of photocatalytic water splitting. To address these issues, we carefully design and construct a metal-free photocatalytic system through grafting 0D nitrogen-doped graphene quantum dots (N-GQDs) on 2D porous ultrathin carbon nitride (PUCN). The incorporated N-GQDs can act as electron collectors to promote the charge separation/transfer on PUCN, and also can extend the photoabsorption region of PUCN. Thus, the metal-free N-GQDs/PUCN photocatalyst exhibits a drastically enhanced hydrogen production rate of 1248 μmol g−1 h−1, which fetches up to about 208 times as high as that of PUCN (6 μmol g−1 h−1). Notably, the photocatalytic performance of N-GQDs/PUCN is close to that of Pt/PUCN with the same cocatalyst amount (1706 μmol g−1 h−1), and metal-free N-GQDs/PUCN photocatalyst outperforms most of the reported carbon nitride-based photocatalysts with metallic cocatalysts for photocatalytic water splitting. This work offers new insight to construct metal-free carbon nitride-based photocatalysts, which will be beneficial for the practical development of photocatalytic water splitting.

Nonredox CO2 Fixation in Solvent-Free Conditions Using a Lewis Acid Metal-Organic Framework Constructed from a Sustainably Sourced Ligand.

CO2 epoxidation to cyclic carbonates under mild, solvent-free conditions is a promising pathway toward sustainable CO2 utilization. Metal-organic frameworks (MOFs) explored for such applications so far are commonly composed of nonrenewable ligands such as benzene dicarboxylate (BDC) or synthetically complex linkers and therefore are not suitable for commercial utilization. Here, we report new yttrium 2,5-furandicarboxylate (FDC)-based MOFs: "UOW-1" and "UOW-2" synthesized via solvothermal assembly, with the former having a unique structural topology. The FDC linker can be derived from biomass and is a green and sustainable alternative to conventionally used BDC ligands, which are sourced exclusively from fossil fuels. UOW-1, owing to unique coordination unsaturation and a high density of Lewis active sites, promotes a high catalytic activity (∼100% conversion; ∼99% selectivity), a high turnover frequency (70 h-1), and favorable first-order kinetics for CO2 epoxidation reactions using an epichlorohydrin model substrate under solvent-free conditions within 6 h and a minimal cocatalyst amount. A systematic catalytic study was carried out by broadening the epoxide substrate scope to determine the influence of electronic and steric factors on CO2 epoxidation. Accordingly, higher conversion efficiencies were observed for substrates with high electrophilicity on the carbon center and minimal steric bulk. The work presents the first demonstration of sustainable FDC-based MOFs used for efficient CO2 utilization.

Imine‐linked covalent organic frameworks coordinated with nickel for ethylene oligomerization

AbstractThe functionalized covalent organic framework materials play an important role in catalytic application. A convenient tactic is developed to design and synthesize an imine‐linked covalent organic frameworks (COFs) material (COF‐PD) with abundant nitrogen atoms, which can provide coordination active site and facilitate the incorporation of COFs with nickel ions. Nickel‐coordinated COF‐PD complex (COF‐PD‐Ni) is prepared and used in ethylene oligomerization. COF‐PD‐Ni displays the highest catalytic activity of 1.98 × 105 g/(mol·Ni·h) in ethylene oligomerization with MAO as co‐catalyst and cyclohexane as solvent. Various reaction parameters including reaction temperature, time, solvent, and the amount of cocatalyst are evaluated in detail, dramatically impacting the catalytic activities as well as the distribution of the products. What is more, the effect of COFs structure on the catalytic performance is also studied, suggesting more coordination sites were more important for high activity.

Hierarchical NiCo2S4/ZnIn2S4 heterostructured prisms: High-efficient photocatalysts for hydrogen production under visible-light

Exploring low-cost co-catalyst to ameliorate the photocatalytic activity of semiconductors sets a clear direction for solving energy crisis and achieving efficient solar-chemical energy conversion. In this work, a unique hierarchical hollow heterojunction was constructed by in-situ growing ZnIn2S4 nanosheets on the porous NiCo2S4 hollow prisms through a low temperature solvothermal method, in which NiCo2S4 with semi-metal property acted as non-noble metal co-catalyst. NiCo2S4 co-catalyst was innovatively encapsulated in ZnIn2S4, which not only relieved the light shielding effect caused by the large loading amount of co-catalyst, but also supplied abundant active sites for H2 evolution. The hierarchical hollow heterostructure of NiCo2S4/ZnIn2S4 provided a highly efficient channel for charge transfer. Combining these advantages, NiCo2S4/ZnIn2S4 composite demonstrated excellent photocatalytic activity. In the absence of sacrificial agent, the NiCo2S4/ZnIn2S4 photocatalyst achieved a remarkable improved H2 yield of 0.77 mmol g−1h−1 under visible light irradiation (λ > 400 nm), which is 6.6 times greater than that of ZnIn2S4. Besides, NiCo2S4 even exhibited better performance on the H2 evolution improvement of ZnIn2S4 than precious metal Pt. This work will offer novel insights into the reasonable design of non-noble metal photocatalysts with respectable activity for water splitting.

Ring‐Opening Copolymerization of Cyclic Anhydrides and Epoxides by bis(amidinate)tin(II) Complex via Binary Catalyst System

AbstractBis(amidinate) tin(II) complex (1) was reported as active catalyst for ring‐opening copolymerization of cyclic anhydrides and epoxides via a binary catalyst system. Polymerizations of six combinations of epoxides and cyclic anhydrides were carried out giving highly alternating poly(anhydride‐alt‐epoxide) with narrow dispersities, except for cyclohexene oxide where significant amount of ether linkage up to 62 % was observed. This ether linkages could be diminished by increasing the amount of cocatalyst to over 3 equiv. Six well‐known cocatalysts were screened where PPNCl was found to be the best cocatalyst.

Virtuous utilization of biochar and carbon dioxide in the thermochemical process of dairy cattle manure

The huge generation of livestock manures has been raised due to the dramatically increasing protein demand. In this study, dairy cattle manure (DCM) was valorized through a pyrolysis platform using CO2 as a co-feedstock, suggesting the conversion of manure to value-added chemicals in a sustainable and renewable way. This work demonstrated that biocrude derived from DCM involves high contents of N-containing hetero-hydrocarbons and aromatic compounds. Because they are not desirable chemicals to be used as fuels due to the challenges during combustion processes, they were further transformed into syngas. CO2 and DCM-derived biochar signified the conversion of biocrude into syngas at ≤ 600 °C, where no gasification reaction works. The gas phase reactions of CO2 with gas phase biocrude led to enhanced CO formation. In addition, alkaline metal(oxide)s in biochar promoted gas phase reactions and chemical bond scissions of biocrude, resulting in more than 5 times higher H2 and CO formations with 3 g DCM biochar than non-catalytic pyrolysis. To evaluate the performance of DCM biochar, pyrolysis of DCM was done with Ni and Co catalysts. The promotion effect of DCM biochar for syngas formation was better than that of equivalent amount of Co catalyst. The performance of DCM biochar was higher than Ni when the additional amount of biochar was used. Considering that DCM is emitted as an agricultural waste material, it is inferred that the waste derived biochar has more economic viability than metal catalysts. Therefore, this study provides that the CO2-driven pyrolysis with DCM biochar could be an environmentally benign means for syngas generation with an economic benefit.

Cocatalysts from types, preparation to applications in the field of photocatalysis.

With the rapid development of society, the burden of energy and the environment is becoming more and more serious. Photocatalytic hydrogen production, the photosynthesis of organic fuel, and the photodegradation of pollutants are three effective ways to reduce these burdens using semiconductor photocatalysts. To improve the reaction efficiency of photocatalysts, a small amount of cocatalyst is often added when photocatalysts participate in the synthesis or decomposition reaction. The addition of this small amount of cocatalyst is like a finishing touch, significantly increasing the activity of the photocatalysts. However, in our common study of photocatalysis, we often pay attention to the study of photocatalysts but ignore the study of cocatalysts. Herein, we summarize the recent application research on cocatalysts in the field of photocatalysis, starting from the types, preparation methods, and reaction mechanisms among others, to remind researchers of the matters needing attention when using cocatalysts.

Sunlight Selective Photodeposition of CoOx(OH)y and NiOx(OH)y on Truncated Bipyramidal BiVO4 for Highly Efficient Photocatalysis.

Facet-engineered monoclinic scheelite BiVO4 particles decorated with various cocatalysts were successfully synthesized by selective sunlight photodeposition of metal or metal oxy(hydroxide) nanoparticles onto the facets of truncated bipyramidal BiVO4 monoclinic crystals coexposing {010} and {110} facets. X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning Auger microscopy revealed that metallic silver (Ag) and cobalt (oxy)hydroxide (CoOx(OH)y) particles were selectively deposited onto the {010} and {110} facets, respectively, regardless of the cocatalyst amount. By contrast, the nickel (oxy)hydroxide (NiOx(OH)y) photodeposition depends on the nickel precursor amount with an unprecedented selectivity for 0.1 wt % NiOx(OH)y/BiVO4 with a preferential deposition onto the {010} facets and the edges between the {110} facets. Moreover, these noble metal-free heterostructures led to remarkable photocatalytic properties for rhodamine B photodecomposition and sacrificial water oxidation reactions. For instance, 0.2 wt % CoOx(OH)y/BiVO4 led to one of the highest oxygen evolution rates, i.e., 1538 μmol h-1 g-1, ever described which is ten times higher than that found for bare BiVO4. The selective deposition of cobalt (oxy)hydroxide species onto the more electron-deficient facet of truncated bipyramidal monoclinic BiVO4 particles favors photogenerated charge carrier separation and therefore plays a key role for efficient photochemical oxygen evolution.

Iron-catalyzed reactions of CO2 and epoxides to yield cyclic and polycarbonates

The catalytic coupling and polymerization of CO2 and epoxides has been studied for over 50 years. While traditionally dominated by catalytic systems containing cobalt, chromium, and zinc, the use of iron catalysts has emerged in the past 10 years. This review provides an overview of the homogeneous iron-catalyzed transformations of carbon dioxide and epoxides to yield cyclic and/or polycarbonates. It is important to note the potential for cyclic carbonates to be used as monomers for polymer formation via transesterification or by ring-opening polymerization in some cases, e.g., cyclohexene carbonate. Typical catalytic systems are composed of a Lewis acidic iron center and an anionic nucleophilic source, either through an anionic group weakly bound to the metal center or the addition of an external cocatalyst, cooperatively described as a binary catalytic system. This review is divided into two sections: (1) iron catalysts for cyclic carbonates and (2) iron catalysts for polycarbonates. At the end of each section, a table summarizes each catalytic system and the reaction conditions utilized in an attempt to provide a clearer comparison across the literature. Focus is given to highlighting differences in product selectivity, reaction conditions, and relative amounts of cocatalyst used. The use of iron catalysts in CO2/epoxide chemistry has been less explored compared with zinc, cobalt, and chromium catalysts. This review highlights recent examples including iron complexes that deoxygenate epoxides in situ and geometry-dependent selectivity towards either polycarbonate or cyclic carbonate production. Reaction conditions (temperature, CO2 pressure, and amount of nucleophilic cocatalyst) and catalyst structure are all critical in accessing efficient catalysis for polycarbonate formation.

Synthesis and Сharacterization of Soft-Bridged Iminopyridyl Iron and Cobalt Complexes and Their Catalytic Behavior toward Ethylene Oligomerization

Two kinds of soft-bridged iminopyridyl ligands and their metal (iron and cobalt) complexes were synthesized. All soft-bridged iminopyridyl ligands and metal complexes were fully characterized by FT-IR, 1H NMR, UV–Vis, ESI-MS, and ICP-MS. Upon activation with methylaluminoxane (MAO), these metal complexes exhibited moderate catalytic activity up to the range of 105 g/(mol Me h) for ethylene oligomerization, and butene was the major product, while for the cobalt complexes, activation with EtAlCl2 in toluene produced Friedel–Crafts toluene alkylation products. In the catalytic systems, cobalt complexes exhibited better catalytic activity and selectivity towards higher carbon number olefins (≥C8) than their iron analogues. The correlations between metal complexes and their catalytic activities and product distribution were investigated in detail under various reaction parameters such as reaction temperature, ethylene pressure and amount of co-catalyst. Under optimized conditions ([Co] = 7 μmol, 35°C, 1.0 MPa, MAO-to-Co = 500), soft-bridged iminopyridyl cobalt catalyst Co1 led to catalytic activity of 6.18 × 105 g/(mol Co h) and 29.97% selectivity for higher carbon number olefins. However, under optimized conditions ([Fe] = 7 μmol, 25°C, 1.0 MPa, MAO-to-Fe = 500), soft-bridged iminopyridyl iron catalyst Fe1 led to catalytic activity of 4.73 × 105 g/(mol Fe h) and 22.60% selectivity for higher carbon number olefins.

Hydrogen-Borrowing Amination of Secondary Alcohols Promoted by a (Cyclopentadienone)iron Complex

Thanks to a highly active catalyst, the scope of the (cyclopentadienone)iron complex-promoted ‘hydrogen-borrowing’ (HB) amination has been expanded to secondary alcohols, which had previously been reported to react only in the presence of large amounts of co-catalysts. A range of cyclic and acyclic secondary alcohols were reacted with aromatic and aliphatic amines giving fair to excellent yields of the substitution products. The catalyst was also able to promote the cyclization of diols bearing a secondary alcohol group with primary amines to generate saturated N-heterocycles.

Aluminum triflate-cocatalyzed radical copolymerization of styrene and ethyl acrylate

Various random copolymers, poly(styrene-co-ethyl acrylate), were synthesized by free radical bulk copolymerization cocatalyzed by aluminum triflate (Al(OTf)3). The experimental conditions for the polymerization reactions, which include the amount of cocatalyst, polymerization time and ratio of styrene to ethyl acrylate, were investigated. The copolymer molecular weights were determined by gel permeation chromatography coupled to multi-angle laser light scattering. Compositional analysis was performed using proton nuclear magnetic resonance spectrometry. Electron paramagnetic resonance spectroscopy was also used to study the radical species which form in the presence or absence of Al(OTf)3. Kinetic studies were performed by determining monomer conversions as a function of time on gas chromatography. It was found that Al(OTf)3 accelerated the rate of polymerization significantly while also increasing the polymer molecular weights for a given conversion compared to the reactions where the triflate was absent. Al(OTf)3 can be a significantly more cost-effective and abundant alternative polymerization cocatalyst compared to some of the rare lanthanide triflates.

1,3-Diene Polymerization Promoted by Half-Sandwich Rare-Earth-Metal Dimethyl Complexes: Active Species Clustering and Cationization/Deactivation Processes.

When activated with fluorinated borate cocatalysts the trimetallic complexes [Cp*LnMe2 ]3 (Ln=Y, Lu; Cp*=C5 Me5 ) promote efficiently the formation of high-cis polybutadiene. Respective polyisoprenes instead bear much less pronounced microstructures, but reveal crosslinked products at lower polymerization temperatures. Varying the amount of cocatalyst, the emerging active species were examined by NMR spectroscopic techniques (incl. 1 H DOSY). The occurrence of donor-solvent and thermally induced degradation products of the highly reactive precatalyst [Cp*YMe2 ]3 and derived catalyst species was revealed by the elucidation of methylidene clusters [Cp*3 Y3 Me4 (CH2 )(thf)2 ] and [Cp*6 Y6 Me4 (CH2 )4 ], as well as [(Cp*Y)2 Me2 (N(Me)2 (C6 H4 )]n [B(C6 F5 )4 ]n , implying a multimetallic active species.

Revisiting cocatalyst/TiO2 photocatalyst in blue light photothermalcatalysis

Coupling heat into photocatalysis (PC) has been found more efficient than PC for removal of volatile organic compounds (VOC). Therein, photothermal synergy induced photothermalcatalysis (PTC) sometimes tells different stories from PC. In this work, we revisit ST-01 TiO2 photocatalyst as photothermalcatalyst under blue light at 333 K and further investigate the role of surface grafted cocatalyst (CrxO, CoxO, CuxO, Pt) in catalytic removal of gaseous acetaldehyde pollutant. By comparison on the amount of cocatalyst, for PC, more CrxO cocatalyst (3 wt%) is favored for higher removal efficiency of acetaldehyde. For PTC, less CrxO cocatalyst (0.3 wt%) is favored. By further comparison on the type of cocatalyst, for PC, hole cocatalyst (CrxO and CoxO) gives inferior performance to that of electron cocatalyst (CuxO and Pt). For PTC, hole cocatalyst gives superior performance to that of electron cocatalyst. The difference between PC and PTC lies in synergistic effect between defect-related blue-light absorption, cocatalyst induced interfacial charge transfer and matched surface red-ox reaction rate. This work may provide new insight into the design and development of photothermalcatalyst for VOC removal.

CH(phenol)-Bridged Bis(imino)pyridines as Compartmental Supports for Diiron Precatalysts for Ethylene Polymerization: Exploring Cooperative Effects on Performance

A family of six CH(phenol)-bridged bimetallic bis(imino)pyridine-iron(II) chlorides, CH(C6H4-4-OH){2′-(4-C6H2-2,6-(R1)2N═CMe)-6′-(2″,6″-(R2)2-4-(R3)C6H2N═CMe)C5H3N}2Fe2Cl4 [R1 = R2 = Me, R3 = H, Fe1; R1 = R2 = Et, R3 = H, Fe2; R1 = Me, R2 = Et, R3 = H, Fe3; R1 = Me, R2 = i-Pr, R3 = H, Fe4; R1 = R2 = R3 = Me, Fe5; R1 = R2 = Et, R3 = Me, Fe6], has been synthesized by the reaction of the corresponding compartmental ligand with 2 equiv of FeCl2·4H2O. The molecular structure of Fe6 reveals an intramolecular Fe···Fe separation of 10.152 Å, with pairs of Fe6 assembling through intermolecular OH···Cl hydrogen bonding interactions. On activation with MAO or MMAO, Fe1–Fe6 exhibited both good thermal stability and very high activity for ethylene polymerization with the least sterically bulky compound, Fe1, being the standout performer (up to 2.43 × 107 g·mol–1(Fe)·h–1 at 60 °C). Notably, Fe1/MAO showed almost double the activity of a structurally related mononuclear catalyst while the resultant polyethylene exhibited much higher molecular weight. In general, the polymeric materials are highly linear and have a tendency to display bimodal distributions that is influenced by the amount of cocatalyst employed. End-group analysis of the polymers generated using MMAO activation reveals chain ends composed of vinyl and saturated groups (propyl and isobutyl), while with MAO, a preference for propyl end groups is observed.

Selective aerobic oxidation of p -cresol with co-catalysts between metalloporphyrins and metal salts

Abstract A green and efficient method for the selective aerobic oxidation of p-cresol to p-hydroxybenzaldehyde catalyzed by co-catalysts between metalloporphyrins and metal salts was investigated and developed. The relationship between the synergistic catalytic effects and the composition as well as amount of co-catalysts was investigated. Moreover, the influence of different reaction conditions was studied in details. A high p-cresol conversion (> 99%) and p-hydroxybenzaldehyde selectivity (83%) were obtained using only 1.125 × 10− 5 mol T(p-CH3O)PPFeIIICl-Co(OAc)2 used under mild, optimized reaction conditions. A possible mechanism for the reaction was also proposed. This work would be meaningful and instructive for the further researches and applications of co-catalyst system on oxidation of cresols and could give some enlightenment on the selectively catalytic oxidation of the side-chain alkyls of aromatics.

Chromium complexes supported by the bidentate PN ligands: synthesis, characterization and application for ethylene polymerization.

Chromium-based complexes are among the most important catalysts in the field of ethylene polymerization and oligomerization. Heterogeneous Cr Phillips catalysts account for more than one-third of the commercialized high density polyethylene (HDPE). In this contribution, chromium complexes, LCrCl3 (Cr1-Cr4: L = 2,6-R1-4-R2-C6H2-N[double bond, length as m-dash]CH-C6H4-2-PPh2; Cr1: R1 = H, R2 = H; Cr2: R1 = Me, R2 = H; Cr3: R1 = iPr, R2 = H; Cr4: R1 = Ph2CH, R2 = iPr), have been synthesized and characterized by elemental analysis, ESI and IR spectroscopy. The molecular structures of Cr3 and Cr4 are defined by X-ray diffraction, revealing a distorted octahedral geometry around the chromium center in both structures. In the presence of an aluminum cocatalyst, complexes Cr1-Cr4 show moderate to high activities toward ethylene polymerization. The nature of the catalysts and various reaction conditions, such as the nature and the amount of cocatalyst, reaction time and temperature, are investigated in detail. The results show that the title complexes have good thermal stability and the substituents on the ligands significantly affect the catalytic properties. Particularly, complex Cr4 can produce HDPE with a high molecular weight up to 68.3 × 104 g mol-1 due to the suppression of the chain transfer/termination by the introduction of bulky Ph2CH groups.