Bis(imino)pyridyl Co(II) and Fe(II) catalysts immobilized on SBA-15 mesoporous material: new highly active supported catalysts for the polymerization of ethylene

A series of bis(imino)pyridyl Co(II) and Fe(II) complexes containing allyloxy group on the pyridine ring were prepared. These metal complexes were heterogenized covalently immobilizing on modified SBA-15 mesoporous material in the presence of Karstedt catalyst. This immobilization technique was demonstrated to be an ideal one since the resulting supported catalysts resembled closely their homogeneous counterparts, mirroring the feature of active sites.     

Effect of N‐methylimidazole and 3,5‐dimethylpyrazole ligands on the polymerization of di(2,6‐dichlorophenolato) Cu(II)/Co(II) complexes in the solid state

The polymerization of 2,6‐dichlorophenol (DCPH) was achieved through the thermal decomposition of copper complexes of DCPH with N‐methylimidazole (NMIz) and 3,5‐dimethylpyrazole (DMPz) ligands. Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), mass spectrometry, ultraviolet–visible spectroscopy, diffuse reflectance spectroscopy, magnetic susceptibility balance, electron spin resonance, X‐ray analysis, and elemental analysis were used to characterize the complexes. The polymerization was achieved either in the solid state or in the melt. The structural analyses were performed with FTIR and NMR spectroscopy analyses. The glass‐transition temperatures were determined by DSC, and the intrinsic viscosities were determined by viscosimetry. The effects of the temperature and time on the conversion percentage and viscosity of the polymers were examined. Varying the decomposition temperature during a 3‐h scan showed that the DMPz complex of Cu decomposed at lower temperatures than the NMIz complex, whereas the NMIz complex yielded a higher conversion to the polymer. Complexes of DCPH with NMIz and DMPz ligands produced 1,2‐ and 1,4‐addition products, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3797–3805, 2004     

Novel nickel(II)-based catalysts for the polymerization of ethylene

A series of Ni(II)-based bidentate -diimine complexes bearing two alkyl (alkyl = methyl, ethyl and isopropyl) substituents on each imine aryl group were studied as precatalysts for the polymerization of ethylene. These new catalysts were observed to show high activity in combination with methyl aluminoxane (MAO) and produced high molecular weight polyethylenes. The effects of the steric bulk of ortho-aryl substituents of the ligand on the catalytic activity and the resulting polyethylene microstructure were investigated. Kinetics of polymerization was also studied by changing important parameters such as temperature and MAO concentration. The polymerization activity, polymer molecular weight and resulting polymer microstructure were drastically changed according to the catalyst structure modification and polymerization parameters.     

Highly active and stereospecific polymerizations of 1,3-butadiene by using bis(benzimidazolyl)amine ligands derived Co(II) complexes in combination with ethylaluminum sesquichloride

A family of cobalt(II) complexes supported on tridentate dibenzimidazolyl ligands having a general formula: [N(CH₃)(CH₂)₂(Bm-R)₂]CoCl₂ (where Bm = benzimidazolyl, R = H; -Me; -Bz), have been prepared by the condensation of o-phenylene diamine with methyliminodiacetic acid. The Co(II) complexes exhibited high activities for the polymerization of 1,3-butadiene, on activation with ethylaluminum sesquichloride (EASC), to yield predominantly cis-1,4 microstructure. The polymers are characterized by high molecular weight with polydispersity values between 2.35 and 3.37. The ligand modification shows remarkable influence on polymerization activity. The stereospecificity of the catalysts is consistent for a wide range of reaction conditions, except temperature. The electronic influence of ligand structure towards metal center is investigated by using cyclic voltammetric analysis and the generation of cationic active centers is identified via UV-vis spectroscopic analysis of the catalyst system.     

Influence of type and positioning of N-aryl substituents on vinyl polymerization of norbornene by Ni(II) α-diimine complexes

Effects of structural variations of the diimine ligand on catalyst activities for vinyl polymerization of norbornene (NB) have been investigated by a series of Ni(II) α-diimine catalysts of the general formula: [{ArN=C(Ac)-C(Ac)=NAr}]NiBr₂ (Ac=acenaphthyl) (Cat(H), Ar=C₆H₅; Cat(2,6-Me), Ar=2,6-C₆H₃Me₂; Cat(2,6-Et), Ar=2,6-C₆H₃Et₂; Cat(2,6- i Pr), Ar=2,6-C₆H₃ i-Pr₂; Cat(2,3-Me), Ar=2,3-C₆H₃Me₂; Cat(2,4-Me), Ar=2,4-C₆H₃Me₂; Cat(2,5-Me), Ar=2,5-C₆H₃Me₂; Cat(3,5-Me), Ar=3,5-C₆H₃Me₂; Cat(2,4,6-Me), Ar=2,4,6-C₆H₂Me₃). In situ reactions with methylaluminoxane generated the active catalysts, and they showed good activity towards NB polymerizations. As indicated by relatively higher activities of Cat(H) and Cat(3,5-Me), it can be generalized that catalysts having 2,6-substituents are less active due to steric interaction between monomer and substituents. In addition, electron donating methyl groups at 2-, 4-or 6-position on the N-aryl have a con effect and that at 3,5-position has a pro effect. This paper was presented at the 11th Korea-Japan Symposium on Catatysis held at Seoul, Korea, May 21–24, 2007.     

Lanthanide(II) amide complexes: Efficient initiators for the living polymerization of methyl methacrylate

Lanthanide(II) complexes supported by amido ligands, [(C₆H₅)(Me₃Si)N]₂Ln(DME)₂ [Ln = Sm ( 1 ) or Yb ( 2 ); DME = 1,2‐dimethoxyethane] and [(C₆H₃? ⁱPr₂‐2,6)(Me₃Si)N]₂Ln(THF)₂ [Ln = Sm ( 3 ) or Yb ( 4 ); THF = tetrahydrofuran], were found to initiate the polymerization of methyl methacrylate (MMA) as efficient single‐component initiators (in toluene for 3 and 4 and in toluene with a small amount of THF for 1 and 2 ) to produce syndiotactic polymers. The catalytic behavior was highly dependent on both the amido ligand and the polymerization temperature. Initiators 3 and 4 initiated MMA polymerization over a wide range of temperatures (20°C to ?40°C), whereas the polymerization with 1 and 2 proceeded smoothly only at low temperatures (≤0°C). The kinetic behavior and some features of the polymerizations of MMA initiated by 3 and 4 were studied at ?40°C. The polymerization rate was first‐order with the monomer concentration. The molar masses of the polymers increased linearly with the increase in the polymer yields, whereas the molar mass distributions remained narrow and unchanged throughout the polymerization; this indicated that these systems had living character. A polymerization mechanism initiated by bimetallic bisenolate formed in situ was proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Neutral Pd(II) and Ni(II) Acetylide Catalysts for the Polymerization of Methyl Methacrylate

Homogenous polymerization of methyl methacrylate using Pd(II)- and Ni(II)-based acetylide complexes as initiators has been investigated. M(PR'₃)₂(CCR)₂ (M=Pd, Ni; R'=PPh₃, Pn-Bu₃; R=Ph, CH₂OH, CH₂OOCCH₃, CH₂OOCPh, CH₂OOCPhOH-o) were found to be a novel type of effective initiators for the polymerization of methyl methacrylate. Among them, Pd(C CPh)₂(PPh₃)₂ (PPP) shows the highest activity in the MMA polymerization and the PMMA obtained is a syndiotactic polymer with high number-average molecular weight (M _n) of 14.1 × 10⁴. Some features and kinetic behavior of MMA polymerization initiated by PPP were studied in detail. The polymerization reaction is first-order with respect to both [PPP] and [MMA]. Radical polymerization mechanism is proposed.     

乙烯聚合用树枝状过渡金属催化剂研究进展

树枝状过渡金属催化剂是在树枝状大分子上负载上过渡金属活性中心,因此,此类催化剂既具有树枝状大分子特有的艺术结构,同时还具有过渡金属配合物的功能化性能,使其两者能够协同发挥作用,兼具均相和非均相催化体系的特点,在催化烯烃聚合方面具有较高的催化活性和良好的催化稳定性,近年来备受关注,催化乙烯聚合就是其中的研究热点之一。本文按其过渡金属活性中心进行分类,综述了近年来国内外树枝状过渡金属催化剂在这乙烯聚合方面的进展,阐述了多种树枝状效应产生的原因,并且对乙烯聚合用树枝状过渡金属催化剂的发展前景进行了展望。     

Neutral Pd(II) and Ni(II) Acetylide Initiators for Polymerization of (Dimethylamino)ethyl Methacrylate

A series of air-stable, late transition, metal-based initiators with the structures ML₂(CCR)₂ (M=Pd and Ni; L=PPh₃ and Pn-Bu₃; R=Ph and CH₂OH) for the polymerization of (dimethylamino)ethyl methylate (DMAEMA) were developed. Transition metal, phosphine, alkynyl, as well as solvents exhibited significant influence on the polymerization. Among them, Pd(CCPh)₂(PPh₃)₂ (PPP) shows the highest activity in CHCl₃ for DMAEMA polymerization. The PDMAEMA obtained is a syndiotactic polymer with high number-average molecular weight (M_n) of 20.2 × 10⁴. A free radical polymerization mechanism with some ATRP characteristics was proposed for the present polymerization.     

Homopolymerization of n‐butyl methacrylate using bis(salicylaldiminate)copper(II)/ methylaluminoxane catalysts

Polymerization catalysts based on copper precursors appear particularly interesting due to the low metal cost, limited toxicity and modest sensitivity to deactivation by polar species. To date, α‐olefin and polar monomer coordination polymerization catalysed using copper catalysts has been scarcely investigated, and a good part of the literature is represented by patents. Here this research has been expanded to the study of the performances of bis(salicylaldiminate)copper(II)/methylaluminoxane (MAO) catalysts in the polymerization of n‐butyl methacrylate. The study of the catalytic activity of bis(salicylaldiminate)copper(II)/MAO systems in n‐butyl methacrylate polymerization was focused on the relationship between the catalytic behaviour and the main reaction conditions and ligand structures. The electronic and steric characteristics of the chelate ligands play an important role in the catalytic performances. The presence of electron‐withdrawing nitro groups on the chelate ligands increased the catalytic activity which reached 36 kg_polymer mol^?1 h^?1, the highest value up to now reported for copper systems in methacrylic or acrylic monomer polymerization. These performances were ascribed to copper catalysts activated by MAO: without copper precursor, working in the presence of MAO and free salicylaldimine ligand, complete inactivity was ascertained. Copyright © 2010 Society of Chemical Industry     

Novel Ni and Pd(benzocyclohexan‐ketonaphthylimino)2 complexes for copolymerization of norbornene with octene

Two novel late transition metals complexes with bidentate O?N chelate ligand, Mt(benzocyclohexan‐ketonaphthylimino)₂ {Mt(bchkni)₂: bchkni ?C₁₀H₈(O)C[N(naphthyl)CH₃]; Mt ? Ni, Pd}, were synthesized. In the presence of B(C₆F₅)₃, both complexes exhibited high activity toward the homo‐polymerization of norbornene (NB) (as high as 2.7 × 10⁵ g_polymer/mol_Ni·h for Ni(bchkni)₂/B(C₆F₅)₃ and 2.3 × 10⁵ g_polymer/mol_Pd·h for Pd(bchkni)₂/B(C₆F₅)₃, respectively). Additionally, both catalytic systems showed high activity toward the copolymerization of NB with 1‐octene under various polymerization conditions and produced the addition‐type copolymer with relatively high molecular weights (0.1–1.4 × 10⁵g/mol) as well as narrow molecular weight distribution. The 1‐octene content in the copolymers can be controlled up to 8.9–14.0% for Ni(bchkni)₂/B(C₆F₅)₃ and 8.8–14.6% for Pd(bchkni)₂/B(C₆F₅)₃ catalytic system by varying comonomer feed ratios from 10 to 70 mol %. The reactivity ratios of two monomers were determined to be r_1‐octene = 0.052, r_NB = 8.45 for Ni(bchkni)/B(C₆F₅)₃ system, and r_1‐octene = 0.025, r_NB = 7.17 for Pd(bchkni)/B(C₆F₅)₃ system by the Kelen‐TÜdÕs method. The achieved NB/1‐octene copolymers were confirmed to be noncrystalline and exhibited good thermal stability (T_d > 400°C, T_g = 244.1–272.2°C) and showed good solubility in common organic solvents. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Improved high‐temperature performance of iron (II) complexes for ethylene polymerization by variation of aluminoxanes

Modification of ethyl‐iso‐butylaluminoxanes (EBAOs) with alkyl boronic acid resulted in different co‐catalytic performances when combined with iron complexes for ethylene polymerization, in particular the preferred high‐temperature performance. The changes in polymerization activity and molecular weight distribution of the resulting polymer derived from the variation of aluminoxane were investigated. The varying performance of the iron complex with different aluminoxanes has proved that the interaction between the late transition metal complex and aluminoxane greatly affects the performance of such bicomponent catalyst systems Copyright © 2003 Society of Chemical Industry     

Polystyrene-supported thiosemicarbazone–transition metal complexes: synthesis and application as heterogeneous catalysts

Functionalized polymers are found to be highly efficient in immobilizing transition metal ions. Crosslinked polystyrene supported Schiff's base complexes of metal ions such as Fe(III), Co(II), Ni(II) and Cu(II) are very effective as heterogeneous catalysts. The catalytic activity of these metal complexes has been studied in the decomposition of H₂O₂ and in the epoxidation of cyclohexene and styrene. The reactions show a first order dependence on the concentration of both the substrates and the catalyst. The influence of the degree of crosslinking of the polymer support on the rate of reactions has been studied. The metal complexes show low catalytic activity at low crosslink density (2% and 5%) but 10% crosslinked resins show higher activity. A possible mechanism for the reactions is suggested. © 1999 Society of Chemical Industry     

Syntheses of group 4 transition metal complexes bearing 2-pyridinethiolate ligands and their catalytic activities for ethylene polymerization

Titanium bis(2-pyridinethiolate) complexes, Ti(6-R-SPy)₂(NMe₂)₂ (6-R-SPy = 6-R-2-pyridinethiolate, 3a: R = H; 3b: R = Me; 3c: R = Ph; 3d: R = C₆H₄-4-Me; 3e: R = C₆H₄-4-t-Bu; 3f: R = C₆H₃-3,5-Me₂), and the titanium bis(2-pyridinolate) complexes, Ti(6-Ph-OPy)₂(NMe₂)₂ (6-Ph-OPy = 6-phenyl-2-pyridinolate, 8) were prepared by treating Ti(NMe₂)₄ with 2 equiv. of 6-R-2-pyridinethiol or 6-Ph-2-pyridinol. The cis-configuration of the diamido moieties in the pseudo octahedral geometry was elucidated by X-ray crystallography for 3a. Reaction of M(NMe₂)₄ (M = Ti, Zr) with 4 equiv. of 2-pyridinethiol cleanly gave tetrakis(pyridinethiolate) complexes, M(6-H-SPy)₄·THF (6: M = Ti; 7: M = Zr). The triangular dodecahedral geometries of 6 and 7 were also revealed by X-ray crystallography. These complexes catalyzed ethylene polymerization upon activation with MAO (methylaluminoxane) or MMAO (modified MAO). The catalytic activities of titanium bis(6-aryl-pyridinethiolate) systems were found to be remarkably higher than that of titanium bis(6-methyl-pyridinethiolate) system. Among the complexes synthesized in this study, Ti[6-(C₆H₃-3,5-Me₂)-SPy]₂(NMe₂)₂ (3f)/MMAO showed the highest activity (1200 kg/Ti-mol h atm) for ethylene polymerization at 60 °C under atmospheric pressure. In contrast, the activity of the corresponding 6-aryl-pyridinolate system 8/MMAO was rather low (9.3 kg/Ti-mol h atm). Both the N-S chelating structure and the bulky aryl substituents are essential for the high activities of the 6-aryl-pyridinethiolate complexes.     

Ferrous and cobaltous chloride complexes bearing 2-(1-(arylimino)methyl)-8-(1H-benzimidazol-2-yl)quinolines: Synthesis, characterization and catalytic behavior in ethylene polymerization

The series of ligands 2-(1-(arylimino)methyl)-8-(1H-benzimidazol-2-yl)quinolines was synthesized and used to prepare new iron(II) and cobalt(II) dichloride complexes. X-ray diffraction studies revealed that the coordination geometry around the metal center can best be described as distorted square-based pyramidal. Upon activation with methylaluminoxane (MAO), both families (Fe and Co) of complexes showed good activities in ethylene polymerization, affording highly linear polyethylenes. Enhanced activities were observed on increasing the reaction temperature to 100 °C. The optimization of the reaction parameters and the influence of the substituents on the imino-bound aryl group of the chelate ligands were investigated.     

Polymerization of 1,3-butadiene by bis(salicylaldiminate)cobalt(II) catalysts combined with organoaluminium cocatalysts

The one-pot reactions of salicylaldehyde or its derivatives with 2,6-dialkyl substituted anilines in the presence of metallating agent, Co(OAc)₂.4H₂O, yield a series of cobalt(II) complex precatalysts (Ar¹-NC-Ar²-O)₂Co (1, Ar¹ = 2,6-dimethylaryl, Ar² = aryl; 2, Ar¹ = 2,6-diethylaryl, Ar² = aryl; 3, Ar¹ = 2,6-diisopropylaryl, Ar² = aryl; 4, Ar¹ = 2,6-dimethylaryl, Ar² = 3-t-butylaryl; 5, Ar¹ = 2,6-diethylaryl, Ar² = 3-t-butylaryl; 6, Ar¹ = 2,6-diisopropylaryl, Ar² = 3-t-butylaryl) in high yields. The treatment of these cobalt(II) salicylaldimine complexes with ethylaluminum sesquichloride (EAS) forms highly active 1,3-butadiene (BD) polymerization catalysts, yielding polybutadienes of moderate molecular weights (MW = 33,900–44,500) with narrow molecular weight distributions (MWD = 1.29–2.36). All Co(II) complexes yield highly cis-1,4-polybutadienes (>94%) with negligible amounts of 1,4-trans (<2.32%) and 1,2-added (<3.37%) products in polymerizations at 30 °C combined with EAS. As the steric bulk at the cobalt center increases by changing the alkyl substituents on the ligand environment, 1,4-cis content decreases. The cis content and MW decrease as polymerization temperature increases. The polymerization yield and the cis content increase as BD concentration increases. The nonlinearity of [BD] to yield and [BD] to MW relationships demonstrates that the narrow MWD comes from uniform active species present in the polymerization system. The activation procedures of the Co(II) complexes in conjunction with EAS are studied by using UV-visible spectroscopy. Suitable correlations are found between polymerization activities and the changes in UV-visible absorption spectra of the complex.     

Synthesis and characterization of monomeric and polymeric pyridinylimine‐based Ni(II) complexes and their catalytic activities in ethylene oligomerization

A new polymeric ligand was synthesized through the reaction of 4‐(pyridinylimine)phenol and formaldehyde in a basic medium, and its corresponding polymer–nickel complexes were formed in a 1:1 molar ratio. The synthesized compounds were characterized using elemental and spectral analyses. The monomeric and polymeric Ni(II) complexes (C₁ and C₂, respectively) were evaluated as catalyst precursors for ethylene oligomerization, using methylaluminoxane as an activator at two different ethylene pressures. C₂ was found to be a more effective pre‐catalyst than C₁, with the co‐catalyst having a similar effect in both cases. C₂ exhibited an activity of 1.282 × 10⁶ g (mol Ni)^?1 h^?1 bar^?1, with an Al:Ni ratio of 2000:1 at room temperature and 1 atm ethylene pressure. Meanwhile C₁ exhibited an activity of 1.126 × 10⁶ g (mol Ni)^?1 h^?1 bar^?1 under similar experimental conditions. At 5 atm ethylene pressure, C₁ favoured the formation of high‐density polyethylene, whereas C₂ favoured the formation of branched low‐density polyethylene. Copyright © 2012 Society of Chemical Industry     

Influence of the metal centers of 2,6‐bis(imino)pyridyl transition metal complexes on ethylene polymerization/ oligomerization catalytic activities

Much work on bis(imino)pyridyl complexes with Fe(II) and Co(II) as ethylene polymerization catalysts has been reported in terms of designing new analogous ligands, while little work has been dedicated to the study of the effect of the metal center on catalyst performance. A series of bis(imino)pyridyl‐MCl₂ (M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II)) transition metal complexes were synthesized, for which single crystals of the Co(II) and Cu(II) complexes were obtained. The crystal structures indicated that these complexes had similar coordination geometries. Being applied to ethylene polymerization at 25 °C and employing 500 equiv. of methylaluminoxane as co‐catalyst, the complexes with Fe(II), Co(II) and Ni(II) centers showed, respectively, catalytic activities of 1.25 × 10⁶ g (mol Fe)^?1 h^?1 Pa for ethylene polymerization, and 3.98 × 10⁵ g (mol Co)^?1 h^?1 Pa and 5.13 × 10³ g (mol Ni)^?1 h^?1 Pa for ethylene oligomerization. In contrast, the complexes with Cu(II) and Zn(II) centers were inactive. Crystal structure data showed that the coordination interactions provided a comparatively reliable quantification of the selectivity of the bis(imino)pyridyl ligand for the studied metal ions, which was in reasonable agreement with the Irving–Williams list. Moreover, for the Ni(II) and Cu(II) complexes, the strong coordination bonds and small N(imino)? M? N(imino) angles were unfavorable for several steps in the mechanism, such as ethylene coordination to the metal center, ethylene migratory insertion and olefin chain growth. All of these will reduce the speed of the overall reaction, indicating a decrease of catalytic efficiency in a given period. The poor activity of the Zn(II) complex for ethylene polymerization may be related to the reduction process by the alkylating agent. Copyright © 2010 Society of Chemical Industry     

Supported catalysts based on 2,6-bis(imino)pyridyl complex of Fe(II): DRIFTS study of the catalyst formation and data on ethylene polymerization

The supported catalysts for ethylene polymerization were prepared by interaction of 2,6-bis[1-(2,6-dimetilphenylimino)-ethyl]pyridineiron(II) dichloride (LFeCl₂) with silica and alumina. The catalysts exhibit high and stable activity at ethylene polymerization in presence of Al(i-Bu)₃ as co-catalyst. LFeCl₂ interaction with surface functional groups of the supports was studied by means of DRIFTS. LFeCl₂ adsorbed on the support surface mainly retains its structure. LFeCl₂ is strongly bounded to the support due to formation of multiple bonds between LFeCl₂ and surface functional groups of the supports. DRIFTS data on the state of the surface iron compounds have been obtained using CO as probe molecule.     

Polymerization of styrene using bis(β‐ketoamino)nickel(II)/methylaluminoxane catalytic systems

Styrene (St) was polymerized in toluene solution by using bis(β‐ketoamino)nickel(II) complex as the catalyst precursor and methylaluminoxane (MAO) as the cocatalyst. The polymerization conditions, such as Al : Ni ratio, monomer concentration, reaction temperature, and polymerization time, were studied in detail. Both of the bis(β‐ketoamino)nickel(II)/MAO catalytic systems exhibited higher activity for polymerization of styrene, and polymerization gave moderate molecular weight of polystyrene with relatively narrow molecular weight distribution (M_w/M_n < 1.6). The obtained polymer was confirmed to be atactic polystyrene by analyzing the stereo‐triad distributions mm, mr, and rr of aromatic carbon C¹ in NMR spectrum of the polymer. The mechanism of the polymerization was also discussed and a metal–carbon coordination mechanism was proposed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007