Synthesis of anilinonaphthoquinone-based nickel complexes and their application for olefin polymerization

A series of anilinonaphthoquinone-based nickel complexes, Ni(C₁₀H₅O₂NAr)(Ph)(PPh₃) (Ar = C₆H₃-2,6-Me (1c); Ar = C₆H₂-2,4,6-Me (2c); Ar = C₆H₃-2,6-Et (3c)), were synthesized and the structures of 1c-3c were confirmed by single crystal X-ray analyses. The anilinonaphthoquinone-ligated nickel complexes activated with B(C₆F₅)₃ showed high activities for ethylene polymerization at 40 °C under atmospheric pressure of ethylene and gave polyethylene with long chain branches and short chain branches. The activity of these systems was decreased by lowering polymerization temperature accompanied by increase in molecular weight. The number of the chain branches was also decreased with lowering polymerization temperature and increasing the bulkiness of the ligand.     

Zirconium complexes in homogeneous ethylene polymerization

This article reviews the recent progress of zirconium complexes for ethylene polymerization. Zirconium complexes are one of the most important types of catalysts for homogeneous ethylene polymerization. Polymerization behavior and polymer structure can be adjusted through the balancing of ligand structure. We surveyed the zirconium complexes synthesized from 2006 to early 2009 and summarize their comparative catalytic activities. Generally, the main factor observed is the steric bulk which on increasing reduces the catalytic activity. Electron count, electronic cloud, and inductive effect also influence the catalytic activity.     

Dinuclear macrocyclic palladium complexes having pincer coordinating groups and their catalytic properties in Mizoroki-Heck reactions

An improved synthetic method of palladium(II) dinuclear macrocyclic complexes have been described. Each of the two isomers of the complexes [Pd₂LBr₂] has a macrocyclic ligand L in which two 2,6-bis(diaminomethyl)phenyl units coordinate to the Pd(II) centers with N, C, N donor atoms. Substitution of the bromo ligands of one of the isomer of the complexes with acetonitrile ligands affords a new dinuclear complex. Catalytic activities of these complexes were studied for the Mizoroki-Heck type reactions of iodobenzene and styrene. High turnover number up to 30,000 was achieved using one of the isomer of the complexes.     

Ethylene polymerization catalyzed by substituted pyrazole nickel complexes

(Pyrazole)nickel dibromide complexes, (3,5-Me₂pz)₂NiBr₂ (1), (3-Mepz)₄NiBr₂ (2), (pz)₄NiBr₂ (3) and (3,5-^tBu₂pz)₂NiBr₂ (4), were prepared by the reaction of the appropriate pyrazole with (DME)NiBr₂. Solid-state structures of these complexes show a direct relation between the steric bulk of the pyrazole ligand and structure, with more bulky ligands forming four-coordinate complexes (1 and 4) whereas the less bulky ligands formed six-coordinate complexes (2 and 3). Activation of selected complexes (1 and 3) with methylaluminoxane (MAO) produced species that catalyzed the polymerization of ethylene to form high density polyethylene.     

Syntheses and structures of non-symmetric guanidinato zirconium and hafnium complexes and their catalytic behavior for ethylene polymerization

Equivalent addition reactions of PhN(Li)SiMe₃ to nitriles, RCN (R = dimethylamido, 1-piperidino), generated non-symmetric guanidinato lithium [(Et₂O)LiN(SiMe₃)C(NMe₂)N(Ph)]₂ (1) or [(THF)LiN(SiMe₃)C(NMe₂)N(Ph)]₂ (2) and [(Et₂O)LiN(SiMe₃)C(N(CH₂)₅)N(Ph)]₂ (5) which further reacted with zirconium or hafnium tetrachloride to form Zr and Hf guanidinato complexes with the general formula [PhNC(R)NSiMe₃]₃MCl (R = dimethylamido, M = Zr (3), Hf (4); R = 1-piperidino, M = Zr (6), Hf (7)). Complexes 1-4, 6 and 7 were well characterized by ¹H, ¹³C NMR and microanalysis, the single crystal X-ray diffraction analysis data for complexes 1, 3, 4 and 7 were also provided. Furthermore, complexes 3, 4, 6 and 7 were found to be active for ethylene polymerization. The influences of cocatalyst, pressure, reaction temperature and Al/M ratio on activity were investigated.     

Mono and bimetallic nickel bromide complexes bearing azolate-imine ligands: Synthesis, structural characterization and ethylene polymerization studies

The synthesis of N-(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-diisopropylaniline (1) and N-(1-(indazol-2-yl)ethylidene)-2,6-diisopropylaniline (2) allowed access to new transition metal complexes. When reacted with dibromo(2,2′-dimethoxyethylether)nickel(II) the complexes [NiBr₂{N-(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-diisopropylaniline}] (3) and [Ni₂Br₂(μ-Br)₂{N-(1-(indazol-1-yl)ethylidene)-2,6-diisopropylaniline}₂] (4) are yielded, respectively. The addition of MAO generates catalytically active species for the homopolymerization of ethylene. The polymer products were low molecular weight (3-6 K) and a monomodal molecular weight distribution, consistent with the presence of a single active site. In addition, the catalyst was found to efficiently oligomerize higher olefins to high molecular weights with narrow PDIs.     

Dinuclear titanium complexes with methylphenylsilylene bridge between cyclopentadienyl rings. Synthesis, characterization and reactivity towards ethylene

The new ansa-titanocene dichloride [{(SiMePh)(η⁵-C₅H₄)₂}TiCl₂] (1) was prepared by one pot reaction, whereas synthesis of its methylated analogue [{(SiMePh)(η⁵-C₅Me₄)₂}TiCl₂] (3) was performed in two steps with isolation of corresponding silane intermediate SiMePh(HC₅Me₄)₂ (2). The reaction of 1 and 3 with TiCl₄ afforded the dinuclear complexes [(SiMePh){(η⁵-C₅R₄)TiCl₃}₂] (R = H (4) and R = Me (5)). The catalysts formed from 4 and 5 after their activation with excess MAO exhibited a modest activity in ethylene polymerization. The polymer products consisted of high molar mass linear polyethylenes with a broad molar mass distribution. The presence of three paramagnetic titanium species in the mixture 4/MAO was revealed by EPR spectroscopy. All new prepared compounds 1-5 were characterized by multinuclear NMR, EI-MS, IR, and solid-state structures of 1, 3 and 5 were determined by X-ray single crystal diffraction.     

Titanium complexes bearing bidentate benzimidazole-containing ligands and their behavior in ethylene polymerization

A series of potentially bidentate benzimidazolyl ligands of the type (Bim)CH₂D (where Bim = benzimidazolyl and D = NMe₂L1, NEt₂L2, NPrⁱ₂L3, OMe L4 and SMe L5) has been reacted with Ti(NMe₂)₄ to give five- and six-coordinate Ti(IV) complexes of the type [(Bim)CH₂D]Ti(NMe₂)₃ and [(Bim)CH₂D]₂Ti(NMe₂)₂, respectively. The X-ray structures of [(Bim)CH₂OMe]Ti(NMe₂)₃, [(Bim)CH₂NMe₂]₂Ti(NMe₂)₂ and [(Bim)CH₂OMe)]₂Ti(NMe₂)₂ are reported along with an evaluation of their behavior in ethylene polymerization.     

Synthesis, characterization and ethylene oligomerization studies of nickel complexes bearing 2-imino-1,10-phenanthrolines

A series of nickel (II) complexes ligated by 2-imino-1,10-phenanthrolines were synthesized and characterized by elemental and spectroscopic analysis as well as by single-crystal X-ray crystallography. X-ray crystallographic analysis reveals complexes 3, 5, 7 and 11 as the five-coordinated distorted trigonal-bipyramidal geometry. Upon activation with Et₂AlCl, these complexes exhibited considerably high activity for ethylene oligomerization (up to 3.76 × 10⁷ g mol⁻¹(Ni) h⁻¹ for 12 with 10 equiv. of PPh₃). The ligand environment and reaction conditions significantly affect the catalytic activity of their nickel complexes.     

Nickel (II) complexes bearing 2-ethylcarboxylate-6-iminopyridyl ligands: synthesis, structures and their catalytic behavior for ethylene oligomerization and polymerization

A series of nickel (II) complexes (L)NiCl₂ (7-9) and (L)NiBr₂ (10-12) were prepared by the reactions of the corresponding 2-carboxylate-6-iminopyridine ligands 1-6 with NiCl₂ · 6H₂O or (DME)NiBr₂ (DME = 1,2-dimethoxyethane), respectively. All the complexes were characterized by IR spectroscopy and elemental analysis. Solid-state structures of 7, 8, 10, 11 and 12 were determined by X-ray diffraction. In the cases of 7, 8 and 10, the ligands chelate with the nickel centers in tridentate fashion in which the carbonyl oxygen atoms coordinate with the metal centers, while the carbonyl oxygen atoms are free from coordinating with the nickel centers in 11 and 12. Upon activation with methylaluminoxane (MAO), these complexes are active for ethylene oligomerization (up to 7.97 × 10⁵ g mol⁻¹ (Ni) h⁻¹ for 11 with 2 equivalents of PPh₃ as auxiliary ligand) and/or polymerization (1.37 × 10⁴ g mol⁻¹ (Ni) h⁻¹ for 9). The ethylene oligomerization activities of 7-12 were significantly improved in the presence of PPh₃ as auxiliary ligands. The effects of the coordination environment and reaction conditions on the ethylene catalytic behaviors have been discussed.     

Bridged bis-pyridinylimino dinickel(II) complexes: Syntheses, characterization, ethylene oligomerization and polymerization

A series of bridged bis(pyridinylimino) ligands were efficiently synthesized through the condensation reaction of 4,4′-methylene-bis(2,6-disubstituted aniline) with 2-pyridinecarboxaldehyde or 2-benzoylpyridine. They reacted with (DME)NiBr₂ to form dinuclear Ni(II) complexes. All resultant compounds were characterized by elemental analysis, IR spectra as well as the single-crystal X-ray diffraction to confirm the structures of ligands and complexes. Activated with methylaluminoxane (MAO), these nickel complexes showed considerably good activities for ethylene oligomerization and polymerization. Their catalytic activities and the properties of PEs obtained were depended on the arched environment of ligand and reaction conditions.     

New o-methoxyphenylcyclopentadienylchromium (III) complexes: Synthesis, structures and catalytic properties for ethylene polymerization

Two new ligands 1-(2-methoxyphenyl)-3,4-diphenylcyclopentadiene (1) and 1-(2-methoxyphenyl)-2,3,4,5-tetramethylcyclopentadiene (2), as well as their corresponding cyclopentadienylchromium complexes η⁵-1-(2-methoxyphenyl)-3,4-diphenylcyclopentadienyl chromium dichloride (3) and η⁵-1-(2-methoxyphenyl)-2,3,4,5-tetramethylcyclopentadienyl chromium dichloride (4) were synthesized and characterized. Molecular structures of 3 and 4 were determined by single-crystal X-ray diffraction. Complexes 3 and 4 were tested as catalyst precursors for ethylene polymerization. When activated with Al(ⁱBu)₃ and , complex 3 shows reasonable catalytic activity while 4 exhibits high catalytic activity for ethylene polymerization. The effects of temperature and Al/Cr ratio on the catalytic activity were studied. The molecular weight and melting temperature of the produced polyethylenes were determined.     

Synthesis,characterization, and reactivity studies in ethylene polymerization of cyclometalated palladium(II) complexes containing terdentate ligands with N,C,N-donors

The reaction of [Na₂PdCl₄] with 3,5-bis(2-pyridoxy)toluene (L_pyH) in acetic acid yields the cyclometalated complex [PdCl(L_py-N, C, N)] (1). Complex 1 can be further converted into neutral species by metathesis reaction exchange of chloride by either iodide or thiocyanate to yield [PdX(L_py-N, C, N)] (X = I (2), SCN (3)). The chloride can be replaced by neutral ligands like pyridine or acetonitrile in the presence of silver tetrafluoroborate to give the corresponding cationic compounds [PdL(L_py-N, C, N)]BF₄ (L = Py (4), MeCN (5)). In contrast, the reaction of [Na₂PdCl₄] with 3,5-bis(3, 5-dimethylpyrazol-1-ylmethyl)toluene (L_pzH) under analogous conditions yields the neutral complex [PdCl₂(L_pzH-N, N)](6) with the ligand bidentate N,N-donor. The cyclometalated palladium complex [PdCl(L_pz-N, C, N)] (7) was prepared by the reaction of Pd(OAc)₂ with L_pzH in acetic acid followed by a metathetic reaction with lithium chloride in acetone/water. Complexes 1, 6, and 7 in the presence of methylaluminoxane (MAO) lead to an active catalyst for the polymerization of ethylene.     

2-Benzoimidazol-8-alkylquinolinylnickel(II) complexes as efficient catalysts for ethylene oligomerization and vinyl polymerization of norbornene

A series of nickel complexes LNiCl₂ (C1–C16), where L represents 2-benzoimidazol-8-alkylquinoline and its derivatives, were prepared as potential catalysts for the oligomerization of ethylene. The molecular structure of a representative complex C2·CH₃CH₂OH was determined by single-crystal X-ray diffraction. Upon treatment with diethylaluminium chloride (Et₂AlCl), all nickel complex pre-catalysts exhibited good activities in the oligomerization of ethylene. Furthermore, in the presence of methylaluminoxane (MAO), the nickel pre-catalysts were suitable for vinyl polymerization of norbornene.     

Titanium(IV) complexes with monocyclopentadienyl and phenoxy-alkoxo ligands: Synthesis,structures and catalytic properties for ethylene polymerization

Three monochlorotitanium complexes Cp′Ti(2,4-^tBu₂-6-(CPh₂O)C₆H₂O)Cl [Cp′ = η⁵-C₅H₅ (2), η⁵-C₅(CH₃)₅ (3), η⁵-C₅H₂Ph₂CH₃ (4)] have been synthesized in high yields (>90%) by the reaction of corresponding Cp′TiCl₃ with the dilithium salt of ligand 2,4-^tBu₂-6-(CPh₂OH)C₆H₂OH (1). When activated by [Ph₃C]⁺[B(C₆F₅)₄]⁻ and AlⁱBu₃, complexes 2–4 exhibit reasonable catalytic activity for ethylene polymerization, producing polyethylenes with moderate molecular weights and melting points. Addition of excess water to complex 2 gave the oxo-bridged complex [Ti(η⁵-C₅H₅)(2,4-^tBu₂-6-(CPh₂O)C₆H₂O)]₂O (5). Complexes 4 and 5 were characterized by single crystal X-ray diffraction.     

The combination of mononuclear metallocene and phenoxyimine complexes to give trinuclear catalysts for the polymerization of ethylene

Trinuclear complexes were synthesized by combination of metallocene and phenoxyimine zirconium complexes. After activation with methylalumoxane (MAO), these catalysts polymerize ethylene with moderate and good activities. Due to the presence of different catalytic centers, polyethylenes with broad or bimodal molecular weight distributions were obtained.     

Synthesis, structure and ethylene polymerization behavior of titanium phosphinoamide complexes

(Phosphinoamide)(cyclopentadienyl)titanium(IV) complexes of the type Cp*TiCl₂(η²-Ph₂PNR) [Cp*=C₅Me₅; R = t-Bu (2a), R = n-Bu (2b), R = Ph (2c)] have been prepared by the reaction of Cp*TiCl₃ with the corresponding lithium phosphinoamides. The structure of Cp*TiCl₂(η²-Ph₂PN^tBu) (2a) and Cp*TiCl₂(η²-Ph₂PNPh) (2c) have been determined by X-ray crystallography. These complexes exhibited moderate catalytic activities for ethylene polymerization in the presence of modified methylaluminoxane (MMAO). Catalytic activity of up to 2.5 × 10⁶ g/(mol Ti h) was observed when activated by i-Bu₃Al/Ph₃CB(C₆F₅)₄.     

Synthesis and characterization of N-(2-pyridyl)benzamide-based nickel complexes and their activity for ethylene oligomerization

A series of N-(2-pyridyl)benzamides (1)-(11) and their nickel complexes, [N-(2-pyridyl)benzamide]dinickel(II) di-μ-bromide dibromide (12)-(16) and (aryl)[N-(2-pyridyl)benzamido](triphenylphosphine)nickel(II) (17)-(24), were synthesized and characterized. The single-crystal X-ray analysis revealed that 12 and 14 are binuclear nickel complexes bridged by bromine atoms and each nickel atom adopts a distorted trigonal bipyramidal geometry. The key feature of the complexes 17, 19 and 23 is each has a six-membered nickel chelate ring including a deprotonated secondary nitrogen atom and an O-donor atom. The nickel complexes show moderate to high catalytic activity for ethylene oligomerization with methylaluminoxane (MAO) as cocatalyst. The activity of 12-16/MAO systems is up to 3.3 × 10⁴ g mol⁻¹ h⁻¹ whereas for 17-24/MAO systems it is up to 4.94 × 10⁵ g mol⁻¹ atm⁻¹ h⁻¹. The influence of Al/Ni molar ratio, reaction temperature, reaction period and PPh₃/Ni molar ratio on catalytic activity was investigated.     

Nickel(II) complexes with mono(imino)pyrrole ligands: preparation,structure and ethylene polymerization behavior

A series of unsymmetrical mono(imine)pyrroles (L1–L3) were synthesized by microwave irradiation from 2-acetylpyrrole and a series of dimethylanilines with two methyl groups at different positions on the aniline ring. A simplified synthetic method was initiated to prepare the corresponding nickel complexes NiL₂ (1–3) with direct condensation of mono(imine)pyrrole and nickel chloride. The compounds were determined using a suite of techniques (i.e. ¹H NMR, ¹³C NMR, IR, EA, MS). L1–L3 and 3 were further characterized by X-ray crystal diffraction. The structure of 3 showed that the ligand chelated to nickel with 2?:?1 M ratio, in spite of a 1?:?1 rate of charge. Application of 1–3 in ethylene polymerization indicated that mono(imino)pyrrole nickel complexes showed low activities. The polymerization reaction time and temperature, as well as the ligand structure, influenced the catalytic performance to some extent. Experimental data showed higher activity as –CH₃ on the aniline ring is closer to the imine group.