Chromium(III) complexes bearing bis(benzotriazolyl)pyridine ligands: synthesis,characterization and ethylene polymerization behavior

Reaction of benzotriazole with 2,6-bis(bromomethyl)pyridine and 2,6-pyridinedicarbonyl dichloride yields the tridentate ligands 2,6-bis(benzotriazol-1-ylmethyl)pyridine (1) and 2,6-bis(benzotriazol-1-ylcarbonyl) pyridine (2). The molecular structures of the ligands were determined by single-crystal X-ray diffraction. These ligands react with CrCl₃(THF)₃ in THF to form neutral complexes, [CrCl₃{2,6-bis(benzotriazolyl)pyridine-N,N,N}] (3, 4), which are isolated in high yields as air stable green solids and characterized by mass spectra (ESI), FTIR spectroscopy, UV–Visible, thermogravimetric analysis (TGA), and magnetic measurements. After reaction with methylaluminoxane (MAO), the chromium(III) complexes are active in the polymerization of ethylene showing a bimodal molecular weight distribution. A DFT computational investigation of the polymerization reaction mechanism shows that the most likely reaction pathway originates from the mer configuration when the spacer is CH₂ (complex 3) and from the fac configuration when the spacer is CO (complex 4).     

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.     

Substituted cyclopentadienylchromium(III) complexes containing neutral donor ligands. Synthesis, crystal structures and reactivity in ethylene polymerization

Lithium derivatives of substituted cyclopentadiene ligands reacted with CrCl₃(THF)₃ in THF solution to afford homodinuclear complexes of the type [{(η⁵-RCp)CrCl(μ-Cl) }₂] [R=SiMe₃ (1), CH₂C(Me)CH₂ (2)]. Complex 1 reacts with pyrazole (C₃H₄N₂) to yield the mononuclear half-sandwich complex [(η⁵-Me₃SiCp)CrCl₂(pyrazole)] (3). The similar complex [Cp*CrCl₂(pyrazole)] (4) was synthesised by reaction of [{Cp*CrCl(μ-Cl)}₂] with pyrazole. Complex 2 reacts with bidentate ligands to give binuclear complexes of the type [{(η⁵-CH₂C(Me)CH₂Cp)CrCl₂ }₂(μ-L-L)] [L-L=Ph₂PCH₂CH₂PPh₂ (5), trans-Ph₂P(O)CHCHP(O)Ph₂ (6)]. All complexes were structurally characterised by X-ray diffraction. After reaction with methylaluminoxane these complexes are active in the polymerization of ethylene. At 25 °C and 4 bar of ethylene, complex 3 yields polyethylene with a bimodal molecular weight distribution centred at 155,000 and 2000 g/mol. Complex 4 shows similar activity, yielding only the low molecular weight fraction. On the other hand, the binuclear complexes 5 and 6 under the same conditions were three times more active than mononuclear complexes. The melting point of the polymers indicates the formation of linear polyethylene.     

Chromium(III) complexes bearing 2-benzoxazolyl-6-arylimino-pyridines: Synthesis and their ethylene reactivity

A series of chromium(III) complexes bearing 2-benzoxazolyl-6-aryliminopyridines was synthesized and characterized by IR spectroscopic and CHN analysis. The X-ray crystallographic analysis of complex Cr3 revealed a distorted octahedral geometry. When activated by Et₂AlCl, MAO or MMAO, these chromium complexes exhibited activities towards ethylene reactivity. High activities of ethylene oligomerization (up to 9.19 × 10⁶ g mol⁻¹ (Cr) h⁻¹) were observed in the catalytic system using MMAO as a cocatalyst, meanwhile good activities of ethylene polymerization were achieved (up to 5.20 × 10⁵ g mol⁻¹ (Cr) h⁻¹) by using MAO as a cocatalyst. Various reaction parameters were investigated in detail, and the steric and electronic effects of ligands were discussed.     

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.     

Titanium complexes with novel triaryl-substituted phosphinimide ligands: Synthesis, structure and ethylene polymerization behavior

A series of titanium phosphinimide complexes [Ph₂P(2-RO-C₆H₄)]₂TiCl₂ (7, R = CH₃; 8, R = CHMe₂) and [PhP(2-Me₂CHO-C₆H₄)][THF]TiCl₃ (9) have been prepared by reaction of TiCl₄ with the corresponding phosphinimines under dehalosilylation. The structure of complex 9 has been determined by X-ray crystallography, and a solvent molecule THF was found to be coordinated with the central metal and the Ti-O bond was consistent with the normal Ti-O (donor) bond length. The complexes 7 and 8 displayed inactive to ethylene polymerization, and the complex 9 displayed moderate activity in the presence of modified methylaluminoxane (MMAO) or i-Bu₃Al/Ph₃CB(C₆F₅)₄, and this should be partly attributed to coordination of THF with titanium and the steric effect of two iso-propoxyl. And catalytic activity up to 32.2 kg-PE/(mol-Ti h bar) was observed.     

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.     

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.     

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.     

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.     

Iron(II)–ethylene polymerization catalysts bearing 2,6-bis(imino)pyrazine ligands: Part II. Catalytic behaviour, homogeneous and heterogeneous insights

A series of new iron(II) complexes bearing tridentate pyrazine-bis(2,6-arylimino) ligands where the aryl groups are 1-naphthyl, 2,6-dimethylphenyl, and 2,6-diisopropylphenyl have been used as ethylene polymerization catalysts after activation with alkylaluminiums. The new complexes display a lesser catalytic activity than those bearing the corresponding pyridine-bis(2,6-arylimino) ligands. Varying the steric bulkiness of the aromatic groups in the tridentate ligands and the polymerization conditions affects the catalytic productivity.     

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.     

Bis(pyrazolyl)pyridine vanadium(III) complexes as highly active ethylene polymerization catalysts

The synthesis, characterization and catalytic activity in ethylene polymerization of novel mononuclear vanadium complexes bearing N^∧N^∧N-tridentate (pyrazolyl-pyridine) ligands are described. With AlEtCl₂ as co-catalyst, complexes 1 and 2 produce single-site catalysts that polymerized ethylene affording high density polyethylene with fairly narrow molecular weight distribution.     

Synthesis, structure and ethylene polymerization behavior of zirconium complexes with chelating ketoiminate ligands

Mixed ketoiminate/ketoimine/pentamethylcyclopentadienyl (Cp*) complex of zirconium, [(η⁵-Cp*){CH₃C(O)CHC(NHR)CH₃}{CH₃C(O)CHC(NR)CH₃}ZrCl₂] (R=4-CF₃Ph) (3) has been prepared in high yield by the reaction of one equivalent of 4-CF₃-phenyl-β-ketoimine (1a) and one equivalent of lithium 4-CF₃-phenyl-β-ketoiminate (2a) with one equivalent of Cp*ZrCl₃ in Et₂O. Bis(ketoiminate)zirconium dichloride complexes, 4 and 6, have been also prepared in high yield by the reaction of amine elimination of ketoimine ligands, respectively 1a and 1b, with Zr(NMe₂)₄ and followed by chlorination reaction with TMSCl. The X-ray crystallography reveals that the compound 3 is based on distorted octahedral geometry containing a ketoimine and a ketoiminate. The ketoiminate ligand coordinates to the zirconium as a bidentate ligand, leaving the metal center coordinatively unsaturated and thus leading to an additional binding of a ketoimine ligand to the metal to stabilize the complex 3. The zirconium complexes 3, 4 and 6 provide the moderate activity for the polymerization of ethylene in the presence of MMAO cocatalyst. Low molecular weight and high density polyethylene was obtained.     

Synthesis, characterization and reactivity of palladium(II) compounds containing terdentate [Csp, N, S] or [Csp, N, S] ligands

The study of the reactivity of R---CH=N---(C₆H₄-2-SMe) with R=C₆H₅ or 2,4,6-Me₃-C₆H₂ with palladium(II) salts is reported. These studies have allowed us to prepare and characterize the coordination complexes: cis-[Pd{R---CH=N---(C₆H₄-2-SMe)}Cl₂] {R=C₆H₅ or 2,4,6-Me₃-C₆H₂} and the cyclopalladated compounds [Pd{C₆H₄---CH=N---(C₆H₄-2-SMe)}Cl] and [Pd{(2-CH₂-4,6-Me₂-C₆H₂)---CH=N---(C₆H₄-2-SMe)}Cl]. The X-ray crystal structures of the latter complexes reveal that the thioimines act as a [Csp², phenyl,N,S]⁻ and as a [Csp³, N,S]⁻ terdentate group, respectively. The study of the reactions of the cyclopalladated compounds with PPh₃ is also reported.     

Titanium complexes with modifiable pyrazolonato and pyrazolonato-ketimine ligands: Synthesis, characterization and ethylene polymerization behavior

Six titanium complexes bearing pyrazolonato and pyrazolonato-ketimine ligands have been synthesized and characterized. It was found that the ligand structure of the synthesized complexes has a significant effect on the catalytic performance of the complexes. The synthesized complexes were activated with MAO and their activities varied from negligible to high (up to 612 kg_PE/(mol_Ti h bar). The pyrazolonato-ketimine complex with a phenyl substituent in the imine part was the most active in the series and it was the only one producing polyethylenes with relatively narrow molecular weight distribution (M_w/M_n from 1.6 to 2.2).     

Transition-metal complexes of phenoxy-imine ligands modified with pendant imidazolium salts: Synthesis, characterisation and testing as ethylene polymerisation catalysts

Reaction between 3-((1R,2R)-2-{[1-(3,5-di-tert-butyl-2-hydroxy-phenyl)-meth-(E)-ylidene]-amino}-cyclohexyl)-1-isopropyl-4-phenyl-3H-imidazol-1-ium bromide (1a) or the derivative 3-((1R,2R)-2-{[1-(2-hydroxy-5-nitro-phenyl)-meth-(E)-ylidene]-amino}-cyclohexyl)-1-isopropyl-4-phenyl-3H-imidazol-1-ium bromide (1b) and metal halides MCl_x.yTHF (M = Zr, x = 4, y = 2; M = V, x = y = 3; M = Cr, x = y = 3), in THF, at −78 °C gives the metal complexes of general formula [MCl_x(κ²-N,O-OC₆H₂R¹R²C(H)N-C₆H₁₀-Im)₂][Br]₂ (where M = Zr, x = 2, R¹ = R² = ^tBu, 2; M = Zr, x = 2, R¹ = H, R² = NO₂, 3; M = V, x = 1, R¹ = R² = ^tBu, 4; M = Cr, x = 1, R¹ = R² = ^tBu, 5; M = Fe, x = 0, R¹ = R² = ^tBu, 6; Im = 1-isopropyl-4-phenyl-3H-imidazol-1-ium-3-yl). ¹H and ¹³C NMR spectroscopy of 2 and 3 indicate κ²-N,O-ligand coordination via the phenoxy-imine moiety with pendant imidazolium salt that is corroborated by a single crystal structure of 6. Compounds 2, 3, 4 and 5 were tested as precatalysts for ethylene polymerisation in the presence of methylaluminoxane (MAO) cocatalyst, showing low activity. Selected polymer samples were characterised by GPC showing multimodal molecular weight distributions.     

Tris(pyrazolyl)methane–chromium(III) complexes as highly active catalysts for ethylene polymerization

Reaction of complex CrCl₃(THF)₃ with the tris(pyrazolyl)methane ligands, HC(Pz)₃, HC(3,5-Me₂Pz)₃ and their substituted derivatives RC(Pz)₃ (R = Me, CH₂OH, CH₂OSO₂Me) in THF lead to the formation of neutral complexes of the types [RC(Pz)₃CrCl₃] and [RC(3,5-Me₂Pz)₃CrCl₃]. After reaction with methylalumoxane (MAO) these complexes are active in the polymerization of ethylene. The substituent on the methane central carbon atom of the ligand has some influence in polymerization behavior. This compounds present higher activities than similar chromium complexes, in the ethylene polymerization reaction.     

Syntheses, characterization and ethylene polymerization of half-sandwich group IV metal complexes with tridentate [O,N,S] ligands

A series of half-sandwich group IV metal complexes with tridentate monoanionic phenoxy-imine arylsulfide [O NS] ligand [2-Bu t 4-Me-6-((2-(SC 6 H 5)C 6 H 4 N = CHC 6 H 2 O)](La) and dianionic phenoxy-amine arylsulfide [O N S] ligand [2-Bu t 4-Me-6-((2-(SC 6 H 5)C 6 H 4 N-CH 2 C 6 H 2 O)] 2(Lb) have been synthesized and characterized.Lb was obtained easily in high yield by reduction of ligand La with excess LiAlH 4 in cool diethyl ether.Half-sandwich Group IV metal complexes CpTi[O NS]Cl 2(1a),CpZr[O NS]Cl 2(1b),CpTi[O N S]Cl(2a),CpZr[O N S]Cl(2b) and Cp * Zr[O N S]Cl(2c) were synthesized by the reactions of La and Lb with CpTiCl 3,CpZrCl 3 and Cp * ZrCl 3,and characterized by IR,1 H-NMR,13 C-NMR and elemental analysis.In addition,an X-ray structure analysis was performed on ligand Lb.The title Group IV half-sandwich bearing tridentate [O,N,S] ligands show good catalytic activities for ethylene polymerization in the presence of methylaluminoxane(MAO) as co-catalyst up to 1.58 × 10 7 g-PE.mol-Zr 1.h 1.The good catalytic activities can be maintained even at high temperatures such as 100 ℃ exhibiting the excellent thermal stability for these half-sandwich metal pre-catalysts.     

Cobalt and nickel complexes bearing 2,6-bis (imino) phenoxy ligands: syntheses, structures and oligomerization studies

A series of new cobalt and nickel complexes LMX₂ (M=Co, X=Cl; M=Ni, X=Br) bearing 2, 6-bis(imino)phenoxy ligands were synthesized. The solid-state structures of 1 and 4 have been determined by single-crystal X-ray diffraction study. Treatment of the complexes LMX₂ with methylaluminoxane (MAO) leads to active catalysts for oligomerization of ethylene with catalytic activities in the range of 1.2×10⁵–2.1×10⁵ g mol⁻¹ h⁻¹ atm⁻¹ for Ni complexes, and 10³ g mol⁻¹ h⁻¹ atm⁻¹ for Co complexes. The oligomers were olefins from C₄ to C₁₆.