Titanium complexes bearing aromatic-substituted β-enaminoketonato ligands: Syntheses, structure and olefin polymerization behavior

A series of titanium complexes [(Ar)NC(CF₃)CHC(R)O]₂TiCl₂ (4b: Ar = -C₆H₄OMe(p), R = Ph; 4c: Ar = -C₆H₄Me(p), R = Ph; 4d: Ar = -C₆H₄Me(o), R = Ph; 4e: Ar = α-Naphthyl, R = Ph; 4f: Ar = -C₆H₅, R = t-Bu; 4g: Ar = -C₆H₄OMe(p); R = t-Bu; 4h: Ar = -C₆H₄Me(p); R = t-Bu; 4i: Ar = -C₆H₄Me(o); R = t-Bu) has been synthesized and characterized. X-ray crystal structures reveal that complexes 4b, 4c and 4h adopt distorted octahedral geometry around the titanium center. With modified methylaluminoxane (MMAO) as a cocatalyst, complexes 4b-c and 4f-i are active catalysts for ethylene polymerization and ethylene/norbornene copolymerization, and produce high molecular weight polyethylenes and ethylene/norbornene alternating copolymers. In addition, the complex 4c/MMAO catalyst system exhibits the characteristics of a quasi-living copolymerization of ethylene and norbornene with narrow molecular weight distribution.     

Zirconium complexes with versatile β-diketiminate ligands: Synthesis, structure, and ethylene polymerization

A series of zirconium complexes (2c, 2d, 2f, 2g, 2h, 2i) containing symmetrical or unsymmetrical β-diketiminate ligands were synthesized by the reaction of ZrCl₄ · 2THF with lithium salt of the corresponding ligand in 1:2 molar ratio. X-ray crystal structures reveal that complexes 2d and 2g adopt distorted octahedral geometry around the zirconium center. These complexes showed moderate activities for ethylene polymerization, when methylaluminoxane (MAO) was used as cocatalyst. The steric and electronic effects of the substituents at the phenyl rings had considerable influence on the catalytic activities of the metal complex, as well as the molecular weights and molecular weight distributions (MWD) of produced polymers. Introduction of electron-withdrawing CF₃ group to phenyls in the ligand led to a significant increase of catalytic activities, and complex 2f (p-CF₃) exhibited the highest catalytic activity of 7.45 × 10⁵ g PE/mol-Zr · h among the investigated complexes. Complexes 2a-d could produce ultra-high molecular weight polyethylenes (UHMWPE) that were hardly dissolvable in decahydronaphthalene or 1,2-dichlorobenzene under the molecular weight measurement conditions. Nevertheless, polyethylenes with broad MWD could be afforded by complexes 2g-i, which was probably due to the introduction of bulky unsymmetrical ligands leading to the formation of multi active species under polymerization conditions. High-temperature ¹³C NMR data indicate the linear structure of obtained polyethylenes.     

Synthesis, structure and norbornene polymerization behavior of nickel complexes bearing two β-ketoiminato chelate ligands

A series of nickel(II) complexes bearing two nonsymmetric bidentate β-ketoiminato chelate ligands have been prepared, and the structures of complexes [(2,6-Me₂C₆H₃)NC(CH₃)C(H)C(Ph)O]₂Ni (4a) and [(2,6-Me₂C₆H₃)NC(CH₃)C(H)C(CF₃)O]₂Ni (4c) have been confirmed by X-ray crystallographic analysis. These nickel(II) complexes were investigated as catalysts for the vinylic polymerization of norbornene. Using modified methylaluminoxane (MMAO) as a cocatalyst, these complexes display very high activities and produce high molecular weight polymers. Catalytic activity of up to 1.16 × 10⁴ kg/mol_Ni · h and the viscosity-average molecular weight of polymer of up to 870 kg/mol were observed. Catalyst activity, polymer yield, and polymer molecular weight could be controlled over a wide range by the variation of the reaction parameters such as Al/Ni molar ratio, norbornene/catalyst molar ratio, monomer concentration, polymerization reaction temperature and time.     

Synthesis and characterization of fluoro-substituted β-enaminoketonato titanium complexes and their catalytic behavior of regioselective ethylene/cyclopentadiene copolymerization

The ethylene/cyclopentadiene (CPD) copolymerization behavior by using fluoro-substituted bis(β-enaminoketonato) titanium complexes [FC₆H₄NC(CH₃)CHCO(CF₃)]₂TiCl₂ (1a–1c) has been investigated in detail. Upon utilizing MMAO as a cocatalyst, complexes 1a–1c exhibit high catalytic activities, affording the copolymers with high molecular weight and unimodal molecular weight distribution. Compared with non-substituted complex [C₆H₅NC(CH₃)CHCO(CF₃)]₂TiCl₂ (1), complexes 1a–1c can produce the copolymers with CPD incorporation adjusted in a wide range due to the enhancement of electrophilicity of metal center caused by introducing electron-withdrawing groups. Especially complex 1c bearing fluorine at the para-position of N-aryl moiety provides the highest CPD incorporation, which is nearly two times (18.5 mol%) higher than the non-substituted complex 1 (8.9 mol%) under the same conditions. The highest CPD incorporation up to 24.6 mol% can be easily achieved using this complex. ¹H- and ¹³C-NMR spectra demonstrate that these fluoro-substituted complexes possess regioselective nature with exclusive 1,2-insertion fashion, and alternating ethylene-CPD sequence can be detected at high CPD incorporation.     

Dendritic β-diketiminato titanium and zirconium complexes: synthesis and ethylene polymerisation

The cyclopentadienyl(β-diketiminato)titanium and zirconium chlorides (η⁵-C₅H₅)MCl₂(CH(C(NC₆H₄-4-OR)CH₃)₂) (M = Ti (4-dend), Zr (5-dend)), where R corresponds to the first generation carbosilane dendron (dendritic wedge) Si(CH₂CH₂SiMePh₂)₃, have been synthesised. After activation with methylaluminoxane, the activity of 4-dend and 5-dend as catalysts for ethylene polymerisation has been determined and compared with that of the non-dedritic counterpart (η⁵-C₅H₅)MCl₂(CH(C(NC₆H₅)CH₃)₂) (M = Ti (4), Zr (5)).     

Novel heteroligated titanium complexes with fluorinated salicylaldiminato and β-enaminoketonato ligands: synthesis, characterization and catalytic behavior in vinyl addition polymerization of norbornene

A series of heteroligated (salicylaldiminato)(β-enaminoketonato)titanium complexes of the general formula [3-Bu(t)-2-OC(6)H(3)CH==N(C(6)F(5))][PhN==C(CF(3))CHC(R)O]TiCl(2) (3a: R==Ph, 3b: R==C(6)H(4)Ph(p), 3c: R==C(6)H(4)Ph(o), 3d: R = 1-naphthyl, 3e: R = C(6)H(4)F2(2,6), 3f: R = C(6)H(4)Cl2(2,5), 3g: R==C(6)F4(2,3,5,6)OMe(4)) were synthesized. The structure of complexes 3d, 3f-g were determined by single crystal X-ray diffraction analysis. The X-ray crystallographic analysis indicated these complexes adopted a distorted octahedral geometry around the titanium center. Upon activation with modified methylaluminoxane, complexes 3a-g exhibited moderate to good catalytic activity for norbornene (NB) vinyl addition polymerization, producing moderate molecular weight polynorbornenes under mild conditions. The introduction of electron-withdrawing groups can greatly enhance the catalytic activity. Significantly, the heteroligated titanium complexes displayed greatly improved activity for vinyl addition polymerization of NB compared to homoligated counterparts, which may stem from the suitable combinations of electronic and steric effects.     

Binuclear titanium complexes coordinated by rigid p-phenylene linked bis-β-carbonylenamine: Synthesis,structure, ethylene polymerization and copolymerization with 1,5-hexadiene

Binuclear complexes for olefin polymerization have attracted great attention due to their unique catalytic properties compared with their mononuclear counterparts. Here a series of p-phenylene-bridgedbis-β-carbonylenamine ligands and their binuclear Ti complexes Ti ₂ L ¹ – Ti ₂ L ³ were prepared and characterized by ¹H NMR, ¹³C NMR, Fourier transform infrared spectroscopy, and elemental analysis. The binuclear complex Ti ₂ L ³ bearing an octylthio sidearm was further investigated by single-crystalX-ray diffraction, which revealed that the ligand was of β-imino enol form, with one titanium atom ligated with six other atoms, forming a deformed octahedral configuration. Furthermore, the ligand in Ti ₂ L ³ adopted a cis configuration, which was different from the trans configuration of its m-phenylene-bridged derivatives. These binuclear complexes ( Ti ₂ L ¹ – Ti ₂ L ³ ) could catalyze ethylene polymerization and copolymerization with 1,5-hexadiene(1,5-HD) efficiently under modified methylaluminoxane activation. Compared with the mononuclear complex TiL ⁵ , the binuclear catalysts were thermally more stable and showed higher activity for ethylene polymerization at higher temperatures. The activity of these titanium complexes for the copolymerization of ethylene with 1,5-HD were over 10⁶ g/mol Ti.h.atm, almost twice as high as for homopolymerization. Compared with the mononuclear analogue TiL ⁵ and the m-substituted binuclear derivative Ti ₂ L ⁴ , binuclear catalyst Ti ₂ L ² showed higher activity and insertion rate of the comonomer. The activity of Ti ₂ L ² was two to three times higher than that of TiL ⁵ and Ti ₂ L ⁴ , indicating that p-substituted binuclear catalysts generate clear bimetallic synergistic effect for the copolymerization of ethylene and 1,5-HD. Meanwhile, 1,5-HD takes 1,3-cyclopentyl form in the polymer by 1,3-insertion. The copolymer prepared by binuclear catalysts had higher molecular weight and wider molecular weight distribution than that prepared by the mononuclear catalyst.     

Synthesis and characterization of novel titanium complexes bearing [ONX]-type β-enaminoketonato ligands and their application to ethylene (co)polymerization

A series of novel titanium complexes bearing tridentate β-enaminoketonato chelating ligands of type, [R(2)NC(CF(3))C(H)CR(1)O]TiCl(3) (2a: R(1) = Ph, R(2) = -C(6)H(4)OMe(o); 2b: R(1) = Ph, R(2) = -C(9)H(6)N; 2c: R(1) = Ph, R(2) = -C(6)H(4)SMe(o); 2d: R(1) = Ph, R(2) = -C(6)H(4)SPh(o); 2e: R(1) = (t)Bu, R(2) = -C(6)H(4)SPh(o)) and [R(2)NC(R(1))C(H)C(CF(3))O]TiCl(3) (2f: R(1) = Ph, R(2) = -C(6)H(4)PPh(2)(o)) were prepared from TiCl(4) by treating with one equiv of deprotonated ligands in toluene. The reaction of 1a with equivalent of TiCl(4) in THF afforded another complex, C(6)H(4)OMeNC(CF(3))C(H)CPhO]TiCl(3)(thf) (3a), in addition to formation of the dichloride complex 4a, [C(6)H(4)(OMe)NC(CF(3))C(H)CPhO](2)TiCl(2). After deprotonation by alkali-metal hydride at -78 °C in diethyl ether, ligand 1a could react with 0.5 equiv of TiCl(4) to form the exclusive and clean dichloride complex 4a in high yield. These complexes were identified by NMR and mass spectra as well as elemental analyses. X-ray diffraction studies on these new trichloride complexes revealed a distorted octahedral coordination of the central metal with three chlorine atoms in a mer disposition. Dichloride complex 4a also adopted a distorted octahedral geometry around the titanium center. Two chlorine atoms are situated in the cis position, as seen in the bond angles for Cl(1)-Ti-Cl(2) (92.64(7)°). The O atom on the heterocyclic group was not coordinated with Ti. When activated by modified methylaluminoxane (MMAO), complexes 2a-e exhibited moderate to high activity towards ethylene (co)polymerization, giving relatively high molecular weight polymers with unimodal molecular weight distribution.     

Synthesis and crystal structures of dichlorocyclopentadienyl β-diketonate titanium complexes

Complexes of acetylacetonatodichlorocyclopentadienyltitanium(IV) (1) and dichlorocyclopentadienyl(2,2,6,6-tetramethyl-3,5-heptanedionato)titanium(IV) (2) have been prepared and their crystal structures determined by X-ray diffraction methods. Complex 1 crystallizes in space group P2₁/m with a?=?7.1893(10), b?=?11.7680(17), c?=?7.6129(11) Å, β?=?109.901(12)°; complex 2 crystallizes in space group P2₁/n with a?=?10.065(2), b?=?16.322(3), c?=?12.219(2) Å, β?=?110.99(3)°. The molecular structures of 1 and 2 can be described as square-based pyramidal, with the centroid of the C₅H₅ ring occupying the apical site and the bidentate β-diketonate and two chloride ligands occupying the basal positions. The average distances between titanium and oxygen atoms are 1.991(2) and 1.967(3) Å in compounds 1 and 2, respectively.     

Syntheses,crystal structure and theoretical modelling of tetrahedral mono-β-diketonato titanocenyl complexes

A comparative investigation on three novel bis(cyclopentadienyl) mono(β-diketonato) titanium(IV) complexes, [Cp₂Ti^IV(R¹COCHCOR²)]⁺ClO₄⁻ (Cp = η⁵-C₅H₅), i.e. [Cp₂Ti(tfba)]⁺, [Cp₂Ti(tfth)]⁺ and [Cp₂Ti(tfba)]⁺ where tfba = CF₃COCHCOC₆H₅⁻, tfth = CF₃COCHCOC₄H₃S⁻ and tffu = CF₃COCHCOC₄H₃O⁻, has been performed based on structural data and DFT calculations. The preparation of [Cp₂Ti^IV(β-diketonato)]⁺ClO₄⁻ involves the reaction of Cp₂TiCl₂ with AgClO₄ and the respective β-diketones. The crystal structures show that the structures are isomorphous. All the complexes exhibit π-stacking between one Cp ring and the aromatic R-group ring, i.e. the C₆H₅, C₄H₃S and C₄H₃O fragments, respectively. The DFT calculations show that the formal 16-electron count of these d⁰ titanium(IV) complexes is increased via Ti ← O π bonding. The bonding mode in the [Cp₂Ti(β-diketonato)]⁺ complexes is different from that in Cp₂Ti(OR)₂ and Cp₂Ti(dioxolene) complexes.     

Convenient Syntheses of Perdeuterioacrylonitrile and β,β-Dideuterioacrylonitrile

Perdeuterioacrylonitrile can be prepared conveniently from succinonitrile in a two-step process. Succinonitrile is exchanged with D₂O to obtain perdeuteriosuccinonitrile, which is then pyrolyzed at ～550°C to obtain perdeuterioacrylonitrile and DCN. CDBCN and CzDsCN are by-products of this reaction. A chemical procedure for separating perdeuterioacrylonitrile from these materials was developed. This involved formation of the Diels-Alder adduct of cyclopentadiene with perdeuterioacrylonitrile, followed by pyrolysis of the purified adduct at -330°C. Cyclopentadiene was removed from the resulting pyrolyzate by reaction with maleic anhydride. Purified perdeuterioacrylonitrile exchanged with H₂O to yield β,β-dideuterioacrylonitrile in good yield and good isotopic purity.     

Study on polymerization and structure of polydiphenylamine

The electrochemical oxidation of diphenylamine in acetonitrile produces an adherent uniform polymer film which exhibits mutiple colour variation(yellow-green-blue) in a wide range of potential scan. The polymerization mechanism and the structure of the polymer were studied by cyclic voltammetry, FT-IR and in situ ESR. The results indicate that the electrochemical polymerization of diphenylamine belongs to a cationic radical polymerization process. During electrolysis, only oligomers were initialy produced, then polymer film was formed on the electrode surface. The electropolymerization performs via the 4,4' C-C phenyl-phenyl coupling mechanism.     

Transition metal complexes bearing 2,6-bis(imino)pyridyl:Synthesis, structure, ethylene polymerization/oligomerization studies

A series of new complexes {2,6-bis[1-((2-methyl-4-methoxyphenyl)imino)ethyl]pyri-dine}MCI2 [M=Fe(Ⅱ) (2), Co(Ⅱ) (3), Ni(Ⅱ) (4), Cu(Ⅱ) (5), Zn(Ⅱ) (6)] have been synthesized. At 25℃, using 500 equiv of methylaluminoxane (MAO), the activities of Fe(Ⅱ), Co(Ⅱ) catalysts can reach 4.02×106 g/mol-Fehatm for ethylene polymerization and 3.98×105 g/mol-Cohatm for ethylene oligomerization. The effects of polymerization conditions such as reaction temperature, Al/M molar ratio and time on the activity of catalyst have been explored.     

Pyridoxylidene aminoguanidine and its copper(II) complexes – Syntheses,structure, and DFT calculations

Two nitrate salts of the well-known, and due to its significant biological activity very important, compound pyridoxylidene aminoguanidine (PLAG) were obtained in the form of single crystals. Thus this ligand is structurally characterized for the first time. In addition, the first data on the structure of a Schiff base of aminoguanidine with the active form of vitamin B₆, i.e. pyridoxal-phosphate, of the formula PLPAG·HCl·2H₂O, are presented. Two new square-pyramidal Cu(II) complexes of PLAG were synthesized and their physicochemical and structural properties analyzed. In these complexes, PLAG is coordinated as a zwitter-ion, in a tridentate ONN manner, via the oxygen atom of the deprotonated phenolic OH-group and nitrogen atoms of the azomethine and imino group of the aminoguanidine moiety. For the first time it was possible to make a comparative analysis of the structural properties of ligand salts and the coordinated ligand, so the effects of coordination could be unequivocally pointed out. Common fragments encountered in ligand structures were compared by half-normal probability plots. Density functional theory calculations have been conducted in order to gain insight into reactive properties of the investigated molecules. Molecular electrostatic potential, average local ionization energy surfaces, and Fukui functions have been calculated in order to obtain further information on the reactive properties.     

Trinuclear zinc β-naphthoate complexes: synthesis and structure

New trinuclear Zn^II β-naphthoate complexes with mono- and bidentate N-donor ligands (2,3-lutidine (lut), 1,10-phenanthroline (phen), and 5,5′-di-tert-butyl-2,2′-bipyridine (dtb-bpy)), (lut)₂Zn₃(μ₂,η²-OOCR)₂(μ₂-OOCR)₄ (1), [(phen)₂Zn₃(μ₂,η²-OOCR)₂(μ₂-OOCR)₄]·2MeCN··2C₆H₆ (2), and (dtb-bpy)₂Zn₃(μ₂,η²-OOCR)₂(μ₂-OOCR)₄ (3) (RCOO⁻ is the anion of β-naphthoic acid C₁₀H₇COOH), were synthesized. The structures of compounds 1–3 were studied by single-crystal X-ray diffraction. In the crystal structures, molecules 1–3 are ordered due to the coplanar arrangement of the aromatic substituents of the acid and the N-donor ligands, as well as through stacking interactions.     

Zirconium and hafnium amide, alkoxide, and pyrrolyl complexes manifesting with pyrrolyl-linked N-donor ligands: Syntheses, characterization, and ring opening polymerization of ε-caprolactone

A series of zirconium and hafnium alkoxide and amide complexes containing symmetrical tridentate pyrrolyl ligand, [C₄H₂NH(2,5-CH₂NMe₂)₂] have been synthesized conveniently by treatment of 2,6-di-tert-butylphenol, tert-butanol or pyrrole in pentane and their reactivity over ring opening polymerization of ε-caprolactone have been carried out. Reactions of [C₄H₂NH(2,5-CH₂NMe₂)₂] with M(NEt₂)₄ (M = Zr or Hf) originate [C₄H₂N(2,5-CH₂NMe₂)₂]M(NEt₂)₃ (1, M = Zr; 2, M = Hf). Furthermore, reactions of [C₄H₂N(2,5-CH₂NMe₂)₂]M(NEt₂)₃ with 2,6-di-tert-butylphenol, tert-butanol or pyrrole afford [C₄H₂N(2,5-CH₂NMe₂)₂]M(OC₆H₃-2,6-^tBu₂)(NEt₂)₂ (3, M = Zr; 4, M = Hf), [C₄H₂N(2,5-CH₂NMe₂)₂]M(O^tBu)₃ (5, M = Zr; 6, M = Hf) and [C₄H₂N(2,5-CH₂NMe₂)₂]M(C₄H₄N)₃ (7, M = Zr; 8, M = Hf), respectively, in satisfactory yield. All the complexes have been characterized by NMR spectra as well 3, 4 and 6 subjected to the X-ray diffraction analysis. Complexes 3-8 have been used as initiators for the ring-opening polymerization of ε-caprolactone and observed broad PDI values (1.84-2.75) representing multiple reactivity centers of these complexes.     

Syntheses,structures and comparative electrochemical study of π-acetylene complexes of cobalt

The preparation and characterization of the complexes [Co₂(CO)₄(μ-dppm)]₂(μ-η²-Me₃SiC₂(CC)₂C₂H) (2), [Co₂(CO)₄(μ-dppm)]₂(μ-η²-HC₂(CC)₂C₂H) (3), Co₂(CO)₄(μ-dmpm)(μ-η²-Me₃SiC₂CCSiMe₃) (4), Co₂(CO)₄(μ-dmpm)(μ-η²-Me₃SiC₂CCH) (5), [Co₂(CO)₄(μ-dmpm)]₂(μ-η²-Me₃SiC₂(CC)₂C₂SiMe₃) (6) and [Co₂(CO)₄(μ-dmpm)]₂(μ-η²-HC₂(CC)₂C₂H) (7) are described. A comparative electrochemical study of all these complexes and the related [Co₂(CO)₄(μ-dppm)]₂(μ-η²-Me₃SiC₂(CC)₂C₂SiMe₃) (1), Co₂(CO)₄(μ-dppm)(μ-η²-Me₃SiC₂CCH) and Co₂(CO)₄(μ-dppm)(μ-η²-HC₂CCH) is presented by means of the cyclic and square-wave voltammetry techniques. Crystals of 2 and 3 suitable for single-crystal X-ray diffraction were grown and the molecular structures of these compounds are discussed.     

Chelating diamide complexes of titanium: new catalyst precursors for the highly active and living polymerization of α-olefins

The reaction of RHN(CH₂)₃NHR (1a,b) (a, R=2,6-ⁱPr₂C₆H₃; b, R=2,6-Me₂C₆H₃) with 2 equiv of BuLi followed by 2 equiv of ClSiMe₃ yields the silylated diamines R(Me₃Si)N(CH₂)₃N(SiMe₃)R (3a,b). The reaction of 3a,b with TiCl₄ yields the dichloride complexes [RN(CH₂)₃NR]TiCl₂ (4a,b) and two equiv of ClSiMe₃. An X-ray study of 4a (P2₁/n, a=9.771(1) Å, b=14.189(1) Å, c=21.081(2) Å, β=96.27(1)°, V=2905.2(5) ų, Z=4, T=25°C, R=0.0701, R_w=0.1495) revealed a distorted tetrahedral geometry about titanium with the aryl groups lying perpendicular to the TiN₂-plane. Compounds 4a,b react with 2 equiv of MeMgBr to give the dimethyl derivatives [RN(CH₂)₃NR]TiMe₂ (5a,b). An X-ray study of 5b (P2₁2₁2₁, a=8.0955(10) Å, b=15.288(4) Å, c=16.909(3) Å, V=2092.8(7) ų, Z=4, T=23°C, R=0.0759, R_w=0.1458) again revealed a distorted tetrahedral geometry about titanium with titanium–methyl bond lengths of 2.100(9) Å and 2.077(9) Å. These titanium dimethyl complexes are active catalysts for the polymerization of 1-hexene, when activated with methylaluminoxane (MAO). Activities up to 350,000 g of poly(1-hexene)/mmol catalyst·h were obtained in neat 1-hexene. These systems actively engage in chain transfer to aluminum. Equimolar amounts of 5a or 5b and B(C₆F₅)₃ catalyze the living aspecific polymerization 1-hexene. Polydispersities (M_w/M_n) as low as 1.05 were measured. Highly active living systems are obtained when 5a is activated with {Ph₃C}⁺[B(C₆F₅)₄]⁻. A primary insertion mode (1,2 insertion) has been assigned based on both the initiation of the polymer chain and its purposeful termination with iodine.     

Synthesis, structure and ring-opening polymerization of macrocyclic arylates containing phthalic unit

A series of maerocyclic arylate diraers have been selectively synthesized by an interfacial polyconden-sation of o-phthaloyldichloride with bisphenols A combination of GPC,FAB-MS,1H and 13C NMR unambiguously confirmed the cyclic nature Although single-crystal X-ray analysis of two such macrocycles reveals no severe strain on the cyclic structures,these macrocycles can undergo facile melt polymerization to give high molecular weight polyary-lates.