Presence Of MAO Research Articles

Synthesis, Characterization, and Catalytic Exploration of Mononuclear Mo(VI) Dioxido Complexes of (Z)-1-R-2-(4',4'-Dimethyl-2'-oxazolin-2'-yl)-eth-1-en-1-ates.

The coordination chemistry of the title ligands with Mo metal centers was investigated. Thus, the synthesis and characterization (NMR, X-ray diffraction) of four mononuclear formally Mo(6+) complexes of (Z)-1-R-2-(4′,4′-dimethyl-2′-oxazolin-2′-yl)-eth-1-en-1-ates (L: R = –Ph, –Ph-p-NO2, –Ph-p-OMe and –t-Bu), derived from the part enols (LH), is described. The resulting air-stable MoO2L2 complexes (1–4) exist, as shown by single-crystal X-ray diffraction experiments, in the cis-dioxido-trans(N)-κ2-N,O-L conformation in the solid state for all four examples. This situation was further probed using semi-empirical PM6(tm) calculations. Complexes 1–4 represent the first Mo complexes of this ligand class and, indeed, of Group 6 metals in general. Structural and spectroscopic comparisons were made between these and related Mo(6+) compounds. Complex 1 (R = –Ph) was studied for its ability to selectively catalyze the production of poly-norbornene from the monomer in the presence of MAO. This, unfortunately, only resulted in the synthesis of insoluble, presumably highly cross-linked, polymeric and/or oligomeric materials. However, complexes 1–4 were demonstrated to be highly effective for catalyzing benzoin to benzil conversion using DMSO as the O-transfer agent. This catalysis work is likewise put into perspective with respect to analogous Mo(6+) complexes.

Alleviation of Iron Corrosion in Chloride Solution by N,N′-bis[2-Methoxynaphthylidene]amino]oxamide as a Corrosion Inhibitor

The alleviation of iron corrosion in 3.5% NaCl sodium chloride solution using N,N′-bis[2-methoxynaphthylidene]amino]oxamide (MAO) as a corrosion inhibitor has been reported. The work was achieved using various investigation techniques. Potentiodynamic cyclic polarization (PCP) displayed a powerful inhibition for the corrosion via reducing the iron’s cathodic and anodic reactions. This was reflected in reduced corrosion currents and increased polarization resistances in the presence and upon the increase of MAO concentration. The electrochemical impedance spectroscopy results indicated that MAO molecules provoke the corrosion resistance via increasing polarization resistance. The power of MAO on decreasing pitting attack was also investigated through measuring the change of current with time at −0.475 V(Ag/AgCl). Scanning electron microscopy images were taken of the surface after the current–time measurements were performed in the absence and presence of MAO. The current-time experiments indicated that MAO highly mitigates the corrosion of iron. The energy dispersive X-ray analyzer reported the products found on the tested surfaces. The effect of extending the exposure time from 1 h to 48 h was also tested and was found to alleviate the corrosion of iron, whether MAO molecules are absent or present.

Synthesis of Anthracene-Bridged Dinuclear Phenoxyiminato Organotitanium Catalysts with Enhanced Activity, Thermal Stability, and Comonomer Incorporation Ability toward Ethylene (Co)polymerization

Dinuclear titanium complexes syn-Ti2 and anti-Ti2 bearing anthracene-bridged bisphenoxyimine ligands (syn-L and anti-L) have been prepared and characterized by NMR and elemental analyses. The molecular structure of syn-Ti2 was defined by X-ray diffraction, revealing a separation of 7.183 A between the two Ti centers. The mononuclear complex [(2,6-iPr2-C6H3NCH-C6H2-3,5-tBu-2-O)­TiCl3(THF)] (Ti1) was also prepared for control experiments. In the presence of MAO as a cocatalyst, syn-Ti2 and anti-Ti2 were active toward ethylene homopolymerization but had distinct catalytic properties. The complex syn-Ti2 with a shorter metal–metal separation exhibited higher activity and produced polymers with higher molecular weights, in comparison to anti-Ti2, having a longer metal–metal separation, and the mononuclear catalyst control Ti1 under identical conditions. More importantly, the complex syn-Ti2 exhibited excellent thermal stability and thus the a greater activity can be obtained at 100 °C, which is a preferred temperature for industrial operations. For ethylene/1-hexene copolymerization, the activity, Mw, and incorporation of 1-hexene by syn-Ti2 were 2.3×, 3.2×, and 6.0× those of anti-Ti2 under identical conditions.

Selective Ethylene Dimerization into 2-Butenes Using Homogeneous and Supported Nickel(II) 2-Iminopyridine Catalysts

In this work, we report a series of novel nickel(II) dibromide and dichloride complexes with 2-iminopyridine and 2-iminoquinoline ligands bearing electron-withdrawing substituents (F, Cl, CF3), that have demonstrated high ethylene dimerization activity [up to 19.2 × 106 g of oligomers·(mol Ni)−1 h−1] in the presence of MAO or Et2AlCl, affording predominantly a mixture of 1-butene and cis- and trans-2-butene (C4 selectivity varies from 89 to 100%; 2-butenes selectivity in the C4 fraction approaches 96%). The effects of ligand substituents and the cocatalyst nature on the activity and selectivity of the nickel(II) complexes in ethylene dimerization have been established. Several nickel complexes were supported on silica-alumina and the resulting heterogeneous catalysts were probed towards ethylene dimerization. These catalysts also afford 2-butenes, with the activity and C4 selectivity being comparable to that of homogeneous catalysts.

Ansa-Metallocenes Bearing 4-(N-Azolyl)-2-methylindenyl and Related Ligands: Development of Highly Isoselective Catalysts for Propene Polymerization at Higher Temperatures

A series of Me2Si-bridged bis(2-Me-indenyl) ansa-zirconocenes containing N-pyrrolyl, N-indolyl, N-carbazolyl, and P-dibenzophospholyl substituents in position 4 of the indenyl moieties has been synthesized. Pd-catalyzed arylation of the azoles with 4-Br-2-Me-indene was used to synthesize the respective 4-(N-azolyl)indenes. 4-(P-Dibenzophospholyl)indene was obtained in high yield by reaction of 5-Cl-dibenzophosphole with (2-Me-inden-4-yl)MgBr. Some of the synthesized zirconocenes were characterized by X-ray crystallography. The rac-zirconocenes were tested in propylene polymerization in the presence of MAO or perfluoroarylborate activators. At 100 °C, the zirconocene rac-Me2Si[2-Me-4-(N-carbazolyl)indenyl]2ZrCl2/MAO afforded highly crystalline isotactic polypropylene with reasonable molecular weight (318 kDa) and a Tm value of 157 °C determined by a remarkably low total number of stereo- and regioerrors, which makes it one of the most isoselective catalysts for high-temperature propylene polymerization.

Highly thermo-stable and electronically controlled palladium precatalysts for vinyl homo/co-polymerization of norbornene-ethylene

In this contribution, the influence of substitutions ranging from electron donating to the electron withdrawing, on the bis(arylimino)acenaphthenes-palladium catalysts is investigated. A series of symmetrical bis(arylimino)acenaphthene-palladium complexes, [1,2-bis[2,6-(CHPh2)2–4-R-C6H2N]C2C10H6]PdMeCl (R = Me L1, Et L2, iPr L3, tBu L4, Cl L5, F L6) has been prepared and investigated toward the polymerization of nobornene as well as its copolymerization with ethylene comonomer. These palladium complexes displayed moderate to high activities for norbornene polymerization in the presence of MAO and (C6F5)4B·C6H5NH(CH3)2 co-catalysts. Specifically, complex Pd4 (R = tBu) displayed a highest activity up to 6.1 × 106 gPNBE mol−1Pd h−1 with 54.2% conversion of monomer at 60 °C and showed exceptionally high thermal stability (act: 4.81 × 105 gPNBE mol−1Pd h−1 with 51.2% conversion at 100 °C), and generating insoluble polynorbornene. Toward the copolymerization of norbornene-ethylene, Pd4 exhibited good activities with high incorporation of ethylene (up to 49.1%) and the resultant copolymer showed high molecular weights as high as 100.3 kg/mol−1 with narrow molecular weights distributions (PDI = 2.15).

Effect of Al Cocatalyst in Ethylene and Ethylene/Norbornene (Co)polymerization by (Imido)vanadium Dichloride Complexes Containing Anionic <i>N</i>-Heterocyclic Carbenes Having Weakly Coordinating Borate Moiety

Effect of Al cocatalyst in ethylene polymerization using (imido)vanadium(V) complexes containing anionic N-heterocyclic carbenes with a weakly coordinating borate moiety in 4-position (WCA-NHC), [V(N-2,6-Me2C6H3)Cl2(WCA-NHC)] [1; NHC=1,3-bis(2,6-dimethylphenyl)-imidazolin-2-ylidene], have been explored. The activities by 1 upon presence of AliBu3 in ethylene polymerization and in the copolymerization with norbornene (NBE) were higher than those in the presence of MAO, and the resultant poly(ethylene-co-NBE)s prepared by 1-AliBu3 catalyst possessed uniform molecular weight distributions and compositions. Formation of vanadium(III) species could be assumed upon presence of AliBu3, especially on the basis of both NMR and ESR spectra (silent) and certain significant changes in the V K-edge XANES (pre-edge and edge region) spectrum, whereas no significant changes in the XANES spectrum were observed from the toluene solution containing 1 upon addition of MAO. It is thus suggested that a difference in the catalyst performances between in the presence of MAO and AliBu3 should be due to a formation of different catalytically active species with different oxidation states.

Oxo-bridged azaallylzirconium complexes: Synthesis, characterization and ethylene polymerization behavior

The oxo-bridged azaallylzirconium chlorides (μ-O){η3-(2,6-Et2-4-R-C6H2) N(Ph)CCHSiMe2NMe2ZrCl2}2, [R=Me (C1) and H (C2)] have been prepared in reasonable yields from the reactions of zirconium tetrachloride and the correspondent ligands, Me2NMe2SiCH2(Ph)CN(2,6-Et2-4-R-C6H2). The representative complex C1 was crystallized and identified by the single-crystal X-ray diffraction, indicating oxo-bridged dinuclear azaallylzirconium structure. Both azaallylzirconium complexes exhibited notable catalytic activities toward ethylene polymerization in the presence of MAO, and obtained polyethylenes possess high molecular weights.

Synthesis and Characterization of Constrained Geometry Oxygen and Sulphur Functionalized Cyclopentadienylchromium Complexes and Their Use in Catalysis for Olefin Polymerization.

A series of constrained geometry O-functionalized cyclopentadienylchromium complexes (1–6) and a S-functionalized cyclopentadienylchromium complex (7) were first synthesized, characterized, and tested as catalyst precursors for the olefin polymerization. In the presence of MAO, the complexes exhibited high catalytic activity for the polymerization of ethylene. It is shown that ligand variations can have a substantial effect on catalyst activity and stability. The effect of Al/Cr ratio on catalytic activity was also studied.

Zirconium complexes based on an ethylene linked amidinate–amido ligand: synthesis, characterization and ethylene polymerization

Monomer/dimer zirconium complexes 4–6 were synthesized by changing the molar ratio of ZrCl4 : ligand. The catalytic behaviors of these zirconium complexes were investigated in the presence of MAO as a cocatalys.

2-Benzimidazol-6-pyrazol-pyridine Chromium(III) Trichlorides: Synthesis, Characterization, and Application for Ethylene Oligomerization and Polymerization

A series of chromium(III) complexes, LCrCl3 (Cr1–Cr4: L = 2-(N-R2-benzimidazol-2-yl)-6-(3,5-R1-pyrazol-1-yl)pyridine; Cr1: R1 = H, R2 = H; Cr2: R1 = Me, R2 = H; Cr3: R1 = Me, R2 = Me; Cr4: R1 = Me, R2 = Bn), were synthesized and characterized by IR spectroscopy and elemental analysis. The studies of the solid state of Cr2 and Cr3 revealed distorted octahedral geometries around the chromium centers by X-ray diffractions. In the presence of MAO, Cr1–Cr4 exhibited high activities toward ethylene oligomerization (up to 2.17 × 106 g·mol–1(Cr)·h–1) and ethylene polymerization (up to 6.78 × 105 g·mol–1(Cr)·h–1). The oligomers were produced with high selectivity for α-olefins (>99%), confirmed by FT-IR and 13C NMR, and the distributions followed the Schulz–Flory equation. Various reaction parameters including the amount of cocatalyst, reaction temperature, and time were evaluated in detail, and it was evident that the title complexes had good thermal stability and the substituents on imidazole-N of the ligands dr...

Synthesis and structural analysis of niobium(V) complexes containing amine triphenolate ligands of the type, [NbCl(X)(O-2,4-R2C6H2-6-CH2)3N] (R = Me, tBu; X = Cl, CF3SO3), and their use in catalysis for ethylene polymerization

Niobium(V) dichloride complexes containing amine triphenolate ligands, [NbCl2{(O-2,4-R2C6H2-6-CH2)3N}] [R=Me (1), tBu (2)], and their mono triflate analog, [NbCl(CF3SO3)(O-2,4-R2C6H2-6-CH2)3N] [R=Me (4), tBu (5)] have been prepared, and structures of complexes 1 and 5 have been determined by X ray crystallography; these complexes fold a distorted octahedral geometry around Nb. Complexes 1 and 2 exhibited catalytic activities for ethylene polymerization in the presence of MAO, and the activity markedly increased at high temperature (100, 120°C); 2 showed the higher activities than 1 (activity by 2 in n-octane at 100°C: 576kg-PE/mol-Nb·h).

Efficient Norbornene (NBE) Incorporation in Ethylene/NBE Copolymerization by Half-Titanocene Catalysts Containing Chlorinated Aryloxo Ligands

Synthesis and structural analysis of a series of half-titanocenes containing chlorinated phenoxy ligands of the type Cp′TiCl2(OAr) [Cp′ = Cp, Ar = 2,6-Cl2C6H3 (1), 2,4,6-Cl3C6H2 (2), C6Cl5 (3); Cp′ = indenyl, Ar = 2,6-Cl2C6H3 (4), 2,4,6-Cl3C6H2 (5), C6Cl5 (6)] and CpTiMe2(OAr) [Ar = 2,4,6-Cl3C6H2 (9), C6Cl5 (10)] have been explored. The Ti–O bond distances in 1–3 are apparently longer than those of the reported aryloxo-modified half-titanocenes, and the Ti–O–C(in phenyl) angles in 1–3 are also rather small. The Cp analogues (1–3) exhibited higher catalytic activities than the reported (indenyl)TiCl2(O-2,6-iPr2C6H3) in ethylene copolymerization with norbornene (NBE) in the presence of MAO; these complexes (1–3) also showed better NBE incorporation than those reported previously.

Synthesis of (Imido)Vanadium(V) Dichloride Complexes Containing Anionic N-Heterocyclic Carbenes That Contain a Weakly Coordinating Borate Moiety: New MAO-Free Ethylene Polymerization Catalysts

Synthesis and structural analysis of (imido)vanadium(V) complexes containing anionic N-heterocyclic carbenes with a weakly coordinating borate [B(C6F5)3] moiety (WCA-NHC) of the type [V(NR)Cl2(WCA-NHC)] [R = 1-adamantyl, C6H5, 2,6-Me2C6H3; NHC = 1,3-bis(2,6-dimethylphenyl)imidazolin-2-ylidene] have been explored; the WCA-NHC forms a σ-bond with vanadium as alkyl ligand (without strong π-donation) on the basis of crystallographic analysis [V–CNHC = 2.039(3)–2.049(2) A]. [V(N-2,6-Me2C6H3)Cl2(WCA-NHC)] exhibited remarkable catalytic activity (e.g., 11000 kg-PE/mol-V·h) for ethylene polymerization in the presence of AliBu3, and the activity was much higher than those in the presence of MAO and Et2AlCl.

Efficient introduction of aromatic vinyl group by incorporation of divinylbiphenyl, p -divinylbenzene in syndiospecific styrene polymerization using aryloxo-modified half-titanocene catalysts

An efficient introduction of aromatic vinyl group into syndiotactic polystyrene has been achieved by incorporation of 3,3′-divinylbiphenyl, p-divinylbenzene (DVB) in syndiospecific styrene polymerization using aryloxo-modified half-titanocenes, Cp′TiCl2(O-2,6-iPr2C6H3) (Cp′ = tBuC5H4, 1,2,4-Me3C5H2), in the presence of MAO. The resultant polymers possessed high molecular weights with uniform molecular weight distributions, and the DVB contents could be varied by the initial feed molar ratios (6–23 mol %) without decrease in the Mn values. The syndiotactic stereo-regularity and presence of the vinyl groups were confirmed by NMR spectra. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1902–1907

Synthesis and Structural Analysis of Zr–Al Heterobimetallic Complexes, [ZrX{(O-2,4-tBu2C6H2-6-CH2)3(μ2-O-2,4-tBu2-C6H2-6-CH2)}N][R2Al(μ2-OiPr)] [X = Cl, Et, iBu; R = Me, Et, iBu]. Unique Reactivity of the iBu Complex

A series of heterobimetallic Zr–Al complexes, [ZrCl{(O-2,4-tBu2C6H2-6-CH2)3(μ2-O-2,4-tBu2-C6H2-6-CH2)}N][R2Al(μ2-OiPr)] [R = Me (3), Et (4)] and [ZrR{(O-2,4-tBu2C6H2-6-CH2)3(μ2-O-2,4-tBu2-C6H2-6-CH2)}N][R2Al(μ2-OiPr)] [R = Et (5), iBu (6)], have been prepared by reactions of Zr(OiPr)[(O-2,4-tBu2C6H2-6-CH2)3N] (1) with 1.0 equiv of Al alkyls (Me2AlCl, Et2AlCl, AlEt3, and AliBu3), and their structures (3, 5, 6) were determined by X-ray crystallography. The isobutyl complex (6) is stable in C6D6 and toluene-d6 at 45 °C; the thermolysis of 6 at >60 °C gradually afforded 1 with liberation of AliBu3. These complexes exhibited remarkable catalytic activities for ethylene polymerization at 80–120 °C in the presence of MAO; only complex 6 exhibited the high activity even at 45–60 °C.

Group IV compounds bearing a novel tridentate N-donor ligand: synthesis, structures and ethylene polymerization

In this paper, treatment of [PhN(CH2)3NC(Ph)NSiMe3]2Li4·2Et2O with group IV metal chlorides yields corresponding compounds 3–5. The catalytic behaviors of 3–5 were investigated in the presence of MAO as co-catalyst for ethylene polymerization.

Copolymerizations of Norbornene and Tetracyclododecene with α-Olefins by Half-Titanocene Catalysts: Efficient Synthesis of Highly Transparent, Thermal Resistance Polymers

Highly efficient synthesis of cyclic olefin (CO) copolymers with high glass transition temperatures (Tg) as well as high catalytic activity have been attained not only by copolymerization of norbornene (NBE) with α-olefins (1-hexene, 1-octene, 1-dodecene), but also by copolymerization of tetracyclododecene (TCD) with α-olefins using half-titanocene catalysts, Cp′TiCl2(N═CtBu2) [Cp′ = tBuC5H4 (1), Cp (2)] in the presence of MAO. Linear relationships between the Tg values and the NBE or TCD contents were observed in all cases; Tg values in poly(TCD-co-α-olefin)s were higher than those in poly(NBE-co-α-olefin)s with the same CO contents. NBE and TCD incorporations in these copolymerization under high NBE or TCD feed conditions (especially by 2) were not affected by α-olefin (number of methylene units in the side chain) employed. An introduction of terminal olefinic double bond into the polymer side chain could be attained, if the copolymerization of NBE with 1-octene by 1 was conducted in the presence of 1,7...

Synthesis of Titanium Complexes Containing an Amine Triphenolate Ligand of the Type [TiX{(O-2,4-R2C6H2)-6-CH2}3N] and the Ti–Al Heterobimetallic Complexes with AlMe3: Effect of a Terminal Donor Ligand in Ethylene Polymerization

The synthesis of various titanatranes containing tris(aryloxo)amine ligands, TiX[{(O-2,4-R2C6H2)-6-CH2}3N] [R = Me (1), tBu (2); X = OiPr (a), OtBu (b), OCH(CF3)2 (c), OC(CF3)3 (d), Cl (e)], and some reactions with Al alkyls have been explored. The Ti–Al heterobimetallic complexes [TiMe{(O-2,4-Me2C6H2-6-CH2)2(μ2-O-2,4-Me2-C6H2-6-CH2)}N]-[Me2Al(μ2-OR′)] [R′ = tBu (3b), CH(CF3)2 (3c), C(CF3)3 (3d)] were isolated by reaction of 1b–d with 1 equiv of AlMe3, whereas reaction of 2b with AlMe3 in toluene did not take place under the same conditions, and the reaction of 2c afforded the methyl complex TiMe[{(O-2,4-tBu2C6H2)-6-CH2}3N]. Structures of 3b,c were determined by X-ray crystallography. These complexes exhibited high catalytic activities for ethylene polymerization in n-octane in the presence of MAO, and the activity by 1 and 2 was affected by the terminal donor ligand (X) as well as the substituent on the atrane ligand (R). The activities by 1c,d increased upon addition of AlMe3, and the corresponding hete...

Synthesis, Structures, and Norbornene Polymerization Behavior of N-Heterocyclic Carbene-Sulfonate-Ligated Palladacycles

A series of new N-heterocyclic carbene-sulfonate (NHC-sulfonate) ligands 5a–e were synthesized. Treatment of the NHC-sulfonate ligands with Ag2O and palladacycles {[Pd(OAc)(8-Me-quin-H)]2 or [Pd(dmba)(μ-Cl)]2 (dmba = Me2NCH2C6H5)} yielded the desired C(sp3),N-chelated and C(sp2),N-chelated NHC-sulfonate palladacycles 6a–e and 7a–e in high yields. All these complexes were fully characterized by 1H and 13C NMR, high-resolution mass spectrometry, and elemental analysis. The molecular structures of compounds 5a, 6d, 6e, and 7e were determined by single-crystal X-ray diffraction analysis. In the presence of MAO, the C(sp3),N-chelated NHC-sulfonate palladacycles 6a–e showed excellent catalytic activities [107 g of polynorbornene (PNB) (mol of Pd)−1 h–1], while the C(sp2),N-chelated palladacycles 7a–e showed moderate catalytic activities [106 g of PNB (mol of Pd)−1 h–1] in the vinyl polymerization of norbornene. The C(sp2),N-chelated palladacycles 7a–e showed high thermal stability and reached the highest activities at high temperature (100 °C).