Metallocene complexes as homogeneous catalysts in olefin polymerization

Ansa metallocene dichloride complexes of titanium, zirconium, and hafnium can be activated by methyl aluminoxane (MAO) to give excellent catalysts for the homogeneous polymerization of ethylene and propylene. The symmetry of the corresponding metaliocene dichloride complexes is essential for the stereospecific polymerization of propylene (isotactic, syndiotactic or atactic). The application of fluorenyl groups instead of cyclopentadienyl groups greatly increases the activity of the catalysts. The first ansa bis(fluorenyl) complexes of zirconium and hafnium, (C₁₃H₈-C₂H₄-C₁₃Hs)MCl₂ (M = Zr, Hf), have been prepared. It was found that after the activation by MAO the zirconium derivative demonstrates a very high activity. Several model complexes are presented in order to discuss the mechanism of the polymerization.This paper was presented at the INEOS-94 Workshop The Modern Problems of Organometallic Chemistry (Moscow, May 21–27, 1994).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 7–14, January, 1995.     

Well-defined vanadium complexes as the catalysts for olefin polymerization

The design and synthesis of well-defined vanadium complexes as efficient catalysts for olefin polymerization remains an attractive project for organometallic and polymeric research. Recently, vanadium complexes with well-defined structures have been explored for olefin (co)polymerization by several groups around the world. This article summarizes our recent progress in well-defined vanadium complexes bearing a variety of chelating β-enaminoketonato, salicylaldiminato, iminopyrrolide and tetradentate amine trihydroxy ligands, and their applications in ethylene polymerization, ethylene/α-olefin copolymerization and ethylene/cycloolefin copolymerization. The application of the optimized catalysts in the copolymerization of ethylene and polar monomer such as 3-buten-1-ol, 5-hexen-1-ol, 10-undecen-1-ol and 5-norbornene-2-methanol is also discussed. Particular attention has been paid to the relationships between the catalytic behavior and the electronic and geometrical structure of the precatalyst.     

Cationic ruthenium allenylidene complexes as catalysts for ring closing olefin metathesis

A series of well accessible cationic ruthenium allenylidene complexes of the general type [(eta6-arene)(R3P)RuCl(=C=CR'2)]+ X- is described which constitute a new class of pre-catalysts for ring closing olefin metathesis reactions (RCM) and provide an unprecedented example for the involvement of metal allenylidenes in catalysis. They effect the cyclization of various functionalized dienes and enynes with good to excellent yields and show a great tolerance towards an array of functional groups. Systematic variations of their basic structural motif have provided insights into the essential parameters responsible for catalytic activity which can be enhanced further by addition of Lewis or Bronsted acids, by irradiation with UV light, or by the adequate choice of the "non-coordinating" counterion X-. The latter turned out to play a particularly important role in determining the rate and selectivity of the reaction. A similarly pronounced influence is exerted by remote substituents on the allenylidene residue which indicates that this ligand (or a ligand derived thereof) may remain attached to the metal throughout the catalytic process. X-ray crystal structures of the catalytically active allenylidene complexes 3b.PF6 and 15.OTf as well as of the chelate complex 10 required for the preparation of the latter catalyst are reported.     

Supported chiral Mo-based complexes as efficient catalysts for enantioselective olefin metathesis

Syntheses and catalytic activities of seven new polymer-supported chiral Mo-based complexes are disclosed. Four of the complexes are polystyrene-based, and three involve polynorbornene supports. Studies concerning the ability of the polymer-bound chiral complexes to promote an assortment of asymmetric ring-closing (ARCM) and ring-opening (AROM) metathesis reactions are detailed. In many instances, levels of reactivity and enantioselectivity are competitive with those of the analogous homogeneous catalysts. The positive effect of lower cross-linking within the polymer backbone on reaction efficiency and asymmetric induction is detailed. The optically enriched products obtained through the use of the supported complexes, after simple filtration and removal of the supported Mo catalysts, contain significantly lower levels of metal impurities as compared to products synthesized with the corresponding homogeneous catalysts.     

Cationic zirconium benzyl complexes as catalysts for olefin polymerization: A comparison among dicyclopentadienyl,monocyclopentadienyl and Cp-free derivatives

Cationic zirconium complexes of formula [Cp₂ZrBz]⁺, [Cp'ZrBz₂]⁺, or [ZrBz₃]⁺ (Cp = η⁵-C₅H₅, Cp' = Cp or η⁵-C₅Me₅, Bz = CH₂C₆H₅) have been tested as catalysts for the polymerization of ethylene and α-olefins. The catalyst performances have been compared with regard to polymer productivities, molecular weights and stereoregularities, and tentatively correlated to the structure of the ionic active species.     

Synthesis of double silylene‐bridged binuclear zirconium complexes and their use as catalysts for olefin polymerization

New double silylene‐bridged binuclear zirconium complexes [(η⁵‐RC₅H₄)ZrCl₂]₂[μ,μ‐(SiMe₂)₂(η⁵‐C₅H₃)₂] [R = H ( 1 ), Me ( 2 ), ⁿPr ( 3 ), ⁱPr ( 4 ), ⁿBu ( 5 ), allyl ( 6 ), 3‐butenyl ( 7 ), benzyl ( 8 ), PhCH₂CH₂ ( 9 ), MeOCH₂CH₂ ( 10 )] were synthesized by the reaction of (η⁵‐RC₅H₄)ZrCl₃·DME with [μ,μ‐(SiMe₂)₂(η⁵‐C₅H₃)₂]^2? ( L^2? ) in THF, and they were all well characterized by ¹H NMR, MS, IR, and EA. The binuclear structure of Complex 3 was further confirmed by X‐ray diffraction, where the two zirconium centers are located trans relative to the bridging [μ,μ‐(SiMe₂)₂(η⁵‐C₅H₃)₂] moiety. When activated with methylaluminoxane (MAO), this series of zirconium complexes are highly active catalysts for the polymerization of ethylene even under very low molar ratio of Al/Zr (Complex 7 , 5.41 × 10⁵ g‐PE/mol‐Zr·h, Al/Zr = 50) and linear polyethylenes (PEs) with broad molecular weight distribution (MWD, M_w/M_n = 7.31–27.6) was obtained. The copolymerization experiments indicate that these complexes are also very efficient in the incorporation of 1‐hexene into the growing PE chain in the presence of MAO (Complex 6 , 3.59 × 10⁶ g‐PE/mol‐Zr·h; 1‐hexene content, 3.65%). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4901–4913, 2007     

Manganese‐based transition metal complexes as new catalysts for olefin polymerizations

Three manganese complexes, Mn(acac)₃ (acac = acetylacetonate), Cp₂Mn (Cp = cyclopentadienyl), and Mn(salen)Cl [salen = 1,2‐cyclohexanediamino‐N,N′‐bis(3,5‐dit‐butyl‐salicylidene)], were used for ethylene and propylene polymerizations. These complexes, in combination with an alkylaluminum cocatalyst such as methylaluminoxane (MAO) or diethyl aluminum chloride (AlEt₂Cl), could promote ethylene polymerizations that yielded extremely high molecular weight linear polymers, but were inactive for propylene polymerizations. The counterparts supported on MgCl₂ showed activities even for propylene polymerizations and had remarkably enhanced activities for ethylene polymerizations. In the presence of an electron donor such as ethylbenzoate, the MgCl₂‐supported manganese‐based catalysts yielded a highly isotactic polypropylene with a high molecular weight. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3733–3738, 2001     

3,4-Dicyano-5-aminopyrazole complexes of anhydrous divalent transition metal chlorides and their triphenylphosphine derivatives

Summary 3,4-Dicyano-5-aminopyrazole, H3,4(CN)₂5NH₂pz (L) reacts either with anhydrous MCl₂ or with [M(PPh₃)₂Cl₂] to yield ML₄Cl₂ complexes (M = Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd or Hg), whose monomeric and covalent natures have been confirmed by their solubility in most non-polar solvents and their low electrical conductivities. The bonding mode of substituted pyrazole is inferred from the position of the (C-N) band in the i.r. spectra. The electronic spectra and the magnetic moments of these compounds were recorded.     

New anilinotropone-based titanium complexes: synthesis, characterization and application as catalysts for olefin polymerization

New titanium(IV) dichloride complexes containing 2-anilinotropone ligands have been synthesized and characterized. Bis(ligand)titanium dichloride complexes 1 and 2 were synthesized from reaction of TiCl4(THF)2 with 2 equivalents of the corresponding sodium salts of 2-(2,6-diisopropylanilino)tropone (L1) and 2-(2,3,4,5,6-pentafluoroanilino)tropone (L2), respectively. The mixed cyclopentadienyl-anilinotropone compound 3 was synthesized by reaction of the lithium salt of with CpTiCl3. The Cp-mixed micro-O bimetallic complex 4 was also isolated as a by-product owing to the adventitious presence of moisture. The molecular structures 1-4 of have been determined by single-crystal X-ray diffraction studies. Complexes 1 and 2 are isostructural and exhibit a C2-symmetric octahedral geometry, with a trans(N,N), cis(O,O) arrangement in complex 1, but with a trans(O,O), cis(N,N) arrangement in complex 2. The Cp-mixed complex 3 has a distorted square-pyramidal structure with the Cp ligand in the apical position. Bimetallic complex 4 shows a similar coordination geometry for the five-coordinate titanium atom and a pseudo-tetrahedral coordination for the second metallic centre. All new complexes, when activated with methylaluminoxane, are active in the polymerization of ethylene and propene.     

An investigation into oxo analogues of molybdenum olefin metathesis complexes as epoxidation catalysts for alkenes

The oxo-imido molybdenum complex 2a is an effective catalyst at low catalyst loadings (0.5 mol % or below) for the epoxidation of a range of alkenes with ^tBuOOH in PhMe at 90 °C. Reactions are complete in less than 4 h and the products are isolated in high yields. The catalytic system is chemoselective for the epoxidation of electron-rich alkenes and allylic alcohols.     

Chelated amines as ligands in olefin hydrogenation catalysts

Activities of catalysts obtained in the reaction of [MCl(C₈H₁₄)₂]₂, (M=Rh, Ir) with amines NH₂(CH₂)_nNH₂, (N=2–5), (CH₃)₂NC₂H₄(CH₃)₂ and 1.8=diaminonaphthalene have been examined. The most efficient catalyst was obtained with 1.3-diaminopropane.

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, [MCl(C₈H₁₄)₂]₂. (M=Rh, Ir) NH₂(CH₂)_nNH₂, (n=2–5). (CH₃)₂NC₂H₄(CH₃)₂ 1,8-. , 1,3-.

     

Non-heme iron(II) complexes are efficient olefin aziridination catalysts

Iron(II) complexes of polydentate nitrogen donor ligands catalyze the rapid aziridination of olefins by PhINTs.     

Molybdenum oxo-imido aryloxide complexes: oxo analogues of olefin metathesis catalysts

The novel 16-electron molybdenum oxo-imido bis(aryloxide) complexes [Mo(NtBu)(O)(2,6-Me2C6H3O)2(py)] (1) and [Mo(NtBu)(O)(2,6-iPr2C6H3O)2(py)] (2) have been prepared by the salt elimination reactions of [Mo(NtBu)(O)Cl2(DME)] with the appropriate lithium aryloxide and from the cycloaddition reactions of tert-butyl isocyanate with the appropriate molybdenum dioxo bis(aryloxide) complex [Mo(O)2(OAr)2(py)n]. Complexes 1 and 2 are the first isolable and crystallographically characterized molybdenum oxo-imido aryloxide complexes. The geometry around the metal in complexes 1 and 2 is best described as a distorted trigonal bipyramid, with the imido and pyridine ligands occupying the axial positions and the oxo and aryloxide ligands in the equatorial plane. X-ray and IR data have confirmed that the imido ligand is the dominant pi donor in the complexes, resulting in an Mo-O bond order of less than 2.5. Reaction of [Mo(NtBu)(O)Cl2(DME)] with Li(OCH2tBu) instead gave the novel complex [Mo(NtBu)(OCH2tBu)3Cl(py)] (3).     

Phosphites as ligands in ruthenium-benzylidene catalysts for olefin metathesis

The use of phosphites in second generation, ruthenium-based olefin metathesis pre-catalysts leads to an improvement in catalyst stability and activity at low catalyst loadings.     

Ruthenium(II) carbonyl complexes with N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives and triphenylphosphine as effective catalysts for oxidation of alcohols

Ruthenium(II) complexes, [RuCl(L)(CO)(PPh₃)₂] {where L?=?N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives}, are prepared from reaction between [RuHCl(CO)(PPh₃)₃] and N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives in toluene and characterized by elemental analysis and spectral data (electronic, infrared, ¹H NMR, and ³¹P NMR). The combination of [RuCl(L)(CO)(PPh₃)₂] (0.01?mmol) and N-methylmorpholine-N-oxide (NMO) (3?mmol) is an active catalyst for the oxidation of primary, secondary, cyclic, allylic, aliphatic, and benzylic alcohols to their corresponding aldehydes and ketones at room temperature. The oxidation protocol is simple to operate and gives the corresponding carbonyl compounds good to excellent yields.     

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.     

Bimetallic phenylene-bridged Cp/amide titanium complexes and their olefin polymerization

Bimetallic dichlorotitanium complexes, {2,6-[eta(5)-2,5-Me2C5H2](2)-4-R-C6H2N-microN}{Ti(IV)Cl2}2 (, R=Me; , R=F) and 4,4'-A[{2-(eta(5)-2,3,5-Me3C5H)C6H3NC6H11-kappaN}Ti(IV)Cl2]2 (, A=CH2; , A=O; , A=ortho-C6H4) are prepared via a key step of the Suzuki-coupling reaction of 2-dihydroxyboryl-3-methyl-2-cyclopenten-1-one () with dibromo-compounds. The solid state structure of was determined by X-ray crystallography. Complexes and are not active for ethylene/1-hexene copolymerization. Meanwhile, the complexes are highly active and their activities are higher than that of the mononuclear analogue, {2-(eta(5)-2,3,5-Me3C5H)C6H3NC6H11-kappaN}Ti(IV)Cl2 (). The molecular weights of the polymers obtained with the bimetallic complexes are higher than that of the polymer obtained using . Slightly higher contents of long-chain-branching are observed for the copolymers obtained using the bimetallic system.     

Oxorhenium complexes as aldehyde-olefination catalysts

Several oxorhenium compounds in the formal oxidation states V and VII are examined as catalysts for the aldehyde-olefination starting from diazo compounds, phosphines, and aldehydes. Of these, [ReMeO2(eta2-alkyne)] complexes provide the simplest catalysts to study, although [ReOCl3(PPh3)2] still remains the most efficient rhenium catalyst for aldehyde-olefination described to date. Prior to the reaction with the Re catalysts the phosphine and the diazo compound react to form a phosphazine. No catalytic reaction occurs in cases where no phosphazine formation is observed. The first step of the catalytic cycle involves the formation of a carbene intermediate by the reaction of phosphazine and catalyst under extrusion of phosphine oxide and dinitrogen. In a second step the carbene reacts with aldehyde under olefin formation and catalyst regeneration. Excess of alkyne as well as the presence of ketones slows down the catalytic reaction. The olefination of 4-nitrobenzaldehyde with diazomalonate is possible with these Re catalysts. In contrast, this reaction does not take place either in the classical Wittig fashion from Ph3P=C(CO2Et)2 and aldehyde or by use of all other catalysts for aldehyde olefination reactions reported to date. Catalytic ylide formation from diazo compounds seems therefore not to be the only pathway through which catalytic aldehyde-olefination reactions can proceed.