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Latent olefin metathesis polymerization catalysts have enormous potential, as they provide access to thermoset polymers. However, developing a novel latent catalyst is difficult because the catalys...

In this report, we apply the chromophore quench-labeling (CQL) technique to living, homogeneous polymerization catalysts and living coordinative chain-transfer polymerization (LCCTP) conditions. We...

An efficient approach to copolymers of glycolic and lactic acids applied in biomedical materials was developed using ring-opening polymerization catalysts based on alkoxy complexes of ‘biometals’ (Mg, Al, and Zn) and 3-methyl- 1,4-dioxane-2,5-dione and glycolide as comonomers.

Chromium(III) complexes {NNZ}CrCl2(THF) (2a-d) (NNZ = pyrazolyl-imine-phenoxy/pyrrolide) have been synthesized and characterized by elemental analysis and X-ray diffraction analysis. Upon activation with methylaluminoxane (MAO), chromium precatalysts 2a-b showed moderate activity in ethylene oligomerization (TOF = 10.9 and 14.5 × 103 (mol ethylene)(mol Cr)− 1·h− 1 at 80 °C, respectively), producing mostly oligomers (78.4–85.7 wt% of total products). On the other hand, under identical oligomerization conditions, 2c-d/MAO behaved as a polymerization catalysts generating predominantly polyethylene (76.6 and 86.1 wt% of the total amount of products, respectively). Under optimized conditions, precatalyst 2a led to TOF = 71,500 mol(C2H4)⋅(mol(Cr)− 1 h− 1 and 95.6 wt% of oligomers.

Originally developed on heterogeneous Ziegler-Natta (ZN) catalysts, the model of "chiral growing chain conformation" developed by Corradini to explain the origin of stereocontrol in propene polymerization was extended to all stereoselective polymerization catalysts. The idea that the chiral recognition is performed by the site-chirality thorough the conformation of growing chain represent the "unusual novelty" of ZN towards e.g. asymmetric catalysis in which a chiral host molecule recognize directly two enantiomeric guest molecules. In this paper, by using DFT calculations, we will show that the origin of the stereocontrol for the new generation of Hf(IV)-pyridylamido based catalysts is somewhat different and more similar to the asymmetric catalysis.

In hopes of extending the existing knowledge on the chemistry of phospholyl and boratabenzene complexes of zirconium, which have shown potential notably as polymerization catalysts, this study aims at exploring the synthesis of mono boratabenzene and mono phospholyl zirconium complexes and at studying their reactivity towards the formation of mixed (boratabenzene)(phospholyl)zirconium complexes. Several derivatives of (η5-phospholyl)Zr(NMe2)xCl3−x and (η6-boratabenzene-NMe2)Zr(NMe2)xCl3−x were synthesized and used as precursors for the formation of mixed (boratabenzene)(phospholyl)zirconium complexes.

International audience; The first three insertion steps of propylene for isoselective metallocenes from the one-carbon-bridged cyclopentadienyl-fluorenyl {Cp/Flu} and silicon-bridged ansa-bis(indenyl) {SBI} families were computed by using a theoretical method implementing the B3PW91 functional in combination with solvent corrections incorporated with the Solvation Model based on Density (SMD) continuum model. For C -symmetric {Cp/Flu}-type metallocenes, two mechanisms of stereocontrol were validated theoretically: more facile and more stereoselective chain "stationary" insertion (or site epimerization backskip) and less stereoselective alternating mechanisms. For the C -symmetric {SBI}-type system, the computation results were in complete agreement with the sole operating chain migratory insertion mechanism. The thermochemical data obtained through the study were used to predict microstructures of polypropylenes by using three-parameter and one-parameter statistical models for the two metallocene systems, respectively. The calculated meso/rac pentad distributions were found to be in good agreement with those determined experimentally for isotactic polypropylene samples obtained at different polymerization temperatures.

Nitrosylruthenium complexes bearing two 2,2'-bipyridine (bpy) or 2-pyridinecarboxylate (pyc) ligands, [Ru(NO)X(bpy)2 ]3+ (X=CH3 CN, CH2 =CHCN, H2 O, Cl, ONO2 ) and [Ru(NO)(OH2 )(pyc)2 ]+ , were used as catalysts for the polymerization of acrylonitrile in N,N-dimethylformamide (DMF) under air without initiators to obtain polyacrylonitrile (PAN) with a high molecular weight and a narrow molecular weight distribution.

This account details externally regulated ring-opening metathesis polymerization (ROMP) methods. Various external stimuli are discussed which collectively span chemical, thermal, photochemical, electrochemical, and mechanical modes of catalyst activation. Specific attention is also given to the recent development of a metal-free approach to ROMP that includes electro-organic and photoredox-mediated systems. 1 Introduction 2 Externally Regulated Ring-Opening Metathesis Polymerization 2.1 Acid-Activated Ring-Opening Metathesis Polymerization Catalysts 2.2 Thermally Activated Ring-Opening Metathesis Polymerization Catalysts 2.3 Mechanically Activated Ring-Opening Metathesis Polymerization Catalysts 2.4 Photochemically Activated Ring-Opening Metathesis Polymerization Catalysts 2.5 Redox-Activated Ring-Opening Metathesis Polymerization Catalysts 3 Metal-Free Ring-Opening Metathesis Polymerization 3.1 Electro-organic Ring-Opening Metathesis Polymerization 3.2 Photoredox-Mediated Ring-Opening Metathesis Polymerization 4 Conclusions and Outlook

International audience; A series of allyl ansa-lanthanidocenes, [{Me2C(C5H4)-(Flu)}Nd(1,3-C3H3(SiMe3)(2))(2)]K (Flu = 9-fluorenyl; 1-Nd-K(allyl)) and {R2C(C5H4)(R'R'Flu)}Ln(1,3-C3H3(SiMe3)(2))(THF)(x) (R = Me, R' = 2,7-tBu(2), Ln = Y (2-Y), Sc (2-Sc), x = 0; Ln = La (2-La), Pr (2-Pr), Nd (2-Nd), Sm (2-Sm), x = 1; R = Me, R' = oct = octamethyloctahydrodibenzo, Ln = Nd, x = 1 (3-Nd); R = Ph, R' = H, Ln = Nd, x = 1 (4-Nd); R = Me, R' = 3,6-tBu(2), Ln = Nd, x = 1 (5-Nd)), were prepared in good yields and characterized by NMR spectroscopy (for diamagnetic complexes 2-Sc, 2-Y, and 2-La) and by single-crystal X-ray diffraction (1-Nd-K(allyl), 2-La, 2-Pr, 2-Nd, 2-Sm, and 4-Nd). Those complexes, especially 1-Nd-K(allyl), 2-Nd, 4-Nd, 2-La, and 2-Sm, act as single-component catalyst precursors for polymerization of styrene (in bulk or in aliphatic hydrocarbon solutions, (nBu)(2)Mg as scavenger, T-polym = 60-140 C), affording highly syndiotactic polystyrene (sPS) ([r](5) = 63-88%; T-m up to 260 C). High productivities (up to 4560 kg(sPS) mol(Ln)(-1) h(-1)) were achieved at 120-140 C, at low catalyst loadings ([St]/[Nd] = 20000-76000 equiv), with 2-Nd and 2-Pr. On the other hand, precursors having bulky substituents on the fluorenyl moieties in 3,6-positions (3-Nd, 5-Nd) or based on small ionic radius metals (2-Y, 2-Sc) were poorly or not active under standard polymerization conditions. These results have been rationalized by DFT computations, which included the solvent, carried out on the putative 1-Nd, and the isolated 2-Nd and 5-Nd complexes. Three consecutive styrene insertions were studied, and it was revealed that (i) the formation of sPS is thermodynamically controlled by two effects-minimization of repulsions between fluorenyl/styrene phenyl ring and (in the initiation phase) fluorenyl/SiMe3 substituents of the allyl ligand-and (ii) the presence of bulky substituents on the fluorenyl moiety does not influence the activation barrier of monomer insertion, but it may destabilize thermodynamically the insertion product.

Research on “post-metallocene” polymerization catalysis ranges methodologically from fundamental mechanistic studies of polymerization reactions over catalyst design to material properties of the polyolefins prepared. A common goal of these studies is the creation of practically useful new polyolefin materials or polymerization processes. This Review gives a comprehensive overview of post-metallocene polymerization catalysts that have been put into practice. The decisive properties for this success of a given catalyst structure are delineated.

The state of Phillips Cr/silica catalyst technology is discussed in this article, including recent advances in the science and also economic and environmental challenges to its continued viability. Although these catalysts have often been described as “mature,” many new innovations have been introduced in the past decade that reduce cost, improve quality, and expand the range of products that can be made. Polymers having unusually high, and low, levels of long-chain branching have been introduced. Several advances in the control of the short-chain branch distribution have also been made. Ways to lower the catalyst costs have been successfully implemented, such that Phillips-type catalysts are still the least expensive in the industry. Finally, new chromium-containing hybrid catalysts have been made that marry attributes from single-site and conventional Cr oxide catalysts.

Many transition metal catalysts including both early and late transition metal ions have been investigated for olefin polymerization and copolymerization reactions. Less attention has been paid to group 7 metal catalysts. Yet, manganese(II)-based catalysts are expected to have features distinct from early and late transition metal catalysts. In this context, the present review summarizes our recent results and strategy about ethylene polymerization and ethylene copolymerization with 1-hexene with manganese(II)-based catalysts.

The cationic tantalum complex {[eta(6)-Ar-CMe2-eta(5)-C5H4]TaPr}[B(C6F5)(4)] (1; Ar = 3,5-Me2C6H3) serves as a starting material for a series of neutral, monocationic, and dicationic derivatives. The cationic hydride {[eta(6)-Ar-CMe2-eta(5)-C5H4]TaH}[B(C6F5)(4)] (2) that results from hydrogenolysis of 1 inserts the di- and trisubstituted olefins cyclopentene and 2-methyl-2-pentene; it reacts with styrene to give the 2,1-insertion product, for which the Ta-CH(Me)Ph group is bound in a sigma(3)-allylic fashion. A neutral complex is obtained from 1 by reaction with Br-, and a dicationic derivative is available by hydride abstraction from 2 using the Lewis acidic trityl cation. All compounds described here retain the unusual ansa-(eta(5)-cyclopentradienyl,eta(6)-arene) coordination mode of the ligand that stabilizes the formally Ta(III) center. X-ray structures and DFT calculations show that the metal-arene interaction contains a significant pi back-donation component (arene

Dynamics of modernization and particularities of suspension production of polypropylene at Tomskteftekhim Company has been presented. Results of commercialization of polymerization catalysts of 2nd and 4th generation have been analyzed.

The reaction of the yttrium dialkyls (C5H4- PPh2=N (C6H3Pr2)-Pr-i)Y(CH2SiMe3)(2)(thf) (1) with an excess of N,N'-diisopropylcarbodiimide gave the yttrium monoalkyl complex (C5H4-PPh2=N-(C6H3Pr2)-Pr-i)Y(CH2SiMe3)[(PrN)-Pr-i= C(CH2SiMe3)-(NPr)-Pr-i] (2). 2 subsequently reacted with 1 equiv of PhSiH3 to generate the CpPN/amidinate heteroleptic yttrium hydride [(C5H4-PPh2=N (C6H3Pr2)-Pr-i)Y(CH2SiMe3)(2)-(NPr)-Pr-i](mu-H)}(2) (3). Hydride 3 showed good reactivity toward various substrates containing unsaturated C C, C-N, and N-N bonds, such as azobenzene, p-tolyacetylene, 1,4-bis(trimethylsily1)-1,3-butanediyne, N,N'-diisopropylcarbodiimide, and 4-dimethylaminopyridine, affording the yttrium hydrazide complex 4 with a rare eta(2)-Cp bonding mode, yttrium terminal alkynyl complex 5, yttrium eta(3)-propargyl complex 6, yttrium amidinate complex 7, and yttrium 2-hydro-4-dimethylaminopyridyl product 8, respectively.

NSFC [20902112, 20972129, 20423002]; China Postdoctoral Science Foundation [20090460748]; Deutsche Forschungsgemeinschaft

Reactions between trimethylaluminum and selected zirconocene and hafnocene polymerization catalysts have been computationally studied at the MP2/TZVP level of theory. Dichloride precatalyst alkylation and the subsequent activation by ligand abstraction with trimethylaluminum were explored as a function of the catalyst structure. The alkylation reactions were found to proceed via two alternative routes depending on the structure of the catalyst. Concerning the activation of the alkylated precatalyst, interaction between trimethylaluminum and metallocene weakens the metal–ligand σ-bond, hence facilitating olefin uptake to some extent. Modification of the chemical environment of the Lewis-acidic Al site towards environments likely present in methylaluminoxane further facilitates the reaction, supporting the critical role of methylaluminoxane in catalyst activation.

Progress in the polymerization of substituted acetylenes and the properties and functions of the formed polymers that have been synthesized in the past several years are surveyed. Polymerization catalysts for substituted acetylenes, new monomers and polymers, controlled polymerizations, and photoelectronic functions and separation membranes of substituted polyacetylenes are discussed. A focus is placed on the development of novel rhodium catalysts for the polymerization of phenylacetylenes, the helical structures of the polymers obtained from chiral monosubstituted acetylenes, and highly gas-permeable polymers prepared from disubstituted acetylenes, in which great advances have been made recently.

Organometallic chemistry has provided the foundation for the development of a wide range of new olefin polymerization catalysts over the last two to three decades. The unraveling of the mechanisms of activation and the mode of action of polymerization catalysts has transformed these former “black-box” systems into some of the best understood catalysts to date. In recent years insight into mechanistic steps such as ligand exchange with main-group-metal alkyls has had particular far-reaching consequences for materials design and new industrial products. This review attempts to summarize the advances made over the last 9−10 years in our understanding of the chemistry of catalyst activation and associated fundamental mechanistic aspects.

Though preparation procedures of heterogeneous Ziegler-Natta catalysts for propylene polymerization are sophisticated, it is uncertain whether the nature of the active sites is similar or different for different preparation procedures. In this study, the effects of preparation procedures on the nature of the active sites were investigated by stopped-flow polymerization in combination with microstructure analysis of polymers. Both basic and advanced types of catalysts showed the same two kinds of isospecific active site, which indicated little influence of the preparation method on the active site structure. On the contrary, the ratios of the two kinds of isospecific sites were not the same, resulting in variation of average polymer properties.

Treatment of the lithium salt of t-BuN(H)PPh2 in THF with CrCl2 (THF)(2) afforded a dinuclear, [(t-BuNPPh2)Cr-2(mu-t-BuNPPh2)(3)]center dot(toluene)(1.5) (1), and a tetrameric cluster, [(t-BuNPPh2)Cr(mu-t-BuNPPh2)(2)Cr(mu-Cl)](2)center dot(toluene)(2) (5), depending on the reagents' stoichiometric ratio. Complex 1 is dimeric with a long intermetallic distance and the ligands adopting an asymmetric and distorted bridging-chelating bonding mode. Complex 5 is instead a symmetry-generated tetramer with two identical dimetallic units, each closely related in geometry to 1, linked by two bridging chlorine atoms. The reactions of 1 with alkyl aluminum activators afforded a series of divalent complexes, [{(mu-AlMe3)(t-BuNPPh2)}(2)Cr]center dot(toluene) (2), [{(mu-AlMe2Cl)(t-BuNPPh2)}(2)Cr]center dot(toluene) (3), and [{(mu-AlEt2Cl)(t-BuNPPh2)}(2)Cr]center dot(toluene) (4), containing organo-aluminum residues. Similarly, reaction of 5 with AlMe3 gave [{(mu-AlMe2)(t-BuNPPh2)(2)}Cr(mu-Cl)(2)center dot(toluene)(1.9) (6), also characterized by an X-ray crystal structure. Finally, the trivalent complex [(t-BuNPPh2)(3)Cr] (7) was readily prepared via reaction of the lithiated ligand with CrCl3(THF)(3). Upon treatment with AlMe3 or Et2AlCl, complexes 2 and [{(mu-AlEtCl2)(t-BuNPPh2)}(2)Cr]center dot(toluene) (8) were isolated and fully characterized. In turn, this indicated that reduction to the divalent state is the primary stage of the activation process of the trivalent species. The catalytic behavior of all of these complexes has been assessed in the presence and absence of cocatalyst and with different solvents. The result showed a pronounced solvent effect, allowing switching from nonselective oligomerization to selective trimerization.

The activation of 2,6-bis(2,6-diisopropylphenylimino)ethylpyridine iron-based catalysts of ethylene polymerization with methylalumoxane (MAO) and aluminum trialkyls has been studied in detail by 1H NMR and EPR spectroscopy. Neutral catalytically active species are formed in LiPrFeCl2/Al(Alk)3 systems. They are complexes [LiPr(−)Fe(+)(μ-Me)2AlMe2] (6) or [LiPr(−)Fe(+)(μ-iBu)(μ-X)Al(iBu)2] (7 or 8, X = iBu or Cl), depending on the activator used (either AlMe3 or Al(iBu)3). On the contrary, when “AlMe3-free” methylalumoxane (PMAO) is used as the activator, catalytically active ion pairs of the type [LFeII(μ-Me)2AlMe2]+[MeMAO]− (3) are formed. Intermediates 6 and 8 are relatively unstable and decay within minutes at room temperature, giving rise to an EPR-active iron species with a signal at g = 2.08, presumably of the type L′FeI−Alk (L′FeI(μ-Alk)2Al(Alk)2) in the low-spin state S = 1/2 (where L′ is a modified bis(imino)pyridine ligand). Polymer properties for the different catalyst/activator systems are pres...

Cs-Symmetric propylene polymerization catalysts 1 with a bridged cyclopentadienyl and fluorenyl architecture are known to produce syndiotactic polymers. On the other hand, related C1-symmetric cata...

Reaction of diimine ligands (Ph2CN)(2)CnH2n (n = 2, a; n = 3, b) with FeCl2 or FeBr2 results in formation of the corresponding high-spin ferrous complexes {Ph2CN)(2)C2H4} FeX2 (1a, X = Cl; 2a, X = Br) and {(Ph2CN)(2)C3H3}FeCl2 (1b). Dialkyl {(Ph2CN)(2)C2H4) Fe(CH2SiMe3)(2) (3a) was prepared by treatment of (py)(2)Fe(CH2SiMe3)(2) with diimine ligand a. Addition of B(C6F5)(3) to 3a at -30 degrees C resulted in Me3SiCH2 abstraction, affording [{(Ph2CN)(2)C2H4} Fe(CH2SiMe3)][Me3SiCH2B(C6F5)(3)] (5a). F-19 NMR spectroscopy revealed that this compound exists as a contact ion-pair in toluene solution. Compound 5a decomposes at room temperature in bromobenzene-d(5) or toluene-d(8), affording dication [{(Ph2CN)(2)CH4)(2)Fe](2+) (6a); at elevated temperatures in toluene-d(8) the formation of [{(Ph2CN)(2)C2H4)Fe(CH2SiMe3)C6F5] (7a) was observed as well. Neither ferrous chloride {(Ph2CN)(2)C2H4} FeCl2 activated with methylaluminoxane nor contact ion-pair 5a is active in the polymerization of ethylene. Instead we were able, for the first time, to observe reversible ethylene binding to a cationic iron alkyl complex.

The influence of the ligand structures of hafnocene polymerization catalysts on ethene insertion and chain propagation was systematically studied by quantum chemical methods. Altogether 54 hafnocenes were studied as a function of the ligand structures. Two consecutive ethene insertions and chain propagations were performed for the catalysts, giving rise to 15 intermediate structures along the reaction pathway. The behavior of the catalysts was analyzed as a function of ancillary ligands, ligand substituents, and bridging units. The differences along the reaction pathway are dominated by the changes in relative stabilities of the catalytic intermediate products. Large aromatic ancillary ligands and electron-donating ligand substituents strongly stabilize the catalyst cations. Steric effects introduced by the ligand framework mostly affect the feasibility of ethene π-coordination and the activation energy for chain propagation. The dominant effect of the relative stabilities of the catalyst intermediates sh...

A number of κ1- and κ3-triazacyclononane RhI, Ir1, RhIII, and IrIII derivatives have been synthesized and characterized, with conversion from κ1-triazacyclononane complexes to κ3-derivatives. The r...

Syntheses and crystal structure of the pyrazolyl complex of the type [1,3-{3,5-R 2 pzCO} 2 C 6 H 4 PdCl 2 (μ-Cl) 2 ] (R= t Bu (1), Ph (2), Me (3)) and general application of these type of complexes in phenylacetylene polymerization is described. Two new compounds 1,3-(3,5-Ph 2 pzCO) 2 C 6 H 4 (L1) and its corresponding complex [1,3-{3,5-Ph 2 pzCO} 2 C 6 H 4 PdCl 2 (μ-Cl) 2 ] (2) were synthesized. Both compounds have structures that are monoclinic, with space group P2 1 /n. This and similar pyrazolyl palladium complexes can be activated to catalyze the polymerization of phenylacetylene.

A statistical model has been employed to determine the unidirectional site epimerization probability, e , during propylene polymerization with the following C 1 -symmetric metallocene precatalysts activated with MAO (MAO = methylaluminoxane): doubly-bridged rac -(1,2-SiMe 2 ) 2 {η 5 -C 5 H 2 -4-(CHMe(CMe 3 ))}{η 5 -C 5 H-3,5-(CHMe 2 ) 2 }ZrCl 2 ( 1 ) and (1,2-SiMe 2 ) 2 {η 5 -C 5 H 2 -4-(1 R ,2 S ,5 R -menthyl)}{η 5 -C 5 H-3,5-(CHMe 2 ) 2 }ZrCl 2 ( 2 ); and singly-bridged Me 2 C(3-(2-adamantyl)-C 5 H 3 )(C 13 H 8 )ZrCl 2 ( 3 ) and Me 2 Si(3-(2-adamantyl)-C 5 H 3 )(C 13 H 8 )ZrCl 2 ( 4 ). For 1 /MAO a steep tacticity dependence on monomer concentration was found, as e increased from 0.114 to 0.909 as [C 3 H 6 ] decreased from 12.5 M to 0.5 M; similarly, e increased for 2 /MAO from 0.177 to 0.709. For 3 /MAO, e was moderately responsive to an increase in polymerization temperature, as e increased from 0.000 to 0.485 from T p = 0–90 °C ([C 3 H 6 ] = 1.1 M). Similarly, e increased for 4 /MAO from 0.709 to 0.913 from T p = 0–40 °C; at higher temperatures, bidirectional site epimerization was implicated.

The intermediates of olefin polymerization over homogeneous catalysts based on bis[N-(3-tert-butylsalicylidene)anilinato]zirconium(IV) dichloride {(LtBu)2ZrCl2} (1-tBu), bis[N-(3-methylsalicylidene)anilinato]zirconium(IV) dichloride {(LMe)2ZrCl2} (1-Me), and bis[N-(salicylidene)anilinato]zirconium(IV) dichloride {(LH)2ZrCl2} (1-H) with different activators {methylaluminoxane (MAO) and AlMe3/[CPh3]+[B(C6F5)4]-} have been studied by 1H and 13C NMR spectroscopy. Heterobinuclear ion pairs [(LtBu)2Zr(μ-Me)2AlMe2]+[Me-MAO]- (2-tBu) and [(LtBu)2Zr(μ-Me)2AlMe2]+[B(C6F5)4]- (2‘-tBu) are formed upon activation of 1-tBu with MAO and AlMe3/[CPh3]+[B(C6F5)4]-, respectively. These species are the precursors of the highly active intermediates of polymerization. In contrast, the activation of 1-Me with MAO results mainly in the formation of the tight ion pair [(LMe)2ZrMe+···Me-MAO-]. This ion pair is the precursor to a poorly active intermediate of polymerization. In the catalytic systems 1-H/MAO and 1-H/AlMe3/[CPh3]+[B(...

An examination has been made of the reaction products obtained by refluxing a mixture of equal weights of styrene and tung oil in xylol solution in the absence of polymerization catalysts. Copolymerization occurs between styrene and tung oil. Saponification of the copolymer yields two main types of styrenated elaeostearic acid. One, which gives an insoluble potassium salt, contains styrene combined with elaeostearic acid in the approximate average molecular ratio of 8 : 1. The other styrenated acid, which is soluble in light petroleum and yields a soluble potassium salt, approximates in composition to a product derived from 1 molecule of styrene and 1 molecule of elaeostearic acid. In the conditions described, about 60% of the styrene remains unpolymerized and none forms a self-polymer. Only about 60% of the available elaeostearic groups take part in copolymer formation, the remaining 40% being recoverable in a styrene-free form. It is believed that the 1 : 1 styrenated acid is formed by a Diels-Alder mechanism.

The reaction of 1,4-bis(diisopropylphenyl)-aza-1,4-butadienenickel dibromide (1a) with stoichiometric amounts of phenyl Grignard or trimethylaluminum affords the purple Ni(I) complexes 1b and 1c, respectively. Single-crystal X-ray diffraction reveals dinuclear species in the solid state for both compounds. UV/vis spectroscopy supports this rare oxidation state of nickel.

Cationic intermediates formed upon activation of an olefin polymerization catalyst based on bis[N-phenylpyrrolylaldiminato]titanium(IV) dichloride (L2TiCl2, I) and [N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato-N‘-phenylpyrrolylaldiminato]titanium(IV) dichloride (L‘LTiCl2, II) with methylalumoxane (MAO) have been identified. Outer-sphere ion pairs of the type [L2TiMe(S)]+[MeMAO]- and [L‘LTiMe(S)]+[MeMAO]- capable of ethene polymerization have been characterized by 1H and 13C NMR spectroscopy. Unlike methyl metallocenium cations, the barrier of the first ethene insertion into the Ti−Me bonds of these species is not significantly higher than that of subsequent insertions. Surprisingly, whereas homoligated catalyst precursors L2TiCl2 in the presence of MAO are prone to ligand transfer to aluminum, under the same conditions the heteroligated system L‘LTiCl2/MAO proved resistant to ligand scrambling.

Simple tribenzyl complexes of lanthanum, [La(CH2C6H4-4-R)(3)(THF)(3)] (R = H (1a), Me (1b)), were prepared in a remarkably straightforward fashion from LaBr3(THF)(4) and potassium benzyl reagents. Single-crystal X-ray diffraction revealed a fac arrangement of the three THF ligands and eta(2) binding of the benzyl groups. These compounds are convenient precursors to other organolanthanum complexes. Reaction of 1a with the amidine ArN=CPhNHAr (Ar = 2,6-Pr-i 2C6H3) affords the corresponding mono(amidinate) dibenzyl derivative 2. Complex 1b reacts with LiCH2C6H4-4-Me to give the THF-free anion [La(CH(2)C(6)H(4-)4- Me)(4)](-) (3). Reactions of 1 with 1 or 2 equiv of [PhNMe2H][B(C6X5)(4)] (X = H, F) generate the corresponding mono- and dicationic benzyl species [La(CH2C6H4-4-R)(2)(THF)(4)](+) ( 4) and [La(CH2C6H4-4- R)(THF)(6)](2+) ( 5), which were structurally characterized. Scouting ethylene polymerization experiments indicate that these species are only modestly active catalysts but suggest that the monocationic dibenzyl species is more efficient. Both neutral and cationic lanthanum benzyl complexes effect the catalytic intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine. It was also observed that polycationic La species without ancillary ligands effectively catalyze the isomerization of the substrate to (E)-2,2-dimethyl-3-pentenylamine.

Two series of new organolanthanide(II) complexes with general formula {η5:η1-[1-R-3-(2-C5H4NCH2)C9H5]}2Ln(II) (R = H–, Ln = Yb (3), Eu (4); R = Me3Si–, Ln = Yb (5), Eu (6)), and {η5:η1-[1-R-3-(3-C5H4NCH2)C9H5]}2Ln(II) (R = H–, Ln = Yb (9), Eu (10); R = Me3Si–, Ln = Yb (11), Eu (12)) were synthesized by silylamine elimination with one-electron reductive reactions of lanthanide(III) amides [(Me3Si)2N]3Ln(μ-Cl)Li(THF)3 (Ln = Yb, Eu) with 2 equiv. 1-R-3-(2-C5H4NCH2)C9H6 (R = H (1), Me3Si– (2)) or 1-R-3-(3-C5H4NCH2)C9H6 (R = H (7), Me3Si– (8)) in good yields. All the complexes were fully characterized by elemental analyses and spectroscopic methods. Complexes 3 and 5 were additionally characterized by single-crystal X-ray diffraction study. The catalytic activities of the complexes for MMA polymerization were examined. It was found that complexes with 3-pyridylmethyl substituent on the indenyl ligands could function as single-component MMA polymerization catalysts with good activities, while the complexes with 2-pyridylmethyl substituent on the indenyl ligands cannot catalyze MMA polymerization. The temperatures and solvents effect on the MMA polymerization have also been examined.

Ethylene polymerization was studied using a variety of iminophosphonamide (PN2) complexes of zirconium. Bis(PN2) dichloride complexes [Ph2P(NR′)2]2ZrX2 (X = Cl; 1a: R′ = p-tolyl; 1b: R′ = Bn; 1c: R′ = C6F5) or dimethyl complexes (X = Me; 2a: R′ = p-tolyl; 2b: R′ = Bn) and cyclopentadienyl(PN2)zirconium dichloride complexes [η5-C5R′′5][R2P(NR′)2]ZrCl2 (3a: R′ = p-tolyl, R = Ph, R′′ = H; 3b: R′ = SiMe3, R = Et, R′′ = H; 3c: R′ = C6F5, R = Ph, R′′ = H; 3e: R′ = 3,5-(CF3)2Ph, R = Ph, R′′ = H; 3f: R′ = 3,5-(CF3)2Ph, R = Ph, R′′ = Me) or dimethyl analogs [η5-C5H5][R2P(NR′)2]ZrMe2 (4a: R′ = p-tolyl, R = Ph; 4b: R′ = SiMe3, R = Et) were evaluated under a range of conditions using methylaluminoxane (PMAO) activator. Complexes 1 and 2 behave as precursors to single-site polymerization catalysts under the conditions studied, while complexes 3 or dialkyls 4 show more complex behavior and formation of poly(ethylene) with a bimodal molecular weight distribution. In contrast, activation of dialkyl complexes 4 with [Ph3C][B(C6F5)4] and polymerization in the presence of small amounts of PMAO or TIBAL as scavenger, led to single-site behavior. PMAO reacts with the neutral dialkyls via ligand abstraction to produce a number of P-containing species that may explain the multi-site behavior observed when using this activator. Dialkyls 4 react cleanly with [Ph3C][B(C6F5)4] in haloarene or even dichloromethane solution to furnish the corresponding cationic alkyls 5, which were characterized by multinuclear NMR spectroscopy. Fluxional dinuclear species are formed in the presence of excess dialkyl and these are susceptible to C—H activation to form µ-Me,µ-CH2 complexes one of which could be isolated in pure form. The cationic alkyls initiate the polymerization of 1-hexene at room temperature in chlorobenzene solution, but extensive chain transfer occurs and the systems are not living.Key words: single site, early metal olefin polymerization catalysis.

Ansa-metallocene complexes have been extensively studied as the precatalysts for olefin polymerization. The bridges have important effects on the activities of the catalysts and polymer properties such as molecular weight and tacticity, mainly by altering the framework of the catalysts. Here, we review the effects of the structures of ansa-metallocene complexes on the catalytic activities, especially the effects of the bridges on the catalytic activities.

A series of half-sandwich aryloxide titanium complexes, [CpTi(OAr)Me2] (Cp = C5H5; OAr = OC6H3Me2-2,6, OC6H3Et2-2,6, OC6H3iPr2-2,6, OC6H3tBu2-2,6, and OC6HPh4-2,3,5,6), have been synthesized. These...

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Intellectually, the advantages that flow from the availability of single-site heterogeneous catalysts (SSHC) are many. They facilitate the determination of the kinetics and mechanism of catalytic turnover—both experimentally and computationally—and make accessible the energetics of various intermediates (including short-lived transition states). These facts in turn offer a rational strategic principle for the design of new catalysts and the improvement of existing ones. It is generally possible to prepare soluble molecular fragments that circumscribe the single-site, thus enabling a direct comparison to be made, experimentally, between the catalytic performance of the same active site when functioning as a heterogeneous (continuous solid) as well as a homogeneous (dispersed molecular) catalyst. This approach also makes it possible to modify the immediate atomic environment as well as the central atomic structure of the active site. From the practical standpoint, SSHC exhibit very high selectivities leading to the production of sharply defined molecular products, just as do their homogeneous analogues. Given that mesoporous silicas with very large internal surface areas are ideal supports for SSHC, and that more than a quarter of the elements of the Periodic Table may be grafted as active sites onto such silicas, there is abundant scope for creating new catalytic opportunities.

Mononuclear Zr complexes CpZrCl2{η5-C5H4(CH2)nCHCH2} (n = 1, 2, 3) undergo intermolecular metathesis of the vinyl group catalyzed by a Ru complex to produce dinuclear complexes with bridging ligand...

In this research communication, we performed the phenol–formaldehyde (PF) resin as an alternative carbon source and various mesostructured silicas as the nano-templates to conveniently prepare the mesoporous carbons of high surface area (850–1500 m 2 g −1 ), large pore size (2.0–22.0 nm) and great pore volume (0.65–1.15 cm 3 g −1 ). It was reasonably supposed that there exist interaction matching between the negative-charged silica surface of the silica template and PF resin. Therefore, the PF oligomers could be homogeneously adsorbed into the nanochannels or cages of the mesoporous silicas via an impregnation process. Because the thermosetting PF resin only requires a simple heat treatment process at 100 °C to form the cross-linked polymeric structure, the replication of the mesostructure of the mesoporous silica template could be readily achieved without adding any polymerization catalysts.

D/A metallocenes constitute a novel unique class of catalysts, in that they are able to express structural information within the elementary steps of the catalytic cycle out of bridged as well as out of unbridged states due to the coexistence of donor (D) and acceptor (A) atoms in complex sandwich structures. Highly polarized transannular bridging interactions as well as Lewis basic and Lewis acidic functionalities in unbridged states are the prerequisites which define a modular highly flexible catalyst system with outstanding options to tailor materials and processes.

The ter- and tetradentate N-alkoxyalkyl-β-ketoimines CH3C(O)CH2C(NCH2CHROH)CH3 {L1-3} react with diethylaluminum chloride to afford the dimeric chloride bridged complexes [{L1-3}AlCl]2 (1a−c), whic...

In this short review we describe some of the main developments of polymer reaction engineering since the early days of polymer science in the 1930's to the current challenges of today.

International audience; Multinuclear aluminum cocatalysts have been obtained by the reaction of various phenols, alcohols or diois with trimethylaluminum and were used in situ or as isolated, welldefined species, for the activation of an iron(ll) or an iron(lll) precatalyst for the oligomerization of ethylene. The best cocatalyst candidate involves 2,2'-biphenol (10) in a 10/AIMe3 ratio of 2/3.

Yttrium alkyl complexes Cp* 2 YR react with CH bonds of alkenes to form either yttrium allyl complexes or yttrium vinyl complexes. Less substituted alkenes react faster, consistent with prior alkene coordination. The selectivity of the reaction of Cp* 2 YR with CH bonds is allylic CH 3 ≫vinyl CH≫allylic CH 2 . Propene is readily metallated by Cp* 2 YR giving the η 3 -allyl complex Cp* 2 Y(η 3 -CH 2 ⋯ CH  CH 2 ) which does not react further with propene. This explains why Cp* 2 YR (R=alkyl, H) complexes make poor propene polymerization catalysts.

Homogeneous polymerization catalysts composed of transition metals have been highly attractive in the last two decades because of their high activity and high selectivity for synthesis of well-defi...