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A series of 20 bis(phenolate-ether) ligands, in combination with Zr and Hf, was tested for performance in propene polymerization, focusing on molecular weight, stereoregularity and regioregularity of the resulting polymer. Ligand variation covers length of the aliphatic linker between the ligand halves, as well as steric bulk of the groups ortho to the phenolate oxygen. The linker length has a dramatic effect on MW: two-carbon linkers produce oligomers (Mn < 2.5 kDa) while three- and four-carbon linkers generate much higher MW (Mn typically 50–500 kDa). Stereoselectivity can be tuned using large, flat substituents in the o-phenolate position; tuning of regioselectivity is much harder. Hf catalysts are slower than their Zr analogs and do not work well with MAO/BHT (BHT = 2,6-di-tert-butyl-4-methylphenol); they are generally more selective (MW, stereo and regio). Density functional calculations agree fairly well with observed selectivities, supporting the involvement of a fac/fac coordinated active species. These O4 catalysts are considerably more flexible than e.g. metallocenes, making accurate prediction of PP microstructure a significant challenge.

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.

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.

Magnesium dichloride and titanium tetrachloride are key components of Ziegler–Natta polymerization catalysts. We report a systematic computational study at M06-2X/def-TZVP level, thus accounting for dispersion, on saturation of magnesium dichloride crystallites by titanium tetrachloride. The crystallites are represented by (MgCl2)n clusters of various sizes and shapes, with n = 4–94, and they show preference for (104)-type edges with five-coordinate Mg atoms. Preferred adsorption modes of TiCl4 upon full saturation of crystallite edges are identified, alongside with adsorption strengths and relative stabilities of the (MgCl2)n-(TiCl4)m products. Consistent with previous literature, both Ti and Mg have tendency of favoring octahedral six-coordination, which can be achieved at all surface sites, including corners, serving as representatives of defect sites on the MgCl2 surfaces. The adsorption strengths of TiCl4 are the strongest for crystallites having (110)-type edges with four-coordinate Mg atoms. The much higher reactivity of (110)-type edges compared to (104)-type edges leads to reversal of the stability order of the crystallites upon TiCl4 adsorption. Saturated (MgCl2)n-(TiCl4)m crystallites thus favor shapes rich in (110)-type edges.

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.

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

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

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.

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.

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.

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.

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.

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...

A simple model is proposed to examine the possible effect of chlorine mobility in titanium chlorides on the dynamics of polymerization rate. The range of value of Cl− diffusivity is estimated to be 10−17 to 10−15 cm2/s. The model was verified by simulation of experimental data were found in the literature.

Three 2-phenylaminopyridine (Ap) complexes of types ApTiCl3 and Ap2TiCl2 were characterized with X-ray diffraction. The complexes were studied as polymerization catalysts using MAO as cocatalyst. In ethylene polymerization, the catalysts showed moderate activities between 65 and 285 kg PE mol−1 Ti−1 h−1 and the molecular weight distributions were between 2.5 and 4.2, and the molar masses were between 135 000 and 804 000 kg/mol.

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...

International audience; A series of new Ni(II) complexes of general formula \L\NiCl [Ni1, L = 2-(C4H3N-2'-CH= N)C2H4NHPh; Ni2, L = 5-tert-butyl-2-(C4H2N-2'-CH=N)C2H4NHPh; Ni3, L = 2-(C4H3N-2'- CH=N)C2H4OPh; Ni4, L = 2-(C4H3N-2'-CH=N)C6H4- 2'-OPh; Ni5, L = 2-(C4H3N-2'-CH=N)C6H4-2'-SPh; Ni6, L = 2-(C4H3N-2'-CH=N)CH2C6H4-2'-OMe] were prepared and fully characterized. All nickel precatalysts, activated with methylaluminoxane (MAO), exhibited moderate to good activities for ethylene oligomerization [TOF = 6.1-71.3 x 10(3) mol (C2H4) (mol (Ni)(-1) h(-1))] and producing high selectivities for 1-butene (68.3-94.0 wt%). The catalytic performance was substantially affected by the ligand environment regarding the pendant oxygen- and sulfur-donor groups, and the substituents on the pyrrolide group. Activation of nickel precatalyst Ni3 with ethylaluminum sesquichloride (Et3Al2Cl3, EASC) instead of MAO produced a significantly more productive catalyst system than Ni2/MAO (TOF = 153 700 vs. 43 500 mol (C2H4) (mol (Ni)(-1) h(-1))); however, the 1- butene selectivity was drastically reduced, attaining only 53 wt% with a concomitant production of larger amounts of internal butenes (38 wt%). Under optimized conditions ([Ni] = 10 mu mol, 30 degrees C, oligomerization time = 20 min, 20 bar ethylene, [Al]/[Ni] = 250), precatalyst Ni3 led to a TOF = 55 900 mol (C2H4) (mol (Ni)(-1) h(-1)) and 82.8 wt% selectivity for 1- butene

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.

The half-sandwich imido tantalum dichloride (η5-C5Me4H)Ta(NtBu)Cl2 is prepared directly from the reaction of the neutral constrained-geometry ligand Me2Si(C5Me4H)(tBuNH) and TaCl5 in refluxing tolu...

As an alternative to the standard Cossee mechanism, in which olefin insertion involves two sites at a single metal centre, we have investigated a true dinuclear alternative where the chain switches between two different metal centres at each insertion. The corresponding dinuclear variations of  hydrogen elimination (BHE) and  hydrogen transfer to monomer (BHT) were also investigated. Surprisingly, calculations indicate that the barriers for both insertion and BHT at two different metal centres are rather similar to those for the more usual mononuclear mechanisms. Dinuclear BHE is more competitive as a chain transfer mechanism, although it always has a higher barrier than BHT. In any system where polymerization at an unknown aluminium active species is believed to occur, dinuclear insertion should be considered as a real alternative to the "standard" mononuclear mechanism. However, from the systems we have studied the prospects for designing highly active, high-MW Al polymerization catalysts (i.e. significantly better than trialkylaluminium) appear just as dim for dinuclear as for mononuclear species.

Direct insertion of ethylene into the chromium−carbon bond in singly charged bis(imido)chromium(VI) cations has been investigated for n-alkyl and benzyl as starting polymer chains. Frontside coordination of ethylene takes place without activation to give a stable complex. Subsequent insertion into the Cr−alkyl bond requires a free energy of activation of 15 kcal/mol and an even higher barrier in the case of a benzyl ligand. Near the transition state, the reaction coordinate is dominated by inversion of the metal complex. Ethylene coordination in the backside mode requires considerable activation, and the additional increase in free energy through loss of entropy makes direct coordination unlikely. An indirect route to the β-agostic backside π-complex is found by inversion of the corresponding frontside ethylene−chromium complex. This rearrangement takes place via a transition state that has comparable or slightly lower free energy than that of direct insertion starting from the frontside π-complex. Howeve...

CpTiCl 2 (OR) (R=Cyclohexyl, CH 2 Ph, C 6 H 4 -Bu t -p, n Bu, i Bu, CH 2 CHCH 2 ) are synthesized, characterized and tested as syndiotactic polymerization catalysts of styrene. The structure and nature of the R group has a great effect on the activity of catalysts. Unsaturated groups and the conjugation of unsaturated groups with oxygen result in the drop of activity; while a more hindered R group increases activity.

A theoretical study has been carried out on two types of olefin polymerization catalysts based on the same M(III) centers (M = Ti, V, Cr) but different (mono) anionic ligand designs. The first system contains a mono-β-diiminato ligand that binds through the two imine nitrogens to the M(III) center and has the nitrogen lone-pairs perpendicular to the NMN coordination plane. It is shown that the generic mono-β-diiminato ligand system without bulky substituents on the nitrogen has barriers (kcal/mol) for insertion (Ti: 10.7; V: 12.2; Cr: 10.4) quite similar to the β-hydrogen transfer process (BHT) (Ti: 11.2; V: 9.8; Cr: 8.4), which serves as the chain-terminating step. The close proximity of the two barriers is in line with findings for other bidentate nitrogen ligands, where bulky aryl groups on the nitrogens were required in order to increase the BHT barrier relative to insertion and ensure acceptable molecular weights. The second system contains a bridged diamide ligand in which the ligand backbone ...

The ligands aminobis(N-ethylenesalicylidenimine) (SalenN3H3) and aminobis(N-propylenesalicylidenimine) (SalpenN3H3) were used to form the bimetallic complexes SalenN3H{AlMe2}2 (1), SalpenN3H{AlMe2}2 (2), SalenN3H{AlMeCl}2 (3) and SalpenN3H{AlMeCl} (4). When extracted in THF 3 and 4 redistribute to form the ionic compounds [SalenN3H{Al(THF)}]+ [AlMe2Cl2]− (5) and [SalpenN3H{Al(THF)}]+ [AlMe2Cl2]− (6). The compounds were characterized by Mp analyses, 1H-NMR and IR, and in the case of 2 and 6 by X-ray crystallography. Additionally, the potential of 5 and 6 to serve as propylene oxide polymerization catalysts was examined.

One-pot synthesis of poly(cyclic ortho ester)s by the reaction of potassium perfluoroalkanoates with epibromohydrin (EBH) using quaternary onium salts is described. The reaction of potassium trifluoroacetate (KTFA) with EBH using quaternary onium salts such as tetrabutylphosphonium bromide (TBPB) produces the polymer with five-membered cyclic ortho ester structure in the backbone. This means that quaternary onium salts act as phase-transfer catalysts in the first step and polymerization catalysts in the second step during the reaction.

The synthesis and characterization of novel bimetallic, neutrally charged dinickel 2,7-diimino-1,8-dioxynaphthalene polymerization catalysts is reported. Ethylene polymerizations as well as ethylene-co-norbornene copolymerizations display increased catalytic activity, methyl branch formation, and comonomer enchainment selectivity versus the monometallic analogues. Furthermore, these systems turn over in the absence of cocatalyst under mild conditions.

The synthesis and catalytic activity in ethylene polymerization of new vanadium complexes of 2,2′-oxydiethanethiolate [O(CH2CH2S)22–] are described; the complexes [V(µ-DIPP)2{O(CH2CH2S)2}Li(MeCN)2] and [V(DIPP){O(CH2CH2S)2}(py)] [DIPP = (OC6H3Pri2-2,6)–] have been structurally characterized.

The present work details the synthesis and structural characterization of six-coordinate aluminium cations derived from the single starting material, Salen(tBu)AlCl 1 [Salen(tBu) = N,N′-ethylenebis(3,5-di-tert-butylsalicylideneimine)]. They are of formula [Salen(tBu)Al(base)2]+X– and contain various combinations of base and counter anion; H2O, Cl– 2, MeOH, Cl– 3, MeOH, BPh4– 4, MeOH, OTs– 5. With thf as base and OTs– as the anion, the neutral complex, Salen(tBu)Al(thf)(OTs) 6 is obtained. MeOH can be added to 6 to displace the thf and produce 5. In contrast the addition of acetophenone to 2 does not displace the H2O but produces the hydrogen-bonded complex 2· · ·2(acetophenone) 7. All of the compounds were characterized spectroscopically and, in the case of 3, 5 and 7, by X-ray crystallography. Compounds 1–3 were examined for activity as oxirane polymerization catalysts.

Ortho lithiation is achieved by the treatment of tBuLi to the lithium carbamate compounds derived from 2-R-1,2,3,4-tetrahydroquinolines (R = H, methyl, n-butyl, tert-butyl, and 6-tert-butoxyhexyl), which enables the facile construction of the o-phenylene-bridged (Me4C5, indenyl, or fluorenyl)/amido titanium complexes. The titanium complex derived from 2-methyltetrahydroquinoline exhibits higher activity, higher 1-octene incorporation, and higher molecular weight in ethylene/1-octene copolymerization than the standard CGC, [Me2Si(η5-Me4C5)(NtBu)]TiCl2.

Exo,exo derivatives of the efficient catalyst precursors (diisodicyclopentadienyl)titanium and -zirconium dichloride substituted at the central position have been synthesized. These compounds have been characterized by solution NMR measurements, which also permitted the calculation of rotational barriers. The solid-state structures of exo,exo-bis(3-diphenylphosphinoisodicyclopentadienyl)titanium and -zirconium dichloride were determined by X-ray crystallography. Unfortunately, after activation by methylalumoxane, these complexes are shown to serve as poor catalysts for the polymerization of propene.

Ethylene-bridged bis(N,N-diisopropyl-1-aminoboratabenzene-4-yl)zirconium dichloride (5a), dimethylsilyl-bridged bis(N,N-diisopropyl-1-aminoboratabenzene-4-yl)zirconium dichloride (7a), and dimethylmethylene-bridged (cyclopentadienyl)(N,N-diisopropyl-1-aminoboratabenzene-4-yl)zirconium dichloride (6a) have been prepared. X-ray crystal structures of the dimethyl derivatives of 5 and 7 show that the complexes closely resemble the corresponding ansa-zirconocenes. When activated by excess methylaluminoxane, 5a, 6a, and 7a are catalysts for the polymerization of olefins.

As modifications of the effective catalyst precursor [dimethylsilanediylbis(benz[e]indenyl)]zirconium dichloride, the ansa-zirconocene complexes Me2Si(cyclopenta[c]phenanthryl)2ZrCl2, Me2Si(cyclope...

Four possible structures of C 2 -symmetric bis(fluorenyl)zirconium complexes are presented. Three bis(fluorenyl)zirconocene complexes have been prepared and tested for the polymerization of propylene and ethylene. rac / meso -Dichloro[ η 10 -(1,2-ethanediyl)bis ( 7H- benzo[c]fluoren -7- ylidene)zirconium ( 10 10 ∗ ) seems to be the most active polymerization catalysts for ethylene.

Temperature-programmed calcination of basic chromium(III) acetate impregnated onto a high surface area silica support and chromium(III) acetylacetonate dry-blended with silica has been studied by quadrupole mass spectrometry and infrared spectroscopy. In both cases the same reactive intermediate has been identified.

Weakening the sidearm donor of amine bis(phenolate) titanium and zirconium polymerization catalysts causes a 10-fold enhancement in activity of the former and no difference in activity of the latter, while increasing the termination to propagation ratios in both.

The coordination strength of various phosphine oxides OPR3 toward the olefin polymerization catalyst (P∧O)PdMe (P∧O = κ2-P,O-Ar2PC6H4SO2O with Ar = 2-MeOC6H4) as compared to that of dmso has been determined. Equilibrium constants KL for the reaction 1-dmso + L ⇆ 1-L + dmso range from 3.5 for electron-rich OPBu3 to 10–3 for electron-poor OP(p-CF3C6H4)3. Complexes derived from more strongly coordinating phosphine oxides, i.e. [(P∧O)PdMe(L)] (1-L; L = OPBu3, OPOct3, OPPh3) have been isolated and fully characterized. Additionally, 1-OPBu3 and 1-OPPh3 were analyzed by X-ray diffraction analyses. Complexes derived from weakly coordinating phosphine oxides have eluded isolation due to loss of phosphine oxide and formation of barely soluble multinuclear palladium complexes 1n by bridging coordination of the sulfonate group to various Pd centers. Hence, the (P∧O)PdMe fragment 1 exhibits an intrinsic limitation with respect to coordination of weak donors. Species 1 generated in situ in the absence of additional lig...

An equimolar mixture of Cp*Ti(CH3)3 (2) and Ph3C+[B(C6F5)4]− (1) forms a highly active and syndioselective catalyst for the polymerization of styrene, producing 96% syndiotactic polystyrene (PS) at an activity of 0.91 × 107 g PS (mol Ti)−1 (mol styrene)−1 h−1. Both activity and syndioselectivity can be increased using tri–isobutylaluminum (TIBA) to scavenge the system. ESR measurements indicate that the polymerization proceeds via titanium(IV) intermediates. Catalysts derived from 2/methylaluminoxane (MAO) as well as Cp*TiCl3/MAO also function as syndioselective styrene polymerization catalysts, but are less active than the ‘cationic’; system derived from 1 and 2.

International audience; Nickel complexes [(X,O)NiR(PPh(3))] (X = N or P), designed for the polymerization of ethylene, were found to be efficient for the homo- and copolymerization of butylacrylate (BuA), methylmethacrylate (MMA), and styrene. Their role as a radical initiator was demonstrated from the calculation of the copolymerization reactivity ratios. It was shown that the efficiency of the radical initiation is improved by the addition of PPh3 to the nickel complexes as well as by increasing the temperature. The dual role of a nickel complex as radical initiator and catalyst was exploited to succeed in the copolymerization of ethylene with BuA and MMA. Multiblock copolymers containing sequences of both ethylene and polar monomers were thus prepared for the first time by a dual radical/catalytic mechanism.