Syndiospecific polymerization of styrene catalyzed by CpTiCl2(OR) complexes

Five new CpTiCl₂(OR) alkoxyl-substituted half-sandwich complexes, where R was methoxyethyl ( 1 ), methoxypropyl ( 2 ), methoxyisopropyl ( 3 ), o-methoxyphenyl ( 4 ), or tetrahydrofurfuryl ( 5 ), were synthesized, characterized, and tested as catalyst precursors for the syndiospecific polymerization of styrene. These precursors were more active than (η⁵-cyclopentadienyl)trichlorotitanium (CpTiCl₃). The different structures of the alkoxyl ligands affected the activity slightly. When the polymerization was carried out in bulk, all the complexes ( 1–5 ) exhibited high activities, even at the low molar ratio of Al/Ti = 300. The syndiotactic polystyrene (s-PS) percentage of the polymer produced by alkoxyl-substituted complexes was much higher than that of CpTiCl₃. The really active center might be described as [CpTiMe]⁺ · [MAOX]⁻ · nMAO (where MAO is methylaluminoxane). The normal active species [CpTiMe]⁺ made up the core and the anion mass [MAOX]⁻ · nMAO surrounded the core and constituted the outer shell circumstance. They activated the syndiospecific polymerization of styrene as a whole. For a high concentration of MAO, the function of the alkoxyl group was weak because of the limited proportion in the outer shell. For a low concentration of MAO, the proportion of alkoxyl ligands in the outer shell increased greatly, and their influence also became significant, as reflected in a higher s-PS percentage of the obtained polymer. The existence of the additional oxygen atom in the alkoxyl ligand stabilized the active species more effectively; this was reflected in the higher temperature of the maximum activities. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1817–1824, 2001     

Highly syndiospecific polymerization of styrene catalyzed by allyl lanthanide complexes

Allylic complexes of lanthanides bearing a fluorenyl-based ligand are active single-component catalysts for the polymerization of styrene, giving highly syndiotactic polymers (rrrr > 99%) with low to high molecular weight (Mn = 8000-135 000) and narrow polydispersities (Mw/Mn = 1.25-2.1).     

(Diisopropylamido) bis (methylcyclopentadienyl) lanthanides as single-component initiators for polymerization of methyl methacrylate

It was first found that (diisopropylamido)bis(methylcyclopentadienyl)lanthanides (MeC₅H₄)₂LnN(i-Pr)₂(THF) (Ln = Yb ( 1 ), Er ( 2 ), Y ( 3 )) exhibit extremely high catalytic activity in the polymerization of methyl methacrylate. The reactions can be carried out over a quite broad range of polymerization temperatures from -78 to 40°C. The catalytic activity of the complexes increases with an increase of ionic radii of the metal elements, i.e. Y > Er > Yb. The results of GPC (gel permeation chromatography) indicate that the number-average molecular weights (M_n) of polymers obtained exceed 100 × 10³ and the molecular weight distribution (M_w/M_n) becomes broad with the increase of temperature. Furthermore highly syndiotactic PMMA (87.7%) can be obtained by lowering the reaction temperature to −78°C. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1593–1597, 1998     

Polymerization of 1,3‐dienes and styrene catalyzed by cationic allyl Ni(II) complexes

Polymerizations of 1,3‐dienes using in situ generated catalyst [(2‐methallyl)Ni][B(Ar_F)₄], 6 , (Ar_F = 3,5‐bis(trifluoromethyl)phenyl) as well as [(2‐methallyl)Ni(mes)][B(Ar_F)₄], 14 , (mes = mesitylene) are reported. Highly sensitive complex 6 polymerizes butadiene (BD) at –30 °C to yield polybutadiene with a M_n of ca. 10 K and 94% cis‐1,4‐enchainment while less reactive isoprene (IP) was polymerized at 23 °C to yield polyisoprene with M_n ca. 7 K. Complex 6 was also shown to polymerize a functionalized diene, 2,3‐bis(4‐trifluoroethoxy‐4‐oxobutyl)‐1,3‐BD, to polymer with M_n = 113 K. The stable and readily isolated arene complex 14 initiates BD and IP polymerizations at somewhat higher temperatures relative to 6 and delivers polymers with higher molecular weights. Complex [(allyl)Ni(mes)][B(Ar_F)₄], 13 , catalyzes polymerization of styrene to yield polystyrene with high conversion, M_n's = ca. 6 K and MWD = 2. The π‐benzyl complex [(η³‐1‐methylbenzyl)Ni(mes)] [B(Ar_F)₄], 19 , was detected as an intermediate following chain transfer by in situ NMR studies. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1901–1912, 2010     

Allyl ansa-lanthanidocenes: single-component, single-site catalysts for controlled syndiospecific styrene and styrene-ethylene (Co)polymerization

A series of new neutral allyl Group 3 metal complexes bearing ansa-bridged fluorenyl/cyclopentadienyl ligands [[Flu-EMe(2)-(3-R-Cp)]Ln(eta(3)-C(3)H(5))(THF)] (E=C, R=H, Ln=Y (2), La (3), Nd (4), Sm (5); R=tBu, Ln=Y (8), Nd (9); E=Si, R=H, Ln=Y (12), Nd (13)) were synthesized in good yields via salt metathesis protocols. The complexes were characterized by elemental analysis, NMR spectroscopy for diamagnetic complexes, and single-crystal X-ray diffraction studies for 2, 4, 9 and 12. Some of the allyl ansa-lanthanidocenes, especially 4, are effective single-component catalysts for the polymerization of styrene, giving pure syndiotactic polystyrenes (rrrr > 99 %) with low to high molecular weights (M(n)=6000-135,000 g mol(-1)) and narrow polydispersities (M(w)/M(n)=1.2-2.6). The catalyst systems are remarkably stable, capable of polymerizing styrene up to 120 degrees C with high activities, while maintaining high syndiotacticity via chain-end control as established by a Bernoullian analysis. Highly effective copolymerization of styrene with ethylene was achieved using neodymium complex 4 (activity up to 2530 kg PS-PE mol(-1) h(-1)) to give true copolymers void of homopolymers with M(n)=9000-152,000 g mol(-1) and narrow polydispersities (M(w)/M(n)=1.2-2.5). The nature of the resultant P(S-co-E) copolymers was ascertained by NMR, size-exclusion chromatography/refractive index/UV, temperature rising elusion fractionation, and differential scanning calorimetry. It is shown that, regardless the amount of ethylene incorporated (1-50 mol %), P(S-co-E) copolymers have a microstructure predominantly made of long highly syndiotactic PS sequences separated by single or few ethylene units. Co-monomers feed and polymerization temperature can be used straightforwardly to manipulate with the physical and mechanical characteristics of the P(S-co-E) copolymers (molecular weights and distributions, co-monomer content, microstructure, T(m), T(g), T(c)).     

Controlled radical polymerization catalyzed by copper(I)–sparteine complexes

Sparteine was found to be an efficient ligand because when complexed with copper(I) halide it generated a homogeneous catalyst for the atom transfer radical polymerization of styrene or methyl methacrylate, which was initiated by (1-bromoethyl)benzene in the former case and by p-toluenesulfonyl chloride in the latter. The plots of ln([M]₀/[M]) versus time and molecular weight versus monomer conversion exhibited linear dependencies, which indicated that the concentration of the living centers throughout polymerization was constant. The polydispersities of polystyrene and poly(methyl methacrylate) in both the bulk and solution polymerizations were quite low. An induction time was observed during the bulk polymerization of styrene; however, it was absent during the solution polymerization. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4191–4197, 1999     

“Living” radical polymerization of styrene catalyzed by cyclometalated ruthenium(II) complexes bearing nonlabile ligands

Cationic substitutionally inert cyclometalated ruthenium (II) and osmium (II) complexes, ([Mt(o‐C₆H₄‐2‐py)(LL)₂]PF₆), where LL‐1,10‐phenanthroline (phen) or 2,2′‐bipyridine (bipy), were used for radical polymerization of styrene. Gradual modification of the complexes within the series allowed comparison of the catalytic activity and the redox properties. There was no correlation between the reducing powers of the complexes and their catalytic activities. The osmium compound of the lowest reduction potential was not active. All the ruthenium complexes catalyzed the polymerization of styrene in a controlled manner; but the level of control and the catalytic activity were different under the same polymerization conditions. [Ru(o‐C₆H₄‐2‐py)(phen)₂]PF₆ demonstrated the best catalytic performance though its redox potential was the highest. It catalyzed the “living” polymerization with a reasonable rate at a catalyst‐to‐initiator ratio of 0.1. 1 equiv. of Al(OiPr)₃ accelerated the polymerization and improved the control, but higher amount of Al(OiPr)₃ did not speed up the polymerization and moved the process into the uncontrollable regime. Under the most optimal conditions, the controlled polymerization occurs fast without any additive and the catalyst degradation. Added free ligands inhibited the polymerization suggesting that the catalytically active ruthenium intermediates are generated via the reversible dechelation of bidentate phen or bipy ligands. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3814–3828, 2009     

Polymerization of styrene catalyzed by rare earth Schiff base complexes

The rare earth Schiff base complex Nd (H₂Salen)₂Cl₃·2C₂H₅OH was synthesized by a simple and convenient method and characterized by IR and elemental analysis. The catalyst system composed of Nd (H₂Salen)₂Cl₃·2C₂H₅OH/Al(i-Bu)₃/CCl₄ is effective for the polymerization of styrene (St). The optimum conditions are as follows: [St]/[Nd] = 1000, [CCl₄]/[Nd] = 9, [Al]/[Nd] = 30, and polymerization at 50°C for 20 h. The resulting polystyrene was characterized by NMR and GPC. The results of NMR show that the polymer obtained had a stereoregularity with 52.3% isotacticity and 47.7% syndiotacticity without any random structure. __________ Translated from Journal of Zhejiang University (Science Edition), 2007, 34(2): 189–196 [译自: 浙江大学学报(理学版)]     

Syndiospecific polymerization of styrene using fluorinated indenyltitanium complexes

Nine new fluorinated half-sandwich titanocene complexes (1b–9b) based on substituted alkylindenes were synthesized, by reacting Me₃SnF with the corresponding chloride species, and employed as catalyst precursors for the syndiospecific polymerization of styrene. When activated with methylaluminoxane (MAO), the new precursors 1b–9b exhibited increased activities by factors of 15-40 compared with the corresponding chlorinated compounds and provided improved syndiotacticity, enhanced melting temperature, and higher polymer molecular weights. The activities of indenyl and methyl- or phenyl-substituted indenyl complexes were found to be higher by factors of 4-12.5 than those of CpTiF₃ and Cp*TiF₃. More importantly, the amount of MAOcan be reduced to an Al : Ti molar ratio of 300 in the temperature range of 10-90°C. It is likely that Ti F, more polarized than the Ti Cl bond in the half-sandwich titanocenes, allows the formation of more active and stable active sites of Ti(III) complexes needed for the syndiospecific polymerization of styrene. Evidence in this direction is brought via the electron paramagnetic resonance (EPR) spectrum and redox titration. The higher activity and syndiospecificity of the fluorinated catalysts are attributable to a greater number, more stable Ti(III) active sites, and/or higher propagation rate constant. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2481–2488, 1999     

Ethylene and propylene polymerization with bis(indenyl)zirconium/Mao catalytic systems modified by sterically demanding alcohols

Ethylene and propylene polymerization using Ind₂ZrCl₂ and Ind₂Zr(CH₃)₂/MAO catalytic systems modified by the sterically demanding bridged alicyclic alcohols, adamantan‐1‐ol, adamantan‐2‐ol, 2‐methyladamantan‐2‐ol, and fenchyl alcohol, was investigated. Lower alcohols like isopropanol completely deactivate the system, whereas in the case of catalysts modified by these voluminous alcohols only a slight decrease in the catalytic activity proportional to alcohol/metallocene molar ratio was observed. The addition of the modifiers gives rise to polymers with higher molecular weights than the nonmodified systems, but no structural changes in the polyethylenes were observed. The addition of the sterically demanding alcohols to the reaction medium changes the regioregularity of polypropylenes, but does not significantly influence their stereoregularity, at 30 °C. Propylene–ethylene copolymers containing up to 8.6% of ethylene units derived from 1,3‐insertion and significant amount of rr‐centered pentads were obtained by single‐monomer polymerization of propylene with Ind₂ZrCl₂/MMAO/adamantan‐1‐ol, at 70 °C. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4248–4259, 2005     

Lanthanide borohydrido complexes for MMA polymerization: syndio‐ vs iso‐ stereocontrol

This paper presents an extensive study of the polymerization of MMA with borohydrido lanthanide complexes for the first time. Catalytic systems are made from a lanthanide derivative bearing zero one, or two bulky ligands: substituted cyclopentadienyl (Cp^*′ = C₅Me₄nPr, Cp⁴ⁱ = C₅HiPr₄, Cp^Ph3 = H₂C₅Ph₃‐1,2,4), and/or diketiminate ([(p‐tol)NN] = [(p‐CH₃C₆H₄)N(CH₃)C]₂CH), in the presence of variable quantities of alkylating agent. With BuLi in apolar medium, highly isotactic polymer (up to 95.6%) is formed. In THF, syndiotactic‐rich PMMA is obtained whatever the nature of the co‐catalyst (BuLi or MgⁿBu₂). The presence of an electron‐withdrawing ligand such as Cp^Ph3 allows high syndioregularity, up to 81.8% at 0 °C, together with the highest conversion. There is quite good concordance between calculated and experimental molecular data in THF. Divalent Cp^*′₂Sm^II(THF) and (Cp^Ph3)₂Sm^II(THF) are active as single‐component initiators; the former affords PMMA 88% syndiotactic at 0 °C. Copyright © 2005 John Wiley & Sons, Ltd.     

The bridged cyclopentadienyl indenyl (fluorenyl) zirconocene complexes for polyethylene macromonomers

The synthesis of long‐chain branched polyethylene includes the generation of vinyl‐terminated polyethylene macromonomers and the copolymerization of these macromonomers with ethylene. Four new bridged cyclopentadienyl indenyl (fluorenyl) zirconocene complexes 1a–b, 2a–b were prepared and showed high activities for ethylene homopolymerization upon the activation of methylaluminoxane. The steric bulk of bridged substituent has a profound effect on the catalytic activity as well as on the molecular weight of resulting polyethylene. Complex 1b showed the highest activity of up to 5.32 × 10⁶ g PE/(mol Zr h) for ethylene homopolymerization at 70 °C, which was higher than that of Cp₂ZrCl₂. The polyethylenes produced with complexes 1a–d/MAO are mostly vinyl‐terminated, possess low molecular weight and fit as macromonomers. The (p‐MePh)₂C‐bridged cyclopentadienyl indenyl zirconocene complex 1a could produce polyethylene macromonomer with selectivity for the vinyl‐terminal as high as 94.9%. Copyright © 2010 John Wiley & Sons, Ltd.     

Styrene polymerization by ziegler-natta catalysts based on bis(salicylaldiminate)nickel(II) complexes and methyl aluminoxane

The homopolymerization of styrene by using different catalytic systems based on bis(salicylaldiminate)nickel(II) and methylaluminoxane was investigated. In particular, the effect on catalyst activity and polymer characteristics by electron withdrawing groups located on the phenolic moiety was studied. The influence of the bulkiness of the substituents on the N-aldimine ligand was also ascertained. Finally the catalytic performances were investigated as a function of the main reaction parameters, such as temperature, Al/Ni molar ratio and duration.     

Syndiotactic polymerization of styrene catalyzed by alkenyl‐substituted cyclopentadienyltitanium trichlorides

CH₂?CHCH₂CpTiCl₃ (1), CH₂?CHCH₂CH₂CpTiCl₃ (2) and CH₃CH₂CH₃CpTiCl₃ (3) have been synthesized and characterized. The influence of the alkenyl substituent groups on the catalyst activities in the syndiotactic polymerization of styrene was investigated. The catalyst activities decreased in the order CH₂?CHCH₂CH₂CpTiCl₃ > CH₃CH₂CH₂CH₂CpTiCl₃ > CH₃CH₂CH₂CpTiCl₃ > CH₂?CHCH₂CpTiCl₃ (Cp?C₅H₄). By using complex 1, the dependence of the activity on the concentration of methylaluminoxane, triisobutylaluminum and diisobutylaluminum hydride was investigated. Copyright © 2003 John Wiley & Sons, Ltd.     

Mechanism of aziridination of styrene catalyzed by copper(I) bis(oxazoline)

Experimental studies show that copper complexes can be effectively anchored onto the pores of mesoporous solids, having a good catalytic performance in several reactions, among them the aziridination of olefins and in particular, styrene. In this work, the mechanism of the aziridination of styrene catalyzed by a bis(oxazoline) copper(I) complex was studied in detail by means of density functional theory (DFT) calculations. For such reactions in the homogeneous phase, our calculations revealed a wide diversity of reaction‐pathways, which have not been considered in previous studies, and should be taken into account due to the small energy differences between them. What is more, our results show that there is a strong dependence on the chosen DFT functional. This has profound implications on the way the heterogeneous reaction is studied. © 2013 Wiley Periodicals, Inc.     

Half-sandwich bis(tetramethylaluminate) complexes of the rare-earth metals: synthesis, structural chemistry, and performance in isoprene polymerization

The protonolysis reaction of [Ln(AlMe(4))(3)] with various substituted cyclopentadienyl derivatives HCp(R) gives access to a series of half-sandwich complexes [Ln(AlMe(4))(2)(Cp(R))]. Whereas bis(tetramethylaluminate) complexes with [1,3-(Me(3)Si)(2)C(5)H(3)] and [C(5)Me(4)SiMe(3)] ancillary ligands form easily at ambient temperature for the entire Ln(III) cation size range (Ln=Lu, Y, Sm, Nd, La), exchange with the less reactive [1,2,4-(Me(3)C)(3)C(5)H(3)] was only obtained at elevated temperatures and for the larger metal centers Sm, Nd, and La. X-ray structure analyses of seven representative complexes of the type [Ln(AlMe(4))(2)(Cp(R))] reveal a similar distinct [AlMe(4)] coordination (one eta(2), one bent eta(2)). Treatment with Me(2)AlCl leads to [AlMe(4)] --> [Cl] exchange and, depending on the Al/Ln ratio and the Cp(R) ligand, varying amounts of partially and fully exchanged products [{Ln(AlMe(4))(mu-Cl)(Cp(R))}(2)] and [{Ln(mu-Cl)(2)(Cp(R))}(n)], respectively, have been identified. Complexes [{Y(AlMe(4))(mu-Cl)(C(5)Me(4)SiMe(3))}(2)] and [{Nd(AlMe(4))(mu-Cl){1,2,4-(Me(3)C)(3)C(5)H(2)}}(2)] have been characterized by X-ray structure analysis. All of the chlorinated half-sandwich complexes are inactive in isoprene polymerization. However, activation of the complexes [Ln(AlMe(4))(2)(Cp(R))] with boron-containing cocatalysts, such as [Ph(3)C][B(C(6)F(5))(4)], [PhNMe(2)H][B(C(6)F(5))(4)], or B(C(6)F(5))(3), produces initiators for the fabrication of trans-1,4-polyisoprene. The choice of rare-earth metal cation size, Cp(R) ancillary ligand, and type of boron cocatalyst crucially affects the polymerization performance, including activity, catalyst efficiency, living character, and polymer stereoregularity. The highest stereoselectivities were observed for the precatalyst/cocatalyst systems [La(AlMe(4))(2)(C(5)Me(4)SiMe(3))]/B(C(6)F(5))(3) (trans-1,4 content: 95.6 %, M(w)/M(n)=1.26) and [La(AlMe(4))(2)(C(5)Me(5))]/B(C(6)F(5))(3) (trans-1,4 content: 99.5 %, M(w)/M(n)=1.18).     

Metathesis polymerization of norbornene and terminal acetylenes catalyzed by bis(acetonitrile) complexes of molybdenum and tungsten

The ring-opening metathesis polymerization (ROMP) of norbornene catalyzed by bis(acetonitrile) molybdenum and tungsten complexes, [M(η³-C₃H₅)Cl(CO)₂(NCMe)₂] (1-Mo: M = Mo, 1-W: M = W), which have two labile acetonitrile ligands, has been investigated. These complexes catalyzed the ROMP of norbornene as a single-component initiator. The highly cis-selective polymerization proceeded in a THF solution (95% for 1-Mo and 96% for 1-W), whereas polymerization in CH₂Cl₂ or toluene resulted in lower cis selectivity. The polymerization of terminal acetylenes using these complexes was also examined. The tungsten complex 1-W showed a high catalytic activity for the polymerization of terminal acetylenes, such as phenyl- and tert-butylacetylene. A highly active catalytic system for the ROMP of norbornene was achieved by the activation of the tungsten complex, 1-W, with one equivalent of phenylacetylene, giving poly(norbornene) with a high molecular weight (M_n = 391 × 10⁴) and a high cis selectivity (cis  89%).