Effect of ketimide ligand for ethylene polymerization and ethylene/norbornene copolymerization catalyzed by (cyclopentadienyl)(ketimide)titanium complexes-MAO catalyst systems: Structural analysis for CpTiCl2(NCPh2)

Ligand effects on the catalytic activity [and norbornene (NBE) incorporation] for both ethylene polymerization and ethylene/NBE copolymerization using half-titanocenes (titanium half-sandwich complexes) containing ketimide ligand of type Cp′TiCl₂[NC(R¹)R²] [Cp′ = Cp (1), C⁵Me⁵ (Cp^∗, 2); R¹,R² = ^tBu,^tBu (a), ^tBu,Ph (b), Ph,Ph (c)]-methylaluminoxane (MAO) catalyst systems have been investigated. CpTiCl₂[NC(^tBu)Ph] (1b) CpTiCl₂(NCPh₂) (1c), and Cp^∗TiCl₂(NCPh₂) (2c) were prepared and identified; the structure of Cp^∗TiCl₂(NCPh₂) (2c) was determined by X-ray crystallography. The catalytic activity for ethylene polymerization increased in the order: 1a > 1b > 1c, suggesting that an electronic nature of the ketimide ligand affects the activity. However, molecular weight distributions for resultant (co)polymers prepared by 1b,c and by 2c-MAO catalyst systems were bi- or multi-modal, suggesting that the ketimide substituent plays a key role in order for these (co)polymerizations to proceed with single catalytically-active species. CpTiCl₂(NC^tBu₂) (1a) exhibited both remarkable catalytic activity and efficient NBE incorporation for ethylene/NBE copolymerization.     

Factors affecting product distributions in ethylene/styrene copolymerization by (aryloxo)(cyclopentadienyl)titanium complexes‐MAO catalyst systems

Ethylene/styrene copolymerizations using Cp′TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) [Cp′ = Cp* (C₅Me₅, 1 ), 1,2,4‐Me₃C₅H₂ ( 2 ), tert‐BuC₅H₄ ( 3 )]‐MAO catalyst systems were explored under various conditions. Complexes 2 and 3 exhibited both high catalytic activities (activity: 504–6810 kg‐polymer/mol‐Ti h) and efficient styrene incorporations at 25, 40°C (ethylene 6 atm), affording relatively high molecular weight poly (ethylene‐co‐styrene)s with unimodal molecular weight distributions as well as with uniform styrene distributions (M_w = 6.12–13.6 × 10⁴, M_w/M_n = 1.50–1.71, styrene 31.7–51.9 mol %). By‐productions of syndiotactic polystyrene (SPS) were observed, when the copolymerizations by 1 – 3 ‐MAO catalyst systems were performed at 55, 70 °C (ethylene 6 atm, SPS 9.0–68.9 wt %); the ratios of the copolymer/SPS were affected by the polymerization temperature, the [styrene]/[ethylene] feed molar ratios in the reaction mixture, and by both the cyclopentadienyl fragment (Cp′) and anionic ancillary donor ligand (L) in Cp′TiCl₂(L) (L = Cl, O‐2,6‐ⁱPr₂C₆H₃ or N=C^tBu₂) employed. Co‐presence of the catalytically‐active species for both the copolymerization and the homopolymerization was thus suggested even in the presence of ethylene; the ratios were influenced by various factors (catalyst precursors, temperature, styrene/ethylene feed molar ratio, etc.). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4162–4174, 2008     

Living copolymerization of ethylene with norbornene catalyzed by bis(pyrrolide-imine) titanium complexes with MAO

Bis(pyrrolide-imine) Ti complexes in conjunction with methylalumoxane (MAO) were found to work as efficient catalysts for the copolymerization of ethylene and norbornene to afford unique copolymers via an addition-type polymerization mechanism. The catalysts exhibited very high norbornene incorporation, superior to that obtained with Me(2)Si(Me(4)Cp)(N-tert-Bu)TiCl(2) (CGC). The sterically open and highly electrophilic nature of the catalysts is probably responsible for the excellent norbornene incorporation. The catalysts displayed a marked tendency to produce alternating copolymers, which have stereoirregular structures despite the C(2) symmetric nature of the catalysts. The norbornene/ethylene molar ratio in the polymerization medium had a profound influence on the molecular weight distribution of the resulting copolymer. At norbornene/ethylene ratios larger than ca. 1, the catalysts mediated room-temperature living copolymerization of ethylene and norbornene to form high molecular weight monodisperse copolymers (M(n) > 500,000, M(w)/M(n) < 1.20). (13)C NMR spectroscopic analysis of a copolymer, produced under conditions that gave low molecular weight, demonstrated that the copolymerization is initiated by norbornene insertion and that the catalyst mostly exists as a norbornene-last-inserted species under living conditions. Polymerization behavior coupled with DFT calculations suggested that the highly controlled living polymerization stems from the fact that the catalysts possess high affinity and high incorporation ability for norbornene as well as the characteristics of a living ethylene polymerization though under limited conditions (M(n) 225,000, M(w)/M(n) 1.15, 10-s polymerization, 25 degrees C). With the catalyst, unique block copolymers [i.e., poly(ethylene-co-norbornene)(1)-b-poly(ethylene-co-norbornene)(2), PE-b-poly(ethylene-co-norbornene)] were successfully synthesized from ethylene and norbornene. Transmission electron microscopy (TEM) indicated that the PE-b-poly(ethylene-co-norbornene) possesses high potential as a new material consisting of crystalline and amorphous segments which are chemically linked.     

Copolymerization of ethylene with styrene catalyzed by a linked bis(phenolato) titanium catalyst

Copolymerization of ethylene with styrene, catalyzed by 1,4‐dithiabutanediyl‐linked bis(phenolato) titanium complex and methylaluminoxane, produced exclusively ethylene–styrene copolymers with high activity. Copolymerization parameters were calculated to be r_E = 1.2 for ethylene and r_S = 0.031 for styrene, with r_E r_S = 0.037 indicating preference for alternating copolymerization. The copolymer microstructure can be varied by changing the ratio between the monomers in the copolymerization feed, affording copolymers with styrene content up to 68%. The copolymer microstructure was fully elucidated by ¹³C NMR spectroscopy revealing, in the copolymers with styrene content higher than 50%, the presence of long styrene–styrene homosequences, occasionally interrupted by isolated ethylene units. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1908–1913, 2006     

Living copolymerization of ethylene with norbornene by fluorinated enolato‐imine titanium catalyst

Complex [Ti(κ²‐N,O‐{2,6‐F₂C₆H₃N?C(Me)C(H) ?C(CF₃) O})₂Cl₂] ( 1 ) was evaluated as catalyst for living copolymerization of ethylene (E) with norbornene (N) upon activation with dried methylaluminoxane (d‐MAO) at temperatures between 25 and 90 °C. Copolymerization performed at different [N]/[E] feed ratios afforded stereoirregular alternating high molar mass P(E‐co‐N) with narrow molar mass distribution. The living nature of E‐co‐N copolymerization by 1 /d‐MAO was demonstrated by kinetics at 50 °C. This catalyst system was used for the synthesis of block copolymers such as polyethylene (PE)‐block‐P(E‐co‐N) with a crystalline PE block and an amorphous P(E‐co‐N) block as well as P(E‐co‐N)₁‐block‐P(E‐co‐N)₂, having different norbornene contents in the segments and thus having different T_g values. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Tuning the active species from syndiospecific styrene polymerisation to ethylene/styrene copolymerisation by (aryloxo)(cyclopentadienyl)titanium complexes-MAO catalysts

Exclusive formation of poly(ethylene-co-styrene)s were observed by introduction of ethylene into the solution of syndiospecific styrene polymerisation using Cp'TiCl(2)(O-2,6-(i)Pr(2)C(6)H(3)) (Cp' = 1,2,4-Me(3)C(5)H(2), tert-BuC(5)H(4))-MAO catalysts without by-production of syndiotactic polystyrene, whereas the styrene polymerisation did not proceed when ethylene was removed from the reaction mixture of ethylene/styrene copolymerisation.     

Olefin polymerization by (cyclopentadienyl)(ketimide)titanium(IV) complexes of the type, Cp′TiCl2(N=CBu2)-methylaluminoxane (MAO) catalyst systems

Effects of substituents on cyclopentadienyl group for homopolymerization of ethylene, 1-hexene, and for ethylene/1-hexene copolymerization using a series of nonbridged (cyclopentadienyl)(ketimide)titanium complexes of the type, Cp′TiCl₂(N=C^tBu₂) [Cp′ = Cp (1), ^tBuC₅H₄ (2), C₅Me₅ (Cp^*, 3), and indenyl (4)] have been explored in the presence of methylaluminoxane (MAO) cocatalyst. Complexes 1–3 showed the similar catalytic activities for ethylene polymerization although the activity by 4 was somewhat low, whereas the activity for 1-hexene polymerization increased in the order 1 > 4 2 > 3. These complexes showed significant activities for ethylene/1-hexene copolymerization affording high molecular weight poly(ethylene-co-1-hexene)s with unimodal molecular weight distributions, and the activity increased in the order: 4 > 1 2, 3. The r_Er_H values in the polymerization by 1–3 at 40 °C were 0.35–0.52 which clearly indicate that the 1-hexene incorporation in the copolymerization did not proceed in a random manner. The r_E values by 1–3 were 6.0–6.4 and the values were independent upon the cyclopentadienyl fragment employed; the r_E values by 4 at 40 °C were 10.2–10.9 which were close to those by ansa-metallocene complex catalysts. These values were influenced by the polymerization temperature, and the 1-hexene incorporation by 1–4 became inefficient at higher temperature, although the observed activities especially by 1, 4 were highly remarkable.     

An experimental and computational evaluation of ethylene/styrene copolymerization with a homogeneous single‐site titanium(IV)‐constrained geometry catalyst

Styrene was copolymerized with ethylene using the geometry constrained Me₂Si(Me₄Cp)(N‐tert‐butyl)TiCl₂ Dow catalyst activated with methylaluminoxane. Increasing the styrene/ethylene ratio in the reactor feed had the effects of reducing both the activity of the catalyst and the molecular weight of the copolymers produced. However, the higher the styrene/ethylene ratio used, the greater the amount of styrene that became incorporated in the copolymer. We discuss these experimental findings within the framework of a computational analysis of ethylene/styrene copolymerization performed through hybrid density functional theory (B3LYP). In general, there was good agreement between the experimental and theoretical results. Our findings point to the suitability of combining experimental and theoretical data for clarifying the copolymerization mechanisms that take place in α‐olefin‐organometallic systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 711–725, 2005     

Enantioselective alkynylation of aldehydes catalyzed by a camphor sulfonylated amino alcohols titanium(IV) catalyst system

A new titanium(IV) complex has been developed for the effective enantioselective alkynylation of phenylacetylene addition to aldehydes. The titanium(IV) complex was readily prepared in situ from (R)‐C‐(7,7‐dimethyl‐2‐oxo‐bicyclo[2.2.1]hept‐1‐yl)‐(1R,2S)‐N‐(2‐hydroxy‐1,2‐diphenyl‐ethyl)‐methanesulfonamide (1h) and tetraisopropyl titanate [Ti(i‐OPr)₄]. A variety of aromatic aldehydes and α,β‐unsaturated aldehydes were found to be suitable substrates in the presence of the camphor sulfonylated amino alcohol titanium(IV) complex [10 mol% 1h, 40 mol% Ti(i‐OPr)₄]. The desired propargylic alcohols were afforded with high isolated yields (up to 90%) and moderate enantioselectivities (up to 65% ee) under mild conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

Living copolymerization of ethylene with norbornene mediated by heteroligated (Salicylaldiminato)(β‐enaminoketonato)titanium catalysts

Three heteroligated (salicylaldiminato)(β‐enaminoketonato)titanium complexes [3‐Bu^t‐2‐OC₆H₃CH?N(C₆F₅)][(p‐XC₆H₄)N?C(Bu^t)CHC(CF₃)O]TiCl₂ ( 3a : X = F, 3b : X = Cl, 3c : X = Br) were synthesized and investigated as the catalysts for ethylene polymerization and ethylene/norbornene copolymerization. In the presence of modified methylaluminoxane as a cocatalyst, these unsymmetric catalysts exhibited high activities toward ethylene polymerization, similar to their parallel parent catalysts. Furthermore, they also displayed favorable ability to efficiently incorporate norbornene into the polymer chains and produce high molecular weight copolymers under the mild conditions, though the copolymerization of ethylene with norbornene leads to relatively lower activities. The sterically open structure of the β‐enaminoketonato ligand is responsible for the high norbornene incorporation. The norbornene concentration in the polymerization medium had a profound influence on the molecular weight distribution of the resulting copolymer. When the norbornene concentration in the feed is higher than 0.4 mol/L, the heteroligated catalysts mediated the living copolymerization of ethylene with norbornene to form narrow molecular weight distribution copolymers (M_w/M_n < 1.20), which suggested that chain termination or transfer reaction could be efficiently suppressed via the addition of norbornene into the reaction medium. Polymer yields, catalytic activity, molecular weight, and norbornene incorporation can be controlled within a wide range by the variation of the reaction parameters such as comonomer content in the feed, reaction time, and temperature. ©2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6072–6082, 2009     

Living polymerization and block copolymerization of alpha-olefins by an amine bis(phenolate) titanium catalyst

An amine bis(phenolate) dibenzyl titanium complex having a methoxy donor on a side arm leads, upon activation with tris(pentafluorophenyl)borane, to unique living properties in alpha-olefin polymerization: exceptionally high molecular weight poly(1-hexene) is obtained in a living fashion at room temperature, living polymerization of 1-hexene is obtained above room temperature, and block copolymerization of 1-hexene and 1-octene at room temperature is described as well.     

Reductions by titanium(II) as catalyzed by titanium(IV)

The cobalt(III) complexes, [(NH3)5CoBr]2+ and [(NH3)5CoI]2+ are reduced by Ti(II) solutions containing Ti(IV), generating nearly linear (zero-order) profiles that become curved only during the last few percent of reaction. Other Co(III)-Ti(II) systems exhibit the usual exponential traces with rates proportional to [Co(III)]. Observed kinetics of the biphasic catalyzed Ti(II)-Co(III)Br and Ti(II)-Co(III)I reactions support the reaction sequence: [Ti(II)(H20)n]2+ + [Ti(IV)F5]- (k1)<==>(k -1) [Ti(II)(H2O)(n-1)]2+ + [(H2O)Ti(IV)F5]-, [Ti(II)(H2O)(n-1)]2+ + Co(III) (k2)--> Ti(III) + Co(II) with rates determined mainly by the slow Ti(IV)-Ti(II) ligand exchange (k1 = 9 x 10(-3) M(-1) s(-1) at 22 degrees C). Computer simulations of the catalyzed Ti(II)-Co(III) reaction in perchlorate-triflate media yield relative rates for reduction by the proposed active [Ti(II)(H2O)(n-1)]2+ intermediate; k(Br)/k(I) = 8.     

Reactions of trichloro(cyclopentadienyl)titanium(IV) with 1,5-diarylthiocarbazones

Summary The synthesis and characterization of the complexes from the reactions of trichloro(cyclopentadienyl)titanium(IV) with 1,5-diarylthiocarbazones (aryl=phenyl,o-tolyl,o-chlorophenyl,p-tolyl,p-chlorophenyl, or 3,5-dimethylphenyl) are reported. They are of the types CpTi(HDz)Cl₂ and CpTi(HDz)₂Cl (Cp=cyclopentadienyl, HDz^–=the mono-anion of a 1,5-diarylthiocarbazone, H₂Dz). The compounds are nonelectrolytes in dimethylformamide (DMF). In solid state, the far i.r. spectra of CpTi(HDz)Cl₂ indicate the complexes to be dimeric, involving Cl-bridges.     

Alternating copolymerization of ethylene and propene with the [ethylene(1-indenyl)(9-fluorenyl)]zirconium dichloridemethylaluminoxane catalyst system

The copolymerization of ethylene and propene was conducted at −40°C with the [ethylene(1-indenyl)(9-fluorenyl)]zirconium dichloride-methylaluminoxane catalyst system, and the microstructure of the resulting copolymers was analyzed in detail by ¹³C NMR. The content of alternating [EP] sequences increased markedly with an increase in the feed ratio of propene to ethylene. A poly(ethylene-co-propene) with a proportion of [EP] sequences over 95% was thus obtained under appropriate copolymerization conditions. It was also demonstrated that the alternating ethylene-propene copolymer is stereoregular and isotactic.     

Reactions of dichloro-bis(cyclopentadienyl)titanium(IV) with bidentate Schiff bases

A series of Cp₂Ti(SB)Cl complexes, whereSB is the anion of bidentate Schiff bases derived from salicylaldehyde and different primary aminesviz o-anisidine,m-anisidine,o-phenetidine,o-chloroaniline,m-chloroaniline,m-nitroaniline, α-naphthylamine and benzylamine, have been synthesised by the reaction of dichloro-bis(cyclopentadienyl) titanium(IV), Cp₂TiCl₂, and bidentate Schiff base (sbh) in a 1:1 molar ratio in refluxingthf in the presence of triethylamine. The new derivatives have been characterised on the basis of their elemental analyses, conductance measurements and spectral (IR,¹Hnmr and electronic) studies     

Reactions of dichlorobis(cyclopentadienyl)titanium (IV) with multidentate Schiff bases

Summary Dichlorobis(cyclopentadienyl)titanium(IV), Cp₂TiCI₂, reacts with bidentate Schiff bases such as salicylideneaniline, salicylidene-o-toluidine, salicylidene-m-toluidine, salicylidene-p-toluidine and 2-hydroxy-l-naphthylReprints of this paper are not available.To whom all correspondence should be addressed.     

Syndiotactic polymerization of styrene and copolymerization with ethylene catalyzed by chiral half-sandwich rare-earth metal dialkyl complexes

The syndiotactic polymerization of styrene(St) and the copolymerization of St with ethylene(E) were carried out by using a series of chiral half-sandwich rare-earth metal dialkyl complexes(Cp~x*) as the catalysts. The complexes are Ln(CH_2SiMe_3)_2(THF)(1-4: Ln = Sc(1), Ln = Lu(2), Ln = Y(3), Ln = Dy(4)) bearing chiral cyclopentadienyl ligand containing bulky cylcohexane derivatives in the presence of activator and AliBu_3. For the St polymerization, a high activity up to 3.1 × 10~6 g of polymer mol Ln~(-1)·h~(-1) and a high syndiotactic selectivity more than 99% were achieved. The resulting syndiotactic polystyrenes(sPSs) have the molecular weights(Mn) ranging from 3700 g·mol~(-1) to 6400 g·mol~(-1) and the molecular weight distributions(Mw/Mn) from 1.40 to 5.03. As for the copolymerization of St and E, the activity was up to 2.4 × 10~6 g of copolymer mol Sc~(-1)·h~(-1)·MPa~(-1), giving random St-E copolymers containing syndiotactic polystyrene sequences with different St content in the range of 15 mol%-58 mol%. These results demonstrate that the bulky cyclopentadienyl ligands of the chiral half-sandwich rare-earth metal complexes effectively inhibit the continued insertion of St monomers into the(co)polymer chain to some extent in comparison with the known half-sandwich rare-earth metal complexes.     

Living carbocationic copolymerization of isobutylene with styrene

The carbocationic copolymerization of isobutylene (IB) and styrene (St), initiated by 2‐chloro‐2,4,4‐trimethylpentane/TiCl₄ in 60/40 (v/v) methyl chloride/hexane at ?90 °C, was investigated. At a low total concentration (0.5 mol/L), slow initiation and rapid monomer conversion were observed. At a high total comonomer concentration (3 mol/L), living conditions (a linear semilogarithmic rate and M_n–conversion plots) were found, provided that the St concentration was above a critical value ([St]₀ ～ 0.6 mol/L). The breadth of the molecular weight distribution decreased with increasing IB concentration in the feed, reaching M_w/M_n ～ 1.1. St homopolymerization was also living at a high total concentration, yielding polystyrene with M_n = 82,000 g/mol, the highest molecular weight ever achieved in carbocationic St polymerization. An analysis of this system by both the traditional gravimetric–NMR copolymer composition method and FTIR demonstrated penultimate effects. IB enrichment was found in the copolymers at all feed compositions, with very little drift at a high total concentration and above the critical St concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1778–1787, 2007     

Homopolymerization of ethylene and copolymerization with 1-butene in the presence of bis(cyclopentadienyl)titanium dichloride and diisobutylaluminum chloride

Ethylene was homopolymerized and copolymerized with 1-butene in benzene at 30°C. with the use of bis(cyclopentadienyl)titanium dichloride and diisobutylaluminum chloride as catalyst. Both freshly prepared catalyst and catalyst which had been aged up to 114 hr. were used. When the catalyst was aged prior to adding the monomer, the yields were lower and the products had higher molecular weights. In the case of copolymers, aging of the catalyst also affected the relative concentrations of the comonomers in the products. 1-Butene was an effective chain transfer agent under all reaction conditions. The data were found to be consistent with the previously suggested mechanism according to which different species initiate polymerizations with freshly mixed and aged catalysts.