Syndioselective propylene polymerization catalyzed by rac-2,2-dimethylpropylidene (1-η5-cyclopentadienyl) (1-η5-fluorenyl) dichlorozirconium

Syndioselective propylene polymerization has been promoted by rac-2,2-dimethylpropylidene (1-η⁵-cyclopentadienyl) (1-η⁵-fluorenyl) dichlorozirconium ( 1 ). The active catalytic species were generated using either triphenylcarbenium tetrakis (pentafluorophenyl) borate ( 2 ) (Zr⁺ method) or methylaluminoxane (MAO method). The former exhibited much higher activity than the latter, especially at low polymerization temperatures (T_p). Syndiotactic poly (propylene) (s-PP) obtained at T_p = ?20°C has T_m approaching 160°C, [rrrr] pentad fraction of 0.92 to 0.95, and 45% crystallinity (X_c). It crystallized in two antichiral unit cells B and C. The C structure is favored by low temperature of polymerization, slow crystallization from melt, and annealing. The s-PP has M?_w/M?_n ranging from 3.6 to 4.4, which can be separated into stereoregular fractions soluble in heptane and hexane and stereoirregular fractions soluble in pentane, ether, and acetone. Therefore, this system cannot be considered to be a single-site catalyst. A parallel study was made on the isopropylidene (1-η⁵-cyclopentadienyl) (1-η⁵-fluorenyl) dichlorozirconium ( 3 )/MAO catalyst. Molecular mechanics calculations were performed for all combinations of the configuration of asymmetric centers. The steric energy favors syndiotactic enchainment for both catalysts 1 and 3 , with 1 forming the more syndioselective catalyst. © 1994 John Wiley & Sons, Inc.     

Silolene-Bridged zirconocenium polymerization catalysts

A new silolene-bridged compound, racemic (1,4-butanediyl) silylene-bis (1-η⁵-in-denyl) dichlorozirconium ( 1 ) was synthesized by reacting ZrCl₄ with C₄H₈Si (IndLi)₂ in THF. 1 was reacted with trialkylaluminum and then with triphenylcarbenium tetrakis (penta-fluorophenyl) borate ( 2 ) to produce in situ the zirconocenium ion ( 1 ⁺). This “constraint geometry” catalyst is exceedingly stereoselective for propylene polymerization at low temperature (T_p = ?55°C), producing refluxing n-heptane insoluble isotactic poly(propylene) (i-PP) with a yield of 99.4%, T_m = 164.3°C, δH_f = 20.22 cal/g and M?_w = 350 000. It has catalytic activities of 10⁷?10⁸ g PP/(mol Zr · [C₃H₆] · h) in propylene polymerization at the T_p ranging from ?55°C to 70°C, and 10⁸ polymer/(mol Zr · [monomer] · h) in ethylene polymerization. The stereospecificity of 1 ⁺ decreases gradually as T_p approaches 20°C. At higher temperatures the catalytic species rapidly loses stereochemical control. Under all experimental conditions 1 ⁺ is more stereospecific than the analogous cation derived from rac-dimethylsilylenebis (1-η⁵-indenyl)dichlorozirconium ( 4 ). The variations of polymerization activities in ethylene and in propylene for T_p from ?55°C to +70°C indicates a Michaelis Mention kinetics. The zirconocenium-propylene π-complex has a larger insertion rate constant but lower thermal stability than the corresponding ethylene π-complex. This catalyst copolymerizes ethylene and propylene with reactivity ratios of comparable magnitude r_E ? 4r_p. Furthermore, r_E.r_p ? 0.5 indicating random copolymer formation. Both 1 and 4 activated with methylaluminoxane (MAO) exhibit much slower polymerization rates, and, under certain conditions, a lower stereo-selectivity than the corresponding 1 ⁺ or 4 ⁺ system. © 1994 John Wiley & Sons, Inc.     

Polar Isotactic and Syndiotactic Polypropylenes by Organozirconium-Catalyzed Masking-Reagent-Free Propylene and Amino–Olefin Copolymerization

Polar functionalized isotactic and syndiotactic polypropylenes (PPs) are synthesized by direct, masking-reagent-free propylene and amino–olefin (AO, CH₂=CH(CH₂)_xNⁿPr₂, x=2, 3, 6) copolymerizations using the activated precatalysts rac-[Me₂Si(indenyl)₂]ZrMe₂ and [Me₂C(Cp)(fluorenyl)]ZrMe₂, respectively. Polymerization activities at 25 °C are as high as 4208 and 535 kg/(mol h atm) with AO incorporation up to 4.0 mol % and 1.6 mol %, respectively. Remarkably, introducing the amino-olefin comonomers significantly enhances stereoselection for both isotactic (mmmm: 59.5 %→91.0 %) and syndiotactic (rrrr: 66.3 %→81.3 %) products.     

Synthesis and characterization of ethylene‐propylene‐1‐pentene terpolymers

Ethylene (E), propylene (P), and 1‐pentene (A) terpolymers differing in monomer composition ratio were produced, using the metallocenes rac‐ethylene bis(indenyl) zirconium dichloride/methylaluminoxane (rac‐Et(Ind)₂ZrCl₂/MAO), isopropyl bis(cyclopentadienyl)fluorenyl zirconium dichloride/methylaluminoxane (Me₂C(Cp)(Flu)ZrCl₂/MAO, and bis(cyclopentadienyl)zirconium dichloride, supported on silica impregnated with MAO (Cp₂ZrCl₂/MAO/SiO₂/MAO) as catalytic systems. The catalytic activities at 25 °C and normal pressure were compared. The best result was obtained with the first catalyst. A detailed study of ¹³C NMR chemical shifts, triad sequences distributions, monomer‐average sequence lengths, and reactivity ratios for the terpolymers is presented. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 947–957, 2008     

Olefin terpolymerizations. III. Symmetry,sterics, and monomer structure in ansa-zirconocenium catalysis of EPDM synthesis

Ethylenebis (η⁵-fluorenyl) zirconium dichloride ( 1 ) and rac-dimethylsilylene bis (1-η⁵-in-denyl) zirconium dichloride ( 2 ) were activated with methylaluminoxane (MAO) to catalyze ethylene (E) propylene (P) copolymerizations. The former produces high MW copolymer at 20°C rich in ethylene with reactivity ratio values of r_E = 1.7 and r_P <0.01, whereas the latter produces lower MW random copolymers with r_E = 1.32 and r_p = 0.36. Ethylidene norbornene (ENB) complexes with 1/MAO but does not undergo insertion in the presence of E and P. In contrast, 2/MAO catalyzes terpolymerization incorporating 9-15 mol % of ENB with slightly lower MW and activity than the corresponding copolymerizations. In comparison, 1,4–hexadiene was incorporated by 2/MAO with much lower A and MW . Terpolymerizations were also conducted with vinylcyclohexene using both catalyst systems. The steric and electronic effects in these processes were discussed. © 1995 John Wiley & Sons, Inc.     

Olefin polymerization and copolymerization with soluble transition‐metal complex catalysts

Olefin polymerizations catalyzed by Cp′TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) ( 1 – 5 ; Cp′ = cyclopentadienyl group), RuCl₂(ethylene)(pybox) { 7 ; pybox = 2,6‐bis[(4S)‐4‐isopropyl‐2‐oxazolin‐2‐yl]pyridine}, and FeCl₂(pybox) ( 8 ) were investigated in the presence of a cocatalyst. The Cp*TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) ( 5 )–methylaluminoxane (MAO) catalyst exhibited remarkable catalytic activity for both ethylene and 1‐hexene polymerizations, and the effect of the substituents on the cyclopentadienyl group was an important factor for the catalytic activity. A high level of 1‐hexene incorporation and a lower r_E · r_H value with 5 than with [Me₂Si(C₅Me₄)(N^tBu)]TiCl₂ ( 6 ) were obtained, despite the rather wide bond angle of Cp Ti O (120.5°) of 5 compared with the bond angle of Cp Ti N of 6 (107.6°). The 7 –MAO catalyst exhibited moderate catalytic activity for ethylene homopolymerization and ethylene/1‐hexene copolymerization, and the resultant copolymer incorporated 1‐hexene. The 8 –MAO catalyst also exhibited activity for ethylene polymerization, and an attempted ethylene/1‐hexene copolymerization gave linear polyethylene. The efficient polymerization of a norbornene macromonomer bearing a ring‐opened poly(norbornene) substituent was accomplished by ringopening metathesis polymerization with the well‐defined Mo(CHCMe₂Ph)(N‐2,6‐ⁱPr₂C₆H₃)[OCMe(CF₃)₂]₂ ( 10 ). The key step for the macromonomer synthesis was the exclusive end‐capping of the ring‐opened poly(norbornene) with p‐Me₃SiOC₆H₄CHO, and the use of 10 was effective for this polymerization proceeding with complete conversion. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4613–4626, 2000     

Polymerizations of olefins and diolefins catalyzed by monocyclopentadienyltitanium complexes containing a (dimethylamino)ethyl substituent and comparison with ansa-zirconocene systems

{[2-(dimethylamino)ethyl]cyclopentadienyl}titanium trichloride (Cp^NTiCl₃, 1 ) was activated with methylaluminoxane (MAO) to catalyze polymerizations of ethylene (E), propylene (P), ethylidene norbornene (ENB), vinylcyclohexene (VCH), and 1,4-hexadiene (HD). The dependence of homopolymerization activity ( A ) of 1 /MAO on olefin concentration ([M]ⁿ) is n = 2.0 ± 0.5 for E and n = 1.8 ± 0.2 for P. The value of n is 2.4 ± 0.2 for CpTiCl₃/MAO catalysis of ethylene polymerization; this system does not polymerize propylene. 1 /MAO catalyzes HD polymerization at one-tenth of A _H for 1-hexene, probably because of chelation effects in the HD case. The copolymerization of E and P has reactivity ratios of r_E = 6.4 and r_P = 0.29 at 20°C, and r_Er_P = 1.9, which suggests 1 /MAO may be a multisite catalyst. The copolymerization activity of CpTiCl₃/MAO is 50 times smaller than that of Cp^NTiCl₃/MAO. Terpolymerization of E/P/ENB has A of 10⁵ g of polymer/(mol of Ti h), incorporates up to 14 mol % (∼ 40 wt %) of ENB, and high MW's of 1 to 3 × 10⁵. All of these parameters are surprisingly insensitive to the ENB concentration. The E/P/VCH terpolymerization has comparable A value of (1.3 ± 0.3) × 10⁵ g/(mol of Ti h). The incorporation of VCH in terpolymer increases with increasing [VCH]. Terpolymerization with HD occurs at about one-third of the A of either ENB or VCH; the product HD–EPDM is low in molecular weight and contains less than 4% of HD. These terpolymerization results are compared with those obtained previously for three zirconocene precursors: rac-ethylenebis(1-η⁵-indenyl)dichlorozirconium ( 6 ), rac-(dimethylsilylene)bis(1-η⁵-indenyl)dichlorozirconium ( 7 ), and ethylenebis(9-η⁵-fluorenyl)dichlorozirconium ( 8 ). The last compound is a particularly poor terpolymerization catalyst; it incorporates very little VCH or HD and no ENB at all. 7 /MAO is a better catalyst for E/P/VCH terpolymerization, while 6 /MAO is superior in E/P/HD terpolymerization. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 319–328, 1998     

Composition distribution of ethylene or propylene–norbornene copolymers obtained with zirconocene catalysts

Copolymerization of ethylene or propylene and norbornene (NB) was carried out with stereospecific zirconocene catalysts rac‐ethylenebis(indenyl)zirconium dichloride, rac‐dimethylsilylenebis(indenyl)zirconium dichloride ( 2 ), rac‐dimethylsilylenebis(2‐methylindenyl)zirconium dichloride, and diphenylmethylene(cyclopentadienyl)(9‐fluorenyl)zirconium dichloride combined with cocatalysts at 40 °C. Temperature‐rising elution fractionation of the copolymers was carried out with cross‐fractionation chromatography with o‐dichlorobenzene as a solvent, and a broad distribution of the copolymer composition was detected. The fraction eluted at lower temperature contained higher NB. The effect of the polymerization time was examined in the ethylene–NB copolymerization with catalyst 2 , and the higher‐temperature elution fraction increased with increasing polymerization time. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 441–448, 2003     

Copolymerization of propylene and 1,5‐hexadiene with stereospecific metallocene/Al(i‐Bu)3/[Ph3C][B(C6F5)4]

Copolymerizations of propylene (P) with 1,5‐hexadiene (1,5‐HD) were carried out with isospecific rac‐1,2‐ethylenebis(1‐indenyl)Zr(NMe₂)₂ [rac‐(EBI)Zr(NMe₂)₂, 1] and syndiospecific isopropylidene(cyclopentadienyl)(9‐fluorenyl)ZrMe₂ [i‐Pr(Cp)(Flu)ZrMe₂, 2] compounds combined with Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄] as a cocatalyst system. Microstructures of poly(propylene‐co‐1,5‐HD) were determined by ¹H NMR, ¹³C NMR, Raman spectroscopies and X‐ray powder diffraction. The isospecific 1/Al(i‐Bu)₃/[Ph₃C][B(C₆F₆)₄] catalyst showed much higher polymerization rate than 2/Al(i‐Bu)₃/[Ph₃C][B(C₆F₆)₄] system, however, the latter system showed higher incorporation of 1,5‐HD (r_P = 8.85, r_1,5‐HD = 0.274) than the former system (r_P = 16.25, r_1,5‐HD = 0.34). The high value of r_P × r_1,5‐HD far above 1 demonstrated that the copolymers obtained by both catalysts are somewhat blocky. The insertion of 1,5‐HD proceeded by enantiomorphic site control; however, the diastereoselectivity of the intramolecular cyclization reaction of 1,2‐inserted 1,5‐HD was independent of the stereospecificity of metallocene compounds, but dependent on the concentration of 1,5‐HD in the feed. The insertion of the monomers by enantiomorphic site control could also be realized by Raman spectroscopy and X‐ray powder diffraction of the polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1590–1598, 2000     

Xantphite: A New Family of Ligands for Catalysis. Applications in the Hydroformylation of Alkenes

The novel bulky diphosphite (P∩P) ligands ( 3 and 4 ) based on the 2,7,9,9‐tetramethyl‐9H‐xanthene‐4,5‐diol ( 2 ) backbone were investigated in the Rh‐catalyzed hydroformylation of oct‐1‐ene, styrene, and (E)‐oct‐2‐ene. These diphosphites gave rise to very active and selective catalysts for the hydroformylation of oct‐1‐ene to nonanal with average rates>10000 (mol aldehyde)(mol Rh)⁻¹h⁻¹ (P(CO/H₂)=20 bar, T=80°, [Rh]=1 mM ) and maximum selectivities of 79% for the linear product. Relatively high selectivities towards the linear aldehyde (up to 70%, linear/branched up to 2.3) but very high activities (up to 39000 (mol aldehyde)(mol Rh)⁻¹h⁻¹) were observed for the hydroformylation of styrene in the presence of these bidentate ligands (P(CO/H₂)=2 – 10 bar, T=120°, [Rh]=0.2 mM ). Remarkable activities (up to 980 (mol aldehyde)(mol Rh)⁻¹h⁻¹) were achieved with these diphosphites for the hydroformylation of (E)‐oct‐2‐ene with selectivities for the linear product of 74% (l/b up to 2.8, P(CO/H₂)=2 bar, T=120°, [Rh]=1 mM ). A detailed study of the solution structure of the catalyst under catalytic conditions was performed by NMR and high‐pressure FT‐IR. The spectroscopic data revealed that under hydroformylation conditions, the bidentate ligands rapidly formed stable, well‐defined catalysts with the structure [RhH(CO)₂(P∩P)]. All the ligands showed a preference for an equatorial‐apical ( ea ) coordination mode in the trigonal bipyramidal Rh‐complexes, indicating that a bis‐equatorial ( ee ) coordination is not a prerequisite for highly selective catalysts.     

Mechanism of electron transfer reaction of ternary nitrilotriacetatocobalt(II) complexes involving succinate and malonate as secondary ligands

The mechanism of oxidation of ternary complexes, [Co^II(nta)(S)(H₂O)₂]^3? and [Co^II(nta)(M)(H₂O)]^3? (nta = nitrilotriacetate acid, S = succinate dianion, and M = malonate dianion), by periodate in aqueous medium has been studied spectrophotometrically over the (20.0–40.0) ± 0.1°C range. The reaction is first order with respect to both [IO₄^?] and the complex, and the rate decreases over the [H⁺] range (2.69–56.20) × 10^?6 mol dm^?3 in both cases. The experimental rate law is consistent with a mechanism in which both the hydroxy complexes [Co^II(nta)(S)(H₂O)(OH)]^4? and [Co^II(nta)(M)(OH)]^4? are significantly more reactive than their conjugate acids. The value of the intramolecular electron transfer rate constant for the oxidation of the [Co^II(nta)(S)(H₂O)₂]^3?, k₁ (3.60 × 10^?3 s^?1), is greater than the value of k₆ (1.54 × 10^?3 s^?1) for the oxidation of [Co^II(nta)(M)(H₂O)]^3? at 30.0 ± 0.1°C and I = 0.20 mol dm^?3. The thermodynamic activation parameters have been calculated. It is assumed that electron transfer takes place via an inner‐sphere mechanism. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 103–113, 2008     

Synthesis, Characterization and Application of Benzyl-substituted Cyclopentadienyl lanthanide Complexes as Catalyst Precursors for the Syndiotactic Polymerization of Methyl Methacrylate

Benzyl-substituted cyclopentadienyl lanthanide complexes were synthesized and characterized by elemental analysis, MS and IR spectroscopy. The analytical data point out the formation of monomeric, unsolvated complexes.In conjunction with AI(Et)3 as co-catalyst, the title complexes are efficient catalysts for the syndiotactic polymerization of methyl methacrylate. For the complex (C6HsCH2C5H4)2YCl, under the optimum polymerization conditions(60℃,n(MMA):n(catalyst):n(co-catalyst)=1000:1:10),a predominantly syndiotactic (rr=66%) polymerof high molecular weight (Mη=105000) was obtained.     

The Measurement of the Gibbs Energy of Transfer Between Oil and Water Using a Nano‐Carbon Paste Electrode

The use of nano‐carbon paste electrodes for the measurement of Gibbs energies of transfer between oil and aqueous phases is reported. In this method the oil of interest is used as the binder for the nano‐carbon paste electrodes and the molecule of interest is dissolved in the organic or aqueous phase. Voltammetry is performed over a period of time and used to monitor the transfer of the molecule between the two phases. The method is illustrated for the transfer of ferrocenemethanol between water and oil using the ferrocenemethanol / ferroceniummethanol (FcCH₂OH/FcCH₂OH⁺) redox couple. Three pairs of voltammetric peaks were observed in a 0.1 M KCl solution when the nano‐carbon paste electrode was modified by dissolution of FcCH₂OH in the binder oil: P1 [E=0.23 V, 0.17 V vs. Ag/AgCl (1 M KCl)], P2 [E=0.36 V, 0.32 V vs. Ag/AgCl (1 M KCl)] and P3 [E=0.55 V, 0.46 V vs. Ag/AgCl (1 M KCl)]. These are assigned to the FcCH₂OH species existing in the aqueous solution [FcCH₂OH(aq)/FcCH₂OH⁺(aq)], originating in the oil (o) [FcCH₂OH(o)/FcCH₂OH⁺(aq)] and to oxidation of adsorbed (ads) material on the nano‐carbon [FcCH₂OH(ads)] respectively. When supporting electrolyte containing the anions Cl^?, NO₃^? or SCN^? was used, an expulsion of the oxidised ferrocene occurred and the difference in midpoint potentials (E_mid) between the peaks P1 and P2 observed in these experiments allowed the calculation of the Gibbs energy (ΔG°) of transfer of ferrocenemethanol from water to oil. The average ΔG° value thus obtained was (?12.7±0.2) kJ mol^?1. For more hydrophobic anions (X^?=PF₆^?, AsF₆^?), the electron transfer is coupled to the transfer of the anion into the oil and the ΔG° for the transfer of the ion pair of FcCH₂OH⁺ and X^? ions from water to oil was found to be ?1.3 and ?3.9 kJ mol^?1 for PF₆^? and AsF₆^? respectively.     

Electrochemical potentials, optical transitions, and frontier orbitals of non-bridged and bridged bent sandwich zirconocene complexes

A linear correlation between the electrochemical gap values (G=E _ox−E _red) and the energies of optical transition in the UV-vis region was found and justified for a series of non-bridged and bridged bent-sandwich zirconocene complexes with the general formula R(η⁵-L)₂ZrX₂, where L=cyclopentadienyl (Cp), indenyl (Ind), fluorenyl (Flu); X=Cl, Me; the bridging group R=SiMe₂, (CH₂)₂.     

The isomers of 3-methyl pentene-2; configurational assignment and molecular structure by electron diffraction

The two isomers of 3-methyl pentene-2 have been investigated in the vapour phase by electron diffraction. The higher boiling isomer (70.4 °C) has the E-configuration and the isomer boiling at 67.7 °C has the Z-configuration. Bond distances in the E-isomer are: r(CC) = 1.349, r(Csp²-Csp³) = 1.511, r(C-C) = 1.551, r(C-H) = 1.116 Å; in the Z-isomer: r(CC) = 1.344, r(Csp²-Csp³) = 1.508, r(C-C) = 1.553, r(C-H) = 1.114 Å. In both compounds the Csp³-Csp³ bond is at approximately right angles to the plane containing the double bond. The possibility of non-planar arrangements around the double bond is discussed.     

Metallocene complexes as homogeneous catalysts in olefin polymerization

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

氮苄叉基苯胺分子的平面扭曲驱动力的DFT研究

为了探索DFT方法中氮苄叉基苯胺分子的扭曲驱动力, 通过把非平面氮苄叉基苯胺(NBA)分子的DFT能量分成π和σ的方法, 分析了垂直离域能ΔE^V(θ)及σ-π轨道作用能ΔE^σπ(θ)的失稳定性, 并讨论了在扭曲过程中它们所起的作用. 在B3LYP/6-31G*, 6-311G*, 6-31G(2d), 6-311G(2d)水平下的计算结果显示: 与经典观点不同, π电子的离域是失稳定的, 且平面时失稳定性最强, 是分子扭曲的动力; 但σ-π轨道作用也是失稳定的, 随着扭角的增大其失稳定性增强, 是分子扭曲的阻力. NBA分子的大扭角构象, 是包含π-π, σ-π轨道作用在内的各种电子相互作用共同作用的结果.     

Redox properties of inorganic nanoparticles

The redox potentials E°(M₁₄₇) (M = Au, Cu) were calculated on the basis of the shell model with inclusion of hybridized electronic configurations of atoms. The prospects for studying E°(M _N ) for nanoparticles of other d metals were outlined.     

Molecular mechanics study of zirconocenium catalyzed isospecific polymerization of propylene

Stereocontrol energy (ΔE⁰) is investigated as a measure of enantioselectivity of ansa-zircoocenium catalyst in propylene polymerization; it was calculated with MM2 (molecular mechanics) force field using π complex (°C) and transition state (TS) geometries obtained by ab initio molecular orbital methods. Both rac-ethylenebis (1-η⁵-indenyl) - ( 1 ) and rac-ethylenebis (1-η⁵-4,5,7,8-tetrahydroindenyl) ( 2 ) zirconocenium species are isospecific in either the π-complexes or the transition states. The stereoselectivity is greater if there is α-agostic interaction; it is lowered in the cases of β and γ agostic interactions. The ¹³C-NMR steric pentad distribution indicates the poly(propylene) to be much less stereoregular than that predicted by ΔE⁰. Following the occurrence of a regiochemical insertion error, the addition of another monomer via any mode is prohibitively unfavorable. The catalyst suffers loss of stereospecificity as temperature of polymerization increases. Insertion via transition states involving different agostic interactions could be one explanation for the observed loss. © 1995 John Wiley & Sons, Inc.     

Olefin terpolymerizations. I. 1,4-hexadiene

Ethylene (E), propylene (P), and 1,4-hexadiene (HD) were terpolymerized with rac-1,2-ethylenebis (1-η⁵-indenyl) zirconium(IV) dichloride and methylaluminoxane (Et[Ind]₂ZrCl₂/MAO), and compared with the copolymerizations of E/P, E/HD, P/HD, and terpolymerization using ethylidene norbornene (ENB) as the termonomer. HD lowers the polymerization activity, the effect is more pronounced for P/HD and E/P/HD using large amount of P, than for E/HD and E/P/HD using feed low in P. The polymer molecular weight is most strongly affected by the temperature of polymerization (T_p), whereas the E/P ratio in the feed has virtually no effect. The reactivity ratios r_E and r_P are 3.0 and 0.3, respectively, at 20°C but r_P becomes larger than r_E at T_P = 70°C. ¹H-NMR spectra showed occurrence of cycloaddition in the homopolymerization of HD; on the other hand, HD is incorporated in the terpolymer only by linear 1,2-addition. © 1995 John Wiley & Sons, Inc.