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Novel complexes [(C5Me5)2Ln][B(C6F5)4] (Ln = Pr, Nd, or Gd) were prepared, which in combination with iBu3Al efficiently induce highly 1,4‐cis‐specific polymerization of butadiene. The activity of the Gd complex/iBu3Al system is high enough to exhibit good catalytic activity even at low temperature. Polymerization at −78 °C gave polybutadiene with nearly perfect 1,4‐cis microstructure (>99.9%) with sharp molecular weight distribution (Mw/Mn = 1.45) and in reasonable yield. ORTEP drawing of 2b. Selected bond distances (Å): Pr‐F1 = 2.549(2), Pr‐F19 = 2.625(2).magnified imageORTEP drawing of 2b. Selected bond distances (Å): Pr‐F1 = 2.549(2), Pr‐F19 = 2.625(2).

A series of bimetallic complexes composed of lanthanide metallocene and trimethylaluminum, Cp*2Ln[(μ-Me)AlMe2(μ-Me)]2LnCp*2 (Cp* = η5-C5Me5, Ln = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Tm, Yb, Lu), were prepared, and the ability to catalyze polymerization of butadiene in the presence of cocatalysts, AlR3 (R = Me, i Bu) and [Ph3C][B(C6F5)4], was studied as a function of the 11 different lanthanide metal species and the kind of alkylaluminum in the cocatalyst. Both catalytic activity and microstructure of polybutadiene depended strongly on the kind of lanthanide metal and the trialkylaluminum. The Gd complex in combination with Al i Bu3/[Ph3C][B(C6F5)4] was extremely active and gave perfectly 1,4-cis regulated polybutadiene at −40 °C. In contrast, the Ce complex with almost similar cocatalysts, AlMe3/[Ph3C][B(C6F5)4], yielded polybutadiene having a very high content of 1,4-trans microstructure (1,4-trans selectivity = 93.8%). With the Al/Ln ratio was 3−5, the polymerization systems, in which the alkylaluminum worked as an activator, showed somewhat living-like nature; the M n of the resulting polybutadiene increased in proportion to monomer consumption, while the molecular weight distribution stayed narrow throughout the reactions. In the presence of a large amount of monomer, molecular weight of polybutadiene was conveniently controlled by additional excess alkylaluminum, which functioned as a chain transfer agent.

Summary: In non‐polar solvents such as toluene, Cp‐Ni and ‐Pd complexes (Cp = η5‐C5H5) with appropriate activators have been found to induce the addition polymerization of norbornene in excellent yields, for example (Cp)Pd(allyl)/[Ph3C][B(C6F5)4] gave 105 120 kg‐polymer/cat‐mol · h at room temperature. While the Cp‐Pd system was not suitable in the presence of ester‐substituted norbornenes, the Cp‐Ni system, for example (Cp)Ni(Cl)(PPh3)/AlMe3/B(C6F5)3 can copolymerize norbornene with 5‐norbornene‐2‐carboxylic acid methyl ester in toluene to give high yields (up to 68% in 2 h at room temperature) of copolymer with variable contents of the methyl ester monomer unit (17.4–60.7 mol‐%). These copolymers have high molecular weights ($\overline M _{\rm n}$ = 234 100–109 500) and narrow molecular weight distributions ($\overline M _{\rm w} /\overline M _{\rm n}$ = 1.78–1.89). In addition, they are soluble in common organic solvents giving flexible and transparent films on casting, that show very high Tg in the range of 352.8 to 316.0 °C. The same Ni‐catalyst system can also copolymerize norbornene derivatives with bulky substituents, i.e., 2‐butyl‐5‐norbornene and 5‐norbornene‐2‐carboxylic acid butyl ester. The Tg of these copolymers are lower (294.9–267.3 °C) than the methyl ester‐based copolymers, demonstrating that the Tg of the polynorbornene copolymer film can be tailored simply by changing the alkyl group of the monomer to within the range of 352 to 267 °C.Figure showing the addition polymerization of norbornene using Cp‐Ni complex with appropriate activators.magnified imageFigure showing the addition polymerization of norbornene using Cp‐Ni complex with appropriate activators.

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Highly efficient cis-polymerization of butadiene was achieved by using new bis(indenyl) silylamide rare earth complexes with the cooperation of both a borate salt and i-Bu3Al; treatment of these complexes with organoboron compounds unexpectedly yielded new cationic mono(indenyl) amido species relevant to polymerization.

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Homo‐ and copolymerizations of butadiene (BD) and styrene (St) were carried out by gadolinium catalysts having various tricarboxylate ligands [Gd(OCOR)3: R = CH3, CH2Cl, CHCl2, CCl3, and CF3], to investigate the effects of ligands and discuss the cis polymerization mechanism. Polymerization of BD with Gd(OCOR)3—(i—Bu)3Al—Et2AlCl catalysts was carried out in hexane at 50°C. By each catalyst, poly(BD) having a high cis content (cis = 97–99%) in 22–85% yields for 2–24 h were obtained. The ligands with low pKa values increased the polymerization activity as follows: R of Gd(OCOR)3: CF3 > CCl3 > CHCl2 > CH2Cl ∼ CH3. On the other hand, in the polymerization of St or copolymerization of BD and St under similar conditions, the highest activity was attained by a Gd(OCOCCI3)3‐ based catalyst. The difference in the optimum ligand among the homo‐ and copolymerization of BD and St was discussed on the basis of energy levels of the catalysts. In the copolymers of BD and St, the cis‐1,4 content of the BD unit decreased with increasing St content. Furthermore, according to the diad analysis of copolymers (St content ∼ 14.5 mol %) by 13C NMR spectroscopy, the low cis value of the BD unit was observed in the St‐BD diad (cis/trans/vinyl = 24/53/23), while the high cis value of the BD unit remained in the BD‐BD diad (cis/trans/vinyl = 89/10/1). These results suggest that the terminal BD unit is controlled by the cis configuration by the coordination between the penultimate cis vinylene unit and the gadolinium metal catalyst, whereas the presence of the penultimate St unit interferes with cis polymerization of the terminal BD unit. The difference in the coordination mechanism in the course of polymerization between rare earth metal and transition metal catalysts such as the Ni(acac)2 and Co(acac)3‐based catalyst was also discussed. © 1995 John Wiley & Sons, Inc.