Polymerization of Propene and Butene with a Chiral Zirconocene and Methylalumoxane As Cocatalyst

Home , Butene, Propene, Zirconocene

Polymerization of Propene and Butene Remarkable is the high activity of the chiral catalyst 1 with a Chid Zirconocene and (Table I). Thus, less than mol/L suffices for the pro- Methylalumoxane as Cocatalyst** duction of 7700 kg polypropylene per mole of Zr per hour at By Walter Kaminsky,* Klaus Kiilper, 60°C. Under comparable conditions only 2730 kg of atactic Hans H. Brintzinger, and Ferdinand R. W. P. Wild polypropylene is formed per mole of Zr per hour with Hitherto, only atactic polypropylene could be prepared bis(cyc1opentadienyl)dimethylzirconium. That is, the chiral with soluble bis(cyclopentadienyl)zirconium(iv)/methyl- zirconocene 1 affords not only isotactic polypropylene, alumoxane Ziegler-Natta catalysts.".'' E~en[~'has recently but also has a polymerization activity 2-3 times greater shown that mixtures of, e.g., 63% isotactic and 37% atactic than catalysts that form only atactic polypropylene. The polypropylene are formed with the sterically rigid ethyl- rates of polymerization of ethylene : propene with bis(cy- enebis( I-indeny1)titanium dichloride (mixture of meso clopentadieny1)zirconium compounds are of the order of form and ra~emate).'~' 25 :1, whereas with zirconocene this ratio drops to ca. If, however, the chiral ethylenebis(4,5,6,7-tetrahydro-l- 10 : l.[7.81This means that propene is polymerized relatively indeny1)zirconium dichloride 1 (Fig. 1) is used in com- far better by zirconocene 1 than by bis(cyc1opentadien- bination with methylalumoxane ([AI(CH3)-O],) as co- y1)zirconium compounds. catalyst, highly isotactic polypropylene is obtained. The racemate of 1 was used for this polymerization. The fraction of polymer soluble in toluene can be reduced to Table 2. Composition of some polypropylenes prepared with 1 (see Table 0.2 wt.45, which is considerably lower than the 2-7% 1). achievable with heterogeneous TiCI,/MgC12/AI(C2H5)3/ M, M, MJM,, Atactic Isotacticity Viscosity C,H,CO,C,H,-based catalysts.1h1 la1 fraction index number 1'4 IbI WI bl [cm'/gl [dl

280000 3osoo0 2.6 0.25 91 242 13oooo 144000 2.4 0.2 88. I 132 55000 62000 2.0 0.7 87.3 I10 41 000 45000 1.9 I .o 86.0 16

[a] GPC measurements at 135°C in trichlorobenzene. [b] Fraction soluble in saturated hydrocarbons (b.p. 130°C) according to Kloos et al. 191. [c] 1R spectroscopically, according to Luongo. [lo] [d] At 135°C in decalin.

Besides the high activity of 1 towards propene, which reaches values at least equal to those achieved by heterogeneous catalysts, the properties of the polypropylene thus formed are also remarkable (Table 2). In contrast to industrial polypropylene, which has a molecular weight distribution M,/M, of at least 5, with 1 we have produced products with molecular weight distributions of only I .9 to 2.6. The fraction soluble in hydrocarbons amounts to less than 1% in all cases. The IR-spectroscopically determined isotacticity index of 86 to 91% is also very high. The crys- Fig. I. Crystal btructure of chiral [C2H,(4,5,6,7-tetrahydro-l-indenyl)2ZrC12] tallinity of the highly isotactic polypropylene is largely de- 1. I51 termined by the stereochemical uniformity of the polymerization. High-resolution I3C-NMR spectroscopy affords an Table I. Polymerization of propene or butene with 1 and methylalumoxane. Conditions: 8.4~lo-' mol/L rac-1 in 330 mL toluene, 70 mL a-olefin, insight into the pattern of the sequences in the polymer 1.6 x lo-' mol/L AI-units of methylalumoxane (M, 1200) at various temper- chain. Isotactic sequences (mm triads) are found to be atures (Pol = polymer, M,, = average molecular weight). present to the extent of 95%, heterotactic sequences (mr triads) to the extent of 3.2%, and syndiotactic sequences (rr triads) to the extent of 0.9%. Notable is the very small amount of rr triads compared to mr triads. In the case of commercially available polypropylene the mr/rr ratio is of Propene - 20 360 1.5 80 300 000 the order of 1, and rr is greater by a factor of about 5. Propene - 10 270 4.5 300 28000o This means that the propene molecules are inserted Propene 0 255 12.5 880 I~OOOO Propene 8 180 13.0 1300 85 000 highly stereospecifically with this homogeneous Ziegler- Propene 15 I 70 26.7 2900 55 000 Natta catalyst. Defects in the insertion are minimal, as is Propene 20 120 31.3 4750 41 000 confirmed by the high isotaxy of 97.5% and an average Propene 60 90 38.7 7700 12000 length of the isotactic sequences of more than 60 monomer I-Butene - 10 330 9.1 500 150000 units. I-Butene + 20 200 29.2 2640 50000 1-Butene can also be polymerized highly effectively with the zirconocene 1 / methylalumoxane catalyst (cf. Table 1). [*] Prof. Dr. W. Kaminsky, Dipl.-Chem. K. Kiilper Thus, polymerization activity is still 2640 kg of polybutene lnstitut fur Technische und Makromolekulare Chemie der Universitat per hour per mole of Zr at 20°C. Although the polymers Martin-Luther-King-Platz 6, D-2000 Hamburg 13 (FRG) have molecular weights of 150000 or 50000, they are sol- Prof. Dr. H. H. Brintzinger, Dr. F. R. W. P. Wild Fakultlit fur Chemie der Universitat uble in toluene. The consistency is wax-like to crystalline, Postfach 5560, D-7750 Konstanz I (FRG) but not clear and viscous like atactic polybutane, which [*+I This work Mias supported by the Deutsche Forschungsgemeinschaft. We was produced with bis(cyc1opentadienyl)zirconium com- thank Hoechst AG for help with the polymer analysis. pounds and measured "C-NMR spectroscopically.

Angew. Chem. Inr. Ed. Enyl. 24 (1985) No. 6 0 VCH Verlagsgesellsc~hajimbH. 0-6940 Weinheim. 1985 0570-0833/85/0606-0507 $ 02.50/0 507 Hence, both unusually highly isotactic polypropylene as and, on the basis of NMR spectroscopic results, found well as isotactic polybutene can be produced with 1 and new applications of the Hiickel 4n + 2 rule for such highly methylalumoxane; the activity of the catalyst is high. The charged perimeter systems. narrow molecular weight distribution, an additional effect, Until now it had not been possible to obtain the corre- might be of interest from an industrial processing point of sponding tetracations either chemically or via electrochem- view. ical oxidation. The highly charged cations react easily with nucleophilic impurities or, as is usually the case, with the Experimental nucleophilic solvent. The proper choice and purification of I : Tetrahydrofuran (THF) (60 mL) was distilled into a three-necked flask at the solvent is therefore even more crucial than for the ca- - 196°C and treated, with stirring, with 4.9 g (21 mmol) of ZrCI,. A solution thodic reduction. In 1979, Tinker and Bard3]described the of the dilithium salt of his(l-indeny1)ethane (21 mmol) in THF (50 mL) was anodic oxidation of thianthrene and other arenes in liquid then added dropwise to the mixture under N:, at room temperature. After 2 SO2 and were able to show that this solvent is excellently hours' stirring, hydrogen chloride was passed into the mixture and, immedi- ately thereafter, the excess HCI was removed in vacuo. The mixture was then suited to the generation of reactive cations owing to its low treated with diethyl ether (20 inL) and petroleum ether (10 mL). The resulting nucleophilicity. light-yellow, crystalline product was filtered off and washed successively It has now been possible, using an optimized sample with 4N hydrochloric acid, water, ethanol, and diethyl ether and dried in va- preparation procedure (purification of SO, solely with cuo: yield 3.1 g of (R,S)-ethylenebis(1-indeny1)zirconiumdichloride. I g of this substance was hydrogenated, as described for the analogous titanium A1203),".41to generate anodically in liquid SO2 the ex- compound [4], for 30 min with 75 mg Pt02and 25 mL CH2CIZat 100 bar H,; tremely reactive dication of anthracene 215' as well as, for yield 650 mg of 1 (characterized by X-ray structure analysis 151). the first time, the tetracation of 1 and to characterize these Polymerization of propene: A solution of methylalumoxane (320 mg, 5.6 species by cyclic voltammetry. mmol Al) and 1 (3.3 x 10 -'mol) in I mL of toluene was added to 330 mL toluene contained in a 1 L glass autoclave fitted with a thermostat and mag- A11 measurements were carried out in S02/Bu4NPF, netic stirrer and previously dried out and purged with argon. After 20 min- with a Pt electrode. The potentials were calibrated using an utes' ageing, purified propene (70 mL) was distilled into the contents of the internal ferrocene standard and then referred to the stand- autoclave at 20°C. The solution gradually clouded, and white polypropylene ard Ag/AgCI reference electrode. precipitated out. After 120 min the contents of the autoclave were treated with ethanol, filtered, and the filter cake washed with dilute HCI and dried in Owing to the high reactivity of 2 +,only quasi-reversible vacuo; yield 31.3 g of isotactic polypropylene. On removal of toluene from voltammograms of the 2/2' redox pair have been ob- the filtrate there remained a further 0.3 g of polypropylene. served for scan rates of 100 mV/s at -70°C. A mean life- time of 0.5 s for the cation was derived from the peak-cur- Received: January 15, 1985; revised: March 13, 1985 [Z I135 IE] rent ratios."' German version: Angew. Chem. 97 (1985) 507 CAS Registry numbers: 1, 96363-63-2; ZrCI1, 10026-1 1-6: dilithium salt of his( I-indenyl)ethane, v: ZOOmV/s 96363-64-3; isotactic polybutene, 25036-29-7; isotactic polypropylene, 25085- T= -50°C 53-4

[I] H. Sinn, W. Kaminsky, Adu. Organomet. Chem. 18 (1980) 99. [2] W. Kaminsky, M. Miri, H. Sinn, R. Woldt, Makromol. Chem. Rapid Commun. 4 (1983) 417. 131 J. A. Ewen, J. Am. Chem. SOL.106 (1984) 6355. 141 F. R. W. P. Wild, L. Zsolnai, G. Huttner, H. H. Brintzinger, J. Organo- I I 1 I met. Chem. 232 (1982) 233. 25 E[V,vs20 Ag/AgCII15 10 (51 F. R. W. P. Wild, M. Wasiucionek, G. Huttner, H. H. Brintzinger, J. Or- ganomet. Chem., in press. [6] P. Pino, R. Mulhaupt, Angew. Chem. 92 (1980) 869: Angew. Chem. ht. Ed. Engl. I9 (1980) 857. Fig. 1. Cyclic voltammogram of the oxidation of' 2 in SO2 (working elec- (71 H. Sinn, W. Kaminsky, H.-J. Vollmer, R. Woldt, Angew. Chem. 52 (1980) trode: Pt). 396; Angew. Chem. Int. Ed. Engl. 19 (1980) 390. 18) W. Kaminsky, Nutiirwissen.Fchafen 71 (1984) 93. [9] F. Kloos, H. G. Lengering, IUPAC Macro Florence, Reprints 2 (1980) 479. Figure 1 shows the voltammogram for the oxidation of 2 [lo] J. P. Luongo, J. Polym. Sci. 42 (1960) 139. at - 50°C. TWOclearly defined reversible steps are appar- ent; a AEo of 770 mV (- 50°C) for these two steps gives a semiquinone formation constant of 2.48 x 10". The peak- current ratios indicate a radical cation life-time that ex- Electrochemical Oxidation of Anthracene and tends far beyond the time scale of cyclic voltammetry; for 9,9'-Bianthryl to the Respective Dication and the dication, the average life-time under the experimental Tetracation** conditions was estimated to be ca. 10 s. The extremely high By Michael Dietrich, John Mortensen, and Jurgen Heinze* reactivity of the dication is shown by the observation that, The electrochemical reduction of unsubstituted arenes in SOz dried with PzOs, 2'+ always reacts via irreversible to stable, highly charged anions was recently described for subsequent reactions. Remarkably, the peak height for the the first time.['] Thus, for example, it was possible to detect dication formation is somewhat smaller than that for the electrochemically the tetraanion of 9,9'-bianthryl 1 and the monocation formation; this indicates a reversible dimeri- hexaanion of decacyclene. Independently, Miillen et a1.[*] zation (K= 50 L.mo1-I) of the radical cation with the sub- had previously converted 1 as well as a series of annulene strate, as is also found for pyrene and other arenes."' derivatives to their tetraanions by the use of alkali metals The oxidation of 1 leads, in four reversible redox steps (Fig. 2), to what is, to the best of our knowledge, the first

[*] Priv.-Doz. Dr. J. Heinze, M. Dietrich, Dr. J. Mortensen tetracation of an unsubstituted arene.Ix1Since formation of Institut fur Physikalische Chemie der Universitat the tetracation also involves the transfer of four electrons, Albertstrasse 21, D-7800 Freiburg (FRG) 1 represents, in principle, an eight-step redox system. The [**I This work was supported by the Fonds der Chemischen Indnstrie. standard potential difference (E: = 1.267; E!== 1.482;

508 0 VCH Verlay~gerell.~chaftmhH. 0-6940 Weinheim, I585 0570-0833/85/0606-05(18 S 02.50/0 Angew. Chem. In(. Ed. Engl. 24 (1588) No. 6