zirconium

Synthesis, Characterization and Monoalkene Polymerization Activity of Bis-[(l,2,3,4-tetraphenyl)-i75-cyclopentadienyl]zirconium(IV) Dichloride G iuseppe C onti3, G uillerm o A rrib a s3, A ngelina A lto m are3, B ernardo M endezb, Francesco C iardelli3 * a D epartm ent of C hem istry and Ind u strial Chem istry, U niversity o f Pisa, via R isorgim ento 35, 56126 Pisa, Italy b E scuela de Q uim ica, Facultad de Ciencias, U n iversidad C entral de V enezuela, Caracas, V enezuela Dedicated to Prof. Dr. Dr. h. c. Günther Wilke on the occasion o f his 70th birthday Z. N aturforsch. 50b, 4 1 1 -4 1 4 (1995); received S ep tem b er 20, 1994 B is-([l,2,3,4-tetraphenyl)-^"’-cyclopentadienyl]zirconium (IV ) D ichloride, M etallocene Catalyst, O lefin Polym erization The title com plex (1) has been p re p a re d by reactio n of Z rC l4 w ith l,2,3,4-(tetraphenyl)cyclopenta-l,3-dienyl lithium (2). T he phenyl su b stitu en ts on th e m etallocene ligands exert b oth steric and electronic effects on th e active site o b tain ed by activation of 1 with MAO. Thus this catalytic system shows low er polym erization activity th an in case of unsubstituted o r m ethyl-substituted ligands and leads to the fo rm atio n of ethylene oligomers.

H om ogeneous catalysts based on group IV m etallocene/m ethylalum oxane (M A O ) system have been the subject of intensive research in re cent years [1 -3 ]. For the ( 775-C 5H 5) 2M tX 2/alum oxane system, ionic or strongly polarized catalytic species [3, 4 -7 ] have been proposed. Structural and catalytic properties of such species can be ex pected to be strongly influenced by th e electronic surroundings and hence by the ligand field of the transition m etal [8-10]. In this general context the title com pound ( 1 ) was prep ared according to the synthetic route described in Schem e 1, and its spectroscopic and catalytic p roperties w ere inves tigated. Z rC l4 + 2 L i(C 5H P h4) R eflux in eth ylbenzene ’ for th ree days (C 5H P h 4)2Z rC l2 + 2 LiCI

1 Scheme 1. Synthesis of bis-[(l,2,3,4-tetraphenyl)-//5-cyclopentadienyljzirconium (IV ) dichloride.

A t room tem p eratu re com pound 1 shows ra th e r different 'H N M R spectra in CDC1 3 and C 6D 6 (Table I).

* R ep rin t requests to Prof. D r. F. C iardelli. 0 9 3 2 -0 7 7 6 /9 5 /0 3 0 0 -0 4 1 1 $06.00

Table I. !H N M R spectral d ata for bis-[(l,2,3,4-tetraphenyl)-?7 5-cyclopentaclienyl]zirconium (IV ) dichloride (1). R eso nance

P ro to n type

CDC13 ö [ppm]

CfiDf, ö [ppm]

a

a a a ß ß ß Cp

6.82 7.04 7.24 6.82 7.04 7.24 6.51

7.14 6.73 6.83 7.63 6.92 6.83 6.80

b c X

y z s

The assignm ents of the 13C N M R spectra have been m ade by analogy with those of sim ilar m etallocene alkali-m etal salts [11] (see E x p e r im ental P art). It is interesting to note th at the singlet resonance of the H -atom of the Cp occurs at 6.51 ppm in CDC13, but at 6.8 ppm in C 6D 6, i.e. 0.5 and 0.2 ppm up-field with respect to (C pPh 4) 2TiC l 2 (7.03 ppm in toluene-d8) [12]. M oreover, in CDC1 3 solution the relative positions of the signals of ortho and meta phenyl protons are inverted with respect to the resonances of the com plex in C 6D 6 solution (Table I). In CDC1 3 (Table I, Fig. 1) the difference of the chem ical surroundings of the protons of the phenyl rings decreases, probably because both the outside (a ) and the inner (ß ) rings assum e a simi-

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G. C o n ti et al. ■S y n th esis, C h a ra c te riz a tio n a n d M o n o a lk e n e P o ly m eriz atio n A ctivity

412

Fig. 1. 'H N M R spectrum in CDC13 of bis-[(l,2,3.4-tetraphenyl)-775-cyclopentadienyl]zirconium (IV ) dichloride.

lar steric position due to a facile and independent rapid ro tatio n in the N M R tim e scale. The solvent effect of benzene seem s to induce a different distribution of ro tational conform ations of the phenyl substituents. Indeed the a and ß ortho p ro to n resonances are now distinguishable. In sum m ary, the N M R spectra suggest an extensive delocalization of the cyclopentadienyl anion charge, rendering the zirconium ce n ter m uch m ore electron-deficient. In o rd er to evaluate the effect of the tetraphenylcyclopentadienyl ligand on the p olym eriza tion activity, com pound 1 was used as catalyst for ethylene and p ropene polym erization und er sim i lar conditions as for C p 2Z rC l 2 and bis-(pentamethyl-? 75-cyclopentadienyl)zirconium (IV ) dichlo ride (C p* 2Z rC l2).

Table II. Polym erization of ethylene by bis-(-?7 5-cyclopentadienyl)zirconium (IV ) dichloride com plexes acti vated with M A O a. Run

C atalyst

[Al]/[Zr]

S.A.b

S.A.*C

HI H2 H3 H4

Cp->ZrCLd C p*2Z rC l2e (C pP h4)2Z rC l2f (C pP h4)->ZrCUf

1500 1500 3000 1500

372.5 185.6 80.4 75.1

0.248 0.124 0.027 0.037

a O ptim um productivity at P c t h y i e n e = 1 bar, T = 25 °C; b kg PE/g atom Z r-h ; c kg PE/g atom Z r-g atom A l-h ; d bis-(-//:’-cyclopentadienyl)zirconium (IV ) dichloride; e bis-(pentam ethyl-/ 7 5-cyclopentadienyl)zirconium (IV ) d ich lo rid e;f bis-(tetraphenyl-?/5-cyclopentadienyl)zirconium (IV ) dichloride.

Typical results are reported in Tables I I - I V and show that 1 is less active than C p 2Z rC l 2 and C p* 2Z rC l 2 in case of both m onom ers. C p* 2Z rC l 2 gave high m olecular weight poly ethylene with good yield, but the SA was about 50% less than w ith C p 2Z rC l 2 (Table II, run H I , H 2 ). A consistent fu rth er decrease of SA was ob served with 1 (Table II, run H 3 ) which gave sim ul tan eo u s oligom erization and polym erization of ethylene [13] (Table III). T he dram atic decrease in the steady-state rate of polym erization of ethylene is probably connected with the decrease of the electron density at the m etal center in 1 which affects the m e ta l-c a rb o n bond strength. In this case the frontier m olecular orbital on the m etallocene m oiety decreases in en ergy leading to a stronger bond betw een zirconium and alkyl ligands. This would then cause a d e crease in the reaction rate due to ground state sta bilization [14-16]. O n the o th er hand under our experim ental conditions the form ation of short chains cannot be m erely attributed to the rather larger am ount of M A O used [17], but rath er to the stro n g er acidity of the active species. It is interesting to note that com pound 1 is inac tive in the oligom erization of propene (Table IV),

Table III. M olecular w eight of polyethylenes obtained with bis-(-? 7 :'-cyclopentadienyl)zirconium (IV ) complexes. C atalyst

^/[dl/g]a Mn -10-5 M w-10-5 Mw/M n

C p?Z rC l2 Cp*2Z rC l2 (C p P h 4),Z rC l2

1.22 7.5 0.31

0.35 _b

-

0.78

0.04

0.17

2.22 4.25c

a V iscosim etric m easu rem en t in decaline at 135 °C; b sam ple was not soluble under the ad o p ted experim en tal conditions; c the sam ple was constituted of solid poly m er and oligom ers of C 6- C 3 0 distribution. Table IV. O ligom erization of p ropene by bis-(-?/5-cyclopentad ien y l)zirco n iu m (IV ) com plexes activated with M A O a. Run

C atalyst

[Al]/[Zr]

H9 H 10 H 11

Cp->ZrCl2 Cp*-.ZrCl2 (C p P h 4)2Z rC l2

3000 3000 2000

S.A.b 700 1200 -

S.A.*C 0.23d 0.40e -

a O p tim u m productivity at P p r 0 p e n e = 1 har, T = 25 °C; b kg PP/g atom Z r-h - b a r; c kg PP/g atom Z r-g atom A l-h -b a r; d oligom er distribution C6- C 30; e oligom er d istrib u tio n C6- C 24.


G. C o n ti et al. • Synthesis, C h a ra c te riz a tio n a n d M o n o a lk e n e P o ly m e riz a tio n A ctiv ity

probably because both an excessive electronic sta bilization of the ^T-olefinic com plex and the high steric hindrance of phenyl substituents [14-16]. These prelim inary results confirm the rem ark ab le influence of substituted m etallocene ligands on the m echanism of olefin polym erization [8 , 9] and the possibility of m odulating the catalytic properties. Experimental Part All m anipulations of m oisture sensitive com pounds were perform ed by using stan d ard vacuum and Schlenk techniques. All solvents w ere dried by distillation on sodium /potassium -benzophenone ketyl under argon atm osphere. M A O (4.5 M in toluene) (W itco), bis-(-^ 5-cyclopentadienyl)zirconium dichloride (A ldrich) and 2,3,4,5-tetraphenylcyclopentadien-l-one (A ldrich) w ere used as received. IR exam inations were carried out with an FTIR Perkin-E lm er 1600 instrum ent co n nected to a personal com puter. N M R spectra w ere obtain ed by using a Varian G E M IN I 200 sp ectro m eter operating at 200 M Hz ('H ) and 50.3 M H z ( 13C). U V /V IS spectra were recorded by m eans of a Jasco 7850 spectrophotom eter. M icroanalyses were p erform ed by the M icroanalytical L ab o rato ry D ep artm en t of P h arm a ceutical Sciences, U niversity of Pisa.

413

E lem ental analysis fo r [Zr(r]5-CSH P h4)2Cl2J', C5HH 42Cl2Z r Calcd C 77.32 H 4.67 Cl 7.88% , Found C 77.86 H 4.89 Cl 8.00%. FT-IR (v): 3065 (m ), 2950 (s), 2900 (s), 2890 (s), 1630 (m ), 1510 (w), 1440 (m), 1400 (w), 1210 (w), 1090 (w), 1020 (w), 980 (s), 890 (w), 830 (w), 785 (m ), 700 (s), 450 (w) cm “ 1. 'H N M R (CDC13) Ö (ppm): 7.24 (2 H , para-H, C 6-ring); 7.04 (4 H , m eta-H, C 6-ring); 6.82 (4H , ortho-H, C 6-ring); 6.51 (1 H , C 5-ring). *H N M R (C 6D 6) d (ppm ): 7.63 (2 H , ortho-H, /3-C6-ring); 7.14 (2 H , ortho-H, a -C 6-ring); 6.92 (2 H , meta-H, /?-C 6-ring); 6.83 (2 H , para-H, a,ßCft-ring); 6.80 (1 H , C 5-ring); 6.73 (2 H , m eta-H, a -C 6-ring). 13C N M R (C D C I 3 ) ö (ppm): 136.56 (quaternaryC, /?-C 6-ring); 133.68 (quaternary-C , a-C 6-ring); 132.32 (ortho-C , /3-Q,-ring); 132.12 (quaternary-C , C 5-ring); 128.78 (ortho-C , a -C 6-ring); 128.00 (meta-C, /3-C6-ring); 127.1 (meta-C, a -C 6-ring); 127.00 (para-C, a,ß-C 6-ring); 107.95 (C H , C 5-ring). U V spectrum (CC14, c = 5.5 -10 -5 M _1): Amax (nm ): 267.5, e (M -1 c m "1) = 5.1 • 104; Amax (nm): 308.7, e (M * 1 c m - 1) - 1.8-104; Amax (nm ): 397.0, e (M - 1 cm “ 1) = 0 .9 -104. Polym erization experim ents

Polym erizations were carried out u nder inert atm osphere by adding the selected am ount of co catalyst to a solution of the Z r com plex in toluene. A fte r the indicated ageing time, gaseous m onom er 3.0 g (13.3 m m ol) of Z rC l 4 was added w ith stir was introduced and its partial pressure kept at ring at 0 °C to 10.0 g (26.6 m m ol) of 2 in 250 ml of 1 b ar during the polym erization tim e; the slurry anhydrous ethylbenzene using a 500 ml th ree-neck was stirred m echanically while th erm ostated at the flask equipped with a co ndenser and m echanical re p o rte d tem p eratu re [17]. stirrer. The reaction m ixture was refluxed for 3 d. The hot deep-red solution was filtered and the sol A c k n ow led gem en ts vent evaporated to give an orange crude product. The title product was o b tain ed by recrystallization Financial support by E U R O N (S. D onato M ila from a toluene//i-heptane 1 :1 m ixture to give nese) is gratefully acknow ledged. G. C. thanks 8.98 g yellow needles (75% with respect to Z rC l4). Scuola N orm ale Superiore/E ni for a Ph.D. grant. Bis-[1,2,3,4-(tetraphenyl)-rf -cyclopentadienyljzirconium (IV ) dichloride (1)


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G. C o n ti et al. ■S ynthesis, C h a ra c te riz a tio n a n d M o n o a lk e n e P o ly m eriz atio n A ctiv ity

1] W. Kaminsky. R. E ngehausen. K. Zoum is, M akro mol. C hem . 193, 1643 (1992). 2] W. Spaleck, F. K über, A. W inter, J. R ohrm ann, B. B achm ann, M. A ntberg, V. D olle, E. F. Paulus. O rganom etallics 13, 954 (1994). 3] J. A. E w en. H. J. E ider, M acrom ol. C hem ., M acromol. Symp. 66, 179 (1993). 4] U. Stehling, J. D iebold. R. K irsten, W. Roll, H. H. B rintzinger, S. Jüngling, R. M ühlhaupt, F. L ang hauser, O rganom etallics 13, 964 (1994). 5] M. B ochm ann. S. J. L ancaster, O rganom etallics 12, 633 (1993). 6] C. Sishtsa, R. M. H ath o rn , T. B. M arks, J. Am. C hem . Soc. 114, 1112 (1992). 7] D. J. C row ther, R. F. Jordan, M acrom ol. C hem ., M acrom ol. Symp. 66, 121 (1993). 8] N. Piccolrovazzi, P. Pino, G. Consiglio, A . Sironi, M. M oret, O rganom etallics 9, 3098 (1990). 9] I. M. Lee, W. J. G au th ier, J. A. M. Ball, B. Iyengar, S. Collins, O rganom etallics 11, 2115 (1992).

[10] M. P. C astellani, J. M. W right. S. J. G eib, A. L. R heingold, W. C. Trogler, O rganom etallics 5, 1116 (1986). [11] H. S chum ann. C. Janiak. J. J. Z uckerm an, Chem. Ber. 121, 207 (1988). [12] M. P. C astellani, J. M. W right. S. J. G eib. A. L. R heingold. W. C. Trogler, O rganom etallics 6, 2524 (1987). [13] C. D enger. U. H aase, G. Fink, M acrom ol. Chem., R apid C om m un. 12, 697 (1991). [14] C. Janiak, J. O rganom et. C hem . 452, 63 (1993). [15] E. P. B ierw agen, J. E. Bercaw, W. A. G oddard, J. A m . C hem . Soc. 116, 1729 (1994). [16] T. K. W oo, L. Fan, T. Z iegler, O rganom etallics 13, 432 (1994). [17] G. C onti, G. A rribas, A. A ltom are, F. Ciardelli, J. Mol. Cat. 89, 41 (1994).
