(η5-Pentamethylcyclopentadienyl)tin(II) tetrakis(pentafluorophenyl)borate: A new cocatalyst for the polymerization of α-olefins

Article abstract of DOI:10.1021/om980153j

The organotin compound (η⁵-pentamethylcyclopentadienyl)tin tetrakis(pentafluorophenyl)borate (1) has been synthesized from a reaction between (pentamethylcyclopentadienyl)tin chloride and lithium tetrakis(pentafluorophenyl)borate. This cation proved to be an effective Ziegler-Natta α-olefin cocatalyst. Activities for ethylene polymerizations using dimethylzirconocene and 1 were 7.3 × 10⁵ g of PE/(mol of 1·[C₂H₄]·h) at 20 °C and 1.2 × 10⁶ g of PE/(mol of 1·[C₂H₄]·h) at 70 °C. This system was also effective for the polymerization of propylene. Activities using rac-ethylenebis(indenyl)-dimethylzirconium with the tin cation were 3.0 × 10⁵ g of PP/(mol of 1·[C₃H₆]·h). Activities increased markedly when using zirconocene dichlorides/tri(i-butyl)aluminum/1. Activities for ethylene polymerization using zirconocene dichloride/tri(i-butyl)aluminum/1 at 20 °C were 7.0 × 10⁶g of PE/(mol of 1·[C₂H₄]·h). Activities for the polymerization of propylene using rac-ethylenebis(indenyl)zirconium dichloride/tri(i-butyl)aluminum/1 at 20 °C were 5.4 × 10⁶ g of PP/(mol of 1·[C₃H₆]·h).

Full text of DOI:10.1021/om980153j

Organometallics 1998, 17, 1931-1933
1931
(η5-P en ta m eth ylcyclop en ta d ien yl)tin (II)
Tetr a k is(p en ta flu or op h en yl)bor a te: A New Coca ta lyst
for th e P olym er iza tion of r-Olefin s
Barrie Rhodes, J ames C. W. Chien,* and Marvin D. Rausch*
Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003
Received March 2, 1998
Summary: The organotin compound (η5-pentamethylcy-
clopentadienyl)tin tetrakis(pentafluorophenyl)borate (1)
has been synthesized from a reaction between (penta-
methylcyclopentadienyl)tin chloride and lithium tetra-
kis(pentafluorophenyl)borate. This cation proved to be
an effective Ziegler-Natta R-olefin cocatalyst. Activities
for ethylene polymerizations using dimethylzirconocene
and 1 were 7.3 × 105 g of PE/ (mol of 1‚[C2H4]‚h) at 20
°C and 1.2 × 106 g of PE/ (mol of 1‚[C2H4]‚h) at 70 °C.
This system was also effective for the polymerization of
propylene. Activities using rac-ethylenebis(indenyl)-
dimethylzirconium with the tin cation were 3.0 × 105 g
of PP/ (mol of 1‚[C3H6]‚h). Activities increased markedly
when using zirconocene dichlorides/ tri(i-butyl)alumi-
num/ 1. Activities for ethylene polymerization using
zirconocene dichloride/ tri(i-butyl)aluminum/ 1 at 20 °C
were 7.0 × 106 g of PE/ (mol of 1‚[C2H4]‚h). Activities
for the polymerization of propylene using rac-ethylenebis-
(indenyl)zirconium dichloride/ tri(i-butyl)aluminum/ 1
at 20 °C were 5.4 × 106 g of PP/ (mol of 1‚[C3H6]‚h).
Research on homogeneous Ziegler (single-site) cataly-
sis began with titanocene dichloride activated by AlR2-
Cl cocatalyst.1 This catalyst system exhibits low eth-
ylene polymerization activity,2 probably because of the
low concentration of ionic catalytic species3 and rapid
reduction of Ti,1a,b,2 and does not polymerize propylene.
Many subsequent studies established the cationic d0
complexes of the type Cp2M+R (M ) group 4 element)
as the catalytically active species.4 They are generally
synthesized by the reactions of metallocene dialkyls
with salts of Ag+ or Cp2Fe+,4b weakly acidic ammonium
salts,4d,e triphenylcarbenium salts,5 and Lewis acids.5d,6
Recent studies suggest that many of the properties of
such catalysts are intimately connected with the nature
of the relatively strong cation-anion pairing.7
We report here the synthesis of (η5-pentamethylcy-
clopentadienyl)tin(II)8 tetrakis(pentafluorophenyl)bo-
rate (1) and an investigation of the polymerization
behavior of single-site zirconocene catalyst systems with
this new cocatalyst.
All operations were performed using standard Schlenk
techniques under an argon atmosphere. The cocatalyst
9
1 was prepared by adding LiB(C6F5)4 (4.27 g, 6.22
mmol) in CH2Cl2 (20 mL) to a solution of Cp*SnCl (2)10
(1.80 g, 6.22 mmol) in CH2Cl2 (50 mL) at room temper-
ature and stirring overnight. The LiCl was removed by
filtration through a Celite plug, giving an intense red
solution. Removal of the solvent followed by extraction
with CHCl3 to remove insoluble impurities and elimina-
tion of chloroform gave crude 1 (4.44 g, 77% yield).
Recrystallization from CH2Cl2/hexane gave elementally
pure 1 (3.89 g, 67% yield): 1H NMR (CDCl3) δ 2.25 (s,
15H); 11B NMR (CDCl3) δ -16.49 (s, B); 13C NMR
(CDCl3) δ 148.12 (d, o-C6F5), 137.26 (d, p-C6F5), 136.66
(d, m-C6F5), 122.97 (s, C5Me5), 9.07 (s, C5Me5); 19F NMR
(CDCl3) δ -132.41 (d, o-F), -162.43 (t, p-F), -166.31
(t, m-F); 119Sn NMR (CDCl3) δ -2219 (s, Sn). Anal.
Found (calcd): C, 43.73 (43.77); H, 1.88 (1.62); F, 41.2
(40.7). The catalyst precursors Cp2ZrMe2 (3),11 rac-
Et(Ind)2ZrMe2 (4),12 and rac-Et(Ind)2ZrCl2 (5)13 were
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1991, 113, 8570. (b) Chien, J . C. W.; Tsai, W.-M. Makromol. Chem.,
Macromol. Symp. 1993, 66, 141. (c) Tsai, W.-M.; Rausch, M. D.; Chien,
J . C. W. Appl. Organomet. Chem. 1993, 7, 71. (d) Ewen, J . A.; Elder,
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Organomet. Chem. 1991, 32, 325 and references in this review. (c)
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references therein. (d) Hlatky, G. G.; Eckman, R. R.; Turner, H. W.
Organometallics 1992, 11, 1413. (e) Sishta, C.; Hathorn, R. M.; Marks,
T. J . J . Am. Chem. Soc. 1992, 114, 1112 and references therein.
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Soc. 1996, 118, 12451 and references therein.
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119, 2582. (b) J ia, L.; Yang, X.; Ishihara, A.; Marks, T. J . Organome-
tallics 1995, 14, 3135. (c) Deck, P. A.; Marks, T. J . J . Am. Chem. Soc.
1995, 117, 6128. (d) Giardello, M. A.; Eisen, M. S.; Stern, C. L.; Marks,
T. J . J . Am. Chem. Soc. 1995, 117, 12114. (e) Chien, J . C. W.; Song,
W.; Rausch, M. D. J . Polym. Sci., Part A: Polym. Chem. 1994, 32, 2387.
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Bott, S. G.; Robinson, K. Makromol. Chem., Macromol. Symp. 1991,
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acids on decamethylstannocene. (a) J utzi, P.; Kohl, F.; Kru¨ger, C.
Angew. Chem., Int. Ed. Engl. 1979, 18, 59. (b) Kohl, F.; J utzi, P. Chem.
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J . M.; Lawless, G. A.; Marziano, I. Organometallics 1997, 16, 793.
S0276-7333(98)00153-8 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 04/23/1998

1932 Organometallics, Vol. 17, No. 10, 1998
Communications
Ta ble 1. Eth ylen e P olym er iza tion w h ile Va r yin g
Zr :Sn Ra tioa
Ta ble 3. Va r ia ble-Tem p er a tu r e Eth ylen e
P olym er iza tion a
c
[3] (mM)
[1] (mM)
yield of PE (g)
activityb
Mw
temperature
(°C)
time
(min)
yield of
PE (g)
Tm
(°C)
c
activityb
Mw
3.0
3.0
3.0
3.0
0
3.0
2.0
1.0
0.50
3.0
0.52
0.89
0.44
0.23
0
2.8 × 105
7.2 × 105
7.1 × 105
7.4 × 105
0
70
50
20
0
-20
2
2
2
10
10
0.36
0.36
0.46
0.18
0.19
1.2 × 106
9.1 × 105
8.6 × 105
5.8 × 104
5.4 × 104
129
129
132
133
132
4.9 × 104
5.1 × 104
1.2 × 105
4.1 × 105
7.3 × 105
1.1 × 105
a
Solvent ) 50 mL of toluene + 1 mL chlorobenzene, P(C2H4) )
b
a
15 psi. Polymerizations were run for 2 min. Tp ) 20 °C. Activity
Solvent ) 50 mL of toluene + 1 mL of chlorobenzene, P(C2H4)
) g of PE/(mol of 1‚[C2H4]‚h). c Mw by viscometry in decalin at
) 15 psi. [3] ) 3.0 mM, [1] ) 0.87 mM. Activity ) g of PE/(mol
b
135 °C.
of 1‚[C2H4]‚h). c Mw by viscometry in decalin at 135 °C.
Ta ble 2. Com p a r ison of 1 a n d 7 a s Coca ta lysts for
th e P olym er iza tion of Eth ylen ea
Ta ble 4. P olym er iza tion of P r op ylen e Usin g
5/TIBA/1a
run
catalyst
yield of
PE (g)
temperature yield of
Tm
[mmmm]
c
c
no.d precursor cocatalyst
activityb
Mw
(°C)
PP (g)
activityb (°C)
Mw
pentadd
1
2
3
4
6
6
3
3
1/TIBA
7/TIBA
1
7
0.88
1.76
0.39
1.15
9.5 × 106 5.0 × 105
1.9 × 107 4.7 × 105
4.2 × 105 2.0 × 105
1.2 × 106 1.3 × 105
70
20
0
2.16
4.47
1.49
0.77
1.5 × 107 101 1.7 × 105
5.4 × 106 140 3.7 × 105
1.4 × 106 148 6.3 × 105
5.3 × 105 152 5.8 × 105
54%
93%
-20
a
a
Solvent ) 50 mL of toluene + 1 mL of chlorobenzene, P(C2H4)
Solvent ) 50 mL of toluene + 1 mL of chlorobenzene, P(C3H6)
) 15 psi. Polymerizations were run for 30 min. Tp ) 20 °C.
) 15 psi. [5] ) [1] ) 50 µM, [TIBA] ) 10 mM. Polymerizations
Activity ) g of PE/(mol of 1‚[C2H4]‚h). c Mw by viscometry in
were run for 30 min. Activity ) g of PP/(mol of 1‚[C2H4]‚h). c Mw
b
b
d
d
decalin at 135 °C. In runs 1 and 2, [6] ) [1] ) [7] ) 10 µM and
by viscometry in decalin at 135 °C. [mmmm] pentads by 13C NMR
[TIBA] ) 200 µM. In runs 2 and 3, [3] ) 1 mM and [1] ) [7] )
100 µM.
spectroscopy in 1,2,4-trichlorobenzene at 100 °C.
Propylene polymerization was also catalyzed by 1/4.
Using the following conditions, [4] ) 3 mM; [1] ) 1 mM;
Tp ) 20 °C; and polymerization time ) 30 min, 4.95 g
of polypropylene was obtained, which corresponds to an
activity of 3.0 × 105 g of PP/(mol of 1‚[C3H6]‚h). The
polymer had a Mw of 3.0 × 105 and a melting point of
133 °C. This system is less active than using 7 as the
cocatalyst, where activities of 8.5 × 106 g of PP/(mol of
7‚[C3H6]‚h) were obtained under similar conditions.5a
Although activities were lower, stereoselectivity was
still very high. Analysis of the methyl pentad distribu-
tions of the polymer by 13C NMR spectroscopy in 1,2,4-
trichlorobenzene at 100 °C showed 85% [mmmm] pen-
tads.
Activities were greatly increased when zirconocene
dichlorides/TIBA/1 catalyst systems were used.14,16 In
this case, TIBA alkylates the zirconocene dichloride and
acts as a scavenger in the reactor. Polymerization of
ethylene using 6/TIBA/1 for 5 min gave 0.54 g of
polyethylene which corresponds to an activity of 7.0 ×
106 g of PE/(mol of 1‚[C2H4]‚h), almost a 10-fold increase
in activity over the 3/1 catalyst system. Polymerizations
for 30 min gave similar activities, but again, activities
using 1 as the cocatalyst were lower than when using 7
(9.5 × 106 g of PE/(mol of 1‚[C2H4]‚h) versus 1.9 × 107
g of PE/(mol of 7‚[C2H4]‚h)) (Table 2).
prepared according to literature procedures. Tri(i-
butyl)aluminum (TIBA) and Cp2ZrCl2 (6) were pur-
chased from Aldrich and used without further purifi-
cation. Ph3C+B(C6F5)4- (7) was also prepared according
to the literature.5a
Initial studies concentrated on finding the ideal
conditions for polymerization with these systems by
varying the ratio of 3:1.14 Ratios of 1:1 to 6:1 were used,
and the results are summarized in Table 1. In this
system, 3 is also acting as a scavenger. Thus, when a
1:1 ratio is used, an excess of 1 is present and the
activity is apparently low. At 1.5:1 ratios or below,
activities are almost constant. If polymerization of
ethylene is attempted in the absence of 3, no polymer
is formed, indicating that 1 is not the catalytically active
species.
A direct comparison of 1 versus 7 as the cocatalyst
was carried out (Table 2). Ethylene polymerization for
30 min showed activities with 7 were higher under
identical conditions ((1.2 × 106 g of PE/(mol of 7‚[C2H4]‚h)
compared to 4.2 × 105 g of PE/(mol of 1‚[C2H4]‚h)).
Ethylene polymerization was also performed from
-20 to +70 °C (Table 3). The 1/3 catalyst system shows
a modest but definite increase in ethylene polymeriza-
tion activity as Tp increases. With this system, poly-
merizations at temperatures of 0 °C and below show a
substantial drop in polymerization activity.
Polymerization of propylene using 5/TIBA/1 for 30
min gave 4.47 g of polypropylene, which corresponds to
an activity of 5.4 × 106 g of PP/(mol of 1‚[C3H6]‚h) (Table
4) which is almost 20 times more active than the 1/4
system. Again, as seen in variable-temperature ethyl-
ene polymerizations, an increase in activity is observed
as polymerization temperature increases. Stereoselec-
tivity of the polymerization catalyst is still high, produc-
ing PP with 93% [mmmm] pentads and a melting point
of 152 °C at a polymerization temperature of -20 °C. If
(11) Samuel, E.; Rausch, M. D. J . Am. Chem. Soc. 1973, 95, 6263.
(12) Horton, A. D.; Orpen, A. G. Organometallics 1991, 10, 3910.
(13) Wild, F. R. W. P.; Wasiucionek, M.; Huttner, G.; Brintzinger,
H. H. J . Organomet. Chem. 1985, 288, 63.
(14) Polymerizations were carried out in a 250 mL crown-capped
glass pressure reactor containing 50 mL of toluene and were equili-
brated with monomer at 15 psi. Known concentrations of 3, 4, 5, 6,
and TIBA were made in toluene. Solutions of the cocatalysts 1 and 7
were prepared in chlorobenzene, due to the very low solubility of 1 in
toluene. One milliliter portions of 3, 4, 5, or 6 and 1 or 7 were added
to the reactor in that order to form the active polymerization catalyst
in situ. If TIBA was used, this was introduced to the reactor first. The
polymerization was quenched with a methanol/2% HCl solution, and
the polymer was worked up as detailed elsewhere.15
(15) Rieger, B.; Mu, X.; Mallin, D. T.; Rausch, M. D.; Chien, J . C.
W.; Macromolecules 1990, 23, 3559.
(16) [Zr], [1] ) 50 µM. TIBA: Zr ) 20:1. Tp ) 20 °C.

Communications
Organometallics, Vol. 17, No. 10, 1998 1933
zirconium is absent during the polymerization (i.e., just
1 and TIBA are present in the polymerization vessel),
no polymer is formed, indicating that TIBA does not
react with 1 to form an active polymerization catalyst.
The reason for the marked increase may be two-fold.
The excess TIBA is probably acting as a superior
scavenger compared to 3 or 4. Also, coordination of the
tin lone pair to the Lewis-acidic aluminum present in
large excess may occur instead of coordination to the
zirconium species. Coordination of the tin lone pair to
aluminum has been observed in similar organotin(II)
compounds.17
An investigation of the mechanism of these processes
as well as further polymerization studies are underway.
Also, extensions to related organotin cocatalyst systems
are under current study.
Ack n ow led gm en t. We would like to thank Dr. L.
C. Dickinson for assistance in setting up NMR studies
and Dr. G. Dabkowski for microanalyses.
(17) Harrison, P. G.; Richards, J . A. J . Organomet. Chem. 1976, 108,
35.
OM980153J