Synthesis of butene - ethylene and hexene - butene - ethylene copolymers from ethylene via tandem action of well-defined homogeneous catalysts [15]

Full text of DOI:10.1021/ja994222c

1830
J. Am. Chem. Soc. 2000, 122, 1830-1831
Table 1. Dimerization of Ethylene by 4a
Synthesis of Butene-Ethylene and
Hexene-Butene-Ethylene Copolymers from
Ethylene via Tandem Action of Well-Defined
Homogeneous Catalysts
percent
entry (atm) (°C) activityb 1-butenec 1-hexenec 2-alkenesc dimersc
P
T
1
2
3
4
5
6
7d
1
1
1
3
3
3
3
0
20
65
0
20
65
20
20
56
140
290
430
560
630
>99
89
64
90
71
36
89
8
12
6
8
7
3
16
4
17
41
3
Zachary J. A. Komon, Xianhui Bu, and Guillermo C. Bazan*
8
Department of Chemistry, UniVersity of California
4
14
Santa Barbara, California 93106
8
ReceiVed December 2, 1999
a [4] ) 125 µmol/L in toluene. Reaction time is 1 h. b Kg ethylene
Recent progress in the chemistry of well-defined organometallic
catalysts has made a significant impact in the manufacture of
polyolefins.1 An ever-growing menu of metal-ligand combina-
tions exists to control the activity, copolymerization aptitude, and
stereoselectivity of the catalytic site.2 Mechanistic and theoretical
studies provide insight into the interactions between the substrate,
metal, and ancillary ligands and how subtle electronic and steric
factors come together to determine the final catalytic perfor-
mance.2
Given the accumulated understanding of these catalysts, it is
reasonable to expect that multiple sites could be coordinated to
offer a performance inaccessible by a single catalyst.3 Within this
concept, we recently reported the use of tandem catalysis to
produce branched polyethylene from a single feedstock of
ethylene.4,5 Mixtures of (C5H5B-OEt)2ZrCl2 (1)6 and [(η5-C5Me4)-
SiMe2(η1-NCMe3)]TiCl2 (2) produce branched polyethylene from
ethylene when activated with methylaluminoxane (MAO). In this
process, 1/MAO produces linear 1-alkenes which insert into the
growing polyethylene chain at the 2/MAO site.7
consumed per mole of catalyst per hour. c Mole percent determined
1
by H NMR spectroscopy. d [4] ) 12.5 µmol/L.
branches were derived from a single 1-alkene source. In this paper
we report how such a tandem catalysis system can be created for
the synthesis of poly(ethylene-co-1-butene) or polyethylene with
ethyl and butyl branches.10
While single-component ethylene oligomerization catalysts have
been reported,11 these either require MAO as activator or do not
achieve activities toward ethylene comparable to metallocene-
type polymerization catalysts. Keim recently reported the synthesis
and reactivity of [(C6H5)2PC6H4C(O)O-κ2P,O]Ni(η3-CH2CMeCH2)
(3).12 Based on the work by Piers,13 we discovered that addition
of one equivalent of B(C6F5)3 to 3 yields [(C6H5)2PC6H4C(OB-
(C6F5)3)O-κ2P,O]Ni(η3-CH2CMeCH2) (4), as shown in eq 1.
Combinations such as 1/2/MAO suffer from two limitations.
First, it is known that the catalytic activity of metallocene and
boratabenzene-based catalysts depends on the ratio of MAO to
transition metal.2,8 As a result, one cannot obtain a linear
relationship between the molar ratio of the precatalysts and the
incorporation of branches onto the backbone. Second, since
oligomerization catalysts generate a statistical distribution of
1-alkenes,6 the precise polymer structure cannot be determined
using simple spectroscopic techniques.9 These complications could
be circumvented by use of well-defined initiators and if the
The molecular structure of 4 (Supporting Information) shows
a square-planar arrangement of ligands on Ni and a strong B-O
interaction (d(B-O) ) 1.541(5) Å), which is intermediate
between that of a B-O single bond and a dative bond.14 The
C-ONi distance (1.240(5) Å) is characteristic of a C-O double
bond, while the C-OB distance (1.289(5) Å) is more indicative
of a single bond; both measurements are consistent with resonance
contribution B in eq 1.
(1) (a) Rotman, D. Chem. Week 1996, 158 (36), 37. (b) Paige, M. M. Chem.
Eng. News 1998, 76 (49), 25.
(2) (a) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth,
R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (b) Transition Metals
and Organometallics as Catalysts for Olefin Polymerization; Kaminsky, W.,
Sinn, H., Eds.; Springer-Verlag: Berlin, 1988. (c) Ziegler Catalysts; Fink,
G., Mu¨lhaupt, R., Brintzinger, H. H., Eds.; Springer-Verlag: Berlin, 1995.
(d) Metallocenes; Togni, A., Halterman, R. L., Eds.; Wiley-VCH: New York,
1998. (e) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int.
Ed. Engl. 1999, 429. (f) Bochmann, M. J. Chem. Soc, Dalton Trans. 1996, 3,
255.
Compound 4 is considerably more active toward ethylene than
3.12 From Table 1, we note that at 0 °C and 1 atm of C2H4, 4
affords exclusively 1-butene (entry 1). Increasing temperature and
(3) For classical systems see: Beach, D. L.; Kissin, Y. V. J. Polym. Sci.
1984, 22, 3027.
(4) Barnhart, R. W.; Bazan, G. C.; Mourney, T. J. Am. Chem. Soc. 1998,
120, 1082.
(5) Branched polymers can also be produced by a single catalyst, see: (a)
Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc. 1995 117,
6414. (b) Pellecchia C.; Pappalardo D.; Gruter G. J. Macromolecules 1999,
32, 4491.
(6) Rogers, J. S.; Bazan, G. C.; Sperry, C. K. J. Am. Chem. Soc. 1997,
119, 9305.
(7) (a) Lai, S.-Y.; Wilson, S. R.; Knight, G. W.; Stevens, J. C.; Chun, P.-
W. S. U.S. Patent 5,272,236, 1993. (b) McKnight, A. L.; Waymouth, R. M.
Chem. ReV. 1998, 98, 2587.
(8) (a) Rogers, J. S.; Lachicotte, R. J.; Bazan, G. C. J. Am. Chem. Soc.
1999, 121, 1288. (b) Bazan, G. C.; Rodriguez, G.; Ashe, A. J., III; Al-Ahmad,
S.; Mu¨ller, C. J. Am. Chem. Soc. 1996, 118, 2291. (c) Bazan, G. C.; Rodriguez,
G.; Ashe, A. J., III; Al-Ahmad, S.; Kampf, J. W. Organometallics 1997, 16,
2492.
(10) For commercial production and applications of these polymers, see:
James, D. E. Linear Low-Density Polyethylene. In Encyclopedia of Polymer
Science and Engineering; Mark, H. F., Bikales, N. M., Overberger, C. G.,
Menges, G., Eds.; Wiley-Interscience: New York, 1986; Vol. 6, pp 429-
454.
(11) (a) Pietsch, J.; Braunstein, P.; Chauvin, Y. New J. Chem. 1998, 22,
467. (b) Britovsek, G. J. P.; Bruce, M.; Gibson, V.; Kimberley, B. S.; Maddox,
P. J.; Mastroianni, S.; McTavish, S. J.; Redshaw, C.; Solan, G. A.; Stro¨mberg,
S.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc. 1999, 121, 8728. (c)
Small, B. L.; Brookhart, M. J. Am. Chem. Soc. 1998, 120, 7143. (d) Skupinska,
J. Chem. ReV. 1991, 91, 3.
(12) Bonnet, M. C.; Dahan, F.; Ecke, A.; Keim, W.; Schultz, R. P.;
Tkatchenko, I. J. Chem. Soc., Chem. Commun. 1994, 615.
(13) Parks, D. J.; Piers, W. E.; Parvez, M.; Atencio, R.; Zaworotko, M. J.
Organometallics 1998, 17, 1369.
(9) Branches from the higher molecular weight 1-alkenes give rise to carbon
resonances that are identical with the backbone. (a) Galland, G. B.; de Souza,
R. F.; Mauler, R. S.; Nunes, F. F. Macromolecules 1999, 32, 1620. (b) Liu,
W.; Ray, D. G.; Rinaldi, P. L. Macromolecules 1999, 32, 3817.
(14) B-O bond length of [HOB(C6F5)3][(C5Me5)2Ta(OH)Me] is 1.490(10)
Å. Schaefer, W. P.; Quan, R. W.; Bercaw, J. E. Acta Crystallogr., Sect. C
1993, 49, 878. The dative BfO bond length in C6H5C(OEt)OB(C6F5)3 is given
in ref 13 as 1.594(5) Å.
10.1021/ja994222c CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/10/2000

Communications to the Editor
J. Am. Chem. Soc., Vol. 122, No. 8, 2000 1831
Table 2. Polymerization Dataa
d
entry
4/5
activityb
% branchingc
Mw (×10-3
)
1
2
3
4
5
6
7
8
9
0.00
0.09
0.27
0.44
0.62
0.70
0.89
1.00
1.78
2.00
140
156
121
112
126
93
126
159
83
0
329
157
152
184
347
191
126
63
1.4
2.1
3.1
4.7
3.5
4.8
7.5e
9.9e
10.9e
102
88
10
78
a Polymerization conditions: T ) 20 °C; P(C2H4) ) 3 atm; [Ti] )
1.25 mmol/L; solvent, toluene; reaction time, 10 min. b Units of Kg
(total mol of metal)-1 h-1 c Determined by 13C NMR spectroscopy;
.
see ref 9a for details. d Determined by GPC. e Includes contribution
from butyl branches.
Figure 1. 13C NMR spectra of polymers obtained with (a) Ni/Ti ) 0.44
and (b) Ni/Ti ) 1.0. Chemical shift assignments were made according
to ref 9a.
Scheme 1
monomer pressure results in an increase in overall ethylene
consumption and loss of selectivity. In addition to 1-butene, one
observes varying amounts of 1-hexene as well as isomerization
products, of which 2-butene is predominant (trans content: 66%
at 65 °C; 72% at 20 °C), and 2-alkyl-1-alkenes (dimerization
products). The ratio of 1-hexene to 1-butene increases with
temperature (from 0.09 at 20 °C to 0.19 at 65 °C) but remains
relatively invariant as a function of pressure (entries 2 vs 5 and
3 vs 6, Table 1). Running the reactions under more dilute
conditions keeps the 1-hexene/1-butene ratio constant and dis-
courages the formation of 2-alkenes and dimers (entry 7). No
activity was observed for 3 under any of the conditions in Table
1.
To complement the reactivity of 4 we targeted {[(η5-C5Me4)-
SiMe2(η1-NCMe3)]TiMe}{MeB(C6F5)3} (5) since, like 2/MAO,
it is effective in copolymerizing 1-alkenes with ethylene,7 it is
generated by addition of B(C6F5)3 to [(η5-C5Me4)SiMe2(η1-
NCMe3)]TiMe2,15 and it has an activity of 140 Kg/(mol‚h) under
our experimental conditions.
Figure 2. Percent branching in polymer as a function of the 4 to 5 ratio.
An asterisk denotes observation of butyl branches.
as a propensity for 1-butene formation, relative to 3. Since 4 and
5 display complementary reactivity, it is possible to coordinate
their action to produce poly(ethylene-co-1-butene) from ethylene.
MAO is no longer required and the branching in the polymer
structure depends linearly on the ratio of the two precatalysts.
The overall process behaves predictably and shows that well-
defined homogeneous catalysts can be coordinated to generate
polymer architectures from a single monomer feedstock that are
not readily obtained by the action of a single catalyst.
Addition of ethylene to a solution containing 4 and 5 results
in the formation of high molecular weight polymers with
monomodal molecular weight distributions (Table 2). In these
reactions the total quantity of ethylene consumed equals (5%
the weight of polymer obtained. Under the appropriate conditions,
this system can generate polymers with exclusively ethyl branches
(Scheme 1). The 13C NMR spectrum of the material obtained
under the conditions in entry 4, Table 2, shows the presence of
branches due to 1-butene insertion (Figure 1a). Increasing the
Ni/Ti ratio results in the appearance of branches due to 1-hexene.
Figure 1b shows the data obtained from the sample in entry 8,
Table 2. Significantly, the simplicity of polymer structure allows
for the percentage of ethyl and butyl branches in the polymer to
be determined9a and, as shown in Figure 2, the percent of 1-butene/
1-hexene in the polymer correlates well against the Ni/Ti ratio.
In summary, compound 4 is readily formed by treating 3 with
B(C5F6)3 and it displays increased activity toward ethylene as well
Acknowledgment. G.C.B. is an Alfred Sloan Fellow and a Henry
and Camille Dreyfus Teacher Scholar. The authors are grateful to these
agencies and to the Department of Energy for financial assistance and to
Professor Griselda Barrera de Galland for assistance with the 13C NMR
analysis of polymers.
Supporting Information Available: Complete details for the syn-
thesis of 4, the oligomerization and polymerization reactions, and the
crystallographic study of 4 (PDF). This material is available free of charge
via the Internet at http://pubs.acs.org.
(15) (a) Deck, P. A.; Beswick, C. L.; Marks, T. J. J. Am. Chem. Soc. 1998,
120, 1772. (b) Lanza, G.; Fragala, I. L.; Marks, T. J. J. Am. Chem. Soc. 1998,
120, 8257.
JA994222C