C O M M U N I C A T I O N S
properties revealed high melting points of the copolymers. Inves-
tigations on the mechanism of the copolymerization and physical
properties of the linear copolymers are currently in progress.
Acknowledgment. The authors are very grateful to Prof.
Richard Jordan for helpful discussions. We also thank Prof.
Zhaomin Hou for high temperature measurements of polymer
molecular weights, and Prof. Takashi Kato for DSC measurements.
This work was supported by a Grant-in-Aid for Scientific Research
on Priority Areas “Advanced Molecular Transformations of Carbon
Resources” from the Ministry of Education, Culture, Sports, Science
and Technology, Japan. T.K. thanks the Japan Society for the
Promotion of Science (JSPS) for a Research Fellowship for Young
Scientists.
Figure 1. 13C NMR assignments for the copolymers of ethylene and
acrylonitrile (in 1,2,4-trichlorobenzene at 120 °C). Chemical shifts for each
carbon atom are listed in parts per million. The ratio of C/D was determined
Note Added after ASAP Publication. Due to a production
error, the units for activity were incorrect in Table 1, column
3, in the version published ASAP on June 27, 2007. The table
was corrected on July 6, 2007.
1
to be ca. 0.25 by H NMR analysis in toluene-d8.
bond because only two types of initiating chain ends, n-alkyl (A)
and 3-cyanobutyl (B) groups, were observed. Insertion of ethylene
into either a Pd-H or a Pd-Me bond should lead to formation of
A, but acrylonitrile insertion should occur into a Pd-H bond, not
a Pd-Me bond, selectively in a 2,1-fashion to generate B as only
one cyano-incorporated initiating end group (Figure 1).
Supporting Information Available: Experimental procedures and
characterization (PDF, CIF). This material is available free of charge
References
(1) Boffa, L. S.; Novak, B. M. Chem. ReV. 2000, 100, 1479-1493.
(2) (a) Acrylonitrile Polymers. Kirk-Othmer Encyclopedia of Chemical
Technology, 4th ed.; Wiley: New York, 1991; Vol. 1, pp 370-411. (b)
Kirk-Othmer Encyclopedia of Chemical Technology Home Page. http://
(3) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100,
1169-1203. (b) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003, 103,
283-315.
There are two types of possible terminating chain ends, vinyl
(C) and 2-cyanoethenyl (D) groups, formed by â-H elimination or
transfer after ethylene and acrylonitrile insertion, respectively. By
1H NMR spectrum of the copolymer obtained in entry 1, the C/D
ratio was determined to be ca. 0.25, which means chain transfer
mostly occurs after acrylonitrile insertion. Reduction of the number
of nitrile groups per polymer chain by decreasing the amount of
acrylonitrile used led to a significant increase in molecular weight
of copolymers (Table 1, entry 4), presumably because it reduced
the frequency of chain transfer. Mn of the copolymer was further
increased to 12 300 by increasing the ethylene pressure to 4.0 MPa
and lowering the reaction temperature to 80 °C (Table 1, entry 5).
The terminating end group analysis also led us to investigate
ethylene homopolymerization because 3 should provide linear
polyethylene with high molecular weight and would be a rare Pd
catalyst which produces linear polyethylene without any activator
such as a large excess of MAO (>60 equiv).8a,g,15 Polymerization
of ethylene using 3 actually produced linear polyethylene (80 °C,
(4) (a) Johnson, L. K.; Mecking, S.; Brookhart, M. J. Am. Chem. Soc. 1996,
118, 267-268. (b) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart,
M. J. Am. Chem. Soc. 1998, 120, 888-899.
(5) Luo, S.; Jordan, R. F. J. Am. Chem. Soc. 2006, 128, 12072-12073.
(6) (a) Wu, F.; Foley, S. R.; Burns, C. T.; Jordan, R. F. J. Am. Chem. Soc.
2005, 127, 1841-1853. (b) Wu, F.; Jordan, R. F. Organometallics 2006,
25, 5631-5637. (c) Groux, L. F.; Weiss, T.; Reddy, D. N.; Chase, P. A.;
Piers, W. E.; Ziegler, T.; Parvez, M.; Benet-Buchholz, J. J. Am. Chem.
Soc. 2005, 127, 1854-1869.
(7) Drent, E.; van Dijk, R.; van Ginkel, R.; van Oort, B.; Pugh, R. I. Chem.
Commun. 2002, 744-745.
(8) (a) Skupov, K. M.; Marella, P. M.; Hobbs, J. L.; McIntosh, L. H.; Goodall,
B. L.; Claverie, J. P. Macromolecules 2006, 39, 4279-4281. (b) Allen,
N. T.; Goodall, B. L.; McIntosh, L. H., III. U.S. Patent US2007049712A1.
(c) Allen, N. T.; Goodall, B. L.; McIntosh, L. H., III. European Patent
EP1760086A2. (d) McIntosh, L. H., III; Allen, N. T.; Kirk, T. C.; Goodall,
B. L. Canadian Patent CA2556356A1. (e) Claverie, J. P.; Goodall, B. L.;
Skupov, K. M.; Marella, P. R.; Hobbs, J. Polym. Prepr. 2007, 48, 191-
192. (f) Goodall, B. L.; Allen, N. T.; Conner, D. M.; Kirk. T. C.; McIntosh,
L. H., III. Polym. Prepr. 2007, 48, 202. (g) Liu, S.; Borkar, S.; Newsham,
D.; Yennawar, H.; Sen, A. Organometallics 2007, 26, 210-216. Theoreti-
cal studies: (h) Haras, A.; Anderson, G. D. W.; Michalak, A.; Rieger,
B.; Ziegler, T. Organometallics 2006, 25, 4491-4497.
15 h, Mn 63 000, Mw/Mn 2.3, 15 g‚mmol-1‚h-1, Tm 131.7 °C). 13
C
NMR spectroscopy showed the exceptional high linearity of
obtained polyethylenes obtained with 3 (<1 branch/1000 C).13
Ethylene-rich copolymers of ethylene and acrylonitrile can be
prepared by high-pressure radical copolymerization at high tem-
perature, but a number of branches are formed with this method.
Therefore, linear copolymers of ethylene and acrylonitrile should
possess different physical properties such as melting points from
copolymers produced by radical methods. For example, the linear
copolymer produced in entry 5 melts at higher temperature than a
copolymer with a similar acrylonitrile incorporation (1.6%) pro-
duced by radical method (107.8 °C).14
(9) (a) Kochi, T.; Yoshimura, K.; Nozaki, K. Dalton Trans. 2006, 25-27.
(b) Kochi, T.; Yoshimura, K.; Noda, S.; Nozaki, K. Polym. Prepr. 2006,
47, 582-583. (c) Nozaki, K.; Kochi, T.; Ida, H. Japanese Patent
JP2007046032A.
(10) Synthesis and use of 3 for olefin polymerization has been discussed in
our patent9a and the following international presentations: (a) Kochi, T.;
Yoshimura, K.; Noda, S.; Nozaki, K. 232th ACS National Meeting; San
Francisco, CA, POLY-263. (b) Kochi, T.; Yoshimura, K.; Nozaki, K.
Pacifichem 2005, Honolulu, HI, ORGN-232.
(11) A modified version of previously reported synthesis of 39c is described.
(12) Similar Pd complexes bearing pyridine ligands and their unique catalytic
activity for olefin polymerization has also been reported on patents and
preprints by Goodall and Claverie.8b-f
(13) (a) Guan, Z.; Cotts, P. M.; McCord, E. F.; McLain, S. J. Science 1999,
283, 2059-2062. (b) Cotts, P. M.; Guan, Z.; McCord. E.; McLain, S.
Macromolecules 2000, 33, 6945-6952.
In conclusion, linear copolymers of ethylene and acrylonitrile
were prepared using palladium complexes bearing phosphine-
sulfonate bidentate ligands. Acrylonitrile units located in the linear
polyethylene backbones were detected for the first time by 13C NMR
spectroscopy. Catalyst systems employing isolated palladium
complexes such as 3 showed much higher activity for the copo-
lymerization than the in situ generation procedures, and molecular
weight of the copolymers and acrylonitrile incorporation were
dependent on the palladium complexes. Preliminary studies on the
(14) Randall, J. C.; Ruff, C. J.; Kelchtermans, M.; Gregory, B. H. Macromol-
ecules 1992, 25, 2624-2633.
(15) Palladium-catalyzed production of linear polyethylene in the presence of
a large excess of MAO has been reported. (a) Tsuji, S.; Swenson, D. C.;
Jordan, R. F. Organometallics 1999, 18, 4758-4764. (b) Li, K.; Darkwa,
J.; Guzei, I. A.; Mapolie, S. F. J. Organomet. Chem. 2002, 660, 108-
115. (c) Chen, R.; Mapolie, S. F. J. Mol. Catal. A: Chem. 2003, 193,
33-40.
JA0725504
9
J. AM. CHEM. SOC. VOL. 129, NO. 29, 2007 8949