Alternating copolymerization of ethylene with 7-methylenebicyclo[4.1.0] heptane promoted by the cobalt complex. Highly regulated structure and thermal rearrangement of the obtained copolymer

Article abstract of DOI:10.1021/ma047943r

The Co complex-catalyzed copolymerization of ethylene with 7-methylenebicyclo[4.1.0]-heptane was investigated as an alternative copolymer with a highly regulated structure. The thermally induced ring opening reaction of the copolymer, which gives a new po

Full text of DOI:10.1021/ma047943r

1528
Macromolecules 2005, 38, 1528-1530
Scheme 1
Alternating Copolymerization of Ethylene
with 7-Methylenebicyclo[4.1.0]heptane
Promoted by the Cobalt Complex. Highly
Regulated Structure and Thermal
Rearrangement of the Obtained Copolymer
Daisuke Takeuchi and Kohtaro Osakada*
Chemical Resources Laboratory, Tokyo Institute of
Technology, 4259 Nagatsuda, Midori-ku,
Yokohama 226-8503, Japan
Received October 6, 2004
Revised Manuscript Received January 10, 2005
160, indicating that the product did not contain olefinic
groups. The signals at δ 26.4 and 40.1 are attributed to
the CH2 carbons bonded to the three-membered ring of
the polymer.12 The former signal is assigned to the
carbon on the same side of the cyclohexane-1,2-diyl
group (carbon d in the formula of Figure 1A), while the
latter is due to that on the opposite side (carbon b).
Difference in the peak positions (14 ppm) is reasonable
by taking difference of shielding effects of these carbons
caused by the six-membered ring attached to the three-
membered ring into consideration.13 The 13C{1H} NMR
spectrum of 2-d shows five sharp signals at δ 19.1, 19.5,
22.7, 25.0, and 26.2, and two weak signals at δ 22.1 and
39.1 with broadening (Figure 1B). The positions of the
latter signals are shifted from the corresponding signals
of 2 (δ 23.0 and 40.1) with large isomer shifts (0.921
and 1.004 ppm, respectively). Thus, they are assigned
to the CD2 carbons derived from C2D4 monomer. All
these results indicate that the copolymer of C2D4 and
7-methylenebicyclo[4.1.0]heptane, 2-d, contains partial
structure i in Scheme 2 almost exclusively among four
possible structures shown in Scheme 1.
Alternating copolymerization of ethylene with sub-
stituted alkenes produces the polymer composed of C4
repeating units, which could hardly be obtained from a
single monomer. Copolymerization of ethylene with
R-olefin by metallocene catalyst forms an alternating
copolymer,1 while metallocenes and Ni and Pd com-
plexes catalyze the copolymerization of ethylene with
norbornene to afford hydrocarbon polymers that exhibit
good optical transparency and high glass transition
temperature.2,3 Methylenecyclopropanes, which undergo
the addition polymerization4 or the ring-opening polym-
erization5,6 depending on the catalyst employed, also
function as the comonomer in the copolymerization with
ethylene. Marks et al. reported the copolymerization of
ethylene with 7-methylenebicyclo[4.1.0]heptane to af-
ford polyethylene containing olefinic groups formed via
insertion of the latter monomer into Zr-polymer bond
and subsequent C-C bond cleavage of the three-
membered ring.7 Recently, we found that the alternating
copolymerization of ethylene with 2-aryl-1-methylene-
cyclopropanes catalyzed by Co-bis(imino)pyridine com-
plexes8 forms polymers with cyclopropylidene groups.9
In this paper, we report Co complex-catalyzed copolym-
erization of ethylene with 7-methylenebicyclo[4.1.0]-
heptane to afford the alternating copolymer with a
highly regulated structure. Thermally induced ring-
opening reaction of the copolymer, giving a new polymer
with trisubstituted CdC bond in the main chain, is also
described.
Scheme 3 depicts the mechanism proposed for the
polymer growth. The growing polymer with the Co-
CH2-CH2- bond (A) undergoes 1,2-insertion of 7-meth-
ylenebicyclo[4.1.0]heptane into the Co-C bond.14 Pre-
coordination of the CdC double bond of the bicyclic
monomer occurs at the opposite side of the six-
Stirring a toluene solution of 7-methylenebicyclo-
[4.1.0]heptane (0.18 g), Co-bis(imino)pyridine complex
(1.7 mM), and modified methylaluminoxane10 (MMAO)
([Al]/[Co] ) 300) for 1 h under ethylene atmosphere (1
atm) affords the alternating copolymer of the two
monomers, 2, at -40 °C (Scheme 1). The reaction using
C2D4 as the comonomer produces the deuterated poly-
mer 2-d. Poor solubility of the copolymer in THF and
chloroform prevented determination of the molecular
weight, although GPC analysis of the product of thermal
isomerization of 2 shows the molecular weight of 5800
(vide infra). The 13C{1H} NMR spectrum was obtained
by dissolving the polymer in C2D2Cl4 at 130 °C, cooling
the resulting solution, and measuring the spectrum at
room temperature soon. The aliphatic carbon region of
the spectrum (Figure 1A) contains seven sharp signals
which are assigned to the carbons of the alternating
copolymer unit based on comparison of the peak posi-
tions with those of 7,7-dibutylmethylenebicyclo[4.1.0]-
heptane.11 No signals were found in the range δ 80-
Figure 1. 13C{1H} NMR spectra of (A) 2, (B) 2-d, and (C) 3
in C2D2Cl4 at room temperature. The samples of 2 and 2-d
were prepared by dissolving the polymers at 130 °C for a short
period (ca. 1 min) in the solvent and cooling the solution
rapidly in order to avoid thermal isomerization of the polymer.
* Corresponding author: e-mail kosakada@res.titech.ac.jp.
10.1021/ma047943r CCC: $30.25 © 2005 American Chemical Society
Published on Web 02/09/2005

Macromolecules, Vol. 38, No. 5, 2005
Communications to the Editor 1529
Scheme 2
Scheme 4
Scheme 5
Scheme 3
polymer after heating showed a pair of the CH carbons
at δ 41.0 and 45.4. Comparison of the spectrum with
those of 2-cyclohexyl-2-butene16 and poly(isoprene)17
indicates that the product of thermolysis is polymer 3,
having a structure of poly(2-cyclohexyl-1,3-butadiene)
(Scheme 4). The appearance of a pair of signals for each
carbon of the cyclohexyl ring suggests the presence of
trans and cis CdC bond in the polymer chain. GPC
analysis of 3, which is soluble in THF, showed that Mn
and Mw/Mn of the polymer are 5800 and 1.69. 2-d also
undergoes the thermal isomerization to afford the
2
corresponding deuterated polymer 2-d. H NMR spec-
trum of 3-d showed broad large signals at δ 1.15 and
1.93 (CD2) and a much smaller signal at δ 5.05 (dCD).
This type of thermal rearrangement of the fused rings
takes place also in organic molecules. 2-Methyl-1-
phenylcyclopropane was reported to undergo photo-
isomerization into 4-phenyl-1-butene.18 We conducted
thermal reactions of 7,7-dimethylbicyclo[4.1.0]heptane
and 7,7-dibutylbicyclo[4.1.0]heptane in C2D2Cl4 at 130
°C for 12 h and observed clean formation of 1-isopro-
pylcyclohexene and (E)-5-cyclohexyl-4-nonene, respec-
tively.19 These isomerization reactions are considered
to proceed via formation of biradical species followed by
1,4-migration of a hydrogen atom. Thus, the thermal
isomerization reaction of 2 and 2-d also causes ho-
molytic cleavage of the C-C bond of three-membered
ring to form biradical species, shown in Scheme 5.
Abstraction of a hydrogen from the CH2 group in the
polymer chain by the radical within the six-membered
ring forms the CdC double bond in the main chain. The
cyclohexyl radical of 2-d abstracts mainly the hydrogen
from the CH2 group on the same side of the cyclohexane-
1,2-diyl group with respect to the cyclopropane plane.
Thus, the repeating unit containing a -HC) group is
contained in much more amount than that with a -DC)
group. Formation of Z- and E-olefinic group indicates
that both hydrogens of the CH2 group undergoes the
1,4-migration.
membered ring in order to avoid steric repulsion be-
tween the ring of the coordinated monomer and that of
the polymer end. The formed intermediate B undergoes
insertion of ethylene preferentially to regenerate A.
Strong coordination of 7-methylenebicyclo[4.1.0]heptane
to the Co center of A prevents double insertion of
ethylene, similar to the copolymerization of ethylene
with 2-phenyl-1-methylenecyclopropane.9 Double inser-
tion of 7-methylenebicyclo[4.1.0]heptane is also inhib-
ited due to steric bulkiness of the monomer. In fact,
homopolymerization of 7-methylenebicyclo[4.1.0]heptane
promoted by the Co complex is quite slow,15 although
the zirconocenes catalyze the smooth polymerization of
the same monomer without ring opening.7 It contrasts
with the results that the copolymerization of ethylene
(1 atm) with 2-phenyl-1-methylenecyclopropane (>150
mM) accompanies double insertion of the cyclic mono-
mer to produce the polymer having oligo(methylene-
cyclopropane) units.
Heating a C2D2Cl4 solution of 2 at 130 °C for 12 h
changes the 13C{1H} NMR spectrum, as shown in Figure
1C. The signals of 2 at δ 18-24 are not observed after
heating, while signals at δ 123 and 145 are newly
generated and assigned to olefinic carbons of the product
of the thermal reaction. The DEPT spectrum of the
The first DSC scan of 2 shows an endothermic peak
at 100 °C on heating, corresponding to the thermal
isomerization of the copolymer, and no exothermic peak
on cooling. The second scan exhibits transition due to

1530 Communications to the Editor
Macromolecules, Vol. 38, No. 5, 2005
Osakada, K. J. Am. Chem. Soc. 2002, 124, 762. (c) Takeuchi,
D.; Yasuda, A.; Osakada, K. Dalton Trans. 2003, 2029.
(7) (a) Jensen, T. R.; Marks, T. J. Macromolecules 2003, 36,
1775. (b) Jensen, T. R.; O’Donnell III, J. J.; Marks, T. J.
Organometallics 2004, 23, 740.
(8) For ethylene polymerization by Co complexes with bis-
(imino)pyridine ligands: (a) Small, B. L.; Brookhart, M.;
Bennett, A. M. A. J. Am. Chem. Soc. 1998, 120, 4049. (b)
Britovsek, G. J. P.; Gibson, V. C.; Kimberley, B. S.; Maddox,
P. J.; McTavish, S. J.; Solan, G. A.; White, A. J. P.; Williams,
D. J. Chem. Commun. 1998, 849. (c) Britovsek, G. J. P.;
Bruce, M.; Gibson, V. C.; 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.
(9) Takeuchi, D.; Anada, K.; Osakada, K. Angew. Chem., Int.
Ed. 2004, 43, 1233.
(10) Chen, E. Y.-X.; Marks, T. J. Chem. Rev. 2000, 100, 1391.
(11) 7,7-Dibutylbicyclo[4.1.0]heptane and 7,7-dimethylbicyclo-
[4.1.0]heptane are synthesized according to the reported
procedure: Corey, E. J.; Posner, G. H. J. Am. Chem. Soc.
1968, 90, 5615.
(12) The polymer obtained for a prolonged reaction sometimes
shows the 13C NMR peak at 30 ppm. It is assigned to the
polyethylene formed after consumption of 7,7-dimethylbicyclo-
[4.1.0]heptane.
Tg at 52 °C. The results suggest that the isomerization
of 2 occurs also in the solid state.
In summary, the Co catalyst does not cause homo-
polymerization of 7-methylenebicyclo[4.1.0]heptane but
promotes alternating copolymerization of ethylene with
it smoothly and stereoselectively at -40 °C to afford the
polymer with a unique structure. The polymer has
entirely different structure from the product of the
copolymerization of the same monomers catalyzed by
zirconocenes. Strained partial structure of the alternat-
ing copolymer facilitates its clean thermal conversion.
Acknowledgment. This work was supported by a
Grant-in-Aid for Young Scientist (No. 16750091) for
Scientific Research from the Ministry of Education,
Science, Sports, and Culture, Japan.
Supporting Information Available: Experimental pro-
cedures for polymerization and thermal isomerization and
NMR and DSC data of the products. This material is available
free of charge via the Internet at http://pubs.acs.org.
(13) Rol, N. C.; Clague, A. D. H. Org. Magn. Res. 1981, 16, 187.
(14) Polymerization of methylenecyclopropane catalyzed by Zr
and Ni complexes was proposed to involve the 1,2-insertion
of the monomer into the M-C σ bond. See refs 4, 5, and 7.
(15) Homopolymerization of 7-methylenebicyclo[4.1.0]heptane
(0.18 g) using the Co complex ([Co] ) 1.7 mM) and MMAO
([monomer]/[Co]/[Al] ) 200/1/300) at -40 °C produced 0.028
g of polymer (16% yield) after 1 h. The amount of the
homopolymer is much smaller than the copolymer obtained
from the reaction under 1 atm of ethylene atmosphere (0.18
g).
References and Notes
(1) Copolymerization of ethylene with acyclic alkenes: (a)
Miyatake, T.; Mizunuma, K.; Kakugo, M. Makromol. Chem.,
Macromol. Symp. 1993, 66, 203. (b) Uozumi, T.; Miyazawa,
K.; Sano, T.; Soga, K. Macromol. Rapid Commun. 1997, 18,
883. (c) Leclerc, M. K.; Waymouth, R. M. Angew. Chem., Int.
Ed. 1998, 37, 922. (d) Shaffer, T. D.; Canich, J. A. M.; Squire,
K. R. Macromolecules 1998, 31, 5145.
(2) (a) Kaminsky, W.; Beulich, I.; Arndt-Rosenau, M. Macromol.
Symp. 2001, 173, 211. (b) McKnight, A. L.; Waymouth, R.
M. Macromolecules 1999, 32, 2816 and references therein.
(3) (a) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich,
S. K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287,
460. (b) Benedikt, G. M.; Elce, E.; Goodall, B. L.; Kalama-
rides, H. A.; McIntosh, III, L. H.; Rhodes, L. F.; Selvy, K.
T.; Andes, C.; Oyler, K.; Sen, A. Macromolecules 2002, 35,
8978. (c) Kiesewetter, J.; Kaminsky, W. Chem.sEur. J.
2003, 9, 1750.
(16) For 13C NMR of (Z)- and (E)-2-cyclohexyl-2-butene: (a)
Vedejs, E.; Cabaj, J.; Peterson, M. J. J. Org. Chem. 1993,
58, 6509. (b) Bangerter, F.; Karpf, M.; Meier, L. A.; Rys, P.;
Skrabal, P. J. Am. Chem. Soc. 1998, 120, 10653.
(17) For 13C NMR of poly(isoprene) with mixture of cis and trans
repeating units: Duch, M. W.; Grant, D. M. Macromolecules
1970, 3, 165.
(18) (a) Kristinsson, H.; Griffin, G. W. J. Am. Chem. Soc. 1966,
88, 378. (b) Mazzocchi, P. H.; Lustig, R. S.; Craig, G. W. J.
Am. Chem. Soc. 1970, 92, 2169.
(19) The assignment of the NMR spectra of the products was
confirmed by comparison of them with the compounds
having similar structures. See ref 16 and Apparu, M.;
Crandall, J. K. J. Org. Chem. 1984, 49, 2125.
(4) (a) Takeuchi, D.; Osakada, K. Chem. Commun. 2002, 646.
(b) Takeuchi, D.; Anada, K.; Osakada, K. Macromolecules
2002, 35, 9628.
(5) (a) Yang, X.; Seyam, A. M.; Fu, P.-F.; Marks, T. J. Macro-
molecules 1994, 27, 4625. (b) Jia, L.; Yang, X.; Seyam, A.
M.; Albert, I. D. L.; Fu, P.-F.; Yang, S.; Marks, T. J. J. Am.
Chem. Soc. 1996, 118, 7900.
(6) (a) Takeuchi, D.; Kim, S.; Osakada, K. Angew. Chem., Int.
Ed. 2001, 40, 2685. See also: (b) Kim, S.; Takeuchi, D.;
MA047943R