Ni-complex-catalysed addition polymerisation of 2-phenyl-1-methylenecylopropane to afford a polymer with cyclopropylidene groups

Article abstract of DOI:10.1039/b111697e

π-Allyl-nickel complexes initiated addition polymerisation of 2-phenyl-1-methylenecyclopropane to give a polymer with three-membered rings; the formed polymer showed a high T_g and negligible thermal decomposition up to 300°C.

Full text of DOI:10.1039/b111697e

Ni-complex-catalysed addition polymerisation of
2-phenyl-1-methylenecylopropane to afford a polymer with
cyclopropylidene groups†
Daisuke Takeuchi and Kohtaro Osakada*
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259, Nagatsuta-cho, Midori-ku, Yokohama,
Japan. E-mail: kosakada@res.titech.ac.jp; Fax: +81-45-924-5224; Tel: +81-45-924-5224
Received (in Cambridge, UK) 2nd January 2002, Accepted 8th February 2002
First published as an Advance Article on the web 25th February 2002
p-Allyl-nickel complexes initiated addition polymerisation
of 2-phenyl-1-methylenecyclopropane to give a polymer
with three-membered rings; the formed polymer showed a
high Tg and negligible thermal decomposition up to 300
°C.
shown below.10 The absence of 13C{1H} NMR signals in the
region of d 100–120 indicates that the polymer does not contain
any olefinic groups formed via C–C bond cleavage of the three-
membered ring. The CH2 carbon signal of the polymer chain
and that of the three-membered ring at the respective positions,
d 31–48 and d 12–23, are inverted under DEPT (135° pulse)
conditions (Fig. 1(C)). Assignment of the latter signal was
confirmed from the 13C{1H} NMR spectrum of the polymer
obtained from 2-phenyl-1-methylene-3[13C]-cyclopropane (I-
13C).11 The existence of four stereoisomers for each monomer
unit of the polymer and the rigidity of the polymer chain (vide
infra) make these signals broad. The signal of the quaternary
carbon of the polymer chain (d 25) is observed as a single sharp
signal in the difference spectrum of 13C{1H} and DEPT (45°
pulse) spectra (Fig. 1(D)), although it severely overlaps with the
CH carbon peaks (d 23–31) in the 13C{1H} NMR spectrum. The
sharp and intense signal of the quaternary carbon is attributed to
a well-regulated head-to-tail linkage of the monomer units.
The reaction of 2-phenyl-1-methylenecyclopropane with [(p-
allyl)NiBr]2 in a molar ratio of [monomer]+[Ni] = 5, followed
by the addition of D2O, produced the polymer whose 2H NMR
spectrum showed a single signal at 1.8 ppm, which was assigned
to the 2CH2D end group (eqn. 1).
Cyclic alkenes such as dialkylcyclopropene and cyclobutene
undergo metal–complex-promoted addition polymerisation1,2
or ring-opening polymerisation,3 in which the release of ring
strain caused by the reaction acts as the major driving force.
Methylenecyclopropanes, also with a highly strained structure,
have been reported to undergo metal–complex-catalysed ring-
opening polymerisation rather than simple addition polymer-
isation.4,5 In this paper, we report the Ni-catalysed polymer-
isation6,7 of 2-phenyl-1-methylenecyclopropane to afford a new
polymer with phenylcyclopropylidene groups, and having good
thermal stability.
[(p-Allyl)NiBr]2 promoted addition polymerisation of
2-phenyl-1-methylenecyclopropane ([monomer]+[Ni] = 70) at
room temperature to give polymer I that contained a cyclopro-
pylidene group in every repeating unit.8 Table 1 summarises the
results of polymerisation. The polymerisation proceeded
smoothly in toluene, THF, NMP, and CH2Cl2. The reaction with
a molar ratio of [monomer]+[Ni] = 200 at 240 °C afforded I
with Mn = 29 000 and Mw/Mn = 1.59 (run 3), while the
reaction at room temperature produced the polymer with a
lower molecular weight. Since 2-methylbut-1-ene is not
polymerised by [(p-allyl)NiBr]2, the strained cyclopropane ring
promotes the polymerisation of 2-phenyl-1-methylenecyclopro-
pane. The polymerisation with a bulky diimine ligand, whose Ni
complexes catalyse the polymerisation of ethylene and a-
olefins,6,9 gave I in lower yield than the reaction without the
addition of the ligand (run 4). Cationic nickel complexes,
prepared in situ by the reaction of [(p-allyl)NiBr]2 with AgPF6
([Ni]+[Ag] = 1+1.2) in the presence of ligands (cod, diimine),
also promoted the polymerisation (runs 5–7). The molecular
weight of the polymer is almost similar to those obtained by the
neutral Ni complex (run 1).
(1)
The regulated head-to-tail linkage of the monomer units of I, as
revealed by 13C{1H} NMR spectroscopy as well as results of the
end group analysis, suggests that the polymerisation proceeds
via successive 1,2-insertion of 2-phenyl-1-methylenecyclopro-
pane to an alkyl–nickel bond of the growing polymer (Scheme
1). This mechanism is in contrast to the ring-opening polymer-
isation of 2-phenyl-1-methylenecyclopropane by Pd com-
plexes, where the polymerisation proceeds via 2,1-insertion of
the monomer to the p-allyl–Pd bond accompanied by C–C bond
cleavage of the three-membered ring.5
The 13C{1H} NMR spectrum of I and the spectrum under
DEPT conditions (Fig. 1) revealed unambiguously the structure
Differential scanning calorimetry (DSC) analysis of I
(obtained in run 3 of Table 1) revealed a glass transition
temperature of 178 °C, which is higher than those of many other
† Electronic supplementary information (ESI) available: full details of the
experimental procedures, DSC and TG profile of I. See http://www.rsc.org/
suppdata/cc/b1/b111697e/
Table 1 Polymerisation of 2-phenyl-1-methylenecyclopropane by nickel complexesa
b
b
Run
Ni complex
Ligand
Solvent
Temp/°C
Time/h
Yield (%)
Mn
Mw/Mn
1
2
3c
4
5
6
7
[(p-allyl)NiBr]2
None
None
None
Toluene
THF
THF
Toluene
THF
Toluene
rt
3
12
24
3
3
3
83
5 700
8 500
29 000
4 700
4 000
4 600
5 200
1.88
1.95
1.59
1.75
1.79
1.99
1.84
[(p-allyl)NiBr]2
240
240
rt
rt
rt
Quant.
Quant.
49
Quant.
Quant.
17
[(p-allyl)NiBr]2
[(p-allyl)NiBr]2
[(p-allyl)NiBr]2 + AgPF6
[(p-allyl)NiBr]2 + AgPF6
[(p-allyl)NiBr]2 + AgPF6
ArN = CH-CH = NArd
e
e
e
cod
cod
ArN = C(1,8-C10H8)C = NArd THF
rt
3
a Reaction conditions: [Ni] = 25 mM, [2-phenyl-1-methylenecyclopropane] = 1.8 M unless otherwise stated. b Determined by GPC in THF vs. polystyrene
standards. c [Ni] = 25 mM, [2-phenyl-1-methylenecyclopropane] = 5.0 M. d Ar = C6H3(iPr)2-2,6. e [Ni]+[Ag] = 1+1.2.
646
CHEM. COMMUN., 2002, 646–647
This journal is © The Royal Society of Chemistry 2002

clopropane produces a polymer with a new structure and high
thermal stability owing to the presence of rigid phenyl-
cyclopropylidene groups. The polymerisation without ring
opening of the growing polymer is caused by smooth repetition
of the 1,2-insertion of the monomer that occurs more rapidly
than the possible b-alkyl elimination of the cyclopropylme-
thylnickel intermediate.5,15
This work was supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports,
Science and Technology.
Notes and references
1 Addition polymerisation of cyclobutene by Ziegler–Natta catalyst: G.
Natta, G. DallAAsta, G. Mazzanti and G. Motroni, Makromol. Chem.,
1963, 69, 163; G. DallAAsta, J. Polym. Sci., Part A1, 1968, 6, 2397; V.
A. Kormer, I. A. Poletayeva and T. L. Yufa, J. Polym. Sci., Part A1,
1972, 10, 251.
2 Addition polymerisation of cyclopropenes: K. B. Wiberg and W. J.
Bartley, J. Am. Chem. Soc., 1960, 82, 6375; S. Rush, A. Reinmuth, W.
Risse, J. OABrien, D. R. Ferro and I. Tritto, J. Am. Chem. Soc., 1996,
118, 12230; ; Polymerisation of cyclopentene by Pd and Ni complexes
has also been reported: S. J. McLain, J. Feldman, E. F. McCord, K. H.
Gardner, M. F. Teasley, E. B. Coughlin, K. J. Sweetman, L. K. Johnson
and M. Brookhart, Macromolecules, 1998, 31, 6705.
3 Ring-opening polymerisation of dialkylcyclobutene by transition metal
catalysts: G. DallAAsta, G. Mazzanti, G. Natta and L. Porri, Makromol.
Chem., 1962, 56, 224; B. R. Maughon and R. H. Grubbs, Macromole-
cules, 1997, 30, 3459.
4 L. Jia, X. Yang, A. M. Seyam, I. D. L. Albert, P-F. Fu, S. Yang and T.
J. Marks, J. Am. Chem. Soc., 1996, 118, 7900.
5 D. Takeuchi, S. Kim and K. Osakada, Angew. Chem., Int. Ed., 2001, 40,
2685.
6 Ni complex catalysed polymerisation of olefins: S. D. Ittel, L. K.
Johnson and M. Brookhart, Chem. Rev., 2000, 100, 1169; G. J. P.
Britovsek, V. C. Gibson and D. F. Wass, Angew. Chem., Int. Ed., 1999,
38, 428; S. Mecking, Coord. Chem. Rev., 2000, 203, 325.
7 Reaction of Ni complexes with methylenecyclopropane: P. Binger, A.
Brinkmann and J. McMeeking, Liebigs Ann. Chem., 1977, 1065.
Recently, nickel complexes with diimine ligands were found to bring
about addition polymerisation of cyclopentene; see ref. 2.
Fig. 1 (A) 13C{1H} NMR and DEPT NMR spectra ((B) 45° pulse, (C) 135°
pulse) of I in CDCl3 at 25 °C. The difference spectrum of (B) from (A) is
shown in (D). The 13C{1H} NMR signal of I-13C is shown in the inset. The
signal marked by an asterisk is due to solvent impurity.
8 The ring strain relieved upon hydrogenation of the double bond in
methylenecyclopropane has been reported to be 53.6 kcal mol21: P.
Binger and H. M. Büch, Top. Curr. Chem., 1987, 135, 77.
9 R. F. de Souza, R. S. Mauler, L. C. Simon, F. F. Nunes, D. V. S. Vescia
and A. Cavagnolli, Macromol. Rapid Commun., 1997, 18, 795.
10 Selected NMR data of the structurally related compound: 1,1-dimethyl-
1
2-phenylcyclopropane: H NMR (CDCl3): d 0.81, 0.84 (2H, m, CH2),
0.85 (3H, s, CH3), 1.28 (3H, s, CH3), 1.93 (1H, m, CH), and 7.18–7.34
(5H, m, Ph). 13C{1H} NMR (CDCl3): d 18.3 (CH2), 19.0 (C), 20.3
(CH3), 27.4 (CH3), 29.7 (CH), 125.4 (p-Ph), 127.8, 128.9 (o, m-Ph), and
140.3 (ipso-Ph).
Scheme 1 A plausible mechanism of polymerisation of 2-phenyl-
1-methylenecyclopropane by Ni complexes.
11 The purity of 13C of the monomer is ca. 99%.
12 N. Ishihara, M. Kuramoto and M. Uoi, Macromolecules, 1988, 21,
3356.
known hydrocarbon polymers, such as thermally resistant
syndiotactic polystyrene.12,13 The results indicate a rigid
polymer chain that serves to render the CH2 and CH carbon
signals of the 13C{1H} NMR spectrum broad. The polymer did
not decompose up to 300 °C in the thermogravimetric (TG)
analysis of I.14 Thus, the produced polymer has good thermal
stability.
13 A hydrocarbon polymer with a cycloalkanediyl moiety in the main chain
has been reported to show the highest glass-transition temperature
among hydrocarbon polymers (231 °C). See: I. Natori, K. Imaizumi, H.
Yamagishi and M. Kazunori, J. Polym. Sci., Part B: Polym. Phys., 1998,
36, 1657.
14 Thermal weight loss of I (obtained in run 3 of Table 1) in 5% is observed
at 353 °C.
15 S. Hajela and J. E. Bercaw, Organometallics., 1994, 13, 1147.
In conclusion, we have demonstrated that Ni-complex-
catalysed addition polymerisation of 2-phenyl-1-methylenecy-
CHEM. COMMUN., 2002, 646–647
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