Alternating ring-opening metathesis copolymerization by grubbs-type initiators with unsymmetrical N-heterocyclic carbenes

Article abstract of DOI:10.1002/chem.200900384

A series of Ru^IV-alkylidenes based on unsymmetrical imidazolin-2ylidenes, that is, [RuCl₂{l-(2,4,6-trimethylphenyl)-3-R- 4,5-dihydro-(3H)-imidazol-l-ylidene}(CHPh)(pyridin)] (R = CH₂Ph (5), Ph (6), ethyl (7), methyl (8)),

Full text of DOI:10.1002/chem.200900384

FULL PAPER
DOI: 10.1002/chem.200900384
Alternating Ring-Opening Metathesis Copolymerization by Grubbs-Type
Initiators with Unsymmetrical N-Heterocyclic Carbenes
Martin Lichtenheldt,[a] Dongren Wang,[b] Kati Vehlow,[a] Ingrid Reinhardt,[b]
Christa Kꢀhnel,[b] Ulrich Decker,[b] Siegfried Blechert,*[a] and
Michael R. Buchmeiser*[b, c]
Abstract: A series of RuIV–alkylidenes
based on unsymmetrical imidazolin-2-
ylidenes, that is, [RuCl2{1-(2,4,6-trime-
thylphenyl)-3-R-4,5-dihydro-(3H)-imi-
dazol-1-ylidene}ACHTUNGTRENNUNG(CHPh)ACHTUNGTRENN(UGN pyridin)] (R=
CH2Ph (5), Ph (6), ethyl (7), methyl
(8)), have been synthesized. These and
the parent initiators [RuCl2ACTHNUTRGEN(UGN PCy3){1-
(2,4,6-trimethylphenyl)-3-R-4,5-dihy-
dro-(3H)-imidazol-1-ylidene}-
ACHTUNGTRENNUNG(CHC6H5)] (R=CH2C6H5 (1), C6H5
(2), ethyl (3)) were used for the alter-
nating copolymerization of norborn-2-
ene (NBE) with cis-cyclooctene (COE)
and cyclopentene (CPE), respectively.
Alternating copolymers, that is, poly-
(NBE-alt-COE)n and poly(NBE-alt-
CPE)n containing up to 97 and 91% al-
ternating diads, respectively, were ob-
tained. The copolymerization parame-
ters of the alternating copolymerization
of NBE with CPE under the action of
initiators 1–3 and 5–8 were determined
by using both a zero- and first-order
Markov model. Finally, kinetic investi-
gations using initiators 1–3, 6, and 7
were carried out. These revealed that
in contrast to the 2nd-generation
Grubbs-type initiators 1–3 the corre-
sponding pyridine derivatives 6 and 7
represent fast and quantitative initiat-
ing systems. Hydrogenation of poly-
(NBE-alt-COE)n yielded a fully satu-
rated, hydrocarbon-based polymer. Its
backbone can formally be derived by
1-olefin polymerization of CPE (1,3-in-
sertion) followed by five ethylene units
and thus serves as an excellent model
compound for 1-olefin polymerization-
derived copolymers.
Keywords:
metathesis
·
polymerization · ring-opening poly-
merization · ruthenium · synthesis
design
Introduction
different monomers, however, is still a challenging task. For
copolymerization to be accomplished by ROMP, a situation
has to be created in which the insertion of a monomer, A,
into the living metal alkylidene is favored in case a second,
different monomer, B, was inserted in the previous step and
in which insertion of a certain monomer A or B is strongly
disfavored in case the same monomer was inserted in the
preceding step. Consequently, reports on the alternating co-
polymers prepared by metathesis copolymerization of two
different monomers are comparably rare.[6–12] In 2005, Chen
et al. reported on the mechanism-based design of a ROMP
initiator for sequence-selective copolymerization.[13,14] Gen-
erally, both selectivity and reactivity of Grubbs- or Grubbs–
Hoveyda-type initiators is governed by the nature of the N-
heterocyclic carbene (NHC),[15–30] the alkylidene,[31–42] or the
(pseudo)halide ligands.[43–53] We recently reported on an al-
ternative system for the synthesis of alternating copolymers
based on Grubbs-type initiators containing an unsymmetri-
cal, chiral NHC.[29] In this contribution, we investigated the
scope and limitations of this concept by using a series of
Ru–alkylidenes based on unsymmetrical NHCs. With these
new initiators in hand, we checked for their capability to co-
Ring-opening metathesis polymerization (ROMP) initiated
by well-defined Schrock carbenes is nowadays a well-estab-
lished polymerization technique.[1–4] Various Schrock-,
Grubbs- and Grubbs–Hoveyda-type initiators may be used
for that purpose.[5] The alternating copolymerization of two
[a] Dr. M. Lichtenheldt, Dr. K. Vehlow, Prof. Dr. S. Blechert
Institut fꢀr Chemie, Technische Universitꢁt Berlin,
Strasse des 17. Juni 135, 10623 Berlin (Germany)
Fax : (+49)30-314-29745
E-mail: blechert@chem.tu-berlin.de
[b] Dr. D. Wang, I. Reinhardt, C. Kꢀhnel, Dr. U. Decker,
Prof. Dr. M. R. Buchmeiser
Leibniz-Institut fꢀr Oberflꢁchenmodifizierung e.V. (IOM)
Permoserstrasse 15, 04318 Leipzig (Germany)
Fax : (+49)341-235-2584
E-mail: michael.buchmeiser@iom-leipzig.de
[c] Prof. Dr. M. R. Buchmeiser
Institut fꢀr Technische Chemie, Universitꢁt Leipzig
Linnꢂstrasse 3, 04103 Leipzig (Germany)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200900384.
Chem. Eur. J. 2009, 15, 9451 – 9457
ꢃ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
9451

polymerize
norborn-2-ene
(NBE) and cis-cyclooctene
(COE) as well as NBE and cy-
clopentene (CPE) in an alter-
nating way.
Results and Discussion
Seven different RuIV–alkyli-
denes (Grubbs-type initiators)
based on unsymmetrical NHCs
were used for the alternating
copolymerization of NBE with
COE and CPE, respectively.
Initiators 2, 3, and 4 have been
prepared as described earli-
er.[30,54] The synthetic protocol
used there was also applied to
Scheme 1. Synthesis of compounds 1–8.
the synthesis of initiator
1
(Scheme 1, PCy3 =tricyclohex-
ylphosphine). This compound
was prepared by means of a
Pd-catalyzed N-arylation reac-
tion of N-benzyl-N-(2-amino-
ethyl)amine with bromomesity-
lene. The resulting diamine
was subject to cyclization by
using triethylorthoformate,[55]
which yielded the correspond-
ing imidazolinium salt. Depro-
tonation with potassium-tert-
amylate and reaction with the
1st-generation Grubbs catalyst
[RuCl2ACHTUNGTRENNUNG(PCy3)2ACHTUNGTRENNUNG(=CHC6H5)] in
the presence of CuCl yielded
1.
In contrast to the PCy3-
based 2nd-generation Grubbs-
type initiators, the correspond-
Figure 1. 13C NMR spectrum (CDCl3) of poly(NBE-alt-COE)n prepared by the action of initiator 5.
ing 3-Br-pyridine and pyridine derivatives of Grubbs-type
initiators have been reported to display excellent initiation
characteristics.[56] Therefore, the corresponding pyridine-con-
taining initiators 5–8 were prepared from the tricyclohexyl-
phosphine-based progenitors 1–4 by using a polymer-bound
triphenylphosphane–CuCl complex as phosphane scavenger
(Scheme 1).[29] In this way, compounds 5–8 were obtained in
45–61% yield. Initiators 5 and 8 were obtained as monopyri-
dine adducts. According to NMR spectroscopy, however, ini-
tiators 6 and 7 were obtained as a mixture of the mono- and
served around d=135.0 and 128.5 ppm. As can be seen,
hardly any signals for poly(NBE) usually occurring at d=
133–134 ppm can be detected.[7,57] The signals around d=
130 ppm belong to the poly(COE) block that is formed after
all the NBE has been consumed. Its formation can, in view
of the very fast polymerization kinetics of 5, not be sup-
pressed. In fact, the copolymerization of NBE with COE by
the action of 5 is finished within less than five seconds. Simi-
lar high activity was also found for initiator 7 (Figure S11,
Supporting Information). The first signal group around
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
À
bis
G
135.0 ppm is assigned to the C=C CH2 carbon atom and
Next we used initiators 1–3 and 4–8 in the copolymeriza-
tion of NBE with COE. By using a NBE/COE ratio of 1:50,
the corresponding copolymers contained 95–97% alternat-
ing diads (Table 1). A representative 13C NMR spectrum of
such a copolymer prepared by the action of 5 is shown in
Figure 1. The signals for the alternating copolymer are ob-
consists of eight different signals at d=135.21, 135.18,
135.07, 135.05, 134.90, 134.88, 134.75, and 134.70 ppm, which
we attribute—without assignment—to the corresponding
ccc, tcc, ctc, cct, ttc, tct, ctt, and ttt diads. The eight signals are
grouped into two sets of different intensity (approx. 60:40)
from which a cis content of 59–64% can be derived for the
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Chem. Eur. J. 2009, 15, 9451 – 9457

Alternating Ring-Opening Metathesis
FULL PAPER
polymers prepared by the action of initiators 1–3 and 5–8
(Table 1). This is in accordance with the H NMR spectro-
scopic data of the polymers, which also shows signals of the
Tg of poly
(NBE)s (40–648C).[59] The different Tg values are a conse-
quence of the poly(COE) block that is formed once the
ACHTUNGTRENNUNG
1
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
cis and trans double bonds in the corresponding ratio at d=
NBE has been consumed. The size of this block strongly af-
fects Tg in that longer poly-
AHCTUNGERTG(NNUN COE) blocks lead to a de-
crease in Tg.
Table 1. Results of the alternating copolymerization of NBE with COE.[a]
Next, we carried out copoly-
merizations of NBE with CPE.
The results are summarized in
Table 2. By using a ratio of
NBE/CPE of only 1:7, copoly-
mers containing 79–91% of al-
ternating diads were obtained.
This percentage of alternating
units is again comparable to
the ones obtained by the use
of 9 (90% alternating units)
and is among the highest
values found so far.[9] This is of
Initiator
cis [%][b]
Alternating
diad [%][b]
Mn [gmolÀ1],
Tg [8C]/
Mn [gmolÀ1]/
Mn of the
[d]
PDI[c]
Dcp [JgÀ1
]
polyACHTNUGRTNEUNG
(COE) block[e]
1
2
3
5
6
7
8
61
60
61
61
59
62
64
95
96
97
97
96
97
96
5.5ꢄ105, 2.0
7.6ꢄ105, 1.9
8.0ꢄ105, 1.6
6.0ꢄ105, 1.9
7.8ꢄ105, 1.8
1.3ꢄ106, 1.4
1.5ꢄ106, 1.6
À50.6/0.35
À52.3/0.38
À47.8/0.44
À56.5/0.47
À53.8/0.37
À47.8/0.37
À58.2/0.34
2.2ꢄ104/4
6.9ꢄ104/10
4.3ꢄ104/6
7.2ꢄ104/14
6.7ꢄ104/10
3.3ꢄ104/3
1.8ꢄ105/14
[a] Initiator/NBE/COE 1:2000:100000. [b] Determined by 13C NMR spectroscopy. [c] Determined by GPC
analysis. [d] Determined by DSC analysis. [e] In% of Mn of the poly(NBE-alt-COE)n blocks.
5.36 and 5.28 ppm, respectively (Figure S1, Supporting Infor-
mation). As already described for [RuCl2A(PCy3)(1-mesityl-3-
{(1’R)-1-phenylethyl}-4,5-imidazolin-2-ylidene)(CHC6H5)]
particular interest, since CPE usually displays a rather limit-
ed propensity to undergo ROMP[60] and homopolymeriza-
tion of CPE is often counterbalanced by backbiting, yielding
cyclic, low molecular weight polymers.[61]
CTHUNGTRENNUNG
AHCTUNGTRENNUNG
(9),[29] such a high cis content is rather unusual for Grubbs-
type initiators and might be connected to the alternating
character of the copolymerization. Thus, most homo- or
block copolymers prepared by Grubbs-type initiators display
a cis/trans ratio of approximately 25:75.[4] The signals
The 13C NMR spectrum of the alternating copolymer is
shown in Figure 3. The signals for the alternating copolymer
are observed around d=135.1 and 128.3 ppm. The first
À
signal group around d=135.1 ppm is assigned to the C=C
CH2 carbon atom. From H NMR spectroscopy, a cis/trans
1
À
around d=129.4 ppm are assigned to the C=C CH2 carbon
atom and are resolved to a minor extent, however, corre-
spond to the same diads. The structure of the polymers
formed is shown in Figure 2.
ratio of 60:40 may be deduced (Figure S2, Supporting Infor-
mation). DSC measurements again revealed only one single
glass transition for each of the alternating polymers in the
range of À39.7<Tg <À27.68C (Table 2). Again, these Tg
values are comparable to the one found for poly(NBE-alt-
CPE)n prepared by the action of 9 (Tg =À37.78C, Dcp =
0.31 JgÀ1).[29] As for poly(NBE-alt-CPE)n (see above), the
different Tg values are a consequence of the different size of
the polyACTHNUTRGENUG(N CPE) block that forms. Again, the size of this
block strongly affects Tg in that longer poly
lead to a decrease in Tg.
ACHTUNGTRENUN(NG CPE) blocks
Hydrogenation of poly(NBE-alt-COE)n with p-toluenesul-
fonylhydrazide in hot xylene yielded a fully saturated, hy-
drocarbon-based polymer the backbone of which formally
consists of CPE (1,3-insertion) followed by an even number
Figure 2. Predominant structures of poly(NBE-alt-COE)n (top) and
poly(NBE-alt-CPE)n (bottom) prepared by the action of initiators 1–3
and 5–8.
Differential scanning calori-
Table 2. Results of the alternating copolymerization of NBE with CPE.[a]
metric (DSC) measurements of
the alternating copolymers re-
vealed one single glass transi-
tion for each polymer in the
[d]
Initiator
Alternating
diad [%][b]
Mn [gmolÀ1],
Tg [8C]/
Mn [gmolÀ1]/Mn
[d]
PDI[c]
Dcp [JgÀ1
]
poly
A
poly
ACHTUNGTRENNUNG
1
2
3
5
6
7
8
79
90
90
85
91
91
86
1.0ꢄ104, 1.9
2.5ꢄ104, 2.3
4.4ꢄ104, 1.9
2.0ꢄ104, 1.9
5.4ꢄ104, 2.4
3.4ꢄ104, 2.6
2.0ꢄ104, 1.9
À39.7/0.457
À29.8/0.333
À28.5/0.332
À30.8/0.239
À29.6/0.262
À27.6/0.291
À31.8/0.471
565/6.3
211/0.9
389/0.9
513/2.8
364/0.7
199/0.6
365/2.0
522/5.8
1211/5.1
2128/5.1
1107/6.0
2551/5.0
1581/4.9
1158/6.2
range
À58.2<Tg <À47.88C
(Table 1) and thus compares to
the one found for the alternat-
ing copolymer prepared by 9
(À50.98C,
The Tg of the alternating co-
Dcp =0.32 JgÀ1).[29]
[a] Initiator/NBE/CPE 1:2000:14000. [b] Determined by 13C NMR spectroscopy. [c] Determined by GPC anal-
polymers is thus in between the ysis. [d] Determined by DSC analysis. [e] In% of size of the poly(NBE-alt-CPE)n blocks.
Chem. Eur. J. 2009, 15, 9451 – 9457
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9453

S. Blechert, M. R. Buchmeiser et al.
Therefore, application of a first-
order Markov model ultimately
leading to the Mayo–Lewis
equation[63] appeared more fa-
vorable. In this case, an r value
for each monomer is obtained.
Thus,
([CPE]/
P21]À1)([NBE]/
r1 =([1/P12]À1)-
[NBE]) and r2 =([1/
[CPE]) with P12
U
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
and P21 being the reactivity
probabilities for CPE to insert
into a growing chain with a ter-
minating NBE and vice versa.
Again, the results are summar-
ized in Table 3. Both P12 and
P21 can be retrieved by
13C NMR spectroscopy.
Finally, kinetic data were re-
corded. Initiators 5 and 8 were
Figure 3. 13C NMR spectrum of poly(NBE-alt-CPE)n prepared by the action of 6.
found to be too fast to allow for
any recording of kinetic data.
(10) of carbon units and that may hardly be realized by any
other polymerization method (Figure 4).
Thus, the copolymerization was finished within less than 10 s
at room temperature. However, initiators 1–3, 6, and 7 could
be investigated in more detail. While initiators 1 and 3
showed the typical non-first-order behavior of a 2nd-genera-
tion Grubbs-type initiator with an increase in kp over time
both in homo- and copolymerization (Figures S3–S8, Sup-
porting Information), catalysts 6 and 7 turned out to be fast
From the 13C NMR spectra we were able to extract the
copolymerization parameter r. Applying
Markov r=(NBE–NBE)(CPE–CPE)/
model,[62]
CPE)(CPE–NBE), in which NBE–NBE and CPE–CPE are
a
zero-order
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
diads for which a NBE is followed by an NBE and a CPE is
followed by a CPE, respective-
ly, and in which NBE–CPE and
CPE–NBE are diads for which
an NBE is followed by a CPE
and vice versa. The higher the
degree of alternating diads, the
lower the r values, which repre-
sent the ratio of the two rate
constants of insertion for both
monomers (k=kp1/kp2), are.
Thus, in a perfectly alternating
copolymerization, (NBE–NBE)
and (CPE–CPE) would be 0
and thus r would be 0. The r
values for initiators 1–3 and 5–8
used in the copolymerization
are summarized in Table 3. As
can be seen, 0.0052<r<0.061,
Figure 4. 13C NMR (bottom) and DEPT spectrum (top) of hydrogenated poly(NBE-alt-COE)n (CDCl3).
which underlines the high
degree of alternating diads that
can be realized with the aid of
these initiators. The zero-order
Markov model is, however,
based on the assumption that
the velocity of insertion of a
monomer is independent of the
previously inserted monomer.
In view of our previous re-
sults,[29] this might not be true.
Table 3. Copolymerization parameters obtained with initiators 1–3 and 5–8 in the alternating copolymerization
of NBE (1) with CPE (2).
Initiator
1
2
3
5
6
7
8
Model
rꢄ10À3
r1
61
7.4
1.2
0.85
6.3
0.96
7.9
1.2
0.85
6.4
0.96
27
5.8
1.2
0.85
4.8
0.97
5.2
1.2
0.85
4.3
0.97
21
zero-order Markov
1.4
0.83
43
1.4
0.83
18
1.5
0.82
14
P12
first-order Markov
r2 ꢄ10À3
P21
0.77
0.88
0.91
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Chem. Eur. J. 2009, 15, 9451 – 9457

Alternating Ring-Opening Metathesis
FULL PAPER
and quantitatively initiating RuIV–alkylidenes (Figure S9–
S11, Supporting Information). Thus, the rate constant for
the homopolymerization of NBE by 6 was 300 sÀ1 and the
one for NBE in the copolymerization with COE was
530 LmolÀ1 sÀ1.
ylidene)
ylidene)
U
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
N-Benzyl-N’-(2,4,6-trimethylphenyl)ethane-1,2-diamine:
[Pd2ACHTUNGTRENNUNG(dba)3]
(dba=dibenzylideneacetone; 1.0 mol%), (Æ)-BINAP (BINAP=2,2’bis-
(diphenylphosphino)-1,1’-binaphthyl; 3.0 mol%), and toluene (25 mL)
were mixed together. After 1 min, 2-bromomesitylene (12.3 mmol) and
N-aminoethylbenzylamine (13.6 mmol), NaOtBu (37.0 mmol), and tolu-
ene (25 mL) were added consecutively. The reaction mixture was stirred
at 808C for 72 h, then cooled to room temperature and dissolved in
15 mL of Et2O. The organic phase was extracted five times with 30 mL
portions of H2O and three times with 15 mL portions of a saturated NaCl
solution. It was then dried over MgSO4. The solvent was removed in
vacuo and the remaining oil was distilled in vacuo to give a yellow oil
(2.37 g, 8.7 mmol, 70.7%). B.p. 2308C (2.1ꢄ10À1 mbar); 1H NMR
(250 MHz, CDCl3): d=7.32 (brs, 2H; H-11), 7.30 (brs, 2H; H-12), 7.25
(m, 1H; H-13), 6.79 (s, 2H; H-3), 3.80 (s, 2H; H-9), 3.03 (t, J=5.6 Hz,
2H; H-8), 2.82 (t, J=5.6 Hz, 2H; H-7), 2.49 (brs, 2H; NH), 2.25 (s, 6H;
H-5), 2.21 ppm (s, 3H; H-6); 13C NMR (75 MHz, CDCl3): d=143.8 (C-1),
140.4 (C-10), 131.0 (C-2), 129.6 (C-4), 129.4 (C-3), 128.4 (C-12), 128.1 (C-
11), 127.0 (C-13), 53.8 (C-9), 49.5 (C-8), 48.3 (C-7), 20.5 (C-6), 18.4 ppm
(C-5); IR (CsF2 plate): n˜ =33520 (m), 3086 (w), 3061 (w), 3026 (m), 2962
(sh), 2939 (m), 2915 (s), 2853 (s), 2824 (sh), 2730 (w), 1486 (vs), 1453 (s),
1373 (w), 1339 (w), 1305 (w), 1234 (m), 1199 (w), 1156 (w), 1115 (m),
1074 (w), 1029 (m), 1013 (w), 907 (w), 854 (m), 735 (s), 698 (s), 604 (w),
583 (w), 567 (w), 542 (w), 504 (w), 462 cmÀ1 (w); MS (EI, 70 eV): m/z
(%): 268 (12) [M]+, 148 (100) [Mes-NH=CH2]+, 120 (23) [Bn-NH=
Conclusions
In summary, we significantly extended the number of Ru–al-
kylidene-based metathesis initiators that allow for the syn-
thesis of highly alternating copolymers of norborn-2-ene
with cis-cyclooctene and cyclopentene, respectively. In terms
of initiation efficiency, the pyridine derivatives turned out to
be superior over the parent PCy3-based compounds. A high
cis-content was observed in poly(NBE-alt-COE)n prepared
by any of the initiators used here. The size of the homopoly-
mer-based blocks, that is, of the polyACHTUNGTREN(NUGN COE) and the poly-
ACHTUNGTRENNUNG(CPE) blocks, strongly affect the thermoelastic properties of
the polymers in that a large fraction of these blocks present
in the corresponding alternating copolymer result in signifi-
cantly lower glass transition temperatures. Finally, hydroge-
nation of the alternating copolymers allows for creating
model systems for polyACHTUNRGTNE(NUG olefin) chemistry, for example, for
the determination of chemical shifts in 1-olefin polymeri-
zation-derived copolymers of cyclopentene and ethylene.
CH2]+, 91 (77) [C7H7]+; elemental analysis calcd
(268.41): C 80.55, H 9.01, N 10.44; found: C 80.27, H 9.22, N 10.60.
% for C18H24N2
3-Benzyl-1-(2,4,6-trimethylphenyl)-4,5-dihydro-3H-imidazolium chloride:
N-Benzyl-N’-(2,4,6-trimethylphenyl)ethane-1,2-diamine
(880.0 mg,
3.3 mmol) dissolved in toluene (9 mL), triethylorthoformate (5.5 mL,
33.0 mmol) and NH4Cl (700 mg, 13.1 mmol) were mixed at 1308C and
stirred for 18 h. After cooling to room temperature, the upper layer was
separated from the lower phase. The latter was dissolved in CH2Cl2. A
white precipitate of NH4Cl formed, which was filtered off. The organic
solvent was removed in vacuo and the resulting residue was recrystallized
from acetone to give colorless, highly hygroscopic crystals (175.5 mg,
0.56 mmol, 16.0%). M.p. 138–1428C; 1H NMR (250 MHz, CDCl3): d=
10.04 (s, 1H; H-1), 7.47–7.36 (m, 5H, H-12, H-13; H-14), 6.90 (s, 2H; H-
6), 5.13 (s, 2H; H-10), 4.11 (s, 2H; H-2), 4.05 (s, 2H; H-3), 2.28 (s, 6H;
H-8), 2.27 ppm (s, 3H; H-9); 13C NMR (75 MHz, CDCl3): d=159.7 (C-1),
140.3 (C-4), 135.1 (C-5), 132.9 (C-12), 130.7 (C-7), 130.1 (C-6), 129.4 (C-
12), 129.1 (C-14), 129.1 (C-13), 52.3 (C-10), 50.9 (C-3), 48.1 (C-2), 21.0
(C-9), 18.0 ppm (C-8); IR (KBr): n˜ =3114 (s), 3002 (s), 2965 (s), 2919 (s),
2856 (s), 1681 (vs), 1636 (vs), 1511(m), 1487 (m), 1452 (s), 1374 (m), 1308
(m), 1286 (m), 1261 (s), 1216 (s), 1181 (m), 1138 (m), 1079 (w), 1043 (w),
1030 (w), 1009 (w), 982 (w), 917 (w), 875 (w), 858 (w), 758 (m), 701 (s),
651 (m), 614 (m), 594 (w), 579 (w), 571 (w), 503 (w), 475 (m), 433 cmÀ1
(w); MS (EI, 70 eV): m/z (%): 314 (3) [M]+, 279 (7) [MÀCl]+, 278 (25)
[MÀHCl]+, 277 (100) [MÀH2Cl]+, 187 (11), 159 (10), 146 (11), 91 (63),
65 (8), 36 (6).
Experimental Section
General: Except where noted, all manipulations were performed under a
dinitrogen atmosphere in a glove box (MBraun LabMaster 130) or by
standard Schlenk techniques. Pentane, toluene, diethyl ether, methylene
chloride, and THF were dried by using a solvent purification system
(SPS, MBraun). Benzene and n-hexane were distilled from sodium/ben-
zophenone ketyl under argon. All commercially available starting materi-
als were purchased from Aldrich or Fluka and were used without any fur-
ther purification. NMR spectra were recorded on a Bruker Avence 600
(600.25 MHz for proton and 150.93 MHz for carbon spectra), a Bruker
DRX 500 Advance (500.2 MHz for proton and 80.5 MHz for carbon
spectra), or a Bruker AM 400 (400.2 MHz for proton and 100.6 MHz for
carbon spectra) spectrometer at room temperature unless specified other-
wise. Proton and carbon spectra were referenced to an internal solvent
resonance and are reported in ppm relative to tetramethylsilane. Mass
spectra were recorded on a MAT 95 SQ and a Varian MAT 71, respec-
tively. 70 eV were used for EI. IR spectra were recorded from 4000–
400 cmÀ1 on a Perkin–Elmer Spectrometer 881 by using ATR technology.
The absorption bands are reported in wave numbers (cmÀ1). Melting
points were determined on a Leica Galen hot stage microscope and are
uncorrected. DSC measurements were carried out on a DSC 7 (Perkin–
Elmer) by using open Al pans. Temperature programme: À100 to 2058C,
108CminÀ1; then at 2058C for 1 min isothermal. All measurements were
carried out under a N2 atmosphere. GPC measurements were performed
on an LC10 AD equipped with an SIL-10 ADVP auto injector, a CTO-
10AC column oven, a SCL-10AVP system controller, and a RID-10A re-
fractive index detector (all Shimadzu). A precolumn and three consecu-
tive Plgel 5 mm MiniMIX-c columns (7.5ꢄ300 mm, Polymer Laborato-
ries) were operated in CHCl3 applying a flow rate of 0.7 mLminÀ1. Mo-
AHCTUNGTRENNUNG
A
R
1
benzyl-1-(2,4,6-trimethylphenyl)-4,5-dihydro-3H-imidazoliumchloride
(205.8 mg, 562.0 mmol) and potassium-tert-amylate (70.9 mg, 562.0 mmol)
dissolved in hexane (40 mL) and [RuCl2ACHTUNGTRNENUG(PCy3)2AHCUTNGTRNE(NUGN CHC6H5)] (231.2 mg,
280.9 mmol) following the procedure described for compounds 2–3 and
was obtained as a purple, microcrystalline solid (211.7 mg, 91.8%). M.p.
1728C (decomp); 1H NMR (250 MHz, CD2Cl2): d=18.85 (s, 1H; H-10),
7.90 (brs, 2H; H-12), 7.78 (dd, J=8.1, 1.7 Hz, 2H; H-22), 7.47–7.35 (m,
3H; H-21, H-23), 7.40 (t, J=7.3 Hz, 1H; H-14), 7.12 (t, J=7.1 Hz, 2H;
H-13), 6.28 (brs, 2H; H-6), 5.35 (s, 2H; H-19), 3.80–3.60 (m, 4H; H-2,
H-3), 2.39–1.05 (m, 33H; PCy3), 2.19 (s, 6H; H-8), 1.91 ppm (s, 3H; H-
9); 31P NMR (250 MHz, CD2Cl2): d=35.8 ppm; 13C NMR (75 MHz,
CD2Cl2): d=294.1 (d, J=7.2 Hz; C-10), 219.4 (d, J=74.3 Hz; C-1), 151.5
(C-11), 138.0 (C-7), 137.3 (C-5), 136.9 (C-4), 136.2 (C-20), 130.9 (brs, C-
6), 129.6 (C-22), 129.2 (C-12), 129.0 (C-21), 128.6 (C-23), 128.6 (C-14),
128.2 (C-13), 55.9 (C-19), 51.8 (C-3), 48.8 (C-2), 31.8 (d, 1JP,C =15.8 Hz;
lecular weights were determined by calibration vs poly
thesis of [RuCl2(1-mesityl-3-phenylimidazolin-2-ylidene)
(2),[54]
ACHTUNGTRENNUNG(PCy3)] [RuCl2(1-mesityl-3-methylimidazolin-2-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
Chem. Eur. J. 2009, 15, 9451 – 9457
ꢃ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9455

S. Blechert, M. R. Buchmeiser et al.
C-15), 29.8 (C-16), 28.2 (d, 3JP, C =9.9 Hz; C-17), 26.9 (C-18), 21.0 (C-9),
18.5 ppm (C-8); IR (KBr): n˜ =3058 (m), 2926 (vs), 2850 (s), 1488 (s),
1447 (s), 1418 (m), 1379 (w), 1344 (w), 1324 (w), 1299 (w), 1267 (s), 1242
(m), 1226 (m), 1174 (m), 1128 (m), 1105 (m), 1073 (m), 1031 (m), 1005
(m), 897 (m), 847 (m), 742 (m), 702 (m), 688 (m), 624 (w), 585 (w), 576
(w), 523 (w), 509 (w), 490 (w), 473 cmÀ1 (w); MS (ESI, 0.5 mLminÀ1
CHCl3,): m/z (%): 820 (36) [M]+, 370 (48), 281 (100) [PCy3].
H-18), 6.98 (t, J=7.8 Hz, 2H; H-15), 6.31 (s, 2H; H-6), 4.55 (q, J=
7.0 Hz, 2H; H-10), 3.89–3.75 (m, 4H; H-2, H-3), 2.19 (s, 3H; H-8),
2.01 ppm (s, 6H; H-9); 13C NMR (150.93 MHz, CD2Cl2): d=311.5 (CH;
C-12), 153.0 (CH; C-17), 151.3 (Cq; C-13), 137.9 (Cq; C-7), 137.2 (Cq; C-
5), 137.0 (CH; C-19), 136.5 (Cq; C-4), 129.3 (CH; C-6), 129.2 (CH; C-
14), 128.5 (CH; C-16), 128.0 (CH; C-15), 124.0 (CH; C-18), 51.5 (CH2, C-
3), 47.5 (CH2; C-10), 46.7 (CH2; C-2), 20.7 (CH3; C-8), 17.7 (CH3; C-9),
13.6 ppm (CH3; C-11); IR (ATR): n˜ =3447 (bm), 2924 (bm), 2739 (w),
1945 (bw), 1700 (bw), 1484 (s), 1446 (s). 1260 (s), 761 cmÀ1 (bw); FAB-
MS: m/z (%): 442 (24) [MÀClÀPyridin]+, 407 (82) [MÀ2ClÀPyridin]+,
391 (100).
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
1.27 mmolP, 3.6 equiv) and CuCl (105.2 mg, 1.06 mmol, 3.0 equiv) were
suspended in CH2Cl2 (3.5 mL) and the mixture was stirred for 16 h at
room temperature. Then, [RuCl
benzyl-4,5-dihydro-3H-imidazol-1-ylidene}
(PCy3){1-(2,4,6-trimethylphenyl)-3-
(CHC6H5)] (290.8 mg,
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
0.354 mmol) and pyridine (9 mL) were added and the color of the reac-
tion mixture changed to green. After 1 h, Et2O (9 mL) was added and
the brownish solid was removed from the green solution. The solvent was
removed in vacuo and the residue was suspended in Et2O and filtered.
Then the solution was evaporated to dryness. The amount of Et2O was
reduced to 1 mL, then hexane was added (3 mL). Evaporation of the sol-
vent yielded a green solid (109.7 mg, 0.177 mmol, 50%). M.p. 2058C
(decomp); 1H NMR (600.25 MHz, CDCl3): d=18.85 (s, 1H; H-15), 8.54
(d, J=5.1 Hz, 2H; H-20), 7.78 (d, J=7.2 Hz, 2H; H-12), 7.56 (t, J=
7.6 Hz, 1H; H-22), 7.52 (d, J=7.6 Hz, 2H; H-17), 7.48–7.43 (m, 3H, H-
13; H-19), 7.37 (t, J=7.3 Hz, 1H; H-14), 7.15–7.06 (m, 4H; H-18, H-21),
6.74 (s, 1H; H-6), 5.84 (s, 2H; H-10), 3.83 (t, J=9.7 Hz, 2H; H-3), 3.68
(t, J=9.4 Hz, 2H; H-2), 2.27 (s, 3H; H-8), 2.17 ppm (s, 6H; H-9);
13C NMR (150.93 MHz, CD2Cl2): d=282.7 (Cq; C-15), 213.9 (Cq; C-1),
153.0 (CH; C-20), 151.4 (Cq; C-16), 149.6 (Cq; C-11), 137.5 (CH; C-22),
136.4 (Cq; C-4), 129.9 (Cq; C-7), 129.3 (CH; C-6), 129.2 (CH; C-19, C-
13), 129.1 (Cq; C-5), 129.0 (CH; C-18), 128.2 (CH; C-14), 128.1 (CH; C-
12), 124.0 (CH; C-21), 65.7 (CH2; C-10), 51.7 (CH2; C-3), 47.7 (CH2; C-
2), 20.8 (CH3; C-8), 17.8 ppm (CH3; C-9); IR (ATR): n˜ =3466 (bw), 2916
(bm), 2740 (w).1950 (bw), 1701 (m), 1484 (s), 1445 (s), 1265 (s), 697 cmÀ1
(m); FAB-MS: m/z (%): 377 (10), 297 (20), 279 (100), 91 (72).
0.632 mmolP, 3.6 equiv) and CuCl (52.2 mg, 0.527 mmol, 3.0 equiv) were
suspended in CH2Cl2 (2 mL) and the mixture was stirred for 16 h at room
temperature. Then, [RuCl
dihydro-3H-imidazol-1-ylidene}AHCUTNGTRENNUNG
(PCy3){1-(2,4,6-trimethylphenyl)-3-methyl-4,5-
(CHC6H5)][30] (130.8 mg, 0.176 mmol) and
pyridin (5 mL) were added. The color of the reaction mixture changed to
dark green within a few minutes. After 1 h, Et2O (5 mL) was added and
the brown solid was removed by filtration. Workup as described for 3
yielded
a green amorphous solid (50.7 mg, 0.093 mmol, 53%). M.p.
1988C (decomp); 1H NMR (600.25 MHz, CDCl3): d=18.79 (s, 1H; H-
11), 8.53 (d, J=4.9 Hz, 2H; H-16), 7.59 (t, J=7.4 Hz, 1H; H-18), 7.46 (d,
J=7.5 Hz, 2H; H-13), 7.39 (t, J=6.3 Hz, 1H; H-15), 7.14 (t, J=6.8 Hz,
2H; H-17), 7.06 (t, J=7.1 Hz, 2H; H-14), 6.73 (s, 2H; H-6), 4.16 (s, 3H;
H-10), 4.00 (d, J=9.5 Hz, 2H; H-3), 3.88 (d, J=10.5 Hz, 2H; H-2), 2.27
(s, 3H; H-8), 2.13 ppm (s, 6H; H-9); 13C NMR (150.93 MHz, CD2Cl2):
d=311.1 (Cq; C-11), 215.2 (Cq; C-1), 152.8 (CH; C-16), 151.2 (Cq; C-12),
138.2 (Cq; C-7), 137.5 (Cq; C-18), 137.1 (Cq; C-5), 136.5 (Cq; C-4), 129.3
(CH; C-13), 129.1 (CH; C-6), 128.5 (CH; C-14), 128.2 (CH; C-14), 127.7
(CH; C-15), 124.0 (CH; C-17), 51.8 (CH2; C-3), 51.4 (CH2; C-2), 37.9
(CH3; C-10), 20.8 (CH3; C-8), 17.8 ppm (CH3; C-9); IR (ATR): n˜ =3459
(bw), 2920 (bm), 2853 (bw), 1945 (bw), 1855 (bw), 1710 (bm), 1445 (s),
1265 (s), 763 cmÀ1 (m); FAB-MS: m/z (%): 509 (4) [MÀCl]+, 391 (20),
297 (20), 20ACTHNUGRTENUNG(100), 154 (48), 137 (52).
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
Copolymerization of NBE and COE: NBE (40 mg, 0.42 mmol) and COE
(2.310 g, 21 mmol) were dissolved in CH2Cl2 (7 mL). The initiator (2.1ꢄ
10À4 mmol) was added and 5 min later the reaction was stopped by the
addition of the ethyl vinyl ether (0.08 mg, 1.1 mmol). The polymer was
precipitated in methanol (50 mL) and was dried in vacuo.
692 mmolP, 3.6 equiv) and CuCl (57 mg, 0.576 mmol, 3.0 equiv) were sus-
pended in CH2Cl2 (2 mL) and the mixture was stirred for 16 h at room
temperature. Then, [RuCl
(PCy3){1-(2,4,6-trimethylphenyl)-3-phenyl-4,5-
(CHC6H5)] (155 mg, 0.192 mmol) and pyr-
dihydro-3H-imidazol-1-ylidene}AHCUTNGTRENNUNG
idine (5 mL) were added. The mixture turned to green within a few mi-
nutes. After 1 h, Et2O (5 mL) was added and the brown solid was re-
moved by filtration. Workup as described for 1 yielded a dark-green
amorphous solid (52.3 mg, 0.086 mmol, 45%). The compound was found
to be unstable in solution, therefore no 13C NMR spectrum is reported.
M. p. 2028C (decomp); 1H NMR (500.2 MHz, CD2Cl2,): d=18.83 (s, 1H;
H-14), 8.54 (d, J=7.7 Hz, 2H; H-19), 8.23 (d, J=5.0 Hz, 2H; H-11), 7.56
(t, J=7.7 Hz, 1H; H-21), 7.50–7.40 (m, 5H; H-12, H-16, H-18), 7.24 (t,
J=7.4 Hz, 1H; H-13), 7.06 (t, J=6.9 Hz, 1H; H-20), 6.99 (t, J=7.7 Hz,
1H; H-17), 6.75 (s, 2H; H-6), 4.35 (t, J=8.9 Hz, 2H; H-3), 3.99 (t, J=
9.6 Hz, 2H; H-2), 2.38 (s, 3H; H-8), 2.09 ppm (s, 6H; H-9); IR (ATR):
n˜ =3455 (bw), 2920 (bm), 2739 (w), 1945 (w), 1902 (bw), 1701 (m), 1600
(m), 1484 (s), 1445 (s), 1276 (s), 1218 (m), 758 cmÀ1 (m); FAB-MS: m/z
(%): 453 (60) [MÀ2ClÀPyridin]+, 297 (100), 154 (65).
Copolymerization of NBE and CPE: NBE (80 mg, 0.84 mmol) and CPE
(405 mg, 5.88 mmol) were dissolved in CH2Cl2 (7 mL). The initiator
(0.42 mmol) was added to this solution and 5 min later the reaction was
stopped by the addition of the ethyl vinyl ether (0.16 mg, 2.2 mmol). The
polymer was precipitated in 50 mL of methanol and dried in vacuo.
Poly(NBE-alt-COE)n: 1H NMR (600.25 MHz, CDCl3): d=5.37–5.27
(brm, 4H); 2.78 (brs, 1H); 2.45 (brs, 1H); 2.02–1.77 (brm, 7H); 1.29
(brs, 10H); 1.09–0.97 ppm (m, 1H); 13C NMR (150.93 MHz, CDCl3): d=
135.2, 135.0, 134.9, 134.7, 130.3 (polyACTHNUGTRNENUG(COE)), 129.9 (polyHCATUNGTREN(NGUN COE)), 128.6,
128.5, 43.5, 43.3, 42.1, 41.7, 41.3, 38.2, 38.0, 32.8, 32.6, 32.5, 32.3, 32.2,
29.9, 29.6, 29.2, 29.1, 27.5 ppm.
Poly(NBE-alt-CPE)n: 1H NMR (600.25 MHz, CDCl3): d=5.37–5.27 (br
m, 4H); 2.78 (brs, 1H); 2.44 (brs, 1H); 2.04–1.77 (brm, 7H); 1.44–1.33
(brs, 4H); 1.09–1.00 ppm (m, 1H); 13C NMR (150.93 MHz, CDCl3): d=
ACHTUNGTRENNUNG
135.4, 135.2, 133.9 (poly
ACHTUNGTRNE(UNGN NBE)), 133.0 (polyACHTUNRTGENG(NUN NBE)), 130.3 (polyACHTUNGTRENNUNG(CPE)),
A
ACHTUNGTRENNUNG
129.8 (poly(CPE)), 128.3, 128.2, 43.5, 43.3, 41.7, 41.3, 38.2, 38.0, 32.6,
AHCTUNGTRENNUNG
0.53 mmolP, 3.6 equiv) and CuCl (43.8 mg, 0.443 mmol, 3.0 equiv) were
suspended in CH2Cl2 (1.5 mL) and stirred for 16 h at room temperature.
32.3, 32.2, 32.0, 29.8, 29.5, 27.1, 26.9 ppm.
Hydrogenation of poly(NBE-alt-COE)n: The polymer (100 mg) was dis-
solved in hot xylene (10 mL), followed by the addition of 500 mg of p-tol-
uenesulfonylhydrazide. The mixture was stirred at 1208C for 2.5 h, then it
was filtered and the hot filtrate was poured into methanol (30 mL). The
precipitated polymer was recovered by centrifugation, washed several
times with methanol, and dried in vacuo to yield the hydrogenated poly-
mer. 1H NMR ([D4]1,2-dichlorobenzene): d=1.90 (brs, 1H), 1.76–1.69
(brs, 4H), 1.28 (brs, 20H), 1.16 (brs, 2H), 0.71–0.65 ppm (brs, 1H);
13C NMR ([D4]1,2-dichlorobenzene): d=41.6, 41.1, 37.5, 32.6, 30.8, 30.5,
29.4 ppm.
Then, [RuCl
dazol-1-ylidene}ACHTUNGTRENNUNG
(PCy3){1-(2,4,6-trimethylphenyl)-3-ethyl-4,5-dihydro-3H-imi-
(CHC6H5)][30] (112 mg, 0.15 mmol) and pyridine (4 mL)
were added. The color of the reaction mixture changed to green within a
few minutes. After 1 h, Et2O (4 mL) was added and the brown solid was
removed by filtration. All solvent was removed and suspended in a mix-
ture of Et2O and CH2Cl2 and filtered. Workup as described for 6 yielded
a bright-green amorphous solid (50.2 mg, 0.09 mmol, 61%). M.p. 2018C
(decomp); 1H NMR (600.25 MHz, CD2Cl2): d=18.72 (s, 1H; H-12), 8.41
(d, J=5.3 Hz, 2H; H-17), 7.55 (t, J=7.8 Hz, 1H; H-19), 7.40 (d, J=
7.8 Hz, 2H; H-14), 7.27 (t, J=6.8 Hz, 1H; H-16), 7.08 (t, J=7.8 Hz, 2H;
9456
www.chemeurj.org
ꢃ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 9451 – 9457

Alternating Ring-Opening Metathesis
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Received: February 11, 2009
Published online: August 7, 2009
Chem. Eur. J. 2009, 15, 9451 – 9457
ꢃ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9457