Supramolecular alternating block copolymers via metal coordination

Article abstract of DOI:10.1002/chem.200900573

A bimetallic ruthenium olefin metathesis initiator was synthesized and used to polymerize functionalized norbornenes, affording polymers that are living at both polymer chainends. Using this bis-ruthenium initiator strategy and combining it with functiona

Full text of DOI:10.1002/chem.200900573

FULL PAPER
DOI: 10.1002/chem.200900573
Supramolecular Alternating Block Copolymers via Metal Coordination
Si Kyung Yang,[a, b] Ashootosh V. Ambade,[a] and Marcus Weck*[a]
Abstract:
A
bimetallic ruthenium
veloped. The terminal functional group
incorporation was confirmed by
1H NMR spectroscopy analyses. The
telechelic polymers were self-assem-
bled into block copolymers by means
of metal coordination between corre-
sponding terminal recognition units.
The self-assembly process was moni-
olefin metathesis initiator was synthe-
sized and used to polymerize function-
alized norbornenes, affording polymers
that are living at both polymer chain-
ends. Using this bis-ruthenium initiator
strategy and combining it with func-
tional chain-terminators, highly-effi-
cient syntheses of either SCS-PdII
pincer- or pyridine-functionalized sym-
metrical telechelic polymers were de-
1
tored by H NMR spectroscopy reveal-
ing nearly quantitative functionaliza-
tion. The resulting supramolecular
block copolymers were further charac-
terized by viscometry and dynamic
light scattering.
Keywords: block copolymers · met-
al coordination · polymerization ·
ring-opening metathesis · rutheni-
um · supramolecular chemistry
Introduction
interactions in multiblock copolymers including hydrogen
bonding and metal coordination. For example, Sijbesma and
Binder have utilized complementary hydrogen bonding to
fabricate supramolecular multiblock copolymers based on
The introduction of noncovalent interactions between poly-
meric constituents[1] allows for the modular construction of
well-defined supramolecular polymeric assemblies including
supramolecular block copolymers, which are of considerable
interest owing to their promise for applications ranging
from electronics to medicine.[2] Supramolecular block co-
polymers can be categorized into diblock[3] and multiblock
copolymers assembled from monotelechelic and ditelechelic
polymers, respectively. Multiblock copolymers are of partic-
ular interest, since unprecedented polymeric blends with
tunable physical properties can be obtained easily by mixing
telechelic polyACTHNUTRGNEUNG
(ester)s and poly(isobutylene)s, respectively.[5]
Schubert has used terpyridine-based metal coordination to
generate diblock copolymers[6] and in combination with
Upy-based hydrogen bonding multiblock copolymers.[7]
Meijer and Zimmerman have employed quadruple hydrogen
bonds with high association constants (Ka ꢀ107 mÀ1) between
diamidonaphthyridine (DAN/Napy) and ureidopyrimidinone
(Upy) or ureidoguanosine (UG), respectively, to generate
supramolecular alternating block copolymers.[8]
Most synthetic strategies towards multiblock copolymers
rely on post-polymerization functionalization steps to intro-
duce the molecular recognition moiety resulting in often
non-quantitative conversions and requiring reaction condi-
tions that may be incompatible with other functionalities
along the polymer. The successful synthesis of telechelic
polymers with complementary binding motifs circumventing
the need for post-polymerization functionalization is a desir-
able prerequisite for the easy and high-yielding preparation
of well-defined supramolecular block copolymers. We sug-
gest that the ring-opening metathesis polymerization
(ROMP) of cyclic olefins in the presence of bifunctional
chain-transfer agents (CTA) is an efficient strategy for the
incorporation of supramolecular functionalities onto both
chain-ends of a polymer.[9] In 2005, we employed this meth-
odology to introduce hydrogen bonding and metal coordina-
two appropriately functionalized homopolymers.[4]
number of noncovalent interactions have been used as key
A
[a] S. K. Yang, Dr. A. V. Ambade, Prof. Dr. M. Weck
Department of Chemistry and Molecular Design Institute
New York University
100 Washington Square East
New York, NY 10003 (USA)
Fax : (+1)212-995-4895
E-mail: marcus.weck@nyu.edu
[b] S. K. Yang
School of Chemistry and Biochemistry
Georgia Institute of Technology
901 Atlantic Drive
Atlanta, GA 30332 (USA)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200900573.
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tion moieties at polymer chain-ends in situ and reported the
self-assembly of the resulting telechelic polymers into supra-
molecular multiblock copolymers.[10] Although highly advan-
tageous over traditional post-polymerization functionaliza-
tion, owing to complete incorporation of almost any termi-
nal recognition unit in situ, the ROMP-CTA strategy limits
full control over the obtained telechelic polymer properties
because it relies on the non-living polymerization of func-
tionalized cyclooctenes. Herein, we report the synthesis of
symmetrically end-functionalized polymers in a single step
by means of ROMP using a bimetallic ruthenium initiator
and functional chain-terminators (CTs). The combination of
a living/controlled polymerization with metal-coordination-
based self-assembly allows for the formation of well-defined
supramolecular alternating block copolymers (Figure 1).
degree of polymerization, and polydispersity. Metal coordi-
nation between SCS-PdII pincer complex-containing poly-
mers and ones containing pyridyl end groups should lead to
À
À
the self-assembly of A A and B B macromonomers with
tunable block length by the controlled addition of the acti-
vating agent AgBF4. Furthermore, use of differently substi-
À
À
tuted norbornene monomers for the A A and B B macro-
monomers allows for the preparation of supramolecular al-
ternating block copolymers.
Results and Discussion
Synthesis of bis-ruthenium initiator 4: A bis-alkylidene ru-
A
ACHTUNGTRENnNUGN ium olefin metathesis initiator was used to afford poly-
AHCTUNGTRENNUNG
thereby allowing for complete incorporation of terminal rec-
ognition units. The synthesis of the bimetallic ruthenium ini-
tiator 4 is outlined in Scheme 1. 6-(4-Vinylphenoxy) hexano-
Scheme 1. Synthesis of bis-ruthenium initiator 4.
ic acid 1 was esterified with hydroquinone using N-(3-dime-
thylaminopropyl)-Nꢁ-ethylcarbodiimide hydrochloride and
4-dimethylaminopyridine to afford bis-styrene 2. Initiator 4
was synthesized by the carbene exchange of 3 with 2 in di-
Figure 1. Schematic representation of the synthetic strategy towards
supramolecular alternating block copolymers.
1
Research design: Our strategy is based on the self-assembly
chloromethane. H NMR analysis indicated 95% conversion
À
À
of A A and B B bifunctional macromonomers by means of
metal coordination. The macromonomers are telechelic
polymers bearing a palladated sulfur-carbon-sulfur (SCS)
pincer complex or a pyridyl end group, respectively, at both
chain-ends. The telechelic polymers are being synthesized
by ROMP using a bis-ruthenium initiator designed to be
living and tolerant to a broad range of functionalities,[11] ter-
minated with functional CTs containing metal coordination
sites resulting in the formation of perfect telechelic poly-
mers. For our study, we employ the coordination of Pd-
pincer complexes to functionalized pyridines as the nonco-
valent interaction. This metal coordination step is unsym-
metrical, highly directional and avoids the problem of ho-
modimerization unlike hydrogen-bonded systems.[12] Fur-
thermore, this interaction has been used extensively in side-
chain supramolecular polymers and can be tuned easily.[12]
The combination of a bis-ruthenium initiator with function-
alized CTs is designed to afford symmetrical telechelic poly-
mers possessing desired recognition motifs with full control
over basic polymer properties, such as molecular weight,
to 4 as seen by a shift of the carbene signals to d=19.4 ppm
in CD2Cl2. After purification by column chromatography, 4
was isolated in 72% yield.
Homopolymerization using initiator 4: We investigated the
polymerization behavior of norbornene octyl ester 10. Mo-
nomer 10 was polymerized quantitatively using 2.5 mol% of
4 within 10 min at room temperature. Full initiation was ob-
served by a complete shift of the carbene signal from d=
19.4 ppm for 4 to 18.6 ppm (for the fully initiated species) in
1
the H NMR spectrum. We carried out a series of homopo-
lymerizations with monomer-to-initiator ratios ([M]/[I])
ranging from 40:1 to 200:1. A linear relationship between
Mn and [M]/[I] was found for polymers 12a–e (Figure 2) in-
dicating the controlled nature of the polymerization of 10
using 4. The gel-permeation chromatography (GPC) data of
12a–e are summarized in Table 1. The living nature of the
polymerization was further confirmed by the synthesis of a
homoblock copolymer. First, a 40 mer was synthesized using
4, which was then used as a macroinitiator for the polymeri-
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Supramolecular Alternating Block Copolymers
FULL PAPER
Scheme 2. Synthesis of CTs 8 and 9.
Figure 2. Plot of Mn vs. monomer 10/initiator 4 ratios for polymer 12a–e.
Table 1. Polymer characterization data (GPC) for 12a–e.[a]
6-Chloro-1-hexenyl methyl ether 5 was reacted with SCS-
PdII pincer precursor 6 or 4-hydroxypyridine 7 by using Wil-
liamson etherification to afford CTs 8 and 9, respectively.
Polymer
[M]/[I]
Mn
Mw
PDI
Preparation and characterization of telechelic polymers:
ROMP of norbornene octyl ester 10 (for 13 and 14) or nor-
bornene methyltriglycol ester 11 (for 15) was carried out
with 2.5 mol% of 4 in CH2Cl2 followed by the addition of
an excess of either 8 to obtain SCS-PdII pincer-functional-
ized telechelic polymer 13 or 9 to yield pyridine-functional-
ized telechelic polymers 14 and 15 (Scheme 3). Complete
12a
12b
12c
12d
12e
40
80
120
160
200
13000
34000
55000
73000
96000
20000
43000
68000
88000
114000
1.56
1.27
1.23
1.20
1.19
[a] Mn =number-average molecular weight; Mw =weight-average molecu-
lar weight; PDI=polydispersity index.
zation of a 1000 mer. The GPC traces of the homoblock co-
polymers were unimodal. Furthermore, we observed a com-
plete shift to high molecular weights without traces of termi-
nated low molecular weight polymer (Figure 3). The new
bis-ruthenium initiator 4 is thus not only active toward
ROMP of norbornenes, but also living at both chain-ends.
Scheme 3. Synthesis of telechelic polymers 12–15.
Figure 3. GPC traces of homoblock copolymers obtained from 10 by
using 4. Dashed line: polymer after complete conversion of the monomer
([M]/[I]=40:1, Mn =13000, PDI=1.56). Solid line: polymer after stand-
ing for 2 h and then continued polymerization of the additional monomer
([M]/[I]=1000:1, Mn =258000, PDI=1.25).
termination of the ROMP was observed by the disappear-
ance of the polymeric carbene signals in the H NMR spec-
tra. Incorporation of each functionality at both the chain-
ends of each telechelic polymer was confirmed by H NMR
1
1
Synthesis of CTs: We can install any desired functionality in
living ROMP through the use of functionalized vinyl ether
derivatives that serve as chain-terminators, that is, they ter-
minate the polymerization by incorporating the desired
functionality at the polymer chain-end.[13] To install supra-
molecular functionalities for metal coordination at both
chain-ends of the polymer, SCS-PdII pincer- and pyridine-
based CTs were synthesized as outlined in Scheme 2.
analysis (Supporting Information). The molecular weights
and PDIs of all the telechelic polymers were determined by
GPC analyses revealing monomodal distributions (Mn =
14000, PDI=1.62 for 13, Mn =13000, PDI=1.57 for 14, and
Mn =18000, PDI=1.51 for 15). Thus our methodology
allows for full control over end group functionalization com-
pared to the CTA-based ROMP in the preparation of sym-
metrical ditelechelic polymers.[8b,10]
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M. Weck et al.
Self-assembly: We also investigated the formation of supra-
molecular multiblock copolymers by means of metal coordi-
nation using telechelic polymers 13–15. AgBF4 is known to
remove the Cl ligand on pincer complexes generating a cat-
ionic Pd species that can coordinate pyridyl units resulting
in the formation of new pincer complexes.[12] We have previ-
ously demonstrated the functionalization of side-chain and
main-chain supramolecular polymers containing Pd-pincer
complexes.[10,12] We envisaged that by controlling the ratio of
AgBF4 in the mixture of complementary telechelic polymers
to activated Pd-pincer moieties we can control the length of
supramolecular block copolymers formed by metal-coordi-
nation.
The preparation of supramolecular homoblock copoly-
mers (SHBCs) 13:14(n) and supramolecular alternating
block copolymers (SABCs) 13:15(n) is outlined in
Scheme 4. SABCs 13:15(n) are based on two chemically dif-
ferent blocks, octyl- and methyltriglycol-substituted poly-
ACHTUNGTRENNUNG(norbornene)s, which may result in phase separation of indi-
vidual blocks whereas the constituent blocks in SHBCs
13:14(n) should be completely miscible. 13:14(n) and
13:15(n) were synthesized by the addition of n equivalents
(n=1, 2, or 3) of AgBF4 to a solution of 1 equivalent of 13
and 1 equivalent of 14 or 15, respectively. The formation of
supramolecular block copolymers was characterized by
1
Figure 4. 1H NMR spectra depicting metal coordination of 13a with 14a
in CD2Cl2. A) Telechelic polymer 13a; B) telechelic polymer 14a; C) a
mixture of telechelic polymers 13a and 14a at a 1:1 ratio: a and b=a-
and b-pyridyl protons, respectively; D) self-assembled telechelic polymer
13a:14a after addition of AgBF4: aꢁ and b’=a- and b-pyridyl protons on
pyridyl pincer complex, respectively.
using H NMR spectroscopy, Ubbelohde viscometry, and dy-
namic light scattering (DLS).
Telechelic polymers 13a and 14a were employed for the
metal coordination because shorter 20 mers allow for easy
1H NMR spectroscopy characterization. SHBC 13a:14a was
prepared by the addition of 3 equivalents of AgBF4 to a so-
lution of 1 equivalent each of 13a and 14a in dichlorome-
thane. The formation of SHBC 13a:14a was confirmed from
ly. A mixture of 13a and 14a at a 1:1 ratio is shown in Fig-
ure 4C; no shifts in the 1H NMR spectra are observed.
1
1
1
characteristic shifts in the H NMR spectrum. The H NMR
Upon addition of AgBF4, the resulting H NMR spectrum of
spectra of 13a and 14a is shown in Figure 4A,B, respective-
SHBC 13a:14a shows the characteristic downfield shifts of
Scheme 4. Self-assembly of telechelic polymers 13–15.
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Supramolecular Alternating Block Copolymers
FULL PAPER
the a- and b-pyridyl signals from d=7.23 (a) and 6.23 ppm
(b) to 7.96 (a’) and 7.29 ppm (b’), respectively. In addition
to the diagnostic shifts of the pyridyl signals, the aromatic
proton signals on the pincer complex broaden and shift
slightly from d=7.79, 7.36, and 6.63 ppm to 7.74, 7.44, and
6.58 ppm, respectively (Figure 4D). These characteristic
shifts indicate quantitative metal coordination between 13a
and 14a, resulting in the formation of SHBC 13a:14a.
Viscometry is a simple yet powerful technique to demon-
strate the formation of supramolecular multiblock poly-
mers.[8] The solution properties of SHBCs 13:14(n) and
SABCs 13:15(n) in dichloromethane were examined by visc-
ometry, and the results are shown in Figure 5. The specific
(Supporting information) supporting our hypothesis that the
increase in hsp values is the direct result of the formation of
supramolecular alternating block copolymers.
To examine the bulk structure of SHBCs 13:14(n) and
SABCs 13:15(n) in more detail, the hydrodynamic radii (Rh)
of these materials were determined by DLS (Table 2). The
Table 2. Hydrodynamic radius (Rh) of SHBCs 13:14(n) and SABCs
13:15(n) measured by DLS at 34 gLÀ1 (258C, CH2Cl2).
SHBC
Rh [nm]
SABC
Rh [nm]
13:14(1)
13:14(2)
13:14(3)
35.8
77.5
79.4
13:15(1)
13:15(2)
13:15(3)
66.8
119.3
142.0
particle size for both classes of materials increases with in-
creased equivalence of AgBF4 from 1 to 2 to 3, indicating
that the polymeric block length can be tuned by the amount
of AgBF4 added. Also, a significant increase in size (almost
two times) from 1 equivalent to 2 equivalents of AgBF4 in-
dicates the formation of supramolecular block copolymers.
The fact that larger aggregates were observed in SABCs
13:15(n) compared to SHBCs 13:14(n), suggests that the
phase separation between the blocks results in increased hy-
drodynamic volume of SABCs with negligible effect on the
metal coordination. Thus, the DLS data are consistent with
the viscometry results strongly suggesting the formation of
supramolecular multiblock copolymers.
Conclusions
We have developed a novel methodology for the synthesis
of symmetrical telechelic polymers bearing terminal recogni-
tion motifs. A bimetallic ruthenium initiator was synthesized
in a straight forward fashion via carbene exchange and used
for the incorporation of supramolecular functionalities onto
polymer chain-ends. The hydroquinone phenyl ring in the
ruthenium initiator offers an opportunity to introduce stimu-
li-responsive functionalities in the middle of the polymeric
backbone. Such functionalities could render these block co-
polymers pH cleavable or light responsive. Further, termina-
tion of the living ROMP with functionalized CTs afforded
the symmetrical telechelic polymers in a single step. Self-as-
sembly of the telechelic polymers to afford block copoly-
mers was achieved by metal coordination between recogni-
tion units. The formation of supramolecular block copoly-
Figure 5. Specific viscosity (hsp) at 258C in CH2Cl2. A) Telechelic poly-
mers 13 and 14, and SHBCs 13:14(n) after addition of n equiv of AgBF4;
B) telechelic polymers 13 and 15, and SABCs 13:15(n) after addition of
n equiv of AgBF4.
viscosity (hsp) of both SHBCs 13:14(n) and SABCs 13:15(n)
increases as the equivalence of AgBF4 increases from 1 to 2
to 3. Additionally, the relatively slight increases from SHBC
13:14(2) and SABC 13:15(2) to SHBC 13:14(3) and SABC
13:15(3), respectively, represent that 2 equivalents of AgBF4
are sufficient for efficient metal coordination leading to the
formation of supramolecular block copolymers. Compared
with SHBCs 13:14(n), SABCs 13:15(n) show much larger hsp
values probably due to, at least partial, phase separation of
the two different blocks. As a control experiment, we also
carried out viscometry experiments on a 1:1 mixture of pyri-
dine-functionalized telechelic polymer 15 and unfunctional-
ized polymer 12a before and after the addition of AgBF4.
The hsp values after addition of AgBF4 were unchanged
1
mers was substantiated using H NMR spectroscopy, viscom-
etry, and DLS. We have also demonstrated that the bulk
properties of the supramolecular block copolymers can be
tuned by the amount of AgBF4 added.
Experimental Section
General Methods. All reagents were purchased either from Acros Organ-
ics, Alfa Aesar, or Sigma–Aldrich and used without further purification
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M. Weck et al.
unless otherwise noted. CH2Cl2 was dried by means of passage through
copper oxide and alumina columns. NMR spectra were recorded by using
a Bruker AV-400 (1H: 400.1 MHz; 13C: 100.6 MHz) spectrometer. Chemi-
cal shifts are reported in ppm and referenced to the corresponding resid-
ual nuclei in deuterated solvents. Elemental analyses were performed by
using a Carlo Erba 1108 elemental analyzer. Mass spectral analyses were
provided by the Georgia Tech Mass Spectrometry Facility using a VG-
70 se spectrometer. Viscosity was measured in dichloromethane using a
Cannon semi-micro Ubbelohde viscometer (9722-G59) at 258C. The hy-
drodynamic radius (Rh) was measured by using a Protein Solutions DLS
(DynaPro) at 258C and analyzed with a Dynamics V6 software. Gel-per-
meation chromatography (GPC) analyses were carried out by using a
Shimadzu pump coupled to a Shimadzu UV detector with tetrahydrofur-
an (THF) as the eluent and a flow rate of 1 mLminÀ1 on an American
Polymer Standards column set (100, 1000, 100 000 ꢂ, linear mixed bed).
CT 9: Potassium carbonate (1.4 g, 10 mmol) was added to a solution of 6-
chloro-1-hexenyl methyl ether 5 (0.55 g, 3.4 mmol) and 4-hydroxypyridine
7 (0.35 g, 3.7 mmol) in anhydrous DMF (10 mL). After the mixture was
stirred at 908C for 12 h, the solvent was removed under reduced pressure.
Water (20 mL) was added and the mixture was extracted with CH2Cl2
(3ꢃ20 mL). The combined organic layers were washed with water, dried
over MgSO4, filtered, and concentrated under reduced pressure. The
crude product was purified by column chromatography (dichlorome-
thane/methanol, 15:1) (0.45 g, 60%). 1H NMR (CDCl3): d=7.25 (d, J=
8.0 Hz, 2H), 6.36 (d, J=8.0 Hz, 2H), 6.26 (d, J=12.0 Hz, 0.6H), 5.86 (d,
J=6.4 Hz, 0.4H), 4.65 (td, J=12.0, 7.2 Hz, 0.6H), 4.33 (dd, J=7.0,
6.4 Hz, 0.4H), 3.73 (t, J=7.2 Hz, 2H), 3.55 (s, 1.2H), 3.48 (s, 1.8H), 2.04
(m, 0.8H), 1.91 (m, 1.2H), 1.75 (m, 2H), 1.35 ppm (m, 4H); 13C NMR
(CDCl3): d=147.5, 146.6, 139.5, 139.5, 118.8, 105.8, 102.2, 59.5, 57.0, 56.9,
56.0, 30.7, 30.5, 30.1, 28.9, 27.3, 25.5, 25.4, 23.3 ppm; EIMS: m/z: calcd
for C13H19NO2, 221.1416; found, 221.1413.
All GPCs were calibrated using polyACTHNUTRGENUGN(styrene) standards and carried out
at 258C. Mw, Mn, and PDI represent the weight-average molecular
weight, number-average molecular weight, and polydispersity index, re-
spectively. 6-(4-Vinylphenoxy) hexanoic acid 1,[14] 6-chloro-1-hexenyl
methyl ether 5,[13b] SCS-PdII pincer precursor 6,[15] and monomers 10 and
11[16] were synthesized according to the previously published procedures.
General polymerization procedure: The desired amount of monomer was
dissolved in anhydrous, degassed CH2Cl2 under an argon atmosphere.
Bis-ruthenium initiator 4 was added as a solution in the corresponding
solvent. Upon complete polymerization, ethyl vinyl ether (for 12), CT 8
(for 13), or CT 9 (for 14 and 15) was added to quench the polymeri-
zation. The polymer was isolated and purified by repeated precipitations
into MeOH (for 12--14) or diethyl ether (for 15).
Bis-styrene 2: To
a solution of 6-(4-vinylphenoxy) hexanoic acid 1
(0.59 g, 2.5 mmol) and hydroquinone (0.13 g, 1.2 mmol) in anhydrous
Self-assembly studies: Polymer 13 was dissolved in CD2Cl2 and polymer
14 or 15 was added until a 1:1 equivalency was reached in relation to the
Pd-pincer complexes as determined by 1H NMR spectroscopy. The de-
sired amount of AgBF4 dissolved in MeNO2 was added to the reaction
mixture. After stirring at 258C for 4 h, the precipitated AgCl(s) was re-
moved by centrifugation. The supernatant liquid was filtered through a
plug of Celite and subsequently through a 0.2 mm syringe filter. The sol-
vent was removed in vacuo to yield the supramolecular block
copolymers.
DMF (8 mL) were added N-(3-dimethylaminopropyl)-Nꢁ-ethylcarbodi-
ACHTUNGTRENNUNGimide hydrochloride (0.55 g, 2.9 mmol) and 4-dimethylaminopyridine
(17 mg, 0.14 mmol). After the mixture was stirred at 258C for 6 h, the
solvent was removed under reduced pressure. Water (30 mL) was added
and the mixture was extracted with CH2Cl2 (3ꢃ30 mL). The combined
organic layers were washed with water, dried over MgSO4, filtered, and
concentrated under reduced pressure to give a yellow oil that was further
purified by column chromatography on silica gel in dichloromethane to
yield 0.59 g of a white solid in 96% yield. 1H NMR (CDCl3): d=7.34 (d,
J=8.8 Hz, 4H), 7.09 (s, 4H), 6.85 (d, J=8.8 Hz, 4H), 6.66 (dd, J=17.6,
11.0 Hz, 2H), 5.61 (d, J=17.6 Hz, 2H), 5.12 (d, J=11.0 Hz, 2H), 3.99 (t,
J=6.4 Hz, 4H), 2.60 (t, J=7.6 Hz, 4H), 1.83 (m, 8H), 1.61 ppm (m, 4H);
13C NMR (CDCl3): d=171.9, 158.8, 148.1, 136.3, 130.4, 127.4, 122.4,
114.5, 111.5, 67.6, 34.2, 28.9, 25.6, 24.6 ppm; elemental anal (%) calcd for
C34H38O6: C 75.25, H 7.06; found: C 74.81, H 7.03; ESI-MS: m/z: calcd
for C34H38O6, 542.2688; found, 543.2741 [M+H]+.
Acknowledgements
We thank the National Science Foundation (CHE-0239385) and New
York University for financial support of this research. This work was sup-
ported partially by the MRSEC Program of the National Science Foun-
dation under Award Number DMR-0820341. MW gratefully acknowledg-
es a Camille Dreyfus Teacher/Scholar Award and an Alfred P. Sloan Fel-
lowship.
Bis-ruthenium initiator 4: Bis-styrene 2 (0.10 g, 0.18 mmol) and Grubbsꢁ
first-generation initiator 3 (0.60 g, 0.73 mmol) were dissolved in anhy-
drous, degassed CH2Cl2 (10 mL) under an argon atmosphere and stirred
at 258C for 1 h. The solvent was removed under reduced pressure and
the crude product was purified by column chromatography (hexanes/
EtOAc, 4:1) to yield 0.26 g of a purple solid in 72% yield. 1H NMR
(CD2Cl2): d=19.44 (s, 2H), 8.41 (br, 4H), 7.07 (s, 4H), 6.79 (d, J=
8.8 Hz, 4H), 4.01 (t, J=6.4 Hz, 4H), 2.58 (m, 16H), 1.94–1.12 ppm (m,
132H). 13C NMR (CD2Cl2): d=290.6, 172.3, 160.0, 148.6, 148.2, 134.3,
122.8, 114.4, 68.3, 34.5, 32.4, 30.0, 29.2, 28.3, 27.0, 25.9, 25.0 ppm; elemen-
tal anal (%) calcd for C104H166O6Cl4P4Ru2: C 63.08, H 8.45; found: C
62.53, H 8.42.
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CT 8. To
a solution of 6-chloro-1-hexenyl methyl ether 5 (0.20 g,
1.2 mmol) and SCS-PdII pincer precursor 6 (0.60 g, 1.3 mmol) in anhy-
drous DMF (10 mL) was added potassium carbonate (0.52 g, 3.8 mmol).
After the mixture was stirred at 908C for 12 h, the solvent was removed
under reduced pressure. Water (20 mL) was added and the mixture was
extracted with CH2Cl2 (3ꢃ20 mL). The combined organic layers were
washed with water, dried over MgSO4, filtered, and concentrated under
reduced pressure. The crude product was purified by column chromatog-
raphy (hexanes/EtOAc, 2:1) (0.38 g, 50%). 1H NMR (CDCl3): d=7.79
(dd, J=7.2, 2.0 Hz, 4H), 7.36 (m, 6H), 6.63 (s, 2H), 6.28 (d, J=12.4 Hz,
0.6H), 5.87 (d, J=6.4 Hz, 0.4H), 4.70 (td, J=12.4, 7.6 Hz, 0.6H), 4.64
(br, 4H), 4.33 (dd, J=7.2, 6.4 Hz, 0.4H), 3.88 (t, J=6.4 Hz, 2H), 3.57 (s,
1.2H), 3.50 (s, 1.8H), 2.08 (m, 0.8H), 1.94 (m, 1.2H), 1.75 (m, 2H),
1.41 ppm (m, 4H); 13C NMR (CDCl3): d=226.8, 157.2, 149.8, 147.2,
146.2, 132.8, 131.7, 129.8, 129.6, 108.0, 106.6, 102.8, 68.1, 59.5, 55.9, 54.5,
30.4, 29.5, 29.2, 27.6, 25.7, 25.4, 23.8 ppm; ESI-MS: m/z: calcd for
C28H31ClO2PdS2, 604.0489; found, 569.0800 [MÀCl]+.
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6610
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Chem. Eur. J. 2009, 15, 6605 – 6611

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Received: March 3, 2009
Published online: June 4, 2009
Chem. Eur. J. 2009, 15, 6605 – 6611
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6611