Self-assembly with block copolymers through metal coordination of SCS-PdII pincer complexes and pseudorotaxane formation

Article abstract of DOI:10.1002/chem.200501028

Poly(norbornene)-based block copolymers containing side chains of palladated pincer complexes/dibenzo[24]crown-8 or palladated pincer complexes/dibenzylammonium salts were synthesized. Noncovalent functionalization was accomplished with their corresponding recognition units through simple 1:1 addition with association constants (K_a) greater than 10 ⁵M^-1. The self-assembly processes were monitored by using both ¹H NMR spectroscopy and isothermal titration calorimetry. In all cases, we found that the self-assembly of the recognition units along each polymer block does not preclude the self-assembly processes along the other block.

Full text of DOI:10.1002/chem.200501028

FULL PAPER
DOI: 10.1002/chem.200501028
Self-Assembly with Block Copolymers through Metal Coordination of
SCS–PdII PincerComplexes and
Pseudorotaxane Formation
AHCTREUNG
Clinton R. South,[a] Mary Nell Higley,[a] Ken C.-F. Leung,[b] Daniela Lanari,[b]
Alshakim Nelson,[c] Robert H. Grubbs,*[c] J. Fraser Stoddart,*[b] and Marcus Weck*[a]
Abstract: Poly(norbornene)-based block copolymers containing side chains of pal-
ladated pincer complexes/dibenzo[24]crown-8 or palladated pincer complexes/di-
benzylammonium salts were synthesized. Noncovalent functionalization was ac-
Keywords: copolymerization
·
·
complished with their corresponding recognition units through simple 1:1 addition
crown compounds
· palladium
with association constants (Ka) greater than 105 mÀ1. The self-assembly processes
pincer complexes · supramolecular
chemistry
1
were monitored by using both H NMR spectroscopy and isothermal titration calo-
rimetry. In all cases, we found that the self-assembly of the recognition units along
each polymer block does not preclude the self-assembly processes along the other
block.
Introduction
tion techniques can be applied to a variety of applications.
Nevertheless, these functionalization strategies should be
tailored to a specific application. For example, a drug deliv-
ery application may require functionalities with weak nonco-
valent attachments to facilitate effective drug release in re-
sponse to a stimulus at a target site.[6] In contrast, materials
for use in electro-optics require strong and dense functional-
ization capable of withstanding thousands of working
hours.[7]
As the field of materials science advances, the demand for
highly functional and versatile materials will soar. Materials
for applications such as organic light-emitting diodes
(OLEDs), photorefractives, solar cells, drug delivery vehi-
cles, sensors, and molecular machines will require fast and
cost effective synthesis and optimization.[1–5] To meet these
demands, future synthetic strategies to produce polymeric
materials should be generic, such that similar functionaliza-
Along the evolutionary pathway, nature has created a
system with incredible fidelity in which a myriad of biomate-
rials can be produced from noncovalent-mediated synthe-
sis.[8] Borrowing from this approach, our system uses similar
noncovalent forces to create functionalized copolymers.
Noncovalent functionalities, such as hydrogen bonding and
metal coordination, have several advantages over traditional
covalent functionalities; such interactions are spontaneous,
allowing for fast functionalization steps. Furthermore, they
are reversible, allowing for “on–off” functionalization. We
have previously reported a polymeric system in which a
weak interaction (hydrogen bonding) and a strong interac-
tion (metal coordination) could be used to functionalize co-
polymers in an orthogonal manner, developing the first gen-
eration of so-called “universal polymer backbones” (UPBs),
that is, polymer backbones that can be functionalized with
multiple small molecules by using noncovalent chemistry
thereby creating libraries of materials.[3,8–10] Herein, we
report the next generation of UPBs by functionalizing an ar-
chitecturally controlled block copolymer with two strong
[a] C. R. South, M. N. Higley, Prof. M. Weck
School of Chemistry and Biochemistry
Georgia Institute of Technology, Atlanta
Georgia 30332–0400 (USA)
Fax : (+1)404-894-7452
E-mail: marcus.weck@chemistry.gatech.edu
[b] Dr. K. C.-F. Leung, Dr. D. Lanari, Prof. J. F. Stoddart
California NanoSystems Institute &
Department of Chemistry and Biochemistry
University of California, Los Angeles, 405 Hilgard Avenue
Los Angeles, California 90095 (USA)
Fax : (+1)310-206-1843
E-mail: stoddart@chem.ucla.edu
[c] Dr. A. Nelson, Prof. R. H. Grubbs
The Arnold and Mabel Beckman Laboratory of Chemical Synthesis
California Institute of Technology, 1200 East California Boulevard
Pasadena, California 91125 (USA)
Fax : (+1)626-564-9297
E-mail: rhg@caltech.edu
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
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noncovalent functionalities based on 1) pseudorotaxane hy-
drogen bonding and 2) metal coordination between palla-
dated sulfur–carbon–sulfur (SCS) pincer complexes and pyr-
idines. This next generation of UPBs possesses unique ad-
vantages. First, the copolymer architecture is defined prior
to functionalization, allowing for the introduction of a varie-
ty of functional groups that might otherwise hinder architec-
tural control if introduced prior to polymerization. Second,
this generation of UPBs rivals covalently functionalized co-
polymers by utilizing two recognition units with high bind-
ing affinities for their corresponding complementary recog-
nition units (small molecules); this fact ensures the produc-
tion of a densely functionalized and monodisperse material.
Finally, our new system retains all the benefits of noncova-
lent modification, including reversibility, self-healing, and
ease of functionalization.
In our search for the next generation of UPBs, depicted
in Figure 1, we sought two important design requirements:
Scheme 1. The two types of molecular recognition pairs employed in this
study.
ing in a myriad of supramolecular structures[44–50] and the
evolution[51] of a “molecular meccano kit”. The driving force
for the formation of threadlike structures from dialkylam-
monium cations and crown ether macrocyles is the forma-
Figure 1. Schematic representation of the next generation of universal
polymer backbones.
+
tion of strong hydrogen bonds between the acidic NH2 pro-
tons and the oxygen atoms in the ring of the crown ether
À
À
macrocyle. In addition to strong N H···O and C H···O hy-
drogen bonding, p–p stacking interactions and electrostatic
forces also contribute to the strong affinity between dialkyl-
1) architectural control of the polymer scaffold, and 2) dis-
tinct recognition partners with sufficiently high noncovalent
binding strengths.
ammonium cations and DB24C8 macrocycles. Such interac-
Block copolymers, which have been used widely in appli-
cations ranging from drug delivery to electro-optics, form
our basis for the architectural control.[11] We achieve such ar-
chitectural control by the use of ring-opening metathesis
polymerization (ROMP)[10,12–19]
tions are highly solvent dependent. In apolar solvents, high
association constants (Ka) are attainable for the dialkylam-
monium and DB24C8 system (vide supra).
The metal coordination system we employ is based on a
SCS–PdII pincer complex 4 which binds pyridines, nitriles,
and phosphines with high efficiencies.[10,52,53] The palladium
pincer complex was chosen because of its high stability and
the ability of the palladium species to undergo substitution
with a variety of ligands.[52] Pyridine 5 was chosen as the
ligand for the pincer complex, because it can be easily dis-
placed by a stronger coordinating phosphorous ligand.[53]
Moreover, a pincer-pyridine self-assembly process can be
characterized easily by using standard methods such as
1H NMR spectroscopy.[9]
to produce block copolymers.
ROMP with the ruthenium–al-
kylidene initiator 1 not only
provides the basis of our archi-
tectural control, but 1 is also
highly functional group toler-
ant.[20–23]
The second requirement is met with the use of two strong
noncovalent interactions involving both metal coordination
and hydrogen bonding as shown in Scheme 1. The hydro-
gen-bonding system is based on the threading of a dialkyl-
A
Results and Discussion
macrocyle 3 to form a pseudorotaxane.[24–42] Since the dis-
covery of rotaxane formation resulting from the threading
of an ammonium cation into a crown ether macrocycle in
1995,[43] a number of interactions between ammonium cat-
Monomer synthesis and homopolymerization reactions: Iso-
merically pure exo-norbornene esters often result in short
polymerization times as well as living polymer growth.[10]
Thus, exo-norbornene acid 6[54–56] was chosen as the starting
A
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Supramolecular Chemistry
FULL PAPER
point in our synthetic pathway. The addition of an alkyl
spacer onto 6 was accomplished by the dicyclohexyl carbo-
diimide/4-dimethylaminopyridine (DCC/DMAP) esterifica-
tion with 1,10-decanediol to yield 7. The exo-decanol 7 was
then oxidized to the corresponding carboxylic acid 8 using
pyridinium dichromate (PDC) in dimethylformamide
(DMF). Compound 8 was functionalized with the Boc-pro-
tected dialkyl amine 9 (Boc=tert-butyloxycarbonyl)[57] or
the DB24C8 derivative 10[49] by using DCC/DMAP esterifi-
cation to afford 11 and 12, respectively. Monomer 12 was
polymerized by using initiator 1 to yield the resulting poly-
meric DB24C8 crown ethers 14a–e. Likewise, monomer 11
was polymerized to give the polymeric Boc protected
amines 13a–e. The synthetic pathway is outlined in
Scheme 2.
Monomers 11 and 12 were found to polymerize in a living
fashion. The absence of chain-transfer and chain-termina-
tion in addition to controlled molecular weights are criteria
for living polymerizations.[58,59] A linear relationship be-
tween Mn and [M]:[I] (M=monomer, I=initiator) was es-
tablished for 11 and 12 (Figure 2). Such a linear relationship
indicates the living nature of the polymerization for mono-
mers 11 and 12. The corresponding gel-permeation chroma-
tography (GPC) data are summarized in Table 1.
We also investigated whether the unprotected amine 11
(11a), could be polymerized in a living fashion. For these
experiments, 11 was deprotected by using trifluoroacetic
acid (TFA), and the resulting 11a was polymerized with 1.
Unfortunately, the polymerization behavior of 11a was un-
controlled, and the formation of high molecular weight poly-
Scheme 2. Synthesis of molecular recognition monomers and subsequent ROMP. Reagents and conditions: a) decane-1,10-diol, DCC/DMAP, CH2Cl2,
reflux, 12 h, 60%; b) PDC, DMF, 48 h, 80%; c) DCC/DMAP, CH2Cl2, reflux, 12 h, 90%; d) 1, CH2Cl2, 8 h, 100%; e) TFA, CH2Cl2, 3 h; f) NH4PF6,
CH2Cl2, 3 h, 92% from 11.
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M. Weck, R. H. Grubbs, J. F. Stoddart et al.
have low polydispersities demonstrating the living character
of the polymerization. Table 1 summarizes the GPC results.
Self-assembly: The aim of this study is to establish the com-
plementarities of polymeric systems bearing the strong non-
covalent recognition motifs 2, 3, and 4. We initially estab-
lished that a polyvalent scaffold does not interfere with the
self-assembly of homopolymers 14c and 15 with their corre-
1
sponding small molecule receptors. Using H NMR spectro-
scopic studies, we were able to prove that both polymers
14c and 15 can be quantitatively functionalized. Figure 3
1
shows the H NMR spectra for the self-assembly of polymer
Figure 2. Plot of Mn versus monomer/initiator ratios for polymers 13 (&)
14c with the small molecule 2. Upon the addition of the di-
*
and 14 ( ).
benzylammonium cation 2 (in the form of 2
[BArF]À) to ho-
G
mopolymer 14c, the fully complexed polymer (2)n·14c
forms. The ammonium benzylic signal moves to d=4.5 ppm
from its original position at d=4.2 ppm (spectra A and C).
In addition, upon the threading of 2 into polymer 14c, the
crown ether signals move from d=4.1, 3.9, and 3.8 ppm to
d=4.0, 3.6, and 3.2 ppm, respectively, indicating the quanti-
tative complexation of the homopolymer (spectrum C).
Table 1. Polymer characterization data (GPC) for 13, 14, 18, and 19.[a]
Polymer
[M]:[I]
Mn [10À3
]
Mw [10À3
]
PDI
13a
13b
13c
13d
13e
14a
14b
14c
14d
14e
18
10
20
50
80
100
10
20
50
80
100
50
11.5
16.0
38.2
59.2
70.3
9.3
11.6
30.0
44.8
57.4
29.5
66.0
14.1
18.6
41.4
68.6
93.3
13.1
17.4
61.7
83.7
138.0
35.6
75.1
1.23
1.16
1.08
1.16
1.33
1.41
1.49
2.05
1.87
2.41
1.21
1.14
After the addition of excess 2
[BArF]À to polymer (2)n·14c, a
A
new signal at 4.2 ppm is observed that corresponds to the
“free” dibenzylammonium salt. Moreover, after the depro-
tonation of the dialkylammonium cation 2 with triethyl-
A
nals disappear along with the complexed crown ether sig-
nals, and the original signals are evident (spectrum D).
These results clearly demonstrate that self-assembly occur-
red and that the self-assembly step is reversible. Similar re-
sults were found for the self-assembly of 3 with polymer 15
(see Supporting Information).
19
50
[a] Mn =number-average molecular weight; Mw =weight-average molecu-
lar weight; PDI=polydispersity index.
mers was observed regardless of the [M]:[I] feed ratios. Ad-
Once the self-assembly of homopolymers 14c and 15 with
their small molecule receptors was found to be independent
of the polymer backbone, the self-assembly behavior of
block copolymers 18 and 20 was examined. Two distinct
routes for the functionalization of copolymers 18 and 20
were investigated, one in which the hydrogen-bonding step
precedes the metal coordination and vice versa. In the case
of both copolymers 18 and 20, the self-assembly was inde-
pendent of the order of functionalization.
ditionally, salt exchange was achieved with 11a by using am-
À
monium hexafluorophosphate, but the monomeric PF6 salt
would not polymerize with initiator 1. Thus, monomer 11
was chosen for all polymerization experiments. The conver-
À
sion of polymer 13c to the dialkylammonium PF6 salt 15
was accomplished by deprotection with TFA followed by
salt exchange by using a 100-fold excess of ammonium hexa-
fluorophosphate. Unfortunately, the resulting polyelectrolyte
15 could not be characterized by GPC; the charges either in-
teracted with the column packing material or the polymer
formed aggregates in an ionomeric fashion and did not
elute.
The DB24C8 recognition moiety 4 assembles spontane-
ously with the dibenzylammonium cation 2 in aprotic sol-
vents. The palladated pincer, however, requires activation
through the addition of silver tetrafluoroborate. Upon acti-
vation, the PdII pincer immediately assembles with pyridines
such as 5. The same behavior was observed for both copoly-
Copolymerizations: After establishing that 11 and 12 could
be polymerized in a controlled manner, AB block copoly-
merizations were carried out with the SCS–Pd pincer mono-
mer 16 (Scheme 3). The synthesis, polymerization, and living
characterization of 16 have been reported previously.[3,9,10,60]
Following the polymerization of 16 by using 1, monomers 11
and 12 were added to 17 to form the bi-functional AB block
copolymers 18 and 19. Following the deprotection of 19 with
TFA and subsequent salt exchange with ammonium hexa-
fluorophosphate, copolymer 20 was obtained. GPC analysis
of copolymers 18 and 19 were carried out. Both copolymers
1
mers. Figure 4 shows the H NMR spectra of the stepwise
self-assembly of copolymer 18 with 5 and 2
[BArF]À and the
A
subsequent stepwise de-functionalization of copolymer
(2)m(5)n·18. Spectrum B shows the copolymer 18 (shown by
itself in spectrum A) with pyridine 5 added. Upon the addi-
tion of silver tetrafluoroborate, the pincer is activated with
removal of the chloride ligand and pyridine 5 rapidly coordi-
nates to the pincer receptor to form copolymer (5)n·18
(spectrum C). The diagnostic a-pyridyl proton moves up-
field to d=8.1 ppm, while the pincer methylene arms
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Supramolecular Chemistry
FULL PAPER
Scheme 3. Synthesis of AB block copolymers bearing DB24C8, DBA+PF6À, and SCS–Pd pincer recognition units. Reagents and conditions: a) initiator 1,
CH2Cl2, 120 min; b) 12, 8 h, 100%; c) 11, CH2Cl2, 8 h, 100%; d) TFA, CH2Cl2, 3 h; e) NH4PF6, CH2Cl2, 3 h, 90% from 19.
become sharper and move slightly downfield from about d=
4.6 to 4.8 ppm. The dibenzylammonium cation 2 is subse-
quently added, and the crown ether complexation occurs, re-
sulting in the fully functionalized copolymer (2)m(5)n·18
(spectrum D). The same characteristic shifts for the com-
a variety of signals corresponding to non-coordinated pyri-
dine, coordinated triphenylphosphine, dibenzylamine, and
triethylamine that are all absent in spectrum A. However,
all signals characteristic of the uncomplexed 18 are evident
in spectrum F. These results clearly demonstrate that the
functionalization of the recognition units are independent of
each other and can be addressed in an orthogonal fashion.
To measure if the bond strengths of the recognition units
are independent of each other, association constants for all
polymers and hydrogen-bonding molecular receptors in
CHCl3 were obtained using isothermal titration calorimetry
(ITC). The results of these experiments are summarized in
Table 2. The measured Ka values were determined by using
a single-site binding model; thus, the association constants
are representative of the average binding strength of a
single side-chain on the polymer, that is, the binding of each
receptor unit is treated as an independent recognition event.
In general, our ITC results show that our polymeric hydro-
gen-bonding system results in very high association
strengths. The highest association constant (Ka =2”106 mÀ1)
plexations of 2
ACHTREUNG
detailed above for the complexation of 2
AHCTREUNG
observed. The noncovalent assembly can then be reversed
in a one-step or step-wise manner with the addition of tri-
ethylamine and triphenylphosphine. Triethylamine deproto-
nates the dibenzylammonium cation 2, resulting in the for-
mation of dibenzylamine, effectively de-threading the crown
complexation but leaving the pyridine fully assembled to the
pincer recognition unit (spectrum E). Finally, upon the addi-
tion of triphenylphospine, the pyridine ligand 5 is quantita-
tively displaced from the pincer complex (spectrum F). The
decomplexation of 5 and 2
[BArF]À from the copolymers is
H
1
evident by the shifting of all signals of 18 in the H NMR
spectrum back to their original position that are detailed in
spectrum A. It is important to note that spectrum F contains
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M. Weck, R. H. Grubbs, J. F. Stoddart et al.
Figure 3. 1H NMR spectra (500 MHz) representing the self-assembly of polymer 14c with 2
N
N
B) 14c: Ha, Hb, Hg =nonequivalent sets of crown ether protons; C) formation of (2)n·14c upon the addition of one equivalent of 2 to polymer 14c (based
on the integration of crown ether/dibenzylammonium signals): Ha =complexed benzylic proton; Ha, Hb, Hg =nonequivalent sets of complexed crown
ether protons; D) regeneration of 14c after the addition of excess Et3N to polymer (2)n·14c: Hb =benzylic protons on dibenzylamine; Ha, Hb, Hg =none-
quivalent sets of uncomplexed crown ether protons.
[61]
Figure 4. 1H NMR spectra (500 MHz, 298 K) in CD2Cl2 showing the stepwise functionalization of copolymer 18 with 2 and 5 and the subsequent recep-
tor removal. A) Copolymer 18: Ha, Hb, Hg =nonequivalent sets of crown ether protons; B) copolymer 18 and receptor 5: Ha =a-pyridyl protons; C) acti-
vation of copolymer 18 with AgBF4 to form copolymer (5)n·18: Ha =a-pyridyl protons on pyridine pincer complex; D) fully functionalized copolymer
(2)m(5)n·18 after addition of 2
A
ether protons; Ha =complexed benzylic protons on 2
A
plexed crown ether protons; Ha =a-pyridyl protons complexed pyridine; Hb =benzylic protons on dibenzylamine. F) copolymer (5)n·18 after addition of
PPh3: Ha, Hb, Hg =nonequivalent sets of uncomplexed crown ether protons; Ha =a-pyridyl protons uncomplexed pyridine.
was measured for homopolymer 14c upon binding with the
dialkylammonium cation 2. Binding of the complementary
homopolymer 15 with the small molecule 3 resulted in a
slightly lower association constant (Ka =1”105 mÀ1). Poten-
tial reasons for the lowered association strength are steric
hinderence created by the bound DB24C8 3 along the sites
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Supramolecular Chemistry
FULL PAPER
Table 2. Association constants for the hydrogen-bonding interactions in
all polymers.
chromatography (GPC) analyses for all polymers were carried out by
using a Waters 1525 binary pump linked to a Waters 2414 refractive
index detector with HPLC grade CH2Cl2 as the eluting solvent on an
American Polymer Standards 10 mm particle size, linear mixed bed pack-
Polymer
Ligand
Ka [104 mÀ1
]
Error [104 mÀ1
]
14c
15
18
(5)n·18
20
(5)n·20
2
3
2
2
3
3
N
286
10
43
54
9
Æ54
Æ4
ing columns (2”). Poly(styrene) standards were used to calibrate all
R
GPCs. Isothermal titration calorimetry (ITC) was performed on a Micro-
cal VP-ITC Isothermal Calorimeter. Degassed, HPLC grade solvents
were used for all ITC experiments.
Æ15
Æ17
Æ4
[62]
Dibenzylammonium BArF (2
[BArF]À): In a degassed flask, NaBArF
A
5
Æ2
(380 mg, 0.43 mmol) was added to a solution of dibenzylammonium
chloride (100 mg, 0.43 mmol) in anhydrous Et2O (10 mL). The mixture
was stirred vigorously for four hours and then filtered. Subsequently, the
filtrate was evaporated to dryness under reduced pressure to afford the
of the polymer backbone, as well as different solubility be-
havior of the two homopolymers. In general, hydrogen-
bonding association constants for all copolymers were less
than the association constants of their homopolymer ana-
logues, in part due to differences in solubility of the individ-
ual blocks of the copolymers in comparison to their homo-
polymer analogues. However, the hydrogen-bonding binding
strengths of both copolymers 18 and 20 were independent of
the metal coordination step. The association constants meas-
ured before and after metal coordination for both polymers
were identical within experimental error. These results clear-
ly demonstrate that the two employed recognition units do
not interfere with each other and that the self-assembly of
our copolymers can be executed orthogonally.
1
product (450 mg, 99%) as a white solid. H NMR (CD2Cl2): d=4.29 (brs,
4H), 7.18 (d, J=8.7 Hz, 4H), 7.45 (t, J=8.7 Hz, 4H), 7.50 (t, J=8.7 Hz,
2H), 7.52 (brs, 4H), 7.68 ppm (brs, 8H); 13C NMR (CD2Cl2): d=51.4,
117.3, 123.4, 125.5, 128.1, 129.1, 130.2, 131.0, 131.5, 134.6 ppm; MS (ESI):
m/z calcd for C14H16N: 198.1277; found: 198.1386 (100) [MÀBArF]+; ele-
mental analysis calcd (%) for C48H28BF24N: C 52.05, H 2.66, N 1.32;
found: C 52.16, H 2.69, N 1.44.
exo-Bicyclo
A
exo-Bicyclo[2.2.1]hept-5-ene-2-carboxylic acid (2.6 g, 19 mmol) and
AHCTREUNG
decane-1,10 diol (9.9 g, 57 mmol) were dissolved in anhydrous CH2Cl2
(25 mL) under an argon atmosphere. DCC (3.92 g, 19 mmol) in CH2Cl2
(5 mL) and DMAP (catalytic amount) were added to the stirred solution
at 258C. Following stirring at reflux for twelve hours, the mixture was
cooled to room temperature, and the precipitate was filtered off. The fil-
trate was dried (MgSO4) and the solvent removed under reduced pres-
sure to give a yellow oil that was further purified by column chromatog-
raphy (SiO2, eluant: 3:1 hexanes/EtOAc) to yield a clear oil (3.35 g,
60%). 1H NMR (CDCl3): d=6.12 (m, 2H), 4.07 (t, J=6.6 Hz, 2H), 3.63
(t, J=6.6 Hz, 2H), 3.03 (m, 1H), 2.92 (m, 1H), 2.21 (m, 1H), 1.91 (m,
1H) 1.67–1.50 (m, 5H) 1.43–1.24 ppm (m, 15H); 13C NMR (CDCl3): d=
176.6, 138.3, 136.0, 64.8, 63.2, 46.8, 46.6, 43.4, 41.9, 33.0, 30.5, 29.7, 29.7,
29.6, 29.4, 28.9, 26.1, 25.9 ppm; MS (ESI+): m/z: 295.2 [M+1]+; elemen-
tal analysis calcd (%) for C18H30O3: C 73.43, H 10.27; found: C 72.99, H
10.29.
Conclusion
In this article, we have reported the next generation of
UPBs that possess recognition moieties which self-assemble
with their complementary receptor molecules with very high
association strengths. We have established that through the
employment of living polymerization techniques, we can
control the architecture of such polymeric systems. In this
contribution, we have demonstrated this control by synthe-
exo-Bicyclo[2.2.1]hept-5-ene-2-carboxylic acid 9-carboxynonyl ester (8):
C
Compound 7 (2.27 g, 7.77 mmol) and PDC (17.13 g, 46.64 mmol) were
dissolved in DMF (50 mL) and stirred at room temperature for 48 h.
Water (20 mL) was added and the mixture was extracted with Et2O (3”
15 mL). The combined organic layers were washed with H2O (2”20 mL)
and dried (MgSO4). The solvent was removed under reduced pressure to
give a brown oil that was further purified by column chromatography
(SiO2, eluant: 2:1 hexanes/EtOAc) to yield a clear oil (1.89 g, 80%).
1H NMR (CDCl3): d=6.12 (m, 2H), 4.07 (t, J=6.6 Hz, 2H), 3.03 (m,
1H), 2.92 (m, 1H), 2.35 (t, J=7.7 Hz, 2H), 2.20 (m, 1H), 1.90 (m, 1H),
1.63 (m, 4H), 1.53 (d, 1H, J=8.3 Hz), 1.39–1.26 ppm (m, 13H);
13C NMR (CDCl3): d=180.3, 176.7, 138.3, 136.0, 64.8, 46.8, 46.6, 43.4,
41.9, 34.3, 30.5, 29.5, 29.4, 29.2. 28.9, 26.1, 24.9 ppm; MS (ESI+): m/z
(%): 309.2 (100), 617.5 (25, dimer); elemental analysis calcd (%) for
C18H28O4: C 70.10, H 9.15; found: C 69.87, H 9.06.
1
sizing block copolymers. Using H NMR spectroscopic and
ITC studies, we have proven that the self-assembly of our
polymers is quantitative, reversible, and can be achieved in
an orthogonal fashion. Our study demonstrates the potential
for the employment of such a functionalization strategy in
polymeric materials. Universal polymer backbones based on
such high-association-constant-based recognition units are a
prerequisite for the employment of the UPB in materials
science and experiments towards this goal are currently
being carried out in our laboratories.
exo-Bicyclo[2.2.1]hept-5-ene-2-carboxylic acid 9-{2,5,8,11,18,21,24,27-oc-
E
taoxatricyclo[26.4.0.012,17]dotriaconta-1(32),12(17),13,15,28,30-hexaen-14-
yl-methoxycarbonyl}nonyl ester (12): Compounds 8 (0.38 g, 1.23 mmol)
and 10 (0.59 g, 1.23 mmol) were dissolved in anhydrous CH2Cl2 (25 mL)
under an argon atmosphere. DCC (0.3 g, 1.45 mmol) in CH2Cl2 (5 mL)
and DMAP (catalytic amount) were added to the stirred solution at
258C. Following stirring at reflux for twelve hours, the mixture was
cooled to room temperature and the precipitate was filtered off. The fil-
trate was dried (MgSO4) and the solvent removed under reduced pres-
sure to give a yellow oil that was further purified by column chromatog-
Experimental Section
General methods: Reagents were purchased either from Acros Organics,
Aldrich Company, or Strem Chemicals and used without further purifica-
tion unless otherwise noted. CH2Cl2 was dried by passage through copper
oxide and alumina columns. Routine NMR spectra were recorded on a
300 MHz (1H, 300 MHz; 13C, 75 MHz) or 500 MHz (1H, 500 MHz; 13C,
125 MHz) Varian Mercury spectrometer; spectra were referenced to re-
sidual proton solvent. The Georgia Tech Mass Spectrometry Facility pro-
vided mass spectral analysis with a VG-70 se spectrometer. Atlanta Mi-
crolabs, Norcross, GA, performed all elemental analysis. Gel-permeation
raphy (SiO2, eluant: EtOAc) to yield
a white solid (0.86 g, 90%).
1H NMR (CDCl3): d=6.90–6.81 (m, 7H), 6.12 (m, 2H), 5.00 (s, 2H), 4.15
(t, J=4.4 Hz, 7H), 4.07 (t, J=7.2 Hz, 2H), 3.92 (t, J=4.4 Hz, 7H), 3.83
(m, 7H), 3.03 (m, 1H), 2.92 (m, 1H), 2.32 (t, J=7.2 Hz, 2H), 2.20 (m,
1H), 1.91 (m, 1H), 1.71–1.51 (m, 8H), 1.40–1.25 ppm (m, 12H);
13C NMR (CDCl3): d=176.0, 174.0, 149.1, 149.0, 138.3, 136.0, 129.3,
Chem. Eur. J. 2006, 12, 3789 – 3797
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3795

M. Weck, R. H. Grubbs, J. F. Stoddart et al.
121.9, 121.6, 114.5, 114.2, 113.8, 71.6, 71.5, 70.2, 70.1, 69.7, 69.6, 66.3, 64.8,
46.8, 46.6, 43.4, 41.9, 34.6, 34.2, 30.5, 29.5, 29.4, 29.3, 28.9, 26.1, 25.9, 25.2,
25.1 ppm; MS (FAB+): m/z (%): 768.5 (30), 154.2 (100); elemental anal-
ysis calcd (%) for C43H60O12: C 67.17, H 7.87; found: C 66.93, H 7.90.
129.4, 121.9, 121.6, 114.5, 114.3, 113.8, 110.4, 109.0, 90.5, 86.6, 71.5, 70.2,
70.1, 69.7, 69.6, 68.3, 66.3, 64.7, 57.8, 51.9, 49.8, 49.4, 47.9, 42.2, 36.6, 34.5,
34.2, 29.8, 29.5, 28.9, 26.3, 26.1, 25.9, 25.2, 24.9 ppm; elemental analysis
calcd (%) for 18: C 63.81, H 6.94; found: C 64.19, H 7.27.
Copolymer19 : 1H NMR (CDCl3): d=7.85 (m, 4H), 7.40–7.10 (m, 13H),
6.55 (s, 2H), 5.45–5.13 (m, 4H), 5.10 (s, 2H), 4.53 (brs, 4H), 4.40 (m,
4H), 4.05 (m, 4H), 3.85 (brt, J=6.6 Hz, 2H), 2.80–2.45 (m, 6H), 2.35 (t,
J=7.6 Hz, 2H), 2.10–1.85 (m, 6H), 1.80–1.55 (m, 18H), 1.50 (s, 9H),
1.49–1.10 ppm (m, 22H); 13C NMR (CDCl3): d=173.9, 168.1, 157.4,
156.4, 152.2, 151.9, 150.5, 135–127, 109.2, 99.8, 86.8, 80.5, 68.6, 66.2, 64.9,
64.0, 61.0, 58.8, 52.1, 39.2, 34.7, 31.3, 31.2, 30.8, 29.9, 29.7, 29.6, 29.3, 29.1,
28.8, 26.5, 26.3, 25.3, 24.2, 23.4, 20.4 ppm; elemental analysis calcd (%)
for 19: C 66.65, H 7.12, N 1.01; found: C 64.96, H 7.12, N 0.83.
exo-Bicyclo
A
carbonylamino)methyl]benzyloxycarbonyl}nonyl ester (11): Compounds
8 (0.76 g, 2.5 mmol) and 9 (0.95 g, 2.90 mmol) were dissolved in anhy-
drous CH2Cl2 (25 mL) under an argon atmosphere. DCC (0.60 g,
2.75 mmol) and DMAP (catalytic amount) were added to the stirred sol-
ution at 258C. Following stirring at reflux for twelve hours, the mixture
was cooled to room temperature and the precipitate was filtered off. The
filtrate was dried (MgSO4) and the solvent removed under reduced pres-
sure to give a yellow oil that was further purified by column chromatog-
raphy (SiO2, eluant: 3:1 Hexanes: EtOAc) to yield a clear oil (1.38 g,
90%). 1H NMR (CDCl3): d=7.33–7.21 (m, 9H), 6.12 (m, 2H), 5.1 (s,
2H), 4.41 (s, 2H), 4.33 (s, 2H), 4.07 (t, J=6.6 Hz, 2H), 3.03 (m, 1H),
2.91 (m, 1H), 2.35 (t, J=7.15 Hz, 2H), 2.20 (m, 1H), 1.91 (m, 1H), 1.71–
1.58 (m, 4H), 1.49 (s, 9H), 1.40–1.23 ppm (m, 13H); 13C NMR (CDCl3):
d=176.7, 174.0, 156.4, 138.4, 136.2, 135.6, 128.9, 128.8, 128.4, 128.0, 127.7,
80.54, 66.21, 64.9, 49.2, 47.0, 46.8, 43.6, 42.0, 34.7, 30.7, 29.7, 29.56, 29.55,
29.5, 29.4, 29.1, 28.9, 26.3, 25.3 ppm; MS (ESI+): m/z (%): 618.5 (50); el-
emental analysis calcd (%) for C38H51NO6: C 73.87, H 8.32, N 2.27;
found: C 73.87, H 8.34, N 2.36.
Copolymer20 : The block copolymer 20 was prepared analogously to
poly
mer 15. 1H NMR (CDCl3): d=9.00 (s, 2H), 7.85 (m, 4H), 7.40 (m,
A
13H), 6.60 (s, 2H), 5.40–5.10 (m, 4H), 5.00 (s, 2H), 4.60 (m, 4H), 4.30
(m, 4H), 4.10 (m, 4H), 3.90 (brt, J=6.6 Hz, 2H), 2.80–2.40 (m, 6H), 2.30
(t, J=7.5 Hz, 2H), 2.10–1.80 (m, 6H), 1.75–1.51 (m, 18H), 1.40–1.10 ppm
(m, 22H); 13C NMR (CDCl3): d=174.5, 173.8, 168.2, 156.8, 156.2, 152.2,
151.3, 150.0, 138.4, 134–127, 108.7, 99.8, 86.8, 80.5, 68.7, 67.9 66.2, 65.0,
64.2, 64.0, 61.0, 68.6, 51.3, 47.5, 45.3, 40.0, 39.1, 37.3, 36.0, 30.8, 30.1, 29.3,
24.2, 23.4 ppm.
General polymerization procedure: An amount of monomer was weighed
into a glass vial with a rubber septum cap, placed under an argon atmos-
phere and dissolved in anhydrous, degassed CD2Cl2 or CDCl3 (1 mL per
100 mg of monomer). A stock solution of the catalyst (in the correspond-
ing solvent) was prepared, and the desired volume of solution was added
to the polymerization vessel. Upon complete polymerization, ethyl vinyl
ether was added to quench the polymerization. The polymer was isolated
and purified by repeated precipitation into cold hexanes or MeOH.
Polymer14 : 1H NMR (CDCl3): d=6.90–6.78 (m, 7H), 5.42–5.10 (brm,
2H), 5.00 (s, 2H), 4.17 (m, 7H), 4.05 (brm, 2H), 3.90 (m, 7H), 3.80 (m,
7H), 2.8–2.4 (brm, 4H), 2.25 (brt, J=7.4 Hz, 2H), 2.2–1.45 (m, 8H),
1.40–1.00 ppm (m, 12H); 13C NMR (CDCl3): d=176.2, 173.9, 149.1,
149.0, 129.4, 121.9, 121.7, 115–113, 72.9, 71.5, 71.4, 70.2, 70.1, 69.7, 69.6,
66.3, 64.7, 49.4, 34.5, 34.2, 29.6, 29–28, 26.1, 25.8, 25.1 ppm; elemental
analysis calcd (%) for 14c: C 76.17, H 7.87; found: C 66.45, H 8.14.
Acknowledgements
Financial support has been provided by the Office of Naval Research
(MURI, Award No. N00014-03-1-0793). M.W. gratefully acknowledges a
3M Untenured Faculty Award, a DuPont Young Professor Award, an
Alfred P. Sloan Fellowship, a Camille Dreyfus Teacher-Scholar Award,
and a Blanchard Assistant Professorship.
´
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1
Polymer13 : H NMR (CDCl3): d=7.41–7.03 (m, 9H), 5.36–5.25 (m, 2H),
5.12 (s, 2H), 4.43 (s, 2H), 4.33 (s, 2H), 4.00 (brt, J=6.5 Hz, 2H), 2.72–
2.51 (m, 2H), 2.35 (t, J=7.5 Hz, 2H), 2.10–1.86 (brm, 2H) 1.60 (m, 4H),
1.50 (s, 9H), 1.47–1.27 ppm (m, 13); 13C NMR (CDCl3): d=173.9, 168.1,
156.3, 152.2, 138.5, 135–127, 99.8, 86.8, 80.5, 68.6, 66.2, 64.8, 64.0, 61.0,
39.2, 34.7, 31.31, 31.26, 30.8, 29.7, 29.6, 29.3, 29.11, 28.8, 26.3, 25.3, 24.2,
23.4, 20.4 ppm; elemental analysis calcd (%) for 13c: C 73.87, H 8.40, N
2.27; found: C 73.79, H 8.40, N 2.31.
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Polymer15 : Polymer 13 (0.53 g, 0.85 mmol) was dissolved in anhydrous
CH2Cl2 (4 mL) under an Argon atmosphere and TFA (1.0 mL,
13.51 mmol) was added. The mixture was stirred for three hours at room
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pressure to yield 15 as a brown oil (85 mg, 93%). 1H NMR (CDCl3): d=
9.10 (brs, 2H), 7.43–6.85 (m, 9H), 5.45–5.10 (m, 2H), 5.00 (s, 2H), 4.15–
3.80 (m, 6H), 3.20–2.20 (m, 5H), 2.19–1.40 (4H), 1.40–1.10 ppm (m,
14H); 13C NMR (CDCl3): d=174.0, 168.2, 156.4, 152.0, 138.5, 134–131,
99.8, 87.0, 80.6, 68.6, 66.2, 64.8, 64.0, 65.0, 61.1, 39.1, 34.7, 31.31, 31.25,
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Copolymer18 . 1H NMR (CDCl3): d=7.80 (m, 4H, SPh), 7.38 (m, 6H,
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3796
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