Functionalized hydrophobic and hydrophilic self-assembled supramolecular rectangles

Article abstract of DOI:10.1021/jo702380b

(Figure Presented) The synthesis of six new, functionalized 180° pyridyl donor ligands and their coordination-driven self-assembly into supramolecular rectangles is reported. Three of the new donors have been functionalized with hydrophobic straight chain alkane units (C₆, C₁₂, and C₁₈) while the remaining three have been functionalized with derivatized di-, tetra-, and hexaethylene glycol hydrophilic units (DEG, TEG, and HEG, respectively). The resulting self-assembled hydrophobic and hydrophilic supramolecular rectangles have been fully characterized by multinuclear NMR and electrospray ionization mass spectrometry. Molecular force field modeling suggests that the functionalized rectangles range in size from roughly 3.0 x 2.9 to 3.0 x 6.0 nm² in size.

Full text of DOI:10.1021/jo702380b

Functionalized Hydrophobic and Hydrophilic Self-Assembled
Supramolecular Rectangles
Brian H. Northrop,* Andreas Glo¨ckner, and Peter J. Stang
Department of Chemistry, UniVersity of Utah, 315 South 1400 East, Salt Lake City, Utah 84112
b.northrop@utah.edu
ReceiVed NoVember 5, 2007
The synthesis of six new, functionalized 180° pyridyl donor ligands and their coordination-driven self-
assembly into supramolecular rectangles is reported. Three of the new donors have been functionalized
with hydrophobic straight chain alkane units (C6, C12, and C18) while the remaining three have been
functionalized with derivatized di-, tetra-, and hexaethylene glycol hydrophilic units (DEG, TEG, and
HEG, respectively). The resulting self-assembled hydrophobic and hydrophilic supramolecular rectangles
have been fully characterized by multinuclear NMR and electrospray ionization mass spectrometry.
Molecular force field modeling suggests that the functionalized rectangles range in size from roughly
3.0 × 2.9 to 3.0 × 6.0 nm2 in size.
Introduction
Coordination-driven transition-metal-mediated self-assembly
involving dative metal-ligand bonding4,5 has become a widely
employed, robust means of preparing supramolecular polygons
and polyhedra with promising electronic, catalytic, photophysi-
cal, and/or redox properties.6 While early examples of such self-
assembled metal-organic structures exhibited little functionality,
there has recently been a drive to incorporate many different
functional moieties into their component building blocks. These
functionalized building blocks are then brought together and
precisely positioned upon spontaneous self-assembly with
appropriately designed complementary components. This pro-
cess has been utilized to prepare, for example, discrete su-
pramolecular metal-organic assemblies functionalized with
dendrimers,7 crown ethers,8 carboranes,9 optical sensors,10
saccharides,11 photoactive perylene diimides12 and azoben-
zenes,13 and polymerizable methyl methacrylate units14 that have
been distributed on their periphery,7-8,11 within building
blocks,9-10,12 and also, in some cases, within interior cavities.13-15
Self-assembly1 is a process ubiquitous throughout nature and
can account for much of the elegant and complex functionality
of biological systems. Over the past few decades, synthetic
chemists have developed various means of achieving abiological
self-assembly2 that have both furthered our understanding of
the self-assembly process itself and also opened the door to a
variety of molecular structures that would have otherwise proven
especially difficult to prepare. Recently, self-assembly has
been shown to play an important role in the development of
molecular materials and in the “bottom-up” approach3 to
nanofabrication.
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10.1021/jo702380b CCC: $40.75 © 2008 American Chemical Society
Published on Web 02/02/2008
J. Org. Chem. 2008, 73, 1787-1794
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Northrop et al.
Building upon molecular self-assembly, self-organization2f,16
is a process by which molecules, often structures such as dual-
character block copolymers17 and the like, are able to arrange
into well-defined configurations in different media. Self-
organization can take place: on surfaces, leading to well-ordered
self-assembled monolayers;18 in solution, giving rise to my-
celles,19 vesicles,20 cylinders,21 spheres,22 etc.; and, using
Langmuir-Blodgett techniques, at the air-water interface.23
There have only recently been examples where both self-
assembly and self-organization involving metallacycles have
been utilized, with the combination allowing for relatively facile
and spontaneous formation of arrays and assemblies of great
complexity. Lu et at., for example, have prepared6g,h alkoxy-
bridged Re(I) supramolecular rectangles that contain long alkyl
chains (C4H9, C8H17, and C12H25). The presence of these hydro-
phobic substituents induces the supramolecular rectangles to
aggregate in solution upon increasing the water content in the
solvent medium, leading to enhanced luminescence6g and the
ability of the rectangles to act as probes for photoluminescence
quenching.6h Recent studies performed by our group, in col-
laboration with Wan et al., have demonstrated24 higher order
assembly in the self-organization of supramolecular polyhedra
and polygons on Au(111) and/or HOPG surfaces. With these
recent advances in mind, we have endeavored to endow a
known25 supramolecular metallacycle with both hydrophobic
as well as hydrophilic functionalities of varying length. Such
structures may then be able to undergo higher order self-
organization in a variety of ways, resulting in control over the
arrangement and distribution of these very important metalla-
cycles.
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Results and Discussion
Synthesis of the 180° Functionalized Donors. New linear
hydrophobic and hydrophilic donor units of varying size were
synthesized according to a divergent approach utilizing 3,6-
diiodobenzene-1,2-diol26 (1) as their core, as shown in Scheme
1. Hydrophobic 3,6-diiodobenzenes 2-4 were prepared by
deprotonation of diol 1 and subsequent nucleophilic attack on
1-bromohexane, 1-bromododecane, and 1-bromooctadecane,
respectively, in 85-96% yield. Related hydrophilic analogues
5-7 were similarly prepared through a reaction of 1 with
monomethylated and bromo-terminated derivatives of diethylene
glycol, tetraethylene glycol, and hexaethylene glycol, respec-
tively, in 91-98% yield. Sonogashira coupling (Scheme 2) of
hydrophobic and hydrophilic diiodibenzenes with 4-ethynylpy-
ridine using Pd(PPh3)2Cl2 afforded the desired linear hydro-
phobic donors [C6 (8), C12 (9), and C18 (10)] and hydrophilic
donors [DEG (11), TEG (12), and HEG (13)] in good yield
(88-98%).
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D. C.; Stang, P. J. J. Am. Chem. Soc. 2006, 128, 10014-10015. (b) Yang,
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M.; Muddiman, D. C.; Stang, P. J. J. Am. Chem. Soc. 2007, 129, 14187-
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Self-Assembly and NMR Studies. With this series of new
functionalized linear donors at hand, the self-assembly of
hydrophobic supramolecular rectangles was performed. Heating
donors 8-10 with the molecular “clip”25 (Scheme 3a) in a 1:1
stoichiometric ratio in a 1.7:1 (v/v) solution of CD3COCD3/
D2O at 55-60 °C for 18 h gave homogeneous orange solutions.
Preliminary analysis of the reaction mixtures with 31P{1H} NMR
showed the presence of one sharp singlet, indicating the
formation of descrete, highly symmetric supramolecular rect-
angles. The rectangles were isolated (95-98% yield) following
counterion exchange of the nitrate anions to hexafluorophosphate
anions to increase the stability26 of the supramolecular com-
plexes. Multinuclear NMR (1H and 31P) analysis of supramo-
lecular rectangles 14-16 was performed and revealed similar
characteristics in each case. Figure 1 displays, as a representative
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Hydrophobic and Hydrophilic Metallacyclic Rectangles
SCHEME 1. Synthesis of Hydrophobic (2-4) and Hydrophilic (5-7) Diiodophenyl Derivatives
of the flanking 195Pt satellite peaks (∆J ) 209 Hz for 14, ∆J )
199 Hz for 15, ∆J ) 187 Hz for 16).
SCHEME 2. Sonogashira Coupling of Diiodophenyls 2-7
To Give New 180° Hydrophobic (8-10) and Hydrophilic
(11-13) Donors
Hydrophilic supramolecular rectangles 17-19 (Scheme 3b)
were similarly prepared and analyzed. Heating donors 11-13
with the molecular clip in a 1:1 stoichiometric ratio in a 1.2:1
(v/v) CD3COCD3/D2O solution at 55-60 °C for 18 h gave
homogeneous orange solutions. Following counterion exchange
to their hexafluorophosphate salts (96-97% isolated yield),
multinuclear (1H and 31P) NMR spectroscopic studies indicated
the presence of highly symmetric species. As with rectangles
14-16, the R- and â-pyridyl hydrogen atoms of hydrophilic
rectangles were downfield shifted relative to donors 11-13 by
0.5-0.6 and 0.72-0.83 ppm, respectively. Single, sharp peaks
were observed in the 31P {1H} NMR spectra, shifted upfield by
∼6 ppm, and coupling of the 195Pt stellite peaks was decreased
by ∆J ) 209 Hz for 17, ∆J ) 219 Hz for 18, and ∆J ) 231
Hz for 19.
Mass Spectrometric Analysis of Functionalized Rect-
angles. Further characterization of the hydrophobic and hydro-
philic supramolecular rectangles was provided by electrospray
ionization mass spectronometry (ESI-MS) studies, which are
able to establish the molecularity of the self-assembled metal-
lacycles. In the cases of the hydrophobic rectangles (Figure 2),
peaks were found at m/z 1664.4, 1832.5, and 1285.5, corre-
sponding to [M - 2PF6]2+of 14, [M - 2PF6]2+ of 15, and [M
- 3PF6]3+ of 16, where M represents the fully intact supramo-
lecular assemblies. Their isotopic distributions are in excellent
agreement with the theoretical distributions.
Well-resolved peaks for hydrophilic rectangles were observed
(Figure 3) at m/z 1700.1, 1876.6, 2052.6 corresponding to [M
- 2PF6]2+ of 17-19, respectively. Again, their isotopic
distributions are in excellent agreement with the theoretical
distributions. These mass spectral results, together with the
multinuclear NMR studies, confirm the self-assembly of both
hydrophobic as well as hydrophilic supramolecular rectangles.
Molecular Force Field Modeling. Attempts to grow single
crystals of supramolecular rectangles 14-19 suitable for X-ray
analysis have so far proven unsuccessful. Therefore, to gain a
greater understanding of the size and shape of these function-
alized metallacycles, molecular force field modeling investiga-
tions were performed. The structures of the supramolecular
rectangles were each constructed within the input mode of the
modeling program Maestro v.8.0.110.28 A 1000 step Monte
Carlo conformational search employing the MMFF force field29
and a solvent model for octane30 was performed to determine
rectangle 16, along with the 31P NMR spectra of 16 and the
molecular clip. For each self-assembled rectangle, proton signals
for the R- and â-pyridyl hydrogen atoms were shifted downfield
by 0.5-0.54 (R-signals) and 0.71-0.79 ppm (â-signals) on
account of the loss of electron density upon coordination. It
was also observed by 1H NMR studies that the R- and â-pyridyl
hydrogen atoms of donors 8-10 were no longer equivalent
following formation of hydrophobic rectangles. This result is
consistent with previous studies involving similar rectangles25,27
and indicates that free rotation of the donor pyridines is slow
on the NMR time scale if not stopped altogether. Analysis of
the 31P {1H} NMR spectra of hydrophobic rectangles 14-16
revealed a single, sharp peak at 8.58, 8.61, and 8.63 ppm,
respectively, each upfield shifted from the molecular clip by
nearly 6 ppm due to back-donation from the platinum atoms.
Back-donation was also observed by the decrease in coupling
(27) (a) Fuss, M.; Siehl, H.-U.; Olenyuk, B.; Stang. P. J. Organometallics
1999, 18, 758-759. (b) Tarkanyi, G.; Jude, H.; Palinkas, G.; Stang, P. J.
Org. Lett. 2005, 7, 4971-4973. (c) Yang, H.-B.; Das, N.; Huang, F.;
Hawkridge, A. M.; Diaz, D. D.; Arif, A. M.; Finn, M. G.; Muddiman, D.
C.; Stang, P. J. J. Org. Chem. 2006, 71, 6644-6647.
J. Org. Chem, Vol. 73, No. 5, 2008 1789

Northrop et al.
SCHEME 3. Coordination-Driven Self-Assembly of (a) Hydrophobic (14-16) and (b) Hydrophilic (17-19) Supramolecular
Rectangles
the lowest energy conformation of each rectangle. In every case,
the most favored conformer was predicted to be the one where
the hydrophobic or hydrophilic “arms” of rectangles 14-19
intertwine or wrap around each other. This result is most
prominently observed (Figure 4a) for rectangles 16 and 19,
which possess the longest chains (C18 and hexaethylene glycol,
respectively). It is important to note, however, that torsional
rotation about the many C-C and C-O bonds that make up
the hydrophobic and hydrophilic arms requires very little energy
and there are many similar conformations within only a few
kilocalories per mole of the found global minimum.
To better gauge the differences in size across the series of
rectangles, a second set of calculations was performed with their
hydrophobic or hydrophilic arms fully elongated (MMFF force
field, solvent model for octanol). These calculations reveal that
the sizes of fully outstretched rectangles range from ∼2.9 nm
for 14 and 17, to ∼4.4 nm for 15 and 18, up to ∼5.9 nm for
16 and 19, each with an anthracene-anthracene (C10-C10′
)
1
FIGURE 1. Representative H NMR spectra (300 MHz, 298 K, CD3COCD3) of the aromatic portion of the (a) molecular clip, (b) hydrophobic
molecular C18Rectangle 16, (c) and hydrophobic C18 donor 10 displaying the characteristic shifts of proton signals associated with the donor and
acceptor units upon coordination as well as (d) the 31P {1H} NMR spectra of the self-assembled C18Rectangle 16 and (e) molecular clip.
1790 J. Org. Chem., Vol. 73, No. 5, 2008

Hydrophobic and Hydrophilic Metallacyclic Rectangles
FIGURE 2. Theoretical (top, red) and experimental (bottom, black) ESI-MS results for hydrophobic rectangles 14-16.
FIGURE 3. Theoretical (top, red) and experimental (bottom, black) ESI-MS results for hydrophilic rectangles 17-19.
distance of roughly 2.9 nm. Representative examples of the
HEGRectangle (19), are shown in Figure 4b. Results for the
longest fully outstretched rectangles, C18Rectangle (16) and
shorter supramolecular rectangles can be found in the Supporting
Information.
(28) Mohamadi, F.; Richards, N. G. J.; Guida, W. C.; Liskamp, R.;
Lipton, M.; Caufield, C.; Chang, G.; Hendrickson, T.; Still, W. C. J. Comput.
Chem. 1990, 11, 440-467.
(30) Currently, there is no solvent model for acetone, the solvent used
for all NMR and ESI-MS analysis, available for the program Maestro
v.8.0.110.
(29) Halgren, T. A. J. Comput. Chem. 1996, 17, 490-641.
J. Org. Chem, Vol. 73, No. 5, 2008 1791

Northrop et al.
FIGURE 4. Computed global minimum (“Relaxed”) (a) and fully stretched (“Elongated”) (b) conformations of C18 hydrophobic and HEG hydrophilic
supramolecular rectangles. Color scheme: C ) gray, N ) blue, O ) red, P ) purple, Pt ) yellow. Hydrogen atoms are omitted for clarity.
1,4-Diiodo-2,3-bis(octadecyloxy)benzene (4). Yield 460 mg
(white solid), 96%. Mp 83-85 °C. 1H NMR (CDCl3, 300 MHz) δ
7.22 (s, 2H), 3.97 (t, 4H, J ) 6.6 Hz), 1.82 (pentet, 4H, J ) 6.9
Hz), 1.49 (pentet, 4H, J ) 7.2 Hz), 1.41-1.17 (m, 36H), 0.88 (t,
6H, J ) 6.6 Hz). 13C NMR (CDCl3, 75 MHz) δ 152.8, 135.5, 93.7,
74.1, 32.2, 30.5, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0,
29.9, 29.7, 29.6, 26.4, 22.9, 14.4. MS (LCMS) m/z 867.2 (M +
H)+. Anal. Calcd for C42H76I2O2: C, 58.19; H, 8.84. Found: C,
58.39; H, 8.87.
1-Bromo-2-(2-methoxyethoxy)ethane. To an acetone solution
(100 mL) of 2-(2-methoxyethoxy)ethyl 4-methylbenzenesulfonate31
(9.5 g, 35.0 mmol) was added LiBr (30 g, 0.35 mol) and the mixture
was brought to reflux. After refluxing for 5 h, the solution was
cooled and the solvent evaporated. The resulting residue was
partitioned between H2O (100 mL) and CH2Cl2 (100 mL) and the
layers were separated. The aqueous layer was extracted further with
CH2Cl2 (3 × 100 mL), the combined organic layers were dried
(MgSO4), filtered, and the solvent was evaporated to give the
desired product as a pale yellow liquid. Yield 6.34 g, 99%. 1H NMR
(CDCl3, 300 MHz) δ 3.80 (t, 2H, J ) 6.6 Hz), 3.68-3.64 (m, 2H),
3.57-3.53 (m, 2H), 3.47 (t, 2H, J ) 6.6 Hz), 3.38 (s, 3H). 13C
NMR (CDCl3, 75 MHz) δ 58.9, 54.2, 31.8, 30.4, 29.3. Anal. Calcd
for C5H11BrO2: C, 32.81; H, 6.06. Found: C, 32.77; H, 6.04.
Conclusion
A series of new hydrophobic and hydrophilic 180° donor
compounds have been prepared and successfully utilized in the
self-assembly of hydrophobic and hydrophilic supramolecular
rectangles of varying sizes. Each rectangle is self-assembled in
nearly quantitative yield despite the presence of long alkyl or
polyethylene glycol chains present on the donor units. All six
supramolecular rectangles have been characterized by multi-
nuclear NMR and ESI mass spectronometry. These hydrophobic
and hydrophilic rectangles represent an important addition to
the now growing class of functionalized metallacyclic assemblies
as their pendant chains will likely promote their self-organization
in solution, at the air-water interface, and on a variety of
surfaces. Such higher order assembly allows for greater control
over the size, shape, orientation, and distribution of the
underlying metallacycles in a variety of environments. Inves-
tigations along these lines are currently underway.
Experimental Section
General Procedure for Preparation of Hydrophobic Diiodides
2 and 4. To a solution of 3,6-diiodobenzene-2,3-diol (126) (200
mg, 0.55 mmol) in anhydrous MeCN (15 mL) was added K2CO3
(380 mg, 2.75 mmol), 18Crown6 (catalytic), and the appropriate
alkyl bromide (1-bromohexane, 456 mg, 2.75 mmol; 1-bromooc-
tadecane, 920 mg, 2.75 mmol) and the mixture was allowed to
reflux under N2(g) for 18 h. The mixture was cooled, the solvent
was evaporated, and the residue was partitioned between H2O (150
mL) and hexanes (100 mL). The layers were separated and the
aqueous layer was extracted with additional hexanes (4 × 60 mL).
The combined organic layers were dried (MgSO4), filtered, and
evaporated to give an off-white residue. The residue was purified
by column chromatography on silica gel (first with pure hexanes
to remove excess alkyl bromide, followed by hexanes/CH2Cl2 95:
2) to give the desired compounds as white solids.
General Procedure for Preparation of Hydropilic Diiodides
5-7. To a solution of 3,6-diiodobenzene-2,3-diol (1) (300 mg, 0.83
mmol) in anhydrous MeCN (20 mL) was added K2CO3 (800 mg,
5.81 mmol), 18Crown6 (catalytic), and either 1-bromo-2-(2-
methoxyethoxy)ethane (909 mg, 4.97 mmol), 13-bromo-2,5,8,11-
tetraoxatridecane32 (1.35 g, 4.97 mmol), or 19-bromo-2,5,8,11,14,-
17-hexaoxanonadecane33 (1.78 g, 4.97 mmol) and the respective
mixtures were allowed to reflux under N2(g) for 18 h. The mixtures
were cooled, the solvent was evaporated, and the residues were
partitioned between H2O (150 mL) and CH2Cl2 (100 mL). The
respective layers were separated and the aqueous layer was extracted
with additional CH2Cl2 (3 × 50 mL). The combined organic layers
were dried (MgSO4), filtered, and evaporated to give, in each case,
a yellow oil. The oils were purified by column chromatography on
silica gel (CH2Cl2/MeOH 97:3) to give the desired compounds as
yellow-orange oils.
2,3-Bis(hexyloxy)-1,4-diiodobenzene (2). Yield 494 mg (white
1
solid), 85%. Mp 48-50 °C. H NMR (CDCl3, 300 MHz) δ 7.22
(s, 2H), 3.98 (t, 4H, J ) 6.6 Hz), 1.83 (pentet, 4H, J ) 7.2 Hz),
1.49 (pentet, 4H, J ) 7.2 Hz), 1.40-1.29 (m, 8H), 0.91 (t, 6H, J
) 6.9 Hz). 13C NMR (CDCl3, 75 MHz) δ 152.8, 135.5, 93.7, 74.1,
31.9, 30.5, 30.4, 26.0, 22.9, 14.3. MS (LCMS) m/z 531.2 (M +
H)+. Anal. Calcd for C18H28I2O2: C, 40.77; H, 5.32. Found: C,
40.91; H, 5.33.
(31) Ouchi, M.; Inoue, Y.; Wada, K.; Iketani, S.; Hakushi, T.; Weber,
E. J. Org. Chem. 1987, 52, 2420-2427.
(32) Inouye, M.; Konishi, T.; Isagawa, J. J. Am. Chem. Soc. 1993, 115,
8091-8095.
(33) Samanta, D.; Sawoo, S.; Sarkar, A. Chem. Commun. 2006, 3438-
3440.
1792 J. Org. Chem., Vol. 73, No. 5, 2008

Hydrophobic and Hydrophilic Metallacyclic Rectangles
1,4-Diiodo-2,3-bis(2-(2-methoxyethoxy)ethoxy)benzene (5). Yield
430 mg (yellow oil), 91%. 1H NMR (CDCl3, 300 MHz) δ 7.22 (s,
2H), 4.20 (t, 4H, J ) 4.8 Hz), 3.86 (t, 4H, J ) 4.8 Hz), 3.71 (t,
4H, J ) 4.8 Hz), 3.56 (t, 4H, J ) 4.8 Hz), 3.38 (s, 6H). 13C NMR
(CDCl3, 75 MHz) δ 152.4, 135.7, 93.4, 72.8, 72.2, 70.8, 70.5, 59.3.
MS (LCMS) m/z 567.0 (M + H)+. Anal. Calcd for C16H24I2O6: C,
33.94; H, 4.27. Found: C, 34.04; H, 4.28.
13,13′-(3,6-Diiodo-1,2-phenylene)bis(oxy)bis(2,5,8,11-tetraox-
atridecane) (6). Yield 594 mg (yellow oil), 96%. 1H NMR (CDCl3),
300 MHz) δ 7.25 (s, 2H), 4.18 (t, 4H, J ) 4.8 Hz), 3.83 (t, 4H, J
) 4.8 Hz), 3.73-3.59 (m, 16H), 3.53 (t, 4H, J ) 4.8 Hz), 3.36 (s,
6H). 13C NMR (CDCl3, 75 MHz) δ 152.3, 135.6, 93.4, 72.7, 72.0,
70.8, 70.8, 70.8, 70.8, 70.7, 70.5, 59.2. MS (LCMS) m/z 742.9 (M
+ H)+. Anal. Calcd for C24H40I2O10: C, 38.83; H, 5.43. Found:
C, 38.94; H, 5.45.
4,4′-(2,3-Bis(2-(2-methoxyethoxy)ethoxy)-1,4-phenylene)bis-
(ethyne-2,1-diyl)dipyridine (11). Reaction scale: 5 (200 mg, 0.353
mmol). Chromatography eluent CH2Cl2/MeOH (96:4). Yield 181
1
mg (off white solid), 98%. Mp 56-59 °C. H NMR (CDCl3, 300
MHz) δ 8.62 (d, 4H, J ) 5.7 Hz), 7.41 (d, 4H, J ) 5.7 Hz), 7.24
(s, 2H), 4.37 (t, 4H, J ) 4.8 Hz), 3.88 (t, 4H, J ) 4.8 Hz), 3.70 (t,
4H, J ) 4.8 Hz), 3.52 (t, 4H, J ) 4.8 Hz), 3.34 (s, 6H). 13C NMR
(CDCl3, 75 MHz) δ 153.8, 150.4, 131.4, 128.3, 125.7, 119.3, 92.7,
89.9, 73.4, 72.2, 70.9, 70.8, 59.2. MS (LCMS) m/z 517.0 (M +
H)+. Anal. Calcd for C30H32N2O6: C, 69.75; H, 6.24; N, 5.42.
Found: C, 69.52; H, 6.23; N, 5.41.
4,4′-(2,3-Bis(2,5,8,11-tetraoxatridecan-13-yloxy)-1,4-phenyle-
ne)bis(ethyne-2,1-diyl)dipyridine (12). Reaction scale: 6 (300 mg,
0.40 mmol). Chromatography eluent CH2Cl2/MeOH (95:5). Yield
246 mg (brown oil), 88%. 1H NMR (CDCl3, 300 MHz) δ 8.61 (br,
4H), 7.51 (s, 4H), 7.24 (s, 2H), 4.35 (t, 4H, J ) 4.8 Hz), 3.86 (t,
4H, J ) 4.8 Hz), 3.72-3.67 (m, 4H), 3.64-3.59 (m, 16H), 3.55-
3.50 (m, 4H), 3.36 (s, 6H). 13C NMR (CDCl3, 75 MHz) δ 153.7,
149.9, 131.2, 128.2, 119.3, 92.7, 89.9, 73.4, 72.1, 70.8, 70.8, 70.8,
70.7, 70.7, 70.7, 59.1, 53.7. MS (LCMS) m/z 692.9 (M + H)+.
Anal. Calcd for C38H48N2O10: C, 65.88; H, 6.98; N, 4.04. Found:
C, 65.67; H, 6.97; N, 4.03.
19,19′-(3,6-Diiodo-1,2-phenylene)bis(oxy)bis(2,5,8,11,14,17-
1
hexaoxanonadecane) (7). Yield 745 mg (orange oil), 98%. H
NMR (CDCl3, 300 MHz) δ 7.26 (s, 2H), 4.18 (t, 4H, J ) 4.8 Hz),
3.84 (t, 4H, J ) 4.8 Hz), 3.75-3.59 (m, 36H), 3.54 (t, 4H, J ) 4.8
Hz), 3.37 (s, 6H). 13C NMR (CDCl3, 75 MHz) δ 152.3, 135.6, 93.4,
72.7, 72.1, 70.8, 70.8, 70.8, 70.8, 70.7, 70.7, 70.7, 70.7, 70.6, 70.5,
59.2. MS (LCMS) m/z 919.3 (M + H)+. Anal. Calcd for
C32H56I2O14: C, 41.84; H, 6.14. Found: C, 41.89; H, 6.15.
General Procedure for Preparation of Hydrophobic and
Hydropilic Donors 8-13. A 100 mL Schlenk flask was charged
with diiodide (2-7, 1.0 equiv), 4-bromopyridine hydrochloride (4.0
equiv), 10 mol % Pd(PPh3)2Cl2, and 15 mol % CuI, degassed, and
back-filled three times with N2(g). Triethylamine (7 mL) and dry
THF (7 mL) were then introduced into the reaction via syringe.
The reaction was allowed to stir at room temperature for 36 h. The
solvent was evaporated and the brown residue was partitioned
between H2O (75 mL) and CH2Cl2 (50 mL). The organic layer was
separated and extracted further with CH2Cl2 (3 × 30 mL). The
combined organic layers were dried (MgSO4), filtered, and evapo-
rated. The resulting brown residues were purified by column
chromatography on silica gel.
4,4′-(2,3-Bis(2,5,8,11,14,17-hexaoxanonadecan-19-yloxy)-1,4-
phenylene)bis(ethyne-2,1-diyl)dipyridine (13). Reaction scale: 7
(340 mg, 0.37 mmol). Chromatography eluent CH2Cl2/MeOH (94:
1
6). Yield 319 mg (orange oil), 98%. H NMR (CDCl3, 300 MHz)
δ 8.57 (br, 4H), 7.51 (s, 4H), 7.24 (s, 2H), 4.35 (t, 4H, J ) 4.8
Hz), 3.86 (t, 4H, J ) 4.8 Hz), 3.72-3.60 (m, 4H), 3.65-3.57 (m,
32H), 3.56-3.51 (m, 4H), 3.36 (s, 6H). 13C NMR (CDCl3, 75 MHz)
δ 153.7, 150.0, 131.2, 128.2, 125.6, 119.2, 92.6, 89.9, 73.3, 72.0,
70.8, 70.8, 70.8, 70.7, 70.0, 70.0, 70.0, 70.0, 70.0, 70.6, 59.1. MS
(LCMS) m/z 868.9 (M + H)+. Anal. Calcd for C46H64N2O14: C,
63.58; H, 7.42; N, 3.22. Found: C, 63.44; H, 7.39; N, 3.20.
General Procedure for Preparation of Hydrophobic Su-
pramolecular Rectangles 14-16. Hydrophobic donors 8-10 (1.0
equiv) and the molecular clip25 acceptor (1.0 equiv) were added to
separate glass vials. To the vials containing donors was added 0.5
mL of a Me2CO/H2O (1.7:1) solution and the resulting suspension
was transferred to the acceptor vial. This process was repeated (3
× 0.4 mL) to ensure quantitative transfer of the donor to the
acceptor. The reaction solution was then stirred at 55 °C for 18 h,
after which time a homogeneous orange solution had formed. The
NO3- counterions were exchanged for PF6- using an H2O solution
of KPF6. The product was washed several times with excess H2O
and the resulting solid collected.
4,4′-(2,3-Bis(hexyloxy)-1,4-phenylene)bis(ethyne-2,1-diyl)dipy-
ridine (8). Reaction scale: 2 (180 mg, 0.34 mmol). Chromatography
1
eluent CH2Cl2/Me2CO (4:1). Yield 151 mg (brown oil), 92%. H
NMR (CDCl3, 300 MHz) δ 8.69 (br, 4H), 7.47 (s, 4H), 7.25 (s,
2H), 4.16 (t, 4H, J ) 6.3 Hz), 1.89-1.75 (m, 4H), 1.60-1.46 (m,
4H), 1.39-1.21 (m, 8H), 0.87 (t, 6H, J ) 6.9 Hz). 13C NMR
(CDCl3, 75 MHz) δ 154.2, 150.0, 131.3, 128.2, 125.6, 119.4, 92.4,
90.2, 74.8, 31.9, 30.6, 26.1, 22.9, 14.3. MS (LCMS) m/z 481.1 (M
+ H)+. Anal. Calcd for C32H36N2O2: C, 79.96; H, 7.55; N, 5.83.
Found: C, 79.69; H, 7.52; N, 5.81.
C6Rectangle (14). Reaction scale: clip (12.7 mg, 10.9 µmol),
donor 8 (5.3 mg, 10.9 µmol). Yield 19 mg (orange solid), 98%. 1H
NMR (CD3COCD3, 300 MHz) δ 9.55 (s, 2H, H9), 9.19 (dd, 8H, J
) 36.0, 5.7 Hz, HR-Pyr), 8.53 (s, 2H, H10), 8.18 (dd, 8H, J ) 36.0,
5.7 Hz, Hâ-Pyr), 7.88-7.78 (m, 8H, H2,4,5,7), 7.53 (s, 4H, ArH),
7.27 (t, 4H, J ) 8.1 Hz, H3,6), 4.30 (t, 8H, J ) 6.3 Hz, PhOCH2),
1.98-1.84 (m, 8H, Halkane), 1.76-1.51 (m, 56H, Halkane and PCH2-
CH3), 1.43-1.28 (m, 16H, Halkane), 1.06-0.92 (m, 64H, PCH2CH3),
0.89 (t, 12H, J ) 6.7 Hz, -CH3). 31P{1H} NMR (CD3COCD3, 121.4
4,4′-(2,3-Bis(dodecyloxy)-1,4-phenylene)bis(ethyne-2,1-diyl)-
dipyridine (9). Reaction scale: 3 (224 mg, 0.32 mmol). Chroma-
tography eluent CH2Cl2/Me2CO (8:1). Yield 194 mg (white solid),
94%. Mp 58-61 °C. 1H NMR (CDCl3, 300 MHz) δ 8.65 (br, 4H),
7.46 (d, 4H, J ) 6.0 Hz), 7.24 (s, 2H), 4.16 (t, 4H, J ) 6.6 Hz),
1.82 (pentet, 4H, J ) 6.9 Hz), 1.52 (pentet, 4H, J ) 6.9 Hz), 1.39-
1.18 (m, 32H), 0.87 (t, 6H, J ) 7.2 Hz). 13C NMR (CDCl3, 75
MHz) δ 154.2, 150.0, 131.4, 128.2, 125.6, 119.4, 92.4, 90.2, 74.8,
32.2, 30.7, 29.9, 29.9, 29.9, 29.9, 29.8, 29.6, 26.5, 22.9, 14.4. MS
(LCMS) m/z 649.1 (M + H)+. Anal. Calcd for C44H60N2O2: C,
81.43; H, 9.32; N, 4.32. Found: C, 81.33; H, 9.35; N, 4.31.
4,4′-(2,3-Bis(octadecyloxy)-1,4-phenylene)bis(ethyne-2,1-diyl)-
dipyridine (10). Reaction scale: 4 (175 mg, 0.2 mmol). Chroma-
tography eluent CH2Cl2/MeOH (10:1). Yield 153 mg (white solid),
93%. Mp 78-79 °C. 1H NMR (CDCl3, 300 MHz) δ 8.64 (br, 4H),
7.39 (d. 4H, J ) 6.0 Hz), 7.26 (s, 2H), 4.16 (t, 4H, J ) 6.3 Hz),
1.82 (pentet, 4H, J ) 6.9 Hz), 1.52 (pentet, 4H, J ) 6.9 Hz), 1.41-
1.14 (m, 48H), 0.87 (t, 6H, J ) 6.9 Hz). 13C NMR (CDCl3, 75
MHz) δ 154.2, 150.0, 131.5, 128.2, 125.7, 119.4, 92.4, 90.2, 74.8,
32.2, 30.7, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 29.9,
29.8, 29.6, 26.5, 22.3, 14.4. MS (LCMS) m/z 817.1 (M + H)+.
Anal. Calcd for C56H84N2O2: C, 82.30; H, 10.36; N, 3.43. Found:
C, 82.01; H, 10.32; N, 3.42.
1
MHz) δ 8.58 (s, JPt-P ) 1325.6 Hz). MS (ESI) calcd for [M -
2PF6]2+ m/z 1664.6, found 1664.4.
C12Rectangle (15). Reaction scale: clip (8.95 mg, 7.7 µmol),
donor 9 (5 mg, 7.7 µmol). Yield 14.7 mg (orange solid), 95%. 1H
NMR (CD3COCD3, 300 MHz) δ 9.55 (s, 2H, H9), 9.19 (dd, 8H, J
) 36.0, 5.7 Hz, HR-Pyr), 8.53 (s, 2H, H10), 8.19 (dd, 8H, J ) 36.0,
5.7 Hz, Hâ-Pyr), 7.90-7.80 (m, 8H, H2,4,5,7), 7.54 (s, 4H, ArH),
7.27 (t, 4H, J ) 8.1 Hz, H3,6), 4.32 (t, 8H, J ) 6.9 Hz, PhOCH2),
2.01-1.87 (m, 8H, Halkane), 1.77-1.53 (m, 56H, Halkane and PCH2-
CH3), 1.48-1.23 (m, 64H, Halkane), 1.07-0.93 (m, 64H, PCH2CH3),
0.88 (t, 12H, J ) 6.6 Hz, -CH3). 31P{1H} NMR (CD3COCD3, 121.4
1
MHz) δ 8.61 (s, JPt-P ) 1330.7 Hz). MS (ESI) calcd for [M -
2PF6]2+ m/z 1832.8, found 1832.5.
C18Rectangle (16). Reaction scale: clip (7.1 mg, 6.1 µmol),
donor 8 (5 mg, 6.1 µmol). Yield 12.8 mg (orange solid), 97%. 1H
J. Org. Chem, Vol. 73, No. 5, 2008 1793

Northrop et al.
NMR (CD3COCD3, 300 MHz) δ 9.56 (s, 2H, H9), 9.18 (dd, 8H, J
) 36.0, 5.7 Hz, HR-Pyr), 8.54 (s, 2H, H10), 8.18 (dd, 8H, J ) 36.0,
5.7 Hz, Hâ-Pyr), 7.90-7.79 (m, 8H, H2,4,5,7), 7.53 (s, 4H, ArH),
7.27 (t, 4H, J ) 8.1 Hz, H3,6), 4.32 (t, 8H, J ) 6.9 Hz, PhOCH2),
2.01-1.86 (m, 8H, Halkane), 1.77-1.50 (m, 56H, Halkane and PCH2-
CH3), 1.46-1.19 (m, 112H, Halkane), 1.07-0.91 (m, 64H, PCH2CH3),
0.87 (t, 12H, J ) 6.3 Hz, -CH3). 31P{1H} NMR (CD3COCD3, 121.4
1H NMR (CD3COCD3, 300 MHz) δ 9.56 (s, 2H, H9), 9.17 (dd,
8H, J ) 24.9, 5.7 Hz, HR-Pyr), 8.53 (s, 2H, H10), 8.23 (dd, 8H, J
) 24.9, 5.7 Hz, Hâ-Pyr), 7.89-7.79 (m, 8H, H2,4,5,7), 7.53 (s, 4H,
ArH), 7.27 (t, 4H, J ) 7.5 Hz, H3,6), 4.56-4.46 (m, 8H, PhOCH2),
4.01-3.91 (m, 8H, Hglycol), 3.76-3.54 (m, 40H, Hglycol), 3.51-
3.43 (m, 8H, Hglycol), 3.27 (s, 12H, -OCH3), 1.79-1.50 (m, 48H,
PCH2CH3), 1.13-0.86 (m, 64H, PCH2CH3). 31P{1H} NMR (CD3-
1
1
MHz) δ 8.63 (s, JPt-P ) 1336.61 Hz). MS (ESI) calcd for [M -
COCD3, 121.4 MHz) δ 8.56 (s, JPt-P ) 1320.50 Hz). MS (ESI)
2PF6]2+ m/z 2001.0, found 2000.7.
calcd for [M - 2PF6]2+ m/z 1876.7, found 1876.6; calcd for [M -
General Procedure for Preparation of Hydrophilic Supramo-
lecular Rectangles 17-19. Hydrophilic donors 11-13 (1.0 equiv)
and the molecular clip25 acceptor (1.0 equiv) were added to separate
glass vials. To the vials containing donors was added 0.5 mL of a
Me2CO/H2O (1.2:1) solution and the resulting suspension was
transferred to the acceptor vial. This process was repeated (3 ×
0.4 mL) to ensure quantitative transfer of the donor to the acceptor.
The reaction solution was then stirred at 55 °C for 18 h, after which
3PF6]3+ m/z 1202.8, found 1202.7.
HEGRectangle (19). Reaction scale: clip (7.9 mg, 6.8 µmol),
donor 8 (5.91 mg, 6.8 µmol). Yield 16.4 mg (orange solid), 96%.
1H NMR (CD3COCD3, 300 MHz) δ 9.55 (s, 2H, H9), 9.17 (dd,
8H, J ) 24.9, 5.7 Hz, HR-Pyr), 8.53 (s, 2H, H10), 8.24 (dd, 8H, J
) 24.9, 5.7 Hz, Hâ-Pyr), 7.88-7.80 (m, 8H, H2,4,5,7), 7.54 (s, 4H,
ArH), 7.27 (t, 4H, J ) 7.5 Hz, H3,6), 4.56-4.47 (m, 8H, PhOCH2),
4.01-3.92 (m, 8H, Hglycol), 3.79-3.51 (m, 72H, Hglycol), 3.49-
3.43 (m, 8H, Hglycol), 3.27 (s, 12H, -OCH3), 1.78-1.48 (m, 48H,
PCH2CH3), 1.12-0.89 (m, 64H, PCH2CH3). 31P{1H} NMR (CD3-
-
time a homogeneous orange solution had formed. The NO3
-
counterions were exchanged for PF6 using an H2O solution of
1
KPF6. The product was washed several times with excess H2O and
the resulting solid collected.
COCD3, 121.4 MHz) δ 8.58 (s, JPt-P ) 1314.52 Hz). MS (ESI)
calcd for [M - 2PF6]2+ m/z 2052.8, found 2052.6; calcd for [M -
3PF6]3+ m/z 1320.2, found 1320.1.
DEGRectangle (17). Reaction scale: clip (10.0 mg, 8.5 µmol),
donor 11 (4.4 mg, 8.5 µmol). Yield 15 mg (orange solid), 96%. 1H
NMR (CD3COCD3, 300 MHz) δ 9.57 (s, 2H, H9), 9.18 (dd, 8H, J
) 24.9, 5.7 Hz, HR-Pyr), 8.53 (s, 2H, H10), 8.24 (dd, 8H, J ) 24.9,
5.7 Hz, Hâ-Pyr), 7.90-7.80 (m, 8H, H2,4,5,7), 7.52 (s, 4H, ArH),
7.27 (t, 4H, J ) 7.5 Hz, H3,6), 4.56-4.46 (m, 8H, PhOCH2), 3.98-
3.89 (m, 8H, Hglycol), 3.72-3.64 (m, 8H, Hglycol), 3.55-3.49 (m,
8H, Hglycol), 3.30 (s, 12H, -OCH3), 1.79-1.48 (m, 48H, PCH2-
CH3), 1.13-0.86 (m, 64H, PCH2CH3). 31P{1H} NMR (CD3COCD3,
Acknowledgment. P.J.S. thanks the NIH (GM-057052) and
the NSF (CHE-0306720) for financial support. B.H.N. thanks
the NIH (GM-080820) for financial support. A.G. thanks the
German Academic Exchange Service for financial support.
Supporting Information Available: Multinuclear NMR spec-
troscopic analysis of compounds 2-19 and full results obtained
from molecular force field modeling studies. This material is
available free of charge via the Internet at http://pubs.acs.org.
1
121.4 MHz) δ 8.53 (s, JPt-P ) 1325.56 Hz). MS (ESI) calcd for
[M - 2PF6]2+ m/z 1700.0, found 1700.1; calcd for [M - 3PF6]3+
m/z 1085.0, found 1085.0.
TEGRectangle (18). Reaction scale: clip (8.6 mg, 7.4 µmol),
donor 12 (5.1 mg, 7.4 µmol). Yield 14.5 mg (orange solid), 97%.
JO702380B
1794 J. Org. Chem., Vol. 73, No. 5, 2008