A new versatile receptor platform

Article abstract of DOI:10.1021/jo015690j

We prepared a molecular receptor based on the molecular tweezer concept. Our system offers versatility, an extremely short synthetic route, good yield, large quantities, and finally having binding constants that equal the best known tweezer molecules when it comes to binding various nitroaromatics such as 1,3,5-trinitrotoluene (24 M^-1), 1,3,5-trinitrobenzene (182 M^-1), and 2,4,7-trinitrofluorenone (490 M^-1) as determined using ¹H NMR in CDCl₃. It is notable that these binding constants are achieved although the molecular framework is not locked in a fixed and rigid conformation. The rigidity has been claimed to be the governing factor when it comes to achieving a large binding constant. We propose that our molecular tweezer system may be preorganized and that this explains the high binding constants observed. Further, we investigated the crystal structures of both the neutral receptor molecule and a complex with 1,3,5-trinitrobenzene and found that the molecule forms a pocket suited to accommodate flat aromatic analytes.

Full text of DOI:10.1021/jo015690j

J . Org. Chem. 2001, 66, 6169-6173
6169
A New Ver sa tile Recep tor P la tfor m
Frederik C. Krebs* and Mikkel J ørgensen
The Danish Polymer Centre, RISØ National Laboratory, P.O. Box 49, DK-4000 Roskilde, Denmark
Frederik.krebs@risoe.dk
Received April 17, 2001
We prepared a molecular receptor based on the molecular tweezer concept. Our system offers
versatility, an extremely short synthetic route, good yield, large quantities, and finally having
binding constants that equal the best known tweezer molecules when it comes to binding various
nitroaromatics such as 1,3,5-trinitrotoluene (24 M-1), 1,3,5-trinitrobenzene (182 M-1), and 2,4,7-
trinitrofluorenone (490 M-1) as determined using 1H NMR in CDCl3. It is notable that these binding
constants are achieved although the molecular framework is not locked in a fixed and rigid
conformation. The rigidity has been claimed to be the governing factor when it comes to achieving
a large binding constant. We propose that our molecular tweezer system may be preorganized and
that this explains the high binding constants observed. Further, we investigated the crystal
structures of both the neutral receptor molecule and a complex with 1,3,5-trinitrobenzene and found
that the molecule forms a pocket suited to accommodate flat aromatic analytes.
In tr od u ction
that the interplanar distance between the two aromatic
plates forms a pocket suitable for binding planar mol-
ecules. The concept has been known for a while,7 and its
applicability has been proven as a viable means of
constructing a molecular receptor. Three schools have
developed so far and have relied on rare8-11 synthetic
chemistry, on lengthy and tedious synthetic chemistry,21
or on relatively simple synthetic chemistry based on
naturally occurring starting materials with fixed stere-
ochemistry but of low versatility.15-17
In this article we present a very versatile type of
receptor platform. In essentially one synthetic step a
large receptor molecule is made (Scheme 1).
A wide range of interactions with an analyte molecule
are easily envisaged for instance specific hydrogen in-
teractions, ionic interactions, and π-π interactions.
During the past 30 years a considerable research effort
has been placed toward obtaining receptor molecules
specific for an analyte which typically is a small func-
tional molecule such as a sugar, a neurotransmitter, a
drug, explosives, etc. By and large most work has been
centered around a family of molecules that have been
used as the host molecule or receptor platform. The
[n]cyclophanes1-6 are an example of a popular molecular
platform. Chemists have many reasons for their choice
of molecular platform but largely the choice is determined
by the ease at which the molecules can be synthesized.
Normally the receptor molecule is much larger and has
a higher level of molecular complexity than the analyte
molecule for which it is specific. Since the platform
molecule often has to be subjected to further synthetic
elaboration to gain specificity it has to be available in
pure form and in large quantities. Most platform mol-
ecules suffer in this respect, as they all have a lengthy
synthetic path behind them before derivatives with
various specificities are arrived at.
(12) Harmata, M.; Tyagarajan, S. Mol. Recognit. Inclusion, Proc. Int.
Symp., 9th 1998, 353-356.
(13) Harmata, M.; Kahraman, M.; Tyagarajan, S.; Barnes, C. L.;
Welch, C. J . Mol. Recognit. Inclusion, Proc. Int. Symp., 9th 1998, 109-
116.
(14) Fleischhauer, J .; Harmata, M.; Kahraman, M.; Koslowski, A.;
Welch, C. J . Tetrahedron Lett. 1997, 38, 8655-8658.
(15) Maitra, U.; D’Souza, L. J . J . Chem. Soc. Chem. Commun. 1994,
2793-2795.
(16) D’Saouza, L. J .; Maitra, U. J . Org. Chem. 1996, 61, 9494-9502.
(17) Maitra, U.; D′Souza, L. J .; Kumar, P. V. Supramol. Chem. 1998,
10, 97-106.
Molecular tweezers7-28 are generally molecules that
have two large aromatic plates connected by a hinge such
(1) Gutsche, C. D. Calixarenes, Monographs in Supramolecular
Chemistry, Stoddart, J . F., Ed., Royal Society of Chemistry: Cam-
bridge, 1989.
(2) Gutsche, C. D. Calixarenes Revisited; Royal Society of Chemis-
try: Cambridge, 1999.
(3) Ikeda, A.; Shinkai, S. Chem. Rev. 1997, 97, 1713-1734.
(4) Vicens, J .; Bo¨hmer, V. Calixarenes, a versatile class of macrocyclic
compounds; Kluwer Academic Publishers: The Netherlands, 1991.
(5) Atwood, J . L.; Koutsantonis, G. A.; Raston, C. L. Nature 1994,
368, 229.
(6) Arduini, A.; Fabbi, M.; Mantovani, M.; Mirone, L.; Pochini, A.;
Secchi, A.; Ungaro, R. J . Org. Chem. 1995, 60, 1454-1457.
(7) Chen, C.-W.; Whitlock J r., H. W. J . Am. Chem. Soc. 1978, 100,
4921-4922.
(8) Harmata, M.; Murray, T. J . Org. Chem. 1989, 54, 3761-3763.
(9) Harmata, M.; Barnes, C. L. Tetrahedron Lett. 1990, 31, 1825-
1828.
(18) J eong, K. S.; Tjivikua, T.; Muehldorf, A.; Deslongchamps, G.;
Famulok, M.; Rebek J r., J . J . Am. Chem. Soc. 1991, 113, 201-209.
(19) Blake, J . F.; J orgensen, W. L. J . Am. Chem. Soc. 1990, 112,
7269-7278.
(20) Zimmerman, S. C.; VanZyl, C. M.; Hamilton, G. S. J . Am. Chem.
Soc. 1989, 111, 1373-1381.
(21) Zimmerman, S. C.; Zeng, Z.; Wu. W.; Reichert, D. E. J . Am.
Chem. Soc. 1991, 113, 183-196.
(22) Zimmerman, S. C.; Wu. W.; Zeng, Z. J . Am. Chem. Soc. 1991,
113, 196-201.
(23) Zimmerman, S C. Top. Curr. Chem. 1993, 165, 71-102.
(24) Zimmerman, S C. Bioorg. Chem. Front. 1991, 2, 33-71.
(25) Zimmerman, S. C.; Mrksich, M.; Baloga, M. J . Am. Chem. Soc.
1989, 111, 8528-8530.
(26) Zimmerman, S. C.; Wu, W. J . Am. Chem. Soc. 1989, 111, 8054-
8055.
(27) Zimmerman, S. C.; VanZyl, C. M. J . Am. Chem. Soc. 1987, 109,
7894-7896.
(28) Potluri, V. K.; Maitra, U. J . Org. Chem. 2000, 65, 7764-7769.
(10) Harmata, M.; Barnes, C. L. J . Am. Chem. Soc. 1990, 112, 5655-
5657.
(11) Harmata, M.; Barnes, C. L.; Karra, S. R.; Elahmad, S. J . Am.
Chem. Soc. 1994, 116, 8392-8393.
10.1021/jo015690j CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/09/2001

6170 J . Org. Chem., Vol. 66, No. 18, 2001
Krebs and J ørgensen
F igu r e 1. ORTEP stereo plots (50% ellipsoids) of the molecular geometry in the solid state as determined by X-ray crystallography.
The neutral host (above) and the host with a 1,3,5-trinitrobenzene guest molecule (below, the solvent CH2Cl2 molecule has been
omitted for clarity).
Sch em e 1
Slight changes in the thickness of the analyte can be
accommodated by the twisting of the large plates with
respect to the hinge. Only strongly electron deficient
molecules bind well. For instance the neutral molecule
4 does not bind solvent dichlorobenzene when crystal-
lizing. The average interplanar distance29 was 6.8(4) Å
(max/min ) 7.672(3)/6.092(3) Å) between the 1-meth-
ylphenanthro[9,10-d]imidazol-2-yl groups which form an
angle of 14.33(4)°. Further, the angle that these groups
form with the hinge region are respectively for the two
groups in the asymmetric unit 49.80(5)° and 55.75(5)°.
In the crystal structure of the complex of 4 with 1,3,5-
trinitrobenzene the interplanar average distance between
the two 1-methyl-phenanthro[9,10-d]imidazol-2-yl groups
is 6.48(13) Å (max/min ) 6.66(1)/6.22(1) Å) which form
angles of 3.76(6)° and 0.61(6)°, respectively. The two
distances between the 1-methylphenanthro[9,10-d]imid-
azol-2-yl groups and the 1,3,5-trinitrobenzene guest
molecule are 3.32(14) Å and 3.23(5) Å, respectively (max/
min ) 3.57(1)/3.05(1) Å and 3.47(1)/3.01(1) Å). The angles
formed between the hinge region and the large aromatic
plates is 42.65(24)° and 61.33(23)°, thus emphasising the
conformational flexibility of this host system. Interest-
ingly, the host molecule on its own seems to prefer having
the aromatic plates in proximity; thus, one does not need
to fix the geometry of the host to make it work as a
Resu lts a n d Discu ssion
Th e Solid Sta te. Our receptor molecule qualifies as
a molecular tweezer and consists of two large aromatic
plates separated at a distance sufficient to host a small
planar molecule. The large plates are held in space by a
linker or hinge region with few conformational degrees
of freedom. In Figure 1 the molecular geometry in the
solid state as determined by X-ray crystallography is
shown for both the neutral molecule 4 as well as the
geometry of 1:1 complex between 4 and 1,3,5-trinitroben-
zene.
(29) In all instances the average interplanar distances were obtained
by least-squares fitting the atoms of one of the planar group to a plane.
The distances of the individual atoms of the other planar group was
the worked out. Angles between planes were obtained by least-squares
fitting the atoms of the individual planar groups to a plane. The angles
between these two planes is then quoted.

A New Versatile Receptor Platform
J . Org. Chem., Vol. 66, No. 18, 2001 6171
Ta ble 1. Bin d in g Con sta n ts for th e 1:1 Com p lex betw een Com p ou n d 4 a n d Va r iou s An a lytes in CDCl3 As Deter m in ed by
NMR Titr a tion s
Sch em e 2
and 8.60 ppm belongs to the A and A′ parts of these
systems. The X and X′ signals are grouped together in a
multiplet around 7.6 ppm. Finally, a multiplet centered
around 8.1 ppm with the intensity of three protons can
be assigned to the A2B system.
A TOCSY spectrum was also obtained to confirm the
assignments. Each spin system is clearly grouped to-
gether using this technique. The ABC system is seen to
be connected through meta couplings to the singlet at 8.75
ppm assigned to the H3 protons. The spectrum in CDCl3
solution is less well resolved since the XX′ parts have
spread out over a larger range, obscuring a doublet of
the ABC system and also overlapping the A2B system.
Bin d in g Stu d ies. When molecules that bind well to
the tweezer (i.e., 1,3,5-trinitrobenzene) are added to the
receptor. Both regions, the aromatic plates and the hinge,
can in principle be tuned with respect to their interaction
with the guest molecule. Comprehensive work by Zim-
merman showed this to be of great importance.20,21 The
available interactions between the aromatic plates and
the analyte are mainly π-π interactions. Through ap-
propriate synthetic elaboration π-donor or π-acceptor
interactions can be envisaged. The interactions between
the hinge region and the analyte that can be envisaged
are specific hydrogen interactions (donor/none/acceptor)
and acid/base interactions. As mentioned above, previous
work on molecular tweezers generally relied on elaborate
synthetic chemistry, making the synthesis of widely
different receptors time-consuming, or relied on naturally
occurring molecules, thus limiting the range of molecular
structures that could be accessed with ease. With the
strategy presented here, the facile synthesis of an array
of receptor molecules with different specificities is pos-
sible. We have exemplified this type of system with a
receptor molecule that binds electron deficient planar
molecules in particular polynitroaromatics such as ex-
plosives.
1
solution, the H spectrum changes dramatically due to
shielding effects. It is notable that the signals arising
from the protons in the 1-methylphenanthro[9,10-d]-
imidazole-2-yl groups are moved to higher field while
those in the bridge are moved to lower field. This is of
course in agreement with the X-ray structure where the
1,3,5-trinitrobenzene molecule is placed in the cleft of the
tweezer. Protons above and below the 1,3,5-trinitroben-
zene plane are shielded (the plate protons) while protons
in the TNB plane are deshielded (the bridge protons). The
1:1 stoichiometry of the complexes between 4 and the
analytes shown in Table 1 was determined by the
continuous variation method shown in the J ob plot in
Figure 2 for 2,4,7-trinitrofluorenone.
Th e An a lytes. NMR titrations with seven guest
molecules (nitro arenes) were carried out in CDCl3, and
the binding constants for the complexes were computed
by least squares nonlinear fitting using the program
EQNMR.30 The results are shown in Table 1. A rather
high binding constant of 490 M-1 was obtained for 2,4,7-
trinitrofluorenone as guest which can be contrasted to
the result obtained by Potluri and Maitra of 220 M-1 with
a host molecule comprised of two pyrene plates bound
together by a 7-deoxycholic acid type bridge via carboxylic
ester hinges.16
We believe that the higher binding constant obtained
with 4 can be ascribed to a tendency for this molecule to
preorganize. A higher binding constant (675 M-1) is
obtained with a totally rigid molecule with fixed confor-
mation as reported by Zimmerman.20
Overall the binding constants obtained are very similar
to the values reported for different and more rigid
receptor systems, suggesting that in the case of 4 the
rigidity of the hinge region is large enough not to impinge
on a strong interaction with guest molecules. The binding
observed is due to the formation of charge-transfer
complexes which is also evident from the dark red to
brownish coloration of the resulting solutions. It is
therefore not surprising that the binding constant in-
1
In Solu tion . The H spectrum of 4 can be subdivided
into 11 independent spin systems as shown in Scheme
2. An A2B (H1 and H2) system arising from the pyridine
ring, two equivalent ABC (H4,H5,H6) systems from the
adjoining benzene rings, equivalent singlets from the H3
protons, equivalent singlets from the N-methyl groups
and two sets of equivalent AA′XX′ (H7,H8,H9,H10)
1
(H11,H12,H13,H14). H spectra were obtained in both
CDCl3 and DMSO-d6, facilitating the assignment. The
singlet at 4.28 ppm in CDCl3 and 4.34 ppm in DMSO-d6
clearly arises from the N-methyl groups. A singlet at 8.69
ppm in CDCl3 and 8.75 ppm in DMSO is also straight-
forwardly assigned to the H3 protons. A COSY spectrum
of the DMSO solution connects doublets at 8.52 and 7.97
ppm and a triplet at 7.79 in one spin system. Since the
integrals of these three signals each corresponds to two
protons, these signals must be assigned to the ABC
system. The COSY spectrum of the DMSO solution also
connects the two AA′XX′ systems. Two doublets at 8.93
and 8.48 ppm together with two distorted doublets at 8.82
(30) Hynes, M. J . J . Chem. Soc., Dalton Trans. 1993, 311.

6172 J . Org. Chem., Vol. 66, No. 18, 2001
Krebs and J ørgensen
F igu r e 2. J ob plot of the chemical shift change of the N-methyl groups of the tweezer molecule (4) as a function of the mole
fraction of 2,4,7-trinitrofluorenone in CDCl3 showing the 1:1 binding stoichiometry.
creases sharply with the number of electron-withdrawing
groups present in the guest molecules. Minor effects on
the substitution pattern of the dinitro benzenes may be
noted. The ortho- and meta-compounds scarcely show any
interaction with 4 while p-dinitrobenzene forms a definite
complex albeit with a low binding constant of 6 M-1. With
one additional nitro group as in 1,3,5-trinitrobenzene the
binding constant increases more than 30 times to 182
M-1. Substitution of one of the three nitro groups with
the less electron-withdrawing cyano group leads to a
smaller binding constant of 55 M-1 underscoring the
sensitivity of the charge-transfer interaction. The seem-
ingly minor change of introducing a methyl group to
obtain 2,4,6-trinitrotoluene again greatly reduces the
binding constant by a factor of more than 7 times to 24
M-1. This effect can only be explained in terms of steric
hindrance. The X-ray crystal structure of 2,4,6-trinitro-
toluene reveals that the methyl group forces the nitro
groups out of plane with the central ring thus increasing
the thickness. The torsion angles reported are in the
range of 30° to 60°.31,32 Close examination of the X-ray
structure of 4 with 1,3,5-trinitrobenzene (Figure 1) shows
a very tight fit between the host and guest. Compound 4
may not readily adapt to a somewhat thicker molecule-
like 2,4,6-trinitrotoluene although it has approximately
the same acceptor properties as 1,3,5-trinitrobenzene.
The very high binding constant of 2,4,7-trinitrofluorenone
may be ascribed to at least two factors. First, the electron-
withdrawing nitro groups have been augmented by the
carbonyl group. Second, the fused three-ring system is
capable of a much larger overlap with the host 1-meth-
ylphenanthro[9,10-d]imidazol-2-yl groups.
mation might be preorganized and flexible enough to
encompass slight differences in interplanar distances.
Further we showed that the binding of planar nitroaro-
matic compounds is comparable to the very rigid tweezer
molecules which has been reported as the compounds
with the highest binding constants.
Exp er im en ta l Section
2-(3-Br om op h en yl)-1H-p h en a n th r o[9,10-d ]im id a zole‚
AcOH (1). Phenanthrenequinone (42 g, 0.20 mol), 3-bro-
mobenzaldehyde (36 g, 0.2 mol), and ammonium hydrogen-
carbonate (32 g, 0.40 mol) were mixed in glacial acetic acid
(250 mL). Initially the mixture foamed due to the effervescence
of CO2(g). After this process had subsided, the mixture was
refluxed for 1 h. During the reaction time, all solids dissolved,
and then the product precipitated toward the end. Water (100
mL) was added carefully and the mixture cooled. The product
was filtered, washed with water and a little hexane, and dried.
This gave the acetate of 1 as colorless material in 82% yield
(71 g). This product was used without further purification. Mp
1
174-175 °C; H NMR (250 MHz, CDCl3, 300 K, TMS): δ 2.2
(s, 3H, CH3), 7.2 (t, 3J (H,H) ) 8 Hz, 1H, ArH), 7.3 (s, 1H, ArH),
7.4 (d, 3J (H,H) ) 8 Hz, 1H, ArH), 7.5 (m, 4H, ArH), 7.9 (d,
3J (H,H) ) 8 Hz, 1H, ArH), 8.1 (s, 1H, ArH), 8.2 (m, 2H, ArH),
8.5 (m, 2H, ArH), 9.2 (bs, 2H, NH/OH); 13C NMR (63 MHz,
DMSO-d6, 300 K, TMS): δ 21.9, 122.8, 123.1, 124.6, 125.0,
125.9, 126.2, 126.3, 126.4, 127.7, 128.0, 128.5, 128.7, 129.2,
132.0, 132.6, 133.4, 137.9, 148.2, 172.8 (two signals are missing
which is ascribed to accidental isochrony). Anal. Calcd for
C
23H17BrN2O2: C, 63.75; H, 3.95; N, 6.47. Found: C, 64.13;
H, 5.64; N, 6.63.
2-(3-Br om op h en yl)-1-m eth yl-p h en a n th r o[9,10-d ]im id -
a zole (2). Compound 1 (69.5 g, 0.16 mol) was suspended in
THF (1400 mL), and tBuOK (53 g, 0.47 mol) was added. The
mixture was stirred for 20 min, and methyl iodide (79.5 g, 0.56
mol) was added. A precipitate formed, and the mixture was
stirred for 1 h more. Water (10 mL) was then added and the
mixture evaporated to dryness. Water (200 mL) and chloroform
(enough to dissolve all the solids) was added. The organic
phase was separated, dried (MgSO4), and evaporated to
dryness leaving the crude product. Recrystallization from
ethanol gave compound 2 as a thin colorless needles in 74%
yield (45.9 g). Mp 167-168 °C; 1H NMR (250 MHz, CDCl3,
Con clu sion s
In conclusion we have shown how a new and versatile
receptor platform based on the concept of molecular
tweezers is easily realized by means of a simple synthetic
strategy. The crystal structures of both the neutral
tweezer molecule and the tweezer molecule with bound
1,3,5-trinitrobenzene indicate that the molecular confor-
3
300 K, TMS): δ 4.2 (s, 3H, CH3), 7.4 (t, J (H,H) ) 8 Hz, 1H,
ArH), 7.5-7.7 (m, 6H, ArH), 7.9 (s, 1H, ArH), 8.3-8.4 (m, 1H,
ArH), 8.6 (d, 3J (H,H) ) 8 Hz,1H, ArH), 8.7 (t, 3J (H,H) ) 8 Hz,
2H, ArH); 13C NMR (63 MHz, CDCl3, 300K, TMS): δ 36.7,
121.3, 123.2, 123.5, 123.7, 124.1, 125.0, 125.6, 126.2, 127.3,
127.92, 127.95, 128.4, 128.7, 129,0. 129.9, 130.8, 133.10,
(31) Barnes, J . C.; Golnazarians, W. Acta Crystallogr. 1987, C43,
549.
(32) Golovina, N. I.; Titkov, A. N.; Raevskii, A. V.; Atovmyan, L. O.
J . Solid State Chem. 1994, 113, 229.

A New Versatile Receptor Platform
J . Org. Chem., Vol. 66, No. 18, 2001 6173
Ta ble 2. Cr ysta llogr a p h ic Da ta for Com p ou n d 4 a n d for
th e 1:1 Com p lex of 4 a n d 1,3,5-Tr in itr oben zen e
133.13, 133.5, 138.2, 151.5. Anal. Calcd for C22H15BrN2: C,
68.23; H, 3.90; N, 7.23. Found: C, 67.87; H, 3.68; N, 7.20.
3-(1-Meth ylp h en a n th r o[9,10-d ]im id a zol-2-yl)-p h en yl-
bor on ic Acid h yd r och lor id e (3). Compound 2 (25 g, 64
mmol) was dissolved in dry THF (400 mL) under argon and
cooled to r70 °C with a CO2(s)/acetone bath. nBuLi (1.6 M,
60 mL, 96 mmol) was added. Triisopropyl borate (24.5 g, 0.13
mol) was added, the cooling bath was removed, and the
mixture was left to stand for 2 h. HCl(aq) 20% 200 mL was
added, and stirring was continued for 0.5 h. The mixture was
evaporated until most of the THF had been removed. The
product was filtered after cooling to ambient temperature,
washed with light petroleum, and dried. The crude product
was dried at a temperature <50 °C. The crude product was
dissolved in a small amount of DMSO and precipitated with
ether. This gave 3 as a colorless powder in 94% yield (23.5 g).
Mp 239-241 °C; 1H NMR (250 MHz, DMSO-d6, 300 K, TMS):
compound
formula
formula wt
4
C
4:(1,3,5-trinitrobenzene)
C56H38N8O6Cl2
989.84
49H33N5
691.80
crystal system
space group
Z
triclinic
P-1
2
triclinic
P-1
2
a, Å
b, Å
10.835(2)
11.104(2)
14.063(3)
91.093(4)
93.404(4)
101.956(4)
1651.4(5)
1.391
10.1412(15)
10.5079(16)
24.330(4)
84.990(4)
79.243(3)
63.291(3)
2275.3(6)
1.445
c, Å
R,o
â,o
γ,o
V, Å3
F, g cm3
crystal dimensions,
mm
0.38 × 0.25 × 0.37 × 0.12 ×
0.13
Mo-KR
0.083
0.12
Mo-KR
0.209
120(2)
29973
12358
3
δ 4.4 (s, 3H, CH3), 7.7-7.9 (m, 5H, ArH), 8.0 (d, J (H,H) ) 8
type of radiation
Hz, 1H, ArH), 8.2 (d, 3J (H,H) ) 8 Hz, 1H, ArH), 8.4 (s, 1H,
µ, cm-1
ArH), 8.7 (d, 3J (H,H) ) 8 Hz,1H, ArH), 8.8 (d, 3J (H,H) ) 8 Hz,
T, K
120(2)
3
3
1H, ArH), 8.9 (d, J (H,H) ) 8 Hz,1H, ArH), 9.0 (d, J (H,H) )
8 Hz, 1H, ArH); 13C NMR (63 MHz, DMSO-d6, 300 K, TMS):
δ 37.9, 122.3, 123.0, 123.4, 123.6, 125.0, 125.6, 127.1, 128.0,
128.6, 128.9, 129.0, 129.1, 129.4, 129.9, 133.1, 137.1, 138.4,
138.5, 150.1 (the signals from two of the carbon atoms could
not be observed. This is ascribed to either accidental isochrony
number of reflections 22171
unique reflections
9104
R(F), Rw(F2) all data 0.0632, 0.1674 0.1222, 0.3423
Crystals of 4‚TNB lost solvent upon exposure to air, and
this impaired the quality of the data due to a degradation of
the crystalline properties. An almost complete sphere of
reciprocal space was covered by a combination of several sets
of exposure frames; each set with a different æ angle for the
crystal, and each frame covering a scan of 0.3° in ω. Data
collection, integration of frame data, and conversion to intensi-
ties corrected for Lorenz, polarization, and absorption effects
were performed using the programs SMART,33 SAINT,33 and
SADABS.34 Structure solution, refinement of the structures,
structure analysis, and production of crystallographic illustra-
tions were carried out using the programs SHELXS97,35
SHELXL97,35 and SHELXTL.36 The structures were checked
for higher symmetry and none was found.37 In both of the
structures H atoms were included in their calculated positions.
Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC-156564 and CCDC-156565. Copies of the
data can be obtained free of charge on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (fax: (+44)1223-
336-033; e-mail: deposit@ccdc.cam.ac.uk).
or to the carbon bonded to boron). Anal. Calcd for C22H18
-
BClN2O2: C, 67.99; H, 4.67; N, 7.21. Found: C, 67.78; H, 4.57;
N, 7.28.
2,6-Bis(3-(1-m eth yl-p h en a n th r o[9,10-d ]im id a zol-2-yl)-
p h en yl)p yr id in e (4). 2,6-Dibromopyridine (1.2 g, 5 mmol),
compound 3 (4.3 g, 11 mmol), water (100 mL), toluene (100
mL), dimethoxyethane (100 mL), Na2CO3 (12 g, 0.11 mol), and
(Ph3P)2PdCl2 (0.25 g, 0.35 mmol, 3.5 mol %) were mixed in a
(500 mL) conical flask and degassed with argon. The mixture
was refluxed overnight under argon. The following day a white
solid had precipitated. The mixture was evaporated to 100 mL,
cooled, and filtered. The product was washed with ether and
light petroleum. The crude product was dissolved in chloroform
and precipitated with ether, giving compound 4 as a white
1
powder in 93% yield (3.2 g). Mp 273-275 °C; H NMR (250
MHz, CDCl3, 300 K, TMS): δ 4.3 (s, 3H, CH3), 7.4-7.7 (m,
3
10H, ArH), 7.8-7.9 (m, 5H, ArH), 8.2 (d, J (H,H) ) 8 Hz, 2H,
ArH), 8.3 (d, 3J (H,H) ) 8 Hz, 2H, ArH), 8.6 (d, 3J (H,H) ) 8
Hz, 2H, ArH), 8.6-8.8 (m, 6H, ArH); 13C NMR (250 MHz,
CDCl3, 300 K, TMS): δ 36.5, 119.6, 120.9, 122.9, 123.4, 124.0,
124.7, 125.2, 125.8, 126.9, 127.6, 127.7, 128.1, 128.3, 128.5,
129.1, 129.5, 129.6, 130.8, 131.4, 137.9, 138.2, 140.3, 152.9,
156.5. Anal. Calcd for C49H33N5: C, 85.07; H, 4.81; N, 10.12.
Found: C, 83.81; H, 4.73; N, 9.94.
J O015690J
(33) Siemens 1995. SMART and SAINT. Area-Detector Control and
Integration Software. Siemens Analytical X-ray Instruments Inc.,
Madison, WI.
(34) Empirical absorption program (SADABS) written by George
Sheldrick for the Siemens SMART platform.
(35) SHELX-97, Program for structure solution and refinement
written by George M. Sheldrick, 1997.
(36) Sheldrick, G. M., 1995 SHELXTL95. Siemens Analytical X-ray
Instruments Inc., Madison, WI.
Cr ysta llogr a p h y. General crystallographic data can be
found in Table 2. The crystals 4 and 4‚TNB were drawn
directly from the mother liquor, coated with a thin layer of
protecting oil, mounted on glass fibers using Apiezon grease,
and transferred quickly to the cold stream of nitrogen (Oxford
Cryostream) on the diffractometer (Siemens SMART CCD
Platform).
(37) Spek, A. L. Acta Cryst. 1990, A46, C-31.