En route to surface-bound electric field-driven molecular motors

Article abstract of DOI:10.1021/jo034169h

Four caltrop-shaped molecules that might be useful as surface-bound electric field-driven molecular motors have been synthesized. The caltrops are comprised of a pair of electron donor-acceptor arms and a tripod base. The molecular arms are based on a carbazole or oligo(phenylene ethynylene) core with a strong net dipole. The tripod base uses a silicon atom as its core. The legs of the tripod bear sulfur-tipped bonding units, as acetyl-protected benzylic thiols, for bonding to a gold surface. The geometry of the tripod base allows the caltrop to project upward from a metallic surface after self-assembly. Ellipsometric studies show that self-assembled monolayers of the caltrops are formed on Au surfaces with molecular thicknesses consistent with the desired upright-shaft arrangement. As a result, the zwitterionic molecular arms might be controllable when electric fields are applied around the caltrops, thereby constituting field-driven motors.

Full text of DOI:10.1021/jo034169h

En Rou te to Su r fa ce-Bou n d Electr ic F ield -Dr iven Molecu la r
Motor s
Huahua J ian and J ames M. Tour*
Department of Chemistry, Department of Mechanical Engineering and Materials Science and
Center for Nanoscale Science and Technology, MS-222, Rice University, 6100 South Main Street,
Houston, Texas 77005
tour@rice.edu
Received February 6, 2003
Four caltrop-shaped molecules that might be useful as surface-bound electric field-driven molecular
motors have been synthesized. The caltrops are comprised of a pair of electron donor-acceptor
arms and a tripod base. The molecular arms are based on a carbazole or oligo(phenylene ethynylene)
core with a strong net dipole. The tripod base uses a silicon atom as its core. The legs of the tripod
bear sulfur-tipped bonding units, as acetyl-protected benzylic thiols, for bonding to a gold surface.
The geometry of the tripod base allows the caltrop to project upward from a metallic surface after
self-assembly. Ellipsometric studies show that self-assembled monolayers of the caltrops are formed
on Au surfaces with molecular thicknesses consistent with the desired upright-shaft arrangement.
As a result, the zwitterionic molecular arms might be controllable when electric fields are applied
around the caltrops, thereby constituting field-driven motors.
In tr od u ction
monly used are chemical9,14,15 and light energy.10-12
Modest AC fields can be used to influence and monitor
intramolecular rotary motion.16 We have been interested
in the force and energy that a dipolar unit generates
under the influence of external electric stimuli. The
change of orientation of dipolar units, originating from
intramolecular rotary motion, could be detected according
to the conformation of the molecules.17-19 In this paper
we detail our design and synthesis of a series of caltrop-
shaped molecules with donor-acceptor functionality,
which might behave as electric field-driven molecular
motors. In all cases, the molecules have thiol-based end
groups for adhesion to a metallic surface, and the
efficiency for their controlled surface assembly is dis-
cussed.
Nature has elegantly constructed mechanical-like de-
vices at the micron-scale such as those in bacteria.1-4 Like
their macroscopic analogues, these tiny machines per-
form numerous functions. In achieving controlled rotary1,2
or translational3,4 movement under the influence of
external stimuli, the natural micron-sized devices can be
highly efficient. Yet they are sufficiently complicated that
reproducing them artificially is beyond present technolo-
gies. Nevertheless, the pursuit of constructing nanosized
machines to augment the basic functions of their natural
counterparts has continued since the concept was first
proposed by Feynman around half a century ago.5-7
Recent developments in organic synthetic methodologies
have allowed chemists to successfully build several
prototypes of nanosized machines in a “bottom-up” ap-
proach.8 For example, several man-made molecular mo-
tors have been reported that can convert external energy
into arranged movement such as ordered rotary9-11 or
translational12,13 motion. The energy sources most com-
In our system (Figure 1), the movement of a molecule
is restricted by attaching the molecule to a surface via a
tripod.20-23 The molecular caltrops are tetrahedral in
shape and can assemble upright on a metallic surface
(13) Harada, A. Acc. Chem. Res. 2001, 34, 456-464.
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10.1021/jo034169h CCC: $25.00 © 2003 American Chemical Society
Published on Web 05/22/2003
J . Org. Chem. 2003, 68, 5091-5103
5091

J ian and Tour
F IGURE 1. Design of electrically driven molecular motor that is assembled on a gold surface.
(such as Au) in the form of self-assembled monolayers
(SAMs). Each of the three legs of the tripodal platform
bears a sulfur-tipped adhesion unit, delivered via an
acetyl-protected benzylic thiol. The acetyl groups can be
readily deprotected in situ to afford free thiols during the
self-assembly process. Once assembled on a metallic
surface, the molecule has no translational degree of
freedom. Instead, the top part (the molecular arms) is
able to rotate about the oligomeric phenylene ethynylene
axis of the molecule (the molecular shaft). With donor-
acceptor functionality attached, the arm possesses a
strong net dipole moment, with the hope of influencing
this dipole to control rotation when subjected to oscillat-
ing electric fields.16
The molecular arms in three of the caltrops are based
on carbazole cores. Functionalized carbazoles have been
used as chromophores and building blocks in organic
photoconductors and photorefractive materials.24,25 The
spectroscopic properties of carbazole and its derivatives
have been widely studied,26,27 which might allow us to
track the movement of the molecular arms by coupled
microscopic/spectroscopic methods.28 Controlling the angle
of the arms by the positions of substitution on the
carbazole and the length of the arms by the number of
conjugated phenylene ethynylene groups allows several
arrangements to be considered. In caltrops 1-3 in Figure
2, one end of the arms carry an N,N-dimethylamino
moiety and the other end a nitro group for the strong
net dipole. Naturally, the strength of the dipole depends
on the separation distance and the electronic arrange-
ment around the carbazole. In caltrop 4, we sought to
have the arms generate another degree of measurable
propeller-like motion that is off-angle to the shaft rota-
tion. The arms and the base are connected together via
the molecular shaft, a rigid oligomeric phenylene ethyn-
ylene. This shaft also separates the arms from the
metallic surface to reduce possible interactions between
them.
We previously synthesized some caltrops that could be
useful as AFM tips; they had no molecular arms atop the
shafts.23 However, our previous study showed that the
caltrops with para-phenylenethiol-terminated tripods
were tilted when attached to the gold surface because
only two of the three potential Au-S bonds could form.
The modified molecular tripod base used here has ben-
zylic thiols at meta-positions relative to the ethynylene
groups, thereby permitting the proper orientation for
assembly.
Resu lts a n d Discu ssion
Syn th esis of th e Molecu la r Tr ip od Ba se. The
construction of the molecular base began with the
synthesis of 7, which was made from 3-iodobenzyl alcohol
(Scheme 1).
The synthesis of the silicon core is shown in Scheme
2. We have previously reported preparation of 8 by
lithiation of 1,4-diiodobenzene and addition of the phe-
nyllithium to tetraethyl orthosilicate.23 It is imperative
that the reaction be conducted in ether and not THF;
otherwise, only traces of 8 are afforded. Coupling of 8
with 3 equiv of 7 gave 9. The 4-iodophenylene moiety of
10 was introduced by addition of n-butyllithium to the
mixture of 1,4-diiodobenzene, 9, and THF at -78 °C.
Neither the addition of 4-iodophenyllithium, generated
in situ by lithium-halogen exchange, to 9 nor the reverse
addition gave 10. Removal of the three TBDMS groups
(22) Guo, W.; Galoppini, E.; Rydja, G.; Pardi, G. Tetrahedron Lett.
2000, 41, 7419-7421.
(23) Yao, Y.; Tour, J . M. J . Org. Chem. 1999, 64, 1968-1971.
(24) Zhu, Z.; Moore, J . S. J . Org. Chem. 2000, 65, 116-123.
(25) Zhang, Y.; Wada, T.; Wang, L.; Sasabe, H. Tetrahedron Lett.
1997, 38, 1785-1788.
(26) Bratcher, M. S.; DeClue, M. S.; Grunnet-J epsen, A.; Wright,
D.; Smith, B. R.; Moerner, W. E.; Siegel, J . S. J . Am. Chem. Soc. 1998,
120, 9680-9681.
(27) Wang, L.; Zhang, Y.; Wada, T.; Sasabe, H. Appl. Phys. Lett.
1996, 69, 728-730.
(28) Mantooth, B. A.; Donhauser, Z. J .; Kelly, K. F.; Weiss, P. S.
Rev. Sci. Instrum. 2002, 73, 313.
5092 J . Org. Chem., Vol. 68, No. 13, 2003

Surface-Bound Electric Field-Driven Molecular Motors
F IGURE 2. Structures of molecular caltrops 1-4.
SCHEME 1
from 10 was completed by TBAF buffered with acetic
acid. When the reaction mixture was not buffered, the
central silicon atom in 10 was fully disrupted. The triol
11 was converted to trithiolacetate 12 by a Mitsunobu-
type reaction.
The thiol groups of 12 are protected by acetyl groups,
which will be removed during the SAM formation process.
The molecular tripod base 12 contains an aryl iodide
moiety that allows coupling with different molecular
shafts to produce various final products for studying
structure-activity relationships.
Syn th esis of Molecu la r Ar m s. The arms of caltrop
1 are based on a 2,7-disubstituted carbazole core. As
shown in Scheme 3, lithiation of 4-bromo-N,N-dimeth-
ylaniline followed by treatment with tributyltin chloride
gives 13.29 Stille coupling of 13 and 2-bromo-5-nitro-
aniline produces 14. The azide 15 was made from 14
through displacement of the diazonium salt. Thermal
decomposition of azide 15 in kerosene gives the function-
(29) Farina, V.; Krishnan, B.; Marshall, D. R.; Roth, G. P. J . Org.
Chem. 1993, 58, 5434-5444.
J . Org. Chem, Vol. 68, No. 13, 2003 5093

J ian and Tour
SCHEME 2
alized carbazole 16.30 Cu-catalyzed coupling of 16 with
1,4-diodobenzene affords 17. Palladium-catalyzed cou-
pling of 17 with TMSA followed by deprotection of the
terminal alkyne affords 19, the “molecular arms” of
caltrop 1. Caltrop 1 was synthesized by Sonogashira
coupling of 19 and tripod base 12.
The arms of caltrop 2 have the same carbazole regio-
chemistry in relation to the shaft as that in caltrop 1,
but 2’s arms are longer. Since 2,7-dibromocarbazole (22)
cannot be conveniently made via bromination of carba-
zole, 22 is prepared in three steps (Scheme 4). Ullmann
coupling of 2,5-dibromo-3-nitrobenzene gives 20,31 which
is subsequently reduced to the diamine 21.31 Cyclization
of 21 in hot acid gives 22.32 The nucleophilic aromatic
substitution reaction of 22 and 4-fluoronitrobenzene
affords 23 that is reduced to 24.
As shown in Scheme 6, the amino group of 24 was
converted to the iodo group through a Sandmeyer reac-
tion. Pd-catalyzed coupling of 28 with 1 equiv of TMSA
gave the dibromo compound 29. This iodide coupling
reaction had quite good selectivity with little reaction
seen at the symmetrical bromo positions. Further cou-
pling of 29 with 1 equiv of 27 gave the monocoupled
product 30. The yield of this coupling reaction was
depressed due to the selectivity problems; however, 40-
50% of 29 could be recovered. Several attempts to couple
30 with (4-nitrophenyl)ethyne44 failed to yield 32.
Lithium-halogen exchange of 30 gave the aryl iodide 31.
Coupling of 31 successfully afforded 32 in good yield.
Removal of the TMS group of 32 gave the free alkyne 33
that was ready for coupling with 12 (molecular base),
yielding caltrop 2.
The synthesis of the donor part of 2’s molecular arms
starts with the reductive alkylation of 4-iodoaniline to
give 25 (Scheme 5).33 Further coupling of 25 with TMSA
affords 26.34 Desilylation of 26 gives 27,35 which will be
used as the donor side of molecular arms of caltrops 2
and 3.
As shown in Scheme 7, preparation of arms of caltrop
3 starts with 34, which was made according to Moore’s
procedure.24 Iodination of 34 by Sandmeyer reaction
affords 3524 that was coupled with TMSA to give 36.
Coupling of 36 with 1 equiv of 1-ethynyl-4-nitrobenzene
gave 37 in a low yield of 36%. However, 50-60% of 36
could be recovered. Further Pd-catalyzed coupling of 37
and 27 afforded 38, desilylation of which gave 39 that
was coupled with the tripod base 12 to afford molecular
caltrop 3.
(30) Smith, P. A. S.; Brown, B. B. J . Am. Chem. Soc. 1951, 73, 2435-
2437.
(31) Yamato, T.; Hideshima, C.; Suehiro, K.; Tashiro, M.; Prakash,
G. K. S.; Olah., G. A. J . Org. Chem. 1991, 56, 6248-6250.
(32) Patrick, D. A.; Boykin, D. W.; Wilson, W. D.; Tanious, F. A.;
Spychala, J .; Bender, B. C.; Hall, J . E.; Dykstra, C. C.; Ohemeng, K.
A.; Tidwell, R. R. Eur. J . Med. Chem. 1997, 32, 781-793.
(33) Giumanini, A. G.; Chiavari, G.; Musiani, M. M.; Rossi, P.
Synthesis 1980, 9, 743-746.
The synthesis of caltrop 4 (Scheme 8) began with the
literature-based preparation of 1,3-dibromo-5-(trimeth-
ylsilylethynyl)benzene (4036) and 41.37 Partial reduction
of 1,3-dinitro-5-bromobenzene38 gave 41. The N,N-di-
(34) Wong, M. S.; Nicoud, J .-F. Tetrahedron Lett. 1994, 35, 6113-
6116.
(35) Leonard, K. A.; Nelen, M. I.; Anderson, L. T.; Gibson, S. L.;
Hilf, R.; Detty, M. R. J . Med. Chem. 1999, 42, 3942-3952.
(36) Xu, Z.; Kahr, M.; Walker, K. L.; Wilkins, C. L.; Moore, J . S. J .
Am. Chem. Soc. 1994, 116, 4537-4550.
5094 J . Org. Chem., Vol. 68, No. 13, 2003

Surface-Bound Electric Field-Driven Molecular Motors
SCHEME 3
SCHEME 4
methylation of aniline 41 gave 4239 followed by Pd-
catalyzed coupling to afford the silyl-protected alkyne 43,
desilylation of which afforded 44. Coupling of 44 with
40 gave 45 (the arms of the caltrop) that was desilylated
to give 46 and coupled with 12 to afford the desired
caltrop 4.
(37) Emokpae, T. A.; Dosunmu, I. M.; Hirst, J . J . Chem. Soc., Perkin
Trans. 2 1974, 1860-1862.
(38) Andrievskii, A. M.; Gorelik, M. V.; Avidon, S. V.; Al’tman, E.
S. Russ. J . Org. Chem. 1993, 29, 1519-1524.
(39) Rosevear, J .; Wilshire, J . F. K. Aust. J . Chem. 1977, 30, 1561-
1572.
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J ian and Tour
SCHEME 5
SCHEME 6
Using the selective addition of aryllithium reagents to
tetraethyl orthosilicate, along with transition-metal-
catalyzed coupling reactions, we have synthesized four
caltrop-shaped molecules that can potentially serve as
molecular motors. These caltrops were designed with
tripod bases containing protected thiols that should allow
the molecules to form Au-S bonds to gold surfaces. The
arms bear donor-acceptor functionalities, which should
make them controllable by an external electric field, to
be confirmed by testing. The synthetic methodology
developed will permit us to easily adjust the structure
of the motors, varying such characteristics as the func-
tional groups of the molecular arms, the length of the
molecular shafts, and the binding moieties of the molec-
ular base. Using the results of the surface testing as
feedback to our synthetic strategy, we can maximize the
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Surface-Bound Electric Field-Driven Molecular Motors
SCHEME 7
TABLE 1. Th eor etica l a n d Actu a l Self-Assem bled
performance of the caltrop-shaped molecules as molecular
motors or rotors in outer low-frequency oscillating electric
fields and on different surfaces.
Mon ola yer Th ick n esses of 1-4 on Au Su r fa cesa
conc
(mM)
time
(h)
theoretical
height (Å)
thickness of
SAM (Å)
caltrop
Self-Assem bly. The four caltrops bear thiolacetate-
terminated ends for adhesion to a metallic surface so that
their behavior can ultimately be studied in the presence
of electric fields. We will use lithographic techniques to
pattern small regions of Au surfaces on which the
caltrops will be deposited. The formation of monolayers
is crucial in order to be able to determine the orientation
of the molecular arms and to detect any movement when
an electric field is applied. Codeposition or insertion into
short alkanethiolate matrixes might be needed to keep
the molecular arms of adjacent molecules from interact-
ing.
In prior work, we have developed both acid- and base-
catalyzed thiol deprotection methods for the in situ
generation of thiols during the self-assembly process, and
we exploit the acid-catalyzed deprotection method here.40
A fresh vapor-deposited Au surface (on silicon with a Cr-
adhesion layer) was incubated with a solution of each
1
2
3
4
1.0
1.0
0.5
1.0
6
4
2
4
29
25
31
25
26
22
31
25
a
Comparison of the theoretical thickness (Spartan, estimating
the Au-S bond to be 2.4 Å) with the ellipsometrically obtained
thicknesses of the monolayers assembled on Au surfaces. Acid-
promoted self-assembly of caltrops where [H2SO4] ) 60 mM.40
caltrop in the presence of dilute sulfuric acid for 2-6 h
to generate SAMs that were investigated by ellipsometry,
the results of which are shown in Table 1. The predicted
heights are based upon minimized structures by Spartan
using force field MMFF94. Our results show that the
thicknesses of the SAMs are consistent with the calcu-
(40) Cai, L.; Yao, Y.; Yang, J .; Price, D. W.; Tour, J . M. Chem. Mater.
2002, 14, 2905-2909.
J . Org. Chem, Vol. 68, No. 13, 2003 5097

J ian and Tour
SCHEME 8
methods.41-43 THF and diethyl ether were distilled from
sodium and benzophenone under a N2 atmosphere. NEt3 and
N,N-diisopropylethylamine were distilled from calcium hydride
under a N2 atmosphere. Column chromatography was carried
out on silica gel (grade 60, mesh size 230-400, EM Science).
Thin-layer chromatography (TLC) was performed using glass
silica gel plates (40 F254 0.25 mm layer thicknesses, Merck).
Infrared spectra (IR) assignments have 2 cm-1 resolution. The
para-substituted benzene ring protons (AA′XX′ system) were
reported as doublets. The residual solvent (CDCl3) proton
signal was used as an internal standard for spectra (δ 7.28
for 1H and δ 77.5 for 13C) unless otherwise stated. All
compounds were named using the Beilstein Autonom feature
of Beilstein Commander software.
lated heights (Table 1). Clearly, the benzylic thiols that
are meta-oriented to the extended base permit self-
assembly in a well-controlled fashion. Previously, when
we had made caltrops (without the molecular arms)23 that
had arylthiols para-oriented to the extended base, self-
assembly was inconsistent (unpublished results); the
ellipsometric thicknesses and surface IR studies suggest
that two of the thiols would bind while the third projected
off the surface.
Con clu sion s
We have designed and successfully synthesized four
caltrop-shaped molecules that bear donor-acceptor func-
tionalities. Our ellipsometry results show that the thiol
moieties on the legs of the molecular caltrops allow them
to form SAMs on Au surfaces, with heights that are
consistent with a monolayer structure. Once assembled,
the structures of these molecules should allow the top
donor-acceptor part (molecular arms) to rotate in re-
sponse to an outer oscillating electric field in testing that
is now underway.28
Gen er a l P r oced u r e for P a lla d iu m -Ca ta lyzed Cou p lin g
Rea ction of Ter m in a l Alk yn es a n d Ar yl Br om id es or
41
Ar yl Iod id es. The palladium catalysts Pd(dba)2 and Pd-
42,43
(PPh3)2Cl2
were prepared according to literature proce-
dures. An oven-dried screw-cap tube was charged with the aryl
halide (1 mol), palladium catalysts (Pd(dba)2 or Pd(PPh3)2Cl2)
(3-5 mol %), and CuI (3-5 mol %). The ligand PPh3 (12-20
mol %) was also added if the catalyst was Pd(dba)2. The tube
was capped with a septum, evacuated, and back-filled with
N2 three times. Triethylamine or N,N-diisopropylethylamine
was added via syringe. A solution of the terminal alkyne in
Exp er im en ta l Section
(41) Coulson, D. R. Inorganic syntheses; Wiley: New York, 1990;
Vol. 28, p 111.
Gen er a l. All reactions were performed under an atmo-
sphere of N2 unless otherwise stated. All chemicals were used
as received from commercial resources without further puri-
fication unless otherwise stated. The palladium catalysts used
in coupling reactions were prepared according to literature
(42) Colquhoun, H. M.; Holton, J .; Thompson, D. J .; Twigg, M. V.
New Pathways for Organic Synthesis: Practical Application of Transi-
tion Metals; Plenum Press: New York, 1984.
(43) Itatani, H.; Bailar, J . C., J r. J . Am. Oil. Chem. Soc. 1967, 44,
147-151.
5098 J . Org. Chem., Vol. 68, No. 13, 2003

Surface-Bound Electric Field-Driven Molecular Motors
THF was transferred via cannula to the tube. The tube was
then capped with its screw cap and the solution was stirred.
According to the reactivity of alkyne and aryl halide, the
reaction temperature varied from room temperature to 70 °C,
and the reaction time varied from 2 h to 3 days. The reaction
mixture was then cooled to room temperature and poured into
H2O in a separatory funnel, and the aqueous layer was
extracted with EtOAc. The organic layer was washed with H2O
three times, dried over MgSO4, and filtered, and the solvent
was removed in vacuo. The residue was purified by column
chromatography to afford the coupled product.
Gen er a l P r oced u r e for Dep r otection of Tr im eth ylsi-
lyl-P r otected Alk yn es. To a stirring solution of the TMS-
protected alkyne in THF were added at room temperature
K2CO3 (0.5-1 equiv) and MeOH/THF (1:1). After the reaction
mixture was stirred at room temperature for 2-4 h, it was
filtered and the solvent was removed in vacuo. The residue
was passed through a plug of silica gel to afford the terminal
alkyne.
Ch em ica l Assem bly of Ca ltr op s on Gold Su r fa ces. To
the freshly prepared solution of caltrop (0.5-1.0 mM) in CH2-
Cl2 (1.5 mL) was added H2SO4 (concentrated, 5.0 µL). The
cleaned Au substrate was immersed into the solution at room
temperature for 2-6 h. The gold sample was removed from
the solution and washed with H2O, followed by CH3CN and
EtOH, and then dried by blowing with N2. Monolayer thickness
was determined by using a Gaertner LSE ellipsometer. The
He-Ne laser (6328 Å) light had an incidence angle of 70°. The
thickness was calculated on the basis of the refractive index
of Nf ) 1.55 and Kf ) 0. The measurement of blank Au
substrate was carried out before assembly to obtain Ns and
Ks values of the substrate. The thickness of the monolayer was
measured immediately after assembly, washing, and drying.
The theoretical height was obtained from molecular models
minimized by SPARTAN SGI version 5.1.3, using force field
MMFF94, with the following assumptions: a Au-S-C bond
angle of 97°, 2.4 Å for the Au-S bond length, and perpendicu-
lar positioning of molecular shafts relative to the Au surface.
122.4, 84.3, 77.4, 64.9, 26.4, 18.9, -4.8; HRMS calcd for C15H22-
OSi 246.1440, found 246.1436.
Eth oxytr i{4-[3-(ter t-bu tyld im eth ylsila n yloxym eth yl)-
p h en yleth yn yl]p h en yl}sila n e (9). According to the general
coupling procedure, 823 (0.153 g, 0.220 mmol), 7 (0.32 g, 1.3
mmol), Pd(dba)2 (0.019 g, 0.033 mmol), CuI (0.006 g, 0.03
mmol), PPh3 (0.029 g, 0.11 mmol), i-Pr2NEt (5 mL), and THF
(15 mL) were employed at room temperature for 2 days to give
9 as a yellow sticky oil (0.223 g, 95%): Rf ) 0.31 (hexanes/
CH2Cl2, 2:1); IR (KBr) 3064, 2931, 2208 cm-1; 1H NMR (CDCl3,
400 MHz) δ 7.65 (d, 6H, J ) 8.2 Hz), 7.61 (d, 6H, J ) 8.2 Hz),
7.54 (d, 3H, J ) 1.4 Hz), 7.47 (td, 3H, J ) 4.5 Hz, 1.4 Hz),
7.36 (m, 6H), 4.79 (s, 6H), 3.94 (q, 2H, J ) 6.9 Hz), 1.31 (t,
3H, J ) 6.9 Hz), 1.00 (s, 27H), 0.17 (s, 18H); 13C NMR (CDCl3,
100 MHz) δ 142.2, 135.6, 134.59, 131.4, 130.7, 129.7, 128.7,
126.6, 125.6, 123.3, 91.3, 89.5, 65.0, 60.4, 26.4, 18.8, 18.7, -4.8;
LRMS calcd for C65H80O4Si4 1036.51, found 1036.51.
Tr is{4-[3-(ter t-b u t yld im et h ylsila n yloxym et h yl)p h en -
yleth yn yl]p h en yl}-4′-iod op h en ylsila n e (10). An oven-dried
50 mL round-bottom flask was charged with 9 (1.25 g, 1.20
mmol), diiodobenzene (0.495 g, 1.50 mmol), and THF (20 mL).
The solution was cooled to -78 °C. n-BuLi (2.39 M in hexane,
0.61 mL) was added dropwise via syringe. The reaction
mixture was stirred at -78 °C after the addition. The dry ice
bath was allowed to warm to room temperature overnight. The
reaction mixture was poured into H2O, and the mixture was
extracted with CH2Cl2. The combined organic layer was dried
over MgSO4 and filtered, and the solvent was removed in
vacuo. The residue was purified by column chromatography
to afford 10 as a slightly yellow clear oil (1.06 g, 88%): Rf )
0.17 (hexanes/CH2Cl2, 3:1); IR (KBr) 2952, 2929, 2211, 1102,
1
840 cm-1; H NMR (CDCl3, 400 MHz) δ 7.80 (d, 2H, J ) 8.0),
7.60-7.54 (m, 15H), 7.47 (td, 3H, J ) 4.6 Hz, 1.1 Hz), 7.36 (d,
6H, J ) 5.0 Hz), 7.31 (d, 2H, J ) 8.0 Hz), 4.78 (s, 6H), 1.00 (s,
27H), 0.17 (s, 18H); 13C NMR (CDCl3, 100 MHz) δ 142.2, 138.3,
137.7, 136.6, 133.7, 133.2, 131.5, 130.7, 129.7, 128.8, 126.7,
125.5, 123.3, 98.0, 91.5, 89.4, 65.0, 26.4, 18.9, -4.8; MALDI-
TOF MS m/z (matrix: dithranol; AgOTf added) found 1303
(M + Ag+), calcd for C69H79IO3Si4Ag 1303.
ter t-Bu tyl(3-iod oben zyloxy)d im eth ylsila n e (5). A mix-
ture of 3-iodobenzyl alcohol (9.17 g, 39.2 mmol), TBDMSCl (7.1
g, 47 mmol), and imidazole (3.1 g, 47 mmol) was dissolved in
CH2Cl2 (250 mL). The reaction mixture was stirred in room
temperature for 2 h and then poured into H2O. The organic
layer was washed with H2O (three times) and dried over
MgSO4 and the solvent removed in vacuo. The residue was
filtered through a plug of silica gel to afford 5 as a clear oil
Tr is{4-[3-(h yd r oxym et h yl)p h en ylet h yn yl]p h en yl}-4′-
iod op h en ylsila n e (11). To the solution of 10 (0.795 g, 0.665
mmol) in THF (100 mL) was added AcOH (0.15 mL, 2.7 mmol),
followed by TBAF (1 M in THF, 2.66 mL, 2.66 mmol). The
reaction mixture was stirred at room temperature for 28 h.
The reaction mixture was poured into H2O, and the mixture
was extracted with EtOAc. The organic layer was washed with
H2O and brine, dried over MgSO4, and filtered and the solvent
removed in vacuo. The residue was purified by column chro-
matography to afford 11 (0.51 g, 90%) as a white oil that
solidified slowly at room temperature: Rf ) 0.25 (hexanes/
EtOAC, 1:2); mp 169-171 °C; IR (KBr) 3414 (br), 2360, 1099,
(13.7 g, 100%): IR (KBr) 2953, 1105, 840 cm-1 1H NMR
;
(CDCl3, 400 MHz) δ 7.70 (s, 1H), 7.59 (d, 1H, J ) 7.7 Hz),
7.30 (t, 1H, J ) 7.7 Hz), 7.09 (t, 1H, J ) 7.7 Hz), 4.71 (s, 2H),
0.97 (s, 9H), 0.13 (s, 6H); 13C NMR (CDCl3, 100 MHz) δ 144.3,
136.3, 135.5, 130.4, 125.6, 94.7, 64.5, 26.3, 18.8, -4.8; HRMS
calcd for C13H21IOSi 348.0406, found 348.0400.
1
1007 cm-1; H NMR (CDCl3, 400 MHz) δ 7.78 (d, 2H, J ) 8.0
Hz), 7.59-7.53 (m. 15H), 7.50 (td, 3H, J ) 5.4 Hz, 1.5 Hz),
7.37 (d, 6H, J ) 4.7 Hz), 7.29 (d, 2H, J ) 7.6 Hz), 4.72 (s, 6H),
1.88 (br, 3H); 13C NMR (CDCl3, 100 MHz) δ 141.6, 138.2, 137.7,
136.5, 133.7, 133.0, 131.5, 131.3, 130.5, 129.0, 127.4, 125.4,
123.7, 98.0, 91.1, 89.7, 65.2; LRMS calcd for C51H37O3ISi 852,
found 852.
Tr ip od Ba se 12. To a solution of PPh3 (3.343 g, 12.76 mmol)
in THF (50 mL), cooled to 0 °C, was added diisopropyl
azodicarboxylate (DIAD) (2.51 mL, 12.8 mmol). A white
precipitate formed after stirring at 0 °C for 5 min. The mixture
was stirred at 0 °C for 30 min, and then a solution of 11 (0.544
g, 0.640 mmol) and thiolacetic acid (0.92 mL, 12.8 mmol) in
THF (20 mL) was added dropwise by pipet. The reaction
mixture became orange, then green, and finally brown during
the addition. The flask that held 11 was rinsed with THF (5
mL × 2), and the rinses were also added to the reaction
mixture. The reaction mixture was stirred in an ice bath
throughout the addition, and the ice bath was then allowed
to warm to room temperature. After 4.5 h, the reaction mixture
was poured into H2O and extracted with EtOAc. The organic
1-(ter t-Bu tyld im eth ylsila n yloxym eth yl)-3-tr im eth ylsi-
la n yleth yn ylben zen e (6). According to the general coupling
procedure, 5 (8.89 g, 25.5 mmol), TMSA (4.4 mL, 31 mmol),
Pd(PPh3)2Cl2 (0.181 g, 0.258 mmol), CuI (0.097 g, 0.51 mmol),
NEt3 (20 mL), and THF (40 mL) were employed at room
temperature to give 6 (7.98 g, 98%) as a yellow oil: Rf ) 0.27
(hexanes/CH2Cl2, 5:1); IR (KBr) 3064, 2956, 2153, 1158, 1107,
841 cm-1 1H NMR (CDCl3, 400 MHz) δ 7.45-7.30 (m, 4H),
;
4.74 (s, 2H), 0.99 (s, 9H), 0.30 (s, 9H), 0.15 (s, 6H); 13C NMR
(CDCl3, 100 MHz) δ 141.9, 130.9, 129.9, 128.6, 126.7, 123.3,
105.7, 94.2, 64.9, 26.4, 18.8, 0.4, -4.8; HRMS calcd for C18H30
OSi2 318.1835, found 318.1809.
-
ter t-Bu tyl(3-eth yn ylben zyloxy)d im eth ylsila n e (7). Ac-
cording to the general deprotection procedure, 6 (5.641 g, 17.67
mmol), K2CO3 (1.22 g, 8.84 mmol), CH3OH (50 mL), and THF
(50 mL) were employed to give 7 (4.15 g, 95%) as a yellow oil:
Rf ) 0.29 (hexanes/CH2Cl2, 5:1); IR (KBr) 3303, 2955, 2100,
1
1105, 838 cm-1; H NMR (CDCl3, 200 MHz) δ 7.53-7.34 (m,
4H), 4.78 (s, 2H), 3.13 (s, 1H), 1.02 (s, 9H), 0.18 (s, 6H); 13C
NMR (CDCl3, 50 MHz) δ 142.1, 131.1, 130.1, 128.7, 127.0,
J . Org. Chem, Vol. 68, No. 13, 2003 5099

J ian and Tour
layer was washed with H2O and brine, dried over MgSO4, and
filtered and the solvent removed in vacuo. The residue was
purified by column chromatography to afford 12 (0.463 g, 70%)
as a colorless sticky oil. The oil solidified slowly at room
temperature to a white solid: Rf ) 0.35 (hexanes/EtOAC, 4:1);
mp 59-61 °C; IR (KBr) 1690 cm-1; 1H NMR (CDCl3, 400 MHz)
δ 7.78 (d, 2H, J ) 8.1 Hz), 7.58-7.49 (m, 15H), 7.44 (dt, 3H,
J ) 6.3 Hz, 2.5 Hz), 7.31-7.28 (m, 8H), 4.14 (s, 6H), 2.39 (s,
9H); 13C NMR (CDCl3, 100 MHz) δ 195.2, 138.4, 138.2, 137.7,
136.5, 133.7, 133.1, 132.4, 131.5, 131.0, 129.4, 129.1, 125.3,
123.8, 98.0, 90.9, 89.8, 33.4, 30.7; MALDI-TOF MS m/z
(matrix: dithranol; AgOTf added) found 1135 (M + Ag+), calcd
for C57H43IO3S3SiAg 1135.
collected by filtration, and washed with petroleum ether (3 ×
10 mL). Recrystallization from benzene gave 16 as a red solid
(0.851 g, 48%, a yield as high as 66% was obtained): Rf ) 0.24
(hexanes/EtOAC, 4:1); mp 245-246 °C; IR (KBr) 3379, 1509,
1
1335 cm-1; H NMR (CDCl3, 400 MHz) δ 8.26 (d, 1H, J ) 1.9
Hz), 8.12 (dd + br, 2H, J ) 8.6 Hz, 2.0 Hz), 7.93 (d, 1H, J )
8.8 Hz), 7.92 (d, 1H, J ) 8.6 Hz), 6.81 (dd, 1H, J ) 8.8 Hz, 2.2
Hz), 6.66 (d, 1H, J ) 2.1 Hz), 3.12 (s, 6H); 13C NMR (DMSO-
d6, 125 MHz) δ 152.2, 145.7, 143.6, 139.0, 129.8, 123.1, 119.0,
114.9, 112.5, 108.8, 106.6, 93.2, 41.2; HRMS calcd for
C
14H13N3O2 255.1008, found 255.1008.
[9-(4-Iod op h en yl)-7-n it r o-9H -ca r b a zol-2-yl]d im et h yl-
a m in e (17). The mixture of 16 (52.7 mg, 0.207 mmol), 1,4-
diiodobenzene (208 mg, 0.630 mmol), Cu powder (29 mg, 0.021
mmol), K2CO3 (29 mg, 0.21 mmol), Na2SO4 (30 mg, 0.21 mmol),
and nitrobenzene (10 mL) was heated at 190 °C for 23 h. After
the mixture was cooled, most of the nitrobenzene was removed
by vacuum distillation. The residue was passed through a
column of silica gel. The desired product 17 was isolated as a
red solid (48 mg, 50%): Rf ) 0.37 (hexanes/CH2Cl2, 3:2); mp
250-251 °C; IR (KBr) 1493, 1298 cm-1; 1H NMR (CDCl3, 400
MHz) δ 8.16 (dd, 1H, J ) 8.5 Hz, 2.0 Hz), 8.10 (d, 1H, J ) 1.9
Hz), 8.01-7.95 (m, 4H), 7.33 (d, 2H, J ) 8.6 Hz), 6.84 (dd, 1H,
Dim eth yl-(4′-n itr o-2′-a m in o-bip h en yl-4-yl)-a m in e (14).
A screw cap tube was charged with 1329 (4.71 g, 11.5 mmol),
2-bromo-5-nitroaniline (1.55 g, 7.14 mmol), Pd(dba)2 (0.122 g,
0.212 mmol), CuI (0.081 g, 0.43 mmol), and PPh3 (0.223 g,
0.851 mmol). The mixture was degassed and back-filled with
N2. THF (50 mL) was added, and the reaction mixture was
heated at 85 °C for 21 h. The reaction mixture was cooled to
room temperature, stirred with aqueous KF (saturated 15 mL)
overnight, and filtered. The solid was discarded after washing
with EtOAc (three times). The liquid was poured into H2O and
extracted with EtOAc. The combined organic layer was washed
with H2O and brine, dried over MgSO4, and filtered and the
solvent removed in vacuo. The residue was purified by column
chromatography to afford 14 as a red solid (1.51 g, 83%):
Rf ) 0.36 (hexanes/EtOAc, 3:1); mp 198-199 °C; IR (KBr)
J ) 8.8 Hz, 2.2 Hz), 6.48 (d, 1H, J ) 2.1 Hz), 3.07 (s, 6H); 13
C
NMR (CDCl3, 100 MHz) δ 152.1, 145.9, 144.4, 139.9, 139.8,
136.9, 130.0, 129.5, 122.7, 118.5, 116.5, 112.6, 109.0, 105.5,
93.6, 91.6, 41.2; HRMS calcd for C20H16IN3O2 457.0287, found
457.0291.
3417, 3323, 1504, 1335 cm-1 1H NMR (CDCl3, 400 MHz) δ
;
Dim eth yl[7-n itr o-9-(4-tr im eth ylsila n yleth yn ylp h en yl)-
9H-ca r ba zol-2-yl]a m in e (18). According to the general cou-
pling procedure, 17 (48 mg, 0.11 mmol), Pd(PPh3)2Cl2 (4 mg,
0.005 mmol), CuI (1 mg, 0.005 mmol), TMSA (50 µL, 0.35
mmol), NEt3 (5 mL), and THF (5 mL) were employed at room
temperature to give 18 as an orange solid (39 mg, 87%): Rf )
0.36 (hexanes/CH2Cl2, 3:2); mp > 232 °C dec; IR (KBr) 2158,
1508, 1328 cm-1; 1H NMR (CDCl3, 500 MHz) δ 8.16-8.13 (m,
2H), 7.98 (d, 1H, J ) 8.8 Hz), 7.97 (d, 1H, J ) 8.4 Hz), 7.77 (d,
2H, J ) 8.5 Hz), 7.53 (d, 2H, J ) 8.5 Hz), 6.84 (dd, 1H, J )
8.8 Hz, 2.2 Hz), 6.50 (d, 1H, J ) 2.1 Hz), 3.06 (s, 6H), 0.33 (s,
9H); 13C NMR (CDCl3, 125 MHz) δ 152.0, 145.9, 144.5, 139.9,
137.1, 134.3, 130.0, 127.3, 123.5, 122.6, 118.5, 116.4, 112.7,
109.0, 105.7, 104.3, 96.5, 91.8, 41.2, 0.33; HRMS calcd for
7.64 (dd, 1H, J ) 8.3 Hz, 2.2 Hz), 7.58 (d, 1H, J ) 2.3 Hz),
7.36 (d, 2H, J ) 8.7 Hz), 7.23 (d, 1H, J ) 8.3 Hz), 6.83 (d, 2H,
J ) 8.7 Hz), 4.10 (br, 2H), 3.04 (s, 6H); 13C NMR (CDCl3, 100
MHz) δ 150.7, 147.8, 145.0, 134.5, 131.1, 129.8, 125.1, 113.8,
113.0, 109.9, 40.8; HRMS calcd for C14H15N3O2 257.1164, found
257.1162.
Dim eth yl-(4′-n itr o-2′-a zid o-bip h en yl-4-yl)-a m in e (15).
To the dark red mixture of 14 (3.63 g, 14.1 mmol), AcOH (70
mL), and H2SO4 (concentrated, 14 mL), cooled to 0 °C, while
stirring, was added dropwise isoamyl nitrite (2.1 mL, 15.5
mmol) over a period of 5 min. The reaction mixture was stirred
at 0 °C for 25 min and then at room temperature for 1 h. H2O
(100 mL) was added to form a dark aqueous solution. Excess
aqueous urea (saturated 6 g) was added to destroy the
remaining nitrous acid, followed by Norit-A (2.5 g). The dark
suspension was stirred at 0 °C for 15 min and filtered. The
dark aqueous solution, after filtration, was stirred in an ice
bath while saturated aqueous NaN3 (1.83 g, 28.2 mmol) was
added dropwise. N2 evolved at once. The reaction mixture
turned from dark to a clear brown solution during the addition.
The reaction mixture was kept stirring in an ice bath for 3 h
after addition of the NaN3. Na2CO3 (powder, 100 g) was added
slowly to the reaction mixture. The resulting red suspension
was extracted with CH2Cl2 (three times). The combined organic
layer was washed with saturated aqueous NaHCO3 and H2O,
dried over MgSO4, and filtered, and the solvent was removed
in vacuo. The residue was purified by column chromatography
to afford 15 as a red solid (2.28 g, 57%, a yield as high as 60%
was obtained): Rf ) 0.25 (hexanes/EtOAC, 8:1); mp 167-168
C
25H25N3O2Si 427.1716, found 427.1719.
[9-(4-Eth yn ylp h en yl)-7-n itr o-9H-ca r ba zol-2-yl]d im eth -
yla m in e (19). According to the general deprotection proce-
dure, 18 (74 mg, 0.17 mmol), K2CO3 (12 mg, 0.086 mmol),
MeOH (20 mL), and THF (20 mL) were employed to give 19
as an orange solid (45 mg, 75%): Rf ) 0.26 (hexanes/CH2Cl2,
1
3:2); IR (KBr) 3278, 2360, 1509, 1318 cm-1; H NMR (CDCl3,
500 MHz) δ 8.17-8.15 (m, 2H), 7.99 (d, 1H, J ) 8.8 Hz), 7.98
(d, 1H, J ) 8.5 Hz), 7.80 (d, 2H, J ) 8.5 Hz), 7.56 (d, 2H, J )
8.5 Hz), 6.85 (dd, 1H, J ) 8.8 Hz, 2.2 Hz), 6.52 (d, 1H, J ) 2.2
Hz), 3.24 (s, 1H), 3.06 (s, 6H); 13C NMR (CDCl3, 125 MHz) δ
152.1, 145.9, 144.5, 139.9, 137.5, 134.5, 130.0, 127.4, 122.7,
122.5, 118.5, 116.5, 112.7, 109.1, 105.6, 91.8, 83.0, 79.1, 41.2;
HRMS calcd for C22H17N3O2 355.1321, found 355.1320.
Ca ltr op 1. According to the general coupling procedure, 19
(42 mg, 0.12 mmol), 12 (121 mg, 0.120 mmol), Pd(dba)2 (4 mg,
0.006 mmol), CuI (1 mg, 0.006 mmol), PPh3 (6.3 mg, 0.024
mmol), NEt3 (5 mL), and THF (5 mL) were employed to give
1 as an orange solid (96 mg, 64%): Rf ) 0.23 (hexanes/EtOAc,
°C; IR (KBr) 2118, 1514, 1342 cm-1 1H NMR (CDCl3, 400
;
MHz) δ 8.10 (d, 1H, J ) 2.2 Hz), 8.04 (dd, 1H, J ) 8.5 Hz, 2.2
Hz), 7.50 (d, 1H, J ) 8.5 Hz), 7.43 (d, 2H, J ) 8.9 Hz), 6.80 (d,
2H, J ) 8.9 Hz), 3.06 (s, 6H); 13C NMR (CDCl3, 100 MHz) δ
151.1, 147.1, 140.8, 138.6, 131.6, 130.7, 123.7, 120.3, 114.5,
112.2, 40.7; HRMS calcd for C14H13N5O2 283.1069, found
283.1071.
Dim eth yl(7-n itr o-9H-ca r ba zol-2-yl)a m in e (16). Odorless
kerosene (250 mL) was purified by shaking with concentrated
H2SO4 (3 × 30 mL). The red powder of 15 (1.958 g, 6.919 mmol)
was added portionwise to hot kerosene (250 mL) while stirring
at 170-190 °C. The heat was maintained for 5 min after the
final addition. The reaction mixture was then cooled to room
temperature and chilled in a refrigerator. The red solid was
2:1); mp 103-106 °C; IR (KBr) 1689, 1511, 1321 1099 cm-1
;
1H NMR (CDCl3, 500 MHz) δ 8.19-8.16 (m, 2H), 7.98 (d + d,
2H, J ) 8.6 Hz, J ) 8.4 Hz), 7.86 (d, 2H, J ) 8.4 Hz), 7.67-
7.29 (m, 30H), 6.85 (dd, 1H, J ) 8.8 Hz, J ) 2.0 Hz), 6.57 (d,
1H, J ) 1.8 Hz), 4.15 (s, 6H), 3.07 (s, 6H), 2.40 (s, 9H); 13C
NMR (CDCl3, 125 MHz, missing one aromatic C due to overlap)
δ 195.3, 152.1, 145.9, 144.5, 139.9, 138.5, 137.2, 136.7, 136.6,
134.5, 134.0, 134.0, 132.4, 131.6, 131.5, 131.0, 130.0, 129.4,
129.1, 127.5, 125.3, 125.0, 123.8, 123.4, 118.5, 116.5, 112.7,
109.1, 105.7, 91.8, 91.1, 91.0, 90.2, 89.9, 41.2, 33.5, 30.8;
5100 J . Org. Chem., Vol. 68, No. 13, 2003

Surface-Bound Electric Field-Driven Molecular Motors
MALDI-TOF MS m/z (matrix: sinapinic acid) found 1253 (M+)
and 1162 (M+ - SAc), calcd for C79H59N3O5S3Si: 1253.
J ) 8.6 Hz), 7.43 (dd, 2H, J ) 8.3, 1.7 Hz), 0.33 (s, 9H); 13C
NMR (CDCl3, 100 MHz) δ 141.9, 136.7, 134.2, 127.2, 124.3,
123.7, 122.2, 121.9, 120.5, 113.4, 104.2, 96.6, 0.36; HRMS calcd
for C23H19Br2NSi 494.9654, found 494.9649.
2,7-Dibr om o-9-(4-n itr op h en yl)-9H-ca r ba zole (23). To a
flask charged with 2,7-dibromocabazole (22)31,32 (4.99 g, 15.3
mmol) and K2CO3 (10.56 g, 76.52 mmol) was added 4-fluoroni-
trobenzene (6.5 mL, 61.4 mmol) and DMF (80 mL). The
reaction mixture was heated at reflux in DMF overnight,
cooled to room temperature, and poured into H2O (500 mL).
The yellow solid was collected by filtration. The crude material
was recrystallized from benzene to afford the product as a light
yellow solid (5.89 g, 86%, a yield as high as 88% was ob-
tained): Rf ) 0.25 (hexanes/CH2Cl2, 3:1); mp 229-230 °C; IR
(KBr) 3073, 1588, 1514, 1346 cm-1; 1H NMR (CDCl3, 400 MHz)
δ 8.56 (d, 2H, J ) 8.9 Hz), 7.98 (d, 2H, J ) 8.3 Hz), 7.77 (d,
2H, J ) 9.0 Hz), 7.58 (d, 2H, J ) 1.5 Hz), 7.49 (dd, 2H,
J ) 8.3 Hz, 1.6 Hz); 13C NMR (CDCl3, 100 MHz) δ 147.0, 142.8,
141.3, 127.5, 126.3, 125.2, 122.8, 122.2, 120.9, 113.3; HRMS
calcd for C18H10Br2N2O2 445.9090, found 445.9091.
4-(2,7-Dibr om ocar bazol-9-yl)ph en ylam in e (24). The mix-
ture of 23 (5.89 g, 13.2 mmol), SnCl2‚2H2O (14.9 g, 660 mmol),
and ethanol (200 mL) was heated at 78-80 °C overnight and
then cooled to room temperature. Most of the ethanol was
removed in vacuo. An aqueous solution of saturated NaOH
(25 g) was poured into the reaction mixture slowly while the
mixture was cooled in an ice bath and stirred vigorously. The
white solid was collected by filtration. The solid was extracted
with benzene several times. The combined benzene solution
was dried over MgSO4 and filtered and the solvent removed
in vacuo. Recrystallization from benzene gave the desired
product as ivory crystals (4.78 g, 87%): Rf ) 0.35 (hexanes/
CH2Cl2, 1:1); mp 185.5-187 °C; IR (KBr) 3469, 3381 cm-1; 1H
NMR (CDCl3, 400 MHz) δ 7.92 (d, 2H, J ) 8.3 Hz), 7.44 (d,
2H, J ) 1.6 Hz), 7.38 (dd, 2H, J ) 8.3 Hz, 1.7 Hz), 7.22 (d, 2H,
J ) 8.7 Hz), 6.89 (d, 2H, J ) 8.7 Hz); 13C NMR (CDCl3, 100
MHz) δ 147.1, 142.9, 128.9, 127.0, 123.6, 121.8, 121.7, 120.2,
116.4, 113.5; HRMS calcd for C18H12N2Br2 415.9348, found
415.9338.
{4-[7-Br om o-9-(4-tr im eth ylsila n yleth yn ylp h en yl)-9H-
ca r ba zol-2-yleth yn yl]p h en yl}d im eth yla m in e (30). Accord-
ing to the general coupling procedure, 29 (0.379 g, 0.766 mmol)
was coupled with 2735 (0.11 g, 0.76 mmol) in the presence of
Pd(dba)2 (22 mg, 0.038 mmol), CuI (7 mg, 0.04 mmol), PPh3
(40 mg, 0.15 mmol), i-Pr2NEt (5 mL), and THF (15 mL) at 60
°C for 11 h to give 30 (0.186 g, 43%) as a yellow solid: Rf )
0.43 (hexanes/EtOAc, 10:1); mp 224-225 °C; IR (KBr) 2204,
1
2160 cm-1; H NMR (CDCl3, 400 MHz) δ 8.05 (d, 1H, J ) 8.1
Hz), 7.95 (d, 1H, J ) 8.3 Hz), 7.75 (d, 2H, J ) 8.6 Hz), 7.51
(m, 4H), 7.48 (dd, 1H, J ) 8.1, 1.3 Hz), 7.45 (m, 3H), 6.68 (d,
2H, J ) 8.6 Hz), 3.02 (s, 6H), 0.33 (s, 9H); 13C NMR (CDCl3,
100 MHz) δ 150.5, 142.3, 141.0, 137.1, 134.1, 133.1, 127.3,
124.6, 124.0, 123.3, 122.7, 122.6, 122.5, 122.0, 120.6, 120.3,
113.3, 113.0, 112.2, 110.3, 104.4, 96.3, 91.4, 88.6, 40.6, 0.35;
HRMS calcd for C33H29N2BrSi 560.1284, found 560.1287.
{4-[7-Iod o-9-(4-tr im eth ylsila n yleth yn ylp h en yl)-9H-ca r -
ba zol-2-yleth yn yl]p h en yl}d im eth yla m in e (31). A dry flask
charged with a solution of 30 (0.214 g, 0.382 mmol) in THF
(10 mL) was cooled to -78 °C, and n-BuLi (2.39 M in pentane,
0.19 mL) was added dropwise. The reaction mixture was
stirred at -78 °C for 30 min. A solution of I2 (0.135 g, 0.531
mmol) in THF (10 mL) was added. The dry ice bath was then
allowed to warm to room temperature overnight. The reaction
mixture was poured into aqueous Na2SO3 and extracted with
EtOAc; the organic layer was washed with H2O three times,
dried over MgSO4, and filtered, and the solvent was removed
in vacuo. The residue was purified by column chromatography
to afford 31 as a white solid (0.116 g, 50%): Rf ) 0.43 (hexanes/
EtOAc, 10:1); IR (KBr) 2203, 2158 cm-1; 1H NMR (CDCl3, 400
MHz) δ 8.04 (d, 1H, J ) 8.1 Hz), 7.84 (d, 1H, J ) 8.1 Hz), 7.75
(d, 2H, J ) 8.5 Hz), 7.71 (d, 1H, J ) 1.2 Hz), 7.60 (dd, 1H,
J ) 8.2 Hz, 1.4 Hz), 7.52-7.44 (m, 6H), 6.68 (d, 2H, J ) 8.7
Hz), 3.02 (s, 6H), 0.33 (s, 9H); 13C NMR (CDCl3, 100 MHz) δ
150.5, 142.5, 140.7, 137.1, 134.1, 133.1, 133.0, 129.7, 127.3,
124.5, 123.3, 123.2, 122.7, 122.6, 122.2, 120.6, 119.2, 113.0,
112.2, 110.3, 104.4, 96.3, 91.2, 88.6, 40.6, 0.36; HRMS calcd
for C33H29IN2Si 608.1145, found 608.1137.
2,7-Dibr om o-9-(4-iod op h en yl)-9H-ca r b a zole (28). The
mixture of 24 (2.54 g, 6.11 mmol), CH3CN (50 mL), and H2O
(50 mL) was stirred in an ice bath while concentrated HCl (3
mL) was added dropwise over 5 min. The reaction mixture
turned from white to yellow. To this mixture, still in an ice
bath, was added a solution of NaNO2 (0.842 g, 12.2 mmol) in
50 mL of H2O. The reaction mixture turned from yellow to
orange. The reaction mixture was then stirred at room
temperature for 50 min. A solution of KI (5.06 g, 30.5 mmol)
in 100 mL of H2O was added. The reaction mixture was then
heated to boiling until no more purple or brown vapor was
evolved. After cooling to room temperature, the reaction
mixture was poured into H2O and extracted with CH2Cl2 three
times. The combined organic layer was washed with aqueous
Na2SO3, followed by H2O, dried over MgSO4, and filtered and
the solvent removed in vacuo. The residue was purified by
column chromatography to afford 28 (2.35 g, 71%, a yield as
high as 78% was obtained) as a white crystalline solid: Rf )
0.48 (hexanes/CH2Cl2, 5:1); mp 189.5-190.5 °C; IR (KBr) 2360,
Dim eth yl-{4-[7-(4-n itr op h en yleth yn yl)-9-(4-tr im eth yl-
sila n yleth yn ylp h en yl)-9H-ca r ba zol-2-yleth yn yl]p h en yl}-
a m in e (32). According to the general coupling procedure, 31
(0.274 g, 0.450 mmol) was coupled with (4-nitrophenyl)ethyne44
(0.11 g, 0.75 mmol) in the presence of Pd(dba)2 (0.014 g, 0.024
mmol), CuI (0.005 g, 0.02 mmol), PPh3 (0.025 g, 0.096 mmol),
NEt3 (5 mL), and THF (15 mL) at room temperature for 15 h
to give 32 (0.235 g, 78%) as red crystals: Rf ) 0.42 (hexanes/
CH2Cl2, 1:1); mp 206-208 °C; IR (KBr) 2359, 2341, 2205, 1514,
1
1384 cm-1; H NMR (CDCl3, 400 MHz) δ 8.22 (d, 2H, J ) 8.8
Hz), 8.07 (d + d, 2H, J ) 8.3 Hz, 8.2 Hz), 7.77 (d, 2H, J ) 8.3
Hz), 7.67 (d, 2H, J ) 8.3 Hz), 7.57-7.42 (m, 8H), 6.68 (d, 2H,
J ) 8.5 Hz), 3.06 (s, 6H), 0.34 (s, 9H); 13C NMR (CDCl3, 100
MHz) δ 150.5, 147.2, 141.6, 141.1, 137.2, 134.1, 133.2, 132.6,
130.8, 127.3, 124.6, 124.6, 124.5, 124.1, 123.3, 123.0, 122.6,
121.0, 120.9, 119.7, 113.7, 113.0, 112.2, 110.3, 104.4, 96.5, 96.3,
91.8, 88.7, 88.2, 40.6, 0.38; HRMS calcd for C41H33N3O2Si
627.2342, found 627.2335.
1
1491 cm-1; H NMR (CDCl3, 400 MHz) δ 7.99 (d, 2H, J ) 8.6
Hz), 7.95 (d, 2H, J ) 8.3 Hz), 7.49 (d, 2H, J ) 1.6 Hz), 7.43
(dd, 2H, J ) 8.3 Hz, 1.6 Hz), 7.27 (d, 2H, J ) 8.6 Hz); 13C
NMR (CDCl3, 100 MHz) δ 141,9, 139.9, 136.6, 129.3, 124.4,
122.2, 122.0, 120.5, 113.3, 93.7; HRMS calcd for C18H10Br2NI
524.8225, found 524.8216.
{4-[9-(4-Eth yn ylp h en yl)-7-(4-n itr op h en yleth yn yl)-9H-
ca r ba zol-2-yleth yn yl]p h en yl}d im eth yla m in e (33). Accord-
ing to the general deprotection procedure, 32 (9.4 mg, 0.014
mmol) with K2CO3 (1.9 mg, 0.014 mmol), MeOH (10 mL), and
CH2Cl2 (10 mL) gave 33 (8.0 mg, 96%) as a red solid: Rf )
0.41 (hexanes/CH2Cl2, 1:1); mp 247-249 °C dec; IR (KBr) 3276,
2,7-Dibr om o-9-(4-tr im eth ylsila n yleth yn ylp h en yl)-9H-
ca r ba zole (29). According to the general coupling procedure,
28 (0.615 g, 1.17 mmol) was coupled with TMSA (0.25 mL,
1.75 mmol) in the presence of Pd(PPh3)2Cl2 (41 mg, 0.58 mmol),
CuI (11 mg, 0.058 mmol), NEt3 (10 mL), and THF (25 mL) at
room temperature for 40 h to give the product 29 as a white
solid (0.49 g, 84%, a yield as high as 86% was obtained): Rf )
0.31 (hexanes/CH2Cl2, 10:1); mp 241-242 °C; IR (KBr) 2161
1
2205, 1512, 1389 cm-1; H NMR (CDCl3, 400 MHz) δ 8.11 (d,
1H, J ) 6.4 Hz), 8.09 (d, 1H, J ) 6.5 Hz), 7.80 (d, 2H, J ) 6.6
Hz), 7.69 (d, 2H, J ) 6.8 Hz), 7.60-7.43 (m, 8H), 6.68 (d, 2H,
1
cm-1; H NMR (CDCl3, 400 MHz) δ 7.95 (d, 2H, J ) 8.3 Hz),
(44) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N.
Synthesis 1980, 8, 627-630.
7.74 (d, 2H, J ) 8.6 Hz), 7.50 (d, 2H, J ) 1.5 Hz), 7.48 (d, 2H,
J . Org. Chem, Vol. 68, No. 13, 2003 5101

J ian and Tour
J ) 7.0 Hz), 3.24 (s, 1H), 3.02 (s, 6H); 13C NMR (CDCl3, 100
MHz) δ 150.6, 147.3, 141.6, 141.1, 137.6, 134.4, 133.2, 132.6,
130.8, 127.5, 124.7, 124.7, 124.6, 124.1, 123.1, 122.6, 122.3,
121.0, 119.7, 113.7, 113.0, 112.2, 110.2, 96.4, 91.8, 88.6, 88.2,
83.1, 78.9, 40.6; HRMS calcd for C38H25N3O2 555.1947, found
555.1942.
88.3, 87.3, 40.6, 0.40; HRMS calcd for C41H33N3O2Si 627.2342,
found 627.2338.
{4-[9-(4-Eth yn ylp h en yl)-6-(4-n itr op h en yleth yn yl)-9H-
ca r ba zol-3-yleth yn yl]p h en yl}d im eth yla m in e (39). Accord-
ing to the general deprotection procedure, 38 (0.235 g, 0.374
mmol) in the presence of K2CO3 (0.026 g, 0.19 mmol), MeOH
(30 mL), and THF (30 mL) for 3 h gave 39 as a red solid (0.126
g, 61%): Rf ) 0.22 (hexanes/CH2Cl2, 3:2); IR (KBr) 3283, 2922,
2203, 1512, 1338 cm-1; 1H NMR (CDCl3, 500 MHz) δ 8.29 (m,
2H), 8.22 (d, 2H, J ) 8.7 Hz), 7.76 (d, 2H, J ) 8.3 Hz), 7.70 (d,
2H, J ) 8.7 Hz), 7.60 (m, 2H), 7.52 (d, 2H, J ) 8.3 Hz), 7.49
(d, 2H, J ) 8.7 Hz), 7.35 (m, 2H), 6.71 (d, 2H, J ) 8.7 Hz),
3.24 (s, 1H), 3.02 (s, 6H); 13C NMR (CDCl3, 125 MHz) δ 150.4,
147.0, 141.3, 140.5, 137.5, 134.3, 133.1, 132.4, 131.2, 130.6,
130.5, 127.1, 125.0, 124.1, 124.0, 123.8, 123.4, 122.2, 117.2,
114.3, 112.3, 110.7, 110.5, 110.4, 96.6, 90.0, 88.3, 87.3, 83.1,
Ca ltr op 2. According to the general coupling procedure, 12
(0.250 g, 0.243 mmol) and 33 (0.151 g, 0.272 mmol) were
coupled in the presence of Pd(dba)2 (8.0 mg, 0.014 mmol), CuI
(2.7 mg, 0.014 mmol), PPh3 (14 mg, 0.054 mmol), NEt3 (5 mL),
and THF (15 mL) at room temperature for 34 h to give 2 as a
red solid (0.147 g, 42%, a yield as high as 76% was obtained):
Rf ) 0.20 (hexanes/EtOAc, 3:1); mp > 130 °C dec; IR (KBr)
2203, 1689, 1515, 1337, 1098 cm-1; 1H NMR (CDCl3, 400 MHz)
δ 8.24 (d, 2H, J ) 8.9 Hz), 8.10 (d, 1H, J ) 8.0 Hz), 8.07 (d,
1H, J ) 8.1 Hz), 7.85 (d, 2H, J ) 8.52 Hz), 7.70-7.44 (m, 34H),
7.33-7.29 (m, 4H), 6.68 (d, 2H, J ) 8.8 Hz), 4.14 (s, 6H), 3.02
(s, 6H), 2.40 (s, 9H); 13C NMR (CDCl3, 100 MHz, missing one
aromatic C due to overlap) δ 195.3, 150.5, 147.2, 141.6, 141.1,
138.5, 137.2, 136.7, 136.6, 134.4, 134.0, 133.9, 133.2, 132.6,
132.4, 131.8, 131.6, 131.5, 131.0, 130.8, 129.5, 129.1, 127.5,
125.3, 125.0, 124.7, 124.7, 124.6, 124.1, 123.8, 123.2, 123.1,
122.7, 121.0, 119.7, 113.8, 113.0, 112.2, 110.2, 96.5, 91.9, 91.0,
90.3, 89.9, 88.8, 88.2, 40.6, 33.5, 30.8; MALDI-TOF MS m/z
(matrix: dithranol) found 1454, calcd for C95H67N3O5S3Si 1454.
79.1, 40.6; HRMS calcd for
555.1946.
C38H25N3O2 555.1947, found
Ca ltr op 3. According to the general coupling procedure, 39
(0.126 g, 0.227 mmol) was coupled with 12 (0.105 g, 0.102
mmol) in the presence of Pd(dba)2 (2.9 mg, 0.0050 mmol), CuI
(1 mg, 0.005 mmol), PPh3 (5 mg, 0.02 mmol), NEt3 (10 mL),
and THF (10 mL) to give 3 as a red solid (0.101 g, 68%): Rf )
0.33 (hexanes/EtOAc, 2:1); mp 143-146 °C; IR (KBr) 2201,
1688, 1515, 1338 cm-1; 1H NMR (CDCl3, 500 MHz) δ 8.33 (m,
2H), 8.24 (d, 2H, J ) 8.7 Hz), 7.82 (d, 2H, J ) 8.3 Hz), 7.71 (d,
2H, J ) 8.7 Hz), 7.65-7.30 (m, 36H), 6.71 (d, 2H, J ) 8.8 Hz),
4.15 (s, 6H), 3.02 (s, 6H), 2.40 (s, 9H); 13C NMR (CDCl3, 125
MHz) δ 195.3, 150.4, 147.1, 141.4, 140.6, 138.5, 137.1, 136.7,
136.6, 134.7, 134.5, 134.0, 133.8, 133.1, 132.4, 132.4, 131.6,
131.5, 131.2, 131.0, 130.6, 130.5, 129.4, 129.1, 127.2, 125.3,
125.0, 125.0, 124.1, 123.8, 123.4, 123.2, 117.2, 114.3, 112.3,
110.7, 110.6, 110.5, 96.7, 91.0, 91.0, 90.2, 90.0, 89.8, 88.3, 88.2,
87.3, 40.6, 33.5, 30.8; MALDI-TOF MS m/z (matrix: sinapinic
acid) found 1455 (M + H+), calcd for C95H67N3O5S3Si 1454.
3,6-Dibr om o-9-(4-tr im eth ylsila n yleth yn ylp h en yl)-9H-
ca r ba zole (36). According to the general coupling procedure,
3524 (4.393 g, 8.834 mmol) was coupled with TMSA (1.3 mL,
9.2 mmol) in the presence of Pd(PPh3)2Cl2 (0.116 g, 0.166
mmol), CuI (0.032 g, 0.17 mmol), NEt3 (30 mL), and THF (50
mL) at room temperature to give 36 as a white solid (3.41 g,
78%): Rf ) 0.22 (hexanes); mp 236-238 °C; IR (KBr) 2162,
1
1509 cm-1; H NMR (CDCl3, 400 MHz) δ 8.21 (d, 2H, J ) 1.7
Hz), 7.72 (d, 2H, J ) 8.5 Hz), 7.53 (dd, 2H, J ) 8.7 Hz, J ) 1.9
Hz), 7.47 (d, 2H, J ) 8.5 Hz), 7.26 (d, 2H, J ) 8.8 Hz), 0.31 (s,
9H); 13C NMR (CDCl3, 100 MHz) δ 139.9, 137.1, 134.1, 129.9,
126.9, 124.5, 123.7, 123.3, 113.8, 111.8, 104.3, 96.5, 0.37;
HRMS calcd for C23H19Br2NSi: 494.9654, found 494.9663.
(3-Br om o-5-n itr op h en yl)d im eth yla m in e (42).39 To an
orange solution of 4139 (1.423 g, 6.557 mmol) in CH3CN (100
mL) was added formaldehyde (37% w/w aqueous, 1.6 mL),
followed by NaBH3CN (1.26 g, 20.0 mmol) and AcOH (6.6 mL).
The reaction mixture was stirred at room-temperature over-
night. Then, a second portion of reagents, formaldehyde (37%
w/w aqueous, 1.6 mL), NaBH3CN (1.26 g, 20.0 mmol), and
AcOH (6.6 mL) were added. Monitoring the reaction by TLC
showed the starting material (41) to be totally consumed after
stirring at room temperature for 24 h. The reaction mixture
was poured into H2O and extracted with EtOAc. The organic
layer was washed with H2O (two times), aqueous Na2CO3 (two
times), and brine (two times) and dried over MgSO4. After
removal of the solvent in vacuo, the residue was purified by
flash column chromatography to afford 42 as a red solid (1.315
3-(4-Nitr op h en yleth yn yl)-6-br om o-9-(4-tr im eth ylsila n -
yleth yn ylp h en yl)-9H-ca r ba zole (37). According to the gen-
eral coupling procedure, 36 (1.385 g, 2.46 mmol) and 4-nitro-
phenylethyne (0.726 g, 4.93 mmol) were coupled in the
presence of Pd(dba)2 (0.080 g, 0.14 mmol), CuI (0.027 g, 0.14
mmol), PPh3 (0.147 g, 0.561 mmol), i-Pr2NEt (20 mL), and THF
(50 mL) at 80 °C to give 37 as a yellow solid (0.56 g, 36%):
Rf ) 0.40 (hexanes/CH2Cl2, 2:1); mp 227-228 °C; IR (KBr)
2192, 2155, 1506, 1338 cm-1 1H NMR (CDCl3, 400 MHz) δ
;
8.28-8.22 (m, 4H), 7.73 (d, 2H, J ) 8.5 Hz), 7.68 (d, 2H, J )
8.8 Hz), 7.61 (dd, 1H, J ) 8.5 Hz, J ) 1.5 Hz), 7.53 (dd, 1H,
J ) 8.7 Hz, J ) 1.9 Hz), 7.47 (d, 2H, J ) 8.5 Hz), 7.35 (d, 1H,
J ) 8.5 Hz), 7.26 (d, 1H, J ) 8.7 Hz), 0.34 (s, 9H); 13C NMR
(CDCl3, 100 MHz) δ 147.1, 141.3, 140.1, 136.9, 134.1, 132.4,
131.1, 130.9, 129.9, 127.0, 125.0, 125.0, 124.1, 123.7, 123.5,
123.0, 114.4, 114.1, 111.9, 110.6, 104.2, 96.6, 96.4, 87.3, 0.35;
HRMS calcd for C31H23BrN2O2Si 564.0698, found 564.0703.
1
g, 82%): Rf ) 0.46 (hexanes/EtOAc, 8:1); mp 100-101 °C; H
NMR (CDCl3, 400 MHz) δ 7.64 (pseudo-t, 1H, J ) 1.8 Hz);
7.42 (pseudo-t, 1H, J ) 2.2 Hz), 7.05 (pseudo-t, 1H, J ) 2.2
Hz), 3.06 (s, 6H); 13C NMR (CDCl3, 100 MHz) δ 151.6, 150.0,
123.6, 120.1, 113.7, 105.5, 40.7.
Dim et h yl-(3-n it r o-5-t r im et h ylsila n ylet h yn ylp h en yl)-
a m in e (43). According to the general coupling procedure, 42
(0.286 g, 1.18 mmol) was coupled with TMSA (0.34 mL, 2.4
mmol) in the presence of Pd(PPh3)2Cl2 (33 mg, 0.047 mmol),
CuI (8.9 mg, 0.047 mmol), i-Pr2NEt (5 mL), and THF (10 mL)
at 50 °C overnight to give 43 as yellow crystals (0.276 g,
89%): Rf ) 0.41 (hexanes/CH2Cl2, 3:1); mp 102.5-103.5 °C;
IR (KBr) 2156, 1529, 1343 cm-1; 1H NMR (CDCl3, 400 MHz) δ
7.58 (pseudo-t, 1H, J ) 1.8 Hz), 7.40 (pseudo-t, 1H, J ) 2.2
Hz), 6.98 (dd, 1H, J ) 2.5 Hz, 1.0 Hz), 3.03 (s, 6H), 0.28 (s,
9H); 13C NMR (CDCl3, 100 MHz) δ 150.7, 149.5, 125.0, 120.5,
114.4, 106.6, 104.0, 95.8, 40.7, 0.24; HRMS calcd for C13H18N2O2-
Si 262.1137, found 262.1134.
Dim eth yl-{4-[6-(4-n itr op h en yleth yn yl)-9-(4-tr im eth yl-
sila n yleth yn ylp h en yl)-9H-ca r ba zol-3-yleth yn yl]p h en yl}-
a m in e (38). According to the general coupling procedure, 37
(0.613 g, 1.09 mmol) and 27 (0.48 g, 3.3 mmol) were coupled
in the presence of Pd(dba)2 (0.044 g, 0.077 mmol), CuI (0.015
g, 0.077 mmol), PPh3 (0.081 g, 0.31 mmol), i-Pr2NEt (10 mL),
and THF (30 mL) to give 38 as a red solid (0.451 g, 65%):
Rf ) 0.28 (hexanes/CH2Cl2, 3:2); mp > 143 °C (decomp.); IR
(KBr) 2202, 2154, 1514, 1338 cm-1; 1H NMR (CDCl3, 400 MHz)
δ 8.28 (m, 2H), 8.21 (d, 2H, J ) 8.9 Hz), 7.72 (d, 2H, J ) 8.5
Hz), 7.68 (d, 2H, J ) 8.9 Hz), 7.59 (m, 2H), 7.48 (m, 4H), 7.33
(d, 1H, J ) 8.5 Hz), 7.31 (d, 1H, J ) 8.5 Hz), 6.70 (d, 2H, J )
8.9 Hz), 3.01 (s, 6H), 0.35 (s, 9H); 13C NMR (CDCl3, 100 MHz)
δ 150.4, 147.0, 141.3, 140.5, 137.1, 134.0, 133.1, 132.4, 131.2,
130.6, 130.5, 127.0, 125.0, 124.1, 124.0, 123.7, 123.3, 123.2,
117.1, 114.3, 112.3, 110.7, 110.5, 110.4, 104.4, 96.7, 96.4, 90.0,
(3-Eth yn yl-5-n itr op h en yl)d im eth yla m in e (44). Accord-
ing to the general deprotection procedure, 43 (0.276 g, 1.05
mmol) was treated with K2CO3 (0.073 g, 0.52 mmol), MeOH
(30 mL), and THF (30 mL) to give 44 as an orange solid (0.196
5102 J . Org. Chem., Vol. 68, No. 13, 2003

Surface-Bound Electric Field-Driven Molecular Motors
g, 98%): Rf ) 0.30 (hexanes/CH2Cl2, 3:1); mp 180.5-181.5 °C;
IR (KBr) 3287, 1539, 1349 cm-1; 1H NMR (CDCl3, 400 MHz) δ
7.57 (pseudo-t, 1H, J ) 1.8 Hz), 7.41 (pseudo-t, 1H, J ) 2.3
Hz), 6.99 (dd, 1H, J ) 2.5 Hz, 1.0 Hz), 3.12 (s, 1H), 3.02 (s,
6H); 13C NMR (CDCl3, 100 MHz) δ 150.7, 149.5, 124.0, 120.7,
114.2, 106.8, 82.8, 78.5, 40.6; HRMS calcd for C10H10N2O2:
190.0742. Found: 190.0740.
{3,5-Bis[3-(N,N-d im eth yl)a m in o-5-n itr op h en yleth yn yl]-
p h en yleth yn yl}tr im eth ylsila n e (45). According to the gen-
eral coupling procedure, 4036 (0.199 g, 0.599 mmol) was coupled
with 44 (0.251 g, 1.32 mmol) in the presence of Pd(dba)2 (27
mg, 0.048 mmol), CuI (9.1 mg, 0.048 mmol), PPh3 (0.050 g,
0.19 mmol), NEt3 (10 mL), and THF (15 mL) to give 45 (0.25
g, 76%) as a yellow solid: Rf ) 0.41 (hexanes/EtOAc, 3:1); mp
253-254 °C; IR (KBr) 2162, 1533, 1342 cm-1; 1H NMR (CDCl3,
400 MHz) δ 7.68 (m, 3H), 7.65 (d, 2H, J ) 1.6 Hz), 7.50 (t, 2H,
J ) 2.3 Hz), 7.07 (dd, 2H, J ) 2.5 Hz, 1.2 Hz), 3.09 (s, 12H),
0.28 (s, 9H); 13C NMR (CDCl3, 100 MHz) δ 150.9, 149.7, 135.3,
134.8, 124.7, 124.6, 123.8, 120.2, 114.1, 106.8, 103.3, 96.7, 89.8,
88.7, 40.8, 0.24; HRMS calcd for C31H30N4O4Si 550.2043, found
550.2037.
149.7, 135.4, 135.2, 124.6, 123.9, 123.6, 120.2, 114.1, 106.9,
90.0, 88.5, 82.1, 79.2, 40.8; HRMS calcd for C28H22N4O4
478.1641, found 478.1642.
Ca ltr op 4. According to the general coupling procedure, 46
(0.075 g, 0.157 mmol) was coupled with 12 (0.093 g, 0.091
mmol) in the presence of Pd(dba)2 (2.6 mg, 0.0045 mmol), CuI
(0.8 mg, 0.005 mmol), PPh3 (0.0047 g, 0.018 mmol), NEt3 (5
mL), and THF (5 mL) to give caltrop 4 as a yellow solid (0.084
g, 68%): Rf ) 0.23 (hexanes/EtOAc, 2:1); mp > 108 °C dec; IR
(KBr) 1691, 1533, 1343 cm-1 1H NMR (CDCl3, 400 MHz) δ
;
7.73 (d, 2H, J ) 1.4 Hz), 7.70 (m, 3H), 7.60-7.56 (m, 16H),
7.50 (m, 5H), 7.45 (dt, 3H, J ) 6.3 Hz, 2.2 Hz), 7.32 (m, 6H),
7.09 (q, 2H), 4.14 (s, 6H), 3.08 (s, 12H), 2.39 (s, 9H); 13C NMR
(CDCl3, 100 MHz, missing one aromatic C due to overlap) δ
195.5, 150.8, 149.7, 138.4, 136.7, 136.6, 135.0, 134.8, 134.7,
133.9, 132.4, 131.6, 131.5, 131.0, 129.4, 129.1, 125.3, 124.7,
124.5, 123.9, 123.8, 120.3, 114.2, 106.9, 91.2, 90.9, 89.9,
89.8, 89.3, 88.8, 40.8, 33.5, 30.8; MS m/z (CI) found 1377.6
(M + H+), calcd for C85H64N4O7S3Si 1377.4.
Ack n ow led gm en t. This work was supported by the
Welch Foundation, Grant C-1489. We thank Dr. I.
Chester of FAR Research for supplying TMSA.
1-Eth yn yl-3,5-bis-[3-(N,N-dim eth yl)am in o-5-n itr oph en -
yleth yn yl]-ben zen e (46). According to the general depro-
tection procedure, 45 (0.064 g, 0.17 mmol) with K2CO3 (0.008
g, 0.06 mmol), MeOH (20 mL), and THF (20 mL) gave 46 (0.045
g, 82%) as a yellow solid: Rf ) 0.34 (hexanes/EtOAc, 3:1);
1
Su p p or tin g In for m a tion Ava ila ble: Copies of H NMR
1
mp > 248 °C dec; IR (KBr) 3247, 1530, 1341 cm-1; H NMR
and 13C NMR spectra for all new compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
(CDCl3, 400 MHz) δ 7.72 (t, 1H, J ) 1.5 Hz), 7.67 (m, 4H),
7.50 (t, 2H, J ) 2.3 Hz), 7.08 (dd, 2H, J ) 2.5 Hz, 1.1 Hz),
3.17 (s, 1H), 3.08 (s, 12H); 13C NMR (CDCl3, 100 MHz) δ 150.9,
J O034169H
J . Org. Chem, Vol. 68, No. 13, 2003 5103