Facile convergent route to molecular caltrops

Article abstract of DOI:10.1021/jo982085g

The convergent syntheses of molecular caltrops are described starting from tetraethyl orthosilicate and using organolithium additions and Pd/Cu- catalyzed coupling methods. The caltrop core is based on a tetrahedral silicon atom, and there are three legs each bearing sulfur-tipped feet for adhesion to metallic surfaces. The forth prong (arm) is non-sulfur-bearing for projection upward from the surface. Rigid phenyleneethynylene segments are used for the legs and arms. These organosilicon caltrops may have utility as scanning probe microscopy tips.

Full text of DOI:10.1021/jo982085g

1968
J . Org. Chem. 1999, 64, 1968-1971
F a cile Con ver gen t Rou te to Molecu la r Ca ltr op s
Yuxing Yao and J ames M. Tour*
Department of Chemistry and Biochemistry, University of South Carolina,
Columbia, South Carolina 29208
Received October 16, 1998
The convergent syntheses of molecular caltrops are described starting from tetraethyl orthosilicate
and using organolithium additions and Pd/Cu-catalyzed coupling methods. The caltrop core is based
on a tetrahedral silicon atom, and there are three legs each bearing sulfur-tipped feet for adhesion
to metallic surfaces. The forth prong (arm) is non-sulfur-bearing for projection upward from the
surface. Rigid phenyleneethynylene segments are used for the legs and arms. These organosilicon
caltrops may have utility as scanning probe microscopy tips.
In tr od u ction
upward when the caltrop is deployed. Iron-made versions
of these structures were formerly used to impede the
progress of advancing enemy cavalry while similar tools
with hollow prongs have been used to erect rapid road-
and airstrip-barricades. The molecular caltrops here were
prepared by a facile convergent route based on a tetra-
hedral silicon atom core with three legs bearing thiol-
tipped feet for adhesion to a metallic surface such as Au,
Pt-Ir, or Ga-As.3,6 The thiols are protected with acetyl
groups to prevent their premature oxidative coupling; we
previously demonstrated the efficacy of NH4OH-based
removal of the acetyl groups during self-assembled
monolayer (SAM) formation.3,5,7 The fourth prong is a
non-sulfur-bearing arm for projection upward from the
surface. Rigid phenyleneethynylene segments are used
for the prong arms. The suitability of these molecular
caltrops to serve as SPM tips will depend on several
factors including the rigidity of the framework,8 the
overall conductances3,5 (which is critical for STM but not
AFM), the ability to be well dispersed on a surface via
insertion into SAMs of short alkane thiols,3 and the
propensity of the three sulfur-bearing arms to align
toward the surface with the fourth arm projected upward.
All of these factors are molecular length-dependent and
an illustration of the proposed tip functionalization
approach is depicted in Scheme 1. The results of SPM
tip usage will be considered separately from the synthetic
details described here.9
Scanning probe microscopy (SPM), which includes
primarily scanning tunneling microscopy (STM) and
atomic force microscopy (AFM), has become a critical tool
for atomic-scale imaging. The application of these tech-
niques has tremendously impacted chemistry, physics,
biology, and materials science.1 However, SPM has
limited resolution for tightly spaced pattern imaging or
atomically sharp surface asperities.2,3 This resolution
deficiency results, in part, from the limited aspect ratio
of the SPM tip. Since imaging sharp surface contours will
be important as molecular systems for nanotechnology
and biology are further investigated, a rigid and high
aspect ratio tip configuration must be developed. An
advance in imaging probe technology was achieved by
attaching carbon nanotubes to the probe tip; however,
methodologies for functionalization of the nanotube ends
and for adhesion of the nanotubes to the cantilever
surfaces are in their infancy.4 As part of our studies
directed toward imaging molecular electronic device
architectures,3,5 we describe here precisely defined mo-
lecular caltrops that may act as SPM probe tips. A
classical caltrop is a tetrahedrally arranged four-pointed
device such that three of the prongs naturally form a
tripod on the ground while the fourth prong projects
* Corresponding author. Email: tour@psc.sc.edu.
(1) (a) Yu, E. T. Chem. Rev. 1997, 97, 1017. (b) Liu, F.; Wu, F.;
Lagally, M. G. Chem. Rev. 1997, 97, 1045. (c) Hwang, R. Q.; Bartelt,
M. C.; Chem. Rev. 1997, 97, 1063. (d) Chiang, S. Chem. Rev. 1997, 97,
1083. (e) Sautet, P. Chem. Rev. 1997, 97, 1097. (f) Poirier, G. E. Chem.
Rev. 1997, 97, 1117. (g) Gewirth, A. A.; Niece, B. K. Chem. Rev. 1997,
97, 1129. (h) Carpick, R. W.; Salmeron, M. Chem. Rev. 1997, 97, 1163.
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Struct. 1994, 23, 115. (b) Bustamante, C.; Keller, D. Phys. Today 1995,
48, 32. (c) Shao, Z.; Yang, J . Quart. Rev. Biophys. 1995, 28, 195. (d)
Itoh, J .; Tohma, Y.; Kanemaru, S.; Shimizu, K. J . Vac. Sci. Technol.
B. 1995, 13, 331.
Resu lts a n d Discu ssion
The caltrops with varying arm and leg lengths and tips
were rapidly synthesized in a convergent manner as
shown in Scheme 2. Slow addition of (p-iodophenyl)-
lithium, generated in situ by lithium-halogen exchange
of p-diiodobenzene in ether using n-BuLi, to tetraethyl
(3) (a) Bumm, L. A.; Arnold, J . J .; Cygan, M. T.; Dunbar, T. D.;
Burgin, T. P.; J ones, L., II; Allara, D. L.; Tour, J . M.; Weiss, P. S.
Science 1996, 271, 1705. (b) Cygan, M. T.; Dunbar, T. D.; Arnold, J .
J .; Bumm, L. A.; Shedlock, N. F.; Burgin, T. P.; J ones, L., II, Allara,
D. L.; Tour, J . M.; Weiss, P. S. J . Am. Chem. Soc. 1998, 120, 2721.
(4) (a) Dai, H.; Hafner, J . H.; Rinzler, A. G.; Colbert, D. T.; Smalley,
R. E. Nature 1996, 384, 147. (b) Wong, S. S.; Harper, J . D.; Lansbury,
P. T., J r.; Lieber, C. M. J . Am. Chem. Soc. 1998, 120, 603. (c) For
application of chemically modified SPM tips for enhanced imaging
sensitivity, see: Wong, S. S.; J oselevich, E.; Woolley, T.; Cheung, C.
L.; Lieber, C. M. Nature 1998, 394, 52.
(6) (a) Ulman, A. An Introduction to Ultrathin Organic Films;
Academic: Boston, 1991. (b) Purcell, S. T.; Garcia, N.; Binh, V. T.;
J ones, L., II.; Tour, J . M. J . Am. Chem. Soc. 1994, 116, 11985-11989.
(c) Dhirani, A.-A.; Zehner, R. W.; Hsung, R. P.; Guyot-Sionnest, P.;
Sita, L. R. J . Am. Chem. Soc. 1996, 118, 3319. (d) Delamarche, E.;
Michel, B.; Biebuyck, H. A.; Gerber, C. Adv. Mater. 1996, 8, 719 and
references therein.
(7) Tour, J . M.; J ones, L., II; Pearson, D. L.; Lamba, J . J . S.; Burgin,
T. P.; Whitesides, G. M.; Allara, D. L.; Parikh, A. N.; Atre, S. V. J .
Am. Chem. Soc. 1995, 117, 9529.
(5) Reed, M. A.; Zhou, C.; Muller, C. J .; Burgin, T. P.; Tour, J . M.
Science 1997, 278, 252.
(8) J ones, L., II; Schumm, J . S.; Tour, J . M. J . Org. Chem. 1997, 62,
1388.
10.1021/jo982085g CCC: $18.00 © 1999 American Chemical Society
Published on Web 02/25/1999

Facile Convergent Route to Molecular Caltrops
J . Org. Chem., Vol. 64, No. 6, 1999 1969
Sch em e 1
orthosilicate afforded ethoxytri(p-iodophenyl)silane (1).10
The use of THF instead of ether as the reaction solvent
gave exclusively tetra(p-iodophenyl)silane. Lithium-
halogen exchange of 1-bromo-4-(trimethylsilylethynyl)-
benzene with tert-BuLi followed by quenching with 1
provided 2. Attempts to prepare 2 through a one-pot
transformation from p-diiodobenzene in ether or THF
failed; only 1-iodo-4-(trimethylsilylethynyl)benzene and
tetra(p-iodophenyl)silane were afforded via an unex-
pected lithium-halogen exchange process. The three legs
bearing the adhesion moieties were affixed in a single
pot using Pd/Cu couplings11 of 2 and 1-ethynyl-4-(thio-
acetyl)benzene to produced the caltrop 3 with a trimeth-
ylsilyl tip. Desilylation of 3 using tetra(n-butyl)ammo-
nium fluoride (TBAF), acetic anhydride and acetic acid
gave the proton-tipped caltrop 4. Deletion of the acetic
anhydride during desilylation resulted in significant loss
of the acetyl moieties on sulfur.8,12 Again, Pd/Cu coupling
of 4 with 4-iodonitrobenzene afforded 5. The terminal
nitro group will provide an efficient handle for monitoring
the tilt angle of the caltrop’s tip-arm via grazing angle
IR.3 Since we have prepared numerous oligo(phenylene-
ethynylene)s ranging from 10 to 140 nm via iterative
doubling strategies,8 we demonstrated the efficacy of 4
to serve as base for tip-elongation using Pd/Cu-catalyzed
coupling with 1-iodo-4-(trimethylsilylethynyl)benzene to
afford 6 and its desilylated counterpart 7.
variable using differing oligo(phenyleneethynylene)s.
Although the caltrop feet used here are based upon
protected thiols, the methodology would permit the
incorporation of numerous surface binding moieties.13
Exp er im en ta l Section
Gen er a l. Unless otherwise noted, all operations were
carried out under a dry, oxygen-free nitrogen atmosphere.
Combustion analyses were obtained from Atlantic Microlab,
Inc. Alkyllithium reagents were obtained from FMC and
(trimethylsilyl)acetylene was obtained from FAR Research
Inc., Melbourne, FL. Reagent grade diethyl ether and tetrahy-
drofuran (THF) were distilled under nitrogen from sodium
benzophenone ketyl. Bulk grade hexane was distilled prior to
use. Flash chromatography was carried out using 230-400
mesh silica gel from EM Science. Thin-layer chromatography
was performed using glass plates precoated with silica gel 60
F254 with a layer thickness of 0.25 mm purchased from EM
Science.
Eth oxytr i(p-iod op h en yl)sila n e (1). To a suspension of
p-diiodobenzene (13.2 g, 40.0 mmol) in ether (250 mL) at -78
°C was added n-BuLi (19.25 mL, 31.00 mmol, 1.61 N in
hexane) via syringe pump (0.57 mL/min for the first 15 mL,
and 0.32 mL/min for the next 4.25 mL). After the addition,
the pale yellow slurry was stirred for 1 h and added via
cannula to a precooled solution (-78 °C) of tetraethyl ortho-
silicate (2.23 mL, 10.00 mmol) in ether (30 mL). The resulting
clear solution was stirred for 30 min at -78 °C and 3 h at
room temperature. 1 N HCl (30 mL, 30 mmol) was added. The
organic layer was separated and washed with water (2×) and
brine (1×). The aqueous solution was extracted with ether
(2×). The combined organic fractions were dried over magne-
sium sulfate and filtered. Removal of solvent in vacuo gave a
crystalline white solid. The solid was purified by flash chro-
matography (silica gel, hexane) to give 1 (3.89 g, 57%) as a
white solid. Mp ) 174-175 °C. FTIR (KBr) 2964, 2872, 1569,
Therefore, the molecular caltrops could be rapidly
prepared with varying tip moieties and differing arm
lengths to serve as potential SPM tips. The silicon core
provides a suitable template for the required construction
of the three legs and the probe arm, each length being
(9) Tetrahedral core-based architectures have attracted much recent
attention for the building of three-dimensional networks. However, the
organosilane approach here permits the simple distinguishing of arms
(i.e. only three of the four bearing sulfur) and is highly convergent.
For other approaches, see: (a) Feldman, K. S.; Mareska, D. A.;
Weinreb, C. K.; Chasmawala, M. J . Chem. Soc., Chem. Commun. 1996,
865. (b) Feldman, K. S.; Weinreb, C. K.; Youngs, W. J .; Bradshaw, J .
D. J . Am. Chem. Soc. 1994, 116, 9019. (c) Sengupta, S.; Sadhukhan,
S. K. Tetrahedron Lett. 1998, 39, 1237. (d) Menger, F. M.; Su, D.
Tetrahedron Lett. 1997, 38, 1485. (e) Wilson, L. M.; Griffin, A. C. J .
Mater. Chem. 1993, 3, 991. (f) Simard, M.; Su, D. Wuest, J . D. J . Am.
Chem. Soc. 1991, 113, 4696. (g) Oldham, W. J .; Lachicotte, R. J .; Bazan
G. C. J . Am. Chem. Soc. 1998, 120, 2987. (h) Mongin, O.; Gossauer, A.
Tetrahedron 1997, 53, 6835. (i) Mongin, O.; Gossauer, A. Tetrahedron
Lett. 1996, 37, 3825. (j) Marsella, M. J .; Li, H.; Reid, R. J . Polym. Prepr.
(Am. Chem. Soc., Div. Polym. Chem.) 1998, 39 (2), 521.
1
1477 cm-1. H NMR (300 MHz, CDCl3) δ 7.74 (d, J ) 8.1 Hz,
6 H), 7.28 (d, J ) 8.2 Hz, 6 H), 3.82 (q, J ) 7.0 Hz, 2 H), 1.21
(t, J ) 7.0 Hz, 3 H). 13C NMR (75 MHz, CDCl3) δ 137.26,
136.73, 132.75, 98.05, 60.00, 18.42. HRMS calcd for C20H17I3-
OSi: 681.8183. Found: 681.8165.
Tr is(4-iod op h en yl)-(4′-(tr im eth ylsilyleth yn yl)p h en yl)-
sila n e (2). To a solution of bromo-4-(trimethylsilylethynyl)-
benzene12 (1.01 g, 4.00 mmol) in ether (15 mL) at -78 °C was
added dropwise t-BuLi (4.32 mL, 8.00 mmol, 1.85 M in
pentane). The solution was stirred for 45 min and added slowly
via cannula to a precooled (-78 °C) solution of 1 (2.05 g, 3.00
mmol) in THF (15 mL). The flask and cannula were rinsed
with ether (10 mL), and the solution was added to the reaction
mixture. The resultant clear yellow solution was stirred for
(10) Tour, J . M.; J ohn, J . A.; Stephens, E. B. J . Organomet. Chem.
1992, 429, 301.
(11) Suffert, J .; Ziessel, R. Tetrahedron Lett. 1991, 32, 757.
(12) Pearson, D. L.; Tour, J . M. J . Org. Chem. 1997, 62, 1376.
(13) Reinerth, W. A.; Tour, J . M. J . Org. Chem. 1998, 63, 2397.

1970 J . Org. Chem., Vol. 64, No. 6, 1999
Yao and Tour
Sch em e 2
1.5 h at -78 °C and poured into water. The organic layer was
separated and washed with water (1×) and brine (1×). The
aqueous solution was extracted with ether (2×). The combined
organic fractions were dried over magnesium sulfate and
filtered. Removal of solvent in vacuo followed by flash chro-
matography (silica gel, hexane) gave 2 (0.85 g, 35%) as a white
solid. Mp ) 168 °C (decomp). FTIR (cast) 3067, 2954, 2154,
(2×) and dried over magnesium sulfate. The solvent was
removed in vacuo, and the residues were purified by column
chromatography on silica gel.
Ca ltr op 3. See the general coupling procedure. The com-
pounds used were 2 (0.772 g, 0.950 mmol), 1-thioacetyl-4-
(trimethylsilylethynyl)benzene (0.88 g, 5.00 mmol), Pd(dba)2
(0.082 g, 0.140 mmol), PPh3 (0.147 g, 0.560 mmol), CuI (0.053
g, 0.280 mmol), i-Pr2NEt (0.66 mL, 3.8 mmol), and THF (10
mL). The reaction mixture was stirred at room temperature
for 3 d. Flash chromatography (silica gel, hexane/Et2O ) 2/1)
gave 3 (0.377 g, 42%) as a white solid. FTIR (cast) 3067, 2954,
1
1564, 1539, 1477 cm-1. H NMR (300 MHz, CDCl3) δ 7.71 (d,
J ) 8.2 Hz, 6 H), 7.45 (d, J ) 8.3 Hz, 2 H), 7.39 (d, J ) 8.3 Hz,
2 H), 7.17 (d, J ) 8.2 Hz, 6 H), 0.24 (s, 9 H). 13C NMR (75
MHz, CDCl3) δ 137.85, 137.50, 136.07, 133.11, 132.22, 131.67,
125.17, 104.90, 98.17, 96.37, 0.29. HRMS calcd for C29H25I3-
Si2: 809.8629. Found: 809.8632.
Gen er a l P r oced u r e for P d /Cu Cou p lin g Rea ction s
betw een Ter m in a l Alk yn es a n d Ar yl Iod id es. To an oven-
dried glass vessel containing the terminal alkyne, aryl iodide,
Pd catalyst, copper iodide, and triphenylphosphine were added
THF and the amine in a drybox which was filled with nitrogen.
The mixture was stirred at room temperature. The reaction
mixture was then poured into water, and the aqueous layer
was extracted with ether, ethyl acetate or dichloromethane
(3×). The combined organic solution was washed with water
1
2154, 1713, 1595, 1539, 1503, 1482, 1395 cm-1. H NMR (300
MHz, CDCl3) δ 7.58 (d, J ) 8.4 Hz, 6 H), 7.56-7.52 (overlap-
ping, 16 H), 7.41 (d, J ) 8.5 Hz, 6 H), 2.42 (s, 9 H), 0.28 (s, 9
H). 13C NMR (75 MHz, CDCl3) δ 193.34, 136.24, 136.10, 134.29,
133.84, 133.69, 132.31, 131.49, 131.20, 128.41, 124.90, 124.68,
124.31, 104.88, 96.05, 90.91, 90.17, 30.34, 0.04. LRMS calcd
for C59H46O3S3Si2: 954. Found: 954. Anal. Calcd for C59H46O3S3-
Si2: C, 74.17; H, 4.85. Found: C, 74.24; H, 4.78.
Ca ltr op 4. A mixture of TBAF (4 mL, 4 mmol, 1.0 M in
THF), acetic anhydride (0.38 mL, 4.00 mmol), and acetic acid
(0.23 mL, 4.00 mmol) was added to a solution of 3 (0.735 g,

Facile Convergent Route to Molecular Caltrops
J . Org. Chem., Vol. 64, No. 6, 1999 1971
0.770 mmol) in THF (10 mL). The green-yellow solution was
stirred for 50 min and then poured into water. The mixture
was washed with water (2×) and brine (1×). The combined
aqueous solution was extracted with ether (1×). The combined
organic solution was dried over magnesium sulfate and
filtered. Removal of solvent in vacuo followed by flash chro-
matography (silica gel, hexane/ethyl acetate ) 2/1) gave 4 as
a white solid (0.68 g, 100%). FTIR (cast) 3292, 3067, 3015,
ylsilylethynyl)benzene (0.56 g, 1.88 mmol), Pd(dba)2 (0.014 g,
0.024 mmol), PPh3 (0.025 g, 0.096 mmol), CuI (0.009 g, 0.048
mmol), i-Pr2NEt (0.16 mL, 0.94 mmol), and THF (11 mL). The
reaction mixture was stirred at room temperature for 24 h.
Flash chromatography (silica gel, hexane/ethyl acetate ) 4/1)
gave 6 (0.34 g, 69%) as a yellow solid. FTIR (cast) 3067, 3026,
2964, 2154, 1713, 1595, 1539, 1503, 1482, 1395 cm-1. 1H NMR
(300 MHz, CDCl3) δ 7.59-7.57 (overlapping, 22 H), 7.48 (s, 4
H), 7.41 (d, J ) 8.2, 6 H), 2.42 (s, 9 H), 0.28 (s, 9 H). 13C NMR
(100 MHz, CDCl3) δ 193.02, 136.00, 134.05, 133.57, 133.48,
132.06, 131.74, 131.31, 130.97, 130.91, 128.17, 124.56, 124.47,
124.09, 122.98, 122.91, 104.49, 96.35, 90.97, 90.72, 90.40,
89.99, 30.28, 0.00. LRMS calcd for C67H50O3S3Si2: 1054.
Found: 1054. Anal. Calcd for C67H50O3S3Si2: C, 76.24; H, 4.77
Found: C, 76.30; H, 4.88.
1
1708, 1595, 1539, 1497, 1482, 1395 cm-1. H NMR (300 MHz,
CDCl3) δ 7.56 (d, J ) 8.6 Hz, 6 H), 7.55-7.52 (m, 16 H), 7.40
(d, J ) 8.4, 6 H), 3.16 (s, 1 H), 2.42 (s, 9 H). 13C NMR (125
MHz, CDCl3) δ 193.40, 136.19, 134.25, 133.69, 132.27, 131.63,
131.17, 128.34, 124.66, 124.28, 123.84, 90.82, 90.11, 83.43,
78.68, 30.32. LRMS calcd for C56H38O3S3Si: 882. Found: 882.
Anal. Calcd for C56H38O3S3Si: C, 76.16; H, 4.34. Found: C,
76.00; H, 4.36.
Ca ltr op 7. A mixture of TBAF (1 mL, 1 mmol, 1.0 M in
THF), acetic anhydride (0.1 mL, 1 mmol), and acetic acid (0.06
mL, 1.00 mmol) was added to a solution of 6 (0.215 g, 0.200
mmol) in THF (5 mL). The solution was stirred for 30 min
and then poured into water. The mixture was washed with
water (2×) and brine (1×). The combined aqueous solution was
extracted with methylene chloride (1×). The combined organic
solution was dried over magnesium sulfate and filtered.
Removal of solvent in vacuo followed by flash chromatography
(silica gel, hexane/methylene chloride/ether ) 10/10/1) gave 7
as a white solid (0.139 g, 71%). FTIR (cast) 3292, 3067, 3015,
1-Iod o-4-(tr im eth ylsilyleth yn yl)ben zen e.14 See the gen-
eral coupling procedure. The compounds used were p-diiodo-
benzene (13.2 g, 40.0 mmol), (trimethylsilyl)acetylene (4.24
mL, 30.00 mmol), Pd(dba)2 (0.86 g, 1.50 mmol), PPh3 (1.57 g,
6.00 mmol), CuI (0.57 g, 3.00 mmol), i-Pr2NEt (20.9 mL, 120.0
mmol), and THF (30 mL). The mixture was stirred at room
temperature for 1.5 d. Flash chromatography (silica gel,
hexane) gave 4.75 g (53%) of the title compound as a white
1
solid. H NMR (300 MHz, CDCl3) δ 7.62 (d, J ) 8.6 Hz, 2 H),
7.16 (d, J ) 8.6 Hz, 2 H), 0.22 (s, 9 H).
1
2923, 1708, 1595, 1533, 1503, 1482, 1395 cm-1. H NMR (300
Ca ltr op 5. See the general coupling procedure. The com-
pounds used were 4 (0.224 g, 0.250 mmol), p-iodonitrobenzene
(0.25 g, 1.00 mmol), Pd(dba)2 (0.008 g, 0.013 mmol), PPh3
(0.014 g, 0.052 mmol), CuI (0.005 g, 0.026 mmol), i-Pr2NEt
(0.09 mL, 0.50 mmol), and THF (8 mL). The reaction mixture
was stirred at room temperature for 17 h. Flash chromatog-
raphy (silica gel, cyclohexane/ethyl acetate ) 4/1) gave 5 (0.182
g, 72%) as a yellow solid. FTIR (cast) 3067, 3026, 2215, 1708,
MHz, CDCl3) 7.58-7.55 (m, 22 H), 7.48 (m, 4 H), 7.40 (d, J )
8.5 Hz, 6 H), 3.17 (s, 1 H), 2.42 (s, 9 H). 13C NMR (125 MHz,
CDCl3) δ 193.38, 136.16, 134.21, 133.72, 132.22, 132.06, 131.53,
131.10, 131.06, 128.27, 124.59, 124.25, 123.48, 122.06, 91.08,
90.76, 90.23, 90.02, 83.20, 79.02, 30.27. LRMS calcd for
C
64H42O3S3Si: 982. Found: 982. Anal. Calcd for C64H42O3S3-
Si: C, 78.17; H, 4.31. Found: C, 77.44; H, 4.34.
1595, 1518, 1503, 1395 cm-1 1H NMR (300 MHz, CDCl3) δ
.
8.21 (d, J ) 8.8, 2 H), 7.66 (d, J ) 8.8, 2 H), 7.59-7.55
(overlapping, 22 H), 7.40 (d, J ) 8.2 Hz, 6 H), 2.42 (s, 9 H).
13C NMR (75 MHz, CDCl3) δ 193.01, 146.83, 136.05, 135.94,
134.65, 134.00, 133.32, 132.16, 132.02, 131.02, 130.95, 129.73,
128.14, 124.50, 124.01, 123.54, 123.45, 94.19, 90.58, 89.99,
88.68, 30.25. LRMS calcd for C62H41NO5S3Si: 1003. Found:
1003. Anal. Calcd for C62H41NO5S3Si: C, 74.15; H, 4.11; N,
1.39. Found: C, 73.92; H, 4.15; N, 1.37.
Ack n ow led gm en t. The Defense Advanced Research
Projects Agency and the Office of Naval Research
supported this work. We thank FMC for a gift of the
alkyllithium reagents and Dr. I Chester of FAR Re-
search Inc., Melbourne, FL, for a gift of (trimethylsilyl)-
acetylene.
Ca ltr op 6. See the general coupling procedure. The com-
pounds used were 4 (0.416 g, 0.47 mmol), 1-iodo-4-(trimeth-
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra for compounds 3-7 (10 pages). This material is
available free of charge via the Internet at http://pubs.acs.org.
(14) Hsung, R. P.; Babcock, J . R.; Chidsey, C. E. D.; Sita, L. R.
Organometallics 1995, 14, 4808.
J O982085G