F IGURE 1. Structures of the target compounds 1-6.
SCHEME 1. Syn th esis of th e S-Boc In ter m ed ia te 7
assembly applications. Thiol-thioacetate derivatized
OPEs were accessed via a convenient Boc protection-
deprotection scheme to afford the free thiol in the
presence of a thioacetate. Self-assembly studies revealed
effective monolayer formation of selected compounds on
gold.
TABLE 1. Ch em ica l Self-Assem bly Da ta for Com p ou n d s
1, 2, a n d 4 in THF for 40 m in
Exp er im en ta l Section
thickness (nm)
Th ioa cetic Acid S-[4-[4-(4-m er ca p top h en yleth yn yl)-3-
n itr op h en yleth yn yl]p h en yl] Ester (1). To a 50 mL round-
bottom flask containing a stir bar were added 12 (0.25 g, 0.47
mmol), CH2Cl2 (6.0 mL), anisole (0.5 mL), and TFA (1.0 mL).
The reaction was allowed to stir at room temperature for 4 h.
EtOAc (25 mL) was then added and washed with water (3×).
The organic layer was dried using anhydrous MgSO4, and the
solvent was removed in vacuo. The residue was dissolved in a
minimum amount of CH2Cl2, and hexanes were then added. Care
was taken to evaporate only the CH2Cl2 on the rotary evaporator.
The solid was filtered, washed with hexanes, and purified by
flash chromatography on silica gel (CH2Cl2) to afford the product
as an orange solid (0.125 g, 70%): mp 105-108 °C; FTIR (KBr)
2564, 2209, 1709, 1587, 1539, 1503, 1398, 1343, 1270, 1119,
compd
founda
calcdb
1
2
4
2.5
2.1
2.2
2.3
2.3
1.8
a
Value measured by ellipsometry with ca. ( 0.2 nm error in
b
the measurement. The theoretical thickness calculated by mo-
lecular mechanics including the Au-S bond and a tilt angle of
20° for the OPEs17and 33° for the alkane.2,18
then form coordination compounds with metallic nano-
rods and nanoparticles. Alkyne 2315 was coupled with 9
to afford the desired compound 24. Intermediate 24 was
then deprotected to give 25 and coupled with 1-iodo-4-
thioacetylbenzene8 to afford the target compound 5 in fair
yield.
Also shown in Scheme 5 is the synthesis of the nitrile-
terminated OPE 6, produced in order to take advantage
of the known bonding interactions between nitriles and
metals.4,16 The alkyne 2616 was coupled with 9 to give
27, followed by deprotection to afford the alkyne 28.
Compound 28 was then coupled with 4-iodothioacetyl-
benzene8 to yield the target compound 6.
With the completed molecules in hand, we carried out
SAM formation on gold for compounds 1, 2, and 4. Using
ellipsometry, we compared the observed and theoretical
thicknesses (Table 1) to assess monolayer formation.
Immersion times were limited to 40 min, due to the rapid
assembly of thiols on gold compared to thioacetates.5,17
Assembly data for all three compounds are close to the
predicted values. Self-assembly data obtained corroborate
with our previous published data.1
1094, 1014, 953, 826, 620, 597, 526 cm-1 1H NMR (400 MHz,
;
CDCl3) δ 8.23 (d, J ) 1.5 Hz, 1H), 7.71 (dd, J ) 8.1, 1.5 Hz, 1H),
7.67 (d, J ) 8.1 Hz, 1H), 7.58 (d, J ) 8.5 Hz, 2H), 7.47 (d, J )
8.6 Hz, 2H), 7.44 (d, J ) 8.6 Hz, 2H), 7.27 (d, J ) 8.5 Hz, 2H),
3.58 (s, 1H), 2.46 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 193.4,
149.6, 135.5, 134.6, 134.5, 134.0, 132.8, 132.5, 129.5, 129.0, 127.9,
123.9, 123.4, 119.4, 118.5, 98.9, 92.9, 88.6, 85.5, 30.6; HRMS
calcd for C24H15NO3S2 429.0493, found 429.0496.
Th ioa cet ic Acid S-[4-[4-(4-m er ca p t op h en ylet h yn yl)-
p h en yleth yn yl]p h en yl] Ester (2). To a 100 mL round-bottom
flask containing a stir bar were added 16 (0.56 g, 1.16 mmol),
CH2Cl2 (18 mL), anisole (1.5 mL), and TFA (3.0 mL). The
reaction was allowed to stir at room temperature for 4 h upon
which time an orange precipitate had formed. Hexanes (50 mL)
was added, and the solid was filtered, washed with hexanes, and
purified by flash chromatography on silica gel (3:1 CH2Cl2/
hexanes) to afford the product as a white solid (0.29 g, 65%):
mp 190 °C dec; FTIR (KBr) 2567, 2209, 1920, 1708, 1689, 1584,
1512, 1479, 1403, 1351, 1304, 1267, 1118, 1094, 1014, 947, 837,
822, 619, 596, 543, 524, 506, 448, 415 cm-1; 1H NMR (400 MHz,
CDCl3) δ 7.56 (d, J ) 8.6 Hz, 2H), 7.50 (m, 4H), 7.40 (d, J ) 8.6
Hz, 2H), 7.39 (d, J ) 8.5 Hz, 2H), 7.24 (d, J ) 8.5 Hz, 2H), 3.54
(s, 1H), 2.45 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 193.7, 134.5,
132.39, 132.38, 131.8, 131.7, 129.1, 128.5, 124.5, 123.5, 122.9,
120.3, 91.1, 90.9, 90.7, 89.7, 30.5; HRMS calcd for C24H16OS2
384.0643, found 384.0636. Anal. Calcd: C, 74.97; H, 4.19.
Found: C, 74.68; H, 4.12.
In conclusion, we have synthesized several new or-
thogonally functionalized compounds for controlled self-
(15) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N.
Synthesis 1980, 8, 627-630.
Th ioa cetic Acid S-[4-[2,5-d ieth yl-4-(4-m er ca p top h en yl-
eth yn yl)p h en yleth yn yl]p h en yl] Ester (3). Compound 20
(0.228 g, 0.4 mmol) was dissolved in CH2Cl2 (5 mL) followed by
addition of anisole (0.5 mL) and TFA (1 mL). The reaction was
stirred at room temperature for 4 h. The mixture was dissolved
in EtOAc, and water (20 mL) was added. The organics were
extracted with EtOAc (3×) and dried over anhydrous MgSO4
(16) Dirk, S. M.; Tour, J . M. Tetrahedron 2003, 59, 287-293.
(17) Tour, J . M.; J ones, L., II; Pearson, D. L.; Lamba, J . S.; Burgin,
T. P.; Whitesides, G. W.; Allara, D. L.; Parikh, A. N.; Atre, S. J . Am.
Chem. Soc. 1995, 117, 9529-9534.
(18) Mbindyo, J . K. N.; Mallouk, T. E.; Mattzela, J . B.; Kratoch-
vilova, I.; Razavi, B.; J ackson, T. N.; Mayer, T. S. J . Am. Chem. Soc.
2002, 124, 4020-4026.
J . Org. Chem, Vol. 69, No. 5, 2004 1753