sufficiently rigid and robust to be visualized using a
conventional AFM tip while laying on an atomically flat mica
surface.
Scheme 1a
Tetrahedrally shaped precursors 516 and 817 were synthe-
sized as follows. Tetraphenyladamantane 3 was prepared by
arylation of 1-bromoadamantane in a mixture of hot benzene,
tert-butyl bromide, and AlCl3. The low solubility of 3 allows
facile purification by washing with CHCl3 in a Soxhlet
extractor. Treatment of adamantane 3 with [bis(trifluoro-
acetoxy)iodo]benzene (4) and iodine gave tetraiodide 5.
Tetraiodide 8 was synthesized from p-tritylaniline (6), which
was diazotized and reacted with KI to give iodide 7. Further
iodination of 7 with 4 in the presence of iodine gave
tetraiodide 8.
We chose a substituted [1,2,5]-dithiazepane unit for
eventual binding of the tips to a gold surface. 4-Iodoaniline
(9) was treated with ethylene oxide to give diol 10, which
was converted into dichoride 11 (Scheme 2).
Scheme 2a
a Reaction conditions: (a) t-BuBr, AlCl3, PhH, ∆ 2 h; (b) 4, I2,
(c) NaNO2, HCl, then KI; (d) 4, I2.
tower-shaped molecule 1 (Scheme 1) as an inroad to a series
a Reaction conditions: (a) Ethylene oxide, MeOH; (b) POCl3,
pyridine; (c) KSCN; (d) KOH; (e) TMSA, Pd(PPh3)2, CuI, THF/
Et3N; (f) K2CO3, MeOH; (g) (4-iodophenylethynyl)trimethylsilane,
Pd(PPh3)2, CuI, THF/Et3N.
of single molecule tips for AFM applications.10,11
Herein, we describe the synthesis of several tetrahedrally
shaped nanoscale molecules built around a 1,3,5,7-tetra-
substituted adamantane unit or else a para-substituted tet-
raarylmethane core.12 Given the high affinity that thiols,13
disulfides,13 and thiolacetates14 display toward gold, we
included S atoms at the termini as a means to eventually
anchor the molecular tip to a thin film of gold placed on a
conventional AFM tip.15 We also demonstrate that 19 is
Reaction of 11 with KSCN gave dithiocyanate 12, which
was converted into [1,2,5]-dithiazepane 13 upon treatment
with hot KOH. Alternatively, reaction of 11 with excess
KSCN afforded 13 directly. Reaction of 13 with trimethyl-
silylacetylene (TMSA) gave 14. Cleavage of 14 gave alkyne
15, which in turn was treated with (4-iodo-phenylethynyl)-
trimethylsilane under Sonogashira coupling conditions to give
TMS derivative 16. Cleavage of 16 gave terminal alkyne
17. Alkynes 15 and 17 were separately coupled to tetraiodide
8 under Sonogashira conditions to give tetraphenylmethane
18 and its larger analogue 19, respectively (Scheme 3).
Alternatively, tetraiodide 5 was coupled to alkyne 15 to give
symmetrically tetrasubstituted adamantane 20.
(10) Keana, J. F. W.; Petukhov, P. A.; Rukavishnikov, A. V.; Phadke,
A.; LaMunyon, D. H.; Lee, M. D. Abstract of Papers, 217th National
Meeting of the American Chemical Society, Anaheim, CA, March
21-25, 1999; American Chemical Society: Washington, DC, 1999; p 72-
ORG.
(11) Rukavishnikov, A. V.; Phadke, A.; Lee, M. D.; LaMunyon, D. H.;
Petukhov, P. A.; Keana. J. F. W. Tetrahedron Lett. 1999, 40, 6353.
(12) See, for example: Constable, E. C.; Eich, O.; Housecroft, C. E.;
Johnston, L. A. Chem. Commun. 1998, 2661. Guo, W.; Galoppini, E.; Rydja,
G.; Pardi, G. Tetrahedron Lett. 2000, 41, 7419. Galoppini, E.; Guo, W.;
Qu, P.; Meyer, G. J. J. Am. Chem. Soc. 2001, 123, 4342. Galoppini, E.;
Guo, W.; Zhang, W.; Hoertz, P. G.; Qu, P.; Meyer, G. J. J. Am. Chem.
Soc. 2002, 124, 7801.
(13) The question of binding of disulfides and thiols to the gold surface
is complicated by the thermodynamic stability of disulfide ring and
monolayer formation kinetics. See the discussion in: Schlenoff, J. B.; Li,
Ming; Ly, Hiep J. Am. Chem. Soc. 1995, 117, 12528.
(14) Kim, S.; Park, S.-K.; Park, C.; Jeon, I. C. J. Vac. Sci. Technol. B.
1996, 14, 1318.
(15) Tour, J. M.; Jones, 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.
(16) (a) Reichert, V. R.; Mathias, L. J. Macromolecules 1994, 27, 7015-
7023; (b) 1994, 27, 7024-7029.
(17) Su, D.; Menger, F. M. Tetrahedron Lett. 1997, 38, 1485.
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Org. Lett., Vol. 4, No. 21, 2002