Suzuki and Heck Catalytic Molecular Coupling
A R T I C L E S
(1s), and Br (3d) were observed at the same binding energies
the region of 1 µm/s, a magnitude that translates into a tip-
as equivalent peaks in the raw material. Specific data points
for the aryl halide SAMs were as follows: Br (3d5/2, 3d3/2) 70.8,
molecule contact time of some 5.6 ms being required to achieve
3
8
substitution, derived using a Hertz model. The grafting of
lipoic or mercaptohexadecanoic acid into alkylthiol monolayers
could be followed by subsequent tagging with an acid reactive
fluorophore, Alexafluor 488 hydrazide (see Supporting Informa-
tion).
7
1.6 eV; S (2p3/ 2, 2p1/2) 163.3, 162.2 eV; C (1s) 285.0 eV; C
(1s, amide) 287.8 eV; N (1s) 399.7 eV. In both the monolayer
and the raw material samples, there is a carbon 1s peak at ∼288
eV, attributed to the amide carbon. The bromine doublet in the
spectrum of the monolayer is weak as expected from its
population on the surface. The position of the sulfur 2p doublet
had shifted to lower energy by ∼1.3 eV as compared to the
unbound sulfur of the raw material. Although the mode of
dialkylsulfide surface assembly remains unclear, this shift is
both indicative of the presence of a thiolate species (with
associated C-S bond cleavage) and consistent with the me-
chanical stability of these SAMs (see below). The N-(3-
AFM-Driven Reactions. It was envisaged that the GPa
pressure developed beneath an AFM probe would facilitate
efficient Suzuki coupling at room temperature. With palladium
film-coated probes, however, no evidence for reaction was
observed. This can be ascribed either to the wearing away of
the metal layer upon scanning, or the comparatively lower
39
number of catalytic sites offered to the halogenated surface.
Although the activity of catalytic nanoparticles can be a sensitive
(methylthio)propyl)-4-benzamide styrene SAM XPS peaks were
40
function of size, shape, and surface modification, it is generally
found to be high, an observation broadly assigned to their high
observed as S (2p3/2, 2p1/2) 163.0, 161.8 eV; C (1s) 285.0 eV;
C (1s, amide) 288.0 eV; N (1s) 399.9 eV.
2
7,39,41-44
surface area:volume ratio.
Colloidal particle-mediated
The amide A and B resonances (N-H stretch and associated
Fermi resonance) in the solid state were absent from grazing
FTIR spectra of the monolayer, consistent with the N-H bonds
being parallel to the surface and intermolecularly hydrogen-
Heck coupling has, for example, been observed to be more facile
than the initial “industry standard” of palladium on activated
4
2
carbon. Both Suzuki and Heck couplings have also been
extensively catalyzed through the use of phosphine-ligated
3
2-34
bonded.
In the monolayer sample, amide III appears at 1265
4
5,46
palladium complexes.
We have found no precedent for the
-
1
32,34
cm , in accordance with literature values.
Amide II appears
successful use of evaporated (“planar”) metallic in these
reactions. (Although there are many examples of ligandless
in the same region as the water bend and is, therefore, obscured.
In polarization modulated spectra, it was resolved at 1543
palladium catalysts in these reactions, these are immobilized
-
1 35,36
cm .
Amide I is not seen, even when a moving average is
on high surface area supports such as activated carbon.4
7,48
)
placed through the data. The presence and absence of these two
peaks is also indicative of hydrogen bonding, with the NH and
CO bonds parallel to the surface, and a trans arrangement of
PVP-Pd nanoparticles are known to adhere to silicon nitride
and to catalyze Suzuki reactions in aqueous solution.4
9-51
There
is also some precedent for their application to Heck catalysis.2
They were prepared from poly(vinylpyrrolidone) (PVP) with a
molecular weight of 40 000, imaged by AFM, and their activity
assessed in fluid-phase Suzuki and Heck coupling reactions,
using reagents subsequently employed in the probe-driven
reaction.
7,28
37
the amide bond. Additional resonances due to the methylene,
C-C, and para-substituted benzene rings were also resolved as
34
expected. Molecular coverages were determined, by stripping
1
4
14
voltammetry, to be (2.0-3.0) × 10 and (2.0-2.5) × 10
-
2
molecules cm for the aryl halide and styrene adlayers,
respectively.
Surface-confined Suzuki reactions were initiated by scanning
a SAM of 4-bromo/iodo-N-(3-(methylthio)propyl)benzamide
with a PVP-Pd nanoparticle-functionalized AFM probe at a force
of 15-25 nN and a speed of 1 µm/s in a methanolic solution
of sodium acetate and 3-aminophenylboronic acid. For the Heck
reaction, a SAM of N-(3-(methylthio)propyl)-4-vinylbenzamide
was scanned with an equivalent probe at a force of 25-40 nN
at a speed of 2 µm/s in a DMF solution of sodium hydrogen
carbonate and 4-iodobenzoic acid. This process catalyzes the
Mechanical Nanolithography and Nanografting. To as-
certain both likely limits of lateral resolution and the limits of
vertical force that could be nondestructively imparted to the
reagent SAM, force tolerances were obtained by lithographic
scanning under MilliQ water (18.2 MΩ). This was performed
at a high scan rate (between 40 and 60 Hz) over an area of 400
nm and at force that was increased stepwise until successful
mechanical lithography was achieved. The dialkylsulfide ad-
layers exhibited the same mechanical stability as analogous
alkanethiol SAMs; they were stable up to 70 ( 5 nN of applied
force, beyond which the adsorbate is removed and the resulting
hole depth measured at low (noncompressional force) to be that
associated with an all-trans molecular configuration and a tilt
angle of 25-30°.
(38) Schwarz, U. D. J. Colloid Interface Sci. 2003, 261, 99-106.
(
39) Narayanan, R.; El-Sayed, M. A. J. Am. Chem. Soc. 2003, 125, 8340-
8347.
(40) Bonnemann, H.; Braun, G. A. Angew. Chem., Int. Ed. Engl. 1996, 35,
1992-1995.
(
41) Beller, M.; Fischer, H.; Kuhlein, K.; Reisinger, C. P.; Herrmann, W. A. J.
Organomet. Chem. 1996, 520, 257-259.
Nanografting experiments were carried out to verify the
feasibility of tagging and locating introduced highly localized
functional groups. Optimal tip velocities were found to be in
(
42) Dhas, N. A.; Gedanken, A. J. Mater. Chem. 1998, 8, 445-450.
(43) Yeung, L. K.; Crooks, R. M. Nano Lett. 2001, 1, 14-17.
(44) Bradley, J. S. In Clusters and Colloids; Schmid, G., Ed.; VCH: Weinheim,
1994; Chapter 6.
(45) Meijere, A. d.; Meyer, F. E. Angew. Chem., Int. Ed. Engl. 1995, 33, 2379-
(
32) Yu, H.-Z.; Ye, S.; Zhang, H.-L.; Uosaki, K.; Liu, Z.-F. Langmuir 2000,
2411.
1
6, 6948-6954.
(46) Cabri, W.; Candiani, I. Acc. Chem. Res. 1995, 28, 2-7.
(47) Mukhopadhyay, S.; Rothenberg, G.; Joshi, A.; Baidossi, M.; Sasson, Y.
AdV. Synth. Catal. 2002, 344, 348-354.
(
33) Clegg, R. S.; Hutchison, J. E. Langmuir 1996, 12, 5239-5243.
34) Lenk, T. J.; Hallmark, V. M.; Hoffmann, C. L.; Rabolt, J. F.; Castner, D.
G.; Erdelen, C.; Ringsdorf, H. Langmuir 1994, 10, 4610-4617.
(
(48) Prckl, S. S.; Kleist, W.; Khler, K. Tetrahedron 2005, 61, 9855-9859.
(49) Van der Putten, A. M. T.; De Bakker, J. W. G.; Fokkink, L. G. J. J.
Electrochem. Soc. 1992, 139, 3475-3480.
(
(
35) Zamlynny, V.; Zawisza, I.; Lipkowski, J. Langmuir 2003, 19, 132-145.
36) Barner, B. J.; Green, M. J.; SBez, E. I.; Corn, R. M. Anal. Chem. 2001,
6
3, 55-60.
(50) Li, Y.; Hong, X. M.; Collard, D. M.; El-Sayed, M. A. Org. Lett. 2000, 2,
2385-2388.
(37) Tam-Chang, S.-W.; Biebuyck, H. A.; Whitesides, G. M.; Jeon, N.; Nuzzo,
R. G. Langmuir 1995, 11, 4371-4382.
(51) Narayanan, R.; El-Sayed, M. A. J. Phys. Chem. B 2004, 108, 8572-8580.
J. AM. CHEM. SOC.
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