Diazirine-modified gold nanoparticle: Template for efficient photoinduced interfacial carbene insertion reactions

Article abstract of DOI:10.1021/la102621h

Photolysis of a 3-aryl-3-(trifluoromethyl)diazirine-modified monolayer-protected gold nanoparticles (2-C₁₂MPNs), with a core size of 1.8 ± 0.3 nm, in the presence of model carbene trapping reagents leads to efficient, essentially quantitative, modification of the interface via carbene insertion reactions. The utility of carbene insertion reactions as a general approach for the modification of Au-MPNs to provide a breadth of new structures available was demonstrated using acetic acid, methanol, benzyl alcohol, phenol, benzylamine, methyl acrylate, and styrene (10a-g, respectively) as electrophilic carbene trapping agents to form the corresponding modified 3a-g-C₁₂MPNs. The 1.8 ± 0.3 nm gold nanoparticles bearing a diazirine group (2-C₁₂MPNs) were synthesized using the ligand exchange reaction with the requisite 3-aryl-3-(trifluoromethyl) diazirinealkylthiol. The 2-C₁₂MPNs and the resulting products of the reaction on the MPN (3a-g-C₁₂MPN) were fully characterized by IR, ¹H NMR, and ¹⁹F NMR spectroscopy and, when applicable, transmission electron microscopy (TEM). Verification for the 3a-g-C ₁₂MPNs was accomplished by comparison of the spectral data to those of obtained for the photoreactions of 3-(3-methoxyphenyl)-3-(trifluoromethyl)- 3H-diazirine as a model with 10a-g.

Full text of DOI:10.1021/la102621h

pubs.acs.org/Langmuir
© 2010 American Chemical Society
Diazirine-Modified Gold Nanoparticle: Template for Efficient Photoinduced
Interfacial Carbene Insertion Reactions
Hossein Ismaili, Soo Lee, and Mark S. Workentin*
Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7
Received June 29, 2010. Revised Manuscript Received August 12, 2010
Photolysis of a 3-aryl-3-(trifluoromethyl)diazirine-modified monolayer-protected gold nanoparticles (2-C12MPNs),
with a core size of 1.8 ( 0.3 nm, in the presence of model carbene trapping reagents leads to efficient, essentially quanti-
tative, modification of the interface via carbene insertion reactions. The utility of carbene insertion reactions as a general
approach for the modification of Au-MPNs to provide a breadth of new structures available was demonstrated using
acetic acid, methanol, benzyl alcohol, phenol, benzylamine, methyl acrylate, and styrene (10a-g, respectively) as
electrophilic carbene trapping agents to form the corresponding modified 3a-g-C12MPNs. The 1.8 ( 0.3 nm gold
nanoparticles bearing a diazirine group (2-C12MPNs) were synthesized using the ligand exchange reaction with
the requisite 3-aryl-3-(trifluoromethyl)diazirinealkylthiol. The 2-C12MPNs and the resulting products of the reaction on
the MPN (3a-g-C12MPN) were fully characterized by IR, 1H NMR, and 19F NMR spectroscopy and, when applicable,
transmission electron microscopy (TEM). Verification for the 3a-g-C12MPNs was accomplished by comparison of the
spectral data to those of obtained for the photoreactions of 3-(3-methoxyphenyl)-3-(trifluoromethyl)-3H-diazirine as
a model with 10a-g.
Introduction
metathesis polymerization (ROMP),9 coupling reaction of ali-
phatic hydroxyl group,10 reductive amination reaction,11 Michael
additions,12 1,3-dipolar cycloadditions,13 Diels-Alder reactions,14
Grignard reactions,15 and olefin cross-metathesis.16 While some
reactions are efficient at ambient temperatures, many reaction
types require refluxing conditions or catalysts and the low stability
of the Au-MPNs in the 1-5 nm in diameter size regime to higher
temperatures (>50 °C) and some catalysts limit the efficacy. The
need to perform reactions on Au-MPNs under relatively mild and
low temperature conditions limits the types of reactions that can be
done efficiently and quantitatively in these systems. In addition,
reactions of the monolayer moieties on the Au-MPNs are typically
slower (less efficient) relative to similar reactions in the solu-
tion phase because of the reaction environment provided at the
interface.12-15 Therefore, finding efficient interfacial reactions that
work under mild reaction conditions is an important challenge in
Au-MPNs applications. In our own attempts to extend the types
of reactions that can be utilized for efficient interfacial modi-
fications of Au-MPNs, we examined some Diels-Alder and
1,3-diploar cycloadditions. These particular reactions were
found to be generally too slow to be useful at ambient tempe-
ratures but showed that high pressure conditions can be used as
an efficient tool to facilitate these reactions on the Au-MPNs
with high yields and with no detrimental effects on the gold
core.13c,d,14
Monolayer-protected gold nanoparticles (Au-MPNs) continue
to be an active area of discovery because of their unique chemi-
cal and physical properties as well as potential applications in
catalysis,1 sensors,2 drug delivery,3 and nanomedicine.4 The key
to their use in any application is the ability to prepare Au-MPNs
with a specific chemical functionality for the interaction or
reaction required. The ability to chemically modify nanoparticles
by a direct interfacial reaction of terminal functional groups,
exposed on the surface of Au-MPNs, with various reactants is a
critical and important goal.5 Because of this, the chemical
modification of Au-MPNs has been the subject of numerous
studies, and a host of reaction types have been explored at the
interface, including esterifications,6 siloxane formation reaction,7
nucleophilic substitutions,8 transition-metal-catalyzed ring-opening
*Corresponding author. E-mail: mworkent@uwo.ca.
(1) (a) Corma, A.; Garcia, H. Chem. Soc. Rev. 2008, 37, 2096 and references
therein . (b) Juarez, R.; Corma, A.; García, H. Green Chem. 2009, 11, 949. (c) Conte, M.;
ꢀ
Miyamura, H.; Kobayashi, S.; Chechik, V. J. Am. Chem. Soc. 2009, 131, 7189. (d)
Raptis, C.; Garcia, H.; Stratakis, M. Angew. Chem., Int. Ed. 2009, 48, 3133.
(2) (a) Wang, Z.; Ma, L. Coord. Chem. Rev. 2009, 253, 1607 and references therein
. (b) Sperling, R. A.; Rivera, P. G.; Zhang, F.; Zanella, M.; Parak, W. J. Chem. Soc. Rev.
2008, 37, 1896 and references therein .
(3) (a) Ghosh, P.; Han, G.; De, M.; Kim, C. K.; Rotello, V. M. Adv. Drug
Delivery Rev. 2008, 60, 1307 and references therein . (b) Nakanishi, J.; Nakayama, H.;
Shimizu, T.; Ishida, H.; Kikuchi, Y.; Yamaguchi, K.; Horiike, Y. J. Am. Chem. Soc.
2009, 131, 3822. (c) Elbakry, A.; Zaky, A.; Liebl, R.; Rachel, R.; Goepferich, A.;
Breunig, M. Nano Lett. 2009, 9, 2059. (d) Prabaharan, M.; Grailer, J. J.; Pilla, S.;
Steeber, D. A.; Gong, S. Biomaterials 2009, 30, 6065.
Photochemical reactions of suitably functionalized Au-MPNs
can also be utilized to perform chemical modifications under
(4) Boisselier, E.; Astruc, D. Chem. Soc. Rev. 2009, 38, 1759.
(5) Daniel, M. C.; Astruc, D. Chem. Rev. 2004, 104, 293.
(6) Brust, M.; Fink, J.; Bethella, D.; Schiffrina, D. J.; Kielyb, C. J. Chem. Soc.,
(11) Otsuka, H.; Akiyama, Y.; Nagasaki, Y.; Kataoka, K. J. Am. Chem. Soc.
2001, 123, 8226.
Chem. Commun. 1995, 1655.
(12) Koenig, S.; Chechik, V. Langmuir 2003, 19, 9511.
(7) Buining, P. A.; Humbel, B. M.; Philipse, A. P.; Verkleij, A. J. Langmuir 1997,
13, 3921.
(8) Templeton, A. C.; Hostetler, M. J.; Kraft, C. T.; Murray, R. W. J. Am.
Chem. Soc. 1998, 120, 1906.
(9) Watson, K. J.; Zhu, J.; Nguyen, S. T.; Mirkin, C. A. J. Am. Chem. Soc. 1999,
121, 462.
(13) (a) Fleming, D. A.; Thode, C. J.; Williams, M. E. Chem. Mater. 2006, 18,
2327. (b) Sommer, W. J.; Weck, M. Langmuir 2007, 23, 11991. (c) Zhu, J.; Lines, B. M.;
Ganton, M. D.; Kerr, M. A.; Workentin, M. S. J. Org. Chem. 2008, 73, 1099. (d) Ismaili,
H.; Alizadeh, A.; Snell, K. E.; Workentin, M. S. Can. J. Chem. 2009, 87, 1708.
(14) Zhu, J.; Ganton., M.; Kerr, M. A.; Workentin, M. S. J. Am. Chem. Soc.
2007, 129, 4904.
(10) Friggeri, A.; Van Manen, H. J.; Auletta, T.; Li, X. M.; Zapotoczny, S.;
(15) Thode, C. J.; Williams, M. E. Langmuir 2008, 24, 5988.
(16) Ornelas, C.; Mery, D.; Cloutet, E.; Aranzaes, J. R.; Astruc, D. J. Am. Chem.
€
ꢀ
Schonherr, H.; Vancso, G. J.; Huskens, J.; Van Veggel, F. C. J. M.; Reinhoudt,
D. N. J. Am. Chem. Soc. 2001, 123, 6388.
Soc. 2008, 130, 1495.
14958 DOI: 10.1021/la102621h
Published on Web 08/24/2010
Langmuir 2010, 26(18), 14958–14964

Ismaili et al.
Article
Scheme 1
ambient (or lower) temperature conditions.17 In the continuation
of our studies on exploring new methods for the modification of
Au-MPNs through interfacial reactions, we report here the
interfacial photoinduced carbene formation from a diazirine-
modified Au-MPN and, as proof of concept, show that the subse-
quent carbene insertions into a selection of model trapping agents
such as alcohols, amines, and alkenes is quantitative (Scheme 1).
Carbene and nitrene insertion reaction approaches have been
considered as feasible strategies to chemically modify surfaces or
immobilize biological molecules on the functionalized surfaces.18
Early in the advent of the use of gold monolayers, Wrighton
and co-workers developed a gold self-assembled monolayer (Au-
SAM) with aryl azide terminal groups that upon irradiation
generated a reactive nitrene that then reacted with amines.19
Surface modification with nylon-6,6,20 protein immobilization
on Fischer carbene-derivatized SAMs,21 and immobilization
of small natural products on a glass slide22 are other examples
of employing carbene insertion approaches on surfaces, but to
date, we are not aware of any reports of generating and utilizing
a reactive carbene moiety on a Au-MPN.
Diazirines are excellent carbene precursors and are well-known
photophores for photoaffinity labeling and photo-cross-linking
probes.23 Diazirines readily generate reactive carbene intermedi-
ates by photoinitiated nitrogen extrusion and, as importantly, are
relatively stable (chemically and thermally) prior to photolysis
and hence do not undergo undesired reactions prior to photo-
lysis or thermal activation.23a,24 Among the diazirine derivatives,
3-aryl-3-(trifluoromethyl)diazirine has received the most wide-
spread use because of its high thermal stability. Because of the
nature of the strong C-F bonds in the CF3 group, fluorine migra-
tions to the carbene carbon do not occur, leaving a stable car-
bene available for quantitative insertion or addition reactions.23a
Scheme 2
The ground state of trifluorophenylcarbene is a triplet, which
is in equilibrium with its higher energy singlet state; it is the
latter that is reactive leading to the observed insertion or addition
reactions.23f,g
In this paper we report the synthesis and characterization of a
3-aryl-3-(trifluoromethyl)diazirine-modified Au-MPN (2-C12MPN)
(Scheme 2). We demonstrate that photolysis leads to a carbene-
modified MPN directly and/or via the diazo-derivative result-
ing from photorearrangement of the diazirine. The carbene-
MPN intermediate is reactive toward X-H (X: O, N) bond
insertion and alkene addition, and this can be used as a temp-
late surface to introduce new functionality at the interface
(3-C12MPNs) (Scheme 1). A further benefit of utilizing the
3-aryl-3-(trifluoromethyl)diazirine as the carbene precursor is
that it demonstrates the usefulness of 19F NMR spectroscopy
to follow the course of the reactions and to further characterize
the resulting products of reactions performed on Au-MPN.
In fact, the use of 19F NMR has some advantages over 1H
NMR characterization where the signals due to ligands on the
Au-MPN are generally very broad.
Results and Discussion
To prepare the desired 3-aryl-3-(trifluoromethyl)diazirine-
modified Au-MPN (2-C12MPN), we utilized a place exchange
reaction incorporating 3-aryl-3-(trifluoromethyl)diazirine dode-
canethiol (9) onto 1.8 ( 0.3 nm dodecanethiolate-modified gold
nanoparticles (1-C12MPN), as illustrated in Scheme 2. The syn-
thetic route to 9 is shown in Scheme 3. Briefly, ortho-lithiation of
3-bromoanisole 1 with n-butyllithium followed by trifluoroace-
tylation of aryllithium intermediate provided ketone 2 in 54%
yield. Reaction of 2 with hydroxylamine hydrochloride gave the
corresponding oxime 3 (90%) which, in turn, was treated with
tosyl chloride to afford p-tolylsulfonyloxime 4 in quantitative
yield. Exposure of 4 to liquid ammonia and the subsequent
oxidation of diaziridine 5 using freshly prepared silver oxide gave
diazirine 6 in 52% overall yield for two steps.25,26 Compound 6
was converted to the corresponding phenol 7 (62%) using BBr3.27
(17) (a) Kell, A. J.; Stringle, D. L. B.; Workentin, M. S. Org. Lett. 2000, 2, 3381.
(b) Kell, A. J.; Workentin, M. S. Langmuir 2001, 17, 7355. (c) Kell, A. J.; Montcalm,
C. C.; Workentin, M. S. Can. J. Chem. 2003, 81, 484. (d) Nakanishi, J.; Nakayama, H.;
Shimizu, T.; Ishida, H.; Kikuchi, Y.; Yamaguchi, K.; Horiike, Y. J. Am. Chem. Soc.
2009, 131, 3822.
€
(18) (a) Jonkheijm, P.; Weinrich, D.; Schroder, H.; Niemeyer, C. M.;
Waldmann, H. Angew. Chem., Int. Ed. 2008, 47, 9618. (b) Browne, W. R. Coord.
Chem. Rev. 2008, 252, 2470.
(19) Wollman, E. W.; Kang, D.; Frisbie, C. D.; Lorkovic, I. M.; Wrighton, M. S.
J. Am. Chem. Soc. 1994, 116, 4395.
(20) Blencowe, A.; Cosstick, K.; Hayes, W. New J. Chem. 2006, 30, 53.
(21) Sawoo, S.; Dutta, P.; Chakraborty, A.; Mukhopadhyay, R.; Bouloussa, O.;
Sarkar, A. Chem. Commun. 2008, 5957.
(22) Kanoh, N.; Kumashiro, S.; Simizu, S.; Kondoh, Y.; Hatakeyama, S.;
Tashiro, H.; Osada, H. Angew. Chem., Int. Ed. 2003, 42, 5584.
(23) (a) Blencowe, A.; Hayes, W. Soft Matter 2005, 1, 178 and references therein .
(b) Hashimoto, M.; Hatanaka, Y. Eur. J. Org. Chem. 2008, 2513. (c) Hatanaka, T.;
€
Hatanaka, Y.; Setou, M. J. Am. Chem. Soc. 2006, 128, 15092. (d) Vila-Perello, M.;
Pratt, M. R.; Tulin, F.; Muir, T. W. J. Am. Chem. Soc. 2007, 129, 8086. (e) Qiu, Z.; Lu,
L.; Jian, X.; He, C. J. Am. Chem. Soc. 2008, 130, 14398. (f) Admasu, A.;
(25) Blencowe, A.; Caiulo, N.; Cosstick, K.; Fagour, W.; Heath, P.; Hayes, W.
Macromolecules 2007, 40, 939.
ꢀ
Gudmundsdottir, A. D.; Platz, M. S.; Watt, D. S.; Kwiatkowski, S.; Crocker, P. J.
J. Chem. Soc., Perkin Trans. 2 1998, 1093. (g)Platz, M.; Admasu, A. S.;Kwiatkowski,
S.; Crocker, P. J.; Imai, N.; Watt, D. S. Bioconjugate Chem. 1991, 2, 337.
(24) Brunner, J.; Senn, H.; Richards, F. M. J. Biol. Chem. 1980, 255, 3313.
(26) Mayer, T.; Maier, M. E. Eur. J. Org. Chem. 2007, 4711.
(27) Hatanaka, Y.; Hashimoto, M.; Kurihara, H.; Nakayama, H.; Kanaoka, Y.
J. Org. Chem. 1994, 59, 383.
Langmuir 2010, 26(18), 14958–14964
DOI: 10.1021/la102621h 14959

Article
Ismaili et al.
Scheme 3
Alkylation of 7 using 1,12-dibromododecane followed by con-
version of the bromide to the thioacetate, and then hydrolysis in
acidic conditions afforded the desired 3-aryl-3-(trifluoromethyl)-
diazirine dodecanethiol (9) in 73% yield.28 The 1-C12MPNs were
prepared using the Brust-Schiffrin two-phase method using
a protocol we have previously reported.29,13d This protocol results
in Au-MPNs with the average core diameter of 1.8 ( 0.3 nm as
shown by TEM analysis (Supporting Information).
methyl group of dodecanethiolate at 0.87 ppm (nonexchanged
ligands) in the 1H NMR spectrum revealed that the ratio of
ligands in 2-C12MPNs is ca. 1:1.3 thiol 9:dodecanethiolate. This
ratio shows that ∼45% of dodecanethiolate of the 1-C12MPNs
has been replaced by 9 through the exchange reaction and can
be verified by degradation of the particles and analyzing the 1H
NMR spectrum of the ligands that are cleaved.13c,d,17a-17c Fur-
ther characterization can be accomplished using 19F NMR where
the spectrum of 2-C12MPN shows a single peak at -65.7 ppm
assigned to the fluorine of the CF3 group, confirming the incor-
poration of 9 on the 2-C12MPNs (see inset of Figure 1).25
The diazirine moiety has major absorptions at 280 and 350 nm
(Supporting Information). Photolysis of 2-C12MPN with wave-
lengths above 300 nm utilizing a medium-pressure Hg lamp
results in photochemical nitrogen extrusion to yield the reactive
carbene, which subsequently can be trapped by a variety of
reagents via X-H (X: O, N) insertion or addition to alkenes.23
In the present case, progress of the reaction (Scheme 1) can be
followed using 19F NMR and IR spectroscopy. As previously
mentioned, the CF3 moiety alpha to the diazirine group of
2-C12MPNs shows a sharp peak at -65.7 ppm in the 19F NMR
spectrum.25 Disappearance of this peak and the emergence of the
new signals in 19F NMR spectrum can be used to reliably follow
the reaction progress. Photolysis of the diazirine can also lead to
the corresponding diazo intermediate via intramolecular rearran-
gement, which upon further irradiation generates the carbene
(Scheme 4).32 The diazo isomer generated from 2-C12MPN can be
detected using IR spectroscopy by the appearance of the strong
NdNdC stretch centered at 2090 cm-1. The diazo stretch
appears after irradiation of 2-C12MPNs, indicating at least partial
conversion of diazirine to the diazo group; therefore, complete
disappearance of the diazo peak in the IR reveals that all of the
carbenes generated from either diazirine or diazo isomer has
undergone insertion reaction. Conversion to the diazo-derivative
is also evident in the 19F NMR spectrum as described below.
The desired 2-C12MPNs were prepared using a ligand exchange
reaction (Scheme 2).30 Stirring a solution of 1-C12MPN (200 mg)
and thiol 9 (206 mg, 0.51 mmol) in benzene for 20 h gave
2-C12MPN. The 1H NMR spectrum of the 2-C12MPN show
broad peaks at 0.87, 0.95-1.74, and 3.89 ppm attributed to the
methyl group of the CH3-terminated dodecanethiolate ligands,
the methylene groups of both ligands (CH3-terminated dodeca-
nethiolate and 9), and the methylene alpha to oxygen (labeled
proton e, Figure 1A), respectively. In addition, the aromatic
region contains broad peaks at 6.65-6.90 ppm (protons labeled
a, b, and d) and 7.27 ppm (proton c) assigned to the aromatic
protons (Figure 1A). Comparison of the 1H NMR spectrum of 9
to that of 2-C12MPN, particularly the excellent agreement of
the signals due to a, b, c, d, and e that are assignable to the 3-aryl-
3-(trifluoromethyl)diazirine moiety in each, illustrates the suc-
cessful exchange reaction and incorporation of 9 onto 1-C12MPN
(Figure 1A). The presence of any free, nonbound 9 would appear
1
as sharp signals in the H NMR spectrum of 2-C12MPN, while
bound 9 (on 2-C12MPN) appear at the same chemical shift;
however, the signals are more broad on the Au-MPN.31 The
purity of 2-C12MPN from the nonbound ligands after exchange
reaction and work-up can thus be confirmed by the lack of sharp
1
signals in the H NMR spectrum of 2-C12MPN (Figure 1). The
integratedareas of the methyleneprotons alpha to oxygen, proton
labeled e (due to 9 attached to 2-C12MPNs), and the terminal
(28) Rothrock, A. R.; Donkers, R. L.; Schoenfisch, M. H. J. Am. Chem. Soc.
2005, 127, 9362.
(29) Brust, M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; Whyman, R. J. J. Chem.
Soc., Chem. Commun. 1994, 801.
(32) (a) Buterbaugh, J. S.; Toscano, J. P.; Weaver, W. L.; Gord, J. R.; Hadad,
C. M.; Gustafson, T. L.; Platz, M. S. J. Am. Chem. Soc. 1997, 119, 3580. (b) Kanoh,
N.; Nakamura, T.; Honda, K.; Yamakoshi, H.; Iwabuchi, Y.; Osada, H. Tetrahedron
2008, 64, 5692.
(30) Hostetler, M. J.; Templeton, A. C.; Murray, R. W. Langmuir 1999, 15, 3782.
(31) Templeton, A. C.; Wuelfing, W. P.; Murray, R. W. Acc. Chem. Res. 2000,
33, 27.
14960 DOI: 10.1021/la102621h
Langmuir 2010, 26(18), 14958–14964

Ismaili et al.
Article
Figure 1. 1H NMR spectra of (A) 2-C12MPN and (B) 9. The asterisk denotes the signal due to residual protons in the solvent, which are
CD2Cl2 in (A) and CDCl3 in (B). Key assignments are indicated.
Scheme 4
As an initial proof of concept of using the reactive carbene to
serve as a template to modify the Au-MPN, the irradiation of an
argon-saturated solution of 2-C12MPN was studied in the pre-
sence of CH3COOH in deuterated benzene (1:10-15 molar ratio,
diazirine group on the 2-C12MPNs:CH3COOH). To monitor the
course of the reaction, 19F NMR and IR spectra were recorded at
various times throughout the reaction. Three distinctive peaks
were observed in the 19F NMR spectra during the course of
the reaction: a peak due to the unreacted diazirine at -65.3 ppm
that decreases in intensity on irradiation that is concomitant with
a peak that appears at -75.9 ppm as a result of the product of
the carbene insertion into the O-H of acetic acid and another
at -57.5 ppm that we assign to the diazo intermediate.25 The peak
at -57.5 ppm initially grows in and then diminishes on continued
photolysis with continued increase in the peak at -75.9 ppm
(Figure 2). The reaction was deemed complete by the disappear-
ance of the peaks at -65.3 and -57.5 ppm in the 19F NMR spec-
trum. After complete reaction the 19F NMR spectrum showed
only a single peak at -75.9 ppm, corresponding to the CF3 group
of 3a-C12MPNs (Table 1). In addition, the IR analysis revealed
the formation and consumption of diazo isomer during the
Figure 2. (A) 19F NMR of 2-C12MPN; (B) 3 h and (C) 7 h after
irradiaton of 2-C12MPNs in the presence of CH3COOH. (D) 19
NMR of product 3a-C12MPN.
F
reaction; the peak at 2090 cm-1 due to the diazo isomer appeared
upon irradiation of 2-C12MPN and disappeared upon continued
irradiation (see Supporting Information). Under our irradiation
conditions the reaction reaches completion within 14 h at room
temperature, andonly productsfromO-H insertionareobtained.
A significant point to be mentioned is that the Au core of 2-C12MPN
is stable under UV irradiation in benzene and TEM taken after
reaction showed no change in the Au core size. Figure 3A shows
the 1H NMR spectrum of 3a-C12MPN. Evidence of the car-
bene insertion was the emergence of new peaks (g) and (f) which
Langmuir 2010, 26(18), 14958–14964
DOI: 10.1021/la102621h 14961

Article
Ismaili et al.
Table 1. Products of Reaction of Photolysis of the Diazirines 2-C12MPN and 6 with a Variety of Carbene Trapping Agents, the Approximate
Time To Complete Conversion To Form 3-C12MPN and 11, Respectively, and the 19F NMR Chemical Shifts of the Products 3-C12MPN
a19F NMR of 3-C12MPNs.
are attributed to the methyl and proton alpha to the CF3 group of
the product, respectively. The broadness of the peaks often makes
the 1H NMR assignments of functionalized MPNs a difficult task.
However, comparing the 1H NMR peaks of functionalized MPNs
with those of the model compound allows for a more confident
assignment. Tothis end, we used compound6 asa modeldiazirine,
and it was irradiated in the presence of the same reagents, in this
case CH3COOH to yield compound 11a (Scheme 5 and Table 1).
The model products 11 can be fully characterized via 1H NMR,
13C NMR, 19F NMR, and IR as well as by mass spectroscopy.
Comparing the NMR data obtained from 11 to that of the
3-C12MPN allows the validation of the product of the inter-
facial reactions performed on 2-C12MPN. In the 1H NMR
spectra (Figure 3) the spectral alignment between 3a-C12MPNs
and 11a, particularly the protons indicated, confirms the modi-
fication of 2-C12MPNs with acetic acid. Further, they both give
the same single peak at -76 ppm in their 19F NMR spectra
(Figure 3). The only difference is that the reaction of 6 with
acetic acid went to completion in 90 min, almost 10 times faster
than the corresponding reaction of 2-C12MPN with similar
optical density between 350 and 360 nm. This is likely due do
to efficient quenching of the excited state of the diazirine on
2-C12MPN by the gold core.33
To investigate the scope of using the photogenerated interfacial
carbene reaction toward X-H insertion and alkene addition as
a template for the modification of 2-C12MPN, its photolysis was
performed in the presence of a number of other reagents contain-
ing alcohol, amine, and alkene moieties (10b-g, Table 1). The
reagents were chosen in part in this proof of concept study to have
structural features that allowed for easier identification of the
products using 1H NMR spectroscopy, specifically having signals
downfield from the alkyl H region of the spectrum. The photo-
reactions of 2-C12MPN in the presence of 10b-g were carried
out under the same conditions as described for the reaction with
acetic acid above, and they were monitored using 19F NMR, 1H
NMR, and IR spectroscopies. The reactions went to completion
in 13-26 h, depending on the substrate (Table 1). Figure 4 shows
the 1H NMR spectra of 3b,c,e,f-C12MPN as representative
examples of the 3-C12MPN products. The appearances of new
1
peaks in H NMR spectra confirm the efficacy of the carbene
(33) (a) Thomas, K. G.; Kamat, P. V. Acc. Chem. Res. 2003, 36, 888. (b) Ghosh,
S. K.; Pal, T. Phys. Chem. Chem. Phys. 2009, 3831.
14962 DOI: 10.1021/la102621h
Langmuir 2010, 26(18), 14958–14964

Ismaili et al.
Article
Figure 3. 1H and 19F NMR spectra of (A) 3a-C12MPN and (B) 11a. The asterisk denotes the signal due to residual protons in the solvent
CD2Cl2. Key assignments are indicated.
Figure 4. 1H NMR spectraof(A) 3b-C12MPN, (B) 3c-C12MPN, (C)3e-C12MPN, and (D) 3f-C12MPN. The asteriskdenotes the signal dueto
residual protons CD2Cl2. Key assignments are indicated.
insertion reactions at modifying the 2-C12MPNs (19F NMR and
Scheme 5
IR data as well as 1H NMR of all 3-C12MPN can be found in the
Supporting Information). We also performed the photoreactions
with 6 in the presence of 10b-g to prepare 11b-g (Scheme 5 and
Table 1) to aid in the characterization of 3-C12MPN. It is these
comparisons that allowed for the characterization of the 1H
NMR of 3-C12MPN and the assignment of the protons identified
Langmuir 2010, 26(18), 14958–14964
DOI: 10.1021/la102621h 14963

Article
Ismaili et al.
in Figure 4 and the 19F in the products indicated in Table 1. In all
cases the reactions were efficient and resulted in quantitative
conversion of the diazirine. For the alkene addition reactions, the
two signals observed in the 19F NMR spectra are from the two
diastereomers. Full characterization is provided in the Supporting
Information.
It is important to note that in none of the reactions of 6 and
2-C12MPNs with 10a-g was the product of the insertion of the
carbene into the deuterated benzene (solvent) detected. Only in
the absence of a trapping reagent was this product observed.
Following 15 h of irradiation of 2-C12MPNs in deuterated
benzene two peaks were observed in the 19F NMR spectra: one
at -57.5 ppm due to the diazo isomer and another at -73.9 result-
ing from insertion into deuterated benzene to yield cyclohepta-
1,3,5-triene.25 Innone ofthe 19F NMRspectra of 3-C12MPNs was
this latter signal observed, suggesting that it was not a major
competing process and that the carbene insertion into benzene-d6
is much slower than X-H insertion or alkene addition. No other
products of other C-H insertion reactions were found.
as a photoreactive template Au-MPN for the introduction of
structural diversity to these particle types. In this study we utilized
Au-MPN with a 1.8 ( 0.3 nm core size; however, the results are
likelyto be general for any similarly modified MPN. Of course, the
efficiency of the photoreactions can also be optimized by utilizing
more intense light sources. Additionally, the ease of generation of
the carbene-modified Au-MPN and its highly reactive nature
makes 2-C12MPN useful for the modification of other surface
types, including carbon nanotubes, graphene, polymers, with Au-
MPN; these studies are currently in progress.
Acknowledgment. We thank the Natural Sciences and Engineer-
ing Research Council (Canada) and the University of Western Ontario
for financial support. S. Lee is grateful to the exchange program
ꢀ
between Universite Pierre et Marie Curie (Paris 6, France) and the
Chemistry Department of the University of Western Ontario.
Supporting Information Available: Full experimental de-
tails and characterization of compounds 2-9, 1-C12MPN, 2-
1
We have prepared and characterized 3-aryl-3-(trifluoromethyl)-
diazirine-modified monolayer-protected gold nanoparticles
(2-C12MPN). Further, these are efficient photoprecursors to
a reactive carbene at an Au-MPN interface that can undergo
efficient X-H insertion and alkene additions leading to the quanti-
tative modification of the Au-MPN. Compound 2-C12MPN serves
C12MPN, 3a-g-C12MPN and 11a-g, H and 19F NMR
spectra of 3a-g-C12MPN and 11a-g, TEM of 2-C12MPN
and 3a-C12MPN, IR of 2-C12MPN, 3a-C12MPN, and diazo
intermediate, and UV-vis spectra of 1-C12MPN, 2-C12-
MPN, and 3a-C12MPN. This material is available free of
charge via the Internet at http://pubs.acs.org.
14964 DOI: 10.1021/la102621h
Langmuir 2010, 26(18), 14958–14964