Boron-dipyrromethene-functionalized hemilabile ligands as turn-on fluorescent probes for coordination changes in weak-link approach complexes

Article abstract of DOI:10.1021/ic400383t

Herein we report a new class of hemilabile ligands with boron-dipyrromethene (Bodipy) fluorophores that, when complexed to Pt(II), can signal changes in coordination mode through changes in their fluorescence. The ligands consist of phosphino-amine or phosphino-thioether coordinating moieties linked to the Bodipy's meso carbon via a phenylene spacer. Interestingly, this new class of ligands can be used to signal both ligand displacement and chelation reactions in a fluorescence turn-on fashion through the choice of weakly binding heteroatom in the hemilabile moiety, generating up to 10-fold fluorescence intensity increases. The Pt(II) center influences the Bodipy emission efficiency by regulating photoinduced electron transfer between the fluorophore and its meso substituent. The rates at which the excited Bodipy-species generate singlet oxygen upon excitation suggest that the heavy Pt(II) center also influences Bodipy's emission efficiency by affecting intersystem crossing from the Bodipy excited singlet to excited triplet states. This signaling strategy provides a quantitative read-out for changes in coordination mode and potentially will enable the design of new molecular systems for sensing and signal amplification.

Full text of DOI:10.1021/ic400383t

Article
pubs.acs.org/IC
Boron-Dipyrromethene-Functionalized Hemilabile Ligands as “Turn-
On” Fluorescent Probes for Coordination Changes in Weak-Link
Approach Complexes
Alejo M. Lifschitz, Chad M. Shade, Alexander M. Spokoyny, Jose Mendez-Arroyo, Charlotte L. Stern,
Amy A. Sarjeant, and Chad A. Mirkin*
Department of Chemistry and International Institute for Nanotechnology, Northwestern University, 2145 Sheridan Road, Evanston,
Illinois 60208, United States
S
* Supporting Information
ABSTRACT: Herein we report a new class of hemilabile
ligands with boron-dipyrromethene (Bodipy) fluorophores
that, when complexed to Pt(II), can signal changes in
coordination mode through changes in their fluorescence.
The ligands consist of phosphino-amine or phosphino-
thioether coordinating moieties linked to the Bodipy’s meso
carbon via a phenylene spacer. Interestingly, this new class of
ligands can be used to signal both ligand displacement and
chelation reactions in a fluorescence “turn-on” fashion through
the choice of weakly binding heteroatom in the hemilabile
moiety, generating up to 10-fold fluorescence intensity
increases. The Pt(II) center influences the Bodipy emission efficiency by regulating photoinduced electron transfer between
the fluorophore and its meso substituent. The rates at which the excited Bodipy-species generate singlet oxygen upon excitation
suggest that the heavy Pt(II) center also influences Bodipy’s emission efficiency by affecting intersystem crossing from the Bodipy
excited singlet to excited triplet states. This signaling strategy provides a quantitative read-out for changes in coordination mode
and potentially will enable the design of new molecular systems for sensing and signal amplification.
ligands for the signaling of coordination changes in WLA
complexes (Scheme 1). When complexed to Pt(II), these novel
ligands create active structures that can be toggled with small
molecules or elemental anions between significantly different
fluorescent states and therefore represent new synthons for the
WLA that can be utilized, in principle, for both stoichiometric
and catalytically amplified sensing strategies. Bodipy was chosen
because its high molar absorption coefficient and fluorescence
quantum yield, and the variety of approaches to modulate the
latter make it an appealing signaling unit.25−29 In particular,
Bodipy has been used for the construction of a wide variety of
fluorescence switches since photoinduced electron transfer
(PeT) between the fluorophore and its meso substituent can be
regulated deliberately via coordination chemistry to either
enhance or quench its fluorescence.30−32 In the case of Pt(II)
complexes, we show that displacement of the Pt−S bond in a
phosphino-thioether (P,S) hemilabile moiety attached to the
Bodipy meso carbon via a phenylene spacer (eq 1, Scheme 1)
impedes PeT, and a fluorescence “turn-on” signal ensues.
Similarly, “turn-on” fluorescence signaling of the opposite
coordination event, ligand chelation, is possible by utilizing
phosphino-amine (P,N) hemilabile moieties in place of P,S (eq
INTRODUCTION
■
The weak-link approach (WLA) is a coordination-chemistry-
based strategy for the synthesis of supramolecular structures
that can be reversibly toggled between different geometries via
ligand displacement reactions at transition metal structural
regulatory sites using small molecule analytes.1−3 Through the
synthetic incorporation of catalysts whose activities depend on
their position and orientation within these frameworks, the
WLA has been employed to regulate various catalytic
properties, including turnover rate and enantioselectivity.4,5
This kind of control over a catalyst offers potential for sensing
and signal amplification applications since the coordination of
an analyte can result in an output that is amplified by the
catalyst in an ELISA-6 or PCR-like fashion.7 In these systems,
sensing and signal amplification are possible since the sensing
analytes produce changes in coordination mode of the WLA
complexes that significantly affect their functionality.
A useful strategy to signal structural changes8−15 and binding
events16−24 in functional molecular and supramolecular systems
is to incorporate fluorescent signaling units, due to the
sensitivity of the fluorescence output and the number of ways
these outputs can be analyzed (e.g., changes in spectral features,
emission intensity, fluorescence lifetimes, and fluorescence
anisotropy). Herein we explore a new strategy of incorporating
boron-dipyrromethene (Bodipy) fluorophores into hemilabile
Received: February 13, 2013
© XXXX American Chemical Society
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Scheme 1. Novel Bodipy-Functionalized Hemilabile Ligands Can Be Used for Signaling Changes in Coordination Mode via
a
Variations in the Bodipy Fluorescence Emission
a
Both ligand displacement (eq 1) and chelation (eq 2) reactions can be signaled in a fluorescence “turn-on” fashion through the choice of
heteroatom (S or N) in the hemilabile moiety.
Scheme 2. Synthesis of P,S-Bodipy Ligands 3 and 6
2, Scheme 1). In all examples studied, the Pt(II) structural
regulatory site directly affects the photophysics of Bodipy by
interacting with the meso substituent, thus establishing a
quantifiable signaling methodology for coordination changes. In
addition, all data suggest that the Pt(II) center may further
modulate the fluorescence emission efficiency of Bodipy via the
heavy atom effect (HAE),33,34 since coordination changes vary
the distance between the fluorophore and the metal cation. By
exploring the fluorescence signaling of coordination changes in
model WLA coordination complexes, we establish a general
Bodipy-containing hemilabile ligand class that can be
incorporated into supramolecular WLA systems and potentially
used for sensing and signal amplification applications.
RESULTS AND DISCUSSION
■
Synthesis. In order to access “turn-on” fluorescence
signaling of both ligand chelation and partial displacement
reactions, we synthesized a set of novel Bodipy-containing
hemilabile ligands in which the nature and electron donating
abilities of the weakly coordinating heteroatom in the
hemilabile moiety are varied (Schemes 2 and 3).
P,S-Bodipy ligands 3 and 6, which differ in the electron
donating ability of the sulfur based on the presence of electron
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Scheme 3. Synthesis of P,N-Bodipy Ligand 12
Scheme 4. Formation of Heteroligated Pt(II) Complexes and Reversible Toggling Between Semiopen (Bottom Left) and
Closed (Bottom Right) Coordination Modes
withdrawing fluorine atoms on the meso phenyl ring, were
synthesized via two different approaches (Scheme 2). Ligand 3
was obtained via nucleophilic aromatic substitution of the para
fluorine in compound 1 by a thiomethoxide nucleophile
generated in situ upon deprotection of 2 in tetrahydrofuran
(THF).35 P,S-Bodipy ligand 6, on the other hand, was obtained
in a one pot reaction starting with benzaldehyde 4 and a
sequence of steps involving an acidic Knoevenagel condensa-
tion with cryptopyrrole 5 catalyzed by trifluoroacetic acid
(TFA),36 oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoqui-
none (DDQ), and treatment with N(i-Pr)2Et and excess
BF3·OEt2. Ligands 3 and 6 were isolated after purification as
analytically pure substances, which exhibit diagnostic 31P{1H}
NMR resonances at δ −16.6 and δ −16.7, respectively.
The synthesis of P,N-Bodipy ligand 12 involves five synthetic
steps from commercially available 2-(methylanilino)ethanol 7
in 5.5% overall yield (Scheme 3). First, electrophilic
bromination of the aromatic ring in amine 7 with N-
bromosuccinimide (NBS) provided 8. Next, the chloride
derivative 9 was obtained via the Appel reaction, and the SN2
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reaction of 9 with potassium diphenylphosphide yielded 10.
The installation of a formyl unit to give 11 was accomplished
via lithium-halogen exchange with n-butyl lithium (n-BuLi)
followed by treatment with N,N-dimethylformamide (DMF).
Finally, the target P,N-Bodipy 12 was obtained via reaction of
11 with cryptopyrrole 5 under similar conditions used to
generate P,S-Bodipy 6. Ligand 12 was isolated as an analytically
pure solid after recrystallization of the crude product mixture
from a 1:1 mixture of CH2Cl2/hexanes (31P{1H} NMR signal: δ
−20.5).
Structures of Complexes 13 and 14. Single crystals of
compounds 13 and 14 suitable for X-ray analysis were grown
by slow diffusion of pentane into CH2Cl2 solutions of the
respective complexes (Figure 1). The solid-state structures are
Bodipy-containing ligands were incorporated into model
WLA complexes that also contain a nonfunctionalized P,S
ligand to highlight the potential to integrate other functional
moieties relevant for sensing and signal amplification into the
system studied herein. Note that although 2-
(diphenylphosphino)ethyl-methyl-thioether (P,S-Me) is used
as a proof-of-concept example, in our previous work, we have
shown that this ligand can be replaced with a wide variety of
isoelectronic structures that have pendant groups consisting of
recognition (i.e., hydrogen-bonding groups)4 and catalytic
moieties (i.e., metallosalens, metalloporphyrins).2 The gen-
eration of Pt(II) semiopen complexes 13, 15, and 17 was
accomplished via sequential addition of P,S-Me and the
appropriate Bodipy-containing ligand to a dichloromethane
solution of dichloro(1,4-cyclooctadiene)platinum(II) (Scheme
4). In all cases, this resulted in the formation of monocationic
complexes in which P,S-Me is chelated to the metal center, and
the Bodipy-functionalized ligand is coordinated through the
phosphorus only. In the case of complexes containing P,S-
Bodipy ligands, the formation of semiopen complexes 13 and
15 was confirmed by the two characteristic set of 31P{1H}
NMR resonances arising from the coordination of chelated P,S-
Me (13, δ 43.1, JP−P = 14 Hz, JP−Pt = 3478 Hz; 15, δ 43.6, JP−P
= 14 Hz, JP−Pt = 3515 Hz) and P-bound P,S-Bodipy ligands
(13, δ 8.9, JP−P = 13 Hz, δ 9.0, JP−Pt = 3199 Hz; 15, JP−P = 13
Hz, JP−Pt = 3168 Hz).37 In the case of semiopen complex 17
containing P,N-Bodipy ligand 12, the 31P{1H} NMR spectrum
shows two sets of resonances centered at δ 43.8 (JP−P = 15 Hz,
JP−Pt = 3515 Hz) and 6.6 (JP−P = 13 Hz, JP−Pt = 3141 Hz),
consistent with a chelated P,S-Me ligand and P-bound P,N-
Bodipy ligand.37
Figure 1. Crystal structures of 13 (left) and 14 (right) drawn with
50% thermal ellipsoid probability. The distances between the center of
the Bodipy moiety and the Pt(II) center were measured from the
crystal structures. Hydrogen atoms and counterions were omitted for
clarity.
consistent with the assignments of the structures in solution,
displaying Pt(II) square planar centers with phosphine ligands
coordinated in a cis-fashion in both 13 and 14. In the case of
13, P,S-Bodipy ligand 3 is coordinated to the Pt(II) center
through the phosphorus only, displaying a Pt−P bond length of
2.279 Å. The distance between the metal center and the center
of the Bodipy moiety is 8.99 Å, and the angle between the
Bodipy plane and the plane of the meso phenyl ring is 83.02°.
In the case of closed complex 14, P,S-Bodipy 3 is chelated to
the Pt(II) center with a bite angle of 85.19° and the Pt−P and
Pt−S bond lengths are 2.278 and 2.354 Å, respectively. The
angle between the planes of the Bodipy and the meso phenyl
ring is slightly lower (83.15°) compared to that observed in 13,
demonstrating that changes in coordination mode at the Pt(II)
center do not appreciably change geometric factors of the dye
that affect its photophysics.38 However, the distance between
the center of the Bodipy moiety and the heavy Pt(II) center in
14 is lowered by 0.4 to 8.6 Å, relative to 13. The degree of
spin−orbit coupling facilitated by the heavy atom center is
highly distance dependent,33,34 and thus, the variation in
Bodipy-Pt(II) distances upon changes in coordination mode
can affect the Bodipy fluorescence efficiency through
intersystem crossing in addition to PeT. Even though the
distances in solution may be different from those observed in
the solid state, the structures in Figure 1 highlight that changes
in the degree of intersystem crossing may also play a role in the
differences in quantum yield between semiopen and closed
complexes.
Fluorescence Efficiency Regulation. The steady-state
luminescence properties of the novel Bodipy-functionalized
hemilabile ligands 3, 6, and 12, and their respective Pt(II)
complexes, were measured in dichloromethane (Table 1).39
P,S-Bodipy ligands 3 and 6 display steady-state quantum yields
of 91% and 84%, respectively, which are within the same
magnitude of reported values for phenyl (77% in acetonitrile)
and tetrafluorophenyl (99% in acetone) meso-substituted
Bodipys.40,41 These results confirm that substitution of Bodipy
in the meso position with P,S hemilabile moieties does not
enable significant PeT between the Bodipy excited state and the
meso substituent in the free ligands. Conversely, the presence
The semiopen complexes were quantitatively converted to
their closed forms via chloride abstraction with 2 equiv of
AgBF4 in dichloromethane. The chelation of the P,S-Bodipy
ligands in complexes 14 and 16 was confirmed by the two
characteristic sets of signals in their 31P{1H} NMR (14, δ 46.6,
J
P−P = 13 Hz, JP−Pt = 3093 Hz and δ 46.2, JP−P = 13 Hz, JP−Pt
3290 Hz; 16, δ 46.3 JP−P = 13 Hz, JP−Pt = 3165 Hz and δ 45.8
P−P = 13 Hz, JP−Pt = 3100 Hz), indicative of two nonequivalent,
=
J
chelated phosphine ligands. Similarly, chelation of P,N-Bodipy
ligand to give closed complex 18 was confirmed by 31P{1H}
NMR resonances at δ 37.9 (JP−P = 16 Hz, JP−Pt = 3397 Hz) and
31.0 (JP−P = 15 Hz, JP−Pt = 3183 Hz), which are highly
diagnostic of two chelated phosphines trans to sulfur and
nitrogen moieties, respectively.37 Complexes 13−18 were also
characterized by 1H, 11B{1H}, 19F NMR spectroscopy and mass
spectrometry (see Experimental Section). Closed complexes
14, 16, and 18 can be quantitatively converted back to their
semiopen forms, 13, 15, and 17, respectively, via addition of 2
equiv of tetrabutylammonium chloride in CH2Cl2, highlighting
the ability of the complexes to toggle reversibly between the
semiopen and closed coordination modes.
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Complex 14 displays a fluorescence quantum yield of 16%, and
16 displays a similar steady-state emission efficiency of 15%.
Therefore, the P,S-Bodipy ligands exhibit “turn-on” florescence
behavior upon substitution-induced breaking of the Pt−S bond.
In the case of P,N-Bodipy ligand 12, incorporation into
semiopen Pt(II) complex 17 also results in a moderate decrease
of the fluorophore’s quantum yield to 3.1%. However,
formation of closed complex 18 results in a fluorescence
quantum yield of 32%, a 10-fold increase relative to semiopen
complex 17. The lack of profile changes observed in the
emission and absorbance spectra of P,N-Bodipy and its Pt(II)
complexes indicates that the Bodipy moieties in 12, 17, and 18
fluoresce from their locally excited singlet state, and that there
are no emissive charge transfer decay pathways (see SI).31 We
can thus ascribe the changes in fluorescence quantum yield to
the stabilization of meso centered orbitals via chelation to
Pt(II), which makes reductive PeT decay less favorable, as
observed in the majority of aniline substituted Bodipy transition
metal sensors.25,31 This is further supported by the fact that the
nature of the fluorescence switch can be reversed by simply
reducing the electron density on the meso phenyl ring upon
exchanging the N moiety for an S group. It is thus likely that
coordination through the sulfur in complexes 14 and 16 lowers
the energy of meso-centered orbitals to the extent that oxidative
PeT effectively diminishes the fluorescence quantum yield (see
Computational Section, SI). Hence, P,S or P,N-Bodipy ligands
can be used to create complexes that signal ligand displacement
or ligand chelation reactions, respectively, both in a
fluorescence “turn-on” fashion. In all cases, the Pt(II) center
directly affects the interaction between the fluorophores and
their meso substituents via changes in coordination mode of
the hemilabile ligands. Thus, inclusion of Bodipy in WLA
Table 1. Spectral Parameters and Quantum Yields for
Bodipy-Containing Hemilabile Ligands and their Respective
a
Pt(II) Complexes
compd
λabs (max/nm)
λabs (max/nm)
Δλ (nm)
ϕf
3
544
540
547
527
527
277
525
525
525
558
556
561
541
541
541
541
544
543
14
16
14
14
14
14
16
19
18
0.91
0.76
0.16
0.83
0.64
0.15
0.066
0.031
0.32
13
14
6
15
16
12
17
18
a
Fluorescence quantum yields for 3, 13, and 14 were calculated in
DCM at room temperature using sulforhodamine B in ethanol as a
standard (λex = 505 nm). For all other compounds, rhodamine 6G in
ethanol at room temperature was used as a standard (λex = 505 nm).
of an aniline moiety on the meso position in 12 results in a
Bodipy species with a much lower quantum yield (6.6%). As
expected on the basis of literature precedent, PeT from the
electron rich aniline substituent to the excited Bodipy efficiently
quenches the fluorophore’s luminescence.42,43
The fluorescence of P,S- and P,N-Bodipy ligands was
similarly measured after the ligands were incorporated into
semiopen and closed Pt(II) complexes (13−18). When
incorporated into semiopen complexes, the quantum yields of
P,S-Bodipy 3 and 6 decrease to 76% in 13 and 64% in 15,
respectively, with minimal absorbance profile changes (see SI).
However, a more dramatic reduction of quantum yields was
observed upon formation of closed complexes 14 and 16.
Figure 2. Addition of tetrabutylammonium chloride to 14 results in quantitative formation of 13. (A) 31P NMR spectroscopy shows structural
changes arising from toggling from closed complex 14 (red) to semiopen complex 13 (green). (B) Fluorescence emission from the mixture increases
upon addition of chloride up to 1 equiv. (C) Correlation between molar fractions of semiopen complex determined by NMR spectroscopy and
integrated fluorescence shows a linear relationship between the two variables.
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systems provides a fluorescence output that is directly
generated by the structural regulatory site, and that can be
toggled between florescence “turn-on” or “turn-on” upon
chelation to Pt(II) simply through the choice of weakly binding
heteroatom.
Quantitative Signaling of Coordination Changes. To
enable the use of Bodipy as a signaling unit for coordination
changes in functional WLA systems, it is paramount to establish
the ability of hemilabile Bodipy ligands to signal these changes
in a quantitative fashion. Toward this end, we studied a system
in which the effector for the coordination changes interacts
directly with the structural regulatory metal center (Figure 2
and Scheme 4). In particular, coordination changes were
effected as tetrabutylammonium chloride was added into closed
complex 14 in dichloromethane, and the reaction mixture was
monitored spectroscopically. Variations in fluorescence signals
throughout the titration were correlated with the 31P NMR
spectrum of the mixture since this characterization technique
has been used previously to quantitatively track coordination
mode changes in WLA systems.37,44 While the Bodipy
absorbance centered at 544 nm only shifts slightly as 14 is
converted to 13, the integration of the Bodipy emission profile
is directly proportional to the fraction of semiopen complex
present as determined by 31P NMR spectroscopy (Figure 2).
Therefore, changes in fluorescence emission provide a
quantitative read-out for determining the fraction of semiopen
complex in a given sample.
Role of Heavy Atom Effect. Several studies have been
carried out in which heavy atoms, such as chalcogens45 and
halides,46 are placed at different positions around and in
proximity to the Bodipy core to populate its excited triplet
state. This has also been shown in molecular arrays in which the
Bodipy excited states interact with a transition metal
coordination complex leading to the population of excited
triplet states.47,48 Among other factors, the degree of spin−orbit
coupling is dependent on the distance between the fluorophore
and the heavy atom. As shown in Figure 1, a variation in
distance between Bodipy and the heavy Pt(II) is observed in
the solid state structures of 13 and 14. In addition, all of the
semiopen complexes in this study display lower quantum yields
than their corresponding free ligands in solution (see Table 1).
These observations suggest that the modulation of PeT
processes might not be the only way in which the model
WLA fluorescence switches operate, but intersystem crossing
into triplet excited states may also diminish emission from the
Bodipy excited singlet state.49
The presence of nonemissive excited triplet states can be
detected indirectly though their ability to generate singlet
oxygen, which in turn can degrade a variety of organic
substrates.50,51 We thus assessed the changes in the degree of
intersystem crossing based on coordination mode by exciting
an oxide-protected version of ligand 3 (3′), semiopen complex
13, and closed complex 14, and observing the effect excitation
has on the oxidation of diphenylbenzofuran (DPBF) by reactive
oxygen species.51 In particular, the photoactivated degradation
of DPBF was tracked by observing the disappearance of the
characteristic band centered at 414 nm in its absorbance profile
upon excitation of the Bodipy species at 545 nm.51 As shown in
Figure 3, we were able to observe a 1.2-fold oxidation rate
increase upon excitation of semiopen complex 13 relative to the
oxygen-protected ligand 3′. Furthermore, the relative rate of
oxidation is increased by 1.7-fold when the Bodipy in closed
complex 14 is excited. The changes in catalytic degradation
Figure 3. Variation in DPBF absorbance at 414 nm upon excitation at
545 nm in 90 × 10−5 M solutions with 5 × 10−5 M oxidized ligand 3′
(purple squares), semiopen complex 13 (red circles), closed complex
14 (blue squares), and no Bodipy species (green triangles).
Absorbance values were normalized to 1 using the initial value prior
to irradiation.
rates thus suggest that intersystem crossing to a triplet manifold
upon irradiation is increased by the proximity to the Pt(II)
heavy atom. Therefore, the 4.5-fold fluorescence decrease in 14
relative to 13 is likely the combined result of the excited singlet
state of Bodipy undergoing PeT to the meso substituent and
intersystem crossing to an excited triplet state, two pathways
which are enabled by the Pt(II) structural regulatory center.
CONCLUSION
■
A new class of Bodipy-functionalized hemilabile ligands has
been developed in which the nature of the weakly coordinating
heteroatom is deliberately varied to allow for fluorescence
“turn-on” signaling of both ligand chelation and partial
displacement reactions. The ligands display high quantum
yields, even when in physical proximity to heavy Pt(II) centers,
and the changes in emission intensity upon coordination
changes are greater than those observed for other fluorophores
previously studied in the context of WLA complexes, such as
anthracene and pyrene.52,53 This new class of Bodipy-
functionalized ligands will allow for fluorescence signaling in
a broader array of sensing strategies amenable to the WLA. For
instance, P,S-Bodipy ligands can be used to signal the binding
of small molecule analytes that displace the Pt−S bond upon
coordination to WLA complexes. Conversely, P,N-Bodipy
ligands can be employed to signal recognition events that
result in the displacement of a receptor ligand by the Bodipy-
functionalized chelating moiety. Further, since the coordination
changes studied herein also result in variations in the degree of
intersystem crossing from the Bodipy excited singlet state, this
study offers the potential to utilize WLA constructs as triplet
sensitizers switches for photo-oxidation processes relevant to
the production of small molecules and photodynamic therapy.
EXPERIMENTAL SECTION
■
General Methods. Phosphino-heteroatom ligands were prepared
and stored using standard Schlenk techniques under an inert nitrogen
atmosphere, unless noted otherwise. The synthesis of Pt(II) complexes
and their manipulations and characterization were performed under
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ambient conditions. All solvents used for synthesis and physical
measurements were purchased as HPLC grade and thoroughly
degassed with a stream of argon gas prior to use. HPLC grade
dichloromethane used for photodegradation measurements of
diphenylbenzofuran was not degassed. Deuterated solvents were
purchased from Cambridge Isotope Laboratories and were degassed
with a stream of argon prior to usage. Freshly distilled pyrrole was
used for the synthesis of all Bodipy species, and N(i-Pr)2Et amine was
distilled over potassium hydroxide prior to use. Dichloro(1,4-
cyclooctadiene)platinum(II) was purchased from Strem Chemicals
Inc. and was used as received. All other chemicals were used as
received from Aldrich Chemical Co.
P,S-Bodipy (6). Benzaldehyde 4 (2.00 g, 5.71 mmol) and pyrrole 5
(1.46 g, 12.0 mmol) were dissolved in CH2Cl2 (600 mL), and
trifluoroacetic acid was added (800 μL). After stirring at room
temperature for 1.5 h, DDQ (1.30 g, 5.71 mmol) was slowly added as
a powder under a stream of nitrogen, and the mixture was stirred for
another 45 min. N(i-Pr)2Et (6.00 mL, 34.3 mmol) was added
dropwise, and after 5 min BF3·OEt2 (5.65 mL, 45.7 mmol) was slowly
added. After 1 h the mixture was filtered through a pad of silica,
washed with water, and dried under MgSO4. Solvent evaporation in
vacuo yielded a dark red oil. Silica-gel column chromatography (9:1 v/
v, petroleum ether/ethyl acetate as eluent) afforded the product as a
1
red solid with a green luster (428 mg, 12% yield). H NMR (400.16
1
MHz, 25 °C, CD2Cl2): δ 7.80−7.30 (m, 12H), 7.01 (d, JH−H = 8 Hz,
2H), 3.05 (m, 2H), 2.50 (s, 6H), 2.37 (m, 2H), 2.32 (q, JH−H = 8 Hz,
4H), 1.32 (s, 6H), 1.00 (t, JH−H = 8 Hz, 6H). 13C{1H} NMR (100.63
MHz, 25 °C, CD2Cl2): δ 153.7 (s), 139.7 (s), 138.43 (s), 137.9 (d,
JC−P = 14 Hz), 137.1 (s), 133.3 (s), 133.0 (s), 132.6 (d, JC−P = 18 Hz),
130.7 (s), 129.6 (s), 128.9 (s), 128.8 (s), 128.5 (d, JC−P = 7 Hz), 29.9
(d, JC−P = 23 Hz), 28.0 (d, JC−P = 16 Hz), 16.9 (s), 14.3 (s), 12.2 (s),
11.6(s). 31P{1H} NMR (161.98 MHz, 25 °C, CD2Cl2): δ −16.7 (s).
19F NMR (376.49 MHz, 25 °C, CD2Cl2): δ −146.2 (q, JF−B = 33 Hz).
11B{1H} NMR (128.38 MHz, 25 °C, CD2Cl2): δ 0.14 (t, JB−F = 33
Hz). ESIMS (m/z): Calcd 625 [M]+. Found 625.
All NMR spectra were recorded on a Bruker Avance 400 MHz. H
and 13C{1H } NMR spectra were referenced to residual proton and
carbon resonances in the deuterated solvents. 11B{1H} NMR spectra
were referenced to neat BF3·OEt2. 19F{1H} NMR spectra were
referenced to CFCl3 in CDCl3. 31P /31P{1H} NMR spectra were
referenced to an 85% H3PO4 aqueous solution. All chemical shifts are
reported in ppm.
UV−vis absorption measurements were performed in a Varian Cary
50 Bio spectrophotometer utilizing 10 mm cell-path quartz cuvettes
(VWR). Fluorescence measurements and photoexcitation experiment
were performed with a Horiba Jovin-Yvonne Fluorolog fluorimeter.
Quantum yield values were determined from the comparative method
using sulforhodamine B or rhodamine 6G in ethanol as standards.
Each quantum yield value was derived from the least-squares fit of a
fluorescence emission versus concentration curve using seven dilutions
yielding r2 values of 0.99. Photoexcitation experiments were performed
under constant stirring and power outputs of 0.2 mW. Electrospray
ionization mass spectra (ESI-MS) were recorded on a Micromas
Quatro II triple quadrapole mass spectrometer.
N-(4-Bromophenyl)-N-(2-chloro)-N-methylamine (9). To a 2-
(methylanilino)ethanol (7.04 g, 46.6 mmol) solution in CCl4 (60
mL) was added N-bromosuccinimide (8.29 g, 46.6 mmol) as a powder
at 0 °C while stirring vigorously. After stirring overnight at room
temperature, the mixture was filtered and passed through a pad of
silica using CH2Cl2 as eluent. The resulting yellow solution of amine 8
was shown to be pure by TLC and was used for the subsequent
reaction without further purification. To the solution of amine 8 in
CCl4/CH2Cl2 (100 mL) were added triphenylphosphine (12.2 g, 46.6
mmol) and molecular sieves at 0 °C. After stirring overnight at room
temperature, the mixture was filtered, washed with water, and
extracted with CH2Cl2. The solution was dried under MgSO4, and
the solvent was removed in vacuo. The crude oil was dissolved in a
minimal amount of CH2Cl2 and passed through a pad of silica, first
using 5:1 v/v, hexanes/CH2Cl2, and then CH2Cl2 as eluents. The
fraction eluted with CH2Cl2 was concentrated in vacuo to give 9 as a
dark yellow oil, which was used for the following synthetic step
Synthesis. P,S-Bodipy (3). Pentafluorophenyl Bodipy 141 (3.85 g,
8.19 mmol) and P,S-TIPS 2 (3.29 g, 8.19 mmol) were dissolved in
THF (40 mL), and cesium fluoride was added (3.80 g, 25.0 mmol).
After stirring for 20 h at room temperature, the mixture was washed
with water, and extracted with CH2Cl2 (2 × 100 mL). Drying under
MgSO4 and solvent evaporation yielded a dark red oil. Silica-gel
column chromatography (9:1 v/v, petroleum ether/ethyl acetate as
eluent) afforded the product as a red solid with a green-golden luster
1
(3.48 g, 61% yield). H NMR (400.16 MHz, 25 °C, CD2Cl2): δ 7.38
1
(m, 10H), 3.11 (m, 2H), 2.51 (s, 6H), 2.34 (q, JH−H = 8 Hz, 4H), 2.32
(m, 2H), 1.46 (s, 6H), 1.01 (t, JH−H = 8 Hz, 6H). 13C{1H} NMR
(100.63 MHz, 25 °C, CD2Cl2): δ 156.0 (s), 148.7 (d, JC−F = 14 Hz),
146.2 (d, JC−F = 14 Hz), 145.0 (d, JC−P = 16 Hz), 142.7 (d, JC−F = 33
Hz), 137.3 (d, JC−P = 11 Hz), 136.9 (s), 134.0 (s), 132.5 (d, JC−P = 19
Hz), 130.0 (s), 128.9 (s), 128.6 (d, JC−P = 7 Hz), 122.0 (s), 31.1 (d,
JC−P = 25 Hz), 28.9 (d, JC−P = 16 Hz), 16.9 (s), 14.2 (s), 12.4 (s), 10.6
(s). 31P{1H} NMR (161.98 MHz, 25 °C, CD2Cl2): δ −16.6 (s). 19F
NMR (376.49 MHz, 25 °C, CD2Cl2): δ −133.0 (q, JF−F = 11 Hz, 2F),
−141.3 (q, JF−F = 11 Hz, 2F), −146.2 (q, JF−B = 33 Hz, 2F). 11B{1H}
NMR (128.38 MHz, 25 °C, CD2Cl2): δ −0.05 (t, JB−F = 33 Hz).
ESIMS (m/z): Calcd 697 [M]+. Found 697.
without further purification (9.50 g, 82% yield over two steps). H
NMR (400.16 MHz, 25 °C, CD2Cl2): δ 7.31 (d, JH−H = 8 Hz, 2H),
6.63 (d, JH−H = 8 Hz, 2H), 3.71 (t, JH−H = 8 Hz, 2H), 3.47 (t, JH−H = 8
Hz, 2H), 2.98 (s, 3H).
P,N-Bromobenzene (10). Amine 9 (4.49 g, 18.1 mmol) was
dissolved in THF (30 mL) and chilled to −78 °C. KPPh2 (33.9 mL,
0.5 M solution in THF, 18.1 mmol) was added dropwise, and the
solution was left to warm up to room temperature. After stirring
overnight, the solvent was removed in vacuo, and the mixture was
extracted with water and CH2Cl2. The solution was dried under
MgSO4, and the solvent was removed in vacuo. Silica-gel column
chromatography (1:1 v/v, hexanes/CH2Cl2) afforded the product as a
white solid (5.74 g, 80%). 1H NMR (400.16 MHz, 25 °C, CD2Cl2): δ
7.56−7.28 (m, 12H), 7.23 (d, JH−H = 8 Hz, 2H), 6.46 (d, JH−H = 7 Hz,
2H), 3.40 (m, 2H), 2.86 (s, 3H), 2.30 (m, 2H). 13C{1H} NMR
(100.63 MHz, 25 °C, CD2Cl2): δ 148.1 (s), 138.7 (d, JC−P = 14 Hz),
133.1 (d, JC−P = 19 Hz), 132.1 (s), 129.2 (s), 129.0 (d, JC−P = 7 Hz),
114.4 (s), 49.9 (d, JC−P = 25 Hz), 38.4 (s), 25.3 (d, JC−P = 15 Hz).
31P{1H} NMR (161.98 MHz, 25 °C, CD2Cl2): δ −20.7. ESIMS (m/z):
Calcd 398 [M]+. Found 398.
P,N-Benzaldehyde (11). A solution of 10 (3.00 g, 7.54 mmol) in
THF (40 mL) was chilled to −78 °C, and n-BuLi (3.15 mL, 2.5 M
solution in THF, 7.87 mmol) was added dropwise over 5 min. The
solution was left to stir at −78 °C for 45 min, and DMF (7.00 mL,
90.8 mmol) was added dropwise. After stirring overnight at room
temperature, the reaction was quenched with water (5 mL), washed
with LiCl(aq) and water, and extracted with CH2Cl2. The solution was
dried under MgSO4, and the solvent was removed in vacuo to give the
pure product as a thick yellow oil (2.46 g, 94% yield). 1H NMR
(400.16 MHz, 25 °C, CD2Cl2): δ 9.70 (s, 1H), 7.64 (d, JH−H = 9 Hz,
P(O),S-Bodipy (3′). Ligand 3 (25.0 mg, 0.0359 mmol) was dissolved
in CH2Cl2 (4 mL), and the solution was stirred while exposed to air
under illumination from a UV lamp (λ = 360 nm, 0.16 W) for 12 h.
The solution volume was then reduced to 1 mL, and pentane was
added to precipitate the oxide. The product was then isolated as a red
solid with a green-golden luster via vacuum filtration (21.0 mg, 82%).
1H NMR (400.16 MHz, 25 °C, CD2Cl2): δ 7.45−7.82 (m, 10H), 3.25
(m, 2H), 2.54 (m, 2H), 2.51 (s, 6H), 2.34 (q, JH−H = 8 Hz, 4H), 1.48
(s, 6H), 1.01 (t, JH−H = 8 Hz, 6H). 13C{1H} NMR (100.63 MHz, 25
°C, CD2Cl2): δ 156.6 (s), 137.2 (d, JC−F = 15 Hz), 134.6 (d, JC−P = 23
Hz), 133.3 (s), 132.8 (s), 132.6 (s), 132.5 (s), 132.3 (s), 131.2 (d, JC−P
= 11 Hz), 131.0 (d, JC−P = 9 Hz), 129.5 (s), 129.3 (d, JC−P = 12 Hz),
115.7 (s), 31.4 (d, JC−P = 66 Hz), 27,8 (s), 17.4 (s), 14.7 (s), 12.9 (s),
11.1 (s). 31P{1H} NMR (161.98 MHz, 25 °C, CD2Cl2): δ 28.9 (s). 19
F
NMR (376.49 MHz, 25 °C, CD2Cl2): δ −133.2 (q, JF−F = 11 Hz, 2F),
−141.3 (q, JF−F = 11 Hz, 2F), −145.9 (q, JF−B = 33 Hz, 2F). 11B{1H}
NMR (128.38 MHz, 25 °C, CD2Cl2): δ −0.05 (t, JB−F = 33 Hz).
ESIMS (m/z): Calcd 713 [M]+. Found 713.
G
dx.doi.org/10.1021/ic400383t | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
2H), 7.42 (m, 10H), 6.55 (d, JH−H = 9 Hz, 2H), 3.53 (m, 2H), 2.99 (s,
3H), 2.39 (m, 2H). 13C{1H} NMR (100.63 MHz, 25 °C, CD2Cl2): δ
190.1 (s), 153.3(s), 138.4 (d, JC−P = 13 Hz), 133.1 (d, JC−P = 19 Hz),
132.1 (s), 129.4 (d, JC−P = 11 Hz), 129.0 (s), 125.8 (s), 111.5 (s), 49.7
(d, JC−P = 25 Hz), 38.5 (s), 25.9 (d, JC−P = 15 Hz). 31P{1H} NMR
(161.98 MHz, 25 °C, CD2Cl2): δ −20.8 (s). ESIMS (m/z): Calcd 347
[M]+. Found 347.
[PtCl(κ2-P,S-Me)(P,S-Bodipy)]Cl (15). 31P{1H} NMR (161.98 MHz,
25 °C, CD2Cl2): δ 43.6 (d, JP−P = 14 Hz, JP−Pt = 3515 Hz, 1P), 9.0 (d,
1
JP−P = 13 Hz, JP−Pt = 3168 Hz, 1P). H NMR (400.16 MHz, 25 °C,
CD2Cl2): δ 8.22−6.78 (m, 24H), 4.0−0.5 (m, 33H). 19F NMR
(376.49 MHz, 25 °C, CD2Cl2): δ −146.2 (q, JF−B = 34 Hz). 11B{1H}
NMR (128.38 MHz, 25 °C, CD2Cl2): δ 0.11 (t, JB−F = 33 Hz). MS
(ESI): m/z calcd for C52H57BClF2N2P2PtS2 [M − Cl]+: 1115. Found:
1115.
P,N-Bodipy (12). The synthesis and purification procedure for 12
was carried out entirely in a glovebox under oxygen- and water-free
conditions. Benzaldehyde 11 (2.00 g, 5.76 mmol) and pyrrole 5 (1.48
g, 12.1 mmol) were dissolved in CH2Cl2 (600 mL), trifluoroacetic acid
was added (800 μL), and the solution was stirred at room temperature
for 1.5 h. DDQ (1.31 g, 5.75 mmol) was added slowly as a powder,
and after 45 min N(i-Pr)2Et (6.05 mL, 34.6 mmol) was added
dropwise. After 5 min, BF3·OEt2 (5.70 mL, 46.1 mmol) was slowly
added, and the mixture was left to stir for 1 h. The whole reaction mix
was then passed through two large pads of silica, first using CH2Cl2
and then hexanes/CH2Cl2 (2:1, v/v) as eluents. Most of the CH2Cl2
was removed in vacuo, and the solution was left overnight at 0 °C. The
product was isolated via vacuum filtration and washed with hexanes
[Pt(κ2-P,S-Me)(κ2-P,S-Bodipy)]2BF4 (16). 31P{1H} NMR (161.98
MHz, 25 °C, CD2Cl2): δ 46.3 (d, JP−P = 13 Hz, JP−Pt = 3165 Hz, 1P),
1
45.8 (d, JP−P = 13 Hz, JP−Pt = 3100 Hz, 1P). H NMR (400.16 MHz,
25 °C, CD2Cl2): δ 8.43−6.71 (m, 24H), 4.25−0.41 (m, 33H). 19F
NMR (376.49 MHz, 25 °C, CD2Cl2): δ −146.1 (q, JF−B = 34 Hz),
−150.5 (s). 11B{1H} NMR (128.38 MHz, 25 °C, CD2Cl2): δ 0.11 (t,
JB−F
= 33 Hz), −1.37 (s). MS (ESI): m/z calcd for
C52H57B2F6N2P2PtS2 [M−BF4]+: 1167. Found: 1167.
[PtCl(κ2-P,S-Me)(P,S-Bodipy)]Cl (17). 31P{1H} NMR (161.98 MHz,
25 °C, CD2Cl2): δ 43.8 (d, JP−P = 15 Hz, JP−Pt = 3515 Hz, 1P), 6.6 (d,
1
JP−P = 13 Hz, JP−Pt = 3141 Hz, 1P). H NMR (400.16 MHz, 25 °C,
CD2Cl2): δ 7.93−6.85 (m, 24 H), 3.94−0.68 (m, 36H). 19F NMR
(376.49 MHz, 25 °C, CD2Cl2): δ −146.2 (q, JF−B = 34 Hz). 11B{1H}
NMR (128.38 MHz, 25 °C, CD2Cl2): δ 0.16 (t, JB−F = 34 Hz). MS
(ESI): m/z calcd for C53H60BClF2N3P2PtS [M − Cl]+: 1112. Found:
1112.
1
which gave a red microcrystalline solid (322 mg, 9% yield). H NMR
(400.16 MHz, 25 °C, CD2Cl2): δ 7.60−7.30 (m, 10H), 7.00 (d, JH−H
=
8 Hz, 2H), 6.61 (d, JH−H = 8 Hz, 2H), 3.52 (m, 2H), 2.93 (s, 3H), 2.48
(s, 6H), 2.37 (m, 2H), 2.33 (q, JH−H = 7 Hz, 4H), 1.40 (s, 6H), 0.99 (t,
JH−H = 7 Hz, 6H). 13C{1H} (100.63 MHz, 25 °C, CD2Cl2): δ 152.8
(s), 148.9 (s), 141.8 (s), 138.7 (s), 138.1 (d, JC−P = 13 Hz), 132.6 (d,
JC−P = 19 Hz), 131.3 (s), 129.0 (s), 128.7 (s), 128.4 (d, JC−P = 5 Hz),
122.7 (s), 112.4 (s), 49.4 (d, JC−P 14 Hz), 37.7 (s), 24.9 (d, JC−P 15
Hz), 16.9 (s), 14.3 (s), 12.1 (s), 11.7 (s). 31P{1H} NMR (161.98 MHz,
25 °C, CD2Cl2): δ −20.5 (s). 19F NMR (376.49 MHz, 25 °C,
CD2Cl2): δ −146.2 (q, JF−B = 33 Hz). 11B{1H} NMR (128.38 MHz,
25 °C, CD2Cl2): δ 0.05 (t, JB−F = 33 Hz). ESIMS (m/z): Calcd 622
[M]+. Found 622.
[Pt(κ2-P,S-Me)(κ2-P,S-Bodipy)]2BF4 (18). 31P{1H} NMR (161.98
MHz, 25 °C, CD2Cl2): δ 37.9 (d, JP−P = 16 Hz, JP−Pt = 3397 Hz, 1P),
1
31.0 (d, JP−P = 15 Hz, JP−Pt = 3183 Hz, 1P). H NMR (400.16 MHz,
25 °C, CD2Cl2): δ 8.18−6.86 (m, 24H), 4.19−0.40 (m, 37H). 19F
NMR (376.49 MHz, 25 °C, CD2Cl2): δ −146.2 (q, JF−B = 34 Hz),
−150.9 (s). 11B{1H} NMR (128.38 MHz, 25 °C, CD2Cl2): δ 0.13 (t,
JB−F
= 34 Hz), −1.50 (s). MS (ESI): m/z calcd for
C53H60B2F6N3P2PtS [M − BF4]+: 1164. Found: 1164.
X-ray Crystallography. Crystallographic data are displayed in the
Supporting Information (Table S1). Single crystals were mounted
using oil (Infineum V8512) on a glass fiber. All measurements were
made on a CCD area detector with graphite monochromated Cu KR
radiation. Data were collected using Bruker APEXII detector and
processed using APEX2 from Bruker. All structures were solved by
direct methods and expanded using Fourier techniques. The non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
included in idealized positions, but not refined. Their positions were
constrained relative to their parent atom using the appropriate HFIX
command in SHELXL-97.
General Procedure for the Generation of Semiopen Complexes.
A solution of P,S-Me (26.1 mg, 0.100 mol) in 3 mL of CH2Cl2 was
added dropwise to a solution of dichloro(1,4-cyclooctadiene)platinum-
(II) (37.4 mg, 0.100 mmol) in 3 mL of CH2Cl2. The solution was left
to stir at room temperature for 5 min, and a solution of Bodipy-
functionalized ligand (1.00 equiv, 0.100 mmol) in 3 mL of CH2Cl2 was
added. The solvent volume was reduced to approximately 1 mL in
vacuo, and the product was then precipitated out of solution with
hexanes. The product was then isolated via vacuum filtration and
washed with hexanes to afford the semiopen complex (in situ 31P{1H}
NMR yields = quantitative, isolated yields >95%).
General Procedure for the Generation of Closed Complexes.
Semiopen complex (0.100 mmol) was dissolved in 2 mL of CH2Cl2,
and AgBF4 (40.9 mg, 2.10 equiv, 0.210 mmol) was added. The mixture
was left to stir vigorously in the dark for 15 min. The mixture was
filtered and the solvent volume reduced to approximately 1 mL in
vacuo. The product was then precipitated out of solution with hexanes
and collected via filtration to yield the closed complex (in situ 31P{1H}
NMR yields = quantitative, isolated yields >95%).
ASSOCIATED CONTENT
* Supporting Information
NMR, absorbance, and emission spectra of compounds 3, 6, 12,
and 13−18; X-ray diffraction crystallographic data for
complexes 13 and 14 in crystallographic table and CIF
forms; and theoretical modeling of a model P,S-Bodipy ligand.
This material is available free of charge via the Internet at
http://pubs.acs.org.
■
S
[PtCl(κ2-P,S-Me)(P,S-Bodipy)]Cl (13). 31P{1H} NMR (CD2Cl2): δ
31P{1H} NMR (161.98 MHz, 25 °C, CD2Cl2): δ 43.1 (d, JP−P = 14 Hz,
1
JP−Pt = 3478 Hz, 1P), 8.9 (d, JP−P = 13 Hz, JP−Pt = 3199 Hz, 1P). H
AUTHOR INFORMATION
Corresponding Author
*E-mail: chadnano@northwestern.edu. Fax: (1) 847-467-5123.
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
■
NMR (400.16 MHz, 25 °C, CD2Cl2): δ 8.40−7.00 (m, 20H), 3.50−
2.00 (m, 21H), 1.50−0.80 (m, 12H). 19F NMR (376.49 MHz, 25 °C,
CD2Cl2): δ −146.1 (q, JF−B = 34 Hz), −140.5 (q, JF−B = 11 Hz),
−131.8 (q, JF−B = 11 Hz). 11B{1H} NMR (128.38 MHz, 25 °C,
CD2Cl2): δ 0.26 (t, JB−F = 33 Hz). MS (ESI): m/z calcd for
C52H53BClF6N2P2PtS2 [M−Cl]+: 1187. Found: 1187.
[Pt(κ2-P,S-Me)(κ2-P,S-Bodipy)]2BF4 (14). 31P{1H} NMR (161.98
MHz, 25 °C, CD2Cl2): δ 46.6 (d, JP−P = 13 Hz, JP−Pt = 3093 Hz, 1P),
1
46.2 (d, JP−P = 13 Hz, JP−Pt = 3290 Hz, 1P). H NMR (400.16 MHz,
Notes
25 °C, CD2Cl2): δ 8.10−7.00 (m, 20H), 4.20−1.20 (m, 27H), 1.01 (t,
JH−H = 8 Hz, 6H). 19F NMR (376.49 MHz, 25 °C, CD2Cl2): δ −127.4
(q, JF−F = 11 Hz), −135.5 (q, JF−F = 11 Hz), −146.0 (q, JF−B = 33 Hz),
−150.2 (s). 11B{1H} NMR (128.38 MHz, 25 °C, CD2Cl2): δ −0.70 (t,
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This material is based upon work supported by NSF Award
CHE-1149314, U.S. Army Award W911NF-11-1-0229, and
JB−F
= 32 Hz), −2.23 (s). MS (ESI): m/z calcd for
C52H53B2F10N2P2PtS2 [M − BF4]+: 1239. Found: 1239.
H
dx.doi.org/10.1021/ic400383t | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(32) Guliyev, R.; Buyukcakir, O.; Sozmen, F.; Bozdemir, O. A.
Tetrahedron Lett. 2009, 50, 5139.
(33) El-Sayed, M. A. Acc. Chem. Res. 1968, 1, 8.
(34) Lower, S. K.; El-Sayed, M. A. Chem. Rev. 1966, 66, 199.
(35) Vives, G.; Giansante, C.; Bofinger, R.; Raffy, G.; Del Guerzo, A.;
Kauffmann, B.; Batat, P.; Jonusauskas, G.; McClenaghan, N. D. Chem.
Commun. 2011, 47, 10425.
DoD/NSSEFF/NPS Awards N00244-09-1-0012 and N00244-
09-1-0071. Any opinions, findings, and conclusions or
recommendations expressed in this publication are those of
the authors and do not necessarily reflect the views of the
sponsors.
(36) Laha, J. K.; Dhanalekshmi, S.; Taniguchi, M.; Ambroise, A.;
Lindsey, J. S. Org. Process Res. Dev. 2003, 7, 799.
(37) Garrou, P. E. Chem. Rev. 1981, 81, 229.
(38) Chen, Y. T.; Wan, L.; Zhang, D. P.; Bian, Y. Z.; Jiang, J. Z.
Photochem. Photobiol. Sci. 2011, 10, 1030.
(39) Beaumont, P. C.; Johnson, D. G.; Parsons, B. J. J. Chem. Soc.,
Faraday Trans. 1998, 94, 195.
(40) Deniz, E.; Battal, M.; Cusido, J.; Sortino, S.; Raymo, F. M. Phys.
Chem. Chem. Phys. 2012, 14, 10300.
(41) Galangau, O.; Dumas-Verdes, C.; Meallet-Renault, R.; Clavier,
G. Org. Biomol. Chem. 2010, 8, 4546.
REFERENCES
■
(1) Wiester, M. J.; Ulmann, P. A.; Mirkin, C. A. Angew. Chem., Int. Ed.
2011, 50, 114.
(2) Gianneschi, N. C.; Masar, M. S.; Mirkin, C. A. Acc. Chem. Res.
2005, 38, 825.
(3) Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40,
2022.
(4) Ulmann, P. A.; Braunschweig, A. B.; Lee, O. S.; Wiester, M. J.;
Schatz, G. C.; Mirkin, C. A. Chem. Commun. 2009, 5121.
(5) Oliveri, C. G.; Gianneschi, N. C.; Nguyen, S. T.; Mirkin, C. A.;
Stern, C. L.; Wawrzak, Z.; Pink, M. J. Am. Chem. Soc. 2006, 128,
16286.
(6) Masar, M. S.; Gianneschi, N. C.; Oliveri, C. G.; Stern, C. L.;
Nguyen, S. T.; Mirkin, C. A. J. Am. Chem. Soc. 2007, 129, 10149.
(7) Yoon, H. J.; Kuwabara, J.; Kim, J. H.; Mirkin, C. A. Science 2010,
330, 66.
(8) Huck, N. P. M.; Feringa, B. L. J. Chem. Soc., Chem. Commun.
1995, 1095.
(9) Pu, S. Z.; Jiang, D. H.; Liu, W. J.; Liu, G.; Cui, S. Q. J. Mater.
Chem. 2012, 22, 3517.
(10) Hurenkamp, J. H.; de Jong, J. J.; Browne, W. R.; van Esch, J. H.;
Feringa, B. L. Org. Biomol. Chem. 2008, 6, 1268.
(11) Browne, W. R.; Pollard, M. M.; de Lange, B.; Meetsma, A.;
Feringa, B. L. J. Am. Chem. Soc. 2006, 128, 12412.
(12) Perez, E. M.; Dryden, D. T. F.; Leigh, D. A.; Teobaldi, G.;
Zerbetto, F. J. Am. Chem. Soc. 2004, 126, 12210.
(13) Vella, S. J.; Tiburcio, J.; Loeb, S. J. Chem. Commun. 2007, 4752.
(14) Armaroli, N.; Balzani, V.; Barigelletti, F.; Decola, L.; Flamigni,
L.; Sauvage, J. P.; Hemmert, C. J. Am. Chem. Soc. 1994, 116, 5211.
(15) Azov, V. A.; Schlegel, A.; Diederich, F. Angew. Chem., Int. Ed.
2005, 44, 4635.
(16) Kaanumalle, L. S.; Gibb, C. L.; Gibb, B. C.; Ramamurthy, V. J.
Am. Chem. Soc. 2005, 127, 3674.
(17) Johansson, M. K.; Cook, R. M.; Xu, J.; Raymond, K. N. J. Am.
Chem. Soc. 2004, 126, 16451.
(18) Knapton, D.; Burnworth, M.; Rowan, S. J.; Weder, C. Angew.
(42) Lager, E.; Liu, J. Z.; Aguilar-Aguilar, A.; Tang, B. Z.; Pena-
Cabrera, E. J. Org. Chem. 2009, 74, 2053.
(43) Lu, H.; Zhang, S. S.; Liu, H. Z.; Wang, Y. W.; Shen, Z.; Liu, C.
G.; You, X. Z. J. Phys. Chem. A 2009, 113, 14081.
(44) Wiester, M. J.; Braunschweig, A. B.; Yoo, H.; Mirkin, C. A. Inorg.
Chem. 2010, 49, 7188.
(45) Fron, E.; Coutino-Gonzalez, E.; Pandey, L.; Sliwa, M.; Van der
Auweraer, M.; De Schryver, F. C.; Thomas, J.; Dong, Z. Y.; Leen, V.;
Smet, M.; Dehaen, W.; Vosch, T. New J. Chem. 2009, 33, 1490.
(46) Kamkaew, A.; Lim, S. H.; Lee, H. B.; Kiew, L. V.; Chung, L. Y.;
Burgess, K. Chem. Soc. Rev. 2013, 42, 77.
(47) Rachford, A. A.; Ziessel, R.; Bura, T.; Retailleau, P.; Castellano,
F. N. Inorg. Chem. 2010, 49, 3730.
(48) Galletta, M.; Puntoriero, F.; Campagna, S.; Chiorboli, C.;
Quesada, M.; Goeb, S.; Ziessel, R. J. Phys. Chem. A 2006, 110, 4348.
(49) Flynn, D. C.; Ramakrishna, G.; Yang, H. B.; Northrop, B. H.;
Stang, P. J.; Goodson, T., III. J. Am. Chem. Soc. 2010, 132, 1348.
(50) Yogo, T.; Urano, Y.; Ishitsuka, Y.; Maniwa, F.; Nagano, T. J. Am.
Chem. Soc. 2005, 127, 12162.
(51) Awuah, S. G.; Polreis, J.; Biradar, V.; You, Y. Org. Lett. 2011, 13,
3884.
(52) Holliday, B. J.; Farrell, J. R.; Mirkin, C. A.; Lam, K. C.;
Rheingold, A. L. J. Am. Chem. Soc. 1999, 121, 6316.
(53) Jeon, Y. M.; Kim, D.; Mirkin, C. A.; Golen, J. A.; Rheingold, A.
L. Tetrahedron 2008, 64, 8428.
Chem., Int. Ed. 2006, 45, 5825.
(19) Wang, M.; Vajpayee, V.; Shanmugaraju, S.; Zheng, Y. R.; Zhao,
Z.; Kim, H.; Mukherjee, P. S.; Chi, K. W.; Stang, P. J. Inorg. Chem.
2011, 50, 1506.
(20) Zhao, G. J.; Northrop, B. H.; Han, K. L.; Stang, P. J. J. Phys.
Chem. A 2010, 114, 9007.
(21) Balzani, V.; Credi, A.; Marchioni, F.; Stoddart, J. F. Chem.
Commun. 2001, 1860.
(22) Credi, A.; Balzani, V.; Langford, S. J.; Stoddart, J. F. J. Am. Chem.
Soc. 1997, 119, 2679.
(23) Dirksen, A.; Kleverlaan, C. J.; Reek, J. N. H.; De Cola, L. J. Phys.
Chem. A 2005, 109, 5248.
(24) Lee, S. J.; Lin, W. J. Am. Chem. Soc. 2002, 124, 4554.
(25) Loudet, A.; Burgess, K. Chem. Rev. 2007, 107, 4891.
(26) Boens, N.; Leen, V.; Dehaen, W. Chem. Soc. Rev. 2012, 41, 1130.
(27) Ulrich, G.; Ziessel, R.; Harriman, A. Angew. Chem., Int. Ed. 2008,
47, 1184.
(28) Esfandiari, N. M.; Wang, Y.; Bass, J. Y.; Cornell, T. P.; Otte, D.
A. L.; Cheng, M. H.; Hemminger, J. C.; McIntire, T. M.;
Mandelshtam, V. A.; Blum, S. A. J. Am. Chem. Soc. 2010, 132, 15167.
(29) Esfandiari, N. M.; Wang, Y.; Bass, J. Y.; Blum, S. A. J. Inorg.
Chem. 2011, 50, 9201.
(30) Chen, Y. T.; Wang, H. L.; Wan, L.; Bian, Y. Z.; Jiang, J. Z. J. Org.
Chem. 2011, 76, 3774.
(31) Rurack, K.; Kollmannsberger, M.; Resch-Genger, U.; Daub, J. J.
Am. Chem. Soc. 2000, 122, 968.
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dx.doi.org/10.1021/ic400383t | Inorg. Chem. XXXX, XXX, XXX−XXX