Photophysical and computational investigations of bis(phosphine) organoplatinum(II) metallacycles

Article abstract of DOI:10.1021/ja3036515

A series of endohedral and exohedral amine-functionalized ligands were synthesized and used in the construction of supramolecular D_2h rhomboids and a D_6h hexagon. These supramolecular polygons were obtained via self-assembly of 120° dipyridyl donors with 180° or 120° diplatinum precursors when combined in 1:1 ratios. Steady-state absorption and emission spectra were collected for each ligand and metallacycle. Density functional theory (DFT) and time-dependent DFT calculations were employed to probe the nature of the observed optical transitions for the rhomboids. The emissive properties of these bis(phosphine) organoplatinum metallacycles arise from ligand-centered transitions involving π-type molecular orbitals with modest contributions from metal-based atomic orbitals. The D_2h rhomboid self-assembled from 2,6-bis(4-pyridylethynyl)aniline and a 60° organoplatinum(II) acceptor has a low-energy excited state in the visible region and emits above 500 nm, properties which greatly differ from those of the parent 2,6-bis(4-pyridylethynyl)aniline ligand.

Full text of DOI:10.1021/ja3036515

Article
pubs.acs.org/JACS
Photophysical and Computational Investigations of Bis(phosphine)
Organoplatinum(II) Metallacycles
J. Bryant Pollock, Timothy R. Cook, and Peter J. Stang*
Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112, United States
S
* Supporting Information
ABSTRACT: A series of endohedral and exohedral amine-functionalized ligands were synthesized and used in the construction
of supramolecular D2h rhomboids and a D6h hexagon. These supramolecular polygons were obtained via self-assembly of 120°
dipyridyl donors with 180° or 120° diplatinum precursors when combined in 1:1 ratios. Steady-state absorption and emission
spectra were collected for each ligand and metallacycle. Density functional theory (DFT) and time-dependent DFT calculations
were employed to probe the nature of the observed optical transitions for the rhomboids. The emissive properties of these
bis(phosphine) organoplatinum metallacycles arise from ligand-centered transitions involving π-type molecular orbitals with
modest contributions from metal-based atomic orbitals. The D2h rhomboid self-assembled from 2,6-bis(4-pyridylethynyl)aniline
and a 60° organoplatinum(II) acceptor has a low-energy excited state in the visible region and emits above 500 nm, properties
which greatly differ from those of the parent 2,6-bis(4-pyridylethynyl)aniline ligand.
to the transition metal ions present in the structure. While
reports for Pt(II)-based self-assemblies are very rare,68 in the
past few years, several reports have demonstrated that
ruthenium-based metallacages show cytotoxicity toward cancer-
ous cell lines in vivo.69−78 However, little is known about the
mechanism of uptake and release for these systems. The
biological systems in which these supramolecular structures are
used are complex, containing many ligands (e.g., amino acids,
glutathione, etc.) that are capable of coordinating to a metal
center and degrading the metal−organic structure. An in vitro
study using several biological ligands and a cationic Ru(III)
trigonal prism supports the previously proposed hypothesis that
the cytotoxicity arises from degradation pathways.80 While this
study was insightful, the current paradigm of having to perform
separate experiments to access information on cytotoxicity and
the species giving rise to cytotoxicity is laborious, and systems
that can streamline this process into a single experiment are
attractive.
INTRODUCTION
■
A breadth of literature can be found on transition metal-
mediated coordination-driven self-assembly, and over the past
decade the development of this field has rapidly grown to
include more complex synthetic designs and applications
ranging from host−guest chemistry1−17 and catalysis18−25 to
light harvesting.26−31 The various design methodologies behind
coordination-driven self-assembly developed by Cotton,32,33
Fujita,34,35 Hupp,36,37 Mirkin,38,39 Raymond,40,41 Stang,42 and
others43−45 have afforded a variety of discrete metallacycles and
metallacages with well-defined shapes and sizes. Using a
strategy dubbed the directional-bonding approach, the archetypal
construction of these structures in the Stang laboratory utilizes
bis(phosphine) Pt(II) metal nodes and pyridyl-based organic
spacers wherein each component has encoded directionality
and angularity which dictates the architectural outcome.42,46−48
Maturation of this field has led to increasingly complex systems,
with single-pot multicomponent systems49−57 and postsyn-
thetic modifications58,59 being at the forefront of structural
design. However, studies which probe the photophysical
properties of supramolecular bis(phosphine) Pt(II) metal−
organic structures, required to effectively develop bioimaging
and sensing applications, are rare.
Monitoring structural integrity in vivo, cell uptake, local-
ization, and cytotoxicity studies of a supramolecular assembly
can be facilitated by using constructs with unique photophysical
properties from their molecular components. One strategy to
imbue emissive properties to a self-assembly is to tether a
known fluorophore using common organic coupling techni-
ques. The issue with such a design is that the emissive signature
The use of discrete, metal−organic supramolecular structures
in biological settings has garnered attention lately, primarily as
vessels or capsules for the trafficking and delivery of therapeutic
agents, biosensing, and bioimaging.60−67 In addition, certain
assemblies have demonstrated inherent drug activity, often due
Received: April 16, 2012
© XXXX American Chemical Society
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Figure 1. Ligand scaffolds employed for metallacycle synthesis. Conditions: (a) 10 mol % Pd(PPH3)4, 10 mol % CuI, acetylene-TMS, Et3N, THF, 60
°C, 24 h; (b) KOH, MeOH, 24 h; (c) 10 mol % Pd(PPH3)4, 10 mol % CuI, 4-bromopyridine hydrochloride, Et3N, THF, 60 °C, 24 h.
of the parent fluorophore-appended building block often
matches that of the constructed assembly. Thus, it is impossible
to distinguish between the self-assembly and decomposition
products on the basis of emission alone, which is typically the
handle used in the aforementioned biological applications. This
problem is avoided by using systems in which the core of the
final assembly is inherently emissive.
with too little, the emissive characteristics of the assembly do
not differ enough from those of the building blocks to allow
them to be distinguished from one another.
In an effort to synthesize a rhomboid-shaped metallacycle
that could satisfy this careful balance, 4-ethynylpyridyl-based
ligands with aniline core motifs were considered. Hooley et
al.108 recently reported the synthesis and photophysical
characterization of 2,6-bis(pyridin-3-ylethynyl)aniline, which
has Φ = 36% with a low-energy absorption band at 441 nm.
Altering the 2,6-bis(pyridin-3-ylethynyl)aniline structure
slightly, a highly emissive ligand with the correct angularity
and directionality was synthesized for the construction of
Pt(II)-incorporated metallacycles.
We now report the synthesis and characterization of a series
of novel bis(pyridyl)aniline ligands and their use in the self-
assembly of rhomboids. Steady-state absorption and fluores-
cence spectra were collected for each ligand and compared to
those of their respective D2h rhomboids synthesized with a 60°
phenanthrene-based Pt acceptor. Rhomboids amine-function-
alized in the interior (endohedral) and on the periphery
(exohedral) were synthesized; however, only the endohedral
aniline metallacycles displayed red-shifted emission compared
to the free ligands. TD-DFT calculations were employed to
probe the nature of the optical transitions for the rhomboids.
Also, a hexagon was synthesized using a 180° organoplatinum-
(II) acceptor to investigate whether size or shape of 2-D
metallacycles affects the photophysical properties. Herein, the
synthesis, photophysical characterization, and quantum me-
chanical description of the electronic transitions are discussed
for a series of metallacycles.
Mono- and multinuclear platinum complexes have been
investigated thoroughly for their inherent photophysical
properties and have exhibited low-energy absorption bands,
long-lived and low-energy excited states, and high quantum
yields.81−101 These properties make a multinuclear Pt(II) self-
assembled metallacycle an attractive target for the proposed
application. Although the photophysics of mono- and multi-
nuclear Pt(II) complexes have been investigated extensively,
the photophysics of Pt-pyridyl metallacycles have largely been
understudied.102−104 One rare example is the study of
rhomboids constructed with 1,2-bis(3-pyridyl)ethyne and 1,4-
bis(3-pyridyl)-1,3-butadiyne using time-dependent density
functional theory (TD-DFT) calculations.105 The low-energy
transitions of both rhomboids correspond to transitions
between molecular orbitals that contain a large amount of
ligand character. It was observed that increasing the size of the
π-system by the addition of ethylene spacers within the ligand
resulted in red-shifted emission of the rhomboids. Goodson et
al. studied the ultrafast optical excitation and relaxation of a
series of Pt-pyridyl rectangles and triangles.106 It was
determined that for self-assemblies with multiple platinum
centers, increased amounts of intersystem crossing (ISC)
occurred due to spin−orbit coupling. This “heavy-atom effect”
manifested itself in decreased excited-state lifetimes, and since
the triplet excited state was plagued by non-emissive decay
pathways, low quantum yields were observed.
Recently, Pistolis et al. synthesized a boron dipyrromethene
(BODIPY) Pt metallacycle whose emission was significantly
red-shifted compared to that of the free ligand (λem = 592
versus 545 nm).107 However, the quantum yield (Φ) of the
metallacycle species was low compared to that of the ligand
(6% versus 47%). When an ethylene spacer was added between
the coordinating pyridyl units and the BODIPY backbone, the
photophysical properties of the BODIPY ligand were conserved
after coordination with the platinum acceptor. This study
demonstrates the delicate balance between the isolation of the
pyridyl-based ligand-centered electronic transitions and the
bis(phosphine) platinum(II) metal center’s ability to perturb
the ligand-centered excited state. Too much Pt character and
spin−orbit coupling open up non-radiative decay pathways;
RESULTS
■
Ligand Synthesis and Photophysical Characterization.
The endohedral, exohedral, and non-functionalized109 ligand
scaffolds employed for metallacycle synthesis are shown in
Figure 1. Each ligand contains three components: (1) a central
ring with or without amino groups for electronic tuning of the
ligand; (2) ethynyl spacers that are meta with respect to each
other, which provides the requisite internal 120° angle for the
synthesis of the D2h rhomboids or D6h hexagons; and (3) 4-
pyridyl moieties at the periphery for metal complexation.
The exohedral and endohedral aniline-based ligands 5 and 6
were prepared stepwise using a Sonogashira coupling,
deprotection, and second Sonogashira coupling. Ligand 6 was
prepared in modest yields due to alternate reaction pathways,
mainly uncontrollable indole formation from the ortho aniline
acetylene core during the Pd-catalyzed 4-pyridyl insertion.108
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Ligand 8 was prepared in modest yield (58%) via a Suzuki
cross-coupling of 2 with 4-bromopyridine HCl (Figure 2).
= 2684 Hz) was observed. Also, the expected downfield shifts
of the α- and β-pyridyl protons upon coordination to the
platinum were observed in the H spectrum, consistent with
1
previous observations of Pt-based metallacycles and
cages.53,110−112 As shown in Figure 5, the α- and β-protons
on the pyridyl ring are split into two sets of two doublets upon
coordination. The Hα-Py of 6, shown in red at δ = 8.62 ppm, is
split into two doublets at δ = 8.89 and 8.69 ppm, while the Hβ-
Py of 6, shown in blue at δ = 7.38, is split into two doublets at δ
= 8.28 and 7.76 ppm. Isotopically resolved peaks for two of the
charge states for 10−12 (see Supporting Information) from the
loss of nitrate counterions in the ESI-MS spectra further
support the formation of a single, discrete rhomboid.
Isotopically resolved signals for [11-2ONO2]2+ and [11-
3ONO2]3+ are shown in Figure 6.
Figure 7 (left) displays the absorption profiles for rhomboids
10, 11, and 12. Each of the rhomboids has two high-energy
absorption bands centered at 258 and 267 nm. Interestingly, 11
has a higher extinction coefficient for the 258 nm band (ε =
135 000 cm−1 M−1) with respect to the 267 nm band (ε = 130
000 cm−1 M−1), while the converse is observed for 12; it has a
higher extinction coefficient for the 267 nm band (ε = 79 900
cm−1 M−1) than the 258 nm band (ε = 73 600 cm−1 M−1). It
should be noted that the overall intensity of both bands
decreases from 12 to 10. Assemblies 10, 11, and 12 all have an
absorption band centered at 288 nm, with ε = 77 500, 85 200,
and 69 900 cm−1 M−1, respectively. Both 10 and 12 have two
absorption bands centered at 288 and 306 nm, while 11 has a
single, broad absorption band centered at 317 nm. There is a
weak shoulder for 12 centered at 356 nm, with ε = 10 200
cm−1 M−1. For metallarhomoid 10, there is a weak, broad
absorption band centered at 370 nm, with ε = 20 100 cm−1
M−1. 11 has the lowest energy absorption band of the three
rhomboids, with a band centered at 430 nm. This absorption
band also has the highest extinction coefficient (ε = 39 900
cm−1 M−1) of the lowest energy absorption bands for 10−12.
Figure 7 displays the emission profiles for 10 and 11, with
both rhomboids having a single, broad emission band centered
at 400 and 522 nm, respectively. The quantum yields of 10 and
11 are 4.0 and 28%, respectively. The emission profile for 12 is
not shown because the quantum yield was too low.
Figure 2. Preparation of ligand 8 via a Suzuki cross-coupling of 2 and
4-bromopyridine HCl.
The absorption profiles of each of the four ligands 5, 6, 7,
and 8 are shown in Figure 3 (left). Ligand 7 has two sharp
absorption bands at 282 and 300 nm with extinction
coefficients (ε) of 52 000 and 45 900 cm−1 M−1, respectively.
These bands are present in both 5 and 6, but with decreased
intensity (see Table 1). 5 and 6 have broad, lower-energy
absorption bands at 347 and 373 nm which are not present in
7. These two absorption bands have ε = 5500 and 13 700 cm−1
M−1, respectively. Ligand 8 does not maintain the two higher-
energy absorption bands (found at 282 and 300 nm) that are
present in 5, 6, and 7, although it does possess a broad
absorption band centered at 329 nm with ε = 5000 cm−1 M−1.
The emission spectra (Figure 3, right) for 5, 6, and 8 all show
similar single, broad bands with λmax = 389, 420, and 397 nm,
respectively. The quantum yields of 5, 6, and 8 are 41, 65, and
34%, respectively. Ligand 7 was determined to be weakly
emissive (Φ = 8.4%), with a sharp band centered at 347 nm and
a broad band at 364 nm with a shoulder at 392 nm.
Metallacycle Synthesis and Photophysical Character-
ization. Rhomboids 10−12. Rhomboids 10, 11, and 12,
shown in Figure 4, were prepared by treating CH2Cl2 solutions
of organoplatinum acceptor 9 with 5, 6, and 7, respectively, in a
1:1 ratio. After 24 h of stirring at room temperature, the
rhomboids were precipitated out of solution using diethyl ether,
isolated, and re-dissolved in CD2Cl2. The final products were
characterized by 1H and 31P{1H} NMR and electrospray
ionization mass spectrometry (ESI-MS). In each 31P{1H} NMR
spectrum of 10, 11, and 12, an intense singlet with concomitant
195Pt satellites was observed (see Supporting Information),
indicating that all the phosphorus atoms in solution were
equivalent. The 31P{1H} NMR of rhomboid 11 is shown in
Figure 5. A singlet at δ = 12.61 ppm with the Pt satellites (1JPt−P
Rhomboid 13. The synthesis of 13 was accomplished by
stirring 8 and 9 in a 1:1 ratio in MeOH at a temperature of 55
°C for 24 h. Diethyl ether was added to the brightly colored,
green solution to precipitate the product. The product was then
Figure 3. Absorption (left) and emission (right) profiles for ligands 5 (blue), 6 (red), 7 (black), and 8 (cyan). The spectra were collected using a 1
cm path length in aerated methylene chloride.
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Table 1. Extinction Coefficients, λemiss, and Quantum Yield for Each Ligand and Self-Assembly
λexc
/
λemis
/
Φ/
a
compd
description
absorption bands λmax/nm [ε × 103/cm−1 M−1
282 [39.0], 300 [35.3], 347 [5.50]
]
nm
nm
%
5
exohedral aniline ligand
endohedral aniline ligand
non-functionalized ligand
ethynyl-free ligand
356
356
324
356
356
430
399
422
41
65
8.4
34
4.0
28

3.7
15
6
282 [28.6], 300 sh [20.7], 373 [13.7]
282 [52.0], 300 [45.9]
329 [5.00]
7
347, 364, 392 sh
8
417
400
522
10
11
12
13
14
exohedral functionalized rhomboid
258 sh [100], 267 [103], 288 [77.5], 306 [86.6], 319 [91.2], 370 sh [20.1]
endohedral functionalized rhomboid 258 [135], 267 sh [130], 288 [85.2], 317 [112], 430 [39.9]
b
non-functionalized rhomboid
ethynyl-free rhomboid
258 sh [73.6], 267 [79.9], 288 [69.9], 306 [95.3], 319 [98.5], 356 sh [10.2] 356
no emiss
285 [167], 314 sh [76.3], 385 [37.8]
284 sh [95.2], 318 [139], 422 [87.6]
385
422
493
505
endohedral functionalized hexagon
a
b
Quinine sulfate and anthracene were used as standards for quantum yield determination. A very weak emission profile was obtained with a signal-
to-noise ratio unsuitable for quantum yield determination.
Figure 4. Solutions of 9 with 5, 6, or 7 are stirred in a 1:1 stoichiometric fashion in CH2Cl2 for 24 h to afford D2h rhomboids 10, 11, and 12.
isolated and re-dissolved in CD2Cl2 for characterization (see
Supporting Information).
when analyzed in conjunction with the NMR spectra (see
Supporting Information).
Figure 11 displays the absorption and emission profiles for
14. The absorption spectrum displays a high-energy, sharp
band centered at 318 nm, with a shoulder at 284 nm, while a
lower-energy broad band is centered at 422 nm. The two
higher-energy bands have extinction coefficients of 139 000 and
95 200 cm−1 M−1, respectively, while the lower-energy band has
an extinction coefficient of 87 600 cm−1 M−1. The emission
profile of 14 (dashed) has a single, broad band centered at 505
nm, and 14 has Φ = 15%.
Figure 9 displays the absorption and emission profiles for
rhomboid 13. In the absorption spectrum there is an intense,
high-energy absorption band centered at 285 nm, with ε = 167
000 cm−1 M−1. This band has a shoulder at 314 nm (ε = 76 300
cm−1 M−1). A broad, low-energy absorption band appears at
385 nm, with ε = 37800 cm−1 M−1. Within this broad band
there are two optical transitions that overlap and have slightly
higher extinction coefficients, at 344 and 362 nm.
Hexagon 14. Hexagon 14 was synthesized by weighing 180°
acceptor 15 and ligand 11 into separate vials and dissolving
both with methylene chloride (Figure 10). The clear solution
containing 15 was then added dropwise to the yellow solution
of 11. The resulting brightly colored, green solution was then
allowed to stir for 24 h at room temperature. The product was
then precipitated with diethyl ether, isolated, and re-dissolved
in CD2Cl2 for characterization (see Supporting Information). It
should be noted that if both compounds are weighed into the
same vial and dissolved together, a low yield will be obtained
due to insoluble kinetic byproducts. Parent ions of the hexagon
structure were not observed in the ESI spectra (both ToF and
FT-ICR detectors were utilized with and without acid) due to
fragmentation; however, several unique fragments were
observed that support the formation of the hexagonal structure
DISCUSSION
■
Ligands. The photophysical properties of aniline have been
widely studied. In general, intense absorption bands for aniline
are due to π → π* transitions.113−116 Typically, there are two
electronic transitions that correspond to the S0 → S1 and S0 →
S2 excited states, with both transitions being red-shifted for
larger arene−aniline systems. For simple anilines, the main
pathway for non-radiative decay is ISC from the S1 to T1 state,
wherein the T1 → S0 conversion does not phosphoresce.113 For
larger arene−anilines the rate constant for ISC is smaller, which
leads to higher quantum yields.117
Ligands 5, 6, and 7 follow a similar trend, where two excited
states S1 and S2 are modulated by the presence and position of
the aniline amine. For 7, we assign the S0 → S1 transition to the
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S1 state for 7 (300 nm); it is possible that a lower-energy,
electronically forbidden state exists for 7. The variation in
quantum yield between 5, 6, and 7 may be rationalized by
considering these two excited states. If the emissive singlet
state, which is S2 in compound 7, is stabilized in compounds 5
and 6, it may be stabilized and approach the S1 state. This
stabilization makes it populated upon excitation of 5 and 6,
leading ultimately to increased emission since ISC is attenuated.
Evidence for this claim comes from the observed quantum
yields for 5 (Φ = 41%) and 6 (Φ = 65%), as well as absorption
features among the series of compounds. The trend for the
band centered at 300 nm to decrease with the growing lower-
energy bands of 5 (347 nm) and 6 (373 nm) suggests that an
intimate relationship between these two electronic transitions
exists. The lack of electronic transitions at 282 and 300 nm in 8
provides evidence linking the two transitions to the presence of
the ethynyl moieties.
The lower-energy excited state of 6 compared to 5 can be
attributed to the position of the amine group on the central
ring. The amine in 5 is meta to the ethynyl moieties, and while
the lone pair on the amine nitrogen is not in direct resonance
with the ethynyl moieties, the σmeta value is negative (−0.16).118
However, when the amine is ortho to the ethynyl moieties, it is
in direct resonance, lowering the energy of the excited state of
6. This is manifested in a 23 nm red-shift of the emission of 6
relative to 5.
Compound 8 lacks the ethynyl moieties responsible for
absorption bands at 282 and 300 nm. It does have a lower-
energy broad absorption band centered at 329 nm; however, it
is blue-shifted compared to those observed for 5 (347 nm) and
6 (373 nm). This blue-shift is attributed to the smaller π-system
present in the ethynyl-free ligand. Interestingly though, the
ethynyl spacer does not seem to have a significant effect on the
emission spectra. When comparing the lowest-energy absorp-
tion bands between 6 (373 nm) and 8 (329 nm), there is a 44
nm red-shift; however, a 5 nm red-shift is observed between the
emission spectra. This indicates that the excited state from
which the radiative pathway decays is similar in energy to that
of 6, despite being a higher-energy transition. Moreover, the
Figure 5. (A) 1H NMR spectra for 6, with the α- and β-pyridyl proton
signals colored in red and blue. (B) 1H NMR spectra for 11,
demonstrating the downfield shift and splitting of the α- and β-protons
on the pyridyl ring upon metal complexation. (C) 31P{1H} spectrum
for 11.
lower-energy band at 300 nm. Decay from this state appears to
be significantly non-radiative compared to the other aniline-
based ligands, which is supported by the lower quantum yield
for 7 (Φ = 8.4%) with respect to 5 (Φ = 41%) and 6 (Φ =
65%). The major pathway for non-radiative decay is believed to
be through ISC, followed by a non-emissive T1 → S0 transition.
The S1 excited state for 5 and 6 is lower in energy than that of
7, while the S2 state (300 nm) is similar in energy to that of the
Figure 6. ESI-MS spectra of [11-2ONO2]2+ and [11-3ONO2]3+ (black) and simulated spectra (red).
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Figure 7. Absorption (left) and emission (right) profiles for 10 (blue), 11 (red), and 12 (black). Spectra were recorded in aerated CH2Cl2.
Figure 8. Compounds 9 and 8 are stirred in a 1:1 stoichiometric fashion in CH2Cl2 for 24 h to afford 13.
blue-shift was observed for 14 when compared to 11. Each of
these observed results will be addressed individually.
When comparing the ligands and their respective self-
assemblies, a red-shift was observed for the lower-energy
electronic transitions. For example, the lowest-energy electronic
transition for endohedral aniline ligand 6 is centered at 373 nm,
while the self-assemblies constructed from this ligand, 11 and
14, have bands centered at 430 and 422 nm. This phenomenon
was attributed to the metal center coordinating with the pyridyl
nitrogen and perturbing the electronic structure of the ligand.
As will be shown in the TD-DFT section, the molecular orbitals
involved with the electronic transitions are of π-type symmetry.
Therefore, it is hypothesized that π-backbonding from the
metal center to the nitrogen π* enriches the ligand π-system
Figure 9. Absorption (solid) and emission (dashed) profiles for 13.
The spectra were collected using 1 cm path length in aerated CH2Cl2.
and lowers the energy required for excitation.
The quantum yield of each self-assembly is lower than the
quantum yields of the ligands from which they are constructed.
As previously discussed, aniline undergoes S1 → T1 ISC and
then non-radiatively decays back to the ground state, S0. Heavy
atoms are known to enhance the rate of spin-forbidden
processes such as ISC. Therefore, inclusion of platinum metal
centers in the self-assemblies will increase the rate constant for
ISC for the ligand-centered transitions. This manifests itself in
the quantum yield being lower in the self-assembly than in the
ligand used for its construction. For example, 8 has Φ = 8.4%,
while 12 is non-emissive. In a more impressive example, 5 has
Φ = 41%, while 10 has Φ = 4.0%.
quantum yield of 8 is almost half that of 6, providing evidence
that the excited state has a much lower rate constant for the
radiative pathway. The major component for the non-radiative
pathway could be attributed to ISC, as a similar phenomenon
has been observed with simple aniline compounds (i.e., a
smaller π-system has a higher rate constant for ISC).
Self-Assemblies. In all cases, the self-assemblies have red-
shifted lower-energy absorption bands and lower quantum
yields than their constituent ligands. However, only self-
assemblies constructed using endohedral aniline ligands 11, 13,
and 14 displayed appreciable red-shifts in the emission spectra
when compared to endohedral aniline ligands 6 and 8. A 17 nm
Interestingly, the exohedral aniline ligand 5 and 10 have
similar λmax for emission, 399 and 400 nm, despite 10 having a
lower-energy absorption band than 5 (370 versus 347 nm).
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Figure 10. Solutions of 15 and 11 were prepared using CH2Cl2. 15 was then added dropwise to a solution of 11 and the mixture stirred for 24 h to
afford 14.
A 17 nm blue-shift in the emission spectrum for 14 was
observed compared to 11. While organoplatinum(II) acceptor
15 is different than 9 and could account for this difference in
the emission spectra, the purpose of making a larger self-
assembly was to determine whether the photophysical
properties and shape or size of the metallacycle were intimately
related. By increasing the size of the metallacycle, there was
only a small blue-shift of 8 nm in the lower-energy absorption
band, which could be attributed to the difference between 15
and 9. Also, the extinction coefficient of this lower-energy band
is higher in 14 (ε = 87 600 cm−1 M−1) than in 11 (ε = 39 900
cm−1 M−1). This is to be expected if each metallacycle consists
of multiple localized π-systems; however, it does not manifest
itself as a strictly linear relationship when comparing the
extinction coefficients for 14 and 11. This does implicate,
though, that the self-assembly’s inherent photophysical proper-
Figure 11. Absorption (solid) and emission (dashed) profiles for 14.
The spectra were collected using 1 cm path length in aerated CH2Cl2.
ties are ligand centered. This is evidence that, for Pt-based
constructs of this type, the specific ligands used in a given self-
assembly have a larger influence on the photophysical
properties than the particular size or shape of the assembly.
DFT and TD-DFT General Information. Single-point
calculations were performed using a split basis set, where Becke
three-parameter hybrid exchange, the Lee−Yang−Parr correla-
tion functional (B3LYP),119,120 and the 6-31G** basis set121
were used for C, H, N, and P atoms, while the Los Alamos
National Laboratories (LANL2DZ)122 basis set and pseudo-
potential were used for Pt. To minimize computational cost,
PH3 ligands were utilized instead of PEt3; therefore, the model
used to approximate self-assembly 10 will be termed 10-PH3.
This implies that 5 and 10 have ligand-centered excited states
with similar energies.
Unlike 10, self-assemblies constructed using endohedral
aniline ligands 11, 13, and 14 displayed appreciable red-shifts in
the emission spectra when compared to endohedral aniline
ligands 6 and 8; however, 15 has an emission profile similar to
that of ligand 5. The low-energy optical transition for 11 in the
absorption spectrum is 430 nm, and the λmax for emission is 522
nm, while 13 has a low-energy absorption band of 385 nm and
a λmax for emission of 493 nm. This trend is continued for 14,
which has a low-energy absorption band of 422, while the λmax
for emission is 505 nm.
Table 2. Wavelength, Molecular Orbitals Involved, Oscillator Strength, and Description for Each of the Three Electronic
Transitions Predicted for 11-PH3
wavelength/nm
458.3
orbital transitions
HOMO−3 → LUMO+1
oscillator strength, f
description
1
349 → 354
350 → 353
345 → 356
346 → 355
345 → 353
346 → 354
1.1438
loss of e− density on aniline nitrogen ethynyl π → 1π*
HOMO−2 → LUMO
HOMO−7 → LUMO+3
HOMO−6 → LUMO+2
HOMO−7 → LUMO
HOMO−6 → LUMO+1
1
353.4
343.0
2.3945
0.8230
e− density increases on aniline nitrogen ethynyl π → 1π*
1
ethynyl π → 1π*
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Figure 12. Predicted TD-DFT transitions for a rhomboid model with oscillator strengths above 0.3. Three excited states are predicted,
corresponding to absorptions at 458.3 (red), 353.4 (green), and 343.0 nm (blue).
This nomenclature was applied to all models. The vertical
singlet transition energies of the complexes were computed at
the TD-DFT level within G09123 using the ground-state
optimized structure. For the structures that were calculated,
1486−1598 molecular orbitals were observed, and each
molecular orbital number that is listed is real and in its
absolute energetic order. The nomenclature that will be utilized
to discuss these molecular orbitals will be relative to the
HOMO and LUMO (i.e., HOMO−1 is the molecular orbital
directly below the HOMO).
TD-DFT Results and Discussion. Rhomboid 11. For
endohedral aniline rhomboid 11-PH3, Table 2 lists the
wavelengths for the theoretical electronic transitions that have
oscillator strengths over 0.3 from the output of the TD-DFT
calculation. For each electronic transition at a particular energy,
the following are listed: the orbitals associated with that
transition, the oscillator strength, and a general description of
the changes between the ground-state and excited-state
molecular orbitals involved in the transition.
Both transitions at 353.4 and 343.0 nm originate from low-lying
(HOMO−6 and HOMO−7) occupied molecular orbitals. The
molecular orbitals for the lowest-energy transition at 458.3 nm
have electron density on the central aniline amine group which
is not present in the corresponding virtual molecular orbitals.
The opposite is observed for the electronic transition at 353.4
nm, where the occupied molecular orbitals have electron
density on the central aniline amine group, while the
unoccupied orbitals have significantly less.
Figure 12 displays the predicted electronic transitions and
the molecular orbitals involved. After comparing the energies of
the eight molecular orbitals involved in the three theoretical
optical transitions, it was observed that there are four subsets of
grouped molecular orbitals, with each subset consisting of two
molecular orbitals that are close in energy. Moreover, each
electronic transition consists of one energetically similar
occupied ground-state “pair” going to an unoccupied excited-
state “pair”. These two energetically similar molecular orbitals
are thought to be degenerate, as discussed below.
Each molecular orbital has π-type symmetry and two regions
of electron density that are ligand-centered and separated by
the phenanthrene moieties of the organoplatinum(II) units on
the D2h rhomboid. Rhomboid 11 has three predicted optical
transitions, at 458.3, 353.4, and 343.0 nm, with oscillator
strengths of 1.1438, 2.3945, and 0.8230, respectively (see Table
2). All three predicted transitions involve filled molecular
orbitals with bonding character between the carbons of the
ethynyl moieties. The corresponding virtual or unoccupied
molecular orbitals have antibonding character between the
carbon atoms in the ethynyl moieties, which leads to a
weakening of the π-system on the ethynyl moiety during the
Rhomboid 11-PH3 has D2h symmetry, and each molecular
orbital has two regions of electron density with π-symmetry.
HOMO−7 and HOMO−6 contain a homologous ligand-
centered π-system that is separated from the second ligand-
centered π-system by the phenanthrene moiety on the Pt
acceptor 9. The second π-system is either identical to the
localized π-system across from it (HOMO−7) or inverted
(HOMO−6), which results in a change in the overall orbital
symmetry.
Performing a population analysis on each molecular orbital
corroborated the experimental conclusion that the optical
transitions arise from ligand-centered transitions; it was
calculated that over 96% of the electron density resides on
1
electronic transition. This transition is ascribed as π → 1π*.
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Table 3. Wavelength, Molecular Orbitals Involved, Oscillator Strength, and Description for Each of the Two Electronic
Transitions Predicted for 10-PH3 and the Three Predicted for 12-PH3
compd
wavelength/nm
361.5
orbital transitions
HOMO−7 → LUMO+3
oscillator strength, f
description
1
10-PH3
345 → 356
346 → 355
345 → 353
346 → 354
337 → 346
339 → 348
340 → 347
339 → 345
340 → 346
335 → 345
337 → 346
338 → 345
340 → 347
2.4633
increase of e− density on aniline nitrogen ethynyl π → 1π*
HOMO−6 → LUMO+2
HOMO−7 → LUMO
HOMO−6 → LUMO+1
HOMO−7 → LUMO+1
HOMO−5 → LUMO+3
HOMO−4 → LUMO+2
HOMO−5 → LUMO
HOMO−4 → LUMO+1
HOMO−9 → LUMO
HOMO−7 → LUMO+1
HOMO−6 → LUMO
HOMO−4 → LUMO+2
1
345.8
361.2
0.7839
1.5737
ethynyl π → 1π*
1
12-PH3
ethynyl π → 1π*
1
342.6
338.7
0.6351
2.5610
ethynyl π → 1π*
ethynyl π → 1π* charge transfer from phenanthrene to ligand
1
ligand-based orbitals. That said, the inclusion of Pt afforded
new photophysical properties relative to those of the free
ligands. This implies that the metal center perturbs the
electronic structure of the ligands. Since each molecular orbital
is of π-type symmetry and extends onto the Pt metal center, it
is hypothesized that π-backbonding from Pt to the pyridyl
nitrogen π* could be stabilizing the ligand-centered excited
state, thus giving rise to the red-shifted absorption and emission
bands.
The emission profile for 11 has a broad band centered at 522
nm, while 10 has a band centered at 400 nm. The difference in
emission wavelength maxima was previously discussed and
attributed to the difference in the σ values and resonance
structures. Further analysis of the molecular orbitals determined
that the unique positioning of the aniline nitrogen ortho to both
ethynyl moieties allows for direct “bridging” of the two π-
systems. This can be seen in molecular orbitals HOMO−3 and
HOMO−2, where the p-orbital of the aniline nitrogen is in
phase with the ethynyl π-system. This allows for the electrons
in the p-orbital on the aniline nitrogen to participate in the π-
system on the ethynyl moieties without having to traverse the
central benzene ring, resulting in the large red-shift observed.
It should be noted that between molecular orbitals 352
(HOMO) and 353 (LUMO) there is a considerable amount of
charge transfer from the metal acceptor unit and ligand; the
organo-Pt(II) acceptor unit includes orbital contributions from
the platinum, phenanthrene, and phosphine. In the HOMO,
98.12% of the electron density resides on the metal acceptor,
while in the LUMO there is only 2.44 (for the ligand, 0.88% in
the HOMO and 97.33% in the LUMO).
Rhomboid 10 and 12. The exohedral aniline rhomboid
model 10-PH3 has two predicted electronic transitions, at
361.53 and 345.8 nm, with oscillator strengths of 2.4633 and
0.7839 (see Table 3). The orbitals utilized in both transitions
are deep, low-lying HOMO−6 and HOMO−7 orbitals, and for
both electronic transitions, the electron is promoted to low-
lying LUMO orbitals.
The occupied molecular orbitals HOMO−7 and HOMO−6
involved with the electronic transition at 361.5 nm have
carbons that are bonding in the ethynyl moieties, while the
unoccupied destination molecular orbitals LUMO+3 and
LUMO+2 have carbons that are antibonding within the ethynyl
moieties. This transition is ascribed as 1π → 1π*. Also,
HOMO−7 and HOMO−6 have little electron density on the
aniline nitrogen, but some electron density is present in the
unoccupied molecular orbitals LUMO+2 and LUMO+3. This
implies that the aniline amine is actively participating in the
electronic transitions, even though it is meta to the ethynyl
moieties.
The electronic transition at 345.8 nm has an oscillator
strength of 0.7839 and is comprised of two molecular orbital
transitions (HOMO−7 → LUMO and HOMO−6 → LUMO
+1). Occupied molecular orbitals HOMO−7 and HOMO−6
both have the carbons in the ethynyl moieties bonding, while
the destination unoccupied molecular orbitals have the carbons
in the ethynyl moieties antibonding (1π → 1π*). Therefore, the
ethynyl moieties seem to be critical to the observed
photophysical properties.
Rhomboid 10-PH3 also displays a significant amount of
charge transfer between the 352 (HOMO) and 353 (LUMO)
molecular orbitals. Molecular orbital 352 has 88.73% of the
electron density residing on the organo-Pt(II) acceptor unit,
with 10.08% on the ligand, while molecular orbital 353 has
2.68% on the organo-Pt(II) acceptor unit and 96.96% on the
ligand.
Rhomboid 12-PH3 has three predicted electronic transitions,
at 361.2, 342.6, and 338.7 nm, with oscillator strengths of
1.5737, 0.6351, and 2.5610 (see Table 3). The electronic
transitions at 361.2 and 342.6 nm both correspond to a
weakening of the ethynyl moieties (1π → 1π*). It was predicted
that 12 would have a higher-energy electronic transition
centered at 338.7 nm that utilizes deep, low-lying HOMO−9
and HOMO−7 molecular orbitals, wherein the ethynyl
moieties (1π → 1π*) are weakened and a phenanthrene
(acceptor)-to-ligand charge transfer occurs. After performing
a population analysis on the molecular orbitals associated with
this charge transfer, it was determined that 41% of electron
density on the phenanthrene moiety of acceptor 9 moiety is
transferred to 5.
It should be noted that there is a considerable amount of
charge transfer from the metal acceptor unit and ligand
between molecular orbitals 344 (HOMO) and 345 (LUMO)
for rhomboid 12. Molecular orbital 344 has 96.63% of the
electron density residing on the organo-Pt(II) acceptor unit,
while in molecular orbital 345 there is only 2.20 (for the ligand,
0.43% in HOMO and 95.64% in the LUMO).
The experimental absorption spectra for 12 and 10 are
shown in Figure 13, with the predicted lower-energy electronic
transition for 10-PH3 overlaid. The theoretical lowest-energy
electronic transition for 10-PH3 (361.53 nm) closely matches
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onto the metal center. Interestingly, an endohedral aniline
rhomboid 11 had markedly different photophysical properties
than those of the ligand 6 used for its construction. Rhomboid
11 has a low-energy excited state that are in the visible regime,
and the assembly emits at wavelengths above 500 nm. This
novel property makes 11 a promising candidate for applications
such as bioimaging and biosensing, since the degradation of the
rhomboid can be monitored by its fluorescence.
Currently, there are ongoing efforts to probe the metal center
and its effect on the photophysical properties of the endohedral
aniline rhomboid 11. By altering the electronic nature of the
ancillary phosphine ligands, it is our intention to synthesize red-
shifted rhomboids that retain the novel properties demon-
strated in this work.
Figure 13. Experimental absorption spectra of 12 (black) and 10 (red)
with the predicted optical transition at 361 nm (blue) overlaid.
EXPERIMENTAL PROCEDURES
■
General Information. 3,5-Diiodoaniline124 (1), m-bis(pyridin-4-
ylethynyl)benzene109 (2), and 2,9-bis[trans-Pt(PEt3)2NO3]-
phenanthrene125 (9) were prepared using known procedures. 2,6-
Dibromoaniline was purchased from Sigma-Aldrich. Deuterated
solvents were purchased from Cambridge Isotope Laboratory
the experimentally observed wavelength maximum for the low-
energy absorption band, 370 nm. Also, the lowest-energy
electronic transition for 12-PH3 was predicted to be centered at
361.2 nm, while it was experimentally observed at 356 nm. The
theoretical oscillator strengths, which are related to the
extinction coefficients, for 10-PH3 and 12-PH3 follow what is
observed experimentally, with 10 having a larger extinction
coefficient, at 361 nm, than that of 12.
Rhomboid 13. Unlike rhomboids 10-PH3, 11-PH3, and 12-
PH3, rhomboid 13-PH3 has C2v symmetry. Rhomboid 13-PH3
was predicted to have a single electronic transition, at 378.2 nm,
with an oscillator strength of 0.5194 (see Table 4). Both
occupied molecular orbitals HOMO−5 and HOMO−4 have
electron density centered on the central aniline core with
density on the nitrogen, while the unoccupied molecular
orbitals LUMO+1 and LUMO have little electron density on
the aniline nitrogen. Moreover, the unoccupied molecular
orbitals have more electron density displaced on the pyridyl
moieties than in the occupied molecular orbitals. This
demonstrates that, without the ethynyl moiety spacers, the
ligand-centered transitions are significantly altered and the
pyridyl π-systems contribution to the observed optical
properties is greatly increased.
1
(Andover, MA). H, 31P{1H}, and 13C NMR spectra were recorded
on a Varian 300 spectrometer, and the mass spectra were recorded on
a Micromass LCT Premier XE ToF mass spectrometer using
electrospray ionization with a MassLynx operating system. The ESI-
MS samples were dissolved in methylene chloride and then diluted
with acetone unless otherwise noted. All 31P{1H} spectra were
referenced using a 10% H3PO4(aq) solution. Elemental Analysis was
performed by Atlantic Microlab, Inc.
Ligand Synthesis. 3,5-Diethynylaniline (3). A Schlenk flask was
charged with 1.035 g (3.001 mmol) of 3,5-diiodo-aniline, 693.5 mg
(20.00 mol %) of Pd(PPh3)4, and 114.3 mg (20.00 mol %) of CuI. The
Schlenk flask was evacuated and placed under positive N2 pressure.
Next, 30 mL of distilled THF, 10 mL of dry Et3N, and 5.0 mL (35
mmol) of trimethylsilylacetylene were added via syringe. The reaction
mixture was stirred for 4 h at room temperature before placing the
Schlenk flask in a 60 °C oil bath for 20 h. The solvent was removed by
reduced pressure. The crude product, yellow oil, was isolated after
column chromatography (mobile phase, 5:1 hexanes/EtOAc). The
crude product was then placed into a round-bottom flask, and 25 mL
of a MeOH/KOH (1 g) solution was added. The mixture was allowed
to stir for 24 h. After removal of the solvent by reduced pressure, the
product was isolated by column chromatography (mobile phase, 2:1
hexanes/EtOAc): 280 mg (65% yield); 1H (CDCl3, 300 MHz) δ 7.02
(t, 1H, ArH, J = 1.32 Hz), δ 6.78 (d, 2H, ArH, J = 1.32 Hz), δ 3.75 (s,
2H, NH2), δ 3.01 (s, 2H, CH); 13C (CDCl3, 75 MHz) δ 146.38 (1C),
δ 126.34 (1C), δ 123.32 (2C), δ 119.06 (2C), δ 83.08 (2C), δ 77.39
(2C); ESI-MS [M+H]+ 142.07. Anal. Calcd for C10H7N: C, 85.08; H,
5.00; N, 9.92. Found: C, 84.07; H, 9.43; N, 4.93.
2,6-Diethynylaniline (4). A Schlenk flask was charged with 3.0 g
(0.012 mol) of 2,6-dibromoaniline, 10 mol % of CuI (0.23 g), and 10
mol % Pd(PPh3)4 (1.4 g). The Schlenk flask was then evacuated via
reduced pressure and backfilled with N2. Next, 20 mL of distilled THF
and 20 mL of dry Et3N were added via syringe. Last, 10 equiv of
acetylene-TMS (17 mL) was added. The reaction was heated to 60 °C
and allowed to stir for 48 h. After cooling, the solvent was removed,
and the compound was purified by column chromatography (mobile
phase, 10% EtOAc/hexanes). The resulting crude mixture, yellow oil,
was used during the next step. A round-bottom flask was charged with
the crude mixture from the previous step. A KOH/MeOH solution
Also, like 10-PH3, 11-PH3, and 12-PH3, it was determined
that rhomboid 13-PH3 has a large charge transfer between
molecular orbitals 328 (HOMO) and 329 (LUMO). Molecular
orbital 328 has 98.79% of the electron density on the organo-
Pt(II) acceptor unit and 0.31% on the ligand, while in
molecular orbital 329 there is 3.35% on the organo-Pt(II)
acceptor unit and 95.48% on the ligand.
CONCLUSION
■
A series of novel Pt(II)-metallacycles were synthesized, and
their photophysical properties were investigated experimentally
and computationally. During this investigation it was
determined that the emissive properties of bis(phosphine)
Pt(II) metallacycles arise from ligand-centered transitions
involving π-type symmetry molecular orbitals that extend
Table 4. Wavelength, Molecular Orbitals Involved, Oscillator Strength, and Description for Each Electronic Transition
Predicted for 13-PH3
wavelength/nm
378.2
orbital transitions
HOMO−5 → LUMO+1
HOMO−4 → LUMO
oscillator strength, f
description
loss of e− density from aniline nitrogen
323 → 330
324 → 329
0.5194
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was prepared by dissolving 1 g into 25 mL. The KOH/MeOH solution
was then added to the round-bottom flask, and the mixture was
allowed to stir overnight. The solvent was then removed by reduced
pressure, and the compound was purified by column chromatography
(mobile phase, 30% EtOAc/hexanes): 0.98 g (58% yield) of a yellow
product, which was then isolated and dried under reduced pressure for
4 h and re-dissolved in CD2Cl2 for characterization.
10: H NMR (CD2Cl2, 300 MHz) δ 9.33 (d, 4H, Hα′-Py, J = 5.58
1
Hz), δ 8.86 (s, 4H, PhenH), δ 8.66 (d, 4H, Hα′′-Py, J = 5.73 Hz), δ
7.91 (d, 4H, Hβ′-Py, J = 5.43 Hz), δ 7.78 (d, 4H, Hβ′′-Py, J = 4.23 Hz),
δ 7.59 (d, 12H, PhenH, J = 5.61 Hz), δ 7.34 (s, 2H, ArH), δ 7.13 (s,
4H, ArH), δ 4.56 (bs, 4H, -NH2), δ 1.3−1.4 (m, 24H, PCH2CH3), δ
1.12−1.27 (m, 36H, PCH2CH3); 31P {1H} NMR (CD2Cl2, 121.4
1
solid was afforded; H (CDCl3, 300 MHz) δ 7.30 (d, 2H, ArH, J =
7.68 Hz), δ 6.61 (t, 1H, ArH, J = 7.71 Hz), δ 4.86 (bs, 2H, NH2), δ
3.41 (s, 2H, CH); 13C (CDCl3, 75 MHz) δ 133.59 (1C), δ 117.14
(2C), δ 106.40 (1C), δ 98.81 (2C), δ 83.16 (2C), δ 80.20(2C); ESI-
MS [M+H]+ 142.07. Anal. Calcd for C10H7N: C, 85.08; H, 5.00; N,
9.92. Found: C, 83.32; H, 5.15; N, 9.63.
1
MHz) δ 8.04 (bs, 195Pt satellites, JPt−P = 2707 Hz); ESI-MS
(C116H162N10O12P8Pt4) m/z [10-2ONO2]2+ 1396.40; [10-3ONO2]3+
909.96. Anal. Calcd for complex (C116H162N10O12P8Pt4): C, 47.77; H,
5.60; N, 4.80. Found: C, 47.56; H, 5.70; N, 4.77.
3,5-Bis(4-pyridylethynyl)aniline (5). A Schlenk flask was charged
with 275 mg (1.95 mmol) of 3,5-diethynylaniline, 225 mg (10.0 mol
%) of Pd(PPh3)4, 37.1 mg (10.0 mol %) of CuI, and 758 mg (3.89
mmol) of 4-bromopyridine hydrochloride. The Schlenk flask was
evacuated and charged with N2. Next, 20 mL of distilled THF and 20
mL of dry Et3N were added via syringe. The reaction mixture was
stirred at 60 °C for 48 h. The solvent was removed by reduced
pressure, and the product was purified via column chromatography
1
11: H (CD2Cl2, 300 MHz) δ 8.87 (d, 4H, Hα′-Py, J = 5.79 Hz), δ
8.67 (d, 4H, Hα′′-Py, J = 5.67 Hz), δ 8.59 (s, 4H, PhenH), δ 8.25 (d,
4H, Hβ′-Py, J = 5.82 Hz), δ 7.74 (d, 4H, Hβ′′-Py, J = 5.88 Hz), δ 7.78 (s,
2H, Hb′-Py), δ 7.62 (d, 8H, PhenH, J = 4.44 Hz), δ 7.61 (s, 4H,
PhenH), δ 7.53 (d, 4H, ArH, J = 7.68 Hz), δ 6.72 (t, 2H, ArH, J = 7.68
Hz), δ 6.31 (bs, 4H, -NH2), δ 1.3−1.4 (m, 24H, PCH2CH3), δ 1.11−
1.27 (m, 36H, PCH2CH3); 31P{1H} NMR (CD2Cl2, 121.4 MHz) δ
1
12.61 (bs, 195Pt satellites, JPt−P
= 2684 Hz); ESI-MS
1
(mobile phase, 10:1 EtOAc/hexanes): 82% yield; H (CDCl3, 300
(C116H162N10O12P8Pt4) m/z [11-2ONO2]2+ 1396.45; [11-3ONO2]3+
909.98. Anal. Calcd for complex + 3DCM (C119H168Cl6N10O12P8Pt4):
C, 45.07; H, 5.34; N, 4.42. Found: C, 45.36; H, 5.55; N, 4.46.
MHz) δ 8.61 (d, 4H, Hα-Py, J = 5.88 Hz), δ 7.36 (d, 4H, Hβ-Py, J =
5.91 Hz), δ 7.13 (bs, 1H, ArH), δ 6.87 (d, 2H, ArH, J = 0.96 Hz), δ
3.82 (bs, 2H, NH2); 13C (CDCl3, 75 MHz) δ 150.06 (4C), δ 146.77
(1C), δ 131.37 (2C), δ 125.76 (5C), δ 123.53 (2C), δ 118.86 (2C), δ
93.4 (2C), δ 86.9 (2C); ESI-MS [M+H]+ 296.03. Anal. Calcd for
C20H13N3: C, 81.34; H, 4.44; N, 14.23. Found: C, 80.25; H, 4.50; N,
13.62.
1
12: H (CD2Cl2, 300 MHz) δ 9.36 (d, 4H, Hα′-Py, J = 5.85 Hz), δ
8.85 (s, 4H, PhenH), δ 8.72 (d, 4H, Hα′′-Py, J = 5.76 Hz), δ 8.06 (s,
2H, ArH), δ 7.97 (d, 4H, Hβ′-Py, J = 5.82 Hz), δ 7.75−7.82 (m, 10H,
Hβ′′-Py and ArH), δ 7.53−7.63 (m, 12H, PhenH), δ 1.28−1.45 (m,
24H, PCH2CH3), δ 1.09−1.23 (m, 36H, PCH2CH3); 31P{1H} NMR
2,6-Bis(4-pyridylethynyl)aniline (6). First, 0.975 g (6.91 mmol) of
2,6-bis(4-pyridylethynyl)aniline was weighed into a Schlenk flask with
132 mg (10.0 mol %) of CuI, 798 mg (10.0 mol %) of Pd(PPh3)4, and
2.50 mol equiv (1.34 g) of 4-bromopyridine HCl. The Schlenk flask
was then evacuated by reduced pressure and backfilled with N2. Next,
20 mL of freshly distilled THF and 20 mL of dry Et3N were added.
The mixture was heated to 60 °C and left to stir for 48 h. The solvent
was removed by reduced pressure and purified via column
chromatography (mobile phase, EtOAc): 450 mg of a bright yellow
1
(CD2Cl2, 121.4 MHz) δ 13.32 (bs, 195Pt satellites, JPt−P = 2704 Hz);
ESI-MS (C116H160N8O12P8Pt4) m/z [12-2ONO2]2+ 1381.44; [12-
3ONO2]3+ 899.97. Anal. Calcd for complex
+ 2DCM
(C118H164Cl4N8O12P8Pt4): C, 46.37; H, 5.41; N, 3.67. Found: C,
46.50; H, 5.78; N, 3.62.
1
13: H (CD2Cl2, 300 MHz) δ 9.06 (d, 4H, Hα′-Py, J = 5.85 Hz), δ
8.77 (s, 4H, PhenH), δ 8.69 (d, 4H, Hα′′-Py, J = 5.67 Hz), δ 8.50 (d,
4H, Hβ′-Py, J = 4.17 Hz), δ 8.02 (bs, 4H, -NH2), δ 7.82 (d, 4H, Hβ′′-Py,
J = 4.14 Hz), δ 7.55−7.65 (m, 12H, PhenH), δ 7.44 (d, 4H, ArH, J =
7.65 Hz), δ 7.03 (t, 2H, ArH, J = 7.62 Hz), δ 1.35−1.45 (m, 24H,
PCH2CH3), δ 1.1−1.27 (m, 36H, PCH2CH3); 31P{1H} NMR
1
solid (23% yield); H (CDCl3, 300 MHz) δ 8.62 (d, 4H, Hα-Py, J =
3.39 Hz), δ 7.41 (d, 2H, Hβ-Py, J = 4.62 Hz), δ 7.38 (d, 4H, ArH, J =
3.48 Hz), δ 6.74 (t, 1H, ArH, J = 4.59 Hz), δ 4.93 (bs, 2H, NH2); 13
C
1
(CD2Cl2, 121.4 MHz) δ 8.97 (bs, 195Pt satellites, JPt−P = 2692 Hz);
ESI-MS (C108H162N10O12P8Pt4) m/z [13-2ONO2]2+ 1348.41; [13-
(CDCl3, 75 MHz) δ 150.13 (4C), δ 149.57 (1C), δ 133.98 (2C), δ
131.26 (1C), δ 125.54 (4C), δ 117.82 (2C), δ 106.74 (2C), δ 94.99
(2C), δ 92.82 (2C), δ 89.99 (2C); ESI-MS [M+H]+ 296.06. Anal.
Calcd for C20H13N3: C, 81.34; H, 14.23; N, 4.44. Found: C, 80.56; H,
13.42; N, 4.67.
3ONO2]3+ 877.27. Anal. Calcd for complex
+ 2DCM
(C110H166Cl4N10O12P8Pt4): C, 44.18; H, 5.59; N, 4.68. Found: C,
44.16; H, 5.80; N, 4.67.
Hexagon 14. First, 180° organoplatinum(II) acceptor μ-1,4-
phenylenetetrakis(triethylphosphine)bis(1,1,1-trifluoromethanesulfo-
nato-κO)diplatinum (15) and ligand 11 were weighed into separate 2
dram vials and dissolved with methylene chloride (0.5 mL for 11 and
1.0 mL for 15). The clear solution containing 15 was then added
dropwise to the yellow solution of 11. The brightly colored, green
solution was then allowed to stir for 24 h at room temperature. The
product was precipitated with diethyl ether, isolated, and redissolved in
2,6-(4-Pyridine)aniline (8). A Schlenk flask was charged with 1.0 g
(4.0 mmol) of 2,6-dibromoaniline and 10 mL of degassed DMF
(purged with N2 for 15 min) and kept under N2 atomosphere. A 2 M
solution of Na2CO3 was prepared, purged with N2 for 15 min, and
added to the Schlenk flask via syringe. Then, a solution containing 2.5
mol equiv (1.2 g) of pyridine-4-boronic acid and 15 mol %
PdCl2(PPh3)2 (280 mg) was prepared using 5 mL of degassed DMF
and added to the Schlenk flask via syringe. The mixture was heated to
100 °C and allowed to stir for 72 h. The solvent was removed by
reduced pressure, and the product was purified via column
chromatography (mobile phase, 10% EtOAc/hexanes): 575 mg of a
light orange solid (58.0% yield); 1H (CDCl3, 300 MHz) δ 8.67 (d, 4H,
Hα-Py, J = 5.7 Hz), δ 7.42 (d, 4H, Hβ-Py, J = 6.03 Hz), δ 7.14 (d, 2H,
ArH, J = 7.62 Hz), δ 6.92 (t, 1H, ArH, J = 7.95 Hz), δ 3.90 (bs, 2H,
NH2); 13C (CDCl3, 75 MHz) δ 150.69 (4C), δ 147.51 (2C), δ 140.49
(1C), δ 130.74 (2C), δ 125.52 (2C), δ 124.29 (4C), δ 119.00 (1C);
ESI-MS [M+H]+ 248.06. Anal. Calcd for C16H13N3: C, 77.71; H,
16.99; N, 5.30. Found: C, 76.94; H, 16.79; N, 5.28.
1
CD2Cl2 for characterization: H (CD2Cl2, 300 MHz) δ 8.61(bs, 24H,
Hα-Py), δ 7.87 (bs, 24H, Hβ-Py), δ 7.49 (d, 24H, ArH, J = 7.8 Hz), δ
7.05 (bs, 12H, ArH), δ 6.72 (bs, 6H, ArH), δ 5.79 (bs, 12H, NH2), δ
1.36 (bs, 144H, PCH2CH3), δ 1.00−1.25 (m, 216H, PCH2CH3);
31P{1H} NMR (CD2Cl2, 121.4 MHz) δ 12.14 (bs, 195Pt satellites,
1JPt−P = 2716 Hz); ESI-MS (C108H162N10O12P8Pt4), see Supporting
Information for spectra of fragments. Anal. Calcd for complex +
4DCM (C316H470Cl8F36N18O36P24Pt12S12): C, 39.81; H, 4.97; N, 2.64.
Found: C, 39.62; H, 4.97; N, 2.69.
UV−Vis and Fluorescence. Absorption spectra were recorded on
a Hitachi U-4100 spectrophotometer, and fluorescence spectra were
recorded on a Horiba Jobin-Yvon Fluoromax-3 instrument using
aerated spectrophotometric-grade dichloromethane (Sigma-Aldrich) at
room temperature. The cells used for the following experiments were
all 1 cm path length quartz cuvettes from Starna Cells, Inc. Exctinction
coefficients were determined by measuring four solutions at
concentrations ranging from 0.6 to 30 μM. The molar absorptivities
for each solution were then calculated using Beer’s law, and the four
General Procedure for Rhomboid Formation (10−13). In a 1:1
stoichiometric fashion, ligand 5, 6, 7, or 8 was added to the 60°
bis(phosphine) organoplatinum(II) acceptor 9 in a 2 dram vial. The
solids were dissolved in dichloromethane (methanol for 13) and
allowed to stir at room temperature overnight. For rhomboid 13, the
solution was allowed to stir at 55 °C for 24 h. To the resulting
homogeneous solution, diethyl ether was added to precipitate the
K
dx.doi.org/10.1021/ja3036515 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
were averaged. Subsequent samples were then prepared to confirm the
extinction coefficients. For fluorescence, metallacycles were freshly
prepared for each measurement. The quantum yield for the instrument
was determined by cross-calibrating with two standards: quinine
sulfate in 0.1 M H2SO4 (Φ = 54%) and anthracene in ethanol (Φ =
27%).
DFT and TD-DFT Calculations. All calculations were performed
using the Gaussian09 (G09) program package revision B.01,123 with
the Becke three-parameter hybrid exchange and the Lee−Yang−Parr
correlation functionals (B3LYP).119,120 The 6-31G** basis set121 was
used for H, C, N, and P atoms, while the Los Alamos National
Laboratories (LANL2DZ)122 basis set and pseudopotential was used
for Pt. All geometry optimizations were performed without a solvent
field in C1 symmetry; the results are in the gas phase. To minimize
computational cost, the PEt3 ligands on Pt were modeled as PH3
ligands. Orbitals were visualized using Chem3D and GaussView 5.0
with an isovalue of 0.02.
(7) Fujita, M.; Yazaki, J.; Ogura, K. Tetrahedron Lett. 1991, 32, 5589.
(8) Muller, C.; Whiteford, J. A.; Stang, P. J. J. Am. Chem. Soc. 1998,
̈
120, 9827.
(9) Murase, T.; Otsuka, K.; Fujita, M. J. Am. Chem. Soc. 2010, 132,
7864.
(10) Sato, H.; Tashiro, K.; Shinmori, H.; Osuka, A.; Murata, Y.;
Komatsu, K.; Aida, T. J. Am. Chem. Soc. 2005, 127, 13086.
(11) Stang, P. J.; Cao, D. H.; Saito, S.; Arif, A. M. J. Am. Chem. Soc.
1995, 117, 6273.
(12) Vajpayee, V.; Kim, H.; Mishra, A.; Mukherjee, P. S.; Stang, P. J.;
Lee, M. H.; Kim, H. K.; Chi, K.-W. Dalton Trans. 2011, 40.
(13) Whiteford, J. A.; Stang, P. J.; Huang, S. D. Inorg. Chem. 1998, 37,
5595.
(14) Yamauchi, Y.; Yoshizawa, M.; Akita, M.; Fujita, M. J. Am. Chem.
Soc. 2009, 132, 960.
(15) Hembury, G. A.; Borovkov, V. V.; Inoue, Y. Chem. Rev. 2007,
108, 1.
(16) Mishra, A.; Vajpayee, V.; Kim, H.; Lee, M. H.; Jung, H.; Wang,
M.; Stang, P. J.; Chi, K.-W. Dalton Trans. 2012, 41.
(17) Resendiz, M. J. E.; Noveron, J. C.; Disteldorf, H.; Fischer, S.;
Stang, P. J. Org. Lett. 2004, 6, 651.
The percentage of platinum, phenanthrene, phosphine, or ligand
character in the occupied (canonical) molecular orbitals (MOs) and
virtual orbitals discussed for the previous complexes was calculated
from a full population analysis,
(18) Breiner, B.; Clegg, J. K.; Nitschke, J. R. Chem. Sci. 2011, 2.
(19) Dydio, P.; Dzik, W. I.; Lutz, M.; de Bruin, B.; Reek, J. N. H.
Angew. Chem., Int. Ed. 2011, 50, 396.
(20) Fiedler, D.; Leung, D. H.; Bergman, R. G.; Raymond, K. N. Acc.
Chem. Res. 2004, 38, 349.
%orbital character(Pt,phen,phosphine,Lig)
∑ ϕ2
(Pt,phen,phosphine,Lig)
=
× 100%
∑ ϕ2
(1)
(all)
(21) Koblenz, T. S.; Wassenaar, J.; Reek, J. N. H. Chem. Soc. Rev.
2008, 37.
(22) Lee, S. J.; Hupp, J. T. Coord. Chem. Rev. 2006, 250, 1710.
(23) Lee, S. J.; Lin, W. Acc. Chem. Res. 2008, 41, 521.
(24) Pluth, M. D.; Bergman, R. G.; Raymond, K. N. Acc. Chem. Res.
2009, 42, 1650.
where ∑φi (i = Pt, phen, phosphine, Lig, or all) is the sum of the
squares of the eigenvalues associated with the atomic orbital of interest
and all of the atomic orbitals in a particular molecular orbital,
respectively. The vertical singlet transition energies of the complexes
were computed at the TD-DFT level within G09 using the ground-
state optimized structure.
(25) Yoshizawa, M.; Klosterman, J. K.; Fujita, M. Angew. Chem., Int.
Ed. 2009, 48, 3418.
(26) Flamigni, L.; Ventura, B.; Oliva, A. I.; Ballester, P. Chem.Eur.
J. 2008, 14, 4214.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra for compounds 3, 4, 5, 6, and 8; H
1
(27) Indelli, M. T.; Chiorboli, C.; Scandola, F.; Iengo, E.; Osswald,
and 31P{1H} NMR spectra and ESI-MS spectra for metalla-
cycles 10−14; atom coordinates for the optimized structures of
10−13; the molecular orbitals involved, wavelength, and
oscillator strength for each theoretical electronic transition
with a non-zero oscillator from the TD-DFT calculation for
10−13. This material is available free of charge via the Internet
at http://pubs.acs.org.
P.; Wurthner, F. J. Phys. Chem. B 2010, 114, 14495.
̈
(28) Jensen, R. A.; Kelley, R. F.; Joong Lee, S.; Wasielewski, M. R.;
Hupp, J. T.; Tiede, D. M. Chem. Commun. 2008, 1886.
(29) Kelley, R. F.; Lee, S. J.; Wilson, T. M.; Nakamura, Y.; Tiede, D.
M.; Osuka, A.; Hupp, J. T.; Wasielewski, M. R. J. Am. Chem. Soc. 2008,
130, 4277.
(30) Oliva, A. I.; Ventura, B.; Wurthner, F.; Camara-Campos, A.;
Hunter, C. A.; Ballester, P.; Flamigni, L. Dalton Trans. 2009, 4023.
(31) Sprafke, J. K.; Kondratuk, D. V.; Wykes, M.; Thompson, A. L.;
AUTHOR INFORMATION
■
Hoffmann, M.; Drevinskas, R.; Chen, W.-H.; Yong, C. K.; Karnbratt, J.;
̈
Corresponding Author
Bullock, J. E.; Malfois, M.; Wasielewski, M. R.; Albinsson, B.; Herz, L.
M.; Zigmantas, D.; Beljonne, D.; Anderson, H. L. J. Am. Chem. Soc.
2011, 133, 17262.
stang@chem.utah.edu
(32) Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001, 34,
759.
(33) Cotton, F. A.; Lin, C.; Murillo, C. A. Proc. Natl. Acad. Sci. U.S.A.
2002, 99, 4810.
(34) Fujita, M. Chem. Soc. Rev. 1998, 27, 417.
(35) Fujita, M.; Tominaga, M.; Hori, A.; Therrien, B. Acc. Chem. Res.
2005, 38, 369.
(36) Farha, O. K.; Hupp, J. T. Acc. Chem. Res. 2010, 43, 1166.
(37) Lee, J.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.;
Hupp, J. T. Chem. Soc. Rev. 2009, 38, 1450.
(38) Gianneschi, N. C.; Masar, M. S.; Mirkin, C. A. Acc. Chem. Res.
2005, 38, 825.
ACKNOWLEDGMENTS
■
We are grateful to NSF-CHE 0820955 for financial support. We
thank Prof. C. D. Poulter for instrumental support and Prof. A.
Orendt for insightful discussions on the quantum mechanical
calculations.
REFERENCES
■
(1) Ghosh, S.; Chakrabarty, R.; Mukherjee, P. S. Inorg. Chem. 2008,
48, 549.
(2) Amouri, H.; Desmarets, C.; Moussa, J. Chem. Rev. 2012, 112,
2015.
(39) Oliveri, C. G.; Ulmann, P. A.; Wiester, M. J.; Mirkin, C. A. Acc.
Chem. Res. 2008, 41, 1618.
(3) Barry, N. P. E.; Therrien, B. Eur. J. Inorg. Chem. 2009, 2009, 4695.
(4) Chen, Y.-Q.; Wang, X.-Z.; Shao, X.-B.; Hou, J.-L.; Chen, X.-Z.;
Jiang, X.-K.; Li, Z.-T. Tetrahedron 2004, 60, 10253.
(40) Caulder, D. L.; Bruckner, C.; Powers, R. E.; Konig, S.; Parac, T.
̈
̈
N.; Leary, J. A.; Raymond, K. N. J. Am. Chem. Soc. 2001, 123, 8923.
(41) Caulder, D. L.; Raymond, K. N. Acc. Chem. Res. 1999, 32, 975.
(42) Chakrabarty, R.; Mukherjee, P. S.; Stang, P. J. Chem. Rev. 2011,
111, 6810.
(5) Freudenreich, J.; Barry, N. P. E.; Suss-Fink, G.; Therrien, B. Eur.
̈
J. Inorg. Chem. 2010, 2010, 2400.
(6) Fujita, M.; Nagao, S.; Iida, M.; Ogata, K.; Ogura, K. J. Am. Chem.
Soc. 1993, 115, 1574.
L
dx.doi.org/10.1021/ja3036515 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
(43) De, S.; Mahata, K.; Schmittel, M. Chem. Soc. Rev. 2010, 39,
1555.
(44) Nitschke, J. R. Acc. Chem. Res. 2006, 40, 103.
(79) Schmitt, F.; Freudenreich, J.; Barry, N. P. E.; Juillerat-Jeanneret,
L.; Suss-Fink, G.; Therrien, B. J. Am. Chem. Soc. 2012, 134, 754.
̈
(80) Paul, L. E. H.; Therrien, B.; Furrer, J. Inorg. Chem. 2011, 51,
(45) Safont-Sempere, M. M.; Fernan
2011, 111, 5784.
́
dez, G.; Wurthner, F. Chem. Rev.
1057.
̈
(81) Hui, C.-K.; Chu, B. W.-K.; Zhu, N.; Yam, V. W.-W. Inorg. Chem.
2002, 41, 6178.
(82) Wong, H.-L.; Tao, C.-H.; Zhu, N.; Yam, V. W.-W. Inorg. Chem.
(46) Northrop, B. H.; Zheng, Y.-R.; Chi, K.-W.; Stang, P. J. Acc.
Chem. Res. 2009, 42, 1554.
(47) Stang, P. J.; Olenyuk, B. Acc. Chem. Res. 1997, 30, 502.
(48) Seidel, S. R.; Stang, P. J. Acc. Chem. Res. 2002, 35, 972.
(49) Bar, A. K.; Mostafa, G.; Mukherjee, P. S. Inorg. Chem. 2010, 49,
7647.
(50) Mahata, K.; Schmittel, M. J. Am. Chem. Soc. 2009, 131, 16544.
́
(51) Solladie, N.; Chambron, J.-C.; Sauvage, J.-P. J. Am. Chem. Soc.
1999, 121, 3684.
(52) Wang, M.; Zheng, Y.-R.; Cook, T. R.; Stang, P. J. Inorg. Chem.
2011, 50, 6107.
(53) Wang, M.; Zheng, Y.-R.; Ghosh, K.; Stang, P. J. J. Am. Chem. Soc.
2010, 132, 6282.
(54) Yamanaka, M.; Yamada, Y.; Sei, Y.; Yamaguchi, K.; Kobayashi,
2010, 50, 471.
(83) Wong, K. M.-C.; Yam, V. W.-W. Acc. Chem. Res. 2011, 44, 424.
(84) Adamson, A. W.; Waltz, W. L.; Zinato, E.; Watts, D. W.;
Fleischauer, P. D.; Lindholm, R. D. Chem. Rev. 1968, 68, 541.
(85) Brooks, J.; Babayan, Y.; Lamansky, S.; Djurovich, P. I.; Tsyba, I.;
Bau, R.; Thompson, M. E. Inorg. Chem. 2002, 41, 3055.
(86) Caspar, J. V. J. Am. Chem. Soc. 1985, 107, 6718.
(87) Chan, S.-C.; Chan, M. C. W.; Wang, Y.; Che, C.-M.; Cheung,
K.-K.; Zhu, N. Chem.Eur. J. 2001, 7, 4180.
(88) Danilov, E. O.; Rachford, A. A.; Goeb, S. b.; Castellano, F. N. J.
Phys. Chem. A 2009, 113, 5763.
(89) Eryazici, I.; Moorefield, C. N.; Newkome, G. R. Chem. Rev.
2008, 108, 1834.
(90) Fleischauer, P. D.; Fleischauer, P. Chem. Rev. 1970, 70, 199.
K. J. Am. Chem. Soc. 2006, 128, 1531.
(55) Yamauchi, Y.; Fujita, M. Chem. Commun. 2010, 46.
(56) Zhao, Z.; Zheng, Y.-R.; Wang, M.; Pollock, J. B.; Stang, P. J.
Inorg. Chem. 2010, 49, 8653.
́
(91) Fornies, J.; Fuertes, S.; Martín, A.; Sicilia, V.; Lalinde, E.;
Moreno, M. T. Chem.Eur. J. 2006, 12, 8253.
(92) Goeb, S.; Prusakova, V.; Wang, X.; Vezinat, A.; Salle, M.;
Castellano, F. N. Chem. Commun. 2011, 47.
(57) Zheng, Y.-R.; Zhao, Z.; Wang, M.; Ghosh, K.; Pollock, J. B.;
Cook, T. R.; Stang, P. J. J. Am. Chem. Soc. 2010, 132, 16873.
(58) Wang, M.; Lan, W.-J.; Zheng, Y.-R.; Cook, T. R.; White, H. S.;
Stang, P. J. J. Am. Chem. Soc. 2011, 133, 10752.
(59) Zhao, D.; Tan, S.; Yuan, D.; Lu, W.; Rezenom, Y. H.; Jiang, H.;
Wang, L.-Q.; Zhou, H.-C. Adv. Mater. 2011, 23, 90.
(60) Fyles, T. M.; Tong, C. C. New J. Chem. 2007, 31.
(61) Hannon, M. J. Chem. Soc. Rev. 2007, 36.
(62) Hannon, M. J.; Moreno, V.; Prieto, M. J.; Moldrheim, E.;
Sletten, E.; Meistermann, I.; Isaac, C. J.; Sanders, K. J.; Rodger, A.
Angew. Chem., Int. Ed. 2001, 40, 879.
(63) Kieltyka, R.; Englebienne, P.; Fakhoury, J.; Autexier, C.;
Moitessier, N.; Sleiman, H. F. J. Am. Chem. Soc. 2008, 130, 10040.
(64) Ma, D.-L.; Che, C.-M.; Yan, S.-C. J. Am. Chem. Soc. 2009, 131,
1835.
(93) Ho, Y.-M.; Koo, C.-K.; Wong, K.-L.; Kong, H.-K.; Chan, C. T.-
L.; Kwok, W.-M.; Chow, C.-F.; Lam, M. H.-W.; Wong, W.-Y. Dalton
Trans. 2012, 41.
(94) Kui, S. C. F.; Hung, F.-F.; Lai, S.-L.; Yuen, M.-Y.; Kwok, C.-C.;
Low, K.-H.; Chui, S. S.-Y.; Che, C.-M. Chem.Eur. J. 2012, 18, 96.
(95) Lees, A. J. Chem. Rev. 1987, 87, 711.
(96) Pomestchenko, I. E.; Luman, C. R.; Hissler, M.; Ziessel, R.;
Castellano, F. N. Inorg. Chem. 2003, 42, 1394.
(97) Rausch, A. F.; Murphy, L.; Williams, J. A. G.; Yersin, H. Inorg.
Chem. 2011, 51, 312.
(98) Wang, Z.; Turner, E.; Mahoney, V.; Madakuni, S.; Groy, T.; Li,
J. Inorg. Chem. 2010, 49, 11276.
(99) Weinstein, J. A.; Tierney, M. T.; Davies, E. S.; Base, K.; Robeiro,
A. A.; Grinstaff, M. W. Inorg. Chem. 2006, 45, 4544.
(100) Wong, K. M.-C.; Yam, V. W.-W. Coord. Chem. Rev. 2007, 251,
2477.
(101) Yam, V. W.-W. Acc. Chem. Res. 2002, 35, 555.
(102) Zhao, G.-J.; Yu, F.; Zhang, M.-X.; Northrop, B. H.; Yang, H.;
Han, K.-L.; Stang, P. J. J. Phys. Chem. A 2011, 115, 6390.
(103) Zhao, G.-J.; Northrop, B. H.; Han, K.-L.; Stang, P. J. J. Phys.
Chem. A 2010, 114, 9007.
(104) Ghosh, S.; Mukherjee, P. S. Organometallics 2008, 27, 316.
(105) Zhao, G.-J.; Northrop, B. H.; Stang, P. J.; Han, K.-L. J. Phys.
Chem. A 2010, 114, 3418.
(106) Flynn, D. C.; Ramakrishna, G.; Yang, H.-B.; Northrop, B. H.;
Stang, P. J.; Goodson, T. J. Am. Chem. Soc. 2010, 132, 1348.
(107) Kaloudi-Chantzea, A.; Karakostas, N.; Raptopoulou, C. P.;
Psycharis, V.; Saridakis, E.; Griebel, J.; Hermann, R.; Pistolis, G. J. Am.
Chem. Soc. 2010, 132, 16327.
(108) Johnson, A. M.; Moshe, O.; Gamboa, A. S.; Langloss, B. W.;
Limtiaco, J. F. K.; Larive, C. K.; Hooley, R. J. Inorg. Chem. 2011, 50,
9430.
(109) Amoroso, A. J.; Thompson, A. M. W. C.; Maher, J. P.;
McCleverty, J. A.; Ward, M. D. Inorg. Chem. 1995, 34, 4828.
(110) Ghosh, K.; Hu, J.; Yang, H.-B.; Northrop, B. H.; White, H. S.;
Stang, P. J. J. Org. Chem. 2009, 74, 4828.
(65) Tashiro, S.; Tominaga, M.; Yamaguchi, Y.; Kato, K.; Fujita, M.
Angew. Chem., Int. Ed. 2006, 45, 241.
(66) Barry, N. P. E.; Edafe, F.; Dyson, P. J.; Therrien, B. Dalton
Trans. 2010, 39.
(67) Horcajada, P.; Gref, R.; Baati, T.; Allan, P. K.; Maurin, G.;
Couvreur, P.; Fer
1232.
(68) Mounir, M.; Lorenzo, J.; Ferrer, M.; Prieto, M. J.; Rossell, O.;
Aviles, F. X.; Moreno, V. J. Inorg. Biochem. 2007, 101, 660.
́
ey, G.; Morris, R. E.; Serre, C. Chem. Rev. 2012, 112,
̀
(69) Ang, W. H.; Grote, Z.; Scopelliti, R.; Juillerat-Jeanneret, L.;
Severin, K.; Dyson, P. J. J. Organomet. Chem. 2009, 694, 968.
(70) Barry, N. P. E.; Edafe, F.; Therrien, B. Dalton Trans. 2011, 40.
(71) Barry, N. P. E.; Zava, O.; Furrer, J.; Dyson, P. J.; Therrien, B.
Dalton Trans. 2010, 39.
(72) Linares, F. T.; Galindo, M. A.; Galli, S.; Romero, M. A.; Navarro,
J. A. R.; Barea, E. Inorg. Chem. 2009, 48, 7413.
(73) Therrien, B.; Suss-Fink, G.; Govindaswamy, P.; Renfrew, A. K.;
̈
Dyson, P. J. Angew. Chem., Int. Ed. 2008, 47, 3773.
(74) Vajpayee, V.; Song, Y. H.; Jung, Y. J.; Kang, S. C.; Kim, H.; Kim,
I. S.; Wang, M.; Cook, T. R.; Stang, P. J.; Chi, K.-W. Dalton Trans.
2012, 41, 3046.
(75) Vajpayee, V.; Song, Y. H.; Yang, Y. J.; Kang, S. C.; Kim, H.; Kim,
I. S.; Wang, M.; Stang, P. J.; Chi, K.-W. Organometallics 2011, 30,
3242.
(111) Zheng, Y.-R.; Northrop, B. H.; Yang, H.-B.; Zhao, L.; Stang, P.
J. J. Org. Chem. 2009, 74, 3554.
(76) Vajpayee, V.; Yang, Y. J.; Kang, S. C.; Kim, H.; Kim, I. S.; Wang,
M.; Stang, P. J.; Chi, K.-W. Chem. Commun. 2011, 47.
(77) Yi, J. W.; Barry, N. P. E.; Furrer, M. A.; Zava, O.; Dyson, P. J.;
Therrien, B.; Kim, B. H. Bioconjugate Chem. 2012, 23, 461.
(78) Zava, O.; Mattsson, J.; Therrien, B.; Dyson, P. J. Chem.Eur. J.
2010, 16, 1428.
(112) Zheng, Y.-R.; Stang, P. J. J. Am. Chem. Soc. 2009, 131, 3487.
(113) Knee, J. L.; Johnson, P. M. J. Chem. Phys. 1984, 80, 13.
(114) Ruckert, I.; Demeter, A.; Morawski, O.; Kuhnle, W.; Tauer, E.;
̈
̈
Zachariasse, K. A. J. Phys. Chem. A 1999, 103, 1958.
(115) Scheps, R.; Florida, D.; Rice, S. A. J. Chem. Phys. 1974, 61,
1730.
M
dx.doi.org/10.1021/ja3036515 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
(116) Yang, J.-S. PATAI’S Chemical Functional Groups; John Wiley &
Sons, Ltd.: New York, 2009.
(117) Lewis, F. D.; Hougland, J. L.; Markarian, S. A. J. Phys. Chem. A
2000, 104, 3261.
(118) Substituent Constants for Correlation Analysis in Chemistry and
Biology; Hansch, C. L. A., Ed.; Wiley-Interscience: New York, 1979.
(119) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(120) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(121) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972,
56, 2257.
(122) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
(123) Frisch, M. J.; G. W. T., Schlegel, H. B.; Scuseria, G. E.; ,; Robb,
M. A.; J. R. C., Scalmani, G.; Barone, V.; Mennucci, B.; ,; Petersson, G.
A.; H. N., Caricato, M.; Li, X.; Hratchian, H. P.; ,; Izmaylov, A. F.; J. B.,
Zheng, G.; Sonnenberg, J. L.; Hada, M.; ,; Ehara, M.; K. T., Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; ,; Honda, Y.; O. K., Nakai, H.;
Vreven, T.; Montgomery, J. A.; , Jr.,; J. E. Peralta, F. O., Bearpark, M.;
Heyd, J. J.; Brothers, E.; ,; K. N. Kudin, V. N. S., Keith, T.; Kobayashi,
R.; Normand, J.; ,; Raghavachari, K.; A. R., Burant, J. C.; Iyengar, S. S.;
Tomasi, J.; ,; Cossi, M.; N. R., Millam, J. M.; Klene, M.; Knox, J. E.;
Cross, J. B.; ,; Bakken, V.; C.A., Jaramillo, J.; Gomperts, R.; Stratmann,
R. E.; ,; Yazyev, O.; A. J. A., Cammi, R.; Pomelli, C.; Ochterski, J. W.; ,;
R. L. Martin, K. M., Zakrzewski, V. G.; Voth, G. A.; ,; Salvador, P.; J. J.
D., Dapprich, S.; Daniels, A. D.; Farkas, O.; J. B. F., Ortiz, J. V.;
Cioslowski, J.; ,; Fox, D. J. Gaussian; Gaussian, Inc.: Wallingford, CT,
2010.
(124) Chimenti, F.; Bolasco, A.; Secci, D.; Chimenti, P.; Granese, A.
Synth. Commun. 2004, 34, 2549.
(125) Kryschenko, Y. K.; Seidel, S. R.; Arif, A. M.; Stang, P. J. J. Am.
Chem. Soc. 2003, 125, 5193.
N
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