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Self-assembly of metal–organic hybrid
nanoscopic rectangles
Sushobhan Ghosh and Partha Sarathi Mukherjee*
Department of Inorganic & Physical Chemistry, Indian Institute of Science,
Bangalore, 560012, India
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Introduction (Ⅰ)
- Self-assembly of nanoscopic assemblies of finite shape by a directional bonding approach
has received special attention by chemists since the discovery of the metallasupramolecular
square in 1990. (a) F. A. Cotton, C. Lin and C. A. Murillo, Acc. Chem. Res., 2001, 34, 759; (b) S. Leininger, B. Olenyuk and P. J. Stang, Chem. Rev., 2000, 100, 853;]
- Square planar Pd(II) and Pt(II) have long been among the favourite metal ions.
- Rectangles needs a speial kind of “clip” type ligand.
M. Bala, P. Thanasekaran, T. Rajendran, R. T. Liao, Y. H. Liu, G. H. Lee, S. M.
Peng, S. Rajagopal and K. L. Lu, Inorg. Chem., 2003, 42, 4795 and references therein
- Amide functionality has proved to useful in self-assembly through hydrogen bonding.
-The self-assembly of a non-symmetric donor with a suitable Pt(II) linker would afford self
selection for a single isomer.
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Introduction (Ⅱ)
< Scheme 1 Self-assembly of rectangle-1 and its alternative isomeric product rectangle-1a >
- Rectangle-1 represents the first example of a Pt(II) based molecular rectangle with amide
functionality
- An example of such a kind of self-assembled geometry can be found in the synthesis of
truncated tetrahedra S.Lelinger, J. Fan, M. Schmitz and P. J. Stang, Proc. Natl. Acad. Sci. USA, 2000, 97, 1380
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Introduction (Ⅲ)
< Scheme 2 Self-assembly of rectangle-2 and its polymeric analogue >
- The use of a purely organic “clip”(clip-2) in conjunction with a metal based linear
acceptor (L2) to obtain a new molecular rectangle (rectangle-2) of Pd(II).
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Experimental
- Synthesis of 1,8-bis[trans-Pt(PEt3)2(NO3)]anthracene (clip-1)
Charged under nitrogen with 1,8-dichloroanthracene (1.0 mmmol) + Pt(PE3)4 (2.5 mmol)
Toluene (40 ml) was added and resulting solution was stirred for 24 h at 110 ℃ in an oil bath
The solvent was removed in vacuo and the residue was stirred with hot methanol (10 mL)
Light yellow microcrystalline 1,8-bis[trans-Pt(PEt3)2Cl]anthracene was obtained upon cooling in a refrigerator for 2 h.
1,8-bis[trans-Pt(PEt3)2Cl]anthracene (0.30 mmol) in acetone (20 mL), was added AgNO3 (0.60 mmol)
The reaction was stirred overnight in the dark, the mixture was filtered through a bed of Celite to remove AgCl
The crude product was taken up in 5 mL of hot ethanol and filtered
The hot filtrate was kept in the refrigerator overnight to obtain yellow microcrystalline pure 1,8-bis[trans- Pt(PEt3)2(NO3)]anthracene (clip-1)
Yield = 85%
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Experimental
- Synthesis of trans-(PEt3)2Pd(CF3SO3)2 (L2)
To a stirred solution of Pd(COD)Cl2 [1 mmol] in dry degassed dichloromethane (20 ml), 1M solution of PEt3 [2 mmol] in THF was added
This solution was stirred for another 2 h and then the solvent was completely removed under vacuum
It was further kept under vacuum for another 3 h to remove all the volatiles, and trans-(PEt3)2PdCl2 was isolated as a greenish
yellow solid. Yield = 88%
Pd(PEt3)2Cl2 [0.39 mmol] in dry degassed dichloromethane (20 ml) silver triflate [0.80 mmol] was
added and the mixture was stirred for 12 h under nitrogen
The white solid was filtered through Celite and the filtrate was concentrated to 2 mL
Diethyl ether was added to the concentrated filtrate to isolate the product as a white precipitate
Yield = 90%
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Experimental
- Synthesis of rectangle-1
To a 3-mL acetone solution containing 11.6 mg (0.010 mmol) of 1,8-bis[trans-Pt(PEt3)2(NO3)]anthracene (clip-1)
Methanol solution of 2.00 mg (2 mL) of L1 (0.01 mmol) was added dropwise with continuous stirring (5 min)
The light yellow solution was stirred for another 30 min
Yield = 82.7%
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Experimental
- Synthesis of rectangle-2
To a 2-mL dichloromethane solution containing 12.8 mg (0.02 mmol) of trans-[(PEt3)2Pd(CF3SO3)2] (L2)
Dichloromethane solution of 7.6 mg (2 mL) of clip-2 (0.02 mmol) was added dropwise with continuous stirring (1 h).
The orange– yellow solution was stirred for another 30 min
The product was isolated as microcrystals upon diffusing ether into the solution of the product
Yield = 80.5%
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Results and discussion
1H
NMR(CDCl3,300 MHz)
:10.89 (s broad, 2H, CO–NH)
:9.65 (s, 2H, H9)
:9.34 (d, 4H, Hα-Py)
:9.28 (d, 4H, Hα -Py)
:8.81 (d, 4H, Hβ-Py)
:8.73 (d, 4H,H β-Py)
:8.23 (s, 2H, H10)
:7.77 (d, 4H, H4,5)
:7.01 (m, 4H, H3,6)
:1.57 (m, 48H, PCH2CH3)
:1.01 (m, 72H, PCH2CH3)
- 1H NMR spectrum
1H
NMR(acetone-d6, 300 MHz)
9.51 (s, 1H)
8.22 (s, 1H)
7.62 (m,4H)
7.15 (m, 2H)
1.65 (m, 24H)
1.03 (m, 36H)
< clip-1 >
<1H NMR of rectancle-1>
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Results and discussion
- 1H NMR spectrum
1H
NMR (CD3 OD, 300 MHz)
:9.12(2H, s,anthracene H9)
:8.85 (8H, d, Py- α)
:8.35 (4H, d, anthracene H2,7)
:7.99 (4H, d, anthracene H3,6)
:7.6–7.9 (14H, m, anthraceneH4,5,10and Py- β)
:2.24 (24H, q, CH2-ethyl)
:1.5 (36H, CH3-ethyl)
1HNMR(CDCl
3,
300 MHz)
1.49 (m,12H, PCH2CH3)
1.04 (m,18H, PCH2CH3)
< L2 >
<1H NMR of rectancle-2>
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Results and discussion
- 31P NMR spectrum of rectancle-1
-The upfield shift of the signals near 5 ppm relative to the clip indicated ligand to Pt coordination
-The 31P NMR data are insufficient for distinguishing the product rectangle-1 from its isomeric relative
rectangle-1a
- It has only one type of H9 and H10 anthracene proton nuclei, while isomer rectangle-1a has two types
- 31P NMR spectrum of rectancle-2
- An upfield shift of 10 ppm of the phosphorus peak and the appearance
of a single peak in the 31P NMRspectrum indicated the formation of a
single product
- Shifts for the proton signals were also found as usual due to complex
formation
<31P NMR of rectancle-2>
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Results and discussion
- Structure analysis
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Results and discussion
- Structure analysis
- C(1)–Pt(1)–P(2) angle of 90.2(4)◦
- N(1)–Pt(1)–P(2) of 90.5(3)◦
- P(1)–Pt(1)–P(2) angle of 170.15(17)◦
- C(1)–Pt(1)–N(1) angle of 179.3(5)◦
- py-N(1)-py-N(3) rings =38.8(8)◦,
- py-N(1)-py- N(3a) rings = 40.8(8)◦
- The coordination planes [N(1)–C(1)–P(1)–P(2)] and [N(3)–
C(11)–P(3)–P(4)] present slight tetrahedral distortions
< Fig. 1 ORTEP (30% probability) of the centrosymmetric rectangle-1>
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Results and discussion
- Structure analysis
<Fig. 2 Packing diagram of rectangle-1>
- The rectangles are packed in layers, which form long channels of rectangular shape of approximately 16.5 A˚
diameter
- The data set was consistent with the formation of a 2 + 2 rectangle and proper connectivity of the linkers was
also established by NMR and ESI
-Each rectangular ensemble hosted a pair of disordered nitrate anions through strong hydrogen bonding
by two amide N–H protons
- Amide functionality is a potential H-bond donor as well as acceptor
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Results and discussion
- ESI mass spectroscopy
< Scheme 2 Self-assembly of rectangle-2 >
- ESI confirmed the M2L2 composition [M= (PEt3)2Pd(OTf)2] for rectangle-2 with a molecular weight of 2043.0
Da despite the possibility of forming 1D chains
- ESI-mass spectrum of rectangle-2 showed a signal corresponding to the consecutive loss of triflate
counterions, [M–3CF3SO3]3+ and [M–4CF3SO3]4+
- The MM2 energy minimized calculation yielded a rectangular shape with an internal length and width
of 18.76A˚ and 4.5A˚
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Conclusion
-The first nanoscopic Pt(II) based molecular rectangle incorporating amide functionality using a
linear non- symmetric amide containing a bridging ligand
- Despite the possibility of forming multiple products L1 prefers to self-assemble predominantly
into one isomeric species
- Pd(II) based molecular rectangle was prepared using a rigid organic clip (clip-2) and a Pd(II)
containing linear acceptor trans-(Et3P)2Pd(OTf)2
- Rectangle-2 is the first Pd(II) based rectangle prepared via a directional bonding approach
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Functionalized Hydrophobic and Hydrophilic
Self-Assembled Supramolecular Rectangles
Seul- A Park
Advanced instrumental analysis lab
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▣ Self-assembly
- A process ubiquitous throughout nature and can account for much of the elegant and complex functionality of
biological systems.
- Recently, self-assembly has been shown to play an important role in the development of molecular materials and
in the “bottom-up” approach to nanofabrication.
- Coordination-driven transition-metal-mediated self-assembly involving dative metal-ligand bonding has become a
widely employed, robust means of preparing supramolecular polygons and polyhedra with promising electronic,
catalytic, photophysical, and/or redox properties.
- Self-assembled metal-organic structures has recently been a drive to incorporate many different functional
moieties into their component building blocks.
- These functionalized building blocks are then brought together and precisely positioned upon spontaneous selfassembly with appropriately designed complementary components.
- This process has been utilized to prepare, for example, discrete supramolecular metal-organic assemblies
functionalized with crown ethers, carboranes, optical sensors, saccharides, photoactive perylene diimide and
azobenzenes, and polymerizable methyl methacrylate units that have been distributed on their periphery, within
building blocks, and also, in some cases, within interior cavities.
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- Building upon molecular self-assembly, self-organization is a process by which molecules, often structures
such as dual character block copolymers and the like, are able to arrange into well-defined configurations in
different media.
- Self-organization can take place: on surfaces, leading to well-ordered self-assembled monolayers; in solution,
giving rise to mycelles, vesicles, cylinders, spheres, etc.; and, using Langmuir-Blodgett techniques, at the airwater interface.
- There have only recently been examples where both self-assembly and self-organization involving
metallacycles have been utilized, with the combination allowing for relatively facile and spontaneous
formation of arrays and assemblies of great complexity.
- Recent studies have demonstrated higher order assembly in the self-organization of supramolecular
polyhedra and polygons on Au(111) and/or HOPG surfaces.
- With these recent advances in mind, we have endeavored to endow a Known supramolecular metallacycle
with both hydrophobic as well as hydrophilic functionalities of varying length.
- Such structures may then be able to undergo higher order self-organization in a variety of ways, resulting in
control over the arrangement and distribution of these very important metallacycles.
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▣ Synthesis of the 180° Functionalized Donors
-New linear hydrophobic and hydrophilic donor units of varying size were synthesized according to a
divergent approach utilizing 3,6-diiodobenzene-1,2-diol
-as their core, as shown in Scheme 1.
Hydrophobic 3,6-diiodobenzenes 2-4 were prepared by deprotonation of diol 1 and subsequent nucleophilic
attack on 1-bromohexane, 1-bromododecane, and 1-bromooctadecane, respectively, in 85-96% yield.
- Hydrophilic analogues 5-7 were similarly prepared through a reaction of 1 with monomethylated and
bromo-terminated derivatives of diethylene glycol, tetraethylene glycol, and hexaethylene glycol, respectively,
in 91-98% yield.
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Hydrophobic doner
Hydrophilic doner
- Sonogashira coupling (Scheme 2)
hydrophobic and hydrophilic diiodibenzenes with 4-ethynylpyridine using Pd(PPh3)2Cl2.
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SCHEME 3. Coordination-Driven Self-Assembly of (a) Hydrophobic
- With this series of new functionalized linear donors at hand, the self-assembly of hydrophobic supramolecular
rectangles was performed.
- Heating donors 8-10 with the molecular “clip”(Scheme 3a) in a 1:1 stoichiometric ratio in a 1.7:1 (v/v) solution of
CD3COCD3/ D2O at 55-60 °C for 18 h gave homogeneous orange solutions.
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1H
NMR
Shift downfied by 0.5-0.54ppm
0.71-0.79 ppm
FIGURE 1. Representative 1H NMR Spectra (300 MHz, 298k, CD3COCD3) of the aromatic protion of the (a)
molecular clip (b) hydrophobic molecular C18 Rectangle 16, (c) and hydrophobic C18 donor 10 displaying the
characteristic shift of proton signals associated with the donor ans acceptor units upon coordination as well as
This result is consistent with previous studies involving similar rectangles and indicates that
free rotation of the donor pyridines is slow on the NMR time scale if not stopped altogether.
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31P
NMR
- Hydrophobic rectangle16 revealed a single,
sharp peak at 8.63 ppm
, upfield shifted from the molecular clip by
nearly 6 ppm
back-donation from the platinum atoms.
- Back-donation was also observed by the
decrease in coupling of the flanking 195Pt
satellite peaks ∆J =187 Hz for 16.
FIGURE 1. (d) The 31P {1H} NMR spectra of the selfassembled C18 Rectangle 16 and (e) molecular clip.
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SCHEME 3. Coordination-Driven Self-Assembly of (b) Hydrophilic (17-19) Supramolecular Rectangles
- Hydrophilic supramolecular rectangles 17-19 (Scheme 3b) were similarly prepared and analyzed.
Heating donors 11-13 with the molecular clip in a 1:1 stoichiometric ratio in a 1.2:1 (v/v) CD3COCD3/D2O
solution at 55-60 °C for 18 h gave homogeneous orange solutions
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1H
NMR
Shift downfied by 0.5-0.54ppm
↔0.5-0.6ppm
0.71-0.79 ppm
↔ 0.72-0.83 ppm
- Following counterion exchange to their hexafluorophosphate salts (96-97% isolated yield), multinuclear (1H and
31P) NMR spectroscopic studies indicated the presence of highly symmetric species.
- As with rectangles 14-16, the α - and β -pyridyl hydrogen atoms of hydrophilic rectangles were downfield shifted
relative to donors 11-13 by 0.5-0.6 and 0.72-0.83 ppm, respectively.
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31P NMR
DEG rectangle 17.
TEG rectangle 18.
HEG rectangle 19.
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ESI-MS
(Hydrophobic)
- Peaks were found at m/z 1664.4, 1832.5, and 1285.5, corresponding to [M - 2PF6]2+of 14, [M - 2PF6]2+ of 15,
and [M- 3PF6]3+ of 16, where M represents the fully intact supramolecular assemblies.
- Their isotopic distributions are in excellent agreement with the theoretical distributions.
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ESI-MS
(Hydrophilic)
- m/z 1700.1, 1876.6, 2052.6 corresponding to [M-2PF6]2+ of 17-19, respectively.
∴These mass spectral results, together with the multinuclear NMR studies, confirm the selfassembly
of both
hydrophobic
as well
hydrophilic
supramolecular
rectangles.
- Again, their
isotopic
distributions
are inasexcellent
agreement
with the theoretical
distributions.
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Molecular Force Field Modeling
- In every case,
the most favored conformer was predicted to be the
one where the hydrophobic or hydrophilic “arms” of
rectangles 14-19 intertwine or wrap around each
other.
- This result is most prominently observed (Figure 4a)
for rectangles 16 and 19, which possess the longest
chains (C18 and hexaethylene glycol, respectively).
FIGURE 4. Computed global minimum
(“Relaxed”) (a) and fully stretched (“Elongated”)
- It is important to note, however, that torsional
rotation about the many C-C and C-O bonds that
make up the hydrophobic and hydrophilic arms
requires very little energy and there are many
similar conformations within only a few kilocalories
per mole of the found global minimum.
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Molecular Force Field Modeling
- To better gauge the differences in size across the series of rectangles, a second set of calculations
was performed with their hydrophobic or hydrophilic arms fully elongated (MMFF force field,
solvent model for octanol).
These subsequent calculations revealed that the size of hydropobic rectangles ranged
from ~2.84-5.88nm and ~2.94-5.93nm for the hydrophilic rectangles. U Li S Au N
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- A series of new hydrophobic and hydrophilic 180° donor compounds have been
prepared and successfully utilized in the self-assembly of hydrophobic and hydrophilic
supramolecular rectangles of varying sizes.
- Each rectangle is self-assembled in nearly quantitative yield despite the presence of
long alkyl or polyethylene glycol chains present on the donor units.
- All six supramolecular rectangles have been characterized by multinuclear NMR and
ESI mass spectronometry.
- These hydrophobic and hydrophilic rectangles represent an important addition to the
now growing class of functionalized metallacyclic assemblies as their pendant chains
will likely promote their self-organization in solution, at the air-water interface, and on
a variety of Surfaces.
- Such higher order assembly allows for greater control over the size, shape,
orientation, and distribution of the underlying metallacycles in a variety of
environments.
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Self-Recognition in the Coordination Driv
en Self-Assembly of 2-D Polygons
Seo Ga Yeong
University Of Ulsan
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The preparation of numerous, discrete 2- and 3-D supramolecular
complexes via coordination-driven self-assembly has been achieved in the
past decade. This was often accomplished by the combination of an organic
donor with a metal acceptor, where one or both reagents possessed welldefined bonding directionality leading to a single, highly symmetrical product.
A more complex situation in self-assembly arises when more than two
starting materials are mixed together in one vessel. Will an ordered system of
discrete supramolecules or an oligomeric product mixture result? To date
many of the systems reported have been 3-D in nature. They generally
contain building blocks which are more restricted in bonding directionality
and/or flexibility (relative to 2-D ensembles), lessening the likelihood of
openchained products. Herein, we report on our own self-recognition
observations in the self-assembly of 2-D supramolecular polygons from
4,4’-dipyridyl and mixtures of organoplatinum acceptors [Scheme 1].
Despite the possibility for open chain oligomers, we demonstrate that closed
macrocycles containing one type of organoplatinum material are strongly
preferred.
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•
Scheme 1. Combination of
Organoplatinum Linkers 1-3
with 4,4’-bipyridine 4 Leads
to Discrete Polygons 5-7
Table 1. Building Block
Combinations and Their
Respective Products
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• Figure 1. 31P{1H} (left) and 1H (center and right) NMR spectra
recorded at various time intervals during the formation of
rectangle 5 and triangle 6.
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Rectangle
Square
•
Figure S1.
31P{1H}
The 31P{1H} spectrum
[Figure S1] displays two
large peaks at 8.31 ppm(5)
and 1.59 ppm (7).
NMR of 5 and 7 after 124 hours heat.
In the 1H spectrum [Figure
S2], well-defined sets of
resonances for 5 and 7 are
observed among minor
amounts of impurity in the
aromatic region.
Figure S2. 1H NMR of 5 and 7 after 124 hours heat.
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•
square
Figure S4. 31P{1H} NMR of
6 and 7(1.56ppm) after
121 hours heat.
Figure S5. 1H NMR of 6 and
7 after 121hours heat.
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•
Figure S3. ESIMS of 5 and 7.
•The mass spectrum [Figure S3] exhibits peaks corresponding to the
consecutive loss of PF6- ions from 5: m/z 2824.1 [5 - PF6-]+ , m/z 1340.1 [5 2PF6-]2+ , and m/z 844.9 [5 - 3PF6-]3+ . Evidence for square 7 is shown by a
weaker, but isotopically resolved, peak at m/z 1024.8 assigned to [7 - 3PF6-]3+
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•
Rectangle
Figure S7. 31P{1H} NMR of
5-7 after 135 hours heat.
5(8.51ppm),7(1.45ppm)
Square
Figure S8. 1H NMR of 5-7 after
135hours heat.
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Figure S9. ESIMS of 5-7.
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Conclusion
In all cases, the NMR data are consistent with that reported previously for 5,21
6,22 and the triflate salt of 7.23 However, extended reaction times (121-135 h)
are necessary in our experiments to reduce the number of products. These are
much longer than those required for the individual assemblies (up to 15 h).
Indeed, after several hours we observe 5-7 in conjunction with other unknown
species. Prolonged heating always simplified the NMR spectra. Apparently, our
systems are able to self-correct themselves to produce the thermodynamically
most stable macrocycles 5-7, although sometimes small amounts of mixed
ligand species remained. In conclusion, we have demonstrated that mixtures of
two or three organoplatinum reagents 1-3 and 4,4’-dipyridyl 4 undergo selfrecognition to give discrete polygons 5-7 as the dominant products.
(21) Kuehl, C. J.; Huang, S. D.; Stang, P. J. J. Am. Chem. Soc. 2001, 123, 9634.
(22) Kryschenko, Y. K.; Seidel, S. R.; Arif, A. M.; Stang, P. J. J. Am. Chem. Soc. 2003, 125, 5193.
(23) Stang, P. J.; Cao, D. H.; Saito, S.; Arif, A. M. J. Am. Chem. Soc. 1995, 117, 6273.
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Self-assembly of Neutral Platinum-Based
Supramolecular Ensembles Incorporating
Oxocarbon Dianions and Oxalate
Lee Kyoung-Eun
University Of Ulsan
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•squarate(C4O42-) and croconate (C5O52-), has been thoroughly
investigated and compared with that of oxalate (C2O42-) for their
planar stereochemistry, oxygen donor atoms, and identical overall
charge.
•Self-assembled platinum(II)-based neutral and finite supramolecular
macrocycles incorporating these interesting functional oxocarbon
dianions, as well as their acyclic analogue, the oxalate moiety.
contain more than two oxygen atoms in different directions, all of
which are capable of coordination to the metal centers.
*reference. Inorganic Chemistry, Vol. 44, No. 20, 2005
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<Synthesis>
Addition of an aqueous solution of linkers 3-5 to an acetone solution of
diplatinum clip 1 in a 1:1 molar ratio resulted in immediate precipitation of the
neutral assemblies 6-8, respectively, in 90-98% isolated yields.
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<X-ray structure>
The molecular rectangle (6) itself is also severely twisted from planarity;
the twist angle between the two anthracene moieties is 39°.
*reference. (2k) Kuehl,C. J.; Huang, S. D.; Stang, P. J J. Am. Chem. Soc. 2001, 123, 9634.
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Crystal structure analyses reveal that the main molecule of 7 is sitting on an
inversion center and that of 8 is sitting on a 2-fold axis.
Both the squarate and croconate groups are essentially planar. The twist angles
between the anthracene moieties are 0° and 1°, and the torsion angles between
the two Pt-C bonds in an anthracene moiety are 7° and 8.9° in 7 and 8,
respectively.
*Reference. (9)Konar, S.; Corbella, M.; Zangrando, E.; Ribas, J.;Chaudhuri, N. R. Chem. Commun. 2003, 1424.
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31P
195pt
31P{1H}
NMR
195pt
NMR (CDCl3, 121.4 MHz): δ13.20 (s, 1JPPt ) 2889 Hz).
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31P
195pt
31P{1H}
NMR
195pt
NMR (CDCl3, 121.4MHz): δ 12.59 (s, 1JPPt ) 2870 Hz).
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31P
NMR
195pt
31P{1H}
195pt
NMR (CDCl3, 121.4MHz): δ 10.95 (s, 1JPPt ) 2922 Hz).
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Conclusion
The formation of discrete platinum-based metallacycles
incorporating flexidentate oxocarbon dianions and oxalate by selfassembly are described. The assembly formed by the oxalate and
clip is the first example of a severely twisted rectangle. The
molecular “clip” were designed in such a way that only the weakly
coordinated nitrate anion can be replaced by the oxygen or nitrogen
donor linkers. Therefore the oxalate and croconate ions were
dictated by the requirement of Pt-based acceptor units to act in a
bismonodentate fashion.
*reference. Inorganic Chemistry, Vol. 44, No. 20, 2005
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Synthesis of a Bis(pyridyl)-Substituted Perylene Diimide
Ligand and Incorporation into a Supramolecular
Rhomboid and Rectangle via Coordination Driven
Self-Assembly
Song HyeYeong
University Of Ulsan
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•Coordination-driven transition-metal-mediated self-assembly of discrete structures
is now a well-established field.
•Recent efforts have focused on incorporating functionality into the final assembly.
•This desire to incorporate functional ligands into supramolecular structures led us
to investigate perylene diimide based dyes.
•Application-oriented areas : laser dyes and fluorescent light collectors,
semiconducting electronic materials, organic field effect transistors, and
photovoltaics.
•Reported several molecular squares containing simple perylene diimide precursors.
•Further investigation into these materials is highly warranted as it may reveal novel
electronic and optical properties not present in the starting material.
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Synthesis of Perylene Diimide 5
① 1(1,6,7,12-tetrachloro-3,4,9,10tetracarboxylic acid dianhydride) +
4-bromo-2,6-dimethylaniline in
propionic acid
② 2(in 71% yield) +
4-(tert-octyl)phenol in 1-methyl-2pyrrolidinone
③ 3(in 80% yield) +
triisopropylsilylacetylene in the
presence of Pd(Ⅱ)/CuI catalysts+
tetrabutylammonium fluoride
④ 4(in 85% yield)+ 4-iodopyridine
⑤ ligand 5 (in 78% yield)
Scheme 1. Synthesis of Perylene Diimide 5
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Self-Assembly of Rhomboid 6 and
Rectangle 7
• Rhomboid 6 was prepared by
combining ligand 5 with
cis-(PMe3)2Pt(Otf)2 8 in a 1:1 ratio in
acetone-d6 at room temperature for 20h
• Rectangle 7 required heating an
aqueous actone-d6 solution of 5 and
clip 9 for 12h.
The product was isolated as the
hexafluorophosphate salt after anion
exchange with KPF6.
Scheme 2. Self-Assembly of Rhomboid 6 and Rectangle 7
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31P
31
P NMR
-27.8 ppm, singlet
195
1
Pt satellites
JPt-P = 3170Hz
•-28ppm due to 6 shifted approximately
8 ppm upfield relative to 8
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1H
1
α-pyidyl
hydrogen
*
H NMR
9.25 ppm
br s, 8H
8.12 ppm
s, 8H
7.81 ppm
d, 8H
7.43 ppm
m, 24H
7.03 ppm
d, 16H
2.13 ppm
s, 24H
1.79 ppm
m, 52H
1.38 ppm
s, 48H
0.77 ppm
s, 72H
Figure S2. 1H NMR spectrum of 6.
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Figure S3. ESIMS spectrum of 6.
A few minor(<5%) byproducts were also formed. Evidence for the 2+2 stoichiometry
was provided by ESIMS. Isotopically resolved peaks centered at m/z 1359.9 and 982.8
were assigned to [6-3OTf-]3+ and [6-4OTf-]4+, respectively.
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31P
31
P NMR
8.96 ppm, singlet
195
1
Pt satellites
JPt-P = 2636Hz
•In the 31P spectrum rectangle 7 gave rise to a singlet 9ppm
with concomitant platinum satellites.
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1H
1
Figure S5. 1H NMR spectrum of 7.
H NMR
9.50 ppm
s, 2H
9.22 ppm
d, 4H
9.10 ppm
d, 4H
8.53 ppm
s, 2H
8.27-7.85 pp
m, 24H
m
7.48 ppm
s, 8H
7.36 ppm
d, 16H
7.26 ppm
t, 4H
6.88 ppm
d, 16H
2.09 ppm
s, 24H
1.77 ppm
s, 16H
1.63 ppm
br s, 48H
1.37 ppm
s, 48H
1.01 ppm
m, 72H
0.77 ppm
s, 72H
•Inequivalent α-pyridine and β-pyridine hydrogens were in
the 1H spectrum, in line with other related rectangles.
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Figure S6. ESIMS spectrum of 7.
In the ESI mass spectrum of the nitrate salt partially resolved signals for [7-3NO3]3+ m/z
1791.9 and [7-4NO3]4+ m/z 1328.5 (base peak) added support to the structure.
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*
is presented starting
materials 5
*
*
*
*
*
*
*
is presented an
anthracene-based
absorption at 268ppm
Fig 1. UV/vis spectra of 5,6,7 and 9 in CH2Cl2.
*is presented π-π* transition of 5 at 288 and 304nm are red-shifted in 6,7 by
30nm as electronic reorganization near the metal sites occurs upon macrocycle
formation
Ref. : (22) Wurthner, F.; Sautter, A. Org. Biomol. Chem. 2003, 1, 240. (23) You, C.-C.; Wu¨ rthner, F. J. Am. Chem. Soc. 2003, 125, 9716.
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•Distance between the Pt atoms is
35.7Å
•Center of the cavity is 7.6Å
Fig 2. Space-filling models of 6 and 7 optimized with the MM2
force-field simulation.
Key: C, N, O, P, Pt. Hydrogens are omitted for clarity.
•Distance between the Pt atoms is
45.9Å
•Center of the cavity is 11.4Å
Ref: (28) CS ChemBats3D Ultra 7.0.0; CambridgeSoft Corp., 2000.
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Inorganic Chemistry, Vol. 41, No. 7, 2002. 1862-1869
Received September 25, 2001
Organometallics, 2009, 28, 2799–2807
Received November 25, 2008
Organic Synthesis Lab
Young-Hwa Choi
Department of Chemistry, University of Ulsan
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• The synthesis of highly ordered supramolecular architectures is of
considerable chemical and structural interest.
• These molecular architectures are typically formed via the self
assembly of simple building blocks.
• Comparing the well-established supramolecular chemistry of late
transition metals with early transition metals, only a few attempts
have been made to adopt the reducing attributes and well-defined
coordination behavior of early transition metals.
• The aim of forming molecular squares and rectangles requires nearly
90° angles at the vertices.
• This is typically available in octahedral or square-planar late
transition metal compounds.
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 Chart 1
• Since 4,4′-azopyridine (8) is well known for its effective bridging
coordination mode, we coupled this structural capability with lowvalent titanocene fragments.
• Generally, azopyridines exhibit two general coordination sites
involving the nitrogen atoms.
• The pyridyl moieties represent the coordination mode A (Chart 1),
and the nitrogen atoms of the azo bridge the coordination mode B
(Chart 1).
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 Scheme 1
• The 4,4′-azobispyridine ligand(8) is efficiently prepared by
oxidative coupling of 4-aminopyridine (9).
• The crude product shows a trans/cis ratio of 4,4′azobispyridine (8) of 37:1 determined by integration of 1H
NMR signals.
• After column chromatography on silica gel, pure red-colored
trans-4,4′-azobispyridine (8) is obtained in 77% yield.
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 Scheme 2
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• The reaction of [Cp*2Ti(η2-C2(TMS)2)] (2) with trans-4,4′-azobispyridine
(8) in benzene is accompanied after 12 h by a color change from orange
to black.
• Within this period of time black crystals of 10, suitable for X-ray analysis,
were obtained directly from the reaction solution in yields of 41%
(170 °C).
• The related complex 11 was obtained from reacting 3 with 8 in THF.
• The color of the reaction solution also became black during the course of
the reaction.
• Black crystals suitable for X-ray analysis are grown within several days at
60 °C from a THF/n-hexane mixture.
• Complex 11 can be obtained in yields of 51% (150°C).
• During the formation of 10 and 11 the azopyridine 8 undergoes a similar
trans to cis rearrangement.
• The resulting tetranuclear complexes 10 and 11 carry exclusively cis-4,4′azobispyridine (8).
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 Figure 1
 Figure 2
•
•
•
•
The molecular structure of 10 is shown in
Figure 1.
The four Ti atoms of 10 adopt a
pseudotetrahedral geometry.
Two metal atoms are aligned by the pyridyl
rings of the 4,4′-azobispyridine ligands (8).
As shown in Figure 2 the titanium atoms
are almost located in one plane, and
therefore complex 10 forms an almost
perfect square with bent titanocene moieties
as corner units.
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 Figure 3
 Figure 4
• The molecular structure of 11 is
shown in Figure 3.
• The molecular square 11 is equally
configured as 10.
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 Figure 5
1H NMR spectrum of 10 recorded
from the reaction of 2 with 8 in
toluene-d8, measured at 214 K.
# solvent signals, * C2(Si(CH3)3)2
(high intensity), traces of silicon
grease (low).
•
•
•
By following the reaction progress for the formation of 10 with 1H NMR
measurements at 214 K in toluene-d8, the release of the acetylene ligand can be
detected immediately.
In this regard, four high-field-shifted signals at 8.57, 8.52, 6.09, and 5.73 ppm are
assigned to the protons of the pyridyl rings.
The downfield singlets at 1.86 and 1.47 ppm arise from the permethylated
titanocene units, reflecting their different coordination environments.
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 Scheme 3
(AZP) 4,4’-azopyridine
(BPE) 1,2-bis(4-pyridyl)ethylene
(dppf) 1,1’-bis(diphenylphosphino)ferrocene
(OTf) trifluoromethanesulfonate anion)
•
•
•
Schemes 3 and 4 illustrate the procedures used for preparation of the macrocyclic squares 5-12.
Tetranuclear squares 5, 7, 8, and 10 were prepared from self-assembly of trans corner components
fac-BrRe(CO)3(trans-AZP)2 or fac-BrRe(CO)3(trans-BPE)2 and (dppf)M(O2H)2(OTf)2 (M＝Pd or
Pt) in CH2Cl2.
Dinuclear squares 6 and 9 were prepared by self-assembly of the cis corner components facBrRe(CO)3(cis-AZP)2 or fac-BrRe(CO)3(cis-BPE)2 and (dppf)Pd(O2H)2(OTf)2 in CH2-Cl2.
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 Scheme 4
•
•
•
 Scheme 5
Squares 11 and 12 were prepared by self-assembly of (dppf)Pd(O2H)2(OTf)2 and trans-AZP or cisAZP in CH2-Cl2, respectively.
Typical yields for the synthesis of these square complexes are greater than 70%, which are
characteristic of thermodynamically driven self-assembly processes.
All of these compounds have been characterized by IR, 1H NMR, 31P NMR, electrospray ionization
mass spectrometry (ESI-MS), and satisfactory elemental analyses.
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•
•
•
A broad shoulder with a maximum around 380nm for each of the AZP-bridged squares and
corner complexes is assigned to Re(dπ) → AZP (π*) metal-to-ligand charge transfer (MLCT).
Upon irradiation of 5 at 313 nm in 293 K CH2Cl2 solution, the bands at 288 and 380 nm
gradually decrease and the band at 504 nm slowly increases.
The spectral changes apparently indicate a trans-cis isomerization of the AZP ligand, as
evidenced by the small growth of the visible band, which is characteristic of cis-azo
compounds.
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• The reactions and compounds discussed in this paper expand the array
of early transition metal based self-assembly processes.
• These new complexes are efficiently synthesized by reacting titanocene
precursors with 4,4′-azobispyridine (8).
• In contrast to cationic and water-soluble polygons of late transition
metal complexes, the presented low-valent titanium compounds are
neutral.
• Moreover, in azobispyridinecontaining late transition metal complexes,
the azo ligands provide only the pyridyl rings for coordination and
coordination on the azo bridge is seldom perfomed.
• In contrast to this, titanocene fragments coordinate on the azo bridge of
azobispyridines.
• This initiates a trans to cis isomerization of the azo ligands and leads to
titanocene-containing molecular squares.
• Due to this, the Ti-Ti distances are notably smaller than the metal-metal
distances in late transition azobispyridine compounds.
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• We have successfully synthesized a series of self-assembly
molecular squares bridged by a photoisomerizable ligand.
• The Pd-Re and Pd tetranuclear squares can be
photochemically converted to their corresponding dinuclear
squares and thermally returned back to the tetranuclear
squares.
• The Pt-Re-based squares are not able to convert to their
corresponding dinuclear squares.
• Instead, photoinduced disassembly of these squares was
observed, although the disassembled components were able
to self-assemble to their original square structures again
upon heating.
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