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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 ((ⅠⅠ))

- 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( )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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- Synthesis of 1,8-bis[trans-Pt(PEt3)2(NO3)]anthracene (clip-1)

Experimental

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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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 greenishyellow solid. Yield = 88%

Pd(PEt3)2Cl2 [0.39 mmol] in dry degassed dichloromethane (20 ml) silver triflate [0.80 mmol] wasadded 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%

Experimental - Synthesis of trans-(PEt3)2Pd(CF3SO3)2 (L2)

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Experimental

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%

- Synthesis of rectangle-1

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Experimental

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%

- Synthesis of rectangle-2

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Results and discussion1H 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 of rectancle-1>

- 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 >

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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)

<1H NMR of rectancle-2>

1HNMR(CDCl3, 300 MHz)1.49 (m,12H, PCH2CH3) 1.04 (m,18H, PCH2CH3) < L2 >

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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

<31P NMR 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

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- Structure analysisResults and discussion

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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)◦

< Fig. 1 ORTEP (30% probability) of the centrosymmetric rectangle-1>

- 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

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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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Seul- A Park Advanced instrumental analysis lab

Functionalized Hydrophobic and Hydrophilic Self-Assembled Supramolecular Rectangles

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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 self-assembly 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 air-water 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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- Sonogashira coupling (Scheme 2)hydrophobic and hydrophilic diiodibenzenes with 4-ethynylpyridine using Pd(PPh3)2Cl2.

Hydrophobic doner

Hydrophilic doner

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- 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.

SCHEME 3. Coordination-Driven Self-Assembly of (a) Hydrophobic

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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

Shift downfied by 0.5-0.54ppm 0.71-0.79 ppm

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.

1H NMR

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FIGURE 1. (d) The 31P {1H} NMR spectra of the self-assembled C18 Rectangle 16 and (e) molecular clip.

- Hydrophobic rectangle16 revealed a single, sharp peak at 8.63 ppm, upfield shifted from the molecular clip by nearly 6 ppmback-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.

31P NMR

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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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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.

1H NMR

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DEG rectangle 17.

TEG rectangle 18.

HEG rectangle 19.

31P NMR

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- 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.

ESI-MS(Hydrophobic

)

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- m/z 1700.1, 1876.6, 2052.6 corresponding to [M-2PF6]2+ of 17-19, respectively.

- Again, their isotopic distributions are in excellent agreement with the theoretical distributions.

ESI-MS(Hydrophilic)

∴These mass spectral results, together with the multinuclear NMR studies, confirm the self-assembly of both hydrophobic as well as hydrophilic supramolecular rectangles.

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- 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).

- 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.

Molecular Force Field Modeling

FIGURE 4. Computed global minimum (“Relaxed”) (a) and fully stretched (“Elongated”)

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- 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).

Molecular Force Field Modeling

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.

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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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Seo Ga YeongUniversity Of Ulsan

Self-Recognition in the Coordination Driven Self-Assembly of 2-D Polygons

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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 well-defined 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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• Figure S1. 31P{1H} NMR of 5 and 7 after 124 hours heat.

The 31P{1H} spectrum [Figure S1] displays twolarge peaks at 8.31 ppm(5) and 1.59 ppm (7).

Figure S2. 1H 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.

RectangleSquare

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• 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.

square

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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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• Figure S7. 31P{1H} NMR of 5-7 after 135 hours heat.

5(8.51ppm),7(1.45ppm)

Figure S8. 1H NMR of 5-7 after 135hours heat.

Rectangle

Square

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• Figure S9. ESIMS of 5-7.

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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 self-recognition to give discrete polygons 5-7 as the dominant products.

Conclusion

(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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Lee Kyoung-EunUniversity Of Ulsan

Self-assembly of Neutral Platinum-Based Supramolecular Ensembles Incorporating

Oxocarbon Dianions and Oxalate

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•squarate(C4O42-) and croconate (C5O5

2-), has been thoroughly investigated and compared with that of oxalate (C2O4

2-) 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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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.

<Synthesis>

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The molecular rectangle (6) itself is also severely twisted from planarity;the twist angle between the two anthracene moieties is 39°.

<X-ray structure>

*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{1H} NMR (CDCl3, 121.4 MHz): δ13.20 (s, 1JPPt ) 2889 Hz).

195pt 195pt

31P NMR

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31P{1H} NMR (CDCl3, 121.4MHz): δ 12.59 (s, 1JPPt ) 2870 Hz).

195pt195pt

31P NMR

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31P{1H} NMR (CDCl3, 121.4MHz): δ 10.95 (s, 1JPPt ) 2922 Hz).

195pt 195pt

31P NMR

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Conclusion The formation of discrete platinum-based metallacycles

incorporating flexidentate oxocarbon dianions and oxalate by self-assembly 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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Song HyeYeongUniversity Of Ulsan

Synthesis of a Bis(pyridyl)-Substituted Perylene Diimide Ligand and Incorporation into a Supramolecular

Rhomboid and Rectangle via Coordination Driven Self-Assembly

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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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Scheme 1. Synthesis of Perylene Diimide 5

Synthesis of Perylene Diimide 5

① 1(1,6,7,12-tetrachloro-3,4,9,10-tetracarboxylic acid dianhydride) + 4-bromo-2,6-dimethylaniline in propionic acid

② 2(in 71% yield) + 4-(tert-octyl)phenol in 1-methyl-2-pyrrolidinone

③ 3(in 80% yield) + triisopropylsilylacetylene in the presence of Pd( )/CuI catalysts+ Ⅱtetrabutylammonium fluoride

④ 4(in 85% yield)+ 4-iodopyridine

⑤ ligand 5 (in 78% yield)

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Scheme 2. Self-Assembly of Rhomboid 6 and Rectangle 7

Self-Assembly of Rhomboid 6 andRectangle 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 thehexafluorophosphate salt after anion exchange with KPF6.

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31P NMR

-27.8 ppm, singlet

195Pt satellites 1JPt-P = 3170Hz

31P

•-28ppm due to 6 shifted approximately8 ppm upfield relative to 8

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1H 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.

1H

*α-pyidyl hydrogen

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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 NMR

8.96 ppm, singlet

195Pt satellites 1JPt-P = 2636Hz

31P

•In the 31P spectrum rectangle 7 gave rise to a singlet 9ppm with concomitant platinum satellites.

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Figure S5. 1H NMR spectrum of 7.

1H 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

ppm m, 24H

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

1H

•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 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

** * is presented ananthracene-basedabsorption at 268ppm

Fig 1. UV/vis spectra of 5,6,7 and 9 in CH2Cl2.

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

•Distance between the Pt atoms is 45.9Å•Center of the cavity is 11.4ÅFig 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.

Ref: (28) CS ChemBats3D Ultra 7.0.0; CambridgeSoft Corp., 2000.

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Organometallics, 2009, 28, 2799–2807 Organometallics, 2009, 28, 2799–2807 Received November 25, 2008Received November 25, 2008

Organic Synthesis LabOrganic Synthesis Lab

Young-Hwa ChoiYoung-Hwa Choi

Department of Chemistry, University of UlsanDepartment of Chemistry, University of Ulsan

Inorganic Chemistry, Vol. 41, No. 7, 2002. 1862-1869Inorganic Chemistry, Vol. 41, No. 7, 2002. 1862-1869Received September 25, 2001Received September 25, 2001

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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 low-valent 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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• 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 fac-BrRe(CO)3(cis-AZP)2 or fac-BrRe(CO)3(cis-BPE)2 and (dppf)Pd(O2H)2(OTf)2 in CH2-Cl2.

Scheme 3

(AZP) 4,4’-azopyridine(BPE) 1,2-bis(4-pyridyl)ethylene(dppf) 1,1’-bis(diphenylphosphino)ferrocene(OTf) trifluoromethanesulfonate anion)

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• Squares 11 and 12 were prepared by self-assembly of (dppf)Pd(O2H)2(OTf)2 and trans-AZP or cis-AZP 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.

Scheme 4

Scheme 5

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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.