DongHun Kim

HyeWoo Lee

Eunji Park

Taewon Kim

Group .ⅤSelf-sorting, Self-selection,

and Self-recognition

1

Wei Jiang, Henrik D. F. Winkler, and Christoph A. Schalley

Institut fur Chemie und Biochemie, Freie UniVersitat Berlin, Takustrasse 3, 14195 Berlin, Germany

Integrative Self-Sorting: Construction of a Cascade-Stoppered

Hetero[3]rotaxane

DongHun Kim

2

Introduction

Nature efficiently uses the principles of noncovalent selfassembly1 together with self-sorting phenomena to generate complex, functional architectures from many different building blocks. Self-sorting thus integrates different subunits into the architecture with precise positional control. In contrast, most synthetic selfasse-mbled architectures repetitively use ever the same bui-lding blocks thus severely restricting the implementa-tion of function. Selfsorting will certainly contribute to solving this problem.

3

Result & Discussion

Recently, Huang et al.3 reported secondary dialkyl ammonium ions to thread through the cavity of benzo-21-crown-7 (C7) to form pseudorotaxanes. Phenyl groups suffice as stoppers to trap C7 on the axle. In contrast, dibenzo-24-crown-8 (C8) forms pseudorotaxanes even with secondary dibenzyl ammonium ions showing the phenyl groups not to be efficient stoppers for C8.4

4

Figure 1. Electrospray-ionization Fourier-transform ion-cyclotron-resonance (ESI-FTICR) mass spectrum of an equimolar mixture of 1-H PF6, 2-H PF6, C7, and C8 in DCM and their chemical structures (inset).

5

Figure 2. Sequence-specific formation of hetero[3]pseudorotaxane 4-2H 2PF6 based on an integrative self-sorting process and the synth- sis of “cascade-stoppered” hetero[3]rotaxane 5-2H 2PF6.

6

Figure 3. Partial 1H NMR spectra (500 MHz, 298 K, CDCl3:CD3CN ) 2:1, 10.0 mM) of (b) 3-2H· 2PF6 alone and equimolar mixtures of (a) 3-2H· 2PF6 and C7; (c) 3-2H· 2PF6 and C8; (d) 3-2H· 2PF6, C7, and C8. Complexed and uncomplexed species are denoted by “c” and “uc” in the parentheses, respectively.

7

Figure 4. (Top) ESI-FTICR mass spectrum of a 1:1:1 DCM solution of 3-2H· 2PF6, C7, and C8; (bottom) infrared-multiphoton dissociation (IRMPD) experiments (MS/MS) of mass-selected [4-2H· PF6]+.

8

Conclusion

In conclusion, we have successfully demonstrated the concept of integrative self-sorting with a hetero[3]pseudorotaxane as a model system. Conceptually, it is derived from a self-sorting system with four discrete components. We applied this concept to the synthesis of a hetero[3]rotaxane with an efficient cascade-stoppering system.

We believe integrative self-sorting, as an important “programming language” in nature, will be highly useful in constructing complex supramolecular assemblies and various artificial smart materials with well-organized structure, distinct topology, and function.

9

Damien Braekers, Christelle Peters, Anca Bogdan, Yuliya Rudzevich, Volker Böhmer, and Jean F. Desreux

J. Org. Chem., 2008, 73 (2), pp 701–706

Self-Sorting Dimerization of Tetraurea Calix[4]arenes

HyeWoo Lee

10

Introduction

Molecular recognition is one of the basic principles of all forms of life and is the first step in fundamental reactions such as replication of DNA or transcription of RNA, etc. Nature combines in a highly sophisticated way a comparatively small number of basic recognition motifs (a surprisingly simple set of complementary structures) to reach an incredible variety/diversity of species. Therefore it is a particular challenge to develop an artificial set of very similar molecules which are able to distinguish themselves and to express this distinction into a result that can be monitored. Calix[4]arenes substituted on their wide rim by four urea functions are self-complementary molecules. In apolar solvents they form quantitatively dimeric capsules held together by a belt of intermolecular hydrogen bonds involving alternately the urea groups of both calixarenes1 (see Figure 1).

Figure 1 Side view (a) and top view (b) of a dimer and its sketchy representation (c) with aromatic arms of the lower and upper calix[4]arenes pointing respectively upward and

downward.

11

It has been shown that tetraurea calixarenes do not interact with another similar self-complementary system formed by triurea derivatives of triphenylmethanes. This may not be very surprising since there is a mismatch between both molecular systems concerning the number of urea functions and the shape of the molecules. However, there are already some selectivities known for the dimerization of tetraurea calix[4]arenes themselves (see Chart 1).

Chart 1.  Structure of the Tetraurea Calix[4]arenes 1−6 and of the Bis[2]catenane 7 (Y = Pentyl)

12

Results and Discussion

General Considerations. Two tetraurea calix[4]arenes are combined in a dimer via their wide rims and are turned by 45° around their common axis with respect to each other as shown in Figure 1. The hydrogen-bonded belt involves alternately the urea groups of the two calixarenes which act simultaneously as donor and acceptor.14 Normally the NHα attached to the urea residue forms a stronger hydrogen bond as indicated by a low field shift of the NMR signal.17 Intermediates between dimer and monomer have not been observed, although the dissociation/association most likely does not occur in one step.

Series I (Addition of 1a to 6a). This combination allows one to compare the results obtained by ESI-MS and 1H NMR. Bis- or tetraloop tetraureas 5 or 6 do not form homodimers because the aliphatic chains connecting adjacent urea groups would have to overlap in a sterically very unfavorable arrangement (Rule 1). However, they easily form heterodimers with 1a since the tolyl residues can pass through the macrocyclic rings.

13

Accordingly, when 1a is added to a solution of a tetracyclic calix[4]arene such as 6a (Figure 2), the 1H NMR signals for the homodimer 1a·1a appear only after the addition of more than an equal amount of 1a relative to 6a. This NMR titration also proves the exclusive formation of the heterodimer 1a·6a and the presence of the homodimer of 6a can be safely excluded.

Figure 2 Sections of the 1H NMR spectra (400 MHz, CDCl3) of tetraloop 6a (a), a 2:1 mixture of tetraloop 6a and tetratolyl 1a (b), a 1:1 mixture of 6a and 1a (c), a 1:2 mixture of 6a and 1a, (d) and 1a alone (e). Peak assignments for compounds 1a and 6a are reported in refs 15 and 8, respectively.

14

An ESI-MS titration of a 6a solution by 1a in chloroform is presented in Figure 3. The tetraethylammonium ion was the guest in this titration experiment while the solvent was most likely the guest in the NMR study. In addition, the ESI-MS measurements were conducted at much lower concentrations (about 10-7 M rather than 1 mM).

Figure 3 Sorting process and electrospray mass spectrometry titration of 6a by 1a in chloroform (red and blue circles:  [1a·6a] dimer; red circles:  [1a·1a] dimer). The peak area of each species was divided by the total ion charge. The sketchy presentation of the sorting process follows the scheme illustrated in Figure 1. The same colors have been used for each capsule and for the corresponding data points.

15

Series II (Addition of 6a to a Mixture of 1a and 4). More complex mixtures of calix[4]arene tetraureas lend themselves to ESI-MS analyses using tetraethylammonium as guest, provided special care is paid to kinetic phenomena (see the Experimental Section). A titration of a chloroform solution of 1a and monoloop 4 by the tetraloop 6 is presented in Figure 4.

Figure 4 Sorting process and electrospray mass spectrometry titration of a mixture of 1a and 4 by 6a in chloroform (red and blue circle:  [1a·4] dimer; red circle:  [1a·1a] dimer; blue circle:  [4·4]; red anf green circle:  [1a·6a] dimer). The peak area of each species was divided by the peak area of reference 7.

16

Series III and IV (Addition of 6a or 6b to a Mixture of 1a and 1b). The nature and distribution of the dimeric capsules drastically depend on the size of the loops grafted onto the calixarene ring and can be anticipated on the basis of the simple rules enunciated above. The tetraloop compounds 6a and 6b form neither homodimers nor heterodimers with each other because this would force two aliphatic chains to be in close contact (“overlapping loops”).

Figure 5 Sorting process and electrospray mass spectrometry titration of a mixture of 1a and 1b by 6a in chloroform (red and blue circle:  [1a·1b] dimer; red circle:  [1a·1a] dimer; blue circle:  [1b·1b] dimer; red and green circle:  [1a·6a] dimer). The peak area of each species was divided by the peak area of reference 7.

17

Furthermore, the tert-butyl substituents of 1b strongly augment the bulkiness of the urea residues attached to this calixarene and it seems unlikely that these groups will be able to intercalate through the small loops of 6a while they might do so in the case of the larger loops of 6b. Figures 5 and 6 present the ESI-MS titrations of a mixture of 1a and 1b by 6a and 6b, respectively. As expected, the starting mixtures contain homodimers of 1a and of 1b as well as the heterodimer [1a·1b], which is the major component most likely because it is entropically favored.

Figure 6 Sorting process and electrospray mass spectrometry titration of a mixture of 1a and 1b by 6b in chloroform (red circle:  [1a·1a] dimer; blue circle:  [1b·1b] dimer; red and blue circle:  [1a·1b]; red and green circle:  [1a·6b] dimer; blue and green circle:  [1b·6b] dimer). The peak area of each species was divided by the peak area of reference 7.

18

Conclusions Tetraurea calix[4]arenes have the remarkable ability to form highly stable

capsules in chloroform even in highly diluted solutions.

These capsules are stabilized by an intricate network of intermolecular hydrogen bonds between the urea groups.

In the presence of an ammonium salt they contain a Et4N+ cation as guest. Relatively small structural changes profoundly modify self-sorting processes in which the steric crowding of the urea substituents seems to play the major role.

Rigidification with ether chains,6 crowding with one or several aliphatic loops, or replacing methyl groups by bulkier tert-butyl moieties prevent or favor the formation of homo- or heterodimeric structures according to simple rules.

One can thus anticipate the outcome of simply mixing together urea calix[4]arenes featuring the same macrocyclic core and obtain capsules of well-defined composition.

19

Thank you for

listening

Thank you for

listening

20

Yao-Rong Zheng, Hai-Bo Yang, Brian H. Northrop, Koushik Ghosh and Peter J. Stang

Inorg. Chem., 2008, 47 (11), pp 4706–4711

Size Selective Self-Sorting in Coordination-Driven Self-Assembly of Finite

Ensembles

Eunji Park

21

Introduction

Self-sorting, the mutual recognition of complementary components within a mixture, is a critical phenomenon in many biological systems. When specific information is encoded within the structural aspects of molecular subunits, multiple higher-order supramolecular structures can be obtained from complex, multicomponent mixtures via self-sorting processes. Through detailed investigations of the self-sorting process, valuable insight into analogous biological self-sorting processes may be obtained. Toward this aim, certain pioneering synthetic self-sorting systems based upon metal–ligand coordination bonding, hydrogen bonding, solvophobic effects, and dynamic covalent chemistry have been developed during the past decade.

In the area of synthetic self-sorting systems driven by metal–ligand coordination bonding, Lehn et al. have previously reported the spontaneous formation of discrete supramolecular double helicates in one vessel as directed by the number of binding sites in oligo-bipyridine strands and by the preferred coordination geometry of metal ions. Raymond et al. later observed self-sorting of supramolecular triple helicates containing two metal centers based solely on the lengths of rigid spacers separating two catecholate ligands. Furthermore, self-sorting also can be directed by chiral ligands and the counteraction of complexes. However, in contrast to numerous literature reports concerning the self-sorting of helicates, only sporadic studies have been reported on the same process involving self-assembled polygons and polyhedra, which comprise some of the most prominent higher-order structures.

22

Results and Discussion

When molecular clip 1 is mixed with two different sized linear bipyridyl linkers 3 (0.72 nm) and 4 (1.65 nm) in a 2:1:1 ratio and heated at 60–65 °C for 45 h in an aqueous acetone solution (v/v 1:1), two molecular rectangles RS and RL of different size are formed as the dominant products (Scheme 1a).

Scheme 1. Graphical Representation of Self-Sorting in the Coordination-Driven Self-Assembly of (a) Supramolecular Rectanglesa and (b) Triangles

23

The self-sorting process was followed by 31P and 1H multinuclear NMR spectroscopy as shown in Figures 1 and 2, respectively. After 1 h, the mixture changes from a suspension to a clear solution. The 31P {1H} NMR spectrum of this reaction mixture shows intense peaks at 8.95 ppm and 9.10 ppm with concomitant 195Pt satellites for RS and RL, flanked by unassignable signals that are representative of oligomeric byproducts. Likewise, peaks attributable to rectangles RS and RL (e.g., δ = 9.52 ppm, H9 in RS; δ = 9.45 ppm, H9 in RL) can be found in the 1H NMR spectrum after 1 h of heating, though broad peaks and unassignable signals belonging to oligomeric byproducts are also observed.

Figure 1. 31P{1H} NMR spectra (Acetone-d6/D2O 1:1) recorded at 1, 7, 21, and 45 h time intervals during the formation of supramolecular rectangles RS and RL.

24

After 21 h, the broad byproduct peaks at 7.89 ppm, 8.22 ppm, 9.30 ppm, and 9.64 ppm have decreased significantly while the intense peaks for RS and RL remain in the 1H NMR spectrum, indicating that most oligomeric byproducts have dynamically self-sorted to the desired products. After 45 h, two sets of sharp signals (consistent with those previously reported for RS and RL) remain in the NMR spectrum, indicating the presence of two highly symmetric Pt(II) supramolecular species obtained as the predominant products in the solution.

Figure 2. Partial 1H NMR spectra (Acetone-d6/D2O 1:1) recorded at 1, 7, 21, and 45 h time intervals during the formation of supramolecular rectangles RS and RL

25

The mixture changes from a suspension to a clear solution after 1 h, though highly disordered 31P {1H} and 1H NMR spectra are observed. After 3 h, initial formation of DTPS and DTPL is clearly indicated by the 31P {1H} NMR spectrum, where two peaks at 11.12 ppm and 10.16 ppm with concomitant 195Pt satellites for DTPS and DTPL appeared. There exist, however, multiple unassignable peaks, such as those at 15.31 ppm, 9.85 ppm, and 8.87 ppm, that are representative of oligomeric byproducts in the solution.

Figure 3. 31P{1H} NMR spectra (Acetone-d6/D2O 1:1) of recorded at 1, 3, 12, and 24 h time intervals during the formation of distorted triangle prisms DTPS and DTPL

26

At the 3 h time interval, signals for DTPS and DTPL cannot be identified in the 1H NMR spectrum because of the breadth of peaks corresponding to the oligomeric byproducts. After 12 h, peaks attributable to discrete DTPS and DTPL can be identified in both the 31P {1H} NMR spectrum and the 1H NMR spectrum, as the intensities of peaks corresponding to oligomeric byproducts are significantly decreased. After 24 h, in the 31P {1H} and 1H NMR spectra, clearly identifiable peaks as shown in Figures 3 and 4 reveal the formation of two different sized discrete supramolecular 3-D cages DTPS and DTPL as the major self-sorted species in the solution.

Figure 4. Partial 1H NMR spectra (Acetone-d6/D2O 1:1) recorded at 1, 3, 12, and 24 h time intervals during the formation of distorted triangle prisms DTPS and DTPL.

27

Conclusions

We have demonstrated that ditopic organoplatinum acceptors 1 or 2, when mixed with two different sized dipyridyl linkers 3 and 4 or tritopic donors 9 and 10, undergo a self-sorting process that results in the formation of discrete 2-D or 3-D superstructures.

The observed self-sorting systems rely on the thermodynamic preferences (enthalpic and entropic) of the supramolecular ensembles, whereby the size of the linkers can direct the self-selection.

These results also help provide an enhanced understanding of the control variables that regulate the self-sorting process and have implications in the related processes that govern the assembly of more complex biological structures in nature.

Scheme 2. Graphical Representation of Self-Sorting in the Coordination-Driven Self-Assembly of Supramolecular Distorted Triangular Prisms 11-12

28

Ki-Whan Chi,*,† Chris Addicott,‡ Atta M. Arif,‡ and Peter J. Stang*,‡

J. Am. Chem. Soc., 2004, 126 (50), pp 16569–16574

Ambidentate Pyridyl-carboxylate Ligands in theCoordination-Driven Self-Assembly of 2D Pt

Macrocycles: Self-Selection for a Single Isomer

Molecular Functional Materials Lab.

Taewon Kim

29

Introduction Most assemblies prepared to date are highly symmetrical in nature

as they are built from simple homodi- and tridentate pyridine-containing donors and metal acceptors.

One problem inherent in the design of lower symmetry discrete self-assembled species containing this type of ligand is the possibility of linkage isomerism.

But, this problem is solved by using self-selection, we get the only one isomer.

Self-selection

is a term used to indicate any situation in which individuals select themselves into a group.

The simplest approach is the combination of an ambidentate ligand (X-Y) with a homotopic bidentate acceptor in a 1:1 ratio (Scheme 2), where only two cyclic products (A/B or C/D) are possible in each case.

Scheme 1. Using self-selection for one isomer 30

Synthesis

N XO

O- M+

1a : M = Na, -X- = none

1b : M = Na, -X- =

1c : M = K, -X- =Pt

Pt

ONO2

ONO2

PEt3

PEt3

PEt3

PEt3

Pt

ONO2

Et3P

PEt3ONO2

XNO

Pt

PEt3Et3P

OO

PtX NO

PEt3PEt3

2+

2PF6-

N XO

O

NXO

O

Pt

PEt3

PEt3

Pt

Pt

Pt

PEt3PEt3

PEt3

PEt3

PEt3PEt3

2+

3a : 2NO3-

3b,c : 2PF6-

2a-2c

3a-3c5

4

Scheme 2. Synthesis of macrocycles 31

Results and Discussion

A B

A contain two inequivalent (and thus coupled) phosphorus nuclei bound to the same platinum atom.

B also possesses two inequivalent phosphorus nuclei, but these are bound to different platinum atoms.

The 31P NMR spectrum of this species would show two uncoupled signals with shifts and intensities similar to what is observed.

Scheme 3. Linkage isomer 2

32

M

X

Y

Y

X

M

PEt3

PEt3

Et3P

Et3P

M

X

X

Y

Y

M

PEt3

PEt3

Et3P

Et3P

Figure 1. 31P NMR of 2a.

The 31P NMR spectra of 2 displayed two coupled doublets of approximately equal intensity with concomitant 195Pt satellites.

The signals near 2 ppm are shifted approximately 4 ppm upfield relative to 4 due to back-donation from the platinum centers.

In contrast, coordination of the carboxylate group does not result in a large 31P chemical shift change.

33

This result means that making macrocycles are structure 2.

Figure 2. 1H NMR of 2a. A multiplet near 8.9 ppm for the pyridine hydrogens adjacent to the

nitrogen nucleus is shifted approximately 0.5 ppm to lower field relative to 1, consistent with the loss of electron density that occurs upon coordination.

34

Figure 3. 31P NMR of 2c.

Figure 4. 1H NMR of 2c.

We have confirmed the same results like 2a which has head-to-tail orientation.

35

M

M

X

Y

Y

X

M

M

M

M

X

X

Y

Y

M

M

C D

C contain two inequivalent (and thus coupled) phosphorus nuclei bound to the same platinum atom like A.

D also possesses two inequivalent phosphorus nuclei, but these are bound to different platinum atoms like B.

We think that macrocycles is confirmed by using 31P NMR, in the same way like recognizing A or B.

Scheme 4. Linkage isomer 3

36

The 31P NMR spectra of 3 gave two sharp singlets of equal intensity with concomitant 195Pt satellites.

The upfield shift of the signals near 8 ppm relative to 5 shows they are bound to the platinum nucleus coordinated to the pyridine rings.

Sadly, in this case, the 31P NMR data are insufficient for distinguishing the products 3 (topology C in Scheme 4) from their isomeric relatives D.

However, this problem was initially solved by examination of the 1H NMR spectra.

Figure 5. 31P NMR of 3a.

37

One unique feature of assemblies C is the presence of an inversion center in the middle of the molecule.

Figure 6-2. 1H NMR of 3a.

Consequently, C has only one type of H9 and H10 anthracene proton nuclei, while isomer D has two types.

Figure 6-1. structure of 3a.

The 1H NMR spectrum reveals one signal each for H9 and H10.

Therefore, isomer is structure 3. 38

X-ray crystallography confirmed that the NMR assignment of 3 was indeed topology C.

Although the isonicotinate moieties show significant disorder in the rectangle 3a, there is no doubt as to their head-to-tail orientation (Figure 7).

Figure 7. X-ray Crystallography of 3a.

39

Evidence for the structures of 2 and 3 was obtained with electro spray ionization mass spectrometry (ESI/MS).

For 2, peaks were observed corresponding to the intact structure minus one counterion.

In the case of 3, peaks were found attributable to the consecutive loss of counterions.

Figure 8. ESI/MS of 2a. Figure 8. ESI/MS of 3a.

These were all isotopically resolved and are in excellent agreement with their theoretical distributions.

40

Why is it selected?-Strain Energy-

Scheme 3. Precursors of A and B

(Using MM2 force field simulation)

Structures E and F are precursors to B.

They are formed when 2 equiv of 1b bond to a single platinum atom via their pyridyl (E) or carboxyl (F) termini.

The largest distance between the carboxyl oxygen atoms is 14.7 Å in the case of E, while in F 7.5 Å separates the pyridine nitrogens.

The analogous gap in G (with one pyridyl and one carboxyl group bound to the same platinum) is only 4.5 Å.

G has the best arrangement of uncoordinated termini to form a closed macrocycle upon reaction with a second platinum center

And G does not experience the same repulsive forces that presumably occur in E and F as two ends of similar polarity approach each other in space.

41

Why is it selected?-Charge Separation

The head-to-tail orientation of the 1b units (topology A) maximizes the charge separation as the closed assembly 2b forms.

The formal charge of 1+ on the pyridine nitrogens is more widely separated in the closed macrocycles 2 and 3 than in their isomers B and D.

42

Conclusion In conclusion, we have prepared discrete macrocycles 2 and 3 from

ambidentate donor ligands 1 and platinum-containing acceptors 4 and 5.

Despite the possibility of forming multiple products that differ only in connectivity, ambidentate ligands 1 and acceptors 4 and 5 prefer to self-assemble predominantly into one closed species.

They are another important example of the relatively few discrete supramolecules made from ambidentate ligands via coordination-driven transition-metalmediated self-assembly.

These results also provide further insights into the coordination-driven self-assembly process.

Moreover, they demonstrate that ambidentate ligands can be used in the self-assembly of discrete metallacycles with some predictability as a consequence of preferred self-recognition due to charge separation as well as strain.

43

Thank you for listening

44