Self-assembly of metal–organic hybrid nanoscopic rectangles

1. 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

2. Introduction (Ⅰ) • Self-assembly of nanoscopic assemblies of finite shape by a directional bonding approachhas 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.

3. 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

4. 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).

5. 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%

6. 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%

7. 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%

8. 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%

9. 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>

10. Results and discussion - 1H NMR spectrum 1HNMR(CDCl3, 300 MHz) 1.49 (m,12H, PCH2CH3) 1.04 (m,18H, PCH2CH3) < L2 > 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>

11. 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>

12. Results and discussion - Structure analysis

13. 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>

14. 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 rectangleand 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

15. 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˚

16. 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

17. Functionalized Hydrophobic and Hydrophilic Self-Assembled Supramolecular Rectangles Seul- A Park Advanced instrumental analysis lab

18. Introduction • ▣ 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.

19. Introduction • - 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.

20. Results and Discussion • ▣ 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.

21. Results and Discussion Hydrophobic doner Hydrophilic doner - Sonogashira coupling (Scheme 2) hydrophobic and hydrophilic diiodibenzenes with 4-ethynylpyridine using Pd(PPh3)2Cl2.

22. Results and Discussion 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.

23. Results and Discussion 1H NMR 0.71-0.79 ppm Shift downfied by 0.5-0.54ppm 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.

24. Results and Discussion 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 self-assembled C18 Rectangle 16 and (e) molecular clip.

25. Results and Discussion 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

26. Results and Discussion 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.

27. Results and Discussion 31P NMR DEG rectangle 17. TEG rectangle 18. HEG rectangle 19.

28. Results and Discussion 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.

29. Results and Discussion ESI-MS (Hydrophilic) • 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. ∴These mass spectral results, together with the multinuclear NMR studies, confirm the self-assembly of both hydrophobic as well as hydrophilic supramolecular rectangles.

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

31. Results and Discussion 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.

32. Conclusion - 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.

33. Self-Recognition in the Coordination Driven Self-Assembly of 2-DPolygons Seo Ga Yeong University Of Ulsan

34. Introduction 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.

35. 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

36. 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.

37. Figure S1. 31P{1H} NMR of 5 and 7 after 124 hours heat. Rectangle Square The 31P{1H} spectrum [Figure S1] displays two large peaks at 8.31 ppm(5) and 1.59 ppm (7). 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.

38. Figure S4. 31P{1H} NMR of 6 and 7(1.56ppm)after 121 hours heat. square Figure S5. 1H NMR of 6 and 7 after 121hours heat.

39. 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+

40. Figure S7. 31P{1H} NMR of 5-7 after 135 hours heat. 5(8.51ppm),7(1.45ppm) Rectangle Square Figure S8. 1H NMR of 5-7 after 135hours heat.

41. Figure S9. ESIMS of 5-7.

42. 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 self-recognition 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.

43. Self-assembly of Neutral Platinum-Based Supramolecular Ensembles Incorporating Oxocarbon Dianions and Oxalate Lee Kyoung-Eun University Of Ulsan

44. Introduction • 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

45. <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.

46. <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.

47. 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.

48. 31P NMR 195pt 195pt 31P{1H} NMR (CDCl3, 121.4 MHz): δ13.20 (s, 1JPPt ) 2889 Hz).

49. 31P NMR 195pt 195pt 31P{1H} NMR (CDCl3, 121.4MHz): δ 12.59 (s, 1JPPt ) 2870 Hz).

50. 31P NMR 195pt 195pt 31P{1H} NMR (CDCl3, 121.4MHz): δ 10.95 (s, 1JPPt ) 2922 Hz).