Construction of Functionalized Metallosupramolecular Tetragonal Prisms via Multicomponent Coordination-Driven Self-Assembly

Abstract

A new approach for the construction of functionalized metallosupramolecular tetragonal prisms via multi-component, coordination-driven, template-free self-assembly is described. The combination of tetra-(4-pyridylphenyl)ethylene, a 90° Pt(II) acceptor, and ditopic bipyridine or carboxylate ligands functionalized with hydroxyl or amine groups, hydrophobic alkyl chains, or electrochemically-active ferrocene, yields a suite of seven self-assembled tetragonal prisms under mild conditions. These 3-D metallosupramolecules were characterized by multinuclear NMR (³¹P and ¹H) and mass spectrometry. Their shapes and sizes were established using MMFF force-field simulations. In addition, their approximate sizes were further supported by PGSE NMR experiments.

Introduction

Multicomponent self-assembly is a ubiquitous phenomenon in biological systems. Nature has demonstrated an extraordinary ability to assemble 2-D and 3-D supramolecular nano-architectures from multiple subunits to effect biological functions.¹ For example, the capsids of Tomato Bushy Stunt Virus are assembled from three protein subunits and serve the role of nucleic acid storage.² Apoferritin is a globular protein comprised of 24 components to store and keep intracellular iron in a soluble and non-toxic form.³ One strategy to mimic biological processes and to develop new biomimetic materials is the synthesis of functionalized supramolecular nanoscale structures with well-defined shapes and sizes, accessible through efficient and predictable multicomponent self-assembly.⁴

In the past two decades, coordination-driven self-assembly has emerged as a powerful tool to construct abiological structures, enabling an efficient route which parallels natural pathways. The rational design of discrete polygons and polyhedra has been achieved by utilizing molecular subunits encoded with specific chemical and geometric information.⁵ In addition, by conjugating chemical functionalities to individual building blocks prior to self-assembly, functionalized supramolecular nano-architectures with predetermined sizes and shapes can be realized.⁶ Despite the efficiency of preparing abiological structures via coordination-driven self-assembly, most reports are limited to a single metal acceptor and a single, electron-rich donor.^5–6 The self-assembly of three or more components is plagued with the formation of entropically-favored, disordered oligomers, and/or dynamic mixtures.⁷ Therefore, efficient methods to self-assemble discrete supramolecular structures with controllable size and shapes from more than two distinct tectons remain underdeveloped.

Recently, an interest in multicomponent coordination-driven self-assembly with an emphasis on constructing discrete supramolecular structures has emerged.^8–12 For example, by employing sterically demanding tectons in the presence of aromatic templates, Fujita et al. have designed multicomponent self-assembled trigonal prisms which are competent for host-guest chemistry.⁹ Severin et al. have described the preparation of macrocycles and cages based on metal-ligand interactions and reversible covalent reactions.¹⁰ Stoddart et al. have developed multicomponent self-assemblies of Borromean rings using complementary imine bond formation and metal-ligand coordination.¹¹ We have previously demonstrated that discrete metallosupramolecular macrocycles and tetragonal prisms can be obtained by controlling the size, shape, and ratio of the multiple subunits used in self-assembly.¹² More recently, we and others have found that three-component systems comprised of square planar platinum(II) or palladium(II) centers, pyridine, and anionic carboxylate donors can self-assemble into multicomponent supramolecular rectangles and prisms with high efficiency.¹³ The isolation of discrete self-assemblies without deleterious side product formation was ascribed to the favorable energetics associated with heteroligated Pt or Pd centers containing one carboxylate and one pyridine ligand. Despite these emerging strategies, which allow the use of multiple building blocks, reports of multicomponent coordination-driven self-assemblies using functionalized tectons are rare. The attachment of specific chemical functionalities to metallosupramolecules is necessary to enable applications in supramolecular catalysis, chemical sensing, and host-guest chemistry, therefore motivating the development of novel routes to functionalized aseemblies.⁶

We report herein the formation and characterization of 3-D tetragonal prisms arising from template-free, multicomponent coordination-driven self-assembly. As shown in Scheme 1, the combination of tetra-(4-pyridylphenyl)ethylene (1),^12b cis-(PEt₃)₂Pt^II(OTf)₂ (2), and functionalized ditopic bipyridine or carboxylate ligands (3a–3g) in a ratio of 2:8:4 results in the formation of functionalized tetragonal prisms (4a–4g). Prisms 4 were characterized by multinuclear NMR and electron-spray ionization mass spectrometry (ESI-MS), supporting their assigned structures. Also, pulsed-field-gradient spin–echo (PGSE) NMR measurements and computational simulations were employed to predict the shapes and approximate sizes of the prisms.

Scheme 1.

Multicomponent Coordination-Driven Self-Assembly of Functionalalized Tetragonal Prismatic cages.

Results and Discussion

Tetragonal prism 4a was prepared by mixing 1, 2, and ditopic 1,2-di(4-pyridyl)glycol (3a) in a 2:8:4 ratio in acetone/nitromethane (v:v=2:1). After 12 h of stirring at room temperature, the reaction mixture appeared yellow. The well-defined NMR signals in both the ³¹P{¹H} and ¹H NMR spectra of 4a support the formation of single, symmetric reaction product. The ³¹P{¹H} NMR spectrum of 4a displays two doublets, occurring at δ = 0.85 ppm and 0.78 ppm (²J_P-P = 20.2 Hz) as well as the expected ¹⁹⁵Pt satellites (Figure 1, A). These doublets are shifted upfield (Δδ = ~ 4.2 ppm) relative to the singlet of the Pt starting material, 2. The two doublets of 4a indicate that the platinum centers each possess two distinct phosphorus environments and that all the Pt centers are themselves symmetry related. These observations are consistent with the assigned tetragonal prismatic structure of 4a, as each platinum binds to both 1 and 3a, breaking the symmetry of the phosphines.^12b,14 The ¹H NMR spectrum of 4a displays sharp, clean signals for the pyridine protons, which exhibit typical down-field shifts relative to free pyridine (Δδ_py-α-H = 0.20 – 0.30 ppm, Δδ_py-β-H = 0.40 – 0.50 ppm) associated with a loss of electron density upon binding (Figure 1, B). Further support of the tetragonal prismatic structure of 4a is given by electron-spray ionization mass spectrometry (ESI-MS). As shown in Figure 2, peaks centered at 1845.4, 1446.5, 1180.6, 848.3, and 515.8, corresponding to [M – 4OTf]⁴⁺, [M – 5OTf]⁵⁺, [M – 6OTf]⁶⁺, [M – 8OTf]⁸⁺, and [M – 12OTf]¹²⁺, for 4a, were observed. Furthermore, the peak arising from [M – 4OTf]⁴⁺ was isotopically resolved and agreed well with its calculated theoretical distribution.

Figure 1.

The ³¹P{¹H} NMR spectrum (A) and partial ¹H NMR spectrum (B; 300 MHz, 298 K) of 4a recorded in acetonitrile-d₃.

Figure 2.

Full ESI-MS spectrum and isotopic resolved peak of [M – 4OTf]⁴⁺ (calculated: red; experimental: blue) for tetragonal prism 4a

Functionalized tetragonal prisms 4b–4e were prepared based on a recently reported strategy for the multicomponent self-assembly of 2-D and 3-D metallosupramolecules using a 90° Pt(II) acceptor with carboxylate and pyridine donors.¹³ The general route involves mixing the tetratopic pyridine donor, 1, Pt^II acceptor, 2, and functionalized isophthalate derivatives (amino (3b), nitro (3c), n-propanyl (3d), or 3-ferrocenylpropanyl (3e)) in a 2:8:4 ratio in acetone/water (v:v = 8:1). In a typical synthesis, the solution is stirred for 4 h at 65 °C, after which the solvent is removed in vacuo and the resulting residue redissolved in neat nitromethane-d₃, followed by an additional 4 h of stirring at 65 °C. This route yielded prisms 4b–4e in solution. ³¹P{¹H} and ¹H NMR multinuclear analyses of the reaction mixtures indicated the formation of single, discrete self-assemblies with high symmetry. For example, the ³¹P{¹H} NMR spectrum of 4b displays two doublets with approximately equal intensities at δ = 6.95 and 1.01 ppm (²J_P-P = 21.9 Hz; Figure 3, A). The presence of doublets indicates distinct phosphorus environments, which would arise from the heteroligated platinum centers containing both pyridine and carboxylate ligands. ^{12, 13} The doublet observed at 6.95 ppm is ascribed to the phosphines trans to carboxylates and displays a small shift relative to the resonance found in 2. The doublet at 1.01 ppm is assigned to the phosphorus atoms trans to the pyridine ligands and is shifted nearly 6.5 ppm relative to that of 2. Similarly to 4b, self-assemblies 4c–4e display two doublets with approximately equal intensities in their ³¹P{¹H} NMR spectra, as shown in Figures S1–S3(SI). In the ¹H NMR spectra of 4b–4e, sharp signals corresponding to the coordinated pyridines were identified around δ = 7.73 and 8.66 ppm, with small downfield shifts relative to those of 1 (Δδ_py-α-H = 0.20 – 0.30 ppm, Δδ_py-β-H = 0.30 – 0.40 ppm; Figure 3, B and Figures S1–S3, SI). The sharp signals in both the ³¹P{¹H} and ¹H NMR spectra support the exclusive formation of single, functionalized tetragonal prisms as products, ruling out other possible assemblies and oligomers. ESI-MS provides further evidence for the tetragonal prismatic structures of 4b–4e. As shown in Figure 4, peaks centered at 2063.5, 1510.6, 1178.6, and 680.7, corresponding to [M – 3OTf]³⁺, [M – 4OTf]⁴⁺, [M – 5OTf]⁵⁺ and [M – 8OTf]⁸⁺, for 4b, were observed. Similarly to 4b, the ESI-MS spectra of 4c–4e display well-defined peaks arising from tetragonal prismatic structures, as shown in Figures S4–S6(SI). All the peaks of [M – 3OTf]³⁺ of 4b–4e are isotopically resolved and in good agreement with their calculated theoretical distributions (Figure 4 and Figures S4–S6, SI).

Figure 3.

The ³¹P{¹H} NMR spectrum (A) and partial ¹H NMR spectrum (B; 300 MHz, 298 K) of 4c recorded in nitromethane-d₃.

Figure 4.

Full ESI-MS spectrum and isotopic resolved peak of [M – 3OTf]³⁺(calculated: red; experimental: blue) for tetragonal prism 4b

To further demonstrate the construction of functionalized metallosupramolecules via the multicomponent self-assembly introduced above, asymmetric terephthalate ligands functionalized with n-hexyl (3f) and 6-ferrocenylhexyl (3g) were self-assembled with the tetratopic pyridine donor (1) and a Pt^II acceptor (2) to afford tetragonal prisms under similar synthetic conditions as for 4b–4e. ³¹P{¹H} and ¹H NMR multinuclear analyses of the reaction mixtures indicated the formation of single, discrete self-assemblies with high symmetry. The ³¹P{¹H} NMR spectra of 4f and 4g display four doublets with approximately equal intensities, corresponding to two sets of coupled phosphorus atoms, at δ = 6.79, 6.12, 1.28, and 1.21 ppm (²J_P-P = 21.4 Hz; Figure 5) for 4f, 6.80, 6.10, 1.28, and 1.21 ppm for 4g (²J_P-P = 21.4 Hz; Figure S7, SI). The presence of four doublets indicates distinct phosphorus environments, which is indicative of heteroligated coordination of pyridine and asymmetric carboxylate to each platinum center. The two doublets observed between 6.5 and 7.2 ppm are ascribed to the phosphines trans to carboxylates and display small shifts relative to 2. Because the functionalized carboxylate linkers are asymmetric, two distinct Pt environments exist in these prisms and therefore two different phosphine environments trans to carboxylates are present. The other two doublets between 1.28 and 1.21 ppm are assigned to the phosphorus atoms trans to the pyridine ligands and are shifted nearly 6.5 ppm relative to 2. The distinct phosphine environments trans to the pyridines also result from the asymmetry of the carboxylate linkers, which breaks the symmetry of the Pt centers.^13,14 In the ¹H NMR spectra of 4f and 4g, sharp signals corresponding to the coordinated pyridines were identified around δ = 7.73 and 8.66 ppm with small downfield shifts relative to 1 (Δδ_py-α-H = 0.20 – 0.30 ppm, Δδ_py-β-H = 0.30 – 0.40 ppm; Figure 5, and Figure S7, SI). ESI-MS also provides further evidence for the tetragonal prismatic structures of 4f and 4g. As shown in Figure 6 and Figure S8 (SI), peaks corresponding to [M – 3OTf]³⁺, [M – 4OTf]⁴⁺, [M – 5OTf]⁵⁺, [M – 6OTf]⁶⁺, and [M – 8OTf]⁸⁺ were observed for 4f and 4g. In addition, the peaks of [M – 3OTf]³⁺ are isotopically resolved and in good agreement with their calculated theoretical distributions. The clean and well-defined signals in both the NMR and MS spectra support the exclusive formation of functionalized tetragonal prisms as products¹⁵.

Figure 5.

The ³¹P{¹H} NMR spectrum (A) and partial ¹H NMR spectrum (B; 300 MHz, 298 K) of 4f recorded in acetone-d₆.

Figure 6.

Full ESI-MS spectrum and isotopic resolved peak of [M – 3OTf]³⁺(calculated: blue; experimental: red) for tetragonal prism 4f.

As attempts to grow single crystals of 4 suitable for X-ray crystallography have so far been unsuccessful, molecular force field simulations and PGSE NMR experiments were used to gain further structural information about 4. Molecular dynamic simulations using MMFF force fields were applied to independently equilibrate cages 4a–4g, followed by energy minimizations of the resulting structures to full convergence. As shown in Figure 7 and Figure S9 (SI), the computed structures of 4 are well defined tetragonal prisms with diameters between 2.30 and 2.70 nm, which are comparable to the sizes determined by PGSE NMR measurements (4a: 2.32 ± 0.06 nm; 4b: 2.48 ± 0.04 nm; 4c: 2.84 ± 0.12 nm; 4d: 2.12 ± 0.04 nm; 4e: 2.26 ± 0.02 nm; 4f: 2.21± 0.11 nm; 4g: 2.43± 0.19 nm).

Figure 7.

Molecular models of tetragonal prisms 4a (A), 4b (B), and 4f(C).

Conclusion

We report here a facile route to functionalized metallosupramolecular tetragonal prisms via multicomponent, coordination-driven, template-free self-assembly. Functionalities were introduced onto 3-D nanostructures by utilizing pre-modified building blocks prior to self-assembly. The methodology developed in this paper extends the emerging strategy of simple, multicomponent self-assembly to allow the integration of specific functionalities onto supramolecules. As such, this chemistry is an important step in designing functional nanoscale architectures which can mimic natural systems.

Experimental Section

General Details

Ligands 3d¹⁶ and 3f¹⁷ were prepared according to reported procedures. Deuterated solvents were purchased from Cambridge Isotope Laboratory (Andover, MA). NMR spectra were recorded on a Varian Unity 300 MHz spectrometer. ¹H NMR chemical shifts are reported relative to residual proteo solvent signals, and ³¹P{¹H} NMR chemical shifts are referenced to an external unlocked sample of 85% H₃PO₄ (δ 0.0). Mass spectra for the self-assemblies were recorded on a Micromass Quattro II triple-quadrupole mass spectrometer using electrospray ionization with a MassLynx operating system. Molecular modeling of tetragonal prisms was performed using the program Maestro v 8.0.110 with MMFF methods. Platinum was modeled using the force field of carbon restrained to have a planar geometry and typical platinum-nitrogen, platinum-oxygen, and platinum-phosphorus bond lengths. For the models of 4e and 4g, ferrocenes were replaced with cyclopentadiene groups.

Synthesis of 3e

Dimethyl-5-hydroxyisophthalate (450.0 mg, 2.1 mmol) and potassium carbonate (0.8 g, 5.8 mmol) were mixed in 20.0 mL of anhydrous DMF and stirred for 1 h under an atmosphere of nitrogen. A solution of 3-bromopropanylferrocene¹⁸ (0.65 g, 2.1 mmol) in 1.0 mL DMF was then added dropwise. The resulting solution was stirred at 60 °C for 24 h, quenched with water and extracted with ethyl acetate (3 × 20 mL). The combined organic phases were dried with anhydrous sodium sulfate and the solvent removed in vacuo. The residue was purified by flash chromatography on silica gel (eluent: hexane/dichloromethane, v:v = 1:10) to afford dimethyl-3-ferrocenylpropanyloxyisophthalate as a reddish oil which was used, as isolated, in future steps. Yield: 43%. ¹H NMR (CDCl₃, 300 MHz, 298 K): δ = 8.27 (m, 1H, Ar-H), 7.76 (m, 2H, Ar-H), 4.05 – 4.15 (m, 11H, Fc and OCH₂), 3.95 (s, 6H, COOCH₃), 2.54 (m, 2H, CH₂CH₃), 2.02 (t, 2H, 6.0 Hz, CH₃).

To a solution of dimethyl-3-ferrocenylpropanyloxyisophthalate, 0.50 g (1.1 mmol) in 5.0 mL of methanol, was added 5.0 mL of aqueous NaOH (0.20 g, 5.0 mmol). The mixture was refluxed for 5 h and the solvent removed under reduced pressure. The resulting aqueous solution was acidified with HCl to afford a yellow precipitate, 3-ferrocenepropanyloxyisophthalic acid. Yield: 82%. ¹H NMR (DMSO-d₆, 300 MHz, 298 K): δ = 8.08 (s, 1H, Ar-H), 7.65 (m, 2H, Ar-H), 4.05 – 4.13 (m, 11H, Fc and OCH₂), 2.47 (m, 2H, CH₂CH₃), 1.99 (t, 3H, 6.1 Hz, CH₃); ¹³C NMR (DMSO-d6, 75 MHz, 298 K): 167.4, 159.6, 133.6, 123.0, 119.7, 89.7, 69.0, 68.4, 67.6, 30.3, 26.1.

The corresponding sodium salt, 3e, was isolated by neutralization of 3-ferrocenepropanyloxyisophthalic acid (111.3 mg) with 2 eq. sodium bicarbonate (45.8 mg) in 3.0 mL aqueous solution and subsequent precipitation with acetone to give a yellow solid.

Synthesis of 3g

Dimethyl-2-hydroxyterephthalate (630.0 mg, 3.0 mmol) and potassium carbonate (0.9 g, 6.9 mmol) were mixed in 20.0 mL of anhydrous DMF and stirred for 3 h under an atmosphere of nitrogen. A solution of 6-bromohexylferrocene¹⁹ (1.24 g, 3.6 mmol) in 1.0 mL DMF was then added dropwise. The resulting solution was stirred at 60 °C for 2 days, quenched with water and extracted with ethyl acetate (3 × 20 mL). The combined organic phases were dried with anhydrous sodium sulfate and the solvent removed in vacuo. The residue was purified by flash chromatography on silica gel (eluent: hexane/dichloromethane, v:v = 2:3) to afford dimethyl-6-ferrocenylhexyloxy-terephthalate as a reddish oil which was used, as isolated, in future steps. Yield: 43%. ¹H NMR (CDCl₃, 300 MHz, 298 K): δ = 7.78 (d, 1H, Ar-H, 8.4 Hz), 7.63 (d, 1H, Ar-H, 8.4 Hz), 7.61 (s, 1H, Ar-H), 4.00 – 4.15 (m, 11H, Fc and OCH₂), 3.94, 3.91 (s, 6H, COOCH₃), 1.40 – 2.35 (m, 11H, alkyl chain).

To a solution of dimethyl-6-ferrocenylhexyloxyterephthalate, 0.47 g (1.0 mmol) in 5.0 mL of methanol, was added 5.0 mL of aqueous NaOH (0.36g, 9.0 mmol). The mixture was refluxed for 5 h and the solvent removed under reduced pressure. The resulting aqueous solution was acidified with HCl to afford a yellow precipitate, 6-ferrocenehexyloxyterephthalic acid. Yield: 82%. ¹H NMR (DMSO-d₆, 300 MHz, 298 K): δ = 7.54 (d, 1H, Ar-H, 8.4 Hz), 7.55 (d, 1H, Ar-H, 8.4 Hz), 7.52 (s, 1H, Ar-H), 4.03 – 4.10 (m, 11H, Fc and OCH₂), 1.35 – 2.28 (m, 11H, alkyl chain); ¹H NMR (DMSO-d6, 5 MHz, 298 K): 168.1, 167.5, 157.6, 135.2, 126.8, 121.6, 114.1, 89.8, 69.1, 68.9, 68.6, 67.6, 31.4, 29.8, 29.3, 29.2, 25.8.

The corresponding sodium salt, 3g, was isolated by neutralization of 6-ferrocenehexyloxyterephthalic acid (102.2 mg) with 2 eq. sodium bicarbonate (38.2 mg) in 3.0 mL aqueous solution and subsequent precipitation with acetone to give a yellow solid.

Self-assembly of tetragonal prism 4a

Tetra-(4-pyridylphenyl)ethylene 1 (1.04 mg, 1.62 μmol), (PEt₃)₂Pt(OTf)₂ (2) (4.72 mg, 6.49 μmol), and dipyridine ligand 3a (0.70 mg, 3.24 μmol) were mixed in 0.9 mL of acetone/nitromethane (v:v = 2:1) and then stirred for 12 h at room temperature. After removing the solvent in vacuo, the resulting residue was washed with dichloromethane three times to afford 4a as yellow solid. Yield: 41%. ³¹P{¹H} NMR (acetonitrile-d₃, 121.4MHz) δ = 0.85 (d, ²J_P-P = 20.2 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: 3082.3 Hz), 0.78 (d, ²J_P-P = 20.2 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: 3080.2 Hz); ¹H NMR (acetonitrile-d₃, 300 MHz, 298 K): δ = 8.67 (m, 16H, H_α-Py for donor 1), 8.67 (m, 16H, H_α-Py for donor 3a),7.75 (m, 16H, H_β-Py for donor 1), 7.58 (m, 16H, H_β-Py for donor 3a), 7.20–7.54 (d, 32H, Ar-H, 8.4 Hz), 4.19 (m, 8H, CH-OH), 3.90 (m, 8H, CH-OH), 1.84 (m, 96H, PCH₂CH₃), 1.23(m, 144H, PCH₂CH₃); MS (ESI) for 4a (C₂₅₂H₃₅₂F₄₈N₁₆O₅₆P₁₆Pt₈S₁₆): m/z: 1845.6.2 [M – 4OTf]⁴⁺; 1446.9 [M – 5OTf]⁵⁺. Anal. Calcd for C₂₅₂H₃₅₂F₄₈N₁₆O₅₆P₁₆Pt₈S₁₆: C, 37.92; H, 4.44; N, 2.81; Found: C, 37.47; H, 4.50; N, 2.83.

General procedure for the self-assembly of tetragonal prisms 4b–4g using functionalized terephthalate ligands

Tetra-(4-pyridylphenyl)ethylene 1, (PEt₃)₂Pt(OTf)₂ 2, and isophthalate derivatives 3b–3g were mixed in 0.9 mL of acetone/H₂O (v:v = 8:1). The mixtures were stirred at 65 °C for 4 h, at which time the solvents were removed and the residues redissolved in nitromechane-d₆, followed by a further 4 h of stirring at 65 °C. Tetragonal prisms 4b–4g were isolable as solids recrystalized from acetone/diethyl ether.

Synthesis and characterization of 4b

Reaction scale: tetratopic ligand (1) (0.94 mg, 1.47 μmol), (PEt₃)₂Pt(OTf)₂ (2) (4.28 mg, 5.87 μmol), and 5-aminoisophthalate (3b) (0.66 mg, 2.94 μmol). Yield: 82%. ³¹P{¹H} NMR(nitromechane-d₃, 121.4MHz) δ = 6.95 (d, ²J_P-P = 21.6 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3220.7 Hz), 1.01 (d, ²J_P-P = 21.5 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3428.3 Hz); ¹H NMR (nitromechane-d₃, 300 MHz, 298 K): δ = 8.79 (m, 16H, H_α-Py for donor 1), 7.78 (m, 16H, H_β-Py for donor 1, Ar-H), 7.56 (m, 16H, Ar-H), 7.34 (m, 4H, Ar-H), 7.30 (m, 16H, Ar-H), 7.24 (m, 8H, Ar-H), 1.98 (m, 96H, PCH₂CH₃), 1.31 (m, 144H, PCH₂CH₃); MS (ESI) for 4b(C₂₂₅H₃₂₄F₁₅N₁₂O₃₁P₁₆Pt₈S₅): m/z: 2063.2 [M – 3OTf]³⁺. Anal. Calcd for C₂₂₈H₃₂₄F₂₄N₁₂O₄₀P₁₆Pt₈S₈: C, 41.23; H, 4.62; N, 2.53; Found: C, 40.52; H, 4.76; N, 2.51.

Synthesis and characterization of 4c

Reaction scale: tetratopic ligand (1) (1.00 mg, 1.56 μmol), (PEt₃)₂Pt(OTf)₂ (2) (4.55mg, 6.24 μmol), and 5-nitroisophthalate (3c) (0.80 mg, 3.12 μmol). Yield: 74%. ³¹P{¹H} NMR(nitromechane-d₃, 121.4MHz) δ = 6.71 (d, ²J_P-P = 21.7 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3203.7 Hz), 1.35 (d, ²J_P-P = 21.6 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3512.3 Hz); ¹H NMR (nitromechane-d₃, 300 MHz, 298 K): δ = 8.82 (m, 16H, H_α-Py for donor 1), 8.83 (m, 8H, Ar-H), 8.36 (m, 4H, Ar-H), 7.79(m, 16H, H_β-Py for donor 1), 7.54 (m, 16 H, Ar-H), 7.26 (m, 16 H, Ar-H), 1.99 (m, 96H,PCH₂CH₃), 1.31 (m, 144H, PCH₂CH₃); MS (ESI) for 4c (C₂₅₂H₃₁₆F₁₅N₁₂O₃₉P₁₆Pt₈S₅): m/z: 2104.5 [M – 3OTf]³⁺. Anal. Calcd for C₂₂₈H₃₁₆F₂₄N₁₂O₄₈P₁₆Pt₈S₈: C, 40.5; H, 4.71; N, 2.49; Found: C, 39.60; H, 4.51; N, 2.42.

Synthesis and characterization of 4d

Reaction scale: tetratopic ligand (1) (0.93 mg, 1.45 μmol), (PEt₃)₂Pt(OTf)₂ (2) (4.25 mg, 5.80 μmol), and 5-(3-propanyl)isophthalate (3d) (0.78 mg, 2.90 μmol). Yield: 86%. ³¹P{¹H} NMR (acetonitrile-d₃, 121.4MHz) δ = 6.71 (d, ²J_P-P = 21.7 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3192.7 Hz), 1.17 (d, ²J_P-P = 21.6 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3448.9 Hz); ¹H NMR (acetonitrile-d₃, 300 MHz, 298 K): δ = 8.67 (m, 16H, H_α-Py for donor 1),7.70 (m, 16H, H_β-Py for donor 1), 7.52 (m, 16H, Ar-H), 7.39 (d, 8H, Ar-H), 7.20 (s, 16H, Ar-H), 3.92 (t, 8H, OCH₂, 5.4Hz), 2.12 (m, 8H, alkyl), 1.79 (m, 96H,PCH₂CH₃), 1.18 (m, 144H, PCH₂CH₃); 1.01 (t, 12H, CH₃, 7.4Hz); MS (ESI) for 4d (C₂₃₇H₃₄₄F₁₅N₈O₃₅P₁₆Pt₈S₅): m/z: 2121.8[M – 3OTf]³⁺. Anal. Calcd for C₂₇₂H₃₅₆F₂₄N₁₂O₆₈P₁₆Pt₈S₈: C, 42.30; H, 5.09; N, 1.64; Found: C, 41.84; H, 4.93; N, 1.68.

Synthesis and characterization of 4e

Reaction scale: tetratopic ligand (1) (0.94 mg, 1.47 μmol), (PEt₃)₂Pt(OTf)₂ (2) (4.29 mg, 5.88 μmol), and 5-(3-Ferrocenylpropanyl)isophthalate (3e) (1.33 mg, 2.94 μmol). Yield: 65%. ³¹P{¹H} NMR(acetonitrile-d₃, 121.4MHz) δ = 6.72 (d, ²J_P-P = 21.6 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3202.7 Hz), 1.19 (d, ²J_P-P = 21.6 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3431.9 Hz); ¹H NMR (acetonitrile-d₃, 300 MHz, 298 K): δ = 8.70 (m, 16H, H_α-Py for donor 1),7.72 (m, 16H, H_β-Py for donor 1), 7.53 (m, 20H, Ar-H), 7.45 (m, 8H, Ar-H), 7.25 (m, 16H, Ar-H), 4.08–4.16(m, 45H, ferrocene), 4.05 (t, 8H, OCH₂, 5.4Hz), 2.54 (m, 8H, CH₂-Fc); 1.89 (m, 104H, PCH₂CH₃, OCH₂CH₂CH₂Fc), 1.15 (m, 144H, PCH₂CH₃); MS (ESI) for 4e (C₂₇₇H₃₇₆F₁₅Fe₄N₈O₃₅P₁₆Pt₈S₅): m/z: 2366.9[M – 3OTf]³⁺. Anal. Calcd for C₂₈₀H₃₇₆F₂₄Fe₄N₈O₄₄P₁₆Pt₈S₈: C, 44.54; H, 5.02; N, 1.48; Found: C, 43.71; H, 4.92; N, 1.48.

Synthesis and characterization of 4f

Reaction scale: tetratopic ligand (1) (1.03 mg, 1.61μmol), (PEt₃)₂Pt(OTf)₂ (2) (4.61mg, 6.44 μmol), and 2-(6-hexyl)terephthalate (3f) (1.00 mg, 3.22 μmol). Yield: 74%. ³¹P{¹H} NMR(acetone-d₆, 121.4MHz) δ = 6.79 (d, ²J_P-P = 21.9 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3228.1 Hz), 6.12 (d, ²J_P-P = 21.9 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3221.9 Hz), 1.28 (d, ²J_P-P = 21.9 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3439.3 Hz), 1.21 (d, ²J_P-P = 21.9 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3445.3Hz); ¹H NMR (acetone-d₆, 300 MHz, 298 K): δ = 8.92 (m, 16H, H_α-Py for donor 1),7.94–8.00 (m, 16H, H_β-Py for donor 1), 7.29 –7.75 (m, 32H, Ar-H), 7.21 (s, 4H, Ar-H), 7.20 (d, 4H, 9.0 Hz), 6.96 (d, 4H, 9.0 Hz), 3.89 (t, 8H, OCH₂, 5.4Hz), 2.13 (m, 44H, alkyl) 1.99 (m, 96H,PCH₂CH₃), 1.31 (m, 144H, PCH₂CH₃); MS (ESI) for 4f (C₂₅₂H₃₆₈F₂₄N₈O₄₄P₁₆Pt₈S₈): m/z: 2177.7 [M – 3OTf]₃₊. Anal. Calcd for C₂₅₂H₃₆₈F₂₄N₈O₄₄P₁₆Pt₈S₈: C, 43.35; H, 5.31; N, 1.60; Found: C, 42.71; H, 5.02; N, 1.62.

Synthesis and characterization of 4g

Reaction scale: tetratopic ligand (1) (0.63 mg, 0.98 μmol), (PEt₃)₂Pt(OTf)₂ (2) (2.87 mg, 3.93 μmol), and 2-(6-Ferrocenylhexyl)terephthalate (3g) (0.97 mg, 1.97 μmol). Yield: 86%. ³¹P{¹H} NMR (acetone-d₆, 121.4MHz) δ = 6.80 (d, ²J_P-P = 21.9 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3215.9 Hz), 6.10 (d, ²J_P-P = 21.9 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3208.6.9 Hz), 1.28 (d, ²J_P-P = 21.9 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3419.3 Hz), 1.21(d, ²J_P-P = 21.9 Hz, ¹⁹⁵Pt satellites,¹J_Pt-P: = 3410.3Hz); ¹H NMR (acetone-d₆, 300 MHz, 298 K): δ = 8.91 (m, 16H, H_α-Py for donor 1),7.93 (m, 16H, H_β-Py for donor 1), 7.27–7.72 (m, 16H, Ar-H), 7.23 (d, 4H, 9.0 Hz), 7.20 (s, 4H, Ar-H), 6.97 (d, 4H, 9.0 Hz), 4.05–4.10 (m, 45H, ferrocene), 3.89 (t, 8H, OCH₂, 5.4Hz),2.12 (m, 40H, alkyl) 1.99 (m, 96H,PCH₂CH₃), 1.32 (m, 144H, PCH₂CH₃); MS (ESI) for 4g (C₂₉₂H₄₀₀F₂₄Fe₄N₈O₄₄P₁₆Pt₈S₈): m/z: 2422.8[M – 3OTf]³⁺. Anal. Calcd for C₂₉₂H₄₀₀F₂₄Fe₄N₈O₄₄P₁₆Pt₈S₈: C, 45.44; H, 5.22; N, 1.45; Found: C, 44.71; H, 5.02; N, 1.44.