Organometallic rotaxane dendrimers with fourth-generation mechanically interlocked branches

Significance

In this study, the preparation of organometallic rotaxane dendrimers with a well-defined topological structure and enhanced rigidity was developed. Starting from a simple rotaxane building block, high-generation rotaxane branched dendrimers were synthesized and characterized. The fourth-generation structure described is among the highest-generation organometallic rotaxane dendrimers reported to date. The introduction of pillar[5]arene rotaxane units activates dynamic features in the dendrimer and enhances the rigidity of each branch of the supermolecules. This research offers a facile approach to the construction of high-generation rotaxane branched dendrimer, which not only enriches the library of rotaxne dendrimer but also provides the further insight into their applications as supramolecular dynamic materials.

Abstract

Mechanically interlocked molecules, such as catenanes, rotaxanes, and knots, have applications in information storage, switching devices, and chemical catalysis. Rotaxanes are dumbbell-shaped molecules that are threaded through a large ring, and the relative motion of the two components along each other can respond to external stimuli. Multiple rotaxane units can amplify responsiveness, and repetitively branched molecules—dendrimers—can serve as vehicles for assembly of many rotaxanes on single, monodisperse compounds. Here, we report the synthesis of higher-generation rotaxane dendrimers by a divergent approach. Linkages were introduced as spacer elements to reduce crowding and to facilitate rotaxane motion, even at the congested periphery of the compounds up to the fourth generation. The structures were characterized by 1D multinuclear (¹H, ¹³C, and ³¹P) and 2D NMR spectroscopy, MALDI-TOF-MS, gel permeation chromatography (GPC), and microscopy-based methods including atomic force microscopy (AFM) and transmission electron microscopy (TEM). AFM and TEM studies of rotaxane dendrimers vs. model dendrimers show that the rotaxane units enhance the rigidity and reduce the tendency of these assemblies to collapse by self-folding. Surface functionalization of the dendrimers with ferrocenes as termini produced electrochemically active assemblies. The preparation of dendrimers with a well-defined topological structure, enhanced rigidity, and diverse functional groups opens previously unidentified avenues for the application of these materials in molecular electronics and materials science.

Dendritic molecules containing rotaxane components are a recently developed subset of mechanically bonded supermolecules (1–3). The combination of the characteristics of both rotaxanes (sliding and rotary motion) and dendrimers (repetitive branching with each generation) provides the resultant rotaxane dendrimers with unusual topological features and potentially useful properties. For example, the introduction of stimuli-responsive rotaxanes (4) such as muscle-like bistable rotaxanes or daisy chains can impart switchable features to the resultant dendrimers that are “smart” to external inputs. The applications of dendrimers in materials science (5, 6) suggest that rotaxane dendrimers could serve as supramolecular dynamic materials.

A variety of rotaxane dendrimers have been designed and constructed over the past few years. For examples, mechanically interlocked units were used either as cores or end groups, by Vögtle and coworkers (7), Stoddart and coworkers (8–13), Gibson et al. (14), Kim and coworkers (15, 16), and Kaifer and coworkers (17, 18). Compared with these simpler systems, rotaxane dendrimers with interlocking ring components on the branches or at the branch points are rare. Specifically, Kim et al. (16) and Leung et al. (19) have reported the only two cases of rotaxane branched dendrimers up to the second generation. Third- or higher-generation rotaxane dendrimers equipped with mechanically interlocked functions on the branches (Fig. 1) are unknown to us.

Fig. 1.

Schematic representation of a rotaxane dendrimer with mechanically interlocked moieties incorporated on the branches.

Herein, we describe the synthesis, characterization, and functionalization of higher-generation (up to fourth-generation) organometallic rotaxane branched dendrimers. A divergent strategy was employed for the dendrimer synthesis in which the host–guest complex of a pillar[5]arene and a neutral alkyl chain were used as the rotaxane subunits. The formation of platinum–acetylide bonds was the growth step in the synthesis; it produced satisfactory yields and allowed construction of the targeted structures. The introduction of macrocyclic wheels enhanced the rigidity of the resultant rotaxane dendrimers and reduced self-folding. Electrochemically active rotaxane dendrimers substituted with different numbered ferrocenes were also prepared by direct surface modification.

Results and Discussion

Synthesis.

To synthesize rotaxane branched dendrimers, the mechanically interlocked functions must be repeating subunits of the targeted structures. The rotaxane building blocks must be stable enough to handle and incorporate repeatedly during the growth processes. We used organometallic [2] rotaxane 1 (Fig. 2) as the basic precursor for the divergent dendrimer growth for the following reasons: (i) 1 can be quickly synthesized by using Ogoshi’s available pillar[5]arene and its neutral alkyl chain guest (20–22); (ii) 1 contains a platinum–acetylide unit that prevents the macrocycle from escaping the thread; (iii) 1 can react with a free alkyne to generate a stable organometallic bond in good yield under mild conditions (23–25); (iv) 1 contains protected alkynes that can be gently exposed for dendrimer growth; and (v) 1 has active alkyne units that can be functionalized to impart further structural diversity and function.

Fig. 2.

Chemical structure of organometallic [2]rotaxane 1, a key building block in the preparation of the rotaxane dendrimers.

We synthesized organometallic [2]rotaxane 1 in a few steps, as indicated in SI Appendix, Scheme S1. The rotaxane formation step proceeded in good yield (86%) from three components and allowed the preparation of 1 on gram scales. The building block 1 proved stable and soluble in common solvents during the dendrimer growth processes. Unlike classic charged rotaxane systems that are constructed by incorporating either charged macrocyclic wheels or axles, organometallic [2]rotaxane 1 is neutral, which simplifies the subsequent reaction and purification processes. The growth processes relied on a Cu(I)-catalyzed coupling reaction of 1 with the corresponding polyacetylene precursors. During this reaction, the bulky phosphine ligands remained inert and the rotaxane remained intact.

Following production of the building block 1, the divergent growth of organometallic dendrimers was carried out by incorporating mechanically interlocked rotaxanes on the branches (Fig. 3). The Cu(I)-catalyzed coupling reaction of 1 and 1,3,5-triethynylbenzene produced the first-generation rotaxane dendrimer G₁ at a yield of 79%, where six protected alkynes were located at the outer periphery of the compound (Fig. 3A). Deprotection of G₁ with tetrabutylammonium fluoride produced the corresponding dendrimer G₁-YNE, in an 87% yield, which bore six acetylene groups. These groups were used to grow the next generation: The coupling of G₁-YNE and 1 produced the second-generation rotaxane dendrimer G₂ with nine pillar[5]arene-based rotaxanes on the branches in 58% yield. The third- and fourth-generation rotaxane dendrimers (G₃ and G₄, respectively) were prepared via sequential deprotection−coupling processes, as shown in Fig. 3B. The fourth-generation rotaxane dendrimer G₄, can be considered as a highly branched [46]rotaxane: 45 rotaxanes located in a dendrimer skeleton of monodisperse distribution. All of the dendrimers G₁−G₄ were soluble in common solvents such as chloroform, dichloromethane, and THF. The purification of these dendrimers was performed using flash column chromatography and recrystallization.

Fig. 3.

(A) Synthesis of organometallic rotaxane dendrimers G₁ by a CuI-catalyzed coupling reaction of 1 and 1,3,5-triethynylbenzene; (B) schematic of a controllable divergent approach for the synthesis of organometallic rotaxane dendrimers G₂–G₄.

Rotaxane Dendrimer Characterization.

The ¹H NMR spectra of these dendrimers, especially G₃ and G₄, showed no proton signals from the terminal acetylenes that would signal structural defects formed during the growth processes. The peaks ascribed to the protons on the linear axle of the rotaxanes were located in a range (below 0.0 ppm) similar to that of [2]rotaxane precursor 1. This result indicates that the structure of the rotaxane was not destroyed during the growth process. More than one set of peaks corresponding to the threaded structures was observed for each subsequent generation. In other words, the rotaxane subunits were located on different branches and were nonequivalent (SI Appendix, Fig. S79). Compared with [2]rotaxane precursor 1, each ³¹P NMR spectrum of the rotaxane dendrimers displayed a downfield shift (Δδ ≃ 2.4 ppm), which also supports the formation of platinum–acetylide bonds during dendrimer growth. As in the ¹H NMR spectra, different chemical shifts were observed for the phosphine ligands in each generation in the growth of the rotaxane dendrimers, indicating the nonequivalent chemical environment of the phosphorous ligands (SI Appendix, Fig. S80).

MALDI-TOF-MS studies were performed on all of the rotaxane dendrimers. The spectra provided direct support for the formation of mechanically interlocked compounds (Fig. 4). For the first-generation rotaxane dendrimer G₁, the MALDI-TOF-MS spectrum in reflectron mode exhibited a single peak at m/z = 6,661.5, which was attributed to [G₁ + H]⁺ with a theoretical monoisotopic mass at 6,661.9 Da. This peak was isotopically resolved and agreed well with the theoretical distribution. The corresponding peaks were also observed in the MS spectra of the higher-generation rotaxane dendrimers G₂ and G₃, confirming the synthesis of the targeted compounds. [With increasing molecular weight (for G₂, theoretical average M_r = 18,760 Da; for G₃, theoretical average M_r = 42,948 Da), the peaks became broader, with a rational deviation from the theoretical mass in linear acquisition mode. This broadening effect was attributed to the binding of sodium and potassium ions to large rotaxane dendrimers, along with the proton signals.] For these high-generation architectures, high charge states, i.e., 2+ and/or 3+, were also observed in MALDI-TOF-MS in addition to singly charged ions, as shown in Fig. 4 B and C. In the MS spectrum of G₃, some fragments were observed. Further experiments with stronger laser power showed that the MS spectrum of G₃ produced a higher abundance of fragments (SI Appendix, Fig. S40). This indicates that such additional peaks may be attributed to the fragments induced in either MALDI source or ionization processes (26). For the fourth-generation rotaxane dendrimer G₄, neither MALDI-TOF nor electrospray ionization-MS provided satisfactory mass data because of the high molecular mass (theoretical average M_r = 91,254 Da) and low ionization efficiency of G₄. A gel permeation chromatography (GPC) analysis of G₃ and G₄ revealed narrow distributions for the number-averaged molecular weight (M_n) and the polydispersity index (PDI) (for G₃, PDI = 1.07; for G₄, PDI = 1.09; SI Appendix, Figs. S81 and S82). The M_n values clearly increased for each dendrimer generation (for G₃, M_n = 32,440; for G₄, M_n = 48,022), as expected for the existence of the fourth-generation rotaxane dendrimer G₄.

Fig. 4.

MALDI-TOF-MS spectra for rotaxane dendrimers G₁ (A)_, G₂ (B), and G₃ (C).

The “Rotaxane Effect.”

The effect of introducing rotaxane units into the dendrimers (the “rotaxane effect”) was investigated by preparing model organometallic dendrimers G_n-c (n = 1, 2, 3) without pillar[5]arene wheels using a parallel approach (SI Appendix, Scheme S2). The absence of the pillar[5]arene wheels resulted in reduced solubility of G_n-c in common solvents (chloroform and THF); the third-generation model dendrimer G₃-c was the highest-generation dendrimer that could be synthesized. We used electron microscopy methods such as atomic force microscopy (AFM) and transmission electron microscopy (TEM), to visualize individual supramolecular dendrimers as described by others (27). These methods can provide structural parameters of dendrimers such as their size, conformation, and rigidity, using direct images on a surface. The AFM analysis of G₁−G₄ showed that the average heights gradually increased with each generation of the rotaxane dendrimers (≃1.6 nm for G₁; ≃2.6 nm for G₂; ≃3.3 nm for G₃; and ≃6.0 nm for G₄), as shown in Fig. 5, although flattened dendrimers were also found on the surface. The introduction of pillar[5]arene rotaxane subunits apparently increased the rigidity of each branch of the dendrimers. We expected that the absence of pillar[5]arene wheels would make the model dendrimers G₁-c–G₃-c “floppier” compared with the corresponding rotaxane dendrimers when exposed on the surface. The average heights of the model dendrimers G₁-c–G₃-c were indeed reduced by nearly one-half (≃0.8 nm for G₁-c; ≃1.0 nm for G₂-c; and ≃1.5 nm for G₃-c) compared with the AFM data for the corresponding rotaxane dendrimers under the same conditions (Fig. 6). The enhanced rigidity induced by the rotaxane subunits was further confirmed by TEM, showing that the individual rotaxane dendrimer structure had a size of ∼3.0 nm for G₃, a value in good agreement with the AFM result. However, the TEM image of G₃-c showed a corresponding size of only ∼1.5 nm (SI Appendix, Fig. S85).

Fig. 5.

AFM images of the rotaxane dendrimers G_n (n = 1, 2, 3, and 4).

Fig. 6.

AFM images of the corresponding model dendrimers G_n-c (n = 1, 2, and 3) without pillar[5]arene wheels.

Dynamic light scattering (DLS) is also a useful technique for determining the dimensions of dendrimers in solution, and we applied it to the new compounds. We were unable to measure the size of the smallest dendrimer G₁ using DLS, possibly because the size of G₁ was below the measuring limit. A size progression was observed with increasing generations for the measured hydrodynamic diameters of the higher-generation dendrimers (2.2 nm for G₂; 3.5 nm for G₃; and 8.7 nm for G₄) (SI Appendix, Fig. S84). No obvious size results were obtained in the DLS studies for the model dendrimers G₁-c–G₃-c, possibly because the sizes of G₁-c–G₃-c were all below the measuring limit. This result is also consistent with dendrimer self-folding in the absence of rotaxane subunits. (Note that the rotaxane dendrimers were not completely spherical in solution, and the samples usually exhibited shrinkage on the surface because of solvent loss, which resulted in the measurement of different dendrimer sizes using the aforementioned three types of techniques. These results are reasonable according to previous reports. For example, see ref. 28.) We also used 2D diffusion-ordered NMR spectroscopy to evaluate the size (hydrodynamic diameter) of the dendrimers in solution. The introduction of the pillar[5]arene wheels resulted in a decrease in the measured weight-averaged diffusion coefficients (D). For example, under the same conditions, the diffusion coefficient of the rotaxane dendrimer G₃ was found to be 5.83 × 10⁻¹¹ m²/s, which was significantly smaller than that of the model dendrimer G₃-c (2.19 × 10⁻¹⁰ m²/s).

These results support a structural role for the rotaxane subunits that enhances the rigidity of the branches and the integrated dendrimers. This “rotaxane effect” may also impart stability in their laser desorption/ionization processes in the MALDI-TOF-MS spectra. For instance, under the same characterization conditions, the G₁ exhibited a complete and single molecular ion peak [G₁+H]⁺, whereas the corresponding model G₁-c displayed additional peak fragments attributed to degradation of the dendrimer skeleton (see SI Appendix, Fig. S21 for G₁ and SI Appendix, Fig. S53 for G₁-c).

Surface Modification.

A subsequent study was performed in which the new dendrimers were subjected to surface modification (29) with functional groups. In this study, a triisopropylsilyl-protected acetylene group was used as the surface group to facilitate dendrimer growth and enable diversity. We chose ferrocene, a robust redox function, which has been extensively explored in applications in the nanoelectronics field (30, 31). The ferrocene subunit was introduced into the rotaxane dendrimers via a coupling reaction of the ferrocenyl monosubstituted platinum–acetylide complex with the multiple alkyne groups in the respective rotaxane dendritic intermediates (G₁-YNE, G₂-YNE, and G₃-YNE) (SI Appendix, Scheme S3). The resultant heterobimetallic dendrimers, G₁-Fc, G₂-Fc, and G₃-Fc, with 6, 12, and 24 ferrocene units, respectively, were characterized by 1D multinuclear (¹H, ¹³C, and ³¹P) NMR spectroscopy and MALDI-TOF-MS.

The cyclic voltammogram studies of the ferrocenyl derivatives revealed that the peak current increased systematically with the increase of the scan rates. The cyclic voltammograms corresponding to the one-electron oxidation of ferrocene groups yielded cathodic/anodic peak current ratios of i_c/i_a ∼ 1. The nearly identical cathodic and anodic peak currents, as well as nearly scan rate-independent peak potentials, indicated that the oxidized complexes were chemically stable on the voltammetric timescale and the oxidation of the ferrocene units in each assembly was chemically reversible (SI Appendix, Fig. S87). The multiple ferrocene groups reacted independently, producing a single voltammetric wave, even though more than one electron was transferred in the overall reaction.

Conclusions

In conclusion, we have reported the synthesis, characterization, and functionalization of a series of organometallic rotaxane dendrimers with mechanically interlocked pillar[5]arene subunits on each branch. We used an organometallic [2]rotaxane precursor, 1, and used sequential coupling–deprotection–coupling processes to obtain organometallic rotaxane dendrimers up to the fourth generation. The largest assembly incorporates 45 rotaxane subunits on the dendritic skeleton in a monodisperse manner. Numerous polymeric rotaxanes, such as rotaxane coordination polymers (32), have been well documented; this study presents discrete, high-generation rotaxane dendrimers with repeating units on each branch. The AFM and TEM studies of the rotaxane dendrimers vs. corresponding model dendrimers indicate that pillar[5]arene “wheels” enhance the rigidity of the branches, reducing self-folding and collapse. Functional rotaxane dendrimers substituted with ferrocenes as termini were prepared through surface chemical transformations. The well-defined topological structures, enhanced rigidity, and diverse functional groups of rotaxane dendrimers should provide a platform for investigations of these molecules in molecular electronics and materials science.

Materials and Methods

General Information.

All reagents were commercially available and were used as supplied without further purification. Deuterated solvents were purchased from Cambridge Isotope Laboratory. NMR spectra were recorded on a Bruker DRX 400 (400-MHz) spectrometer. ¹H and ¹³C NMR chemical shifts were reported relative to the residual solvent signals, and ³¹P{¹H} NMR chemical shifts were referenced to an external unlocked sample of 85% (vol/vol) H₃PO₄ (δ 0.0). The 2D rotating-frame Overhauser enhancement spectroscopy NMR spectra were recorded on a Bruker DRX500 spectrometer. DLS measurements were performed using a Malvern Zetasizer Nano-ZS light scattering apparatus (Malvern Instruments) with a He–Ne laser (633 nm, 4 mW). The TEM images were obtained using a Philips TECNAI-12 instrument with an accelerating voltage of 120 kV. AFM images were obtained on a Dimension FastScan (Bruker), using the ScanAsyst mode under ambient conditions. UV−vis spectra were recorded in a quartz cell (with a light path of 10 mm) on a Cary 50Bio UV–vis spectrophotometer. Steady-state fluorescence spectra were recorded using a conventional quartz cell (with a light path of 10 mm) and a Cary Eclipse fluorescence spectrophotometer. MALDI-MS experiments were carried out using a Bruker UltrafleXtreme MALDI TOF/TOF mass spectrometer (Bruker Daltonics) equipped with a Smartbeam-II laser. Cyclic voltammetry (CV) was performed using a three-electrode cell and a RST electrochemical work station. The working electrode was a glassy carbon disk with surface area of about 7.0 mm². A saturated calomel electrode was used as reference electrode and a Pt wire as the counterelectrode. The CV measurements were carried out in a dichloromethane solution containing 0.2 M tetra-n-butylammoniumhexafluorophosphate (n-Bu₄NPF₆). The concentration of redox molecule in solution was 2.00 mM.

General Procedure for Synthesis of Rotaxane Dendrimers G_n.

A mixture of multiyne complexes (1,3,5-triethynylbenzene for G₁; G₁-YNE for G₂; G₂-YNE for G₃; and G₃-YNE for G₄) and 1 (for each terminal acetylene moiety, 1.1 eq 1 was added) in degassed diethylamine was stirred overnight at room temperature in the presence of a catalytic amount of CuI (∼5 mol %). The solvent was evaporated under reduced pressure and purified by column chromatography on SiO₂ using petroleum ether/CH₂Cl₂ (1:1–0:1) as an eluent to produce a pale-yellow solid as the target compound (recrystallization was necessary for G₃ and G₄).

G₁: Light yellow solid, 79%, ¹H NMR (CDCl₃, 400 MHz): δ 7.25 (d, J = 8.8 Hz, 6H), 7.19 (s, 3H), 7.02 (s, 3H), 6.93 (s, 6H), 6.92 (s, 15H), 6.90 (s, 15H), 6.73 (d, J = 8.8 Hz, 6H), 3.90 (m, 30H), 3.76 (s, 30H), 3.72 (m, 30H), 3.38 (m, 6H), 3.29 (m, 6H), 2.21 (m, 36H), 1.89–1.75 (m, 78H), 1.25 (m, 45H), 1.16 (s, 108H), 1.08–1.01 (m, 98H), 0.81 (m, 6H), 0.48 (m, 6H), 0.16 (m, 2H), 0.15 (m, 6H), −0.05 (m, 18H), −0.68 (m, 6H), −0.76 (m, 6H); ³¹P NMR (CDCl₃, 161.9 MHz): δ 11.4 (J = 2379.9 Hz); ¹³C NMR (CDCl₃, 100 MHz): δ 158.8, 157.1, 149.7, 149.6, 131.8, 128.3, 128.2, 127.7, 124.5, 117.9, 114.2, 114.1, 113.8, 106.3, 90.9, 69.7, 69.6, 68.6, 68.1, 30.59, 30.56, 30.4, 30.1, 29.33, 29.27, 29.1, 25.3, 24.0, 23.3, 23.2, 18.6, 18.3, 18.1, 16.5, 16.3, 16.2, 11.8, 11.3, 10.70, 10.66, 8.4; MS: (MALDI-TOF-MS) 6,667.15 ([M+H]⁺).

G₂: Light yellow solid, 58%, ¹H NMR (CDCl₃, 400 MHz): δ 7.22 (d, J = 8.8 Hz), 7.19 (s), 7.04 (s), 6.92 (s), 6.92 (s), 6.90 (s), 6.73 (d, J = 8.8 Hz), 6.68 (d, J = 8.8 Hz), 6.64 (s), 3.89 (m), 3.76 (s), 3.74 (m), 3.40 (m), 3.28 (m), 2.71 (m), 2.22 (m, –PCH₂CH₃), 1.87–1.75 (m), 1.26 (m), 1.16 (s), 1.12–0.98 (m), 0.82 (m), 0.73 (m), 0.48 (m), 0.38 (m), 0.15 (m), −0.05 (m), −0.33 (m), −0.69 (m), −0.77 (m), −1.35 (m), −1.77 (m); ³¹P NMR (CDCl₃, 161.9 MHz): δ 11.5 and 11.3; ¹³C NMR (CDCl₃, 100 MHz): δ 158.8, 157.2, 149.70, 149.65, 149.6, 131.8, 131.6, 128.3, 128.23, 128.16, 127.7, 124.5, 117.9, 114.2, 114.1, 113.8, 113.6, 106.3, 90.9, 69.7, 69.6, 69.5, 68.6, 68.1, 30.9, 30.8, 30.6, 30.4, 30.3, 30.2, 30.1, 29.33, 29.31, 29.27, 29.1, 25.3, 24.0, 23.30, 23.25, 23.22, 23.18, 18.6, 18.3, 18.1, 16.5, 16.4, 16.2, 11.8, 11.3, 10.8, 10.69, 10.66, 8.4; MS: (MALDI-TOF-MS) 18,768 (broad, [M+H]⁺, [M+Na]⁺).

G₃: Light yellow solid, 49%, ¹H NMR (CDCl₃, 400 MHz): δ 7.22 (d, J = 8.8 Hz), 7.19 (s), 7.04 (s), 6.92 (s), 6.92 (s), 6.90 (s), 6.73 (d, J = 8.8 Hz), 6.69 (d, J = 8.8 Hz), 6.64 (s), 3.90 (m), 3.76 (s), 3.73 (m), 3.39 (m), 3.28 (m), 2.72 (m), 2.23 (m), 1.89–1.73 (m), 1.26 (m), 1.16 (s), 1.12–0.98 (m), 0.82 (m), 0.73 (m), 0.48 (m), 0.38 (m), 0.15 (m), −0.04 (m), −0.33 (m), −0.68 (m), −0.77 (m), −1.35 (m), −1.77 (m); ³¹P NMR (CDCl₃, 161.9 MHz): δ 11.44, 11.38 and 11.2; ¹³C NMR (CDCl₃, 100 MHz): δ 158.8, 157.2, 149.69, 149.65, 149.58, 131.8, 131.6, 128.3, 128.23, 128.16, 127.7, 124.5, 117.9, 114.2, 114.1, 113.8, 113.6, 106.3, 90.9, 69.78, 69.70, 69.6, 69.5, 68.6, 68.1, 30.9, 30.8, 30.6, 30.4, 30.3, 30.2, 30.1, 29.33, 29.31, 29.27, 29.1, 25.3, 24.0, 23.30, 23.25, 23.22, 23.18, 18.6, 18.3, 18.07, 18.02, 16.5, 16.4, 16.2, 11.8, 11.3, 10.8, 10.69, 10.65, 10.60, 8.4; MS: (MALDI-TOF-MS) 42,959 (broad, [M+H]⁺, [M+Na]⁺, [M+K]⁺), 21,501 (broad, [M+2H]²⁺, etc.).

G₄: Light yellow solid, 83%, ¹H NMR (CDCl₃, 400 MHz): δ 7.22 (d), 7.18 (s), 6.93 (s), 6.92 (s), 6.90 (s), 6.81 (s), 6.73 (d), 6.69 (d), 6.65 (s), 3.90 (m), 3.76 (s), 3.73 (m), 3.38 (m), 3.29 (m), 2.71 (m), 2.22 (m), 1.89–1.68 (m), 1.16 (m), 1.16 (s), 1.12–0.86 (m), 0.82 (m), 0.73 (m), 0.48 (m), 0.37 (m), 0.14 (m), 0.07 (s), −0.05 (m), −0.33 (m), −0.68 (m), −0.76 (m), −1.34 (m), −1.77 (m); ³¹P NMR (CDCl₃, 161.9 MHz): δ 11.48 and 11.43; ¹³C NMR (CDCl₃, 100 MHz): δ 158.8, 157.1, 149.70, 149.66, 149.60, 131.8, 131.6, 128.31, 128.25, 128.18, 124.5, 118.0, 114.2, 114.1, 113.8, 113.6, 106.3, 90.9, 90.1, 69.8, 69.7, 69.6, 69.5, 68.6, 68.1, 30.8, 30.6, 30.4, 30.1, 29.69, 29.65, 29.5, 29.3, 29.1, 23.30, 23.25, 23.22, 23.18, 18.6, 18.3, 18.1, 16.5, 16.4, 16.2, 14.1, 11.8, 11.3, 10.8, 10.69, 10.65, 10.60, 8.4.