Organometallic rotaxane dendrimers withfourth-generation mechanically interlocked branchesWei Wanga, Li-Jun Chena, Xu-Qing Wanga, Bin Suna,b, Xiaopeng Lib, Yanyan Zhangc, Jiameng Shic, Yihua Yuc, Li Zhangd,Minghua Liud, and Hai-Bo Yanga,1

aShanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, Shanghai 200062, People’sRepublic of China; bDepartment of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666; cShanghai Key Laboratory of MagneticResonance, Department of Physics, East China Normal University, Shanghai 200062, People’s Republic of China; and dKey Laboratory of Colloid, Interface andChemical Thermodynamics, Institute of Chemistry, The Chinese Academy of Sciences, Beijing 100080, People’s Republic of China

Edited by Vivian Wing-Wah Yam, The University of Hong Kong, Hong Kong, China, and approved March 31, 2015 (received for review January 11, 2015)

Mechanically interlocked molecules, such as catenanes, rotaxanes,and knots, have applications in information storage, switchingdevices, and chemical catalysis. Rotaxanes are dumbbell-shapedmolecules that are threaded through a large ring, and the relativemotion of the two components along each other can respond toexternal stimuli. Multiple rotaxane units can amplify responsiveness,and repetitively branched molecules—dendrimers—can serve as vehi-cles for assembly of many rotaxanes on single, monodisperse com-pounds. Here, we report the synthesis of higher-generation rotaxanedendrimers by a divergent approach. Linkages were introduced asspacer elements to reduce crowding and to facilitate rotaxane motion,even at the congested periphery of the compounds up to the fourthgeneration. The structures were characterized by 1D multinuclear (1H,13C, and 31P) and 2D NMR spectroscopy, MALDI-TOF-MS, gel perme-ation chromatography (GPC), and microscopy-based methods in-cluding atomic force microscopy (AFM) and transmission electronmicroscopy (TEM). AFM and TEM studies of rotaxane dendrimersvs. model dendrimers show that the rotaxane units enhance therigidity and reduce the tendency of these assemblies to collapseby self-folding. Surface functionalization of the dendrimers withferrocenes as termini produced electrochemically active assemblies.The preparation of dendrimers with a well-defined topologicalstructure, enhanced rigidity, and diverse functional groups openspreviously unidentified avenues for the application of these mate-rials in molecular electronics and materials science.

rotaxane dendrimer | controllable divergent approach | platinumacetylide | surface modification | dynamic supramolecular systems

Dendritic molecules containing rotaxane components are arecently developed subset of mechanically bonded super-

molecules (1–3). The combination of the characteristics of bothrotaxanes (sliding and rotary motion) and dendrimers (repetitivebranching with each generation) provides the resultant rotaxanedendrimers with unusual topological features and potentially use-ful properties. For example, the introduction of stimuli-responsiverotaxanes (4) such as muscle-like bistable rotaxanes or daisy chainscan impart switchable features to the resultant dendrimers that are“smart” to external inputs. The applications of dendrimers inmaterials science (5, 6) suggest that rotaxane dendrimers couldserve as supramolecular dynamic materials.A variety of rotaxane dendrimers have been designed and con-

structed over the past few years. For examples, mechanicallyinterlocked units were used either as cores or end groups, by Vögtleand 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 dendrimerswith interlocking ring components on the branches or at the branchpoints are rare. Specifically, Kim et al. (16) and Leung et al. (19)have reported the only two cases of rotaxane branched dendrimersup to the second generation. Third- or higher-generation rotaxanedendrimers equipped with mechanically interlocked functions onthe branches (Fig. 1) are unknown to us.

Herein, we describe the synthesis, characterization, and func-tionalization of higher-generation (up to fourth-generation) organ-ometallic rotaxane branched dendrimers. A divergent strategy wasemployed for the dendrimer synthesis in which the host–guestcomplex of a pillar[5]arene and a neutral alkyl chain were used asthe rotaxane subunits. The formation of platinum–acetylide bondswas the growth step in the synthesis; it produced satisfactory yieldsand allowed construction of the targeted structures. The introductionof macrocyclic wheels enhanced the rigidity of the resultant rotaxanedendrimers and reduced self-folding. Electrochemically activerotaxane dendrimers substituted with different numbered ferroceneswere also prepared by direct surface modification.

Results and DiscussionSynthesis. To synthesize rotaxane branched dendrimers, themechanically interlocked functions must be repeating subunits ofthe targeted structures. The rotaxane building blocks must bestable enough to handle and incorporate repeatedly during thegrowth processes. We used organometallic [2] rotaxane 1 (Fig. 2)as the basic precursor for the divergent dendrimer growth forthe following reasons: (i) 1 can be quickly synthesized by usingOgoshi’s available pillar[5]arene and its neutral alkyl chain guest(20–22); (ii) 1 contains a platinum–acetylide unit that preventsthe macrocycle from escaping the thread; (iii) 1 can react with afree alkyne to generate a stable organometallic bond in goodyield under mild conditions (23–25); (iv) 1 contains protectedalkynes that can be gently exposed for dendrimer growth; and

Significance

In this study, the preparation of organometallic rotaxane den-drimers with a well-defined topological structure and enhancedrigidity was developed. Starting from a simple rotaxane buildingblock, high-generation rotaxane branched dendrimers were syn-thesized and characterized. The fourth-generation structure de-scribed is among the highest-generation organometallic rotaxanedendrimers reported to date. The introduction of pillar[5]arenerotaxane units activates dynamic features in the dendrimer andenhances the rigidity of each branch of the supermolecules. Thisresearch offers a facile approach to the construction of high-gen-eration rotaxane branched dendrimer, which not only enriches thelibrary of rotaxne dendrimer but also provides the further insightinto their applications as supramolecular dynamic materials.

Author contributions: W.W. and H.-B.Y. designed research; W.W., L.-J.C., X.-Q.W., B.S.,X.L., Y.Z., J.S., Y.Y., L.Z., and M.L. performed research; W.W. contributed new reagents/analytic tools; W.W., X.L., and H.-B.Y. analyzed data; and W.W., X.L., and H.-B.Y. wrotethe paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.1To whom correspondence should be addressed. Email: hbyang@chem.ecnu.edu.cn.

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1500489112/-/DCSupplemental.

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(v) 1 has active alkyne units that can be functionalized to impartfurther structural diversity and function.We synthesized organometallic [2]rotaxane 1 in a few steps,

as indicated in SI Appendix, Scheme S1. The rotaxane formation stepproceeded in good yield (86%) from three components and allowedthe preparation of 1 on gram scales. The building block 1 provedstable and soluble in common solvents during the dendrimer growthprocesses. Unlike classic charged rotaxane systems that are con-structed by incorporating either charged macrocyclic wheels or axles,organometallic [2]rotaxane 1 is neutral, which simplifies the sub-sequent reaction and purification processes. The growth processesrelied on a Cu(I)-catalyzed coupling reaction of 1 with the corre-sponding polyacetylene precursors. During this reaction, the bulkyphosphine 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 in-corporating mechanically interlocked rotaxanes on the branches(Fig. 3). The Cu(I)-catalyzed coupling reaction of 1 and 1,3,5-trie-thynylbenzene produced the first-generation rotaxane dendrimerG1at a yield of 79%, where six protected alkynes were located at theouter periphery of the compound (Fig. 3A). Deprotection of G1with tetrabutylammonium fluoride produced the correspondingdendrimer G1-YNE, in an 87% yield, which bore six acetylenegroups. These groups were used to grow the next generation: Thecoupling of G1-YNE and 1 produced the second-generation rotax-ane dendrimer G2 with nine pillar[5]arene-based rotaxanes on thebranches in 58% yield. The third- and fourth-generation rotaxanedendrimers (G3 and G4, respectively) were prepared via sequentialdeprotection−coupling processes, as shown in Fig. 3B. The fourth-generation rotaxane dendrimer G4, can be considered as a highlybranched [46]rotaxane: 45 rotaxanes located in a dendrimer skele-ton of monodisperse distribution. All of the dendrimers G1−G4were soluble in common solvents such as chloroform, dichloro-methane, and THF. The purification of these dendrimers was per-formed using flash column chromatography and recrystallization.

Rotaxane Dendrimer Characterization. The 1H NMR spectra ofthese dendrimers, especially G3 and G4, showed no proton sig-nals from the terminal acetylenes that would signal structuraldefects formed during the growth processes. The peaks ascribedto the protons on the linear axle of the rotaxanes were located ina range (below 0.0 ppm) similar to that of [2]rotaxane precursor1. This result indicates that the structure of the rotaxane was notdestroyed during the growth process. More than one set of peakscorresponding to the threaded structures was observed for eachsubsequent generation. In other words, the rotaxane subunitswere 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 adownfield shift (Δδ ’ 2.4 ppm), which also supports the forma-tion of platinum–acetylide bonds during dendrimer growth. As inthe 1H NMR spectra, different chemical shifts were observed forthe phosphine ligands in each generation in the growth of therotaxane dendrimers, indicating the nonequivalent chemical en-vironment 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 formationof mechanically interlocked compounds (Fig. 4). For the first-gen-eration rotaxane dendrimer G1, the MALDI-TOF-MS spectrum inreflectron mode exhibited a single peak at m/z = 6,661.5, which wasattributed to [G1 + H]+ with a theoretical monoisotopic mass at6,661.9 Da. This peak was isotopically resolved and agreed well withthe theoretical distribution. The corresponding peaks were also ob-served in the MS spectra of the higher-generation rotaxane den-drimers G2 and G3, confirming the synthesis of the targetedcompounds. [With increasing molecular weight (for G2, theoreticalaverage Mr = 18,760 Da; for G3, theoretical average Mr = 42,948Da), the peaks became broader, with a rational deviation from thetheoretical mass in linear acquisition mode. This broadening effectwas attributed to the binding of sodium and potassium ions to largerotaxane dendrimers, along with the proton signals.] For these high-generation architectures, high charge states, i.e., 2+ and/or 3+, werealso observed in MALDI-TOF-MS in addition to singly chargedions, as shown in Fig. 4 B and C. In the MS spectrum of G3, somefragments were observed. Further experiments with stronger laserpower showed that the MS spectrum of G3 produced a higherabundance of fragments (SI Appendix, Fig. S40). This indicates thatsuch additional peaks may be attributed to the fragments induced ineither MALDI source or ionization processes (26). For the fourth-generation rotaxane dendrimer G4, neither MALDI-TOF nor elec-trospray ionization-MS provided satisfactory mass data because ofthe high molecular mass (theoretical average Mr = 91,254 Da) andlow ionization efficiency of G4. A gel permeation chromatography(GPC) analysis of G3 and G4 revealed narrow distributions for thenumber-averaged molecular weight (Mn) and the polydispersity in-dex (PDI) (forG3, PDI = 1.07; forG4, PDI = 1.09; SI Appendix, Figs.S81 and S82). The Mn values clearly increased for each dendrimergeneration (for G3, Mn = 32,440; for G4, Mn = 48,022), as expectedfor the existence of the fourth-generation rotaxane dendrimer G4.

The “Rotaxane Effect.” The effect of introducing rotaxane unitsinto the dendrimers (the “rotaxane effect”) was investigated bypreparing model organometallic dendrimers Gn-c (n = 1, 2, 3)without pillar[5]arene wheels using a parallel approach (SI Ap-pendix, Scheme S2). The absence of the pillar[5]arene wheelsresulted in reduced solubility of Gn-c in common solvents(chloroform and THF); the third-generation model dendrimerG3-c was the highest-generation dendrimer that could be syn-thesized. We used electron microscopy methods such as atomicforce microscopy (AFM) and transmission electron microscopy(TEM), to visualize individual supramolecular dendrimers as

Rotaxane

Dendrimer

Rotaxane Dendrimer

Fig. 1. Schematic representation of a rotaxane dendrimer with mechan-ically interlocked moieties incorporated on the branches.

Synthesized in 0.55 g batches in 86% yieldSynthesized in 2.07 g batches in 80% yield

1

Facile and scalable preparat ion

Neutrality

Excellent stability and solubility

React ive end sites for dendrimer growth

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

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described by others (27). These methods can provide structuralparameters of dendrimers such as their size, conformation, andrigidity, using direct images on a surface. The AFM analysis ofG1−G4 showed that the average heights gradually increased witheach generation of the rotaxane dendrimers (’1.6 nm for G1;’2.6 nm forG2;’3.3 nm forG3; and’6.0 nm forG4), as shown inFig. 5, although flattened dendrimers were also found on thesurface. The introduction of pillar[5]arene rotaxane subunitsapparently increased the rigidity of each branch of the den-drimers. We expected that the absence of pillar[5]arene wheelswould make the model dendrimers G1-c–G3-c “floppier” comparedwith the corresponding rotaxane dendrimers when exposed on thesurface. The average heights of the model dendrimers G1-c–G3-cwere indeed reduced by nearly one-half (’0.8 nm for G1-c;’1.0 nmfor G2-c; and ’1.5 nm for G3-c) compared with the AFM data forthe corresponding rotaxane dendrimers under the same conditions(Fig. 6). The enhanced rigidity induced by the rotaxane subunits wasfurther confirmed by TEM, showing that the individual rotaxanedendrimer structure had a size of ∼3.0 nm for G3, a value in goodagreement with the AFM result. However, the TEM image of G3-cshowed a corresponding size of only ∼1.5 nm (SI Appendix, Fig. S85).Dynamic light scattering (DLS) is also a useful technique for

determining the dimensions of dendrimers in solution, and weapplied it to the new compounds. We were unable to measurethe size of the smallest dendrimer G1 using DLS, possibly be-cause the size of G1 was below the measuring limit. A size pro-gression was observed with increasing generations for themeasured hydrodynamic diameters of the higher-generationdendrimers (2.2 nm for G2; 3.5 nm for G3; and 8.7 nm for G4) (SIAppendix, Fig. S84). No obvious size results were obtained in theDLS studies for the model dendrimers G1-c–G3-c, possibly be-cause 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 den-drimers were not completely spherical in solution, and thesamples usually exhibited shrinkage on the surface because ofsolvent loss, which resulted in the measurement of differentdendrimer sizes using the aforementioned three types of tech-niques. These results are reasonable according to previous re-ports. For example, see ref. 28.) We also used 2D diffusion-ordered NMR spectroscopy to evaluate the size (hydrodynamicdiameter) of the dendrimers in solution. The introduction of thepillar[5]arene wheels resulted in a decrease in the measured weight-averaged diffusion coefficients (D). For example, under the sameconditions, the diffusion coefficient of the rotaxane dendrimer G3was found to be 5.83 × 10−11 m2/s, which was significantly smallerthan 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 den-drimers. This “rotaxane effect”may also impart stability in their laserdesorption/ionization processes in the MALDI-TOF-MS spectra.For instance, under the same characterization conditions, the G1exhibited a complete and single molecular ion peak [G1+H]+,whereas the corresponding model G1-c displayed additional peakfragments attributed to degradation of the dendrimer skeleton (seeSI Appendix, Fig. S21 for G1 and SI Appendix, Fig. S53 for G1-c).

Surface Modification. A subsequent study was performed in whichthe new dendrimers were subjected to surface modification (29)

G1

G2

G3

G4

G1

CuI, Et2NH, rt, 12h

79%

I II

III: (I) (a) TBAF, THF,

rt. 12h, 87%; (b) CuI, 1, Et2NH, rt, 12h,58%; (II) ) (a) TBAF, THF, rt. 12h, 67%;(b) CuI, 1, Et2NH, rt, 12h, 49%; (II) ) (a)TBAF, THF, rt. 12h, 63%; (b) CuI, 1,Et2NH, rt, 12h, 83%;

A

B

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

B

A

C8000 12000 16000 20000 m/z

[G2+H]+[G2+Na]+

9380

18768

[G2+2H]+

20000 30000 40000 m/z

[G3+H]+[G3+Na]+[G3+K]+

42959

21501

[G3+2H]2+[G3+H+Na]2+[G3+H+K]2+[G3+2Na]2+[G3+2K]2+

3000 4000 5000 6000 7000 m/z

6661.5

6658 6666 6674 m/z

[G1+H]+

Fig. 4. MALDI-TOF-MS spectra for rotaxane dendrimersG1 (A), G2 (B), andG3 (C).

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with functional groups. In this study, a triisopropylsilyl-protectedacetylene group was used as the surface group to facilitatedendrimer growth and enable diversity. We chose ferrocene, arobust redox function, which has been extensively explored inapplications in the nanoelectronics field (30, 31). The ferrocenesubunit was introduced into the rotaxane dendrimers via acoupling reaction of the ferrocenyl monosubstituted platinum–

acetylide complex with the multiple alkyne groups in the respectiverotaxane dendritic intermediates (G1-YNE, G2-YNE, and G3-YNE) (SI Appendix, Scheme S3). The resultant heterobimetallicdendrimers, G1-Fc, G2-Fc, and G3-Fc, with 6, 12, and 24 ferro-cene 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 theincrease of the scan rates. The cyclic voltammograms corre-sponding to the one-electron oxidation of ferrocene groupsyielded cathodic/anodic peak current ratios of ic/ia ∼ 1. Thenearly identical cathodic and anodic peak currents, as well asnearly scan rate-independent peak potentials, indicated that theoxidized complexes were chemically stable on the voltammetrictimescale and the oxidation of the ferrocene units in each as-sembly was chemically reversible (SI Appendix, Fig. S87). Themultiple ferrocene groups reacted independently, producing asingle voltammetric wave, even though more than one electronwas transferred in the overall reaction.

ConclusionsIn conclusion, we have reported the synthesis, characterization,and functionalization of a series of organometallic rotaxanedendrimers with mechanically interlocked pillar[5]arene subunitson each branch. We used an organometallic [2]rotaxane pre-cursor, 1, and used sequential coupling–deprotection–couplingprocesses to obtain organometallic rotaxane dendrimers up tothe fourth generation. The largest assembly incorporates 45rotaxane subunits on the dendritic skeleton in a monodispersemanner. Numerous polymeric rotaxanes, such as rotaxane co-ordination polymers (32), have been well documented; this studypresents discrete, high-generation rotaxane dendrimers with

repeating units on each branch. The AFM and TEM studies ofthe rotaxane dendrimers vs. corresponding model dendrimersindicate that pillar[5]arene “wheels” enhance the rigidity of thebranches, reducing self-folding and collapse. Functional rotaxanedendrimers substituted with ferrocenes as termini were preparedthrough surface chemical transformations. The well-defined to-pological structures, enhanced rigidity, and diverse functionalgroups of rotaxane dendrimers should provide a platform forinvestigations of these molecules in molecular electronics andmaterials science.

Materials and MethodsGeneral Information. All reagents were commercially available and were usedas suppliedwithout further purification. Deuterated solvents were purchasedfrom Cambridge Isotope Laboratory. NMR spectra were recorded on a BrukerDRX 400 (400-MHz) spectrometer. 1H and 13C NMR chemical shifts werereported relative to the residual solvent signals, and 31P{1H} NMR chemicalshifts were referenced to an external unlocked sample of 85% (vol/vol)H3PO4 (δ 0.0). The 2D rotating-frame Overhauser enhancement spectroscopyNMR spectra were recorded on a Bruker DRX500 spectrometer. DLS mea-surements were performed using a Malvern Zetasizer Nano-ZS light scat-tering apparatus (Malvern Instruments) with a He–Ne laser (633 nm, 4 mW).The TEM images were obtained using a Philips TECNAI-12 instrument withan accelerating voltage of 120 kV. AFM images were obtained on a Di-mension FastScan (Bruker), using the ScanAsyst mode under ambient condi-tions. UV−vis spectra were recorded in a quartz cell (with a light path of 10mm) on a Cary 50Bio UV–vis spectrophotometer. Steady-state fluorescencespectra were recorded using a conventional quartz cell (with a light path of10 mm) and a Cary Eclipse fluorescence spectrophotometer. MALDI-MS ex-periments were carried out using a Bruker UltrafleXtreme MALDI TOF/TOFmass spectrometer (Bruker Daltonics) equipped with a Smartbeam-II laser.Cyclic voltammetry (CV) was performed using a three-electrode cell and a RSTelectrochemical work station. The working electrode was a glassy carbon diskwith surface area of about 7.0 mm2. A saturated calomel electrode was used asreference electrode and a Pt wire as the counterelectrode. The CV measurementswere carried out in a dichloromethane solution containing 0.2 M tetra-n-buty-lammoniumhexafluorophosphate (n-Bu4NPF6). The concentration of redox mol-ecule in solution was 2.00 mM.

General Procedure for Synthesis of Rotaxane Dendrimers Gn. A mixture ofmultiyne complexes (1,3,5-triethynylbenzene for G1; G1-YNE for G2; G2-YNEfor G3; and G3-YNE for G4) and 1 (for each terminal acetylene moiety, 1.1 eq1 was added) in degassed diethylamine was stirred overnight at roomtemperature in the presence of a catalytic amount of CuI (∼5 mol %). Thesolvent was evaporated under reduced pressure and purified by columnchromatography on SiO2 using petroleum ether/CH2Cl2 (1:1–0:1) as an eluentto produce a pale-yellow solid as the target compound (recrystallization wasnecessary for G3 and G4).

Fig. 5. AFM images of the rotaxane dendrimers Gn (n = 1, 2, 3, and 4).

Fig. 6. AFM images of the corresponding model dendrimers Gn-c (n = 1, 2,and 3) without pillar[5]arene wheels.

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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.

ACKNOWLEDGMENTS. We thank Prof. Kun Huang at East China NormalUniversity for assistance with the GPC analysis. H.-B.Y. thanks NationalNatural Science Foundation of China (Grants 21322206, 21132005, and91027005), the Key Basic Research Project of the Shanghai Science and Tech-nology Commission (Grant 13JC1402200), and the Program for ChangjiangScholars and Innovative Research Team in University for financial support.

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