& Supramolecular Chemistry

Unexpected Self-Assembly of a HomochiralMetallosupramolecular M4L4 Catenane

Rainer Hovorka,[a] Georg Meyer-Eppler,[a] Torsten Piehler,[a] Sophie Hytteballe,[a]

Marianne Engeser,[b] Filip Topic,[c] Kari Rissanen,[c] and Arne L�tzen*[a]

Abstract: Two enantiomerically pure 9,9’-spirobifluorene-based bis(pyridine) ligands 1 and 2 were prepared to studytheir self-assembly behavior upon coordination to cis-pro-tected palladium(II) ions. Whereas the sterically more de-

manding ligand, 2, gave rise to the expected dinuclear met-allosupramolecular M2L2 rhombi, the sterically less demand-ing ligand, 1, acts as a template to give rise to a homochiralmetallosupramolecular M4L4 catenane.

Introduction

The combination of palladium(II) and platinum(II) metal centersand highly directional bridging pyridyl ligands has proven tobe one of the most successful and reliable coordination motifsin metallosupramolecular chemistry.[1] Usually, the outcome ofthe coordination-driven self-assembly can be predicted both interms of size and composition by assuming that the smallestassembly is formed according to the maximum occupancy rulethat does not experience too much destabilizing steric strain.As part of our ongoing program to elucidate general guide-lines for the (diastereoselective) self-assembly of metallosupra-molecular aggregates,[2–6] we have recently started a systematicstudy on the influence of rigid chiral concave building blockson the outcome of the self-assembly of bis(pyridine) ligandsand palladium(II) and platinum(II) ions in the sense of chiralself-sorting.[4, 5] Cis-protected [(dppp)Pd(OTf)2] or [(dppp)Pt-(OTf)2] (dppp = 1,3-bis(diphenylphosphino)propane) complexes,for example, self-assembled into dinuclear metallosupramolec-ular rhombi upon coordination to bis(pyridine) ligands basedon Trçger’s base,[4d,e] the 2,2’-dihydroxy-binaphthyl,[4f] and the9,9’-spirobifluorene scaffold.[4g]

Now, we have prepared an elongated version of the previ-ously reported bis(pyridine) ligand based on the 9,9’-spirobi-fluorene skeleton in order to learn more about the underlyingprinciples of the self-assembly of these metallosupramolecularaggregates.

Results and Discussion

The synthesis of spirobifluorene based ligand 1 starts fromenantiomerically pure or racemic 2,2’-diethynyl-9,9’-spirobi-fluorene, which was prepared according to literature methods(Scheme 1).[7] Two-fold Sonogashira cross-coupling reaction ofthis compound with 4-iodopyridine hydrochloride affordedtarget compound 1 in enantiomerically pure and racemic formin good yield.

According to our previous results,[4d–g] we expected thestraight-forward formation of a homochiral [(dppp)2Pd2{(R)-1}2](OTf)4 complex when we mixed enantiomerically pureligand (R)-1 with an equimolar amount of [(dppp)Pd(OTf)2] inacetonitrile.[8] Hence, we were surprised to obtain an ESI massspectrum (Figure 1) and a 1H NMR spectrum that clearly re-vealed the formation of a tetranuclear [(dppp)4Pd4{(R)-1}4] com-

Scheme 1. Synthesis of ligand (R)-1 (dba = dibenzylideneacetone,dppf = 1,1’-bis(diphenylphosphino)ferrocene).

[a] Dipl.-Chem. R. Hovorka, Dipl.-Chem. G. Meyer-Eppler, Dipl.-Chem. T. Piehler,S. Hytteballe, Prof. Dr. A. L�tzenKekul�-Institut f�r Organische Chemie und BiochemieUniversit�t BonnGerhard-Domagk-Str. 1 53121 Bonn (Germany)Fax: (+ 49) 228-73-9608E-mail : arne.luetzen@uni-bonn.de

[b] Dr. M. EngeserKekul�-Institut f�r Organische Chemie und BiochemieUniversit�t BonnGerhard-Domagk-Str. 1, 53121 Bonn (Germany)

[c] F. Topic, Prof. Dr. K. RissanenDepartment of Chemistry, Nanoscience CenterUniversity of Jyv�skyl� (Finland)

Supporting information for this article is available on the WWW underhttp ://dx.doi.org/10.1002/chem.201403414.

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Full PaperDOI: 10.1002/chem.201403414

plex of lower symmetry besides the expected dinuclear aggre-gate in an equilibrated mixture. Such signals were not ob-served with a similar spirobifluorene-based ligand that lacksthe ethynyl groups and has the pyridyl groups directly at-tached to the spirobifluorene core.[4g]

Interestingly, we observed this behavior of 1 not only in ace-tonitrile but also in acetone, and mixtures of dichloromethaneand acetonitrile (see the Supporting Information). Further31P NMR experiments (see the Supporting Information) corro-borated these results as they clearly revealed the presence oftwo different aggregates, one of which contains two magneti-cally non-equivalent phosphorus nuclei that couple with eachother. Temperature-dependent NMR experiments indicatedthat these two species can interconvert as the relative ratiochanges reversibly. As expected under the assumption that thelarger aggregate is destabilized for entropic reasons with in-creasing temperature, the fraction of the M4L4 aggregate islarger at lower temperatures (Figure 2). However, even at243 K, both species are still present in solution.

In principle, one could think of three kinds of structures forsuch an [(dppp)4Pd4(1)4] aggregate (Figure 3): The first onewould be a sandwich-type aggregate of two [(dppp)2Pd2(1)2]

rhombi (Figure 3, left) that would be held together by weaknon-covalent interactions such as dispersive interactions, p–p

and CH–p interactions, and maybe some electrostatic interac-tions between the cationic complexes and some of the coun-terions in the organic solvents. However, such a structurewould hardly give rise to the 31P NMR signals we observed.The second would be a (folded) tetranuclear metallamacrocy-cle [(dppp)4Pd4(1)4] (Figure 3, middle), although such a structureis usually only observed with rather rigid bridging ligands ofalmost linear shape[1, 3a, 9, 10] but not with strongly bent ligandslike 1. Nevertheless, one could still think of a strongly foldedstructure that might also explain the unexpected shifts of theNMR signals. In light of the fact, however, that the slightlysmaller spirobifluorene ligand, which lacks the ethynyl bridgesbetween the spirobifluorene and the pyridyl moieties that wehave studied before, did not form any of these structures, theyseem unlikely. The third possibility would be a [(dppp)4Pd4(1)4]complex where two [(dppp)2Pd2(1)2] rhombi are catenated(Figure 3, right). This kind of structure would nicely explain thesplitting of the 31P NMR signals and the extraordinary upfieldshifts of some of the 1H NMR signals owing to the fact thatsome of the nuclei come into close proximity to the p-systemsand experience their strong magnetic anisotropy. Such metal-losupramolecular [(dppp)4Pd4(L)4] catenanes have indeed beendescribed in the literature before. However, their formationwas observed in aqueous solution, and hence, it was explainedto be a result of the hydrophobic effect that causes the thread-ing of one ligand through a dinuclear metallosupramolecularmacrocycle.[11]

To gain some structural insight on the tetranuclear complex,we investigated it by infrared multiphoton dissociation(IRMPD) MS/MS studies. In such an experiment a sandwich-type complex could be expected to lose an [M2L2] fragment asthe most likely first fragmentation because the lowest bindingenergy would be expected to be between the two [2:2] com-plexes, whereas in case of the macrocyclic or the catenated ag-gregate, more stable coordinative or even covalent bondshave to be broken. Please note, however, that we recentlyhave shown that rearrangements during fragmentation caneasily lead to false structural conclusions especially in weaklybound metallosupramolecular systems. In particular, supra-molecular {[(bisphosphane)4M4(L)4](OTf)5}3 + (M = Pd, Pt) sand-wich aggregates do not necessarily split symmetrically intohalves when fragmented by a soft method like IRMPD in thegas phase.[6d] Nevertheless, IRMPD fragmentations gave accessto valuable structural and mechanistic information in many

Figure 1. ESI mass spectrum (positive mode) of a solution of [(dppp)Pd-(OTf)2] and ligand (R)-1 mixed in a 1:1 stoichiometry in acetonitrile.

Figure 2. 1H NMR spectra (500.1 MHz, [D2]dichloromethane/[D3]acetonitrile3:1, 243 K) of a) an equimolar mixture of [(dppp)Pd(OTf)2] and ligand (R)-1 and b) (R)-1 (signs in spectrum a) indicate selected signals arising from thePd4(1)4 complex; for more details see the Supporting Information).

Figure 3. Schematic representation of possible [(dppp)4Pd4(L)4] aggregates:sandwich-type aggregate of two [(dppp)2Pd2(L)2] complexes (left), tetranu-clear metallamacrocycle (middle), and tetranuclear catenane (right).

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other cases.[3a,b, 12] Figure 4 shows the mass spectra of the iso-lated complex fragmented by IRMPD with different irradiationtimes of the laser.

What can be seen is that the first fragmentation at low irra-diation times is the loss of a [(dppp)Pd(OTf)]+ fragment fol-lowed by subsequent losses of a ligand and another[(dppp)Pd(OTf)]+ fragment at higher irradiation times. This be-havior surely is in accordance with a macrocyclic or catenanestructure. Nevertheless, it also very closely resembles the frag-mentation pattern we recently observed for formally similar{[(dppp)4Pd4(L)4](OTf)5}3 + sandwich aggregates that unsymmet-rically split into {[(dppp)3Pd3(L)3](OTf)4}2 + and {[(dppp)Pd(L)]-(OTf)}+ complexes.[6d]

Hence, it is unfortunately not possible to distinguish themacrocyclic from the catenated and the sandwich structure bythis technique. Initially, we thought that a couple of fragmen-tations could finally lead to a {[(dppp)3Pd3(1)2](OTf)6-n}(6�n) +

fragment that would be unique for the macrocyclic species.However, such a fragmentation pathway does obviously notoccur under the conditions of the IRMPD-MS/MS experiment.Hence, the fact that this fragment is not observed cannot beused as a proof that the catenated species must have formed.Especially, as there is also no other specific unique fragment ofthe catenated structure that might not also occur in the frag-mentation processes of the other species, and thus, may serveas a proof for this structure.

Fortunately, we finally succeeded in growing single crystalsof the unknown aggregate by slow diffusion of ethyl acetateinto a solution of the complex in dichloromethane/acetonitrile(2:1). These were suitable for X-ray diffraction analysis to finallysolve the problem. As shown in Figure 5 the [(dppp)4Pd4(1)4]aggregate is indeed a catenane. This structure is in accordancewith all of our experimental observations and nicely explainsthe unusual chemical shifts in the NMR spectra. It is the firstexample of a homochiral tetranuclear metallosupramolecularcatenane.

A closer look suggests that the spirobifluorene moiety nicelyfills the cavity of the metallosupramolecular rhombus in termsof size and shape in a perfect orientation to ensure strainlessthreading. Hence, the formation of the catenane obviously is

a result of a template effect here, rather than the result of a sol-vophobic effect.

In order to prove this we also prepared a slightly larger de-rivative of ligand 1 that carries two additional methyl groupsin the 7,7’-positions (2, Scheme 2). The synthesis started fromliterature-known (S)-2,2’-dibromo-7,7’-dimethyl-9,9’-spirobi-fluorene[7] in enantiomerically pure form. Two-fold Suzukicross-coupling of this dibromide with the in situ preparedTMS-acetylene boronic acid ester afforded the diethynylatedcompound, which was desilylated with potassium fluoride togive the terminal alkynes. These terminal alkynes were subject-ed to a two-fold Sonogashira cross-coupling reaction with 4-io-dopyridine hydrochloride to afford target ligand 2.

Owing to these two methyl groups, the spirobifluorene isnow slightly too large to be accommodated in the metallosu-pramolecular rhombus’s cavity. Hence, catenane formation is

Figure 4. IRMPD FTICR MS/MS spectra of the {[(dppp)4Pd4(1)4](OTf)5}3+ ionafter different irradiation times (* mark overtone signals, § marks electronicnoise).

Figure 5. Supramolecular structure of [(dppp)4Pd4{(R)-1}4](OTf)8 as deter-mined by X-ray diffraction analysis: top ball and stick representation (colorcode: grey carbon, white hydrogen, blue nitrogen, yellow phosphorus, andpetrol palladium; solvent molecules and anions are omitted for viewingclarity), bottom CPK representation of the two catenated rhombi in greenand red.

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prevented and we only observed the formation of the dinu-clear rhombi (Figure 6 and the Supporting Information).

Conclusion

In conclusion, we were able to synthesize two enantiomericallypure dissymmetric bis(pyridine) ligands (R)-1 and (S)-2 basedon a 9,9’-spirobifluorene core and studied their self-assemblybehaviour upon coordination to cis-protected palladium(II)ions. Unexpectedly, sterically less demanding ligand (R)-1 gaverise not only to the initially expected dinuclear metallosupra-molecular aggregates but also forms a homochiral tetranuclear[(dppp)4Pd4{(R)-1}4](OTf)8 catenane. This structure is obviouslythe result of an efficient template effect of the spirobifluorenemoiety, which nicely fits the cavity of the dinuclear rhombus ina perfect orientation to thread the metallamacrocycle andclose the catenane. Sterically more demanding ligand (S)-2,however, is slightly too large to be accommodated in the

rhombus’ cavity. Hence it cannot act as a template and gaverise to the expected homochiral dinuclear metallosupramolecu-lar [(dppp)2Pd2{(S)-2}2](OTf)4 rhombi.

Experimental Section

Reactions under inert gas atmosphere were performed underargon by using standard Schlenk techniques and oven-dried glass-ware prior to use. Thin-layer chromatography was performed onaluminum TLC plates silica gel 60F254 from Merck. Detection wascarried out under UV light (254 and 366 nm). Products were puri-fied by column chromatography on silica gel 60 (70–230 mesh)from Merck. The 1H and 13C NMR spectra were recorded ona Bruker DRX 500 spectrometer at 500.1 and 125.8 MHz or ona Bruker AM 400 at 400.1 MHz and 100.6 MHz, respectively. The1H NMR chemical shifts are reported on the d scale (ppm) relativeto residual non-deuterated solvent as the internal standard. The13C NMR chemical shifts are reported on the d scale (ppm) relativeto deuterated solvent as the internal standard. Signals were as-signed on the basis of 1H, 13C, HMQC, and HMBC NMR experiments(for the numbering of the individual nuclei see the Supporting In-formation). Mass spectra were recorded at a microOTOF-Q ora Apex IV FT-ICR from Bruker. For IRMPD spectra, a CO2 laser (max.25 W) has been used. Elemental analyses were carried out witha Heraeus Vario EL. However, CHN analyses could only be conduct-ed with fluorine-free compounds. Most solvents were dried, dis-tilled and stored under argon according to standard procedures.(R)- and (rac)-2,2’-diethynyl-9,9’-spirobifluorene and (S)-2,2’-dibro-mo-7,7’-dimethyl-9,9’-spirobifluorene were prepared by a literature-known procedure.[7] For experimental details of (S)-2,2’-di({trime-thyl)silylethynyl)-7,7’-dimethyl-9,9’-spirobifluorene and (S)-2,2’-di-ethynyl-7,7’-dimethyl-9,9’-spirobifluorene, see the Supporting Infor-mation.

(R)- and (rac)-2,2’-(4-pyridylethynyl)-9,9’-spirobifluorene (1)

A flame-dried two-neck flask was charged with 221.6 mg(0.61 mmol) of (R)-2,2’-diethynyl-9,9’-spirobifluorene, 6 mg (5mol- %) of CuI, 296 mg (1.52 mmol, 2.5 equiv) of 4-bromopyridinehydrochloride, 17 mg (5 mol- %) dppf, and 15 mg (5 mol- %) of[Pd2dba3]·CHCl3 was evacuated and flushed with argon twice.15 mL of dry THF and 2.42 mL of (iPr)2NH were added by syringe.The resulting mixture was stirred at 60 8C for 72 h. After that time,the mixture was cooled to room temperature, quenched with15 mL of brine, and subsequently filtrated through Celite. Afterrinsing the filter with dichloromethane, the layers were separatedand the aqueous layer was extracted with dichloromethane (4 �15 mL). The combined organic phases were washed with sat. aq.NaHCO3 and dried with Na2SO4. After removing the solvents underreduced pressure, the residue was subjected to column chroma-tography on silica gel using a gradient of cyclohexane/ethyl ace-tate (1:1 v/v) + 0.5 % of Et3N (Rf = 0.28)!ethyl acetate + 0.5 % ofEt3N (Rf = 0.66) as eluent to afford 210.4 mg (67 %) of the desiredproduct as a slightly yellow amorphous solid. 1H NMR: (400.1 MHz,CDCl3, 293 K) d= 8.52 (d, 4 H, 3J17,18 = 4.8 Hz, H-18), 7.87 (m, 4 H, H-4, H-5), 7.57 (dd, 2 H, 3J3,4 = 7.9 Hz, 4J1,3 = 1.2 Hz, H-3), 7.41 (ddd, 2 H,3J5,6 = 7.6 Hz, 3J6,7 = 7.6 Hz, 5J6,8 = 0.8 Hz, H-6), 7.24 (d, 4 H, 3J17,18 =4.8 Hz, H-17), 7.17 (ddd, 2 H, 3J6,7 = 7.6 Hz,3J7,8 = 7.8 Hz, 3J5,7 = 0.9 Hz,H-7), 6.94 (d, 2 H,4J1,3 = 1.2 Hz, H-1), 6.76 ppm (d, 2 H,3J7,8 = 7.8 Hz, H-8); 13C NMR: (100.6 MHz, CDCl3, 293 K) d= 149.5 (C-18), 148.3 (C-13), 148.3 (C-10), 142.8 (C-11), 140.7 (C-12), 137.2 (C-16), 131.9 (C-3),128.6 (C-7), 128.2 (C-6), 127.4 (C-1), 125.3 (C-2), 124.1 (C-8), 121.2(C-17), 120.5 (C-4), 120.2 (C-5), 94.2 (C-15), 87.1 (C-14), 65.5 ppm (C-

Scheme 2. Synthesis of ligand (S)-2 (dba = dibenzylideneacetone, dppf= 1,1’-bis(diphenylphosphino)ferrocene).

Figure 6. 1H NMR spectra (400.1 MHz, [D6]acetone, 293 K) of a) an equimolarmixture of [(dppp)Pd(OTf)2] and ligand (S)-2 and b) (S)-2 (arrows indicatecomplexation induced shifts upon formation of the dinuclear metallosupra-molecular rhombi).

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9); MS (ESI, 10 eV) m/z : 519.3 [M + H]+ ; HR-ESI : m/z calcd for[C39H22N2 + H]+ : 519.1861; found: 519.1870; elemental analysiscalcd (%) for C34H28N2O4·1=3 H2O: C 89.29, H 4.35, N 5.34; found: C89.40, H 4.68, N 5.45; specific optical rotation: (+)-(R)-1: [a]20

D = +6218 (c = 0.49, THF).

(S)-2,2’-di(4-pyridylethynyl)-7,7’dimethyl-9,9’-spirobifluorene

A flame-dried two-neck flask was charged with 113 mg (0.29 mmol)of (S)-2,2’-diethynyl-7,7’-dimethyl-9,9’-spirobifluorene, 8 mg (15mol- %) of CuI, 348 mg (1.44 mmol, 5 equiv) of 4-bromopyridine hy-drochloride, 20 mg (12.5 mol- %) dppf, and 16 mg (5 mol- %) of[Pd2dba3]·CHCl3 was evacuated and flushed with argon twice. 8 mLof dry THF and 1.2 mL of (iPr)2NH were added by syringe. The re-sulting mixture was stirred at 60 8C for 36 h. After that time, themixture was cooled to room temperature, quenched with 15 mL ofbrine, and subsequently filtrated through Celite. After rinsing thefilter with dichloromethane, the layers were separated and theaqueous layer was extracted with dichloromethane (4 � 15 mL). Thecombined organic phases were washed with sat. aq. NaHCO3 anddried with Na2SO4. After removing the solvents under reducedpressure, the residue was subjected to column chromatography onsilica gel using n-hexane/ethyl acetate (1:1 v/v) + 0.5 % of Et3N (Rf =0.18) as eluent to afford 69 mg (44 %) of the desired product asa slightly yellow amorphous solid. 1H NMR: (400.1 MHz, CDCl3,293 K) d= 8.52 (d, 4 H, 3J17,18 = 4.6 Hz, H-18), 7.82 (dd, 2 H, 3J3,4 =7.9 Hz, 5J1,4 = 0.5 Hz, H-4), 7.76 (d, 2 H, 3J5,6 = 7.8 Hz, H-6), 7.58 (dd2 H, 3J3,4 = 7.9 Hz, 4J1,3 = 1.5 Hz, H-3), 7.26 (d, 4 H, 3J17,18 = 4.6 Hz, H-17), 7.23 (d, 2 H, 3J5,6 = 7.8 Hz, H-5), 6.91 (m, 2 H, H-1), 6.65 (s, 2 H, H-8), 2.23 ppm (S, 6 H, H-19); 13C NMR: (100.6 MHz, CDCl3, 293 K) d=149.2 (C-18), 148.8 (C-13), 148.4 (C-10), 143.0 (C-11), 139.0 (C-7),138.1 (C-12), 131.9 (C-3), 131.7 (C-16), 129.1 (C-5), 127.4 (C-1), 125.4(C-17), 124.7 (C-8), 120.6 (C-6), 120.3 (C-4), 119.8 (C-2), 94.8 (C-15),86.8 (C-14), 65.2 (C-9), 21.5 ppm (C-19); MS (ESI, 10 eV): m/z : 547.2[M + H]+ ; HR-ESI : m/z calcd for [C41H26N2 + H]+ : 547.2169; found:547.2167; elemental analysis calcd (%) for C34H28N2O4·5/3 H2O: C85.39, H 5.31, N 4.68; found: C 85.29, H 5.26, N 4.62; specific opti-cal rotation: (�)-(S)-2 : [a]25

D =�5058 (c = 0.26, CH2Cl2).

Preparation and characterization of the metal complexes

9.5 mmol of a ligand were dissolved in 0.6 mL of CD2Cl2. This solu-tion was then added to a solution of 9.5 mmol or [(dppp)Pd(OTf)2] ,respectively, in 0.2 mL of CD3CN. The resulting solution was charac-terized by NMR spectroscopy. For the ESI-MS studies, 30 mL of theNMR solution were diluted with 970 mL of a 1:1 mixture of CH2Cl2

and CH3CN.

Crystal structure determination of [(dppp)4Pd4{(R)-1}4](OTf)8

Data were collected on an Agilent SuperNova Dual diffractometerwith an Atlas detector equipped with an Oxford Cryostream low-temperature device by using mirror-monochromated CuKa radia-tion (l= 1.54184 �). CrysAlisPro[13] software was used for data col-lection, integration, reduction, and applying the analytical absorp-tion correction. The structure was solved by charge flipping (Super-flip[14]) and refined by full-matrix least squares on F2 (SHELXL-2014[15]) through the OLEX2[16] and WinGX[17] interface. All non-hy-drogen atoms were refined anisotropically. Hydrogen atoms atcarbon were placed in calculated positions and refined isotropicallyby using a riding model. Appropriate restraints or constraints wereapplied to the geometry and the atomic displacement parametersof the atoms in the catenane, as well as in the counter anions andthe solvent molecules. Triflate anions and the ethyl acetate solvent

were fitted and refined as rigid fragments. Contribution of the dis-ordered regions to the structure factors was calculated by usingSQUEEZE[18] procedure of PLATON[19] and the resulting FAB file wassubsequently used in the refinement.

Crystal dimensions 0.558 � 0.235 � 0.078 mm, colorless plate,C276.75H208F14.25N8O18.25P8Pd4S4.75, M = 5033.89, monoclinic, spacegroup P21, a = 29.5654(5), b = 16.7651(5), c = 32.7076(6) �, a= 90,b= 93.6735(16), g= 908, V = 16 178.8(6) �3, Z = 2, 1= 1.033 g cm�3,m= 3.200 mm�1, F(000) = 5158, 54 425 reflections (2Vmax = 135.508)measured (39 045 unique, Rint = 0.0479, completeness = 98.6 %),Final R indices (I>2s(I)): R1 = 0.1183, wR2 = 0.3351, R indices (alldata): R1 = 0.1305, wR2 = 0.3710. GOF = 1.314 for 2524 parametersand 4353 restraints, largest diff. peak and hole 1.986/�1.107 e��3,Flack parameter x = 0.099(7). CCDC-999739 contains the supple-mentary data for this structure. These data can be obtained free ofcharge via www.ccdc.cam.ac.uk/data_request/cif, or by emailingdata request@ccdc.cam.ac.uk, or by contacting The CambridgeCrystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ,UK; fax: + 44 1223 336033.

Acknowledgements

Financial support from the DFG (SFB 624), the Academy of Fin-land (KR, grant. no. 265328 and 263256) and the National Doc-toral Program in Nanoscience, Finland (F.T. , PhD fellowship) isgratefully acknowledged. We are grateful to the EAST NMR-Project and Dr. Janez Plavec from the Slovenian NMR Center ofthe National Institute of Chemistry in Ljubljana, Slovenia forthe opportunity to perform some NMR experiments at their fa-cility.

Keywords: 9,9’-spirobifluorenes · catenanes ·metallosupramolecular chemistry · palladium complexes · self-assembly

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cause the self-assembly process was not diastereoselective, and thus,gave rise to a mixture of stereoisomeric complexes.

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Received: May 6, 2014Published online on August 25, 2014

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