Abstract
The binding of Zn(II) cations to a pentafoil (51) knotted ligand allows the synthesis of otherwise inaccessible metalated molecular pentafoil knots via transmetalation, affording the corresponding “first-sphere” coordination Co(II), Ni(II), and Cu(II) pentanuclear knots in good yields (≥85%). Each of the knot complexes was characterized by mass spectrometry, the diamagnetic (zinc) knot complex was characterized by 1H and 13C NMR spectroscopy, and the zinc, cobalt, and nickel pentafoil knots afforded single crystals whose structures were determined by X-ray crystallography. Lehn-type circular helicates generally only form with tris-bipy ligand strands and Fe(II) (and, in some cases, Ni(II) and Zn(II)) salts, so such architectures become accessible for other metal cations only through the use of knotted ligands. The different metalated knots all exhibit “second-sphere” coordination of a single chloride ion within the central cavity of the knot through CH···Cl– hydrogen bonding and electrostatic interactions. The chloride binding affinities were determined in MeCN by isothermal titration calorimetry, and the strength of binding was shown to vary over 3 orders of magnitude for the different metal-ion–knotted-ligand second-sphere coordination complexes.
Introduction
Molecular knots and entanglements occur in DNA,1 some proteins,2 and form spontaneously in polymer chains3 of sufficient length and flexibility.4 Synthetic routes to several small-molecule knots have been developed,5,6 or serendipitously discovered,7 and physical and chemical consequences of knotting have been demonstrated,4 including anion binding,7h,8 asymmetric,9 and allosteric regulation10 of catalysis, and the securing of a threaded structure by the increase in steric bulk that accompanies tying a knot in a molecular strand.11 However, despite metal template synthesis being a common route to molecular knots,4a,4c,4f,4h,5a,5c−5k,7d,8 effects on metal-ion coordination induced by knotting of the ligand strand have rarely10,12 been described.
We recently reported that a pentafoil (51) knot could be prepared by ring-closing olefin metathesis (RCM) of a pentameric circular Fe(II)5-helicate.10 The framework of this 51 knot contains only kinetically robust covalent bonds, and so, unlike previous examples,5e,5f the metal ions can be removed from a molecular pentafoil knot without destroying the knot topology. Direct remetalation of the knotted ligand proved only possible with Zn(II) cations, presumably because the coordination dynamics of other metal(II) cations is too slow to allow “mistakes” regarding which bipyridine moieties coordinate to which metal ion to be corrected. However, complexation of the five Zn(II) cations holds the knotted ligand in the conformation necessary to bind to five metal ions. We reasoned that this might enable sequential substitution of other metal(II) cations12 for Zn(II) without permitting the knotted ligand to adopt conformations that can bind to incoming metal ions through “wrong” combinations of bipyridine units.13 Here, we show that this enables the efficient synthesis of the otherwise inaccessible Co(II), Ni(II), and Cu(II) metalated knots, enabling the exploration of the coordination chemistry of the knotted ligand. The unknotted ligand monomer only forms circular helicates with Fe(II) and Zn(II),10 and so the transmetalation strategy, and resulting breadth of coordination chemistry, is only achievable with a knotted ligand.
Results and Discussion
Direct Metalation of Knotted Ligand 1
The coordination chemistry of pentafoil knot 1 was investigated by first probing the rate of metalation of 1 with different zinc(II) salts (Scheme 1, steps a,b). The rate and efficiency of introduction of the zinc(II) ions proved to be highly dependent on the salt used (Table 1). Treatment of 1 with Zn(BF4)2 in MeOH/CH2Cl2 (most conveniently followed using deuterated solvents) generated [Zn51·Cl](BF4)9 in 98% yield after 2 h at 40 °C followed by work-up with 1 equiv of Bu4NCl (Table 1, entry 1). Introducing the metal ions with Zn(CF3SO3)2 proved more sluggish, resulting in a 44% yield of [Zn51·Cl](CF3SO3)9 after 16 h and work-up (Table 1, entry 2). However, treatment of 1 with ZnCl2 afforded [Zn51·Cl](BF4)9 quantitatively in less than 5 min at room temperature, followed by exchange of the nine noncavity bound Cl– anions for BF4– for solubility reasons (Table 1, entry 3).
Scheme 1. Metallation of Knotted Ligand 1 To Generate the Corresponding M(II)5–1 Knot Complexes.
Reagents and conditions: (a) ZnCl2, dichloromethane/methanol (1:1), room temperature, <5 min; (b) saturated NH4BF4 (quantitative yield over two steps); (c) M(BF4)2 (M = Fe(II), Co(II), Ni(II), Cu(II)), acetonitrile/methanol (10:1), 80 °C, 2–4 days; (d) NBu4Cl 1 equiv per metalated pentafoil knot (94% [Fe51·Cl](BF4)9, 92% [Co51·Cl](BF4)9, 88% [Ni51·Cl](BF4)9, 85% [Cu51·Cl](BF4)9).
Table 1. Synthesis of [Zn51·Cl]9+ from 1 with Various Zinc Salts.
| entry | Zn salts | solvent | temp (°C) | time (h) | yield (%) |
|---|---|---|---|---|---|
| 1 | Zn(BF4)2 | MeOH/CH2Cl2 | 40 | 2 | 98a |
| 2 | Zn(CF3SO3)2 | MeOH/CH2Cl2 | 40 | 16 | 44a |
| 3 | ZnCl2 | MeOH/CH2Cl2 | rt | <5 min | quant.b |
After workup with 1 equiv of Bu4NCl.
After anion exchange with KBF4.
The X-ray crystal structure of [Zn51·Cl](PF6)9 features a chloride anion tightly bound in the central cavity as a consequence of electrostatic interactions and 10 CH···Cl– hydrogen bonds (Figure 2c and f).10 Given the very different rates of metalation with the different zinc salts, it seems likely that halide binding in the central cavity plays a significant role in facilitating the metalation of the knotted ligand, encouraging rapid rearrangement of wrongly coordinated bipyridine residues. In the 1H NMR spectrum of the titration of ZnCl2 into knot 1, free ligand and [Zn51·Cl]9+ signals dominate. Asymmetric species, that is, partially metalated pentafoil knots [Zn1–41·Cl]1–7+, are only present in very minor amounts (Figure S13). Coordination of the first zinc cations to the knotted ligand appears to preorganize the remaining empty coordination pockets, expediting the subsequent coordination events.
Figure 2.
X-ray crystal structures of [Co51·Cl](BF4)9, [Ni51·Cl](BF4)9, and [Zn51·Cl](BF4)9. (a–c) Views from above the central cavity, (d–f) views in the plane of the metalated knots: (a,d) [Co51·Cl](BF4)9, (b,e) [Ni51·Cl](BF4)9, and (c,f) [Zn51·Cl](BF4)9. In each structure, carbon atoms are light gray (except for one building block strand in which the C atoms are colored turquoise); N, blue; Co, teal; Ni, dark green; Zn, deep blue; the central chloride ion is shown at 99% van der Waals radius as a green sphere. Other anions, residual solvent molecules, and hydrogen atoms are omitted for clarity.
In contrast to the complexation of the knotted ligand with Zn(II), direct metalation of 1 with some other first row transition metal salts (Fe(II), Co(II), Ni(II), or Cu(II)) failed to generate isolable quantities of fully metalated knots, even over extended reaction times (up to 60 h) at elevated temperatures (up to 80 °C).14 Rather than start from metal-free ligand 1, we reasoned that as the Zn(II) cations in [Zn51·Cl](BF4)9 organize the binding sites of 1 in the correct arrangement, the labile Zn(II) ions of that complex might be exchanged for a less labile metal (introduced in large excess) in a stepwise process. Such stepwise transmetalation could allow the knotted ligand to retain the relative positions of its bipyridine chelating groups as the metals are successively exchanged, and hence reduce the degree of ligand strand rearrangement required.
Transmetalation of [Zn51·Cl](BF4)9
The Zn5-pentafoil knot complex [Zn51·Cl](BF4)9 was treated with a 20-fold excess of Fe(BF4)2 in CH3CN:CH3OH (1:0.1), and heated to 80 °C (Scheme 1, steps c,d). After 24 h, electrospray ionization mass spectrometry (ESI–MS) indicated almost complete conversion to a mixture of [Fe51·Cl](BF4)9 and [Fe51](BF4)10, with a small quantity of [ZnFe41·Cl](BF4)9 and [ZnFe41](BF4)10 also present. To ensure full exchange of Zn(II) for Fe(II) in the knot, a further 20-fold excess of Fe(BF4)2 was added, and heating continued for another 24 h. After this time, the addition of 1 equiv of NBu4Cl with respect to [Fe51]10+ (to avoid having a mixture of anions in the knot coordination complex) afforded [Fe51·Cl](BF4)9 as a red-purple solid. High-resolution (HR) ESI–MS (Figure S5) and 1H NMR spectroscopy (Figure S11) confirmed the product composition.
1H NMR (Figure S14) and ESI–MS (Table 2 and Figures S15–18) monitoring of the transmetalation process were consistent with the stepwise replacement of the Zn(II) cations in the knot. 1H NMR shows the signals corresponding to [Zn51·Cl](BF4)9 broadening after addition of Fe(BF4)2(H2O)6 and their intensity decreasing. Concomitantly, signals corresponding to [Fe51·Cl](BF4)9 emerge.
Table 2. ESI–MS Characterization of [Zn51](BF4)10 Treated with 10 equiv of Fe(BF4)2.
| 4+ charged
species |
5+ charged species |
6+ charged species |
7+ charged species |
|||||
|---|---|---|---|---|---|---|---|---|
| pentafoil knot intermediates | calcd | obsd | calcd | obsd | calcd | obsd | calcd | obsd |
| {[Zn4Fe11·Cl](BF4)9-nBF4}n+ | 1137.77 | 892.85 | 892.50 | 729.57 | 729.50 | 612.95 | 613.00 | |
| {[Zn3Fe21·Cl](BF4)9-nBF4}n+ | 1135.38 | 1136.08 | 890.94 | 890.92 | 727.98 | 728.00 | 611.59 | 610.92 |
| {[Zn2Fe31·Cl](BF4)9-nBF4}n+ | 1133.00 | 889.04 | 888.80 | 726.40 | 726.61 | 610.22 | 610.71 | |
| {[Zn1Fe41·Cl](BF4)9-nBF4}n+ | 1130.62 | 1130.67 | 887.13 | 887.08 | 724.81 | 724.83 | 608.86 | 608.83 |
Upon addition of 10 equiv of Fe(BF4)2(H2O)6 to an acetonitrile solution of [Zn51·Cl](BF4)9, aliquots were analyzed every hour by ESI–MS (Table 2, Figures S15–18), and the evolution of hetero penta-metalated knots {[Zn4Fe1·Cl](BF4)9–n}n+, {[Zn3Fe21·Cl](BF4)9–n}n+, {[Zn2Fe31·Cl](BF4)9–n}n+, and {[ZnFe41·Cl](BF4)9–n}n+ followed. No species featuring four or less metal ions were detected. The results are consistent with a stepwise transmetalation process where one zinc cation is substituted by an iron center at a time without the need for major reorganization of the knotted ligand.15
In analogous fashion, knots [Co51·Cl](BF4)9, [Ni51·Cl](BF4)9, and [Cu51·Cl](BF4)9 were formed by the transmetalation of [Zn51·Cl](BF4)9 with the respective metal tetrafluoroborate salts, followed by work-up with 1 equiv of Bu4NCl (Scheme 1, steps c,d). Longer reaction times were required for the complete exchange with Zn(II) in the order: Co(BF4)2 (2 days) < Ni(BF4)2 ≈ Cu(BF4)2 (4 days). Reaction progress was monitored by mass spectrometry until no heterometallic species were detected. The paramagnetic nature of Co(II), Ni(II), and Cu(II) precluded obtaining structural information for those pentametallic knots by NMR spectroscopy, but ESI–MS confirmed the isolation of homometallic coordination complexes (e.g., Figure 1 and Figures S4–10). The mass spectrometry results show selective association of each metalated knot with a single chloride anion. The UV–vis spectra of the Fe(II), Zn(II) Co(II), Ni(II), and Cu(II) knot complexes are similar to those of the known Fe(II), Zn(II), Co(II), Ni(II), and Cu(II) [M(5,5′-dimethyl-2,2′-bipy)3]2+ complexes (Figures S25–S29).
Figure 1.
(a) Low-resolution ESI–MS of pentafoil knot [Cu51·Cl](BF4)9. Calculated peaks (m/z): 1138.1 [M – 4BF4]4+; 893.1 [M – 5BF4]5+; 729.7 [M – 6BF4]6+; 613.2 [M – 7BF4]7+; 525.4 [M – 8BF4]8+. The minor peaks observed at m/z = 532.1, 620.3, 738.4, 903.2, and 1150.5 are corresponding to the {[Cu51](BF4)10-nBF4}n+ species and mainly originated from exchanges of cavity chloride and tetrafluoroborate anions. (b) High-resolution ESI–MS of the [M – 7BF4]7+ peak of [Cu51·Cl](BF4)9. Experimental spectrum (top) and calculated spectrum (bottom).
X-ray Crystal Structures of Metalated Pentafoil Knots
Slow diffusion of diisopropylether or toluene into a concentrated acetonitrile solution of [M51·Cl](BF4)9 (M = Co, Zn, or Ni) afforded crystals of suitable quality for X-ray diffraction on beamline I19 at the Diamond light Source (UK). The three crystal structures are broadly similar (Figure 2) but with slightly different conformations of the knotted ligand to accommodate the different sized metal ions. In each structure, the 190-atom-long pentafoil knotted ligand wraps around each of the metal ions in a closed loop double helicate. Five of the 15 bipyridine groups form an inner cavity lined with 10 electron-poor hydrogen atoms that form an array of hydrogen bonds with the chloride anion located inside the cavity (CH···Cl– distances given in Table 3). The cavity diameters vary depending on the metal cation: Fe(II), Zn(II), and Ni(II), 3.3(1) Å cavities; Co(II), 3.5(1) Å. The cobalt pentafoil knot dimensions are also more distorted from that of a regular pentagon than the other metalated knots: standard deviations of the metal–metal distances 0.6 Å for the cobalt knot as compared to 0.1, 0.1, and 0.2 Å in the iron, nickel, and zinc complexes, respectively; standard deviations of the metal–metal–metal angles (from the ideal 108° of a pentagon) 2.2° for the cobalt knot as compared to 0.7° (iron), 1.5° (nickel), and 1.7° (zinc) pentafoil knots. The chloride anion is located at different distances from the plane of the metal ions in the different knot complexes, illustrating how the size, electrostatics, and shape of the knotted ligand cavity change with coordination to the different metal cations (Figure 2d–f).
Table 3. X-ray Crystal Structure Parameters of Pentametalated Knotsa.
| cation | M–N distance (Å) | M–M distance (Å) | M–M–M angles (deg) | cavity size (Å) | CH···Cl distance (Å) |
|---|---|---|---|---|---|
| FeII | 2.0(1) | 8.3(1) | 108.8, 108.3, 108.8, 107.9, 106.7 | 3.3(1) | 2.8(1) |
| CoII | 2.1(1) | 8.6(6) | 105.3, 105.5, 106.5, 110.2, 110.5 | 3.5(1) | 2.8(1) |
| NiII | 2.1(1) | 8.4(1) | 106.3, 107.0, 107.1, 109.4, 110.2 | 3.4(1) | 2.8(1) |
| ZnII | 2.2(1) | 8.5(2) | 106.7, 107.1, 107.1, 107.8, 111.3 | 3.3(1) | 2.7(1) |
Distances are averages; standard deviations shown in parentheses.
The packing of the zinc pentafoil knot [Zn51·Cl](BF4)9 differs from that of the other pentafoil knot coordination complexes. The crystal structure of [Zn51·Cl](BF4)9 features pairs of knots close-packed through π-stacking of phenyl rings of each ligand (shown in turquoise in Figure 3), with the knots separated by a layer of six tetrafluoroborate anions (shown in space-filling representation in Figure 3). Five of the anions are located between the metal centers, forming an array of CH1···F bonds with the electron-poor CH1 atoms of the coordinated bipy ligands, with the sixth BF4– anion directly between the two chloride anions. The sandwiched complexes stack in the unit cell, forming cationic pillars with anionic cores.
Figure 3.
Packing of two [Zn51·Cl](BF4)9 complexes in the X-ray crystal structure, one shown with carbon atoms in gray, one with carbon atoms in red. Anions (chloride and tetrafluoroborate) depicted in space-filling representations. The phenyl rings shown in turquoise are involved in π-stacking between the two Zn5-pentafoil knots.
Chloride Binding Affinity of Metalated Pentafoil Knots
Isothermal titration calorimetry (ITC) was used to compare the chloride binding properties of the various metalated pentafoil knots (Table 4). Tetrabutylammonium chloride (Bu4NCl) was titrated into solutions of each chloride-free knot, [M51](BF4)10, in dry acetonitrile. Each of the different metalated knots was found by ITC to strongly bind chloride ions (Figures S30 and 31). The knot:chloride stoichiometry in each case is 1:1, although the number of chloride binding sites determined for each knot (N values, Table 4) was slightly lower than 1.0, probably as a result of scavenging of traces of chloride ions from glassware/solvents by the “empty” knots prior to the ITC measurements. In all cases, the chloride binding was both enthalpically and entropically favorable. The chloride affinities were high and similar for the iron(II), cobalt(II), and nickel(II) pentafoil knots (Ka (2.3–3.3) × 107 M–1), an order of magnitude lower for the zinc(II) knot (Ka 5 × 106 M–1), and significantly lower for the copper(II) knot (Ka 8 × 104 M–1).
Table 4. Determination of Cl– + [M51]10+ → [M51·Cl]9+ Binding by Isothermal Titration Calorimetry in MeCN.
| [[M51](BF4)10] (mol L–1) | [NBu4Cl] (mol L–1) | N (sites) | Ka (L mol–1) | ΔG (kJ mol–1) | ΔH (kJ mol–1) | –ΤΔS (kJ mol–1) | |
|---|---|---|---|---|---|---|---|
| [Fe51](BF4)10 | 2.5 × 10–5 | 2.0 × 10–4 | 0.79 | 3.3(9) × 107 | –43.0 | –33.0(5) | 10.1 |
| [Co51](BF4)10 | 2.5 × 10–5 | 2.0 × 10–4 | 0.59 | 2.3(6) × 107 | –42.1 | –25.6(4) | 16.5 |
| [Ni51](BF4)10 | 1.0 × 10–4 | 1.0 × 10–3 | 0.86 | 3(3) × 107 | –42.9 | –28.1(6) | 14.8 |
| [Cu51](BF4)10 | 1.0 × 10–4 | 1.0 × 10–3 | 0.72 | 8(2) × 104 | –28.1 | –22(2) | 5.8 |
| [Zn51](BF4)10 | 2.5 × 10–5 | 2.0 × 10–4 | 0.75 | 5(1) × 106 | –38.4 | –36.8(8) | 1.6 |
The different Cl– affinities of the various metalated pentafoil knots presumably result from several factors, including (but not restricted to): how coordination to the different size and electronic geometries of the cations affects the conformation of the cavity, the strength of coordination bonds influencing the polarization of the H1 atoms, the strength of the long-range M(II)···Cl– electrostatic attraction, and the tolerance of distortion of six-coordinate geometries by the different metal ions. In the absence of definitive structural data from X-ray crystallography, we cannot be sure as to the reasons why the Cu(II) pentafoil knot complex is a much more modest binder of chloride ions than the other metalated pentafoil knots. It may be that accommodating the size and shape of the five Cu(II) ions distorts the folded geometry of the pentafoil knotted ligand to such an extent that the cavity is no longer of appropriate size or shape (e.g., no longer directs all of the polarized H1 protons toward a single point in space) to bind Cl–.
Conclusions
A pentafoil knotted ligand 1, containing 15 bipyridine chelate residues in a 190-atom-long closed loop, forms “first-sphere” pentanuclear coordination complexes with a range of first row transition metal dications. The resulting complexes exhibit strong second-sphere coordination to a single chloride anion. Zn(II) ions,14 but not Fe(II), Co(II), Ni(II), or Cu(II), can be introduced directly into the knotted ligand, but the Zn(II) can be smoothly transmetalated with other metal(II) tetrafluoroborate salts to the pentanuclear Fe(II), Co(II), Ni(II), and Cu(II) knot complexes. The stepwise metal-ion-for-metal-ion substitution mechanism prevents the ligand from ever having sufficient vacant metal binding sites for incorrect binding modes to be adopted. The knotted ligands wrap around the five metal ions in a circular double helicate motif. Lehn-type circular helicates only form with tris-bipy strands and Fe(II) ions (and, in some cases, Ni(II)16 and Zn(II)10), and so this motif is only accessible with other metal(II) cations through such a knotted ligand. The X-ray crystal structures of the different pentanuclear knot complexes show conformational changes in the entangled ligand to accommodate the different sized metals. This results in a range of second-sphere coordination binding affinities for chloride ions that varies according to the metal ion over nearly 3 orders of magnitude, from Ka = 8 × 104 M–1 (Cu51) to Ka = 3.3 × 107 M–1 (Fe51) in acetonitrile. Knotting ligand strands imparts coordination chemistry that is inaccessible with constitutionally similar but unknotted ligands, a significant example4a,8−11 of the potential chemical consequences of molecular topology.
Acknowledgments
We thank the China 1000 Talents Plan, East China Normal University, the Engineering and Physical Sciences Research Council (EPSRC) (EP/P027067/1), the European Research Council (ERC) (Advanced Grant no. 339019), and the Biotechnology and Biological Sciences Research Council (BBSRC) (BB/M017702/1) for funding, the Diamond Light Source (UK) for Synchrotron beam time on I19 (XR029), and the University of Manchester for a President’s Doctoral Scholar Award (to L.Z.). D.A.L. is a Royal Society Research Professor and a Thousand Talents Professor.
Supporting Information Available
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.8b12548.
Experimental section, synthetic overview, synthetic procedures and characterization details, NMR spectra, UV–vis spectra, ITC experiments, X-ray crystal structure information, and additional references (PDF)
X-ray crystallographic details for [Zn51·Cl](BF4)9] (CIF)
X-ray crystallographic details for [Co51·Cl](BF4)9] (CIF)
X-ray crystallographic details for [Ni51·Cl](BF4)9] (CIF)
The authors declare no competing financial interest.
Supplementary Material
References
- a Wasserman S. A.; Cozzarelli N. R. Biochemical topology: applications to DNA recombination and replication. Science 1986, 232, 951–960. 10.1126/science.3010458. [DOI] [PubMed] [Google Scholar]; b Vinograd J.; Lebowitz J. Physical and topological properties of circular DNA. J. Gen. Physiol. 1966, 49, 103–125. 10.1085/jgp.49.6.103. [DOI] [PMC free article] [PubMed] [Google Scholar]; c Champoux J. J. DNA topoisomerases: structure, function, and mechanism. Annu. Rev. Biochem. 2001, 70, 369–413. 10.1146/annurev.biochem.70.1.369. [DOI] [PubMed] [Google Scholar]
- Lim N. C. H.; Jackson S. E. Molecular knots in biology and chemistry. J. Phys.: Condens. Matter 2015, 27, 354101. 10.1088/0953-8984/27/35/354101. [DOI] [PubMed] [Google Scholar]
- Frank-Kamenetskii M. D.; Lukashin A. V.; Vologodskii A. V. Statistical mechanics and topology of polymer chains. Nature 1975, 258, 398–402. 10.1038/258398a0. [DOI] [PubMed] [Google Scholar]
- a Fielden S. D. P.; Leigh D. A.; Woltering S. L. Molecular knots. Angew. Chem., Int. Ed. 2017, 56, 11166–11194. 10.1002/anie.201702531. [DOI] [PMC free article] [PubMed] [Google Scholar]; For other reviews on molecular knots, see:; b Fenlon E. E. Open problems in chemical topology. Eur. J. Org. Chem. 2008, 2008, 5023–5035. 10.1002/ejoc.200800578. [DOI] [Google Scholar]; c Beves J. E.; Blight B. A.; Campbell C. J.; Leigh D. A.; McBurney R. T. Strategies and tactics for the metal-directed synthesis of rotaxanes, knots, catenanes, and higher order links. Angew. Chem., Int. Ed. 2011, 50, 9260–9327. 10.1002/anie.201007963. [DOI] [PubMed] [Google Scholar]; d Forgan R. S.; Sauvage J.-P.; Stoddart J. F. Chemical topology: complex molecular knots, links, and entanglements. Chem. Rev. 2011, 111, 5434–5464. 10.1021/cr200034u. [DOI] [PubMed] [Google Scholar]; e Amabilino D. B.; Sauvage J.-P. The beauty of knots at the molecular level. Top. Curr. Chem. 2011, 323, 107–126. 10.1007/128_2011_292. [DOI] [PubMed] [Google Scholar]; f Ayme J.-F.; Beves J. E.; Campbell C. J.; Leigh D. A. Template synthesis of molecular knots. Chem. Soc. Rev. 2013, 42, 1700–1712. 10.1039/C2CS35229J. [DOI] [PubMed] [Google Scholar]; g Horner K. E.; Miller M. A.; Steed J. W.; Sutcliffe P. M. Knot theory in modern chemistry. Chem. Soc. Rev. 2016, 45, 6432–6448. 10.1039/C6CS00448B. [DOI] [PubMed] [Google Scholar]; h Sauvage J.-P. From chemical topology to molecular machines (Nobel lecture). Angew. Chem., Int. Ed. 2017, 56, 11080–11093. 10.1002/anie.201702992. [DOI] [PubMed] [Google Scholar]
- a Dietrich-Buchecker C. O.; Sauvage J.-P. A synthetic molecular trefoil knot. Angew. Chem., Int. Ed. Engl. 1989, 28, 189–192. 10.1002/anie.198901891. [DOI] [Google Scholar]; b Ashton P. R.; Matthews O. A.; Menzer S.; Raymo F. M.; Spencer N.; Stoddart J. F.; Williams D. J. A template-directed synthesis of a molecular trefoil knot. Liebigs Ann. Recueil 1997, 1997, 2485–2494. 10.1002/jlac.199719971210. [DOI] [Google Scholar]; c Guo J.; Mayers P. C.; Breault G. A.; Hunter C. A. Synthesis of a molecular trefoil knot by folding and closing on an octahedral coordination template. Nat. Chem. 2010, 2, 218–222. 10.1038/nchem.544. [DOI] [PubMed] [Google Scholar]; d Barran P. E.; Cole H. L.; Goldup S. M.; Leigh D. A.; McGonigal P. R.; Symes M. D.; Wu J. Y.; Zengerle M. Active metal template synthesis of a molecular trefoil knot. Angew. Chem., Int. Ed. 2011, 50, 12280–12284. 10.1002/anie.201105012. [DOI] [PubMed] [Google Scholar]; e Ayme J.-F.; Beves J. E.; Leigh D. A.; McBurney R. T.; Rissanen K.; Schultz D. A synthetic molecular pentafoil knot. Nat. Chem. 2012, 4, 15–20. 10.1038/nchem.1193. [DOI] [PubMed] [Google Scholar]; f Ayme J.-F.; Beves J. E.; Leigh D. A.; McBurney R. T.; Rissanen K.; Schultz D. Pentameric circular iron(II) double helicates and a molecular pentafoil knot. J. Am. Chem. Soc. 2012, 134, 9488–9497. 10.1021/ja303355v. [DOI] [PubMed] [Google Scholar]; g Ayme J.-F.; Gil-Ramírez G.; Leigh D. A.; Lemonnier J.-F.; Markevicius A.; Muryn C. A.; Zhang G. Lanthanide template synthesis of a molecular trefoil knot. J. Am. Chem. Soc. 2014, 136, 13142–13145. 10.1021/ja506886p. [DOI] [PubMed] [Google Scholar]; h Danon J. J.; Krüger A.; Leigh D. A.; Lemonnier J.-F.; Stephens A. J.; Vitorica-Yrezabal I. J.; Woltering S. L. Braiding a molecular knot with eight crossings. Science 2017, 355, 159–162. 10.1126/science.aal1619. [DOI] [PubMed] [Google Scholar]; i Zhang L.; August D. P.; Zhong J.; Whitehead G. F. S.; Vitorica-Yrezabal I. J.; Leigh D. A. A molecular trefoil knot from a trimeric circular helicate. J. Am. Chem. Soc. 2018, 140, 4982–4985. 10.1021/jacs.8b00738. [DOI] [PubMed] [Google Scholar]; j Danon J. J.; Leigh D. A.; Pisano S.; Valero A.; Vitorica-Yrezabal I. J. A six-crossing doubly interlocked [2]catenane with twisted rings, and a molecular granny knot. Angew. Chem., Int. Ed. 2018, 57, 13833–13837. 10.1002/anie.201807135. [DOI] [PMC free article] [PubMed] [Google Scholar]; k Zhang L.; Stephens A. J.; Nussbaumer A. L.; Lemonnier J.-F.; Jurček P.; Vitorica-Yrezabal I. J.; Leigh D. A. Stereoselective synthesis of a composite knot with nine crossings. Nat. Chem. 2018, 10, 1083–1088. 10.1038/s41557-018-0124-6. [DOI] [PubMed] [Google Scholar]
- a Fujita M.; Ibukuro F.; Hagihara H.; Ogura K. Quantitative self-assembly of a [2]catenane from two preformed molecular rings. Nature 1994, 367, 720–723. 10.1038/367720a0. [DOI] [Google Scholar]; b For selected examples of the synthesis of other interlocked molecular architectures featuring metal ion coordination, see:Leigh D. A.; Lusby P. J.; Teat S. J.; Wilson A. J.; Wong J. K. Y. Benzylic imine catenates: Readily accessible octahedral analogues of the Sauvage catenates. Angew. Chem., Int. Ed. 2001, 40, 1538–1543. . [DOI] [PubMed] [Google Scholar]; c Chichak K. S.; Cantrill S. J.; Pease A. R.; Chiu S.-H.; Cave G. W. V.; Atwood J. L.; Stoddart J. F. Molecular Borromean rings. Science 2004, 304, 1308–1312. 10.1126/science.1096914. [DOI] [PubMed] [Google Scholar]; d Li F.; Clegg J. K.; Lindoy L. F.; Macquart R. B.; Meehan G. V. Metallosupramolecular self-assembly of a universal 3-ravel. Nat. Commun. 2011, 2, 205. 10.1038/ncomms1208. [DOI] [PubMed] [Google Scholar]; e Li S.; Huang J.; Cook T. R.; Pollock J. B.; Kim H.; Chi K.-W.; Stang P. J. Formation of [3]catenanes from 10 precursors via multicomponent coordination-driven self-assembly of metallarectangles. J. Am. Chem. Soc. 2013, 135, 2084–2087. 10.1021/ja3118812. [DOI] [PubMed] [Google Scholar]; f Huang S.-L.; Lin Y.-J.; Hor T. S. A.; Jin G.-X. Cp* Rh-based heterometallic metallarectangles: size-dependent Borromean link structures and catalytic acyl transfer. J. Am. Chem. Soc. 2013, 135, 8125–8128. 10.1021/ja402630g. [DOI] [PubMed] [Google Scholar]; g Huang S.-L.; Lin Y.-J.; Li Z.-H.; Jin G.-X. Self-assembly of molecular Borromean rings from bimetallic coordination rectangles. Angew. Chem., Int. Ed. 2014, 53, 11218–11222. 10.1002/anie.201406193. [DOI] [PubMed] [Google Scholar]; h Lincheneau C.; Jean-Denis B.; Gunnlaugsson T. Self-assembly formation of mechanically interlocked [2]-and [3] catenanes using lanthanide ion [Eu (III)] templation and ring closing metathesis reactions. Chem. Commun. 2014, 50, 2857–2860. 10.1039/c3cc49640f. [DOI] [PubMed] [Google Scholar]; i Schouwey C.; Holstein J. J.; Scopelliti R.; Zhurov K. O.; Nagornov K. O.; Tsybin Y. O.; Smart O. S.; Bricogne G.; Severin K. Angew. Chem., Int. Ed. 2014, 53, 11261–11265. 10.1002/anie.201407144. [DOI] [PubMed] [Google Scholar]; j Wood C. S.; Ronson T. K.; Belenguer A. M.; Holstein J. J.; Nitschke J. R. Two-stage directed self-assembly of a cyclic [3]catenane. Nat. Chem. 2015, 7, 354–358. 10.1038/nchem.2205. [DOI] [PubMed] [Google Scholar]; k Thorp-Greenwood F. L.; Kulak A. N.; Hardie M. J. An infinite chainmail of M6L6 metallacycles featuring multiple Borromean links. Nat. Chem. 2015, 7, 526–531. 10.1038/nchem.2259. [DOI] [PubMed] [Google Scholar]; l Zhu R.; Lübben J.; Dittrich B.; Clever G. H. Stepwise halide-triggered double and triple catenation of self-assembled coordination cages. Angew. Chem., Int. Ed. 2015, 54, 2796–2800. 10.1002/anie.201408068. [DOI] [PubMed] [Google Scholar]; m Beves J. E.; Danon J. J.; Leigh D. A.; Lemonnier J.-F.; Vitorica-Yrezabal I. J. A Solomon link through an interwoven molecular grid. Angew. Chem., Int. Ed. 2015, 54, 7555–7559. 10.1002/anie.201502095. [DOI] [PMC free article] [PubMed] [Google Scholar]; n Galli M.; Lewis J. E. M.; Goldup S. M. A stimuli responsive rotaxane-Au catalyst: Regulation of activity and diastereoselectivity. Angew. Chem., Int. Ed. 2015, 54, 13545–13549. 10.1002/anie.201505464. [DOI] [PMC free article] [PubMed] [Google Scholar]; o Denis M.; Pancholi J.; Jobe K.; Watkinson M.; Goldup S. M. Chelating rotaxane ligands as fluorescent metal ion sensors. Angew. Chem., Int. Ed. 2018, 57, 5310–5314. 10.1002/anie.201712931. [DOI] [PMC free article] [PubMed] [Google Scholar]
- a Safarowsky O.; Nieger M.; Fröhlich R.; Vögtle F. A molecular knot with twelve amide groups—one-step synthesis, crystal structure, chirality. Angew. Chem., Int. Ed. 2000, 39, 1616–1618. . [DOI] [PubMed] [Google Scholar]; b Feigel M.; Ladberg R.; Engels S.; Herbst-Irmer R.; Fröhlich R. A trefoil knot made of amino acids and steroids. Angew. Chem., Int. Ed. 2006, 45, 5698–5702. 10.1002/anie.200601111. [DOI] [PubMed] [Google Scholar]; c Ponnuswamy N.; Cougnon F. B. L.; Clough J. M.; Pantos G. D.; Sanders J. K. M. Discovery of an organic trefoil knot. Science 2012, 338, 783–785. 10.1126/science.1227032. [DOI] [PubMed] [Google Scholar]; d Prakasam T.; Lusi M.; Elhabiri M.; Platas-Iglesias C.; Olsen J.-C.; Asfari Z.; Cianférani-Sanglier S.; Debaene F.; Charbonnière L. J.; Trabolsi A. Simultaneous self-assembly of a [2]catenane, a trefoil knot, and a Solomon link from a simple pair of ligands. Angew. Chem., Int. Ed. 2013, 52, 9956–9960. 10.1002/anie.201302425. [DOI] [PubMed] [Google Scholar]; e Ponnuswamy N.; Cougnon F. B. L.; Pantos G. D.; Sanders J. K. M. Homochiral and meso figure eight knots and a Solomon link. J. Am. Chem. Soc. 2014, 136, 8243–8251. 10.1021/ja4125884. [DOI] [PubMed] [Google Scholar]; f Kim D. H.; Singh N.; Oh J.; Kim E.-H.; Jung J.; Kim H.; Chi K.-W. Coordination-driven self-assembly of a molecular knot comprising sixteen crossings. Angew. Chem., Int. Ed. 2018, 57, 5669–5673. 10.1002/anie.201800638. [DOI] [PubMed] [Google Scholar]; g Leigh D. A.; Lemonnier J.-F.; Woltering S. L. Comment on “Coordination-driven self-assembly of a molecular knot comprising sixteen crossings. Angew. Chem., Int. Ed. 2018, 57, 12212–12214. 10.1002/anie.201804904. [DOI] [PubMed] [Google Scholar]; h Cougnon F. B. L.; Caprice K.; Pupier M.; Bauza A.; Frontera A. A strategy to synthesize molecular knots and links using the hydrophobic effect. J. Am. Chem. Soc. 2018, 140, 12442–12450. 10.1021/jacs.8b05220. [DOI] [PubMed] [Google Scholar]
- a Ayme J.-F.; Beves J. E.; Campbell C. J.; Gil-Ramírez G.; Leigh D. A.; Stephens A. J. Strong and selective anion binding within the central cavity of molecular knots and links. J. Am. Chem. Soc. 2015, 137, 9812–9815. 10.1021/jacs.5b06340. [DOI] [PubMed] [Google Scholar]; b Bilbeisi R. A.; Prakasam T.; Lusi M.; El-Khoury R.; Platas-Iglesias C.; Charbonnière L. J.; Olsen J.-C.; Elhabiri M.; Trabolsi A. [C–H···Anion] Interactions mediate the templation and anion binding properties of topologically non-trivial metal-organic structures in aqueous solutions. Chem. Sci. 2016, 7, 2524–2532. 10.1039/C5SC04246A. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Gil-Ramírez G.; Hoekman S.; Kitching M. O.; Leigh D. A.; Vitorica-Yrezabal I.; Zhang G. Tying a molecular overhand knot of single handedness and asymmetric catalysis with the corresponding pseudo-D3-symmetric trefoil knot. J. Am. Chem. Soc. 2016, 138, 13159–13162. 10.1021/jacs.6b08421. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Marcos V.; Stephens A. J.; Jaramillo-Garcia J.; Nussbaumer A. L.; Woltering S. L.; Valero A.; Lemonnier J.-F.; Vitorica-Yrezabal I. J.; Leigh D. A. Allosteric initiation and regulation of catalysis with a molecular knot. Science 2016, 352, 1555–1559. 10.1126/science.aaf3673. [DOI] [PubMed] [Google Scholar]
- Leigh D. A.; Pirvu L.; Schaufelberger F.; Tetlow D. J.; Zhang L. Securing a supramolecular architecture by tying a stopper knot. Angew. Chem., Int. Ed. 2018, 57, 10484–10488. 10.1002/anie.201803871. [DOI] [PMC free article] [PubMed] [Google Scholar]
- a Dietrich-Buchecker C. O.; Sauvage J.-P.; Armaroli N.; Ceroni P.; Balzani V. Knotted heterodinuclear complexes. Angew. Chem., Int. Ed. Engl. 1996, 35, 1119–1121. 10.1002/anie.199611191. [DOI] [Google Scholar]; b Dietrich-Buchecker C. O.; Hwang N. G.; Sauvage J.-P. A trefoil knot coordinated to two lithium ions: synthesis and structure. New J. Chem. 1999, 23, 911–914. 10.1039/a904476k. [DOI] [Google Scholar]; c Prakasam T.; Bilbeisi R. A.; Lusi M.; Olsen J.-C.; Platas-Iglesias C.; Trabolsi A. Postsynthetic modification of cadmium-based knots and links. Chem. Commun. 2016, 52, 7398–7401. 10.1039/C6CC02423H. [DOI] [PubMed] [Google Scholar]
- Miyake H.; Tsukube H. Coordination chemistry strategies for dynamic helicates: time-programmable chirality switching with labile and inert metal helicates. Chem. Soc. Rev. 2012, 41, 6977–6991. 10.1039/c2cs35192g. [DOI] [PubMed] [Google Scholar]
- In response to a reviewer’s suggestion, preliminary results show that direct metalation of the pentafoil knotted ligand 1 with MnCl2 for 2 days at room temperature, followed by anion exchange, successfully generates the corresponding [Mn51·Cl](BF4)9 complex. This is consistent with the relatively fast coordination dynamics of typical Mn(II) complexes (first-sphere coordination water exchange is faster for Mn(II) than Fe(II), for example, although slower than Zn(II)). Similarly, direct metalation of 1 with Cd(OAc)2, another metal salt with fast ligand exchange dynamics, resulted in the formation of [Cd51](OAc)10. These preliminary results will be reported fully in due course.
- Carnes M. E.; Collins M. S.; Johnson D. W. Transmetalation of self-assembled, supramolecular complexes. Chem. Soc. Rev. 2014, 43, 1825–1834. 10.1039/C3CS60349K. [DOI] [PubMed] [Google Scholar]
- a Hasenknopf B.; Lehn J.-M.; Kneisel B. O.; Baum G.; Fenske D. Self-assembly of a circular double helicate. Angew. Chem., Int. Ed. Engl. 1996, 35, 1838–1840. 10.1002/anie.199618381. [DOI] [Google Scholar]; b Hasenknopf B.; Lehn J.-M.; Boumediene N.; Dupont-Gervais A.; Van Dorsselaer A.; Kneisel B.; Fenske D. Self-assembly of tetra- and hexanuclear circular helicates. J. Am. Chem. Soc. 1997, 119, 10956–10962. 10.1021/ja971204r. [DOI] [Google Scholar]; c Hasenknopf B.; Lehn J.-M.; Boumediene N.; Leize E.; Van Dorsselaer A. Kinetic and thermodynamic control in self-assembly: sequential formation of linear and circular helicates. Angew. Chem., Int. Ed. 1998, 37, 3265–3268. . [DOI] [PubMed] [Google Scholar]
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