Double trefoil knot

Use of structural differences between the two isomeric ligand syntones 396 and 397 allowed obtaining [196] both the non-intertwined Pd2L4 coordination capsule 775 and its intertwined PdsLe analog 776, respectively (Scheme 4.190). The double trefoil knot-mimicking capsule 776... 

Engelhard DM, Freye S, Grohe K, John M, Clever GH (2012) NMR-Based structure determination of an intertwined coordination cage resembhng a double trefoil knot. Angew Chem Int Ed 51(19) 4747 750... 

Figure 16. Precursor and reaction scheme leading to the dicopper(I) trefoil knot (Cu2(K-86)2+). Formation of the double helix is essential this step is the weak point of the present synthesis.

We realized that improvement in the yields of trefoil knots would be determined by (i) the proportion of double helix precursor formed compared with face-to-face open chain complex (Figure 18) (ii) the spatial arrangement of the four reacting ends of the helical dinuclear complex. This latter factor will reflect the extent of winding of the two molecular strings interlaced around the copper atoms. The various complexes synthesized and studied are depicted in Figure 21 [96]. 

Figure 9. The relationship between a half-turn and a node. A trefoil knot has been drawn with thick lines its polarity is shown by the arrowheads along the knot. A dashed box has been drawn about each node, so that the strands of the knot divide the boxes into four regions, two between antiparallel strands, two between parallel strands. A half-turn of base pairs is drawn between antiparallel strands the helix axes are shown as double-headed arrows and dyad axes normal to them are represented by dotted lines ending in two ellipses.

Figure 7-50. The reaction of the molecular thread 7.67 with copper(i) salts gives a double-helical precursor with three crossing points. Reaction with ICH2(CH2OCH2)5CH2I gives the dinuclear trefoil knot 7.68.

The initial structural assignment of the above trefoil knot was based on mass spectral as well as H NMR data. However, its structure was subsequently confirmed by an X-ray diffraction study of the dinuclear copper(I) precursor (see Figure 6.38). The two copper(I) ions are located 6.3 A apart inside the double helix. 

Following on from the preparation of [2]catenate 10.103 (Scheme 10.27a), Sauvage realised that replacing the single Cu(l) core in [Cu(10.102)2] with a bimetallic double helicate would result in a precursor that, if it was stable enough to be cyclised, would immediately give a trefoil knot via a double auxiliary linkage approach (Scheme 10.27b). 

Scheme 10.27 (a) Schematic diagram of the synthesis of a [2] catenane via the auxiliary linkage approach, (b) Extension of this approach to the formation of a trefoil knot via a bimetallic double helicate. ... 

Fig. 9. The dinuclear double-stranded helical complex [Cu2(L,3)2](BF4)2 is utilized as the precursor of the trefoil knot system. (From Scheme 1 in Dietrich-Buchecher, C. D. Sauvage, J.-P. Cian, A. D. Fischer, J. J. Chem. Soc., Chem. Commun. 1994, 2231.)...

Mobius strip were formed exclusively. The synthesis of the more highly twisted belts 42 and 43 would be very interesting because subsequent cleavage of the double bonds by ozonolysis would lead to a catenane 44 and a molecular trefoil knot 45, respectively. 

Sauvage and coworkers have continued their elegant intertwining of macromolecules in order to better understand the construction of molecular knots. A double-stranded helix built around two Cu(I) centers was transformed (74%) into a trefoil knot by Ru(II)-catalyzed ring-closure metathesis <97CC2053>. The electrochemically triggered rearrangement of a copper... 

The same authors later studied the evolution of the radicals formed after rupture of a single knotted alkane molecule using first-principles molecular dynamics calculation [284]. In knotted chains, recombination of the radicals is totally bypassed in favor of ultrafast (about several hundred femtoseconds) phenomena such as diradicals which generate cyclic alkanes, and disproportionation to form carbon-carbon double bonds. Saitta and Klein suggested that the trefoil knot imposes topological constraints to the velocity distribution of the recoiling radicals at rupture, leading to deviations from the canonical recombination reaction. 

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