Dicopper trefoil knots

Fig. 35 a, b. Crystal structure of the dicopper trefoil knot 852 + a) stereo view of a single molecule (the circles representing the atoms are given in black for oxygen, dotted for nitrogen and crosshatched for copper) b) stereoview of the unit cell. It contains two homochiral molecules, four PFg anions and two benzene molecules... 

In an attempt to improve the very poor yield (the dicopper trefoil knot was obtained in 3% yield only), we investigated the effect of structural parameters on the course of the reaction. The results obtained have recently been reported as a preliminary communication [43]. 

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.

Figure 18. Scheme of the two main cyclization reactions leading to the unknotted complex and the dicopper(I) trefoil knot. 

Figure 22. Reaction scheme leading to the dicopper(I) trefoil knot Cn2(K-84) f.

High-Yield Synthesis of a Dicopper(I) Trefoil Knot using Ring-Closing Metathesis Methodology... 

The dicopper(I) trefoil knot 36 was first obtained as a mixture of isomers (cis-cis, cis-trans and tra.ns-tra.ns products), because of the cis or trans nature of the two cyclic olefins formed. These olefins can be easily and quantitatively reduced at room temperature by catalytic hydrogenation yielding the knot 37. 

Although the preparative yields for most of the dicopper(I) trefoil knots described above were modest (0.5 to 8% for the methylene-bridged knots, 30% for the phe-nylene-bridged knot Cu2(K-84)p+) the amounts obtained were sufficient to undertake the study of their specific properties. 

Figure 28. Principle of the resolution of the dicopper(I) molecular trefoil knot Cu2(K-84) +. The chiral auxiliary used is S-(+)-l,l -binaphthyl-2,2 -diyl phosphate (BNP-).

Synthetic scheme for dicopper and free trefoil knots. From C. O. Dietrich-Buchecker, J. Guilhem, C. Pascard and J.-P. Sauvage, Angew. Chem. Int. Ed. 29, 1154-6 (1990). 

Fig. 33. a) Demetallation of the dicopper(I) trefoil knot 852 + leading to the trefoil knot 86. b) Two topological stereoisomers trefoil knot 86 and unraveled macrocycle 87... 

Figure 11. Dicopper(I) trefoil knots and related acyclic monocopper(I) complex.

Meyer, M. Albrecht-Gary, A.-M. Dietrich-Buchecker. C.O. Sauvage. J.-P. Dicopper(I) trefoil knots Topological and structural effects on the demetalation rates and mechanism. J. Am. Cheni. Soc. 1997, 119 (20). 4599-4607. and references cited therein. 

Dietrich-Buchecker, C.O. Sauvage. J.-P. De Cian. A. Fischer, J. High-yield synthesis of a dicopper(I) trefoil knot containing 1,3-phenylene groups as bridges between the chelate units. J. Chern. Soc., Chern. Commun. 1994, (19). 2231-2232. 

Dietrich-Buchecker CO, Rapenne G, Sauvage J-P, De Cian A, Fisher J (1999) A dicopper(l) trefoil knot with m-phenylene bridges between the ligand subunits synthesis, resolution, and absolute configuration. Chem Eur J 5 1432-1439... 

Therefore, combining the quantitative formation and high stability of the helical precursor composed of Cu(I) bis-phenanthroline units linked by 1,3-phenylene units and the highly efficient RCM methodology developed by Grubbs and coworkers, the dicopper(l) trefoil knot 7 + could be obtained in seven steps from commercially available 1,10-phenanthroline, with an overall yield of 35%. The cis or trans nature of the two cyclic olefins formed in the... 

Trefoil knots, and therefore the molecular knots discussed in this section, are chiral (Figure 4-29). The resolution of a dicopper(I) knot prepared from a helical precursor containing the 1,3-phenylene-linked bis-phenanthroline ligand described above (LI 198) has been achieved by crystallisation of the racemic cation with (5)-(+)-l,l -binaphthyl-2,2 -diyl phosphate [343]. As commented by these authors, the preparation of optically pure knot complexes is of great potential interest in relation both to interactions with biological molecules and, where the complexed metal has more than one accessible oxidation state, to enantioselective electron transfer [344]. 

Figure 4-29. Enantiomers of a trefoil knot and of a dicopper knot.

Meskers CJ, Dekkers HPJM, Rapenne G, Sauvage JP (2000) Chiroptical properties of an optically pure dicopper(I) trefoil knot and its enantioselectivity in luminescence quenching reactions. Chem Eur J 6 2129... 

Demetallation of the dicopper knotted complex 5.72 occurs by treatment with KCN to give the trefoil 5.73 which acquires a topological chirality. The CD curve of this species was recorded and shows a pronounced signal in the range 280-340 nm. Unfortunately no X-ray strucmres could be determined for any of three compounds 5.71-5.73. 

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