Copper-complexed catenane

ELECTROCHEMICALLY DRIVEN MOTIONS IN COPPER-COMPLEXED CATENANES... 

The Archetype Electrochemically Induced Ring Gliding Motions in a Two-Geometry Copper-Complexed Catenanes... 

Figure 14.4 The three forms of the copper-complexed catenane, each species being either a monovalent or a divalent complex, (a) Four-coordinate complex, (b) five-coordinate complex, and (c) six-coordinate complex.

When either the 2(6)2 + solution resulting from this process or a solution prepared from a sample of isolated solid 2(6)2 + (BF4 )2 were electrochemically reduced at — IV, the tetracoordinate catenate was quantitatively obtained. The cycle depicted in Fig. 14.3 was thus completed. The changeover process for the monovalent species is faster than the rearrangement of the Cu(II) complexes, as previously observed for the previously reported simpler catenate.16 In fact, the rate is comparable to the CV timescale, and three Cu species are detected when a CV of a CH3CN solution of 2(6)2 + (BF4 )2 is performed. The waves at + 0.63 V and —0.41V correspond, respectively, to the tetra- and hexacoordinate complexes mentioned above. By analogy with the value found for the previously reported copper-complexed catenane,16 the wave at —0.05 V is assigned to the pentacoordinate couple (Fig. 14.4b). 

A Copper-Complexed [2]Catenane in Motion with Three Distinct Geometries... 

When the copper complex of 7.62 reacts with ICH2(CH2OCH2)4CH2l in the presence of base, an intramolecular cyclisation occurs to form the macrocyclic ether 7.63. However, because of the arrangement of the starting ligands about the copper(i) centre, the two macrocycles are interlinked, and the consequence is the formation of the copper(i) complex of the catenand (catenand = catenane ligand) (Fig. 7-41). 

Keywords Catenanes Copper complexes Interlaced design Knots Kuratowski s graphs Mobius strip Topological chirality Topology... 

Copper complexes are known in oxidation states ranging from 0 to +4, although the +2 (cupric) and the +1 (cuprous) oxidation states are by far the most common, with the divalent state predominating. Only a relatively small number of Cu complexes have been characterized and the Cu° and oxidation states are extremely rare. A few mixed valence (see Mixed Valence Compounds) polynuclear species have also been isolated examples include a CuVCu species and a Cu /Cu catenane. The coordination numbers and geometries (see Coordination Numbers Geometries) of copper complexes vary with oxidation state. Thus, the majority of the characterized Cu complexes are square planar and diamagnetic, as is common for late transition metals with d electronic configurations. 

The other examples of electrochemically driven ring motions in [2]catenanes are from the class of metal complexed catenanes (i.e., catenates) that have been synthesized and studied in our groups. These compounds, the synthesis of which relies on the ability of copper( I) to gather the bidentate phenanthroline ligand around its tetrahedral coordination sphere, are produced in remarkable yield [9, 28, 57f]. The principle of operation is essentially based on the different stereoelectronic requirements of copper(I) and copper(II). Whereas a coordination number of 4, with a tetrahedral or distorted tetrahedral arrangement is preferred by copper(I),... 

The systems studied by Schuster and Guldi are reported in Fig. 22 56 and 57" are analogous to rotaxanes 33 and 40 with two zinc(II) porphyrins as stoppers, a Cu(I)(dpp)2 as the spacer and a C6o as the electron acceptor are appended to the macrocycle or included in it. SS is a catenane derived from 56 upon axial binding by a bidentate ligand to the zinc ions of the porphyrin stoppers. Rotaxanes 59" and 60 differ from 56 and 57" in having two 50 electron acceptors as stoppers and a zinc porphyrin electron donor appended to the macrocycle and differ from each other in the distance between the electron donor and the copper complex, which has been increased by insertion of a phenylamido group. 

The remarkable efficiency of these RCM reactions pointed to this new cyclization methodology as an attractive and versatile approach for the synthesis of more complex catenanes and knots. Due to the very mild and highly preservative conditions in which RCM reactions occur, the latter compounds could be obtained by using much weaker templates (lithium or iron) than copper (I). ... 

The metallo-carbene catalysts for ring-closing metathesis (RCM) reactions are ideal for this purpose. As a result of the mild reaction conditions and lack of competition with the coordination chemistry of the intermediate helical complex, the RCM strategy is particularly well adapted to the synthesis of copper(I)-complexed catenanes. A natural extension of this work was the preparation of a trefoil knot following the strategy depicted in Figure 11. 

Although the number of applications of olefin metathesis to transition metal complexes is small compared to the number of applications in organic synthesis, this field is becoming increasingly important. Spectacular examples are the double RCM reactions of copper phenanthroline complexes as a synthetic route to catenanes [113] or a recently reported approach to steric shielding of rhenium complex terminated sp-carbon chains [114]. 

Two interlocked macrocyclic ligands as in (15) are topologically related to the catenanes, whence the name catenand derives.34,186 187 These macrocycles complex a variety of metals, presumably in a tetrahedral geometry.34,186 The stabilizing effect of the catenand topology is evident in the observed redox stability of the nickel(I) complex186 as well as the reluctance toward demetallation, observed for the copper(I) complexes.187... 

In an example of a [3]-catenane formed by this methodology, the compound 7.64 is formed from the coupling of the copper(i) complex formed from the reaction of [Cu(MeCN)4]+ with one equivalent of 7.63 and one equivalent of 7.65 in 58 % yield (Fig. 7-44) The conformation of the [3]-catenane is partially controlled by intramolecular 7i-stacking interactions (Fig. 7-45). A number of other strategies have also been adopted... 

The assembly of the pseudo-tetrahedral intermediate 2 is clearly the key to the successful formation of the catenane 4. The process is based on the well documented tendency of copper(I), with its symmetrical d configuration, to adopt a tetrahedral co-ordination geometry. Indeed, the copper(I) complex of the parent ligand, 1,10-phenanthroline, is a stable classical tetrahedral species that was first investigated in 1933. ... 

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