Copper complexes catenates

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). 

Cesario, M., Dietrich-Buchecker, C.O., Gui Them, J., Pascard, C. and Sauvage, J.P. 1985. Molecular structure of a catenand and its copper (I) catenate complete rearrangement of the interlocked macrocyclic ligands by complexation, J. Chem. Soc. Chem. Commun., 244-247. 

Figure 3. Cyclic voltammograms of bis-chelate copper complexes (a) [Cu(phen)2] and (b) [Cu(dmbp)2] in CH3CN- n-C4H9)4NC104 (0.1 M), and (c) of copper-catenate Cu.5 in CH3CN for oxidation, in DMF for reduction. Oxidation on Pt, reduction on the hanging mereury electrode.

Fig. 13. Electrochemically triggered rearrangement of a [2]catenate containing two different rings. The principle is the same as the one described for the copper complex rotaxane (Fig. 10)...

The effect of interlocking on the properties of molecules is dramatic. For example, the basicity of the 2,9-diphenyl-1.10-phenanthroline unit is enhanced by several orders of magnitude when it is present in a [2]catenand. The proton catenate displays a similar molecular structure to that of the corresponding copper(I) catenate, whereas that of the catenand is completely different. The special topology of the catenands and knots makes them unique ligands, with strong complexes being formed with a variety of metal ions. ° ... 

To our knowledge, topologically chiral molecules have not yet been resolved into enantiomers. However, we may anticipate that their energy barrier to racemization will be extremely high, compared to Euclidean chiral molecules. Therefore they are expected to be useful in enantioselective interactions or reactions. For example, it has been shown that tetrahedral copper(I) bis-2,9-diphenyl-l,10-phenanthroline complexes (which form the catenate subunits) are good reductants in the excited state [97] therefore the chiral Cu(I) catenates could be used for enantioselective electron-transfer reactions. Alternatively, the resolution of topologically chiral molecules would allow to answer fundamental questions, such as what are the chiroptical properties of molecular trefoil knots ... 

The coordination of catenated nitrogen ligands to transition metals also dates back to the early work of Griess 89, 90), which included references to copper and silver derivatives of 1,3-diphenyltriazene. Around the turn of the century Meldola and Streatfeild 146-148), Meunier 150-152), Niemen-towski and Roszkowski 159), Cuisa and Pestalozza 55,56), and others reported extensively on triazene complexes of copper, silver, and mercury, and in the late 1930s and early 1940s Dwyer and colleagues 69-74) extended this work to include derivatives of nickel and palladium. However, most work on the coordination chemistry of triazenes and other catenated... 

In CH3CN or CH2CI2, all copper]I) [2]catenates are reversibly oxidized to the divalent complexes (Figure 3). The oxidation potentials are high ( 0.6 V versus SCE), making the Cu species relatively strong oxidants. 

In the case of the phen complex, reduction of the monovalent state leads to copper metal, the initial electron transfer occurring either in the Cu 4s orbital or via a phen n orbital. Fast dissociation follows this monoelectronic reduction step. The redox orbitals involved during the reduction process of the copper catenate are likely to be ligand-localized. This is also supported by the small difference between the redox potentials of the Cu+ / and Cu°/ couples (A i/2 200 mV). Electrolysis of Cu.5+ in the cavity of an EPR spectrometer confirms the radical anion nature of the formally copper(O) complex obtained by one-electron reduction of the catenate g = 2.000 + 0.002, Ai/ = 39 G. 

It is noteworthy that, due to the topologically different properties of the copper-catenate and the copper-entwined complex [Cu(dap)2]+, electrolysis of the second leads only to copper metal and free dap. 

As expected, the redox potential of the Cu +/Cu+ couple is slightly shifted towards anodic values in CuAg.l0 + as compared to Cu.S" ". This effect is even more pronounced in CuCo.l0 + the copper(II) state is significantly more difficult to electro-generate than for the mono-nuclear species Cu.5+. The positive shift of the Cu +/Cu+ redox potential in di-metallic species as compared to Cu.5+ shows that the two metal complex subunits of the [3]catenates do interact. This may reflect an... 

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),... 

Figure 34. Square scheme illustrating the response of the catenate Cu-lS" " to an electrochemical signal. Oxidation and reduction generates metastable complexes which rearranges to adopt the best coordination mode for the new oxidation state of the copper center. Cu is a black circle and Cu is an open circle. (For the notation used here, see Figure 33.)...

Bauerle and coworkers have also prepared the catenate 3 (Chart 5.2) and characterized this species by electrospray ionization Fourier transform ion cyclotron resonance (ESI-F TlCR) mass spectrometry [32]. Reductive elimination of the platinum centers from this complex yielded a Cu+-linked conjugated catenate, which was also characterized by mass spectrometry, and the Cu could be removed with KCN to give the pure conjugated, metal-lfee catenane. The copper could not be removed from the terthiophene analogue of 3 which was prepared earlier by the same group [33]. 

The luminescence properties of a 3-catenand (20) and related 3-catenates containing a copper(I) center [Cu 20]+ were reported in 1991 [96]. The photophysical data are summarized in Table 5. It is interesting to note that while the mononuclear [Cu 20]+ shows ligand-centered tctc, and MLCT emission, the dinuclear complex [Cu2 20] + only reveals a single MLCT phosphorescence band at 700 nm in CH2CI2. The mixed-metal complex [CuCo 20] + is not lumi-... 

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