Copper -templated synthesis 2 -rotaxanes

Figure 2.28. Copper(I)-templated synthesis of [2]-rotaxane 81 from the thread 77, macrocycle 58, and Ru(II)-complex precursor 79.

Figure 2.30. Copper(I)-templated synthesis of Cu(I)-complexed [3]-rotaxane 86 and compartmental [5]-rotaxane 87, bearing free-base porphyrins as stoppers.

Figure 2.37. Copper(I)-templated synthesis of a Zn(II)/Au(III) bis-porphyrin-stoppered [2]-rotaxane as its Cu(I) complex (102) and as free [2]-rotaxane (107).

Figure 35 Copper (I)-templated synthesis of metal-complexed [2]-rotaxane (105) bearing...

Figure 51 Principle of transition metal-templated synthesis of a [3]-rotaxane, from two chelating macrocycles (B) and a bis-chelate-containing molecular thread (A) functionalized with reactive end groups X (same conventions as in Figure 43). (ii) Threading step, affording prerotaxane (C) construction of the porphyrin stoppers providing copper(I)-complexed [3]-rotaxane (D).

Abstract The approach based on the copper(I)-templated synthesis of porphyrin catenanes and rotaxanes developed by the authors group is here reviewed. Zn(II) porphyrins and gold(III) porphyrins were chosen as electron donors and electron acceptors, respectively, to constitute the electro- and photoactive parts of the present systems. The processes—energy and electron transfer reactions—occiuring in the interlocked structures upon light absorption in the presence or absence of Cu(I) are presented, their rates and efficiencies critically compared and discussed with respect to properties of the components and of the ensemble. A detailed examination of differences and analogies in photoreactivity between the present and closely related systems reported by others is presented. 

Several examples of photo-active porphyrin-containing catenanes and rotaxanes have been reported recently [84-86], but we will here examine only the few cases based on copper(I) template synthesis of the interlocked structure and as such, strictly related to the structures here discussed [87-90]. These reports, by Schuster and Guldi, present both the synthetic procedure and an account of the photoinduced processes taking place in the array. The latter will be briefly summarized and discussed with reference to the main results on the systems presented in the previous chapters. 

An intriguing series of electro- and photoactive porphyrin catenanes and rotaxanes, obtained by the authors through copper(I)-templated synthesis, is reviewed in the sixth chapter by Lucia Flamigni, Valerie Heitz, and Jean-Pierre Sauvage. The photo-induced processes - energy and electron transfer reactions - occurring in the interlocked structures upon light absorption are discussed in detail and critically compared to closely related systems reported by others. 

Flamigni L, Heitz V, Sauvage J-P (2006) Porphyrin Rotaxanes and Catenanes Copper(I)-Templated Synthesis and Photoinduced Processes 121 217-261... 

Scheme 14,19 Proposed catalytic cycle for the copper (I) template synthesis of rotaxane 68...

The situation could have been markedly different when the precursors contain coordinating moieties or transition metals, which could perturb the course of the reaction by interacting with the copper(I) catalyst or act as competitors, respectively. Interestingly, the presence of various transition metal-complexed fragments in the precursors is not particularly detrimental and does not seem to lower the preparative yields. Click chemistry has been successfully used with various transition metal complexes as precursors (Cu(I) or Fe(II)). The iron(II)-templated synthesis of a [3]rotaxane is remarkably efficient since the yield of a 4-fold stoppering reaction is close to quantitative. An impressive example... 

Flamigni L, Heitz V, Sauvage J-P (2006) Porphyrin Rotaxanes and Catenanes Copper(I)-Templated Synthesis and Photoinduced Processes 121 217-261 Flamigni L, see Baranoff E (2007) 123 41-78 Fontal B, see Contreras RR (2003) 106 71-79 Forr6 L, see Brouet V (2004) 109 165-199... 

Another way of templating the chromophore assembly, based on the copper(I) assisted synthesis of catenanes and rotaxanes developed by Dietrich-Buchecker and Sauvage in the 1980s, has led to the rotaxanes 118-120 represented in Figure 13.62. In this case, excitation of either the zinc or the gold porphyrins leads to photoinduced charge transfer to generate [(ZnP)2] -AuP . 

SCHEME 10.3 Synthesis of Stoddart s rotaxane 3 templated using charge transfer donor-acceptor interactions and stoppered dioxynaphthalene using copper-catalyzed alkyne-azide cycloaddition (CuAAC). 

By combining the catalytic and template effect of copper(I), Leigh et al. have developed a new powerful tool, which permits to use only catalytic amounts of the template agents for the synthesis of mechanically interlocked architectures. In theory, this concept can be applied to many other metal-mediated reactions, such as cross-couplings, condensations or other cycloaddition reactions.This new development may be the seminal idea that could lead to a whole new range of catenane- and rotaxane-forming protocols. 

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