Copper -templated synthesis catenanes

Copper(I)-Templated Synthesis of [2]Catenanes Bearing Pendant... 

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. 

Fig. 17 Two strategies for the transition metal-templated synthesis of a [2]catenane made with Zn and Au porphyrin-incorporating interlocked macrocycles. The thick lines represent chelating fragments, the black disk symbolises copper(I), the empty diamonds are Zn(II) porphyrins, and the hatched diamonds are Au(III) porphyrins...

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. 

The first template synthesis of catenanes made use of ligands that were turns and a copper(I) ion as anchor (Fig. 4). Terminal phenolic functions provided the... 

Figure 8 Principle of template synthesis of a [3]catenane. Copper (I) holds the two coordination fragments (thick line) perpendieular to one another. The cyclization involves two additional short linear links (thin line) and requires the connection of eight reacting center.

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

The use of metal coordination in the template-directed synthesis of knots and links is one of the earliest successful strategies employed by chemists. The first example of metal-templated synthesis of a [2]catenane was reported in Strasbourg by Sauvage et al. who first used the method to assemble two phenanthroline-based strands around a tetrahedral copper(I) cation (Scheme 17.1). 

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... 

Considering the efficiency of the 3D-template effect induced by transition metals in the synthesis of [2]catenanes, we tried to generalize our eoneept for obtaining [3]catenanes. Still relying on the copper(I)/l,10-phenanthroline couple, we eould develop two different strategies. 

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). ... 

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 . 

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