Organometallic cyclophane

Formation of organic and organometallic cyclophane capsules by triple RCM + triple CM and its inhibition to yield functional dendrimers by CM in the presence of CH2=CHC02R (R = H or CH3)... 

Figure 11 Examples of organometallic cyclophanes characterized by sensing behavior.

Cyclophanes or 7r-spherands have played a central role in the development of supramolecular chemistry forming an important class of organic host molecules for the inclusion of metal ions or organic molecules via n-n interactions. Particular examples are provided by their applications in synthesis [80], in the development of molecular sensors [81], and the development of cavities adequate for molecular reactions with possible applications in catalysis [82]. The classical organic synthesis of cyclophanes can be quite complex [83], so that the preparation of structurally related molecules via coordination or organometallic chemistry might be an interesting alternative. 

Cyclophane ruthenium complexes are of interest as possible monomeric components in the construction of multilayered organometallic polymers such as 262, which might show extended ir-electron delocalization (Scheme 25). 

Of great importance in transition metal chemistry of cyclophanes is that the complexes provide suitable building blocks to construct an organometallic polymer of general structure D (Fig. 3), monomeric and oligomeric units of which are already known (Figs. 25, 27). 

Complex chemistry of cyclophanes links the two best examined two-layered molecules of organic and organometallic chemistry, namely [22 ]para-cyclophane and ferrocene. The rich redox chemistry of ruthenium, cobalt, rhodium and iridium therefore provides a basis for constructing polymeric structures, of which some oligomeric building units are already known. 

From the standpoint of molecular complexity, the most intriguing applications of thiophene and its derivatives focus either on the occurrence of the thiophene moiety in naturally occurring molecules or in pharmacological agents. Transformation of thiophene into other moieties also produces some remarkable molecules. From a commercial view, the unique electronic and physical properties of thiophene make it ideal for applications in polymers, liquid crystals and dyes. Examples of thiophene-containing cyclophanes and other macrocycles as well as organometallic derivatives complete this chapter. 

Organometallic derivatives of poly-p-xylylene (PPX) with Ge and Sn atoms covalently bonded to polymer chains have been synthesized by a vapor deposition technique using bridged [2,2]-paracyclophanes with corresponding organometallic groups [32, 33]. Pyrolysis of these cyclophanes, along with polymerization of the /7-xylylene monomer mixture, is shown in Scheme 2.2. 

Very recently, Gmeiner and co-workers prepared metallocene-derived receptor ligands for G-protein-coupled receptors (GPGRs) such as dopamine and serotonin receptor subtypes. They used ruthenocene and ferrocene derivatives, in which the metallocenes replaced cyclophanes as so-called fancy bioisosters. In particular, compound 31 (Scheme 32) showed sub-nanomolar affinity and high specificity for the dopamine D4 and serotonin HTia receptor subtypes, and may thus be a suitable lead structure for the further development of selective organometallic GPCR ligands. 

Carcerands and Hemicarcerands, p. 189 Concave Reagents, p. i /1 Crown Ethers, p. 326 Cryptophanes, p. 340 Cyclodextrins, p. 398 Cyclodextrins, Applications, p. 405 Cyclophanes Definition and Scope, p. 414 Enzyme Mimics, p. 546 Macrocycle Synthesis, p. 830 Organometallic Anion Receptors, p. 1006 Soft and Smart Materials, p. 1302 X-Ray Crystallography, p. 1586... 

Popeney, C.S., Rheingold, A.L., and Guan, Z.B. (2009) Nickel(II) and palladiumfll) polymerization catalysts bearing a fluorinated cyclophane ligand stabilization of the reactive intermediate. Organometallics, 28,4452 4463. 

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