Pyrrole-based macrocycles

Pyrrole-based macrocyclic assemblements were also utilized as functionalizing units for fuller-enes. Despite the fact that the first example coming to mind is a porphyrine macrocycle, the ability of such 7t-electron-rich systems to strongly bind fullerenes in a convex-planar supramolecular association will be discussed in Section 2.22.2. 

Other pyrrole-based macrocyclic anion receptors include the cyclo[n]pyrroles that consist solely of an array of p3rrole groups linked directly to each other via the 2- and 5-positions of the rings [127]. For example, cyclo [8] pyrrole 66a-d can be prepared by direct coupling of bipyrroles 65a-d in the presence of iron(III) chloride in 1 M sulfuric acid (Scheme 5.1). 

Mani et al. also studied the anion binding of amine-linked pyrrole-based macrocycles 71 and 72 using NMR titration in acetone-de [134]. The smaller macrocycle 71 complexed F in a 1 1 binding mode with a Ka of 1,138 IVT. A 1 2 stoichiometry was obtained for the binding of CF and Br with the first A ai being 3,182 and 243 respectively. The larger macrocycle 72 could form more 1 1 complexes with CF and Br K = 13,586 for CF and 1,181 for Br ). 

Silver(I) complexes with macrocyclic nitrogen ligands are also very numerous. Mono- or homodi-nuclear silver-containing molecular clefts can be synthesized from the cyclocondensation of functionalized alkanediamines or triamines with 2,6-diacetylpyridine, pyridine-2,6-dicarbalde-hyde, thiophene-2,5-dicarbaldehyde, furan-2,5-dicarbaldehyde, or pyrrole-2,5-dicarbaldehyde in the presence of silver(I).486 97 The clefts are derived from bibracchial tetraimine Schiff base macrocycles and have been used, via transmetallation reactions, to complex other metal centers. The incorporation of a range of functionalized triamines has provided the conformational flexibility to vary the homodinuclear intermetallic separation from ca. 3 A to an excess of 6 A, and also to incorporate anions as intermetallic spacers. Some examples of the silver(I) complexes obtained are shown in Figure 5. 

Subjecting 2 or 3 to strongly acidic conditions (e.g. 1 M CF3CO2H or concentrated HQ) leads to rapid demetalation and the production of two isomeric free-base macrocycles 10 and 11 [11, 12]. The structure of 10 was conflrmed by its spectral properties and its remetalation to form the nickel complex 5. On the other hand, the structure of 11 was determined solely by its spectral properties. For instance, the NMR spectrum of 11 demonstrated the presence of a fully unsaturated system. Typical also was the presence of pyrrolic proton signals in the 6-7 ppm range of the NMR spectrum [12]. Compound 11 was very unstable... 

The last class of Schiff base macrocycles to be discussed in this subsection are the only ones which can truly be called expanded porphyrins. This is because in all cases reliance is not made on simple pyrroles but on linked polypyrroles. The first... 

The metal-free condensation of fr(2-formylphenyl)telluride with a series of diamines afforded the macrocyclic tellurium Schiff base macrocycles attempted complexation with Pt(II) and Hg(II) afforded transmetalated products <04JOM1452>. Reduction of the Schiff base components of these chalcogenaza macrocycles gave rise to more robust and flexible macrocycles, which form the desired Pd(II) Tie,iV,jV, Tie-complex <04CC322>. The related Se-derivatives are also therein reported. 5,10-Diphenyl-15,20-di(4-methoxyphenyl)-21-tellura-porphyrin was prepared (18%) by the acid-catalyzed condensation of 2,5-6w(l-phenyl-l-hydroxymethyl)tellurophene, pyrrole, and 4-methoxybenzaldehyde, followed by oxidation with /j-chloranil <04OM4513>. 

The first pyrrole-based moiety able to interact with Cgo through n-n interactions was described by Sessler et al. " and consisted of a calix[4]pyrrole scaffold fused with four units of TTF (Figure 2.11b). This molecule interacted with Cgo very weakly in its open form, but is able to switch in a cone conformation after the addition of Cl ions, forming an electron-rich deep cavity defined by the TTF arms. Indeed, a 2 1 complex was formed after the addition of tetrabutylammonium chloride to a solution of Cgo and the macrocycle."" ... 

Beer PD, Cheetham AG, Drew MGB, Fox OD, Hayes EJ, Rolls TD (2003) Pyrrole-based metallo-macrocycles and cryptands. Dalton Trans 603-611... 

Eigure 189. Pyrrole-based nickel(ll)-containing macrocycles and crytands. 

In an exciting development. Beer and co-workers prepared a range of novel compounds incorporating copper(ll) bis(dithiocarbamate) units (Fig. 220). These include macrocyclic complexes based on terphenyl diamines (439-442) (326, 1468, 1469) and ferrocenyl amines (443) (1468), pyrrole-based metallo-cryptands (444) (492), cyclic amide complexes (445), and monometallic complexes with crown-ether substituents (446) (492), a number of which have been... 

As with any metalloprotein, the chemical and physical properties of the metal ion in cytochromes are determined by the both the primary and secondary coordination spheres (58-60). The primary coordination sphere has two components, the heme macrocycle and the axial ligands, which directly affect the bound metal ion. The pyrrole nitrogen donors of the heme macrocycle that are influenced by the substitutents on the heme periphery establish the base heme properties. These properties are directly modulated by the number and type of axial ligands derived from the protein amino acids. Typical heme proteins utilize histidine, methionine, tyrosinate, and cysteinate ligands to affect five or six coordination at the metal center. 

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