Metal template

Poly(ether sulfone) and poly(ether ketone) rotaxanes 77, 78, 79, and 80 were reported by Xie and Gong via solution polymerization in a mixture of toluene and DMF in the presence of metal ions (K+ or Na+) and 30C10 [114, 123]. The min values depended on the reaction conditions and the amount of BG applied [114, 123]. Polyrotaxanes 77 and 78 were difficult to purify because these polymers formed emulsions in water or methanol. Because of different preparation conditions between those with or without BG, the absolute m/n values are not comparable and thus the effect of the BG on threading remains unknown. However, considering that a polar solvent, i.e., DMF, was used for polymerization, these m/n values are still significant. 

By use of proton NMR techniques Parsons and coworkers studied a similar system in more detail in terms of the threading process and molecular motion 

Swager and coworkers also applied the self-assembly process in side-chain systems [131, 132]. The bisphenylene crown ether was incorporated into a conjugated backbone, polyphenyleneacetylene 87. This polymer complexes with paraquat 88 to give a novel polyrotaxane structure (89). With a polythiophene backbone, a similar polyrotaxane was synthesized by the same approach. 

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The yield of 7 might have been higher had a transition metal template been used, but to our knowledge, this has not been tried. 

Shinkai [15] concluded that p-zert-butyl calix[n]ar-ene tetra esters form stable monolayers at the air-water interface and the metal responds, therein, quite differently from that in solution. They reported that examination of the metal template effect on the conformer distribution established that when the metal cation present in the base used serves as a template, the cone conformer results are predominant [16]. Hence, Na in... 

The yield of the cyclization step under the influence of a metal template can be increased when the corresponding dialdehyde 19 of the tetrapyrrole 16 is used. The reaction sequence is initiated by insertion of palladium(II) or nickel(II) into the tetrapyrrole to give 20 followed by Michael addition of one acrylaldehyde side chain to the other yielding the macrotetracycle 21 from which in a retro-Michael reaction acetaldehyde is eliminated to give 22. 

Metal template reactions, 1, 416, 433 equilibrium kinetic, 1, 434 thermodynamic, 1, 434 Metal tolerance amino acid complexes, 2, 964 plants, 2, 963 Metal toxicity... 

Scheme 1 [3+2+1 ] -Benzannulation reaction as the first example of a metal-templated coupling of three different ligands...

The formal [3+2+1]-cycloaddition involves an a,ft-unsaturated carbene ligand (C3-synthon),an alkyne (C2-synthon) and a carbonyl ligand (Cl-synthon) and takes place within the coordination sphere of the chromium(O), which acts as a metal template (Scheme 2). 

A completely different kind of macro cycle, a calix-salen type macrocycle, was obtained in good yield by microwave irradiation of various dialdehydes and diamines [165]. This was the first example of a calix-type synthesis under microwave conditions and without the presence of a metal template. An example of a [3 -1- 3] cyclocondensed macrocycle 265, obtained from a bis aldehyde and a chiral diamine is reported in Scheme 97. 

Macrocyclic complexes of zinc have inspired interest in varied areas such as supramolecular and biomimetic chemistry including hydrolysis enzymes, such as phosphatases and esterases, and also for the fluorescent detection of zinc. The polyaza macrocycles and their A--functionalized derivatives are particularly well represented. An important aspect of macrocycle synthesis is the use of metal templates to form the ligand. Examples of zinc as a template ion will be discussed where relevant. 

An 18-membered N3O3 macrocycle could not be synthesized with transition metal templates but the N402 analog (85) was successfully synthesized with a zinc template. This gave dinuclear /r-hydroxy bridged zinc complexes including a rare example of a single unsupported... 

The preparation of metallophthalocyanines under solvent-free conditions from 1,2-phthalonitrile or phthalic anhydride and urea in the presence of metal templates... 

Apart from this one-reaction type, the routine use of metal template procedures for obtaining a wide range of macrocyclic systems stems from 1960 when Curtis discovered a template reaction for obtaining an isomeric pair of Ni(n) macrocyclic complexes (Curtis, 1960). Details of this reaction are discussed later in this chapter. The template synthesis of these complexes marked the beginning of renewed interest in macrocyclic ligand chemistry which continues to the present day. 

Blanco, M.-J., Transition-Metal-Templated Synthesis of Rotaxanes, 23, 125. 

Aucagne V, Bema J, Crowley JD, Goldup SM, Hanni KD, Leigh DA, Lusby PJ, Ronaldson VE, Slawin AMZ, Viterisi A, Walker DB (2007) Catalytic active-metal template synthesis of [2]rotaxanes, [3]rotaxanes, and molecular shuttles, and some observations on the mechanism of the Cu(I)-catalyzed azide-alkyne 1, 3-cycloaddition. J Am Chem Soc 129 11950-11963... 

The use of transition metal templates represents a particularly intriguing strategy to selectively accomplish [6 + 4] cycloadditions, as was shown first in the Kreiter laboratories302. Chromium(O) has emerged as the metal of choice in this kind of cycloaddition reaction which is either thermally or photochemically activated291. 

The role of transition metals in the chemical synthesis of corrins is more than just adding a touch of inorganic elegance to organic synthesis- leave elegance to tailors and cobblers , a physicist once said — it is a vital role in the sense that perhaps no synthetic corrin would as yet exist without recourse to metal templates. Beside the purely topological function of arranging the proximity of reaction centres, metal ions have served this purpose as follows ... 

Goral, V. Nelen, M. I. Eliseev, A. V. Lehn, J. M. Double-level orthogonal dynamic combinatorial libraries on transition metal template. Proc. Natl. Acad. Sci. U.S.A. 2001,98,1347-1352. 

Complexes with cyclic polydentate ligands containing NHC donor groups like 92 and 93 have been obtained in metal template-controlled reactions [223-225]. Related complexes (94 and 95) have been synthesized directly from polyimidazo-lium salts [226, 227] (Fig. 31). 

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