Supramolecular catalysis complex

Cacciapaglia, R., Di Stefano, S., Kelderman, E. and Mandolini, L. (1999) Supramolecular catalysis of ester and amide cleavage by a dinuclear barium(II) complex. Angew. Chem., Int. Ed., 38, 348. 

Enolase type activity is displayed in the efficient supramolecular catalysis of H/D exchange in malonate and pyruvate bound to macrocyclic polyamines [5.32]. Other processes that have been studied comprise for instance the catalysis of nucleophilic aromatic substitution by macrotricyclic quaternary ammonium receptors of type 21 [5.33], the asymmetric catalysis of Michael additions [5.34], the selective functionalization of doubly bound dicarboxylic acids [5.35] or the activation of reactions on substituted crown ethers by complexed metal ions [5.36]. 

Supramolecular catalysis may also involve the combination of a host cavity and a metal active site as in the bis(diphenylphosphino)calix[4]arene nickel(II) complex 12.40 which acts as an efficient catalyst for ethylene and propylene polymerisation, and in tandem with zirconocene dichloride, for the formation of linear low-density polyethylene. In the latter case the complex gives very little branching - a significant advantage. The key to the effectiveness of the catalyst involves calixarene-induced changes in the bite angle at the Ni(II) centre, which is square planar in the active form of the catalyst.29... 

Ballester, Vidal-Ferran, and van Leeuwen evaluate concepts and strategies in the field of supramolecular catalysis. The authors describe what characterizes supramolecular catalysts, formulating a definition on the basis of the nature of interactions between catalyst and substrate or between building blocks of the catalyst. Examples are cited that demonstrate how supramolecular catalysts are superior to simple molecular catalysts in a broad range of reactions. Ballester et al. consider supramolecular catalysts as enzyme models, guided in their comparisons by the various mechanisms by which enzymes accelerate chemical transformations such as the binding of a reactant next to the catalytic site, the simultaneous complexation of two reactants, or desolvation. Addressing the synthesis of supramolecular catalysts, the authors describe how... 

The use of cyclodextrins14 has provided the ability to conduct the Strecker reaction with TMSCN in water via supramolecular catalysis involving reversible guest-host interactions. Activation of imine 16 by complexation with the hydroxyl groups present in cyclodextrins was found to work best with p-cyclodextrin. This chemically green reaction could be applied to ketones as well as aldehydes. 

Supramolecular chemistry has been a very popular research topic for three decades now. Most applications are foreseen in sensors and opto-electronical devices. Supramolecular catalysis often refers to the combination of a catalyst with a synthetic receptor molecule that preorganizes the substrate-catalyst complex and has also been proposed as an important possible application. The concept, which has proven to be powerful in enzymes, has mainly been demonstrated by chemists that investigated hydrolysis reactions. Zinc and copper in combination with cyclodextrins as the receptor dramatically enhance the rate ofhydrolysis. So far, the ample research devoted to transition metal catalysis has not been extended to supramolecular transition metal catalysis. A rare example of such a supramolecular transition metal catalyst was the results of the joined efforts of the groups of Nolte and Van Leeuwen [SO], They reported a basket-shaped molecule functionalized with a catalytically active rhodium complex that catalyzed hydrogenation reactions according to the principles of enzymes. The system showed substrate selectivity, Michaelis Menten kinetics and rate enhancement by cooperative binding of substrate molecules. The hydroformylation of allyl catachol substrates resulted in a complex mixture of products. 

SUPRAMOLECULAR CATALYSIS BY METAL COMPLEXES BASED ON CALIXARENES... 

One of the essential impetuses to cyclic dye architectures is the development of artificial model systems of the light-harvesting complexes in purple bacteria, where cychc arrays of chromophores provide the fundamental structural feature for their functionahty [2], On the other hand, cavities of variable sizes and shapes are accessible upon the formation of macrocycles. The assemblies of this kind, thus, possess also potentials in substrate binding, molecular recognition, matter transportation and even supramolecular catalysis. 

This review is dedicated to the synthesis of water-soluble cryptophanes and of the closely related hemicryptophane derivatives that were developed more recently. The study of their binding properties with different species and some peculiar properties related to their chiral structure are also described. A particular attention is given to xenon-cryptophane complexes since, as above mentioned, these complexes have played a major role in the development of water-soluble cryptophane derivatives. We describe in a concise manner the different approaches, which have been reported in the literature to introduce hydrophilic moieties onto the cryptophane structure. Finally, we report some physical properties of the water-soluble cryptophane complexes. This mainly concerns the study of their binding properties with neutral molecules or charged species. The preparation of enantiopure cryptophanes has also contributed to the development of this field. Indeed, it was stressed that cryptophanes exhibit remarkable chiroptical and binding properties in water [11]. These properties are also described. The last part of this review is devoted to hemicryptophane derivatives, which are closely related to the cryptophane structure and which allow the functionalization of the inner space of the molecular cavity. These show a renewed interest in their applications in chiral recognition and supramolecular catalysis. 

Water-Soluble Metal Hemicryptophane Complexes Towards Supramolecular Catalysis in Water... 

Metal complexes have attractive optical, magnetic, redox and catalytic properties, expanding the application of metal-mediated self-assembled containers in research areas such as supramolecular catalysis, development of redox and photoactive capsular systems, etc. 

Brown CJ, Miller GM, Johnson MW, Bergman RG, Raymond KN (2011) High-tumover supramolecular catalysis by a protected ruthenium(II) complex in aqueous solution. J Am Chem Soc 133(31) 11964-11966... 

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. 

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