Cyclodextrin, supramolecular catalysis complex

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. 

This short compilation of the recent literature results convincingly demonstrates the usefulness of water-soluble supramolecular complexing agents in biphasic aqueous organometalHc catalysis. Due to their availability, cyclodextrins play a major role in this field. Thinking of the relatively low price of these chemicals (a few per kg in 1998 [2]) their use on a larger scale can also be envisaged in fine chemicals production. 

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