Dynamic covalent chemistry

Dynamic covalent chemistry is a strategy in chemistry in which a reversible reaction is under thermodynamic

reaction control and a specific reaction product out of many possible reaction products is captured [1]. Because all

the components in the reaction mixture are able to equilibrate quickly, some degree of error checking and proof

reading is enabled. The concept of dynamic covalent chemistry was demonstated in the development of specific

molecular Borromean rings.

The concept is also demonstrated in a reaction sequence involving polyacetal macrocycles [2]. The

cyclophane C2 can be prepared by the irreversible highly diluted reaction of a diol with

chlorobromomethane in the presence of sodium hydride. The dimer however is part of series of

equilibria between polyacetal macrocycles of different size brought about by acid catalyzed (triflic

acid) transacetalization. This particular type of transacetalization goes by the name of formal me

tathesis because it is reminiscent of olefin metathesis but then with formaldehyde. Regardless of the

starting material, C2, C4 or a high molar mass product, the equilibrium will eventually produce an

identical product distribution. In this system it is also possible to amplify the presence of C2 in the

mixture when the catalyst is silver triflate because the silver ion fits ideally and irreversibly in its

cavity.

References

1. ↑  Dynamic covalent chemistry Rowan SJ, Cantrill SJ, Cousins GR, Sanders JK, Stoddart JF. Angewandte Chem

ie International Edition 2002 41 898-952. PubMed Abstract

2. ↑  Metathesis reaction of formaldehyde acetals: an easy entry into the dynamic covalent chemistry of

cyclophane formation. Cacciapaglia R, Di Stefano S, Mandolini L. J. Am. Chem. Soc. 2005 39 13666-71 PubMed Abstract