Anion exchange type resins in preparative organic chemistry: structure-activity relationships

A critical overview is presented on the use of anion-exchange type resins, conventional and modified, including also polymeric crown ethers and related moieties, as catalysts in organic synthesis. The analysis of the available material has been organized to highlight the effects of specific structural and physical parameters of the polymer matrix, such as loading extent and topology of active sites, degree of crosslinking, porosity, surphace area and particle size. Semiquantitative evaluation of the above parameters has been done by comparing the specific activity and selectivity of polymer catalysts with their low molar mass analogs, in standard nucleophilic substitution, addition and elimination reactions. Examples have been included of polymer catalysts that are more active and sometimes more selective than the corresponding low molecular weight analogs. Cooperative effects of polymer constrained structural units play a key role in determining the reported behaviour.