Engineering uniform active sites in inorganic solid catalysts

One of the reasons why such remarkable progress has been achieved in understanding the mechanisms of enzyme action is because crystalline enzymes, replete with their uniform active sites, are amenable to X-ray structural elucidation in a time-resolved fashion. The same is true of the catalytic behaviour of ribozymes, where the precise location and stereochemistry of crucially important cations within the RNA may be identified by synchrotron-based X-ray studies. When certain, carefully chosen, organometallic species are appropriately heterogenised on selected, high-area solid hosts, new, high-performance catalysts may be designed, and their structures may be elucidated-generally under in situ conditions-by synchrotron radiation supplemented by other lex situ) techniques. Armed with precise knowledge of the nature of the active site, improvements may be engineered so as to boost the performance of the original catalyst. In addition, related studies may be carried our on homogeneous analogues of the identified (heterogeneous) catalytically active site, thereby deepening further our understanding of catalysis. Novel designed catalysts (derived from mesoporous silica) that effect such processes as epoxidation land hydrogenation) of alkenes on the one hand, and allylic amination tin regio- and stereoselective modes) on the other are described, along with the de novo design of high-area redox molecular sieve catalysts that preferentially oxyfunctionalise linear alkanes tin air under mild conditions) at terminal carbon atoms. The increasing importance of computational chemistry in the broad landscape of catalysis is also adumbrated. (C) 1999 Elsevier Science B.V. All rights reserved.