A series of cationic manganese complexes of 1,4,7-triazacyclononane (tacn) of varying nuclearity (number of metal centers = 1, 2, or 4) have been immobilized in situ onto the surface of acid-modified solid supports.  Alkyl and aryl carboxylic acids have been incorporated onto silica either by grafting or by sol-gel synthesis, and these acid sites act as both anchoring points and necessary co-catalysts.  Comparison of catalytic activity upon addition of H2O2 towards the epoxidation/dihydroxylation of linear and cyclic alkenes (e.g. n-octene, cyclohexene, cyclooctene and styrene) showed enhanced total turnovers with heterogeneous rather than soluble carboxylic acid co-catalysts.  The use of a solid support such as silica introduces the ability to fine-tune the performance (selectivity and throughput) of these catalysts upon variation of parameters such as the structure and surface density of the carboxylic acid, as well as the structure and surface density of silanol-capping moieties.  Moreover, our heterogeneous system offers the advantages of ease of handling and separation of products.

Immobilized manganese triazacyclononane catalysts for epoxidation

245th National Meeting (2013)

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