Oxidation of Alkenes to Give Corresponding Enol or Enone

4 a-Oxidation of Alkenes to Give Corresponding Enol or Enone 

The use of MIL-lOl-encapsulated polyoxometallate (POM) has also been reported for the a-oxidation of cyclohexene and a-pinene [113]. Both Ti- and Co-POM/MIL-101 catalysts showed fairly good activity and selectivity toward a-pinene oxidation with 40% and 45% conversion, respectively, and an average selectivity of 30% for both verbenol and verbenone compared with unmodified MIL-101 (14-18% conversion). 

In the MOF PIZA-3 (PIZA, porphyrinic Illinois zeolite analog), Mn(III) is found both in the porphyrin struts and as a structural metal node. The framework is structurally stable and is used for the oxidation of cycUc alkanes and alkenes with iodosylbenzene or peracetic acid as the oxidant [117]. Reaction is found to take place at the outer surface, which is justified by the authors by the unfavorable hydrophilic properties of the pore interior. Yields were similar to those obtained with homogeneous Mn(III) porphyrin systems or those immobilized inside inorganic supports as heterogeneous catalysts. Less than 0.1 mM of metalloporphyrin or degradation products were observed in the reaction mixtures, with no loss of oxidation activity observed in a second run when peracetic acid was used. 

I 70 Application of Metal-Organic Frameworks in Fine Chemical Synthesis 

Rosseinsky and coworkers reported the postmodification of IRMOF-3 with sali-cylaldehyde by imine condensation, leading to the formation of the MOF-supported Schiffbase with 13% yield. The resulting salicylidene-functionalized IRMOF-3 was used as an N-O ligand for a vanadium oxide complex and characterized by liquid-state NMR and PXRD analyses. The obtained MOF-supported vanadium catalyst was found to be active for cyclohexene a-oxidation with tBuOOH, although both conversion and TOF were relatively low, a possible problem involving framework coUapse was identified [118]. 

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