Zeolite-encapsulated cobalt salophen complexes as efficient oxygen-activating catalysts in palladium-catalyzed aerobic 1,4-oxidation of 1,3-dienes

Different cobalt salophen catalysts 1, 2, 3, and 4 were prepared and studie d as oxygen-activating agents in the palladium-quinone catalyzed aerobic ox idation of 1,3-dienes. These cobalt salophen catalysts were also encapsulat ed into the supercage of zeolite Y by the template synthesis method (ship-i n-the-bottle technique). The cobalt salophen catalyst 2 from 3,5-di-tert-bu tylsalicylaldehyde and 1,2-diaminobenzene was found to be more active than the unsubstituted parent cobalt salophen and the zeolite-encapsulated varia nt 2-ZeY showed remarkably high activity. With this catalyst, palladium-cat alyzed aerobic oxidation of 1,3-cyclohexadiene afforded 1,4-diacetoxy-2-cyc lohexene in high yield (95 %) at room temperature within three hours. It wa s demonstrated that the zeolite-encapsulated catalyst 2-ZeY can be isolated and reused several times and still show good conversion in the third run.