Selective oxidation of cyclooctene over copper-containing metal-organic frameworks

The selective oxidation of cyclooctene with tert-butylhydroperoxide (TBHP) was studied over Cu-containing MOFs at 348 K in liquid toluene. With Cu-3(BTC)(2), complete conversion was achieved after 120 h. The epoxide selectivity steadily increases to >80%. The conversion is accelerated by a radical initiator and decelerated by a radical inhibitor. A radical-based mechanism is proposed with alkoxy- or polyperoxides being formed as intermediates to the epoxide. The comparison of the cyclooctene conversion with TBHP over Cu-3(BTC)(2) with FeBTC, the ion-exchanged zeolites Na,Cu-Y and Na,Fe-Y and TS-1 proves that Cu-3(BTC)(2) is active for radicals generation from TBHP, but less suitable for catalyzing alkene epoxidation. The two recently reported Cu-MOFs 3(infinity)[Cu (Me - 4py - trz - ia)] and 3(infinity)[Cu-4(mu(4) - O)(mu(2) - OH)(2) (Me(2)trz - pba)(4)] are up to four times more active for cyclooctene oxidation than Cu-3(BTC)(2). This was attributed to the specific coordination geometry of the catalytically active Cu sites within these materials. Moreover, the liquid-phase conversion of cyclooctene with TBHP is shown to be a sensitive test reaction to evaluate the potential of new solid oxidation catalysts, especially of transition metal-containing MOFs. (C) 2015 Elsevier Inc. All rights reserved.