Redox-Active Cobalt(II/III) Metal–Organic Framework for Selective Oxidation of Cyclohexene

We
report herein a new cobalt­(II/III) mixed-valence metal–organic
framework formulated as [CoIICo2III(μ3-O)­(bdc)3(tpt)]·guest 1, where bdc = benzene-1,4-dicarboxylate and tpt = 2,4,6-tri­(4-pyridinyl)-1,3,5-triazine,
which can be used as a redox-active heterogeneous catalyst for selective
oxidation of cyclohexene on the allylic position without destroying
the adjacent double bond. Two oxidants were chosen to demonstrate
this result. For using tert-butyl hydroperoxide,
the conversion rate is 63% and only allylic oxidation products (tert-butyl-2-cyclohexenyl-1-peroxide, 86%; 2-cyclohexen-1-one,
14%) are found, whereas if using O2 as oxidant, a total
conversion of 38% is achieved and also only the allylic oxidation
products (cyclohexenyl hydroperoxide, 72%; 2-cyclohexen-1-one, 20%;
and cyclohex-2-en-1-ol, 8%) are found. The absence of any adduct on
the double bond may be due to the unique radical chain mechanism triggered
by the mixed-valent [CoIICo2III(μ3-O)] centers.