Abstract
Nine metal-organic frameworks, [M(PDA), M(BTC), M(PTC)] (M=Cu, Co, Mn; H2PDA= pyridine-2,6- dicarboxylic, H3BTC= 1,3,5-benzenetricarboxylic acid , H3PTC= pyridine-2,4,6-tricarboxylate), containing respectively Cu2+, Co2+, Mn2+ ions and carboxylate ligands (H2PDA, H3BTC, H3PTC). They can be used as valuable heterogeneous catalysts since they are easily separated and reused from the reaction systems, and possess single catalytic active sites in their frameworks which are characteristic of the homogenous catalysts. In addition, N-hydroxyphthalimide (NHPI) has been also revealed to be valuable organocatalyst for free-radical processes and found ample applications in promoting the aerobic oxidation of a wide range of organic compounds. We present here a heterogeneous protocol by adsorbing NHPI in MOFs to obtain the novel NHPI/MOFs catalytic system. The allylic oxidation of α-isophorone (α-IP) into ketoisophorone (KIP) utilizing the NHPI/MOFs as heterogeneous catalysts with moleular oxygen as primary terminal oxidant under solvent- free condition was conducted. The results show that NHPI/Co(BTC) obtain optimum catalytic efficiency affording 36.6% conservation of α-IP and 81.7% KIP selectivity. The catalyst can be isolated easily from the reaction system by simple filtration and recycle without significant degradation in activity. The oxidations fulfill the requirement of green chemistry concept in terms of environmental benignity and sustainability.
Keywords: Allylic oxidation, dioxygen, heterogeneous, metal-organic frameworks, N-hydroxyphthalimide, solvent-free.
Graphical Abstract
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