Room-temperature olefin epoxidation reaction by two 2D cobalt metal-organic complexes under O2 atmosphere: coordination and structural regulation

Selective oxidation of olefin to epoxides is an important reaction in industry, however, developing heterogeneous catalysts to achieve the effective catalysis for this reaction under O2 atmosphere at room temperature is challenging but highly desired. In this work, two novel 2D cobalt metal-organic complexes, namely [Co(L)(5-HIP)]·2H2O (Co-MOC-1) and [Co(L)(BTEC)0.5]·H2O (Co-MOC-2) (L = (E)-4,4′-(ethene-1,2-diyl)bis(N-(pyridin-3-yl)benzamide; 5-H2HIP = 5-hydroxyisophthalic acid; H4BTEC = pyromellitic acid) were designed and synthesized through hydrothermal method, which exhibited different metal coordination modes (4-coordinate and 5-coordinate, respectively) and 2D layer structures directed by different carboxylates co-ligands. Two Co-MOCs can serve as heterogeneous catalysts for the selective oxidation of olefins to epoxides at room temperature using O2 as oxidant. Furthermore, a higher catalysis activity of Co-MOC-1 than Co-MOC-2 (96.7% vs 90.2% yield of 1,2-epoxycyclooctane) was observed, which may be attributed to the coordination unsaturated Co centers, the less coordination number and larger interlayer spacing of Co-MOC-1.