Structural design of Mn-metal-organic frameworks toward highly efficient solvent-free cycloaddition of CO₂

Three new manganese-based metal-organic frameworks (Mn-MOFs), [Mn(L)(H2O)]·2DMA (1), [Mn2(L)2(H2O)3]·2DMA (2), and [Mn2(L)2(DMF)2(H2O)]·3DMF (3), have been synthesized with the ligand H2L (N-phenyl-N′-phenylbicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxdiimide dicarboxylic acid). The secondary building units (SBUs) of the Mn-MOFs are controlled by changing the anions of the manganese salts, and the structures are modified from two-fold interpenetrating to non-interpenetrating by adjusting the mixed solvent systems. Along with the structural modification of the Mn-MOFs, we optimized their catalytic activities for the reaction of CO2 and epoxides toward cyclic carbonates. Both the activity and reusability of the Mn-MOFs are successfully improved in the solvent-free cycloaddition of CO2 with various epoxides under the mild conditions of atmospheric pressure and 70 °C.