Chiral porous metal-organic frameworks with dual active sites for sequential asymmetric catalysis

Abstract

Metal-organic frameworks (MOFs) are a class of organic-inorganic hybrid materials built from metal-connecting nodes and organic-bridging ligands. They have received much attention in recent years owing to the ability to tune their properties for potential applications in various areas. Properly designed MOFs with uniform, periodically aligned active sites have shown great promise in catalysing shape-, size-, chemo-, regio-and stereo-selective organic transformations. This study reports the synthesis and characterization of two chiral MOFs (CMOFs 1 and 2) that are constructed from Mn-salen-derived dicarboxylic acids [salen is (R,R)-N,N'-bis(5-tert-butylsalicylidene)-1,2- cyclohexanediamine], bis(4-vinylbenzoic acid)-salen manganese(III) chloride (H2L4) or bis(benzoic acid)-salen manganese(III) chloride (H2L 3) and [Zn4(μ4-O)(O2CR)6] or [Zn5(H2O)2(μ3-OH) 2(O2CR)8] secondary building units (SBUs), respectively. The SBUs in CMOF-1 are connected by the linear ditopic Mn-salen-derived linkers to construct a fourfold interpenetrated isoreticular MOF (IRMOF) structure with pcu topology. In CMOF-2, the Mnsalen centres dimerize in a cross-linking way to form a diamondoid structure with threefold interpenetration. CMOF-1 was examined for highly regio-and stereo-selective tandem alkene epoxidation/epoxide ring-opening reactions by using the Mn-salen and Zn4(μ4-O)(carboxylate)6 active sites, respectively. Our work demonstrated the potential utility of chiral MOFs with multiple active sites in the efficient synthesis of complex molecules with excellent regio-and stereo-controls. © 2012 The Royal Society.