Abstract
Two novel pillared MOFs containing a urea-functional group are introduced and their efficiency as organocatalysts is evaluated in methanolysis of epoxides.
Highlights
Supramolecular organocatalysis is an interdisciplinary research area that includes elements from organic chemistry, supramolecular chemistry and biochemistry.[1,2] The design of a supramolecular catalyst is based on using hydrogen bonding and other intermolecular interactions in recognition and activation of substrates for triggering a variety of chemical transformations.[3,4] supramolecular catalysis o en suffers from drawbacks such as the lack of catalyst recycling and low efficiency due to the self-aggregation of the catalyst.[3]
Two novel urea-containing metal-organic frameworks (MOFs) were synthesized by combining the ditopic urea “strut”, pillaring struts, and Zn(NO3)2$6H2O using the solvothermal method at 90 C for 120 h to give suitable X-ray quality crystals of [Zn2(ubl)2(bipy)]$DMF (TMU-18) and [Zn2(ubl)2(bpe)]$DMF (TMU-19), where the ubl is 4,40-(carbonylbis(azanediyl))dibenzoic acid, and bipy and bpe are 4,40bipyridine and 1,2-bis(4-pyridyl)ethane, respectively, Fig. 1
TMU-18 and TMU-19 were synthesized by combining the ditopic urea ligand, pillaring struts, and Zn(NO3)2$6H2O using the solvothermal method at 90 C for 120 h to give suitable X-ray quality crystals
Summary
Supramolecular organocatalysis is an interdisciplinary research area that includes elements from organic chemistry, supramolecular chemistry and biochemistry.[1,2] The design of a supramolecular catalyst is based on using hydrogen bonding and other intermolecular interactions in recognition and activation of substrates for triggering a variety of chemical transformations.[3,4] supramolecular catalysis o en suffers from drawbacks such as the lack of catalyst recycling and low efficiency due to the self-aggregation (self-quenching) of the catalyst.[3]. Methanolysis of epoxides, which was traditionally attained using corrosive sulfuric acid,[32] has been widely investigated in heterogeneous catalytic systems including polymers and silica-based materials.[33,34] In recent years, some noteworthy attempts for the methanolysis reaction using MOFs have been reported, in which the epoxide activation is mostly achieved by the function of metal Lewis acidity centers within the MOF structures.[20,22,23] Generally, the coordinating ability of solvents such as MeOH which can act as a nucleophile and the requisite vacant metal sites within the MOF catalyst led to the low structural stability of these kinds of catalysts, even those which provided excellent catalytic activity and selectivity.[35] incorporating the linkers containing Brønsted acids[36] or hydrogen-bond donating (HBD) moieties into a MOF structure which involves locked metal centers such as paddle-wheel nodes can hopefully provide a MOF catalytic system that would be durable even for recycling purposes.
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