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Water Stability of Metal–Organic Frameworks
Published in T. Grant Glover, Bin Mu, Gas Adsorption in Metal-Organic Frameworks, 2018
In addition to hydrophobicity, functional groups can also provide steric effects to improve water stability. An interesting example of this combined stability mechanism is the mixed-ligand MOF, Zn-TMBDC-DABCO, or DMOF-TM.54–56 The parent form of this MOF is stable at humidity levels below 40%RH, but it undergoes complete degradation at higher humidity levels. Jasuja et al.56 showed that functionalizing the BDC ligand with four methyl groups (TMBDC) to obtain DMOF-TM results in a fully stable MOF under all humidity levels. Further, DMOF-TM was shown to be cyclically stable after humidity exposure up to 95%RH. Isotherms for both MOFs are shown in Figure 8.9. Molecular simulations showed a stark difference in how adsorbed water clusters in the pore space of the parent DMOF versus DMOF-TM.55 Adsorbed water in the parent structure clusters near the Zn-BDC coordination site and eventually degrades the material. On the other hand, the methyl groups in DMOF-TM clearly force the adsorbed water to remain in the center of the pore space, away from the coordination site. Notably, DMOF-TM adsorbs large quantities of water at saturation, reaching a loading of approximately 24 mol/kg. This loading is on par with water adsorption saturation in BPL carbon and the mesoporous silica SBA-1 and greater than loadings in UiO-66 and zeolites 5A and 13X (Figure 8.2). A summary of governing structural parameters for each stability mechanism is shown in Figure 8.8.
Surface Activation and Modification
Published in Benny K.G. Theng, Clay Mineral Catalysis of Organic Reactions, 2018
The ability of Dabco2+-exchanged montmorillonite to catalyze the conversion of acetonitrile to acetamide has been reported by Mortland and Berkheiser (1976). Similarly, Stul et al. (1983) have found Zn-Dabco-montmorillonite to be highly efficient in catalyzing the isomerization of cis-2-butene to trans-2-butene and 1-butene (at 150°C) whereas TMA+-montmorillonite is comparatively inactive. We should mention that the free, neutral Dabco base can serve as a homogeneous catalyst for various organic conversions, including the coupling of functionalized aldehydes to acrylic esters (Hoffmann and Rabe 1983), and that of acrylonitrile to α-keto esters (Basavaiah et al. 1987). This compound can also catalyze the Baylis−Hillman reaction between aromatic aldehydes and activated olefins (Basavaiah et al. 2003; Chandrasekhar et al. 2004; de Souza et al. 2008), and the synthesis of quinoxalines by reacting 1,2-diamines with phenacyl bromides (Meshram et al. 2010). More recently, Meshram et al. (2012a, 2012b) used Dabco to promote the synthesis of pyrrole by reacting phenacyl bromides, pentane-2,4-dione and amine, and that of benzofurans from phenacyl halides and o-hydroxy benzaldehyde. Whether or not such reactions can be efficiently and selectively catalyzed by clay-intercalated Dabco awaits investigation.
Introduction
Published in Andrew M. Harned, Nonnitrogenous Organocatalysis, 2017
In 1968, Morita described a reaction between an aldehyde and an electron-deficient alkene (acrylates and acrylonitrile).32 The reaction was catalyzed by tricyclohexylphosphine and afforded α-hydroxyalkylated products 9 (Figure 1.5). Several years later, Baylis and Hillman33 reported that this same reaction could be carried out using a highly nucleophilic tertiary amine catalyst (DABCO). This reaction has since become known as the Morita–Baylis–Hillman (MBH) reaction and has been the subject of intense research in recent decades owing to the highly functionalized nature of the products. It should be mentioned that Rauhut and Currier described a related dimerization of acrylates in a 1963 patent.34 This reaction was also promoted by a trialkylphosphine.
Review. Inverse coordination. Organic nitrogen heterocycles as coordination centers. A survey of molecular topologies and systematization. Part 2. Six-membered rings
Published in Journal of Coordination Chemistry, 2019
1,4-Diazabicylo(2,2,2)octane, also known as DABCO, is a versatile molecule for the synthesis of inverse coordination complexes. Its iron (391) [667], palladium (392) [668], cadmium (393) [669], organoaluminium and organogallium (394) [670] inverse coordination complexes are illustrated in Scheme 134. Other DABCO centered inverse coordination complexes include analogous compounds with manganese [655(a)], manganese-iron pair [671], iron [655(a)], ruthenium [24], osmium [24, 672], cobalt [673], rhodium [264], nickel [674], copper [547, 675], silver [676], zinc [655(a), 677], cadmium [655(a), 669], mercury [678], bismuth [679], lithium [680] and more can be expected.