Sonia Aguado

Metal-organic frameworks: opportunities for catalysis.

The role of metal-organic frameworks (MOFs) in the field of catalysis is discussed, and special focus is placed on their assets and limits in light of current challenges in catalysis and green chemistry. Their structural and dynamic features are presented in terms of catalytic functions along with how MOFs can be designed to bridge the gap between zeolites and enzymes. The contributions of MOFs to the field of catalysis are comprehensively reviewed and a list of catalytic candidates is given. The subject is presented from a multidisciplinary point of view covering solid-state chemistry, materials science, and catalysis.

MOF-Supported Selective Ethylene Dimerization Single-Site Catalysts through One-Pot Postsynthetic Modification

The one-pot postfunctionalization allows anchoring a molecular nickel complex into a mesoporous metal-organic framework (Ni@(Fe)MIL-101). It is generating a very active and reusable catalyst for the liquid-phase ethylene dimerization to selectively form 1-butene. Higher selectivity for 1-butene is found using the Ni@(Fe)MIL-101 catalyst than reported for molecular nickel diimino complexes.

Guest-induced gate-opening of a zeolite imidazolate framework

The zinc benzimidazolate coordination polymer (ZIF-7) shows a reversible gate-opening effect upon variation of partial pressure of CO2 or temperature. This phenomenon, which is unique for a MOF with sodalite topology, arises from a phase-to-phase transformation upon guest adsorption–desorption.

Dynamic Nuclear Polarization Enhanced Solid‐State NMR Spectroscopy of Functionalized Metal–Organic Frameworks

Dynamic nuclear polarization (DNP) is applied to enhance the signal of solid-state NMR spectra of metal-organic framework (MOF) materials. The signal enhancement enables the acquisition of high-quality 1D 13C solid-state NMR spectra, 2D 1H-13C dipolar HETCOR and 1D 15N solid-state NMR spectra with natural isotopic abundance in experiment times on the order of minutes.

Solvent free base catalysis and transesterification over basic functionalised Metal-Organic Frameworks

Metal-Organic Frameworks (post-)functionalised with nitrogen containing moieties undergo solvent free aza-Michael condensation and transesterification, surpassing molecular and functionalised MCM-type analogues.

Facile synthesis of an ultramicroporous MOF tubular membrane with selectivity towards CO2

A substituted imidazolate-based MOF (SIM-1) membrane has been crystallized in situ on a tubular asymmetric alumina support that can be exploited for gas separation through preferential adsorption.

Engineering structured MOF at nano and macroscales for catalysis and separation

Here, we present for the first time the combination of the postfunctionalization of a MOF with its shaping as structured bodies. This study deals with the porous zinc carboxylimidazolate material known as SIM-1. A great advantage of this method is that the aldehyde moieties present on the structure walls allow organic modifications in the solid state, such as imine synthesis by condensation with primary amines to give the corresponding imino-functionalized SIM-2. We show that this postfunctionalization can be carried out on shaped SIM-1 bodies and films. The parent SIM-1 structured materials are prepared by direct in situ synthesis on a variety of supports for catalysis such as alumina beads and cordierite monoliths, and for separation applications using supports such as alumina tubes, fibers and anodic alumina disks. The hydrophobic SIM-2(C12) prepared on alumina beads is found to be an active catalyst for the Knoevenagel condensation, while its analogous supported membrane on alumina tube is efficient for CO2/N2 separation under humid conditions.

Absolute molecular sieve separation of ethylene/ethane mixtures with silver zeolite A.

Absolute ethylene/ethane separation is achieved by ethane exclusion on silver-exchanged zeolite A adsorbent. This molecular sieving type separation is attributed to the pore size of the adsorbent, which falls between ethylene and ethane kinetic diameters.

Engineering the Environment of a Catalytic Metal–Organic Framework by Postsynthetic Hydrophobization

Heterogeneous catalysis is of paramount importance in many areas of the chemical and energy industries. Often, however, reactions can be hindered or reaction rates limited by poisoning effects originating from moisture in the air or from the water formed during the organic transformation. Water can be adsorbed and block catalytic sites, leading to their deactivation. This drawback has motivated the design and engineering of catalytic materials with hydrophobic features, such as the hydrophobic outer shell of enzymes, to prevent water-induced catalyst poisoning. Metal–organic frameworks (MOFs) represent an extensive class of porous organic–inorganic crystalline materials. Due to their calibrated pore size, they are regarded as new shapeselective catalysts analogous to zeolites. MOFs have already been reported to catalyze a broad range of organic transformations involving their Lewis acid nodes as well as their Brønsted acid–base properties. 13] Many reports have dealt with carbon–carbon bond formation catalyzed by unmodified MOFs through reactions such as Suzuki–Miyaura cross-coupling, the Mukaiyama aldol reaction, alkylation 17] or polymerization. 19] To obtain more sophisticated MOF catalysts, many research groups have examined the functionalization of these materials. The post-synthetic modification (PSM) of MOFs, an appealing route toward functionalized frameworks, involves chemical modification of the solid after formation of the crystalline structure, assuming that the primitive MOFs employed are sufficiently porous and robust. Post-synthetic modification can provide a wide range of isotopological structures from a single MOF by treating it as a substrate with a variety of organic reagents. The insertion of pendant groups onto or into the MOF makes it possible to add chemical functionality while retaining the MOF’s overall framework. Cohen and co-workers extensively studied the covalent organic PSM of a variety of amino-functionalized MOFs. This strategy was used by his group and others to generate metal complexes on MOFs, creating a new class of Lewis acid catalysts. 23, 30] Furthermore, Cohen extended his study to the hydrophobization of amino-containing MOFs through amide coupling, in order to increase their moisture resistance. In a parallel work, Yaghi et al. also reported the functionalization of porous materials and especially the reactivity of ZIF-90 against an amine or a reducing agent. The effect of the functionalization of a MOF by hydrophobic agents on its catalytic activity has, however, not been reported to date. In contrast to previous studies, our methodology is based on the modification of the environment of the catalytic centers and not on the insertion of new sites onto the MOF structure. We therefore studied the ability of modified zeolitic imidazolate framework (ZIF) materials to accelerate the rate of a reaction involving water formation. We chose the Knoevenagel condensation, which is a crossed aldol condensation of a carbonyl compound with an active methylene compound leading to C=C bond formation. This reaction is widely applied in the synthesis of fine chemicals and is classically catalyzed by bases in solution. This reaction can also be catalyzed by solid bases, such as metal oxides. The water that is produced in the course of the reaction usually competes with substrates for adsorption, however, thereby acting as a poison. Porous solids such as modified SBA-1, zeolites, 37] MIL-101 (TOF= 328 h ), 39] IRMOF-3 (TOF = 180 h ) or MIL-53, and others have already been employed as active heterogeneous catalysts for the Knoevenagel reaction. We report herein the fine tuning of hydrophobic properties of a MOF by post-synthetic modification to optimize its catalytic properties. To our knowledge, this is the first study showing that the engineering of the hydrophobic/hydrophilic environment can enhance the catalytic activity of a MOF by an order of magnitude. Our work focused on a porous substituted imidazolate material (SIM-1, formulated C10H10N4O2Zn) discovered by our group and belonging to the class of ZIFs. SIM-1 is a robust material, isostructural to ZIF-8 and consisting of ZnN4 tetrahedra linked by carboxylimidazolates. The aldehyde moiety present on the structure walls allows organic modification in the solid state, such as imine synthesis by condensation with primary amines to give the corresponding imino-functionalized SIM-2. This SIM-1 functionalization by imine condensation proceeds under mild conditions. In a typical experiment, a sample of desorbed SIM-1 (50 mg) was suspended in anhydrous methanol (5 mL) and the desired amine (1 mmol) was added under stirring. The suspension was allowed to react at room temperature for 24 h. After reaction, the solid was centrifuged and washed three times with ethanol and then dried under vacuum, providing the corresponding SIM-2 as a crystalline offwhite powder. In this manner, SIM-1 was treated with the primary amines dodecylamine to give SIM-2(C12) (Scheme 1). The C12 aliphatic chains present at the surface of the material create a hydrophobic shell surrounding the framework. Powder XRD analysis of the SIM-2(C12) sample showed a slight loss of crystallinity despite retention of the initial structure. Notably, the porosity of the SIM materials was maintained [a] Dr. J. Canivet, Dr. S. Aguado, C. Daniel, Dr. D. Farrusseng Universit Lyon 1, IRCELYON, Institut de Recherches sur la Catalyse et l’Environnement de Lyon, UMR CNRS 5256 Avenue Albert Einstein 2, 69626 Villeurbanne (France) Fax: (+ 33) 4-72-44-54-36 E-mail : david.farrusseng@ircelyon.univ-lyon1.fr Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201000386.

Homogeneity of flexible metal–organic frameworks containing mixed linkers

Very sophisticated porous materials known as multivariate functional MOFs (also known as MixMOFs) can be designed using a synthesis method that starts from solutions composed of two or more different linkers. For this procedure to be successful, one must have access to techniques that characterize the homogeneity of MOF crystallites containing two different linkers. This is of particular relevance for MOFs made of 2-aminobenzene-1,4-dicarboxylate (abdc), which are excellent platforms for the introduction of additional functions by post-modification. In this paper, we show that adsorption/desorption isotherms and thermodiffraction studies on flexible structures can indirectly characterize the homogeneity of MOFs made from a mixture of linkers. Breathing pressures and temperatures for a series of MIL-53(Al) functionalized with amino tags, i.e. Al(OH)(bdc)1−n(abdc)n, were measured as a function of the amino content. The linear relationship between the CO2 breathing pressure and the amine content in the MIL-53(Al) structure clearly illustrates the homogeneity of the crystallite composition; in other words, the crystallites have the same abdc : bdc ratio. On the other hand, the functionalization of MIL-53(Al) with low amine content (10% abdc) results in a profound modification of the breathing properties triggered by the temperature. Much higher temperatures are required for full conversion of the np (narrow pore) to the lp (large pore) phase. We also suggest an interplay between coexisting np and lp microcrystalline domains that may “smooth” the breathing properties at the macroscopic level.