Reductive electrosynthesis of crystalline metal-organic frameworks

Electroreduction of oxoanions affords hydroxide equivalents that induce selective deposition of crystalline metal–organic frameworks (MOFs) on conductive surfaces. The method is illustrated by cathodic electrodeposition of Zn[subscript 4]O(BDC)[subscript 3] (MOF-5; BDC = 1,4-benzenedicarboxylate), which is deposited at room temperature in only 15 min under cathodic potential. Although many crystalline phases are known in the Zn[superscript 2+]/BDCsuperscript 2–] system, MOF-5 is the only observed crystalline MOF phase under these conditions. This fast and mild method of synthesizing MOFs is amenable to direct surface functionalization and could impact applications requiring conformal coatings of microporous MOFs, such as gas separation membranes and electrochemical sensors.Massachusetts Institute of Technology. Energy Initiative (Seed Fund Program)National Science Foundation (U.S.) (Grant CHE-9808061)National Science Foundation (U.S.) (Grant DBI-9729592)National Science Foundation (U.S.) (Grant DMR- 0819762

Metal-organic frameworks as kinetic modulators for branched selectivity in hydroformylation.

Finding heterogeneous catalysts that are superior to homogeneous ones for selective catalytic transformations is a major challenge in catalysis. Here, we show how micropores in metal-organic frameworks (MOFs) push homogeneous catalytic reactions into kinetic regimes inaccessible under standard conditions. Such property allows branched selectivity up to 90% in the Co-catalysed hydroformylation of olefins without directing groups, not achievable with existing catalysts. This finding has a big potential in the production of aldehydes for the fine chemical industry. Monte Carlo and density functional theory simulations combined with kinetic models show that the micropores of MOFs with UMCM-1 and MOF-74 topologies increase the olefins density beyond neat conditions while partially preventing the adsorption of syngas leading to high branched selectivity. The easy experimental protocol and the chemical and structural flexibility of MOFs will attract the interest of the fine chemical industries towards the design of heterogeneous processes with exceptional selectivity

Influence of Water in the Synthesis of the Zirconium-Based Metal-Organic Framework UiO-66: Isolation and Reactivity of [ZrCl(OH)2(DMF)2]Cl

We recently discovered that aging a solution of zirconium(IV) tetrachloride (ZrCl4) in N,N-dimethylformamide (DMF) in the presence of water, followed by the addition of a terephthalic acid linker, reduces the crystallite size of the metal-organic framework UiO-66 (Chem. Commun. 2016, 52, 6411-6414). In an effort to shed light on the nature of the aging effect and on its relationship with the crystallite size of UiO-66, we report here the isolation and structural characterization of a microcrystalline zirconium-based compound of the formula [ZrCl(OH)2(DMF)2]Cl, which is formed during the aging process. The Zr(IV) ions are coordinated by hydroxide, DMF, and chloride to produce a one-dimensional polymer. Thanks to the presence of two -OH groups per zirconium atom, [ZrCl(OH)2(DMF)2]Cl is a suitable precursor for the synthesis of UiO-66 in dry DMF, affording a product having a smaller crystallite size than that obtained from a reaction mixture having the same chemical composition but using ZrCl4 as the Zr(IV) source. By starting from ZrCl4 and generating [ZrCl(OH)2(DMF)2]Cl in situ in solution through aging, we obtained smaller crystallites as the aging time increased, proving that [ZrCl(OH)2(DMF)2]Cl plays a role in the aging process. The possible role of [ZrCl(OH)2(DMF)2]Cl in the crystallization mechanism of UiO-66 is also discussed, with emphasis on its relationship with the amount of water in the reaction mixture

Aging of the reaction mixture as a tool to modulate the crystallite size of UiO-66 into the low nanometer range

Nanosized UiO-66 with an unprecedented crystallite size of 10 nm was synthesized by exploiting controlled aging of stock solutions of Zr4+ in N,N-dimethylformamide in the presence of variable amounts of water and acetic acid prior to the addition of the ligand. The yield of the synthesis is not affected, affording high conversion of the starting reagents into the product

Synthesis of Water-Soluble Phosphine Oxides by Pd/C-Catalyzed P–C Coupling in Water

Cross-coupling between diphenylphosphine oxide and halogenated benzoic acids catalyzed by Pd/C in water is a green, simple, and fast protocol to obtain water-soluble tertiary phosphine oxides without the addition of ligands and additives. Low reaction times and microwave irradiation make this method general and excellent for laboratory and large-scale synthesis without the need to use organic solvents in reactions and workup

Phosphine and phosphine oxide groups in metal-organic frameworks detected by P K-edge XAS

Phosphine metal–organic frameworks (P-MOFs) are crystalline porous coordination polymers that contain phosphorus functional groups within their pores. We present the use of X-ray absorption spectroscopy (XAS) at the P K-edge to determine the phosphine to phosphine oxide ratio in two P-MOFs with MIL-101 topology. The phosphorus oxidation state is of particular interest as it strongly influences the coordination affinity of these materials for transition metals. This method can determine the oxidation state of phosphorus even when the material contains paramagnetic nuclei, differently from NMR spectroscopy. We observed that phosphine in LSK-15 accounts for 72 ± 4% of the total phosphorus groups and that LSK-12 contains only phosphine oxide.ISSN:1463-9084ISSN:1463-907

In situ high-resolution powder X-ray diffraction study of UiO-66 under synthesis conditions in a continuous-flow microwave reactor

Large scale synthesis of metal-organic frameworks (MOFs) is of high interest, due to their potential for industrial applications. The capacity to synthesize large amounts of MOFs should be combined with the ability to control their properties. Understanding how process parameters influence the formation of the product is necessary to synthesize tailor-made materials. The crystallization process of a MOF from the reaction mixture can be conveniently monitored in real time by performing in situ studies using synchrotron radiation. This yields insight into the formation of the product under the actual reaction conditions. In this work, we performed an in situ high-resolution powder X-ray diffraction study of the crystallization of UiO-66 in a recently developed continuous-flow microwave reactor that provided excellent performances in terms of space-time yield and atom economy. The effect of the addition of different amounts of water and acetic acid to the reaction mixture on the yield and crystallite size of the product was investigated over a range of residence times. UiO-66 was the only crystalline phase observed and two stages of the process were identified, namely, a preliminary stage, where the crystallite size of the MOF increases, and a steady state one where the quality of the product is constant. The yield and crystallite size of the product primarily depended on the water/acetic acid ratio, which was the most important parameter determining the rate of product formation. Increasing the absolute amounts of additives at fixed ratios led to a higher yield of larger crystallites, whereas aging of the metal stock solution led to a higher yield of smaller crystallites. Selected experiments were performed offline isolating the solid at the steady state and characterizing it after workup. In this way, we demonstrated that large scale synthesis of UiO-66 with controlled properties can be performed with a continuous-flow microwave reactor

Efficient microwave assisted synthesis of metal–organic framework UiO-66: optimization and scale up

A highly efficient and scalable microwave assisted synthesis of zirconium-based metal–organic framework UiO-66 was developed. In order to identify the best conditions for optimizing the process, a wide range of parameters was investigated. The efficiency of the process was evaluated with the aid of four quantitative indicators. The properties of the materials prepared by microwave irradiation were compared with those synthesized by conventional heating, and no significant effects on morphology, crystal size, or defects were found from the use of microwave assisted heating. Scale up was performed maintaining the high efficiency of the process