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A palladium diphosphine pincer complex H3(PNNNP-PdI) has been encapsulated in the benzotriazolate metal-organic framework MFU-4l-OH ([Zn5(OH)4(btdd)3], btdd2− = bis(1,2,3-triazolo)dibenzodioxin), and the resulting materials were investigated as Lewis acid catalysts for cyclization of citronellal to isopulegol. Rapid catalyst immobilization is facilitated by a Brønsted acid–base reaction between the H3(PNNNP-PdI) benzoic acid substituents and Zn–OH groups at the framework nodes. Catalyst loading can be controlled up to a maximum of 0.5 pincer complexes per formula unit [ PdI-x , Zn5(OH)4−nx(btdd)3(H3−nPNNNP-PdI)xx = 0.06–0.5, n ≈ 2.75]. Oxidative ligand exchange was used to replace I− with weakly coordinating BF4− anions at the Pd–I sites, generating the activated PdBF4-x catalysts (x = 0.06, 0.10, 0.18, 0.40). The Lewis acid catalytic activity of the PdBF4-x series decreases with increasing catalyst density as a result of the appearance of mass transport limitations. Initial catalytic rates show that the activity of PdBF4-0.06 approaches the intrinsic activity of a homogeneous PNNNP-PdBF4 catalyst analogue. In addition, PdBF4-0.06 exhibits better catalytic activity than the metallolinker-based MOF Zr-PdBF4 and was not subject to leaching or catalyst degradation processes observed for the homogeneous analogue. [ABSTRACT FROM AUTHOR]

The effect of solvent has been investigated for the synthesis of bismuth gallate compounds, of which the water-based bismuth subgallate has been used as an active pharmaceutical ingredient (API) for over a century. Using methanol as a solvent, two new bismuth gallates were acquired: first a flexible 3-periodic metal–organic framework (MOF) forms, which transforms upon extended synthesis times into a layered 2-periodic coordination polymer of the same bismuth-to-gallate ratio. The structures were determined by three-dimensional electron diffraction. Synthesis in ethanol resulted in the formation of the MOF phase, but not the layered phase. The layered material of the methanol-based synthesis was used as a Lewis acid catalyst due to its higher stability, showing a comparatively quick and regiospecific conversion of styrene oxide to 2-methoxy-2-phenylethanol, indicating the presence of open metal sites in the material. The acquisition of bismuth gallate structures of varying periodicity highlights the prospect of acquiring novel MOFs and coordination polymers from the same components of APIs. [ABSTRACT FROM AUTHOR]

In a one-pot self-assembly reaction of Co(OAc)2·4H2O, thiophene-2,5-dicarboxylic acid (H2tdc) and four different bis(tridentate) polypyridyl spanning ligands under ambient conditions, a series of structurally diverse metal–organic frameworks has been synthesised and characterized by single crystal X-ray diffraction: {[Co2(tdc)2(tpbn)(H2O)2]·solvent}n (solvent = 2H2O, 1; solvent = 2CH3OH, 2H2O, 1a), {[Co2(tdc)2(tphn)]·solvent}n (solvent = H2O, 2; solvent = CH3OH, 2.5H2O, 2a), {[Co2(tdc)2(tpchn)(H2O)2]·solvent}n (solvent = 5H2O, 3; solvent = C2H5OH, 2H2O, 3a), and {[Co2(tdc)2(tpxn)]·solvent}n (solvent = 6H2O, 4; when no solvent, 4a), where tpbn (N,N′,N′′,N′′′-tetrakis(2-pyridylmethyl)-1,4-diaminobutane), tphn = N,N′,N′′,N′′′-tetrakis(2-pyridylmethyl)-1,6-diaminohexane, tpchn = N,N′-(cyclohexane-1,4-diylbis(methylene))bis(1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine) and tpxn = N,N′-(1,4-phenylenebis(methylene))bis(1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine). There is a profound effect of the nature of spacer between the alkyl nitrogens in the spanning ligands (flexible vs. semiflexible) on the molecular structures of 1a–4a. The notable differences are (a) the binding mode of the tridentate part of polypyridyl ligands to the Co(II) center is facial in 1a, 3a and 4a but meridional in 2a, (b) the Co(II) centers in 1a–3a are hexacoordinated (with a coordinated water in 1a and 3a) but are pentacoordinated in 4a, and (c) the binding mode of tdc linker is bis(monodentate) in 1a, 3a and 4a but chelated in one end and monodentate in the other end in 2a. Thus, the overall framework structure of 1a, 2a, 3a and 4a is cis-decalin type 2D polymer, ladder-shaped 1D polymer, hexagonal 2D net and cis-decalin type 2D polymer, respectively. Their thermal stabilities have been established by thermogravimetric analysis (TGA). The presence of an unsaturated metal center in 4 has provided us an opportunity for its use as an efficient Lewis acid catalyst for the Knoevenagel condensation reaction of malononitrile with various aldehydes (100% conversion in 60 minutes with 2 mol% catalyst in methanol). [ABSTRACT FROM AUTHOR]

A Cu-BTC (MOF-199) [copper(II)-benzene-1,3,5-tricarboxylate] catalyst has been synthesized and evaluated for imine synthesis from amine compounds under neat conditions. The performance of the Cu-BTC MOF was significantly higher than that of the CuO supported on Al2O3, TiO2 and SiO2 catalysts. The role of surface Lewis acid sites on the catalyst in the formation of imine products was illustrated by the pyridine-IR studies. The recovered Cu-BTC catalyst demonstrated consistent activity for five cycles under similar experimental conditions. The physicochemical properties of the catalysts were analyzed by XRD, BET-SA, FT-IR, UV-DRS, SEM, TEM, XPS and pyridine adsorbed DRIFT spectroscopy. [ABSTRACT FROM AUTHOR]

A straightforward and efficient methodology for the one-pot multicomponent synthesis of 1,4-dihydropyridine has been developed using MIL-101-SO3H metal–organic framework as a solid Brønsted acid. The presence of the uniformly distributed Brønsted acidic sulfonic acid sites throughout the framework and the high stability bestow the catalyst with excellent reactivity towards the synthesis of 1,4-dihydropyridine under simple reaction conditions using renewable ethanol as the solvent. The present methodology tolerates various functional groups and allows the synthesis of 1,4-dihydropyridine derivatives in good to excellent yields through Hantzsch reaction. The developed methodology proceeds under mild conditions, avoids corrosive reagents and special reaction conditions, and is amenable to gram scale synthesis. The sustainable nature of the catalyst was proved by the easy recovery and the reusability of the catalyst, as it was reused several times without loss in activity, which was confirmed from the FTIR, PXRD and SEM analyses of the reused catalyst. [ABSTRACT FROM AUTHOR]

Functionalized metal–organic frameworks (MOFs) have been used in a wide range of applications. Although the development of functionalized MOFs with plentiful open metal sites (defects) provides an avenue for targeted reactions, creating such defects remains challenging. Herein, a UiO-type MOF with hierarchical porosity and plentiful Zr–OH/OH2 sites (capping 35% Zr coordination sites) was synthesized within 40 min by a solid-phase synthesis route without the use of solvent and template. The optimal sample converted 5.7 mmol benzaldehyde to (dimethoxymethyl)benzene within 2 min at 25 °C. The turnover frequency number and activity per unit mass reached 2380 h−1 and 8568 mmol g−1 h−1, respectively, outperforming all previously reported catalysts at room temperature. This excellent catalytic activity was correlated with the defect density in functionalized UiO-66(Zr) and the accessibility of plentiful Zr–OH/OH2 sites as acid sites. [ABSTRACT FROM AUTHOR]

Conversion of 5-hydroxymethylfurfural (HMF) into 5-ethoxymethylfurfural (EMF) and ethyl levulinate (EL) is an attractive biomass transformation due to its potential application in the energy and chemical industries. Here, we report on the conversion with MOF-based polyoxometalate [Cu–BTC][HPM] (NENU-5) as the catalyst. The homogeneous distribution of HPM in the pores of Cu–BTC makes the composite combine the properties of the catalytic activity of HPM and the insolubility, large surface area and hierarchical pores of Cu–BTC. The catalyst demonstrates reusability and catalytic activity with 55% yield of EMF and 11% yield of EL. [ABSTRACT FROM AUTHOR]

Herein, two novel Evans–Showell-type polyoxometalate (POM)-based metal–organic complexes, namely, {[Cu(L)(H2O)3][Cu(L)0.5(H2O)][Cu(L)0.5(H2O)4][Co2Mo10H4O38]}·5H2O (1) and [(H2L)0.5]2{[Zn(L)0.5(H2O)4]2[Co2Mo10H4O38]}·2H2O (2) (L = N,N′-bis(3-pyridinecarboxamide)-piperazine), were hydrothermally synthesized using a semi-rigid bis-pyridyl-bis-amide ligand and structurally characterized via single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). The single-crystal X-ray diffraction analysis shows that complex 1 is a 3D Evans–Showell-type POM-based metal–organic network. In complex 1, the 1D infinite double chain structure constructed from {{Cu[Co2Mo10H4O38]}4-L} units and the μ4-bridging L ligand are linked by quadrate Cu2L2 loops to form a 2D layer, which is further connected by μ2-bridging L ligands, forming a 3D (2,3,4)-connected metal–organic framework. Complex 2 displays 3D supramolecular networks based on 1D {[Co2Mo10H4O38]–Zn–L}n infinite chains, which are constructed from Evans–Showell-type polyoxoanions and μ2-bridging 3-bpfp ligands (via ligation of pyridyl nitrogen atoms). The different coordination modes of the POM polyanions, bis(pyridylformyl)piperazine ligands and ratios play key roles in the construction of the title complexes. Significantly, the ligand L shows a μ4-bridging coordination mode in complex 1, which is observed for the first time in a POM system. Compounds 1 and 2 represent the first examples of metal–organic complexes based on Evans–Showell-type polyoxoanion and transition metal-bis-pyrazine–bis-amide coordination complexes. The fluorescence properties of the title complexes are reported herein. In addition, the title complexes act as heterogeneous Lewis acid catalysts for the oxidation of benzyl alcohol, and can also be recovered and reused without any significant loss in activity. Significantly, compound 1 with a 3D metal–organic framework showed higher catalytic performance with 99.4% conversion and 98.8% selectivity for benzoic acid at 10 h than compound 2 with 3D supramolecular networks. [ABSTRACT FROM AUTHOR]