N-Heterocyclic carbene–rhodium complexes as catalysts for hydroformylation and related reactions

Rhodium(I) complexes with N-heterocyclic carbenes (Rh–NHC) can be considered as important candidates for catalysts of hydroformylation of olefins. The high stability of Rh-C(NHC) bonding under reaction conditions allow to expect that NHC ligand will be present in coordination sphere of the catalytically active rhodium complex and therefore influences the reaction yield and regioselectivity. The potential applicability of Rh–NHC complexes containing chiral carbene ligand in asymmetric hydroformylation can be also considered. The excellent review articles relevant to application of Rh–NHC in hydroformylation have been published recently [1], [2], [3]. After that, important contributions to this subject, concerning theoretical and experimental studies, both structural and catalytic, have been reported. Therefore, the reactivity of Rh–NHC complexes can be discussed now in term of these new data. The up to now reported results indicate that the most promising and selective systems for hydroformylation can be composed from Rh–NHC complex and stoichiometric amount of electron-withdrawing phosphorus ligand.     

Metal–organic framework derived hierarchical porous TiO_2 nanopills as a super stable anode for Na-ion batteries

Hierarchical porous TiO_2 nanopills were synthesized using a titanium metal-organic framework MIL-125(Ti) as precursor. The as-synthesized TiO_2 nanopills owned a large specific surface area of 102 m~2/g and unique porous structure. Furthermore, the obtained TiO_2 nanopills were applied as anode materials for Na-ion batteries for the first time. The as-synthesized TiO_2 nanopills achieved a high discharge capacity of 196.4 m Ah/g at a current density of 0.1 A/g. A discharge capacity of 115.9 m Ah/g was obtained at a high current density of 0.5 A/g and the capacity retention was remained as high as 90% even after 3000 cycles. The excellent electrochemical performance can be attributed to its unique hierarchical porous feature.     

Palladium supported on metal–organic framework as a catalyst for the hydrogenation of nitroarenes under mild conditions

Sustainable development demands an environmentally friendly and efficient method for the hydrogenation of organic molecules, including the hydrogenation of functionalized nitroarenes. In this study, a highly active and selective metal–organic framework-supported palladium catalyst was prepared for the catalytic hydrogenation of nitroarenes. High selectivity (>99%) and excellent yield (98%) of aniline were realized after 2 hours in ethanol under hydrogen (1 atm) at room temperature. The reductions were successfully carried out in the presence of a wide range of other reducible functional groups. More importantly, the catalyst was very stable without the loss of its catalytic activity after five cycles.     

2-Mercaptoimidazole selectively etching and thiol-functionalized ZIF-8 metal–organic framework to serve as a multifaceted platform for radical scavenging and Au loading

Zeolite imidazole frameworks (ZIF-8) are a group of metal–organic frameworks (MOFs) that harbor application potential due to their unique high porosity and other physicochemical properties. However, the small cavities, unstable dispersion, and the lack of surface functional groups hinder the practical application of ZIF-8. In this study, we aimed to develop a ZIF-8-based multifaceted platform with hollow structure and abundant functional groups via a simple one-pot method. We synthesized the ZIF-8 with thiol functionalization (ZSH), while 2-mercaptoimidazole was served as both etching agent and functional counterpart. The hollow morphology and the thiol-groups modification were validated by scanning electron microscopy, transmission electron microscopy with energy-disperse X-ray mapping and X-ray photoelectron spectroscopy. The interparticle structure was estimated by Brunauer–Emmmett–Teller and ultraviolet–visible spectroscopy. The hollow architecture, colloidal stable, and thiol-abundant surface endow ZSHs exploiting the antioxidant and anti-inflammatory ability than pristine ZIF-8 toward a broad scale of morphological change with high functionalization degree. Moreover, ZSHs can specifically encapsulate gold nanoparticles in large quantities for further applications. Finally, ZSHs possess good biocompatibility in human cells and in vivo zebrafish model and could potentially protect human cells against oxidative stress. This concept valuably elucidated the new era for functionalized ZIF-8 to apply as the next generation of multifunctional biomaterials.     

Metal organic framework–organic polymer monolith stationary phases for capillary electrochromatography and nano-liquid chromatography

In this study, metal organic framework (MOF)–organic polymer monoliths prepared via a 5-min microwave-assisted polymerization of ethylene dimethacrylate (EDMA), butyl methacrylate (BMA), and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) with the addition of various weight percentages (30–60%) of porous MOF (MIL-101(Cr)) were developed as stationary phases for capillary electrochromatography (CEC) and nano-liquid chromatography (nano-LC). Powder X-ray diffraction (PXRD) patterns and nitrogen adsorption/desorption isotherms of these MOF–organic polymer monoliths showed the presence of the inherent characteristic peaks and the nano-sized pores of MIL-101(Cr), which confirmed an unaltered crystalline MIL-101(Cr) skeleton after synthesis; while energy dispersive spectrometer (EDS) and micro-FT-IR spectra suggested homogenous distribution of MIL-101(Cr) in the MIL-101(Cr)–poly(BMA–EDMA) monoliths. This hybrid MOF–polymer column demonstrated high permeability, with almost 800-fold increase compared to MOF packed column, and efficient separation of various analytes (xylene, chlorotoluene, cymene, aromatic acids, polycyclic aromatic hydrocarbons and trypsin digested BSA peptides) either in CEC or nano-LC. This work demonstrated high potentials for MOF–organic polymer monolith as stationary phase in miniaturized chromatography for the first time.     

Porous organic polymer immobilized copper nanoparticles as heterogeneous catalyst for efficient benzylic C–H bond oxidation

A facile and practical heterogeneous copper nanoparticles catalyst (Cu@AEPOP) was prepared by the incorporation of Cu(OAc)₂ to amide and ether functionalized porous organic polymers (AEPOP) that were efficiently prepared by condensation of 4,4′-diaminodiphenyl ether with 1,3,5-benzenetricarbonyl chloride. The prepared AEPOP and Cu@AEPOP were characterized by SEM, BET, TEM, ICP, FT-IR and XRD. With TBHP (70 wt% in water) as oxidant and solvent, Cu@AEPOP showed excellent catalytic activity for the selective oxidation of benzylic C–H bonds. Among the oxidation of alkyl benzenes to ketones, secondary alcohols to ketones, and primary alcohols to acids, the copper catalyst exhibited remarkable selectivity and reactivity for a broad range of substrates in excellent yields. Furthermore, the experimental operation was very facile and the heterogeneous catalyst could be easily recovered by filtration separation.     

Diastereoselective hydroformylation of Δ4-steroids with rhodium–phosphite catalysts

The hydroformylation of two steroidal substrates, namely 17β-acetoxyandrost-4-ene 1 and 3β,17β-diacetoxyandrost-4-ene 2, with a rhodium tris(O-tert-butylphenyl)phosphite catalyst was investigated. In both cases, the major reaction product was 4β-formyl-17β-acetoxy-5β-androstane 3, which was isolated and characterized by X-ray diffraction and NMR techniques. This reaction is the first example of catalytic carbonylation to the β face of a steroid backbone. The effect of reaction temperature, the pressure at which the reaction was completed and the ligand:Rh ratio on the regio- and stereoselectivity of the reaction is also discussed.     

Integration of zeolite@metal–organic framework: a composite catalyst for isopropyl alcohol conversion to aromatics

In this study, a Zn-based metal-organic framework (MOF)-zeolite composite ZSM-5@IRMOF-1 was synthesized for the alternative production of BTX from isopropyl alcohol (IPA). Incorporation ensured the capacity to tune the Lewis acidity at a framework level and design accessible pore structures, making composites highly attractive to be used as catalysts. The combination of monodispersed HZSM-5 zeolites on and within acidic IRMOF-1 provided the highly selective production of lower aromatics from IPA. The interaction of IPA with catalysts was investigated at different temperatures in a fixed-bed continuous flow reactor. The obtained product was analyzed using a standard test method ASTM D6730 through gas chromatography-detail hydrocarbon analyser. The results indicated that the reaction between IPA and MOF-supported zeolite occurred without substantial participation of MOFs. The maximum aromatic (BTEX) selectivity of 38.2% was achieved among all hydrocarbons at 92.3% carbon conversion. In addition, the gas yield was <20% for this catalyst system. The appropriate density of Brønsted and Lewis acidic sites and hierarchical pore structures provided the composite catalyst with outstanding aromatic selectivity yield and high stability.     

Chiral metal–organic framework used as stationary phases for capillary electrochromatography

Metal–organic frameworks (MOFs) have received great attention as novel media in separation sciences because of their fascinating structures and unusual properties. However, to the best of our knowledge, there has been no attempt to utilize chiral MOFs as stationary phases in capillary electrochromatography (CEC). In this study, a homochiral helical MOF [Zn₂(D-Cam)₂(4,4′-bpy)]_n (D-Cam = D-(+)-camphoric acid, 4,4′-bpy = 4,4′-bipyridine) was explored as the chiral stationary phase in open tubular capillary electrochromatography (OT-CEC) for separation of chiral compounds and isomers. The MOFs coated column has been developed using a simple procedure via MOFs post-coated on the sodium silicate layer. The baseline separations of flavanone and praziquantel were achieved on the MOFs coated column with high resolution of more than 2.10. The influences of pH, organic modifier content and buffer concentration on separation were investigated. Besides, the separations of isomers (nitrophenols and ionones) were evaluated. The relative standard deviations (RSDs) for the retention time of run-to-run, day-to-day and column-to-column were 1.04%, 2.16% and 3.07%, respectively. The results demonstrated that chiral MOFs are promising for enantioseparation in CEC.     

Immobilization of palladium nanoparticles as a recyclable heterogeneous catalyst for the Suzuki–Miyaura coupling reaction

This work describes the synthesis of Pd nanoparticles that are stabilized on CaAl-layered double hydroxide functionalized with Tris (tris(hydroxymethyl)aminomethane). The synthesized catalyst is characterized by several different analyses and has been successfully applied to the Suzuki–Miyaura reaction.     

Asymmetric hydroformylation of vinyl acetate with BINAP–rhodium(I) complexes

Complexes of (R)-BINAP (BINAP=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) derived from the available rhodium precursors Rh(acac)(CO)₂ and [Rh(μ-OMe)(cod)]₂ are used for the asymmetric hydroformylation of vinyl acetate. Enantiomeric excesses of up to 60% are achieved with regioselectivities of up to 99%. Only a BINAP/Rh ratio of 2 is required. Effects of pressure and temperature on catalyst stability, enantio- and chemoselectivity are discussed.     

Metal organic framework–derived core-shell CuO@NiO nanosphares as hole transport material in perovskite solar cell

Journal of Solid State Electrochemistry - Cu-Ni bimetallic organic frameworks were synthesized by a facile and stepwise solvothermal method, utilizing metal organic framework as precursor....     

Synthesis of new α-aminophosphonates using nanoscale nickel-based metal–organic framework as a heterogeneous catalyst and their antibacterial activity

An elegant approach was presented for the synthesis of novel α-aminophosphonates: a three-component one-pot condensation of 3-(trifluoromethyl)aniline, substituted aromatic aldehydes, and diethyl phosphite using a nickel-based metal–organic framework (Ni-MOF). The Ni-MOF was synthesized using 4,4′-biphenyldicarboxylic acid and further characterized using various techniques such as X-ray diffraction, Fourier-transform infrared, thermogravimetry/differential thermal analysis, Brunauer–Emmett–Teller, and field-emission scanning electron microscopy analyses. Ni-MOF seems to be an eco-friendly, an easily recyclable, and heterogeneous catalyst up to the eighth run with minimal reduction in its catalytic activity. The synthesized α-aminophosphonates were also investigated for antibacterial and antioxidant activities. In few cases, compounds 4a–4x show similar as well as higher antibacterial activity. Among the synthesized α-aminophosphonates, 4a–4x had more potent antibacterial activity against pathogenic bacteria while compounds 4h, 4m, 4n, 4q, 4u, 4v, and 4w exhibited significant antioxidant activity.     

Bridging nitrile groups in a metal–organic framework

This article describes two coordination polymers based on sodium and nickel triflates, respectively, and the linker adiponitrile (1,4-butanedinitrile). Sodium triflate forms a coordination network with adiponitrile, where the nitriles bridge the sodium ions, a rare coordination mode for a nitrile. Crystal structures of alkali metal complexes of linear aliphatic dinitriles have not been reported previously. With nickel triflate, a cationic 1-D coordination polymer results upon coordination of adiponitrile.     

Pd–Co bimetallic nanoparticles supported on graphene as a highly active catalyst for Suzuki–Miyaura and Sonogashira cross-coupling reactions

Graphene (G) supported Pd–Co bimetallic nanoparticles (NPs) as a highly active catalyst was prepared by a chemical reduction method and used for coupling reactions. With the characterization of X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and Raman spectrum, the composition of resulting Pd–Co material was identified to be alloy structural. The Pd–Co (1:1)/G exhibited the highest catalytic activity for the Sonogashira-type coupling reactions and also exerted satisfied catalytic activity and recycle stability for Suzuki–Miyaura cross-coupling reactions. This Pd–Co/G material also possessed other advantages such as low-cost, easy recycled from reaction system by a magnet for their magnetic property, and easy experimental handling.     

Conversion of carbon dioxide to propionaldehyde over cobalt and rhodium nanoparticles supported on MIL-53 (Al) metal–organic framework

The two-step conversion of carbon dioxide to propionic acid and propionaldehyde has been studied in the presence of novel catalysts, cobalt and rhodium nanoparticles supported on MIL-53(Al) microporous metal–organic framework. The first step is hydrogenation of carbon dioxide with formation of synthesis gas over cobalt-containing catalyst Co/MIL-53(Al) (500°C, 1 atm), and the second step is continuous (without separation) Rh/MIL-53 (Al)-catalyzed hydroformylation of ethylene with the synthesis gas formed in the first step.     

Embedding antimony nanoparticles into metal–organic framework derived TiO2@carbon nanotablets for high-performance sodium storage

Titanium dioxide (TiO₂) has been widely investigated as a candidate for anode materials of sodium-ion batteries (SIBs) due to its low cost and high abundance. However, the intrinsic sluggish ion/electron transfer rate hinders its practical applications for high energy density storage devices. In contrast, antimony (Sb) shows high specific theoretical capacity (660 mAh/g) as well as excellent electron conductivity, but the large volume variation upon cycling usually leads to severe capacity fading. Herein, with the objective of achieving high-performance sodium storage anode materials, TiO₂@C-Sb nanotablets with a small amount of Sb content (6.4 wt%) are developed through calcination Ti-metal–organic framework (MIL-125) derived TiO₂@C/SbCl₃ mixture under reductive atmosphere. Benefitting from the synergetic effect of well-dispersed Sb nanoparticles as well as robust porous TiO₂@C substrate, the TiO₂@C-Sb shows enhanced electron/ion transfer rate and predominantly pseudocapacitive sodium storage behavior, delivering a reversible capacity of 219 mAh/g at 0.5 A/g even after 1000 cycles. More significantly, this method may be commonly used to incorporate other alloy-based high-theoretical materials into MIL-125-derived TiO₂@C, which is promising for developing high-energy-density TiO₂-based energy storage devices.     

Hexamethylenetetramine-based ionic liquid anchored onto the metal–organic framework MIL-101(Cr) as a superior and reusable heterogeneous catalyst for the preparation of hexahydroquinolines

Research on Chemical Intermediates - Regarding the significance of medicinal and pharmacological sciences, we explored one-pot multicomponent reaction of aromatic aldehydes, aryl amines,...     

Nitrogen-doped mesoporous carbon nanospheres loaded with cobalt nanoparticles for oxygen reduction and Zn–air batteries

Mesoporous carbon supported with transition metals nanoparticles performs desired activities for oxygen reduction reaction (ORR) and clean energy conversion devices such as Zn–air batteries. In this work, we synthesized N-doped mesoporous carbon loaded with cobalt nanoparticles (CoMCN) through self-assembly method. There are sufficient mesopores on the carbon substrate which stem from the pore-forming agent. These mesopores can provide enough accessible active sites and profitable charge/mass transport for ORR. The high content of pyridinic and graphitic N is beneficial for promoting O₂ adsorption and reduction. The smaller value of I_D/I_G indicates the higher degree of graphitization of CoMCN, providing better electronic conductivity. The half-wave potential of CoMCN is 0.865 V in basic solution, which is 24 mV more positive than that of the commercial Pt/C (0.841 V). In addition, CoMCN performs excellent methanol tolerance and stability under both basic and acidic conditions. The Zn–air battery assembled with CoMCN performs the larger power density and open-circuit voltage than the commercial Pt/C-based battery, indicating the potential application in energy conversion systems. This work provides thoughtful ideas for fabricating transition metal nanoparticles based porous carbon for electrocatalysis and metal–air batteries.     

A stable organic triradical with truncated π-conjugation as a model for single-component organic molecule-based ferrimagnetics

As a novel molecular design for genuinely organic molecule-based ferrimagnets, we have proposed a strategy of ‘single-component ferrimagnetics.’ When a π-biradical with an S=1 ground state and a π-monoradical with S=1/2 are united by σ-bonds, the π-conjugation between the biradical and the monoradical moieties should be truncated in the resultant triradical. This gives magnetic degrees of freedom for both S=1 and S=1/2 in the single molecule, serving as a building block for organic molecular ferrimagnets. We have designed and synthesized a triradical, 2,2,6,6-tetramethyl-pipelidine-1-N-oxyl-4-carboxylic acid 2,4-bis(1-oxyl-3-oxido-4,4,5,5-tetramethyl-2-imidazolin-2-yl)-phenyl ester (2) as a model compound for single-component ferrimagnetics. Solution-phase ESR spectra from 2 are explained by a perturbation treatment assuming that the exchange interaction within the biradical moiety is much larger than those between the biradical and the monoradical moieties, which is suitable for single-component ferrimagnetics. From susceptibility measurements for a cyclohexane-substituted biradical, cyclohexane carboxylic acid 2,4-bis(1-oxyl-3-oxido-4,4,5,5-tetramethyl-2-imidazolin-2-yl) phenyl ester (4) as a biradical analogue of 2, it is shown that the intramolecular ferromagnetic interaction has been found to be unaffected by the chemical modification for anchoring the monoradical moiety.