Monodentate Phosphinoamine Nickel Complex Supported on a Metal-Organic Framework for High-Performance Ethylene Dimerization.

Ethylene dimerization is an efficient industrial chemical process to produce 1-butene, with demanding selectivity and activity requirements on new catalytic systems. Herein, a series of monodentate phosphinoamine-nickel complexes immobilized on UiO-66 are described for ethylene dimerization. These catalysts display extensive molecular tunability of the ligand similar to organometallic catalysis, while maintaining the high stability attributed to the metal-organic framework (MOF) scaffold. The highly flexible postsynthetic modification method enables this study to prepare MOFs functionalized with five different substituted phosphines and 3 N-containing ligands and identify the optimal catalyst UiO-66-L5-NiCl2 with isopropyl substituted nickel mono-phosphinoamine complex. This catalyst shows a remarkable activity and selectivity with a TOF of 29 000 (molethyl/molNi/h) and 99% selectivity for 1-butene under ethylene pressure of 15 bar. The catalyst is also applicable for continuous production in the packed column micro-reactor with a TON of 72 000 (molethyl/molNi). The mechanistic insight for the ethylene oligomerization has been examined by density functional theory (DFT) calculations. The calculated energy profiles for homogeneous complexes and truncated MOF models reveal varying rate-determining step as ß-hydrogen elimination and migratory insertion, respectively. The activation barrier of UiO-66-L5-NiCl2 is lower than other systems, possibly due to the restriction effect caused by clusters and ligands. A comprehensive analysis of the structural parameters of catalysts shows that the cone angle as steric descriptor and butene desorption energy as thermodynamic descriptor can be applied to estimate the reactivity turnover frequency (TOF) with the optimum for UiO-66-L5-NiCl2. This work represents the systematic optimization of ligand effect through combination of experimental and theoretical data and presents a proof-of-concept for ethylene dimerization catalyst through simple heterogenization of organometallic catalyst on MOF.

Democratizing the Assessment of Thermal Robustness of Metal-Organic Frameworks.

With the pressing need of having reliable materials for carbon dioxide capture, metal-organic frameworks (MOFs) have shown promising performance due to their flexible sign and tunable functionality by applying reticular chemistry principles. One of the main characteristics of practical MOFs is to design thermally robust candidates for sustainable functionality. Here, we introduce a comprehensive methodology for examining the thermal stability of MOFs by combining theoretical calculations and affordable experimental methods to fully describe their performance under thermal variations. We chose the prototypical MOF, HKUST-1, to assess the methodology by performing density functional theory and classical molecular dynamics simulations and validating with experiments such as in situ powder X-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. HKUST-1 shows thermal robustness until a temperature of 240 °C at different atmospheric gases with a reversible breathing trend with temperature. This methodology is affordable as it uses minimal experimental testing and can be applied to any MOF materials to explore its suitability for practical applications.

Site-Isolated Azobenzene-Containing Metal-Organic Framework for Cyclopalladated Catalyzed Suzuki-Miyuara Coupling in Flow.

Sites isolation of active metals centers, systematically studied in homogeneous systems, has been an alternative to develop low metal consuming, highly active next generation catalysts in heterogeneous condition. Because of the high porosity and facile synthetic procedures, MOF-based catalysts are excellent candidates for heterogenization of well-defined homogeneous catalysts. Herein, we report the direct Pd coordination on the azobenzene linker within a MOF catalyst through a postsynthetic modification method for a Suzuki-Miyaura coupling reaction. The immobilized cyclopalladated complexes in MOFs were analyzed by a series of characterization techniques including XPS, PXRD, and deuterium NMR (2H NMR) spectroscopy. The heterogeneous nature of the catalyst as well as its stability were demonstrated though "hot filtration" and recycling experiments. Furthermore, we demonstrate that the MOF packed column promoted the reaction between phenyl boronic acid and bromobenzene under microflow conditions with a 85% yield continuously for 12 h. This work sheds light on the potential of site-isolated MOF catalysts in efficient, recyclable and continuous flow systems for industrial application.

Green Synthesis, Experimental and Theoretical Studies to Discover Novel Binders of Exosomal Tetraspanin CD81 Protein.

A new class of benzothiazole-appended quinoline derivatives (6-8) was synthesized via one-pot TPGS micellar-mediated acid-catalyzed nucleophilic addition, followed by aerobic oxidative cyclization of 3-formylquinoline-2-one (2), 3-formylquinoline-2-thione (3), and 2-azidoquinoline-3-carbaldehyde (4) individually with 2-amino thiophenol (5). The structures of the prepared compounds were confirmed using suitable spectroscopic methods complemented with single-crystal X-ray diffraction analysis. Time-dependent density functional theory-based optimization of molecular structures, bond lengths, bond angles, HOMO-LUMO energy gaps, and molecular electrostatic potential maps was theoretically computed at the B3LYP/6-311++g(d) level. The molecular docking studies recommended that 6-8 bound to the active site cavity of CD81 effectively with the binding energies of -6.9, -6.3, and -6.5 kcal mol-1, respectively. Further, MD simulation studies of compound 6 suggested that the binding resulted in the stabilization of the CD81 molecule. Thus, all theoretical predictions associated with the experimental verifications motivated to discover novel approaches for cancer therapy.

In Situ Solution-State Characterization of MOF-Immobilized Transition-Metal Complexes by Infrared Spectroscopy.

Transition-metal catalysts immobilized on the surface of Metal-organic frameworks (MOFs) are being utilized for an ever-increasing number of reactions ranging from couplings to olefin oligomerization. While these reactions are usually performed in solution, unlike their homogeneous counterparts, the insolubility of the MOF systems makes it difficult to obtain detailed mechanistic information by in situ spectroscopic analysis in solution. In this report, we present a synthetic method to solubilize these systems by grafting oligomers on the surface of the MOF particles, making it possible to characterize these species by transmission infrared (IR) spectroscopy. The fundamental photochemistry of these catalysts was also studied and compared to that of their homogeneous counterparts. This work establishes a proof of principle for in-solution monitoring of heterogeneous catalysts.

Recyclable and Reusable Heteroleptic Nickel Catalyst Immobilized on Metal-Organic Framework for Suzuki-Miyaura Coupling.

Metal-organic frameworks (MOFs) provide highly versatile platforms to stabilize molecular catalysts that are not readily accessible under homogeneous conditions, thus enabling access to a new set of catalytic materials. Herein, we describe a recyclable and highly active nickel catalyst immobilized on MOF for Suzuki-Miyaura coupling reaction, which operates under mild conditions. This mixed ligand catalyst forms from the combination of 1 equiv of MOF-immobilized ligand, 1 equiv of nickel source, and 1 equiv of PPh3. The nature of the catalyst was verified through a series of analytical tests and catalysis experiments. The immobilized catalyst was reusable for at least up to 7 cycles without decrease in the yield of the coupled product. We also verified that this reaction does not work under homogeneous conditions and that the reaction is truly heterogeneous through "hot filtration" experiments. We identified that the reaction is first order in arylborane concentration and negative order in arylbromide concentration through the effect of substrate concentrations on the initial rate. This informed us to conduct the catalysis under slow addition of the arylbromide and reduce the catalyst loading to 1% from 3%, without detriment to the yield or rate of the reaction. The catalyst gave good to excellent isolated yields with a range of functionalities, including heterocycles on aryl bromide with widely varying electronic properties.

Exposed Equatorial Positions of Metal Centers via Sequential Ligand Elimination and Installation in MOFs.

Metal-organic frameworks (MOFs) provide highly designable platforms to construct complex coordination architectures for targeted applications. Herein, we demonstrate that trans-coordinated metal centers with exposed equatorial positions can be placed in a MOF matrix. A Zr-based MOF, namely, PCN-160, was initially synthesized as a scaffold structure. Postsynthetic linker labilization was subsequently implemented to partially remove the original dicarboxylate linkers and incorporate pyridinecarboxylates. A pair of neighboring pyridyl groups was arranged at proper proximity within the framework to form trans-binding sites that accommodate different metal cations including Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Pd2+. Furthermore, the trans-coordinated Ni2+ sites in porous frameworks can be readily accessed by substrates along the equatorial plane, facilitating the catalysis as manifested by the superior activity in ethylene dimerization over that observed for a cis-chelated catalyst.

Flexible ligated ruthenium(II) self-assemblies sensitizes glioma tumor initiating cells in vitro.

The tumorigenic potentials of residual cancer stem-like cells within tumors represent limitations of current cancer therapies. Here, the authors describe the effects of synthesized flexible, ligated, supramolecular self-assembled chair type tetranuclear ruthenium (II) metallacycles (2-5) on glioblastoma and glioma stem like cells. These self-assemblies were observed to be selectively toxic to glioma cells and CD133-positive glioma stem like cells population. Of the self-assembled compounds tested, metallacycle 4 more efficiently induced glioma stem like cells death within a brain cancer cell population and simultaneously inhibited the formation of free-floating gliospheres by reducing the sphere size. Detailed cell death studies revealed that treatment with metallacycle 4 reduced mitochondrial membrane potentials (an indicator of apoptosis) of glioma stem like cells. These results shows the elimination of cancer stem-like cells using an appropriate ligand binding adaptor offers a potential means of developing metal-based compounds for the treatment of chemo-resistant tumors.

Aggregation induced enhanced and exclusively highly Stokes shifted emission from an excited state intramolecular proton transfer exhibiting molecule.

The inner filter effect due to self-quenching dominates the normal emission of dyes at higher concentrations, which would limit their applications. Since normal emission was also observed with aggregation induced emission enhancement (AIEE) active excited state intramolecular proton transfer (ESIPT) exhibiting molecules, two new molecules are synthesized and studied to obtain normal emission free AIEE. The molecules are 4-(3-(benzo[d]thiazol-2-yl)-5-tert-butyl-4-hydroxybenzyl)-2-(benzo[d]thiazol-2-yl)-6-tert-butyl phenol (bis-HPBT) and its oxazole analogue (bis-HPBO). Of these molecules, bis-HPBT, which is weakly fluorescent in tetrahydrofuran solution, shows a sudden high enhancement in fluorescence upon addition of 70% water due to the formation of aggregates. Though the normal emission is also observed in tetrahydrofuran, it is completely eliminated in the aggregates, and the aggregates display exclusive tautomer emission. However, bis-HPBO does not emit such an exclusive tautomer emission in the water/tetrahydrofuran mixture. The enhancement in the fluorescence quantum yield of bis-HPBT in 70% water is ∼300 times higher than that in tetrahydrofuran. The modulated molecular structure of bis-HPBT is the cause of this outstanding AIEE. The observation of almost exclusive tautomer emission is a new additional advantage of AIEE from bis-HPBT over other ESIPT molecules. Since the tautomer emission is highly Stokes shifted, no overlap with the absorption spectrum occurs and therefore, the inner filter effect is averted. The aggregated structure acts as a good fluorescence chemosensor for metal ions as well as anions. The aggregated structure is cell permeable and can be used for cell imaging.

Antitumor and biological investigation of doubly cyclometalated ruthenium(II) organometallics derived from benzimidazolyl derivatives.

In this study, we report the synthesis, anticancer and biological properties of three doubly cyclometalated phenylbenzimidazole derived ruthenium(ii) organometallics () and their corresponding three organic ligands. The structures of were fully characterized by various analytical techniques, and the meso stereoisomer of the doubly cyclometalated ruthenacycle was unambiguously confirmed by single crystal X-ray diffraction. The anticancer effects of the newly synthesized compounds were tested against selected human cancer cell lines AGS (gastric carcinoma), SK-hep-1 (hepatocellular carcinoma), and HCT-15 (colorectal carcinoma). The growth inhibitory effects of ruthenacycles on cancer cells were found to be considerably more effective against the abovementioned cancer cells than the reference drug oxaliplatin. Compound exhibited a more specific effect on the AGS cells. Gene-fishing and ELISA array were performed to analyze the target genes and cytokine secretion by . As a result, a significant reduction was observed in RPS21 by . Moreover, increased the secretion of cytokines such as IFNγ in macrophages and reduced the release of cytokines such as rantes and IGF-1. These results show that could be a very good anticancer drug through the regulation of the RPS21 gene and cytokines.

Rhenium(I)-Based Monocyclic and Bicyclic Phosphine Oxide-Coordinated Supramolecular Complexes.

Neutral, flexible ditopic phosphine (P-P) or phosphine oxide (O=P-P=O) donors, rigid anionic bis-chelating oxygen donors, and Re2(CO)10 were used to assemble ten phosphine oxide (P=O)-donor-based neutral monocyclic M2LL'-, bicyclic M4L2L″-, and bicyclic M4LL'2-type supramolecular coordination complexes (SCCs). A soft ditopic phosphine donor was transformed into a hard ditopic phosphine oxide donor, during the formation of the cyclic complexes 1-3, 5-6, and 9-10. Complexes 4, 7, and 8 were obtained using a hard P=O donor ligand. These SCCs were characterized using elemental analysis, FTIR, NMR, and single-crystal X-ray diffraction analysis. The absorption properties of 1-8 were studied using absorption UV-vis spectroscopic methods, and the results were analyzed using theoretical calculations. The results revealed that the neutral P=O donor significantly influenced the photophysical properties by enhancing the absorption coefficient in the visible region.

Rhenium(I)-based bridgeless double metallocalix[4]arenes.

Bridgeless double metallocalix[4]arenes possessing two orthogonally arranged dinuclear cavitands were obtained from a Re2(CO)10, rigid bis-chelating OO donor (H2-L), and a flexible bis-ditopic NN donor (L') by a one-pot approach.

Selective synthesis of ruthenium(II) Metalla[2]catenane via solvent and guest-dependent self-assembly.

The coordination-driven self-assembly of an anthracene-functionalized ditopic pyridyl donor and a tetracene-based dinuclear Ru(II) acceptor resulted in an interlocked metalla[2]catenane, [M2L2]2, in methanol and a corresponding monorectangle, [M2L2], in nitromethane. Subsequently, guest template, solvent, and concentration effects allowed the self-assembly to be reversibly fine-tuned among monorectangle and catenane structures.

Spheroid metallocavitands with eight calixarene-shaped receptors on the surface.

Spheroid metallocavitands [((Re(CO)3L)3)2L'] with a diameter of ~17 Å, possessing eight solvent-accessible calixarene-shaped receptors on the surface, were obtained from a Re2(CO)10, rigid NN donors (H-L), and flexible hexatopic N donors (L') in a one-step process.

Luminescent dirhenium(I)-double-heterostranded helicate and mesocate.

The semirigid ligands 1,4-bis(2-(2-hydroxyphenyl)benzimidazol-1-ylmethyl)benzene (H2-pBC) and 1,3-bis(2-(2-hydroxyphenyl)benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene (H2-mBC), containing two hydroxyphenylbenzimidazolyl units as bis-chelating (or bis(bidentate)) N∩OH donor, were synthesized and were used to assemble neutral, luminescent heteroleptic, unsaturated double-hetero-stranded, rhenium(I)-based helicate (1) and mesocate (2) with the flexible bis(monodentate) nitrogen donor (1,4-bis(benzimidazol-1-ylmethyl)benzene/1,3-bis(benzimidazol-1-ylmethyl)benzene), and Re2(CO)10. The photophysical properties of the complexes were studied. Both complexes 1 and 2 exhibit dual emissions in both solution and solid state. In solution, these complexes show both fluorescence and phosphorescence. Complex 1 undergoes a predominantly ligand-centered oxidation, resulting in the generation of phenoxyl radicals.

Four-component domino strategy for the combinatorial synthesis of novel 1,4-dihydropyrano[2,3-c]pyrazol-6-amines.

An efficient one-pot four-component domino protocol for the combinatorial synthesis of novel 1,4-dihydropyrano[2,3-c]pyrazol-6-amines has been achieved. This transformation presumably occurs via cyclization-Knoevenagel condensation-Michael addition-tautomerism-intramolecular O-cyclization-elimination sequence of reactions. The significant features of this reaction include expedient one-pot process, short reaction time, no column chromatographic purification, excellent yield, and readily available starting materials.

New class of phosphine oxide donor-based supramolecular coordination complexes from an in situ phosphine oxidation reaction or phosphine oxide ligands.

A one-pot, multicomponent, coordination-driven self-assembly approach was used to synthesize the first examples of neutral bridging phosphine oxide donor-based supramolecular coordination complexes. The complexes were self-assembled from a fac-Re(CO)3 acceptor, an anionic bridging O donor, and a neutral soft phosphine or hard phosphine oxide donor.

Rhenium(I) based metallocalix[4]arenes decorated with free functionalized benzimidazolyl units.

Neutral and heteroleptic metallocalix[4]arenes with covalently attached free functionalized benzimidazolyl units were synthesized using Re2(CO)10, a flexible tritopic N donor and rigid bis-chelating unit, via a one-pot process.

Dual role of acetate as a nucleophile and as an internal base in cycloplatination reaction of sym-N,N',N″-triarylguanidines.

Reaction of cis-[Cl(2)Pt(S(O)Me(2))(2)] with 1 equiv of sym-N,N',N″-triarylguanidines, ArN═C(NHAr)(2) (sym = symmetrical; Ar = 2-MeC(6)H(4) (LH(2)(2-tolyl)), 2-(MeO)C(6)H(4) (LH(2)(2-anisyl)), 4-MeC(6)H(4) (LH(2)(4-tolyl)), 2,5-Me(2)C(6)H(3) (LH(2)(2,5-xylyl)), and 2,6-Me(2)C(6)H(3) (LH(2)(2,6-xylyl))) in toluene under reflux condition for 3 h afforded cis- or trans-[Cl(2)Pt(S(O)Me(2))(ArN═C(NHAr)(2))] (Ar = 2-MeC(6)H(4) (1), 2-(MeO)C(6)H(4) (2), 4-MeC(6)H(4) (3), 2,5-Me(2)C(6)H(3) (4), and 2,6-Me(2)C(6)H(3) (5), respectively) in 83-96% yield. Reaction of cis-[Cl(2)Pt(S(O)Me(2))(2)] with 1 equiv of LH(2)(2-tolyl) and LH(2)(4-tolyl) in the presence of 1 equiv of NaOAc in methanol under reflux condition for 3 h afforded acetate-substituted products, cis-[(AcO)ClPt(S(O)Me(2))(ArN═C(NHAr)(2))] (Ar = 2-MeC(6)H(4) (6) and 4-MeC(6)H(4) (7)) in 83% and 84% yields, respectively. Reaction of cis-[Cl(2)Pt(S(O)Me(2))(2)] with 1 equiv of LH(2)(2-anisyl) and LH(2)(2-tolyl) in the presence of 1 equiv of NaOAc in methanol under reflux condition for 3 and 12 h afforded six-membered [C,N] platinacycles, [Pt{κ(2)(C,N)-C(6)H(3)R-3(NHC(NHAr)(═NAr))-2}Cl(S(O)Me(2))] (Ar = 2-RC(6)H(4); R = OMe (8) and Me (9)), in 92% and 79% yields, respectively. The new complexes have been characterized by analytical and spectroscopic techniques, and further the molecular structures of 1, 2, 4, 5, 6, and 8 have been determined by single-crystal X-ray diffraction. The platinum atom in 1, 4, and 5 exhibited the trans configuration, while that in 2, 6, and 8 exhibited the cis configuration. Complex 6 is shown to be the precursor for 9, and the former is suggested to transform to the latter possibly via an intramolecular C-H activation followed by elimination of AcOH. The solution behavior of new complexes has been studied by multinuclear NMR ((1)H, (195)Pt, and (13)C) spectroscopy. The new complexes exist exclusively as a single isomer (trans (1 and 5) and cis (6 and 7)), a mixture of cis and trans isomers with the former isomer being predominant in the case of 2 and the latter isomer being predominant in the case of 3. Complex 5 in the trans form revealed the presence of one isomer at 0.007 mM concentration and two isomers in about 1.00:0.12 ratio at 0.154 mM concentration as revealed by (1)H NMR spectroscopy, and this has been ascribed to the restricted Pt-S bond rotation at higher concentration. Platinacycle 8 exists as one isomer, while 9 exists as a mixture of seven isomers in solution. The influence of steric factor, π-acceptor property of the guanidine, subtle solid-state packing forces upon the configuration of the platinum atom, and the number of isomers in solution have been outlined. Factors that accelerate or slow down the cycloplatination reaction, the role of NaOAc, and a plausible mechanism of this reaction have been discussed.