Metal-free directed sp2-C-H borylation.

Organoboron reagents are important synthetic intermediates that have a key role in the construction of natural products, pharmaceuticals and organic materials1. The discovery of simpler, milder and more efficient approaches to organoborons can open additional routes to diverse substances2-5. Here we show a general method for the directed C-H borylation of arenes and heteroarenes without the use of metal catalysts. C7- and C4-borylated indoles are produced by a mild approach that is compatible with a broad range of functional groups. The mechanism, which is established by density functional theory calculations, involves BBr3 acting as both a reagent and a catalyst. The potential utility of this strategy is highlighted by the downstream transformation of the formed boron species into natural products and drug scaffolds.

A Green Environmental Protection Photocatalytic Molecular Reactor for Aerobic Oxidation of Sulfide to Sulfoxide.

The design and synthesis of metal-organic frameworks (MOFs) as photocatalytic molecular reactors for varied reactions have drawn great attention. In this work, we designed a novel photoactive perylenediimides-based (PDI) carboxylate ligand N,N'-di(3',3",5',5"-tetrakis(4-carboxyphenyl))-1,2,6,7-tetrachloroperylene-3,4,9,10-tetracarboxylic acid diimide (Cl-PDI-TA) and use it to successfully synthesize a novel Zr(IV)-based MOF 1 constructed from [Zr6 O8 (H2 O)8 ]8+ clusters bridged by Cl-PDI-TA ligands. Structural analysis revealed that Zr-MOF 1 manifests a 3D framework with (4,8)-connected csq topology and possesses triangular channels of ~17 Šand mesoporous hexagonal channels of ~26 Šalong c-axis. Moreover, the synthesized Zr-MOF 1 exhibits visible-light absorption and efficient photoinduced free radical generation property, making it a promising photocatalytic molecular reactor. When Zr-MOF 1 was used as a photocatalyst for the aerobic oxidation of sulfides under irradiation of visible light, it could afford the corresponding sulfoxides with high yield and selectivity. Experimental results demonstrated that the substrate sulfides could be fixed in the pores of 1 and directly transformed to the products sulfoxides in the solid state. Furthermore, the mechanism for the photocatalytic transformation was also investigated and the results revealed that the singlet oxygen (1 O2 ) and superoxide radical (O2 ⋅- ) generated by the energy transfer and electron transfer from the photoexcited Zr-MOF to oxidants were the main active species for the catalytic reactions. This work offers a perceptive comprehension of the mechanism in PDI-based MOFs for further study on photocatalytic reactions.

High-nuclearity Luminescent Lanthanide Nanocages for Tumor Drug Delivery.

There is an unmet need for easy-to-visualize drug carriers that can deliver therapeutic cargoes deep into solid tumors. Herein, we report the preparation of ultrasmall luminescent imine-based lanthanide nanocages, Eu60 and Tb60 (collectively Ln60 ), designed to encapsulate anticancer chemotherapeutics for tumor therapy. The as-prepared nanocages possess large cavities suitable for the encapsulation of doxorubicin (DOX), yielding DOX@Ln60 nanocages with diameters around 5 nm. DOX@Ln60 are efficiently internalized by breast cancer cells, allowing the cells to be visualized via the intrinsic luminescent property of Ln(III). Once internalized, the acidic intracellular microenvironment promotes imine bond cleavage and the release of the loaded DOX. DOX@Ln60 inhibits DNA replication and triggers tumor cell apoptosis. In a murine triple negative breast cancer (TNBC) model, DOX@Ln60 was found to inhibit tumor growth with negligible side effects on normal tissues. It proved more effective than various controls, including DOX and Ln60 . The present nanocages thus point the way to the development of precise nanomedicines for tumor imaging and therapy.

Single-Site Metal-Organic Framework and Copper Foil Tandem Catalyst for Highly Selective CO2 Electroreduction to C2 H4.

Tandem catalysis is a promising way to break the limitation of linear scaling relationship for enhancing efficiency, and the desired tandem catalysts for electrochemical CO2 reduction reaction (CO2 RR) are urgent to be developed. Here, a tandem electrocatalyst created by combining Cu foil (CF) with a single-site Cu(II) metal-organic framework (MOF), named as Cu-MOF-CF, to realize improved electrochemical CO2 RR performance, is reported. The Cu-MOF-CF shows suppression of CH4 , great increase in C2 H4 selectivity (48.6%), and partial current density of C2 H4 at -1.11 V versus reversible hydrogen electrode. The outstanding performance of Cu-MOF-CF for CO2 RR results from the improved microenvironment of the Cu active sites that inhibits CH4 production, more CO intermediate produced by single-site Cu-MOF in situ for CF, and the enlarged active surface area by porous Cu-MOF. This work provides a strategy to combine MOFs with copper-based electrocatalysts to establish high-efficiency electrocatalytic CO2 RR.

Designing Heteroatom-Codoped Iron Metal-Organic Framework for Promotional Photoreduction of Carbon Dioxide to Ethylene.

Rational engineering active sites and vantage defects of catalysts are promising but grand challenging task to enhance photoreduction CO2 to high value-added C2 products. In this study, we designed an N,S-codoped Fe-based MIL-88B catalyst with well-defined bipyramidal hexagonal prism morphology via a facile and effective process, which was synthesized by addition of appropriate 1,2-benzisothiazolin-3-one (BIT) and acetic acid to the reaction solution. Under simulated solar irradiation, the designed catalyst exhibits high C2 H4 evolution yield of 17.7 µmol g-1 ⋅h, which has been rarely achieved in photocatalytic CO2 reduction process. The synergistic effect of Fe-N coordinated sites and reasonable defects in the N,S-codoped photocatalyst can accelerate the migration of photogenerated carriers, resulting in high electron density, and this in turn helps to facilitate the formation and dimerization of C-C coupling intermediates for C2 H4 effectively.

Coordination Polymers with 2,2':6',2″-Terpyridine Earth-Abundant Metal Complex Units for Selective CO2 Photoreduction.

Combining molecular metal complexes into coordination polymers (CPs) is an effective strategy for developing photocatalysts for CO2 reduction; however, most such reported catalysts are noble metal-containing CPs. Herein, two novel Zr-containing bimetallic CPs, Co-Zr and Ni-Zr, were designed and successfully synthesized by connecting 2,2':6',2″-terpyridine-based molecular earth-abundant metal (Co or Ni) complexes with ZrO8 nodes. Both CPs were applied as catalysts for CO2 photoreduction to selectively produce CO. The catalytic performance of Co-Zr is better than that of Ni-Zr with a yield of 3654 µmol (g of catalyst)-1 for CO in 6 h (TON = 18.2). The difference between these two catalysts was analyzed with respect to band structure and charge migration ability. This work provides an effective way to introduce molecular earth-abundant metal complexes into coordination polymers for the construction of efficient noble metal-free CO2 photocatalysts.

Pillar-Layered Metal-Organic Frameworks for Sensing Specific Amino Acid and Photocatalyzing Rhodamine B Degradation.

Metal-organic frameworks (MOFs) have presented potential for detection of specific species and catalytic application due to their diverse framework structures and functionalities. In this work, two novel pillar-layered MOFs [Cd6(DPA)2(NTB)4(H2O)4]n·n(DPA·5DMA·H2O) (1) and [Cu2(DPA)(OBA)2]n·n(2.5DMF·H2O) (2) [DPA = 2,5-di(pyridin-4-yl)aniline, H3NTB = 4,4',4''-nitrilotribenzoic acid, H2OBA = 4,4'-oxydibenzoic acid, DMA = N,N-dimethylacetamide, DMF = N,N-dimethylformamide] were successfully synthesized and structurally characterized. Both 1 and 2 have three-dimensional framework structures. The fluorescent property of 1 makes it possible for sensing specific amino acid such as L-glutamic acid (Glu) and L-aspartic acid (Asp). While MOF 2 was found to be suitable for photocatalytic degradation of Rhodamine B (RhB) in the presence of H2O2. The results imply that MOFs are versatile and metal centers are important in determining their properties.

Potential Applications of Cucurbit[n]urils and Their Derivatives in the Capture of Hazardous Chemicals.

Cucurbit[n]urils (Q[n]s) are a relatively young family of macrocycles, consisting of glycoluril units bridged by methylene groups, and their unique structures have attracted extensive attention from chemists in recent decades. Due to the presence of a rigid hydrophobic inner cavity and two polar outer portals lined with carbonyl groups, Q[n]s not only encapsulate guest species into the cavity, but also coordinate with metal ions/clusters. Considerable achievements have been obtained in the fields of Q[n]s-based host-guest chemistry, coordination chemistry, as well as the combination of host-guest and coordination chemistry. Furthermore, the outer surface of Q[n]s has been demonstrated to be capable of interacting with definite species to generate supramolecular architectures in recent years. With more in-depth research into Q[n]s, their application studies have also emerged as a hot topic. This Minireview focuses on recent advances in the potential applications of solid-state materials based on Q[n]s and their derivatives for the capture and adsorption of hazardous chemicals from a solution or a gas mixture.

Cobalt-Based Metal-Organic Frameworks for Adsorption of CO2 and C2 Hydrocarbons: Effect of Auxiliary Ligands with Different Functional Groups.

Recently, metal-organic frameworks (MOFs) have been investigated as potential materials for CO2 capture and light hydrocarbon storage/separation due to their high porosity, large surface area, and tunable skeleton structures. In this work, the six cobalt-based MOFs 1-6 were successfully synthesized under solvothermal conditions by a mixed-ligand strategy. 1 and 2 have the same framework structure with a topology of {42·5}2{44·510·67·76·8}, while the structures of the 3-6 frameworks are the same with a topology of {42·5}2{44·510·69·74·8}. The adsorption properties of these MOFs for CO2 and C2 hydrocarbons were then investigated, and the effect of the functional groups was discussed. The results revealed that the introduction of amino and bromo groups could effectively strengthen the adsorption performance.

Sensing Properties of NH2-MIL-101 Series for Specific Amino Acids via Turn-On Fluorescence.

Metal-organic frameworks (MOFs) have been demonstrated to be desired candidates for sensing definite species owing to their tunable composition, framework structure and functionality. In this work, the NH2-MIL-101 series was utilized for sensing specific amino acids. The results show that cysteine (Cys) can significantly enhance the fluorescence emission of NH2-MIL-101-Fe suspended in water, while NH2-MIL-101-Al exhibits the ability to sense lysine (Lys), arginine (Arg) and histidine (His) in aqueous media via turn-on fluorescence emission. Titration experiments ensure that NH2-MIL-101-Fe and NH2-MIL-101-Al can selectively and quantitatively detect these amino acids. The sensing mechanism was examined and discussed. The results of this study show that the metal centers in MOFs are crucial for sensing specific amino acids.

Cucurbit[7]uril-Based Metal-Organic Rotaxane Framework for Dual-Capture of Molecular Iodine and Cationic Potassium Ion.

Metal-organic rotaxane frameworks (MORFs) attracted much attention in the past years for construction of intelligent functional materials. Herein, a one-pot synthesis is reported of a three-dimensional (3D) cucurbit[7]uril (Q[7])-based MORF under hydrothermal conditions, namely Q[7]-MORF-1, formed by encapsulating the anionic benzoate moieties of the tricarboxylate ligand into the cavity of Q[7]. Furthermore, Q[7]-MORF-1 shows dual-capture capacity for iodine and K+ selectively among the alkali metal ions. The captured molecular iodine is included in the cavity of Q[7] through halogen-bonding interactions and the K+ cations are positioned at the carbonyl port of the Q[7] through K-O coordination interactions.

Rh(III)-Catalyzed meta-C-H Alkenylation with Alkynes.

Rh(III)-catalyzed meta-C-H functionalization reactions are still rare. Herein, we report the first example of Rh(III)-catalyzed meta-C-H alkenylation with disubstituted alkynes directed by a U-shaped nitrile template. Exclusive regio-selectivity has been achieved using unsymmetrical aryl and alkyl-disubstituted alkynes to afford synthetically valuable trisubstituted olefins. Propargyl alcohols are also compatible, affording complex allylic alcohols. Notably, transition metal-catalyzed meta-alkenylation with alkynes has not been successful with Pd catalysts.

Solvent-Free Photoreduction of CO2 to CO Catalyzed by Fe-MOFs with Superior Selectivity.

It is deemed as a desired approach to utilize solar energy for the conversion of CO2 into valuable products, and the majority of the MOFs-based photocatalytic reductions of CO2 have focused on formic acid (HCOOH) production with an organic solvent as the reaction medium. Herein, we report a solvent-free reaction route for the photoreduction of CO2 catalyzed by Fe-MOFs, namely, NH2-MIL-53(Fe) [(Fe(OH)(NH2-BDC)]•G, NH2-MIL-88B(Fe) [Fe3O(H2O)3(NH2-BDC)3]Cl•G, and NH2-MIL-101(Fe) [Fe3O(H2O)3(NH2-BDC)3]Cl•G (NH2-BDC = 2-aminoterephthalic acid; G = guest and/or solvent molecules). Compared with the orthodox reaction route, the present out-of-the-way photocatalytic reduction of CO2 with superior selectivity to CO occurs at the gas-solid interface. The reaction procedure is environmentally friendly and provides a possibility to address the CO2 emission problem. Importantly, NH2-MIL-101(Fe) shows the highest photocatalytic activity among these Fe-MOFs due to its efficient charge separation and electron transfer.

Ligand-Promoted RhIII -Catalyzed Thiolation of Benzamides with a Broad Disulfide Scope.

A ligand-promoted RhIII -catalyzed C(sp2 )-H activation/thiolation of benzamides has been developed. Using bidentate mono-N-protected amino acid ligands led to the first example of RhIII -catalyzed aryl thiolation reactions directed by weakly coordinating directing amide groups. The reaction tolerates a broad range of amides and disulfide reagents.

Porous Metal-Organic Frameworks with Chelating Multiamine Sites for Selective Adsorption and Chemical Conversion of Carbon Dioxide.

A combination of carbon dioxide (CO2) capture and chemical fixation in a one-step process is attractive for chemists and environmentalists. In this work, by incorporating chelating multiamine sites to enhance the binding affinity toward CO2, two novel metal-organic frameworks (MOFs) [Zn2(L)(2,6-NDC)2(H2O)]·1.5DMF·2H2O (1) and [Cd2(L)(2,6-NDC)2]·1.5DMF·2H2O (2) (L = N1-(4-(1 H-1,2,4-triazole-1-yl)benzyl)- N1-(2-aminoethyl)ethane-1,2-diamine, 2,6-H2NDC = 2,6-naphthalenedicarboxylic acid, DMF = N, N-dimethylformamide) were achieved under solvothermal conditions. Both 1 and 2 possess high selectivity for adsorption of CO2 over CH4 at room temperature under atmospheric pressure. Moreover, 1 has one-dimensional tubular channels decorated with multiactive sites including NH2 groups and coordination unsaturated Lewis acid metal sites, leading to efficient catalytic activity for chemical fixation of CO2 by reaction with epoxides to give cyclic carbonates under mild conditions.

Bottom-up Construction of π-Extended Arenes by a Palladium-Catalyzed Annulative Dimerization of o-Iodobiaryl Compounds.

A straightforward method was developed for construction of aromatic compounds with a triphenylene core. The method involves Pd-catalyzed annulative dimerization of o-iodobiaryl compounds by double C-I and C-H bond cleavage steps. Simple reaction conditions are needed, requiring neither a ligand nor an oxidant, and the reaction tolerates a wide range of coupling partners without compromising efficiency or scalability. Significantly, the tetrachloro-substituted synthon, 1,6,11-trichloro-4-(4-chlorophenyl)triphenylene, can be generated and used to prepare a series of fully fused, small graphene nanoribbons by a late-stage arylation with arylboronic acids and a subsequent Scholl reaction. The synthetic strategy enables bottom-up access to extended π-systems in a controlled manner.

Enantioselective Palladium-Catalyzed Intramolecular α-Arylative Desymmetrization of 1,3-Diketones.

An efficient enantioselective protocol has been reported to build highly oxygenated and densely substituted bicyclo[m.n.1] skeletons through intramolecular asymmetric α-arylative desymmetrization of 1,3-diketones. Employing Pd catalyst and FOXAP ligand, various bicyclo[m.n.1] skeleton with different size can be accessed with high enantio- and diastereoselectivities. Utilizing the present method as a key step, formal asymmetric total synthesis of the (-)-parvifoline has been demonstrated.

Rh(III)-Catalyzed meta-C-H Olefination Directed by a Nitrile Template.

A range of Rh(III)-catalyzed ortho-C-H functionalizations have been developed; however, extension of this reactivity to remote C-H functionalizations through large-ring rhodacyclic intermediates has yet to be demonstrated. Herein we report the first example of the use of a U-shaped nitrile template to direct Rh(III)-catalyzed remote meta-C-H activation via a postulated 12-membered macrocyclic intermediate. Because the ligands used for Rh(III) catalysts are significantly different from those of Pd(II) catalysts, this offers new opportunities for future development of ligand-promoted meta-C-H activation reactions.

Zinc(II) and Copper(II) Hybrid Frameworks via Metal-Ion Metathesis with Enhanced Gas Uptake and Photoluminescence Properties.

The fabrication of metal-organic frameworks with controlled structure and desired properties is important but still a challenge. In this work, a zinc(II) framework, {[Zn3(L)2(DABCO)(H2O)]·9DMF} (named as Zn-1), has been synthesized based on [1,1':3',1″-terphenyl]-4,4″,5'-tricarboxylic acid (H3L) and 1,4-diazabicyclo[2.2.2]octane (DABCO), which is isostructural to the previously reported copper(II) analogue, {[Cu3(L)2(DABCO)(H2O)]·15H2O·9DMF} (named as Cu-1). Interestingly, hybrid zinc(II) and copper(II) bimetallic frameworks have been obtained via metal-ion metathesis and found to show enhanced adsorption and photoluminescence properties. Such a post-metal-ion metathesis method can be used to synthesize new and desired frameworks that could not be obtained by direct synthesis.

Ligand-Promoted Rhodium(III)-Catalyzed ortho-C-H Amination with Free Amines.

Ligand development for rhodium(III)-catalyzed C-H activation reactions has largely been limited to cyclopentadienyl (Cp) based scaffolds. 2-Methylquinoline has now been identified as a feasible ligand that can coordinate to the metal center of Cp*RhCl to accelerate the cleavage of the C-H bond of N-pentafluorophenylbenzamides, providing a new structural lead for ligand design. The compatibility of this reaction with secondary free amines and anilines also overcomes the limitations of palladium(II)-catalyzed C-H amination reactions.