NiMn‐Based Bimetal–Organic Framework Nanosheets Supported on Multi‐Channel Carbon Fibers for Efficient Oxygen Electrocatalysis

Developing noble‐metal‐free bifunctional oxygen electrocatalysts is of great significance for energy conversion and storage systems. Herein, we have developed a transformation method for growing NiMn‐based bimetal–organic framework (NiMn‐MOF) nanosheets on multi‐channel carbon fibers (MCCF) as a bifunctional oxygen electrocatalyst. Owing to the desired components and architecture, the MCCF/NiMn‐MOFs manifest comparable electrocatalytic performance towards oxygen reduction reaction (ORR) with the commercial Pt/C electrocatalyst and superior performance towards oxygen evolution reaction (OER) to the benchmark RuO₂ electrocatalyst. X‐ray absorption fine structure (XAFS) spectroscopy and density functional theory (DFT) calculations reveal that the strong synergetic effect of adjacent Ni and Mn nodes within MCCF/NiMn‐MOFs effectively promotes the thermodynamic formation of key *O and *OOH intermediates over active NiO₆ centers towards fast ORR and OER kinetics.     

Sulfonic and Phosphonic Acid and Bifunctional Organic–Inorganic Hybrid Membranes and Their Proton Conduction Properties

Hybrid organic–inorganic approaches are used for the synthesis of bifunctional proton exchange membrane fuel cell (PEMFC) membranes owing to their ability to combine the properties of a functionalized inorganic network and an organic thermostable polymer. We report the synthesis of both sulfonic and phosphonic acid functionalized mesostructured silica networks into a poly(vinylidenefluoride‐co‐hexafluoropropylene) (poly(VDF‐co‐HFP) copolymer. These membranes, containing different amounts of phosphonic acid and sulfonic acid groups, have been characterized using FTIR and NMR spectroscopy, SA‐XRD, SAXS, and electrochemical techniques. The proton conductivity of the bifunctional hybrid membranes depends strongly on hydration, increasing by two orders of magnitude over the relative humidity (RH) range of 20 to 100 %, up to a maximum of 0.031 S cm⁻¹ at 60 °C and 100 % RH. This value is interesting as only half of the membrane conducts protons. This approach allows the synthesis of a porous SiO₂ network with two different functions, having  SO₃H and  PO₃H₂ embedded in a thermostable polymer matrix.     

Chiral Ammonium Betaine‐Catalyzed Highly Stereoselective Aza‐Henry Reaction of α‐Aryl Nitromethanes with Aromatic N‐Boc Imines

A highly stereoselective aza‐Henry reaction of α‐aryl nitromethanes with aromatic N‐Boc imines was established by using C₁‐symmetric chiral ammonium betaine as a bifunctional organic base catalyst. Various substituted aryl groups for both imines and nitromethanes were tolerated in the reaction, and a series of precursors for the synthesis of unsymmetrical anti‐1,2‐diaryl ethylenediamines was provided.     

Palladium‐Catalyzed Oxidative C≡C Triple Bond Cleavage of 2‐Alkynyl Carbonyl Compounds Toward 1,2‐Dicarbonyl Compounds†

A new, general palladium‐catalyzed oxidative strategy for the cleavage of the C≡C triple bond is presented. By employing PdCl₂, CuBr₂, TEMPO and air as the catalytic system and H₂O as the carbonyl oxygen atom source, a wide range of 2‐alkynyl carbonyl compounds, including 1,3‐disubstituted prop‐2‐yn‐1‐ones, propiolamides and propiolates, lost an alkynyl carbon to access various 1,2‐dicarbonyl compounds, e.g., 1,2‐diones, 2‐keto amides and 2‐keto esters, through Wacker oxidation, intramolecular cyclization and C—C bond cleavage cascades.     

Highly luminescent diyne (?CC?CC?) containing hybrid polyphenyleneethynylene/poly(p‐phenylenevinylene) polymer: Synthesis and characterization

Luminophoric dialdehyde 1,4‐bis[4‐formylphenylethynyl‐(2,5‐dioctadecyloxyphenyl)‐buta‐1,3‐diyne] ( 4 ) enables the synthesis of diyne‐containing hybrid polyphenyleneethynylene/poly(p‐phenylenevinylene) polymer poly[1,4‐phenylene‐ethynylene‐1,4‐(2,5‐dioctadecyloxy)phenylene‐butadi‐1,3‐ynylene‐1,4‐(2,5‐dioctadecyloxy)phenylene‐ethynylene‐1,4‐phenylene‐ethene‐1,2‐diyl‐1,4‐(2,5‐dioctadecyloxy)phenylene‐ethene‐1,2‐diyl] ( 7 ) with a well‐defined general structure (? Ph? C?C? Ar? C?C? C?C? Ar? C?C? Ph? CH?CH? Ar? CH?CH? )_n, which was confirmed by NMR and infrared spectroscopy. The highly luminescent material is thermostable, soluble in usual organic solvents through the grafting of octadecyloxy side groups, and can be processed into transparent films. With the aim to investigate the effect of ? C?C? C?C? in the photophysical behavior of 7 , a comparison of the photophysics of monomers 3 [1,4‐bis(4‐formylphenylethynyl)‐2,5‐dioctadecyloxybenzene] and 4 and subsequently of their respective polymers 6 and 7 has been carried out. Similar photophysical behaviors for 6 (poly[1,4‐phenylenethynylene‐1,4‐(2,5‐dioctadecyloxyphenylene)ethene‐1,2‐diyl]) and 7 were observed in dilute CHCl₃ solution as a result of an identical chromophore system responsible for the absorption (λ_a = 448 nm) and emission (λ_f = 490 nm) in both compounds. The increased planarization and enhanced rigidity of the conjugated backbone in the solid state at room temperature as well as in frozen dilute tetrahydrofuran solution at 77 K cause the bathochromic shift of the absorption and emission spectra. The large octadecyloxy side chains obviously limit strong π‐π interchain interactions in the solid films, which explains the high fluorescence quantum yields of 35 and 52% obtained for 6 and 7 , respectively. The energetically arduous migration of the π electron through the diyne units not only requires a higher threshold voltage for the detection of photoconductivity in 7 but could possibly limit radiationless deactivation channels of the exciton, which explains the approximate 20% fluorescence quantum yields difference between 6 and 7 in the solid state. The electron‐withdrawing effect of the triple bonds confer both 6 and 7 with a good electron‐accepting property (E^ox = 1.39 V vs Ag/AgCl) if used in light‐emitting diode devices. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2670–2679, 2002     

Photo‐Organocatalysis of Atom‐Transfer Radical Additions to Alkenes

We have found that an organic molecule as simple as p‐anisaldehyde efficiently catalyzes the intermolecular atom‐transfer radical addition (ATRA) of a variety of haloalkanes onto olefins, one of the fundamental carbon–carbon bond‐forming transformations in organic chemistry. The reaction requires exceptionally mild reaction conditions to proceed, as it occurs at ambient temperature and under illumination by a readily available fluorescent light bulb. Initial investigations support a mechanism whereby the aldehydic catalyst photochemically generates the reactive radical species by sensitization of the organic halides by an energy‐transfer pathway.     

Highly Emissive Luminogens Based on Imidazo[1,2‐a]pyridine for Electroluminescent Applications

A search for novel organic luminogens led us to design and synthesize some N‐fused imidazole derivatives based on imidazo[1,2‐a]pyridine as the core and arylamine and imidazole as the peripheral groups. The fluorophores were synthesized through a multicomponent cascade reaction (A³ coupling) of a heterocyclic azine with an aldehyde and alkyne, followed by Suzuki coupling and a multicomponent cyclization reaction. All of the compounds exhibited interesting photophysical responses, especially arylamine‐containing derivatives, which displayed strong positive solvatochromism in the emission spectra that indicated a more polar excited state owing to an efficient charge migration from the donor arylamine to the imidazo[1,2‐a]pyridine acceptor. The quantum yields ranged from 0.2 to 0.7 and depended on the substitution pattern, most notably that based on the donor group at the C2 position. Moreover, the influence of general and specific solvent effects on the photophysical properties of the fluorophores was discussed with four‐parameter Catalán and Kamlet–Taft solvent scales. The excellent thermal, electrochemical, and morphological stability of the compounds was explored by cyclic voltammetry, thermogravimetric analysis, and AFM methods. Furthermore, to understand the structure, bonding, and band gap of the molecules, DFT calculations were performed. The performance of the electroluminescence behavior of the imidazo[1,2‐a]pyridine derivative was investigated by fabricating a multilayer organic light‐emitting diode with a configuration of ITO/NPB (60 nm)/EML (40 nm)/BCP (15 nm)/Alq₃ (20 nm)/LiF (0.5 nm)/Al(100 nm) (ITO=indium tin oxide, EML=emissive layer, BCP=2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline, Alq₃=tris(8‐hydroxyquinolinato)aluminum), which exhibited white emission with a turn‐on voltage of 8 V and a brightness of 22 cd m^?2.     

2‐Chloro‐Azaborolyl Anion: A Source of 1,2‐Azaborole Isosteric to Cyclopentadienylidene

Azaborolyl anions, the five‐membered BN heterocycles, have attracted a considerable attention due to their aromaticity and isoelectronic relationship with ubiquitous cyclopentadienyl ligands. Besides their syntheses and applications in the preparation of metal complexes, the other aspects of their chemistry have been virtually unexplored. Reduction of the azabutadienyl chelate boron dichloride [ArN?C(R)CH?C(R)]BCl₂ ( 2 , Ar=2,6‐Me₂C₆H₃, R=tBu) with two equivalents of potassium yielded the novel 2‐chloro‐azaborolyl anion [ArNC(R)CHC(R)BCl]K(thf) ( 3 ) as a stable product in good yield. Reaction of 3 with 1,3,4,5‐tetramethylimidazol‐2‐ylidene (NHC) yielded the first NHC–azaborole adduct with the elimination of KCl. The salt elimination reaction was also observed in the reactions with H₂O and the organic azide ArN₃, leading to the formation of an oxo‐bridged 3H‐1,2‐diazaborole and an intramolecular donor‐stabilized iminoborane, demonstrating that 3 is a source of the unexplored 1,2‐azaborole isosteric to cyclopentadienylidene.     

Visible‐Light‐Enabled Trifluoromethylative Pyridylation of Alkenes from Pyridines and Triflic Anhydride

A general strategy for visible‐light‐enabled site‐selective trifluoromethylative pyridylation of unactivated alkenes has been developed using pyridines and triflic anhydride (Tf₂O). Intriguingly, the N‐triflylpyridinium salts, generated in situ from pyridines and Tf₂O, serve as effective modular bifunctional reagents to install both CF₃ and pyridyl groups to various olefins while controlling C4‐selectivity in radical addition to the pyridine core. This synthetic route exhibited broad substrate scope under metal‐free and mild photocatalytic conditions, granting efficient access to valuable C4‐alkylated pyridines and quinolines without requiring prefunctionalization of the reaction site.     

On the Mechanism of Bifunctional Squaramide‐Catalyzed Organocatalytic Michael Addition: A Protonated Catalyst as an Oxyanion Hole

A joint experimental–theoretical study of a bifunctional squaramide‐amine‐catalyzed Michael addition reaction between 1,3‐dioxo nucleophiles and nitrostyrene has been undertaken to gain insight into the nature of bifunctional organocatalytic activation. For this highly stereoselective reaction, three previously proposed mechanistic scenarios for the critical C?C bond‐formation step were examined. Accordingly, the formation of the major stereoisomeric products is most plausible by one of the bifunctional pathways that involve electrophile activation by the protonated amine group of the catalyst. However, some of the minor product isomers are also accessible through alternative reaction routes. Structural analysis of transition states points to the structural invariance of certain fragments of the transition state, such as the protonated catalyst and the anionic fragment of approaching reactants. Our topological analysis provides deeper insight and a more general understanding of bifunctional noncovalent organocatalysis.     

Strategies for Synthesis of Imidazo[1,2‐a]pyridine Derivatives: Carbene Transformations or C−H Functionalizations

The imidazo[1,2‐a]pyridines are an important target in organic synthetic chemistry and have attracted critical attention of chemists mainly due to the discovery of the interesting properties exhibited by a great number of imidazo[1,2‐a]pyridine derivatives. Although lots of synthetic methods of imidazo[1,2‐a]pyridines have been developed in the past years, the chemistry community faces continuing challenges to use green reagents, maximize atom economy and enrich the functional group diversity of product. Undoubtedly, with its low cost and lack of environmentally hazardous byproducts, cascade reactions and C?H functionalizations are ideal strategies for this field. In this record we highlight some of our progress toward the goal to synthesis of imidazo[1,2‐a]pyridine derivatives through carbene transformations or C?H functionalizations.     

Mechanism and scope of salen bifunctional catalysts in asymmetric aldehyde and α-ketoester alkylation

Metal complexes of C₂-symmetric Lewis acid/Lewis base salen ligands provide bifunctional activation resulting in rapid rates in the enantioselective addition of diethylzinc to aldehydes (up to 92% ee). Further experiments probed the reactivity of the individual Lewis acid and Lewis base components of the catalyst and established that both moieties are essential for asymmetric catalysis. These catalysts are also effective in the asymmetric addition of diethylzinc to α-ketoesters. This finding is significant because α-ketoesters alone serve as their own ligands to accelerate racemic 1,2-carbonyl addition of Et₂Zn and racemic carbonyl reduction. The latter proceeds via a metalloene pathway, and often accounts for the predominant product. Singular Lewis acid catalysts do not accelerate enantioselective 1,2-addition over these two competing paths. The bifunctional amino salen catalysts, however, rapidly provide enantioenriched 1,2-addition products in excellent yield, complete chemoselectivity, and good enantioselectivity (up to 88% ee). A library of the bifunctional amino salens was synthesized and evaluated in this reaction. The utility of the α-ketoester method has been demonstrated in the synthesis of an opiate antagonist.     

Synthesis and characterization of soft–hard stereoblock polybutadiene with Fe(2‐EHA)3/Al(i‐Bu)3/DEP catalyst system

Stereoblock polybutadiene (PBD) composed of amorphous equibinary cis?1,4/1,2 PBD (e‐PBD, soft) and crystalline syndiotactic 1,2‐PBD (s‐1,2‐PBD, hard) segments is synthesized through one‐pot sequential polymerization with iron(III)2‐ethylhexanoate/triisobutylaluminum/diethyl phosphate [Fe(2‐EHA)₃/Al(i‐Bu)₃/DEP] catalyst system. The first‐stage polymerization of 1,3‐butadiene (BD) is carried out at a low [Al]/[Fe] ratio to give amorphous e‐PBD block, and sequentially, the in situ addition of excessive Al(i‐Bu)₃ and BD to the living polymerization system give rise to a second crystalline s‐1,2‐PBD block. The length of each block is controllable by adjusting cocatalyst and monomer feed ratio. The syndiotactic pentad content is in the range of 63.8–76.6% and increases with the length of s‐1,2‐PBD block. The copolymer exhibits glass transition temperature (T_g) around ?40 °C and melting point (T_m) around 168 °C originating from e‐PBD and s‐1,2‐PBD blocks, respectively. The incompatibility between s‐1,2‐PBD and e‐PBD blocks as well as the crystallization of s‐1,2‐PBD block induce the microphase separation in stereoblock PBD. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1182–1188     

Synthesis and Reactivity of Cyclic Borane‐Amidine Conjugated Molecules Formed by Direct 1,2‐Carboboration of Carbodiimides with 9‐Borafluorenes

Efficient 1,2‐carboboration reactions to the C=N bond of carbodiimides with 9‐borafluorenes, which give rise to cyclic borane‐amidine conjugates with a seven‐membered BNC₅ ring, are reported. The resulting cyclic borane‐amidine conjugates can be hydrolyzed into an acyclic bifunctional biaryl compound carrying both boronic acid and amidine groups, rendering the utility of the two‐step protocol for the synthesis of multi‐functionalized molecular systems with a potential as a supramolecular building block. Furthermore, the conjugated structure of the cyclic boron‐amidine compounds can be changed upon alkylation of the boron atom that increases the coordination number of boron. The combination of Lewis acid (borane) and conjugated base (amidine) provides rich structural diversity of heteroatom‐containing π‐conjugated systems.     

Calcium Hydride Reactivity: Formation of an Anionic N‐Heterocyclic Olefin Ligand

An anionic N‐heterocyclic olefin ligand was serendipitously obtained by reaction of an amidinate calcium hydride complex with 1,3‐dimethyl‐2‐methyleneimidazole (NHO). Instead of anticipated addition to the polarized C=CH₂ bond to form an unstabilized alkylcalcium complex, deprotonation of the NHO ligand in the backbone was observed. Preference for deprotonation versus addition is explained by loss of aromaticity in the latter conversion. Theoretical calculations demonstrate the substantially increased ylidic character of this anionic NHO ligand which, like N‐heterocyclic dicarbenes, shows strong bifunctional coordination.     

Di‐tert‐Butyl Peroxide‐Mediated Atom‐Transfer Radical Addition of 2‐Chlorodithiane to Aryl Alkynes under Mild Conditions

Atom transfer radical addition (ATRA) of 2‐chlorodithiane onto aryl alkynes through the use of di‐tert‐butyl peroxide as an oxidant at room temperature directly affords a variety of synthetically valuable β‐chloro‐(Z)‐vinyl dithianes in good yields with high regioselectivities and without the assistance of any transition metals. It provides an operationally simple pathway to access vinyl dithianes with controlled formation of a new C(sp²)?C bond and a C(sp²)?Cl bond.     

Metal‐Organic Frameworks as Platform for Lewis‐Acid‐Catalyzed Organic Transformations

Metal‐organic frameworks (MOFs) are highly promising Lewis acid catalysts; they either inherently possess Lewis acid sites (LASs) on it or the LASs can be generated through various post‐synthetic methods, the later can be performed in MOFs in a trivial fashion. MOFs are suitable platform for catalysis because of its highly crystalline and porous nature. Moreover, with recent advancements, thermal and chemical stability is not a problem with many MOFs. In this Minireview, an enormous versatility of MOFs, in terms of their microporosity/mesoporosity, size/shape selectivity, chirality, pore size, etc., has been highlighted. These are advantageous for designing and performing various targeted organic transformations. Although, many organic transformations catalyzed by MOFs with LASs have been reported in the recent past. In this Minireview, we have restricted ourselves to four important organic reactions: (i) cyanosilylation, (ii) Diels–Alder reaction, (iii) C?H activation, and (iv) CO₂‐addition. The discussion focuses mostly on the recent reports (42 examples).     

2‐Iminopyridylpalladium dichloride as highly active catalyst for the Heck reaction

Heck reactions of bromoarenes with various olefins catalyzed by 2‐iminopyridylpalladium (II) have been investigated. The scope of a coupling reaction has been tested in 1‐methyl‐2‐pyrrolidinone at 140 °C using K₂CO₃ as base. Using 0.1% molar ratio of palladium catalysts, aryl bromides were converted into 1,2‐substitutedethene products in good to high yields through coupling with both vinylarenes and alkylolefins. With butyl vinyl ether, an electron‐rich olefin, however, the effective coupling reaction produced a mixture of two regio‐isomers, 1,2‐ and 1,1‐substitutedethenes. Copyright © 2007 John Wiley & Sons, Ltd.     

A ladder coordination polymer based on Ca2+ and (4,5‐dicyano‐1,2‐phenylene)bis(phosphonic acid): crystal structure and solution‐state NMR study

The preparation of coordination polymers (CPs) based on either transition metal centres or rare‐earth cations has grown considerably in recent decades. The different coordination chemistry of these metals allied to the use of a large variety of organic linkers has led to an amazing structural diversity. Most of these compounds are based on carboxylic acids or nitrogen‐containing ligands. More recently, a wide range of molecules containing phosphonic acid groups have been reported. For the particular case of Ca²⁺‐based CPs, some interesting functional materials have been reported. A novel one‐dimensional Ca²⁺‐based coordination polymer with a new organic linker, namely poly[[diaqua[μ₄‐(4,5‐dicyano‐1,2‐phenylene)bis(phosphonato)][μ₃‐(4,5‐dicyano‐1,2‐phenylene)bis(phosphonato)]dicalcium(II)] tetrahydrate], {[Ca₂(C₈H₄N₂O₆P₂)₂(H₂O)₂]·4H₂O}_n, has been prepared at ambient temperature. The crystal structure features one‐dimensional ladder‐like _∞¹[Ca₂(H₂cpp)₂(H₂O)₂] polymers [H₂cpp is (4,5‐dicyano‐1,2‐phenylene)bis(phosphonate)], which are created by two distinct coordination modes of the anionic H₂cpp²⁻ cyanophosphonate organic linkers: while one molecule is only bound to Ca²⁺ cations via the phosphonate groups, the other establishes an extra single connection via a cyano group. Ladders close pack with water molecules through an extensive network of strong and highly directional O—H…O and O—H…N hydrogen bonds; the observed donor–acceptor distances range from 2.499 (5) to 3.004 (6) Å and the interaction angles were found in the range 135–178°. One water molecule was found to be disordered over three distinct crystallographic positions. A detailed solution‐state NMR study of the organic linker is also provided.     

Synthesis of 2‐Hydroxy‐1,4‐oxazin‐3‐ones through Ring Transformation of 3‐Hydroxy‐4‐(1,2‐dihydroxyethyl)‐β‐lactams and a Study of Their Reactivity

The reactivity of 3‐hydroxy‐4‐(1,2‐dihydroxyethyl)‐β‐lactams with regard to the oxidant sodium periodate was evaluated, unexpectedly resulting in the exclusive formation of new 2‐hydroxy‐1,4‐oxazin‐3‐ones through a C3? C4 bond cleavage of the intermediate 4‐formyl‐3‐hydroxy‐β‐lactams followed by a ring expansion. This peculiar transformation stands in sharp contrast with the known NaIO₄‐mediated oxidation of 3‐alkoxy‐ and 3‐phenoxy‐4‐(1,2‐dihydroxyethyl)‐β‐lactams, which exclusively leads to the corresponding 4‐formyl‐β‐lactams without a subsequent ring enlargement. In addition, this new class of functionalized oxazin‐3‐ones was further evaluated for its potential use as building blocks in the synthesis of a variety of differently substituted oxazin‐3‐ones, morpholin‐3‐ones and pyrazinones. Furthermore, additional insights into the mechanism and the factors governing this new ring‐expansion reaction were provided by means of density functional theory calculations.