Electronic Structure of Monodithiolated Iron?Oxotungsten Heterometallic Complexes: Integer‐Spin Fe?W Assembly

Fe? W heterometallic complexes, in which an FeX₂ (X=Cl, SPh) moiety is attached to monodithiolene oxotungsten through a sulfide bridge, that is, [Ph₄P]₂[Cl₂Fe(S)₂WOS₂] ( 1 ), [Ph₄P]₂[Cl₂Fe(S)₂WOS₂(DMED)] ( 2 , DMED=dimethylethylenedicarboxylate), [Ph₄P]₂[Cl₂Fe(S)₂WO(tdt)] ( 3 , tdt=toluenedithiolate), [Ph₄P]₂[(SPh)₂Fe(S)₂WO(tdt)] ( 4 ), and [Ph₄P]₂[Cl₂Fe(S)₂WO(edt)] ( 5 , edt=ethanedithiolate), are reported. Mössbauer and EPR spectroscopy, magnetism, electrochemistry, and electronic structural analysis based on DFT and TD‐DFT calculations show the transfer of electron from the iron center to the tungsten center, thus resulting in a ferromagnetically coupled Fe^IIIW^V unit, along with antiferromagnetic intermolecular interactions, from the starting Fe^II and W^VI compounds. A net spin of a S=3 ground state, which arises from ferromagnetically coupled Fe^III and W^V atoms, displays a rare X‐band EPR in normal mode at g≈7 in the solid state.     

meso‐Tritolylcorrole‐Functionalized Single‐walled Carbon Nanotube Donor?Acceptor Nanocomposites for NO2 Detection

meso‐Tritolylcorrole‐functionalized single‐walled carbon nanotubes (TTC‐SWNT) donor‐acceptor (D–A) heterojunction nanocomposite film was fabricated on a polycarbonate membrane through filtration and non‐covalent functionalization, providing an excellent sensing platform with low‐cost, high flexibility and good gas accessibility. The TTC‐SWNTs nanocomposite displays a fast and sensitive response to nitrogen dioxide with a limit of detection of 10 ppb (S/N=3). The sensing response was significantly amplified compared to the unmodified one, which was ascribed to a D–A heterojunction at the interface between electron donor TTC and electron acceptor SWNTs. This study provides a simple route to fabricate low‐cost and highly sensitive donor‐acceptor nanocomposite‐based gas sensors.     

Gold for C?C Coupling Reactions: A Swiss‐Army‐Knife Catalyst?

For organic chemists, the construction of C C bonds is the most essential aspect of the assembly of molecules. Transition‐metal‐catalyzed coupling reactions have evolved as one of the key tools for this task. Lately, gold has also emerged as a catalyst for this kind of transformation. Gold, with its special properties as a mild carbophilic π Lewis acid, its ability to insert into C H bonds, and, as discovered recently, its ability to undergo redox transformations, offers the opportunity to apply all this potent proficiency for the construction of compounds in an efficient and economical way. This Minireview critically presents the C C coupling reactions enabled by gold catalysts to encourage further research activities in this promising area of oxidation/reduction gold catalysts.     

A Radical Process towards the Development of Transition‐Metal‐Free Aromatic Carbon?Carbon Bond‐Forming Reactions

Transition‐metal‐free cross‐coupling reactions have been a hot topic in recent years. With the aid of a radical initiator, a number of unactivated arene C? H bonds can be directly arylated/functionalized by using aryl halides through homolytic aromatic substitution. Commercially available or specially designed promoters (e.g. diamines, diols, and amino alcohols) have been used to make this synthetically attractive method viable. This protocol offers an inexpensive, yet efficient route to aromatic C? C bond formations since transition metal catalysts and impurities can be avoided by using this reaction system. In this article, we focus on the significance of the reaction conditions (e.g. bases and promoters), which allow this type of reaction to proceed smoothly. Substrate scope limitations and challenges, as well as mechanistic discussion are also included.     

Elevating the Triplet Energy Levels of Dibenzofuran‐Based Ambipolar Phosphine Oxide Hosts for Ultralow‐Voltage‐Driven Efficient Blue Electrophosphorescence: From D?A to D?π?A Systems

A series of donor (D)–π–acceptor (A)‐type phosphine‐oxide hosts ( DBF _x POPhCz _n ), which were composed of phenylcarbazole, dibenzofuran ( DBF ), and diphenylphosphine‐oxide (DPPO) moieties, were designed and synthesized. Phenyl π‐spacer groups were inserted between the carbazolyl and DBF groups, which effectively weakened the charge transfer and triplet‐excited‐state extension. As the result, the first triplet energy levels (T₁) of DBF _x POPhCz _n are elevated to about 3.0 eV, 0.1 eV higher than their D? A‐type analogues. Nevertheless, the electrochemical analysis and DFT calculations demonstrated the ambipolar characteristics of DBF _x POPhCz _n . The phenyl π spacers hardly influenced the frontier molecular orbital (FMO) energy levels and the carrier‐transporting ability of the materials. Therefore, these D? π? A systems are endowed with higher T₁ states, as well as comparable electrical properties to D? A systems. Phosphorescent blue‐light‐emitting diodes (PHOLEDs) that were based on DBF _x POPhCz _n not only inherited the ultralow driving voltages (2.4 V for onset, about 2.8 V at 200 cd m^?2, and <3.4 V at 1000 cd m^?2) but also had much‐improved efficiencies, including about 26 cd A^?1 for current efficiency, 30 Lm W^?1 for power efficiency, and 13 % for external quantum efficiency, which were more than twice the values of devices that are based on conventional unipolar host materials. This performance makes DBFDPOPhCz _n among the best hosts for ultralow‐voltage‐driven blue PHOLEDs reported so far.     

Rhodium(III)‐Catalyzed C?C and C?O Coupling of Quinoline N‐Oxides with Alkynes: Combination of C?H Activation with O‐Atom Transfer

[Cp*Rh^III]‐catalyzed C H activation of arenes assisted by an oxidizing N O or N N directing group has allowed the construction of a number of hetercycles. In contrast, a polar N O bond is well‐known to undergo O‐atom transfer (OAT) to alkynes. Despite the liability of N O bonds in both C H activation and OAT, these two important areas evolved separately. In this report, [Cp*Rh^III] catalysts integrate both areas in an efficient redox‐neutral coupling of quinoline N‐oxides with alkynes to afford α‐(8‐quinolyl)acetophenones. In this process the N O bond acts as both a directing group for C H activation and as an O‐atom donor.     

A New Dynamic Covalent Bond of Se?N: Towards Controlled Self‐Assembly and Disassembly

A new kind of Se? N dynamic covalent bond has been found that can form between the Se atom of a phenylselenyl halogen species and the N atom of a pyridine derivative, such as polystyrene‐b‐poly(4‐vinylpyridine). This Se? N dynamic covalent bond can be reversibly and rapidly formed or cleaved under acidic or basic conditions, respectively. Furthermore, the bond can be dynamically cleaved by heating or treatment with stronger electron‐donating pyridine derivatives. The multiple responses of Se? N bond to external stimuli has enriched the existing family of dynamic covalent bonds. It can be used for controlled and reversible self‐assembly and disassembly, which may find potential applications in a number of areas, including self‐healing materials and responsive assemblies.     

Palladium‐Catalyzed Cyanation of Carbon?Carbon Triple Bonds Under Aerobic Conditions

Essential oxygen : The title transformation involves two different modes of cyanation, syn and anti cyanopalladation, as the key steps in this catalytic reaction. These processes enable successful dicyanative cyclization of diyne and enyne derivatives (see scheme).

     

Solid‐State Luminescence of Au?Cu?Alkynyl Complexes Induced by Metallophilicity‐Driven Aggregation

A new series of homoleptic alkynyl complexes, [{Au₂Cu₂(C₂R)₄}_n] (R=C₃H₇O ( 1 ), C₆H₁₁O ( 2 ), C₉H₁₉O ( 3 ), C₁₃H₁₁O ( 4 )), were obtained from Au(SC₄H₈)Cl, Cu(NCMe)₄PF₆, and the corresponding alkyne in the presence of a base (NEt₃). Complexes 1 – 4 aggregate upon crystallization into polymeric chains through extensive metallophilic interactions. The cluster that contains fluorenolyl functionalities, C₁₃H₉O ( 5 ), crystallizes in its molecular form as a disolvate, [Au₂Cu₂(C₂C₁₃H₉O)₄] ? 2 THF. The substitution of weakly bound THF molecules with pyridine molecules leads to the complex [Au₂Cu₂(C₂C₁₃H₉O)₄] ? 2 py ( 6 ), thus giving two polymorphs in the solid state. Such structural diversity is established through metal‐chain and hydrogen‐bond formation, which depends on the stereochemical characteristics of the organic ligands. More interestingly, this solid‐state structural arrangement affords good emission properties, such as intensity and spectroscopic profile, which are otherwise very weakly emissive in solution. Metallophilic aggregation of the {Au₂Cu₂} cluster units, as observed in the crystals, results in dramatic enhancement of the room‐temperature phosphorescence, thereby reaching a maximum quantum efficiency of 95 % ( 4 ). A theoretical approach further indicates a synergistic effect of the array of the metal chain upon aggregation, which greatly enhances the spin‐orbit coupling and, hence, the phosphorescence, thereby opening up a new direction in the field of aggregate‐enhanced emission.     

The Morita?Baylis?Hillman Reaction of Chiral Highly Oxygenated Cyclopent‐2‐enones

The Morita? Baylis? Hillman (MBH) reactions of (4S,5R,7R,8R)‐ and (4R,5R,7R,8R)‐4‐hydroxy‐7,8‐dimethoxy‐7,8‐dimethyl‐6,9‐dioxaspiro[4.5]dec‐2‐en‐1‐ones ( 2 and 3 , resp.) with aldehydes using various catalysts were studied. A combination of Bu₃P/phenol in THF was found being optimum conditions giving the corresponding MBH adducts with high diastereoisomeric ratios. After separation, each stereomerically pure isomer of the MBH adducts was subjected to hydrolysis employing 1% aq. CF₃COOH (TFA) in a water bath of an ultrasonic cleaner to afford the corresponding polyhydroxylated cyclopentenones in good yields.     

Dioctylamine‐Sulfonamide‐Modified Carbon Nanoparticles as High Surface Area Substrates for Coenzyme Q10?Lipid Electrochemistry

Dioctylaminesulfonamide‐modified carbon nanoparticles are characterised and employed as high surface area substrate for (i) coenzyme Q10 and (ii) 1,2‐dimyristoyl‐sn‐glycero‐3‐phosphocholine (or DMPC) ‐ Q10 redox processes. The carbon nanoparticles provide a highly hydrophobic substrate with ca. 25 Fg^?1 capacitance when bare. Q10 or DMPC‐Q10 immobilised onto the carbon nanoparticles lower the capacitance, but give rise to well‐defined pH‐dependent voltammetric responses. The DMPC‐Q10 deposit shows similar characteristics to those of Q10, but with better reproducibility and higher sensitivity. Both redox systems, Q10 and DMPC‐Q10, are sensitive to the Na⁺ concentration in the electrolyte and mechanistic implications are discussed.     

Rhodium‐Catalyzed ortho‐Selective C?F Bond Borylation of Polyfluoroarenes with Bpin?Bpin

An ortho‐selective C F bond borylation between N‐heterocycle‐substituted polyfluoroarenes and Bpin‐Bpin with simple and commercially available [Rh(cod)₂]BF₄ as a catalyst is now reported. The reaction proceeds under mild reaction conditions with high efficiency and broad substrate scope, even toward monofluoroarene, thus providing a facile access to a wide range of borylated fluoroarenes that are useful for photoelectronic materials. Preliminary mechanistic studies reveal that a Rh^III/V catalytic cycle via a key intermediate rhodium(III) hydride complex [(H)Rh^IIIL_n(Bpin)] may be involved in the reaction.     

Amide‐Directed Tandem C?C/C?N Bond Formation through C?H Activation

The transformation of C? H bonds into other chemical bonds is of great significance in synthetic chemistry. C? H bond‐activation processes provide a straightforward and atom‐economic strategy for the construction of complex structures; as such, they have attracted widespread interest over the past decade. As a prevalent directing group in the field of C? H activation, the amide group not only offers excellent regiodirecting ability, but is also a potential C? N bond precursor. As a consequence, a variety of nitrogen‐containing heterocycles have been obtained by using these reactions. This Focus Review addresses the recent research into the amide‐directed tandem C? C/C? N bond‐formation process through C? H activation. The large body of research in this field over the past three years has established it as one of the most‐important topics in organic chemistry.     

Catalytic C?C,C?N,and C?O Ullmann‐Type Coupling Reactions

Copper‐catalyzed Ullmann condensations are key reactions for the formation of carbon–heteroatom and carbon–carbon bonds in organic synthesis. These reactions can lead to structural moieties that are prevalent in building blocks of active molecules in the life sciences and in many material precursors. An increasing number of publications have appeared concerning Ullmann‐type intermolecular reactions for the coupling of aryl and vinyl halides with N, O, and C nucleophiles, and this Minireview highlights recent and major developments in this topic since 2004.