A Monomeric Stannabenzene: Synthesis,Structure, and Electronic Properties

A tin‐containing benzene, stannabenzene, was synthesized and isolated as a monomeric form. The X‐ray crystallographic analysis revealed the planar structure of the stannabenzene ring and unsaturated Sn?C and C?C bonds without bond alternation. Low‐field shifted NMR signals and negative nuclear‐independent chemical shifts (NICS) values are in agreement with the features of aromatic compounds. The narrow HOMO–LUMO gap of stannabenzene has been revealed by UV/Vis spectroscopy and electrochemistry.     

Non‐Pincer‐Type Mononuclear Scandium Alkylidene Complexes: Synthesis,Bonding, and Reactivity

The first non‐pincer‐type mononuclear scandium alkylidene complexes were synthesized and structurally characterized. These complexes exhibited short Sc?C bond lengths and even one of the shortest reported to date (2.1134(18) Å). The multiple character of the Sc?C bond was highlighted by a DFT calculation. This was confirmed by experimental reactivity study where the complex underwent [2+1] cycloaddition with elemental selenium and [2+2] cycloaddition with imine. DFT calculation also revealed a strong nucleophilic behavior of the alkylidene complex that was experimentally demonstrated by the C?H bond activation of phenylacetylene.     

A Two‐Coordinate Cobalt(II) Imido Complex with NHC Ligation: Synthesis,Structure, and Reactivity

The synthesis, structural characterization, and reactivity of the first two‐coordinate cobalt complex featuring a metal–element multiple bond [(IPr)Co(NDmp)] ( 4 ; IPr=1,3‐bis(2′,6′‐diisopropylphenyl)imidazole‐2‐ylidene; Dmp=2,6‐dimesitylphenyl) is reported. Complex 4 was prepared from the reaction of [(IPr)Co(η²‐vtms)₂] (vtms=vinyltrimethylsilane) with DmpN₃. An X‐ray diffraction study revealed its linear C? Co? N core and a short Co? N distance (1.691(6) Å). Spectroscopic characterization and calculation studies indicated the high‐spin nature of 4 and the multiple‐bond character of the Co? N bond. Complex 4 effected group‐transfer reactions to CO and ethylene to form isocyanide and imine, respectively. It also facilitated E? H (E=C, Si) σ‐bond activation of terminal alkyne and hydrosilanes to produce the corresponding cobalt(II) alkynyl and cobalt(II) hydride complexes as 1,2‐addition products.     

1,4‐Iron Migration for Expedient Allene Annulations through Iron‐Catalyzed C−H/N−H/C−O/C−H Functionalizations

C?H activation bears great potential for enabling sustainable molecular syntheses in a step‐ and atom‐economical manner, with major advances having been realized with precious 4d and 5d transition metals. In contrast, we employed earth abundant, nontoxic iron catalysts for versatile allene annulations through a unique C?H/N?H/C?O/C?H functionalization sequence. The powerful iron catalysis occurred under external‐oxidant‐free conditions even at room temperature, while detailed mechanistic studies revealed an unprecedented 1,4‐iron migration regime for facile C?H activations.     

Cobalt‐Catalyzed Tandem C−H Activation/C−C Cleavage/C−H Cyclization of Aromatic Amides with Alkylidenecyclopropanes

A cobalt‐catalyzed chelation‐assisted tandem C?H activation/C?C cleavage/C?H cyclization of aromatic amides with alkylidenecyclopropanes is reported. This process allows the sequential formation of two C?C bonds, which is in sharp contrast to previous reports on using rhodium catalysts for the formation of C?N bonds. Here the inexpensive catalyst system exhibits good functional‐group compatibility and relatively broad substrate scope. The desired products can be easily transformed into polycyclic lactones with m‐CPBA. Mechanistic studies revealed that the tandem reaction proceeds through a C?H cobaltation, β‐carbon elimination, and intramolecular C?H cobaltation sequence.     

Copper‐Catalyzed Reaction Cascade of Thiophenol Hydroxylation and S‐Arylation through Disulfide‐Directed C−H Activation

Copper‐catalyzed thiophenol C?H activation is described. Through an initial attempt to conduct C‐arylation with arylboronic acid, a rather surprising sequential C?H activation and S‐arylation was discovered. Mechanistic investigation revealed the disulfide intermediate as the key component in directing C?H oxidation. The overall reaction proceeded under mild conditions with molecular oxygen as the oxidant. Discovery of disulfide as the directing group provides a potential new direction for catalytic C?H functionalization under mild conditions.     

Micro‐ and Nanometer‐Scale Porous,Fibrous, and Sheet Architectures Constructed by Supramolecular Assemblies of Dipyrrolyldiketones

X‐ray analysis of some 1,3‐dipyrrolyl‐1,3‐propanediones synthesized from pyrroles and malonyl chloride derivatives revealed 1D supramolecular networks formed by N? H???O?C interactions in the solid state. Micro‐ and nanometer‐scale morphologies of porous, fibrous, and sheet structures were fabricated by hydrogen‐bonding interactions and determined by fine‐tuning the substituents and the solvents used. Of the unique polymorphs, ordered 2D lamellar sheet structures of the derivatives with long alkyl chains (C₁₆H₃₃, C₁₄H₂₉, and so on) were constructed by van der Waals hydrophobic effects between aliphatic chains as well as hydrogen bonding.     

A Three‐Dimensional Capsule‐like Carbon Nanocage as a Segment Model of Capped Zigzag [12,0] Carbon Nanotubes: Synthesis,Characterization, and Complexation with C70

Herein we report the synthesis and photophysical and supramolecular properties of a novel three‐dimensional capsule‐like hexa‐peri‐hexabenzocoronene (HBC)‐containing carbon nanocage, tripodal‐[2]HBC, which is the first synthetic model of capped zigzag [12,0] carbon nanotubes (CNTs). Tripodal‐[2]HBC was synthesized by the palladium‐catalyzed coupling of triboryl hexabenzocoronene and L‐shaped cyclohexane units, followed by nickel‐mediated C?Br/C?Br coupling and subsequent aromatization of the cyclohexane moieties. The physical properties of tripodal‐[2]HBC and its supramolecular host–guest interaction with C₇₀ were further studied by UV/Vis and fluorescence spectroscopy. Theoretical calculations revealed that the strain energy of tripodal‐[2]HBC was as high as 55.2 kcal mol^?1.     

Arene‐Free Ruthenium(II/IV)‐Catalyzed Bifurcated Arylation for Oxidative C−H/C−H Functionalizations

Experimental and computational studies provide detailed insight into the selectivity‐ and reactivity‐controlling factors in bifurcated ruthenium‐catalyzed direct C?H arylations and dehydrogenative C?H/C?H functionalizations. Thorough investigations revealed the importance of arene‐ligand‐free complexes for the formation of biscyclometalated intermediates within a ruthenium(II/IV/II) mechanistic manifold.     

Luminescent Pincer Platinum(II) Complexes with Emission Quantum Yields up to Almost Unity: Photophysics,Photoreductive CC Bond Formation,and Materials Applications

Luminescent pincer‐type Pt^II complexes supported by C‐deprotonated π‐extended tridentate R? C^N^N? R′ ligands and pentafluorophenylacetylide ligands show emission quantum yields up to almost unity. Femtosecond time‐resolved fluorescence measurements and time‐dependent DFT calculations together reveal the dependence of excited‐state structural distortions of [Pt(R? C^N^N? R′)(C?C‐C₆F₅)] on the positional isomers of the tridentate ligand. Pt complexes [Pt(R‐C^N^N? R′)(C?C‐Ar)] are efficient photocatalysts for visible‐light‐induced reductive C? C bond formation. The [Pt(R‐C^N^N? R′)(C?C‐C₆F₅)] complexes perform strongly as phosphorescent dopants for green‐ and red‐emitting organic light‐emitting diodes (OLEDs) with external quantum efficiency values over 22.1 %. These complexes are also applied in two‐photon cellular imaging when incorporated into mesoporous silica nanoparticles (MSNs).     

Pronounced stereospecificity of 1H, 13C, 15N and 77Se shielding constants in the selenophenyl oximes as shown by NMR spectroscopy and GIAO calculations

In the ¹H and ¹³C NMR spectra of 1‐(2‐selenophenyl)‐1‐alkanone oximes, the ¹H, the ¹³C‐3 and ¹³C‐5 signals of the selenophene ring are shifted by 0.1–0.4, 2.5–3.0 and 5.5–6.0 ppm, respectively, to higher frequencies, whereas those of the ¹³C‐1, ¹³C‐2 and ¹³C‐4 carbons are shifted by 4–5, ～11 and ～1.7 ppm to lower frequencies on going from the E to Z isomer. The ¹⁵N chemical shift of the oximic nitrogen is larger by 13–16 ppm in the E isomer relative to the Z isomer. An extraordinarily large difference (above 90 ppm) between the ⁷⁷Se resonance positions is revealed in the studied oxime isomers, the ⁷⁷Se peak being shifted to higher frequencies in the Z isomer. The trends in the changes of the measured chemical shifts are well reproduced by the GIAO calculations of the ¹H, ¹³C, ¹⁵N and ⁷⁷Se shielding constants in the energy‐favorable conformation with the syn orientation of the? C?N? O? H group relative to the selenophene ring. Copyright © 2009 John Wiley & Sons, Ltd.     

HFIP‐Assisted C−H Functionalization by Cp*CoIII: Access to Key Reactive Cobaltacycles and Implication in Catalysis

Described here is a synthetic approach to access two of the most widely invoked cationic cobaltacycles in Cp*Co^III‐catalyzed C?H functionalization reactions by C?H activation. The unique stabilizing capability of MeCN was used to surmount the previously proposed reversible nature of the C?H metalation step. Moreover, it is revealed the boosting effect of 1,1,1,3,3,3‐hexafluoroisopropanol in the metalation step and in the reaction between N‐pyrimidinylindole and diphenylacetylene under catalytic conditions.     

Molecular Structure,Vibrational Spectra,and Hydrogen Bonding of the Ionic Liquid 1‐Ethyl‐3‐methyl‐1H‐imidazolium Tetrafluoroborate

The IR and Raman spectra and conformations of the ionic liquid 1‐ethyl‐3‐methyl‐1H‐imidazolium tetrafluoroborate, [EMIM] [BF₄] ( 6 ), were analyzed within the framework of scaled quantum mechanics (SQM). It was shown that SQM successfully reproduced the spectra of the ionic liquid. The computations revealed that normal modes of the EMIM⁺?BF ion pair closely resemble those of the isolated ions EMIM⁺ and BF , except for the antisymmetric BF stretching vibrations of the anion, and the out‐of‐plane and stretching vibrations of the H? C(2) moiety of the cation. The most plausible explanation for the pronounced changes of the latter vibrations upon ion‐pair formation is the H‐bonding between H? C(2) and BF . However, these weak H‐bonds are of minor importance compared with the Coulomb interactions between the ions that keep them closely associated even in dilute CD₂Cl₂ solutions. According to the ‘gas‐phase’ computations, in these associates, the BF anion is positioned over the imidazolium ring of the EMIM⁺ cation and has short contacts not only with the H? C(2) of the latter, but also with a proton of the Me? N(3) group.     

Eosin Y as a Direct Hydrogen‐Atom Transfer Photocatalyst for the Functionalization of C−H Bonds

Eosin Y, a well‐known economical alternative to metal catalysts in visible‐light‐driven single‐electron transfer‐based organic transformations, can behave as an effective direct hydrogen‐atom transfer catalyst for C?H activation. Using the alkylation of C?H bonds with electron‐deficient alkenes as a model study revealed an extremely broad substrate scope, enabling easy access to a variety of important synthons. This eosin Y‐based photocatalytic hydrogen‐atom transfer strategy is promising for diverse functionalization of a wide range of native C?H bonds in a green and sustainable manner.     

Substituent effect on electron affinity,gas‐phase basicity,and structure of monosubstituted propynyl radicals and their anions: A theoretical study

The substituent effect of electron‐withdrawing groups on electron affinity and gas‐phase basicity has been investigated for substituted propynl radicals and their corresponding anions. It is shown that when a hydrogen of the α‐CH₃ group in the propynyl system is substituted by an electron‐withdrawing substituent, electron affinity increases, whereas gas‐phase basicity decreases. These results can be explained in terms of the natural atomic charge of the terminal acetylene carbon of the systems. The calculated electron affinities are 3.28 eV (?C?C? CH₂F), 3.59 eV (?C?C? CH₂Cl) and 3.73 eV (?C?C? CH₂Br), and the gas‐phase basicities of their anions are 359.5 kcal/mol (^?:C?C? CH₂F), 354.8 kcal/mol (:C?C? CH₂Cl) and 351.3 kcal/mol (^?:C?C? CH₂Br). It is concluded that the larger the magnitude of electron‐withdrawing, the greater is the electron affinity of radical and the smaller is the gas‐phase basicity of its anion. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Synthesis and Reactivity of a Neutral,Three‐Coordinate Platinum(II) Complex Featuring Terminal Amido Ligation

A crystallographically characterized three‐coordinate, formally 14 electron Pt^II complex 1 featuring terminal amido ligation is reported. Computational analysis revealed relatively weak π donation from the amide lone pair to platinum and supports a 14‐electron assignment for 1 . Stoichiometric reactivity studies confirmed the viability of net O? H and C? H addition across, as well as isonitrile insertion into, the terminal platinum–amido linkage of 1 .     

Mono‐, bis‐, and trismaleimides having electron‐donating chromophores: Fluorescence,electrochemical properties,polymerization, and cure monitoring

Mono‐, bis‐, and trismaleimides (MM‐2, BM‐4, and TM‐6, respectively) bearing electron‐donating chromophores generally displayed strong fluorescence quenching. The quenching mechanism of fluorescence was revealed by electrochemical studies. On the basis of the electrochemical data, an energy level diagram was established for these maleimides. The electron‐donating ability increased in the order of TM‐6 < BM‐4 < MM‐2. The electron‐accepting ability increased in the opposite order, that is, from MM‐2 to BM‐4 to TM‐6. The copolymerization of multimaleimides with diamine could be well monitored by fluorescence spectroscopy. Compared with fluorescence probe techniques, the fluorescence monitoring could directly reflect the consumption of C?C bonds. Furthermore, a novel trismaleimide resin was preliminarily studied, in which TM‐6 was a dual‐purpose functional monomer acting not only as a crosslinker but also as an intrinsic fluorophore to monitor its crosslinking or cure process. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 304–313, 2006     

Iridium‐Catalyzed,Silyl‐Directed,peri‐Borylation of C−H Bonds in Fused Polycyclic Arenes and Heteroarenes

peri‐Disubstituted naphthalenes exhibit interesting physical properties and unique chemical reactivity, due to the parallel arrangement of the bonds to the two peri‐disposed substituents. Regioselective installation of a functional group at the position peri to 1‐substituted naphthalenes is challenging due to the steric interaction between the existing substituent and the position at which the second one would be installed. We report an iridium‐catalyzed borylation of the C?H bond peri to a silyl group in naphthalenes and analogous polyaromatic hydrocarbons. The reaction occurs under mild conditions with wide functional group tolerance. The silyl group and the boryl group in the resulting products are precursors to a range of functional groups bound to the naphthalene ring through C?C, C?O, C?N, C?Br and C?Cl bonds.     

Synthesis, Structure and Photophysical Properties of Silole-Oxadiazole Copolymers

A new conjugated copolymer (PTST‐DyOXD) derived from 1,1‐dimethyl‐3,4‐diphenyl‐2,5‐bis(5‐bromo‐2‐thienyl)‐silole (TST) and 2,5‐bis(4‐ethynylphenyl)‐1,3,4‐oxadiazole (DyOXD) was synthesized by Pd(0)‐catalyzed Sonogashira coupling reaction. For comparison, another copolymer without acetenyl group (PTST‐OXD) was also synthesized by Pd(0)‐catalyzed Suzuki coupling reaction. Chemical structures and optoelectronic properties of the copolymers were characterized by ¹H NMR, ¹³C NMR, IR, UV‐vis absorption, photoluminescence and cyclic voltammetry. The number‐average molecular weight (M_n) is 4010 Da for PTST‐DyOXD and 3890 Da for PTST‐OXD, respectively. The thermogravimetric analysis (TGA) measurements show that they have good thermal stability with decomposition temperature at 312 and 318°C, respectively. The optical band gap is 2.21 eV for PTST‐DyOXD and 2.10 eV for PTST‐OXD based on the absorption onset. CV analysis revealed the LUMO level of PTST‐DyOXD is ?3.04 eV, lower than that of PTST‐OXD (about ?2.89 eV), which is attributed to the introduction of acetylene group in PTST‐DyOXD, increasing the system of the conjugate chain length.     

The Proportion of Fe‐NX,N Doping Species and Fe3C to Oxygen Catalytic Activity in Core‐Shell Fe‐N/C Electrocatalyst

A bifunctional oxygen electrocatalyst composed of iron carbide (Fe₃C) nanoparticles encapsulated by nitrogen doped carbon sheets is reported. X‐ray photoelectron spectroscopy and X‐ray absorption near edge structure revealed the presence of several kinds of active sites (Fe?N_x sites, N doping sites) and the modulated electron structure of nitrogen doped carbon sheets. Fe₃C@N‐CSs shows excellent oxygen evolution and oxygen reduction catalytic activity owing to the modulated electron structure by encapsulated Fe₃C core via biphasic interfaces electron interaction, which can lower the free energy of intermediate, strengthen the bonding strength and enhance conductivity. Meanwhile, the contribution of the Fe?N_x sites, N doping sites and the effect of Fe₃C core for the electrocatalytic oxygen reaction is originally revealed. The Fe₃C@N‐CSs air electrode‐based zinc‐air battery demonstrates a high open circuit potential of 1.47 V, superior charge‐discharge performance and long lifetime, which outperforms the noble metal‐based zinc‐air battery.