Bio-inspired tetracarbene compounds as a new family of energy saving catalysts

Efficient use of energy is a pressing issue.Improvement of chemical processes is currently an important target for energy efficiency.Although chemical processes are independent of pathways with respect to the final energy output or consumption,the application of catalysts can reduce involved activation energies considerably and therefore save large amounts of energy.

N-heterocyclic carbene as a promising metal-free electrocatalyst with high efficiency for nitrogen reduction to ammonia

Electrocatalytic nitrogen reduction reaction(NRR)at ambient conditions holds great promise for sustainably synthesizing ammonia(NH3),while developing highly-efficient,long-term stable,and inexpensive catalysts to activate the inert N≡N bond is a key scientific issue.In this work,on the basis of the concept"N-heterocyclic carbenes(NHCs)",we propose a carbon decorated graphitic-carbon nitride(C/g-C3N4)as novel metal-free NRR electrocatalyst by means of density functional theory(DFT)computations.Our results reveal that the introduced C atom in g-C3N4 surface can be regarded as NHCs and catalytic sites for activating N≡N bond,and are stabilized by the g-C3N4 substrate due to sterically disfavored dimerization.Especially,this NHCs-based heterogeneous catalysis can efficiently reduce the activated N2 molecule to NH3 with a low overpotential of 0.05 V via an enzymatic mechanism.Our work is the first report of NHCs-based electrocatalyst for N2 fixation,thus opening an alternative avenue for advancing sustainable NH3 production.

Synthesis, Crystal Structure and Catalytic Behavior of 1-Ethyl-3-benyl-imidazolyl Tetranuclear N-Heterocyclic Carbene Silver Bromide

The title complex [Ag（carbene）2]2[Ag2Br4] has been synthesized by the reaction of Ag2O with 1-ethyl-3-benyl-imidazolium bromide in DMSO at room temperature, and characterized by elemental analysis, 1H NMR and single-crystal X-ray diffraction analysis. It crystallizes in triclinic, space group P with a = 10.1597（10）, b =11.0646（11）, c = 13.0245（14） , α = 102.230（2）, β = 90.606, γ = 113.9250（10）o, V = 1300.3（2） 3, Mr = 748.06, Z = 2, Dc = 1.911 g/cm3, μ（MoKα） = 4.60 mm-1 and F（000） = 728. The structure was refined to R = 0.0316 and wR = 0.0835 for 3744 observed reflections with I 〉 2σ（I）. The title compound crystallizes as a centrosymmetric tetranuclear compound. One half of the molecule comprises the asymmetric unit of the structure. The Ag（1） atom is nearly linear or T-shaped when the Ag（1）-Ag（2） interaction is taken into consideration, which is bi-coordinated by two carbene carbon atoms. The Ag（2） atom adopts tetrahedral geometry. The catalytic behavior of the title complex has been investigated, and the results indicate it has a highly catalytic activation for L-lactide polymerization.

Synthesis and Structural Study of a N-Heterocyclic Carbene Trinuclear Silver(Ⅰ)Complex

The bis-benzimidazolium salt bis[2-（N-ethylbenzimidazoliumyl）ethyl]amine hexafluorophosphate（LH2·（PF6）2） and its N-heterocyclic carbene silver（Ⅰ） complex[L2Ag3]（PF6）3（1）have been prepared and characterized.In complex 1,a trinuclear silver（Ⅰ） architecture is formed by two tridentate ligands and three silver（I） atoms,in which one 12- and two 7-membered rings are contained.In the crystal packing of 1,1D chain and 2D supramolecular layer are formed via intermolecular weak interactions,including π…π interactions and C-H…π contacts.Additionally,the fluorescence emission spectra of LH2-（PF6）2 and 1 are described.

Transformations of biomass-based levulinate ester into γ-valerolactone and pyrrolidones using carbon nanotubes-grafted N-heterocyclic carbene ruthenium complexes

As a renewable biomass-based compound with wide applications in food additives,fine chemical synthesis and fuels,γ-valerolactone(GVL)has attached much attention.While,pyrrolidones are widely used in pharmaceutical,agrochemical,material industrial and other chemical production.In this research,we demonstrated transformations of biomass-based ethyl levulinate(EL)into GVL and pyrrolidones by using heterogeneous catalysts(CNT-Ru-1)with N-heterocyclic carbene ruthenium(NHC-Ru)complex grafted on multi-walled carbon nanotube(CNT).The Ru catalyst showed high efficiency on EL hydrogenation to GVL with both EL conversion and GVL yield exceeding 99%.Moreover,the Ru catalyst readily promoted reductive amination of EL in the presence of various amines for pyrrolidone synthesis.Finally,the Ru catalyst was also applicable to hydrogenation of various carbonyl compounds for the synthesis of the corresponding alcohols with excellent catalytic performance.The research provides insight for heterogenizing the homogeneous noble metal-based catalysts with high catalytic active for biomass-based transformations.

Rh(Ⅱ) carbene S-H insertion into H_2S via the stepwise mechanism

The mechanism of Rh（Ⅱ） carbene S-H insertion into H2S in gas phase has been studied by B3LYP functional. Calculation results showed that the Rh（Ⅱ） carbene S-H insertion into H2S took only stepwise channels and no concerted channels had been located, which was different from the Rh（Ⅱ） carbene C-H and O-H insertions.

A New Palladium Complex Containing the Mixture of Carbene and Phosphine Ligands: Synthesis, Crystal Structure and Spectral FT-IR, NMR and UV-Vis Researches

In this paper,a new Pd-based complex that contains A^-heterocyclic carbene(NHC)and triphenylphosphine(PPh?)ligands was synthesized.The c/5-(NHC)PdBr2(PPh3)complex has been prepared by the substitution of 3?chloropyridine ligand in(NHC)PdBr2(3-chloropyridine)complex with triphenylphosphine.This complex has been characterized by using 1^H NMR,^31P{^1H}NMR,^13C{^1H}NMR,FTIR,UV-Vis spectroscopy and elemental analysis techniques.The molecular and crystal structures of the cz5-(NHC)PdBr2(PPh3)complex were determined by singlecrystal X-ray diffraction method.

Synthesis and Catalytic Activity of a Two-core Ruthenium Carbene Complex: a Unique Catalyst for Ring Closing Metathesis Reaction

The reaction of a ruthenium carbide complex RuCl2（C：）（PCy3）2 with [H（Et2O）x]＋[BF4]- at a molar ratio of 1：2 produced a two-core ruthenium carbene complex, {[RuCl（=CHPCy3）（PCy3）]2（μ-Cl）3}＋·[BF4]-, in the form of a yellow-green crystalline solid in a yield of 94%. This two-core ruthenium complex is a selective catalyst for ring closing metathesis of unsubstituted terminal dienes. More importantly, no isomerized byproduct was observed for N-substrates when the two-core ruthenium complex was used as the catalyst at an elevated temperature（137 °C）, indicating that the complex is a chemo-selective catalyst for ring closing metathesis reactions.

Comparison of the Kinetics of 1-Hexene Metathesis by Ruthenium Carbene Catalysts

A kinetic study of two ruthenium carbene catalysts, （PCy3）2Cl2Ru=CHPh 1 （Grubbs catalyst） and a new catalyst [1,3-bis（2,6-dimethylphenyl）4,5-dihydroimidazol-2-ylidene]（PPh3） （Cl）2Ru-CHPh 3, were conducted in metathesis of 1-hexene. The kinetic behavior of these catalysts at 40, 50, 60 and 70℃ was compared. Complex 3 has the more active catalytic effect at temperatures 40-70℃.

A New Rearrangement Reaction of 2-Phenyl Substituted Benzothiazepine with Ethoxycarbonyl Carbene─Mechanism of the Reaction and Structure of the Product

2,3-Dihydro-2-phenyl-4-(4-methoxyphenyl)-1, 5-benzothiazepine reacts with ethoxycarbonyl carbene to give an unexpected compound 2,3-disubstituted-4H-1,4-benzothiazine Ⅲ. It was found to be a new rearrangement reaction and the structure of the product was confirmed by IR, NMR, MS.

Insertion of O—H Bond of Rh(Ⅱ)-methylene Carbene into Alcohols: A Stepwise Mechanism More Plausible than a Concerted Mechanism

The mechanisms of insertion of O-H bond of Rh（ Ⅱ ）-methylene carbene into methanol and ethanol were studied by using B3LYP functional both in gas phase and in CH2 C12. The formation of free alcoholic oxonium ylides is found to be impossible. Alcoholic oxonium ylide are formed as the intermediates before beth the stepwise and the concerted transition states of insertion of O-H bend of Rh（ Ⅱ ）-methylene carbene into methanol and ethanol. With re- gard to the mechanisms of insertion of O-H of Rh（ Ⅱ ） -methylene carbene into alcohols, analysis of the energy bartiers of the two mechanisms indicate that the stepwise mechanism is more plausible than the concerted mechanism.

THE ELECTRIC PROPERTY OF SINGLET CARBENE AND ITS ISOELECTRONIC SYSTEM^1——Electrophilic and Nucleophilic Directions of an Atom in the Molecule

The electrostatic potential of carbene and nitrene,have been calculated by AB INITIO method with 6-31G** basis set,there are positive potential regions in the directions of vacant P orbitals,and negative regions in the directions of lone-pair electrons. Therefore,atoms in these molecules have different electric properties in different directions.The idea of electrophilic and nucleophilic directions of an atom in molecules should be introduced.

Hydrogenation of CO_(2) to formate catalyzed by SBA-15-supported cyclic(alkyl)(amino)carbene-iridium

Recently,cyclic(alkyl)(amino)carbenes(CAACs)have been widely used as ligands to enhance the catalytic reactivity of center metal,but the problem of recycling this expensive ligand remains to be solved.In this work,the heterogeneous SBA-15-CAAC-Ir catalyst was prepared by a covalent attachment method.and using SBA-15 as the carrier.It shows high reactivity for the hydrogenation of CO_(2) to formate.After immobilization,the ordered mesoporous structure and the overall rod-like morphology of the original SBA-15 have been preserved very well.Using SBA-15-CAAC-Ir as catalyst,up to 21050 TON can be obtained at 60℃.In addition,the catalyst can be separated easily by centrifugation,and the catalytic activity of SBA-15-CAAC-Ir can still remain very high after multiple cycles.

NEW HETEROCYCLIC SYSTEM SYNTHESIS I REACTION OF DIHYDRO-1,5-BENZO-DIAZEPINES AND THIAZEPINES WITH (ETHOXYCARBONYL)CARBENES

Dihydro-1-benzoyl-1,5-benzodiazepines react with (ethoxycarbonyl)carbenes to give 4H-azirino-[1,2-a][1,5]-benzodiazepines and unexpected new tin9 system 1H-pyrrolo-[1,2-a][1,5]-benzodiazepines. Dihydro-1,5-benzothiazepines react with (ethoxycarbonyl)carbenes in cyclohexane to gire unexpected rin9 cleavage products ethyl (2E, 4E)-3-aryl-2-arylthiohexadienoates.

一种新型的重要试剂——卡宾(carbene)

卡宾(亚甲基)尽管早在三十年代就用来解说某些有机化学反应,但直至一九五九年通过光谱研究才被让实它的存在。嗣后,卡宾作为一类反应活性中间体,一直成为活跃的研究领域。它不仅在有机合成中得到了广泛的应用和发展,而且有力地推动了硅烯(>Si:)、锗烯(>Ge:)、卡拜或称碳炔(—C:)等新型活性中间体的研究。同时对卡宾本身的研究也在不断地发展和深入。目前,卡宾已成为一类新型的重要化学试剂被广泛地应用在有机研究领域里。

Theoretical Study on the Molecular Orbital and Stabilization Energy of Substituted Lithium Carbene Cations

The stabilization energies of substituted lithium carbene cations were calculated by using ab initio molecular orbital theory, and the relationship between the stabilization energies and molecular orbitals was discussed. The substituents with pi donor engender strong stabilization to CH2Li+. The calculations show the Y-C* bond lengths of cations become shorter and H-Y bond lengths longer than those of corresponding neutral molecules.

N-Heterocyclic carbene-catalyzed enantioselective(dynamic) kinetic resolutions and desymmetrizations

N-heterocyclic carbene-catalyzed enantioselective kinetic resolutions,dynamic kinetic resolutions,and desymmetrization reactions are systematically reviewed.The content is organized according to the activation modes involved in these transformations.Future advances within this highly active research field are discussed from our perspectives on the topic.

Recent advances in the synthesis and application of N-heterocyclic carbene-based molecular cages

N-Heterocyclic carbene(NHC)-based cages have emerged as a prominent and dynamic research area within the research field of chemistry. Leveraging the distinctive electronic and steric properties of NHC ligands, the design, synthesis, and application of these corresponding cages have garnered substantial scholarly interest. In recent years, we have witnessed the successful fabrication of diverse NHC-based cages through a range of synthetic methodologies, which hold significant potential for applications in molecular recognition and catalysis. In this review, we delve into the foundational synthetic strategies that underlie the creation of NHC-based cages, employing approaches encompassing metal–NHC chelation, coordination assembly,and covalent bonding. Additionally, we compile the diverse applications of these cages within catalytic processes and molecular recognition. Lastly, we shed light on the current limitations of synthesis and outline future trends in the development of NHCbased cages.

Carbene-catalyzed enantioselective seleno-Michael addition as access to antimicrobial active Se-containing heterocycles

Organoseleniums exhibit a diverse set of biological activities that are pivotal for drug discovery and are widely explored in synthetic chemistry and material science.While many transformations have been developed for non-enantioselective C–Se bond formations,the catalyst-controlled stereoselective preparation of chiral organoseleniums continues to be of considerable challenge.In particular,there are limited studies on the enantioselective seleno-Michael addition reactions to access chiral selenium functional molecules.Here,we disclose a carbene-catalyzed highly enantioselective nucleophilic C–Se bond construction through formal[3+3]annulations between selenocarboxamides and bromoenals,affording seleno-thiazinone products with good yields and excellent enantioselectivities.The choice of a weak inorganic base was pivotal to suppressing the unproductive racemization and decomposition of the selenium products.Notably,the catalytically generated chiral selenium-containing heterocyclic products feature remarkable antimicrobial activities that could serve as promising lead scaffolds for further agrochemical development.

Photoluminescent nickel(Ⅱ)carbene complexes with ligand-to-ligand charge-transfer excited states

While nickel(II)complexes have been widely used as catalysts for carbon-carbon coupling reactions,the exploration of their photophysical and photochemical properties is still in the infancy.Here,a series of square-planar Ni(II)complexes[(diNHC)NiX2]bearing chelating benzimidazole-based bis(N-heterocyclic carbene)ligands and varying anionic coligands(1,X=Cl;2,X=Br;3,X=I)are synthesized and structurally characterized.In solid state,both 1 and 2 exhibit orange-red photoluminescence under ambient conditions.The photophysical and electrochemical measurements along with density functional theory(DFT)calculations reveal that the low-energy emissions can be attributed to singlet excited states with ligand-to-ligand charge-transfer(LLCT)character.This work suggests that strong-field N-heterocyclic carbene ligands play a crucial role to achieve the luminescence of Ni(II)complexes.