Structural Variability of R2C Adducts of 3a,6a‐Diaza‐1,4‐diphosphapentalene: Tuning the N→P Bonding

3a,6a‐Diaza‐1,4‐diphosphapentalene (DDP) reacts with hexachlorocyclopentadiene to form a stable adduct (ClC)₄C=DDP ( 4 ). The phosphorus atom involved into coordination has a pyramidal arrangement but retains partial double bonding with carbon [1.752(3) Å]. At the same time, the P–N bond remains covalent [1.824(3) Å]. The adduct 4 is better described as a zwitterionic compound with strongly delocalized positive and negative charges. A similar zwitterionic adduct DDP=C(CN)₂ was prepared by the reactions of dichloro‐DDP ( 7 ) with malononitrile in the presence of Et₃N. DFT calculations showed that related structures are formed in the case of the substituents (ClC)₄C=, (HC)₄C=, (NC)₂C=, and (MeCO)₂C=, possessing electron‐delocalizing properties. Compounds with other R₂C groups (R = Ph, Me, C₆F₅, Cl), possessing electronegative properties as well, but insufficient e‐delocalization, demonstrate the noncovalent P–N bonding and a little shorter R₂C–P bond lengths (ca. 1.70 Å).     

Hydrogen‐Bond‐Mediated Asymmetric Cascade Reaction of Stable Sulfur Ylides with Nitroolefins: Scope,Application and Mechanism

A hydrogen‐bond‐mediated asymmetric [4+1] annulation/rearrangement cascade of stable sulfur ylides and nitroolefins was developed. This reaction provides a facile route to enantioenriched 4,5‐substituted oxazolidinones in moderate to excellent isolated yields (65–96 %) with excellent stereocontrol (up to more than 95:5 d.r. and 97:3 e.r.). This methodology was successfully applied to the concise synthesis of two bioactive molecules. The stereocontrolled modes and mechanism have been proposed to explain the origin of this stereochemistry.     

Asymmetric Friedel–Crafts Alkylation of Electron‐Rich N‐Heterocycles with Nitroalkenes Catalyzed by Diphenylamine‐Tethered Bis(oxazoline) and Bis(thiazoline) ZnII Complexes

The asymmetric Friedel–Crafts alkylation of electron‐rich N‐containing heterocycles with nitroalkenes under catalysis of diphenylamine‐tethered bis(oxazoline) and bis(thiazoline)‐Zn^II complexes was investigated. In the reaction of indole derivatives, the complex of ligand 4 f with trans‐diphenyl substitutions afforded better results than previously published ligand 4 e with cis‐diphenyl substitutions. Excellent yields (up to greater than 99 %) and enantioselectivities (up to 97 %) were achieved in most cases. The complex of ligand 4 d bearing tert‐butyl groups gave the best results in the reactions of pyrrole. Moderate to good yields (up to 91 %) and enantioselectivities (up to 91 %) were achieved in most cases. The origin of the enantioselectivity was attributed to the NH–π interaction between the catalyst and the incoming aromatic system in the transition state. Such an interaction was confirmed through comparison of the enantioselectivity and the absolute configuration of the products in the reactions catalyzed by designed ligands.     

Pivaloylmetals (tBu‐COM: M=Li,MgX, K) as Equilibrium Components

Short‐lived pivaloylmetals, (H₃C)₃C‐COM, were established as the reactive intermediates arising through thermal heterolytic expulsion of O=CtBu₂ from the overcrowded metal alkoxides tBuC(=O)‐C(‐OM)tBu₂ (M=MgX, Li, K). In all three cases, this fission step is counteracted by a faster return process, as shown through the trapping of tBu‐COM by O=C(tBu)‐C(CD₃)₃ with formation of the deuterated starting alkoxides. If generated in the absence of trapping agents, all three tBu‐COM species “dimerize” to give the enediolates MO‐C(tBu)=C(tBu)‐OM along with O=CtBu₂ (2 equiv). A common‐component rate depression by surplus O=CtBu₂ proves the existence of some free tBu‐COM (separated from O=CtBu₂); but companion intermediates with the traits of an undissociated complex such as tBu‐COM & O=CtBu₂ had to be postulated. The slow fission step generating tBu‐COMgX in THF levels the overall rates of dimerization, ketone addition, and deuterium incorporation. Formed by much faster fission steps, both tBu‐COLi and tBu‐COK add very rapidly to ketones and dimerize somewhat slower (but still fairly fast, as shown through trapping of the emerging O=CtBu₂ by H₃CLi or PhCH₂K, respectively). At first sight surprisingly, the rapid fission, return, and dimerization steps combine to very slow overall decay rates of the precursor Li and K alkoxides in the absence of trapping agents: A detailed study revealed that the fast fission step, generating tBu‐COLi in THF, is followed by a kinetic partitioning that is heavily biased toward return and against the product‐forming dimerization. Both tBu‐COLi and tBu‐COK form tBu‐CH=O with HN(SiMe₃)₃, but only tBu‐COK is basic enough for being protonated by the precursor acyloin tBuC(=O)‐C(‐OH)tBu₂.     

Novel Bis(2‐cyanoketene‐S,S‐/S,N‐acetals): Versatile Precursors for Novel Bis(aminopyrazole) Derivatives

A synthesis of novel bis(aminopyrazoles) by the reaction of hydrazine hydrate with the appropriate bis(2‐cyanoketene‐S,N‐acetals) was reported. The latter compounds were prepared by treatment of bis(cyanoacetamides) with phenyl isothiocyanate in KOH/EtOH and subsequent alkylation with methyl iodide. The utility of bis(2‐cyanoketene‐S,S‐acetals) as building blocks for novel bis(aminopyrazoles) was also investigated.     

From an Isolable Acyclic Phosphinosilylene Adduct to Donor‐Stabilized SiE Compounds (E=O,S, Se)

Reaction of the arylchlorosilylene‐NHC adduct ArSi(NHC)Cl [Ar=2,6‐Trip₂C₆H₃; NHC=(MeC)₂(NMe)₂C:] 1 with one molar equiv of lithium diphenylphosphanide affords the first stable NHC‐stabilized acyclic phosphinosilylene adduct 2 (ArSi(NHC)PPh₂), which could be structurally characterized. Compound 2 , when reacted with one molar equiv selenium and sulfur, affords the silanechalcogenones 4 a and 4 b (ArSi(NHC)(?E)PPh₂, 4 a : E=Se, 4 b : E=S), respectively. Conversion of 2 with an excess of Se and S, through additional insertion of one chalcogen atom into the Si?P bond, leads to 3 a and 3 b (ArSi(NHC)(?E)‐E‐P(?E)Ph₂, 3 a : E=Se, 3 b : E=S), respectively. Additionally, the exposure of 2 to N₂O or CO₂ yielded the isolable NHC‐stabilized silanone 4 c , Ar(NHC)(Ph₂P)Si?O.     

Breslow Intermediates from Aromatic N‐Heterocyclic Carbenes (Benzimidazolin‐2‐ylidenes,Thiazolin‐2‐ylidenes)

We report the first generation and characterization of elusive Breslow intermediates derived from aromatic N‐heterocyclic carbenes (NHCs), namely benzimidazolin‐2‐ylidenes (NMR, X‐ray analysis) and thiazolin‐2‐ylidenes (NMR). In the former case, the diamino enols were generated by reaction of the free N,N‐bis(2,6‐diisopropylphenyl)‐ and N,N‐bis(mesityl)‐substituted benzimidazolin‐2‐ylidenes with aldehydes while the dimer of 3,4,5‐trimethylthiazolin‐2‐ylidene served as the starting material in the latter case. The unambiguous NMR identification of the first thiazolin‐2‐ylidene‐based Breslow intermediate rests on double ¹³C labeling of both the NHC and the aldehyde component. The acyl anion reactivity was confirmed by benzoin formation with excess aldehyde.     

Na2S–Carbon Nanotube Fabric Electrodes for Room‐Temperature Sodium–Sulfur Batteries

A unique sodium sulfide (Na₂S) cathode is developed, which will allow the use of sodium‐free anodes for room‐temperature sodium–sulfur (Na–S) batteries. To overcome the “inert” nature of the Na₂S, a special cathode structure is developed by spreading the multi‐walled carbon nanotube (MWCNT)‐wrapped Na₂S particles onto MWCNT fabrics. Spectroscopic and electrochemical analyses reveal a series of polysulfide intermediates involved in the charge/discharge of the cell. The Na–S battery prepared in full discharge state with the Na₂S/MWCNT cathode provides a remarkable capacity of 500 A h kg^?1 (based on sulfur mass) after 50 cycles.     

Atomically Dispersed Nickel(I) on an Alloy‐Encapsulated Nitrogen‐Doped Carbon Nanotube Array for High‐Performance Electrochemical CO2 Reduction Reaction

Single‐atom catalysts (SACs) show great promise for electrochemical CO₂ reduction reaction (CRR), but the low density of active sites and the poor electrical conduction and mass transport of the single‐atom electrode greatly limit their performance. Herein, we prepared a nickel single‐atom electrode consisting of isolated, high‐density and low‐valent nickel(I) sites anchored on a self‐standing N‐doped carbon nanotube array with nickel–copper alloy encapsulation on a carbon‐fiber paper. The combination of single‐atom nickel(I) sites and self‐standing array structure gives rise to an excellent electrocatalytic CO₂ reduction performance. The introduction of copper tunes the d‐band electron configuration and enhances the adsorption of hydrogen, which impedes the hydrogen evolution reaction. The single‐nickel‐atom electrode exhibits a specific current density of ?32.87 mA cm^?2 and turnover frequency of 1962 h^?1 at a mild overpotential of 620 mV for CO formation with 97 % Faradic efficiency.     

Cationic Five‐Coordinate Bis(guanidinato)silicon(IV) Complexes with SiN4El Skeletons (El=S,Se): “Heterolytic Activation” of S−S and Se−Se Bonds

The donor‐stabilized silylene [iPrNC(NiPr₂)NiPr]₂Si ( 2 ) reacts with PhEl?ElPh (El=S, Se) to form the respective cationic five‐coordinate bis(guanidinato)silicon(IV) complexes {[iPrNC(NiPr₂)NiPr]₂SiSPh}⁺PhS^? ( 4 ) and {[iPrNC (NiPr₂)NiPr]₂SiSePh}⁺PhSe^? ( 5 ). Compounds 4 and 5 were characterized by crystal structure analyses and NMR spectroscopic studies in the solid state.     

Enantioselective Synthesis of N,S‐Acetals by an Oxidative Pummerer‐Type Transformation using Phase‐Transfer Catalysis

Reported is the first enantioselective oxidative Pummerer‐type transformation using phase‐transfer catalysis to deliver enantioenriched sulfur‐bearing heterocycles. This reaction includes the direct oxidation of sulfides to a thionium intermediate, followed by an asymmetric intramolecular nucleophilic addition to form chiral cyclic N,S‐acetals with moderate to high enantioselectivites. Deuterium‐labelling experiments were performed to identify the stereodiscrimination step of this process. Further analysis of the reaction transition states, by means of multidimensional correlations and DFT calculations, highlight the existence of a set of weak noncovalent interactions between the catalyst and substrate that govern the enantioselectivity of the reaction.     

O(3P)原子与CS2反应可见化学发光研究

在交叉分子束装置上研究了基态氧原子O(3P)与二硫化碳反应的可见光区(380～500 nm)化学发光，得到的光谱标识为SO2分子 3B1→ 1A1自旋禁阻跃迁发射谱，实验中得到的上态主要是振动基态和弯曲模ν2激发的振动激发态，通过对不同压力情况下光谱的分析和反应通道的讨论，确认 3B1态的SO2来自于反应的多级过程.