Relative Stability of Multiple Bonds between Germanium and Stibium. A Theoretical Study

Substituent effects on the potential energy surface of XGeSb (X=H, Li, Na, BeH, MgH, BH₂, AlH₂, CH₃, SiH₃, NH₂, PH₂, OH, SH, F, and Cl) were investigated by using B3LYP/Def2‐TZVP, B3PW91/Def2‐ TZVPP CCSD (T)//B3LYP/Def2‐TZVP methods. The isomers include structures with formal double (Ge=SbX) and triple (Xge=Sb) bonds to germanium‐stibium, so a direct comparison of these types of species is possible. Our model calculations indicate that electropositively substituted Ge=SbX species are thermodynamically and kinetically more stable than their isomeric Xge=Sb molecules. Moreover, the theoretical findings suggest that only the organic substitutions (such as CH₃) can make triply bonded Xge=Sb molecule more stable than the doubly bonded Ge=SbX species.     

Reductive Insertion of Elemental Chalcogens into Boron–Boron Multiple Bonds

The syntheses of sulfur‐ and selenium‐bridged cyclic compounds containing boron stabilized by N‐heterocyclic carbenes (NHCs) have been achieved by the reductive insertion of elemental chalcogens into boron–boron multiple bonds. The three pairs of bonding electrons between the boron atoms in the triply bonded diboryne enabled six‐electron reduction reactions, resulting in the formation of [2.2.1]‐bicyclic systems wherein bridgehead boron atoms are spanned by three chalcogen bridges. A similar reaction using a diborene (boron–boron double bond) resulted in the reductive transfer of both pairs of bonding electrons to three sulfur atoms, yielding a NHC‐stabilized trisulfidodiborolane. The demonstration of these six‐ and four‐electron reductions lends support to the presence of three and two pairs of bonding electrons between the boron atoms of the diboryne and diborene, respectively, a fact that may be useful in future discussions on bond order.     

Highly Strained Heterocycles Constructed from Boron–Boron Multiple Bonds and Heavy Chalcogens

The reactions of a diborene with elemental selenium or tellurium are shown to afford a diboraselenirane or diboratellurirane, respectively. These reactions are reminiscent of the sequestration of subvalent oxygen and nitrogen in the formation of oxiranes and aziridines; however, such reactivity is not known between alkenes and the heavy chalcogens. Although carbon is too electronegative to affect the reduction of elements with lower relative electronegativity, the highly reducing nature of the B?B double bond enables reactions with Se⁰ and Te⁰. The capacity of multiple bonds between boron atoms to donate electron density is highlighted in reactions where diborynes behave as nucleophiles, attacking one of the two Te atoms of diaryltellurides, forming salts consisting of diboratellurenium cations and aryltelluride anions.     

非经典多重键

在难以形成经典多重键的重原子（第三周期以下）之间可以形成一种非经典多重键。由于构成双键的两部分（即两个分子片）的基态分别是单线态,这种电子结构导致非经典双键由两个配位键构成,非经典三键则是在此基础上再加上一个π键。这种多重键的强度和键级较经典多重键为低。与两个配位键的电子结构相对应,含有非经典多重键的分子具有反式弯曲的几何构型。     

On‐Demand Electrochemical Epoxidation in Nano‐Electrospray Ionization Mass Spectrometry to Locate Carbon–Carbon Double Bonds

Reported here is the first on‐demand electrochemical epoxidation incorporated into the standard nano‐electrospray ionization mass spectrometry (nanoESI‐MS) workflow for double‐bond identification. The capability lies in a novel tunable electro‐epoxidation of double bonds, where onset of the reaction can be controlled by simply tuning the spray voltage. On‐demand formation of mono‐/multiple epoxides is achieved at different voltages. The electro‐epoxidized products are then fragmented by tandem MS to generate diagnostic ions, indicating the double bond position(s). The process is completed within seconds, holding great potential for high‐throughput analysis. The rapid switch‐on/off electro‐epoxidation of a single sample, the low sample consumption, the demonstrated applicability to complex lipids containing multiple double bonds, and the advantage of not requiring extra apparatus make this method attractive for use in lipid‐related biological studies.     

Sulfur‐Impregnated Core–Shell Hierarchical Porous Carbon for Lithium–Sulfur Batteries

Core–shell hierarchical porous carbon spheres (HPCs) were synthesized by a facile hydrothermal method and used as host to incorporate sulfur. The microstructure, morphology, and specific surface areas of the resultant samples have been systematically characterized. The results indicate that most of sulfur is well dispersed over the core area of HPCs after the impregnation of sulfur. Meanwhile, the shell of HPCs with void pores is serving as a retard against the dissolution of lithium polysulfides. This structure can enhance the transport of electron and lithium ions as well as alleviate the stress caused by volume change during the charge–discharge process. The as‐prepared HPC‐sulfur (HPC‐S) composite with 65.3 wt % sulfur delivers a high specific capacity of 1397.9 mA h g^?1 at a current density of 335 mA g^?1 (0.2 C) as a cathode material for lithium–sulfur (Li‐S) batteries, and the discharge capacity of the electrode could still reach 753.2 mA h g^?1 at 6700 mA g^?1 (4 C). Moreover, the composite electrode exhibited an excellent cycling capacity of 830.5 mA h g^?1 after 200 cycles.     

Metal–Metal Distances at the Limit: Cr–Cr 1.73 Å – the Importance of the Ligand and its Fine Tuning

The synthesis and structure of a homobimetallic chromium complex is reported. The ligand used to stabilise the quintuply bonded metals is a sterically fine‐tuned guanidinate. A chromium–chromium bond length of 1.7293(12) Å was observed. It is the shortest metal–metal distance reported for a stable compound yet.     

Coordination Bonds and Diels–Alder Bonds Dual Crosslinked Polymer Networks of Self‐healing Polyurethane

A dual crosslinked self‐healing polyurethane was prepared with robust mechanical properties through the dynamic reversible pyridine‐Fe³⁺ coordination bonds and Diels–Alder (DA) covalent bonds dual crosslinking strategy. Moreover, the mechanical properties and self‐healing ability of polyurethane can be tuned readily by different ratio of the coordination bonds and DA bonds. Under external load, the coordination bonds serve as sacrificial bonds are broken to dissipate energy, the DA bonds can keep the shape of sample. With the coordination bonds participation, the damaged samples can be healed under moderate heating treatment or with the aid of FeCl₃ solution. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2228–2234     

Access to Stable Metalloradical Cations with Unsupported and Isomeric Metal–Metal Hemi‐Bonds

Metalloradical species [Co₂Fv(CO)₄]^.+ ( 1 ^.+, Fv=fulvalenediyl) and [Co₂Cp₂(CO)₄]^.+ ( 2 ^.+, Cp=η⁵‐C₅H₅), formed by one‐electron oxidations of piano‐stool cobalt carbonyl complexes, can be stabilized with weakly coordinating polyfluoroaluminate anions in the solid state. They feature a supported and an unsupported (i.e. unbridged) cobalt–cobalt three‐electron σ bond, respectively, each with a formal bond order of 0.5 (hemi‐bond). When Cp is replaced by bulkier Cp* (Cp*=η⁵‐C₅Me₅), an interchange between an unsupported radical [Co₂Cp*₂(CO)₄]^.+ (anti‐ 3 ^.+) and a supported radical [Co₂Cp*₂(μ‐CO)₂(CO)₂]^.+ (trans‐ 3 ^.+) is observed in solution, which cocrystallize and exist in the crystal phase. 2 ^.+ and anti‐ 3 ^.+ are the first stable thus isolable examples that feature an unsupported metal–metal hemi‐bond, and the coexistence of anti‐ 3 ^.+ and trans‐ 3 ^.+ in one crystal is unprecedented in the field of dinuclear metalloradical chemistry. The work suggests that more stable metalloradicals of metal–metal hemi‐bonds may be accessible by using metal carbonyls together with large and weakly coordinating polyfluoroaluminate anions.     

Alkylidyne–Metal Templated Triboronate Condensation

Under exceptionally mild conditions the alkylidyne metallatetraborane 1 undergoes an intriguing conversion into the dodecaboronate dianion in a rare example of metal-templated boronate condensation.     

Oxidative Addition of Carbon–Carbon Bonds to Gold

The oxidative addition of strained C? C bonds (biphenylene, benzocyclobutenone) to DPCb (diphosphino‐carborane) gold(I) complexes is reported. The resulting cationic organogold(III) complexes have been isolated and fully characterized. Experimental conditions can be adjusted to obtain selectively acyl gold(III) complexes resulting from oxidative addition of either the C(aryl)? C(O) or C(alkyl)? C(O) bond of benzocyclobutenone. DFT calculations provide mechanistic insight into this unprecedented transformation.     

The Transition Metal-Nitrogen Multiple Bond

Numerous nitrido complexes of transition metals show very short metal-nitrogen bond lengths, suggesting M?N-triple bonds. At present, compounds of this type are being intensively investigated. In particular the molybdenum complexes are considered as model substances for the study of at least an intermediate step of N₂-assimilation. This article contains a review of the structure and bonding, as well as syntheses and reactions of these complexes.     

Activation of Strong Boron–Fluorine and Silicon–Fluorine σ‐Bonds: Theoretical Understanding and Prediction

The oxidative addition of BF₃ to a platinum(0) bis(phosphine) complex [Pt(PMe₃)₂] ( 1 ) was investigated by density functional calculations. Both the cis and trans pathways for the oxidative addition of BF₃ to 1 are endergonic (ΔG°=26.8 and 35.7 kcal mol^?1, respectively) and require large Gibbs activation energies (ΔG°^≠=56.3 and 38.9 kcal mol^?1, respectively). A second borane plays crucial roles in accelerating the activation; the trans oxidative addition of BF₃ to 1 in the presence of a second BF₃ molecule occurs with ΔG°^≠ and ΔG° values of 10.1 and ?4.7 kcal mol^?1, respectively. ΔG°^≠ becomes very small and ΔG° becomes negative. A charge transfer (CT), F→BF₃, occurs from the dissociating fluoride to the second non‐coordinated BF₃. This CT interaction stabilizes both the transition state and the product. The B?F σ‐bond cleavage of BF₂Ar^F (Ar^F=3,5‐bis(trifluoromethyl)phenyl) and the B?Cl σ‐bond cleavage of BCl₃ by 1 are accelerated by the participation of the second borane. The calculations predict that trans oxidative addition of SiF₄ to 1 easily occurs in the presence of a second SiF₄ molecule via the formation of a hypervalent Si species.     

Main Group Multiple Bonds for Bond Activations and Catalysis

Since the discovery that the so-called “double-bond” rule could be broken, the field of molecular main group multiple bonds has expanded rapidly. With the majority of homodiatomic double and triple bonds realised within the p-block, along with many heterodiatomic combinations, this Minireview examines the reactivity of these compounds with a particular emphasis on small molecule activation. Furthermore, whilst their ability to act as transition metal mimics has been explored, their catalytic behaviour is somewhat limited. This Minireview aims to highlight the potential of these complexes towards catalytic application and their role as synthons in further functionalisations making them a versatile tool for the modern synthetic chemist.