Superhalogens as Building Blocks of Halogen‐Free Electrolytes in Lithium‐Ion Batteries

Most electrolytes currently used in Li‐ion batteries contain halogens, which are toxic. In the search for halogen‐free electrolytes, we studied the electronic structure of the current electrolytes using first‐principles theory. The results showed that all current electrolytes are based on superhalogens, i.e., the vertical electron detachment energies of the moieties that make up the negative ions are larger than those of any halogen atom. Realizing that several superhalogens exist that do not contain a single halogen atom, we studied their potential as effective electrolytes by calculating not only the energy needed to remove a Li⁺ ion but also their affinity towards H₂O. Several halogen‐free electrolytes are identified among which Li(CB₁₁H₁₂) is shown to have the greatest potential.     

Nonsymmetrical 3,4‐Dithienylmaleimides by Cross‐Coupling Reactions with Indium Organometallics: Synthesis and Photochemical Studies

The synthesis and photochemical study of novel nonsymmetrical 1,2‐dithienylethenes (DTEs) with a maleimide bridge have been carried out. The synthetic approach to the DTEs was based on successive selective palladium‐catalyzed cross‐coupling reactions of 5‐susbtituted‐2‐methyl‐3‐thiophenyl indium reagents with 3,4‐dichloromaleimides. The required organoindium reagents were prepared from 2‐methyl‐3,5‐dibromothiophene by a selective (C‐5) coupling reaction with triorganoindium compounds (R₃In) and subsequent metal–halogen exchange. The coupling reactions usually gave good yields and have a high atom economy with substoichiometric amounts of R₃In. The results of photochemical studies show that these novel dithienylmaleimides undergo a photocyclization reaction upon irradiation in the UV region and a photocycloreversion after excitation in the visible region, thus they can be used as photochemical switches. ON–OFF operations can be repeated in successive cycles without appreciable loss of effectiveness in the process.     

Understanding the Unconventional Effects of Halogenation on the Luminescent Properties of Oligo(Phenylene Vinylene) Molecules

It is commonly known that halogenation tends to decrease the luminescence quantum yield of an organic dye, owing to the high electronegativity and heavy‐atom effect of the halogen atom. However, based on an investigation of the effects of halogenation on the luminescence of the oligo(phenylene vinylene) (OPV) framework, we demonstrate that halogenation can have positive impact on the solid‐state fluorescence and electrochemiluminescence (ECL) properties of OPV derivatives. The chlorinated OPV exhibits a very high solid‐state fluorescence quantum yield (91 %), whilst the brominated analogue gives the highest ECL emission intensity. Time‐dependent density functional theory calculations, natural bond orbital analysis, and natural transition orbital analysis were performed to assist the understanding of the origin of these positive halogenation effects, which provide insight into the rational design of highly luminescent halogenated organic materials for solid‐state devices and ECL applications.     

Rational Modification of the Hierarchy of Intermolecular Interactions in Molecular Crystal Structures by Using Tunable Halogen Bonds

A family of 16 isomolecular salts (3‐XpyH)₂[MX′₄] (3‐XpyH=3‐halopyridinium; M=Co, Zn; X=(F), Cl, Br, (I); X′=Cl, Br, I) each containing rigid organic cations and tetrahedral halometallate anions has been prepared and characterized by X‐ray single crystal and/or powder diffraction. Their crystal structures reflect the competition and cooperation between non‐covalent interactions: N? H???X′? M hydrogen bonds, C? X???X′? M halogen bonds and π–π stacking. The latter are essentially unchanged in strength across the series, but both halogen bonds and hydrogen bonds are modified in strength upon changing the halogens involved. Changing the organic halogen (X) from F to I strengthens the C? X???X′? M halogen bonds, whereas an analogous change of the inorganic halogen (X′) weakens both halogen bonds and N? H???X′? M hydrogen bonds. By so tuning the strength of the putative halogen bonds from repulsive to weak to moderately strong attractive interactions, the hierarchy of the interactions has been modified rationally leading to systematic changes in crystal packing. Three classes of crystal structure are obtained. In type A (C? F???X′? M) halogen bonds are absent. The structure is directed by N? H???X′? M hydrogen bonds and π‐stacking interactions. In type B structures, involving small organic halogens (X) and large inorganic halogens (X′), long (weak) C? X???X′? M interactions are observed with type I halogen–halogen interaction geometries (C? X???X′ ≈ X???X′? M ≈155°), but hydrogen bonds still dominate. Thus, minor but quite significant perturbations from the type A structure arise. In type C, involving larger organic halogens (X) and smaller inorganic halogens (X′), stronger halogen bonds are formed with a type II halogen–halogen interaction geometry (C? X???X′ ≈180°; X???X′? M ≈110°) that is electrostatically attractive. The halogen bonds play a major role alongside hydrogen bonds in directing the type C structures, which as a result are quite different from type A and B.     

Selective C−H Halogenation with a Highly Fluorinated Manganese Porphyrin

The selective C?H functionalization of aliphatic molecules remains a challenge in organic synthesis. While radical chain halogenation reactions provide efficient access to many halogenated molecules, the use of typical protocols for the selective halogenation of electron‐deficient and strained aliphatic molecules is rare. Herein, we report selective C?H chlorination and fluorination reactions promoted by an electron‐deficient manganese pentafluorophenyl porphyrin catalyst, Mn(TPFPP)Cl. This catalyst displays superior properties for the aliphatic halogenation of recalcitrant, electron‐deficient, and strained substrates with unique regio‐ and stereoselectivity. UV/Vis analysis during the course of the reaction indicated that an oxo‐Mn^V species is responsible for hydrogen‐atom abstraction. The observed stereoselectivity results from steric interactions between the bulky porphyrin ligand and the intermediate substrate radical in the halogen rebound step.     

Polysaccharide‐based chiral stationary phases as halogen bond acceptors: A novel strategy for detection of stereoselective σ‐hole bonds in solution

In the last few years, halogen bonds have been exploited in a variety of research areas both in the solid state and in solution. Nevertheless, several factors make formation and detection of halogen bonds in solution challenging. Moreover, to date, few chiral molecules containing electrophilic halogens as recognition sites have been reported. Recently, we described the first series of halogen‐bond‐driven enantioseparations performed on cellulose tris(3,5‐dimethylphenylcarbamate) by high‐performance liquid chromatography. Herein the performances of amylose tris(3,5‐dimethylphenylcarbamate) as halogen bond acceptor were also investigated and compared with respect to cellulose tris(3,5‐dimethylphenylcarbamate). With the aim to explore the effect of polysaccharide backbone on the enantioseparations, the thermodynamic parameters governing the halogen‐dependent enantioseparations on both cellulose and amylose polymers were determined by a study at variable temperature and compared. Molecular dynamics were performed to model the halogen bond in polysaccharide‐analyte complexes. Chiral halogenated 4,4′‐bipyridines were used as test compounds (halogen bond donors). On this basis, a practical method for detection of stereoselective halogen bonds in solution was developed, which is based on the unprecedented use of high‐performance liquid chromatography as technical tool with polysaccharide polymers as molecular probes (halogen bond acceptors). The analytical strategy showed higher sensitivity for the detection of weak halogen bonds.     

“Anti‐Electrostatic” Halogen Bonding

Halogen bonding is often described as being driven predominantly by electrostatics, and thus adducts between anionic halogen bond (XB) donors (halogen‐based Lewis acids) and anions seem counterintuitive. Such “anti‐electrostatic” XBs have been predicted theoretically but for organic XB donors, there are currently no experimental examples except for a few cases of self‐association. Reported herein is the synthesis of two negatively charged organoiodine derivatives that form anti‐electrostatic XBs with anions. Even though the electrostatic potential is universally negative across the surface of both compounds, DFT calculations indicate kinetic stabilization of their halide complexes in the gas phase and particularly in solution. Experimentally, self‐association of the anionic XB donors was observed in solid‐state structures, resulting in dimers, trimers, and infinite chains. In addition, co‐crystals with halides were obtained, representing the first cases of halogen bonding between an organic anionic XB donor and a different anion. The bond lengths of all observed interactions are 14–21 % shorter than the sum of the van der Waals radii.     

Computational design of S‐nitrosothiol “click” reactions

To address a long‐standing problem of finding efficient reactions for chemical labeling of protein‐based S‐nitrosothiols (RSNOs), we computationally explored hitherto unknown (3+2) cycloaddition RSNO reactions with alkynes and alkenes. Nonactivated RSNO cycloaddition reactions have high activation enthalpy (>20 kcal/mol at the CBS‐QB3 level) and compete with alternative S—N bond insertion pathway. However, the (3+2) cycloaddition reaction barriers can be dramatically lowered by coordination of a Lewis acid to the N atom of the —SNO group. To exploit this effect, we propose to use reagents with Lewis acid and a strain‐activated carbon–carbon multiple bond linked by a rigid scaffold, which can react with RSNOs with small activation enthalpies (～5 kcal/mol) and high reaction exothermicities (～40 kcal/mol). The proposed efficient RSNO cycloaddition reactions can be used for future development of practical RSNO labeling reactions. © 2013 Wiley Periodicals, Inc.     

2,3,17,18‐Tetrahalohexaphyrins and the First Phlorin‐type Hexaphyrins

1‐(Triisopropylsilyl)‐3,4‐dichloropyrrole and 1‐(triisopropylsilyl)‐3,4‐difluoropyrrole were conveniently prepared from the corresponding 3,4‐dibromopyrrole by lithiation followed by halogenation. 2,3,17,18‐Tetrahalogeno [26]‐ and [28]hexaphyrins have been prepared by condensation of 3,4‐dihalopyrroles and a dipyrromethane‐dicarbinol. 2,3,17,18‐Tetrahalogenated hexaphyrins display variable structural and electronic properties depending upon the halogen atom and the number of π‐electrons. Tetrabromo[28]hexaphyrin and tetrachloro[28]hexaphyrin were further reduced with excess NaBH₄ to furnish meso‐reduced hexaphyrins as the first example of phlorin‐type meso‐aryl‐substituted hexaphyrins.     

Aromatic Superhalogens

No organic molecules with electron affinities near or above those of halogens are known. We show for the first time that aromaticity rules can be used to design molecules with electron affinities far exceeding those of halogen atoms either by tailoring the ligands of cyclopentadienyl or by multiple benzoannulations of cyclopentadienyl in conjunction with the substitution of CH groups with isoelectronic N atoms. Results based on density functional theory revealed that the electron affinities of some of these organic molecules can reach as high as 5.59 eV, thus opening the door to new class of superhalogens that contain neither a metal nor a halogen atom.     

Haloaza‐closo‐dodecaboranes

The bromo‐ and iodoaza‐closo‐dodecaboranes HNB₁₁H₁₀Hal (Hal = Br, I), MeNB₁₁H₉Br₂, and MeNB₁₁H₈Br₃ are formed from [NB₁₁H₁₁]^– and MeNB₁₁H₁₁, respectively, by electrophilic halogenation with elementary halogen in the presence of acidic catalysts. Hydrogen in para‐ or in para‐ and meta‐position with respect to the cluster‐N atom is substituted by halogen. With iodine chloride as halogenation agent, all the 11 boron bound H atoms of MeNB₁₁H₁₁ are substituted to give HNB₁₁Cl₅I₆ with iodine in the para‐ and meta‐ and chlorine in the ortho‐positions, presumably via electrophilic (I) and nucleophilic substitution (Cl). The products are characterized by their NMR spectra, the product HNB₁₁Cl₅I₆ also by crystal structure analysis.     

Halogen bonding: a theoretical study based on atomic multipoles derived from quantum theory of atoms in molecules

Atomic multipole moments derived from quantum theory of atoms in molecules are used to study halogen bonds in dihalogens (with general formula YX, in which X refers to the halogen directly interacted with the Lewis base) and some molecules containing C–X group. Multipole expansion is used to calculate the electrostatic potential in a vicinity of halogen atom (which is involved in halogen bonding) in terms of atomic monopole, dipole, and quadrupole moments. In all the cases, the zz component of atomic traceless quadrupole moments (where z axis taken along Y–X or C–X bonds) of the halogens plays a stabilizing role in halogen bond formation. The effects of atomic monopole and dipole moments on the formation of a halogen bond in YX molecules depend on Y and X atoms. In Br₂ and Cl₂, the monopole moment of halogens is zero and has no contribution in electrostatic potential and hence in halogen bonding, while in ClBr, FBr, and FCl it is positive and therefore stabilize the halogen bonds. On the other hand, the negative sign of dipole moment of X in all the YX molecules weakens the corresponding halogen bonds. In the C–X-containing molecules, monopole and dipole moments of X atom are negative and consequently destabilize the halogen bonds. So, in these molecules the quadrupole moment of X atom is the only electrostatic term which strengthens the halogen bonds. In addition, we found good linear correlations between halogen bonds strength and electrostatic potentials calculated from multipole expansion.     

Stereoselective Halogenation in Natural Product Synthesis

At last count, nearly 5000 halogenated natural products have been discovered. In approximately half of these compounds, the carbon atom to which the halogen is bound is sp³‐hybridized; therefore, there are an enormous number of natural products for which stereocontrolled halogenation must be a critical component of any synthesis strategy. In this Review, we critically discuss the methods and strategies used for stereoselective introduction of halogen atoms in the context of natural product synthesis. Using the successes of the past, we also attempt to identify gaps in our synthesis technology that would aid the synthesis of halogenated natural products, as well as existing methods that have not yet seen application in complex molecule synthesis. The chemistry described herein demonstrates yet again how natural products continue to provide the inspiration for critical advances in chemical synthesis.     

Synthesis and Crystal Structures of Neutral Complexes of Tellurium(IV) – [PhTeX3L](X = Br,I; L = ethylenethiourea)

A three‐step one‐pot synthetic procedure to synthesize the neutral tellurium(IV) coordination compounds PhTeX₃L (X = Br, I and L = ethylenethiourea) has been developed and is described in this article. Oxidative halogenation of PhTeTePh in methanol generates the tellurium(II) derivative, PhTeX, which is subsequently complexed with ethylenethiourea, and, finally, further oxidative addition of additional halogen affords the corresponding tellurium(IV) compound PhTeX₃L in good yields. The final product was obtained by the slow evaporation of the reaction mixture as black crystals. The X‐ray structural analyses of the compounds show Te···X and X···X secondary interactions in the solid state and suggest a weak dependence of the formation of supramolecular assemblies on the nature of the halogen bonded to the tellurium atom.     

卤过氧化物酶在绿色卤化反应中的研究进展

卤化反应是一类极其重要的有机合成反应,在实验室研究和化工生产领域占据重要地位.传统卤化反应因存在使用有毒有害试剂、反应缺乏选择性等问题而亟待改进,生物酶催化策略则为突破上述瓶颈提供了可能.自然界已经进化出多种可对有机物中催化引入卤素的卤化酶.酶催化卤化反应的突出优势在于常温常压下,可使用来源温和的卤素进行高效的催化反应.催化范围包括卤化、羟卤化、卤环合和氧化脱羧等多种具有挑战性的反应.鉴于酶催化卤化反应展示出巨大的潜力,从催化活性、酶稳定性、底物浓度、催化范围等几个方面着重介绍了卤过氧化物酶在绿色卤化反应中的最新研究进展,为进一步开发绿色的卤化酶催化卤化反应提供参考.     

Cyclic Haloiodanes: Syntheses,Applications and Fundamental Studies

Hypervalent iodine reagents are powerful tools in contemporary organic synthesis. They have found numerous applications in modern oxidative transformations. The unique reactivity of hypervalent iodine allows access to unconventional electrophilic synthons. For example, electrophilic halogenation chemistry has been greatly expanded by the study of various haloiodanes. Cyclic λ³-haloiodanes are versatile reagents which can promote reactions such as halogenations, halocyclizations and oxidations. Their peculiar reactivity sets them apart from traditional sources of electrophilic halogens. Furthermore, they offer a broad range of reactivities which have been exploited in more diversified transformations. This review summarizes the different syntheses and derivatives of these cyclic haloiodanes, their applications and mechanistic insights as well as the relevant computational, structural and kinetic studies.     

Some measures for mediating the strengths of halogen bonds with the B–B bond in diborane(4) as an unconventional halogen acceptor

A series of halogen‐bonded complexes with diborane(4) 1 and its derivatives (Li 2 , methyl 3 , CN 4 ) as the halogen acceptors as well as with XCN, XCCH, XCF₃, XF (X = Cl, Br, I) as the halogen donors have been investigated by means of quantum chemical calculations at the MP2/aug‐cc‐pVTZ level. The result shows that the B?B bond is a good electron donor in halogen bonding, particularly for the halogen donor XF. Interestingly, for the halogen donor XF, the halogen bond becomes stronger in order of IF < BrF < ClF. It is found that the addition of electron‐donating substituents greatly strengthens the halogen bonding interaction to the point where it exceeds that of the majority of H‐bonds. When the N atom in 2 ‐BrCN is combined with another interaction, its strength has a further increase due to the cooperative effect. This study combines the boron compounds with halogen bonds and would be significant for expanding their applied fields. © 2013 Wiley Periodicals, Inc.     

Preparation of halogenated derivatives of thiazolo[5,4‐d]thiazole via direct electrophilic aromatic substitution

Chlorination and bromination reactions of thiazolo[5,4‐d]thiazole led to the generation of its mono‐ and dihalogenated derivatives. These are the first instances of successful direct electrophilic aromatic substitution in the thiazolo[5,4‐d]thiazole ring system. X‐ray analysis demonstrates that both 2‐bromothiazolo[5,4‐d]‐thiazole and 2,5‐dibromothiazolo[5,4‐d]thiazole are planar structures, with strongly manifested π‐stacking in the solid state. Theoretical analysis of the pyridine‐catalyzed halogenation (MP2/6‐31+G(d) and B3LYP/6‐31+G(d) calculations) reveals that introduction of one halogen actually leads to a slightly enhanced reactivity towards further halogenation. Several halogenation mechanisms have been investigated: 1) The direct C‐halogenation with N‐halopyridine as electrophile; 2) C‐halogenation via intermediate N‐halogenation, and 3) C‐halogenation following an addition ‐ elimination pathway, with intermediate formation of a cyclic halonium ion. The theoretical studies suggest that the direct C‐halogenation is the favored mechanism.     

Competition between hydrogen and halogen bonding in halogenated 1‐methyluracil: Water systems

The competition between hydrogen‐ and halogen‐bonding interactions in complexes of 5‐halogenated 1‐methyluracil (XmU; X = F, Cl, Br, I, or At) with one or two water molecules in the binding region between C5‐X and C4?O4 is investigated with M06‐2X/6‐31+G(d). In the singly‐hydrated systems, the water molecule forms a hydrogen bond with C4?O4 for all halogens, whereas structures with a halogen bond between the water oxygen and C5‐X exist only for X = Br, I, and At. Structures with two waters forming a bridge between C4?O and C5‐X (through hydrogen‐ and halogen‐bonding interactions) exist for all halogens except F. The absence of a halogen‐bonded structure in singly‐hydrated ClmU is therefore attributed to the competing hydrogen‐bonding interaction with C4?O4. The halogen‐bond angle in the doubly‐hydrated structures (150–160°) is far from the expected linearity of halogen bonds, indicating that significantly non‐linear halogen bonds may exist in complex environments with competing interactions. © 2016 Wiley Periodicals, Inc.     

Direct through anionic,cationic, and radical active species: Terminal carbon–halogen bond for “controlled”/living polymerizations of styrene

In this work, we examined the synthesis of novel block (co)polymers by mechanistic transformation through anionic, cationic, and radical living polymerizations using terminal carbon–halogen bond as the dormant species. First, the direct halogenation of growing species in the living anionic polymerization of styrene was examined with CCl₄ to form a carbon–halogen terminal, which can be employed as the dormant species for either living cationic or radical polymerization. The mechanistic transformation was then performed from living anionic polymerization into living cationic or radical polymerization using the obtained polymers as the macroinitiator with the SnCl₄/n‐Bu₄NCl or RuCp^*Cl(PPh₃)/Et₃N initiating system, respectively. Finally, the combination of all the polymerizations allowed the synthesis block copolymers including unprecedented gradient block copolymers composed of styrene and p‐methylstyrene. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 465–473