The Na⋅⋅⋅B Bond in NaBH3−: A Different Type of Bond

A newly introduced Na−B bond in NaBH₃⁻ has been a challenge for the chemical bonding community. Here, a series of MBH₃⁻ (M=Li, Na, K) species and NaB(CN)₃⁻ are studied within the context of quantum chemical topology approaches. The analyses suggest that M–B interaction cannot be classified as an ordinary covalent, dative, or even simple ionic interaction. The interactions are controlled by coulombic forces between the metals and the substituents on boron, for example, H or CN, more than the direct M–B interaction. On the other hand, while the characteristics of the (3, −1) critical points of the bonds are comparable to weak hydrogen bonds, not covalent bonds, the metal and boron share a substantial sum of electrons. To the best of the author's knowledge, the characteristics of these bonds are unprecedented among known molecules. Considering all paradoxical properties of these bonds, they are herein described as ionic-enforced covalent bonds.     

PCM Study of Bond Dissociation Energies of the S–NO Bond: A DFT Study

Quantum chemical calculations are used to estimate the equilibrium S–NO bond dissociation energies (BDEs) for seven S-nitro-N-acetyl-d,l-penicillamine dipeptides (SNAP-two peptides) in acetonitrile solution. These compounds were studied by employing the hybrid density functional theory (B3LYP, B3P86 and B3PW91) methods together with the 6-31G** basis set. The obtained results are compared with available experimental results. It is demonstrated that B3PW91 method is the best method to compute the bond dissociation energies of SNAP-two peptides. The substituent and solvent effects of the S–NO BDEs are further analyzed. The results show that S–NO BDE increases with the increment of isoelectric points of substituted groups. In addition, the S–NO BDE decreases due to the inclusion of solvent effects. Furthermore, SNAP-two peptides and the other NO-donors are compared.     

Aliphatic Phosphenium Canon Featuring A P-S Bond

ThefirstStablephOSphenlU门nCatlonWaSfoUndlfl1972．TheirCXteflslVeCheffilstTyWererespectivelyreviewedbyCowley－In1985andbySanchez三In1990．RecentInteresthasfocusedontheroleoffunctlonalllzatlonofthephosphoruscenterInthestabllltvandreactlvlty‘－”．yur...     

Macrocyclic β-Sheets Stabilized by Hydrogen Bond Surrogates

Mimics of protein secondary and tertiary structure offer rationally-designed inhibitors of biomolecular interactions. β-Sheet mimics have a storied history in bioorganic chemistry and are typically designed with synthetic or natural turn segments. We hypothesized that replacement of terminal inter-β-strand hydrogen bonds with hydrogen bond surrogates (HBS) may lead to conformationally-defined macrocyclic β-sheets without the requirement for natural or synthetic β-turns, thereby providing a minimal mimic of a protein β-sheet. To access turn-less antiparallel β-sheet mimics, we developed a facile solid phase synthesis protocol. We surveyed a dataset of protein β-sheets for naturally observed interstrand side chain interactions. This bioinformatics survey highlighted an over-abundance of aromatic–aromatic, cation-π and ionic interactions in β-sheets. In correspondence with natural β-sheets, we find that minimal HBS mimics show robust β-sheet formation when specific amino acid residue pairings are incorporated. In isolated β-sheets, aromatic interactions endow superior conformational stability over ionic or cation-π interactions. Circular dichroism and NMR spectroscopies, along with high-resolution X-ray crystallography, support our design principles.     

Convenient Synthesis of Host Molecule Containing Se-Se Bond

OrganoseleniumcompoundscontaininganSe-Sebondareofparticularinterest1-3.In1990,ShujiTomodaandco-workerfirstlysynthesizedaclassofcrown-ethertypehostmoleculesintowhichtheSe-Sebondsareincorporated.Thisndghtprovideauniqueopportunityforanewmoleculardevice,whichwouldactasacatalystinaphotochendcallyinducedredoxcycleorundergoselectivemembranetransportofspecificmetalionsunderlightirradiation.Inthispaper,aconvenientapproachtosynthesizethiskindofmoleculewasreported.Thehostmoleculewhichwassynthesizedcon…     

Can Dative Bond Between Two Anions Possible?

Formation of a genuine chemical bond between two similarly charged fragments is beyond expectation. Any such interaction generally lies in the realm of non-covalent interaction. Herein, formation of a strong dative covalent bond between two anionic fragments is reported for the first time. Calculation using ab initio coupled cluster theory reveals the formation of an unprecedented strong H₃Be⁻←X⁻ (X⁻=CH₃⁻, CN⁻, OH⁻, F⁻) dative covalent bond. The calculated bond dissociation energies in polar solvents are significant, which indicates the possibility of their experimental realization.     

Carbon Monoxide Activation by a Molecular Aluminium Imide: C−O Bond Cleavage and C−C Bond Formation

Anionic molecular imide complexes of aluminium are accessible via a rational synthetic approach involving the reactions of organo azides with a potassium aluminyl reagent. In the case of K₂[( NON )Al(NDipp)]₂ ( NON =4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethyl-xanthene; Dipp=2,6-diisopropylphenyl) structural characterization by X-ray crystallography reveals a short Al−N distance, which is thought primarily to be due to the low coordinate nature of the nitrogen centre. The Al−N unit is highly polar, and capable of the activation of relatively inert chemical bonds, such as those found in dihydrogen and carbon monoxide. In the case of CO, uptake of two molecules of the substrate leads to C−C coupling and C≡O bond cleavage. Thermodynamically, this is driven, at least in part, by Al−O bond formation. Mechanistically, a combination of quantum chemical and experimental observations suggests that the reaction proceeds via exchange of the NR and O substituents through intermediates featuring an aluminium-bound isocyanate fragment.     

Nickel-Catalyzed Suzuki-Miyaura Cross-Coupling Involving C−O Bond Activation

An efficient Suzuki-Miyaura cross-coupling reaction of ortho-phenoxy-substituted aromatic amides with aryl boronates is described. The use of LiO^tBu is crucial for the success of the reaction. An amidate anion, which is formed through deprotonation of the amide NH bond by LiO^tBu, functions as a directing group to activate a C−O bond.     

π-Acceptor induced thermal reactions: Bond cleavage reactions

TCNQ, TCNQF4, and DDQ have been found to initiate unusual bond breakage reactions. Benzylphenyl sulfide (BPS) and benzylphenyl ether (BPE) undergo cleavage of their interaryl bonds while bibenzyl (BB) does not cleave the interaryl bond and forms only trans-stilbene (TS) when reacted under the same conditions.     

New Organotin Compounds Including a Tin–Zinc Bond

Abstract

The reaction of dialkyltinhydrides with dialkylzinc results in a tin metal bond formation. Crystal structures of 1,1,1,2,3,3,3-hepta-phenyl-2-(ethylzincio)tristannane *TMEDA 1, 1,1,2,2,3,3,4,4-octaphenyl-1,4-(ethylzincio)tetrastannane*2TMEDA 2, and triphenyl(phenylzincio)stannane*TMEDA 3 could be obtained.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

GRAPHICAL ABSTRACT     

Synthetic Advantages of Defluorinative C−F Bond Functionalization

Much progress has been made in the development of methods to both create compounds that contain C−F bonds and to functionalize C−F bonds. As such, C−F bonds are becoming common and versatile synthetic functional handles. This review summarizes the advantages of defluorinative functionalization reactions for small molecule synthesis. The coverage is organized by the type of carbon framework the fluorine is attached to for mono- and polyfluorinated motifs. The main challenges, opportunities and advances of defluorinative functionalization are discussed for each class of organofluorine. Most of the text focuses on case studies that illustrate how defluorofunctionalization can improve routes to synthetic targets or how the properties of C−F bonds enable unique mechanisms and reactions. The broader goal is to showcase the opportunities for incorporating and exploiting C−F bonds in the design of synthetic routes, improvement of specific reactions and advent of new methods.     

ChemInform Abstract: How Strong Is the GalliumGallium Triple Bond? Theoretical Compliance Matrices as a Probe for Intrinsic Bond Strengths.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

An Efficient Synthesis of Cyclopeptides Bridged with Aliphatic-aryl Ether Bond

Based on the pseudo-dilution effect (PDE) on solid support, three cyclopeptides with an aliphatic-aryl ether bond as the bridge were synthesized via SN2 reaction between bromoacetylated at N-terminal and the phenol -OH group in C-terminal Tyr residue. All the products were obtained in good overall yields and characterized by related analytic data.     

An Analytical Bond Order Potential for Mg−H Systems

Magnesium-based materials provide some of the highest capacities for solid-state hydrogen storage. However, efforts to improve their performance rely on a comprehensive understanding of thermodynamic and kinetic limitations at various stages of (de)hydrogenation. Part of the complexity arises from the fact that unlike interstitial metal hydrides that retain the same crystal structures of the underlying metals, MgH₂ and other magnesium-based hydrides typically undergo dehydrogenation reactions that are coupled to a structural phase transformation. As a first step towards enabling molecular dynamics studies of thermodynamics, kinetics, and (de)hydrogenation mechanisms of Mg-based solid-state hydrogen storage materials with changing crystal structures, we have developed an analytical bond order potential for Mg−H systems. We demonstrate that our potential accurately reproduces property trends of a variety of elemental and compound configurations with different coordinations, including small clusters and bulk lattices. More importantly, we show that our potential captures the relevant (de)hydrogenation chemical reactions 2H (gas)→H₂ (gas) and 2H (gas)+Mg (hcp)→MgH₂ (rutile) within molecular dynamics simulations. This verifies that our potential correctly prescribes the lowest Gibbs free energies to the equilibrium H₂ and MgH₂ phases as compared to other configurations. It also indicates that our molecular dynamics methods can directly reveal atomic processes of (de)hydrogenation of the Mg−H systems.     

N?O Bond as a Glycosidic‐Bond Surrogate: Synthetic Studies Toward Polyhydroxylated N‐Alkoxypiperidines

A series of novel polyhydroxylated N‐alkoxypiperidines has been synthesized by ring‐closing double reductive amination (DRA) of highly functionalized 1,5‐dialdehydes with various hydroxylamines. The required saccharide‐based dialdehydes were prepared efficiently from sodium cyclopentadienylide in seven steps. A two‐step protocol has been developed for the DRA; it led, after deprotection, to isofagomine, 3‐deoxyisofagomine, and numerous other N‐alkoxy analogues. The barrier to inversion in these polyhydroxylated N‐alkoxypiperidine derivatives was found by variable‐temperature NMR methods to be approximately 15 kcal mol^?1. With the exception of N‐hydroxyisofagomine itself, none of the compounds prepared showed significant inhibitory activity against sweet almond β‐glucosidase.     

When Is a Bond Broken? The Polarizability Perspective.

The question of when a chemical bond can be said to be broken is of fundamental chemical interest but has not been widely studied. Herein we propose that the maxima of static polarizability along bond dissociation coordinates naturally define cutoff points for bond rupture, as they represent the onset of localization of shared electron density into constituent fragments. Examples of computed polarizability maxima over the course of bond cleavage in main-group and transition metal compounds are provided, across covalent, dative and charge-shift bonds. The behavior along reaction paths is also considered. Overall, the static polarizability is found to be a sensitive reporter of electronic structure reorganization associated with bond stretching, and thus can serve as a metric for describing bond cleavage (or diagnose the absence of a chemical bond).