Derivatization of Undecahalogenated -Dodecaborates [BXNH] (X = F-I): Attaching Isocyanate, Amidinium, and Formamide Functionalities.

Halogenated -dodecaborates are very robust and versatile weakly coordinating anions for numerous applications. The introduction of additional substituents, e.g.

Generation and reactivity of the fragment ion [BIS(CN)] in the gas phase and on surfaces.

Gaseous fragment ions generated in mass spectrometers may be employed as "building blocks" for the synthesis of novel molecules on surfaces using ion soft-landing. A fundamental understanding of the reactivity of the fragment ions is required to control bond formation of deposited fragments in surface layers. The fragment ion [BX] (X = halogen) is formed by collision-induced dissociation (CID) from the precursor [BX] dianion.

Binding Properties of Small Electrophilic Anions [B X ] and [B X ] (X=Cl, Br, I): Activation of Small Molecules Based on π-Backbonding.

Superelectrophilic anions constitute a special class of molecular anions that show strong binding of weak nucleophiles despite their negative charge. In this study, the binding characteristics of smaller gaseous electrophilic anions of the types [B X ] and [B X ] (with X=Cl, Br, I) were computationally and experimentally investigated and compared to those of the larger analogues [B X ] . The positive charge of vacant boron increases from [B X ] via [B X ] to [B X ] , as evidenced by increasing attachment enthalpies towards typical σ-donor molecules (noble gases, H O).

Binding of saturated and unsaturated C-hydrocarbons to the electrophilic anion [BBr]: a systematic mechanistic study.

The highly reactive gaseous ion [BBr] is a metal-free closed-shell anion which spontaneously forms covalent bonds with hydrocarbon molecules, including alkanes. Herein, we systematically investigate the reaction mechanism for binding of [BBr] to the five hexane isomers yielding [BBr(CH)], as well as to cyclohexane and several hexene isomers (yielding [BBr(CH)]) using collision-induced dissociation (CID), infrared photodissociation spectroscopy (IRPD) and computational methods. CID of the different [BBr(CH)] ions results in distinct fragmentation patterns dependent on the structure of the hexane isomer.

Anion-Anion Chemistry with Mass-Selected Molecular Fragments on Surfaces.

While reactions between ions and neutral molecules in the gas phase have been studied extensively, reactions between molecular ions of same polarity remain relatively unexplored. Herein we show that reactions between fragment ions generated in the gas phase and molecular ions of the same polarity are possible by soft-landing of both reagents on surfaces. The reactive [B I ] anion was deposited on a surface layer built up by landing the generally unreactive [B I ] .

Relevance of π-Backbonding for the Reactivity of Electrophilic Anions [B X ] (X=F, Cl, Br, I, CN).

Electrophilic anions of type [B X ] posses a vacant positive boron binding site within the anion. In a comparatitve experimental and theoretical study, the reactivity of [B X ] with X=F, Cl, Br, I, CN is characterized towards different nucleophiles: (i) noble gases (NGs) as σ-donors and (ii) CO/N as σ-donor-π-acceptors. Temperature-dependent formation of [B X NG] indicates the enthalpy order (X=CN)>(X=Cl)≈(X=Br)>(X=I)≈(X=F) almost independent of the NG in good agreement with calculated trends.

Gaseous cyclodextrin--dodecaborate complexes χCD·BX (χ = α, β, and γ; X = F, Cl, Br, and I): electronic structures and intramolecular interactions.

A fundamental understanding of cyclodextrin-closo-dodecaborate inclusion complexes is of great interest in supramolecular chemistry. Herein, we report a systematic investigation on the electronic structures and intramolecular interactions of perhalogenated closo-dodecaborate dianions B12X122- (X = F, Cl, Br and I) binding to α-, β-, and γ-cyclodextrins (CDs) in the gas phase using combined negative ion photoelectron spectroscopy (NIPES) and density functional theory (DFT) calculations. The vertical detachment energy (VDE) of each complex and electronic stabilization of each dianion due to the CD binding (ΔVDE, relative to the corresponding isolated B12X122-) are determined from the experiments along α-, β- and γ-CD in the form of VDE (ΔVDE): 4.

Activation of CS and CO by Silylium Cations.

The hydride-bridged silylium cation [Et Si-H-SiEt ] , stabilized by the weakly coordinating [Me NB Cl ] anion, undergoes, in the presence of excess silane, a series of unexpected consecutive reactions with the valence-isoelectronic molecules CS and CO . The final products of the reaction with CS are methane and the previously unknown [(Et Si) S] cation. To gain insight into the entire reaction cascade, numerous experiments with varying conditions were performed, intermediate products were intercepted, and their structures were determined by X-ray crystallography.

Synthesis, Electronic Properties and Reactivity of [B X (NO )] (X=F-I) Dianions.

Nitro-functionalized undecahalogenated closo-dodecaborates [B X (NO )] were synthesized in high purities and characterized by NMR, IR, and Raman spectroscopy, single crystal X-diffraction, mass spectrometry, and gas-phase ion vibrational spectroscopy. The NO substituent leads to an enhanced electronic and electrochemical stability compared to the parent perhalogenated [B X ] (X=F-I) dianions evidenced by photoelectron spectroscopy, cyclic voltammetry, and quantum-chemical calculations. The stabilizing effect decreases from X=F to X=I.

Direct functionalization of C-H bonds by electrophilic anions.

Alkanes and [BX] (X = Cl, Br) are both stable compounds which are difficult to functionalize. Here we demonstrate the formation of a boron-carbon bond between these substances in a two-step process. Fragmentation of [BX] in the gas phase generates highly reactive [BX] ions which spontaneously react with alkanes.

Properties of gaseous closo-[BX] dianions (X = Cl, Br, I).

Electronic structure, collision-induced dissociation (CID) and bond properties of closo-[BX] (X = Cl-I) are investigated in direct comparison with their closo-[BX] analogues. Photoelectron spectroscopy (PES) and theoretical investigations reveal that [BX] dianions are electronically significantly less stable than the corresponding [BX] species. Although [BCl] is slightly electronically unstable, [BBr] and [BI] are intrinsically stable dianions.

First steps towards a stable neon compound: observation and bonding analysis of [B(CN)Ne].

Noble gas (Ng) containing molecular anions are much scarcer than Ng containing cations. No neon containing anion has been reported so far. Here, the experimental observation of the molecular anion [B(CN)Ne] and a theoretical analysis of the boron-neon bond is reported.

[Se(CHC(O)CH)][BFNH]: The first selenium cation with three β-ketone substituents.

The reaction of [Se][BFNH] with acetone and subsequent crystallization from acetone/diethyl ether yielded the selenium cation [Se(CHC(O)CH)] as a by-product, which is stabilized by the weakly coordinating undeca-fluorinated anion [BFNH]. While attempting to crystallize pure [Se][BFNH], the structure of the isolated product, namely, tris-(2-oxoprop-yl)selenium 1-ammonio-undeca-fluoro-dodeca-borate, was surprising. The cation [Se(CHC(O)CH)] represents the first example for a cationic selenium compound with three ketone functional groups located in the β-position with respect to the selenium atom.

Na[MeNBCl]·SO: a rare example of a sodium-SO complex.

In the title compound, Na[MeNBCl]·SO [systematic name: sodium 1-(trimethylammonio)-undeca-chloro--dodeca-borate sulfur dioxide], the SO mol-ecule is --coordinated to the Na cation. Surprisingly, the SO mol-ecule is more weakly bound to sodium than is found in other sodium-SO complexes and the SO mol-ecule is essentially undistorted compared to the structure of free SO. The Na cation has a coordination number of eight in a distorted twofold-capped trigonal prism and makes contacts to three individual boron cluster anions, resulting in an overall three-dimensional network.

Rational design of an argon-binding superelectrophilic anion.

Chemically binding to argon (Ar) at room temperature has remained the privilege of the most reactive electrophiles, all of which are cationic (or even dicationic) in nature. Herein, we report a concept for the rational design of anionic superelectrophiles that are composed of a strong electrophilic center firmly embedded in a negatively charged framework of exceptional stability. To validate our concept, we synthesized the percyano-dodecoborate [B(CN)], the electronically most stable dianion ever investigated experimentally.

Self-organizing layers from complex molecular anions.

The formation of traditional ionic materials occurs principally via joint accumulation of both anions and cations. Herein, we describe a previously unreported phenomenon by which macroscopic liquid-like thin layers with tunable self-organization properties form through accumulation of stable complex ions of one polarity on surfaces. Using a series of highly stable molecular anions we demonstrate a strong influence of the internal charge distribution of the molecular ions, which is usually shielded by counterions, on the properties of the layers.

Electronic Structure and Stability of [BX] (X = F-At): A Combined Photoelectron Spectroscopic and Theoretical Study.

The stability and electron loss process of numerous multiply charged anions (MCAs) have been traditionally explained in terms of the classical Coulomb interaction between spatially separated charged groups. An understanding of these processes in MCAs with not well-separated excess charges is still lacking. We report the surprising properties and physical behavior of [BX], X = F, Cl, Br, I, At, which are MCAs with not well-separated excess charges and cannot be described by the prevailing classical picture.

The First Step of the Oxidation of Elemental Sulfur: Crystal Structure of the Homopolyatomic Sulfur Radical Cation [S ].

The oxidation of elemental sulfur in superacidic solutions and melts is one of the oldest topics in inorganic main group chemistry. Thus far, only three homopolyatomic sulfur cations ([S ] , [S ] , and [S ] ) have been characterized crystallographically although ESR investigations have given evidence for the presence of at least two additional homopolyatomic sulfur radical cations in solution. Herein, the crystal structure of the hitherto unknown homopolyatomic sulfur radical cation [S ] is presented.

Superelectrophilic Behavior of an Anion Demonstrated by the Spontaneous Binding of Noble Gases to [B Cl ].

It is common and chemically intuitive to assign cations electrophilic and anions nucleophilic reactivity, respectively. Herein, we demonstrate a striking violation of this concept: The anion [B Cl ] spontaneously binds to the noble gases (Ngs) xenon and krypton at room temperature in a reaction that is typical of "superelectrophilic" dications. [B Cl Ng] adducts, with Ng binding energies of 80 to 100 kJ mol , contain B-Ng bonds with a substantial degree of covalent interaction.

Reaction of the Tricyanoborate Dianion [B(CN)] with HgCl.

The very reactive [B(CN)] dianion has a strongly nucleophilic boron atom and can be used for the synthesis of tricyanoborates, which otherwise are difficult to access. Herein the reaction of this anion with HgCl is reported. The main product is the anionic mercury complex [Hg(B(CN))].

Improving the Solubility of Halogenated 1-Ammonio-closo-dodecaborate Anions.

The partly halogenated and N-alkylated closo-dodecaborates [BClHN(propyl)] and [BBrHNR] (R = ethyl-pentyl) were prepared by alkylation of [BHNH] and subsequent halogenation with elemental chlorine or N-bromosuccinimide. Simple metathesis reactions yielded the [HNMe], [Cmim], [NBu], and Na salts, which were characterized by heteronuclear NMR and IR spectroscopy as well as electrospray ionization mass spectrometry. The crystal structures of the salts [HNMe][BBrHN(ethyl)]·CHCN, [HNMe][BBrHN(propyl)], Na[BBrHN(butyl)], and [HNMe][BClHN(propyl)]·CHCN were determined by single-crystal X-ray diffraction.

The Me NB Cl Radical: A Strong One-Electron Oxidizing Agent.

Strong oxidizing agents often contain fluorine and are not compatible with substrates forming strong element-fluorine bonds. Therefore, there is need for new strong oxidizers. Cyclic voltammetric measurements on the weakly coordinating anion [Me NB Cl ] in liquid SO revealed an oxidation wave at +2.

Evidence for an intrinsic binding force between dodecaborate dianions and receptors with hydrophobic binding pockets.

A gas phase binding study revealed strong intrinsic intermolecular interactions between dianionic halogenated closo-dodecaborates [B12X12](2-) and several neutral organic receptors. Oxidation of a tetrathiafulvalene host allowed switching between two host-guest binding modes in a supramolecular complex. Complexes of β-cyclodextrin with [B12F12](2-) show remarkable stability in the gas phase and were successfully tested as carriers for the delivery of boron clusters into cancer cells.

Theoretical and Synthetic Study on the Existence, Structures, and Bonding of the Halide-Bridged [B2X7](-) (X = F, Cl, Br, I) Anions.

While hydrogen bridging is very common in boron chemistry, halogen bridging is rather rare. The simplest halogen-bridged boron compounds are the [B2X7](-) anions (X = F, Cl, Br, I), of which only [B2F7](-) has been reported to exist experimentally. In this paper a detailed theoretical and synthetic study on the [B2X7](-) anions is presented.

Alkoxy substituted halogenated closo-dodecaborates as anions for ionic liquids.

Halogenated and alkoxylated closo-dodecaborates [B12X11OR](2-) (X = Cl, Br; R = propyl, octyl, dodecyl) have been synthesized by halogenation of the known [B12H11OH](2-) anion followed by alkylation in the superbasic medium DMSO/KOH. The obtained sodium salts were transformed by simple metathesis reactions in aqueous solution to the tetrabutylammonium ([NBu4](+)) and 1-hexyl-3-methylimidazolium ([C6mim](+)) salts. All compounds were fully characterized by heteronuclear NMR, IR and Raman spectroscopy, ESI mass spectrometry, and thermal analytical measurements.