Functionalization of closo‐Borates via Iodonium Zwitterions

A simple method for the functionalization of closo‐borates [closo‐B₁₀H₁₀]^2? ( 1 ), [closo‐1‐CB₉H₁₀]^? ( 2 ), [closo‐B₁₂H₁₂]^2? ( 3 ), [closo‐1‐CB₁₁H₁₂]^? ( 4 ), and [3,3′‐Co(1,2‐C₂B₉H₁₁)₂]^? ( 5 ) is described. Treatment of the anions and their derivatives with ArI(OAc)₂ gave aryliodonium zwitterions, which were sufficiently stable for chromatographic purification. The reactions of these zwitterions with nucleophiles provided facile access to pyridinium, sulfonium, thiol, carbonitrile, acetoxy, and amino derivatives. The synthetic results are augmented by mechanistic considerations.     

Substituent‐Stabilized Organic Dianions in the Gas Phase and Their Potential Use as Electrolytes in Lithium‐Ion Batteries

Using density functional theory and a hybrid exchange‐correlation functional, a systematic study of the stability and electronic structure of neutral and multiply charged organic molecules, B_nC_6?nX₆ (n=0, 1, 2; X=H, F, CN) and B_nC_5?nX₅ (n=0, 1; X=H, F, CN) is performed. The results show that in addition to the aromaticity of the molecules, substituents play an important role in stabilizing the organic dianion complexes. In particular, it is demonstrated that CN groups are responsible for the stability of organic dianions as it has recently been found to be the case in B‐cage compounds such as B₁₂(CN)₁₂^2? and CB₁₁(CN)₁₂^2?. It is also shown that the stable organic dianions B₂C₄(CN)₆^2? and BC₄(CN)₅^2? might be halogen‐free electrolytes in Li‐ion batteries.     

Borane Derivatives: A New Class of Super‐ and Hyperhalogens

Super‐ and hyperhalogens are a class of highly electronegative species whose electron affinities far exceed those of halogen atoms and are important to the chemical industry as oxidizing agents, biocatalysts, and building blocks of salts. Using the well‐known Wade–Mingos rule for describing the stability of closo‐boranes B_nH_n^2? and state‐of‐the‐art theoretical methods, we show that a new class of super‐ and hyperhalogens, guided by this rule, can be formed by tailoring the size and composition of borane derivatives. Unlike conventional superhalogens, in which a central metal atom is surrounded by halogen atoms, the superhalogens formed according to the Wade–Mingos rule do not have to have either halogen or metal atoms. We demonstrate this by using B₁₂H₁₃ and its isoelectronic cluster CB₁₁H₁₂ as examples. We also show that while conventional superhalogens containing alkali atoms require at least two halogen atoms, a single borane‐like moiety is sufficient to give M(B₁₂H₁₂) clusters (M=Li, Na, K, Rb, Cs) superhalogen properties. In addition, hyperhalogens can be formed by using the above superhalogens as building blocks. Examples include M(B₁₂H₁₃)₂ and M(CB₁₁H₁₂)₂ (M=Li–Cs). This finding opens the door to an untapped source of superhalogens and weakly coordinating anions with potential applications.     

Difunctionalized {closo‐1‐CB11} Clusters: 1‐ and 2‐Amino‐12‐ethynylcarba‐closo‐dodecaborates

Carba‐closo‐dodecaborate anions with two functional groups have been synthesized via a simple two‐step procedure starting from monoamino‐functionalized {closo‐1‐CB₁₁} clusters. Iodination at the antipodal boron atom provided access to [1‐H₂N‐12‐I‐closo‐1‐CB₁₁H₁₀]^? ( 1 a ) and [2‐H₂N‐12‐I‐closo‐1‐CB₁₁H₁₀]^? ( 2 a ), which have been transformed into the anions [1‐H₂N‐12‐RC?C‐closo‐1‐CB₁₁H₁₀]^? (R=H ( 1 b ), Ph ( 1 c ), Et₃Si ( 1 d )) and [2‐H₂N‐12‐RC?C‐closo‐1‐CB₁₁H₁₀]^? (R=H ( 2 b ), Ph ( 2 c ), Et₃Si ( 2 d )) by microwave‐assisted Kumada‐type cross‐coupling reactions. The syntheses of the inner salts 1‐Me₃N‐12‐RC?C‐closo‐1‐CB₁₁H₁₀ (R=H ( 1 e ), Et₃Si ( 1 f )) and 2‐Me₃N‐12‐RC?C‐closo‐1‐CB₁₁H₁₀ (R=H ( 2 e ), Et₃Si ( 2 f )) are the first examples for a further derivatization of the new anions. All {closo‐1‐CB₁₁} clusters have been characterized by multinuclear NMR and vibrational spectroscopy as well as by mass spectrometry. The crystal structures of Cs 1 a , [Et₄N] 2 a , K 1 b , [Et₄N] 1 c , [Et₄N] 2 c , 1 e , and [Et₄N][1‐H₂N‐2‐F‐12‐I‐closo‐1‐CB₁₁H₉]?0.5 H₂O ([Et₄N ]4 a ?0.5 H₂O) have been determined. Experimental spectroscopic data and especially spectroscopic data and bond properties derived from DFT calculations provide some information on the importance of inductive and resonance‐type effects for the transfer of electronic effects through the {closo‐1‐CB₁₁} cage.     

Formation and Structure of an Anionic Ruthenaborane Compound:[Et4N][(PPh3)2ClRuB12H12]

在研究RuCl2(PPh3)3 和 closo-B10H102- 在乙醇中的反应时,意外分离得到一个阴离子型的钌硼烷化合物[Et4N][(PPh3)2ClRuB12H12], 并且经过红外光谱和单晶X射线衍射分析确证. 在其结构中,闭式B12H122-配体与Ru(II)中心通过三个B-H-Ru三中心-二电子键结合. 分析原因应是在通过文献方法制备闭式B10H102-时的少量副产物闭式B12H122-在反应体系中与RuCl2(PPh3)3反应而生成了标题化合物. 根据硼烷簇合物的电子计数规则, 标题化合物也可以看成是含有2n (n为簇顶点数)个骨架电子的pileo型簇合物, 具有加帽(capped)的闭式多面体骨架构型. 这是第一个阴离子型的含有闭式B12H122- 的钌化合物.     

ChemInform Abstract: Stability of B12(CN)122‐: Implications for Lithium and Magnesium Ion Batteries.

DFT calculations are used to calculate the binding energies of the second electron of the closo‐borane B₁₂H₁₂^2‐ and B₁₂(CN)₁₂^2‐.     

Fragmentation of the tryptophan cluster [Trp9-2H]2- induced by different activation methods

Electrospray ionization (ESI) of tryptophan gives rise to multiply charged, non‐covalent tryptophan cluster anions, [Trp_n–xH]^x?, in a linear ion trap mass spectrometer, as confirmed by high‐resolution experiments performed on a Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometer. The smallest multiply charged clusters that can be formed in the linear ion trap as a function of charge state are: x = 2, n = 7; x = 3, n = 16; x = 4, n = 31. The fragmentation of the dianionic cluster [Trp₉–2H]^2? was examined via low‐energy collision‐induced dissociation (CID), ultraviolet photodissociation (UVPD) at 266 nm and electron‐induced dissociation (EID) at electron energies ranging from >0 to 30 eV. CID proceeds mostly via charge separation and evaporation of neutral tryptophan. The smallest doubly charged cluster that can be formed via evaporation of neutral tryptophans is [Trp₇–2H]^2?, consistent with the observation of this cluster in the ESI mass spectrum. UVPD gives singly charged tryptophan clusters ranging from n = 2 to n = 9. The latter ion arises from ejection of an electron to give the radical anion cluster, [Trp₉–2H]^?.. The types of gas‐phase EID reactions observed are dependent on the energy of the electrons. Loss of neutral tryptophan is an important channel at lower energies, with the smallest doubly charged ion, [Trp₇–2H]^2?, being observed at 19.8 eV. Coulomb explosion starts to occur at 19.8 eV to form the singly charged cluster ions [Trp_x–H]^? (x = 1–8) via highly asymmetric fission. At 21.8 eV a small amount of [Trp₂–H–NH₃]^? is observed. Thus CID, UVPD and EID are complementary techniques for the study of the fragmentation reactions of cluster ions. Copyright © 2010 John Wiley & Sons, Ltd.     

Boron‐Containing Protoporphyrin IX Derivatives and Their Modification for Boron Neutron Capture Therapy: Synthesis,Characterization, and Comparative In Vitro Toxicity Evaluation

A novel series of boronated porphyrins for potential use in boron neutron capture therapy (BNCT) and photodynamic therapy (PDT) for tumor suppression is described. Protoporphyrin IX {i.e., bis(α‐methyl‐β‐pentylethylether)protoporphyrin IX, and bis(α‐methyl‐β‐dodecanylethylether)protoporphyrin IX} bearing polyhedral borane anions (B₁₂H₁₁SH^2?, B₁₂H₁₁NH₃^?, or B₁₂H₁₁OH^2?) were synthesized with reasonable yields. Modification of the protoporphyrin IX structure was achieved by variation of the lengths of the alkyl chains (pentyl and dodecanyl) attached through ether linkages to the former vinyl groups. The goal of this modification was to develop boronated porphyrins with chemical and physical properties that differed from those of protoporphyrin IX. Performance of an MTT assay with each derivative revealed that the synthesized boronated porphyrins showed low cytotoxicities in a variety of cancer cells. Of these compounds, B₁₂H₁₁NH₂^2?‐conjugated porphyrin induced a significant increase in the level of boron accumulation and PDT efficacy against HeLa cells.     

Theoretical study of H2 elimination from [B n H n + 1]− monoanions (n = 6–9, 11)

Transition states of elementary reactions of H₂ molecule elimination from [B _n H _{n + 1}]^? anions (n = 6–9, 11) in which nucleophilic/electrophilic vacancies form at boron atoms have been localized by the density functional theory method (in the B3LYP/6-311++G** approximation). For a series of [B _n H _{n + 1}]^? anions (n = 6–12), the activation barriers to H2 elimination have been compared to consider the possibility of substitution for exopolyhedral hydrogen atoms by the mechanism with the first rate-limiting stage of formation of [B _n H _{n ? 1}]^? (n = 6–12) intermediates with a vacant “bare” vertex of the boron cluster. For the [B _n H _n ]^2?, [B _n H _{n + 1}]^?, and [B _n H _{n ? 1}]^? anions (n = 6–12), the electronic chemical potential μ and Pearson hardness η have been evaluated since these characteristics make it possible to assess the propensity of different reagents to react with each other in terms of the empirical HSAB principle (soft with soft and hard with hard). The application of this principle is exemplified by the interaction of the [B₁₀H₉]^? and [B₁₂H₁₁]^? anions with acetonitrile CH₃CN, furan C₄H₄O, and 18-crown-6.     

Protonation of the Dodecahydro-<Emphasis Type="Italic">closo</Emphasis>-Dodecaborate Anion in CH<Subscript>3</Subscript>CN/CF<Subscript>3</Subscript>COOH

The behavior of the [B₁₂H₁₂]^2– anion in CH₃CN, CF₃COOH, and the CH₃CN/CF₃COOH system is studied by IR spectroscopy. Based on the IR spectroscopy data correlated with the data obtained when studying the protonation processes of boron cluster anions [B₆H₆]^2– and [B₁₀H₁₀]^2–, the possibility to prepare the protonated form of the closo-dodecaborate anion, namely monoanion [B₁₂H₁₃]^–, is concluded in CF₃COOH and the CH₃CN/CF₃COOH system. In the IR spectra of salts of the protonated forms of anions [B_nH_n]^2– (n = 6, 10, 12) in solutions and Nujol mulls, a high-frequency shift of the ν(BH) absorption bands is observed as compared with the spectra of salts of non-protonated anions Cat₂[B_nH_n] (Δν = 70–100 cm^–1).     

Binding Matter with Antimatter: The Covalent Positron Bond

We report sufficient theoretical evidence of the energy stability of the e⁺?H₂^2? molecule, formed by two H^? anions and one positron. Analysis of the electronic and positronic densities of the latter compound undoubtedly points out the formation of a positronic covalent bond between the otherwise repelling hydride anions. The lower limit for the bonding energy of the e⁺?H₂^2? molecule is 74 kJ mol^?1 (0.77 eV), accounting for the zero‐point vibrational correction. The formation of a non electronic covalent bond is fundamentally distinct from positron attachment to stable molecules, as the latter process is characterized by a positron affinity, analogous to the electron affinity.     

Colossal Stability of Gas‐Phase Trianions: Super‐Pnictogens

Multiply charged negative ions are ubiquitous in nature. They are stable as crystals because of charge compensating cations; while in solutions, solvent molecules protect them. However, they are rarely stable in the gas phase because of strong electrostatic repulsion between the extra electrons. Therefore, understanding their stability without the influence of the environment has been of great interest to scientists for decades. While much of the past work has focused on dianions, work on triply charged negative ions is sparse and the search for the smallest trianion that is stable against spontaneous electron emission or fragmentation continues. Stability of BeB₁₁(X)₁₂³⁻ (X=CN, SCN, BO) trianions is demonstrated in the gas phase, with BeB₁₁(CN)₁₂³⁻ exhibiting colossal stability against electron emission by 2.65 eV and against its neutral adduct by 15.85 eV. The unusual stability of these trianions opens the door to a new class of super‐pnictogens with potential applications in aluminum‐ion batteries.     

The Hexacyanodiborane(6) Dianion [B2(CN)6]2−

Diborane(6) dianions with substituents that are bonded to boron via carbon are very reactive and therefore only a few examples are known. Diborane(6) derivatives are the simplest catenated boron compounds with an electron‐precise B–B σ‐bond that are of fundamental interest and of relevance for material applications. The homoleptic hexacyanodiborane(6) dianion [B₂(CN)₆]²⁻ that is chemically very robust is reported. The dianion is air‐stable and resistant against boiling water and anhydrous hydrogen fluoride. Its salts are thermally highly stable, for example, decomposition of (H₃O)₂[B₂(CN)₆] starts at 200 °C. The [B₂(CN)₆]²⁻ dianion is readily accessible starting from 1) B(CN)₃²⁻ and an oxidant, 2) [BF(CN)₃]⁻ and a reductant, or 3) by the reaction of B(CN)₃²⁻ with [BHal(CN)₃]⁻ (Hal=F, Br). The latter reaction was found to proceed via a triply negatively charged transition state according to an S_N2 mechanism.     

New coordination polymers of silver(I) based on dodecahydro-<Emphasis Type="Italic">closo</Emphasis>-dodecaborate anion: Synthesis and structure

It has been demonstrated that the reaction of Cat[Ag[B₁₂H₁₂]] or [Ag₂[B₁₂H₁₂]] with chelating ligands L (L = bipy, phen) leads to the selective formation of stable [(Ag₂(L)₂[B₁₂H₁₂]] _n 1D polymers irrespective of the nature of cation (Cat) in the starting reagent, the ratio of the reaction components, and the solvent used. The structures of [Ag₂(bipy)₂[B₁₂H₁₂]] _n · 2CH₃CN and [Ag₂(phen)₂[B₁₂H₁₂]] _n · DMF have been determined by X-ray crystallography. It has been demonstrated that the [B₁₂H₁₂]^2? anion in polymer chains acts as a bridging ligand coordinated to silver atoms through edges or through an edge and a vertex of the icosahedron. The Ag–B(H) and Ag–H(B) distances are within 2.638(3)–3.074(3) and 1.90–2.80 Å, respectively. These complexes are the first examples of 1D coordination polymers based on the [B₁₂H₁₂]^2? anion and azaheterocyclic ligands L.     

1‐Oxa‐nido‐dodecaborate [OB11H12]− from the Controlled Oxidation of the closo‐Borates [B11H11]2− and [B12H12]2−

The closo‐dodecaborate [B₁₂H₁₂]^2? is degraded at room temperature by oxygen in an acidic aqueous solution in the course of several weeks to give B(OH)₃. The degradation is induced by Ag²⁺ ions, generated from Ag⁺ by the action of H₂S₂O₈. Oxa‐nido‐dodecaborate(1?) is an intermediate anion, that can be separated from the reaction mixture as [NBzlEt₃][OB₁₁H₁₂] after five days in a yield of 18 %. The action of FeCl₃ on the closo‐undecaborate [B₁₁H₁₁]^2? in an aqueous solution gives either [B₂₂H₂₂]^2? (by fusion) or nido‐B₁₁H₁₃(OH)^? (by protonation and hydration), depending on the concentration of FeCl₃. In acetonitrile, however, [B₁₁H₁₁]^2? is transformed into [OB₁₁H₁₂]^? by Fe³⁺ and oxygen. The radical anions [B₁₂H₁₂] ^{˙ ?} and [B₁₁H₁₁] ^{˙ ?} are assumed to be the primary products of the oxidation with the one‐electron oxidants Ag²⁺ and Fe³⁺, respectively. These radical anions are subsequently transformed into [OB₁₁H₁₂]^? by oxygen. The crystal structure analysis shows that the structure of [OB₁₁H₁₂]^? is derived from the hypothetical closo‐oxaborane OB₁₂H₁₂ by removal of the B3 vertex, leaving a non‐planar pentagonal aperture with a three‐coordinate O vertex, as predicted by NMR spectra and theory.     

Darstellung und Charakterisierung von Thiocyanatderivaten der Hydroboratanionen B10H102− und B12H122−

Preparation and Characterization of Thiocyanate Derivatives of the Hydroborate Anions B₁₀H₁₀^2? and B₁₂H₁₂^2? The reaction of B₁₀H₁₀^2? or B₁₂H₁₂^2? with (SCN)₂ in dichloromethane yields mixtures of thiocyanatohydroborates from which the pure isomers 1-and 2-(SCN)B₁₀H₉^2?, 1, 10-(SCN)₂B₁₀H₈^2?, and 1-(SCN)B₁₂H₁₁^2? are isolated by ion exchange chromatography on diethylaminoethyl cellulose. The structures are determined by ¹¹B and ¹¹B{¹H}NMR spectroscopy. There are characteristic chemical shifts due to apical and equatorial substituents, respectively. In B₁₀H₁₀^2? the substitution at apical positions is prefered. The IR and Raman spectra are similar to those of isosteric halogeno derivatives in the region of ν(BH) and of the borate cages. Because of the high frequencies of ν(CN): 2120–2140 cm^?1 S coordination of SCN^? is supposed.     

The reaction of pentaborane(9) with sodium cyanide and sodium cyanotrihydroborate

The reaction of pentaborane(9) with NaCN occurs in a 1:1 molar ratio at temperatures between ? 30° and + 10°C to yield the complex Na[B₅H₉CN], which can be isolated in the form of a dioxanate. When excess pentaborane(9) is used the reaction is relatively clean and yields predominantly the [B₉H₁₄]^? ion. With NaBH ₃CN no intermediates of the type Na[B₅H₉CN] are detected, and the major product is the [B₉H₁₄]^? ion, but no hydrogen is evolved in the reaction. Structures for the intermediate anions are suggested. No monocarbon carbaboranes were detected in any of the reactions.     

Bismuth Undecahydro‐closo‐dodecaborane: A Retainable Intermediate of B−H Bond Activation by Bismuth(III) Cations

The [B₁₂H₁₂]^2? anion shows an extensive substitutional chemistry based on its three‐dimensional aromaticity. The replacement of functional groups can be attained by electrophilically induced substitution caused by Brønsted or Lewis acidic electrophiles (e.g. Pt²⁺). Until now, it was impossible to structurally characterize a metal‐substituted [B₁₂H₁₂]^2? cage. When an aqueous solution containing both Bi³⁺ cations and [B₁₂H₁₂]^2? anions was heated, the charge‐neutral bismuth undecahydro‐closo‐dodecaborane BiB₁₂H₁₁ was obtained, representing a new class of metalated [B₁₂H₁₂]^2? clusters. The title compound was characterized by single‐crystal X‐ray diffraction and NMR spectroscopic methods. Compared to the typical B?H bond, the short B?Bi single bond (230 pm) exhibits inverted polarity.     

Synthesis,crystal structure,and thermal stability of ionic cluster compounds (phenH)4[Re4Q4(CN)12]·nH2O (Q = S,Se, n = 6; Q = Te,n = 10)

Three new salts of tetrahedral rhenium chalcocyanide cluster anions [Re₄Q₄(CN)₁₂]^4? (Q = S, Se, Te) and 1,10-phenanthroline-1-ium cations, (phenH)₄[Re₄S₄(CN)₁₂]·6H₂O (1), (phenH)₄[Re₄Se₄(CN)₁₂]·6H₂O (2), and (phenH)₄[Re₄Te₄(CN)₁₂]·10H₂O (3), have been synthesized by reactions of K₄[Re₄Q₄(CN)₁₂]·nH₂O with 1,10-phenanthroline in the presence of Nd³⁺ in an acidic aqueous medium (pH 4). 1 and 2 exhibit similar 2-D layered supramolecular architectures based on hydrogen bonds between water molecules, CN-groups of cluster anions, and phenH⁺ cations. The latter are involved in π–π and C–H?π stacking interactions, connecting the adjacent layers with each other. Complex 3 demonstrates a 3-D framework based on hydrogen bonds between water molecules and CN-groups, π–π and C–H?π interactions. Notably short O···Te contacts of 3.40 and 3.50 Å are found in the structure of 3. The thermal properties of 1–3 have been investigated by TG-DTG.     

Cluster bonding and energetics of the borane anions,BnHn2− (n = 5–12): A comparative study using bond length—bond enthal

Cluster bond enthalpies, E_L(BB), and orders, n?(BB), for the structurally characterised closo anions, B_nH_n^2? (n = 6 and 8–12), have been estimated using the logarithmic length—enthalpy and enthalpy—order relationships E_L(BB) (kJ mol^?1) = 1.766 × 10¹¹ [L(BB)]^?4.0 and E_L(BB) (kJ mol^?1) = 318.8[n?(BB)]^0.697, respectively. In a parallel study, the molecular-orbital bond index CNDO-based calculation method has been used to give BB and BH bond indices, I(BB) and I(BH), from which bond index based bond enthalpies, E_I, have been calculated using the relationships E_I(BB) = 297.9 I(BB) and E_I(BH) = 374.8I(BH) (enthalpies in kJ mol^?1; lengths in pm). From these, total skeletal bond enthalpies Σ E(BB), and total bond enthalpies, Σ E(BB) + Σ E(BH), have been calculated. Although calculated values of E_L and Σ E_L generally exceed those of E_I and Σ E_I by some 8% and calculated values of I generally exceed those of n? by a greater amount, the trends in these parameters for the series of B_nH_n^2? anions are very similar, showing the greater efficiency with which the n + 1 skeletal electron pairs are used as n increases. However, the two approaches differ in that, whereas the Σ E_I values suggest that the anions are all of comparable stability, the ΣE_L values clearly show B₆H₆^2?, B₁₀H₁₀^2? and B₁₂H₁₂^2? to be more stable than B₈H₈^2?, B₉H₉^2? and B₁₁H₁₁^2?. The interatomic distances in B₇H₇^2? and in the unknown B₅ H₅^2? are estimated and used to assess their relative stabilities. The E_L values suggest that B₇ H₇^2? is of comparable stability to B₈H₈^2? etc., but show B₅H₅^2? as relatively unstable. The E_I values suggest that both of these anions should be relatively stable members of the series of closo anions.