Influence of the solvent and R groups on the structure of (carboranyl)R2PI2 compounds in solution. Crystal structure of the first iodophosphonium salt incorporating the anion [7,8-nido-C2B9H10]-

The influence of the electron-donor or electron-acceptor capacity of the R groups (R = (i)Pr, Ph, Et) and the solvent on the molecular geometry in solution of adducts of carboranylphosphanes [(carboranyl)(i)Pr2P, (carboranyl)Ph2P and (carboranyl)Et2P] with I2 in 1 : 1 ratios, has been studied in detail by 31P{1H} and 11B{1H} NMR spectroscopies. The more electron-accepting Ph groups make the (carboranyl)Ph2P less nucleophilic, thus stabilizing the I2 encapsulated neutral biscarboranylphosphane-diiodine adducts in solution, such as (carboranyl)Ph2PI-IPPh2(carboranyl), generating P---I-I---P motifs. Even in a polar solvent, such as EtOH, the arrangement is preserved. The expected basicity of these carboranylphosphanes is: (carboranyl)(i)Pr2P > (carboranyl)Et2P > (carboranyl)Ph2P. Thus, the comparatively higher basicity of (carboranyl)Et2P vs. (carboranyl)Ph(2)P facilitates a higher transfer of electron density to the I2 sigma*, generating the ionic species, [(carboranyl)Et2PI]+I-, even in low polar solvents, such as CH2Cl2 and toluene, with no degradation of the cluster. However, in EtOH, the formation of the anionic [7,8-nido-C2B(9)H10]- cluster takes place by removal of one boron atom from the closo cluster. The basicity of (carboranyl)(i)Pr(2)P should be the highest, superior to (carboranyl)Et2P. This is observed in the reaction of these carboranylphosphanes with I(2) in EtOH. Whereas the formation of P four-coordinated molecular "spoke" charge-transfer complexes, (carboranyl)(i)Pr2P-I-I, are suggested for (carboranyl)(i)Pr2P in low polarity solvents, ionic species are formed in ethanolic solutions, which deboronate in a few days, faster than (carboranyl)Et2P, to yield the zwitterionic species. This is attributed to the higher basicity of (carboranyl)(i)Pr2P vs. (carboranyl)Et2P. The X-ray crystal structure of [7-PI(i)Pr2-8-Ph-7,8-nido-C2B9H10], 2c, obtained from the reaction of 1-P(i)Pr2-2-Ph-closo-1,2-closo-C2B10H10 with I(2) in EtOH, confirms the formation of the zwitterion. These results prove that minor changes in the nature of the R substituents on the P atom in carboranylphosphanes, along with the solvent in which the reaction takes place, produce major alterations in the geometry of the (carboranyl)R2P-I-I species in solution, and in their possible further reactivity.     

Visible-Light-Induced Photoreduction of Carborane Phosphonium Salts: Efficient Synthesis of Carborane-Oxindole-Pharmaceutical Hybrids

Visible-light-induced photoreaction of carboranes is an effective approach to prepare carborane-containing compounds. While several methods involving boron-centered carboranyl radicals have been established, those for carbon-centered carboranyl radicals are underdeveloped, except for the UV-light-promoted photohomolysis. Herein, we describe a simple but effective approach to access carbon-centered carboranyl radicals by photoreduction of carborane phosphonium salts under blue light irradiation without using transition metals and photocatalysts. The utility of the method was demonstrated by successfully preparing a range of carborane-oxindole-pharmaceutical hybrids by radical cascade reactions. Computational and experimental studies suggest that the carbon-centered carboranyl radicals are generated by single-electron transfer of the photoactive charge-transfer complexes between the salts and the additive potassium acetate.     

Preparation of a new carboranyl lactoside for the treatment of cancer by boron neutron capture therapy: synthesis and toxicity of fluoro carboranyl glycosides for in vivo 19F-NMR spectroscopy

The synthesis of new ortho-carboranyl lactosides 8, 17, 19 and glucosides 22 and 23 for the use in boron neutron capture therapy is reported. Carboranyl lactosides 17 and 19 as well as the glucosides 22 and 23 contain a fluorine atom to allow a noninvasive determination of these compounds in tumor cells by 19F-NMR spectroscopy. In cloning efficiency tests on human bronchial carcinoma cells the carboranyl lactosides 17 and 19 displayed almost no cytotoxicity. Thus, the considerably cytotoxic carboranyl alcohol 11 is detoxified when linked to a sugar moiety such as in carboranyl glucoside 22.     

Aggregation‐Induced Electrochemiluminescence of Carboranyl Carbazoles in Aqueous Media

The aggregation‐induced electrochemiluminescence (AIECL) of carboranyl carbazoles in aqueous media was investigated for the first time. Quantum yields, morphologies, and particle sizes were observed to determine the electrochemiluminescence (ECL) performance of these aggregated organic dots (ODs). All compounds exhibit much higher ECL stability and intensity than the carborane‐free compound, demonstrating the essential role of the carboranyl motif. Moreover, the results of cyclic voltammetry (CV) suggest that oxidation/reduction reactions take place at the carboranyl motif. The excited states of ODs were proposed to be generated by the mechanism of surface state transitions. More importantly, these compounds show a reductive–oxidative mechanism in contrast to other organic materials that show oxidative–reductive mechanisms. Our experiments and data have established the relation between AIE organic structures and ECL properties that has a strong potential for biological and diagnostic applications.     

Synthesis,Characterization, and Thermal Behavior of Carboranyl–Styrene Decorated Octasilsesquioxanes: Influence of the Carborane Clusters on Photoluminescence

Novel polyhedral oligomeric silsesquioxanes (POSS) or octasilsesquioxanes with carboranyl–styrene fragments attached to each corner are described. These compounds have been synthesized by olefin‐metathesis reactions between octavinylsilsesquioxane and carboranyl–styrene compounds that possess different substituents (Ph, Me, or H). In all cases, these reactions, which were catalyzed by the Grubbs catalyst, are highly regioselective and yield exclusively the E isomers. The existence of the carborane cage in the POSS structure induces a remarkable thermal stability in these compounds. After combustion at 1000 °C, these carboranyl–POSS compounds exhibit a mass loss lower than 10 %. The UV/Vis absorption data of these carboranyl–POSS compounds shows a slight bathochromic shift with respect to the carboranyl–styrene monomers, with an absorption maximum around 262 nm. Nevertheless, important differences in the emission spectra of the carboranyl–POSS compounds with regard to their carboranyl–styrene precursors are observed; the phenyl‐o‐carborane‐containing POSS compound exhibits the highest fluorescence intensity (Φ_F=44 %), whereas for the POSS compound bearing the methyl substituent, and for the unsubstituted o‐carborane clusters, the fluorescence intensity is much lower (Φ_F=9 and 2 %, respectively). This is precisely the reverse of what occurs with the monomers, in which the unsubstituted o‐carboranyl–styrene compound exhibits the highest Φ_F, and a quenching of the fluorescence is observed in the phenyl‐o‐carboranyl–styrene compound. In addition, a large red shift of around 100 nm is observed for the POSS compounds with respect to their precursors. These experimental results can only be accounted for by the spatial ordering induced by the POSS core that eases interactions, which otherwise would not occur. These results have been confirmed by time‐dependent density functional theory (TDDFT) calculations that exclude a photoinduced electron transfer (PET) process in the POSS compounds.     

Simple, high-yield methods for the synthesis of aldehydes directly from o-, m-, and p-carborane and their further conversions

Aldehydes have long served as important building blocks for synthetic chemists, and carboranyl aldehydes are no exception. Recent literature reports, for example, illustrate their application as intermediates in biomedicine, materials science, and basic organic chemistry. We report here new methods for the single-step preparation of C-monoformyl and C,C-diformyl derivatives directly from o-, m-, and p-carborane, as well as improved synthetic routes to homologated carboranyl aldehydes. Additionally, reductive amination is used to transform these aldehydes into a series of 2 degrees amines of alpha-amino acid esters.     

Bis（C—p—carboranyl）（C2B10H11）2振动光谱的从头算研究

BiS（C-p-carboranyl）（C2B10H11）2是一种稠合型碳硼烷，由2个C2B10H11集团通过C-C键联结构成．Leites已发表了其实验振动光谱[1]，理论计算尚未见报道，本文对其几何优化、振动光谱及其指认进行从头计算研究．1计算方法首先在STO－3G下对标题化合物D5d与D5h两种构型进行从头算，确定D5d为其稳定构型，进而保持D5d对称性不变，并在6－31G下进行几何优化及振动光谱的理论研究，全部计算采用Gaussion－94程序，在CrayS－MP／11型计算机上完成．2结果与讨论2．1几何优化优化几何及部分实验键长列于表1．标题化合物在D5d与D5h两种…     

Determination of pKR+ values for cyclobutadieneiron tricarbonyl-substituted carbocations

pK_R⁺ values for a series of cyclobutadieneiron tricarbonyl-substituted carbocations have been determined by a Hammett-Deno indicator acidity study utilizing trifluoroacetic acid-water solutions. The results show that these carbocations are considerably more stable than a variety of similar organic and organometallic carbocations but less stable than the corresponding ferrocene systems.     

Synthesis, structural, spectroscopic and electrochemical studies of carborane substituted naphthyl selenides

New unsymmetrical selenides bearing an o-carborane and a naphthalene ring as the substituents were prepared by the cleavage of the corresponding diselenides. The compounds were characterized by means of spectroscopic and analytical methods. (77)Se NMR signals of the selenium atoms attached to the carbon atoms of the carborane cages are shifted downfield in comparison to those bonded only to the aromatic rings, indicating an electron withdrawing effect of the o-carboranyl substituent. Compounds 1-(2-R-1,2-dicarba-closo-carboranyl)naphthyl selenides (R = Me, 1; Ph, 2) were characterized by means of single crystal X-ray diffraction. The influence of the electronic nature of the substituents attached to the selenium atoms on the structural parameters and packing properties of naphthyl selenides are discussed. Theoretical calculations and cyclic voltammetry (CV) studies were carried out to compare the bonding nature of carboranyl and analogous aryl selenium compounds. Cyclic voltammetry studies of naphthyl carboranyl mono and diselenides have shown that the carboranyl fragment polarizes the Se lone pair making it less prone to generate a Se-Se bond.     

Bis-pyrene carbocations for chromogenic and fluorogenic dual-detection of fluoride anion in situ

We have designed and synthesized a new carbocation precursor (carbinol) based on bis-pyrene derivative. The carbinol can be transformed to stable carbocations with quenched fluorescence and long wavelength absorption. The stable carbocations can be further used as fluoride anion detection in acidic environment, which show both chromogenic and fluorogenic responses in the presence of fluoride anion. UV–vis and fluorescence spectroscopy were utilized to monitor the changes during detection process. The responsive mechanism was studied by quantum chemical calculations and the results indicate that the carbocation mediated formation of C–F covalent bond leads to this dual responsive phenomenon. The bis-pyrene carbocations and corresponding F adduct was confirmed MALDI-TOF mass spectrum. The successful elucidation of this new mechanism opens a new avenue for carbocation-based sensor or biological labeling in the future.     

Basic concepts of "cation pool" and "cation flow" methods and their applications in conventional and combinatorial organic synthesis

Carbocations have been generally considered to be relatively unstable and transient species. But the "cation pool" method enables the easy accumulation of carbocations in conventional reaction media such as dichloromethane. In the "cation pool" method, carbocations are generated by low-temperature electrochemical oxidation and accumulated in a solution. In the next step, the carbocations thus produced are allowed to react with various nucleophiles. Combinatorial parallel synthesis based upon the "cation pool" method has also been developed. The applicability of the "cation pool" method depends upon the stability of the cation that is accumulated. This problem can be overcome by the "cation flow" method. In the "cation flow" method, carbocations are generated in a microflow electrochemical system. Short residence times and efficient temperature control of the microflow system are advantageous. Combinatorial sequential synthesis has been achieved based on the "cation flow" method.     

Synthesis and Certain Reactions of Primary Carboranyl Acetates and Tosylates

Acetates and tosylates of primary carboranyl alcohols were prepared, and their reactions with nucleophilic reagents were investigated. Some specific features of these processes were revealed, and preparative procedures for previously unknown carboranyl amines were developed.     

Generation and trapping reaction of an efficient 1,2-dehydrocarborane precursor, phenyl[o-(trimethylsilyl)carboranyl]iodonium acetate

An efficient 1,2-dehydrocarborane precursor, phenyl[o-(trimethylsilyl)carboranyl]iodonium acetate, was readily prepared by reaction of [o-(trimethylsilyl)carboranyl]lithium and IPh(OAc)2. The facile 2+4 cycloaddition of with dienes such as anthracene, naphthalene, norborna-2,5-diene and 2,5-dimethylfuran gave high yields of the 1,2-dehydrocarborane adducts in the presence of a desilylating agent. The reaction of with a cyclic alkene and strained cycloalkynes afforded the adducts formed by the ene reaction and the 2+2 cycloaddition reaction. The reaction of with a bicyclopalladacycle yielded the cyclization product. The structures of compounds and were determined by single-crystal X-ray crystallography.     

Carborane‐Induced Excimer Emission of Severely Twisted Bis‐o‐Carboranyl Chrysene

The synthesis of a highly twisted chrysene derivative incorporating two electron deficient o‐carboranyl groups is reported. The molecule exhibits a complex, excitation‐dependent photoluminescence, including aggregation‐induced emission (AIE) with good quantum efficiency and an exceptionally long singlet excited state lifetime. Through a combination of detailed optical studies and theoretical calculations, the excited state species are identified, including an unusual excimer induced by the presence of o‐carborane. This is the first time that o‐carborane has been shown to induce excimer formation ab initio, as well as the first observation of excimer emission by a chrysene‐based small molecule in solution. Bis‐o‐carboranyl chrysene is thus an initial member of a new family of o‐carboranyl phenacenes exhibiting a novel architecture for highly‐efficient multi‐luminescent fluorophores.     

Substituent effects in benz[a]anthracene carbocations: a stable ion, electrophilic substitution (nitration, bromination), and DFT study

A series of novel carbocations were generated from isomeric monoalkylated and dialkylated benz[a]anthracenes (BAs) by low-temperature protonation in FSO(3)H/SO(2)ClF. With the monoalkyl derivatives (5-methyl, 6-methyl, 7-methyl, and 7-ethyl) as well as the D-ring methylated analogues (9-methyl, 10-methyl, and 11-methyl), the C-7 or the C-12 protonated carbocations were observed (as the sole or major carbocation) in all cases. Protonation of the 12-methyl derivative (9) gave the C-7 protonated carbocation (9H+) as the kinetic species and the ipso-protonated carbocation (9aH+) as the thermodynamic cation. With the 12-ethyl derivative (10), relief of steric strain in the bay-region greatly favors ipso-protonation (10aH+). With 3,9-dimethyl (14), C-7 protonation (14H+) is strongly favored (with <10% protonation at C-12), and with 1,12-dimethyl (15) the sole species observed is the C-7 protonated carbocation (15H+). For 7-methyl-12-ethyl, 7-ethyl-12-methyl, and 7,12-diethyl derivatives (16, 17, and 18), two ipso-protonated carbocations were initially formed (C-7/C-12), rearranging in time to give the C-12 protonated carbocations exclusively (16aH+, 17aH+, and 18aH+). Protonation outcomes are compared with the computed relative energies by DFT. Charge delocalization paths in the resulting carbocations were deduced based on the magnitude of Deltadelta13C values. For the thermodynamically more stable C-12 protonated carbocations, the charge delocalization path is analogous to those derived based on computed NPA charges for the benzylic carbocations formed by 1,2-epoxide (bay-region) and 5,6-epoxide (K-region) ring opening. Nitration (and bromination) of the 4-methyl, 7-methyl, 7-ethyl, 3,9-dimethyl, and 1,12-dimethyl derivatives resulted in isolation and characterization of several novel derivatives. Excellent agreement is found between low-temperature protonation selectivities and the regioselectivities observed in model substitution reactions.     

Synthesis of S-carboran-9-YL esters of pentavalent phosphorus acids

Conclusions New carboranyl thioesters of pentavalent phosphorus acids were synthesized, in which the carboranyl group is attached at the B-9 atom.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 719–721, March, 1986.     

Quantum chemical study of solvent and substituent effects on the 1,5-hydride shift in 2,6-dimethyl-2-heptyl cations

The mechanism of the degenerate 1,5-hydride shift in 2,6-dimethyl-2-heptyl cations has been investigated using ab initio MP2 and density functional theory (DFT) hybrid (B3LYP) calculations. The potential-energy profile for the 1,5-hydride shift consists of three minima corresponding to two equivalent acyclic carbocations and one symmetrically mu-hydrido-bridged carbocation, while two equivalent unsymmetrically hydrido-bridged carbocations were located as transition-state structures. The calculated relative energy differences between acyclic carbocations and symmetrically mu-hydrido-bridged structure are significantly affected by introduction of alkyl and (CH2)n-substituents at the C4 position of the 2,6-dimethyl-2-heptyl cation structure. DFT self-consistent isodensity polarizable continuum method (SCI-PCM) and MP2 PCM continuum methods have been used to calculate the effect of solvation on geometries and relative energies of the species involved in the 1,5-hydride shift. It is found that relative energies of acyclic and mu-hydrido-bridged carbocation structures as well as the energy barriers for 1,5-hydride shifts are in accord with experimental data if solvation effects are taken into account.     

On the Edge of the Known: Extremely Electron-Rich (Di)Carboranyl Phosphines

The syntheses of the first B9-connected carboranylphosphines (B9-Phos) featuring two carboranyl moieties as well as access to B9-Phos ligands with bulky electron-donating substituents, previously deemed unattainable, is reported. The electrochemical properties of the B9-Phos ligands were investigated, revealing the ability of the mesityl derivatives to form stabilized phosphoniumyl radical cations. The B9-Phos ligands display an extremely electron-releasing character surpassing that of alkyl phosphines and commonly used N-heterocyclic carbenes. This is demonstrated by their very small Tolman electronic parameters (TEPs) as well as extremely low P−Se coupling constants. Cone angles and buried volumes attest to the high steric demand exerted by the (di)carboranyl phosphines. The dicarboranyl phosphine Au^I complexes show superior catalytic performance in the hydroamination of alkynes compared to the monocarboranyl phosphine analogs.     

A new method for empirical force field calculations on localized and delocalized carbocations

A new empirical force field method for localized and delocalized carbocations is described. Additional geometry parameters for carbocations were added to Allinger's MMP2 molecular mechanics program, which can treat delocalized π-systems. The effect of hyperconjugation in carbocations is introduced via a quantum chemical term into force field calculations for the first time. The calculated heats of formation are in excellent agreement with a wide range of experimental data; the largest deviations are about 3.5 kcal/mol. The calculated structures agree very well with those computed at correlated ab initio levels (MP2(full)/6-31G*). The relative energies and geometries of different conformations of representative carbocations also were in good agreement with MP4/6-31G*//MP2(full)/6-31G* results. © 1996 by John Wiley & Sons, Inc.     

Stable ion and electrophilic chemistry of the sterically crowded stilbene 1,1'-Bi(benzocyclobutenylidene) and its derivatives

Generation and NMR studies of novel carbocations and carboxonium ions are reported from sterically hindered stilbene 1,1'-bi(benzocyclobutenylidene) 1, its dimethoxy derivative 5, and from their skeletally rearranged derivatives, namely, the spirocyclic ketone 6, diastereomeric alcohols 7 and isomeric diols 8. Quenching experiments on the carbocations under various conditions resulted in the formation/isolation of several novel covalent adducts. Acid-catalyzed isomerization of the diols 8 produced a remarkable dimeric molecule, whose structure was confirmed by X-ray analysis. Reactions of hindered stilbenes 1 and 5 with Br 2/CDCl 3 were examined via NMR experiments. The experimentally observed carbocations were also studied computationally by GIAO-DFT and by NICS.