硼中子捕获疗法中使用的1,2-C2B10H12异腈衍生物的结构和电子特性

利用密度泛函方法在B3LYP/6-31G(d)水平上对1,2-C2B10H12的两种异腈类衍生物的结构特性进行了研究. 结果表明, 1,2-C2B10H11NC的活性较强; 1,2-C2B10H11NC和1,2-C2B10H11CH2NC可以通过结构中的C4原子与过渡金属原子成键而形成碳硼烷异腈金属配合物. 1,2-C2B10H11NC和1,2-C2B10H11CH2NC的分子极性均比1,2-C2B10H12的弱, 这不利于它们在硼中子捕获疗法中的应用.     

Helical β-isoindigo-Based Chromophores with B−O−B Bridge: Facile Synthesis and Tunable Near-Infrared Circularly Polarized Luminescence

It is essential to create organic compounds that exhibit circularly polarized luminescence (CPL) in the near-infrared (NIR) range. Helicene-type emitters possess appealing chiroptical features, however, such NIR molecules are scarce due to a paucity of synthetic strategies. Herein, we developed a series of helical β-isoindigo-based B−O−B bridged aza-BODIPY analogs that were synthesized conveniently. The reaction of diimino-β-isoindigo with a heteroaromatic amine produced a restricted ligand cavity, which triggered off the generation of a B−O−B bridge. The B−O−B bridge led to distorted conformations that satisfy the helical requirements, resulting in excellent spectroscopic and chiroptical properties. Tunable CPL with the highest luminescence dissymmetry factor (g_lum) of 1.3×10⁻³ and a CPL brightness (B_CPL=11.5 M⁻¹ cm⁻¹) in the NIR region was achieved. This synthetic approach is expected to offer a new opportunity to chiral chemistry and increase flexibility for chiroptical tuning.     

Non-spectator behavior of carborane ligands in icosahedral metallacarboranes

Icosahedral metallacarboranes with closo-3,1,2-MC₂B₉ frameworks are formally derived by η⁵ coordination of the open face of a nido-7,8-C₂B₉ cage to a metal atom. Recent work has established that the boron vertices of these faces readily form exo-polyhedral bonds of various kinds. These include linkages to other metal-ligand systems via either three-center two-electron B---H metal of two-center B-metal σ interactions, as well as attachments to organic groups with B---C or B---O bonds. Many new types of molecular structure have been identified, thereby opening a new domain of metallacarborane chemistry which merits further study.     

Metal complexes of monocarbon carboranes bearing C-amine or -amino substituents

Icosahedral metal-monocarbollide complexes in which the carbon atom of the {nido-CB₁₀} fragment carries an exo-polyhedral -NR₃ or -NR₂ group have an extensive chemistry. This is illustrated with complexes of ruthenium, osmium, rhodium, molybdenum, tungsten and rhenium. Many complexes with molecular structures new to the metallacarborane field have been discovered, and it has been shown that it is possible to introduce functional groups into the {nido-CB₁₀} cage system in many different ways.     

First example of the formation of a Si-C bond from an intramolecular Si-H?H-C diyhydrogen interaction in a metallacarborane: A theoretical study

The recently reported crystal structure of [NMe₄][1-SiMe₂H-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] shows short contacts between the Si-H proton acceptor group and the C_c-H proton donor moiety in the dicarbollide ligand. These short contacts were studied within the framework of the Quantum Theory of Atoms in Molecules (QTAIM) at different levels of DFT theory (B3LYP/6-311(d,p) and BP86/TZ2P(+)) that shows the existence of a bifurcated Si-H?H-C_c dihydrogen bond. This paper presents the study of an experimental uncommon Si-H group playing as proton acceptor bond in a dihydrogen bond where hydrides like M-H (M, as metal transition), B-H or Al-H usually perform this role. Furthermore, this paper accounts with a new simple method to estimate bonding energies for closed-shell intramolecular interactions in the scheme of Voronoi charge population analysis and Coulomb′s Law.     

Coordination of a closo‐Cluster at Rhodium and Iridium

Stanna‐closo‐dodecaborate [Bu₃MeN]₂[SnB₁₁H₁₁] reacts as a nucleophile with the rhodium and iridium electrophiles of type [Cp*M(bipy′)Cl][BF₄] under formation of a transition metal tin bond. The zwitterionic molecules [Cp*M(bipy′)(SnB₁₁H₁₁)] (with M = Rh, Ir) were characterized by NMR spectroscopy, elemental analyses and X‐ray crystal structure analyses. A high dipole moment of 25.67 D was calculated by DFT methods in the case of the rhodium derivative.     

Heptagon-Containing Nanographene Embedded into [10]Cycloparaphenylene

We report the synthesis and characterization of a novel type of nanohoop, consisting of a cycloparaphenylene derivative incorporating a curved heptagon-containing π-extended polycyclic aromatic hydrocarbon (PAH) unit. We demonstrate that this new macrocycle behaves as a supramolecular receptor of curved π-systems such as fullerenes C₆₀ and C₇₀, with remarkably large binding constants (ca. 10⁷ M⁻¹), as estimated by fluorescence measurements. Nanosecond and femtosecond spectroscopic analysis show that these host-guest complexes are capable of quasi-instantaneous charge separation upon photoexcitation, due to the ultrafast charge transfer from the macrocycle to the complexed fullerene. These results demonstrate saddle-shaped PAHs with dibenzocycloheptatrienone motifs as structural components for new macrocycles displaying molecular receptor abilities and versatile photochemical responses with promising electron-donor properties in host-guest complexes.     

Synthesis of adenosine containing carborane modification

The carboranyl cage is a new modifying entity for nucleosides and DNA-oligonucleotides. Most of carborane–nucleoside conjugates described so far belong to pyrimidine series. Herein, the first synthesis of adenosine, nucleoside containing purine nucleic base, modified with carborane cluster, is described.     

Structural, spectroscopic, electrochemical and computational studies of C,C′-diaryl-ortho-carboranes, 1-(4-XC6H4)-2-Ph-1,2-C2B10H10 (X = H, F, OMe, NMe2, NH2, OH and O−)

The influence of aryl ring substituents X (F, OMe, NMe₂, NH₂, OH and O⁻) on the physical and electronic structure of the ortho-carborane cage in a series of C,C′-diaryl-ortho-carboranes, 1-(4-XC₆H₄)-2-Ph-1,2-C₂B₁₀H₁₀ has been investigated by crystallographic, spectroscopic [nuclear magnetic resonance (NMR), UV–vis], electrochemical and computational methods. The cage C1–C2 bond lengths in this carborane series show small variations with the electron-donating strength of the substituent X, but there is no evidence of a fully evolved quinoid form within the aryl substituents in the ground state. In the ¹¹B and ¹³C NMR spectra, the ‘antipodal’ shift at B12, and the C1 shift correlates with the Hammett σ _p value of the substituent X. The UV–visible absorption spectra of the cluster compounds show marked differences when compared with the spectra of the analogous substituted benzenes. These spectroscopic differences are attributed to variation in contributions from the cage orbitals to the unoccupied/virtual orbitals involved in the transitions responsible for the observed absorption bands. Electrochemical studies (cyclic and square-wave voltammetry) carried out on the diarylcarborane series reveal that one-electron reduction takes place at the cage in every case with the voltage required for reduction of the cage influenced by the electron-donating strength of the substituent X, affording a series of carborane radicals with formal [2n + 3] electron counts. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis,molecular structure and reactivity of the dimethyl sulfide adduct of a 1,3,2-diselenaborolane with an annelated dicarba-closo-dodecaborane(12) unit

The reaction of 1,2-diselenolato-1,2-dicarba-closo-dodecaborane(12) dianion [1,2-(1,2-C₂B₁₀H₁₀)Se₂]²⁻ with HBBr₂–SMe₂ affords the dimethyl sulfide adduct of 4,5-[1,2-dicarba-closo-dodecaborano(12)]-1,3-diselena-2-borolane in good yield. The molecular structure was determined by X-ray diffraction, and the solution-state structure was established by NMR spectroscopy (¹H, ¹¹B, ¹³C, ⁷⁷Se NMR). ¹¹B and ⁷⁷Se chemical shifts were reproduced by DFT calculations. Attempts were made to abstract dimethyl sulfide, and the parent donor-free compound could be detected in solution. The reactivity of the title compound was studied towards pyridine, Me₃SnF, [Pt(PPh₃)₂(C₂H₄)], tert-Bu-OH, AlMe₃ and AlH₃-N(Et)Me₂ as well as a hydroborating reagent.     

Synthesis, characterization and DFT calculations of new ethynyl-bridged C60 derivatives

A new series of soluble C₆₀ derivatives for organic electronic application has been synthesized by ethynylation reaction using different electron-donating and electron-withdrawing groups of varying length.     

General method for the synthesis of 2′-O-carboranyl-nucleosides

The carboranyl cage is a new modifying entity for nucleosides, DNA oligonucleotides, and other biomolecules. Herein, the first reliable method for the synthesis of nucleosides modified with a carborane cluster at the 2′-position is described.     

Measurement of Nanometer Distances in Solution via 13C NMR Spectroscopy—Shrinking of Macrocycles with Increasing Temperature

For a molecular system, size and shape are of elementary importance for its function and properties. Therefore, the determination of distances within a molecule is essential. However, the commonly used methods are only suitable for distances smaller than 4 Å or larger than 15 Å. Here, we show that by incorporating a molecular spring, we can measure distances in macrocycles in the range of 10 Å using ¹³C NMR spectroscopy. The accuracy of the method also allows to determine the temperature dependence of the distances. In one case, we find a contraction of the length by almost 10 % upon heating. This shrinking due to heating can be considered as inverse thermoelasticity at the molecular level and is a previously completely overlooked phenomenon that can be used in the future as a tool to change the length and, thus, the function of a system.     

Synthese von Germanium(I)‐bromid. Ein erster Schritt zu neuen Clusterverbindungen des Germaniums?

Synthesis of Germanium(I) Bromide. A First Step towards New Gemanium Cluster Compounds? Thermodynamic data for gaseous GeBr, derived from quantum chemical (DFT)‐calculations show that this monohalide should be formed at 1550 °C as a product of the reaction of elemental germanium with HBr at 1×10^—2 mbar. Herein the design of an apparatus is described in which GeBr can be synthesized under these conditions and cocondensed with toluene at —196 °C. Using this technique 3 g of a dark red X‐ray amorphous solid could be prepared over a period of 3 hours and was identified to be GeBr. It is shown to undergo disproportionation at 90 °C to give elemental germanium and germanium tetrabromide.     

Boron-Copper 1,3-Rearrangement: the New Concept Behind the Boryl Migration from C(sp2) in Alkenyl Boranes to C(sp3)

Regioselective borylcupration of borylated skipped (Z)-dienes generates diborylated alkylcopper species that are involved in an intramolecular stereospecific B/Cu 1,3-rearrangement by migration of Bpin moiety from C(sp²) to C(sp³). DFT mechanistic studies showed that boryl migration occurs through the formation of 4-membered boracycle intermediate with a moderate free-energy barrier. Moreover, the use of KOMe forms stable Lewis base adducts with Bpin moieties that blocks the reaction. Subsequently to the 1,3-boron shift, the in situ electrophilic trapping allows selective C−H, C−C and C−X bonds, followed by intramolecular cross coupling giving access to cyclic functionalized alkylidenecyclohexanes or alkylidenecyclobutanes.     

Dimethylaluminum and gallium amino alkoxides

An S,S′-thioether—thioester chelating ligand [7,8-μ-SCH₂C(O)S-7,8-C₂B₉H₁₀]⁻ (L₁), incorporating the unit [—(C)₂B₉H₁₀]⁻ has been synthesized. Reactions have been conducted with RhCl(PPh₃)₃ and PdCl₂(PPh₃)₂ complexes in ethanol. With Rh, L₁ maintains its original cyclic nature and most probably chelation via thioether—thioester takes place. The carborane negative charge may stabilize this original thioether—thioester complex. The other two Rh positions are occupied by two PPh₃ ancillary ligands forming [Rh(L₁)(PPh₃)₂]. The reaction of L₁ with Pd induces ligand modifications and the cyclic nature of L₁ is lost. A transesterification process leading to a dianionic ligand L₂, [7-S-8-SCH₂C(O)OCH₂CH₃−7,8-C₂B₉H₁₀]²⁻ has taken place. In this way L₂ is capable of compensating the dipositive Pd charge. The other two Pd positions are occupied by two PPh₃. This reaction has been extended to methanol and isopropanol solvents. The crystal structure of [Pd(L₂)(PPh₃)₂] has been determined.     

A DFT study of the Huisgen 1,3-dipolar cycloaddition between hindered thiocarbonyl ylides and tetracyanoethylene

The mechanism for the 1,3-dipolar cycloaddition between the hindered thiocarbonyl ylide 1 and tetracyanoethylene 2 has been studied at the B3LYP/6-31G^∗ level. Formation of the [3+2] cycloadduct 4 takes place through a stepwise mechanism that is initiated by the nucleophilic attack of the thiocarbonyl ylide 1 to the ethylene derivative 2 to give a zwitterionic intermediate IN. The subsequent cyclization of IN yields a seven-membered cyclic ketene imine 6, which equilibrates with the thermodynamically more stable [3+2] cycloadduct 4. The computed free energies are in agreement with the experimental outcomes.     

Chalcogen-Bond-Induced Double Helix Based on Self-Assembly of a Small Planar Building Block

As a rule, helical structures at the molecular level are formed by non-planar units. This makes the design of helices, starting from planar building blocks via self-assembly, even more fascinating. Until now, however, this has only been achieved in rare cases, where hydrogen and halogen bonds were involved. Here, we show that the carbonyl-tellurium interaction motif is suitable to assemble even small planar units into helical structures in solid phase. We found two different types of helices: both single and double helices, depending on the substitution pattern. In the double helix, the strands are connected by additional Te⋅⋅⋅Te chalcogen bonds. In the case of the single helix, a spontaneous enantiomeric resolution occurs in the crystal. This underlines the potential of the carbonyl-tellurium chalcogen bond to generate complex three-dimensional patterns.     

Photoluminescence of boron carbide

The excitation of B_4.3C with an Ar-laser () yields a photoluminescence spectrum between about 1.56 and 1.58 eV with its main maximum at 1.563 eV and a weaker maximum at 1.572 eV. It is attributed to the indirect-allowed recombination of free excitons.