Selective Oxygen and Hydrogen Functionalization of the h-BN/Rh(111) Nanomesh

We present detailed studies on the covalent adsorption of molecular oxygen and atomic hydrogen on the hexagonal boron nitride (h-BN) nanomesh on Rh(111). The functionalization of this two-dimensional (2D) material was investigated under ultra-high vacuum conditions using synchrotron radiation-based in situ high-resolution X-ray photoelectron spectroscopy, temperature-programmed X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. We are able to provide a deep insight into the adsorption behavior and thermal stability of oxygen and hydrogen on h-BN/Rh(111). Oxygen functionalization was achieved via a supersonic molecular beam while hydrogen functionalization was realized using an atomic hydrogen source. Adsorption of the respective species was observed to occur selectively in the pores of h-BN leading to spatially defined modification of the 2D layer. The adsorption of the observed molecular oxygen species was found to be an activated process that requires high-energy oxygen molecules. Upon heating to 700 K, oxygen functionalization was observed to be almost reversible except for small amounts of boron oxides evolving due to the reaction of oxygen with the 2D material. Hydrogen functionalization of h-BN/Rh(111) was fully reversed upon heating to about 640 K.     

High‐Density DNA Functionalization by a Combination of Cu‐Catalyzed and Cu‐Free Click Chemistry

We report the regioselective Cu‐free click modification of styrene functionalized DNA with nitrile oxides. A series of modified oligodeoxynucleotides (nine base pairs) was prepared with increasing styrene density. 1,3‐Dipolar cycloaddition with nitrile oxides allows the high density functionalization of the styrene modified DNA directly on the DNA solid support and in solution. This click reaction proceeds smoothly even directly in the DNA synthesizer and gives exclusively 3,5‐disubstituted isoxazolines. Additionally, PCR products (300 and 900 base pairs) were synthesized with a styrene triphosphate and KOD XL polymerase. The click reaction on the highly modified PCR fragments allows functionalization of hundreds of styrene units on these large DNA fragments simultaneously. Even sequential Cu‐free and Cu‐catalyzed click reaction of PCR amplicons containing styrene and alkyne carrying nucleobases was achieved. This new approach towards high‐density functionalization of DNA is simple, modular, and efficient.     

Opportune gem‐Silylborylation of Carbonyl Compounds: A Modular and Stereocontrolled Entry to Tetrasubstituted Olefins

An easy access to highly versatile gem‐silylboronate synthons is achieved by means of a new olefination reagent, HC(Bpin)₂(SiMe₃). Subsequent silicon or boron‐based selective functionalization allows for the modular and stereocontrolled synthesis of all‐carbon tetrasubstituted alkenes. A particular attraction of this approach is the iododesilylation reaction, which becomes a pivotal tool for C?Si functionalization.     

Coordination compounds of electron-deficient boron cluster anions BnH n2? (n = 6, 10, 12)

This survey concerns the coordination ability of B _n H _n ²⁻ (n = 6, 10, 12) boron cluster anions and their derivatives in complex formation. Boron cluster anions form four types of compounds: salts of organic cations and alkali-metal cations, including Cat₂B _n H _n , where specific interactions can be observed between a cation Cat and a boron cluster anion; salts of protonated anions CatB₆H₇ and CatB₁₀H₁₁, analogues of Cat[MB _n H _n ] complexes, where an extra hydrogen atom appears bound with the BBB face of a boron polyhedron and performs as a hard acceptor; metal complexes with outer-sphere boron cluster anions where specific ligand-ligand interactions may be observed between a boron cluster anion and an inner-sphere ligand; and true metal complexes with boron cluster anions that enter the inner coordination sphere. The last case characterizes closo-hydroborate anions as polydentate ligands whose denticity can vary widely under the effect of substituents or other ligands in the complex.     

Hexagonal Bipyramidal [Ta2B6]−/0 Clusters: B6 Rings as Structural Motifs

It has been a long‐sought goal in cluster science to discover stable atomic clusters as building blocks for cluster‐assembled nanomaterials, as exemplified by the fullerenes and their subsequent bulk syntheses. ¹ , ² Clusters have also been considered as models to understand bulk properties, providing a bridge between molecular and solid‐state chemistry. ³ Because of its electron deficiency, boron is an interesting element with unusual polymorphism. While bulk boron is known to be dominated by the three‐dimensional (3D) B₁₂ icosahedral motifs, ⁴ new forms of elemental boron are continuing to be discovered. ⁵ In contrast to the 3D cages commonly found in bulk boron, in the gas phase two‐dimensional (2D) boron clusters are prevalent. ⁶ – ⁸ The unusual planar boron clusters have been suggested as potential new bulking blocks or ligands in chemistry. ^6a Herein we report a joint experimental and theoretical study on the [Ta₂B₆]⁻ and [Ta₂B₆] clusters. We found that the most stable structures of both the neutral and anion are D_6h bipyramidal, similar to the recently discovered MB₆M structural motif in the Ti₇Rh₄Ir₂B₈ solid compound. ⁹      

Hydrogenation of Borylated Arenes

A cis‐selective hydrogenation of abundant aryl boronic acids and their derivatives catalyzed by rhodium cyclic (alkyl)(amino)carbene (Rh–CAAC) is reported. The reaction tolerates a variety of boron‐protecting groups and provides direct access to a broad scope of saturated, borylated carbo‐ and heterocycles with various functional groups. The transformation is strategically important because the versatile saturated boronate products are difficult to prepare by other methods. The utility of the saturated cyclic building blocks was demonstrated by post‐functionalization of the boron group.     

From Mono‐ to Poly‐Substituted Frameworks: A Way of Tuning the Acidic Character of Cc?H in o‐Carborane Derivatives

The incorporation of iodine atoms onto the boron vertices of the o‐carborane framework causes, according to spectroscopic data, a uniform increase in the acidic character of the C_c? H (C_c= cluster carbon) vertices, whereas the incorporation of methyl groups onto the boron vertices of the o‐carborane framework reduces their acidity. Methyl groups when attached to boron are electron‐withdrawing in boron clusters, whereas iodine atoms bonded to boron act as electron donors. This has been proven on B‐methyl and B‐iodinated o‐carboranes with NMR spectroscopy measurements and DFT calculations of natural bond orbital (NBO) charges, which show a cumulative buildup of positive cluster‐only total charge (CTC) on B‐methyl o‐carboranes and a cumulative buildup of negative cluster‐only total charge for B‐iodinated o‐carboranes.     

X-Ray Photoelectron Spectra and Electronic Structure of Solid Solutions Based on Cubic Boron Nitride

The electronic energy structure of substitution solid solutions based on boron nitride B _1-x NR _x and BN _1-x R_x (R = C, O) (x=0.25) in a diamond-like modification of ZnS type has been investigated by the local coherent potential method in terms of multiple-scattering theory. The total and partial densities of states were calculated for each element in a solid solution. The crystalline potential was calculated using an MT approximation. The lattice parameter was chosen based on X-ray diffraction data for c-BN: 0.3615 nm. The electronic energy structures of the solid solutions and binary c-BN are compared in the framework of a single approximation. The calculated partial densities of states are compared with the experimental X-ray emission and photoelectron spectra of boron, nitrogen, and oxygen in these compounds. The calculated partial charges of electrons at the top of the valence band show that charge transfer from boron to nitrogen takes place in the solid solutions. An analysis of the electronic structures of the solid solutions of boron nitride indicates that the quasicore resonances inherent in binary c-BN are delocalized and that chemical bonding in the solid solutions of boron nitride is weakened.     

Controlling the Dual-Emission Character of Aryl-Modified o-Carboranes by Intramolecular CH⋅⋅⋅O Interaction Sites

It is still challenging to realize a dual-emission system, in which two luminescent bands simultaneously appear by photoexcitation, in solid with organic dyes due to the difficulty in regulation of electronic properties in the excited state and concentration quenching. o-Carborane is known to be a versatile platform for constructing solid-state emitters since the sphere boron cluster is favorable for suppressing intermolecular interactions and subsequently concentration quenching. Here, we show solid-state dual-emissive o-carborane derivatives. We prepared 4 types of o-carborane derivatives and found dual-emission behaviors both in solution and solid states. By regulating the rotation at the o-carborane unit with the intramolecular C_cageH⋅⋅⋅O interaction, the dual-emission intensity ratios were changed. Finally, it was demonstrated that the overall photoluminescence spectra can be estimated using the binding energy of intramolecular interactions.     

Boron Difluoride Complexes of Expanded N‐Confused Calix[n]phyrins That Demonstrate Unique Luminescent and Lasing Properties

Complexation of novel multiply N‐confused expanded calix[n]phyrins with boron difluoride afforded a new class of cyclic BODIPY (boron‐dipyrromethene) arrays. The structures of circularly arranged BODIPY subunits linked in an N‐confused fashion give rise to such photophysical properties unique to the macrocycles as redshifted emission wavelengths along with apparent large Stokes shifts, long emission lifetimes, and solid‐state lasing. The DFT calculations support the size‐dependent excited‐state dynamics of the macrocycles.     

碳硼烷硼氢键选择性官能团化的研究进展

由于独特的三维立体结构、硼含量高、良好的热稳定性和化学稳定性等特点,碳硼烷及其衍生物在材料、催化、医药、超分子和配位化学等领域应用广泛,因此发展高效、高区域选择性的碳硼烷B-H键的官能团化的方法学备受硼化学家的关注。本文对近年来碳硼烷B-H键的官能团化的反应类型及相关反应机理予以论述,希望为后续研究提供可靠的参考。     

A Dynamic Thermodynamic Resolution Strategy for the Stereocontrolled Synthesis of Streptonigrin

We report that axially chiral biaryl boronic esters can be generated with control of atroposelectivity by a Binol-mediated dynamic thermodynamic resolution process. These intermediates can be progressed to enantioenriched products through stereoretentive functionalization of the carbon–boron bond. Finally, we have exploited this method in the first highly stereoselective total synthesis of P-streptonigrin.     

1,3‐Dehydro‐o‐Carborane: Generation and Reaction with Arenes

Like the importance of benzyne, witnessed in modern arene chemistry for decades, 1,2‐dehydro‐o‐carborane (o‐carboryne), a three‐dimensional relative of benzyne, has been used as a synthon for generating a wide range of cage, carbon‐functionalized carboranes over the past 20 years. However, the selective B functionalization of the cage still represents a challenging task. Disclosed herein is the first example of 1,3‐dehydro‐o‐carborane featuring a cage C? B bond having multiple bonding characters, and is successfully generated by treatment of 3‐diazonium‐o‐carborane tetrafluoroborate with non‐nucleophilic bases. This presents a new methodology for simultaneous functionalization of both cage carbon and boron vertices.     

Synthesis of a Tyr-octreotate conjugated closo-carborane [HC2B10H10]: a potential compound for boron neutron capture therapy

A novel Tyr³-octreotate conjugated closo-carborane as a potential compound for boron neutron capture therapy was obtained via Fmoc solid phase peptide synthesis. The boron cluster [C₂B₁₀H₁₁] was introduced through the reaction of 6,9-bis(acetonitrile)decaborane and 5-hexynoic acid yielding a new closo-carborane conjugated carboxylic acid which was coupled subsequently with solid phase conjugated Tyr³-octreotate. The final boron-containing peptide was purified by preparative reverse phase HPLC and structural identity was proved applying MALDI-TOF mass spectrometry.     

Resonating valence bond ground state in oxygen-functionalized phenalenyl-based neutral radical molecular conductors

We report the preparation, crystallization, and solid-state characterization of the first two members of a new family of spiro-bis(1,9-disubstituted phenalenyl)boron neutral radicals based solely on oxygen functionalization, and we show that this strategy significantly lowers the electrochemical disproportionation potentials (DeltaE), in comparison with other spiro-bis(1,9-disubstituted phenalenyl)boron salts. In the solid state, these radicals pack in a continuous array of pi-pi-stacked phenalenyl units with very short intermolecular carbon...carbon contacts. These two radicals are among the most highly conducting neutral organic solids, with room temperature conductivities reaching 0.3 S/cm. Magnetic susceptibility measurements show that the radicals do not exist as isolated free radicals, and there is significant spin-spin interaction between the molecules in the solid state as expected from the crystal structures and the calculated band structures; the solid-state properties are best rationalized in terms of the resonating valence bond model.     

Facial Synthesis of o‐Carborane‐Substituted Alkenes and Allenes by a Regioselective Ene Reaction of 1,3‐Dehydro‐o‐carborane

1,3‐Dehydro‐o‐carborane is a useful synthon for selective cage boron functionalization of o‐carboranes. It reacts readily with alkenes or alkynes to give a variety of cage B(3)‐alkenyl/allenyl o‐carboranes by ene reactions in very high yields and excellent regioselectivity. This can be ascribed to the highly polarized cage C?B multiple bond, which lowers the activation barriers of the ene reaction.     

Copper(I)-Catalyzed Enantioselective Nucleophilic Borylation of Aliphatic Ketones: Synthesis of Enantioenriched Chiral Tertiary α-Hydroxyboronates

A new method was developed for the first catalytic enantioselective borylation of aliphatic ketones. A variety of substrates reacted efficiently with bis(pinacolato)diboron in the presence of a copper(I)/chiral N-heterocyclic carbene complex catalyst to furnish optically active tertiary α-hydroxyboronates with moderate to high enantioselectivities (up to 94 % ee). Notably, the product could be converted into the chiral tertiary alcohol derivative using a stereospecific boron functionalization process. The theoretical study of the mechanism for the enantioselectivity is also described.     

BODIPY Dyes Bearing Multibranched Fluorinated Chains: Synthesis,Structural, and Spectroscopic Studies

A small series of boron-dipyrromethene (BODIPY) dyes, characterized by the presence of multibranched fluorinated residues, were designed and synthesized. The dyes differ in both the position (para-perfluoroalkoxy-substituted phenyl ring or boron functionalization) and number of magnetically equivalent fluorine atoms (27 or 54 fluorine atoms per molecule). Photophysical and crystallographic characterization of the synthesized BODIPYs was carried out to evaluate the effect of the presence of highly fluorinated moieties on the optical and morphological properties of such compounds.     

Ab initio study on the noncovalent adsorption of camptothecin anticancer drug onto graphene, defect modified graphene and graphene oxide

The application of graphene and related nanomaterials like boron nitride (BN) nanosheets, BN-graphene hybrid nanomaterials, and graphene oxide (GO) for adsorption of anticancer chemotherapeutic camptothecin (CPT) along with the effect on electronic properties prior to functionalization and after functionalization has been reported using density functional theory (DFT) calculations. The inclusion of dispersion correction to DFT is instrumental in accounting for van der Waals π–π stacking between CPT and the nanomaterial. The adsorption of CPT exhibits significant strain within the nanosheets and noncovalent adsorption of CPT is thermodynamically favoured onto the nanosheets. In case of GO, surface incorporation of functional groups result in significant crumpling along the basal plane and the interaction is basically mediated by H-bonding rather than π–π stacking. Docking studies predict the plausible binding of CPT, CPT functionalized graphene and GO with topoisomerase I (top 1) signifying that CPT interacts through π stacking with AT and GC base pairs of DNA and in presence of nano support, DNA bases preferentially gets bound to the basal plane of graphene and GO rather than the edges. At a theoretical level of understanding, our studies point out the noncovalent interaction of CPT with graphene based nanomaterials and GO for loading and delivery of anticancer chemotherapeutic along with active binding to Top1 protein.     

Evidence from Circular Dichroism and from Melting Behavior for Helix‐Inducing Complexation of a Designed β3‐Pentadecapeptide with DNA Duplexes. Preliminary Communication

Inspired by naturally occurring DNA‐binding proteins and their artificial α‐peptidic mimics reported to date, a research project was initiated aiming at creating a new class of β‐peptides capable of binding to and ultimately regulating the functions of DNA. As an initial foray, a β³‐pentadecapeptide 1 , which bears H‐bonding Asn side chains and positively charged Lys side chains, was designed and synthesized on the solid support. DNA‐Complexation studies by means of circular dichroism and DNA‐melting‐temperature measurements revealed the first preliminary indications that support the existence of ordered interactions between β‐peptides and DNA.