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Special Issue "Boron Chemistry and Its Development in the 21st Century: In Memory of Professor Bohumil Štíbr (1940-2020)"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Inorganic Chemistry".

Deadline for manuscript submissions: 30 June 2020.

Special Issue Editors

Prof. Dr. Igor B. Sivaev
Website
Guest Editor
Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, Russia
Interests: Chemistry and application of polyhedral boron hydrides, including boranes, carboranes, and metallacarboranes
Prof. Dr. Narayan S. Hosmane
Website
Guest Editor
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL, United States
Interests: Synthetic and structural chemistry of polyhedral boron cage biomolecules and nanostructured materials for cancer therapy, catalysis and extraction of radionuclides
Dr. Bohumír Grűner
Website
Guest Editor
Institute of Inorganic Chemistry, v.v.i., Czech Academy of Sciences, Řež, Czech Republic
Interests: Chemistry of boranes, carboranes and metallacatboranes; main focus on synthesis of derivatives designed as pharmacologically relevant enyzme inhibitors, polyhedral anions for extraction of radionuclides and chiral compounds

Special Issue Information

Dear Colleagues,

Prof. Dr. Bohumil Štíbr, born 15.07.1940 in Slaný, Czech Republic, is one of the most distinguished inorganic chemists who has made key contributions to the areas of boron chemistry. He graduated in Inorganic Chemistry at the University of Pardubice in 1962, where he also pursued his PhD (= CSc.), finishing in 1968 with a first-class degree award. Simultaneous to his studies, he was also very active in the area of boron cluster chemistry at Řež. He has been employed at the Institute of Inorganic Chemistry (IIC) at Řež since 1962. He has been in charge of the IIC's boron group for ~25 years. In 1997 he defended his DrSc thesis. Essentially, he is employed in the Institute of Inorganic Chemistry of the Czech Academy of Sciences of the Czech Republic as Leading Research Scientist. Over this whole period of time he was working in the area of cluster-boron chemistry. He is author/co-author of ~300 scientific papers in impacted journals and several book contributions, mostly in the area of carboranes, main-group heteroboranes, and macropolyhedral boranes. He participated in the invention of ~30 new parent (unsubstituted) carboranes. In 1995 he discovered a new genre of carborane compounds (11-vertex tricarbaboranes, so called tricarbollides). Recently, he was involved in the area of alkylation reactions in the ten-vertex borane and carborane series.

Prof. Dr. Štíbr has received several awards, including two medals of the University of Pardubice, two prizes of the Czech Academy of Sciences of the Czech Republic, and the Alexander von Humboldt Prize (D, 2001). He has held several Visiting Professorships worldwide: University of California at LA, 6 months Research Fellow (1972); University of Leeds, UK, 6 months, Visiting Professor (1987); Institute of Materials, Bellaterra, Spain, 18 months, Visiting Professor (1995–6); and University of Bayreuth, D, Alex. von Humbolld Stifftung, 1 year, Visiting Professor (2001).

Molecules is pleased to announce a Special Issue honoring Bohumil Štíbr on the occasion of his 80th birthday for his outstanding achievements in boron chemistry. This Special Issue is dedicated to all aspects of boron chemistry, including cluster and inorganic boron chemistry (including boranes, carboranes, metallaboranes, metallacarboranes, aminoboranes, transition metal complexes of boron, etc.), organic and bioorganic boron chemistry (including boron-based Lewis acids, boronic acids and its complexes, benzoxaboroles, the application of boron reagents in organic synthesis), boron in materials (including polymers, dendrimers, ionic liquids, liquid crystals, hydrogen storage, catalysis, etc.), and boron in medicine (including boron neutron capture of cancer, carborane pharmacophores, boron-containing drugs, boronic acid-based sugar sensors, etc.).

It is a pleasure to invite you to submit a manuscript to this Special Issue; regular articles, communications, as well as reviews are all welcome.

Special Statement: This Issue and collection of articles are dedicated to the memory of the Prof. Dr. Bohumil Štíbr, who unfortunately passed away on January 7th 2020, soon before he could reach the age of 80. Bohumil was among the founding fathers of boroh hydride chemistry in the Czech Republic, and was responsible for many important developments in the field.  The following articles are a celebration of Bohumil's great efforts.  May he rest in peace.

Prof. Dr. Igor B. Sivaev
Prof. Dr. Narayan S. Hosmane
Dr. Bohumír Grűner
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Boranes
  • Carboranes
  • Metallaboranes
  • Metallacarboranes
  • Transition metal–boron complexes
  • Boron-based Lewis acids
  • Aminoboranes
  • Boronic acids
  • Boron-based materials
  • Boron-based drugs
  • Boron neutron capture therapy

Published Papers (16 papers)

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Research

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Open AccessArticle
Blue Emitting Star-Shaped and Octasilsesquioxane-Based Polyanions Bearing Boron Clusters. Photophysical and Thermal Properties
Molecules 2020, 25(5), 1210; https://doi.org/10.3390/molecules25051210 - 07 Mar 2020
Abstract
High boron content systems were prepared by the peripheral functionalisation of 1,3,5-triphenylbenzene (TPB) and octavinylsilsesquioxane (OVS) with two different anionic boron clusters: closo-dodecaborate (B12) and cobaltabisdicarbollide (COSAN). TPB was successfully decorated with three cluster units by an oxonium ring-opening reaction, [...] Read more.
High boron content systems were prepared by the peripheral functionalisation of 1,3,5-triphenylbenzene (TPB) and octavinylsilsesquioxane (OVS) with two different anionic boron clusters: closo-dodecaborate (B12) and cobaltabisdicarbollide (COSAN). TPB was successfully decorated with three cluster units by an oxonium ring-opening reaction, while OVS was bonded to eight clusters by catalysed metathesis cross-coupling. The resulting compounds were spectroscopically characterised, and their solution-state photophysical properties analysed. For TPB, the presence of COSAN dramatically quenches the fluorescence emission (λem = 369 nm; ΦF = 0.8%), while B12-substituted TPB shows an appreciable emission efficiency (λem = 394 nm; ΦF = 12.8%). For octasilsesquioxanes, the presence of either COSAN or B12 seems to be responsible for ∼80 nm bathochromic shift with respect to the core emission, but both cases show low emission fluorescence (ΦF = 1.4–1.8%). In addition, a remarkable improvement of the thermal stability of OVS was observed after its functionalisation with these boron clusters. Full article
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Open AccessArticle
The Influence of Halogenated Hypercarbon on Crystal Packing in the Series of 1-Ph-2-X-1,2-dicarba-closo-dodecaboranes (X = F, Cl, Br, I)
Molecules 2020, 25(5), 1200; https://doi.org/10.3390/molecules25051200 - 06 Mar 2020
Abstract
Although 1-Ph-2-X-closo-1,2-C2B10H10 (X = F, Cl, Br, I) derivatives had been computed to have positive values of the heat of formation, it was possible to prepare them. The corresponding solid-state structures were computationally analyzed. Electrostatic potential [...] Read more.
Although 1-Ph-2-X-closo-1,2-C2B10H10 (X = F, Cl, Br, I) derivatives had been computed to have positive values of the heat of formation, it was possible to prepare them. The corresponding solid-state structures were computationally analyzed. Electrostatic potential computations indicated the presence of highly positive σ-holes in the case of heavy halogens. Surprisingly, the halogen•••π interaction formed by the Br atom was found to be more favorable than that of I. Full article
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Open AccessArticle
Complexes Between Adamantane Analogues B4X6 -X = {CH2, NH, O ; SiH2, PH, S} - and Dihydrogen, B4X6:nH2 (n = 1–4)
Molecules 2020, 25(5), 1042; https://doi.org/10.3390/molecules25051042 - 26 Feb 2020
Cited by 1
Abstract
In this work, we study the interactions between adamantane-like structures B4X6 with X = {CH2, NH, O ; SiH2, PH, S} and dihydrogen molecules above the Boron atom, with ab initio methods based on perturbation theory [...] Read more.
In this work, we study the interactions between adamantane-like structures B4X6 with X = {CH2, NH, O ; SiH2, PH, S} and dihydrogen molecules above the Boron atom, with ab initio methods based on perturbation theory (MP2/aug-cc-pVDZ). Molecular electrostatic potentials (MESP) for optimized B4X6 systems, optimized geometries, and binding energies are reported for all B4X6:nH2 (n = 1–4) complexes. All B4X6:nH2 (n = 1–4) complexes show attractive patterns, with B4O6:nH2 systems showing remarkable behavior with larger binding energies and smaller B···H2 distances as compared to the other structures with different X. Full article
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Open AccessArticle
Focus on Chemistry of the 10-Dioxane-nido-7,8-dicarba-undecahydrido Undecaborate Zwitterion; Exceptionally Easy Abstraction of Hydrogen Bridge and Double-Action Pathways Observed in Ring Cleavage Reactions with OH as Nucleophile
Molecules 2020, 25(4), 814; https://doi.org/10.3390/molecules25040814 - 13 Feb 2020
Abstract
Ring cleavage of cyclic ether substituents attached to a boron cage via an oxonium oxygen atom are amongst the most versatile methods for conjoining boron closo-cages with organic functional groups. Here we focus on much less tackled chemistry of the 11-vertex zwitterionic [...] Read more.
Ring cleavage of cyclic ether substituents attached to a boron cage via an oxonium oxygen atom are amongst the most versatile methods for conjoining boron closo-cages with organic functional groups. Here we focus on much less tackled chemistry of the 11-vertex zwitterionic compound [10-(O-(CH2-CH2)2O)-nido-7,8-C2B9H11] (1), which is the only known representative of cyclic ether substitution at nido-cages, and explore the scope for the use of this zwitterion 1 in reactions with various types of nucleophiles including bifunctional ones. Most of the nitrogen, oxygen, halogen, and sulphur nucleophiles studied react via nucleophilic substitution at the C1 atom of the dioxane ring, followed by its cleavage that produces six atom chain between the cage and the respective organic moiety. We also report the differences in reactivity of this nido-cage system with the simplest oxygen nucleophile, i.e., OH. With compound 1, reaction proceeds in two possible directions, either via typical ring cleavage, or by replacement of the whole dioxane ring with -OH at higher temperatures. Furthermore, an easy deprotonation of the hydrogen bridge in 1 was observed that proceeds even in diluted aqueous KOH. We believe this knowledge can be further applied in the design of functional molecules, materials, and drugs. Full article
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Open AccessArticle
Synthesis, Properties and Antimicrobial Activity of 5-Trifluoromethyl-2-formylphenylboronic Acid
Molecules 2020, 25(4), 799; https://doi.org/10.3390/molecules25040799 - 12 Feb 2020
Cited by 1
Abstract
2-Formylphenylboronic acids display many interesting features, not only from synthetic but also from an application as well as structural points of view. 5-Trifluoromethyl-2-formyl phenylboronic acid has been synthesized and characterized in terms of its structure and properties. The presence of an electron-withdrawing substituent [...] Read more.
2-Formylphenylboronic acids display many interesting features, not only from synthetic but also from an application as well as structural points of view. 5-Trifluoromethyl-2-formyl phenylboronic acid has been synthesized and characterized in terms of its structure and properties. The presence of an electron-withdrawing substituent results in a considerable rise in the acidity in comparison with its analogues. In some solutions, the title compound isomerizes with formation of the corresponding 3-hydroxybenzoxaborole. Taking into account the probable mechanism of antifungal action of benzoxaboroles, which blocks the cytoplasmic leucyl-tRNA synthetase (LeuRS) of the microorganism, docking studies with the active site of the enzymes have been carried out. It showed possible binding of the cyclic isomer into the binding pocket of Candida albicans LeuRS, similar to that of the recently approved benzoxaborole antifungal drug (AN2690, Tavaborole, Kerydin). In case of Escherichia coli LeuRS, the opened isomer displays a much higher inhibition constant in comparison with the cyclic one. The antimicrobial activity of the title compound was also investigated in vitro, showing moderate action against Candida albicans. The compound reveals higher activity against Aspergillus niger as well as bacteria such as Escherichia coli and Bacillus cereus. In case of Bacillus cereus, the determined Minimum Inhibitory Concentration (MIC) value is lower than that of AN2690 (Tavaborole). The results confirm potential of 2-formylphenylboronic acids as antibacterial agents and give a hint of their possible mechanism of action. Full article
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Open AccessFeature PaperCommunication
Exopolyhedral Ligand Orientation Controls Diastereoisomer in Mixed-Metal Bis(Carboranes)
Molecules 2020, 25(3), 519; https://doi.org/10.3390/molecules25030519 - 24 Jan 2020
Abstract
Heterobimetallic derivatives of a bis(carborane), [μ7,8-(1′,3′−3′-Cl-3′-PPh3-closo-3′,1′,2′-RhC2B9H10)-2-(p-cymene)-closo-2,1,8-RuC2B9H10] (1) and [μ7,8-(1′,3′−3′-Cl-3′-PPh3-closo-3′,1′,2′-RhC2B9H [...] Read more.
Heterobimetallic derivatives of a bis(carborane), [μ7,8-(1′,3′−3′-Cl-3′-PPh3-closo-3′,1′,2′-RhC2B9H10)-2-(p-cymene)-closo-2,1,8-RuC2B9H10] (1) and [μ7,8-(1′,3′−3′-Cl-3′-PPh3-closo-3′,1′,2′-RhC2B9H10)-2-Cp-closo-2,1,8-CoC2B9H10] (2) have been synthesised and characterised, including crystallographic studies. A minor co-product during the synthesis of compound 2 is the new species [8-{8′-2′-H-2′,2′-(PPh3)2-closo-2′,1′,8′-RhC2B9H10}-2-Cp-closo-2,1,8-CoC2B9H10] (3), isolated as a mixture of diastereoisomers. Although, in principle, compounds 1 and 2 could also exist as two diastereoisomers, only one (the same in both cases) is formed. It is suggested that the preferred exopolyhedral ligand orientation in the rhodacarboranes in the non-observed diastereoisomers would lead to unacceptable steric crowding between the PPh3 ligand and either the p-cymene (compound 1) or Cp (compound 2) ligand of the ruthenacarborane or cobaltacarborane, respectively. Full article
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Open AccessArticle
Synthesis and Structure of Methylsulfanyl Derivatives of Nickel Bis(Dicarbollide)
Molecules 2019, 24(24), 4449; https://doi.org/10.3390/molecules24244449 - 04 Dec 2019
Cited by 1
Abstract
Symmetrically and unsymmetrically substituted methylsulfanyl derivatives of nickel(III) bis(dicarbollide) (Bu4N)[8,8′-(MeS)2-3,3′-Ni(1,2-C2B9H10)2], (Bu4N)[4,4′-(MeS)2-3,3′-Ni(1,2-C2B9H10)2], and (Bu4N)[4,7′-(MeS)2-3,3′-Ni(1,2-C2B [...] Read more.
Symmetrically and unsymmetrically substituted methylsulfanyl derivatives of nickel(III) bis(dicarbollide) (Bu4N)[8,8′-(MeS)2-3,3′-Ni(1,2-C2B9H10)2], (Bu4N)[4,4′-(MeS)2-3,3′-Ni(1,2-C2B9H10)2], and (Bu4N)[4,7′-(MeS)2-3,3′-Ni(1,2-C2B9H10)2] were synthesized, starting from [Ni(acac)2]3 and the corresponding methylsulfanyl derivatives of nido-carborane (Bu4N)[10-MeS-7,8-C2B9H11] and (Bu4N)[10-MeS-7,8-C2B9H11]. Structures of the synthesized metallacarboranes were studied by single-crystal X-ray diffraction and quantum chemical calculations. The symmetrically substituted 8,8′-isomer adopts transoid conformation stabilized by two pairs of intramolecular C–H···S hydrogen bonds between the dicarbollide ligands. The unsymmetrically substituted 4,7′-isomer adopts gauche conformation, which is stabilized by two nonequivalent C–H···S hydrogen bonds and one short chalcogen B–H···S bond (2.53 Å, −1.4 kcal/mol). The gauche conformation was found to be also preferred for the 4,7′-isomer. Full article
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Open AccessArticle
Photophysical Properties of Spirobifluorene-Based o-Carboranyl Compounds Altered by Structurally Rotating the Carborane Cages
Molecules 2019, 24(22), 4135; https://doi.org/10.3390/molecules24224135 - 15 Nov 2019
Abstract
9,9′-Spirobifluorene-based o-carboranyl compounds C1 and C2 were prepared and fully characterized by multinuclear nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. The solid-state structure of C1 was also determined by single-crystal X-ray diffractometry. The two carboranyl compounds display major absorption bands that [...] Read more.
9,9′-Spirobifluorene-based o-carboranyl compounds C1 and C2 were prepared and fully characterized by multinuclear nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. The solid-state structure of C1 was also determined by single-crystal X-ray diffractometry. The two carboranyl compounds display major absorption bands that are assigned to ππ* transitions involving their spirobifluorene groups, as well as weak intramolecular charge-transfer (ICT) transitions between the o-carboranes and their spirobifluorene groups. While C1 only exhibited high-energy emissions (λem = ca. 350 nm) in THF at 298 K due to locally excited (LE) states assignable to ππ* transitions involving the spirobifluorene group alone, a remarkable emission in the low-energy region was observed in the rigid state, such as in THF at 77 K or the film state. Furthermore, C2 displays intense dual emissive patterns in both high- and low-energy regions in all states. Electronic transitions that were calculated by time-dependent-DFT (TD-DFT) for each compound based on ground (S0) and first-excited (S1) state optimized structures clearly verify that the low-energy emissions are due to ICT-based radiative decays. Calculated energy barriers that are based on the relative energies associated with changes in the dihedral angle around the o-carborane cages in C1 and C2 clearly reveal that the o-carborane cage in C1 rotates more freely than that in C2. All of the molecular features indicate that ICT-based radiative decay is only available to the rigid state in the absence of structural fluctuations, in particular the free-rotation of the o-carborane cage. Full article
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Open AccessFeature PaperArticle
Insertion of Carbenes into Deprotonated nido-Undecaborane, B11H13(2-)
Molecules 2019, 24(20), 3779; https://doi.org/10.3390/molecules24203779 - 21 Oct 2019
Abstract
We have examined the insertion of carbenes carrying leaving groups into the [nido-B11H13]2− dianion to form the [closo-1-CB11H12] anion. The best procedure uses CF3SiMe3 and LiCl [...] Read more.
We have examined the insertion of carbenes carrying leaving groups into the [nido-B11H13]2− dianion to form the [closo-1-CB11H12] anion. The best procedure uses CF3SiMe3 and LiCl as the source of CF2. It is simple, convenient and scalable and proceeds with 70–90% yield. Density functional calculations have been used to develop a mechanistic proposal that accounts for the different behavior of CF2, requiring only one equivalent of base for successful conversion of Na[nido-B11H14] to [closo-1-CB11H12], and CCl2 and CBr2, which require more. Full article
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Open AccessArticle
Enlargement of a Modular System—Synthesis and Characterization of an s-Triazine-Based Carboxylic Acid Ester Bearing a Galactopyranosyl Moiety and an Enormous Boron Load
Molecules 2019, 24(18), 3288; https://doi.org/10.3390/molecules24183288 - 10 Sep 2019
Cited by 1
Abstract
The amount of boron accumulated in tumor tissue plays an important role regarding the success of the boron neutron capture therapy (BNCT). In this article, we report a modular system, combining readily available starting materials, like glycine, 1,3,5-triazine and the well-known 9-mercapto-1,7-dicarba-closo [...] Read more.
The amount of boron accumulated in tumor tissue plays an important role regarding the success of the boron neutron capture therapy (BNCT). In this article, we report a modular system, combining readily available starting materials, like glycine, 1,3,5-triazine and the well-known 9-mercapto-1,7-dicarba-closo-dodecaborane(12), as well as α-d-galactopyranose for increased hydrophilicity, with a novel boron-rich tris-meta-carboranyl thiol. Full article
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Open AccessArticle
A Reversible Phase Transition of 2D Coordination Layers by B–H∙∙∙Cu(II) Interactions in a Coordination Polymer
Molecules 2019, 24(17), 3204; https://doi.org/10.3390/molecules24173204 - 03 Sep 2019
Cited by 2
Abstract
Materials that combine flexibility and open metal sites are crucial for myriad applications. In this article, we report a 2D coordination polymer (CP) assembled from CuII ions and a flexible meta-carborane-based linker [Cu2(L1)2(Solv)2]•xSolv (1-DMA, 1-DMF, and [...] Read more.
Materials that combine flexibility and open metal sites are crucial for myriad applications. In this article, we report a 2D coordination polymer (CP) assembled from CuII ions and a flexible meta-carborane-based linker [Cu2(L1)2(Solv)2]•xSolv (1-DMA, 1-DMF, and 1-MeOH; L1: 1,7-di(4-carboxyphenyl)-1,7-dicarba-closo-dodecaborane). 1-DMF undergoes an unusual example of reversible phase transition on solvent treatment (i.e., MeOH and CH2Cl2). Solvent exchange, followed by thermal activation provided a new porous phase that exhibits an estimated Brunauer-Emmett-Teller (BET) surface area of 301 m2 g−1 and is capable of a CO2 uptake of 41 cm3 g−1. The transformation is reversible and 1-DMF is reformed on addition of DMF to the porous phase. We provide evidence for the reversible process being the result of the formation/cleavage of weak but attractive B–H∙∙∙Cu interactions by a combination of single-crystal (SCXRD), powder (PXRD) X-ray diffraction, Raman spectroscopy, and DFT calculations. Full article
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Open AccessCommunication
N-Heterocyclic Carbene Adducts of Alkynyl Functionalized 1,3,2-Dithioborolanes
Molecules 2019, 24(9), 1690; https://doi.org/10.3390/molecules24091690 - 30 Apr 2019
Cited by 1
Abstract
Alkynyl functionalized boron compounds are versatile intermediates in the areas of medicinal chemistry, materials science, and optical materials. In particular, alkynyl boronate esters [R1−C≡C−B(OR2)2] are of interest since they provide reactivity at both the alkyne entity, with [...] Read more.
Alkynyl functionalized boron compounds are versatile intermediates in the areas of medicinal chemistry, materials science, and optical materials. In particular, alkynyl boronate esters [R1−C≡C−B(OR2)2] are of interest since they provide reactivity at both the alkyne entity, with retention of the B−C bond or alkyne transfer to electrophilic substrates with scission of the latter. The boron atom is commonly well stabilized due to (i) the extraordinary strength of two B−O bonds, and (ii) the chelate effect exerted by a bifunctional alcohol. We reasoned that the replacement of a B−O for a B−S bond would lead to higher reactivity and post-functionalization in the resulting alkynyl boronate thioesters [R1−C≡C−B(S2X)]. Access to this poorly investigated class of compounds starts form chloro dithioborolane cyclo-Cl−B(S2C2H4) as a representative example. Whereas syntheses of three coordinate alkynyl boronate thioesters [R1−C≡C−B(S2X)] proved to be ineffective, the reactions of NHC-adducts (NHC = N-heterocyclic carbene) of cyclo-Cl-B(S2C2H4) afforded the alkyne substituted thioboronate esters in good yield. The products NHC−B(S2C2H4)(C≡C-R1) are remarkably stable towards water and air, which suggests their use as boron-based building blocks for applications akin to oxygen-based boronate esters. Full article
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Open AccessCommunication
NNB-Type Tridentate Boryl Ligands Enabling a Highly Active Iridium Catalyst for C–H Borylation
Molecules 2019, 24(7), 1434; https://doi.org/10.3390/molecules24071434 - 11 Apr 2019
Cited by 1Correction
Abstract
Boryl ligands play a very important role in catalysis because of their very high electron-donating property. In this paper, NNB-type boryl anions were designed as tridentate ligands to promote aryl C–H borylation. In combination with [IrCl(COD)]2, they generate a highly active [...] Read more.
Boryl ligands play a very important role in catalysis because of their very high electron-donating property. In this paper, NNB-type boryl anions were designed as tridentate ligands to promote aryl C–H borylation. In combination with [IrCl(COD)]2, they generate a highly active catalyst for a broad range of (hetero)arene substrates, including highly electron-rich and/or sterically hindered ones. This work provides a new NNB-type tridentate boryl ligand to support homogeneous organometallic catalysis. Full article
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Open AccessArticle
The Studies on Structure and Stability of CaBn Clusters
Molecules 2019, 24(6), 1011; https://doi.org/10.3390/molecules24061011 - 13 Mar 2019
Cited by 1
Abstract
Calcium-boron systems have excellent properties of hardness, strength, and chemical stability, and we studied a series of CaBn clusters to investigate their structures and relative stability. The results showed the most stable structures of CaBn clusters are not planar. The B [...] Read more.
Calcium-boron systems have excellent properties of hardness, strength, and chemical stability, and we studied a series of CaBn clusters to investigate their structures and relative stability. The results showed the most stable structures of CaBn clusters are not planar. The B atoms tend to get together and form the planar ring to stabilize the structure, and the Ca atoms are coordinated to the periphery of the formations. The average binding energy (Eb), fragmentation energy (EF), second-order energy difference (Δ2E), adiabatic detachment energy (ADE), and adiabatic electron affinity (AEA) of the CaBn clusters were calculated to investigate the relative stability and the ability of removing or obtaining an electron. As shown by the results, EF and Δ2E values had obvious odd-even alteration as n increased, which indicated that the formations CaB4, CaB6, and CaB8 were more stable. The ADE values for CaBn clusters with even values of n were higher than those with odd values of n, which indicated CaBn clusters with even values of n had difficultly removing an electron. The AEA values of CaB3 and CaB7 were larger than the others, which meant CaB3 and CaB7 easily obtained an electron. These results provide a useful reference for understanding the formation mechanism and stability of the alkaline earth metal boride as well as guidance for synthesizing the CaBn clusters. Full article
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Review

Jump to: Research

Open AccessFeature PaperReview
Boron Chemistry for Medical Applications
Molecules 2020, 25(4), 828; https://doi.org/10.3390/molecules25040828 - 13 Feb 2020
Cited by 1
Abstract
Boron compounds now have many applications in a number of fields, including Medicinal Chemistry. Although the uses of boron compounds in pharmacological science have been recognized several decades ago, surprisingly few are found in pharmaceutical drugs. The boron-containing compounds epitomize a new class [...] Read more.
Boron compounds now have many applications in a number of fields, including Medicinal Chemistry. Although the uses of boron compounds in pharmacological science have been recognized several decades ago, surprisingly few are found in pharmaceutical drugs. The boron-containing compounds epitomize a new class for medicinal chemists to use in their drug designs. Carboranes are a class of organometallic compounds containing carbon (C), boron (B), and hydrogen (H) and are the most widely studied boron compounds in medicinal chemistry. Additionally, other boron-based compounds are of great interest, such as dodecaborate anions, metallacarboranes and metallaboranes. The boron neutron capture therapy (BNCT) has been utilized for cancer treatment from last decade, where chemotherapy and radiation have their own shortcomings. However, the improvement in the already existing (BPA and/or BSH) localized delivery agents or new tumor-targeted compounds are required before realizing the full clinical potential of BNCT. The work outlined in this short review addresses the advancements in boron containing compounds. Here, we have focused on the possible clinical implications of the new and improved boron-based biologically active compounds for BNCT that are reported to have in vivo and/or in vitro efficacy. Full article
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Open AccessReview
Synthesis of Polyhedral Borane Cluster Fused Heterocycles via Transition Metal Catalyzed B-H Activation
Molecules 2020, 25(2), 391; https://doi.org/10.3390/molecules25020391 - 17 Jan 2020
Abstract
Aromatic heterocycles are ubiquitous building blocks in bioactive natural products, pharmaceutical and agrochemical industries. Accordingly, the carborane-fused heterocycles would be potential candidates in drug discovery, nanomaterials, metallacarboranes, as well as photoluminescent materials. In recent years, the transition metal catalyzed B-H activation has been [...] Read more.
Aromatic heterocycles are ubiquitous building blocks in bioactive natural products, pharmaceutical and agrochemical industries. Accordingly, the carborane-fused heterocycles would be potential candidates in drug discovery, nanomaterials, metallacarboranes, as well as photoluminescent materials. In recent years, the transition metal catalyzed B-H activation has been proved to be an effective protocol for selective functionalization of B-H bond of o-carboranes, which has been further extended for the synthesis of polyhedral borane cluster-fused heterocycles via cascade B-H functionalization/annulation process. This article summarizes the recent progress in construction of polyhedral borane cluster-fused heterocycles via B-H activation. Full article
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