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New Developments in Boron Chemistry: From Oxidoborates to Hydrido(hetero)borane Derivatives – in Celebration of Professor John D. Kennedy’s 80th Birthday

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

Deadline for manuscript submissions: closed (31 July 2023) | Viewed by 34684

Special Issue Editors

School of Natural Sciences, Bangor University, Bangor LL57 2UW, UK
Interests: agricultural bio-stimulants; boron-11 NMR; computational studies; hydrogen bonding; Lewis acidity measurement; organoborates and silicates; polyborates and silicates; synthesis; supramolecular self-assembly; transition-metal chemistry
Special Issues, Collections and Topics in MDPI journals
Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, Russia
Interests: chemistry and application of polyhedral boron hydrides; including boranes; carboranes and metallacarboranes
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Professor John D. Kennedy, born 28th March 1943, is a leading and influential British inorganic chemist who made key contributions to the area of borane and metallaborane chemistry. He began his scientific career with research in the field of organotin chemistry and soon became a recognized expert not only in the field of organometallic synthesis, but also in NMR spectroscopy of organometallic compounds. He received his BSc (1965) and PhD (1968) from University College London, and his doctoral studies were supervised by Prof. Alwyn G. Davies. He then spent a 3-year period at the State University of New York in Albany as a research associate, where he studied with Prof. Henry G. Kuivila. He returned to the UK in 1971 and worked for a time as a lecturer in organic chemistry at King's Сollege, London, after which he was appointed for 3 years as a research associate at the City of London Polytechnic, with Prof. William McFarlane.

In 1975, he moved from London to the University of Leeds, where he started to work on borane and metallaborane chemistry as a research fellow with Prof. Norman N. Greenwood. This partnership resulted in 100 influential publications. Soon after his arrival in Leeds, John Kennedy also established himself as an independent researcher and was promoted to Senior Lecturer, Reader, and then to Professor in 2000. He has published more than 400 papers, mainly on boron chemistry, and has an h-index of 44. John Kennedy retired in 2008 and now holds the title Emeritus Professor of Inorganic Chemistry. The ‘metallaborane’ group at Leeds oversaw significant developments in metallaborane, heteroborane, metallaheteroborane and carborane chemistry. In these studies, metals from both p and d blocks of the periodic table were incorporated into borane/heteroborane clusters with products both spectroscopically and structurally fully characterized . This research also allowed significant advances to be made in macropolyhedral chemistry, ‘disobedient skeletons’, supramolecular chemistry, and cluster fluxional processes. At the same time, John Kennedy developed an active collaboration with the Czech boron group at the Institute of Inorganic Chemistry of the Czech Academy of Sciences, which was named "the Anglo-Czech Polyhedral Collaboration" and continues to this day.

Professor John Kennedy has always taken an active part in the life of the boron community. He founded and organized a series of annual UK meetings for young boron chemists, known as the INTRABORON, with which he was associated for several years. For many years, he was a member of the international advisory boards for the international boron conferences, IMEBORON and EUROBORON. In 1993, he received the J.E. Purkynĕ Medal from the Academy of Sciences of the Czech Republic, and in 2000, he was awarded the Royal Society of Chemistry 1999 Silver Medal for Main-Group Chemistry.

Molecules is pleased to announce a Special Issue, due for publication in March 2023, to honour Professor John D. Kennedy for his outstanding achievements in boron chemistry and to celebrate his 80th birthday.

This Special Issue is dedicated to all aspects of boron chemistry, including all fields of inorganic boron chemistry from oxidoborates to hydrido(hetero)borane derivatives (including boranes, carboranes, metallaboranes, and metallacarboranes), transition metal complexes of boron-containing ligands, organic and bio-organic boron chemistry (including boron-based Lewis acids, boronic acids, benzoxaboroles, aminoboranes, and the application of boron reagents in organic synthesis), boron in materials (including polymers, dendrimers, ionic liquids, liquid crystals, hydrogen storage, and catalysis), and boron in medicine (including boron neutron capture of cancer, carborane pharmacophores, boron-containing drugs, and boronic acid-based sugar sensors.).

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.

Prof. Dr. Michael A. Beckett
Prof. Dr. Igor B. Sivaev
Guest Editors

Manuscript Submission Information

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Keywords

  • boranes
  • boron-containing ligands
  • carboranes
  • heteroboranes
  • hydridoborates
  • metalla(car)boranes
  • organoboron compounds
  • oxidoborates

Published Papers (25 papers)

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14 pages, 3939 KiB  
Article
New Boron Containing Acridines: Synthesis and Preliminary Biological Study
by Anna A. Druzina, Nadezhda V. Dudarova, Ivan V. Ananyev, Anastasia A. Antonets, Dmitry N. Kaluzhny, Alexey A. Nazarov, Igor B. Sivaev and Vladimir I. Bregadze
Molecules 2023, 28(18), 6636; https://doi.org/10.3390/molecules28186636 - 15 Sep 2023
Viewed by 812
Abstract
The synthesis of the first conjugates of acridine with cobalt bis(dicarbollide) are reported. A novel 9-azido derivative of acridine was prepared through the reaction of 9-methoxyacridine with N3CH2CH2NH2, and its solid-state molecular structure was determined [...] Read more.
The synthesis of the first conjugates of acridine with cobalt bis(dicarbollide) are reported. A novel 9-azido derivative of acridine was prepared through the reaction of 9-methoxyacridine with N3CH2CH2NH2, and its solid-state molecular structure was determined via single-crystal X-ray diffraction. The azidoacridine was used in a copper (I)-catalyzed azide-alkyne cycloaddition reaction with cobalt bis(dicarbollide)-based terminal alkynes to give the target 1,2,3-triazoles. DNA interaction studies via absorbance spectroscopy showed the weak binding of the obtained conjugates with DNA. The antiproliferative activity (IC50) of the boronated conjugates against a series of human cell lines was evaluated through an MTT assay. The results suggested that acridine derivatives of cobalt bis(dicarbollide) might serve as a novel scaffold for the future development of new agents for boron neutron capture therapy (BNCT). Full article
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16 pages, 2673 KiB  
Article
The Synthesis, Characterization, and Fluxional Behavior of a Hydridorhodatetraborane
by Fatou Diaw-Ndiaye, Pablo J. Sanz Miguel, Ricardo Rodríguez and Ramón Macías
Molecules 2023, 28(18), 6462; https://doi.org/10.3390/molecules28186462 - 06 Sep 2023
Cited by 1 | Viewed by 760
Abstract
The octahydridotriborate anion plays a crucial role in the field of polyhedral boron chemistry, facilitating the synthesis of higher boranes and the preparation of diverse transition metal complexes. Among the stable forms of this anion, CsB3H8 (or (n-C4H [...] Read more.
The octahydridotriborate anion plays a crucial role in the field of polyhedral boron chemistry, facilitating the synthesis of higher boranes and the preparation of diverse transition metal complexes. Among the stable forms of this anion, CsB3H8 (or (n-C4H9)4N)[B3H8] have been identified. These salts serve as valuable precursors for the synthesis of metallaboranes, wherein the triborate anion acts as a ligand coordinating to the metal center. In this study, we have successfully synthesized a novel rhodatetraborane dihydride, [Rh(η2-B3H8)(H)2(PPh3)2] (1), which represents a Rh(III) complex featuring a bidentate chelate ligand fasormed by B3H8. Extensive characterization of this rhodatetraborane complex has been performed using NMR spectroscopy in solution and X-ray diffraction analysis in the solid state. Notably, the complex exhibits intriguing fluxional behavior, which has been investigated using NMR techniques. Moreover, we have explored the reactivity of complex 1 towards pyridine (py) and dimethylphenylphosphine (PMe2Ph). Our findings highlight the labile nature of this four-vertex rhodatetraborane as it undergoes disassembly upon attack from the corresponding Lewis base, resulting in the formation of borane adducts, LBH3, where L = py, PMe2Ph. Furthermore, in these reactions, we report the characterization of new cationic hydride complexes, such as [Rh(H)2(PPh3)2 (py)]+ (2) and [Rh(H)2(PMe2Ph)4]+. Notably, the latter complex has been characterized as the octahydridotriborate salt [Rh(H)2(PMe2Ph)4][B3H8] (3), which extends the scope of rhodatetraborane derivatives. Full article
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20 pages, 7866 KiB  
Article
Synthesis, Reactivity and Coordination Chemistry of Group 9 PBP Boryl Pincer Complexes: [(PBP)M(PMe3)n] (M = Co, Rh, Ir; n = 1, 2)
by Philipp M. Rutz, Jörg Grunenberg and Christian Kleeberg
Molecules 2023, 28(17), 6191; https://doi.org/10.3390/molecules28176191 - 22 Aug 2023
Viewed by 1053
Abstract
The unsymmetrical diborane(4) derivative [(d(CH2P(iPr)2)abB)–Bpin] (1) proved to be a versatile PBP boryl pincer ligand precursor for Co(I) (2a, 4a), Rh(I) (23b) and Ir(I/III) (23c [...] Read more.
The unsymmetrical diborane(4) derivative [(d(CH2P(iPr)2)abB)–Bpin] (1) proved to be a versatile PBP boryl pincer ligand precursor for Co(I) (2a, 4a), Rh(I) (23b) and Ir(I/III) (23c, 56c) complexes, in particular of the types [(d(CH2P(iPr)2)abB)M(PMe3)2] (2ac) and [(d(CH2P(iPr)2)abB)M–PMe3] (2bc). Whilst similar complexes have been obtained before, for the first time, the coordination chemistry of a homologous series of PBP pincer complexes, in particular the interconversion of the five- and four-coordinate complexes 2ac/3ac, was studied in detail. For Co, instead of the mono phosphine complex 2a, the dinitrogen complex [(d(CH2P(iPr)2)abB)Co(N2)(PMe3)] (4a) is formed spontaneously upon PMe3 abstraction from 2a in the presence of N2. All complexes were comprehensively characterised spectroscopically in solution via multinuclear (VT-)NMR spectroscopy and structurally in the solid state through single-crystal X-ray diffraction. The unique properties of the PBP ligand with respect to its coordination chemical properties are addressed. Full article
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13 pages, 5383 KiB  
Communication
1,8-Dihydroxy Naphthalene—A New Building Block for the Self-Assembly with Boronic Acids and 4,4′-Bipyridine to Stable Host–Guest Complexes with Aromatic Hydrocarbons
by Chamila P. Manankandayalage, Daniel K. Unruh, Ryan Perry and Clemens Krempner
Molecules 2023, 28(14), 5394; https://doi.org/10.3390/molecules28145394 - 14 Jul 2023
Viewed by 758
Abstract
The new Lewis acid–base adducts of general formula X(nad)B←NC5H4-C5H4N→B(nad)X [nad = 1,8-O2C10H6, X = C6H5 (2c), 3,4,5-F3-C6H2 (2d)] [...] Read more.
The new Lewis acid–base adducts of general formula X(nad)B←NC5H4-C5H4N→B(nad)X [nad = 1,8-O2C10H6, X = C6H5 (2c), 3,4,5-F3-C6H2 (2d)] were synthesized in high yields via reactions of 1,8-dihydroxy naphthalene [nadH2] and 4,4′-bipyridine with the aryl boronic acids C6H5B(OH)2 and 3,4,5-F3-C6H2B(OH)2, respectively, and structurally characterized by multi-nuclear NMR spectroscopy and SCXRD. Self-assembled H-shaped Lewis acid–base adduct 2d proved to be effective in forming thermally stable host–guest complexes, 2d × solvent, with aromatic hydrocarbon solvents such as benzene, toluene, mesitylene, aniline, and m-, p-, and o-xylene. Crystallographic analysis of these solvent adducts revealed host–guest interactions to primarily occur via π···π contacts between the 4,4′-bipyridyl linker and the aromatic solvents, resulting in the formation of 1:1 and 1:2 host–guest complexes. Thermogravimetric analysis of the isolated complexes 2d × solvent revealed their high thermal stability with peak temperatures associated with the loss of solvent ranging from 122 to 147 °C. 2d, when self-assembled in an equimolar mixture of m-, p-, and o-xylene (1:1:1), preferentially binds to o-xylene. Collectively, these results demonstrate the ability of 1,8-dihydroxy naphthalene to serve as an effective building block in the selective self-assembly to supramolecular aggregates through dative covalent N→B bonds. Full article
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16 pages, 2680 KiB  
Article
Synthesis and Structural Characterization of Copper Complexes Containing “R-Substituted” Bis-7-Azaindolyl Borate Ligands
by Miriam Jackson, Simon D. Thomas, Graham J. Tizzard, Simon J. Coles and Gareth R. Owen
Molecules 2023, 28(12), 4825; https://doi.org/10.3390/molecules28124825 - 17 Jun 2023
Viewed by 1087
Abstract
The coordination chemistry of scorpionate ligands based on borates containing the 7-azaindole heterocycle is relatively unexplored. Thus, there is a requirement to further understand their coordination chemistry. This article outlines the synthesis and characterization of a family of complexes containing anionic flexible scorpionate [...] Read more.
The coordination chemistry of scorpionate ligands based on borates containing the 7-azaindole heterocycle is relatively unexplored. Thus, there is a requirement to further understand their coordination chemistry. This article outlines the synthesis and characterization of a family of complexes containing anionic flexible scorpionate ligands of the type [(R)(bis-7-azaindolyl)borohydride] ([RBai]), where R = Me, Ph or naphthyl. The three ligands were coordinated to a series of copper(I) complexes containing a phosphine co-ligand to form the complexes, [Cu(MeBai)(PPh3)] (1), [Cu(PhBai)(PPh3)] (2), [Cu(NaphthBai)(PPh3)] (3), [Cu(MeBai)(PCy3)] (4), [Cu(PhBai)(PCy3)] (5) and [Cu(NaphthBai)(PCy3)] (6). Additional copper(II) complexes, namely, [Cu(MeBai)2] (7) and [Cu(PhBai)2] (8), were obtained during attempts to obtain single crystals from complexes 4 and 2, respectively. Complexes 7 and 8 were also prepared independently from CuCl2 and two equivalents of the corresponding Li[RBai] salt alongside an additional complex, namely, [Cu(NaphthBai)2] (9). The copper(I) and copper(II) complexes were characterized using spectroscopic and analytical methods. Furthermore, a crystal structure was obtained for eight of the nine complexes. In all cases, the boron-based ligand was found to bind to the metal centers via a κ3-N,N,H coordination mode. Full article
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23 pages, 3546 KiB  
Article
Synthesis and In Vitro Biological Evaluation of p-Carborane-Based Di-tert-butylphenol Analogs
by Sebastian Braun, Sanja Jelača, Markus Laube, Sven George, Bettina Hofmann, Peter Lönnecke, Dieter Steinhilber, Jens Pietzsch, Sanja Mijatović, Danijela Maksimović-Ivanić and Evamarie Hey-Hawkins
Molecules 2023, 28(11), 4547; https://doi.org/10.3390/molecules28114547 - 04 Jun 2023
Viewed by 1590
Abstract
Targeting inflammatory mediators and related signaling pathways may offer a rational strategy for the treatment of cancer. The incorporation of metabolically stable, sterically demanding, and hydrophobic carboranes in dual cycloxygenase-2 (COX-2)/5-lipoxygenase (5-LO) inhibitors that are key enzymes in the biosynthesis of eicosanoids is [...] Read more.
Targeting inflammatory mediators and related signaling pathways may offer a rational strategy for the treatment of cancer. The incorporation of metabolically stable, sterically demanding, and hydrophobic carboranes in dual cycloxygenase-2 (COX-2)/5-lipoxygenase (5-LO) inhibitors that are key enzymes in the biosynthesis of eicosanoids is a promising approach. The di-tert-butylphenol derivatives R-830, S-2474, KME-4, and E-5110 represent potent dual COX-2/5-LO inhibitors. The incorporation of p-carborane and further substitution of the p-position resulted in four carborane-based di-tert-butylphenol analogs that showed no or weak COX inhibition but high 5-LO inhibitory activities in vitro. Cell viability studies on five human cancer cell lines revealed that the p-carborane analogs R-830-Cb, S-2474-Cb, KME-4-Cb, and E-5110-Cb exhibited lower anticancer activity compared to the related di-tert-butylphenols. Interestingly, R-830-Cb did not affect the viability of primary cells and suppressed HCT116 cell proliferation more potently than its carbon-based R-830 counterpart. Considering all the advantages of boron cluster incorporation for enhancement of drug biostability, selectivity, and availability of drugs, R-830-Cb can be tested in further mechanistic and in vivo studies. Full article
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15 pages, 2843 KiB  
Article
A Window into the Workings of anti-B18H22 Luminescence—Blue-Fluorescent Isomeric Pair 3,3′-Cl2-B18H20 and 3,4′-Cl2-B18H20 (and Others)
by Marcel Ehn, Dmytro Bavol, Jonathan Bould, Vojtěch Strnad, Miroslava Litecká, Kamil Lang, Kaplan Kirakci, William Clegg, Paul G. Waddell and Michael G. S. Londesborough
Molecules 2023, 28(11), 4505; https://doi.org/10.3390/molecules28114505 - 01 Jun 2023
Cited by 3 | Viewed by 1779
Abstract
The action of AlCl3 on room-temperature tetrachloromethane solutions of anti-B18H22 (1) results in a mixture of fluorescent isomers, 3,3′-Cl2-B18H20 (2) and 3,4′-Cl2-B18H20 (3 [...] Read more.
The action of AlCl3 on room-temperature tetrachloromethane solutions of anti-B18H22 (1) results in a mixture of fluorescent isomers, 3,3′-Cl2-B18H20 (2) and 3,4′-Cl2-B18H20 (3), together isolated in a 76% yield. Compounds 2 and 3 are capable of the stable emission of blue light under UV-excitation. In addition, small amounts of other dichlorinated isomers, 4,4′-Cl2-B18H20 (4), 3,1′-Cl2-B18H20 (5), and 7,3′-Cl2-B18H20 (6) were isolated, along with blue-fluorescent monochlorinated derivatives, 3-Cl-B18H21 (7) and 4-Cl-B18H21 (8), and trichlorinated species 3,4,3′-Cl3-B18H19 (9) and 3,4,4′-Cl3-B18H19 (10). The molecular structures of these new chlorinated derivatives of octadecaborane are delineated, and the photophysics of some of these species are discussed in the context of the influence that chlorination bears on the luminescence of anti-B18H22. In particular, this study produces important information on the effect that the cluster position of these substitutions has on luminescence quantum yields and excited-state lifetimes. Full article
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10 pages, 8811 KiB  
Article
Two New Aluminoborates with 3D Porous-Layered Frameworks
by Chen Wang, Juan Chen, Chong-An Chen, Zhen-Wen Wang and Guo-Yu Yang
Molecules 2023, 28(11), 4387; https://doi.org/10.3390/molecules28114387 - 27 May 2023
Viewed by 822
Abstract
Two new aluminoborates, NaKCs[AlB7O13(OH)]·H2O (1) and K4Na5[AlB7O13(OH)]3·5H2O (2), have been hydro(solvo)thermally made with mixed alkali metal cationic templates. Both 1 and [...] Read more.
Two new aluminoborates, NaKCs[AlB7O13(OH)]·H2O (1) and K4Na5[AlB7O13(OH)]3·5H2O (2), have been hydro(solvo)thermally made with mixed alkali metal cationic templates. Both 1 and 2 crystallize in the monoclinic space group P21/n and contain similar units of [B7O13(OH)]6− cluster and AlO4 tetrahedra. The [B7O13(OH)]6− cluster is composed of three classical B3O3 rings by vertex sharing, of which two of them connect with AlO4 tetrahedra to constitute monolayers, and one provides an O atom as a bridging unit to link two oppositely orientated monolayers by Al-O bonds to form 3D porous-layered frameworks with 8-MR channels. UV-Vis diffuse reflectance spectra indicate that both 1 and 2 exhibit short deep-UV cutoff edges below 190 nm, revealing that they have potential applications in deep-UV regions. Full article
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11 pages, 2751 KiB  
Article
The Nature of the (Oligo/Hetero)Arene Linker Connecting Two Triarylborane Cations Controls Fluorimetric and Circular Dichroism Sensing of Various ds-DNAs and ds-RNAs
by Lidija-Marija Tumir, Dijana Pavlović Saftić, Ivo Crnolatac, Željka Ban, Matea Maslać, Stefanie Griesbeck, Todd B. Marder and Ivo Piantanida
Molecules 2023, 28(11), 4348; https://doi.org/10.3390/molecules28114348 - 25 May 2023
Viewed by 970
Abstract
A series of tetracationic bis-triarylborane dyes, differing in the aromatic linker connecting two dicationic triarylborane moieties, showed very high submicromolar affinities toward ds-DNA and ds-RNA. The linker strongly influenced the emissive properties of triarylborane cations and controlled the fluorimetric response of dyes. The [...] Read more.
A series of tetracationic bis-triarylborane dyes, differing in the aromatic linker connecting two dicationic triarylborane moieties, showed very high submicromolar affinities toward ds-DNA and ds-RNA. The linker strongly influenced the emissive properties of triarylborane cations and controlled the fluorimetric response of dyes. The fluorene-analog shows the most selective fluorescence response between AT-DNA, GC-DNA, and AU-RNA, the pyrene-analog’s emission is non-selectively enhanced by all DNA/RNA, and the dithienyl-diketopyrrolopyrrole analog’s emission is strongly quenched upon DNA/RNA binding. The emission properties of the biphenyl-analog were not applicable, but the compound showed specific induced circular dichroism (ICD) signals only for AT-sequence-containing ds-DNAs, whereas the pyrene-analog ICD signals were specific for AT-DNA with respect to GC-DNA, and also recognized AU-RNA by giving a different ICD pattern from that observed upon interaction with AT-DNA. The fluorene- and dithienyl-diketopyrrolopyrrole analogs were ICD-signal silent. Thus, fine-tuning of the aromatic linker properties connecting two triarylborane dications can be used for the dual sensing (fluorimetric and CD) of various ds-DNA/RNA secondary structures, depending on the steric properties of the DNA/RNA grooves. Full article
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17 pages, 4165 KiB  
Article
Metallacarborane Synthons for Molecular Construction—Oligofunctionalization of Cobalt Bis(1,2-dicarbollide) on Boron and Carbon Atoms with Extendable Ligands
by Krzysztof Śmiałkowski, Carla Sardo and Zbigniew J. Leśnikowski
Molecules 2023, 28(10), 4118; https://doi.org/10.3390/molecules28104118 - 16 May 2023
Cited by 1 | Viewed by 1180
Abstract
The exploitation of metallacarboranes’ potential in various fields of research and practical applications requires the availability of convenient and versatile methods for their functionalization with various functional moieties and/or linkers of different types and lengths. Herein, we report a study on cobalt bis(1,2-dicarbollide) [...] Read more.
The exploitation of metallacarboranes’ potential in various fields of research and practical applications requires the availability of convenient and versatile methods for their functionalization with various functional moieties and/or linkers of different types and lengths. Herein, we report a study on cobalt bis(1,2-dicarbollide) functionalization at 8,8′-boron atoms with different hetero-bifunctional moieties possessing a protected hydroxyl function allowing further modification after deprotection. Moreover, an approach to the synthesis of three and four functionalized metallacarboranes, at boron and carbon atoms simultaneously via additional functionalization at carbon to obtain derivatives carrying three or four rationally oriented and distinct reactive surfaces, is described. Full article
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11 pages, 2584 KiB  
Article
Synthesis and Structural Characterization of p-Carboranylamidine Derivatives
by Nicole Harmgarth, Phil Liebing, Volker Lorenz, Felix Engelhardt, Liane Hilfert, Sabine Busse, Rüdiger Goldhahn and Frank T. Edelmann
Molecules 2023, 28(9), 3837; https://doi.org/10.3390/molecules28093837 - 30 Apr 2023
Viewed by 1203
Abstract
In this contribution, the first amidinate and amidine derivatives of p-carborane are described. Double lithiation of p-carborane (1) with n-butyllithium followed by treatment with 1,3-diorganocarbodiimides, R–N=C=N–R (R = iPr, Cy (= cyclohexyl)), in DME or THF afforded [...] Read more.
In this contribution, the first amidinate and amidine derivatives of p-carborane are described. Double lithiation of p-carborane (1) with n-butyllithium followed by treatment with 1,3-diorganocarbodiimides, R–N=C=N–R (R = iPr, Cy (= cyclohexyl)), in DME or THF afforded the new p-carboranylamidinate salts p-C2H10B10[C(NiPr)2Li(DME)]2 (2) and p-C2H10B10[C(NCy)2Li(THF)2]2 (3). Subsequent treatment of 2 and 3 with 2 equiv. of chlorotrimethylsilane (Me3SiCl) provided the silylated neutral bis(amidine) derivatives p-C2H10B10[C{iPrN(SiMe3)}(=NiPr)]2 (4) and p-C2H10B10[C{CyN(SiMe3)}(=NCy)]2 (5). The new compounds 3 and 4 have been structurally characterized by single-crystal X-ray diffraction. The lithium carboranylamidinate 3 comprises a rare trigonal planar coordination geometry around the lithium ions. Full article
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13 pages, 5709 KiB  
Article
DFT Surface Infers Ten-Vertex Cationic Carboranes from the Corresponding Neutral closo Ten-Vertex Family: The Computed Background Confirming Their Experimental Availability
by Michael L. McKee, Jan Vrána, Josef Holub, Jindřich Fanfrlík and Drahomír Hnyk
Molecules 2023, 28(8), 3645; https://doi.org/10.3390/molecules28083645 - 21 Apr 2023
Viewed by 982
Abstract
Modern computational protocols based on the density functional theory (DFT) infer that polyhedral closo ten-vertex carboranes are key starting stationary states in obtaining ten-vertex cationic carboranes. The rearrangement of the bicapped square polyhedra into decaborane-like shapes with open hexagons in boat conformations is [...] Read more.
Modern computational protocols based on the density functional theory (DFT) infer that polyhedral closo ten-vertex carboranes are key starting stationary states in obtaining ten-vertex cationic carboranes. The rearrangement of the bicapped square polyhedra into decaborane-like shapes with open hexagons in boat conformations is caused by attacks of N-heterocyclic carbenes (NHCs) on the closo motifs. Single-point computations on the stationary points found during computational examinations of the reaction pathways have clearly shown that taking the “experimental” NHCs into account requires the use of dispersion correction. Further examination has revealed that for the purposes of the description of reaction pathways in their entirety, i.e., together with all transition states and intermediates, a simplified model of NHCs is sufficient. Many of such transition states resemble in their shapes those that dictate Z-rearrangement among various isomers of closo ten-vertex carboranes. Computational results are in very good agreement with the experimental findings obtained earlier. Full article
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11 pages, 2212 KiB  
Article
Synthesis of Novel Carborane-Containing Derivatives of RGD Peptide
by Alexander V. Vakhrushev, Dmitry A. Gruzdev, Alexander M. Demin, Galina L. Levit and Victor P. Krasnov
Molecules 2023, 28(8), 3467; https://doi.org/10.3390/molecules28083467 - 14 Apr 2023
Cited by 1 | Viewed by 1316
Abstract
Short peptides containing the Arg-Gly-Asp (RGD) fragment can selectively bind to integrins on the surface of tumor cells and are attractive transport molecules for the targeted delivery of therapeutic and diagnostic agents to tumors (for example, glioblastoma). We have demonstrated the possibility of [...] Read more.
Short peptides containing the Arg-Gly-Asp (RGD) fragment can selectively bind to integrins on the surface of tumor cells and are attractive transport molecules for the targeted delivery of therapeutic and diagnostic agents to tumors (for example, glioblastoma). We have demonstrated the possibility of obtaining the N- and C-protected RGD peptide containing 3-amino-closo-carborane and a glutaric acid residue as a linker fragment. The resulting carboranyl derivatives of the protected RGD peptide are of interest as starting compounds in the synthesis of unprotected or selectively protected peptides, as well as building blocks for preparation of boron-containing derivatives of the RGD peptide of a more complex structure. Full article
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16 pages, 2810 KiB  
Article
Dehydroborylation of Terminal Alkynes Using Lithium Aminoborohydrides
by P. Veeraraghavan Ramachandran and Henry J. Hamann
Molecules 2023, 28(8), 3433; https://doi.org/10.3390/molecules28083433 - 13 Apr 2023
Viewed by 1326
Abstract
Dehydrogenative borylation of terminal alkynes has recently emerged as an atom-economical one-step alternative to traditional alkyne borylation methodologies. Using lithium aminoborohydrides, formed in situ from the corresponding amine-boranes and n-butyllithium, a variety of aromatic and aliphatic terminal alkyne substrates were successfully borylated [...] Read more.
Dehydrogenative borylation of terminal alkynes has recently emerged as an atom-economical one-step alternative to traditional alkyne borylation methodologies. Using lithium aminoborohydrides, formed in situ from the corresponding amine-boranes and n-butyllithium, a variety of aromatic and aliphatic terminal alkyne substrates were successfully borylated in high yield. The potential to form mono-, di-, and tri-B-alkynylated products has been shown, though the mono-product is primarily generated using the presented condition. The reaction has been demonstrated at large (up to 50 mmol) scale, and the products are stable to column chromatography as well as acidic and basic aqueous conditions. Alternately, the dehydroborylation can be achieved by treating alkynyllithiums with amine-boranes. In that respect, aldehydes can act as starting materials by conversion to the 1,1-dibromoolefin and in situ rearrangement to the lithium acetylide. Full article
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15 pages, 2790 KiB  
Article
Structural (XRD) Characterization and an Analysis of H-Bonding Motifs in Some Tetrahydroxidohexaoxidopentaborate(1-) Salts of N-Substituted Guanidinium Cations
by Michael A. Beckett, Simon J. Coles, Peter N. Horton and Thomas A. Rixon
Molecules 2023, 28(7), 3273; https://doi.org/10.3390/molecules28073273 - 06 Apr 2023
Cited by 1 | Viewed by 1132
Abstract
The synthesis and characterization of six new substituted guanidium tetrahydroxidohexaoxidopentaborate(1-) salts are reported: [C(NH2)2(NHMe)][B5O6(OH)4]·H2O (1), [C(NH2)2(NH{NH2})][B5O6(OH)4] ( [...] Read more.
The synthesis and characterization of six new substituted guanidium tetrahydroxidohexaoxidopentaborate(1-) salts are reported: [C(NH2)2(NHMe)][B5O6(OH)4]·H2O (1), [C(NH2)2(NH{NH2})][B5O6(OH)4] (2), [C(NH2)2(NMe2)][B5O6(OH)4] (3), [C(NH2)(NMe2)2][B5O6(OH)4] (4), [C(NHMe)(NMe2)2][B5O6(OH)4]·B(OH)3 (5), and [TBDH][B5O6(OH)4] (6) (TBD = 1,5,7-triazabicyclo [4.4.0]dec-5-ene). Compounds 16 were prepared as crystalline salts from basic aqueous solution via self-assembly processes from B(OH)3 and the appropriate substituted cation. Compounds 16 were characterized by spectroscopic (NMR and IR) and by single-crystal XRD studies. A thermal (TGA) analysis on compounds 13 and 6 demonstrated that they thermally decomposed via a multistage process to B2O3 at >650 °C. The low temperature stage (<250 °C) was endothermic and corresponded to a loss of H2O. Reactant stoichiometry, solid-state packing, and H-bonding interactions are all important in assembling these structures. An analysis of H-bonding motifs in known unsubstituted guanidinium salts [C(NH2)3]2[B4O5(OH)4]·2H2O, [C(NH2)3][B5O6(OH)4]·H2O, and [C(NH2)3]3[B9O12(OH)6] and in compounds 16 revealed that two important H-bonding R22(8) motifs competed to stabilize the observed structures. The guanidinium cation formed charge-assisted pincer cation–anion H-bonded rings as a major motif in [C(NH2)3]2[B4O5(OH)4]·2H2O and [C(NH2)3]3[B9O12(OH)6], whereas the anion–anion ring motif was dominant in [C(NH2)3][B5O6(OH)4]·H2O and in compounds 16. This behaviour was consistent with the stoichiometry of the salt and packing effects also strongly influencing their solid-state structures. Full article
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9 pages, 1218 KiB  
Communication
Facile Attachment of Halides and Pseudohalides to Dodecaborate(2-) via Pd-catalyzed Cross-Coupling
by Mahmoud K. Al-Joumhawy, Jui-Chi Chang, Fariba Sabzi and Detlef Gabel
Molecules 2023, 28(7), 3245; https://doi.org/10.3390/molecules28073245 - 05 Apr 2023
Cited by 1 | Viewed by 1371
Abstract
Cross-coupling reactions with [B12H11I]2− as one partner have been used successfully for Kumada and Buchwald Hartwig couplings with Pd catalysis. Here, we found that the iodide could be substituted easily, and unexpectedly, with other halides such as Br [...] Read more.
Cross-coupling reactions with [B12H11I]2− as one partner have been used successfully for Kumada and Buchwald Hartwig couplings with Pd catalysis. Here, we found that the iodide could be substituted easily, and unexpectedly, with other halides such as Br and Cl, and with pseudohalides such as cyanide, azide, and isocyanate. We found that for Cl, Br, N3, and NCO, tetrabutylammonium salts—or sodium salts—were successful halide sources, whereas for cyanide, CuCN was the only halide source that allowed a successful exchange. The azide could be reacted further in a click reaction with triazoles. While no substitution with fluoride occurred, tetrabutylammonium fluoride in the presence of water led to [B12H11OH]2−. Yields were high to very high, and reaction times were short when using a microwave oven as a heating source. Full article
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17 pages, 3666 KiB  
Article
Polyhedral Dicobaltadithiaboranes and Dicobaltdiselenaboranes as Examples of Bimetallic Nido Structures without Bridging Hydrogens
by Amr A. A. Attia, Alexandru Lupan and Robert Bruce King
Molecules 2023, 28(7), 2988; https://doi.org/10.3390/molecules28072988 - 27 Mar 2023
Viewed by 1126
Abstract
The geometries and energetics of the n-vertex polyhedral dicobaltadithiaboranes and dicobaltadiselenaboranes Cp2Co2E2Bn−4Hn−4 (E = S, Se; n = 8 to 12) have been investigated via the density functional theory. Most of [...] Read more.
The geometries and energetics of the n-vertex polyhedral dicobaltadithiaboranes and dicobaltadiselenaboranes Cp2Co2E2Bn−4Hn−4 (E = S, Se; n = 8 to 12) have been investigated via the density functional theory. Most of the lowest-energy structures in these systems are generated from the (n + 1)-vertex most spherical closo deltahedra by removal of a single vertex, leading to a tetragonal, pentagonal, or hexagonal face depending on the degree of the vertex removed. In all of these low-energy structures, the chalcogen atoms are located at the vertices of the non-triangular face. Alternatively, the central polyhedron in most of the 12-vertex structures can be derived from a Co2E2B8 icosahedron with adjacent chalcogen (E) vertices by breaking the E–E edge and 1 or more E–B edges to create a hexagonal face. Examples of the arachno polyhedra with two tetragonal and/or pentagonal faces derived from the removal of two vertices from isocloso deltahedra were found among the set of lowest-energy Cp2Co2E2Bn−4Hn−4 (E = S, Se; n = 8 and 12) structures. Full article
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12 pages, 3283 KiB  
Article
Thermal Polymorphism in CsCB11H12
by Radovan Černý, Matteo Brighi, Hui Wu, Wei Zhou, Mirjana Dimitrievska, Fabrizio Murgia, Valerio Gulino, Petra E. de Jongh, Benjamin A. Trump and Terrence J. Udovic
Molecules 2023, 28(5), 2296; https://doi.org/10.3390/molecules28052296 - 01 Mar 2023
Cited by 1 | Viewed by 1901
Abstract
Thermal polymorphism in the alkali-metal salts incorporating the icosohedral monocarba-hydridoborate anion, CB11H12, results in intriguing dynamical properties leading to superionic conductivity for the lightest alkali-metal analogues, LiCB11H12 and NaCB11H12. As such, [...] Read more.
Thermal polymorphism in the alkali-metal salts incorporating the icosohedral monocarba-hydridoborate anion, CB11H12, results in intriguing dynamical properties leading to superionic conductivity for the lightest alkali-metal analogues, LiCB11H12 and NaCB11H12. As such, these two have been the focus of most recent CB11H12 related studies, with less attention paid to the heavier alkali-metal salts, such as CsCB11H12. Nonetheless, it is of fundamental importance to compare the nature of the structural arrangements and interactions across the entire alkali-metal series. Thermal polymorphism in CsCB11H12 was investigated using a combination of techniques: X-ray powder diffraction; differential scanning calorimetry; Raman, infrared, and neutron spectroscopies; and ab initio calculations. The unexpected temperature-dependent structural behavior of anhydrous CsCB11H12 can be potentially justified assuming the existence of two polymorphs with similar free energies at room temperature: (i) a previously reported, ordered R3 polymorph stabilized upon drying and transforming first to R3c symmetry near 313 K and then to a similarly packed but disordered I43d polymorph near 353 K and (ii) a disordered Fm3 polymorph that initially appears from the disordered I43d polymorph near 513 K along with another disordered high-temperature P63mc polymorph. Quasielastic neutron scattering results indicate that the CB11H12 anions in the disordered phase at 560 K are undergoing isotropic rotational diffusion, with a jump correlation frequency [1.19(9) × 1011 s−1] in line with those for the lighter-metal analogues. Full article
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16 pages, 2632 KiB  
Article
Synthesis: Molecular Structure, Thermal-Calorimetric and Computational Analyses, of Three New Amine Borane Adducts
by Kevin Turani-I-Belloto, Rodica Chiriac, François Toche, Eddy Petit, Pascal G. Yot, Johan G. Alauzun and Umit B. Demirci
Molecules 2023, 28(3), 1469; https://doi.org/10.3390/molecules28031469 - 03 Feb 2023
Cited by 1 | Viewed by 1497
Abstract
Cyclopropylamine borane C3H5NH2BH3 (C3AB), 2-ethyl-1-hexylamine borane CH3(CH2)3CH(C2H5)CH2NH2BH3 (C2C6AB) and didodecylamine borane (C12H25)2NHBH3 ((C12)2AB) are [...] Read more.
Cyclopropylamine borane C3H5NH2BH3 (C3AB), 2-ethyl-1-hexylamine borane CH3(CH2)3CH(C2H5)CH2NH2BH3 (C2C6AB) and didodecylamine borane (C12H25)2NHBH3 ((C12)2AB) are three new amine borane adducts (ABAs). They are synthesized by reaction of the corresponding amines with a borane complex, the reaction being exothermic as shown by Calvet calorimetry. The successful synthesis of each has been demonstrated by FTIR, Raman and NMR. For instance, the 11B NMR spectra show the presence of signals typical of the NBH3 environment, thereby implying the formation of B–N bonds. The occurrence of dihydrogen bonds (DHBs) for each of the ABAs has been highlighted by DSC and FTIR, and supported by DFT calculations (via the Mulliken charges for example). When heated, the three ABAs behave differently: C3AB and C2C6AB decompose from 68 to 100 °C whereas (C12)2AB is relatively stable up to 173 °C. That means that these ABAs are not appropriate as hydrogen carriers, but the ‘most’ stable (C12)2AB could open perspectives for the synthesis of advanced materials. Full article
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15 pages, 2716 KiB  
Article
Incorporation of a Boron–Nitrogen Covalent Bond Improves the Charge-Transport and Charge-Transfer Characteristics of Organoboron Small-Molecule Acceptors for Organic Solar Cells
by Jie Yang, Wei-Lu Ding, Quan-Song Li and Ze-Sheng Li
Molecules 2023, 28(2), 811; https://doi.org/10.3390/molecules28020811 - 13 Jan 2023
Cited by 6 | Viewed by 2123
Abstract
An organoboron small-molecular acceptor (OSMA) MB←N containing a boron–nitrogen coordination bond (B←N) exhibits good light absorption in organic solar cells (OSCs). In this work, based on MB←N, OSMA MB-N, with the incorporation of a boron–nitrogen covalent bond (B-N), [...] Read more.
An organoboron small-molecular acceptor (OSMA) MB←N containing a boron–nitrogen coordination bond (B←N) exhibits good light absorption in organic solar cells (OSCs). In this work, based on MB←N, OSMA MB-N, with the incorporation of a boron–nitrogen covalent bond (B-N), was designed. We have systematically investigated the charge-transport properties and interfacial charge-transfer characteristics of MB-N, along with MB←N, using the density functional theory (DFT) and the time-dependent density functional theory (TD-DFT). Theoretical calculations show that MB-N can simultaneously boost the open-circuit voltage (from 0.78 V to 0.85 V) and the short-circuit current due to its high-lying lowest unoccupied molecular orbital and the reduced energy gap. Moreover, its large dipole shortens stacking and greatly enhances electron mobility by up to 5.91 × 10−3 cm2·V−1·s−1. Notably, the excellent interfacial properties of PTB7-Th/MB-N, owing to more charge transfer states generated through the direct excitation process and the intermolecular electric field mechanism, are expected to improve OSCs performance. Together with the excellent properties of MB-N, we demonstrate a new OSMA and develop a new organoboron building block with B-N units. The computations also shed light on the structure–property relationships and provide in-depth theoretical guidance for the application of organoboron photovoltaic materials. Full article
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11 pages, 1792 KiB  
Communication
Room Temperature Reduction of Titanium Tetrachloride-Activated Nitriles to Primary Amines with Ammonia-Borane
by P. Veeraraghavan Ramachandran and Abdulkhaliq A. Alawaed
Molecules 2023, 28(1), 60; https://doi.org/10.3390/molecules28010060 - 21 Dec 2022
Cited by 3 | Viewed by 2791
Abstract
The reduction of a variety of aromatic and aliphatic nitriles, activated by a molar equivalent of titanium tetrachloride, has been achieved at room temperature using ammonia borane as a safe reductant. The corresponding methanamines were isolated in good to excellent yields following a [...] Read more.
The reduction of a variety of aromatic and aliphatic nitriles, activated by a molar equivalent of titanium tetrachloride, has been achieved at room temperature using ammonia borane as a safe reductant. The corresponding methanamines were isolated in good to excellent yields following a simple acid-base workup. Full article
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Review

Jump to: Research

67 pages, 34211 KiB  
Review
Chemistry of Carbon-Substituted Derivatives of Cobalt Bis(dicarbollide)(1) Ion and Recent Progress in Boron Substitution
by Lucia Pazderová, Ece Zeynep Tüzün, Dmytro Bavol, Miroslava Litecká, Lukáš Fojt and Bohumír Grűner
Molecules 2023, 28(19), 6971; https://doi.org/10.3390/molecules28196971 - 07 Oct 2023
Cited by 1 | Viewed by 1157
Abstract
The cobalt bis(dicarbollide)(1) anion (1), [(1,2-C2B9H11)2-3,3′-Co(III)](1), plays an increasingly important role in material science and medicine due to its high chemical stability, 3D shape, aromaticity, diamagnetic character, ability [...] Read more.
The cobalt bis(dicarbollide)(1) anion (1), [(1,2-C2B9H11)2-3,3′-Co(III)](1), plays an increasingly important role in material science and medicine due to its high chemical stability, 3D shape, aromaticity, diamagnetic character, ability to penetrate cells, and low cytotoxicity. A key factor enabling the incorporation of this ion into larger organic molecules, biomolecules, and materials, as well as its capacity for “tuning” interactions with therapeutic targets, is the availability of synthetic routes that enable easy modifications with a wide selection of functional groups. Regarding the modification of the dicarbollide cage, syntheses leading to substitutions on boron atoms are better established. These methods primarily involve ring cleavage of the ether rings in species containing an oxonium oxygen atom connected to the B(8) site. These pathways are accessible with a broad range of nucleophiles. In contrast, the chemistry on carbon vertices has remained less elaborated over the previous decades due to a lack of reliable methods that permit direct and straightforward cage modifications. In this review, we present a survey of methods based on metalation reactions on the acidic C-H vertices, followed by reactions with electrophiles, which have gained importance in only the last decade. These methods now represent the primary trends in the modifications of cage carbon atoms. We discuss the scope of currently available approaches, along with the stereochemistry of reactions, chirality of some products, available types of functional groups, and their applications in designing unconventional drugs. This content is complemented with a report of the progress in physicochemical and biological studies on the parent cobalt bis(dicarbollide) ion and also includes an overview of recent syntheses and emerging applications of boron-substituted compounds. Full article
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54 pages, 28158 KiB  
Review
Decaborane: From Alfred Stock and Rocket Fuel Projects to Nowadays
by Igor B. Sivaev
Molecules 2023, 28(17), 6287; https://doi.org/10.3390/molecules28176287 - 28 Aug 2023
Cited by 2 | Viewed by 1672
Abstract
The review covers more than a century of decaborane chemistry from the first synthesis by Alfred Stock to the present day. The main attention is paid to the reactions of the substitution of hydrogen atoms by various atoms and groups with the formation [...] Read more.
The review covers more than a century of decaborane chemistry from the first synthesis by Alfred Stock to the present day. The main attention is paid to the reactions of the substitution of hydrogen atoms by various atoms and groups with the formation of exo-polyhedral boron–halogen, boron–oxygen, boron–sulfur, boron–nitrogen, boron–phosphorus, and boron–carbon bonds. Particular attention is paid to the chemistry of conjucto-borane anti-[B18H22], whose structure is formed by two decaborane moieties with a common edge, the chemistry of which has been intensively developed in the last decade. Full article
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18 pages, 8081 KiB  
Review
Recent Progress in Crystalline Borates with Edge-Sharing BO4 Tetrahedra
by Jing-Jing Li, Wei-Feng Chen, You-Zhao Lan and Jian-Wen Cheng
Molecules 2023, 28(13), 5068; https://doi.org/10.3390/molecules28135068 - 28 Jun 2023
Cited by 1 | Viewed by 856
Abstract
Crystalline borates have received great attention due to their various structures and wide applications. For a long time, the corner-sharing B–O unit is considered a basic rule in borate structural chemistry. The Dy4B6O15 synthesized under high-pressure is the [...] Read more.
Crystalline borates have received great attention due to their various structures and wide applications. For a long time, the corner-sharing B–O unit is considered a basic rule in borate structural chemistry. The Dy4B6O15 synthesized under high-pressure is the first oxoborate with edge-sharing [BO4] tetrahedra, while the KZnB3O6 is the first ambient pressure borate with the edge-sharing [BO4] tetrahedra. The edge-sharing connection modes greatly enrich the structural chemistry of borates and are expected to expand new applications in the future. In this review, we summarize the recent progress in crystalline borates with edge-sharing [BO4] tetrahedra. We discuss the synthesis, fundamental building blocks, structural features, and possible applications of these edge-sharing borates. Finally, we also discuss the future perspectives in this field. Full article
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24 pages, 11487 KiB  
Review
Towards the Application of Purely Inorganic Icosahedral Boron Clusters in Emerging Nanomedicine
by Francesc Teixidor, Rosario Núñez and Clara Viñas
Molecules 2023, 28(11), 4449; https://doi.org/10.3390/molecules28114449 - 30 May 2023
Cited by 3 | Viewed by 1601
Abstract
Traditionally, drugs were obtained by extraction from medicinal plants, but more recently also by organic synthesis. Today, medicinal chemistry continues to focus on organic compounds and the majority of commercially available drugs are organic molecules, which can incorporate nitrogen, oxygen, and halogens, as [...] Read more.
Traditionally, drugs were obtained by extraction from medicinal plants, but more recently also by organic synthesis. Today, medicinal chemistry continues to focus on organic compounds and the majority of commercially available drugs are organic molecules, which can incorporate nitrogen, oxygen, and halogens, as well as carbon and hydrogen. Aromatic organic compounds that play important roles in biochemistry find numerous applications ranging from drug delivery to nanotechnology or biomarkers. We achieved a major accomplishment by demonstrating experimentally/theoretically that boranes, carboranes, as well as metallabis(dicarbollides), exhibit global 3D aromaticity. Based on the stability–aromaticity relationship, as well as on the progress made in the synthesis of derivatized clusters, we have opened up new applications of boron icosahedral clusters as key components in the field of novel healthcare materials. In this brief review, we present the results obtained at the Laboratory of Inorganic Materials and Catalysis (LMI) of the Institut de Ciència de Materials de Barcelona (ICMAB-CSIC) with icosahedral boron clusters. These 3D geometric shape clusters, the semi-metallic nature of boron and the presence of exo-cluster hydrogen atoms that can interact with biomolecules through non-covalent hydrogen and dihydrogen bonds, play a key role in endowing these compounds with unique properties in largely unexplored (bio)materials. Full article
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