New approaches to the synthesis of aminoalkyl-o-carboranes

International audienceAminoalkyl-o-carboranes have attracted interest due to their potential use in boron neutron capture therapy (BNCT) 1 and as ligands for transition metal catalysts. 2 The synthesis of aminoalkyl-o-carboranes is commonly carried out by the addition of terminal alkynes to activated boranes B 10 H 12 L 2. 3 However this methodology often gives low yields. Other approaches include the reaction of lithio-o-carborane with preformed amines. 4 It is therefore of interest to investigate new synthetic routes that produce aminoalkyl-o-carboranes in good yields and from other functional groups that allow the preparation of a variety of amines. In this sense, we have recently reported a synthesis of amines by Lewis acid-catalyzed direct amination of benzylic alcohols. 5 Thus, we are now interested in utilizing this organic synthetic procedure to introduce the o-carborane fragments, as part of several projects directed towards the preparation of new metal complexes and their application in catalysis and materials science

Merging Icosahedral Boron Clusters and Magnetic Nanoparticles: Aiming toward Multifunctional Nanohybrid Materials

All-inorganic-made nanohybrid icosahedral boron cluster magnetic nanoparticles have been prepared. These magnetic nanoparticles (MNPs) consist of a magnetic core and an inorganic carboranylphosphinate shell. The phosphinate is directly bonded to the iron atoms of the surface in a bidentated coordination mode. The nanoparticles have been characterized by TEM, X-ray powder diffraction, infrared spectroscopy, energy dispersive X-ray analysis, high resolution X-ray photoelectron spectroscopy, magnetometry measurements, and redox titration, among other techniques. These studies have led to a composition (1-OPH­(O)-1,7-<i>closo</i>-C₂B₁₀H₁₁)₈(2Fe₃O₄·Fe₂O₃)₁₃ that implies a surface coverage of 61.3 ± 7.4% by the ligand. When these MNPs go through sterilization in one autoclave, the magnetic hysteresis studies suggest minimal change before and after sterilization; this could erroneously indicate that there have not been any changes in the MNP composition. However, the Fe²⁺ titration demonstrates that after sterilization only 1/7 of the Fe is Fe²⁺, leading to a core formula of Fe₃O₄·2Fe₂O₃ with a concomitant loss of ligand to a final ratio of 1:70 (carborane: Fe), and a final coverage by the ligand of 11.2 ± 1.4%. These studies bring relevant information on the behavior of the widely used MNPs and clearly show how the sterilization process needed for biological tests may alter the composition of the core and the loading of a peripheral ligand. In the particular case reported here, the liberated ligand has not been oxidized nor altered through the sterilization process

Redox-active metallacarborane-decorated octasilsesquioxanes. Electrochemical and thermal properties

Polyanionic and electroactive hybrids based on octasilsesquioxanes bearing metallacarborane units are developed. They show remarkable solubility in organic solvents and outstanding thermal stability. The metallacarboranes act as independent units simultaneously undergoing the reversible redox process.Ministerio de Economía, Comercio y Empresa“Severo Ochoa” Program for Centers of Excellence in R&DGeneralitat de CatalunyaDepto. de Química en Ciencias FarmacéuticasFac. de FarmaciaTRUEpu

closo-o-carboranylmethylamine?pyridine associations: synthesis, characterization, and first complexation studies

The synthesis of new pyridine-substituted carboranylmethylamines is described. The strategy involved mesylation of carboranylmethanols prior to amination reaction and is particularly adapted to the reactivity of o-carborane derivatives bearing a 2-pyridinyl substituent. Preparation and characterization of a corresponding N,N-ligand?palladium complex as well as first results in a Suzuki coupling reaction are illustrated.<br/

SingleNot Double3D-Aromaticity in an Oxidized <i>Closo</i> Icosahedral Dodecaiodo-Dodecaborate Cluster

3D-aromatic molecules with (distorted) tetrahedral, octahedral, or spherical structures are much less common than typical 2D-aromatic species or even 2D-aromatic-in-3D systems. Closo boranes, [BnHn]2– (5 ≤ n ≤ 14) and carboranes are examples of compounds that are singly 3D-aromatic, and we now explore if there are species that are doubly 3D-aromatic. The most widely known example of a species with double 2D-aromaticity is the hexaiodobenzene dication, [C6I6]2+. This species shows π-aromaticity in the benzene ring and σ-aromaticity in the outer ring formed by the iodine substituents. Inspired by the hexaiodobenzene dication example, in this work, we explore the potential for double 3D-aromaticity in [B12I12]0/2+. Our results based on magnetic and electronic descriptors of aromaticity together with 11B{1H} NMR experimental spectra of boron-iodinated o-carboranes suggest that these two oxidized forms of a closo icosahedral dodecaiodo-dodecaborate cluster, [B12I12] and [B12I12]2+, behave as doubly 3D-aromatic compounds. However, an evaluation of the energetic contribution of the potential double 3D-aromaticity through homodesmotic reactions shows that delocalization in the I12 shell, in contrast to the 10σ-electron I62+ ring in the hexaiodobenzene dication, does not contribute to any stabilization of the system. Therefore, the [B12I12]0/2+ species cannot be considered as doubly 3D-aromatic

<i>m</i>‑Carboranylphosphinate as Versatile Building Blocks To Design all Inorganic Coordination Polymers

The first examples of coordination polymers of manganese­(II) and a nickel­(II) complex with a purely inorganic carboranylphosphinate ligand are reported, together with its exhaustive characterization. X-ray analysis revealed 1D polymeric chains with carboranylphosphinate ligands bridging two manganese­(II) centers. The reactivity of polymer <b>1</b> with water and Lewis bases has also been studied

Metallosupramolecular Chemistry of Novel Chiral <i>closo</i>-<i>o</i>‑Carboranylalcohol Pyridine and Quinoline Ligands: Syntheses, Characterization, and Properties of Cobalt Complexes

The cobalt­(II) complexes CoCl₂(LOH)₂ (LOH = 1-[R­(hydroxy)­methyl]-2-R′-1,2-dicarba-<i>closo</i>-dodecaborane (R′ = H or Me; R = 2-pyridyl <b>3a</b> or <b>4a</b>, 3-pyridyl <b>3b</b> or <b>4b</b>, 4-pyridyl <b>3c</b> or <b>4c</b>, 2-quinolyl <b>3d</b> or <b>4d</b>, 4-quinolyl <b>3e</b> or <b>4e</b>)) and CoCl₂(LOH)₄ (<b>5</b>, R′ = H; R = 4-pyridyl) were synthesized and characterized. Deprotonation of alcohol in <b>3a</b> afforded the square-planar complex Co^II(LO)₂ (<b>6</b>) that oxidized slowly in solution and under air to give the cobaltacarborane complex Co^III{(η⁵-C₂B₉H₁₀)­(CHOH)­(η¹-NC₅H₄)}­(η²-NC₅H₄COO) (<b>7</b>). Crystal structures for <b>3a</b>, <b>3a·2MeOH</b>, <b>3b</b>, <b>3e</b>, <b>4c</b>, <b>4e</b>, <b>5</b>, <b>6</b>, and <b>7</b> have been determined by X-ray diffraction (XRD). Molecular structures show octahedral (<b>3a</b>, <b>3a·2MeOH</b>, <b>5</b>), tetrahedral (<b>3b</b>, <b>3e</b>, <b>4c</b>, <b>4e</b>), and square-planar (<b>6</b>) coordination around Co^II centers, whereas 2-pyridyl and quinolyl ligands favor a bidentate <i>N</i>,<i>O</i>-coordination mode and 3- and 4-pyridyl and quinolyl ligands favor a monodentate <i>N</i>-coordination. The supramolecular structures are dominated by intermolecular O–H···Cl/O hydrogen bonds and π–π interactions in the case of tetrahedral complexes. The magnetic properties of <b>3a</b>–<b>c</b> were investigated in the temperature range 2–300 K by means of χ_M<i>T</i>, which corroborated coordination numbers and geometries as well as provided information on the supramolecular interactions among neighboring molecules for all three compounds. Complex <b>3a</b> shows solvent accessible channels running parallel to the hydrogen bonding network and is able to uptake methanol vapors to convert into <b>3a·2MeOH</b>. The structure of <b>3a</b> is related to that for <b>3a·2MeOH</b> by rotation of complex molecules within the 1D O–H···Cl hydrogen bonding networks and insertion of methanol into it

Metallosupramolecular Chemistry of Novel Chiral <i>closo</i>-<i>o</i>‑Carboranylalcohol Pyridine and Quinoline Ligands: Syntheses, Characterization, and Properties of Cobalt Complexes

The cobalt­(II) complexes CoCl₂(LOH)₂ (LOH = 1-[R­(hydroxy)­methyl]-2-R′-1,2-dicarba-<i>closo</i>-dodecaborane (R′ = H or Me; R = 2-pyridyl <b>3a</b> or <b>4a</b>, 3-pyridyl <b>3b</b> or <b>4b</b>, 4-pyridyl <b>3c</b> or <b>4c</b>, 2-quinolyl <b>3d</b> or <b>4d</b>, 4-quinolyl <b>3e</b> or <b>4e</b>)) and CoCl₂(LOH)₄ (<b>5</b>, R′ = H; R = 4-pyridyl) were synthesized and characterized. Deprotonation of alcohol in <b>3a</b> afforded the square-planar complex Co^II(LO)₂ (<b>6</b>) that oxidized slowly in solution and under air to give the cobaltacarborane complex Co^III{(η⁵-C₂B₉H₁₀)­(CHOH)­(η¹-NC₅H₄)}­(η²-NC₅H₄COO) (<b>7</b>). Crystal structures for <b>3a</b>, <b>3a·2MeOH</b>, <b>3b</b>, <b>3e</b>, <b>4c</b>, <b>4e</b>, <b>5</b>, <b>6</b>, and <b>7</b> have been determined by X-ray diffraction (XRD). Molecular structures show octahedral (<b>3a</b>, <b>3a·2MeOH</b>, <b>5</b>), tetrahedral (<b>3b</b>, <b>3e</b>, <b>4c</b>, <b>4e</b>), and square-planar (<b>6</b>) coordination around Co^II centers, whereas 2-pyridyl and quinolyl ligands favor a bidentate <i>N</i>,<i>O</i>-coordination mode and 3- and 4-pyridyl and quinolyl ligands favor a monodentate <i>N</i>-coordination. The supramolecular structures are dominated by intermolecular O–H···Cl/O hydrogen bonds and π–π interactions in the case of tetrahedral complexes. The magnetic properties of <b>3a</b>–<b>c</b> were investigated in the temperature range 2–300 K by means of χ_M<i>T</i>, which corroborated coordination numbers and geometries as well as provided information on the supramolecular interactions among neighboring molecules for all three compounds. Complex <b>3a</b> shows solvent accessible channels running parallel to the hydrogen bonding network and is able to uptake methanol vapors to convert into <b>3a·2MeOH</b>. The structure of <b>3a</b> is related to that for <b>3a·2MeOH</b> by rotation of complex molecules within the 1D O–H···Cl hydrogen bonding networks and insertion of methanol into it

Surface Activity and Molecular Organization of Metallacarboranes at the Air–Water Interface Revealed by Nonlinear Optics

Because of their amphiphilic structure, surfactants adsorb at the water–air interface with their hydrophobic tails pointing out of the water and their polar heads plunging into the liquid phase. Unlike classical surfactants, metallabisdicarbollides (MCs) do not have a well-defined amphiphilic structure. They are nanometer-sized inorganic anions with an ellipsoidal shape composed of two carborane semicages sandwiching a metal ion. However, MCs have been shown to share many properties with surfactants, such as self-assembly in water (formation of micelles and vesicles), formation of lamellar lyotropic phases, and surface activity. By combining second harmonic generation and surface tension measurement, we show here that cobaltabis­(dicarbollide) anion {[(C₂B₉H₁₁)₂Co]⁻ also named [COSAN]⁻} with H⁺ as a counterion, the most representative metallacarborane, adsorbs vertically at the water surface with its long axis normal to the surface. This vertical molecular orientation facilitates the formation of intermolecular and nonconventional dihydrogen bonds such as the B–H^δ−···^δ+H–C bond that has recently been proven to be at the origin of the self-assembly of MCs in water. Therefore, it appears here that lateral dihydrogen bonds are also involved in the surface activity of MCs