Boron Cations Research Articles

Construction of heterogeneous frustrated lewis pairs based on covalent organic frameworks stabilized boron cations and investigation of cycloaddition reaction performance

Frustrated Lewis Pairs (FLPs) catalysts have been widely designed and synthesized in current chemistry, with the key being the selection of boron-based Lewis acids. Among novel boron-based Lewis acids, boron cations with higher Lewis acidity caused by cationic charge have been proven to have special reactivity. However, the current boron cations have only been used to construct homogeneous FLPs, which would be difficult to meet the industrial process demand for FLPs catalysts, possibly due to the lack of suitable stabilizers. In this paper, we propose a strategy to construct heterogeneous FLPs using covalent organic frameworks (COFs) stabilized boron cations as Lewis acid. Firstly, heterogeneous Lewis acid COFs@[B(C6F5)2]+[Al2Cl7]- was prepared by stabilizing boron cations with CN bonds in COFs, followed by introducing tBu3P to construct heterogeneous FLPs COFs@[B(C6F5)2]+[Al2Cl7]-/tBu3P. Meanwhile, these FLPs catalysts exhibited excellent catalytic and cyclic performance in the preparation of cyclic carbonates by CO2 addition from epoxy compounds.

Formation of Delocalized Linear M-B-M Covalent Bonds: A Combined Experimental and Theoretical Study of BM2(CO)8+ (M = Co, Rh, Ir) Complexes.

Investigations of transition-metal boride clusters not only lead to novel structures but also provide important information about the metal-boron bonds that are critical to understanding the properties of boride materials. The geometric structures and bonding features of heteronuclear boron-containing transition metal carbonyl cluster cations BM(CO)6+ and BM2(CO)8+ (M = Co, Rh, and Ir) are studied by a combination of the infrared photodissociation spectroscopy and density functional calculations at B3LYP/def2-TZVP level. The completely coordinated BM2(CO)8+ complexes are characterized as a sandwich structure composed of two staggered M(CO)4 fragments and a boron cation, featuring a D3d symmetry and 1Eg electronic ground state as well as metal-anchored carbonyls in an end-on manner. In conjunction with theoretical calculations, multifold metal-boron-metal bonding interactions in BM2(CO)8+ complexes involving the filled d orbitals of the metals and the empty p orbitals of the boron cation were unveiled, namely, one σ-type M-B-M bond and two π-type M-B-M bonds. Accordingly, the BM2(CO)8+ complexes can be described as a linear conjugated (OC)4M═B═M(CO)4 skeleton with a formal B-M bond index of 1.5. The three delocalized d-p-d covalent bonds render compensation for the electron deficiency of the cationic boron center and endow both metal centers with the favorable 18-electron structure, thus contributing much to the overall structural stability of the BM2(CO)8+ cations. As a comparison, the saturated BRh(CO)6+ and BIr(CO)6+ complexes are determined to be a doublet Cs-symmetry structure with an unbridged (OC)2B-M(CO)4 pattern, involving a two-center σ-type (OC)2B → M(CO)4+ dative single bond along with a weak covalent B-M half bond. This work offers important insight into the structure and bonding of late transition metal boride carbonyl cluster cations.

Saturated NHC-Stabilized Borenium, Boronium, Hydride-Bridged Boron Cations, and a Bora-Acyl Chloride

Saturated NHC-Stabilized Borenium, Boronium, Hydride-Bridged Boron Cations, and a Bora-Acyl Chloride

A Tamed Intermediate: The Pivotal Role of Cp* in Hypercoordinate Boron Cation Catalysis

A Tamed Intermediate: The Pivotal Role of Cp* in Hypercoordinate Boron Cation Catalysis

A chelated borinium cation.

Two coordinate boron cations are rare. Herein we report the synthesis of [RNSiMe2CH2]2BF (R = Dipp 3, 1-Ad 5) (Dipp = C6H3(iPr)2, Ad = C10H15) via the reaction of BF3 with the corresponding dilithiated diamides. Subsequent abstraction of fluoride provided the corresponding borinium salts, [(RNSiMe2CH2)2B][B(C6F5)4] (R = Dipp 6, 1-Ad 8). While the former was generated, the latter proved isolable and was crystallographically characterized.

Influence of Doping Technology on the Stoichiometry and Features of the Localization of B3+ Cations in LiNbO3:B Single Crystals

We have established that relatively simple calculations of the Coulomb interaction in the lattice of doped lithium niobate (LN, LiNbO3) can confirm the physical properties of real crystals. We have developed a method for the double adjustment of real XRD data for calculations of Coulomb interaction in a LN cluster. The study considers two crystals doped with boron (LN:B); LN:B(1) has been grown from a charge with 0.02 mol% B2O3, boron has been introduced by homogeneous doping, LN:B(2) has been grown from a charge with 0.547 mol% B2O3, and boron has been introduced by direct solid-state doping. XRD and Rietveld method data have been obtained for these crystals. The obtained data have been used to build a model of the LN cluster; the cluster in the calculations consists of six oxygen octahedra of the LN structure. The cluster configuration has been chosen in such a way that the structure contains two tetrahedral voids. We have studied 10 variants of filling a cluster with intrinsic cations (Li, Nb), defects, and vacancies. There are 10 of them because, in addition to the basic cations in their positions, defects are present in the structure. In terms of the defects used (NbLi, NbV), we have used only those that Rietveld found for these exact LN:B crystals, and the vacancy in the niobium octahedron (VNb) compensates for these defects, according to the models known for LN. The energy of the Coulomb interaction between the cluster structure of a real crystal and the boron cation localized in it in different positions has been calculated for each of the configurations. Calculations have demonstrated that B is more likely to be embedded near a defect than in a regular structure. This means that boron positively influences the local substructure of doped LN crystals, not only structures the melt during crystal growth. Calculations have shown that the type and location of structural defects affect the position of boron in the structure of a LN crystal. Calculations have also shown that LN:B(1) has a more stable structure, including optical damage resistance. The photoinduced light scattering (PILS) patterns and conoscopic patterns confirm this conclusion for the studied LN:B crystals. The information obtained in this study may be useful for interpreting the defective structure of LN crystals co-doped with boron and metals (Mg, Zn, etc.). This will supplement the knowledge available in the literature regarding models that describe the structure of complexly doped LN crystals.

ВЛИЯНИЕ КОНЦЕНТРАЦИИ КАТИОНОВ БОРА В КРИСТАЛЛАХ НИОБАТА ЛИТИЯ НА ТИП И КОНЦЕНТРАЦИЮ ТОЧЕЧНЫХ СТРУКТУРНЫХ ДЕФЕКТОВ КАТИОННОЙ ПОДРЕШЕТКИ

Doping a charge of congruent composition (R = [Li]/[Nb] = 0,946) by boric acid leads to an increase in stoichiometry (R = 0,96) of the LiNbO3:B (144·10-5 wt % B in the cone) crystal. The LiNbO3:B crystal was studied by the X-ray diffraction analysis. It was found that in the LiNbO3:B crystal there are no NbLi defects, but there are NbV defects. It has been shown that the localization of the boron cation in the structure of the LiNbO3:B crystal near the NbV defect will be most preferable in the faces of vacant tetrahedral voids common with lithium or vacant oxygen octahedra O6.

Skeletal rearrangement of a boron-containing annulenic molecule into a macrocycle bridged by an electronically stabilized boron cation.

An annulenic molecule containing a three-coordinate chloroborane moiety, which exhibits a borane-olefin proximity effect, undergoes a skeletal rearrangement upon chloride abstraction, to generate a three-dimensional macrocyclic molecule featuring a borocenium (η5-cyclopentadienyl-B+-R) structure.

An Iridium-Stabilized Borenium Intermediate.

Exploration of new organometallic systems based on polyhedral boron clusters has the potential to solve challenging chemical problems such as the stabilization of reactive intermediates and transition-state-like species postulated for E-H (E = H, B, C, Si) bond activation reactions. We report on facile and clean B-H activation of a hydroborane by a new iridium boron cluster complex. The product of this reaction is an unprecedented and fully characterized transition metal-stabilized boron cation or borenium. Moreover, this intermediate bears an unusual intramolecular B···H interaction between the hydrogen originating from the activated hydroborane and the cyclometallated metal-bonded boron atom of the boron cluster. This B···H interaction is proposed to be an arrested insertion of hydrogen into the Bcage-metal bond and the initiation step for iridium "cage-walking" around the upper surface of the boron cluster. The "cage-walking" process is supported by the hydrogen-deuterium exchange observed at the boron cluster, and a mechanism is proposed on the basis of theoretical methods with a special focus on the role of noncovalent interactions. All new compounds were isolated and fully characterized by NMR spectroscopy and elemental analysis. Key compounds were studied by single crystal X-ray diffraction and X-ray photoelectron spectroscopy.

Calculated substantiation of isolation of boron and sodium cations from molten working and heating medium during hardening of restored parts

Scientific and technological research in the development of the technical process for the restoration and strengthening of worn parts using calculated justification allowed us to make an optimal technical decision on the development of a method for surfacing and electrolysis borating of parts to increase their service life. The working medium for strengthening the restored tillage organs of agricultural aggregates is substantiated theoretically using the developed mathematical model describing the working medium as a thermodynamic system consisting of boron cations, sodium and oxygen anions. The creation of a potential difference in this medium will provide a process in which boron and sodium ions are discharged at the cathode, and oxygen ions at the anode. For this, it is necessary to theoretically determine the electromotive forces of polarization of electrolytic cells and compare them. The solution to this problem requires an assessment of the change in the Gibbs energy during the decomposition of sodium oxide and boric anhydride for the temperature of the borating process, taking into account its change under standard conditions, the chemical potentials of the reacting components and phase transitions, the melting of substances and their sublimation. The order in which boron and sodium are separated at the cathode is determined by comparing the electromotive forces of polarization of boric anhydride and sodium oxide. It was found that sodium oxide is more stable than boric anhydride. Consequently, boron atoms are reduced on the cathode surface, and calculations have confirmed the possibility of its use.

Unraveling the reactivity of a cationic iminoborane: avenues to unusual boron cations.

A cationic terminal iminoborane [Mes*N Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> B ← IPr2Me2][AlBr4] (3+[AlBr4]−) (Mes* = 2,4,6-tri-tert-butylphenyl and IPr2Me2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) has been synthesized and characterized. The employment of an aryl group and N-heterocyclic carbene (NHC) ligand enables 3+[AlBr4]− to exhibit both B-centered Lewis acidity and BN multiple bond reactivities, thus allowing for the construction of tri-coordinate boron cations 5+–12+. More importantly, initial reactions involving coordination, addition, and [2 + 3] cycloadditions have been observed for the cationic iminoborane, demonstrating the potential to build numerous organoboron species via several synthetic routes.

Bringing out the potential of organoboron compounds by designing the chemical bonds and spaces around boron.

Since the structures, reactivity and properties of organoboron compounds stem from the electron deficiency and low electronegativity of boron, the design of the chemical bonds attached to boron as well as the space provided by substituents around boron leads to particular reactivity and functions of organoboron compounds. Based on the concept of vacant boron p-orbital engineering in combination with peripheral space design for boron, we have developed new organoboron compounds, which exhibit exotic reactivity and properties and boron-mediated organic transformations capable of constructing large π-conjugated systems. Here we describe our recent study by focusing on three topics: (i) the synthesis and its derivatization, small-molecule activation and application to materials science of a two-coordinate boron cation (borinium ion), (ii) a 9-borafluorene-mediated benzannulation reaction of alkyne derivatives and (iii) BN-substituted molecules featuring a 4nπ heterocycle exhibiting unique electronic and emission properties. The molecules and reactions appearing in this article are unprecedented, yet feature very simple systems, and therefore clearly demonstrate intrinsic and new potential of organoboron compounds.

Electrochromic Polycationic Organoboronium Macrocycles with Multiple Redox States.

Polycationic macrocycles are attractive as they display unique molecular switching capabilities arising from their redox properties. Although diverse polycationic macrocycles have been developed, those based on cationic boron systems remain very limited. We present herein the development of novel polycationic macrocycles by introducing organoboronium moieties into a conjugated organoboron macrocyclic framework. These macrocycles consist of four bipyridylboronium units that are connected by fluorene and either electron-deficient arylborane or electron-rich arylamine moieties. Electrochemical studies reveal that the macrocycles undergo reversible multi-step redox processes with transfer of up to 10 electrons. Switchable electrochromic behavior is demonstrated via spectroelectrochemical studies and the observed color changes are rationalized by correlation with computed electronic transitions using DFT methods.

Visualization of the Effect of an Impurity on the Optical Homogeneity of Lithium Niobate Doped with Boron Cations

The laser conoscopy method confirms the high optical uniformity of LiNbO3:B crystals in the range of B2O3 concentrations from 0.008 to 1.24 mol. %. Minor signs of anomalous optical biaxiality appear in the conoscopic patterns of crystals at boron concentrations of 0.12 and 0.83 mol. % at a laser power of 90 mW. The maximum value of the angle of anomalous optical axes for the studied samples is 2V = 10 ́ for the sample (0.12 mol. %), аnd the value of anomalous birefringence corresponds to ∆n = 0.02·10-5.

Study of the chromium doping effect in boron phosphide semiconductors

According to the firs-principles theory-based spin-density functional calculations within the framework of Wu–Cohen generalized gradient approximation (WC-GGA), we examine the structural and electronic properties of ternary alloys of zinc-blende boron phosphide doped with chromium. We compare the materials with aluminum phosphide that exhibits half-metallic properties at various concentrations. The curves of total and partial densities of states and the band structures show that [Formula: see text][Formula: see text]P are purely metallic and can be possible candidates for use in light emitting diodes (LEDs). These compounds are not polarized on spins; the main cause is the nature of chemical bond located between the boron cations and the phosphorus anion, whereas the ternary materials of [Formula: see text][Formula: see text]P all have various uses in spintronic science according to many studies because of their half-metallicity behavior.

Generation and Identification of the Linear OCBNO and OBNCO Molecules with 24 Valence Electrons.

Two structural isomers containing five second‐row element atoms with 24 valence electrons were generated and identified by matrix‐isolation IR spectroscopy and quantum chemical calculations. The OCBNO complex, which is produced by the reaction of boron atoms with mixtures of carbon monoxide and nitric oxide in solid neon, rearranges to the more stable OBNCO isomer on UV excitation. Bonding analysis indicates that the OCBNO complex is best described by the bonding interactions between a triplet‐state boron cation with an electron configuration of (2s)0(2pσ)0(2pπ)2 and the CO/NO− ligands in the triplet state forming two degenerate electron‐sharing π bonds and two ligand‐to‐boron dative σ bonds.

Organic Transformations Using Electron-Deficient Boron Compounds

The molecular structures and chemical reactivity of boron compounds are characterized by the electron deficiency and low electronegativity of boron. Based on simple molecular design strategy taking advantage of the unique properties of boron, we have developed new chemical species and new organic transformations. This article describes our recent studies of (i) a two-coordinate boron cation (borinium ion) and (ii) a 9-borafluorene-mediated benzannulation reaction of alkyne derivatives. In the former, we successfully isolated a diarylborinium ion (Mes2B+), which had been considered impossible to be isolated as a stable species without introducing particular electron-donating groups to boron. We found several unique small-molecule activation reactions mediated by Mes2B+ such as C=O double bond cleavage of CO2. Moreover, we revealed that Mes2B+ serves as an excellent hole-doping reagent for carbon nanotube, graphene, and transition metal dichalcogenide. In the latter topic, we discovered a new efficient boron-mediated benzannulation reaction of alkyne derivatives, which enables the synthesis of a wide variety of extended π-conjugated molecules and polymers. The boron compounds used in these studies are simple but enable powerful organic transformations.

η5-Cp*B-Mes]+: A Masked Potent Boron Lewis Acid

The chemistry of the boron cation has been revitalized in the past decade due to its newfound application in stoichiometric and catalytic organic reactions. To extend the frontier of boron cation c...

Isolation of an N-Heterocyclic Carbene Complex of a Borasilene.

Borasilenes, that is complexes which contain a boron-silicon double bond, have scarcely been isolated to date. In pursuit of such species, (Me3 Si)3 SiB(Cl)NHI (2, NHI=bulky N-heterocyclic imine) was prepared and treated with KOtBu to achieve formal extrusion of ClSiMe3 . The formation of an elusive borasilene (3int ) is postulated and it was verified by isolation of the N-heterocyclic carbene adduct (Me3 Si)2 SiB(I )NHI (4, I =1,3,4,5-tetramethyl-imidazolin-2-ylidene). X-ray crystallographic study and theoretical calculations on 4 diagnosed a boron-silicon double bond with marked zwitterionic character. The negative charge resides at the Si atom which marks the apex of a trigonal pyramid. Structural comparison of 4 with boron cation congeners (5+ , 6+ ) suggests that the positive charge is mainly located at the trigonal planar-coordinated B center. The conversion of 4 with pinacolborane (HBpin, 2 equiv) resulted in cleavage of the double bond to produce (Me3 Si)2 Si(Bpin)2 and (NHI)BH2 (I ).

Optical properties and structure particularities of LiNbO3 crystals grown from a boron-doped melt

A series of LiNbO3:B crystals was grown from the melt doped by boron. It is shown that LiNbO3:B crystals possess an increased resistance to optical damage. We have found changes according to Raman spectra confirming the ordering of Li+, Nb5+ cations and vacancies along the polar axis. The chemical interactions were studied in the system Li2O–B2O3–Nb2O5. Boron cations are unable to incorporate into a cation sublattice of LiNbO3, but they change the physic-chemical structure of a melt. It contributes to an increased structure and optical uniformity of LiNbO3:B.