Boron-nitrogen Bond Research Articles

Supramolecular gels based on boronate esters and imidazolyl donors.

Dative boron-nitrogen bonds can be used for the controlled assembly of boronate esters and N-donor ligands. So far, most investigations have focused on crystalline assemblies. In contrast, there are very few reports about soft materials based on dative B-N bonds. Here, we describe the formation of gels by aggregation of diboronate esters and ditopic bisimidazolyl donor ligands. Analyses of low molecular weight model compounds by NMR spectroscopy, isothermal titration calorimetry, and X-ray crystallography reveal that imidazolyl ligands form particularly strong dative bonds with boronate esters. The strong interaction allows gel formation in competitive polar solvents such as THF and acetone. In less polar solvents, very low critical gel concentrations of down to 0.02 wt% are observed. By using a diboronate ester linked by an azobenzene group, it is possible to form a photoresponsive gel.

Efficient synthetic methods for the installation of boron-nitrogen bonds in conjugated organic molecules.

Polycyclic aromatic hydrocarbons in which one or more CC units have been replaced by isoelectronic BN units have attracted interest as potentially improved organic materials in various devices. This promise has been hampered by a lack of access to gram quantities of these materials. However, the exploitation of keystone reactions such as ring closing metathesis, borylative cyclization of amino styrenes and electrophilic borylation has lead to strategies for access to workable amounts of material. These strategies can be augmented by judicious postfunctionalization reactions to diversify the library of materials available. This Frontier article highlights some of the recent successes and shows that the long promised applications of BN-doped PAHs are beginning to be explored in a meaningful way.

Beyond Dehydrocoupling: Group 2 Mediated Boron-Nitrogen Desilacoupling

The alkaline-earth element bis(trimethylsilyl)amides, [Ae{N(SiMe3)2}2(thf)2] [Ae=Mg, Ca, Sr], are effective precatalysts for boron–nitrogen bond formation through the desilacoupling of amines, RR′NH (R=alkyl, aryl; R′=H, alkyl, aryl), and pinBSiMe2Ph. This reactivity also yields a stoichiometric quantity of Me2PhSiH and provides the first example of a catalytic main-group element–element coupling that is not dependent on the concurrent elimination of H2.

Beyond Dehydrocoupling: Group 2 Mediated Boron-Nitrogen Desilacoupling.

The alkaline-earth element bis(trimethylsilyl)amides, [Ae{N(SiMe3 )2 }2 (thf)2 ] [Ae=Mg, Ca, Sr], are effective precatalysts for boron-nitrogen bond formation through the desilacoupling of amines, RR'NH (R=alkyl, aryl; R'=H, alkyl, aryl), and pinBSiMe2 Ph. This reactivity also yields a stoichiometric quantity of Me2 PhSiH and provides the first example of a catalytic main-group element-element coupling that is not dependent on the concurrent elimination of H2 .

Dynamic NMR and Twisted Intramolecular Charge Transfer Excited States

In this paper the results of dynamic NMR studies on ethylmethylamino-tertiary-butyl-phenylborane (EMABPB) with or without light are reported. The NMR data were recorded on a Bruker 400 MHz NMR equipped with our custom-made optical probe and with our custom-made 450 watts (W) monochromatic light sources. The molecular photochemistry including twisted intramolecular charge-transfer-excited-state (TICT) of the EMABPB in several solvents has been investigated. These results indicate that the aminoborane demonstrates multiple configurations in CD3Cl and CD2Cl2 resulting in the shifts of the signals of the alkyl groups on the nitrogen and boron. This indicates that there are some time-dependent changes at constant temperature over the irradiation interval. At ﹣60°C and the presence of light (λ = 265 nm), we observed a large change in the populations of the two sites, and this by itself indicates a modification in the rotation around the boron nitrogen bond in the excited state. By considering the existence of the TICT state, many important energy technologies may be developed with higher efficiency by controlling the back-electron transfer processes.

The Thermal Stability of Tris(methimazolyl)borates and Their Germanium Complexes

AbstractA series of methimazole‐based soft scorpionate anions ([RTmMe]–, R = H, Ph, Me, nBu) bearing substitution at the bridgehead boron have been used to produce a series of germanium complexes of general formulae [Ge(RTmMe)2]I2. Structural analyses of the germanium complexes by X‐ray crystallography reveal that they all contain an octahedral S6 coordination sphere. The scorpionate anions (as their Li or Na salts) and their germanium complexes have been studied by thermogravimetric analysis. This analysis suggests that the degradation pathway for the free scorpionate anions differs from that of the complexes. Both pathways involve the loss of a methimazole ring thereby supporting the view that cleavage of the boron–nitrogen bonds can occur under thermally aggressive conditions. As expected, the presence of the germanium alters the degradation profile of the anion. In contrast to the free anions, the four complexes all display a similar mechanism for degradation. Although the presence of the germanium enforces a conformational change in the anions, its presence does not significantly increase the stability of the boron–nitrogen bonds.

A four-component organogel based on orthogonal chemical interactions.

A thermoresponsive organogel was obtained by orthogonal assembly of four compounds using dynamic covalent boronate ester and imine bonds, as well as dative boron-nitrogen bonds. It is shown that the gel state can be disrupted or reinforced by chemicals which undergo exchange reactions with the gel components.

Microwave assisted synthesis of 10b-aza-10c-borapyrene

The synthesis of 10b-aza-10c-borapyrene, an analog of the polycyclic aromatic hydrocarbon pyrene with an internal boron–nitrogen bond, has been improved. We have dramatically reduced the reaction times and ease of workup for the synthesis of this molecule by using a microwave reactor and carefully controlling reaction conditions.

Self‐Assembly of Arylboronate Esters with Pyridyl Side Chains

AbstractBoronate esters that contain N‐donor groups are self‐complementary structures, which can assemble by means of dative boron–nitrogen bonds to form macrocycles or polymers. Herein, we describe the synthesis of dioxaborinanes and benzodioxaboroles containing pyridyl side chains. In the solid state, the dioxaborinanes were found to exist predominantly as monomers. Upon crystallization, aggregation into one‐dimensional polymers was observed, but only for boronate esters that contained electron‐withdrawing groups. The more Lewis acidic benzodioxaboroles, on the other hand, were found to form macrocycles both in solution and in the solid state.

Highly Emissive Boron Ketoiminate Derivatives as a New Class of Aggregation‐Induced Emission Fluorophores

A series of boron ketoiminate derivatives that exhibited clear aggregation-induced emission (AIE) characteristics (in THF: Φ(PL)≤0.01; in the solid state: Φ(PL)=0.30-0.76) were prepared by the reactions of 1,3-enaminoketone derivatives with boron trifluoride-diethyl etherate. The structures and optical properties were investigated by UV-visible spectroscopy, photoluminescent (PL) spectroscopy, and X-ray single-crystal measurements. These results indicate that the AIE characteristics were derived from molecular motions of the boron-chelating rings with a boron-nitrogen (B-N) bond. Furthermore, the optical properties were controllable by steric hindrance of the substituted groups on the nitrogen atom.

ChemInform Abstract: Supramolecular Assemblies Based on Dative Boron—Nitrogen Bonds

AbstractReview: 31 refs.

Supramolecular Assemblies Based on Dative Boron–Nitrogen Bonds

Dative boron-nitrogen bonds were found to be a useful binding motif in structural supramolecular chemistry. Crystalline cages were formed using a diboronate ester and 2,4,6-tri(4-pyridyl)-1,3,5-triazine. These cages can act as hosts for electron-rich planar aromatic systems such as triphenylene. Further, crystalline two-dimensional polymers were formed via dative B-N bonds between a triboronic ester and a ditopic pyridyl ligand. Use of an extended triboronate ester resulted in formation of a gel in toluene with a minimum gelation concentration of 0.5 wt%.

Supramolecular polymers based on dative boron–nitrogen bonds

Heteroditopic monomers containing an arylboronate ester and a dialkyl-4-aminopyridine group aggregate via dative boron-nitrogen bonds to give main chain supramolecular polymers. The degree of polymerization can be tuned by changing the electronic and steric properties of the boronate ester.

Molecular Networks Based on Dative Boron–Nitrogen Bonds

Die BN-Verbindung: Kristalline und weiche molekulare Netzwerke lassen sich mithilfe dativer B-N-Bindungen aufbauen (siehe Bild). Sie entstehen in einer einstufigen Dreikomponentenreaktion zwischen einer Triboronsäure, einem Catechol und einem Bipyridyllinker. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Molecular Networks Based on Dative Boron–Nitrogen Bonds

The BN connection: Crystalline and soft molecular networks can be constructed using dative BN bonds (see picture). The networks are obtained in a one-step, three-component reaction involving a triboronic acid, a catechol, and a bipyridyl linker. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

On the multiple B–N bonding in boron compounds using the topological analysis of electron localization function (ELF)

Topological analysis of the Electron Localization Function (ELF) within the framework of Quantum Chemical Topology (QCT) has been applied to study the nature of the boron–nitrogen bonds. A series of 10 compounds have been chosen, with the B–N bond length ranging between 1.698 A (B–N) and 1.258 A (BN). According to the Lewis formula three types of bonds have been recognized. These are: the single B–N bond with a basin population of 1.91 ÷ 2.09e, the double BN bond with a population of 3.78 ÷ 4.28e, and the triple BN bond with a basin population of 5.72 ÷ 5.74e. In the case of partial double bonds (BN), where formally two or more resonance hybrids have to be considered, our calculations strongly support the concept of double boron–nitrogen bonding (BN).

Dative boron–nitrogen bonds in structural supramolecular chemistry: multicomponent assembly of prismatic organic cages

The multicomponent reaction of diboronic acids with a catechol and a tripyridyl linker results in the formation trigonal prismatic cages. The cages feature six dative boron–nitrogen bonds as structure-directing elements. The size of the cages can be varied by changing the diboronic acid building block. The cages are able to encapsulate polyaromatic molecules such as triphenylene or coronene.

BENZENE STAND-INS

WITH A SYSTEMATIC SERIES of X-ray crystal structures, chemist Shih-Yuan Liu and coworkers at the University of Oregon, Eugene, provide evidence that a family of six-membered rings featuring a boron-nitrogen bond has a benzenelike nature ( J. Am. Chem. Soc. 2008 , 130 , 7250). The compounds, 1,2-dihydro-1,2-azaborines, feature bonding characteristics and other properties that could make them valuable substitutes for benzenes in biomedical and materials research. Benzene is the quintessential aromatic compound, stabilized by virtue of delocalized electrons freely moving about its circular array of atoms. Liu’s work indicates that 1,2-dihydro-1,2-azaborines, related to benzene through substitution of one of the ring’s bonds with a B–N bond, share that special stability. Liu and coworkers synthesized a derivative of 1,2-dihydro-1,2-azaborine with substituents at the boron and nitrogen atoms. They also made four reference heterocycles designed to be nonaromatic. They then obtained X-ray crystal structures of a...

Reaction of closo-dodecaborate anion B12H 12 2− with iminium salts

The reaction of the closo-dodecaborate anion with iminium salts was studied. The iminium salts were either formed in situ or introduced into the reaction in an individual state. Mono-and disubstituted products with an exopolyhedral boron-nitrogen bond were found to form. The structures of compounds 1,7-[NMe2(CH2Cl)]2B12H10 and 1,7-[MeNPh(CH2Cl)]2B12H10 were determined using X-ray crystallography.

Interaction of closo-decaborate anion B10H 10 2− with iminium salts

The interaction of closo-decaborate anions with iminium salts, either formed in situ or introduced into the reaction as individual compounds, has been studied. The reaction leads to products with an exopolyhedral boron-nitrogen bond. The formation of compounds with exopolyhedral boron-chlorine and boron-carbon bonds is also possible. The crystal structures of [NMe2(CH2Cl)]2B10H8 and 3-CH3-2,8-[NMe2(CH2Cl)]2-7-ClB10H6 have been studied.