The Dewar Isomer of 1,2-Dihydro-1,2-azaborinines: Isolation, Fragmentation, and Energy Storage.

The photochemistry of 1,2-dihydro-1,2-azaborinine derivatives was studied under matrix isolation conditions and in solution. Photoisomerization occurs exclusively to the Dewar valence isomers upon irradiation with UV light (>280 nm) with high quantum yield (46 %). Further photolysis with UV light (254 nm) results in the formation of cyclobutadiene and an iminoborane derivative. The thermal electrocyclic ring-opening reaction of the Dewar valence isomer back to the 1,2-dihydro-1-tert-butyldimethylsilyl-2-mesityl-1,2-azaborinine has an activation barrier of (27.0±1.2) kcal mol-1 . In the presence of the Wilkinson catalyst, the ring opening occurs rapidly and exothermically (ΔH=(-48±1) kcal mol-1 ) at room temperature.

1,2-Azaborine: The Boron-Nitrogen Derivative of ortho-Benzyne.

The BN analogue of ortho-benzyne, 1,2-azaborine, is generated by flash vacuum pyrolysis, trapped under cryogenic conditions, and studied by direct spectroscopic techniques. The parent BN aryne spontaneously binds N2 and CO2, thus demonstrating its highly reactive nature. The interaction with N2 is photochemically reversible. The CO2 adduct of 1,2-azaborine is a cyclic carbamate which undergoes photocleavage, thus resulting in overall CO2 splitting.

Protecting group-free synthesis of 1,2-azaborines: a simple approach to the construction of BN-benzenoids.

The protecting group-free synthesis of a versatile 1,2-azaborine synthon 5 is described. Previously inaccessible 1,2-azaborine derivatives, including the BN isostere of phenyl phenylacetate and BN1 triphenylmethane were prepared from 5 and characterized. The structural investigation of BN phenyl phenylacetate revealed the presence of a unique NH-carbonyl hydrogen bond that is not present in the corresponding carbonaceous analogue. The methyne CH in BN triphenylmethane was found to be less acidic than the corresponding proton in triphenylmethane. The gram-quantity synthesis of the parent 1,2-azaborine 4 was demonstrated, which enabled the characterization of its boiling point, density, refractive index, and its polarity on the ET(30) scale.

Crystal structure and Hirshfeld surface analysis of tri-aza-triborinotris[1,3,2]benzodi-aza-borole acetone disolvate.

The title compound, alternatively known as benzodi-aza-borole trimer, C18H15B3N6·2C3H6O, at 100 K crystallizes in the triclinic system, space group P . The structure displays N-H⋯O hydrogen bonding connecting the main mol-ecule with the crystallization solvent. Disorder of the main mol-ecule is observed with occupancy factors refined to 0.8922 (14):0.1078 (14). The packing of the crystal shows a parallel-displaced atom-centered orientation with 3.30 (2) Šbetween the planes of the rings. In the solid state, the title compound is linked with weak C-H⋯π inter-actions, which is supported by Hirshfeld surface analysis.

UV-photoelectron spectroscopy of 1,2- and 1,3-azaborines: a combined experimental and computational electronic structure analysis.

We present a comprehensive electronic structure analysis of structurally simple BN heterocycles using a combined UV-photoelectron spectroscopy (UV-PES)/computational chemistry approach. Gas-phase He I photoelectron spectra of 1,2-dihydro-1,2-azaborine 1, N-Me-1,2-BN-toluene 2, and N-Me-1,3-BN-toluene 3 have been recorded, assessed by density functional theory calculations, and compared with their corresponding carbonaceous analogues benzene and toluene. The first ionization energies of these BN heterocycles are in the order N-Me-1,3-BN-toluene 3 (8.0 eV) < N-Me-1,2-BN-toluene 2 (8.45 eV) < 1,2-dihydro-1,2-azaborine 1 (8.6 eV) < toluene (8.83 eV) < benzene (9.25 eV). The computationally determined molecular dipole moments are in the order 3 (4.577 D) > 2 (2.209 D) > 1 (2.154 D) > toluene (0.349 D) > benzene (0 D) and are consistent with experimental observations. The λ(max) in the UV-vis absorption spectra are in the order 3 (297 nm) > 2 (278 nm) > 1 (269 nm) > toluene (262 nm) > benzene (255 nm). We also establish that the measured anodic peak potentials and electrophilic aromatic substitution (EAS) reactivity of BN heterocycles 1-3 are consistent with the electronic structure description determined by the combined UV-PES/computational chemistry approach.

Nucleophilic aromatic substitution reactions of 1,2-dihydro-1,2-azaborine.

Could go either way: the addition of nucleophiles to the parent 1,2-dihydro-1,2-azaborine and subsequent quenching with an electrophile generates novel substituted 1,2-azaborine derivatives. Mechanistic studies are consistent with two distinct nucleophilic aromatic substitution pathways depending on the nature of the nucleophile.

Crystal structure of 2,2'-bi-pyrrole.

The complete mol-ecule of the title compound, C8H8N2, is generated by a crystallographic center of symmetry. In the crystal, short N-H⋯π [H⋯π = 2.499 (19) Å] inter-actions link the mol-ecules into a herringbone structure.

Correction: Synthesis by free radical polymerization and properties of BN-polystyrene and BN-poly(vinylbiphenyl).

Correction for 'Synthesis by free radical polymerization and properties of BN-polystyrene and BN-poly(vinylbiphenyl)' by Wen-Ming Wan et al., Chem. Commun., 2016, 52, 13616-13619.

Synthesis by free radical polymerization and properties of BN-polystyrene and BN-poly(vinylbiphenyl).

Free radical polymerization of B-vinyl- and B-styryl-functionalized azaborinine monomers gives well-defined hybrid polymers that were fully characterized by multinuclear NMR and GPC analysis; their solubility, thermal characteristics, and photophysical properties are dramatically different from those of the all-carbon polystyrene analogues.

How stable are 1,2-dihydro-1,2-azaborines toward water and oxygen?

The stability of 1,2-dihydro-1,2-azaborines toward oxygen and water was investigated as a function of their ring substituents: while generally 1,2-dihydro-1,2-azaborines are compatible with water, their stability toward oxygen is dependent on the boron and the C(3) substituents, and we found that electron withdrawing groups enhanced the heterocycle's ability to resist oxidative degradation.