Ashley N. Lamm

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.

BN-substituted diphenylacetylene: a basic model for conjugated π-systems containing the BN bond pair

We report the synthesis, structural characterization, and optoelectronic properties of BN-Tolan 1 and Bis-BN-Tolan 2, one of the simplest conjugated systems containing the BN bond pair. BN-tolans 1 and 2 display absorption and emission properties that are distinct from their carbonaceous analogue, tolan. In addition, Bis-BN-Tolan 2 exhibits unique N–H⋯π(C≡C) hydrogen bonding in the solid state.

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.

1,2-Azaborine, the BN 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.

Photoisomerization of 1,2-Dihydro-1,2-Azaborine: A Matrix Isolation Study†

Boron-nitrogen heterocycles have received much interest in recent years, due to their wide applications as ligands[1] and potential use in organic optical and electronic devices.[2] 1,2-Dihydro-1,2-azaborine compounds are six membered heterocycles and are isoelectronic to benzene, with a C=C unit replaced by a B=N unit.[3] These compounds were initially reported in the 1960’s by Dewar and White,[4] and during the last ten years, examples of substituted 1,2-dihydro-1,2-azaborines[1c,5] as well as their potential in coordination chemistry were explored by Ashe et al.[6] Renewed interest in 1,2-dihydro-1,2-azaborine chemistry,[1c,7] properties[8] and applications[9] led to the synthesis and isolation of parent 1,2-dihydro-1,2-azaborine (1), a benzene isostere, in 2009.[10]