New Triazaborine Chromophores: Their Synthesis via Oxazaborines and Electrochemical and DFT Study of Their Fundamental Properties

Abstract

Eight new and stable triazaborine chromophores featuring various substituents as donor and acceptor moieties were prepared and investigated. An interpretation of the measured electrochemical data (CV, RDV, and dc polarography) and UV−vis spectra and quantum chemical calculations are presented. In the homologous series the first reduction proceeds as a one-electron reversible process localized at the −NC–CN– part of the central heterocycle being in conjugation with the attached carbonyl. The first oxidation of triazaborines proceeds as a two-electron irreversible process, most probably of the ECE type, localized at the negatively charged boron atom and surrounding unsaturated structures, including the substituted phenyl ring. For a better understanding of the relationship between the structure and redox properties, the LFER approach was applied for the first oxidation as well as reduction potential using the Hammett σ (para) substituent constants. The energies of the longest-wavelength absorption bands taken from UV–vis spectra were compared with the experimentally found differences E ox – E red and with calculated HOMO–LUMO gaps, and no systematic influence of substitution was found. The calculated optimized structures and displacement of the frontier orbitals confirmed the interpretations presented above.

Innocent BN bond substitution in anthracene derivatives

“…Similar results have been observed in triazaborine heterocycles. 33 That we don't observe a linear free energy relationship between substituent and the peak oxidation potential may reflect the rapid decomposition of the BN anthracene radical cation, which results in a broad and unstable peak oxidation potential and contributing to the scatter in the Hammett analysis.…”

Recent Advances in the Synthesis of Borinic Acid Derivatives

“…The synthesis of bicyclic oxazaborinines 176 has been described starting from cyclic β-enaminones 175 , bearing a secondary amino group, and benzenediazonium tetraphenylborates 174 ( Scheme 59 ) [ 180 , 181 ]. The corresponding oxazaborinines 176 were obtained in modest to good yields, depending on the nature of the 4-substituted benzenediazonium and the size of the cyclic enaminones 175 .…”

Synthesis and Characterization of New Boron Compounds Using Reaction of Diazonium Tetraphenylborate with Enaminoamides

“…We have studied the reactions of polarized ethylenes, such as β-enaminones, β-enaminonitriles, and β-enaminoamides, with substitution on the amino group, with diazonium salts, leading to heterocyclic compounds. These compounds are pyridazines [20][21][22], pyrazoles [23][24][25][26], oxazaborines, diazaborinones, and triazaborines [27][28][29][30][31]. In 2009, we published work on the reaction of β-enaminoamides 1 (Figure 1, R 3 = Ph) and 4-methylbenzenediazonium tetraphenylborate to give compounds I-III (Scheme 2) [28].…”