A Crystalline Diazadiborinine Radical Cation and Its Boron‐Centered Radical Reactivity

Abstract

One-electron oxidation of 1,4,2,5-diazadiborinine 1 has been studied. While the reaction of 1 a bearing phenyl groups on the B atoms with AgAl{OC(CF ) } afforded a complex mixture, the same oxidation reaction with 1 b featuring bulky mesityl substituents on the B atoms rendered the corresponding cation radical 2 b as an isolable species. X-ray diffraction analysis, EPR spectroscopy, and DFT calculations of 2 b revealed the delocalization of the unpaired electron over the entire π-system of 2 b, as well as a large spin density (0.76 in total) on the two equivalent boron atoms. The chemical trapping reaction of 2 b with p-benzoquinone and triphenyltin hydride afforded the dicationic species 3 containing two newly formed B-O bonds and the monocationic product 2b-H containing a B-H bond, respectively, thus confirming the boron-centered radical reactivity of 2 b.

A Neutral and Aromatic Boron‐Rich Inorganic Benzene

“…In the UV/Vis absorption spectrum, an absorption band with a maximum at a wavelength of 607 nm was observed (Figure S21, Supporting Information). The cyclic voltammogram (CV) of 3 shows an irreversible oxidation wave at E OX 1 =−1.45 V (Figure S25), indicating the electron‐rich nature of 3 …”

Designs of Singlet Fission Chromophores with a Diazadiborinine Framework**

“…Our calculated adiabatic and vertical E(S) 1 s correspond to λ = 454 and 425 nm and are within the lowest energy broad hump ranging from 525 to 425 nm in the UV-Vis spectrum of 2. [49] The non-perfect agreement is attributed to the negligence of solvent effects. Our TDDFT calculated E(S) 1 with the polarizable continuum medium (PCM) [64] solvent model of hexane is redshifted by 0.13 eV compared to the corresponding gas phase calculation.…”

“…[48] While 1 is just a theoretical model, the diazadiborinine molecule 2 with two side rings was synthesized by the Kinjo group. [46,49] And the core structure of 2 resembles 1. This synthesis inspired us to carry out the present work: we use quantum chemistry calculations to propose a few more SF chromophores based on the framework of 2.…”

Persistent Borafluorene Radicals

“…Boron-centered radicals have been studied extensively in recent years because of their importance in both pure and applied chemistry. [13] Neutral boryl radicals germane to this report include Lewis base stabilized BH 2 C, [14] BR 1 R 2 C, [15] and borole radicals. [16] In order to expand the radical-based chemistry to molecular platforms that are stable and relevant to materials, we report the synthesis, molecular structures, UV/Vis absorption, electrochemistry, electron paramagnetic resonance (EPR) spectroscopy, and theoretical studies of N-heterocyclic carbene (NHC)-and cyclic (alkyl)(amino)carbene (CAAC)-stabilized borafluorene radicals (2 and 4; Figure 1 d).…”