Isolation of Stable Borepin Radicals and Anions

Abstract

Borepin, a 7‐membered boron‐containing heterocycle, has become an emerging molecular platform for the development of new materials and optoelectronics. While electron‐deficient borepins are well‐established, reduced electron‐rich species have remained elusive. Herein we report the first isolable, crystalline borepin radical (2 a, 2 b) and anion (3 a, 3 b) complexes, which have been synthesized by potassium graphite (KC8) reduction of cyclic(alkyl)(amino) carbene‐dibenzo[b,d]borepin precursors. Borepin radicals and anions have been characterized by EPR or NMR, elemental analysis, X‐ray crystallography, and cyclic voltammetry. In addition, the bonding features have been investigated computationally using density functional theory.

Synthesis, Characterization, and Properties of Three-Dimensional Analogues of 9-Borafluorenes

“…9-Borafluorene is composed of an antiaromatic borole unit and two fused aromatic benzene rings, representing a prominent class of boron-doped polycyclic π-conjugated hydrocarbons . 9-Borafluorenes have been the focus of intense research in the past two decades not only due to their fundamental significance in terms of aromaticity/antiaromaticity and Lewis acidity but also because of their appealing photophysical properties, which stimulates the related investigation on exploiting their potential for applications in electronic materials and devices. , Moreover, the pronounced Lewis acidity, which can presumably be attributed to the antiaromatic nature of the central borole unit, enables the sensory applications (Figure a). − , Besides, 9-borafluorenes exhibit fascinating aspects in reaction chemistry, , being extensively utilized as synthetic precursors for diverse boracycles such as borepin, ,, phosphaborepin, BP-phenanthryne, BN-phenanthrenes, ,,, etc. More recently, the challenge of synthetic approach to carbene-stabilized 9-borafluorene radical and monoanion species was addressed by Pan and co-workers (Figure b). , …”

Designing a Four-Ring Tubular Boron Motif through Metal Doping

“…The size of the orbital interaction can be taken as a probe to select the right fragmentation scheme. The fragments that give the smallest Δ E orb are the most appropriate ones because they suggest that the fragments are very nearly prepared like those in the overall complex. − Table S10 presents the results of EDA, taking Be 2 and B 24 in different charge and electronic states as interacting fragments. The relative size of the Δ E orb value suggests that the most appropriate fragments to describe the Be 2 –B 24 interaction in Be 2 B 24 + are those that consider triplet Be 2 2+ (1s 4 2p z 2 ) and quartet B 24 – .…”

Probing borafluorene B–C bond insertion with gold acetylide and azide

“…1–4 The reactivity of 9-borafluorenes often mirrors that of boroles but there are some different reaction outcomes attributed to the diminished Lewis acidity at boron or the lack of a true diene that renders the BC 4 unit resilient to Diels–Alder chemistry. 5–22 Both boroles and 9-borafluorenes have been recognized as effective reagents for accessing boracycles larger than five atoms via intermolecular ring expansion reactions. 22–41…”

“…[1][2][3][4] The reactivity of 9-borafluorenes often mirrors that of boroles but there are some different reaction outcomes attributed to the diminished Lewis acidity at boron or the lack of a true diene that renders the BC 4 unit resilient to Diels-Alder chemistry. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Both boroles and 9-borafluorenes have been recognized as effective reagents for accessing boracycles larger than five atoms via intermolecular ring expansion reactions. [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] Two widely investigated reactions with 9-borafluorenes have been with organic azides and alkynes.…”