Extensive Structural Rearrangements upon Reduction of 9H‐9‐Borafluorene

Abstract

Common wisdom has it that organoboranes are readily oxidized. Described herein is that also their reduction can result in remarkable chemistry. Treatment of dimeric 9H-9-borafluorene with Li metal in toluene yields two strikingly different classes of compounds. One part of the sample reacts in a way similar to B2H6, thus affording an aryl(hydro)borane cluster reminiscent of the [B3H8](-) anion. The other part furnishes a dianionic boron-doped graphene flake devoid of hydrogen substituents at the boron centers and featuring a central B=B bond. A change in the solvent to THF allows an isolation of this dibenzo[g,p]chrysene analogue in good yields.

The 9H‐9‐Borafluorene Dianion: A Surrogate for Elusive Diarylboryl Anion Nucleophiles

“…The key to success is to maintain a temperature of À78 8C during the first hour of the reaction in order to avoid the formation of unwanted side products, primarily [1H] À and [3] 2À (Figure 2 a and b, top vs. middle). [25] Why is an initial low temperature of such critical importance, given that further stirring of the respective mixture at room temperature for a much longer time span is still required to drive the reaction to completion?…”

Deprotonation of a Seemingly Hydridic Diborane(6) To Build a B−B Bond

“…[8][9][10][11] Specifically,o ur group generated the compound K[1H] from diborane 1H 2 [12,13] through ar eduction/hydride elimination sequence (Scheme 2). [8][9][10][11] Specifically,o ur group generated the compound K[1H] from diborane 1H 2 [12,13] through ar eduction/hydride elimination sequence (Scheme 2).…”

“…Indeed, this concept has been successfully applied to prepare the entire sequence of products shown in Scheme 1b. [8][9][10][11] Specifically,o ur group generated the compound K[1H] from diborane 1H 2 [12,13] through ar eduction/hydride elimination sequence (Scheme 2). [11] Thea nion [1H] À contains acentral BÀBsingle bond, supported by one residual m-Ha tom, and may therefore be regarded as af ormal deprotonation product of 1H 2 .Examples of clear-cut BÀBcoupling reactions through the deprotonation of neutral B(m-H)B fragments are so far restricted to higher clusters B n H m with n !…”

“…Af ourth resonance structure,f eaturing two protons and aB = Bdouble bond, possesses arelative weight of 6%. [25] Given this background, we started our investigation by titrating a[ D 8 ]THF solution of the B = B-bonded species Li 2 [1] [9,11] with ethereal HCl (Scheme 3). According to 1 HNMR spectroscopy (Figure 1), the gradual addition of the acid resulted first in clean conversion of the starting material to Li [1]through reduction of 1H 2 with M = Li or K; [11] the reverse reaction through titration of Li 2 [1]with ethereal HCl;and the comproportionation of 1H 2 and Li 2 [1]toafford Li[1H].A ll reactions were carried out in THF at room temperature.…”

Boron‐Containing Polycyclic Aromatic Hydrocarbons: Facile Synthesis of Stable, Redox‐Active Luminophores

“…[5] Moreover,w es ucceeded in the synthesis of ad ianionic dibenzo[g,p]chrysene (cf.F igure 2) derivative with ac entral B = Bbond. [6] Forthe next stage,weare aiming at an extension of the p-conjugated frameworks.The new target compound F ( Figure 2) can be regarded as a7 ,14-dihydro-7,14-diborabisanthene and consequently as stretched version of the 9,10dihydro-9,10-diboraanthracene scaffold. Alternatively,o ne may view F as adoubly boron-bridged dibenzo[g,p]chrysene.…”