Oligo(borolyl)benzenes—Synthesis and Properties

Abstract

Herein, we report the synthesis of boroles that are linked by a conjugated phenylene spacer. The characterization of these compounds was completed by NMR and UV/Vis spectroscopy, as well as X-ray crystal diffraction. Furthermore, the coordination behavior of these oligoboroles towards five electronically and sterically disparate pyridine derivatives was studied and revealed fundamental differences in the properties of the resulting adducts. The experimental results were supported by density functional theory (DFT) calculations that showed a charge-transfer effect upon formation of the pyridine-4-carbonitrile adduct. By chemical reduction of a tris(borolyl)-substituted benzene derivative, a hexaanion was isolated as a result of a two-electron reduction of each borolyl moiety. The interaction of the borolyl units through the aryl spacer, and the possible increase of the Lewis acidity due to the conjugation of the borolyl moieties, were investigated by base transfer reactions.

Ring Expansions of Boroles with Diazo Compounds: Steric Control of C or N Insertion and Aromatic/Nonaromatic Products

“…The uptake of one or two electrons results in the formation of radical monoanions or aromatic dianions, respectively 3a. f–h, 4 The metal‐free activation of small molecules such as dihydrogen is also possible with boroles 5. Moreover, the activated butadiene backbone is accessible for cycloaddition reactions, for example with alkynes or boroles, to give boranorbornadienes or borole dimers, respectively 4b.…”

Synthesis of Zwitterionic Cobaltocenium Borate and Borata‐alkene Derivatives from a Borole‐Radical Anion

“…[11] Meanwhile, this twoelectron reduction protocol has been expanded to generate a series of other borole dianions. [9,[12][13][14][15] Our group has recently studied the electrochemistry of borole reduction in closer detail. It was shown by cyclic-voltammetry measure-ments that reduction of 1-ferrocenyl-2,3,4,5-tetraphenylborole (2) [16] and 1-mesityl-2,3,4,5-tetraphenylborole (3) [17] proceeds through a sequence of two separate one-electron reduction steps involving radical-anion intermediates [2] *À and [3] *À , respectively.…”

A theoretical study of the aromaticity in neutral and anionic borole compounds

“…[51,55,[57][58][59] Figure 7 displays all derivatives used for this study. By comparing the 1,3-and 1,4-disubstituted bis(borolyl)benzenes 10 and 11, [57] respectively, compound 11 was found to be 4.3 kcal/mol more stable than 10. The reason for the decreased thermodynamic stability of 10 is likely due to the destabilizing π-conjugation of the two π-accepting borolyl units through the phenylene bridge.…”