Azidoborolate anions and azidoborole adducts: isolable forms of an unstable borole azide

Abstract

Boroles are well known to undergo ring expansion reactions with organic azides to yield 1,2-azaborinines. A synthon featuring both azide and borole moieties within the same molecule, 1-azido-2,3,4,5-tetraphenylborole, was found...

A Three‐Dimensional Inorganic Analogue of 9,10‐Diazido‐9,10‐Diboraanthracene: A Lewis Superacidic Azido Borane with Reactivity and Stability

“…The N 2 elimination of 9‐azido‐9‐borafluorene could be thermally induced, affording a BN‐phenanthryne intermediate, which can undergo cyclotrimerization to give a structurally characterized tetramer, or be trapped with trimethylchlorosilane or the second equivalent of 9‐azido‐9‐borafluorene [1g] . Considerable efforts towards the combination of an azido group and a non‐fused borole moiety in one molecule can be seen in a very recent report by Braunschweig and co‐workers [2] . However, the 1‐azido‐2,3,4,5‐tetraphenylborole turned out to be even less stable than 9‐azido‐9‐borafluorene and had to be trapped at −75 °C with a Lewis base as evidence for its formation [2] .…”

“…[2] However, the 1-azido-2,3,4,5-tetraphenylborole turned out to be even less stable than 9-azido-9-borafluorene and had to be trapped at À 75 °C with a Lewis base as evidence for its formation. [2] Thus overall, the knowledge about the reactivity of strongly Lewis acidic azido boranes is still limited. The dearth of related research is presumably attributed to the pronounced instability, capricious nature or poor solubility caused by aggregation.…”

A Three‐Dimensional Inorganic Analogue of 9,10‐Diazido‐9,10‐Diboraanthracene: A Lewis Superacidic Azido Borane with Reactivity and Stability

“…The reported reactivity patterns of azido boranes are mostly azido‐based, including the [3+2]‐dipolar cycloaddition reactions, [1b–d] Staudinger reactions, [1v] 1,1‐addition, [1a] and R‐group migration reactions that are associated with N 2 elimination [1e–h] . There are notably less reactions of azido boranes in which boron is a non‐spectator, perhaps because the azido boranes of enough stability usually require electronic stabilization either by quaternization with a σ‐donating ligand [1b,c,h,i,l, 2] or by substitution with π‐donating groups, [1a,d,j,k,m] which nevertheless turns off the reactivity at boron. The azido boranes with boosted Lewis acidity but lacking steric hindrance tend to aggregate via intermolecular B−N interaction [1n–u] .…”

“…[1g] Considerable efforts towards the combination of an azido group and a non-fused borole moiety in one molecule can be seen in a very recent report by Braunschweig and co-workers. [2] However, the 1-azido-2,3,4,5-tetraphenylborole turned out to be even less stable than 9-azido-9-borafluorene and had to be trapped at À 75 °C with a Lewis base as evidence for its formation. [2] Thus overall, the knowledge about the reactivity of strongly Lewis acidic azido boranes is still limited.…”

“…The dearth of related research is presumably attributed to the pronounced instability, capricious nature or poor solubility caused by aggregation. 9,10-Dihydro-9,10-diboraanthracenes (DBAs) are boron congeners of anthracenes in which the sp 2 -hybridized carbons at 9-and 10-positions are replaced by a trigonal planar boron center, respectively, leading to a neutral conjugated π-system but with two fewer π electrons than anthracene. DBAs, their doubly reduced derivatives (DBA) 2À as well as the N-heterocyclic carbene (NHC) stabilized derivatives demonstrated unique photophysical properties and diverse reactivity, allowing for the applications in ligand design, [3] olefin polymerization, [4] luminescent materials, [5] dihydrogen-and hydride-transfer catalysis, [6] small molecule activation, [6,7] and fluoride complexation.…”