Azaborines: synthesis and use in the generation of stabilized boron-substituted carbocations

Abstract

A formal N-heterocyclic carbene insertion into the B-H bond of 9-BBN followed by a ring expansion reaction is reported. NHC-9-BBN adducts were reacted in one or two steps to give the corresponding di- or triazaborines. Hydride abstraction of selected species with [PhC] is facile, giving rise to 6π-aromatic cations with Lewis acidity comparable to Lewis acids commonly employed in frustrated Lewis pairs.

N-Heterocyclic Carbenes in Materials Chemistry

“…This reaction is predicted to occur by initial complexation of the nucleophilic NHC with a surface silicon atom, followed by subsequent migration of the hydride to the carbene carbon. This reaction profile parallels exactly that observed in the reaction of NHCs with isolated main group compounds containing Si–H or B–H bonds. − …”

B−B Cleavage and Ring‐Expansion of a 1,4,2,3‐Diazadiborinine with N‐Heterocyclic Carbenes

“…[17,18] It has since become apparent that NHCs readily undergo ring-expansion reactions (RERs) in the presence of variousE ÀHh ydrides at elevated temperatures, generating the wide variety of ring-expanded products shown in Scheme1.E arly reports by the groupso fH ill [19] and Radius [20] established that beryllium and silicon hydridesc ould insert into the CÀNb onds of both bulkya nd non-bulky NHCs, with concomitant hydride migration to the carbeneCatom. Later work by the research groups of Crudden, [21] Inoue, [22] Marder, [23,24] Radius, [25][26][27] Rivard, [28] and Stephan [29] were able to extend this reactivity pattern to other EÀHs ubstrates (E = Al and B) and NHCs, [25,28] as well as demonstrate that diboron(4) reagentss uch as bis(catecholato)diboron(4)c an participate in ar elatedB ÀBb ond activation/B insertion reaction. [23,24,27,30] Despite the growing number of RERs reported in the literature, to the best of our knowledge,C ÀNb ond activation of NHCs with heterocycles containing endocyclicE ÀHf unctionalities remains completely unknown.…”

Synthesis and Tunable Optical Properties of C,N‐Chelated Borate Luminophores Derived from Potassium Acyltrifluoroborates

“…Hydrazone 4 a reacts with BF 3 ⋅ Et 2 O in the presence of methanol to give the cyclized product ( 1 a ) in 91 % yield . To the best of our knowledge, this is the first example of the formation of a borate compound consisting of a six‐membered B‐N‐C‐N‐N‐C heterocycle . 1 a is a pale‐yellow air‐ and moisture‐stable solid, which can be isolated by column chromatography on silica gel and exhibits blue luminescence under irradiation from UV light (see below).…”

“…[9] To the best of our knowledge, this is the first example of the formation of ab orate compound consisting of as ix-memberedB -N-C-N-N-C heterocycle. [11] 1a is ap ale-yellow air-and moisture-stable solid, which can be isolatedb yc olumn chromatography on silica gel and exhibits blue luminescenceu nder irradiation from UV light (see below).…”