A Chemiluminescent Tetraaryl Diborane(4) Tetraanion

Abstract

Two subvalent, redox‐active diborane(4) anions, [3]4− and [3]2−, carrying exceptionally high negative charge densities are reported: Reduction of 9‐methoxy‐9‐borafluorene with Li granules without stirring leads to the crystallization of the B(sp3)−B(sp2) diborane(5) anion salt Li[5]. [5]− contains a 2,2′‐biphenyldiyl‐bridged B−B core, a chelating 2,2′‐biphenyldiyl moiety, and a MeO substituent. Reduction of Li[5] with Na metal gives the Na+ salt of the tetraanion [3]4− in which two doubly reduced 9‐borafluorenyl fragments are linked via a B−B single bond. Comproportionation of Li[5] and Na4[3] quantitatively furnishes the diborane(4) dianion salt Na2[3], the doubly boron‐doped congener of 9,9′‐bis(fluorenylidene). Under acid catalysis, Na2[3] undergoes a formal Stone–Wales rearrangement to yield a dibenzo[g,p]chrysene derivative with B=B core. Na2[3] shows boron‐centered nucleophilicity toward n‐butyl chloride. Na4[3] produces bright blue chemiluminescence when exposed to air.

Bringing out the potential of organoboron compounds by designing the chemical bonds and spaces around boron

“…8), 38 which exhibits exceptional chemical stability and distinctive emission properties. The transformation of Mes 2 B + into Mes 4 B 2 can be achieved by reductive B–B coupling 39 that occurs upon treatment of Mes 2 B + with Li metal in 1,2-DCB, followed by oxidation of the resulting radical anion [Mes 4 B 2 ]˙ − using 1,2-dibromoethane (Fig. 8a).…”

Systematic Electronic and Structural Studies of 9-Carbene-9-Borafluorene Monoanions and Transformations into Luminescent Boron Spirocycles

“…However, through chemical reduction reactions, boron-based compounds can be designed such that they become electron-rich nucleophiles. The initial reports on boron nucleophiles (or boryl anions) − spawned new investigations into understanding the chemistry and reactivity of group 13 Lewis bases (Figure a). These compounds are isoelectronic to N-heterocyclic carbenes (NHC) but are weaker sigma-donors and are generally used for the formation of novel B–E bonds (E = transition metal, main-group element, or lanthanide).…”

“…Recently, we have been investigating the structure and bonding, reactivity, and materials properties of 9-carbene-9-borafluorenes. ,− While 9-borafluorene has become a popular building block in molecular chemistry, studies of chemically reduced borafluorenes are still rare. ,,, Previously, we reported the formation of borafluorene-based spirocycles resulting from the reaction of diketones and 9-carbene-9-borafluorene monoanion (Figure b) . Although the electronic structures differ significantly, the R 2 BO 2 moiety of our closed-shell compounds bear resemblance, in terms of connectivity, to open-shell boracyclic radicals and salts synthesized by Stephan (Figure c). , Most notably, the incorporation of borafluorene in the spirocycle produces fluorescent materials .…”

Synthesis of Symmetrically and Unsymmetrically Substituted Cationic Diborane(4) Compounds with Distinct Structural Motifs and Properties

“…[12] for details), and a tetraaryl diborane(4) tetraanion (right, see ref. [15] for details). b) The nucleophilic ditriflato-diborane [B(hpp)(OTf)] 2 (1) and dibromido-diborane [B(hpp)Br] 2 (2) used in this work (see ref.…”