A Chemiluminescent Tetraaryl Diborane(4) Tetraanion. (20th July 2021)

• Record Type: Journal Article
• Authors: Budy, Hendrik; Kaese, Thomas; Bolte, Michael; Lerner, Hans‐Wolfram; Wagner, Matthias
• Is Part Of: Angewandte Chemie. Volume 133:Number 35(2021)
• Page Start: 19546
• Page End: 19554
• Publication Date: 2021-07-20
• Subjects: 9-borafluorene -- boryl anions -- chemiluminescence -- redox chemistry -- subvalent compounds; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.202106980
• Languages: English
• ISSNs: 0044-8249

Abstract

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(sp 3 )−B(sp 2 ) 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. Abstract : Combination of boron doping with an antiaromaticity/aromaticity switch allowed the preparation of a unique diborane(4) tetraanion. Air oxidation leads to blue chemiluminescence, while controlled two‐electron oxidation furnishes a dianionic diborene. The reactivities of the compounds are characterized by boron‐centered nucleophilicity, C−H activation, single electron transfers, and Stone–Wales‐type rearrangements.