A Chemiluminescent Tetraaryl Diborane(4) Tetraanion.

Two subvalent, redox-active diborane(4) anions, [3] and [3] , 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 )-B(sp ) 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] in which two doubly reduced 9-borafluorenyl fragments are linked via a B-B single bond.

The 9H-9-Borafluorene Dianion: A Surrogate for Elusive Diarylboryl Anion Nucleophiles.

Double reduction of the THF adduct of 9H-9-borafluorene (1⋅THF) with excess alkali metal affords the dianion salts M [1] in essentially quantitative yields (M=Li-K). Even though the added charge is stabilized through π delocalization, [1] acts as a formal boron nucleophile toward organoboron (1⋅THF) and tetrel halide electrophiles (MeCl, Et SiCl, Me SnCl) to form B-B/C/Si/Sn bonds. The substrate dependence of open-shell versus closed-shell pathways has been investigated.

A redox-active diborane platform performs C(sp)-H activation and nucleophilic substitution reactions.

Organoboranes are among the most versatile and widely used reagents in synthetic chemistry. A significant further expansion of their application spectrum would be achievable if boron-containing reactive intermediates capable of inserting into C-H bonds or performing nucleophilic substitution reactions were readily available. However, current progress in the field is still hampered by a lack of universal design concepts and mechanistic understanding.

Deprotonation of a Seemingly Hydridic Diborane(6) To Build a B-B Bond.

Deprotonation of the doubly arylene-bridged diborane(6) derivative 1H with (Me Si) CLi or (Me Si) NK gives the B-B σ-bonded species M[1H] in essentially quantitative yields (THF, room temperature; M=Li, K, arylene=4,4'-di-tert-butyl-2,2'-biphenylylene). With nBuLi as the base, the yield of Li[1H] drops to 20 % and the 1,1-bis(9-borafluorenyl)butane Li[2H] is formed as a side product (30 %). In addition to the 1,1-butanediyl fragment, the two boron atoms of Li[2H] are linked by a μ-H bridge.

Hydroboration as an Efficient Tool for the Preparation of Electronically and Structurally Diverse N→B-Heterocycles.

Ladder-type organoboranes featuring intramolecular N→B coordination have been prepared through hydroboration of a 2-(ortho-styryl)pyridine (PhPy) with a series of hydroboranes, including 9H-9-borabicyclo[3.3.1]nonyl (9H-BBN), BH3 ⋅THF, HBCl2 ⋅SMe2 , HB(C6 F5 )2 , and a 9H-9-borafluorene derivative.

Forming B-B Bonds by the Controlled Reduction of a Tetraaryl-diborane(6).

Dimeric aryl(hydro)boranes can provide suitable platforms for the synthesis of boron-containing graphene flakes through reductive B-B coupling. Two-electron reduction of 1,2:1,2-bis(4,4'-di-tert-butyl-2,2'-biphenylylene)diborane(6) (4) with LiNaph/THF establishes a B-B σ bond but can be accompanied by substituent redistribution. In the singly rearranged product, Li2[6], only one 1,2-phenyl shift has occurred.

A preorganized ditopic borane as highly efficient one- or two-electron trap.

Reduction of the bis(9-borafluorenyl)methane 1 with excess lithium furnishes the red dianion salt Li2[1]. The corresponding dark green monoanion radical Li[1] is accessible through the comproportionation reaction between 1 and Li2[1]. EPR spectroscopy on Li[1] reveals hyperfine coupling of the unpaired electron to two magnetically equivalent boron nuclei (a((11)B) = 5.