Synthesis and Structural Characterization of Carbene-Stabilized Carborane-Fused Azaborolyl Radical Cation and Dicarbollyl-Fused Azaborole

Abstract

The carbene-stabilized electron-rich iminocarboranyl boron­(I) compound [(Dipp)­NC­(Bu t )­C2B10H10]­B­(NHC) (1) (Dipp = 2,6-diisopropylphenyl, NHC = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) is an excellent precursor for the preparation of the unprecedented carborane-fused azaborolyl radical cation [{(Dipp)­NC­(Bu t )­C2B10H10}­B­(NHC)]•+ ([2]•+) and dicarbollyl-fused azaborole 7,8-nido-C2B9H9-7,8-C­(Bu t )­N­(Dipp)­B­(NHC) (3) via controlled single-electron oxidation and two-electron oxidative deboration, respectively. Single-crystal X-ray analyses and DFT calculations indicate that the unpaired electron in [2]•+ is delocalized over the BNC unit, and the two fused five-membered rings in 3 form a sort of π-conjugated system.

Tuning the Electrochemical Potential of Perfunctionalized Dodecaborate Clusters Through Vertex Differentiation

“…The readily-accessible isolable radical cluster also represents a new addition to the boroncentered radical molecules. [26][27][28][29][30][31][32][33][34] The pentafluoroaryl groups decorating the cluster were demonstrated to be amenable to facile post-functionalization with thiol-containing groups via S N Ar chemistry, thus enabling the possibility of orthogonal substitution without affecting the B-NO 2 vertex. Overall, this chemistry provides another unique entry towards robust and redox-active 3D aromatic building blocks for potentially designing new photoredox reagents 19 and hybrid materials.…”

Reactions of Dihaloboranes with Electron-Rich 1,4-Bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadienes

“…Nonetheless, the synthetic approach to low-valent boron species is severely limited [ 11 , 12 , 13 ]. Almost all of the reported synthetic strategies require a strong metallic reducing agent (e.g., Li, K, Na, KC 8 ) [ 3 , 4 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ], harsh reaction conditions, and a strict moisture- and oxygen-free atmosphere. Therefore, the exploration of metal-free reductants to access low-valent boron species is highly desirable [ 24 , 25 , 26 ].…”

Crystalline boron-linked tetraaminoethylene radical cations

“…By stark contrast, isolable boron radical cations are extremely rare probably due to the intrinsic electron deficient nature of boron. Indeed, only a handful of boron radical cations supported by the strong electron donors L have been isolated and structurally characterized by the Bertrand ( I ), 4 Braunschweig ( II ), 5 Xie ( III ), 6 Himmel ( IV ), 7 and Harman ( V ) 8 groups ( Fig. 1a ).…”