Extensive Structural Rearrangements upon Reduction of 9H‐9‐Borafluorene

Abstract

Common wisdom has it that organoboranes are readily oxidized. Described herein is that also their reduction can result in remarkable chemistry. Treatment of dimeric 9H-9borafluorene with Li metal in toluene yields two strikingly different classes of compounds. One part of the sample reacts in a way similar to B 2 H 6 , thus affording an aryl(hydro)borane cluster reminiscent of the [B 3 H 8 ] À anion. The other part furnishes a dianionic boron-doped graphene flake devoid of hydrogen substituents at the boron centers and featuring a central B=B bond. A change in the solvent to THF allows an isolation of this dibenzo [g,p]chrysene analogue in good yields.

Coordination and Ring Expansion of 1,2-Dipolar Molecules with 9-Phenyl-9-borafluorene

“…19− 7.13 (m, 1H), 7.08−7.02 (m, 1H), 6.97−6.92 (m, 1H), 6.88 (t, J = 6.0 Hz, 1H), 6.83 (t, J = 6.0 Hz, 1H), 6.75 (d, J = 12.0 Hz, 1H), 6.72−6.65 (m, 2H); 13 C{ 1 H} NMR (151 MHz, CDCl 3 ) δ 146. 81, 146.40, 145.00, 144.81, 141.70, 136.45, 135.68, 131.62, 131.26, 130.29, 129.92, 129.53, 128.92, 128.72, 128.47, 128.24, 127.86, 127.68, 127.62, 127.32, 127.24, 126.75, 126.62, 126.57, 125.74, 87.01; 11 B{ 1 H} NMR (193 MHz, CDCl 3 ) δ 45.5; FT-IR (cm −1 (ranked intensity)): 1595 (10), 1489 (14), 1439 (5), 1331 (7), 1265 (4), 989 (6), 947 (12), 910 (9), 766 (8), 740 (3), 697 (1), 647 (2), 592 (11), 535 (13), 503 (15); high-resolution mass spectroscopy (HRMS) electrospray ionization (ESI) calcd for C 31 H 23 BONa [M + Na] + 445.1739, found 445.1731; UV−vis (CH 2 Cl 2 ) λ max (235 nm) ε = 6,700 L mol −1 cm −1 ; fluorescence (CH 2 Cl 2 ) λ em 344 nm.…”

“…3H),3H),7.40 (d,J = 8.0 Hz,2H),2H),5H), 7.16 (t, J = 8.0 Hz, 1H), 7.08 (d, J = 8.0 Hz, 1H), 7.04−6.97 (m, 1H), 6.94 (t, J = 4.0 Hz, 3H), 6.77−6.70 (m, 2H); 13 C{ 1 H} NMR (101 MHz, CDCl 3 ) δ 148. 17, 145.94, 141.42, 140.34, 139.49, 139.05, 137.25, 136.55, 131.49, 131.21, 130.82, 130.57, 128.98, 128.87, 127.93, 127.75, 127.73, 127.44, 127.10, 127.00, 126.55; 11 B{ 1 H} NMR (128 MHz, CDCl 3 ) δ 45.6; FT-IR (cm −1 (ranked intensity)) 2095 (4), 1594 (6), 1493 (10), 1436 (5), 1275 (2), 1184 (15), 1130 (12), 1028 (11), 910 (9), 739 (3), 694 (1), 647 (8), 603 (7), 511 (14), 481 (13); high-resolution mass spectroscopy (HRMS) electrospray ionization (ESI) calcd for C 32 H 24 BO [M + H] + 435.1920, found 435.1914; UV−vis (CH 2 Cl 2 ) λ max (234 nm) ε = 35200 L mol −1 cm −1 ; fluorescence (CH 2 Cl 2 ) λ em 351 nm.…”

“…Single crystals for X-ray diffraction studies were grown by vapor diffusion of a CH 2 Cl 2 solution of 1Ph•N(Ph)CH(Ph) into toluene: yield 43.0 mg, 94%; mp 183−186 °C; 1 H NMR (600 MHz, CDCl 3 ) δ 9.11 (s, 1H), 7.66 (d, J = 12.0 Hz, 2H), 7.61 (d, J = 6.0 Hz, 2H), 7.43 (t, J = 6.0 Hz, 1H), 7.33 (d, J = 6.0 Hz, 2H), 7.26−7.16 (m, 10H), 7.08 (t, J = 6.0 Hz, 2H), 6.97 (d, J = 12.0 Hz, 2H), 6.65 (d, J = 12.0 Hz, 2H); 13 C{ 1 H} NMR (151 MHz, CDCl 3 ) δ 166. 80,160.55,152.26,149.46,145.86,143.37,143.25,136.29,133.99,133.37,132.84,132.78,131.94,131.60,131.53,129.85,129.30,129.12,128.96,128.61,128.47,128.31,127.77,127.52,126.97,126.84,126.07,126.01,124.20,121.01,119.37;11 B{ 1 H} NMR (193 MHz,CDCl 3 ) δ 3.2; FT-IR (cm −1 (ranked intensity)) 1595 ( 7), 1490 (11), 1438 (5), 1331 (8), 1267 (3), 1246 (15), 989 (6), 947 (12), 910 (10), 763 (9), 739 (2), 696 (1), 648 (4), 592 (13), 506 (14); highresolution mass spectroscopy (HRMS) electrospray ionization (ESI) calcd for C 31 H 24 BNNa [M + Na] + 444.1899, found 444.1891.; UV− vis (CH 2 Cl 2 ) λ max (238 nm) ε = 31600 L mol −1 cm −1 , (316 nm): ε = 12800 L mol −1 cm −1 ; fluorescence (CH 2 Cl 2 ) λ em 371 nm.…”

“…7b,8 Wagner demonstrated that reduction of the dimeric 9-H-9-borafluorene (1H 2 ) resulted in dehydrogenation and formation of six-membered B 2 C 4 rings with the two boron atoms in the bridging positions (C). 9 Wagner, Wang, and coworkers 10 studied the photolysis of tetra-coordinate anionic 9-borafluorenes 1Mes(Ar) that resulted in selective insertion of the α-carbon of one of the aryl groups to form boratanorcaradienes (D).…”

Single and Double Hydroboration of B–B Triple Bonds and Convergent Routes to a Cationic Tetraborane

“…16 Wagner and coworkers then showed that such monoanions, C, (and indeed their diborane(6) precursors) can be reduced to dianionic diborenes [B2R4] 2-(D) by using alkali metals to isolate a biphenylene-bridged diborene. [17][18][19] The inherent electron deficiency of boron in diboron compounds can also be satiated by neutral Lewis bases. For example, neutral diborenes of the form L(R)B=B(R)L (I) are now accessible with a wide variety of bases and covalent substituents via Wurtz coupling of dihaloboranes or reduction of dihalodiboranes.…”