Syntheses and Characterization of o‐Carboranes Containing Fused exo‐Polyhedral Di‐ and Triboraheterocycles

Abstract

Reaction of dilithio‐o‐carborane Li2C2B10H10 (generated in situ from o‐carborane 1 and butyllithium) with the 1, 2‐diborylbenzene derivative 1, 2‐C6H4(iPr2NBCl)2 yielded the o‐carborane compound 3 having the fused exo‐polyhedral C2B2C2 heterocycle. The analogous reactions with 1, 1‐bis(dimethylaminochloroboryl)ethane and with 1, 3‐dichloro‐1, 2,3‐tris(dimethylamino)triborane(5) afforded the o‐carborane compounds 5 and 7 containing the fused exo‐polyhedral five‐membered C2B2C and C2B3 rings, respectively. Attempts to use 1, 2‐dichloro‐1, 2‐bis(dimethylamino)diborane(4) for the synthesis of the o‐carborane compound 10 with a fused exo‐polyhedral C2B2 ring instead led to the diborane(4)yl‐o‐carborane species 9c and 9d (the latter in trace amount), which contain a diborane(4)yl moiety bonded to the o‐carborane. The molecular compositions of the new o‐carborane derivatives follow from NMR spectroscopic and mass spectrometric data as well as from X‐ray diffraction analyses of 3, 7 and 9c. The structures exhibit weak intramolecular C–H···H–B hydrogen‐hydrogen interactions.

trans‐Selective Insertional Dihydroboration of a cis‐Diborene: Synthesis of Linear sp3‐sp2‐sp3‐Triboranes and Subsequent Cationization

“…These are significantly downfield-shifted from 2-Pyr owing to the electron-withdrawing nature of the aryl versus the electrondonating nature of the amino substituent. Comparison with other literature-known amino-and aryl(diboryl)boranes (d(R 2 NB(BX 2 ) 2 ) % 50-62 ppm, [2,17] d(ArB(BX 2 ) 2 ) % 70-85 ppm) [18] shows that the central boron nuclei of 2-R are unusually deshielded, that is, particularly electron-poor. This was confirmed by density functional theory (DFT) calculations at the OLYP/TZ2P level of theory on 2-Mes in the gas phase, which gave negative Hirshfeld charges of À0.093 for B1 and B3 and a positive charge of 0.050 for B2 ( Figure 3).…”

“…The presence of the two boronbound hydrogen atoms was confirmed by IR bands attributable to terminal B-H vibrations in the 2160 to 2200 cm À1 region. These are the first examples of sp 3 -sp 2 -sp 3 -hybridized triboranes, previous examples of electron-precise triboranes being limited to sp 2 -sp 2 -sp 2 [2,17,18] or sp 3 -sp 3 -sp 2 hybridization patterns. [11,13] Unlike Nçths tris(aminoboryl)-[3]ferrocenophane, in which the central B2 atom is tilted out of the B1B3Fe plane, [20] the iron center and all three boron atoms of 2-R lie in the same plane.…”

“…X-ray diffraction analysis of single crystals obtained from a freshly irradiated solution of 2-Mes (Figure 1 b) [23] revealed the structure of the cis-isomer 2'-Mes, in which H1 has shifted from a terminal position trans to H2 to a bridging position cis to the terminal H2. [19] This is accompanied by a shortening of the B1ÀB2 bond from 1.720(3) to 1.650(3) , a lengthening of the B2 À B3 bond from 1.738(3) to 1.774(3) and a slight widening of the B1-B2-B3 angle from 118.72 (17) to 122.69- (16)8. Furthermore, the Fe atom no longer lies in the B 3 plane.…”

Synthesis and Structure of an o‐Carboranyl‐Substituted Three‐Coordinate Borane Radical Anion

“…[107,108] A variety of BÀ N type borylated carboranes were reported featuring a strong interaction between boron and nitrogen. [109][110][111][112][113][114] The elasticity of the C1À C2 bond of o-carborane (1.629(6) Å) was studied in the presence of bulky substituents [115][116][117] (1.712(7) to 2.156(4) Å) and as a function of the C1À C2 σ*-anti-bonding orbital population by donating groups at C1 and C2 (1.723(2) to 2.065(7) Å). [118][119][120][121][122][123][124][125][126][127] The interest in electrochemical reduction [105,[128][129][130][131][132] to populate this antibonding orbital has led to its application in reversible electrochemical uranium capture.…”

“…Recently, 9‐borafluorene analogues of carborane‐fused “boroles” resulted in strong Lewis acidity while eliminating the rotational freedom of ortho ‐carborane [107,108] . A variety of B−N type borylated carboranes were reported featuring a strong interaction between boron and nitrogen [109–114] . The elasticity of the C1−C2 bond of o ‐carborane (1.629(6) Å) was studied in the presence of bulky substituents [115–117] (1.712(7) to 2.156(4) Å) and as a function of the C1−C2 σ *‐anti‐bonding orbital population by donating groups at C1 and C2 (1.723(2) to 2.065(7) Å) [118–127] .…”