Synthesis and Structures of Two New Types of Boronium Salts
FULL PAPER
to –20 °C, most of the B(NHPh)3 separated as a solid, which was
removed by filtration. The filtrate exhibited red brown fluorescence.
It was then reduced in volume to 20 mL. At –50 °C, only a few
additional crystals of B(NHPh)3 separated, which were removed
by filtration. All the volatile material from the filtrate was then
evaporated under vacuum to leave behind a light brown powder of
7. C18H20BN5 (317.18): calcd. C 68.10, H 6.35, N 22.07; found C
units. As far as we know, this N–C bond cleavage is rather
unusual, although this step must occur in order to reason-
ably explain the formation of 8. Obviously, aminoboron ha-
lides are better suited[8] to generate borenium cations than
triaminoborane systems. However, there is no doubt that
this result opens up new aspects for the chemistry of cat-
ionic boron compounds. Reactions that take unexpected
routes are certainly more interesting than those that occur
along a “normal” route, and this example shows that BN
chemistry still offers surprises.
1
68.29, H 5.22, N 22.20. H NMR (400 MHz, C6D6): δ1 = 2.11 (N–
Me2), 2.82 (br., N–H), 6.42, 6.70, 6.72, 6.96, 7.63, 7.97 (Ar-H, Ph-
H) ppm. 11B NMR (64 MHz, toluene): δ = 2.0 ppm (h1/2 = 83 Hz).
Di(pyrid-2-yl)aminotrimethylsilane (6): To a solution of 1 (1.712 g,
10.1 mmol) in toluene (80 mL) was added a solution of nBuLi
(6.4 mmol, 1.56 , 10 mmol) at –78 °C. A precipitate of (pyЈ)2NLi
formed immediately. At room temperature, the suspension was
treated with Me3SiCl (1.3 mL, 10 mmol). After stirring for 2 h, the
insoluble material (LiCl) was removed by filtration, and the filtrate
reduced in volume to about 15 mL. White needles of 6 separated
over a week by keeping the solution at 0 °C. Yield: 1.97 g (81%).
C13H17N3Si (243.59): calcd. C 64.17, H 6.99, N 17.28; found C
Experimental Section
All experiments have been performed under anhydrous conditions
using N2 or Ar as protective gases. All compounds were freshly
crystallized or distilled. Solvents were dried by conventional meth-
ods. NMR spectroscopy: Bruker ACP-200 and Jeol EX 400. Stan-
dards for 11B, 14N and 27Al: external BF3·OEt2, nitromethane, and
1 AlCl3 in water, respectively. UV/Vis Spectroscopy: Varian Cray
60 CONC spectrometer. Elemental analysis: microanalytical labo-
ratory of the department. X-ray structure determinations: Bruker
P4 four circle diffractometer equipped with an area detector and
a LT2 cooling device; Mo-Kα radiation, graphite monochromator.
Thermal ellipsoids are represented at a 25% probability level.
1
66.18, H 7.06, N 17.88. H NMR (400 MHz, C6D6): δ = 0.44 (s, 9
3
H, Si–Me3), 6.38 [br. d, J(1H1H) = 8.5 Hz, 2 H, py-C3–H], 6.48
3
3
4
[ddd, J(1H1H) = 6.5 Hz, J(1H1H) = 5.6 Hz, J(1H1H) = 1.3 Hz,
2 H, py-C5–H], 7.02 [ddd, J(1H1H) = 7.0 Hz, J(1H1H) = 1.1 Hz,
2 H, py-C4–H], 8.27 [dd, br, 3J(1H1H) = 5.4 Hz, 4J(1H1H) = 2.1 Hz,
2 H, py-C6–H] ppm. 13C NMR (100 MHz, C6D6): δ = 1.3 (Si–
Me3), 116.9 (py-C5), 117.7 (py-C3), 137.6 (py-C4), 149.0 (py-C6),
160.0 (py-C2) ppm. 29Si NMR (80 MHz, C6D6): δ = 6.8 ppm. 14N
NMR (28.9 MHz, toluene): δ = –85.9 (py-N), –266.6 (N–Si) ppm.
3
4
Compound 4: To a stirred solution of 1 (1.59 g, 9.3 mmol) in toluene
(40 mL) was added tris(dimethylamino)borane (1.6 mL, 9.3 mmol).
After heating to reflux for 20 h, a bright yellow fluorescing solution
formed, which presented an 11B NMR signal at 4.7 ppm (h1/2
=
Reaction of 6 with Chlorobis(dimethylamino)borane: A solution of 6
(2.44 g, 10 mmol) in toluene (40 mL) was cooled to 0 °C. (Me2N)2-
BCl (1.35 mL, 10 mmol) in toluene (20 mL) was then added. After
stirring the solution for several hours and warming to ambient tem-
perature, a single 11B NMR signal at 4.7 ppm was observed in the
spectrum, which shows a quantitative conversion to 4. All other
NMR spectroscopic data were identical to those found for 4. Yield:
2.6 g of 4 (97%).
57 Hz). The solvent was removed, and a yellow powder of 4 re-
mained. Yield: 2.3 g (91%). C14H20BN5 (269.22): calcd. C 63.46, H
7.48, N 26.02; found C 61.87, H 7.53, N 25.92. 1H NMR
(270 MHz, C6D6): δ = 2.36 (N–Me)2 ppm. 13C NMR (100 MHz):
δ = 39.5 (N–Me)2 ppm, as well as the resonances listed for 5. 11B
NMR (64 MHz): δ = 4.7 (h1/2 = 57 Hz) ppm.
Compound 5: The yellow solid that remained after evaporation of
the solvent from 4 was dissolved in CHCl3 (30 mL). After 10 d,
addition of pentane (20 mL) to the top of the solution led to the
formation of only a few very small crystals in two days. A few
days later, the homogeneous solution was cooled to –78 °C. Yellow
fluorescing crystals of 5·(CHCl3)4 separated. On drying the crystals
in vacuo, they turned turbid as they lost weight. Yield: 2.19 g
(83%). M.p. 180 °C. C14H21BClN5 (305.62): calcd. C 55.02, H 6.93,
N 22.92, Cl 11.60; found C 54.12, H 6.88, N 21.75, Cl 10.74. 1H
NMR (400 MHz, C6D6): δ = 2.54 (s, 6 H, HN–Me), 5.47 (br. s, 1
Diboroniumbis(tetrachloroaluminate) 8(AlCl4)2: To a solution of 4
(2.05 g, 7.6 mmol) in toluene (70 mL) was added AlCl3 powder
(1.00 g, 7.6 mmol). The suspension was stirred for 1 d. The 11B
NMR spectrum shows that no reaction had occurred. The mixture
was then kept at reflux for 20 h. During this period, a green-yellow
precipitate formed. The yellow solution presented a 11B NMR sig-
nal at δ = 26.5 ppm (70%) and a multiplet at 0.7 ppm (≈30%). Two
signals were observed in the 27Al NMR spectrum at 80.4 and
68 ppm, in addition to overlapping bands in the range 92–104 ppm.
After filtration, the solid material was dried and treated with
CH2Cl2. Only part of the material dissolved. The concentrated
solution was then cooled to –20 °C. Fairly large yellow-orange crys-
tals with an octahedral shape formed over a few days. As revealed
by the X-ray structure determination, the crystals have the compo-
sition 8(AlCl4)2·2CH2Cl2. Yield: not determined. M.p. 200 °C.
C34H34Al2B3Cl12N11 (1108.51): calcd. C 36.81, H 3.07, N 13.90, Cl
38.38; found C 36.00, H 2.78, N 12.84, Cl 37.89. 1H NMR
(400 MHz, CH2Cl2/C6D6): δ = 2.l3 (s, C–Me) ppm. 13C NMR
(100 MHz, CH2Cl2/C6D6): δ = 21.2 (N–Me) ppm. 11B NMR
H, N–H), 6.06 [td, J (1H1H) = 6.6 Hz, J (1H1H) = 1.2 Hz, 2 H,
C2–H], 6.81 [td, 3J (1H1H) = 8.3 Hz, 4J (1H1H) = 3.1 Hz, 2 H, C3–
H], 7.06 [br. d, 3J (1H1H) = 8.7 Hz, 2 H, C4–H], 7.64 [dd, 3J
(1H1H) = 6.4, 4J (1H1H) = 1.7 Hz, 2 H, C1–H] ppm. 13C NMR
(100 MHz): δ = 48.7 (N–Me2), 111.7 (py-C2), 121.9 (py-C4), 131.8
(py-C3), 138.4 (py-C1), 156.5 (py-C5) ppm. 11B NMR (64 MHz):
δ = 5.0 ppm. 14N NMR (28.9 MHz): δ = –92.5 (py-N), –203.8 (N–
H), –356.2 (N–Me2, HN–Me2) ppm. UV/Vis (toluene): λmax = 320,
393 cm–1.
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4
Compound 7: A mixture of B(NMe2)3 (3.45 mL, 20 mmol) and ani-
line (3.65 mL, 40 mmol) in toluene (150 mL) was kept at reflux for
20 h. After cooling the solution, 11B NMR signals (1:1 intensity)
–
(64 MHz): δ = 2.0, –26.5 ppm. 27Al NMR: δ = 106.4 (AlCl4 , h1/2
= 20 Hz) ppm.
at 24.9 ppm for (Me2N)2BNHPh[10] and at 23.6 ppm for X-ray Structure Determinations: Single crystals were suspended in
B(NHPh)3 were observed in the spectrum.[6] 1 (3.42 g, 20 mmol)
was added to the reaction mixture, which was kept at reflux for
another 20 h. The 11B NMR spectrum showed a signal for
B(NHPh)3 in addition to one at 2.0 ppm. On cooling the mixture
perfluoro ether oil, and a suitable crystal was selected, fixed on a
glass fibre and mounted on the goniometer head flushed with nitro-
gen gas cooled to –80 °C. The unit cell was determined from the
reflections recorded on 5 sets of 15 different exposures each. Data
Eur. J. Inorg. Chem. 2007, 2296–2302
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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