Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7649
chemicals were purchased and used as received. 1H, 11B, 13C,
and 29Si NMR spectra were recorded on a Bruker Avance
DRX 500 MHz instrument and referenced to the deuterated
solvent in the case of the 1H and 13C NMR spectra. 11B and
Synthesis of 6 and 6a. A solution of N2CHSiMe3 (0.7 mL, 2 M,
in n-hexane) was added to a solution of 3 (0.49 g, 1.0 mmol) in n-
hexane (10 mL) at room temperature. Then the flask was kept at
room temperature for 3 days and after that yellow crystals of 6
were obtained, which are suitable for X-ray structural analysis.
Yield: 0.53 g (88%). Mp 244 °C. 1H NMR (500 MHz, C6D6): δ
7.09-7.17 (m, 6H, Ar-H), 4.51 (s, 1H, γ-CH), 3.63 (sept, 2H,
CH(CH3)2), 3.60 (sept, 2H, CH(CH3)2), 1.62 (s, 6H, CH3), 1.58
(d, 6H, CH(CH3)2), 1.43 (d, 6H, CH(CH3)2), 1.25 (d, 6H,
CH(CH3)2), 1.13 (d, 6H, CH(CH3)2), -0.07 (Si(CH3)3) ppm.
13C{1H} NMR (125.77 MHz, C6D6): δ 166.43 (CN), 146.92,
143.76, 139.99, 127.56, 124.98, 124.76 (Ar-C), 95.35 (γ-C),
31.91 (CN2), 29.60 (CH(CH3)2), 27.39 (CH(CH3)2), 25.34
(CH(CH3)2), 25.32 (CH(CH3)2), 24.68 (CH(CH3)2), 23.68
(CH(CH3)2), 0.03 (Si(CH3)3) ppm. 29Si{1H} NMR (99.35 Hz,
C6D6): δ -2.43 (Si(CH3)3) ppm EI-MS (70 eV): m/z (%): 561
(100) [M-iPr)]þ. Anal. Calcd for C33H50GeN4Si (603.50): C,
65.68; H, 8.35; N, 9.28. Found: C, 64.96; H, 8.62; N, 8.87. For
6a: After keeping the supernatant solution of 6 for about 3
months at room temperature we observed the conversion of 6 to
6a. Mp 210 °C. 1H NMR (500 MHz, C6D6): δ 7.06-7.18 (m, 6H,
Ar-H), 4.75 (s, 1H, γ-CH), 3.89 (sept, 2H, CH(CH3)2), 3.39
(sept, 2H, CH(CH3)2), 1.66 (s, 6H, CH3), 1.57 (d, 6H, CH-
(CH3)2), 1.37 (d, 6H, CH(CH3)2), 1.26 (d, 6H, CH(CH3)2), 1.07
(d, 6H, CH(CH3)2), -0.04 (Si(CH3)3) ppm. 13C{1H} NMR
(125.77 MHz, C6D6): δ 167.04 (CN), 147.39, 143.37, 139.81,
127.80, 125.34, 124.53 (Ar-C), 97.23 (γ-C), 29.76 (CH(CH3)2),
28.59 (NC), 27.35 (CH(CH3)2), 25.85 (CH(CH3)2), 25.22
(CH(CH3)2), 24.44 (CH(CH3)2), 23.93 (CH(CH3)2), 0.03
(Si(CH3)3) ppm. 29Si{1H} NMR (99.35 Hz, C6D6): δ 12.50
(Si(CH3)3) ppm EI-MS (70 eV): m/z (%): 604 (100) [M]þ.
Crystallographic Details for Compounds 4, 6, and 6a. The data
sets of 4, 6, and 6a were collected on a Bruker TXS-Mo rotating
anode equipped with INCOATEC Helios mirror optics (Mo KR
29Si NMR spectra were referenced to BF3 Et2O and SiMe4,
3
respectively. Elemental analyses were performed by the Ana-
lytisches Labor des Instituts fur Anorganische Chemie der
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Universitat Gottingen. EI-MS were measured on a Finnigan
Mat 8230 or a Varian MAT CH5 instrument. Melting points
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were measured in sealed glass tubes with a Buchi melting
point B 540 instrument and are not corrected.
Synthesis of 2 and 3. A solution of B(C6F5)3 (0.51 g, 1.0 mmol)
in toluene (10 mL) was added drop by drop to a stirred solution
of 1 (0.49 g, 1.0 mmol) in toluene (10 mL) at room temperature.
Immediately the red color of the reaction mixture changed to
colorless. The reaction mixture was stirred for additional
10 min. After that a solution of 1,3-di-tert-butylimidazol-2-
ylidene (0.18 g, 1.0 mmol) in toluene (10 mL) was added drop
by drop to the reaction mixture. During this time the reaction
mixture turned to brown-red with the formation of a white
precipitate. After another 10 min the solvent was removed in
vacuum, and the residue was extracted with n-hexane (15 mL).
The extracted brown-red solution contained compound 2. The
insoluble part was collected and identified as imidazolium
borate salt 3. Both are formed almost quantitatively, and the
NMR data matches with the previously reported samples.3c,9
Synthesis of 4. A solution of B(C6F5)3 (0.51 g, 1.0 mmol) in
toluene (10 mL) was added to a solution of 3 (0.49 g, 1.0 mmol)
in toluene (10 mL) at room temperature. The brown-red color of
the solution of 3 vanished slowly, and pale yellow crystals of 4
were formed after 2 days at room temperature. Yield: 0.78 g
(78%). Mp 265 °C. 1H NMR (500 MHz, THF-D8): δ 7.37-7.44
(m, 6H, Ar-H), 6.50 (s, 1H, γ-CH), 2.73 (sept, 2H, CH(CH3)2),
2.61 (sept, 2H, CH(CH3)2), 2.47 (s, 2H, CH2), 1.84 (s, 3H, CH3),
1.39 (d, 6H, CH(CH3)2), 1.25 (d, 6H, CH(CH3)2), 1.19 (d, 6H,
CH(CH3)2), 1.15 (d, 6H, CH(CH3)2) ppm. 13C{1H} NMR
(125.77 MHz, THF-D8): δ 180.93, 166.74 (CN), 145.62,
137.35, 130.25, 129.65, 128.89, 126.02 (Ar-C), 149.13, 139.52,
137.41 (C6F5), 108.96 (γ-C), 29.42 (CH(CH3)2), 29.32
(CH(CH3)2), 27.50 (CH(CH3)2), 25.85 (CH(CH3)2), 25.62
(CH(CH3)2), 25.46 (CH(CH3)2), 25.30 (CH3) ppm. 11B{1H}
NMR (96.29 MHz, THF-D8): δ -14.82. 19F{1H} NMR
(188.31 MHz, THF-D8): δ -131.60 (d, 6F, o-F), -163.40 (t,
6F, m-F), -167.28 (t, 3F, p-F). EI-MS (70 eV): m/z (%): 475
(100) [M-(B(C6F5)3, Me)] þ. Anal. Calcd for C47H40BF15GeN2
(1001.26): C, 56.38; H, 4.03; N, 2.80. Found: C, 56.27; H, 3.82;
N, 2.68.
˚
λ = 0.71073 A). The crystal was mounted in a shock-cooled oil
drop at the tip of a fiber.26 The data was integrated with
SAINT V7.46A (4, 6a) and SAINTV7.60A (6),27 and an em-
pirical absorption correction (SADABS-2008/2) was applied.28
The structure was solved by direct methods (SHELXS)29 and
refined on F2 using the full-matrix least-squares methods of
SHELXL.30 All non-hydrogen atoms were refined with aniso-
tropic displacement parameters. All hydrogen atoms bonded to
sp2 (sp3) carbon atoms were assigned ideal positions and refined
using a riding model with Uiso constrained to 1.2 (1.5) times the
U
eq value of the parent carbon atom.
Acknowledgment. This work was supported by the Deutsche
Forschungsgemeinschaft.
Synthesis of 5. A solution of 1,3-di-tert-butylimidazol-2-yli-
dene (0.18 g, 1.0 mmol) in toluene (10 mL) was added to a
solution of 4 (0.49 g, 1.0 mmol) in toluene (10 mL) at room
temperature. Immediately the reaction mixture turns to red in
color. After 10 min the solvent was removed in vacuum, and the
product was isolated as a red oil. 1H NMR (500 MHz, C6D6): δ
7.32 (s, 1H, NCH), 6.99-7.20 (m, 6H, Ar-H), 6.33 (s, 2H, NCH),
5.87 (s, 1H, γ-CH), 3.86 (sept, 2H, CH(CH3)2), 3.63(s, 1H, CH),
3.60 (sept, 2H, CH(CH3)2), 2.96 (s, 1H, CH), 2.45 (s, 2H, CH2),
1.70 (d, 6H, CH(CH3)2), 1.35 (d, 12H, CH(CH3)2), 1.32 (d, 6H,
CH(CH3)2), 0.75 (s, 18H, C(CH3)3) ppm. 11B{1H} NMR (96.29
MHz, C6D6): δ -13.66. 19F{1H} NMR (188.31 MHz, C6D6):
δ -130.65 (br, 6F, o-F), -163.77 (t, 6F, m-F), -167.32 (br, 3F,
p-F). From the analytical data we do not obtain satisfactory results.
Supporting Information Available: X-ray data for 4, 6, and 6a
(CIF). This material is available free of charge via the Internet at
(26) (a) Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1993, 26, 615–619. (b)
Kottke, T.; Lagow, R. J.; Stalke, D. J. Appl. Crystallogr. 1996, 29, 465–468.
(27) SAINT v7.46A/v7.60A in Bruker APEX v2.2-0; Bruker AXS Inst.
Inc.: Madison, WI, 2005.
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(28) Sheldrick, G. M. SADABS 2008/2; University of Gottingen: Gottingen,
Germany, 2008.
(29) Sheldrick, G. M. SHELXS in SHELXTL v6.10; Bruker AXS Inst. Inc.:
Madison, WI, 2000.
(30) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.