Exocyclic Unsaturated Heterodiborolanes and Their Diborylhexadiene Precursors
FULL PAPER
filtered off and washed twice with 20 mL of hexane. The filtrates
1-Aza-2,5-di-tert-butyl-3,4-diisopropylidene-1-methyl-2,5-diborolane
(5c): tert-Butyllithium (24 mmol, 1.7 in pentane) was added to a
5 mmol, 40%) precipitated from the solution. Ϫ H NMR (C6D6, solution of 5a (2.74 g, 12 mmol) in hexane at Ϫ50 °C. The mixture
were concentrated and cooled to Ϫ30 °C. Colorless 4c (2.31 g,
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200 MHz): δ ϭ 1.77, 1.82 (2 s, 2 ϫ 6 H, (CH3)2C), 2.09, 2.10 (2 s,
was stirred for 15 h at room temp., the liquid separated from the
2 ϫ 6 H, m-aryl-CH3), 2.24, 2.42 (2 s, 2 ϫ 6 H, o-aryl-CH3), 6.88 precipitate and the solvent removed in vacuo. The remaining oil
(s, 2 H, aryl). Ϫ 11B NMR (C6D6, 64 MHz): δ ϭ 61. Ϫ 13C NMR was distilled at 10Ϫ2 mbar and a bath temperature of 50Ϫ90 °C
(C6D6, 50 MHz): δ ϭ 19.4 (aryl-CH3), 26.7, 23.7 [2 ϫ C(CH3)2], yielding 2.06 g (7.5 mmol, 63%) of 5c. Part of the product decom-
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131.5, 131.8, 132.5, 133.8, 134.2 (5 ϫ Caryl), 145, 147 [both br,
BCC(CH3)2 and BCaryl], 164.1 [C(CH3)2]. Ϫ EI-MS: m/z (%) ϭ 467
[Mϩ], (19), 432 [Mϩ Ϫ Cl] (100), 413 (71), 332 [Mϩ Ϫ Dur] (23).
posed under these conditions to a dark brown solid. Ϫ H NMR
(CDCl3, 200 MHz): δ ϭ1.19 (s, 18 H, tBu), 1.66, 1.82 [2 s, 2ϫ6 H,
(CH3)2C], 2.88 (s, 3 H, NϪCH3). Ϫ 11B NMR (C6D6, 64 MHz):
δ ϭ 58. Ϫ 13C NMR (C6D6, 50 MHz): δ ϭ 21.4 [C(CH3)2], 22.9,
3,4-Bis[(2,6-dimethylphenyl)methoxyboryl]-2,5-dimethyl-2,4-
hexadiene (4d) and 3,4-bis[(duryl)methoxyboryl]-2,5-dimethyl-2,4-
hexadiene (4e): The same procedure as described for 4c was used.
Instead of recrystallization the solvent was stripped off and the
remaining viscous product was distilled under high vacuum. Yields:
790 mg (2 mmol, 70%) of 4d and 100 mg (0.2 mmol, 13%) of 4e.
Compound 4e crystallizes at room temp. after a few hours, whereas
4d becomes a glass-like solid
26.9 [2
ϫ C(CH3)2], 28.6 [C(CH3)3], 32.9 (NϪCH3), 126.0
[C(CH3)2], 150 [br, BCC(CH3)2]. Ϫ EI-MS: m/z (%) ϭ 273 (28)
[Mϩ], 216 (24) [Mϩ Ϫ tBu], 174 (10) [Mϩ Ϫ C(CH3)2], 160 (16),
41 (100) [C3H5ϩ].
2,5-Diduryl-3,4-diisopropylidene-1-oxa-2,5-diborolane (6): A sample
of 4c (400 mg) was refluxed for six hours in 10 mL of hexamethyl-
disiloxane. After removal of all volatile components, pure 6 re-
mained as a colorless solid. Ϫ 1H NMR (C6D6, 200 MHz): δ ϭ
1.69, 1.86 [2 s, 2ϫ6 H, (CH3)2C], 2.12, 2.33 (2 s, 2ϫ12 H, aryl-
CH3), 6.94 (s, 2 H, duryl). Ϫ 11B NMR (C6D6, 64 MHz): δ ϭ 54.
4d: 1H NMR (CDCl3, 200 MHz): δ ϭ 1.65, 1.69 [2 s, 2 ϫ 6 H,
C(CH3)2], 2.15 (s, broad, 12 H, aryl-CH3), 3.38 (OϪCH3), 6.91 (d,
3
3JHH ϭ 7.5 Hz, 4 H, aryl), 7.08 (t, JHH ϭ 7.5 Hz, 2 H, aryl). Ϫ
Ϫ
13C NMR (C6D6, 50 MHz): δ ϭ 19.5, 19.3 (2 ϫ aryl-CH3), 23.5,
11B NMR (CDCl3, 64 MHz): δ ϭ 47. Ϫ 13C NMR (CDCl3,
25.6 [2 ϫ C(CH3)2], 132.1, 133.5, 134.5 (CarylH), 147.5 [C(CH3)2].
Ϫ m.p. 190 °C (dec.). Ϫ EI-MS: m/z (%) ϭ 412 (100) [Mϩ], 278
(25) [Mϩ Ϫ Dur], 252 (38) [Mϩ Ϫ DurBO].
50 MHz):
δ ϭ 21.3 (aryl-CH3), 22.4, 24.0 [C(CH3)2], 53.5
(OϪCH3), 126.1, 127.1, 137.9 (3 ϫ Caryl), 141, 143 [both br,
BCC(CH3)2 and BCaryl], 147.3 [C(CH3)2]. Ϫ EI-MS: m/z (%) ϭ 402
(22) [Mϩ], 298 (8) [Mϩ Ϫ xylyl], 224 (66) [Mϩ Ϫ (BXylOMe) Ϫ
OMe], 209 (58) [Mϩ Ϫ (BXylOMe) Ϫ OMe Ϫ Me], 147 (100)
[XylBOMeϩ].
2,5-Diduryl-3,4-diisopropylidene-1-thia-2,5-diborolane (7): A sample
of 4c (800 mg, 1.71 mmol) was heated for 4 h to 120 °C in 5 mL of
hexamethyldisilathiane. The yellow solution was cooled to room
temp. which caused the product to precipitate. The colorless solid
7 (610 mg, 1.4 mmol, 83%) was separated and washed with cold
hexane. Ϫ 1H NMR (CDCl3, 200 MHz): δ ϭ 1.77, 1.82 [2 s, 2 ϫ 6
H, (CH3)2C], 2.07 (s, 6 H, aryl-CH3), 2.21 (s, 18 H, aryl-CH3), 6.92
(s, 2 H, duryl). Ϫ 11B NMR (CDCl3, 64 MHz): δ ϭ 72. Ϫ 13C
NMR (CDCl3, 50 MHz): δ ϭ 18.9, 19.3 (2 ϫ m-aryl-CH3), 19.5,
19.8 (2 ϫ o-aryl-CH3), 22.8, 25.4 [2 ϫ C(CH3)2], 131.2, 132.3,
132.5, 133.1, 133.5 (5 ϫ Caryl), 145 [br, BCϪC(CH3)2 or BCaryl],
145.5 [C(CH3)2], 148 [br, BCϪC(CH3)2 or BCaryl]. Ϫ EI-MS: m/z
4e: 1H NMR (C6D6, 200 MHz): δ ϭ 1.84, 1.86 [2 s, 2 ϫ 6 H,
(CH3)2C], 2.17 (s, 12 H, m-aryl-CH3), 2.22 (s, br, 12 H, o-aryl-
CH3), 3.32 (s, 6 H, OϪCH3), 6.90 (s, 2 H, duryl). Ϫ 11B NMR
(C6D6, 64 MHz): δ ϭ 49. Ϫ 13C NMR (CDCl3, 50 MHz): δ ϭ 18.3,
19.6 (aryl-CH3), 22.7, 24.4 [2 ϫ C(CH3)2], 53.4 (OϪCH3), 131.1,
133.3, 133.7 (3 ϫ Caryl), 147.6 [C(CH3)2]. ؊ EI-MS: m/z (%) ϭ
458 (12) [Mϩ], 325 (9) [Mϩ Ϫ duryl], 309 (4), 252 (37) [Mϩ
Ϫ
DurB(OMe)2], 237 (31), 175 (100) [DurBOMeϩ].
1-Aza-2,5-dichloro-3,4-diisopropylidene-1-methyl-2,5-diborolane
(5a): Heptamethyldisilazane (1.52 g, 8.69 mmol) was added at room
temp. to a solution of 4b (2.36 g, 8.69 mmol) in 50 mL of hexane.
The mixture was refluxed for 4 h, the solvent evaporated and the
residue distilled at 58 °C/8 ؋
10Ϫ3 mbar to give 1.80 g (7.8 mmol,
(%) ϭ 428 (100) [Mϩ], 294 (20) [Mϩ Ϫ Dur], 253 (69) [Mϩ
C(CH3)2 Ϫ Dur].
Ϫ
2-Aza-4,5-dicarba-3-duryl-4,5-diisopropyl-2-methyl-nido-hexa-
borane(6) (10a): Lithium durylborate (990 mg, 6.2 mmol) was sus-
pended in 60 mL of hexane. Compound 5a (720 mg, 3.1 mmol) was
added at room temp. and the mixture was stirred for 48 h. The
solution was separated from the precipitate, the solvent evaporated
and the residue distilled at 90Ϫ100 °C/8 ϫ 10Ϫ3 mbar to yield
142 mg of a colorless oil consisting mostly of 10a. Ϫ 1H NMR
(CDCl3, 200 MHz): δ ϭ 0.95, 0.99, 1.17, 1.20 [4 d, 4ϫ3 H,
CH(CH3)2, 3JHH ϭ 8 Hz], 2.16, 2.19 (2 s, 2 ϫ 3 H, m-methyl), 2.21,
2.23 (2 s, 2 ϫ 3 H, o-methyl), 2.62 (s, 3 H, N-methyl), 6.88 (s, 1 H,
p-aryl-CH). Ϫ 11B NMR (C6D6, 64 MHz): δ ϭ 23.1 (s, B-duryl),
13.5 (d, BeqH, 1JBH ϭ 130 Hz), Ϫ41.5 (d, BapicalH, 1JBH ϭ 202 Hz).
Ϫ EI-MS: m/z (%) ϭ 295 (20) [Mϩ Ϫ B], 280 (3) [Mϩ Ϫ B Ϫ CH3],
252 (10) [Mϩ Ϫ B Ϫ C3H7], 43 (100) [C3H7ϩ], 41 [C3H5ϩ].
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90%) of colorless, air-sensitive 5a. Ϫ H NMR (C6D6, 200 MHz):
δ ϭ 1.71, 2.15 [2 s, 2 ϫ 6 H, (CH3)2C, exo and endo], 2.89 (s, 3 H,
NϪCH3). Ϫ 11B NMR (C6D6, 64 MHz): δ ϭ 44. Ϫ 13C NMR
(C6D6, 50 MHz): δ ϭ 23.1, 26.4 [2 ϫ C(CH3)2, exo and endo], 29.7
(NϪCH3), 137 [br, BCϪC(CH3)2], 146.0 [C(CH3)2]. Ϫ EI-MS: m/z
(%) ϭ 229 (51) [Mϩ], 214 (100) [Mϩ Ϫ CH3], 200 (7) [Mϩ Ϫ C2H5],
122 (25) [Mϩ Ϫ C8H11].
1-Aza-2,5-diduryl-3,4-diisopropylidene-1-methyl-2,5-diborolane (5b):
Heptamethyldisilazane (325 mg, 1.85 mmol) was added to a solu-
tion of 4c (650 mg, 1.4 mmol) in 25 mL of hexane. The mixture
was stirred for 15 h, filtered and the solvent removed in vacuo.
According to the 1H NMR spectrum the reaction was almost
quantitative. Recrystallization from hexane at Ϫ80 °C gave 425 mg
(1 mmol, 70%) of colorless 5b. Ϫ H NMR (C6D6, 200 MHz): δ ϭ (10b): Li[BH4] (155 mg, 5.75 mmol) was suspended in 50 mL of
2-Aza-4,5-dicarba-4,5-diisopropyl-2-methyl-nido-hexaborane(6)
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1.81, 1.84 [2 s, 2 ϫ 6 H, (CH3)2C], 2.16, 2.26 [2 s, 2ϫ12 H, aryl-
hexane and 5a (660 mg, 2.88 mmol) was added at room temp. After
5 h of stirring at 40 °C, the solvent was removed at 1 mbar and the
CH3], 2.56 (NϪCH3), 6.94 (s, 2 H, duryl). Ϫ 11B NMR (C6D6,
64 MHz): δ ϭ 55. Ϫ 13C NMR (C6D6, 50 MHz): δ ϭ 19.0, 19.6 remaining colorless oil condensed into a dry-ice cooled trap. Ϫ 11B
(aryl-CH3), 25.9, 23.2 [C(CH3)2], 31.6 (NϪCH3), 131.3, 133.5 (2 ϫ NMR (C6D6, 64 MHz): δ ϭ Ϫ45.2 (d, Bapical, 1JBH ϭ 202 Hz), 13.6
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Caryl), 142.5 (CarylH), 143, 144 [both br, BCC(CH3)2 and BCAryl].
(d, Beq, JBH ϭ 155 Hz). Ϫ EI-MS: m/z (%) ϭ 175 (22) [Mϩ], 160
Ϫ EI-MS: m/z (%) ϭ 425 (100) [Mϩ], 382 (17) [Mϩ Ϫ C(CH3)2], (10) [Mϩ Ϫ Me], 146 (11) [Mϩ Ϫ NMe], 132 (45) [Mϩ Ϫ iPr], 41
356 (12), 291 (17) [Mϩ Ϫ Dur].
(100) [C3H5ϩ].
Eur. J. Inorg. Chem. 2001, 381Ϫ386
385