H.-J. Frohn et al. / Journal of Organometallic Chemistry 598 (2000) 127–135
133
C, 28.2; H, 0.44; F, 52.2%. IR w (cm−1): 3084, 1761,
1647, 1608, 1526, 1460, 1383, 1340, 1302, 1284, 1252,
1194, 1107, 1072, 1018, 976, 879, 845, 812, 744, 710,
625, 572, 534, 523, 484.
Extraction with MeCN (2×15 ml) followed by drying
with MgSO4 and removal of the solvent gave a colorless
solid. Pure borate (11) was obtained in 83% yield (4.08
g) after drying over P4O10 in vacuum. Anal. Calc. for
C6H2BF6K: C, 30.3; H, 0.85; F, 47.9%; found: C, 29.7;
H, 0.83; F, 48.5%. IR w (cm−1): 3078, 1614, 1529, 1412,
1331, 1283, 1232, 1213, 1136, 1034, 999, 889, 750, 737,
625, 532.
3.5. Potassium 2,4,6-trifluorophenyltrifluoroborate (10)
2,4,6-C6H2F3Li was prepared from 1-bromo-2,4,6-
trifluorobenzene (4.20 g, 20 mmol) and BuLi (2.5 M in
hexane; 8 ml, 20 mmol) in ether (30 ml) at −75°C and
added gradually to a cold solution of B(OCH3)3 (5.5 g,
53 mmol) in ether (40 ml) at −70°C. After stirring for
1 h the reaction mixture was warmed to 10°C within 3
h followed by hydrolysis with 10% HCl (60 ml). The
organic layer was separated, the aqueous one was ex-
tracted with ether (2×10 ml) and the combined ex-
tracts were dried with MgSO4. The solvent was
removed to give the crude arylboronic acid (3.4 g).
19F-NMR (acetone): −99.6 (F-2,6), −106.6 (F-4)
3.7. Potassium 2,6-difluorophenyltrifluoroborate (8)
2,6-C6H3F2Li was prepared from 1-bromo-2,6-di-
fluorobenzene (3.86 g, 20 mmol) and BuLi (2.5 M in
hexane; 8 ml, 20 mmol) in ether (30 ml) at −78°C and
added gradually to the cold solution of B(OCH3)3 (4.20
g, 40 mmol) in ether (20 ml) at −70°C. After stirring at
−70°C for 1 h the reaction mixture was warmed to
10°C within 20 min followed by hydrolysis with 5%
HCl (20 ml). The organic layer was separated, the
aqueous one was extracted with ether (2×10 ml) and
the combined extracts were dried with MgSO4. After
removal of the solvent the crude arylboronic acid (3.0
g) was obtained. 19F-NMR (acetone): −102.59 (F-2,6)
ppm; 1H-NMR (acetone): 7.07 (H-4), 6.61 (H-3,5) ppm.
A solution of the arylboronic acid in MeOH (5 ml)
was added to the solution of K[HF2] (4.7 g, 60 mmol)
in water (40 ml). After stirring for 1 h, the precipitate
was filtered off, washed with water and with dry ether
(2×10 ml) and dried over Sicapent to give compound
8 (3.6 g, 82%). The product was slightly soluble in
acetone, MeCN, MeOH. Anal. Calc. for C6H3BF5K: C,
32.8; H, 1.37; F, 43.2%; found: C, 33.2; H, 1.56; F,
43.0%. IR w (cm−1): 3089, 1626, 1587, 1570, 1446,
1290, 1264, 1218, 1176, 1005, 970, 775, 712, 547, 516.
1
ppm; H-NMR (acetone): 7.41 (OH), 6.78 (H-3,5) ppm.
A solution of the arylboronic acid in MeOH (10 ml)
was added to the solution of K[HF2] (5.6 g, 72 mmol)
in water (45 ml). After stirring overnight the precipitate
was filtered off, washed with water and dried over
Sicapent to give borate (10) (3.6 g, 76%). Anal. Calc.
for C6H2BF6K: C, 30.3; H, 0.85; F, 47.9%; found: C,
30.0; H, 0.90; F, 48.2%. IR w (cm−1): 3106, 1644, 1617,
1595, 1520, 1490, 1412, 1293, 1221, 1176, 1159, 1115,
1005, 970, 837, 727, 614, 575, 550, 519.
3.6. Potassium 3,4,5-trifluorophenyltrifluoroborate (11)
3,4,5-Trifluorophenylmagnesium bromide was pre-
pared from 1-bromo-3,4,5-trifluorobenzene (4.34 g, 20.5
mmol) and magnesium (0.51 g, 21.0 mmol) in ether (35
ml) and added dropwise to the solution of B(O-i-
C3H7)3 (4.17 g, 22.1 mmol) in ether (30 ml) at −30°C.
The white suspension was warmed to 10°C within 30
min. The 19F-NMR spectrum displayed resonances at
−135.9 (F-3,5) and −160.4 (F-4) ppm which were
assigned to 3,4,5-C6H2F3B(O-i-Pr)2. The reaction mix-
ture was poured into 10% HCl (90 ml) and stirred at r.t.
for 1 h. The organic phase was separated, the aqueous
one extracted with ether (40 ml) and the combined
extracts were dried with MgSO4. After evaporation of
the solvent at reduced pressure the crude arylboronic
acid (4.3 g) was obtained.
3.8. Potassium 3,5-difluorophenyltrifluoroborate (9)
3,5-Difluorophenylmagnesium bromide was prepared
from 1-bromo-3,5-difluorobenzene (3.80 g, 19.7 mmol)
and magnesium (0.48 g, 19.7 mmol) in ether (40 ml)
and added dropwise to the solution of B(OCH3)3 (5.5 g,
53 mmol) in ether (40 ml) at −25°C. The white suspen-
sion was warmed to 20°C overnight. The reaction mix-
ture was poured into 5% HCl (110 ml). The organic
phase was separated, the aqueous one extracted with
ether (2×10 ml) and the combined extracts were dried
with MgSO4. After evaporation of the solvent at re-
duced pressure the crude arylboronic acid (3.0 g) was
obtained.
19F-NMR (ether): −137.1 (F-3,5), −160.4 (F-4)
ppm {3,4,5-C6H2F3B(OH)2} and −135.3 (F-3,5),
−162.0 (F-4) ppm {probably 3,4,5-C6H2F3B(O-i-Pr)2}
(7:1).
The crude product was treated with K[HF2] (5.19 g,
65 mmol) in 70% aqueous methanol (120 ml) overnight.
The mother liquor was decanted, the residue was ex-
tracted with MeCN (10 ml) and the combined extracts
were evaporated to dryness under reduced pressure.
19F-NMR (acetone): −111.0 (F-3,5) ppm {3,5-
C6H3F2B(OH)2} and admixtures at −110.0 and
−107.6 ppm. 1H-NMR (acetone): 7.37 (H-2,6) and
6.90 (H-4) ppm.
The crude product was treated with K[HF2] (5.6 g, 72
mmol) in water–methanol (4:1) (50 ml) overnight. The
reaction solution was saturated with KF·2H2O and