J. Pecyna et al. / Polyhedron 30 (2011) 2505–2513
2511
173–174 °C; 1H NMR d 1.20 (br q, J = 144 Hz, 4H), 1.69 (dtt,
J1 = 11.6 Hz, J2 = 11.0 Hz, J3 = 3.0 Hz, 1H), 1.89–1.95 (m, 1H), 1.90
(br q, J = 157 Hz, 4H), 1.98–2.08 (m, 2H), 2.33 (dm, J = 12.0 Hz,
2H), 3.38 (ddd, J1 = 12.9 Hz, J2 = 12.3 Hz, J2 = 2.5 Hz, 2H), 3.68 (dt,
J1 = 12.4 Hz, J2 = 2.4 Hz, 2H), 3.96 (s, 3H); 11B NMR d ꢀ20.3 (d,
J = 143 Hz, 4H), ꢀ14.8 (d, J = 158 Hz, 4H), 32.2 (s, 1H). HRMS, calcd
for C8H22B9O2S m/z 281.2178; found m/z 281.2198.
for 1 h where the yellow/orange color dissipated after ꢄ30 min.
Reaction progress was monitored by following 11B NMR spectrum
of an aliquot taken directly from the reaction mixture [11B {1H}
NMR (D2O) d ꢀ1.2 (1B), ꢀ3.8 (1B), ꢀ23.3 (1B), ꢀ26.5 (2B), ꢀ29.4
(2B), ꢀ30.3 (2B)]. Solid Na2S2O5 (123.8 g, 0.651 mol) and
[NEt4]+Brꢀ (68.41 g, 0.3255 mol) were then added, and after
15 min, 20% HCl (85 mL) was added slowly via the addition funnel
until a pH of ꢄ3 was obtained. A white precipitate was filtered,
washed with water (5 ꢃ 100 mL), press dried, and further dried
in air overnight giving 27–37 g (42–58% yield) of [closo-2-CB9H9-
2-COOH]ꢀ [NEt4]+ (4) in purity greater than 90% by 11B NMR. The
filtrate is a yellow solution. 11B NMR was consistent with that re-
ported in the literature [10,11].
The more polar fraction (6.3 mg) was eluted with CH2Cl2: 1H
NMR (CD3CN) d major signal 3.96 (s); 11B NMR (CD3CN) major sig-
nals d ꢀ24.5 (d, J = 135 Hz, 4B), ꢀ18.5 (d, J = 156 Hz, 4B), 48.0 (s,
1B). HRMS, calcd for C8H22B9O2S m/z 281.2175; found m/z
281.2215.
4.7. Preparation of [closo-1-CB9H8-1-COOMe-10-(4-C3H7C5H9S)]
(3[3]b)
4.9. Preparation of [arachno-6-CB9H13-6-COOH]ꢀ [NEt4]+ (5)
Glyoxylic acid (200.0 g, 2.16 mol) was slowly added in 15 g por-
tions to a cooled solution (0 °C) of KOH (251.3 g, 4.48 mol) in water
(300 mL) containing 200 g of crushed ice in a 3-L three-necked
flask equipped with an addition funnel, mechanical stirrer, and
internal thermometer. Vigorous stirring and slow addition of gly-
oxylic acid is important to maintain the temperature of the solu-
tion below 5 °C. Finely crushed B10H14 (40.0 g, 0.327 mol) was
then slowly added in two portions, while maintaining the temper-
ature of the solution around 5 °C. Once all B10H14 had dissolved, the
solution was vigorously stirred for an additional 2 h (<5 °C). Reac-
tion progress was monitored by following 11B NMR spectrum of an
aliquot taken directly from the reaction mixture [11B {1H} NMR
(D2O) d ꢀ3.2 (1B), ꢀ4.7 (2B), ꢀ14.6 (1B), ꢀ16.2 (1B), ꢀ19.8 (1B),
ꢀ20.8 (1B), ꢀ26.7 (1B), ꢀ38.3 (1B), ꢀ38.7 (1B)]. Solid [NEt4]+Brꢀ
(47.9 g, 0.228 mol) was added, and after 10 min, freezer-cold
(ꢀ15 °C) 20% solution of HCl (340 mL) was slowly added via the
addition funnel until a pH of ꢄ3 was obtained. Addition of HCl re-
sulted in vigorous bubbling, foaming, and release of H2. Occasion-
ally, manual breaking up of large clumps of the product was
necessary for thorough neutralization of the product and decom-
position of the flammable boron hydride byproducts. At pH ꢄ3,
the bubbling and foaming begins to subside. The resulting white
precipitate was filtered, washed with H2O (10 ꢃ 100 mL), press
dried, and further dried in air overnight giving 64–72 g (66–74%
yield) (see footnote 1) of [arachno-6-CB9H13-6-COOH]ꢀ [NEt4]+
(5) in purity greater than 90% by NMR: 11B {1H} NMR (CD3CN) d
major signals ꢀ0.5 (1B), ꢀ9.2 (3B), ꢀ20.1 (1B), ꢀ27.8 (1B), ꢀ39.0
(2B); (acetone-d6) d major signals ꢀ0.3 (1B), ꢀ9.0 (2B), ꢀ9.6 (1B),
ꢀ19.6 (1B), ꢀ27.6 (1B), ꢀ38.8 (2B) [lit. [10] (acetone-d6) ꢀ0.6
(1B), ꢀ9.4 (1B), ꢀ10.3 (3B), ꢀ19.3 (1B), ꢀ27.9 (2B), ꢀ39.1 (1B)].
When an acetone solution of 5 is filtered, evaporated, and redis-
solved in acetone-d6 the spectrum changes: 11B {1H} NMR (ace-
tone-d6) d major signals 3.0 (2B), 0.5 (1B), ꢀ4.6 (2B), ꢀ11.9 (2B),
ꢀ29.1 (1B), ꢀ36.2 (1B).
4.7.1. Method A
A solution of methyl ester 16 (250 mg, 1.22 mmol) in 4-propyl-
thiane (17[3], 2.0 mL) was stirred at 120 °C for 3 h. Excess thiane
was removed and the semisolid residue was passed through a silica
gel plug (hexane/CH2Cl2, 1:2). The first fraction containing the
product was evaporated giving 192 mg (49% yield) of ester 3[3]b
as a white solid.
4.7.2. Method B
Crude acid 2[3] (2.40 g, 7.8 mmol), obtained by hydrolysis of
the reaction products as described in Section 4.4. Method A, was
dissolved in CH2Cl2 (20 mL) and (COCl)2 (2.60 mL, 30 mmol)
was added followed by a catalytic amount of DMF. The mixture
was stirred for 1 h at ambient temperature, volatiles were
removed, the resulting acid chloride was dissolved in MeOH
(20 mL) and the solution was gently refluxed for 1 h. MeOH was
evaporated and the crude methyl ester 3[3]b was purified by col-
umn chromatography (SiO2, hexane/CH2Cl2, 1:1) to give 1.47 g
(58% yield) of 3[3]b as a white solid, which was recrystallized from
hexane/CH2Cl2: m.p. 95–103 °C; 1H NMR major signals: d 0.60–
2.50 (m, 8H), 0.93 (t, J = 7.0 Hz, 3H), 1.27–1.45 (m, 4H), 1.65–1.75
(m, 2H), 2.04–2.15 (m, 1H), 2.33 (dm, J = 11.8 Hz, 2H), 3.39 (t,
J = 11.9 Hz, 2H), 3.74 (dm, J = 12.2 Hz, 2H), 3.956 (s, 3H); minor
signals: d 3.47–3.56 (m), 3.960 (s); 11B NMR major signals: d
ꢀ20.3 (d, J = 141 Hz, 4B), ꢀ14.8 (d, J = 158 Hz, 4B), 32.6 (1B); minor
signal: d 30.6 (s). Anal. Calc. for C11H27B9O2S: C, 41.20; H, 8.49.
Found: C, 41.40; H, 8.60%.
4.8. Preparation of [closo-2-CB9H9-2-COOH]ꢀ [NEt4]+ (4)
[Arachno-6-CB9H13-6-COOH]ꢀ [NEt4]+ (5, 64.5 g, 0.217 mol) was
suspended in a biphasic system of Et2O (500 mL) and ice-cold 18%
HCl (400 mL) in a 2-L Erlenmeyer flask. The mixture was stirred
vigorously in an ice-bath and slowly warmed to room temperature
until only traces of solid remained (ꢄ2 h). The Et2O was separated
in a 2-L separatory funnel, and the aqueous layer was further ex-
tracted with additional Et2O (3 ꢃ 150 mL). Any remaining solid
material was drained into the aqueous layer. The Et2O layers were
combined in a 1-L round-bottom flask and evaporated to approxi-
mately one-half its volume. A cooled (0 °C) solution of KOH (2.7 M,
645 mL) was then added, and the remaining Et2O was removed,
and the last remnants of Et2O were removed in vacuum (<5 mm
Hg) until vigorous bubbling was no longer observed. The solution
was then poured into a 3-L three-necked flask equipped with an
addition funnel and mechanical stirrer and cooled down to ꢄ5 °C
in an ice-bath. Elemental I2 (126.5 g, 0.500 mol) was slowly added
in ꢄ10 g portions every 5–10 min, or as often as solid iodine was
no longer visible. Towards the last few additions, the solution
developed a yellow/orange color. The solution was further stirred
4.10. Preparation of [closo-2-CB9H8-2-COOH-7-I]ꢀ [NEt4]+ (6) [4]
A red solution of N-iodosuccinimide (35.23 g, 0.157 mol) and
[closo-2-CB9H9-2-COOH]ꢀ [NEt4]+ (4, 30.82 g, 0.104 mol) in anhy-
drous MeCN (150 mL) was stirred vigorously for 1 h at 0 °C and
then stored for 72 h in a freezer (ꢀ10 to ꢀ20 °C). MeCN was re-
moved at 0 °C under reduced pressure (<10 mm Hg). Solid Na2S2O5
(29.8 g, 0.157 mol) and 10% HCl (350 mL) were added and the reac-
tion mixture turned green/yellow and a yellow precipitate began
to form. If solution does not turn green/yellow, more Na2S2O5
should be added. The mixture was stirred vigorously. Once all
red residue dissolved, Et2O (100 mL) was added and the mixture
was vigorously stirred until the yellow precipitate redissolved
leaving an orange organic layer. The Et2O layer was separated
and the aqueous layer was further extracted with Et2O