S. Aldridge et al. / Journal of Organometallic Chemistry 614–615 (2000) 188–194
189
2.2. ClBO2C6H2O2BCl (4)
molecular sieves (THF) or KOH (40:60 petrol–toluene)
and purged with nitrogen prior to distillation. THF,
toluene and petrol were all distilled from sodium before
use. Triethylamine was dried over sodium wire prior to
use. Starting materials 2,5-dihydroxy-para-quinone,
chloranilic acid, trimethylsilyl chloride, BH3·THF and
BCl3 were used as received (Aldrich) without further
purification. 1,2,4,5-Tetrahydroxybenzene (2) was pre-
pared in essentially quantitative yield from 2,5-dihy-
droxy-para-quinone by the method of Hegedus and
coworkers [12].
To a solution of 2.5 g (5.8 mmol) of 3 in petrol at r.t.
was added dropwise by syringe four equivalents of BCl3
(14.5 cm3 of a 1.0 M solution in heptane, 14.5 mmol).
The initially colourless solution became pale yellow but
lost its colour on heating to 60°C for 3 h. At this point
volatiles were removed in vacuo and the residual solid
extracted with 15 cm3 of petrol. Cooling to −30°C for
48 h resulted in the formation of 4 as colourless acicu-
lar crystals in 89% yield. Compound 4 was character-
1
ised by H-, 13C- and 11B-NMR, IR, EIMS, elemental
NMR spectra were measured on a Bruker AM-400
or Bruker AMX-360 FT-NMR spectrometer. Residual
1
analysis and single crystal X-ray diffraction. H-NMR
(benzene, 20°C): l 6.45 (sl, 2H, aromatic). 13C-NMR
(benzene, 20°C): l 99.1 (CH aromatic), 144.2 (quater-
nary aromatic). 11B-NMR (petrol, 20°C): l 29.2. IR
(cm−1): 3123 m, 1463, s sh, 1410 s, 1341 s, 1108 s, 980
m, 859 m, 822 m. EIMS P+: 230 (100%) expected
isotopic distribution for two boron and two chlorine
atoms. Anal. Calc. for C6H2B2Cl2O4: C, 31.25; H, 0.87.
Found: C, 30.83; H, 0.79%.
1
protons of solvent were used as the reference for H-
and 13C-NMR, while
a
sealed tube containing
[(nBu4N)(B3H8)] was used as an external reference for
11B-NMR. IR spectra were measured for each com-
pound pressed into a disk with an excess of dried KBr
on a Nicolet 500 FT-IR spectrometer. Mass spectra
were measured by the EPSRC National Mass Spec-
trometry Service Centre, University of Wales Swansea.
Perfluorotributylamine was used as the standard for
high-resolution EIMS. Elemental analyses were carried
out both by the departmental analysis service and by
Warwick Analytical Service, University of Warwick.
Abbreviations: s, strong; m, medium; w, weak; sh,
shoulder; sl, singlet; d, doublet; pcq, partially collapsed
quartet; b, broad.
2.3. HBO2C6H2O2BH (7)
To a rapidly stirred solution/suspension of 1.12 g (9.7
mmol) of 2,5-dihydroxy-para-quinone in THF at r.t.
were added dropwise by syringe four equivalents of
BH3·THF (38.7 cm3 of a 1.0 M solution in THF, 38.7
mmol). Within 1 h the reaction mixture became a
yellow solution, which lost its colour on stirring for a
further 12 h. Removal of volatiles in vacuo at −20°C
followed by sublimation at 40°C onto a cold finger held
at −20°C gave 7 as large colourless crystals in yields of
40–60%. Higher yields of a less pure product could be
achieved by extraction of the crude product into petrol
and cooling the resultant solution, rather than by subli-
2.1. 1,2,4,5-(Me3SiO)4C6H2 (3)
A 2.0 g (14 mmol) sample of 1,2,4,5-(HO)4C6H2 (2)
was suspended in toluene (20 cm3) and ten equivalents
of trimethylsilyl chloride (17.8 cm3, 140 mmol) and ten
equivalents (19.6 cm3, 140 mmol) of triethylamine were
then added by syringe to the rapidly stirred reaction
mixture. After 12 h at room temperature (r.t.) the
supernatant toluene solution was separated from the
(Et3NH)Cl precipitate by filtration. The precipitate was
washed with toluene (2×10 cm3) and the combined
washings reduced to dryness in vacuo. Extraction with
petrol (15 cm3) and cooling to −30°C for 48 h resulted
in the formation of 3 as pale pink acicular crystals in
mation. Compound 7 was characterised by H-, 13C-
1
and 11B-NMR, IR, EIMS (including exact mass deter-
1
mination) and elemental analysis. H-NMR (benzene,
20°C): l 6.94 (sl, 2H, aromatic), ca. 4.6 (b pcq, 2H,
BH). 13C-NMR (benzene, 20°C): l 97.2 (CH aromatic),
141.9 (quaternary aromatic). 11B-NMR (petrol, 20°C):
1
l 29.4 (d, JBꢀH=191 Hz). IR (cm−1): 2678 m sh, 2660
s [w(BꢀH)]. EIMS P+: 162 (100%) expected isotopic
distribution for two boron atoms. Exact mass calc. for
C6H4B2O4: 162.0296; found: 162.0296. Anal. Calc. for
C6H4B2O4: C, 44.56; H, 2.49. Found: C, 44.22; H,
2.43%.
1
78% yield. Compound 3 was characterised by H- and
13C-NMR, IR, EIMS, elemental analysis and single
1
crystal X-ray diffraction. H-NMR (chloroform, 20°C):
l 0.05 (sl, 36H, Me3Si), 6.13 (sl, 2H, aromatic). 13C-
NMR (chloroform, 20°C): l 0.2 (Me3Si), 113.4 (CH
aromatic), 139.9 (quaternary aromatic). IR (cm−1):
2957 m, 2900 w [w(CꢀH)], 1401 m, 1186 s [l(CH3)],
1505 s, 1249 s, 1217 m, 945 s, 917 s, 83.9 s. EIMS P+:
431 (100%). Anal. Calc. for C18H38O4Si4: C, 50.18; H,
8.89. Found: C, 50.42; H, 8.64%.
2.4. HBO2C6Cl2O2BH (8)
Compound 8 was prepared from 2,5-dihydroxy-3,6-
dichloro-para-quinone (chloranilic acid) by a method
analogous to that described above for 7. By contrast to
7, crude 8 was best purified by recrystallisation from
petrol (yield ca. 45%), as sublimation invariably re-