Facile and reliable synthesis of tetraphenoxyborates and their properties

Article abstract of DOI:10.1002/ejic.200600074

Tetraphenoxyborates are reliably prepared in a two-step sequence, exploiting less corrosive reagents like boric acid and the corresponding phenols. The broad scope of this transformation is demonstrated in 22 examples. Several solid-state structures reveal the preferential conformation of the phenoxy moieties allowing cation interaction. Furthermore, a novel architecture of a phenoxy-substituted tetraborate was found. Surprisingly, the tetraphenoxyborates exhibit a good stability in neutral and basic media. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200600074

FULL PAPER
DOI: 10.1002/ejic.200600074
Facile and Reliable Synthesis of Tetraphenoxyborates and Their Properties
Itamar M. Malkowsky,[a] Roland Fröhlich,[b] Ulrich Griesbach,[c] Hermann Pütter,[c] and
Siegfried R. Waldvogel*[a]
Keywords: Borates / Sodium / Anions / Phenolates
Tetraphenoxyborates are reliably prepared in a two-step se-
quence, exploiting less corrosive reagents like boric acid and
the corresponding phenols. The broad scope of this transfor-
mation is demonstrated in 22 examples. Several solid-state
structures reveal the preferential conformation of the phen-
oxy moieties allowing cation interaction. Furthermore, a
novel architecture of a phenoxy-substituted tetraborate was
found. Surprisingly, the tetraphenoxyborates exhibit a good
stability in neutral and basic media.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
phenoxyborates requires the prior construction of the tri-
esters of boric acid followed by the conversion with phenol-
ates. In order to obtain soluble phenolate equivalents of
divalent cations like barium, sophisticated reagent mixtures
were applied.[8] However, the direct use of barium metal
ameliorated the process to barium-linked dimeric borates.[9]
We present a reliable protocol for the synthesis of a wide
scope of tetraphenoxyborates. The simple two-step se-
quence can be performed in a one-pot process and is feas-
ible for large quantities of the desired tetragonal boron
compound.
Introduction
Tetracoordinated borates play an important role in na-
ture.[1] In particular, these natural products are involved in
the communication among bacterial microorganisms.[2]
Size, oxophilic nature, and a maximum coordination
number of four predestine boron for templating alkoxy or
phenoxy moieties in an efficient manner. The synthesis and
properties of tetracoordinated borates are well established,
whereas the corresponding tetraphenoxy derivatives are
only little explored. Tetraphenoxyborates are commonly
used as bulky and inert counterions for catalysts[3] or as
electrolytes in batteries.[4]
The formation of such tetragonal-coordinated com-
pounds involves the reaction of Lewis acidic boron species
with a nucleophilic phenoxy system. If very electron-de-
ficient boranes are applied with no additional base, a tetrag-
onal boron derivative is observed, incorporating an unusual
tautomeric form of the phenolate.[5] Treatment of the corre-
sponding phenol with boron trichloride in the presence of
a nitrogen base leads to the triphenoxyborane by a direct
displacement of chlorine and subsequently to the anionic
tetragonal derivative. This approach requires very electron-
deficient phenols and a highly corrosive boron reagent.[6]
When employing sodium tetrahydridoborate as boron
source in the reaction with phenol a variety of different bo-
rates is observed. Herein the counterion plays a crucial role,
because the sodium cations link the borate subunits to infi-
nite polymeric structures.[7] The stepwise formation of tetra-
Results and Discussion
The synthesis of tetraphenoxyborates began with the es-
terification of the corresponding phenol with boric acid
(Scheme 1). The transformation was performed in refluxing
toluene with the use of a Dean–Stark trap. With the re-
moval of water the reaction mixture became homogeneous.
The amount of water received was slightly lower than antic-
ipated from a stoichiometric condensation reaction.
[a] Kekulé-Institut für Organische Chemie und Biochemie,
Gerhard-Domagk-Str. 1, 53121 Bonn, Germany
Fax: +49-228-73-9608
Scheme 1. a) B(OH)3, toluene, 12 h reflux with a Dean–Stark trap.
E-mail: waldvogel@uni-bonn.de
Removal of the solvent under reduced pressure yielded a
mixture of phenyl esters of boric acid. Mass spectrometric
investigation of the crude product indicated the presence of
several trigonal boron species as depicted in Figure 1.
[b] Westfälische Wilhelms-Universität Münster, Organisch-Chem-
isches Institut,
Corrensstr. 40, 48149 Münster, Germany
[c] BASF Aktiengesellschaft,
GCI/E-M311, 67056 Ludwigshafen, Germany
1690
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Facile and Reliable Synthesis of Tetraphenoxyborates and Their Properties
FULL PAPER
Figure 1. Major products by the condensation reaction of 1 with
boric acid.
The presence of abundant 1 gives rise to a fast equilib-
rium among the ester species 2–4.[10] When the crude mate-
Figure 2. Left: X-ray structure of the tetraborate 28; right: coordi-
rial was carefully distilled under high vacuum (10–4–
10–5 mbar), the pure triester 2 could be obtained. However,
this step turned out to be time-consuming. Furthermore, it
was only feasible on smaller quantities, limited to substrates
of low molecular weight and involved an unacceptable loss
of material. Therefore, the crude mixture was directly sub-
jected to the corresponding phenolate in THF (Scheme 2).
nation pattern.
(Table 1). Three sodium cations link the borate fragments
through the phenol oxygen atoms and compensate the
negative charge. In addition, each sodium cation is coordi-
nated by two THF molecules, which are omitted in Figure 2
for clarity. The architecture of the depicted tetraborate 28
is unique. Remarkably, 28 exhibits no C3 symmetry, due to
the deviated orientation of the methoxy substituents in its
periphery.
As shown in Table 2, the parent phenol (Entry 1) as well
as mono-, di- and trisubstituted substrates were applied in
the synthesis of their tetraphenoxyborates in moderate to
excellent yields. The reaction outcome is determined by the
steric demand and electronic nature of the individual phe-
nol derivative. The conversion of para- and ortho-cresol to
Scheme 2. a) B(OH)3, toluene, 12 h reflux with a Dean–Stark trap;
b) Na, 1, THF, room temp.
THF proved to be the appropriate solvent for this par- the corresponding borates 7 and 14, respectively, shows a
ticular transformation including the reaction of phenol with lower yield for the latter one, due to the steric demand close
sodium as well as the formation of the desired tetraphen- to the borate centre (Entries 2 and 9). This trend is reflected
oxyborate 5, which precipitated and could easily be isolated in the conversion of almost all ortho-alkyl-substituted phe-
by simple filtration. The formation of anionic borates re- nols compared to the congeners with free ortho positions.
sults in a fast equilibrium of the corresponding trigonal Interestingly, thymol and 4-chlorothymol, both exhibiting
compounds 2–4 and strongly favours the formation of the an isopropyl group at C-2, provide the borates 16 and 26 in
mononuclear borate species 5. Noteworthy, performing the high yields (Entries 11 and 21).
transformation at high concentration led almost exclusively
Phenols with a single tert-butyl substituent were success-
to 5. However, application of 4-methoxyphenol in this reac- fully subjected to the condensation reaction with boric acid
tion sequence yielded the desired borate 9 besides the tetra- followed by salt formation to yield 8, 17, 19 or 25 in good
nuclear borate 28 as by-product in very low yields. Fortu- yields (Entries 3, 12, 14 and 20), whereas two tert-butyl
nately, a suitable single crystal for X-ray analysis was ob- groups dramatically disfavour the arrangement of four phe-
tained (Figure 2). Further spectroscopic investigation was nolates around the boron centre (Entry 13). Furthermore,
not possible because not sufficient pure material of 28 was electronic effects can lower the nucleophilicity of the inter-
available.
mediate sodium phenolate, resulting in a lower yield for the
Compound 28 represents an intermediate in the forma- desired borate. Therefore, substrates like 4-fluorophenol, 4-
tion of 5 from higher aggregates similar to 3 or 4. The mo- chlorophenol and 2-bromo-4-methylphenol were converted
lecular structure reveals a mixed tetraborate. In the centre, into the corresponding borates 10, 11 and 20, respectively,
a trigonal boric anhydride unit is connected to three tetrag- in moderate yields (Entries 5, 6 and 15). In contrast, tetra-
onal anionic borate moieties. The tetrahedral symmetry of phenoxyborates of electron-rich phenols were obtained in
the borates is distorted and shows two pairs of angles good to excellent yields (Entries 4, 7 and 17).
Table 1. Selected geometric parameters [Å, °] for a subunit of 28.
Btrig–O1
1.3624(1)
1.4630(1), 1.4647(1), 1.4888(1)
1.4610(1)
2.3255(2)
2.6439(2)
O–Btrig–O
119.542(5)
126.218(10)
102.450(8)
99.389(12)
Btetr–O(Ar)
Btetr–O1
Btrig–O1–Btetr
O1–Btetr–O(Na1)
(Na2)O–Btetr–O(Na2)
(Na1)O–Btetr–O(Na2)
Na1–O1
Na1–O(Ar)
Na2–O(Ar)
113.274(5), 115.317(5)
2.4078(2), 2.4635(2)
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Table 2. Substrates for the synthesis of tetraphenoxyborates.
compound 30 could easily be separated from the phenolate
of 29 by chilling the reaction mixture. Compound 30 was
filtered off and obtained as pure colourless solid. Thus, tri-
phenoxyboranes of phenol derivatives exhibiting two alkyl
substituents in the ortho positions are far too shielded to
undergo addition with a further phenolate equivalent.
Because suitable crystals for X-ray analysis of both, tri-
phenoxyborane (6a) and the corresponding tetraphen-
oxyborate (6b) were available, a direct comparison of the
structural features was possible (Figure 3). The obtained
geometric data are representative for most analogues.
Figure 3. Molecular structure of triphenoxyborane (6a) and the tet-
raphenoxyborate (6b) determined by X-ray analysis.
Triphenoxyborane (6a) exhibits a trigonal-planar boron
centre with three phenyl units symmetrically arranged
around the boron atom. The planes of the aromatic rings
are oriented almost perpendicular to the BO3 plane, re-
sulting in a water-wheel-shaped molecule. Three almost
similar distances of about 2.35 Å between the oxygen atoms
of 6a emphasise the expected C3 symmetry of 6a. In con-
trast, the tetraphenoxyborate (6b) reveals a slight deviation
from the tetrahedral symmetry by elongation in one direc-
tion. The pair of oxygen atoms bridged by the sodium cat-
ion forms the shorter side of the tetrahedron and exhibits
an interatomic distance of about 2.26 Å. Interestingly, the
opposite side shows the same oxygen–oxygen distance with-
out a coordinating counterion. The corresponding in-
teratomic distances on the longer side are in the range of
2.44–2.48 Å. Compared to 6a, neighboured ortho-carbon
atoms come closer to each other up to 4.28 Å. The sodium
cation in 6b has in fact a coordination number of five. Two
positions are held by phenoxy oxygen atoms, represented in
Figure 3 by dashed lines. The remaining three ligands are
THF molecules, which are omitted for clarity. Almost the
same assembly can be found in the X-ray structure of tetra-
Phenols with two ortho substituents smoothly undergo
the condensation reaction to the triphenoxyborane, whereas
the subsequent formation of the tetraphenoxyborates was
not observed (Scheme 3).
Scheme 3. a) B(OH)3, toluene, 24 h reflux with a Dean–Stark trap;
b) 29, NaH, THF.
The conversion of 2,4,6-trimethylphenol (29) with so- phenoxyborate 10 as shown in Figure 4. Again, THF mole-
dium metal was sluggish, therefore sodium hydride was em- cules are not depicted for clarity.
ployed for deprotonation. Still, the addition of 30 to the
The tetraphenoxyborate 10 exhibits very similar struc-
phenolate of 29 gave no indication for the formation of the tural features compared to 6b according to geometry and
sodium tetraphenoxyborate 31. The reaction mixture was complexation of the sodium cation by the substrate and
analyzed by 11B NMR spectroscopy, as the signals for a three THF molecules. In contrast, the tetranaphthoxybor-
trigonal and a tetragonal boron atom clearly differ from ate 27 (Figure 4) is no longer able to coordinate to the so-
each other. Only a broad signal at δ = 15.89 ppm was ob- dium cation itself, due to the highly crowded boron centre.
served, indicating the triphenoxyborane 30. Remarkably, Therefore, the cation is coordinated by five THF molecules
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Facile and Reliable Synthesis of Tetraphenoxyborates and Their Properties
FULL PAPER
borates span a significantly wider oxygen–boron–oxygen
angle than the opposite angle between the cation-bridged
oxygen atoms.[9]
It turned out that tetraphenoxyborates are much less
prone to hydrolysis than the corresponding trigonal tri-
phenoxyborane species. Consequently, 5 can be handled for
short times at ambient conditions,[11] whereas the triphenyl
ester of boric acid is almost immediately affected by moist-
ure. The enhanced stability of the tetragonal boron systems
is based on the saturated coordination sphere of the boron
centre. However, protic media or strongly coordinating sol-
vents like methanol or acetonitrile might affect the stability
of 5. In this context, 11B NMR studies proved to be a versa-
tile tool. Besides the chemical shift as an indicator for the
electronic properties, the line full width at half maximum
can individually characterize the structure of a specific bo-
rate derivative. The comparison of different triphenoxybor-
anes is not facile to accomplish, due to extremely broad
signals. However, triphenoxyboranes and tetraphenoxybo-
rates can easily be distinguished as presented in Figure 5.
The 11B NMR spectrum of triphenoxyborane in chloro-
form (Figure 5, top) shows a broad signal at δ Ϸ 15 ppm
with a line full width at half maximum of 320 Hz, which
represents a typical value for a trigonal boron species. When
the same substrate is recorded in methanol, a shift to δ Ϸ
18 ppm is observed accompanied by a significantly de-
creased line full width at half maximum of 85 Hz. Methanol
is a particular solvent since an adduct formation with the
ester of boric acid can occur.[12] Thus, the electrophilic bo-
ron centre experiences a tetragonal environment which is
clearly supported by the NMR spectroscopic data. Interest-
ingly, only a single species is detected revealing that no ex-
change of the phenolate groups occurs. When recording the
corresponding tetraphenoxyborate in methanol, the protic
Figure 4. Molecular structures of tetraphenoxyborates 10 and 27
determined byX-ray analysis.
and reveals a boron–sodium distance of 8.97 Å, which is
about 3 times longer than for 6b or 10. The boron–oxygen
bond lengths in 27 are comparable with those observed for
6b and 10, whereas the distance between the phenoxy car-
bon atoms increases by 6% (Table 3). The oxygen atoms in
27 are almost equidistant, resulting in a consistent tetrahe-
dral symmetry of the BO4 unit.
Table 3. Selected geometric parameters [Å (shortest), ° (largest)] for
6a, 6b, 10 and 27.
6a
6b
10
27
B–O
1.3570(1)
–
1.4505(1)
2.3422(2)
3.5017(2)
1.4500(1)
2.3469(2)
3.4752(2)
99.052(4)[a]
1.4595(1)
8.1432(5)
3.6991(2)
114.254(4)
O–Na
C1–C1Ј 4.1062(4)
O–B–O 120.454(20) 98.510(4)[a]
102.130(4)[b] 103.291(4)[b]
115.489(5)
114.775(4)
126.102(4)
B–O–C1 122.382(15) 126.445(4)
126.247(4)
[a] Sodium-bridged pair of oxygen atoms. [b] Non-bridged pair of
oxygen atoms.
The geometric data for the described sodium tetraphen- and nucleophilic properties have no significant impact on
oxyborates correspond to earlier reports on complex archi- the NMR spectroscopic data. The chemical shift as well as
tectures of sodium hydrido(phenoxy)borates concerning the line width of the signal correspond to the data collected
oxygen–boron and oxygen–sodium bond lengths as well as for a THF solution. Furthermore, the typical line full width
the angle for the sodium-chelating oxygen–boron–oxygen at half maximum for a tetraphenoxyborate of 20–40 Hz in
cleft at about 100°.[7] In contrast to sodium borates, the THF or MeOH was also observed in acetonitrile (Figure 5,
non-coordinating oxygen atoms in barium-linked dimeric bottom).
Figure 5. 11B NMR studies of trigonal and tetragonal boron species (Ar = 2,4-dimethylphenyl).
Eur. J. Inorg. Chem. 2006, 1690–1697
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FULL PAPER
change of colour. The obtained tetraphenoxyborates exhibit good
stability. However, the microanalyses of most borates show slight
deviations from 0.4% and therefore, HRMS data are given.[13]
Conclusion
A reliable and easy to perform two-step-one-pot se-
quence for the synthesis of tetraphenoxyborates was elabo-
rated. The protocol is applicable to a broad scope of phe-
nols and useful for larger scale as well. Interestingly, the
tetraphenoxyborates exhibit a much higher stability than
the trigonal congeners. Consequently, tetraphenoxyborates
can be handled in methanol, THF and acetonitrile.
Sodium Tetraphenoxyborate (6b): 33.3 g, 82%. 1H NMR (300 MHz,
CD3CN): δ = 6.64–6.70 (m, 4 H, 4-H), 7.06–7.08 (m, 16 H, 2-H,
3-H) ppm. 13C NMR (75 MHz, CD3CN): δ = 119.26 (C-4), 120.14
(C-2), 129.64 (C-3), 158.93 (C-1) ppm. 11B NMR (64 MHz,
CD3CN): δ = 2.79 ppm. HRMS: calcd. for C24H20BO4 383.1453
[M – Na+]–; found 383.1417.
Sodium Tetrakis(4-methylphenoxy)borate (7): 38.8 g, 84%. 1H
NMR (400 MHz, [D8]THF): δ = 2.14 (s, 12 H, CH3), 6.74–6.78 (m,
8 H, 2-H), 6.87–6.91 (m, 8 H, 3-H) ppm. 13C NMR (75 MHz, [D8]-
THF): δ = 20.76 (CH3), 120.62 (C-2), 127.56 (C-4), 129.53 (C-3),
156.62 (C-1) ppm. 11B NMR (64 MHz, CD3CN): δ = 2.34 ppm.
HRMS: calcd. for C28H28BO4 439.2080 [M – Na+]–; found
439.2066.
Furthermore, a novel tetranuclear borate system was
found, consisting of trigonal and tetragonal boron moieties.
The structural comparison of the corresponding tetraphen-
oxyborates and triphenyl esters of boric acid reveals that
the tetragonal arrangement yields in a superb organisation
of the ortho positions in the aryl moieties. Oxidative coup-
ling reactions of these boron-templated phenolates are cur-
rently studied and will be reported in due course.
Sodium Tetrakis(4-tert-butylphenoxy)borate (8): 35.9 g, 57%. 1H
NMR (300 MHz, [D8]THF): δ = 1.22 (s, 36 H, CH3), 6.90–6.93 (m,
8 H, 2-H), 6.99–7.02 (m, 8 H, 3-H) ppm. 13C NMR (75 MHz, [D8]-
THF): δ = 32.16 (CH3), 34.45 [C(CH3)3], 120.27 (C-2), 125.64 (C-
3), 141.07 (C-4), 156.67 (C-1) ppm. 11B NMR (64 MHz, [D8]-
THF): δ = 2.04 ppm. HRMS: calcd. for C40H52BO4 607.3971
[M – Na+]–; found 607.3979.
Experimental Section
General Remarks: All reagents were used in analytical grades. Sol-
vents were desiccated if necessary by standard methods. Micro-
analyses were performed with a Vario EL III (Elementar-Analyse-
Sodium Tetrakis(4-methoxyphenoxy)borate (9): 34.7 g, 66%. 1H
NMR (300 MHz, CD3CN): δ = 3.79 (s, 12 H, OCH3), 6.75–6.78
(m, 8 H, arom. H), 7.07–7.10 (m, 8 H, arom. H) ppm. 13C NMR
(75 MHz, CD3CN): δ = 56.16 (OCH3), 114.92, 120.65 (C-2, C-3),
152.69, 153.33 (C-1, C-4) ppm. 11B NMR (64 MHz, CD3CN): δ =
1
nsysteme, Hanau, D). H and 13C NMR spectra were recorded at
25 °C with a Bruker ARX 300, AM 360 or AMX 400. Chemical
shifts (δ) are reported in parts per million (ppm) relative to traces
of CHCl3, [D7]THF or CD2HCN in the corresponding deuterated
solvents. 11B NMR spectra were recorded at 25 °C with a Bruker
AC 200 by external calibration. Mass spectra were obtained with
a Quattro LC (Waters-Micromass) or Micro TOF (Bruker) by em-
ploying ESI and HRMS (negative mode).
2.30 ppm. MS (ESI): m/z (%)
= 503 (100) [M –
Na+]–.
C28H28BNaO8 (526.2): calcd. C 63.90, H 5.36; found C 63.60, H
5.26.
Sodium Tetrakis(4-fluorophenoxy)borate (10): 5.9 g, 37%. 1H NMR
(300 MHz, CD3CN): δ = 6.77–6.83 (m, 8 H, 2-H), 6.97–7.02 (m, 8
H, 3-H) ppm. 13C NMR (75 MHz, CD3CN): δ = 115.61 [d, 2J(F,C)
= 24.8 Hz, C-3], 120.79 [d, 3J(F,C) = 7.9 Hz, C-2], 155.20 (C-1),
156.85 [d, 1J(F,C) = 247.4 Hz, C-4] ppm. 11B NMR (64 MHz,
CD3CN): δ = 2.66 ppm. HRMS: calcd. for C24H16BF4O4 455.1072
[M – Na+]–; found 455.1103.
Triphenoxyborane (6a): Phenol (9.4 g, 0.10 mol) and boric acid
(2.1 g, 0.03 mol) were suspended in toluene (50 mL) and the reac-
tion mixture was heated for a period of 12 h (Dean–Stark trap).
Toluene was removed under reduced pressure and the crude prod-
uct was purified by distillation to yield a colourless oil, which solid-
ified upon cooling; yield 5.8 g, 67%. B.p. 150 °C, 5·10–6 mbar; m.p.
1
82 °C. H NMR (300 MHz, CDCl3): δ = 6.94–6.99 (m, 3 H, 4-H),
7.00–7.04 (m, 6 H, 2-H), 7.15–7.21 (m, 6 H, 3-H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 120.20 (C-2), 123.50 (C-4), 129.26 (C-3),
152.85 (C-1) ppm. 11B NMR (64 MHz, CDCl3): δ = 15.65 ppm.
MS (EI = 70 eV): m/z (%) = 290.0 (100) [M]+·, 197.0 (44) [M –
C6H5O]+·, 94.0 (75) [C6H5O]+·, 77.0 (81) [C6H5]+·.
Sodium Tetrakis(4-chlorophenoxy)borate (11): 7.4 g, 41%. 1H NMR
(300 MHz, CD3CN): δ = 6.98–7.06 (m, 16 H, 2-H, 3-H) ppm. 13C
NMR (75 MHz, CD3CN): δ = 121.51 (C-2), 123.41 (C-4), 129.38
(C-3), 157.75 (C-1) ppm. 11B NMR (64 MHz, CD3CN): δ =
2.57 ppm. HRMS: calcd. for C24H16BCl4O4 517.9927 [M – Na+]–;
found 517.9906.
General Procedure for the Preparation of Sodium Tetraphenoxybo-
1
rates:
A suspension of the corresponding phenol derivative
Sodium Tetrakis(4-methylthiophenoxy)borate (12): 19.5 g, 99%. H
(0.32 mol) and boric acid (0.10 mol) in toluene (200 mL) was
heated for a period of 12 h (Dean–Stark trap). Toluene was re-
moved under reduced pressure and the excess of phenol was re-
moved by distillation, solid phenols were removed by sublimation.
The crude product was dissolved in THF (40 mL) and added drop-
wise to a solution of the sodium phenolate, which was prepared by
deprotonation of the corresponding phenol (0.09 mol) with 1 equiv.
of sodium (0.09 mol) in THF (70 mL). After stirring for additional
1–12 h, the precipitated product was filtered off and washed sub-
sequently with diethyl ether (40 mL) and pentane (40 mL). The fil-
trate was stored at 4 °C for another 12 h and a second crop was
isolated as described above. Drying under high vacuum provided
the desired products as colourless solids that were stored under
inert conditions at ambient temperature. For 10, 11, 12, 17, 20, 21
and 26 the scale of the protocol was reduced by a factor of three.
All borates decomposed at temperatures above 200 °C under
NMR (400 MHz, CD3CN): δ = 2.05 (s, 12 H, SCH3), 6.64–6.70
(m, 16 H, 2-H, 3-H) ppm. 13C NMR (100 MHz, CD3CN): δ =
18.37 (SCH3), 120.85 (C-2), 126.78 (C-3), 130.66 (C-4), 157.09 (C-
1) ppm. 11B NMR (128 MHz, CD3CN): δ = 4.07 ppm. HRMS:
calcd. for C28H28BO4S4 567.0969 [M – Na+]–; found 567.0955.
1
Sodium Tetrakis(3,4-dimethylphenoxy)borate (13): 43.0 g, 83%. H
NMR (300 MHz, CD3CN): δ = 2.04 (s, 12 H, 4-CH3), 2.07 (s, 12
H, 3-CH3), 6.72–6.76 (m, 8 H, 5-H, 6-H), 6.78 (s, 4 H, 2-H) ppm.
13C NMR (75 MHz, CD3CN): δ = 18.84 (3-CH3), 20.18 (4-CH3),
117.27 (C-6), 121.35 (C-2), 126.54 (C-4), 130.49 (C-5), 137.19 (C-
3), 156.94 (C-1) ppm. 11B NMR (64 MHz, CD3CN): δ = 2.60 ppm.
HRMS: calcd. for C32H36BO4 495.2718 [M – Na+]–; found
495.2720.
Sodium Tetrakis(2-methylphenoxy)borate (14): 29.6 g, 64%. 1H
NMR (400 MHz, [D8]THF): δ = 2.10 (s, 12 H, CH3), 6.51 [dd,
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Facile and Reliable Synthesis of Tetraphenoxyborates and Their Properties
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3
3
3J3,4(H,H) = J4,5(H,H) = 7.4 Hz, 4 H, 4-H], 6.76 [ddd, J4,5(H,H) Sodium Tetrakis(5,6,7,8-tetrahydro-2-naphthoxy)borate (21): 12.9 g,
3
4
1
= 7.4 Hz, J5,6(H,H) = 8.4 Hz, J3,5 = 1.6 Hz, 4 H, 5-H], 6.87 [d,
62%. H NMR (400 MHz, [D8]THF): δ = 1.79 (m, 16 H, 7-H, 6-
3J3,4(H,H) = 7.4 Hz, 4 H, 3-H], 7.19 [d, J5,6(H,H) = 8.4 Hz, 4 H, H), 2.67 (m, 16 H, 8-H, 5-H), 6.54 [d, 4J1,3(H,H) = 1.7 Hz, 4 H, 1-
3
6-H] ppm. 13C NMR (100 MHz, [D8]THF): δ = 17.78 (CH3),
H], 6.75 [dd, J3,4(H,H) = 8.4 Hz, J1,3(H,H) = 1.7 Hz, 4 H, 3-H],
3
4
118.86 (C-4), 120.59 (C-6), 126.38 (C-5), 129.11 (C-2), 130.19 (C- 6.88 [d, 3J3,4(H,H) = 8.4 Hz, 4 H, 4-H] ppm. 13C NMR (100 MHz,
3), 157.55 (C-1) ppm. 11B NMR (64 MHz, CD3CN): δ = 2.92 ppm.
HRMS: calcd. for C28H28BO4 439.2080 [M – Na+]–; found
439.2065.
[D8]THF): δ = 26.68, 29.72 (C-6, C-7), 29.83, 30.76 (C-5, C-8),
118.84 (C-3), 121.26 (C-1), 127.11 (C-4), 129.53 (C-4a), 137.06 (C-
8a), 156.88 (C-2) ppm. 11B NMR (100 MHz, [D8]THF): δ =
3.99 ppm. HRMS: calcd. for C40H44BO4 599.3338 [M – Na+]–;
found 599.3312.
1
Sodium Tetrakis(2,4-dimethylphenoxy)borate (15): 38.9 g, 75%. H
NMR (360 MHz, [D8]THF): δ = 2.03 (s, 12 H, 2-CH3), 2.10 (s, 12
3
4
H, 4-CH3), 6.55 [dd, J5,6(H,H) = 8.3 Hz, J3,5(H,H) = 1.8 Hz, 4
H, 5-H], 6.68 [d, 4J3,5(H,H) = 1.8 Hz, 4 H, 3-H], 6.98 [d, 3J5,6(H,H)
= 8.3 Hz, 4 H, 6-H] ppm. 13C NMR (75 MHz, CD3CN): δ = 17.56
(2-CH3), 20.57 (4-CH3), 119.06 (C-6), 126.49 (C-5), 127.02 (C-2),
127.94 (C-4), 131.05 (C-3), 155.62 (C-1) ppm. 11B NMR (64 MHz,
CD3CN): δ = 3.21 ppm. HRMS: calcd. for C32H36BO4 494.2737
[M – Na+]–; found 494.2785.
Sodium Tetrakis(1,3-benzodioxol-5-yloxy)borate (22): 47.7 g, 82%.
1H NMR (400 MHz, [D8]THF): δ = 5.83 (s, 8 H, OCH2O), 6.48
3
4
[dd, J6,7(H,H) = 8.4 Hz, J4,6(H,H) = 2.2 Hz, 4 H, 6-H], 6.55 [d,
3J6,7(H,H) = 8.4 Hz, 4 H, 7-H], 6.74 [d, J4,6(H,H) = 2.2 Hz, 4 H,
4
4-H] ppm. 13C NMR (100 MHz, [D8]THF): δ = 101.39 (OCH2O),
102.96 (C-4), 107.88 (C-6), 112.00 (C-7), 141.09 (C-7a), 148.50 (C-
3a), 153.88 (C-5) ppm. 11B NMR (128 MHz, [D8]THF): δ =
4.03 ppm. HRMS: calcd. for C28H20BO12 559.1053 [M – Na+]–;
found 559.1033.
Sodium Tetrakis[5-methyl-2-(1-methylethyl)phenoxy]borate (16):
1
3
56.8 g, 90%. H NMR (400 MHz, CD3CN): δ = 1.35 [d, J(H,H)
= 6.9 Hz, 24 H, CH(CH3)2], 2.23 (s, 12 H, 5-CH3), 3.64 [sept,
Sodium Tetrakis(2,4,5-trimethylphenoxy)borate (23): 40.8 g, 71%.
1H NMR (300 MHz, CD3CN): δ = 2.03 (s, 12 H, 5-CH3), 2.04 (s,
12 H, 4-CH3), 2.09 (s, 12 H, 2-CH3), 6.67 (s, 4 H, 3-H), 7.19 (s, 4
H, 6-H) ppm. 13C NMR (75 MHz, CD3CN): δ = 17.22 (2-CH3),
18.94 (4-CH3), 19.99 (5-CH3), 121.08 (C-6), 125.16 (C-4), 124.43
(C-2), 131.72 (C-3), 133.88 (C-5), 155.99 (C-1) ppm. 11B NMR
(64 MHz, CD3CN): δ = 2.85 ppm. HRMS: calcd. for C36H44BO4
551.3344 [M – Na+]–; found 551.3342.
3J(H,H) = 6.9 Hz, 4 H, CH(CH3)2], 6.48 [d, J3,4(H,H) = 7.8 Hz,
3
3
4 H, 4-H], 6.99 [d, J3,4(H,H) = 7.5 Hz, 4 H, 3-H], 7.52 (s, 4 H, 6-
H) ppm. 13C NMR (100 MHz, CD3CN): δ = 21.62 [CH(CH3)2],
23.79 [CH(CH3)2], 27.98 (5-CH3), 118.24 (C-6), 120.22 (C-4),
125.64 (C-3), 135.16 (C-2), 135.55 (C-5), 156.98 (C-1) ppm. 11B
NMR (64 MHz, CD3CN): δ = 3.22 ppm. HRMS: calcd. for
C40H52BO4 607.3971 [M – Na+]–; found 607.3981.
Sodium Tetrakis(2-tert-butyl-4-methylphenoxy)borate (17): 14.4 g,
Sodium Tetrakis(2,3,5-trimethylphenoxy)borate (24): 39.1 g, 68%.
1H NMR (300 MHz, CD3CN): δ = 2.06 (s, 12 H, 5-CH3), 2.07 (s,
12 H, 3-CH3), 2.11 (s, 12 H, 2-CH3), 6.25 (s, 4 H, 6-H), 7.14 (s, 4
H, 4-H) ppm. 13C NMR (75 MHz, CD3CN): δ = 12.54 (2-CH3),
20.63 (3-CH3), 21.59 (5-CH3), 118.11 (C-6), 120.43 (C-4), 123.61
(C-2), 134.67 (C-3), 136.67 (C-5), 157.95 (C-1) ppm. 11B NMR
(64 MHz, CD3CN): δ = 2.99 ppm. HRMS: calcd. for C36H44BO4
551.3344 [M – Na+]–; found 551.3352.
1
63%. H NMR (400 MHz, [D8]THF): δ = 1.58 [s, 36 H, C(CH3)3],
3
4
2.04 (s, 12 H, CH3), 6.40 [dd, J5,6(H,H) = 8.6 Hz, J3,5(H,H) =
4
2.1 Hz, 4 H, 5-H], 6.70 [d, J3,5(H,H) = 2.1 Hz, 4 H, 3-H], 7.64 [d,
3J5,6(H,H) = 8.6 Hz, 4 H, 6-H] ppm. 13C NMR (100 MHz, [D8]-
THF): δ = 21.20 (CH3), 31.47 [C(CH3)3], 35.42 [C(CH3)3], 120.21
(C-6), 123.29 (C-3), 125.98 (C-5), 126.62 (C-4), 136.99 (C-2), 156.04
(C-1) ppm. 11B NMR (128 MHz, [D8]THF): δ = 4.87 ppm. HRMS:
calcd. for C44H60BO4 663.4590 [M – Na+]–; found 663.4571.
Sodium Tetrakis(2-tert-butyl-4,5-dimethylphenoxy)borate (25):
47.5 g, 64%. 1H NMR (400 MHz, [D8]THF): δ = 1.63 [s, 36 H,
C(CH3)3], 1.91 (s, 12 H, 5-CH3), 1.93 (s, 12 H, 4-CH3), 6.63 (s, 4
H, 3-H), 7.61 (s, 4 H, 6-H) ppm. 13C NMR (100 MHz, [D8]THF):
δ = 19.08 (5-CH3), 19.33 (4-CH3), 31.80 [C(CH3)3], 35.24 [C-
(CH3)3], 121.70 (C-6), 121.76 (C-5), 126.70 (C-3), 132.81 (C-4),
134.81 (C-2), 156.17 (C-1) ppm. 11B NMR (64 MHz, [D8]THF): δ
= 2.75 ppm. HRMS: calcd. for C48H68BO4 719.5205 [M – Na+]–;
found 719.5225.
Sodium Tetrakis(3,5-di-tert-butylphenoxy)borate (18): 31.6 g, 37%.
1H NMR (300 MHz, CD3CN): δ = 1.21 [s, 72 H, C(CH3)3], 6.71
4
4
[d, J2,4(H,H) = 1.5 Hz, 4 H, 4-H], 6.98 [d, J2,4(H,H) = 1.5 Hz, 8
H, 2-H] ppm. 13C NMR (75 MHz, CD3CN): δ = 32.13 [C(CH3)3],
35.47 [C(CH3)3], 112.63 (C-2), 114.86 (C-4), 151.49 (C-3), 159.14
(C-1) ppm. 11B NMR (64 MHz, CD3CN): δ = 2.75 ppm. HRMS:
calcd. for C56H84BO4 831.6468 [M – Na+]–; found 831.6431.
Sodium Tetrakis(2-tert-butyl-4-methoxyphenoxy)borate (19): 42.8 g,
1
57%. H NMR (400 MHz, CD3CN): δ = 1.57 [s, 36 H, C(CH3)3],
3
4
Sodium Tetrakis[4-chloro-5-methyl-2-(1-methylethyl)phenoxy]borate
(26): 23.8 g, 93%. 1H NMR (300 MHz, [D8]THF): δ = 1.18 [d,
3J(H,H) = 6.9 Hz, 24 H, CH(CH3)2], 2.09 (s, 12 H, 5-CH3), 3.47
3.56 (s, 12 H, OCH3), 6.29 [dd, J5,6(H,H) = 8.8 Hz, J3,5(H,H) =
4
2.6 Hz, 4 H, 5-H], 6.64 [d, J3,5(H,H) = 2.6 Hz, 4 H, 3-H], 7.64 [d,
3J5,6(H,H) = 8.8 Hz, 4 H, 6-H] ppm. 13C NMR (100 MHz,
CD3CN): δ = 31.15 [C(CH3)3], 35.91 (OCH3), 56.45 [C(CH3)3],
110.77 (C-5), 113.98 (C-6), 120.18 (C-3), 139.29 (C-2), 151.73 (C-1),
152.34 (C-4) ppm. 11B NMR (128 MHz, CD3CN): δ = 2.99 ppm.
HRMS: calcd. for C44H60BO8 727.4387 [M – Na+]–; found
727.4364.
3
[sept, J(H,H) = 6.9 Hz, 4 H, CH(CH3)2], 6.80 (s, 4 H, 3-H), 7.42
(s, 4 H, 6-H) ppm. 13C NMR (75 MHz, [D8]THF): δ = 20.00 (5-
CH3), 22.93 [CH(CH3)2], 28.09 [CH(CH3)2], 121.76 (C-6), 121.82
(C-4), 125.58 (C-3), 132.05 (C-2), 137.62 (C-5), 155.53 (C-1) ppm.
11B NMR (64 MHz, [D8]THF): δ = 2.54 ppm. HRMS: calcd. for
C40H48BCl4O4 743.2405 [M – Na+]–; found 743.2378.
Sodium Tetrakis(2-bromo-4-methylphenoxy)borate (20): 11.1 g,
43%. 1H NMR (400 MHz, [D8]THF): δ = 2.12 (s, 12 H, CH3), 6.78
Sodium Tetrakis(1-naphthoxy)borate (27): Boric acid (0.62 g,
3
4
[dd, J5,6(H,H) = 8.4 Hz, J3,5(H,H) = 1.7 Hz, 4 H, 5-H], 7.13 [d,
0.01 mol) was added to a solution of 1-naphthol (4.61 g, 0.032 mol)
4J3,5(H,H) = 1.7 Hz, 4 H, 3-H], 7.46 [d, J5,6(H,H) = 8.4 Hz, 4 H, in toluene (40 mL) and the reaction mixture was heated for 12 h
3
6-H] ppm. 13C NMR (100 MHz, [D8]THF): δ = 20.26 (CH3),
114.29 (C-2), 120.95(C-6), 129.29 (C-5), 129.82 (C-4), 132.96 (C-3),
152.24 (C-1) ppm. 11B NMR (128 MHz, [D8]THF): δ = 2.12 ppm.
(Dean–Stark trap). Toluene was removed under reduced pressure
and the crude product was dissolved in THF (15 mL). First, 1-
naphthol (1.33 g, 0.9 mol) and then sodium hydride (0.37 g, 60%
HRMS: calcd. for C28H24BBr4O4 750.8507 [M – Na+]–; found suspension in paraffin, 0.9 mol) was added to the solution at 0 °C.
750.8503.
After completion of the reaction, the solution was stored at 4 °C
Eur. J. Inorg. Chem. 2006, 1690–1697
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1695

I. M. Malkowsky, R. Fröhlich, U. Griesbach, H. Pütter, S. R. Waldvogel
FULL PAPER
for 12 h. The precipitated product was isolated by filtration and
subsequent washing with diethyl ether (5 mL) and pentane (5 mL);
yield: 3.4 g, 57%. 1H NMR (400 MHz, CD3CN): δ = 7.13–7.18 (m,
8 H, 7-H and 8-H), 7.36–7.41 (m, 8 H, 4-H and 5-H), 7.67–7.72
(m, 8 H, 2-H and 6-H), 8.55–8.57 (m, 4 H, 3-H) ppm. 13C NMR
(100 MHz, CD3CN): δ = 112.28 (C-2), 117.60 (C-8), 124.58 (C-3),
124.74 (C-5), 126.30 (C-4), 127.74 (C-7 and C-8a), 128.14 (C-6),
135.92 (C-4a), 155.63 (C-1) ppm. 11B NMR (64 MHz, CD3CN): δ
= 4.05 ppm. HRMS: calcd. for C40H28BO4 583.2086 [M – Na+]–;
found 583.2090.
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
X-ray Crystal Structure Analysis for 27: C60H68BNaO9 (966.94),
colourless crystal 0.30 × 0.25 × 0.15 mm, a = 17.904(1), b =
17.710(1), c = 16.789(1) Å, β = 91.69(1)°, V = 5321.1(5) Å3, ρcalcd.
= 1.207 g cm–3, µ = 0.703 mm–1, empirical absorption correction
(0.817 Յ T Յ 0.902), Z = 4, monoclinic, space group C2/c (no. 15),
λ = 1.54178 Å, T = 223 K, ω and φ scans, 16055 reflections col-
lected ( h, k, l), [(sinθ)/λ] = 0.59 Å–1, 4362 independent (Rint
=
Tris(2,4,6-trimethylphenoxy)borane (30): 2,4,6-Trimethylphenol (29)
(15 g, 0.11 mol) and boric acid (2.1 g, 0.03 mol) were suspended in
toluene (100 mL) and the reaction mixture was heated for a period
of 24 h (Dean–Stark trap). Toluene was distilled off under reduced
pressure and excess of 29 was removed by sublimation. The crude
product was purified by crystallisation in toluene to yield a colour-
less solid; yield 9.1 g, 64%; m.p. 245 °C (toluene). 1H NMR
(300 MHz, CDCl3): δ = 2.20 (s, 9 H, 4-CH3), 2.28 (s, 18 H, 2-CH3
and 6-CH3), 6.80 (s, 6 H, 3-H and 5-H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 16.95 (2-CH3 and 6-CH3), 20.59 (4-CH3), 127.71 (C-
2 and C-6), 129.15 (C-3 and C-5), 132.45 (C-4), 148.26 (C-1) ppm.
11B NMR (64 MHz, CDCl3): δ = 15.89. MS (EI = 70 eV): m/z (%)
= 416.2 (100) [M]+·, 281.2 (12) [M – (CH3)3C6H2O]+·.
0.034) and 2748 observed reflections [I Ն 2σ(I)], 323 refined param-
eters, R = 0.075, wR2 = 0.258, max. residual electron density 0.56
(–0.28) e·Å–3, the THF solvent molecules are heavily disordered,
refinement with split positions did not improve the model, hydro-
gen atoms calculated and refined as riding atoms.
X-ray Crystal Structure Analysis for 28: C87H111B4Na3O27
(1700.97), colourless crystal 0.40 × 0.30 × 0.30 mm, a = 14.658(1),
b = 16.913(1), c = 19.312(1) Å, α = 85.15(1), β = 87.80(1), γ =
70.01(1)°, V = 4482.9(5) Å3, ρcalcd. = 1.260 g cm–3, µ = 0.878 mm–1,
empirical absorption correction (0.720 Յ T Յ 0.779), Z = 2, tri-
¯
clinic, space group P1 (no. 2), λ = 1.54178 Å, T = 223 K, ω and φ
scans, 17206 reflections collected ( h, k, l), [(sinθ)/λ] = 0.59 Å–1,
14334 independent (Rint = 0.040) and 10777 observed reflections [I
Ն 2σ(I)], 1156 refined parameters, R = 0.055, wR2 = 0.164, max.
residual electron density 0.33 (–0.25) e· Å–3, C67 and THF mole-
cule O211–C215 disordered and refined with split positions, hydro-
gen atoms calculated and refined as riding atoms.
X-ray Crystal Structure Analysis for 6a: C18H15BO3 (290.11),
colourless crystal 0.30 × 0.25 × 0.15 mm, a = 11.650(1), b =
15.897(2), c = 19.724(2) Å, α = 113.31(1), β = 106.59(1), γ =
90.19(1)°, V = 3186.9(6) Å3, ρcalcd. = 1.209 g cm–3, µ = 0.648 mm–1,
empirical absorption correction based on ψ scan data (0.829 Յ T
¯
Յ 0.909), Z = 8, triclinic, space group P1 (no. 2), λ = 1.54178 Å,
Acknowledgments
T = 223 K, ω/2θ scans, 13476 reflections collected ( h, +k, l),
[(sinθ)/λ] = 0.62 Å–1, 12986 independent (Rint = 0.043) and 8143
observed reflections [I Ն 2σ(I)], 794 refined parameters, R = 0.049,
wR2 = 0.143, max. residual electron density 0.23 (–0.27) e·Å–3, four
almost identical independent molecules in the asymmetric unit, hy-
drogen atoms calculated and refined as riding atoms.
Financial support by the BASF AG and the International Gradu-
ate College “Template-Directed Chemical Synthesis” (DFG) is
highly appreciated.
[1] A. Ricardo, M. A. Carrigan, A. N. Olcott, S. A. Benner, Sci-
ence 2004, 303, 196 and literature cited therein.
[2] M. F. Semmelhack, S. R. Campagna, C. Hwa, M. J. Federle,
B. L. Bassler, Org. Lett. 2004, 6, 2635–2637 and literature cited
therein; M. Berger, J. Mulzer, J. Am. Chem. Soc. 1999, 121,
8393–8394.
[3] W. Funakoshi, K. Sasaki, M. Abe, Japan Patent No. 07207017,
1995.
[4] S. Yoshimura, T. Noma, I. Yonetsu, Japan Patent No.
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[5] D. Vagedes, R. Fröhlich, G. Erker, Angew. Chem. 1999, 111,
3561–3565; Angew. Chem. Int. Ed. 1999, 38, 3362–3365.
[6] F. A. R. Kaul, G. T. Puchta, H. Schneider, M. Grosche, D. Mi-
halios, W. A. Herrmann, J. Organomet. Chem. 2001, 621, 184–
189.
[7] M. Bishop, S. G. Bott, A. R. Barron, J. Chem. Soc., Dalton
Trans. 2000, 3100–3105.
X-ray Crystal Structure Analysis for 6b: C36H44BNaO7 (622.51),
colourless crystal 0.70 × 0.50 × 0.30 mm, a = 18.299(1), b =
9.803(1), c = 19.287(1) Å, β = 100.09(1)°, V = 3406.3(4) Å3, ρcalcd.
= 1.214 g cm–3, µ = 0.772 mm–1, empirical absorption correction
(0.614 Յ T Յ 0.801), Z = 4, monoclinic, space group P21/c (no.
14), λ = 1.54178 Å, T = 223 K, ω and φ scans, 25313 reflections
collected ( h, k, l), [(sinθ)/λ] = 0.59 Å–1, 5816 independent (Rint
= 0.055) and 4546 observed reflections [I Ն 2σ(I)], 481 refined pa-
rameters, R = 0.051, wR2 = 0.153, max. residual electron density
0.30 (–0.27) e·Å–3, two of the three THF solvent molecules are
disordered and refined with split positions, hydrogen atoms calcu-
lated and refined as riding atoms.
X-ray Crystal Structure Analysis for 10: C36H40BF4NaO7 (694.48),
colourless crystal 0.60 × 0.60 × 0.45 mm, a = 12.955(1), b =
17.126(1), c = 16.242(1) Å, β = 99.17(1)°, V = 3557.5(4) Å3, ρcalcd.
= 1.297 g cm–3, µ = 0.963 mm–1, empirical absorption correction
(0.596 Յ T Յ 0.671), Z = 4, monoclinic, space group P21/n (no.
14), λ = 1.54178 Å, T = 223 K, ω and φ scans, 10815 reflections
collected ( h, k, l), [(sinθ)/λ] = 0.59 Å–1, 6038 independent (Rint
= 0.026) and 4264 observed reflections [I Ն 2σ(I)], 443 refined pa-
rameters, R = 0.053, wR2 = 0.163, max. residual electron density
0.38 (–0.32) e· Å–3, the THF solvent molecules are partly disor-
dered, refinement with split positions did not improve the model,
hydrogen atoms calculated and refined as riding atoms.
[8] K. G. Caulton, M. H. Chisholm, S. R. Drake, K. Folting, J. C.
Huffman, W. Streib, Inorg. Chem. 1993, 32, 1970–1976.
[9] R. J. Errington, M. Tombul, G. L. P. Walker, W. Clegg, S. L.
Heath, L. Horsburgh, J. Chem. Soc., Dalton Trans. 1999, 3533–
3534.
[10] Maldi-TOF analysis of the crude product. 11B NMR studies
turned out to be less useful since the equilibration is fast on
the NMR timescale and the particular shifts are very similar.
[11] For longer times and storage purposes, an anhydrous environ-
ment is recommended to avoid hydrolysis.
[12] H. I. Schlesinger, H. C. Brown, D. L. Mayfield, J. R. Gilbreath,
J. Am. Chem. Soc. 1953, 75, 213–215.
[13] NMR spectroscopic data gave no indication of impurities such
as remaining solvent molecules or other borate species. Since
X-ray Crystallography Study: Data sets were collected with Enraf
Nonius CAD4 and Nonius KappaCCD diffractometers. For the
programs used see ref.[14] CCDC-285239 to -285243 contain the
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 1690–1697

Facile and Reliable Synthesis of Tetraphenoxyborates and Their Properties
FULL PAPER
these compounds are considered to be very moisture-sensitive
no elemental analyses can be given (compare: T. Alaviuhkola,
J. Bobacka, M. Nissinen, K. Rissanen, A. Ivaska, J. Pursiainen,
Chem. Eur. J. 2005, 11, 2071–2080).
tallogr. 1997, 30, 421–426) and Denzo (Z. Otwinowski, D.
Borek, W. Majewski, W. Minor, Acta Crystallogr., Sect. A 2003,
59, 228–234), structure solution SHELXS-97 (G. M. Sheldrick,
Acta Crystallogr., Sect. A 1990, 46, 467–473), structure refine-
ment SHELXL-97 (G. M. Sheldrick, University of Göttingen,
1997), graphics DIAMOND 3.0d (Crystal Impact GbR, Bonn,
Germany).
[14] Data collection EXPRESS (Nonius B.V., 1994) and COL-
LECT (Nonius B.V., 1998), data reduction MolEN (K. Fair,
Enraf–Nonius B.V., 1990) and Denzo-SMN (Z. Otwinowski,
W. Minor, Methods Enzymol. 1997, 276, 307–326), absorption
correction for CCD data SORTAV (R. H. Blessing, Acta Crys-
tallogr., Sect. A 1995, 51, 33–37; R. H. Blessing, J. Appl. Crys-
Received: January 24, 2006
Published Online: February 28, 2006
Eur. J. Inorg. Chem. 2006, 1690–1697
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1697