Unusual interaction of alkynes with nine-vertex arachno-monocarbaboranes 4-CB8H14 and [4-CB8H13]-

Article abstract of DOI:10.1039/b613237e

Alkynes R¹R²C₂ react with the neutral monocarbaborane arachno-4-CB₈H₁₄ (1) at elevated temperatures (115-120 °C) under the formation of the derivatives of the ten-vertex dicarbaborane nido-5,6-C₂B₈H₁₂ (2) of general formula 9-Me-5,6-R¹,R²-nido-5,6-C ₂B₈H₉ (where R¹,R² = H,H 2a; Me,Me 2b; Et,Et 2c, H,Ph 2d, and Ph,Ph 2e) in moderate yields (26-52%). Side reaction with PhC₂H also yields 1-Ph-6-Me-closo-1,2-C ₂B₈H₈ (3d). In contrast, the reaction between [arachno-4-CB₈H₁₃]^- anion (1^-) and PhC₂H produces a mixture of the closo anions [1-CB₇H ₈]^- (4^-) and [1-CB₆H ₇]^- (5^-) (yields 32 and 24%, respectively). Individual compounds were isolated and purified by liquid chromatography and characterized by NMR spectroscopy (¹¹B, ¹H and ¹³C) combined with two-dimensional [¹¹B- ¹¹B]-COSY and ¹H-{¹¹B(selective)}NMR techniques. The Royal Society of Chemistry 2007.

Full text of DOI:10.1039/b613237e

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
Unusual interaction of alkynes with nine-vertex arachno-monocarbaboranes
4-CB8H14 and [4-CB8H13]−
ˇ
Bohumil St´ıbr,* Josef Holub, Mario Bakardjiev and Zbyneˇk Janousˇek
Received 12th September 2006, Accepted 8th December 2006
First published as an Advance Article on the web 3rd January 2007
DOI: 10.1039/b613237e
Alkynes R1R2C2 react with the neutral monocarbaborane arachno-4-CB8H14 (1) at elevated
temperatures (115–120 ◦C) under the formation of the derivatives of the ten-vertex dicarbaborane
nido-5,6-C2B8H12 (2) of general formula 9-Me-5,6-R1,R2-nido-5,6-C2B8H9 (where R1,R2 = H,H 2a;
Me,Me 2b; Et,Et 2c, H,Ph 2d, and Ph,Ph 2e) in moderate yields (26–52%). Side reaction with PhC2H
also yields 1-Ph-6-Me-closo-1,2-C2B8H8 (3d). In contrast, the reaction between [arachno-4-CB8H13]−
anion (1−) and PhC2H produces a mixture of the closo anions [1-CB7H8]− (4−) and [1-CB6H7]− (5−)
(yields 32 and 24%, respectively). Individual compounds were isolated and purified by liquid
chromatography and characterized by NMR spectroscopy (11B, 1H and 13C) combined with
11
two-dimensional [11B–11B]–COSY and 1H–{ B(selective)}NMR techniques.
Introduction
The nine-vertex monocarbaborane arachno-4-CB8H14 (1), was
prepared for the first time in 1976 via oxidative degradation of
the [nido-6-CB9H12]− anion.1 Improved synthesis is based on the
reaction between [nido-7,9-C2B10H13]− and Me2S in the presence
of concentrated hydrochloric acid.2 The most convenient route to
carborane 1 is, however, the acidic oxidation of the [arachno-6-
CB9H14]− anion.3,4 Kennedy et al. reported the preparation of the
Scheme 1 Formation of the 9-Me-5,6-R1,R2-nido-5,6-C2B8H9 derivatives
and 1-Ph-6-Me-closo-1,2-C2B8H8 (3d) from 4-CB8H14 (1) via alkyne
C-phenyl derivative, 4-Ph-4-CB8H13.5 Deprotonation of 11,6 leads
to anions [arachno-4-CB8H13]− (1−) and [arachno-4-CB8H12]2−,
and treatment with Et3N generates the [closo-1-CB7H8]− anion.4
Dehydrogenation of 1 at elevated temperatures produces a useful
carborane nido-1-CB8H12,1 which was employed for the synthesis
of the closo anions [1-CB8H9]− and [2-CB6H7]−.3,7 In this work
we would like to extend the non-metallic chemistry of 1 and
1− by reactions with selected alkynes that, instead of expected
formation of tricarbaboranes, lead to derivatives of the ten-vertex
dicarbaborane nido-5,6-C2B8H128 and to removal of boron vertices,
respectively.
insertion and dehydrogenation.
The reactions are carried out in refluxing toluene or by heating
in hexane at 120 ◦C using a stainless steel vessel and the products
were isolated by liquid chromatography in hexane.
Although no detailed mechanistic studies have been done, the
reactions are in agreement with the dicarbon insertion pathway
shown in Scheme 2 (extra hydrogen atoms omitted for clarity).
According to this scheme, both alkyne carbons are inserted into
the area identified by B-vertices 5,6,7, and 8 in the cage of 1, while
the C4 vertex is expelled into the exoskeletal site, forming thus a
Me substituent at position B9 (numbering as in 1). This process is
evidently associated with interruption of the original C4–B1 and
C4–B5 connectivities. One of the alkyne carbons (at R1) becomes
three-coordinate (C6 in compound 2 formed) and that at R2 forms
the tetra-coordinate C5 vertex in 2. It should be noted that a
similar removal of the cluster carbon atom, called de-insertion,
was observed recently in the [nido-C2B10H13]− → [closo-CB9H10]−
Results and discussion
Syntheses
Treatment of the neutral monocarbaborane arachno-4-CB8H14 (1)
with alkynes R1R2C2 at elevated temperatures (115–120 ◦C) did
9
not yield the expected eleven-vertex tricarbaboranes C3B8H12
but the main reaction mode was the formation of the ten-vertex
dicarbaboranes 9-Me-5,6-R1,R2-nido-5,6-C2B8H9 (where R1,R2 =
H,H 2a; Me,Me 2b; Et,Et 2c, H,Ph 2d, and Ph,Ph 2e) in moderate
yields (26–52%, see Scheme 1). The process is thus consistent with
the stoichiometry as in eqn (1):
R1R2C2 + 4-CB8H14 → 9-CH3-5,6-R1,R2-5,6-C2B8H9 + H2 (1)
Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic,
250 68, Rezˇ, Czech Republic. E-mail: stibr@iiccas.cz; Fax: +420 220940157;
Tel: +420 266173106
Scheme 2 Proposed mechanism of the alkyne insertion.
Dalton Trans., 2007, 581–584 | 581
This journal is
The Royal Society of Chemistry 2007
©

View Article Online
conversion.10a The reaction with PhC2H is highly regiospecific,
giving only 5-Ph-9-Me-nido-5,6-C2B8H10 (2d). It should also be
noted that, in this case, the formation of 2d is accompanied by
its dehydrogenation to 1-Ph-6-Me-closo-1,2-C2B8H8 (3d). Partial
dehydrogenation of 2e to 1,2-Ph2-6-Me-closo-1,2-C2B8H7 (3e) at
the reaction temperature was also observed in the reaction with
Ph2C2, but the product could not be isolated in pure state from the
mixture of other trace components.
Also the reaction between [arachno-4-CB8H13]− anion (1−)
and PhC2H in THF at reflux did not produce tricarbaboranes.
Instead of these, a mixture of the closo anions [1-CB7H8]−
(4−) and [1-CB6H7]− (5−) (yields 32 and 24%, respectively) was
isolated. Both anions were separated as their PPh4+ salts by liquid
chromatography in CH2Cl2 and identified by NMR spectroscopy
as reported earlier.4,7 It seems highly probable that the reaction
is based on removal of one (B6) or two (B6,8) boron vertices via
hydroboration, followed by closure of the rest of the cage (see
Scheme 3 and eqn (2) and (3)):
Fig. 1 Stick representation of the 11B NMR spectra of compounds 2a–2e.
[4-CB8H13]− + PhC2H → [1-CB7H8]−
=
+ PhCH CH–BH2 + H2
(2)
−
−
=
[4-CB8H13] + 2 PhC2H → [1-CB6H7] + 2 PhCH CH–BH2 (3)
Fig. 2 Stick representation of the 13C NMR spectra of compounds 2a–2e.
remarkable combined a + b effects at the substituted carbon sites
Scheme 3 Formation of anions [1-CB7H8]− (4−) and [1-CB6H7]− (5−) from
[4-CB8H13]− (1−).
with shieldings decreasing in the order H > Ph > Me > Et. The 13
C
NMR spectroscopy
NMR spectrum of the closo compound 3d exhibits two distinct C1
and C2 resonances (62.4 and 54.9 ppm) along with typical 1-Ph
(range 133.5–128.8 ppm) and 6-Me (30.5 ppm) resonances of these
exosleletal substituents.
Graphical intercomparison of the11B NMR shifts (see Fig. 1)
shows that the positions of the B9 singlet and the B4 doublet
are remarkably affected by combined antipodal (A) and c effects
from the organic substituents on the C6 and C5 vertices. Most
remarkably affected by the vicinal (b) C-substitution are the B2-
shifts, followed by vicinal B7, B10, and B1 shifts. The 11B NMR
spectrum of the closo compound 3d exhibits seven different doublet
resonances and one B6 singlet due to Me-substitution. The four
high-field doublets assigned to B5,6,7 and 9 coincidentally overlap.
Graphical interrelations of the 13C NMR properties (see Fig. 2)
of derivatives of type 2 shows that, besides signals attributed to the
organic C-substituents, the spectra consist of downfield resonances
of the cage C6 atoms (range 158–128 ppm), intermediate-field
C5-resonances (range 89–65 ppm), and little varying high-field
resonances of the exoskeletal 9-Me group (range −1.4 to −3.5
ppm). It is readily seen that the organic C-substituents exert
1
The H NMR spectrum of compound 2a exhibits two typical
low-field singlet resonances of the cage CH6 and CH5 units, while
that of 2d shows only one CH6 singlet due to 5-Ph substitution.
The spectra of all compounds of type 2 show a typical resonance
of intensity 3 due to the 9-Me subsitution (range 0.62–0.78 ppm)
along with two different, broad high-field resonances of the l-
9,10 (range −1.03 to −1.90) and l-8,9 (range −1.61 to −2.22)
1
11
hydrogen bridges. Beside these resonances, the H–{ B} NMR
spectra reveal seven singlet signals due to unsubstituted BH units.
1
The H NMR spectrum of the closo compound 3d exhibits one
distinct H2 resonance (3.19 ppm) along with typical 1-Ph (7.83 and
7.57 ppm) and 6-Me (0.24 ppm) resonances due to the exoskeletal
substituent.
582 | Dalton Trans., 2007, 581–584
This journal is
The Royal Society of Chemistry 2007
©

View Article Online
being defined as in as in ref. 14. Solvent resonances were used
as internal secondary standards. NMR data for all compounds
isolated are listed in Table 1.
Experimental
General
All reactions were carried out with use of standard vacuum or
inert-atmosphere techniques as described by Shriver,10b although
some operations, such as column LC, were carried out in air. The
starting carborane 1 was prepared according to the literature.4
Fluka dichloromethane and hexane were dried over CaH2 and
freshly distilled before use. Other chemicals were of reagent or
analytical grade and were used as purchased. Column chromatog-
raphy was carried out using silica gel (Aldrich, 130–270 mesh) as
the stationary phase. The purity of individual chromatographic
fractions was checked by analytical TLC on Silufol (silica gel on
aluminium foil; detection by I2 vapour, followed by 2% aqueous
AgNO3 spray). Low-resolution mass spectra were obtained using a
Finnigan MAT Magnum ion-trap quadrupole mass spectrometer
equipped with a heated inlet option, as developed by Spectronex
AG, Basel, Switzerland (70 eV, EI ionisation). 1H and 11B, NMR
spectroscopy was performed at 9.4 T on a Varian Mercury
Synthesis of 9-CH3-5,6-R1,R2-nido-5,6-C2B8H9 (2) compounds
(where R1,R2 = H,H 2a; Me,Me 2b; Et,Et 2c, H,Ph 2d, and Ph,Ph
2e)
A solution of alkynes R1R2C2 (6 mmol, excess) and compound
1 (225 mg, 2 mmol) in hexane (20 ml) was heated in a 100 ml-
stainless steel vessel at 120 ◦C for 2 h. In the case of acetylene the
reaction was carried out by bubbling through the solution of 1 in
toluene (20 ml) for 2 h at reflux. After cooling to room temperature,
the solvents were evaporated and the desired compounds of type
2 were isolated by liquid chromatography on silica gel, using
hexane as a mobile phase. Yields, Rf values, and other properties
of compounds 2 isolated in this manner are in Table 2.
Alternative synthesis of closo anions [1-CB7H8]− (4−) and
[2-CB6H7]− (5−)
1
11
12
400 instrument. The [11B–11B]–COSY11 and H–{ B(selective)}
NMR experiments were made essentially as described earlier.13
Chemical shifts are given in ppm to high-frequency (low field)
of N = 32.083971 MHz (nominally F3B.OEt2 in CDCl3) for 11B
(quoted 0.5 ppm), N = 25.144 MHz (SiMe4) for 13C (quoted 0.5
ppm), and N = 100 MHz (SiMe4) for 1H (quoted 0.05 ppm), N
A solution of compound 1 (171 mg, 1.52 mmol) in THF (30 ml)
was treated with NaH (100 mg, 4.16 mmol) under stirring for
ca. 2 h until the hydrogen evolution ceased. The mixture was
filtered and the filtrate treated with phenylacetylene (932 mg,
9.12 mmol) and then heated at reflux for 120 h. After cooling
Table 1 NMR data
Compound
Nucleus
Chemical. shifts
1
a
5,6-C2B8H12 (2)
13C{ H}
137.5 (q, JCB = 55 Hz, C6), 69.5 (s, C5)
9-Me-5,6-C2B8H11 (2a)
11Ba,b
9.6 (s, −, B9), 6.5 (d, 149, B7), 4.5 (d, 159, B1), 1.1 (d, 155, B8), −4.6 (d, 144, B3), −11.4 (d,
152/43, B10), −31.0 (d, 177, B2), −36.4 (d, 152, B4), all [11B–11B]–COSY cross-peaks observed
6.37 (s, H6), 4.91 (s, H5), 3.50 (s, 2H,H1,7), 2.96 (s, H8), 2.87 (s, H3), 2.48 (s, H10), 0.91 (s, H4),
0.86 (s, H2), 0.67 (s, 3H,9-Me), −1.69 (s, l-H9,10), −1.99 (s, l-H8,9)
128.5 (br. s, C6), 64.7 (s, C5), −3.5 (s, 9-Me)
11
a,c
1H{ B}
1
a,c
13C{ H}
5,6-Me2-9-Me-5,6-C2B8H9 (2b)
5,6-Et2-9-Me-5,6-C2B8H9 (2c)
5-Ph-9-Me-5,6-C2B8H10 (2d)
11Ba,b
7.5 (s, −, B9), 4.4 (d, ca. 160, B1), 3.2 (d, ca. 150, B7), −0.9 (d, 150, B8), −5.0 (d, ca. 150, B3),
−6.6 (d, ca. 160/37, B10), −24.0 (d, 174, B2), −37.4 (d, 149, B4), all [11B–11B]-COSY
cross-peaks observed
11
a,c
1H{ B}
3.39 (s, H1), 3.23 (s, H7), 2.71 (s, H8), 2.63 (s, H3), 2.42 (s, H10), 2.15, 2.08 (s, 3H, 5- and
6-Me), 0.80 (s, H2), 0.70 (s, H4), 0.62 (s, 3H, 9-Me), −1.78 (s, lH8,9), −2.21 (s, lH9,10)
152.0 (br. s, C6), 84.0 (s, C5), 23.0, 21.7 (5- and 6-Me) −2.5 (s, 9-Me)
6.6 (s, −, B9), 2.2 (d, 144, B1), 1.3 (d, 131, B7), −1.2 (d, 149, B8), −6.0 (d, 144, B3), −8.5 (d,
149/27, B10), −26.6(d, 177, B2), −38.6 (d, 150, B4), all [11B–11B]-COSY cross-peaks observed
3.36 (s, H1), 3.26 (s, H7), 2.76 (s, H8), 2.62 (s, H3), 2.57 (s, H10), 2.50, 2.38 (s, 2H, 5- and 6-Et),
1.20, 1.13 (s, 3H, 5- and 6-Et), 0.81 (s, H2), 0.70 (s, H4), 0.62 (s, 3H, 9-Me), −1.90 (s, l-H9,10),
−2.22 (s, l-H8,9)
1
a
13C{ H}
11Ba,b
11
a,c
1H{ B}
1
a
13C{ H}
158.0 (br. s, C6), 89.3 (s, C5), 28.5, 28.2 (5- and 6-Et), 14.2, 13.9 (5- and 6-Et) −2.1 (s, 9-Me)
10.7 (s, −, B9), 4.6 (d, ca. 150, B7), 3,7 (d, ca. 150, B1), −0.3 (d, 146, B8), −3.2 (d, 147, B3),
−6.8 (d, 155, B10), −28.3 (d, 177, B2), −36.8 (d, 153, B4), all [11B–11B]–COSY cross-peaks
observed
11Ba,b
11
a,c
1H{ B}
7.60–7.39 (m, 5H, Ph), 6.66 (s, H6), 3.90 (s, H1), 3.59 (s, H7), 2.99 (s, 2H, H3,8), 2.67 (s, H10),
1.03 (s, 2H, H2,4), 0.71 (s, 3H, 9-Me), −1.16 (s, l-H9,10), −1.82 (s, l-H8,9)
133.6 (br. s, C6), 132.0 − 127 (m, 6C, Ph), 92.7 (s, C5), −1.8 (s, 9-Me)
32.0 (d, 168, B10), −7.3 (d, 144, B4), −9.3 (s, −, B6), −17.3 (d, 177, B3), −24.7 (d, 4B, 177,
B5,7 and 6,9), all [11B–11B]–COSY cross-peaks observed except for B6–B10
7.83 (s, 3H, Ph), 7.57 (s, 2H, Ph), 5.92 (s, H10), 3.19 (s, H2), 2.87 (s, H4), 2.51 (s, H3), 1.26,
1.21, 1.16 (s, 2H, 1H, 1H, H5,6,7, 9), 0.24 (s, 3H, 6-Me)
1
a
13C{ H}
1-Ph-6-Me-5,6-C2B8H10 (3d)
5,6-Ph2-9-Me-5,6-C2B8H9 (2e)
11Ba,b
11
a,c
1H{ B}
1
a
13C{ H}
133.5–128.8 (m, 5-Ph), 62.4 (s, C1), 54.9 (s, C2), 30.5 (s, 6-Me)
11Ba,b
8.6 (s, −, B9), 3.6 (d, 2B, ca. 150, B1,7), 0.2 (d, 133, B8), −5.0 (d, 153, B3), −6.6 (d, ca. 155,
B10), −20.3 (d, 177, B2), −36.6 (d, 152, B4), all [11B–11B]–COSY cross-peaks observed
7.58–6.82 (m, 10H, Ph), 3.71 (s, H1), 3.50 (s, H7), 2.81 (s, H10), 1.72 (s, H2), 1.04 (s, H4), 0.78
(s, 3H, 9-Me), −1.03 (s, l-H9,10), −1.61 (s, l-H8,9)
11
a,c
1H{ B}
1
a
13C{ H}
153.7 (br. s, C6), 139.6–126.9 (m, 12C, Ph), 91.6 (s, C5), −1.4 (s, 9-Me)
a In CDCl3. b d(11B) (multiplicity, 1JBH in Hz, assignment). c d(1H and 13C) (multiplicity, assignment).
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 581–584 | 583
©

View Article Online
Table 2 Characteristics of products of reactions between alkynes R1R2C2 and arachno-4-CB8H14 (1) at 115–120 ◦
C
Alkyne
Product(s)
Yield (%)
Rfa
mp/◦C
m/z (found)b
Calcdc
Foundc
C2H2
Me2C2
Et2C2
2a
2b
2c
2e
3d
2e
26
29
37
32
14
52
0.25
0.26
0.40
0.45
0.61
0.16
ca. −10
ca. −20
32
74
78
138(50), 137(100)
166(50), 165(100)
194(55), 193(100)
214(55), 213(100)
212(55), 211(100)
290(60), 289(100)
26.37, 10.33
36.47, 11.02
43.62, 11.51
50.82, 8.53
50.94, 7.60
62.38, 7.68
25.92, 10.15
36.20, 10.95
43.33, 11.24
50.71, 8.41
51.01, 7.42
61.94, 7.41
PhC2H
Ph2C2
82
a In hexane. b Ordered as m/z values corresponding to M+ (%), most intensive m/z (%). c Ordered as %C, %H.
to ambient temperature, the volatiles were evaporated using a
rotary evaporator and the remaining materials were digested with
References
ˇ
1 (a) B. St´ıbr, K. Basˇe, S. Herˇma´nek and J. Plesˇek, J. Chem. Soc., Chem.
a mixture of water (30 ml) and dichloromethane (30 ml) under
stirring. The aqueous layer was separated, treated with a solution
of PPh4Cl (570 mg, 1.52 mmol) in water (30 ml) and the resulting
white precipitate was isolated by filtration and dried in vacuo. The
ˇ
Commun., 1976, 150; (b) K. Basˇe, S. Herˇma´nek and B. St´ıbr, Chem. Ind.
(London), 1977, 951; (c) K. Basˇe, B. St´ıbr, J. Dolansky´ and J. Duben,
Collect. Czech. Chem. Commun., 1981, 46, 2345; (d) S. Herˇma´nek,
J. Fusek, B. St´ıbr, J. Plesˇek and T. Jel´ınek, Polyhedron, 1986, 5,
1873.
2 A. E. Wille, J. Plesˇek, J. Holub, B. St´ıbr, P. J. Carroll and L. G. Sneddon,
ˇ
ˇ
mixture of the PPh4 salts of anions 4− and 5− thus obtained was
+
ˇ
separated on a silica gel column using dichloromethane as a mobile
phase. Fractions of Rf 0.12 and 0.05 were collected and compounds
obtained by evaporation were identified by NMR spectroscopy as
Inorg. Chem., 1996, 35, 5342.
ˇ
3 (a) T. Jel´ınek, B. St´ıbr, J. Holub, M. Bakardjiev, D. Hnyk, D. L. Ormsby,
C. A. Killner, M. Thornton-Pett, H.-J. Schanz, B. Wrackmeyer and J. D.
Kennedy, Chem. Commun., 2001, 1756; (b) B.
4 (a) Brellochs, J. Bacˇkovsky´, B. St´ıbr, T. Jel´ınek, J. Holub, M. Bakardjiev,
D. Hnyk, M. Hofmann, I. C´ısarˇova´ and B. Wrackmeyer, Eur. J. Inorg.
PPh4 [2-CB6H7]− (5−) (154 mg, 24%) and PPh4 [1-CB7H8]− (4−)
+
+
ˇ
(212 mg, 32%), respectively, as reported earlier.4,7
ˇ
Chem., 2004, 3605; (b) J. Plesˇek, T. Jel´ınek, B. St´ıbr and S. Herˇma´nek,
J. Chem. Soc., Chem. Commun., 1988, 348.
5 (a) T. Jel´ınek, M. Thornton-Pett and J. D. Kennedy, Collect. Czech.
Chem. Commun., 2002, 67, 1035; (b) A. Franken, C. A. Kilner, M.
Thornton-Pett and J. D. Kennedy, J. Organomet. Chem., 2002, 657,
180.
Conclusions
We have shown that the insertion of alkynes R1R2C2 to the nine-
vertex monocarbaborane arachno-4-CB8H14 (1) at elevated tem-
peratures results in the formation of the ten-vertex dicarbaboranes
9-Me-5,6-R1,R2-nido-5,6-C2B8H9, the typical feature being the
extrusion of the cage CH2 vertex in 1 into the exoskeletal position.
In this respect this reaction reminds us of the reaction between
R1R2C2 and 4-(Me2S)–B9H13, also generating C-substituted 5,6-
R1,R2-nido-5,6-C2B8H10 derivatives under complete elimination
of one boron vertex from the nine-vertex arachno core.15 It was
also demonstrated that the reaction between [arachno-4-CB8H13]−
anion (1−) and PhC2H proceeds in an entirely different manner,
producing a mixture of the closo anions [1-CB7H8]− (4−) and [1-
CB6H7]− (5−) under elimination of one or two boron vertices. This
reaction represents an improved access to the seven-vertex anion
5− that has so far been hardly available.7 In general, we hope
that the substituted derivatives of 2 reported in this paper can be
used as source compounds for various mechanistic studies and
the preparation of C- and B-substituted compounds in the area of
dicarbaborane and tricarbaborane chemistry. Relevant studies in
these areas of cluster-boron chemistry are in progress.
6 D. E. Kadlecek and L. G. Sneddon, Inorg. Chem., 2002, 41,
4239.
ˇ
7 B. St´ıbr, O. L. Tok, W. Milius, M. Bakardjiev, J. Holub, D.
Hnyk and B. Wrackmeyer, Angew. Chem., Int. Ed., 2002, 41,
2126.
8 (a) J. Plesˇek and S. Herˇma´nek, Chem. Ind. (London), 1971, 1267; (b) J.
Plesˇek and S. Herˇma´nek, Collect. Czech. Chem. Commun., 1974, 39,
821.
ˇ
9 (a) B. St´ıbr, J. Holub, F. Teixidor and C. Vin˜as, J. Chem. Soc., Chem.
ˇ
Commun., 1995, 795; (b) B. St´ıbr, J. Holub, I. C´ısarˇova´, F. Teixidor,
C. Vin˜as, J. Fusek and Z. Plza´k, Inorg. Chem., 1996, 35, 3635; (c) J.
ˇ
Holub, B. St´ıbr, D. Hnyk, J. Fusek, I. C´ısarˇova´, F. Teixidor, C.
Vin˜as, Z. Plza´k and P. v. R. Schleyer, J. Am. Chem. Soc., 1997, 119,
7750.
10 (a) A. Laromaine, F. Teixidor and C. Vin˜as, Angew. Chem., Int.
Ed., 2005, 44, 2220; (b) D. F. Shriver and M. A. Drezdon, Ma-
nipulation of Air Sensitive Compounds, 2nd edn, Wiley, New York,
1986.
11 See, for example: (a) J. D. Kennedy, in Multinuclear NMR, ed. J. Mason,
Plenum Press, New York, 1987, p. 221; (b) W. C. Hutton, T. L. Venable
and R. N. Grimes, J. Am. Chem. Soc., 1984, 106, 29; (c) J. Schraml
and J. M. Bellama, Two-Dimensional NMR Spectroscopy, Wiley, New
York, 1982 and references therein.
12 X. L. R. Fontaine and J. D. Kennedy, J. Chem. Soc., Dalton Trans.,
1987, 1573.
Acknowledgements
ˇ
13 J. Plesˇek, B. St´ıbr, X. L. R. Fontaine, J. D. Kennedy, S. Herˇma´nek and
T. Jel´ınek, Collect. Czech. Chem. Commun., 1991, 56, 1618.
The work was supported by the Grant Agency of the Czech
Republic (project no. 203/05/2646) and Ministry of Education
of the Czech Republic (project no. LC 523).
14 W. McFarlane, Proc. R. Soc. London, Ser. A, 1968, 306, 185.
ˇ
15 B. St´ıbr, B. F. Teixidor, C. Vinˇas and J. Fusek, J. Organomet. Chem.,
1998, 550, 125–130.
584 | Dalton Trans., 2007, 581–584
This journal is
The Royal Society of Chemistry 2007
©