Practical synthesis of 1,12-difunctionalized o-carborane for the investigation of polar liquid crystals

Article abstract of DOI:10.1021/ic5014494

Two isomerically pure 1,12-difunctionalized derivatives of o-carborane, 12-iodo-1-vinyl (1b) and 12-iodo-1-phenyl (1c), are conveniently obtained on a practical scale in yields of 22% and 32%, respectively, by monoiodination of the corresponding o-carborane derivatives (4b and 4c) followed by separation of the regioisomers by crystallization (1b) and chromatography (1c). Subsequent functional group transformations gave access to other derivatives, including two liquid-crystalline compounds, in which o-carborane is a linear structural element. Regioselectivity of substitution on the carborane cage and on the benzene ring correlates with the inductive effect parameter of the substituent. The preparation of analogous derivatives of m-carborane was also investigated.

Full text of DOI:10.1021/ic5014494

Article
pubs.acs.org/IC
Practical Synthesis of 1,12-Difunctionalized o‑Carborane for the
Investigation of Polar Liquid Crystals
Aleksandra Jankowiak† and Piotr Kaszynski*,†,‡
́
†Organic Materials Research Group, Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, United States
‡Section of Heteroorganic Compounds, University of Łod
́
z, Tamka 12, 91403 Łodz, Poland
́
́
́
ABSTRACT: Two isomerically pure 1,12-difunctionalized derivatives of o-
carborane, 12-iodo-1-vinyl (1b) and 12-iodo-1-phenyl (1c), are conveniently
obtained on a practical scale in yields of 22% and 32%, respectively, by
monoiodination of the corresponding o-carborane derivatives (4b and 4c)
followed by separation of the regioisomers by crystallization (1b) and
chromatography (1c). Subsequent functional group transformations gave access
to other derivatives, including two liquid-crystalline compounds, in which o-
carborane is a linear structural element. Regioselectivity of substitution on the
carborane cage and on the benzene ring correlates with the inductive effect
parameter of the substituent. The preparation of analogous derivatives of m-
carborane was also investigated.
In addition, the carbon atoms in the 2,9-disubtituted m-
carborane (IC) are enantiotopic, which raises the possibility of
coupling of the electric dipole with molecular chirality, a feature
important for some applications including ferroelectric liquid
crystals.16 Wider use of carboranes B and C in the design of soft
materials is hampered, however, by the lack of general access to
appropriately functionalized derivatives IB and IC. Our interest
in these compounds is related to liquid crystals and stems from
the fundamental question of the role of the molecular electric
dipole in liquid-crystalline phase stabilization.10,17 A compar-
ison of the properties of isosteric mesogenic derivatives IA−IC
would provide an interesting opportunity for such an
investigation with possible practical implications.
INTRODUCTION
■
Among three 12-vertex carboranes, [closo-C2B10H12],1 only the
p-carborane (A; Figure 1) has been broadly used as a linear
The synthesis of p-carborane derivatives IA substituted at
antipodal 1,12 positions is accomplished easily by taking
advantage of the acidic C−H groups and nucleophilicity of the
resulting carbanions.18 In contrast, the preparation of analogous
o-carborane derivatives IB requires two electrophilic substitu-
tion steps: at the boron and carbon atoms, which raises the
issue of regioselectivity, regardless of the order of these
transformations. As a consequence, a mixture of 1,12 and 1,9
regioisomers (IB and IIB, respectively; Figure 2) is typically
formed, which necessitates isomer separation.
Thus far, five compounds of the general structure IB have
been reported in the literature. Unfortunately, compounds 1a−
1c are lacking any preparative details, and their characterization
is incomplete.14,19−21 Compound 2 was separated from a 1:1
mixture of the two isomers,22 while 3 was isolated in small
amounts by crystallization of the isomeric mixture.23
Figure 1. Structures of three isomeric carboranes A−C and their
derivatives IA− IC. Each vertex represents a BH fragment, and the
sphere is a carbon atom. The arrow represents the vector of the
cluster’s electric dipole.
structural element in the design of molecular-size objects,2−5
liquid crystals,6−10 and pharmacological compounds.11−13 In
contrast, there is only one report of o-carborane (B) as a linear
structural element,14 and no report of such use of m-carborane
(C) substituted in the antipodal positions. In spite of focus on
p-carborane, it can be argued that the remaining two isomeric
and essentially isosteric carboranes have additional properties
that are of particular interest for certain molecular and
functional designs. Thus, unlike A, o- and m-carboranes have
moderate ground-state dipole moments of 4.45 and 2.76 D
(benzene), respectively,15 which are oriented about 30° of the
1,12 axis in B and nearly parallel to the 2,9 axis in C (Figure 1).
Received: June 19, 2014
Published: August 4, 2014
© 2014 American Chemical Society
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a
Scheme 1. Iodination of o-Carboranes
a
Reagents and conditions: (i) ICl, CH2Cl2, rt for 4a; I2, AlCl3 catalyst,
CH2Cl2, rt, protected from light for 4b; ICl, MeSO3H, 60 °C for 4c.
chromatography (SiO2) or gradient sublimation were un-
successful.
Iodination of 1-vinyl-o-carborane (4b)25,26 was accomplished
using the conditions (I2, catalyst AlCl3, CH2Cl2, protected from
light) reported for iodination of the parent o-carborane (B)27
and resulted in a mixture of isomers 1b and 5b in a 3:4 ratio
obtained in 80% yield. The two isomers could not be separated
by chromatography (SiO2 untreated or treated28 with AgNO3).
However, the desired isomer 1b was isolated in 22% yield by
recrystallization of the mixture from hexane. Interestingly, when
iodination of 4b was conducted in the presence of ambient
light, two byproducts were formed in significant quantities for
Figure 2. Two isomeric products IB and IIB obtained from o-
carborane (B) and the structures of the reported isomerically pure
1,12-disubstituted derivatives IB.
The preparation of m-carborane derivatives IC requires yet
another synthetic approach and can, in principle, be achieved
by deboronation of [closo-1,7-C2B10H12] (C) followed by
reboronation of the [nido-C2B9H11]2− dianion tandem to install
a substituent at the B(2) position and the subsequent
electrophilic substitution at the antipodal boron atom. Both
of these methods are known in the literature1 but have not been
used in the same sequence to obtain disubstituted derivatives.
Similar to the case of o-carborane, a mixture of regioisomers 2,9
(IC) and 2,10 (IIC) is expected (Figure 3), and methods for
separation need to be developed.
1
which structures 6 and 7 were assigned on the basis of H
NMR spectra.
1-Phenyl-o-carborane (4c)25,29,30 was iodinated with ICl in
MeSO3H at 60 °C, giving a mixture of isomers 1c and 5c in a
4:5 ratio isolated in 80% yield. Thin-layer chromatography
(TLC) analysis demonstrated reasonable separation of the
isomers (Rf = 0.39 for 5c and Rf = 0.32 for 1c in 4:1 hexane/
CH2Cl2), and 9-iodo 5c was isolated in 48% yield while the 12-
iodo isomer 1c was obtained in 32% yield as the more polar
fraction by column chromatography.
Figure 3. Two isomeric products IC and IIC formed from m-
carborane (C).
Thus, isomerically pure compounds 1b and 1c were prepared
by iodination of the corresponding 1-substituted o-carborane
and isolated in 22% and 32% yield, respectively.
For the purpose of general intermediates, B-iodo derivatives
provide the most versatility. Therefore, we initially focused on
compounds 1 and expanded our investigation to derivatives IC.
Here we provide practical synthesis of 1b and 1c and
demonstrate their further transformations including two
examples of liquid-crystalline derivatives. Regioslectivity of the
transformations (iodination and nitration) is discussed in terms
of the substituent effect. Finally, we describe our attempts at the
preparation of 2,9-difunctionalized derivatives of m-carborane
(IC).
Functional Group Transformation in 12-Iodo-1-phenyl-o-
carborane (1c). The iodine atom in 1c was used for the
Negishi C−C coupling reaction31−33 to install a pentyl group at
the B(12) position, and 12-pentyl-1-phenyl-o-carborane (8)
was obtained in 58% yield (Scheme 2). Subsequent nitration of
8 with HNO3/H2SO4, according to an analogous method for
4c,34 resulted in a mixture of isomers 1-(4-nitrophenyl)-12-
pentyl-o-carborane (9) and 1-(3-nitrophenyl)-12-pentyl-o-
carborane (10) in a ratio of 3:1. Chromatographic separation
gave the desired 9 isolated in 61% yield as the less polar
fraction.
RESULTS
■
Synthesis. 1,12-Difunctionalized o-Carborane. Isomer
Separation. Initially, we concentrated on three iodo derivatives
1a−1c accessible by iodination of appropriate 1-substituted o-
carborane derivatives 4a−4c (Scheme 1). Thus, iodination of 1-
methyl-o-carborane (4a)21,24 with ICl at ambient temperature
gave a mixture of isomers 1a and 5a in a nearly 1:1 ratio and
60% yield. Attempts at separation of the isomers using
Catalytic reduction of the nitro group in the 4-nitrophenyl
derivative 9 gave aniline 11 in 86% yield. Subsequent
diazotization of 11 using t-BuONO in the presence of
35
CuBr2 yielded the 4-bromophenyl derivative 12, which was
contaminated with ∼20% of the 3,4-dibromophenyl derivative
13. Separation of the pure bromo 12 from the mixture was
problematic. To obtain a pure halogen derivative, the amino
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a
Scheme 2. Synthesis of 1,12-disubstituted o-carboranes
a
Reagents and conditions: (i) C5H11MgBr, ZnCl2, Pd(OAc)2, [HPCy3]+[BF4]−, THF, reflux, 24 h; (ii) HNO3/H2SO4 (15:85), CH2Cl2, 0 °C; (iii)
H2, Pd/C, THF, rt; (iv) t-BuONO, CuBr2, MeCN, 0 °C; (v) (1) [NO]+[PF6]− and (2) [Bu4N]+[I]−, MeCN, 0 °C.
compound 11 was converted to 1-(4-iodophenyl)-12-pentyl-o-
carborane (14) in 70% yield by diazotization using
[NO]+[PF6]− followed by treatment with [Bu4N]+I−, according
to a general method (Scheme 2).36
The 12-iodo-1-phenyl derivative 1c was nitrated, giving a 1:2
mixture of isomers 15 and 16, from which the 4-nitro derivative
15 was isolated in 21% yield by chromatography (Scheme 3).
(pentyloxy)phenylzinc chloride to give 1-vinyl-12-[4-
(pentyloxy)phenyl]-o-carborane (19) in 65% yield (Scheme 5).
a
Scheme 5. Negishi Arylation of 1b
a
Scheme 3. Nitration of 1c
a
Reagents and conditions: (i) (1) 4-C5H11OC6H4Br, Mg, (2) ZnCl2,
and (3) Pd(OAc)2, [HPCy3]+[BF4]−, THF, reflux, 6 h.
a
Reagents and conditions: (i) HNO3/H2SO4 (15:85), CH2Cl2, 0 °C.
Liquid-Crystalline Compounds. The application of function-
alized linear derivatives of o-carborane, 1a and 1b, was
demonstrated by the preparation of two liquid-crystalline
compounds. Thus, the impure bromide 12 or iodide 14 was
used in Negishi coupling reactions with a 4-(octyloxy)-
phenylzinc reagent, resulting in biphenyl 20 isolated in 64%
yield (Scheme 6). A similar reaction under Suzuki−Miyaura38
The 3-nitro isomer 16 was obtained in 41% yield as the more
polar compound. An alternative method for the preparation of
15 was briefly investigated. Thus, the reaction of 9-iodo-o-
carborane with (4-nitrophenyl)diazonium salt using general
literature conditions29 gave a complex mixture of products,
which contained about 10% of the expected product 15.
Attempted butoxycarbonylation reaction37 of 5c using (i-
Pr)2NEt (Hunig’s base), a non-nucleophilic amine, in n-BuOH
and the formation of ester 17 resulted in deboronation of 5c
and formation of the nido derivative 18 (Scheme 4). No
carbonylation was observed.
a
Scheme 6. Synthesis of Biphenyl 20
Functional Group Transformations in 1b. The iodine atom
in 1b was used to install an aryl group at the B(12) position.
Thus, 12-iodo-1-vinyl-o-carborane (1b) was reacted with 4-
a
Scheme 4. Attempted Synthesis of Ester 17
a
Reagents and conditions: (i) (1) 4-C8H17OC6H4Br, Mg, (2) ZnCl2,
and (3) Pd(dba)2, [HPCy3]+[BF4]−, THF, reflux, 15 h.
conditions39 (aqueous K2CO3, toluene, 100 °C) resulted in
deboronation of the carborane cage and formation of a highly
polar compound, presumably the corresponding nido deriva-
tive.
The vinyl derivative 19 was employed in a Heck C−C
coupling reaction,40 leading to the styrene derivative 21 isolated
in 50% yield (Scheme 7). The reaction was conducted in the
presence of (i-Pr)2NEt (Hunig’s base) under anhydrous
a
Reagents and conditions: (i) CO, PdCl2, Bnap, (i-Pr)2NEt, n-BuOH,
100 °C, 16 h.
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conditions to avoid deboronation and formation of a nido
derivative.
a
Scheme 7. Synthesis of Styrene 21
Figure 5. Optical textures of 20 obtained upon cooling from the
isotropic phase: (a) nematic phase at 138 °C; (b) SmA phase at 100
°C.
a
Reagents and conditions: (i) 4-C5H11OC6H4I, Pd(OAc)2, (o-
MeOPh)3P, NMP, (i-Pr)2NEt, 100 °C, 3 h.
Figure 6. Target compund 22.
Analysis of these two derivatives, 20 and 21, by differential
scanning calorimetry (DSC) and polarized optical microscopy
revealed their mesogenic behavior. The biphenyl derivative 20
exhibits SmA and nematic phases (Figure 4a) identified by their
characteristic schlieren and fan textures, as shown in Figure 5.
The styrene derivative 21 displays only a nematic phase with
the clearing temperature of 101 °C. Interestingly, the crystalline
polymorph obtained from solution melts at 121 °C, and the
nematic phase is monotropic (Figure 4b). However, the
crystalline polymorph formed from the nematic phase has a
significantly lower melting temperature, 63 °C, and the nematic
phase is enantitropic.
Attempts at 2,9-Difunctionalized m-Carborane. Com-
pound 9-iodo-2-phenyl-m-carborane (22; Figure 6) was
envisioned as a key intermediate to linear molecular materials
derived from m-carborane (C), in analogy to the o-carborane
derivative 1c, and two possible routes were briefly explored.
The first route to 22 involved iodination of 2-phenyl-m-
carborane (23),41 which was prepared by deboronation of m-
carborane (C)42 and subsequent boronation with PhBCl2.41
Initially, m-carborane (C) was deboronated according to a
literature procedure42 using KOH in EtOH at 150 °C, giving
the nido salt 24[Me3NH] in 56% yield (Scheme 8). The
method was modified by using a higher boiling solvent, 2-
EtOC2H4OH instead of EtOH, which allowed for the reaction
to be carried out under normal pressure. The cation in the
resulting salt 24[Me3NH] was exchanged for Cs+, more
suitable for further transformation, and 24[Cs] was isolated
in 76% yield. Lithiation of 24[Cs] with n-BuLi and
reboronation with PhBCl2, according to a literature proce-
dure,41 gave 23 in 57% yield.
a
Scheme 8. Synthesis of 23
a
Reagents and conditions: (i) KOH, 2-EtOC2H4OH, [Me3NH]+Br−,
reflux 3 h; (ii) CsOH, MeCN; (iii) n-BuLi, PhBCl2, THF, −78 °C.
Attempts at iodination of 23 were unsuccessful, and no
desired 22 was isolated or observed. Mild conditions such as I2
in AcOH at 60 °C and ICl in CH2Cl2 or acetic acid at room
temperature (rt) or in refluxing CH2Cl2 or MeSO3H at 60 °C
gave no reaction. Raising the temperature of the reaction in
MeSO3H to 100 °C resulted in the formation of a complex
mixture of starting 23 and several products, presumably
resulting from iodination of the phenyl ring, as suggested by
1H NMR spectra. Manipulation with the temperature did not
result in selective iodination, and it appears that the benzene
ring is substituted preferentially under these conditions. A
complex mixture was also obtained when CF3SO3H was used as
the solvent.
The second attempt at the synthesis of 22 was envisioned
with a reversed sequence of reactions: iodination of m-
carborane (C) followed by deboronation and finally reborona-
tion with PhBCl2. Thus, C was iodinated to form 25 in 80%
yield using a mixture of iodine and periodic acid in acetic acid
in the presence of sulfuric acid.43 The resulting 9-iodo-m-
Figure 4. DSC trace for (a) biphenyl 20 and (b) styrene 21. The high-temperature portion of trace a is enlarged 10 times. The numbers in
parentheses indicate transition temperatures. Graph b is a superimposition of three traces: first heating (a), cooling (b), and second heating (c).
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carborane (25)44 was deboronated using the 2-EtOC2H4OH
method to give Cs+ salt 26[Cs] as a mixture of isomers B(6)-I
and B(1)-I in a ratio of ∼2:1 and 57% yield (Scheme 9), which
substituent parameter.48 Quantitative analysis of the data
suggests a better fit of ln K values with the inductive parameter
I(R) rather than with σp(R), which is in agreement with our
recent results in the transmission of electronic effects through
the [closo-1-CB11H12]− cluster.49 Although a trend is observed,
more data points are necessary for a meaningful analysis and a
better understanding of the effect of the antipodal substituent
in o-carborane on the benzene ring reactivity. Such compounds
are now, in principle, available from the iodo derivative 1c.
A much weaker substituent effect was observed in iodination
of 1-substituted o-carborane derivatives. For all three derivatives
4a−4c, the ratio of the 12-iodo and 9-iodo isomers (1 and 5,
respectively) was diminishing in the order 4a (1.12), 4c (0.78),
and 4b (0.76), which follows a trend in the substituent’s
inductive parameter I(R) value:48 −0.01 (methyl), 0.12
(phenyl), and 0.13 (vinyl).50 These results suggest that
electron-withdrawing substituents on the benzene ring would
disfavor antipodal substitution and should be avoided to
maximize the yield of the desired 1,12-disubstituted derivatives
and make the process practical. For instance, substituents at the
C(1) positions such as 4-I-C6H4 (I(R) = 0.18)48 or 4-NO2-C6H4
(I(R) = 0.26)48 are expected to give more than 60% of the 1,9
isomer. On the other hand, electron-donating substituents on
the benzene ring will favor the antipodal substitution but also
activate the aromatic ring toward electrophilic substitution.
While iodination of 4c is selective for the cluster, iodination
of 23 suffers from a more balanced nucleophilicity of the
benzene ring and carborane cage compared to the o-carborane
analogue 4c. The m-carboran-2-yl group is less electron-
withdrawing (σp = 0.15) than the o-carboran-1-yl group (σp =
0.43),48 and the benzene ring is not as deactivated toward
electrophilic substitution. At the same time, the m-carborane
cage has diminished reactivity in 23. Conceivably, 2-iodo-m-
carborane could be successfully monoiodinated, although on
the basis of the results for iodination of o-carborane derivatives
(vide supra), poor selectivity for the desired 2,9-diiodo
derivative can be expected (I(R) = 0.42 for iodine).48
a
Scheme 9. Preparation of the Nido Anion 26
a
Reagents and conditions: (i) I2, HIO3, AcOH, CCl4, H2SO4; (ii)
KOH, 2-EtOC2H4OH, [Me3NH]+Br−, reflux 3 h; (iii) CsOH, MeCN.
is similar to previously reported results.45 Unfortunately,
attempts at reboronation of 26[Cs] using PhBCl2 under the
same conditions as those for 24[Cs] with or without
tetramethylethylenediamine did not give the desired 22, and
only unreacted 26 was observed by NMR. In some experi-
ments, however, analysis of the nonpolar fraction revealed
possible traces of the expected product 22, while the polar
fraction (MeOH eluent) contained the B(6)-I isomer of 26.
DISCUSSION
■
The preparation of isomerically pure derivatives of o-carborane
1b and 1c relies on simple separation methods: crystallization
and chromatographic separation. The former method often
appears moderately effective, as demonstrated for 1b and 1,12-
diaryl-o-carborane 3,23 while the latter permits the quantitative
separation of isomers. Among the three isomeric mixtures
investigated here, only that obtained from 4c showed the
separation of products on TLC, permitting separation by
classical chromatographic methods (Rf values in a 4:1 hexane/
CH2Cl2 system: 1a and 5a, Rf = 0.37; 1b and 5b, Rf = 0.43; 1c,
Rf = 0.32; 5c, Rf = 0.39). Overall, two important building blocks
for linear molecules, compounds 1b and 1c, containing
functionalizable phenyl, vinyl, and iodine groups, are available
in three steps from B10H14 and estimated yields of about 16%
and 26%, respectively, taking advantage of the recently
discovered high-yield procedure30 for alkyne insertion to
B10H12·(MeCN)2.
CONCLUSIONS
■
We have demonstrated that two 1,12-difunctionalized deriva-
tives of o-carborane, 1b and 1c, can conveniently be obtained
on a practical scale in the pure form. Through standard
chemical transformations, this opens up access to a number of
derivatives in which o-carborane plays the role of a linear
structural element with a moderate dipole moment. Application
of these building blocks, 1b and 1c, has been demonstrated
with two examples of liquid-crystalline materials 20 and 21.
Results suggest that regioselectivity of substitution on the
carborane cage and benzene ring correlates with the inductive
effect parameter I(R) of the substituent.
Functional group transformations in o-carborane derivatives
revealed that nitration of the benzene ring in derivatives of 1-
phenyl-o-carborane is sensitive to the nature of the antipodal
substituent46 at the B(12) position, as is evident from variation
of the ratio K of the two isomers 4-nitro and 3-nitro (Figure 7).
Analysis of the results for 1c, 8, and the parent 4c47 shows that
the observed trend in ln K follows that of the Hammett
Attempts at the preparation of m-carborane with two
substituents in the antipodal positions (the 2,9 pattern) have
been unsuccessful thus far, largely because of the more balanced
nucleophilicity of the molecular fragments and hence poor
regioslectivity.
EXPERIMENTAL SECTION
■
Reactions were carried out under argon, and subsequent manipulations
were conducted in air. NMR spectra were obtained at 128.4 MHz
(11B) and 400.1 MHz (1H) in CDCl3 unless otherwise specified. H
1
NMR spectra were referenced to the solvent and 11B NMR chemical
shifts to an external boric acid sample in CH3OH that was set to 18.1
ppm.
Figure 7. Ratio K of two regioisomers obtained by nitration of 1-
phenyl-o-carborane derivatives and selected substituent parameters.
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12-Iodo-1-methyl-o-carborane (1a) and 9-Iodo-1-methyl-o-
carborane (5a).19 A mixture of 4a (50 mg, 0.3 mmol)21,24 and ICl
(73 mg, 0.45 mmol) in CH2Cl2 (2 mL) was stirred at rt for 3 days.
The solvent was evaporated, and the resulting solid residue was passed
through a silica gel plug (4:1 hexane/CH2Cl2; Rf = 0.37), giving 52 mg
(60% yield) of a mixture of isomers 1a and 5a in a ratio of 10:11
established by H NMR (400 MHz, CDCl3, characteristic signals):
major isomer, δ 2.06 (s, CH3), 3.85 (br s, 1H); minor isomer, δ 1.92
(s, CH3), 3.67 (br s, 1H).
rt; the resulting mixture was stirred at rt for 15 min, and then
Pd(OAc)2 (200 mg, 0.3 mmol) and tricyclohexylphosphonium
tetrafluoroborate (220 mg, 0.6 mmol) were added, followed by 1c
(1.98 g, 5.72 mmol). The mixture was refluxed for 24 h, 5% HCl was
added, the products were extracted into Et2O, the extracts were dried
(Na2SO4), and the solvents were evaporated. The oily residue was
passed through a silica gel plug (hexane), giving 0.95 g (58% yield) of
1
1
8 as a colorless oil. H NMR (400 MHz, CDCl3): δ 0.70−0.78 (m,
2H), 0.87 (t, J = 6.8 Hz, 3H), 1.20−1.32 (m, 6H), 1.5−3.5 (m, 9H),
3.91 (br s, 1H), 7.29−7.35 (m, 2H), 7.36−7.40 (m, 1H), 7.48−7.52
(m, 2H). 11B NMR (128 MHz, CDCl3): δ −12.4 (d, J = 156 Hz, 2B),
−11.2 (d, J = 154 Hz, 4B), −8.2 (d, J = 150 Hz, 2B), −1.3 (d, J = 149
Hz, 1B), 7.7 (s, 1B). HRMS. Calcd for C13H26B10: m/z 292.2973.
Found: m/z 292.2995.
12-Iodo-1-vinyl-o-carborane (1b) and 9-Iodo-1-vinyl-o-car-
borane (5b).20 A mixture of 4b (288 mg, 1.16 mmol),25,26 iodine
(310 mg, 1.20 mmol), and catalytic amounts of AlCl3 (16 mg, 0.12
mmol) in dry CH2Cl2 (5 mL) was stirred at rt, overnight, under an
argon atmosphere, and protected from light (aluminum foil). The
solvent was evaporated, and the residue was passed through a silica gel
plug (4:1 hexane/CH2Cl2; Rf = 0.43), giving 280 mg (80% yield) of a
mixture of 1b and 5b in a 3:4 ratio. Crystallization (hexane, 3 mL, rt)
gave 60 mg of 1b, while subsequent crystallization of the mother liquor
(hexane, 1 mL, 0 °C) gave an additional 15 mg (22% combined yield)
of pure 1b as colorless crystals. Mp: 148−149 °C (lit.20 mp 148−148.5
1-(4-Nitrophenyl)-12-pentyl-o-carborane (9) and 1-(3-Nitro-
phenyl)-12-pentyl-o-carborane (10). A mixture of fuming HNO3
and concentrated H2SO4 (10 mL, 15:85) was added to a solution of 8
(600 mg, 2.1 mmol) in CH2Cl2 (10 mL) at 0 °C. The reaction mixture
was stirred at 0 °C for 4 h, kept at −15 °C overnight, and poured into
water. The products were extracted (CH2Cl2), the extracts were dried
(Na2SO4), and the solvent was evaporated. The solid residue was
separated on a silica gel column (12:1 hexane/AcOEt), giving 423 mg
(61% yield) of 9, which was further recrystallized from hexane, giving
white crystals. Mp: 91−92 °C. 1H NMR (400 MHz, CDCl3): δ 0.72−
0.79 (m, 2H), 0.87 (t, J = 6.8 Hz, 3H), 1.21−1.32 (m, 6H), 1.50−3.3
(m, 9H), 3.97 (br s, 1H), 7.68 (d, J = 9.1 Hz, 2H), 8.19 (d, J = 9.1 Hz,
2H). 11B NMR (128 MHz, CDCl3): δ −11.3 (m, 6B), −7.7 (d, J = 148
Hz, 2B), −1.0 (d, J = 151 Hz, 1B), 8.8 (s, 1B). Anal. Calcd for
C13H25B10NO2: C, 46.55; H, 7.51; N, 4.25. Found: C, 46.79; H, 7.74;
N, 4.25.
1
°C). H NMR (400 MHz, CDCl3): δ 1.5−3.3 (m, 9H), 3.73 (br s,
1H), 5.43 (d, J = 10.5 Hz, 1H), 5.60 (d, J = 16.7 Hz, 1H), 5.87 (dd, J1
= 16.9 Hz, J2 = 10.4 Hz, 1H). 11B NMR (128 MHz, CDCl3): δ −17.3
(s, 1B), −11.6 (d, J = 146 Hz, 4B), −10.6 (d, J = 152 Hz, 2B), −7.0 (d,
J = 155 Hz, 2B), −0.1 (d, J = 151 Hz, 1B).
The mother liquor contained both isomers 5b and 1b in a 4:1 ratio.
1H NMR (400 MHz, CDCl3, major characteristic signals): δ 3.93 (br s,
1H), 5.44 (d, J = 10.5 Hz, 1H), 5.65 (d, J = 16.3 Hz, 1H), 5.97 (dd, J1
= 16.8 Hz, J2 = 10.5 Hz, 1H). {1H}11B NMR (128 MHz, CDCl3, major
characteristic signals): δ −15.9 (1B), −12.0 (2B), −11.7 (4B), −7.0
(2B), −3.2 (1B).
Further elution of the column (12:1 hexane/AcOEt) gave 148 mg
(21% yield) of the meta isomer 10, which was recrystallized from
Iodination run in the presence of ambient light resulted in a mixture
1
1
hexane, giving white crystals. Mp: 95−96 °C. H NMR (400 MHz,
containing ∼25% of two byproducts identified as 6 and 7. H NMR
CDCl3): δ 0.72−0.79 (m, 2H), 0.87 (t, J = 6.8 Hz, 3H), 1.21−1.33 (m,
6H), 1.50−3.3 (m, 9H), 3.97 (br s, 1H), 7.56 (t, J = 8.1 Hz, 1H), 7.87
(dd, J1 = 8.0 Hz, J2 = 1.1 Hz, 1H), 8.27 (dd, J1 = 9.0 Hz, J2 = 2.0 Hz,
1H), 8.35 (t, J = 2.0 Hz, 1H). 11B NMR (128 MHz, CDCl3): δ −11.3
(m, 6B), −7.8 (d, J = 154 Hz, 2B), −0.9 (d, J = 152 Hz, 1B), 8.5 (s,
1B). Anal. Calcd for C13H25B10NO2: C, 46.55; H, 7.51; N, 4.25.
Found: C, 46.79; H, 7.51; N, 4.13.
(400 MHz, CDCl3, major characteristic signals): δ 1.70 (d, J = 6.8 Hz,
1
3H), 4.22 (br s, 1H), 4.48 (q, J = 6.7 Hz, 1H). H NMR (400 MHz,
CDCl3, minor characteristic signals): δ 1.76 (d, J = 6.7 Hz, 3H), 4.42
(br s, 1H), 4.56 (q, J = 6.8 Hz, 1H).
12-Iodo-1-phenyl-o-carborane (1c) and 9-Iodo-1-phenyl-o-
carborane (5c).19 A mixture of 4c (1.50 g, 6.8 mmol) and ICl (1.10
g, 6.8 mmol) in MeSO3H (8 mL) was stirred at 60 °C overnight. The
resulting mixture was cooled and poured into ice water. The products
were extracted (CH2Cl2), the extracts were dried (Na2SO4), and the
solvents were evaporated. The solid residue (2.11 g) was separated on
a silica gel column (10:1 hexane/CH2Cl2) to give (1.11 g, 48% of
yield) of 5c as the first fraction (4:1 hexane/CH2Cl2; Rf = 0.39).
Recrystallization from hexane gave pure 5c as white crystals. Mp: 102−
103 °C (lit.19 mp 93−94 °C). 1H NMR (400 MHz, CDCl3): δ 1.5−3.3
(m, 9H), 4.25 (br s, 1H), 7.33−7.38 (m, 2H), 7.40−7.45 (m, 1H),
7.46−7.50 (m, 2H). 11B NMR (128 MHz, CDCl3): δ −15.9 (s, 1B),
−12.4 (d, J = 162 Hz, 2B), −11.1 (d, J = 172 Hz, 2B), −9.7 (d, J = 169
Hz, 2B), −7.1 (d, J = 158 Hz, 2B), −2.8 (d, J = 150 Hz, 1B). Anal.
Calcd for C8H15B10I: C, 27.75; H, 4.37. Found: C, 27.94; H, 4.18.
Isomer 1c was isolated as the second fraction (750 mg, 32% yield;
4:1 hexane/CH2Cl2; Rf = 0.32) and purified by recrystallization from
hexane, giving 1c as white crystals. Mp: 149−150 °C (lit.19 145−146
°C. 1H NMR (400 MHz, CDCl3): δ 1.5−3.3 (m, 9H), 4.05 (br s, 1H),
7.31−7.37 (m, 2H), 7.39−7.46 (m, 3H). 11B NMR (128 MHz,
CDCl3): δ −16.7 (s, 1B), −11.5 (d, 2B), −10.8 (d, 2B), −10.2 (d, 2B),
−6.9 (d, J = 157 Hz, 2B), −0.2 (d, J = 159 Hz, 1B). Anal. Calcd for
C8H15B10I: C, 27.75; H, 4.37. Found: C, 27.92; H, 4.29.
1-(4-Aminophenyl)-12-pentyl-o-carborane (11). A mixture of
9 (318 mg, 0.95 mmol) and 10% Pd/C (25 mg) in THF (5 mL) was
stirred overnight under positive pressure of H2. The solvent was
evaporated, and the residue was passed through a silica gel plug
(CH2Cl2), giving 250 mg (86% yield) of amine 11. An analytically
pure sample was obtained by recrystallization from hexane, giving
white crystals. Mp: 91−92 °C. 1H NMR (400 MHz, CDCl3): δ 0.65−
0.78 (m, 2H), 0.85 (t, J = 6.8 Hz, 3H), 1.20−1.35 (m, 6H), 1.5−3.3
(m, 9H), 3.77 (br s, 1H), 4.4 (br s, 2H), 6.60 (d, J = 8.7 Hz, 2H), 7.30
(d, J = 8.7 Hz, 2H). 11B NMR (128 MHz, CDCl3): δ −11.7 (m, 6B),
−8.5 (d, J = 147 Hz, 2B), −1.2 (d, J = 152 Hz, 1B), 7.1 (s, 1B). Anal.
Calcd for C13H27B10N: C, 51.11; H, 8.91; N, 4.59. Found: C, 51.30; H,
8.93; N, 4.66.
1-(4-Bromophenyl)-12-pentyl-o-carborane (12). According to
a general literature procedure,35 a solution of 11 (100 mg, 0.33 mmol)
in MeCN (0.5 mL) was slowly added to a solution of t-BuONO (0.50
mmol) in dry MeCN (1.5 mL) containing CuBr2 (90 mg, 0.40 mmol)
at 0 °C. The resulting mixture was stirred for 10 min, then warmed to
rt, and stirred for 1 h. 10% HCl was added, the products were
extracted (CH2Cl2), the organic layer was dried (Na2SO4), and the
solvents were evaporated. The residue was passed through a silica gel
plug (hexane), giving 102 mg (84% yield) of bromide 12 as a white
1-Phenyl-o-carborane (4c).29,30 4c was prepared in 67% yield by
arylation of o-carborane (B) according to a literature procedure.29 1H
NMR (400 MHz, CDCl3): δ 1.5−3.6 (m, 10H), 4.05 (br s, 1H), 7.31−
7.36 (m, 2H), 7.39−7.46 (m, 3H). 11B NMR (128 MHz, CDCl3): δ
−12.5 (d, J = 172 Hz, 2B), −11.0 (d, 2B), −10.5 (d, J = 168 Hz, 2B),
−8.7 (d, J = 156 Hz, 2B), −4.1 (d, J = 152 Hz, 1B), −1.8 (d, J = 147
Hz, 1B).
12-Pentyl-1-phenyl-o-carborane (8). A solution of C5H11MgBr
(22 mmol) was added to a solution of dry ZnCl2 (3.60 g, 26.4 mmol)
in dry tetrahydrofuran (THF; 30 mL) under an argon atmosphere at
1
solid, contaminated with dibromo derivative 13 (∼20% based on H
NMR). The mixture was inseparable either by chromatography or by
1
distillation, and crude 12 was used for further transformations. H
NMR (400 MHz, CDCl3, major signals): δ 0.68−0.77 (m, 2H), 0.87
(t, J = 6.8 Hz, 3H), 1.20−1.32 (m, 8H), 1.5−3.3 (m, 9H), 3.86 (br s,
2H), 7.36 (d, J = 8.8 Hz, 2H), 7.45 (d, J = 8.8 Hz, 2H). 1H NMR (400
MHz, CDCl3, minor signals): δ 7.29 (dd, J1 = 8.6 Hz, J2 = 2.4 Hz, 1H),
7.56 (d, J = 8.6 Hz, 1H), 7.73 (d, J = 2.3 Hz, 1H). {1H}11B NMR (128
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MHz, CDCl3): δ −11.3 (m, 6B), −8.1 (2B), −1.1 (1B), 8.1 (1B).
HRMS. Calcd for C13H24B10Br: m/z 369.2048. Found: m/z 369.2025.
1-(4-Iodophenyl)-12-pentyl-o-carborane (14). According to a
modified general literature procedure,36 a solution of 11 (130 mg, 0.43
mmol) in MeCN (1 mL) was added dropwise to a solution of
[NO]+[PF6]− (82 mg, 0.47 mmol) in dry MeCN (3 mL) at −15 °C.
The mixture was stirred for 1 h at −15 °C, then [Bu4N]+I− (173 mg,
0.47 mmol) was added in one portion, and stirring was continued for 1
h at 0 °C. The mixture was warmed to rt and stirred for 15 min, and
the solvent was evaporated. The resulting residue was passed through a
silica gel plug (hexane), and the crude product was purified further on
a silica gel column (hexane), giving 130 mg (70% yield) of iodide 14.
An analytically pure sample was obtained by recrystallization from
hexane as white crystals. Mp: 54−55 °C. 1H NMR (400 MHz,
CDCl3): δ 0.68−0.77 (m, 2H), 0.87 (t, J = 6.9 Hz, 3H), 1.22−1.32 (m,
6H), 1.5−3.3 (m, 9H), 3.86 (br s, 1H), 7.22 (d, J = 8.8 Hz, 2H), 7.66
(d, J = 8.8 Hz, 2H). 11B NMR (128 MHz, CDCl3): δ −11.9 (m, 6B),
−8.1 (d, J = 151 Hz, 2B), −1.2 (d, J = 150 Hz, 1B), 8.1 (s, 1B). Anal.
Calcd for C13H25B10I: C, 37.50; H, 6.05. Found: C, 38.07; H, 6.07.
12-Iodo-1-(4-nitrophenyl)-o-carborane (15) and 12-Iodo-1-
(3-nitrophenyl)-o-carborane (16). To a solution of 1c (100 mg, 0.3
mmol) in CH2Cl2 (2 mL) was added at 0 °C a mixture of HNO3
(fuming) and concentrated H2SO4 (1.5 mL, 15:85). The reaction
mixture was stirred at 0 °C and poured into water. The products were
extracted (CH2Cl2), the extracts were dried (Na2SO4), and the solvent
was evaporated. The 100 mg of residue, containing isomers 15 and 16
in a 1:2 ratio, was separated by column chromatography (SiO2; 8:1
hexane/AcOEt).
15 (4-nitro isomer): 25 mg (21% yield). Rf = 0.27. Mp: 199−201
°C. 1H NMR (400 MHz, CDCl3): δ 1.5−3.3 (m, 9H), 4.12 (br s, 1H),
8.21 (d, J = 8.8 Hz, 2H), 7.63 (d, J = 8.8 Hz, 2H). 11B NMR (128
MHz, CDCl3): δ −16.1 (s, 1B), −11.2 (d, J = 115 Hz, 4B), −10.2 (d, J
= 154 Hz, 2B), −6.4 (d, J = 158 Hz, 2B), 0.1 (d, J = 155 Hz, 1B).
HRMS. Calcd for C8H14B9INO2 (M-BH): m/z 382.0914. Found: m/z
382.0917.
16 (3-nitro isomer): 48 mg (41% yield). Rf = 0.23. Mp: 174−176
°C. 1H NMR (500 MHz, CDCl3): δ 1.5−3.3 (m, 9H), 4.13 (br s, 1H),
7.59 (t, J = 7.6 Hz, 1H), 7.81 (d, J = 7.5 Hz, 1H), 8.26−8.34 (m, 2H).
11B NMR (128 MHz, CDCl3): δ −16.3 (s, 1B), −11.2 (d, J = 135 Hz,
2H), 5.40 (d, J = 10.5 Hz, 1H), 5.63 (d, J = 16.9 Hz, 1H), 6.05 (dd, J1
= 16.9 Hz, J2 = 10.5 Hz, 1H), 6.77 (d, J = 8.6 Hz, 2H), 7.26 (d, J = 8.4
Hz, 2H). 11B NMR (128 MHz, CDCl3): δ −12.1 (m, 6B), −8.2 (d, J =
153 Hz, 2B), −1.3 (d, J = 155 Hz, 1B), 6.1 (s, 1B). Anal. Calcd for
C15H28B10O: C, 54.18; H, 8.49. Found: C, 54.45; H, 8.48.
1-[4-(Octyloxy)-4-biphenylyl]-12-pentyl-o-carborane (20). A
solution of 4-C8H17OC6H4MgBr (2.0 mmol, freshly prepared from
C8H17OC6H4Br and Mg in 5 mL of THF) was added to a solution of
ZnCl2 (0.36 mmol) in THF (5 mL) under an argon atmosphere. The
mixture was stirred at rt for 15 min, and Pd2(dba)3 (0.005 mmol) was
added, followed by either impure bromide 12 or iodide 14 (0.1
mmol). The mixture was stirred at 50 °C overnight, 5% HCl was
added, the products were extracted (Et2O), the organic layers were
dried (Na2SO4), the solvents were evaporated, and the crude product
was purified using a silica gel column (10:1 hexane/CH2Cl2), giving 25
mg (64% yield) of biphenyl 20 as white crystals, which was
recrystallized from hexane. Mp: 58 °C. 1H NMR (400 MHz,
CDCl3): δ 0.70−0.79 (m, 2H), 0.87 (t, J = 6.8 Hz, 3H), 0.89 (t, J =
6.7 Hz, 3H), 1.21−1.41 (m, 14H), 1.42−1.51 (m, 2H), 1.5−3.3 (m,
9H), 1.80 (quint, J = 7.0 Hz, 2H), 3.92 (br s, 1H), 3.99 (t, J = 6.6 Hz,
2H), 6.96 (d, J = 8.8 Hz, 2H), 7.47 (d, J = 8.8 Hz, 2H), 7.48 (d, J = 8.9
Hz, 2H), 7.52 (d, J = 8.7 Hz, 2H). 11B NMR (128 MHz, CDCl3): δ
−11.1 (m, 6B), −8.2 (d, J = 149 Hz, 2B), −1.2 (d, J = 145 Hz, 1B), 8.2
(s, 1B). Anal. Calcd for C27H46B10O2: C, 65.28; H, 9.74. Found: C,
65.47; H, 9.56.
1-[2-[4-(Pentyloxy)phenyl]ethenyl]-12-[4-(pentyloxy)-
phenyl]-o-carborane (21). A mixture of 19 (94 mg, 0.28 mmol), 1-
iodo-4-(pentyloxy)benzene (81 mg, 0.28 mmol), and Hunig’s base
(0.07 mL, 0.42 mmol) in dry NMP (3 mL) was stirred for 3 h at 100
°C and cooled, 5% HCl was added, the organic products were
extracted (hexane), the organic layer was dried (Na2SO4), and the
solvents were evaporated. The product was separated by chromatog-
raphy (10:1 hexane/EtOAc), giving 70 mg (50% yield) of 21 as white
crystals, which were recrystallized (hexane and then MeCN). Mp: 121
°C. 1H NMR: δ 0.77−0.87 (m, 2H), 0.92 (t, J = 6.8 Hz, 3H), 0.93 (t, J
= 6.8 Hz, 3H), 1.20−1.49 (m, 6H), 1.5−3.3 (m, 9H), 1.71−1.83 (m,
4H), 3.76 (br s, 1H), 3.92 (t, J = 6.6 Hz, 2H), 3.96 (t, J = 6.6 Hz, 2H),
6.19 (d, J = 15.7 Hz, 1H), 6.77 (d, J = 8.6 Hz, 2H), 6.83 (d, J = 15.6
Hz, 1H), 6.85 (d, J = 8.7 Hz, 2H), 7.23−7.32 (m, 4H). 11B NMR (128
MHz, CDCl3): δ −11.2 (m, 6B), −8.3 (d, J = 150 Hz, 2B), −1.2 (d, J
= 151 Hz, 1B), 6.0 (s, 1B). Anal. Calcd for C26H42B10O2: C, 63.12; H,
8.65. Found: C, 63.21; H, 8.54.
4B), −10.2 (d, J = 145 Hz, 2B), −6.4 (d, J = 158 Hz, 2B), 0.3 (d, J =
155 Hz, 1B). HRMS. Calcd for C8H14B9INO2 (M-BH): m/z 382.0914.
Found: m/z 382.0916.
Cesium 1,7-Dicarbadodecahydroundecaborate (24[Cs]). A
mixture of m-carborane (C; 2.0 g, 13.7 mmol) and KOH (1.54 g, 27.5
mmol) in freshly distilled 2-ethoxyethanol (15 mL) was refluxed for 3
h under an argon atmosphere. The solvent was evaporated and water
was added, followed by [Me3NH]+Br− (14 mmol). The resulting
precipitation of the nido salt 24[Me3NH] was filtered, washed with
water, and dried. The crude salt (2.0 g, 76% yield) was dissolved in
MeCN, CsOH (10.5 mmol) was added, and the solvent was
evaporated to dryness, giving salt 24[Cs]. {1H}11B NMR (128
MHz, CD3CN): δ −35.3 (1B), −34.2 (1B), −22.6 (2B), −21.4 (2B),
−5.7 (1B), −4.5 (2B).
Attempted Preparation of 17 by Butoxycarbonylation of 5c.
A solution of 5c (100 mg, 0.29 mmol), Hunig’s base (0.45 mmol),
PdCl2 (1.0 mg, 2 mol %), and Bnap (7 mg) in n-butanol (1 mL) was
saturated with CO, and the mixture was kept at 100 °C under positive
pressure for 16 h. The mixture was cooled, the solvent was evaporated,
and the residue was passed through a silica gel plug (CH2Cl2), giving
1
90 mg of the nido salt 18. H NMR (400 MHz, CDCl3): δ 1.5−3.3
(m, 10H), 1.50 (d, J = 6.6 Hz, 6H), 1.55 (d, J = 6.7 Hz, 6H), 1.57 (t, J
= 7.3 Hz, 3H), 2.53 (br s, 1H), 3.23−3.32 (m, 1H), 3.80−3.90 (m,
1H), 7.05−7.10 (m, 2H), 7.16 (t, J = 7.5 Hz, 2H), 7.25−8.29 (m, 2H).
{1H}11B NMR (128 MHz, CD3CN): δ −33.6 (1B), −29.7 (1B),
−24.8 (1B), −21.1 (1B), −18.4 (1B), −15.8 (1B), −13.2 (1B), −10.2
(1B), −7.8 (1B).
2-Phenyl-m-carborane (23).41 A solution of 1.6 M n-BuLi in
hexane (0.48 mmol) was added to a solution of 24[Cs] (100 mg, 0.37
mmol) in THF under an argon atmosphere at −40 °C. After 1 h, the
mixture was warmed to rt, stirred for 1 h, and cooled to −40 °C, and
neat PhBCl2 (158 mg, 0.50 mmol) was added. Stirring was continued
for 1 h, and the mixture was warmed to rt and stirred for 1 h. 5% HCl
was added, the products were extracted (Et2O), the extracts were dried
(Na2SO4), and the solvents were evaporated. The crude product was
purified on a silica gel plug (hexane), giving 50 mg (60% yield) of 23
as a viscous oil. 1H NMR (400 MHz, CDCl3): δ 1.5−3.3 (m, 9H), 3.21
(s, 2H), 7.28−7.42 (m, 3H), 7.63 (d, J = 6.8 Hz, 2H). {1H}11B NMR
(128 MHz, CDCl3): δ −15.8 (1B), −12.8 (3B), −11.9 (2B), −10.5
(1B), −7.1 (1B), −5.6 (2B).
1-Vinyl-12-[4-(pentyloxy)phenyl]-o-carborane (19). A solu-
tion of 4-C5H11OC6H4MgBr (3.35 mmol, freshly prepared from 4-
C5H11OC6H4Br and Mg in 5 mL of THF) was added under an argon
atmosphere to a solution of dry ZnCl2 (545 mg, 4.0 mmol) in dry
THF (5 mL). The resulting mixture was stirred at rt for 15 min, and
then Pd(OAc)2 (23 mg, 0.034 mmol) and [HPCy3]+[BF4]− (25 mg,
0.068 mmol) were added followed by 1b (200 mg, 0.67 mmol). The
reaction mixture was refluxed for 6 h, 5% HCl was added, the products
were extracted (Et2O), the extracts were dried (Na2SO4), and the
solvents were evaporated. The residue was passed through a silica gel
column (6:1 hexane/CH2Cl2), giving 150 mg (65% yield) of 19 as a
white solid. An analytically pure sample was obtained by
recrystallization from hexane. Mp: 65 °C. 1H NMR (400 MHz,
CDCl3): δ 0.91 (t, J = 7.1 Hz, 3H), 1.30−1.42 (m, 4H), 1.5−3.3 (m,
9H), 1.76 (quint, J = 7.1 Hz, 2H), 3.70 (br s, 1H), 3.91 (t, J = 6.6 Hz,
9-Iodo-m-carborane (25).44 A mixture of m-carborane (C; 100
mg, 0.68 mmol), HIO3 (66 mg, 0.38 mmol), I2 (132 mg, 0.52 mmol),
acetic acid (0.9 mL), CCl4 (0.1 mL), and H2SO4 (0.05 mL) was stirred
at 80 °C for 36 h. Water was added, the products were extracted into
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hexane, the organic layers were dried (Na2SO4), and the solvents were
evaporated. The crude product was passed through a silica gel plug
(hexane and then 6:1 hexane/CH2Cl2), giving 140 mg (76% yield) of
25 as a white crystalline solid. 11B NMR (128 MHz, CD3CN): δ −23.6
(s, 1B), −18.4 (d, J = 183 Hz, 1B), −16.3 (d, J = 184 Hz, 1B), −12.8
(d, J = 159 Hz, 2B), −11.6 (d, J = 158 Hz, 2B), −8.5 (d, J = 153 Hz,
1B), −5.4 (d, J = 166 Hz, 2B).
(19) Zakharkin, L. I.; Kalinin, V. N. Bull. Acad. Sci. USSR, Div. Chem.
Sci. 1966, 549−551.
(20) Zakharkin, L. I.; Kalinin, V. N. Bull. Acad. Sci. USSR, Div. Chem.
Sci. 1967, 908−910.
(21) Zakharkin, L. I.; Kalinin, V. N.; Kozlova, V. S.; Antonovich, V. A.
Russ. J. Gen. Chem. 1973, 43, 844−847.
(22) Plese
46, 687−692.
̌ ̌ ́
k, J.; Hermanek, S. Collect. Czech. Chem. Commun. 1981,
Cesium 6-Iodo-7,9-carborate and 1-Iodo-7,9-carborate
(26[Cs]). 26[Cs] was prepared in 57% yield by deboronation of 25
according to the procedure described for 24.
(23) Fox, M. A.; Wade, K. J. Mater. Chem. 2002, 12, 1301−1306.
(24) Alekseyeva, E. S.; Batsanov, A. S.; Boyd, L. A.; Fox, M. A.;
Hibbert, T. G.; Howard, J. A. K.; MacBride, J. A. H.; Mackinnon, A.;
Wade, K. Dalton Trans. 2003, 475−482.
1-Iodo derivative (minor isomer). {1H}11B NMR (128 MHz,
CD3CN): δ −35.6 (1B), −32.2 (1B), −22.0 (2B), −19.4 (2B), −4.0
(1B), −2.7 (2B).
(25) Fein, M. M.; Grafstein, D.; Paustian, J. E.; Bobinski, J.;
Lichtstein, B. M.; Mayes, N.; Schwartz, N. N.; Cohen, M. S. Inorg.
Chem. 1963, 2, 1115−1119.
(26) Semioshkin, A. A.; lnyushin, S. G.; Ermanson, L. V.; Petrorskii,
P. V.; Lemmen, P.; Bregadze, V. I. Russ. Chem. Bull. 1998, 47, 1985−
1988.
6-Iodo derivative (major isomer). {1H}11B NMR (128 MHz,
CD3CN): δ −40.0 (1B), −31.1 (1B), −20.5 (2B), −19.5 (2B), −5.8
(1B), −2.7 (2B).
AUTHOR INFORMATION
■
(27) Andrews, J. S.; Zayas, J.; Jones, M., Jr. Inorg. Chem. 1985, 24,
3715−3716.
Corresponding Author
*E-mail: piotr.kaszynski@vanderbilt.edu.
(28) Nikolova-Damayanova, B. Silver ion chromatography, http://
lipidlibrary.aocs.org/Silver/bnd_rev/index2.htm.
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This project was supported by the NSF (Grant DMR-
1207585).
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