Synthesis of closo- and nido-biscarboranes with rigid unsaturated linkers as precursors to linear metallacarborane-based molecular rods

Article abstract of DOI:10.1039/c3dt52596a

Several biscarborane-type derivatives of 8-iodo-1,2-dicarba-closo- dodecaborane (1), suitable as the precursors of linear metallacarborane-based molecular rods, were prepared. The synthesized closo-compounds contained two carborane moieties connected through a rigid linear unsaturated linker. The linkers were based on ethynylene and para-phenylene fragments and their combinations. The deboronation of all reported closo-compounds was selective and afforded nido-products with open pentagonal faces on opposite sides of the molecule, parallel to each other and perpendicular to the main molecular axis. All of the closo and nido products were characterized by a variety of physical methods (NMR, HRMS, IR). The structures of closo-carboranes 3, 6, 9, and 14 and nido-carboranes 15 and 17 were established by X-ray diffraction.

Full text of DOI:10.1039/c3dt52596a

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PAPER
Synthesis of closo- and nido-biscarboranes with
rigid unsaturated linkers as precursors to linear
metallacarborane-based molecular rods†
Cite this: Dalton Trans., 2014, 43,
4969
Alexander V. Safronov, Yulia V. Sevryugina, Kothanda Rama Pichaandi,‡
Satish S. Jalisatgi and M. Frederick Hawthorne*
Several biscarborane-type derivatives of 8-iodo-1,2-dicarba-closo-dodecaborane (1), suitable as the pre-
cursors of linear metallacarborane-based molecular rods, were prepared. The synthesized closo-
compounds contained two carborane moieties connected through a rigid linear unsaturated linker. The
linkers were based on ethynylene and para-phenylene fragments and their combinations. The deborona-
tion of all reported closo-compounds was selective and afforded nido-products with open pentagonal
faces on opposite sides of the molecule, parallel to each other and perpendicular to the main molecular
axis. All of the closo and nido products were characterized by a variety of physical methods (NMR, HRMS,
IR). The structures of closo-carboranes 3, 6, 9, and 14 and nido-carboranes 15 and 17 were established
by X-ray diffraction.
Received 19th September 2013,
Accepted 16th October 2013
DOI: 10.1039/c3dt52596a
www.rsc.org/dalton
Progress in molecular electronic applications of molecular
rods has occurred parallel to advances in physics, where
Introduction
Rigid-rod molecules—organic, organometallic, or inorganic— theoretical and practical approaches to single-molecule con-
have received attention during the past two decades. Numer- ductivity measurements and other types of characterization
ous reviews and articles are dedicated to the design, synthesis, have been developed.10
and application of these molecules, which can be discreet or
Several reports have been previously published on the
oligomeric in nature.1 The rigid molecules of fixed length can design and synthesis of rigid-rod molecules based on carbo-
be used as building blocks for supramolecular assemblies;2 rane fragments called “carbo(ra)rods”.11 Dimers and tetramers
i.e., as “molecular tinkertoys”.3 The discovery of porous coordi- of para-carborane containing direct Ccarborane–Ccarborane bonds
nation polymers, also known as metal–organic frameworks were prepared and characterized,11c as well as several deriva-
(MOFs), was the direct result of the development of molecular- tives of para- and meta-carboranes in which the polyhedral
rod chemistry. Transition-metal-containing MOFs show cata- moieties were connected through ethynylene and butadiyne-
lytic activity in a variety of organic reactions.4 Although they 1,4-diyl linkers attached both to cage carbon and to boron
are best known for their application as gas storage and separ- atoms.11a,b This line of investigation was continued in the
ation materials,5 MOFs also form thin films that can be used current study with the molecular rods based on metallacarbor-
as sensors.6
ane fragments. The synthesis of such molecules seemed attrac-
The application of molecular rods in molecular electronics tive due to the numerous known bis(dicarbollide)metal
is even more promising. Such molecules can potentially be complexes, many of which exist in more than one oxidation
used as unimolecular diodes,7 rectifiers,8 molecular wires that state.12 Rigid-rod molecules with metallacarboranes connected
provide electron transfer through a molecule, components of through rigid unsaturated linkers might be conductive and
computer memory devices, and in several additional areas.9 possibly serve as molecular wires.
There are two possible ways to prepare these compounds:
(1) Pd-catalyzed cross-coupling copolymerization of diiodo-
International Institute of Nano and Molecular Medicine (I2NM2), University of
substituted metallacarboranes with metal derivatives of the
desired linker molecules, and (2) connection of nido-biscarbor-
ane compounds containing the desired linkers via π-coordi-
nation with metals (Fig. 1).
Missouri, Columbia, MO 65211, USA. E-mail: hawthornem@missouri.edu
†Electronic supplementary information (ESI) available. CCDC 961327–961332.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3dt52596a
To maintain structural rigidity, the metallacarborane units
in rod molecules must be substituted at the apical positions,
‡Present address: Department of Chemistry and Energy Center, Purdue Univer-
sity, 560 Oval Drive, West Lafayette, IN 47907, USA.
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Since then, several important discoveries have been made con-
cerning the differences in reactivity of arylhalides and halocar-
boranes. First, in contrast to organic chemistry, only
compounds with B–I bonds participate in cross-coupling reac-
tions. Other derivatives (B–Cl, B–Br) appeared to be completely
nonreactive towards the oxidative addition to palladium.
Second, unlike organic cross-couplings, which can be catalyzed
by complexes of different transition metals, in borane and car-
borane chemistry, these reactions are exclusively palladium-
catalyzed. Third, in addition to the nature of the nucleophile,
the nature of the additive plays an important role the yield of
the product. For example, cross-coupling according to the
Suzuki protocol15 in the presence of CsF (a transmetallation-
assisting agent) proceeds with high yields only in the case of
para-carborane because meta- and ortho-carboranes react faster
with fluoride anion to form of nido-carboranes. Fourth, in
some cases, cross-coupling reactions are accompanied by
undesirable side reactions, most often by dehalogenation of
the starting material.16
Fig. 1 Two possible routes to metallacarborane-based molecular rods.
In the current study, four compounds of interest were
modeled; all of them contained two 1,2-dicarba-closo-dodeca-
boran-8-yl moieties connected through an unsaturated linker:
ethynylene, 1,4-phenylene, phenylene-1,4-diethynyl, or buta-
diyn-1,4-diyl. For simplicity, the synthesis of most of the target
molecules was performed via a one-step cross-coupling reac-
tion, i.e. through the coupling of two iodocarborane molecules
with one linker molecule containing two nucleophilic centers.
This approach has never been used in carborane cross-coup-
ling chemistry where reactions of a single carborane molecule
with one or several nucleophiles are the most common case.
This study began with the synthesis of a bis(carboranyl)-
acetylene compound. The commercially available bis-
(trimethylstannyl)acetylene (2, Scheme 1) was chosen as an
acetylene-containing nucleophile. The reaction of 8-iodo-1,2-
dicarba-closo-dodecaborane (1) with 2 in dioxane in the pres-
ence of Pd(PPh3)4 gave target compound 3 with 47% isolated
yield. The use of less-volatile bis(tributylstannyl)acetylene in
this reaction did not increase the reaction yield. In addition to
the coupling product 3, 20–30% of deiodinated product (ortho-
carborane) was regularly observed in this reaction. Analysis of
the literature data showed that this reaction represents the
first example of Stille cross-coupling in the carborane series.
Synthesis of the next target compound was achieved
through the generation of an organozinc derivative from
1,4-dibromobenzene (4, Scheme 2). The recently discovered
cobalt-assisted synthesis of organozincs17 appeared to be the
most convenient way to produce labile compound 5. The reac-
tion of 5 with 1 in acetonitrile in the presence of a Pd(0) cata-
lyst gave 6 in moderate yield. Most likely, side reactions of 5,
Fig. 2 Selective deboronation of 1 and the formation of metallacarbor-
anes with apical functionalization.
B(10) and B(10′), as shown in Fig. 1. In this case, conformational
interconversions of metallacarborane units have no effect on
the rod geometry. However, until recently, no reliable pro-
cedure has existed for the preparation of a carborane precursor
that would allow for synthesis of axially functionalized metalla-
carborane complexes.
In 2012 publication,13 a convenient synthetic route to a
less-common iodinated ortho-carborane molecule, 8-iodo-1,2-
dicarba-closo-dodecaborane, was described (1, Fig. 2). The
compound revealed an unusual and selective deboronation
pattern: in the resulting 1-iodo-7,8-dicarba-nido-undecaborate
anion, the B–I bond was perpendicular to the plane of the
open pentagonal C2B3 face. The compound formed the corres-
ponding bis(dicarbollide)cobalt and nickel complexes in high
yields. In these complexes, both the B–I bonds and the metal
atom were collinear, as required for the synthesis of molecular
rods. Cross-coupling polymerization of these complexes is
currently under investigation in our laboratory.
Reported here is the synthesis and characterization of closo
and nido precursors to metallacarborane-based molecular
rods via a single-step cross-coupling of 8-iodo-1,2-dicarba-
closo-dodecaborane with ethynylene and phenylene-based
nucleophiles.
Results and discussion
Synthesis of closo-biscarboranes
Palladium-catalyzed cross-coupling reactions using carborane
and borane substrates were discovered in the early 1980s.14
Scheme 1
4970 | Dalton Trans., 2014, 43, 4969–4977
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of acetylenes—is usually conducted in the presence of copper
compounds in air in an amine solution at elevated tempera-
tures. In the case of ortho-carboranes, these reaction con-
ditions are not favorable because amines cause cage
deboronation at elevated temperatures.19 Instead, oxidative
coupling of 13 was performed in DMSO in air in the presence
of Pd/C and CuI catalysts20 to produce the target compound 14
in 91% isolated yield. The overall yield of compound 14 was
84% based on the initial amount of the starting carborane 1.
Scheme 2
2. Synthesis of nido-biscarboranes
Several reagents can be used for deboronation of closo-carbor-
anes. Alkali-metal alkoxides and cesium and tetrabutyl-
ammonium (TBAF) fluorides are most commonly used
because they are inexpensive and produce target nido-carbor-
anes in very high yields.21 In the current study, TBAF was used
for two reasons. First, the products after reaction with TBAF
are easy to isolate, and product loss during the isolation
process is minimal. Second, TBA salts of nido-carboranes are
soluble in most organic solvents. In this study, solubility was
important for proper characterization of the target compounds
bearing double negative charge.
Scheme 3
With an excess of 1 M TBAF in THF at reflux, the reactions
of compounds 3, 6, 9, and 14 were complete within 5 h and
produced single products according to NMR analyses
(see below). The corresponding nido-biscarboranes 15–18
(Scheme 5) were isolated with excellent yields after water treat-
ment of the evaporated reaction mixtures (see Experimental
section).
Scheme 4
3. Characterization of closo- and nido-biscarboranes
such as polymerization and decomposition, can explain the
reduced yield of 6.
All of the new closo- and nido-biscarboranes were characterized
by multinuclear NMR. Because of the symmetry of the com-
pounds and the unsaturated nature of the linkers, both 1H and
13C{1H} spectra provided limited structural information.
Compared with the syntheses of 3 and 6, the synthesis of
compound 9 was relatively simple because the acetylenes in
the linker were separated by a 1,4-phenylene fragment. The
organozinc compound 8 was produced from the commercially
available 1,4-diethynylbenzene (7, Scheme 3) by an exchange
reaction of the initially generated bis(ethynyllithium) with
anhydrous zinc bromide. The subsequent cross-coupling reac-
tion of 8 with closo-carborane 1 in the presence of Pd(0) gave
product 9 with a 75% isolated yield.
Initially, synthesis the last target compound (14) containing
the butadiyn-1,4-diyl linker was planned through the double
cross-coupling of 1,4-trimethylstannylbutadiyne with com-
pound 1. However, a more efficient step-by-step synthetic route
was chosen because of the cost of the corresponding organotin
derivative and the possible low yield of the product.
1
For example, in the H NMR spectra of compounds 3 and 14,
which contain ethynylene and butadiyne linkers, respectively,
only one sharp signal corresponding to the carborane C–H
and a broad signal corresponding to the B–H bonds were
observed. In the 1H NMR of compounds 6 and 9, additional
signals were observed from the phenyl rings of the linkers,
which appeared as singlets at δ 7.39 and 7.34 ppm, respecti-
1
vely. The same trend was observed in the H NMR spectra of
nido-biscarboranes 15–18 (see Experimental section).
TMS-protected acetylenes18 can be coupled with iodo-
carboranes in a variety of ways with excellent yields. The reaction
of compound 1 with the organozinc derivative of ethynyltri-
methylsilane (11, Scheme 4) in the presence of Pd(PPh3)4
afforded compound 12 in 93% isolated yield. Deprotection of
12 was achieved quantitatively by a standard procedure
using K2CO3 in methanol. The next step—oxidative coupling
Scheme 5
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In the 13C{1H} NMR spectra of all the compounds, signals which is characteristic of nido-carboranes. Most importantly,
from the cage carbon atoms were observed in the normal the 11B NMR spectra of all compounds contained just one set
range for closo-compounds (see Experimental section). of signals which implied formation of a single nido-isomer for
However, spectra of both the closo and nido compounds both carborane cages. Assignment of the signals via the
acquired under standard conditions did not contain signals [11B–11B] COSY NMR spectrum of 3 confirmed that the result-
corresponding to the carbon atoms connected directly to ing compounds contain nido-carborane fragments substituted
boron. This absence of signal could result from a number of at position B(1) and that the regioselectivity characteristic of
causes. First, all of the carbons connected to carborane cages deboronation of the parent 8-iodo-1,2-dicarba-closo-dodecabor-
were quaternary, and the resonances of such atoms are some- ane persisted in its coupling products.
times difficult to acquire, even in relatively simple organic
High-resolution mass spectral data provided additional
systems. Second, quaternary carbons were connected to boron support to the NMR characterization of the reported closo and
atoms that contain two quadrupolar isotopes, 10B and 11B. The nido compounds. For all of the closo-biscarboranes, molecular
splitting on these nuclei significantly decreases the intensity ion peak envelopes with the expected isotope distribution pat-
of the carbon signal, which makes it difficult to distinguish terns were observed. The spectra of the nido-biscarboranes
them from the background. Signals from the rest of the contained two peak envelopes corresponding to the molecular
linkers’ carbon atoms were acquired without any difficulties ion bearing a double negative charge (Δm/z = 0.5) and to its
and corresponded to the expected structures. In the case of the agglomerate with the TBA cation bearing an overall single
intermediate compound 13, a 2J coupling of the terminal negative charge (Δm/z = 1) (see Experimental section).
carbon atom with the 11B isotope of the B(8) atom of the car-
X-ray quality crystals of the closo-biscarborane compounds,
borane cage was observed. The corresponding signal appeared 3, 6, 9, and 14 and the two nido-biscarborane compounds, 15
2
as a quartet with a J value of 21 Hz. Such coupling had been and 17 were obtained. A graphic representation of the refined
observed previously for carboranes with ethynyl substituents structures is shown in Fig. 3–8. In all of the structures, two car-
in different positions on the cage.18
borane units were connected to a linker fragment by a B–C
The 1H and 13C{1H} NMR spectra of nido-biscarboranes bond. The boron cluster cages showed no distortion, with the
1
15–18 also provided limited structural information. In the H B–B and B–C distances within the normal range. Similarly, the
NMR spectra of all of the compounds, signals of TBA counter para-substituted phenyl rings in compounds 6, 9, and 17
ions partially overlapped with resonances of carborane C–H were undistorted, displaying averaged C–C bond distances of
and B–H vertices. In the case of compounds 6 and 9, signals 1.395, 1.389, and 1.380 Å, respectively.
from the phenyl rings of the linkers were also observed. All
The B–C distances between the carborane cages and the
spectra contained a broad characteristic peak in the range of δ linker carbon atoms differed slightly for all of the compounds
−2–(−3) ppm, corresponding to the bridging or “extra” hydro- (Table S2†). The shortest B–C distance was observed for closo-
gen. Similarly, in the 13C{1H} NMR spectra of 15–18, signals
from all of the carbon atoms except for the ones directly con-
nected to the boron atoms were observed.
The majority of the structural information for the prepared
compounds was provided by their 11B, 11B{1H}, and [11B–11B]
COSY NMR spectra. The spectra of closo compounds 3, 9, and
14 were very similar and had the expected signal pattern of
2 : 1 : 1 : 2 : 3 : 1 in the typical range for closo-carboranes
between δ 0 and −20 ppm. A singlet corresponding to the B–C
bond appeared in the 11B NMR spectra of 3, 9, and 14 at δ
−8.1, −8.0, and −9.2 ppm, respectively. The assignment of the
signals was based on the [11B–11B] COSY NMR spectrum of 3.
This assignment confirmed that all of the reported com-
Fig. 3 The ORTEP representation of compound 3, drawn at the 40%
probability level.
pounds contained a closo-carborane fragment substituted at
the B(8) position of the cage. Because of the nature of the
linker in 6, its 11B spectra were slightly different. Similar to the
previously reported 11B NMR of 9-aryl-substituted carbor-
anes,22 the signal corresponding to the B–C bond was observed
in the positive part of the spectrum at δ +2.56 ppm. The sym-
metry of resonances corresponding to the remainder of the
molecule stayed unchanged.
Similar to the spectra of closo-biscarboranes, the 11B NMR
of the nido products provided more structural information.
The spectra of all of the nido-biscarboranes contained the
Fig. 4 The ORTEP representation of compound 6, drawn at the 40%
same 2 : 2 : 1 : 2 : 1 : 1 pattern in the range of 0 to −40 ppm, probability level.
4972 | Dalton Trans., 2014, 43, 4969–4977
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Fig. 5 The ORTEP representation of compound 9, drawn at the 40% probability level. Only one of the two molecules in the asymmetric unit is dis-
played. Chloroform molecules are omitted for clarity.
In 3, 9, 14, 15, and 17, the CuC bond length decreased in
the order 3 > 15 > 14 > 9 > 17. For an analogous carborane/
nido-carborane pair, such as 3/15 or 9/17, the CuC distance
was slightly longer in the neutral closo-biscarborane com-
pounds (3 and 9), and an insertion of the para-phenylene
linker shortened the CuC distance by approximately 0.02 Å,
such as in 9 vs. 3 and in 17 vs. 15. These effects can also be
observed in the overall lengths of the prepared molecules. The
Fig. 6 The ORTEP representation of compound 14, drawn at the 40%
probability level.
distances, measured between the most remote B-atoms in 3, 6,
and 9, or between the centroids of the open pentagonal C2B3
faces of nido-carboranes in 15 and 17, decreased in the order
9 (17.967 Å) > 17 (16.024 Å) > 14 (13.654 Å) > 6 (12.855 Å) >
3 (10.999 Å) > 15 (9.241 Å).
The degree of linearity of the linkers connecting the carbor-
ane cages was also examined. The angles between the lines
connecting substituted B-atoms and the centers of mass of the
molecules were compared. In all compounds containing the
benzene ring—6, 9, and 17—the linkers formed straight lines
with almost perfect 180.0° angles between the substituted
B-atoms and centroids of the para-phenylene ring. Similarly,
the linker in compound 14 displayed an ideal 180.0° angle,
whereas that in compound 15 demonstrated a slight bend
Fig. 7 The ORTEP representation of compound 15, drawn at the 40%
(177.6°). The bend in the crystal structure of 3 containing the
ethynylene linker was even more pronounced with the corres-
ponding angle equal to 171.7°.
probability level. The B(21)–B(31) nido-carborane cage exhibits a dis-
order due to averaging of two rotamers [in gauche- and trans-orien-
tations with respect to the B(1)–B(11) cage], modeled with the 0.5 : 0.5
ratio. For clarity purposes, only trans-rotamer is displayed, and two
NBu4+ cations are omitted.
In their solid states, the compounds also differed by the
rotational conformations of their carborane cages. To describe
the relative orientation of the carborane cage carbon atoms
with respect to each other around the axis of the linker, the
use of the well-established for alkane chemistry cis-, trans-, and
gauche-nomenclature is convenient. The carborane carbons
adopted the trans-conformation in 6, 9, 14, and 17 and the
gauche-conformation in compound 3. In the crystal structure
of 15, the trans- and gauche-conformers were averaged to
compound 3 (1.527(5) Å) with an ethynylene linker, whereas
the longest was observed for closo-compound 6 (1.584(3) Å)
containing a para-phenylene linker. In closo-biscarborane com-
pounds 9 and 14, the B–C distances were nearly identical:
1.544 and 1.545 Å, respectively. In the nido-biscarboranes 15
and 17, the B–C distances were 1.553 and 1.550 Å, respectively.
Fig. 8 The ORTEP representation of compound 17, drawn at the 40% probability level. Two NBu4+ cations are omitted for clarity.
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cause a positional disorder, which was modeled in the form of Synthesis of closo-biscarboranes
two equally present rotamers.
1,2-Bis(1′,2′-dicarba-closo-dodecaboran-8′-yl)ethyne (3). In
a glove-box, 8-iodo-1,2-dicarba-closo-dodecaborane (1, 0.500 g,
1.85 mmol), bis(trimethylstannyl)acetylene (2, 0.325 g,
0.925 mmol), Pd(PPh3)4 (0.107 g, 0.0925 mmol), anhydrous
LiCl (0.235 g, 5.55 mmol), and a few crystals of BHT were
combined in a flame-dried reaction tube and sealed with a
septum. Anhydrous ACN (5 mL) was added, and the reaction
mixture was stirred at 80 °C for 48 h (TLC and 11B NMR
control). The reaction mixture was co-evaporated with 10 mL
of silica and treated by column chromatography (40 mL of
silica) using EtOAc gradient (0 → 50%) in hexane. After evapor-
ation and drying, compound 3 was isolated as a beige solid
(0.134 g, 47%). NMR δH (500 MHz; CDCl3) 3.47 (4 H, br s, Ccb–
H), 2.9–1.5 (18 H, m, B–H); δB (160 MHz; CDCl3; BF3·Et2O) −1.4
(2 B, d, JB–H 151), −8.1 (1 B, s, B–C), −10.2 (1 B, d, JB–H 152),
−13.2 (2 B, d, JB–H 160), −14.5 (3 B, d, JB–H 163), −17.6 (1 B, br
d, JB–H 159); δC (125 MHz; CDCl3) 52.7 (Ccb–H); m/z (–APCI)
Conclusions
Several closo-biscarboranes were prepared starting from 8-iodo-
1,2-dicarba-closo-dodecaborane. In all of the reported com-
pounds both carborane cages were deboronated selectively in
the para-positions with respect to the substituent. Structural
analysis of the nido-compounds showed that the open penta-
gonal faces of the nido-cages were parallel to each other. This
fact makes the synthesized compounds attractive starting
materials for the preparation of linear molecular rods with
metallacarborane fragments in the main chain.
Experimental section
Materials
311.3741 [M
+
H]− (calcd for C6H22B20 310.3726); mp
338–340 °C; νmax/cm−1 (nujol) 3072, 3062 (CH), 2648, 2635,
2604, 2570 (BH).
Unless otherwise stated, all reactions were carried out under
an argon atmosphere using standard Schlenk-line techniques.
8-Iodo-1,2-dicarba-closo-dodecaborane (1) was prepared
according to the published procedure.13 Bis(trimethylstannyl)-
acetylene (2) was purchased from Acros Organics. 1,4-Dibromo-
benzene (4), 1,4-diethynylbenzene (7), and trimethylsilylacetyl-
ene (10) were purchased from Aldrich and were used without
further purification. Tetrabutylammonium fluoride (TBAF) was
purchased from TCI America as a 1 M solution in THF and
was used as received. Tetrahydrofuran (THF) was distilled in
an argon atmosphere from sodium benzophenone ketyl before
use. Acetonitrile (ACN) was distilled under an argon atmos-
phere from calcium hydride before use. Anhydrous methanol
was purchased from Taylor Scientific (St. Louis, MO) and was
used without further purification. Chromatography separ-
ations were performed in air using SorbTech silica (60 Å,
63–200 μm). Thin-layer chromatography was performed using
Merck precoated glass plates (Silica 60 F254) using a palla-
dium stain solution for spot developing.
1,4-Bis(1′,2′-dicarba-closo-dodecaboran-8′-yl)benzene (6). In
a glove-box, activated Zn powder (0.453 g, 6.93 mmol), anhy-
drous ZnBr2 (52.0 mg, 0.231 mmol), and anhydrous CoCl2
(30.0 mg, 0.231 mmol) were combined in a flame-dried one-
necked round-bottom flask equipped with a stirring bar and a
septum, and anhydrous ACN (2 mL) was added. A drop of TFA
was added to the suspension followed by the addition of 4-bromo-
toluene (42.0 μL, 0.345 mmol), and the reaction mixture
was stirred at RT for 30 min. A solution of 1,4-dibromobenzene
(4, 0.546 g, 2.31 mmol) in ACN (4 mL) was added dropwise,
and the resulting reaction suspension was stirred at RT for 3 h.
The solution of 5 was added to a suspension of 1 (1.00 g,
3.70 mmol) and Pd(PPh3)4 (0.427 g, 0.370 mmol) in ACN
(5 mL), and the resulting reaction mixture was stirred at 80 °C
for 48 h (TLC and 11B NMR control). The reaction mixture was
co-evaporated with 20 mL of silica and treated by column
chromatography (80 mL of silica) using EtOAc gradient
(0 → 50%) in hexane. After evaporation and drying, compound
6 was isolated as a white solid (0.154 g, 23%). NMR δH
(500 MHz; acetone-d6) 7.39 (4 H, s, C6H4), 4.59 (4 H, br s, Ccb–
H), 2.9–1.6 (18 H, m, B–H); δB (160 MHz; acetone-d6; BF3·Et2O)
Physical measurements
1
The H, 11B, 11B{1H}, and 13C{1H} NMR spectra were obtained 2.5 (1 B, s, B–C), −1.5 (2 B, d, JB–H 146), −9.4 (1 B, d, JB–H 149),
using a Bruker Avance-300, DRX 500 and Avance-500 NMR −12.4 (2 B, d, JB–H 125), −13.1 (3 B, d, JB–H 208), −16.7 (1 B,
spectrometers; 2D spectra were recorded on a Bruker Avance- br d, JB–H 175); δC (125 MHz; acetone-d6) 133.1 (C6H4), 55.8
500 NMR spectrometer. Boron NMR spectra were referenced to (Ccb–H); m/z (–APCI) 363.4056 [M + H]− (calcd for C10H26B20
1
15% BF3·Et2O in CDCl3 taken as 0 ppm. H and 13C{1H} NMR 362.4041); mp >350 °C (decomp); νmax/cm−1 (nujol) 2515br
spectra were referenced to the residual peak of the nondeuter- (BH).
ated solvent. Chemical shifts were reported in ppm, and the
1,4-Bis((1′,2′-dicarba-closo-dodecaboran-8′-yl)ethynyl)benzene
coupling constants were reported in Hz. Mass spectra were (9). A 2.5 M solution of BuLi in hexane (450 μL, 1.12 mmol)
obtained on an ABI QSTAR and Mariner Biospectrometry was added dropwise to a solution of 1,4-diethynylbenzene
Workstation by PerSeptive Biosystems. Melting points were (7, 74.0 mg, 0.586 mmol) in THF (3 mL) at 0 °C over a period
measured in sealed capillaries with an SRS OptiMelt appar- of 5 min. The reaction mixture was allowed to warm to RT, was
atus. IR spectra were recorded on a Nicolet Nexus 470 FT-IR stirred for 1 h, and was subsequently cooled to −70 °C; a solu-
spectrometer.
tion of anhydrous ZnBr2 (0.291 g, 1.29 mmol) in THF (4 mL)
4974 | Dalton Trans., 2014, 43, 4969–4977
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was then added over a period of 5 min. The reaction mixture for C4H12B10 168.1939); mp 148–150 °C; νmax/cm−1 (nujol)
was allowed to warm to RT and was then mixed with a solution 3064br (CH), 2609, 2582 (B–H), 2129 (CuC).
of
1
(0.316 g, 1.11 mmol) and Pd(PPh3)4 (65.0 mg,
(c) To a solution of 13 (0.200 g, 1.19 mmol) in 4 mL of
0.056 mmol) in THF (3 mL). The reaction mixture was stirred DMSO were added 10% Pd/C (64.0 mg, 60.0 μmol) and CuI
at reflux for 24 h (TLC and 11B NMR control). The reaction (12.0 mg, 60.0 μmol), and the resulting suspension was stirred
mixture was co-evaporated with 5 mL of silica and treated by in air for 24 h (TLC control). The reaction mixture was filtered,
column chromatography (20 mL of silica) using EtOAc gradi- poured into 20 mL of water, and extracted with ethyl acetate
ent (0 → 50%) in hexane. After evaporation and drying, com- (3 × 10 mL). The combined extracts were washed with water
pound 9 was isolated as a beige solid (0.173 g, 75%). NMR δH (2 × 20 mL) and brine (5 mL), dried over Na2SO4, and co-evap-
(500 MHz; CDCl3) 7.37 (4 H, s, C6H4), 3.56 (4 H, br s, Ccb–H), orated with 4 mL of silica. The compound was isolated by
3.3–1.6 (18 H, m, B–H); δB (160 MHz; CDCl3; BF3·Et2O) −1.5 column chromatography (16 mL of silica) using EtOAc (0 →
(2 B, d, JB–H 151), −8.0 (1 B, s, B–C), −10.1 (1 B, d, JB–H 152), 50%) in hexane to give, after evaporation and drying, 14
−13.3 (2 B, d, JB–H 160), −14.5 (3 B, d, JB–H 151), −17.0 (br d, (0.180 g, 91%) as a beige solid. NMR δH (500 MHz; acetone-d6)
1B); δC (125 MHz; CDCl3) 131.7, 123.5 (C6H4), 52.9 (Ccb–H); m/z 4.59 (4 H, br s, Ccb–H), 3.1–1.5 (18 H, m, B–H), 2.27 (1 H, s,
(–APCI) 410.4075 [M]− (calcd for C14H26B20 410.4044); mp uC–H); δB (160 MHz; CDCl3, BF3·Et2O) −1.0 (2 B, d, JB–H 148),
222–224 °C (decomp); νmax/cm−1 (nujol) 3069 (CH), 2598, 2571 −8.4 (1 B, s, B–C), −9.5 (1 B, d, JB–H 159), −13.1 (2 B, d), −13.9
(BH), 2191 (CuC).
(3 B, d, JB–H 158), −17.0 (1 B, d); δC (125 MHz; CDCl3) 82.4 (br,
1,4-Bis(1′,2′-dicarba-closo-dodecaboran-8′-yl)butadiyne (14). uC–Cu), 55.9 (Ccb–H); m/z (–TIS) 334.3712 [M]− (calcd for
(a) A 2.5 M solution of BuLi in hexane (1.56 mL, 3.89 mmol) C8H22B20 334.3727); mp >350 °C (decomp); νmax/cm−1 (nujol)
was added dropwise to a solution of trimethylsilylacetylene 3064 (CH), 2641, 2628, 2610, 2581 (BH), 2108 (CuC).
(10, 549 μL, 3.89 mmol) in THF (10 mL) at 0 °C over a period
Synthesis of nido-biscarboranes
of 5 min. The reaction mixture was allowed to warm to RT, was
stirred for 1 h, and was cooled to −70 °C. A solution of anhy-
General procedure for the synthesis of TBA salts of nido-bis-
drous ZnBr2 (1.01 g, 4.47 mmol) in THF (10 mL) was sub- carboranes 15–18. To a solution of the corresponding closo-
sequently added over a period of 5 min. After warming to RT, carborane (1 mmol) in 3 mL of THF was added 10 mL of 1 M
the prepared solution of trimethylsilylethynylzinc bromide 11 TBAF in THF (10 mmol). The reaction mixture was heated to
was mixed with a solution of 1 (0.700 g, 2.59 mmol) and Pd- reflux until the TLC analysis showed the absence of the start-
(PPh3)4 (0.150 g, 0.129 mmol) in THF (10 mL), and the reaction ing material (2–5 h). The reaction mixture was evaporated to
mixture was stirred at reflux for 24 h (TLC and 11B NMR dryness, and 5 mL of water was added to the residue in one
control). The reaction mixture was co-evaporated with 10 mL portion. The formed precipitate was filtered on a glass frit,
of silica and treated by column chromatography (40 mL of washed with water (3 × 3 mL) and ether (5 mL), and dried
silica) using DCM gradient (0 → 30%) in hexane. After evapor- under vacuum.
ation and drying, TMS-protected compound 12 was isolated as
Tetrabutylammonium 1,2-bis(7′,8′-dicarba-nido-undecaborate-
a white solid (0.580 g, 93%). NMR δH (500 MHz; CDCl3) 3.51 1′-yl)ethyne (15). White solid (94%). NMR δH (500 MHz;
(2 H, br s, Ccb–H), 3.3–1.5 (9 H, m, B–H), 0.15 (9 H, s, TMS); δB acetone-d6) 3.44 (16 H, m, TBA–CH2), 2.34–(−0.21) (16 H, br m,
(160 MHz; CDCl3; BF3·Et2O): δ −1.5 (2 B, d, JB–H 151), −8.7 B–H), 1.82 (16 H, m, TBA–CH2), 1.73 (4 H, br s, Ccarb–H), 1.43
(1 B, s, B–C), −10.1 (1 B, d, JB–H 175), −13.3 (2 B, d, JB–H 154), (16 H, m, TBA–CH2), 0.98 (24 H, m, TBA–CH3), −2.40 (2 H, br
−14.4 (3 B, d, JB–H 148), −17.3 (1 B, br d, JB–H 165); δC m, B–H–B); δB (160 MHz; acetone-d6; BF3·Et2O): −12.8 [2 B, d,
(125 MHz; CDCl3) 104.8 (TMC–Cu), 52.9 (Ccb–H), 0.24 (TMS); JB–H 132, B(9,11)], −16.5 [2 B, d, JB–H 137, B(5,6)], −18.2 (1 B, d,
m/z (–TIS) 240.2409 [M − H]− (calcd for C7H20B10Si 240.2337); JB–H 159, B(3)], −22.6 (2 B, d, JB–H 147, B(2,4)], −34.9 [1 B, dd,
mp 110–112 °C; νmax/cm−1 (nujol) 3070, 3065 (νC–H), 2663, JB–H
123, JB–H
38, B(10)], −35.5 [1 B, s, B(1)]; δC
term
bridge
2652, 2638, 2608, 2586, 2567 (BH), 2073 (CuC).
(125 MHz; acetone-d6) 59.4 (TBA), 43.1 (br, Ccarb–H), 24.4, 20.4,
(b) Anhydrous methanol (5 mL) was added to a solid 13.8 (TBA); m/z (–APCI) 144.7116 [M]2−, 531.7629 [M + TBA]−
mixture of 12 (0.200 g, 0.833 mmol) and anhydrous K2CO3 (calcd for C14H26B18 289.3504, M2−144.6749,
(0.173 g, 1.25 mmol), and the resulting suspension was stirred 531.6363); νmax/cm−1 (nujol): 2534, 2507 (BH).
M + TBA
at RT for 2 h (TLC control). The reaction mixture was dissolved
Tetrabutylammonium 1,4-bis(7′,8′-dicarba-nido-undecabo-
in water (10 mL) and extracted with ether (3 × 5 mL). The com- rate-1′-yl)benzene (16). White solid (92%). NMR δH (500 MHz;
bined organic extracts were passed through a plug containing acetone-d6) 7.53 (4 H, s, C6H4), 3.30 (16 H, m, TBA–CH2), 2.46–
0.5 mL of silica and 4 mL of anhydrous Na2SO4 and were evap- (−0.08) (16 H, m, B–H), 1.88 (Ccarb–H), 1.74 (16 H, m, TBA–
orated to dryness to give 13 (0.134 g, 96%) as a white solid. CH2), 1.40 (16 H, m, TBA–CH2), 0.96 (24 H, m, TBA–CH3),
NMR δH (500 MHz; CDCl3) 3.56 (2 H, br s, Ccb–H), 2.9–1.6 (9 H, −2.23 (2 H, br m, B–H–B); δB (160 MHz; acetone-d6; BF3·Et2O)
m, B–H), 2.27 (1 H, s, uC–H); δB (160 MHz; CDCl3; BF3·Et2O) −11.5 (2 B, d, JB–H 134), −15.6 (2 B, d, JB–H 134), −17.5 (1 B, d,
−1.4 (2 B, d, JB–H 151), −8.9 (1 B, s, B–C), −9.8 (1 B, d, JB–H JB–H 154), −21.8 (2 B, d, JB–H 145), −25.9 [1 B, s, B(1)], −33.6
154), −13.1 (2 B, d, JB–H 163), −14.2 (2 B, d, JB–H 166), −14.7 (1 B, dd, JB–H term 127, JB–H bridge 43); δC (125 MHz; acetone-d6)
(1 B, d), −17.0 (1 B, d, JB–H 180); δC (125 MHz; CDCl3) 85.6 (q*, 134.7 (C6H4), 59.2 (TBA), 43.9 (br, Ccarb–H), 24.4, 20.3, 13.8
2J 21, uC–H), 53.2 (Ccarb–H); m/z (–TIS) 168.2075 [M]− (calcd (TBA); m/z (–TIS) 170.7397 [M]2−, 583.8452 [M + TBA]− (calcd
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for C8H22B18 341.3820, M2− 170.6907, M + TBA 583.6679); positions. Therefore, the refinement of the H-atoms was
νmax/cm−1 (thin film) 2962, 2934, 2875 (CH), 2507br (BH).
mixed. In 17, only the hydrogens of the nido-carborane groups
Tetrabutylammonium 1,4-bis((7′,8′-dicarba-nido-undecabo- were located in the difference Fourier maps and refined indivi-
rate-1′-yl)ethynyl)benzene (17). Beige solid (96%). NMR δH dually, whereas the hydrogens of the aromatic group and the
(500 MHz; acetone-d6) 7.24 (4 H, s, C6H4), 3.41 (16 H, m, TBA– TBA cations were included at geometrically idealized positions;
CH2), 2.43–(−0.15) (16 H, br m, B–H), 1.80 (20 H, m, Ccarb–H, therefore, the refinement of the H-atoms was mixed. The
TBA–CH2), 1.42 (16 H, m, TBA–CH2), 0.93 (24 H, m, TBA–CH3), crystal structure of 15 revealed two types of disorder. One type
−2.34 (2 H, br m, B–H–B); δB (160 MHz; acetone-d6; BF3·Et2O) of disorder was caused by the three fluxional arms of the TBA
−10.3 (2 B, d, JB–H 135), −14.7 (2 B, d, JB–H 136), −16.4 (1 B, d, cation. This disorder was modeled to provide the 0.6 : 0.4 ratio
JB–H 163), −20.7 (2 B, d, JB–H 145), −32.9 (1 B, dd, JB–H term 127, of the superimposed forms. In the second type of disorder,
JB–H bridge 42), −34.5 [1 B, s, B(1)]; δC (125 MHz; acetone-d6) one of the nido-carborane cages exhibited rotational disorder,
131.9, 125.7 (C6H4), 59.4 (TBA), 43.4 (br, Ccarb–H), 24.4, 20.4, which made distinguishing between the boron and carbon
13.8 (TBA); m/z (–APCI) 194.7012 [M]2−, 631.6817 [M + TBA]− atoms at two atom sites difficult. This disorder was modeled
(calcd for C14H26B18 389.3818, M2− 194.6909, M + TBA using partial occupancies for the boron and carbon atoms,
631.6666); νmax/cm−1 (nujol) 2576, 2552, 2515 (BH), 2183 which provided a 0.5 : 0.5 ratio for the superimposed rotamers.
(CuC).
The TBA cation in the crystal structure of 17 exhibited disorder
Tetrabutylammonium 1,4-bis(7′,8′-dicarba-nido-undecaborate- of its the two fluxional arms. This disorder was modeled to
1′-yl)butadiyne (18). Beige solid (95%). NMR δH (500 MHz; provide 0.65 : 0.35 and 0.52 : 0.48 ratios for the two super-
acetone-d6) 3.44 (16 H, m, TBA–CH2), 2.39–(−0.19) (16 H, br m, imposed forms of each arm. The crystal structure of 9 contained
B–H), 1.82 (20 H, m, Ccarb–H, TBA–CH2), 1.44 (16 H, m, TBA– two disordered molecules of chloroform in an asymmetric
CH2), 0.98 (24 H, m, TBA–CH3), −2.39 (2B, br m, B–H–B); δB unit. The disorders were modeled in the form of four rotamers
(160 MHz; acetone-d6; BF3·Et2O) −11.4 (2 B, d, JB–H 134), −15.8 in a 0.60 : 0.14 : 0.11 : 0.15 ratio for one of the chloroform mole-
(2 B, d, JB–H 135), −17.5 (1 B, d, JB–H 165), −21.7 (2 B, d, JB–H cules and in the form of two rotamers in a 0.5 : 0.5 ratio for the
146), −33.9 (1 B, dd, JB–H term 127, JB–H bridge 43), −35.8 [1 B, s, other molecule. The crystal structure of 3 was solved in space
B(1)]; δC (125 MHz; acetone-d6) 59.4 (TBA), 43.4 (br, Ccarb–H), group Pnn2; however, because the compound is a weak ano-
24.5, 20.4, 13.9 (TBA); m/z (–TIS) 156.7275 [M]2−, 555.8129 malous scatterer (i.e., in contains only light atoms B, C, and H)
[M + TBA]− (calcd for C8H22B18 313.3506, M2− 156.6750, and because data were collected using Mo Kα radiation, its
M + TBA 555.6364); νmax/cm−1(thin film) 2962, 2934 (CH), absolute configuration could not be reliably determined.
2518br (BH).
Therefore, Friedel pairs were merged, and any references to
the Flack parameter were removed. The crystallographic data
and the details of the data collection and structure refine-
X-ray diffraction studies
The X-ray quality crystals of 3, 6, 9, 14, 15, and 17 were ments of 3, 6, 9, 14, 15, and 17 are provided in Table S1.†
obtained by slow evaporation of chloroform (3, 9, 14) or CCDC 961327 (3), CCDC 961328 (6), CCDC 961329 (9), CCDC
acetone (6, 15, 17) solutions. Data collection for the crystals 961330 (14), CCDC 961331 (15) and CCDC 961332 (17) contain
was performed at −100 °C on a Bruker SMART 1000 CCD area the supplementary crystallographic data for this paper.
detector system using the ω scan technique with Mo Kα radi-
ation (λ = 0.71073 Å) from a graphite monochromator. Data
reduction and integration were performed with the software
package SAINT.23 Data were corrected for absorption using
SADABS.24 The crystal structures were solved with the direct
methods program SHELXS-97 and were refined by full matrix
least squares techniques with the SHELXTL25 suite of pro-
grams. All non-hydrogen atoms were refined with anisotropic
thermal parameters, except for the disordered chlorine atoms
in the crystal structure of 9. The hydrogen atoms in 3, 6, and
14 were located in the difference Fourier maps and were
refined individually. In 9, all hydrogen atoms, except those of
the disordered chloroform, were located in the difference
Fourier maps and were refined individually, whereas the
chloroform hydrogens were included at geometrically idealized
positions; therefore, the refinement of H-atoms was mixed. In
15, only the hydrogens of the open pentagonal C2B3 faces of
the nido-carboranes were located in the difference Fourier
maps and were refined individually, whereas the remaining
BH hydrogens, as well as those of the tetrabutylammonium
(TBA) cations, were included at geometrically idealized
Acknowledgements
The authors gratefully acknowledge the National Science Foun-
dation (CHE-0702774) for financial support of this work,
Dr Mark Lee and Mr Brett Meyers for measuring the mass
spectra of the prepared compounds. The authors also thank
Dr Ilia Guzei (UW-Madison) for the in-house crystallographic
program “ModiCIFer”.
References
1 See, for example: (a) P. F. H. Schwab, M. D. Levin and
J. Michl, Chem. Rev., 1999, 99, 1863; (b) P. F. H. Schwab,
J. R. Smith and J. Michl, Chem. Rev., 2005, 105, 1197.
2 P. J. Stang and B. Olenyuk, Acc. Chem. Res., 1997, 30, 502.
3 J. Michl and T. F. Magnera, Proc. Natl. Acad. Sci. U. S. A.,
2002, 99, 4788.
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Dalton Transactions
Paper
4 J.-Y. Lee, O. K. Farha, J. Roberts, K. A. Scheidt,
S.-B. T. Nguyen and J. T. Hupp, Chem. Soc. Rev., 2009, 38,
1450.
5 See, for example: (a) J.-R. Li, Y. Ma, M. C. McCarthy,
J. Sculley, J. Yu, H.-K. Jeong, P. B. Balbuena and
Nauk. SSSR, Ser. Khim., 1980, 1691; (b) L. I. Zakharkin,
A. I. Kovredov, V. A. Ol’shevskaya and Zh.
S. Shaugumbekova, J. Organomet. Chem., 1982, 226, 217;
(c) L. I. Zakharkin, A. I. Kovredov and V. A. Ol’shevskaya,
Izv. Akad. Nauk. SSSR, Ser. Khim., 1985, 888.
H.-C. Zhou, Coord. Chem. Rev., 2011, 255, 1791; 15 L. Eriksson, I. P. Beletskaya, V. I. Bregadze, I. B. Sivaev and
(b) L. J. Murray, M. Dinca and J. R. Long, Chem. Soc. Rev., S. Sjöberg, J. Organomet. Chem., 2002, 657, 267.
2009, 38, 1294; (c) X.-J. Wang, P.-Z. Li, Y. Chen, Q. Zhang, 16 (a) W. J. Marshall, R. J. Young and V. V. Grushin, Organo-
H. Zhang, X. X. Chan, R. Ganguly, Y. Li, J. Jiang and
Y. Zhao, Sci. Rep., 2013, 3, 1149, DOI: 10.1038/srep01149.
6 A. Bétard and R. A. Fischer, Chem. Rev., 2012, 112, 1055.
7 See, for example: (a) M. Elbing, R. Ochs, M. Koentopp,
M. Fischer, C. von Hänisch, F. Weigend, F. Evers,
metallics, 2001, 20, 523; (b) L. I. Zakharkin, E. V. Balagurova
and V. N. Lebedev, Russ. J. Gen. Chem., 1998, 68, 972.
17 (a) H. Fillon, C. Gosmini and J. Périchon, J. Am. Chem. Soc.,
2003, 125, 3867; (b) I. Kazmierski, C. Gosmini, J.-M. Paris
and J. Périchon, Tetrahedron Lett., 2003, 44, 6417.
H. Weber and M. Mayor, Proc. Natl. Acad. Sci. U. S. A., 18 H. Himmelspach and M. Finze, Eur. J. Inorg. Chem., 2010,
2005, 102, 8815; (b) M. J. Kumar, Recent Pat. Nanotechnol.,
2007, 1, 51.
2012 and references therein.
19 L. I. Zakharkin and V. N. Kalinin, Tetrahedron Lett., 1965,
8 R. M. Metzger, Chem. Rev., 2003, 103, 3803.
407.
9 R. L. Carroll and C. B. Gorman, Angew. Chem., Int. Ed., 20 T. Kurita, M. Abe, T. Maegawa, Y. Monguchi and H. Sajiki,
2001, 41, 4378. Synlett, 2007, 2521.
10 (a) D. K. James and J. M. Tour, Chem. Mater., 2004, 16, 21 (a) M. F. Hawthorne, D. C. Young, P. M. Garrett,
4423; (b) B. A. Mantooth and P. S. Weiss, Proc. IEEE, 2003,
91, 1785.
11 (a) A. Herzog, S. S. Jalisatgi, C. B. Knobler, T. J. Wedge and
M. F. Hawthorne, Chem.–Eur. J., 2005, 11, 7155;
(b) W. Jiang, D. E. Harwell, M. D. Mortimer, C. B. Knobler
D. A. Owen, S. G. Schwerin, F. N. Tebbe and P. A. Wegner,
J. Am. Chem. Soc., 1968, 90, 862; (b) M. A. Fox, W. R. Gill,
P. L. Herbertson, J. A. H. MacBride, K. Wade and
H. M. Colquhoun, Polyhedron, 1996, 15, 565; (c) J. Yoo,
J.-W. Hwang and Y. Do, Inorg. Chem., 2001, 40, 568.
and M. F. Hawthorne, Inorg. Chem., 1996, 35, 4355; 22 See, for example, ESI† to A. M. Spokoyny, T. C. Li,
(c) X. Yang, W. Jiang, C. B. Knobler and M. F. Hawthorne,
J. Am. Chem. Soc., 1992, 114, 9719.
12 M. F. Hawthorne, Acc. Chem. Res., 1968, 1, 281.
O. K. Farha, C. W. Machan, C. She, C. L. Stern, T. J. Marks,
J. T. Hupp and C. A. Mirkin, Angew. Chem., Int. Ed., 2010,
49, 5339.
13 A. V. Safronov, Y. S. Sevryugina, S. S. Jalisatgi, 23 Bruker, SAINT v 7.68A, Bruker AXS Inc., Madison, WI,
R. D. Kennedy, C. L. Barnes and M. F. Hawthorne, Inorg.
Chem., 2012, 51, 2629.
2009.
24 G. M. Sheldrick, SADABS 2008/1, Gottingen, 2008.
14 See, for example: (a) L. I. Zakharkin, A. I. Kovredov, 25 G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystal-
V. A. Ol’shevskaya and Zh. S. Shaugumbekova, Izv. Akad.
logr., 2008, 64, 112.
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