Syntheses and structural characterization of o-carboranylamides with direct cage-amide bond

Article abstract of DOI:10.1039/c3dt52785a

Reactions of lithio-o-carborane with isocyanates under various conditions were studied, and the structural features of the resulting carboranylamides are described. The reactions of o-carborane (o-C₂B₁₀H ₁₂), n-BuLi (two equiv.) and two equiv. of (substituted) phenylisocyanate, pentylisocyanate and p-ethylphenylthioisocyanate in diethyl ether, respectively, led, after workup, to the corresponding mono-substituted carboranylamide 2a-g and carboranylthioamide 5 in low to moderate yields, and only with RNCO (R = Ph, m-MeOC₆H₄, pentyl) could disubstituted products 3a-c be isolated. The reaction with phenylisocyanate afforded the mono-amide and di-amide products in a ratio of approximately 1:2, whereas in the other two reactions the ratios are approximately 4:1 and 32, respectively. In tetrahydrofuran all the reactions attempted with RNCO (R = Ph, p-IC₆H₄, m-NCC₆H₄ and pentyl) gave more monoamide products than those in diethyl ether. With phenylisocyanate no diamide product was isolated and with pentylisocyanate the ratio between monoamide and diamide is approximately 3.5:1. The new carboranylamides were characterized by means of elemental analyses, IR and NMR spectroscopy and mass spectrometry, as well as single-crystal X-ray diffraction analyses of 2a-f, 3a and 5.

Full text of DOI:10.1039/c3dt52785a

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Syntheses and structural characterization of
o-carboranylamides with direct cage–amide bond†
Cite this: Dalton Trans., 2014, 43,
5083
Yong Nie,* Yafeng Wang, Jinling Miao, Deqian Bian, Zhenwei Zhang, Yu Cui and
Guoxin Sun
Reactions of lithio-o-carborane with isocyanates under various conditions were studied, and the struc-
tural features of the resulting carboranylamides are described. The reactions of o-carborane (o-C2B10H12),
n-BuLi (two equiv.) and two equiv. of (substituted) phenylisocyanate, pentylisocyanate and p-ethyl-
phenylthioisocyanate in diethyl ether, respectively, led, after workup, to the corresponding mono-substi-
tuted carboranylamide 2a–g and carboranylthioamide 5 in low to moderate yields, and only with RNCO
(R = Ph, m-MeOC6H4, pentyl) could disubstituted products 3a–c be isolated. The reaction with phenyl-
isocyanate afforded the mono-amide and di-amide products in a ratio of approximately 1 : 2, whereas in
the other two reactions the ratios are approximately 4 : 1 and 3 : 2, respectively. In tetrahydrofuran all
the reactions attempted with RNCO (R = Ph, p-IC6H4, m-NCC6H4 and pentyl) gave more monoamide
products than those in diethyl ether. With phenylisocyanate no diamide product was isolated and with
pentylisocyanate the ratio between monoamide and diamide is approximately 3.5 : 1. The new carboranyl-
amides were characterized by means of elemental analyses, IR and NMR spectroscopy and mass
spectrometry, as well as single-crystal X-ray diffraction analyses of 2a–f, 3a and 5.
Received 7th October 2013,
Accepted 29th November 2013
DOI: 10.1039/c3dt52785a
www.rsc.org/dalton
Introduction
Polyhedral carborane cluster compounds have been widely
studied because of their three-dimensional aromatic structures
and unique physical and chemical properties.1 Among the
most studied carborane systems are the icosahedral 1,2-
dicarba-closo-dodecaborane(12) (C2B10H12, o-carborane (1))
and its m- and p-isomers (Fig. 1). Due mainly to the diverse
potential applications in biomedical, catalysis and materials
Fig. 1 Structures of o-, m-, and p-carborane isomers (unmarked
vertices are BH).
sciences, the syntheses and properties of functionalized are a number of papers concerning such carboranylamide
carboranes have become an increasingly important subfield. compounds, there has been a relatively small portion of such
compounds in which the carborane skeleton and the amide
To that end the reactions of carborane–metal species with
small unsaturated molecules (aldehyde, ketone, alkene, alkyne, moieties are directly linked at the cage carbon8,9 or boron10,11
carbodiimide, and so on) have proven a straightforward and atom. Moreover, there has been much less work on the crystal-
effective way.2–5
lographic studies of such carboranylamide species (some
The structure of amide is pervasive in proteins and pep- of which belong to carborane carbamoyl compounds such as
tides, and is an important fragment in organic medicines. The carboranylcarbamates derived from C- or B-aminocarboranes).
The general approach to amide compounds is the conden-
carborane-substituted amides or carboranylamides have great
potential in medicinal chemistry such as the boron neutron sation reaction of amine and carboxylic acid or its derivatives,
capture therapy (BNCT) of tumors and the boron neutron which also applies to the synthesis of carboranylamides (reac-
capture synovectomy (BNCS)6,7 of rheumatoid. Although there
tions of carboranyl acid halides and amines (or ammonia)
or, carboranylamine and carboxylic acid halides).1 The reac-
tion of lithiocarborane with amino-substituted acid chloride
School of Chemistry and Chemical Engineering, University of Jinan, 106 Jiwei Road,
(Me2NC(O)Cl) also led to the formation of the corresponding
250022 Jinan, P. R. China. E-mail: chm_niey@ujn.edu.cn; Tel: +86-531-82767937
carboranylamide.12 Recently a new synthesis of carboranyl-
†Electronic supplementary information (ESI) available. CCDC 937467, 952824,
amides has be reported by transition metal catalysis. For
950184, 937468, 958414, 958415, 937469 and 963492. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c3dt52785a
instance, Bregadze and Beletskaya et al.13 developed the
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palladium catalyzed cross coupling of B-iodinated m- and p-
carboranes with sodium amidates which afforded the corres-
ponding carboranylamide products. Llop et al.14 reported
some m-carboranylamides via palladium catalyzed reactions of
C-iodinated carborane with amine and CO.
Table 1 The amounts of reactants and product distribution in the reac-
tions of lithiocarborane and isocyanatesa
Isolated
yield/%
n-BuLi/ RNCO/
Entry
R
1/mmol mmol
mmol
2
3
Another straightforward route to amide is the reaction of
organolithium and isocyanates. In this direction, Zakharkin
et al.8b reported that o-(RC)(CLi)B10H10 (R = Me, Ph) react with
phenylisocyanate and phenylthioisocyanate, respectively, to
give the corresponding carboranylamide and -thioamide pro-
ducts. Wade et al.9c studied similar reactions of Li2C2B10H10
and phenylisocyanate and methylisocyanate, respectively, and
obtained the corresponding disubstituted carboranylamides.
To further explore the reactions of lithiocarboranes with
different isocyanates and the detailed structures of the carbor-
anylamides with direct cage–amide bond(s), we have investi-
gated the reactions of lithio-o-carboranes with (substituted)
phenylisocyanates, pentylisocyanate and p-ethyl-phenylthioiso-
cyanate under various conditions, in which it was found that
the solvent effect (diethyl ether and THF) and steric effect of
isocyanates influence the product distribution (monoamide
and/or diamide) and the yields. The isolation, spectral charac-
terization and crystal structures of these carboranylamides are
reported herein.
1
m-MeOC6H4
m-MeOC6H4
C6H5
C6H5
n-C5H11
n-C5H11
o-FC6H4
p-IC6H4
p-IC6H4
m-NCC6H4
m-NCC6H4
0.99
1.00
1.01
1.01
0.99
1.03
1.00
1.01
0.42
1.01
1.02
2.20
1.10
2.02
2.15
2.20
2.20
2.05
2.20
0.88
2.20
2.20
2.20
2.20
2.11
1.09
2.09
2.27
2.15
2.18
2.13
2.15
0.86
2.19
2.20
2.12
2.07
55.4 14.6
61.1
26.7 59.0
81.6
58.5 38.7
70.5 20.8
2b
3
—
4c
5
—
6c
7
58.6
10.4
65.3
17.5
64.4
23.3
65.8
—
—
—
—
—
—
—
8d
9c
10e
11c
12
13c
p-Cl-o-CF3C6H3 1.01
p-Cl-o-CF3C6H3 1.01
a Unless otherwise stated, diethyl ether was used as the solvent, the
yields are isolated ones based on the amount of 1. b The reaction
mixture was cooled by liq. N2, then warmed to room temperature.
c THF was used as the solvent. d p-IC6H4NCO was added as a solid,
toluene as the solvent. e m-NCC6H4NCO was added as a solid.
To understand our results on 3-methoxyphenylisocyanate,
we repeated the same reaction as Wade et al.9c of dilithiocar-
borane with two equiv. of phenylisocyanate in diethyl ether
under reflux, and obtained the corresponding diamide 3b as
the major product, together with a relatively small amount of
the monoamide 2b8a,e (Scheme 1, Table 1). Compounds 2b and
3b were characterized by IR, NMR and MS, as well as single-
crystal X-ray analysis of 2b (see below).
Comparing with Wade’s results, the reactions were carried
out under almost the same conditions and 3-methoxyphenyl-
isocyanate has only one more 3-OMe substituent on the phenyl
ring, but the product distribution is different. This difference
may be attributed to the presence of the electron-donating
3-OMe group, which results in slightly lower electrophilicity of
the isocyanate, meanwhile the steric effect of the carboranyl
skeleton and the isocyanate compound may also play a role in
such transformations, leading to monoamide as the major product.
As the monoamide is the major product in the reaction
with 3-methoxyphenylisocyanate, we carried out a similar
reaction to Planas et al.15 (LiC2B10H11 and pyridylaldehyde
form carboranylalcohol at low temperature) by reacting
LiC2B10H11 with 3-methoxyphenylisocyanate in a 1 : 1 ratio
(Scheme 2 and entry 2 in Table 1). Under such conditions,
compound 2a was obtained in a yield of 61%, without any
diamide 3a isolated.
Results and discussion
Syntheses and spectral characterization
Wade et al.9c reacted Li2C2B10H10 with two equivalents of
RNCO and obtained the corresponding carboranyl diamide
products (yields 77%, R = Ph; 65%, R = Me), and characterized
them by IR and MS methods. We studied the corresponding
reaction of o-carborane (1), n-BuLi and 3-methoxyphenyliso-
cyanate (in a ratio of = 1 : 2 : 2 or 1 : 2.2 : 2.2) and isolated, after
workup, the corresponding monoamide 2a and diamide 3a
(Scheme 1, Table 1), but with 2a as the major product, which
is different from Wade’s results.9c Compounds 2a and 3a
were characterized by IR and NMR spectroscopy and mass
spectrometry, as well as single-crystal X-ray analyses (see
below).
In order to further optimize the reaction conditions, we
tried the reaction of 1 and 3-methoxyphenylisocyanate in the
presence of tetrabutylammonium fluoride (TBAF) at room
temperature, and 2a was isolated only in a low yield (6.5%)
with the discovery of the starting carborane 1. Moreover, elev-
ated temperature did not improve the yield of 2a, leading
instead to the deboronation product [Bu4N][C2B9H12]16 (4)
(Scheme 3). Comparing the results with those of Yamamoto
et al.,17 who reported that in the presence of TBAF, 1 and
Scheme 1 Reactions of lithiocarborane with isocyanates.
5084 | Dalton Trans., 2014, 43, 5083–5094
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Scheme 2 Reaction of LiC2B10H11 with one equiv. of 3-methoxyphenyl-
isocyanate.
Scheme 4 Reaction of dilithiocarborane with 4-ethylphenyl-
thioisocyanate.
remarkably different to that in diethyl ether (Table 1). In the
case of pentylisocyanate, more monoamide and somewhat less
diamide were isolated. These results may probably be attribu-
ted to the better solubility of both the isocyanates and lithio-
carborane in THF and steric reason of the isocyanates. In THF
all the reactions attempted gave more monoamide products
than the corresponding diamide (if any).
Scheme 3 Reaction of 1, 3-methoxyphenylisocyanate with TBAF.
aldehyde/ketone produced the corresponding carboranylalco-
hols, it suggests that due to the weaker electrophilicity of the
isocyanate function than the aldehyde/ketone, the addition of
lithiocarborane to isocyanate is sluggish, leading to nido-car-
borane 4 via deboronation instead.
It was described by Teixidor et al.18 that the monolithio-
o-carborane species in different ethereal solvents (diethyl
ether, dimethoxyethane and THF) show different reactivity
towards S/Se and halogen-containing reagents, one of the
main reason being the different property of contact ion pairs
of solvated lithiocarboranes. In the present case of phenyl-
isocyanate, similarly the different property of the contact ion
pairs of solvated dilithiocarborane species (with THF or
diethyl ether) may play a major role.
Apart from the reactions with isocyanates, we also investi-
gated a similar reaction with 4-ethylphenylthioisocyanate (in a
ratio of 1 : 2.2 : 2.2) and obtained the corresponding mono-
thioamide product 5 in good yield (Scheme 4). Compound 5
was characterized by IR, NMR and EI-MS, and its crystal struc-
ture has been determined by X-ray diffraction (see below).
To extend the scope and limitations of this type of reaction,
we carried out similar reactions of dilithiocarborane
Li2C2B10H11 with two equivalents of pentylisocyanate, and iso-
lated the corresponding monoamide 2c and diamide 3c, with
the former as the major product (Scheme 2, Table 1), which is
again different with Wade et al.’s results on methylisocyanate,
presumably the different steric effect between methyl and
pentyl groups plays some role. It is apparent that there is a
subtle substituent effect in these seemingly straightforward
transformations. We then studied the same reactions with sub-
stituted phenylisocyanates (with electron-withdrawing groups
2-F, 4-I, 3-CN, 4-Cl-2-CF3 on the benzene ring) from which only
monoamides were isolated, however, the corresponding yields
were only from medium (2d) to low (2e–g) (Scheme 1, Table 1),
although in principle phenylisocyanates with electron-
withdrawing groups on the phenyl ring should exhibit
better activity towards organolithium than those with electron-
donating groups. Apart from the isolation of 2e–g, some un-
identified solid products were obtained at the bottom of the
preparative TLC plates which by 11B-NMR were tentatively
assigned to be deboronated species. Compounds 2c–g were
characterized by IR and NMR spectroscopy and mass spectro-
metry, and the solid-state structures have been established by
single-crystal X-ray diffraction analyses of 2c–f (see below).
Most probably the low yields of compounds 2e–g is because
RNCO (R = p-IC6H4, m-NCC6H4) are not soluble in diethyl
ether or toluene. We then carried out the same reactions in the
more polar solvent tetrahydrofuran (THF) in which the two iso-
cyanates are soluble. The yields of compound 2e–g are much
better that those from the reactions in diethyl ether (Table 1).
In the case of p-Cl-o-CF3C6H4NCO, the yield is also increased
(Table 1). Moreover, when we repeated the same reactions of
phenylisocyanate and pentylisocyanate in THF, respectively,
the solvent effect is more apparent. With phenylisocyanate, the
monoamide product was isolated in 70.5% and 81.6% (two
runs), whereas no diamide product was obtained, which is
X-ray structures of 2a–f, 3a and 5
Colorless crystals of compounds 2a–f and 3a were obtained by
solvent (diethyl ether) evaporation, and yellow crystals of com-
pound 5 were grown in a solution of hexane–dichloromethane
(4/1, v/v) at room temperature. The corresponding crystal data
and refinement parameters are shown in Tables 2 (2a–b, 3a), 4
(2c–e) and 6 (2f, 5), respectively. Selected bond lengths and
bond angles are listed in Tables 3, 5 and 7, and the related
hydrogen bond information is given in Table S1.†
In the structure (Fig. 2) of compound 2a, the carbonyl
carbon of the amide moiety is directly attached to the cage
carbon with the C2–C3 bond length of 1.526(3) Å, showing
that it is essentially a single bond. The amide part and the
phenyl ring are coplanar (torsion angles of both O2–C3–N1–C4
and C3–N1–C4–C5 are 0.000(1)°) and the molecule is sym-
metric about the plane passing through C1, C2 and the amide
moiety. The intramolecular O2⋯H1A (2.51 Å) and O2⋯H5
(2.28 Å) interactions fix the orientation of the amide fragment
respective to the carborane cage. The cage C1–C2 bond length
is 1.631(3) Å, essentially the same as that in o-carborane (1,
1.629(6) Å19), probably due to the conjugation effect of the
amide moiety that balances the steric hindrance of the amide
substituent which usually makes the cage carbon–carbon
bond somewhat longer than that in 1. There exists
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Table 2 Crystal data and structure refinement parameters of 2a, 3a and
Table 3 Selected bond lengths (Å) and bond angles (°) in 2a, 3a and 2b
2b
2a
C(1)–C(2)
C(2)–C(3)
C(3)–O(2)
1.631(3)
1.526(3)
1.204(3)
1.343(3)
C(2)–B(5)
C(2)–B(3)
C(1)–B(3)
C(1)–B(4)
1.699(3)
1.729(2)
1.716(2)
1.689(3)
2a
3a
2b
Empirical
formula
Formula weight
Temperature/K
Crystal system
Space group
a/Å
b/Å
c/Å
α/°
β/°
C
10H19B10NO2
C18H26B10N2O4
C9H17B10NO
C(3)–N(1)
C(4)–N(1)
1.418(3)
293.36
293.15
442.51
293.15
263.34
293.15
Triclinic
C(3)–C(2)–C(1)
B(5)–C(2)–C(3)
B(3)–C(2)–C(3)
O(2)–C(3)–C(2)
N(1)–C(3)–C(2)
3a
C(1)–C(10)
C(2)–C(1)
C(2)–O(1)
C(2)–N(1)
113.55(18)
124.97(14)
114.88(11)
119.9(2)
O(2)–C(3)–N(1)
C(3)–N(1)–C(4)
C(1)–C(2)–B(3)
C(1)–C(2)–B(5)
126.5(2)
128.2(2)
61.35(9)
110.43(14)
Orthorhombic
Cmca
7.2645(7)
21.8580(13)
20.1778(15)
90.00
90.00
90.00
3204.0(4)
8
1.216
0.069
1216.0
0.42 × 0.41 ×
0.32
5.5 to 52.74°
Monoclinic
P21/c
10.9013(10)
15.5194(10)
14.2472(10)
90.00
98.225(7)
90.00
2385.6(3)
4
1.232
0.077
920.0
0.56 × 0.43 ×
0.034
ˉ
P1
7.1110(7)
9.6524(8)
12.4183(8)
104.922(6)
104.856(7)
103.257(8)
755.24(11)
2
1.158
0.062
272.0
0.43 × 0.22 ×
0.18
113.68(19)
1.659(3)
1.532(3)
1.214(3)
1.334(3)
1.431(3)
1.523(4)
1.214(3)
114.6(2)
120.8(2)
115.9(2)
124.5(2)
119.2(2)
124.1(2)
116.8(2)
C(11)–N(2)
N(2)–C(12)
C(1)–B(1)
C(1)–B(2)
C(1)–B(5)
C(1)–B(6)
1.329(3)
1.428(3)
1.686(4)
1.725(4)
1.733(4)
1.699(4)
γ/°
Volume/Å3
Z
C(3)–N(1)
C(10)–C(11)
C(11)–O(3)
ρcalc/mg mm−3
m/mm−1
F(000)
C(1)–C(10)–C(11)
C(2)–C(1)–C(10)
C(1)–C(2)–N(1)
N(1)–C(2)–O(1)
C(1)–C(2)–O(1)
C(3)–N(1)–C(2)
C(10)–C(11)–N(2)
2b
C(1)–C(10)
C(2)–C(1)
C(2)–O(1)
C(2)–N(1)
C(3)–N(1)
C(10)–C(11)
C(11)–O(3)
C(1)–C(10)–C(11)
C(2)–C(1)–C(10)
C(1)–C(2)–N(1)
N(1)–C(2)–O(1)
C(1)–C(2)–O(1)
C(3)–N(1)–C(2)
C(10)–C(11)–N(2)
C(10)–C(11)–O(3)
N(2)–C(11)–O(3)
C(11)–N(2)–C(12)
B(1)–C(1)–C(10)
B(1)–C(1)–B(6)
B(1)–C(1)–B(2)
118.8(3)
124.2(3)
126.0(2)
110.9(2)
63.2(2)
Crystal size/
mm3
2Θ range for
data collection
Index ranges
5.14 to 52.74°
6.24 to 52.74°
62.20(19)
−8 ≤ h ≤ 7
−27 ≤ k ≤ 27
−17 ≤ l ≤ 25
5366
−13 ≤ h ≤ 13
−17 ≤ k ≤ 19
−17 ≤ l ≤ 17
14 790
−8 ≤ h ≤ 8
−12 ≤ k ≤ 12
−15 ≤ l ≤ 15
7825
1.659(3)
1.532(3)
1.214(3)
1.334(3)
1.431(3)
1.523(4)
1.214(3)
114.6(2)
120.8(2)
115.9(2)
124.5(2)
119.2(2)
124.1(2)
116.8(2)
C(11)–N(2)
N(2)–C(12)
C(1)–B(1)
C(1)–B(2)
C(1)–B(5)
C(1)–B(6)
1.329(3)
1.428(3)
1.686(4)
1.725(4)
1.733(4)
1.699(4)
Reflections
collected
Independent
reflections
Data/restraints/
parameters
Goodness-of-fit
on F2
Final R indexes
[I ≥ 2σ(I)]
Final R indexes
[all data]
1753 [R(int) =
0.0475]
1753/0/127
4877 [R(int) =
0.0635]
4877/0/309
3071 [R(int) =
0.0401]
3071/0/190
1.060
1.036
1.031
C(10)–C(11)–O(3)
N(2)–C(11)–O(3)
C(11)–N(2)–C(12)
B(1)–C(1)–C(10)
B(1)–C(1)–B(6)
B(1)–C(1)–B(2)
118.8(3)
124.2(3)
126.0(2)
110.9(2)
63.2(2)
R1 = 0.0556
wR2 = 0.1479
R1 = 0.0688
wR2 = 0.1613
0.26/−0.27
R1 = 0.0704
wR2 = 0.1693
R1 = 0.1235
wR2 = 0.2088
0.37/−0.23
R1 = 0.0590
wR2 = 0.1537
R1 = 0.0935
wR2 = 0.1761
0.22/−0.19
62.20(19)
Largest diff.
peak/hole/e Å−3
intermolecular C–H⋯O hydrogen bonds that link the mole- have a dihedral angle of 17.9(8)°. The cage C1–C2 bond length
cules of 2a into a one-dimensional chain structure (Fig. S12, is 1.624(2) Å, essentially the same as those in o-carborane and
Table S1†).
2a, but slightly shorter than that in 3a. Similar to that in the
In the structure (Fig. 3) of the diamide 3a, the C2–C1 and structure of 2a, the intramolecular O1⋯H1A (2.54 Å) and
C10–C11 bond lengths are found to be 1.532(3) and 1.523(4) Å, O1⋯H5 (2.32 Å) interactions fix the relative orientations of the
respectively. Because of the steric effect of the amide groups, amide fragment and the carborane cage, a feature also found
the cage C1–C10 bond length is 1.659(3) Å, slightly longer than in other monoamide structures herein. In the solid state there
those in 1 and 2a. The two amide moieties are not as planar as exist intermolecular C–H⋯O hydrogen bonds linking the
that in the structure of 2a, with the torsion angles C3–N1–C2– molecules of 2b into a dimeric structure (Fig. S14, Table S1†).
O1 and C12–N2–C11–O3 being 3.9(5)° and −8.1(5)°, respect-
In the structure (Fig. 5) of compound 2c with a pentyl
ively. The dihedral angles between the two amide moieties group, the C2–C3 bond length is found to be 1.519(3) Å and
is 80.1(2)°, and those between O3–C11–N2–C12/phenyl and the cage C1–C2 bond length is 1.626(3) Å, respectively, the
between O1–C2–N1–C3/phenyl are 20.0(1)° and 46.6(1)°, latter being essentially the same as those in o-carborane and
respectively. In crystal of 3a there are intramolecular C–H⋯O 2a,b. The amide moiety is essentially planar (torsion angle
and intermolecular C–H⋯O and N–H⋯O hydrogen bond inter- O1–C3–N1–C4 is −3.8(4)°). Similar to those in the structures of
actions, and the latter link the molecules of 3a into a one- 2a,b, the intramolecular O1⋯H1A (2.55 Å) and O1⋯H4A
dimensional chain structure (Fig. S13, Table S1†).
(2.48 Å) interactions are present . In crystal of 2c the intermole-
In the structure (Fig. 4) of compound 2b, the C2–C3 bond cular N–H⋯O hydrogen bonds interaction link the molecules
length is 1.525(3) Å. The amide moiety is essentially planar of 2c into a one-dimensional chain (Fig. S15, Table S1†).
(torsion angle O2–C3–N1–C4 = 7.1(3)°) and also coplanar both
Compounds 2d–f have monoamide structures and electron-
cage carbon atoms, and this plane and that of the phenyl ring withdrawing substituents (o-F (2d), p-I (2e) and m-CN (2f)) on
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Table 4 Crystal data and structure refinement parameters of 2c–e
Table 5 Selected bond lengths (Å) and bond angles (°) in 2c–e
2c
2d
2e
2c
C(1)–C(2)
C(2)–C(3)
C(3)–O(1)
C(3)–N(1)
C(1)–C(2)–C(3)
C(2)–C(3)–O(1)
C(2)–C(3)–N(1)
N(1)–C(3)–O(1)
2d
C(1)–C(2)
C(2)–C(3)
C(3)–O(1)
C(3)–N(1)
C(1)–C(2)–C(3)
C(2)–C(3)–O(1)
C(2)–C(3)–N(1)
N(1)–C(3)–O(1)
2e
C(1)–C(2)
C(2)–C(3)
C(3)–O(1)
C(3)–N(1)
1.626(3)
1.519(3)
1.222(3)
1.321(3)
115.22(17)
119.6(2)
114.73(19)
125.6(2)
C(4)–N(1)
C(1)–B(3)
C(2)–B(3)
C(2)–B(4)
C(3)–N(1)–C(4)
C(1)–C(2)–B(3)
C(1)–C(2)–B(4)
C(1)–C(2)–B(5)
1.452(3)
1.700(4)
1.719(4)
1.702(3)
123.1(2)
61.01(15)
110.47(17)
110.91(18)
Empirical
formula
Formula weight
Temperature/K
Crystal system
Space group
a/Å
b/Å
c/Å
α/°
β/°
C8H23B10NO
C9H16B10FNO
C9H16B10INO
257.37
293.15
Orthorhombic
Pbca
11.6375(6)
10.1626(6)
27.496(2)
90.00
90.00
90.00
3251.8(3)
8
1.051
281.33
293.15
Triclinic
389.23
293.15
Monoclinic
P21/n
7.2249(2)
22.8107(10)
10.5504(4)
90.00
109.334(4)
90.00
1640.71(11)
4
1.576
1.941
752.0
0.41 × 0.36 ×
0.15
ˉ
P1
6.735(2)
11.253(4)
11.649(4)
114.63(3)
90.84(3)
106.42(3)
760.9(4)
2
1.228
0.074
288.0
0.38 × 0.32 ×
0.28
1.624(3)
1.533(3)
1.212(3)
1.327(3)
114.17(17)
121.0(2)
113.66(19)
125.3(2)
C(4)–N(1)
C(1)–B(4)
C(2)–B(4)
C(2)–B(5)
C(3)–N(1)–C(4)
C(1)–C(2)–B(4)
C(1)–C(2)–B(5)
C(1)–C(2)–B(6)
1.419(3)
1.708(4)
1.716(4)
1.700(3)
127.57(19)
61.43(15)
111.15(17)
110.97(17)
γ/°
Volume/Å3
Z
ρcalc/mg mm−3
m/mm−1
F(000)
0.055
1088.0
Crystal size/mm3 0.38 × 0.36 ×
0.23
1.624(4)
1.725(5)
1.208(4)
1.336(4)
114.1(2)
119.8(3)
114.7(3)
125.4(3)
C(4)–N(1)
C(1)–B(3)
C(2)–B(3)
C(2)–B(11)
C(3)–N(1)–C(4)
C(1)–C(2)–B(6)
C(1)–C(2)–B(11)
B(7)–C(2)–B(11)
1.416(3)
1.710(5)
1.725(5)
1.696(4)
127.7(3)
61.5(2)
2Θ range for
data collection
Index ranges
6.1 to 52.74°
6.38 to 52.74°
6.28 to 52.74°
C(1)–C(2)–C(3)
C(2)–C(3)–O(1)
C(2)–C(3)–N(1)
N(1)–C(3)–O(1)
−13 ≤ h ≤ 14
−12 ≤ k ≤ 12
−33 ≤ l ≤ 34
10 775
−8 ≤ h ≤ 8
−13 ≤ k ≤ 14
−14 ≤ l ≤ 14
7806
−9 ≤ h ≤ 9
−28 ≤ k ≤ 28
−13 ≤ l ≤ 13
19 725
111.3(2)
62.6(2)
Reflections
collected
Independent
reflections
Data/restraints/
parameters
Goodness-of-fit
on F2
3326 [R(int) =
0.0500]
3326/0/182
3110 [R(int) =
0.0485]
3110/0/199
3340 [R(int) =
0.0394]
3340/0/199
Table 6 Crystal data and structure refinement parameters of 2f and 5
1.044
1.077
1.044
2f
5
Final R indexes
[I ≥ 2σ(I)]
R1 = 0.0744
wR2 = 0.2061
R1 = 0.1169
wR2 = 0.2380
0.39/−0.22
R1 = 0.0623
wR2 = 0.1672
R1 = 0.0986
wR2 = 0.2001
0.20/−0.21
R1 = 0.0340
wR2 = 0.0744
R1 = 0.0456
wR2 = 0.0806
0.53/−0.88
Empirical formula
Formula weight
Temperature/K
Crystal system
C10H16B10N2O
288.35
293.15
Orthorhombic
P212121
C11H21B10NS
307.45
293(2)
Monoclinic
P21/c
Final R indexes
[all data]
Largest diff.
peak/hole/e Å−3
Space group
a/Å
b/Å
c/Å
α/°
7.1169(6)
8.6634(5)
25.2552(15)
90.00
11.4931(16)
18.880(2)
8.6737(10)
90.00
the phenyl rings (Fig. 6–8, respectively). Different from all other
structures in this paper molecules of compound 2f crystallize in
the chiral space group (P212121). The corresponding cage
carbon–carbon bonds in 2d–f are found to be similar (1.624(3),
1.624(4) and 1.639(3) Å, respectively), also similar to those in 1
and the above monoamides, suggesting that the amide groups
have no significant influence on the geometries of the icosahedra.
The amide moieties in the structures of 2d–f are essentially planar
(torsion angles O1–C3–N1–C4 are 4.5(4), 8.5(6), −1.7(5)°,
respectively). The fluorine atom in 2d participates in intramo-
lecular N–H⋯F hydrogen bond interaction, and the intermole-
cular C–H⋯O hydrogen bonds link the molecules of 2d into a
dimer (Fig. S16, Table S1†). There is no significant intermole-
cular hydrogen bond interaction in the structure of 2e, but
intramolecular C–H⋯O one exists (Fig. 7, Table S1†). The
molecules of 2f are linked together by intermolecular N–H⋯N
hydrogen bond interactions to form a one-dimensional chain
structure (Fig. S17, Table S1†).
β/°
90.00
90.00
1557.14(19)
4
1.230
0.068
592.0
0.38 × 0.34 × 0.12
5.94 to 52.74°
−8 ≤ h ≤ 5
−6 ≤ k ≤ 10
−31 ≤ l ≤ 31
5365
3104 [R(int) =
0.0429]
3104/0/208
1.028
R1 = 0.0606
wR2 = 0.1135
R1 = 0.1019
wR2 = 0.1320
0.16/−0.17
110.802(13)
90.00
1759.4(4)
4
1.161
0.172
γ/°
Volume/Å3
Z
ρcalc/mg mm−3
m/mm−1
F(000)
640.0
Crystal size/mm3
2Θ range for data collection
Index ranges
0.42 × 0.26 × 0.23
6.62 to 52.74°
−14 ≤ h ≤ 14
−23 ≤ k ≤ 22
−10 ≤ l ≤ 10
9305
3591 [R(int) =
0.0419]
3591/0/209
1.036
R1 = 0.0601
wR2 = 0.1508
R1 = 0.0939
wR2 = 0.1812
0.23/−0.20
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indexes [I ≥ 2σ(I)]
Final R indexes [all data]
Largest diff. peak/hole/e Å−3
In the structure (Fig. 9) of compound 5, the carborane skele-
ton is directly linked to the thioamide moiety with the C2–C3
bond length of 1.519(3) Å. The cage carbon–carbon bond
is found to be 1.641(3) Å, similar to those in 1 and the
monoamide 2a–f. The thioamide moiety is essentially planar
(torsion angle S1–C3–N1–C4 6.6(4)°). Interestingly, in crystal of
5 there exists intramolecular C–H⋯S hydrogen bond and weak
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Table 7 Selected bond lengths (Å) and bond angles (°) in 2f and 5
2f
C(1)–C(2)
C(2)–C(3)
C(3)–O(1)
C(3)–N(1)
C(1)–C(2)–C(3)
C(2)–C(3)–O(1)
C(2)–C(3)–N(1)
N(1)–C(3)–O(1)
5
1.639(3)
1.525(3)
1.191(3)
1.347(3)
113.7(2)
120.3(2)
114.0(2)
125.7(3)
C(4)–N(1)
C(1)–B(3)
C(2)–B(6)
C(2)–B(11)
C(3)–N(1)–C(4)
C(8)–C(10)–N(2)
C(1)–C(2)–B(6)
C(1)–C(2)–B(11)
1.423(3)
1.699(5)
1.711(5)
1.696(4)
127.2(2)
178.9(3)
113.4(2)
123.9(2)
C(1)–C(2)
C(2)–C(3)
C(3)–S(1)
1.641(3)
1.519(3)
1.635(2)
C(4)–N(1)
C(2)–B(4)
C(2)–B(6)
1.434(3)
1.701(3)
1.731(3)
C(3)–N(1)
1.327(3)
C(1)–C(2)–C(3)
C(2)–C(3)–S(1)
C(2)–C(3)–N(1)
N(1)–C(3)–S(1)
116.95(19)
121.13(18)
113.2(2)
C(3)–N(1)–C(4)
C(1)–C(2)–B(6)
C(1)–C(2)–B(4)
125.3(2)
60.85(15)
109.76(19)
125.66(18)
Fig. 3 Molecular structure of compound 3a with numbering scheme,
the ellipsoids are drawn at the 30% probability.
Fig. 2 Molecular structure of compound 2a with numbering scheme,
the ellipsoids are drawn at the 30% probability.
Fig. 4 Molecular structure of compound 2b with numbering scheme,
the ellipsoids are drawn at the 30% probability.
N–H⋯H–B dihydrogen bond (Table S1†), which fix the orien-
tation of the thioamide moiety relative to the carborane cage.
The H1⋯H4 distance is found to be 2.21 Å, lying in the range
of the reported values (typically 1.7–2.2) for X–H⋯H–B (X = C,
N, O, S) dihydrogen bonds.20 Additionally, the cage C–H peak
(4.97 ppm) in the 1H NMR of 5 indicates the presence of intra-
molecular C–H⋯S bond in solution, similar to that with
C–H⋯N intramolecular bond in solution.20h
THF were dried over sodium/benzophenone and distilled
under nitrogen prior to use. Other analytically pure reagents
were commercially available. IR spectra were recorded in the
range 400–4000 cm−1 on a Perkin Elmer Spectrum RX I
spectrometer using KBr pellets. NMR analyses were performed
on a Bruker Avance 400 III MHz spectrometer with tetramethyl-
silane (TMS) and the deuterated solvent as internal standard
(1H) and BF3·OEt2 as external standard (11B). Melting points
were measured with a SGW X-4 apparatus and are not cor-
rected. The mass spectra were recorded on an Agilent 5973N
MSD (low resolution) and Agilent 6890-Micromass GCT
(GC-MS, high resolution) instruments. Elemental analyses
Experimental section
General
All reactions were carried out under dry Ar using standard
Schlenk techniques. The solvents diethyl ether, toluene and
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Fig. 5 Molecular structure of compound 2c with numbering scheme,
the ellipsoids are drawn at the 20% probability.
Fig. 7 Molecular structure of compound 2e with numbering scheme,
the ellipsoids are drawn at the 50% probability.
Fig. 6 Molecular structure of compound 2d with numbering scheme,
the ellipsoids are drawn at the 30% probability.
were performed on an Elementar Vario EL III instrument
(Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences).
Fig. 8 Molecular structure of compound 2f with numbering scheme,
the ellipsoids are drawn at the 30% probability.
Reaction of dilithiocarborane with two equiv. of 3-
methoxyphenylisocyanate
colorless precipitate was stirred for 30 min at 0 °C and 30 min
at room temperature. It was cooled to 0 °C and a solution of
3-methoxyphenylisocyanate (315 mg, 2.11 mmol) in diethyl
ether (10 mL) was added. On addition the precipitate dis-
appeared and the reaction mixture became light yellow. It was
A portion of n-BuLi (2.2 m in n-hexane, 1.0 mL, 2.20 mmol)
was added dropwise to a solution of o-carborane (143 mg,
0.99 mmol) in diethyl ether (30 mL) at 0 °C. The resulting
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[M]+ (10), 294 [M − C7H8NO + H]+ (15), 123 [MeOC6H4NH2]+
(100).
Reaction of lithiocarborane with one equiv. of 3-
methoxyphenylisocyanate at low temp
A portion of n-BuLi (2.2 m in n-hexane, 0.44 mL, 0.97 mmol)
was added dropwise to a solution of o-carborane (145 mg,
1.00 mmol) in diethyl ether (20 mL) pre-cooled with liq. N2.
The resulting colorless precipitate was stirred at low tempera-
ture for 1 h and a solution of 3-methoxyphenylisocyanate
(162 mg, 1.09 mmol) in diethyl ether (10 mL) was added. On
addition the precipitate disappeared and the reaction mixture
became colorless. It was stirred for 4 h and then at room temp-
erature for 11 h during which the solution became yellow.
After quenching with dilute HCl and neutralization with
aqueous NaOH, the organic phase was separated and the water
phase extracted with diethyl ether (3 × 10 mL). The organic
portions were combined, dried (anhydrous NaSO4) and con-
centrated in vacuo. The light yellow solid residue was further
purified by preparative TLC on silica gel. Elution with
n-hexane–dichloromethane (1/2, v/v) gave 2a (179 mg, 61.1%)
as a colorless solid.
Fig. 9 Molecular structure of compound 5 with numbering scheme
(only the hydrogen atoms involved in hydrogen bonds are shown), the
ellipsoids are drawn at the 30% probability.
Reaction of o-carborane with one equiv. of 3-
methoxyphenylisocyanate and TBAF
heated at reflux for 5 h during which a white precipitate
appeared. After cooling to room temperature the reaction
mixture was quenched with dilute HCl and then neutralized
with aqueous NaOH. The organic phase was separated and the
water phase extracted with diethyl ether (3 × 10 mL). The
organic portions were combined, dried (anhydrous MgSO4)
and concentrated in vacuo. The resulting light yellow solid
residue was further purified by preparative TLC on silica gel.
Elution with n-hexane–dichloromethane (1/2, v/v) gave 2a
(161 mg, 55.4%) and 3a (64 mg, 14.6%) as colorless solids.
2a: Rf = 0.62; m.p. 161–164 °C; IR (KBr): ν = 3410, 3068,
2936, 2838, 2632, 2596, 2555, 1714, 1685, 1609, 1543, 1496,
To a solution of o-carborane (101 mg, 0.70 mmol) in THF
(30 mL) at room temperature was added a solution of 3-meth-
oxyphenylisocyanate (104 mg, 0.70 mmol) in THF (10 mL). To
the resulting solution TBAF in THF (1.7 mL, 1 mol L−1
,
1.7 mmol) was added which resulted in a light yellow solution.
It was stirred for 10 min at room temperature and heated at
70 °C for 50 min. After cooling to room temperature the reac-
tion mixture was quenched with saturated NH4Cl solution.
The organic phase was separated and the water phase extracted
with diethyl ether (3 × 10 mL). The organic portions were com-
bined, dried (anhydrous MgSO4) and concentrated in vacuo.
The light yellow solid residue was dissolved with ethyl acetate
(5 mL) and diethyl ether (30 mL), the resulting white solid was
filtered and washed with ether and water, and dried to give
compound 416 as a white solid (149 mg, 56.6%). From the fil-
trate, a small amount of 2a (10 mg, 4.9%) was isolated by pre-
parative TLC on silica gel (eluent: n-hexane–dichloromethane
(1/2, v/v)). Compound 4 was identified by a comparison of the
IR and NMR data with those reported.16 X-ray analysis of 4:
1460, 1419, 1265, 1040, 827, 782, 727, 718, 683 cm−1 11B{1H}
;
NMR (128.4 MHz, CDCl3, 291.3 K): δ = −3.2 (2B), −8.6 (2B),
−11.6 (2B), −13.1 (4B) ppm; 1H NMR (400.1 MHz, CDCl3,
291.2 K): δ = 7.57 (s, 1H, NH), 7.27 (t, 1H, J = 8.0 Hz, ArH), 7.14
(m, 1H, ArH), 6.94 (dd, 1H, J = 8.0, 2.0 Hz, ArH), 6.76 (dd, 1H,
J = 8.0, 2.0 Hz, ArH), 4.35 (s, 1H, CcageH), 3.81 (s, 3H, OCH3),
1.6–3.3 (br, 10H, BH) ppm; EI-MS (70 eV) m/z (%): 293 [M]+
(100), 278 [M − CH3]+ (2), 261 [M − OCH3 − H]+ (6), 141
[C2B10H9]+ (12); HRMS (EI): calcd for C10H19B10NO2 [M]+
295.2346, found 295.2422; Calcd (%) for C10H19B10NO2:
C 40.65, H 6.49, N 4.74%; found: C 41.14, H 6.55, N 4.74%.
3a: Rf = 0.15; m.p. 146–152 °C; IR (KBr): ν = 3414, 3353,
2933, 2590, 1693, 1609, 1537, 1494, 1453, 1425, 1235, 1042,
ˉ
formula C18H48B9N (M.W. 375.86), triclinic, space group P1;
cell parameters a = 10.851(3), b = 10.875(3), c = 12.556(2) Å; α =
75.596(17), β = 84.333(17), γ = 67.11(2)°.
Reaction of dilithiocarborane with two equiv. of
phenylisocyanate in Et2O
846, 779, 721, 683 cm−1 11B{1H} NMR (128.4 MHz, CDCl3,
;
Similar procedures were used to those for compound 2a.
o-Carborane (146 mg, 1.01 mmol), n-BuLi (2.2 m in n-hexane,
0.92 mL, 2.02 mmol), phenylisocyanate (249 mg, 2.09 mmol).
Compounds 2b8a,e (71 mg, 26.7%) and 3b9c (228 mg, 59.0%)
were obtained as colorless solids after TLC separation (eluent:
n-hexane–dichloromethane (2/1, v/v)).
290.9 K): δ = −1.7 (4B), −9.0 (3B), −10.3 (3B) ppm; 1H NMR
(400.1 MHz, CDCl3, 291.1 K): δ = 7.81 (s, 2H, NH), 7.24 (t, 2H,
J = 8.4 Hz, ArH), 7.15 (m, 2H, ArH), 6.95 (dd, 2H, J = 8.0,
1.2 Hz, ArH), 6.74 (dd, 2H, J = 8.0, 2.0 Hz, ArH), 3.79 (s, 6H,
OCH3), 1.8–3.3 (br, 10H, BH) ppm; EI-MS (70 eV) m/z (%): 442
5090 | Dalton Trans., 2014, 43, 5083–5094
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2b: Rf = 0.58; m.p. 127–128 °C; IR (KBr): ν = 3409, 3066,
3c: m.p. 99–102 °C; IR (KBr): ν = 3322, 2950, 2931, 2877,
2591, 2554, 1699, 1605, 1532, 1444, 1314, 1248, 1138, 1014, 2858, 2597, 1676, 1535, 1433, 1266, 721 cm−1 11B{1H} NMR
;
751 cm−1 11B{1H} NMR (128.4 MHz, CDCl3, 293.4 K): δ = −3.2 (128.4 MHz, CDCl3, 293.4 K): δ = −2.6 (4B), −9.8 (2B), −11.1
;
(2B), −8.5 (2B), −11.7 (2B), −13.1 (4B) ppm; 1H NMR (4B) ppm; 1H NMR (400.1 MHz, CDCl3, 293.4 K): δ = 6.18 (s,
(400.1 MHz, CDCl3, 293.4 K): δ = 7.59 (s, 1H, NH), 7.45 (d, 2H, 2H, NH), 3.26 (q, 4H, J = 6.8 Hz, NCH2), 1.7–3.1 (br, 10H, BH),
J = 8.0 Hz, ArH), 7.38 (t, J = 7.8 Hz, 2H, ArH), 7.22 (t, 1H, J = 1.53 (quint, 4H, J = 7.2 Hz, NCH2CH2), 1.25–1.33 (m, 8H,
7.4 Hz, ArH), 4.36 (s, 1H, CcageH), 1.6–3.3 (br, 10H, BH) ppm; CH2CH2CH3), 0.90 (t, 6H, J = 7.0 Hz, CH3) ppm; EI-MS (70 eV)
EI-MS (70 eV) m/z (%): 263 [M]+ (100), 141 [C2B10H9]+ (24); m/z (%): 370 [M]+ (4), 341 [M − C2H5]+ (2), 328 [M − C3H6]+ (2),
Calcd (%) for C9H17B10NO: C 40.72, H 6.46, N 5.28%; found: 315 [M − C4H7]+ (7), 284 [M − C5H11NH]+ (24), 256 [M −
C 41.18, H 6.51, N 5.25%.
3b: Rf = 0.16; m.p. 168–170 °C; IR (KBr): ν = 3395, 3341, C5H11NHCO − C3H6]+ (16), 201 [M − C5H11NHCO − C4H8]+ (6),
2578, 1697, 1597, 1514, 1443, 1314, 1242, 1114, 740, 691 cm−1
C5H11NHCO]+ (4), 242 [M − C5H11NHCO − CH2]+ (3), 214 [M −
;
185 [M − C5H11NHCO − C5H12]+ (4), 171 [M − C5H11NHCO −
11B{1H} NMR (128.4 MHz, CDCl3, 293.6 K): δ = −2.0 (4B), −9.2 C5H11N]+ (9), 141 [C2B10H9]+ (9), 114 [C5H11NHCO]+ (27),
(3B), −10.8 (3B) ppm; 1H NMR (400.1 MHz, CDCl3, 293.5 K): 86 [C5H11NH]+ (100); Calcd (%) for C14H34B10N2O2: C 45.38,
δ = 7.84 (s, 2H, NH), 7.45 (d, 4H, J = 8.0 Hz, ArH), 7.35 (t, 4H, H 9.25, N 7.56%; found: C 45.56, H 9.38, N 7.16%.
J = 8.0 Hz, ArH), 7.19 (t, 2H, J = 7.4 Hz, ArH), 1.8–3.5 (br, 10H,
Reaction of dilithiocarborane with two equiv. of
pentylisocyanate in THF
BH) ppm.
Similar procedures to those for compound 2a, except that the
reaction was carried out in dry THF (30 mL). o-Carborane
(148 mg, 1.03 mmol), n-BuLi (2.5 M in hexane, 0.88 mL,
2.20 mmol), pentylisocyanate (246 mg, 2.18 mmol) in THF
(10 mL). The reaction mixture was heated at 40 °C for 4.5 h,
and the light yellow crude product was further purified by TLC
separation (eluent: petroleum ether (b.p. 30–60 °C)–dichloro-
methane (1/1, v/v) to give compound 2c (186 mg, 70.5%) and
3c (79 mg, 20.8%).
Reaction of dilithiocarborane with two equiv. of
phenylisocyanate in THF
Similar procedures to those for compound 2a, except that the
reaction was carried out in dry THF (25–30 mL). o-Carborane
(147 mg, 1.02 mmol), n-BuLi (2.2 M in hexane, 1.0 mL,
2.20 mmol), phenylisocyanate (253 mg, 2.12 mmol) in THF
(10 mL). The reaction mixture was heated at 40 °C for 5.5 h,
and the light yellow crude product was further purified by TLC
separation (eluent: n-hexane–dichloromethane (2/1, v/v) to give
compound 2b (190 mg, 70.5%). Another run was with o-carbor-
ane (146 mg, 1.01 mmol), n-BuLi (newly obtained, 2.5 M in
hexane, 0.86 mL, 2.15 mmol), phenylisocyanate (270 mg,
2.27 mmol) in THF (10 mL), 2b (218 mg, 81.6%) was obtained
after workup.
Reaction of dilithiocarborane with two equiv. of 2-
fluorophenylisocyanate
Similar procedures were used to those for compound 2a. o-Car-
borane (142 mg, 0.98 mmol), n-BuLi (2.2 m in n-hexane,
1.0 mL, 2.20 mmol), 2-fluorophenylisocyanate (308 mg,
2.25 mmol). The orange red oily crude product was further
purified by TLC separation (eluent: n-hexane–dichloromethane
(4/1, v/v) to give compound 2d (153 mg, 55.5%) as a colorless
Reaction of dilithiocarborane with two equiv. of
pentylisocyanate in Et2O
Similar procedures were used to those for compound 2a. o-Car- solid. 2d: Rf = 0.43; m.p. 106–110 °C; IR (KBr): ν = 3427, 3062,
borane (143 mg, 0.99 mmol), n-BuLi (2.2 m in n-hexane, 2621, 2583, 1709, 1623, 1540, 1481, 1457, 1322, 1261, 1239,
1.0 mL, 2.20 mmol), pentylisocyanate (243 mg, 2.15 mmol). 1190, 1017, 823, 755, 723 cm−1 11B{1H} NMR (128.4 MHz,
;
The white crude product was further purified by column CDCl3, 291.7 K): δ = −3.1 (2B), −8.5 (2B), −11.7 (2B), −13.1 (4B)
1
chromatography (eluent: petroleum ether (b.p. 30–60 °C)– ppm; H NMR (400.1 MHz, CDCl3, 291.6 K): δ = 8.06–8.11 (m,
dichloromethane (1/1, v/v)) to give compounds 2c (149 mg, 1H, ArH), 7.94 (s, 1H, NH), 7.14–7.18 (m, 3H, ArH), 4.35 (s, 1H,
58.5%) and 3c (142 mg, 38.7%) as colorless solids.
CcageH), 1.7–3.3 (br, 10H, BH) ppm; EI-MS (70 eV) m/z (%): 281
2c: m.p. 79–81 °C; IR (KBr): ν = 3346, 3080, 2934, 2859, [M]+ (100), 261 [M − HF]+ (4), 171 [M − NHC6H4F]+ (10), 141
2605, 2586, 2552, 1674, 1543, 1458, 1274, 1018, 721 cm−1 11B [C2B10H9]+ (10); HRMS (EI) calcd for C9H16B10NOF: [M]+
;
{1H} NMR (128.4 MHz, CDCl3, 294.6 K): δ = −3.5 (2B), −8.8 283.2146, found 283.2198; Calcd (%) for C9H16B10NOF:
1
(2B), −12.0 (2B), −13.3 (4B) ppm; H NMR (400.1 MHz, CDCl3, C 38.13, H 5.69, N 4.94%; found: C 38.29, H 5.87, N 4.70%.
294.7 K): δ = 5.98 (s, 1H, NH), 4.29 (s, 1H, CcageH), 3.27 (q, J =
6.7 Hz, 2H, NCH2), 1.6–3.2 (br, 10H, BH), 1.52 (quint, 2H, J =
7.2 Hz, NCH2CH2), 1.22–1.38 (m, 4H, CH2CH2CH3), 0.90 (t, 3H,
Reaction of dilithiocarborane with two equiv. of 4-
iodophenylisocyanate
J = 7.0 Hz, CH3) ppm; EI-MS (70 eV) m/z (%): 257 [M]+ (5), 242 Similar procedures to those for compound 2a, except that the
[M − CH3]+ (3), 228 [M − C2H5]+ (10), 214 [M − C3H7]+ (43), 201 reaction was carried out in dry THF (30 mL). o-Carborane
[M − C4H8]+ (100), 188 [M − C5H9]+ (12), 171 [M − C5H11NH]+ (61 mg, 0.42 mmol), n-BuLi (2.2 M in hexane, 0.4 mL,
(46), 142 [M − C6H13NO]+ (32), 114 [C5H11NHCO]+ (34); Calcd 0.88 mmol), 4-iodophenylisocyanate (210 mg, 0.86 mmol). The
(%). for C8H23B10NO: C 37.35, H 8.95, N 5.40%; found: reaction mixture was heated at 40 °C for 5.5 h and the light
C 37.30, H 8.95, N 5.42%.
yellow crude product was further purified by TLC separation
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(eluent: n-hexane–dichloromethane (2/1, v/v) to give compound Reaction of dilithiocarborane with two equiv. of 4-
2e (107 mg, 65.3%) as a colorless solid. 2e: Rf = 0.67; m. ethylphenylthioisocyanate
p. 144–147 °C; IR (KBr): ν = 3318, 3044, 2573, 1703, 1597, 1524,
Similar procedures were used to those for compound 2a. o-Car-
1489, 1393, 1314, 1239, 930, 812, 731 cm−1 11B{1H} NMR
;
borane (148 mg, 1.03 mmol), n-BuLi (2.2 m in n-hexane,
1.0 mL, 2.20 mmol), 4-ethylphenylthioisocyanate (343 mg,
2.10 mmol). The yellow oily crude product was further purified
by TLC separation (eluent: n-hexane–dichloromethane (4/1,
v/v) to give compound 5 (239 mg, 75.4%) as a yellow solid. 5:
Rf = 0.62; m.p. 69–71 °C; IR (KBr): ν = 3322, 3045, 2963, 2928,
(128.4 MHz, CDCl3, 294.0 K): δ = −3.2 (2B), −8.5 (2B), −11.5
(2B), −13.0 (4B) ppm; 1H NMR (400.1 MHz, CDCl3, 293.8 K):
δ = 7.68 (d, 2H, J = 8.8 Hz, ArH), 7.56 (s, 1H, NH), 7.23 (d, 2H,
J = 8.8 Hz, ArH), 4.34 (s, 1H, CcageH), 1.6–3.1 (br, 10H, BH)
ppm; EI-MS (70 eV) m/z (%): 389 [M]+ (65), 262 [M − I]+ (7),
171 [M − IC6H4NH]+ (17), 142 [C2B10H10]+ (100); Calcd (%)
for C9H16B10NOI: C 27.61, H 4.12, N 3.58%; found: C 27.74,
H 4.18, N 3.52%.
2598, 1512, 1491, 1367, 1127, 1014, 930, 731 cm−1 11B{1H}
;
NMR (128.4 MHz, CDCl3, 292.6 K): δ = −3.5 (2B), −8.8 (2B),
−10.4 (2B), −12.9 (4B) ppm; 1H NMR (400.1 MHz, CDCl3,
292.5 K): δ = 9.06 (s, 1H, NH), 7.50 (d, 2H, J = 8.4 Hz, ArH),
7.26 (d, 2H, J = 8.4 Hz, ArH), 4.97 (s, 1H, CcageH), 2.67 (q, 2H,
J = 7.6 Hz, CH2), 1.6–3.4 (br, 10H, BH), 1.24 (t, 3H, J = 7.6 Hz,
CH3) ppm; EI-MS (70 eV) m/z (%): 307 [M]+ (32), 138 [PhNHCS
+ 3H]+ (100); Calcd (%) for C11H21B10NS: C 42.69, H 6.84,
N 4.53%; found: C 43.04, H 7.00, N 4.38%.
Reaction of dilithiocarborane with two equiv. of
3-cyanophenylisocyanate
Similar procedures to those for compound 2e. o-Carborane
(148 mg, 1.02 mmol), n-BuLi (2.2 M in hexane, 1.0 mL,
2.20 mmol), 3-cyanophenylisocyanate (317 mg, 2.20 mmol). Crystal structure determination
The light yellow crude product was further purified by TLC
Suitable crystals were selected and mounted on an Oxford
separation (eluent: n-hexane–dichloromethane (1/3, v/v) to give
compound 2f (186 mg, 64.4%) as a colorless solid. 2f: Rf =
0.76; m.p. 246–247 °C; IR (KBr): ν = 3333, 3069, 2613, 2593,
2232, 1705, 1588, 1549, 1430, 1295, 1247, 1129, 1017, 938,
Gemini E diffractometer for data collection (graphite-mono-
chromated MoKα radiation (λ = 0.71073 Å), ω scan mode) at
293(2) K. The structures were solved at the interface of Olex221
using Superflip22 and Shelxs23 and expanded using Fourier
difference techniques with the Shelxtl-9723 program package.
The non-hydrogen atoms were refined anisotropically by full-
matrix least-squares calculations on F2. The hydrogen atoms
were placed in geometric positions and refined isotropically.
CCDC 937467, 952824, 950184, 937468, 958414, 958415,
937469 and 963492 contain the information of 2a–f, 3a and 5,
respectively.
792 cm−1 11B{1H} NMR (128.4 MHz, CDCl3, 294.1 K): δ = −3.1
;
(2B), −8.4 (2B), −11.8 (2B), −13.1 (4B) ppm: 1H NMR
(400.1 MHz, CDCl3, 294.0 K): δ = 7.92 (m, 1H, ArH), 7.69 (s,
1H, NH), 7.63 (dt, 1H, J = 2.6, 6.8 Hz, ArH), 7.52–7.49 (m, 2H,
ArH), 4.35 (s, 1H, CcageH), 1.6–3.1 (br, 10H, BH) ppm; EI-MS
(70 eV) m/z (%): 288 [M]+ (100), 261 [M − CN + H]+ (10), 171
[M − NC C6H4NH]+ (41), 141 [C2B10H9]+ (57); Calcd (%)
for C10H16B10N2O: C 41.35, H 5.56, N 9.65%; found: C 41.98,
H 5.63, N 9.61%.
Conclusions
It is clear from the present work that both the substituent and
the solvent have an effect on the product (monoamide and/or
diamide) distribution and the corresponding yields. In most of
Reaction of dilithiocarborane with two equiv. of 4-chloro-
3-trifluoromethylphenyl-isocyanate
Similar procedures to those for compound 2e. o-Carborane the reactions of dilithiocarborane with two equiv. of isocya-
(145 mg, 1.01 mmol), n-BuLi (2.2 M in hexane, 1.0 mL, nates in diethyl ether or THF only carboranyl monoamide pro-
2.20
mmol),
4-chloro-2-trifluoromethylphenylisocyanate ducts or more monoamide than the corresponding diamide
(459 mg, 2.07 mmol) in THF (10 mL). The light yellow product (in the cases of 3-methoxyphenylisocyanate and penty-
crude product was further purified by TLC separation (eluent: lisocyanate) are isolated. The only exception is found in the case
n-hexane–dichloromethane (2/1, v/v) to give compound 2g of phenylisocyanate, in which the product distribution of mono-
(242 mg, 65.8%) as a colorless solid. 2g: Rf = 0.61; m. amide and diamide is opposite in diethyl ether and in THF.
p. 83–85 °C; IR (KBr): ν = 3296, 3073, 2589, 1692, 1519, 1506, Similar to the corresponding monolithio-o-carborane system,18
1413, 1308, 1129, 1055, 816, 723 cm−1
;
11B{1H} NMR it is apparent that ethereal solvents also play an important role
(128.4 MHz, CDCl3, 294.1 K): δ = −2.9 (2B), −8.5 (2B), −11.7 in the dilithio-o-carborane system, which merits further detailed
(2B), −13.0 (4B) ppm; 1H NMR (400.1 MHz, CDCl3, 294.1 K): investigation, both experimentally and theoretically.
δ = 8.02 (s, 1H, NH), 7.98 (d, 1H, J = 8.8 Hz, ArH), 7.65 (d, 1H,
The structural studies of the carboranylamide compounds
J = 2.0 Hz, ArH), 7.57 (dd, 1H, J = 2.4, 8.8 Hz, ArH), 4.30 (s, 1H, show that the amide moieties do not have significant influence
C
cageH), 1.6–3.3 (br, 10H, BH) ppm; EI-MS (70 eV) m/z (%): 366 on the directly linked cage structure due to the electron deloca-
[M]+ (83), 296 [M − CF3]+ (13), 171 [M − NHC6H3CF3Cl]+ (70), lization of the amide fragments. In both the monoamide and
141 [C2B10H9]+ (100); Calcd (%) for C10H15B10NOF3Cl: C 32.68, diamide structures, the amide moieties are essentially planar
H 4.12, N 3.81%; found: C 33.82, H 4.26, N 3.79%.
and the carbonyl oxygen atoms participate in intramolecular
5092 | Dalton Trans., 2014, 43, 5083–5094
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and/or intermolecular hydrogen interactions of different type.
Moreover, in the monoamide structures, the Ccage–H⋯O inter-
actions have helped to fix the orientation of the amide moi-
eties with respect to the carborane cage. In the monoamide
(c) N. Vázquez, V. G. Vallejo, J. Calvo, D. Padro and J. Llop,
Tetrahedron Lett., 2011, 52, 615–618; (d) S. C. Jonnalagadda,
J. S. Cruz, R. J. Connell, P. M. Scott and V. R. Mereddy,
Tetrahedron Lett., 2009, 50, 4314–4317; (e) H. S. Ban,
K. Shimizu, H. Minegishi and H. Nakamura, J. Am. Chem.
Soc., 2010, 132, 11870–11871.
8 (a) T. L. Heying, J. W. Ager, S. L. Clark, R. P. Alexander,
S. Papetti, J. A. Reid and S. I. Trotz, Inorg. Chem., 1963, 2,
1097–1105; (b) L. I. Zakharkin and A. V. Kazantsev, Zh.
Obshch. Khim., 1967, 37, 554–560; (c) V. I. Stanko,
A. I. Klimova and V. A. Brattsev, Zh. Obshch. Khim., 1970,
40, 1523; (d) M. Scholz, A. L. Blobaum, L. J. Marnett and
E. Hey-Hawkins, Bioorg. Med. Chem., 2012, 20, 4830–4837;
(e) H. S. Wong, E. I. Tolpin and W. N. Lipscomb, J. Med.
Chem., 1974, 17, 785–791.
compounds 2a,b,d and the thioamide
5 the Ccage–H
groups participate in intermolecular C–H⋯O (2a,b,d) or
intramolecular C–H⋯S (5) hydrogen bond interactions. In the
monoamides 2e and 5 there is no intermolecular weak inter-
actions, whereas in other structures intermolecular hydrogen
bonds of different type link the molecules into dimeric (2b,d)
or one-dimensional chain structures (2a,c,f and 3a).
Acknowledgements
We thank the National Natural Science Foundation of
China (grant 20702020) and the Natural Science Foundation of
Shandong Province (grant ZR2010BM020) for support of this
work. We also thank the referees for helpful suggestions.
9 (a) L. I. Zakharkin, V. N. Kalinin and V. V. Gedymin, J. Orga-
nomet. Chem., 1969, 16, 371–379; (b) L. I. Zakharkin,
V. N. Kalinin and V. V. Gedymin, Tetrahedron, 1971, 27,
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J. A. Hugh MacBride, I. R. Stephenson and K. Wade,
J. Mater. Chem., 1992, 2, 793–804; (d) N. Vázquez,
V. G. Vallejo and J. Llop, Tetrahedron Lett., 2012, 53, 4743–
4746; (e) H. Beall, Inorg. Nucl. Chem. Lett., 1977, 13, 111–
114.
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