Facile Deboronation of Some o-Carboranylamides

Article abstract of DOI:10.1002/ejic.201700612

The crystal structures of the known closo-carboranylamide 1,2-(PhNHCO)₂-o-C₂B₁₀H₁₀ (3) as diethyl ether and toluene/water solvates are reported. Compound 3 undergoes gradual deboronation in wet diethyl ether lea

Full text of DOI:10.1002/ejic.201700612

A Journal of
Accepted Article
Title: Facile Deboronation of Some o-Carboranylamides
Authors: Yong Nie
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10.1002/ejic.201700612
European Journal of Inorganic Chemistry
FULL PAPER
These carboranylamide compounds are interesting with respect
to the direct amide bond to the carboranyl cluster, which in turn
may undergo various transformations, providing possible
compounds for the boron neutron capture therapy (BNCT) of
tumors and related biomedical applications[3] and ligands for
metal coordination.[4] On the other hand, the structures of these
carboranylamides merit further investigation as only few related
structures have been studied in detail. During our investigation
we have successfully obtained crystals of the diamide 3 as
diethyl ether and toluene/water solvates, respectively, and found
that the deboronation of 3 under very mild condition (diethyl
ether solution, room temperature) leads to the product
[PhNH3][7,8-(PhNHCO)2-nido-C2B9H10] (4). Herein we report on
the structures of these carboranylamides and some related
results on the transformation of related compounds.
Facile Deboronation of Some o-
Carboranylamides
Yong Nie,*[a] Yafeng Wang,[a] Jinling Miao,[a]
Chunhua Hu,[b] Zhenwei Zhang,[a] Yu Cui,[a] Yexin
Li[a]
Abstract: The crystal structures of the known closo-carboranylamide
1,2-(PhNHCO)2-o-C2B10H10 (3) as diethyl ether and toluene/water
solvates, respectively, are reported. Compound 3 was found to
undergo gradual deboronation in wet diethyl ether leading to the
formation of the corresponding nido-carboranylamide [PhNH3][7,8-
(PhNHCO)2-nido-C2B9H10] (4). The structure of
4 has been
confirmed by an X-ray analysis. Further experimental and theoretical
evidence showed that the presence of the electron-withdrawing Results and discussion
amide moieties facilitates the facile deboronation of these closo-
carboranylamides in certain solvents affording the corresponding
Structures of closo-carboranylamide
3 as different
nido-carboranylamides.
solvates
o
At room temperature (23 C), colorless solid 3 was dissolved in
diethyl ether and the resulting solution was allowed to stand
overnight, colorless plate crystals were grown as (3)2·Et2O, as
proved by an X-ray structure analysis. In a separate reaction of
Introduction
dilithio-o-carborane
(Li2C2B10H12)
with
two
equiv.
of
We have recently studied the one-pot reactions of o-carborane
(C2B10H12, 1), n-BuLi (2 equiv.) and two equiv. of isocyanates in
diethyl ether or tetrahydrofuran (THF), and found that there are
interesting substituent and solvent effects on the distribution of
the carboranylamide products.[1] In particular, with phenyliso-
cyanate the reaction gave both the mono-substituted carboranyl-
amide 1-PhNHCO-closo-C2B10H11 (2) and the disubstituted 1,2-
(PhNHCO)2-closo-C2B10H10 (3) (Scheme 1),[1,2] whereas in the
case of substituted phenylisocyanates, the reactions all led to
monoamide compounds as the major or only carborane products.
phenylisocyanate in toluene, a small amount of colorless plate
crystals was isolated as (3)2·H2O·2C7H8 after the reaction was
quenched with dilute HCl and then neutralized with aqueous
NaOH solution and the resulting mixture was left at room
temperature. After further workup both the monoamide 2 and
diamide 3 were isolated, but somewhat less in yields than those
from the same reaction in Et2O or THF.[1]
The molecular structure of compound 3 in (3)2·Et2O is shown
in Fig. 1, selected bond lengths, bond angles, torsion angles and
dihedral angles are listed in Table 1. The corresponding crystal
data and structure refinement parameters are presented in
Table 2, and the information on hydrogen bonding interactions is
shown in Table 3.
As shown in Fig. 1, the asymmetric unit contains two
crystallographically independent molecules of 3. In both
molecules the amide moieties adopt planar configuration, and
the Ccage-Ccage bond lengths and other interatomic bond lengths
and bond angles are similar to each other. The main difference
between the two molecules of 3 lie in the relative positions of the
exo-cluster amide/phenyl groups and the cage. The Ccage-Ccage
and other bond lengths in 3 are very similar to that in 1,2-(m-
CONHC6H5
CONHC6H5
1) 2 n-BuLi, Et2O
CH
CH
C
C
C
C
+
2)
C6H5NCO
H
CONHC6H5
3) H+
2
1
3
Scheme 1. Reaction of dilithio-o-carborane with phenylisocyanate leading to
carboranylamides 2 and 3
[1]
CH3OC6H4NHCO)2C2B10H10 (1.659(3) Å). In molecule 1 (C1,
C2), the dihedral angle between the amide moiety (C10, N2, O2)
and the plane C1-C2-C10 is found to be 25.2(1)°, and the
dihedral angle between C3-C1-C2/N1-C3-O1 is 71.1(2)°,
whereas the corresponding dihedral angles in molecule 2 (C17,
C18) are 18.8(1)° (amide (C19, N3, O3)/plane C19-C17-18) and
74.6(1)° (amide C17-C18-C26/N4-C26-O4). Due to the steric
reason the relative positions of both amide moieties in each
molecule are also different, in molecule 1 the dihedral angle
between the two amide planes is 67.4(2)° while the
[a] Dr. Y. Nie, Y. F. Wang, Dr. J. L. Miao, Z. W. Zhang, Prof. Y. Cui, Dr.
Yexin Li
School of Chemistry and Chemical Engineering, University of Jinan,
336 West Nanxinzhuang Road, 250022 Jinan, P. R. China
E-mail: chm_niey@ujn.edu.cn (YN); URL:
http://chem.ujn.edu.cn/showjiaoshi.asp?jiaoshiid=144
[b] Dr. C. H. Hu
Department of Chemistry, New York University, 100 Washington
Square East, New York, NY 10003, USA
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10.1002/ejic.201700612
European Journal of Inorganic Chemistry
FULL PAPER
corresponding dihedral angle for molecule 2 is 73.4(2)°. In
addition, the dehedral angle between the amide planes and the
the phenyl groups are somewhat different: the corresponding
valules are 30.6(1)° and 38.6(1)° in molecule 1 and 50.8(1)° and
37.2(1)° in molecule 2, respectively (Table 1).
Fig. 1. Structure of 3 in (3)2·Et2O, diethyl ether and hydrogen atoms are
omitted for clarity.
Table 1. Selected bond lengths, bond angles, dihedral and torsion angles of (3)2·Et2O.
Molecule 2
Molecule 1
bond lengths (Å)
C(1)-C(2)
1.659(2)
C(17)-C(18)
1.665(2)
115.98(13)
bond angles (°)
C(1)-C(2)-C(10)
C(2)-C(1)-C(3)
C(2)-C(10)-O(2)
C(1)-C(3)-O(1)
C(2)-C(10)-N(2)
C(1)-C(3)-N(1)
O(2)-C(10)-N(2)
O(1)-C(3)-N(1)
115.36(13)
119.97(13)
118.85(15)
119.71(15)
115.73(14)
114.87(15)
125.40(16)
125.23(16)
C(18)-C(17)-C(19)
C(17)-C(18)-C(26)
C(17)-C(19)-O(3)
C(18)-C(26)-O(4)
C(17)-C(19)-N(3)
C(18)-C(26)-N(4)
O(3)-C(19)-N(3)
O(4)-C(26)-N(4)
121.08(13)
119.55(15)
119.84(15)
114.69(14)
115.01(15)
125.74(16)
124.91(16)
torsion angles (°)
C10-C2-C1-C3
C4-N1-C3-O1
-9.1(2)
-2.9(3)
0.7 (3)
C26-C18-C17-C19
C27-N4-C26-O4
C20-N3-C19-O3
8.7(2)
-0.1(3)
-1.4(3)
C11-N2-C10-O2
dihedral angles (°)
C1-C2-C10/N2-C10-O2
C3-C1-C2/N1-C3-O1
N2-C10-O2/N1-C3-O1
25.2(1) C17-C18-C26/N4-C26-O4 74.6(1)
71.1(2) C19-C17-C18 /N3-C19-O3 18.8(1)
67.4(2) N4-C26-O4/N3-C19-O3 73.4(2)
N2-C10-O2/phenyl (C11-16) 30.6(1) N4-C26-O4/phenyl (C27-32)
N1-C3-O1/phenyl (C4-9) 38.6(1) N3-C19-O3/phenyl (C20-25)
50.8(1)
37.2(1)
phenyl (C11-16)/phenyl (C4-9) 34.0(1) phenyl (C27-32)/phenyl(C20-25) 33.5(1)
In the solid state structure of (3)2·Et2O both intramolecular and
intermolecular hydrogen bonding interactions involving the
amide groups are present (Fig. 2, Table 3). The intermolecular
hydrogen bonds (N(3)-H(3)···O(1), N(2)-H(2)···O(4), C(16)-
H(16A)···O(4), N(4)-H(4)···O(2)) link the molecules of 3 into a 2D
network structure (Fig. 2).
Fig. 2. Hydrogen bonding interactions in (3)2·Et2O, only the hydrogen atoms
involved in hydrogen bonds are shown.
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10.1002/ejic.201700612
European Journal of Inorganic Chemistry
FULL PAPER
Table 2. Crystal data and structure refinement parameters of (3)2·Et2O, (3)2·H2O·2C7H8 and (4)2·2Et2O
(3)2·Et2O (3)2·H2O·2C7H8 (4)2·2Et2O
C36H54B20N4O5 C39H54B20N4O5 C52H80B18N6O6
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
839.03
120.05(10)
monoclinic
P21/n
875.06
293(2)
monoclinic
P21/n
1079.80
293(2)
triclinic
P-1
a/Å
b/Å
c/Å
α/°
β/°
γ/°
Volume/Å3
Z
11.83661(15)
16.9357(2)
23.0517(3)
90.00
93.6391(12)
90.00
4611.66(10)
4
1.208
11.9758(6)
17.4738(7)
23.230(2)
90.00
93.939(6)
90.00
4849.7(6)
4
1.198
11.4781(11)
12.5873(14)
24.400(2)
87.665(8)
82.728(8)
63.274(10)
3122.8(6)
2
ρcalc/mg·mm-3
m/mm-1
1.148
0.069
0.548
0.071
F(000)
1752.0
1824.0
1144.0
Crystal size/mm3
0.36 × 0.31 × 0.19 0.38 × 0.28 × 0.22 0.38 × 0.36 × 0.23
6.052~ 52.744°
-14 ≤ h ≤ 13
2Θ range for data collection 6.48~133.196° 6.64~52.744°
Index ranges
-11 ≤ h ≤ 14
-19 ≤ k ≤ 20
-25 ≤ l ≤ 27
21560
-14 ≤ h ≤ 14
-21 ≤ k ≤ 21
-28 ≤ l ≤ 29
26193
-15 ≤ k ≤ 15
-30 ≤ l ≤ 30
23821
Reflections collected
Independent reflections
Data/restr./parameters
Goodness-of-fit on F2
Final R indexes [I ≥ 2σ (I)]
8146[R(int) = 0.0275] 9867[R(int) = 0.0371] 12689[R(int) = 0.0606]
8146/24/595
1.033
9867/25/598
1.033
12689/0/777
1.031
R1 = 0.0571
wR2 = 0.1536
R1 = 0.0658
wR2 = 0.1630
R1 = 0.0665
wR2 = 0.1717
R1 = 0.1038
wR2 = 0.2019
0.55/-0.53
R1 = 0.1062
wR2 = 0.2509
R1 = 0.1979
wR2 = 0.3122
0.38/-0.27
Final R indexes [all data]
Largest diff. peak/hole /e Å-3 0.54/-0.45
Table 3. Information on the hydrogen bond interactions in (3)2·Et2O, (3)2·H2O·2C7H8 and (4)2·2Et2O
Compounds
D-H···A
d(H···A)/ Å
d(D-A)/Å
∠(D-H···A)/o
(3)2·Et2O
N(2)-H(2)···O(4)i
N(3)-H(3)···O(1)
N(4)-H(4)···O(2)ii
2.25(2)
2.24(2)
2.34(2)
2.50
2.36
2.48
2.997(2)
2.961(2)
3.056(2)
2.902(2)
2.863(2)
3.114(2)
2.877(6)
2.875(6)
3.041(3)
2.968(3)
3.137(3)
2.985(3)
2.908(3)
2.855(3)
3.183(3)
3.384(3)
2.895(3)
3.12
154(2)
153(2)
145.5(2)
106
114
126
C(5)-H(5)···O(1)
C(12)-H(12A)···O(2)
C(16)-H(16A)···O(4)i
C(12)-H(12)···O(1)
C(32)-H(32)···O(3)
N(1)-H(1)···O(3)
N(2)-H(2)···O(4)
N(3)-H(3)···O(1)iii
N(4)-H(4)···O(5)
O(5)-H(5B)···O(2)
C(21)-H(21)···O(3)
C(25)-H(25)···O(1) iii
C(25)-H(25)···O(2) iii
C(28)-H(28)···O(4)
C(44)-H(44)···H(19)iv
C(46)-H(46)···H(8A)v
C(21)-H(21)···O(3)
N(2)-H(2)···H(8)-B(8)
N(4)-H(4)···H(13)-B(13)
N(5)-H(5B)···O(6)vi
N(5)-H(5C)···O(3)vii
N(5)-H(5D)···O(4)
N(6)-H(6B)···O(1)
N(6)-H(6C)···O(5)
N(6)-H(6D)···O(2)
(3)2·H2O·2C7H8
2.30
2.31
120
118
2.28(2)
2.19(2)
2.35(2)
2.14(2)
2.09(3)
2.37
2.46
2.59
2.43
2.21
2.21
2.48
2.24
2.02
1.97
1.90
1.88
1.93
147(2)
151(2)
152.0(2)
165(2)
160(3)
112
135
143
111
168
150
110
115
126
174
159
169
160
3.08
2.929(3)
2.72(4)
(4)2·2Et2O
2.62(4)
2.852(7)
2.745(5)
2.758(6)
2.778(5)
2.841(6)
2.715(5)
1.95
1.83
173
174
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10.1002/ejic.201700612
European Journal of Inorganic Chemistry
FULL PAPER
The structure of 3 in (3)2·H2O·2C7H8 is shown in Fig. 3, and
selected bond lengths, bond angles, torsion angles and dihedral
angles are listed in Table 4. The corresponding crystal data and
structure refinement parameters and the information on
hydrogen bonding interactions are presented in Tables 2 and 3,
respectively. There are also two independent molecules of 3 in
the asymmetric unit. The Ccage-Ccage bond lengths and the main
intramolecular interatomic bond lengths and angles are
essentially the same as those in the afore-mentioned ether
solvate. The four amide moieties are each essentially planar as
those in the ether solvate. The dihedral angles involving the
amide and phenyl moieties are somewhat different (Table 4).
These interactions may limit the mutual motions of the amide
and the phenyl rings. Compared with that of the ether solvate,
the two molecules of 3 in the toluene/water solvate is a little
nearer to each other, as evidenced from the intermolecular
hydrogen bond N(1)···O(3) distance of 3.041(3) Å.
Symmetry codes: (i) 3/2 - x, 1/2 + y, 1/2 - z; (ii) 1+ x, y, z; 1/2 – x, - 1/2 + y,
1/2 – z; 3/2 – x, - 1/2 + y, 1/2 – z; 2 + x, y, z; (iii) - 1 + x, y, z; - 2 + x, y, z; (iv)
1/2 - x, - 1/2 + y, 1/2 - z; - 1/2 - x, - 1/2 + y, 1/2 - z; (v) 1 - x, - y, 1 - z; (vi) - 1/2 -
x, - 1/2 + y, 1/2 - z; 1/2 - x, - 1/2 + y, 1/2 - z; (vii) - 1/2 - x, - 1/2 + y, 1/2 - z; 1/2 -
x, - 1/2 + y, 1/2 - z;
Figure 3. Structure of 3 in (3)2·H2O·2C7H8, water and toluene molecules and
hydrogen atoms are omitted for clarity.
Table 4. Selected bond lengths, bond angles, dihedral and torsion angles of (3)2·H2O·2C7H8
Molecule 2
Molecule 1
bond lengths (Å)
C(1)-C(2)
C(2)-C(3)
C(3)-N(1)
C(10)-N(2)
C(26)-N(4)
C(26)-C(18)
C(19)-N(3)
1.668(3)
1.541(2)
1.343(2)
1.340(2)
1.341(2)
1.538(2)
1.341(2)
C(17)-C(18)
C(3)-O(1)
1.667(3)
1.210(2)
1.527(2)
1.221(2)
1.215(2)
1.218(2)
1.529(2)
C(1)-C(10)
C(10)-O(2)
C(26)-O(4)
C(19)-O(3)
C(19)-C(17)
bond angles (°)
C(1)-C(2)-C(3)
C(2)-C(1)-C(10)
C(2)-C(3)-N(1)
C(1)-C(10)-N(2)
C(2)-C(3)-O(1)
C(1)-C(10)-O(2)
O(1)-C(3)-N(1)
O(2)-C(10)-N(2)
torsion angles (°)
C3-C2-C1-C10
C4-N1-C3-O1
C11-N2-C10-O2
dihedral angles (°)
121.99(18)
C(18)-C(17)-C(19)
C(17)-C(18)-C(26)
C(17)-C(19)-N(3)
C(18)-C(26)-N(4)
C(17)-C(19)-O(3)
C(18)-C(26)-O(4)
O(3)-C(19)-N(3)
O(4)-C(26)-N(4)
114.81(17)
116.29(18)
114.8(2)
115.10(19)
120.1(2)
119.5(2)
124.9(2)
125.4(2)
118.74(17)
115.50(18)
114.99(19)
119.44(19)
119.0(2)
125.0(2)
125.9(2)
6.6(3)
-1.9 (4)
1.8(4)
C19-C17-C18-C26
C20-N3-C19-O3
C27-N4-C20-O4
-8.4(3)
-1.6(4)
0.3(4)
C2-C1-C10/N2-C10-O2
C3-C2-C1/N1-C3-O1
N2-C10-O2/N1-C3-O1
N2-C10-O2/phenyl (C11-16) 48.1(1) N4-C26-O4/phenyl (C27-32)
N1-C3-O1/phenyl (C4-9) 60.8(2) N3-C19-O3/phenyl (C20-25)
13.2(1)
76.9(2)
76.2(2)
C19-C17-C18/N3-C19-O3
C17-C18-C26/N4-C26-O4
N4-C26-O4/N3-C19-O3
32.9(1)
67. (2)
60.0(3)
31.7(1)
30.5 (1)
phenyl (C11-16)/phenyl (C4-9) 46.4(1) phenyl (C27-32)/phenyl (C20-25) 35.9(1)
As in the structure of the ether solvate, both intramolecular C-
H···O and intermolecular hydrogen bonds (N(1)-H(1)···O(3),
N(2)-H(2)···O(4), N(3)-H(3)···O(5), O(5)-H(5B)···O(2), C(25)-
H(25)···O(1), C(25)-H(25)···O(2), C(46)-H(46A)···H(8A), C(44)-
H(44)···H(19) exist in the solid state structure of (3)2·H2O·2C7H8,
with the latter linking molecules of 3 into a 2D network. The
water and disordered toluene molecules may take part in the
intermolecular dihydrogen bonds (C(44)-H(44)···H(19) and
C(46)-H(46A)···H(8A)) with 3 in the crystals (Table 3).
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10.1002/ejic.201700612
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Fig. 4. Packing of (3)2·H2O·2C7H8, only the hydrogen atoms involved in the hydrogen bonds are shown.
plate crystals were grown and determined by an X-ray analysis
to be (4)2·2Et2O. The product [PhNH3][7,8-(PhNHCO)2-nido-
C2B9H10] (4) was obviously formed by the partial degradation of
3 under very mild condition. The nido-cage of 4 was also
indicated by the 11B-NMR spectrum which exhibited signals
(128.4 MHz, -7.5, -15.9, -21.4, -29.9, -31.6, -34.5 ppm) of a
Formation
and
structure
of
the
nido-
carboranylamide 4
The formation of the deboronated compound 4 from 3 under
mild condition was unexpected. About 3 days after the X-ray
analysis for 3, the residue solid originally from the etheral
solution that was left over was redissolved in a small amount of
wet diethyl ether and again allowed to stand overnight, colorless
-
partially degraded C2B9 cluster. Presumabley because of the
mixed cations from the deboronation a satisfactory elemental
anaysis of 4 was not obtained.
Fig. 5. Structure of (4)2·2Et2O, diethyl ether and most hydrogen atoms are omitted for clarity.
The structure of (4)2·2Et2O is shown in Fig. 5, and the selected
bond lengths, bond angles, torsion angles and dihedral angles
are listed in Table 5. The corresponding crystal data and
structure refinement parameters and the information on
hydrogen bonding interactions are also shown in Tables 2 and 3,
respectively. Two independent ion pairs of nido-carborane 4 and
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10.1002/ejic.201700612
European Journal of Inorganic Chemistry
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anilinium are present in the asymmetric unit. The Ccage-Ccage
bond lengths and other interatomic bond lengths and angles are
essentially the same in each cage. The Ccage-Ccage bond lengths
(1.573(6), 1.582(6) Å) are considerably shorter that those in 3,
but are similar to those reported for such nido-C2B9 cages (~
1.57 Å),[5] although shorter than that reported for a nido-
32)/phenyl(C20-25) (73.8(2)°, cage 2). Two amide groups, one
in each cage, are all not as well planar as those in 3 mentioned
above, as the the torsion angles of C4-N2-C3-O2 and C20-N4-
C19-O4 are -5.4(7)° and 5.1(9)°, respectively. In the crystals
both intramolecular N-H···O and C-H···O and intermolecular
hydrogen bonds (N(5)-H(5B)···O(6), N(5)-H(5C)···O(3), N(5)-
monoamide (1.67 Å).[6] The dihedral angle for C1-C2-C3/N2-C3- H(5D)···O(2),
O2 (2.1(4)°) in cage 1 (left, Fig. 5) is smaller than that for C19- H(6D)···O(2)) and the latter link a pair of the cages into two
C18-C17/N4-C19-O4 (9.5(4)°) in cage 2 (right, Fig. 5). Similar independent symmetry-related dimers, both dimers further
N(6)-H(6B)···O(1),
N(6)-H(6C)···O(5),
N(6)-
differences are also found for other dihedral angles of N1-C10-
inteact with the anilinium moieties and/or disordered ether
molecule (Fig. 6). Weak intramolecular dihydrogen bonding
interactions of (N(2)-H(2)···H(8)–B(8), and N(4)-H(4)···H(13)-
B(13)) exist involving the amide moieties.
O1/phenyl(C11-16)
O3/phenyl(C27-32)
(74.3(3)°,
(17.1(3)°,
cage
cage
1)
and
N3-C26-
2),
phenyl(C11-
16)/phenyl(C4-9) (36.8(2)°, cage 1) and phenyl(C27-
Fig. 6. Hydrogen bonding interactions in the crystals of (4)2·2Et2O, only those hydrogens involved in the hydrogen bonds are shown.
Table 5. Selected bond lengths, bond angles, dihedral and torsion angles of (4)2·2Et2O
cage 1
cage 2
bond lengths (Å)
C(1)-C(2)
1.573(6)
C(17)-C(18)
1.582(6)
117.3(3)
120.4(3)
124.2(4)
123.1(4)
115.4(4)
113.5(4)
120.3(4)
123.2(4)
bond angles (°)
C(2)-C(1)-C(10)
C(1)-C(2)-C(3)
C(1)-C(10)-O(1)
C(2)-C(3)-O(2)
C(1)-C(10)-N(1)
C(2)-C(3)-N(2)
O(1)-C(10)-N(1)
O(2)-C(3)-N(2)
torsion angles (°)
C10-C1-C2-C3
C11-N1-C10-O1
C4-N2-C3-O2
120.0(3)
C(17)-C(18)-C(19)
C(18)-C(17)-C(26)
C(18)-C(19)-O(4)
C(17)-C(26)-O(3)
C(18)-C(19)-N(4)
C(17)-C(26)-N(3)
O(4)-C(19)-N(4)
O(3)-C(26)-N(3)
116.9(3)
123.2(4)
123.2(4)
113.6(3)
117.4(4)
123.1(4)
119.3(4)
-1.2(5)
-1.4(7)
-5.4(7)
C19-C18-C17-C26
C27-N3-C26-O3
C20-N4-C19-O4
-0.1(6)
-0.4(8)
5.1(9)
dihedral angles (°)
C1-C2-C3/N2-C3-O2
C10-C1-C2/N1-C10-O1
N2-C3-O2/N1-C10-O1
N2-C3-O2/phenyl (C4-9)
N1-C10-O1/phenyl (C11-16)
2.1(4)
C19-C18-C17/N4-C19-O4
C18-C17-C26/N3-C26-O3
N4-C19-O4/N3-C26-O3
N4-C19-O4/phenyl (C20-25)
N3-C26-O3/phenyl (C27-32)
9.5 (4)
87.9(3)
81.5(5)
79.9(3)
17.1(3)
87.2(3)
89.9(3)
83.2(3)
74.3(3)
phenyl (C11-16)/phenyl (C4-9) 36.8(2)
phenyl (C27-32)/ phenyl (C20-25) 73.8(2)
characterized nido-C2B9 carborane which has two directly linked
amide moieties. The amide (carbonyl) carbon-nitrogen bond
might have been cleaved to afford 4 and aniline molecules, while
the proton needed to finally form the nido-cage and the anilium
Compound 3 is one of the few structurally characterized o-
carboranyldiamide with
a
direct cage-amide bond and
compound is to our knowledge the first structurally
4
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10.1002/ejic.201700612
European Journal of Inorganic Chemistry
FULL PAPER
could be from trace water or moisture around, although this
assumption can not rule out the possibility that the workup of the
reaction (involving phenylisocyanate) might leave trace amount
of aniline molecule in the product, but this latter assumption is
much less likely. Usually the amide bond is not easily broken,
unless in the presence of some certain precious metal or Lewis
acid catalysts,[7] or strong base.[8]
20.6, -6.8, -15.6, -31.3, -34.5 ppm, respectively. Then we tested
the monoamide compounds 2 and 7. In wet diethyl ether the two
compounds are stable at least up to five days. But it was further
found that these monoamides could be partially degraded in wet
methanol or THF, and somewhat faster than that in diethyl ether.
Similar changes occurred to the monothioamide 8. No attempt
was made to isolate the deboronation products of the o-
caboranylamides mentioned here.
The deboronation of a closo-C2B10 cluster to afford the
corresponding nido-C2B9 cage is well known,[9] the common
applicable pathway is under strong basic condition (e.g. either
KOH/EtOH or organic amines) or in the presence of F-.[10]
Recently there have been some examples in which the
degradation occurs under mild conditions such as wet DMSO,
MeOH or mixed aqueous solution.[10] In the latter cases, mainly
polar and protic solvents could work. In addition, these
carborane compounds usually have electron-withdrawing
moieties such as ester or formyl, facilitating the solvent-
mediated deboronation. In 2014/2015 Valliant et al. reported the
facile deboronation of a few closo-carboranyl monoamides in
water or DMSO-H2O mixed solvents. In the latter case, the
transformation was complete within 30 min, in an nmr tube at 37
oC, while larger amout of sample could be deboronated in
MeCN/H2O at 35 oC for 24 h, to give an isolated yield of 62%.[11]
In our case the presence of the two amide groups directly linked
to the cluster could be a more promoting factor for the
It appears that the facile deboronation of the o-
caboranylamides depends on both the mono or disubstitution
mode and the nature of the solvents, and the deboronation is
relatively faster for diamide in polar, protic solvents while much
slower for monoamide in aprotic and less polar solvents. That
the diamide
3 is more prone to deboronation than the
monoamide 2 and o-carborane may be explained on the basis of
the Density Functional Theory (DFT) calculations (see
Supporting information). The LUMO of compound 3 delocalizes
over the exo-polyhedral amide moieties and the cluster boron
atoms in which the most electropostive vertices B3 and B6 are
heavily involved. The computed Mulliken atomic charges for B3
and B6 is +0.041 each for 3, because of the two electron-
withdrawing amide groups, while those for the monoamide 2 and
o-carborane are +0.036 and +0.017 each, respectively. The
more positive charges on the B3 and B6 vertices in 3 indicate
that 3 would exhibit higher reactivity than 2 and o-carborane
deboronation even in much less polar dietheyl ether as a solvent. towards nucleophiles such as water or methanol.
It was noted that during the preparation of 3 in ether or THF,
there was no apparent deboronation during the reaction or the
workup process including the preparative TLC separation using
dichloromethane/hexane as the eluent, normally the whole
Conclustion
workup process was done as soon as possible. The
recrystallization process in diethyl ether to furnish crystals
suitable for X-ray analysis is also relatively fast. Based on such
results we may conclude that while 3 is stable as a solid, the
safe storage time for 3 in wet diethyl ether in air at room
temperature is actually less than 3 days.
We have reported the structures of the known o-
carboranyldiamide 3 as different solvates. Unexpectedly we
discovered that in wet diethyl ether 3 could be converted to the
corresponding nido-prodcut 4. The formation/presence of the
anilinium moiety in the structure of 4 is still a question for further
analysis. Further tests on related carboranyl(thio)amide
compounds indicate that the electron-withdrawing amide groups
in these compounds could facilitate such transfromation, but
depending on the number of amide moieties and the nature of
the solvents present, and probably the temperature as well.
These findings demonstrate the complexity of handling these
compounds but also provide a convenient approach to the
Some related transformations
In order to investigate whether 3 is unstable in other solvents
and whether other carboranylamides could also exhibit similar
reactivity, we tested some related compounds by simply
dissolving them in some common organic solvents at room
temperature and monitoring the process using analytical TLC
method, in some cases by 11B{1H}-NMR.
corresponding
circumstances.
nido-carboranylamides
under
certain
CONHC6H4-3-OMe
CONHC5H11
C
C
C
C
Experimental section
CONHC6H4-3-OMe
CONHC5H11
General information: The preparative reaction in toluene was carried
out under dry Ar using standard Schlenk techniques. The solvent
toluene was dried over sodium/benzophenone and distilled under
nitrogen prior to use. Preparative TLC plate was made on glass plates
(20 × 20 cm) with silica gel GF254. All other reagents were commercially
available and were used as received. NMR analyses were performed on
a Bruker Avance III 400 MHz spectrometer with tetramethylsilane (TMS)
and the deuterated solvent as internal standard (1H) and BF3·OEt2 as
external standard (11B).
5
6
CSNHC6H4-4-Et
CONHC5H11
H
C
C
C
C
H
7
8
In wet diethyl ether diamide 5 could also be gradually
deboronated, and the 11B-NMR exhibited the typical signals
(20.6, -6.8, -15.6, -31.3, -34.5 ppm, the signal at 20.6 ppm is for
the boron-oxygen species) for the nido-product. Similar results
were obtained for compound 6, and the 11B-NMR signals are
Reaction of dilithiocarborane with phenylisocyanate in toluene
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10.1002/ejic.201700612
European Journal of Inorganic Chemistry
FULL PAPER
[7] Y.-F. Wei, D.-X. Shi, Z. Wei, J. Xu, J.-R. Li, Chin. J. Org. Chem. 2012, 32,
1126-1130.
[8] Y. Sevryugina, R. L. Julius, M. F. Hawthorne, Inorg. Chem. 2010, 49,
10627-10634.
[9] R. A. Wiesboeck, M. F. Hawthorne, J. Am. Chem. Soc. 1964, 86, 1642.
[10] a) R. N. Grimes, Carboranes, Second Edition, Academic Press, Oxford,
2011; b) V. I. Bregadze, Chem. Rev., 1992, 92, 209-223.
[11] a) M. E. El-Zaria, A. R. Genady, N. Janzen, C. I. Petlura, D. R. Beckford
Vera, J. F. Valliant, Dalton Trans. 2014, 43, 4950-4961.
b) A. R. Genady, J. Tan, M. E. El-Zaria, A. Zlitni, N. Janzen, J. F. Valliant, J.
Organomet. Chem. 2015, 798, 278-288.
o-carborane 1 (144 mg, 1.00 mmol) was dissolved in dry toluene (25 mL),
the colorless solution was cooled with an ice-bath, to which was added
dropwise n-BuLi (2.2 M, 0.92 mL, 2.02 mmol), and the resulting colorless
solution was stirred for 30 min. and then 30 min at room temperature,
followed by the addition of phenylisocyanae (247 mg, 2.07 mmol) in
toluene (10 mL) and then heated (oil bath 38oC) for 7h, during which time
white precipitate appeared. After cooling to room temperature dilute HCl
was added and the aqueous phase was neutralized with aqueous NaOH
solution, the resulting mixture was left at room temperature for 3d and a
small amount of crystals of (3)2·H2O·2C7H8 was grown. The further
standard workup gave a yellow brownish solid as the crude product,
[12] O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H.
Puschmann, J. Appl. Cryst. 2009, 42, 339-341.
[13] L. Palatinus, G. Chapuis, J. Appl. Cryst. 2007, 40, 786-790.
[14] G. M. Sheldrick, Acta. Crystallogr. 2008, A64, 112-122.
which
was
separated
using
preparative
TLC
(eluent:
dichloromethane/hexane 1/2, V/V) to give compound 2 (54.5 mg, 20.9%)
and 3 (83 mg, 21.7%) both as colorless solids. The materials left on the
baseline of the TLC plate was dissolved with ethanol, and the 11B{1H}
NMR (128.4 MHz, 291.5 K) gave signals at δ = -7.5, -15.9, -21.4, -29.9, -
31.6, -34.5 ppm, indicating the deboronation of the closo-product, most
likely 3. In addition, from this same fraction a very small amount of
colorless crystals of PhNHCONHPh was grown and identified by X-ray
analysis.
Crystal structure determination
Suitable crystals of (3)2·Et2O, (4)2·Et2O and (3)2·H2O·2C7H8 were
selected and mounted on an Oxford Gemini E diffractometer for data
collection (graphite-monochromated MoKα radiation (λ = 0.71073 Å), ω
scan mode) at 120
K ((3)2·OEt2), 293 K ((4)2·OEt2), and 293 K
((3)2·H2O·2C7H8). The structures were solved at the interface of Olex2[12]
using Superflip[13] and Shelxs[14] and expanded using Fourier difference
techniques with the SHELXTL-97[14] 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 (974224, 974225, 974226)
contain the supplementary crystallographic data for (3)2·Et2O, (4)2·2Et2O,
(3)2·H2O·2C7H8, respectively. These data can be obtained free of charge
from
the
Cambridge
Crystallographic
Data
Centre
via
http://www.ccdc.cam.ac.uk/data_request/cif.
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.
Keywords: Boron, Carborane, Amide, Deboronation, X-ray
structure
References
[1]. Y. Nie, Y.-F. Wang, J.-L. Miao, D.-Q. Bian, Z.-W. Zhang, Y. Cui, G.-X. Sun.
Dalton Trans. 2014, 43 5083-5094.
[2] D. A. Brown, H. M. Colquhoun, J. A. Daniels. J. A. Hugh MacBride, I. R.
Stephenson, K. Wade, J. Mater. Chem.1992, 2, 793-804.
[3] a) M. Scholz, E. Hey-Hawkins, Chem. Rev. 2011, 111, 7035-7062;
b) F. Issa, M. Kassiou, L. M. Rendina, Chem. Rev. 2011, 111, 5701-5722;
c) Y.-H. Zhu, N. S. Hosmane, J. Organomet. Chem. 2017,
http://dx.doi.org/10.1016/j.jorganchem.2017.02.020
[4] a) Y.-P.Wang, L. Zhang, Y.-J. Lin, Z.-H. Li, G.-X. Jin, Chem. Eur. J. 2017,
23, 1814-1819; b). B. Xu, Y.-P. Wang, Z.-J. Yao, G.-X. Jin, Dalton Trans.
2015, 44, 1530-1533; c) Z.-J. Yao, W.-B. Yu, Y.-J. Lin, S.-L. Huang, Z.-H.
Li, G.-X. Jin, J. Am. Chem. Soc. 2014, 136, 2825-2832; d) Z.-J. Yao, G.-X.
Jin, Coord. Chem. Rev. 2013, 257, 2522-2535; e) Z.-J. Yao, X.-K. Huo, G.-
X. Jin, Chem. Commun. 2012, 48, 6714-6716; f) Y. Gao, Y.-J. Lin, Y.-F.
Han, G.-X. Jin, Dalton Trans. 2017, 46, 1585-1592.
[5] For example, R. Sillanpaa, J. Pedrajas, C. Vinas, F. Teixidor, R. Kivekas,
Acta Crystallogr. 1999, C55, 1008-1009.
[6] A. S. Louie, L. E. Harrington, J. F. Valliant, Inorg. Chim. Acta 2012, 389
159-167.
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Carborane
Page No. – Page No.
Title
((Insert TOC Graphic here: max.
width: 5.5 cm; max. height: 5.0 cm;
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not be less than 2 mm.))
*one or two words that highlight the emphasis of the paper or the field of the study
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Carboranylamide 1,2-(PhNHCO)2-o-C2B10H10 (3) in diethyl ether undergoes gradual
deboronation leading to [PhNH3][7,8-(PhNHCO)2-nido-C2B9H10] (4). Further evidence
showes that such closo-carboranylamides in some certain solvents tend to undergo
facile deboronation, depending on the number of amide groups and the nature of the
solvents.
Carborane
Yong Nie,* Yafeng Wang,Jinling Miao,
Chunhua Hu, Zhenwei Zhang,Yu Cui,
Yexin Li
Page No. – Page No.
Facile Deboronation of Some o-
Carboranylamides
*one or two words that highlight the emphasis of the paper or the field of the study
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