Poly-iodinated closo 1,2-C2B10 and nido [7,8-C2B9]- carborane frameworks: Synthesis and consequences

Article abstract of DOI:10.1016/j.jorganchem.2015.05.053

The preparation of C_c-monosubstituted closo and nido carborane derivatives, mono-, di and tetraiodinated is reported. Some of these mono-to poly-iodinated nido carboranes are studied in terms of the acidity of the open face bridging proton, the

Full text of DOI:10.1016/j.jorganchem.2015.05.053

Journal of Organometallic Chemistry 798 (2015) 171e181
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Poly-iodinated closo 1,2-C2B10 and nido [7,8-C2B9]ꢀ carborane
frameworks: Synthesis and consequences
a
a
a
a, *
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Marius Lupu , Adnana Zaulet , Francesc Teixidor , Reijo Sillanpaa , Clara Vinas
a Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC) Campus UAB, 08193, Bellaterra, Spain
Department of Chemistry, University of Jyvaskyla, FIN-40014, Jyvaskyla, Finland
b
€
€
€
€
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 April 2015
Received in revised form
26 May 2015
The preparation of Cc-monosubstituted closo and nido carborane derivatives, mono-, di and tetraiodi-
nated is reported. Some of these mono-to poly-iodinated nido carboranes are studied in terms of the
acidity of the open face bridging proton, their chemical shift position in the 1H NMR, and the lesser
tendency to h
5-coordination in parallel to a larger number of iodo groups.
Accepted 27 May 2015
© 2015 Elsevier B.V. All rights reserved.
Available online 20 June 2015
Dedicated to Prof. Russell N. Grimes, a true
pioneer in the field of Boron chemistry that
contributed substantially to the under-
standing and evolution of Boron clusters, on
the occasion of his 80th birthday.
Keywords:
Carboranes
Iodination
Acidity
Solvent free
1. Introduction
counterparts require slightly shorter reaction times, for the same
degree of iodination, than the parent o-carborane. This result is
consistent with both theoretical [6] and experimental data [7] re-
ported by Lipscomb and co-workers, which showed that the
electron-donating effect of methyl groups bonded to the Ccluster
atoms (Cc) causes a uniform increase in electron density on the B
atoms, while having little or no effect on the sequence of
substitution.
Highly iodinated molecules have been of interest in materials
science and medical applications [1] including the potential use of
iodinated ortho-carboranes as next-generation radiopaque contrast
agents for X-ray diagnostic imaging [2]. These compounds have a
much larger ratio of iodine in their structures than the iodinated
organic compounds currently used in X-ray contrast agents. Clean
and effective syntheses are still the critical issue for the consider-
ation of highly iodinated o-carboranes as realistic candidates for X-
ray contrast agents [3]. However, the recent development of a fast,
solvent free synthetic procedure has allowed the preparation of 1-
R-8,9,10,12-I4-1,2-closo-C2B10H7 and 1,2-R2-8,9,10,12-I4-1,2-closo-
C2B10H6 (R ¼ H, Me, Ph) derivatives by direct reaction of o-car-
boranes (1,2-closo-C2B10H12, 1-R-1,2-closo-C2B10H11 and 1,2-R2-1,2-
closo-C2B10H10) and iodine in sealed tubes [4,5]. Appealingly, the
procedure does not require any solvent-based workup and the
iodine excess is recovered and re-utilized. The C-substituted
Although halogenated nido carboranes have potential relevance
to important topics such as radioiodine carrier [8] and as boron
neutron capture therapy (BNCT) reagents [9], relatively few B-
iodinated [7,8-nido-C2B9]ꢀ derivatives are known. Two ways have
been reported for the synthesis of nido B-iodine o-carborane de-
rivatives: i) by electrophilicꢀiodination of the boron vertexes of the
anionic [7,8-nido-C2B9H12
]
cluster, leading to nido carboranes
substituted at the 9 and 11 positions, that are the sites of highest
electron density as a result of their position in the open pentagonal
face of the nido cluster [10] and, ii) by partial deboronation of
related BeI closo clusters. The reported BeI nido carboranes are: the
monoiodinated [5ꢀ-I-nido-7,8-nido-C2B9H11
]
ꢀ [11e13] and [9-I-nido-
7,8-nido-ꢀC2B9H11
]
[11,14], the diiodiꢀnated [7,8-I2-7,8-nido-
* Corresponding author.
E-mail address: clara@icmab.es (C. Vinas).
C2B9H10
]
[11], [9,11-I2-7,8-nido-C2B9H10
]
[11,14,15] and [5,6-I2-
~
http://dx.doi.org/10.1016/j.jorganchem.2015.05.053
0022-328X/© 2015 Elsevier B.V. All rights reserved.

172
M. Lupu et al. / Journal of Organometallic Chemistry 798 (2015) 171e181
ꢀ
7,8-nido-C2B9H10
]
[13], triiodinated [5,6,9-I3-7,8-nido-C2B9H9]ꢀ
(d, 1J(B,H)
¼
88), ꢀ11.7 (d, 1J(B,H)
¼
130), ꢀ12.9 (d,
[13], and tetraiodinated [1,5,6,10-I4-7,8-nido-C2B9H8]ꢀ [16]. The
1J(B,H) ¼ 118), ꢀ16.3 (br s, 1B, BeI), ꢀ19.4 (br s, 1B, BeI).
vertexes numbering of neutral 1,2-closo-C2B10H12 and anionic [7,8-
nido-C2B9H12]ꢀ/[7,8-nido-C2B9H11
]
2ꢀ
platforms are indicated in
2.2. Synthesis of the mixture 1-Ph-9-I-1,2-closo-C2B10H10 and 1-Ph-
12-I-1,2-closo-C2B10H10
Chart 1.
In this paper, we describe the syntheses of a set of closo B-
iodinated derivatives of monosubstituted 1-R-closo-C2B10H11 clus-
ters and the consequences of their deboronation that lead to highly
regioselective B-iodinated nido counterparts, and to study the in-
fluence of the iodo groups in their acidity particularly on the open
face bridging hydrogen.
The initial procedure was as before, in a 25 mL flask, 1-Ph-1,2-
closo-C2B10H10 (50 mg, 0.22 mmol) and iodine (574 mg, 2.25 mmol).
The flask was then introduced in an oil bath at a temperature of
120 ꢁC, maintained for 75 min at this temperature, and then
allowed to cool slowly to room temperature. Then, diethyl ether
enough to dissolve the product and a 10% aqueous solution of so-
dium metabisulphite were added to the residue. The mixture was
vigorously shaken and the two layers were separated. The organic
layer was washed in this way several times, until the complete
quenching of the excess iodine. The organic phase was then dried
over MgSO4, filtered and the solvent removed under reduced
pressure, to give 1-Ph-9-I-1,2-closo-C2B10H10/1-Ph-12-I-1,2-closo-
2. Materials and methods
All manipulations were carried out under inert atmosphere. 1,2-
dimethoxyethane (DME) and THF were distilled from sodium
benzophenone prior to use. Reagents were obtained commercially
and used as purchased. 1,2-closo-C2B10H12
C2B10H11, 1-Ph-1,2-closo-C2B10H11 were obtained from Katchem. IR
spectra (
, cmꢀ1; ATR or KBr pellets) were obtained on a Shimadzu
, 1-Me-1,2-closo-
C2B10H10 as a yellowish oil (59 mg, 75%). IR (KBr):
matic CH), 2932 (Cc-H), 2601 (BeH). 1H NMR (CDCl3):
(m, 5H, C6H5), 4.29 (s, 1H, Cc-H), 4.09 (s, 1H, Cc-H), 2.99e2.38 (BeH).
1H{11B} (CD3COCD3):
¼ 7.52e7.39 (m, 5H, C6H5), 4.29 (s, 1H, Cc-H),
4.09 (s, 1H, Cc-H), 2.99 (s, BeH), 2.80 (s, BeH), 2.70 (s, BeH), 2.61(s,
n
¼ 3040 (aro-
n
d
¼ 7.52e7.39
FTIR-8300 spectrophotometer. The 1H- and 1H{11B}-NMR
(300.13 MHz), 13C{1H}-NMR (75.47 MHz) and 11B- and 11B{1H}-NMR
(96.29 MHz) spectra were recorded on a Bruker ARX 300 instru-
ment equipped with the appropriate decoupling accessories. All
NMR spectra were performed in acetone-d6 at 22 ꢁC. The 11B- and
11B{1H}-NMR shifts were referenced to external BF3$OEt2, while the
1H, 1H{11B} and 13C{1H}-NMR shifts were referenced to SiMe4.
Chemical shifts are reported in units of parts per million downfield
from reference, and all coupling constants in Hz. The mass spectra
were recorded in the negative ion mode using a BrukerBiflex
MALDI-TOF-MS [N2 laser; lexc 337 nm (0.5 ns pulses); voltage ion
source 20.00 kV (Uis1) and 17.50 kV (Uis2)].
d
BeH), 2.38 (s, BeH). 11B NMR (CDCl3):
d
¼
ꢀ0.7 (d,
1J(B,H) ¼ 159), ꢀ3.3 (d, 1J(B,H) ¼ 151), ꢀ7.5 (d, 1J(B,H) ¼ 158), ꢀ10.7
(d, 1J(B,H) ¼ 130), ꢀ11.4 (d, BeH), ꢀ12.7 (d, BeH), ꢀ16.4 (br s, 1B,
BeI), ꢀ17.1 (br s, 1B, BeI).
2.3. Synthesis of 1-Me-9,12-I2-1,2-C2B10H9
A
thick-walled Pyrex tube charged with 1-Me-1,2-closo-
C2B10H11 (250 mg, 1.57 mmol) and iodine (4.00 g, 15.79 mmol) was
put under vacuum, cooled down with liquid nitrogen and sealed.
The tube was then placed in a furnace and the temperature was
raised to 170 ꢁC during 30 min, maintained at this temperature for
3.5 h and then allowed to cool slowly to room temperature. Excess
of iodine was effectively separated by sublimation from the reac-
tion mixture at 50 ꢁC under reduced pressure to give 1-Me-9,12-I2-
1,2-closo-C2B10H9 as a yellowish solid. (485 mg, 75%). IR (KBr):
2.1. Synthesis of the mixture 1-Me-9-I-1,2-closo-C2B10H10 and 1-
Me-12-I-1,2-closo-C2B10H10
A 25 mL round-bottomed flask was charged with 1-Me-1,2-
closo-C2B10H10 (250 mg, 1.57 mmol) and iodine (4.00 g,
15.97 mmol), closed and sealed to air with Teflon. The flask was
then introduced in an oil bath at a temperature of 120 ꢁC, main-
tained for 45 min and then allowed to cool slowly to room tem-
perature. Excess iodine was effectively separated by sublimation
from the reaction mixture at 50 ꢁC under reduced pressure to give
n
¼ 3041 (Cc-H), 2936, 2863 (Calkyl-H), 2621, 2575 (BeH).1H NMR
(CDCl3):
d
¼ 4.01 (br s, 1H, Cc-H), 3.75e1.75 (BeH), 1.98 (s, 3H, CH3).
1H{11B} (CD3COCD3):
d
¼ 4.01 (br s, 1H, Cc-H), 2.85 (br s, 2H, BeH),
1-Me-9-I-1,2-closo-C2B10H10/1-Me-12-I-1,2-closo-C2B10H10 as
yellowish solid. (330 mg, 74%). IR (KBr):
¼ 3040 (Cc-H), 2932, 2868
(Calkyl-H), 2579 (BeH). 1H NMR (CDCl3):
¼ 3.91 (s, 1H, Cc-H), 3.72
(s, 1H, Cc-H), 2.66e2.27 (BeH), 2.08 (s, 3H, CH3), 1.94 (s, 3H, CH3). 1H
11B} (CD3COCD3):
¼ 3.88 (s, 1H, Cc-H), 3.69 (s, 1H, Cc-H), 2.66 (s,
BeH), 2.60 (s, BeH), 2.42 (s, BeH), 2.30 (s, BeH), 2.27 (s, BeH), 2.08
a
2.78 (br s, 4H, BeH), 2.49 (br s, 2H, BeH), 1.98 (s, 3H, CH3). 13C{1H}
n
(CDCl3):
(CDCl3):
d
¼ 68.11 (s, Cc-CH3), 59.17 (s, Cc-H), 25.49 (s, CH3). 11B NMR
d
d
¼ ꢀ10.5 (d, 1J(B,H) ¼ 156, 2B), ꢀ14.8 (d, 1J(B,H) ¼ 177,
2B), ꢀ15.9 (d, 1J(B,H) ¼ 173, 2B), ꢀ16.7 (d, 1J(B,H) ¼ 184, 2B), ꢀ18.4
(br s, 1B), ꢀ21.7 (br s, 1B). MALDI-TOFMS: m/z ¼ 408.69 (23%) [M],
525.09 [M þ I -B] (100%), 536.25 [M þ I] (75%). Crystals suitable for
X ray diffraction study were grown from mixture hexane/ethyl
acetate (1/1).
{
d
(s, 3H, CH3), 1.94 (s, 3H, CH3). 11B NMR (CDCl3):
d
¼ ꢀ0.4 (d,
1J(B,H) ¼ 152), ꢀ5.6 (d, 1J(B,H) ¼ 201), ꢀ7.7 (d, 1J(B,H) ¼ 165), ꢀ10.4
ꢀ
2ꢀ
Chart 1. Icosahedral neutral 1,2-closo-C2B10H12, monoanionic [7,8-nido-C2B9H12
]
and dianionic [7,8-nido-C2B9H11
]
platforms with their numbering. Vertexes with numbers
correspond to B. All vertexes, also including C, have external H or substituent.

M. Lupu et al. / Journal of Organometallic Chemistry 798 (2015) 171e181
173
2.4. Synthesis of 1-Ph-9,12-I2-1,2-closo-C2B10H9
1J(B,H) ¼ 140, 1B).
A thick-walled Pyrex tube charged with 1-Ph-1,2-closo-C2B10H11
(250 mg, 1.12 mmol) and iodine (4.00 g, 11.29 mmol) was put under
vacuum, cooled down with liquid nitrogen and sealed. The tube
was then placed in a furnace and the temperature was raised to
170 ꢁC during 30 min, maintained for 3.5 h at this temperature, and
then allowed to cool slowly to room temperature. Then, diethyl
ether enough to dissolve the product and a 10% aqueous solution of
sodium metabisulphite were added to the residue. The mixture was
vigorously shaken and the two layers were separated. The organic
layer was washed in this way several times, until the complete
quenching of the excess iodine. The organic phase was then dried
over MgSO4, filtered and the solvent removed under reduced
pressure, to give 1-Ph-9,12-I2-1,2-closo-C2B10H9 as a brownish oil.
2.6.2. Characterization of [HNMe3][9,11-I2-7,8-nido-C2B9H10]
The [HNMe3][9,11-I2-7,8-nido-C2B9H10] was prepared according
to the general procedure described in the literature [14]. IR (KBr):
(cmꢀ1) 3140 (Cc-H), 3032, 2960 (Calkyl-H), 2766 (Me3NeH), 2584,
n
2561, 2539, 2521 (BH), 1474, 1449 (d
Me3NeH). 11B NMR (CDCl3):
d
¼ ꢀ12.8 (d, 1J(B,H) ¼ 143, 2B: B5þB6), ꢀ15.5 (d, 1J(B,H) ¼ 166, 1B:
B3), ꢀ18.5 (d, 1J(B,H)
¼ 154, 2B: B4þB7), ꢀ19.9 (s, 2B:
B9þB11), ꢀ28.1 (br d, 1J(B,H)
¼ 133, 1B: B10), ꢀ35.2 (d,
1J(B,H) ¼ 144, 1B: B1). 1H NMR (CD3COCD3):
d
3.23 (s, NMe3, 9H),
3.23
2.33 (s, Cc-H,1H),1.78 (s, Cc-H,1H). 1H{11B} NMR (CD3COCD3):
d
(s, NMe3, 9H), 2.33 (s, Cc-H, 1H), 1.78 (s, Cc-H, 1H), 2.25, 1.98, 1.76,
1.43, 0.86, 0.65 (br s, BeH), ꢀ2.98 (t, 1J(H,H) ¼ 6, BeHeB).
(470 mg, 79%). IR (KBr):
n
¼ 3042 (aromatic CH), 2923 (Cc-H), 2610
2.7. X-ray structure analysis
(BeH).1H (CDCl3):
d
¼ 7.47 (d, 3H, 3J(H,H) ¼ 6, Caryl-H), 7.39 (dd, 2H,
3J(H,H) ¼ 6, Caryl-H), 4.38 (br s, 1H, Cc-H), 3.75e1.75 (BeH). 1H{11B}
X-ray crystal structure analyses for 1-Me-9,12-I2-1,2-closo-
C2B10H9 and [NHMe3][7-Ph-1,5,6,10-I4-7,8-nido-C2B9H7] were done
with an EnrafNonius CCD area detector diffractometer with MoKa
NMR (CD3COCD3):
d
¼ 7.47 (d, 3H, 3J(H,H) ¼ 6, Caryl-H), 7.39 (dd, 2H,
3J(H,H) ¼ 6, Caryl-H), 4.38 (br s, 1H, Cc-H), 4.38 (br s, 1H, Cc-H), 3.09
(br s, 2H, BeH), 3.00 (br s, 2H, BeH), 2.86 (br s, 2H, BeH), 2.76 (br s,
radiation (
l
¼ 0.71073 Å) at 123 K. The data sets were corrected for
2H, BeH). 13C{1H} NMR (CDCl3):
d
¼ 131.81, 131.00, 130.79, 130.05,
absorption using SADABS program [17]. X-ray crystal structure
analysis for [NHMe3][5,6,11-I3-7,8-nido-C2B9H8] was done with an
Agilent Supernova diffractometer equipped with Atlas CCD area-
129.30, 127.52 (C6H5), 57.91 (Cc-H). 11B NMR (CDCl3):
d
¼ ꢀ5.8 (d,
1J(B,H) ¼ 160, 2B), ꢀ10.4, ꢀ11.4, ꢀ12.1 (6B), ꢀ14.0 (br s,1B), ꢀ15.1 (br
s, 1B).
detector using MoKa radiation (
l
¼ 0.71073 Å) at 123 K. The data
set was corrected for absorption using a multifaceted crystal model
as implemented in CrysAlisPro program package [18]. The struc-
tures were solved with the program SIR97 [19]; full-least-squares
refinements on F2 were performed with SHELXL97 [20] using
anisotropic displacement parameters for most of the non-H atoms:
The hydrogen atoms were treated as riding atoms using the
SHELX97 default parameters or their positional parameters were
refined isotropically according to the riding model. All calculations
and graphics were done at WinGX platform [21]. Crystallographic
data and structure refinement details are shown in Table 1. Crys-
tallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC-1058310e1058314. Copies of the data can be obtained free of
charge from www.ccdc.cam.ac.uk/conts/retrieving.html.
2.5. Synthesis of 1-Bz-2-Me-8,9,10,12-I4-1,2-closo-C2B10H6
The procedure was as for 1-Ph-9,12-I2-1,2-closo-C2B10H9 (R ¼ Me,
Ph) with1-Bz-2-Me-C2B10H10 (0.2 g, 0.805 mmol) and iodine
(2.043 g, 8.052 mmol). The tube was then placed in a furnace and
the temperature gradually raised to 270 ꢁC during 20 min, main-
tained for 3 h and allowed to drop slowly to room temperature. The
mixture was then dissolved in diethyl ether (4 mL), and the excess
of iodine quenched by addition of 5% aqueous solution Na2S2O5
(4 mL). The mixture was thoroughly shaken and the two layers
separated. The aqueous layer was extracted with diethyl ether
(3 ꢂ 5 mL). The combined organic phase was dried over NaSO4,
filtered and evaporated in vacuum. The resulting solid, 1-Bz-2-Me-
8,9,10,12-I4-1,2-C2B10H6, was obtained in 77% yield (470 mg). Good
crystals for X ray diffraction were grown from the mixture hexane/
ethyl acetate (1/1). FTIR (KBr),
NMR (CD3COCD3): 7.44 (5H, Caryl-H), 3.80 (2H, s, CH2), 2.43 (3H, s,
Cc-CH3). 1H{11B} NMR (CD3COCD3):
7.44 (5H, Caryl-H), 3.80 (2H, s,
n
(cmꢀ1): 2625, 2607 (s, BeH). 1H
3. Results and discussion
d
d
3.1. B-iodinated closo 1-R-o-carborane (R ¼ Me, Ph) derivatives:
CH2), 3.35, 3.20, 2.93 (s, BeH), 2.43 (3H, s, Cc-CH3). 11B NMR
mono, di and tetraiodinated
(CD3COCD3):
(CDCl3):
d
ꢀ8.1, ꢀ9.5 (br s, 8B), ꢀ17.8 (br s, 2BeI). 13C{1H} NMR
d
134.39, 130.52, 128.92, 128.55 (s, Caryl), 79.37 (s, Cc), 76.77
As described in a previous communication, a solvent-free
regioselective tetraiodination on o-carboranes is effectively ach-
ieved by reaction of 1,2-R2-1,2-closo-C2B10H10 (R ¼ H, Me, Ph) and
1-R-1,2-closo-C2B10H11 (R ¼ Me, Ph) with excess iodine in sealed
tubes (Scheme 1) [4].
(s, Cc), 39.74 (s, CH2), 22.18 (s, CH3).
2.6. Deboronation of the Cc-monosubstituted mono or
polyiodinated closo o-carboranes
In this paper, an extension of this fast, efficient and solvent free
procedure was used to explore the versatility of the method in the
iodination reaction to synthesize the closo monoiodinated com-
pounds 1-R-9-I-1,2-closo-C2B10H10/1-R-12-I-1,2-closo-C2B10H10 and
diiodinated 1-R-9,12-I2-1,2-closo-C2B10H9 as well as the Cc hetero-
disubstituted 1-Me-2-Bz-8,9,10,12-I4-1,2-closo-C2B10H6. We have
tested the reaction of 1-R-1,2-closo-C2B10H11 (R ¼ Me, Ph) and
iodine in a ratio 1:10 in sealed tubes under various experimental
conditions (temperature and reaction time). The best results are
shown in Table 2. Always, after the reaction is completed, volatiles,
including HI, are carefully removed first by natural diffusion after
mindful opening of the reaction flask glass tube, then by evapora-
tion leaving the crude product as a solid that is analysed by 1H{11B}
NMR spectra. Almost all of the iodine in excess (95%) could be
The carboranes described in the preceding sections have been
deboranated as described in Refs. [13] and [16]. The crystal struc-
tures of [HNMe3][5-I-7,8-nido-C2B9H11
]
and [HNMe3][7-Ph-
1,8,9,12-I4-7,8-nido-C2B9H7] are reported in this paper.
2.6.1. Characterization of [NMe4][9-I-7,8-nido-C2B9H11
The [NMe4][9-I-7,8-nido-C2B9H11] was prepared according to
the general procedure described in the literature [14]. IR (KBr):
(cmꢀ1) 3181, 3168 (Cc-H), 3097, 3037, 2958 (Calkyl-H), 2574, 2518,
]
n
2430 (BH), 1474, 1467, 1446. 11B NMR (CDCl3):
d
¼ þ18.3 (s,
B(9)), ꢀ5.2 (d, 1J(B,H) ¼ 138, 1B), ꢀ16.0 (d, 1J(B,H) ¼ 136, 1B), ꢀ17.8
(d, 1J(B,H) ¼ 148, 2B), ꢀ21.6 (d, 1J(B,H) ¼ 152, 1B), ꢀ24.9 (d,
1J(B,H)
¼
138, 1B), ꢀ29.5 (d, 1J(B,H)
¼ 131, 1B), ꢀ37.4 (d,

174
M. Lupu et al. / Journal of Organometallic Chemistry 798 (2015) 171e181
Table 1
Crystallographic data and structure refinement details for neutral closo carborane derivatives 1-Me-9,12-I2-1,2-closo-C2B10H9, 1; 1-Me-2-Bz-8,9,10,12-I4-1,2-closo-C2B10H6, 2
compounds and the anionic nido derivatives [NMe4][5-I-7,8-nido-C2B9H11], 3; [HNMe3][5,6,11-I3-7,8-nido-C2B9H9], 4 and [HNMe3][7-Ph-1,5,6,10-I4-7,8-nido-C2B9H7], 5.
Compound
1
2
3
4
5
Formula
Mr
Crystal system
Space group (no.)
a (Å)
C3H12B10 2
410.05
I
C10H16B10 4
751.93
monoclinic
P21/c (14)
9.421(13)
16.59(2)
15.685(17)
90
I
C6H22B9IN
332.44
monoclinic
P21/n (14)
15.29(2)
13.259(18)
15.56(2)
90
C5H19B9I3N
571.2
C11H22B9I4N
749.19
monoclinic
P21/n (14)
8.9345(3)
12.7332(3)
11.4559(3)
90
monoclinic
P21/n (14)
6.9919(2)
17.5061(5)
14.3988(3)
90
monoclinic
P21/c (14)
13.5502(2)
12.3860(2)
14.9886(2)
90
b (Å)
c (Å)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
97.6710(10)
90
113.05(6)
90
93.48(2)
90
92.382(10)
90
113.7250(10)
90
V (Å)
1291.61(6)
4
2.109
2256(5)
4
2.214
3149(7)
8
1.394
1760.90(8)
4
2.155
2302.98(6)
4
2.23
Z
Dc (g cmꢀ1
)
m
(MoKa) (mmꢀ1
)
4.821
5.517
2.005
5.301
5.409
T/K
123(2)
2514
0.03
137
0.0222
0.0487
0.877, ꢀ0.567
300(2)
5249
0.0417
218
0.0605
0.1646
1.611, ꢀ1.286
173.5(2)
5329
0.0648
310
0.1060
0.3011
7.235, ꢀ3.241
123(2)
3026
0.0264
184
0.0282
0.0592
1.962, ꢀ0.743
123(2)
4500
0.0333
235
0.0267
0.0518
1.385, ꢀ0.818
Observed reflections
Rint
Parameters
R[F2 > 2
wR(F2)a
s
(F2)]
Largest peak, hole (e Åꢀ3
)
w ¼ 1=½s2ðFo2Þ þ ðaPÞ2 þ bPꢃ where P ¼ ðFo2 þ 2Fc2Þ=3
a
1H and 11B NMR spectra of the isomers mixture.
No attempt to separation regioisomers, 1-Me-9-I-1,2-closo-
C2B10H10 and 1-Me-12-I-1,2-closo-C2B10H10, was made because our
goal was to discern if the Me substituent bonded at one of the Cc
would produce a major regioselective isomer. 1H and 11B NMR
spectra of the mixture confirm same amount of each regioisomer
and no antipodal influence of the Cc-Me on the electrophilic boron
vertex substitution. The 1-R-9-I-1,2-closo-C2B10H10 and 1-R-12-I-
1,2-closo-C2B10H10 (R ¼ Ph, vinyl) regioisomers separation was
recently reported for the investigation of polar liquid crystals [22].
In this paper, we report the single-crystal X-ray structure
determination of 1-Me-9,12-I2-1,2-closo-C2B10H9 and 1-Me-2-Bz-
8,9,10,12-I4-1,2-closo-C2B10H6.
Scheme 1. General tetraiodination of 1-R-1,2-closo-C2B10H11 (R ¼ Me, Ph) by reaction
with iodine in sealed tubes (R, R’ ¼ H, Me or Ph).
recovered from the mixture by sublimation under reduced pressure
allowing further reuse of reagents.
3.2. Deboronation process of mono, di and tetraiodinated
derivatives of closo 1-R-o-carborane (R ¼ Me, Ph)
As a representative example of these compounds, the 1H NMR
spectrum of the mixture of 1-Me-9-I-1,2-closo-C2B10H10 and 1-Me-
12-I-1,2-closo-C2B10H10 display two broad singlets of the same in-
tensity at 3.91 and 3.72 ppm and two singlets at 2.08 and 1.94 ppm
corresponding to the Cc-H and the methyl groups (Cc-Me) of the
two geometrical isomers. The 11B{1H} NMR spectra of these com-
pounds also display two different resonances at high field that do
not split when running 11B NMR spectra in agreement with the
presence of the two geometrical isomers with a BeI vertex. Fig. 1
shows the geometry of the two isomers while Fig. 2 displays the
We have reported recently the partial deboronation reaction of
closo 1-R-9-I-1,2-C2B10H10, 1-R-12-I-1,2-C2B10H10, 1-R-9,12-I2-1,2-
C2B10H9 and 1-R-8,9,10,12-I4-1,2-C2B10H7 (R ¼ Me, Ph) derivatives
with KOH/EtOH under reflux conditions for
5
h
that
following precipitation with [HNMe3]Cl leads to the formation of
[HNMe3][7-R-5-I-7,8-nido-C2B9H10], [HNMe3][7-R-6-I-7,8-nido-
C2B9H10], [HNMe3][7-R-5,6-I2-7,8-nido-C2B9H9] and [HNMe3][7-R-
1,5,6,10-I4-7,8-nido-C2B9H7] in good to high yield [13]. The nucle-
ophilic attack is produced selectively over one of the boron atoms
that are directly bonded to the cluster carbons, because these boron
Table 2
Mono, di and tetra iodination reaction of 1-R-1,2-closo-C2B10H11 using iodine in a 1/
10 M ratio.
R
T (ꢁC)
t (h)
9-I-
9,12-I2-
8,9,10,12-I4-
H [5]
Me
Ph
H [5]
Me [4]
Ph [4]
H [4]
Me [4]
Ph [4]
115
120
120
170
170
170
265
265
265
2.5
0.75
1.25
3.5
3.5
3.5
3.5
3.5
3.5
97%
74%
75%
82%
75%
79%
75%
>75%
<75%
Fig. 1. The two mono B-iodinated isomers: 1-Me-12-I-closo-1,2-C2B10H10 and 1-Me-9-
I-closo-1,2-C2B10H10
.

M. Lupu et al. / Journal of Organometallic Chemistry 798 (2015) 171e181
175
Fig. 3. ORTEP drawing of 1-Me-9,12-I2-1,2-closo-C2B10H9. Thermal displacement el-
lipsoids are drawn at 20% probability level. Selected bond lengths (Å): I9
e
B9 ¼ 2.174(4), I12 e B12 ¼ 2.179(5), C1eC2 ¼ 1.643(4). C1eC13 ¼ 1.517(5).
atoms, either B(3) or B(6), are the ones most electronically
impoverished (Scheme 2). The non-equivalence of the initial Cc
substituents of the [7,8-nido-C2B9]ꢀ cluster resulted in the prepa-
ration of four isomers. No attempt to resolve the nido-carborane
ligands into their enantiomers was made and the ligand racemic
mixture was isolated.
Fig. 2. 1H and 11B{1H} NMR spectra of the mixture of isomers 1-Me-12-I-closo-1,2-
All synthesized compounds, closo and nido, were characterized
C2B10H10 and 1-Me-9-I-closo-1,2-C2B10H10
.
by 1H-, 11B, 13C NMR and MALDI-TOF-MS spectroscopy [13]. The
3
4
CH3
8
C1
H
7
9
C2
5
12
6
11
10
I
-B(6)
-B(3)
H
CH3
CH3
C
C
H
H
C
C
I
I
H
H
H
CH3
H3C
11
11
10
C7
C7
10
H
H
9
6
C8
C8
9
6
2
2
5
3
3
5
4
1
4
1
I
I
ꢀ
ꢀ
.
Scheme 2. Anionic iodinated chiral ligands, [7-R-5-I-7,8-nido-C2B9H10
]
and [7-R-6-I-7,8-nido-C2B9H10
]

176
M. Lupu et al. / Journal of Organometallic Chemistry 798 (2015) 171e181
Fig. 6. ORTEP drawing of [HNMe3][5,6,11-I3-7,8-nido-C2B9H9]. Thermal displacement
ellipsoids are drawn at 20% probability level. Selected bond lengths (Å): I5
B5 2.183(5), I6 B6 2.185(5), C7eC8 1.555(7), C8eB9 1.624(7),
B9eB10 ¼ 1.854(8), B10eB11 ¼ 1.797(7), B11eC7 ¼ 1.597(7).
e
¼
e
¼
¼
¼
[NHMe3][7-Ph-1,5,6,10-I4-7,8-nido-C2B9H7] (Fig. 7) were grown
from ethanol, water and chloroform solutions, respectively. The
structural parameters in the compounds are normal. However,
bond distances B11eC7 and B11eB10 are longer in tetra B-iodine
compound than in tri B-iodine one (see the captions in Figs. 6 and
7).
Fig. 4. ORTEP drawing of 1-Me-2-Bz-8,9,10,12-I4-1,2-closo-C2B10H6. Thermal
displacement ellipsoids are drawn at 20% probability level.
Figs.
8 and 9 display the crystal packing showing the
periodical weak Cc-H/IeB and Cc-H/HeB interactions of 1-Me-
9,12-I2-1,2-closo-C2B10H9 and [7-Ph-1,5,6,10-I4-7,8-nido-C2B9H7]ꢀ,
respectively.
single-crystal X-ray structure determination for [NMe4][5-I-7,8-
nido-C2B9H11], [HNMe3][5,6,11-I3-7,8-nido-C2B9H9] and [HNMe3]
[7-Ph-1,5,6,10-I4-7,8-nido-C2B9H7] are reported.
3.3. X-ray structure determination
Closo B-iodinated derivatives: Crystals suitable for X-ray
diffraction of 1-Me-9,12-I2-1,2-closo-C2B10H9 (Fig. 3), and 1-Me-2-
Bz-8,9,10,12-I4-1,2-closo-C2B10H6 (Fig. 4) were grown from a solu-
tion of hexane:ethyl acetate (1:1). Nido B-iodinated derivatives:
Crystals suitable for X-ray diffraction of [NMe4][5-I-7,8-nido-
C2B9H11] (Fig. 5), [HNMe3][5,6,11-I3-7,8-nido-C2B9H9] (Fig. 6) and
Fig. 7. ORTEP drawing of [HNMe3][7-Ph-1,5,6,10-I4-7,8-nido-C2B9H7]. Thermal
displacement ellipsoids are drawn at 20% probability level. Selected bond lengths (Å):
Fig. 5. ORTEP drawing of [NMe4][5-I-7,8-nido-C2B9H11]. Thermal displacement ellip-
soids are drawn at 20% probability level.
I1
e
B1 ¼ 2.178(4), I5 eB5
¼
2.190(4), I6
e
B6
¼
2.173(5), C7eC8
¼
1.566(6),
C8eB9 ¼ 1.611(6), B9eB10 ¼ 1.838(6), B10eB11 ¼ 1.824(6), B11eC7 ¼ 1.625(6).

M. Lupu et al. / Journal of Organometallic Chemistry 798 (2015) 171e181
177
Fig. 8. Crystal structure of 1-Me-9,12-I2-1,2-C2B10H9 showing the CceH/I hydrogen bonding (I/H is 2.962 Å) of molecules forming an infinite zig-zag chains running parallel to the
b crystallographic axis.
An examination of Cambridge Structural Database [23] shows
just 28 X-ray structures of iodinated closo 1,2-C2B10 carborane
framework and 8 X-ray structures of iodinated nido [7,8-C2B9]ꢀ
carborane framework that have been summarized in Table 3.
NMR spectrum but the largest upfield shift is always due to the BeI
[5,28]. In this paper the influence of BeI in the 11B{1H}-NMR as well
as in the acidity of the hydrogen bridge has been studied.
4.1. Influence of the number of BeI vertexes of nido species on the
4. NMR spectral considerations on B-iodinated [7,8-nido-
11B{1H}-NMR spectrum
¡
C2B9H12
]
derivatives
The 11B{1H}-NMR spectra of [HNMe)3][7,8-nido-C2B9H12],
[HNMe3][5,6-I2-7,8-nido-C2B9H10], and [HNMe3][1,5,6,10-I4-7,8-
nido-C2B9H8], are in the range ꢀ7 to ꢀ38 ppm, characteristic to o-
carborane derived nido species [29]. Fig. 10 shows the influence of
the successive B-iodinations on the chemical shifts of 11B{1H} NMR
spectra of the nido o-carborane derivatives. The [HNMe3][5,6-I2-
7,8-nido-C2B9H10] spectrum displays the same number of reso-
nances (2:1:2:2:1:1) of the non-iodinated [HNMe3][7,8-nido-
C2B9H12] cluster parent (2:2:1:2:1:1) from low to high field but
different pattern. Conversely, for the case of [HNMe3][1,5,6,10-I4-
7,8-nido-C2B9H8], the pattern is 2:1:4:2 (low to high field). Neither
The sensitivity of the electron distribution in carboranes to the
presence of substituents has long been apparent [24]. For icosa-
hedral carborane derivatives of 1-R-1,2-closo-C2B10H11, 11B NMR
studies have shown that the chemical shifts of the cage boron
atoms vary with the substituent R [25], particularly on the boron
atom opposite to the point of attachment of the substituent, the
“antipodal atom” [26]. The 11B NMR spectrum of o-carborane was
rationalised in 1986 following a set of empirical rules incorporating
antipodal, rhomboidal, butterfly and neighbour effects [27]. It was
also reported that the presence of iodine atoms bonded to Boron
vertexes in closo o-carborane modifies all the resonances of the 11
B
the resonance at
d
¼ ꢀ24.0 ppm for [HNMe3][5,6-I2-7,8-nido-
Fig. 9. Crystal packing of [7-Ph-1,5,6,10-I4-7,8-nido-C2B9H7]ꢀ showing the periodical Cc-H/IeB interactions (2.897 Å). White ¼ H, pink ¼ B, grey ¼ C). Contacts shorter than the sum
of Van der Waals radii (ꢀ0.2 Å) are plotted as dashed dark lines.

178
M. Lupu et al. / Journal of Organometallic Chemistry 798 (2015) 171e181
Table 3
Crystal structures reported on iodinated neutral closo 1,2-C2B10 and monoanionic nido [7,8-C2B9]ꢀ carborane frameworks.
Compound
CCDC code
Reference
1,2-closo-C2B10 framework
Mono-iodinated
[12-IPh-1,2-closo- C2B10H11]I
CARLAI
[34]
[35]
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[42]
[38]
[43]
[42]
[44]
[45]
[46]
[47]
[4]
9-I-1-SiMe2tBu-1,2-closo-C2B10H10
12-I-1-SiMe2tBu-1,2-closo-C2B10H10
9-I-1-CHMeOEt-1,2-closo-C2B10H10
9-I-1,2-Ph2-1,2-closo-C2B10H10
9-Et-12-I-1,2-closo-C2B10H10
12-I-1,2-closo-C2B10H11
HAWPAY
HAWPEC
IZEYAO
KIYCUQ
LICJOW
WUNDEP
WUNDEP01
XARHUU
12-I-1,2-closo-C2B10H11
9-X-12-Y-3,4,5,6,7,8,10,11-Me8-1,2-closo-C2B10H2 (X,Y ¼ I,Cl)
8-I-1,2-closo-C2B10H11
8-I-1-COOEt-1,2-closo-C2B10H10
9,12-I2-1,2-closo-C2B10H10
9,12-I2-1,2-closo-C2B10H10
Di-iodinated
LICJUC
WURVOU
3,10-I2-1,2-closo-C2B10H10
9,12-I2-1,2-Ph2-1,2-closo-C2B10H8
9,12-I2-8,10-Ph2-1,2-closo-C2B10H8
9,12-I2-1,2-Ni(PPh3)2e1,2-closo-C2B10H8
9,12-I2-1,2-(HgR)2e1,2-closo-C2B10H8
8,9,10,12-I4-1,2-closo-C2B10H8
BAQZUP
ULOYAW
OLIQEC
YAWKIQ
GERGAM
WUNDUF
GERGEQ
WUNFAN
WUNFER
WUNDIT
HAFZOE
CEHWOC
WUNDAL
WUNDOZ
Tetra-iodinated
8,9,10,12-I4-1-Me-1,2-closo-C2B10H7
8,9,10,12-I4-1-Ph-1,2-closo-C2B10H7
8,9,10,12-I4-1,2-Me2-1,2-closo-C2B10H6
8,9,10,12-I4-1,2-Ph2-1,2-closo-C2B10H6
4,5,7,8,9,10,11,12-I8-1,2-closo-C2B10H4
3,4,5,7,8,9,10,11,12-I9-1,2-closo-C2B10H3
3,4,5,6,7,8,9,10,11,12-I10-1,2-closo-C2B10H2
3,4,5,6,7,8,9,10,11,12-I10-1,2-closo-C2B10H2
3,4,5,6,7,8,9,10,11,12-Iꢀ10-1,2-closo-C2B10H2
[39]
[4]
[39]
[39]
[39]
[48]
[49]
[28]
[39]
[42]
[44]
[50]
[50]
[50]
[16]
[33]
Octa-iodinated
Nona-iodinated
Deca-iodinated
[7,8-nido-C2B9]ꢀ framework
Mono-iodinated
[1-I-7,8-nido-C2B9H11
]
[6-I-7,8-Ph2-7,8-nido-C2B9H9]ꢀ
BARBEC
ꢀ
]
[9-I-11-PPh3-7,8-nido-C2B9H10ꢀ
[6-I-9-PPh3-7,8-nido-C2B9H10
]
[5-I-6,9-(PPh3)2-7,8-nido-C2B9H9]ꢀ
Tetra-iodinated
Octa-iodinated
[1,5,6,10-I4-7,8-nido-C2B9H8]ꢀ
FAKGAB
RICLUL
[1,2,4,5,6,9,10,11-I8-7,8-nido-C2B9H4]ꢀ
C2B9H10] nor these at
d
¼ ꢀ16.4 and ꢀ33.9 ppm for [HNMe3]
4.2. Influence on the acidity of nido derivatives when increasing the
number of BeI vertexes
[1,5,6,10-I4-7,8-nido-C2B9H8] split into doublets in the 11B NMR
spectra, thus indicating that they correspond to BeI vertexes,
respectively. The iodo groups affect more importantly the ipso
Treatment of 1,5,6,10-I4-1,2-closo-C2B10H8 with potassium hy-
droxide in ethanol yielded the corresponding tetraiodo nido cluster
boron atoms. The average chemical shift value, <d>, remains
practically unaltered upon the increment of the number of BeI
vertexes.
Fig. 11. 11B{1H} (black lines) and 11B (red lines) NMR spectra of the acid/base pair
[1,5,6,10-I4-7,8-nido-C2B9H8]ꢀ/[1,5,6,10-I4-7,8-nido-C2B9H7]2ꢀ in water. The highest
field peak in the spectra at pH ¼ 3 (ꢀ33.9 ppm) is assigned to the overlapped signals of
B(1) and B(10). At pH ¼ 10, the peak of B(1) is shifted to higher field, whereas that of
B(10) is shifted to low field (ca. ꢀ8.0 and þ 12.0 ppm, respectively). (For interpretation
of the references to colour in this figure legend, the reader is referred to the web
version of this article.)
Fig. 10. Raw 11B{1H}spectra with the peak assignments for unsubstituted [HNMe3][7,8-
nido-C2B9H12] and two iodinated derivatives [HNMe3][5,6-I2-7,8-nido-C2B9H10] and
[HNMe3][1,5,6,10-I4-7,8-nido-C2B9H8] from solutions of the samples in acetone-d6.
Substitution of hydrogen with iodine causes significant shielding on boron atoms
attached to the substituent.

M. Lupu et al. / Journal of Organometallic Chemistry 798 (2015) 171e181
179
Fig. 12. 11B{1H} NMR spectra of the acid/base pairs: a) [7,8-nido-C2B9H12
]
ꢀ/[7,8-nido-C2B9H11
]
2ꢀ; b) [5,6-I2-7,8-nido-C2B9H10
]
ꢀ/[5,6-I2-7,8-nido-C2B9H9]2ꢀ; c) [1,5,6,10-I4-7,8-nido-
C2B9H8]ꢀ/[1,5,6,10-I4-7,8-nido-C2B9H7]2ꢀ in EtOH: H2O at the pH range 11e1.
Table 4
1H NMR chemical shift of bridge BHB protons in iodinated nido-carboranes derivatives related to the parent nido-o-carborane. Spectra were run in acetone-d6.
Entry
Compounds
d
1H NMR of bridge BHB protons (ppm)
Dd relative to o-carborane
ꢀ
1
2
3
4
5
6
7
8
[7,8-nido-C2B9H12
]
ꢀ2.90
e
ꢀ
ꢀ
ꢀ
[9-I-7,8-nido-C2B9H10
[3-I-7,8-nido-C2B9H11
[5-I-7,8-nido-C2B9H11
]
]
]
ꢀ2.98
ꢀ0.08
þ0.23
þ0.49
þ1.28
þ0.75
þ0.65
þ2.81
þ0.22
þ1.01
þ3.09
þ0.50
þ1.32
þ3.30
ꢀ2.67 [16]
ꢀ2.41 [11]
ꢀ1.62
[9,11-I2-7,8-nido-C2B9H9]ꢀꢀ
[5,6-I2-7,8-nido-C2B9H10
]
ꢀ2.15 [16]
ꢀ2.25 [11]
ꢀ0.09 [16]
ꢀ2.68
[5,6,9-I3-7,8-nido-C2B9H9]ꢀ
[1,5,6,10-I4-7,8-nido-C2B9H8]ꢀ
ꢀ
9
[7-Me-7,8-nido-C2B9H11]
10
11
12
13
14
[7-Me-5,6-I2-7,8-nido-C2B9H9]ꢀ
ꢀ1.89 [11]
þ0.19 [11]
ꢀ2.40
[7-Me-1,5,6,10-I4-7,8-nido-C2B9H7]ꢀ
ꢀ
[7-Ph-7,8-nido-C2B9H11
]
[7-Ph-5,6-I2-7,8-nido-C2B9H9]ꢀ
ꢀ1.58 [11]
þ0.40 [11]
[7-Ph-1,5,6,10-I4-7,8-nido-C2B9H7]ꢀ
[1,5,6,10-I4-7,8-nido-C2B9H8]ꢀ, able to generate
sandwich type compounds. It was isolated for characterization as
the trimethylammonium salt of the protonated monoanion,
h
5-ligands for
deprotonation, the B(10) resonance is shifted to low field,
whereas that of B(1) is shifted upfield, as occurs for [7,8-nido-
2ꢀ
[32], [7,8-m
eSCH2CH2Se7,8-nido-C2B9H9]2ꢀ [32] and
C2B9H11
]
[NHMe3][1,5,6,10-I4-7,8-nido-C2B9H8]. The bridging proton in pris-
[1,2,3,4,5,6,9,10,11-I9-7,8-nido-C2B9H2]2ꢀ [33].
ꢀ
tine [7,8-nido-C2B9H12
]
anion is relatively acidic and can be
For a matꢀter of comparison [7,8-nido-C2B9H12]ꢀ, [5,6-I2-7,8-
removed by the addition of strong base.
nido-C2B9H10]
and [1,5,6,10-I4-7,8-nido-C2B9H8]ꢀ have been stud-
Although it is possible to approximately calculate nido-carbor-
ane pKa values from DFT methods [30], there exists few experi-
mental data in the literature [31]. We undertook a study in order to
determine the acidity of the anion [1,5,6,10-I4-7,8-nido-C2B9H8]ꢀ.
We wanted to avoid a typical titration to be able to observe struc-
tural changes upon the pH modification. The 11B NMR spectra of its
potassium salt in aqueous solution could be very informative as a
function of pH. Significant shifts were observed from acidic to basic
solutions. Fig. 11 shows a comparison of two spectra of K[1,5,6,10-
I4-7,8-nido-C2B9H8] recorded at pH 3 and 10. The former is iden-
tical to that of [NHMe3][1,5,6,10-I4-7,8-nido-C2B9H8] in acetone,
indicating that the monoanion is present. The one at pH 10 shows a
quite different pattern; but importantly, however, is that both
the monoanion [1,5,6,10-I4-7,8-nido-C2B9H8]ꢀ and the dianion
[1,5,6,10-I4-7,8-nido-C2B9H7]2ꢀ are stable in aqueous media. Upon
ied by 11B{1H}-NMR in a mixture of EtOH: H2O in a range of pH
between 11 and 1 (Fig. 12). At the lowest pH (higher concentration
of acid), it was assumed that all three anions had the bridging
proton on the open face, thus they were monoanions. In Fig. 12a,
dedicated to [7,8-nido-C2B9H12]ꢀ, it is definitely observed that the
11B{1H}-NMR is invariant through all pH values. When the number
of B-iodinated vertexes increases, case of [5,6-I2-7,8-nido-
C2B9H10]ꢀ, the situation is different. As can be seen in Fig. 12b, the
11B{1H}-NMR spectrum is identical from pH ¼ 1 to pH ¼ 8 indi-
cating that within this pH interval the bridging proton is on the
open face, but the spectrum shows signs of alteration at pH ¼ 11
suggesting that two species, most probably [5,6-I2-7,8-nido-
C2B9H10
]
ꢀ and [5,6-I2-7,8-nido-C2B9H9]2ꢀ coexist at pH ¼ 11. Finally,
the same studies were performed in a higher iodo containing anion,
[1,5,6,10-I4-7,8-nido-C2B9H8]ꢀ, see Fig. 12c. In this case, the 11B{1H}-

180
M. Lupu et al. / Journal of Organometallic Chemistry 798 (2015) 171e181
NMR at a very low pH (between 1 and 3) show identical spectra, but
this dramatically changes at pH ¼ 5 at which pH the two species,
monoanionic [1,5,6,10-I4-7,8-nido-C2B9H8]ꢀ and dianion [1,5,6,10-
I4-7,8-nido-C2B9H7]2ꢀ, coexist. At pH 8, only the dianionic species
is present. The new and very distinct resonance near ꢀ43 ppm
appears at the same chemical shift as the new resonance found in
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