Designed synthesis of new ortho-carborane derivatives: From mono- to polysubstituted frameworks

Article abstract of DOI:10.1021/ic800362z

The use of nucleophilic and electrophilic processes allow the designed synthesis of several B-iodinated derivatives of o-carborane. Because of the straightforward Pd-catalyzed conversion of B-I to B-C bond with Grignard reagents, such as methylMgBr and biPhenylMgBr, both, symmetrical 3,6-R ₂-1,2-closo-C₂B₁₀H₁₀ and asymmetrical 3-I-6-Me-1,2-closo-C₂B₁₀H₁₀ could be obtained. Not only conventional reactions in solution have been studied but also a highly efficient, clean and fast solvent-free procedure has provided successful results to regioselectively produce B-iodinated o-carborane derivatives by a careful control of the reaction conditions. The high number of nonequivalent leaving groups in boron iodinated o-carborane derivatives opens the possibility through B-C coupling to materials with novel possibilities and to self-assembling due to the enhanced polarizability of the C-H bond.

Full text of DOI:10.1021/ic800362z

Inorg. Chem. 2008, 47, 7309-7316
Designed Synthesis of New ortho-Carborane Derivatives: from Mono- to
Polysubstituted Frameworks
Gemma Barbera`,† Albert Vaca,† Francesc Teixidor,† Reijo Sillanpa¨a¨,‡ Raikko Kiveka¨s,§
and Clara Vin˜as*,†
Institut de Ciencia de Materials de Barcelona (CSIC) Campus UAB, 08193 Bellaterra, Spain,
Department of Chemistry, UniVersity of JyVa¨skyla¨, 40351 JyVa¨kyla¨, Finland, and Department of
Chemistry, UniVersity of Helsinki, 00014 Helsinki, Finland
Received February 26, 2008
The use of nucleophilic and electrophilic processes allow the designed synthesis of several B-iodinated derivatives
of o-carborane. Because of the straightforward Pd-catalyzed conversion of B-I to B-C bond with Grignard reagents,
such as methylMgBr and biPhenylMgBr, both, symmetrical 3,6-R2-1,2-closo-C2B10H10 and asymmetrical 3-I-6-Me-
1,2-closo-C2B10H10 could be obtained. Not only conventional reactions in solution have been studied but also a
highly efficient, clean and fast solvent-free procedure has provided successful results to regioselectively produce
B-iodinated o-carborane derivatives by a careful control of the reaction conditions. The high number of nonequivalent
leaving groups in boron iodinated o-carborane derivatives opens the possibility through B-C coupling to materials
with novel possibilities and to self-assembling due to the enhanced polarizability of the C-H bond.
Introduction
Because the utility of carborane units is dependent upon
their functionalization,1 the introduction of functional groups
at the boron atoms is an important target. The substitution
of the carbon hydrogen in carborane clusters is easy because
Figure 1. Vertex numbering in 1,2-closo-C2B10H12, o-carborane.
the C-H vertices may be deprotonated with strong bases.
Conversely, the chemistry of boron-substituted carboranes
is less developed than that of the carbon-substituted ana-
logues because of the higher difficulty of introducing
functional groups at the boron atoms of the carborane cage.
Calculated Mulliken charges on 1,2-closo-C2B10H12 by
geometry optimizations at B3LYP/6-31G* level of theory2,3
show that B(8,9,10,12) are richer in electron density than
B(3,6). Figure 1 shows vertex numbering in o-carborane.
Zakharkin et al. reported the synthesis of 3-isonitrile-1,2-
closo-C2B10H11, which was prepared from 3-amino-1,2-closo-
C2B10H11.4 The electrophilic monoiodination at the 9 posi-
tion5,6 and diiodination at the 9 and 12 vertices5,7 of the
o-carborane cage is achieved by treatment with I2 in the
presenceofAlCl3.7,8Ahighlyiodinatedo-carborane,4,5,7,8,9,10,11,12-
I8-1,2-closo-C2B10H4, was later obtained by reaction with ICl
(4) (a) Zakharkin, L. I.; Kalinin, V. N.; Gedymin, V. V. Synth. Inorg.
Met.-Org. Chem. 1971, 1, 45. (b) Zakharkin, L. I.; Kalinin, V. N.;
Gedymin, V. V.; Dzarasova, G.S. J. Organomet. Chem. 1969, 16, 371.
(c) Valliant, J. F.; Schaffer, P. J. Inorg. Biochem. 2001, 85, 43.
(5) Zakharkin, L. I.; Kalinin, V. N. IzV. Akad. Nauk SSSR, Ser. Khim.
1966, 3, 575.
*
To whom correspondence should be addressed. E-mail:
clara@icmab.es.
†
Institut de Ciencia de Materials de Barcelona (CSIC) Campus UAB.
University of Jyva¨skyla¨.
University of Helsinki.
‡
§
(6) (a) Zakharkin, L. I.; Ol’shevskaya, V. A.; Poroshin, T. Y.; Balagurova,
E. V. Zh. Obshch. Khim. 1987, 57, 2012. (b) Andrews, J. S.; Zayas,
J.; Jones, M., Jr. Inorg. Chem. 1985, 24, 3715.
(1) (a) Grimes, R. N. Carboranes, Academic Press: New York, 1970. (b)
Mehta, S. C.; Lu, D. R. Pharm. Res. 1996, 13, 344. (c) Barth, R. F.;
Soloway, A. H.; Brugger, R. M. Cancer InVest. 1996, 14, 534. (d)
Grimes, R. N. J. Chem. Educ. 2004, 81, 658. (e) Plesˇek, J. Chem.
ReV. 1992, 92, 269.
(7) Li, J.; Logan, C. F.; Jones, M., Jr. Inorg. Chem. 1991, 30, 4866.
(8) (a) Zakharkin, L. I.; Kalinin, V. N. IzV. Akad. Nauk. SSSR. Ser. Khim.
1968, 3, 685. (b) Brattsev, V. A.; Stanko, V. I. Zh. Obshch. Khim.
1970, 40, 1664. (c) Zakharkin, L. I.; Kalinin, V. N. IzV. Akad. Nauk.
SSSR. Ser. Khim. 1970, 40, 2653. (d) Zakharkin, L. I.; Kovredov, A. I.;
Ol’shevskaya, V. A.; Shaugumbekova, Z. S. J. Organomet. Chem.
1982, 226, 217.
(2) Gaussian 98; Gaussian, Inc.: Pittsburgh, PA, 1998.
(3) Teixidor, F.; Barbera`, G.; Vaca, A.; Vin˜as, C.; Kiveka¨s, R.; Sillanpa¨a¨,
R. J. Am. Chem. Soc. 2005, 127, 10158.
10.1021/ic800362z CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 16, 2008 7309
Published on Web 07/17/2008

Barbera` et al.
and triflic acid.9 The recent development of a fast, solvent-
free synthetic procedure has allowed the preparation of
8,9,10,12-I4-1,2-closo-C2B10H8 derivatives by direct reaction
of o-carborane and iodine in sealed tubes.10 Not only are
iodinated carboranes the derivatives obtained by electrophilic
substitution but also B-methylated carboranes11,12 have also
been successfully produced.
Scheme 1. - General Tetraiodination of 1-R-2-R′-1,2-closo-C2B10H10
by Reaction with Iodine in Sealed Tubes (R, R′ ) H, Me or Ph)
under varied experimental conditions (reagents ratio, tem-
perature, and reaction time). The results given as a molar
fraction (%) of the different iodinated compounds are shown
in Table 1. Always, after the reaction is complete, the Pyrex
tube is carefully opened and gaseous HI is removed by
evaporation, leaving the crude product as a solid that is
analyzed by ESI-MS and 1H{11B} NMR. The latter technique
allows the determination of the molar ratio of the different
iodinated compounds from the integration of the Ccluster-H
peaks. Almost all of the excess iodine (95%) could be
recovered from the mixture by sublimation under reduced
pressure, avoiding the need for quenching with NaHSO3 and
allowing further re-use of reagents.
From the results in Table 1, it can be observed that this
method is regioselective for the synthesis of 9-I-1,2-closo-
C2B10H11, 9,12-I2-1,2-closo-C2B10H10, and 8,9,10,12-I4-1,2-
closo-C2B10H8, depending on the experimental conditions.
The best results were obtained using a 1:10 o-carborane/I2
ratio. As expected, the first boron vertices to be iodinated
are those furthest removed from the cluster carbon atoms.
Thus, B(9) monoiodination can be achieved with high
selectivity (97%) after 2.5 h at 115 ( 2 °C (entry 1). The
crude product was >97% pure in 9-I-1,2-closo-C2B10H11
because the remaining starting ortho-carborane is removed
in the iodine sublimation step. Enhanced purity can be
achieved by recrystallization in hexane.
Alternatively, another way to B-functionalize the o-
carborane, specifically at the 9 position, is by activating a
B-I bond via conversion of a B-carboranyl iodide.13
Using the procedures named above, it is possible to
derivatize all o-carborane cluster positions except B(3)/B(6)
because these boron atoms, adjacent to both cluster carbons,
are not susceptible to electrophilic substitution. Although
studies of a metal-induced selective B(3)/B(6)-disubstitution
of ortho-carborane-1,2-dithiolate have been done,14 the
disubstitution of C-unsubstituted 1,2-C2B10H12 requires a
combination of nucleophilic and boron-insertion reactions.
The synthesis of 3,6-I2-1,2-closo-C2B10H10 has been recently
achieved starting from 3-I-1,2-closo-C2B10H11 by combining
nucleophilic and boron-insertion processes.15,16 Electrophilic
iodination of these 3-iodo and 3,6-diiodo species led to nona-
and deca-B-iodinated o-carboranes, respectively.15,17
B-iodinated o-carboranes have an elevated versatility to
obtain B-derivatives by performing the Pd-catalyzed B-C
cross-coupling reaction with Grignard reagents.18
As each vertex possesses different electron density, each
vertex has different reactivity. This leads to boron regiose-
lective designed synthesis methods to selectively achieve the
different B-substituted o-carborane derivatives in high yields.
Results and Discussion
Synthetic Studies.
Small increments in temperature, keeping the reagents ratio
constant, lead to important changes in the outcome of the
reaction. Above 160 ( 2 °C, the major product is 9,12-I2-
1,2-closo-C2B10H10 (entry 3). The optimized conditions for
the preparation of this compound are 170 °C and 3.5 h (entry
6). Nevertheless, significant amounts of the isomer 8,9-I2-
1,2-closo-C2B10H10 are found in the composition of the crude
product. Therefore, recrystallization in hexane/chloroform
(6:1 by volume) is needed for the isolation of pure 9,12-I2-
1,2-closo-C2B10H10.
a) Boron Iodinated closo-o-Carborane Derivatives by
Electrophilic Iodination in Solvent-Free Reactions. As
described in a previous communication, a solvent-free
regioselective tetraiodination on o-carboranes is effectively
achieved by reaction of 1-R-2-R′-1,2-closo-C2B10H10 (R, R′
) H, Me, Ph) and elemental iodine in excess into sealed
tubes (Scheme 1).10 In this article, an extension of this fast,
efficient, and solvent-free procedure is described. We have
tested the reaction of o-carborane and iodine in sealed tubes
After 3.5 h at 270 ( 2 °C (entry 11), the crude solid
contained ca. 3% of 8,9,12-I3-1,2-closo-C2B10H9, ca. 93%
of 8,9,10,12-I4-1,2-closo-C2B10H8, and ca. 4% of higher
(9) Srivastava, R. R.; Hamlin, D. K.; Wilbur, D. S. J. Org. Chem. 1996,
61, 9041.
1
iodinated ortho-carboranes, based on H{11B} NMR spec-
(10) Vaca, A.; Teixidor, F.; Kiveka¨s, R.; Sillanpa¨a¨, R.; Vin˜as, C. Dalton
Trans. 2006, 4884.
troscopy. As previously reported,10 this is the first efficient
synthetic procedure for the preparation of 8,9,10,12-I4-1,2-
closo-C2B10H8. Longer reaction times did not substantially
improve this result. Although being less regioselective (entry
10), this species could also be produced by the reaction of
1,2-closo-C2B10H12 with the stoichiometric amount of el-
emental iodine (4 equiv) at 270 ( 2 °C for 24 h. The crude
product contained 74% of 8,9,10,12-I4-1,2-closo-C2B10H8.
The crude solids were recrystallized from 1:1 ethanol/water
to give pure 8,9,10,12-I4-1,2-closo-C2B10H8 in a high yield.
To explore the versatility of the method, mono- and di-
C-alkyl- and C-aryl-substituted ortho-carboranes were iodi-
(11) Herzog, A.; Maderna, A.; Harakas, G. N.; Knobler, C. B.; Hawthorne,
M. F. Chem.sEur. J. 1999, 5, 1212.
(12) Zheng, Z.; Knobler, C. B.; Mortimer, M. D.; Kong, G.; Hawthorne,
M. F. Inorg. Chem. 1996, 35, 1235.
(13) Grushin, V. V. Acc. Chem. Res. 1992, 25, 529.
(14) Herberhold, M.; Yan, H.; Milius, W.; Wrackmeyer, B. Angew. Chem.,
Int. Ed. 1999, 38, 24.
(15) Teixidor, F.; Barbera`, G.; Vin˜as, C.; Sillanpa¨a¨, R.; Kiveka¨s, R. Inorg.
Chem. 2006, 45, 3496.
(16) (a) Barbera`, G. Doctoral Thesis, Universitat Auto`noma de Barcelona,
Bellaterra, 2002,http://www.tdcat.cesca.es/. (b) Yamazaki, H.; Ohta,
K.; Endo, Y. Tetrahedron Lett. 2005, 46, 3119.
(17) Barbera`, G.; Teixidor, F.; Vin˜as, C.; Sillanpa¨a¨, R.; Kiveka¨s, R. Eur.
J. Inorg. Chem. 2003, 1511.
(18) Zheng, Z.; Jiang, W.; Zinn, A. A.; Knobler, Hawthorne, M. F. Inorg.
Chem. 1995, 34, 2095.
7310 Inorganic Chemistry, Vol. 47, No. 16, 2008

ortho-Carborane DeriWatiWes
Table 1. Composition (%) of Iodination Crude Products of ortho-Carborane as a Function of I2 Molar Ratio (1,2-closo-C2B10H12/I2), Temperature, and
Reaction Timea
Exp.
I2 ratio
T (°C)
t (h)
9-I-
8,9-I2-
9,12-I2-
8,9,12-I3-
8,9,10,12-I4-
In > -
4
1
2
3
4
5
6
7
8
(1:10)
(1:10)
(1:10)
(1:10)
(1:8)
(1:10)
(1:10)
(1:10)
(1:2)
115
120
160
170
170
170
180
195
270
270
270
290
300
2.5
2.5
3.5
3
3.5
3.5
3.5
4.5
24
97b
95
23
4
4
1
5
14
16
16
13
16
62
77
72
82
70
57
54
1
3
5
4
14
43
37
18
3
9
8
1
10
11
12
13
(1:4)
24
74
93
83
21
8
4
17
77
(1:10)
(1:10)
(1:15)
3.5
2.5
110
2
a The molar ratio of the iodinated products has been calculated based on the integration of the peaks of Cclu´ster-H from 1H NMR spectra. b The remaining
3% was starting material, removed by sublimation.
Scheme 2. - Syntheses of Asymmetric 3-I-6-Me-1,2-closo-C2B10H10 via a Cross-Coupling Reaction and via a B-I Boron Insertion Reaction on the
[3-Me-7,8-nido-C2B9H10]2- Anion
nated under similar conditions. Slightly shorter reaction times
were needed for the same degree of substitution compared
to the parent o-carborane. Heating 1-R-1,2-closo-C2B10H11
(R ) Me, Ph) with I2 at 270 ( 2 °C for 3.5 h gave the
corresponding 1-R-8,9,10,12-I4-1,2-closo-C2B10H7 (R ) Me,
Ph) derivatives selectively in high yields (>75%). The
C-disubstituted counterparts, 1,2-R2-1,2-closo-C2B10H10 (R
) Me, Ph) were iodinated in an analogous way, and the crude
products obtained were analyzed by ESI-MS. 1,2-Ph2-1,2-
closo-C2B10H10 underwent tetraiodination selectively after
3.5 h, whereas 1,2-Me2-1,2-closo-C2B10H10 was more sus-
ceptible to electrophilic substitution and only 2.5 h were
required for completion of the reaction. This result is
consistent with both theoretical19 and experimental data20
reported by Lipscomb and co-workers, which showed that
the electron-donating effect of methyl groups bonded to the
Ccluster atoms causes a uniform increase in electron density
on the B atoms while having little, or no effect on the
sequence of substitution.
in the presence of [PdCl2(PPh3)2] and CuI, using the
appropriate aryl or alkylmagnesium bromide reagent as a
source of the organic group, in THF solution under reflux.
Using 3,6-I2-1,2-closo-C2B10H10/Grignard reagent in a 1:10
ratio, new 3,6-R2-1,2-closo-C2B10H10 (R ) methyl, biphenyl)
species were obtained in high yields (97, 96%, respectively).
Referring to asymmetric carborane derivatization, 3-I-6-
Me-1,2-closo-C2B10H10 could be obtained following two
synthetic procedures (Scheme 2). The first one, based on the
reaction of 3,6-I2-1,2-closo-C2B10H10 with methylmagnesium
bromide in a 1:5 ratio, produces the asymmetric compound
in low yield (16%). The second one, that afforded a higher
yield (81%), consisted of the combination of deboronation
on 3-Me-1,2-closo-C2B10H11, and subsequent B-I insertion
through the reaction of [3-Me-7,8-nido-C2B9H10]2- with BI3.
Following a reported procedure on methylation reaction,21
3-Me-1,2-C2B10H11 reacted with methyl iodide in the pres-
ence of aluminum trichloride under reflux for 2 days. After
working up, 3,4,5,7,8,9,10,11,12-Me9-1,2-closo-C2B10H3 was
obtained in 98% yield.17 Treatment of 3,6-Me2-1,2-C2B10H10
The synthesis of penta- and hexa-iodinated derivatives,
taking 3-I-1,2-closo-C2B10H11 and 3,6-I2-1,2-closo-C2B10H10
as starting materials, has also been achieved.
with MeI/AlCl3 at reflux for 2 days produces 9-I0.707H0.293
-
12-Cl0.566H0.434-3,4,5,6,7,8,10,11-Me8-1,2-closo-C2B10H2, whose
11B-NMR spectrum indicates a mixture of species.3 The
11B{1H}-NMR spectrum was practically identical, suggesting
b) Boron Alkylated and Arylated o-Carborane Deriva-
tives: Alkyl and Aryl-Dehalogenation Reactions at B(3)
and B(6). In extending the chemistry of 3-R-6-R′-o-
carborane derivatives, aryl and alkyl-dehalogenation reactions
were performed on 3,6-I2-1,2-closo-C2B10H10, using either
an alkyl or an aryl reagent. The reaction consists of the B-C
cross coupling Kumada reaction on 3,6-I2-1,2-closo-C2B10H10
1
that all or most of the BHs had been substituted. The H
NMR spectrum confirmed this observation. The carborane
C-H region between 2.6 and 4.6 ppm was very informative.
Resonances due to C-H, in ppm with relative areas in
parentheses, were observed at 4.47 (2.97), 3.16 (1), 2.99 (1),
3.04 (5), 2.94 (5), 2.77 (2.65), and 2.74 (2.65). This indicates
that four dominant species, one of them being symmetrical,
(19) (a) Newton, M. D.; Boer, F. P.; Lipscomb, W. N. J. Am. Chem. Soc.
1966, 88, 2353. (b) Boer, F. P.; Potenza, J. A.; Lipscomb, W. N. Inorg.
Chem. 1966, 5, 1301.
(21) Jiang, W.; Knobler, C. B.; Mortimer, M. D.; Hawthorne, M. F. Angew.
Chem., Int. Ed. Engl. 1995, 34, 1332.
(20) Potenza, J. A.; Lipscomb, W. N. Inorg. Chem. 1966, 5, 1483.
Inorganic Chemistry, Vol. 47, No. 16, 2008 7311

Barbera` et al.
are formed in this reaction. The most abundant compound
displays its cluster C-H’s at 3.04 and 2.94 ppm, the second
in importance at 2.77 and 2.74 ppm, the third at 4.47 ppm,
this being most probably symmetrical, and the less abundant
at 3.16 ppm and 2.99 ppm. The abundances would be
approximately 49%, 26%, 15%, and 10%, respectively.
Suitable colorless crystals were obtained from hexane that
indicated that octaboron methyl substitution of the C2B10
icosahedron at positions 3,4,5,6,7,8,10 and 11 had taken
place. The remaining positions at B(9) and B(12) are partially
occupied by halogen and hydrogen atoms. Similarly to
4,5,7,8,9,10,11,12-Me8-C2B10H4,11 there are only eight Me
groupsonthecluster9-I0.707H0.293-12-Cl0.566H0.434-3,4,5,6,7,8,10,11-
Me8-1,2-closo-C2B10H2. It may appear that boron permethy-
lation in 1,2-closo-C2B10H12 is severely hampered due to the
-I effect of Me.
Figure 2. Molecular structure of 3,6-I2-1,2-closo-C2B10H10. Hydrogen
atoms are omitted.
The existence of three species with H in the 9,12 positions,
(I,H), (H,H), and (H,Cl), whereas all other B positions are
methyl substituted, could induce to reason that positions 9,12
are not the first to suffer electrophilic attack in 3,6-Me2-1,2-
C2B10H10. To discard this possibility, a careful monitoring
of the methylation reaction by 11B-NMR has allowed us to
find a synthetic procedure for 3,6,8,9,10,12-Me6-1,2-C2B10H6
in 68% yield. Reducing the reaction time to 4 h, 3,6,8,9,10,12-
Me6-1,2-closo-C2B10H6 could be produced with high selec-
tivity. This experiment proves that B(9) and B(12) are among
the first four boron positions to be methylated. There is no
evidence of at which stage of the methylation process the
attack by other nucleophiles to the B(9)-Me and B(12)-Me
groups takes place, but what seems clear is that the cluster
evolves to remove the high load of positive charge (created
by the Me groups bonded to the B vertexes) by incorporating
groups (Cl, I, H) that either are less electron-withdrawing
(H) or that by back-donation (Cl, I) can refill the cluster of
electron density. Substitution of antipodal to cluster carbon
B-Me group by nucleophiles had been observed in methyl
derivatives of [closo-CB11Me12]-.22
c) Study of the Deboronation Process of B-Methy-
lated and B-Iodinated Derivatives. All of these boron-
substituted carboranes were reacted with KOH/EtOH. Under
these conditions, the low electron density at B(3) in pristine
o-carborane facilitates its removal, whereas with 3,6-Me2-
1,2-closo-C2B10H10, the presence of methyl groups in B(3)
and B(6) prevents its deboronation. The same happens for
3,6-(biPh)2-1,2-closo-C2B10H10. Moreover, 3,4,5,7,8,9,10,11,12-
Me9-1,2-closo-C2B10H3 remained also unreacted under the
typical deboronation conditions, even though B(6) is still
bonded to a hydrogen atom.
Figure 3. Molecular structure of 3,6-Me2-1,2-closo-C2B10H10. Hydrogen
atoms are omitted. Small letter “a” refers equivalent position -x, y, -z +
3/2.
in 86% yield. In this case, the MALDI-TOF-MS spectrum
shows only one envelope of peaks centered at 1266.8 m/z
that corresponds to [1,2,3,4,5,6,9,10,11-I9-7,8-nido-C2B9H3]-.
Inthesameway,thedeboronationreactionof4,5,7,8,9,10,11,12-
I8-closo-C2B10H4 produces pure [1,2,4,5,6,9,10,11-I8-7,8-
nido-C2B9H3]2- in 86% yield. Conversely, the deboronation
of 3,4,5,7,8,9,10,11,12-I9-1,2-closo-C2B10H3 produced a mix-
ture of the fully B-iodinated [1,2,3,4,5,6,9,10,11-I9-7,8-nido-
C2B9H2]2- and [1,2,4,5,6,9,10,11-I8-nido-7,8-C2B9H3]2- di-
anions in approximately a 50:50 mixture.
Then, deboronation studies confirm that either B(3)-I or
B(6)-I vertices on o-carborane can be easily removed under
nucleophilic conditions. This deboronation process is in
contrast to the case of having B(3)-alkyl/B(6)-alkyl or
B(3)-aryl/B(6)-aryl vertices for which no reaction has taken
place, not even with a crowded species such as 3,4,5,7,8,9,
10,11,12-Me9-C2B10H3.
All boron-substituted o-carborane derivatives were ob-
tained in good yields and were initially characterized by
microanalysis and IR spectroscopy. 11B-, 13C{1H}-, and 1H-
NMR and MS for the compounds are fully consistent with
the proposed formulas.
Molecular and Crystal Structures of 3,6-I2-1,2-closo-
C2B10H10, 3,6-Me2-1,2-closo-C2B10H10 and 3-I-6-Me-1,2-
closo-C2B10H10. The species 3,6-I2-1,2-closo-C2B10H10, 3,6-
Me2-1,2-closo-C2B10H10, and 3-I-6-Me-1,2-closo-C2B10H10
have been studied in crystalline state. Their molecular
structures are presented in Figures 2, 3, and 4, respectively.
Selected bond lengths and angles for the compounds are
listed in Table 2, and crystallographic data are summarized
in Table 3.
However, the deboronation of the 3,6-diiodinated com-
pound with EtO- under reflux conditions and subsequent
precipitation with [HNMe3]Cl led to the formation of
[HNMe3][3-I-7,8-nido-C2B9H11]. In the deboronation reaction
on the per-B-iodinated compound, 3,4,5,6,7,8,9,10,11,12-I10-
1,2-closo-C2B10H2, that has both B(3) and B(6) atoms bonded
to iodine, the nucleophilic attack takes place on one of these
vertices, producing [1,2,3,4,5,6,9,10,11-I9-7,8-nido-C2B9H2]2-
The structures of 3,6-I2-closo-1,2-C2B10H10, 3,6-Me2-closo-
1,2-C2B10H10, and 3-I-6-Me-1,2-closo-C2B10H10 are formed
of well-separated molecules without any strong intermolecu-
(22) Janousek, Z.; Lehmann, U.; Castul´ık, J.; C´ısarova, I.; Michl, J. J. Am.
Chem. Soc. 2004, 126, 4060.
7312 Inorganic Chemistry, Vol. 47, No. 16, 2008

ortho-Carborane DeriWatiWes
removal follows the order: B-H > B-I . B-alkyl, B-aryl.
Selective asymmetric disubstitution at the equivalent B(3)
and B(6) vertexes of the o-carborane that opens a new route
for cluster application uses has been achieved. These boron-
substituted o-carborane derivatives can in turn serve as
synthons for many others.
Experimental Section
General Procedures. Elemental analyses were performed using
a Carlo Erba EA1108 microanalyser. IR spectra were recorded from
KBr pellets on a Shimadzu FTIR-8300 spectrophotometer. 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 with a
Bruker ARX 300 instrument equipped with the appropriate decou-
pling accessories. Chemical shift values for 11B NMR spectra were
referenced to external BF3 r OEt2 and those for 1H, 1H{11B}, and
13C{1H} NMR spectra were referenced to SiMe4. Chemical shifts
are reported in units of parts per million downfield from the
reference, and all coupling constants in hertz. MS spectra for ionic
species were recorded using a Bruker Biflex MALDI-TOF mass
spectrometer and using a FIA-ES/MS (Shimadzu AD VP/ API 150)
instrument for neutral species.
Unless otherwise noted, all manipulations were carried out under
a nitrogen atmosphere using standard vacuum-line techniques.
Diethyl ether and THF were distilled from sodium benzophenone
prior to use. Hexane was dried over molecular sieves and deoxy-
genated before use. A 1.6 M solution of n-butyllithium in hexanes,
iodine monochloride, aluminum trochloride, triflic acid, 4-biPhe-
nylmagnesium bromide, methylmagnesium bromide, methyl iodide
from Aldrich; BI3 from Alfa and 1,2-closo-C2B10H12 from Katchem
Ltd. (Prague) were used as purchased. 3-I-1,2-closo-C2B10H11,7 3,6-
I2-1,2-closo-C2B10H10,15 and [HNMe3][3-I-7,8-nido-C2B9H11]25 were
synthesized according to the literature.
Synthesis of 1,2-I2-1,2-closo-C2B10H10. To a stirring solution
of 1,2-closo-C2B10H12 (98 mg, 0.68 mmol) in diethyl ether (10 mL)
cooled to 0 °C in an ice-water bath was added, dropwise, a solution
of butyllithium in hexane (0.89 mL, 1.6 M, 1.43 mmol) under
nitrogen atmosphere. The suspension was stirred at room temper-
ature for 0.5 h, then cooled again to 0 °C, at which point I2 (365.8
mg, 1.44 mmol) was added in a single portion. The resulting
solution was stirred at 0 °C for 30 min and at room temperature
for further 30 min, then extracted with 5% aqueous Na2S2O3 (10
mL) and washed with water (2 × 5 mL). The organic phase was
dried over MgSO4, filtered, and evaporated in vacuo to give a pale-
yellow solid. The crude product was purified by silica gel flash
chromatography at -10 °C under argon atmosphere, using diethyl
ether as the eluting solvent to yield 1,2-I2-1,2-closo-C2B10H10 (188
mg, 70%). Elemental analysis of C2B10H10I2: Calcd C, 6.07; H,
2.55; found C, 6.29; H, 2.55. ESI-MS: 394.8 (M - H+, 100%). FTIR
(KBr), ν (cm-1) ) 2596 (s, B-H), 2574 (s, B-H). 1H NMR
(CDCl3), δH ) 4.6-2.2 (6 H, br m, BH). 1H{11B} NMR (CDCl3),
δH ) 2.99 (6 H, br s), 2.72 (2 H, br s), 2.24 (2 H, br s). 13C{1H}
NMR (CDCl3), δC ) 21.8 (s). 11B NMR (CDCl3), δC ) -1.5 (2
B, d, overlapped), -3.4 (2 B, d).
Figure 4. Molecular structure of 3-I-6-Me-1,2-closo-C2B10H10. Hydrogen
atoms are omitted. Small letter “b” refers equivalent position -x, y, z.
lar interactions. Only some weak interactions can be found
in the three compounds like the I · · · I contact of 3.5918(13)
Å in 3,6-I2-closo-1,2-C2B10H10 and a BH· · · I contact, with
the H · · · I and B · · · I distances of 3.03 and 4.150(3) Å, in
3-I-6-Me-1,2-closo-C2B10H10.
The molecule of 3,6-I2-closo-1,2-C2B10H10 has approxi-
mate C2V symmetry but the crystallographic symmetry of the
compound is C1. 3,6-Me2-closo-1,2-C2B10H10 assumes crys-
tallographic 2-fold symmetry with the axis going through
the midpoints of the bonds C1-C1a and B9-B9a (a refers
equivalent position -x, y, -z + 3/2). However, approximate
symmetry of the latter molecule is C2V. 3-I-6-Me-1,2-closo-
C2B10H10 assumes mirror symmetry with the symmetry plane
containing the atoms I3, B3, B6, C6, B8, and B10. Therefore,
the symmetry element is bisecting the C1-C1b and B9-B9b
bonds (b refers equivalent position -x, y, z).
In these three compounds, the Ccluster-Ccluster distances vary
in the range 1.613(5)-1.625(4) Å. These values agree well
with the corresponding values observed for the 1,2-unsub-
stituted o-carborane derivatives.23 Ccluster-Ccluster distances
can be modified by substituting the cluster carbons. Thus,
the shortest distances are found for o-carborane derivatives
carrying H atoms at both cluster carbons, like the present
compounds, but much longer distances have been found for
the derivatives bearing aryl groups, phosphorus, or sulfur
substituents at the cluster carbons.23a,24
Conclusions
The combination of nucleophilic and electrophilic reactions
and the choice of the proper experimental conditions allow
the designed synthesis of several o-carborane derivatives with
different patterns of substitution. Several iodinated com-
pounds, from mono- to per-B-substituted, are now accessible
on demand. The synthetic importance of B-iodo-o-carboranes
relies on the possibility of exchanging iodine with organic
moieties using the Kumada cross-coupling reaction, opening
new possibilities of constructing macromolecules. The study
of the boron-degradation reaction on several B-substituted
o-carborane derivatives shows that the ease of boron vertex
Synthesis of 9-I-1,2-closo-C2B10H11. A thick-walled Pyrex tube
charged with 1,2-closo-C2B10H12 (0.279 g, 1.93 mmol) and iodine
(4.911 g, 19.3 mmol) was put under vacuum, cooled down with
liquid nitrogen, and sealed. The tube was then placed in a furnace,
and the temperature was gradually raised to 115 °C during 30 min,
(23) (a) Teixidor, F.; Vin˜as, C. In Science of Synthesis, Ed.; Thieme:
Stuttgart, 2005, Vol. 6, p 1235,and references therein. (b) Nova´k, C.;
sˇubrtova´, C.; L´ınek, A.; Hasˇek, J. Acta Crystallogr. 1983, C39, 1393.
(c) sˇubrtova´, C.; L´ınek, A.; Hasˇek, J. Acta Crystallogr. 1980, B36,
858.
(24) Kiveka¨s, R.; Flores, M. A.; Vin˜as, C.; Sillanpa¨a¨, R. Acta Crystallogr.
2002, C58, 570, and references cited therein.
(25) Barbera`, G.; Vin˜as, C.; Teixidor, F.; Welch, A. J.; Rosair, G. M. J.
Organomet. Chem. 2002, 657, 217.
Inorganic Chemistry, Vol. 47, No. 16, 2008 7313

Barbera` et al.
Table 2. Selected Bond Lengths (Angstroms) and Angles (Degrees) for 3,6-I2-1,2-closo-C2B10H10, 3,6-Me2-1,2-closo-C2B10H10, and
3-I-6-Me-1,2-closo-C2B10H10
3,6-I2-1,2-closo-C2B10H10
I3-B3 2.156(11)
3,6-Me2-1,2-closo-C2B10H10
C1-C1a
1.613(5)
3-I-6-Me-1,2-closo-C2B10H10
I3-B3
C1-C1b
C1-B3
C1-B6
C6-B6
2.132(3)
I6-B6
2.146(9)
1.623(13)
1.723(14)
1.711(12)
1.700(14)
1.727(13)
120.1(7)
119.4(7)
128.8(7)
119.8(6)
119.9(6)
129.5(6)
3
C1-B3
1.738(4)
1.742(4)
1.572(4)
1.625(4)
1.718(4)
1.736(4)
1.571(5)
C1-C2
C1-B3a
C3-B3
C1-B3
C1-B6
C2-B3
C2-B6
C1-B3-I3
C2-B3-I3
I3-B3-B8
C1-B6-I6
C2-B6-I6
I6-B6-B10
C3-B3-C1
C3-B3-C1a
C3-B3-B8
119.4(2)
119.8(2)
132.1(2)
C1-B3-I3
C1b-B3-I3
I3-B3-B8
C1-B6-C6
C1b-B6-C6
C6-B6-B10
121.5(2)
121.5(2)
127.7(3)
120.8(2)
120.8(2)
130.9(3)
Equivalent position -x, y, -z + /2. b Equivalent position -x, y, z.
a
Table 3. Crystallographic Data and Structural Refinement Details for
3,6-I2-1,2-closo-C2B10H10 (1), 3,6-Me2-1,2-closo-C2B10H10 (2), and
3-I-6-Me-1,2-closo-C2B10H10 (3)
the crude product from hexane/CHCl3 6:1 by volume. FTIR (KBr),
ν (cm-1) ) 3032 (s, Ccluster-H), 2615, and 2584 (s, B-H). 1H NMR
(CD3COCD3), δH ) 5.15 (2 H, br s, CH) and 3.8-1.5 (8 H, m,
compound
(1)
(2)
(3)
1
BH). H{11B} NMR (CD3COCD3), δH ) 5.15 (2 H, br s, CH),
2.73, 2.65, and 2.95 (8 H, br s, BH). 11B NMR (CD3COCD3), δB
) -5.1 (2 B, d, 1J(B,H) ) 156, B(8,10)), -11.6 (4 B, d,
B(4,5,7,11)), -13.0 (2 B, d, B(3,6)) and -13.8 (2 B, s, B(9,12)).
13C{1H} NMR (CD3COCD3), δC ) 54.5 (Ccluster-H).
empirical formula
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
ꢀ (deg)
V (Å3)
Z
C2H10B10I2
396.00
orthorhombic
P212121
9.0602(4)
17.4247(17)
7.7457(16)
90
C2H16B10
172.27
monoclinic
C2/c
14.8528(7)
6.8281(3)
11.5332(6)
114.220(5)
1066.70(9)
4
C3H13B10I
284.13
orthorhombic
Pmn21
7.2615(2)
9.6534(3)
8.0861(2)
90
Synthesis of 3,8,9,10,12-I5-1,2-closo-C2B10H7. A thick-walled
Pyrex tube charged with 3-I-1,2-closo-C2B10H11 (0.060 g, 0.22
mmol) and iodine (0.558 g, 2.20 mmol) was put under vacuum,
cooled down with liquid nitrogen, and sealed. The tube was then
placed in a furnace, and the temperature was gradually raised to
270 °C during 15 min, maintained for 6 h, and allowed to drop
slowly to room temperature. Excess iodine was effectively separated
by sublimation from the reaction mixture at 50 °C under reduced
pressure. The resulting solid was recrystallized from 1:1 ethanol/
water mixture to yield 3,8,9,10,12-I5-1,2-closo-C2B10H7 (0.135 g,
79%). MALDI-TOF MS: m/z ) 773 (M - H+). FTIR (KBr), ν
(cm-1) ) 3015 (s, Ccluster-H), 2613 and 2572 (s, B-H). 1H NMR
(CD3COCD3), δH ) 5.98 (2 H, br s, CH). 1H{11B} NMR
(CD3COCD3), δH ) 3.13, 3.25, and 3.54 (5 H, br s, BH) and 5.98
(2 H, br s, CH). 11B NMR (CD3COCD3), δB ) -25.7 (1 B, s,
B(3)), -15.3 (2 B, s), -8.9, (5 B, m) and -2.0 (2 B, d, 1J(B,H) )
161).
Synthesis of 3,6,8,9,10,12-I6-1,2-closo-C2B10H6. A thick-walled
Pyrex tube charged with 3,6-I2-1,2-closo-C2B10H10 (0.080 g, 0.20
mmol) and iodine (0.508 g, 2.00 mmol) was put under vacuum,
cooled down with liquid nitrogen, and sealed. The tube was then
placed in a furnace and the temperature gradually raised to 270 °C
during 15 min, maintained for 6 h, and allowed to drop slowly to
room temperature. Excess iodine was effectively separated by
sublimation from the reaction mixture at 50 °C under reduced
pressure. The resulting solid was recrystallized from a 1:1 ethanol/
water mixture to yield 3,6,8,9,10,12-I6-1,2-closo-C2B10H6 (0.138
g, 76%). MALDI-TOF MS: m/z ) 899 (M - H+). FTIR (KBr), ν
(cm-1) ) 3012 (s, Ccluster-H), 2613 (s, B-H). 1H NMR
(CD3COCD3), δH ) 6.22 (2 H, br s, CH). 1H{11B} NMR
(CD3COCD3), δH ) 3.25 (4 H, br s, BH) and 6.22 (2 H, br s, CH).
11B NMR (CD3COCD3), δB ) -23.7 (2 B, s, B(3,6)), -12.0 (2 B,
s), -8.7 (2 B, s), and -3.4 (4 B, d, 1J(B, H) ) 188, B(4, 5, 7,11)).
Synthesis of 3-Me-1,2-closo-C2B10H11. To a stirred solution of
3-I-1,2-closo-C2B10H11 (0.5 g, 1.85 mmol) in THF (20 mL) at 0
°C, was added, dropwise, a solution of methylmagnesium bromide
(3.1 mL, 3 M, 9.3 mmol). After stirring at room temperature for
30 min, cis-[PdCl2(PPh3)2] (52.0 mg, 4% equiv) and CuI (14.1 mg,
4% equiv) were added in a single portion; then the reaction was
1222.8(3)
4
566.82(3)
2
T (°C)
21
0.71069
2.151
50.88
1.071
-100
0.71073
1.073
0.46
1.044
-100
0.71073
1.665
27.66
1.076
0.0278
0.0560
2
λ (Å)
F (g·cm-3
)
µ (cm-1
)
GOF
Ra [I > 2σ(I)]
0.0332
0.0847
0.0965
0.2576
b
Rw [I > 2σ(I)]
a R ) Σ|Fo| - |Fc|/Σ|Fo|. b Rw ) {Σ[w(Fo - Fc )2]/Σ[w(Fo )2]}1/2
.
2
2
maintained for 2.5 h, and allowed to drop slowly to room
temperature. Excess of both iodine and 1,2-closo-C2B10H12 were
effectively separated by sublimation from the reaction mixture at
50 °C under reduced pressure, yielding practically pure (<1% of
I2-1,2-C2B10H11 based on 1H NMR) 9-I-1,2-closo-C2B10H11 (0.505
g, 97%). Elemental analysis of C2H11B10I: Calcd C, 8.89; H, 4.10;
found: C, 9.06; H, 3.92. ESI-MS: m/z 268.9 (M - H+, 100%). FTIR
(KBr), ν (cm-1) ) 3047 (s, Ccluster-H), 2584 (vs, B-H). 1H NMR
(CD3COCD3), δH 4.96 (1 H, br s, CH), 4.75 (1 H, br s, CH) and
1
3.8 - 1.2 (9 H, m BH). H{11B} NMR (CD3COCD3), δH 4.96 (1
H, br s, CH), 4.75 (1 H, br s, CH), 2.82, 2.65, 2.52, 2.40, and 2.16
(9 H, br s, BH). 11B NMR (CD3COCD3), δB -1.1 (1 B, d, 1J(B,H)
1
) 151), -7.2 (2 B, d, J(B,H) ) 153), -12.0, -12.7 and -13.6
(7 B, m) and -16.4 (1 B, s, B(9)I). 13C{1H} NMR (CD3COCD3),
δC ) 57.9 and 53.2 (Ccluster-H).
Synthesis of 9,12-I2-1,2-closo-C2B10H10. A thick-walled Pyrex
tube charged with 1,2-closo-C2B10H12 (0.253 g, 1.75 mmol) and
iodine (4.451 g, 17.5 mmol) was put under vacuum, cooled down
with liquid nitrogen, and sealed. The tube was then placed in a
furnace and the temperature gradually raised to 170 °C during 30
min, maintained for 3.5 h, and allowed to drop slowly to room
temperature. Excess iodine was effectively separated by sublimation
from the reaction mixture at 50 °C under reduced pressure. The
residual solid was composed of 9-I-1,2-closo-C2B10H11 (2%), 8,9-
I2-1,2-closo-C2B10H10 (13%), 9,12-I2-1,2-closo-C2B10H10 (82%), and
8,9,12-I3-1,2- C2B10H9 (3%) based on 1H NMR. 9,12-I2-1,2-closo-
C2B10H10 could be obtained pure by fractional recrystallization of
7314 Inorganic Chemistry, Vol. 47, No. 16, 2008

ortho-Carborane DeriWatiWes
heated to reflux overnight. The solvent was removed and 20 mL
of diethyl ether was added to the residue. The excess of Grignard
reagent was destroyed by slow addition of dilute HCl. The organic
layer was separated from the mixture, and the aqueous layer was
extracted with diethyl ether (3 × 10 mL). The combined organic
phase was washed with water and dried over MgSO4. The final
compound was purified by flash silica gel chromatography using
hexane as the eluting solvent to give 3-Me-1,2-closo-C2B10H11.
Yield: 285 mg (97%). Elemental analysis of C3B10H14: Calcd C,
22.77; H, 8.92; found C, 22.38; H, 8.48. FTIR (KBr), ν (cm-1) )
3063 (Ccluster-H), 2957, 2924, 2855 (Calkyl-H), 2629, 2598, 2575
(B-H). 1H NMR (CDCl3), δH ) 3.43 (2H, br s, Ccluster-H), 3.0-1.0
(8H, br m, B-H), 0.65 (3H, s, CH3).1H{11B} NMR (CDCl3), δH
) 3.43 (2H, br s, Ccluster-H), 2.26 (br s, B-H), 2.15 (br s, B-H),
0.65 (3H, s, CH3). 13C{1H} NMR (CDCl3), δC ) 58.1 (s; Ccluster),
(10 mL) at 0 °C, was added, dropwise, a solution of 4-biphenyl-
magnesium bromide (5 mL, 2 M, 10 mmol) in the same solvent.
After stirring at room temperature for 30 min, cis-[PdCl2(PPh3)2]
(28 mg, 4% equiv) and CuI (7.6 mg, 4% equiv) were added in a
single portion, following which the reaction was heated to reflux
for 4 days. The solvent was removed, and 20 mL of diethyl ether
was added to the residue. The excess of Grignard reagent was
destroyed by slow addition of dilute HCl. The organic layer was
separated from the mixture, and the aqueous layer was extracted
with diethyl ether (3 × 10 mL). The combined organic phase was
washed with water and dried over MgSO4. The solvent was
removed, and the residue was extracted with hexane. The final
compound was purified by flash silica gel chromatography using
dicloromethane/hexane (4:1) as the eluting solvent to give 3,6-
(biPh)2-1,2-closo-C2B10H10. Yield 0.43 g (96%). Elemental analysis
of C26H28B10: Calcd C, 69.60; H, 6.29; found C, 69.90; H, 6.30.
FTIR (KBr), ν (cm-1) ) 3076, 3049, 3044 (Caryl-H), (Ccluster-H),
2584, 2547 (B-H). 1H NMR (CDCl3), δH ) 7.73-7.30 (m, 18H;
1
-0.2 (br q, CH3). 11B NMR (CDCl3), δB ) -1.8 (d, J(B,H) )
1
148, 2B), -4.0 (s, 1B), -7.8 (d, J(B,H) ) 150, 1B), -11.7 (d,
1
1J(B,H) ) 126, 2B), -12.9 (d, J(B,H) ) 150, 4B).
H
aryl), 3.92 (br s, 2H; Ccluster-H), 3.00-1.50 (8H, br m, B-H).
Synthesis of 3-I-6-Me-1,2-closo-C2B10H10.
1H{11B} NMR (CDCl3), δH ) 7.73-7.30 (18H, m, Haryl), 3.92 (2H,
br s, Ccluster-H), 2.62 (br s, B-H), 2.47 (br s, B-H). 13C{1H} NMR
(CDCl3), δC ) 143.4, 142.0, 141.2, 134.3, 130.3, 129.4, 128.4, 127.8
(Caryl), 59.8 (s, Ccluster). 11B NMR (CDCl3), δB ) -2.0 (d, 1J(B,H)
) 150, 2B), -4.7 (s, 2B), -12.6 (d, 6B).
Method A. In an analogous manner, 3,6-I2-1,2-closo-C2B10H10
(0.50 g, 1.26 mmol) in THF (20 mL) at 0 °C, was added, dropwise,
a solution of methylmagnesium bromide (2.1 mL, 3 M, 6.3 mmol).
After stirring at room temperature for 30 min, cis-[PdCl2(PPh3)2]
(17.7 mg, 4% equiv) and CuI (4.8 mg, 4% equiv) were added in a
single portion, and then the reaction was heated at reflux for 5 h. The
solvent was removed and 20 mL of diethyl ether were added to the
residue. The excess of Grignard reagent was destroyed by slow addition
of dilute HCl. The organic layer was separated from the mixture, and
the aqueous layer was extracted with diethyl ether (3 × 10 mL). The
combined organic phase was washed with water and dried over
MgSO4. The final compound was purified by flash silica gel chroma-
tography using dicloromethane/hexane (3:5) as the eluting solvent to
give 3-I-6-Me-1,2-closo-C2B10H10. Yield 57.3 mg (16%).
Synthesis of [HNMe3][3-Me-7,8-nido-C2B9H12]. To a solution
of KOH (0.89 g, 15.79 mmol) in degassed EtOH (50 mL), 3-Me-
1,2-closo-C2B10H11 (500 mg, 3.16 mmol) was added. The solution
was refluxed for 3 h. After cooling down to room temperature, the
solvent was removed under reduced pressure, and the solid residue
was dissolved in 20 mL of water. The solution was neutralized
with HCl 1 M. Afterward, aqueous [HNMe3]Cl was added dropwise
to the solution to precipitate the compound. The white solid was
rinsed with water and diethyl ether obtaining [HNMe3][3-Me-7,8-
nido-C2B9H12]. Yield: 550 mg (84%). Elemental analysis of
C6H24B9N: Calcd C, 34.72; H, 11.65; N, 6.74; found C, 34.69; H,
11.56; N, 5.62. FTIR (KBr), ν (cm-1) ) 2908, 2856 (Calkyl, H),
2513 (B-H). 1H NMR (CD3COCD3), δH ) 3.21 (s, 9H; [HNMe3]),
2.08 (br s, 2H; Ccluster-H), 2.09 (s; 3H, CH3), -2.71 (1H; B-H-B).
13C{1H} NMR (CD3COCD3), δC ) 47.5 (m; Ccluster), 45.1 (s;
[HNMe3]), 25.24 (s; CH3). 11B NMR (CD3COCD3), δB ) -10.0
Method B. To the stirred solution of [HNMe3][3-Me-7,8-nido-
C2B9H11] (3.5 g, 16.9 mmol) in anhydrous diethyl ether (40 mL)
at 0 °C was added dropwise n-butyllithium (21.1 mL, 1.6 M, 33.8
mmol). Once the addition was completed, the reaction mixture was
stirred at room temperature for an additional 2 h and then heated
to reflux for 4 h. After evaporation of the solvent, anhydrous hexane
(40 mL) was added to the remaining solid. A solution of BI3 (9.9
g, 25.35 mmol) in 40 mL of hexane was then added dropwise with
stirring at 0 °C. Stirring was continued for 5 h at room temperature
once the addition was completed. The excess boron triiodide was
carefully decomposed by the addition of 10 mL of water. The
organic layer was separated from the mixture and the aqueous layer
extracted with hexane (3 × 10 mL). The combined organic phase
was dried over MgSO4, and the solvent was removed at the rotary
evaporator. The crude product was recrystallized from hexane to
obtain 3-I-6-Me-1,2-closo-C2B10H10. Yield 3.9 g (81%). Crystals
suitable for an X-ray diffraction experiment were grown by slow
evaporation from a concentrated dichloromethane solution. El-
emental analysis of C3H13B10I: Calcd C, 12.68; H, 4.61; found C,
12.58; H, 4.60. FTIR (KBr), ν (cm-1) ) 3032 (Ccluster-H), 2964,
2930 (Calkyl-H), 2594, 2586 (B-H). 1H NMR (CDCl3), δH ) 3.73
(2H, s, Ccluster-H), 3.00-1.00 (8H, br m, B-H), 0.70 (s, 3H; CH3).
1H{11B} NMR (CDCl3), δH ) 3.73 (2H, s, Ccluster-H), 2.70 (1H,
s, B-H), 2.50 (2H, s, B-H), 2.35 (2H, s, B-H), 2.24 (2H, s, B-H),
2.12 (1H, s, B-H), 0.70 (3H, s, CH3). 13C{1H} NMR (CDCl3), δC
1
1
(s, 1B), -10.0 (d, J(B,H) ) 138, 2B), -15.6 (d, J(B,H) ) 130,
2B), -20.3 (d, 1J(B,H) ) 147, 2B), -35.6 (d, 1J(B,H) ) 149, 2B).
X-ray Structure Determinations of 3,6-I2-closo-1,2-C2B10H10,
3,6-Me2-closo-1,2-C2B10H10, and 3-I-6-Me-1,2-closo-C2B10H10.
Single-crystal data collection for 3,6-I2-1,2-closo-C2B10H10 was
performed at ambient temperature on a Rigaku AFC5S diffracto-
meter, and data collections for 3,6-Me2-closo-1,2-C2B10H10 and 3-I-
6-Me-closo-1,2-C2B10H10 were performed with Enraf Nonius FR590
diffractometer at -100 °C using monochromatic Mo KR radiation.
The structures were solved by direct methods and refined on F2
by the SHELXL97 program.26
For 3,6-I2-1,2-closo-C2B10H10 and 3,6-Me2-1,2-closo-C2B10H10,
non-hydrogen atoms were refined with anisotropic displacement
parameters, and hydrogen atoms were treated as riding atoms using
the SHELX97 default parameters. 3,6-I2-1,2-closo-C2B10H10 crystal-
lizes in non-centrosymmetric space group and absolute configuration
of the compound was determined by refinement of Flack’s x
parameter.
) 62.5 (s, Ccluster). 11B NMR (CDCl3), δB ) -1.7 (d, J(B,H) )
For 3-I-6-Me-1,2-closo-C2B10H10, non-hydrogen atoms were
refined with anisotropic displacement parameters, and hydrogen
atoms were treated as riding atoms using the SHELX97 default
parameters. The methyl group is disordered showing rotational
disorder with each hydrogen atom occupying two positions. 3-I-
1
162, 2B), -3.0 (s, 1B; B(6)), -11.4 (d,1J(B,H) ) 155, 6B), -28.8
(s, 1B, B(3)).
Synthesis of 3,6-(biPh)2-1,2-closo-C2B10H10. To a stirring
solution of 3,6-I2-1,2-closo-C2B10H10 (396 mg, 1 mmol) in THF
Inorganic Chemistry, Vol. 47, No. 16, 2008 7315

Barbera` et al.
6-Me-1,2-closo-C2B10H10 crystallizes in non-centrosymmetric space
group and absolute configuration of the compound was assigned
by refinement of Flack’s x parameter.
lographic Data Centre as supplementary publications no. CCDC
641600-641602 for 3,6-I2-1,2-C2B10H10, 3,6-Me2-1,2-C2B10H10,
and 3-I-6-Me-C2B10H11, respectively. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif or at http://pubs.acs.org/.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. . This work was supported by CICYT
(Project MAT2006-05339), Generalitat de Catalunya (2005/
SGR/00709).
IC800362Z
Supporting Information Available: Crystallographic data for
the structures have been deposited with the Cambridge Crystal-
(26) Sheldrick G. M. SHELX97. University of Go¨ttingen: Germany, 1997.
7316 Inorganic Chemistry, Vol. 47, No. 16, 2008