Are halocarboranes suitable for substitution reactions? The case for 3-I-1,2-closo-C2B10H11: Molecular orbital calculations, aryldehalogenation reactions, 11B NMR interpretation of closo-carboranes, and molecular structures of 1-Ph-3-Br-1,2-closo-C2B10H10 and 3-Ph-1,2-closo-C2B10H11

Article abstract of DOI:10.1021/ic010493o

In this paper, the chemistry of 3-X-1,2-closo-C₂B₁₀H₁₁ (X = halogen) derivatives is extended. Molecular orbital and ¹¹B and ¹³C NMR calculations on these species are presented. A qualitative interpretation of the ¹¹B NMR spectra of closo o-carborane derivatives is also provided. The synthesis of 3-X-1-R-o-carborane (X = I, Br and R = Me, Ph) derivatives is reported, and aryldehalogenation at the B3 position is reported for the first time. The molecular and crystal structures of 1-phenyl-3-bromo- 1,2-dicarba-closo-dodecaborane and 3-phenyl-1,2-dicarba-closo-dodecaborane are described.

Full text of DOI:10.1021/ic010493o

Inorg. Chem. 2001, 40, 6555-6562
6555
Are Halocarboranes Suitable for Substitution Reactions? The Case for
3-I-1,2-closo-C2B10H11: Molecular Orbital Calculations, Aryldehalogenation Reactions,
11B NMR Interpretation of closo-Carboranes, and Molecular Structures of
1-Ph-3-Br-1,2-closo-C2B10H10 and 3-Ph-1,2-closo-C2B10H11
Clara Vin˜as,*,† Gemma Barbera`,† Josep M. Oliva,† Francesc Teixidor,† Alan J. Welch,‡ and
Georgina M. Rosair‡
Institut de Cie`ncia de Materials de Barcelona (CSIC),Campus U.A.B., E-08193 Bellaterra, Spain, and
Department of Chemistry, Heriot-Watt University, Edinburgh EH14 4AS, U.K.
ReceiVed May 9, 2001
In this paper, the chemistry of 3-X-1,2-closo-C2B10H11 (X ) halogen) derivatives is extended. Molecular orbital
and 11B and 13C NMR calculations on these species are presented. A qualitative interpretation of the 11B NMR
spectra of closo o-carborane derivatives is also provided. The synthesis of 3-X-1-R-o-carborane (X ) I, Br and
R ) Me, Ph) derivatives is reported, and aryldehalogenation at the B3 position is reported for the first time. The
molecular and crystal structures of 1-phenyl-3-bromo-1,2-dicarba-closo-dodecaborane and 3-phenyl-1,2-dicarba-
closo-dodecaborane are described.
Introduction
carboranes, and in many aspects the latter better resemble their
organic analogues, e.g., 3-amino-o-carborane shows reactions
The icosahedral carborane 1,2-closo-C2B10H12 (o-carborane)
can be viewed as an aromatic moiety,1 in many respects
resembling organic molecules.2 For example, the acidity and
subsequent reactivity of the C-H group of 1,2-closo-C2B10H12
is reminiscent of that of R-C≡C-H and arises because of the
similar nature of the C atomic orbitals in both HCCB10H11 and
HCCR, each carbon atom contributing two sp hybrid and two
perpendicular p AO’s to the molecular orbital set.3
typical of aliphatic and aromatic primary amines.6 Furthermore,
the boron atoms in the cluster are susceptible to electrophilic
alkylation in the presence of AlCl3, under conditions similar to
those required for aromatic compounds. The formation of a B-S
bond by the action of elemental sulfur on carborane, in the
presence of AlCl3, has also been reported.7 These reactions can
be better described, however, by the EINS (electrophilic induced
nucleophilic substitution) mechanism.
However, the chemistry of boron-substituted carboranes is
not as well developed as that of carbon-substituted carboranes
because of the difficulty of introducing functional groups at the
boron atoms of the carborane cage. In general, boron-
halogenated carboranes,4 the most accessible boron-substituted
derivatives, are of limited value in synthesis due to the low
reactivity of the halogen linked to boron, but if this problem
could be overcome it would open up many new possibilities in
boron cluster chemistry. The strong electron-withdrawing (-I)
effect of the cluster on the R substituent at carbon is well
established, explaining why it is difficult to add HCl to
C-carboranylethene in the presence of AlCl3 while B-carbora-
nylethylenes readily react under similar conditions.5 Thus
C-substituted carboranes behave differently from B-substituted
Given that resemblances do exist between B-substituted
carboranes and organic analogues, it is difficult to understand
why the B-substitution chemistry of carboranes is relatively
unexplored. The formation of a B-C bond from B-X through
the reaction of iodocarboranes with organomagnesium com-
pounds in the presence of Ni and Pd complexes has been
reported.8,9 This reaction and a modification introducing CuI
as a cocatalyst10 has become a route to B-substituted o-carborane
derivatives and has been applied in several systems, mostly on
the readily available B9 and/or B12 iodinated species. It could,
probably, be extended to the B8 and B10 positions as these
(5) Zakharkin, L. I.; Kalinin, V. N. IzV. Akad. Nauk SSSR, Ser. Khim.
1968, 1423.
(6) Zakharkin, L. I.; Kalinin, V. N. IzV. Akad. Nauk SSSR, Ser. Khim.
* Author to whom correspondence should be addressed. Fax: Int. Code
+93 5805729. E-mail: clara@icmab.es.
1967, 2585.
(7) Plesek, J.; Hermanek, S. Collect. Czech. Chem. Commun. 1981, 46,
687.
† Institut de Cie`ncia de Materials de Barcelona (CSIC).
‡ Heriot-Watt University.
(8) Li, J.; Logan, C. F.; Jones, M., Jr. Inorg. Chem. 1991, 30, 4866.
(9) (a) Zakharkin, L. I.; Kovredov, A. I.; Ol’shevskaya, V. A.; Shaugum-
bekova, Zh. S. IzV. Akad. Nauk SSSR, Ser. Khim. 1980, 1691. (b)
Kovredov, A. I.; Shaugumbekova, Zh. S.; Petrovskii, P. V.; Zakharkin,
L. I. Zh. Obshch. Khim. 1989, 59, 607. (c) Zakharkin, L. I.; Kovredov,
A. I.; Ol’shevskaya, V. A.; Shaugumbekova, Zh. S. J. Organomet.
Chem. 1982, 226, 217. (d) Gru¨ner, B.; Janousek, Z.; King, B. T.;
Woodford, J. N.; Wang, C. H.; Vsetecka, V.; Michl, J. J. Am. Chem.
Soc. 1999, 121, 3122.
(10) (a) Zheng, Z.; Jiang, W.; Zinn, A. A.; Knobler, C. B.; Hawthorne, M.
F. Inorg. Chem. 1995, 34, 2095. (b) Jiang, W.; Knobler, C. B.; Curtis,
C. E.; Mortimer, M. D.; Hawthorne, M. F. Inorg. Chem. 1995, 34,
3491. (c) Peyman, T.; Knobler, C. B.; Hawthorne, M. F. Inorg. Chem.
1998, 37, 1544.
(1) (a) Schleyer, P. v. R.; Najafian, K. Inorg. Chem. 1998, 37, 3454. (b)
Olah, G. A.; Prakash, G. K. S.; Williams, R. E.; Fidd, L. E.; Wade,
K. Hypercarbon Chemistry; Wiley: New York, 1987. (c) Gimarc, B.
J.; Zhao, M. Inorg. Chem. 1996, 35, 825. (d) Nu´n˜ez, R.; Vin˜as, C.;
Teixidor, F.; Sillanpa¨a¨, R.; Kiveka¨s, R. J. Organomet. Chem. 1999,
592, 22.
(2) Grimes, R. N. Carboranes; Academic Press: New York, 1970.
(3) (a) Wade, K. AdV. Inorg. Chem. Radiochem. 1976, 18, 1. (b) Fox, M.
A.; Wade, K. The borane, carborane, carbocation continuum; John
Wiley: New York, 1998. (c) Kiveka¨s, R.; Sillanpa¨a¨, R.; Teixidor, F.;
Vin˜as, C.; Nun˜ez, R. Acta Crystallogr. 1994, C50, 2027.
(4) (a) Bregadze, V. I. Chem. ReV. 1992, 92, 209. (b) Fox, M. A.; Wade,
K. J. Organomet. Chem. 1999, 573, 279.
10.1021/ic010493o CCC: $20.00 © 2001 American Chemical Society
Published on Web 11/20/2001

6556 Inorganic Chemistry, Vol. 40, No. 26, 2001
Vin˜as et al.
have also been iodinated. However, the cluster carbon atoms
and the boron atoms adjacent to carbon do not appear to be
susceptible to electrophilic substitution. Thus compounds 3-I-
1,2-closo-C2B10H11,8 3-Br-1,2-closo-C2B10H11,11,12 and 3-F-1,2-
closo-C2B10H1112 have been synthesized by the alternate strategy
of reacting [C2B9H11]2- with BX3 or their adducts. From 3-I-
1,2-C2B10H11 may be formed species with B3-C(alkyl) bonds,
and 3-R-1,2-closo-C2B10H11 (R ) ethyl, allyl) have been
synthesized.8 However, no aryl substitution at B3 has been
reported to this time, although 3-Ph-1,2-closo-C2B10H11 does
exist, the result of the reaction between [C2B9H11]2- and
PhBCl2.13
Figure 1. Structure of the 1,2-closo-C2B10H12 cluster showing number-
ing of the cage atoms.
Density-functional and Hartree-Fock (HF) calculations are
also reported on 3-X-1,2-closo-C2B10H11 (X ) F, Cl, Br, I) and
related carboranes. The availability of codes for calculating
NMR shielding constants and other magnetic properties from
first principles (ab initio)14,15 allows experimentalists to check,
correlate, and compare between experimental and computed
NMR shifts, thus assigning NMR signals to the corresponding
nuclei. The model calculations assume a single molecule (0 K
temperature) in the presence of a constant magnetic field B.
In this paper we extend the chemistry of 3-X-1,2-closo-
C2B10H11 derivatives. We present molecular orbital calculations
(within the framework of density-functional and Hartree-Fock
theory) on these species. The synthesis of 1-R-3-X-o-carborane
derivatives (X ) I, Br and R ) Me, Ph) is reported, and
aryldehalogenation at the B3 position is reported for the first
time. The molecular and crystal structures of 1-phenyl-3-bromo-
1,2-dicarba-closo-dodecaborane and 3-phenyl-1,2-dicarba-closo-
dodecaborane are described.
Figure 2. 3D contour plots ((0.075 wave function amplitude units)
of HOMO and LUMO orbitals in X-C6H5 (X ) F, Cl, Br, I)
compounds.
Results and Discussion
basis set as “Gen”. As described in section 4 below, the HF
and B3LYP theoretical levels were used with basis sets “Gen”
and LANL2DZ20 (which consists of a Dunning/Huzinaga full
double-ú basis set for H, B, and C atoms, and Los Alamos
effective core potential (ECP) plus double-ú for I) for the
calculation of 11B NMR chemical shifts in 3-I-1,2-closo-
C2B10H11. Figure 1 shows the structure of 1,2-closo-C2B10H12
with the numbering of the cage atoms.
All optimized molecular geometries are minima in the
potential energy hypersurface, that is, all energy second-
derivative matrices showed no imaginary frequencies. The NMR
spectra calculations were performed on the optimized molecular
geometries with gauge-including atomic orbitals (GIAO) and
the same level of theory and basis sets noted above.
1. Electronic Structures of 3-X-1,2-closo-C2B10H11 (X )
F, Cl, Br, I) and Related Carboranes. A. Theoretical
Approach. All calculations in this work were performed with
the Gaussian98 suite of programs.15 The methodology used in
the geometry optimizations and NMR calculations is based on
density-functional theory (DFT) with Becke’s three parameter
hybrid functional16 and the Lee-Yang-Parr correlation func-
tional17,18 denoted as B3LYP.19 The 6-31G* basis set was used
for all atoms, except for bromine and iodine, where the 3-21G*
and 3-21G** basis sets were used, respectively. These are
double-ú type basis sets with an additional set of polarization
functions in all atoms, except hydrogen. We will refer to this
B. Electronic Structure. In this section the electronic
structure of the 3-X-1,2-closo-C2B10H11 carboranes (X ) F, Cl,
Br, I) is discussed. For comparative purposes on possible
chemical reactivity in the former species, and considering the
similarity invoked between the carborane cluster and the
aromatic ring, discussion of the X-benzene (X ) F, Cl, Br, I)
molecules is also included.
As shown in Figure 2, the two electrons in the highest-
occupied molecular orbital (HOMO) of X-benzene are delo-
calized around the phenyl ring with wave function amplitudes
decreasing in the order F > Cl > Br > I. These HOMOs are
similar to the 2-fold degenerate (e1g) HOMO in benzene.
Notwithstanding this, HOMO pz wave function amplitudes also
appear on the halogen atom in the X-benzene species, increasing
(11) Li, J.; Jones, M., Jr. Inorg. Chem. 1990, 29, 4162.
(12) Roscoe, J. S.; Kongpricha, S.; Papetti, S. Inorg. Chem. 1970, 9, 1561.
(13) Hawthorne, M. F.; Wegner, P. A. J. Am. Chem. Soc. 1968, 90, 896.
(14) Helgaker, T.; Jensen, H. J. Ja.; Jørgensen, P.; Olsen, J.; Ruud, K.;
Ågren, H.; Andersen, T.; Bak, K. L.; Bakken, V.; Christiansen, O.;
Dahle, P.; Dalskov, E. K.; Enevoldsen, T.; Ferna´ndez, B.; Heiberg,
H.; Hettema, H.; Jonsson, D.; Kirpekar, S.; Kobayashi, R.; Koch, H.;
Mikkelsen, K. V.; Norman, P.; Packer, M. J.; Saue, T.; Taylor, P. R.;
Vahtras, O. Dalton: An electronic structure program, release 1.0;
1997.
(15) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels,
A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone,
V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.;
Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;.
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R.
L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara,
A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B. G.;
Chen, W.; Wong, M. W.; Andre´s, J. L.; Head-Gordon, M.; Replogle,
E. S.; Pople, J. A. Gaussian 98; Gaussian, Inc.: Pittsburgh, PA, 1998.
(16) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(17) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785.
(18) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989,
157, 200.
(19) See http://www.gaussian.com/00000432.htm.
(20) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.

Are Halocarboranes Suitable for Substitution Reactions?
Inorganic Chemistry, Vol. 40, No. 26, 2001 6557
Figure 4. HOMO and LUMO energy levels for (a) X-C6H5 and (b)
3-X-1,2-closo-C2B10H11 carborane.
Scheme 1
Figure 3. 3D contour plots ((0.075 wave function amplitude units)
of HOMO and LUMO orbitals of 3-X-1,2-closo-C2B10H11 (X ) F, Cl,
Br, I) compounds.
C2B10H11 carboranes have larger HOMO-LUMO gaps, as
shown in Figure 4, and therefore they are expected to be less
reactive than X-benzene species.
Thus, our calculations suggest that the reactivity of the
X-benzene and 3-X-1,2-closo-C2B10H11 carboranes should
increase in the order F < Cl < Br < I. The 3-I-1,2-closo-
C2B10H11 compound is predicted to be the best 3-halogenated
starting compound for derivative chemistry.
2. Synthetic Studies. A. New 3-X-o-carborane Derivatives.
That B3, in 1-R1-2-R2-1,2-closo-C2B10H10 compounds, is the
atom most susceptible to nucleophilic attack was demonstrated
long ago by Hawthorne and co-workers.21 Removal of B3 leads
to the nido [7-R1-8-R2-7,8-C2B9H10]- anion and its rich deriva-
tive chemistry. The low electron density at B3 that facilitates
its removal is also what prevents the formation of B3-X bonds
by normal electrophilic substitution, a process that readily takes
place first at B9, B12 followed by B8 and B10.22 Thus there
exists clear evidence that not all the boron atoms in o-carborane
and its derivatives should be regarded equally. Our calculations
suggest that B3-X should have a chemistry comparable to that
of C(aryl)-X, an idea supported by the organic-like behavior
of 3-NH2-1,2-closo-C2B10H11 and 3-CH2CH-1,2-closo-C2B10H11.
in the order F < Cl < Br < I. Therefore the lone-pair (or less
aromatic) character of the HOMOs in X-benzene is largest for
iodobenzene. Turning now to the LUMOs shown in Figure 2,
the “hole” amplitudes are also delocalized around the phenyl
ring for X ) F, Cl, and Br, with very similar amplitudes (all
orbitals in Figure 2 and Figure 3 are plotted in a contour of
(0.075 wave function amplitude units). These LUMOs are also
similar to the 2-fold degenerate (e2u) LUMO in benzene.
However, when X ) I the LUMO is completely different from
the above cases, with wave function amplitude along the I-C
bond (σ* symmetry).
Figure 3 depicts HOMOs and LUMOs in the 3-X-1,2-closo-
C2B10H11 carboranes (X ) F, Cl, Br, I). It is immediately
apparent that the two electrons in the HOMOs are also
delocalized, in this case around the carborane cage. As in
X-benzene species, the HOMO amplitudes in 3-X-1,2-closo-
C2B10H11 carboranes also decrease in the order F > Cl > Br >
I. Moreover, no HOMO amplitude whatsoever (at (0.075
contour levels) is found in the carborane cage for X ) Br, I.
Note also that the HOMO pz amplitude on X also increases in
the order F < Cl < Br < I.
Turning now to the LUMOs in 3-X-1,2-closo-C2B10H11
carboranes, Figure 3 shows very similar shapes and amplitudes
for all X. Careful inspection of the LUMOs in Figure 3 reveals
π*-type lobes on C1, C2 and on the antipodal atoms B9, B12.
LUMO “hole” amplitudes are also found along the B3-B4,
B3-B7, B5-B6, and B6-B11 connectivities.
In extending the chemistry of 3-halogeno o-carborane we have
first investigated the synthesis of 3-I and 3-Br species which
additionally have an electron-donating (-Me) or electron-
withdrawing (-Ph) substituent on one of the cage carbon atoms.
The reaction is shown in Scheme 1.
Figure 4 shows the HOMO-LUMO energy levels for (a)
X-benzene and (b) 3-X-1,2-closo-C2B10H11 carborane. As shown
in this figure the HOMO-LUMO energy gaps decrease in the
order F > Cl > Br > I for a and b. Moreover, the gaps are
larger in b than in a.
All four new carboranes 3-Br-1-Ph-1,2-closo-C2B10H10, 3-I-
1-Ph-1,2-closo-C2B10H10, 3-Br-1-Me-1,2-closo-C2B10H10, and
3-I-1-Me-1,2-closo-C2B10H10 were produced in good yields.
Compounds were initially characterized by microanalysis and
From the data above and comparing the orbital pictures shown
in Figure 2 and Figure 3 we conclude that similar chemical
reactivities for both X-benzene and 3-X-1,2-closo-C2B10H11
carborane species are expected. Electrophiles will thus attack
near the HOMO-amplitude region and nucleophiles on the
LUMO-amplitude region. Nevertheless, the 3-X-1,2-closo-
(21) (a) Wiesboeck, R. A.; Hawthorne, M. F. J. Am. Chem. Soc. 1964, 86,
1642. (b) Garret, P. M.; Tebbe, F. N.; Hawthorne, M. F. J. Am. Chem.
Soc. 1964, 86, 5016. (c) Hawthorne, M. F.; Young, D. C.; Garret, P.
M.; Owen, D. A.; Schwerin, S. G.; Tebbe, F. N.; Wegner, P. M. J.
Am. Chem. Soc. 1968, 90, 862.
(22) Dixon, D. A.; Kleier, D. A.; Halgren, T. A.; Hall, J. H.; Lipscomb,
W. N. J. Am. Chem. Soc. 1977, 99, 6226.

6558 Inorganic Chemistry, Vol. 40, No. 26, 2001
Vin˜as et al.
Scheme 2
IR spectroscopy. NMR spectra (11B, 13C, 1H) of the compounds
are fully consistent with the proposed formulas.
Thus it may be concluded that the insertion of a BX2+
fragment into the open C2B3 face of nido [7-R-7,8-C2B9H10]2-
derivatives is not much dependent on either the bulkiness of
the C-substituent or their electronic properties.
Figure 5. Structure of 1-Ph-3-Br-1,2-closo-C2B10H10 showing the atom-
labeling scheme.
B. Aryldehalogenation Reactions at B(3). Aryldehaloge-
nation reactions were performed on 3-I-1,2-closo-C2B10H11,
using three aryl substituents of differing volume: phenyl,
biphenyl, and anthracenyl.
Table 1. Selected Interatomic Distances (Å) and Interbond and
Dihedral Angles (deg) in 1-Ph-3-Br-1,2-closo-C2B10H10
Br(1)-B(3)
C(1)-C(11)
C(1)-C(2)
C(1)-B(5)
C(1)-B(4)
C(1)-B(6)
C(1)-B(3)
C(2)-B(7)
C(2)-B(11)
C(2)-B(3)
C(2)-B(6)
B(3)-B(8)
B(3)-B(4)
B(3)-B(7)
B(4)-B(5)
B(4)-B(9)
B(4)-B(8)
B(5)-B(9)
B(5)-B(10)
1.927(5)
1.521(6)
1.671(6)
1.711(6)
1.712(6)
1.732(6)
1.769(6)
1.696(6)
1.703(6)
1.721(7)
1.730(6)
1.765(7)
1.769(7)
1.780(7)
1.775(7)
1.775(7)
1.779(7)
1.774(7)
1.780(7)
B(5)-B(6)
1.793(7)
1.770(7)
1.782(7)
1.780(7)
1.782(7)
1.790(7)
1.792(7)
1.796(7)
1.782(8)
1.785(7)
1.779(8)
1.785(8)
1.779(7)
1.382(6)
1.383(6)
1.370(7)
1.392(7)
1.381(7)
1.387(6)
B(6)-B(10)
B(6)-B(11)
B(7)-B(11)
B(7)-B(12)
B(7)-B(8)
The procedure used was a modification of that reported by
Hawthorne and Jones for alkyl substitution and consisted of
the attack of the appropriate arylmagnesium bromide reagent
(prepared from the corresponding aryl bromide) on 3-I-1,2-
closo-C2B10H11 in the presence of [PdCl2(PPh3)2] and CuI, in
THF solution under refluxing conditions, as denoted in Scheme
2. The compounds 3-R-1,2-closo-C2B10H11 (R ) aryl) were
obtained in good to high yields (=90%) and were fully
B(8)-B(9)
B(8)-B(12)
B(9)-B(10)
B(9)-B(12)
B(10)-B(12)
B(10)-B(11)
B(11)-B(12)
C(11)-C(16)
C(11)-C(12)
C(12)-C(13)
C(13)-C(14)
C(14)-C(15)
C(15)-C(16)
1
characterized by multinuclear NMR data (11B, 13C, H).
These reactions thus demonstrate that B-C coupling is a valid
route to produce, in addition to B3-C(alkyl) carboranes already
described, new B3-C(aryl) derivatives. On the other hand,
attempts to produce this B-C coupling but in the reverse way,
that is, reaction of a B-carboranylmagnesium reagent with R-X
(R ) aryl), did not succeed, mainly yielding mostly unreacted
reagent. An attempted dehalogen coupling reaction with Cu,23
intended to lead to B-B formation, was similarly unsuccessful.
However, hydrodehalogen reactions of 3-I-1,2-closo-C2B10H11
in DMF in the presence of Ni24 or Pd25 in stoichiometric
quantities yielded o-carborane.
C(11)-C(1)-C(2) 118.4(3)
C(11)-C(1)-B(5) 122.3(3)
C(11)-C(1)-B(4) 122.9(4)
C(11)-C(1)-B(6) 116.9(3)
C(11)-C(1)-B(3) 117.6(3)
C(2)-B(3)-Br(1) 119.3(3)
B(8)-B(3)-Br(1) 130.0(3)
C(1)-B(3)-Br(1) 118.0(3)
B(4)-B(3)-Br(1) 123.9(3)
B(7)-B(3)-Br(1) 124.5(3)
C(2)-C(1)-C(11)-C(16)
B(3)-C(1)-C(11)-C(16)
C(2)-C(1)-C(11)-C(12)
B(3)-C(1)-C(11)-C(12)
-159.2(4)
-90.2(5)
25.6(5)
3. Molecular and Crystal Structures of 1-Ph-3-Br-1,2-
closo-C2B10H10 and 3-Ph-1,2-closo-C2B10H11. As an adjunct
to our theoretical and synthetic work we have studied the species
1-Ph-3-Br-1,2-closo-C2B10H10 and 3-Ph-1,2-closo-C2B10H11 by
single-crystal X-ray diffraction.
94.5(5)
we define the orientation of the Ph substituent by the angle θ,
the modulus of the average Ccage-Ccage-C11-C torsion angle.28
In the present compound θ is 66.8(5)°, twisted from its
optimum29a value of ca. 25° by the steric requirements of the
Br substituent (the potential energy barrier to complete rotation
of the Ph substituent in 1-Ph-1,2-closo-C2B10H11 is only 6 kJ
mol-1 at the DZ//HF/6-31G* level of theory29a). Thus in the
conformation adopted the torsion angles B3-C1-C11-C12 and
B3-C1-C11-C16 are nearly equal and opposite, 94.5(5)° and
-90.2(5)°, respectively. The B3-Br distance is 1.927(5) Å, in
excellent agreement with other such distances in the literature.30
A. 1-Ph-3-Br-1,2-closo-C2B10H10. A perspective view of a
single molecule is shown in Figure 5, and Table 1 lists key
molecular parameters determined. The compound crystallizes
as well-separated, individual molecules. There is no relationship
between the crystallographic packing in 1-Ph-3-Br-1,2-closo-
C2B10H10 and its isomer species 1-Ph-2-Br-1,2-closo-C2B10H10.26
The cage has the expected near-icosahedral geometry with the
lengths of the differing types of connectivity increasing in the
expected sequence C-C < C-B < B-B, the magnitudes of
these connectivities standing in close comparison with those
determined for 1,2-closo-C2B10H12.27 In C-Ph 1,2-carboranes
(27) Davidson, M. G.; Hibbert, T. G.; Howard, J. A. K.; Mackinnon, A.;
Wade, K. Chem. Commun. 1996, 2285.
(28) Cowie, J.; Reid, B. D.; Watmough, J. M. S.; Welch, A. J. Organomet.
Chem. 1994, 481, 283.
(23) (a) Fuson, R. C.; Cleveland, E. A. Organic Syntheses; Wiley: New
York, 1955; Collect. Vol. 3, p 339. (b) Brown, E.; Robin, J. P.
Tetrahedron Lett. 1978, 3613.
(24) Kende, A. S.; Liedeskind, L. S.; Braitsch, D. M. Tetrahedron Lett.
1975, 16, 3375.
(25) Grigg, R.; Stevenson, P.; Worakun, T. Tetrahedron 1988, 44, 2049.
(26) McGrath, T. D.; Welch, A. J. Acta Crystallogr., Sect. C 1995, 51,
649
(29) (a) R-form: Brain, P. T.; Cowie, J.; Donohoe, D. J.; Hynk, D.; Rankin,
D. W. H.; Reed, D.; Reid, B. D.; Robertson, H. E.; Welch, A. J.;
Hofmann, M.; Schleyer, P. v. R. Inorg. Chem. 1996, 35, 1701. (b)
â-form: Thomas, Rh. Ll.; Rosair, G. M.; Welch, A. J. Acta
Crystallogr., Sect. C 1996, 52, 1024.

Are Halocarboranes Suitable for Substitution Reactions?
Inorganic Chemistry, Vol. 40, No. 26, 2001 6559
Figure 6. Structure of 3-Ph-1,2-closo-C2B10H11 showing the atom-
labeling scheme.
Table 2. Selected Interatomic Distances (Å) and Interbond and
Dihedral Angles (deg) in 3-Ph-1,2-closo-C2B10H11
C1-C2
C1-B4
C1-B5
C1-B6
C1-B3
C2-B7
C2-B11
C2-B6
C2-B3
B3-C31
B3-B8
B3-B4
B3-B7
B4-B8
B4-B9
B4-B5
B5-B9
1.626(3)
1.692(3)
1.699(3)
1.725(3)
1.734(3)
1.695(3)
1.700(3)
1.724(3)
1.740(3)
1.566(3)
1.774(3)
1.791(3)
1.793(3)
1.774(3)
1.780(3)
1.781(3)
1.779(3)
B5-B6
1.782(3)
1.787(3)
1.766(3)
1.779(3)
1.774(3)
1.780(3)
1.786(3)
1.789(3)
1.791(3)
1.786(3)
1.786(3)
1.783(3)
1.790(3)
1.778(3)
1.396(2)
1.400(3)
B5-B10
B6-B10
B6-B11
B7-B12
B7-B11
B7-B8
Figure 7. 11B and 11B{1H} spectra of 3-I-1,2-closo-C2B10H11.
the chemical shifts of the cage boron atoms vary with the
substituent R,31 particularly the boron atom opposite to the point
of attachment of the substituent, the “antipodal atom”.32
The 11B NMR spectrum of 3-I-1,2-closo-C2B10H11 presents
a 2:1:3:3:1 pattern in the range -1.04 to -29.02 ppm. Figure
7 shows the 11B and 11B{1H} NMR spectra of 3-I-1,2-closo-
C2B10H11. The resonance at -29.02 ppm does not split into a
doublet in the 11B NMR spectrum, indicating that this resonance
corresponds to the B-I vertex. Once the B3 resonance is known,
the two-dimensional 2D-COSY NMR spectrum33 is helpful for
the assignment of the remaining peaks. Figure 8 shows a typical
spectrum, that of 3-I-1,2-closo-C2B10H11, with the assignments
deduced from the off-diagonal resonances.
B8-B9
B8-B12
B9-B12
B9-B10
B10-B11
B10-B12
B11-B12
C31-C32
C31-C36
C31-B3-C1
C31-B3-C2
C31-B3-B8
C31-B3-B4
121.44(14)
122.33(15)
128.74(15)
123.50(16)
C31-B3-B7
B3-C31-C32
B3-C31-C36
C32-C31-C36
125.27(15)
120.04(16)
122.64(16)
117.12(17)
A. Qualitative Description of the 11B NMR Spectra. The
11B NMR spectra of icosahedral closo-carboranes could be easily
understood if dominated by the diamagnetic shielding term σd:
the further a boron atom was from the more electronegative
carbon atoms, the more shielded it would be and the more
negative its chemical shift. Thus, 1,2-closo-C2B10H12 would
display a 2:4:2:2 pattern from high to low frequency due to
B(3,6), B(4,5,7,11), B(8,10), and B(9,12), respectively. How-
ever, this is not the case as the experimental spectrum has
resonances at -2.1:-8.9:-13.4:-14.5 (2:2:4:2) ppm arising
from atoms B(9,12), B(8,10), B(4,5,7,11), and B(3,6), respec-
tively; thus the real spectrum is the reverse of that predicted on
the basis of σd.34 This certainly implies that a paramagnetic
deshielding term σp is very relevant as has been stated
earlier,35,36 the magnitude of this term decreasing as B(9,12) >
B(8,10) > B(4,5,7,11) > B(3,6). The strong σp term is a
C1-B3-C31-C32 155.93(16)
C2-B3-C31-C32 89.0(2)
C1-B3-C31-C36 -29.3(3)
C2-B3-C31-C36 -96.2(2)
B. 3-Ph-1,2-closo-C2B10H11. Figure 6 shows a perspective
view of a single molecule of 3-Ph-1,2-closo-C2B10H11, and Table
2 lists key interatomic distances, interbond angles, and torsion
angles determined.
The molecule crystallizes with no imposed symmetry. The
plane of the Ph substituent is more or less symmetrically
disposed with respect to C2 but lies in no special orientation
with respect to C1 (and C1 and C2 are unambiguously located).
There are no significant intermolecular contacts, and the crystal
structure of 3-Ph-1,2-closo-C2B10H11 bears no relationship to
those of two crystalline modifications of 1-Ph-1,2-closo-
C2B10H11 recently reported.29
C1-C2 is 1.626(3) Å, C(cage)-B distances lie in the range
1.69-1.74 Å, and B-B lies in the range 1.76-1.80 Å. The
phenyl ring is attached to B3 at B3-C31 1.566 (3) Å.
4. NMR Spectral Considerations. The sensitivity of the
electron distribution in carboranes to the presence of substituents
has long been apparent.2 For icosahedral carborane derivatives
of 1-R-1,2-closo-C2B10H11, 11B NMR studies have shown that
(31) Hermanek, S.; Plesek, J.; Stibr, B.; Grigor, V. J. Chem. Soc., Chem.
Commun. 1977, 561.
(32) (a) Hermanek, S.; Gregor, V.; Stibr, B.; Plesek, J.; Janousek, Z.;
Antonovich, V. A. Collect. Czech. Commun. 1976, 41, 1492. (b)
Stanko, V. I.; Babushkina, T. A.; Klimova, T. P.; Goltyapin, Y. U.;
Klimova, A. I.; Vasilev, A. M.; Alymov, A. M.; Khrapov, V. V. Zh.
Obshch. Khim. 1976, 46, 1071.
(33) (a) Reed, D. J. Chem. Res. 1984, 198. (b) Venable, T. L.; Hutton, W.
C.; Grimes, R. N. J. Am. Chem. Soc. 1984, 106, 29.
(34) (a) Jameson, C. J.; Mason, J. Multinuclear NMR; Plenum: New York,
1987. (b) Harris, R. K. Nuclear Magnetic Resonance Spectroscopy;
Pitman: London, 1983.
(30) (a) The United Kingdom Chemical Database Service: Fletcher, D.
A.; McMeeking, R. F.; Parkin, D. J. Chem. Inf. Comput. Sci. 1996,
36, 746. (b) Allen, F. H.; Kennard, O. Chem. Des. Autom. News 1993,
8, 1.
(35) Hermanek, S. Chem. ReV. 1992, 92, 325.
(36) Oliva, J. M.; Vin˜as, C. J. Mol. Struct. 2000, 556, 33.

6560 Inorganic Chemistry, Vol. 40, No. 26, 2001
Vin˜as et al.
Figure 10. Raw 11B NMR spectra with the peak assignments for the
compounds: (a) 3-I-1,2-closo-C2B10H11, (b) 1,2-closo-C2B10H12, and
(c) 9,12-I2-1,2-closo-C2B10H10.
above provides a rationale for these effects. Now, if the 11B
NMR spectrum of 3-I-1,2-closo-C2B10H11, with resonances at
-1.04 (B9,B12), -6.82 (B8), -10.73 (B4,B7,B10), -12.18
(B5,B11,B6), and -29.02 (B3) ppm, is compared to that for
o-carborane, we note that all resonances are shifted about 3 ppm
to lower field, except that due to B3, considerably shifted to
higher field, by about 14 ppm. Figure 10 shows how the
resonances attributable to the different types of boron nuclei in
compounds 1,2-closo-C2B10H12, 3-I-1,2-closo-C2B10H11, and
9,12-I2-1,2-closo-C2B10H10 change in chemical shift. All the
resonances show some changes, but the largest upfield shift,
over 14 ppm, is always due to the B-I resonances.
Figure 8. 11B{1H}-11B{1H} 2D-COSY NMR spectrum of 3-I-1,2-
closo-C2B10H11.
We will not discuss the smaller shifts, a general phenomenon
when a heteroatom participating with more electrons than BH
is incorporated into the cluster, this already anticipating that
B3 is electron rich compared to BH’s in the molecule.
Figure 9. 11B NMR in closo carboranes. (a) In 1,2-C2B10H12,
perpendicular disposition of the occupied σBH and the atomic p orbitals.
The last one participates in the low-lying ψ* unoccupied orbital. Only
some atomic orbitals are represented. (b) In 3-I-1,2-C2B10H11, lone-
pair electron back-donation from the I atom to the ψ*, largely spread
on the cluster.
Let us focus on the B3 shift. It is known that the σ/p
combination is more efficient the closer in energy are the
participating orbitals. Considering that lone pairs of non-
electronegative elements like iodine are reasonably basic in
terms of Lewis acid/base theory, they should interact efficiently
with the p orbitals on B3. See Figure 9b. This will enrich
considerably the electron density at B3 enhancing its shielding
σd term, and consequently shifting the B3 resonance to high
field. This back-donation to B3 will diminish in the sequence I
> Br > Cl > F, thus shifting the B3 resonance to lower field
upon substitution of one halogen by another. The increasing
electronegativity in the former sequence will, moreover, cause
B3 to become even more deshielded, explaining its considerable
downfield shift. This qualitative explanation suffices to explain
the 11B NMR pattern of these icosahedral closo species. Their
main novelty is the inclusion of a local σp contribution, thus
avoiding the concept of tangential px and py, “π” orbitals which
are NMR active, and radial pz orbitals which are chemically
active.35,39 The π back-donation power (the mesomeric (+M)
effect) had been invoked earlier to explain an increase in the
electron density at the antipodal position.31
consequence of low-lying unoccupied p orbitals allowed
efficient combination with appropriate energy-rich occupied
orbitals. Figure 9a depicts the σBH/p combination, possibly
responsible for the strong 11B NMR dependency of the σp term.
According to selection rules the combination of an occupied
and an unoccupied orbital is magnetically active only when the
corresponding (hypothetical) electron transfer comprises an
angular momentum.37 Thus, perpendicularly placed σ/p com-
binations are active in NMR, yielding deshielding contributions
perpendicular to the σ/p plane of charge circulation. It is also
reasonable to assume that the magnitude of the individual σp
contributions will depend on the electron density in the particular
B-H bond. The last follows the pattern B-H(9,12) > B-H(8,10)
> B-H(4,5,7,11) > B-H(3,6); thus the largest individual σp
contribution would be for B-H(9,12), the smallest for B-H(3,6),
corresponding very well with the observed pattern indicated
above.
The 11B NMR spectrum of o-carborane was rationalized in
1986 following a set of empirical rules incorporating antipodal,
rhomboidal, butterfly, and neighbor effects.38 The description
B. Quantitative Description of the 11B and 13C NMR
Spectra. To our knowledge no comprehensive literature exists
(39) Hermanek, S.; Jelinek, T.; Plesek, J.; Stibr, B.; Fusek, J.; Mares, F. In
Boron Chemistry; Hermanek, S. Ed.; World Scientific: Singapore,
1987; p 26.
(37) Dahn, H. J. Chem. Educ. 2000, 77, 905.
(38) Teixidor, F.; Vin˜as, C.; Rudolph, R. W. Inorg. Chem. 1986, 25, 3339.

Are Halocarboranes Suitable for Substitution Reactions?
Inorganic Chemistry, Vol. 40, No. 26, 2001 6561
Table 3. Experimental 11B{1H} and 13C{1H} Chemical Shifts (ppm) in Carboranes 3-X-1,2-C2B10H11 (X ) F, Cl, Br, I, Ph) and
3-X-1-R-1,2-C2B10H10 (X ) Br, I and R ) Me, Ph)a
nuclei
11B
Fb
Clc
Br
I
Ph
(Br, Me)
(Br, Ph)
(I, Me)
(I, Ph)
0.0 (1)
-5.4 (2)
-12.1 (1)
-14.0 (1)
-14.4 (2)
-15.5 (2)
-19.2 (1)
6.02
-3.1
-10.10
-15.02
-16.55
-17.7
-1.42 (2)
-7.56 (1)
-11.27 (3)
-12.5 (4)
-1.04 (2)
-6.82 (1)
-10.73 (3)
-12.18 (3)
-29.02 (1)
-2.06 (2)
-4.71 (1)
-8.16 (1)
-12.62 (3)
-13.29 (3)
-2.32 (1)
-5.60 (1)
-7.74 (1)
-9.10 (1)
-9.97 (4)
-12.31 (1)
-13.14 (1)
-3.26 (2)
-7.80 (1)
-8.61 (1)
-9.59 (1)
-10.53 (3)
-11.38 (1)
-13.88 (1)
-1.24 (1)
-5.06 (1)
-6.41 (1)
-8.17 (1)
-10.05 (4)
-12.09 (1)
-24.32 (1)
-1.98 (1)
-3.00 (1)
-6.49 (1)
-9.43 (5)
-12.75 (1)
-23.19 (1)
11B
11B
11B
11B
11B
11B
13C cluster
13C cluster
13C
59.17
59.17
60.30
60.30
56.69
56.69
133.06
132.03
129.77
128.30
72.04
66.24
25.73
78.23
62.32
132.70
130.77
129.53
127.79
71.47
66.84
28.35
78.15
62.59
134.24
130.78
129.53
127.67
13C
13C
13C
a The numbers within parentheses correspond to the equivalent boron atoms. b Reference 46. c Reference 47.
on GIAO/IGLO calculations of 11B NMR spectra in B(3)-
substituted o-carboranes.40 We should emphasize here the IGLO
calculations of Brain et al.29 on the C-substituted 1-Ph-1,2-closo-
C2B10H11. Their computed 11B NMR chemical shift results agree
well with experiment up to a difference of ca. 4 ppm (B(8,10))
for the minimum energy conformer (II′′//HF/6-31G* calcula-
tions). Similar results are found in a recent work Oliva et al.36
where 11B and 13C NMR experimental and computed chemical
shifts for dodecaborane, o-carborane, and 1,2-(SH)2-o-carborane
are reported. Also, Diaz et al.41 report experimental/calculational
correlations of 13C NMR signals in a series of carboranes and
derivatives, including o-carborane.
instrument equipped with the appropriate decoupling accessories. All
NMR spectra were recorded from CDCl3 solutions at 25 °C. Chemical
shift values for 11B NMR spectra were referenced to external BF3‚
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 reference, and all coupling constants are
reported in hertz.
Unless otherwise noted, all manipulations were carried out under a
dinitrogen 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 deoxygenated prior to
use. A 1.6 M solution of n-butyllithium in hexanes from Lancaster
was used as purchased. BI3 and BBr3 were used as purchased from
Table 3 shows 11B and 13C NMR experimental chemical shifts
for the carboranes 3-X-1,2-closo-C2B10H11 (X ) F, Cl, Br, I,
Ph) and 3-X-1-R-1,2-closo-C2B10H10 (X ) Br, I; R ) Me, Ph).
Attempts to reproduce these 11B and 13C NMR chemical shifts
using rigorous calculational methods42 have been used. All of
them broadly reproduce trends for most cage atoms except B3.
Possible solvent molecule-molecule interactions of the iodo-
carboranes when measuring the 11B NMR signals, and/or
intermolecular hydrogen bonding noted in the crystal structure
of 3-I-1,2-closo-C2B10H11,43 should not be disregarded to explain
the degree of inaccuracy found. However, it is necessary to
consider that small differences (up to 2 ppm) are experimentally
observed when recording 11B NMR spectra of o-carborane
derivatives in different solvents.
8
11
Alfa. 3-I-1,2-closo-C2B10H11 and 3-Br-1,2-closo-C2B10H11 were
synthesized according to the literature.
3-Bromo-1-methyl-1,2-dicarba-closo-dodecaborane. To a solution
of [HNMe3][7-Me-7,8-C2B9H11] (5.0 g, 24 mmol) in anhydrous diethyl
ether (50 mL) at 0 °C was added dropwise with stirring butyllithium
(30 mL, 48 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 (100 mL) was added to the remaining solid. BBr3 (9.0 g, 36
mmol) 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 tribromide was decomposed by careful addition of
20 mL of water. The organic layer was separated from the mixture
and the aqueous layer extracted with hexane (3 × 15 mL). The
combined organic phase was dried over MgSO4 and the solvent removed
at the water pump. The crude product was purified by flash silica gel
chromatography using dichloromethane/hexane (2:1) as the eluting
solvent to give 3-bromo-1-methyl-1,2-dicarba-closo-dodecaborane.
Yield: 3.5 g (62%). Anal. Calcd for C3H13B10Br: C, 15.19; H, 5.53.
Experimental Section
General Considerations. Elemental analyses were performed using
a Carlo Erba EA1108 microanalyzer. 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
NMR (96.29 MHz) spectra were recorded with a Bruker ARX 300
Found: C, 15.50; H, 5.64. IR: ν [cm-1] ) 3057 (Ccluster-H), 2960-
1
2854 (CMe-H), 2590 (B-H). H NMR: δ ) 3.56 (br s, 1H, Ccluster
-
H), 2.17 (s, 3H, CH3), 3.50-1.50 (br m, 9H, B-H). 13C{1H} NMR:
δ ) 72.04, 66.24 (s, Ccluster), 25.73 (s, CH3). 11B NMR: δ ) - 2.32
(d, 1J(B,H) ) 151, 1B), -5.60 (d, 1J(B,H) ) 151, 1B), -7.74 (d,
1J(B,H) ) 110, 1B), -9.10 (s, 1B, B(3)), -9.97 (d, 4B), -12.31 (d,
(40) Non-boron-substituted nido-undecaborates and icosahedral closo o-
carboranes have respectively chemical shift windows ca. (0:-40 ppm)
and (0:-15 ppm). More extensive literature is found for the GIAO-
MP2/GIAO/IGLO computations of 11B NMR spectra in the nido and
related carboranes; see, e.g.: (a) Schleyer, P. v. R.; Gauss, J.; Buehl,
M.; Greatrex, R.; Fox, M. A. J. Chem. Soc., Chem. Commun. 1993,
23, 1766. (b) Onak, T.; Tran, D.; Tseng, J.; Diaz, M.; Arias, J.; Herrera,
S. J. Am. Chem. Soc. 1993, 115, 9210. (c) Jaballas, J.; Onak, T. J.
Organomet. Chem. 1998, 550, 101. (d) Hosmane, N. S.; Maguire, J.
A. In Organometallic and Organometalloidal Compounds: Borane,
Carbocation Continuum; Casanova, J. Ed.; Wiley: New York, 1998;
p 397.
(41) Diaz, M.; Jaballas, J.; Arias, J.; Lee, H.; Onak, T. J. Am. Chem. Soc.
1996, 118, 4405.
(42) We have used the following GIAO methods: HF/LANL2DZ, HF/
Gen, B3LYP/LANL2DZ, and B3LYP/Gen.
(43) Vin˜as, C.; Barbera`, G.; Teixidor, F.; Welch, A. J., Rosair, G. M. To
be published.
1
1B), -13.14 (d, J(B,H) ) 96, 1B).
3-Bromo-1-phenyl-1,2-dicarba-closo-dodecaborane. Similarly were
reacted [HNMe3][7-Ph-7,8-C2B9H11] (5.0 g, 19 mmol) and butyllithium
(24 mL, 38 mmol) in anhydrous diethyl ether (50 mL) at 0 °C, followed
by addition of anhydrous hexane (100 mL) and BBr3 (7.1 g, 28.5 mmol).
Workup and purification as previously gave 3-bromo-1-phenyl-1,2-
dicarba-closo-dodecaborane. Yield: 3.1 g (55%). Anal. Calcd for
C8H15B10Br: C, 32.11; H, 5.05. Found: C, 32.42; H 5.07. IR: ν [cm-1
]
) 3068 (Ccluster-H), 3056, 3040 (Caryl-H), 2642, 2609, 2599, 2589,
2577, 2558 (B-H). 1H NMR: δ ) 7.47-7.27 (m, 5H, Haryl), 4.23 (br
s, 1H, Ccluster-H), 3.90-2.10 (br m, 9H, B-H). 13C{1H} NMR: δ )
132.70, 130.77, 129.53, 127.79 (Caryl), 78.23, 62.32 (s, Ccluster). 11B
1
NMR: δ ) -3.26 (d, J(B,H) ) 143, 2B), -7.80 (d, 1B), -8.61 (s,

6562 Inorganic Chemistry, Vol. 40, No. 26, 2001
Vin˜as et al.
1B, B(3)), -9.59 (d, 1B), -10.53 (d, 3B), -11.38 (d, 1B), -13.88 (d,
1J(B,H) ) 164, 1B).
3-Anthracenyl-1,2-dicarba-closo-dodecaborane. An entirely analo-
gous reaction, but using 9-anthracylmagnesium bromide (25 mmol) and
chromatography using dichloromethane/hexane (1:4) as eluting solvent,
gave 3-anthracyl-1,2-dicarba-closo-dodecaborane. Yield: 1.50 g (94%).
Anal. Calcd for C16 H20 B10: C, 59.97; H, 6.29. Found: C, 58.41; H,
6.11. IR: ν [cm-1] ) 3089 (Ccluster-H), 3010 (Caryl-H), 2603-2550
3-Iodo-1-methyl-1,2-dicarba-closo-dodecaborane. In an analogous
manner were reacted [HNMe3][7-Me-7,8-C2B9H11] (5.0 g, 24 mmol)
and butyllithium (30 mL, 48 mmol) in anhydrous diethyl ether (50
mL) at 0 °C, followed by addition of anhydrous hexane (100 mL) and
BI3 (14.1 g, 36 mmol). Workup as previously and purification by flash
silica gel chromatography using dichloromethane/hexane (4:1) as the
eluting solvent gave 3-iodo-1-methyl-1,2-dicarba-closo-dodecaborane.
Yield: 4.8 g (71%). Anal. Calcd for C3H13B10I: C, 12.68; H, 4.61.
1
2
(B-H), 1436 (γ (C-C)aryl). H NMR: δ ) 8.80 (d, J(H,H) ) 8.80,
2H, Haryl), 8.47 (s, 1H, Haryl), 8.01 (d, 2J(H,H) ) 7.5, 2H, Haryl), 7.54-
7.46 (m, 4H, Haryl), 3.86 (s, 2H, Ccluster-H), 3.50-1.50 (br m, 9H,
B-H). 13C{1H} NMR: δ ) 137.41, 132.22, 131.91, 130.15, 127.92,
126.95, 125.62 (Caryl), 59.0 (s, Ccluster). 11B NMR: δ ) -2.15 (d, 1J(B,H)
) 147, 2B), -3.89 (s, 1B, B(3)), -7.83 (d, 1J(B,H) ) 150, 1B), -11.02
Found: C, 13.04; H 4.56. IR: ν [cm-1] ) 3058 (Ccluster-H), 2956-
1
2857 (CMe-H), 2594 (B-H). H NMR: δ ) 3.60 (br s, 1H, Ccluster
-
1
1
H), 2.24 (s, 3H, CH3), 3.50-1.10 (br m, 9H, B-H). 13C{1H} NMR:
δ ) 71.47, 66.84 (s, Ccluster), 28.35 (s, CH3). 11B NMR: δ ) -1.24 (d,
1J(B,H) ) 151, 1B), -5.06 (d, 1J(B,H) ) 156, 1B), -6.41 (d, 1J(B,H)
) 122, 1B), -8.17 (d, 1J(B,H) ) 176, 1B), -10.05 (d, 1J(B,H) ) 180,
(d, J(B,H) ) 134, 1B), -11.81 (d, J(B,H) ) 132, 2B), -13.34 (d,
1J(B,H) ) 159, 3B).
Crystallographic Studies. Intensity data collected on a Bruker P4
diffractometer, with Mo KR radiation (λ ) 0.71073 Å) to 2θmax
)
1
50°, ω scans, corrections for absorption (æ scans), Lorentz and
polarization effects,44 and structures were solved by direct methods and
refined (against F2) by full-matrix least-squares refinement.45 Cage C
atoms were unambiguously identified by inspection of U values
following isotropic refinement of all cage vertexes as boron, and
confirmed by C-C distances. H atoms were treated as riding model.
For 1-Ph-3-Br-1,2-closo-C2B10H10, C8H15B10Br, 160(2) K, Mr )
299.21: crystal size 0.25 × 0.38 × 0.30 mm, monoclinic, P21/n, a )
7.0131(6) Å, b ) 20.213(3) Å, c ) 10.5327(14) Å, â ) 107.005(9)°,
V ) 1427.8(3) Å3, Z ) 4, Fcalcd ) 1.392 g cm-3, F(000) ) 592, µ )
2.848 mm-1, of 3332 unique reflections 2500 were observed [Fo >
2σ(Fo)], 173 parameters, R1 ) 0.0455, wR2 ) 0.1176 (for observed
data), S ) 1.080; maximum and minimum residual electron density,
0.601 and -1.404 eÅ-3 (near Br3).
4B), -12.09 (d, J(B,H) ) 161, 1B), -24.32 (s, 1B, B(3)).
3-Iodo-1-phenyl-1,2-dicarba-closo-dodecaborane.
Similarly,
[HNMe3][7-Ph-7,8-C2B9H11] (5.0 g, 19 mmol) was deprotonated with
butyllithium (24 mL, 38 mmol) in anhydrous diethyl ether (50 mL),
followed by evaporation of the solvent and addition of anhydrous
hexane (100 mL) and BI3 (11.1 g, 28.5 mmol) in hexane (50 mL).
After reaction and workup as previously, chromatography using
dichloromethane/hexane (1:1) as eluting solvent gave 3-iodo-1-phenyl-
1,2-dicarba-closo-dodecaborane. Yield: 3.42 g (52%). Anal. Calcd for
C8H15B10I: C, 27.75; H, 4.37. Found: C, 27.64; H, 4.34. IR: ν [cm-1
) 3059 (Ccluster-H), 2544 (B-H). 1H NMR: δ ) 7.50-7.00 (m, 5H,
aryl), 4.22 (br s, 1H, Ccluster-H), 3.10-1.50 (br m, 9H, B-H). 13C{1H}
NMR: δ ) 134.24, 130.78, 129.53, 127.67 (Caryl), 78.15, 62.59 (s,
]
H
C
cluster). 11B NMR: δ ) -1.98 (d, 1J(B,H) ) 140, 1B), -3.00 (d,
For 3-Ph-1,2-closo-C2B10H11, C8H16B10, 293(2) K, Mr ) 220.31:
crystal size 0.10 × 0.68 × 0.24 mm, monoclinic, P21/c, a ) 10.405(2)
Å, b ) 9.779(2) Å, c ) 12.746(2) Å, â ) 99.26(2) °, V ) 1280.0 (4)
Å3, Z ) 4, Fcalcd ) 1.143 cm-3, F(000) ) 356, µ ) 0.053 mm-1, of
2246 unique reflections 1724 were observed [Fo > 4σ(Fo)], 197
parameters, R1 ) 0.0708, wR2 ) 0.1399 (for observed data), S ) 1.042;
maximum and minimum residual electron density, 0.237 and -0.202
1J(B,H) ) 114, 1B), -6.49 (d, 1J(B,H) ) 164, 1B), -9.43 (d, 1J(B,H)
1
) 158, 5B), -12.75 (d, J(B,H) ) 169, 1B), -23.19 (s, 1B, B(3)).
3-Phenyl-1,2-dicarba-closo-dodecaborane. To a stirring solution
of 3-iodo-1,2-dicarba-closo-dodecaborane (1.35 g, 5 mmol), in THF
(50 mL) at 0 °C, was added, dropwise, a solution of phenylmagnesium
bromide (20 mmol) in the same solvent. After stirring at room
temperature for 30 min, [PdCl2(PPh3)2] (140 mg, 4% equiv) and CuI
(38 mg, 4% equiv) were added in a single portion, following which
the reaction mixture was heated to reflux for 3 days. The solvent was
removed, and 100 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 purified by flash silica gel
chromatography using dicloromethane/hexane (1:4) as the eluting
solvent to give 3-phenyl-1,2-dicarba-closo-dodecaborane. Yield: 0.95
g (86%). Anal. Calcd for C8H16B10: C, 43.61; H, 7.32. Found: C, 43.75;
H, 7.34. IR: ν [cm-1] ) 3064 (Ccluster-H), 3010 (Caryl-H), 2646, 2635,
e Å-3
.
Acknowledgment. This work was supported by CICYT
(Project MAT98-0921), Generalitat de Catalunya (Grant
2000SGR00108 and CESCA), and the Spanish Ministerio de
Ciencia y Tecnolog´ıa (a contract) (J.M.O.).
Supporting Information Available: Crystallographic data for 1-Ph-
3-Br-1,2-C2B10H10 and 3-Ph-1,2-C2B10H11 in CIF format. GIAO
calculated 11B and 13C NMR chemical shifts in carboranes 3-X-1,2-
closo-C2B10H11 (X ) F, Cl, Br, I, Ph) and 3-X-1-R-1,2-closo-C2B10H10
(X ) Br, I and R ) Me, Ph). Experimental and GIAO computed 11B
NMR chemical shifts in 3-I-1,2-closo-C2B10H11 using the Hartree-
Fock and B3LYP approaches with the “Gen” and LANL2DZ basis sets.
This material is available free of charge via the Internet at http://
pubs.acs.org. Crystallographic data (excluding structure factors) for the
structures reported in this paper also have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publications
no. CCDC-162671 and CCDC-154906 for 1-Ph-3-Br-1,2-C2B10H10 and
3-Ph-C2B10H11, respectively. Copies of the data can be obtained free
of charge on application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. (fax, (+44) 1223-336-033; E-mail,
deposit@ccdc.cam.ac.uk).
1
2619, 2608, 2602, 2596, 2556 (B-H). H NMR: δ ) 8.00-7.30 (m,
5H, Haryl), 3.71 (br s, 2H, Ccluster-H), 3.50-0.50 (br m, 9H, B-H).
13C{1H} NMR: δ ) 133.06, 132.03, 129.77, 128.30 (Caryl), 56,69 (s,
1
C
cluster). 11B NMR: δ ) -2.06 (d, J(B,H) ) 149, 2B), -4.71 (s, 1B,
B(3)), -8.16 (d, 1J(B,H) ) 147, 1B), -12.62 (d, 3B), -13.29 (d,
1J(B,H) ) 169, 3B).
3-Biphenyl-1,2-dicarba-closo-dodecaborane. An entirely analogous
reaction, but using 4-biphenylmagnesium bromide (20 mmol) and
chromatography using dichloromethane/hexane (4:1) as eluting solvent,
gave 3-biphenyl-1,2-dicarba-closo-dodecaborane. Yield: 1.4 g (94%).
Anal. Calcd for C14H20B10: C, 56.73; H, 6.80. Found: C, 56.64; H,
6.78. IR: ν [cm-1] ) 3060 (Ccluster-H), 3028 (Caryl-H), 2623, 2601,
IC010493O
1
(44) XSCANS, Data collection and reduction programme, version 2.3;
Bruker AXS: Madison, WI, 1994.
(45) SHELXTL: Sheldrick, G. M. Structure determination and refinement
programmes, version 5.1; Bruker AXS: Madison, WI, 1999.
(46) Todd, L. J.; Siedle, A. P. Prog. Nucl. Magn. Reson. Spectrosc. 1979,
13, 87.
2567 (B-H), 1479 (γ (C-C)aryl). H NMR: δ ) 7.70-7.20 (m, 9H,
H
aryl), 3.73 (br s, 2H, Ccluster-H), 2.50-1.10 (br m, 9H, B-H). 13C{1H}
NMR: δ ) 142.66, 141.24, 140.43, 134.28, 129.44, 128.43, 127.86,
127.68 (Caryl), 57.35 (s, Ccluster). 11B NMR: δ ) -2.01 (d, J(B,H) )
1
150, 2B), -4.75 (s, 1B, B(3)), -8.14 (d, 1J(B,H) ) 150, 1B), -12.63
(d, 6B).
(47) From Jones, M., Jr., private communcation.