Palladium-catalyzed amination of 2-Iodo-para-carborane

Article abstract of DOI:10.1021/om0611756

The palladium-catalyzed Buchwald-Hartwig amination of B-iodocarborane by various azoles and amines is described for the first time. The reactions of 2-iodo-p-carborane with indole, imidazole, benzimidazole, or carbazole in the system Pd(dba)₂-BINAP-Bu^tONa in dioxane at 100 °C gave 2-p-carboranyl derivatives of these azoles in high yields together with 2-hydroxy-p-carborane as a side product. The reactions of 2-iodo-p-carborane with aromatic amines in the same system gave the amination products in 60-70% yields and also were accompanied by the formation of hydroxy derivatives (up to 30% yields). In a special investigation it was shown that the base Bu ^tONa was responsible for its formation. The principle possibility of the amination of 2-iodo-p-carborane by morpholine (with 30% yield) as an example of aliphatic amination was shown. The structures of N-(1,12-dicarba-closo- dodecaboran-2-yl)carbazole (1), N-(1, 12-dicarba-closo-dodecaboran-2-yl) benzimidazole (2), N-(1, 12-dicarba-closo-dodecaboran-2-yl)indole (4), and 2-hydroxy-1,12-dicarba-closo-dodecaborane (5) have been established by X-ray diffraction studies.

Full text of DOI:10.1021/om0611756

2340
Organometallics 2007, 26, 2340-2347
Palladium-Catalyzed Amination of 2-Iodo-para-carborane
Irina P. Beletskaya,*,† Vladimir I. Bregadze,*,‡ Kuanysh Z. Kabytaev,†
Galina G. Zhigareva,‡ Pavel V. Petrovskii,‡ Ivan V. Glukhov,‡ and Zoya A. Starikova‡
Chemistry Department, M. V. LomonosoV Moscow State UniVersity, Leninskye Gory, 119992, Moscow,
Russian Federation, and A. N. NesmeyanoV Institute of Organoelement Compounds, 28 VaViloV Street,
119991 Moscow, Russian Federation
ReceiVed December 25, 2006
The palladium-catalyzed Buchwald-Hartwig amination of B-iodocarborane by various azoles and
amines is described for the first time. The reactions of 2-iodo-p-carborane with indole, imidazole,
benzimidazole, or carbazole in the system Pd(dba)2-BINAP-ButONa in dioxane at 100 °C gave 2-p-
carboranyl derivatives of these azoles in high yields together with 2-hydroxy-p-carborane as a side product.
The reactions of 2-iodo-p-carborane with aromatic amines in the same system gave the amination products
in 60-70% yields and also were accompanied by the formation of hydroxy derivatives (up to 30% yields).
In a special investigation it was shown that the base ButONa was responsible for its formation. The
principle possibility of the amination of 2-iodo-p-carborane by morpholine (with 30% yield) as an example
of aliphatic amination was shown. The structures of N-(1,12-dicarba-closo-dodecaboran-2-yl)carbazole
(1), N-(1,12-dicarba-closo-dodecaboran-2-yl)benzimidazole (2), N-(1,12-dicarba-closo-dodecaboran-2-
yl)indole (4), and 2-hydroxy-1,12-dicarba-closo-dodecaborane (5) have been established by X-ray
diffraction studies.
routes for attaching the carborane cluster to the organic moiety,
using either the carbon atom or the boron atom of the carborane
cage.
Introduction
There is a growing interest in the synthesis of compounds
that combine carborane clusters and organic units, due to their
potential applicability for nanoarchitectural and supramolecular
constructions,1-4 nonlinear optical materials,2,5,6 or medicinal
chemistry.7 The nature of the carborane cage opens two different
The substitution at the carbon atom in carborane derivatives
is widely described,8 while the preparation of boron derivatives
is more challenging. New possibilities for the carborane cage
functionalization at the boron atom are opened by the palladium-
catalyzed cross-coupling reactions of B-halogen carboranes, in
spite of the fact that there is a great difference in behavior
between the Csp2-Hal bond and the carborane B-Hal bond in
oxidative addition. Until now all attempts to detect the formation
of a Pd-intermediate with a B-Pd-I bond have failed;9 however
a few Pd-catalyzed cross-coupling reactions at the B-I bond
have been carried out.10,11
* To whom correspondence should be addressed. E-mail: (I.B.)
beletska@org.chem.msu.ru; (V.B.) bre@ineos.ac.ru.
† Chemistry Department, M. V. Lomonosov Moscow State University.
‡ A. N. Nesmeyanov Institute of Organoelement Compounds.
(1) (a) Yang, X.; Jiang, W.; Knobler, C. B.; Hawthorne, M. F. J. Am.
Chem. Soc. 1992, 114, 9719. (b) Mueller, J.; Base, K.; Magnera, T. F.;
Michl, J. J. Am. Chem. Soc. 1992, 114, 9721. (c) Scho¨berl, U.; Magnera,
T. E.; Harrison, R. M.; Fleischer, F.; Pflug, J. L.; Schwab, P. F. H.; Meng,
X.; Lipiak, D.; Noll, B. C.; Allured, V. S.; Rudalevige, T.; Lee, S.; Michl,
J. J. Am. Chem. Soc. 1997, 119, 3907. (d) Schwab, P.; Levin, M. D.; Michl,
J. Chem. ReV. 1999, 99, 1863.
The carborane derivatives with a boron-carbon bond can be
prepared by cross-coupling reactions of B-iodocarboranes with
active organometallic compounds,3,10-12 terminal alkynes,3,12 and
(2) (a) Murphy, D. M.; Mingos, D. M. P.; Forward, J. M. J. Mater. Chem.
1993, 3, 67. (b) Murphy, D. M.; Mingos, D. M. P.; Haggitt, J. L.; Powell,
H. R.; Westcott, S. A.; Marder, T. B.; Taylor, N. J.; Kanis, D. R. J. Mater.
Chem. 1993, 3, 139.
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R. F.; Codogni, I. M.; Wilson, J. G. Chem. ReV. 1998, 98, 1515. (b)
Hawthorne, M. F.; Maderna, A. Chem. ReV. 1999, 99, 3421. (c) Valliant,
J. F.; Guenther, K. J.; King A. S. Coord. Chem. ReV. 2002, 232, 173. (d)
Endo, Y.; Iijima, T.; Yamakoshi, Y.; Fukasawa, H.; Miyaura, C.; Inada,
M.; Kubo, A.; Itai, A. Chem. Biol. 2001, 8, 341. (e) Bregadze, V. I.; Sivaev,
I. B.; Glazun, S. A. Anti-Cancer Agents Med. Chem. 2006, 6, 75.
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Hawthorne, M. F. Inorg. Chem. 1995, 34, 3491. (b) Jiang, W.; Knobler, C.
B.; Hawthorne, M. F. Inorg. Chem. 1996, 35, 3056. (c) Jiang, W.; Harwell,
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30, 267. (e) Bayer, M. J.; Herzog, A.; Diaz, M.; Harakas, G. A.; Lee, H.;
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10.1021/om0611756 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 03/27/2007

Palladium-Catalyzed Amination of 2-Iodo-para-carborane
Organometallics, Vol. 26, No. 9, 2007 2341
Table 1. Reaction of 2-Iodo-p-carborane with Carbazolea
Scheme 1
Pd(dba)2/
ligand, %
time,
h
yieldb
yieldb
entry
base
B-N (1), % B-OH (5), %
1
2
3
4
5
5/5 BINAP
ButONa
ButONa
48
48
48
48
69 (57)
67
29
28
31
3
5/7.5 BINAP
5/7.5 Tol-BINAP ButONa
58
5/5 BINAP
5/5 BINAP
NaH
Cs2CO3 48
90c (78)
7
0
a Reaction conditions: 0.1 mmol of 2-iodo-p-carborane, 0.1 mmol of
b
carbazole, 1.2 mmol of base, catalyst, 1 mL of dioxane, 100 °C. Yield
determined by 11B NMR; the yield of isolated product is shown in
c
parentheses. Carbazole pretreated with NaH was added to the reaction
mixture.
Scheme 2
arylboronic acids,13 as well as by the carboranylation of styrenes
(i.e., the boron analogue of the Heck reaction).14 Recently we
have demonstrated that boron-substituted pyridyl- and quinolyl-
ethynyl derivatives of m- and p-carboranes can be prepared by
the palladium-catalyzed cross-coupling of 9-iodo-m- and 2-iodo-
p-carborane and the corresponding acetylenes or their magne-
sium derivatives.15
These results allowed us to anticipate a possible extension
of Pd-catalyzed reactions to boron-heteroatom bond forming
processes and especially to the amination of carboranes at the
boron atom using the Buchwald-Hartwig procedure.16 Herein
we report that this type of reaction has been accomplished for
the first time for 2-iodo-1,12-dicarba-closo-dodecaborane (2-
iodo-p-carborane) under the action of azoles or aromatic and
aliphatic amines. The catalytic cycle of this reaction is presented
in Scheme 1.
or by the reaction of 1,7-C2H2B10H9(2-COOH) with HN3.19a,b
The only known B-substituted amino derivative of p-carborane,
2-amino-p-carborane, was obtained by the latter method.19c
Results and Discussion
Amination of 2-Iodo-p-carborane by Azoles. It is known
that almost each Pd-catalyzed amination requires its “own”
ligand depending on the nature of haloarenes and amine. The
yields of such reactions usually depend on the L/Pd ratio and
the nature of the base. Therefore we have carried out a wide
optimization of the reaction conditions, mainly using carbazole
as an example. It was shown that the Buchwald-Hartwig
reaction can be applied to the amination of 2-iodo-p-carborane
by azoles (Scheme 2).
However there is a peculiarity in the reaction with carbazole.
Under classical conditionssPd(dba)2-BINAP-ButONa in di-
oxane at 100 °Csa comparable amount of the hydroxy
derivative of carborane (B-OH) (5) (∼30%) was formed along
with the amination product (∼70%) (Table 1, entries 1-3). The
formation of phenols has been never described during the
amination of haloarenes. The application of Cs2CO3, commonly
used in the arylation of azoles, turned out to be inefficient (Table
1, entry 5). The problem was solved by the use of NaH as a
base, resulting in a high yield of the product (∼90%) (Table 1,
entry 4). The isolated yields are generally much lower than the
yields estimated by 11B NMR due to losses during the
chromatography.
It is known that the amino group can be introduced at the
boron atom of o-carborane by the reaction of ammonia with
o-carborane dianion in liquid ammonia solution.17 In the same
way the N-piperidyl derivative of o-carborane was obtained.17b
Although the mechanism of this reaction is unknown, it was
suggested that two additional electrons in the o-carborane
dianion increase the hydride lability of hydrogen at the boron
atom, and the reaction of this dianion with ammonia leads to
the evolution of H2 and the formation of the B-N bond.17b,c
The mechanism of this reaction was also considered as the
bimolecular nucleophilic substitution of the hydride anion with
an amide anion.17c Only the amino derivatives of o-carborane
can be obtained by this method because m- and p-carborane
dianions undergo isomerization into o-carborane under these
conditions.17b Amino derivatives of m-carborane with the B-N
bond could be prepared by indirect ways: either by insertion
ofdiphenylaminodichloroboraneintonido-carborane[m-C2B9H12]- 18
(13) Eriksson, L.; Beletskaya, I. P.; Bregadze, V. I.; Sivaev, I. B.; Sjo¨berg,
S. J. Organomet. Chem. 2002, 657, 267.
Unlike carbazole, all other azoles with different values of
pKa (benzimidazole 12.8, imidazole 14.5, indole 17) in the
presence of ButONa gave good results and formation of B-OH
(5) was negligible. In some cases less expensive MeONa can
also be used successfully (Table 2, entry 4; Table 3, entry 4).
The best results have been obtained for 5 mol % [Pd]
(Pd:BINAP ) 1:1). The decrease of catalyst concentration leads
to a reduction of product yields (Table 2, entries 2 and 5; Table
(14) Eriksson, L.; Winberg, K.-J.; Claro, R. T.; Sjo¨berg, S. J. Org. Chem.
2003, 68, 3569.
(15) (a) Beletskaya, I. P.; Bregadze, V. I.; Ivushkin, V. A.; Petrovskii,
P. V.; Sivaev, I. B.; Sjo¨berg, S.; Zhigareva, G. G. J. Organomet. Chem.
2004, 689, 2920. (b) Beletskaya, I. P.; Bregadze, V. I.; Ivushkin, V. A.;
Zhigareva, G. G.; Petrovskii, P. V.; Sivaev, I. B. Russ. J. Org. Chem. 2005,
41, 1359.
(16) (a) Hartwig, J. F. Angew. Chem., Int. Ed. 1998, 37, 2046. (b) Wolfe,
J. P.; Wagaw, S.; Marcous, J.-F.; Buchwald, S. L. Acc. Chem. Res. 1998,
31, 805.
(17) (a) Zakharkin L. I.; Kalinin V. N. IzV. Akad. Nauk SSSR, Ser. Khim.
1967, 2585. (b) Zakharkin L. I.; Kalinin V. N.; Gedymin V. V. J.
Organomet. Chem. 1969, 16, 371. (c) Brattsev, V. A.; Stanko, V. I. Russ.
J. Gen. Chem. 1969, 39, 2144.
(19) (a) Zakharkin L. I.; Kalinin, V. N.; Gedymin, V. V. Synth. React.
Inorg. Met. Org. Chem. 1973, 3, 93. (b) Zakharkin, L. I.; Kalinin, V. N.;
Gedymin, V. V. Russ. J. Gen. Chem. 1973, 43, 1974. (c) Zakharkin, L. I.;
Kalinin, V. N.; Kobelkova, N. I. Russ. J. Gen. Chem. 1980, 50, 919.
(18) Roscoe J. S.; Kongpricha S.; Papetti S. Inorg. Chem. 1970, 9, 1561.

2342 Organometallics, Vol. 26, No. 9, 2007
Beletskaya et al.
Table 2. Reaction of 2-Iodo-p-carborane with
Table 4. Reaction of 2-Iodo-p-carborane with Imidazole and
Benzimidazolea
Triazolesa
a Reaction conditions: 0.1 mmol of 2-iodo-p-carborane, 0.1 mmol of
azole, 1.2 mmol of ButONa, catalyst 5% Pd(dba)2/5% BINAP, 1 mL of
b
dioxane, 100 °C, 48 h. Yield determined by 11B NMR; the yield of isolated
product is shown in parentheses.
Table 5. Amination of 2-Iodo-p-carborane by Aromatic
Aminesa
yieldb
yieldb
entry
amine
C6H5NH2
p-ClC6H4NH2
base (equiv)
product B-N,% 5, %
1
2
3
4
5
6
7
ButONa (1.2)
ButONa (1.2)
6
7
8
8
8
8
8
68 (59)
68c
66 (47)
11
25
34
32
32
34
7
0
5
p-MeOC6H4NH2 ButONa (1.2)
p-MeOC6H4NH2 MeONa (1.2)
p-MeOC6H4NH2 Cs2CO3 (1.2)
p-MeOC6H4NH2 NaOH (1.6)
p-MeOC6H4NH2 K2CO3 (1.4) +
18-crown-6 (1.4)
56
0
a Reaction conditions: 0.1 mmol of 2-iodo-p-carborane, 0.1 mmol of
b
benzimidazole, 1.2 mmol of base, catalyst, 1 mL of dioxane, 100 °C. Yield
a Reaction conditions: 0.1 mmol of 2-iodo-p-carborane, 0.1 mmol of
determined by 11B NMR; the yield of isolated product is shown in
parentheses.
amine, base, Pd(dba)2 5 mol %, BINAP 5 mol %, 1 mL of dioxane, 100
b
°C. Yield determined by 11B NMR; isolated yield is shown in parentheses.
cCannot be separated from 5.
Table 3. Reaction of 2-Iodo-p-carborane with Indolea
Pd(dba)2/
ligand, %
time,
h
yieldb
yieldb
azole under formation of an anion. The use of CuI as a well-
known cocatalyst in the arylation of azoles16 was not successful
in this case.
Amination of 2-Iodo-p-carborane by Aromatic Amines.
The reaction of 2-iodo-p-carborane with aromatic amines
p-XC6H4NH2 (X ) H, Cl, OMe) in the system 5% Pd(dba)2-
5% BINAP-ButONa in dioxane (100 °C) gave the products in
good yields but was also accompanied by the formation of 5 in
30% yield (Scheme 3).
entry
base
B-N (4), % B-OH (5), %
1
2
3
4
5
6
5/5 BINAP ButONa
2/2 BINAP ButONa
5/5 BINAP MeONa
5/5 BINAP MeONa
2/2 BINAP MeONa
48
48
24
72
72
24
89 (63)
13
59
64
8
10
0
0
0
0
5/5 dppf
MeONa
27
0
a Reaction conditions: 0.1 mmol of 2-iodo-p-carborane, 0.1 mmol of
b
indole, 1.2 mmol of base, catalyst, 1 mL of dioxane, 100 °C. Yield
determined by 11B NMR; the yield of isolated product is shown in
parentheses.
The yield of amination product is practically the same for
amines with both electron-withdrawing and electron-donating
substituents (Table 5).
3, entries 2 and 5). An attempt to change BINAP to other mono-
or bidentate ligands including Buchwald’s ligands (Table 2,
entries 6-10) has been unsuccessful. Increasing the amount of
ligand or the use of Tol-BINAP in place of BINAP has led to
no improvement of yields and selectivity (Table 1, entries 2
and 3).
The attempt to replace ButONa by other bases and avoid the
formation of B-OH product was not successful. In all cases
Scheme 3
Thus for azoles having pKa values in the range 12.8-17 we
found the conditions for N-carboranylation in high yields. It is
difficult to discuss the influence of the pKa value on the
reactivity of azoles because the high acidity produces the
N-anion more easily but decreases at the same time the
nucleophilicity of this anion.
(Table 5, entries 4-7) a decrease in the yields was observed.
The only exception is the system K2CO3-18-crown-6 ether,
which allowed an increase in yield of up to 56% (Table 5,
entry 7).
Amination of 2-Iodo-p-carborane by Aliphatic Amines.
The amination of 2-iodo-p-carborane by morpholine (Scheme
Very acidic azoles, triazole and benzotriazole (pKa 10.3 and
8.2, correspondingly), gave poor yields due to their low
nucleophilicity (Table 4, entries 2 and 3). A small amount of 5
is formed in these reactions due to consumption of ButONa by

Palladium-Catalyzed Amination of 2-Iodo-para-carborane
Organometallics, Vol. 26, No. 9, 2007 2343
Table 6. Reaction of 2-Iodo-p-carborane with Morpholinea
Figure 1. Molecular structure of one of the independent molecules
(B) of N-(1,12-dicarba-closo-dodecaboran-2-yl)carbazole (1) (50%
probability thermal ellipsoids). Selected bond distances (Å) for A[B]
molecules: N(1)-B(2) 1.481(5) [1.472(5)], C(1)-B(2) 1.743(6)
[1.725(6)], C(1)-B(3) 1.745(5) [1.655(6)], C(1)-B(4) 1.747(6)
[1.677(6)], C(1)-B(5) 1.673(8) [1.691(6)], C(1)-B(6) 1.660(8)
[1.719(6)], C(12)-B(7) 1.687(6) [1.651(7)], C(12)-B(8) 1.704(6)
[1.718(9)], C(12)-B(9) 1.704(6) [1.705(7)], C(12)-B(10) 1.659-
(7) [1.659(6)], C(12)-B(11) 1.713(6) [1.648(7)]. Bond angle C(2)-
N(1)-C(14): 105.0(5)° [107.5(5)°].
a Reaction conditions: 0.1 mmol of 2-iodo-p-carborane, 0.12 mmol of
morpholine, 0.1 mmol of ButONa, 1 mL of dioxane, 100 °C, 48 h, 5 mol
b
c
% Pd(dba)2, yield based on 11B NMR. Solvent: toluene. 5 mol %
Pd(OAc)2, solvent toluene.
Table 7. Preparation of 2-Hydroxy-p-carborane (5)a
entry
base (equiv)
time, h
5, %
ButONa (1)
ButONa (3)
K3PO4b (2)
NaOH (2)
20
20
65
40
16
90
0
Figure 2. Structure of N-(1,12-dicarba-closo-dodecaboran-2-yl)-
benzimidazole (2) (50% probability thermal ellipsoids). Selected
bond distances (Å): N(1)-B(2) 1.481(2), C(1)-B(3) 1.713(3),
C(1)-B(4) 1.700(3), C(1)-B(5)1.707(3), C(1)-B(6) 1.6933, C(12)-
B(7) 1.700(3), C(12)-B(8) 1,702(3), C(12)-B(9) 1.707(3), C(12)-
B(10) 1.714(3), C(12)-B(11) 1.705(3). Selected bond angles
(deg): C(2)-N(1)-C(3) 104.4(2), C(2)-N(2)-C(8) 106.5(2).
1
2
3
4
0
a Reaction conditions: 0.1 mmol of 2-iodo-p-carborane, 5% Pd(dba)2,
5% BINAP, 1 mL of dioxane, 100 °C, yield based on 11B NMR. In the
b
presence of 0.2 mmol of water.
6, entries 2, 3). The use of toluene as solvent and Pd(OAc)2 as
catalyst precursor gave worse results (Table 6, entry 10). It is
known that the amination of haloarenes by aliphatic amines
containing â-hydrogen atoms is often accompanied by the
reduction of the halogen-carbon bond.16 This process was found
to compete (together with formation of 5) with the amination
of 2-iodo-p-carborane by morpholine. Neither BINAP nor other
ligands carried out this reaction selectively (Table 6).
4) as an example of the reaction with aliphatic amines under
the same conditions gave poor results. The system Pd(dba)2-
BINAP-ButONa has been found to be unselective, giving along
with the B-N compound significant amounts of 5 and the
product of reduction (p-carborane) (Table 6, entry 1). After
48 h we have found 30% 9, 20% 5, and 19% p-carborane.
Scheme 4
Reaction of 2-Iodo-p-carborane with Different Bases. A
special investigation has been carried out in order to elucidate
the source of the hydroxy group in 2-hydroxy-p-carborane (5).
For this purpose we have studied the reactions of 2-iodo-p-
carborane with different bases (Table 7). The reactions of
2-iodo-p-carborane with NaOH (Table 7, entry 4) and with K3-
PO4 in the presence of water (Table 7, entry 3) did not lead to
the formation of 5. In the case of a 3-fold excess of ButONa, 5
was formed in 90% yield (Table 7, entry 2).
The use of other ligands such as P(o-tolyl)3, PCy3, and IMes‚
HCl, as well as the bidentate ligand Cy2Xantphos was also
ineffective (Table 6, entries 4-6, 9). Only in the presence of
di(tert-butyl)biphenylphosphine or (t-Bu)3P‚HBF4 did the de-
sired product yield increase to 39% and 43%, respectively (Table
The process of hydroxy derivative formation is still uncertain.
It is known that this compound was formed as a side product

2344 Organometallics, Vol. 26, No. 9, 2007
Beletskaya et al.
Figure 3. Structure of one of the independent molecules (B) of
N-(1,12-dicarba-closo-dodecaboran-2-yl)indole (4) (50% probability
thermal ellipsoids). Selected bond distances (Å) for A [B] mol-
ecules: N(1)-B(2) 1.468(3) [1.478(3)], C(1)-B(2) 1.737(4) [1.737-
(4)], C(1)-B(3) 1.717(4) [1.709(4)], C(1)-B(4) 1.701(4) [1.717(4)],
C(1)-B(5) 1.702(4) [1.698(4)], C(1)-B(6) 1.695(4) [1.703(4)],
C(12)-B(7) 1.707(4) [1.710(4)[. C(12)-B(8) 1.698(5) [1.718(4)],
C(12)-B(9) 1.714(4) [1.702(4)], C(12)-B(10) 1.710(4) [1.697-
(4)], C(12)-B(11) 1.714(4) [1.705(4)]. Bond angle C(2)-N(1)-
C(9): 106.8(2)° [106.5(2)°].
Figure 5. Molecular structure of one of the independent molecules
in the crystal of 2-hydroxy-1,12-dicarba-closo-dodecaborane (5)
(30% probability thermal ellipsoids). Selected average bond
distances (Å, the average deviation is equal to 0.003): O(2)-B(2)
1.381, C(1)-B(2) 1.734, C(1)-B(3) 1.698, C(1)-B(4) 1.701,
C(1)-B(5) 1.704, C(1)-B(6) 1.700, C(12)-B(7) 1.699, C(12)-
B(8) 1.702, C(12)-B(9) 1.701, C(12)-B(10) 1.701, C(12)-B(11)
1.701.
The crystals 1 and 4 contain two crystallographically inde-
pendent molecules in the unit cell (A and B), which have the
same structures in 4, but in 1 the independent molecules differ
in the relative disposition of the aromatic system with respect
to the carborane moiety by 30.4°; namely, they are rotamers.
The dihedral angle (deg) between the plane of the B(2)-B(3)-
B(4)-B(5)-B(6) atoms and the plane of the heterocyclic system
is 28.2° and 58.6° (for A and B) and 24.2°, 29.0°, and 32.4°
(for A and B), respectively, in the structures 1, 2, and 4.
Heterocyclic systems in all structures have conventional planar
structures with the standard geometrical parameters.
In 1, 2, and 4 the B-B bonds in the p-carborane moiety
located in the parallel five-membered rings (B(2), B(3), B(4),
B(5), B(6) and B(7), B(8), B(9), B(10), B(11)) are equal (av
1.783 Å) and slightly longer than the B-B bonds between the
cycles (av 1.769 Å). This means that the introduction of a
substituent in position 2 of the p-carborane icosahedron does
not change the B-B bond’s nature and influences only the
carbon-boron bond, increasing the bond length B(2)-C(1) (av
1.734 Å) in comparison with all other C(1)-B bonds (1.693-
1.717 Å) and C(12)-C (1.697-1.718 Å) bonds. This can be
explained by the π-electron back-donation from the aromatic
ring to the antibonding orbital of the C-B bond, similar to the
one found for C- and B-aryl derivatives of o- and m-
carboranes.21 In the unsubstituted p-caborane22 the bond length
distribution is the same as in 1, 2, and 4: the B-B bonds in
the B5-cycles are longer (av 1.781 Å) in comparison to the bonds
between the cycles (av 1.760 Å), and on average the B-C bond
lengths are equal to 1.705 Å. We have not found any structure
of N-substituted o-, m-, and p-carboranes similar to 1, 2, and 4
in the Cambridge Structural Database [The Cambridge Structural
Figure 4. Centosymmetric H-bonded dimer in 2 (H-bond param-
eters: C(1)-H(1A) 0.95(2) Å, distances N(2)‚‚‚C(1) and H(1A)‚
‚‚N(2) 3.239(3) and 2.46(2) Å, respectively, C(1)-H(1A)‚‚‚N(2)
bond angle 139°).
in the Heck reaction in the presence of water when K3PO4 was
used as catalyst.20 In our case the reactions of 2-iodo-p-carborane
with NaOH and K3PO4 in the presence of water did not lead to
the formation of hydroxy derivative 5 (Table 7, entries 3, 4).
So, namely, ButONa is the source of the hydroxy derivative in
the reaction. Indeed, we showed that the hydroxy derivative
was formed in almost quantitative yield in usual reaction
conditions using an excess of ButONa (Table 7, entry 2). We
could suggest that unlike ArPdXL2 the palladium intermediate
p-C2H11B10-PdL2I is able to react with ButO-, giving p-
C2H11B10-Pd-OBut, which decomposes with elimination of
isobutene to give p-C2H11B10OH (5). Compound 5 was isolated
and its structure has been investigated.
The structures of the compounds obtained were confirmed
by 1H and 11B NMR, mass spectrometry, and elemental analysis.
The X-ray crystal structures of compounds 1, 2, 4, and 5 were
determined.
Description of the Structures. Molecular structures of N-(1,-
12-dicarba-closo-dodecaboran-2-yl)carbazole (1), N-(1,12-di-
carba-closo-dodecaboran-2-yl)benzimidazole (2), and N-(1,12-
dicarba-closo-dodecaboran-2-yl)indole (4) are given in Figures
1, 2, and 3.
(21) Glukhov, I. V.; Lyssenko, K. A.; Korlyukov, A. A.; Antipin, M.
Yu. Faraday Discuss. 2007, 203
(20) Beletskaya, I. P.; Davydov, D. V., Moreno-Manas, M. Tetrahedron
Lett. 1998, 39, 5617.
(22) Davidson, M. G.; Hibbert, T. G.; Howard, J. A. K.; Mackinnon,
A.; Wade, K. Chem. Commun. 1996, 2285.

Palladium-Catalyzed Amination of 2-Iodo-para-carborane
Organometallics, Vol. 26, No. 9, 2007 2345
Figure 6. Double layers in the structure 5 (average H-bond parameters: O(2A)-H(2A) 0.82(2) Å, distances O(2A)‚‚‚O(2B) and H(2A)‚
‚‚O(2B) 2.617 and 1.81 Å, respectively, O(2A)-H(2A)‚‚‚O(2B) bond angle 170.2°).
Table 8. Crystal Data and Structure Refinement for 1, 2, 4, and 5
1
2
4
5
formula
mol wt
C14H19B10N
309.40
C9H16B10N2
260.34
C10H17B10N
259.35
C2H12B10O
160.22
cryst color, habit
cryst size, mm
cryst syst
space group
cell constants
a, Å
colorless, needle
0.25 × 0.20 × 0.15
monoclinic
P21
colorless, plate
0.4 × 0.3 × 0.2
triclinic
colorless, needle
0.6 × 0.4 × 0.2
monoclinic
P21
colorless, prism
0.21 × 0.17 × 0.13
monoclinic
C2/c
P1h
13.922(4)
7.835(2)
15.145(4)
90
90.420(5)
90
1651.9(8)
4
1.244
7.167(1)
9.142(1)
10.977(1)
86.316(3)
76.466(3)
77.876(3)
683.5(2)
2
9.834(2)
13.467(2)
10.802(2)
90
90.274(3)
90
1430.5(4)
4
24.445(2)
13.346(1)
23.753(2)
90
104.829(2)
90
7491.4(11)
32
1.136
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
D
calcd, g cm-3
1.265
1.204
2θmax, deg
54
0.063
12 005
0.972
56
0.064
5372
0.982
54
0.059
8512
0.969
54
0.055
35 537
1.000
abs coeff, µ(Mo KR), mm-1
no. reflns collected
completeness
no. indep reflns
no. obsd reflns (I > 2σ(I))
abs struct param
no. of params
6343 (Rint ) 0.0680)
3174 (Rint ) 0.0433)
5494 (Rint ) 0.0315)
8179
3666
4461
1977
4780
0(2)
4(4)
451
190
379
657
R1 (on F for obsd reflns)
wR2 (on F2 for all reflns)
weighting scheme
A
0.0780
0.1338
0.0606
0.1182
0.0556
0.1230
0.0547
0.1287
w-1 ) σ2(Fo ) + (aP)2 + bP, P ) 1/3(Fo2 + 2Fc )
2
2
0.0016
0.0212
0.0166
0.018
B
1.1889
0.3550
1.2683
F(000)
640
268
536
2624
GOOF
1.019
0.197 and -0.241
1.016
0.271 and -0.208
1.015
0.252 and -0.218
1.046
0.263 and -0.272
largest diff peak and hole, e Å-3
Database, release 1.8 (November 2005)]. In the structures of
N-substituted o-carboranes the B-N bond lenghts in 3-cyano-
(1.46323 and 1.467 Å24) and 3-aminocarbonyl-1,2-dicarba-closo-
dodecaboranes (1.46924 and 1.460 Å25) are shorter than the
N(1)-B(2) bond (av 1.476 Å) in 1, 2, and 4.
structure 2 are centrosymmetric dimers formed (see Figure 4)
due to the presence of rather weak hydrogen bonds C(1)-
H(1A)‚‚‚N(2).
The structure of 2-hydroxy-p-carborane (5) is given in Figure
5. So far there have not been reported any crystal structures of
monohydroxy derivatives of carboranes. The crystal 5 is
monoclinic with four independent molecules in the unit cell,
which have the same structure. The B-O bond lengths are
within the range 1.391-1.385 Å (av 1.389 Å). The same B-O
bond lengths were found for B-decahydroxy-p-carborane 1,12-
H2-1,12-C2B10(OH)10 (av 1.394 Å),26 in closo-2,3,4,5,6,7,8,9,-
10,11-decamethoxy-1,12-bis(sulfonic acid)-1,12-dicarbadode-
caborane, and for its sodium and potassium salts (av 1.390 Å).27
The packing of molecules in structures 1, 2, and 4 is defined
by the van der Waals interactions between the atoms. Only in
(23) Morel, P.; Schaffer, P.; Valliant, J. F. J. Organomet. Chem. 2003,
668, 25.
(24) Valliant, J. F.; Schaffer, P. J. Inorg. Biochem. 2001, 85, 43.
(25) Krasnov, V. P.; Levit, G. L.; Charushin, V. N.; Grishakov, A. N.;
Kodess, M. I.; Kalinin, V. N.; Ol’shevskaya, V. A.; Chupakhin, O. N.
Tetrahedron: Asymmetry 2002, 13, 1833.

2346 Organometallics, Vol. 26, No. 9, 2007
Beletskaya et al.
2.99 (s, 1H, cage C-H), 7.30 (t, 2H, J ) 7.7 Hz, carbazole), 7.44
(t, 2H, J ) 7.7 Hz, carbazole), 8.01 (d, 2H, J ) 8.1 Hz, carbazole),
8.09 (d, 2H, J ) 7.7 Hz, carbazole). Anal. Calcd for C14H19B10N:
C, 54.34; H, 6.19; B, 34.94; N, 4.53. Found: C, 54.39; H, 6.19; B,
35.21; N, 4.06. MS: m/z 309 [M+].
All interatomic distances in 5 are typical for p-carboranes.
The C-B bond lengths are within the range 1.691-1.711Å with
the exception of the C(1)-B(2) bonds, which are longer by ca.
0.03 Å (1.731-1.737 Å) due to the electron lone pair donation
from the oxygen atom of the hydroxy group to the antibonding
orbital of the corresponding C-B bond. Earlier, its existence
was shown by quantum-chemical calculations.28 In the crystal
5 molecules linked by the O-H‚‚‚O hydrogen bond network
(see Figure 6) in the double layers are placed parallel to the ab
plane.
(B) A carbazole was added (66 mg, 0.4 mmol) to a suspension
of sodium hydride (60% dispersion in mineral oil; 0.35 mmol) in
dioxane (3 mL). The mixture was stirred at 100 °C for 15 min,
and then 2-iodo-p-carborane, Pd(dba)2 (8.6 mg, 5%), and BINAP
(9.3 mg, 5%) were added to the mixture. The stirring was continued
at 100 °C for 48 h. The resulting mixture was diluted with 5 mL
of diethyl ether and filtered through a pad of silica gel, and the
solvent was removed under reduced pressure. The crude product
was purified by flash chromatography on silica gel with an eluent
of petroleum ether to afford a colorless crystalline solid (78%).
Conclusion
The palladium-catalyzed cross-coupling of 2-iodo-p-carborane
with various NH nucleophiles (azoles, anilines, and morpholine)
at the boron atom is described for the first time. The best yields
of aminated p-carboranes were reached using the system Pd-
(dba)2-BINAP-ButONa in dioxane at 100 °C. A significant
amount (up to 30%) of 2-hydroxy-p-carborane as a side product
was formed in some of these reactions, most likely due to
reaction of iodo-carborane with ButONa. The compounds with
carbazole, benzimidazole, indole, and hydroxy fragments at the
boron atom of p-carborane have been characterized by X-ray
structural analysis to be the first examples of B-N derivatives
of p-carborane with resolved structures.
N-(1,12-Dicarba-closo-dodecaboran-2-yl)benzimidazole (2)
was prepared according to the general procedure to give a colorless
crystalline solid (71%), mp ) 196-197 °C. 11B NMR: -18.6 (d,
1B, J ) 164 Hz), -16 (d, 2B, J ) 133 Hz), -15.1 (d, 6B, J ) 139
Hz), -5.1 (s, 1B). 1H NMR: 0.8-3.5 (m, 9 H, B-H), 3.01 (s, 1H,
cage C-H), 3.31 (s,1H, cage C-H), 7.29 (t, 1H, J ) 7.0 Hz,
benzimidazole), 7.33 (t, 1H, J ) 7.0 Hz, benzimidazole), 7.81 (d,
1H, J ) 7.0 Hz, benzimidazole), 7.83 (d, 1H, J ) 7.0 Hz,
benzimidazole), 8.07 (s, 1H, benzimidazole). Anal. Calcd for
C9H16B10N2: C, 41.52; H, 6.19; B, 41.53; N, 10.76. Found: C,
41.61; H, 6.28; B, 41.74; N, 10.48. MS: m/z 260 [M+].
N-(1,12-Dicarba-closo-dodecaboran-2-yl)imidazole (3) was
prepared according to the general procedure to give a colorless
crystalline solid (68%), mp ) 115-117 °C. 11B NMR: -19.1 (d,
1B, J ) 178 Hz), -16.2 (d, 2B, J ) 159 Hz), -15.1 (d, 4B, J )
149 Hz), -14.7 (s, 2B J ) 93 Hz), -4.8 (s, 1B). 1H NMR: 1.5-
3.3 (m, 9H, B-H), 3.02 (s, 1H, cage C-H), 3.23 (s, 1H, cage
C-H), 7.09 (s, 1H, imidazole), 7.12 (s, 1H, imidazole), 7.71 (s,
1H, imidazole). Anal. Calcd for C5H14B10N2: C, 28.56; H, 6.71;
N, 13.32. Found: C, 29.02; H, 7.01; N, 12.94. MS: m/z 210 [M+].
Experimental Section
General Comments. All reactions were performed under argon
in oven-dried glassware. Flash chromatography was carried out on
Merck silica gel 60 (4360 mesh), and Merck silica 60 F254 was
used for thin-layer chromatography (TLC). The TLC plates were
developed with palladium chloride in acidified (hydrochloric acid)
methanol solution. Dioxane was dried over sodium benzophenone
ketyl and distilled under argon prior to use. The 1H and 11B NMR
spectra were recorded on Bruker AMX-400 and Varian XL-400
spectrometers at 400 and 128.3 MHz, respectively, from solutions
in CDCl3. The 11B chemical shifts were measured relative to Et2O‚
BF3 as external reference. The mass spectra were obtained on a
Finnigan SSQ-7000 instrument. Elemental analyses were performed
in the Microanalytical Laboratory of INEOS RAS, Moscow, Russia.
General Procedure for Amination Reaction. An oven-dried 5
mL tube was charged with 2-iodo-p-carborane (81 mg, 0.3 mmol),
amine (0.3 mmol), ButONa (34.6 mg, 0.36 mmol), Pd(dba)2 (8.6
mg, 5%), and BINAP (9.3 mg, 5%), and 3 mL of dry dioxane was
added. The tube was evacuated and back-filled with argon. Then
the tube was immersed in a preheated oil bath and stirred at 100
°C for 24-48 h. The reaction was monitored by TLC using
petroleum ether as eluent. The reaction was stopped either after
precipitation of palladium black or when all 2-iodo-p-caborane was
consumed. The resulting mixture was diluted with 5 mL of diethyl
ether and filtered through a pad of silica gel, and the solvent was
removed under reduced pressure. The crude product was purified
by flash chromatography using chloroform or petroleum ether as
eluent.
N-(1,12-Dicarba-closo-dodecaboran-2-yl)indole (4) was pre-
pared according to the general procedure to give a colorless
crystalline solid (63%), mp ) 151-153 °C. 11B NMR: -19.6 (d,
1B, J ) 164 Hz), -16.6 (d, 2B, J ) 155 Hz), -15.5 (d, 4B, J )
147 Hz), -14.7 (d, 2B, J ) 111 Hz), -3.8 (s, 1B). 1H NMR: 1.5-
3.4 (m, 9H, B-H), 2.98 (s, 1H, cage C-H), 3.32 (s, 1H, cage
C-H), 6.63 (d, 1H, J ) 3.3 Hz, indole), 7.19 (t, 1H, J ) 7.6 Hz,
indole), 7.29 (t, 1H, J ) 7.6 Hz, indole), 7.36 (d, 1H, J ) 3.3 Hz,
indole), 7.65 (d, 1H, J ) 7.6 Hz, indole), 7.93 (d, 1H, J ) 7.6 Hz,
indole). Anal. Calcd for C10H17B10N: C, 46.31; H, 6.61; N, 5.40.
Found: C, 46.26; H, 6.53; N, 5.01. MS: m/z 259 [M+].
N-(1,12-Dicarba-closo-dodecaboran-2-yl)benzenamine (6) was
prepared according to the general procedure to give a colorless
crystalline solid (59%), mp ) 93-94 °C. 11B NMR: -21.6 (d,
1B, J ) 167 Hz), -17.2 (d, 2B, J ) 170 Hz), -15.8 (d, 4B, J )
155 Hz), -14.9 (d, 2B, J ) 135 Hz), -3.1 (s, 1B). 1H NMR: 1.5-
3.2 (m, 9H, B-H), 2.82 (s, 1H, cage C-H), 3.08 (s, 1H, cage
C-H), 3.90 (s, 1H, NH), 6.77 (t, 1H, J ) 7.3 Hz, Ph), 6.96 (d, 2H,
J ) 7.7 Hz, Ph), 7.18 (m, 2H, J ) 7.3 Hz, J ) 7.7 Hz, Ph). Anal.
Calcd for C8H17B10N: C, 40.83; H, 7.28; B, 45.94; N, 5.95.
Found: C, 41.10; H, 7.32; B, 46.05; N, 5.62. MS: m/z 235 [M+].
N-(1,12-Dicarba-closo-dodecaboran-2-yl)carbazole (1) was
prepared in two ways. (A) According to the general procedure a
colorless crystalline solid (57%) was obtained, mp ) 166-167 °C.
11B NMR: -18.9 (d, 1B, J ) 169 Hz), -16.4 (d, 2B, J ) 131
Hz), -15.5 (d, 4B, J ) 150 Hz), -14.2 (d, 2B, J ) 167 Hz), -3.7
(s, 1B). 1H NMR: 1.3-3.4 (m, 9 H, B-H), 2.70 (s, 1H, cage C-H),
N-(1,12-Dicarba-closo-dodecaboran-2-yl)-4-methoxybenze-
namine (8) was prepared according to the general procedure to
give a colorless crystalline solid (47%), mp ) 100-102 °C. 11B
NMR: -21.6 (s, 1B), -17.4 (d, 2B, J ) 178 Hz), -15.9 (d, 4B,
J ) 157 Hz), -14.9 (d, 2B, J ) 137 Hz), -2.7 (s, 1B). 1H NMR:
1.3-3.5 (m, 9H, B-H), 2.85 (s, 1H, cage C-H), 3.10 (s, 1H, cage
C-H), 3.71 (s, 1H, NH), 3.78 (s, 3H, OMe), 6.80 (d, 2H, J ) 8.4
Hz, C6H4), 6.92 (d, 2H, J ) 8.4 Hz, C6H4). Anal. Calcd for
C9H19B10NO: C, 40.74; H, 7.22; B, 40.74; N, 5.28. Found: C,
41.07; H, 7.44; B, 40.40; N, 4.93. MS: m/z 256 [M+].
(26) Peymann, T.; Herzog, A.; Knobler, C. B.; Hawthorne, M. F. Angew.
Chem., Int. Ed. 1999, 38, 1062.
(27) Herzog, A.; Knobler, C. B.; Hawthorne, M. F. J. Am. Chem. Soc.
2001, 123, 12791.
(28) Oliva, J. M.; Allan, N. L.; Schleyer, P. v. R.; Vinˇas, C.; Teixidor,
F. J. Am. Chem. Soc. 2005, 127, 13538.

Palladium-Catalyzed Amination of 2-Iodo-para-carborane
Organometallics, Vol. 26, No. 9, 2007 2347
N-(1,12-Dicarba-closo-dodecaboran-2-yl)morpholine (9) was
prepared according to the general procedure, but 10% of (t-Bu)3P‚
HBF4 was used instead of BINAP. Yield: 33%, a colorless
crystalline solid, mp )74-76 °C. 11B NMR: -22.5 (d, 1B, J )
177 Hz), -17.9 (d, 2B, J ) 173 Hz), -16.2 (d, 6B, J ) 211 Hz),
integrated using SAINT software29,30 and the semiempirical method
of SADABS.31
The structures were solved by the direct method and refined by
full-matrix least-squares against F2 in anisotropic (for non-hydrogen
atoms) approximation. All hydrogen atoms of the carborane moiety
and OH groups were located from the difference Fourier syntheses,
and the H(C) atoms were placed in geometrically calculated
positions. All hydrogen atom positions were refined in isotropic
approximation in a riding model with the Uiso(H) parameters equal
to 1.2Ueq(Ci), where U(Ci) are the equivalent thermal parameters
of the atoms to which corresponding H atoms are bonded. All
calculations were performed on an IBM PC/AT using the SHELX-
TL software.32 Crystallographic data and refinement parameters for
compounds are presented in Table 8.
1
1.1 (s, 1B). H NMR: 1.3-3.1 (m, 9H, B-H), 2.76 (s, 1H, cage
C-H), 2.95 (s, 1H, cage C-H), 2.95 (t, 4H, J ) 4.2 Hz,
morpholine), 3.64 (t, 4H, J ) 4.2 Hz, morpholine). Anal. Calcd
for C6H19B10NO: C, 31.42; H, 8.35; N, 6.11. Found: C, 31.80; H,
8.34; N, 5.82. MS: m/z 229 [M+].
2-Hydroxy-1,12-dicarba-closo-dodecaborane (5). To an oven-
dried 5 mL tube charged with 2-iodo-p-carborane (81 mg, 0.3
mmol), ButONa (87 mg, 0.9 mmol), Pd(dba)2 (8.6 mg, 5%), and
BINAP (9.3 mg, 5%) was added 3 mL of dry dioxane. The tube
was evacuated, back-filled with argon, and stirred at 100 °C for 20
h. The reaction mixture was diluted with 3 mL of diethyl ether,
filtered through a pad of silica gel, and concentrated to leave a
crude oil. The resulting oil was purified by flash chromatography
on silica gel with chloroform as eluent to afford a colorless
crystalline solid (78%), mp ) 162-163 °C. 11B NMR: -24.7 (d,
1B, J ) 167 Hz), -18.1 (d, 2B, J ) 194 Hz), -16.4 (d, 4B, J )
187 Hz), -14.5 (d, 2B, J ) 163 Hz), 2.3 (s, 1B). 1H NMR: 1.3-
3.5 (m, 9H, B-H); 2.50 (s, 1H, cage C-H), 2.72 (s, 1H, cage
C-H), 3.14 (s, 1H, O-H). MS: m/z 160 [M+].
Acknowledgment. Financial support by the Russian Foun-
dation for Basic Researches (Grant No. 05-03-32359) is
gratefully acknowledged.
Supporting Information Available: Crystallographic data for
the structures 1, 2, 4, and 5 (atomic coordinates, bond lengths, bond
angles, and thermal parameters). This material is available free of
charge via the Internet at http://pubs.acs.org. These data have also
been deposited at the Cambridge Crystallographic Data Centre
(CCDC). Deposition numbers for the structures 1, 2, 4, and 5 are
615616, 615615, 615617, and 629064 correspondingly. These data
can be obtained free of charge on application to the CCDC (e-mail
deposit@ccdc.cam.ac.uk).
X-ray Crystal Structure Determination of Compounds 1, 2,
4, and 5. Crystals of 1, 2, 4, and 5 suitable for X-ray crystal
structure determination were grown by slow crystallization from
the chloroform solution at room temperature. Single-crystal X-ray
diffraction experiments for 1, 2, 4, and 5 were carried out with a
Bruker SMART 1000 CCD area detector, using graphite-mono-
chromated Mo KR radiation (λ ) 0.71073 Å, ω-scans with a 0.3°
step in ω and 10 s per frame exposure) at 120 K. Low temperature
of the crystals was maintained with a Cryostream (Oxford Cryo-
systems) open-flow N2 gas cryostat. Reflection intensities were
OM0611756
(29) SAINTPlus, Data Reduction and Correction Program v. 6.01; Bruker
AXS: Madison, WI, 1998.
(30) SMART, Bruker Molecular Analysis Research Tool, v. 5.059; Bruker
AXS: Madison, WI, 1998.
(31) Sheldrick G. M. SADABS v.2.01, Bruker/Siemens Area Detector
Absorption Correction Program; Bruker AXS: Madison, WI, 1998.
(32) Sheldrick G. M. SHELXTL-97, Version 5.10; Bruker AXS Inc.:
Madison, WI, 1997.