Catalytic amidation of 9-iodo-m-carborane and 2-iodo-p-carborane at a boron atom

Article abstract of DOI:10.1021/om800635d

The palladium-catalyzed amidation of B-iodocarboranes by various amides is described for the first time. The reactions of 2-iodo-1,12-dicarba-closo- dodecaborane (2-iodo-p-carborane) with acetamide, 2-pyrrolidinone, caprolactam, p-methylbenzamide, and 2-phenylacetamide using the system Pd(dba) ₂/BINAP/NaH (dba = dibenzylideneacetone; BINAP = rac-2,2′- bis(diphenylphosphino)-1,1′-binaphthyl) in dioxane at 100°C gave 2-p-carboranyl derivatives of these amides in good to high yields. Similar reactions of 9-iodo-1,7-dicarba-closo-dodecaborane (9-iodo-m-carborane) with corresponding amides afforded 9-m-carboranyl derivatives in good to high yields. The structures of N-(1,12-dicarba-closo-dodecaboran-2-yl)pyrrolidin-2-one (5), N-(1,7-dicarba-closo-dodecaboran-9-yl)acetamide (6), and N-(1,7-dicarba-closo- dodecaboran-9-yl)-2-phenylacetamide (7) have been established by X-ray diffraction studies.

Full text of DOI:10.1021/om800635d

Organometallics 2008, 27, 5937–5942
5937
Catalytic Amidation of 9-Iodo-m-carborane and 2-Iodo-p-carborane
at a Boron Atom
Sergey N. Mukhin,† Kuanysh Z. Kabytaev,† Galina G. Zhigareva,‡ Ivan V. Glukhov,‡
Zoya A. Starikova,‡ Vladimir I. Bregadze,*,‡ and Irina P. Beletskaya*,†
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 July 6, 2008
The palladium-catalyzed amidation of B-iodocarboranes by various amides is described for the first
time. The reactions of 2-iodo-1,12-dicarba-closo-dodecaborane (2-iodo-p-carborane) with acetamide,
2-pyrrolidinone, caprolactam, p-methylbenzamide, and 2-phenylacetamide using the system Pd(dba)2/
BINAP/NaH (dba ) dibenzylideneacetone; BINAP ) rac-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl)
in dioxane at 100 °C gave 2-p-carboranyl derivatives of these amides in good to high yields. Similar
reactions of 9-iodo-1,7-dicarba-closo-dodecaborane (9-iodo-m-carborane) with corresponding amides
afforded 9-m-carboranyl derivatives in good to high yields. The structures of N-(1,12-dicarba-closo-
dodecaboran-2-yl)pyrrolidin-2-one (5), N-(1,7-dicarba-closo-dodecaboran-9-yl)acetamide (6), and N-(1,7-
dicarba-closo-dodecaboran-9-yl)-2-phenylacetamide (7) have been established by X-ray diffraction studies.
studied,8 alternative routes involving reactions at the boron
center are still a challenge.
Introduction
The unique properties of carboranes account for many
applications in materials science,1-4 nonlinear optics,2,5,6 and
medicinal chemistry,7 especially in boron neutron capture
therapy (BNCT). The last method requires the development of
new routes to incorporate carborane groups into biologically
active compounds. Carborane units can be attached to other
molecule either via their C or B atoms. While substitution at
the carbon atom in carborane derivatives has been extensively
Palladium-catalyzed cross-coupling provides a novel route
for the introduction of functionality at the boron atoms.9
However, the study of this palladium-catalyzed boron-carbon
bond formation revealed significant differences between the
reactivity of C-Hal10 and carborane B-Hal bonds. Thus, all
attempts to detect the formation of a [C2H11B10-PdL2I]
complex, which could in principle be formed as a result of
oxidative addition of the B-I bond to the Pd(0) center, have
failed thus far.11 DFT calculations also indicate that B-I bond
reactivity is much lower than the reactivity of an aromatic C-Cl
bond.12
* To whom correspondence should be addressed. E-mail: beletska@
org.chem.msu.ru (I.P.B.); bre@ineos.ac.ru (V.I.B.).
† 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.
In comparison with cross-coupling reactions such as the
Suzuki and Sonogashira reactions, amination and especially
amidation reactions are much more challenging and complicated
processes.13 It is known that even with aryl iodides these
reactions require an appropriate choice of base and ligand 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.
(7) (a) Soloway, A. H.; Tjarks, W.; Barnum, B. A.; Rong, F.-G.; Barth,
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.
(8) (a) Grimes, R. N. Carboranes; Academic Press: New York, 1970.
(b) Bregadze, V. I. Chem. ReV. 1992, 92, 209.
(9) (a) Zakharkin, L. I.; Kovredov, V. A.; Ol’shevskaya, V. A.;
Shaugumbekova, Z. S. J. Organomet. Chem. 1982, 226, 217. (b) Vinas,
C.; Barbera, G.; Oliva, J. M.; Teixidor, F.; Welch, A. J.; Rosair, G. M.
Inorg. Chem. 2001, 40, 6555. (c) Jiang, W.; Harwell, D. E.; Mortimer,
M. D.; Knobler, C. B.; Hawthorne, M. F. Inorg. Chem. 1996, 35, 4355. (d)
Li, J.; Logan, C. F.; Jones, M. Inorg. Chem. 1991, 30, 4866. (e) Zheng, Z.;
Jiang, W.; Zinn, A. A.; Knobler, C. B.; Hawthorne, M. F. Inorg. Chem.
1995, 34, 2095. (f) Eriksson, L.; Beletskaya, I. P.; Bregadze, V. I.; Sivaev,
I. B.; Sjo¨berg, S. J. Organomet. Chem. 2002, 657, 267.
(3) (a) Jiang, W.; Knobler, C. B.; Curtis, C. E.; Mortimer, M. D.;
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, D. E.; Mortimer, M. D.; Knobler, C. B.; Hawthorne, M. F. Inorg.
Chem. 1996, 35, 4355. (d) Hawthorne, M. F.; Zheng, Z. Acc. Chem. Res.
1997, 30, 267. (e) Bayer, M. J.; Herzog, A.; Diaz, M.; Harakas, G. A.;
Lee, H.; Knobler, C. B.; Hawthorne, M. F. Chem. Eur. J. 2003, 9, 2732.
(4) (a) Colquhoun, H. M.; Herbertson, P. L.; Wade, K.; Baxter, I.;
Williams, D. J. Macromolecules 1998, 31, 1694. (b) Alekseyeva, E. S.;
Fox, M. A.; Howard, J. A. K.; Macbride, J. A. H.; Wade, K. Appl.
Organomet. Chem. 2003, 17, 499.
(5) (a) Lamrani, M.; Hamasaki, R.; Mitsuishi, M.; Miyashita, T.;
Yamamoto, Y. Chem. Commun. 2000, 1595. (b) Tsuboya, N.; Lamrani,
M.; Hamasaki, R.; Ito, M.; Mitsuishi, M.; Miyashita, T.; Yamamoto, Y. J.
Mater. Chem. 2002, 12, 2701.
(6) (a) Kaszynski, P.; Douglas, A. G. J. Organomet. Chem. 1999, 581,
28. (b) Piecek, W.; Kaufman, J. M.; Kaszynski, P. A. Liq. Cryst. 2003, 30,
39. (c) Pahomov, S.; Young, V. G.; Kaszynski, P. Inorg. Chem. 2000, 39,
2243. (d) Kaszynski, P.; Pahomov, S.; Young, V. G. Collect. Czech. Chem.
Commun. 2002, 67, 1061.
(10) Negishi, E., Ed. Handbook of Organopalladium Chemistry for
Organic Synthesis; Wiley: New York, 2002.
(11) Marshall, W. J.; Young, R. J., Jr.; Grushin, V. V. Organometallics
2001, 20, 523.
(12) Vinˇas, C.; Barbera, G.; Oliva, J. M.; Teixidor, F.; Welch, A. J.;
Rosair, G. M. Inorg. Chem. 2001, 40, 6555.
10.1021/om800635d CCC: $40.75
2008 American Chemical Society
Publication on Web 10/24/2008

5938 Organometallics, Vol. 27, No. 22, 2008
Mukhin et al.
Scheme 2. Amidation of 2-Iodo-p-carborane
Table 1. Reaction of 2-Iodo-p-carborane with Acetamidea
entry
base
yieldb of B-N(1), %
1
2
3
4
Cs2CO3
K3PO4
NaOBut
NaH
10
16
77
95c
a Reaction conditions: 0.1 mmol of 2-iodo-p-carborane, 0.15 mmol of
acetamide, 0.15 mmol of base, catalyst, 2.5 mol % of Pd(dba)2, 2.5 mol
% of BINAP, 1 mL of dioxane, 100 °C, 72 h. b Yield determined by
11B NMR. c Reaction conditions: 0.1 mmol of 2-iodo-p-carborane and
catalyst (2.5 mol % of Pd(dba)2, 2.5 mol % of BINAP) were added to
0.14 mmol of acetamide pretreated with 0.12 mmol of NaH in 1 mL of
dioxane, 100 °C.
Scheme 1. Proposed Catalytic Cycle for 2-Iodo-p-carborane
Amidation
Table 2. Amidation of 2-Iodo-p-carborane by Different Amidesa
are often accompanied by competitive side processes such as
reductive dehalogenation.10 Nevertheless, we have successfully
realized the amination of iodo-p-carborane (although the reaction
is accompanied by unusual hydroxyl derivative formation).14
This encouraged us to attempt the amidation of carboranes at
the boron atom, especially since the products may be expected
to possess some interesting properties.
a Reaction conditions: 0.37 mmol of 2-iodo-p-carborane and catalyst
were added to 0.52 mmol of corresponding amide pretreated with 0.42
mmol of NaH in 3 mL of dioxane, 100 °C, 72 h. b Isolated yields. The
yield determined by 11B NMR is shown in parentheses. c Decreased
isolated yields are due to the poor separation of products from dba.
Results and Discussion
Amidation of 2-Iodo-p-carborane. It is known that the Pd-
catalyzed amidation of aryl halides is more difficult to effect
than their amination and that it often requires bulky, electron-
rich phosphine ligands and a thorough optimization of reaction
conditions.15 However, in the case of carboranes B-I bond
amidation proceeds under the same conditions as amination.
Initial attempts using the catalytic system Pd(dba)2/BINAP/
NaOBut/dioxane (100 °C), which we reported earlier for
amination, were successful for amidation. Reaction of 2-iodo-
p-carborane with acetamide as a model reagent afforded the
10 and 16% product yields, respectively (Table 1, entries 1 and
2). The reason could be that a high concentration of amidate
anion is required for realization of the reaction in which
equilibrium a is moved to initial compounds (Scheme 1).
Otherwise, a side process leading to degradation of catalytic
system occurs, and palladium black precipitation is observed
under prolonged heating.
The use of NaH which can fully deprotonate amides results
in some formation of the reduced product C2H2B10H10 in
addition to the desired product. However, pretreatment of amides
with NaH before the reaction resulted in an almost quantative
yield of the product 1 (Table 1, entry 4).
Using these optimized reaction conditions, we have carried
out the amidation of 2-iodo-p-carborane by different types of
amides: aliphatic amides (acetamide, 2-phenylacetamide), aro-
matic amides (p-methylbenzamide), and lactams (caprolactam,
pyrrolidin-2-one) (Scheme 2). In all of these reactions high
yields of the expected products were obtained. In some cases
the isolation of pure compounds was difficult, due to contamina-
tion with trace amounts of dba. Consequently, the isolated yield
of analytically pure product was significantly lower (50-70%)
than the yield determined by NMR spectroscopy (Table 2).
Amidation of 9-Iodo-m-carborane. The same protocol used
for amidation of 2-iodo-p-carborane was employed for amidation
expected coupling product in 77% yield (as determined by 11
B
NMR) (Table 1, entry 3). However, although a 77% yield
usually is quite acceptable, taking in consideration the high cost
and limited availability of both p-carborane and its iodo
derivative, it was necessary to improve the yield of this reaction.
Attempts to change the base and to use bases weaker than
t-BuONa, such as Cs2CO3 and K3PO4, were not successful.
These bases are conventionally employed in Pd-catalyzed
amidation reactions, but in our case they gave only poor resultss
(13) (a) Fujita, K.; Yamashita, M.; Puschmann, F.; Alvarez-Falcon,
M. M.; Incarvito, C. D.; Hartwig, J. F. J. Am. Chem. Soc. 2006, 128, 9044.
(b) Ikawa, T.; Barder, T. E.; Biscoe, M. R.; Buchwald, S. L. J. Am. Chem.
Soc. 2007, 129, 13001.
(14) Beletskaya, I. P.; Bregadze, V. I.; Kabytaev, K. Z.; Zhigareva, G. G.;
Petrovskii, P. V.; Glukhov, I. V.; Starikova, Z. A. Organometallics 2007,
26, 2340.
(15) Miyaura, N., Ed. Cross-coupling Reactions, A Practical Guide;
Springer: Berlin, Germany, 2002; Top. Curr. Chem. 219.

Catalytic Amidation of Carboranes
Organometallics, Vol. 27, No. 22, 2008 5939
Scheme 3. Amidation of 9-Iodo-m-carborane
The lengths of the B(9)-N(13) bond in the studied com-
pounds vary slightly and are 1.485(2) Å for 6 and 1.472(5) and
1.480(4) Å in the two independent molecules of 7, respectively.
Analysis of the Cambridge Crystallographic Data Base has
shown that in the literature only nine monosubstituted carborane
derivatives with B-N bonds are described. Among them six
are o-carborane derivatives, while the other three are p-
carboranes. For the latter the B-N bond varies in the range of
1.457-1.482 Å, which is in a good agreement with the values
found for 6 and 7.
In the crystal structures of these compounds a main role is
played by the H bonds of N-H · · · O type. In both 6 and 7 they
lead to formation of infinite chains along the a axis in the case
of 6 and the b axis in the case of 7. Such chain formation in the
structure of 6 is shown on Figure 2. Both independent molecules
of 7 participate in formation of the same chain. Parameters of
the H bonds are given in Table 5.
Table 3. Amidation of 9-Iodo-m-carborane by Various Amidesa
Thestructureofthethirdboron-substitutedcarboranylamidesN-
(p-carboran-2-yl)pyrrolidine-2-one (5)sis shown in Figure 3.
The unit cell contains two independent molecules. Analysis of
their geometries has shown that they have comparable geo-
metrical parameters (see Table 6).
The lengths of B-N bonds are 1.4824(18) and 1.4767(19) Å in
the two independent molecules, respectively, in good agreement
with the range found for B-N bonds in similar compounds (see
above). The five-membered 2-pyrrolidone rings have an enve-
lope conformation. The deviations of the N1, C′(1), C′(2), and
C′(4) atoms from the corresponding mean planes are 0.001 and
0.002 Å, respectively. At the same time, C′(3) atoms are shifted
from the planes by 0.408 and 0.423 Å, respectively.
It is noteworthy that if one superimposes both independent
molecules so that B(2), N(1), and O(1) atoms coincide, then
the flaps of the envelope (atoms C′(3)) are pointed in different
directions (see Figure 4). At the same time, the atoms of the
carborane moieties also do not coincide. This allows us to state
that the two independent molecules present in the crystal of 5
differ in the relative conformation of the five-membered rings
as well as in the relative disposition of the ring and the carborane
moiety.
a Reaction conditions: 0.37 mmol of 9-iodo-m-carborane and catalyst
were added to 0.52 mmol of corresponding amide pretreated with 0.42
mmol of NaH in 3 mL of dioxane, 100 °C, 72 h. b Isolated yields.
of 9-iodo-m-carborane. It is known that 9-iodo-m-carborane is
less reactive in cross-coupling reactions than 2-iodo-p-carbo-
rane.16 Nevertheless, the amidation of 9-iodo-m-carborane with
acetamide, 2-phenylacetamide, and p-methylbenzamide (Scheme
3) afforded practically the same high yields of the products as
did the reaction of 2-iodo-p-carborane, and pure compounds
were isolated in 63-67% yields (Table 3).
Description of the Structures. We have investigated the
crystal structures of carboranylamides 5-7 obtained in this
study. The crystals of compounds 6 and 7 have one and two
independent molecules in the unit cell, respectively (Figure 1).
In general, the structures of the central amide fragment are
similar. Atoms N(13), C(14), O(15), and C(16) are almost
coplanar. The deviation of the atoms from the mean planes is
equal to 0.002 Å or 6 and 0.002 and 0.001 Å for the two
independent molecules of 7, respectively. A comparison of bond
lengths in these fragments is given in Table 4. It should be noted
that the largest variation is observed by the analysis of the
relative disposition of the amide fragments and the carborane
moiety. Usually for such an analysis the value of the dihedral
angle θ is used, which in the present case was chosen as a
modulus of the B(12)-B(9)-N(13)-C(14) angle. In the studied
compounds the θ angle values are equal to 12.1° for 6 and 108.3
and 65.2° for the two independent molecules of 7, respectively.
It is evident that this fact is caused by the free rotation of the
amide fragment around the B(9)-N(13) bond in solution, which
leads to the absence of a preferred conformation upon the
crystallization and is also the reason for the presence of two
independent molecules in the crystal.
Conclusion
Using the system Pd(dba)2/BINAP/NaH in dioxane at 100
°C, an amide group was directly introduced at a boron atom of
a carborane cage via a nitrogen atom in one step. It is worth
noting that the easiness of amidation at the B atom compared
to amination is in contrast with the same reactions at the C atom.
On the basis of the reaction developed, the convenient one-
step method of synthesis of N-(9-m- and 2-p-carboranyl)amides
was proposed. N-(2-p-Carboranyl)amides have not been known
until now.17 Only one N-(9-m-carboranyl)amide was described
by the example of 9-(N-formylamino)-m-carborane, which was
prepared in several steps.18
Experimental Section
General Comments. All reactions were performed under argon
in oven-dried glassware. Flash chromatography was carried out on
(17) (a) Grushin, V. V.; Bregadze, V. I.; Kalinin, V. N. In Journal of
Organometallic Chemistry Library, Organometallic Chemistry ReViews;
Davies, A. G., Fisher, E. O., Reutov, O. A., Eds.; Elsevier: Amsterdam,
1988; Vol. 20, pp 1-68. (b) ComprehensiVe Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G. W., Eds.; Pergamon Press:
Oxford, U.K., 1995; Vol. 1, pp 217-255. (c) ComprehensiVe Organome-
tallic Chemistry III; Mingos, D. M. P., Crabtree, R. H., Eds.; Elsevier:
Amsterdam, 2007; Vol. 3, pp 49-112.
(16) 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.
(18) Kalinin, V. N.; Kobel’kova, N. I.; Krasnokutskaya, E. V.; Zakharkin,
L. I. Bull. Acad. Sci. USSR, DiV. Chem. Sci. 1983, 1084.

5940 Organometallics, Vol. 27, No. 22, 2008
Mukhin et al.
Figure 1. General view of molecules of 6 (a) and one of the independent molecules of 7 (b) in the crystal form. Thermal ellipsoids are
shown at the 50% probability level.
Table 4. Selected Bond Lengths (Å) of the Amide Fragment in
Crystals of 6 and 7 (for Two Independent Molecules)
B(9)-N(13)
N(13)-C(14)
C(14)-O(15)
C(14)-C(16)
6
7
1.485(2)
1.472(5)
1.480(4)
1.344(2)
1.345(4)
1.344(4)
1.233(2)
1.232(4)
1.208(4)
1.507(2)
1.529(5)
1.522(4)
Table 5. Parameters of the H Bonds in Crystals of 6 and 7
N(13)-H(13) · · · O(15)
H(13) · · · O(15) (Å) N(13) · · · O(15) (Å)
(deg)
6
7
2.16
2.06
2.22
2.953(2)
2.899(5)
3.019(4)
157
162
153
Merck silica gel 60 (4360 mesh), and Merck silica 60 F254 was
used for thin-layer chromatography (TLC). Carborane spots were
visualized on TLC by dipping in a 0.5% w/v PdCl2 in 10%
concentrated HCl/MeOH solution followed by heating, which gave
black spots on a yellow background. All starting amides were
recrystallized before use. Dioxane was dried over sodium ben-
Figure 3. General view of a molecule of 5 in the crystal form.
Thermal ellipsoids are shown at the 50% probability level.
Table 6. Selected Bond Lengths (Å) in Two Independent Molecules
of 5
B(2)-N(1)
N(1)-C′(1)
N(1)-C′(4)
C′(1)-O(1)
1.4824(18)
1.4767(19)
1.3647(16)
1.3679(16)
1.4771(19)
1.4740(19)
1.2227(16)
1.2318(16)
1
zophenone ketyl and distilled under argon prior to use. The H,
13C, and 11B NMR spectra were recorded on a Bruker AMX-400
spectrometer at 400, 100.61, and 128.3 MHz, respectively, from
solutions in CDCl3; all shifts are given in units of ppm. 11B chemical
shifts were measured relative to Et2O · BF3 as external reference.
Mass spectra were obtained on a Finnigan SSQ-7000 instrument.
Elemental analyses were performed in the Microanalytical Labora-
tory of the INEOS RAS, Moscow, Russia.
General Procedure for Amidation Reactions. The amide (0.52
mmol) was added to a suspension of sodium hydride (60%
dispersion in mineral oil, used without washing out; 17.4 mg, 0.44
mmol) in dioxane (3 mL). The mixture was stirred at 100 °C for
60 min, and then the corresponding iodocarborane (100 mg, 0.37
mmol), Pd(dba)2 (5.32 mg, 2.5%), and BINAP (5.8 mg, 2.5%) were
added to the mixture. Stirring was continued at 100 °C for 72 h.
The progress of the reaction was monitored by TLC using
chloroform as eluent. Heating was stopped after all iodocarborane
was consumed. The resulting mixture was diluted with 5 mL of
dichloromethane and filtered through a paper filter. The solvent
was carefully removed under vacuum. The crude product was
purified by flash chromatography on silica gel using diethyl ether
or chloroform as eluent.
N-(1,12-Dicarba-closo-dodecaboran-2-yl)acetamide (1). Yield:
51%. Mp: 172-173 °C. 11B NMR: -19.8 (d, 1B, J ) 166 Hz), -16.8
(d, 2B, J ) 94 Hz), -15.5 (d, 4B, J)160 Hz), -14 (d, 2B, J ) 144
Figure 2. Infinite chains, formed by the N-H · · · O bonds in the
crystal form of 6.
1
Hz), -5.6 (s, 1B). H NMR: 1.3-3.0 (m, 9H, B-H), 2.03 (s, 3H,

Catalytic Amidation of Carboranes
Organometallics, Vol. 27, No. 22, 2008 5941
C), 65.01(carborane cage C), 127.40 (benzene ring C, opposite to
-CH2CONH-), 129.05 (2C, benzene ring), 129.41 (2C, benzene
ring), 134.88 (benzene ring C, C-CH2CONH-), 174.05 (CO).
Anal. Calcd for C10H19B10NO: C, 43.30; H, 6.90; N, 5.05. Found:
•
C, 43.41; H, 6.94; N, 4.89. MS: m/z (%) 92 (100) (PhCH2 ), 156
(3) (NH-C2B10H11), 186 (15) (CONH-C2B10H11), 277 (0.4) [M]+.
N-(1,12-Dicarba-closo-dodecaboran-2-yl)-p-methylbenza-
mide (3). Yield: 73%. Mp: 164-165 °C. 11B NMR: -19.7 (d, 1B,
J ) 155 Hz), -16.7 (d, 2B, J ) 96 Hz), -15.4 (d, 4B, J ) 159
Hz), -13.9 (d, 2B, J ) 141 Hz), -5.1 (s, 1B). 1H NMR: 1.3-3.3
(m, 9H, B-H), 2.42 (s, 3H, p-toluamide CH3), 2.76 (s, 1H, cage
C-H), 3.84 (s, 1H, cage C-H), 6.09 (s, 1H, p-toluamide NH),
7.25 (d, 2H, J ) 8 Hz, p-toluamide benzene ring), 7.71 (d, 2H, J
) 8 Hz, p-toluamide benzene ring). 13C NMR: 21.40 (p-methyl-
benzamide Me), 60.61 (carborane C), 65.25 (carborane C), 127.12
(2C near CONH2 group), 129.19 (2C near CH3 group), 132.00
(C-CONH2), 142.22 (C-Me), 169.81 (CONH2). Anal. Calcd for
C10H19B10NO: C, 43.30; H, 6.90; N, 5.05. Found: C, 43.61; H, 6.97;
N, 4.78. MS: m/z 277 [M]+.
N-(1,12-Dicarba-closo-dodecaboran-2-yl)caprolactam (4).
Yield: 73%. Mp: 64-65 °C. 11B NMR: -19.7 (d, 1B, J ) 167
Hz), -17.1 (d, 2B, J ) 123 Hz), -15.7 (d, 2B, J ) 120 Hz), -15
(d, 2B, J ) 117 Hz), -13.7 (d, 2B, J ) 157 Hz), -2.8 (s, 1B). 1H
NMR: 1.4-3.1 (m, 9H, B-H), 1.6-1.8 (m, 6H, caprolactam),
2.49-2.56 (m, 2H, caprolactam), 2.71 (s, 1H, cage C-H), 3.71 (s,
2H, caprolactam), 4.41 (s, 1H, cage C-H). 13C NMR: 23.48
(caprolactam C), 28.51 (caprolactam C), 29.35 (caprolactam C),
38.46 (caprolactam C, CH2-CO), 49.56 (caprolactam C,
CH2-N-), 59.39 (carborane cage C), 65.09 (carborane cage C),
180.45 (caprolactam CO). Anal. Calcd for C8H21B10NO: C, 37.63;
H, 8.29; B, 42.33; N, 5.48. Found: C, 37.49; H, 8.36; B, 42.49; N,
5.34. MS: m/z 255 [M]+.
Figure 4. Projection of two independent molecules in the unit cell
of 5, superposed by the atoms B(2), N(1), and O(1).
acetamide CH3), 2.71 (s, 1H, cage C-H), 3.69 (s, 1H, cage C-H),
5.53 (s, 1H, acetamide NH). 13C NMR: 25.11 (corresponds to Me in
AcNH-), 60.51 (cage C), 65.07 (cage C), 173.31 (CO from AcNH-).
Anal. Calcd for C4H15B10NO: C, 23.87; H, 7.51; B, 53.71; N, 6.96.
Found: C, 23.48; H, 7.56; B, 53.48; N, 6.62.
N-(1,12-Dicarba-closo-dodecaboran-2-yl)2-phenylacetamide
(2). Yield: 73%. Mp: 155-156 °C. 11B NMR: -19.8 (d, 1B, J )
164 Hz), -16.8 (d, 2B, J ) 91 Hz), -15.5 (d, 4B, J ) 160 Hz),
1
-14.1 (d, 2B, J ) 142 Hz), -5.5 (s, 1B). H NMR: 1.4-3.1 (m,
9H, B-H), 2.68 (s, 1H, cage C-H), 3.60 (s, 2H, 2-phenylacetamide
CH2), 3.68 (s,1H, cage C-H), 5.29 (s, 1H, NH), 7.31-7.34 (m,
1H, benzene ring), 7.38-7.41 (m, 2H, benzene ring). 13C NMR:
45.16 (2-phenylacetamide, -NHCOCH2-), 60.58 (carborane cage
N-(1,12-Dicarba-closo-dodecaboran-2-yl)pyrrolidin-2-one (5).
Yield: 51%. Mp: 120-121 °C. 11B NMR: -19.4 (d, 1B, J ) 168
Hz), -16.6 (d, 2B, J ) 159 Hz), -16.2 (d, 2B, J ) 162 Hz), -15.4
(d, 2B, J ) 170 Hz), -13.9 (d, 2B, J ) 159 Hz), -4.9 (s, 1B). 1H
Table 7. Crystal Data and Structure Refinement Details for 5-7
5
6
7
formula
mol wt
C6H17B10NO
227.31
C4H15B10NO
201.27
C
10.5H20B10ClNO
319.83
cryst color, habit
cryst size, mm
cryst syst
space group
colorless, plate
0.55 × 0.40 × 0.20
orthorhombic
Pca21
colorless, needle
0.45 × 0.30 × 0.20
orthorhombic
P212121
colorless, prism
0.23 × 0.17 × 0.14
orthorhombic
P212121
cell constants
a, Å
16.7029(8)
8.8115(9)
11.0222(16)
b, Å
7.4094(4)
10.4327(10)
15.039(2)
c, Å
19.8847(9)
12.6598(13)
20.857(3)
R, deg
90
90
90
2460.9(2)
90
90
90
1163.8(2)
90
90
90
3457.4(9)
ꢀ, deg
γ, deg
V, Å3
Z
8
4
8
Dcalcd, g cm-3
2θmax, deg
1.227
54
0.064
30 182
1.149
60
0.060
13 313
1.229
52
0.215
30 307
0.990
6746 (Rint ) 0.0503)
4830
-0.01(11)
424
0.0649
abs coeff (Mo KR), mm-1
no. of rflns collected
completeness
no. of indep rflns
no. of obsd rflns (I > 2(I))
abs structure param
no. of params
R1 (on F for obsd rflns)
wR2 (on F2 for all rflns)
weighting scheme
A
0.993
0.999
3664 (Rint ) 0.0243)
3494
n/a
409
0.0343
0.0956
1778 (Rint ) 0.0518)
1605
n/a
193
0.0394
0.0992
0.1473
0.051
0.051
0.015
B
0.975
0.5
8.0
F(000)
944
416
1320
GOF
1.039
0.306 and -0.284
0.985
0.338 and -0.262
0.975
0.275 and -0.456
largest diff peak and hole, e Å-3

5942 Organometallics, Vol. 27, No. 22, 2008
Mukhin et al.
NMR: 1.3-3.1 (m, 9H, B-H), 2.08 (quintet, 2H, pyrrolidin-2-one),
2.38 (t, 2H, pyrrolidin-2-one), 2,74 (s, 1H, cage C-H), 3.65 (t,
2H, pyrrolidin-2-one), 4.05 (s, 1H, cage C-H). 13C NMR: 19.90
(2-pyrrolidinone C), 32.65 (2-pyrrolidinone C), 50.45 (2-pyrroli-
dinone C, CH2-NHCO), 60.35 (carborane cage C), 63.69 (carbo-
rane cage C), 179.54 (2-pyrrolidinone CO). Anal. Calcd for
C6H17B10NO: C, 31.70; H, 7.54; B, 47.56; N, 6.16. Found: C, 31.51;
H, 7.79; B, 47.26; N, 5.98. X-ray-quality crystals were obtained
by slow diffusion of warm hexane into a hot chloroform solution
of 5. MS: m/z 227 [M]+.
solution. Crystal data and details of the structure refinement are
given in Table 7. Single-crystal X-ray diffraction experiments for
5 and 6 were carried out with a Bruker SMART APEX2 CCD area
detector and for 7 with a Bruker SMART 1000 CCD area detector
diffractometer, using graphite-monochromated Mo KR radiation (λ
) 0.710 73 Å, ω-scans) at 100 K (5 and 6) and 120 K (7). The
low temperature of the crystals was maintained with a Cryostream
(Oxford Cryosystems) open-flow N2 gas cryostat. Reflection
intensities were integrated using SAINT software19,20 and the
semiempirical method SADABS.21
N-(1,7-Dicarba-closo-dodecaboran-9-yl)acetamide (6). Yield:
67%. Mp: 150-151 °C. 11B NMR: -22 (d, 1B, J ) 182 Hz), -18.7
(d, 1B, J ) 182 Hz), -15.5 (d, 2B, J ) 176 Hz), -14 (d, 2B, J )
148 Hz), 11.2 (d, 1B, J ) 149 Hz), -7.1 (d, 2B, J ) 164 Hz),
-0.9 (s, 1B). 1H NMR: 1.3-3.3 (m, 9H, B-H), 2.02 (s, 3H, CH3),
2.87 (s, 2H, cage C-H), 5.18 (s, 1H, NH). 13C NMR: 25.12 (Me,
AcNH-), 51.83 (2C, carborane cage), 172.81 (CO). Anal. Calcd
for C4H15B10NO: C, 23.87; H, 7.51; N, 6.96; B,53.71. Found: C,
23.89; H, 7.49; N, 6.69; B, 53.57.
N-(1,7-Dicarba-closo-dodecaboran-9-yl)-2-phenylacetamide (7).
Yield: 63%. Mp: 85-86 °C. 11B NMR: -22 (d, 1B, J ) 180 Hz),
-18.7 (d, 1B, J ) 182 Hz), -15.5 (d, 2B, J ) 174 Hz), -14 (d,
2B, J ) 145 Hz), -11.2 (d, 1B, J ) 149 Hz), -7.1 (d, 2B, J )
163 Hz), -0.8 (s, 1B). 1H NMR: 1.3-3.3 (m, 9H, B-H), 2.84 (s,
2H, cage C-H), 3.60 (s, 2H, 2-phenylacetamide CH2), 5.16 (s, 1H,
NH), 7.27-7.31 (m, 3H, benzene ring), 7.34-7.38 (m, 2H, benzene
ring). 13C NMR: 45.09 (PhCH2CONH-), 51.84 (carborane cage
C), 127.09 (benzene ring C, opposite to -CH2CONH-), 128.86
(2C, benzene ring), 129.46 (2C, benzene ring), 135.49 (benzene
ring C, C-CH2CONH-), 173.61 (CO). Anal. Calcd for
C10H19B10NO: C, 43.30; H, 6.90; N, 5.05. Found: C, 43.52; H, 6.67;
N, 4.79.
The structures were solved by direct methods and refined by
full-matrix least squares against F2 in an anisotropic (for non-
hydrogen atoms) approximation. All carborane hydrogen atoms
were located from the difference Fourier syntheses; the H(C) atoms
were placed in geometrically calculated positions. Some carborane
hydrogen atom positions were refined in an isotropic approximation
in the riding model with the Uiso(H) parameters equal to
1.2[Ueq(Xi)], where U(Xi) values are respectively the equivalent
thermal parameters of the atoms to which corresponding H atoms
are bonded. All calculations were performed on an IBM PC/AT
computer using SHELXTL software.22
Acknowledgment. Financial support by the Russian
Foundation for Basic Research (Grant No. 05-03-32359) is
gratefully acknowledged. S.N.M. thanks Dr. Andrei V.
Cheprakov for his generous advice and helpful discussions.
Supporting Information Available: CIF files giving crystal-
lographic data for the structures 5-7 (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 5-7
are 693268-693270. These data can be obtained free of charge on
application to the CCDC (e-mail deposit@ccdc.cam.ac.uk).
N-(1,7-Dicarba-closo-dodecaboran-9-yl)-p-methylbenza-
mide (8). Yield: 66%. Mp: 93-94 °C. 11B NMR: -21.9 (d, 1B, J
) 180 Hz), -18.6 (d, 1B, J ) 182 Hz), -15.4 (d, 2B, J ) 173
Hz), -13.8 (d, 2B, J ) 148 Hz), -11.1 (d, 1B, J ) 150 Hz), -6.9
1
(d, 2B, J ) 162 Hz), -0.4 (s, 1B). H NMR: 1.3-3.5 (m, 9H,
B-H), 2.38 (s, 3H, p-toluamide CH3), 2.91 (s, 2H, cage C-H),
5.91 (s, 1H, NH), 7.22 (d, 2H, J ) 8 Hz), 7.72 (d, 2H, J ) 8 Hz).
13C NMR: 21.42 (CH3-C6H4-), 51.93 (carborane cage C), 127.22
(2C near CONH2 group), 129.07 (2C near CH3 group), 132.57
(C-CONH2), 141.68 (C-Me), 169.46 (CONH2). Anal. Calcd for
C10H19B10NO: C, 43.30; H, 6.90; N, 5.05; B, 38.98. Found: C,
43.14; H, 6.91; N, 4.99; B, 38.87.
X-ray Crystal Structure Determination of Compounds 5-7.
Crystals of 5-7 suitable for X-ray crystal structure determination
were grown by slow diffusion of warm hexane into a hot chloroform
OM800635D
(19) SAINTPlus, Data Reduction and Correction Program, v. 6.01;
Bruker AXS, Madison, WI, 1998.
(20) SMART, Bruker Molecular Analysis Research Tool, v. 5.059;
Bruker AXS, Madison, WI, 1998.
(21) Sheldrick, G. M. SADABS, Bruker/Siemens Area Detector Absorp-
tion Correction Program v.2.01; Bruker AXS, Madison, WI, 1998.
(22) Sheldrick, G. M. SHELXTL-97, Version 5.10; Bruker AXS Inc.,
Madison, WI, 1997.