Boron - Oxygen bond formation by palladium-catalyzed etheration of 2-iodo-para-carborane

Article abstract of DOI:10.1021/om9001044

For the first time, the palladium-catalyzed etheration of 2-iodo-p-carborane with phenolates and alkoxides has been demonstrated. The reactions of 2-iodo-1,12-dicarba-closo-dodecaborane (2-iodo-p-carborane) with sodium salts of phenol, p-cresol, α- and β-

Full text of DOI:10.1021/om9001044

4758 Organometallics 2009, 28, 4758–4763
DOI: 10.1021/om9001044
Boron-Oxygen Bond Formation by Palladium-Catalyzed Etheration of
2-Iodo-para-carborane
Kuanysh Z. Kabytaev,†,§ Sergey N. Mukhin,†,§ 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. §These authors contributed equally to this work.
Received February 11, 2009
For the first time, the palladium-catalyzed etheration of 2-iodo-p-carborane with phenolates and
alkoxides has been demonstrated. The reactions of 2-iodo-1,12-dicarba-closo-dodecaborane (2-iodo-
p-carborane) with sodium salts of phenol, p-cresol, R- and β-naphthol, 3-methyl-4-chlorophenol, and
3,4-dimethylphenol using the Pd(dba)2/BINAP (dba = dibenzylideneacetone; BINAP = rac-2,20-bis-
(diphenylphosphino)-1,10-binaphthyl) system in dioxane at 90 °C afforded the corresponding 2-
p-carboranyl aryl ethers in good to high yields. 2-Methoxy-p-carborane and 2-ethoxy-p-carborane have
also been obtained in good yield. The structures of 2-(4-methylphenoxy)-p-carborane and 2-methoxy-
p-carborane have been established by X-ray diffraction studies.
Introduction
leading to monosubstituted o-, m-, and p-carboranes.4,5 The
forming B-I bond proved to be closer to aromatic Csp2-I (or
to Csp2-Cl) than to the B-I bond in alkyl or aryl boron
halides.6 However, this bond is significantly less reactive
than the Csp2-I bond or even less reactive than Csp2-Cl, and
its reactivity decreases in the series 2-iodo-p-carborane >
9-iodo-m-carborane > 9-iodo-o-carborane.6
Polyhedral boron compounds and particularly icosahe-
dral carboranes, being known for 45 years, still attract the
attention of chemists working in different fields including
medicine1 and materials science2 and also in the construction
of molecular devices.3
A certain analogy between the B-I bond and sp2 C-Hal
bonds promoted the development of Pd-catalyzed boron-
carbon bond-forming reactions similarly to Kumada,4
Suzuki,7 Negishi,8 Sonogashira,5,8 and Heck9 reactions.
Recently, we have successfully accomplished amination10
and amidation11 B-N bond-forming reactions of p- and
m-iodo-carboranes with different amines (aliphatic, aro-
matic, and NH-heterocycles) and amides (aliphatic, lactams,
One of the most important features of carboranes is their
ability to undergo an electrophilic substitution, which allows
considering them as nonplanar aromatic compounds. How-
ever, the mechanism of such reactions should be different
from that for their arene counterparts. One of the most
important reactions of this kind is electrophilic iodination
*To whom correspondence should be addressed. E-mail: beletska@
elorg.chem.msu.ru (I.P.B.); bre@ineos.ac.ru (V.I.B.).
(1) (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.; Morel, P.; Schaffer, P.; Sogbein, O. O.;
Stephenson, K. A. 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. (f) Yinghuai, Z.; Peng, A. T.;
Carpenter, K.; Maguire, J. A.; Hosmane, N. S.; Takagaki, M. J. Am. Chem.
Soc. 2005, 127, 9875.
(2) (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) Schoberl, 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. (e) Farha, O. K.; Spokoyny, A. M.; Mulfort, K. L.;
Hawthorne, M. F.; Mirkin, C. A.; Hupp, J. T. J. Am. Chem. Soc. 2007,
129, 12680. (f ) Simon, Y. C.; Ohm, C.; Zimny, M. J.; Coughlin, E. B.
Macromolecules 2007, 40, 5628.
(4) (a) Zakharkin, L. I.; Kalinin, V. N. Izv. Akad. Nauk SSSR, Ser.
Khim. 1966, 575. (b) Seickhaus, J. F.; Semenuk, N. S.; Knowles, T. A.;
Schroeder, H. Inorg. Chem. 1969, 8, 2452. (c) Zakharkin, L. I.; Kovredov, A. I.;
Ol'shevskaya, V. A.; Shaugumbekova, Zh. S. J. Organomet. Chem. 1982, 226,
217.
(5) Jiang, W.; Knobler, C. B.; Curtis, C. E.; Mortimer, M. D.;
Hawthorne, M. F. Inorg. Chem. 1995, 36, 3491.
(6) (a) Marshall, W. J.; Young, R. J., Jr.; Grushin, V. V. Organome-
~
tallics 2001, 20, 523. (b) Vinas, C.; Barbera, G.; Oliva, J. M.; Teixidor, F.;
Welch, A. J.; Rosair, G. M. Inorg. Chem., 2001, 40, 6555.
(7) Eriksson, L.; Beletskaya, I. P.; Bregadze, V. I.; Sivaev, I. B.;
Sjoberg, S. J. Organomet. Chem. 2002, 657, 267.
(8) (a) Yang, X.; Jiang, W.; Knobler, C. B.; Mortimer, M. D.;
Hawthorne, M. F. Inorg. Chim. Acta 1995, 240, 371. (b) Beletskaya, I.
€
P.; Bregadze, V. I.; Ivushkin, V. A.; Petrovskii, P. V.; Sivaev, I. B.; Sjoberg, S.;
Zhigareva, G. G. J. Organomet. Chem. 2004, 689, 2920. (c) 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.
(9) Eriksson, L.; Winberg, K.-J.; Claro, R. T.; Sjoberg, S. J. Org.
(3) (a) Tour, J. M. J. Org. Chem. 2007, 72, 7477. (b) Morin, J.-F.;
Sasaki, T.; Shirai, Y.; Guerrero, J. M.; Tour, J. M. J. Org. Chem. 2007, 72,
9481. (c) Morin, J.-F.; Shirai, Y.; Tour, J. M. Org. Lett. 2006, 8, 1713. (d)
Sasaki, T.; Tour, J. M. Tetrahedron Lett. 2007, 48, 5821. (e) Sasaki, T.; Tour,
J. M. Org. Lett. 2008, 10, 897. (f) Sasaki, T.; Guerrero, J. M.; Tour, J. M.
Tetrahedron 2008, 64, 8522. (g) Sasaki, T.; Morin, J.-F.; Lu, M.; Tour, J. M.
Tetrahedron Lett. 2007, 48, 5817.
Chem. 2003, 68, 3569.
(10) 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.
(11) Mukhin, S. N.; Kabytaev, K. Z.; Zhigareva, G. G.; Glukhov, I.
V.; Starikova, Z. A.; Bregadze, V. I.; Beletskaya, I. P. Organometallics
2008, 27, 5937.
r
pubs.acs.org/Organometallics
Published on Web 07/24/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 16, 2009 4759
Figure 1. General view of molecules of 4 (a) and 1 (b) in the crystal. Thermal ellipsoids are shown for p = 50%.
Scheme 1. Etheration of 2-Iodo-p-carborane
and aromatic) analogously to Buchwald-Hartwig amina-
tion12 and amidation13 of aryl iodides.
During the course of our amination studies employing
t-BuONa as a base, we have observed the formation of
unusual 2-hydroxy-para-carborane along with the expected
amination product.10 This compound was isolated and
characterized by X-ray crystallography. We have shown that
tert-butoxide was the source of a hydroxy group; however no
formation of 2-hydroxy-p-carborane was observed in the
in the presence of two alkoxides: MeONa and EtONa. In
presence of NaOH or KOH in aqueous or organic solvents.10
both reactions, only the product of alkoxylation was formed
This result is somewhat contradictory to that obtained in
without any traces of hydroxylation product, as proved
aromatic substitution in the presence of a similar Pd cata-
by 11B NMR studies.
The structure of 2-MeO-p-carborane is shown in Figure 1.
The reaction of 2-I-p-C2B10H11 with various phenols and
naphthols except for β-naphthol under the same conditions
proceeded very smoothly to give the products in good to high
isolated yields. In the case of β-naphthol, the reaction was
not completed within 3 days, but no byproduct was detected.
The structure of 2-(4-methylphenoxy)-p-carborane is gi-
ven in Figure 1.
To validate our protocol, we have performed the test
lyst,14 where only aryl-tert-butyl ether was obtained. It
should be mentioned that the formation of phenols is a much
more difficult task, which requires employment of sophisti-
cated monodentate ligands.15
The direct Pd-catalyzed hydroxylation and etheration of
iodo-carborane still needs to be explored due to the poor
selectivity and low yields of the oxidation method (the only
exception is exhaustive oxidative hydroxylation16). We sup-
pose that formation of a hydroxy derivative employing
t-BuONa as a hydroxy group source is the best available
reaction in the absence of catalyst. No reaction occurred after
procedure thus far.
48 h of stirring, as confirmed by 11B NMR spectroscopy.
On the basis of these observations, it was reasonable to
It is known that palladium-catalyzed etheration of aryl
propose the palladium-catalyzed etheration of iodo-carbor-
halides by alcohols or phenols requires the application of
electron-rich and bulky monodentate ligands,17 while in the
case of 2-iodo-p-carborane, this process proceeds well
anes with alkoxides and phenolates. Indeed, we have shown
that 2-iodo-p-carborane can successfully be etherated by
phenolates and alkoxides in the presence of the Pd(dba)2/
with the same catalyst as that used in amination reaction.
BINAP system.
The amination of aryl halides in the presence of MeONa,
i-PrONa, or t-BuONa employing the Pd/BINAP catalyst
system gives the amination product only.18 Thus, appar-
ently, there are some differences between palladium-cata-
Results and Discussion
Using a similar catalytic system (Pd(dba)2/BINAP in
lyzed coupling reactions of 2-iodo-p-carborane and aryl
dioxane at 90 °C) to that applied for amination and hydro-
xylation of 2-iodo-p-carborane,10 we examined the reaction
halides. Unfortunately, the main obstacle for gaining in-
sights into the catalytic cycle of cross-coupling processes
with iodo-carborane is an impossibility to detect or isolate
the intermediate oxidative addition step,6 which is well
characterized for aryl halides.
(12) (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.
(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) Palucki, M.; Wolfe, J. P.; Buchwald, S. L. J. Am. Chem. Soc.
1997, 119, 3395.
(15) Anderson, K. W.; Ikawa, T.; Tundel, R. E.; Buchwald, S. L. J.
Am. Chem. Soc. 2006, 128, 10694.
(16) Herzog, A.; Knobler, C. B.; Hawthorne, M. F. J. Am. Chem. Soc.
(17) (a) Parrish, C. A.; Buchwald, S. L. J. Org. Chem. 2001, 66, 2498.
(b) Vorogushin, A. V.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc. 2005,
127, 8146. (c) Burgos, C. H.; Barder, T. E.; Huang, X.; Buchwald, S. L.
Angew. Chem., Int. Ed. 2006, 45, 4321. (d) Schwarz, N.; Pews-Davtyan, A.;
Alex, K.; Tillack, A.; Beller, M. Synthesis 2007, 23, 3722. (e) Mann, G.;
Shelby, Q.; Roy, A. H.; Hartwig, J. F. Organometallics 2003, 22, 2775.
ꢀ
(18) Prashad, M.; Hu, B.; Lu, Y.; Draper, R.; Har, D.; Repic, O.;
2001, 123, 12791.
Blacklock, T. J. J. Org. Chem. 2000, 65, 2612–2614.

4760 Organometallics, Vol. 28, No. 16, 2009
Kabytaev et al.
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) for Crystal
Structures of 1 and 4
Scheme 2. Reaction of 2-Iodo-p-carborane with Phenols
1
4
B(2)-C(1)
1.744(2)
1.804(2)
1.802(2)
1.780(2)
1.781(2)
1.3884(16)
1.4324(14)
119.76(10)
1.721(2)
1.798(2)
1.799(2)
1.784(2)
1.777(2)
1.4016(19)
1.3789(17)
127.42(11)
B(2)-B(3)
B(2)-B(6)
B(2)-B(7)
B(2)-B(11)
B(2)-O(13)
O(13)-C(14)
B(2)-O(13)-C(14)
Table 1. Reaction of 2-Iodo-p-carborane with Phenolsa
Figure 2. Formation of puckered layers in 4 through C-H
interactions.
π
3 3 3
It is known that reaction of aryl halides with alcohols or
phenols can be effectively catalyzed by copper complexes
and nanoparticles.21 However, all our attempts to perform
the reaction of 2-iodo-p-carborane with t-BuONa in the
presence of copper complexes were unsuccessful.
It deserves mentioning that p-carborane derivatives sub-
stituted by one alkoxy or aryloxy group at the boron atom
have not been known until now. Thus, only closo-2,3,4,5,-
6,7,8,9,10,11-decahydroxy-1,12-bis(sulfonic acid)-1,12-dicar-
badodecaborane(12) was prepared by Hawthorne.16 Ex-
haustive methylation of this compound by methyl triflate
furnished closo-B-decamethoxy-1,12-bis(methylsulfonate)-
p-carborane.
Description of Structures. The structures of studied
compounds, 2-methoxy-p-carborane (1) and 2-(4-methyl-
phenoxy)-p-carborane (4), are shown in Figure 1. The
selected bond lengths and angles are given in Table 2.
From Table 2, it is apparent that, in general, the geome-
trical parameters of the studied molecules are quite similar.
The main difference is the B(2)-C(1) bond length, which in 4
is 0.023 A shorter than that in 1. As it is known from the
literature for the carborane derivatives, containing atoms
with electron lone pairs (LP) (oxygen, nitrogen, sulfur, etc.)
bonded to carboranes, the electron back-donation of LP to
the antibonding orbital of the bond of the icosahedron can
occur.22 On the basis of the literature analysis of the studied
a Reaction conditions: 0.37 mmol of 2-iodo-para-carborane and
catalyst were added to 1.48 mmol of the corresponding phenol pre-
treated with 1.11 mmol of NaH in 3 mL of dioxane, 90 °C. b Yield
determined by 11B NMR is 98%.
Of all dicarba-closo-dodecaborane isomers (p-, m-, and
o-carboranes), only the 2-iodo derivative of p-carborane
gives the coupling products with alcohols and phenols under
the mentioned conditions. 9-Iodo-m-carborane is not reac-
tive enough, though it can participate in amination19 and
amidation11 reactions. It was found that 9-iodo-o-carborane
quantitatively decomposes under basic conditions, forming
nido-undecaborate.20
(21) (a) Beletskaya, I. P.; Cheprakov, A. V. Coord. Chem. Rev. 2004,
248, 2337. (b) Hosseinzadeh, R.; Tajbakhsh, M.; Mohadjerani, M.; Alikarami,
M. Synlett2005, 7, 1101. (c) Kidwai, M.;Mishra, N. K.; Bansal, V.;Kumar, A.;
Mozumdar, S. Tetrahedron Lett. 2007, 48, 8883.
(19) Kabytaev, K. Z.; Bregadze, V. I.; Beletskaya, I. P. Unpublished
results
ꢀ
(20) Plesek, J.; Hermanek, S.; Stı
ꢀ
ꢀ
ꢁ
~
€€
€
´
br, B. J.; Waksman, L.; Sneddon, L.
(22) Teixidor, F.; Flores, M. A.; Vinas, C.; Sillanpaa, R.; Kivekas, R.
G. Inorg. Synth. 1983, 22, 231.
J. Am. Chem. Soc. 2000, 122, 1963.

Article
Organometallics, Vol. 28, No. 16, 2009 4761
Figure 3. Formation of infinite chains in the crystal of 1.
Table 3. Crystal Data and Structure Refinement for 1 and 4
1
4
formula
mol wt
C3H14B10
174.24
O
C9H18B10
250.33
O
cryst color, habit
cryst size, mm
cryst syst
Colorless, plate
0.13 ꢀ 0.11 ꢀ 0.08
monoclinic
Colorless, block
0.17 ꢀ 0.13 ꢀ 0.11
monoclinic
space group
C 2/c
P 2(1)/n
Cell Constants
a, A
b, A
c, A
R, deg
β, deg
26.432(5)
6.5980(17)
12.095(2)
90.00
108.445(7)
90.00
2001.0(7)
8
1.157
56
0.057
8250
0.998
2406 (Rint = 0.0322)
1561
172
7.0460(8)
10.8128(12)
18.763(2)
90.00
94.115(2)
90.00
1425.8(3)
4
1.166
58
0.060
15 385
0.999
3799 (Rint = 0.0453)
2679
226
γ, deg
V, A3
Z
Dcalcd, g cm-3
2θmax, deg
abs coeff., μ(Mo KR), mm-1
no. reflns collected
completeness
no. indep reflns
no. obsd reflns (I > 2σ(I))
no. of params
R1 (on F for obsd reflns)
wR2 (on F2 for all reflns)
0.0412
0.1127
0.0524
0.1159
w )
-1=σ2(Fo2) + (aP)2 + bP, P = 1/3(Fo2 + 2Fc
2
Weighting Scheme
a
0.06
0
720
0.02
1.0
520
0.998
b
F(000)
GOOF
largest diff peak and hole, e A-3
1.014
0.244 and -0.196
0.349 and -0.225
compounds it is reasonable to propose that the antibonding
orbital of the B(2)-C(1) bond should be involved in such
interaction, for which the highest difference in bond length is
observed.23 Thus, it is possible to suggest that the bond
length variation is caused by the difference in the extent of
the LP-carborane charge transfer. Analysis of the bond
lengths also shows that variation of the bond lengths in the
Bcarb-O-C fragment takes place, which can indicate that
the LP of oxygen atoms are involved in conjugation with
the aromatic ring. It is clear from the values of the O(13)-
C(14) bond lengths that for 1 it is 0.053 A longer than that
in 4, while the B(2)-O(13) bond, in contrast, is shorter by
0.014 A. Thus, it is possible to conclude that the conjugation
of oxygen LP with the aromatic ring leads to the decrease in
the extent of the charge transfer to the antibonding orbital of
the B(2)-C(1) bond.
The crystal packings of two studied p-carboranes deriva-
tives are different. Thus, in the crystal of 4 molecules form
weak intermolecular C-H π interactions by both C-H
3 3 3
(23) Glukhov, I. V.; Lyssenko, K. A.; Korlyukov, A. A.; Antipin, M.
Yu. Faraday Discuss. 2007, 135, 203.

4762 Organometallics, Vol. 28, No. 16, 2009
Kabytaev et al.
hydrogen atoms of the carborane moiety, which are more
acidic than the B-H ones. This type of interaction for
carboranes plays an important role in the formation of
crystal structures, as described in a number of papers dedi-
cated to the cocrystals of carboranes.24 Distances between
the hydrogen atoms and centroids of the aromatic rings are
equal to 2.489 and 2.514 A for interactions formed by H(1)
and H(12) atoms, respectively. The mentioned interactions
lead to the formation of a sandwich-like structure (see
Figure 2), in which a given carborane icosahedron is sur-
rounded by two aromatic rings in a metallocene fashion. This
results in the formation of puckered layers, which are inter-
linked by weak van der Waals interactions only.
eluent. The reaction was stopped after all 2-iodo-p-carborane
was consumed. The resulting mixture was diluted with dichloro-
methane and filtered through a paper filter, and the solvent was
carefully removed under vacuum. The crude product was pur-
ified by flash chromatography on silica gel using petroleum
ether or chloroform as eluent (h=10 cm, i=2 cm).
2-Methoxy-1,12-dicarba-closo-dodecaborane (1). The mixture
of MeONa (60 mg, 1.11 mmol), 2-iodo-p-carborane (100 mg,
0.37 mmol), Pd(dba)2 (10.6 mg, 5.0%), and BINAP (11.6 mg,
5.0%) was stirred for 72 h at 90 °C in dioxane and then worked
up as stated in General Procedures. Yield: 63%; colorless oil
crystallizes upon cooling. 11B NMR: -24.5 (d, 1B, J=169 Hz),
-18.3 (d, 2B, J=171 Hz), -17.4 (d, 2B, J=128 Hz), -16.9
1
(d, 2B, J=172 Hz), -15.4 (d, 2B, J=155 Hz), 3.3 (s, 1B). H
NMR: 0.9-3.1 (m, 9H, B-H), 2.64 (s, 1H, cage C-H), 3.04 (s,
1H, cage C-H), 3.58 (s, 3H, Me). Anal. Calcd for C3H14B10O:
C, 20.68; H, 8.10. Found: C 20.59; H 8.21.
In the crystal of 1 molecules are held together by C-
H
O interactions of two types (see Figure 3): C(12)-
3 3 3
H(12) O(13C) (H(12) and C(14)-H(14A) O(13A).
3 3 3
3 3 3
2-Ethoxy-1,12-dicarba-closo-dodecaborane (2). Ethanol was
added by micropipet (35.5 μL, 28 mg, 0.6 mmol) to a suspension
of NaH (60% dispersion in mineral oil; 24 mg, 0.6 mmol) in
dioxane (1 mL). The mixture was stirred at 90 °C for 30 min, and
then 2-iodo-p-carborane (54 mg, 0.2 mmol), Pd(dba)2 (6 mg,
5.0%), and BINAP (6 mg, 5.0%) were added to the mixture. The
stirring was continued for 22 h at 90 °C in dioxane and then
worked up as stated in General Procedures. Yield: 61%, color-
less oil. 11B NMR: -24.3 (d, 1B, J = 167 Hz), -18.4 (d, 2B, J =
122 Hz), -16.9 (d, 2B, J = 140 Hz), -15.3 (d, 2B, J = 64 Hz),
-14.7 (d, 2B, J = 184 Hz), 3.1 (s, 1B). 1H NMR: 1.0-3.0 (m,
9H, B-H), 1.29 (t, 3H, CH3, J=7.0 Hz), 2.67 (s,1H, cage C-H),
3.06 (s, 1H, cage C-H), 3.84 (q, 2H, CH2, J=7.0 Hz). 13C NMR:
17.1, 59.4, 64.9, 66.4. Anal. Calcd for C4H16B10O: C, 25.52; H,
8.57. Found: C, 25.69; H, 8.33.
2-(Phenoxy)-1,12-dicarba-closo-dodecaborane (3). Yield: 66%,
colorless oil. 11B NMR: -23.7 (d, 1B, J=169 Hz), -18.0 (d, 2B,
J = 170 Hz), -16.7 (d, 4B, J = 172 Hz), -14.8 (d, 2B, J = 175
Hz), 1.9 (s, 1B). 1H NMR: 1.4-3.3 (m, 9H, B-H), 2.73 (s, 1H,
carborane cage C-H), 3.22 (s, 1H, carborane cage C-H), 7.09-
7.11 (m, 3H, benzene ring), 7.34 (t, 2H, benzene ring, J = 7.9 Hz).
13C NMR: 59.9, 64.8, 120.2, 123.0, 129.6, 157.4. Anal. Calcd for
C8H16B10O: C, 40.66; H, 6.82; B, 45.75. Found: C, 41.03; H, 6.73;
B, 45.73. MS: m/z 236 [M]þ.
Geometrical parameters of the hydrogen bonds: C(12)-
H(12), H(12) O(13C), and C(12) O(13C) bond lengths
are equal to 0.968, 2.551, and 3.276(2) A, respectively. The
C(12)-H(12)-O(13C) angle is 132°. C(14)-H(14A), H-
(14A) O(13A), and C(14) O(13A) bond lengths are
3 3 3
3 3 3
3 3 3
3 3 3
equal to 0.980, 2.659, and 3.475(2) A. The C(14)-H-
(14A)-O(13A) angle is 141°. These interactions are rather
weak, but they lead to the formation of infinite chains
parallel to b axis. These chains are interlinked by van der
Waals interactions only.
Conclusion
We have described an efficient method for introduction of
an alkoxy or aryloxy group at a boron atom of p-carborane.
Using the Pd(dba)2/BINAP system in dioxane at 90 °C, the
etheration of 2-iodo-p-carborane at the boron atom with
various O-nucleophiles (sodium salts of phenols, MeONa,
and EtONa) was accomplished for the first time. Impor-
tantly, p-carboranes substituted by one alkoxy or aryloxy
group at the boron atom have not been known until now.
2-(4-Methylphenoxy)-1,12-dicarba-closo-dodecaborane (4).Yield:
68%, colorless crystalline solid, mp 43-44 °C. 11B NMR: -23.8
(d, 1B, J=158 Hz), -18.0 (d, 2B, J=168 Hz), -16.7 (d, 4B, J=
171 Hz), -14.9 (d, 2B, J = 171 Hz), 2.0 (s, 1B). 1H NMR: 1.4-3.1
(m, 9H, B-H), 2.35 (s, 3H, Me group), 2.72 (s, 1H, carborane cage
C-H), 3.21 (s, 1H, carborane cage C-H), 6.98 (d, 2H, benzene
ring, J= 8.5 Hz), 7.13 (d, 2H, benzene ring, J=8.5Hz). 13CNMR:
20.7, 59.9, 64.7, 119.9, 130.0, 132.3, 155.3. Anal. Calcd for
C9H18B10O: C, 43.18; H, 7.25; B, 43.18. Found: C, 42.99; H, 7.09;
B, 43.28.
2-(3,4-Dimethylphenoxy)-1,12-dicarba-closo-dodecaborane (5).
Yield 92%, white crystalline solid, mp 54 °C. 11B NMR: -23.9
(d, 1B, J = 171 Hz), -18.1 (d, 2B, J = 174 Hz), -16.8 (d, 4B, J =
171 Hz), -14.9 (d, 2B, J = 175 Hz), 2.0 (s, 1B). 1H NMR: 1.4-
3.3 (m, 9H, B-H), 2.24 (s, 3H, Me), 2.26 (s, 3H, Me) 2.72 (s,1H,
cage C-H), 3.20 (s, 1H, cage C-H), 6.81-6.85 (m, 2H, benzene
ring), 7.07 (d, 1H, benzene ring, J = 8.0 Hz). 13C NMR: 19.0,
20.0, 59.8, 64.7, 117.2, 121.4, 130.4, 131.0, 137.9, 155.4. Anal.
Calcd for C10H20B10O: C, 45.43; H, 7.63. Found: C, 45.59;
H, 7.76.
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). Car-
borane 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 phenols were recrystallized before use. Dioxane was
dried over sodium benzophenone ketyl and distilled under argon
prior to use. The 1H, 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. 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 Experimental Procedures. A phenol was added
(1.48 mmol) to a suspension of NaH (60% dispersion in mineral
oil; 44.4 mg, 1.11 mmol) in dioxane (3 mL). The mixture was
stirred at 90 °C for 30 min, and then 2-iodo-p-carborane (100
mg, 0.37 mmol), Pd(dba)2 (10.6 mg, 5.0%), and BINAP (11.6
mg, 5.0%) were added to the mixture. The stirring was con-
tinued at 90 °C for 24-72 h, depending on the phenol substrate.
The reaction was monitored by TLC using petroleum ether as
2-(r-Naphthoxy)-1,12-dicarba-closo-dodecaborane (6). Yield:
85%, yellowish crystalline solid, mp 72-73 °C. 11B NMR:
-23.7 (d, 1B, J=166 Hz), -18.0 (d, 2B, J=144 Hz), -16.7
1
(d, 4B, J=171 Hz), -14.8 (d, 2B, J=170 Hz), 2.2 (s, 1B). H
NMR: 1.4-3.3 (m, 9H, B-H), 2.75 (s, 1H, cage C-H), 3.32
(s,1H, cage C-H), 7.28 (t, 1H, naphthoxy, J=3.5 Hz), 7.44 (t,
1H, naphthoxy, J=7.9 Hz), 7.50-7.54 (m, 2H, naphthoxy), 7.60
(d, 1H, naphthoxy, J = 8.2 Hz), 7.83-7.87 (m, 1H, naphthoxy),
8.10-8.16 (m, 1H, naphthoxy). 13C NMR: 60.0, 65.0, 114.3,
(24) Blanch, R. J.; Williams, M.; Fallon, G. D.; Gardiner, M. G.;
Kaddour, R.; Raston, C. L. Angew. Chem., Int. Ed. Engl. 1997, 36, 504.

Article
Organometallics, Vol. 28, No. 16, 2009 4763
122.2, 122.8, 125.6, 125.7, 125.8, 126.3, 127.6, 127.8, 134.9.
Anal. Calcd for C12H18B10O: C, 50.33; H, 6.34; B, 37.75. Found:
C, 50.54; H, 6.36; B, 37.40.
resulting mixture was diluted with chloroform and filtered
through a paper filter, and then solvent was carefully removed
under vacuum. The residue was dissolved in CDCl3 and
analyzed by 11B NMR spectroscopy. No reaction product was
observed.
2-(β-Naphthoxy)-1,12-dicarba-closo-dodecaborane (7). Yield:
36%, colorless crystalline solid, mp 67-68 °C. 11B NMR: -23.6
(d, 1B, J=161 Hz), -17.9 (d, 2B, J=176 Hz), -16.7 (d, 4B,
J=172 Hz), -14.8 (d, 2B, J = 165 Hz), 2.0 (s, 1B). 1H NMR:
1.4-3.3 (m, 9H, B-H), 2.75 (s, 1H, cage C-H), 3.27 (s, 1H, cage
C-H), 7.26-7.29 (m, 1H, naphthoxy), 7.42 (t, 1H, naphthoxy,
J=7.5 Hz), 7.46-7.50 (m, 2H, naphthoxy), 7.78-7.84 (m, 3H,
naphthoxy). 13C NMR: 60.0, 64.8, 115.7, 121.4, 124.5, 126.3,
127.1, 127.7, 129.6, 130.1, 134.4, 155.2. Anal. Calcd for
C12H18B10O: C, 50.33; H, 6.34; B, 37.75. Found: C, 50.29; H,
6.36; B, 37.60.
2-(3-Methyl-4-chlorophenoxy)-1,12-dicarba-closo-dodecabor-
ane (8). Yield: 95%, colorless oil. 11B NMR: -23.7 (d, 1B, J=
160 Hz), -18.0 (d, 2B, J=145 Hz), -16.7 (d, 4B, J=151 Hz),
-14.9 (d, 2B, J = 164 Hz), 1.8 (s, 1B). 1H NMR: 1.4-3.3 (m,
9H, B-H), 2.37 (s, 3H, Me), 2.74 (s, 1H, cage C-H), 3.20 (s, 1H,
cage C-H), 6.86 (dd, 1H, benzene ring, J = 2.8 Hz and J=
8.8 Hz), 6.94 (d, 1H, benzene ring, J = 2.7 Hz), 7.27 (s, 1H,
benzene ring). 13C NMR: 20.3, 60.0, 64.7, 118.8, 122.6, 128.2,
129.8, 137.3, 155.9. Anal. Calcd for C9H17B10OCl: C, 37.96; H,
6.02. Found: C, 37.80; H, 5.86.
X-ray Crystal Structure Determination of Compounds 1 and 4.
Crystals of 1 were obtained by cooling of 1 in liquid state (oil)
to 4 °C. The crystals of 4 suitable for X-ray study were grown
by diffusion of warm hexane into a hot chloroform solution.
Single-crystal X-ray diffraction experiments for 1 and 4 were
carried out with a Bruker SMART 1000 CCD area detector
diffractometer, using graphite-monochromated Mo KR radia-
tion (λ = 0.71073 A, ω-scans) at 120 K. The low temperature of
the crystals was maintained with a Cryostream (Oxford
Cryosystems) open-flow N2 gas cryostat. Reflection intensities
were integrated using SAINT software25 and absorption correc-
tion was applied semi-empirically using SADABS program.26
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 carborane hydrogen
atoms were located from difference Fourier syntheses; the H(C)
atoms were placed in geometrically calculated positions. All
calculations were performed on an IBM PC/AT using
SHELXTL software.27 Crystallographic data and refinement
parameters for compounds are presented in Table 3.
Control Experiment: Reaction of 2-Iodo-p-carborane with
Sodium tert-Butoxide with No Catalyst. The mixture of
t-BuONa (29 mg, 0.3 mmol) and 2-iodo-p-carborane (27 mg,
0.1 mmol) was stirred for 48 h at 100 °C in dioxane. The resulting
mixture was diluted with diethyl ether and filtered through a
paper filter, and then solvent was carefully removed under
vacuum. The residue was dissolved in CDCl3 and analyzed by
11B NMR spectroscopy. Only starting material was found.
Attempt to Perform Copper-Catalyzed Reaction of 2-Iodo-p-
carborane with tert-Butoxide. The mixture of t-BuONa (29 mg,
0.3 mmol), 2-iodo-p-carborane (27 mg, 0.1 mmol), CuI (2 mg,
10% mol), and phenanthroline (2 mg, 10% mol) or trans-1,2-
diaminocyclohexane (1.2 mg, 10% mol) was stirred for 24 h at
100 °C in dioxane. The resulting mixture was diluted with
diethyl ether and filtered through a paper filter, and then solvent
was carefully removed under vacuum. The residue was dissolved
in CDCl3 and analyzed by 11B NMR spectroscopy. No new
product was formed.
Acknowledgment. Financial support by the Russian
Foundation for Basic Research and support of the Pre-
sident of the Russian Federation for leading schools
(project NSh-3019.2008.3) are acknowledged. We thank
Dr. Alexei D. Averin for acquiring NMR spectra.
Supporting Information Available: Crystallographic data for
structures 1 and 4 (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 and 4 are 712095 and 712094. These data can be obtained free
of charge on application to the CCDC (e-mail deposit@ccdc.
cam.ac.uk).
Attempt to Perform Reaction of 9-Iodo-m-carborane with
Phenol. Phenol was added (28 mg, 0.3 mmol) to a suspension
of NaH (60% dispersion in mineral oil; 8 mg, 0.2 mmol) in
dioxane (1 mL). The mixture was stirred at 90 °C for 20 min,
and then 9-iodo-m-carborane (27 mg, 0.1 mmol), Pd(dba)2
(3 mg, 5.0%), and BINAP (3 mg, 5.0%) were added to the
mixture. The stirring was continued at 90 °C for 48 h. The
(25) (a) SAINTPlus, Data Reduction and Correction Program, v. 6.01;
Bruker AXS: Madison, WI, 1998. (b) SMART, Bruker Molecular Analysis
Research Tool, v. 5.059; Bruker AXS: Madison, WI, 1998.
(26) Sheldrick, G. M. SADABS, Bruker/Siemens Area Detector
Absorption Correction Program, v.2.01; Bruker AXS: Madison, WI, 1998.
(27) Sheldrick, G. M., SHELXTL-97, Version 5.10; Bruker AXS Inc.:
Madison, WI, 1997.