Practical synthesis of aminoethyl-o-carboranes

Article abstract of DOI:10.1021/om020803q

A convenient synthesis of [(N,N′-dibenzylamino)ethyl]-o-carboranes (3) is reported. Under catalytic hydrogenolysis conditions (H₂/Pd-C), o-carboranylamines with N-benzyl groups were selectively removed to give the corresponding secondary amines (4). Thus, a highly selective cleavage of one N-benzyl group was achieved by using Pd catalyst under mild and acidic reaction conditions. This method is efficient and compatible with other o-carboranyl alkyl groups such as methyl and phenyl groups present in the substrate. Alternatively, primary aminoethyl-o-carborane (7) can be prepared by monoalkylation of o-carborane, followed by selective deprotection of the silyl group.

Full text of DOI:10.1021/om020803q

Organometallics 2003, 22, 445-449
445
P r a ctica l Syn th esis of Am in oeth yl-o-ca r bor a n es
J ong-Dae Lee,† Young-J oo Lee,† Hee-J un J eong,† J i Sun Lee,‡ Chai-Ho Lee,*,‡
J aejung Ko,*,† and Sang Ook Kang*,†
Department of Chemistry, Korea University, 208 Seochang, Chochiwon,
Chung-nam 339-700, Korea, and Department of Chemistry, Wonkwang University,
Iksan, J eonbuk 570-749, Korea
Received September 26, 2002
A convenient synthesis of [(N,N′-dibenzylamino)ethyl]-o-carboranes (3) is reported. Under
catalytic hydrogenolysis conditions (H2/Pd-C), o-carboranylamines with N-benzyl groups
were selectively removed to give the corresponding secondary amines (4). Thus, a highly
selective cleavage of one N-benzyl group was achieved by using Pd catalyst under mild and
acidic reaction conditions. This method is efficient and compatible with other o-carboranyl
alkyl groups such as methyl and phenyl groups present in the substrate. Alternatively,
primary aminoethyl-o-carborane (7) can be prepared by monoalkylation of o-carborane,
followed by selective deprotection of the silyl group.
In tr od u ction
functionally substituted substrates are used. In 1997,
Quintana9 reported the formation of functionalized
aminoalkyl-o-carboranes by the reaction of lithio-o-
carborane with N-(bromoalkyl)phthalimides and their
application to the preparation of isocyanate-substituted
o-carboranes. Hughes and co-workers10 later described
the successful deprotection of N-phthalimidoalkyl-o-
carboranes with hydrazine hydrate; however, the puri-
fication of the resultant aminoalkyl-o-carboranes was
unreliable, and the yields after recrystallization were
consistently low as a result of the formation of debor-
onated coproducts.11 Thus, we chose to explore alterna-
tive procedures for the introduction of the aminoalkyl
functional group into the carboranes. With the aim of
obtaining a convenient and high-yielding route to the
monosubstituted aminoalkyl-o-carborane derivatives,
N-(2-chloroethyl)dibenzylamine (2) was chosen as the
starting material. The benzyl moiety is one of the most
commonly employed protecting groups for amine func-
tionality in organic synthesis12 due to its ease of
deprotection and inherent stability. Thus, the [(N,N′-
dibenzylamino)ethyl]-o-carboranes 3 were prepared by
the addition of lithio-o-carborane to N-(2-chloroethyl)-
dibenzylamine (2). Subsequent hydrogenolysis caused
N-debenzylation to produce the corresponding secondary
amines. Alternatively, the reaction between lithio-o-
carborane 1a and ClCH2CH2N(SiMe3)2 (5) followed by
hydrolysis of the resultant disilazane with aqueous HCl
yielded the primary amine, aminoethyl-o-carborane (7),
quantitatively. Therefore, an alternative and convenient
synthetic methodology for the synthesis of aminoalkyl-
o-carboranes has been developed. The carborane prod-
ucts were analyzed by NMR spectroscopy and X-ray
crystallography where appropriate.
Aminoalkyl-o-carboranes (CabN) have attracted inter-
est due to their potential use in boron neutron capture
therapy (BNCT).1 Moreover, the coordination behavior
of these potentially bidentate ligands has been the focus
of extensive studies.2 Furthermore, the corresponding
deboronated compounds (DcabN) are the common start-
ing materials for the preparation of new half-sandwich
complexes, (DcabN)ML2 (M ) Ti, Zr, Hf, L ) Cl;3 M )
Fe, Ru, L ) Lewis base;4 M ) Ni, L ) PPh35), with
metals possessing specific structures and reactivities.
Hence, there is considerable interest in the synthesis
of aminoalkyl-o-carboranes.
The synthesis of aminoalkyl-o-carboranes is com-
monly achieved by the addition of terminal alkynes to
activated boranes B10H12L2.6 However, despite recent
modifications,7,8 low yields of the desired aminoalkyl-
o-carboranes are not uncommon, especially when highly
† Korea University.
‡ Wonkwang University.
(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)
Carlsson, J .; Gedda, L.; Gronvik, C.; Hartman, T.; Lindstro¨m, A.;
Lindstro¨m, P.; Lundqvist, H.; Lo¨vqvist, A.; Malmqvist, J .; Olsson, P.;
Essand, M.; Ponten, J .; Sjo¨berg, S.; Westermark, B. Int. J . Radiat.
Oncol., Biol., Phys. 1994, 30, 105. (c) Spielvogel, B. F.; Sood, A. US
Patent, 5272250, 1993.
(2) (a) Ko, J .; Kang, S. O. Adv. Organomet. Chem. 2001, 47, 61. (b)
Lee, J .-D.; Kim, S.-J .; Yoo, D.; Ko, J .; Cho, S.; Kang, S. O. Organome-
tallics 2000, 19, 1695. (c) Lee, J .-D.; Baek, C.-K.; Ko, J .; Park, K.; Cho,
S.; Min, S.-K.; Kang, S. O. Organometallics 1999, 18, 2189.
(3) Kim, D.-H.; Won, J . H.; Kim, S.-J .; Ko, J .; Kim, S. H.; Cho, S.;
Kang, S. O. Organometallics 2001, 20, 4298.
(4) Park, J .-S.; Kim, D.-H.; Ko, J .; Kim, S. H.; Cho, S.; Lee, C.-H.;
Kang, S. O. Organometallics 2001, 20, 4632.
(5) Park, J .-S.; Kim, D.-H.; Kim, S.-J .; Ko, J .; Kim, S. H.; Cho, S.;
Lee, C.-H.; Kang, S. O. Organometallics 2001, 20, 4483.
(6) Heying, T. L.; Ager, J . W., J r.; Clark, S. L.; Mangold, D. J .;
Goldstein, H. L.; Hilman, M.; Polark, R. J .; Szymanski, J . W. Inorg.
Chem. 1963, 2, 1089.
(9) Wu, Y.; Carroll, P. J .; Kang, S. O.; Quintana, W. Inorg. Chem.
1997, 36, 4753.
(7) Wilson, J . G.; Anisuzzaman, A. K. M.; Alam, F.; Soloway, A. H.
Inorg. Chem. 1992, 31, 1955.
(8) (a) Malmquist, J .; Ghaneolhosseini, H.; Sjo¨berg, S. Acta Chem.
Scand. 1996, 50, 958. (b) Malmquist, J .; Sjo¨berg, S. Acta Chem. Scand.
1994, 58, 886. (c) Malmquist, J .; Sjo¨berg, S. Inorg. Chem. 1992, 31,
2534.
(10) Batsanov, A. S.; Goeta, A. E.; Howard, J . A. K.; Hughes, A. K.;
Malget, J . M. J . Chem. Soc., Dalton Trans. 2001, 1820.
(11) Nagakawa, T.; Watanabe, H.; Yoshizaki, T. J pn. Pat.
J P45031940, 1970.
(12) Greene, T. W.; Wuts, P. G. M. Protecting Groups in Organic
Synthesis, 3rd ed.; Wiley: New York, 1999.
10.1021/om020803q CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/21/2002

446 Organometallics, Vol. 22, No. 3, 2003
Lee et al.
Sch em e 1. Syn th esis of 3a
Ta ble 1. X-r a y Cr ysta llogr a p h ic Da ta a n d
P r ocessin g P a r a m eter s for Com p ou n d s 3a a n d 4a
3a
4a
formula
fw
C
18H29B10
N
C11H24B10ClN
313.86
367.52
cryst class
space group
Z
monoclinic
P21/c
4
orthorhombic
P212121
4
cell constants
a, Å
b, Å
10.2077(6)
15.2630(9)
14.7009(12)
2263.3(3)
6.8687(7)
11.6255(8)
23.1877(13)
1851.6(3)
a
Legend: (i) BunLi, benzene, 25 °C.
c, Å
Resu lts a n d Discu ssion
V, Å3
â, deg
98.818(6)
0.055
Syn th esis of [(N,N′-Diben zyla m in o)eth yl]-o-ca r -
bor a n e (3). The carborane 3 was obtained from the
direct reaction of lithio-o-carborane with N-(2-chloro-
ethyl)dibenzylamine (2) as described in Scheme 1.
The synthesis was initiated by the monolithiation of
the o-carborane derivatives 1.13 When o-carborane was
treated with an equimolar quantity of n-butyllithium
in benzene followed by N-(2-chloroethyl)dibenzylamine
(2), [(N,N′-dibenzylamino)ethyl]-o-carborane (3) was
formed in high yield. In this case, no color change was
observed and the reaction was monitored by TLC;
complete disappearance of the starting material was
observed after 12 h of vigorous stirring at room tem-
perature. Compounds 3 are moderately stable in air and
can be purified by low-temperature recrystallization in
ethanol. The identification of all products 3 isolated was
accomplished by IR and 1H, 11B, and 13C NMR spec-
troscopy. Accordingly, the compounds 3 have distinct
µ, mm-1
cryst size, mm
D
0.196
0.4 × 0.45 × 0.45
0.3 × 0.35 × 0.5
calcd, g/cm3
F(000)
radiation
θ range, deg
h, k, l collected
no. of reflns collected/
unique
1.079
1.126
656
776
Mo KR (λ ) 0.7170 Å)
1.94-25.97
+12,+18,(18
4694/4442
1.76-25.97
+8,+14,+28
2146/2109
no. of data/restraints/
params
4442/0/283
2109/0/232
goodness-of-fit on F2
0.321
1.106
final R indices [I > 2σ(I)] R1 ) 0.0389a
R1 ) 0.0594a
wR2 ) 0.1565b
R1 ) 0.1345a
wR2 ) 0.1879b
wR2 ) 0.0886b
R indices (all data)
R1 ) 0.2565a
wR2 ) 0.1142b
R1 ) ∑||Fo| - |Fc| (based on reflections with Fo2 > 2σF2). wR2
a
b
) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2; w ) 1/[σ2(Fo2) + (0.095P)2]; P )
2
[max(Fo2,0) + 2Fc2]/3 (also with Fo > 2σF2).
2
Ta ble 2. Selected In ter a tom ic Dista n ces (Å) in 3a
a n d 4a
1
resonances in the H NMR spectrum for each proton of
the CH2 units: δ 3.4-3.6 (s, 2H, N-CH2-Ph), δ 2.5-2.7
(t, 2H, N-CH2-CH2), and δ 2.0-2.4 (t, 2H, Cab-CH2).
Product identification was further supported by a single-
crystal X-ray diffraction analysis of 3a . The structural
parameters (Table 2) fall within the normal range for
the monosubstituted closo-derivatives. Finally, satisfac-
tory elemental analyses were also obtained for com-
pounds 3.
P r ep a r a t ion of [(N-Ben zyla m in o)et h yl]-o-ca r -
bor a n e Hyd r och lor id e (4). The benzyl group is a
commonly used protecting group in organic synthesis,14
and its removal is in most cases carried out by hydro-
genolysis using Pd-C catalysts with H2 as the reducing
agent. Although simple hydrogenolysis of the mono-
and/or dibenzylamine derivatives by a conventional
method, Pd-C/H2, has been reported,15 the [(N,N′-
dibenzylamino)ethyl]-o-carborane derivatives in this
study failed to undergo complete cleavage under such
conditions as discussed below.16 In 1996, Blaser and
Studer reported that with catalytic amounts of HCl as
a modifier, the mono- or dibenzyl derivatives can rapidly
and selectively undergo debenzylation.17 Thus, with the
aid of HCl, the mono-debenzylation of 3 occurred cleanly
to afford the secondary benzyl amine 4 in >80% yield
after recrystallization (Scheme 2).
3a
4a
N(1)-C(5)
N(1)-C(4)
N(1)-C(12)
C(1)-C(3)
C(3)-C(4)
C(5)-C(6)
C(12)-C(13)
1.461(3)
1.464(3)
1.468(3)
1.532(3)
1.519(3)
1.502(3)
1.505(3)
N(1)-C(4)
N(1)-C(5)
C(1)-C(3)
C(3)-C(4)
C(5)-C(6)
1.483(7)
1.515(7)
1.531(7)
1.521(7)
1.479(8)
Ta ble 3. Selected In ter a tom ic An gles (d eg) in 3a
a n d 4a
3a
4a
C(5)-N(1)-C(4)
C(5)-N(1)-C(12)
C(4)-N(1)-C(12)
C(4)-C(3)-C(1)
N(1)-C(4)-C(3)
N(1)-C(5)-C(6)
N(1)-C(12)-C(13)
110.4(2)
109.8(2)
109.9(2)
116.6(2)
115.1(2)
114.5(2)
111.9(2)
C(4)-N(1)-C(5)
C(4)-C(3)-C(1)
N(1)-C(4)-C(3)
C(6)-C(5)-N(1)
114.7(5)
115.1(5)
107.7(5)
112.4(5)
Sch em e 2. Syn th esis of 4a
Compounds 4 were isolated as white, transparent
crystals. These compounds are both air- and moisture-
stable in the solid state. The structural identity of 4 was
confirmed by a single-crystal X-ray structural analysis
of 4a (Figure 2). The reaction of 3a in acidic ethanol
with H2 (60 psi) and Pd-C catalyst caused selective
mono-debenzylation and produced a quantitative yield
of the corresponding secondary amine 4a . The at-
tempted deprotection of the second N-benzyl group
a
Legend: (i) H2, Pd/C, HCI, EtOH, 25 °C.
proved unsuccessful under these reaction conditions,
with no evidence for the formation of primary amines
even upon treatment with excess Pd catalyst and
extended reaction times. Similarly, the use of the
corresponding methyl- or phenyl-o-carborane derivative
in Scheme 2 yielded the mono-debenzylated product 4b

Practical Synthesis of Aminoethyl-o-carboranes
Organometallics, Vol. 22, No. 3, 2003 447
Sch em e 3. Syn th esis of 7a
a
Legend: (i) Methylene chloride, 25 °C; (ii) BunLi, benzene,
25 °C; (iii) HCI, Et2O, 25 °C.
of o-carborane. The HCl-promoted deprotection of silyl
groups is well established and was exploited in our
preparation of 7. The disilyl group was therefore selec-
tively cleaved to give the corresponding parent amine
in high yield. In terms of selectivity and efficiency, this
mild disilazane protection/deprotection protocol is su-
perior to other conventional methods using, for example,
phthalimide/hydrazine.9 The major drawback of the
latter method is the significant formation of byproducts
as a result of the use of the deprotecting reagents.
However, under our reaction conditions, only the desired
amines were obtained in quantitative yields, with no
trace of deboronated compounds.
F igu r e 1. Molecular structure of 1-[(dibenzylamino)ethyl]-
o-carborane (3a ). The thermal ellipsoids are drawn at the
30% probability level.
The treatment of 1a with 1 equiv of n-butyllithium
followed by 1 equiv of 5 yielded the monoalkylated
product 6 in high yield. Desilylation of a diethyl ether
suspension of the N-protected product 6 with 6 N HCl
at 25 °C afforded 7 directly as microcrystalline solids
in high yield. Product identification was confirmed by
comparison of spectroscopic properties with those re-
ported by Quintana.9 Thus, we have developed an
efficient alternative synthetic route to primary o-car-
boranylethylamine.
Con clu sion s
Large quantities of starting materials 3 and 6 are
readily obtained in high yield, and the subsequent
hydrogenolytic debenzylation of 3 gives the correspond-
ing secondary aminoethyl-o-carboranes 4 in high purity.
In addition, we have described a chemoselective method
for the cleavage of nitrogen-silicon bonds to generate
primary amino-o-carborane.7 The main advantage of our
protocol is the high yields of deprotected products
obtained. Thus, our synthesis provides the first practi-
cal, unequivocal synthesis of aminoalkyl-o-carboranes
adaptable for large-scale production.
F igu r e 2. Molecular structure of 1-[(benzylamino)ethyl]-
o-carborane‚HCl (4a ). The thermal ellipsoids are drawn at
the 30% probability level.
or 4c, in yields comparable to 4a . Thus, the treatment
of 3 with H2 in acidic ethanol resulted in the mono-
debenzylation to exclusively afford, based on an 1H
NMR spectroscopic analysis of the crude reaction mix-
ture, the corresponding secondary amine [(N-benzyl-
amino)ethyl]-o-carborane hydrochloric acid salts (4).
Since the debenzylation approach is not ideal for the
generation of the primary aminoethyl-o-carborane, we
felt that alternative strategies were worthy of investiga-
tion. A reported synthesis of 1-aminoethyl-o-carborane
(7) consists of the treatment of Li[1,2-C2B10H11] (1a )
with commercially available N-(bromoethyl)phthalimide
in glyme.9 We believe that the synthesis of carborane 7
shown in Scheme 3 is more convenient. There was no
substantial difference observed for the monoalkylation
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
under a dry, oxygen-free nitrogen or argon atmosphere using
standard Schlenk techniques. Ether and benzene were dried
and distilled from sodium/benzophenone. The 1H, 11B, and 13C
NMR spectra were recorded on a Varian Mercury 300 spec-
trometer operating at 300.1, 96.3, and 75.4 MHz, respectively.
All proton and carbon chemical shifts were measured relative

448 Organometallics, Vol. 22, No. 3, 2003
Lee et al.
to internal residual chloroform from the lock solvent (99.5%
CDCl3) and then referenced to Me4Si (0.00 ppm). The chemical
shift values for the 11B NMR spectra were referenced relative
to external BF3‚OEt2. IR spectra were recorded on a Biorad
FTS-165 spectrophotometer. The elemental analyses were
performed with a Carlo Erba Instruments CHNS-O EA 1108
analyzer. All melting points are uncorrected. The carboranes
and N-(2-chloroethyl)dibenzylamine were purchased from
Katechem and Aldrich, respectively, and used without puri-
fication. Palladium on carbon catalyst was purchased from
Aldrich and used without purification.
Syn th esis of 1-[(Diben zylam in o)eth yl]-o-car bor an e (3a).
To a stirred solution of o-carborane (1a ; 4.3 g, 30 mmol) in
benzene (600 mL) was added 2.5 M n-BuLi (13.2 mL, 33 mmol)
via a syringe through a serum cap at 25 °C. The resulting
white suspension was stirred at 25 °C for 10 min and then
placed in an ice bath. When the benzene solution was cold,
the N-(2-chloroethyl)dibenzylamine 2 (7.8 g, 30 mmol) was
added to the lithio-o-carborane. The reaction temperature was
maintained at 0 °C for 1 h. The reaction mixture was then
slowly warmed to room temperature. After stirring for an
additional 12 h, the reaction mixture was filtered. Diethyl
ether was added, and the organic layer was washed with
distilled water, dried with anhydrous MgSO4, and then dried
in vacuo to give a white crystalline powder. The resulting
residue was taken up in a minimum of ethanol and then
recrystallized from this solution by cooling it to -10 °C to
afford 3a (10.5 g, 95%) as colorless crystals. Anal. Calcd for
instead of 3a to yield 4b (5.8 g, 89%) as a white powder. Anal.
Calcd for C12H26B10NCl: C, 43.96; H, 7.99; N, 4.27. Found: C,
44.40; H, 8.08; N, 4.37. Mp: 230-231 °C. IR spectrum (KBr
pellet, cm-1): 2592(s), 3344(w), 3440(w). 1H NMR (DMSO-
d6): δ 2.13 (3H, s), 2.83-2.89 (2H, t), 3.10-3.13 (2H, t), 4.17
(2H, s), 7.41-7.58 (5H, m), 9.69 (2H, s). 13C NMR (DMSO-d6):
δ 22.89, 30.87, 49.85, 75.60, 76.68, 132.04.
1-[(Ben zylam in o)eth yl]-2-ph en yl-o-car bor an e‚HCl (4c).
The procedure was analogous to that described for 4a but using
3c instead of 3a to give 4c (6.3 g, 81%) as a white powder.
Anal. Calcd for C17H28B10NCl: C, 52.36; H, 7.24; N, 3.59.
Found: C, 52.47; H, 7.32; N, 3.64. Mp: 215-216 °C. IR
spectrum (KBr pellet, cm-1): 2588(s), 3327(w), 3451(w). 1H
NMR (DMSO-d6): δ 1.95-2.00 (2H, t), 2.66-2.71 (2H, t), 3.61
(2H, s), 7.41-7.61 (10H, m), 9.69 (2H, s). 13C NMR (DMSO-
d6): δ 31.59, 51.24, 75.98, 77.59, 132.05, 134.24.
P r ep a r a tion of N,N′-Bis(tr im eth ylsilyla m in o)eth ylen e
Ch lor id e (5). A 500 mL flask was charged with 2-chloro-
ethylamine hydrochloride (11.6 g, 100 mmol), NEt3 (46.4 mL,
330 mmol), and freshly distilled methylene chloride (300 mL).
A solution of chlorotrimethylsilane (28.0 mL, 220 mmol) in
methylene chloride (50 mL) was added to the vigorously stirred
slurry of chloroethylamine slowly over 1 h via a cannula. The
reaction mixture was stirred overnight, and the precipitate of
NEt3‚HCl was filtered off. The methylene chloride solution was
evaporated, and the residue was extracted with hexane. The
extracts were combined, and the solvent was removed in vacuo.
The residue was dried in vacuo to give the product as a slightly
1
C
18H29B10N: C, 58.82; H, 7.95; N, 3.81. Found: C, 58.96; H,
yellow liquid (18.1 g, 81%). H NMR (CDCl3): δ 0.12 (18H, s),
8.00; N, 3.85. Mp: 83 °C. IR spectrum (KBr pellet, cm-1):
2588(s), 3031(w), 3064(w), 3086(w). 1H NMR (CDCl3): δ 2.36-
2.41 (2H, t), 2.58-2.63 (2H, t), 3.52 (2H, s), 3.95 (1H, s), 7.27-
7.39 (10H, m). 13C NMR (CDCl3): δ 34.18, 51.92, 58.72, 73.83,
138.23.
3.04-3.09 (2H, t), 3.23-3.29 (2H, t). 13C NMR (CDCl3): δ 3.02,
44.52, 45.61.
Syn th esis of 1-[Bis(tr im eth ylsilyl)a m in oeth yl]-o-ca r -
bor a n e (6). To a stirred solution of o-carborane (1a ; 4.3 g, 30
mmol) in benzene (600 mL) was added 2.5 M n-BuLi (13.2 mL,
33 mmol) via a syringe through a serum cap at 25 °C. The
resulting white suspension was stirred at 25 °C for 10 min
and then placed in an ice bath. When the benzene solution
was cold, ClCH2CH2N(SiMe3)2 (6.7 g, 30 mmol) was added to
the lithio-o-carborane. The reaction mixture was maintained
at 0 °C for 1 h and then slowly warmed to room temperature.
After stirring for an additional 12 h, the reaction mixture was
filtered. The filtrate volume was reduced under vacuum, and
the resulting residue was taken up in a minimum of hexane
and then recrystallized from this solution by cooling it to -10
°C to afford 6 (7.7 g, 78%) as a white powder. Anal. Calcd for
1-[(Diben zyla m in o)eth yl]-2-m eth yl-o-ca r bor a n e (3b).
The same method as described for 3a but with 1b instead of
1a produced 3b (11.2 g, 98%) as white crystals. Anal. Calcd
for C19H31B10N: C, 59.81; H, 8.19; N, 3.67. Found: C, 59.90;
H, 8.23; N, 3.73. Mp: 55 °C. IR spectrum (KBr pellet, cm-1):
1
2579(s), 3029(w), 3061(w), 3085(w). H NMR (CDCl3): δ 1.71
(3H, s), 2.17-2.23 (2H, t), 2.62-2.67 (2H, t), 3.63 (2H, s), 7.27-
7.38 (10H, m). 13C NMR (CDCl3): δ 22.87, 33.01, 59.26, 74.65,
76.69, 138.99.
1-[(Diben zyla m in o)eth yl]-2-p h en yl-o-ca r bor a n e (3c).
The procedure was analogous to that described for 3a but using
1c instead of 1a to give 3c (13.0 g, 98%) as white crystals.
Anal. Calcd for C24H33B10N: C, 64.98; H, 7.50; N, 3.16.
Found: C, 65.06; H, 7.60; N, 3.24. Mp: 67 °C. IR spectrum
(KBr pellet, cm-1): 2588(s), 3030(w), 3064(w), 3084(w). 1H
NMR (CDCl3): δ 2.00-2.06 (2H, t), 2.56-2.61 (2H, t), 3.46 (2H,
s), 7.27-7.38 (15H, m). 13C NMR (CDCl3): δ 31.85, 58.37,
80.74, 83.64, 138.78.
P r ep a r a t ion of 1-[(Ben zyla m in o)et h yl]-o-ca r b or a n e‚
HCl (4a ). The Pd-C catalyst (1.5 g, 20 wt %) was introduced
into a reactor together with an equimolar quantity of concen-
trated HCl, ethanol (60 mL), and the starting material 3a (7.35
g, 20 mmol) under a hydrogen atmosphere (60 psi) at room
temperature. The reaction mixture was shaken for 5 h at room
temperature. The suspended solid was then collected by
filtration, and the solvent was removed under vacuum. The
resulting residue was taken up in a minimum of ethanol and
then recrystallized from this solution by cooling it to -10 °C
to afford 4a (4.6 g, 74%) as colorless crystals. Anal. Calcd for
C
10H33B10NSi2: C, 36.22; H, 10.03; N, 4.22. Found: C, 36.62;
H, 10.18; N, 4.33. Mp: 53 °C. IR spectrum (KBr pellet, cm-1):
1
2598(s), 2957(m), 3069(w). H NMR (CDCl3): δ 0.24 (18H, s),
2.43-2.50 (2H, t), 2.96-3.04 (2H, t), 3.34 (1H, br s). 13C NMR
(CDCl3): δ 0.20, 33.81, 37.98, 54.56.
P r ep a r a tion of 1-[(Am in o)eth yl]-o-ca r bor a n e‚HCl (7).
A 100 mL flask was charged with 1-[bis(trimethylsilyl)-
aminoethyl]-o-carborane (1.66 g, 5.0 mmol) and diethyl ether
(50 mL). The reaction flask was cooled in an ice bath, and 6 N
HCl (15 mL) was slowly added to the ethereal solution. After
12 h, the ether and water layer were separated, and the latter
was washed with ether (330 mL). The water was removed on
a rotary evaporator to give a yellowish-white powder. This
residue was taken up in a minimum of acetone and then
recrystallized from this solution by cooling it to -10 °C to
afford 7 (0.94 g, 84%) as a white crystalline powder. Anal.
Calcd for C4H18B10NCl: C, 21.47; H, 8.11; N, 6.26. Found: C,
21.73; H, 8.25; N, 6.42. Mp: 121-122 °C. IR spectrum (KBr
pellet, cm-1): 2578(s), 2909(w), 2958(w), 3070(s). 1H NMR
(DMSO-d6): δ 2.57-2.63 (2H, t), 2.83-2.89 (2H, t), 5.38 (1H,
br s), 8.04 (3H, br s). 13C NMR (DMSO-d6): δ 35.74, 37.50,
63.13.
C
11H24B10NCl: C, 42.09; H, 7.71; N, 4.46. Found: C, 42.60; H,
7.83; N, 4.54. Mp: 250-251 °C. IR spectrum (KBr pellet, cm-1):
2602(s), 3340(w), 3422(w). 1H NMR (DMSO-d6): δ 2.77-2.83
(2H, t), 3.01-3.07 (2H, t), 4.13 (2H, s), 5.42 (1H, s), 7.41-7.56
(5H, m), 9.69 (1H, s). 13C NMR (DMSO-d6): δ 44.84, 49.88,
63.13, 72.51, 131.86.
X-r a y Cr ysta llogr a p h y. Details of the crystal data and a
summary of the intensity data collection parameters for 3a
and 4a are given Table 1 in the Supporting Information. The
crystals of 3a and 4a were grown from ethanol solutions stored
1-[(Ben zylam in o)eth yl]-2-m eth yl-o-car bor an e‚HCl (4b).
The method was similar to that described for 4a but using 3b

Practical Synthesis of Aminoethyl-o-carboranes
Organometallics, Vol. 22, No. 3, 2003 449
at -10 °C. The crystals of 3a and 4a were mounted in thin-
walled glass capillaries and sealed under argon. The data sets
of 3a and 4a were collected using an Enraf CAD4 automated
diffractometer. Mo KR radiation (λ ) 0.7107 Å) was used for
all the structures. Each structure was solved by the application
of direct methods using the SHELXS-96 program18a and least-
squares refinement using SHELXL-97.18b The absolute con-
figuration of 4a was confirmed by the refinement of the Flack
parameter.
Ack n ow led gm en t. We are grateful to the Korea
Atomic Energy Research Institute for a grant (number
M20204330044-02A1102-00421).
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
distances and angles, atomic coordinates, and thermal param-
eters for compounds 3a and 4a . This material is available free
of charge via the Internet at http://pubs.acs.org.
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OM020803Q
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Sheldrick, G. M. SHELXL, Program for Crystal Structure Refinement;
University of Go¨ttingen: Germany, 1997.