Palladium/nickel-cocatalyzed cycloaddition of 1,3-dehydro-o-carborane with alkynes. Facile synthesis of C,B-substituted carboranes

Article abstract of DOI:10.1021/ja1058789

o-Carboryne (1,2-dehydro-o-carborane) has been reported as a very reactive intermediate and regarded as a three-dimensional relative of benzyne, whereas the 1,3-dehydro-o-carborane has remained elusive. In this article, we present the preparation of 1,3-dehydro-o-carborane from 3-iodo-1-lithio-o-carborane mediated by palladium(0). This reactive intermediate can be trapped by alkynes via Pd/Ni-cocatalyzed [2 + 2 + 2] cycloaddition reaction, leading to the formation of C,B-substituted-o-carborane derivatives. The possible reaction mechanism involving the formation of metal-1,3-dehydro-o-carborane followed by stepwise insertions of 2 equiv of alkyne and reductive elimination is proposed, and the relative reactivity of M-C versus M-B bond in metal-1,3-dehydro-o- carborane complexes is also discussed. This work offers a new methodology for B-functionalization of carboranes and demonstrates that metal-1,3-dehydro-o- carborane can be viewed as a new kind of boron nucleophile.

Full text of DOI:10.1021/ja1058789

Published on Web 10/27/2010
Palladium/Nickel-Cocatalyzed Cycloaddition of
1,3-Dehydro-o-Carborane with Alkynes. Facile Synthesis of
C,B-Substituted Carboranes
Zaozao Qiu and Zuowei Xie*
Department of Chemistry and Center of NoVel Functional Molecules, The Chinese UniVersity of
Hong Kong, Shatin, New Territories, Hong Kong, China
Received July 2, 2010; E-mail: zxie@cuhk.edu.hk
Abstract: o-Carboryne (1,2-dehydro-o-carborane) has been reported as a very reactive intermediate and
regarded as a three-dimensional relative of benzyne, whereas the 1,3-dehydro-o-carborane has remained
elusive. In this article, we present the preparation of 1,3-dehydro-o-carborane from 3-iodo-1-lithio-o-carborane
mediated by palladium(0). This reactive intermediate can be trapped by alkynes via Pd/Ni-cocatalyzed [2
+ 2 + 2] cycloaddition reaction, leading to the formation of C,B-substituted-o-carborane derivatives. The
possible reaction mechanism involving the formation of metal-1,3-dehydro-o-carborane followed by stepwise
insertions of 2 equiv of alkyne and reductive elimination is proposed, and the relative reactivity of M-C
versus M-B bond in metal-1,3-dehydro-o-carborane complexes is also discussed. This work offers a new
methodology for B-functionalization of carboranes and demonstrates that metal-1,3-dehydro-o-carborane
can be viewed as a new kind of boron nucleophile.
Chart 1. Benzyne, o-Carboryne, and 1,3-Dehydro-o-carborane
Introduction
o-Carboryne (1,2-dehydro-o-carborane), a three-dimensional
relative of benzyne (Chart 1), was first reported as a very
reactive intermediate in 1990.1 It can react with alkenes, dienes,
alkynes, and aromatics in [2 + 2], [4 + 2] cycloaddition and
ene-reaction patterns,2 similar to those of benzyne.3 This reactive
species can be stabilized by transition metals, leading to the
formation of metal-o-carboryne complexes.4 Molecular orbital
calculations on the Zr-carboryne complex suggest that the
bonding interactions between the Zr atom and carboryne ligand
are best described as a resonance hybrid of both the Zr-C σ
and Zr-C π bonding forms (Chart 2),4b which is similar to that
Chart 2. Bonding Description of Metal-Carboryne Complex
(1) Gingrich, H. L.; Ghosh, T.; Huang, Q.; Jones, M., Jr. J. Am. Chem.
Soc. 1990, 112, 4082–4083.
(2) (a) Ghosh, T.; Gingrich, H. L.; Kam, C. K.; Mobraaten, E. C. M.;
Jones, M., Jr. J. Am. Chem. Soc. 1991, 113, 1313–1318. (b) Huang,
Q.; Gingrich, H. L.; Jones, M., Jr. Inorg. Chem. 1991, 30, 3254–3257.
(c) Cunningham, R. J.; Bian, N.; Jones, M., Jr. Inorg. Chem. 1994,
33, 4811–4812. (d) Ho, D. M.; Cunningham, R. J.; Brewer, J. A.;
Bian, N.; Jones, M., Jr. Inorg. Chem. 1995, 34, 5274–5278. (e) Barnett-
Thamattoor, L.; Zheng, G.; Ho, D. M.; Jones, M., Jr.; Jackson, J. E.
Inorg. Chem. 1996, 35, 7311–7315. (f) Jeon, J.; Kitamura, T.; Yoo,
B.-W.; Kang, S. O.; Ko, J. Chem. Commun. 2001, 2110–2111. (g)
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S. R.; Qiu, Z.; Xie, Z. J. Am. Chem. Soc. 2010, 132, 9988–9989.
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91, 6411–6415.
observed in Zr-benzyne complex.5 This type of metal-o-
carboryne complex can react with unsaturated molecules in a
controlled manner to produce alkenylcarboranes,6 benzocarbo-
ranes,7 dihydrobenzocarboranes,8 and other functionalized car-
boranes.9
Theoretical studies suggest that the formation of o-carboryne
is energetically very comparable to that of benzyne. The
(5) Buchwald, S. L.; Watson, B. T. J. Am. Chem. Soc. 1986, 108, 7411–
7413.
(6) Qiu, Z.; Xie, Z. Angew. Chem., Int. Ed. 2008, 47, 6572–6575.
(7) Deng, L.; Chan, H.-S.; Xie, Z. J. Am. Chem. Soc. 2006, 128, 7728–
7729.
(4) (a) Sayler, A. A.; Beall, H.; Sieckhaus, J. F. J. Am. Chem. Soc. 1973,
95, 5790–5792. (b) Wang, H.; Li, H.-W.; Huang, X.; Lin, Z.; Xie, Z.
Angew. Chem., Int. Ed. 2003, 42, 4347–4349. (c) Ren, S.; Deng, L.;
Chan, H.-S.; Xie, Z. Organometallics 2009, 28, 5749–5756. (d) Qiu,
Z.; Deng, L.; Chan, H.-S.; Xie, Z. Organometallics 2010, 29, 4541–
4547.
(8) Qiu, Z.; Xie, Z. J. Am. Chem. Soc. 2009, 131, 2084–2085.
(9) (a) Deng, L.; Chan, H.-S.; Xie, Z. J. Am. Chem. Soc. 2005, 127, 13774–
13775. (b) Ren, S.; Chan, H.-S.; Xie, Z. J. Am. Chem. Soc. 2009,
131, 3862–3863. (c) Ren, S.; Chan, H.-S.; Xie, Z. Organometallics
2009, 28, 4106–4114.
9
10.1021/ja1058789  2010 American Chemical Society
J. AM. CHEM. SOC. 2010, 132, 16085–16093 16085

A R T I C L E S
Qiu and Xie
a
Table 1. Catalytic Deiodination of 1-Li-2-Me-3-I-1,2-C2B10H9
calculated cage C-C bond distance in o-carboryne is 1.356 Å,
indicating the multiple bond character.10 We wondered if the
unknown species 1,3-dehydro-o-carborane could be generated.
It might feature a cage C-B multiple bond (Chart 1). In view
of the characteristics of o-carboryne and the important applica-
tion of boron-centered nucleophiles,11 we then initiated a
research program to explore the chemistry of 1,3-dehydro-o-
carborane.
yield (%)b
1b 3b
entry
catalyst
loading (mol %) reaction time (h)
As o-carboryne can be generated in situ by heating 1-Li-2-
X-1,2-C2B10H10 (X ) Br,1,2 I12) via the elimination of LiX, we
attempted to produce 1,3-dehydro-o-carborane in a similar
manner using 1-Li-3-X-1,2-C2B10H10 as precursors. Unfortu-
nately, both 1-Li-3-X-1,2-C2B10H10 and 1-Li-2-CH3-3-X-1,2-
C2B10H9 are all very thermally stable even after prolonged
heating in THF or toluene. Considering that the cage B-I bond
can undergo oxidative addition in the presence of Pd(0),13 we
speculated that an oxidative addition of the cage B-I in 1-Li-
3-I-1,2-C2B10H10 on Pd(0), followed by a subsequent elimination
of LiI, would afford the target complex Pd-1,3-dehydro-o-
carborane, which could possibly be trapped by alkynes. Herein,
we report our work on palladium/nickel-cocatalyzed reaction
of 1,3-dehydro-o-carborane with 2 equiv of alkynes to afford
[2 + 2 + 2] cycloaddition products, C,B-substituted carboranes.
1
2
3
4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4/Ni(cod)2
Ni(cod)2
10
5
5/5
5
14
30
30
30
<1 >99
10 90
<1 >99
>99 <1
a
n
Conditions: (1) BuLi (1 equiv), toluene, r.t., 0.5 h; (2) catalyst, 110
°C. b Yields determined by GC-MS on the crude product mixture.
Table 2. Optimization of Pd/Ni-Cocatalyzed Cycloaddition
Reactiona
yieldb
loading (mol %) reaction time 1b 3b 4b
Results and Discussion
entry
catalyst
1,3-Dehydro-o-Carborane. In an initial attempt, a toluene
solution of 1-Li-2-Me-3-I-1,2-C2B10H9, prepared in situ by
treatment of 2-Me-3-I-1,2-C2B10H10 (1b) with 1 equiv of nBuLi,
was heated in the presence of 10 mol % Pd(PPh3)4 to give
1-methyl-o-carborane (3b) in almost quantitative yield in 14 h
as indicated by 11B NMR spectrum of the reaction mixture. This
catalytic deiodination may result from the thermal decomposition
of Pd-2-methyl-1,3-dehydro-o-carborane presumably via radical
process (Table 1, entry 1).2g,7 The solvent acts as the hydrogen
source. If the catalyst loading was reduced to 5 mol %, the
reaction was slowed down (Table 1, entry 2). Ni(cod)2 (cod )
1,5-cyclooctadiene) was almost inactive in the activation of the
cage B-I bond (Table 1, entry 4). However, a combination of
5 mol % of Ni(cod)2 and 5 mol % of Pd(PPh3)4 can enhance
the reaction rate (Table 1, entry 3) (vide infra). Grignard reagent
(MeMgBr) is less effective than nBuLi in the reaction with cage
CH. On the other hand, MeMgBr is known to react with 3-iodo-
o-carborane in the presence of Pd(0) to give 3-methyl-o-
carborane.13a It is noted that no reaction proceeded at T < 70
°C, and compound 3b can only be generated at higher tem-
1
2
3
4
5
6
7
8
9
none
Pd(OAc)2
PdCl2(PPh3)2
PdCl2(cod)
PdCl2(cod)/2PPh3
Pd(CH2TMS)2(cod)
[Pd(Ally)Cl]2
[Pd(Ally)Cl]2/4PPh3
Pd(dba)2
0
10
10
10
10
10
5
5
10
7 d
3 d
3 d
3 d
30 h
3 d
3 d
1 h
7 d
7 h
7 d
3 h
3 d
0.5 h
2 h
2 h
4 h
3 h
100
56 19 25
12 79
9
87 12 <1
<1
90
6
8
9
91
<1
25 69
<1
7 92
21 36 43
10 Pd(PPh3)4
11 Ni(cod)2
10
10
2
8
90
72 13 15
91
25 43 32
12 Pd(PPh3)4/Ni(PPh3)4
13 Pd(dba)2/Ni(cod)2
14 Pd(PPh3)4/Ni(cod)2
15 Pd(PPh3)4/Ni(cod)2
16 Pd(PPh3)4/Ni(cod)2/2PPh3
17 Pd(PPh3)4/Ni(cod)2
18 PdCl2(PPh3)2/Ni(cod)2
10/10
10/10
10/10
5/5
5/5
2/2
10/10
3
6
<1
<1
<1
<1
9
6
3
4
6
7
93
96
95
93
84
a Conditions: (1) nBuLi (1 equiv), toluene, r.t., 0.5 h; (2) catalyst,
3-hexyne (4 equiv), 110 °C. b Yields determined by GC-MS on the
crude product mixture.
peratures as indicated by 11B NMR spectroscopy in the reaction
of 1-Li-2-Me-3-I-1,2-C2B10H9 with a catalytic amount of Pd-
(PPh3)4. Many attempts to isolate pure (η2-1,3-o-
C2B10H9Me)Pd(L), an analogue of (η2-1,2-o-C2B10H10)Ni(L),4a
from a stoichiometric reaction in the presence of PPh3 or dppe
(dppe ) 1,2-bis(diphenylphosphino)ethane) failed as the reaction
did not occur at T < 70 °C and the resultant metal complex
slowly decomposed at higher temperatures. It is noteworthy that
3-bromo-o-carborane and 3-chloro-o-carborane are incompatible
with this reaction because the oxidative addition between the
B-Br or B-Cl bond and Pd(0) is inefficient.14
Subsequent work focused on trapping the 1,3-dehydro-o-
carborane intermediate by 3-hexyne. The optimization of this
reaction was listed in Table 2. No reaction was observed after
heating at 110 °C for 7 days in the absence of a catalyst. Most
of the Pd(II) species examined can catalyze the [2 + 2 + 2]
(10) Kiran, B.; Anoop, A.; Jemmis, E. D. J. Am. Chem. Soc. 2002, 124,
4402–4407.
(11) (a) Braunschweig, H.; Dewhurst, R. D.; Schneider, A. Chem. ReV.
2010, 110, 3924–3957. (b) Mkhalid, I. A. I.; Barnard, J. H.; Marder,
T. B.; Murphy, J. M.; Hartwig, J. F. Chem. ReV. 2010, 110, 890–931.
(c) Hartwig, J. F. Nature 2008, 455, 314–322. (d) Coombs, D. L.;
Aldridge, S. Coord. Chem. ReV. 2004, 248, 535–559. (e) Braunsch-
weig, H.; Colling, M. Coord. Chem. ReV. 2001, 223, 1–51. (f) Irvine,
G. J.; Lesley, M. J. G.; Marder, T. B.; Norman, N. C.; Rice, C. R.;
Robins, E. G.; Roper, W. R.; Whittell, G. R.; Wright, L. J. Chem.
ReV. 1998, 98, 2685–2722. (g) Braunschweig, H. Angew. Chem., Int.
Ed. 1998, 37, 1786–1801. (h) Segawa, Y.; Yamashita, M.; Nozaki,
K. Science 2006, 314, 113–115. (i) Segawa, Y.; Suzuki, Y.; Yamashita,
M.; Nozaki, K. J. Am. Chem. Soc. 2008, 130, 16069–16079. (j)
Spokoyny, A. M.; Reuter, M. G.; Stern, C. L.; Ratner, M. A.;
Seideman, T.; Mirkin, C. A. J. Am. Chem. Soc. 2009, 131, 9482–
9483.
(12) Qiu, Z.; Wang, S. R.; Xie, Z. Angew. Chem., Int. Ed. 2010, 49, 4649–
4652.
(13) (a) Li, J.; Logan, C. F.; Jones, M., Jr. Inorg. Chem. 1991, 30, 4866–
4868. (b) Eriksson, L.; Winberg, K. J.; Claro, R. T.; Sjo¨berg, S. J.
Org. Chem. 2003, 68, 3569–3573.
(14) Vin˜as, C.; Barbera`, G.; Oliva, J. M.; Teixidor, F.; Welch, A. J.; Rosair,
G. M. Inorg. Chem. 2001, 40, 6555–6562.
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16086 J. AM. CHEM. SOC. VOL. 132, NO. 45, 2010

1,3-Dehydro-o-carborane
A R T I C L E S
Table 3. Pd/Ni-Cocatalyzed Cycloaddition of
1,3-Dehydro-o-carborane with Alkynesa
Scheme 1. Pd/Ni-Cocatalyzed Cycloaddition of
1,3-Dehydro-o-carborane with Diynes
entry
R1/1
R2/R3/2
Et/Et/2a
Et/Et/2a
Et/Et/2a
Et/Et/2a
Et/Et/2a
product
4a
4b
4c
4d
4e
4f
4g
4h
4i
yield (%)b
1
2
3
4
5
6
7
8
9
H/1a
12
79
67
69
43
58
51
55
43
85
Me/1b
nBu/1c
TMS/1d
Ph/1e
(CH2)2OMe/1f Et/Et/2a
(CH2)2NMe2/1g Et/Et/2a
more demanding alkynes bearing a trimethylsilyl or o-tolyl
group, in which only the deiodination product 3b was observed
(entries 10 and 15). Alkynes bearing a carbonyl group such as
2e and 2f were incompatible with this reaction because they
reacted with the carboryne precursor 1-Li-2-Me-3-I-1,2-C2B10H9
(entries 11 and 12). Unsymmetrical alkynes 2j,k gave two
isomers of 4l,m and 5l,m with 4 being the major ones (entries
16 and 17).
Me/1b
Me/1b
nPr/nPr/2b
nBu/nBu/2c
10 Me/1b
11 Me/1b
12 Me/1b
13 Me/1b
14 Me/1b
15 Me/1b
16 Me/1b
17 Me/1b
nBu/TMS/2d
COOMe/COOMe/2e
Me/COOMe/2f
Ph/Ph/2g
3b
NR
NR
4j
c
c
55
51
83
p-tolyl/p-tolyl/2h
o-tolyl/o-tolyl/2i
Me/Ph/2j
4k
3b
4l+5l
The palladium/nickel-cocatalyzed cycloaddition reaction was
also extended to diynes (Scheme 1). Under the same reaction
condition mentioned above, 2-methyl-1,3-dehydro-o-carborane
underwent cycloaddition with diynes 6 to provide the 1,3-benzo-
o-carboranes, 7a-c in 6-34% yields with a good fused-ring
size tolerance. A dimerization product of 6a was isolated from
the reaction mixture, which probably resulted in the rather low
yield for the five-membered ring system 7a.
d
49 (4l/5l ) 62/38)
47 (4m/5m ) 80/20)
d
Et/Ph/2k
4m+5m
a
n
Conditions: (1) BuLi (1 equiv), toluene, r.t., 0.5 h; (2) Pd(PPh3)4 (5
mol %), Ni(cod)2 (5 mol %), alkyne (4 equiv), 110 °C, overnight.
b Isolated yields. c 1 was recovered. Ratio was determined by H NMR
d
1
spectroscopy on the crude product mixture.
1
All products were fully characterized by H, 13C, and 11B
cycloaddition reaction of 2-methyl-1,3-dehydro-o-carborane with
2 equiv of 3-hexyne to afford 1,3-benzocarborane 4b (entries
2-8). Addition of PPh3 to PdCl2(cod) or [Pd(Ally)Cl]2 led to a
significant improvement of the reactions probably due to the
effective reduction of Pd(II) to Pd(0) by PPh3 (entries 5 and
8).15 In fact, Pd(PPh3)4 can catalyze the [2 + 2 + 2] cyclo-
addition reaction, affording 4b in 90% yield (entry 10). Pd(dba)2
(dba ) dibenzylideneacetone), however, gave 4b in 43% yield
even after prolonged heating, suggesting large ligand effects
(entry 9). On the other hand, Ni(cod)2 exhibited very low
catalytic activity (entry 11), but the addition of nickel(0) species
to palladium catalyst can significantly accelerate the reactions
(entries 12-18).16 The combination of Pd(PPh3)4 with Ni(cod)2
exhibited the highest catalytic activity. If the catalyst loading
was decreased from 10 mol % to 2 mol %, the reaction rate
was slowed down, but the yield still remained very high (entries
14-17). Ni(cod)2 can also accelerate the catalytic reaction of
PdCl2(PPh3)2, giving 4b in 84% yield in 3 h (entry 18).
Various alkynes were compatible with this palladium/nickel-
cocatalyzed cycloaddition reaction under the optimal conditions
(Table 2, entry 15). The results were compiled in Table 3. 1,3-
Dehydro-o-carborane without a substituent at 2-C position gave
a very low isolated yield (12%) of 4a, whereas 2-methyl-1,3-
dehydro-o-carborane afforded 4b in 79% isolated yield (entry
1 vs 2). Steric effects of substituents on the 2-C position of the
cage were much less significant than electronic effects; for
example, the electron-withdrawing group phenyl led to a big
drop in the yield of 4e (entries 5 vs 2-4). Both aliphatic and
aromatic alkynes underwent [2 + 2 + 2] cycloaddition reactions,
and steric factors of alkynes played an important role in such
reactions. No cycloaddition reaction proceeded for sterically
NMR spectra, high-resolution mass spectrometry as well as
elemental analyses. In the H NMR spectrum of 4a, the cage
1
CH signal was overlapped with that of CH2 of the Et groups at
2.63 ppm when CDCl3 was used as solvent, whereas a clear
broad singlet corresponding to the cage CH was observed at
1.83 ppm in benzene-d6. The cage C-CH3 and cage C-Si(CH3)3
protons appeared as singlet each at 1.29 and 0.03 ppm,
1
respectively, in the H NMR spectra of 4b and 4d. The 13C
NMR spectra of 4, 5, and 7 showed two peaks in the range
70-80 ppm assignable to the two cage carbons and three olefinic
carbon resonances in the period 120-150 ppm, respectively.
The olefinic carbon bonded to the cage boron atom was not
observed probably due to the quadrupolar broadening effect.17
The 11B{1H} NMR spectra exhibited a 3:5:2 pattern spanning
between -7 to -13 ppm for 4b,h-m, 5, and 7, whereas 1:2:
1:3:1:1:1, 3:4:1:1:1, 1:4:3:1:1, 2:1:1:3:3, 1:1:5:1:1:1, and 3:5:
1:1 patterns were observed for those of 4a,c,d,e,f,g, respectively.
It is noteworthy that the signal of the BC vertex was overlapped
1
with the BH signals and was unable to be identified in the H
coupled 11B NMR spectra.
The molecular structures of 4a,b,d,j,m, 5m, and 7b were
further confirmed by single-crystal X-ray analyses (Figure 1).
Table 4 summarizes the selected bond distances. The six-
membered C5B ring is coplanar in these molecules with
alternative short and long bonds, similar to those observed in
1,2-benzocarboranes.7,12 These data suggest that there is no
substantial π-delocalization in such rings. Thus, the C4 unit may
be best described as a butadiene moiety.
Reaction Mechanism. As shown in Table 1, a catalytic
amount of Pd(0) species can quantitatively convert 1-Li-2-
Me-3-I-1,2-C2B10H9 to 3b in refluxing toluene. On the other
hand, refluxing 1b and 4 equiv of 3-hexyne in toluene in the
(15) Miyaura, M. Cross-Coupling Reactions. A Practical Guide. In Topics
in Current Chemistry; Springer: Berlin Heidelberg, 2002.
(16) Cho, C. S.; Lee, J. W.; Lee, D. Y.; Shim, S. C.; Kim, T. J. Chem.
Commun. 1996, 2115–2116.
(17) Cook, K. S.; Piers, W. E.; McDonald, R. J. Am. Chem. Soc. 2002,
124, 5411–5418.
9
J. AM. CHEM. SOC. VOL. 132, NO. 45, 2010 16087

A R T I C L E S
Qiu and Xie
Figure 1. Molecular Structures of 4a,b,d,j,m, 5m, and 7b.
presence of 5 mol % Pd(PPh3)4 and 5 mol % Ni(cod)2 or 1
equiv of Pd(PPh3)4 and Ni(cod)2 did not give any alkyne
insertion products; rather, it afforded the isomers of 1b with
iodo being located at different cage boron positions as
indicated by GC-MS analyses. These results suggest that the
cage B-I can undergo oxidative addition reaction on Pd(0)
and the resultant cage B-Pd(I) bond is inert toward 3-hexyne.
Thus, it is most likely that the above [2 + 2 + 2]
cycloaddition reactions proceed through a metal-1,3-dehydro-
o-carborane intermediate.
9
16088 J. AM. CHEM. SOC. VOL. 132, NO. 45, 2010

1,3-Dehydro-o-carborane
A R T I C L E S
Table 4. Selected Bond Lengths (Å) in 4a,b,d,j,m, 5m and 7b
4a
4b
4d
4j
4m
5m
7b
C(1)-C(2)
C(1)-B(3)
C(1)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-B(3)
1.680(4)
1.706(5)
1.507(4)
1.340(4)
1.482(4)
1.351(4)
1.524(5)
1.728(4)
1.708(4)
1.502(4)
1.353(4)
1.479(4)
1.351(4)
1.527(5)
1.726(2)
1.707(2)
1.518(2)
1.366(3)
1.498(2)
1.366(3)
1.546(3)
1.723(4)
1.706(4)
1.520(4)
1.347(3)
1.487(3)
1.357(3)
1.527(4)
1.684(5)
1.707(5)
1.481(5)
1.350(4)
1.481(5)
1.344(5)
1.537(6)
1.721(4)
1.701(4)
1.514(4)
1.352(4)
1.492(4)
1.351(4)
1.531(4)
1.722(5)
1.689(5)
1.508(5)
1.359(5)
1.483(5)
1.356(5)
1.533(5)
Scheme 2. Proposed Mechanism for Pd/Ni-Cocatalyzed [2 + 2 + 2] Cycloaddition Reaction
Having the aforementioned experimental data, a plausible
mechanism for palladium/nickel-cocatalyzed [2 + 2 + 2]
cycloaddition is proposed in Scheme 2. Since Ni(0) can hardly
insert into the B-I bond (Table 1, entry 4), the Pd-1,3-dehydro-
o-carborane B is formed by the oxidative addition of B-I on
Pd(0), followed by LiI elimination. As a two-component catalyst
system is much more effective than Pd species alone in the
reaction of 1,3-dehydro-o-carborane with alkynes, it is rational
to propose a transmetalation process between Pd and Ni,18
affording a more reactive nickel-1,3-dehydro-o-carborane C.
yield. The relatively higher activity of the Ni species may
probably be ascribed to the fact that the Pd-B bond is stronger
than the Ni-B bond or the Ni-B bonding pair is more
nucleophilic than that of Pd-B.20 In the reaction with PhCt CEt,
the electronically controlled regioselective insertion of unsym-
metrical alkyne21 into the Ni-B bond gives the nickelacyclo-
pentene intermediate D. The absence of 2-Me-1,3-{1′,4′-
[EtCdC(C6H5)-C(Et)dC(C6H5)]}-1,2-C2B10H10 in the products
indicates the exclusive insertion into the Ni-B bond. This is
consistent with the results reported in the literature.17,20,22 As
an M-B bond is much more nucleophilic than an M-C bond,20
the alkyne insertion into an M-B bond could be considered as
a nucleophilic attack of the M-B σ-bond (the bonding electron
pair) on one of the two alkyne carbons. The nucleophilic attack
in nature also explains the regioselectivity observed in the
unsymmetrical alkynes; that is, in the insertion product D, boron
is bonded to the carbon having electron-donating ethyl sub-
stituent. Since the insertion of alkynes into the M-C(cage) bond
This hypothesis was supported by the following experiments.
4d,19
An 1:1 mixture of (η2-o-C2B10H10)Pd(PPh3)2
and Ni(cod)2
in toluene at room temperature afforded (η2-o-C2B10H10)-
4a
Ni(PPh3)2 as indicated by 31P NMR. On the other hand, (η2-
o-C2B10H10)Pd(PPh3)2 did not show any activity toward 3-hex-
yne. However, the addition of 20 mol % of Ni(cod)2 to the above
solution led to the isolation of [2 + 2 + 2] cycloaddition product
7
1,2-{1′,4′-[EtCdC(Et)-C(Et)dC(Et)]}-1,2-C2B10H10 in 18%
(18) Reduction potentials: Ni2+/Ni )-0.25 V, Pd2+/Pd ) 0.95 V, see
Housecroft, C. E.; Sharpe, A. G. Inorganic Chemistry; Pearson
Education: New York, 2001, pp 752-754.
(19) Deng, L. Synthesis, structural characterization and reactivity study of
novel twelve-, thirteen-, and fourteen-vertex carboranes and their
derivatives. Ph.D. Thesis. The Chinese University of Hong Kong, 2006.
(20) Dang, L.; Lin, Z.; Marder, T. B. Chem. Commun. 2009, 3987–3995.
(21) (a) Bennett, M. A.; Wenger, E. Organometallics 1995, 14, 1267–1277.
(b) Bennett, M. A.; Macgregor, S. A.; Wenger, E. HelV. Chim. Acta
2001, 84, 3084–3104.
(22) Selander, N.; Willy, B.; Szabo´, K. J. Angew. Chem., Int. Ed. 2010,
49, 4051–4053.
9
J. AM. CHEM. SOC. VOL. 132, NO. 45, 2010 16089

A R T I C L E S
Qiu and Xie
m/z calcd for C6H19B10I+: 326.1529. Found: 326.1532. Anal. Calcd
for C6H19B10I: C, 22.09; H, 5.87. Found: C, 22.42; H, 5.76.
3-Iodo-1-trimethylsilyl-o-carborane (1d). This compound was
prepared as a white solid from Me3SiCl using the same procedures
as reported for 1c. Yield: 87%. Mp: 74.2-74.9 °C. 1H NMR (400
MHz, CDCl3): δ 3.64 (s, 1H) (cage H), 0.41 (s, 9H) (CH3). 13C{1H}
NMR (100 MHz, CDCl3): δ 67.4, 64.1 (cage C), -0.9 (CH3).
11B{1H} NMR (128 MHz, CDCl3): δ -0.2 (1B), -1.7 (1B), -4.7
(1B), -9.0 (2B), -9.7 (1B), -11.0 (1B), -12.1 (1B), -13.0 (1B),
-28.1 (1B). HRMS: m/z calcd for C5H20B10ISi+ ([M + H]+):
342.1298. Found: 342.1302. Anal. Calcd for C5H19B10ISi: C, 17.54;
H, 5.59. Found: C, 17.41; H, 5.49.
3-Iodo-1-methoxyethyl-o-carborane (1f). This compound was
prepared as colorless oil from 2-chloroethyl methyl ether using the
same procedures reported for 1c. Yield: 85%. 1H NMR (400 MHz,
CDCl3): δ 3.87 (s, 1H) (cage H), 3.56 (m, 2H) (OCH2), 3.32 (s,
3H) (OCH3), 2.79 (m, 1H), 2.63 (m, 1H) (OCH2CH2). 13C{1H}
NMR (100 MHz, CDCl3): δ 72.8, 64.4 (cage C), 70.0 (OCH2), 58.7
(OCH3), 38.3 (OCH2CH2). 11B{1H} NMR (128 MHz, CDCl3): δ
-2.2 (1B), -4.7 (1B), -7.7 (1B), -9.7 (1B), -11.3 (4B), -12.9
(1B), -24.5 (1B). HRMS: m/z calcd for C5H17B10IO+: 328.1322.
Found: 328.1323. Anal. Calcd for C5H17B10IO: C, 18.30; H, 5.22.
Found: C, 18.68; H, 5.14.
in metal-carboranyl complexes is prohibited due to steric
reasons,23 the second equivalent of alkyne inserts into the
Ni-C(vinyl) bond in both a head-to-tail (major) and head-to-
head (minor) manner. Subsequent reductive elimination yields
the final products 4m/5m (80/20) and regenerates the Ni(0) to
complete the catalytic cycle. Compound 4m is the major isomer
although the regioselectivity in the second insertion is relatively
poor.
Conclusion
We have shown for the first time the generation of 1,3-
dehydro-o-carborane, which can be regarded as a new kind of
boron nucleophile. This reactive species can be trapped by
alkynes in the presence of a catalytic amount of transition metals.
The present work offers a new methodology for C,B-function-
alization of carboranes and demonstrates the relative reactivity
of cage M-C versus M-B bond in metal-1,3-dehydro-o-
carborane complexes toward alkynes.
Experimental Section
3-Iodo-1-dimethylaminoethyl-o-carborane (1g). This com-
pound was prepared as light yellow oil from 2-chloro-N,N′-
dimethylethylamine using the same procedures reported for 1c.
Yield: 66%. 1H NMR (400 MHz, CDCl3): δ 4.00 (s, 1H) (cage H),
2.59 (m, 2H), 2.41 (m, 2H) (CH2), 2.23 (s, 6H) (N(CH3)2). 13C{1H}
NMR (100 MHz, CDCl3): δ 73.7, 64.4 (cage C), 57.8 (NCH2), 45.4
(NCH3), 35.8 (CH2CH2N). 11B{1H} NMR (96 MHz, CDCl3): δ
-1.9 (1B), -4.3 (1B), -7.4 (1B), -9.5 (1B), -11.0 (4B), -12.5
(1B), -24.2 (1B). HRMS: m/z calcd for C6H20B10IN+: 341.1638.
Found: 341.1639. Anal. Calcd for C6H20B10IN: C, 21.12; H, 5.91;
N, 4.10. Found: C, 21.59; H, 6.03; N, 3.83.
General Procedures. All reactions were carried out in flame-
dried glassware under an atmosphere of dry nitrogen with the rigid
exclusion of air and moisture using standard Schlenk or cannula
techniques or in a glovebox. All organic solvents were freshly
distilled from sodium benzophenone ketyl immediately prior to use.
1H NMR spectra were recorded on a Bruker DPX 400 spectrometer
at 400 MHz. 13C{1H} NMR spectra were recorded on either a
Bruker DPX 300 spectrometer at 75 MHz or a Bruker DPX 400
spectrometer at 100 MHz. 11B{1H} NMR spectra were recorded
on either a Bruker DPX 300 spectrometer at 96 MHz or a Bruker
DPX 400 spectrometer at 128 MHz. All chemical shifts were
reported in δ units with references to the residual solvent resonances
of the deuterated solvents for proton and carbon chemical shifts,
and to external BF3 ·OEt2 (0.00 ppm) for boron chemical shifts.
Mass spectra were obtained on a Thermo Finnigan MAT 95 XL
spectrometer. Melting points were determined using an Electro-
thermal M-IA9000 melting point apparatus and the values reported
were uncorrected. NiCl2(PPh3)2,24 3-iodo-o-carborane (1a),13a 3-iodo-
1-methyl-o-carborane (1b),14 and 3-iodo-1-phenyl-o-carborane
(1e)14 were prepared according to the literature procedures. Alkynes
were freshly distilled from CaH2 or P2O5 prior to use. All other
chemicals were purchased from either Aldrich or Acros Chemical
Co. and used as received unless otherwise specified. Elemental
analyses were performed by the Shanghai Institute of Organic
Chemistry, CAS, China.
Palladium/Nickel-Cocatalyzed Cycloaddition Reaction of 1,3-
Dehydro-o-carborane with Alkynes. A Representative Procedure.
To a toluene solution (5 mL) of 2-Me-3-I-1,2-C2B10H10 (0.5 mmol)
n
was added 1 equiv of BuLi (0.5 mmol), and the reaction mixture
was stirred at room temperature for 0.5 h. After addition of
Pd(PPh3)4 (5 mol %), Ni(cod)2 (5 mol %), and alkyne (2.0 mmol)
[or diyne (1.0 mmol)], the reaction vessel was closed and heated
at 110 °C overnight. The reaction was quenched with water and
extracted with ether. After removal of organic solvents, the residue
was subject to column chromatography on silica gel (230-400
mesh) using hexane as eluent to give the cycloaddition product,
1,3-benzo-o-carborane.
1,3-(1,2,3,4-Tetraethyl-1,3-butadiene-1,4-diyl)-o-carborane (4a).
Yield: 12%. Colorless crystals. Mp: 88.9-90.1 °C. 1H NMR (400
MHz, CDCl3): δ 2.61 (m, 4H), 2.39 (m, 5H) (cage CH & CH2),
1.19 (t, J ) 7.2 Hz, 3H), 1.10 (t, J ) 7.2 Hz, 3H), 1.03 (t, J ) 7.2
3-Iodo-1-n-butyl-o-carborane (1c). To an ether solution (5 mL)
n
of 3-iodo-o-carborane (1a; 400 mg, 1.5 mmol) was added BuLi
1
(1.6 M, 0.93 mL, 1.5 mmol) and the mixture was stirred at 0 °C
Hz, 3H), 1.01 (t, J ) 7.2 Hz, 3H), (CH3). H NMR (400 MHz,
n
for 1 h. After adding BuBr (0.16 mL, 1.5 mmol), the reaction
benzene-d6): δ 2.54 (q, J ) 7.6 Hz, 2H), 2.23 (m, 2H), 2,15 (m,
2H), 2.02 (m, 2H) (CH2), 1.83 (s, 1H) (cage CH), 1.15 (t, J ) 7.6
Hz, 3H), 0.87 (t, J ) 7.6 Hz, 3H), 0.82 (t, J ) 7.6 Hz, 3H), 0.74
(t, J ) 7.6 Hz, 3H), (CH3). 13C{1H} NMR (75 MHz, CDCl3): δ
143.3, 142.0, 130.6 (olefinic C), 60.4 (cage C), 28.3, 27.0, 23.3,
21.9 (CH2), 15.5, 15.1, 15.0, 14.8 (CH3), the olefinic C connected
to the cage B atom and another cage C were not observed. 11B{1H}
NMR (96 MHz, CDCl3): δ -4.8 (1B), -7.8 (2B), -10.0 (1B),
-11.7 (3B), -13.2 (1B), -14.0 (1B), -16.8 (1B). HRMS: m/z
calcd for C14H30B10+: 306.3345. Found: 306.3349. Anal. Calcd for
C14H30B10: C, 54.86; H, 9.87. Found: C, 54.80; H, 10.17.
mixture was stirred for 5 h at 0 °C and then hydrolyzed with water.
The organic layer was separated, dried over MgSO4, and concen-
trated. The residue was subject to column chromatography on silica
gel (230-400 mesh) using hexane as eluent to give 1c as a colorless
1
oil (254 mg, 53%). H NMR (400 MHz, CDCl3): δ 3.61 (s, 1H)
(cage H), 2.47 (m, 1H), 2.30 (m, 1H), 1.50 (m, 2H), 1.35 (m, 2H)
(CH2), 0.94 (t, J ) 7.2 Hz, 3H) (CH3). 13C{1H} NMR (100 MHz,
CDCl3): δ 75.0, 64.7 (cage C), 38.9, 30.9, 22.0 (CH2), 13.6 (CH3).
11B{1H} NMR (128 MHz, CDCl3): δ -2.6 (1B), -5.2 (1B), -7.5
(1B), -10.0 (1B), -11.3 (4B), -13.3 (1B), -25.3 (1B). HRMS:
2-Methyl-1,3-(1,2,3,4-tetraethyl-1,3-butadiene-1,4-diyl)-o-carbo-
rane (4b). Yield: 54%. Colorless crystals. Mp: 129.2-130.1 °C.
1H NMR (400 MHz, CDCl3): δ 2.54 (m, 3H), 2.44 (m, 5H) (CH2),
1.29 (s, 3H) (CH3), 1.15 (t, J ) 7.6 Hz, 3H), 1.12 (t, J ) 7.6 Hz,
3H), 1.05 (t, J ) 7.6 Hz, 3H), 1.04 (t, J ) 7.6 Hz, 3H) (CH2CH3).
13C{1H} NMR (100 MHz, CDCl3): δ 145.6, 143.5, 128.8 (olefinic
C), 81.3, 67.9 (cage C), 28.2, 26.9, 23.5, 21.9 (CH2), 20.2 (CH3),
(23) (a) Xie, Z. Coord. Chem. ReV. 2006, 250, 259–272. (b) Sun, Y.; Chan,
H.-S.; Zhao, H.; Lin, Z.; Xie, Z. Angew. Chem., Int. Ed. 2006, 45,
5533–5536. (c) Sun, Y.; Chan, H.-S.; Xie, Z. Organometallics 2006,
25, 3447–3453. (d) Qiu, Z.; Xie, Z. Sci. China Ser. B-Chem. 2009,
52, 1544–1558. (e) Shen, H.; Xie, Z. Chem. Commun. 2009, 2431–
2445.
(24) Venanzi, L. M. J. Inorg. Nucl. Chem. 1958, 8, 137–142.
9
16090 J. AM. CHEM. SOC. VOL. 132, NO. 45, 2010

1,3-Dehydro-o-carborane
A R T I C L E S
15.6, 15.3, 15.2, 14.7 (CH2CH3), the olefinic C connected to the
cage B atom was not observed. 11B{1H} NMR (96 MHz, CDCl3):
δ -8.0 (3B), -9.9 (1B), -11.2 (3B), -12.8 (1B), -14.4 (2B).
HRMS: m/z calcd for C15H32B10+: 320.3502. Found: 320.3504.
Anal. Calcd for C15H32B10: C, 56.21; H, 10.06. Found: C, 56.16;
H, 10.15.
377.4076. Anal. Calcd for C18H39B10N: C, 57.25; H, 10.41; N, 3.71.
Found: C, 57.32; H, 10.63; N, 3.53.
2-Methyl-1,3-(1,2,3,4-tetra-n-propyl-1,3-butadiene-1,4-diyl)-o-
carborane (4h). Yield: 55%. A white solid. Mp: 85.1-86.0 °C. 1H
NMR (400 MHz, CDCl3): δ 2.48 (m, 3H), 2.27 (m, 5H) ()CCH2),
1.51 (m, 4H), 1.36 (m, 4H) (CH2CH2), 1.26 (s, 3H) (CH3), 0.98
(m, 12H) (CH2CH3). 13C{1H} NMR (100 MHz, CDCl3): δ 144.4,
142.4, 127.8 (olefinic C), 81.3, 68.0 (cage C), 37.9, 36.5, 33.2, 31.6
()CCH2), 24.6, 24.2, 23.6 (CH2CH2), 20.2 (CH3), 14.8, 14.7, 14.6,
14.4 (CH2CH3), the olefinic C connected to the cage B atom was
not observed. 11B{1H} NMR (96 MHz, CDCl3): δ -8.3 (3B), -11.4
2-n-Butyl-1,3-(1,2,3,4-tetraethyl-1,3-butadiene-1,4-diyl)-o-carbo-
rane (4c). Yield: 67%. Colorless oil. 1H NMR (400 MHz, CDCl3):
δ 2.43 (m, 10H), 1.33 (m, 2H), 1.25 (m, 2H) (CH2), 1.15 (t, J )
7.2 Hz, 3H), 1.11 (t, J ) 7.2 Hz, 3H), 1.04 (t, J ) 7.2 Hz, 3H),
1.02 (t, J ) 7.2 Hz, 3H), 0.79 (t, J ) 7.2 Hz, 3H) (CH3). 13C{1H}
NMR (100 MHz, CDCl3): δ 145.8, 143.3, 128.7 (olefinic C), 82.9,
72.7 (cage C), 31.4, 31.2, 28.1, 27.0, 23.5, 22.4, 21.8 (CH2), 15.4,
15.3, 15.2, 14.8, 13.6 (CH3), the olefinic C connected to the cage
B atom was not observed. 11B{1H} NMR (128 MHz, CDCl3): δ
-7.8 (3B), -11.2 (5B), -14.4 (1B), -16.2 (1B). HRMS: m/z calcd
for C18H38B10+: 362.3971. Found: 362.3967. Anal. Calcd for
C18H38B10: C, 59.62; H, 10.56. Found: C, 59.82; H, 10.72.
(5B), -14.6 (2B). HRMS: m/z calcd for C19H41B10 ([M+H]+):
+
376.4128. Found: 376.4114. Anal. Calcd for C19H40B10: C, 60.59;
H, 10.70. Found: C, 60.56; H, 10.84.
2-Methyl-1,3-(1,2,3,4-tetra-n-butyl-1,3-butadiene-1,4-diyl)-o-car-
borane (4i). Yield: 33%. Colorless oil. 1H NMR (400 MHz, CDCl3):
δ 2.48 (m, 3H), 2.31 (m, 5H), 1.40 (m, 16H) (CH2), 1.27 (s, 3H)
(CH3), 0.95 (m, 12H) (CH2CH3). 13C{1H} NMR (75 MHz, CDCl3):
δ 144.4, 142.3, 127.6 (olefinic C), 81.4, 68.0 (cage C), 35.4, 34.0,
33.4, 33.2, 32.9, 32.4 30.7, 29.1, 23.4, 23.3, 23.2, 23.1(CH2), 20.2
(CH3), 14.0, 13.9, 13.8, 13.7 (CH2CH3), the olefinic C connected
to the cage B atom was not observed. 11B{1H} NMR (96 MHz,
CDCl3): δ -8.4 (4B), -11.5 (4B), -14.6 (2B). HRMS: m/z calcd
for C23H48B10+: 432.4754. Found: 432.4758. Anal. Calcd for
C23H48B10: C, 63.84; H, 11.18. Found: C, 64.15; H, 11.62.
2-Trimethylsilyl-1,3-(1,2,3,4-tetraethyl-1,3-butadiene-1,4-diyl)-
o-carborane (4d). Yield: 69%. Colorless crystals. Mp: 109.0-110.5
°C. 1H NMR (400 MHz, CDCl3): δ 2.46 (m, 8H) (CH2), 1.26 (t, J
) 7.6 Hz, 3H), 1.18 (t, J ) 7.6 Hz, 3H), 1.08 (t, J ) 7.6 Hz, 3H),
1.06 (t, J ) 7.6 Hz, 3H) (CH2CH3), 0.03 (s, 9H) (Si(CH3)3). 13C{1H}
NMR (100 MHz, CDCl3): δ 144.4, 142.2, 131.5 (olefinic C), 83.8,
68.5 (cage C), 29.0, 27.8, 23.5, 21.8 (CH2), 15.2, 15.0, 14.7, 14.6
(CH2CH3), 0.56 (Si(CH3)3), the olefinic C connected to the cage B
atom was not observed. 11B{1H} NMR (128 MHz, CDCl3): δ -2.6
(1B), -7.2 (2B), -7.8 (2B), -11.1 (3B), -12.3 (1B), -14.3 (1B).
HRMS: m/z calcd for C17H38B10Si+: 378.3740. Found: 378.3748.
Anal. Calcd for C17H38B10Si: C, 53.92; H, 10.11. Found: C, 53.91;
H, 10.16.
2-Methyl-1,3-(1,2,3,4-tetraphenyl-1,3-butadiene-1,4-diyl)-o-car-
borane (4j). Yield: 55%. Yellow crystals. Mp: 251.7-252.5 °C.
1H NMR (400 MHz, CDCl3): δ 7.09 (m, 9H), 6.89 (d, J ) 8.0 Hz,
1H), 6.77 (m, 10H) (aromatic CH), 2.12 (s, 3H) (CH3). 13C{1H}
NMR (100 MHz, CDCl3): δ 147.5, 145.4, 142.2, 139.7, 139.5,
139.0, 131.9, 131.5, 130.4, 130.1, 129.7, 128.7, 127.5, 127.3, 127.2,
127.1, 126.8, 126.6, 126.5, 126.0, 125.9, 125.7 (aromatic and
olefinic C), 78.7, 67.8 (cage C), 21.0 (CH3), the olefinic C connected
to the cage B atom was not observed. 11B{1H} NMR (96 MHz,
CDCl3): δ -8.2 (3B), -10.5 (4B), -13.6 (3B). HRMS: m/z calcd
for C31H32B10+: 512.3502. Found: 512.3520. Anal. Calcd for
C31H32B10: C, 72.62; H, 6.29. Found: C, 72.68; H, 6.23.
2-Phenyl-1,3-(1,2,3,4-tetraethyl-1,3-butadiene-1,4-diyl)-o-carbo-
rane (4e). Yield: 43%. Colorless crystals. Mp: 100.2-101.5 °C.
1H NMR (400 MHz, CDCl3): δ 7.24 (m, 3H), 7.14 (m, 2H) (Ph),
2.63 (m, 4H), 2.13 (m, 3H), 1.98 (m, 1H) (CH2), 1.27 (t, J ) 7.6
Hz, 3H), 1.15 (t, J ) 7.6 Hz, 3H), 0.64 (t, J ) 7.6 Hz, 3H), 0.49
(t, J ) 7.6 Hz, 3H) (CH3). 13C{1H} NMR (100 MHz, CDCl3): δ
145.3, 143.4, 130.3, 129.9, 129.4, 128.8, 127.4 (olefinic C & Ph),
84.9, 75.5 (cage C), 28.5, 27.5, 23.1, 21.6 (CH2), 15.0, 14.7, 14.6,
14.0 (CH3), the olefinic C connected to the cage B atom was not
observed. 11B{1H} NMR (128 MHz, CDCl3): δ -6.0 (2B), -7.6
(1B), -10.0 (1B), -11.4 (3B), -13.7 (3B). HRMS: m/z calcd for
C20H34B10+: 382.3658. Found: 382.3657. Anal. Calcd for C20H34B10:
C, 62.79; H, 8.96. Found: C, 62.80; H, 8.96.
2-Methyl-1,3-(1,2,3,4-tetra-p-tolyl-1,3-butadiene-1,4-diyl)-o-car-
borane (4k). Yield: 51%. A white solid. Mp: 227.1-227.9 °C. 1H
NMR (400 MHz, CDCl3): δ 6.90 (m, 6H), 6.83 (d, J ) 7.6 Hz,
1H), 6.73 (d, J ) 7.6 Hz, 1H), 6.50 (m, 8H) (aromatic CH), 2.23
(s, 3H), 2.21 (s, 3H), 2.03 (s, 6H), 2.00 (s, 3H) (CH3). 13C{1H}
NMR (100 MHz, CDCl3): δ 147.7, 145.5, 139.6, 137.0, 136.8,
136.5, 136.4, 135.1, 135.0, 134.8, 131.6, 131.3, 130.2, 129.9, 129.5,
128.6, 128.2, 127.9, 127.7, 127.5, 127.2 (aromatic and olefinic C),
79.1, 67.9 (cage C), 21.0, 20.9 (CH3), the olefinic C connected to
the cage B atom was not observed. 11B{1H} NMR (128 MHz,
CDCl3): δ -7.8 (4B), -10.1 (4B), -13.3 (2B). HRMS: m/z calcd
for C35H40B10+: 568.4128. Found: 568.4150. Anal. Calcd for
C35H40B10: C, 73.91; H, 7.09. Found: C, 74.14; H, 7.38.
2-Methoxyethyl-1,3-(1,2,3,4-tetraethyl-1,3-butadiene-1,4-diyl)-o-
1
carborane (4f). Yield: 58%. Colorless oil. H NMR (400 MHz,
CDCl3): δ 3.25 (t, J ) 7.2 Hz, 2H) (OCH2), 3.23 (s, 3H) (OCH3),
2.52 (m, 3H), 2.38 (m, 5H), 1.64 (m, 2H) (CH2), 1.16 (t, J ) 7.6
Hz, 3H), 1.12 (t, J ) 7.6 Hz, 3H), 1.05 (t, J ) 7.6 Hz, 3H), 1.03
(t, J ) 7.6 Hz, 3H) (CH3). 13C{1H} NMR (100 MHz, CDCl3): δ
146.0, 143.6, 128.7 (olefinic C), 82.8, 69.5 (cage C), 70.7 (OCH2),
58.5 (OCH3), 31.1, 28.2, 27.0, 23.5, 21.9 (CH2), 15.4, 15.2, 15.1,
14.7 (CH3), the olefinic C connected to the cage B atom was not
observed. 11B{1H} NMR (128 MHz, CDCl3): δ -7.1 (1B), -7.8
(1B), -11.1 (5B), -12.7 (1B), -14.2 (1B), -16.1 (1B). HRMS:
m/z calcd for C17H36B10O+: 364.3764. Found: 364.3760. Anal. Calcd
for C17H36B10O: C, 56.01; H, 9.95. Found: C, 56.01; H, 9.96.
2-Methyl-1,3-(1,3-diphenyl-2,4-dimethyl-1,3-butadiene-1,4-diyl)-
o-carborane (4l) + 2-Methyl-1,3-(1,4-dimethyl-2,3-diphenyl-1,3-
butadiene-1,4-diyl)-o-carborane (5l). Yield: 49%. A white solid.
4l: 5l ) 62: 38 by 1H NMR spectrum of the crude mixture.
Compound 4l was isolated as a pure product whereas 5l was always
contaminated with 4l. For 4l: 1H NMR (400 MHz, CDCl3): δ 7.36
(m, 6H), 7.12 (m, 2H), 6.93 (m, 2H) (aromatic CH), 1.93 (s, 3H),
1.70 (s, 3H), 1.34 (s, 3H) (CH3). 13C{1H} NMR (75 MHz, CDCl3):
δ 144.8, 140.8, 139.8, 130.8, 129.6, 128.7, 128.5, 128.2, 128.1,
127.7, 126.9 (aromatic and olefinic C), 79.8, 67.9 (cage C), 22.9,
21.7, 20.5 (CH3), the olefinic C connected to the cage B atom was
not observed. 11B{1H} NMR (96 MHz, CDCl3): δ -7.3 (3B), -10.4
(5B), -13.2 (2B). HRMS: m/z calcd for C21H28B10+: 388.3189.
Found: 388.3189. Anal. Calcd for C21H28B10: C, 64.92; H, 7.26.
Found: C, 64.75; H, 7.33.
2-Dimethylaminoethyl-1,3-(1,2,3,4-tetraethyl-1,3-butadiene-1,4-
1
diyl)-o-carborane (4g). Yield: 51%. Colorless oil. H NMR (400
MHz, CDCl3): δ 2.44 (m, 10H) (CH2), 2.10 (s, 6H) (N(CH3)2),
1.54 (m, 2H) (CH2), 1.16 (t, J ) 7.6 Hz, 3H), 1.14 (t, J ) 7.6 Hz,
3H), 1.08 (t, J ) 7.6 Hz, 3H), 1.04 (t, J ) 7.6 Hz, 3H) (CH3).
13C{1H} NMR (100 MHz, CDCl3): δ 146.0, 143.6, 128.7 (olefinic
C), 83.1, 70.5 (cage C), 58.4 (NCH2), 45.3 (N(CH3)2), 29.1, 28.2,
27.0, 23.5, 21.9 (CH2), 15.5, 15.4, 15.3, 14.9 (CH3), the olefinic C
connected to the cage B atom was not observed. 11B{1H} NMR
(128 MHz, CDCl3): δ -7.6 (3B), -10.9 (5B), -14.1 (1B), -16.2
(1B). HRMS: m/z calcd for C18H39B10N+: 377.4080. Found:
9
J. AM. CHEM. SOC. VOL. 132, NO. 45, 2010 16091

A R T I C L E S
Qiu and Xie
Scheme 3. The Correlations in HMBC Analyses of 4m and 5m
(s, 3H), 2.02 (s, 3H) ()CCH3), 1.83 (m, 2H) (CH2CH2), 1.24 (s,
3H) (CH3). 13C{1H} NMR (75 MHz, CDCl3): δ 147.2, 145.3, 118.7
(olefinic C), 81.7, 67.7 (cage C), 33.1, 31.3 ()CCH2), 23.8
(CH2CH2), 20.3, 20.1, 19.5 (CH3), the olefinic C connected to the
cage B atom was not observed. 11B{1H} NMR (96 MHz, CDCl3):
δ -6.2 (1B), -7.3 (2B), -9.6 (1B), -11.0 (3B), -12.6 (1B), -13.8
(2B). HRMS: m/z calcd for C12H24B10+: 276.2876. Found: 276.2867.
Anal. Calcd for C12H24B10: C, 52.14; H, 8.75. Found: C, 52.39; H,
8.64.
2-Methyl-1,3-(1,3-diphenyl-2,4-diethyl-1,3-butadiene-1,4-diyl)-
o-carborane (4m) + 2-Methyl-1,3-(1,4-diethyl-2,3-diphenyl-1,3-
butadiene-1,4-diyl)-o-carborane (5m). Yield: 47%. A white solid.
4m/5m ) 80:20 by 1H NMR spectrum of the crude mixture. Both
4m and 5m were isolated in the pure form via many times of
column chromatographic separation on silica gel. For 4m: Mp:
2-Methyl-1,3-[1,4-dimethyl-2,3-(1,4-butanediyl)-1,3-butadiene-
1,4-diyl]-o-carborane (7b). Yield: 34%. Colorless crystals. Mp:
1
127.5-128.0 °C. H NMR (400 MHz, CDCl3): δ 2.45 (m, 4H)
()CCH2), 2.11 (s, 3H), 2.04 (s, 3H) ()CCH3), 1.65 (m, 4H)
(CH2CH2), 1.23 (s, 3H) (CH3). 13C{1H} NMR (75 MHz, CDCl3):
δ 140.8, 139.0, 121.3 (olefinic C), 81.1, 67.4 (cage C), 29.3, 27.2
()CCH2), 22.1, 21.9 (CH2CH2), 21.0, 20.1, 19.3 (CH3), the olefinic
C connected to the cage B atom was not observed. 11B{1H} NMR
(96 MHz, CDCl3): δ -7.5 (3B), -9.3 (1B), -10.9 (3B), -12.2
(1B), -14.0 (2B). HRMS: m/z calcd for C13H26B10+: 290.3032.
Found: 290.3029. Anal. Calcd for C13H26B10: C, 53.76; H, 9.02.
Found: C, 53.85; H, 9.28.
1
128.5-130.7 °C. H NMR (400 MHz, CDCl3): δ 7.32 (m, 6H),
7.20 (d, J ) 7.2 Hz, 1H), 7.16 (m, 1H), 7.06 (m, 1H), 6.97 (m,
1H) (aromatic CH), 2.27 (m, 2H), 1.78 (m, 2H) (CH2), 1.73 (s,
3H) (CH3), 1.01 (t, J ) 7.6 Hz, 3H), 0.55 (t, J ) 7.6 Hz, 3H)
(CH2CH3). 13C{1H} NMR (100 MHz, CDCl3): δ 146.9, 144.7,
139.6, 139.2, 131.1, 129.9, 129.4, 128.0, 127.9, 127.8, 127.7, 127.6,
127.0 (aromatic and olefinic C), 79.7, 67.5 (cage C), 28.4, 26.8
(CH2), 20.6 (CH3), 14.3 (CH2CH3), the olefinic C connected to the
cage B atom was not observed. 11B{1H} NMR (96 MHz, CDCl3):
δ -7.7 (3B), -10.9 (4B), -13.6 (3B). HRMS: m/z calcd for
C23H32B10+: 416.3502. Found: 416.3489. Anal. Calcd for C23H32B10:
C, 66.31; H, 7.74. Found: C, 66.46; H, 7.91. For 5m: Mp:
2-Methyl-1,3-[1,4-dimethyl-2,3-(1,5-pentanediyl)-1,3-butadiene-
1,4-diyl]-o-carborane (7c). Yield: 23%. A white solid. Mp: 88.7-89.9
1
°C. H NMR (400 MHz, CDCl3): δ 2.61 (m, 4H) ()CCH2), 2.16
(s, 3H), 2.11 (s, 3H) ()CCH3), 1.67 (m, 1H), 1.58 (m, 4H), 1.48
(m, 1H) (CH2CH2), 1.30 (s, 3H) (CH3). 13C{1H} NMR (75 MHz,
CDCl3): δ 146.0, 144.0, 124.4 (olefinic C), 81.1, 68.3 (cage C),
31.0, 29.0 ()CCH2), 28.3, 28.0 (CH2CH2), 21.6, 20.2, 19.9 (CH3),
the olefinic C connected to the cage B atom was not observed.
11B{1H} NMR (96 MHz, CDCl3): δ -7.9 (3B), -9.9 (1B), -11.2
1
129.1-130.2 °C. H NMR (400 MHz, CDCl3): δ 7.03 (m, 6H),
6.86 (d, J ) 7.6 Hz, 1H), 6.81 (d, J ) 6.4 Hz, 1H), 6.73 (d, J )
8.0 Hz, 1H), 6.61 (m, 1H) (aromatic CH), 2.23 (m, 4H) (CH2),
1.71 (s, 3H) (CH3), 0.98 (t, J ) 7.6 Hz, 3H), 0.81 (t, J ) 7.6 Hz,
3H) (CH2CH3). 13C{1H} NMR (100 MHz, CDCl3): δ 146.1, 144.8,
140.0, 130.6, 129.7, 129.6, 129.5, 129.1, 127.4, 127.3, 127.2, 126.4,
126.0 (aromatic and olefinic C), 80.7, 68.0 (cage C), 29.0, 28.2
(CH2), 20.5 (CH3), 14.5, 14.4 (CH2CH3), the olefinic C connected
to the cage B atom was not observed. 11B{1H} NMR (96 MHz,
CDCl3): δ -7.4 (3B), -10.6 (4B), -13.6 (3B). HRMS: m/z calcd
for C23H32B10+: 416.3502. Found: 416.3506. Anal. Calcd for
C23H32B10: C, 66.31; H, 7.74. Found: C, 66.52; H, 7.80. The
regiochemical assignments of 4m and 5m were further confirmed
by HMBC analyses and the diagnostic correlations are shown in
Scheme 3.
+
(3B), -12.6 (1B), -14.4 (2B). HRMS: m/z calcd for C14H29B10
([M + H]+): 304.3189. Found: 304.3179. Anal. Calcd for C14H28B10:
C, 55.23; H, 9.27. Found: C, 55.00; H, 9.58.
X-ray Structure Determination. Data were collected at 293 K
on a Bruker SMART 1000 CCD diffractometer using Mo-KR
radiation. An empirical absorption correction was applied using the
SADABS program.25 All structures were solved by direct methods
and subsequent Fourier difference techniques and refined aniso-
tropically for all non-hydrogen atoms by full-matrix least-squares
calculations on F2 using the SHELXTL program package.26 The
cage carbon atoms were located by comparing the bond lengths as
the average distance between the carbon and carbon/boron atoms
would appear shorter than that between the boron atoms. Crystal
2-Methyl-1,3-[1,4-dimethyl-2,3-(1,3-propanediyl)-1,3-butadiene-
1,4-diyl]-o-carborane (7a). Yield: 6%. A white solid. Mp: 62.3-63.5
1
°C. H NMR (400 MHz, CDCl3): δ 2.57 (m, 4H) ()CCH2), 2.09
Table 5. Crystal Data and Summary of Data Collection and Refinement
4a
C14H30B10
4b
C15H32B10
4d
4j
C31H32B10
4m
C23H32B10
5m
C23H32B10
7b
C13H22B10
formula
C17H38B10Si
crystal size (mm)
fw
crystal system
space group
a, Å
b, Å
c, Å
R, deg
ꢀ, deg
0.50 × 0.40 × 0.30 0.40 × 0.30 × 0.20 0.50 × 0.40 × 0.30 0.50 × 0.40 × 0.30 0.40 × 0.30 × 0.20 0.50 × 0.40 × 0.30 0.50 × 0.40 × 0.30
306.48
monoclinic
P21/c
320.51
orthorhombic
Pna21
17.164(15)
9.756(9)
12.097(11)
90
378.66
orthorhombic
P212121
9.771(3)
14.550(5)
16.814(6)
90
512.67
416.59
monoclinic
P21
416.59
monoclinic
P21/n
286.41
monoclinic
P21/c
trigonal
j
R(3)
9.626(6)
17.645(12)
12.048(8)
90
38.990(1)
38.990(1)
12.161(1)
90
12.641(1)
8.951(1)
22.288(2)
90
8.939(1)
17.671(2)
16.068(2)
90
9.311(6)
7.728(5)
24.422(16)
90
111.74(1)
90
90
90
90
90
90
120
98.53(1)
90
91.45(1)
90
91.05(1)
90
γ, deg
V, Å3
1901(2)
4
2026(3)
4
2390(1)
4
16011(1)
18
2493.8(4)
4
2537.3(5)
4
1757(2)
4
Z
Dcalcd, Mg/m3
radiation (λ), Å
2θ range, deg
µ, mm-1
F(000)
1.071
1.051
1.052
0.957
0.71073
3.5 to 50.0
0.050
4824
1.110
1.091
1.083
0.71073
4.3 to 50.0
0.052
0.71073
4.7 to 50.0
0.051
0.71073
3.7 to 50.5
0.100
0.71073
1.8 to 50.0
0.056
0.71073
3.4 to 50.5
0.055
0.71073
3.3 to 50.0
0.052
656
688
816
880
880
600
no. of obsd reflns
3355
2873
4328
6196
8299
4575
3092
no. of params refnd 217
226
253
371
595
298
208
goodness of fit
R1
wR2
1.044
0.075
0.161
1.082
0.048
0.106
1.049
0.039
0.108
1.056
0.069
0.205
1.001
0.052
0.103
1.094
0.082
0.248
1.035
0.090
0.251
9
16092 J. AM. CHEM. SOC. VOL. 132, NO. 45, 2010

1,3-Dehydro-o-carborane
A R T I C L E S
data and details of data collection and structure refinements are
given in Table 5.
tion Region (Project No. 404108) and The Chinese University of
Hong Kong. We thank Ms. Hoi-Shan Chan for single-crystal X-ray
analyses.
Acknowledgment. This work was supported by grants from
the Research Grants Council of the Hong Kong Special Administra-
Supporting Information Available: Crystallographic data in
CIF format for 4a,b,d,j,m, 5m, and 7b. This material is available
free of charge via the Internet at http://pubs.acs.org.
(25) Sheldrick, G. M. SADABS: Program for Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen: Germany,
1996.
(26) Sheldrick, G. M. SHELXTL 5.10 for Windows NT: Structure Deter-
mination Software Programs; Bruker Analytical X-ray Systems, Inc.:
Madison, Wisconsin, USA, 1997.
JA1058789
9
J. AM. CHEM. SOC. VOL. 132, NO. 45, 2010 16093