Ionic-liquid-promoted decaborane dehydrogenative alkyne-insertion reactions: A new route to o-carboranes

Article abstract of DOI:10.1021/ic800999y

Unlike in conventional organic solvents, where Lewis base catalysts are required, decaborane dehydrogenative alkyne-insertion reactions proceed rapidly in biphasic ionic-liquid/toluene mixtures with a wide variety of terminal and internal alkynes, thus providing efficient, one-step routes to functional o-carborane 1-R-1,2-C₂B₁₀H₁₁ and 1-R-2-R′-1,2-C₂B₁₀H₁₀ derivatives, including R = C₆H₅- (1), C₆H₁₃- (2), HC≡C-(CH₂)₅- (3), (1-C₂B ₁₀H₁₁)-(CH₂)₅-(4), CH ₃CH₂C(O)OCH₂- (5), (C₂H ₅)₂NCH₂- (6), NC-(CH₂)₃- (7), 3-HC≡C-C₆H₄- (8), (1-C₂B ₁₀H₁₁)-1,3-C₆H₄-(9), HC≡C-CH₂-O-CH₂- (10); R,R′ = C ₂H₅- (11); R = HOCH₂-, R′ = CH ₃- (12); R = BrCH₂-; R′ = CH₃- (13); R = H₂C=C(CH₃)-, R′ = C₂H₅- (14). The best results were obtained from reactions with only catalytic amounts of bmimCl (1-butyl-3-methylimidazolium chloride), where in many cases reaction times of less than 20 min were required. The experimental data for these reactions, the results observed for the reactions of B₁₀H ₁₃^- salts with alkynes, and the computational studies reported in the third paper in this series all support a reaction sequence involving (1) the initial ionic liquid promoted formation of the B ₁₀H₁₃^- anion, (2) addition of B ₁₀H₁₃^- to the alkyne to form an arachno-R,R′-C₂B₁₀H₁₃^- anion, and (3) protonation of arachno-R,R′-C₂B₁₀H ₁₃^- to form the final neutral 1-R-2-R′-1,2-C ₂B₁₀H₁₀ product with loss of hydrogen.

Full text of DOI:10.1021/ic800999y

Inorg. Chem. 2008, 47, 9193-9202
Ionic-Liquid-Promoted Decaborane Dehydrogenative Alkyne-Insertion
Reactions: A New Route to o-Carboranes
Yuqi Li, Patrick J. Carroll, and Larry G. Sneddon*
Department of Chemistry, UniVersity of PennsylVania, Philadelphia, PennsylVania 19104-6323
Received May 31, 2008
Unlike in conventional organic solvents, where Lewis base catalysts are required, decaborane dehydrogenative
alkyne-insertion reactions proceed rapidly in biphasic ionic-liquid/toluene mixtures with a wide variety of terminal
and internal alkynes, thus providing efficient, one-step routes to functional o-carborane 1-R-1,2-C2B10H11 and 1-R-
2-R′-1,2-C2B10H10 derivatives, including R ) C6H5- (1), C6H13- (2), HC≡C-(CH2)5- (3), (1-C2B10H11)-(CH2)5-
(4), CH3CH2C(O)OCH2- (5), (C2H5)2NCH2- (6), NC-(CH2)3- (7), 3-HC≡C-C6H4- (8), (1-C2B10H11)-1,3-C6H4-
(9), HC≡C-CH2-O-CH2- (10); R,R′ ) C2H5- (11); R ) HOCH2-, R′ ) CH3- (12); R ) BrCH2-; R′ )
CH3- (13); R ) H2CdC(CH3)-, R′ ) C2H5- (14). The best results were obtained from reactions with only
catalytic amounts of bmimCl (1-butyl-3-methylimidazolium chloride), where in many cases reaction times of less
than 20 min were required. The experimental data for these reactions, the results observed for the reactions of
s
B10H13 salts with alkynes, and the computational studies reported in the third paper in this series all support a
s
reaction sequence involving (1) the initial ionic liquid promoted formation of the B10H13 anion, (2) addition of
B10H13s to the alkyne to form an arachno-R,R′-C2B10H13s anion, and (3) protonation of arachno-R,R′-C2B10H13s to
form the final neutral 1-R-2-R′-1,2-C2B10H10 product with loss of hydrogen.
Introduction
neutron capture therapy) to materials science.2 The syntheses
of mono- and di-C-substituted o-carborane derivatives have
previously been most conveniently achieved (eqs 1 and 2)3
through the reactions of alkynes with either decaborane/
Lewis-base (L) mixtures or 6,9-B10H12 · L2 (e.g., L ) SEt2,
CH3CN) compounds. Reaction times are normally several
Because of their high boron content and excellent chemical
and thermal stabilities, o-carborane clusters are important
components in applications ranging from medicine1 (boron
*
To whom correspondence should be addressed. E-mail:
lsneddon@sas.upenn.edu.
(2) For reviews of carborane polymers and other application of carboranes,
see: (a) Williams, R. E Pure Appl. Chem 1972, 29, 569–583. (b)
Heying, T. L. Progress in Boron Chemistry; Pergamon: New York,
1970; Vol. 2, Chapter 3. (c) Schroeder, H. A. Inorg. Macromol. ReV.
1970, 1, 45. (d) Korshak, V. V.; Sarishvili, I. G.; Zhigach, A. F.;
Sobolevskii, M. V. Russ. Chem. ReV. 1967, 36, 903. (e) Green, J.;
Mayers, N.; Korshak, A. P.; Fein, M. M.; O’Brien, E. L.; Cohen, M. S.
Polymer Letters 1964, 2, 109. (f) Teixidor, F.; Vinas, C.; Demonceau,
A.; Nunez, R. Pure Appl. Chem. 2003, 75, 1305–1313. (g) Grimes,
R. N. J. Chem. Ed. 2004, 81, 657–672.
(3) (a) Heying, T. L.; Ager, J. W.; Clark, S. L.; Mangold, D. J.; Goldstein,
H., L.; Hillman, M.; Polak, R. J.; Szymanski, J. W. Inorg. Chem 1963,
2, 1089–1092. (b) Fein, M. M.; Bobinski, J.; Mayers, N; Schwartz,
N. N.; Cohen, M. S. Inorg. Chem. 1963, 2, 1111–1115. (c) Potenza,
J. A.; Lipscomb, W. N. Inorg. Chem. 1966, 5, 1471–1477. (d) Ott,
J. J.; Gimarc, B. M. J. Am. Chem. Soc. 1986, 108, 4303–4308. (e)
Vondrak, T.; Plesek, J.; Hermanek, S.; Stibr, B. Polyhedron 1989, 8,
805–811. (f) Petrov, E. S.; Yakovleva, E. A.; Isaeva, G. G.; Kalinin,
V. N.; Zakharkin, L. I.; Shatenshtein, A. I. Dokl. Akad. Nauk SSSR
1970, 191, 617–619. (g) Bregadze, V. I. Chem. ReV. 1992, 92, 209–
233. (h) Bould, J.; Laromaine, A; Bullen, N. J.; Vinas, C.; Thornton-
Pett, M.; Sillanapaa, R.; Kivekas, R.; Kennedy, J. D.; Teixidor, F.
Dalton Trans. 2008, 1552–1563.
(1) For reviews of boron neutron capture therapy, see: (a) Barth, R. F.;
Soloway, A. H.; Fairchild, R. G.; Brugger, R. M. Cancer 1992, 70,
2995–3007. (b) Barth, R. F. J. Neuro-Oncology 2003, 62, 1–5. (c)
Hawthorne, M. F.; Lee, M. W. J. Neuro-Oncol. 2003, 62, 33–35. (d)
Soloway, A. H.; Barth, R. F.; Gahbauer, R. A.; Blue, T. E.; Goodman,
J. H. J. Neuro-Oncol. 1997, 33, 9–18. (e) Sweet, W. H. J. Neuro-
Oncol. 1997, 33, 19–26. (f) Moss, R. L.; Aizawa, O.; Beynon, D.;
Brugger, R.; Constantine, G.; Harling, O.; Liu, H. B.; Watkins, P.
J. Neuro-Oncol. 1997, 33, 27–40. (g) Sjoberg, S.; Carlsson, J.;
Ghaneolhosseini, H.; Gedda, L.; Hartman, T.; Malmquist, J.; Naeslund,
C.; Olsson, P.; Tjarks, W. J. Neuro-Oncol. 1997, 33, 41–52. (h) Barth,
R. F.; Soloway, A. H.; Fairchild, R. G. Cancer Res. 1990, 50, 1061–
1070. (i) The Clinical State of Boron Neutron Capture Therapy.
Presented at the Department of Energy, Office of Medical Sciences
Division Workshop, November 3-5, 1997, Charlotte, NC. (j) Haw-
thorne, M. F. Angew. Chem., Int. Ed. Engl. 1993, 32, 950–984. (k)
Soloway, A. H.; Tjarks, W.; Barnum, B. A.; Rong, F.-G.; Barth, R. F.;
Codogni, I. M.; Wilson, J. G. Chem. ReV. 1998, 98, 1515–1562. (l)
Lesnikowski, Z. J.; Shi, J.; Schinazi, R. F. J. Organomet. Chem. 1999,
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2002, 232, 173–230.
10.1021/ic800999y CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 20, 2008 9193
Published on Web 09/19/2008

Li et al.
Table 1. Comparison of Decaborane Reactions with Phenylacetylene in
hours with typical yields of <75% for terminal alkynes and
with much lower yields (or not work at all) for internal
alkynes.
Different Biphasic Systemsa
time (h)
for B10H14
consumption
time (h)
for B10H14
consumption
ionic phase
(g, mmol)
ionic phase
(g, mmol)
B10H14 + 2L
9
∆8 B10H12L2 (L ) SEt2or CH3CN) + H2 (1)
bmimBF4 (0.9, 3.9)
bmimPF6 (1.0, 3.5)
thtdpBF4 (1.1, 1.9)
bmpyBF4 (0.9, 3.9)
bmimBr (0.34, 0.7)
bpyPF6 (0.31, 1.1)
96
72
48
24
20
16
bmimCl (0.21, 1.2)
bmimI (0.33, 1.2)
bmimOTf (0.23, 0.8) no reaction
Bu4NCl (0.26, 0.9)
Bu4NPF6 (1.0, 2.6)
PPNCl (1.1, 1.9)
Me4NF (0.18, 2.2)
0.1
no reaction
0.5
20
1
B10H12L2 + RCtCH f 1-R-1,2-C2B10H11 + 2L + H2 (2)
We report in this paper that, in contrast to the conventional
routes, decaborane dehydrogenative alkyne-insertion reac-
tions in biphasic ionic-liquid/toluene mixtures proceed rapidly
(in many cases in less than 20 min) with both terminal and
internal alkynes without the need of any added Lewis base
catalyst and thus provide improved, one-step routes to an
array of C-substititued, 1-R-1,2-C2B10H11 and 1-R-2-R′-1,2-
C2B10H10, o-carborane derivatives.
20
a All reactions were performed at 120 °C and used ∼0.4 g (3.2 mmol)
of B10H14, an excess (∼0.6 g, 5.9 mmol) of phenylacetylene, and ∼10 mL
of toluene.
Robertson Microlit Laboratories, Madison, NJ. Melting points were
obtained on a standard melting point apparatus and are uncorrected.
Reaction of B10H14 and an Alkyne in the Absence of an
Ionic Liquid. A 50 mL, 2-neck round bottom flask equipped with
a septum, stir bar, and vacuum adapter was charged under an inert
atmosphere with 0.102 g (0.83 mmol) of B10H14, 0.4 mL (3.6 mmol)
of phenylacetylene and ∼10 mL of toluene. After heating the
reaction mixture at 120 °C for 1 h, analysis by 11B NMR of an
aliquot of the toluene layer showed only unreacted B10H14.
General Synthetic Procedures. A 50 mL, 2-neck round bottom
flask equipped with a septum, stir bar, and vacuum adapter was
charged in a dry box with an ionic liquid, inorganic salt or nitrogen
base. The flask was sealed, taken out of the box and then charged
under Ar with the indicated amounts of B10H14, alkyne and toluene.
Using the vacuum adapter, the flask was attached to a water
condenser open to argon and the body of the flask then submerged
in an oil bath (usually at 120 °C) equipped with a magnetic stir
plate. The mixture was vigorously stirred during reaction to form
an emulsion. The reaction was monitored by 11B NMR analysis of
the toluene layer and stopped when all starting decaborane had been
consumed. The top organic layer of the reaction mixture was
separated by pipette. The ionic liquid layer was then extracted with
10-20 mL of ether. The combined toluene and ether extracts were
vacuum concentrated and then flash-filtered through a silica gel
column.
Experimental Section
General Procedures and Materials. Unless otherwise noted,
all reactions and manipulations were performed in dry glassware
under nitrogen or argon atmospheres using the high-vacuum or
inert-atmosphere techniques described by Shriver.4
Phenylacetylene, 3-hexyne, 1-octyne, bis(triphenylphosphora-
nylidene) ammonium chloride [PPNCl], 2-methyl-1-hexen-3-yne,
Bu4NCl, 1,8-bis(dimethylamino)naphthalene [Proton Sponge, PS],
Me4NF, Bu4NPF6 (Aldrich), methyl propiolate, 1,8-nonadiyne
(Chemical Samples), propargylpropionate, 2-butyn-1-ol (Lancaster),
3-diethylamino-1-propyne, 5-cyano-1-pentyne and m-diethynyl-
benzene (GSF Chemicals) were used as received. The literature
method was used to prepare [Et3NH+][B10H13s].5 The 1-butyl-3-
methyl-imidazolium chloride [bmimCl], 1-butyl-3-methyl-imida-
zolium bromide [bmimBr], 1-butyl-3-methylimidazolium iodide
[bmimI], 1-butyl-3-methylimidazolium hexafluorophosphate
[bmimPF6],
1-butyl-3-methylimidazolium
tetrafluoroborate
[bmimBF4], trihexyl(tetradecyl)phosphonium tetrafluoroborate [th-
tdpBF4], 1-butyl-4-methylpyridinium tetrafluoroborate [bmpyBF4],
1-butylpyridimiun hexafluorophosphate [bpyPF6], 1-butyl-3-meth-
ylimidazolium trifluoromethanesulfonate [bmimOTF] (Fluka) were
dried by carrying out azetropic distillations with toluene, followed
by in vacuo drying. They were then stored in the dry box until
use. Decaborane, B10H14 (Callery), was sublimed prior to use. HPLC
or ACS grade hexanes, toluene, ethyl acetate, CH2Cl2, NEt3, and
silica gel with mesh sizes of 230-400 (Fisher) were used as
received. C6D6 (D, 99.5%) and CD2Cl2 (D, 99.9%) (Cambridge
Isotope) were used as received.
Physical Measurements. 1H NMR at 400.1 MHz and 11B NMR
spectra at 128.4 MHz were obtained on a Bruker DMX 400
spectrometer. All 11B NMR chemical shifts are referenced to
external BF3 ·OEt2 (0.00 ppm) with a negative sign indicating an
upfield shift. All 1H chemical shifts were measured relative to
residual protons in the lock solvents and are referenced to Me4Si
(0.00 ppm). High- and low-resolution mass spectra (HRMS and
LRMS) using negative chemical ionization (NCI) techniques were
recorded on a Micromass Autospec Spectrometer. Infrared spectra
were recorded on a Perkin-Elmer Spectrum 100 FT-IR spectrometer
using KBr pellets or NaCl plates and are listed in Table S1
(Supporting Information). Elemental analyses were performed at
Syntheses in Ionic Liquids. 1-C6H5-1,2-C2B10H11 (1).3,6 Re-
action of B10H14 (0.307 g, 2.51 mmol) with 0.674 g (6.60 mmol)
of phenylacetylene in biphasic toluene (∼10 mL)/bmimCl (0.209
g, 1.20 mmol) at 120 °C for 7 min gave, following hexanes elution
from a silica gel column, 0.400 g (1.78 mmol, 71% yield) of 1 as
a white solid. mp: 66-67 °C (lit. 66-67 °C).6 NCI-HRMS (m/e)
11
calcd for 12C8
B
1H16: 222.2182; found 222.2185. Anal. Calcd:
10
C, 43.61; H, 7.32. Found: C, 43.80; H, 7.60. The 1H and 11B NMR
and IR data (Tables S1 and S2, Supporting Information) are
consistent with literature values.6
The reactions of B10H14 (∼0.4 g, 3.2 mmol) with phenylacetylene
(∼0.6 g, 5.9 mmol) in biphasic mixtures of toluene (∼10 mL) and
other ionic liquids are compared in Table 1.
1-C6H13-1,2-C2B10H11 (2).7 Reaction of B10H14 (0.251 g, 2.06
mmol) with 0.720 g (6.53 mmol) of 1-octyne in biphasic toluene
(∼10 mL)/bmimCl (0.194 g, 1.11 mmol) at 120 °C for ∼7 min
gave, following hexanes elution from a silica gel column, 0.430 g
(1.86 mmol, 91% yield) of 2 as an oily liquid. NCI-HRMS (m/e)
11
calcd for 12C8
B
1H24: 230.2802; found 230.2819. Anal. Calcd:
10
(6) (a) Stanko, V. I.; Kopylov, V. V.; Klimova, A. I. Z. Obshchei Khim.
1965, 35, 1433–1436. (b) Brain, P. T.; Cowie, J.; Donohoe, D. J.;
Hnyk, D.; Rankin, W. H.; Reed, D.; Reid, B. D.; Robertson, H. E.;
Welch, A. J. Inorg. Chem. 1996, 35, 1701–1708.
(4) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-SensitiVe
Compounds, 2nd ed.; Wiley: New York, 1986.
(5) Graybill, B. M.; Pitochelli, A. R.; Hawthorne, M. F. Inorg. Chem.
1962, 1, 622–623.
(7) Dunks, G. B.; Ordonez, K. P. U.S. Patent 4100199, 1978.
9194 Inorganic Chemistry, Vol. 47, No. 20, 2008

New Route to o-Carboranes
C, 42.07; H, 10.59. Found: C, 42.98; H, 10.43. Spectral data for 2
were not previously reported. 11B NMR (128.4 MHz, C6D6, ppm,
J ) Hz): δ -3.1 (d, 1B, J 147), -6.5 (d, 1B, J 143), -10.1 (d,
2B, J 151), -12.2 (d, 2B, J 160), -13.2 (d, 2B, J undefined), -13.9
(d, 2B, J 156). 1H NMR (400.1 MHz, C6D6, ppm, J ) Hz): δ 2.53
(s, 1H, cage C-H), 1.62-1.57 (2H, CH2), 1.24-1.15 (m, 4H,
CH2CH2), 1.07-1.00 (m, 4H, CH2CH2), 0.88 (t, 3H, J 7.2, CH3).
1-(HC≡C-(CH2)5)-1,2-C2B10H11 (3). Reaction of B10H14 (0.228
g, 1.86 mmol) with 0.7 mL (∼4.6 mmol) of 1,8-nonadiyne in
biphasic toluene (∼10 mL)/bmimCl (0.138 g, 0.79 mmol) at 120 °C
for 10 min gave, following CH2Cl2 elution from a silica gel column,
1H NMR (400.1 MHz, C6D6, ppm, J ) Hz): 3.34 (s, 1H, cage
C-H), 2.50 (s, 2H, N-CH2), 2.03 (q, 4H, J7.1, CH2CH3), 0.56 (t,
6H, J 7.1, CH3).
1-NC-(CH2)3-1,2-C2B10H11 (7).10 Reaction of B10H14 (0.180 g,
1.47 mmol) with 0.4 mL (∼3.8 mmol) of 5-cyano-1-pentyne in
biphasic toluene (∼10 mL)/bmimCl (0.095 g, 0.54 mmol) at 120
°C for ∼30 min gave, following ethyl acetate elution from a silica
gel column, 0.200 g (0.95 mmol, 65% yield) of 7 as a white solid.
mp: 81-82 °C (lit. 81-82 °C).10 NCI-HRMS (m/e) calcd for
11
12C6
B
10
1H1714N: 213.2291, found 213.2298. Anal. Calcd: C, 34.10;
H, 8.11; N, 6.63. Found: C, 34.35; H, 8.14; N, 6.71. The 11B and
1H NMR and IR data (Tables S1 and S2, Supporting Information)
are consistent with literature values.10
0.282 g (1.18 mmol, 63% yield) of 3 as an oily liquid. NCI-HRMS
11
(m/e) calcd for 12C9
B
10
1H22: 240.2652; found 240.2643. 11B NMR
(128.4 MHz, C6D6, ppm, J ) Hz): δ -2.8 (d, 1B, J 146), -6.1 (d,
1B, J 138), -9.8 (d, 2B, J 151), -12.1 (d, 2B, J 157), -13.0 (d,
2B, J undefined), -13.6 (d, 2B, J undefined). 1H NMR (400.1 MHz,
C6D6, ppm, J ) Hz): δ 2.46 (s, 1H, cage C-H), 1.89 (m, 2H, CH2),
1.80 (m, 2H, CH2), 1.49 (m, 2H, CH2), 1.22 (s, 1H, HCtC), 1.10
(m, 2H, CH2), 0.88 (m, 2H, CH2).
1-(3-HCtC-C6H4)-1,2-C2B10H11 (8). Reaction of B10H14 (0.295
g, 2.42 mmol) with 0.6 mL (∼3.8 mmol) of m-diethynylbenzene
in biphasic toluene (∼10 mL)/bmimCl (0.240 g, 1.37 mmol) at 120
°C for ∼20 min gave, following hexanes elution from a silica gel
column, 0.250 g (1.02 mmol, 42% yield) of 8 as a light yellow
1H16:
12
11
solid. mp: 59-61 °C. NCI-HRMS (m/e) calcd for
C
B
10 10
1,1′-(CH2)5-(1,2-C2B10H11)2 (4).8 Reaction of B10H14 (0.447 g,
3.66 mmol) with 0.215 g (1.79 mmol) of 1,8-nonadiyne in biphasic
toluene (∼10 mL)/bmimCl (0.150 g, 0.86 mmol) at 120 °C for
∼10 min gave, following CH2Cl2 elution from a silica gel column,
0.379 g (1.06 mmol, 59% yield) of 4 as a white solid. mp: 177-179
246.2182; found 246.2187. Anal. Calcd: C, 49.16; H, 6.60. Found:
C, 48.88; H, 6.62. 11B NMR (128.4 MHz, C6D6, ppm, J ) Hz):
-2.4 (d, 1B, J 151), -4.6 (d, 1B, J 151), -9.4 (d, 2B, J 153),
-11.7 (d, 2B, J 163), -12.3 (d, 2B, J undefined), -14.7 (d, 2B, J
1
158). H NMR (400.1 MHz, CD2Cl2, ppm, J ) Hz): δ 7.61 (m,
8
11
°C (lit. 177-179 °C). NCI-HRMS (m/e) calcd for 12C9
B
1H32:
20
1H, C6H4), 7.50 (m, 2H, C6H4), 7.33 (t, 1H, J 7.8, C6H4), 4.07 (s,
360.4364; found 360.4386. Anal. Calcd: C, 30.32; H, 9.05. Found:
1H, cage C-H), 3.19 (s, 1H, -C≡CH).
1
C, 30.60; H, 9.34. The 11B and H NMR and IR data (Tables S1
1,1′-(1,3-C6H4)-(1,2-C2B10H11)2 (9).11 Reaction of B10H14 (0.337
g, 2.75 mmol) with 0.5 mL (0.169, 1.33 mmol) of m-diethynyl-
benzene in biphasic toluene (∼10 mL)/bmimCl (0.168 g, 0.95
mmol) at 120 °C for ∼20 min gave, following hexane elution from
a silica gel column, 0.168 g (0.46 mmol, 35% yield) of 9 as a white
and S2, Supporting Information) are consistent with literature
values.8
1-CH3CH2C(O)OCH2-1,2-C2B10H11 (5).9 Reaction of B10H14
(0.245 g, 2.01 mmol) with 0.4 mL (∼2.5 mmol) of propargylpropionate
in biphasic toluene (∼10 mL)/bmimCl (0.120 g, 0.69 mmol) at 120
°C for ∼10 min gave, following ethyl acetate elution from a silica gel
1
solid. The 11B and H NMR data (Tables S1 and S2, Supporting
Information) are consistent with the literature values.11
column, 0.337 g (1.46 mmol, 73% yield) of 5 as an oily liquid. NCI-
1-(HC≡C-CH2-O-CH2)-1,2-C2B10H11 (10). Reaction of B10H14
(0.351 g, 2.87 mmol) with 0.7 mL (6.8 mmol) of dipropargyl ether
in biphasic toluene (∼10 mL)/bmimCl (0.308 g, 1.76 mmol) at 120
°C for ∼20 min gave, following CH2Cl2/hexane (1:4 ratio) elution
from a silica gel column, 0.333 g (1.56 mmol, 55% yield) of 10 as
11
HRMS (m/e) calcd for 12C6
B
10
1H1816O2: 232.2236; found 232.2225.
Anal. Calcd: C, 31.28; H, 7.92. Found: C, 31.52; H, 7.96. Spectral
data for 5 were not previously reported. 11B NMR (128.4 MHz, C6D6,
ppm, J ) Hz): δ 2.5 (d, 1B, J 149), -5.0 (d, 1B, J 148), -10.0 (d,
1
an oily liquid. NCI-HRMS (m/e) calcd for 12C611B10 H16O: 214.2131;
1
2B, J 151), -12.2 (d, 2B, J 158), -13.8 (d, 4B, J 169). H NMR
(400.1 MHz, C6D6, ppm, J ) Hz): δ 4.00 (s, 2H, -CH2-O-), 3.13
(s, 1H, cage C-H), 1.88 (q, 2H, J 7.5, CH2CH3), 0.85 (t, 3H, J 7.5,
CH3).
found 214.2127. Anal. Calcd: C, 33.95; H, 7.60. Found: C, 34.37;
H, 7.84. 11B NMR (128.4 MHz, C6D6, ppm, J ) Hz): δ -3.5 (d,
1B, J 153), -5.3 (d, 1B, J 140), -9.8 (d, 2B, J 157), -12.4 (d,
1-(C2H5)2NCH2-1,2-C2B10H11 (6).3 Reaction of B10H14 (0.170
g, 1.39 mmol) with 0.25 mL (∼1.8 mmol) of 3-diethylamino-1-
propyne in biphasic toluene (∼10 mL)/bmimCl (0.090 g, 0.51
mmol) at 120 °C for ∼30 min gave, following hexanes elution from
a silica gel column, 0.146 g (0.64 mmol, 46% yield) of 6 as a white
1
2B, J 168), -13.9 (d, 4B, J 156). H NMR (400.1 MHz, C6D6,
ppm, J ) Hz): δ 3.47 (s, 2H, -O-CH2-), 3.32 (s, 2H,
-O-CH2-), 3.18 (s, 1H, cage C-H), 1.98 (s, 1H, -C≡CH).
1,2-Et2-1,2-C2B10H10 (11).12 Reaction of B10H14 (0.468 g, 3.83
mmol) with 0.682 g (8.30 mmol) of 3-hexyne in biphasic toluene
(∼10 mL)/bmimCl (0.204 g, 1.17 mmol) at 120 °C for ∼7 min
gave, following hexane elution from a silica gel column, 0.537 g
(2.68 mmol, 70% yield) of 11 as a white solid. mp: 74-75 °C.
solid. mp: 33-34 °C (lit. 33-35 °C).3 NCI-HRMS (m/e) calcd for
11
12C7
B
10
1H2314N: 231.2761; found 231.2764. Anal. Calcd: C, 36.66;
H, 10.11; N, 6.11. Found: C, 36.51; H, 10.30; N, 5.89. Spectral
data for 6 were not previously reported. 11B NMR (128.4 MHz,
C6D6, ppm, J ) Hz): δ -3.1 (d, 1B, J 149), -5.6 (d, 1B, J 149),
-9.5 (d, 2B, J 150), -11.9 (d, 2B, J 161), -13.6 (d, 4B, J 158).
NCI-HRMS (m/e) calcd for 12C611B10 H20: 202.2802; found 202.2819.
1
Anal. Calcd: C, 35.97; H, 10.06. Found: C, 35.91; H, 10.27. The
(10) (a) Wong, H. S.; Tolpin, E. I.; Lipscomb, W. N. J. Med. Chem. 1974,
17, 785–791. (b) Berry, J. M.; Watson, C. Y.; Whish, W. J. D.;
Threadgill, M. D. J. Chem. Soc., Perkin Trans. 1997, 1, 1147–1156.
(11) Endo, Y.; Songkram, C.; Ohta, K.; Yamaguchi, K. J. Organomet.
Chem. 2005, 690, 2750–2756.
(12) Vinas, C.; Pedrajas, J.; Bertran, J.; Teixidor, F.; Kivekas, R.; Sillanpaa,
R. Inorg. Chem. 1997, 36, 2482–2486.
(8) Gomez, F. A.; Johnson, S. E.; Knobler, C. B.; Hawthorne, M. F. Inorg.
Chem. 1992, 31, 3558–3567.
(9) (a) Churkina, L. A.; Zvereva, T. D.; Shingel, I. A.; Ol’dekop, Yu, A.
Inst. Fiz.-Org. Khim., Minsk, USSR. Vestsi Akad. Nauk. BSSR, Seryya
Khimichnykh NaVuk 1983, 1, 56–64. (b) Cai, J.; Nemoto, H.; Singaram,
B.; Yamamoto, Y. Tetrahedron Lett. 1996, 37, 3383–3386.
Inorganic Chemistry, Vol. 47, No. 20, 2008 9195

Li et al.
11B and 1H NMR and IR data (Tables S1 and S2, Supporting
Information) are consistent with literature values.12
of 1. In a similar manner, reactions of (1) B10H14 (0.309 g, 2.53
mmol) with 0.5 mL (∼4.5 mmol) of phenylacetylene and 1.087 g
of (1.9 mmol) bis(triphenylphosphoranylidene) ammonium chloride
(PPNCl) in toluene (∼10 mL) at 120 °C for ∼1 h gave 0.159 g
(0.70 mmol, 28% yield) of 1; (2) B10H14 (0.158 g, 1.29 mmol) with
0.5 mL (∼4.5 mmol) of phenylacetylene and 0.176 g (1.89 mmol)
of Me4NF in toluene (∼10 mL) at 110 °C for 10 h gave 0.065 g
(0.30 mmol, 23% yield) of 1; and (3) B10H14 (0.327 g, 2.68 mmol)
with ∼0.5 mL (∼4.5 mmol) of phenylacetylene and 1.019 g (2.63
mmol) of Bu4NPF6 in toluene (∼10 mL) at 110 °C for ∼20 h gave
0.376 g (1.71 mmol, 64% yield) of 1.
1,2-Et2-1,2-C2B10H10 (11). Reaction of B10H14 (0.221 g, 1.81
mmol) with ∼0.4 mL (∼3.5 mmol) of 3-hexyne and 0.466 g (1.68
mmol) of Bu4NCl in toluene (∼10 mL) at 110 °C for ∼0.5 h, gave
0.194 g (0.97 mmol, 53% yield) of 11, and reaction of B10H14 (0.196
g, 1.60 mmol) with ∼0.4 mL (∼3.5 mmol) of 3-hexyne and 0.835
g (1.45 mmol) of PPNCl in toluene (∼10 mL) at 110 °C for ∼1 h
gave 0.091 g (0.45 mmol, 28% yield) of 11.
1-HOCH2-2-Me-1,2-C2B10H10 (12).13 Reaction of B10H14 (0.181
g, 1.48 mmol) with 0.402 g (5.74 mmol) of 2-butyn-1-ol in biphasic
toluene (∼10 mL)/bmimCl (0.113 g, 0.65 mmol) at 60 °C for ∼10
h gave, following CH2Cl2 elution from a silica gel column, 0.179
g (0.95 mmol, 64% yield) of 12 as a white solid. mp: 270-272 °C
(lit. 268-269 °C).13 NCI-HRMS (m/e) calcd for 12C4
B
10
1H1616O:
11
190.2131; found 190.2138. Anal. Calcd: C, 25.52; H, 8.57. Found:
C, 25.80; H, 8.76. Spectral data for 12 were not previously reported.
11B NMR (128.4 MHz, C6D6, ppm, J ) Hz): δ -4.5 (d, 1B, J
153), -6.2 (d, 1B, J 144), -10.5 (d, 2B, J 162), -11.0 (d, 2B, J
1
undefined), -11.7 (d, 4B, J 151). H NMR (400.1 MHz, C6D6,
ppm, J ) Hz): δ 3.27 (d, 2H, J 7.3, CH2OH), 1.29 (s, 3H, CH3),
1.0 (t, 1H, J 7.3, OH).
1-BrCH2-2-Me-1,2-C2B10H10 (13).3 Reaction of B10H14 (0.271
g, 2.22 mmol) with 0.4 mL (∼4.6 mmol) of 1-bromo-2-butyne in
biphasic toluene (∼10 mL)/bmimCl (0.094 g, 0.54 mmol) at 120
°C for ∼4 h gave, following ethyl acetate elution from a silica gel
column, 0.490 g (1.95 mmol, 88% yield) of 13 as a white solid.
Syntheses via [Et3NH+][B10H13s] Salts. 1-C6H5-1,2-C2B10H11 (1).
Reaction of [Et3NH+][B10H13-] (0.362 g, 1.62 mmol) with ∼0.5
mL (∼4.5 mmol) of phenylacetylene and ∼10 mL toluene at 110
°C for 10 min gave 0.233 g (1.06 mmol, 66% yield) of 1.
1-C6H13-1,2-C2B10H11 (2). Reaction of [Et3NH+][B10H13-] (0.369
g, 1.65 mmol) with 0.4 mL (∼2.7 mmol) of 1-octyne in toluene
(∼10 mL) at 120 °C for ∼10 min gave 0.215 g (0.87 mmol, 57%
mp: 126-127 °C (lit. 125-127 °C).3 NCI-HRMS (m/e) calcd for
11
12C4
B
1H1580Br: 252.1288; found 252.1269. Anal. Calcd: C,
10
19.14; H, 6.02. Found: C, 18.88; H, 5.92. Spectral data for 13 were
not previously reported. 11B NMR (128.4 MHz, C6D6, ppm, J )
Hz): δ -3.8 (d, 1B, J 159), -5.5 (d, 1B, J 157), -10.4 (d, 8B, J
undefined). 1H NMR (400.1 MHz, C6D6, ppm, J ) Hz): δ 3.02 (s,
2H, CH2), 1.15 (s, 3H, CH3).
yield) of 2.
1-H2CdC(CH3)-2-Et-1,2-C2B10H10 (14). Reaction of B10H14
(0.129 g, 1.06 mmol) with 0.187 g (∼2.0 mmol) of 2-methyl-1-
hexen-3-yne in biphasic toluene (∼10 mL)/bmimCl (0.120 g, 0.69
mmol) at 120 °C for ∼10 min gave, following pentane elution from
-
1-(C2H5)2NCH2-1,2-C2B10H11 (6). Reaction of [Et3NH+][B10H13
]
(0.411 g, 1.84 mmol) with ∼0.5 mL (∼3.6 mmol) of 3-diethy-
lamino-1-propyne in toluene (∼10 mL) at 120 °C for ∼10 min
gave 0.134 g (0.06 mmol, 32% yield) of 6.
1-NC-(CH2)3-1,2-C2B10H11 (7). Reaction of [Et3NH+][B10H13
a silica gel column, 0.184 g (0.87 mmol, 82% yield) of 14 as an
-
]
11
oily liquid. NCI-HRMS (m/e) calcd for 12C7
B
1H20: 214.2495;
10
(0.378 g, 1.69 mmol) with 0.5 mL (∼4.8 mmol) of 5-cyano-1-
pentyne in toluene (∼10 mL) at 110°C for ∼10 min, gave, following
ethyl acetate elution from a silica gel column and recrystallization
from hot pentane, 0.189 g (0.89 mmol, 53% yield) of 7.
1,2-Et2-1,2-C2B10H10 (11). Reaction of [Et3NH+][B10H13-] (0.361
g, 1.62 mmol) with 0.4 mL (∼3.5 mmol) of 3-hexyne in toluene
(∼10 mL) at 120 °C for ∼10 min gave 0.108 g (1.13 mmol, 70%
yield) of 11.
found 214.2489. Anal. Calcd: C, 39.59; H, 9.49. Found: C, 39.58;
H, 9.88. 11B NMR (128.4 MHz, C6D6, ppm, J ) Hz): δ -4.2 (d,
1B, J 150), -4.9 (d, 1B, J 149), -10.7 (d, 4B, J 148), -11.8 (d,
4B, J 155). 1H NMR (400.1 MHz, C6D6, ppm, J ) Hz): δ 4.99 (d,
2H, J 29.7, dCH2), 1.54 (q, 2H, J 7.6, CH2CH3), 1.43 (s, 3H,
CH3-CdCH2), 0.69 (t, 3H, J 7.6, CH2CH3).
arachno-8-(NC)-7,8-C2B10H14 (15).14 Analysis by 11B NMR
s
of aliquots of both the toluene and ionic liquid layers following
the reaction of B10H14 (0.125 g, 1.02 mmol) with 0.25 mL of
cyanoacetylene in biphasic toluene (∼10 mL)/bmimCl (0.168 g,
Syntheses via in Situ Generation of [PSH+][B10H13-] or
[Et3NH+][B10H13-]. 1-C6H5-1,2-C2B10H11 (1). Reaction of B10H14
(0.233 g, 1.90 mmol) with 0.5 mL (∼4.5 mmol) of phenylacetylene
and 0.413 g (1.93 mmol) of Proton Sponge in toluene (∼10 mL)
at 110 °C for 1 h gave 0.086 g (0.38 mmol, 20% yield) of 1.
Likewise, reaction of B10H14 (0.249 g, 2.03 mmol) with ∼0.4 mL
(∼3.4 mmol) of phenylacetylene and 0.292 g (2.8 mmol) of Et3N
in toluene (∼10 mL) at 110 °C for ∼10 min gave 0.118 g (0.54
mmol, 26% yield) of 1.
0.96 mmol) at 120 °C for ∼30 min showed the formation of
-
arachno-8-(NC)-7,8-C2B10H14
.
Reaction of B10H14 with Phenylacetylene in Acidic
bmimCl/Toluene. HCl was bubbled through a mixture of B10H14
(0.253 g, 2.1 mmol), bmimCl (0.157 g, 0.9 mmol), and toluene
(10 mL) for 15 min; then 0.6 mL (5.4 mmol) of phenylacetylene
was added, and the mixture heated at 115 °C for 20 min. Analysis
by11B NMR of the toluene layer showed only unreacted B10H14.
Syntheses with Halide Salts. 1-C6H5-1,2-C2B10H11 (1). The
reaction of B10H14 (0.326 g, 2.67 mmol) with 0.5 mL (∼4.5 mmol)
of phenylacetylene and 0.689 g (2.48 mmol) of Bu4NCl in toluene
(∼10 mL) at 120 °C for 30 min resulted in the formation of two
layers. Extraction of the toluene layer gave, following hexane
elution from a silica gel column, 0.196 g (0.89 mmol, 34% yield)
1,2-Et2-1,2-C2B10H10 (11). Reaction of B10H14 (0.242 g, 1.98
mmol) with ∼0.4 mL (∼3.5 mmol) of 3-hexyne and 0.538 g (2.51
mmol) of Proton Sponge in toluene (∼10 mL) at 110 °C for ∼30
min gave 0.093 g (0.47 mmol, 23% yield) of 11, and reaction of
of B10H14 (0.278 g, 2.27 mmol) with ∼0.5 mL (∼4.4 mmol) of
3-hexyne and 0.220 g (2.2 mmol) of Et3N in toluene (∼10 mL) at
110 °C for ∼10 min gave 0.141 g (0.70 mmol, 31% yield) of 11.
Reaction with [Bu4N+][B10H13-]. 11B NMR analysis indicated
reaction of [Bu4N+][B10H13-] (0.249 g, 0.7 mmol) with ∼0.3 mL
(13) (a) Zakharkin, L. I.; Kazantsev, A. V. IzV. Akad. Nauk SSSR, Ser.
Khim. 1966, 3, 568–570. (b) Zhu, Y.; Maguire, J. A.; Hosmane, N. S.
Inorg. Chem. Commun. 2002, 5, 296–299. (c) Cheung, M-S.; Chan,
H-S.; Xie, Z. Organometallics 2004, 23, 517–526.
(14) (a) Su, K; Carroll, P. J.; Sneddon, L. G. J. Am. Chem. Soc. 1993,
115, 10004–10017. (b) Su, K; Barnum, B.; Carroll, P. J.; Sneddon,
L. G. J. Am. Chem. Soc. 1992, 114, 2730–2731.
(∼2.7 mmol) of phenylacetylene in ∼10 mL of toluene at 110 °C
-
for 30 min, resulted in complete consumption of [Bu4N+][B10H13
to form the B9H14 anion.
]
15
-
9196 Inorganic Chemistry, Vol. 47, No. 20, 2008

New Route to o-Carboranes
Table 2. Crystallographic Data Collection and Structural Refinement Information for 4, 8, and 9
4
8
9
empirical formula
fw
C9B20H32
356.55
C10B10H16
244.33
C10B20H26
362.51
crystal class
space group
Z
monoclinic
P21/c (No. 14)
4
orthorhombic
Pca21 (No. 29)
4
monoclinic
C2/c (No. 15)
4
a, Å
b, Å
c, Å
13.537(6)
11.577(5)
13.750(6)
106.01(3)
2071.3(15)
0.45
11.138(2)
11.504(2)
10.857(2)
14.756(2)
15.817(2)
11.4501(13)
128.506(3)
2091.3(4)
0.50
ꢀ, deg
V, Å3
1391.1(4)
0.55
µ, cm-1
cryst size, mm
Dcalcd, g/cm3
F(000)
0.45 × 0.27 × 0.01
0.30 × 0.18 × 0.03
0.40 × 0.28 × 0.03
1.143
1.167
1.151
744
504
744
radiation
temp, K
2θ angle, deg
hkl collected
Mo ΚR
Mo ΚR
Mo KR
143
143
143
5.14-48.1
-15 e h e 13
-13 e k e 11
-11 e l e 15
6516
5.1-50.08
-12 e h e 13
-13 e k e 12
-12 e l e 11
5538
5.16-50.1
-17e h e 15
-18 e k e 18
-12 e l e 13
7865
reflns measured
unique reflns
3150
2071
1852
(Rint ) 0.0528)
(Rint ) 0.0280)
(Rint ) 0.0448)
observed reflns (F > 4σ)
reflns used in refinement
params
2046
1896
1396
3150
263
2071
246
1852
189
Ra indices (F > 4σ)
R1 ) 0.1180
wR2 ) 0.2601
R1 ) 0.1781
wR2 ) 03136
1.136
R1 ) 0.0457
wR2 ) 0.1149
R1 ) 0.0507
wR2 ) 0.1218
1.041
R1 ) 0.0553
wR2 ) 0.1239
R1 ) 0.0805
wR2 ) 0.1410
1.110
Ra indices (all data)
GOFb
final difference peaks, e/Å3
+0.587, -0.407
+0.166, 0.192
+0.244, -0.190
a R1 ) ∑|Fo| - |Fc|/∑|Fo|; wR2 ) {∑w(Fo s Fc )2/∑w(Fo )2}1/2
.
b GOF ) {Σw(Fo - Fc )2/n - p)}1/2, where n ) no. of reflections and p ) no. of
2
2
2
2 2
parameters refined.
Crystallographic Data for 1,1′-(CH2)5-(1,2-C2B10H11)2 (4),
1-(3-HCtC-C6H4)-1,2-C2B10H11 (8), and 1,1′-(1,3-C6H4)-(1,2-
C2B10H11)2 (9). Single crystals of 4 (Upenn no. 3219), 8 (Upenn
no. 3267), and 9 (Upenn no. 3271) were grown from hexane
solutions at room temperature.
Collection and Reduction of the Data. X-ray intensity data
(Table 2) were collected on a Rigaku Mercury CCD area detector
employing graphite-monochromated Mo KR (λ ) 0.71069 Å)
radiation. Rotation images were processed to produce a listing of
unaveraged F2 and σ(F2) values, which were then passed to the
CrystalStructure16 program package for further processing and
structure solution on a Dell Pentium III computer. The intensity
data were corrected for Lorentz and polarization effects and for
absorption.
Results
As summarized in Table 3, decaborane was found to react
with a variety of internal and terminal alkynes in mixtures
of toluene and an ionic liquid, such as 1-butyl-3-methylim-
idiazolium chloride, bmimCl, to give the corresponding 1-R-
1,2-C2B10H11 and 1-R-2-R′-1,2-C2B10H10 o-carborane de-
rivatives, 1-14 (eq 3).
Solution and Refinement of the Structures. The structures were
solved by direct methods (SIR97).17a Refinements were by full-
matrix least squares based on F2 using SHELXL-97.17b All
reflections were used during refinement (F2 values that were
experimentally negative were replaced by F2 ) 0). Non-hydrogen
atoms were refined anisotropically, cage hydrogen atoms were
refined isotropically, and chain hydrogen atoms were included as
constant contributions to the structure factors and were not refined.
The biphasic reaction mixtures, with an ionic liquid layer
at the bottom and the alkyne-toluene layer at the top, were
heated at ∼120 °C with vigorous stirring to form an
emulsion. In many cases, as shown in the NMR spectra in
Figure 1 for the reaction of decaborane with 1-octyne in
toluene/bmimCl, reactions were complete in only a few
minutes. The bottom spectrum shows the initial B10H14
starting material in the toluene layer above the ionic liquid.
The 1-octyne was added, and the stirred emulsion was heated
at 120 °C. The middle spectrum is of the reaction mixture
after 4 min, where the peaks of the 1-C6H13-1,2-C2B10H11
product are clearly visible. The top spectrum shows that the
reaction was complete after only 7 min. The toluene layer
(15) Greenwood, N. N.; Gysling, H. J.; McGinnety, J. A.; Owen, J. D.
Chem. Commun. 1970, 505–506.
(16) CrystalStructure, Crystal Structure Analysis Package; Rigaku Corpora-
tion: The Woodlands, TX, 2002.
(17) For SIR97, see: (a) Altomare, A.; Burla, M. C.; Camalli, M.;
Cascarano, G.; Giacovazzo, C.; Moliterni, A.; Polidori, G.; Spagna,
R. J. Appl. Cryst. 1999, 32, 115–119. (b) Sheldrick, G. M. SHELXL-
97, Program for the Refinement of Crystal Structures; University of
Go¨ttingen: Go¨ttingen, Germany, 1997.
Inorganic Chemistry, Vol. 47, No. 20, 2008 9197

Li et al.
Table 3. Summary of B10H14 Dehydrogenative Alkyne Insertions in
bmimCl/Toluene
Figure 1. 11B{1H} spectra of the toluene layer showing the progress of
the reaction of B10H14 with 1-octyne at 120 °C to produce 1-C6H13-1,2-
C2B10H11 (2) when employing bmimCl/toluene biphasic media.
was separated by pipette, and then the ionic liquid was
extracted several times with Et2O. The toluene and ether
solutions were combined, vacuum-concentrated, and then
flash filtered through a silica gel column using a hexanes
eluent. Removal of the solvent afforded a ∼90% yield of 2.
As typical of o-carborane derivatives, compounds 1-14
were air and water stable and showed good solubilities in
polar solvents including THF, methylene chloride, and ethyl
acetate. The less polar products 1, 2, 6, 8, 9, 11, and 14
were also soluble in hexanes, benzene, and toluene. Com-
pounds 1, 2, 4-7, 9, and 11-13 were previously known,
but 3, 8, 10, and 14 had not been reported. All products were
1
characterized by 11B and H NMR, NCl-MS, FT-IR, and
elemental analysis.
The Cs symmetric monosubstituted 1-R-1,2-C2B10H11
derivatives 1-10 have a mirror plane containing the C1, C2,
B9, and B12 atoms and should exhibit six doublets in 1:1:
2:2:2:2 ratios in their 11B NMR spectra arising from the B9,
B12, B8,10, B4,5, B7,11, and B3,6 boron atoms. However,
overlap of the B4,5 and B7,11 resonances was usually
observed producing a pattern with five doublets in 1:1:2:4:2
ratios.18 The ∼C2V symmetric disubstituted 1-R-2-R′-1,2-
C2B10H10 derivatives 11-14 should have four doublets in
(18) (a) Fielding, T. E. Ph.D. thesis, University of Pittsburgh, Pittsburgh,
PA, 1971. (b) Todd, L. J.; Siedle, A. R. Prog. NMR Spectrosc. 1993,
13, 87–176.
a New compound. b The previous synthesis was via lithiocarborane, not
by alkyne insertion.
9198 Inorganic Chemistry, Vol. 47, No. 20, 2008

New Route to o-Carboranes
Figure 3. ORTEP drawing of 1-(3-HC≡C-C6H4)-1,2-C2B10H11 (8). Selected
bond lengths (Å) and angles (deg): C1-C13, 1.504(3); C13-C14, 1.392(4);
C14-C15, 1.393(3); C15-C16, 1.404(3); C16-C17, 1.381(4); C17-C18,
1.388(4); C18-C13, 1.394(3); C15-C19, 1.437(4); C19-C20, 1.194(4);
C1-C2, 1.648(3); C1-B3, 1.743(3); C1-B4, 1.720(4); C1-B5, 1.716(4);
C1-B6, 1.734(4); C2-B3, 1.722(4); B3-B4, 1.790(4); B4-B5, 1.780(4);
B5-B6, 1.768(4); B6-C2, 1.722(4); C13-C1-C2, 117.8(2); C13-C1-B3,
115.9(2); C13-C1-B4, 122.0(2); C13-C1-B5, 123.4(2); C13-C1-B6,
117.3(2);C1-C13-C14,120.6(2);C13-C14-C15,120.9(2);C14-C15-C16,
119.3(2); C16-C17-C18, 121.0(2); C18-C13-C14, 119.3(2).
Figure 2. ORTEP drawing of the structure of 1,1′-(CH2)5-(1,2-C2B10H11)2
(4).19
ionic liquids, the highest reactivities were for the chloride
containing Bu4NCl (eq 4) and PPNCl salts. Nevertheless,
the yields with these salts were much lower (∼20-30%)
than those obtained from the analogous bmimCl reactions
with these alkynes (90% 1 and 70% 2).
2:2:4:2 ratios because of the B9,12, B8,10, B4,5,7,11, and
B3,6 boron atoms, but resonances again overlap. The
crystallographically determined structures of 1,1′-(CH2)5-(1,2-
C2B10H11)2 (4), 1-(3-HC≡C-C6H4)-1,2-C2B10H11 (8), and 1,1′-
(1,3-C6H4)-(1,2-C2B10H11)2 (9) are shown in Figures 2-4.
The distances and angles observed in these structures are
all in the expected ranges.
No reaction was observed when decaborane was heated
in an alkyne/toluene solution at 120°C without an ionic
liquid. While many ionic liquids showed reactivity for B10H14
dehydrogenative alkyne-insertion when employed in the
biphasic ionic-liquid/toluene mixtures, reactions employing
bmimCl were remarkably fast. Thus as shown in Table 1
for reactions with phenylacetylene, although the bmimCl
reaction was complete in 7 min, the reactions with bmimBF4,
bmimPF6, thtdpBF4, bmpyBF4, bmimBr, and bmpyPF6
required between 16 and 96 h for completion, with the
basicity of the anionic component of the ionic liquid
appearing to be the key in determining the reactivity (e.g.,
Cl- > Br- > I-). In this regard, it was also found that upon
heating, toluene solutions of several halide salts formed
“ionic liquid”-like biphasic mixtures that promoted B10H14
dehydrogenative-alkyne insertions with both phenylacetylene
and 3-hexyne. Consistent with the trend observed with the
Thus, in terms of both rates and yields, the most effective
agent for inducing B10H14 dehydrogenative-alkyne insertion
was bmimCl. It is also important to note that the best yields
were obtained when only catalytic amounts (∼0.2-0.4 equiv
relative to B10H14) of bmimCl were employed. When bmimCl
was used in larger amounts, the product yields dropped
because of B10H14 degradation reactions.
Syntheses via the Reactions of Alkynes with B10H13
-
.
-
The reactions of several alkynes with the B10H13 anion
were investigated to test the possible role of this anion in
the ionic liquid-mediated reactions. Reactions of phen-
ylacetylene, 1-octyne, 3-diethylamino-1-propyne, 5-cyano-
1-pentyne, and 3-hexyne with the [Et3NH+][B10H13-] salt
(19) Because of the poorer quality of the structure determination of 4, the
distances and angles information are not listed.
Inorganic Chemistry, Vol. 47, No. 20, 2008 9199

Li et al.
Discussion
Ionic liquids (ILs) are generally defined as salts that are
relatively low viscosity liquids at temperatures below
100°C.20 Some of the most common ILs are composed of
inorganic anions, X-, BF4 , PF6 , and nitrogen-containing
organic cations, such as RN,R′N-imidazolium or RN-
pyridinium. ILs have been shown20 to have a number of
unusual properties that make them attractive substitutes for
conventional solvents for organic and inorganic syntheses,
including (1) negligible vapor pressures, (2) thermal stability
to elevated temperatures, (3) the ability to dissolve a wide
range of organic and inorganic compounds, salts, and gases,
(4) immiscibility with many hydrocarbons, water, or both,
thus enabling two-phase reaction systems, (5) weakly-
coordinating anions and cations that provide a polar reaction
medium, and (6) the ability to stabilize polar intermediates
and transition states. Examples of the numerous organic
reactions that have been carried out in ILs include hydro-
genations, hydrodimerizations, hydroformylations, oxida-
tions, Heck reactions, carbonylations, Suzuki-couplings,
Trost-Tsuji couplings, Friedel-Crafts reactions, alkylations,
halogenations, cycloaddtions, reductions, and metathesis
reactions. These prior studies suggested to us that ionic
liquids might have similar advantages for carrying out many
polyborane transformations, including hydroborations, alkyne-
insertions, dehydrogenations, dehydrocondensations, alky-
lations, and transition metal catalyzed reactions.21
The results reported herein have clearly demonstrated that
decaborane dehydrogenative alkyne-insertion reactions pro-
ceed in biphasic bmimCl/toluene mixtures to give good to
excellent yields of o-carborane products without the need
of the Lewis base catalysts required in the conventional
syntheses. Likewise, both terminal and internal alkynes
showed comparable reactivities. Thus, as illustrated in the
two examples given in Figure 5, the reactions of decaborane
in bmimCl/toluene with 3-hexyne and 1-octyne gave their
1,2-Et2-1,2-C2B10H10 (11) (70%, 10 min) and 1-C6H13-1,2-
C2B10H11 (2) (91%, 7 min) products in good yields and
comparable reaction rates. In contrast, Heying3a reported that
3-hexyne does not react at all using the conventional process
in eqs 1 and 2.
-
-
Figure 4. ORTEP drawing of 1,1′-(1,3-C6H4)-(1,2-C2B10H11)2 (9). Selected
bond length (Å) and bond angles (deg): C1-C13, 1.511(3); C13-C14,
1.397(3); C14-C15, 1.382(3); C13-C16, 1.392; C1-C2, 1.692(3); C1-B3,
1.740(3); C1-B4, 1.685(3); C1-B5, 1.725(3); C1-B6, 1.723(3); C2-B3,
1.749(3); B3-B4, 1.755(3); B4-B5, 1.746(3); B5-B6, 1.744(3); B6-C2,
1.746(3); C13-C1-C2, 120.8(2); C13-C1-B3, 117.6(2); C13-C1-B4,
119.8(2); C13-C1-B5, 118.7(2); C13-C1-B6, 120.5(2); C1-C13-C14,
120.3(2);C1-C13-C16,120.5(2);C13-C14-C15,119.7(2);C14-C13-C16,
119.2(2).
in toluene solution gave the o-carborane derivatives 1, 2,
6, 7, and 11 in comparable rates, but in most cases, with
somewhat lower yields than the analogous B10H14-bmimCl/
toluene reactions. Reactions of phenylacetylene and
3-hexyne with the B10H13- anion generated in situ via the
reaction of B10H14 with catalytic amounts of either Et3N
or Proton Sponge likewise produced 1 and 11 (eq 5), but
the yields were much lower (∼20-30%) than either the
[Et3NH+][B10H13-] or B10H14-bmimCl/toluene reactions.
As shown in Table 3, a variety of functionalized alkynes were
found to react to produce the corresponding C-functionalized
(20) For general reviews, see: (a) Ionic Liquids in Synthesis; 2nd ed.;
Wasserscheid, P., Welton, T., Eds.; Wiley-VCH: Weinheim, Germany,
2007. (b) Dyson, P. J. Appl. Organomet. Chem. 2002, 16, 495–500.
(c) Zhao, H.; Malhotra, S. V. Aldrich Chim. Acta 2002, 35, 75–83.
(d) Sheldon, R. Chem. Commun. 2001, 2399–2407. (e) Wasserscheid,
P.; Keim, W. Angew. Chem., Int. Ed. 2002, 39, 3772–3789. (f) Dupont,
J.; de Souza, R. F.; Suarez, P. A. Z. Chem. ReV. 2002, 102, 3667–
3692.
Unlike with [Et3NH+][B10H13-] and [PSH+][B10H13
]
,
-
when [Bu4N+][B10H13-] was reacted with phenylacetylene
in toluene solution, no o-carborane products were produced.
Instead, 11B NMR analysis of the solution after only 30 min
at 110 °C showed cage degradation to the B9H14- anion and
other minor products (eq 6).
(21) Kusari, U.; Li, Y.; Bradley, M. G.; Sneddon, L. G. J. Am. Chem. Soc.
2004, 126, 8662–8663.
9200 Inorganic Chemistry, Vol. 47, No. 20, 2008

New Route to o-Carboranes
Figure 7. Reactions of enynes give only dehydrogenative alkyne-insertion
rather than olefin-hydroboration products
product 8 and the di-insertion products 4 and 9 are shown
in Figures 3, 2, and 4. Endo’s previous synthesis11 of 9 via
the reaction of B10H14 with m-diethynylbenzene and aceto-
nitrile in benzene solution required 2 days of reflux to achieve
a 44% yield, whereas the bmimCl/toluene reaction gave a
35% yield after only 10 min.
Figure 5. Reactions of B10H14 with 3-hexyne and 1-octyne in bmimCl/
toluene show comparable reaction times/yields.
The following paper22 reports that ionic liquids also
promote decaborane olefin-hydroboration reactions, but with
rates that are much slower than those found for the ionic-
liquid-promoted dehydrogenative alkyne insertion reactions.
Consistent with this lower olefin reactivity, it was found
(Figure 7) that the reaction of decaborane with 2-methyl-1-
hexen-3-yne gave exclusively the dehydrogenative alkyne-
insertion product 1-H2CdC(CH3)-2-Et-1,2-C2B10H10 14 rather
than the 6-EtCtC(Me)CHCH2-B10H13 olefin-hydroboration
product. Thus, reactions with enynes can provide convenient
routes to olefin-substituted o-carboranes.
Decaborane has been shown to be a monoprotic Bronsted
acid in polar solvents, such as water (pKa ) 2.7), dioxane,
and acetonitrile.23 The experimental observations for both
the ionic liquid-mediated dehydrogenative alkyne-insertion
reactions and decaborane-olefin hydroborations22 indicate
that the ionic liquid promoted ionization of decaborane to
form the B10H13- anion is the essential first step in both the
alkyne and olefin reactions. Supporting the above hypothesis,
it was found that the reactions of B10H13- salts with alkynes,
either starting with the isolated [Et3NH+][B10H13-] salt or
with B10H13- generated in situ from the reactions of B10H14
with either Et3N or Proton Sponge, resulted in dehydroge-
native alkyne insertion to produce the o-carborane pro-
ducts. Both the yields and rates of the reaction with
[Et3NH+][B10H13-] salts were comparable to those of the
bmimCl/toluene reactions. Likewise, when the reaction of
B10H14 with alkynes in bmimCl was carried out under
conditions where B10H14 ionization was suppressed by the
addition of added HCl acid, no reaction was observed.
Figure 6. Depending upon the reaction stoichiometry, reactions with diynes
give either mono- or di-insertion products.
o-carboranes with faster rates and with either comparable or
significantly higher yields than those obtained with the con-
ventional Lewis base methods. It should also be noted that while
compounds 4, 5, 11, and 12 were previously known, they have
apparently not been prepared directly from alkyne/B10H14
reactions but were instead prepared via the reaction of [Li+][1,2-
C2B10H11-] or [Li+]2[1,2-C2B10H102-] o-carborane anions with
the corresponding RX reagents (4, Br(CH2)5Br;8 5,
BrCH2CO2Et;9 11, EtBr12) and formaldehyde13a,b or ethylene
oxide13c (12). Thus, the ionic liquid reactions are the first report
of their direct preparation from decaborane.
As illustrated for the reactions with m-diethynylbenzene
and 1,8-nonadiyne given in Figure 6, depending on the
reaction stoichiometries, decaborane reactions with diynes
yield either mono or dicarborane products. The crystallo-
graphically established structures of the monoinsertion
(22) Kusari, U.; Carroll, P. J.; Sneddon, L. G. Inorg. Chem. 2008, 47, 9203–
9215.
(23) (a) Guter, G. A.; Schaeffer, G. W. J. Am. Chem. Soc. 1956, 78, 3546.
(b) Hawthorne, M. F.; Pitochelli, A. R.; Strahm, R. D.; Miller, J. J.
J. Am. Chem. Soc. 1960, 82, 1825–1829. (c) Hermanek, S.; Plotova,
H. Coll. Czech. Chem. Comm. 1971, 36, 1639–1643.
Inorganic Chemistry, Vol. 47, No. 20, 2008 9201

Li et al.
Su14 had previously shown that K+B10H13 will add to
-
the polar-alkyne, cyanoacetylene, in THF solution to form
the arachno-dicarbaborane anion, arachno-8-(NC)-7,8-
-
C2B10H14 (eq 7). We likewise confirmed (eq 8) that the
reaction of B10H14 with cyanoacetylene in bmimCl/toluene
gave the same arachno-8-(NC)-7,8-C2B10H14- product, again
-
supporting the initial bmimCl-mediated formation of B10H13
in the ionic liquid reactions.
Figure 8. Proposed overall reaction scheme for ionic liquid promoted
dehydrogenative alkyne-insertion
organic solvents.26 Thus, HCl dissolved in the ionic-liquid/
toluene could then serve as the proton source for the final
step in the bmimCl/toluene mixture reactions. As indicated
in Figure 8, this reaction would then regenerate bmimCl,
which could go back into the cycle to promote the ionization
of additional B10H14. The strong activating effect of Cl-
compared to the other ionic liquid anions in Table 1 is
consistent with its stronger base strength relative to the other
anions and, accordingly, to its ability to promote decaborane
ionization.
-
However, the nature of the reaction of B10H13 with the
strongly polarized cyanoacetylene would be expected to be
quite different than its reaction with the nonpolar alkynes
reported herein. Thus, in contrast to cyanoacetylene, the
alkynes employed herein would be expected to be susceptible
to electrophilic, not nucleophilic attacks. The third paper24
in this series utilizes computational methods to explore both
-
the nucleophilic and electrophilic reactions of the B10H13
It is clear from the results reported herein that decaborane
dehydrogenative alkyne-insertions are activated in ionic
liquids and that these reactions now provide an important
new synthetic route to a wide variety of o-carborane
derivatives. The following two papers demonstrate that ionic
liquids also activate decaborane olefin-hydroborations and,
in addition, present the results of further experimental and
computational studies that provide more detailed insights into
the mechanistic steps involved in both the decaborane
dehydrogenative alkyne-insertion and olefin-hydroboration
reactions.
anion, and there it is demonstrated that it is energetically
feasible for B10H13 to rearrange to an electrophilic-type
-
structure having a LUMO orbital highly localized at the B6
boron (Figure 8). Alkyne binding at this site serves as a
prelude to the dehydrogenative alkyne-insertion reaction with
the proposed structure of the key alkyne-B10H13 adduct being
quite similar to that previously established5,25 for L-B10H13
-
Lewis acid/base adducts (L ) R3N, R3P, RCN).
The final step in the scheme in Figure 8 requires a proton
-
source to react with the intermediate arachno-R,R′-C2B10H13
anion to form the final neutral o-carborane products with
loss of H2. For reactions with [Et3NH+][B10H13-] and
[PSH+][B10H13-], this can be accomplished, as shown in eq
9,byprotontransferfromthecationsofthe[Et3NH+][arachno-
Acknowledgment. We thank the National Science Foun-
dation for the support of this project.
-
-
R,R′-C2B10H13
]
and [PSH+][arachno-R,R′-C2B10H13
]
Supporting Information Available: Tables of infrared data for
all compounds, NMR characterization data for the previously
reported compounds 1, 4, 7, 9, and 11, and X-ray crystallographic
data structure determinations of compounds 4, 8, and 9 in CIF
format. This material is available free of charge via the Internet at
http://pubs.acs.org.
intermediates with liberation of the free amines and
two equivalents of hydrogen. The requirement of a proton
source in the final step explains why reactions with
[Bu4N+][B10H13-] could not produce o-carboranes.
[Et2NH+][arachno-R,R′C2B10H13-] f
1,2-R,R′-1,2-C2B10H10 + Et3N + 2H2 (9)
IC800999Y
(24) Yoon, C. W.; Kusari, U.; Sneddon, L. G. Inorg. Chem. 2008, 47, 9216–
9227.
(25) Hofmann, M.; Schleyer, P. v. R. Inorg. Chem 1998, 37, 5557–5565.
(26) Bos, M.; Dahmen, A. M. F. Anal. Chim. Acta 1973, 63, 185–196.
The dissociation of B10H14 in bmimCl would lead to the
formation of B10H13 and HCl. While HCl is of course a
strong acid in water, it is only partially disassociated in many
-
9202 Inorganic Chemistry, Vol. 47, No. 20, 2008