Synthesis of new arylcarboranes as precursors for oligomers

Article abstract of DOI:10.1016/S0022-328X(99)00277-6

Some new aryl o-carboranes have been synthesized. From methyl 3-iodo-5-(trimethylsilyl-ethynyl)-benzoate (1) or butyl 3-(3,3-diethyltriazeno)-5-ethynyl-benzoate (2), 5-ethynyl-3-iodo-benzoates (3a, 3b) were obtained, which after the reaction with the deca

Full text of DOI:10.1016/S0022-328X(99)00277-6

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 587 (1999) 67–73
Synthesis of new arylcarboranes as precursors for oligomers
Beate Fo¨rster, Josep Bertran, Francesc Teixidor *, Clara Vin˜as
Institut de Cie`ncia de Materials de Barcelona, CSIC, Campus UAB, E-08193 Bellaterra, Spain
Received 19 February 1999
Abstract
Some new aryl o-carboranes have been synthesized. From methyl 3-iodo-5-(trimethylsilyl-ethynyl)-benzoate (1) or butyl
3-(3,3-diethyltriazeno)-5-ethynyl-benzoate (2), 5-ethynyl-3-iodo-benzoates (3a, 3b) were obtained, which after the reaction with the
decaborane–acetonitrile complex led to the corresponding 5-(1%-(1%,2%-dicarba-closo-dodecaboranyl))-3-iodo-benzoates (4a, 4b).
Furthermore, the methyl 3-iodo-5-(trimethylsilyl-ethynyl)-benzoate (1) is the starting material for the synthesis of a bis-carborane.
Compound 1 is modified to the methyl 3,5-bis(trimethylsilyl-ethynyl)-benzoate (5), which is deprotected to give the methyl
3,5-bis(ethynyl)-benzoate (6). Compound 6 reacted with the decaborane–acetonitrile complex to the methyl 3,5-bis(1%-(1%,2%-di-
carba-closo-dodecaboranyl))-benzoate (7), which was partially degraded to the bis(tetramethylammonium)-3,5-bis(7%-(7%,8%-di-
carba-nido-undecaboranyl))methoxycarbonylphenyl (8). © 1999 Elsevier Science S.A. All rights reserved.
Keywords: o-Carboranes; Arylcarboranes; Oligomers
ethynylbenzene oligomers are produced leaving the
cluster formation as the very last step, and a second
1. Introduction
alternative that consists of introducing the cluster in the
The icosahedral carboranes C2B10H12 may be re-
early stages, followed by their oligomerization. A dis-
garded as excellent molecular building blocks with re-
cussion suggesting the first as the better choice is
markable chemical stability and high boron content [1].
included.
When they are substituted by suitable functionalized
groups, they can be used in many applications. They
serve as precursors for boron–carbide type ceramics [2],
in the cancer treatment by boron neutron capture ther-
2. Results and discussions
apy (BNCT) [3], as polymers for high-temperature ap-
The methyl-3-(3,3-diethyltriazeno)-5-(trimethylsilyl-
plications [4], in neutron shielding purposes [5], in
ethynyl)-benzoate is a monomer that contains a diethyl-
connection with their non-linear optical (NLO) proper-
triazene group and a terminal ethynyl moiety protected
ties [6], as ligands in metallaborane catalysts [4,7], as
by a trimethylsilyl group. It also contains an ester
metal complexing agents for solvent extraction [8] and
group, which is a very versatile function. This is a good
as carriers for radioactive metals in radioimmunodetec-
tion and radioimmunotherapy [9].
starting material to synthesize oligomers that have peri-
odic segments, the chain growth being able to take
With the aim of finding a convenient and control-
place at both ends. This idea has been used in the
lable pathway to carboranylbenzene oligomers, we have
synthesis of alkane oligomers [10] and polyurethane
begun an exploratory research leading to these com-
segments [11].
pounds. These results are presented in this paper. Basi-
cally two pathways are considered, one in which
Starting
with
methyl-3-(3,3-diethyltriazeno)-5-
(trimethylsilyl-ethynyl)-benzoate, the formerly describ-
ed methyl 3-iodo-5-(trimethylsilyl-ethynyl)-benzoate (1)
[12] and butyl 3-(3,3-diethyltriazeno)-5-ethynyl-ben-
zoate (2) have been prepared. These compounds are
good precursors for oligomers and macrocycles [12,13].
* Corresponding author. Tel.: +34-3-5801853; fax: +34-3-
5805729.
E-mail address: teixidor@icmab.es (F. Teixidor)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00277-6

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B. Fo¨rster et al. / Journal of Organometallic Chemistry 587 (1999) 67–73
Scheme 1. General procedure for the synthesis of the new aryl-o-carboranes.
The reagents for these syntheses are based on terminal
acetylenes protected as the corresponding trimethylsilyl
derivative and aryl iodide precursors based on a di-
alkyltriazene, respectively. They allow for the stepwise
synthesis of well-defined sequences of phenylacetylene
units with the possibility to control the chain length
and the functional group placement.
2.1. Triazene group deprotection (A)
Removal of the triazene groups to introduce the
iodide is carried out with an excess of methyl iodide in
an autoclave at 110°C for 17 h [12,14] (see Scheme 2).
We have used the same strategy, shown in Scheme 1,
in the synthesis of new aryl-o-carboranes. Four reac-
tions, A, B, C and D, have been carried on to synthe-
size the compounds. Reactions
A
and
B
are
deprotecting ones, C is a coupling reaction, and D
corresponds to the o-carborane derivatives formation.
Scheme 2. Triazene group removal and iodide insertion (A).

B. Fo¨rster et al. / Journal of Organometallic Chemistry 587 (1999) 67–73
69
Scheme 3. Trimethylsilylacetylene group deprotection (B).
2.2. Trimethylsilylacetylene group deprotection (B)
Scheme 5. Reaction of acetylenic group aryl compounds (3a, 3b) with
decaborane B10H14
.
The deprotection at the acetylenic group is carried
out in good yield by a catalytic amount of a weak base
like potassium carbonate in the presence of methanol
using dichloromethane as a co-solvent to improve the
solubility of the ester [12,15] (see Scheme 3).
The iodide group in the starting material 1 also offers
the possibility to synthesize a selected diacetylene com-
pound 5.
can be found. It was concluded that the trimethylsilyl
group disturbed the cluster formation [19].
The reaction of 2 with the decaborane–acetonitrile
complex also yields a complicated mixture of several
products, which could not be isolated. In this case, it
seems that the triazene group behaves as a degrading
agent.
On the contrary the less sterically encumbered
acetylene compounds 3a and 3b react with a decabo-
rane–acetonitrile complex produced as earlier described
[18], in toluene to the corresponding 4a and 4b carbo-
rane derivatives (Scheme 5). It has been found that for
RꢀBu, the reaction requires more time than for RꢀMe,
but the reaction yield of the carborane 4b is better too.
The two acetylenic groups of compound 6 then react
with a decaborane–acetonitrile complex [18] to the
methyl 3,5-bis(1%-(1%,2%-dicarba-closo-dodecaboranyl))-
benzoate (7) (Scheme 6). The yield of the end product,
however, is very low. One reason for this may be the
competing partial degradation of 7 to yield 8. Com-
pound 8 has been separated by changing the polarity of
2.3. Coupling of acetylenic groups in the aromatic ring
(C)
For this purpose, 1 is converted to the corresponding
bis-trimethylsilylacetylene compound 5. The reaction is
conducted in a similar way as to produce the precursor
of 1 [12,16], which is reacted with trimethylsily-
lacetylene in the presence of bis(dibenzylideneace-
tone)palladium(0), Pd(dba)2 [17], cuprous iodide and
triphenylphosphine in catalytic amounts. Scheme 4
shows the pathway to yield bis-trimethylsilylacetylene
compounds. Triethylamine is used as a solvent. Due to
the higher reactivity of the aryliodides, as compared
with the arylbromides, the reaction proceeds in a rela-
tively short time. Compound 5 is easily deprotected
using potassium carbonate as a weak base in a catalytic
amount to yield the methyl 3,5-bis(ethynyl)benzoate
(6). The methyl 3,5-bis(trimethylsilyl-ethynyl)benzoate
the eluent from pure dichloromethane to
a
dichloromethane–methanol (1:1) mixture during the
chromatographic purification of the reaction mixture. It
was isolated with tetramethylammonium chloride as its
bis-tetramethylammonium salt (8). The acetonitrile,
which is used as a Lewis base in the complex with
decaborane, may be the reason for the degradation.
This nido species 8 incorporates two anionic carbo-
rane cluster units with a pentagonal opened face linked
by an aromatic ring with an ester group. The total
charge of −2 may be delocalized in this pseudoaro-
matic system.
(5) shows
a good solubility in methanol and,
dichloromethane used as a co-solvent is not necessary.
2.4. Reaction of the acetylenic group of aryl
compounds with decaborane (D)
It is reported [18] that decaborane reacts with
acetylenic compounds in the presence of Lewis bases to
produce 1-R-2-R%-1,2-C2B10H10 derivatives with the ac-
companying elimination of a molecule of hydrogen.
However, in the reaction of the protected acetylene (1)
and the decaborane–acetonitrile complex, no carborane
2.5. Characterisation of the compounds
2.5.1. Acetylene deri6ati6es
The NMR spectra of the bis(ethynyl)benzoates 5 and
6 reflect the high symmetry of the molecules. Com-
pound 5 displays two singlet signals in a ratio of 2:1 for
the three aryl protons: at 8.01 ppm for the two protons
in o-position to the carboxyl group and at 7.7 ppm for
the one in p-position; a single signal whose relative area
is 18 appears at 0.22 ppm, corresponding to the protons
of the trimethylsilyl groups. Compound 6 also displays
Scheme 4. Coupling of acetylenic groups in the aromatic ring (C).

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B. Fo¨rster et al. / Journal of Organometallic Chemistry 587 (1999) 67–73
Scheme 6. Reaction of acetylenic group aryl compound 6 with decaborane B10H14
.
two singlet signals in a ratio of 2:1 at 8.07 ppm and at
7.72 ppm, corresponding to the protons in o-position
and p-position to the carboxyl group, respectively, and
at 3.12 ppm, a singlet for the protons of the trimethylsi-
lyl group. In the 13C{1H}-NMR spectra only four
signals can be found at low field corresponding to the
aromatic carbons (from 139 to 123 ppm).
cluster carbon atoms in the 13C{1H} spectrum are
missing [21].
3. Conclusions
The procedure reported in this paper for the synthe-
sis of adequately substituted ethynylbenzene derivatives
seemed to be convenient to produce poly-o-carboranyl
oligomers. The process is based on a series of controlled
protection/deprotection steps aiming at producing the
desired polyethynyl precursors. The carboxyl group
bisecting the 3,5-positions of the aryl ring is adequately
placed as a blocking agent and as a solubilizing group.
Compound 6, incorporating two ethynyl groups, is a
representative example of the lower member of a series
of polyethynylbenzene compounds. At this point two
strategies could be followed: starting from the ethynyl
compounds as a means to enlarge the number of
ethynyl benzene units to finally incorporate the carbo-
rane cluster, or taking in consideration the somehow
similar reactivity of ethyne and o-carborane to perform
the protective/deprotective process on the cluster con-
taining molecule, e.g. 4b. To choose which of the two
strategies was more suitable we succeeded in preparing
the dicluster compound 7. The yield, however, did not
allow further studies on it. Yields of 4a or 4b were
neither high enough. Thus it seems that if this proce-
dure is applicable to produce polycarboranylbenzene
oligomers it is more convenient first to produce the
alkynylbenzene oligomers followed by cluster formation
than the opposite.
2.5.2. Carborane deri6ati6es
These compounds have been characterized by ele-
mental analyses, IR, NMR and mass spectroscopies.
The IR spectra show, for compounds 4a and 4b, the
typical w(B–H) absorption at frequencies near 2580
cm−1, characteristic of closo 1-R-1,2-C2B10H11 deriva-
tives. The monosubstitution at CH is supported by the
presence of a w(C–H) carborane band at 3044 cm−1
.
The 11B-NMR spectra of compounds 4a and 4b present
an spectral data pattern (1:1:2:4:2) for both compounds
in the typical range (−1 and −13 ppm) for closo
C2B10H12 derivatives. The 1H-NMR spectra of the
mono o-carboranes 4a and 4b display, in addition to
the aromatic proton signals at 8.3–7.9 ppm, a broad
signal for the proton, connected with the carbon of the
carborane at 4.0 ppm. In both compounds, the
13C{1H}-NMR spectra display two resonances at-
tributed to the cluster’s carbon atoms, one at 59.7 ppm
and the second at 74.0 ppm.
Due to the low reaction yield, purification and char-
acterization of the bis-carborane cluster derivates 7 and
8 has been difficult. The infrared spectrum of the closo
carborane 7 exhibited a B–H stretching absorption at
2599 cm−1, whereas the corresponding absorption of
the nido compound 8 appears at 2532 cm−1. The
1H-NMR spectrum of 7 displays a broad signal at 5.5
ppm for the proton, connected to the carbon of the
cluster, and the 13C{1H} spectrum shows the two car-
bon atoms of the carborane substituent at 76.3 and 62.1
ppm. The 11B-NMR patterns of both compounds 7 and
8 are consistent with the high symmetry of the
molecule.
4. Experimental
4.1. General
Microanalyses were performed using a Perkin–Elmer
240-B microanalyzer. IR spectra were obtained as KBr
pellets on a Nicolet 710-FT spectrophotometer. The
1H-, 13C{1H}- and 11B-NMR spectra were recorded
with a Bruker ARX 300 WB, operating at 300.13 MHz
for 1H, 75.47 MHz for 13C and 96.29 MHz for 11B
The 1H-NMR spectrum of 8 displays the B–H–B
resonance at −2.4 ppm, which unambiguously proves
the nido character of the cluster [20]. This is supported
by the 11B-NMR spectrum, which shows nine equally
weighted resonances in the range −8.4 to −35.4 ppm,
typical for a nido-C2B9H1−2 derivative carborane. Con-
trarily to the closo equivalent (7), the signals of the two
1
spectra. Chemical shift values for H and 13C spectra
were referenced relative to tetramethylsilane, and to
BF3·OEt2 for 11B spectra. Mass spectra were recorded
on a Hewlett–Packard 5989 X.

B. Fo¨rster et al. / Journal of Organometallic Chemistry 587 (1999) 67–73
71
All organic and inorganic salts were analytical
reagent grade and used as received. Absolute MeOH
(ppm): 8.3 (m, 1H, Caryl–H), 8.1 (m, 1H, Caryl–H), 8.0
(m, 1H, Caryl–H), 4.3 (t, 3J(H,H)=6.6 Hz, 2H,
CO2CH2–), 3.2 (s, 1H, Cethynyl–H), 1.7 (m, 2H,
CO2CH2CH2–), 1.4 (m, 2H, CO2(CH2)2CH2–), 1.0 (t,
3J(H,H)=7.3 Hz, 3H, CO2(CH2)3CH3). 13C{1H}-NMR
(CDCl3), l (ppm): 164.4 (CO2), 144.4, 138.6, 132.3,
129.0, 124.3 (Caryl), 93.1 (Caryl–I), 81.0, 79.4 (Cethynyl),
65.5 (CO2CH2–), 30.7 (CO2CH2CH2–), 19.2
(CO2(CH2)2CH2–), 13.7 (CO2(CH2)3CH3).
,
was kept over 3 A molecular sieves. Methyl iodide and
trimethylsilylacetylene were obtained from Aldrich and
,
also dried over 3 A molecular sieves. The methyl 3-
iodo-5-(trimethylsilyl-ethynyl)-benzoate (1), the butyl 3-
(3,3-diethyltriazeno)-5-ethynyl-benzoate (2) [12] and
Pd(dba)2 [17] were prepared according to the literature.
Triethylamine was freshly distilled over calcium hy-
dride. Potassium carbonate, triphenylphosphine, copper
iodide, magnesium sulfate and tetramethylammonium
chloride were obtained from Fluka. The decaborane
B10H14 was obtained from Dexsil Corporation and
purified by sublimation at 0.01 mmHg before use.
All reactions were carried out under a dinitrogen
atmosphere.
4.4. Synthesis of methyl 5-(1%-(1%,2%-dicarba-closo-dode-
caboranyl))-3-iodo-benzoate (4a)
A total of 0.105 g (0.86 mmol) of decaborane was
dissolved in 10 ml of acetonitrile and refluxed for 2 h
under nitrogen. After cooling, 0.1 g (0.35 mmol) of 3a,
dissolved in 5 ml of toluene, was added and the reac-
tion mixture was heated under reflux for 12 h more.
The solvents were removed in vacuo, and the residue
was treated with 5 ml of methanol for 30 min under
stirring. Upon the evaporation of the solvent, the
product was purified by chromatography on a silica gel
column with dichloromethane:n-hexane (3:1) as eluent
(Rf=0.67). The solvent mixture was evaporated to
dryness to afford 0.04 g of 4a (29%). Anal. Calc. for
C10H17B10IO2 (%): C, 29.71; H, 4.24. Found: C, 29.93;
H, 4.14. EI-MS (m/z): 404.0 (100%, M+). IR, w
(cm−1): 3044 (Ccluster–H), 2959, 2931 (Calkyl–H), 2615,
2573 (B–H), 1722 (CꢀO), 1567 (C–C)aryl, 1300, 1237
4.2. Synthesis of methyl 5-ethynyl-3-iodo-benzoate (3a)
Potassium carbonate (0.02 g, 0.13 mmol) was added
to a solution of 0.461 g (1.29 mmol) of methyl 3-iodo-5-
(trimethylsilyl-ethynyl)-benzoate (1) in 2.5 ml
dichloromethane and 10 ml methanol. The reaction
mixture was stirred at room temperature for 18 h. After
the evaporation of the solvents, the residue was chro-
matographed on
a
silica gel column with
dichloromethane as eluent (Rf=0.67). Evaporation to
dryness gave 0.341 g of (3a) (93%). Anal. Calc. for
C10H7IO2 (%): C, 41.99; H, 2.47. Found: C, 42.06; H,
2.27. EI-MS (m/z): 285.9 (100%, M+). IR, w (cm−1):
3275, 3240 (Cethynyl–H), 3064, 3008 (Caryl–H), 2952
(Calkyl–H), 1714 (CꢀO), 1560 (C–C)aryl, 1285 (C–O).
1H-NMR (CDCl3), l (ppm): 8.3 (m, 1H, Caryl–H), 8.0
(m, 1H, Caryl–H), 7.9 (m, 1H, Caryl–H), 3.9 (s, 3H,
CO2CH3), 3.2 (s, 1H, Cethynyl–H). 13C{1H}-NMR
(CDCl3), l (ppm): 164.6 (CO2), 144.4, 138.5, 132.3,
131.7, 124.2 (Caryl), 93.1 (Caryl–I), 80.8, 79.6 (Cethynyl),
52.5 (CO2CH3).
1
4
(C–O). H-NMR (CDCl3), l (ppm): 8.4 (t, J(H,H)=
1.5 Hz, 1H, Caryl–H), 8.0 (m, 1H, Caryl–H), 7.9 (m, 1H,
Caryl–H), 4.0 (s, broad, 1H, Ccluster–H), 3.9 (s, 3H,
CO2CH3), 3.2–0.8 (broad, 10H, B–H). 13C{1H}-NMR
(CDCl3), l (ppm): 164.4 (CO2), 140.4, 139.8, 135.8,
132.3, 127.5 (Caryl), 94.1 (Caryl–I), 73.9, 59.7 (Ccluster),
52.8 (CO2CH3). 11B-NMR (CDCl3), l (ppm): −1.5 (d,
1J(B,H)=151 Hz, 1B), −3.5 (d, 1J(B,H)=175 Hz,
1
1B), −8.3 (d, J(B,H)=154 Hz, 2B, B(8,10)), −10.7
(d, 1J(B,H)=175 Hz, 4B, B(4,5,7,11)), −12.3 (d,
1J(B,H)=153 Hz, 2B, B(3,6)).
4.3. Synthesis of butyl 5-ethynyl-3-iodo-benzoate (3b)
In an autoclave (125 ml of volume) was placed 1.39 g
(4.6 mmol) of butyl 3-(3,3-diethyltriazeno)-5-ethynyl-
benzoate (2). After evacuation, 30 ml of methyl iodide
was filled in, and the autoclave was saturated with
nitrogen. The stirring solution was heated at 110°C,
kept at this temperature for 17 h and cooled down. The
methyl iodide was evaporated and the residue was
4.5. Synthesis of butyl 5-(1%-(1%,2%-dicarba-closo-dode-
caboranyl))-3-iodo-benzoate (4b)
A total of 0.155 g (1.24 mmol) of decaborane are
dissolved in 10 ml of acetonitrile and refluxed for 2 h.
After cooling, 0.37 g (1.13 mmol) of 3b, dissolved in 5
ml toluene, was added and the reaction mixture was
heated under reflux for 72 h. The solvents were re-
moved in vacuo and the residue was treated with 5 ml
of methanol for 30 min under stirring. The mixture was
then extracted with n-hexane and the combined n-hex-
ane phases were concentrated. For purification, it was
chromatographed on a preparative silica thin layer with
dichloromethane–n-hexane (1:1) as eluent (Rf=0.81).
The evaporation of the solvent gave 0.177 g of product
chromatographed on
a
silica gel column with
dichloromethane as eluent (Rf=0.73). After the evapo-
ration of the solvent, 1.32 g of 3b could be obtained
(88%). Anal. Calc. for C13H13IO2 (%): C, 47.57; H,
3.99. Found: C, 46.37; H, 3.99. EI-MS (m/z): 327.9
(18%, M+). IR, w (cm−1): 3254 (Cethynyl–H), 3071
(Caryl–H), 2959, 2931, 2868 (Calkyl–H), 1721 (CꢀO),
1560 (C–C)aryl, 1278 (C–O). 1H-NMR (CDCl3), l

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B. Fo¨rster et al. / Journal of Organometallic Chemistry 587 (1999) 67–73
4b (35%). Anal. Calc. for C13H23B10IO2 (%): C, 34.98;
H, 5.19. Found: C, 35.94; H, 5.09. EI-MS (m/z): 446.25
(4%, M+). IR, w (cm−1): 3044 (Ccluster–H), 2959, 2931,
2875 (Calkyl–H), 2580 (B–H), 1722, 1708 (CꢀO), 1567
(C–C)aryl, 1293, 1237 (C–O). 1H-NMR (CDCl3), l
in 10 ml of dichloromethane and filtered through silica
gel. The removing of the solvent afforded 0.038 g of 6
(79%). Anal. Calc. for C12H8O2 (%): C, 29.71; H, 4.24.
Found: C, 29.93; H, 4.14. EI-MS (m/z): 184.00 (70%,
M+). IR, w (cm−1): 3282 (Cethynyl–H), 2958 (Calkyl–H),
1728 (CꢀO), 1602, 1568 (C–C)aryl, 1233 (C–O). 1H-
4
(ppm): 8.3 (t, J(H,H)=1.5 Hz, 1H, Caryl–H), 8.0 (m,
4
4
1H, Caryl–H), 7.9 (t, J(H,H)=1.9 Hz, 1H, Caryl–H),
NMR (CDCl3), l (ppm): 8.1 (d, J(H,H)=1.5 Hz, 2H,
3
4
4.3 (t, J(H,H)=6.8 Hz, 2H, CO2CH2–), 4.0 (s, broad,
Caryl–H), 7.7 (t, J(H,H)=1.5 Hz, 1H, Caryl–H), 3.9 (s,
1H, Ccluster–H), 1.7 (m, 2H, CO2CH2CH2–), 1.4 (m,
2H, CO2(CH2)2CH2–), 1.0 (t, 3J(H,H)=7.3 Hz, 3H,
CO2(CH2)3CH3), 3.3–0.8 (broad, 10H, B–H). 13C{1H}-
NMR (CDCl3), l (ppm): 163.9 (CO2), 140.2, 139.7,
135.6, 132.6, 127.5 (Caryl), 94.1 (Caryl–I), 74.0 (Ccluster),
65.8 (CO2CH2–), 59.7 (Ccluster), 30.6 (CO2CH2CH2–),
19.1 (CO2(CH2)2CH2–), 13.7 (CO2(CH2)3CH3). 11B-
3H, CO2CH3), 3.1 (s, 2H, Cethynyl–H). 13C{1H}-NMR
(CDCl3), l (ppm): 165.4 (CO2), 139.2, 133.2, 130.8,
122.9 (Caryl), 81.5, 78.9 (Cethynyl), 52.4 (CO2CH3).
4.8. Synthesis of the methyl 3,5-bis(1%-(1%,2%-dicarba-
closo-dodecaboranyl))benzoate (7) and the bis(tetra-
methylammonium) salt of 3,5-bis(7%-(7%,8%-dicarba-
nido-undecaboranyl))methoxycarbonylphenyl (8)
1
NMR (CDCl3), l (ppm): −1.5 (d, J(B,H)=151 Hz,
1B), −3.5 (d, 1J(B,H)=172 Hz, 1B), −8.3 (d,
1
1J(B,H)=162 Hz, 2B, B(8,10)), −10.7 (d, J(B,H)=
A solution of 0.045 g (0.369 mmol) of decaborane in
5 ml of acetonitrile was refluxed for 2 h. After cooling,
the solvent was evaporated and the residue dissolved in
10 ml of toluene. To the stirring solution was added
0.033 g (0.18 mmol) of 6 and the solution was heated at
110°C for 15 h. The cooled reaction mixture was evap-
orated to dryness and the residue dissolved in 5 ml of
methanol. After stirring for 30 min, the solvent was
removed under vacuo and the crude products were
chromatographed on a silica gel column. The starting
eluent was CH2Cl2–n-hexane 1:1, then CH2Cl2, with
which 0.015 g of product 7 (20%) could be obtained
(Rf(CH Cl )=0.48). Increasing the polarity of the eluent
1
186 Hz, 4B, B(4,5,7,11)), −12.1 (d, J(B,H)=142 Hz,
2B, B(3,6)).
4.6. Synthesis of methyl
3,5-bis(trimethylsilyl-ethynyl)benzoate (5)
In a Schlenk was placed 0.002 g (0.004 mmol) of
Pd(dba)2, 0.006 g (0.024 mmol) of triphenylphosphine,
0.001 g (0.004 mmol) of cuprous iodide and 0.140 g
(0.39 mmol) of 1. The Schlenk was evacuated and filled
with nitrogen. 0.077 g (0.78 mmol) of trimethylsily-
lacetylene, dissolved in 5 ml of freshly distilled dry
triethylamine, was added. The suspension was stirred at
70°C for 15 h. After cooling, the suspension was filtered
in order to remove the catalyst, which was washed
carefully with diethylether. The washing solution and
the filtrate were combined, washed with water and
dried over magnesium sulfate. After removing the sol-
vents in vacuum, the crude product was chro-
2
2
to CH2Cl2:methanol 1:1, a further fraction was col-
lected and the solvent evaporated. The residue was
treated with an aqueous solution of tetramethylammo-
nium chloride, product 8 precipitated, was filtered and
dried to give 0.01 g of the bis(tetramethylammonium)
salt of 3,5-bis(7%-(7%,8%-dicarba-nido-undecaboranyl))-
methoxycarbonylphenyl 8 (10%). Characterization of 7:
IR, w (cm−1): 3058 (Ccluster/aryl–H), 2953, 2924, 2853
matographed in
a
silica gel column with
dichloromethane–n-hexane (2:1) as eluent (Rf=0.40).
Evaporation to dryness afforded 0.092 g of 5 (72%).
Anal. Calc. for C18H24O2Si2 (%): C, 65.80; H, 7.36.
Found: C, 65.80; H, 7.17. EI-MS (m/z): 328.15 (27%,
M+). IR, w (cm−1): 3038 (Caryl–H), 2994, 2949, 2898
(Calkyl–H), 1732 (CꢀO), 1469 (Calkyl–H), 1276 (C–O).
1H-NMR (CDCl3), l (ppm): 8.0 (m, 2H, Caryl–H), 7.7
(m, 1H, Caryl–H), 3.9 (s, 3H, CO2CH3), 0.2 (s, 18H,
Si(CH3)3). 13C{1H}-NMR (CDCl3), l (ppm): 165.6
(CO2), 139.0, 132.6, 130.5, 123.9 (Caryl), 102.9, 96.1
(Cethynyl), 52.4 (CO2CH3), −0.22 (Si(CH3)3).
(Calkyl–H), 2599 (B–H), 1721 (CꢀO), 1598 (C–C)aryl,
1
1248 (C–O). H-NMR (CD3COCD3), l (ppm): 8.3 (d,
4
4J(H,H)=1.9 Hz, 2H, Caryl–H), 8.0 (t, J(H,H)=1.9
Hz, 1H, Caryl–H), 5.5 (s, broad, 2H, Ccluster–H), 4.0 (s,
3H, CO2CH3), 2.9–0.2 (broad, 20H, B–H). 13C{1H}-
NMR (CD3COCD3), l (ppm): 165.6 (CO2), 136.4,
133.3, 131.4, 130.8 (Caryl), 76.3, 62.1 (Ccluster), 53.7
(CO2CH3). 11B-NMR (CD3COCD3), l (ppm): −2.4 (d,
1J(B,H)=144 Hz, 1B), −3.9 (d, 1J(B,H)=150 Hz,
1
1B), −8.6 (d, J(B,H)=169 Hz, 2B, B(8,10)), −10.6
(d, 1J(B,H)=187 Hz, 4B, B(4,5,7,11)), −12.3 (d,
1J(B,H)=156 Hz, 2B(3,6)). Characterization of 8:
Anal. Calc. for C20H52B18N2O2·2CH3COCH3 (%): C,
47.10; H, 9.66; N, 4.22. Found: C, 47.54; H, 8.86; N,
3.74. EI-MS (m/z): 414 (2%, M −132,-cluster). IR, w
(cm−1): 3030 (Ccluster/aryl–H), 2955 (Calkyl–H), 2532 (B–
H), 1715 (CꢀO), 1445 (C–H)alkyl, 1251 (C–O). 1H-
NMR (CD3COCD3), l (ppm): 7.6 (m, 2H, Caryl–H),
4.7. Synthesis of methyl 3,5-bis(ethynyl)benzoate (6)
A solution of 0.085 g (0.26 mmol) of 5 and 0.004 g
(0.026 mmol) of potassium carbonate in 10 ml of
methanol was stirred for 18 h at room temperature.
After evaporation to dryness, the residue was dissolved

B. Fo¨rster et al. / Journal of Organometallic Chemistry 587 (1999) 67–73
73
Hagitt, H.R. Powell, S.A. Westcott, T.B. Marder, N.J. Taylor,
D.R. Kanis, J. Mater. Chem. 3 (1993) 139.
7.4 (m, 1H, Caryl–H), 3.8 (s, 3H, CO2CH3), 3.4 (s, 24H,
N(CH3)4), 3.0–0.2 (broad, 18H, B–H), −2,4 (broad,
2H, B–H–B). 13C{1H}-NMR (CD3COCD3), l (ppm):
168.3 (CO2), 146.9, 131.1, 129.5, 125.2 (Caryl), 56.3
(N(CH3)4), 52.2 (CO2CH3). 11B-NMR (CD3COCD3), l
(ppm): −8.4 (d, 1J(B,H)=139 Hz, 1B), −9.9 (d,
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1
1J(B,H)=141 Hz, 1B), −13.4 (d, J(B,H)=161 Hz,
1B), −16.2 (d, 1J(B,H)=148 Hz, 1B), −17.6 (d,
1
1J(B,H)=143 Hz, 1B), −19.4 (d, J(B,H)=153 Hz,
1B), −22.5 (d, 1J(B,H)=147 Hz, 1B), −32.4 (dd,
1J(B,H)=135 Hz, 1J(B,H)=36 Hz, 1B), −35.4 (d,
1J(B,H)=138 Hz, 1B).
Acknowledgements
This work was supported by the CIRIT (Project
QFN95-4721) and the DGICYT (Project PB94-0226).
B.F. thanks the EU for a Postdoctoral Fellowship in
the HCM-programme (ERBCHBGCT930345). J.B.
thanks the Generalitat de Catalunya for a Predoctoral
Grant (1996-FI-98469 APQF).
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