Synthesis of Bu4NB11H14 by the reaction of tetrabutylammonium octahydrotriborate with diborane in diglyme

Article abstract of DOI:10.1023/B:RUCO.0000025997.76929.34

The method for synthesis of Bu₄NB₁₁H₁₄ by dehydrocondensation of Bu₄NB₃H₈ with diborane in diglyme in the temperature range of 70-90°C was developed. The product is formed in 75-85% yield.

Full text of DOI:10.1023/B:RUCO.0000025997.76929.34

Russian Journal of Coordination Chemistry, Vol. 30, No. 5, 2004, pp. 307–308. Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 5, 2004, pp. 329–330.
Original Russian Text Copyright © 2004 by Gavrilova, Titov, Petrovskii.
Synthesis of Bu4NB11H14 by the Reaction
of Tetrabutylammonium Octahydrotriborate
with Diborane in Diglyme
L. A. Gavrilova*, L. V. Titov*, and P. V. Petrovskii**
*Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia
**Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
ul. Vavilova 28, Moscow, GSP-1, 117813 Russia
Received April 7, 2003
Abstract—The method for synthesis of Bu4NB11H14 by dehydrocondensation of Bu4NB3H8 with diborane in
diglyme in the temperature range of 70–90°ë was developed. The product is formed in 75–85% yield. The con-
–
ditions that ensure complete conversion of the anions, namely, initial Ç3H– and intermediate arachno-Ç9H ,
8
14
–
–
into nido-Ç11H and prevent further dehydrocondensation of Ç11H to closo-Ç12H2– were established.
14
14
12
Development of methods for synthesis and study of
The reaction between Bu4NB3H8 and diborane was
the properties of salts with polyhedral boron hydride carried out in the following way. The Bu4NB3H8 salt
anions, including Ç11H–14 , are of interest for the prepa-
was charged into a 600-ml glass vessel, and dyglime
was added until octahydrotriborate completely dis-
ration of coordination compounds containing these
solved. The solution was cooled to –196°ë and the ves-
anions as ligands and of metalloboranes and carbo-
sel was evacuated and filled with diborane. The
ranes.
Bu4NB3H8 : B2H6 molar ratio was 1 : 8 and the initial
Previously, we studied dehydrocondensation of tet-
raalkylammonium octahydrotriborates with Ç2ç6 [1]
and Ç5ç9 [2]. Dehydrocondensation of Bu4NB3H8 with
these boranes yields a mixture of tetrabutylammonium
Ç2ç6 pressure in the vessel was 200–300 mmHg. The
reaction mixture was kept at a specified temperature for
24 or 48 h. After completion of the exposure, transpar-
ent yellow-colored solutions were obtained. The final
gas pressure in the reaction vessel was not higher than
atmospheric pressure.
salts with the arachno-Ç9H–14 and nido-Ç11H1–4 anions.
The quantitative ratio of the anions depends on the con-
ditions of dehydrocondensation. Salts with the Ç9H1–4
According to 11Ç {1H} NMR data, depending on the
temperature and the exposure time, the reaction solu-
tions contained anions with the following chemical
and Ç11H–14 anions have not been obtained in a pure
state.
shifts (ppm): Ç3H8– (–29.8) [4]; B9H1–4 (–8.4, –20.6,
−23.9) [5]; and Ç11H–14 (–14.2, –16.5) [6, 7]. The spec-
The purpose of this study was to select the optimal
conditions for the formation of Bu4NB11H14 in the
dehydrocondensation reaction of Çu4NB3H8 with dibo-
rane.
tra also exhibited weak unidentified signals whose total
intensity corresponded to not more than 3–5% of the
overall amount of boron added to the solution. The rel-
ative contents of hydroborates in the solutions (mol %)
were calculated from the integrated intensities of sig-
nals in the 11Ç {1H} NMR spectra. The unidentified sig-
nals were not taken into account. The compositions of
the solutions determined on the basis of NMR data are
summarized in table. The solid Çu4NB11H14 was iso-
lated from solutions that contained, according to NMR
EXPERIMENTAL
The study was carried out using Bu4NB3H8 prepared
and purified by the known procedure [3]. Diborane was
prepared by the reaction of NaBH4 with boron trifluo-
ride etherate in diglyme. Diglyme and pentane were
dehydrated and distilled from LiAlH4. All operations
were carried out in an atmosphere of dry nitrogen.
data, only Ç11H–14 .
The IR spectra of solutions in diglyme were mea-
Synthesis of Bu4NB11H14. The reaction vessel con-
sured on a UR-20 spectrophotometer. 11B NMR spectra taining Bu4NB3H8 (0.35 g, 1.24 mmol), diglyme
were recorded on a Bruker WP-200-SY instrument (17 ml), and Ç2ç6 (9.95 mol) was kept at 80°C for
(64.2 MHz) using BF3 · OEt2 as an external standard.
24 h. The solid product was precipitated by pentane,
1070-3284/04/3005-0307 © 2004 åÄIä “Nauka /Interperiodica”

308
GAVRILOVA et al.
reaction products contain lower amount of Ç9H–14 and
Composition of the products formed in dehydrocondensation
of Bu4NB3H8 with diborane
higher amount of Ç11H1–4 as compared to the previous
case (table). When the temperature is elevated to 75°ë,
both the initial Ç3H8– anion and the intermediate Ç9H–14
anion are fully consumed. After 48 h, the solution con-
tains only Ç11H–14 .
Content, mol %
T, °C
Time, h
B9H–14
B3H–8
B11H–14
60
60
60
75
75
90
90
24
48
96
24
48
24
48
59.9
27.7
0.0
16.9
9.1
3.5
5.6
0.0
0.0
0.0
23.2
63.2
96.3
91.8
100
The IR spectra of the solutions exhibit an intense
absorption band at 2540 cm–1 that corresponds to the
stretching vibrations of the B–H bonds in Ç11H–14 . The
2.6
ν(Ç–ç) modes typical of the Ç9H–14 anion cannot be
seen, as they are overlapped by the intense ν(Ç–ç)
mode for Ç11H–14 . Irrespective of the exposure time, no
0.0
0.0
100
0.0
100
Ç3H–8 or Ç9H1–4 anions are found in the reaction prod-
washed, and dried in a vacuum. The product was ucts obtained at 90°ë. In the temperature range from 60
recrystallized from isopropyl alcohol. The yield was to 90°ë, a minor impurity of unidentified boronhy-
75–85%. On heating in an atmosphere of argon at 220– drides can be detected in solutions; at 105°ë, the pro-
240°ë, the salt Bu4NB11H14 decomposes with vigorous portion of these compounds increases to 20% of the
gas evolution.
total boron taken for the reaction.
Thus, a temperature of 75–90°ë and an exposure
time of 24 to 48 h are considered to be the optimal con-
ditions for the synthesis of Bu4NB11H14. Under these
For C16H40NB11
anal. calcd. (%):
Found (%):
C, 51.18;
C, 49.57;
H, 13.42;
H, 13.02;
B, 31.67.
B, 30.69.
conditions, the Ç11H–14 anion does not undergo further
dehydrocondensation to Ç12H–12 . The reaction can be
represented by the following overall equation
The 11Ç {1H} NMR spectrum of a dyglime solution
of the salt exhibits only signals with chemical shifts of
Bu4NB3H8 + 4B2H6
Bu4NB11H14 + 9H2. (1)
–14.2 and –16.2 ppm, typical of the Ç11H1–4 anion [6, 7].
ACKNOWLEDGMENTS
RESULTS AND DISCUSSION
This study was supported by the Russian Founda-
tion for Basic Research, project no. 02-03-32794.
The known method [8] used for the preparation of
salts with the Ç11H–14 anion is based on the reaction of
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RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 5 2004