Mild C-C bond cleavage in cycloalkanes by the action of new lanthanide catalysts LnCl3?3H2O?3(EtO)2AlOH

Full text of DOI:10.1134/s1070428008030275

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2008, Vol. 44, No. 3, pp. 470–471. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © R.G. Bulgakov, D.S. Karamzina, S.P. Kuleshov, U.M. Dzhemilev, 2008, published in Zhurnal Organicheskoi Khimii, 2008, Vol. 44,
No. 3, pp. 470–471.
SHORT
COMMUNICATIONS
Mild C–C Bond Cleavage in Cycloalkanes by the Action of New
Lanthanide Catalysts LnCl ·3H O·3(EtO) AlOH
3
2
2
R. G. Bulgakov, D. S. Karamzina, S. P. Kuleshov, and U. M. Dzhemilev
Institute of Petroleum Chemistry and Catalysis, Russian Academy of Sciences,
pr. Oktyabrya 141, Ufa, 450075 Bashkortostan, Russia
e-mail: ink@anrb.ru
Received July 4, 2007
DOI: 10.1134/S1070428008030275
Different ways of hydrocarbon processing (crack-
ing, hydrogen cracking, skeletal isomerization, re-
forming) involve transformations of saturated hydro-
carbons through activation and cleavage of carbon–
carbon bonds. Therefore, an important relevant prob-
lem is search for new methods for activation of
thermodynamically stable nonpolar C–C bonds. Non-
catalytic dissociation of C–C bonds in alkanes and un-
strained cycloalkanes requires fairly severe conditions:
high temperature (300–1000°C) and pressure (more
than 50 atm) [1]. Various transition metal compounds,
especially those derived from VI–VIII Group ele-
ments, in combination with organoaluminums make it
possible to perform such reactions at 150–180°C.
Superacids and superelectrophilic reagents based on
polyhalomethanes activate C–C bonds under even
milder conditions (20–200°C) [2]. However, wide ap-
plication of superacids in practice is strongly limited
because of their corrosion activity and high cost.
NaBH , [Bu N][Pr(BH ) ·DME] (where DME stands
4 4 4 4
for 1,2-dimethoxyethane), and molecular hydrogen
(bubbling at a flow rate of 0.4 ml/s). The reactions
were performed under mild conditions: 80°C, 760 mm,
6 h. Experiments with molecular hydrogen were car-
ried out under more drastic conditions: a high-pressure
reactor was continuously shaken over a period of 5 h at
215°C and a hydrogen pressure of 16 atm.
We found that [Ln] in combination with (i-Bu) AlH
2
is a highly selective and fairly efficient catalyst (see
table). The conversion of cyclohexane (strain energy
E = 0 kJ/mol) over [Tb] was 67%, while the known
s
catalyst Re (CO) –(i-Bu) AlH ensured only 22% con-
2
10
2
version [1]. The conversions of cycloheptane and cy-
clooctane (E = 3.7 and 5.1 kJ/mol, respectively) were
s
7
2 and 78%. In the reactions with other hydrogenating
agents, the conversion of cyclohexane over [Tb] did
not exceed 10%.
The examined lanthanides rank as follows with re-
spect to the conversion of cyclohexane (%): Ce (38) <
Nd (40) < Eu (52) < Tb (67). This series coincides with
the known series of complexing power of lanthanide
ions [4].
In the present communication we report on the first
example of using lanthanide complexes as catalysts for
low-temperature activation of C–C bonds in hydro-
genolysis of cycloalkanes. The catalysts, LnCl ·3H O·
3
2
3
(EtO) AlOH complexes ([Ln], Ln = Ce, Nd, Eu, Tb),
2
The conversion of cyclohexane in the presence of
simpler lanthanide compounds, such as LnCl , LnCl ·
were generated in situ according to the procedure de-
3
3
scribed in [3], i.e., by reaction of LnCl ·6H O with
3
2
6
H O, LnCl ·3TBP (TBP is tributyl phthalate), and
2 3
Al(OEt) . As hydrogenating agents we used LiAlH ,
3
4
aluminum alkoxides Al(OR) (R = Et, i-Bu), was con-
3
+
siderably lower (15%). Our results led us to presume
that the catalytically active center in the hydrogenol-
ysis process includes both metal ions, lanthanide and
aluminum.
[
Ln], H /H O
2
Me
+
(i-Bu) AlH
2
( )
n
(
)
Me
n
I–III
IV–VI
Typical procedure for hydrogenolysis of cyclo-
[
3 2 2
Ln] = LnCl ·3H O·3(EtO) AlOH; Ln = Ce, Nd, Eu, Tb;
I, IV, n = 1; II, V, n = 2; III, VI, n = 3.
alkanes. A solution of 0.24 mmol of Al(OEt) in
3
4
70

MILD C–C BOND CLEAVAGE IN CYCLOALKANES
471
1
0
2.5 ml of dioxane was added under argon to
.08 mmol of LnCl · 6 H O, and the mixture was
Hydrogenolysis of cycloalkanes with the system LnCl ·
3
3
H
2
O·3(EtO) AlOH–(i-Bu) AlH in dioxane
2
2
3
2
stirred until it became homogeneous and LnCl ·6H O
3
2
Initial compound no. Ln Conversion, % Product
disappeared. Cycloalkane I–III, 4.8 mmol, and
i-Bu) AlH, 7.2 mmol, were added, and the mixture was
(
I
Tb
Eu
Nd
Ce
Tb
Tb
67
52
40
38
72
78
IV
IV
IV
IV
V
2
heated for 6 h at 80°C. The mixture was then cooled to
0°C, treated with 15 ml of 10% hydrochloric acid,
I
1
I
and extracted with diethyl ether, The extract was dried
over Na SO , and the solvent was distilled off.
I
2
4
II
III
2
0
1
Hexane (IV). n = 1.3752 (1.3751 [5]). H NMR
D
VI
spectrum, δ, ppm: 0.96 t (6H, CH ), 1.35 br.s (8H,
3
1
3
1
6
CH ). C NMR spectrum, δ , ppm: 14.03 q (C , C ),
2
C
4
providing the complex [Bu N][Pr(BH ) ·DME]. The
2
5
3
4
4 4
2
3.04 t (C , C ), 32.13 t (C , C ).
authors also thank B.I. Kutepov and A.N. Khazipova
(Institute of Petroleum Chemistry and Catalysis, Rus-
sian Academy of Sciences, Ufa) for their help in per-
forming high-pressure hydrogenation experiments.
2
0
1
Heptane (V). n = 1.3879 (1.3878 [5]). H NMR
D
spectrum, δ, ppm: 1.02 t (6H, CH ), 1.42 br.s (10H,
3
1
3
1
7
CH ). C NMR spectrum, δ , ppm: 14.09 q (C , C ),
3.18 t (C , C ), 29.43 t (C ), 32.29 t (C , C ).
2
C
2
6
4
3
5
2
2
0
1
REFERENCES
Octane (VI). n = 1.3976 (1.3974 [5]). H NMR
D
spectrum, δ, ppm: 0.92 t (6H, CH ), 1.45 br.s (12H,
3
1
3
1
8
1. Akhrem, I.S. and Vol’pin, M.E., Usp. Khim., 1990,
CH ). C NMR spectrum, δ , ppm: 14.19 q (C , C ),
2
C
vol. 59, p. 1906.
2
7
4
5
3
6
2
2.90 t (C , C ), 29.45 t (C , C ), 32.30 t (C , C ).
2
. Zhorov, Yu.M., Termodinamika khimicheskikh protsessov
(Thermodynamics of Chemical Processes), Moscow:
Khimiya, 1985, p. 135.
1
13
The H and C NMR spectra were recorded on
a JEOL FX 90Q spectrometer at 89.5 and 22.5 MHz,
respectively, using tetramethylsilane as internal refer-
ence and chloroform-d as solvent. The products were
analyzed by GLC on a Tsvet 500M chromatograph
equipped with a flame ionization detector and a steel
column, 2 m×3 mm (stationary phase 30.5% of SE on
Chromaton N-AW-HMDS; oven temperature program-
ming from 50 to 270°C at a rate of 8 deg/min).
3. Bulgakov, R.G., Kuleshov, S.P., Karamzina, D.S., Makh-
mutov, A.R., Vafin, R.R., Shestopal, Ya.L., Mullagali-
ev, I.R., Monakov, Yu.B., and Dzhemilev, U.M., Kinet.
Katal., 2006, vol. 47, p. 760.
4
. Yatsimirskii, B.K., Kostromina, N.A., Sheka, Z.A., Davi-
denko, N.K., Kriss, E.E., and Ermolenko, V.I., Khimiya
kompleksnykh soedinenii redkozemel’nykh elementov
(
Chemistry of Rare-Earth Coordination Compounds),
The authors are grateful to V.D. Makhaev and
A.P. Borisov (Institute of Chemical Physics Problems,
Russian Academy of Sciences, Chernogolovka) for
Kiev: Naukova Dumka, 1966, p. 493.
5. Gordon, A.J. and Ford, R.A., The Chemist’s Companion,
New York: Wiley, 1972.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 3 2008