Selective oxidation of methane and its homologues to alcohols catalyzed by gold compounds and a proposed reaction mechanism

Full text of DOI:10.1134/S0012500810020059

ISSN 0012ꢀ5008, Doklady Chemistry, 2010, Vol. 430, Part 2, pp. 50–53. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © L.A. Levchenko, N.G. Lobanova, V.M. Martynenko, A.P. Sadkov, A.F. Shestakov, A.K. Shilova, A.E. Shilov, 2010, published in Doklady Akademii Nauk,
010, Vol. 430, No. 6, pp. 773–775.
2
CHEMISTRY
Selective Oxidation of Methane and Its Homologues
to Alcohols Catalyzed by Gold Compounds
and a Proposed Reaction Mechanism
L. A. Levchenko, N. G. Lobanova, V. M. Martynenko, A. P. Sadkov,
A. F. Shestakov, A. K. Shilova, and Academician A. E. Shilov
Received July 27, 2009
DOI: 10.1134/S0012500810020059
Gold complexes with the bioflavonoid rutin in
Figure 1 shows the kinetic curve of propane oxidaꢀ
water catalyze the selective oxidation of methane to tion to 2ꢀpropanol by the Au–rutin complex. The iniꢀ
methanol by air at room temperature and atmospheric tial acceleration of the reaction is likely associated
pressure like it occurs in bacteria Micrococcus luteus with the reduction of Au(III) to Au(I). The reaction
[
1]. The present work is aimed at extending the scope
mechanism can only be suggested at present. In studyꢀ
ing this mechanism for methane, we will proceed from
the proposed structure of another catalytically active
of substrates to the nearest methane homologues,
ethane and propane, and at studying the mechanism
of oxidation of methane and its homologues.
complex, the Au(I) complex with quercetin (
reported by us in [5]. In the first step, the activation of
a methane C–H bond ( ) occurs upon its oxidaꢀ
1)
The experimental procedure used in this study was
analogous to that in [2], where methane oxidation was
catalyzed by the Au(I) complex with rutin. The
reagent concentrations were on the same order as in
the reaction in [1]. The reaction requires the presence
of the reducing agent NADH; therefore, as in [3], gold
2
→
3
tive addition to the gold complex. Inasmuch as methꢀ
ylgold complexes are rather resistant to hydrolysis, it
should be assumed that the C–O bond formation (
3
→
4) is caused by the participation of water or oxygen in
active toward a hydrocarbon should be in the Au(I) the process. Gold is not an oxophilic element; thereꢀ
state.
fore, its direct interaction with an oxygen molecule is
improbable. If it is assumed that the oxygen molecule
in the next step detaches an H atom from the methyl
The oxidation of ethane and propane was studied
under the same conditions. The reaction products
were, respectively, ethanol and 2ꢀpropanol. Chroꢀ
matographic analysis showed the absence of 1ꢀproꢀ
panol. The yield of the products per mole of Au at
3
Yield of 2ꢀpropanol, mM
×
10−
2
5
°
С
over a period of time of 48 h was 30 mol for methꢀ
ane, 200 mol for ethane, and 220 mol for propane; at
, the yields (72 h) were 15, 40, and 141 mol,
300
250
200
150
100
5
°
С
D O
2
respectively. The yield increases in the series of alkanes
C –C3. The observed increase in the reactivity along
1
this series is consistent with the decrease in the C–H
bond cleavage energy (table).
Ethane and propane are also oxidized without
rutin, in the presence of O2, NADH, HAuCl4, and the
Tris–HCl buffer (pH 7.8). The yields of ethanol and 2ꢀ
propanol in this case decrease to, respectively, 40 and
50
25 mol per mole of Au (48 h at 25 С).
°
0
10 20 30
40 50
60 70 80
Time, h
Institute of Problems of Chemical Physics, Russian Academy
of Sciences, pr. Akademika Semenova 1, Chernogolovka,
Moscow oblast, 142432 Russia
Fig. 1. Kinetic curve of propane oxidation catalyzed by the
Au(I)–rutin complex at 25 C.
°
50

SELECTIVE OXIDATION OF METHANE AND ITS HOMOLOGUES
51
ligand to produce the carbene complex Au–CH2, the assume reversible water addition followed by oxygen
addition.
latter could react with water to give CH OH. However,
3
The question of why only the Au(I) complexes with
rutin and quercetin do catalyze methane oxidation [5]
can be clarified by that the remote gold atom (at ring
in the system where H O was replaced by D O
2
2
(
99.9%), formation of the isopropyl group in 2ꢀproꢀ
panol rules out such a possibility (mass spectrometric
data). The mass spectra in H O and D O turned out to
C
) is in conjugation with two gold atoms (through
rings and ). This can be explained by the mechaꢀ
be almost identical (Fig. 2). Therefore, we should nism shown in Scheme 1.
2
2
A
B
O
O
O
O
O
O
C
Au
Au
Au
HO
O
B
HO
O
O
HO
O
O
H O
CH4
2
A
O
O
O
O
O
O
O
Au(I)
Au(I)
Au(I)
H
Au
Au
Au
H
1
CH3
CH3
2
O
H
H
O2
O
O
O
O
O
Au
Au
Au
HO
O
O
HO
O
O
HO
O
O
O
Au(I)
O
O
O
O
O
O
Au(I)
Au (( II )I I)
Au
6
Au
Au
5
4
CH OH H O
3
2
2
CH3
H
CH3
H
O
O
O
HO
H O
O
H
H
CH4
H O
2
O
O
Au
HO
O
O
O
O
Au(I)
Au
2
CH OH + 2H O
3 2
Scheme 1.
Due to the presence of ring C conjugated with
rings A and B, intermediate structure 4 should be peroxide, which then goes into solution (stage
more stable than in the absence of this ring or conjuꢀ From this point on,
Stage
4
→
5
of this mechanism yields hydrogen
).
acts as the oxidant instead of
5
→
6
H O
2 2
gation with it.
O
2
(stage
3
→
4).
DOKLADY CHEMISTRY Vol. 430
Part 2
2010

52
LEVCHENKO et al.
C–H bond cleavage energies in methane, ethane, and propane [4]
Alkane
E, kcal/mol
Alkane
E, kcal/mol
CH –H
3
104.0
98.1
CH CH CH –H
2
97.9
94.5
3
2
C H –H
2
(CH ) CH–H
3 2
5
The oxidative addition of methane to the binuclear
moiety of trinuclear Au(I) complex with quercetin
Au(I) Au(III)
1
CH2
H
O
was theoretically studied by the PBE density funcꢀ
tional method [7] with the use of the extended SBK
pseudopotential basis set [8] and the PRIRODA
program [9]. The optimized structure of the oxidaꢀ
tion product is shown in Fig. 3. The formation of
H
O
H
H
O
H
Methyl group transfer from CH ReO to Os O4 folꢀ such a structure leads to a decrease in free energy by
3
3
3
lowed by formation of CH OH was observed in [6].
28 kcal/mol. The isomeric structure in which the
3
(а)
(b)
3
2
1
50
50
50
3
50
250
150
50
5
0
30
40 50 60 70 80 90 100
m
30 40 50 60 70 80 90 100
/z
m/z
Fig. 2. Mass spectra of gaseous propane oxidation products. Solvents: (a) H O and (b) D O.
2
2
Au
2.20
2.45
O
1
.30
1
.50
O
C
1.40
C
1.27
1.44
H
C
C
H
C
1.42
H
C
H
1.42
C
O
O
C
1.37
1
.44
C
C
C
C
C
H
A
B
C
1.25
H
O
C
C
1
.29
1.27
2.80
2
.26
O
O
2.25
2
.55
Au
1
H
.57
Au
2.05
H
C
H
H
Fig. 3. Calculated structure of the product of methane oxidation catalyzed by the Au(I)–quercetin complex (2). Bond lengths are
in angstroms.
DOKLADY CHEMISTRY Vol. 430
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2010

SELECTIVE OXIDATION OF METHANE AND ITS HOMOLOGUES
53
methyl and hydride ligands change places has almost
the same energy. The character of the C–C bond
124 [Dokl. Akad. Nauk, 2001, vol. 377, no. 5, pp. 700–
01].
7
length distribution in the pyrocatechol ring of
dence of its tendency to rearrange into quinoid form
Thus, in this work, which is conceptually biomiꢀ
metic, we succeeded in simplifying the reaction mechꢀ
anism and explaining the methane activation at room
temperature. The same mechanism is proposed for the
oxidation of ethane and propane.
1
is eviꢀ
2. Levchenko, L.A., Sadkov, A.P., Lariontseva, N.V.,
Kulikov, A.V., Shilova, A.K., and Shilov, A.E., Dokl.
Biochem. Biophys., 2004, vol. 394, nos. 1–6, pp. 33–34
4.
[Dokl. Akad. Nauk, 2004, vol. 394, no. 2, pp. 272–273].
3
. Shulpin, G.B., Shilov, A.E., and SussꢀFink, G., Tetraꢀ
hedron Lett., 2001, vol. 42, pp. 7253–7256.
4. Gurvich, L.V., Karachintsev, G.B., Kondrat’ev, V.N.,
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ionizatsii i srodstvo k elektronu (Energies of the Chemiꢀ
cal Bond Cleavage, Ionization Potentials, and Electron
Affinity), Moscow: Nauka, 1974.
ACKNOWLEDGMENTS
The experiments on ethane oxidation were carried
out with the participation of Z.M. Bukhmetdinova, a
student of Ufa State University.
We are grateful to D.N. Sokolov for his help with
the chromatographic analysis.
5. Levchenko, L.A., Kartsev, V.G., Sadkov, A.P., Shestaꢀ
kov, A.F., Shilova, A.K., and Shilov, A.E., Dokl. Chem.
007, vol. 412, part 2, pp. 35–37 [Dokl. Akad. Nauk
007, vol. 412, no. 4, pp. 500–502].
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Chem., Int. Ed. Engl., 2008, vol. 47, pp. 7849–7852.
This work was supported by the Russian Foundaꢀ
tion for Basic Research, project no. 06–03–32252.
7. Perdew, J.P., Burke, K., and Ernzerhof, M., Phys. Lett.
A., 1996, vol. 77, p. 3865.
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DOKLADY CHEMISTRY Vol. 430
Part 2
2010