Heterogeneous Shvo-type ruthenium catalyst: Dehydrogenation of alcohols without hydrogen acceptors

Article abstract of DOI:10.1016/j.tetlet.2004.04.113

A Shvo-type diruthenium complex is heterogenized by a sol-gel process, which catalyzes the conversion of alcohols to carbonyl compounds and molecular hydrogen without any additive. The heterogeneous catalyst is recoverable by simple filtration, stable in the air, and reusable.

Full text of DOI:10.1016/j.tetlet.2004.04.113

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 4607–4610
Heterogeneous Shvo-type ruthenium catalyst:
dehydrogenation of alcohols without hydrogen acceptors
Jun Ho Choi, Namdu Kim, Yong Jun Shin, Jung Hye Park and Jaiwook Park*
Center for Integrated Molecular System, Department of Chemistry, Division of Molecular and Life Science,
Pohang University of Science and Technology (POSTECH), San 31 Hyoja Dong, Pohang 790–784, Republic of Korea
Received 10 March 2004; revised 20 April 2004; accepted 22 April 2004
Abstract—A Shvo-type diruthenium complex is heterogenized by a sol–gel process, which catalyzes the conversion of alcohols to
carbonyl compounds and molecular hydrogen without any additive. The heterogeneous catalyst is recoverable by simple filtration,
stable in the air, and reusable.
Ó 2004Elsevier Ltd. All rights reserved.
The Shvo complex, [(g5-Ph4C4CO)2H]Ru2((CO)4)(l-H)
(1), is a versatile catalyst.1 It has been used for many
homogeneous hydrogen-transfer reactions such as the
disproportionation of aldehydes to esters,2 the reduction
of aldehydes and ketones,3 the Oppenauer-type oxida-
tion of alcohols and amines,4;5 and the racemization of
alcohols and amines.6;7 During our study on the dy-
namic kinetic resolution of alcohols with the catalytic
activity for the racemization of alcohols,6 we recognized
that 1 catalyzes also the dehydrogenation of alcohols
and found a brief report that describes the catalytic
dehydrogenation of 2-octanol and cyclohexanol at
the sol–gel process to give a recoverable and reusable
catalyst. First, we examined the dehydrogenation of
1-phenylethanol with 1–3 to see the substituent effect of
the pentadienyl ring on the catalytic activity (Scheme 1).
Interestingly, 1 having phenyl substituents showed the
highest activity; under the conditions of the entry 5
in Table 1, acetophenone was produced in 60% yield
by 2 and in 68% by 3. Then, the efficiency of the
OH
R2
O
[Ru]
Toluene, 110 C
145 °C by
Ph4C4CO)(CO)2Ru]2, which readily converts into 1 in
a
dimeric ruthenium complex, [(g5-
R1
R1
R2
°
the reaction with alcohols.8
Scheme 1.
H
Table 1. Dehydrogenation of 1-phenylethanol by
conditions
1
in various
O
R
O
R
R
R
1: R = Ph
2: R = Me
Ph
Ph
Entry mol %
Concentration Time
(M)
Solvent
Yield
(%)a
Ru
CO
Ru
Ph
OC
Ph
CO
CO
3: R = 1-Naphthyl
H
(h)
1
4.0
0.1
24
Ethyl
acetate
22.8
For practical uses, heterogeneous catalysts are prefera-
ble to homogeneous one, thus we planned to synthesize
a simple derivative of 1, which can be easily employed in
2
4.0
4.0
0.1
0.1
9
24
24
Benzene 49.5
Heptane 59.7
3
440.1
.0
Octane
98.0
5
6
7
8
9
4.0
2.0
1.0
8.0
4.0
0.1
0.1
0.1
0.1
0.5
9
9
9
6
9
Toluene 89.3
Toluene 81.0
Toluene 65.9
Toluene 94.0
Toluene 95.4
Keywords: Silica sol–gel; Diruthenium; Dehydrogenation; Alcohols.
* Corresponding author. Tel.: +82-54-279-2117; fax: +82-54-279-3399;
e-mail: pjw@postech.ac.kr
a By GC.
0040-4039/$ - see front matter Ó 2004Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.04.113

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J. H. Choi et al. / Tetrahedron Letters 45 (2004) 4607–4610
dehydrogenation was optimized with using 1 with
varying conditions (Table 1).9 The reaction rate de-
pended on the reaction temperature; it was almost
completed in 9 h in refluxing octane (bp 126 °C) while in
refluxing benzene (bp 80 °C) the reaction proceeded in
less than 50% even after 24h, (entry 2 vs entry 4). It was
notable that a more concentrated solution led to a
higher yield (entry 8 vs entry 9).
able by simple filtration, and reusable several times.
Although the activity decreased gradually, over 90% of
the original activity was maintained in the fourth use:
1st, 100%; 2nd, 97.4%; 3rd, 96.0%; 4th, 90.5%; 5th,
86.8%. The catalyst 11 was effective for various alcohols
(Table 2). Aliphatic alcohols as well as benzylic alcohols
were dehydrogenated to the corresponding ketones in
high yields. The production of a c-lactone from 1,2-
benzenedimethanol implicates the dehydrogenation of
the intermediate hemiacetal. However, the reaction of
benzyl alcohol was relatively slow, and produced benzyl
benzoate in less than 0.5%. In comparison to the known
We thought that the derivatives of 1, which contain
hydroxy groups, would be suitable for sol–gel processes
to afford robust catalysts.10 The Shvo-type diruthenium
complex 10, which has two (hydroxylmethyl)phenyl
groups, was synthesized from the cyclopetadienone 7
by the procedure reported by Shvo and Menashe2;11
Table 2. Dehydrogenation of alcohols with 11a
Meanwhile,
7 was prepared from 4-(phenylethy-
Entry
Substrate
Time (h) Yield (%)b
nyl)benzaldehyde (4)12 through a three-step process: (1)
protection of the formyl group of 4; (2) oxidation of the
triple bond to give the 1,2-diketone 6;13 (3) coupling of 6
and diphenylacetone (Scheme 2).14 The silica gel
entrapping 10 was prepared by the sol–gel process
involving a mixture of 10, tetramethyl orthosilicate,
methanol, water and THF. The resulting gel was washed
with methanol and dried under vacuum to give 11 as
yellow powder entrapping 10 in 77% yield.15
1
2
3
1-Phenylethanol
1-(4-Chlorophenyl)ethanol
1-(4-Methoxyphenyl)ethanol
6
6
6
97
97
97
41-Cyclohexylethanol
8
97
5
6
7
8
2-Octanol
Cyclohexanol
6
20
6
97
100c
96d
41e
1,2-Benzenedimethanol
Benzyl alcohol
6
a In refluxing toluene (0.1 M) with 4.4 mol % of 11.
b Isolated yield.
c By GC.
The heterogeneous catalyst 11 showed a better activity
than 1 in the dehydrogenation of 1-phenylethanol,
which was completed in 6 h. The catalyst was recover-
d The product was 3H-isobenzofuran-1-one.
e By GC with using biphenyl as the internal standard.
Neopentyl glycol (1.5 equiv),
p-TsCl (0.7 mol%)
O
H
O
O
Toluene, 100 oC, 24 h; 99 %
4
5
I
2 (0.7 equiv)
DMSO, 120 oC, 8 h
O
(1.0 euqiv)
O
66%
O
Ph
Ph
O
O
O
Ph
Ph
KOH (0.5 equiv),
7
EtOH, 80 oC, 3 h; 82 %
O
6
Ph
O
1) Ru3(CO)12, Benzene, 80 o
2) Acetone/aq. Na2CO3
3) aq. NH4Cl; 98 %
C
H
CF3CO2H
H
O
O
Ph
Ph
O
O
Ph
Ph
Ph
rt, 24 h; 98 %
Ph
Ru
Ph
Ru
Ph
Ph
Ru
Ru
Ph
Ph
OC
OC
Ph
O
O
O
O
H
H
OC
CO
CO
OC
CO
CO
O
8
O
H
9
H
H2(1 atm), Toluene
90 oC, 24 h; 73 %
H
O
Ph
O
Ph
Ph
Tetramethyl orthosilicate
[Ru]-SiO2
Ph
Ph
CH3OH, H2O, THF
rt, 24 h
Ru
11
Ru
Ph
CO
HO
OH
H
OC
OC
CO
10
Scheme 2.

J. H. Choi et al. / Tetrahedron Letters 45 (2004) 4607–4610
4609
€
B. A.; Larsson, A. L. E.; Ray, M. L.; Backvall, J.-E.
J. Am. Chem. Soc. 1999, 121, 1645–1650; (c) Kim, M.-J.;
Ahn, Y.; Park, J. Curr. Opin. Biotechnol. 2002, 13, 578–
Ph
Ph
Ph
O
Ph
1A
Ru
OH
R2
O
OC
ꢂ
587; (d) Pamies, O.; Backvall, J.-E. Chem. Rev. 2003, 103,
3247–3261.
€
OC
R1
R1
1
+
ꢁ
ꢂ
7. Pamies, O.; Ell, A. H.; Samec, J. S. M.; Hermanns, N.;
Ph
Ph
Ph
€
Backvall, J.-E. Tetrahedron Lett. 2002, 43, 4699–4702.
8. Blum, Y.; Shvo, Y. J. Organomet. Chem. 1985, 282, C7–
C10.
9. A typical procedure for dehydrogenation: In a 50 mL flask
equipped with a grease-free high vacuum stopcock, 1
(8.6 mg, 0.0080 mmol) and 1-phenylethanol (0.20 mmol)
were mixed with dry toluene (2 mL) under Ar atmosphere.
The mixture was heated to reflux. The reaction was
checked by GC.
OH
R2
H2
Ph
H
1B
Ru
OC
OC
Scheme 3.
dehydrogenation catalysts such as RuH2(PPh3)4,16
IrH5(iPrP)2,17 IrH2{C6H3-2,6-(CH2P-t-Bu2)2},18 Ru(OC
OCF3)2(CO)(PPh3)2,19 Ru3(CO)12/PPh3,20 11 has several
advantages: stable in the air and easy to handle; active
without additives; active under mild conditions.
10. (a) Zehl, G.; Bischoff, S.; Mizukami, F.; Isutzu, H.;
€
Bartoszek, M.; Jancke, H.; Lucke, B.; Maeda, K. J. Mater.
Chem. 1995, 5, 1893–1897; (b) Lu, Z.; Lindner, E.; Mayer,
H. A. Chem. Rev. 2002, 102, 3543–3578; (c) Kawano, S.;
Tamaru, S.; Fujita, N.; Shinkai, S. Chem. Eur. J. 2004, 10,
343–351.
11. Compound 5: yield: 99%; mp: 115 °C; 1H NMR (CDCl3) d
7.46–7.57 (m, 6H), 7.30–7.37 (m, 3H), 5.39 (s, 1H), 3.78 (d,
J ¼ 11:2 Hz, 2H), 3.65 (d, J ¼ 10:7 Hz, 2H), 1.29 (s, 3H),
0.80 (s, 3H); 13C NMR (CDCl3) d 138.6, 131.8, 131.8,
128.8, 128.5, 126.4, 124.0, 123.4, 101.5, 89.9, 89.5, 77.8,
30.5, 23.3, 22.1; MS (EI): m=z: 292.14(M þ); Anal. Calcd
for C20H20O2: C, 82.16; H, 6.89. Found: C, 82.25; H, 6.81.
A possible pathway for the catalytic dehydrogenation is
proposed in Scheme 3: The diruthenium complex 1 is in
equilibrium with mononuclear species 1A and 1B.21 An
alcohol reacts with the 16-electron species 1A to give the
hydride complex 1B and the corresponding ketone.
Then, 1B loses molecular hydrogen with being coupled
with another 1B to form 1.
1
Compound 6: yield: 66%; mp: 95.5 °C; H NMR (CDCl3)
d 7.92–8.0 (m, 4H), 7.63–7.67 (m, 3H), 7.47–7.53 (m, 2H),
5.44 (s, 1H), 3.78 (d, J ¼ 11:1 Hz, 2H), 3.66 (d,
J ¼ 11:0 Hz, 2H), 1.27 (s, 3H), 0.81 (s, 3H); 13C NMR d
194.7, 194.6, 145.3, 135.1, 133.4, 133.2, 130.2, 130.1, 129.2,
127.1, 100.7, 77.9, 30.5, 23.2, 22.1; FT-IR (KBr)
1667 cmꢀ1; MS (EI): m=z: 324.15 (Mþ); Anal. Calcd for
C20H20O4: C, 74.06; H, 6.21. Found: C, 74.02; H, 6.13.
Compound 7: yield: 82%; mp: 200–202 °C; 1H NMR d
7.10–7.36 (m, 15H), 6.88–6.98 (m, 4H), 5.33 (s, 1H), 3.76
(d, J ¼ 11:2 Hz, 2H), 3.63 (d, J ¼ 10:7 Hz, 2H), 1.28 (s,
3H), 0.79 (s, 3H); 13C NMR d 200.5, 154.7, 154.0, 238.8,
133.7, 133.2, 130.9, 130.8, 129.7, 129.5, 128.7, 128.3, 128.2,
127.7, 127.6, 126.1, 125.9, 125.6, 101.8, 77.9, 23.3, 22.1,
FT-IR (KBr) 1707 cmꢀ1; MS (EI): m=z: 498.31 (Mþ); Anal.
Calcd for C35H30O3: C, 84.31; H, 6.06. Found: C, 84.11;
H, 6.24.
In summary, we synthesized a heterogeneous version of
the versatile Shvo complex through sol–gel process, and
demonstrated that it is a recoverable and reusable cat-
alyst for the efficient dehydrogenation of alcohols.
Acknowledgements
This work was supported financially by the Center for
Integrated Molecular System, the National Laboratory
of Chirotechnology and MOE through the BK21 pro-
ject.
Compound 8: yield: 98%; mp: 143 °C; 1H NMR (CDCl3) d
6.90–7.50 (m, 38H), 5.21 (s, 2H), 3.68 (d, J ¼ 10:9 Hz,
4H), 3.54 (d, J ¼ 11:1 Hz, 4H), 1.22 (s, 6H), 0.75 (s, 6H),
)18.43 (s, 1H); 13C NMR d 201.0, 200.9, 200.8, 200.7,
154.6, 138.1, 132.2, 132.1, 131.4, 131.3, 131.3, 131.2, 130.7,
130.6, 130.4, 130.4, 130.3, 128.1, 128.0, 127.8, 127.0, 125.6,
103.5, 103.1, 103.0, 101.6, 88.1, 88.1, 88.0, 87.9, 77.7, 30.4,
23.2, 22.0; FT-IR (KBr) 2030, 2005, 1977 cmꢀ1; MS
(FAB): m=z: 1314.16 (Mþ+1); Anal. Calcd for
C74H62O10Ru2: C, 67.67; H, 4.76. Found: C, 67.65; H,
4.83.
References and notes
1. (a) Shvo, Y.; Czarkie, D.; Rahamim, Y.; Chodosh, D. F.
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allics 2002, 21, 5674–5677.
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€
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Compound 9: yield: 98%; mp: 139.5 °C (dec); 1H NMR
(CDCl3) d 9.85 (s, 2H), 7.49–7.56 (m, 4H), 6.93–7.22 (m,
34H), )18.37 (s, 1H); 13C NMR (CDCl3) d 200.8, 200.9,
200.6, 200.5, 191.6, 154.8, 137.7, 135.7, 132.8, 132.1, 131.2,
130.2, 130.0, 129.9, 129.0, 128.5, 128.2, 128.0, 127.4, 127.2,
104.4, 104.3, 101.9, 101.7, 88.7, 88.5, 87.8, 87.6; FT-IR
(KBr) 2035, 2007, 1978 cmꢀ1; MS (FAB): m=z: 1142.17
(Mþ+1); Anal. Calcd for C64H42O8Ru2:C, 67.36; H, 3.71.
Found: C, 67.35; H, 3.73.
Compound 10: yield: 73%; mp: 83 °C; 1H NMR (CDCl3) d
7.20–6.90 (m, 38 H), 4.48 (s, 4H), )18.39 (s, 1H); 13C
NMR (CDCl3) d 201.0, 154.5, 140.7, 132.3, 132.2, 132.1,
131.4, 131.3, 131.2, 131.1, 130.8, 130.4, 130.0, 128.1, 128.0,
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4610
J. H. Choi et al. / Tetrahedron Letters 45 (2004) 4607–4610
to afford 11 (1.639 g); 0.362 wt % Ru by Induced Coupled
127.9, 127.0, 126.2, 103.6, 103.5, 103.4, 103.4, 88.2, 88.1,
88.0, 87.9, 64.8; FT-IR (KBr) 2034, 2006, 1976 cmꢀ1; MS
(FAB): m=z: 1146.76 (Mþ+1); Anal. Calcd for
C64H46O8Ru2:C, 67.12; H, 4.05. Found: C, 67.36; H, 4.04.
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15. The silica sol–gel process for 11: A mixture of 1 (50 mg),
tetramethyl orthosilicate (3.5 mL), degassed methanol
(2.5 mL), degassed water (2.5 mL) and degassed THF
(5.0 mL) in 50 mL flask equipped with a grease-free high
vacuum stopcock was stirred at room temperature for 24h
under Ar and then it was stand aside for 24h at room
temperature, which yielded homogeneous sol–gel. After
removing volatiles under vacuum, the resulting yellow
solid was washed with methanol and dried under vacuum
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