Olefin isomerization reactions catalyzed by ruthenium hydrides bearing Schiff base ligands

Article abstract of DOI:10.1002/aoc.1808

A series of in situ-generated ruthenium hydride complexes Ru(PPh ₃)₂(CO)H(Lⁿ) (n = a-h) incorporating a Schiff base ligand was investigated for the isomerization of olefins. ¹H-NMR was used to characterize the new hydride species in combination with ³¹P-NMR. Allylbenzene and 1-octene were used as model substrates. Temperature, solvents and catalyst/substrate mole ratio were taken into account as parameters to optimize the isomerization reaction. All catalysts showed the best performance in 2-butanol, suggesting that the catalytic activity depends not only strongly on the steric and electronic environment of the ruthenium but also on the chosen solvent.

Full text of DOI:10.1002/aoc.1808

Full Paper
Received: 10 December 2010
Revised: 13 April 2011
Accepted: 13 April 2011
Published online in Wiley Online Library: 30 May 2011
(wileyonlinelibrary.com) DOI 10.1002/aoc.1808
Olefin isomerization reactions catalyzed by
ruthenium hydrides bearing Schiff base ligands
Fu Dinga,b, Sabine Van Doorslaerc, Peggie Coold and Francis Verpoortb,e∗
A series of in situ-generated ruthenium hydride complexes Ru(PPh3)2(CO)H(Ln) (n = a–h) incorporating a Schiff base ligand
1
was investigated for the isomerization of olefins. H-NMR was used to characterize the new hydride species in combination
with 31P-NMR. Allylbenzene and 1-octene were used as model substrates. Temperature, solvents and catalyst/substrate mole
ratio were taken into account as parameters to optimize the isomerization reaction. All catalysts showed the best performance
in 2-butanol, suggesting that the catalytic activity depends not only strongly on the steric and electronic environment of the
c
ruthenium but also on the chosen solvent. Copyright ꢀ 2011 John Wiley & Sons, Ltd.
Keywords: isomerization; ruthenium hydride; organometallic compounds; Schiff base
Introduction
dride compounds to afford an extensive range of ruthenium
complexes that would subsequently show improved catalytic ac-
tivities and stabilities for isomerization compared with their parent
compound, RuH2(CO)(PPh3)3.
Since all kinds of unsaturated hydrocarbons play an important role
in organic synthesis, the isomerization of double/triple bonds has
been one of the highlights of transition-metal-catalyzed synthesis
in terms of both academic curiosity and industrial interests.[1]
Certain transition metal complexes based on Fe,[2–4] Pd,[2,3] Rh,[4]
Pt,[5] Ni,[3,6] Ir,[7] Ru,[8–11] and Cr[12,13] are known as catalysts for
isomerization. For instance, the Wilkinson catalyst (PPh3)3RhCl is
frequently employed in the isomerization of allylic ethers.[14]
Ruthenium hydride has been applied as a catalyst for the
olefin isomerization[11,15–20] since Ewing et al. reported on the
double bond migration of 1-pentene to give cis-2-pentene
(60%) and trans-2-pentene (40%) making use of RuHCl(PPh3)3.[21]
Although many elegant applications corroborate the idea that
ruthenium hydride complexes may perform isomerization in a
more conventional approach,[24–29] in most cases they only exist
as intermediate species. Furthermore, the instability of the hydride
retards the application of this kind of catalyst. In order to discover
an effective catalyst applicable under mild conditions, variation
of the ligand environment is expected to tune the stability, the
reactivity and even the selectivity of those compounds.
As all the properties of the catalysts are dictated primarily by the
coordination environment around the metal center, complexation
oftransitionmetalcompoundswithspecificligandsisofsignificant
importance for the catalytic activity. In addition, Schiff bases
bearing transition metal complexes offer a powerful synthetic
methodology for organic transformations. In particular, they play
a crucial role in ligand optimization strategies, resulting in a novel
class of robust and active ruthenium catalysts.[22–27] By the proper
choice of the substituents on the Schiff base, the desired physical
and chemical properties could be induced into the prepared
complexes.
Experimental
General
Unless otherwise stated, all reactions were carried out under a
dry argon atmosphere following conventional Schlenk techniques
and all solvents were distilled from the appropriate drying agents
and deoxygenated prior to use. 1H, 13C and 31P NMR spectra
were recorded on a Varian 300 spectrometer in CDCl3 (δ, ppm).
The salicylaldehydes and aromatic amines to synthesize the Schiff
Base ligands and RuCl3·nH2O to synthesize the precursor were
all purchased from Aldrich and used as received. The precursor
RuH2(CO)(PPh3)3 was prepared according to the literature.[33] All
other chemicals used were of analytical grade without further
purification.
Yields and selectivities were obtained using a Finnigan Trace GC
Ultra with an Ultra Fast Column Module (PH-5 5% diphenyl–95%
dimethyl poly-siloxane capillary, helium carrier gas, 1 ml/min),
∗
Correspondence to: Francis Verpoort, Organometallics and Catalysis, Depart-
ment of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281-S3,
B-9000, Belgium. E-mail: Francis.Verpoort@UGent.be
a
b
c
Laboratory of Coordination Chemistry, Shenyang University of Chemical
Technology, Shenyang, 100142, People’s Republic of China
Organometallics and Catalysis, Department of Inorganic and Physical
Chemistry, Ghent University, Krijgslaan 281-S3, B-9000, Belgium
Although Schiff base ruthenium hydride complexes have been
reported for several decades,[28,29] study of their isomerization ac-
tivity remains relatively scarce. Their antibacterial activities and ox-
idation activities in alcohols have been widely investigated..[30–32]
With the intention of developing long-lived, highly active ruthe-
nium isomerization catalysts, we explored the substitution of
tertiary phosphines by Schiff bases in situ from ruthenium hy-
Department of Physics, University of Antwerp, Universiteitsplein 1, B-2610
Wilrijk, Belgium
d
e
Laboratory of Adsorption and Catalysis, Department of Chemistry, University
of Antwerp, Universiteitsplein 1, B-2610 Wilrijk, Belgium
StateKeyLaboratoryofFineChemicals,DalianUniversityofTechnology,Dalian
116024, People’s Republic of China
c
Appl. Organometal. Chem. 2011, 25, 601–607
Copyright ꢀ 2011 John Wiley & Sons, Ltd.

F. Ding et al.
CHO
OH
R
R
R'
N
Ethanol
+
H2NR'
80°C, 2hr
OH
R = H R'= 2-Me-phenyl
R = H R'= 4-tBu-phenyl
R = H R'= 2,6-dimethylphenyl
(a) R = NO2 R'= 2-Me-phenyl
(b) R = NO2 R'= 4-tBu-phenyl
(c) R = NO2 R'= 2,6-dimethylphenyl
(e)
(f)
(g)
R = H R'= 4-bromo-2,6-dimethylphenyl (d) R = NO2 R'= 4-bromo-2,6-dimethylphenyl (h)
Scheme 1. Synthesis of Schiff bases.
H
CO
R'
Ru
PPh3
R'
Ph3P
N
OH
PPh3
O
N
Toluene
H
H
CO
H
+
Ru
70°C, 8h
H
PPh3
R
R
R = H R'= 2-Me-phenyl
R = H R'= 4-tBu-phenyl
R = H R'= 2,6-dimethylphenyl
(1)
(2)
(3)
R = NO2 R'= 2-Me-phenyl
R = NO2 R'= 4-tBu-phenyl
R = NO2 R'= 2,6-dimethylphenyl
(5)
(6)
(7)
R = H R'= 4-bromo-2,6-dimethylphenyl (4)
R = NO2 R'= 4-bromo-2,6-dimethylphenyl (8)
Scheme 2. Synthesis of the ruthenium hydride Schiff base catalysts 1–8.
column (10 m × 0.10 mm, 0.40 µm) and an FID = Flame Ionization
Detector detection system. The temperature program started at
50 ◦C and heated at 20 ◦C/min up to 255 ◦C.
Preparation of Schiff Base Ruthenium Hydride Complexes
The new hexa-coordinated ruthenium (II) complexes of the
type RuH(CO)(PPh3)2(Ln) (L = Schiff base ligand, n = a–h)
were prepared according the reaction depicted in Scheme 2.
To a toluene solution of the bidentate salicylaldimine ligand
a–h (1.1 equiv.) was added drop-wise a toluene solution of
RuH2(CO)(PPh3)3 (1 equiv.). After addition, the mixture was heated
to 65–80 ◦C for about 5 h to afford a pale yellow solution. The new
species were evidenced by 1H and 31P NMR and yields between
50 and 90%, based on 31P NMR measurements, were obtained. 1H
and 31P NMR also confirmed that the starting hydride compound
was no longer present.
Pretreatmentofthesubstrateswasnecessarybeforestartingthe
isomerization reaction. 1-Octene was passed through a column of
neutral alumina (Acros, 50–200 µm), containing 15 g of alumina
per 100 ml of 1-octene, into a Schlenk flask; then, 1-octene was
deoxygenated. In an empty 15 ml reaction vessel, an appropriate
quantity of the catalyst under investigation and solvent was
transferred under a constant Ar flow. Then the substrate was
added and the vessel was immersed in an oil bath, allowing
equilibration to the desired temperature before timing.
Prior to GC-analysis, the reaction mixture was purified over a
silica filter in order to remove the catalyst. Hexane was used as
solvent to prepare the GC samples and 1-dodecane was added as
internal standard.
Results and Discussion
Synthesis and Characterization
Preparation of Schiff Base Ligand
Since ruthenium hydrides were found to be active catalysts for
isomerization, a series of ruthenium hydride Schiff base complexes
RuH(PPh3)2(CO)(Ln) (with n = a–h) were developed. Compound
1 was reported by Vart A, et al., although without any further
exploration of application.[28]
The Schiff bases were prepared using conventional methods.[34]
The resultant crude products were isolated as yellow solids and
purifiedbywashingwithcoldpentanefollowedbydrying invacuo,
affording salicylaldimines in quantitative yields. The spectroscopic
properties[35] of the synthesized Schiff bases, see Scheme 1, are in
agreement with the literature data.[34]
Based on the NMR data given in Table 1, the stereochemical
structure of compounds 1–8 was in agreement with the general
structure depicted in Scheme 2. From the 1H NMR data [1H, δRuH
ca. −10 ppm, 2J(PH) ca. 20–22 Hz, 4J(HH) ca. 2 Hz], especially, the
Preparation of Ruthenium Hydride Precursor
4
coupling J(HHꢁ) between hydridic and azomethine (–N CH–)
The precursor RuH2(CO)(PPh3)3 was prepared according to the
literature and the characterization was in good agreement with
the literature data.[33]
protonsfavorsthestructurebetweenthealternativearrangements
withthehydride transtotheO-donorsite. The 31P NMRresonances
1
[
31P{ H}, δPPH3, ca. 38.9–43.0 ppm (s)] were found to be singlets,
c
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Copyright ꢀ 2011 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2011, 25, 601–607

Olefin isomerization reactions catalyzed by ruthenium hydrides
Schiff base exert opposite electronic effects: the phenolate oxygen
is a hard donor stabilizing the higher oxidation state of the
ruthenium whereas the imine nitrogen is a softer donor and,
consequently, will better stabilize the lower oxidation state of the
ruthenium atom. In this way a flexible interaction between these
two binding sites can be achieved.
It follows from Table 2 that a higher catalyst loading results in
a higher substrate conversion. However, the variance is not linear
and some differences in conversion are less than 1%, i.e. there are
no significant differences between these two mole ratios (1 : 1000
to 1 : 5000). Since a lower catalyst loading is much more attractive
in comparison to other reported catalysts, this is a noteworthy
improvement.[42–44]
Table 1. The 1H and 31P NMR data of RuH2(CO)(PPh3)3 and 1–8
1H (ppm)
31P(ppm)
RuH2(CO)(PPh3)3
−6.885(t), −8.905(m)
−11.336(t)
58.245(d), 45.732(t)
38.936(s)
1
2
3
4
5
6
7
8
−10.931(t)
41.273(s)
−16.394(t)
40.213(s)
−14.364(t)
38.075(s)
−11.263(t)
38.940(s)
−10.891(t)
41.657(s)
−16.748(t)
40.205(s)
−14.534(t)
39.926(s)
The temperature has a drastic influence on the activity;
increasing the temperature did not lead to increased conversion. A
higher temperature promoted the decomposition of the catalyst,
resulting in a lower yield. Complexes 1, 2 and 5–7 performed best
at 80 ◦C, while complexes 3 and 4 needed 100 ◦C to complete
the isomerization reaction. Only complex 8 showed excellent
performance at 60 ◦C.
because for bulky phosphines, e.g. PPh3, no effective coupling
was observed between the two phosphine ligands (31P–31P).[36]
Furthermore, these observations indicate that the phosphine
ligands are orientated trans to each other. The Schiff base ligands
coordinate in a bidentate fashion with the N,O donors forming
a six-membered chelating ring.[10,11,22–27] All above observations
support the general structure depicted in Scheme 2.
The respective 1H resonances relative to the hydride in
complexes 1–8 were strongly shifted downfield or upfield (−10.9
to −16.7 ppm), depending on the electronic properties of the
Rꢁ-group on the Schiff base.
Furthermore, a number of features of Schiff base ligands
make them attractive for catalytic applications, particularly the
decreased liability and/or higher stability in comparison to the
precursor compound. For complexes 1–8, no changes were found
in the NMR spectrum after several days, even in open air. In
addition, the new compounds are more stable than most of the
reported ruthenium hydrides, which degrade in less than 24 h
in air.
The conversion of 1-octene in the presence of RuH2(CO)(PPh3)3
andcomplexes1–8withoutsolventisdepictedinFig. 1. Exceptfor
complexes 1 and 2, all complexes achieved over 95% conversion.
Using complex 8, a conversion of 98.1% was reached, and
complexes 3, 4 and 6–8 reached >95% conversion within the
first half-hour. Complexes 1, 2 and 5 showed a much slower rate
of reaction. All nitro-containing complexes displayed a higher
activity compared with the non-nitro-containing compounds.
As discussed above, it seems that, after adjusting the steric
and electronic effects around the ruthenium center through an
appropriate selection of the substituents on the Schiff base unit,
the activity of ruthenium hydride complexes depended on the
Rꢁ-group of the Schiff base. The experimental data suggest that
the electronic influence of the Schiff base has a greater impact on
the catalytic performance than the steric bulk of the Schiff base.
Based on the results discussed above, most of the catalysts
demonstrated an excellent performance at a catalyst–substrate
mole ratio of 1 : 1000. The same ratio was used to study the
influence of the solvent.
Isomerization Activities
Since hydride complexes have been corroborated in the literature
as isomerization catalysts,[37–41] by applying different R or Rꢁ
groups in the Schiff base ligand, the influence of electronic and
steric factors of the ligand in the ruthenium hydride complexes
was the subject of this study. To elucidate the source of the
activity differences and establish relative stabilities of the various
complexes, the reactivities of the ruthenium hydrides 1–8 were
examined using 1-octene and allylbenzene as model substrates.
Complexes 1–8 were treated with an excess of 1-octene at
differenttemperatures(60,80and100 ◦C)for12 handtheactivities
were investigated. The results are summarized in Tables 2–4. To
compare and optimize their activities, different catalyst–substrate
ratios (1 : 1000, 1 : 5000 and 1 : 10000) and different solvents were
applied.
During the isomerization reaction, three products were gen-
erated – 2-octene, 3-octene and 4-octene – indicating that 1–8
catalyzed the isomerization of 1-octene. Initial GC and NMR results
proved that neither metathesis nor dimerization took place.
Each of the new species, 1–8, were superior to RuH2(CO)(PPh3)3
under the experimental conditions described in Table 2. High
conversions were mostly achieved by the new complexes.
Moreover, the increased activity of these catalysts was not
accompanied by a decrease in stability towards towards air and
moisture. This observation results from the contribution of the
Schiff base ligand. Two donor atoms, N and O, in the coordinated
Comparing the percentage conversion of 1-octene depicted
in Table 3, it can be seen that the various solvents affected the
isomerization in different ways. 2-Butanol was the unique solvent
for all catalysts. For the other solvents, it was difficult to observe
a general trend. Moreover, the solvent effect on this series of
catalysts was not affected by the temperature.
Because of the distinct thermal stability in different solvents, the
best performance of the catalyst did not always appear at higher
temperatures. The same catalyst could generate higher yields at
a different temperatures depending on the solvent. For instance,
catalyst 1 gave 97.4 and 95.2% yields in CHCl3 and CH3CHClCH2Cl,
respectively, at60 ◦C, whileinmethanoland2-butanol, thehighest
yields obtained at 80 ◦C were, respectively, 87.2 and 95.9%. This
phenomenon appears to be true for all catalysts. Furthermore, it
seems that the solvent effect improved the activity of catalysts
containing a small substituent on the Schiff base (1 and 5).
Using allylbenzene as substrate, 2-butanol was still the solvent
ofchoicesinceallthecatalystswerepromoted. Varying thesolvent
resulted in a significant change in conversion, e.g. for catalyst 1 a
conversion of 32.3% was obtained in CH3CHClCH2Cl at 60 ◦C, while
when using 2-butanol a conversion of 86.6% was reached at 60 ◦C.
For catalyst 7, at all temperatures high conversions were obtained
when CHCl3 or 2-butanol was used as the solvent. For catalyst 6,
c
Appl. Organometal. Chem. 2011, 25, 601–607
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F. Ding et al.
Table 2. 1-Octene conversion by RuH2(CO)(PPh3)3 (precursor) and 1–8, without solvent
Temperature
(◦C)
Precursor
1
2
3
4
5
6
7
8
C : Sa ratio 1 : 1000
60
80
42.0
86.5
88.7
62.5
96.1
94.8
90.6
96.6
96.5
96.9
96.3
97.5
95.2
97.3
97.4
89.6
97.4
97.3
97.1
97.4
97.4
95.7
97.4
96.9
98.1
97.4
97.4
100
C : Sa ratio 1 : 5000
60
80
36.0
40.4
60.3
39.6
87.6
92.3
86.4
96.5
94.6
71.4
91.5
94.9
93.2
97.0
96.8
73.1
97.3
97.2
96.7
96.2
97.1
60.2
92.1
95.6
96.6
96.7
97.2
100
C : Sa ratio 1 : 10 000
60
80
1.8
19.1
40.3
32.9
26.2
81.7
20.4
87.0
92.7
10.3
35.9
86.2
20.3
84.0
94.3
42.6
91.2
92.3
89.4
91.2
96.9
24.7
85.9
95.6
89.9
96.1
97.2
100
a C : S ratio, catalyst/substrate mole ratio.
Table 3. Percentage conversion for the isomerization of 1-octene by complexes 1–8 with solvent
Solvent
Temperature
(◦C)
No solvent
CHCl3
CH3CHClCH2Cl
MeOH
2-Butanol
Toluene
Catalyst 1
60
62.5
96.1
94.8
92.2
96.7
97.0
95.2
91.0
92.9
37.9
87.2
60.8
92.1
95.9
94.0
92.1
96.4
96.9
80
100
Catalyst 2
60
90.6
96.6
96.5
65.1
58.0
83.0
57.7
74.0
74.0
96.1
89.8
94.0
93.2
89.5
95.3
50.2
66.4
61.7
80
100
Catalyst 3
60
96.9
96.3
97.5
95.8
92.3
96.3
72.5
88.5
77.8
52.0
65.8
76.0
97.8
96.5
96.3
38.3
54.4
75.3
80
100
Catalyst 4
60
95.2
97.3
97.4
89.9
98.0
98.8
75.1
77.9
80.8
97.2
97.7
95.7
90.8
95.5
96.6
15.8
17.0
36.4
80
100
Catalyst 5
60
89.6
97.4
97.3
71.3
88.4
84.0
59.2
67.7
59.3
45.1
62.6
63.7
94.1
98.6
96.4
72.5
86.8
90.6
80
100
Catalyst 6
60
97.1
97.4
97.4
93.2
93.2
94.4
85.5
96.0
96.3
56.3
63.2
60.3
96.2
96.7
97.1
69.3
75.0
85.8
80
100
Catalyst 7
60
95.7
97.4
96.9
77.5
74.8
75.6
53.3
54.3
66.3
91.1
95.5
96.4
87.4
87.9
94.5
57.9
61.3
60.9
80
100
Catalyst 8
60
98.1
97.4
97.4
91.0
91.0
71.2
59.9
68.9
43.9
33.3
19.5
96.2
96.6
95.8
63.9
76.3
76.9
80
100
100.0
c
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Copyright ꢀ 2011 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2011, 25, 601–607

Olefin isomerization reactions catalyzed by ruthenium hydrides
RuH2
100
95
90
85
80
75
70
65
60
1
2
3
4
5
6
7
8
Table 4. Percentage conversion for the isomerization of allylbenzene
by complexes 1–8 with solvent
Solvent
Temperature
(◦C)
CHCl3 CH3CHClCH2Cl MeOH 2-Butanol Toluene
Catalyst 1
60
33.4
27.6
61.2
32.3
62.5
50.2
56.7
69.7
76.3
86.6
97.6
93.0
50.7
75.6
84.6
98.0
97.6
97.2
96.8
80
100
Catalyst 2
60
12.8
17.4
37.2
15.3
45.9
65.1
69.1
53.1
48.6
99.8
97.8
99.7
10.9
15.4
18.8
80
4
8
12
12
100
0
2
4
6
8
10
Catalyst 3
60
Time (h)
99.7
99.9
96.4
57.9
58.1
59.2
95.5
95.7
92.1
98.4
99.7
99.6
18.2
29.8
34.1
Figure 1. Isomerization results of 1-octene using RuH2(CO)(PPh3)3
RuH2) and complexes 1–8 (without solvent, temperature 80 ◦C, C : S
80
(
100
ratio 1 : 1000).
Catalyst 4
60
81.5
96.6
95.2
82.5
97.2
99.7
21.7
51.2
76.7
99.4
99.7
99.8
15.0
35.7
26.8
80
100
(a)
Catalyst 5
60
26.0
56.8
52.9
23.4
45.4
66.2
80.1
85.2
95.9
90.9
99.8
99.4
10.6
71.4
82.9
80
100
Catalyst 6
60
49.3
40.3
64.1
46.9
75.3
70.6
15.6
18.7
13.2
99.8
99.9
99.9
30.8
57.1
72.2
(b)
(c)
80
100
Catalyst 7
60
92.6
92.9
92.5
47.8
53.0
50.6
98.9
94.9
99.2
77.0
65.2
79.3
14.0
20.9
27.4
80
100
Catalyst 8
60
95.7
94.0
89.9
9.6
17.7
43.8
59.0
47.1
73.8
75.7
85.5
96.2
9.8
39.1
34.9
80
100
the solvent of choice was 2-butanol; at 60 ◦C full conversion was
achieved. In general, it can be concluded that 2-butanol is the
preferred solvent for this series of ruthenium Schiff Base hydrides.
Because many hydride complexes, such as RuH4(PPh3)3 and
RuH(BH4)(PMe2Ph)3, are able to decarbonylate alcohols, it was
expected that this decarbonylation would also occur here. Some
analogous reactions have been reported in the literature describ-
ing the decarbonylation of methanol by applying RuHCl(PPh3)3,
where a ruthenium hydride complex RuH2(η2-HCHO)(PPh3)3
was suggested as an intermediate.[45] Furthermore, adding
methanol to WH(η2-CH2PMe2)(PMe3)4, a well-characterized η2-
formaldehyde complex WH2(η2-HCHO)(PMe3)4 was formed.[46]
Therefore, notwithstanding the unknown intermediates, based on
the H NMR observation (Fig. 2a–c), it is reasonable to suppose
that the alcohol decarbonylation occurred by a metal–aldehyde
dihydride complex, RuH(η2-OCH2R)(PPh3)2 (Ln).
Furthermore,aftertheeliminationofhydrogenfromthecatalyst,
the intermediate reacted with H2 produced during the reaction,
to recover the catalysts. Owing to these possible interactions, the
Figure 2. Hydride
region
of
the
1HNMR
spectrum
of
(a) precursor–RuH2(CO)(PPh3)3, (b) catalyst 1–RuH(CO)(PPh3)2 (La)
and (c) intermediate, catalyst 1-RuH(CO)(PPh3)2 (La) and precur-
sor–RuH2(CO)(PPh3)3.
higher activity in alcohol is unsurprising. A proposed mechanism
for the reaction of the ruthenium hydride with alcohol is depicted
in Scheme 3.
The fact that the activity in methanol was not as high as in
2-butanol as solvent is a consequence of the difference in vapor
pressure. At 80 ◦C methanol evaporates, excluding the mechanism
described above almost completely. Moreover, performing the
same experiments in open air using solvents and substrates
directly from the bottle (as received), similar conversions were
obtained. Thehighstabilityofthenewcatalystsmakesthereaction
conditions very convenient, enhancing the catalyst lifetime and
allowing lower catalyst loadings to be applied.
1
c
Appl. Organometal. Chem. 2011, 25, 601–607
Copyright ꢀ 2011 John Wiley & Sons, Ltd.
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F. Ding et al.
Acknowledgments
CO
I
H
Ru
Ru
VII
H2
F.D. is indebted to the Research Fund of Ghent University and
Shenyang University of Chemical Technology for a research grant.
F.V., S.V.D and P.C. are grateful to the FWO-Flanders (Fund for
Scientific Research – Flanders) for financial support.
H
R
Ru
RCH2OH
H
H2
H2
H
H
VIII
H
VI
2-OCHR
II
Ru
Ru
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