Tandem hydroformylation-acetalization with a ruthenium catalyst immobilized in ionic liquids

Article abstract of DOI:10.1016/j.molcata.2014.04.009

For the first time, a ruthenium catalyzed hydroformylation-acetalization reaction of olefins is presented. The tandem reaction proceeds well with 1,2- or 1,3-diols, trapping the intermediary formed aldehydes as cyclic acetals. In this manner the hydrogenation of the aldehydes to the corresponding alcohols usually observed with Ru catalysts is prevented. The optimized catalytic system consisting of Ru catalyst, ionic liquids, acetic acid and ammonium salt can be recycled and reused for at least two further runs. Interestingly, styrenes as substrate give preferentially terminal acetals.

Full text of DOI:10.1016/j.molcata.2014.04.009

Journal of Molecular Catalysis A: Chemical 391 (2014) 139–143
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Tandem hydroformylation–acetalization with a ruthenium catalyst
immobilized in ionic liquids
Jakob Norindera, Claudia Rodriguesa, Armin Börnera,b,∗
a Leibniz-Institut für Katalyse an der Universität Rostock e.V., A.-Einstein-Str. 29a, 18059 Rostock, Germany
b Institut für Chemie, Universität Rostock, A. Einstein-Str. 3a, 18059 Rostock, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
For the first time, a ruthenium catalyzed hydroformylation–acetalization reaction of olefins is presented.
The tandem reaction proceeds well with 1,2- or 1,3-diols, trapping the intermediary formed aldehydes
as cyclic acetals. In this manner the hydrogenation of the aldehydes to the corresponding alcohols usu-
ally observed with Ru catalysts is prevented. The optimized catalytic system consisting of Ru catalyst,
ionic liquids, acetic acid and ammonium salt can be recycled and reused for at least two further runs.
Interestingly, styrenes as substrate give preferentially terminal acetals.
Received 3 February 2014
Received in revised form 31 March 2014
Accepted 6 April 2014
Available online 24 April 2014
Keywords:
Ruthenium
© 2014 Published by Elsevier B.V.
Hydroformylation
Tandem reaction
Acetalization
1. Introduction
properties of several ruthenium catalysts. Thus, reduction of start-
ing olefins or product aldehydes may become a serious issue
Hydroformylation, the addition of synthesis gas (CO/H2) to
olefins, is one of the most important homogeneously catalyzed pro-
cesses in industrial scale [1]. The aldehydes formed are used as
final products or intermediates in bulk chemistry as well for the
production of fine chemicals such as pharmaceuticals or aroma
compounds [1,2]. In this respect exclusively cobalt and rhodium
complexes have been used. In particular rhodium has seen broad
application due the high activity and selectivity of the relevant cat-
alysts. A special problem concerns its extremely high and volatile
price.
Ruthenium catalysts attract increasing attention as a much
cheaper alternative [3]. Already Wilkinson and co-workers sporad-
ically suggested their use in their pioneering work on Rh catalyzed
hydroformylation [4]. In general, the activity of ruthenium com-
plexes in hydroformylation is lower than that of the corresponding
rhodium congeners [3,5]. By use of appropriate organic ligands
like amines or phosphines this disadvantage may be partly over-
come [6]. A crucial problem concerns the high hydrogenation
[6c,7]. This effect may be desired, when alcohols are the final
target of the hydroformylation [8]. In addition, ruthenium cata-
lysts tend to isomerize olefins [9]. Recently both properties have
been advantageously employed for highly efficient hydroformy-
lation/hydrogenation tandem reactions of terminal and internal
olefins by groups of Nozaki and Beller [6e,10]. Moreover, as another
example of tandem reactions covering a hydroformylation step,
recently the first Ru catalyzed hydroaminomethylation was dis-
closed [11].
To our knowledge, in contrast to rhodium catalysis [12] the
combination of hydroformylation with acetalization under the
assistance of a ruthenium catalyst has never been reported
(Scheme 1) [13]. Yielding acetals should be of particular value in
perfume manufacture, since they protect the aldehyde group reli-
ably toward oxidation or reaction with amines. Both reactions affect
significantly the overall odor impression [2b]. Moreover, glycerol
acetals of aliphatic aldehydes have been reported as pesticides and
additives for diesel fuels [14].
In order to increase the turnover number (TON) of the Ru cat-
alyst with respect to the yield of the acetals we attempted to
recycle and to reuse the catalyst. Therefore, a special focus was
given to the reaction in ionic liquids taking in mind the excel-
lent results reported by Tominaga and Sasaki for their use in the
hydroformylation with CO2 catalyzed by unmodified Ru clusters
[15,16].
∗
Corresponding author at: Leibniz-Institut für Katalyse an der Universität Rostock
e.V., A.-Einstein-Str. 29a, 18059 Rostock, Germany. Tel.: +49 381 1281 202;
fax: +49 381 1281 5202.
E-mail addresses: jakob.norinder@catalysis.de
(J. Norinder), armin.boerner@catalysis.de (A. Börner).
http://dx.doi.org/10.1016/j.molcata.2014.04.009
1381-1169/© 2014 Published by Elsevier B.V.

140
J. Norinder et al. / Journal of Molecular Catalysis A: Chemical 391 (2014) 139–143
Table 1
Effect of acids on the hydroformylation–acetalization tandem reaction of 1-octene (1a, R = C6H13) with ethylene glycol.
.
Entry
Acid
2a + 3aa (%)
4aa (%)
5aa (%)
6aa [%]
n/isob
49:51
7aa [%]
1
2
HOAc
–
H3PO4
p-TsOH
p-Cresol
8
12
36
39
2
0
0
0
0
0
5
3
30
0
87
57
2
46
72
1
28
10
8
50:50
–
47:53
54:46
3
4c
5
11
15
a
Determined by GC.
Linear product versus branched isomer of acetal 6a.
10% of p-TsOH was used.
b
c
isomer was observed. Increasing the syngas pressure to 100 bar did
not affect yield or regioselectivity.
2.2. Influence of solvents
Next, the effect of different solvents was investigated under the
optimized conditions described in Table 1. Both [BMIM]NTf2 and
[BMIM]BF4 as solvents resulted in high yields of acetal 6a (Table 2,
entries 1 and 2).
For practical reasons, [BMIM]BF4 was chosen for further studies,
since the crude product could be best extracted with organic sol-
vent from the ionic liquid, giving promise for reusing the ionic liquid
and the ruthenium catalyst therein. In other polar solvents such as
THF, EtOAc or NMP (entries 3–5) isomerization and hydrogenation
of the olefin increased. The use of tetrabutylphosphonium bromide
as a solvent resulted in nonanols as the major product (64%), deplet-
ing the desired acetal product (entry 6). The reaction in propylene
carbonate (PC) [18] predominantly led to isomerization and reduc-
tion of the substrate (entry 7). With the exception of the reaction in
PC and NMP, the regioselectivity was not strongly affected by the
choice of the solvent (typically 47–58% linear product).
Scheme 1. Principle of the ruthenium catalyzed hydroformylation–acetalization
tandem reaction.
2. Results and discussion
2.1. Screening of reaction conditions
For the screening of reaction conditions, 1-octene (1a) was used
as a substrate (Table 1). The catalyst was in situ generated by treat-
ment of Ru3(CO)12 with CO/H2 in a ratio of 1:1 at 20 bar. Preliminary
trials with methanol and ethanol afforded complex mixtures of
products. Therefore, we turned our focus on the use of diols, such
as ethylene glycol, with the hope to achieve an improved trapping
of the intermediary formed aldehyde by generation of more sta-
ble cyclic acetals. The reaction was performed in the ionic liquid
[BMIM]BF4. Since the hydroformylation with ruthenium catalysts
often benefits from the presence of halide ions [15a], NEt4Cl was
added, which is characterized by a high solubility in organic sol-
vents.
2.3. Variation of alcohols for acetalization
A series of commercially available diols and glycerol were exam-
ined (Table 3). By use of neopentyl glycol the relevant acetal 6b was
achieved in 93% GC-yield (entry 2).
Also propane-1,3-diol afforded a higher yield of the corre-
sponding acetal than ethylene-1,2-glycol (compare entries
1
It was found that the presence of acetic acid improved the for-
mation of the desired acetal 6a over the ester 7a and in this way 87%
of acetal 6a was observed according to GC (Table 1, entry 1). With-
out acid added, 57% of the desired acetal 6a was formed together
with considerable amounts (26%) of alkoxycarbonylation product
7a (entry 2) [17]. Inspired by this finding, other protic acids were
examined as additives. By addition of phosphoric acid the formation
of isomeric nonanols was favored (entry 3). Simultaneously, isom-
erization and hydrogenation of the starting olefin became major
reactions. By using 10 mol % of p-TsOH, a moderate yield of acetal
6a was observed together with a considerable amount of internal
n-octenes (entry 4). Next, p-Cresol was examined as a mild pro-
tic acid (entry 5). Hydrogenation of the intermediate nonanals (4a)
leading to nonanols (5a) and the formation of alkoxycarbonylation
products 7a diminished the yield of the desired acetal. Indepen-
dent of acid used about equal amounts of linear versus branched
and 3). Apparently the formation of the six membered ring is
Table 2
Effect of solvents on the hydroformylation–acetalization tandem reaction of 1-
octene (1a) with ethylene glycol.a
Entry Solvent
2a + 3ab [%] 4ab [%] 5ab [%] 6ab (%) n/isoc 7ab [%]
1
2
3
4
5
6
7
[BMIM]BF4
[BMIM]NTf2
THF
EtOAc
NMP
PBu4Br
PC
8
2
24
25
18
1
0
0
7
7
12
0
5
7
2
1
7
87
88
66
65
53
27
7
49:51
47:53
58:42
53:47
75:25
53:47
90:10
1
0
1
1
1
1
0
64
5
59
6
a
b
c
Reaction conditions, as indicated in Table 1, using HOAc as additive.
Determined by GC.
Linear product versus branched isomer.

J. Norinder et al. / Journal of Molecular Catalysis A: Chemical 391 (2014) 139–143
141
Table 3
Variation of diols used for the hydroformylation–acetalization tandem reaction with 1-octene (1a, R = C6H13).a
Entry
Diol
2a + 3ab (%)
5ab [%]
Acetal
Product
Yieldb [%]
87 (36)
n/isoc
1
8
5
6a
49:51
51:49
2
3
0
3
4
2
6b
6c
93 (58)
93 (45)
51:49
e
4
0
3
2
6d
6e
95 (52)d
–
5
18
74 (55)
64:36
a
Reaction conditions, as indicated in Table 1, using HOAc as additive.
Determined by GC. Isolated yields in parentheses.
Linear product versus branched isomer of acetal 6.
In order to separate the glycerol derived acetals 6d from the ionic liquid reaction mixture, addition of 3 mL of water revealed to be advantageous.
Not determined, since 16 isomers could not be clearly separated.
b
c
d
e
thermodynamically favored over the five membered acetal. Like-
wise the corresponding glycerol acetal was formed in excellent
yield (entry 4). In this case a mixture of all 16 possible isomers
was produced. Pinacol was less apt for acetalization compared
to the other diols examined (entry 5). A considerable amount of
nonanols was formed as by-product, decreasing the yield of the
desired acetal 6e. However, the increased n/iso-regioselectivity is
remarkable. The apparently high selectivity for the linear acetal
Table 4
Substrates used in the hydroformylation–acetalization with neopentyl glycol.a
Entry
Substrate
Acetal
Product
6b
Yieldb [%]
93 (58)
n/isoc
51:49
49:51
1
2
6b
90 (45)
3
4
5
6
6f
80 (56)
75 (60)
75 (56)
89 (52)
84:16
78:22
77:23
84:16
6g
6h
6i
7
6j
69 (38)
79:21
a
Reaction conditions as indicated in Table 1, using HOAc and neopentyl glycol as additives. For octenes, the reaction time was 20 h and in case of styrene derivatives 2 h.
With styrenes in all cases full conversion was noted.
b
Determined by GC. Isolated yields in parentheses.
Linear product versus branched isomeric acetals 6.
c

142
J. Norinder et al. / Journal of Molecular Catalysis A: Chemical 391 (2014) 139–143
Table 5
4. Experimental
Reusing the catalytic system in the hydroformylation/acetalization of 1-octene (1a).a
All reagents were supplied from commercial sources. They were
transferred to Schlenk vessels and used without further purifica-
tion. The experiments were carried out in 25 mL Parr autoclaves or
in a HEL 8 × 16 mL parallel reactor. Proton and carbon NMR spectra
were carried out in CDCl3, using residual CHCl3 as internal standard.
Gas chromatography was carried out using an Agilent HP-5 col-
umn (30 m, 0.32 mm diam., 0.25 ␮m film); carrier gas; H2, flow
rate; 0.9 mL/min. GC program for octene derivatives: 35 ◦C (0 min)
5 ◦C/min until 180 ◦C, thereafter 30 ◦C/min until 320 (10 min). GC
program for styrene derivatives: 50 ◦C (2 min) 10 ◦C/min until 320
(10 min).
Entry
Recycle
2a + 3a (%)
5a (%)
6bb (%)
n/isoc
TON
TTN
1
2
3
–
1st
2nd
0
5
10
4
1
2
93 (58)
94 (58)
88 (50)
51:49
49:51
50:50
139
140
131
139
279
410
a
Reaction conditions as indicated in Table 1, using HOAc and neopentyl glycol as
additives.
b
Determined by GC. Isolated yields in parentheses.
Linear product versus branched isomeric acetals 6b.
c
in this experiment is likely due to preferential acetalization of
the linear aldehyde isomer. In general, the isolated yields of
acetals were less than the yields determined by GC. This is prob-
ably due to the polar products and the polar reaction medium,
which did not allow isolating the whole amount of reaction
products.
4.1. A typical experiment using 4-tert-butylstyrene and
neopentyl glycol
Ruthenium dodecacarbonyl (17.3 mg, 27 ␮mol), NEt4Cl
(663 mg, 4.00 mmol), neopentyl glycol (2.08 mL, 20 mmol), HOAc
(229 ␮L, 4.00 mmol), 4-tert-butylstyrene (733 ␮L, 4.00 mmol) and
[BMIM]BF4 (5 mL) were added to a HEL parallel reactor. The reactor
was purged with Ar (5× 2 bar) and with syngas (5× 5 bar). The
autoclave was filled with 16 bar syngas (CO/H2 = 1:1) and heated to
140 ◦C. The pressure was kept automatically at 20 bar after reach-
ing 140◦ C. After 2 h, the reactor was cooled to room temperature.
The crude product was extracted with 3× 5 mL pentane/Et2O (1:1).
The organic phase was washed with aqueous NaHCO3 (2× 5 mL).
The crude product was analyzed on GC and thereafter purified
by flash chromatography using 25 g silica and cyclohexane/EtOAc
100:1 to 10:1. This gave 613 mg (56% yield) of acetal product as an
isomeric mixture (n/iso ratio 84:16). Analytical samples of the two
isomers were separated by column chromatography. The linear
product (2-(4-(tert-butyl)phenethyl)-5,5-dimethyl-1,3-dioxane)
was isolated as a colorless oil. 1H NMR (300 MHz, CDCl3): ı 7.23
(d, J = 9.0 Hz, 2H), 7.07 (d, J = 9.0 Hz, 2H), 4.36 (t, J = 4.5 Hz, 1H), 3.55
(dm, J = 12.0 Hz, 2H), 3.36 (dm, J = 12.0 Hz, 2H), 2.67–2.61 (m, 2H),
1.91–1.84 (m, 2H), 1.23 (s, 9H), 1.14 (s, 3H), 0.65 (s, 3H). 13C NMR
(75 MHz, CDCl3): ı 148.67, 138.78, 128.23, 125.36, 101.61, 77.36,
36.40, 34.49, 31.56, 30.35, 29.65, 23.17, 22.00. MS (EI 70 eV) m/z
(%): 276 (M+, 14), 261 (8), 189 (10), 175 (98), 142 (100), 131 (42),
115 (89). The branched isomer 2-(1-(4-(tert-butyl)phenyl)ethyl)-
5,5-dimethyl-1,3-dioxane was isolated as a colorless oil. 1H NMR
(300 MHz, CDCl3) ı 7.30 (d, J = 8.4 Hz, 2H), 7.20 (d, J = 8.4 Hz, 2H),
4.50 (d, J = 4.6 Hz, 1H), 3.67–3.52 (m, 2H), 3.44–3.29 (m, 2H), 2.95
(qd, J = 7.2, 4.6 Hz, 1H), 1.43–1.22 (m, 12H), 1.16 (s, 3H), 0.68 (s,
3H). 13C NMR (75 MHz, CDCl3) ı 148.97, 140.01, 127.84, 125.17,
104.86, 77.43, 77.39, 44.00, 34.47, 31.54, 30.26, 23.09, 21.94, 15.95.
MS (EI 70 eV) m/z (%): 275 (2), 175 (2), 161 (17), 146 (9), 131 (14),
115 (100), 69 (55).
2.4. Variation of substrates
In turn other olefins were subjected to the optimized reac-
tion conditions (Table 4). In comparison to 1-octene (entry 1) also
the internal olefin trans-2-octene gave the corresponding termi-
nal acetal (entry 2) as the major product. The n/iso ratio did not
significantly differ from that observed with the terminal octene
showing the high isomerization activity of the Ru catalyst. Styrene
derivatives which cannot isomerize gave unexpectedly high yield
of the terminal aldehydes. Under Rh catalysis usually an iso-
regiodirecting effect of the substrate is observed [19]. An influence
of the electronic properties of the para substituent on the yield
could not be noted (entries 3–7). Furthermore, the styrenes exam-
ined showed to be most reactive under the present condition and
full conversion was observed within 2 h in all cases.
2.5. Reuse of the catalyst
The ionic liquid, ruthenium and tetraethylammonium chloride
are non-volatile. After separating the crude product from the polar
ionic liquid by extraction with organic solvent, the ionic liquid was
purified by bulb-to-bulb distillation. The residual ionic liquid, con-
taining the ruthenium catalyst and tetraethylammonium chloride,
was reused in further experiments (Table 5). The turnover number
(TON) in each experiment was 131–140 (mol product/mol catalyst)
and the total turnover number (TTN) after three cycles reached 410
(total mol of product/mol catalyst).
3. Summary and conclusion
For the first time,
a
ruthenium catalyzed hydrofor-
Acknowledgements
mylation–acetalization tandem reaction has been developed.
The optimized catalytic system consisting of Ru3(CO)12, acetic
acid, NEt4Cl and an ionic liquid exhibits a similar reactivity to both
terminal as well as internal aliphatic olefins and gives acetals with
good yields. The reaction only proceeds with diols affording cyclic
acetals. Styrene derivatives were also successfully converted.
Remarkably, with these substrates the hydroformylation step
occurred with preferential selectivity for the linear product, which
overrides the iso-directing effect of the substrate commonly
observed with rhodium catalysts. The catalyst could be reused
at least two times, which enhances the overall efficiency of the
process. By this manner a total turnover number (TTN = total mol
of product/mol catalyst) of 410 could be reached.
We appreciate valuable discussion with Dr. D. Selent. DC C.
Rodrigues is grateful to CAPES (Coordenac¸ ão de Aperfeic¸ oamento
de Pessoal de Nível Superior, Brazil. Project 18782/12-4) for a
grant. We thank Leibniz-Gemeinschaft (Pakt für Innovation und
Forschung) for financial support.
Appendix A. Supplementary data
Supplementary material related to this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.molcata.
2014.04.009.

J. Norinder et al. / Journal of Molecular Catalysis A: Chemical 391 (2014) 139–143
143
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