Highly linear-selective hydroformylation of 1-alkenes using formaldehyde as a syngas substitute

Article abstract of DOI:10.1002/adsc.200900713

A highly linear-selective hydroformylation of 1-alkenes using formaldehyde without the direct use of syngas is described. One rhodium(I) complex catalyzes two processes in the overall hydroformylation of 1-alkenes using formaldehyde as the syngas substitute to give hydroformylated aldehydes with excellent regioselectivities. A high regioselectivity (linear/branched=up to 98/2) and chemical yield (up to 95%) can be achieved by the simultaneous use of two types of phosphanes as ligands.

Full text of DOI:10.1002/adsc.200900713

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DOI: 10.1002/adsc.200900713
Highly Linear-Selective Hydroformylation of 1-Alkenes using
Formaldehyde as a Syngas Substitute
Gouki Makado,a Tsumoru Morimoto,a,* Yasuko Sugimoto,a Ken Tsutsumi,a
Natsuko Kagawa,b and Kiyomi Kakiuchia
a
Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), Takayama, Ikoma, Nara
630-0192, Japan
Fax : (+81)-743-72-6081; e-mail: morimoto@ms.naist.jp
Department of Medicinal Organic Chemistry, Chiba University Yayoi, Inage, Chiba 263-8522, Japan
b
Received: October 14, 2009; Revised: November 30, 2009; Published online: February 9, 2010
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.200900713.
Abstract: A highly linear-selective hydroformyla-
tion of 1-alkenes using formaldehyde without the
direct use of syngas is described. One rhodium(I)
complex catalyzes two processes in the overall hy-
droformylation of 1-alkenes using formaldehyde as
the syngas substitute to give hydroformylated alde-
hydes with excellent regioselectivities. A high regio-
selectivity (linear/branched=up to 98/2) and chemi-
cal yield (up to 95%) can be achieved by the simul-
taneous use of two types of phosphanes as ligands.
appeared regarding the use of paraformaldehyde in
hydroformylation reactions without the direct use of
syngas,[4,5,6] although they have not yet afforded syn-
thetically useful levels of productivity and regioselec-
tivity.[7] The method using formaldehyde consists of
two cooperative catalytic processes: the catalytic de-
carbonylation of formaldehyde to give a carbonyl
moiety and hydrogen, and their use in the subsequent
hydroformylation of alkenes. Regardless of the com-
plexity involved in the overall catalysis, the aforemen-
tioned reports have used only a single catalyst for the
two different processes. It is, however, possible that
two discrete catalysts could be used in the decarbony-
lation and hydroformylation processes. Herein we
wish to report on a highly selective, highly efficient
hydroformylation without the direct use of syngas by
using two different types of catalysts, which are suita-
Keywords: alkenes; formaldehyde; homogeneous
catalysis; hydroformylation; rhodium
Hydroformylation involves the addition of carbon ble for each process.
monoxide and hydrogen (CO/H2, syngas) to alkenes
In order to simultaneously generate two types of
in the presence of a transition metal catalyst to give rhodium catalysts in one reaction system, we adopted
homologous linear (l) and/or branched (b) alde- a strategy in which two different rhodium species are
hydes.[1] Because of its versatility, it represents syn- generated in situ by adding two phosphanes to a
thetic routes to various aldehydes that are useful in a single rhodium complex. For the success of the strat-
wide range of areas from fine and specialty chemicals egy, it is essential that the decarbonylation process is
production to pharmaceuticals synthesis.[2] Since the controlled by one phosphane more strongly than the
discovery of the reaction by Roelen in 1938,[3] consid- other and that the hydroformylation process is re-
erable efforts have been devoted to the development versed. BINAP was a promising candidate as an effec-
of new catalysts including new ligands and the utiliza- tive ligand for a rhodium catalyst in the decarbonyla-
tion of novel reaction media, such as the use of an tion process, because it is known that the rhodium
aqueous biphase, supercritical carbon dioxide, fluo- complex having BINAP is a more efficient catalyst
rous biphase, or ionic liquids, in attempts to improve for the decarbonylation of aldehydes than xantphos.[8]
the efficiency and selectivity (regio- and enantioselec- In addition, we also have recently reported that the
tivity) of the reaction. A recent innovation in this use of BINAP ligand facilitates a rhodium(I)-cata-
chemistry involves the development of a protocol lyzed CO gas-free carbonylation reaction using para-
using formaldehyde (HCHO) as a syngas substitute.
formaldehyde as the CO substitute.[5e] Towards a re-
ACHTUNGTRENNUNG
This promises to be an experimentally convenient al- gioselective hydroformylation process, we selected
ternative to the transformation. Some reports have xantphos, which is a representative ligand for the ex-
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299

Gouki Makado et al.
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tremely highly linear-selective hydroformylation cata-
lyzed by a rhodium complex.[9]
Next, we investigated the effect of BINAP or xant-
phos on the efficiency and selectivity of hydroformy-
We initially carried out the rhodium-catalyzed hy- lation using syngas. Using BINAP and/or xantphos as
droformylation reaction of 1-decene (1) with formalin ligand(s), the turnover frequency (TOF) in the early
under the catalytic conditions consisting of [RhCl- stage (1 h) of the hydroformylation of 1-decene (1)
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
BINAP (0.02 mmol), xantphos (0.02 mmol) in toluene pheric syngas (CO/H2 =1/1) at 908C for 1 h. When
(6 mL) at 908C for 20 h. The reaction proceeded with only BINAP was used as a ligand, linear (2-l) and
an extremely high regioselectivity to give the linear branched (2-b) aldehydes were formed in a ratio of 2-
aldehyde 2-l and the branched aldehyde 2-b in 80% l/2-b=65/35 (TOF=3.05 hÀ1). When only xantphos
yield in a ratio of 2-l/2-b=97/3, along with 18% of was used, the reaction proceeded much more smooth-
isomers of 1-decene (Table 1, entry 1).[10] In contrast, ly (TOF=19.9 hÀ1) to give these aldehydes with a
the use of BINAP or xantphos resulted in a low selec- high linear-selectivity of 2-l/2-b=93/7. Furthermore,
tivity or a low efficiency (entries 2 and 3). These re- the use of a combination of BINAP (0.01 mmol) and
sults indicate that, when a combination of BINAP xantphos (0.01 mmol) resulted in a slight decrease in
and xantphos was used, each phosphane functions the reaction rate (TOF=10.9 hÀ1), although the
uniquely and specifically (BINAP in the decarbonyla- linear-selectivity (2-l/2-b=94/6) remained the same.
tion and xantphos in the hydroformylation), to ach- These findings suggest that, for the simultaneous use
ieve the highly linear-selective hydroformylation, as of BINAP and xantphos, the rhodium species associ-
we expected.
ated with the xantphos ligand controls the regioselec-
tivity and the efficiency of the overall reaction.
Furthermore, 31P NMR experiments (Figure 1) im-
plied that two rhodium species participate in the reac-
Table 1. Effective use of a combination phosphanes in
Rh(I)-catalyzed hydroformylation of 1-decene 1 using for-
malin.[a]
tion of entry 1 in Table 1. A mixture of [RhClACHTUNGTRENNUNG(cod)]2,
(R)-BINAP, and xantphos (1:2:2) in toluene-d8 at
room temperature showed two signals at d=49.5 ppm
(d, JP,Rh =195 Hz) and 2.3 ppm (d, JP,Rh =91 Hz),
[11]
which correspond to [RhCl((R)-BINAP)]2
and
RhCl(cod)ACTHNUTRGNEUNG
G
(xantphos),[12] respectively. When 100
equivalents of formalin were added to the mixture,
these signals vanished, and two new signals appeared
at d=45.6 ppm (dd, JP, P =45 Hz, JP,Rh =160 Hz) and
20.9 ppm (d, JP,Rh =127 Hz), which are assigned to
RhCl(CO)((R)-BINAP)[11b]
AHCTUNGTRENNUNG
and
(xantphos),[9] respectively. These two rhodium species,
RhCl(CO)((R)-BINAP) and RhH(CO)2A(xantphos),
RhH(CO)2
CTHUNGTRENNUNG
would be directly involved in the linear-selective hy-
droformylation catalysis using formaldehyde in the
presence of both BINAP and xantphos.
From the above results, an acceptable reaction
pathway is as follows. Thus, the present reaction in-
cludes two catalytic processes: the decarbonylation of
formaldehyde leading to the formation of a carbonyl
moiety and H2 and subsequent hydroformylation
using the resulting carbonyl moiety and H2
(Scheme 1). Each process proceeds in a general
Entry
BINAP
xantphos
Conv.[b]
Yield (2-l/2-b)[b]
1
2
3
2 mol%
4 mol%
–
2 mol%
–
4 mol%
98%
85%
77%
80% (97/3)
85% (64/36)
8% (88/12)
À
manner. Oxidative addition of the aldehydic C H
[a]
Conditions: (1 mmol), formalin (37%; 0.37 mL,
1
bond in formaldehyde to Rh, followed by decarbony-
lative hydride migration and subsequent reductive
elimination, yields an Rh-CO species and H2. On the
other hand, addition of in situ generated Rh-H species
to 1-alkene and subsequent insertion of the carbonyl
formed earlier, followed by hydrogenolysis by H2,
afford the aldehyde with the regeneration of the Rh-
H species. These are taken up by two different rhodi-
5 mmol), [RhClACHTUNGTRENNUNG(cod)]2 (0.01 mmol), ligand (0.04 mmol),
toluene (6 mL), 908, 20 h.
[b]
Yields are the sum of 2-l and 2-b. Values in parentheses
are the ratios of 2-l/2-b. Conversions, yields, and ratios
were determined by GC. cod=1,5-cyclooctadiene;
BINAP=2,2’-bis(diphenylphosphino)-1,1’-binaphthyl;
xantphos=9,9-dimethyl-4,5-bis(diphenylphosphino)xan-
thene.
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Highly Linear-Selective Hydroformylation of 1-Alkenes using Formaldehyde
Figure 1. 31P NMR spectra of (a) a mixture of [RhCl
ACTHNUTRGEN(UNG cod)]2, (R)-BINAP, and xantphos (1:2:2) in toluene-d8 solution and (b)
the reaction of the mixture with formalin.
um species, [RhCl
(xantphos), which are formed from a mixture of the was possible to perform a similar transformation
catalyst precursors [RhCl(cod)]2, BINAP, and xant- more simply and conveniently. Furthermore, under
phos. From the known property that a rhodium cata- the catalytic conditions employed, even when para-
lyst associated with the BINAP ligand has a higher formaldehyde was used instead of formalin, 2-l regio-
ability to decarbonylate aldehydes,[5e,7] [RhCl- selectivity was observed, although with somewhat
(BINAP)]2 is responsible for the decarbonylation of lower efficiency (76% conversion) [Scheme 2(b)].
formaldehyde to yield RhCl(CO)(BINAP) and H2 Prolonging the reaction time to 40 h led to the regio-
[process (a)]. RhCl(cod)(xantphos) receives the re- selective formation of 2-l [Scheme 2(c)] in high yield.
sulting carbonyl and H2 “formally” from the process Reactions of other 1-alkenes also proceeded effi-
(a), to afford RhH(CO)2A
(xantphos),[13] and then cata- ciently with a high regioselectivity to yield the corre-
(cod)- pressurized synthesis gas.[14] Thus, using this system, it
ACHUTGTNRNE(NUG BINAP)]2 and RhClACHUTNGTRENNUGN
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
CTHUNGTRENNUNG
lyzes the hydroformylation of 1-decene [process (b)]. sponding linear aldehydes. In all cases, no side reac-
The finding obtained from the kinetic study suggests tion products, except for linear/branched aldehydes
the consideration that, for the combined use of and isomers of 1-alkenes, were detected. Under the
BINAP and xantphos, the rhodium species associated above standard conditions, the reaction of 1-octene
with xantphos controls the efficiency and regioselec- proceeded well to give nonanal (l) and 2-methylocta-
tivity of the hydroformylation process. The origin of nal (b) in 90% yield in a ratio of l/b=97/3 (Table 2,
the high linear-selectivity follows the mechanism re- entry 1). The present method using formalin tolerates
ported by van Leeuwen.[9] Consequently, the sequence not only simple alkenes, but also functionalized al-
of events leads to a highly regioselective hydroformy- kenes. Thus, for reactions of 1-alkenes having func-
lation without the direct use of syngas.
tional groups, such as an ether (entry 3), an ester
The best result was obtained when BIPHEP and (entry 5), a siloxy (entry 7), and a phthaloyl (entry 9)
Nixantphos were used instead of BINAP and xant- group, linear aldehydes were formed predominantly
phos: the yield of products increased dramatically to in ratios of l/b=94/6 up to 97/3, however substantial
95% GC yield without any detectable loss in linear- isomerization of the substrates to internal alkenes was
selectivity (2-l/2-b=97/3) [Scheme 2(a)]. The ob- observed. Importantly, during the course of the reac-
served high linear selectivity is almost the same as the tion, these functional groups in the remaining sub-
selectivity (l/b=98/2) in the Rh
ACHTUNGTRENN(UGN acac)(CO)2/nixant- strates and their isomers as well as in products (alde-
phos-catalyzed hydroformylation of 1-octene using hydes) remained intact. Regarding Scheme 1, when
Adv. Synth. Catal. 2010, 352, 299 – 304
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Gouki Makado et al.
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Scheme 1. Possible reaction pathway of hydroformylation using formaldehyde catalyzed by two different Rh species.
Scheme 2. Rh(I)-catalyzed highly linear-selective hydroformylation of 1-decene (1) with formaldehyde.
paraformaldehyde was used, instead of formalin, in formaldehyde as a syngas substitute. The high regiose-
all of the reactions, the regioselectivity remained ex- lectivity (linear/branched=up to 98/2) and efficiency
tremely high with a slightly slower consumption of (up to 95%) can be attributed to the simultaneous
substrates (entries 2, 4, 6, 8, and 10).
use of two types of phosphanes as ligands. Two rhodi-
In conclusion, we have reported on the highly um species associated with each phosphane separately
linear-selective hydroformylation of 1-alkenes using catalyze the decarbonylative decomposition of form-
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Adv. Synth. Catal. 2010, 352, 299 – 304

Highly Linear-Selective Hydroformylation of 1-Alkenes using Formaldehyde
Table 2. Highly linear-selective hydroformylation of 1-al-
Et2O=5/1) to afford the linear (Rf 0.71) and branched (Rf
0.70) aldehydes as colorless oils.
kenes using formaldehyde.[a]
Acknowledgements
This work was financially supported, in part, by a Grant-in-
Aid for Scientific Research on Priority Areas “Advanced Mo-
lecular Transformations of Carbon Resouces” from MEXT.
We acknowledge technical advice for analyzing the strcuture
of the rhodium complex, from Dr. Koji Itagaki and Prof. Dr.
Kotohiro Nomura. We also thank Ms. Yoshiko Nishikawa,
Mr. Fumio Asanoma, and Mr. Shouhei Katao for assistance
in obtaining HR-MS, elemental analyses, and X-ray data, re-
spectively.
Entry
R
HCHO[b] Conv.[c] Yield (l/b)[c]
À
C6H13
1
2
3
4
5
6
7
8
9
10
A
B
A
B
A
B
A
B
A
B
94%
76%
94%
71%
96%
90%
94%
77%
93%
80%
90% (97/3)
72% (97/3)
68% (97/3)
47% (96/4)
79% (97/3)
73% (98/2)
85% (97/3)
68% (97/3)
37% (94/6)
26% (92/8)
À
ACHTUNGTRENNUNG(CH2)7CH2OBn
À
ACHTUNGTRENNUNG(CH2)7CH2OPiv
À
ACHTUNGTRENNUNG(CH2)7CH2OTBS
References
À
ACHTUNGTRENNUNG(CH2)7CH2NPhth
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[a]
Conditions: 1-alkene (1 mmol), formaldehyde (5 mmol),
[RhCl(cod)]2 (0.01 mmol), BIPHEP (0.02 mmol), Nixant-
ACHTUNGTRENNUNG
phos (0.02 mmol), toluene (6 mL), 908C, 20 h.
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[b]
[c]
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Experimental Section
Typical Procedure for the Hydroformylation of 1-
Decene (1) Using Formalin
A 10-mL Schlenk tube containing a stirring bar was charged
with [RhCl
(cod)]2 (4.93 mg, 0.01 mmol), BIPHEP (10.5 mg,
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Adv. Synth. Catal. 2010, 352, 299 – 304
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303

Gouki Makado et al.
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À
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any anticipated product except for desired aldehydes
and isomers of 1-decene; for examples, aldol and
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[13] There are the following three possibilities for the origin
of carbonyl ligands in the formation of RhH(CO)2
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
a Rh-xantphos species traps free carbon monoxide
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