Hydroformylation of internal olefins to linear aldehydes with novel rhodium catalysts

Article abstract of DOI:10.1002/(SICI)1521-3773(19990201)38:3<336::AID-ANIE336>3.0.CO;2-P

Unprecedented high activities and selectivities were observed in the hydroformylation of internal octenes to linear products using rhodium catalysts with rigid diphosphane ligands. Dibenzophosphole 1 and a phenoxaphosphane analogue with bite angles of 120 and 119°, respectively, are suited for this.

Full text of DOI:10.1002/(SICI)1521-3773(19990201)38:3<336::AID-ANIE336>3.0.CO;2-P

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[4] R. G. Pearson, Coord. Chem. Rev. 1990, 100, 403 ± 425.
[5] S. M. Azad, S. M. W. Bennett, S. M. Brown, J. Green, E. Sinn, C. M.
Topping, S. Woodward, J. Chem. Soc. Perkin Trans 1 1997, 687 ± 694.
[6] A. E. Shirk, D. F. Shriver, Inorg. Synth. 1977, 17, 45 ± 47.
[7] Data for structure 5 are given in the supporting information. BINOL
analogues are known, see a) M. Shibasaki, H. Sasai, T. Arai, Angew.
Chem. 1997, 109, 1290 ± 1310; Angew. Chem. Int. Ed. Engl. 1997, 36,
1237 ± 1256; b) T. Iida, N. Yamamoto, H. Sasai, M. Shibasaki, J. Am.
Chem. Soc. 1997, 119, 4783 ± 84; c) T. Iida, N. Yamamoto, S.
Matsunaga, H.-G. Woo, M. Shibasaki, Angew. Chem. 1998, 110,
2383 ± 2386; Angew. Chem. Int. Ed. 1998, 37, 2223 ± 2226.
[8] For related chemistry, see a) C. W. Lindsley, M. DiMare, Tetrahedron
Lett. 1994, 35, 5141 ± 5144; b) A. Arase, M. Hoshi, T. Yamaki, H.
Nakanishi, J. Chem. Soc. Chem. Commun. 1994, 855 ± 856.
[9] a) G. Giffels, C. Dreisbach, U. Kragl, M. Weigerding, H. Waldmann, C.
Wandrey, Angew. Chem. 1995, 107, 2165 ± 2166; Angew. Chem. Int. Ed.
Engl. 1995, 34, 2005 ± 2006; b) F. Almqvist, L. Torstensson, A.
Gudmundsson, T. Frejd, Angew. Chem. 1997, 109, 388 ± 389; Angew.
Chem. Int. Ed. Engl. 1997, 36, 376 ± 377.
weeks did not affect the ee value for the reduction of 1a,
neither did deliberate addition of water to the reaction (one
equivalent per Ga, to simulate impure ªwetº ketones).
The enantioselectivity in the reduction of 1a shows an
unusual temperature dependence: a maximum ee value is
attained at 20 to 158C, both the chemical yield and ee
value decrease steadily at temperatures below this range. At
788C an 18% yield of racemic alcohol is realized. One
explanation of this behavior is that transmetalation of 4 to 3
(X ˆ MTB dianion) is slow below 208C and that an achiral
catalytic process begins to compete. Support for this hypo-
thesis comes from the observation that added lithium
alkoxides do catalyze catecholborane reduction of 1a via
the borate 6.[8] The use of the MTB ligand is vital to the
reaction; LiGaH4 with either 1,1'-bi(2-naphthol) or 1,1'-bi(2-
thionaphthol) leads to low selectivities (3 ± 34% ee). The
probable causes are decomplexation of the chiral ligand by
catecholborane and poor lithium coordination. Both the
presence of 6 and removal of the chiral ligand may account,
in part, for the lower enantioselectivities encountered in some
recent titanium work.[9]
[10] a) Review: C. Girard, H. B. Kagan, Angew. Chem. 1998, 110, 3088 ±
3127; Angew. Chem. Int. Ed. 1998, 37, 2922 ± 2959; b) D. G. Black-
mond, J. Am. Chem. Soc. 1997, 119, 12934 ± 12937; c) D. Guillaneux,
S. H. Zhao, O. Samuel, D. Rainford, H. B. Kagan, J. Am. Chem. Soc.
1994, 116, 9430 ± 9439.
The solid-state structure of the pre-catalyst 5[7] is not
retained in solution during the catalysis. The new species
formed are currently still under investigation. However, the
absence of a nonlinear effect[10] in the reduction of 1a by 5
suggests that a mononuclear catalyst with a single active MTB
ligand is responsible for the enantioselection. In Noyoriꢁs
BINAL reagent[3] the (Ra)-ligand gives the (R)-alcohol
because of repulsion between the n electrons of the reagent
and the p electrons of the substrate. The similarity in the ee
value for the reduction of 1a ± d suggests a related electronic
control with 5, but steric factors cannot be ruled out.
Hydroformylation of Internal Olefins to Linear
Aldehydes with Novel Rhodium Catalysts**
Lars A. van der Veen, Paul C. J. Kamer, and
Piet W. N. M. van Leeuwen*
Hydroformylation is one of the worldꢁs largest homoge-
neously catalyzed processes in industry, which produces more
than six million tons of aldehydes and alcohols annually.[1]
Since linear aldehydes are the most desired products a key
issue in this process is the control of regiochemistry. High
selectivities in the hydroformylation of terminal alkenes have
been reported for both diphosphites and diphosphanes.[2]
Selective hydroformylation of internal alkenes, which is of great
interest in industry and in synthetic organic chemistry, on the
other hand is still a relatively unexplored terrain (Scheme 1).
Experimental Section
All operations were performed under argon. A solution of MTB (15 mg,
0.05 mmol) in THF (5 mL) was treated with LiGaH4 (100 mL of a 0.25m
solution in Et2O) and the mixture stirred (208C, 25 min). The reaction was
cooled to 208C and catecholborane (1.1 mL of a 1m THF solution,
1.1 mmol) and ketone (1.0 mmol) were added. The solution was stirred at
208C for 18 h (method A), or sealed and stored at 208C (method B;
158C and 4 mol% catalyst for 1d). Alternatively, the catecholborane and
ketone were added at 788C and the reaction mixture stirred as it warmed
to room temperature overnight (method C). Normal workup procedures
afforded the alcohols 2 as essentially single products (the ee values were
determined by gas chromatography on a chiral column (LIPODEX A or
CYCLODEX B) or the a-methoxy-a-(trifluoromethyl)phenyl acetate
analyzed for the alcohol of 1h).
Scheme 1. The hydroformylation of trans-4-octene to linear and branched
aldehydes.
Received: July 28, 1998 [Z12216IE]
German version: Angew. Chem. 1999, 111, 347 ± 349
Keywords: asymmetric reductions ´ gallium ´ hydrides ´
ketones
[*] Prof. Dr. P. W. N. M. van Leeuwen, L. A. van der Veen,
Dr. P. C. J. Kamer
Institute of Molecular Chemistry
University of Amsterdam
Nieuwe Achtergracht 166, 1018 WV Amsterdam (The Netherlands)
Fax: (‡31)20-525-6456
[1] a) Review: E. J. Corey, C. J. Helal, Angew. Chem. 1998, 110, 2092 ±
2118; Angew. Chem. Int. Ed. 1998, 37, 1987 ± 2012; b) E. J. Corey, R. K.
Bakshi, S. Shibata, C.-P. Chen, V. K. Singh, J. Am. Chem. Soc. 1987,
109, 7925 ± 7926.
E-mail: pwnm@anorg.chem.uva.nl
[**] This work was supported by SON/STW.
[2] Review: R. Noyori, S. Hashiguchi, Acc. Chem. Res. 1997, 30, 97 ± 102.
[3] R. Noyori, I. Tomino, Y. Tanimoto, M. Nishizawa, J. Am. Chem. Soc.
1984, 106, 6709 ± 6716.
Supporting information for this article is available on the WWW
under http://www.wiley-vch.de/home/angewandte/ or from the au-
thor.
336
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Angew. Chem. Int. Ed. 1999, 38, No. 3

COMMUNICATIONS
Very few rhodium catalysts have been reported that will
hydroformylate internal alkenes at acceptable rates, and even
fewer that will produce linear aldehydes preferentially.[3]
Considerable progress in this field has been made by using
bulky diphosphites as modifying ligands.[4] However, because
of the intrinsicly low long-term stability of phosphites the
development of new efficient catalysts for the hydroformyla-
tion of internal alkenes continues to be an important goal.
In our effort to develop ligands that induce high regiose-
lectivity in the rhodium-catalyzed hydroformylation, we have
reported on new diphosphanes with large bite angles.[2f] This
work and studies done by Casey and co-workers[2c, 5] showed
that high selectivities towards linear aldehydes can be obtained
with rigid diphosphanes with chelate bite angles close to 1208.
Herein we describe the synthesis of new dibenzophospholyl-
and phenoxaphosphanyl-substituted xanthene ligands 2b and
2c, and their high activity and selectivity in the rhodium-
catalyzed hydroformylation of 1-octene. More importantly,
2b and 2c exhibit an unprecedented high activity and
selectivity in the hydroformylation of trans-2- and -4-octene
Scheme 2. Synthesis of diphosphanes 2a ± c and the monophosphane 4.
a) nBuLi, THF, 1 h at 608C; b) Ph2PCl, 3 or 4, THF, 1 h at 608C then
16 h at 208C, 81% (2a), 67% (2b), or 75% (2c); c) nBuLi, TMEDA, Et2O/
hexanes (1/2), 1 h at 08C then 16 h at 208C; d) iPr2NPCl2, hexanes, 1 h at
608C then 16 h at 208C; e) PCl3, 16 h at reflux, 54%.
phanes known. Since large steric differences in the catalyst
complexes of the ligands 2b and 2c are not anticipated, the
higher activity of 2c relative to 2b might be ascribed to very
subtle effects in the bite angle or
electronic characteristics of the phos-
phorus heterocycles.
Although the high l:b ratios of
ligands 2b and 2c are in good agree-
ment with our earlier observations
that diphosphanes with natural bite
angles close to 1208 give very selec-
tive catalysts,[2f] the selectivity for the
formation of the linear aldehyde of
both 2b and 2c is considerably lower
than that of 2a. This is a consequence
of a dramatic increase in the rate of
isomerization of 1-octene to form
internal alkenes, which are not hydro-
Table 1. Hydroformylation of 1-octene.[a]
to linear nonanal. To the best of our knowledge diphosphanes
2b and 2c constitute the first rhodium catalysts with modified
phosphane groups for the selective linear hydroformylation of
internal olefins.
The diphosphanes 2a ± c were synthesized by dilithiation of
4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylxanthene 1 with n-
butyllithium in THF at 608C, followed by reaction with the
corresponding chlorophosphane (Scheme 2).[6] The natural
bite angles of 2a ± c are 110, 120, and 1198, respectively.[7] 9-
Ligand
Isomerization l:b[b,c]
[%][b]
Selectivity
[%][b,d]
TOF[e]
PPh3
2a
1.2
3.9
3.1
49
74
94
83
86
1880
250
360
2b
2c
16
13
65
68
1100
[a] Reactions were carried in a 180 mL stainless steel autoclave in toluene
at 808C under an atmosphere of CO/H2 (1:1) with an initial pressure of
20 bar, catalyst precursor: [Rh(CO)2(dipivaloylmethanoate)], [Rh] ˆ
1.0mm, Rh:P:1-octene ˆ 1:10:673. [b] Determined by GC with decane as
the internal standard. [c] l:b ratio includes all branched aldehydes.
[d] Selectivity for the linear aldehyde. [e] Turnover frequencies (TOF)
Chlorodibenzo[b, d]phosphole (3) was prepared from
a
literature procedure.[8] 10-Chlorophenoxaphosphane (4) was
obtained in 54% yield by dilithiation of diphenyl ether with n-
butyllithium and N,N,N',N'-tetramethylethylenediamine
(TMEDA) in diethyl ether/hexanes (1/1) at room temper-
ature, followed by reaction with diisopropylphosphoramidous
dichloride at 608C, and refluxing the resulting 10-(diiso-
propylamino)phenoxaphosphane in phosphorus trichloride.
The activity and selectivity of ligands 2a ± c were first tested
in the hydroformylation of 1-octene (Table 1). Under mild
reaction conditions the diphosphanes 2b and 2c both showed
a higher activity and a higher linear:branched (l:b) ratio
compared to the parent diphosphane 2a. The extraordinary
high activity of 2c places it among the most active diphos-
were calculated as (mol aldehyde)(mol catalyst) 1h at 20 ± 30% conver-
sion.
1
formylated as long as 1-octene is present. The reason why 2b
and 2c display such a high isomerization activity relative to 2a
is not completely clear yet, but we speculate that it could be
caused by the higher rigidity and the larger bite angles of the
former ligands.
The high activity of diphosphanes 2b and 2c, combined
with the very high l:b ratio and rate of isomerization that leads
to the internal olefins, prompted us also to test the ligands in
Angew. Chem. Int. Ed. 1999, 38, No. 3
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337

COMMUNICATIONS
Paulsen, E. W. Beuttenmueller, B. R. Proft, L. M. Petrovich, B. A.
Matter, D. R. Powell, J. Am. Chem. Soc. 1997, 119, 11817 ± 11825;
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[3] a) P. W. N. M. van Leeuwen, C. F. Roobeek, J. Organomet. Chem. 1983,
258, 343 ± 350; b) A. van Rooy, E. N. Orij, P. C. J. Kamer, P. W. N. M.
van Leeuwen, Organometallics 1995, 14, 34 ± 43; c) B. Breit, R. Winde,
K. Harms, J. Chem. Soc. Perkin Trans. 1 1997, 2681 ± 2682.
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C. B. Hansen (DSM, Du Pont), WO 97/33854, 1997 [Chem. Abstr. 1997,
127, 294939r].
the hydroformylation of simple internal alkenes of low
reactivity. A relatively high temperature and low pressure
were used to enhance the rate of isomerization and to prevent
hydroformylation of the internal alkenes. In the hydroformy-
lation of trans-2-octene both ligands 2b and 2c showed a high
activity and selectivity towards the formation of linear
nonanal (Table 2). The hydroformylation of 1-octene formed
Table 2. Hydroformylation of trans-2- and -4-octene.[a]
Ligand Substrate
t
Conversion l:b[d]
[%][b]
1-Nonanal TOF[d]
[%][c]
[h]
PPh3
2b
2c
PPh3
2b
2c
2-octene
2-octene
2-octene
4-octene
4-octene
4-octene
1.0
1.0
1.0
17
17
17
8.5
10
22
9.0
54
67
0.9
9.5
9.2
0.3
6.1
4.4
46
90
90
23
86
81
39
65
112
2.4
15
[5] C. P. Casey, L. M. Petrovich, J. Am. Chem. Soc. 1995, 117, 6007 ± 6014.
[6] All new compounds were fully characterized. See the supporting
information for the experimental details.
[7] C. P. Casey, G. T. Whiteker, Isr. J. Chem. 1990, 30, 299 ± 304.
[8] H. T. Teunissen, F. Bickelhaupt, Phosphor Sulphur Silicon 1996, 118,
309 ± 312.
20
[a] As Table 1, but at 1208C and with an initial pressure of CO/H2 (1/1) of
2 bar. [b] Determined by GC with decane as an internal standard.
[c] Percentage of linear nonanal in all products other than octenes.
[d] See Table 1.
in situ by isomerization was highly favored over the hydro-
formylation of the large excess of 2-octene, and no hydro-
genation was observed. The high selectivity of ligands 2b and
2c was even more pronounced in the hydroformylation of
trans-4-octene; selectivities in the formation of linear nonanal
still exceeded 80% although three consecutive double bond
isomerizations had to precede hydroformylation. From these
remarkable results it can be concluded that diphosphane
rhodium complexes can be very efficient for the selective
linear hydroformylation of internal alkenes, an area that
seemed hardly accessible. The high activity and selectivity of
diphosphanes 2b and 2c may open up a new range of
applications for hydroformylation catalyzed by diphosphane
rhodium complexes. One of the possible interesting industrial
applications could be the linear hydroformylation of ªRaffi-
nate 2º, a mixture of butenes that originates from steam
crackers.[1d]
a-Chloroalkylmagnesium Reagents of
>90%ee by Sulfoxide/Magnesium Exchange**
Reinhard W. Hoffmann* and Peter G. Nell
a-Heterosubstituted organometallic reagents such as 1 are
attractive chiral d1-synthons[1] provided that they have suffi-
cient configurational stability and that they can be generated
in high stereochemical purity (Scheme 1). The (a-alkoxy)-
Scheme 1. The organolithium compounds 1a ± h and the Grignard
reagents 2a ± h. Boc ˆ tert-butoxycarbonyl.
Received: August 17, 1998 [Z12298IE]
German version: Angew. Chem, 1999, 111, 349 ± 351
alkyllithium reagents 1a,b[2] and (a-amino)alkyllithium re-
agents 1c, d[3] are prominent examples. Reagents 1, in which
X is a heteroatom of the second row of the periodic table (see
1e,f) have much lower barriers to racemization.[4] Their
diminished configurational stability limits their use in stereo-
selective synthesis. Higher configurational stability may be
expected for the corresponding magnesium reagents 2, since
previous studies[5, 6] indicated compounds of the type 2h to be
configurationally stable on a macroscopic time scale at or
above 788C. We have therefore explored diastereoselective
and enantioselective routes to reagents of the type 2. We
Keywords: homogeneous catalysis
phosphorus heterocycles ´ rhodium
´ hydroformylations ´
[1] a) G. W. Parshall, Homogeneous Catalysis: The Applications and
Chemistry of Catalysis by Soluble Transition Metal Complexes, Wiley,
New York, 1980; b) C. A. Tolman, J. W. Faller in Homogeneous
Catalysis with Metal Phosphine Complexes (Ed.: L. H. Pignolet),
Plenum, New York, 1983, pp. 81 ± 109; c) M. Beller, B. Cornils, C. D.
Frohning, C. W. Kohlpaintner, J. Mol. Catal. A 1995, 104, 17 ± 85;
d) C. D. Frohning, C. W. Kohlpaintner in Applied Homogeneous
Catalysis with Organometallic Compounds: a comprehensive handbook
in two volumes, Vol. 1 (Eds.: B. Cornils, W. A. Herrmann), VCH,
Weinheim, New York, 1996, pp. 27 ± 104.
[2] a) G. J. H. Buisman, E. J. Vos, P. C. J. Kamer, P. W. N. M. van Leeuwen,
Tetrahedron: Asymmetry 1995, 6, 719 ± 738; b) A. van Rooy, P. C. J.
Kamer, P. W. N. M. van Leeuwen, K. Goubitz, J. Fraanje, N. Veldman,
A. L. Spek, Organometallics 1996, 15, 835 ± 847; c) C. P. Casey, G. T.
Whiteker, M. G. Melville, L. M. Petrovich, J. A. Gavney Jr., D. R.
Powell, J. Am. Chem. Soc. 1992, 114, 5535 ± 5543; d) C. P. Casey, E. L.
[*] Prof. Dr. R. W. Hoffmann, Dipl.-Chem. P. G. Nell
Fachbereich Chemie der Universität
Hans-Meerwein-Strasse, D-35032 Marburg (Germany)
Fax: (‡49)6421/28-8917
E-mail: RWHO@ps1515.chemie.uni-marburg.de
[**] This study was supported by the Deutsche Forschungsgemeinschaft
(SFB 260) and the Fonds der Chemischen Industrie. We thank Dr. K.
Harms for the crystal structure analysis.
338
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Angew. Chem. Int. Ed. 1999, 38, No. 3