Hydroformylation of alkenes employing rhodium(I) complexes and a phosphine oxide ligand

Article abstract of DOI:10.1021/jo011093l

Following the facile synthesis of a novel phosphine oxide compound, (diphenylphosphinoyl)phenylmethanol (1), this compound was employed as a ligand in the rhodium-catalyzed hydroformylation of alkenes, with good conversions and regioselectivities. This ligand was partially resolved using an enzyme, and enantioselective hydroformylation was carried out with the addition of a rhodium(I) complex. The rhodium(I) complex containing ligand 1 was not isolated, although it was subjected to low-temperature NMR studies.

Full text of DOI:10.1021/jo011093l

the reaction of diphenylphosphine and benzaldehyde in
tetrahydrofuran (THF) (eq 1).
Hyd r ofor m yla tion of Alk en es Em p loyin g
Rh od iu m (I) Com p lexes a n d a P h osp h in e
Oxid e Liga n d
Helen J . Clark, Ruiping Wang, and Howard Alper*
Centre for Catalysis Research and Innovation,
Department of Chemistry, University of Ottawa,
Ottawa, Ontario K1N 6N5, Canada
This ligand was investigated for the hydroformylation
of several substrates catalyzed by chloro(dicarbonyl)-
rhodium(I) dimer, and the results are presented in Table
1. The hydroformylation of olefins bearing aryl substit-
uents was performed in chloroform, using a 2:1 ratio of
1/[Rh(CO)2Cl]2 and 1:1 CO/H2 at a total pressure of 600
to 1000 psi and usually at 40 °C. The ratio of substrate
to rhodium was 167/1.
halper@science.uottawa.ca
Received November 21, 2001
Abstr a ct: Following the facile synthesis of a novel phos-
phine oxide compound, (diphenylphosphinoyl)phenylmethanol
(1), this compound was employed as a ligand in the rhodium-
catalyzed hydroformylation of alkenes, with good conversions
and regioselectivities. This ligand was partially resolved
using an enzyme, and enantioselective hydroformylation was
carried out with the addition of a rhodium(I) complex. The
rhodium(I) complex containing ligand 1 was not isolated,
although it was subjected to low-temperature NMR studies.
The hydroformylation reaction of styrene proceeded
well at 40 °C and in good selectivity (96/4 branched/linear
aldehydes, Table 1, entry 1). However little conversion
occurred at 25 °C (Table 1, entry 2). Note that in the
absence of 1, there is virtually no reaction (Table 1, entry
3). Furthermore, significantly lower conversions, but
comparable selectivities (Table 1, entries 4 and 5) were
observed if ligand (1) was replaced by PPh3 and BzP(O)-
Ph2 under the same reaction conditions as entry 1. The
hydroformylation reaction, carried out with p-methyl-
styrene and p-chlorostyrene as substrates, also proceeded
in good conversion and regioselectivity (Table 1, entries
6 and 7). This catalyst system is particularly excellent
for phenyl vinyl ether (Table 1, entry 8) and for vinyl
benzoate with only the branched aldehyde formed in
quantitative yield (Table 1, entry 9). Although the
regioselectivity was good for vinyl acetate, the conversion
was only 31% (Table 1, entry 10). Nevertheless, the latter
result was superior to that obtained using PPh3 or BzP-
(O)Ph2 as the ligands (Table 1, entries 11 and 12).
The structure of the active species is not known. The
ligand could be coordinated to the rhodium solely through
the oxygen of the phosphine oxide or through both the
oxygen of the phosphine oxide and the hydroxyl oxygen.
It is also conceivable that the ligand may function as a
monodenate ligand, with more than one ligand molecule
coordinated to the rhodium. Low-temperature 31P NMR
suggests that the rhodium is in fact coordinating through
the oxygen of the phosphine oxide. All the signals are
singlets indicating no coupling to rhodium. A broad
singlet at δ 30.9 ppm, recorded at room temperature,
splits into two singlets, at δ 32.5 and 48.9, when the
spectrum is recorded at -70 °C. The 31P chemical shift
of the free ligand (1) in DMSO-d6 occurs at 33.2 ppm,
and thus, the chemical shift at 32.5 ppm (CDCl3) was
assigned to the phosphorus resonance in the uncoordi-
nated ligand (1). These results can be compared to those
of Grim and co-workers,13 who report a complex with
phosphine oxide coordination to (1,5-cyclooctadiene)-
[bis(diphenylphosphinoyl)(diphenylthiophosphinoyl)-
methanido]rhodium(I)-2-propanol. At room temperature,
they observe a broad singlet at δ 36.2. However at -50
As hydroformylation is one of the most extensively
studied homogeneous catalytic reactions, there has been
a large body of research into the ligands used for this
transformation. For example, there is increasing interest
in the use of mixed bidentate ligands in a variety of
metal-catalyzed processes, such as ligands containing
P-S, P-N, N-S, N-O, or P-O groups.1-8 Mixed phos-
phine-phosphine oxide ligands have been used for the
carbonylation of methanol,9 and mixed amino-phosphine
oxide complexes have also out performed their phosphine
analogues for the hydroformylation of aryl alkenes.10,11
However, the use of monodentate phosphine oxides as
ligands has received little attention. Indeed, it has been
thought that phosphine oxides decrease the rate of
hydroformylation and as such have not been further
investigated.12
We report the successful use of a novel phosphine oxide
ligand for olefin hydroformylation. The synthesis of this
ligand is extremely facile and the compound is easy to
handle due to its lack of sensitivity to air. (Diphenylphos-
phinoyl)phenylmethanol (1) is formed in 67% yield from
* To whom correspondence should be addressed. Tel: 613-562-5189.
Fax: 613-562-5871.
(1) Alcock, N. W.; Brown, J . M.; Hulmes, D. L. Tetrahedron:
Asymmetry 1993, 4, 743.
(2) Bader, A.; Linder, E. Coord. Chem. Rev. 1991, 108, 27.
(3) Baker, R. W.; Rea, S. O.; Sargent, M. V.; Schenkelaars, E. M.
C.; Skelton, B. W.; White, A. H. Tetrahedron: Asymmetry 1994, 5, 45.
(4) Chelucci, G.; Cabras, M. A.; Botteghi, C. Tetrahedron: Asymmetry
1994, 5, 299.
(5) Frost, C. G.; Williams, J . M. J . Tetrahedron: Asymmetry 1993,
4, 1785.
(6) Gladiali, S.; Pinna, L.; Arena, C. G.; Rotondo, E.; Faraone, F. J .
Mol. Catal. 1991, 66, 183.
(7) Gladiali, S.; Dore, A.; Fabbri, D. Tetrahedron: Asymmetry 1994,
5, 1143.
(8) Saleem, A. M.; Hodali, H. A. Synth. React. Inorg. Met-Org. Chem.
1990, 20, 9.
(9) Wegman, R. W.; Abatjoglou, A. G.; Harrison, A. M. J . Chem. Soc.,
Chem. Commun. 1987, 1891.
(10) Abu-Gnim, C.; Amer, I. J . Chem. Soc., Chem. Commun. 1994,
115.
(11) Basoli, C.; Botteghi, C.; Cabras, M. A.; Chelucci, G.; Marchetti,
M. J . Organomet. Chem. 1995, 488, C20.
(12) Abu-Gnim, C.; Amer, I. J . Organomet. Chem. 1996, 516, 235.
(13) Grim, S. O.; Kettler, P. B.; Thoden, J . B. Organometallics 1991,
10, 2399.
10.1021/jo011093l CCC: $22.00 © 2002 American Chemical Society
Published on Web 07/20/2002
6224
J . Org. Chem. 2002, 67, 6224-6225

TABLE 1. Hyd r ofor m yla tion of Olefin s Em p loyin g (Dip h en ylp h osp h in oyl)p h en ylm eth a n ol (1)
entry
ligand
substratea
T (°C)
pressureb (psi)
conversionc (%)
(% branched)d
1
2
3
4
5
6
7
8
9
1
1
styrene
styrene
styrene
sryrene
40
25
40
40
40
40
40
60
50
40
40
40
600
600
600
600
600
600
600
600
1000
600
600
600
77
8
96
97
95
95
96
97
95
97
>99
97
90
95
2.5
15
27
93
74
93
100
31
7
PPh3
BzP(O)Ph2
1
1
1
1
1
styrene
p-chlorostyrene
p-methoxystyrene
phenylvinyl ether
vinyl benzoate
vinyl acetate
vinyl acetate
vinyl acetate
10
11
12
PPh3
BzP(O)Ph2
26
a
All experiments were run with 2 mmol of substrate, 2 mL of chloroform, 0.012 mmol of [Rh(CO)2Cl]2, and 0.024 mmol of ligand for
20 h. Total pressure for a 1:1 mixture of CO and H2. c Determined by 1H NMR/GC. Determined by 1H NMR/GC, remainder of which
b
d
is linear aldehyde.
TABLE 2. En a n tioselective Hyd r ofor m yla tion
entry
substratea
T (°C)
pressureb (psi)
time (h)
conversionc (%)
(% branched)d
% ee of branched aldehydee
1f
2f
3g
4g
styrene
styrene
p-chlorostyrene
vinyl benzoate
40
60
50
50
600
800
600
20
20
20
20
15
22
96
99
95
93
95
97
25
35
23
52
1000
a
All experiments were run with 2 mmol of substrate, 2 mL of chloroform, 0.012 mmol of Rh[(CO)2Cl]2, and 0.024 mmol of ligand.
Total pressure always a 1:1 mixture of CO and H2. c Determined by 1H NMR/GC. Determined by 1H NMR/GC, remainder of which is
b
d
linear aldehyde. e Determined by the addition of chiral shift reagent into the 1H NMR sample or chiral GC. f Ligand was 18%
g
enantiomerically pure. Ligand was 23% enantiomerically pure.
stirred in a THF (10 mL) solution overnight. The solvent was
removed in vacuo, and the resulting off white solid was recrys-
°C, the singlet splits to give signals at δ 26.5 and 46.3,
similar to the data we observed. These results were
tallized in methanol affording a white crystalline solid (2.069 g,
attributed to the fast exchange between the coordination
67%): IR (KBr, cm-1) 3210, 3059, 1435, 1163, 722, 693; 1H NMR
of the phosphine oxide and then the decomplexation to
(200 MHz, DMSO-d6) δ 7.9-7.0 (m, 15H, ArH), δ 5.5 (d, J )
4.6, 1H, CH); 13C NMR (75 MHz, DMSO-d6) 138.1, 131.9 (d, J )
8.5 Hz), 131.6 (m), 131.3 (d, J ) 8.8 Hz), 128.3 (d, J ) 10.7 Hz),
128.1 (d, J ) 10.7 Hz), 127.7 (d, J ) 4.4 Hz), 127.5 (d, J ) 2.2
give the uncoordinated phosphine oxide. Nevertheless,
it is conceivable that the labile nature of this ligand
explains the excellent regioselectivity seen.
Hz), 127.4 (d, J ) 2.7 Hz), (ArC), 72.1 (d, J ) 86.4 Hz, CH); 31
P
The hydroxyphosphine oxide (1) contains a chiral
center. The resolution of this alcohol was carried out
using porcine pancreatic lipase in a transesterification
reaction with methyl propionate. This reaction did not
go to completion and therefore the enantiomerically pure
alcohol was not obtained, as some racemic alcohol was
always present. However, some optically active alcohol
with 18-23% ee was extracted from the mixture during
two experiments. The optical purity was determined by
a combination of chiral HPLC and optical rotation.
Several hydroformylation reactions were effected under
the same conditions as previously employed using race-
mic diphenylphosphinoyl)phenylmethanol (Table 2).
With styrene as the substrate, the conversions appear
to be lower than with the racemic ligand. However, with
both p-chlorostyrene and vinyl benzoate (Table 2, entries
3 and 4) the conversions and regioselectivity are compa-
rable to previous hydroformylation reactions. For vinyl
benzoate, the enantioselectivity (52%) observed displayed
is very encouraging considering the ligand employed is
of 23% ee.
NMR δ 33.2; electrospray MS calc. for C19H17O2P (M + H+) 309,
(2M + H+) 617.
Gen er a l Hyd r ofor m yla tion . The following is a typical
procedure: The catalyst was placed in a stainless steel autoclave
with a glass liner equipped with a stirring bar, under a nitrogen
atmosphere. The olefin (2 mmol), [Rh(CO)2Cl]2 (0.012 mmol), and
(diphenylphosphinoyl)phenylmethanol (0.024 mmol) were mixed
with chloroform (2 mL). The autoclave was purged three times
with carbon monoxide, to displace any air, and then charged with
a 1:1 ratio of carbon monoxide and hydrogen. The autoclave was
placed in an oil bath with sufficient silicone oil to cover the
majority of the autoclave and heated to the appropriate tem-
perature. After the reaction was complete, the contents of the
autoclave were cooled to room temperature, opened and then
passed through a small column of neutral alumina and washed
with chloroform. The analysis was carried out without removal
of solvent. Identical reaction conditions were employed using
0.024 mmol of benzyldiphenylphosphine oxide or triphenylphos-
phine as the ligand.
Tr a n sester ifica tion of (Dip h en ylp h osp h in oyl)p h en yl-
m eth a n ol. (Diphenylphosphinoyl)phenylmethanol (0.1 g, 0.325
mmol), methyl propionate (0.035 mL, 0.36 mmol), and porcine
pancreatic lipase (0.2 g) were added to diethyl ether (10 mL).
This suspension was stirred in a water bath at 30 °C for 3 days.
The mixture was then filtered to remove the enzyme and washed
with methanol and then ethanol. The washings were concen-
trated in vacuo to give a white solid.
In conclusion, (diphenylphosphinoyl)phenylmethanol
was prepared and used as a ligand for the rhodium-
catalyzed hydroformylation of aryl alkenes. This ligand
is not only readily synthesized, but air stable. It enables
one to attain aldehydes in high regioselectivity using
[Rh(CO2)Cl]2 as a catalyst.
The experimental data were the same as for the previous
compound.
Ack n ow led gm en t. We are grateful to the NSERC/
NRC research grants program for support of this
research.
Exp er im en ta l Section
(Dip h en ylp h osp h in oyl)p h en ylm eth a n ol. Benzaldehyde (1
mL, 10 mmol) and diphenylphosphine (1.75 mL, 10 mmol) were
J O011093L
J . Org. Chem, Vol. 67, No. 17, 2002 6225