A new, efficient, and in some cases highly regioselective water-soluble polymer rhodium catalyst for olefin hydroformylation

Article abstract of DOI:10.1021/ja973048u

A water-soluble complex Rh/PPA(Na⁺)/DPPEA 1 was obtained from poly(4- pentenoic acid) (PPA) and bis[2-(diphenylphosphino)ethyllamine (DPPEA). Complex 1 is a highly active catalyst for the hydroformylation of olefins. Some selectively for linear aldehydes was observed in the hydroformylation of aliphatic olefins, while high ratios of branched aldehydes resulted in the case of vinyl ethers. Complex 1 is also the first polymeric water-soluble metal complex which can catalyze the conversion of vinylarenes to 2- arylpropanals in a highly chemoselective and regioselective manner.

Full text of DOI:10.1021/ja973048u

1466
J. Am. Chem. Soc. 1998, 120, 1466-1468
A New, Efficient, and in Some Cases Highly Regioselective
Water-Soluble Polymer Rhodium Catalyst for Olefin
Hydroformylation
Abdelaziz Nait Ajjou and Howard Alper*
Contribution from the UniVersity of Ottawa, Department of Chemistry, 10 Marie Curie,
Ottawa, Ontario, Canada K1N 6N5
ReceiVed August 29, 1997
Abstract: A water-soluble complex Rh/PPA(Na+)/DPPEA 1 was obtained from poly(4-pentenoic acid) (PPA)
and bis[2-(diphenylphosphino)ethyl]amine (DPPEA). Complex 1 is a highly active catalyst for the
hydroformylation of olefins. Some selectivity for linear aldehydes was observed in the hydroformylation of
aliphatic olefins, while high ratios of branched aldehydes resulted in the case of vinyl ethers. Complex 1 is
also the first polymeric water-soluble metal complex which can catalyze the conversion of vinylarenes to
2-arylpropanals in a highly chemoselective and regioselective manner.
Introduction
are effective for the hydroformylation of olefins.8 The enhance-
ment of the catalytic activity was achieved by the addition of
water-soluble organic ligands such as P(Ph(SO3))3 and inorganic
salts which increase the concentration of the catalyst at the
interface.9 Among several new ligands with surfactant
structures,10a-d surface active phosphines,10b,c and poly(enolate-
co-vinyl alcohol-co-vinyl acetate) (PEVV),10d have shown high
activities for the hydroformylation of olefins. Recently, new
water-soluble phosphine ligands were easily prepared by reaction
of diphenylphosphine moieties, with coupling of triphenylphos-
phine moieties to water-soluble polymers.11 We report, herein,
the synthesis of a new water-soluble polymeric rhodium
complex and its application for the hydroformylation of higher
olefins especially vinylarenes.
Aqueous organometallic catalysis has recently become a very
active field of research.1 Processes using water as the solvent
are environmentally and economically attractive. Indeed, in
addition to the ease of catalyst separation from the products,
water is environmentally safe and inexpensive.
Water-soluble transition metal complexes have been used as
catalysts in several significant commercial processes.2 For
example, the water-soluble catalyst HRh(CO)(TPPTS)3
(TPPTS: trisodium tris(m-sulfonatophenyl)phosphine) is used
for the hydroformylation of propene.3 In the case of higher
olefins, the hydroformylation reactions are limited by the
solubility of the substrate in the aqueous phase where the
reaction is presumed to occur.4 To solve this problem, several
approaches have been taken to increase the rate of the hydro-
formylation reaction by improving the affinities between the
two phases. Surfactants5 and modified cyclodextrins6 as well
as polar solvents such as an alcohol7 were added in order to
enhance the reaction rates. Supported aqueous phase catalysts
Results and Discussion
(1) Synthesis of the Water-Soluble Rhodium Catalyst Rh/
PPA(Na+)/DPPEA 1. Poly(4-pentenoic acid) (PPA) (Mw )
4900, Mw/Mn ) 2.96) was prepared by the catalytic hydro-
carboxylation of 1,2-polybutadiene using Pd(OAc)2/DPPB/
HCOOH system (eq 1).12
(1) (a) Cornils, B.; Herrmann, W. A. Applied Homogeneous Catalysis
with Organometallic Compounds; VCH: Weinheim, Germany, 1996; Vol.
2, p 573. (b) Beller, M.; Cornils, B.; Frohning, C. D.; Kohlpainter, C. W.
J. Mol. Catal. 1995, 104, 17. (c) Herrmann, W. A.; Kohlpainter, C. W.
Angew. Chem., Int. Ed. Engl. 1993, 32, 1524. (d) Ungva´ry, F. Coord. Chem.
ReV. 1997, 160, 123. (e) Joo´, F.; Katho´, AÄ . J. Mol. Catal. 1997, 116, 3.
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(b) Cornils, B.; Wiebus, E. Chemtech 1995, 25, 33. (c) Cornils, B.; Konkol,
W.; Bach, H.; Daembkes, G.; Gick, W.; Wiebus, E.; Bahrmann, H. German
Patent, 3,415,968, 1985. (d) Mercier, C.; Mignani, G.; Aufrand, M.;
Allmang, G. Tetrahedron Lett. 1991, 32, 1433. (e) Mercier, C.; Chabardes,
P. Pure Appl. Chem. 1994, 66, 1509. (f) Morel, D.; Jenck, J. French Patent,
2,550,202, 1982. (g) Varre, C.; Desbois, M.; Nouvel, J. French Patent,
2,561,650, 1985. (h) Kuntz, E. German Patent, 2,627,354, 1976. (i) Kuntz,
E. U.S. Patent, 4,248,802, 1981.
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S0002-7863(97)03048-5 CCC: $15.00 © 1998 American Chemical Society
Published on Web 02/07/1998

Water-Soluble Polymer Rh Catalyst for Olefin Hydroformylation
J. Am. Chem. Soc., Vol. 120, No. 7, 1998 1467
Table 1. Hydroformylation of Aliphatic Olefins Using
Scheme 1
Water-Soluble Rh/PPA(Na+)/DPPEA as the Catalysta
entry
substrate
1-dodecene
1-dodecene
1-octene
4-vinylcyclohexene
n-butylvinyl ether
time (h) convn % selectivityb % L/Bc
1
2
3
4
5
1.5
16
16
4
45
100
100
21
40d
53d
2.9
2
2
5
60e
96
16
16
25
17
>99
>99
0.2
B only
6f phenyl vinyl ether
a Reaction conditions: substrate (10 mmol), Rh/PPA(Na+)/DPPEA
(50 mg, 0.015 mmol of Rh) in 3 mL of water, CO/H2 (1/1) 600 psi, 90
°C. b Selectivity for aldehydes. c Molar ratio of linear (L) to branched
aldehyde (B) as determined by 1H NMR. d The other product was
2-dodecene. e The other product was 2-octene f The reaction was
performed using 2 mmol of phenyl vinyl ether in the presence of Rh/
PPA(Na+)/DPPEA (10 mg, 0.003 mmol of Rh).
energies Rh 3d3/2 and Rh 3d5/2 at 313.5 and 308.5 eV,
respectively. The full width at half-maximum (fwhm) of Rh
3d5/2 is ∆1/2 ) 3 eV. These values, in agreement with the ESCA
data for Rh(I) supported catalysts,14 show that the rhodium in
the catalyst 1 is in the monovalent state.
The phosphorus content was determined by elemental analysis
and corresponded to 1.8% (0.58 mmol of phosphorus per gram
of 1), while absorption atomic spectroscopy (AAS) gave the
rhodium content as 3.19% (0.3 mmol of rhodium per gram of
1) (P/Rh ) 1.93).
Bis[2-(diphenylphosphino)ethyl]amine (DPPEA)13 was acy-
lated with PPA using dicyclohexylcarbodiimide (DCC) as the
coupling agent in THF. The resulting PPA/DPPEA ligand was
characterized by 31P NMR which shows the presence of two
signals at d ) -20.05 and -21.10 ppm. The splitting observed,
consistent with occurrence of the acylation reaction (31P NMR
spectrum of HCl‚NH(CH2CH2PPh2)2 shows only one signal at
d ) -18 ppm), is a consequence of slow rotation about the
amide bond.13d PPA/DPPEA was reacted, in THF, with the
rhodium dimer [Rh(COD)Cl]2 to give the polymeric complex
Rh/PPA/DPPEA with an average molecular weight of 7712 and
a polydispersity of 3.1. After the addition of aqueous NaHCO3
followed by ethyl acetate, the reaction mixture separated into
two phases, in which the aqueous phase became yellow while
the organic phase changed from yellow to colorless indicating
that the rhodium complex was transferred to the aqueous phase.
(2) Hydroformylation of Olefins Catalyzed by Rh/PPA-
(Na+)/DPPEA 1. The hydroformylation of neat 1-dodecene
catalyzed by the water-soluble complex 1 at 90 °C under 600
psi of CO/H2 (CO/H2 ) 1/1) for 1.5 h resulted in 45%
conversion of the substrate and 40% selectivity for hydroformy-
lation with a 2.9/1.0 ratio of linear to branched aldehyde (Table
1, entry 1) and a turnover frequency of 80 mol/mol(Rh)/h. These
data indicate that 1 is as active and selective as the water-soluble
complex Rh/PEVV.10d The increase of reaction time to 16 h
led to full conversion and 53% selectivity for the aldehydes
with L/B ) 2 (Table 1, entry 2). The catalyst gave the same
activity and selectivity for three cycles, and the analysis of the
organic phase by atomic absorption indicated that no rhodium
was leached from the aqueous to the organic phase. The
hydroformylation of 1-octene, under the same conditions,
afforded similar results (Table 1, entry 3), while 4-vinylcyclo-
hexene gave the aldehydes in 21% conversion and 96%
selectivity with L/B ratio of 5 (Table 1, entry 4), the internal
double bond being inert. Branched aldehydes were obtained
as the major or only product in the case of vinyl ethers. While
n-butyl vinyl ether gave the aldehydes in 25% conversion and
a B/L molar ratio of 5, only the branched aldehyde was formed
in the case of phenyl vinyl ether although the conversion of the
substrate was low (Table 1, entries 5 and 6). The increase of
reaction time or the amount of the catalyst, in the case of phenyl
vinyl ether, resulted in the decomposition and polymerization
of the substrate, and no improvement in the yield of 2-phenoxy-
propanal was observed.
1
This is further supported by H and 31P NMR analyses of the
organic phase after evaporation, which did not show any traces
of phosphine ligand. After evaporation of water to dryness,
the water-soluble complex thus obtained (Rh/PPA(Na+)/DP-
PEA; 1 (Scheme 1) was characterized using different techniques.
The 31P NMR (D2O) spectrum of 1 displays a new broad
signal at d ) +20 ppm (94%) indicating that the complexation
reaction occurred. Another small signal was observed at d )
+32 ppm (6%) and was due to the corresponding phosphine
oxide. The broadening of the signals due to the physical
properties of this material limits the information (i.e., coupling
constants) assignably by this method. The 13C NMR (D2O)
spectrum of 1 did not show any signal characteristic of 1,5-
cyclooctadiene. However, it exhibits the signal of the aromatic
carbons centered at 130 ppm, the amide signal at 160 ppm, and
the carbonyl signals at 180 and 182 ppm. The small signal at
180 ppm is attributed to the carboxylate groups which are,
probably, coordinating to the rhodium atom, while the signal
at 182 ppm is assigned to the sodium carboxylate groups (the
13C NMR spectra of the polyacid (PPA) and its sodium salt
show the carbonyl signals at 175 and 182 ppm, respectively).
The X-ray photoelectron spectrum for the rhodium in the
catalyst 1 shows a well-resolved spin doublet with binding
When styrene was hydroformylated under the same conditions
as for 1-dodecene (except the reaction temperature was 70 °C),
aldehydes were obtained in 98% selectivity with 13% conversion
of styrene after 2 h, 2-phenylpropanal being the major aldehyde
(B/L ) 93/7) (Table 2, entry 1). The increase of the reaction
time to 16 h led to full conversion of starting material with
B/L ) 95/5 (Table 2, entry 2). This interesting result proves
that the water-soluble catalyst Rh/PPA(Na+)/DPPEA is more
active and much more regioselective than the water-soluble
system Rh-PEVV which gave very low conversion of styrene10d
and Rh(acac)(CO)2/TPPTS or Rh(acac)(CO)2/PR[(CH2)8C6H4-
(12) Nait Ajjou A.; Alper, H. Macromolecules 1996, 29, 1784.
(13) (a) Sacconi, L.; Morassi, R. J. Chem. Soc. A 1968, 2997. (b) Wilson,
M. E.; Nozzo, R. G.; Whitesides, G. M. J. Am. Chem. Soc. 1978, 100,
2269. (c) Nuzzo, R. G.; Feilter, D.; Whitesides, G. M. J. Am. Chem. Soc.
1979, 101, 3683. (d) Nuzzo, R. G.; Haynie, S. L.; Wilson, M. E.; Whitesides,
G. M. J. Org. Chem. 1981, 46, 2861.
(14) (a) Andersson, S. L. T.; Watters, K. L.; Howe, R. F. J. Catal. 1981,
69, 212. (b) Andersson, S. L. T.; Scurrell, M. S. J. Catal. 1981, 71, 233.
(c) Okamoto, Y.; Ishida, N.; Imanaka, T.; Teranishi, S. J. Catal. 1979, 58,
82.

1468 J. Am. Chem. Soc., Vol. 120, No. 7, 1998
Ajjou and Alper
Table 2. Hydroformylation of Vinyl Arenes Using Water-Soluble
Molecular weights and molecular weight distributions were measured
at 45 °C by gel permeation chromatography (Waters high-pressure
instrument Model 510 pump), using a series of 10 microns particle
size µ.Styragel Columns HT 3, HT 4, and HT 5 with the effective
molecular weight ranges of 500-30 000; 5 000-600 000; and 50 000
to 4 × 106, respectively, and a differential refractometer (Model 410).
Tetrahydrofuran was used as eluant at a flow rate of 1 mL/min, and a
sample concentration of 1 mg/mL was used. Polybutadiene narrow
standards were used for calibration.
Synthesis of Rh/PPA(Na+)/DPPEA, 1. Preparation of Bis[(2-
diphenylphosphino)ethyl]amine. Bis[(2-diphenylphosphino)ethyl]-
amine was prepared from bis(2-chloroethyl)amine using a literature
method.13a The compound was purified as an air-stable hydrochloride
after recrystallization from acetonitrile.13c,d Before the acylation
reaction, the amine hydrochloride was dissolved in degassed methylene
chloride and then treated with a degassed aqueous solution containing
a stoichiometric amount of sodium hydroxide. The organic phase was
dried (MgSO4) and then evaporated to yield the free amine which was
kept under nitrogen.
Preparation of Rh/PPA(Na+)/DPPEA. To a solution of polyacid
(PPA) (2 g, equivalent to 20 mmol of CO2H groups) in dry THF (50
mL) was added 1,3-dicyclohexylcarbodiimide (DCC) (577 mg, 2.8
mmol) and then a solution of HN(CH2CH2PPh2)2 (884 mg, 2 mmol) in
dry THF (20 mL) (N2 atm). The reaction mixture was stirred at room
temperature for 24 h, the volume of the mixture was then reduced to
20 mL (rotary evaporation), and dicyclohexylurea (DHU) was precipi-
tated and removed by filtration under nitrogen. The filtrate was then
evaporated affording the phosphinated polyacid (PPA/DPPEA) which
was analyzed by 31P NMR. PPA/DPPEA ligand was dissolved in THF
(50 mL) under N2 and a solution of freshly16 prepared [Rh(COD)Cl]2
(493 mg, 1 mmol), in THF (20 mL) was added by syringe. The yellow
solution was stirred at room temperature for 24 h. An aqueous degassed
solution of NaHCO3 (1.5 g, 18 mmol) was added followed by ethyl
acetate (50 mL). After 30 min, the mixture consisted of a yellow
aqueous solution and colorless organic phase. The former phase was
evaporated to dryness to give the water-soluble rhodium complex (Rh/
PPA(Na+)/DPPEA, 1) as a yellow powder. The organic phase was
also evaporated and analyzed by 1H and 31P NMR which did not show
any traces of phosphine ligand.
Rh/PPA(Na+)/DPPEA as the Catalysta
time convn selectivityb isolated
entry
substrate
styrene
styrene
p-methoxystyrene
p-methylstyrene
p-bromostyrene
p-fluorostyrene
(h)
%
%
yields % B/Lc
1
2
3
4
5
6
2
16
24
24
24
24
13
100
100
100
100
100
100
98
98
97
93/7
98
94
96
99
98
98
95/5
88/12
92/8
95/5
94/6
96/4
98
>99
>99
>99
7d 2-vinylnaphthalene 24
a Reaction conditions: substrate (10 mmol), Rh/PPA(Na+)/DPPEA
(50 mg, 0.015 mmol of Rh) in 3 mL of water, CO/H (1/1) 600 psi, 70
°C. b Selectivity for aldehydes. c Molar ratio of branched (B) to linear
1
aldehyde (L) as determined by H NMR. d THF (3 mL) was added in
order to dissolve 2-vinylnaphthalene.
p-SO3Na]2, which afforded the products in B/L ratios ranging
from 66/34 to 73/27.10b This system is also more active and
appreciably more regiselective than the supported aqueous phase
catalyst8e and shows comparable regioselectivity with some
homogeneous systems such as Rh(cod)(η6-PhBPh3)15 and [Rh-
(NBD)(L-L)]BF4 where L-L is 1,2-bis[bis(pentafluorophenyl)-
phosphino]ethane.16 The generality of Rh/PPA(Na+)/DPPEA
activity and regioselectivity was tested using a variety of
substituted styrenes and 2-vinylnaphthalene (Table 2, entries
3-7). These results demonstrate the high activity of the catalyst
(full conversion in all the cases after 24 h) and excellent
regioselectivity with B/L ratios which range from 92/8 to 96/4,
except in the case of p-methoxystyrene where B/L ) 88/12.
To our knowledge, this is the first highly active polymeric water-
soluble catalyst which convertes vinylarenes to the correspond-
ing 2-arylpropanals in a highly regioselective manner.
Conclusions
The water-soluble complex Rh/PPA(Na+)/DPPEA is a new,
highly active catalyst for the hydroformylation of olefins and
constitutes the first polymeric water-soluble catalyst leading to
2-arylpropanals in a highly regioselective manner.
Catalytic Hydroformylation Procedure. In a 45 mL autoclave
equipped with a glass liner containing a stirring bar was placed an
aqueous solution of Rh/PPA(Na+)/DPPEA (10-50 mg, 0.003-0.015
mmol of Rh) and the olefin (2-10 mmol) (in the case of 2-vinylnaph-
thalene, 3 mL of THF were added to dissolve the substrate). The
autoclave was flushed three times with carbon monoxide and pressur-
ized to 400 psi, and then hydrogen was introduced up to a total pressure
of 600 psi. The reactor was then placed in an oil bath at the desired
reaction temperature for the required reaction time (see Tables 1 and
2). The autoclave was cooled to room temperature, excess CO/H2 was
released, and the organic phase was separated from the aqueous phase,
Experimental Section
Materials. All olefins were purchased from Aldrich Chemical Co.
and used without further purification.
[Rh(COD)Cl]2 was prepared according to the literature method.17
Solvents were dried and distilled prior to use by known methods.
Instruments. IR spectra were recorded using a Bomem MB100-
C15 (FT-IR) instrument. 1H, 31P, and 13C NMR spectral determinations
were made on either a Varian Gemini 200 or Bruker 500 MHz
spectrometer using D2O and CDCl3 as the solvents. Phosphorus
chemical shifts are relative to external 85% H3PO4.
1
diluted with diethyl ether, dried (MgSO4), and then analyzed by H
The rhodium content of the catalysts was obtained by atomic
absorption spectroscopy (AAS), using a Varian Spectr. Plus 250.
X-ray photoelectron spectroscopy (XPS) measurements were ob-
tained using Phi 5500 system instrument with MgKa radiation (1253.6
eV). The binding energies for Rh were referenced to carbon (1s )
284.5 eV).
NMR spectroscopy after the solvent was evaporated. The isolated
yields were obtained after purification by silica gel chromatography
using 9/1 petroleum ether/ethyl acetate as the eluant (under N2) and
then analyzed by NMR.
Acknowledgment. We are indebted to the Natural Sciences
and Engineering Research Council of Canada for financial
support of this research.
(15) Amer, I.; Alper, H. J. Am. Chem. Soc. 1990, 112, 3674.
(16) Chan, A. S. C.; Pai, C.-C.; Yang, T.-K.; Chen, S.-M. J. Chem. Soc.,
Chem. Commun. 1995, 2031.
(17) Giordano, G.; Crabtree, R. H. Inorganic Syntheses; John Wiley &
Sons: New York, 1979; Collect. vol. 19.
JA973048U