A novel water-soluble rhodium-poly(enolate-co-vinyl alcohol-co-vinyl acetate) catalyst for the hydroformylation of olefins

Article abstract of DOI:10.1021/ja9623875

The water-soluble polymer, poly(enolate-co-vinyl alcohol-co-vinyl acetate) (PEVV), prepared by controlled oxidation of poly(vinyl alcohol-co-vinyl acetate), is a valuable ligand for the rhodium biphasic catalytic hydroformylation of olefins. The average turnover frequency for the catalytic hydroformylation of 1-octene was 5.46 x 10^-5 kmol (kg(Rh)s)^-1 at 90°C, and that of 1-dodecene was 2.36 x 10^-4 kmol (kg(Rh)s)^-1 at 60°C. Selective hydroformylation of styrene and its derivatives gave up to 97% of branched-chain aldehyde using Rh-PEVV under biphasic reaction conditions but at low conversions.

Full text of DOI:10.1021/ja9623875

J. Am. Chem. Soc. 1997, 119, 893-895
893
A Novel Water-Soluble Rhodium-Poly(enolate-co-vinyl
alcohol-co-vinyl acetate) Catalyst for the Hydroformylation of
Olefins
Jinhua Chen and Howard Alper*
Contribution from the Department of Chemistry, UniVersity of Ottawa, 10 Marie Curie PriVate,
Ottawa, Ontario, Canada K1N 6N5
ReceiVed July 11, 1996X
Abstract: The water-soluble polymer, poly(enolate-co-vinyl alcohol-co-vinyl acetate) (PEVV), prepared by controlled
oxidation of poly(vinyl alcohol-co-vinyl acetate), is a valuable ligand for the rhodium biphasic catalytic
hydroformylation of olefins. The average turnover frequency for the catalytic hydroformylation of 1-octene was
5.46 × 10-5 kmol (kg(Rh)s)-1 at 90 °C, and that of 1-dodecene was 2.36 × 10-4 kmol (kg(Rh) s)-1 at 60 °C.
Selective hydroformylation of styrene and its derivatives gave up to 97% of branched-chain aldehyde using Rh-
PEVV under biphasic reaction conditions but at low conversions.
Homogeneous catalysis has many advantages over hetero-
geneous catalysis.1 However, the recovery of homogeneous
catalysts from high-boiling products is difficult. The idea of
biphasic catalysis, which simplifies the separation of catalysts
from products by decantation, has attracted great attention in
recent years.2-6 Biphasic catalysis relies on the transfer of
organic substrates into the aqueous phase containing the catalyst.
The reaction rate could be reduced to such an extent that it
becomes unacceptable when the solubility of the substrates in
the aqueous phase is low, preventing adequate transfer of organic
substrates into the aqueous catalytic phase or at the phase
boundary.3 Therefore, studies have focused on improving the
affinities between the two phases.2,3 The addition of cosolvents,
such as alcoholic solvents, surfactants, and modified cyclodex-
trins, to enhance mutual solubility or mobility of the components
across the phase boundary can increase the reaction rate by more
than 10 times.2-5 Addition of water-soluble organic ligands,
such as P(Ph(SO3))3, and inorganic salts to increase the
concentration of the catalyst to the interface enhances the
catalytic reactivity as well.2-5 Extensive studies have been
undertaken to improve the ligands for these reactions. One
example is the use of a catalyst bearing partially fluorinated
“ponytail” ligands bound via phosphorus in a fluorous biphasic
system.7 The fluorous biphasic system becomes a one-phase
system by increasing the temperature.7 A similar idea for “smart
ligands” has been reported for biphasic hydrogenation.8 Re-
cently, ligands with surfactant structures, such as Ph2P(CH2)2-
C(O)NHC(CH3)2CH2SO3Li, P[(CH2)nC6H4SO3Na]3, P[C6H4-
(CH2)nC6H4SO3Na]3, (menthyl)P[(CH2)8C6H4-p-SO3Na]2, and
Ph2P(CH2)nSO3Na, have been used in catalytic hydroformyla-
tion.9 These ligands are superior to P(C6H4-p-SO3Na)3 (TPPTS)
for the catalytic hydroformylation of olefins.9 As the structure
of the surfactant ligands implies, the lipophilic phosphine ligand
coordinated to the catalytic active center is concentrated close
to the interface while the hydrophilic part of the component
aids in the solubilization of the catalyst into the aqueous solution.
This concept encouraged us to develop a water-soluble, polymer-
anchored, rhodium catalyst having a structure of a lipophilic
rhodium center and a hydrophilic long chain for the catalytic
hydroformylation of olefins. Such a catalyst, with the noted
features, could offer significant advantages over conventional
ligands in terms of regioselectivity, reactivity, and separation
of reaction mixtures. The chemical modifications of polymers
have been used to prepare polymers with various functional
groups.10 Therefore, a polymer composed of both lipophilic
and hydrophilic structures, such as lipophilic functionality
grafted polyvinyl alcohol (PVA), may be ideal for such a
purpose.
The controlled oxidation of PVA using sodium hypochlorite
has been reported to afford lipophilic poly(methylene ketone)
(PMK).11 Under basic conditions, tautomerization of PMK gave
the enolate which chelated metal ions such as nickel.11 Thus,
oxidation of PVA affords poly(vinyl alcohol-co-methylene
ketone) composed of both lipophilic and hydrophilic components
of methylene ketone and vinyl alcohol. The strong chelating
ability of the PMK enolate results in a rhodium complex which
can serve as a biphasic hydroformylation catalyst precursor,
while the unoxidized hydroxyl groups promote the dissolution
of the catalyst in aqueous solution.
Results and Discussion
(1) Preparation of Rhodium-Poly(enolate-co-vinyl alcohol-
co-vinyl acetate) (Rh-PEVV) Complexes. Oxidation of
secondary alcohols with NaOCl affords ketones in high yields.12
X Abstract published in AdVance ACS Abstracts, November 15, 1996.
(1) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.; John
Wiley: New York, 1992.
(2) Chaudhari, R. V.; Bhanage, B. M.; Deshpande, R. M.; Delmas, H.
Nature 1995, 373, 501.
(3) Cornils, B. Angew. Chem., Int. Ed. Engl. 1995, 34, 1575.
(4) Monteil, F.; Queau, R.; Kalck, P. J. Organomet. Chem. 1994, 480,
177.
(5) (a) Beller, M.; Cornils, B.; Frohning, C. D.; Kohlpaintner, C. W. J.
Mol. Catal. 1995, 104, 17 and references therein. (b) Cornils, B.; Kuntz,
E. G. J. Organomet. Chem. 1995, 502, 177.
(9) (a) Fremy, G.; Castanet, Y.; Grzybek, R.; Monflier, E.; Mortreux,
A.; Trzeciak, A. M.; Ziolkowski, J. J. J. Organomet. Chem. 1995, 505, 11.
(b) Burtik, T.; Bartik, B.; Hanson, B. E. J. Mol. Catal. 1994, 88, 43 (c)
Fell, B.; Papadogianakis, G. J. Prakt. Chem. 1994, 7, 591. (d) Abatjoglou,
A. G. U.S. Pat. 5180854, 1993. (e) Bartik, T.; Ding, H.; Bartik, B.; Hanson,
B. E. J. Mol. Catal. 1995, 98, 117.
(10) MacGrath, M. D.; Sall, E. D.; Tremont, S. J. Chem. ReV. 1995, 95,
381 and references therein.
(6) Kalck, P.; Monteil, F. AdV. Organomet. Chem. 1992, 34, 219.
(7) Horvath, I. T.; Rabai, J. Science 1994, 266, 72.
(8) Bergbreiter, D. E.; Zhang, L.; Mariagnanam, V. M. J. Am. Chem.
Soc. 1993, 115, 9295.
(11) Huang, S. J.; Wang, I.-F.; Quinga, E. In Modification of Polymers;
Canahes, C. E., Moore, J. E., Jr., Eds.; Plenum Press: New York, 1983; p
75.
(12) Nwaukwa, S. O.; Keehn, P. M. Tetrahedron Lett. 1982, 23, 35.
S0002-7863(96)02387-6 CCC: $14.00 © 1997 American Chemical Society

894 J. Am. Chem. Soc., Vol. 119, No. 5, 1997
Chen and Alper
Table 1. 13C NMR Chemical Shifts for P(VA-co-VAc), Its
Oxidized Product, PEVV, and Rh-PEVV (DMSO-d6, ppm)
Table 3. Catalytic Hydroformylation of 1-Octene Using Different
Catalyst Precursors Under the Same Reaction Conditionsa
P(VA-co-VAc) P(MK-co-VA-co-VAc)
PEVV
Rh-PEVV
conversion (%)
(CHO selectivity)
entry
catalyst
L/Bb
206.9; 204.9
207.2, 204.9, 207.9, 204.2
1
2
3
RhCl3
<1
1.00
1.00
1.14
193.2
169.9
159.5
100.6, 98.2
69-62
51-46
20.7
174.4, 173.9
169.7
165.8
RhCl3 + P(VA-co-VAc)
<1
169.7
169.7
Rh-PEVVc
49 (98)
100.4
66.7
51-44
20.7
98.4
a Reaction conditions: H2/CO, 1:1, 41.4 bar, 40 °C, 22 h, [Rh]/n-
1-octene ) 0.2 mol %. b 1-Nonanal/2-methyloctanal ratio (L/B ) linear
to branched) determined by NMR spectroscopy. c Reaction time of 28
h.
66.7
45.8
20.7
69-62
51-46
21.6; 20.8
Table 4. Catalytic Hydroformylation of Aliphatic Olefins Using
Rh-PEVV as the Catalyst Precursora
Table 2. Molecular Weight Data for P(MK-co-VA-co-VAc) at
Different Conversions
aldehyde
conversion selectivity
polymer
conversion (%)
Mw
Mn
Mw/Mn
t
1
2
3
20
31
48
7380
7353
7255
3120
3145
2961
2.37
2.34
2.45
entry
substrate
(h)
(%)
(%)
L/B
1
2
3
4
5
6
7
8
1-octeneb
22
4
1.5
1.5
1.5
4
89
70
38
25
43
14
24
23
67g
70h
44g
28g
28g
85g
100
93
2.45
1.95
2.69
2.96
2.50
1.61
5.65
L only
1-dodecenec
1-octene
1-octened
Scheme 1. Complex of Rh-PEVV
1-octenee
1-octenec
4-vinyl cyclohexenef
methyl 3,3-dimethyl-
4-pentenoate
n-butyl vinyl ether
2
2
OH
O
O
OH
O
O
O
Rh
Rh
O
9
2
8
5
12
100
92
0.35
0.41
10 n-butyl vinyl ether
This reaction has been applied to the oxidation of PVA to give
PMK.11 Controlled oxidation of poly(vinyl alcohol-co-vinyl
acetate) (P(VA-co-VAc)) with NaOCl affords poly(methylene
ketone-co-vinyl alcohol-co-vinyl acetate) (P(MK-co-VA-co-
VAc)). The 13C NMR spectrum (Table 1) of P(MK-co-VA-
co-VAc) showed ketone signals at 206.9 and 204.9 ppm. This
is in agreement with an intense band in the infrared spectrum
at 1704 cm-1, overlapped with the absorption of the acetyl group
at 1724 cm-1, and the intensity of the C-O stretching band at
1043 cm-1 decreased significantly compared to that of P(VA-
co-VAc). The infrared spectrum of poly(enolate-co-vinyl
alcohol-co-vinyl acetate) (PEVV), formed by treatment of
P(MK-co-VA-co-VAc) with Et3N, showed a broad absorption
at 1581 cm-1 with the disappearance of the band of 1704 cm-1
compared to that of P(MK-co-VA-co-VAc). The 13C NMR
spectrum of PEVV gave signals at 193.2, 159.5, 100.6, and 98.2
ppm for the R,â-unsaturated carbonyl and the CdCsO-
carbons, respectively. These spectroscopic data clearly indicate
the formation of PEVV (Table 1). The 13C NMR integration
ratio of carbonyl groups between ketone and acetyl in P(MK-
co-VA-co-VAc) gave the percentage conversion of alcohol to
ketone listed in Table 2. It is seen that no chain degradation
and cross-linking took place, as implied by the weight average
molecular weight data and number average molecular weight
for the conversion of the alcohol (Table 2).
Reaction of PEVV with RhCl3 in aqueous solution afforded
Rh-PEVV. The 13C NMR spectrum (Table 1) of Rh-PEVV
gave new signals at 174.4, 173.9, and 98.4 ppm assigned to the
rhodium-chelated enolate. The signals for the acetyl groups
shifted from 169.7 to 165.8 ppm for the carbonyl carbons and
from 20.8 to 21.6 ppm for the methyl group. These signals
suggest the coordination of rhodium to both enolate and acetyl
groups in PEVV. Therefore, the complex of Rh-PEVV can
be represented as in Scheme 1.
(2) Catalytic Hydroformylation of Olefins Using Rh-
PEVV. Treatment of neat 1-octene (10 mmol) with 1:1 CO/
H2 (41.4 bar, 40 °C, 22 h) and an aqueous solution of RhCl3
(0.02 mmol), with and without P(VA-co-VAc) as the catalyst
precursor, gave less than 1% conversion and poor selectivity
for the hydroformylation of 1-octene (entries 1 and 2, Table 3).
a Reaction conditions: substrate (10 mmol)/Rh ) 500:1 in 3 mL of
H2O; temperature ) 100 °C; H2/CO ) 1:1, 41.4 bar, L/B ratio was
1
determined by H NMR. b T ) 90 °C. c T ) 60 °C. d H2/CO ) 1:3,
f
27.6 bar. e H2/CO ) 3:1, 27.6 bar. No hydroformylation of the internal
double bond occurred here. g The other product was 2-octene. h The
other product was 2-dodecene.
In contrast, treatment of 1-octent with Rh-PEVV under the
same conditions for 28 h resulted in 49% conversion and 98%
selectivity for hydroformylation with a small preference for
n-nonanal (Table 3). The organic phase, upon reuse, did not
show any catalytic activity. Reuse of the aqueous phase (three
times) did not diminish the activity and selectivity for the
hydroformylation reaction, indicating no rhodium leaching to
the organic phase. The average turnover frequency (TOF) is
2.36 × 10-5 kmol (kg(Rh) s)-1 (entry 3, Table 3) for the
catalytic hydroformylation of 1-octene at 40 °C, and the value
increased to 5.46 × 10-5 (entry 1, Table 4) at 90 °C. The
catalytic hydroformylation of 1-dodecene proceeded at 60 °C
at an excellent TOF of 2.36 × 10-4 (entry 2, Table 4).
Comparing these results with the TOF values of 8.6 × 10-6
and 7.8 × 10-5 for the catalytic hydroformylation of 1-octene
using [Rh(m-StBu)(CO)(TPPTS)]2 with and without ethanol as
the cosolvent, respectively,4 one can conclude that Rh-PEVV
is a very reactive biphasic catalyst. The TOF was 7.85 × 10-6
when HRh(CO)(TPPTS)3 was used as the catalyst precursor for
the hydroformylation of 1-octene at 100 °C.2 The reactivity of
Rh-PEVV compares well with the best TOF of 5.11 × 10-4
using the PPh3 ligand promoted HRh(CO)(TPPTS)3 biphasic
catalytic system for 1-octene at 100 °C.2 The selectivity for
the linear aldehyde improved as the temperature was raised to
90 °C (entry 3, Table 3; entry 1, Table 4). However, the rate
of isomerization of 1-octene to 2-octene was greater than the
hydroformylation reaction rate at higher temperature (entries
3-5, Table 4). Changing the H2/CO ratio affected the rates of
linear/branched aldehydes with a 1:3 ratio of H2/CO being the
most selective for the linear product (entries 3-5, Table 4).
These excellent results led us to apply the Rh-PEVV catalyst
to the selective catalytic hydroformylation of other olefins.
Substitution at the allylic position markedly increases the
selectivity for the linear aldehyde product (entries 7 and 8, Table

A NoVel Water-Soluble Rhodium Catalyst
J. Am. Chem. Soc., Vol. 119, No. 5, 1997 895
Table 5. Catalytic Hydroformylation of Olefins Using Rh-PEVV
4). The catalytic hydroformylation of methyl 3,3-dimethyl-
penten-4-onate gives only the linear product (entry 8, Table 4).
While the conversion was low, the vinyl ether n-butyl vinyl
ether afforded the branched chain aldehyde as the major product
(entries 9 and 10, Table 4).
as the Catalyst Precursora
conversion selectivity
entry
1
substrate
t (h)
(%)
(%)
B/Lb
17.3
22
13
>99
Although the hydroformylation of styrene gave poor selectiv-
ity at 90 °C using Rh-PEVV as the catalyst precursor, excellent
selectivity (up to a 36.7 ratio of B/L) for the catalytic
hydroformylation of styrene and its derivatives was achieved
at 40 °C (Table 5). These results can be compared with the
homogeneous system using a zwitterionic rhodium complex13
and the rhodium complex of electron deficient phosphine ligands
as catalyst precursors.14 Change of the H2/CO ratio or addition
of PPh3, did not improve the B/L selectivity and reactivity
(entries 2-5, Table 5) as was found in the hydroformylation of
aliphatic olefins. Unfortunately the conversion of styrenes is
low after reaction times of 22-24 h.
2
3
4
5
6
c
d
e
f
24
22
22
22
24
12
7
4
10
12
>99
>99
>99
>99
>99
17.9
9
9
9
15.3
Cl
7
8
22
24
14
4
>99
>99
9
Me
g
36.7
a Reaction conditions: substrate 10 mmol, Rh 0.2 mol %, H2/CO )
1:1, 41.4 bar, 40 °C. b L ) 1-phenylpropanal; B ) 2-phenylpropanal.
Ratio is based on 1H NMR data. c Rh/PPh3 ) 1:10. d Rh/PPh3 ) 1:57.
e H2/CO ) 1:3, 27.6 bar. f H2/CO ) 3:1, 27.6 bar. g Reaction temper-
ature ) 28 °C.
Conclusion
In conclusion, Rh-PEVV is a novel, highly active, water-
soluble catalyst for the hydroformylation of olefins, especially
for aliphatic olefins. Excellent selectivity for the preparation
of branched-chain aldehydes was found for styrene and its
derivatives, albeit at low conversion.
General Procedures for the Preparation of Rh-PEVV. To a
solution of P(MK-co-VA-co-VAc) (4.55 g) in methanol (30 mL) was
added Et3N (4.0 mL) at room temperature under N2 to give a red-
brown solution of PEVV which was immediately treated with an
aqueous solution of RhCl3‚3H2O (320.5 mg, 40 mL). The reaction
mixture was stirred for 5 h at room temperature under N2. The resulting
solution was dried in vacuum to afford 4.88 g of Rh-PEVV. The
concentration of Rh in Rh-PEVV is 2.56 mg/100 mg.
Experimental Section
General Considerations. All chemicals were purchased from
Aldrich and were used as received. P(VA-co-VAc) has the micro-
structure of 80% vinyl alcohol and 20% vinyl acetate. P(MK-co-VA-
co-VAc) was prepared according to the literature procedure by the
controlled oxidation of P(VA-co-VAc).12 All 1H and 13C NMR spectra
were recorded on either a Gemini-200 or AMX-500 NMR spectrometer
using CDCl3 or DMSO-d6 as the solvent and TMS as the internal
standard. The 1H NMR spectra of the hydroformylation products were
analyzed by comparison with authentic samples. The yield of hydro-
formylation products was calculated using either anisole or tert-
butylbenzene as the internal standard by 1H NMR integration. Infrared
spectra were recorded on a Bomem-100 FT-IR spectrometer. Gel
permeation chromatography (GPC) was run using a Waters 510 HPLC
pump operating on 1 mL/min flow rate with three consecutive Styragel
HT columns effective from 5 × 102 to 4 × 106 and detected using a
Waters 410 differential refractometer detector. HPLC grade THF was
used as eluant. The molecular weights of the polymers are based on
calibration with polybutadiene standards.
General Procedure for the Hydroformylation Reactions. A glass
liner containing an aqueous solution of Rh-PEVV (84.0 mg, 3 mL,
0.02 mmol of Rh) and olefin (10 mol) was placed in a 45 mL autoclave
equipped with a magnetic stirring bar. The autoclave was flushed three
times with CO and then pressurized to the desired level. The hydrogen
line was attached to the autoclave, the autoclave was flushed three times
with H2, and then the pressure was gradually increased to the desired
level. The autoclave was placed in an oil bath on a heater/stirrer preset
to the reaction temperature. After the appropriate reaction time, the
autoclave was cooled to room temperature, the excess H2/CO gas was
released, and the resulting solution was separated and immediately
1
analyzed by H NMR spectroscopy.
Acknowledgment. We are grateful to the Environmental
Science and Technology Alliance Canada for support of this
research.
(13) Amer, I.; Alper, H. J. Am. Chem. Soc. 1990, 112, 3674.
(14) Chan, A. S. C.; Pai, C.-C.; Yang, T.-K.; Chen, S.-M. J. Chem. Soc.,
Chem. Commun. 1995, 2031.
JA9623875