Hydroformylation of 1-octene under atmospheric pressure catalyzed by rhodium carbonyl thiolate complexes tethered to silica

Article abstract of DOI:10.1021/om9800795

The silica-tethered rhodium thiolate complex catalysts Rh-S/SiO₂ and Rh-S-P/SiO₂ were prepared by the condensation of SiO₂ with Rh₂[μ-S(CH₂)₃Si(OCH₃) ₃]₂(CO)₄ (Rh-S) or Rh₂[μ-S(CH₂)₃Si(OCH₃) ₃]₂[Ph₂P(CH₂)₃Si(OC ₂H₅)₃]₂(CO)₂ (Rh-S-P). These tethered complex catalysts exhibit high activity for the hydroformylation of 1-octene in the presence of phosphine donor ligands under the mild conditions of 60°C and 1 atm. IR (DRIFT) spectral studies of the catalysts used indicate that tethered monorhodium dicarbonyl thiolate complexes of the type Rh(SR)(CO)₂(PR′₃) are the predominant species on the surface for the catalysts that have the highest hydroformylation activity. The catalysts are easily separated from the reaction mixtures, and the Rh-S/SiO₂ catalyst maintains its activity through at least three cycles over a total period of 69 h, during which time there are 1273 (mol of aldehyde/mol of Rh) turnovers. Effects of the phosphine ligand and PR′₃/Rh mole ratio on the hydroformylation rate, conversion, and chemo- and regioselectivity for aldehyde products were also investigated.

Full text of DOI:10.1021/om9800795

Organometallics 1998, 17, 3063-3069
3063
Hyd r ofor m yla tion of 1-Octen e u n d er Atm osp h er ic
P r essu r e Ca ta lyzed by Rh od iu m Ca r bon yl Th iola te
Com p lexes Teth er ed to Silica
Hanrong Gao and Robert J . Angelici*
Department of Chemistry and Ames Laboratory, Iowa State University, Ames, Iowa 50011
Received February 5, 1998
The silica-tethered rhodium thiolate complex catalysts Rh-S/SiO2 and Rh-S-P/SiO2 were
prepared by the condensation of SiO2 with Rh2[µ-S(CH2)3Si(OCH3)3]2(CO)4 (Rh-S) or Rh2[µ-
S(CH2)3Si(OCH3)3]2[Ph2P(CH2)3Si(OC2H5)3]2(CO)2 (Rh-S-P). These tethered complex cata-
lysts exhibit high activity for the hydroformylation of 1-octene in the presence of phosphine
donor ligands under the mild conditions of 60 °C and 1 atm. IR (DRIFT) spectral studies of
the catalysts used indicate that tethered monorhodium dicarbonyl thiolate complexes of the
type Rh(SR)(CO)2(PR′3) are the predominant species on the surface for the catalysts that
have the highest hydroformylation activity. The catalysts are easily separated from the
reaction mixtures, and the Rh-S/SiO2 catalyst maintains its activity through at least three
cycles over a total period of 69 h, during which time there are 1273 (mol of aldehyde/mol of
Rh) turnovers. Effects of the phosphine ligand and PR′3/Rh mole ratio on the hydroformyla-
tion rate, conversion, and chemo- and regioselectivity for aldehyde products were also
investigated.
In tr od u ction
for the hydroformylation of alkenes under conditions of
low pressure and temperature (5 bar, 80 °C).8-12 How-
ever, only two reports dealing with the application of
immobilized rhodium thiolate complex catalysts in
hydroformylation have appeared so far. Blum et al.13
reported that a silica-bound rhodium complex with one
bridging thiolate and one bridging chloro ligand (Rh2-
Hydroformylation of olefins is an important and well-
known process for the production of aldehydes and
alcohols.1 Much effort has been focused on the use of
rhodium complexes as catalysts, because they often
exhibit high activity as compared to other transition-
metal catalysts.2-7 Although homogeneous rhodium
catalysts, in many cases, are more active and selective
in the hydroformylation of olefins than are heteroge-
neous ones, an important technical problem is the
separation and recovery of the soluble catalysts. Espe-
cially in the case of rhodium-complex-catalyzed hydro-
formylations of higher olefins, the separation of the
catalyst from the high-boiling aldehydes requires vigor-
ous distillation conditions which result in the degrada-
tion of the catalyst with concomitant loss of rhodium.
One approach to solving this problem is to anchor the
homogeneous complex catalyst on an insoluble support.
It is well-known that the rhodium thiolate complexes
[Rh(µ-SR)(L)(L′)]2 (L, L′ ) COD or L ) CO, L′ ) PR3;
COD ) cyclooctadiene) are active catalyst precursors
(CO)2(PBut ) (µ-Cl)(µ-SR), R ) CH2CH2CH2Si(OC2H5)3)
3 2
is active for the hydroformylation of cyclohexene under
80 atm of CO/H2 and 120 °C. Also, the immobilized
rhodium thiolate catalyst prepared from phosphinated
cross-linked polystyrene and Rh2(µ-S-t-Bu)2(CO)4 was
used to catalyze the hydroformylation (80 °C, 5 bar) of
olefins.8b In the present paper, we report that silica-
tethered rhodium carbonyl thiolate complex catalysts
prepared by the condensation of silica with Rh2[µ-
S(CH2)3Si(OCH3)3]2(CO)4 or Rh2[µ-S(CH2)3Si(OCH3)3]2-
[Ph2P(CH2)3Si(OC2H5)3]2(CO)2 efficiently catalyze the
(8) (a) Kalck, Ph.; Frances, J . M.; Pfister, P. M.; Southern, T. G.;
Thorez, A. J . Chem. Soc., Chem. Commun. 1983, 510. (b) Kalck, Ph.;
Spirau, F. S. New J . Chem. 1989, 13, 515. (c) Dedieu, A.; Escaffre, P.;
Frances, J . M.; Kalck, Ph.; Thorez, A. New J . Chem. 1986, 10, 631.
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M. T.; Apreda, M. C.; Cano, F. H.; Foces-Foces, C. J . Chem. Soc., Dalton
Trans. 1988, 1523.
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Richards, R. L.; Sosa, P.; Terreros, P.; Terrens, H. J . Organomet. Chem.
1989, 359, 219.
(11) (a) Claver, C.; Masdeu, A. M.; Ruiz, N.; Foces-Foces, C.; Cano,
F. H.; Apreda, M. C.; Oro, L. A.; Garcia-Alejandre, J .; Torrens, H. J .
Organomet. Chem. 1990, 398, 177. (b) Bayo´n, J . C.; Esteban, P.; Read,
J .; Claver, C.; Ruiz, A. J . Chem. Soc., Chem. Commun. 1989, 1056. (c)
Polo, A.; Claver, C.; Castillo´n, S.; Ruiz, A.; Bayo´n, J . C.; Read, J .; Mealli,
C.; Masi, D. Organometallics 1992, 11, 3525. (d) Polo, A.; Fernandez,
E.; Claver, C.; Castillo´n, S. J . Chem. Soc., Chem. Commun. 1992, 639.
(12) (a) Aaliti, A.; Masdeu, A. M.; Ruiz, A.; Claver, C. J . Organomet.
Chem. 1995, 489, 101. (b) Masdeu, A. M.; Orejio´n, A.; Ruiz, A.;
Castillo´n, S.; Claver, C. J . Mol. Catal. 1994, 94, 149.
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lation: Direct Synthesis of Carbonyl Compounds; Plenum: New York,
1991. (b) Cornils, B. In Hydroformylation in New Syntheses with
Carbon Monoxide; Falbe, J ., Ed.; Springer-Verlag: Berlin, 1980; pp
1-225. (c) Beller, M.; Cornils, B., Frohning, C. D.; Kohlpaintner, C.
W. J . Mol. Catal. A: Chem. 1995, 104, 17-85. (d) Frohning, C. D.;
Kohlpaintner, C. W. In Applied Homogeneous Catalysis with Organo-
metallic Compounds; Cornils, B.; Herrman, W. A., Eds.; VCH: Wein-
heim, Germany, 1996; pp 29-104.
(2) Amer, I.; Alper, H. J . Am. Chem. Soc. 1990 112, 3674.
(3) Gladiali, S.; Pinna, L.; Arena, C. G.; Rotondo, E.; Faraone, F.
J . Mol. Catal. 1991, 66, 183.
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S0276-7333(98)00079-X CCC: $15.00 © 1998 American Chemical Society
Publication on Web 06/11/1998

3064 Organometallics, Vol. 17, No. 14, 1998
Gao and Angelici
oily residue was washed with pentane (2 mL) and dried under
vacuum at room temperature to give the oily red complex Rh-
S-P. Anal. Calcd for C56H92O14P2S2Si4Rh2: C, 46.37; H, 6.59.
Found: C, 46.92; H, 6.47. IR (ν(CO) in toluene): 1970 (s), 1956
hydroformylation (eq 1) of 1-octene in the presence of a
(s) cm-1 31P {1H} NMR (in CDCl3, 200 MHz): δ 21.92 (d, J Rh-P
.
) 122 Hz). The J Rh-P value is about the same as that (J Rh-P
) 121 Hz) of the rhodium phosphine complex RhCl(CO)(Ph2-
PCH3)2, which was prepared according to a literature proce-
dure.16
phosphine or phosphite ligand under the mild conditions
of 60 °C and 1 atm total pressure of H2 and CO. To our
knowledge, these are the first examples of immobilized
rhodium complex catalysts that exhibit high activities
for the hydroformylation of olefins under atmospheric
pressure.
P r ep a r a tion of th e Teth er ed Ca ta lyst Rh -S/SiO2. The
rhodium thiolate complex Rh-S (46 mg, 0.065 mmol) was
refluxed with SiO2 (0.8 g), which had been dried under vacuum
at 100 °C for 2 h, in 15 mL of toluene for 4 h. After filtration,
the solid was washed with toluene (4 × 10 mL) and then dried
under vacuum at room temperature. The resulting silica-
tethered rhodium carbonyl thiolate complex catalyst Rh-S/
SiO2 (Rh content 1.50 wt %) gave an IR spectrum (DRIFTS)
Exp er im en ta l Section
with ν(CO) bands at 2081 (m), 2064 (s), and 2020 (s) cm-1
,
All syntheses of rhodium complex catalysts were performed
using standard Schlenk techniques under an argon atmo-
sphere. Rh2Cl2(CO)4 was purchased from Strem. Silica gel
100 (BET surface area, 400 m2/g) and (3-mercaptopropyl)-
trimethoxysilane were obtained from Fluka. Ph2P(CH2)3Si-
(OC2H5)3 was prepared according to the literature method.14
Solvents were dried by refluxing over CaH2 under nitrogen
prior to use. All other reagents were commercial samples and
were used as purchased.
FTIR and DRIFT spectra were recorded on a Nicolet 560
spectrophotometer equipped with a TGS detector in the main
compartment and an MCT detector in the auxiliary experiment
module (AEM). The AEM housed a Harrick diffuse-reflectance
accessory. The solution IR spectra were measured in the main
compartment using a solution cell with NaCl salt plates. The
DRIFT spectra were recorded on samples in the Harrick
microsampling cup. A Varian 3400 GC interfaced to a Finni-
gan TSG 700 high-resolution magnetic sector mass spectrom-
eter with electron ionization (70 eV) was used for all GC-MS
measurements. Gas chromatographic analyses were per-
formed with a HP-6890 GC using a 32 m HP-1 capillary
column with an FID detector.
which are very similar in position and relative intensity to
those (2074 (m), 2056 (s), and 2004 (s) cm-1 in toluene) of the
free Rh2[µ-S(CH2)3Si(OCH3)3]2(CO)4 complex.
P r ep a r a tion of th e Teth er ed Ca ta lyst Rh -S-P /SiO2.
Rh-S-P/SiO2 was prepared in the same way as that used for
the preparation of Rh-S/SiO2 but using Rh-S-P instead of
Rh-S. The rhodium content of the catalyst was 2.45 wt %.
The IR spectrum (DRIFTS) of Rh-S-P/SiO2 exhibits one
ν(CO) band at 1978 cm-1, which is quite different from that
(1970 (s), 1956 (s) cm-1 in toluene) for the precursor cis-Rh2[µ-
S(CH2)3Si(OCH3)3]2[Ph2P(CH2)3Si(OC2H5)3]2(CO)2 complex. How-
ever, the 1978 cm-1 band is very similar to that (1975 cm-1
)
of the trans isomer of the dirhodium complex [Rh(µ-SC6H5)-
(PPh3)(CO)]2.15 According to the literature,17 the product of
the reaction between Rh2(µ-SC6F5)2(CO)4 and 2 equiv of PPh3
at low temperature (-5 °C) is cis-[Rh(µ-SC6F5)(PPh3)(CO)]2
(ν(CO) 1994, 1977 cm-1), but the product is trans-[Rh(µ-SC6F5)-
(PPh3)(CO)]2 (ν(CO) 1984 cm-1) when the reaction is run at
room temperature. Our IR experiments show that cis-Rh-
S-P also isomerizes to trans-Rh-S-P upon heating in toluene
at 80 °C for 40 min. So, it appears that the tethering reaction
in refluxing toluene causes the cis-Rh-S-P complex to
isomerize to trans-Rh-S-P.
Hyd r ofor m yla tion of 1-Octen e. The hydroformylation
reactions were carried out in a three-necked, jacketed vessel
closed with a self-sealing silicon rubber cap; the vessel was
connected to a vacuum/CO-H2 line and a constant-pressure
gas buret. The temperature of the ethylene glycol that
circulated through the vessel jacket was maintained with a
constant-temperature bath. The reaction temperature and the
pressure of CO-H2 (1/1) were 60 °C and 1 atm, respectively.
After the catalyst and phosphorus ligand were added and the
atmosphere in the vessel was replaced with CO-H2, toluene
and 1-octene were added by syringe with vigorous stirring and
the uptake of CO-H2 was followed with the constant-pressure
gas buret. After the reaction was stopped, the reaction
mixture was analyzed by GC. When the Rh-S/SiO2 catalyst
was used in three successive hydroformylations of 1-octene,
the reaction mixture after the first cycle was filtered and the
solid catalyst was washed with toluene, dried under vacuum,
and used for the hydroformylation of a new batch of 1-octene
by following the same procedure as that in the first cycle. After
the second cycle, the catalyst was treated as after the first
cycle; the isolated catalyst was used for the third cycle.
To determine if any of the rhodium leached from the solid
catalyst, the rhodium contents of the liquid phases from the
first and second cycles were analyzed by atomic emission
spectroscopy. It was found that 1.5% of the total rhodium on
The rhodium contents of the silica-tethered catalysts were
determined by atomic emission spectroscopy. Each sample
was prepared for analysis by first treating the catalyst (50 mg)
with 5 mL of aqua regia at 90 °C for 5-10 min; then 5 mL of
aqueous HF (5%) was added to the mixture, which was heated
at 90 °C for 5-10 min. The resulting solution was diluted with
water to 25 mL.
P r ep a r a tion of [Rh 2(µ-S(CH2)3Si(OCH3)3)2(CO)4] (Rh -
S). Rh2[µ-S(CH2)3Si(OCH3)3]2(CO)4 was prepared by a proce-
dure similar to that used for the preparation of other rhodium
alkane- or arenethiolato carbonyl complexes Rh2(µ-SR)2(CO)4.15
To a stirred suspension of sodium hydride (11 mg (60 wt %),
0.27 mmol) in THF (30 mL) cooled by an ice bath was added
dropwise (3-mercaptopropyl)trimethoxysilane (47 µL, 0.26
mmol). After the mixture was stirred for 20 min, a solution
of Rh2Cl2(CO)4 (50 mg, 0.13 mmol) in THF (10 mL) was added
dropwise, and this mixture was stirred at room temperature
for 30 min. The mixture was evaporated and chromato-
graphed on silica gel. Elution with ether/hexanes (1/1) gave
the yellow-brown Rh-S complex. IR (ν(CO) in toluene): 2074
(m), 2056 (s), 2004 (s) cm-1
.
1H NMR (in CDCl3): δ 3.57 (s,
18H, OCH3), 3.11 (t, 4H, SCH2), 1.91 (m, 4H, CH2CH2CH2),
0.82 (m, 4H, CH2Si). Anal. Calcd for C16H30O10S2Rh2: C,
27.12; H, 4.27. Found: C, 27.48; H, 4.82.
P r ep a r a t ion of cis-R h 2[µ-S(CH 2)3Si(OCH 3)3]2[P h 2P -
(CH2)3Si(OC2H5)3]2(CO)2 (Rh -S-P ). A solution of Rh-S
(0.10 g, 0.14 mmol) and Ph2P(CH2)3Si(OC2H5)3 (0.11 g, 0.28
mmol) in 10 mL of toluene was stirred at room temperature
for 2 h. After the solvent was evaporated under vacuum, the
(16) Mann, B. E.; Masters, C.; Shaw, B. L. J . Chem. Soc. A 1971,
1104.
(14) Capka, M. Synth. React. Inorg. Met.-Org. Chem. 1977, 7, 347.
(15) Bolton, E. S.; Havlin, R.; Knox, G. R. J . Organomet. Chem. 1969,
18, 153.
(17) Fierro, J . J . G.; Mart´ınez-Ripoll, M.; Mercha´n, M. D.; Rodr´ıguez,
A.; Terreros, P.; Torrens, H.; Vivar-Cerrato, M. A. J . Organomet. Chem.
1997, 544, 243.

Hydroformylation of 1-Octene Catalyzed by Rh
Organometallics, Vol. 17, No. 14, 1998 3065
a
Ta ble 1. Hyd r ofor m yla tion of 1-Octen e over Rh -S/SiO2
P ligand
none
P(OPh)3
P(C6H4F-p)3
PPh3
reacn time (h)
TOFb (min-1
)
TOc
conversnd (%)
aldehyde selectivity (%)e
n/if
isomerizn product (%)g
12
11
22
22
23
24
8
0
0
504
564
415
271
80
0
0
0
0
0
28.0
5.8
3.1
1.5
1.9
0
1.19
0.66
0.39
0.25
0.07
0
85.8
70.5
51.1
32.5
11.0
0
68.5
91.6
93.9
95.4
82.7
12.0
4.2
4.1
4.5
1.4
P(C6H4OMe-p)3
P(C6H11
PMe3
)
3
dppeh
12
21
0
0
0
0
0
0
dppmh
a
Reaction conditions: Rh-S/SiO2 (50 mg, 7.26 × 10-3 mmol of Rh), 1-octene (1.00 mL, 6.38 mmol), P/Rh ) 7.8, toluene (5 mL), 60 °C,
1 atm (1/1, H2-CO). The maximum turnover frequency defined as moles of aldehyde formed per mole of rhodium per minute. c Turnover
b
d
(moles of aldehyde formed per mole of rhodium) corresponds to the reaction time. The conversion of 1-octene measured by GC corresponds
to the reaction time. e Aldehyde selectivity (total yield of moles of 1-nonanal and 2-methyloctanal per mole of 1-octene converted) determined
by GC. f Mole ratio of 1-nonanal/2-methyloctanal. The yield of isomerization byproducts (total of 2-, 3-, and 4-octene) determined by GC
g
h
analysis. dppe ) Ph2PCH2CH2PPh2; dppm ) Ph2PCH2PPh2.
the catalyst leached into the liquid phase in the first cycle. In
the second cycle, 0.75% of the rhodium complex leached into
the liquid phase. The liquid phases separated from the first
and second cycles were also used for the hydroformylation of
1-octene under the same conditions as those used with the solid
catalyst. After the first cycle (22 h), during which time 0.80
mL of 1-octene was converted, 0.80 mL of 1-octene was added
to the solution phase. The hydroformylation rate (milliliters
of CO and H2 uptake per minute) of the solution phase was
only one-sixth of that of the first cycle with the solid catalyst
(Rh-S/SiO2). The rate of hydroformylation of the solution
phase from the second cycle was only one-seventh of that of
the second cycle with the Rh-S/SiO2 catalyst. Thus, less than
17% of the hydroformylation is catalyzed by the Rh that
leaches into the solution. No ν(CO) absorptions were detected
F igu r e 1. Kinetic curves for the hydroformylation of
1-octene by Rh-S/SiO2 with the P-donor cocatalysts: (a)
P(OPh)3; (b) P(C6H4F-p)3; (c) PPh3; (d) P(C6H4OMe-p)3; (e)
in IR spectra of solutions after the first cycle, despite the
observation that the solution showed catalytic activity.
In all experiments, the hydroformylation products were
1-nonanal and 2-methyloctanal. In most cases the only
P(C6H11)3. For reaction conditions, see Table 1.
isomerization products observed were cis- and trans-2-octene.
are generally performed under high pressure (normally
g40 atm) of H2 and CO.18-23 In comparison to the other
catalyst systems in Table 1, that involving P(OPh)3 also
gives the highest regioselectivity (n/i, mole ratio of
1-nonanal/2-methyloctanal), a value of 12, which is
about 3 or 8 times greater than those observed with
PPh3 or P(C6H11)3, respectively. However, with regard
to the chemoselectivity for aldehyde, P(OPh)3 is much
worse than the phosphine ligands. While the P(OPh)3
catalyst system gives a conversion of 85.7%, its selectiv-
ity for aldehyde is only 68.5% and the yield of isomer-
ization byproducts is 28.0%. When the P(OPh)3/Rh ratio
was increased from 7.8 to 15, the percent of isomeriza-
tion increased to 34.5% while the n/i ratio was un-
changed (12.1) in a 20 h run. Decreasing the P(OPh)3/
Rh ratio to 3.6 affected the isomerization (32.6%)
slightly, but the n/i ratio decreased to 7.7 in a 21.5 h
run.
However, when the P(OPh)3 cocatalyst was used, cis- and
trans-3-octene and cis- and trans-4-octene were also formed.
No hydrogenation products of the aldehydes or 1-octene were
detected. There was no evidence for products resulting from
the hydroformylation of the internal olefins 2-, 3-, and 4-octene.
Resu lts a n d Discu ssion
Rh -S/SiO2 a s Ca ta lyst P r ecu r sor . The silica-
tethered rhodium carbonyl thiolate catalyst Rh-S/SiO2
was used for the hydroformylation of 1-octene in toluene
solvent in the presence of a phosphine or phosphite
donor under the conditions of 60 °C and 1 atm of H2
and CO (1:1). As the data in Table 1 show, the
hydroformylation rate, conversion, and selectivity for
aldehyde products are strongly affected by the nature
of the phosphorus ligand. Rh-S/SiO2 alone is inactive
for both the hydroformylation and the isomerization of
1-octene. The highest hydroformylation rate (TOF )
1.19 min-1) was achieved when P(OPh)3 was used as
the cocatalyst. This TOF is about 3 or 17 times higher
than those of the catalyst systems using PPh3 or
P(C6H11)3, respectively. To our knowledge, this is the
most active immobilized rhodium complex catalyst
system for the hydroformylation of olefins under such
mild conditions. Hydroformylations of olefins over
anchored rhodium complex catalysts reported previously
The arylphosphine ligands are better cocatalysts than
the more basic alkylphosphines for both the hydro-
formylation rate and the chemo- and regioselectivities.
For the three aryl phosphine ligands, the hydroformyl-
ation rates decrease in the order P(C6H4F-p)3 > PPh3
>P(C6H4OMe-p)3, while the selectivities for aldehyde
decrease in the opposite order: P(C6H4OMe-p)3 > PPh3
(20) Lee, B.; Alper. H. J . Mol. Catal. A: Chem. 1996, 111, 17.
(21) Cauzzi, D.; Lanfranchi, M.; Marzolini, G.; Predieri, G.; Tirip-
icchio, A.; Costa, M.; Zanoni, R. J . Organomet. Chem. 1995, 488, 115.
(22) Hartley, F. R.; Murray, S. G.; Nicholson, P. N. J . Mol. Catal.
1982, 16, 363.
(18) (a) Blum, J .; Rosenfeld, A.; Polak, N.; Israelson, O.; Schumann,
H.; Avnir, D. J . Mol. Catal. A: Chem. 1996, 107, 217. (b) Pittman, C.
U., J r.; Hirao, A. J . Org. Chem. 1978, 43, 640.
(19) Hong, L.; Ruckenstein, E. J . Mol. Catal. 1994, 90, 303.
(23) Arai, H. J . Catal. 1978, 51, 135.

3066 Organometallics, Vol. 17, No. 14, 1998
Gao and Angelici
Ta ble 2. Effect of P P h 3/Rh Mole Ra tio on th e
Ca ta lytic Beh a vior of Rh -S/SiO2 in th e
Hyd r ofor m yla tion of 1-Octen ea
reacn
aldehyde
isomerizn
products
(%)g
time TOFb
conversnd selectivity
P/Rh (h) (min-1) TOc
(%)
(%)e
n/if
1.3 22
2.6 23
5.2 12.5
7.8 22
0.45 301
0.95 720
1.25 673
0.39 415
89.6
98.1
85.4
51.1
38.6
84.1
90.4
93.9
3.0
3.4
3.8
4.1
55.0
15.6
8.2
3.1
a
For reaction conditions, see Table 1. Footnotes are the same
as in Table 1.
> P(C6H4F-p)3. These trends demonstrate that electron-
withdrawing substituents on the phenyl rings accelerate
both the hydroformylation and the side reaction of
isomerization. The regioselectivity (n/i) of the three
arylphosphine catalyst systems is about the same. The
catalyst systems Rh-S/SiO2-PMe3, Rh-S/SiO2-dppe,
and Rh-S/SiO2-dppm, are inactive for the hydroformyl-
ation of 1-octene under these mild reaction conditions.
Figure 1 shows kinetic curves for the hydroformyla-
tion of 1-octene over Rh-S/SiO2 with different phos-
phorus ligand cocatalysts. Except for Rh-S/SiO2-
P(C6H4F-p)3, which is active from the outset (Figure 1b),
the catalyst systems with the other phosphorus ligands
exhibit an induction period. The length of the induction
period decreases as the basicity of the phosphorus ligand
F igu r e 2. Comparison of the DRIFT spectra of the used
Rh-S/SiO2-PPh3 catalyst with different PPh3/Rh mole
ratios after hydroformylations of 1-octene: (a) unreacted
Rh-S/SiO2; (b) P/Rh ) 1.3; (c) P/Rh ) 2.6; (d) P/Rh ) 5.2;
(e) P/Rh ) 7.8.
predominant species on the surface change with in-
creasing PPh3/Rh ratio, as illustrated in eq 2. Since Rh-
decreases: P(C6H11 3
P(OPh)3.
)
> P(C6H4OMe-p)3 > PPh3 >
The effect of the P/Rh ratio on the rate, conversion,
and selectivity of 1-octene hydroformylation was inves-
tigated using the PPh3 ligand. As the data illustrate
in Table 2, the catalyst system with the highest P/Rh
mole ratio gives the highest chemoselectivity for alde-
hydes and highest regioselectivity for the linear alde-
hyde. The maximum hydroformylation rate (TOF) is
obtained at a P/Rh mole ratio of about 5. To gain some
insight into the structures of species formed during the
hydroformylation reactions, IR spectra (DRIFTS) (Fig-
ure 2) were recorded in air on the used catalysts, which
were isolated at the end of the reaction time (Table 2)
by filtering the catalysts from the reaction mixtures,
washing with toluene, and drying under vacuum. Spec-
tra of the isolated Rh-S/SiO2-PPh3 catalysts used with
different PPh3/Rh mole ratios are shown in Figure 2.
When the mole ratio of P/Rh is 1.3, the spectrum of the
used catalyst is very similar to that of the unreacted
Rh-S/SiO2. As the P/Rh ratio increases, the ν(CO) band
at around 2081 cm-1 gradually disappears. When the
P/Rh ratio reaches 5.2, the used catalyst exhibits bands
at 2060 and 1975 cm-1 with similar intensities. The
positions of these bands are lower than those (2090 and
(SR)(CO)2(PPh3) is the predominant species present
when the PPh3/Rh ratio (5.2) gives the most active
catalyst, it appears that a Rh(SR)(CO)2(PPh3) type of
complex, although not necessarily involved in the ca-
talysis, is associated with the activity of the catalyst.
DRIFT spectra of isolated Rh-S/SiO2 catalysts that
had been used with different phosphorus ligand cocata-
lysts (P/Rh ratio of 7.8) for the reaction times given in
Table 1 are shown in Figure 3. When no phosphorus
ligand was added, the IR spectrum of the used catalyst
remains the same as that of the unreacted Rh-S/SiO2.
The IR spectrum of the used Rh-S/SiO2-dppe catalyst
gives three ν(CO) bands at 2080 (m), 2060 (s), and 2010
(s) cm-1. These are very similar to those of the unre-
acted catalyst Rh-S/SiO2, which suggests that dppe
does not react nor cleave the thiolate bridge of the
tethered rhodium carbonyl complex Rh-S/SiO2. Both
Rh-S/SiO2 alone and Rh-S/SiO2-dppe are inactive for
the hydroformylation of 1-octene (Table 1). Spectra of
the isolated catalysts using PPh3, P(OPh)3, P(C6H4OMe-
p)3, and P(C6H4F-p)3 as cocatalyst show two ν(CO) bands
at 2055-2065 and 1965-1975 cm-1 (Figure 3b-e). For
P(C6H4F-p)3 and P(C6H4OMe-p)3, the intensities of the
two bands are similar. However, for PPh3 and P(OPh)3,
the 1965-1975 cm-1 band is more intense than that of
the 2055-2065 cm-1 band. These results suggest, as
discussed for the spectra of catalysts using different
PPh3/Rh ratios (Figure 2), that two types of complexes
are present, one of the type Rh(SR)(CO)2(PR′3) with two
bands (one in each of the 2055-2065 and 1965-1975
cm-1 regions). The other complex is of the type trans-
2005 cm-1 24
) of cis-RhCl(CO)2(PPh3), which is consistent
with the stronger donor ability of RS- ligands25 and
suggests that the structure of the complex on the surface
is of the type Rh(SR)(CO)2(PPh3). When the P/Rh ratio
is increased to 7.8, the relative intensity of the band at
2060 cm-1 decreases substantially and a new band at
1970 cm-1 grows in. The position of this latter band is
very similar to that (1969 cm-1) in Rh(SCH3)(CO)-
(PPh3)2.15 These spectral changes suggest that the
(24) Uguagliati, P.; Deganello, G.; Belluco, U. Inorg. Chim. Acta
1974, 9, 203.
(25) Lever, A. B. P. Inorg. Chem. 1990, 28, 1271.

Hydroformylation of 1-Octene Catalyzed by Rh
Organometallics, Vol. 17, No. 14, 1998 3067
Ta ble 3. Effect of P P h 3/Rh Mole Ra tio on th e
Ca ta lytic Beh a vior of Rh -S-P /SiO2 in th e
Hyd r ofor m yla tion of 1-Octen ea
reacn
aldehyde
isomerizn
products
(%)g
time TOFb
conversnd selectivity
P/Rh (h) (min-1) TOc
(%)
(%)e
n/if
none 18.5
0
0
13.3
97.5
98.2
98.2
97.9
0
13.3
27.9
10.0
4.7
1.6
3.2
7.4
10
24.0
24.0
21.0
25.0
0.33 370
0.35 470
0.49 499
0.46 492
71.4
89.8
95.2
94.1
3.4
3.4
4.2
4.6
5.8
a
Reaction conditions are the same as those in Table 1. Footnotes
are the same as in Table 1.
cm-1 overlaps with that of the unreacted rhodium
complex Rh-S) indicate the presence of some Rh(SR)-
(CO)2(PR′3). It seems that there is no rhodium complex
species of the type Rh(SR)(CO)(P(C6H11)3)2 on the used
catalyst surface. This indicates that it is more difficult
for the larger P(C6H11)3 ligand to react with Rh-S/SiO2,
compared to the other monophosphine ligands. The
used catalyst isolated from the Rh-S/SiO2-PMe3 cata-
lyst system does not show any detectable ν(CO) bands
in its DRIFT spectrum. All of these results suggest that
the structure of the rhodium species on the SiO2 surface
after hydroformylation is sensitive to the phosphorus
ligand used.
Rh -S-P /SiO2 a s Ca ta lyst P r ecu r sor . The hydro-
formylation reactions catalyzed by Rh-S/SiO2 required
the addition of a phosphorus donor cocatalyst. In
principle, it seemed possible that the phosphine cocata-
lyst could also be anchored to the support. Thus, the
F igu r e 3. Comparison of the DRIFT spectra of the Rh-
S/SiO2 catalysts with different phosphorus ligands after
being used in the hydroformylation of 1-octene: (a) dppe;
(b) PPh3; (c) P(OPh)3; (d) P(C6H4OMe-p)3; (e) P(C6H4F-p)3;
(f) P(C6H11)3; (g) no PR3.
complex
Rh2[µ-S(CH2)3Si(OCH3)3]2[Ph2P(CH2)3Si-
Rh(SR)(CO)(PR′3)2 with one band in the 1965-1975
cm-1 region. On the basis of these ν(CO) data, we
conclude that in the cases of P(C6H4F-p)3 and P(C6H4-
OMe-p)3, the major species present on the used catalyst
is the mononuclear dicarbonyl complex cis-Rh(SR)(CO)2-
(PR′3), on the basis of the fact that the two bands (2055-
2065 and 1965-1975 cm-1) are very similar to those
(2060 and 1975 cm-1) assigned to cis-Rh(SR)(CO)2(PPh3)
in the PPh3/Rh ratio studies (Figure 2). However, for
the P(OPh)3 and PPh3 cocatalysts, the single 1965-1975
cm-1 band suggests that the major species formed on
the used catalyst surface has a structure similar to that
of Rh(SCH3)(CO)(PPh3)2,15 which has a band at 1969
cm-1 as discussed above; the smaller band at 2055-
2065 cm-1 suggests that some of the Rh(SR)(CO)2(PR′3)
complex is also present. As is evident in Figure 3, the
relative intensity of the ν(CO) band at 2055-2065 cm-1
increases with the phosphorus ligand in the order PPh3
< P(OPh)3 < P(C6H4OMe-p)3 ≈ P(C6H4F-p)3, which
suggests that the fraction of the dicarbonyl species Rh-
(SR)(CO)2(PR′3) on the used catalyst surfaces decreases
in the order P(C6H4F-p)3 ≈ P(C6H4OMe-p)3 > P(OPh)3
> PPh3. Thus, it appears that the hydroformylation
activity of the Rh(SR)(CO)2(PR′3) species is strongly
affected by the basicity of the phosphorus ligand: the
weaker the basicity of the ligand, the higher the activity
of the complex.
(OC2H5)3]2(CO)2 (Rh-S-P), with anchoring siloxy groups
on both the thiolate and phosphine ligands, was teth-
ered to the SiO2 to give the Rh-S-P/SiO2 catalyst,
which was used to catalyze the hydroformylation of
1-octene at 60 °C and 1 atm of CO-H2. It was observed
(Table 3) that, as for Rh-S/SiO2, Rh-S-P/SiO2 alone
is inactive for the hydroformylation of 1-octene under
these mild conditions, although it exhibits a low activity
for the isomerization of 1-octene. Thus, anchoring both
the sulfur and phosphine ligands in Rh-S-P/SiO2 does
not give an active hydroformylation catalyst. However,
Rh-S-P/SiO2 is active for hydroformylation in the
presence of added PPh3 (Table 3). With an increase in
the PPh3/Rh mole ratio, the hydroformylation rate (TOF
and TO), aldehyde selectivity, and 1-nonanal/2-methyl-
octanal (n/i) mole ratio increase. When PPh3/Rh is 7.4,
the hydroformylation rate and the regio- and chemose-
lectivity reach a maximum but decline only slightly
when the PPh3/Rh mole ratio is increased to 10. Figure
4 shows the IR (DRIFT) spectra of the isolated Rh-S-
P/SiO2-PPh3 catalysts that had been used with differ-
ent PPh3/Rh mole ratios at the end of the reaction times
in Table 3. When PPh3 was not added to the reaction
mixture, the spectrum of the used catalyst showed three
ν(CO) bands at 2078 (m), 2060 (s), and 2011 (s) cm-1
,
which are within experimental error the same as those
of the Rh-S/SiO2 catalyst. This result indicates that
the phosphine in the tethered Rh-S-P complex is
replaced by CO to give tethered Rh-S in the absence
of PPh3 under the hydroformylation conditions. As for
the Rh-S/SiO2 catalyst, the ν(CO) band at 2078 cm-1
disappears with an increase in the PPh3/Rh mole ratio.
When a PPh3/Rh mole ratio of 7.4 is achieved, the used
For the Rh-S/SiO2-P(C6H11)3 catalyst system (Figure
3f), after the hydroformylation proceeds for 24 h, there
is still some of the original rhodium carbonyl complex
Rh-S on the catalyst surface, as indicated by the ν(CO)
bands at 2078 (sh), 2056 (s), and 2008 (br); the ad-
ditional bands at 2054 and 1954 cm-1 (the band at 2056

3068 Organometallics, Vol. 17, No. 14, 1998
Gao and Angelici
PPh3 was added at a PPh3/Rh mole ratio of 6, the
isolated catalyst showed two ν(CO) bands at 2054 (s)
and 1978 (s) cm-1. The positions and intensities of these
bands are very similar to those (2055-2065 and 1965-
1975 cm-1) that were assigned to a Rh(SR)(CO)2(PR′3)
species in the Rh-S/SiO2-PR′3 and Rh-S-P/SiO2-
PPh3 catalyst systems, which suggests that the same
type of species is generated in the Rh-S/P-SiO2-PPh3
system.
Although several reports on the homogeneous hydro-
formylation of alkenes catalyzed by [Rh(µ-SR)(CO)-
(PR′3)]2 indicate that the dinuclear rhodium catalyst
precursors maintain their integrity throughout the
catalytic cycle,8,9,13 recent kinetic evidence27 strongly
suggests that a mononuclear complex is involved.
Spectroscopic studies show, however, that Rh2(µ-SR)2-
(CO)2(PR′3)2 complexes are the predominant species
observed during the homogeneous hydroformylation of
olefins.28 We also used the homogeneous catalyst Rh-
S/PPh3 to catalyze the hydroformylation of 1-octene
under the same conditions as in Table 1. The results
show that when the PPh3/Rh mole ratio is 5, the
maximum TOF and the TO during a 24 h period are
0.26 and 275, respectively, which are lower than those
(1.25 and 673 (in 12.5 h), 0.49 and 499 (in 21 h))
obtained using the Rh-S/SiO2-PPh3 (PPh3/Rh ) 5.2)
and Rh-S-P/SiO2-PPh3 (PPh3/Rh ) 7.4) catalyst
systems. The IR spectrum of the hydroformylation
solution exhibits two ν(CO) bands at 1973 (s) and 1965
(s) cm-1, which are similar to those (1966 (s) and 1952
(s) cm-1 in hexadecane) of cis-[Rh(S-t-C4H9)(CO)(PMe2-
Ph)]2;26 this suggests that the rhodium complex species
formed in the homogeneous hydroformylation reaction
is cis-Rh2[µ-S(CH2)3Si(OCH3)3]2(PPh3)2(CO)2, analogous
to the [Rh(µ-SR)(CO)(PR′3)]2 system.8,9,13 It is clear that
the predominant species present in the homogeneous
Rh-S/PPh3 catalyst system is different from that (Rh-
(SR)(CO)2(PR′3)) in the tethered catalyst systems, Rh-
S/SiO2-PPh3 and Rh-S-P/SiO2-PPh3. Thus, the teth-
ering of Rh-S to SiO2 stabilizes the complex in different
forms (Rh(SR)(CO)2(PR′3) and Rh(SR)(CO)(PR′3)2) than
what exists in the homogeneous catalyst system (Rh2-
(µ-SR)2(CO)2(PR′3)2). This stabilization of Rh(SR)(CO)2-
(PR′3) by SiO2 attachment may be the reason for the
higher activity of the Rh-S/SiO2-PR′3 and Rh-S-P/
SiO2-PPh3 catalyst systems as compared with the
homogeneous Rh-S/PPh3 catalyst system.
F igu r e 4. Comparison of the DRIFT spectra of the used
Rh-S-P/SiO2-PPh3 catalyst with different PPh3/Rh mole
ratios after hydroformylations of 1-octene: (a) no PPh3; (b)
P/Rh ) 1.6; (c) P/Rh ) 3.2; (d) P/Rh ) 7.4; (e) P/Rh ) 10;
(f) unreacted Rh-S-P/SiO2.
catalyst exhibits two ν(CO) bands, at 2058 and 1975
cm-1, with similar intensities. The positions and rela-
tive intensities of these bands are similar to those
(Figure 2) of the used Rh-S/SiO2-PPh3 with a PPh3/
Rh mole ratio of approximately 5. Thus, the Rh-S-P/
SiO2-PPh3 catalyst is largely converted to the Rh-S/
SiO2-PPh3 catalyst under the conditions of hydro-
formylation. Also, the conversions of the tethered Rh-
S-P complex with increasing PPh3 concentration follow
the pattern (eq 2) observed for the tethered Rh-S
complex. In both cases, a Rh(SR)(CO)2(PPh3) species
is the major complex on the surface at a PPh3/Rh ratio
(5-7) that gives a maximum hydroformylation activity.
In a further attempt to generate a hydroformylation
catalyst in which both the rhodium complex and phos-
phine cocatalyst were tethered to the SiO2, we first
tethered Ph2P(CH2)3Si(OC2H5)3 to SiO2 by reacting 0.64
mmol of the ligand with SiO2 (0.8 g) in refluxing toluene
for 4 h. The resulting P-SiO2 solid was treated with
the Rh-S complex in toluene at room temperature for
2 h to form the Rh-S/P-SiO2 (Rh, 1.7 wt %) catalyst.
The IR (DRIFT) spectrum of this catalyst, which shows
three ν(CO) bands at 2056 (s), 1995 (s), and 1975 (s)
cm-1, is clearly different from those of Rh-S (2074 (m),
2056 (s), 2004 (s) cm-1), Rh-S-P (1970 (s), 1956 (s)
cm-1) or Rh-S-P/SiO2 (1978 cm-1); however, they are
similar to those (2050 (s), 1990 (s), and 1972 (s) cm-1 in
hexadecane) of [Rh(µ-S-t-C4H9)(CO)2(PMe2Ph)]2,26 in
which the Rh centers are 5-coordinate. This suggests
that the major species on the Rh-S/P-SiO2 catalyst is
the five-coordinate rhodium thiolate complex Rh2[µ-
S(CH2)3Si(OCH3)3]2[Ph2P(CH2)3Si(OC2H5)3]2(CO)4. In
hydroformylation studies using the conditions in Table
1, Rh-S/P-SiO2 alone is unfortunately inactive for the
hydroformylation of 1-octene; however, it is active in the
presence of PPh3. After Rh-S/P-SiO2 was used for the
hydroformylation of 1-octene for 24 h, the DRIFT
spectrum of the isolated catalyst showed that when no
PPh3 was added, the ν(CO) bands remained the same
as those of the unreacted Rh-S/P-SiO2; however, when
Finally, the durability of the Rh-S/SiO2-PPh3 cata-
lyst with a PPh3/Rh ratio of 7.8 was evaluated in three
successive hydroformylations of 1-octene under the
conditions in Table 1. In the first cycle, the maximum
TOF was 0.39 and the TO was 415 after 22 h. Then,
the catalyst was filtered from the mixture, washed with
toluene, and dried under vacuum at room temperature.
It was observed that in the second hydroformylation
cycle the addition of PPh3 is still essential for the
reaction. Using the same PPh3/Rh mole ratio as in the
first cycle, this catalyst system gave a maximum TOF
of 0.30 and a TO value of 307 after 21.5 h. After the
catalyst was treated as described after the first cycle,
it was used in a third cycle for which the maximum TOF
(27) Davis, R.; Epton, J . W.; Southern, T. G. J . Mol. Catal. 1992,
77, 159.
(26) Kalck, Ph.; Poilblanc, R. Inorg. Chem. 1975, 14, 2779.
(28) Kalck, Ph. Polyhedron 1988, 7, 2441.

Hydroformylation of 1-Octene Catalyzed by Rh
Organometallics, Vol. 17, No. 14, 1998 3069
was 0.49 and the TO was 551 after 25.5 h. Thus, during
the third cycle, the catalyst had essentially the same
TO activity as in the first cycle. For the three cycles
over 69 h, the total turnover number was 1273 mol of
aldehyde/mol of Rh. The DRIFT spectrum of the used
catalyst after the third cycle is about the same as that
of the used catalyst in the first cycle (ν(CO) at 2060 (w)
and 1970 (s) cm-1), even though excess PPh3 (PPh3/Rh
) 7.8) was added to the reaction solution for each cycle.
affected by the phosphine donor and the mole ratio of
P/Rh. The high activity of the tethered catalysts may
result from the stabilization of a monorhodium dicar-
bonyl thiolate type of complex, Rh(SR)(CO)2(PR′3), which
is the predominant species on the most active form of
the catalysts using PPh3 as cocatalyst. These tethered
catalysts are easy to separate from the reaction mixture
and exhibit good durability for the hydroformylation of
1-octene. Attempts to tether both Rh-S and the phos-
phine cocatalyst on the SiO2 did not give a catalyst that
was active for hydroformylation, unless another phos-
phine cocatalyst was added to the solution.
Su m m a r y
The silica-tethered rhodium thiolate complex cata-
lysts, Rh-S/SiO2 and Rh-S-P/SiO2, discussed in this
paper are very active for the hydroformylation of
1-octene in the presence of a phosphine cocatalyst under
the mild conditions of 60 °C and 1 atm. The hydro-
formylation rate (TOF and TO), conversion, and chemo-
and regioselectivity for aldehyde products are markedly
Ack n ow led gm en t. This work was supported by the
U.S. Department of Energy, Office of Basic Energy
Sciences, Chemical Sciences Division, under Contract
W-7405-Eng-82 to Iowa State University.
OM9800795