A silica-supported, switchable, and recyclable hydroformylation - Hydrogenation catalyst

Article abstract of DOI:10.1021/ja010150p

A homogeneous hydroformylation catalyst, designed to produce selectively linear aldehydes, was covalently tethered to a polysilicate support. The immobilized transition-metal complex [Rh(A)CO]⁺ (1⁺), in which A is N-(3-trimethoxysila

Full text of DOI:10.1021/ja010150p

8468
J. Am. Chem. Soc. 2001, 123, 8468-8476
A Silica-Supported, Switchable, and Recyclable
Hydroformylation-Hydrogenation Catalyst
Albertus J. Sandee, Joost N. H. Reek,* Paul C. J. Kamer, and
Piet W. N. M. van Leeuwen*
Contribution from the Institute of Molecular Chemistry, UniVersity of Amsterdam, Nieuwe Achtergracht
166, 1018 WV Amsterdam, The Netherlands
ReceiVed January 17, 2001
Abstract: A homogeneous hydroformylation catalyst, designed to produce selectively linear aldehydes, was
covalently tethered to a polysilicate support. The immobilized transition-metal complex [Rh(A)CO]+ (1+), in
which A is N-(3-trimethoxysilane-n-propyl)-4,5-bis(diphenylphosphino)phenoxazine, was prepared both via
the sol-gel process and by covalent anchoring to silica. 1+ was characterized by means of 31P and 29Si MAS
NMR, FT-IR, and X-ray photoelectron spectroscopy. Polysilicate immobilized Rh(A) performed as a selective
hydroformylation catalyst showing an overall selectivity for the linear aldehyde of 94.6% (linear to branched
aldehyde ratio of 65). In addition 1-nonanol, obtained via the hydrogenation of the corresponding aldehyde,
was formed as an unexpected secondary product (3.6% at 20% conversion). Under standard hydroformylation
conditions, 1+ and HRh(A)(CO)2 (1) coexist on the support. This dual catalyst system performed as a
hydroformylation/hydrogenation sequence catalyst (Z), giving selectively 1-nonanol from 1-octene; ultimately,
98% of 1-octene was converted to mainly 1-nonanal and 97% of the nonanal was hydrogenated to 1-nonanol.
The addition of 1-propanol completely changes Z in a hydroformylation catalyst (X), which produces 1-nonanal
with an overall selectivity of 93%, and completely suppresses the reduction reaction. If the atmosphere is
changed from CO/H2 to H2 the catalyst system is switched to the hydrogenation mode (Y), which shows a
clean and complete hydrogenation of 1-octene and 1-nonanal within 24 h. The immobilized catalyst can be
recycled and the system can be switched reversibly between the three “catalyst modes” X, Y, and Z, completely
retaining the catalyst performance in each mode.
Introduction
ticularly suited as heterogeneous catalyst supports because of
their high physical strength and chemical inertness.
The development of well-defined catalyst systems that allow
rapid and selective chemical transformations and at the same
time can be completely recovered from the product is still a
paramount challenge.1 Although highly active and selective
reusable catalyst systems have been reported, key problems for
many systems comprise catalyst stability and leaching of
catalytic material in the product phase.2 An intensively studied
and promising approach to facilitate catalyst-product separation
is the attachment of homogeneous catalysts to polymeric organic,
inorganic, or hybrid supports,3,4 and more recently to dendri-
meric5,6 supports. Inorganic materials such as silica are par-
In the past three decades much research has been devoted
to recyclable catalyst systems for the hydroformylation of
higher alkenes. In the late seventies, alkoxysilane function-
alized monophosphine ligands were used to tether a rhodium-
phosphine complex to commercially available silica.7 An
interesting alternative for the preparation of silica-immobilized
catalysts was presented by Panster et al., who used the sol-gel
process,8 i.e., a co-condensation of tetraalkoxysilanes and
functionalized trialkoxysilanes.9 The sol-gel technique is an
ideal method for catalyst immobilization because of its diversity
and its mildness.10-13 The selectivity of the catalyst reported in
(1) Baker, R. T.; Tumas, W. Science 1999, 284, 1477.
(2) Herrmann, W. A.; Cornils, B. Angew. Chem., Int. Ed. Engl. 1997,
36, 1048.
(5) For a review on this topic, see: Oosterom, G. E.; Reek, J. N. H.;
Kamer, P. C. J.; van Leeuwen, P. W. N. M. Angew. Chem., Int. Ed. 2001,
40, 1829.
(3) Extensive reviews on polymer immobilized catalysts include the
following: (a) Hartley, F. R.; Vezey, P. N. AdV. Organomet. Chem. 1977,
15, 189. (b) Hartley, F. R. Supported Metal Complexes. A New Generation
of Catalysts; Reidel: Dordrecht, The Netherlands, 1985. (c) Iwasawa, Y.
Tailored Metal Catalysts; Ugo, R., James, B. R., Eds.; Reidel: Dordrecht,
The Netherlands, 1986. (d) Keim, W.; Driessen-Ho¨lscher, B. Handbook of
heterogeneous catalysis; Ertl, G., Kno¨zinger, H., Weitkamp, J., Eds.; Wiley-
VCH: Weinhein, Germany, 1997; Vol. 1, p 231.
(4) Alternative approaches toward catalyst-product separation include
the following: (a) Aqueous biphasic catalysis: Cornils, B.; Herrmann, W.
A. Applied homogeneous catalysis with organometallic compounds; Cornils,
B., Herrmann, W. A., Eds.; VCH: Weinhein, Germany, 1996; Chapter 3.
(b) Supported aqueous phase catalysis: Arhanchet, J. P.; Davis, M. E.;
Merola, J. S.; Hanson B. E. Nature 1989, 339, 454. (c) Fluorous phase
catalysis: Horva´th, I. T.; Ra´bai, J. Science 1994, 266, 72. (d) Smart
polymers: Bergbreiter, D. E.; Chandra, R. J. Am. Chem. Soc. 1987, 109,
174.
(6) (a) Knapen, J. W. J.; van der Made, A. W.; de Wilde, J. C.; van
Leeuwen, P. W. N. M.; Wijkens, P.; Grove, D. M.; van Koten, G. Nature
1994, 372, 659. (b) Reetz, M. T.; Lohmer, G.; Schwickardi, R. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1526. (c) de Groot, D.; Eggeling, E. B.; de
Wilde, J. C.; Kooijman, H.; van Haaren, R. J.; van der Made, A. W.; Spek,
A. L.; Vogt, D.; Reek, J. N. H.; Kamer, P. C. J.; van Leeuwen, P. W. N.
M. Chem. Commun. 1999, 1623. (d) Bourque, S. C.; Maltais, F.; Xiao,
W.-J.; Tardiff, O.; Alper, H.; Arya, P.; Manzer, L. E. J. Am. Chem. Soc.
1999, 121, 3035. (e) Bourque, S. C.; Alper, H.; Manzer, L. E.; Arya, P. J.
Am. Chem. Soc. 2000, 122, 956.
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Organomet. Chem. 1979, 172, 367.
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Soc. 1994, 116, 348.
(10) Lindner, E.; Schneller, T.; Auer, F.; Mayer, H. A. Angew. Chem.,
Int. Ed. 1999, 38, 2154.
10.1021/ja010150p CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/10/2001

A Silica-Supported Hydroformylation-Hydrogenation Catalyst
J. Am. Chem. Soc., Vol. 123, No. 35, 2001 8469
Pansters’ work is rather low, but metal leaching was suppressed
to a large extent. Blum et al. reported a sol-gel immobilized
hydroformylation catalyst that is free of metal-leaching.14 In
the latter case no directing ligands were used which resulted in
a lack of control over the product distribution. Immobilized
hydroformylation catalysts that combine a high selectivity and
activity with the absence of leaching of the catalytic material
in the product phase have not been reported yet. For this
purpose, catalysts containing monophosphines have proven not
to be suitable thus far. A single ligand-to-metal bond appeared
to be too weak and monophosphines generally give rise to a
low selectivity. Diphosphines bind more strongly to rhodium
than monophosphines due to the chelate effect.15 Many rhodium
diphosphine complexes give rise to a low selectivity in
hydroformylation reactions, but Devon et al. described a
diphosphine, BISBI, that showed a very high regioselectivity
for the formation of linear aldehydes.16 Casey et al. reported
that rhodium diphosphine complexes with a large P-Rh-P
(bite) angle can give rise to a high regioselectivity for the linear
aldehyde.17 We have designed a new generation of diphosphine
ligands based on xanthene backbones that give extremely
regioselective rhodium catalysts producing the linear alde-
hyde.18,19
Chart 1
Scheme 1. Schematic Representation of Different Routes to
Prepare Silica-Immobilized [Rh(A)(CO)]+ (1+)
The application of catalysts with large P-Rh-P bite angles
in multiphase hydroformylation reactions appeared very suc-
cessful as with these ligands a good catalyst performance was
combined with a high ligand-to-metal bond strength. These
properties resulted in selective two- and three-phase catalyst
systems that were completely separated from the product phase
and reused in numerous consecutive runs.20 Preliminary results
showed that under proper conditions a polysilicate immobilized
rhodium complex, containing a xanthene-based diphosphine,
gave rise to a very selective and sustainable hydroformylation
process.20b Here we report a detailed study showing that the
performance of such an immobilized catalyst is largely depend-
ent on the conditions applied. Under standard conditions the
system performed as a regioselective hydroformylation-
hydrogenation cascade catalyst, which yielded a clean one-pot
synthesis of 1-nonanol from 1-octene. Furthermore we will show
that with small and simple manipulations, which affect the
catalyst-support interactions, the system can be switched
between three different catalyst modes. Depending on the
conditions applied, the catalyst system can either function as a
hydroformylation, a hydrogenation, or a hydroformylation/
hydrogenation sequence catalyst. Moreover, upon recycling and
reusing the system we can reversibly switch between these
catalyst modes, thus using the same batch of catalyst for different
types of reactions.
Results and Discussion
Catalyst Immobilization. The rhodium-diphosphine com-
plex Rh(A) was immobilized on silica using the sol-gel
technique and by a direct anchoring to commercially available
silica. The latter method has been studied using different
conditions. Both techniques are relatively straightforward
procedures. Via the sol-gel process, Rh(A) was immobilized
on a polysilicate support by stirring a solution of A, [Rh(acac)-
(CO)2], and tetramethyl orthosilicate (TMOS) in THF/H2O to
obtain [Rh(A)CO]+ (1(I)+) (Scheme 1-I).20b The resulting gel
was dried and crushed into a free-flowing silica.
The immobilization of Rh(A) on commercially available silica
was performed in four different ways to obtain 1(II) to 1(V)
(11) Lindner, E.; Schneller, T.; Auer, F.; Weger, P.; Mayer, H. A. Chem.
Eur. J. 1997, 3, 1833.
+
+
(Scheme 1-II to 1-V). In the first three approaches, A was
covalently tethered to silica (to obtain silica(A)) by refluxing a
suspension of A and silica in toluene for 2 h. The subsequent
complexation of the rhodium precursor was performed under
three different conditions. In the first approach the rhodium
precursor [Rh(acac)(CO)2] and silica(A) were simply mixed
together and stirred in a THF suspension (Scheme 1-II). In the
second way, silica(A) was first reacted with dimethoxydimeth-
ylsilane to modify the acidic silanols on the silica surface.24 To
this end a suspension of silica(A) and dimethoxydimethylsilane
was refluxed for 2 h in toluene and subsequently stirred in a
solution of [Rh(acac)(CO)2] in THF at room temperature for
(12) Schubert, U. New J. Chem. 1994, 18, 1049.
(13) Blum, J.; Avnir, D.; Schumann, H. Chemtech 1999, 32.
(14) Blum, J.; Rosenfeld, A.; Polak, N.; Israelson, O.; Schumann, H.;
Avnir, D. J. Mol. Catal. A 1996, 107, 217.
(15) Shriver, D. F.; Atkins, P. W.; Langford, C. H. Inorganic Chemistry;
Oxford University Press: Oxford, 1994.
(16) Devon, T. J.; Phillips, G. W.; Puckette, T. A.; Stavinoha, J. L.;
Vanderbilt, J. J. U.S. Patent to Texas Eastman 4,694,109, 1987; Chem. Abstr.
1988, 108, 7890.
(17) Casey, C. P.; Whiteker, G. T.; Melville, M. G.; Petrovich, L. M.;
Gavey, J. A.; Powell, D. R. J. Am. Chem. Soc. 1992, 114, 5535.
(18) Kranenburg, M.; van der Burgt, Y. E. M.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M.; Goubitz, K.; Fraanje, J. Organometallics 1995, 14,
3081.
(19) van der Veen, L. A.; Boele, M. D. K.; Bregman, F. R.; Kamer, P.
C. J.; van Leeuwen, P. W. N. M.; Goubitz, K.; Fraanje, J.; Schenk, H.; Bo,
C. J. Am. Chem. Soc. 1998, 120, 11616.
(21) Allum, K. G.; Hancock, R. D.; Howell, I. V.; McKenzie, S.;
Pitkethley, R. C.; Robinson, P. J. J. Organomet. Chem. 1975, 87, 203.
(22) Bemi, L.; Davies, J. A.; Fyfe, C. A.; Wasylishen, R. E. J. Am. Chem.
Soc. 1982, 104, 438.
(23) Capka, M.; Czakoova´, M.; Urbaniak, W.; Schubert, U. J. Mol. Catal.
1992, 74, 335.
(24) This method was reported to be equally efficient in the modification
of silica surfaces as the use of chloroalkylsilanes: Sindorf, D. W.; Marciel,
G. E. J. Am. Chem. Soc. 1983, 105, 3767.
(20) (a) Sandee, A. J.; Slagt, V. F.; Reek, J. N. H.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M. Chem. Commun. 1999, 17, 1633. (b) Sandee, A. J.;
van der Veen, L. A.; Reek, J. N. H.; Kamer, P. C. J.; Lutz, M.; Spek, A.
L.; van Leeuwen, P. W. N. M. Angew. Chem., Int. Ed. Engl. 1999, 38,
3231. (c) Schreuder Goedheijt, M.; Hanson, B. E.; Reek, J. N. H.; Kamer,
P. C. J.; van Leeuwen, P. W. N. M. J. Am. Chem. Soc. 2000, 220, 1650.
(d) Meehan, N. J.; Sandee, A. J.; Reek, J. N. H.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M.; Poliakoff, M. Chem. Commun. 2000, 1497.

8470 J. Am. Chem. Soc., Vol. 123, No. 35, 2001
Sandee et al.
Table 1. Charactaristic Data of Immobilized [Rh(A)CO]+ (1(I)
)
+
Compared with Those of the Homogeneous Analoguesa
+
(1)(I)
(2)+(OTf)
(2)+(BF4)
31P NMR
δ ppm (JP-Rh
FT-IR
38 (br)b
36(br)b
)
37.4 (d, 122 Hz)c
2003
37.2 (d, 122 Hz)c
1998
2011
ν(CO) (cm-1
)
b
a For more details see the Experimental Section. Obtained by MAS
solid-state NMR; JP-Rh is too small for detection in the solid state.c
Obtained by liquid-state NMR.
Table 2. Qualitative XPS Identification of the Elements Present in
[Rh(A)CO]+ Immobilized via the Sol-Gel Technique (1(I)+) Using
[Rh(B)CO]+(BF)4 (2+(BF4)) as a Reference Compound and the
Observed Binding Energies of the Specific Orbitals
Figure 1. 31P NMR spectra obtained during the sol-gel processing
of [Rh(B)(acac)(CO)]: (A) [Rh(B)(acac)(CO)] in a soluble prepolymer
mixture; (B) transformation from [Rh(B)(acac)(CO)] to [Rh(B)(CO)]+;
(C) transformation has been completed to [Rh(B)(CO)]+ (the polymer
has gelled at this stage); and (D) HRh(B)(CO)2 in a wet polymer gel,
obtained from [Rh(B)(CO)]+ upon applying a CO/H2 atmosphere.
binding energies (eV)
elements
[Rh(A)CO]+ in sol-gel
[Rh(B)CO]+(BF)4
Si2p
P2p
B1s
C1s
Rh3d
Rh3d
N1s
O1s
F1s
107.9
137a
134.1
191.5
287.1
311.2
315.1
289.3
312.9
317.4
404.1
537.2
relative intensity of 3.3 and 2. This is comparable to the results
of 2+(BF4), for which binding energies of 311 and 316 eV with
a relative intensity of 3.2 and 2 were found.20b These data are
in good agreement with two-level-degenerated energy levels of
the rhodium-3d electrons found for rhodium(I) compounds.30
The cationic complex formed during the sol-gel process,
which was started by mixing B and [Rh(acac)(CO)2] in a TMOS/
H2O/THF solution, was monitored using liquid-state 31P NMR
spectroscopy (Figure 1).31 After [Rh(B)(acac)CO] was formed,
as indicated by a broad doublet at 10 ppm and JP,Rh ) 92 Hz,
this complex quantitatively transformed into [Rh(B)CO]+ (2+)
(doublet at 37 ppm; JP,Rh ) 122 Hz) during the gelation process
(Figure 1), having a siloxate as its counterion. Probably acidic
silanols, formed during the hydrolysis of TMOS, protonate the
acetylacetonate to acetylacetone. As a consequence 2+ is formed
having a silicate counterion.32 On exposing the gel containing
2+ to 1 bar of CO/H2 (1:1) for 3 h at room temperature the
color of the gel changed from orange to yellow. 31P NMR studies
elucidated the quantitative transformation of 2+ to [HRh(B)-
(CO)2] (2) (doublet at 22 ppm; JP,Rh ) 123 Hz), which is the
key intermediate for a selective hydroformylation catalyst in a
homogeneous phase (Figure 1).18,19
Since Si(OMe)4 (Q elements) was used as the major silica
precursor with only 5% of RSi(OMe)3 (T elements) a dense
silicate network was expected to be formed.9 The presence of
a rhodium complex in the sol-gel matrix can even give rise to
a further increase in network density. The composition of the
sol-gel manufactured silica was investigated by means of 29Si
MAS NMR (Figure 2). With this technique, the ratio of Si-
O-Si versus Si-OH and Si-OR groups can be determined
and the density of the network can be estimated from the ratio
of silica atoms having a branching point of 4, 3, 2, or 1 (Q4,
536.4
687.1
a Very weak signal.
30 min (Scheme 1-III). In the third approach, [Rh(acac)(CO)2]
was added to a prestirred mixture of silica(A) and triethylamine
in THF. The resulting suspension was stirred for 30 min at room
temperature (Scheme 1-IV). For the last method the diphosphine
rhodium complex was synthesized prior to the immobilization
by adding [Rh(acac)(CO)2] to a solution of A in THF and stirring
the mixture for 30 min at room temperature. Predried silica was
added to this reaction mixture and the suspension was stirred
for 18 h (Scheme 1-V). All above-described catalyst systems
were washed thoroughly and dried under reduced pressure before
use.
+
Catalyst Characterization. System 1(I) was characterized
by means of solid-state 31P MAS NMR and FT-IR, and the data
were in good agreement with the fully characterized (homoge-
neous) cationic complexes 2+(OTf) and 2+(BF4); 2+ ) [Rh-
(B)CO]+ (Table 1).20b,25,26 1(I) showed a broad singlet at 38
+
ppm (versus a broad singlet at 36 ppm, observed for 2+(OTf))
in the 31P MAS NMR spectrum. In the IR spectrum the carbonyl
vibration was found at 2011 cm-1, which is close to those found
for 2+(OTf) (2003 cm-1) and 2+(BF4) (1998 cm-1).
X-ray photoelectron spectroscopy (XPS) qualitatively identi-
fied the elements in 1(I)+, and the characteristic electron binding
energies compared well with those of 2+(BF4) (Table 2).27,28
From XPS it was also determined that rhodium is only present
in the oxidation state (I); no traces of metallic rhodium(0) were
found in the samples.29 The binding energies of the rhodium
+
3d electrons in 1(I) were found to be 312 and 317 eV with a
Q3, Q2, and Q1, respectively) by deconvoluting the relative peak
areas.10 For the silica material, prepared in the presence of 1(I)
,
+
(25) It was observed that the stretch frequency of the carbonyl is
influenced by the counterion of the complexes. The influence of the SiO-
counterion of our immobilized complexes was found to be sensitive to the
presence of traces of a protic solvent.
we found a relative ratio of Q4, Q3, Q2 of 49.0/40.5/10.2. (no
terminal Q1 was observed, and the amount of T elements was
(26) van der Veen, L. A.; Keeven, P. H.; Schoemaker, G. C.; Reek, J.
N. H.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Lutz, M.; Spek, A. L.
Organometallics 2000, 19, 872.
(27) Tang, L.; Huang, M.; Liang, Y. Chin. J. Polym. Sci. 1996, 14, 199.
(28) Valuable information on transition metal complexes on a silica
support was recently obtained using EXAFS: Bianchini, C.; Burnaby, D.
G.; Evans, J.; Frediani, P.; Meli, A.; Oberhauser, W.; Psaro, R.; Sordelli,
L.; Vizza, F. J. Am. Chem. Soc. 1999, 121, 5961.
(30) Niemantsverdriet, J. W. Spectroscopy in Catalysis; Weinheim,
Germany, 1995.
(31) Nonimmobilized complexes can be studied easily during the sol-
gel process by means of liquid-state NMR. This is not possible for the
immobilized rhodium siloxantphos complex (Rh(A)).
(32) Ion pairs of cationic rhodium-phosphine species on silica were
previously observed by Basset et al. via the protonation of rhodium-allyl
groups by the silica: Scott, S. L.; Dufour, P.; Santini, C. C.; Basset, J.-M.
J. Chem. Soc., Chem. Commun. 1994, 2011.
(29) Besson, M.; Gazelot, P.; Pinel, C.; Neto, S. Heterog. Catal. Fine
Chem. IV 1997, 215.

A Silica-Supported Hydroformylation-Hydrogenation Catalyst
J. Am. Chem. Soc., Vol. 123, No. 35, 2001 8471
Figure 2. 29Si MAS NMR spectra of the Si-support of the sol-gel immobilized [Rh(A)(CO)]+ (1(I)+) (A) and [Rh(B)(CO)]+ (2+) (B).
Table 3. Hydroformylation of 1-Octene Using Polysilicate-Immobilized [Rh(A)CO]+ (1(I)
)
+
a
entry/
(method of
preparation)
time
(h)
conversion
(%)
TOFb
l/b
ratio
l-aldehyde
(%)
b-aldehyde
(%)
l-alcohol
(%)
octene isomers/
octane (%)
(h-1
)
1/(I)
2
0.5
23
22
22
2
20
97
24
18
37
19
72
18.3
n.d.
8.0
65
2
19
37
37
32
2
94.6
40.1
85.5
96.2
90.7
93.3
70.0
1.5
22.0
4.5
3.6
0
0.2
37.9
9.9
2/(II)
3/(III)
0
4/(IV)
8.7
2.6
1.0
5.1
0
0.2
5/(V)
13.2
283
119
2.6
1.6
6/(homog.)
7/(no ligand)
2.9
3.7
2
28.9
0.1
1.0
a P(CO/H2) (1:1) ) 50 bar, temperature ) 80 °C, ligand:Rh ) 10, substrate:Rh ) 637:1, Rh content 10 µmol. Samples were analyzed by means
of GC and GC-MS analysis. b Average turnover frequencies were calculated as (mol product)(mol catalyst)-1h-1, n.d. ) not determined.
too low to detect, Figure 2A). For the silica material, prepared
in the presence of 2+, comparable results were obtained; a Q4,
Q3, Q2 ratio of 57.5/37.5/4.9 was observed (Figure 2B).34 These
results indicate that the network density of these systems is
indeed very high and the copolymerization of 5% of RSi(OMe)3
(A) yields only slightly less dense networks.
The Impact of the Catalyst Preparation Procedure on
Catalysis. The method of catalyst immobilization appeared to
affect its performance in catalysis. When the catalyst was
synthesized via route II the catalyst showed a low selectivity
in the hydroformylation of 1-octene (the linear to branched
aldehyde ratio was even lower than 2) (Table 3, entry 2),
whereas the route V catalyst is highly selective toward the linear
aldehyde (with a linear-to-branched ratio of 37) (Table 3, entry
5). In accordance with examples from literature it is likely that
the former preparation procedure gives rise to the ionic bonding
of ligand-free rhodium cations on the slightly acidic silica
surface.22,35 If the rhodium phosphine complex is prepared prior
to anchoring (route V) no ligand-free rhodium is attached to
the silica. We also succeeded in eliminating the disturbing effect
of the acidic silanols on the catalyst preparation via the chemical
modification of the silica surface (route III) or upon addition
of a neutralizing base (route IV). Premodification of the silica
using dimethoxydimethylsilane (III) largely improved the
catalyst selectivity (linear to branched aldehyde ratio of 19,
Table 3, entry 3) at the cost of some activity.22 The addition of
triethylamine (IV) also resulted in a very good hydroformylation
catalyst (with a linear to branched aldehyde ratio of 37, Table
3, entry 4).
System 1(I)+, immobilized via the sol-gel process (Scheme
1-I), performed very well in the hydroformylation of 1-octene.
The selectivity for the linear aldehyde of 1(I)+ was found to be
as high as 94.6%, which equals that of its homogeneous
analogue (Table 3, entries 1 and 6). Again, the preformation of
the rhodium diphosphine complex before immobilization avoided
the formation of ligand free rhodium cations on the silica
surface. This approach gives rise to a well-defined, very selective
hydroformylation catalyst.
The high network density of immobilized 1(I)+, obtained via
the sol-gel process, was expected to have implications on the
catalysis; it can result in a good recyclability due to its rigidity,
but at the same time it might decrease the catalyst activity due
to the blocking of catalyst sites.9 The sol-gel immobilized
(33) A transition metal can serve as an extra junction in the silica network
and it can also catalyze the polycondensation process. This was previously
observed by Lambert and Gonzalez: Lambert, C. K.; Gonzalez, R. D.
Microporous Mater. 1997, 179.
(34) The resolution of Figure 2A is better than that of Figure 2B due to
a difference in the number of scans.
(35) Yao, J.-Z.; Chen, Y.-Y.; Tian, B.-S. J. Organomet. Chem. 1997,
534, 51.

8472 J. Am. Chem. Soc., Vol. 123, No. 35, 2001
Sandee et al.
Table 4. Hydroformylation of 1-Octene Using Sol-Gel and Silica-Immobilized Catalyst [Rh(A)CO]+ (1+) in Subsequent Catalytic Runsa
entry
[cycle]
meth of
prep.
time
(h)
conversion
(%)
TOFb
l/b
ratio
l-aldehyde
(%)
b-aldehyde
(%)
l-alcohol
(%)
octene isomers/
octane (%)
(h-1
)
1 [1]
I
I
I
I
2
2
2
2
20
19
19
12
18
26
25
12
65
43
35
62
94.6
90.0
87.6
89.6
1.5
2.2
2.7
1.6
3.6
5.1
6.7
8.8
0.2
2.6
3.0
0
2 [2]
3 [3]
4 [4]
5 [1]
6 [2]
I
I
18
18
38
30
23
17
22
25
61.0
77.9
4.1
3.7
29.6
15.1
5.3
3.4
7 [1]
8 [2]
9 [3]
V
V
V
22
22
72
37
41
61
13
15
8
37
45
27
90.7
91.5
79.9
2.6
2.1
3.5
5.1
4.0
13.2
1.6
2.4
3.4
10 [1]
11 [2]
12 [3]
13[4]
III
III
III
III
23
23
23
72
24
23
22
44
8
8
8
5
19
20
16
16
85.5
87.3
83.7
84.8
4.5
4.5
5.2
5.4
0
0
0
0
9.9
8.3
11.1
9.8
14 [1]
15 [2]
16 [3]
17 [4]
Ic
Ic
Ic
Ic
Ie
24
24
24
24
2.5
69
69
69
67
7
35d
36d
36d
35d
4
32
36
35
35
33
92.8
94.1
94.0
94.5
92.0
3.0
2.7
2.7
2.7
2.8
2.5
1.2
1.0
1.3
0
1.7
2.0
2.3
2.2
5.2
18(silica/Et3N)
a P(CO/H2) (1:1) ) 50 bar, temperature ) 80 °C, ligand:Rh ) 10, substrate:Rh ) 637:1, Rh content 10 µmol. Samples were analyzed by means
of GC and GC-MS analysis. b Average turnover frequencies were calculated as (mol product)(mol catalyst)-1 h-1
the catalyst mixture. d Initial turnover frequency. e 1 mL of triethylamine added to the catalyst mixture.
.
c 1 mL of 1-propanol added to
catalyst, however, was slightly faster than the silica immobilized
analogue (Table 3, entries 1 and 5), indicating that the catalytic
sites are fully accessible.12
(Table 4, entries 10-13). The modification of the surface
silanols with alkylsilanes did not yield an optimal catalyst
system. The overall selectivity for the linear aldehyde (ranging
from 83.7 to 87.3%) was slightly lower compared with the other
catalysts; more isomerization (8.3 to 11.1%) and branched
aldehyde (4.5 to 5.4%) was obtained. As yet we do not have a
plausible explanation for this.
Interestingly, we found a more subtle method to reduce the
influence of the silica. In the presence of 1 mL of 1-propanol,
which is approximately 7% of the total volume of the reaction
mixture, an efficient suppression of hydrogenation activity has
been realized; a high overall selectivity for the linear aldehyde
(ranging from 92.8 to 94.5%) was obtained in subsequent batch-
wise runs (Table 4, entries 14-17). The effect of the presence
of 1-propanol is in contrast with previously reported examples
of hydroformylation catalysts, to which alcohols or amines were
added to promote the hydrogenation of aldehydes via a transfer
hydrogenation reaction.38 In the present case the alcohol prevents
the formation of the hydrogenation catalyst from the hydro-
formylation catalyst by deactivating the acidic silanols on the
silica surface. The addition of triethylamine as a base also
enabled the suppression of the hydrogenation activity (Table 4,
entry 18).
Influence of the Silica on the Catalyst Recycling Proper-
ties. Sol-gel and silica immobilized Rh(A) were tested in
successive hydroformylations of 1-octene to investigate the
effect of the support on the recyclability of the catalyst (Table
4, entries 1-6 and 7-9, respectively). For both systems the
ratio of linear aldehyde, branched aldehyde, and octene isomers
was found to be comparable with the homogeneous analogue
(Table 3, entry 6). Upon recycling, the high regioselectivity for
the linear aldehyde was maintained (linear-to-branched ratios
ranging from 22 to 65) while only a few percent of alkene
isomers was formed as a side product (ranging from 0 to 3.4%).
Interestingly, we observed a small decrease in hydroformylation
activity upon recycling along with an increasing formation of
1-nonanol (4-9%), an effect that becomes more pronounced
(up to 30%) at longer reaction times (Table 4, entries 5 and 6).
We have not observed this phenomenon in analogous homo-
geneous hydroformylation reactions, suggesting that the silica
support plays a key role in this secondary reaction. We suggest
that the acidic silica increasingly blocks the formation of HRh-
(A)(CO)2 1(I) from 1(I)+ (vide infra), resulting in an increase in
hydrogenation activity39 and a small decrease in hydroformy-
lation activity.36,37
It is evident that the silica support influences the catalytic
performance and in the following part we describe experiments
that provide a better insight into the processes involved. In the
sol-gel state the immobilized cationic complex 1(I)+ completely
transforms to the rhodium hydride species 1(I) under a CO/H2
atmosphere (Figure 1) (vide supra). On dried silica, however,
this conversion might not be complete since the dried support
When the silica material with the capped (acidic) silanols
was used (Scheme 1-III), the influence of the silica on the
recyclability of the hydroformylation catalyst was largely
suppressed. No hydrogenation of the aldehyde was observed
as a secondary reaction in any of the successive catalytic runs
is more acidic.40 Hence, 1(I) and 1(I) probably coexist on the
+
(36) Rhodium Catalyzed Hydroformylation; van Leeuwen, P. W. N. M.,
Claver, C., Eds.; Kluwer Acedemic Publishers: Dordrecht, The Netherlands,
2000.
(37) Homogeneous Hydrogenation; Chaloner, P. A., Esteruelas, M. A.,
Joo´, F., Oro, L. A., Eds.; Kluwer Acedemic Publishers: Dordrecht, The
Netherlands, 1994.
(38) (a) Kaneda, K.; Imanaka, T.; Teranishi, S. Chem. Lett. 1983, 1465.
(b) Anderson, J.-A.; Currie, A. W. S. Chem. Commun. 1996, 1543.
(39) Although rhodium-catalyzed hydrogenation of carbonyl groups is
not a commonly used synthetic route for the production of alcohols, the
mechanism of this reaction is well understood. See (besides ref 36) for
example: To¨ro¨s, S.; Lolla´r, L.; Heil, B.; Marko´, L. J. Organomet. Chem.
1983, 255, 377.
silica support. To investigate the effect of dried silica on these
types of complexes, several experiments in solution were
performed using Rh(B).
Upon the addition of predried silica to a yellow solution of
2 in toluene, the solution slowly decolorized and the silica turned
(40) The decrease in the capacity of silica to form hydrogen bridges on
drying gives rise to an increase in acidic sites on the silica surface. The
addition of a protic solvent (water or alcohol) to dried silica will facilitate
hydrogen bond formation and thereby neutralize the acidity: van Roosmalen,
A. J.; Mol, J. C. J. Phys. Chem. 1979, 83, 2485.

A Silica-Supported Hydroformylation-Hydrogenation Catalyst
J. Am. Chem. Soc., Vol. 123, No. 35, 2001 8473
Table 5. Hydroformylation (X) and Hydrogenation (Y) Activities of [Rh(B)(CO)]+(CF3COO)- (2+) and HRh(B)(CO)2 (2)a
catalyst
(reaction)
time
(h)
conversion
(%)
TOFb
(h-1
L/b
ratio
l-aldehyde
(%)
b-aldehyde
(%)
l-alcohol
(%)
octane/octene
isomersc (%)
)
2+ (X)
2′e (X)
2+ (Y)
2 (Y)
2
12
20
16
0
21
187
22
>50
52
75.3
94.5
0
1.8
0
0
100
0
24.7d
3.7
2
2
0
a Temperature ) 80 °C, ligand:Rh ) 10, Rh content 10 µmol, substrate:Rh ) 637:1, using 1 mL of 1-octene (in case of X) and 1 mL of
1-nonanal (in case of Y) as the substrate, P(CO/H2) (1:1) ) 50 bar (in case of X) and P(H2) ) 50 bar (in case of Y), unless else stated. Samples
were analyzed by means of GC and GC-MS analysis. b Average turnover frequencies were calculated as (mol product)(mol catalyst)-1 h-1 c Octane
.
and alkene isomers are not quantitatively separable on GC. d Of which approximately 50% was octane. e Data taken from ref 19, reaction performed
under 20 bar of CO/H2 and 80 °C at a ligand-to-metal ratio of 5.
Scheme 2. Representation of the Interconversion of the
orange. This silica “adsorbed” rhodium diphosphine complex
Catalyst Systems [Rh(A)(CO)]+ (1+) and [HRh(A)(CO)2] (1)
indeed appeared to be the cationic species 2+ as indicated by
and the Products Generated from Each Catalyst Species
the carbonyl vibration at 1972 cm-1 in the IR spectrum.25 The
rhodium-hydrido complex 2 is converted to 2+ by the silica,
probably via a protonation of the rhodium hydride, which after
elimination of H2 yields the cationic species.41 Upon the addition
of 20 µL of trifluoroacetic acid to a mixture of 2 in d6-benzene
a similar protonation resulted in the formation of 2+(CF3COO-),
as indicated by 31P NMR that showed a broad doublet at 38
ppm; JP,Rh ) 111 Hz.42 This supports the idea that the conversion
of 2 to 2+ indeed occurs via a simple protonation.
The catalytic performance of 2+ is significantly different from
that of the rhodium hydride analogue, 2. The activity of
2+(CF3COO-) in the hydroformylation of 1-octene was inves-
tigated by monitoring a mixture of 2, CF3COOH, and 1-octene
in toluene under standard hydroformylation conditions (Table
5, entry 1). After 2 h, 12% of 1-octene was converted; 75% of
the products were aldehydes (TOF ) 21 mol‚mol-1‚h-1) while
the remaining 25% was octane, obtained by hydrogenation of
The hydrogenation activity of both 2+(CF3COO-) and 2 was
1-octene. Compared to 2 (Table 5, entry 2), the hydroformylation
further compared in the hydrogenation of 1-nonanal under 50
rate of 2+ was a factor 10 lower, but the hydrogenation activity
bar of H2. Catalyst 2+(CF3COO-) showed a significant hydro-
was significantly higher.39
genation of the aldehyde to the corresponding alcohol (16%
Generally, the catalyst for hydroformylation is a neutral
rhodium(I) hydride species36 that is clearly distinct from the
species that are active for hydrogenation.37 The hydrogenation
catalysts are cationic Rh(I)+ or neutral Rh(I)Cl species. Often
rhodium(I) salts are used as the precursor for hydroformylation
catalysts. Although there are several papers that seem to invoke
cationic species as the catalysts, under the reaction conditions
(H2, CO, temperature > 25 °C) these salts are converted to a
rhodium hydride complex.43 Anions that have been used include
halides, conjugate bases of weak acids, thiolates, alkoxides, etc.
The frequently reported “promoting” effect of bases such as
amines is based on more efficient formation of the active
rhodium hydride by neutralizing the formed strong acids (HI,
HCl, HBr, HBF4). Rhodium salts of weaker acids, like thiolates,
are smoothly converted into the rhodium hydride without the
addition of base.44-46 Stanley reported hydroformylation cata-
lysts that differ from the rhodium hydride species consisting of
bimetallic rhodium complexes.47
conversion within 2 h reaction time, Table 5, entry 3), whereas
the rhodium hydride complex 2 is completely inactive in this
reaction (Table 5, entry 4). The presence of both complexes on
the silica support thus explains the observed cascade of a
hydroformylation followed by a hydrogenation reaction. These
experiments support the proposal that in the silica-immobilized
system 1+ and 1 coexist on the polysilicate surface and that 1+
must be formed from 1 by a protonation of the rhodium-hydride
by the silica support since this is the only acid present in the
reaction mixture.
The neutralizing effect of alcohols on the silica-supported
cationic rhodium species was illustrated by the addition of
1-propanol (under 1 atm of CO/H2) to a suspension of silica
“adsorbed” 2+ in toluene. This resulted in a decolorization of
the silica while the toluene turned yellow; Rh(B) was “desorbed”
from the silica under formation of the rhodium hydride 2 as
indicated by the appearance of a doublet at 21 ppm; JRh,P
)
125 Hz in the 31P NMR spectrum (Scheme 2). The presence of
alcohol sufficiently decreases the acidity of the silica, which
becomes unable to protonate the rhodium hydride species.40
Hence 2+ is completely transformed to the rhodium hydride 2
under a CO/H2 atmosphere in the presence of alcohol.42
Consequently, the catalytic performance using Rh(A), im-
mobilized on polysilicates, can be controlled by the addition of
small amounts of alcohol.
(41) The bonding of a rhodium phosphine carbonyl complex to a silica
surface was previously applied via the protonation of a rhodium-methyl
bond: Scott, S. L.; Szpakowicz, M.; Mills, A.; Santini, C. C. J. Am. Chem.
Soc. 1998, 120, 1883.
(42) The reversible protonation and hydrogenation of a comparable
rhodium hydride viz. HRh(CO)(TPPTS)3 was previously observed: Her-
rmann, W. A.; Kulpe, J. A. J. Organomet. Chem. 1990, 389, 85.
(43) Kwok, T. J.; Wink, D. J. Organometallics 1993, 12, 1954.
(44) Park, H. S.; Alberico, E.; Alper, H. J. Am. Chem. Soc. 1999, 121,
11697.
(45) Die´gues, M.; Claver, C.; Masdeu-Bulto´ A. M.; Ruiz, A.; van
Leeuwen, P. W. N. M.; Schoemaker, G. C. Organometallics 1999, 18, 2107.
(46) Pa`mies, O.; Net, G.; Ruiz, A.; Bo, C.; Poblet, J. M.; Claver, C. J.
Organomet. Chem. 1999, 586, 125.
Hydroformylation-Hydrogenation Cascade Reaction. Un-
der standard hydroformylation conditions, the cationic species
(47) Broussard, M. E.; Juma, B.; Train, S. G.; Peng, W. J.; Laneman, S.
A.; Stanley, G. G. Science 1993, 260, 1784.

8474 J. Am. Chem. Soc., Vol. 123, No. 35, 2001
Sandee et al.
Figure 3. Course of the hydroformylation-hydrogenation sequence reaction of 1-octene using sol-gel immobilized Rh(A). The black line represents
the 1-octene concentration, the black dotted line 1-nonanal, the gray line the sum of 1-nonanal and 1-nonanol, and the gray dotted line 1-nonanol.
For detailed information about the conditions applied, see the Experimental Section.
1+ and the hydridic complex 1 coexist on the support. Hence
hydroformylation and hydrogenation will both proceed under a
CO/H2 atmosphere. Via a hydroformylation-hydrogenation of
1-octene using Rh(A), immobilized via the sol-gel process
(Scheme 1-I), we performed a clean one-pot reaction of 1-octene
to 1-nonanol. 98% of the 1-octene was converted in the
hydroformylation reaction and 97% of the linear nonanal was
subsequently hydrogenated to 1-nonanol resulting in an overall
selectivity of 90% for the linear alcohol after 328 h.48 Since
both reactions are rate dependent in substrate, the overall
reactivity of the cascade reaction is low. For commercial
purposes, the reactivity of the current system, applied as a
cascade reactor, is too slow as yet. Importantly, no heavy-end
side products were observed in this reaction owing to the mild
conditions applied.
On monitoring such a cascade reaction, mainly the hydro-
formylation of 1-octene to the aldehyde was observed in the
first few hours (Figure 3). The hydrogenation toward the
corresponding alcohol started at higher aldehyde concentrations.
When approximately 90% of the 1-octene was consumed (at
60 h) the hydroformylation activity had decreased significantly,
which is in line with the first-order rate dependency in substrate.
In contrast, the hydrogenation of the aldehyde product pro-
ceeded. As a result, the aldehyde concentration decreased again
after approximately 40 h, which in turn caused a decrease of
the hydrogenation rate. After 175 h the hydroformylation of
1-octene has proceeded up to 97% and the subsequent aldehyde
hydrogenation up to 75% conversion.49
with a high regioselectivity, is uncommon for rhodium cata-
lysts.51 Moreover, we can control the ratio of the two coexisting
catalyst species 1+ and 1 and we are able to recycle the catalyst
completely as a result of the heterogeneous nature of the system.
The combination of these properties can be utilized for a
multipurpose system that can be switched between a pure
hydroformylation catalyst (X), a pure hydrogenation catalyst
(Y), and a hydroformylation-hydrogenation (Z) sequence
catalyst (Scheme 3).
Modulation of the Catalyst Functionality. We started a
series of catalyst experiments on 1-octene, using polysilicate
immobilized Rh(A), with a reaction under standard conditions,
thus with the catalyst system in the Z mode. The reaction was
stopped after 172 h, which resulted in a product mixture that
consisted of 66.7% of 1-nonanol and 18.5% of 1-nonanal (Table
6, entry 1). After this reaction we recycled the system and
transformed it into a hydrogenation catalyst (Y) just by washing
it with toluene and subsequently adding a mixture of 1-octene
and 1-nonanal in toluene to the catalyst mixture. After a reaction
time of 24 h under an H2-atmosphere a complete hydrogenation
of both substrates was observed to octane and 1-nonanol,
respectively (Table 6, entry 2). This shows that the switch from
the Z to the Y mode was accomplished by simply replacing
(50) For a review on tandem reaction sequences under hydroformylation
conditions see: Eilbracht, P.; Ba¨rfacker, L.; Buss, C.; Hollmann, C.; Kitsos-
Rzychon, B. E.; Kranemann, C. L.; Rische, T.; Roggenbuck, R.; Schmidt,
A. Chem. ReV. 1999, 99, 3329.
(51) Examples of rhodium-catalyzed hydrocarbonylation include the
following: (a) Johnson, P.; Lawrenson, M. J. Fr. Dem. 1.549.414, 1968;
Chem. Abstr. 1970, 72, 2995. (b) Lawrenson, M. J. UK Patent 1.284.615,
1972; Chem. Abstr. 1972, 77, 125 982. (c) Lawrenson, M. J. UK Patent
1.254.222, 1971; Chem Abstr. 1972, 76, 33 787. (d) Fell, B.; Barl, M. J.
Mol. Catal. 1977, 2, 301. (e) Zhou, J.-Q.; Alper, H. J. Chem. Soc., Chem.
Commun. 1991, 233. (f) MacDougall, J. K.; Simpson, M. C.; Green, M. J.;
Cole-Hamilton, D. J. J. Chem. Soc., Dalton Trans. 1996, 1161. (g) Anderson,
J.-A. M.; Currie, A. W. S. Chem. Commun. 1996, 1543. The cobalt-
phosphine based Shell hydroformylation process produces alcohols with
linearities up to 80% in a similar reaction sequence: Arnoldy, P. Rhodium
catalyzed hydroformylation; van Leeuwen, P. W. N. M., Claver C., Eds.;
Kluwer Acedemic Publishers: Dordrecht, The Netherlands, 2000; p 203.
Such a clean, one-pot hydroformylation-hydrogenation
cascade system,50 producing a high yield of the linear product
(48) This result was obtained using a reaction mixture of 14 mL of
toluene, 0.5 mL of 1-octene, and 0.5 mL of decane. The obtained exact
product distribution was the following: 1-nonanol (89.8%), octane (4.5%),
l-nonanal (2.3%), b-nonanal (0.7%), and b-alcohol (0.7%).
(49) The decreased hydrogenation activity at higher conversions is most
probably caused by the increased alcohol concentration; the silica becomes
less acidic and the hydrogenation catalyst 1+ transforms to 1. Full conversion
to the alcohol is obtained at lower substrate concentration, see ref 48.

A Silica-Supported Hydroformylation-Hydrogenation Catalyst
J. Am. Chem. Soc., Vol. 123, No. 35, 2001 8475
Table 6. Results from Switching between Hydrogenation (Y), Hydroformylation (X), and Hydroformylation-Hydrogenation Sequence (Z)
Reactions Using Sol-Gel Immobilized [Rh(A)CO]+ (1(I)
)
+
a
entry/
(reaction)
time
(h)
conversion
octene (%)
conversion
aldehyde (%)
l-aldehyde
(%)
b-aldehyde
(%)
l-alcohol
(%)
octaneb
(%)
l/b
23
1/(Z)
2/(Y)
3/(Z)
4/(Y)
5/(X)
172
24
68
2
97
100
60
98
96
75
100
16
10
0
18.5
0
65.2
0
3.6
0
4.5
0
66.7
100
13.7
9.7
11.2
100
16.6
98
18
18
96
90.7
5.1
0
4.3
a Temperature ) 80 °C, ligand:Rh ) 10, Rh content 10 µmol, substrate:Rh ) 637:1, using 1 mL of 1-octene (X and Z) (plus 1 mL of 1-nonanal
in the case of Y) as the substrate(s), P(CO/H2) (1:1) ) 50 bar (X and Z) or P(H2) ) 50 bar (Y). Samples were analyzed by means of GC and
GC-MS analysis. b Numbers include isomers of 1-octene since these are not separable from octane on GC.
Scheme 3. Control over Catalyst Function by Changing the
Conclusion
Reaction Conditionsa
We have developed a polysilicate immobilized homogeneous
catalyst system that can act both as a hydrogenation and a
regioselective hydroformylation catalyst. This system has been
used for a clean one-pot synthesis of 1-nonanol from 1-octene
via a hydroformylation-hydrogenation cascade reaction and
could be quantitatively recovered from the product. The
catalyst-support interactions were fully controlled and easily
manipulated by simple changes in the reaction conditions. This
enabled a reversible switching of the catalyst mode between a
hydroformylation, a hydrogenation, and a hydroformylation/
hydrogenation cascade catalyst. In view of the increasing
demand for greener chemical processes the current system
exhibits several important properties: (1) it affords a quantitative
and straightforward separation of the catalyst from the products,
(2) it is reusable in numerous catalytic cycles without any
deterioration of the catalytic activity,20d and (3) it enables clean
and selective reactions for different important catalytic processes
using only one catalyst system.
a X ) hydroformylation, Y ) hydrogenation and Z ) hydrofor-
mylation/hydrogenation sequence.
the CO/H2 for an H2 atmosphere. More importantly, we observed
that this modulation is reversible; in the third catalyst cycle the
system was applied again as a Z-sequence catalyst by changing
the atmosphere from H2 to CO/H2 and using 1-octene as the
substrate. This resulted in a switch of the catalyst from the
hydrogenation mode back to the hydroformylation-hydrogena-
tion sequence mode. The regioselectivity for the linear aldehyde
and alcohol (overall linear-to-branched ratio of 18) was largely
restored (Table 6, entry 3). This indicates that the catalyst did
not decompose upon switching between these two modes, since
even a few percent of decomposed rhodium catalyst would
generally result in a dramatic drop in regioselectivity.
Experimental Section
Materials. 4,5-Bis(diphenylphosphino)phenoxazine19 and 9,9-dim-
ethyl-4,5-bis(diphenylphosphino)xanthene18 were synthesized according
to literature procedures. 1-Octene was purified over neutral alumina
prior to its use. All other chemicals were purchased commercially and
used without further purification. Solvents were dried prior to their
use. Hexane, pentane, diethyl ether, THF, toluene, and benzene were
distilled from sodium. Dichloromethane and triethylamine were distilled
from calcium hydride. All solutions and solvents not stated above were
degassed under argon prior to their use. All reactions were performed
under Schlenk conditions using Argon as the inert atmosphere.
Analytical Techniques. NMR spectra were recorded on a Bruker
AMX 300 or DRX 300 spectrometer. Chemical shifts are in ppm
relative to TMS as external standard unless otherwise stated. Solid-
state 31P MAS NMR chemical shifts are relative to NH4H2PO4 (at 0.8
ppm) and 29Si MAS NMR chemical shifts are relative to Zeolite A (at
-89 ppm) and Q8M8 (at 11.85 ppm). The correct pulse delays were
determined at 20 s for the 31P MAS NMR and 5 min for the 29Si MAS
NMR at a spinning rate of 10.000-11.000 Hz. FT-IR spectra were
obtained on a Bio-Rad FTS-7 spectrophotometer. Mass spectra (FAB)
were recorded on a JEOL JMS SX/SX102A. Elemental Analysis was
performed on an Elementar Vario EL apparatus (Foss Electric). XPS
spectra were obtained with a VG Escalab 200 spectrometer equipped
with an Al KR source and a hemispherical analyzer connected to a
five-channel detector. Measurements were carried out at 20 eV pass
energy. Charging was corrected for by using the C1s peak (284.6 eV)
as a reference. Samples were ground and pressed in indium foil, which
was placed on an iron stub. The XPS spectra have been fitted with a
VGS program fit routine and with XPSPEAK software version 3.1.
Synthesis of N-(3-Trimethoxysilane-n-propyl)-4,5-bis(diphe-
nylphosphino)phenoxazine (A). A solution of 500 mg (0.907 mmol)
of 4,5-bis(diphenylphosphino)phenoxazine in 5 mL of dimethylforma-
mide was added to a suspension of 44 mg (1.833 mmol) of NaH in 5
mL of dimethylformamide. The orange mixture was stirred 90 min at
70 °C. 3-Chloropropyltrimethoxysilane (362 mg; 1.819 mmol) was
In the fourth cycle, once more the system was switched back
from the Z to the Y mode (Table 6, entry 4). This time, the
hydrogenation reaction of a 1:1 mixture of 1-octene and
1-nonanal was stopped after 2 h and a chemoselectivity for the
alkene reduction over aldehyde reduction was observed (96%
alkene and 10% aldehyde was hydrogenated).52 From these four
catalytic runs it can be concluded that the immobilized catalyst
system is switched easily and repeatedly between the hydro-
genation mode and the hydroformylation-hydrogenation cas-
cade mode. We subsequently investigated, in the fifth run, the
switch of the system to a pure hydroformylation catalyst (Table
6, entry 5). The atmosphere was changed from H2 to CO/H2
and 1 mL of 1-propanol was added to the catalyst along with a
fresh batch of 1-octene in toluene. After 96 h 1-octene was
almost completely converted to the linear aldehyde with a
complete suppression of its hydrogenation to the alcohol! Hence,
the catalyst modulation between all three catalyst functionalities
was successfully accomplished upon small changes of the
reaction conditions.
(52) This is in contrast with Rh(A) performing as a Z-sequence catalyst
with which the aldehyde is preferentially reduced. The preference of
aldehyde hydrogenation under a CO/H2 atmosphere has previously been
observed on different cationic complexes; see refs 51e and 51g. It is assumed
that under hydroformylation conditions aldehyde coordination to the cationic
species will be kinetically favored over alkene coordination.

8476 J. Am. Chem. Soc., Vol. 123, No. 35, 2001
Sandee et al.
added at room temperature. The mixture was stirred for 18 h at 70 °C.
The brown-yellow suspension was filtered and the solvent was removed
under reduced pressure. The product was washed with several portions
of pentane until an off-white powder was obtained. Solvent and
impurities were removed in vacuo (1 × 10-5 bar) at 60 °C for 18 h
Catalysts were prepared freshly before use for catalysis. silica(A)
(1 g) and 1 × 10-5 mol of [Rh(acac)(CO)2] were stirred in 5 mL of
THF for 30 min at room temperature. The resulting catalyst-support
system was washed with THF and dried under reduced pressure (1(II)+).
1(III)+ was prepared, on modified silica, similar to method I. To prepare
1(IV)+, 1 g of silica(A) was suspended in a mixture of 1 mL of
triethylamine and 5 mL of THF and stirrer at room temperature for 30
min. After 1 × 10-5 mol of [Rh(acac)(CO)2] was added the reaction
mixture was stirred for another 30 min at room temperature. Workup
was analogues to other methods. To prepare 1(v)+, A and [Rh(acac)-
(CO)2] were stirred in 10 mL of THF for 30 min. Predried silica was
added to the yellow reaction mixture and the resulting suspension was
stirred for 18 h at room temperature. The resulting yellow-brown
catalyst-support system was washed with THF and dried under reduced
pressure.
Effect of Silica on HRh(B)(CO)2. CO/H2 was bubbled through a
solution of 5 mg of [Rh(acac)(CO)2] and 20 mg of B in 5 mL of toluene
for 10 min. Predried silica (250 mg) was added to the yellow reaction
mixture. As a result the solution decolorized and the silica turns orange.
FT-IR (KBr): ν(CO) 1972 cm-1. Under continuous bubbling of CO/
H2, 1 mL of 1-propanol was added to the reaction mixture. The solution
slowly became yellow. After 20 min a 31P NMR spectrum was
acquired: δ 21 (d, J(P,Rh) ) 125 Hz).
Effect of CF3COOH on HRh(B)(CO)2. CO/H2 was bubbled through
a solution of 5 mg of [Rh(acac)(CO)2] and 20 mg of B in d6-benzene
for 10 min. CF3COOH (20 µL) was added to the reaction mixture under
continuous bubbling of CO/H2. 31P NMR: δ 38 (br d, J(P,Rh) ) 111
Hz). A hydroformylation and a hydrogenation experiment were
performed using a catalyst mixture of 1 × 10-5 mol of [Rh(acac)-
(CO)2], 1 × 10-4 mol of B, and 20 µL of CF3COOH in toluene (see
below for details).
Hydroformylation of 1-Octene. A typical catalysis experiment was
used: A stainless steel 50 mL autoclave, equipped with a mechanical
stirrer, a substrate vessel, a cooling spiral, and a sample outlet was
charged with 1 g of 1 × 10-5 mol rhodium catalyst containing silica
in 10 mL of toluene. The suspension was incubated for 1 h at 80 °C
under 20 bar of CO/H2 (1:1). A mixture of 1 mL of 1-octene and 1 mL
of decane in 3 mL of toluene was added and the CO/H2 pressure was
brought to 50 bar. The mixture was stirred for 24 h. The autoclave
was cooled to 10 °C and the pressure was reduced to 1.8 bar. With
this small overpressure the liquid is slowly removed from the catalyst
with a 1.2 mm syringe. After the catalyst was washed with 5 mL of
toluene, 10 mL of toluene is added and the pressure was brought to 20
bar. Finally the mixture was heated to 80 °C and the second cycle was
performed.
1
(Yield 76.9%). Mp 138 °C dec. H NMR (300 MHz, CDCl3): δ 7.20
(m, 20H; ArH), 6.66 (t, 2H, 3J ) 7.9 Hz; CP-CH-CH), 6.49 (d, 2H,
3
3J ) 1.0 Hz; CH-CH-CH), 5.97 (dd, 2H, J ) 1.6, 7.8 Hz; CH-
3
CH-CC), 3.61 (s, 9H; CH3-O), 3.49 (t, 2H, J ) 8 Hz; N-CH2),
1.80 (m, 2H, 3J ) 8.1 Hz; CH2-CH2-CH2), 0.72 (t, 2H, 3J ) 8.0 Hz;
Si-CH2). 31P{1H} NMR (121.4 MHz, CDCl3, versus H3PO4): δ -18.5.
13C{1H} NMR (75.5 MHz, CDCl3): δ 146.7 (t, J(P,C) ) 10.9 Hz;
CO), 136.8 (t, J(P,C) ) 12.8 Hz; PC), 133.5 (t, J(P,C) ) 10.5 Hz;
PCCH), 132.9 (CN), 128.0 (CH), 127.9 (CH), 124.9 (CH), 124.4 (t,
J(P,C) ) 8.5 Hz; C), 123.5 (CH), 111.6 (CH), 50.4 (CH3-O), 46.6
(CH2-N), 17.7 (CH2-CH2-CH2), 5.8 (CH2-CH2-Si). 29Si{1H} NMR
(59.6 MHz, CDCl3): δ -43. FT-IR (KBr): 3058 cm-1 (w), 2940 cm-1
(w), 2839 cm-1 (w), 1553 cm-1 (m), 1461 cm-1 (s), 1417 cm-1 (s),
1377 cm-1 (m), 1226 cm-1 (m), 1087 cm-1 (s), 696 cm-1 (s). Exact
mass (FAB): 714.2353 [M + 1] (calcd for C42H42NO2P2Si, 714.2358).
Anal. Calcd for C42H41NO2P2Si H2O: C, 68.93; H 5.92; N, 1.92.
Found: C, 69.08; H, 5.70; N, 1.76.
Synthesis of [Rh(B)CO](BF4). Xantphos (B) (242 mg; 0.4182
mmol) was added to a clear yellow solution of 80 mg (0.2094 mmol)
of [Rh(µ-Cl)(CO)2]2 in 5 mL of EtOH. An orange precipitate was
formed and collected by filtration and washed with EtOH and Et2O
(yield 78.5%). The orange compound was dissolved in dichloromethane
and 63.6 mg (0.3267 mmol) of AgBF4 was added. A white precipitate
was filtered off and the solvent was removed under reduced pressure.
The yellow solid compound was recrystallized from dichloromethane/
pentane (yield 92.6%). (The triflate analogue was synthesized according
to the same procedure). 31P NMR (121.4 MHz, CDCl3, versus H3PO4):
δ 37.2 (d, J(P,Rh) ) 121 Hz). 1H NMR (300.0 MHz, CDCl3): δ 7.88
(dd, 2H, ArH), δ 7.66-7.54 (m, 24H, ArH), δ 1.81 (s, 6H, 2Me). FT-
IR (KBr): 1997.8 cm-1 ν(CO). Exact mass (FAB): 709.0942 [M] (calcd
for C40H32O2P2Rh, 709.0923). Anal. Calcd for C40H32O2P2Rh‚BF4‚0.5CH2-
Cl2: C 57.99, H 3.97. Found: C 58.68, H 3.90.
Synthesis of Sol-Gel Immobilized [Rh(A)CO]+ (1(I)+). A mixture
of 5.0 mg (0.0195 mmol) of Rh(acac)(CO)2 and 138.7 mg (0.1946
mmol) of A was dissolved in 6 mL of THF. H2O (2 mL) and 2 mL of
TMOS were subsequently added and a red-brown two-phase system
was formed. MeOH was added until a clear red-brown solution was
formed. Gelation took place within 1 h. After 36 h the gel was carefully
dried under reduced pressure. The dried gel was powdered and
thoroughly washed with MeOH, THF, and Et2O. The resulting pink-
red silicas were stored at -20 °C. The exact rhodium and phosphine
contents of the immobilized catalysts were determined by means of
Switching of Catalyst Functionality. Hydroformylation-reduction
sequence reactions were performed as described above. Hydroformy-
lations were also performed under the same conditions, but 1 mL of
propanol was added to the reaction mixture. Hydrogenations were
performed on a reaction mixture of 1 mL of 1-octene, 1 mL of
1-nonanal, and 1 mL of decane in 12 mL of toluene under 50 bar of
H2 at 80 °C. The catalyst recycling procedure was performed as
described above.
AES. FT-IR (KBr): ν(CO) 2011 cm-1 31P MAS NMR (121.4 MHz,
.
versus NH4H2PO4 ) 0.8 ppm): δ 38 br (some phosphine oxide (δ 26)
br and protonated phosphine (δ 51) was observed).
+
Synthesis of Silica Immobilized Catalyst 1(II) to 1(v)+. A typical
catalyst immobilization procedure on silica was used: 2 g of silica
(Silica 60 from sds, 70-200 µm, surface area 550 m2/g), which is stored
at 180 °C, was predried at 180 °C under reduced pressure for 2 h. A
(250 mg; 0.351 mmol) was added to a suspension of the silica in 20
mL of toluene and the resulting mixture was refluxed for 2 h. The
silica(A) was washed with toluene, dried under reduced pressure, and
stored under an inert atmosphere. The silica modification (Scheme 1-III)
was performed by refluxing a mixture of 2 g of silica(A) and 2 mL of
dimethoxydimethylsilane in 20 mL of toluene for 2 h. The resulting
modified silica(A) was washed with toluene, dried under reduced
pressure, and stored under an inert atmosphere.
Acknowledgment. We thank Dr. A. Kentgens for perform-
ing the solid-state NMR experiments, Prof. Dr. J. W. Niemants-
verdriet and L. Coulier for the help with the XPS measurements,
and J. Elgersma for performing the AES analyses. We are
grateful to the Innovation Oriented Research Program (IOP-
katalyse) for the financial support of this research.
JA010150P