Immobilized rhodium hydrogenation catalysts

Article abstract of DOI:10.1016/S0022-328X(01)00696-9

The showcase catalyst for olefin hydrogenations is Wilkinson's complex ClRh(PPh₃)₃ (1). Here, the Wilkinson-type catalyst ClRh[Ph₂P(CH₂)₃Si(OEt)₃]₃ (2), trans-ClRh(CO)[Ph₂P(CH₂)₃Si(OEt) ₃]₂ (3), and the chelate complex ClRh(PPh₃)[Ph₂PCH₂CHOHCH₂PPh ₂] (4) have been synthesized using the bifunctional ligands Ph₂P(CH₂)₃Si(OEt)₃ (5) and Ph₂PCH₂CHOHCH₂PPh₂ (6), and fully characterized. The dihydride complex 4(H)₂ has been generated in situ and characterized with NMR. Complexes 2, 3, and 4 have been immobilized on silica, giving 2i, 3i, and 4i, respectively, which have been studied by solid-state NMR. The catalytic activities of 2i-4i for the hydrogenation of 1-dodecene (7), 2-cyclohexen-1-one (8), and 4-bromostyrene (9) are compared with those of the homogeneous analogs 2 and 3, as well as with 1. While there are no substantial differences between 1 and 2 concerning TON and TOF, 2i shows reversed activity for the three test samples: dodecene gives the lowest TOF, followed by bromostyrene and cyclohexenone. However, TON and maximal yield are the same for 1, 2, and 2i. In contrast to 1 and 2, the immobilized catalyst 2i can be recycled seven times, 4i three times. Catalysts 3 and 3i give maximal TOF for the hydrogenation of 7, followed by 8 and 9. The yields are below 100% for the homogeneous catalyst 3, but immobilization (3i) gives maximum yields for all substrates.

Full text of DOI:10.1016/S0022-328X(01)00696-9

Journal of Organometallic Chemistry 627 (2001) 44–54
www.elsevier.nl/locate/jorganchem
Immobilized rhodium hydrogenation catalysts
Christof Merckle, Simone Haubrich, Janet Blu¨mel *
Organisch-Chemisches Institut der Ruprecht-Karls-Uni6ersita¨t Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Received 31 August 2000; received in revised form 16 January 2001
Abstract
The showcase catalyst for olefin hydrogenations is Wilkinson’s complex ClRh(PPh3)3 (1). Here, the Wilkinson-type catalyst
ClRh[Ph2P(CH2)3Si(OEt)3]3 (2), trans-ClRh(CO)[Ph2P(CH2)3Si(OEt)3]2 (3), and the chelate complex ClRh(PPh3)[Ph2PCH2-
CHOHCH2PPh2] (4) have been synthesized using the bifunctional ligands Ph2P(CH2)3Si(OEt)3 (5) and Ph2PCH2CHOHCH2PPh2
(6), and fully characterized. The dihydride complex 4(H)2 has been generated in situ and characterized with NMR. Complexes 2,
3, and 4 have been immobilized on silica, giving 2i, 3i, and 4i, respectively, which have been studied by solid-state NMR. The
catalytic activities of 2i–4i for the hydrogenation of 1-dodecene (7), 2-cyclohexen-1-one (8), and 4-bromostyrene (9) are compared
with those of the homogeneous analogs 2 and 3, as well as with 1. While there are no substantial differences between 1 and 2
concerning TON and TOF, 2i shows reversed activity for the three test samples: dodecene gives the lowest TOF, followed by
bromostyrene and cyclohexenone. However, TON and maximal yield are the same for 1, 2, and 2i. In contrast to 1 and 2, the
immobilized catalyst 2i can be recycled seven times, 4i three times. Catalysts 3 and 3i give maximal TOF for the hydrogenation
of 7, followed by 8 and 9. The yields are below 100% for the homogeneous catalyst 3, but immobilization (3i) gives maximum
yields for all substrates. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Immobilized catalysts; Olefin hydrogenation; Rhodium complexes; Bifunctional ligands; Silica support; Solid-state NMR
polymer matrix [12–16], or subjecting them to microen-
capsulation [10,17]. The key feature of all these differ-
ent approaches is to improve the possibility of catalyst
recovery and recycling.
1. Introduction
In a world of rapidly shrinking resources the so-
called ‘‘green’’ chemistry becomes more and more im-
portant. Homogeneous catalysts are the showcase
materials being studied in this direction for many
decades, and they are still improved following different
strategies: they are tailored according to the needs of
the catalytic reaction, and are made more and more
efficient [1,2], also by combining two different catalysts
[3,4]. Furthermore, several approaches have been devel-
oped to combine the advantages of homogeneous and
heterogeneous catalysts like easy separation of reac-
tants, products, and catalysts, as well as high activity
and selectivity: For example, water soluble catalysts
[5–7] for use in biphasic media have been applied in the
Rhoˆne–Poulenc process [5]. Biphasic fluorous catalysis
makes progress [8–10], and also immobilizing catalysts
via the sol–gel process [11], by anchoring them to a
For some time our group, like others, has pursued
this idea [12,13] by immobilizing homogeneous catalysts
on silica supports [18,19] via bifunctional linkers like
Ph2P(CH2)3Si(OEt)3 (5). Silica is an inexpensive, rea-
sonably well-defined material [20–22], and its reaction
with ethoxysilane groups has been studied in detail
[23,24], and applied in countless cases recently [25–29].
The real breakthrough for clean immobilization came
when we learned how to avoid side-products stemming
from the immobilization procedure [30,31]. Suspension
NMR [32] and multinuclear solid-state NMR [18,22,31]
have served as powerful tools for investigating the
amorphous solid materials. At the present state we are
able to immobilize any arbitrary phosphine complex on
the silica surface via covalent bonding, cleanly and in a
well-defined manner. As an example, here we present
the immobilized catalysts of the Wilkinson type, which
can easily be separated from the reaction mixture, and
recycled many times. Their activity with respect to the
* Corresponding author. Tel.: +49-6221-548470; fax: +49-6221-
544904.
E-mail address: j.bluemel@urz.uni-heidelberg.de (J. Blu¨mel).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00696-9

C. Merckle et al. / Journal of Organometallic Chemistry 627 (2001) 44–54
45
hydrogenation of standard substrates is studied, be-
cause hydrogenation is one of the most important and
best developed areas of catalysis [33]. We find that the
hydrogenation activity of our immobilized species can
favorably compete with the activity of corresponding
homogeneous analogs. Furthermore, an immobilized
rhodium carbonyl complex is studied, and in this case
turn over numbers (TON) are even higher than for the
analog in solution.
obtained quantitatively, and in analytically pure form.
Attempts to synthesize 2 by ligand exchange starting
from ClRh(PPh3)3 (1) were not successful, because PPh3
could not be removed from the reaction product, and
furthermore dimers were formed. Using RhCl3·3H2O as
a precursor [34] was unsuccessful, because of cross-link-
ing of the ethoxysilane groups under the acidic reaction
conditions. In principle, 2 can be synthesized in its
immobilized form 2i by treating silica modified with
Ph2P(CH2)3Si(OEt)3 (5) with Wilkinson’s catalyst [35],
and removing PPh3 by washing the solid. However, a
threefold ligand exchange would not be guaranteed due
to steric reasons, leading to a less well-defined catalyst.
Furthermore, 2i cannot be removed from the silica
surface to give 2 without destruction, because of the
harsh conditions needed to break the strong covalent
siloxane bonds [24]. Similarly, a second catalyst,
ClRh(CO)[Ph2P(CH2)3Si(OEt)3]2 (3), could be synthe-
sized starting from [(CO)2RhCl]2, as depicted in Scheme
1b. Another catalyst, ClRh(PPh3)[Ph2PCH2CH-
OHCH2PPh2] (4), was obtained by reacting
2. Results and discussion
2.1. Synthesis of molecular catalysts
As shown in Scheme 1a, the most efficient synthesis
of the rhodium complex ClRh[Ph2P(CH2)3Si(OEt)3]3 (2)
uses [(COD)RhCl]2 (COD=cyclooctadiene) as the
starting material. Without further purification, which
would be difficult due to the ethoxysilane groups, low
volatility, and missing inclination of 2 to crystallize, it is
Scheme 1. Syntheses of the catalysts 2–4i.

46
C. Merckle et al. / Journal of Organometallic Chemistry 627 (2001) 44–54
chelate ligand cannot assume two trans positions, one
of the coupling partners must be PPh3. The second
phosphine moiety of coordinated 6 has to be in position
1
2 due to its characteristic small J(Rh,P) value of 87.2
Hz. The latter comes very close to the corresponding
value in H2ClRh(PPh3)3 (1(H)2) [39], or the fluorinated
phosphine complex [8], both with 90 Hz. The positions
1 and 3 for PPh3 and P3 are furthermore corroborated
by the coupling constants 1J(Rh,P1)=110.7 Hz and
1J(Rh,P3)=109.9 Hz, which are comparable to the
values in 1(H)2 (114 Hz) [39] and the fluorinated ver-
sion (108 Hz) [8]. Additionally, the cis coupling con-
stants 2J(P1,P2), and 2J(P2,P3) with 24.2 Hz both lie
well within the typical range of 9–35 Hz [38], and
correspond, e.g. very well with the value of 17.5 Hz
found for 1(H)2 [39] or 24 Hz given for the fluorous
analog [8]. In order to investigate the exact positions of
hydride ligands, elegant methods can be applied nowa-
days, which make use of the parahydrogen [37,40]. In
our case, however, the assignment is already unambigu-
ous, due to the characteristic trans coupling
2J(P2,HA)=162.2 Hz, which comes close to the value in
1(H)2 (152 Hz) [39,41]. So, interestingly, the chelating
ligand 6 does not assume the two positions trans to Cl
and PPh3, but rather one coordination site trans to
PPh3, and one trans to H; perhaps this accommodates
its sterical demand better due to the four phenyl groups
and the large bite angle of about 91° (value of the
analog 1,3-bis(diphenyl-phosphino)propane [42]) as
compared to, e.g. 85° in bis(diphenyl-phosphino)ethane
[42].
Fig. 1. 121.4 MHz 31P CP/MAS NMR spectra of polycrystalline 1,
and the immobilized catalysts 2i and 4i, recorded with spinning
speeds of 8 (1), 12 (2i), and 15 kHz (4i). Rotational sidebands are
denoted by asterisks.
2.2. Immobilization of catalysts
The molecular catalysts 2 and 3 have been immobi-
lized on silica to give 2i and 3i by stirring the support
material in toluene with the appropriate amount of 2 or
3 at 60°C for about 5 h. As shown previously, the
bonding to the support via siloxane bonds is sufficiently
strong to prevent leaching due to linker detachment
from the surface [23,24,30], even if there is just one
siloxane bond formed [31]. Less robust is the CꢀOꢀSi
bond formed, when 4 is immobilized [20,30] to give 4i.
In toluene, however, even with prolonged washing, no
leaching could be detected by NMR, or coloring of the
supernatant solution, prior to catalysis. The 31P suspen-
sion NMR spectra [32] of the materials 2i–4i showed
rather broad signals in toluene as the suspension
medium, probably due to a larger chemical shift an-
isotropy (CSA) as compared to nickel carbonyl com-
pounds [32], and further efforts will be needed to
improve the spectrum quality for rhodium complexes.
However, the classical solid-state 31P CP/MAS NMR
spectra were readily recorded, and they prove the high
quality of the immobilized species. As shown in Fig. 1,
the 31P-NMR signals of 2i and 4i correspond very well
Cl(PPh3)Rh(COD) with the chelating phosphine 6
(Scheme 1c). The characterization and NMR signal
assignments were straightforward, and the l and J data
are in the expected areas (see Section 4), and therefore
do not need any detailed discussion.
Since it is known that in dihydride complexes chelat-
ing ligands can assume other than the expected coordi-
nation sites [36,37], we also investigated the reaction of
4 with molecular hydrogen in situ. When treating 4
within an NMR tube with 1 bar hydrogen pressure, a
1:1 mixture of 4 and 4(H)2 (Scheme 1) is obtained, as
determined by 31P-NMR spectroscopy. The reaction is
not fully reversible, even when 4(H)2 is treated with
fresh solvent and subjected to vacuum. The geometry
shown in Scheme 1c can be deduced from the NMR
2
data: the very large and characteristic J(P,P) value of
376.2 Hz indicates the trans arrangement of two phos-
phine moieties, which typically display coupling con-
stants in the range of 370–567 Hz [38]. Since the

C. Merckle et al. / Journal of Organometallic Chemistry 627 (2001) 44–54
47
become smaller, while the residual linewidth increases
due to the immobilization. The linewidth in the spec-
trum of 4i excludes mere physisorption of 4 on the
silica surface ([23] and references cited therein). Fig. 2
shows the 31P CP/MAS NMR spectrum of 3i, and of
crystalline trans-Cl(CO)Rh(PPh3)2 (13) for comparison.
In every respect, the situation is the same as with 2i and
4i.
to the isotropic line of the signal of 1, which was first
described by Veeman’s group [43]. Of course in the case
of 2i and 4i the line splittings due to the PꢀP and RhꢀP
couplings are no longer visible. The silica surface is too
inhomogeneous to allow as good a resolution as in the
case of crystalline material. Interestingly, as in the case
of immobilized nickel complexes [18], the rotational
sidebands of the signals of 2i and 4i have lower inten-
sity than the ones of crystalline 1. So, the CSA seems to
There is no 31P-NMR signal of uncomplexed phos-
phine in the shift region of −12 to −25 ppm visible in
any of the cases, 2i–4i. Additionally, there is no oxidic
species [30] present in any case. Therefore, we can be
sure that the molecular catalysts 2–4 have been immo-
bilized cleanly and in a well-defined manner. The chem-
ical shifts of 2i, 3i, and 4i are about the same as the
ones for 2, 3, and 4 in solution; slight differences might
be due to the different surroundings of the molecules,
solvent molecules or silica surface.
2.3. Catalytic hydrogenation beha6ior of all catalysts
We sought to test all catalysts with a range of simple
representative alkenes (Scheme 2). 1-Dodecene (7) was
chosen as a monofunctional alkene, which could be a
candidate for isomerization besides hydrogenation. 2-
Cyclohexen-1-one (8) is a test reagent for chemoselec-
tivity of the catalysts, because the CꢁO functionality
could, in principle, be reduced as well. Furthermore,
special behavior of this substrate might be detectable,
because a,b-unsaturated ketones are more nucleophilic
than monofunctional alkenes, and should bind to the
Rh centers more readily. Finally, 4-bromostyrene (9)
was chosen as a sterically, and from the standpoint of
chemoselectivity, more demanding olefin with a bromo
substituent as an additional functionality, as well as an
aromatic ring system adjacent to the alkene double
bond. One has to observe chemoselectivity especially
carefully when studying supported catalysts, because
due to our earlier [30] and ongoing experience, unex-
pected and quite weird transformations of substrates
can happen on oxidic surfaces. Finally, this set of
olefins guaranteed us easy comparison with other sys-
tems of immobilized catalysts, e.g. the fluorous catalysts
[8].
Fig. 2. 161.9 MHz 31P CP/MAS NMR spectra of polycrystalline
trans-(PPh3)2Rh(CO)Cl (13) and 3i, both recorded with a spinning
speed of 8 kHz. For further details see Section 4.
The only hydrogenation products of these substrates
with all the catalysts presented in this paper are dode-
cane (10), cyclohexanone (11), and 4-bromoethylben-
zene (12), as proved by NMR and GC–MS (Scheme 2).
Only in the case of 3 (but not with 3i!), the hydrogena-
tion of 1-dodecene gave B5% 2- and 3-dodecene as
by-products, as found in Ref. [8], too. However, no
isomerization whatever could be detected with the
Wilkinson-type catalysts.
First of all, Wilkinson’s catalyst 1 served as a refer-
ence for the catalytic hydrogenation activity with 7–9,
using the conditions described in Section 4, and the
Scheme 2. The substrates dodecene, cyclohexenone, and bro-
mostyrene, and their hydrogenation products dodecane, cyclohex-
anone, and ethylbromobenzene.

48
C. Merckle et al. / Journal of Organometallic Chemistry 627 (2001) 44–54
Fig. 4. Graphical representation of the substrate conversion (hydro-
gen uptake) during the catalytic hydrogenation of dodecene, cyclo-
hexenone, and bromostyrene with 2i (top), 3i (middle), and 4i
(bottom). For details see Section 4 and supplementary material;
yields, reaction temperatures and times see Table 1.
Fig. 3. Graphical representation of the substrate conversion (corre-
sponding to hydrogen uptake) during the catalytic hydrogenation of
dodecene, cyclohexenone, and bromostyrene with 1 (top), 2 (middle),
and 3 (bottom). For details see Section 4 and supplementary material;
yields, reaction temperatures and times see Table 1.
bromostyrene needed about 100 h for the completion of
the reaction, and there is an induction period of about
20 h. Although it is well known that alkyl phosphines
give much less effective Wilkinson-type catalysts than
aryl phosphines [44], complex 2 performs nearly as well
as 1 with all three substrates, and the same characteris-
apparatus displayed in Fig. 7. The results are shown in
Fig. 3.
While dodecene and cyclohexenone were both hydro-
genated equally rapidly with 100% yield within 20 h,

C. Merckle et al. / Journal of Organometallic Chemistry 627 (2001) 44–54
49
Table 1
Product yields and reaction times for the hydrogenation of substrates dodecene, cyclohexenone, and bromostyrene. The reactions were run at
ambient temperature, if not stated otherwise. In all experiments 0.01 mmol of free or immobilized catalyst in 5 ml THF (1) or toluene (2–4i) was
stirred with 1 mmol of substrate, while hydrogen was admitted (Fig. 7, and Section 4)
Catalyst
Dodecene
Reaction time (h)
14
Cyclohexenone
Bromostyrene
Product yield (%) Reaction time (h)
Product yield (%)
100
Reaction time (h)
Product yield (%)
1
2
100
100
20
16
100
100
100
100
100
100
100
79
46
100
–
8 (45°C)
30 (70°C)
62
15
100
6 (45°C)
18 (70°C)
9
141 (45°C)
305
2i
3
3i
4i
17
46
100
68
100
99
13
100
94
100
100
231 (70°C)
190 (70°C)
23 (60°C)
168
12 (60°C)
–
tics are seen in the curves (Fig. 3). Obviously it does not
make too much of a difference, when just one of the
substituents at the P ligand is an alkyl one, and two
phenyl groups remain. Furthermore, the longer alkyl
chains and bulky ethoxy groups do not seem to interfere
with the catalytic activity of 2 by, e.g. decreasing mobility
in solution. An interaction of the oxygen atoms with the
rhodium centers via hemilabile coordination, as found
with Ru complexes [11], also does not seem to take place.
Interestingly, in the case of 3, dodecene and bro-
mostyrene are hydrogenated to give the same products
as with 1 and 2, but the reaction with cyclohexenone is
substantially more sluggish now.
The immobilization of 2 and 3 changes the picture
somewhat (Fig. 4): with 2i, the reaction rates of cyclo-
hexenone and bromostyrene are still comparable to the
ones obtained with 2. Only the hydrogenation of do-
decene proceeds at a slower pace now. This is probably
due to the fact that the long molecule dodecene has to
diffuse with the right end into the pores of the support
now, in order to find the catalytic center, an effect that
is well known and exploited with polymer-supported
catalysts [45]. The yields, however, are still very high in
all cases (Table 1). Interestingly, immobilization of 3
increases the reaction times, but also the yields for all
three substrates (Fig. 4, Table 1). Here, the catalyst 3i
might profit from the strict separation of the reaction
centers on the silica surface, since it is well known that
one mechanism of deactivation of hydroformylation
catalysts is dimerization [46].
Catalyst 4i performs in the same way as 2i towards
dodecene and cyclohexenone, concerning yield, and just
needs a little higher temperature of 60°C for the reaction
(Fig. 4, Table 1). The chelating ligand obviously does not
impede the catalytic reaction. Using higher temperatures
in the system 1/bromostyrene and 2/bromostyrene re-
moves the induction periods, and substantially reduces
the reaction times (Fig. 5). However, the catalytic activity
Fig. 5. Graphical representation of the substrate conversion (hydro-
gen uptake) during the catalytic hydrogenation of bromostyrene with
1 (top) and 2 (bottom), at 25, 45, and 70°C. For details see Section 4,
supplementary material, and Table 1.

50
C. Merckle et al. / Journal of Organometallic Chemistry 627 (2001) 44–54
Table 2
Yields and reaction times, when the immobilized catalysts 2i and 4i are recycled. After each cycle the support is washed and fed with fresh solvent
and dodecene as the substrate using the same conditions as described in Table 1
Number of cycles
2i (RT)
4i (60°C)
Reaction time (h)
Product yield (%)
Reaction time (h)
Product yield (%)
1
2
3
4
5
6
7
17
22.5
77.5
67
248
302
480
100
100
100
91
77
60
12
24
24
99
64
53
49
does not increase linearly when raising the temperature,
but there is an optimum temperature range around
45°C.
ethoxysilane group [11] for robust anchoring of the
catalyst on the support. There is an ongoing effort in
our labs to find easy syntheses for this type of ligand
[50].
As compared to Wilkinson’s catalyst, and other im-
mobilized catalyst systems, e.g. the fluorous one [8], the
performance of 2i, 3i, and 4i is very good, and the
chemoselectivity is not changed by the anchoring to
silica. Furthermore, in contrast to 1, the catalyst can
easily be removed from the reaction mixture by letting
it settle down and decanting the supernatant solution.
In this respect our immobilized catalysts are already
superior to homogeneous catalysts, which cannot be
recycled easily.
3. Conclusions
To sum it up, we demonstrate with Wilkinson-type
complexes that, using the proper conditions and linkers,
they can easily be immobilized on commercial silica. They
are still very active with respect to the hydrogenation of
different substrates, and the chemoselectivities are not
changed by the immobilization. The catalysts can easily
be removed from the reaction mixtures, and recycled
many times before they gradually lose catalytic activity.
Therefore, they can be compared favorably with other
systems of immobilized catalysts. In addition to that, the
immobilization procedure is quite simple, and the linkers
needed for it are easy to synthesize. The simplification of
syntheses also for chelating ligands containing ethoxysi-
lane groups for still stronger bonding to the support and
therefore longer lifetime of the immobilized catalysts is
part of our ongoing research interests.
2.4. Recycling of immobilized catalysts
Next, the possibility of recycling of 2i and 4i was
tested, using dodecene as the substrate. When catalyst
2i is recycled batch-wise six times, the yields are high
for the first four times, and even 100% for the first three
times. Then, the reactions slow down gradually, and the
yield drops to about 50% after the seventh run (for
details see Table 2 and Fig. 6). In order to check,
whether this drop in the yield was due to the repeated
opening and closing of the hydrogenation apparatus
(Fig. 7, Section 4), or whether the maximum possible
TON (sometimes called ‘‘natural lifetime’’) of 2i had
already been reached, the sixfold amount of substrate
was added at once. The yield was 100% in this case, and
the reaction rate was high, which rules out the latter
assumption. Future attempts indeed could improve the
‘‘recycling’’ characteristics of the hydrogenation reac-
tion with a continuous catalysis setting in a closed
system. Unfortunately, the type of deactivation could
not readily be determined, because the solid-state NMR
spectrum of used catalyst only shows the signals of
intact catalyst. With 4i, the recycling behavior is not
quite as satisfactory as with 2i (Table 2), in this case
probably due to the weak bonding of the ligand to the
support via a CꢀOꢀSi bond. Here, the situation could
be improved by using chelating ligands containing an
Fig. 6. Graphical representation of the recycling behavior of 2i with
respect to hydrogenation of dodecene (for details see Section 4,
supplementary material, and Table 2).

C. Merckle et al. / Journal of Organometallic Chemistry 627 (2001) 44–54
51
Fig. 7. Schematic presentation of the experimental setting used for the hydrogenation reactions (work principle see text and Section 4).
4. Experimental
Bruker AC 300, Bruker DRX 300, and Bruker DRX 500
NMR spectrometers. The deuterated solvents served as
internal standards for 1H- and 13C-NMR spectra, and the
chemical shifts were recalculated with respect to TMS.
H3PO4 (85%) was the external chemical shift standard for
31P-NMR measurements. When necessary, the shift as-
signments were corroborated by 2D COSY NMR spectra.
4.1. General comments
All catalytic reactions were performed under inert gas
using Schlenk techniques, prior to admitting hydrogen.
They were proved to be fully reproducible by being
repeated several times. Solvents were dried by standard
methods, and oxygen was removed. The identity of
molecular compounds was checked by elemental analysis,
mass spectrometry, and their solution-state NMR spec-
tra, and IR spectra where appropriate. Immobilized
species were studied by solid-state NMR. For GC
analyses of the hydrogenation products a Chrompack
Model CP-9003 instrument was used. All starting mate-
rials were commercially available, if not described below.
As a support Merck silica 40 (specific surface area 750
4.3. Solid-state NMR spectroscopy
All solid-state 31P-NMR spectra were recorded on a
Bruker MSL 300 or a digital Bruker Avance 400 NMR
spectrometer equipped with an ultrashield widebore
magnet, and a 4 mm multinuclear double-bearing MAS
probehead. The modified silica was loosely filled into the
ZrO2 rotors in a glove box. Cross polarization (CP) and
magic angle spinning (MAS) with rotational speeds up
to 15 kHz were applied. The contact time was 1 ms, and
the relaxation delay was 10 s for all surface-immobilized
compounds. The 31P CP/MAS NMR spectra were refer-
enced with respect to 85% H3PO4(aq.) by setting the
31P-NMR peak of solid (NH4)H2PO4 to +0.81 ppm. The
Hartmann–Hahn match was set by using solid
ClRh(PPh3)3 (1). For the exponential multiplication
line-broadening factors of up to 100 Hz was applied.
m2 g−1; average pore size 40 A; particle size 0.063–0.2
,
mm) that was dried at 600°C in vacuo (10−2 Pa for 12 h) in
order to condense surface silanol groups [20], was used.
4.2. Liquid-state NMR spectroscopy
All the spectra were recorded on Bruker WH 200,

52
C. Merckle et al. / Journal of Organometallic Chemistry 627 (2001) 44–54
4.4. Synthesis of ClRh[PPh2(CH2)3Si(OEt)3]3 (2)
18H, CH3, 3J(H,H)=7.1 Hz); 0.86 (t, 4H, CH2Si,
3J(H,H)=7.9 Hz). 13C{1H}-NMR (benzene-d6, 75.47
MHz, 23°C, l ppm): 188.39 (dt, CO, J(Rh,C)=73.5
1
The ligand PPh2(CH2)3Si(OEt)3 (5) was synthesized
as described in Ref. [30]. A solution of 5 (143 mg, 0.366
mmol) in 3 ml of toluene was added to a solution of
[Rh(COD)Cl]2 (30 mg, 0.061 mmol) in 5 ml of toluene.
The color changed from yellow to dark orange. After
all volatile substances were removed in vacuo an or-
ange-brown viscous oil was obtained. Yield: 79 mg
(0.060 mmol, 100% with respect to [Rh(COD)Cl]2).
2
1
Hz, J(P,C)=15.8 Hz); 134.85 (t, Cipso, J(P,C)=21.0
Hz); 133.95 (t, Cmeta
3J(P,C)=6.1 Hz); 133.58 (t,
Cortho
,
,
2J(P,C)=10.5 Hz); 129.93 (Cpara); 58.50
(OCH2); 30.86 (t, PCH2, 1J(P,C)=13.3 Hz); 19.29
(CH2CH2CH2); 18.66 (CH3); 12.85 (t, CH2Si,
3J(P,C)=7.2 Hz).
HR-MS
(FAB+)
1273.4440
(Calc.
for
4.6. Synthesis of
ClRh(PPh3)[Ph2PCH2CHOHCH2PPh2] (4)
C63H93O9P3RhSi3: 1273.4396). Anal. Found: C, 58.15;
H, 7.49; P, 6.81. Calc. for C63H93ClO9P3RhSi3
(1308.408 g mol−1): C, 57.76; H, 7.16; P, 7.09%.
31P{1H}-NMR (toluene-d8, 121.49 MHz, 23°C, l ppm):
To a solution of Cl(PPh3)Rh(COD) (76 mg, 0.149
mmol) [47] in 20 ml of THF, a solution of ligand 6 (64
mg, 0.149 mmol) [48] in THF was added. The color
changed from yellow to orange. After the mixture was
stirred for 1 h the solvent and COD were removed in
vacuo, and 4 was yielded quantitatively as an orange
oil.
2
1
39.85 (dt, J(P, Ptrans)=39.6 Hz, J(Rh,Ptrans)=186.9
Hz); 25.62 (dd, 2J(P,Ptrans)=39.6 Hz, 1J(Rh,Pcis)=
138.9 Hz). 1H-NMR (toluene-d8, 300.13 MHz, 23°C,
nuclei of the ligand trans to Cl carry a prime, l ppm):
7.74–6.57 (m, 20H, PPh2); 7.04–6.92 (m, 10H, PPh2);
3.76–3.65 (2 overlapping q, 18 H, ꢀCH%CH3,
2
ꢀCH2CH3, 3J(H,H)=6.8 Hz); 2.50 (m, 4H, PCH2ꢀ);
2.14 (m, 4H, PCH2CH2CH2); 2.03 (t, 2H, PCH%,
2
3J(H,H)=6.8 Hz); 1.98–1.85 (m, 2H, CH2CH%CH2);
2
1.12 (t, 27H, CH3, CH%, 3J(H,H)=6.8 Hz); 0.71 (t, 4H,
3
CH2Si, 3J(H,H)=7.9 Hz); 0.46 (t, 2H, CH%Si,
2
3J(H,H)=7.9 Hz). 13C{1H}-NMR (toluene-d8, 75.47
MHz, 23°C, nuclei of the ligand trans to Cl carry a
prime, l ppm): 135.60 (Cipso); 135.31 (C%ipso); 131.54
(C%ortho, C%meta); 131.42 (Cortho, Cmeta); 129.52 (C%para);
129.21 (Cpara); 58.80 (OCH2, OC%H2); 33.77 (PC%H2);
32.83 (PCH2); 19.06 (CH3); 18.90 (C%H3); 16.45
(CH2C%H2CH2); 16.41 (CH2CH2CH2); 12.85 (C%H2Si);
12.69 (CH2Si).
MS (FAB): 793.1 [M−Cl]+. HR-MS (FAB+)=
793.1448 [M−Cl]+ (Calc. for C45H41OP3Rh 793.1426).
Anal. Found: C, 64.09; H, 5.55. Calc. for
C45H41OP3ClRh (829.099 g mol−1): C, 65.19; H, 4.98%.
31P{1H}-NMR (toluene-d8, 121.49 MHz, l ppm): 40.19
(ddd, P2, 2J(P2,P1)=36.1 Hz, 2J(P2,P3)=51.1 Hz,
2
1J(Rh,P2)=177.6 Hz); 32.81 (ddd, P1, J(P2,P1)=36.1
2
1
Hz, J(P1,P3)=357.2 Hz, J(Rh,P1)=133.9 Hz); 24.45
(ddd, P3, 2J(P2,P3)=51,1 Hz, 2J(P1,P3)=357.2 Hz,
1J(Rh,P3)=136.2 Hz. The signal assignment is addi-
4.5. Synthesis of trans-Cl(CO)Rh[PPh2(CH2)3Si(OEt)3]2
(3)
1
tionally corroborated by a 31P,31P-COSY spectrum. H-
NMR (benzene-d6, 500.13 MHz, l ppm): 8.0–6.8 (m,
35H, aryl-H); 3.68 (broad, 1H, OH); 3.07 (m, 1H, Ha);
2.70* (m, 1H, Hb2, 2J(Hb2,Hb%2)=14.6 Hz); 2.60 (m, 1H,
A solution of 5 (100 mg, 0.257 mmol) in 3.5 ml of
toluene was added to a solution of [Rh(CO)2Cl]2 (25
mg, 0.064 mmol) in toluene. After the mixture was
stirred for 25 min, during which time the color changed
from yellow to dark brown, all volatile substances were
removed in vacuo, and a dark brown viscous oil was
obtained. Yield: 125 mg (0.128 mmol, 100% with re-
spect to [Rh(CO)2Cl]2). HR-MS (FAB+) 918.2360
[M−CO]+ (Calc. for C42H62ClO6Si2P2Rh: 918.2304).
Anal. Found: C, 54.30; H, 6.74; P, 6.26. Calc. for
C43H62ClO7P2RhSi2 (947.440 g mol−1): C, 54.51; H,
Hb3, 2J(Hb3,Hb%3)=14.6 Hz); 2.05* (m, 1H, Hb%3
,
,
2J(Hb%3,Hb3)=14.6 Hz); 1.91 (m, 1H, Hb%2 2J(Hb%2
,
Hb2)=14.6 Hz); *signal assignments of Hb%3, Hb3 and
Hb%2, Hb2 pairwise interchangeable. 13C{1H}-NMR
(benzene-d6, 125.77 MHz, l ppm): 137.22 (d, Cipso
,
1
1J(P,C)=20.7 Hz); 136.41 (d, Cipso, J(P,C)=25.4 Hz);
136.11 (d, Cipso,1J(P,C)=21.7 Hz); 135.46 (d, Cipso of
PPh3, 1J(P,C)=11 Hz); 134.88 (d, Cortho, 2J(P,C)=13.1
Hz); 134.24 (d, Cortho
,
2J(P,C)=10.4 Hz); 134.10 (d,
2
2
6.60; P, 6.54%. IR (neat, cm−1): wCO=1970, wRhCl
960. 31P{1H}-NMR (benzene-d6, 121.49 MHz, 23°C, l
=
Cortho, J(P,C)=14.1 Hz); 133.57 (d, Cortho, J(P,C)=
2
10.4 Hz); 132.10 (d, Cortho of PPh3, J(P,C)=9.4 Hz);
1
1
3
ppm): 24.11 (d, J(Rh,P)=123.6 Hz). H-NMR (ben-
131.65 (d, Cmeta, J(P,C)=11.3 Hz); 131.33 (d, Cmeta,
3
zene-d6, 300.13 MHz, 23°C, l ppm): 7.86 (d, 8H, Hortho
,
3J(P,C)=11.3 Hz); 130.84 (d, Cmeta, J(P,C)=9.4 Hz);
3
3J(H,H)=6.4 Hz); 7.1–6.95 (m, 12H, Hmeta, Hpara);
130.60 (d, Cmeta, J(P,C)=9.4 Hz); 127.10 (d, Cmeta of
3
3.77 (q, 12H, OCH2, J(H,H)=7.1 Hz); 2.90–2.75 (m,
PPh3, 3J(P,C)=9.4 Hz; 129.49 (s, Cpara); 128.82 (s,
4H, PCH2); 2.11–1.95 (m, 4H, CH2CH2CH2); 1.14 (t,
Cpara); 128.72 (s, Cpara); 128.38 (d, Cpara of PPh3,

C. Merckle et al. / Journal of Organometallic Chemistry 627 (2001) 44–54
53
4J(P,C)=1.8 Hz); 128.1 (signal overlapping with sol-
vent peak); 65.61 (t, Ca, 2J(P,C)=7.5 Hz); 33.09*
(broad, s, P2-CH2); 28.88* (broad, s, P3-CH2); *signal
assignments interchangeable.
Fig. 7. Hereby, the weighed homogeneous or immobi-
lized catalyst is placed into a Schlenk flask, the atmo-
sphere of which is changed from nitrogen to pure
hydrogen. Then, the solvent is added, and the mixture
is stirred vigorously. Hydrogen is held at a predeter-
mined level in a calibrated storage area sealed with
degassed paraffin oil. After adding the olefin through
the septum of the Schlenk flask with a syringe, the
reaction is started by opening the valve connecting the
reaction vessel with the hydrogen reservoir. The hydro-
gen uptake could then be monitored at the scale of the
hydrogen reservoir.
After the hydrogenation reactions, the immobilized
catalysts were allowed to settle down for about 3 min.
The results of the hydrogenation were checked by direct
GC–MS of the supernatant solutions. Only in case of
1, 2, and 3, the catalysts had to be removed by flash
chromatography prior to the application of GC, and
determination of the yield by the removal of the solvent
in vacuo. In the cases of 2i, 3i, and 4i, the product
yields could be determined directly after removal of
solvent from the supernatant solutions.
4.7. In situ generation of the dihydrogen complex 4(H)2
Fifty-seven milligrams (0.069 mmol) of 4 were placed
into a 5 mm NMR tube and dissolved in about 2 ml of
toluene-d8. Then, oxygen free hydrogen was gently bub-
bled into the solution at room temperature via a capil-
lary. The color changed from orange to yellow. After
the NMR tube was sealed with a glass stopper, the
31P-NMR spectrum was recorded, which showed that
about 50% of the complex has been transformed into
4(H)2 (see Scheme 1, also for numbering). Besides the
residual signals of 4, the following ones of 4(H)2 show
up in the spectra: 31P{1H}-NMR (toluene-d8, 121.49
MHz, l ppm): 42.27 (ddd, P1, 2J(P1,P2)=24.2 Hz,
2J(P1,P3)=376.2 Hz, 1J(Rh,P1)=110.7 Hz); 29.31
(ddd, P3, 2J(P3,P2)=24.2 Hz, 2J(P3,P1)=376.2 Hz,
1J(Rh,P3)=109.9 Hz); 15.09 (dt, P2, 2J(P2,P1)=
2J(P2,P3)=24.2 Hz, 1J(Rh,P2)=87.2 Hz). 1H-NMR
(toluene-d8, 300.13 MHz, l ppm): −7.63 (d, broad,
2
HA, J(HA,P2)=162.2 Hz); −17.02 (s, broad, HB).
Acknowledgements
4.8. Immobilization procedure
We thank the Deutsche Forschungsgemeinschaft
(DFG) for support via the Landesforschungsschwer-
punktprogramm, and the Fonds der Chemischen Indus-
trie for financial support. Furthermore we thank the
company Bruker for a very generous gift of an acces-
sory for our new Avance 400 NMR instrument. Finally
Dr G. Raudaschl-Sieber (TU Munich) has to be
thanked for recording one of the 31P-CP/MAS NMR
spectra.
The complexes 2, 3, and 4 were immobilized accord-
ing to the standard procedure given in Ref. [18], taking
care to use the right solvent [24], here toluene, and the
surface coverage with the corresponding complexes 2i,
3i, and 4i was determined by weighing back the residual
complex from the supernatant solution. The surface
coverage corresponds to 129 mg of 2i per gram of silica
(3i: 117 mg g−1; 4i: 73 mg g−1), or eight molecules of
catalyst 2i per 100 nm2 of silica surface (3i: 10
molecules per 100 nm2; 4i: 7 molecules per 100 nm2).
The supported catalysts were washed several times with
toluene, and then with THF, and finally dried in vacuo
for 4 h at room temperature.
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