Recent progress in asymmetric heterogeneous catalysis: Use of polymer-supported catalysts

Article abstract of DOI:10.1016/S0022-328X(00)00050-4

The asymmetric heterogeneous catalytic reduction of carbonyl bonds by hydrogen transfer reduction or hydrogenation by means of molecular hydrogen as well as the asymmetric allylic substitution of allylic acetates are reported. In order to perform these reactions, new polymer-supported catalysts were employed. These polymers are either a Merrifield resin with a chiral pendent ligand or a chiral main chain polymer with ureas, thioureas and a diphosphine as functional groups. Comparison of the results obtained in these heterogeneous asymmetric reactions was made with those obtained in the homogeneous ones.

Full text of DOI:10.1016/S0022-328X(00)00050-4

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 603 (2000) 30–39
Recent progress in asymmetric heterogeneous catalysis: use of
polymer-supported catalysts
Christine Saluzzo, Rob ter Halle, Franc¸ois Touchard, Fabienne Fache,
Emmanuelle Schulz, Marc Lemaire *
Laboratoire de Catalyse et Synthe`se Organique, UMR 5622, UCBL/CPE, Baˆt. 308, 43 bd. du 11 No6embre 1918,
69622 Villeurbanne Cedex, France
Received 23 November 1999; received in revised form 21 January 2000
Abstract
The asymmetric heterogeneous catalytic reduction of carbonyl bonds by hydrogen transfer reduction or hydrogenation by
means of molecular hydrogen as well as the asymmetric allylic substitution of allylic acetates are reported. In order to perform
these reactions, new polymer-supported catalysts were employed. These polymers are either a Merrifield resin with a chiral
pendent ligand or a chiral main chain polymer with ureas, thioureas and a diphosphine as functional groups. Comparison of the
results obtained in these heterogeneous asymmetric reactions was made with those obtained in the homogeneous ones. © 2000
Elsevier Science S.A. All rights reserved.
Keywords: Heterogeneous catalysis; Asymmetric catalysis; Polymers
1. Introduction
dation [6] and hydrogenation [7]. This method consists
of the ‘heterogenization’ of an homogeneous catalyst by
anchoring the catalyst on a solid support, i.e. an inor-
ganic material [8] or an organic polymer [9], in order to
perform the separation of the catalyst from the reaction
mixture, by filtration. However, lower activities and
selectivities are mostly observed. In all cases, the choice
of the polymer is crucial: a large swelling with the
reaction solvent is necessary. Moreover, the active sites
must be at the proper location [10]. Most of the existing
systems involves crosslinked polystyrene, polyacrylate
or polypeptide supported reagents [11]. In order to
combine the advantages of homogeneous (mobility,
accessibility of the active sites) and heterogeneous catal-
ysis (easy separation), soluble polymer-supported cata-
lysts could be employed [6a,12]. Then, by precipitation
upon addition of an appropriate solvent followed by
filtration, the catalyst is recovered.
Over the past three decades, homogeneous asymmet-
ric catalysis was subjected to a successful development.
Nevertheless, only few examples have been developed
to an industrial scale. Pharmaceuticals, agrochemicals,
flavors and flagrances [1] are the principal areas which
require the synthesis of optically pure chiral com-
pounds. Most of them are still synthesized starting
from the chiral pool or in their racemic form, followed
by resolution.
The lack of employment of the homogeneous asym-
metric catalysis is probably and essentially due to prob-
lems of separation and recycling of the expensive chiral
catalyst. To overcome these drawbacks, very early after
the discovery of homogeneous asymmetric catalysis,
heterogeneous catalysis has been employed, particularly
polymer-supported homogeneous catalysis. This
methodology was brought out by Kagan et al. [2] and
Stille et al. [3], in the 1970s and was used for reactions
like hydroformylation [3c,4], dihydroxylation [5], epoxi-
We herein report our efforts to develop new reusable,
partly soluble or non-soluble polymer-supported cata-
lysts for allylic substitution of allylic acetates and asym-
metric reduction by means of hydrogen transfer or
molecular hydrogen. Different kinds of polymers were
involved in these reactions. Asymmetric allylic substitu-
* Corresponding author. Fax: +33-4-7243 1408.
E-mail address: marc.lemaire@univ-lyon1.fr (M. Lemaire)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00050-4

C. Saluzzo et al. / Journal of Organometallic Chemistry 603 (2000) 30–39
31
Scheme 1.
tion was performed with polyamides and polyureas
with main chain chirality presenting a pseudo C2 sym-
metry. Hydrogen transfer reductions were thus per-
formed with catalysts synthesized from a sulfonamide-
supported Merrifield resin, from polyureas and poly-
thioureas. Finally, hydrogenation with molecular hy-
drogen was tested with a polyurea containing in its
main chain the BINAP structure.
soluble in THF whereas polyamide 4a is insoluble in
organic solvents. Unfortunately, attempts to recover
and reuse the catalytic systems were ineffective.
To our knowledge, it was the first time that such
polyamide and polyurea ligands were employed to af-
ford enantioselective alkylations. Actually, much atten-
tion was focused on the nature of this kind of polymer
in order to stabilize the Pd°. It should be noted that one
of the best ligands so far tested is the ligand developed
by Trost et al. which possesses two phosphine and two
amide functional groups in order to form a ‘chiral
pocket’ [17].
2. Enantioselective allylic substitution
Palladium catalyzed allylic substitution has received
considerable attention because it is a very useful
method for carbon–carbon bond formation. Numerous
soluble, non-polymeric phosphine-containing ligands
were tested in order to effect highly enantioselective
reactions [13]. On the opposite, only a few nitrogen-
ligands with s-donor character have been used [14].
In 1995, we showed that the use of N,N%-dimethyl-
1,2-diphenylethylene diamine as ligand for the homoge-
neous allylic substitution of allylic acetates (1) led to
interesting results (Scheme 1, Table 1) [15].
Indeed, the transformation of acetates 1a and 1b into
compounds 2a and 2b yields to high conversions (up to
85%) and 16% and 95% ee, respectively (runs 1 and 2,
Table 1). Then, we decided to develop a new strategy
which consists of using polymeric nitrogen-ligands like
polyamide 4a and polyureas 5a and 5b, in order to
study the catalytic asymmetric allylic substitution by
means of a polymer-supported catalyst [15,16]. These
polymers were easily obtained in good yield by copoly-
merization of C2 symmetric chiral diamines with a
diarylchloride or various diisocyanates respectively
(Scheme 2, Table 2).
Polyamide 4a shows the highest enantioselectivity but
the lowest catalytic activity (run 2) compared to the
polyureas 5a and 5b (runs 1 and 3). It is noteworthy
that contrary to what was generally observed, better
results were obtained with the heterogeneous system
(run 1, Table 2) compared to the homogeneous one for
the allylic substitution of acetate 1a with (1S,2S) N,N%-
dimethyl-1,2-diphenylethylenediamine (Table 1, run 1).
A difference in solubility was observed between
polyamide and polyureas. Polyureas 5a and 5b are
3. Reduction
3.1. Reduction by hydrogen transfer catalysis
The hydrogen transfer reduction (HTR) is an attrac-
tive method because it avoids the use of hydrogen
pressure which requires specific equipment. Several dif-
ferent substrates have been successfully reduced by
transfer hydrogenation in the presence of both hetero-
geneous [18] and homogeneous catalysts [19]. This reac-
tion includes generally as hydrogen acceptors, ketones,
a,b-unsaturated carbonyl compounds, a,b-unsaturated
acids and esters, imines and nitro compounds and as
hydrogen donors, alcohols (mainly i-PrOH) and the
formic acid/triethylamine system. Chiral ligands first
employed in this asymmetric reaction were chiral phos-
phines (DIOP, CHIRAPHOS, NORPHOS, BINAP),
then, since the beginning of the 1990s, chiral bidentate
nitrogen ones have been mainly used.
Encouraging results were obtained in homogeneous
asymmetric catalysis when we used diamine ligands in
the reduction of prochiral ketones by means of hydro-
gen transfer reduction [20] (Scheme 3).
Table 1
Homogeneous alkylation of allylic acetates
Run Acetate
Product Conversion (%)
ee (%)
(configuration)
1
2
1a
1b
2a
2b
85
90
16 (S)
95 (S)

32
C. Saluzzo et al. / Journal of Organometallic Chemistry 603 (2000) 30–39
Scheme 2.
Table 2
Pd-catalyzed allylic substitution with polyamide and polyureas as ligands
Run
Acetate
Ligand
Product
Conversion (%)
ee (%) (configuration)
1
2
3
1a
1b
1b
5b
4a
5a
2a
2b
2b
80
38
72
25 (R)
80 (R)
38 (R)
Then, two types of ligands derived from diamines
had been used with success; the first one having a C2
symmetry like diureas and dithioureas, the second one
without such symmetry like an amino sulfonamide. We
have synthesized heterogeneous catalysts by means of
organic polymers. In the case of the ligand without C2
axial symmetry, we prepared materials presenting the
ligand moiety as a pendent group on a polystyren
matrix. With other polymeric ligands, chirality and
ligand were included in the main chain of the polymer.
This last type of structure allows the conservation of a
pseudo C2 axis along the polymer chain.
equivalents of metal precursor and i-PrOH–KOH for
Ir or i-PrOH–Et3N for Ru, at 70°C for 2 days.
When the chiral non-crosslinked polymer 6 was used
with Ru as metal, we have observed that conversion
and ee were dependent on the nature of the precursor
employed (runs 2 and 3). Similar observations (runs 5
and 6) were made with crosslinked polymer 7. How-
ever, a different behavior between polymers 6 and 7
was pointed out. In the case of polymer 6, with
[Ru(benzene)Cl2]2 better ee and lower conversion than
[Ru(p-cym)Cl2]2 were obtained (runs 2 and 3) contrary
to polymer 7 which presented with [Ru(p-cym)Cl2]2
better conversion but lower ee than [Ru(benzene)Cl2]2
(runs 5 and 6). This difference of behavior remains
unexplained. However, when the chiral polysulfon-
amides 6 and 7 were used with Ir as metal, excellent
conversions and enantioselectivities were obtained (runs
1 and 4). Moreover, heterogeneous Ir catalysts showed
higher enantioselectivities compared to the homoge-
neous analog for which only 75% of conversion and
89% of enantiomeric excess were obtained. This differ-
ence could be explained by the formation of chiral
microenvironments upon polymerization.
3.1.1. Aminosulfonamide as a pendent group on
Merrifield-type materials
In 1995, Noyori et al. reported the use of (1S,2S)-N-
(toluene-p-sulfonyl)-1,2-diphenylethylene diamine with
very high ee [21] in the Ru-catalyzed hydrogen transfer
reduction of ketones (97% ee for acetophenone). On the
other hand, Knochel et al. obtained ee up to 92% with
N-monotosylated 1,2-diaminocyclohexane derivatives
[22]. We considered the synthesis of chiral polymers
containing Noyori’s monomer in a polymeric matrix
(Scheme 4). These polymers were subsequently tested as
ligands for the IrI and RuII catalyzed hydrogen transfer
reduction of acetophenone [23].
Table 3 summarizes the data of the asymmetric hy-
drogen transfer reduction of acetophenone carried out
in the presence of polymers 6 and 7.
Both polymers were used for the catalytic transfer
hydrogenation of acetophenone in the presence of 0.025
Scheme 3.

C. Saluzzo et al. / Journal of Organometallic Chemistry 603 (2000) 30–39
33
Scheme 4.
Table 3
Reduction of acetophenone with polymers 6 and 7 and [Ir(COD)Cl]2 or [Ru(benzene)Cl2]2 as metal precursors
Run
Ligand
Metal precursor
Time (days)
Conversion (%)
ee (%) (configuration)
1
2
3
4
5
6
6
6
6
7
7
7
[Ir(COD)Cl]2
3
2
2
3
2
2
94
20
72
96
96
23
92 (S)
64 (S)
40 (S)
94 (S)
31 (S)
84 (S)
[Ru(benzene)Cl2]2
[Ru(p-cym)Cl2]2
[Ir(COD)Cl]2
[Ru(benzene)Cl2]2
[Ru(p-cym)Cl2]2
Attempts to reuse the catalysts showed that the Ru-
containing one, although less selective, is more stable
upon reuse than the Ir derivative.
of [Rh(COD)Cl]2 with a diamine polymer unit/Rh ratio
of 10, i-PrOH as hydrogen donor and KOH. The
results are summarized in Table 4.
More recently, Bayston et al. [24], with a similar
objective have prepared the polymer 8 (Scheme 5)
starting from the aminostyrene Merrifield-type poly-
mer. They used ruthenium precursors and obtained
91% ee with 88% conversion. Compared to ligand 7
with ruthenium catalyst (run 3) this ligand showed
better conversion and selectivity. Nevertheless, conver-
sion and selectivity were comparable with Ir catalyst
(runs 1 and 4, Table 3).
It is noteworthy that the pseudo C2 symmetry seems
to be important. When using the dissymmetric polyurea
9a, synthesized with the dissymmetrical 2,4-toluene di-
isocyanate, no ee was observed (run 2) contrary to its
analog 9b (13% ee) (run 3) obtained with the symmetri-
3.1.2. Asymmetric ligands in main chain polymer
3.1.2.1. Polyureas, new materials for polymer supported
catalysis. Diureas were tested as ligands for asymmetric
hydrogen transfer. The best results were obtained with
phenylisocyanides as precursors (for propiophenone,
87% conversion and 80% ee were observed) (Scheme 6)
[25].
Scheme 5.
We have heterogenized chiral diamines (1,2-cyclo-
hexyldiamine, 1,2-diphenylethylene diamine and N,N%-
dimethyl-1,2-diphenylethylene diamine) by their
incorporation into polymer backbones by polyconden-
sation with diisocyanates (as shown in Scheme 1). Thus
pseudo C2 symmetric polyurea ligands were obtained
(Scheme 4) [15,26]. Their molecular weight was about
2000 g mol−1 (determined by NMR spectroscopy).
The study of the hydrogen transfer reduction was
performed at 70°C, with acetophenone in the presence
Scheme 6.

34
C. Saluzzo et al. / Journal of Organometallic Chemistry 603 (2000) 30–39
Table 4
Hydrogen transfer reduction of acetophenone with polyamide 4a and polyureas
Run
Chiral polymer–rhodium catalyst
Conversion
Time (days)
ee (%) (configuration)
1
2
3
4
5
Polyamide 4a
Polyurea 9a
Polyurea 9b
Polyurea 9c
Crosslinked polyurea 9c
22
80
50
97
100
7
4
4
3
1
28 (R)
0
13 (S)
39 (R)
60 (R)
homogeneous catalytic reaction [29]. The molecular
imprinting effect seems to be an interesting tool in
order to reach high enantioselectivity. We have pre-
pared a new catalyst by polymerization of the chiral
rhodium ([(N,N%-dimethyl-1,2-diphenylethylene di-
amine, COD) rhodium]) complex in the presence of
sodium 1-(S)-phenylethanolate (template) with di- and
triisocyanates [30] (Scheme 8).
The hydrogen transfer using non-templated or tem-
plated polymer was performed in the presence of 5
mol% of Rh-polymer with a KOH/[Rh] ratio of 4, at
60°C. Results are presented in Table 5.
The molecular imprinting effect was noted by an
increasing ee in the case of the acetophenone reduction
(runs 1 and 2). The best results are obtained in the case
of the propiophenone reduction; the ee increased from
47% with non-templated polymerized complex (run 3)
to 67% with the templated polymerized complex (run
4). Optimization of the crosslinking ratio led to the best
compromise between activity and selectivity (70% ee)
[30c]. One of the main advantages of this method is
that, in most cases, it allows an increase of the obtained
ee compared to the homogeneous phase. Nevertheless,
it is noteworthy that in the case of sterically demanding
substrates such as tert-butyl phenyl ketone, little or no
reduction was observed, indicating a substrate specific-
ity different from that observed in homogeneous
catalysis.
Finally, in most cases, for the reduction of ketones
by hydrogen transfer, we have shown that the chiral
supported-polymer catalysis, involving polymers such
as aminosulfonamide Merrifield-type materials or chiral
main chain polyureas and polythioureas, led to similar
or better results, compared to those of homogeneous
catalysis. The imprinting effect is obvious for molecules
similar to the structure of the template and is not
efficient if the substrate structure is very different from
the template one.
Scheme 7.
cal 2,6-toluene diisocyanate (Scheme 7). Rigidity of the
polymer appeared to be another important parameter.
Polyurea 9c (run 5), crosslinked by a mixture of 70% of
diisocyanate and 30% of different triisocyanates,
showed higher catalytic activity as well as higher enan-
tioselectivity than the polyamide 4a or other polyureas.
Moreover, this chiral crosslinked polyurea presents a
slightly increased enantioselectivity over the amine
monomer analog (55% ee and 94% conversion in simi-
lar conditions). These results could be explained by the
rigidity of the active site which is crucial for the selec-
tivity and the stability of the catalytic system. On the
other hand, this crosslinked polyurea 9c was recovered
by filtration and reused twice with no loss of either
catalytic activity or enantioselectivity.
The importance of the rigidity of the material led us
to be interested in the molecular imprinting technique
for which crosslinking is required. The principle of
molecular imprinting consists of copolymerization and
cross-coupling of a polymer in the presence of a chiral
molecule used as a printed molecule (PM). The latter,
included into the polymer by means of a covalent or a
non-covalent bond, can be removed in order to let its
chiral imprint in the polymeric matrix. This chiral
cavity is then able to act as a center of molecular
recognition [27]. This methodology has intensively been
used in the chromatography area especially for resolu-
tion of racemates by HPLC [28]. Catalysis has also
been investigated but on a smaller scale and has shown
an increase of activity compared to the corresponding
3.1.2.2. Polythioureas as material for asymmetric cataly-
sis. Conversely, for oxygen-containing functional
groups, the sulfur-containing molecules are more or less
considered as poison for transition metal catalysis. On
the other hand, stronger interactions with ‘soft’ transi-
tion metals could be expected with the sulfur atom
compared to the oxygen donor.

C. Saluzzo et al. / Journal of Organometallic Chemistry 603 (2000) 30–39
35
Scheme 8.
Table 5
Molecular imprinting effect in reduction by using Rh catalyst with templated and non-templated polymer 10
Run
Substrate
Catalyst
Inductor configuration
Conversion
Time (days)
ee (%) (configuration)
25 (R)
1
2
3
Polymerized
(R) templated
Polymerized
(S,S)
(S,S)
(S,S)
98
98
96
1
1
6
43 (R)
47 (R)
4
(R) templated
(S,S)
91
9
66 (R)
We were also interested in the hydrogen transfer
reduction of prochiral ketones with thioureas [31] as
ligand in homogeneous catalysis (Scheme 9). Encourag-
ing results obtained with acetophenone in the presence
of Rh and Ru catalysts (Rh catalyst gives 98% conver-
sion and 66% ee instead of 98% conversion and 89% ee
for the Ru analog) led us to synthesize and test poly-
thioureas for heterogeneous catalysis.
isothiocyanates (Scheme 10). In such cases, the best
results were obtained when using rigid diisothiocyanate
although crosslinking does not increase selectivity of
the reduction.
Elemental analysis provides an evaluation of the
DP of polymer 12 which is about 13 and of the
molecular weight of ca. 7700 g mol−1. The reduction
of acetophenone was carried out at 70°C in the pres-
ence of a t-BuOK/metal ratio of 4 and 5 mol% of
metal.
Polythioureas were easily obtained by polyaddition
of N,N%-dimethyl-1,2-diphenylethylene diamine with

36
C. Saluzzo et al. / Journal of Organometallic Chemistry 603 (2000) 30–39
Table 7
Aryl-alkyl ketones (RCOR%) reduced with polymer 12 in the presence
of [Ru(benzene)Cl2]2
Run
R
R%
Time (days)
Conversion (%)
ee (%)
1
2
3
Ph
Ph
Ph
Me
Et
i-Pr
1
1
1
92
95
87
70
80
84
Scheme 9.
4. Reduction with molecular hydrogen
The polymer 12 was tested with different catalyst
precursors. The ratio L/M (ligand/metal) was increased
until the ee reaches its highest value. Only the best
results are reported in Table 6.
The results presented in Table 6 show that rhodium
led to weaker selectivities (run 1). The nature of ruthe-
Hydrogen transfer presents several distinct advan-
tages as a reducing process, nevertheless, it requires
basic or acidic conditions not always compatible with
useful substrates. On the contrary, the use of molecular
hydrogen as a reducing agent could be performed in
neutral conditions. Thus, hydrogenation using molecu-
lar hydrogen is of more general industrial application
[32].
Asymmetric hydrogenation reactions catalyzed by
rhodium or ruthenium complexes containing chiral
phosphines have been successfully performed and con-
stitute examples of well established catalytic method-
ologies. Among them, BINAP metal complexes were
extensively studied and applied from both academic
and industrial points of view [33]. Heterogenization of
such asymmetric catalytic systems containing phospho-
rus ligands has received an increasing interest in recent
years.
nium-containing
catalyst
precursors,
[Ru(p-
cymene)Cl2]2 or [Ru(benzene)Cl2]2, did not furthermore
influence the selectivity (63% ee in both cases) (runs 2
and 3). Then, further reduction of acetophenone was
carried out with [Ru(benzene)Cl2]2 as metallic precursor
after 1 day at 70°C with an L/M ratio of 1.5; 92% of
conversion and 70% ee was obtained.
This polymer was recovered by filtration and from
the first to the fourth recycled polymer, no loss of
catalytic activity was observed contrary to selectivity
which decreased slightly from 70% to 61% ee.
The use of polymer 12 in hydrogen transfer reduction
of other aryl ketones was also studied (reaction condi-
tions: L/M=1.5, Ru/substrate=4, t-BuOK=4, 70°C)
(Table 7). For all ketones tested, conversions up to 85%
and ee up to 70% were observed.
Recently Bayston et al. have succesfully performed
the heterogenization of BINAP by anchoring it onto an
Scheme 10.
Table 6
Influence of the catalyst precursor on the enantioselectivity of the reduction of acetophenone
Run
Precursor
L/M
Time (h)
Conversion (%)
ee (%)
1
2
3
[Rh(COD)Cl]2
[Ru(p-cymene)Cl2]2
[Ru(benzene)Cl2]2
3
2
2
15
15
15
96
93
98
47
63
63

C. Saluzzo et al. / Journal of Organometallic Chemistry 603 (2000) 30–39
37
Scheme 11.
existing polymer (Merrifield resin type) (Scheme 11)
[34]. This ligand was used in the hydrogenation of
carbonyl compounds as b-ketoesters with conversions
of about 80–100% using a substrate/catalyst ratio of
500/1 and ee values up to 90%. Acrylic acid was also
hydrogenated; conversion up to 90% and ee about 60%
were observed. On the other hand, Chan et al. [35] have
chosen the strategy which includes the BINAP in the
main chain of a polymer (Scheme 11), in order to study
the hydrogenation of acrylic acid derivatives (conver-
sion from 65% to 100% with a ratio substrate/catalyst
of 200, and ee values from 88 to 95% were obtained).
At the same time, we have chosen this second possi-
bility, i.e. the inclusion of BINAP in the backbone of
the polymer. We have synthesized diam-BINAP (6,6%-
dimethylamino-2,2%-diphosphino-1,1%-binaphtalene)
(Scheme 12) as a precursor of heterogenized BINAP.
diam-BINAP was obtained from enantiopur binol in
five steps in about 20% overall yield [36]. Then, by
polyaddition with 2,6-diisocyanatotoluene, diam-BI-
NAP was transformed into poly-NAP, a polyurea
which presents a pseudo C2 symmetry (Scheme 13) and
which is soluble in polar aprotic solvents (DMF,
DMSO) [36].
system was filtered and reused four times. We have
observed only a slight loss of enantioselectivity (from
68% to 61%).
The hydrogenation reaction in the presence of poly-
NAP–ruthenium as catalyst was extended to ethylenic
substrates (Table 9). Comparable results, concerning
activity and enantioselectivity, were obtained for poly-
NAP and BINAP for the reduction of a-acetamido
acrylic acid. Conversions are about 95% and ee up to
70% which is close to that observed in similar condi-
tions with BINAP itself.
Poly-NAP proved to be an efficient ligand for hydro-
genation of b-ketoesters, ketones and ethylenic
substrates.
5. Conclusion
The renewed interest for homogeneous supported
catalysis is partly due to the development of nitrogen-
containing ligands. The chemistry of this functional
group is much more adapted to the formation of poly-
mers than their phosphorus counterparts. Even in the
case of phosphine-containing ligands, the introduction
of an amine group onto the homogeneous ligand allows
the formation of efficient and selective materials.
We have shown that polymer-supported analogs such
as polysulfonamide Merrifield resins and chiral main
chain polymers, such as polyureas or polythioureas
presenting a pseudo C2 symmetry were suitable for
different types of asymmetric heterogeneous catalytic
reactions: allylic substitution and hydrogen transfer
reduction of ketones. Moreover, the heterogenization of
We have used poly-NAP as a ruthenium ligand in
asymmetric hydrogenation of CꢀO and CꢀC bonds.
The results are summarized in Tables 8 and 9. Compar-
ative results with BINAP are presented.
In the case of the b-keto-ester (runs 1 and 2, Table
8), similar activity and selectivity (99%) were observed.
An attempt to reuse the poly-NAP–RuBr2 was per-
formed with this substrate and after four times, no loss
of either selectivity or activity was observed.
In 1995, Noyori et al. [38] reported the use of both
BINAP–Ru catalyst and a chiral diamine (mainly
diphenylethylene diamine: DPEDA) as an additional
ligand allowing reduction of various prochiral ketones.
They have shown a synergetic effect of the amine, as
BINAP–Ru catalyst alone was unable to reduce un-
functionalized ketones. Then, we carried out the reduc-
tion of acetophenone in the presence of DPEDA. The
reaction conditions employed with poly-NAP (run 4),
even though different from Noyori’s conditions (run 3),
yielded total conversion (100%) and an interesting
enantioselectivity (68%). For this reaction, the catalytic
Scheme 12.

38
C. Saluzzo et al. / Journal of Organometallic Chemistry 603 (2000) 30–39
Scheme 13.
Table 8
Reduction of carbonyl compounds with H2, at 50°C under 40 bar
Run Substrate
Catalyst
Solvent
Time (h) S/C
Conversion (%) ee (%)
1
2
BINAP-RuBr2
MeOH
MeOH
14
14
18
1000 100
99 (S) [37]
Poly-NAP–RuBr2
1000 100
500 99
1000 100
99 (S)
3
(S) BINAP–RuCl2·dmfa+(S,S) DPEDA i-PrOH–KOH
87 (R) [38]
68 (S)
4
(S) Poly-NAP–RuBr2+(S,S) DPEDA
i-PrOH–t-BuOK 18
a Hydrogen pressure: 4 bar.
Table 9
Hydrogenation of olefinic substrates at 50°C under 10 bar
Run
Substrate
Catalyst
Solvent
Time (h)
S/C
Conversion (%)
ee (%)
1
2
BINAP–RuCl2·dmf
MeOH
MeOH
14
14
100
100
95
95
78
70
(S) Poly-NAP–RuCl2·dmf
BINAP into poly-NAP (polyurea) was successful and
allowed the efficient hydrogenation of carbonyl and
ethylenic compounds.
From the synthetic point of view, in most cases, the
use of polymer-supported ligands in these reactions is
interesting because high conversions and enantioselec-
tivities were obtained. On the other hand, they offer
easy separation of the catalyst from the reaction prod-
ucts and their reuse is mostly effective without any loss
either of conversion or enantioselectivity.
Yi [39]) are dissolved in a minimal volume of CH2Cl2
and 2.09 mmol of diamine in 1 ml of CH2Cl2 are then
added. The reaction mixture is stirred for 12 h under
argon, then 50 ml of i-PrOH is added and the solution
is stirred for 12 h again. The polymer then precipitates.
It is washed twice with 50 ml of i-PrOH and dried for
2 days under vacuum (20 mmHg) at room temperature
(r.t.) in the presence of P2O5.
Yield: 56%, [h]D= −200.2 (c=0.52, DMSO); Fp=
1
215°C; H-RMN ((CD3)2SO): 2.23; 2.42; 3.13; 7.2–7.6;
8.07; 9.01. Elemental analysis: Anal. Found: C, 72.06;
H, 6.36; N, 9.87; S, 11.71. Calc.: C, 72.11; H, 6.33; N,
9.76; S, 11.8%.
6. Experimental
6.1. Example of polymer synthesis
6.2. Example of hydride transfer reduction
6.1.1. Synthesis of polymer 12
Typically, 2.06 mmol of 2,6,2%,6%-tetramethylbiphenyl-
4,4%-diisothiocyanate (synthesized according to Kim and
The catalyst precursor (6×10−3 mmol of metal) and
the appropriate quantity of ligand are mixed in 2 ml of
a 0.012 M solution of t-BuOk. After 1 h of stirring

C. Saluzzo et al. / Journal of Organometallic Chemistry 603 (2000) 30–39
39
under argon, the ketone is added (6×10−2 M). After
12 h of stirring at r.t., the system is heated at 70°C. The
conversion is followed by GC (cydex b SGE 25 m×
0.25 mm).
The catalysts poly-NAP–RuBr2 and poly-NAP–
RuCl2·dmf were respectively prepared according to
Genet et al. [37] and Noyori et al. [40].
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2 ml of methanol. The resulting suspension was stirred
for 14 h at 50°C under 40 bar of hydrogen pressure.
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