Heterogenization of ferrocene palladacycle catalysts on ROMP-derived monolithic supports and application to a Michael addition

Article abstract of DOI:10.1039/c4nj01253d

The anchoring of well-defined molecular catalysts on a surface is an attractive strategy to develop sustainable catalytic processes. This article describes the first syntheses of monolith-supported ferrocene palladacycle catalysts. Monolithic supports were prepared via ring-opening metathesis polymerization (ROMP) using the 1st generation Grubbs catalyst . Fluorinated carboxylates were surface-grafted utilizing living Ru-termini. The immobilization of the palladacycles onto the monolithic support was accomplished by ligand substitution on the fluorinated carboxylates of the graft polymer. An investigation of these supported catalysts on the efficiency and reusability under different reaction conditions in a direct Michael addition generating a quaternary C-atom is reported. Whereas stereoselectivity was found to be significantly lower than in a comparable homogeneous system, Pd-leaching was not detected in all analyzed samples indicating a permanently immobilized catalyst system. This journal is

Full text of DOI:10.1039/c4nj01253d

NJC
View Article Online
View Journal
PAPER
Heterogenization of ferrocene palladacycle
catalysts on ROMP-derived monolithic supports
Cite this:DOI: 10.1039/c4nj01253d
and application to a Michael addition†
a
b
a
Mavila Sudheendran,‡ Simon H. Eitel,‡ Stefan Naumann,
ac
b
Michael R. Buchmeiser* and Rene Peters*
´
The anchoring of well-defined molecular catalysts on a surface is an attractive strategy to develop
sustainable catalytic processes. This article describes the first syntheses of monolith-supported ferrocene
palladacycle catalysts. Monolithic supports were prepared via ring-opening metathesis polymerization (ROMP)
using the ‘‘1st generation Grubbs catalyst’’. Fluorinated carboxylates were surface-grafted utilizing living
Ru-termini. The immobilization of the palladacycles onto the monolithic support was accomplished by
ligand substitution on the fluorinated carboxylates of the graft polymer. An investigation of these
supported catalysts on the efficiency and reusability under different reaction conditions in a direct
Michael addition generating a quaternary C-atom is reported. Whereas stereoselectivity was found to be
significantly lower than in a comparable homogeneous system, Pd-leaching was not detected in all
analyzed samples indicating a permanently immobilized catalyst system.
Received (in Montpellier, France)
2
7th July 2014,
Accepted 16th September 2014
DOI: 10.1039/c4nj01253d
www.rsc.org/njc
inorganic or organic support is considered to be the most
promising way to overcome these difficulties. In this context,
Introduction
2
Asymmetric synthesis using chiral catalysts is, in principle, monolithic supports prepared by ROMP have received con-
3
the most efficient way to synthesize optically active compounds siderable attention in recent years. The monolithic supports
and is therefore of great importance for both industrial appli- of this class having suitable porous properties and func-
1
cations and academic research. However, the application of tional groups can be prepared easily and have been widely
these often expensive chiral catalysts in commercial syntheses used in heterogeneous catalysis as well as in separation
4
is severely limited owing to difficulties in separation and science. The low back pressure, easily accessible surface-
recycling. Therefore, a catalytic system that allows for the bound catalytic sites as well as the fast mass transfer of the
straightforward separation of expensive chiral catalysts from support allow for the running of such devices in a conti-
the reaction mixture with minimum product contamination nuous flow-through set-up with high TONs and low catalyst
2
b
by metal leaching and which can be recycled efficiently is highly leaching. Quite recently, a variety of heterogenization techni-
desirable. Since most of these difficulties are primarily due ques for the immobilization of expensive catalysts and enzymes
to the homogeneous nature of the catalysts, the heterogeniza- on a ROMP-derived monolithic support has been reported by
4
b,5
tion by the immobilization of homogeneous catalysts on an Buchmeiser et al.
The use of mono- and bimetallic planar chiral palladacycle
catalysts in the asymmetric direct conjugate addition of
a-cyanoacetates to cyclic enones, forming adjacent quaternary
and tertiary stereocenters, has recently been reported by Peters
a
Institut f u¨ r Polymerchemie, Lehrstuhl f u¨ r Makromolekulare Stoffe und
Faserchemie, Universit a¨ t Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart,
Germany. E-mail: michael.buchmeiser@ipoc.uni-stuttgart.de;
Fax: +49 (0)711 68564050; Tel: +49 (0)711 68564074
6
b
c
et al. Here we report the immobilization of these catalysts: the
Institut f u¨ r Organische Chemie, Universit a¨ t Stuttgart, Pfaffenwaldring 55,
D-70569 Stuttgart, Germany. E-mail: rene.peters@oc.uni-stuttgart.de;
Fax: +49 (0)711 68554330; Tel: +49 (0)711 68564330
7
–10
bimetallic ferrocene bisimidazoline bispalladacycle FBIP
and the monometallic ferrocene imidazoline palladacycle
11
Institut f u¨ r Textilchemie und Chemiefasern (ITCF), K o¨ rschtalstr. 26,
D-73770 Denkendorf, Germany. Fax: +49 (0)711 9340185;
Tel: +49 (0)711 9340101
FIP on a ROMP-derived monolithic support. The goal of this
immobilization technique has been to facilitate the efficient
recovery and reuse of the noble-metal catalysts along with high
stereoselectivities, comparable to those for the homogeneous
catalyst systems.
†
Electronic supplementary information (ESI) available: Synthetic and spectral
information. See DOI: 10.1039/c4nj01253d
These authors contributed equally.
‡
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem.

View Article Online
Paper
NJC
Results and discussion
Transformation of the dimeric precatalysts into monomeric
obtained by the analogous reaction of the precatalyst [FBIP-Cl]
2
with silver tetrafluoroborate–acetonitrile in dichloromethane.
complexes suitable for catalyst grafting
Synthesis of monolithic supports
The chiral bimetallic precatalyst [FBIP-Cl]
precatalyst [FIP-Cl] exist as dimeric, chloride-bridged species
Scheme 1), which are relatively inert towards ligand exchange.
However, catalytically active monomeric complexes FBIP-
CC and FIP-O CC can be obtained by activation with
2
and the monometallic
The ROMP-derived monolithic support was prepared from NBE
and (NBE–CH O) SiCH in a suitable mixture of porogens by
using the ‘‘1st generation Grubbs catalyst’’, RuCl
2
2
3
3
(
2
(PCy
3
)
2
(Q CHPh),
3a,5d,13
according to a previously published protocol.
After rod
O
2
3
F
7
2
3 7
F
formation, the ‘living’ ruthenium termini located at the surface
were used for the grafting of the functional monomers. Earlier,
Buchmeiser et al. reported a successful immobilization of a
Ru-based metathesis initiator via the halogen exchange by a
silver heptafluorobutyrate in dichloromethane containing aceto-
6
a
nitrile (Scheme 1). These activated palladacycles offer high
catalytic activity along with a high level of stereocontrol in
1,4-additions of a-cyanoacetates to cyclic enones. In the case of
5d
fluorinated carboxylate ligand. This approach was more straight-
the bis-Pd catalyst a highly organized transition state, in which
both metal centers cooperate, has been proposed to be respon-
forward and convenient as there are no intermediate steps involved.
In addition, the unreacted catalyst can be fully recovered.
6
,12
sible for the good stereocontrol.
We envisaged that catalyst
immobilization might be achieved through a ligand exchange
of these complexes with the carboxylate groups of the grafted
polymer.
Synthesis of supported catalyst C1a via surface grafted
monomer M1
We began the immobilization following a previously published
In addition, we have investigated the use of the biscationic
5d
ꢀ
procedure, where mono(norborn-5-ene-2-ylmethyl) hexafluoro-
glutarate (M1) was used as the functional monomer. Monomer
M1 can be readily obtained by a simple ring-opening of hexa-
fluoroglutaric anhydride with 5-norbornene-2-methanol (1) in
complex FBIP-BF
4
containing BF
4
as counterion. FBIP-BF
4
was
5d
dichloromethane (Scheme 2).
After the reaction, the solution containing M1 was used
as such without further purification and grafted on to the
monolithic surface via the living Ru-termini (Scheme 3). The
initiator was removed by extensive flushing with a mixture of
DMSO : THF : EVE (ethylvinylether) (40 : 40 : 20), which results in
a ruthenium free monolithic matrix as evidenced by inductively
coupled plasma optical emission spectroscopy (ICP-OES) measure-
3a,c
ments. The amount of chemically accessible carboxylate groups
of the graft polymer were quantified at this stage by acid–base
titration using phenolphthalein as indicator. For this purpose,
a known volume of standard KOH solution was injected into
the monolith. The amount of carboxylate groups were deter-
mined by comparing the concentration of this solution with the
one of a standard KOH solution. This way, a carboxylic acid
ꢀ1
content of 370 mmol g , was found.
The potassium carboxylate groups of the graft polymer were
directly utilized for the immobilization of the activated complex
ꢀ
FBIP-BF . The remaining BF counterion in the grafted complex
4
4
Scheme 1 Activation of the precatalysts [FBIP-Cl]
2 2
and [FIP-Cl] by silver
salts to form the monomeric homogeneous catalysts.
Scheme 2 Synthesis of functional monomer M1.
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
NJC
Paper
Table 1 Results of the Michael addition reaction using the supported
a
catalyst C1a
b
c
c,d
c,e
Entry
Yield [%]
ee(R,R) [%]
ee(S,R)/(R,S)
[%]
dr
f
1
99
41
29
54
36
94
68
50
22
28
65
ꢀ4
5
5
4
89 : 11
41 : 59
41 : 59
52 : 48
57 : 43
2
3
4
5
Scheme 3 Synthesis of monolith-supported catalyst C1a via immobiliza-
tion of FBIP-BF by carboxylate groups.
4
a
Conditions: diglyme, 92 mmol of 2, 10 equiv. of 3, 0.2 equiv. of HOAc,
0
.2 mL of diglyme. All results (if not indicated otherwise) were produced
b
1
was subsequently substituted by an excess of silver heptafluoro- with identical monolithic support. c Determined by H NMR spectro-
d
scopy using an internal standard. Determined by HPLC. A minus
sign indicates that the (R,S)-enantiomer is formed in excess. (R,R +
butyrate. Following this procedure, FBIP was bound to the
e
ꢀ1
support with a concentration of 20 mg g . Since the complex
f
S,S):(S,R + R,S). Under optimized conditions using the homogeneous
6
a
is intensively dark-red, any leaching of the complex would be FBIP-O C F catalyst, 92 mmol of 2, 2 equiv. of 3, 1 mol% of FBIP-
2
4 7
2 4 7
O C F , 0.2 equiv. of HOAc, 0.17 mL of diglyme.
easily determined in the eluent. To our pleasure, no leaching
of the catalyst was observed, indicative for a successful immobi-
lization of the catalyst (Scheme 3).
Alternative route to the supported catalyst C1b by direct
immobilization and application of C1b
Catalytic performance of the supported catalyst C1a
To study the activity of the FBIP derived monolith-supported In order to overcome the inconsistencies in the catalytic
catalyst C1a, the 1,4-addition of tert-butyl-2-cyano-2-phenyl- activities of the supported catalyst, the immobilization was
acetate (2) to 2-cyclohexen-1-one (3) was carried out in diglyme carried out via an approach, by which the supported catalyst
at 35 1C. All catalytic experiments using supported catalysts was obtained directly carrying the desired heptafluorobutyrate
described in this article have been done under sealed condi- counterion. This alternative synthesis of the supported catalyst
tions. In the optimized homogeneous version of this reaction used the direct substitution of one heptafluorobutyrate ligand
using FBIP-O CC F as catalyst the (R,R)-diastereomer 4 is of FBIP-O C F by free carboxylic acid groups of the graft
2 3 7 2 4 7
formed in excess with high enantioselectivity, whereas the polymer thus releasing heptafluorobutyric acid as side product
enantioselectivity for the epimer is only moderate (Table 1, (Scheme 4).
entry 1). The results of the same transformation using the
The driving force of this method is the almost 30-fold excess
monolith-supported catalyst C1a are also summarized in of free acid groups on the monolith relative to the injected
Table 1. Despite the successful immobilization, variations in catalyst. The difference of the pK values of heptafluorobutyrate
a
1
4
the results of four identical experiments in terms of conversion (pK
and selectivity (Table 1, entries 2 to 5) indicate that a gradual (pK
a
a
E 0.63) and of the carboxylate group of the graft polymer
1
4
E 0.6) is very small and should only slightly influence
was
2 4 7
decomposition of the catalytic species or the linker between the equilibrium. Following this procedure, FBIP-O C F
ꢀ1
monolith and catalyst might occur.
bound to the support with a concentration of 20 mg g .
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem.

View Article Online
Paper
NJC
Table 2 Results of the Michael addition reactions using the supported
a
catalyst C1b
b
c
c,d
c,e
Entry
Yield [%]
ee(R,R) [%]
ee(S,R)/(R,S)
[%]
dr
f
1
2
3
4
5
6
7
99
56
51
27
27
40
35
94
56
60
27
52
87
38
65
0
3
89 : 11
50 : 50
48 : 52
48 : 52
42 : 58
52 : 48
52 : 48
g
ꢀ14
4
h
Scheme 4 Alternative route to the monolith-supported catalyst C1b via
ꢀ5
7
h
direct immobilization of FBIP-O
2
CC
3
F
7
.
a
Conditions: diglyme, 92 mmol of 2, 10 equiv. of 3, 0.2 equiv. of HOAc,
0
.2 mL of diglyme. All results (if not indicated otherwise) were produced
No catalyst leaching was observed indicative of a quantitative
immobilization of the catalyst. In contrast to the first synthesis
b
1
with identical monolithic support. c Determined by H NMR spectro-
d
scopy using an internal standard. Determined by HPLC. A minus
e
of the supported catalyst, no base was necessary for catalyst sign indicates that the other enantiomer is formed in excess. (R,R +
f
S,S):(S,R + R,S). Under optimized conditions using the homogeneous
immobilization. Thus no base-catalyzed product formation has
6
a
FBIP-O C F catalyst, 92 mmol of 2, 2 equiv. of 3, 1 mol% of FBIP-
2 4 7
to be expected as competing reaction pathway, which might
have been an issue in the previous approach.
g h
O
2
C
4
F
7
, 0.2 equiv. of HOAc, 0.17 mL of diglyme. 5 equiv. of 3. 180 mmol
of 2, 10 equiv. of 3, 0.2 equiv. of HOAc, 0.2 mL of solvent.
The results of the enantioselective Michael additions using
this supported catalyst C1b are summarized in Table 2. Under
the studied conditions moderate to good enantiomeric excess way that the geometry of the homogeneous catalyst is main-
was obtained for the (R,R)-diastereomer, while the (S,R)/(R,S)- tained in the heterogeneous mode. In fact this is a critical issue
isomer was formed in almost racemic form. However, the ee’s, due to the interactions of the catalyst with the support, which
2
d
diastereomeric ratios, as well as the yields of the conjugate often leads to a negative change in enantioselectivity. At this
addition product 4 were changing from run to run and no stage, both the stability and accessibility of the linker ligand
obvious trend was found.
should be taken into account. Hydrolyzable groups such as
Nevertheless, there is some improvement of the enantio- ester moieties at the functionalized monomer should ideally be
selectivity for the (R,R)-isomer compared to the previous avoided to guarantee stability of the linker under the condi-
approach and an ee of up to 87% could be attained in one tions of catalysis. Furthermore, a homogeneous distribution of
run (Table 2, entry 6). However, there are several important the catalyst over the support is an important issue. Analysis of
criteria that an immobilized chiral catalyst should fulfil in the support after usage showed in the above-described case an
order to be useful for a chemical process. In general, it is of inhomogeneous distribution of the catalyst with a decreasing
interest to evaluate a supported catalyst in terms of activity, catalyst concentration from the top to the bottom of the
stereoselectivity, stability, homogeneous distribution on the column (Fig. 1). The reaction rate on the top and bottom of
solid support and reusability. In order to fulfil the above out- the column can be expected to differ significantly and the
lined features, the catalyst should ideally be immobilized in a consequence might be an incomplete conversion.
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
NJC
Paper
Fig. 1 Left: monolithic support without immobilized catalyst. Right: mono-
2 3 7
lithic support with immobilized FBIP-O CC F (monolith supported catalyst
C1b). Flow direction from top to bottom, indicated by the arrow.
Synthesis of the supported catalyst C2 via surface-grafted
monomer M2
To overcome the above issues, the fluorinated monomer (M2)
having a sufficient chain length with no readily hydrolyzable
groups was synthesized in six steps from 1 (Scheme 5). The
synthesis of the functionalized monomer M2 was accomplished
by the coupling of fragment 6 with the sodium alcoholate of 7 in dry
15
16
DMF. Compounds 6 and 7 were in turn synthesized starting
from 5-norbornene-2-methanol (1) and 1H,1H,7H-dodecafluoro-1-
heptanol, respectively, following a previously published protocol.
The new designed monomer M2 was expected to have a sufficient
chain length to connect the complex and the support, so that the
complex can move far away from the solid surface and into the
liquid phase. This should maintain the geometry of the supported
catalysts to a better extent similar to the homogeneous system,
while the CF -groups of the linker contribute to the electronic
2
structure of the palladium-center similar as the heptafluorobutyrate
counterion, which has significant influence on the stereoselectivity
outcome of the homogeneous reaction. In addition, the absence of
6
Scheme 5 Synthesis of the functional monomer M2.
any hydrolyzable groups in monomer M2 should improve the
stability of the linker ligand thereby reducing the leaching of both
the metal and ligand. Therefore monomer M2 should also improve
the reusability of the supported-catalysts.
performed catalysis reactions was calculated from the Pd-amount
of the monolith, determined by ICP-OES (see the ESI†). The excess
of acid groups on the monolith was transformed into the corre-
As described above, monomer M2 was surface-grafted onto
the ROMP-derived monolith and then treated with the activated
complex FBIP-O C F to achieve the supported catalyst C2
2 a
sponding methyl esters by TMSCHN , because the pK value of the
Brønsted-acid co-catalyst (usually HOAc) has previously been shown
to have a strong influence on the selectivity of the reaction and a
negative influence has been observed for strong acids such as
2
4 7
(
Scheme 6). The amount of grafted monomer M2 and thereby
the amount of free acid groups of the monolith was reduced to
0 mmol to provide a more uniform distribution of the catalyst
6a
trifluoroacetic acid. With the new monomer M2 and a reduced
5
amount of free carboxylic acid groups on the monolith a consistent
all over the monolith.
distribution of the catalyst FBIP-O CC F has been achieved (Fig. 2,
Immobilization was again achieved through the direct sub-
stitution of the heptafluorobutyrate counterion of the activated
complex FBIP-O CC F by the free acid groups of the function-
2
3 7
supported catalyst C2 shown after use in catalysis).
2
3 7
Catalytic performance of the supported catalyst C2
alized monolith. This way, 83% (3.67 mmol) of the FBIP-O C F
4 7
2
complex used were bound to the support. The remaining 17% The catalytic activity of the supported catalyst C2 was again
were recovered as precatalyst [FBIP-Cl] , indicating a successful investigated by the asymmetric Michael addition of tert-butyl-2-
immobilization. The amount of immobilized catalyst after the cyano-2-phenylacetate (2) to 2-cyclohexen-1-one (3) to form the
2
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem.

View Article Online
Paper
NJC
Table 3 Results of the Michael addition reactions carried out by using the
a
supported catalyst C2 and different solvents
b
c
c,d
c,e
Entry Solvent
Yield [%] ee(R,R) [%] ee(S,R)/(R,S) [%] dr
f
1
2
3
4
5
Diglyme 99
CH Cl
Diglyme 29
94
69
66
72
12
65
ꢀ22
27
4
89 : 11
73 : 27
63 : 37
59 : 41
59 : 41
2
2
2
Et
2
O
15
98
EtOAc
0
a
Conditions: 92 mmol of 2, 10 equiv. of 3, 0.2 equiv. of HOAc, 0.2 mL of
Scheme 6 Synthesis of the FBIP-containing monolith-supported catalyst C2.
solvent. All results (if not indicated otherwise) were produced with
b
1
identical monolithic support.c Determined by H NMR spectroscopy
d
using an internal standard. Determined by HPLC. A minus sign
e
indicates that the (R,S)-enantiomer has been formed in excess. (R,R +
f
S,S):(S,R + R,S). Under optimized conditions using the homogeneous
6a
FBIP-O
2 4 7
C F catalyst, 92 mmol of 2, 2 equiv. of 3, 1 mol% of FBIP-
2 4 7
O C F , 0.2 equiv. of HOAc, 0.17 mL of diglyme.
(Table 3, entry 2). More promising were the results of reactions
carried out in diglyme and diethylether (Table 3, entries 3
2
0
and 4), where 66% and 72% ee were obtained for the major
diastereomer, while the minor diastereomer was formed in
almost racemic form. High yields were obtained with ethyl
acetate as solvent (Table 3, entry 5), but the product was formed
in almost racemic form. Diglyme was chosen as solvent for
further experiments to examine the stability and reusability of
the catalyst system (Table 4).
Fig. 2 Left: monolithic support without immobilized catalyst. Right: mono-
The results showed varying yields between 9 and 80% of
the Michael addition product 4, while the ee of the (R,R)-
diastereomer maintained in a moderate range and was still not
constant. The enantioselectivity of the (S,R)/(R,S)-diastereomer
The results of a solvent was rather low. Interestingly, starting from the second run this
2 3 7
lithic support with immobilized FBIP-O CC F (monolith supported catalyst
C2). Flow direction from top to bottom, indicated by the arrow.
1
7,18
densely functionalized product 4.
screening using 3.67 mmol of the immobilized catalyst C2 isomer was formed as the major product, whereas in the first run
(
Table 3, entries 2 to 5) and the results with diglyme as preferred the (R,R)-diastereomer was preferred.
1
9
solvent are summarized in Tables 3 and 4, respectively.
All analysed reaction samples did not show any palladium-
2 2
The reaction in CH Cl proceeded with poor yield while leaching and only negligible Fe-amounts were determined by
the enantioselectivity was good for the major (R,R)-isomer ICP-OES (see the ESI†). Loss of Pd in the catalyst and cleavage
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
NJC
Paper
Table 4 Results of the Michael addition reactions carried out by using
a
diglyme and the supported catalyst C2
b
c
c,d
c,e
Run
Yield [%]
ee(R,R) [%]
ee(S,R)/(R,S)
[%]
dr
1
2
3
4
5
6
7
8
9
29
9
66
50
43
54
34
24
46
39
40
17
41
27
16
13
9
11
8
4
10
7
63 : 37
48 : 52
44 : 56
37 : 63
30 : 70
Scheme 7 Synthesis of the FIP-containing monolith-supported catalyst C3.
23
26
68
14
44
80
53
47
38
2 3 7 2 3 7
of FIP-O CC F was accomplished in analogy to FBIP-O CC F via
42 : 58 direct immobilization using the free acid groups of the monolithic
32 : 68
28 : 72
30 : 70
31 : 69 (1.71 mmol) of the injected catalyst (4.4 mmol) were immobilized,
28 : 72
support, followed by esterification of the residual carboxylic acid
groups with TMSCHN (Scheme 7). Following this procedure, 39%
2
1
1
0
1
2
2
while the rest was recovered as precatalyst [FIP-Cl] . Again, the
2
a
Conditions: 92 mmol of 2, 10 equiv. of 3, 0.2 equiv. of HOAc, 0.2 mL of amount of immobilized catalyst was calculated after the cata-
diglyme. All results were produced with identical monolithic support.
lytic runs from the Pd-amount of the monolith, determined by
ICP-OES (see the ESI†).
b
c
1
Determined by H NMR spectroscopy using an internal standard.
Determined by HPLC. A minus sign indicates that the (R,S)-
d
e
enantiomer has been formed in excess. (R,R + S,S):(S,R + R,S).
Catalytic performance of the supported catalyst C3
Diglyme was used as solvent for catalysis, to allow for a direct
comparison with the catalytic performance of the monolith-
supported catalyst C2 (vide supra). In the first two runs almost
quantitative yields of 4 were obtained (Table 5, entries 2 and 3).
However, in the subsequent reactions the yield dropped to o10%
of the linker unit between catalyst and monolith under the
reaction conditions can thus be excluded. On the other side, the
permanently changing stereoselectivity might be partly explained
by a changing environment of the Pd-centers, e.g. caused by
product ligation.
(Table 5, entries 4 to 8). The (R,R)-diastereomer was formed with low
to moderate enantioselectivity, while the (S,R)/(R,S)-diastereomer
was formed in almost racemic form. As expected the latter
Synthesis of the supported catalyst C3 via surface-grafted M2
A highly enantioselective preferred formation of the (S,R)/(R,S)- (S,R)/(R,S)-diastereomer is formed in excess.
diastereomer of 4 has been previously described with the Albeit the immobilization of the monometallic catalyst FIP
monometallic catalyst FIP-O CC in a homogeneous reaction proceeds with lower yield (39% immobilization compared to
2
3 7
F
6a
system. Since the results presented above show similar pre- 88% immobilization with the bimetallic catalyst FBIP under
ferences for the (S,R)/(R,S)-diastereomer after the first run in otherwise identical conditions) no palladium leaching occurred
diglyme, the immobilization of the monometallic palladacycle during the catalytic runs. The analyzed catalysis reaction samples
2 3 7
FIP-O CC F on the M2-based graft-polymer was investigated contained no Pd and only negligible amounts of Fe were deter-
and applied to the conjugate addition of tert-butyl-2-cyano-2- mined by ICP-OES (see the ESI†). The loss of enantioselectivity
phenylacetate (2) to 2-cyclohexen-1-one (3). The heterogenization compared to the homogeneous reaction can be tentatively
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem.

View Article Online
Paper
NJC
Table 5 Results of the Michael addition reactions carried out by using the of the heptafluorobutyrate counterion by carboxylate-groups of
a
supported catalyst C3
the functionalized monolith. Activity, selectivity and reusability
of the monolith-supported catalysts were studied for the Michael
addition of tert-butyl-2-cyano-2-phenylacetate (2) to 2-cyclohexen-
1-one (3) to form the addition product 4 with adjacent quaternary
and tertiary stereocenters. Moderate to good enantiomeric
excesses were attained for the (R,R)-isomer, while the (S,R)/
(
R,S)-diastereomer was usually formed in almost racemic form.
Often this latter diastereomer was formed in excess, comparable
to the monometallic catalyst FIP-O CC in the homogeneous
2
3 7
F
reaction. The loss of the immobilized catalysts was investigated
by ICP-OES measurements: no Pd-leaching and negligible
Fe-amounts were detected in all analyzed reaction samples,
indicating a permanently immobilized catalyst system. However,
the steadily changing stereoselectivity data from run to run suggest
that the nature/composition of the catalyst is also changing from
run to run. Compared to the recently developed homogeneous
version of this reaction, both the diastereoselectivity as well as
the enantioselectivity are considerably lower. This indicates
that interactions between the catalytically active centers and
either the monolithic support or the linkers used have a
negative impact. Nevertheless, this study has established the
proof of principle for a successful immobilization of ferrocene
derived planar chiral palladacycles. The new immobilization
procedure and the novel graft-polymer system might be inter-
esting for other catalytic reactions.
b
c
c,d
c,e
Entry
Yield [%]
ee(R,R) [%]
ee(S,R)/(R,S)
[%]
dr
f
1
90
99
97
6
9
8
33
59
45
20
17
23
25
12
89
1
ꢀ1
ꢀ7
ꢀ2
4
29 : 71
35 : 65
31 : 69
32 : 68
39 : 61
31 : 69
2
3
4
g
5
Experimental
30 : 70 General remarks
6
7
8
6
6
4
10
33 : 67
All reactions were performed under a nitrogen atmosphere in a
glovebox or in oven dried (150 1C) glassware and were magne-
tically stirred. A positive pressure of nitrogen (ca. 0.2 bar) was
a
Conditions: 92 mmol of 2, 10 equiv. of 3, 0.2 equiv. of HOAc, 0.2 mL of
diglyme. All results (if not indicated otherwise) were produced with
identical monolithic support.c Determined by H NMR spectroscopy
b
1
d
using an internal standard. Determined by HPLC. A minus sign used as protective atmosphere for Schlenk technique. For all
e
indicates that the (R,S)-enantiomer has been formed in excess. (R,R +
reactions liquids and solutions were added via syringe and
f
S,S):(S,R + R,S). Under optimized conditions using the homogeneous
6a
septa. Working with the PEEK columns all solvents, reagents and
reaction mixtures were injected by luer lock syringe technique
using a syringe pump. Solvents were removed by rotary evapora-
tion at 40 1C bath temperature and 600–10 mbar pressure or by a
constant stream of nitrogen. Non-volatile compounds were dried
in vacuo at 0.1 mbar.
Diethyl ether, tetrahydrofuran (THF), toluene, n-pentane,
acetonitrile and dichloromethane were distilled and further
purified by an MBraun solvent purification system. Diglyme
FIP-O
0
2
C F catalyst, 92 mmol of 2, 2 equiv. of 3, 1 mol% of FIP-O CC F ,
4
7
2
3
7
g
.2 equiv. of HOAc, 0.17 mL of diglyme. Reaction time of 3 d.
ascribed to the different catalyst environment, affected by the
monolithic support, and the lower amount of immobilized
catalyst. Nevertheless, the diastereoselectivity was comparable
to the homogeneous reaction.
(
anhydrous, 499.5%) was stored over 4 Å molecular sieves in
Conclusions
crown capped bottles under nitrogen atmosphere. 2-Cyclohexen-
Two methodologies are described for the heterogenization of 1-one (3, 498%) was distilled in vacuum prior to use and stored
planar chiral palladacycle catalysts on ROMP-derived mono- at ꢀ30 1C under inert atmosphere. The precatalysts [FBIP-Cl]
2
21
11a
lithic supports using either potassium carboxylate groups or (ref. 7a and c) and [FIP-Cl]
free acid groups (to avoid traces of basic impurities) on the 2 and the activated catalysts FBIP-O CC F and FIP-O CC F
3 7
2
,
tert-butyl-2-cyano-2-phenylacetate
2
3
7
2
monolith. Furthermore, the application of the new, hydrolysis- (ref. 6a) were prepared according to literature procedures.
stable monomer M2 in the graft-polymers was examined in Preparation of the monolithic support inside a PEEK column
terms of stability and influence on the activity of the bound (100 ꢁ 7 mm i.d.) and grafting of functionalized monomer
catalyst. Immobilization of the mono- and bimetallic catalysts M1 to the monolithic support was performed according to
5
b,d
FIP-O
2
CC
3
F
7
and FBIP-O
2
CC
3
F
7
was accomplished via substitution literature procedures.
All other chemicals were purchased
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
NJC
Paper
and used without any further purification. For work-up procedures was added and the suspension was stirred overnight at room
and column chromatography distilled technical grade solvents temperature. Afterwards the suspension was filtrated over celite
(
CH Cl , diethyl ether, petrol ether and ethyl acetate) were used.
and the solvent was removed in vacuo at room temperature to give
2
2
Reactions were either monitored by HPLC (Hewlett Packard pure FBIP-BF as a red solid (26.7 mg, 18 mmol, quantitative).
4
ꢀ
1
1
Series 1050, reverse phase, acetonitrile–water as eluent) or by thin C H B F FeN O Pd S , MW: 1483.59 g mol . Mp.: decomposi-
62
56
2
8
8
4
20
2 2
layer chromatography (TLC) with silica-plates (silica gel 60 F254). tion 4 200 1C. [a]
Visualization was achieved by fluorescence quenching under UV CDCl , 25 1C): d = 7.46–7.44 (m, 8H, arom. H), 7.33 (b, 4H, arom.
light (l = 254 nm) and/or by staining with basic KMnO -solution H), 7.27–7.25 (m, 4H, arom. H), 7.21–7.18 (m, 4H, arom. H), 7.08
1.5 g KMnO , 10 g K CO , 5 mL 1 M NaOH in 200 mL water). (t, J = 7.5, 4H, arom. H), 6.58 (t, J = 7.4, 4H, arom. H), 5.59 (b, 2H),
Preparative column chromatography for compound purification 4.93 (b, 4H), 4.54 (b, 2H), 2.47 (s, 6H, CH ), 2.12 (s, free CH CN),
was performed on silica (0.040–0.063 mm), using a positive 1.71 (b, 6H, Pd ’ CH CN), 1.51 (b, 6H, Pd ’ CH CN). C NMR
D 2 2
: +22.4 (c = 0.10, CH Cl ) H NMR (500 MHz,
3
4
(
4
2
3
3
3
13
3
3
pressure of nitrogen (ca. 0.2 bar). Yields refer to pure isolated (125 MHz, CDCl , 25 1C): d = 144.7, 138.2, 131.1, 128.8, 127.9,
3
products and are calculated in mol% of the used starting material. 127.4, 127.1, 126.9, 125.7, 124.3, 123.6, 121.3, 73.6, 71.9, 51.6, 20.0.
1
9
Conversions refer to unconsumed cyanoacetate 2 and were either
F NMR (235 MHz, CDCl
determined by H-NMR using an internal standard or by RP-HPLC (in CDCl ): 3142, 3064, 3033, 2937, 2324, 2296, 1595, 1553, 1465,
with a corresponding calibration curve. The dr- and ee-values 1453, 1365, 1305, 1260, 1171, 1100, 1051, 970. MS (ESI) m/z: 122.03
3
, 25 1C): d = ꢀ151.6, ꢀ151.7. IR
1
3
+
2+
of the Michael addition products 4 were determined by chiral ([M ꢀ 4CH
3
CN ꢀ BF
4
] , 11%), 573.01 ([M ꢀ 4CH
3
CN ꢀ 2BF
4
] ,
4
] :
2
+
stationary phase HPLC (ELITE LaChrom with Hitachi-modules 100%). HRMS (ESI) m/z: calcd for [M ꢀ 4CH
3
CN ꢀ 2BF
+
and a Chiracel OD-H column, iPrOH : heptane (99 : 1) as eluent at 573.0119; found: 573.0106; calcd for [M ꢀ 4CH CN ꢀ BF ] :
3
4
ꢀ1
a flow of 0.9 mL min , room temperature, 210 nm). The assign- 1233.0280; found: 1233.0282.
ment of the configuration of product 4 is based on comparison of
6a
Immobilization of planar chiral palladacycle catalysts on
ROMP-derived monolithic supports
the HPLC retention times with literature data.
1
13
19
H, C and F NMR spectra were recorded on a Bruker
Avance 250, Bruker Avance 500 or Bruker Avance III 400 spectro-
4
Immobilization of FBIP-BF via potassium carboxylate groups
1
meter at 25 1C operating at 250, 500 or 400 MHz for H and 63, on the graft-polymer with M1: monolith-supported catalyst C1a.
1
3
19
1
2
25 or 100 MHz for C. F NMR spectra were recorded at An aqueous solution of KOH (10 mL, 5.2 mM) was introduced to
35 MHz. CDCl was distilled from CaH and stored over mole- the monolith grafted with M1 (B120 mmol) at a flow rate of
3
2
ꢀ
1
cular sieves (4 Å). Other deuterated solvents were used without 0.1 mL min and flushed with water until reaching a neutral
further purification and are mentioned after the corresponding eluent. The column was then flushed with methanol followed by
ꢀ
1
frequency. Chemical shifts in ppm refer to tetramethylsilane CH
d = 0) as internal standard. Coupling constants J are given in of FBIP-BF
Hz and the following abbreviations are used for multiplicities: monolith by using luer syringe technique at a flow rate of
2
Cl
2
, each for 30 min at a flow rate of 0.2 mL min . A solution
(
4
(4.2 mmol) in dry CH Cl (1 mL) was injected to the
2
2
ꢀ
1
s (singlet), d (doublet), t (triplet), q (quartet), p (pentet), 0.05 mL min . The column was then sealed and kept at room
m (multiplet), b (broad signal). GC-MS data were recorded on an temperature overnight. Then silver heptafluorobutyrate (32.1 mg,
Agilent Technologies device consisting of a 7693 autosampler, a 100 mmol) in anhydrous CH CN (1.5 mL) was introduced into the
3
7890A GC and a 5975C quadrupole mass detector. Dodecane was monolith, which was again sealed and kept at room temperature
used as internal standard. An SPB-5 fused silica column (34.13 m ꢁ for 1 h for anion exchange. Finally, the monolith was first flushed
0
.25 mm ꢁ 0.25 mm film thickness) was used. The injection with acetonitrile (3 mL, colourless eluent) followed by dichloro-
temperature was set to 150 1C. The column temperature ramped methane (30 min). Monolith-supported catalyst C1a was used
from 45 1C to 250 1C within eight minutes, and was then held for directly for catalysis.
further five minutes. The column flow was 1.05 mL min . IR
ꢀ1
2 3 7
Direct immobilization of FBIP-O CC F via carboxylic acid
spectra were recorded with a Bruker Vector 22 with an Mk II Golden groups on graft-polymer with M1: monolith-supported catalyst
Gate ATR-unit from Speace. Signals are listed by wave numbers C1b. The catalyst FBIP-O CC F was prepared from the precatalyst
2
3 7
ꢀ
1
(
cm ). Metal contents of the columns and of catalysis samples [FBIP-Cl] (5.0 mg, 2.1 mmol, 1 equiv.) and AgO CC F (2.6 mg,
2 2 3 7
were determined by ICP-OES measurements on an Ametek Spektro 8.4 mmol, 4 equiv.) with acetonitrile in CH Cl according to the
2
2
6a
Arcos instrument. High resolution mass spectra were recorded on a literature procedure. A solution of FBIP-O
Bruker MicroTOFQ instrument using ESI for ionization. dry CH Cl (1 mL) was introduced to the monolith (grafted with
Activation of the precatalyst [FBIP-Cl] with silver tetrafluoro- monomer M1, B120 mmol) at a flow rate of 0.1 mL min . The
borate–acetonitrile: bis(diacetonitrile)[l-(1S
2 3 7
CC F (4.2 mmol) in
2
2
ꢀ
1
2
0
0
p
,1 S
,5-dihydro-1-[(4-methyl-phenyl)sulfonyl]-4,5-diphenyl-1H-imidazol- the column was flushed with dry CH
p
)-2,2 -bis[(4R,5R)- column was then sealed and kept at room temperature. After 24 h,
Cl at a flow rate of
-yl-jN3]-1,1 -ferrocendiyl-jC1:jC1 ]di-palladium(II) di-tetrafluoro- 0.1 mL min for 30 min (colourless eluent). The prepared
4
2
2
2
0
0
ꢀ1
borate (FBIP-BF ). Silver tetrafluoroborate (7.04 mg, 36 mmol, monolith-supported catalyst C1b was used directly for catalysis.
4
4
equiv.) was dissolved in acetonitrile (B2 mL) and the solution
was stirred for a few minutes. The solvent was then removed by a groups on graft-polymer with M2: monolith-supported catalyst
constant stream of nitrogen. A solution of the precatalyst [FBIP-Cl] C2. The catalyst FBIP-O CC was prepared from the pre-
3 7
22.0 mg, 9 mmol, 1 equiv.) in CH Cl (1 mL per 5 mg silver salt) catalyst [FBIP-Cl] (5.0 mg, 2.1 mmol, 1 equiv.) and AgO CC F
Direct immobilization of FBIP-O CC F via carboxylic acid
2 3 7
2
2
3 7
F
(
2
2
2
2
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem.

View Article Online
Paper
NJC
(
2.6 mg, 8.4 mmol, 4 equiv.) with acetonitrile in CH
2
Cl
2
accord- Afterwards the column was washed with diglyme–solvent (4 mL)
6
a
ing to the literature procedure. A solution of FBIP-O
2
CC
4.4 mmol) in dry CH Cl (1 mL) was introduced to the monolith removed in vacuo to give a mixture of Michael addition product
3
F
7
to elute the reaction mixture. The solvent of the eluent was
(
2
2
(
0
grafted with monomer M2, B50 mmol) at a flow rate of 4 and residual tert-butyl-2-cyano-2-phenylacetate 2. The samples
ꢀ
1
.1 mL min . The column was then sealed and kept at room were used for analytics without further purification.
The dr- and ee-values of the Michael addition products
at a flow rate of 0.1 mL min for 30 min so that the 4 were determined by chiral stationary phase HPLC (Chiracel
temperature. After 24 h, the column was flushed with dry
ꢀ
1
CH
eluent was colourless (elution of excess catalyst as [FBIP-Cl]
In order to transform residual carboxylic acid groups of the room temperature, 210 nm, t(R,R) = 13.3 min, t(S,S) = 41.3 min,
2 2
Cl
ꢀ
1
2
). OD-H column, iPrOH : heptane (99 : 1), 0.9 mL min
flow,
6
a
monolith support into the corresponding methyl ester the column
t(S,R) = 17.8 min, t(R,S) = 12.1 min) according to the literature.
was first washed with a MeOH–benzene mixture (4.5 mL, 2/7), The yield of Michael addition product 4 was determined
6a
then trimethylsilyldiazomethane (TMSCHN , 50 mmol, 1 equiv. according to the literature by RP-HPLC (RP-18 column, gradient
2
corresponding to the determined carboxylic acid groups amount, of acetonitrile–water as eluent, detection at 210 nm, tcyanoacetate 2
=
2
M in hexane) was injected and the column was further washed 2.0 min, tMichael addition product 4 = 2.3 min) using a corresponding
with a MeOH–benzene mixture (4.5 mL, 2/7), followed by CH
2
Cl
2
calibration curve.
ꢀ1
at a flow rate of 0.1 mL min for 30 min. The prepared monolith-
supported catalyst C2 was used directly for catalysis. The
amount of immobilized catalyst on the functionalized column
C2 (3.67 mmol FBIP-O CC F ) after the performed catalysis reac-
Acknowledgements
2
3 7
This project was financially supported by the Deutsche
Forschungsgemeinschaft (DFG, PE 818/6-1). The Landesgra-
duiertenf o¨ rderung Baden-W u¨ rttemberg is kindly acknowledged
for a PhD fellowship to S.H.E.
tions was calculated by the palladium amount in the monolith,
determined by ICP-OES (see ESI†).
Direct immobilization of FIP-O
groups on graft-polymer with M2: monolith-supported catalyst
C3. The catalyst FIP-O CC was prepared from the precatalyst
FIP-Cl] (4.5 mg, 2.1 mmol, 1 equiv.) and AgO CC (2.6 mg,
.4 mmol, 4 equiv.) with acetonitrile in CH Cl according to the
literature procedure. A solution of FIP-O CC F (4.4 mmol) in
2 3 7
CC F via carboxylic acid
2
3 7
F
[
2
2
3 7
F
Notes and references
8
2
2
6
a
1 (a) E. N. Jacobsen, Comprehensive Asymmetric Catalysis,
Springer, Berlin, 1999, vol. I–III; (b) R. Noyori, Asymmetric
Catalysis in Organic Synthesis, Wiley-Interscience, New York,
1994; (c) I. Ojima, Catalytic Asymmetric Synthesis, Wiley-VCH
Verlag GmbH, New York, 2nd edn, 2000.
2 (a) C. Baleiz ˜a o and H. Garcia, Chem. Rev., 2006, 106, 3987;
(b) M. R. Buchmeiser, Polymeric Materials in Organic Synthesis
and Catalysis, Wiley-VCH, 1st edn, 2003; (c) D. E. De Vos,
I. F. J. Vankelecom and P. A. Jacobs, Chiral Catalyst Immobi-
lization and Recycling, Wiley-VCH Verlag GmbH, Weinheim,
2000; (d) K. Ding and Y. Uozumi, Handbook of Asymmetric
Heterogeneous Catalysis, Wiley-VCH Verlag GmbH & Co. KGaA,
Weinheim, 2008; (e) Q.-H. Fan, Y.-M. Li and A. S. C. Chan,
Chem. Rev., 2002, 102, 3385; ( f ) J. A. Gladysz, Chem. Rev., 2002,
102, 3215; (g) M. Heitbaum, F. Glorius and I. Escher, Angew.
Chem., Int. Ed., 2006, 45, 4732.
2
3 7
dry CH Cl (1 mL) was introduced to the monolith (grafted with
2
2
ꢀ
1
monomer M2, B50 mmol) at a flow rate of 0.1 mL min . The
column was then sealed and kept at room temperature. After
2
4 h, the column was flushed with dry CH
2
Cl
2
at a flow rate of
ꢀ1
0.1 mL min for 30 min so that the eluent was colourless. In
order to transform residual carboxylic acid groups of the mono-
lith support into the corresponding methyl ester the column was
first washed with a MeOH–benzene mixture (4.5 mL, 2/7), then
TMSCHN (50 mmol, 1.0 equiv. corresponding to the determined
2
carboxylic acid groups amount, 2 M in hexane) was injected and
the column was further washed with a MeOH–benzene mixture
ꢀ1
2 2
(4.5 mL, 2/7), followed by CH Cl at a flow rate of 0.1 mL min
for 30 min. The prepared monolith-supported catalyst C3
was used directly for catalysis. The amount of immobilized
catalyst on the functionalized column C3 (1.71 mmol FIP-O CC F )
2 3 7
after the performed catalysis reactions was calculated by the
palladium amount in the monolith, determined by ICP-OES
3 (a) M. R. Buchmeiser, Macromol. Rapid Commun., 2001,
22, 1081; (b) M. R. Buchmeiser, Polymer, 2007, 48, 2187;
(c) F. Sinner and M. R. Buchmeiser, Macromolecules, 2000,
(see ESI†).
3
3, 5777; (d) F. Sinner and M. R. Buchmeiser, Angew. Chem.,
Asymmetric Michael additions with immobilized palladacycle
catalysts on monolithic supports (general procedure)
Int. Ed., 2000, 39, 1433.
4
(a) M. R. Buchmeiser, J. Mol. Catal. A: Chem., 2002, 190, 145;
(b) M. R. Buchmeiser, R. Bandari, A. Prager-Duschke,
A. L o¨ ber and W. Knolle, Macromol. Symp., 2010, 287, 107;
(c) M. R. Buchmeiser, J. Sep. Sci., 2008, 31, 1907; (d) M. R.
Buchmeiser, J. Chromatogr. A, 2004, 1060, 43; (e) S. Lubbad,
B. May, M. Mayr and M. R. Buchmeiser, Macromol. Symp.,
2004, 210, 1.
tert-Butyl-2-cyano-2-phenylacetate 2 (20 mg, 92 mmol, 1 equiv.)
was dissolved in anhydrous diglyme–solvent (100 mL) and HOAc
dissolved in diglyme–solvent (21.1 mL, 18 mmol, 0.2 equiv.,
ꢀ
1
c = 0.87 mol L ) and 2-cyclohexen-1-one 3 (89 mL, 0.92 mmol,
0 equiv.) were added successively. The mixture was injected
1
into the prepared corresponding column (C1 to C3) followed by
additional diglyme–solvent (100 mL) using the luer lock syringe
technique. The column was sealed and heated for 20 h at 35 1C.
5 (a) M. R. Buchmeiser, Bioorg. Med. Chem. Lett., 2002,
12, 1837; (b) M. Mayr, B. Mayr and M. R. Buchmeiser,
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
NJC
Angew. Chem., Int. Ed., 2001, 40, 3839; (c) M. R. Buchmeiser,
Paper
W. Frey and R. Peters, Organometallics, 2012, 31, 6365;
(i) K. Hyodo, S. Nakamura and N. Shibata, Angew. Chem., Int.
Ed., 2012, 51, 10337; ( j) K. Hyodo, M. Kondo, Y. Funahashi and
S. Nakamura, Chem. – Eur. J., 2013, 19, 4128; (k) S. Nakamura,
K. Hyodo, M. Nakamura, D. Nakane and H. Masuda,
Chem. – Eur. J., 2013, 19, 7304.
Chem. Rev., 2008, 109, 303; (d) J. O. Krause, S. H. Lubbad,
O. Nuyken and M. R. Buchmeiser, Macromol. Rapid
Commun., 2003, 24, 875; (e) R. M. Kroll, N. Schuler,
S. Lubbad and M. R. Buchmeiser, Chem. Commun., 2003,
2742; ( f ) M. Sudheendran and M. R. Buchmeiser,
Macromolecules, 2010, 43, 9601.
(a) S. H. Eitel, S. Jautze, W. Frey and R. Peters, Chem. Sci.,
11 Ferrocenyl imidazoline monopalladacycles: (a) M. E. Weiss,
D. F. Fischer, Z.-q. Xin, S. Jautze, W. B. Schweizer and
R. Peters, Angew. Chem., Int. Ed., 2006, 45, 5694;
(b) D. F. Fischer, Z.-q. Xin and R. Peters, Angew. Chem.,
Int. Ed., 2007, 46, 7704; (c) Z.-q. Xin, D. F. Fischer and
R. Peters, Synlett, 2008, 1495; (d) D. F. Fischer, A. Barakat,
Z.-q. Xin, M. E. Weiss and R. Peters, Chem. – Eur. J., 2009,
15, 8722; (e) R. Peters, Z.-q. Xin and F. Maier, Chem. – Asian
J., 2010, 5, 1770; ( f ) S. H. Eitel, M. Bauer, D. Schweinfurth,
N. Deibel, B. Sarkar, H. Kelm, H.-J. Kr u¨ ger, W. Frey and
R. Peters, J. Am. Chem. Soc., 2012, 134, 4683; (g) M. Weber
and R. Peters, J. Org. Chem., 2012, 77, 10846; (h) J. M. Bauer,
W. Frey and R. Peters, Angew. Chem., Int. Ed., 2014, 53, 7634.
6
7
2013, 4, 2218; (b) vinylketones as substrates: S. Jautze and
R. Peters, Angew. Chem., Int. Ed., 2008, 47, 9284.
(a) S. Jautze, P. Seiler and R. Peters, Angew. Chem., Int. Ed.,
2007, 46, 1260; (b) S. Jautze, P. Seiler and R. Peters,
Chem. – Eur. J., 2008, 14, 1430; (c) S. Jautze, S. Diethelm,
W. Frey and R. Peters, Organometallics, 2009, 28, 2001;
(d) M. Weber, S. Jautze, W. Frey and R. Peters, J. Am. Chem.
Soc., 2010, 132, 12222; (e) M. Weber, S. Jautze, W. Frey and
R. Peters, Adv. Synth. Catal., 2012, 354, 1443; ( f ) M. Weber,
W. Frey and R. Peters, Chem. – Eur. J., 2013, 19, 8342;
(
g) M. Weber, W. Frey and R. Peters, Angew. Chem., Int.
Ed., 2013, 52, 13223; (h) M. Weber, J. E. M. N. Klein, 12 For selected studies on cooperative catalysis by the Peters
B. Miehlich, W. Frey and R. Peters, Organometallics, 2013,
2, 5810.
Reviews on palladacycles: (a) J. Dupont and M. Pfeffer,
Palladacycles, Wiley-VCH, Weinheim, Germany, 2008;
group, see e.g.: (a) F. M. Koch and R. Peters, Chem. – Eur. J.,
2011, 17, 3679; (b) T. Kull, J. Cabrera and R. Peters,
Chem. – Eur. J., 2010, 16, 9132; (c) P. S. Tiseni and
R. Peters, Chem. – Eur. J., 2010, 16, 2503.
3
8
9
(
b) J.-P. Djukic, A. Hijazi, H. D. Flack and G. Bernardinelli, 13 J. O. Krause, S. Lubbad, O. Nuyken and M. R. Buchmeiser,
Chem. Soc. Rev., 2008, 37, 406. Adv. Synth. Catal., 2003, 345, 996.
Reviews about ferrocene palladacycles in asymmetric 14 For pK -values of heptafluorobutyric acid and hexafluoro-
a
catalysis: (a) C. J. Richards, in Chiral Ferrocenes in Asym-
metric Catalysis, ed. L.-X. Dai and X.-L. Hou, Wiley-VCH,
Weinheim, 2010, pp. 337–368; (b) R. Peters, D. F. Fischer
glutaric acid see: W. A. Herrmann, W. R. Thiel, F. E. Kuehn,
R. W. Fischer, M. Kleine, E. Herdtweck, W. Scherer and
J. Mink, Inorg. Chem., 1993, 32, 5188.
and S. Jautze, Top. Organomet. Chem., 2011, 33, 139; for 15 H. Liu, S. Wan and P. E. Floreancig, J. Org. Chem., 2005,
selected applications, see e.g.: (c) L. E. Overman, C. E. Owen, 70, 3814.
M. M. Pavan and C. J. Richards, Org. Lett., 2003, 5, 1809; 16 (a) T. Nguyen, M. Rubinstein and C. Wakselman’, Synth.
(
d) R. S. Prasad, C. E. Anderson, C. J. Richards and L. E.
Commun., 1983, 13, 81; (b) Z. Szl ´a vik, G. T ´a rk ´a nyi,
Z. Skribanek, E. Vass and J. R ´a bai, Org. Lett., 2001, 3, 2365.
Overman, Organometallics, 2005, 24, 77; (e) H. Nomura and
C. J. Richards, Chem. – Eur. J., 2007, 13, 10216; ( f ) H. Nomura 17 Recent reviews about conjugate additions: (a) J. Christoffers
and C. J. Richards, Chem. – Asian J., 2010, 5, 1726.
0 Review about the application of imidazolines in asymmetric
catalysis: (a) H. Liu and D.-M. Du, Adv. Synth. Catal., 2009,
and A. Baro, Angew. Chem., Int. Ed., 2003, 42, 1688;
(b) J. Christoffers, G. Koripelly, A. Rosiak and M. R o¨ ssle,
Synthesis, 2007, 1279; (c) S. Jautze and R. Peters, Synthesis,
2010, 365.
1
351, 489; selected recent applications of bisimidazoline
ligands: (b) S. Nakamura, K. Hyodo, Y. Nakamura, 18 (a) Quaternary Stereocenters: Challenges and Solutions
N. Shibata and T. Toru, Adv. Synth. Catal., 2008, 350, 1443;
c) H. Huang and R. Peters, Angew. Chem., Int. Ed., 2009,
for Organic Synthesis, ed. J. Christoffers and A. Baro, Wiley-
VCH, Weinheim, Germany, 2005; (b) J. Christoffers and
A. Baro, Adv. Synth. Catal., 2005, 347, 1473.
(
48, 604; (d) H. Liu and D.-M. Du, Adv. Synth. Catal., 2010,
352, 1113; (e) L. Cheng, J. Dong, J. You, G. Gao and J. Lan, 19 For additional solvents and solvent mixtures see the ESI†.
Chem. – Eur. J., 2010, 16, 6761; ( f ) M. Ohara, S. Nakamura 20 For further experiments using monolith-supported catalyst
and N. Shibata, Adv. Synth. Catal., 2011, 353, 3285;
g) K. Hyodo, S. Nakamura, K. Tsuji, T. Ogawa, Y. Funahashi
C2 with diethylether as solvent under otherwise identical
see the ESI†.
(
and N. Shibata, Adv. Synth. Catal., 2011, 353, 3385; (h) M. Weiss, 21 J. P. Albarella, J. Org. Chem., 1977, 42, 2009.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem.