Mixing and matching chiral cobalt- and manganese-based calix-salen catalysts for the asymmetric hydrolytic ring opening of epoxides

Article abstract of DOI:10.1016/j.tetasy.2016.02.006

Homochiral oligomeric salen macrocycles possessing aromatic spacers have been prepared as new calix-salen derivatives. The corresponding cobalt and manganese complexes were synthesized and characterized, and their catalytic activities have been studied in the challenging hydrolysis of meso epoxides. While manganese calix-salen complexes were not active in the studied reactions, the dual heterobimetallic system, using an equimolar combination of cobalt and manganese calix-salen derivatives proved to be more enantioselective than the sole cobalt system. Furthermore, as heterogeneous complexes, the catalytic mixture could be easily recovered by simple filtration and successfully reengaged in subsequent catalytic runs. Interestingly, no need for cobalt reactivation was noticed to maintain maximum efficiency of this dual system. The matched Co/Mn dual catalyst was also used to promote the dynamic hydrolytic kinetic resolution of epibromohydrin.

Full text of DOI:10.1016/j.tetasy.2016.02.006

Tetrahedron: Asymmetry xxx (2016) xxx–xxx
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Mixing and matching chiral cobalt- and manganese-based calix-salen
catalysts for the asymmetric hydrolytic ring opening of epoxides
Hiba Dandachi a,b, Elena Zaborova a,d, Emilie Kolodziej a,c, Olivier R. P. David d, Jérôme Hannedouche a,c
,
Mohamed Mellah a, , Nada Jaber b, , Emmanuelle Schulz a,c,
⇑
⇑
⇑
a Equipe de Catalyse Moléculaire, Université Paris-Sud, ICMMO, UMR 8182, Orsay F-91405, France
b Laboratoire de chimie médicinale et des produits naturels, Université Libanaise, Faculté des Sciences (I) et PRASE-EDST, Hadath, Beyrouth, Lebanon
c CNRS, Orsay F-91405, France
d Laboratoire Synthèse & Réactivité, Institut Lavoisier, UMR 8180, Université de Versailles SQY, 45 Av. des Etats-Unis, 78035 Versailles, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Homochiral oligomeric salen macrocycles possessing aromatic spacers have been prepared as new calix-
salen derivatives. The corresponding cobalt and manganese complexes were synthesized and character-
ized, and their catalytic activities have been studied in the challenging hydrolysis of meso epoxides. While
manganese calix-salen complexes were not active in the studied reactions, the dual heterobimetallic sys-
tem, using an equimolar combination of cobalt and manganese calix-salen derivatives proved to be more
enantioselective than the sole cobalt system. Furthermore, as heterogeneous complexes, the catalytic
mixture could be easily recovered by simple filtration and successfully reengaged in subsequent catalytic
runs. Interestingly, no need for cobalt reactivation was noticed to maintain maximum efficiency of this
dual system. The matched Co/Mn dual catalyst was also used to promote the dynamic hydrolytic kinetic
resolution of epibromohydrin.
Received 20 January 2016
Accepted 12 February 2016
Available online xxxx
Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction
salen-type linear oligomers or polymers.8 Macrocyclic structures
have also been described to show undeniable activity enhance-
The high efficiency in terms of both the activity and enantiose-
lectivity of salen-derived complexes to achieve the formation of
new bonds is well-established, for the synthesis of valuable enan-
tioenriched synthons,1 even on a large industrial scale.2 Conse-
quently, numerous research teams have already described
different methods to heterogenize and, thus, recycle these cata-
lysts.3 Moreover, they have been proven to be particularly efficient
for promoting epoxide ring-opening.4 Precisely in this context,
Jacobsen et al. demonstrated that catalysis occurred through coop-
erative bimetallic activation.5 Numerous efforts have since been
devoted to the specific preparation of such catalysts for efficient
dual activation. Some of them are based on the formation of
bimetallic complexes arising from the association of two ligands
by non-covalent interactions.6 Other research teams have pro-
posed the immobilization of various salen-complexes on insoluble
supports, with the aim of enhancing cooperativity by specific spa-
tial arrangement while also promoting easy recovery.7 Some valu-
able examples also imply the formation of soluble or insoluble
ment.9 These examples have in common the use of polysalen com-
plexes, in which the same metal is used to promote the bimetallic
activation.
We have recently developed a heterobimetallic dual-catalyst
system based on the preparation and use of various salen com-
plexes, for the hydrolytic kinetic resolution of terminal epoxides.10
A combination of cobalt-salen and manganese-salen complexes,
generated from ligands possessing the same stereochemical con-
figuration, produced highly enantioselective catalysts for the
hydrolysis of epibromohydrin, or other terminal epoxides and also
for the more challenging ring opening of cyclohexene oxide. Fur-
thermore, we have reported the efficient synthesis of new macro-
cyclic salen complexes (calix-salen complexes), containing either
chromium, cobalt or copper salts, and their use as catalysts to pro-
mote various enantioselective reactions, such as Diels–Alder and
Henry reactions, the additions of dimethylzinc to aldehydes, nucle-
ophilic ring-openings of epoxides and hydrolytic kinetic resolution
reactions.11 Efficient reactivities were recorded, leading in some
specific cases to enhanced isolated yields and enantioselectivities,
especially for those transformations in which cooperative catalysis
was already reported to be operative. Furthermore, all macrocyclic
catalysts were easily recovered by simple filtration at the end of
⇑
Corresponding authors.
E-mail addresses: Mohamed.mellah@u-psud.fr (M. Mellah), nada.jaber@ul.edu.lb
(N. Jaber), emmanuelle.schulz@u-psud.fr (E. Schulz).
http://dx.doi.org/10.1016/j.tetasy.2016.02.006
0957-4166/Ó 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Dandachi, H.; et al. Tetrahedron: Asymmetry (2016), http://dx.doi.org/10.1016/j.tetasy.2016.02.006

2
H. Dandachi et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
the reactions and could be reused in renewed runs, thus proving
their recyclability and following, at best, the principles of green
chemistry.
Herein we report our investigations toward the use of such
macrocyclic complexes containing different metals and their effi-
ciency in their dual use for the ring opening of epoxides. Special
attention will also be drawn for evaluating their recovery and
reuse in these transformations.
the pentamer (8%), with the tetramer being formed as the major
species (82%).
The macrocycles were further characterized by Maldi-TOF anal-
yses, proving that the condensation occurred together with the loss
of two water molecules, and thus confirming the formation of cyc-
lic structures. As for compound 4 a repetitive unit of m/z 508.31
was observed; this value was m/z 596.34, which is characteristic
for the targeted structure of 5. For this fluorene containing com-
pound, the dimer, the trimer, and the tetramer could be detected
but the presence of the corresponding pentamer was not noticed
(see SI). Accordingly for the calix-salen 6, the cyclic oligomers were
observed with a repetitive mass unit of 566.27. Although this spec-
troscopic technique is not quantitative, it demonstrates that the
production of cyclic structures can be efficiently extended to the
use of structurally varied disalicylaldehydes, possessing rigid link-
ers (see Scheme 2).
Finally, cobalt salts were incorporated into these cyclic salen
ligands (used as mixtures of differently sized macrocycles) follow-
ing classical procedures,13 with the aim of forming active catalytic
sites in each coordinating salen. The cobalt complexes 7, 8, and 9
were easily recovered in quantitative yields as brown powders
by filtration and subsequent washing with methanol. Accordingly,
the corresponding manganese complexes were also prepared from
manganese acetate tetrahydrated in an ethanol/toluene mixture
under an argon atmosphere. Subsequent aerobic oxidation
occurred in the presence of brine to give the targeted manganese
complexes 10, 11, and 12 in up to quantitative yield as brown pow-
ders (see Scheme 3).14
Characterization of the obtained complexes was mainly per-
formed via ATR–IR spectroscopy of the insoluble species. Before
complexation of any metals, the vibrational elongation wavelength
of the imine function was observable at ca. 1628 cmÀ1. The coordi-
nation steps, leading to the formation of Co(III) complexes were
accompanied with a shift of the wavelength and a splitting of
two bands at approximately 1604 cmÀ1 and 1637 cmÀ1 in each
case. For the manganese complexes this imine vibration is visible
at approximately 1606–1611 cmÀ1 (see SI for more information).
The nucleophilic ring opening of meso-epoxides is a valuable
synthetic transformation, leading to the formation of two stere-
ogenic centers.15 The control of the enantioselectivity, for instance
in the case of the hydrolysis, is not so straightforward and typical
homogeneous enantiopure cobalt-salen complexes struggle to pro-
vide high enantioselectivities. In this context, Jacobsen et al. pre-
pared salen-based macrocycles with Co-OTs active sites, and
demonstrated their ability to perform this transformation effi-
ciently.9a,f The hydrolytic enantioselective opening of cyclohexene
oxide was thus chosen as a benchmark reaction to evaluate the
catalytic efficiency of the new cobalt- and manganese-based
calix-salen complexes.
2. Results and discussion
We have previously reported a straightforward synthesis of
calix-salen ligands, based on the condensation of the chiral, enan-
tiopure (S,S)-cyclohexane-1,2-diamine with a disalicylaldehyde
compound linked by a phenyl group. The judicious choice of the
concentration of the reaction mixture allowed us to control the
macrocycle size; a concentrated solution led to the formation of
large rings, whereas dilution led to the main formation of dimeric
structures.12 Other macrocycles, possessing aromatic spacers with
various structures, have also been prepared, following the same
procedure. The synthesis of the targeted dialdehydes is depicted
in Scheme 1. The boronic ester (3-tert-butyl-2-hydroxy-5-
(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-benzaldehyde) was
synthesized in three steps, starting from 2-tert-butyl-phenol, by
para-bromination, ortho-carbonylation and the final introduction
of the boron ester, in 63% overall yield, as previously reported. Sub-
sequent Suzuki–Miyaura type coupling with 1,4-dibromobenzene,
2,7-dibromofluorene or 4,7-dibromobenzo[c]-1,2,5-thiadiazole
gave the targeted triaromatic structures 1, 2, and 3 in good yields.
With the aim of preparing macrocycles with a large ring size,
dilute conditions used for the condensation reactions were chosen
in accordance with those used for the preferential synthesis of the
tetrameric benzene containing structures.12 The reactions occurred
for all compounds in THF in which an equimolar mixture of the
chosen dialdehyde 1 to 3 was engaged with the enantiopure (S,
S)-cyclohexane-1,2-diamine (each compound 0.112 M), at 70 °C
in the presence of molecular sieves for 24 h. The corresponding
macrocycles were recovered by precipitation in methanol and sub-
sequent filtration, to give the expected compounds in quantitative
yields for the three calix-salen derivatives 4 to 6 (Scheme 2). These
ligands have been characterized by 1H NMR spectroscopy (DOSY
experiments), following a characterization method we developed
for analyzing the parent macrocycle with the phenyl spacer. The
chemical shift of the imine protons in these structures and compar-
ison with the values obtained in the previous case (see Supporting
information) indicated that the tetrameric species was indeed that
mainly formed. According to these NMR studies, the macrocycle 5
produced from 2 did not contain any dimeric species and was only
the tetramer (76%) and the pentamer (24%). The same trend as
observed for the calix-salen 6 from 3, although in this specific case,
a small amount of the trimer could be detected (10%) along with
The hydrolysis of cyclohexene oxide was performed in a small
amount of THF (0.33 M) with 1.3 equiv of water and the reaction
O
O
O
K2CO3 (2 equiv.)
O
Pd(PPh3)4 (6 mol%)
Ar
B
Br
Br
OH
+
Ar
S
HO
OH
O
DME/H2O
24h, 100 °C
tBu
tBu
tBu
N
N
Ar
48 % yield,
63 % yield,
80 % yield
=
1
3
2
Scheme 1. Synthesis of dialdehydes 1, 2, and 3 by a Suzuki cross-coupling.
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H. Dandachi et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
3
N
N
N
N
OH HO
OH HO
tBu
tBu
tBu
tBu
4
5
n
n
n=4 (76%), n=5 (24%)
n=2 (11%), n=3 (15%), n=4 (70%), n=5 (4%)
S
N
N
N
N
OH HO
tBu
tBu
6
n
n=3 (10%), n=4 (82%), n=5 (8%)
Scheme 2. Synthesis of calix-salen derivatives.
1) Co(OAc)2.4H2O (1.3 equiv.)
N
O
N
O
THF/MeOH
25 °C, 72 h
Ar
Co
OAc
2) AcOH, O2, THF
25 °C, 18 h
tBu
tBu
n
S
N
N
Ar
=
N
N
Ar
OH HO
tBu
8
9
7
quantitative yield
tBu
n
1) Mn(OAc)2.4H2O (3 equiv.)
toluene/EtOH
N
O
N
Mn
Cl
85 °C, 5 h
O
Ar
2) NaCl/H2O
25 °C, 18 h
tBu
tBu
n
S
N
N
Ar
=
12
88 % yield
11
10
95 % yield
quantitative yield
Scheme 3. Synthesis of calix-salen cobalt and manganese complexes.
was run at 50 °C for four days, in the presence of chlorobenzene as
the internal standard. Under these conditions, the Jacobsen salen
cobalt–acetate complex prepared from (S,S)-cyclohexane-1,2-dia-
mine (6 mol %), gave the expected diol with an (R,R)-configuration
in 80% isolated yield and with 18% ee (see Scheme 4).
Complexes 7, 8, and 9 were tested to evaluate their ability to
perform this transformation, and all species proved active to pro-
duce the targeted diol, albeit with low conversions and selectivities
(see Table 1). The recorded enantioselectivities remained modest,
but in each case better selectivities were observed compared to
those obtained with the Jacobsen monomeric counterpart, specifi-
cally by using catalyst 9 which gave diol 13 with up to 58% ee. The
configuration of 13 was also assigned as (R,R) according to co-elu-
tion tests performed by chiral gas chromatography analyses.
Catalysts 7, 8, and 9, as insoluble species, were easily recovered
by filtration after the first reaction run. They were subsequently
washed with a THF/pentane mixture, vacuum dried and then
reused in the same transformation to evaluate their stability and
their catalytic activities. Unfortunately, these macrocyclic com-
plexes proved to be poorly recyclable since the second use of 7
or 8 in the hydrolysis of cyclohexene oxide was accompanied with
a substantial loss of activity, thus preventing the possibility to
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4
H. Dandachi et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
Table 2
Cyclohexene oxide hydrolysis promoted by cobalt (S,S)-calix-salen complexes 7, 8 and
9 together with manganese calix-salen complexes 10, 11, 12 and ent-12a
N
O
N
O
Co
Run
7 and 10
8 and 11
9 and 12
9 and ent-12
tBu
tBu
Conv.b
(%)
eec
(%)
Conv.b
(%)
eec
(%)
Conv.b
(%)
eec
(%)
Conv.b
(%)
eec
(%)
OAc
tBu
tBu
1
2
3
16
19
52
42
88
5
50
34
53
39
12
70
75
71
37
24
48
26
OH
OH
7
8
9
or , or , or (6 mol %)
O
H2O (1.3 equiv.), PhCl (1 equiv.)
50°C, 4 days, THF
a
Substrate 0.4 mmol, 3 mol % cobalt (S,S)-calix-salen and 3 mol % manganese
13
(S,S)-calix-salen (or (R,R)-calix-salen), 1.3 equiv H2O, 4 days, THF, 50 °C.
b
Determined by GC analysis, with chlorobenzene as internal standard.
Determined by chiral GC analysis (see SI).
Scheme 4. Hydrolysis of cyclohexene oxide by salen-based cobalt complexes.
c
Table 1
Cyclohexene oxide hydrolysis promoted by cobalt (S,S)-calix-salen complexes 7, 8,
to an optimized spatial shape necessary for obtaining high enan-
tioselectivities. We propose that in the case of the macrocyclic
calix-salen involved herein, the manganese species is used as an
epoxide activator, whereas the cobalt complex activates the water.
This heterobimetallic activation leads thus to the reduction of the
alternative less enantioselective monometallic pathway and allows
selectivity enhancement.5a Furthermore, each mixture of catalysts
could be recovered by simple filtration and used in a new run
with fresh substrates; the combination 9 and 12 could be reused
up to three times.
These cooperative effects were successfully applied to the
transformation of other substrates, to study the scope of their
application. Since the combination 9 and 12 led to the best results
for the hydrolysis of cyclohexene oxide, it seemed important to
verify this effect with the analogous substrate, cyclopentene oxide
(see Scheme 5).
and 9a
Run
7
8
9
Conv.b (%)
eec (%)
Conv.b (%)
eec (%)
Conv.b (%)
eec (%)
1
2
3
33
15
28
21
41
17
26
4
66
40
16
58
46
30
a
Substrate 0.4 mmol, 6 mol % cobalt (S,S)-calix-salen, 1.3 equiv H2O, 4 days, THF,
50 °C.
b
Determined by GC analysis, with chlorobenzene as internal standard.
Determined by chiral GC analysis (see SI).
c
realize a third run; in the case of 8, diol 13 was recovered in its
nearly racemic form. The use of the benzothiadiazole-containing
calix-salen 9 improved these results since three runs could be per-
formed, albeit with a decrease in both the conversion and selectiv-
ity of the reaction.
Accordingly, manganese derivatives 10, 11, and 12 were also
evaluated as presumed non-catalysts in these hydrolytic ring-
opening reactions,16 and as expected under the same reaction con-
ditions, no reaction occurred even after prolonged reaction times.
The cooperativity of cobalt and manganese species was then
explored and both cyclic catalysts containing cobalt and man-
ganese metals, respectively, were thus mixed, in an equimolar
ratio, to evaluate any potential beneficial effect of their dual use
on the course of the transformation.
9
(6 mol %)
or and
OH
9
12
O
(3 mol % each)
OH
H2O (1.3 equiv.)
PhCl (1 equiv.)
50°C, 4 days, THF
14
Scheme 5. Hydrolysis of cyclopentene-oxide by salen-based cobalt complexes.
(S,S)-Cobalt calix salen 9 was first used to promote this transfor-
mation to provide diol 14 with 38% ee and 39% conversion of the
epoxide. This macrocyclic catalyst could be recovered by precipita-
tion and filtration and its reuse gave the targeted product albeit
with a decreased yield and enantioselectivity (see Table 3). Analo-
gously to the transformation of cyclohexene oxide, the dual use of
an equimolecular mixture of (S,S)-cobalt calix salen 9 and (S,S)-
manganese calix salen 12 drastically improved the course of the
reaction, leading in this case again to a matched effect and pro-
duced 14 both in high conversion (90%) and with an increased ee
of 58%. The catalyst was recovered and reused three times, still
supplying 14 with 52% ee in the third run.
Accordingly, each cobalt calix-salen complex 7–9 was again
employed in the hydrolytic kinetic resolution of cyclohexene oxide
with its corresponding manganese analogue, possessing the same
configuration at the stereogenic centers. Although no major
improvement could be detected concerning the activity of the
implied catalysts, in each case however, an important increase in
the selectivity of the reaction could be observed. The use of addi-
tional manganese (S,S)-calix-salen, gave diol 13 with 52% ee instead
of 28% in the case of the cobalt calix-salen 7, and with 50% ee,
instead of 26% for the transformation in the presence of 8. The best
system was obtained for the catalyst combination 9 and 12, result-
ing in a large enantioselectivity enhancement. The importance of
the configuration of the additional cyclic manganese complex was
checked by carrying out the synthesis and characterization of ent-
6 and its corresponding Mn complex ent-12 (see SI). As can be
deduced from Table 2, the combination of (S,S)-cobalt calix-salen
together with an (R,R)-manganese calix-salen led to poorer results.
We already observed such cooperative positive or negative effects
by studying homogeneous salen-type complexes,10 confirming
the involvement of the manganese additive in the selectivity-deter-
mining transition state and the importance of its configuration. We
proposed, by using our previously described monomeric salen com-
plexes species that a matched combination of the cobalt and the
manganese complexes resulted exclusively from the arrangement
of species with ligands possessing the same configuration leading
Table 3
Cyclopentene-oxide hydrolysis promoted by 9, or 9 and 12a
Run
9
9 and 12
Conv.b (%)
Conv.b (%)
ee (%)c
ee (%)c
1
2
3
39
19
38
18
90
66
49
58
60
52
a
Substrate 0.4 mmol, 6 mol % 9 or 3 mol % 9 and 3 mol % 12, 1.3 equiv H2O,
4 days, THF, 50 °C.
b
Determined by GC analysis, with chlorobenzene as internal standard.
Determined by chiral GC analysis (see SI).
c
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H. Dandachi et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
5
7
(2 mol%)
or 7 and 10
MeO
HO
O
O
(each 1 mol%)
OMe
OH
Br
Br
O
Br
H2O (1.5 equiv.)
PhCl (0.3 equiv.)
20°C, 24 h, THF
amberlyst 15
DCM, 20°C, 16 h
15
16
Scheme 6. Dynamic hydrolytic kinetic resolution of epibromohydrin.
The last benchmark transformation used to evaluate this heter-
obimetallic enhancement effect, was the hydrolytic kinetic resolu-
tion of epibromohydrin (see Scheme 6). This substrate undergoes
fast racemization under the hydrolytic kinetic resolution condi-
tions and the resulting diol 15 was obtained with complete conver-
sion since, in this case, kinetic hydrolytic resolution proceeded in
dynamic mode. The product was recovered and analyzed as ace-
tonide derivative 16 for a straightforward determination of the
transformation selectivity. Jacobsen et al. reported that 3-bromo-
propane-1,2-diol was isolated in 93% yield and 96% ee, with
1.5 equiv of H2O in THF, in the presence of 2 mol % of the classical
chiral bis-tert-butyl-cyclohexyl-salen Co(III)-OAc catalyst.17
Cobalt catalyst 7 (2 mol %) was used in the hydrolytic kinetic res-
olution of epibromohydrin, and complete conversion toward the for-
mation of the expected diol was observed after 24 h reaction time,
with compound 16 being isolated with 88% ee. The macrocyclic insol-
uble catalyst was easily recovered and reused in subsequent runs
while showing no loss in selectivity after each reuse. The catalytic
activity could be maintained for three runs, but a significant decrease
was observed after the fourth use of the catalyst (see Table 4). Such a
deactivation is well described in the bibliography, due to the transfor-
mation of essential Co(III)-OAc sites into Co(III)-OH species, due to
the nucleophilicity of the acetate counteranion. Treatment is then
necessary for reactivation,5a,18 and catalyst 7 was thus triturated
with acetic acid before its reuse for a fifth run and provided high
activity for this last transformation. On the other hand, the
combination of 7 and 10 was tested for the same transformation by
using an equimolar mixture (1 mol % each) of both cyclic
complexes. An important match effect could again be observed
since an almost complete conversion gave compound 16 with 92%
ee at the first run. More interestingly, this mixture of catalyst was
recovered and reused up to eight times with only a slight decrease
in its efficiency. Notably in this case, no reactivation step was
needed; we assume this indicates the heterobimetallic activation,
the Mn-complex probably substituting the through time
disappearing cobalt–acetate complex, for activating the epoxide.
Table 5
Cyclohexene oxide hydrolysis promoted by cobalt (S,S)-calix-salen complex
9
together with manganese (S,S)-calix-salen complex 12a
Run
9 and 12
Conv.b (%)
eec (%)
1
2
3
4
5
6
38
38
39
38
10
8
78
78
78
78
47
46
a
4 mmol cyclohexene oxide, 3 mol % 9 and 3 mol % 12, 1.3 equiv H2O, 4 days,
THF, 50 °C.
b
Determined by GC analysis, with chlorobenzene as internal standard.
Determined by chiral GC analysis (see SI).
c
system 9 and 12 was used to hydrolyze cyclohexene oxide at a ten
times larger scale (see Table 5).
The preceding experiment (see Table 2) could only be per-
formed for three runs with concomitant loss of activity. In this
case, the catalysts mixture performed better, since six runs could
be achieved, four of them with no loss of selectivity or activity.
3. Conclusion
We have thus demonstrated that the use of heterogeneous
heterobimetallic catalytic systems was particularly effective to
promote the hydrolytic kinetic resolution of cyclohexene oxide,
cyclopentene oxide and epibromohydrin. A matched effect was
obtained using an equivalent catalytic mixture of cobalt and man-
ganese-based calix-salen derivatives generated from macrocycles
possessing the same structural configuration. This approach
allowed for better enantioselectivities than the ones obtained with
the use of the homometallic cobalt-based calix-salen catalyst, for
each targeted products. In addition, this mixture of catalyst could
be easily recovered by filtration and reused in subsequent runs
with reasonable stability in terms of activity and selectivity. In
these cases, the known cobalt reactivation step, unavoidable in
many procedures involving such catalyst recovery, was not neces-
sary here to maintain high catalytic activity along with the reuse.
Although manganese-based calix-salen proved to be inactive in
the studied reactions when used alone, we suggest that their use
together with the cobalt-based calixsalen analogues inhibits the
competitive monometallic, less enantioselective, reaction pathway.
We propose in this case that the manganese-based calix-salen
serves as a Lewis activator for the epoxides, and catalyzes the
hydrolytic kinetic resolution together with the Co-OH species gen-
erated from cobalt acetate-based calix-salen, by hydrolysis.
Table 4
Hydrolytic kinetic resolution of epibromohydrin hydrolysis promoted by 7, or 7 and
10a
Run
7
7 and 10
Conv.b (%)
Conv.b (%)
eec (%)
eec (%)
1
2
3
4
5
6
7
8
>99
88
83
88
89
93
91
89d
97
97
97
97
97
82
83
83
92
90
90
90
90
90
86
82
68
85d
a
4. Experimental
4.1. General
Substrate 1.7 mmol, 2 mol % 7 or 1 mol % 7 and 1 mol % 10, 1.5 equiv H2O, 24 h,
THF, 20 °C.
b
Determined by GC analysis, with chlorobenzene as internal standard.
Determined by chiral GC analysis (see SI).
The catalyst has been reactivated in the presence of AcOH before reuse.
c
d
Reactions (except catalytic transformations) were carried out
under argon in oven-dried glassware with magnetic stirring. THF
was distilled from sodium/benzophenone and DCM was distilled
from CaH2 before use. 1H NMR spectra and 13C NMR spectra were
Since chiral catalysts stability issues in recovery studies are
often caused by small-scale handling difficulties, the best optimized
Please cite this article in press as: Dandachi, H.; et al. Tetrahedron: Asymmetry (2016), http://dx.doi.org/10.1016/j.tetasy.2016.02.006

6
H. Dandachi et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
recorded on either a Bruker AM 360 (360 MHz), AM 300 (300 MHz)
or AM 250 (250 MHz) instrument with samples dissolved in CDCl3
and data are reported in ppm with the solvent signal as reference
(7.24 ppm for 1H NMR and 77 ppm for 13C NMR). MALDI-TOF anal-
yses were performed by the service of mass spectrometry of the
Institut de Chimie des Substances Naturelles, Gif sur Yvette, on a
Voyager DE-SFR spectrometer with a solution of dithranol in THF
(10 g/L) as matrix. High resolution mass spectra were recorded
on a Bruker MicrOTOF-Q spectrometer using electrospray ioniza-
tion (ESI) and tandem quadrupole coupled with a time-of-flight
mass analyzer. FTIR spectra were measured on a Vertex 70 Bruker
spectrometer with a germanium gate ATR accessory. Optical rota-
tions were determined on a Perkin–Elmer 241 digital polarimeter
with a sodium lamp (489 nm, D line). Achiral gas chromatography
analyses were performed on a Varian 430-GC chromatograph using
helium as a carrier gas. Chiral gas chromatography analyses were
performed on a GC Shimadzu 2010-Plus, FID, SSL using hydrogen
as a carrier gas. For the hydrolysis of cyclohexene oxide, the con-
version was determined by using the column VF1-MS
13C NMR (91 MHz, CDCl3) d (TMS, ppm): 197.3 (2COH), 160.7
(2Cq arom-OH), 144.4 (2Cq arom), 140.6 (2Cq arom), 139.0 (4Cq
arom), 133.3 (2CH arom), 132.9 (2Cq arom), 130.2 (2CH arom),
125.9 (2CH arom), 123.5 (2CH arom), 121.0 (2Cq arom), 120.5
(2CH arom), 37.3 (CH2), 35.3 (2Cq-tBu), 29.5 (2tBu).
Benzothiadiazole dialdehyde 3 was prepared from 4,7-dibro-
mobenzo[c]-1,2,5-thiadiazole (20.4 mmol, 6.0 g). The residue was
collected to afford 8.0 g of dialdehyde
3 as a yellow solid
(16.3 mmol, 80% yield). Rf (pentane/Et2O: 94/6) = 0.31. 1H NMR
(250 MHz, CDCl3) d (TMS, ppm): 12.00 (s, 2H, OH), 10.04 (s, 2H,
CHO), 8.14 (s, 4H), 7.79 (s, 2H), 1.52 (s, 18H). 13C NMR (63 MHz,
CDCl3) d (TMS, ppm): 197.4 (2COH), 161.5 (2Cq arom-OH), 154.2
(2Cq arom), 138.9 (2Cq arom), 135.1 (2CH arom), 132.9 (2CH
arom), 132.1 (2Cq arom), 128.5 (2Cq arom), 127.5 (2CH arom),
120.9 (2Cq arom), 35.3 (2Cq-tBu), 29.4 (2tBu).
4.3. Synthesis of calix-salen derivatives
A 100 mL, two-necked, round-bottomed flask equipped with a
reflux condenser was charged with a solution of dialdehyde
(0.9 mmol, 400 mg) in THF (8 mL). Molecular sieves (4 Å) and (R,
R)- or (S,S)-cyclohexane-1,2-diamine (1 equiv, 0.9 mmol,
106.1 mg) were added under argon with continuous stirring. The
reaction mixture was further stirred for 24 h at 70 °C. After cooling
to room temperature and filtration to remove the molecular sieves,
the filtrate was concentrated by rotary evaporation. The crude pro-
duct was then precipitated with methanol, filtered and washed
with cold methanol.
15 m  0.25 mm  0.25
2 min). The enantioselectivity of the reactions were determined
m, iso-
lm
(50 °C, 5 min, 10 °C/min, 250 °C,
with a Chiraldex column B-PM 50 m  0.25 mm  0.12
l
therm, 130 °C. For the hydrolysis of cyclopentene oxide, the con-
version was determined by using the column UB-624
30 m  0.32 mm  1.8
20 min). The enantioselectivity of the reactions were determined
m, iso-
lm
(50 °C, 1 min, 10 °C/min, 250 °C,
with a Chiraldex column B-PM 50 m  0.25 mm  0.12
l
therm, 90 °C. For the hydrolytic kinetic resolution of epibromohy-
drin, the conversion was determined by using the column VF1-MS
(S,S)-Calix-salen 4 was prepared from phenyl dialdehyde 1
(0.9 mmol, 400 mg). The residue was collected to afford 472 mg
of a mixture of macrocyclic compounds as a yellow powder
(0.9 mmol, quantitative crude yield). Macrocyclic oligomers distri-
bution d (ppm) (%): 8.56 pentamer (4%), 8.35 tetramer (70%), 8.23
trimer (15%), 7.88 dimer (11%). Maldi-Tof (m/z): 1017.36 (n = 2),
15 m  0.25 mm  0.25
lm (110 °C, 10 min to 250 °C, 2 min). The
enantioselectivity of the reactions were determined with a Chi-
raldex column B-PM 50 m  0.25 mm  0.12
lm, isotherm, 110 °C.
4.2. Suzuki cross-coupling
1526.49 (n = 3), 2034.50 (n = 4), 2542.59 (n = 5). IR (ATR,
m )
cmÀ1
A Schlenk tube was charged with boronic ester (2 equiv,
40.8 mmol, 12.4 g), dibromoaryl (1 equiv, 20.4 mmol), Pd(PPh3)4
(0.06 equiv, 1.2 mmol, 1.4 g) and K2CO3 (2 equiv, 40.8 mmol,
5.6 g) and kept under argon by successive vacuum-argon cycles.
Degassed DME (73 ml) and degassed water (30 ml) were trans-
ferred via cannula into the Schlenk flask. The reaction mixture
was further heated at 100 °C, with stirring for 24 h. Water
(200 ml) was then added and the aqueous layer was extracted with
DCM. The organic layer was dried over magnesium sulfate and fil-
tered. The solvent was removed by rotary evaporation. The crude
product was filtered through a silica plug and washed with DCM
and acetone. The filtrate was concentrated by rotary evaporation.
The product was then precipitated with Et2O and filtered.
Phenyl dialdehyde 1 was prepared from 1,4-dibromobenzene
(20.4 mmol, 4.8 g). The residue was collected to afford 4.22 g of
dialdehyde 1 as a yellow solid (9.8 mmol, 48% yield). Rf (pentane/
Et2O: 95/5) = 0.46. 1H NMR (360 MHz, CDCl3) d (TMS, ppm):
11.82 (s, 2H, OH), 9.99 (s, 2H, CHO), 7.81 (d, Jmeta = 2.3 Hz, 2H),
7.65 (d, Jmeta = 2.3 Hz, 2H), 7.64 (s, 4H), 1.49 (s, 18H). 13C NMR
(62.5 MHz, CDCl3) d (TMS, ppm): 197.4 (2COH), 160.9 (2Cq arom-
OH), 139.1 (2Cq arom), 133.2 (2CH arom), 132.1 (2Cq arom),
131.5 (2Cq arom), 130.1 (2CH arom), 128.4 (4CH arom), 120.9
(2Cq arom), 35.3 (2Cq-tBu), 29.5 (2tBu).
2953, 2932, 2864, 1628, 1441. [
a]
20 = À242.8 (c 0.01, DCM).
D
(S,S)-Calix-salen 5 was prepared from fluorene dialdehyde 2
(0.9 mmol, 481.9 mg). The residue was collected to afford
554.5 mg of a mixture of macrocyclic compounds as a yellow pow-
der (0.9 mmol, quantitative crude yield). Macrocyclic oligomers
distribution d (ppm) (%): 8.52 pentamer (24%), 8.39 tetramer
(76%). Maldi-Tof (m/z): 1193.58 (n = 2), 1789.97 (n = 3), 2386.27
(n = 4). IR (ATR,
(c 0.01, DCM).
m
cmÀ1) 2932, 2863, 1628, 1441. [
a]
20 = À423.9
D
(S,S)-Calix-salen 6 was prepared from benzothiadiazole dialde-
hyde 3 (0.9 mmol, 454 mg). The residue was collected to afford
526.6 mg of a mixture of macrocyclic compounds as a red powder
(0.9 mmol, quantitative crude yield). Macrocyclic oligomers distri-
bution d (ppm) (%): 8.57 pentamer (8%), 8.45 tetramer (82%), 8.35
trimer (10%). Maldi-Tof (m/z): 1133.46 (n = 2), 1699.85 (n = 3),
2266.12 (n = 4), 2833.35 (n = 5). IR (ATR,
m
cmÀ1) 2945, 2863,
1626, 1441. [
a]
20 = À467.6 (c 0.0025, DCM).
D
(R,R)-Calix-salen ent-6 was prepared from benzothiadiazole
dialdehyde 3 (0.9 mmol, 454 mg). The residue was collected to
afford 437.1 mg of a mixture of macrocyclic compounds as an
orange powder (0.8 mmol, 83% yield). Macrocyclic oligomers
distribution d (ppm) (%): 8.45 tetramer (100%). HRMS (ESI+): calcd
for
136H152N16NaO8S4: 2288.0746; found: 2289.0802. IR (ATR,
cmÀ1) 2951, 2864, 1626, 1441. [ 20 = +603.0 (c 0.005, DCM).
C68H76N8NaO4S2: 1155.5323; found: 1155.5341, calcd for
Fluorene dialdehyde 2 was prepared from 2,7-dibromofluorene
(20.4 mmol, 6.6 g). Purification by silica-gel column chromatogra-
phy (pentane/Et2O: 94/6) afforded 6.7 g of dialdehyde 2 as an
orange solid (12.9 mmol, 63% yield). Rf (pentane/Et2O: 94/6)
= 0.13. 1H NMR (250 MHz, CDCl3) d (TMS, ppm): 11.81 (s, 2H,
OH), 9.99 (s, 2H, CHO), 7.88 (d, 2H, Jortho = 7.8 Hz), 7.85 (d, 2H,
Jmeta = 2.0 Hz), 7.76 (br s, 2H), 7.67 (d, 2H, Jmeta = 2.2 Hz), 7.60
(dd, 2H, Jortho = 7.8 Hz, Jmeta = 2.0 Hz), 4.05 (s, 2H), 1.50 (s, 18H).
C
m
a
]
D
4.4. Synthesis of (S,S)-calix-salen cobalt(III) complexes
A Schlenk tube thoroughly maintained under a dry argon atmo-
sphere was charged with a solution of calix-salen (0.7 mmol) in
degassed THF (16 mL). A solution of Co(OAc)2Á4H2O (1.3 equiv,
Please cite this article in press as: Dandachi, H.; et al. Tetrahedron: Asymmetry (2016), http://dx.doi.org/10.1016/j.tetasy.2016.02.006

H. Dandachi et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
7
0.9 mmol, 226.7 mg) in degassed methanol (8 mL) was then trans-
ferred via cannula into the Schlenk flask. The reaction mixture was
further stirred for 72 h at 25 °C. Acetic acid (3.5 mL) was added to
the reaction medium. The reaction mixture was further stirred
under an oxygen atmosphere for 18 h at 25 °C with the formation
of a precipitate. The product was filtered and the residue was
washed with methanol.
(1.5 mL) and pentane (5 mL) were added and the catalyst was pre-
cipitated for 2 h. A drop of the supernatant was dissolved in THF
(0.5 mL) and analyzed by GC analysis. The supernatant was then
removed using a micro immersion filter for reverse filtration, fil-
tered through a plug of Celite and washed with EtOAc. The recov-
ered filtrate was gently concentrated by removing the solvent by
slow rotary evaporation without heating the water bath. The cata-
lyst was washed with THF/pentane 1.5 mL/5 mL (4 times), dried
under vacuum and then reused for the next cycle.
(S,S)-Calix-salen cobalt(III) 7 was prepared from (S,S)-calix-
salen 4 (0.7 mmol, 356.1 mg). The residue was collected to afford
437.3 mg of the catalyst mixture
(0.7 mmol, quantitative yield). IR (ATR,
1638, 1605, 1534, 1435.
(S,S)-Calix-salen cobalt(III) 8 was prepared from (S,S)-calix-
salen 5 (0.7 mmol, 417.8 mg). The residue was collected to afford
498.9 mg of the catalyst mixture
7
as
a
dark brown solid
Cyclohexane-1,2-diol 13 was prepared from cyclohexene oxide
m
cmÀ1) 2945, 2866, 1715,
(0.4 mmol, 40
(1.2 mL) and H2O (0.5 mmol, 9.3
from cyclohexene oxide (4.0 mmol, 0.4 mL), chlorobenzene
(4.0 mmol, 0.4 mL) in THF (9.7 mL) and H2O (5.1 mmol, 93 L).
Cyclopentane-1,2-diol 14 was prepared from cyclopentene
l
L), chlorobenzene (0.4 mmol, 40.2
lL) in THF
lL) or for the test at a larger scale
l
8
as
a dark brown solid
(0.7 mmol, quantitative yield). IR (ATR,
1607, 1532, 1435.
m
cmÀ1) 2949, 2864, 1638,
oxide (0.5 mmol, 40
lL), chlorobenzene (0.5 mmol, 46.6
lL) in
THF (1.2 mL) and H2O (0.6 mmol, 10.7
l
L).
(S,S)-Calix-salen cobalt(III) 9 was prepared from (S,S)-calix-
salen 6 (0.7 mmol, 396.7 mg). The residue was collected to afford
4.7.
Catalytic
test—hydrolytic
kinetic
resolution
of
477.9 mg of the catalyst mixture
(0.7 mmol, quantitative yield). IR (ATR,
1603, 1528, 1437.
9
as
a dark brown solid
epibromohydrin
m
cmÀ1) 2951, 2866, 1634,
Epibromohydrin (1.7 mmol, 141
standard—0.3 equiv, 0.5 mmol, 50
lL), chlorobenzene (internal
l
L) and THF (197.5 L) were
l
4.5. Synthesis of calixsalen manganese(III) complexes
introduced into a screw-capped vial. A reference sample was pre-
pared by adding a small drop of the solution to THF. On the other
hand, the solution was introduced in a tube containing calix-salen
catalyst(s) (0.02 equiv, 0.03 mmol, 20 mg), and then H2O
A Schlenk tube thoroughly maintained under a dry argon atmo-
sphere was charged with a solution of calix-salen (0.5 mmol) in
degassed toluene (4 mL). A solution of Mn(OAc)2Á4H2O (3 equiv,
1.5 mmol, 367.6 mg) in degassed ethanol (8 mL) was then trans-
ferred via cannula into the Schlenk flask. The reaction mixture
was further stirred for 5 h at 85 °C. A saturated aqueous sodium
chloride solution (5 mL) was added to the reaction medium. The
reaction mixture was further stirred under an air atmosphere for
18 h at 25 °C with the formation of a precipitate. The product
was filtered and the residue was washed with ethanol.
(1.5 equiv, 2.5 mmol, 44.5 lL) was added. The reaction mixture
was further stirred for approximately 24 h at room temperature.
At the end of the reaction, the catalyst was filtered off, washed
with THF, dried under vacuum and then reused for the next cycle.
The recovered filtrate was concentrated by removing the solvent
by rotary evaporation. Dimethoxypropane (3.3 equiv, 5.5 mmol,
677.4 lL), DCM (7.3 mL) and 27 mg of Amberlyst 15 were added
to the crude product. The reaction mixture was further stirred for
16 h at room temperature. The solution was filtered through a plug
of Celite and then analyzed by chiral GC analysis.
(S,S)-Calix-salen manganese(III) 10 was prepared from (S,S)-
calix-salen 4 (0.5 mmol, 254.3 mg). The residue was collected to
afford 283.6 mg of the catalyst mixture 10 as a dark brown solid
(0.47 mmol, 95% yield). IR (ATR,
1539, 1429.
m
cmÀ1) 3387, 2945, 2864, 1611,
Acknowledgments
(S,S)-Calix-salen manganese(III) 11 was prepared from (S,S)-
calix-salen 5 (0.5 mmol, 298.4 mg). The residue was collected to
afford 342.6 mg of the catalyst mixture 11 as a dark brown solid
(0.5 mmol, quantitative yield). IR (ATR,
1611, 1539, 1427.
The CNRS, the Ministère de l’Enseignement Supérieur et de la
Recherche, the Direction des Relations Internationales de l’Univer-
sité Paris Sud, the Agence Universitaire de la Francophonie, Leba-
non, the Lebanese Association for Scientific Research, and the
Research Grant Program at the Lebanese University are acknowl-
edged for financial support. The French authors are also thankful
to the LabEx Charmmmat for support and the postdoctoral position
for E.Z.
m
cmÀ1) 3416, 2955, 2866,
(S,S)-Calix-salen manganese(III) 12 was prepared from (S,S)-
calix-salen 6 (0.5 mmol, 283.4 mg). The residue was collected to
afford 288.3 mg of the catalyst mixture 12 as a dark brown solid
(0.4 mmol, 88% yield). IR (ATR,
1533, 1431.
m
cmÀ1) 3414, 2949, 2864, 1607,
Supplementary data
(R,R)-Calix-salen manganese(III) ent-12 was prepared from
(R,R)-calix-salen ent-6 (0.5 mmol, 283.4 mg). The residue was col-
lected to afford 271.9 mg of the catalyst mixture ent-12 as a dark
brown solid (0.41 mmol, 83% yield). IR (ATR,
1609, 1535, 1441.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetasy.2016.02.
006.
m
cmÀ1) 2945, 2863,
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