Chiral ion pairs in catalysis: lithium salts of chiral metallocomplex anions as catalysts for asymmetric C-C bond formation

Article abstract of DOI:10.1016/j.tetasy.2009.06.006

A series of Co(III) anionic complexes of Schiff bases obtained from substituted salicylaldehydes and optically active amino acids has been synthesized. The ion pairing of these anions to a lithium cation can be used to induce asymmetry into lithium-cataly

Full text of DOI:10.1016/j.tetasy.2009.06.006

Tetrahedron: Asymmetry 20 (2009) 1746–1752
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Chiral ion pairs in catalysis: lithium salts of chiral metallocomplex anions
as catalysts for asymmetric C–C bond formation
Yuri N. Belokon’ a, , Victor I. Maleev , Dmitri A. Kataev , Tatiana F. Saveleva , Tatiana V. Skrupskaya ,
a
a
a
a
*
a
b
Yulia V. Nelyubina , Michael North
a
A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28, Vavilova str., 119991 Moscow, Russian Federation
School of Chemistry and University Research Centre in Catalysis and Intensified Processing, Bedson Building, University of Newcastle upon Tyne,
b
Newcastle upon Tyne, NE1 7RU, United Kingdom
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of Co(III) anionic complexes of Schiff bases obtained from substituted salicylaldehydes and opti-
cally active amino acids has been synthesized. The ion pairing of these anions to a lithium cation can be
used to induce asymmetry into lithium-catalyzed trimethylsilylcyanation of aldehydes and Michael reac-
tions. The influence of the temperature, solvent polarity and structural modification of the chiral anion on
the enantioselectivity of the catalysis has been investigated.
Received 14 May 2009
Accepted 8 June 2009
Available online 25 July 2009
Ó 2009 Elsevier Ltd. All rights reserved.
1
. Introduction
3,3 -dichlorobinaphthol in asymmetric aldol reactions.9 Among
other alkali metal cations, the lithium cation is considered to have
0
1
0
Asymmetric synthesis using metal catalysts with the source of
the highest Lewis acidity. For example, the lithium cation is a
1
1
chirality residing in their cations has been the focus of great inter-
well-known catalyst for pericyclic reactions. The group of Michl
showed that a solution of the lithium salt of the permethylated ico-
sahedral monocarbododecaborate, LiCB11Me12, in benzene is a
much more effective catalyst than the usual solution of lithium
perchlorate in diethyl ether. A practically important application
of LiCB11Me12 is catalysis of the radical polymerization of alkenes
1
est for many years. However, little attention has been paid to
complexes with chiral counteranions, although they have great po-
tential as a novel type of asymmetric metal-based catalysts. In
these complexes, the achiral cation can activate substrates and
the chiral counteranion, being positioned away from the metal
1
1
2
12
centre, is incorporated into the stereodetermining step. The Lewis
also reported by Michl.
1
3
acidity of the cation in combination with the chiral, weakly coordi-
nated anion should be enhanced in comparison with traditional
metal complexes. Therefore, even alkali metal cations which are
usually considered as weak Lewis acids, might become efficient
catalysts in asymmetric transformations if chiral counteranions
with delocalized charges were employed.
In previous work we demonstrated that chiral anionic com-
plexes of potassium and silver - or -bis[N-salicylidene-(S)-
aminoacidato]cobaltates can be used as Lewis acid catalysts in
asymmetric trimethylsilylcyanation of aldehydes and Mukayama
aldol reaction. It was deemed interesting to extend this approach
K
D
1
4
to examine C–C bond-forming reactions catalyzed by lithium
or -bis[N-salicylidene-(S)-aminoacidato]cobaltates.
K-
The strategy of chiral anion-mediated catalysis has only re-
cently started to be explored.3 A few examples exist of asymmet-
ric reactions catalyzed by salts of alkali metal cations with chiral
D
–5
6
–9
counteranions.
Shibasaki et al. reported the synthesis of bime-
2. Results and discussion
tallic rare earth-alkali metal BINOL complexes and their successful
application in catalytic asymmetric Michael additions and aldol
reactions. A mono-lithium BINOL salt in organic solvent was used
Bis(N-salicylideneaminoacidato)cobaltates are coordinatively
saturated anionic cobalt complexes with two perpendicular tri-
dentate ligands, which are the Schiff bases of salicylaldehyde and
6
3+
in the asymmetric trimethylsilylcyanation of aldehydes by Kagan
7
a
and Holmes. Ishihara et al. studied the same reaction in water
(S)-amino acids. These complexes were used earlier (by some of
7
b
3+
as a cosolvent and described the enantioselective cyanosilylation
of ketones in the presence of chiral lithium salts of phosphoric
us) as chiral substrates for anionic Co ligand alkylation in the
1
5
syntheses of enantiomerically enriched amino acids. The chiral
cobaltate anion is stereochemically stable and retained its chiral
8
acids. Nakajima et al. reported the use of the dilithium salt of
1
5
integrity during the amino acid synthesis. The complexes were
1
6
synthesized by a modified literature procedure as shown in
Scheme 1.
*
Corresponding author. Tel./fax: +7 499 135 63 56.
E-mail address: yubel@ineos.ac.ru (Y.N. Belokon’).
0
957-4166/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2009.06.006

Y. N. Belokon’ et al. / Tetrahedron: Asymmetry 20 (2009) 1746–1752
1747
O
R2
+
1
O
+
R (S)
OH
Na [Co(CO ) ]
3
3 3
H N
H
2
i,ii,iii
Λ
(S,S)
R
Δ
R2
(S,S)
2
O
O
R1
H
O O
Co
O O
Co
H
R1
N
H
R
N
1
R
N
N
1
H
Li
O
Li
O
O
O
O
O
R2
-(1-4)] Li
R2
-
+
-
+
[Λ
[Δ-(1-4)] Li
Figure 2. General view of compound [
K
-2]Na illustrating sodium to anion binding.
Both the components of the superimposed solvent molecule, that is, water (shown
as O(2W)) and methanol (shown as O(1S)) molecules, are given. Hydrogen atoms of
the ligand are omitted for clarity. Green spheres represent the remaining hydrogen
atoms.
Scheme 1. Reagents and conditions: (i) EtOH, reflux, 3 h; (ii) separation and
purification by gel chromatography on Sephadex LH-20 (C /EtOH, 3:1); (iii) ion-
exchange and gel chromatography on Sephadex LH-20 (C /EtOH, 3:1).
6
H
6
H
6
The lithium salt also crystallizes as a solvate with one ethanol
molecule per five complex species, but the ethanol does not bind
to a cation. Although the exchange of lithium by sodium atom
has only a small effect on the geometry of the complex anion, it
leads to a variation of the supramolecular patterns in the corre-
6
The complexes exist as meridional
D- and K
-stereoisomers,14
which are not interconverted under normal conditions (i.e., they
are stereochemically inert) and can be separated chromatographi-
sponding crystals. Thus, the [K-3]Li salt has a typical isle structure.
There are two independent moieties in its crystal: the cobaltate an-
ions of the first type are connected with two alkali metal cations,
while methoxysalicylidene fragments of the other species remain
unbound, and thus the whole system is neutral. These structural
units are held together by various H-bonds of intermediate
strength (OꢀꢀꢀO 2.714(4)–3.032(4) Å), which, with a number of
cally on Al
have higher R
2
O
3
. The
values than the
K
(S,S)-complexes were always observed to
(S,S)- diastereomers. The general
f
D
stereoselectivity trend was that an excess of the
D(S,S)-isomer al-
ways formed during the synthesis.15 The X-ray analyses of lithium
salt with the chiral anion, bis[N-(3-methoxysalicyliden)-(S)-tert-
leucinato]cobaltate [
K
-3]Li (Fig. 1) and its sodium analogue [
K
-
weak C–HꢀꢀꢀO and C–Hꢀꢀꢀ
p
contacts, result in the formation of the
-2]Na are
2]Na (Fig. 2) have been carried out. Although both salts crystallize
3D framework. In contrast, the cobaltate anions in [
K
in the same space group (C2) and have very similar unit cell
parameters (see Table 8), the binding of the cation to the complex
anion is different. The coordination sphere of the alkali metal in
assembled into infinite chains through the sodium cations. The lat-
ter link the neighbouring complexes in such a way that species
with two Na–OC bonds per anionic ligand and those with only
one Na–OC bond alternate. These supramolecular associates are
also interconnected with each other by means of H-bonds (OꢀꢀꢀO
[
2
K
-3]Li is filled by four oxygen atoms (LiꢀꢀꢀO 1.877(5)–
.119(12) Å): two of which belong to the methoxysalicylidene
fragment of the ligand, while the others are from water molecules
Fig. 1). In the case of the [
2.818(3)–3.265(5) Å) and weaker C–HꢀꢀꢀO and C–Hꢀꢀꢀ
p contacts.
(
K
-2]Na salt (NaꢀꢀꢀO 2.330(3)–2.415(3) Å)
Comparison of the Li and Na complexes indicates that the coor-
dination of the Li cation is much more clearly defined and its ste-
reochemical surrounding is easily predicted. In addition, the
crystal structure of the Li complex has an alternation of separate
an additional M–O bond of 2.223(3) Å is formed with the carboxyl-
ate group of the neighbouring cobaltate anion. The crystal struc-
ture of [
with two water molecules in the first coordination sphere of the
sodium cation and one with H O(2W) replaced by methanol
NaꢀꢀꢀO 2.645(7) Å).
K-2]Na is actually a superimposition of the complex
+
ꢁ
[LiALi] and [A] moieties. One could envisage the anion [A] substi-
tuted by another anion, for example, a strongly basic one. This
would constitute the typical catalytic pair of a Lewis acid and basic
component of most nucleophilic additions of CH-acids to electro-
philes. In addition, a water molecule coordinates to the Li cation
in the structure, supporting the notion of the cation possessing Le-
wis acidity and modelling substrate coordination. Evidently, the
lithium salts held the promise of becoming efficient chiral Lewis
acids in a set of C–C forming reactions.
2
(
The asymmetric addition of trimethylsilyl cyanide to benzalde-
hyde was chosen as the first model reaction (Scheme 2). The reac-
tion was carried out in methylene chloride under argon at 20 °C.
No reaction was observed under these experimental conditions
without a catalyst.
(
R)
Ph
CN
2
2
mol% cat
2
PhCHO + Me SiCN
3
CH Cl , Ar, 1h, r.t.
H OSiMe3
Figure 1. General view of compound [
Hydrogen atoms of the ligand as well as unbound water and ethanol molecules are
omitted for clarity. Green spheres represent the remaining hydrogen atoms.
K
-3]Li illustrating lithium to anion binding.
chemical yield >98%
Scheme 2.

1
748
Y. N. Belokon’ et al. / Tetrahedron: Asymmetry 20 (2009) 1746–1752
Table 1
Enantiomeric purity of (R)-mandelonitrile trimethylsilyl ether in the reaction catalyzed by lithium complexes 1–4b
a
Catalyst
1-Li
2-Li
2-Nac
3-Li
4-Li
Product ee (%) with catalyst of
Product ee (%) with catalyst of
D
K
configuration
configuration
23
22
24
40
9
16
0
12
0
d
e
50 (60 )
a
For details of chiral GLC analysis see Section 4.
b
c
Reaction conditions: PhCHO (1 mmol), TMSCN (1.1 mmol), catalyst (0.02 mmol), CH
0% chemical yield.
S)-Mandelonitrile trimethylsilyl ether was formed.
2 2
Cl (1 mL), rt, under Ar, 1 h.
9
(
d
e
Reaction was carried out for 24 h at ꢁ20 °C.
Catalyst screening (Table 1) revealed that all the lithium com-
Table 3
The addition of TMSCN to a series of aldehydes catalyzed by [
K
-4]Li catalysta
plexes were catalytically active in this reaction. The chemical yield
determined by NMR spectroscopy was >98% in the case of lithium
salts and was 90% in the case of sodium salts (Table 1). The reaction
proceeded quantitatively, but no chiral induction was observed,
eeb (%)
Run
Carbonyl compounds
4-F–C CHO
2-Cl–C CHO
PhCH@CHCHO
PhCOMe
Yield (%)
1
2
3
4
6
H
4
>90
>90
>90
53
32
42
37
27
6 4
H
when [
The general trend was that low enantioselectivities were ob-
served when complexes with a configuration were used (Table
, row 1). Complexes with a -configuration showed moderate
enantioselectivity (Table 1, row 2). Notably, (S)-valine-derived
complex [ -2]Na generated a product with 16% enantiomeric ex-
cess, whereas its [ -2]Li analogue produced mandelonitrile tri-
D
-3]Li, or [
D
-4]Li complexes were used (Table 1).
D
K
a
Reaction conditions: carbonyl compounds (1 mmol), TMSCN (1.1 mmol), cata-
Cl
Results of chiral GLC analysis, (S)-configurations.
1
lyst (0.02 mmol), CH
2
2
(1 mL), under Ar, 24 h at ꢁ20 °C.
b
K
K
O
methylsilyl ether with an enantiomeric excess of 40%. Increasing
the steric bulk of the amino acid substituent (catalyst 3) inverted
the absolute configuration of trimethylsilylmandelonitrile into
O
5
mol% catalyst,
CO Et
5
mol% base
r.t., 48 h
+
2
(
S)
CO Et
2
CO Et
2
the (S)-form. Only one complex, [
K-4]Li-containing allyl groups
CO Et
in the salicylidene fragment, afforded an enantioselectivity of
2
5
0%. A slightly better enantioselectivity (60%) was observed with
-4]Li at ꢁ20 °C.
Scheme 3.
[K
Increasing the amount of catalyst to 5 mol % or decreasing it to
.5 mol % did not affect the enantioselectivity significantly (Table
, entries 1–4). The stereoselectivity fell to only 19% when
The next reaction studied with our catalyst system was the
asymmetric Michael reaction. The addition is an efficient method
for enantioselective carbon–carbon bond formation. An initial
reaction of cyclohex-2-enone with diethyl malonate (Scheme 3)
catalyzed by all the Li-complexes without any additional bases
added failed to give the desired product after 48 h at ambient
temperature.
As expected (vide infra), Li salts of phenols were efficient co-
catalysts of the reaction. Thus, premixing [
,6-di-(tert-butyl)-4-methylphenolate in Et O, followed by addi-
0
2
0
2
17
.1 mol % of [
K-2]Li was used, but the yield was still high (Table
, entry 5). Decreasing the amount of catalyst to 0.05 mol % further
resulted in a relatively small change in ee (from 19% to 18%), but
the chemical yield was only 78% (Table 2, entry 6). The catalyst
(
2 mol %) efficiently catalyzed the reaction without any added sol-
vent, giving O-trimethylsilylmandelonitrile in quantitative yield
and with 36% ee (Table 2, entry 7).
D-1]Li with lithium
2
2
tion of cyclohex-2-enone and diethyl malonate, afforded the de-
sired product in 99% yield with 24% ee after 48 h. It should to be
noted that there were no changes in the H NMR spectrum of com-
Table 2
Influence of the amount of catalyst on the enantioselectivity of benzaldehyde
trimethylsilylcyanation with [K-2]Li as a catalyst
a
1
eeb (%)
plex [D-1]Li after the addition of the phenolate. Thus, it appeared
Entry
Catalyst (mol %)
Yield (%)
that the octahedral structure of the complex anion remained intact
during the course of the reaction. Different solvents (Table 4), bases
(Table 5) and temperatures were screened. Entries 2–9 in Table 4
1
2
3
4
5
6
5
2
1
0.5
0.1
0.05
2
99
99
99
99
99
78
99
40
40
36
35
19
18
36
show the effect of the solvent on the reaction catalyzed by [
D-
1]Li at room temperature. The solvent was seen to play a role in
c
7
Table 4
a
Reaction conditions: PhCHO (1 mmol), TMSCN (1.1 mmol), CH
2
Cl
2
(1 mL), rt,
Asymmetric Michael addition catalyzed by [D-1]Li and lithium 2,6-di(tert-butyl)-4-
under Ar, 1 h.
methylphenolate
a
b
c
Results of chiral GLC analysis, (S)-configuration.
Reaction was carried out without solvent.
b
Run
Solvent
Ether
Yield (%)
ee (%)
1
2
3
4
5
6
7
8
9
99
40
30
72
83
58
40
96
98
24
0
2
1
7
31
39
65–69
37
To evaluate the scope of the [K-4]Li catalyst system, the trim-
CH
CH
3
CN
Cl
ethylsilylcyanation of various aldehydes and acetophenone was
examined (Table 3).
2
2
Toluene
Bu
2
O
With aldehyde substrates, total conversion was observed after
4 h at ꢁ20 °C. The reaction of acetophenone occurred in the low-
t
MeO Bu
2
THF
Dioxane
Dimethoxyethane
est yield. The introduction of electronegative substituents onto the
aromatic ring of benzaldehyde resulted in a significant loss of
enantioselectivity (Table 1, Table 3, runs 1 and 2). Cinnamaldehyde
also gave lower asymmetric induction than benzaldehyde (Table 3,
entry 3).
a
Reactionconditions:cyclohex-2-enone(0.3 mmol), diethylmalonate(0.3 mmol),
solvent (1 mL), under Ar, 48 h.
b
Results of chiral HPLC analysis, (S)-configuration.

Y. N. Belokon’ et al. / Tetrahedron: Asymmetry 20 (2009) 1746–1752
1749
Table 5
3
. Conclusion
The strategy described in the present work has demonstrated
Asymmetric Michael addition catalyzed by
[
D
-1]Li and
a
number of lithium
phenolates in dioxanea
Run
1
Base
Yield (%)
96
ee (%)b
65
the ability of a chiral lithium ion-pair catalyst to promote the enan-
tioselective cyanation of aldehydes and ketones, and an asymmet-
ric Michael reaction, which might provide a new direction for the
design of chiral catalysts for asymmetric catalysis. The ease of
preparation and structural modification of the metallocomplex an-
ions may improve the performance of the catalytic systems. Stud-
ies directed toward this are currently underway.
tBu
OLi
tBu
2
3
87
97
69
52
OLi
4
. Experimental
X-ray diffraction experiments for [
K
-3]Li and [
K
-2]Na were car-
(Mo
ried out with a Bruker SMART APEX2 CCD diffractometer [
) = 0.71072 Å, -scans] at 100 K.
Structures were solved by the direct method and refined by the
K
OLi
K
a
x
2
4
20
55
full-matrix least-squares technique against F in the anisotropic–
isotropic approximation. The hydrogen atoms of water molecules
OLi
and those of the methanol molecule in [K-2]Na were located from
the Fourier synthesis of the electron density and refined in the iso-
tropic approximation. The hydrogen atoms of the O3W water mol-
HO
ecule in [
K-2]Na and that of the OH group of the ethanol molecule
in [ -3]Li were not localized due to their strong disorder. The H(C)
atom positions were calculated. The hydrogen atoms H(C) were re-
fined in the isotropic approximation in riding model. Crystal data
K
a
Reaction conditions: cyclohex-2-enone (0.3 mmol), diethyl malonate
(
0.3 mmol), dioxane (1 mL), under Ar, 48 h.
b
Results of chiral HPLC analysis.
and structure refinement parameters for [K-3]Li and [K-2]Na are
given in Table 8. All calculations were performed using the SHELXTL
both the activity and the enantioselectivity, and dioxane gave the
best results (Table 4, run 8). The variation of base led to PhOLi as
the base of choice (Table 5, run 2). Finally, different Li-salts of
bis-[N-salicyliden-(S)-valinato]cobaltates were tested as catalysts
for the reaction (Table 6).
1
8
software.
1H NMR spectra were recorded on a Bruker Avance 300
300 MHz) spectrometer. Chemical shifts are reported in ppm on
(
the d scale relative to the signal of residual protons of the deuter-
ated solvent, spin-coupling constant in Hertz.
The results are summarized in Table 6. When the temperature
was lowered to ꢁ20 °C, the enantioselectivity dropped signifi-
cantly (Table 6, run 7). Raising the temperature to 50 °C also led
to a significant decrease in enantioselectivity (Table 6, entry 8). Ta-
ble 7 summarizes the influence of the dilution of the reaction on
the catalyst efficiency. When the concentration of the catalyst
was decreased to 0.015 M from 0.03 M, better enantioselectivity
could be obtained (Table 7, entry 1 vs entry 2). Further decrease
in the concentration of the catalyst and reagents led to less satisfy-
ing enantioselectivities (Table 7, entry 3). It seems that the catalyt-
ically active species might involve both dimeric and monomeric
species, the relative amounts of which depend on the concentra-
tion of the catalyst. The dilution of the reaction mixture was found
to result in an increase in enantioselectivity. This might indicate
that the catalytically active species responsible for the asymmetric
induction is a monomeric complex.
Optical rotations were measured on a Perkin–Elmer 241 polar-
imeter in a thermostated cell (5 cm) at 25 °C. The solvent and con-
centration in grams per 100 mL of the solvent are given for all
compounds. Melting points were determined in open capillary
tubes and are uncorrected. Elemental analyses were carried out
by the laboratory of Microanalysis of INEOS RAS.
2 3
Silica Gel Kieselgel 60 (Merck), Al O (Chemapol) and Sephadex
LH-20 were used. Solvents were purified by standard procedures.
Freshly distilled reagents were used for chromatographic
separations.
Enantiomeric analysis of the synthesized trimethylsilyl ethers
of cyanohydrins was carried out on a gas chromatograph (model
3
700-00) equipped with a flame-ionization detector on a DP-
TFA-
c
-cD chiral stationary phase (32 m ꢂ 0.20 mm). The standard
for each compound was its racemic form. The absolute configura-
tion of the major product was determined by comparison with
1
3
the reported value of the specific rotation.
Table 6
The enantiomeric purity of the synthesized Michael adducts
was determined by chiral HPLC analysis (Chiralpak AS-H chiral sta-
tionary phase, iPrOH–hexane/1:9, 210 nm). The absolute configu-
ration of the major product was determined by comparison with
Asymmetric Michael addition catalyzed by lithium complexes 1, 2 and 4 with lithium
phenolate as cocatalysta
Entry
Catalyst
Yield (%)
ee (%) (configuration)b
1
2
3
4
5
6
[
[
[
[
[
[
[
[
D
K
D
K
D
K
D
D
-1]Li
-1]Li
-2]Li
-2]Li
-4]Li
-4]Li
96
11
57
17
68
80
98
97
69(S)
4(R)
58(S)
10(R)
56(S)
0
19
the reported value of the specific rotation.
3 3 3
4.1. Synthesis of Na [Co(CO ) )
] (modified method20
A
solution of Co(NO
(12.5 mL) and 30% H (5 mL) was added dropwise with cooling
to 0 °C to a suspension of Na CO (13.4 g, 0.126 mol) in H
3
)
2
ꢀ6H
2 2
O (7.27 g, 0.025 mol) in H O
c
7
-1]Li
-1]Li
0
d
2 2
O
8
49(S)
2
3
2
O
a
Reaction conditions: cyclohex-2-enone (0.3 mmol), diethyl malonate
0.3 mmol), dioxane (1 mL), under Ar, 48 h.
(
12.5 mL). The reaction mixture was stirred for 20 h at ꢃ20 °C.
(
b
The dark-green precipitate that formed was filtered off and washed
with water and EtOH to give the title compound (7.5 g) as a dark
green solid with mp >300 °C.
Results of chiral HPLC analysis.
Reaction was carried out at ꢁ20 °C.
c
d
Reaction was carried out at 50 °C for 7 h.

1
750
Y. N. Belokon’ et al. / Tetrahedron: Asymmetry 20 (2009) 1746–1752
Table 7
The influence of dilution on the performance of the [
D
-1]Li catalyst in the addition of diethyl malonate to cyclohex-2-enonea
Run
Dioxane volume (mL)
Concentration (M) of
Yield (%)
ee (%)
[
D
-1]Li
O
2 2
CH (COOEt)
1
2
3
0.5
1
2
0.03
0.015
0.0075
0.6
0.3
0.15
0.6
0.3
0.15
99
99
99
55
65
62
a
The experimental conditions are the same as in run 1 (Table 6) with the exception of varying volumes of dioxane.
4
.2. Synthesis of lithium
K
- and
D
-bis(N-salicylidene-
3.28 (s, 6H, OMe); 4.49 (d, J 7.5, 2H,
CHAr); 6.56 (d, J 7.8, 2H, CHAr); 7.03 (d, J 7.8 Hz, 2H, CHAr); 8.31
s, 2H, CH@N). Anal. Calcd for C26 CoNa: C, 53.80; H, 5.21;
N, 4.83. Found: C, 53.5; H, 5.45; N, 4.42.
a-H-Val); 6.41 (t, 2H, J 7.8,
aminoacidato)cobaltates (general procedure)
(
30 2 8
H N O
Salicylaldehyde (10 mmol) was added with stirring to a mixture
3 3 3
of Na [Co(CO ) ] (5 mmol) and an amino acid (10 mmol) in EtOH.
The reaction mixture was refluxed for 3 h, then filtered. The filtrate
was concentrated in vacuo, and the residue was washed with
diethyl ether and dissolved in EtOH. The isomers were separated
4.2.2. Sodium
cobaltate [ -2]Na
84% Yield. Mp >300 °C. ½
(CD OD): 1.16–1.27 (m, 12H, CH
3.61 (s, 6H, OMe); 4.13 (d, J 8.1, 2H,
CHAr); 6.69 (d, 2H, J 7.5, CHAr); 7.06 (d, J 8.1, 2H, CHAr); 8.29 (s,
2H, CH@N). Anal. Calcd for C26 CoNa: C, 53.80; H, 5.21; N,
4.83. Found: C, 53.75; H, 5.34; N, 4.62.
D-bis[N-(3-methoxysalicylidene)-(S)-valinato]
D
2
D
5
1
a
ꢄ
¼ ꢁ8046 (c 0.035, MeOH). H NMR
and purified by column chromatography on Al
2
O
3
(EtOH as eluent).
3
3
-Val); 2.79–2.89 (m, 2H, b-H-Val);
An additional purification was carried out by gel chromatography
on Sephadex LH-20 using an EtOH–benzene (1:3) mixture as
eluent.
a-H-Val); 6.47 (t, 2H, J 7.8,
30 2 8
H N O
A resulted sodium complex (100 mg) was dissolved in 10 mL
5
0% aqueous solution of EtOH and slowly passed through a
DOWEX-50 ꢂ 8 ion-exchange resin filled column, containing lith-
ium cations as counterions. The resulting solution was concen-
trated, and the target product was purified by gel
chromatography on Sephadex LH-20 using an EtOH–benzene
4.2.3. Lithium
1]Li
K-bis[N-salicylidene-(S)-valinato]cobaltate [K-
2
D
5
1
89% Yield. Mp >300 °C. ½
(CD OD): 1.17–1.29 (m, 12H, CH
4.49–4.6 (d, J 7.2, 2H, -H-Val); 6.49–6.60 (m, 4H, CHAr); 6.85 (t,
H, J 6.9, CHAr); 7.48 (d, J 7.1, 2H, CHAr); 8.43 (s, 2H, CH@N). Anal.
Calcd for C24 O: C, 53.34; H, 5.60; N, 5.18. Found:
CoLiꢀ2H
C, 53.15; H, 5.66; N, 5.11.
aꢄ
¼ ꢁ4031 (c 0.032, MeOH); H NMR
3
3
-Val); 2.50–2.65 (m, 2H, b-H-Val);
(
1:3) mixture as eluent.
a
2
4
.2.1. Sodium
cobaltate [ -2]Na
0% Yield. Mp >300 °C. ½
OD): 1.24–1.27 (m, 12H, CH
K
-bis[N-(3-methoxysalicylidene)-(S)-valinato]
H
26
N
2
O
6
2
K
25
1
9
a
ꢄ
¼ ꢁ3697 (c 0.035, MeOH). H NMR
D
(
CD
3
3
-Val); 2.45–2.58 (m, 2H, b-H-Val);
4.2.4. Lithium
]Li
D
-bis[N-salicylidene-(S)-valinato]cobaltate [D-
1
2
D
5
1
8
4% Yield. Mp >300 °C. ½
aꢄ
¼ ꢁ8631 (c 0.032, MeOH). H NMR
Table 8
Crystal data and structure refinement parameters for [
3 3
(CD OD): 1.21–1.27 (m, 12H, CH -Val); 2.52–2.65 (m, 2H, b-H-Val);
K
-3]Li and [
K-2]Na complexes
4
2
.27 (d, J 6.6, 2H,
H, CHAr); 7.07 (t, J 6.9, 2H, CHAr); 7.43 (d, 2H, J 7.8, CHAr); 8.39
CoLiꢀ2H O: C, 53.34; H,
.60; N, 5.18. Found: C, 53.11; H, 5.72; N, 5.09.
a-H-Val); 6.56 (t, J 6.9, 2H, CHAr); 6.77 (d, J 8.4,
Compound
[
K
-3]Li
82Co
[K
-2]Na
(
s, 2H, CH@N). Anal. Calcd for C24
H
26
N
2
O
6
2
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Z
C
56.80
H
2
Li
N
2 4
O
22.40
52.70 2 4 2 20.36
C H69.40Co N Na O
1248.36
100
Monoclinic
C2
2
5
1311.00
100
Monoclinic
C2
4.2.5. Lithium
cobaltate [ -2]Li
0% Yield. Mp >300 °C. ½
K-bis[N-(3-methoxysalicylidene)-(S)-valinato]
2
K
a (Å)
b (Å)
c (Å)
21.0102(10)
14.6857(8)
14.4266(8)
132.654(5)
3273.8(4)
1380
19.1457(10)
14.0064(8)
13.7010(7)
129.359(5)
2840.8(3)
1305
25
D
1
9
aꢄ
¼ ꢁ3458 (c 0.031, MeOH). H NMR
(
CD
3
OD): 1.26–1.27 (m, 12H, CH
3
-Val); 2.43–2.54 (m, 2H, b-H-Val);
3
.26 (s, 6H, OMe); 4.47 (d, J 7.3, 2H,
a-H-Val); 6.38 (t, 2H, J 7.8,
b (°)3
V (Å )
CHAr); 6.56 (d, J 7.6, 2H, CHAr); 6.97 (d, J 7.8, 2H, CHAr); 8.32 (s,
F(0 0 0)
2
H, CH@N). Anal. Calcd for C26
30
H N
2
O
8 2
CoLiꢀ3.5H O: C, 49.77; H,
ꢁ
D
calc (g cm 1
)
1.330
5.83
1.459
6.79
5
.94; N, 4.46. Found: C, 49.78; H, 5.93; N, 4.3.
ꢁ
Linear absorption,
l
(cm 1
)
2
h
max (°)
57
58
99.6
16,341
7484
6813
Completeness of dataset (%) 100
4.2.6. Lithium
cobaltate [ -2]Li
6% Yield. Mp >300 °C. ½ ꢄ
D-bis[N-(3-methoxysalicylidene)-(S)-valinato]
Reflections measured
Independent reflections
Observed reflections
20,065
8661
7692
D
25
D
¼ ꢁ6982 (0.034, MeOH). 1H NMR
8
a
(
3 3
CD OD): 1.18–1.28 (m, 12H, CH -Val); 2.75–2.86 (m, 2H, b-H-
[
I > 2r(I)]
Val); 3.56 (s, 6H, OMe); 4.16 (d, J 8.3, 2H,
2H, J 7.8, CHAr); 6.64 (d, 2H, J 7.5, CHAr); 7.04 (d, J 8.1, 2H,
CHAr); 8.32 (s, 2H, CH@N). Anal. Calcd for C26
CoLiꢀ
O: C, 53.62; H, 5.54; N, 4.81. Found: C, 54.10; H, 5.54; N,
.92.
a-H-Val); 6.48 (t,
Parameters
384
389
R
1
0.0560
0.1535
1.007
1.006/ꢁ1.375
0.0373
0.0882
0.998
0.659/ꢁ0.448
wR
GOF
D
2
30 2 8
H N O
H
2
min (e Å 3
ꢁ
)
q
max
,
D
q
4

Y. N. Belokon’ et al. / Tetrahedron: Asymmetry 20 (2009) 1746–1752
1751
4
.2.7. Lithium
tertleucinato]cobaltate [
4% Yield. Mp >300 °C. ½
O): 1.13 (s, 18H, Me
K
-bis[N-(3-methoxysalicylidene)-(S)-
The enantiomeric composition of the product was determined by
gas chromatography.
K
a
-3]Li
25
1
8
ꢄ
¼ ꢁ4500 (c 0.027, MeOH). H NMR
D
(
D
2
3
C); 3.08 (s, 6H, OMe); 4.52 (s, 2H,
a
-H-Val);
4
.5. Asymmetric Michael reaction (general procedure)
6
.43-6.54 (m, 4H, CHAr); 6.99 (d, J 6.4, 2H, CHAr); 8.24 (s, 2H,
CH@N). Anal. Calcd for C28 O: C, 52.02; H, 6.24;
CoLiꢀ3H
N, 4.33. Found: C, 51.89; H, 6.51; N, 4.39.
H
34
N
2
O
8
2
A Schlenk flask was evacuated and filled with argon, whilst
being heated with a heatgun. Then the flask was cooled to room
temperature under a flow of argon. A catalyst (0.015 mmol) and
a base (0.015 mmol) were added to the flask and cyclohex-2-enone
4
.2.8. Lithium
tertleucinato]cobaltate [
2% Yield. Mp >300 °C. ½
O): 1.17 (s, 18H, Me
D
-bis[N-(3-methoxysalicylidene)-(S)-
D
-3]Li
(
0.03mL, 0.3 mmol) solution in dioxane (1 mL) was added. Then
the solution was stirred for 2 min and diethyl malonate
0.046 mL, 0.049 g, 0.3 mmol) was added. The reaction mixture
2
D
5
1
8
a
ꢄ
¼ ꢁ5763 (c 0.027, MeOH). H NMR
(
D
2
3
C); 3.62 (s, 6H, OMe); 4.29 (s, 2H,
a
-H-Val);
(
6
.22 (t, J 7.3, 2H, CHAr); 6.84 (d, J 7.9, 2H, CHAr); 7.14 (d, J 7.9, 2H,
CHAr); 8.34 (s, 2H, CH@N). Anal. Calcd for C28 O: C,
CoLiꢀ3H
2.02; H, 6.24; N, 4.33. Found: C, 52.19; H, 6.37; N, 4.10.
was stirred for 48 h under an argon atmosphere. The catalyst was
removed from the reaction mixture by column chromatography
on silica gel (column 60 ꢂ 5 mm), using EtOAc as an eluent. The
enantiomeric purity of the product was determined by chiral HPLC.
H
34
N
2
O
8
2
5
4
.2.9. Lithium
-4]Li
4% Yield. Mp >300 °C. ½
K-bis[N-(3-allylsalicylidene)-(S)-valinato]
cobaltate [
K
2
D
5
¼ ꢁ4633 (c 0.06, MeOH). 1H NMR
8
a
ꢄ
4.6. Crystallographic data
(
3 3
CD OD): 1.18–1.28. (m, 12H, CH -Val); 2.55 (m, 2H, b-H-Val);
2
.76 (AB part of ABX, JAB 15.0, JAX 8.0, JBX 6.6, 4H, CH
-H-Val); 4.64–4.72 (m, 4H, H C@); 5.32 (m, 2H, X part
of ABX, @CH–); 6.41 (t, J 7.4, 2H, CHAr); 6.74 (d, J 6.5, 2H, CHAr);
2
-Allyl); 4.38
The crystallographic data have been deposited with the Cam-
(
m, 2H,
a
2
bridge Crystallographic Data Centre, CCDC 729876 for [
K-3]Li
and CCDC 729877 for [ -2]Na. Copies of this information may be
K
7
C
.22 (d, 2H, J 7.7, CHAr); 8.33 (s, 2H, CH@N). Anal. Calcd for
CoLiꢀ4H O: C, 54.88; H, 6.45; N, 4.27. Found: C, 55.08;
obtained free of charge from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ,UK (Fax: +44-1223-336033; e-mail: depos-
it@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
30
H
34
N
2
O
6
2
H, 5.72; N, 3.90.
4
.2.10. Lithium
cobaltate [ -4]Li
4% Yield. Mp >300 °C. ½
D-bis[N-(3-allylsalicylidene)-(S)-valinato]
Acknowledgements
D
2
D
5
¼ ꢁ732 (c 0.044, MeOH). 1H NMR
8
a
ꢄ
This work was financially supported by an ISTC Grant G-1361,
RFBR Grant 09-03-00730-a and RAS Presidium Program P18. The
authors thank Dr. M. Ilyin for conducting chiral GLC analyses of
the cyanohydrins and for HPLC analyses of the Michael adducts.
(
3 3
CD OD): 1.22–1.38 (m, 12H, CH -Val); 2.86 (m, 2H, b-H-Val);
2
.92, 3.18 (AB part of ABX, JAB 15.1, JAX 5.0, JBX 7.2, 4H, CH
2
-Allyl);
4
.46 (m, 2H, -H-Val); 4.60–4.73 (m, 4H, H C@); 5.46 (m, 2H, X
a
2
part of ABX, @CH–); 6.48 (t, J 7.2, 2H, CHAr); 6.89 (d, J 7.2, 2H, CHAr);
7
C
5
.34 (d, 2H, J 7.9, CHAr); 8.50 (s, 2H, CH@N). Anal. Calcd for
CoLiꢀ1.25H O: C, 59.36; H, 6.06; N, 4.62. Found: C,
9.25; H, 6.12; N, 4.29.
30
H
34
N
2
O
6
2
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