Synthesis and metal complexes of chiral C2-symmetric diamino-bisoxazoline ligands

Article abstract of DOI:10.1002/chem.200700826

A synthetic route to tetradentate chiral N₄ ligands has been developed with the aim to study the potential of corresponding iron and manganese complexes as catalysts for enantioselective epoxidation. These ligands, which contain two oxazoline rings and two trialkylamino groups as coordinating units, are readily prepared in enantiomerically pure form by the reaction of chiral 2-chloromethyloxazolines with achiral N,N′- dimethylethane-1,2-diamine or chiral (R,R)-N,N′-dimethylcyclohexane-1,2- diamine. The ligands derived from N,N′-dimethylethane-1,2-diamine reacted with anhydrous metal halides MnCl₂ and FeCl₂ in a stereoselective manner to give octahedral mononuclear complexes that have the general formula Δ-[(L)MCl₂]. In contrast, the ligands derived from N,N′-dimethylcyclohexane-1,2-diamine formed complexes with different coordination modes depending on the diastereomer employed: in one case the metal ion was found to be pentacoordinate, in the other case a hexacoordinated complex was observed. The structure of a series of Fe and Mn complexes was determined by X-ray analysis. The coordination chemistry of these ligands was further studied by X-ray and NMR analyses of the diamagnetic isostructural complexes [(L)ZnCl₂]. Analogous ionic complexes, which were prepared by removing chloride with silver trifluoromethanesulfonate or hexafluoroantimonate, were tested as catalysts for the epoxidation of olefins.

Full text of DOI:10.1002/chem.200700826

DOI: 10.1002/chem.200700826
Synthesis and Metal Complexes of Chiral C2-Symmetric Diamino–
Bisoxazoline Ligands
Geoffroy Guillemot,[a] Markus Neuburger,[b] and Andreas Pfaltz*[a]
Abstract: A synthetic route to tetra-
dentate chiral N4 ligands has been de-
veloped with the aim to study the po-
tential of corresponding iron and man-
ganese complexes as catalysts for enan-
tioselective epoxidation. These ligands,
which contain two oxazoline rings and
two trialkylamino groups as coordinat-
ing units, are readily prepared in enan-
tiomerically pure form by the reaction
of chiral 2-chloromethyloxazolines with
amine reacted with anhydrous metal
halides MnCl2 and FeCl2 in a stereose-
lective manner to give octahedral
the other case a hexacoordinated com-
plex was observed. The structure of a
series of Fe and Mn complexes was de-
termined by X-ray analysis. The coordi-
nation chemistry of these ligands was
further studied by X-ray and NMR
analyses of the diamagnetic isostructur-
al complexes [(L)ZnCl2]. Analogous
ionic complexes, which were prepared
by removing chloride with silver tri-
fluoromethanesulfonate or hexafluoro-
mononuclear complexes that have the
A
general formula D-[(L)MCl2]. In con-
trast, the ligands derived from N,N’-di-
methylcyclohexane-1,2-diamine formed
complexes with different coordination
modes depending on the diastereomer
employed: in one case the metal ion
was found to be pentacoordinate, in
achiral
N,N’-dimethylethane-1,2-di-
ACHTREUNG
ACHTREUNG
Keywords: chiral ligands · iron ·
manganese · N ligands · oxazolines
clohexane-1,2-diamine. The ligands de-
rived from N,N’-dimethylethane-1,2-di-
Introduction
examples are the chiral Mn(salen) catalysts for the epoxida-
C
Iron and manganese complexes with nitrogen ligands have
been extensively studied as models of active sites of mono-
oxygenases and as oxidation catalysts for organic synthe-
sis.[1–5] To mimic metal porphyrins such as cytochrome P-
450,[2] which play a central role in many biological processes,
a variety of synthetic ligands were developed. Two of the
most widely used classes of ligand are the porphyrins[4] and
tetradentate Schiff base derivatives,[5] exemplified in
More recently, inspired by the remarkable oxidative prop-
erties of non-heme iron enzymes such as methane monooxy-
genase[7] or Rieske dioxygenases,[8] more flexible N4 ligands
containing sp3-hybridized N atoms have been synthesized. In
particular, Fe and Mn complexes derived from N,N’-dimeth-
yl-N,N’-bis(2-pyridylmethyl)ethane-1,2-diamine
(bpmen)
and (R,R)-N,N’-dimethyl-N,N’-bis(2-pyridylmethyl)cyclohex-
ane-1,2-diamine [(R,R)-bpmcn] have emerged as efficient
catalysts for the epoxidation of certain olefins.[9,10] However,
attempts to use bpmcn or other chiral ligands of this type
for enantioselective epoxidation have met limited suc-
Figure 1 by [Mn
N
N
raphenylporphyrin dianion; salen: N,N’-ethylene-bis(salicyli-
deneiminato) dianion]. With the growing importance of
asymmetric catalysis, many efforts have been made to
devise chiral variants of these ligands, the most successful
AHCTREUNG
gands[12,13] we have prepared a series of N4 ligands that are
structurally related to bpmen and bpmcn, but contain two
oxazoline instead of pyridine rings. Here we report the syn-
thesis of (S,S)-bomen and (S,R,R,S)-bomcn (Figure 1) li-
gands, the preparation and structure of various metal com-
plexes and preliminary epoxidation studies using manganese
and iron catalysts derived from these ligands.
[a] Dr. G. Guillemot, Prof. Dr. A. Pfaltz
Department of Chemistry, University of Basel
St. Johanns-Ring 19, 4056 Basel (Switzerland)
Fax : (+41)61-267-1103
E-mail: andreas.pfaltz@unibas.ch
[b] M. Neuburger
Ligands of this type have several attractive features:
i) they possess a relatively simple C2-symmetric structure
Laboratory for Chemical Crystallography, University of Basel
Spitalstrasse 51, 4056 Basel (Switzerland)
8960
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FULL PAPER
Scheme 1. Synthesis of 2-chloromethyl-2-oxazoline 6a and 6b. i) NEt3,
CH2Cl2, À208C, (83–89%); ii) Burgess reagent, THF, reflux, (51–66%);
iii) MeOH, Et2O·HCl, (>95%); iv) amino alcohol 2, CH2Cl2, RT, (55–
62%).
Figure 1. Structures of porphyrin, salen, and pyridine- and oxazoline-de-
rived N4 ligands.
and are readily assembled from commercially available
enantiomerically pure amino alcohols; ii) the steric proper-
ties and conformational flexibility can be tuned by variation
of the diamine bridge; iii) introduction of a chiral backbone
like trans-cyclohexane-1,2-diamine allows further variation
of the stereochemical properties; iv) the steric constraints
generated by the substituents at the oxazoline rings provide
a means for controlling the stereochemistry of metal com-
plex formation. In this way the number of possible isomers
that can arise through coordination to a octahedral metal
center can be reduced.
Scheme 2. Synthesis of bisoxazoline ligands 9 and 10. i) N,N’-dimethyl-
ethane-1,2-diamine, K2CO3, CH3CN, reflux; ii) (R,R)-N,N’-dimethylcyclo-
hexane-1,2-diamine, K2CO3, CH3CN, reflux, (39–51%).
attractive, as it involves less expensive, simpler reagents, and
because different oxazolines can be prepared from chloro-
AHCTREUNG
Results and Discussion
converted to the corresponding ligands 9a, 9b, 10a and 10b
by treatment with N,N’-dimethylethane-1,2-diamine (7) or
(R,R)-N,N’-dimethylcyclohexane-1,2-diamine (8), respective-
ly, and anhydrous K2CO3 in acetonitrile under reflux
(Scheme 2).[19] NMR analysis of the crude products showed
essentially quantitative formation of the desired ligands. Li-
gands (S,R,R,S)- and (R,R,R,R)-10a and (S,R,R,S)-10b were
purified by flash chromatography on silica gel and isolated
as analytically pure colorless or slightly yellowish oils. Li-
gands 9a and 9b proved to be difficult to purify by chroma-
tography, but according to NMR and mass spectrometry the
crude products were of high purity and used as such for the
preparation of the metal complexes. To study the influence
of the additional stereogenic centers in the chiral bridge on
Ligands synthesis and complex formation: 2-Chlorometh-
yloxazolines 6a and 6b were chosen as the central inter-
A
mediates in this synthesis, because they readily react with
secondary diamines to afford the desired tetradentate li-
gands. Among the various possible routes to these inter-
mediates[14–17] we investigated the two synthetic sequences
shown in Scheme 1. Amide formation from chloroacetyl
chloride and amino alcohol 2a or 2b, and subsequent cyliza-
tion using Burgessꢁ reagent afforded the chloromethyloxazo-
lines 6a and 6b in 42–59% overall yield.[18] The alternative
route, starting from chloroacetonitrile, also comprised two
steps and led to the desired oxazolines 6a and 6b in similar
overall yields (52–59%). However, the latter route is more
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A. Pfaltz et al.
the geometry and reactivity of metal complexes derived
from ligands of type 10, the (S,R,R,S)- and (R,R,R,R)-diaste-
reomers of ligand 10a were prepared from (R)- and (S)-
chloromethyloxazoline 6a and commercially available
(R,R)-N,N’-dimethylcyclohexane-1,2-diamine.
Complexation of ligands 9a,b and 10a,b with anhydrous
salts (MCl2; M=Fe, Mn, Zn) in acetonitrile at room temper-
ature under N2 proceeded smoothly to give colorless or
slightly yellow solutions of the desired metal complexes.
After removal of the solvent and washing with diethyl ether,
complexes 11a,b–13a,b (Scheme 3) and 17a,b–19a,b and
20–22 (Scheme 4) were isolated in high yields (70 to 90%)
as microcrystalline solids, which were characterized by mass
mental analyses and crystal structures were consistent with
the general formula [(L)M][X]2 (X=SbF6 or PF6).[20]
Structural characterization of metal complexes: The ZnII
complexes 11a and 11b were prepared for NMR studies, as
they were expected to be isostructural to the corresponding
paramagnetic FeCl2 and MnCl2 complexes. The 1H NMR
spectra of the diamagnetic zinc complexes in CD2Cl2 were
consistent with a C2 symmetric structure with a single set of
signals for the iP r (11a) and tBu (11b) substituents, respec-
tively, and also only one signal for the methylamino groups.
Notably, the ethylene protons, which appear as singlet-like
signals in the NMR spectra of the free ligands, now give rise
to pairs of doublets, as a conse-
quence of the more rigid struc-
ture of the metal complexes, in
which the diastereotopic pro-
tons experience distinctly differ-
ent environments. Analysis of
the NMR and MS data clearly
confirms the structural formulas
of complexes 11a and 11b.
The flexible tetradentate
Scheme 3. Preparation of metal complexes derived from ligands 9a and 9b. i) Anhydrous MCl2, CH3CN;
ligand can adopt different con-
formations when coordinating
to a metal center (Figure 2) and
form three diastereomeric com-
plexes (trans, cis-a and cis-b).
In order to establish the coordi-
nation mode in complexes 12a
and 13a by means of X-ray
analysis, the compounds were
recrystallized from a mixture of
acetonitrile and diethyl ether,
to yield colorless and pale
green crystals, respectively,
which were used for crystal
structure determination.
ii) 2 equiv of silver salt, CH3CN.
Scheme 4. Preparation of metal complexes derived from ligands 10a and 10b. i) Anhydrous MCl2, (S,R,R,S)-
10a,b, CH3CN, RT; ii) anhydrous MCl2, (R,R,R,R)-10, CH3CN, RT.
spectroscopy (FAB or ESI) and elemental analysis. More-
over, crystallization from acetonitrile or acetonitrile/diethyl
ether solutions provided crystals suitable for X-ray analysis
for several complexes.
For catalytic studies, we also prepared ionic versions of
the Fe and Mn complexes with weakly coordinating anions
to generate two vacant coordination sites (Scheme 3). Start-
ing from the dichloro complexes, the chloride anions were
removed by precipitation as AgCl to give the corresponding
trifluoromethanesulfonate (OTfÀ), hexafluoroantimonate, or
hexafluorophosphate complexes. All complexes were char-
acterized by elemental analysis and mass spectroscopy (FAB
or ESI). The mass spectra of the hexafluoroantimonate or
hexafluorophosphate salts generally showed a main signal
corresponding to a monofluoro complex [(L)M(F)]+ (L=
Figure 2. Stereoisomers of octahedral metal complexes.
As expected, the Mn and Fe complexes formed analogous
structures (Figure 3; crystallographic data: Table 5). Com-
plex 13a possesses crystallographically imposed C2 symme-
try, the twofold axis running through the metal ion and bi-
À
À
secting the Cl Fe Cl angle. The ligand is tetracoordinated
to the metal center, which adopts a distorded octahedral ge-
ometry with two oxazoline N atoms in axial positions, and
the two amine N atoms in equatorial positions. The remain-
À
ligand; M=Mn, Fe). The abstraction of fluoride from SbF6
À
or PF6 most likely occurs in the mass spectrometer, as ele-
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Chiral Metal Complexes
FULL PAPER
Table 1. Selected bond lengths [Š] and angles [8] for complexes 12a, 13a
and 16b(PF6)2.
A
Complex 12a
À
À
À
Mn1 Cl1
2.4231(5)
2.4272(5)
2.2413(14)
2.2599(14)
2.4304(13)
2.4030(13)
N1 Mn1 N2
72.22(5)
72.49(5)
74.81(5)
96.11(5)
95.97(5)
À
À
À
Mn1 Cl2
N3 Mn1 N4
À
À
À
Mn1 N1
N2 Mn1 N3
À
À
À
Mn1 N4
N1 Mn1 N3
À
À
À
Mn1 N2
N2 Mn1 N4
À
À
À
Mn1 N3
Cl1 Mn1 Cl2
113.684(16)
165.68(4)
À
À
N1 Mn1 N4
Complex 13a
À
À
À
Fe1 Cl1
2.3917(5)
2.3917(5)
2.1816(17)
2.1816(17)
2.3383(18)
2.3383(18)
N1 Fe1 N2
74.43(6)
74.43(6)
77.19(9)
97.85(6)
97.85(6)
112.61(3)
170.33(9)
[a]
À
À
À
Fe1 Cl1A
N2A Fe1 N1A
À
À
À
Fe1 N1
N2 Fe1 N2A
À
À
À
Fe1 N1A
N1 Fe1 N2A
À
À
À
Fe1 N2
N2 Fe1 N1A
À
À
À
Fe1 N2A
Cl1 Fe1 Cl1A
À
À
N1 Fe1 N1A
Complex 16b(PF6)2
AHCTREUNG
À
À
À
Fe1 N5
2.1404(18)
2.1466(18)
2.1608(15)
2.1748(15)
2.2909(18)
2.2931(17)
N1 Fe1 N2
78.19(6)
78.23(6)
80.56(6)
90.15(6)
91.60(6)
93.74(6)
165.73(6)
À
À
À
Fe1 N6
N3 Fe1 N4
II
Figure 3. ORTEPdrawing of Mn complex 12a (top) and FeII complex
13a (50% thermal ellipsoids). The hydrogen atoms have been omitted
for clarity.
Fe1 N1
N2 Fe1 N3
À
À
À
À
À
À
Fe1 N4
N1 Fe1 N3
À
À
À
Fe1 N2
N2 Fe1 N4
À
À
À
Fe1 N3
N5 Fe1 N6
À
À
N1 Fe1 N4
[a] The symmetry operator to generate the positions of Cl1A and N2A is
x, Ày, Àz.
ing two equatorial coordination sites are occupied by the
two chloride ions. This arrangement, the cis-a-configuration,
is by far the most frequently observed coordination mode
for ligands of this type.[9a,10a,21–32]
Table 2. Deviation [Š] of atoms from the calculated equatorial least-
squares mean plane[a] for complexes 12a, 13a, 16b
(PF6)2 and 18b.
R
The chiral ligand can chelate the metal ion in two differ-
ent ways, forming two helical diastereomers of D and L hel-
icity. By analysis of the crystal structures, the D configura-
tion was assigned to both the Mn and Fe complexes 12a and
13a. As mentioned above, the NMR spectrum of the Zn
complexes 11a and 11b was consistent with the selective for-
mation of only one diastereomer, this suggests that the coor-
dination mode observed in complexes 11–13 is thermody-
namically favored. Apparently, the stereoselectivity of com-
plex formation is controlled by the substituents at the ste-
reogenic centers of the oxazoline rings.
12a
13a
16b
A
18b
Cl1
Cl1A
Cl2
N1
N2
N2A
N3
N5
N6
M
0.2404(4)
–
0.2297(5)
–
–
–
–
–
–
À0.2297(5)
À0.2411(4)
–
–
0.1409(4)
–
À0.1798(12)
À0.3395(14)
À0.3190(18)
À0.1426(18)
0.2092(13)
–
0.3190(18)
–
–
0.3402(14)
–
–
–
–
–
0.1424(18)
0.135(2)
À0.1348(18)
0.0287(3)
À0.1703(13)
–
–
0.0076(3)
0.0000
0.6472(2)
Selected structural parameters of the two structures are
listed in Table 1. The bond lengths and angles in the
[MN4Cl2] core are very similar. The mean value of the
metal–nitrogen distances are; 2.33 Š for the Mn and 2.26 Š
for the Fe complex, and are consistent with the presence of
high-spin MnII and FeII atoms. This is in agreement with the
NMR spectrum of iron complex 13a in CD3CN. As expect-
ed, the metal bonds to the oxazoline N atoms are shorter
than those to the amino groups, as a consequence of the sp2-
hybridization of the oxazoline N atom and the metal-oxazo-
line p interaction. An edge-on perspective of the two com-
plexes shows a severe distortion from a pseudo-square
planar arrangement, defined by two amine N atoms and the
two chloride atoms. Deviations from the least-squares mean
plane are indicative of this distortion (Table 2; mean devia-
[a] Atoms used to calculate the least-squares mean plane are as follows:
Cl1, Cl2, N2, N3 for 12a; Cl1, N2, Cl1A, N2A for 13a; N2, N3, N5, N6
for 16b(PF6)2; Cl2, N1, N2, N3 for 18b.
A
teristic of the distorted octahedral geometry. This deforma-
tion most likely results from geometrical constraints im-
posed by the two oxazoline rings and the presence of five-
membered metallacycles, which enforce an angle around the
metal atom close to 758. An additional characteristic of the
À À
two complexes is the rather large Cl M Cl angle of 113.78
and 112.68 in 12a and 13a, respectively.
Crystals of 16b(PF6)2, the ionic analogue of 13b, that
A
were suitable for X-ray analysis, were obtained in acetoni-
trile/diethylether (see Figure 4; crystallographic data:
Table 5). The conformation of the ligand and the pseudo-oc-
tahedral coordination geometry are quite similar in the di-
chloro and the ionic complex, although some deviations of
À
tion of 0.29 Š for 12a and 0.27 Š for 13a). The angles N1
À
À À
À À
M N2 (72.38) and N4 M N2 (96.08) for 12a and N1 M
À À
N2 (74.48) and N1A M N2 (97.98) for 13a, are also charac-
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8963

A. Pfaltz et al.
gands such as a 6-methylpyridine derivative of a bpmcn
complex (Figure 1), namely [Fe(6-Me2-bpmcn)
(CF3SO3)2].[33]
G
Crystals suitable for X-ray analysis were obtained for the
manganese derivative (S,R,R,S)-18b by means of crystalliza-
tion from acetonitrile (Figure 5; crystallographic data:
II
Figure 4. ORTEPdrawing of Fe complex 16b(PF6)2 (50% thermal ellip-
A
soids). The hydrogen atoms and the counterions have been omitted for
clarity.
Figure 5. ORTEPdrawing of Mn II complex 18b (50% thermal ellipsoids).
the metal–nitrogen distances and angles are observed. The
two vacant sites generated by abstraction of the two chlo-
ride ions are occupied by two molecules of acetonitrile,
while the hexafluorophosphate counteranions are located at
the periphery and do not interact with the metal ion. The N6
pseudo-octahedral core is less distorted than in the dichloro
complex, as revealed by the deviations from the least-square
mean plane defined by N2, N3, N5, and N6 (0.14 Š; see
The hydrogen atoms have been omitted for clarity.
Table 5). The general structural features of the complexed
ligand are consistent with the NMR spectra of (S,R,R,S)-
17b, but, notably, the metal center is only pentacoordinated,
since one oxazoline ring is positioned too distant from the
À
Mn atom to form a bond (Mn N4=3.39 Š). The coordina-
À
À
Table 2). The N Fe N angles in the five-membered chelate
tion geometry of (S,R,R,S)-18b can be described as a dis-
torted square pyramidal structure (t=0.45)[34] with the
apical position occupied by one chloride, Cl1, and the dis-
torted square formed by the second chloride atom Cl2, the
two tertiary amino groups, N2 and N3, and the oxazoline N1
atom. The deviation of the Mn atom from the calculated
least square plane is 0.6472(2) Š (Table 2; for main structur-
al parameters: see Table 3).
À
À
À À
rings, namely N1 Fe N2 (78.28), N3 Fe N4 (78.28) and
À
À
N2 Fe N3 (80.68) are still smaller than the ideal 908, but to
a lesser extent than in the case of the dichloro complex 13a.
À
À
À À
Furthermore, the N1 Fe N3 and N2 Fe N4 angles are
both close to 908 (90.28 and 91.68, respectively), and the
À
À
À À
N5 Fe N6 angle is also distinctly smaller than the Cl Fe
Cl angle in 13a (93.78 vs. 112.68). As expected, the metal–
amine bonds in the ionic complex are ꢀ0.05 Š shorter than
in the neutral complex 13a. Although there is no crystallo-
graphically imposed C2 symmetry, the symmetry of the
ligand is largely retained, with a pseudo axis across the Fe
atom and the center of the diamine bridge.
The remarkably different behavior of the diastereomeric
ligand, (R,R,R,R)-10a, is illustrated by the Zn complex
(R,R,R,R)-20. The NMR spectra in CD2Cl2 and [D8]THF
were consistent with a C2-symmetric structure. At ambient
temperature some signal broadening was observed, but at
À188C in [D8]THF, a well resolved spectrum was obtained,
with sharp signals that could be fully assigned (see the Ex-
perimental Section). Colorless crystals of (R,R,R,R)-20 suit-
able for X-ray analysis were grown from a concentrated so-
lution in acetonitrile at room temperature (Figure 6; crystal-
lographic data: Table 5; selected bond lengths and angles:
Table 3). The three-dimensional arrangement of the ligand
backbone and the oxazoline moieties in this complex closely
resembles that found in Fe and Mn complexes 12a and 13a
(Figure 3). As expected from the R configuration of the oxa-
zoline rings, the ligand forms a L-helix, confirming that
steric effects of the oxazoline substituents determine the
helical chirality.
Ligands 10a and 10b showed a distinctly different coordi-
nation behavior than their analogues 9a and 9b. Depending
on whether the (S,R,R,S)- or (R,R,R,R)-isomer was used,
different coordination modes were observed upon complex-
ation with ZnCl2, FeCl2, or MnCl2 (Scheme 4).
The 1H and 13C NMR spectra of the Zn complexes
(S,R,R,S)-17a and (S,R,R,S)-17b showed two distinct sets of
signals for the oxazoline moities as well as for the methyla-
mino groups. This implies that the C2-symmetry of the
ligand was lost in the complex. Studies of the 2-D NMR
spectra indicated a cis-b configuration for the complex with
a cis arrangement of the two oxazoline rings. A preference
for this coordination mode over the cis-a configuration has
been reported for metal complexes of similar tetradentate li-
Crystals of the cationic bis-acetonitrile Mn complex 21-
(SbF6)2 were grown by slow diffusion of diethylether into a
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Chiral Metal Complexes
FULL PAPER
Table 3. Selected bond lengths [Š] and angles [8] for complexes 18b, 20
and 21(SbF6)2.
N
Complex 18b
À
À
À
Mn1 Cl1
2.3822(5)
2.4003(5)
2.1926(13)
2.3974(14)
2.3170(14)
3.3924(14)
N1 Mn1 N2
73.55(5)
113.93(4)
75.18(5)
157.27(3)
94.04(3)
105.71(4)
130.42(5)
108.552(19)
À
À
À
Mn1 Cl2
N1 Mn1 Cl1
À
À
À
Mn1 N1
N2 Mn1 N3
À
À
À
Mn1 N2
Cl2 Mn1 N2
À
À
À
Mn1 N3
N2 Mn1 Cl1
À
À
À
Mn1 N4
N3 Mn1 Cl1
À
À
N1 Mn1 N3
À
À
Cl1 Mn1 Cl2
Complex 20
À
À
À
Zn1 Cl1
2.3316(7)
2.3764(7)
2.211(2)
2.231(2)
2.331(2)
2.356(2)
N1 Zn1 N2
74.67(8)
73.07(9)
75.29(8)
92.92(8)
92.33(8)
104.09(3)
163.12(8)
À
À
À
Zn1 Cl2
N3 Zn1 N4
À
À
À
Zn1 N1
N2 Zn1 N3
À
À
À
Zn1 N4
N1 Zn1 N3
À
À
À
Zn1 N2
N2 Zn1 N4
À
À
À
Zn1 N3
Cl1 Zn1 Cl2
À
À
N1 Zn1 N4
Complex 21(SbF6)2
AHCTREUNG
A
B
A
B
À
À
À
Mn1 N5 2.220(5) 2.281(4) N1 Mn1 N2
75.54(13)
75.83(13)
78.98(12)
98.08(13)
99.03(13)
87.83(17)
76.36(13)
À
À
À
Mn1 N6 2.248(4) 2.233(4) N3 Mn1 N4
75.55(13)
77.97(12)
99.28(13)
98.25(13)
88.64(17)
À
À
À
Mn1 N1 2.215(4) 2.188(4) N2 Mn1 N3
À
À
À
Mn1 N4 2.199(4) 2.204(3) N1 Mn1 N3
À
À
À
Mn1 N2 2.311(3) 2.301(3) N2 Mn1 N4
À
À
À
Mn1 N3 2.289(3) 2.305(4) N5 Mn1 N6
À
À
N1 Mn1 N4 172.66(13) 173.34(14)
saturated acetonitrile solution. The solid-state structure of
this complex, determined by X-ray diffraction, is very simi-
lar to the structure of the dichloro-Zn complex, as shown in
Figure 6 (crystallographic data: Table 5; selected bond
lengths and angles: Table 3).
II
Figure 6. ORTEPdrawing of Zn complex 20 (top) and MnII complex 21-
AHCTREUNG
ions have been omitted for clarity.
The remarkably different coordination chemistry of the
(S,R,R,S)- and (R,R,R,R)-diastereomers of ligand 10 may be
attributed to the rigid conformation imposed by the trans-di-
aminocyclohexane unit. While the R,R,R,R configuration
allows the formation of C2-symmetric tetracoordinated com-
plexes with a cis-a configuration, which is also favored by
the more flexible ligand 9, the S,R,R,S configuration pre-
vents this coordination mode and impedes the coordination
of both oxazoline rings.
12b were used, the same conversions and yields were ob-
tained.
We next tested complexes derived from ligands 10a,b,
which we expected to behave differently, based on their co-
ordination chemistry discussed above. We hoped that the
conformationally more rigid trans-diaminocyclohexane
bridge would enhance the kinetic and thermodynamic stabil-
ity of the complexes and prevent degradation during epoxi-
dation.[9a] In addition, we were interested to see if the differ-
ent coordination modes of the two diastereomeric ligands
(R,R,R,R)-10 and (S,R,R,S)-10 had an effect on the catalytic
Catalysis: Stack et al. have shown that manganese com-
plexes derived from (R,R)-bpmcn are efficient catalysts for
the epoxidation of a wide range of olefins by using peracetic
acid as oxidant.[9] Therefore, we decided to test our manga-
nese complexes prepared from ligands 9a,b and 10a,b as
catalysts for analogous enantioselective epoxidations. In a
typical run, 1.5 equivalents of 32% aqueous peracetic acid
solution were slowly added to a mixture of 1.0 equivalent of
alkene and 5 mol% of catalyst in acetonitrile at À308C.
Using cationic complexes 14a and 14b, almost complete
conversion of vinyl-cyclohexane, indene or trans-b-methyl-
styrene was observed after 30 min and epoxides were ob-
tained in yields of up to 94% (97% for indene). However,
no asymmetric induction was achieved (<6% ee in all
cases). Surprisingly, when the dichloro complexes 12a and
Table 4. Epoxidation studies with MnII catalysts.
Catalyst
(R,R,R,R)-21(Cl)2
(R,R,R,R)-21(OTf)2
(S,R,R,S)-18a(Cl)2
(S,R,R,S)-18a(OTf)2
(S,R,R,S)-18a(SbF6)2
[a] Based on conversion.
Conversion [%]
Yield[a] [%]
ee [%]
G
<10
20
<4
38
–
86
–
96
97
–
<6
–
18
21
G
ACHTREUNG
U
E
G
C
N
99
Chem. Eur. J. 2007, 13, 8960 – 8970
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8965

A. Pfaltz et al.
Table 5. Crystallographic data of complexes 12a, 13a, 16b
N
G
Complex
12a
13a
N
18b
20
21(SbF6)2
N
formula
Mr
C18H34Cl2Mn1N4O2
464.33
4
C18H34Cl2Fe1N4O2
465.25
2
C22H40Cl2N4O2Zn1
528.87
4
C26H46F12Mn1N6O2Sb2
1001.09
4
1629.9
2
1.504
546.47
4
1.300
Z
1calc [gcmÀ3
]
1.375
1.402
1.380
1.764
F
A
980
492
1686
1164
1120
1980
pale pink block
pale green plate
0.04”0.20”0.20
orthorhombic
P22121
7.5728(7)
8.9244(4)
16.3012(15)
90
purple plate
0.23”0.26”0.36
orthorhombic
P22121
10.6449(1)
14.9076(1)
22.6736(2)
90
pale red block
0.22”0.24”0.25
orthorhombic
P212121
9.9811(2)
13.9113(3)
20.1114(4)
90
colorless plate
0.10”0.12”0.31
orthorhombic
P212121
9.0648(1)
12.2302(1)
22.9624(3)
90
pink block
0.30”0.30”0.32
monoclinic
P21
9.0474(2)
35.9055(8)
11.7475(2)
90
crystal size [mm3] 0.22”0.24”0.27
crystal system
space group
a [Š]
b [Š]
c [Š]
orthorhombic
P212121
9.0262(8)
15.2617(15)
16.2781(9)
90
a [8]
b [8]
90
90
90
90
90
90
90
90
90
90
99.0743(6)
90
3768.43(13)
0.71073
173
g [8]
V [Š3]
l [Š]
2242.4(3)
0.71073
173
1101.68(15)
0.71073
173
3598.07(5)
0.71073
173
2792.47(10)
0.71073
173
2545.71(5)
0.71073
173
T [8C]
m [mmÀ1
]
0.847
0.947
0.604
0.691
1.200
1.846
min/max trans-
mission
0.82/0.83
0.83/0.96
0.85/0.87
0.85/0.86
0.87/0.89
0.57/0.57
q range [8]
3.37–32.502
93522
8089 (merging
r=0.039)
4490
3.385–31.994
30061
3822 (merging
r=0.066)
1953
1.635–27.835
31475
8542 (merging
r=0.084)
5750
1.780–30.079
25975
8177 (merging
r=0.057)
6416
1.774–27.899
21500
6069 (merging
r=0.074)
5068
1.134–27.489
28237
16981 (merging
r=0.043)
13684
N collected[a]
N independent[b]
N observed[c]
N parameters[d]
R[e]
245
0.0205
192
0.0234
494
0.0259
299
0.0287
281
0.0339
884
0.0309
wR2
0.0357
0.0256
0.0398
0.0386
0.0427
0.0430
GOF
1.0713
1.0793
1.0740
1.0952
0.9209
1.1212
[a] N collected is the number of reflections collected. [b] N independent is the number of independent reflections. [c] N observed is the total number of
the independent reflections having I>3.00s(I). [d] Number of parameters that have been refined using the reflections considered as observed. [e] Calcu-
lated on the reflections considered as observed.
properties. With the C2-symmetric tetracoordinated ionic
complex 21(OTf)2, no enantiomeric excess and low conver-
Conclusion
ACHTREUNG
sion was observed (Table 4). The dichloro complex 21(Cl)2
was even less active (<10% conv), in contrast to the analo-
gous complexes 12a and 12b, based on diaminoethane-de-
rived ligands. The different activities of 12a,b and 21 may
be the result of the stabilizing effect of the diaminocyclohex-
ane unit,[9a] which prevents dissociation of a chloride from
the inactive dichloro complex 21(Cl)2, whereas in the more
labile complexes 12a and 12b partial dissociation of one or
Two classes of readily accessible modular chiral diamino–
bisoxazoline ligands have been prepared and converted to a
A
series of FeII, MnII, and ZnII complexes. The coordination
chemistry of these ligands strongly depends on the back-
bone. Bisoxazolines containing a diaminoethane bridge act
as tetradentate ligands and selectively form metal complexes
[MN4L2] with cis-a configuration of the [MN4] core. The
same behavior is observed for ligands assembled from two
(R)-oxazolines and (R,R)-1,2-diaminocyclohexane, whereas
the corresponding diastereomeric (S,R,R,S)-ligands prefer a
different coordination mode, leading to pentacoordinated
[MN3L2] complexes with only one coordinated oxazoline
ring. The pentacoordinated manganese complexes with
weakly coordinating anions proved to be active catalysts for
the epoxidation of olefins with peracetic acid. Although the
enantioselectivities were modest, the modular structure of
the ligands, which can be easily modified, should leave room
for improvement. Moreover, ligands of this type may prove
useful for other applications in asymmetric catalysis.
À
more M N bonds generates vacant sites that are necessary
for catalytic activity.
Manganese complexes 18a,b(Cl)2 derived from the diaste-
reomeric ligands (S,R,R,S)-10a,b also showed no catalytic
activity, whereas the corresponding trifluoromethanesulfo-
nate 18a
ACHTREUNG
fluoroantimonate 18a
AHCTREUNG
methanesulfonate and hexafluoroantimonate salts both in-
duced modest, but reproducible enantiomeric excesses of
ꢀ20%, which, notably, remained constant during the course
of the reaction.
We also carried out preliminary catalytic studies with iron
complexes. However, all complexes were found to be less
active and less enantioselective (up to 12% ee) than analo-
gous manganese-based catalysts.
8966
www.chemeurj.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 8960 – 8970

Chiral Metal Complexes
FULL PAPER
A
(CH3)2), 18.4 ppm (CH
U
A
Experimental Section
339 (100) [M+H]+.
Compound 9b: Compound
7
General: All chemicals were purchased from commercial sources and
used as received, unless noted otherwise. Anhydrous solvents were ob-
tained in sure-seal bottles from Fluka or purified using standard meth-
ods.[35] All reactions were carried out in an atmosphere of purified nitro-
gen by using a glovebox and standard Schlenk techniques.
NMR: Bruker Advance DRX 500 (1H: 500 MHz, 13C: 125.8 MHz),
Bruker AMX 400 (1H: 400 MHz, 13C: 100.6 MHz) or Bruker AC 250.
Chemical shifts (d are listed relative to tetramethylsilane as an internal
standard; ox=oxazoline).
19.2 mmol), (S)-6b (1.69 g, 9.62 mmol), CH3CN (12 mL), yield: 1.31 g
(75%). [a]D =À73.5 (c=1.2 in CHCl3); 1H NMR (500 MHz, CDCl3,
258C): d=4.17 (m, 2H; OCHH), 4.02 (m, 2H; OCHH), 3.84 (m, 2H;
NCH
NCH3), 0.87 ppm (s, 18H; C
d=164.4 (C=N(Ox)), 75.7 (CH(Ox)), 68.5 (CH2(Ox)), 54.8
(NCH2CH2N), 54.3 (NCH2), 42.7 (NCH3), 33.4 (C(CH3)3), 25.9 ppm (C-
(CH3)3); MS
(FAB): m/z (%): 367 (100) [M+H]+.
ACHTREUNG
AHCTREUNG
AHCTREUNG
A
ACHTREUNG
General procedure for the synthesis of ligands 10: (R,R)-N,N’-dimethyl-
cyclohexane-1,2-diamine (8) and K2CO3 were added to a solution of the
chloromethyloxazoline 6 in CH3CN at room temperature. The resulting
reaction mixture was refluxed for 3 h. The solid was filtered off and vola-
tiles removed in vacuo. Acetone was added and the resulting colorless
precipitate filtered off again. Removal of acetone gave a yellow oil,
which was purified by flash chromatography (silica gel, EtOAc, 3 vol%
NEt3).
Mass spectrometry: Finnegan MAT 312 (FAB), VG 70-SE (70 eV) (EI)
in m/z (% of base peak).
Optical rotation: Perkin–Elmer 341 polarimeter (sodium lamp, 1-dm cuv-
ette, c in g/100 mL, 208C).
Gas chromatography: Carlo Erba HRGC Mega2 series MFC 800.
Elemental analyses: were performed by the Microanalytical Laboratory
of the Department of Chemistry, University of Basel.
Compounds 3,[18] 5[36] and 6[18] were prepared following published proce-
dures.
Compound (S,R,R,S)-10a: Compound 8 (440 mg, 3.09 mmol), K2CO3
(1.72 g, 12.44 mmol), (S)-6a (1.00 g, 6.19 mmol), CH3CN (10 mL), yield:
0.56 g (46%). Rf =0.29 (EtOAc, 3 vol% NEt3); [a]D =À78.0 (c=0.98 in
CH2Cl2); 1H NMR (500 MHz, CDCl3, 258C): d=4.24 (m, 2H; OCHH),
Synthesis of (4R)-2-chloromethyl-4-isopropyl-4,5-dihydrooxazole ((R)-
6a)—procedure starting from chloroacetamide: Burgess reagent (methyl-
N-triethylammoniosulfonylcarbamate; 3.78 g, 15.86 mmol) was added to
a solution of amide (R)-3a (2.77 g, 15.42 mmol) in THF (30 mL) at room
temperature. After refluxing the reaction mixture for 5 h, the volatiles
were evaporated and the residue was dissolved in CH2Cl2 (20 mL). The
solution was washed with water (2”20 mL). After separation of the or-
ganic phase, the aqueous layer was extracted twice with CH2Cl2. The
combined organic layers were dried over MgSO4 and concentrated to
give a yellowish oil, from which analytically pure (R)-6a was obtained by
distillation (b.p. 428C, 0.04 mbar) as a colorless oil (1.55 g, 62%).
3.95 (m, 2H; OCHH), 3.89 (m, 2H; NCH
14.2 Hz, 2H; CH2), 3.42 (bd, J
A
(H,H)=
2
ACHTREUNG
AHCTREUNG
AHCTREUNG
6H; CH
N
A
ACHTREUNG
32.6 (CH
ACHTREUNG
A
N
ACHTREUNG
Synthesis of (R)-6a—procedure starting from methyl chloroacetimidate
hydrochloride (5): Methyl chloroacetimidate hydrochloride (1.72 g,
11.9 mmol) and d-valinol (1.23 g, 11.9 mmol) were mixed in CH2Cl2
(40 mL), and the resulting suspension stirred at room temperature for
4 h. The solid was filtered off and the volatiles removed in vacuo to give
a yellowish oil, from which analytically pure (R)-6a was obtained by dis-
tillation (b.p. 428C, 0.04 mbar) as a colorless oil (1.1 g, 57%). [a]D =
+99.2 (c=1.19 in CHCl3); 1H NMR (500 MHz, CDCl3, 258C): d=4.33
(m, 1H; OCHH), 4.09 (m, 2H; ClCH2), 4.04 (m, 1H; OCHH), 3.95 (m,
elemental analysis calcd (%) for C22H40N4O2 (392.58): C 67.31, H 10.27,
N 14.27; found: C 66.27, H 10.51, N 14.12.
Compound (R,R,R,R)-10a: Compound 8 (311 mg, 2.19 mmol), K2CO3
(1.21 g, 8.75 mmol), (R)-6a (0.705 g, 4.36 mmol), CH3CN (8 mL), yield:
0.33 g (39%). Rf =0.29 (EtOAc, 3 vol% NEt3); [a]D =++56.6 (c=0.96 in
CH2Cl2); 1H NMR (500 MHz, CDCl3, 258C): d=4.23 (m, 2H; OCHH),
3.94 (m, 2H; OCHH), 3.88 (m, 2H; NCH
(m, 2H; NCHCH2), 2.35 (m, 6H; NCH3), 1.81 (m, 2H; NCHCH2CH2),
1.74 (m, 2H; CH(CH3)2), 1.66 (m, 2H; NCHCH2CH2), 1.19 (m, 2H;
NCHCH2CH2), 1.07 (m, 2H; NCHCH2CH2), 0.94 (d, 3J
(H,H)=6.8 Hz,
6H; CH (H,H)=6.8 Hz, 6H; CH
(CH3)2), 0.87 (d, 3J (CH3)2); 13C NMR
A
AHCTREUNG
1H; NCH
CH
(CH3)2), 0.87 ppm (d, 3J
(125 MHz, CDCl3, 258C, TMS): d=162.3 (C=N(Ox)), 72.42 (NCH
71.18 (CH2O), 36.44 (ClCH2), 32.46 (CH(CH3)2), 18.66 (CH(CH3)2),
18.07 ppm (CH(CH3)2); MS
(FAB): m/z (%): 162 (100) [M+H]+; elemen-
A
G
A
AHCTREUNG
A
N
ACHTREUNG
A
N
ACHTREUNG
AHCTREUNG
(125 MHz, CDCl3, 258C): d=165.9 (C=N(Ox)), 71.9 (CH(Ox)), 69.9
(CH2(Ox)), 63.2 (NCHCH2), 51.6 (NCH2), 37.2 (NCH3), 32.5 (CH-
A
ACHTREUNG
A
ACHTREUNG
AHCTREUNG
tal analysis calcd (%) for C7H12ClNO (161.6): C 52.02, H 7.48, N 8.67;
found: C 51.86, H 7.38, N 8.67.
A
G
ACHTREUNG
mental analysis calcd (%) for C22H40N4O2 (392.58): C 67.31, H 10.27, N
14.27; found: C 67.08, H 10.13, N 14.35.
General procedure for the synthesis of ligands 9: N,N’-Dimethylethylene-
1,2-diamine (7) and K2CO3 were added to a solution of chloromethyloxa-
zoline 6 in CH3CN at room temperature, and the reaction mixture re-
fluxed for 3 h. The solid was filtered off and volatiles removed in vacuo.
EtOAc was added and the resulting colorless precipitate filtered off
again. Removal of the solvents gave a yellowish oil which was used for
the preparation of metal complexes without further purification. Elemen-
tal analyses were unsatisfactory and difficulties were encountered in puri-
fying 9a and 9b by chromatography; however, according to NMR analy-
ses the products were pure.
Compound (S,R,R,S)-10b: Compound 8 (704 mg, 4.95 mmol), K2CO3
(2.82 g, 20.4 mmol), (S)-6b (1.73 g, 9.85 mmol), CH3CN (18 mL), yield:
1.06 g (51%). Rf =0.32 (EtOAc, 3 vol% NEt3); [a]D =À69 (c=0.81 in
CH2Cl2); 1H NMR (500 MHz, CDCl3, 258C): d=4.17 (m, 2H; OCHH),
4.02 (m, 2H; OCHH), 3.80 (m, 2H; NCH
(tBu)), 3.50 (d, 2J
G
14 Hz, 2H; CH2), 3.38 (d, 2J
AHCTREUNG
NCHCH2), 2.36 (m, 6H; NCH3), 1.71 (m, 2H; NCHCH2CH2), 1.65 (m,
2H; NCHCH2CH2), 1.19 (m, 2H; NCHCH2CH2), 1.05 (m, 2H;
NCHCH2CH2), 0.87 (s, 18H; C
258C): d=166.1 (C=N(Ox)), 75.4 (CH(Ox)), 68.6 (CH2(Ox)), 63.2
(NCHCH2), 52.0 (NCH2), 36.9 (NCH3), 33.6 (C(CH3)3), 27.5
(FAB): m/z
(CH3)3); 13C NMR (125 MHz, CDCl3,
Compound 9a: Compound
7 (597 mg, 6.77 mmol), K2CO3 (4.12 g,
AHCTREUNG
29.8 mmol), (S)-6a (2.21 g, 13.7 mmol), CH3CN (16 mL), yield: 1.78 g
(78%). [a]D =À82.7 (c=1.2 in CHCl3); 1H NMR (400 MHz, CDCl3,
258C): d=4.24 (m, 2H; OCHH), 3.95 (m, 2H; OCHH), 3.90 (m, 2H;
(NCHCH2CH2), 26 (C
(CH3)3), 25.6 ppm (NCHCH2CH2); MS
ACHTREUNG
(%): 421 (100) [M+H]+; elemental analysis calcd (%) for C24H44N4O2
(420.64): C 68.53, H 10.54, N 13.32; found: C 67.93, H 10.34, N 13.16.
NCH
NCH3), 1.74 (m, 2H; CH
(CH3)2), 0.87 ppm (d, 3J
(H,H)=6.8 Hz, 6H; CH
ACHTREUNG
A
ACHTREUNG
General procedure for the preparation of dichloro–zinc complexes: One
equivalent of [ZnCl2(dioxane)] was added to a solution of ligand (9a,b or
G
G
ACHTREUNG
N
(100 MHz, CDCl3, 258C): d=164.5 (C=N(Ox)), 72.2 (CH(Ox)), 70.1
(CH2(Ox)), 54.9 (NCH2CH2N), 54.4 (NCH2), 42.9 (NCH3), 32.6 (CH-
10a,b) in MeCN (3 mL). The reaction mixture was stirred at room tem-
perature for one hour. Remaining traces of solid were filtered off and
Chem. Eur. J. 2007, 13, 8960 – 8970
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8967

A. Pfaltz et al.
volatiles were removed in vacuo. The residue was washed with Et2O
(5 mL) and dried in vacuo to give a colorless solid which was analyzed by
using NMR spectroscopy.
10.59; found: C 49.99, H 7.45, N 10.54. Crystals suitable for X-ray analy-
sis were grown from acetonitrile at room temperature.
Preparation of dichloro manganese and iron complexes of ligands 9a,b—
synthesis of 12a: A solution of (S,S)-9a (0.5 g, 1.477 mmol) in MeCN
(5 mL) was added to a suspension of MnCl2 (0.176 g, 1.399 mmol) in
MeCN (5 mL) at room temperature to give, after a few minutes, a bright
orange solution which was stirred for further 3 h. The volatiles were re-
moved and the residue washed with Et2O (10 mL) to give a colorless
compound, which was dried in vacuo; yield: 0.55 g (81%) of 12a. MS-
Complex 11b: [ZnCl2(dioxane)] (120 mg, 0.53 mmol), (S,S)-9b (208 mg,
R
0.57 mmol), MeCN (3 mL), yield: 180 mg (67%). 1H NMR (250 MHz,
CDCl3, 258C): d=4.30 (m, 2H; OCHH), 4.23 (m, 2H; OCHH), 4.02 (m,
2H; NCH
(d, 2J(H,H)=16.7 Hz, 2H; exo-H of NCH2), 3.12 (d, 2J
2H; endo-H of NCH2CH2N), 2.79 (d, 2J
(H,H)=9.8 Hz, 2H; exo-H of
NCH2CH2N), 2.62 (s, 6H; NCH3), 0.91 ppm (s, 18H; C
(CH3)3); 13C NMR
A
ACHTREUNG
A
ACHTREUNG
AHCTREUNG
(FAB): m/z (%): 428 (100) [MÀCl]+; elemental analysis calcd (%) for
AHCTREUNG
C18H34Cl2MnN4O2 (464.33): C 46.56, H 7.38, N 12.07; found: C 46.30, H
7.37, N 12.07. Crystals suitable for X-ray analysis were grown in MeCN/
Et2O solution at room temperature.
(125 MHz, CDCl3, 258C): d=173 (C=N(Ox)), 73.6 (CH(Ox)), 70.6
(CH2(Ox)), 54.0 (NCH2CH2N), 53.6 (NCH2), 45.6 (NCH3), 33.8 (C-
A
(CH3)3); MS
A
Complex 13a: FeCl2 (0.176 g, 1.389 mmol), (S,S)-9a (0.495 g,
2(dioxane)] (136 mg, 0.606 mmol),
1.462 mmol), MeCN (10 mL), yield: 0.47 g (73%). MS(FAB): m/z (%):
A
(S,R,R,S)-10a (0.250 g, 0.637 mmol), MeCN (3 mL), yield: 160 mg
(50%). 1H NMR (500 MHz, CD2Cl2, 258C): d=4.85 (bd, 1H; CHH),
4.67 (m, 1H; OCHH), 4.45 (m, 4H; 3H of OCH2 and 1H from CHH),
429 (100) [MÀCl]+; elemental analysis calcd (%) for C18H34Cl2FeN4O2
(465.25): C 46.47, H 7.37, N 12.04; found: C 46.20, H 7.10, N 12.02. Crys-
tals suitable for X-ray analysis were grown in a MeCN/Et2O solution at
room temperature.
4.32 (m, 1H; NCH
NCHCH2CH2), 3.13 (d, J
17.0 Hz, 1H; CHH), 2.49 (m, 1H; NCHCH2CH2), 2.45 (s, 3H; NCH3),
2.26 (s, 3H; NCH3), 2.13 (m, 1H; CH(CH3)2), 1.94–1.81 (overlapping m,
3H, NCHCH2CH2, CH(CH3)2), 1.72 (m, 1H; NCHCH2CHH), 1.62 (m,
(iPr)), 4.02 (m, 1H; NCH
A
2
2
ACHTREUNG
N
Preparation of OTf and SbF6 salts 14a,b–16a,b—synthesis of 15a(OTf)2:
G
AgOTf (0.16 g, 0.623 mmol) was added to a solution of 13a (0.149 g,
0.320 mmol) in MeCN (5 mL) at room temperature. The reaction mixture
was stirred for 2 d protected from light by aluminum foil. The solid was
filtered off and the red-brown solution concentrated to ꢀ0.5 mL. Et2O
was added to precipitate a light brown solid, which was dried in vacuo to
AHCTREUNG
ACHTREUNG
1H; NCHCH2CHH), 1.45 (bm, 2H; NCHCH2CHH overlapping with
NCHCHHCH2), 1.28 (m, 1H; NCHCHHCH2), 1.07 (m, 1H;
NCHCH2CHH), 0.89 (d, 3J
(H,H)=6.9 Hz, 3H; CH
7 Hz, 6H; CH
(CH3)2); 13C NMR (125 MHz, CD2Cl2, 258C): d=174.5
(C=N(Ox)), 172.7 (C=N(Ox)), 72.2 (CH2(Ox)), 71.2 (CH2(Ox)), 66.8
(NCH(iPr)), 65.7 (NCH(iPr)), 62.9 (NCH of cyclohexane), 62.5 (NCH of
cyclohexane), 54.0 (CH2), 49.1 (CH2), 45.1 (NCH3), 37.9 (NCH3), 30.7
(CH(CH3)2), 30.4 (CH(CH3)2), 24.6 (NCHCH2CH2), 23.8 (NCHCH2CH2),
23.5 (NCHCH2CH2), 23.2 (NCHCH2CH2), 19.4 (CH(CH3)2), 18.7 (CH-
(CH3)2); MS(FAB): m/z (%):
A
ACHTREUNG
yield 190 mg (86%) of 15a
C
G
G
G
ACHTREUNG
ACHTREUNG
C 34.69, H 4.95, N 8.09; found: C 34.95, H 5.37, N 7.90.
Complex 15a
0.314 mmol), MeCN (5 mL), yield: 220 mg (74%) of an orange solid.
MS
A
A
ACHTREUNG
A
N
ACHTREUNG
mental analysis calcd (%) for C18H34F12FeN4O2Sb2·1MeCN (906.9): C
AHCTREUNG
26.49, H 4.11, N 7.72; found: C 26.13, H 4.12, N 8.35.
(CH3)2), 14.6 (CH
(CH3)2), 14.4 ppm (CH
A
ACHTREUNG
491 (100) [MÀCl]+.
Complex 15b(SbF6)2: AgSbF6 (0.118 g, 0.343 mmol), 13b (0.100 g,
U
0.203 mmol), MeCN (3 mL), yield: 123 mg (75%) of an orange solid. El-
emental analysis calcd (%) for C20H38F12FeN4O2Sb2·1.5MeCN (955.45): C
28.91, H 4.48, N 8.06; found: C 29.14, H 4.75, N 7.78.
Complex (S,R,R,S)-17b: [ZnCl2(dioxane)] (77 mg, 0.343 mmol),
T
(S,R,R,S)-10b (0.150 g, 0.357 mmol), MeCN (2 mL), yield: 70 mg (37%).
1H NMR (500 MHz, CD2Cl2, 258C): d=4.58 (m, 1H; OCHH of coordi-
nated oxazoline [Oxc]), 4.45 (m, 1H; OCHH [Oxc]), 4.30 (d, 1H; endo-H
Fe
0.205 mmol), MeCN (2 mL), yield: 0.12 g (74%) of a yellowish solid. MS-
(FAB): m/z (%): 441 (100) [(9b)Fe(F)]+; elemental analysis calcd (%)
A
of CH2) overlapping with 4.29 (m, 1H; NCH
U
AHCTREUNG
ping with 4.03 (m, 1H; OCHH [Oxn]), 3.61 (m, 1H; NCH(tBu) [Oxn])
for C22H38F12FeN4O2P2·2MeCN (794.33): C 36.29, H 5.58, N 10.58; found:
C 36.03, H 5.47, N 10.73. Crystals suitable for X-ray analysis were grown
from a saturated acetonitrile solution at room temperature.
overlapping with 3.60 (m, 1H; NCH of cyclohexane), 3.29 (d, 2J
2
17.2 Hz, 1H; CHH), 2.85 (d, J
(H,H)=16.7 Hz, 1H; exo-H of CH2), 2.74
(dt, 3J
G
G
Preparation of dichloro–manganese and –iron complexes of ligands
10a,b—synthesis of (S,R,R,S)-18a(Cl)2: MnCl2 (0.076 g, 0.60 mmol) was
added to a solution of (S,R,R,S)-10a (0.240 g, 0.611 mmol) in MeCN
(5 mL). The resulting slightly orange solution was stirred at room temper-
ature overnight. Volatiles were removed in vacuo and THF (5 mL) was
added and then evaporated. This procedure was repeated twice to give a
colorless solid, which was washed with Et2O (5 mL) and dried in vacuo;
(s, 3H; NCH3), 2.48 (s, 3H; NCH3), 2.20 (m, 1H; NCHCHHCH2), 1.97
(m, 1H; NCHCHHCH2), 1.87 (m, 1H; NCHCH2CHH), 1.83 (m, 1H;
NCHCH2CHH), 1.30 (m, 1H; NCHCHHCH2), 1.21 (m, 1H;
NCHCH2CHH), 1.13 (m, 1H; NCHCH2CHH), 1.10 (m, 1H;
NCHCHHCH2), 1.0 (s, 9H;
C
(CH3)3), 0.84 ppm (s, 9H;
C(CH3)3);
A
13C NMR (125 MHz, CD2Cl2, 258C): d=173.3 (C=N [Oxc]), 164.7 (C=N
[Oxn]), 76.9 (CH [Oxn]), 73.8 (CH2 [Oxc]), 70.7 (CH [Oxc]), 68.4 (CH2
[Oxn]), 63.1 (NCH of cyclohexane), 60.1 (NCH of cyclohexane), 51.7
yield: 0.22 g (70%). MS
analysis calcd (%) for C22H40Cl2MnN4O2 (518.42): C 50.97, H 7.78, N
10.81; found: C 50.73, H 7.91, N 10.42.
A
(CH2), 48.6 (CH2), 45.2 (NCH3), 41.7 (NCH3), 34.8 (C
(C
(CH3)3 [Oxn]), 26.3 (C(CH3)3 [Oxn]), 26.2 (C(CH3)3 [Oxc]), 25.8
(NCHCH2CH2), 25.2 (NCHCH2CH2), 24.7 (NCHCH2CH2), 23.2 ppm
(NCHCH2CH2); MS
(FAB): m/z (%): 519 (100) [MÀCl]+.
Complex (R,R,R,R)-20: [ZnCl2(dioxane)] (110 mg, 0.49 mmol),
A
G
A
ACHTREUNG
Complex (S,R,R,S)-18b(Cl)2: MnCl2 (0.1 g, 0.79 mmol), (S,R,R,S)-10b
(0.35 g, 0.83 mmol), MeCN (5 mL), yield: 0.3 g (67%) of colorless solid.
N
MS
A
for C24H44Cl2MnN4O2 (546.48): C 52.75, H 8.12, N 10.25; found: C 52.51,
H 8.02, N 9.96. Crystals suitable for X-ray analysis were grown in a solu-
tion of acetonitrile at room temperature.
AHCTREUNG
(R,R,R,R)-10a (0.204 g, 0.519 mmol), MeCN (3 mL), yield: 0.21 g (81%).
3
1H NMR (500 MHz, [D8]THF, À188C): d=4.38 (dd, 3J
A
Complex (S,R,R,S)-19a(Cl)2: FeCl2 (0.046 g, 0.363 mmol), (S,R,R,S)-10a
(0.150 g, 0.382 mmol), MeCN (3 mL), yield: 0.126 g (67%) of a slightly
G
G
OCHH), 3.76 (d, 2J
(H,H)=15.4 Hz, 2H; exo-H of CH2) overlapping with 3.19 (m, 2H; CH-
(CH3)2), 2.45 (s, 6H ; NCH3), 2.27 (m, 2H ; NCHCH2), 1.94 (m, 2H;
(H,H)=15.4 Hz, 2H; endo-H of CH2), 3.21 (d, 2J-
orange solid. MS
A
ACHTREUNG
calcd (%) for C22H40Cl2FeN4O2 (519.33): C 50.88, H 7.76, N 10.79; found:
C 50.07, H 7.55, N 10.17.
ACHTREUNG
NCHCHHCH2), 1.73 (m, 2H; NCHCH2CHH), 1.28 (m, 2H;
NCHCHHCH2), 1.12 (m, 2H; NCHCH2CHH), 0.90 (d, 3J
ACHTREUNG
Complex (S,R,R,S)-19b(Cl)2: FeCl2 (0.114 g, 0.903 mmol), (S,R,R,S)-10b
(0.4 g, 0.95 mmol), MeCN (4 mL), yield: 0.4 g (81%) of an off-white
3
6H; CH
(CH3)2), 0.78 ppm (d, J
(H,H)=6.8 Hz, 6H; CH
ACHTREUNG
tal analysis calcd (%) for C22H40N4O2Cl2Zn (528.87): C 49.96, H 7.62, N
solid. MS
A
8968
www.chemeurj.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 8960 – 8970

Chiral Metal Complexes
FULL PAPER
(%) for C24H44Cl2FeN4O2 (547.39): C 52.66, H 8.10, N 10.24; found: C
52.46, H 7.94, N 10.11.
finement against F was carried out on all non-hydrogen atoms using the
program CRYSTALS.[41] Chebychev polynomial weights[42] were used to
complete the refinement. CCDC-626347 (12a), -626346 (13a), -626348
Complex (R,R,R,R)-21(Cl)2: MnCl2 (0.081 g, 0.644 mmol), (R,R,R,R)-
10a (0.262 g, 0.667 mmol), MeCN (5 mL), yield: 0.27 g (81%) of a color-
(16b
N
N
the supplementary crystallographic data for this paper. These data can be
obtained free of charge from the Cambridge Crystallographic Data
Center via www.ccdc.cam.ac.uk/data_request/cif.
less solid. MS
A
calcd (%) for C22H40Cl2MnN4O2 (518.42): C 50.97, H 7.78, N 10.81;
found: C 51.04, H 7.55, N 10.71.
Preparation of the OTf and SbF6 salts (S,R,R,S)-18a,b, (S,R,R,S)-19a,b
and (R,R,R,R)-21a,b—synthesis of (S,R,R,S)-18a(OTf)2: AgOTf
G
(0.104 g, 0.405 mmol) was added to a solution of (S,R,R,S)-18a(Cl)2
(0.11 g, 0.212 mmol) in MeCN (5 mL) at room temperature. The reaction
mixture was stirred for 1 d protected from light by aluminum foil. The
colorless solid was filtered off and the volatiles removed in vacuo. THF
(5 mL) was added and then evaporated. This procedure was repeated
twice and the resulting colorless residue was washed with Et2O; yield:
Acknowledgements
We thank Dr. Axel Franzke and Dr. ClØment Mazet for 500 MHz NMR
spectra. Financial support by the Swiss National Science Foundation is
gratefully acknowledged.
64 mg (41%). MS
N
ysis calcd (%) for C24H40F6MnN4O8S2·0.5THF (781.71): C 39.95, H 5.67,
N 7.17; found: C 40.06, H 5.63, N 7.52.
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3947–3980.
Complex (S,R,R,S)-18a
18a(Cl)2 (0.231 g, 0.446 mmol), MeCN (4 mL), yield 270 mg (64%) of a
colorless solid. MS
A
A
analysis calcd (%) for C22H40F12MnN4O2Sb2·0.5meCN·0.5THF (975.6): C
30.78, H 4.70, N 6.46; found: C 30.85, H 4.87, N 6.12.
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Complex (S,R,R,S)-18b
18b(Cl)2 (0.13 g, 0.238 mmol), MeCN (5 mL), yield: 0.1 g (55%) of a col-
orless solid. MS
calcd (%) for C26H44F6MnN4O8S2 (773.72): C 40.36, H 5.73, N 7.24;
found: C 40.31, H 5.87, N 7.00.
G
U
Complex (S,R,R,S)-18b
18b(Cl)2 (0.35 g, 0.64 mmol), MeCN (7 mL), yield: 0.48 g (75%) of color-
less solid. MS
(FAB): m/z (%): 710 (100) [MÀSbF6]+, 494 (86) [(S,R,R,S-
10b)Mn(F)]+;
elemental analysis calcd (%) for
A
ACHTREUNG
C24H46F12MnN4O2Sb2·2CH3CN (1029.2): C 32.68, H 4.90, N 8.17; found:
C 32.83, H 4.89, N 8.08.
Complex (S,R,R,S)-19a
19a(Cl)2 (0.1 g, 0.192 mmol), MeCN (5 mL), yield: 0.18 g (95%) of an
orange solid. MS
(FAB): m/z (%): 683 (15) [MÀSbF6]+, 467 (17)
[(S,R,R,S-10a)Fe(F)]+;
elemental analysis calcd (%) for
A
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ACHTREUNG
C22H40F12FeN4O2Sb2·CH3CN·0.5Et2O (998.04): C 31.29, H 4.85, N 7.02;
found: C 31.25, H 4.90, N 7.23.
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Complex (S,R,R,S)-19b
19b(Cl)2 (0.2 g, 0.365 mmol), MeCN (4 mL), yield: 270 mg (76%) of a
colorless solid. MS
(FAB): m/z (%): 711 (30) [MÀSbF6]+, 495 (100)
[(S,R,R,S-10b)Fe(F)]+;
elemental analysis calcd (%) for
C24H44F12FeN4O2Sb2·CH3CN (989.03): C 31.57, H 4.79, N 7.08; found: C
31.47, H 4.88, N 7.03.
(SbF6)2: AgSbF6 (0.248 g, 0.722 mmol), (S,R,R,S)-
ACHTREUNG
Complex (R,R,R,R)-21
21(Cl)2 (0.12 g, 0.230 mmol), MeCN (5 mL), yield: 126 mg (76%) of col-
orless solid. MS
A
A
calcd (%) for C24H40F6MnN4O8S2 (745.66): C 38.66, H 5.41, N 7.51;
found: C 38.90, H 5.46, N 7.38.
Epoxidation procedure: To a solution of alkene (0.2 mmol, 0.2m) and cat-
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through a plug of silica gel. Conversion and yields were determined
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N
E
tals were measured on a Enraf Nonius Kappa CCD diffractometer at
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Received: May 31, 2007
Published online: August 23, 2007
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