New pyridylene-bridged bisoxazoles - Synthesis and structural study

Article abstract of DOI:10.1515/znb-2011-0213

The bisoxazoles 1a - 1c that feature structures with two oxazole moieties connected to a 2,6- pyridylene central linker and contain different aryl substituents in 4- and 5-positions of the oxazole rings have been synthesized. Single-crystal X-ray structur

Full text of DOI:10.1515/znb-2011-0213

New Pyridylene-bridged Bisoxazoles – Synthesis and Structural Study
Marika Felsmann, Jo¨rg Hu¨bscher, Frank Eißmann, Wilhelm Seichter, and Edwin Weber
Institut fu¨r Organische Chemie, Technische Universita¨t Bergakademie Freiberg, Leipziger Str. 29,
09596 Freiberg/Sachsen, Germany
Reprint requests to Prof. Dr. Edwin Weber. Fax: +49 (0)3731 393170.
E-mail: Edwin.weber@chemie.tu-freiberg.de
Z. Naturforsch. 2011, 66b, 197 – 204; received September 27, 2010
The bisoxazoles 1a – 1c that feature structures with two oxazole moieties connected to a 2,6-
pyridylene central linker and contain different aryl substituents in 4- and 5-positions of the oxazole
rings have been synthesized. Single-crystal X-ray structure determinations of the free ligand 1a, con-
taining the NiCl2 complex of 1c as the CH3COOH solvate as well as the 1,4-dioxane-solvated di-
ester intermediate 2a are reported, which show specific molecular conformations and packings in the
crystals. The conformation of 1a is syn with reference to the oxazole nitrogen atoms and anti with
reference to the oxazole and pyridine nitrogen atoms. In the Ni2+ complex, the metal ion is in an oc-
tahedral coordination environment with the nitrogens of 1c and an oxygen of an acetic acid molecule
in the basal plane, while two chloride ions occupy the axial positions of three additional acetic acid
molecules one is hydrogen-bonded to a chloride and two form a carboxylic dimer, thus giving rise
to a 1 : 1 : 4 (1c : NiCl2 : HOAc) stoichiometric ratio. The crystalline 1 : 1 inclusion compound of 2a
with 1,4-dioxane suggests a typical clathrate owing to the bulkyness of the host molecule.
Key words: Pyridine Derivatives, Oxazole Derivatives, Nickel, Coordination Compound,
X-Ray Diffraction Analysis
Introduction
Aryl-substituted oxazoles are an interesting class of
compounds due to their high fluorescence [1]. Ow-
ing to this property, some particular 2,5-diaryloxazoles
have found commercial application as solutes in
liquid scintillators [2] and as optical brighten-
ing agents [3]. A well-known compound of this
type is 1,4-bis(5-phenyloxazol-2-yl)benzene, usually
termed POPOP [4]. On the other side, analogous
bis(benzoxazole)s featuring a 2,6-substituted pyridine
ring as a linker between the benzoxazole moieties, thus
corresponding to the tridentate 2,2ꢀ,6ꢀ,2ꢀꢀ-terpyridine
structure, have proven to be effective ligands for the
complexation of Fe(II) and Zn(II) [5] or as receptors
for dialkylammonium cations [6]. They have also been
used for the separation of lanthanides and actinides [7],
and as ancillary ligands for the formation of particular
ruthenium [8] or model copper-dioxygen complexes
[9]. However, as far as we know, bisoxazoles having
a central 2,6-pyridylene bridge and aryl residues at-
tached to the 4- and 5-positions of the oxazole units,
such as illustrated in Scheme 1, are not documented
Scheme 1. The bisoxazoles studied in this paper.
this substance type is mentioned as a potential sensi-
tizer in a recent patent [10].
Here we describe the synthesis of the bisoxazoles
1a – c (Scheme 1) and report on the X-ray crystal
structures of bisoxazole 1a, the complex of 1c with
nickel(II) chloride and also the diester intermediate 2a.
Results and Discussion
Compound preparation
Although there are different methods for the prepa-
in the literature. Only one special compound related to ration of oxazoles in general [11, 12], only a very lim-
c
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M. Felsmann et al. · New Pyridylene-bridged Bisoxazoles
Scheme 2. Synthetic pathway for the
preparation of the bisoxazoles.
ited number among them give potential access [13 –
15] to the compounds under consideration (Scheme 1).
Perhaps the most promising one makes use of a ring
condensation reaction between a 2-acyl ketone and am-
monium acetate in acetic acid [16, 17], developed in
close analogy to the Paal-Knorr cyclization [18]. Em-
ployment of the respective bis(ketoester)s 2a – c under
the mentioned conditions successfully indeed yielded
the corresponding bisoxazoles 1a – c (Scheme 2). The
bis(ketoester)s 2a – c were synthesized from benzoins
3a – c and acid dichloride 4 following a procedure for
related compounds [17]. The benzoins 3a – c were ob-
tained by the usual benzoin condensation [19] from
the respective benzaldehyde. The Ni2+ complex of
1c, [Ni(1c)Cl2(HOAc)] · 3HOAc, was prepared from
1c and NiCl2 · 6H2O in acetic acid, and the inclusion
complex 2a · 1,4-dioxane was obtained on crystalliza-
tion of 2a from this solvent.
Fig. 2. Packing diagram of 2a · 1,4-dioxane (1 : 1). Oxygen
atoms are displayed as dotted, nitrogen atoms as hatched and
carbon atoms of the guest molecules as grey circles. Broken
lines represent hydrogen bond interactions.
information about the molecular structures and pack-
ing behavior of the various components in the solid
state. Crystal and refinement data are summarized in
Table 1. Perspective views of the molecular structures
including the numbering schemes of atoms are shown
in Figs. 1, 3 and 5. In order to simplify structural char-
acterizations, the rings of the molecules are marked
by capital letters in the illustrations of the molecular
structures. Packing diagrams are presented in Figs. 2
and 4, while Fig. 6 presents the basic supramolecular
unit of 1c. Following the course of the synthesis, the
structures of the compounds are described in the order
2a · 1,4-dioxane (1 : 1), 1a and 1c · NiCl2 · 4AcOH.
The 1 : 1 complex of the diester 2a with 1,4-dioxane,
the structure of which is displayed in Fig. 1, crystal-
X-Ray diffraction studies
The crystal structures of the compounds 1a,
1c · NiCl2 · 4AcOH and 2a · 1,4-dioxane (1 : 1), have
been determined from single crystals in order to collect
¯
lizes as colorless plates in the space group P1 with
Z = 2. The two CO2 fragments within the pyridine-
2,6-dicarboxylate unit are twisted in the same direc-
tion at angles of 12.9(3) and 13.5(3)◦ with respect
to the mean plane of the pyridine ring. The inter-
planar angles between the terminal phenyl rings are
84.0(1)◦ for the pair of rings A/B and 83.2(1)◦ for
Fig. 1. Perspective view of 2a · 1,4-dioxane (1 : 1), including
numbering scheme of atoms and ring specification. Displace- A’/B’. The torsion angles C(1)–C(2)–O(2)–C(15) and
C(24)–C(23)–O(5)–C(22) are 73.3(2) and −79.8(2)◦,
ment ellipsoids are at the 50 % probability level.
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M. Felsmann et al. · New Pyridylene-bridged Bisoxazoles
199
Fig. 4. Packing diagram of 1a viewed along the crystallo-
graphic b axis. Broken double lines represent aromatic face-
to-face interactions.
Fig. 3. Perspective view of 1a, including numbering scheme
of atoms and ring specification. Displacement ellipsoids are
at the 50 % probability level.
◦
˚
rings [C(12)–H(12)···centroid(B) 2.95 A, 142.9 ] and
πpyridine ···πoxazole interactions [24] with a distance of
˚
respectively. Compound 2a has opposite chirality at
the stereogenic centers C(2) and C(23). This means,
that under the given conditions of crystal growth only
the meso-stereoisomer could be obtained in the crys-
talline state. Due to the inherent mirror symmetry
of 2a, the 1 : 1 stoichiometry of the complex of 2a
with 1,4-dioxane appears unusual as it implies an
asymmetric binding behavior of the crystal compo-
nents. The oxygen atom O(1G) of the solvent molecule
is linked via a relatively strong C–H···O hydrogen
bond [20] to the methine hydrogen H(2) [d(H···O)
3.54 A between the centroids of interacting rings. As
depicted in Fig. 4, the crystal structure of 1a is con-
structed of molecular stacks extending in direction of
the crystallographic c axis.
Crystallization of the tert-butyl-substituted bisox-
azole 1c from acetic acid in the presence of Ni(II)
chloride, in the course of three month, yields green
rods which turned out to be a complex of the composi-
tion [Ni(1c)Cl2(HOAc)]· 3HOAc. A perspective view
of the complex, which crystallizes in the space group
¯
P1 with Z = 2, is illustrated in Fig. 5. The central tri-
˚
2.40 A], while the oxygen atom O(2G) acts as a bi-
cyclic part of the complex ligand is approximately pla-
nar with largest atomic distances from the mean plane
of this fragment being 0.093(1) for C(3) and −0.074(1)
for C(16). As contrasted with 1a, in the complex of
furcated acceptor for a neighboring dioxane molecule
◦
˚
[C(3G)–H(3G2)···O(2G) 2.61 A, 158.5 ] as well as
to a further molecule of 2a [C(28)–H(28)···O(2G)
◦
˚
2.61 A, 152.2 ]. Lacking conventional strong hydro-
gen bond donors [21], the host lattice is dominated
by C–H···O=C interactions (Fig. 2) with H···O dis-
˚
tances ranging between 2.44 – 2.71 A. Contrary to ex-
pectations π ···π stacking [22] is not observed.
Crystallization of the pyridine-linked bisoxazole 1a
from chloroform yields colorless crystals of the or-
thorhombic space group Pbcn with the asymmetric
unit containing one half of the molecule. A perspective
view of the molecule is presented in Fig. 3. The hete-
rocyclic rings are inclined at an angle of 12.4(1)◦ with
respect to the plane of the pyridine ring. The dihedral
angle between the phenyl rings B and C is 41.1(1)◦.
Noteworthy, in the molecular structure of 1a, the nitro-
gen of the pyridine is flanked by the oxygens of the ox-
azole rings. Moreover, neither the pyridine nor the ox-
azole heteroatoms are involved in hydrogen bond-type
interactions. Instead, the packing of molecules is con-
trolled by multiple arene interactions. They comprise
C–H···π contacts [23] between peripheral aromatic
Fig. 5. Perspective view of [Ni(1c)Cl2(HOAc)] · 3HOAc, in-
cluding numbering scheme of atoms and ring specification.
Displacement ellipsoids are at the 50 % probability level.
Thus lines represent coordinative bonds, broken lines hydro-
gen bond-type interactions.
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M. Felsmann et al. · New Pyridylene-bridged Bisoxazoles
Fig. 6. Representation of the dimeric unit of
the Ni(II) complex of 1c. Hydrogen bond in-
teractions are displayed as broken lines; bro-
ken double lines represent arene face-to-face
interactions. Non-relevant hydrogen atoms
of the bisoxazole molecules are omitted for
clarity.
1c now the nitrogen atoms of the oxazoles are in syn cated at the periphery of these dimeric units, only van
orientation with reference to the nitrogen atom of the der Waals forces exist between these large dimers.
pyridine ring, thus giving rise to the geometry of a typ-
ical tridentate nitrogen donor ligand. The dihedral an-
gles formed by the pairs of peripheric aromatic rings
are 58.1(1) and 58.3(1)◦.
Conclusions
The bisoxazoles 1a – c featuring 2,6-pyridylene
linkers between the oxazole moieties were synthesized
in reasonable overall yields using a combination of es-
terification and ring condensation methods. With ref-
erence to the characteristic aryl substituents in the 4,5-
positions of the oxazoles, they represent a new struc-
tural type of this particular compound class. As ex-
emplary cases, the bis(oxazolyl)pyridine 1a, the Ni2+
complex of 1c, and the intermediate compound 2a,
have been studied with reference to their crystal struc-
tures, and the following features have emerged.
In the crystal structure of 1a, the molecular confor-
mation shows the nitrogen atom of the pyridine ring
flanked by the oxygen atoms of the oxazoles, and the
pyridine and oxazole units involved in intramolecular
stacking contacts.
The coordination environment of the nickel cation
shows a distorted octahedral geometry of the type
N3OCl2 with the nitrogens of the tridentate ligand and
the oxygen of one molecule of acetic acid located
in the equatorial plane, while the chloride ions oc-
cupy the axial positions of the polyhedron. The Ni–
˚
Npyridine distance is significantly shorter [2.041(1) A]
˚
than the Ni–Noxazole distances [2.208(1), 2.277(1) A];
˚
the Ni–O distance is 2.066(1) A, and the Ni–Cl bond
lengths are 2.376(1) and 2.390(1) A. The hydroxy
˚
hydrogen of the complexed acetic acid molecule is
linked to one of the chloride anions by a strong
◦
˚
hydrogen bond [O(4)–H(4)···Cl(2) 2.08 A, 171.2 ]
[21], while the second chloride is associated with a
further molecule of acetic acid [O(6)–H(6)···Cl(1)
◦
2.28 A, 172.2 ]. The location of the methyl carbon
As was to be expected, in the Ni2+ complex of 1c the
˚
of this solvent molecule near the aromatic ring B nitrogen atoms of the oxazole rings and of the pyridine
˚
of the ligand [C(55)···centroid(B) 3.45 A] indicates ring are all in syn conformation and coordinated to the
C–H···π(arene) bonding [23] which may also ex- Ni2+ ion. Thus 1c behaves as a typical tridentate lig-
plain the unusual conformation of the acid molecule and, comparable with 2,2ꢀ,6ꢀ,2ꢀꢀ-terpyridine [8] and re-
[C(55)–C(54)–O(6)–H(6) 3.0(2)◦]. The remaining two lated bisbenzoxazoles [5, 7]. However, unlike the usual
molecules of acetic acid form a slightly distorted, complexes of these latter ligands, in the present case,
non-centrosymmetric dimer [25] [O(8)–H(8)···O(9) the coordination octahedron can not be formed by us-
◦
◦
˚
˚
1.77 A, 175.0 ; O(10)–H(10)···O(7) 1.78 A, 172.0 ]. ing two of the bulkily substituted tridentate molecules
Dimeric units of the complex are formed by a relatively 1c for sterical reasons. Therefore, the three N donors
strong hydrogen bond between chloride Cl(1) and a of 1c together with an oxygen atom of an acetic acid
pyridine hydrogen of a symmetry related complex molecule are located in the equatorial plane, while two
◦
˚
molecule [26] [C(17)–H(17)···Cl(1) 2.69 A, 164.4 ] chloride ions occupy the axial positions of the coordi-
as well as by π ···π interactions [24] with a distance nation polyhedron. The second molecule of acetic acid
˚
of 3.614 A between the centroids of pyridine and ox- is hydrogen-bonded to one of the chloride ions, and
azole rings (Fig. 6). As the tert-butyl groups are lo- the remaining two acetic acid molecules form carb-
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M. Felsmann et al. · New Pyridylene-bridged Bisoxazoles
201
oxylic dimers that fill interstitial lattice space created other common reagents were purchased from commercial
sources.
in the packing of stacked complex dimers. Hence, on
the one side, the bulky p-tert-butylphenyl substituents
of 1c prevent the common coordination mode of simple
tridentate ligands and, on the other side, support lattice
inclusion of solvent molecules [27] such as acetic acid
in an unusually high 1 : 4 stoichiometric ratio.
Being in accordance with the construction principle
of a bulkily substituted clathrate host [28], the crys-
talline diester intermediate 2a also turned out to be
a 1 : 1 stoichiometric inclusion compound with 1,4-
dioxane. In this complex, the structure of 2a shows a
twisted conformation with reference to the aryl rings
and a meso configuration regarding the methine stere-
ogenic centers.
Preparation of bis(keto ester)s 2a – c
General procedure
To a refluxing solution of the corresponding benzoin
3a – c (20 mmol) and 2,6-pyridinedicarbonyl dichloride (4)
(2.04 g, 10 mmol) in dry toluene (20 mL), triethylamine
(15 mL, 0.11 mol) was slowly added during 3 h. After evap-
oration of the solvent, ethanol (10 mL) was added to the oily
residue and the mixture stirred for 2 h. The solid which was
formed was collected and crystallized. Details for the indi-
vidual compounds are given below.
2a: Compound 3a (4.24 g) was reacted. Crystallization
from 1,4-dioxane yielded 2.45 g (44 %) of colorless crystals;
m. p. 151 C. – 1H NMR (400 MHz, CDCl3): δ = 7.13 (s,
◦
This latter property invites asking whether com-
pounds of these structural types permit a development 2 H, CH), 7.35 – 7.44 (m, 10 H, Ar-H), 7.51 – 7.60 (m, 6 H,
Ar-H), 7.99 – 8.02 (m, 5 H, Ar-H), 8.35 (d, JHH = 8.0 Hz,
2 H, Ar-H). – 13C NMR (100 MHz, CDCl3): δ = 79.1, 128.5,
128.6, 128.7, 28.9, 129.1, 129.3, 133.2, 133.5, 134.5, 138.2,
147.9, 163.6, 193.2. – IR (KBr): ν = 3065, 2980, 2944, 1752,
1727, 1699, 1599, 1581, 1235, 1146, 760, 696 cm−1. – MS
(ESI): m/z = 556 (calcd. 556.4 for C35H25NO6, [M]+). –
Analysis for C35H25NO6 · H2O (573.60): calcd. C 73.29,
H 4.74, N 2.44; found C 73.51, H 4.81, N 2.80.
of a new class of clathrate hosts in general, capable of
a variety of inclusions [27, 28]. E. g., structural mod-
ification of the aryl substituents of these bisoxazoles
can lead to a tailored selectively in the complexation
of particular metal cations such as lanthanides and
actinides [7] or dialkylammonium cations [6], which
may then allow specific separations via extraction pro-
cesses [29]. In this frame, the extraction of Am(III) and
Ln(III) is mentioned as an important part of the pro-
cessing of nuclear fuel [30]. It is also an interesting as-
pect to study potential conditions where the oxazoles
tend to use the oxygen instead of the nitrogen atoms
as donors. Moreover, the compounds are promising for
their use as optical brightening agents [3] or as build-
ing blocks for light-emitting devices [31].
2b: Compound 3b (5.45 g) was reacted. Crystallization
from ethanol yielded 4.94 g (73 %) of a brownish pow-
der; m. p. 214 – 216 ◦C. – 1H NMR (400 MHz, CDCl3,
[D6]DMSO): δ = 3.78, 3.84, (2 s, 12 H, CH3), 6.89 – 6.95
3
(m, 8 H, Ar-H), 7.14 (s, 2 H, CH), 7.51 (d, JHH = 8.4 Hz,
3
4 H, Ar-H), 8.02 (d, JHH = 8.8 Hz, 4 H, Ar-H), 8.13 (t,
3
3JHH = 8.0 Hz, 1 H, Ar-H), 8.33 (d, JHH = 8.0 Hz, 2 H,
Ar-H). – 13C NMR (100 MHz, CDCl3 [D6]DMSO): δ =
53.8, 54.1, 76.8, 112.6, 113.0, 124.1, 125.6, 128.8, 129.7,
137.3, 146.4, 158.8, 162.0, 162.0, 162.3, 190.0. – IR (KBr):
ν = 3079, 2962, 2937, 2840, 1727, 1681, 1631, 1599, 1517,
1265, 1242, 1171, 1146 cm−1. – MS (ESI): m/z = 676.4
(calcd. 676.2 for C39H33NO10, [M+H]+). – Analysis for
C39H33NO10 (675.21): calcd. C 69.33, H 4.92, N 2.07; found
C 69.69, H 5.00, N 2.20.
Experimental Section
General
Melting points: Kofler melting point microscope (uncor-
rected). IR: Nicolet FT-IR 510. 1H and 13C NMR (chemi-
cal shifts δ in ppm vs. TMS as internal standard): Bruker
Avance DPX 400. MS (ESI): Quattro-LC (positive ion) and
Esquire-LC (solvent: chloroform). Elemental analysis: Her-
aeus CHN rapid analyzer. TLC analysis: aluminum sheets
precoated with silica gel 60 F254 (Merck). Toluene was dried
over sodium and freshly distilled before use. Triethylamine
was dried over potassium hydroxide.
2c: Compound 3c (6.44 g) was reacted. Crystallization
from 1,4-dioxane yielded 6.7 g (86 %) of a colorless powder;
m. p. 182 ◦C. – 1H NMR (400 MHz, CDCl3): δ = 1.28, 1.29
3
(2 s, 36 H, CH3), 7.11 (s, 2 H, CH), 7.40, 7.43 (2d, JHH
=
8.4 Hz, 8 H, Ar-H), 7.54 (d, 3JHH = 8.4 Hz, 4 H, Ar-H), 7.94 –
8.00 (m, 5 H, Ar-H), 8.34 (d, JHH = 8.0 Hz, 2 H, Ar-H). –
3
The starting benzoins 3a [32], 3b [33] and 3c [34] were 13C NMR (100 MHz, CDCl3): δ = 31.0, 31.2, 34.7, 35.1,
synthesized via benzoin condensation from the correspond- 78.7, 125.6, 126.1, 128.3, 128.4, 129.0, 130.6, 132.0, 138.0,
ing benzaldehydes following the described procedures. The 148.2, 152.4, 157.3, 163.6, 192.7. – IR (KBr): ν = 3090,
2,6-pyridinedicarbonyl dichloride (4) was prepared form 2,6- 3062, 3030, 2962, 2905, 2865, 1751, 1730, 1695, 1602,
pyridinedicarboxylic acid and thionyl chloride according to 1233, 1141 cm−1. – MS (ESI): m/z = 780 (calcd. 780.69 for
the literature method [35]. 2,6-Pyridinedicarboxylic acid and C51H57NO6, [M]+). – Analysis for C51H57NO6 · 0.5 H2O
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M. Felsmann et al. · New Pyridylene-bridged Bisoxazoles
Table 1. Crystal data and parameters pertinent to data collection and structure refinement of 1a, [Ni(1c)Cl2(HOAc)] · 3HOAc
and 2a.
Compound
1a
[Ni(1c)Cl2(HOAc)] · 3HOAc
C51H55N3O2Cl2Ni · 4 C2H4O2
1111.80
2a
Empirical formula
Formula weight, g mol−1
Crystal data
C35H23N3O2
517.56
C35H25NO6 · C4H8O2
643.66
Crystal system
orthorhombic
Pbcn
30.1367(6)
10.1127(2)
8.4746(2)
90
triclinic
P1
triclinic
P1
¯
¯
Space group
˚
a, A
13.156(2)
13.369(3)
16.826(3)
96.367(6)
99.817(5)
96.344(6)
2872.6(9)
2
9.2390(3)
10.7711(4)
17.0938(6)
80.771(3)
77.743(2)
86.650(3)
1640.26(10)
2
˚
b, A
˚
c, A
α, deg
β, deg
90
90
γ, deg
3
˚
V, A
2582.75(9)
4
Z
F(000), e
1080
1.33
0.1
1176
1.29
0.5
676
1.30
0.1
Dcalcd, Mg m−3
µ(MoKα ), mm−1
Data collection
Temperature, K
θ limits, deg
133(2)
1.3 – 29.1
153(2)
2.4 – 30.1
93(2)
2.3 – 29.4
Index ranges hkl
No. of coll. / unique refl. / Rint
No. of refl. with [I ≥ 2 σ (I)]
Refinement
−41/41, −13/11, −11/11
28675 / 3457 / 0.0271
2957
−18/18, −18/18, −23/23
46707 / 16867 / 0.0700
11213
−12/12, −14/14, −23/23
34925 / 8937 / 0.0825
4788
No. of refined parameters
R1 (F) / wR2 (F2)a,b
Weighting scheme x / yb
S (Goodness of fit on−F32)c
182
715
433
0.0442 / 0.1507
0.0806 / 0.8470
1.070
0.0385 / 0.0956
0.0391 / 0.0
0.972
0.52 / −0.39
0.0526 / 0.1516
0.0631 / 0.8486
0.923
0.34 / −0.27
˚
Final ∆ρmax/min, e A
0.38 / −0.32
a
2
R1 = ΣꢁFo|−|Fcꢁ/Σ|Fo|; b wR2 = [Σw(Fo −Fc2)2/Σw(Fo2)2]1/2, w = [σ2(Fo2) + (xP)2 + yP]−1, where P = (Max(Fo2, 0)+2Fc2)/3;
c
2
GoF = [Σw(Fo −Fc2)2/(nobs −nparam)]1/2
.
(788.43): calcd. C 77.63, H 7.41, N 1.78; found C 77.50, IR (KBr): ν = 3051, 3033, 1677, 1606, 1592, 1502, 1028
H 7.50, N 2.02.
cm−1. – MS (ESI): m/z = 518 (calcd. 518.0 for C35H23N3O2,
[M]+). – Analysis for C35H23N3O2 · 0.5 H2O (526.77):
calcd. C 79.83, H 4.59, N 7.98; found C 79.68, H 4.97,
N 8.36.
Preparation of bisoxazoles 1a – c
General procedure
1b: Compound 2b (5.06 g) was used for the reaction. Af-
The corresponding bis(ketoester)s 2a – c (7.5 mmol) and ter cooling the reaction mixture to r. t., water (55 mL) was
ammonium acetate (3.46 g, 45 mmol) were dissolved in conc. added followed by aqueous sodium hydrogen carbonate for
acetic acid (55.0 mL) and refluxed for 3.5 h. Work-up of the
neutralization. The organic layer was separated, washed with
reaction mixture, purification methods and other details for water and treated with n-hexane to form a solid. Crystalliza-
the individual compounds are given below.
tion from 1,4-diox◦ane yielded 1.15 g (24 %) of a pale-yellow
powder; m. p. 68 C. – 1H NMR (400 MHz, CDCl3): δ =
3.83 (s, 12 H, CH3), 6.87 – 6.97 (m, 10 H, Ar-H), 7.48 – 7.56
(m, 9 H, Ar-H). – 13C NMR (100 MHz, DCCl3): δ = 55.3,
55.3, 114.0, 114.1, 121.0, 125.2, 127.9, 129.0, 132.4, 133.8,
144.6, 159.3, 159.6. – IR (KBr): ν = 3047, 2997, 2958, 2930,
2833, 1590, 1520, 1498, 1251, 1034, 833 cm−1. – MS (ESI):
m/z = 638 (calcd. 638.0 for C39H31N3O6, [M]+). – Analysis
for C39H31N3O6 · 3.5 H2O (700.92): calcd. C 66.83, H 5.46,
N 6.02; found C 66.66, H 5.26, N 6.01.
1a: Compound 2a (4.17 g) was used for the reaction.
The hot reaction mixture was poured into ice (150 mL) and
neutralized with aqueous ammonia. The precipitate which
was formed was collected, washed several times with wa-
ter and dried. Crystallization from 1,4-dioxane yielded 1.0 g
◦
1
(26 %) of colorless crystals; m. p. 215 – 218 C. – H NMR
(400 MHz, CDCl3): δ = 7.35 – 7.43 (m, 12 H, Ar-H),
3
7.75 – 7.78 (m, 8 H, Ar-H), 7.97 (t, JHH = 7.9 Hz, 1 H,
3
Ar-H), 8.30 (d, JHH = 7.9 Hz, 2 H, Ar-H). – 13C NMR
(100 MHz, CDCl3): δ = 123.1, 127.2, 128.1, 128.3, 128.6,
1c: Compound 2c (5.84 g) was used for the reaction. Af-
128.6, 128.9, 132.1, 137.2, 137.8, 146.4, 147.3, 158.5. – ter cooling of the reaction mixture to r. t., the precipitate
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M. Felsmann et al. · New Pyridylene-bridged Bisoxazoles
203
which was formed was collected, neutralized with aqueous ter with graphite-monochromatized MoKα radiation (λ =
˚
sodium hydrogen carbonate, washed several times with wa- 0.71073 A) using ω and φ scans. Reflections were corrected
ter and dried. Crystallization from 1,4-dioxane yielded 4.33 g for background, Lorentz and polarization effects. Prelimi-
(78 %) of a colorless powder; m. p. 315 ◦C. – 1H NMR nary structure models were derived by application of Direct
(400 MHz, CDCl3): δ = 1.33 (s, 36 H, CH3), 7.44 (d, 3JHH
=
Methods [36], and the structures were refined by full-matrix
8.4 Hz, 8 H, Ar-H), 7.72 – 7.76 (m, 8 H, Ar-H), 7.96 (t, least-squares calculation based on F2 for all reflections [36].
3
3JHH = 7.6 Hz, 1 H, Ar-H), 8.29 (d, JHH = 7.6 Hz, 2 H, With the exception of H(8) and H(10) in the structure of
Ar-H). – 13C NMR (100 MHz, DCCl3): δ = 31.2, 31.3, 34.7, [Ni(1c)Cl2(HOAc)] · 3HOAc, all other hydrogen atoms were
34.8, 123.0, 125.5, 125.6, 125.7, 126.0, 126.8, 127.8, 129.5, included in the models in calculated positions and were re-
136.8, 137.6, 146.6, 147.2, 151.3, 152.1, 158.3. – IR (KBr): fined as constrained to the bonding atoms.
ν = 3087, 3069, 3037, 2962, 2905, 2869, 1627, 1570, 1495,
The crystal data and parameters pertinent to data collec-
1267, 839 cm−1. – MS (ESI): m/z = 742 (calcd. 742.5 for tion and structure refinement of the compounds studied are
C51H55N3O2, [M]+. – Analysis for C51H55N3O2 · 0.5 H2O summarized in Table 1.
(751.20): calcd. C 81.54, H 7.51, N 5.62; found C 81.07,
H 7.47, N 5.54.
Supplementary material
CCDC 781694, 781695 and 781696 contain the crys-
tallographic data for 1a, [Ni(1c)Cl2(HOAc)] · 3 HOAc and
2a, respectively. These data can be obtained free of charge
from the Cambrigde Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data request/cif.
Further details on the crystal structures, including tables
of structure parameters and geometric parameters for non-
covalent contacts are given as Supplementary Material avail-
able online (www.znaturforsch.com/ab/v66b/c66b.htm).
X-Ray structure determinations
Single crystals of 1a were grown by slow isothermal
evaporation of saturated solutions in chloroform, 2a · 1,4-
dioxane on crystallization of 2a from 1,4-dioxane. Single
crystals of the metal complex [Ni(1c)Cl2(HOAc)] · 3HOAc
were obtained by isothermal evaporation of a saturated solu-
tion of 1c and nickel(II) chloride in acetic acid. The inten-
sity data were collected on a Bruker APEX II diffractome-
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204
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S1
New Pyridylene Bridged Oxazoles – Synthesis and Structural Study
Marika Felsmann, Jörg Hübscher, Frank Eißmann, Wilhelm Seichter, and Edwin Weber
Institut für Organische Chemie, TU Bergakademie Freiberg, Leipziger Straße 29, D-09596
Freiberg/Sachsen, Germany
Supplementary Material
Table S1. Interplanar angles (°) of aromatic units in the compounds studied.
Table S2. Geometric parameters of the Ni(II) involved interactions in [Ni(1c)Cl2(HOAc)] ·
HOAc.
Table S3. Geometric parameters for non-covalent contacts in the compounds studied.
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S2
Table S1. Interplanar angles (°) of aromatic units in the compounds studied.
[Ni(1c)Cl2(HOAc)] · 3HOAc
Compound
1a
2a
Interplanar angles
A/B
25.2(1)
32.0(1)
12.4(1)
41.1(1)
44.9(1)
48.9(1)
22.9(1)
24.5(1)
6.9(1)
A'/B'
A/C
85.0(1)
64.9(1)
A’/C’
A/D
A’/D
B/C
2.5(1)
58.1(1)
58.3(1)
82.7(1)
58.2(1)
B’/C’
Table S2. Geometric parameters of the Ni(II) involved interactions in
[Ni(1c)Cl2(HOAc)] · 3HOAc.
Bond lengths (Å)
Bond angles (°)
Ni(1)–N(1)
Ni(1)–N(2)
Ni(1)–N(3)
Ni(1)–O(3)
Ni(1)–Cl(1)
Ni(1)–Cl(2)
2.277(1)
2.041(1)
2.208(1)
2.066(1)
2.376(1)
2.390(1)
N(1)–Ni(1)–N(3)
N(2)–Ni(1)–O(3)
Cl(1)–Ni(1)–Cl(2)
154.0(1)
179.6(1)
179.5(1)
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S3
Table S3. Geometric parameters for non-covalent contacts in the compounds studied.
Atoms involved
D–H···A
Symmetry
Distance (Å)
Angle (°)
D–H···A
D···A
H···A
1a
C(12)–H(12)···centroid(ring B)a
x, –y, 0.5+z
3.756(3)
2.95
143
[Ni(1c)Cl2(HOAc)]·3HOAc
O(4)–H(4)···Cl(2)
x, y, z
2.917(2)
3.116(2)
3.616(2)
2.613(2)
2.632(2)
3.303(2)
3.540(2)
3.626(2)
3.447(3)
3.802(3)
3.405(3)
2.08
2.28
2.69
1.77
1.78
2.66
2.73
2.66
2.89
2.84
2.59
171
172
164
175
172
125
144
166
117.1
166
139
O(6)–H(6)···Cl(1)
x, y, z
C(17)–H(17)···Cl(1)
1–x, 1–y, 1–z
x, y, z
O(8)–H(8)···O(9)
O(10)–H(10)···O(7)
x, y, z
C(19)–H(19)···O(5)
1+x, y, z
C(28)–H(28)···O(7)
–x, 1–y, 1–z
1+x, –1+y, 1+–z
1–x, 1–y, 1–z
x, y, z
C(51)–H(51B)···O(10)
C(55)–H(55B)···centroid(ring B)a
C(57)–H(57B)···centroid(ring C)a
C(43A)–H(43E)···C(3)b
1–x, 2–y, 1–z
2a
C(26)–H(26)···O(1)
C(11)–H(11)···O(3)
C(6)–H(6)···O(3)
C(23)–H(23)···O(4)
1–x, 2–y, 1–z
1–x, y, z
3.213(3)
3.466(3)
3.327(3)
3.364(3)
2.54
2.71
2.63
2.52
128
137
130
142
2–x, 2–y, –z
1–x, 1–y, 1–z
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S4
C(34)–H(34)···O(4)
C(21)–H(21)···O(6)
C(2)–H(2)···O(1G)
C(28)–H(28)···O(2G)
C(3G)–H(3G2)···O(2G)
–x, 1–y, 1–z
–1+x, y, z
1+x, y, z
3.112(3)
2.956(3)
3.394(3)
3.481(3)
3.552(3)
2.47
2.44
2.40
2.61
2.61
124
114
173
152
158
x, y, 1+z
1–x, 1–y, –z
a
Means centre of the aromatic ring. Ring B: C(4)…C(9), ring C: C(10)…C(15), ring B’:
C(25)…C(30), ring C’: C(31)…C(36).
b
To achieve a reasonable hydrogen bond geometry, an individual atom instead the ring
centroid was chosen as acceptor
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