The formation of overlooked compounds in the reaction of methyl amine with the diethyl ester of o-phenylenebis(oxamic acid) in MeOH

Article abstract of DOI:10.1039/c2dt32259e

The treatment of the diethyl ester of o-phenylenebis(oxamic acid) (opbaH₂Et₂) with 2/3 of an equivalent of MeNH₂ in MeOH does not result in the formation of the methyl ester of o-phenylene(N′-methyloxamide)(oxamic acid) (opooH₃Me, 1) in pure state, as reported previously. The colourless crude material formed by this reaction was confirmed to be composed of 1 (89% content), the dimethyl ester of o-phenylenebis(oxamic acid) (opbaH₂Me₂, 2, 6%), 1,4-dihydro-2,3-quinoxalinedione (3, 3%) and o-phenylenebis(N′- methyloxamide) (opboH₄Me₂, 4, 1%), respectively. The identities of 1-4 have been verified by IR, ¹H and ¹³C NMR spectroscopy as well as elemental analysis. In addition, the solid state structures of 1 and 2·2DMSO, respectively, were determined by single-crystal X-ray diffraction studies. Successive recrystallization of the crude material from MeOH and MeOH : THF (1 : 1), respectively, does not give pure 1, but a mixture of 1 and 2. It is shown further that out of this mixture pure bis(oxamato) complexes cannot be obtained, as previously reported. Instead, treatment of the mixture with Ni^II or Cu^II salts, followed by the addition of [ⁿBu₄N]OH, results in the formation of two mixtures of [ⁿBu₄N]₂[Ni(opba)] (5) and [ⁿBu₄N]₂[Ni(opooMe)] (6) as well as [ⁿBu₄N]₂[Cu(opba)] (7) and [ⁿBu ₄N]₂[Cu(opooMe)] (8), respectively. The simultaneous formation of 5/6 and 7/8, respectively, has been verified by crystallization of the obtained mixtures and X-ray diffraction studies of the obtained single crystals. Co-crystallization of mixtures of 5/6 (99 mass%) and 7/8 (1 mass%), respectively, results in the formation of single-crystals of diamagnetically diluted 7 in the host lattice of 5 (7@5) accompanied by single-crystal formation of diamagnetically diluted 8 in the host lattice of 6 (8@6), as verified by EPR spectroscopy. It is finally shown that the ethyl ester of o-phenylene(N′- methyloxamide)(oxamic acid) (opooH₃Et, 9), a homologue of 1, can be obtained in pure state by the treatment of opbaH₂Et₂ with 5/6 of an equivalent of MeNH₂ in EtOH. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c2dt32259e

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The formation of overlooked compounds in the
reaction of methyl amine with the diethyl ester of
Cite this: Dalton Trans., 2013, 42, 1798
o-phenylenebis(oxamic acid) in MeOH†
Mohammad A. Abdulmalic,a Azar Aliabadi,b Andreas Petr,b Vladislav Kataevb and
Tobias Rüffer*a
The treatment of the diethyl ester of o-phenylenebis(oxamic acid) (opbaH2Et2) with 2/3 of an equivalent
of MeNH2 in MeOH does not result in the formation of the methyl ester of o-phenylene(N’-methylox-
amide)(oxamic acid) (opooH3Me, 1) in pure state, as reported previously. The colourless crude material
formed by this reaction was confirmed to be composed of 1 (89% content), the dimethyl ester of o-phe-
nylenebis(oxamic acid) (opbaH2Me2, 2, 6%), 1,4-dihydro-2,3-quinoxalinedione (3, 3%) and o-phenylene-
bis(N’-methyloxamide) (opboH4Me2, 4, 1%), respectively. The identities of 1–4 have been verified by IR,
1H and 13C NMR spectroscopy as well as elemental analysis. In addition, the solid state structures of 1 and
2·2DMSO, respectively, were determined by single-crystal X-ray diffraction studies. Successive recrystalliza-
tion of the crude material from MeOH and MeOH : THF (1 : 1), respectively, does not give pure 1, but a
mixture of 1 and 2. It is shown further that out of this mixture pure bis(oxamato) complexes cannot be
obtained, as previously reported. Instead, treatment of the mixture with NiII or CuII salts, followed by the
addition of [nBu4N]OH, results in the formation of two mixtures of [nBu4N]2[Ni(opba)] (5) and
[nBu4N]2[Ni(opooMe)] (6) as well as [nBu4N]2[Cu(opba)] (7) and [nBu4N]2[Cu(opooMe)] (8), respectively.
The simultaneous formation of 5/6 and 7/8, respectively, has been verified by crystallization of the
obtained mixtures and X-ray diffraction studies of the obtained single crystals. Co-crystallization of mixtures
of 5/6 (99 mass%) and 7/8 (1 mass%), respectively, results in the formation of single-crystals of diamagneti-
cally diluted 7 in the host lattice of 5 (7@5) accompanied by single-crystal formation of diamagnetically
diluted 8 in the host lattice of 6 (8@6), as verified by EPR spectroscopy. It is finally shown that the ethyl
ester of o-phenylene(N’-methyloxamide)(oxamic acid) (opooH3Et, 9), a homologue of 1, can be obtained in
pure state by the treatment of opbaH2Et2 with 5/6 of an equivalent of MeNH2 in EtOH.
Received 7th August 2012,
Accepted 25th October 2012
DOI: 10.1039/c2dt32259e
www.rsc.org/dalton
form monometallic complexes.1 Due to the flexidentate prop-
erties of these complexes, that is, to bind exogenous further
Introduction
o-Arylene or alkylene bis(oxamate or oxamide) derivatives re- metal ions via the exo-cis oxygen atoms, many kinds of bi- and
present versatile synthetic building blocks and have been trinuclear as well as polymeric complexes are achievable.
broadly used as tetradentate ligands.1 These compounds are These complexes are of manifold interest, for example, due to
able to coordinate metal ions via the N2O2 or N4 donor sets to their supramolecular relevance or in the field of materials
sciences.1
Already in 1936, Gaade2 synthesized diethyl-N,N′-ethylene-
aTechnische Universität Chemnitz, Fakultät für Naturwissenschaften, Strasse der
bis(oxamate) as a first example of a starting material for the
preparation of CuII–bis(oxamato) complexes. In general, the
Nationen 62, D-09111 Chemnitz, Germany.
E-mail: tobias.rueffer@chemie.tu-chemnitz.de
treatment of appropriate diamines with two equivalents of
bLeibniz-Institut für Festkörper- und Werkstoffforschung IFW Dresden, PF 27 01 16,
ethyloxalyl chloride or an excess of diethyl oxalate in the case
D-01171 Dresden, Germany
†Electronic supplementary information (ESI) available: Fig. S1–S15 give the 1H,
13C NMR and IR spectra, respectively, of analyzed material and synthesized com-
pounds. Fig. S16 gives an optical photograph of different kinds of single-crystals
of diamagnetically diluted complexes. Transesterification reactions in the
context of the investigated reaction are summarized in S17. CCDC
888732–888735. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c2dt32259e
of aliphatic diamines leads to diethyl-N,N′-diaminoalkylene- or
arylene-bis(oxamates), of which a broad variety has been
already synthesized.2–10
A survey of perhaps the simplest heteroatomsubstituted
derivatives of diethyl-bis(oxamates), namely the bis(oxamides),
in which the two O–Et groups are replaced by N(H)–R
1798 | Dalton Trans., 2013, 42, 1798–1809
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Scheme 1 Utilization of opbaH2Et2 for the synthesis of its derivatives 1 and 4 and their CuII complexes.11a
(R = alkyl) groups, reveals astonishingly few reports.11,12 The hydrogen atoms refers to N–H bonded ones.11a The use of this
synthesis of opboH4Me2 (4), obtained by the treatment of abbreviation is incorrect. Furthermore, information given in
opbaH2Et2 with an excess of MeNH2, was reported in 1997, cf. the experimental part implies a yield of 90%, although
Scheme 1.11a Out of the bis(oxamide) 4, the corresponding opbaH2Et2 was treated with 2/3 of an equivalent of MeNH2,
CuII complex was synthesized and subsequently oxidized to its which should result in a maximum yield of 66%.11a The higher
corresponding CuIII complex.11a The same report describes yield of 1 then implies the presence of further compounds in
that the treatment of opbaH2Et2 with substoichiometric the isolated material taken for pure 1.11a This listing makes
amounts of MeNH2 in MeOH should result in the exclusive for- already clear that the synthesis of 1 reported so far in the litera-
mation of opooH3Me2 (1), cf. Scheme 1. Starting from 1 in a ture11a,b cannot give rise to pure 1 without additional effort. Our
supposed pure state, the synthesis of the corresponding CuII initial studies to access pure 1 and subsequent work with
complexes in the form of Na+, Me4N+ and PPh4+ salts, respecti- obtained materials are schematically illustrated in Scheme 2.
vely, is described as well.11a
With the aim to obtain pure 1, we recrystallized the
In our trials to synthesize [nBu4N]2[M(opooMe)] (M = Ni (6), obtained crude twice from MeOH and MeOH : THF (1 : 1),
Cu (8)) using 1 prepared as described previously11a and to respectively, cf. Scheme 2. The elemental analysis data of the
obtain single-crystals of 8@6, we were confronted with distinc- recrystallized material neither deviate significantly from those
tive problems. These problems originate from impure 1 pre- obtained for the crude nor supposed pure 1. The H and 13C
1
pared according to the literature,11a and commented in the NMR characterization of the recrystallized material reveals,
following.
however, that besides 1 one further compound is present,
namely opbaH2Me2 (2), cf. Fig. S2.† The presence of 2 is con-
cluded, for example, from its 1H NMR chemical shifts at
3.87 ppm for the two O–CH3 groups and at 10.40 ppm for the
two N–H protons. Of course, 1H NMR resonances of 2 do
overlap with those of 1, although from the ratio of the intensi-
ties of 2 compared to 1 the presence of ca. 5% of 2 and
ca. 95% of 1 is concluded. Thus, even recrystallization of the
crude does not give rise to pure 1. Indeed, after inspecting the
1H and 13C NMR spectra of the recrystallized material for the
first time we were unaware of the presence of 2 and could not
explain the origin of its NMR resonances. We thus started with
the synthesis of the NiII and CuII complexes 6 and 8 of
assumed pure 1, cf. Scheme 2.
The recrystallized material obtained as described above was
thus treated in MeOH with one equivalent of [Ni(OAc)2(H2O)4]
or half an equivalent of [Cu2(OAc)4(H2O)2]. Four equivalents of
[nBu4N]OH were then added to the reaction mixtures. After
appropriate workup, orange and purple coloured materials
were isolated, respectively. The elemental analysis of the orange
and purple coloured materials agrees with the formation of 6
and 8, respectively. Afterwards, a mixture of 99 mass% of the
orange material and 1 mass% of the purple coloured material
was co-crystallized under diffusion controlled conditions from a
combined MeCN solution against Et2O with the aim to obtain
8@6. Besides the formation of a small amount of well-shaped,
orange coloured single-crystals, having clearly identifiable and
addressable crystal faces required for orientation in EPR
Results and discussion
Synthesis
The work undertaken in this report is a continuation of our
recent research which dealt with the synthesis and EPR studies
of [M(opooMe)]2+ (M = NiII, CuII) type complexes.13
We repeated the synthesis of opooH3Me2 (1) first according
to the procedure described in the literature and obtained in
analogy a solid material.11a That solid material is referred to in
the following as “crude”. The elemental analysis data of the
crude are in agreement with the values calculated for 1 and do
not deviate significantly from the data given in the litera-
ture.11a 1H and 13C NMR spectra of the crude reveal, however,
that 1 was not obtained in pure state. For pure 1, for example,
the 13C NMR should indicate the presence of up to ten dis-
tinguishable resonances originating from sp2 hybridized
carbon atoms, however, eighteen different resonances could
be detected instead (Fig. S1†). Furthermore, for pure 1 three
different N–H resonances with a ratio of 1 : 1 : 1 in the 1H NMR
are expected, whereas six different signals were detected
instead (Fig. S1†).
In the report which describes the synthesis of proposed
pure 1, it is surprising to read that three different N–H reson-
ances with a ratio of 1 : 2 : 2 are given.11a The thus supposed
pure 1 is then abbreviated as H4L2, where the number of
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Scheme 2 Synthesis of NiII and CuII complexes out of the recrystallized crude and the formation of 7@5 and 8@6 during co-crystallization.
experiments,
a large amount of less well-shaped orange
coloured single-crystals has been noticed.14
One of the well-shaped single crystals was selected for EPR
measurements. Its typical EPR spectrum is shown in Fig. 1.
The lines in the spectrum are grouped into four subsets due to
the on-site hyperfine (HF) coupling of the CuII electron spin
with its own nuclear spin. A clearly resolved structure of
subsets arises due to the transferred HF coupling with the
N-donor atoms. Considering the number of the lines in the
subsets most likely only two N-donor atoms are coordinated to
CuII. The g-factor of 2.074, a Cu hyperfine (HF) coupling con-
stant of 116 G and a N HF-coupling constant of 16 G were
obtained from modelling of the spectrum, cf. Fig. 1.
The obtained result of the EPR measurement verified that
the well-shaped crystals represent 7@5, which was already
studied by EPR measurements.15 One of the less well-shaped
single crystals was then separated and studied by EPR. The
results obtained thereof agree with the formation of 8@6 and
are identical to those recently reported.13 The orange and
purple coloured materials were then separately subjected to
diffusion controlled crystallization from CH2Cl2, acetone and
DMF solutions, respectively, against Et2O.
Fig. 1 Experimental (top) and simulated (bottom) EPR spectra of 7@5. The
magnetic field was oriented at an angle of 50° with respect to the AII axis of the
crystal to obtain the best resolved hyperfine patterns.
For all performed crystallizations the orange and purple
coloured materials gave rise to two even optically different
kinds of single-crystals of pure 5 and pure 6, as well as pure 7
and pure 8, respectively.
From the co-crystallization experiments we became aware
that the recrystallized material is a mixture of 1 and 2. That
prompted us to start with a resolution procedure of the
1800 | Dalton Trans., 2013, 42, 1798–1809
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originally obtained crude material in order to identify its referred to as residue C. The NMR characterization of residue
different components and to get access to pure 1.
C did reveal that this material is composed of two different
compounds (Fig. S8†), one in major and the other in minor
quantity. For example, in the 1H NMR of C between ca. 9 to
11 ppm three resonances, attributed to N–H protons, with a
ratio of intensities of 1 : 1 : 1 can be seen at 8.97, 10.33 and
10.57 ppm, whereas an additional resonance with minor inten-
sity appears at 10.48 ppm.
Residue C was thus subjected to a further Soxhlet-extraction
with 100 mL EtOH for ca. 10 hours. After the collection of the
EtOH-insoluble material, referred to as residue F, the charac-
terization (Fig. S9 and S10†) reveals this material to be exclu-
sively opboH4Me2 (4), in 1% yield. The EtOH extract E was
evaporated to dryness to obtain a colourless solid. The charac-
terization of E reveals now that the desired opooH3Me2 (1) is
isolated in pure state in 89% yield (Fig. S11 and S12†).
The separation process of the crude
The only satisfactory method of separation employed in order
to isolate the different compounds forming the crude in their
pure states was to use recurring Soxhlet-extractions under opti-
mized conditions. The whole separation process, giving rise to
the isolation of opbaH2Me2 (2), 1,4-dihydro-2,3-quinoxaline-
dione (3), opboH4Me2 (4) and finally opbooH3Me (1), respect-
ively, in pure state is summarized in Scheme 3.
A first Soxhlet-extraction of the crude with THF for three
hours (ca. 6 runs) was performed. After removal of all THF the
obtained residue A, cf. Scheme 3, could be analyzed as pure
opbaH4Me2 (2) in 6% yield based on the amount of the crude
used (Fig. S3 and S4†). The THF-insoluble residue B was dried
with a steam of argon. The NMR characterization indicates
that residue B is free of 2 (Fig. S5†).
Synthesis of the ethyl ester of o-phenylene(N′-methyloxamide)
(oxamic acid) (opooH3EtMe, 9)
Residue B was then subjected to a Soxhlet-extraction with
100 mL of MeOH. This extraction did resolve nearly all residue The isolation of pure 1 according to Scheme 3 is a very time
B. After ca. seven hours extraction time the MeOH-insoluble consuming procedure. In order to have instant access to an
material in the Soxhlet thimble, referred to as residue D asymmetric N′-alkyloxamide oxamic acid ester, several exper-
(Scheme 3), was dried on air, recrystallized from MeOH : iments were performed. It turned out that the treatment of
DMSO (2 : 1) and finally dried in vacuo. The characterization of opbaH2Et2 with 5/6 of an equivalent of MeNH2 in absolute
residue D refers this material as pure 1,4-dihydro-2,3-quinoxa- EtOH according to Scheme 4 is sufficient to gain 9 in ca. 50%
linedione (3) in 3% yield (Fig. S6 and S7†).
yield in pure state (Fig. S13 and S14†).13 The comparatively low
The MeOH solution, obtained from the Soxhlet-extraction yield of 9 could indicate that besides 9 further compounds
of B, was evaporated to dryness. The obtained material is were formed. In order to check this, the following experiment
Scheme 3 Separation process to resolve the crude into its pure components 1–4.
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Selected bond lengths, bond and torsion angles of 1 are given
in Table 1, whereas Table 5 summarizes crystal and structural
refinement data. The molecular structure of 1 is shown in
Fig. 2 from two different perspective views. The chiral confor-
mer of 1 observed in the solid state could be described as a
planar chiral, with the chiral plane going through the C6H4N2
fragment. As the oxamate unit possesses then a higher priority
compared to the oxamidate unit, the observed conformer can
be described as Rp. Both the oxamate group (group I: N1, O1–
O3, C1, C2, C11) and the oxamidate group (group II: N2, N3,
O4, O5, C3, C4, C12) point to the same directions with respect
to the central aromatic ring, cf. Fig. 2. Furthermore, the confor-
mation of both groups I and II could be described as the exo
(anti)-conformation. Both group I (root-mean-square deviation
from planarity {rmsd in the following} = 0.0455 Å) and group II
(rmsd = 0.0063 Å), respectively, are nearly planar. The inter-
planar angle between both groups amounts to 81.6(1)°. With
respect to the central aromatic ring (C5–C10), group I is
rotated by 55.4(°) and group II by 43.9(2)°.
No intramolecular hydrogen bonds between group I and
group II are observed, cf. Fig. 2. This observation is in contrast
to the finding for the related opbaH2Et2, where both oxamate
groups interact by an intramolecular hydrogen bond.17
However, as observed for opbaH2Et2,17 compound 1 forms 1D
chains along the crystallographic c-axes in the solid state due
to intermolecular hydrogen bonds. A selected part of one 1D
chain is shown in Fig. 3 together with a graphical illustration
of the orientation of the 1D chains to each other and with
respect to the unit cell. Data of the intermolecular hydrogen
bonds are summarized in Table 2. As shown in Fig. 3, interact-
ing molecules of 1 are parallel displaced superimposed with
respect to each other and the interactions between all mol-
ecules of 1 within a 1D chain are always achieved by intermole-
cular hydrogen bonds of the type N–H⋯O. The 1D chains of
opbaH2Et2, however, are formed by dimeric units of
opbaH2Et2 with N–H⋯O type hydrogen bonds which are con-
nected further to zigzag chains by means of C–H⋯O hydrogen
bonds. This structural difference might show and underline
that slight changes of the nature of a supramolecular synthon
have fundamental impact on the supramolecular arrangement.
THE MOLECULAR AND CRYSTAL STRUCTURE OF OPBAH2Me2·2DMSO
(2·2DMSO). Single crystals of 2 have been obtained from
Scheme 4 Synthesis of opooH3EtMe (9).
was performed: after the reaction had come to an end and the
colourless solid formed was filtered off, the solvent of the fil-
trate was removed in vacuo. The NMR characterization of the
obtained material revealed that besides a trace of 9 only
unreacted opbaH2Et2 could be observed (Fig. S15†). That
clearly indicates that the use of MeOH for the reaction of
opbaH2Et2 with substoichiometric amounts of MeNH2 is
responsible for the formation of further products. The for-
mation of 1 and 2 is clearly due to a transesterification reac-
tion. The observation that 1 and 2 are formed comparatively
quickly may open a new access to catalyzed transesterification
reactions, cf. remarks given in S17.†
Structural descriptions
In order to prove the identities of the above separated com-
pounds and complexes, especially of 1 and 2 and the com-
plexes formed thereof, we tried to grow their single crystals
suitable for X-ray diffraction studies. As mentioned above,
single crystals of 5–8 have been obtained. In the following we
report on the solid state structures of 1, 2, 5 and 7, those of 6
and 8 have been recently reported.13
THE MOLECULAR AND CRYSTAL STRUCTURE OF OPOOH3Me2 (1). Single
crystals of 1 have been obtained from DMSO : nitrobenzene
(1 : 1) solutions of 1 layered by Et2O. Compound 1 crystallizes
in the non-centrosymmetric orthorhombic space group Pna2
(1). The absolute structure of 1 has been refined with respect
to the Flack x parameter which is 0.0(5), whereas for the
inverted structure a Flack x parameter of 0.8(5) is observed.16
Table 1 Selected bond lengths (Å), bond and torsion angles (°) of 1
Bond lengths
C1–N1
C1–O1
C1–C2
C2–O2
C2–O3
C5–N1
C5–C10
Torsion angles
O1–C1–C2–O3
N1–C1–C2–O3
O1–C1–C2–O2
N1–C1–C2–O2
Bond angles
1.340(6)
1.211(6)
1.544(7)
1.216(6)
1.308(6)
1.417(6)
1.413(7)
C3–N2
C3–O4
C3–C4
C4–O5
C4–N3
C10–N2
1.340(6)
1.248(6)
1.543(7)
1.236(6)
1.303(7)
1.425(6)
O1–C1–N1
O1–C1–C2
N1–C1–C2
O3–C2–O2
O3–C2–C1
O2–C2–C1
C1–N1–C5
C1–N1–H1N
C5–N1–H1N
127.1(5)
121.6(4)
111.3(5)
125.7(5)
112.2(5)
122.1(4)
123.8(4)
118(4)
O4–C3–N4
O4–C3–C4
N2–C3–C4
O5–C4–N3
O5–C4–C3
N3–C4–C3
C3–N2–C10
C3–N2–H2N
C10–N2–H2N
126.2(5)
119.7(4)
114.1(4)
126.2(5)
119.6(4)
114.2(4)
124.1(5)
121(3)
−6.7(7)
174.5(4)
174.9(6)
−3.9(7)
O4–C3–C4–N3
N2–C3–C4–N3
O4–C3–C4–O5
N2–C3–C4–O5
0.9(7)
179.8(4)
0.1(5)
118(4)
115(3)
−1.1(6)
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Fig. 2 ORTEP diagrams (50% ellipsoid probability) of the molecular structure of 1. Left: top view. Right: side view.
Fig. 3 Left: graphical representation of a selected part of a 1D chain formed by 1 in the solid state due to intermolecular hydrogen bonds. Label ‘A’ to ‘C’ refers to
a first to the third symmetry generated molecule of 1. Right: graphical representation of the orientation of the 1D chains formed by 1 along the crystallographic c-
axes. All C-bonded hydrogen atoms are omitted for clarity.
DMSO : CHCl3 (1 : 9) solutions of 2 layered by nhexane. Com-
Table 2 Selected bond lengths (Å) and angles (°) of the intermolecular hydro-
gen bonds of 1
pound 2 crystallizes in the centrosymmetric monoclinic space
group C2/c in the form of a DMSO adduct as 2·2DMSO.
Selected bond lengths, bond and torsion angles of 2·2DMSO
are given in Table 3, whereas Table 5 summarizes crystal and
structural refinement data. The molecular structure of
2·2DMSO is shown in Fig. 4 together with those of the
opbaH2Me2 fragment, which is denoted in the following as 2A.
Compound 2·2DMSO possesses crystallographically imposed
D–H⋯A
D–H
H⋯A
D⋯A
D–H⋯A
N1–H1N⋯O4A
N2–H2N⋯O4A
N3–H3N⋯O5A
0.92(7)
0.91(3)
1.06(6)
1.99(8)
1.96(3)
1.82(6)
2.850(6)
2.827(6)
2.856(6)
154(6)
162(3)
165(5)
Symmetry code ‘A’: x, y, 1 + z.
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C2 symmetry. The interaction of the two DMSO molecules orig- 0.0091 Å) is rotated by 19.7(3)° with respect to the N(H)–CvO
inates from hydrogen bonds between the N–H protons of 2A unit (N1, H1N, C1, O1; rmsd = 0.0199 Å). The non-planarity of
and the oxygen atoms of DMSO, cf. Fig. 4. The donor⋯accep- the oxamate group is expressed in addition by the torsion
tor distance N1⋯O4 amounts to 2.8777(17) Å and the N1– angles given in Table 4 with, for example, the value for N1–C1–
H1N⋯O4 angle to 162.8(17)°. The interactions of the DMSO C2–O2 with 19.3(2)°. The N(H)–CvO unit of 2A is furthermore
molecules rule out any possible formation of intermolecular rotated by 44.7(2)° with respect to the C6H4 aromatic ring. All
hydrogen bonds and/or π interactions between molecules of 2. other structural features of 2A agree very well with the corre-
The two oxamate groups of 2A adopt the same conformation sponding data given for opbaH2Et2.17
in the solid state, which could be described as an exo(anti)-
THE MOLECULAR STRUCTURES OF [nBU N]2[M(OPBA)] (M = Ni (5),
4
conformation, although these groups point to opposite direc- Cu(7)). Complexes 5 and 7 crystallize in the centrosymmetric
tions with respect to the plane of the aromatic ring. For the monoclinic space group C2/c. Both complexes are isomorphic
closely related opbaH2Et2 the two oxamate groups adopt to each other, as related unit cell parameters are only slightly
different conformations, namely an endo(anti)- and an different. Selected bond lengths, bond and torsion angles of 5
exo(syn)-conformation,17 although in the case of this com- and 7 are given in Table 4, whereas Table 5 summarizes crystal
pound no cocrystallization of any solvent molecule is and structural refinement data of 5 and 7.
observed.
The crystal structure of 5 and 7 consists of discrete [nBu4N]+
The crystallographically independent oxamate group of 2A cations and [M(opba)]2− anions, respectively. The anionic enti-
is not planar, as the OvC–OMe unit (O2, O3, C2, C6; rmsd = ties [Ni(opba)]2− (5A) and [Cu(opba)]2− (7A), respectively,
possess crystallographically imposed C2 symmetry and are
both not perfectly planar as indicated in Fig. 5. Accordingly,
the MO2N2 coordination setups are not strictly planar and the
largest deviations are observed for the N atoms (5A: 0.0459(9)
Table 3 Selected bond lengths (Å), bond and torsion angles (°) of 2·2DMSO
Å; 7A: 0.0713(14) Å). The M atoms are otherwise precisely in
the plane of calculated mean planes of their surrounding O2N2
donor atom setups. The M–N bond lengths of the MO2N2
coordination units of 5A and 7A are significantly shorter com-
pared to the M–O bond lengths (5A: Ni1–N1 = 1.8338(13) Å vs.
Ni1–O2 = 1.8933(12) Å; 7A: Cu1–N1 = 1.910(2) Å vs. Cu1–O2 =
1.9428(19) Å).
There are already reports of complexes with discrete [Ni-
(opba)]2− complex fragments, namely [Ni(meso-cth)][Ni-
(opba)]·2H2O (10) (meso-cth = meso-5,7,7,12,14,14-hexamethyl-
1,4,8,11-tetraazacyclotetradecane),18 and of complexes with
discrete [Cu(opba)]2− complex fragments, namely [Ni(meso-
cth)][Cu(opba)]·2H2O (11),19 [PPh4]2[Cu(opba)] (12),20 and [Ru-
Bond lengths
C1–N1
C1–O1
C1–C2
C2–O2
Bond angles
O1–C1–N1
1.3463(18)
1.2188(17)
1.531(2)
1.2023(18)
1.3287(17)
1.416(2)
126.16(15)
121.68(13)
112.16(13)
125.45(15)
110.30(13)
124.24(13)
123.02(13)
118.3(11)
O1–C1–C2
N1–C1–C2
O3–C2–O2
O3–C2–C1
O2–C2–C1
C1–N1–C3
C1–N1–H1N
C3–N1–H1N
C2–O3
C3–N1
C3–C3Aa
1.406(3)
1.5084(12)
S1–O4
Torsion angles
O1–C1–C2–O3
N1–C1–C2–O3
O1–C1–C2–O2
N1–C1–C2–O2
117.1(11)
18.11(19)
−161.83(12)
−160.79(15)
19.3(2)
a Symmetry operation used to generate equivalent atoms ‘A’: −x, y, −z
− 1/2.
Fig. 4 ORTEP diagrams (50% ellipsoid probability, respectively) of the molecular structure of 2·2DMSO (left, side view) and of 2A (right, top view, C-bonded hydro-
gen atoms are omitted for clarity). Symmetry operation used to generate equivalent atoms ‘A’: −x, y, −z − 1/2.
1804 | Dalton Trans., 2013, 42, 1798–1809
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Table 4 Selected bond lengths (Å), bond and torsion angles (°) of 5A and 7A
Bond lengths
N1–M1
O2–M1
C1–N1
C1–O1
C1–C2
C2–O2
C2–O3
5Aa
7Ab
Bond angles
N1–M1–N1Ac
N1–M1–O2
N1A–M1–O2
O2–M1–O2Ac
O1–C1–N1
O1–C1–C2
N1–C1–C2
O3–C2–O2
O3–C2–C1
O2–C2–C1
C1–N1–C3
C1–N1–M1
C3–N1–M1
C2–O2–M1
5Aa
85.79(8)
86.18(5)
7Ab
1.8338(13)
1.8933(12)
1.332(2)
1.246(2)
1.552(2)
1.294(2)
1.232(2)
1.406(2)
1.422(3)
1.910(2)
1.9428(19)
1.326(4)
1.242(3)
1.558(4)
1.295(3)
1.235(3)
1.396(3)
1.430(6)
84.19(13)
84.87(9)
168.24(9)
106.34(11)
128.5(3)
121.1(2)
110.4(2)
124.6(3)
119.0(3)
116.5(2)
130.2(2)
115.79(18)
113.97(18)
112.34(17)
171.49(6)
101.97(7)
128.59(16)
122.07(14)
109.35(14)
124.74(16)
120.02(15)
115.24(14)
128.83(14)
116.58(11)
114.59(10)
112.61(11)
C3–N1
C3–C3Ac
Torsion angles
O1–C1–C2–O3
N1–C1–C2–O3
O1–C1–C2–O2
N1–C1–C2–O2
1.2(2)
−0.2(3)
179.4(2)
179.3(2)
−1.0(3)
−179.48(14)
−179.51(13)
−0.16(18)
a M1 = Ni1. b M1 = Cu1. c Symmetry operation used to generate equivalent atoms ‘A’. 5A: −x + 2, y, −z + 3/2. 7A: −x + 1, y, −z + 5/2.
Table 5 Crystal and structural refinement data of 1, 2·2DMSO, 5 and 7
1
2·2DMSO
5
7
Chemical formula
Formula weight (g mol−1
Crystal system
C12H13N3O5
279.25
Orthorhombic
Pna2(1)
C16H24N2O8S2
436.49
Monoclinic
C2/c
C42H76N4NiO6
791.78
Monoclinic
C2/c
C42H76CuN4O6
796.61
Monoclinic
C2/c
)
Space group
Unit cell dimensions (Å, °)
a = 10.1175(11)
b = 25.335(3)
c = 5.0430(4)
α = 90.0
15.3163(5)
9.0186(3)
14.8471(5)
90.0
a = 18.5088(4)
b = 17.1731(4)
c = 14.2230(4)
α = 90.0
18.5716(9)
17.2023(7)
14.1556(5)
90.0
β = 90.0
γ = 90.0
98.034(4)
90.0
β = 91.997(3)
γ = 90.0
91.897(4)
9.0
Volume (Å3)
1292.7(2)
100
Cu Kα
1.54184
2030.72(12)
100
Mo Kα
0.71073
4518.08(19)
115
Cu Kα
1.54184
4519.9(3)
115
Cu Kα
1.54184
Measurement temperature (K)
Radiation source
Wavelengths (Å)
Z
4
4
4
4
Density (calculated) (Mg m−3
)
1.435
0.967
584
1.428
0.308
920
1.164
0.983
1728
1.171
1.045
1732
Absorption coefficient (mm−1
F(000)
)
Reflections collected
Independent reflections/Rint
Index ranges
4032
3450
7198
6968
a
1633, 0.0618
−11 ≤ h ≤ 11,
−28 ≤ k ≤ 24,
−5 ≤ l ≤ 4
3.49 to 63.07
1633/2/193
0.953
R1 = 0.0598, wR2 = 0.1448
R1 = 0.0752, wR2 = 0.1521
0.0(5)
1790, 0.0188
−18 ≤ h ≤ 18,
−10 ≤ k ≤ 10,
−17 ≤ l ≤ 12
3.58 to 25.05
1790/0/131
1.0062
R1 = 0.0290, wR2 = 0.0703
R1 = 0.0357, wR2 = 0.0720
—
3542, 0.0204
−21 ≤ h ≤ 21,
−19 ≤ k ≤ 19,
−11 ≤ l ≤ 16
3.51 to 62.71
3542/0/240
1.005
R1 = 0.0391, wR2 = 0.1042
R1 = 0.0445, wR2 = 0.1069
—
3440, 0.0333
−21 ≤ h ≤ 21,
−16 ≤ k ≤ 19,
−16 ≤ l ≤ 7
4.64 to 62.76
3440/0/240
0.943
R1 = 0.0496, wR2 = 0.1246
R1 = 0.0639, wR2 = 0.1300
—
θ range for data collection (°)
Data/restraints/parameters
Goodness-of-fit on F2 b
Final R indices [I > 2σ(I)]c
R indices (all data)c
Flack x parameter16
Largest diff. peak/hole (e Å−3
)
0.313, −0.300
0.002/0.000
0.236, −0.302
0.000/0.000
0.407, −0.387
0.000/0.000
0.594, −0.310
0.000/0.000
Average/maximum shift/error
a Rint = Σ|Fo − Fo2(mean)|/ΣFo2, where Fo (mean) is the average intensity of symmetry equivalent diffractions. b S = [∑w(Fo − Fc2)2]/(n − p)1/2
,
2
2
2
where n = number of reflections, p = number of parameters. c R = [∑(|Fo| − |Fc|)/∑|Fo|); wR = [∑(w(Fo2 − Fc ) )/∑(wFo4)]1/2
.
2 2
(bpy)3] [Cu(opba)]·9H2O (13).21 The observation that the M–N when comparing related bond lengths of 10 with those of
bonds of 5A and 7A are shorter compared to the M–O bonds is 11–13.18–21
due to the greater basicity of the N (amide) compared to the
O (carboxylate) donor atoms,20 and has been observed for
10–13 as well.18–21 The Ni–N and Ni–O bond lengths of 5A are
Experimental part
significantly shorter compared to the related bond lengths of
7A which reflects nicely the shorter ionic radius of NiII ions in
All chemicals were purchased from commercial sources and
a planar coordination environment compared to CuII ions
used as received without further purification. The solvents
(NiII: 63 pm vs. CuII: 71 pm).22 The same tendency is observed were purified according to standard procedures.23 NMR
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Fig. 5 ORTEP diagrams (50% ellipsoid probability) of the molecular structures of 5A (left) and 7A (right). Above: top view. Below: side view. Sign ∢ refers to the
interplanar angle and rmsd to the root-mean-square deviation from planarity of calculated mean planes of atoms adjoining differently coloured areas. Symmetry
operation used to generate equivalent atoms ‘A’ 5A: −x + 2, y, −z + 3/2. 7A: −x + 1, y, −z + 5/2.
1
spectra were recorded at room temperature with a Bruker material: 1.71 g. The H and 13C NMR spectra of the recrystal-
Avance III 500 UltraShield spectrometer (1H at 500.300 MHz lized material are given in Fig. S2.† The elemental analysis of
and 13C{1H} at 125.813 MHz) in the Fourier transform mode. the recrystallized material does not deviate significantly from
Chemical shifts are reported in δ (ppm) vs. SiMe4 with the the values obtained from the crude. According to the analytical
1
solvent as the reference signal ([D6]-DMSO: H NMR, δ = 2.54; characterization of the recrystallized material it is composed of
and 13C{1H}NMR, δ = 40.45). FT-IR spectra were recorded in the methyl ester of o-phenylene(N′-methyloxamide)(oxamic
the range of 400–4000 cm−1 on a Thermo Scientific Smart iTR acid) (opooH3Me2, 1) to ca. 95% content and the dimethyl
spectrophotometer. Elemental analyses for C, H and N were ester of o-phenylenebis(oxamic acid) (opbaH2Me2, 2) to ca. 5%
performed using a Thermo FlashAE 1112 series. The diethyl content.
ester of N,N′-o-phenylene-bis(oxamic acid) (opbaH2Et2) was
synthesized according to a published procedure.4 EPR spec-
Synthesis and characterization of CuII and NiII complexes by
troscopy was done with an X-band spectrometer EMX (Bruker)
using the recrystallized material obtained from the reaction of
at ambient temperature. The angular dependent measure-
opbaH2Et2 and MeNH2 in MeOH
ments were done using a H103 cavity equipped with a
goniometer.
The recrystallized material has been obtained as described
above and is composed of opooH3Me2 (1, ca. 95%) and
opbaH2Me2 (2, ca. 5%). In the following descriptions the used
masses of the recrystallized material are given. The given
molar amounts refer to assumption that this material is
Repeated reaction of opbaH2Et2 with MeNH2 according to
[11a]
A solution of opbaH2Et2 (0.01 mol, 3.08 g) in MeOH (50 mL) pure 1.
II
was treated with MeNH2 (0.56 g, 0.0066 mol, 33% in EtOH) at
NI COMPLEXES. A hot solution (ca. 50 °C) of [Ni(OAc)2(H2O)4]
room temperature. The mixture was kept at 65 °C for half an (0.49 g, 0.002 mol) in MeOH (50 mL) was added dropwise with
hour with vigorous stirring and the white precipitate was fil- stirring to a hot suspension (ca. 50 °C) of the recrystallized
tered off, washed with MeOH and Et2O, and dried under material (0.55 g, 0.002 mol) in MeOH (50 mL). Then, [nBu4N]-
vacuum. That material is referred to in the following as crude. OH (5.18 g, 40% in MeOH, 0.008 mol) was added with continu-
1
Yield of crude: 1.53 g. Fig. S1† gives the H and 13C NMR as ous stirring. The resulting mixture was stirred at 60 °C for a
well as the IR spectra of the crude. Elemental analysis of the further 15 minutes, filtered and the solvent evaporated to
crude: anal. calcd (%) for C12H13N3O5 (279.25 g mol−1): C dryness. The resulting oily material was treated with THF
51.61, H 4.69, N 15.05; found: C 51.62, H 4.65, N 14.70.
(25 mL) and filtered to eliminate [nBu4N]OAc. The solid
The crude (ca. 3 g) was recystallized twice from MeOH and material was precipitated by addition of Et2O (200 mL) as an
MeOH : THF (1 : 1), respectively. Yield of recrystallized orange powder, filtered and dried in vacuo. Yield: 1.07 g (66%).
1806 | Dalton Trans., 2013, 42, 1798–1809
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Anal. calcd (%) for C43H79NiN5O5 (803.54 g mol−1): C 64.17, Resolution process of the material obtained from the reaction
H 9.89, N 8.70; found: C 63.01, H 9.89, N 8.57%. (Remark: the of opbaH2Et2 with MeNH2 into its components
elemental analysis is calculated by assuming the formation of
[nBu4N]2[Ni(opooMe)] (6) in pure state. The observed values do The reaction of opbaH2Et2 with MeNH2 in MeOH has been
not deviate severely from calculated ones, indicating that the repeated as described before, giving identical analytical
measurement of the elemental analysis of the obtained orange results. Solvent extraction was carried out in a standard
powder alone is not suited to decide whether pure 8 is formed Soxhlet apparatus of 250 mL volume, using THF, MeOH and
or not.)
The orange powder was dissolved in MeCN, acetone and
EtOH as solvents, successively.
EXTRACTION WITH THF. The Soxhlet thimble was charged with
DMF, respectively, and the solutions obtained were subjected 2 g of finely ground crude, and extracted first with 100 mL of
to diffusion controlled crystallizations against Et2O. In all THF for three hours. The solvent was removed using a rotary
three cases the whole amount of the orange powder did crystal- evaporator and the solid material obtained dried in vacuo.
lize, as finally colourless solvent mixtures were obtained. Fur- Crop A (opbaH2Me2, 2): yield: 0.13 g (6%), based on the used
thermore, in all three cases one kind of crystal in minority has crude. Anal. calcd (%) for C12H12N2O6 (280.23 g mol−1): C 51.43,
been obtained. Unit cell measurements by single-crystal X-ray H 4.32, N 10.00; found: C 51.40, H 4.19, N 9.91. IR: ν = 3345(s),
1
diffraction studies revealed the crystals formed in minority to 3236(b) (NH); 1717(s), 1682(s), 1600(s) (CO). H NMR: δ = 3.87
be identical. A full characterization in one selected case did (s, 6H, H1,1′), 7.31 (dd, 2H, H6,6′), 7.57 (dd, 2H, H5,5′), 10.40 (s,
prove the formation of [nBu4N]2[Ni(opba)] (5). Thus, indepen- 2H, NH). 13C{1H} NMR: δ = 53.2 (C1,1′), 125.6 (C6,6′), 126.3 (C5,5′),
1
dent of the solvent used to dissolve the orange coloured 129.6 (C4,4′), 155.3 (C3,3′), 160.7 (C2,2′). The IR, H and 13C NMR
powder for crystallization, 5 is always formed in pure state. The spectra of 2 are given in Fig. S3 and S4,† respectively.
second kind of crystal formed in majority has been subjected
The prevailed residue in the Soxhlet thimble after THF
1
to analogous X-ray studies as well. These studies did reveal extraction (B) was dried by a steam of argon. The H and 13C
these crystals to be [nBu4N]2[Ni(opooMe)] (6), as reported NMR spectra of residue B are given in the ESI in Fig. S5.†
earlier.13 No further characterization of 5 and 6 has been per-
EXTRACTION WITH MeOH. After drying B, this residue was
formed, as the identities of both NiII complexes are established extracted with 100 mL of MeOH for 7 hours to leave insoluble
unambiguously by the X-ray studies. off-white material in the Soxhlet thimble, referred to as
II
CU COMPLEXES. The previous procedure was employed to syn- residue D. The solid D was collected and recrystallized from
thesize the CuII complexes with [Cu2(OAc)4(H2O)2] (0.27 g, MeOH : DMSO (2 : 1) and dried in vacuo. According to the
0.0007 mol), the recrystallized material (0.41 g, 0.0014 mol) analytical data given below, D refers to exclusively 1,4-dihydro-
and [nBu4N]OH (3.62 g, 0.0056 mol). The solid material 2,3-quinoxalinedione (3): yield: 0.06 g (3%), based on the used
obtained after precipitation was purple coloured. Anal. calcd crude. Anal. calcd (%) for C8H6N2O2 (162.15 g mol−1): C 59.26,
(%) for C43H79CuN5O5 (809.77 g mol−1): C 63.79, H 9.83, H 3.73, N 17.28; found: C 59.28, H 3.70, N 17.24%. IR: ν = 3023
N 8.65; found: C 63.04, H 9.80, N 8.43%. (Remark: the elemen- (m) (NH); 2865(m), 2833(m) (CH); 1655(s), 1605(m) (CO). 1H
tal analysis is calculated by assuming the formation of NMR: δ = 7.09 (dd, 2H, H1,1′), 7.12 (dd, 2H, H2,2′), 11.90 (s, 2H,
[nBu4N]2[Cu(opooMe)] (8) in pure state. The observed values do NH). 13C{1H} NMR: δ = 115.0 (C1,1′), 122.9 (C2,2′), 125.5 (C3,3′),
1
not deviate severely from calculated ones, indicating that the 155.1 (C4,4′). The IR, H and 13C NMR spectra of 3 are given in
measurement of the elemental analysis of the obtained purple Fig. S6 and S7,† respectively.
powder is not suited to guarantee the formation of a pure
The MeOH extract (C) was evaporated to dryness. The 1H
complex.) As described for the NiII complexes, the purple and 13C NMR spectra of C are given in Fig. S8.† According to
powder was subjected to different crystallizations. Similarly in its NMR characterization, C was found to be composed of at
all three cases two different kinds of crystals in minority least two different compounds. Therefore, C was subjected to a
([nBu4N]2[Cu(opba)], 7) and majority ([nBu4N]2[Cu(opooMe)], 8) further Soxhlet extraction.
were formed, as analyzed by X-ray studies as described before.
EXTRACTION WITH EtOH. C was placed in a Soxhlet extractor
COCRYSTALLIZATION OF THE ORANGE AND PURPLE POWDERS. A mixture again and extracted with 100 mL of EtOH for 10 hours. The
of the orange powder (99 mg) and the purple powder (1 mg) EtOH insoluble material F was collected and dried in vacuo.
was dissolved in MeCN and the resulting solution was sub- According to the analytical data given below, F refers exclu-
jected to diffusion controlled crystallization against Et2O. sively to o-phenylenebis(N′-methyloxamide) (opboH4Me2, 4):
Large, orange coloured crystals were formed in minority pos- yield: 0.02 g (1%), based on the used crude. Anal. calcd (%) for
sessing well shaped faces (Fig. S16†). The crystals formed in C12H14N4O4 (278.26 g mol−1): C 51.80, H 5.07, N 20.14; found:
minority were subjected to EPR measurements, establishing C 51.81, H 5.02, N 20.09. IR: ν = 3378(s), 3318(s), 3258(sh)
the formation of 7@5. The results obtained from these (NH); 1705(m), 1681(s), 1655(s), 1601(s) (CO). 1H NMR: δ = 2.74
measurements agree completely with already reported ones.15 (d, 6H, H1,1′), 7.30 (dd, 2H, H6,6′), 7.60 (dd, 2H, H5,5′), 8.96 (q,
The crystals formed in majority were subjected to EPR 2H, NHCH3), 10.47 (s, 2H, NHAr). 13C{1H} NMR: δ = 26.0 (C1,1′),
measurements as well, establishing the formation of 8@6. The 125.3 (C6,6′), 126.0 (C5,5′), 129.8 (C4,4′), 158.6 (C2,2′), 160.0 (C3,3′).
1
results obtained from these measurements agree completely The IR, H and 13C NMR spectra of 4 are given in Fig. S9 and
with that in our recent report.13
S10,† respectively.
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The EtOH extract E was evaporated in a rotary evaporator formation of solely the methyl ester opooH3Me2, 1. This obser-
and the white solid obtained was collected and dried in vacuo. vation could be generalized in the sense that for amide for-
According to the analytical data given below, E refers exclu- mations of bis(oxamic acid) esters with primary alkylamines
sively to methyl ester of o-phenylene(N′-methyloxamide) the use of MeOH should be avoided. Instead, absolute EtOH
(oxamic acid) (opooH3Me2, 1): yield: 1.78 g (89%), based on as a solvent should be applied, as shown for the formation of
the used crude. Anal. calcd (%) for C12H13N3O5 (279.25 g the ethyl ester opooH3EtMe, 9. Moreover, the observed for-
mol−1): C 51.61, H 4.69, N 15.05; found: C 51.56, H 4.63, N mation of 1 together with those of opbaH2Me2 (2) by reacting
14.99. IR: ν = 3303(sh), 3254(m) (NH); 1732(m), 1709(s), 1654 opbaH2Et2 with MeNH2 in MeOH may give stimulation for the
1
(s), 1597(s), (CO). H NMR: δ = 2.74 (d, 3H, H12), 3.87 (s, 3H, research of amine catalyzed related transesterification
H1), 7.30 (m, 2H, H6,7), 7.54 (dd, 1H, H8), 7.66 (dd, 1H, H5), reactions.
8.96 (m, 1H, NHC12), 10.33 (s, 1H, NHC9), 10.57 (s, 1H, NHC4).
The observation that from dissolved mixtures of the com-
13C{1H} NMR: δ = 26.0 (C12), 53.3 (C1), 125.0 (C7), 125.8 (C6), plexes 5–8 single crystals of 7@5 together with single crystals
125.9 (C8), 126.4 (C5), 129.1 (C9), 130.2 (C4), 155.2 (C11), 158.5 of 8@6 are formed is a nice example for the supramolecular
(C10), 160.0 (C3), 160.2 (C2). The IR, 1H and 13C NMR spectra of recognition of structurally related complexes.
1 are given in Fig. S11 and S12,† respectively.
Synthesis of the ethyl ester of o-phenylene(N′-methyloxamide)-
(oxamic acid) (opooH3EtMe, 9)
According to the literature,13
Acknowledgements
a solution of opbaH2Et2
This work has been supported by the Deutsche Forschungsge-
meinschaft through project FOR 1154 “Towards Molecular
Spintronics”. M. A. A. thanks the DAAD for a scholarship.
(0.006 mole, 1.84 g) in absolute EtOH (50 mL) was treated with
MeNH2 (0.15 g, 0.005 mole, 33% in EtOH) under continuous
vigorous stirring at 25 °C. After stirring for 30 minutes, the
white precipitate obtained was filtered off, washed with EtOH
and Et2O, and dried in vacuo. Yield: 0.91 g (52%). Anal. calcd
(%) for C13H15N3O5 (293.28 g mol−1): C 53.24, H 5.16, N 14.33;
found: C 53.45, H 5.20, N 14.91. IR: ν = 3308(m), 3257(m)
(NH); 1732(sh), 1711(s), 1655(s), 1595(s), (CO). 1H NMR: δ =
1.33 (t, 3H, H1), 2.75 (d, 3H, H13), 4.32 (q, 2H, H2), 7.30 (m,
2H, H7,8), 7.55 (dd, 1H, H9), 7.67 (dd, 1H, H6), 8.96 (m, 1H,
NHCH3), 10.35 (s, 1H, NHAr10) and 10.52 (s, 1H, NHAr5). 13C
{1H} NMR: δ = 13.7 (C1), 26.0 (C13), 62.6 (C2), 125.0 (C8), 125.8
(C7), 125.9 (C9), 126.4 (C6), 129.2 (C10), 130.1 (C5), 155.4 (C12),
158.5 (C11), 160.0 (C4), 160.2 (C3).
Notes and references
1 E. Pardo, R. Ruiz, J. Cano, X. Ottenwaelder, R. Lescouezec,
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The IR, H and 13C NMR spectra of 9 are given in Fig. S13
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X-ray crystallography
Intensity data for 1, 2·2DMSO, 5 and 7, respectively, were col-
lected on an Oxford Gemini S diffractometer with Mo Kα radi-
ation (2·2DMSO) or Cu Kα radiation (1, 5 and 7). The
structures were solved by direct methods and refined by full-
matrix least-squares methods on F2 with the SHELXTL-97
program package.24 All non-hydrogen atoms were refined an-
isotropically. All C-bonded hydrogen atoms were geometrically
placed and refined isotropically in riding modes using default
SHELXTL parameters. The positions of N-bonded hydrogen
atoms were taken from difference Fourier maps and refined
isotropically. CCDC numbers 888732 (1), 888733 (2·2DMSO),
888734 (5) and 888735 (7).
Conclusion
It could be shown that the use of MeOH as a solvent for the
amide formation reaction of opbaH2Et2 with sub-stoichio-
metric amounts of MeNH2 is not suited to guarantee the
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