Chelate [2-(iminoethyl)pyridine N-oxide]metal complexes - Synthesis and structural comparison with their chemically related 2-(iminoethyl)pyridine- derived systems

Article abstract of DOI:10.1002/ejic.200500645

The N,O-chelate ligands 2-(iminoethyl)pyridine N-oxide (2a) and 2-(iminoethyl)-6-isopropylpyridine N-oxide (2b) were prepared by conventional synthetic routes, the latter involving a variant of the Reissert-Henze reaction. Treatment of 2a with FeCl₂ resulted in a deoxygenation reaction of the ligand and formation of the salt (bis{2-(iminoethyl)-pyridine}FeCl] ⁺[FeCl₄]^- (18a). In contrast, the reaction of 2a with PdCl₂ or CoCl₂ cleanly furnished the six-membered chelate [κN,O-2(iminoethyl)pyridine N-oxide]MCl₂ complexes (19a, M = Pd) or (20a, M = Co), respectively, which were both characterised by X-ray diffraction. Treatment of 2b with [NiBr₂ (dme)], followed by crystallisation from THF, gave the complex [κN,O-2b)NiBr₂(THF)] (21b), which features a distorted trigonal-bipyramidal coordination geometry of the central metal atom. The reaction of 2a with [NiBr₂(dme)] gave the structurally related complex [(κN,O-2a)NiBr₂(κO-2a)] (21a). The N,O-chelate Pd complex 19a was shown to be an active catalyst for the Suzuki coupling reaction. The ligand systems 2a,b and their related 2-(iminoethyl)-pyridines 3a,b and a variety of metal complexes of ligands 3 were also prepared and characterised for comparison by X-ray diffraction. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200500645

FULL PAPER
DOI: 10.1002/ejic.200500645
Chelate [2-(Iminoethyl)pyridine N-oxide]metal Complexes – Synthesis and
Structural Comparison with Their Chemically Related
2-(Iminoethyl)pyridine-Derived Systems
Katrin Nienkemper,[a] Vasily V. Kotov,[a] Gerald Kehr,[a] Gerhard Erker,*[a] and
Roland Fröhlich[a]
Keywords: Chelates / Coordination chemistry / N,O ligands / Transition metals
The N,O-chelate ligands 2-(iminoethyl)pyridine N-oxide (2a)
and 2-(iminoethyl)-6-isopropylpyridine N-oxide (2b) were
gave the complex [(κN,O-2b)NiBr2(THF)] (21b), which fea-
tures a distorted trigonal-bipyramidal coordination geometry
prepared by conventional synthetic routes, the latter involv- of the central metal atom. The reaction of 2a with
ing a variant of the Reissert–Henze reaction. Treatment of 2a
with FeCl2 resulted in a deoxygenation reaction of the ligand
[NiBr2(dme)] gave the structurally related complex [(κN,O-
2a)NiBr2(κO-2a)] (21a). The N,O-chelate Pd complex 19a was
shown to be an active catalyst for the Suzuki coupling reac-
tion. The ligand systems 2a,b and their related 2-(iminoethyl)-
pyridines 3a,b and a variety of metal complexes of ligands 3
were also prepared and characterised for comparison by X-
ray diffraction.
and
formation
of
the
salt
[bis{2-(iminoethyl)-
pyridine}FeCl]+[FeCl4]– (18a). In contrast, the reaction of 2a
with PdCl2 or CoCl2 cleanly furnished the six-membered
chelate [κN,O-2(iminoethyl)pyridine N-oxide]MCl2 com-
plexes (19a, M = Pd) or (20a, M = Co), respectively, which
were both characterised by X-ray diffraction. Treatment of
2b with [NiBr2(dme)], followed by crystallisation from THF,
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
and compared their structural features with those of the
related [2-(iminoethyl)pyridine]metal complex systems 3.
Introduction
Chelating ligand systems are of considerable importance
in metal-catalysed organic reactions[1] and in polymerisa-
tion catalysis.[2] Among the various chelating ligand types,
many salicylaldimine-derived bi- and multidentate ligands
have been found to be very useful. The monoanionic biden-
tate systems 1, which feature various types of substituent
patterns at the central framework, have been employed ex-
tensively in homogeneous Ziegler–Natta-type polymerisa-
tion catalysis[3–5] as well as in asymmetric organic reac-
tions,[6] and they form the basis of the many salen-type li-
gands whose metal complexes have found extensive catalytic
uses.[7]
The neutral pyridine N-oxide aldimines or ketimines 2
(see Scheme 1) are the neutral analogues of the ubiquitous
anionic ligand systems 1. A variety of such examples and
their metal complexes have been described so far[8–12] but
overall much less is known about these interesting bidentate
ligand systems than their phenolic counterparts, especially
with a bulky alkyl substituent (R1) in the 6-position. We
have therefore prepared several examples of metal com-
plexes of this class of neutral bidentate ligand systems 2
Scheme 1.
Results and Discussion
Preparation of the Chelating Ligand Systems
For this study two general lines of acetylpyridine (R2 =
CH3) derived ligands were employed, namely the parent
systems (R1 = H) and the 6-isopropyl analogue (R1 = iPr).
We also briefly investigated the corresponding tert-butyl
system (R1 = tBu), but encountered some difficulties that
will be described below. All the imine systems of this study
were derived from 2,6-diisopropylaniline as the coupling
component of the Schiff-base synthesis. 2-Acetylpyridine
(4) was, thus, condensed with 2,6-diisopropylaniline to yield
the Schiff-base product 3a (see Scheme 2).[13] Oxidation of
4 with m-chloroperbenzoic acid in chloroform gave the cor-
[a] Organisch-Chemisches Institut der Universität Münster,
Corrensstrasse 40, 48149 Münster, Germany
E-mail: erker@uni-muenster.de
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
366
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Chelate [2-(Iminoethyl)pyridine N-oxide]metal Complexes
FULL PAPER
responding 2-acetylpyridine N-oxide (5a),[14] which was ucts 9b (61%) and 9c (65%) in good yield. The products 9
then treated with diisopropylaniline to yield 2a.
were then converted into the corresponding 2-acetyl-6-
alkyl-pyridines 10b (25%) and 10c (36%) by treatment with
methyllithium in diethyl ether (–25 °C), followed by aque-
ous workup and distillation. Subsequent treatment of com-
pounds 10 with 2,6-diisopropylaniline (MeOH, catalysed by
formic acid) eventually gave the 6-alkyl-substituted 2-(imino-
ethyl)pyridine ligands 3b (R = iPr) and 3c (R = tBu),
respectively.
2-Acetyl-6-isopropylpyridine (10b) was converted into
the corresponding pyridine N-oxide product 11b. First
attempts to achieve the selective oxidation by treatment
with m-chloroperbenzoic acid were unsuccessful, and
stronger oxidation conditions, such as 30% H2O2 at 80 °C
in acetic acid for 20 h, were required to achieve the conver-
sion of 10b into 11b (61% isolated). The tert-butyl-substi-
tuted analogue 10c even proved inert under these forcing
oxidation conditions and could not be converted into the
corresponding N-oxide under the applied reaction condi-
tions. Eventually, condensation of 11b with 2,6-diisopro-
pylaniline gave the N-aryl-2-(iminoethyl)-6-isopropylpyri-
dine N-oxide system 2b, which was used as a sterically more
hindered chelate ligand in this study.
The chelate ligands 3a, 3b and 3c and the pyridine N-
oxide systems 2a and 2b were characterised by X-ray dif-
fraction. Details of 3c are given in the Supporting Infor-
mation. The structures of the chelate ligand pairs 3a/2a and
3b/2b are depicted for comparison in Figures 1 and 2,
respectively.
Scheme 2.
The synthesis of the 6-isopropyl and 6-tert-butyl deriva-
tives of 2 and 3 started from 2-ethylpyridine (6, see
Scheme 3). Deprotonation of 6 with n-butyllithium at
–30 °C followed by treatment with methyl iodide at –50 °C
furnished 2-isopropylpyridine (7b, 67%).[15] Subsequent α-
deprotonation of 7b was achieved by treatment with the
stronger base potassium diisopropylamide (generated in
situ from isopropylamine, KOtBu and nBuLi) at –50 °C.
Quenching with MeI at –75 °C then gave 7c in 68% yield.[15]
The 2-cyano substituent was introduced by a modified Reis-
In the crystal, the ligand system 3a features a close to
sert–Henze reaction.[16] For that purpose, compounds 7b planar central (iminoethyl)pyridine framework with an s-
and 7c were first converted into their respective pyridine N- trans arrangement of the pyridyl and the imino subunits
oxides 8b and 8c by treatment with m-chloroperbenzoic [dihedral angle θ1 = –177.1(1)° (see Table 1)]. The C7–N9
acid in chloroform at 0 °C.[17] The selective CN introduc- bond length [1.280(2) Å] is in the typical C=N double bond
tion was achieved by treatment of compounds 8 with range,[18] which is (E)-configured in 3a, i.e. the bulky pyri-
Me3SiCN in the presence of dimethylcarbamoyl chloride in dyl and 2,6-diisopropylphenyl substituents are oriented
CH2Cl2 at ambient temperature. Distillation gave the prod- trans to each other. The plane of the 2,6-diisopropylphenyl
Scheme 3.
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367

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Figure 1. Comparison of the molecular structures of the ligand systems 3a (left) and 2a (right).
Figure 2. Comparison of the conformational arrangements of the chelating ligand systems 3b (left) and 2b (right).
Table 1. Selected structural parameters of the chelate ligands 2 and 3.[a]
3a
2a
3b
2b[b]
C7–N9
1.280(2)
–177.1(1)
–177.9(1)
104.0(2)
–81.9(2)
74.2
1.278(2)
174.3(1)
143.2(1)
93.1(2)
–92.5(2)
128.8
1.274(2)
–179.0(1)
173.0(1)
98.0(2)
–88.5(2)
91.0
1.283(4)
177.4(3)
133.7(3)
88.1(3)
–96.9(3)
143.1
1.276(4)
–177.7(2)
–137.4(3)
97.2(4)
–90.0(4)
135.6
C2–C7–N9–C10 [θ1]
N1–C2–C7–N9 [θ2]
C7–N9–C10–C15 (C11) [θ3]
pyridyl vs. aryl plane
[a] Bond lengths in Å and angles in °. [b] Two independent molecules.
ring is rotated close to normal from the central C=N plane is close to normal to the C=N plane [θ3 = 98.0(2)/–88.5(2)°;
[θ3 = 104.0(2)/–81.9(2)°].
see Table 1].
The conformational arrangement of the corresponding
In the pyridine N-oxide derivative 2b the C=N double
N-aryl[2-(iminoethyl)]pyridine N-oxide system 2a is related. bond is again substantially rotated away from planarity. Ac-
The attachment of the oxygen atom to the pyridyl nitrogen tually, the observed dihedral angle θ2 in 2b [averaged abso-
atom [N1–O = 1.301(1) Å] causes the adjacent imino moi- lute value 135.6(3)°] is very close to that observed in 2a (see
ety to rotate away from the central plane by about 140° (θ2, above and Table 1). Thus, compound 2b has almost the
see Table 1 and Figure 1). This conformational arrange- same optimal rotational angle around the C2–C7 vector,
ment appears to be the best compromise between compet- which probably leads to an optimal compensation of the
ing repulsive interactions between the bulky =N-aryl group N–O vs. C7–CH3 and C7–N9(Ar) steric interactions. Again,
attached at the (sp2) carbonyl carbon atom C7 or its CH3 the 2,6-diisopropylphenyl substituent plane is oriented close
group, respectively, with the newly introduced N–O func- to normal to the C=N substituent plane [averaged θ3 =
tionality. Again, the 2,6-diisopropylphenyl plane is oriented –93.1(4)°; see Table 1].
close to normal [θ3 = 93.1(2)/–92.5(2)°] to the C=N plane
in 2a.
The ligand systems 2 and 3 seem to adopt similar confor-
mational structures in solution. A perpendicular arrange-
In the ligand system 3b the bulky isopropyl substituent ment between the C=N and 2,6-diisopropylphenyl planes
is attached to the pyridyl 6-position. The framework con- would create an axially prochiral subunit in all these com-
formation in 3b is s-trans [θ1 = –179.0(1)°; see Table 1]. The pounds. This would be monitored by the occurrence of
central trisubstituted imino C=N double bond [1.274(2) Å] pairwise diastereotopic methyl groups of the isopropyl sub-
remains (E)-configured and the 2,6-diisopropylphenyl plane stituents of the N-aryl substituent. For 3b, the iPr2C6H3
368
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Chelate [2-(Iminoethyl)pyridine N-oxide]metal Complexes
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methyl resonances in the 1H NMR spectrum are, by chance,
isochronous in CDCl3 at ambient temperature, but they
split upon cooling of the sample to –65 °C {1H NMR: δ =
2.74 [sept, 2 H, CH(CH3)2ar], 1.12 and 1.10 [each d, 6 H,
CH(CH3)2ar] ppm; 13C NMR: δ = 27.7 [CH(CH3)2ar], 23.1,
1
23.0 [CH(CH3)2]ar ppm}. The H NMR resonances of the
remaining isopropyl group at C6 of the pyridyl ring occur
at δ = 3.08 [sept, 1 H, CH(CH3)2py] and 1.32 [d, 6 H,
CH(CH3)2py] ppm {13C NMR: δ = 36.2 [CH(CH3)2py], 22.7
[CH(CH3)2py] ppm}.
The corresponding pyridine N-oxide derivative 2b also
shows a single CH(CH3)2py 1H NMR resonance even at
–60 °C in CDCl3 [δ = 1.28 (d, 6 H) ppm; 13C: δ = 20.5
(25 °C) ppm]. In contrast, the CH(CH3)2ar methyl groups
of 2b are diastereotopic at room temperature [1H: δ = 1.23,
1.16 (each d, each 6 H) ppm; 13C: δ = 23.5, 22.9 ppm] which
indicates that the rotation around the imino =N–C(aryl)
vector is “frozen” on the NMR timescale under these con-
ditions and that the N-aryl substituent plane is oriented
substantially out of the N=C plane in solution, as was ob-
served in this and the related systems in the crystal.
Scheme 4.
Metal Complex Formation and Structural Characterisation
First, we treated the ligand system 3b (R = iPr) with
FeCl2, CoCl2, and NiBr2(dme). In clean reactions the corre-
sponding 1:1 chelate complexes [(3b)MX2] were obtained in
high yields. Single crystals were obtained from all the three
complexes 12b [(3b)FeCl2], 13b [(3b)CoCl2] and 14b [(3b)
NiBr2], and their molecular structures in the solid state de-
termined (see Table 2 and Scheme 4). Since the three com-
Figure 3. Molecular structure of the nickel chelate complex 14b.
In complex 14b the ligand system adopts a cisoid confor-
pounds are structurally analogous, we will briefly describe mation [θ(N1–C2–C7–N9) = 2.8(3)°] that allows both the
only the nickel system 14b (see Figure 3 for the structure). nitrogen centres N1 and N9 to coordinate to the nickel
The structural data of 12b, 13b and 14b are listed in Table 2. atom. The C7–N9 bond length in the ligand system is not
For additional information see the Supporting Information. affected by the coordination and retains its value of
Table 2. Selected structural data of the [2-(iminoethyl)pyridine]metal complexes 12–16.[a]
12b (Fe)[b]
13b (Co)[b]
14b (Ni)[c]
15a (Fe)[b]
16a (Co)[b]
C2–C7
C7–N9
M–N1
M–N9
M–Hal1
M–Hal2
M–Hal1*
N1–M–N2
Hal1–M–Hal2
Hal1–M–Hal1*
C2–C7–N9–C10
C7–N9–C10–C11 (C15)
1.497(5)
1.271(5)
2.108(3)
2.111(3)
2.209(1)
2.223(1)
–
77.3(1)
118.68(5)
–
–179.0(3)
–89.1(5)
94.3(5)
93.1
1.484(5)
1.288(4)
2.034(3)
2.044(3)
2.200(1)
2.209(1)
–
81.1(1)
113.78(5)
–
–178.6(3)
–89.7(5)
94.5(4)
85.9
1.474(4)
1.286(3)
1.994(2)
1.995(2)
2.3577(5)
2.3169(5)
–
81.7(1)
123.64(2)
–
–178.0(2)
97.7(3)
–84.0(3)
99.7
1.483(11)
1.294(10)
2.126(7)
2.201(6)
2.385(2)
2.278(3)
2.484(2)
74.8(2)
105.3(1)
84.9(1)
–175.4(7)
–89.0(9)
90.3(9)
1.482(2)
1.290(2)
2.093(1)
2.123(1)
2.3419(5)
2.2878(6)
2.4589(5)
76.64(5)
103.42(2)
86.01(2)
175.2(1)
89.8(2)
–88.8(2)
97.9
pyridyl vs. aryl plane
98.6
[a] Bond lengths in Å; angles and dihedral angles in °. [b] Hal = Cl. [c] Hal = Br.
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1.286(3) Å. The metal–nitrogen bond lengths amount to
1.994(2) Å (Ni–N1) and 1.995(2) Å (Ni–N9). In complex
14b the nickel atom has a pseudo-tetrahedral coordination
geometry with a small N1–Ni–N9 angle of 81.7(1)° inside
the five-membered chelate ring and, consequently, a much
larger complementary Br1–Ni–Br2 angle of 123.64(2) Å.
Again, an (E)-trisubstituted C=N unit is found and the 2,6-
diisopropylphenyl substituent at the imine nitrogen atom is
rotated close to perpendicular to the plane of the central
(iminoethyl)pyridine moiety (angle between the planes:
99.7°).
The less bulky parent ligand system 3a also reacts readily
with the metal dihalides FeCl2 or CoCl2. In both cases we
were able to obtain single crystals and characterise the
structures of the products (15a and 16a, respectively) by X-
ray diffraction. The coordination of the cisoid chelate ligand
in 15a and 16a (see Scheme 4) is very similar to that in 12b
and 13b (see Table 2). However, use of the less bulky ligand
3a results in the formation of a chloro-bridged dimer.[19] In
both 15a and 16a the coordination geometry of the central
metal atom can best be described as distorted trigonal-bipy-
ramidal with two equivalent half molecules in an overall
C2-symmetric framework. The pyridyl nitrogen atom (N1)
and Cl1 mark the apical centres of the distorted trigonal
bipyramid {15a: N1–Fe–Cl1 = 155.6(2)° [163.77(4)°]; the
value in brackets is the corresponding value of the iso-
structural cobalt complex 16a}. The angles between the
three equatorial ligands amount to 126.0(2)° (N9–Fe–Cl1*)
[122.86(4)°], 116.7(2)° (N9–Fe–Cl2) [114.03(4)°] and
115.5(1) (Cl1*–Fe–Cl2) [119.79(2)°], which amounts to a
sum of the three bonding angles of 358.2° in the iron com-
plex 15a [356.68° in the cobalt complex 16a]. Most angles
between the apical and basal ligands are rather close to the
expected value of 90° [Fe complex 15a: between 84.1(2)°
and 99.1(2)°; Co complex 16a: between 83.18(4)° and
99.41(4)°] with the exception of the smaller chelate nitrogen
angle [N1–Fe–N9 = 74.8(2)°; N1–Co–N9 = 76.64(5)°] and
the correspondingly enlarged angle between the bridging
halide ligands [Cl1–Fe–Cl2 = 105.3(1)°; Cl1–Co–Cl2 =
103.42(2)°]. The structure of the dimeric (chelate ligand)
FeCl2 complex 15a is depicted in Figure 4 (for further de-
tails of the isostructural cobalt system 16a see the Support-
ing Information).
Figure 4. View of the molecular structure of the dimeric iron com-
plex 15a.
Scheme 5.
dine ligand [(3a)2FeCl]+[FeCl4]– (18a; see Scheme 6 and
Figure 5). The X-ray crystal structure analysis of 18a, al-
though of a rather poor quality, shows a distorted trigonal-
bipyramidal coordination geometry around the FeII centre
in the cation (the FeIII centre in the [FeCl4]– ion is tetrahe-
drally coordinated) with the pyridine nitrogen atoms ori-
ented trans to each other at the apical positions [N1A–Fe1–
N1B = 159.5(3)°] and a sum of the basal ligand angles [Cl1–
Fe1–N9A = 117.2(2)°; Cl1–Fe–N9B = 117.8(2)°; N9A–Fe–
N9B = 124.9(3)°] of 359.9°.
The reaction of 3a with [NiBr2(dme)] in dichloromethane
at room temperature takes a slightly different course. We
isolated the 2:1 reaction product 17a (see Scheme 5) of the
composition [(3a)2NiBr]+Br– as a green-yellow solid.[20] The
general trigonal-bipyramidal structural type of 17a with the
pyridyl nitrogen atoms was determined by X-ray diffraction
but the quality of the X-ray crystal structure analysis of 17a
was too poor to allow for any detailed discussion.
Scheme 6.
The reaction of the N,O-chelate ligand 2a with PdCl2
gave complex 19a (see Scheme 7), which was isolated as a
Let us now turn to the reactions of the chelate pyridine yellow solid in 75% yield. The X-ray crystal-structure
N-oxide ligands with the metal halides. The reaction of 2a analysis showed a six-membered chelate structure where
with FeCl2 did not give an (iminoethyl)pyridine N-oxide both the pyridine N-oxide oxygen atom and the imino ni-
complex as one might have expected. Instead, it turned out trogen atom are coordinated to the palladium atom [Pd–O1
that the N-oxide is reduced by part of the iron. Crystallisa- = 2.029(1) Å; N9–Pd = 2.035(2) Å]. In complex 19a both
tion of the crude reaction product furnished single crystals the N–O [1.343(2) Å] and the C7–N9 [1.284(2) Å] bond
of the FeII/FeIII salt of the deoxygenated (iminoethyl)pyri- lengths are almost unchanged relative to the free ligand (see
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Chelate [2-(Iminoethyl)pyridine N-oxide]metal Complexes
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Figure 6. Molecular structure of palladium complex 19a.
Figure 5. Molecular structure of the salt [(3a)2FeCl]+[FeCl4]– (18a).
atom [1H NMR: δ = 1.59, 1.19 (each d, each 6 H) ppm;
13C: δ = 24.9, 23.8 ppm].
Table 3 and Table 1). The palladium atom in complex 19a
features a square-planar coordination geometry with Pd–Cl
bond lengths of 2.2945(5) Å (Cl1) and 2.2678(5) Å (Cl2).
The bond angles at Pd amount to 91.52(2)° (Cl1–Pd–Cl2),
90.46(4)° (Cl1–Pd–O1), 84.92(6)° (O1–Pd–N9) and
93.12(4)° (N9–Pd–Cl2) (sum of bonding angles at Pd:
360.02°). In contrast to the free ligand 2a, the chelate core
of complex 19a is markedly rotated away from planarity,
with central dihedral angles of 40.7(3)° (N9–C7–C2–N1)
and –1.5(3)° (C7–C2–N1–O1). The six-membered core of
complex 19a features a twist-boat-like conformation (see
Figure 6), and the 2,6-diisopropylphenyl substituent at the
imine nitrogen centre N9 is rotated almost as far out of the
adjacent imine C=N plane as in the free ligand 2a [C7–N9–
C10–C11 = –77.3(2)° in 19a and –92.5(2)° in 2a].
The [2-(N-aryliminoethyl)pyridine N-oxide]cobalt com-
plex 20a was obtained from the reaction of 2a with CoCl2
(see Scheme 7). The X-ray crystal structure analysis of 20a
features a pseudo-tetrahedral coordination geometry of the
central transition metal atom. The intact chelate ligand is
again N,O-coordinated, with the 2,6-diisopropylphenyl sub-
stituent oriented close to normal to the C=N plane (see
Table 3 and Figure 7). The complex framework also fea-
tures a twist-boat-type six-membered ring conformation
with dihedral angles of –22.6(4)° (N1–C2–C7–N9) and
2.2(4)° (C7–C2–N1–O1).
Scheme 7.
Figure 7. View of the molecular structure of the cobalt complex
20a.
Complex 19a is one of the few diamagnetic chelate sys-
tems obtained in this study, and could thus be characterised
by NMR spectroscopy. Its most prominent feature is the
The reaction of the N,O-chelate ligand 2b with
observation of pair-wise diastereotopic methyl groups of [NiBr2(dme)] takes a different course. Again, a 1:1 addition
the 2,6-diisopropylphenyl substituent at the C=N nitrogen product (21b, see Scheme 8) was obtained. Single crystals
Table 3. Selected structural data of the metal complexes 19–23.[a]
19a (Pd)
20a (Co)
21b (Ni)
21a (Ni)
22a (Zn)
1.499(6)
23a (Cu)
C2–C7
C7–N9
N1–O1
N9–M
1.489(3)
1.284(2)
1.343(2)
2.035(2)
2.029(1)
121.8(1)
84.92(6)
109.9(1)
175.9(2)
–54.9(2)
40.7(3)
1.496(4)
1.291(4)
1.340(3)
2.020(2)
1.957(2)
123.7(2)
87.84(9)
118.2(2)
174.4(2)
40.8(4)
1.486(4)
1.285(4)
1.336(3)
2.041(3)
2.005(2)
123.6(2)
82.9(1)
113.8(2)
–175.3(3)
57.6(3)
1.485(5)
1.284(4)
1.332(4)
2.073(3)
2.049(2)
123.8(2)
81.7(1)
1.491(5)[b]
1.500(6)
1.285(6)
1.332(5)
2.076(4)
2.005(3)
121.6(3)
83.7(1)
1.490(4)
1.281(4)
1.340(3)
1.985(2)
1.919(2)
123.2(2)
87.07(9)
115.4(2)
–179.8(3)
49.0(3)
1.272(4)[b]
1.282(5)
1.340(5)
2.072(4)
1.976(3)
121.6(3)
84.3(1)
113.0(3)
–174.1(4)
–52.3(5)
26.8(7)
1.337(3)[b]
–
O1–M
2.055(2)[b]
C7–N9–M
N9–M–O1
M–O1–N1
C2–C7–N9–C10
C2–N1–O1–M
N1–C2–C7–N9
–
–
–
113.6(2)
–179.3(4)
53.5(4)
113.2(3)
174.2(4)
50.4(5)
–176.6(3)[b]
–
–22.6(4)
–32.0(4)
–32.4(6)
–126.8(4)[b]
–26.9(7)
–29.7(4)
[a] Bond lengths in Å and angles and dihedral angles in °. [b] κO-coordinated ligand 2a.
Eur. J. Inorg. Chem. 2006, 366–379
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371

K. Nienkemper, V. V. Kotov, G. Kehr, G. Erker, R. Fröhlich
FULL PAPER
were obtained from THF solution. In 21b (see Figure 8)
the (iminoethyl)pyridine N-oxide ligand coordinates to the
nickel atom through both the oxygen atom and the imino
nitrogen atom to form a favoured six-membered chelate
ring. The ring conformation is twisted, with the core atoms
N1–C2–C7–N9 deviating from coplanarity by about –32°
(see Table 3). The corresponding dihedral angles amount to
57.6(3)° (C2–N1–O1–Ni), 5.9(4)° (C2–C7–N9–Ni), 31.8(2)°
(C7–N9–Ni–O1) and –62.2(2)° (N1–O1–Ni–N9). The N1–
O1 bond length in complex 21b is 1.336(3) Å, which is sim-
ilar to that found in the free ligand 2b. The nickel atom in
complex 21b features a distorted trigonal-bipyramidal coor-
dination geometry, with the pyridine N-oxide oxygen atom
O1 [Ni–O1 = 2.005(2) Å] and the oxygen atom of a coordi-
nated THF ligand [Ni–O25 = 2.160(2) Å] being at the apical
positions [O1–Ni–O25 = 174.1(1)]. The imino-nitrogen
atom N9 [Ni–N9 = 2.041(3) Å] and the pair of bromide
ions [Ni–Br1 = 2.4407(6) Å; Ni–Br2 = 2.4173(6) Å] are ori-
ented in the central plane [N9–Ni–Br1 = 96.17(7)°; N9–Ni–
Br2 = 126.67(8)°; Br1–Ni–Br2 = 136.84(3)°]. The 2,6-di-
isopropylphenyl substituent at N2 is rotated almost normal
to the C=N imine plane [C7–N9–C10–C11 = –94.3(4)°] as
is the bulky CHMe2 group at the α-position of the pyridine
N-oxide ring.
Figure 8. Molecular geometry of the nickel(ii) complex 21b.
Figure 9. View of the molecular structure of complex 21a.
In addition to the metal complexes described above, we
also prepared a zinc and a copper complex of the unsubsti-
tuted N,O-ligand 2a (see Scheme 9).
Scheme 8.
The reaction of the less bulky chelate pyridine N-oxide
ligand 2a with [NiBr2(dme)] takes a similar course, except
that a 2:1 adduct (21a, see Scheme 8 and Figure 9) was ob-
tained after recrystallisation. The X-ray crystal-structure
analysis of 21a revealed the presence of a six-membered
chelate ring that is very similar to the corresponding sub-
Scheme 9.
The reaction of ligand 2a with ZnBr2 in acetonitrile at
structural unit in 21b (see above and Table 3), but instead room temperature yielded a bright yellow solid (22a). The
of the THF solvent the nickel atom in 21a has picked up molecular structure is depicted in Figure 10 and shows a
a second (iminoethyl)pyridine N-oxide ligand (2a) and is monomeric complex with a four-coordinate zinc atom. The
coordinated to it only through the N–O oxygen atom (κO) geometry around the metal centre can be described as dis-
to complete its distorted trigonal-bipyramidal coordination torted tetrahedral with an N9–Zn–O1 angle of 84.3(1)° and
sphere [Ni–O1a = 2.055(2) Å; N1a–O1a–Ni = 123.2(2)°]. a Br1–Zn–Br2 angle of 121.60(4)°. Again, the six-mem-
The κO-coordinated ligand 2a in 21a features a conforma- bered metallacycle features a twist-boat-type conformation
tion that is similar to that of the free ligand [N1a–C2a– [dihedral angles C2–N1–O1–M = –52.3(5)° and N1–C2–
C7a–N9a = –126.8(4)°].
C7–N9 = 26.8(7)°; all values for molecule A].
372
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Chelate [2-(Iminoethyl)pyridine N-oxide]metal Complexes
FULL PAPER
Conclusion
We have shown that pyridine N-oxide systems can readily
be obtained in a straightforward synthetic way. The systems
2a and 2b in many cases serve as rather stable chelate li-
gands, cleanly forming the respective κN,O-coordinated
complexes with a variety of metal systems. Only in an ex-
ceptional case did we observe a redox reaction that resulted
in loss of the pyridine N-oxide oxygen atom with concur-
rent formation of a corresponding (iminoethyl)pyridine che-
late metal complex. The (iminoethyl)pyridine N-oxide com-
plexes are structural analogues of the ubiquitous (salicylimi-
no)metal complexes. However, the (iminoethyl)pyridine N-
oxides are neutral ligands in contrast to their negatively
charged salicylimino ligand analogues. Therefore, one
might envision a variety of complementary use of these che-
lating ligand systems, both in coordination chemistry and
catalysis.
Figure 10. View of the molecular structure of complex 22a.
Compound 23a was obtained from the reaction of Cu-
(OTf)2 with 2a in dichloromethane (see Figure 11). In this
case the metal centre is five-coordinate. The geometry can
be regarded as distorted square-pyramidal, with the nitro-
gen atom of the imino bridge, the pyridine N-oxide oxygen
atom, the oxygen atom of one triflate group and the oxygen
atom of an additional water molecule as the four basal
atoms [O2–Cu–N9 = 167.5(1)°; O1–Cu–O6 = 168.1(1)°].
Experimental Section
General: All reactions involving air- or moisture-sensitive com-
The oxygen atom of the second triflate group occupies the pounds were carried out under an inert gas using Schlenk-type
glassware or in a glovebox. Solvents were dried and distilled prior
to use. The following instruments were used for physical characteri-
sation of the compounds: melting points: DSC 2010 TA-instru-
ments; elemental analyses: Foss–Heraeus CHNO-Rapid; MS:
Micromass Quattro LC-Z electrospray mass spectrometer; NMR:
Bruker AC 200 P (1H: 200 MHz; 13C: 50 MHz), ARX 300 (1H:
300 MHz; 13C: 75 MHz), Varian UNITY plus NMR spectrometer
(1H: 600 MHz; 13C: 151 MHz). 2-Isopropylpyridine (7b),[15] 2-tert-
butylpyridine (7c),[15] 2-acetylpyridine N-oxide (5a)[14] and (2,6-di-
isopropylphenyl)(1-pyridin-2-ylethylidene)amine (3a)[13] were syn-
thesised according to methods published elsewhere. Compounds 8b
and 8c were synthesised by a general procedure for the preparation
of amine N-oxides.[17] Compounds 9b and 9c were synthesised ac-
cording to a modified Reissert–Henze reaction.[16]
axial coordination site.
X-ray Crystal Structure Determinations: Data sets were collected
with Enraf Nonius CAD4 and Nonius KappaCCD diffractometers,
with Mo-Kα radiation, equipped with a rotating anode generator.
Programs used: data collection EXPRESS (Nonius B.V., 1994) and
COLLECT (Nonius B.V., 1998); data reduction MolEN (K. Fair,
Enraf–Nonius B.V., 1990) and Denzo-SMN;[21] absorption correc-
tion for CCD data SORTAV[22] and Denzo;[23] structure solution
SHELXS-97;[24] structure refinement SHELXL-97;[25] graphics XP
(BrukerAXS, 2000). CCDC-277028 to -277044 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Figure 11. View of the molecular structure of complex 23a.
We have only begun to investigate the chemistry of the
(iminoethyl)pyridine N-oxide chelate metal complexes. In a
first experiment, the (N,O-chelate)PdCl2 system 19a was
employed as a catalyst in the Suzuki coupling reaction of 2-Isopropylpyridine N-Oxide (8b):
A solution of 7b (70.0 g,
578 mmol) in chloroform (700 mL) was cooled to 0 °C and m-chlo-
roperbenzoic acid (143 g, 578 mmol), dissolved in chloroform
(400 mL), was added dropwise. The resulting mixture was warmed
to ambient temperature within 3 h, then passed through a column
of alkaline alumina. Evaporation of the solvent yielded the product
bromobenzene with phenylboronic acid to yield biphenyl.
With 3 mol-% of 19a in the presence of the base K2CO3
(toluene, 80 °C, 8 h) a practically quantitative yield of the
Ph-Ph coupling product was obtained, which is superior to
the reaction catalysed by PdCl2 alone in the absence of a
supporting ligand, which gives only a 62% yield of biphenyl
under these general reaction conditions. This makes it prob-
ably worthwhile to explore the catalytic potential of the
[(iminoalkyl)pyridine N-oxide]metal complexes described in
this article and related systems.
1
as a yellow oil (63.0 g, 79%). H NMR (200 MHz, CDCl3, 25 °C):
3
δ = 8.19 (d, J = 6.4 Hz, 1 H, 6-H), 7.18 (m, 2 H, 3-H/5-H), 7.12–
3
7.01 (m, 1 H, 4-H), 3.74 [sept, J = 6.8 Hz, 1 H, CH(CH3)2], 1.24
[d, 3J = 6.9 Hz, 6 H, CH(CH3)2] ppm. 13C{1H} NMR (75 MHz,
CDCl3, 25 °C): δ = 157.7 (C-2), 139.6 (C-6), 125.5 (C-5), 122.9 (C-
4), 122.6 (C-3), 27.4 [CH(CH3)2], 20.1 [CH(CH3)2] ppm.
Eur. J. Inorg. Chem. 2006, 366–379
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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373

K. Nienkemper, V. V. Kotov, G. Kehr, G. Erker, R. Fröhlich
FULL PAPER
2-tert-Butylpyridine N-Oxide (8c): In an analogous procedure, reac-
tion of 7c (33.0 g, 244 mmol) in chloroform (750 mL) with m-chlo-
7.7, 4J = 1.3 Hz, 1 H, 5-H), 2.69 (s, 3 H, COCH3), 1.36 [s, 9 H,
C(CH3)3] ppm. 13C{1H} NMR (75 MHz, CDCl3, 25 °C): δ = 201.0
(CO), 168.7 (C-6), 152.4 (C-2), 136.8 (C-4), 122.4 (C-5), 118.1 (C-
roperbenzoic acid (60.2 g, 244 mmol) yielded 8c as a yellow oil
1
(29.0 g, 79%). H NMR (200 MHz, CDCl3, 25 °C): δ = 8.15 (dd, 3), 37.6 [C(CH3)3], 30.5 [C(CH3)3], 25.6 (COCH3) ppm. C11H15NO
4
3
4
3J = 6.1, J = 1.8 Hz, 1 H, 6-H), 7.29 (dd, J = 7.9, J = 2.4 Hz, 1 (177.24): calcd. C 74.54, H 8.53, N 7.90; found C 74.30, H 8.64, N
3
4
H, 3-H), 7.15 (dt, J = 7.9, J = 1.8 Hz, 1 H, 4-H), 7.11–7.02 (m, 7.85.
1 H, 5-H), 1.48 [s, 9 H, C(CH3)3] ppm. 13C{1H} NMR (75 MHz,
2-Acetyl-6-isopropylpyridine N-Oxide (11b): Compound 10b
CDCl3, 25 °C): δ = 157.9 (C-2), 141.6 (C-6), 125.3 (C-5), 123.5 (C-
4), 123.4 (C-3), 36.1 [C(CH3)3], 26.8 [C(CH3)3] ppm.
(6.00 g, 36.8 mmol), dissolved in glacial acetic acid (25 mL), was
treated with hydrogen peroxide solution (5.6 mL, 30%). The mix-
ture was allowed to react at 70–80 °C for 10 h. Additional hydrogen
peroxide solution (4.6 mL, 30%) was then added and the mixture
6-Isopropylpyridine-2-carbonitrile (9b): Dimethylcarbamoyl chlo-
ride (52.7 mL, 574 mmol) was added dropwise to a solution of 8b
(62.3 g, 454 mmol) and trimethylsilyl cyanide (71.8 mL, 574 mmol) was heated for another 10 h. After cooling to room temperature,
in dichloromethane (400 mL). The resulting mixture was stirred at
room temperature for 2 d and the progress of the reaction was mon-
itored by TLC (pentane/chloroform/triethylamine, 20:5:1). Then, a
10% aqueous K2CO3 solution was added and stirring continued
for 15 min. The organic phase was separated and the aqueous layer
extracted with dichloromethane. The combined organic layers were
dried (MgSO4), the solvent was evaporated and the crude product
distilled to give the 9b as a bright-yellow oil (40.2 g, 61%). 1H
the solvent was evaporated and the crude residue was treated with
sodium carbonate solution. The aqueous phase was extracted with
dichloromethane, the combined organic layers dried (Na2SO4) and
the solvent evaporated. The product was obtained as a yellow oil
1
(3.99 g, 61%). H NMR (200 MHz, CDCl3, 25 °C): δ = 7.40 (dd,
4
3
4
3J = 7.8, J = 2.2 Hz, 1 H, 3-H), 7.30 (dd, J = 7.8, J = 2.2 Hz, 1
3
3
H, 5-H), 7.21 (t, J = 7.8 Hz, 1 H, 4-H), 3.72 [sept, J = 7.1 Hz, 1
H, CH(CH3)2], 2.71 (s, 3 H, COCH3), 1.26 [d, 3J = 7.1 Hz, 6 H,
CH(CH3)2] ppm. 13C{1H} NMR (75 MHz, CDCl3, 25 °C): δ =
196.1 (CO), 158.6 (C-6), 147.5 (C-2), 124.9 (C-4), 124.3 (C-5), 123.4
(C-3), 30.2 (COCH3), 27.2 [CH(CH3)2], 20.1 [CH(CH3)2] ppm.
3
NMR (200 MHz, CDCl3, 25 °C): δ = 7.71 (t, J = 7.9 Hz, 1 H, 4-
3
4
3
H), 7.47 (dd, J = 7.9, J = 1.0 Hz, 1 H, 3-H), 7.36 (dd, J = 7.9,
4J = 1.0 Hz, 1 H, 5-H), 3.06 [sept, J = 7.0 Hz, 1 H, CH(CH3)2],
3
1.25 [d, 3J = 7.0 Hz, 6 H, CH(CH3)2] ppm. 13C{1H} NMR C10H13NO2 (179.22): calcd. C 67.02, H 7.31, N 7.82; found C
(75 MHz, CDCl3, 25 °C): δ = 169.3 (C-6), 137.1 (C-4), 133.0 (C-2), 66.63, H 7.49, N 8.11.
125.8 (C-3), 124.3 (C-5), 117.5 (CN), 36.2 [CH(CH3)2], 22.1
General Procedure for the Preparation of the Ketimines 3a, 3b, 2a,
[CH(CH3)2] ppm.
2b: A mixture of the appropriate 2-acetylpyridine compound
6-tert-Butylpyridine-2-carbonitrile (9c):[26] Analogously to the prep-
aration of 9b, reaction of 8c (29.0 g, 192 mmol), trimethylsilyl cya-
nide (30.4 mL, 243 mmol) and dimethylcarbamoyl chloride
(22.3 mL, 243 mmol) in dichloromethane (200 mL) yielded 9c as a
bright-yellow oil (20.0 g, 65%). 1H NMR (200 MHz, CDCl3,
(12 mmol), 2,6-diisopropylaniline (16 mmol), a catalytic amount of
formic acid and sodium sulfate in methanol was refluxed for several
hours. The progress of the reaction was monitored by TLC. After
cooling to room temperature, the precipitate was removed by fil-
tration, the solvent was evaporated and the crude product purified
3
3
4
25 °C): δ = 7.72 (t, J = 7.9 Hz, 1 H, 4-H), 7.53 (dd, J = 7.9, J = by column chromatography on silica gel. In most cases crystals
3
4
1.1 Hz, 1 H, 3-H), 7.46 (dd, J = 7.9, J = 1.1 Hz, 1 H, 5-H), 1.32
suitable for the X-ray crystal structure analysis were grown from
[s, 9 H, C(CH3)3] ppm. 13C{1H} NMR (75 MHz, CDCl3, 25 °C): δ pentane at room temperature by means of solvent evaporation.
= 171.4 (C-6), 137.0 (C-4), 132.7 (C-2), 125.3 (C-3), 122.7 (C-5),
(2,6-Diisopropylphenyl)[1-(pyridin-2-yl)ethylidene]amine (3a): For-
117.7 (CN), 37.9 [C(CH3)3], 29.8 [C(CH3)2] ppm.
mula C19H24N2,
M
=
280.40, light yellow crystal
2-Acetyl-6-isopropylpyridine (10b):
A
solution of 9b (38.0 g,
0.50×0.30×0.10 mm, a = 8.469(1), b = 9.503(1), c = 11.790(1) Å,
α = 108.47(1), β = 103.82(1), γ = 100.68(1)°, V = 838.1(2) Å3, ρcalcd.
= 1.111 gcm–3, μ = 0.65 cm–1, no absorption correction (0.968 Յ
260 mmol) in diethyl ether (400 mL) was cooled to –25 °C and
methyllithium (179 mL, 286 mmol, 1.6 m solution in diethyl ether)
was added dropwise. The reaction mixture was warmed to ambient
¯
T Յ 0.994), Z = 2, triclinic, space group P1 (no. 2), λ = 0.71073 Å,
temperature within 2 h and then quenched with a mixture of aque- T = 198 K, ω and φ scans, 5134 reflections collected ( h, k, l),
ous ammonium chloride solution and hydrochloric acid. The or-
ganic phase was separated and the aqueous phase extracted with
diethyl ether. The ethereal solution was dried (Na2SO4) and the
solvent evaporated. Distillation yielded the product as a colourless
oil (10.6 g, 25%). 1H NMR (200 MHz, CDCl3, 25 °C): δ = 7.79
(dd, J = 7.7, J = 1.2 Hz, 1 H, 5-H), 7.67 (t, J = 7.7 Hz, 1 H, 4-
H), 7.28 (dd, 3J = 7.7, 4J = 1.2 Hz, 1 H, 3-H), 3.07 [sept, 3J =
7.0 Hz, 1 H, CH(CH3)2], 2.68 (s, 3 H, COCH3), 1.29 [d, 3J =
7.0 Hz, 6 H, CH(CH3)2] ppm. 13C{1H} NMR (75 MHz, CDCl3,
25 °C): δ = 200.8 (CO), 166.6 (C-6), 153.0 (C-2), 136.8 (C-4), 124.2
(C-3), 118.6 (C-5), 36.0 [CH(CH3)2], 25.5 (COCH3), 22.4
[CH(CH3)2] ppm. C10H13NO (163.22): calcd. C 73.59, H 8.03, N
8.58, found C 73.30, H 8.21, N 8.94.
[(sinθ)/λ] = 0.62 Å–1, 3372 independent (Rint = 0.019) and 2651 ob-
served reflections [I Ն 2σ(I)], 195 refined parameters, R = 0.047,
wR2 = 0.124, max. residual electron density 0.18 (–0.16) eÅ–3, hy-
drogen atoms calculated and refined as riding atoms.
(2,6-Diisopropylphenyl)[1-(6-isopropylpyridin-2-yl)ethylidene]amine
(3b): Reaction of 2-acetyl-6-isopropylpyridine (10b; 3.51 g,
21.5 mmol) with 2,6-diisopropylaniline (5.4 mL, 28.7 mmol)
yielded a yellow solid (5.87 g, 85%) after column chromatography
(SiO2; pentane/ethyl acetate, 20:1). M.p. 81 °C. 1H NMR
3
4
3
3
(600 MHz, CDCl3, 25 °C): δ = 8.18 (br. d, 1 H, 3-Hpy), 7.71 (t, J
3
= 7.7 Hz, 1 H, 4-Hpy), 7.25 (d, J = 7.7 Hz, 1 H, 5-Hpy), 7.16 (m,
3
2 H, 3-/5-Har), 7.09 (m, 1 H, 4-Har), 3.12 [sept, J = 6.9 Hz, 1 H,
3
CH(CH3)2py], 2.77 [sept, J = 6.9 Hz, 2 H, CH(CH3)2ar], 2.22 (s, 3
3
3
2-Acetyl-6-tert-butylpyridine (10c): Analogously to the preparation
of 10b, 10c was prepared from the reaction of 9c (18.4 g, 115 mmol)
with methyllithium (79.4 mL, 127 mmol, 1.6 m solution in diethyl
ether) in diethyl ether (180 mL). After aqueous workup and distil-
lation, the product was obtained as a colourless oil (7.33 g, 36%).
H, CNCH3), 1.35 [d, J = 6.9 Hz, 6 H, CH(CH3)2py], 1.15 [d, J =
6.9 Hz, 12 H, CH(CH3)2ar] ppm. 1H NMR (600 MHz, CDCl3,
3
–65 °C): δ = 8.14 (d, J = 7.6 Hz, 1 H, 3-Hpy), 7.75 (t, 3J = 7.6 Hz,
3
1 H, 4-Hpy), 7.29 (d, J = 7.6 Hz, 1 H, 5-Hpy), 7.19 (m, 2 H, 3-/5-
Har), 7.14 (m, 1 H, 4-Har), 3.08 [sept, 3J = 6.7 Hz, 1 H, CH-
3
4
3
1H NMR (200 MHz, CDCl3, 25 °C): δ = 7.79 (dd, J = 7.7, J =
(CH3)2py], 2.74 [sept, J = 6.7 Hz, 2 H, CH(CH3)2ar], 2.22 (s, 3 H,
3
3
1.3 Hz, 1 H, 3-H), 7.69 (t, J = 7.7 Hz, 1 H, 4-H), 7.46 (dd, J =
CNCH3), 1.32 [d, 3J = 6.7 Hz, 6 H, CH(CH3)2py], 1.12 [d, 3J =
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Chelate [2-(Iminoethyl)pyridine N-oxide]metal Complexes
FULL PAPER
6.7 Hz, 6 H, CH(CH3ACH3 )ar], 1.10 [d, 3J = 6.7 Hz, 6 H, 3.85 [sept, J = 6.9 Hz, 1 H, CH(CH3)2py], 2.92 [sept, J = 6.9 Hz,
B
3
3
CH(CH3ACH3 )ar] ppm. 13C{1H} NMR (150 MHz, CDCl3, 2 H, CH(CH3)2ar], 2.17 (s, 3 H, CNCH3), 1.31 [d, J = 6.9 Hz, 6
B
3
–65 °C): δ = 167.7 (CN), 165.9 (C-6py), 154.7 (C-2py), 145.9 (C-1ar), H, CH(CH3)2py], 1.23 [d, 3J = 6.9 Hz, 6 H, CH(CH3ACH3 )ar], 1.16
B
136.7 (C-4py), 135.8 (C-2/–6ar), 123.1 (C-4ar), 122.7 (C-3/–5ar), 121.7 [d, 3J = 6.9 Hz, 6 H, CH(CH3ACH3 )ar] ppm. 1H NMR (600 MHz,
B
3
4
(C-5py), 118.2 (C-3py), 36.2 [CH(CH3)2py], 27.7 [CH(CH3)2ar], 23.1 CDCl3, –60 °C): δ = 7.46 (dd, J = 7.7, J = 2.1 Hz, 1 H, 3-Hpy),
B
B
3
3
4
[CH(CH3ACH3 )ar], 23.0 [CH(CH3ACH3 )ar], 22.7 [CH(CH3)2py], 7.41 (t, J = 7.7 Hz, 1 H, 4-Hpy), 7.37 (dd, J = 7.7, J = 2.1 Hz, 1
17.5 (CNCH3) ppm. MS (ESI): m/z (%) = 345.3 (100) [M + Na]+,
323 (12) [M + H]+. C22H30N2 (322.49): calcd. C 81.94, H 9.38, N
8.69; found C 81.75, H 9.32, N, 8.64.
H, 5-Hpy), 7.19 (m, 2 H, 3-/5-Har), 7.15 (m, 1 H, 4-Har), 3.84 [sept,
3J = 6.8 Hz, 1 H, CH(CH3)2py], 2.87 [sept, 3J = 6.8 Hz, 2 H,
CH(CH3)2ar], 2.15 (s, 3 H, CNCH3), 1.28 [d, 3J = 6.8 Hz, 6 H,
CH(CH3)2py], 1.19 [d, 3J = 6.8 Hz, 6 H, CH(CH3ACH3 )ar], 1.14
B
X-ray Crystal Structure Analysis of 3b: Formula C22H30N2, M =
322.48, colourless crystal 0.45×0.30×0.20 mm, a = 11.486(1), b =
17.360(1), c = 11.529(1) Å, β = 117.34(1)°, V = 2042.1(3) Å3, ρcalcd.
= 1.049 gcm–3, μ = 4.59 cm–1, no absorption correction (0.820 Յ
T Յ 0.914), Z = 4, monoclinic, space group P21/c (no. 14), λ =
1.54178 Å, T = 223 K, ω and φ scans, 11145 reflections collected
( h, k, l), [(sinθ)/λ] = 0.59 Å–1, 3444 independent (Rint = 0.022)
and 2708 observed reflections [I Ն 2σ(I)], 225 refined parameters,
R = 0.046, wR2 = 0.133, max. residual electron density 0.28
(–0.18) eÅ–3, hydrogen atoms calculated and refined as riding
atoms.
[d, 3J = 6.8 Hz, 6 H, CH(CH3ACH3 )ar] ppm. 13C{1H} NMR
B
(150 MHz, CDCl3, 25 °C): δ = 165.8 (CN), 158.3 (C-6py), 149.5 (C-
2py), 144.2 (C-1ar), 136.3 (C-2/–6ar), 125.4 (C-4py), 124.2 (C-4ar),
123.2 (C-3py), 123.1 (C-3/–5ar, C-5py), 28.0 [CH(CH3)2ar], 27.2
B
B
[CH(CH3)2py], 23.5 [CH(CH3ACH3 )ar], 22.9 [CH(CH3ACH3 )ar],
20.5 [CH(CH3)2py], 19.9 (CNCH3) ppm. MS (ESI): m/z (%) = 361
(45) [M + Na]+, 339 (100) [M + H]+. C22H30N2O (338.49): calcd.
C 78.06, H 8.93, N 8.28; found C 77.92, H 9.05, N 8.16.
X-ray Crystal Structure Analysis of 2b: Formula C22H30N2O, M =
338.48, colourless crystal 0.40×0.25×0.20 mm, a = 8.534(1), b =
14.593(1), c = 16.546(1) Å, β = 92.64(1)°, V = 2058.4(3) Å3, ρcalcd.
= 1.092 gcm–3, μ = 5.14 cm–1, empirical absorption correction
(0.821 Յ T Յ 0.904), Z = 4, monoclinic, space group P21 (no. 4),
λ = 1.54178 Å, T = 293 K, ω/2θ scans, 4517 reflections collected
( h, –k, +l), [(sinθ)/λ] = 0.62 Å–1, 4369 independent (Rint = 0.035)
and 3210 observed reflections [I Ն 2σ(I)], 466 refined parameters,
R = 0.045, wR2 = 0.136, Flack parameter 0.0(4), max. residual
electron density 0.21 (–0.16) eÅ–3, hydrogen atoms calculated and
refined as riding atoms.
2-[1-(2,6-Diisopropylphenylimino)ethyl]pyridine N-Oxide (2a): Reac-
tion of 2-acetylpyridine N-oxide (5.77 g, 42.1 mmol) with 2,6-diiso-
propylaniline (10.6 mL, 56.0 mmol) yielded a yellow solid (8.36 g,
67%) after column chromatography (SiO2; pentane/chloroform/tri-
ethylamine/methanol, 4:1:1:1). M.p. 80 °C. 1H NMR (600 MHz,
3
3
CDCl3, 25 °C): δ = 8.23 (m, J = 6.4 Hz, 1 H, 6-Hpy), 7.62 (dd, J
4
3
4
= 7.6, J = 2.3 Hz, 1 H, 3-Hpy), 7.35 (dt, J = 7.6, J = 1.3 Hz, 1
3
3
4
H, 4-Hpy), 7.32 (ddd, J = 7.6, J = 6.4, J = 2.3 Hz, 1 H, 5-Hpy),
7.16 (m, 2 H, 3-/5-Har), 7.10 (m, 1 H, 4-Har), 2.88 [sept, 3J = 6.8 Hz,
3
General Procedure for the Preparation of Metal Complexes: The me-
tal precursor (1 mmol) was suspended in the appropriate solvent
(20 mL), stirred, and a solution of the ligand (1 mmol) in the same
solvent (10 mL) was added. The resulting mixture was stirred for
several hours. For workup, the mixture was filtered, the solvent
evaporated, the crude product washed with pentane and dried in
vacuo. In most cases crystals suitable for X-ray analyses were
grown from a concentrated solution of the complex in a mixture
of acetonitrile/dichloromethane/THF layered with pentane.
2 H, CH(CH3)2ar], 2.19 (s, 3 H, CNCH3), 1.22 [d, J = 6.8 Hz, 6
H, CH(CH3ACH3 )ar], 1.16 [d, 3J
= 6.8 Hz, 6 H, CH-
B
(CH3ACH3 )ar] ppm. 1H NMR (600 MHz, CDCl3, –60 °C): δ =
B
8.27 (d, 3J = 6.3 Hz, 1 H, 6-Hpy), 7.66 (d, 3J = 7.6 Hz, 1 H, 3-Hpy),
3
7.46 (t, J = 7.6 Hz, 1 H, 4-Hpy), 7.41 (m, 1 H, 5-Hpy), 7.19 (m, 2
H, 3-/5-Har), 7.16 (m, 1 H, 4-Har), 2.82 [sept, 3J = 6.8 Hz, 2 H,
CH(CH3)2ar], 2.17 (s, 3 H, CNCH3), 1.19 [d, 3J = 6.8 Hz, 6 H,
CH(CH3ACH3 )ar], 1.13 [d, 3J = 6.8 Hz, 6 H, CH(CH3ACH3 )ar]
ppm. 13C{1H} NMR (150 MHz, CDCl3, 25 °C): δ = 164.9 (CN),
149.4 (C-2py), 144.4 (C-1ar), 140.1 (C-6py), 136.1 (C-2/–6ar), 128.0
(C-4py), 126.9 (C-5py), 126.1 (C-3py), 124.3 (C-4ar), 123.1 (C-3/–5ar),
B
B
Reaction of Ligand 3b with FeCl2; Synthesis of Compound 12b: A
suspension of anhydrous FeCl2 (393 mg, 3.1 mmol) in THF was
heated to 70 °C and a solution of 3b (1.00 g, 3.1 mmol) in THF
was added. The resulting mixture was stirred for 2 h. After workup
and drying, the product was obtained as brown powder (1.22 g,
87%). MS (ESI): m/z (%) = 535.3 (100) [FeCl2(3b) + BF4]–.
C22H30Cl2FeN2 (449.24): calcd. C 58.82, H 6.73, N 6.24; found C
57.01, H 6.67, N, 5.71.
28.1 [CH(CH3)2ar], 23.4 [CH(CH3ACH3 )ar], 22.9 [CH-
B
(CH3ACH3 )ar], 19.8 (CNCH3) ppm. MS (ESI): m/z (%) = 319
B
(100) [M + Na]+, 297 (85) [M + H]+. C19H24N2O (296.41): calcd.
C 76.99, H 8.16, N 9.45; found C 76.87, H 8.10, N 9.37.
X-ray Crystal Structure Analysis of 2a: Formula C19H24N2O, M =
296.40, yellow crystal 0.35×0.25×0.15 mm, a = 8.698(1), b =
8.800(1), c = 11.502(1) Å, α = 103.05(1), β = 95.07(1), γ = 97.15(1)°,
V = 844.8(2) Å3, ρcalcd. = 1.165 gcm–3, μ = 5.62 cm–1, empirical
absorption correction (0.828 Յ T Յ 0.920), Z = 2, triclinic, space
X-ray
Crystal
C22H30Cl2FeN2·C4H8O,
Structure
Analysis
=
of
521.33,
12b:
red
Formula
crystal
M
0.30×0.25×0.15 mm, a = 8.701(1), b = 15.738(1), c = 20.229(1) Å,
β = 97.33(1)°, V = 2747.4(4) Å3, ρcalcd. = 1.260 gcm–3, μ =
7.63 cm–1, empirical absorption correction (0.803 Յ T Յ 0.894), Z
= 4, monoclinic, space group P21/c (no. 14), λ = 0.71073 Å, T =
198 K, ω and φ scans, 16643 reflections collected ( h, k, l),
[(sinθ)/λ] = 0.66 Å–1, 6533 independent (Rint = 0.047) and 4332 ob-
served reflections [I Ն 2σ(I)], 282 refined parameters, R = 0.069,
wR2 = 0.226, max. residual electron density 1.19 (–0.74) eÅ–3, sol-
vent molecule disordered, refined with split positions, geometrical
restraints, fixed occupancies (0.67:0.33) and one common isotropic
displacement parameter, hydrogen atoms calculated and refined as
riding atoms.
¯
group P1 (no. 2), λ = 1.54178 Å, T = 223 K, ω/2θ scans, 3610
reflections collected ( h, k, -l), [(sinθ)/λ] = 0.62 Å–1, 3433 inde-
pendent (Rint = 0.023) and 2840 observed reflections [I Ն 2σ(I)],
205 refined parameters, R = 0.043, wR2 = 0.126, max. residual elec-
tron density 0.20 (–0.20) eÅ–3, hydrogen atoms calculated and re-
fined as riding atoms.
2-[1-(2,6-Diisopropylphenylimino)ethyl]-6-isopropylpyridine N-Oxide
(2b): Reaction of 2-acetyl-6-isopropylpyridine N-oxide (3.21 g,
17.9 mmol) with 2,6-diisopropylaniline (4.5 mL, 23.9 mmol)
yielded, after column chromatography (SiO2; pentane/chloroform/
1
methanol, 20:3:1), 2.47 g (41%) of a yellow solid. M.p. 117 °C. H
NMR (600 MHz, CDCl3, 25 °C): δ = 7.46 (br. m, 1 H, 3-Hpy), 7.31 Reaction of Ligand 3b with CoCl2; Synthesis of Compound 13b:
(m, 2 H, 4-/5-Hpy), 7.16 (m, 2 H, 3-/5-Har), 7.10 (m, 1 H, 4-Har), Complex 13b was prepared in an analogous procedure. Reaction
Eur. J. Inorg. Chem. 2006, 366–379
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
375

K. Nienkemper, V. V. Kotov, G. Kehr, G. Erker, R. Fröhlich
FULL PAPER
of CoCl2 (402 mg, 3.1 mmol) and 3b (1.00 g, 3.1 mmol) in THF
yielded a green-blue powder (1.05 g, 74%). MS (ESI): m/z (%) =
10.132(1), c = 14.308(1) Å, β = 110.48(1)°, V = 1919.2(3) Å3, ρcalcd.
= 1.420 gcm–3, μ = 11.75 cm–1, empirical absorption correction
451.1 (100) [CoCl2(3b)]+. C22H30Cl2CoN2 (452.33): calcd. C 58.42, (0.719 Յ T Յ 0.892), Z = 4, monoclinic, space group P21/n (no.
H 6.69, N 6.19; found C 58.63, H 7.00, N 5.25.
X-ray Crystal Structure Analysis of
C22H30Cl2CoN2·0.5CH2Cl2·0.5C4H8O, M = 530.83, turquoise crys-
tal 0.40×0.05×0.05 mm, a = 8.679(1), = 15.655(1), c =
14), λ = 0.71073 Å, T = 198 K, ω and φ scans, 21540 reflections
collected ( h, k, l), [(sinθ)/λ] = 0.66 Å–1, 4559 independent (Rint
= 0.044) and 3700 observed reflections [I Ն 2σ(I)], 222 refined pa-
rameters, R = 0.031, wR2 = 0.070, max. residual electron density
0.30 (–0.32) eÅ–3, hydrogen atoms calculated and refined as riding
atoms.
13b:
Formula
b
20.196(1) Å, β = 97.93(1)°, V = 2717.8(4) Å3, ρcalcd. = 1.297 gcm–3,
μ = 9.42 cm–1, empirical absorption correction (0.704 Յ T Յ
0.954), Z = 4, monoclinic, space group P21/c (no. 14), λ =
0.71073 Å, T = 198 K, ω and φ scans, 15372 reflections collected
( h, k, l), [(sinθ)/λ] = 0.59 Å–1, 4789 independent (Rint = 0.091)
and 2800 observed reflections [I Ն 2σ(I)], 323 refined parameters,
R = 0.056, wR2 = 0.116, max. residual electron density 0.33
(–0.45) eÅ–3, solvent molecules sharing same side refined with split
positons and fixed occupancies (0.5), hydrogen atoms calculated
and refined as riding atoms.
Reaction of Ligand 3a with [NiBr2(dme)]; Synthesis of Compound
17a: A suspension of [NiBr2(dme)] (680 mg, 2.22 mmol) in dichlo-
romethane was treated with a solution of 3a (622 mg, 2.22 mmol)
in dichloromethane. The resulting mixture was stirred at room tem-
perature for 2 d, then another 300 mg of 3a (1.07 mmol) was added,
and stirring was continued for 2 d. After workup, compound 17a
was isolated as a green solid (1.46 g, 84%). MS (ESI): m/z (%) =
699.4 (100) [NiBr(3a)2]+. C38H48Br2N4Ni (779.32): calcd. C 58.57,
H 6.21, N 7.19; found C 57.46, H 6.48, N 6.82.
Reaction of Ligand 3b with [NiBr2(dme)]; Synthesis of Compound
14b: A suspension of [NiBr2(dme)] (948 mg, 3.1 mmol) in dichloro-
methane was treated with a solution of 3b (1.0 g, 3.1 mmol) in
dichloromethane. The resulting mixture was stirred at room tem-
perature for 24 h. After workup, the product was isolated as a light-
brown powder (1.19 g, 71%). MS (ESI) m/z (%) = 461.3 (83)
[NiBr(3b)]+, 323.4 (25) [3b + H]+, 189.1 (100). C22H30Br2N2Ni
(540.99): calcd. C 48.84, H 5.59, N 5.18; found C 48.81, H 5.51, N
5.04.
Reaction of Ligand 2a with FeCl2; Synthesis of Compound 18a: The
reaction of FeCl2 (107 mg, 0.84 mmol) with 2a (500 mg,
1.69 mmol) in THF at room temperature yielded a black powder
(0.52 mmol, 62%). MS (ESI): m/z (%) = 651.4 (100) [FeCl(3a)]+,
102.0 (45). C38H48Cl5Fe2N4 (849.77): calcd. C 53.71, H 5.69, N
6.59; found C 53.02, H 5.78, N 6.58.
X-ray
C38H48ClFeN4·FeCl4,
Crystal
Structure
Analysis
of
18a:
red
Formula
crystal
M
=
849.76,
X-ray Crystal Structure Analysis of 14b: Formula C22H30Br2N2Ni,
M = 541.01, yellow crystal 0.50×0.30×0.08 mm, a = 8.685(1), b =
19.351(1), c = 27.866(1) Å, V = 4683.3(6) Å3, ρcalcd. = 1.535 gcm–3,
μ = 42.50 cm–1, empirical absorption correction (0.225 Յ T Յ
0.727), Z = 8, orthorhombic, space group Pbca (no. 61), λ =
0.71073 Å, T = 198 K, ω and φ scans, 10395 reflections collected
( h, k, l), [(sinθ)/λ] = 0.66 Å–1, 5573 independent (Rint = 0.036)
and 4039 observed reflections [I Ն 2σ(I)], 251 refined parameters,
R = 0.038, wR2 = 0.079, max. residual electron density 0.91
(–0.89) eÅ–3, hydrogen atoms calculated and refined as riding
atoms.
0.30×0.30×0.10 mm, a = 8.835(1), b = 15.414(1), c = 15.138(1) Å,
β = 95.31(1)°, V = 2052.7(3) Å3, ρcalc = 1.375 gcm–3, μ =
10.64 cm–1, empirical absorption correction (0.741 Յ T Յ 0.901),
Z = 2, monoclinic, space group P21 (no. 4), λ = 0.71073 Å, T =
198 K, ω and φ scans, 17177 reflections collected ( h, k, l),
[(sinθ)/λ] = 0.59 Å–1, 6886 independent (Rint = 0.064) and 6040 ob-
served reflections [I Ն 2σ(I)], 452 refined parameters, R = 0.099,
wR2 = 0.267, Flack parameter 0.01(4), max. residual electron den-
sity 2.42 (–0.56) eÅ–3, very poor, partly amorphous crystal leads to
an analysis of limited accuracy, hydrogen atoms calculated and re-
fined as riding atoms.
Reaction of Ligand 3a with FeCl2; Synthesis of Compound 15a: Re-
action of FeCl2 (1.00 g, 7.89 mmol) in THF with 3a (2.21 g,
7.89 mmol) at 80 °C yielded a black solid (1.99 g, 62%).
Reaction of Ligand 2a with PdCl2; Synthesis of Compound 19a: A
suspension of PdCl2 (500 mg, 2.82 mmol) in acetonitrile was
treated with a solution of 2a (836 mg, 2.82 mmol) in acetonitrile.
After workup, the product was obtained as an orange solid (1.0 g,
75%). 1H NMR (600 MHz, CH3CN, 25 °C): δ = 8.68 (dd, 3J = 6.5,
X-ray Crystal Structure Analysis of 15a: Formula C19H24Cl2FeN2,
M = 407.15, red crystal 0.30×0.25×0.15 mm, a = 14.151(1), b =
10.073(1), c = 14.431(1) Å, β = 109.97(1)°, V = 1933.4(3) Å3, ρcalcd.
= 1.399 gcm–3, μ = 10.59 cm–1, empirical absorption correction
(0.742 Յ T Յ 0.857), Z = 4, monoclinic, space group P21/n (no.
14), λ = 0.71073 Å, T = 198 K, ω and φ scans, 6709 reflections
collected ( h, k, l), [(sinθ)/λ] = 0.62 Å–1, 3913 independent (Rint
= 0.043) and 2907 observed reflections [I Ն 2σ(I)], 222 refined pa-
rameters, R = 0.096, wR2 = 0.291, max. residual electron density
1.97 (–0.62) eÅ–3, the remaining electron density is located around
x,0,z, all attempts to refine these in a chemically meaningful way
failed, analysis only done to confirm the geometry of the complex,
hydrogen atoms calculated and refined as riding atoms.
3
4
4J = 1.3 Hz, 1 H, 6-Hpy), 8.18 (dd, J = 8.0, J = 1.8 Hz, 1 H, 3-
3
4
3
Hpy), 8.08 (dt, J = 8.0, J = 1.3 Hz, 1 H, 4-Hpy), 7.82 (ddd, J =
8.0, 3J = 6.5, 4J = 1.8 Hz, 1 H, 5-Hpy), 7.33 (m, 2 H, 3-/5-Har), 7.28
3
(m, 1 H, 4-Har), 3.32 [sept, J = 6.8 Hz, 2 H, CH(CH3)2ar], 2.23 (s,
3 H, CNCH3), 1.59 [d, J = 6.8 Hz, 6 H, CH(CH3ACH3 )ar], 1.19
3
B
3
B
[d, J = 6.8 Hz, 6 H, CH(CH3ACH3 )ar] ppm. MS (ESI): m/z (%)
= 561.0 (100) [PdCl2(2a) + BF4]–. C19H24Cl2N2OPd (473.73): calcd.
C 48.17, H 5.11, N 5.91; found C 47.94, H 5.49, N 5.97.
X-ray
Crystal
Structure
Analysis
of
514.76,
19a:
red
Formula
crystal
C19H24Cl2N2OPd·C2H3N,
M
=
Reaction of Ligand 3a with CoCl2; Synthesis of Compound 16a: In
an analogous procedure, complex 16a was obtained by treating
CoCl2 (1.0 g, 7.70 mmol) with compound 3a (2.16 g, 7.70 mmol) in
THF and collected as a green powder (2.10 g, 66%). MS (ESI):
m/z (%) = 496.1 (100) [CoCl2(3a) + BF4]–. C19H24Cl2CoN2
(410.25): calcd. C 55.63, H 5.90, N 6.83; found C 56.96, H 6.90, N
5.10.
0.50×0.40×0.30 mm, a = 9.307(1), b = 17.942(1), c = 13.611(1) Å,
β = 97.51(1)°, V = 2253.4(3) Å3, ρcalcd. = 1.517 gcm–3, μ =
10.77 cm–1, empirical absorption correction (0.615 Յ T Յ 0.738),
Z = 4, monoclinic, space group P21/n (no. 14), λ = 0.71073 Å, T =
198 K, ω and φ scans, 14417 reflections collected ( h, k, l),
[(sinθ)/λ] = 0.66 Å–1, 5323 independent (Rint = 0.034) and 5074 ob-
served reflections [I Ն 2σ(I)], 259 refined parameters, R = 0.026,
X-ray Crystal Structure Analysis of 16a: Formula C19H24Cl2CoN2, wR2 = 0.068, max. residual electron density 1.04 (–0.83) eÅ–3, hy-
M = 410.23, pink crystal 0.30×0.25×0.10 mm, a = 14.132(1), b = drogen atoms calculated and refined as riding atoms.
376
www.eurjic.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 366–379

Chelate [2-(Iminoethyl)pyridine N-oxide]metal Complexes
FULL PAPER
Reaction of Ligand 2a with CoCl2; Synthesis of Compound 20a: Re-
action of CoCl2 (1.0 g, 77 mol) with 2a (2.28 g, 77 mmol) in THF
0.712), Z = 8, monoclinic, space group P21/c (no. 14), λ =
0.71073 Å, T = 198 K, ω and φ scans, 29515 reflections collected
yielded a blue powder (3.12 g, 95%). C19H24Cl2CoN2O (426,25): ( h, k, l), [(sinθ)/λ] = 0.68 Å–1, 11531 independent (Rint = 0.075)
calcd. C 53.54, H 5.68, N 6.57; found C 54.79, H 6.65, N 5.95.
and 5668 observed reflections [I Ն 2σ(I)], 506 refined parameters,
R = 0.062, wR2 = 0.144, max. residual electron density 1.34
(–1.25) eÅ–3, hydrogen atoms calculated and refined as riding
atoms.
X-ray
C19H24Cl2CoN2O·C5H12,
0.60×0.10×0.05 mm,
Crystal
Structure
Analysis
498.38,
32.646(1), b = 10.395(1), c =
of
20a:
green
Formula
crystal
M
=
a
=
13.788(1) Å, β = 93.73(1)°, V = 4669.1(6) Å3, ρcalcd. = 1.418 gcm–3,
μ = 9.83 cm–1, empirical absorption correction (0.590 Յ T Յ
0.953), Z = 8, monoclinic, space group C2/c (no. 15), λ =
0.71073 Å, T = 198 K, ω and φ scans, 24564 reflections collected
( h, k, l), [(sinθ)/λ] = 0.67 Å–1, 5836 independent (Rint = 0.054)
and 3644 observed reflections [I Ն 2σ(I)], 251 refined parameters,
R = 0.052, wR2 = 0.166, max. residual electron density 0.48
(–0.41) eÅ–3, solvent molecule refined as pentane with geometrical
restraints, hydrogen atoms calculated and refined as riding atoms.
Reaction of Ligand 2a with Cu(OTf)2; Synthesis of Compound 23a:
Cu(OTf)2 (1.0 g, 2.76 mmol) was treated with ligand 2a (0.82 g,
2.76 mmol) at room temperature in dichloromethane. After workup
a green powder was isolated (1.38 g, 76%).
X-ray Crystal Structure Analysis of 23a: Formula C19H24CuN2O-
(H2O)(CF3SO3)2·CH2Cl2,
M
=
761.02,
green
crystal
0.40×0.15×0.05 mm, a = 8.881(1), b = 19.970(1), c = 18.480(1) Å,
β = 97.77(1)°, V = 3247.4(4) Å3, ρcalcd. = 1.557 gcm–3, μ =
10.44 cm–1, empirical absorption correction (0.680 Յ T Յ 0.950),
Z = 4, monoclinic, space group P21/n (no. 14), λ = 0.71073 Å, T =
198 K, ω and φ scans, 22468 reflections collected ( h, k, l),
[(sinθ)/λ] = 0.68 Å–1, 8157 independent (Rint = 0.052) and 5356 ob-
served reflections [I Ն 2σ(I)], 399 refined parameters, R = 0.052,
wR2 = 0.132, max. residual electron density 0.71 (–0.51) eÅ–3, hy-
drogen atoms at water from difference Fourier calculations, other
calculated and all refined as riding atoms.
Reaction of Ligand 2a with [NiBr2(dme)]; Synthesis of Compound
21a: A solution of the ligand 2a (0.77 g, 26 mmol) in dichlorometh-
ane was added to a suspension of [NiBr2(dme)] (1.0 g, 26 mmol) in
dichloromethane. The resulting mixture was refluxed for 2 h. After
workup, compound 21a was obtained as a brown solid (1.17 g,
54%). MS (ESI): m/z (%) = 731.3 (40) [NiBr(2a)2]+, 325.2 (80),
297.2 (100), 178.0 (70), 101.9 (70).
Supporting Information (see footnote on the first page of this arti-
cle): X-ray crystal structure analyses of 3c, 12b, 13b and 16a, and
additional spectroscopic information for 2a,b, 3b,c and 19a.
X-ray
Crystal
Structure
Analysis
of
21a:
Formula
C38H48Br2N4NiO2, M = 811.33, red crystal 0.35×0.30×0.20 mm,
a = 11.156(1), b = 30.146(1), c = 12.011(1) Å, β = 109.81(1)°, V =
3800.4(5) Å3, ρcalcd. = 1.418 gcm–3, μ = 26.50 cm–1, empirical ab-
sorption correction (0.457 Յ T Յ 0.619), Z = 4, monoclinic, space
group P21/c (no. 14), λ = 0.71073 Å, T = 198 K, ω and φ scans,
22711 reflections collected ( h, k, l), [(sinθ)/λ] = 0.62 Å–1, 7688
independent (Rint = 0.059) and 4718 observed reflections [I Ն
2σ(I)], 434 refined parameters, R = 0.047, wR2 = 0.103, max. resid-
ual electron density 0.63 (–0.52) eÅ–3, hydrogen atoms calculated
and refined as riding atoms.
Acknowledgments
Financial support from the Fonds der Chemischen Industrie and
the Deutsche Forschungsgemeinschaft is gratefully acknowledged.
V. V. K. thanks the Alexander von Humboldt-Stiftung for a sti-
pend.
Reaction of Ligand 2b with [NiBr2(dme)]; Synthesis of Compound
21b: [NiBr2(dme)] (453 mg, 1.48 mmol) was suspended in dichloro-
methane and 2b (500 mg, 1.48 mmol) in dichloromethane was
added. After workup compound 21b was isolated as dark-brown
solid (610 mg, 74%). MS (ESI) m/z (%) = 477.3 (100) [NiBr(2b)]+,
339.4 (61) [2b + H]+. C22H30Br2N2NiO (556.99): calcd. C 47.44, H
5.43, N 5.03; found C 48.02, H 5.40, N 4.83.
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X-ray
Crystal
Structure
Analysis
of
21b:
Formula
C26H38Br2N2NiO2, M = 629.11, red crystal 0.75×0.15×0.10 mm,
a = 8.744(1), b = 33.910(1), c = 9.367(1) Å, β = 95.39(1)°, V =
2765.1(4) Å3, ρcalcd. = 1.511 gcm–3, μ = 36.16 cm–1, empirical ab-
sorption correction (0.172 Յ T Յ 0.714), Z = 4, monoclinic, space
group P21/n (no. 14), λ = 0.71073 Å, T = 198 K, ω and φ scans,
19041 reflections collected ( h, k, l), [(sinθ)/λ] = 0.68 Å–1, 6690
independent (Rint = 0.054) and 5100 observed reflections [I Ն
2σ(I)], 305 refined parameters, R = 0.045, wR2 = 0.115, max. resid-
ual electron density 1.20 (–1.30) eÅ–3, hydrogen atoms calculated
and refined as riding atoms.
Reaction of Ligand 2a with ZnBr2; Synthesis of Compound 22a: Re-
action of ZnBr2 (0.76 g, 3.37 mmol) with ligand 2a (1.0 g,
3.37 mmol) in acetonitrile yielded after workup a bright yellow
powder (1.70 g, 97%).
X-ray
C19H24Br2N2OZn·0.5C4H8O
0.30×0.12×0.08 mm,
Crystal
Structure
Analysis
557.64, colourless crystal
15.943(1), 10.254(1),
of
22a:
Formula
M
=
a
=
b
=
c =
28.396(1) Å, β = 97.36(1)°, V = 4603.9(6) Å3, ρcalcd. = 1.609 gcm–3,
μ = 45.54 cm–1, empirical absorption correction (0.342 Յ T Յ
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378
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Eur. J. Inorg. Chem. 2006, 366–379

Chelate [2-(Iminoethyl)pyridine N-oxide]metal Complexes
FULL PAPER
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Received: July 20, 2005
Published Online: December 1, 2005
Eur. J. Inorg. Chem. 2006, 366–379
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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