Synthesis and transition metal coordination chemistry of a novel hexadentate bispidine ligand

Article abstract of DOI:10.1039/c4dt03262d

Reported is the new bispidine-derived hexadentate ligand L (L = 3-(2-methylpyridyl)-7-(bis-2-methylpyridyl)-3,7-diazabicyclo[3.3.1]nonane) with two tertiary amine and four pyridine donor groups. This ligand can form heterodinuclear and mononuclear complexes and, in the mononuclear compounds discussed here, the ligand may coordinate as a pentadentate ligand, with one of the bispyridinemethane-based pyridine groups un- or semi-coordinated, or as a hexadentate ligand, leading to a pentagonal pyramidal coordination geometry or, with an additional monodentate ligand, to a heptacoordinate pentagonal bipyramidal structure. The solution and solid state data presented here indicate that, with the relatively small Cu^II and high-spin Fe^II ions the fourth pyridine group is only semi-coordinated for steric reasons and, with the larger high-spin Mn^II ion genuine heptacoordination is observed but with a relatively large distortion in the pentagonal equatorial plane. This journal is

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Synthesis and transition metal coordination
chemistry of a novel hexadentate bispidine ligand†
Cite this: DOI: 10.1039/c4dt03262d
Peter Comba,* Henning Rudolf and Hubert Wadepohl
Reported is the new bispidine-derived hexadentate ligand L (L = 3-(2-methylpyridyl)-7-(bis-2-methylpyri-
dyl)-3,7-diazabicyclo[3.3.1]nonane) with two tertiary amine and four pyridine donor groups. This ligand
can form heterodinuclear and mononuclear complexes and, in the mononuclear compounds discussed
here, the ligand may coordinate as a pentadentate ligand, with one of the bispyridinemethane-based pyri-
dine groups un- or semi-coordinated, or as a hexadentate ligand, leading to a pentagonal pyramidal
coordination geometry or, with an additional monodentate ligand, to a heptacoordinate pentagonal
bipyramidal structure. The solution and solid state data presented here indicate that, with the relatively
small CuII and high-spin FeII ions the fourth pyridine group is only semi-coordinated for steric reasons
and, with the larger high-spin MnII ion genuine heptacoordination is observed but with a relatively large
distortion in the pentagonal equatorial plane.
Received 22nd October 2014,
Accepted 14th November 2014
DOI: 10.1039/c4dt03262d
www.rsc.org/dalton
nate to a single metal ion, leading to a pentagonal pyramidal
structure and possibly to heptacoordination, when a mono-
Introduction
The 3,7-diaza-bicyclo[3.3.1]nonane (bispidine) motif offers a dentate ligand completes the distorted pentagonal bipyrami-
rigid ligand backbone, resulting in a high degree of preorgani- dal coordination sphere, or behave as a dinucleating ligand
zation and rigidity, combined with a wide synthetic variability (see Chart 1). We discuss two different synthesis strategies for
for tailor-made ligand systems. The bispidine itself was first the ligand – the classical double Mannich reaction sequence
discovered by Mannich and Mohs1 and appears as a substruc- and the alkylation of the secondary amine at N7 of the tetra-
ture of the natural product sparteine. The general synthesis of dentate bispidone precursor. Also, in order to suppress retro
bispidines involves two consecutive double Mannich reactions Mannich ligand decay and hence enhance the stability of the
via the piperidone intermediate.1 Based on the possibility to formed complexes, ligand L was reduced at C9 to produce the
enforce specific coordination geometries and therefore stabil- corresponding alcohol derivative LOH. Here, we report the first
ize complexes with specific properties,2,3 the bispidine tran- row transition metal coordination chemistry of the new bispi-
sition metal coordination chemistry has developed into a dines as mononucleating ligands, and in particular we discuss
particularly broad field, with applications in catalytic the solid state and solution structures based on X-ray crystallo-
aziridination,4–6
sulfoxidation7–9
and
C–H-activation graphy, electrochemistry and EPR as well as ligand field
processes,10–12 molecular magnetism,13–16 the development of spectroscopy.
new ionophores,17 radiotracers for positron emission tomo-
graphy (PET),18–20 and copper sensors.21,22 Typical bispidine
ligands and the main structural features of their transition
Results and discussion
Ligand synthesis
metal complexes are shown in Chart 1.
Here, we present the new bispine ligand L with a bis(2-
pyridyl)methyl substituent, leading to a hexadentate ligand, an
isomer of the known hexadentate bispidine L2, with strikingly
different complexing properties: this ligand can either coordi-
The typical procedure to build up a bispidone is by two con-
secutive double Mannich reactions. The precursor for the syn-
thesis of the desired ligand L, the known di(2-pyridyl)amine
(2), is obtained in a two-step procedure from the commercially
available di(2-pyridyl)ketone.23 This was reacted with the
common Npy2 piperidone (pL) to obtain L in up to 16% yield
(Scheme 1). Due to the modest yield, L was alternatively
obtained by alkylation of the secondary amine N7 of the bispi-
dine precursor with the halogenated dipyridyl building block
(Scheme 1). For this convergent synthesis, we decided to insert
Universität Heidelberg, Anorganisch-Chemisches Institut and Interdisciplinary
Center for Scientific Computing (IWR), INF 270, D-69120 Heidelberg, Germany.
E-mail: peter.comba@aci.uni-heidelberg.de; Fax: +49-6221-546617
†Electronic supplementary information (ESI) available. CCDC 1030274–1030279.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c4dt03262d
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Chart 1 Ligands discussed in this publication, and the two isomeric hexacoordinate structures with L2 and L (if X = void), as well as the two coordi-
nation modes (mono- and dinucleating) of the hexadentate bispidine L.
a latent benzyl protecting group at N7 by choosing benzyl Transition metal coordination chemistry
amine as the amine component in the second Mannich reac-
tion.17 The resulting benzylated bispidine (5) was hydrogen- All syntheses were carried out under ambient conditions in
ated with palladium on activated charcoal, to remove the methanol, if not mentioned otherwise. Equimolar solutions of
benzyl group and yield the secondary amine precursor (6). The the ligand and the metal salt were combined and stirred at
di(2-pyridyl)methyl chloride (4) was obtained by a slightly room temperature overnight. Suitable crystals for X-ray crystal
modified published procedure,24 where the di(2-pyridyl)ketone structure determination were obtained by diffusion of diethyl-
was reduced to the corresponding alcohol (3) with sodium ether into the methanolic complex solutions.
borohydride and subjected to an Apple reaction, to obtain the
Copper complexes. In the structures of the CuII complexes
di(2-pyridyl)methyl chloride (4). After refluxing the bispidine [CuII(L)]2+ and [CuII(LOH)]2+, shown in Fig. 1 (selected struc-
precursor (6) with the chloride (4) in acetonitrile with sodium tural data presented in Table 1), only five donors of the hexa-
carbonate as base and a catalytic amount of sodium iodide, dentate ligands are coordinated (in both cases, a fluorine atom
the desired ligand L was obtained in yields up to 53%, i.e. this of the tetrafluoroborate counterion is interacting with CuII at
procedure is clearly more efficient than the double Mannich the open position trans to N7 with a Cu–F distance of approx.
reaction. Reduction of the ketone L at C9 to the corresponding 2.6 Å, see Table 1). One of the two pyridine groups attached to
alcohol LOH with sodium borohydride, to prevent the retro N7 (py4) is dangling, similar to the phenyl group in the ana-
Mannich reaction, resulting in ligand decomposition under logous pentadentate ligand L3 (see Chart 1), from which struc-
acidic (pH < 3) or alkaline conditions (pH > 10), produced tures of hexacoordinate FeII complexes similar to those in
(LOH) in 93% yield (Scheme 2).
Fig. 1 – with one monodentate ligand trans to N7 – are
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Scheme 1 Two different synthetic routes to ligand L.
known.25 That is, the coordination geometry around CuII is
comparable to that observed with L1 (see Table 1).4,26,27
However, the dangling pyridine donor py4 of L and LOH clearly
points in the direction of the CuII center with a Cu⋯N distance
of 3.89 Å and 3.85 Å (L and LOH, respectively), which is an
important difference to the structure of the FeII complex with
L3.25 The third pyridine donor py3 is coordinated trans to N3,
and this defines the pseudo-Jahn–Teller axis along Cu–N7.
Since the second apical position is unoccupied in contrast to
the structures with L1, the Cu–N7 distances are as expected
Scheme 2 Reduction of L to LOH
.
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Fig. 1 ORTEP plots of [CuII(L)]2+ (left) and [CuII(LOH)]2+ (right), hydrogen atoms are omitted for clarity, ellipsoids are shown with 50% probability.
comparably short (see Table 1) – the pseudo-Jahn–Teller axis
of the complex with the hexadentate isomer of L, L2 (also pre-
Table 1 Selected distances and angles of the CuII complexes of L and
LOH in comparison with those of L1 and L2 (ref. 4 and 28)
sented in Table 1), is oriented along the py1–Cu–py2 axis.
Interestingly, the position of the py3 donor in [CuII(L)]2+ and
[CuII(LOH)]2+ is significantly different to that in [CuII(L1)Cl]+,
with a shorter Cu–N distance (1.98 Å, 1.98 Å vs. 2.03 Å) and a
compressed py1–Cu–py3 angle (96.2°, 96.0°, vs. 110.0°).
Together with the significant tilt of the Cu–N7 axis with
respect to the CuN4 plane (increase of the py1–Cu–N7 angle of
approx. 15°), this indicates that the particular distortion may
be due to the Cu⋯py4 interaction and that the pentagonal-
pyramidal coordination geometry (hexacoordination of L and
[CuII(L)]2+
[CuII(LOH)]2+
[CuII(L1)Cl]+
[Cu(L2)]2+
Distances [Å]
Cu–N3
Cu–N7
Cu–py1
Cu–py2
Cu–py3
Cu–py4
Cu–F11
N3⋯N7
py1⋯py2
2.003(3)
2.237(3)
2.047(3)
2.040(3)
1.984(3)
3.893(3)
2.637(3)
2.934(5)
3.986(5)
1.993(2)
2.233(2)
2.052(2)
2.039(2)
1.976(2)
3.854(2)
2.653(2)
2.930(3)
3.994(3)
2.036(2)
2.368(2)
2.028(2)
2.029(2)
2.029(2)
—
—
2.915
3.995
2.087(3)
2.045(3)
2.573(3)
2.208(3)
2.028(3)
2.009(3)
—
L
OH) is prevented by ligand-induced strain (crowding in the
2.83
4.67
basal plane due to relatively short metal–donor distances), i.e.,
a larger metal ion could lead to the desired coordination
geometry.
Angles [°]
N3–Cu–N7
N3–Cu–py1
N3–Cu–py2
N3–Cu–py3
N7–Cu–py1
N7–Cu–py2
py1–Cu–py2
N7–Cu–py3
py1–Cu–py3
py2–Cu–py3
87.41(13)
80.89(14)
80.73(14)
168.79(14)
104.53(14)
91.97(12)
154.62(13)
82.81(12)
96.2(1)
87.57(8)
80.84(9)
80.79(9)
169.18(9)
103.72(8)
92.52(8)
154.84(9)
83.11(8)
96.02(9)
105.02(9)
82.53(6)
81.39(7)
80.94(7)
160.82(7)
88.32(6)
98.43(6)
160.07(7)
79.27(7)
110.00(6)
97.02(6)
86.43(12)
—
—
154.39(13)
—
—
148.53
—
The redox potentials and electronic properties of the new
complexes and of selected reference compounds are listed in
Table 2. It appears that as a whole, the solution properties are
very similar to those of the L1-based CuII complex and there-
fore, we conclude that the solution structure is similar to that
in the solid (see Fig. 1), i.e. square pyramidal (or pseudo-
octahedral) with a dangling but weakly interacting py4. This is
supported by the axial EPR spectrum (see Fig. 2) and the spin
105.0(1)
Table 2 Redox potentials (MeCN vs. Fc/Fc+, vs. Ag/AgNO3; H2O vs. K3[Fe(CN)6]a or vs. Ag/AgClb) and spectroscopic data of the CuII complexes of L
and LOH, in comparison with other CuII bispidine complexes2,28,30,44
CuI/CuII [mV]
dd CuII [nm]
EPR (gx,y, gz; Ax,y, Az)
MeOH–EtOH, 5K A in 10−4 cm−1
SOPHE simulation45,46
,
MeCN
H2O
MeOH (ε [M−1 cm−1])
[Cu(L)](BF4)2
[Cu(LOH)](BF4)2
[Cu(L)](ClO4)2
[Cu(L1)]2+
−651 (−602)
−671 (−538)
−678 (−594)
−776 (−603)
−745 (−573)
—
−786a; −515b
−730a; −459b
—
626 (119)
630 (112)
—
617 (108)
620 (125)
573
2.061, 2.237; 8.5, 172.9
—
—
2.060, 2.217; −178
2.069, 2.208; −169
—
−523b
[Cu(L2)]2+
−502b
[Cu(L3)]2+
−433b
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donors) leads to the expectation that L might enforce seven-
coordination and a distorted pentagonal bipyramidal geometry
with FeII. From the two crystal structures of the [FeII(L)X]n+
complexes (X = Cl, OHMe, see Fig. 3 and Table 3) obtained, it
emerges, however, that the fourth in-plane pyridine donor
(py4), similar to the CuII structures discussed above, is dan-
gling but with an even shorter distance to the metal center
(3.03 Å vs. 3.85 Å) and therefore may be considered semi-co-
ordinated. Also presented in Fig. 3 and Table 3 is an FeIII
complex of L, obtained by reaction of the ligand with an FeII
salt under ambient conditions – all other complexation reac-
tions were performed under inert atmosphere. For compari-
son, selected structural data of other iron-amine/pyridine
complexes are also listed in Table 3.
In the structures of the FeII complexes of L and LOH, an
octahedral coordination geometry is completed by a mono-
dentate Cl− or methanol solvent molecule, respectively, co-
ordinated trans to N7. Semi-coordination of py4 again leads to
a distortion of the remaining FeII–N2py3X chromophore,
similar to but more pronounced as that discussed above for
the CuII complexes, in particular for the unreduced L-based
system (reduction of the ketone leads to a slight increase of
Fig. 2 X-band EPR spectrum of [CuII(L)]2+ in MeOH–EtOH (9 : 1) at 5 K
and 9.423336 GHz, black line (bottom): experimental spectrum, red line
(top) simulated spectrum.
Hamiltonian parameters. As expected, the ligand field of the the donor strength; the discussion refers to the ketone-based
CuII complex is slightly reduced by reduction of the ligand ligand L):27–29 (i) the data in Table 3 suggest that the Fe⋯py4
from L to LOH, and the redox potentials are consequently more interaction tends to reduce the Fe–N7 distance (and concomi-
positive (destabilization of the CuII state).29 More importantly, tantly increases the Fe–N3 distance);28,30 (ii) the Fe⋯py4 inter-
the ligand field exerted by L is significantly smaller than that actions leads to an asymmetry with respect to the coordination
of L1, and the corresponding redox potentials therefore are of the two pyridine donors py1 and py2, i.e., the two angles
less negative, i.e. CuII is less stabilized by L than by L1. This is py1,2–Fe–py3 are strikingly different (85° vs. 137° and 87° vs.
in agreement with the structural properties enforced by L, i.e. 130°, respectively).
the weak interaction of py4 leads to a distortion of the pseudo-
square pyramidal coordination geometry.
Due to problems with the solubility of the various com-
plexes, the redox potentials (see Table 4) could not all be deter-
Due to the fact that the stability constants of CuII complexes mined in the same solvent, and the electronic spectra in
vary over a wide range and those of CuI are much less variable, solution (also given in Table 4) are, as expected for high spin
there is an approximate linear correlation between CuII/I FeII systems, relatively feature-less and therefore not fully
redox potentials and the corresponding CuII stability con- assigned. Qualitatively, it appears however, that there is a sig-
stants.31 For ligands with a similar organic backbone and a nificant difference between the solution properties of the com-
constant donor set, this type of correlation offers an ideal plexes with L and LOH in comparison to the complexes of the
possibility for an accurate prediction of stability constants analogues L1, L2 and L3, suggesting also a semi-coordination
and, for the very rigid bispidine scaffold it has been demon- of the additional pyridine group py4. Specifically, there is the
strated that this is the case.30,32 Based on these established expected reduction of the ligand field and a concomitant
correlations and the redox potentials reported in Table 2, the destabilization of the reduced FeII form.
expected stability constants for the two complexes are log K-
Interestingly, when the complex synthesis is performed
{[CuII(L)]2+} = 16.0 and log K {[CuII(LOH)]2+} = 16.3 (see ESI†). As under ambient atmosphere, spontaneous oxidation of the FeII
discussed above, these values are comparable but slightly complex to FeIII takes place,37 and the corresponding complex
smaller than the experimentally determined value for could be isolated and crystallized; the structure of the mole-
[CuII(L1)]2+, and we believe that this is due to the distortion cular cation is also shown in Fig. 3 and selected structural
induced by semi-coordination of py4.
parameters are given in Table 3 together with those of a
Iron complexes. Most of the reported FeII bispidine com- similar published structure with another pentadentate bispi-
plexes exist in the S = 2 spin state (high spin), most are close to dine ligand L1′ (L1′ is an isomer to L1 with the pyridine group
the spin crossover limit, and only one genuine low spin (S = 0) attached to N3 instead of N7). The complex has the expected
complex has been reported so far;29,33,34 intermediate spin distorted octahedral geometry with L coordinated as a tetra-
(S = 1) electronic configuration is extremely rare for FeII and dentate ligand to a high spin FeIII center with a semi-
may be imposed by a pentagonal bipyramidal coordination coordinated py4 donor. The metal donor distances are very
geometry. The generally larger metal donor distances with similar to those of the corresponding high spin FeII complex
high spin FeII compared to CuII (approx. 2.2 vs. 2.0 Å for amine (see Table 3) but, as in the similar L1′ based system, the OMe−
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Fig. 3 ORTEP plots of the complex cations (a) [FeII(L)OHMe]2+, (b) [FeII(LOH)Cl]+, and (c) [FeIII(L)OMe]2+; hydrogen atoms are omitted for clarity, ellip-
soids are shown with 50% probability.
donor, coordinated as an anionic coligand has, as expected, a 5/2) electronic ground state with a spin only moment of µeff
relatively short metal–ligand bond (FeIII–O = 1.79 Å). Other 5.916 B.M.
=
FeIII methoxy complexes with similar amine/pyridine ligands
Manganese complexes. There are a number of MnII bispi-
(e.g. N4py = N,N-bis(2-pyridyl)methyl)-N-(bis-2-pyridylmethyl)- dine complexes known, especially with tetradentate bispidine
amine39 and bztpen = N-benzyl-N,N′,N′-tris(2-methylpyridyl)- ligands and, as expected for high spin d5 systems, their geome-
ethylendiamine)40 have similar structural features, especially tries are generally octahedral with Mn–N distances signifi-
also with respect to the Fe–O–CH3 angle of 149°, which is cantly larger than those of the FeII complexes.27,29,41 Therefore
typical for a high spin FeIII electronic configuration:33,34,39,40 and since heptacoordinate MnII complexes (pentagonal bipyra-
typical Fe–O–CH3 angles for low spin FeIII are around 130°, midal and monocapped trigonal prismatic) are not
those for high spin FeIII are around 150–170°.38,39
uncommon,42–44 the hexacoordinating bispidine L was co-
Confirmation of the electronic ground state in solution ordinated to MnII. Diffusion of diethylether into the methano-
arises from magnetic moment determinations (Evans-NMR, lic solution of [MnII(L)Cl]+, obtained by the combination of a
CD3CN). For the two high spin FeII complexes, the effective methanolic solution of MnCl2 with an equimolar amount of
magnetic moments are: µeff = 4.9612 B.M. for [FeII(L)OHMe]2+ ligand, produced practically colorless needles, suitable for
and µeff = 4.8734 B.M. for [FeII(LOH)Cl]+, and this is typical for X-ray diffraction. A plot of the molecular cation of [MnII(L)Cl]+,
high spin d6 configuration, with S = 2 and a spin only moment obtained by X-ray crystal structure analysis, is shown in Fig. 4;
of µeff = 4.899 B.M. The magnetic moment of [FeIII(L)OMe]2+ in selected structural parameters are presented in Table 5, which
solution is µeff = 5.1882 B.M., typical for a high spin d5 (S = also lists relevant data for comparison (there are two indepen-
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Table 3 Selected bond distances and angles of the FeII and FeIII complexes of L, LOH and other bispidine ligands
[FeII(L)-
[FeII(L1)OHMe]2+
(ref. 41)
[FeII(L1)Cl]+
(ref. 33)
[FeII(L2)-
SO4]33
[FeII(L3)Cl]+
(ref. 25)
[FeIII(L)-
OMe]2+
[FeIII(L1′)OCH2CF3]2+ a
(ref. 36)
OHMe]2+
[FeII(LOH)Cl]+
Distances [Å]
Fe–N3
Fe–N7
Fe–py1
Fe–py2
Fe–py3
Fe–py4
Fe–XA
2.289(2)
2.2482(18)
2.265(2)
2.184(2)
2.209(2)
3.025(1)
2.0939(19)b
2.897(6)
4.150(6)
2.235(2)
2.309(2)
2.294(2)
2.189(2)
2.174(2)
3.352(3)
2.3954(7)b
2.908(6)
4.260(6)
2.177(3)
2.293(3)
2.163(3)
2.231(3)
2.110(3)
—
2.194(2)
2.362(2)
2.182(2)
2.142(2)
2.134(2)
—
2.215(9)
2.274(10)
2.206(10)
2.172(10)
2.195(10)
1.957(8)
1.957(8)c
2.883(9
2.213(2)
2.342(2)
2.232(2)
2.173(2)
2.143(2)
4.058(3)d
2.3616(7)b
2.938(3)
4.265(3)
2.1916(15)
2.2951(15)
2.2281(17)
2.1425(16)
2.1099(16)
3.240(2)
2.202(2)
2.193(2)
2.106(2)
2.095(2)
2.093(2)
—
2.120(3)b
2.923
2.416(1)b
2.879(2)
4.195(2)
1.7923(14)b
2.861(2)
1.791(2)c
2.893(3)
4.090(3)
N3⋯N7
py1⋯py2
4.245(10)
4.177(2)
Angles [°]
N3–Fe–N7
N3–Fe–py1
N3–Fe–py2
N7–Fe–py1
N7–Fe–py2
py1–Fe–py2
py1–Fe–py3
py2–Fe–py3
Fe–O–CH3
79.50(7)
70.92(7)
72.05(7)
99.06(7)
93.61(7)
137.70(7)
84.87(8)
137.41(8)
130.97(18)
79.44(7)
72.56(8)
73.59(8)
97.21(8)
89.51(8)
143.54(8)
86.56(8)
129.70(9)
—
81.6(1)
77.0(1)
76.5(1)
78.27(5)
76.00(5)
76.48(6)
94.12(5)
86.15(5)
151.82(6)
93.68(6)
113.73(6)
—
79.94(3)
76.32(3)
76.01(3)
89.18(3)
91.75(3)
151.70(4)
92.1(4)
77.1(4)
—
80.29(7)
76.07(8)
75.35(8)
87.21(7)
92.41(7)
151.05(8)
92.18(8)
115.83(8)
—
79.19(6)
73.59(6)
74.18(6)
95.66(6)
89.48(6)
145.73(5)
86.85(6)
127.20(6)
149.12(12)
82.33(7)
153.64(8)
—
a L1′ is an isomer to L1 with the pyridine group attached to N3 instead of N7. b trans zu N7. c trans zu N3. d C-atom of the phenylring pointing in
direction of the metal center.
Table 4 Redox potentials (MeCN vs. Fc/Fc+a; vs. Ag/AgNO3b; H2O vs.
K3[Fe(CN)6]c; vs. Ag/AgClb) and spectroscopic data of the FeII complexes
of L and LOH, in comparison with other FeII bispidine complexes33,35,36
and py3, py4), and this results in N3, py3, py4 all being above
the mean equatorial plane (0.57 Å, 0.06 Å, 0.19 Å, respectively,
all for molecule 1; Mn is by 0.38 Å above the plane; py1 and
py2 are by 0.49 Å and 0.35 Å below the plane; the corres-
ponding values for molecule 2 are similar, see ESI†). As a
result, the repulsion between the pyridyl groups py3 (and py4)
and the α hydrogen atoms of py1 (and py2) is reduced. In
order to visualize the similarity between the 7-coordinated
MnII and the 6-coordinated FeII structures and to justify the
“semi-coordination” of py4 in the FeII and CuII structures, an
overlay plot of [MnII(L)(Cl)]+ and [FeII(L)(HOMe)]2+ is also
shown in Fig. 4.
FeIII/FeII [mV]
dd FeII [nm]
MeCN
H2Oa
MeOHb
MeCN
[Fe(L)OHMe]2+
[Fe(LOH)Cl]+
[Fe(L1)Cl]2+
[Fe(L2)]2+
474
225
—
—
—
—
364
341, 412
309; 402
376; 402; 457; 564
—
222c
—
156
—
661b
773c
[Fe(L3)OTf]+
a vs. K3[Fe(CN)6]. b vs. Ag/AgNO3. c vs. Fc/Fc+.
The redox potential (MnII/III couple vs. SCE) of [MnII(L)(Cl)]+
is significantly more positive than that of the hexacoordinate
dent complex cations, in the unit cell, and the parameters of [Mn(tpen)Cl]+ with a similar donor set, indicating that the
extra pyridine donor prevents oxidation and concomitant com-
both are tabulated).
As hoped for, the structure of [MnII(L)(Cl)]+ is heptacoordi- pression of the coordination sphere. For the 7-coordinated
nated with the hexacoordinating bispidine and a Cl− complet- EDTA and NOTA complexes with H2O as an extra ligand, steric
effects are of lesser importance (possible dissociation of the
ing the distorted pentagonal bipyramidal coordination sphere.
In terms of the coordination of the two dipyridinamine-based 7th ligand and reduction of the coordination number) and the
carboxylates obviously stabilize the oxidized form (Table 6).
Squid magnetometry was used to analyze the electronic
pyridine donors py3 and py4, the structure is, due to ligand-
enforced strain, still significantly distorted but the longer Mn–
py3,4 distances of 2.34, 2.4, 2.53 and 2.65 Å all can be con- ground state of [MnII(L)(Cl)]2[MnCl4] (Fig. 5). It follows that
zero field splitting is neglectable and the magnetic suscepti-
sidered as genuine bonds. The trans angle N7–Mn–Cl of 165°
(167°) is in agreement with a (distorted) bipyramidal structure.
bility at room temperature per [MnII(L)(Cl)]+ cation (S = 5/2 for
The intra-donor angles in the pentagonal plane indicate a rela- the [MnCl4]2− complex ion)45 is 4.168 cm3 K mol−1, typical for
a high spin d5 center (S = 5/2, 4.337 cm3 K mol−1 for g = 2). It
tively symmetrical distribution with an ideal value of 72° and
appears that spin pairing to result in possible S = 3/2 (inter-
an observed distribution between 67° and 82°, and the average
deviation of 0.38 Å from a mean plane is significant but not mediate spin) and S = 1/2 (low spin) states, due to (distorted)
pentagonal bipyramidal coordination geometry, is prevented
very large. The most extensive distortion is related to the posi-
by the long metal–donor distances and the resulting relatively
tion of N3 (rigid N3–Mn–N7 angle) and the two pyridine
groups py3 and py4 (tight and rigid chelate rings involving N7 weak ligand field.
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Table 5 Selected structural parameters of [MnII(L)Cl]+ and relevant
data for comparison
[MnII(L1)Cl]+
(ref. 41)
[MnII(tpen)-
Cl]+ b
[MnII(L)Cl]+ a
Distance [Å]
Mn–N3
Mn–N7
Mn–py1
Mn–py2
Mn–py3
Mn–py4
Mn–Cl
2.435(2)
2.326(2)
2.307(2)
2.389(2)
2.346(2)
2.647(2)
2.3933(8)
2.926(3)
4.273(3)
2.485(2)
2.344(2)
2.362(2)
2.342(2)
2.415(2)
2.529(2)
2.4064(8)
2.926(3)
4.246(3)
2.2829(1)
2.4151(1)
2.2714(1)
2.2622(1)
2.1910
—
2.3914(1)(2)
2.943
—
2.485(2)
2.444(2)
2.262(2)
2.490(2)
2.297(2)
2.498(2)
2.4544(7)
—
N3⋯N7
py1⋯py2
—
Angle [°]
N3–Mn–N7
N3–Mn–py1
N3–Mn–py2
N3–Mn–py3
N3–Mn–py4
N7–Mn–py1
N7–Mn–py2
N7–Mn–py4
N7–Mn–py3
py1–Mn–py2
N7–Mn–Cl
75.80(7)
68.29(7)
67.51(7)
133.62(7)
127.55(7)
93.98(7)
94.85(7)
69.62(7)
73.15(7)
131.00(8)
164.62(6)
75.98(8)
70.56(7)
81.76(8)
74.51(6)
66.82(7)
66.81(7)
132.42(7)
127.15(7)
92.24(7)
94.95(7)
70.63(7)
73.16(7)
129.00(7)
166.62(7)
80.55(8)
71.45(8)
77.93(8)
77.507(2)
73.599(2)
74.010(2)
149.085(2)
—
—
85.5(1)
—
—
—
—
—
—
—
—
—
—
—
—
144.4(1)
112.147(1)
139.44(6)
py1–Mn–py4
py3–Mn–py4
py2–Mn–py3
a Two independent molecules. b tpen
pyridylmethyl)ethylene-1,2-diamine.68
=
N,N,N′,N′-tetrakis(2-
Table 6 Redox potentials of [Mn(L)Cl]+ and relevant data for compari-
son in MeCN, vs. SCE
MnII/III [mV]
Fig. 4 (a) ORTEP plot of the complex cation [MnII(L)(Cl)]+ (only one of
the two independent molecules is shown, hydrogen atoms are omitted
for clarity, ellipsoids are shown with 50% probability); (b) overlay plot of
[MnII(L)(Cl)]+ (red, M = MnII) and [FeII(L)(HOMe)]2+ (green, M = FeII).
[Mn(L)Cl]+
1171d
911a
1050
496e
566e
Mn(L″)Cl2]a
[Mn(tpen)Cl]+ b
[Mn(NOTA)]− c
[Mn(EDTA)]2− c
a L″ is a tetradentate bispidine derivative;69 E(Ag/AgNO3) = 343 mV vs.
SCE.70 b tpen = N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylene-1,2-diamine.68
Conclusion
c NOTA
=
1,4,7-triacetato-1,4,7-triazanonane; EDTA
=
N,N,N′,N′-
tetraacetatoethylene-1,2-diamine.71 d E(Fc/Fc+) = 380 mV vs. SCE.70 e E
(SHE) = −244 vs. SCE.70
The hexadentate bispidine ligands L and LOH have been shown
to be able to form heptacoordinated pentagonal bipyramidal
structures. For the relatively small CuII and high spin FeII ions
the fourth pyridine group is only semi-coordinated for steric
reasons and, with the larger high spin MnII ion genuine hepta-
coordination is observed but with a relatively large distortion
in the pentagonal equatorial plane. It appears that an elonga-
tion of chelate rings involving the dipyridylamine group might
lead to the desired enforcement of pentagonal (bi)pyramidal
structures, even for smaller metal ions, and this also emerges
from similar effects observed with 6- vs. 5-membered chelate
rings involving the N7-appended pyridine donor in L1-based
pentadentate bispidine ligands.46,47 Moreover, an expansion of
the linker between N7 and the pyridine donors py3 and py4
would also lead to less distortion in the equatorial plane, even
with relatively large metal–donor distances.
Experimental section
All chemicals were purchased from Sigma Aldrich and Acros.
Analytical grade solvents were used without further purifi-
cation and all reactions were carried out under air if not
mentioned otherwise. The piperidone precursor pL was syn-
thesized according to a published procedure.29
Caution! Metal perchlorates in presence of organic ligands are
potentially explosive and sensitive to heat and impact. No
problem occurred for the work described here but these com-
pounds need in general to be handled with extreme care.
Electrochemistry was performed on
a CH Instruments
CHI660D electrochemical workstation, equipped with a CH
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ESI-MS spectra were recorded on a Bruker ApexQe hybrid
9.4 T FT-ICR instrument.
Elemental analyses were obtained from a CHN-O-vario EL
instrument by the “Mikroanalytisches Labor” of the chemical
institutes, University of Heidelberg.
EPR measurements were performed on a Bruker ELEX-
SYS-E-500 instrument and collected at liquid helium tempera-
ture in frozen methanol–ethanol (9 : 1) solution. The spin
Hamiltonian parameters were obtained by simulation of the
experimental data with the XSophe software package.48,49
X-ray crystal structure determinations
Crystal data and details of the structure determinations are
listed in the ESI (Table S3†). Full shells of intensity data were
collected at low temperature with a Bruker AXS Smart 1000
CCD diffractometer (Mo-Kα radiation, sealed tube, graphite
monochromator; compounds [FeII(L)OHMe]2+ and [FeIII(L)-
OMe]2+) or a Agilent Technologies Supernova-E CCD diffracto-
meter (Mo- or Cu-Kα radiation, microfocus tube, multilayer
mirror optics; compounds [CuII(L)]2+, [CuII(LOH)]2+ and
[FeII(LOH)Cl]+) or STOE IPDS I diffractometer (Mo-Kα radiation,
graphite monochromator; compound [MnII(L)Cl]+). Data were
corrected for air and detector absorption, Lorentz and polariz-
ation effects;50,51 absorption by the crystal was treated numeri-
cally (Gaussian grid)51 (compounds [CuII(L)]2+ and
[CuII(LOH)]2+) or with a semiempirical multiscan method3,52,53
(all others).The structures were solved by conventional direct
methods54,55 (compound [MnII(L)Cl]+) or by the charge flip
procedure56,57 (all others) and refined by full-matrix least
squares methods based on F2 against all unique reflec-
tions.55,58 All non-hydrogen atoms were given anisotropic dis-
placement parameters. Hydrogen atoms were generally input
at calculated positions and refined with a riding model. Where
Fig. 5 (a) Temperature dependent susceptibility and (b) reduced mag-
netization of [MnII(L)(Cl)]2[MnCl4].
Instruments Picoamp Booster. All electrochemical measure-
ments were performed in a glass cell, covered with a teflon possible, hydrogen atoms of solvent water were taken from
cap, situated in a Faraday cage. All complex solutions were difference Fourier syntheses or else placed to maximize hydro-
gen bonding59,60 with atomic charges calculated from partial
prepared in degassed and with Argon saturated solvents. The
supporting electrolyte for acetonitrile was: 0.1 M tetra-n- equalization of orbital electronegativity.61 Water molecules
butylammonium tetrafluoroborate; for acetonitrile (MeCN):
0.1 M tetra-n-butylammonium hexafluorophosphate. Cyclovol-
were then refined as rigid groups. When found necessary, dis-
ordered groups and/or solvent molecules where subjected to
tammograms (CVs) in non-aqueous media were recorded with suitable geometry and adp restraints.
an Ag/AgNO3 reference electrode, a glassy carbon working elec-
In the structure of [FeII(LOH)Cl]+ a cluster of 3 strong differ-
trode and a platinum wire as counter electrode. Aqueous solu-
ence Fourier peaks was assigned to partially occupied sites of
tions contained 3 M sodium chloride (NaCl) as supporting the chloride ion. Their total population refined to close to 1.0.
electrolyte and were measured with an Ag/AgCl reference elec-
trode, a glassy carbon working electrode and a platinum wire
The smtbx solvent masking procedure was then used to
remove the electronic contribution of residual solvent mole-
as counter electrode. Electrochemical measurements in non- cules (water and/or methanol) from the Fobs
.
62,63 During refine-
aqueous media were normalized vs. ferrocene, where ferrocene
had the following potential: MeCN (50 mV); in H2O, potentials
ment against the solvent-corrected data the sum of
populations for the chlorides was restrained to 1.00(1). Due to
were normalized against potassium hexacyano ferrate (K3[Fe(CN)6]) severe disorder and fractional occupancy, electron density
with 270 mV.
attributed to solvent of crystallization (methanol and/or water)
was removed from the structure of [MnII(L)Cl]+ with the
BYPASS procedure,62 as implemented in PLATON
(SQUEEZE).64,65 Partial structure factors from the solvent
masks were included in the refinement as separate contri-
UV/vis spectra were recorded with a Jasco V-570 UV-vis-NIR
spectrometer as methanolic solutions.
NMR spectra were recorded with
a Bruker Avance I
(200 MHz) instrument; chemical shifts of 1H and 13C were
referenced to solvent resonances (CDCl3).
butions to Fobs
.
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Syntheses
90 minutes drop wise. The solution was stored at +4 °C over-
night and quenched with methanol (6.0 ml) for 15 minutes at
Di(2-pyridyl)oxime.66,67 (C11H9N3O, MW: 199.21 g mol−1): room temperature. The initial volume was concentrated to
To sodium acetate (2.96 g, 21.71 mmol, 2 eq.) in water 25.0 ml, dissolved in water (52.0 ml) and washed with chloro-
(20.00 ml) was added hydroxylamine hydrochloride (1.51 g, form (2 × 52.0 ml). The aqueous phase was neutralized with
21.71 mmol, 2 eq.) and heated to 60 °C for one hour. Di(2- potassium carbonate and extracted with diethyl ether (4 ×
pyridyl)ketone (2.0 g, 10.86 mmol, 1 eq.) was added in metha- 35.0 ml). The combined ether extracts were dried with sodium
nol (4.0 ml) and the brown solution was stirred at 60 °C over- sulfate and evaporated. The crude product was obtained as a
night. The light red reaction mixture was cooled at 0 °C and brown oil and purified by column chromatography (silica, 30 ×
the product precipitated in light-rose crystals. The product 6 cm, methylene chloride–methanol 10 : 1, Rf 0.46). The ana-
(2.10 g, 97% yield) was filtered, washed with a little cold water lytically pure product was obtained as light-rose crystals
1
and dried in vacuo. FAB-MS: m/z = 200.10 (calc.: 200.08) [M + (2.37 g, 47% yield). H-NMR (200 MHz, CDCl3) δ[ppm] = 6.24
H]+; elemental analysis (report no.: 28891, C11H11N3O2) calc.: (s, CHCl, 1H); 7.14–7.21 (m, 2H); 7.61–7.74 (m, 4H); 8.48–8.51
C(60.82), H(5.10), N(19.34), obs.: C(61.10), H(5.04), N(19.28).
(m, 2H); 13C-NMR (50 MHz, CDCl3): δ[ppm] = 63.76 (, 123.10,
137.36, 148.79, 158.29, elemental analysis (C11H9ClN2): calc.: C
Di(2-pyridyl)methylamine. (C11H11N3, MW: 185.23 g mol−1
)
The di(2-pyridyl)oxime (2.08 g, 10.44 mmol, 1 eq.), ammonium (64.56), H(4.43), N(13.69), obs.: C(64.48), H(4.56), N(13.54).
acetate (1.37 g, 17.75 mmol, 1.7 eq.) and concentrated Dimethyl-(7-benzyl-3-methyl-9-oxo-2,4-bis(2-pyridyl)-3,7-di-
ammonia (3.3 ml) were dissolved in ethanol–water (2 : 1, azabicyclo[3.3.1]nonane)-1,5-dicarboxylate. (C29H30N4O5, MW:
63.0 ml) and heated to 80 °C. Zinc dust (3.07 g, 47.0 mmol, 4.5 514.57 g mol−1): Benzylamine (3.44 ml, 31.55 mmol, 1.2 eq.)
eq.) was added in small portions during 30 minutes and the and formaldehyde (37% wt in water, 4.7 ml, 63.09 mmol, 2.4
mixture was refluxed for additional 3 hours. After stirring at eq.) were added to a suspension of the piperidone pL (10.0 g,
room temperature overnight, solids were removed by filtration, 26.29 mmol, 1 eq.) in ethanol (60.0 ml) and refluxed for
washed with a little water, and ethanol was removed at the 4 hours. The black solution was stirred overnight at room
rotary evaporator. The remaining solution was alkalized with temperature and the precipitated product was filtered and
10 M sodium hydroxide solution and the amine was extracted washed with ethanol. After recrystallization from ethanol, the
with methylene chloride. The combined extracts were washed product was obtained as a white powder (6.69 g, 49% yield).
with brine, dried over sodium sulfate and evaporated. The 1H-NMR (200 MHz, CDCl3) δ[ppm] = 2.01 (s, CH3, 3H),
2
2
crude product (1.37 g, 71% yield), a yellow-brown oil was used 2.56–2.62 (d, JH–H = 11.87 Hz, CH2,eq, 2H), 3.06–3.13 (d, JH–H
without further purification. 1H-NMR (400 MHz, CDCl3) = 12.09 Hz, CH2,ax, 2H), 3.40 (s, NCH2Ph, 2H), 3.86 (s, OCH3,
δ[ppm] = 2.50 (br s, NH2, 2H), 5.34 (m, CH, 1H), 7.14–7.17 (m, 6H), 4.73 (s, CH, 2H), 7.13–7.20 (m, Harom., 2H), 7.43–7.55 (m,
3
Harom., 2H), 7.39–7.41 (m, Harom., 2H), 7.62–7.66 (m, Harom.
,
Harom., 7H), 7.90–7.94 (d, JH–H = 7.80 Hz, Harom., 2H),
2H), 8.57–8.58 (m, Harom., 2H), 13C-NMR (100 MHz, CDCl3): 8.46–8.49 (m, Harom., 2H), 13C-NMR (50 MHz, CDCl3): δ[ppm] =
δ[ppm] = 62.29, 121.73, 122.05, 136.66, 149.14, 162.69.
Di(2-pyridyl)methanol.66,67 (C11H10N2O, MW: 186.21
43.26, 52.46, 59.01, 61.17, 62.47, 73.81, 122.87, 123.45, 127.65,
128.43, 130.42, 136.16, 136.94, 149.08, 158.47, 168.53, 203.65.
g
mol−1): Sodium borohydride (1.03 g, 27.10 mmol, 1 eq.) was ESI-MS, elemental analysis (C29H30N4O5, report no.: 31987):
added in small portions to a solution of di(2-pyridyl)ketone calc. C(67.88), H(5.88), N(10.89), obs.: C(67.83), H(5.90), N
(5.00 g, 27.10 mmol, 1 eq.) in methanol (50.0 ml) at 0 °C. The (10.82).
solution was warmed and stirred at room temperature over-
Dimethyl-(3-methyl-9-oxo-2,4-bis(2-pyridyl)-3,7-diazabicyclo-
night. The solvent was evaporated to dryness and the residue [3.3.1]nonane)-1,5-dicarboxylate. (C22H24N4O5, MW: 424.45 g
was taken up in water (20.0 ml) and acidified with 2 N hydro- mol−1) To a solution of 5 (4.0 g, 7.77 mmol, 1 eq.) in ethyl
chloride acid. After stirring for 10 minutes, the solution was acetate (100.0 ml) was added palladium on activated charcoal
alkalized with concentrated ammonia and extracted with (10%, 0.40 g) and the mixture was hydrated at 70 °C and 1 atm
methylene chloride (3 × 50.0 ml). The combined organic hydrogen overnight. The solvent was evaporated, the residue
extracts were dried with sodium sulfate and evaporated. The taken up in methylene chloride and the catalyst was removed
product (4.93 g, 98% yield), a brown oil was dried in vacuuo by filtration over celite pad. After evaporation of the solvent,
and used without further purification. 1H-NMR (200 MHz, the crude product was recrystallized from ethanol as colorless
CDCl3) δ[ppm] = 6.01 (s, CH, 1H), 6.05 (s, OH, 1H), 7.22–7.30 needles (2.53 g, 77% yield). 1H-NMR (200 MHz, CDCl3) δ[ppm]
(m, Harom., 2H), 7.60–7.64 (m, Harom., 2H), 7.70–7.77 (m, = 1.73 (s, NCH3, 3H); 3.07–3.21 (m, CH2 ax/eq, 2H); 3.64 (s,
Harom., 2H), 8.58–8.61 (m, Harom., 2H), 13C-NMR (50 MHz, OCH3, 6H); 3.82–3.89 (m, CH2 ax/eq, 2H); 4.56 (s, CH, 2H);
CDCl3): δ[ppm] = 74.66, 121.65, 122.80, 125.10, 126.23, 136.62, 7.18–7.20 (m, Hpy, 2H); 7.33–7.37 (m, Hpy, 2H); 7.59–7.67 (m,
137.55, 147.56, 149.13, 154.53, 160.42.
Di(2-pyridyl)methyl chloride.66,67 (C11H9ClN2, MW: 204.6 g CDCl3) δ[ppm] = 41.61, 52.20, 55.06, 64.42, 73.73, 123.22,
Hpy, 2H); 8.60–8.62 (m, Hpy, 2H) ppm. 13C-NMR (50 MHz,
mol−1): To
a solution of di(2-pyridyl)methanol (4.61 g, 124.39, 136.53, 150.05, 157.29, 168.70, 202.91. ESI-MS: m/z =
24.76 mmol, 1 eq.) in acetonitrile (52.0 ml) was added a solu- 425.1 (100%), 426.1 (24%) [M + H]+, elemental analysis
tion of triphenylphosphine (7.79 g, 29.71 mmol, 1.2 eq.) in (C22H24N4O5, report no.: 31986): calc.: C(62.25), H(5.70),
carbon tetrachloride (42.0 ml) at 0 °C over a period of N(13.20), obs.: C(62.39), H(5.75), N(13.20).
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Dimethyl-(3-methyl-7-bis(2-pyridyl)methyl-9-oxo-2,4-bis- K3[Fe(CN)6]), Elemental analysis (report no.: 32312): calc. (%):
(2-pyridyl)-3,7-diazabicyclo[3.3.1]nonane)-1,5-dicarboxylate (L). C(44.84), H(4.33), N(9.51); obs. (%): C(44.66), H(4.35), N(9.38).
(C33H32N6O5, MW: 592.64 g mol−1): Method A: to a suspension
[CuII(LOH)](BF4)2·2H2O. (C33H34B2CuF8N6O5, MW: 831.82 g
of the piperidone pL (2.74 g, 2.7 mmol, 1 eq.) in methanol mol−1): LOH (0.05 g, 0.08 mmol, 1 eq.) was dissolved in hot
(15.0 ml) was added di(2-pyridyl)methylamine (1.60 g, acetonitrile (4.0 ml), after addition anhydrous Cu(BF)4 (0.02 g,
8.64 mmol, 1.2 eq.) and formaldehyde (37% wt in water, 0.08 mmol, 1 eq.) in acetonitrile (1.0 ml), the deep blue solu-
1.3 ml, 17.28 mmol, 2.4 eq.) and was refluxed for 1 hour. After tion was heated to reflux once and stirring was continued at
evaporation of the solvent, the residue was recrystallized from room temperature overnight. The blue solution was subjected
hot ethanol to obtain the product as a white powder (0.67 g, to diethyl ether diffusion to obtain blue needles (39 mg, 54%
16% yield). Method B: di(2-pyridyl)methyl chloride (0.50 g, yield) suitable for X-ray diffraction. UV/vis λ = 630 nm
2.44 mmol, 1 eq.) was refluxed for 24 hours with 6 (1.03 g, (15 873 cm−1), ε = 112 M−1 cm−1; CV: −671 mV (MeCN vs.
2.44 mmol, 1 eq.), sodium carbonate (0.52 g, 4.89 mmol, 2 eq.) Fc/Fc+), −728 mV (H2O vs. K3[Fe(CN)6]). Elemental analysis
and a catalytic amount of sodium iodide in acetonitrile (report no. 32312) calc. (%): C(45.67), H(4.41), N(9.68); obs.
(10.0 ml). After complete evaporation of the solvent, the (%) C(45.67), H(4.52), N(9.72).
residue was partitioned between water and methylene chlor-
[CuII(L)](ClO4)2·MeOH. A suspension of L (0.15 g, 253.10
ide, the organic phase was separated, the aqueous phase was µmol, 1 eq.) in MeOH (1.5 ml) was combined with a solution
extracted with methylene chloride and the combined organic of Cu(ClO4)2·6H2O in MeOH–H2O (1 : 1, 3.0 ml) and the result-
extracts were dried over sodium sulfate. After evaporation of ing blue solution was refluxed for 60 minutes. After the solu-
the solvent the residue was recrystallized from ethanol to tion was concentrated to one half of the initial volume and
obtain the product as a white powder (0.76 g, 53% yield). stored at +4 °C the product crystallized as blue plates (180 mg,
1H-NMR (200 MHz, CDCl3) δ[ppm] = 1.89 (s, NCH3, 3H), 80% yield). CV: −678 mV (MeCN vs. Fc/Fc+). Elemental analysis
2
2
3.03–3.09 (d, JH–H = 12.3 Hz, CH2,ax, 2H), 3.46–3.52 (d, JH–H
=
(report no. 32341) calc. (%): C(46.03), H(4.09), N(9.47); obs.
11.4 Hz, CH2,eq, 2H), 3.67 (s, OCH3, 6H), 4.47 (s, CH, 2H), 4.75 (%) C(45.85), H(4.26), N(9.63).
(s, NCH, 1H), 7.03–7.10 (m, Hpy, 4H), 7.49–7.66 (m, Hpy, 6H),
[Fe(LOH)Cl](Cl). (C33H34Cl2FeN6O5, MW: 721.41 g mol−1):
3
7.76–7.80 (d, JH–H = 7.8 Hz, Hpy, 2H), 8.36–8.49 (m, Hpy, 4H), LOH (25 mg, 0.04 mmol, 1 eq.) was suspended in dry aceto-
13C-NMR (50 MHz, CDCl3) δ[ppm] = 42.45, 52.36, 56.31, 63.08, nitrile (2.0 ml), anhydrous FeCl2 was added under argon
74.34, 77.95, 122.46, 122.84, 124.20, 124.48, 136.26, 149.08, atmosphere, and the yellow solution was stirred at room temp-
149.18, 157.90, 159.23, 168.82, 202.73, elemental analysis erature overnight. The yellow solution was subjected to diethyl
(C33H32N6O5, report no.: 32196): calc.: C(66.88), H(5.44), ether diffusion to obtain yellow needles (15.9 mg, 52%),
N(14.18), obs.: C(66.67), H(5.56), N(14.08).
suitable
for
X-ray
diffraction.
Elemental
analysis
Dimethyl-(3-methyl-7-bis(2-pyridyl)methyl-9-hydroxo-2,4-bis- (C66H74Cl4Fe2N12O13, report no. 32313) calc. C(52.96), H(4.98),
(2-pyridyl)-3,7-diazabicyclo[3.3.1]nonane)-1,5-dicarboxylate (LOH). N(11.23), obs. C(53.03), H(4.91), N(11.11), UV/vis (MeCN): λ =
(C33H34N6O5, MW: 594.66 g mol−1): The ligand L (0.32 g, 412 nm (24 271 cm−1),
ε = , 341 nm
1381 M−1 cm−1
0.54 mmol, 1 eq.) was dissolved in 1,4-dioxane–water-mixture (29 326 cm−1), ε = 1712 M−1 cm−1, 259 nm (38 610 cm−1), ε =
3 : 1 (12.0 ml) an cooled to −5 °C, sodium borohydride (0.01 g, 10 996 M−1 cm−1; CV: 225 mV (MeCN vs. Fc/Fc+), FAB-MS
0.27 mmol, 0.5 eq.) in 1,4-dioxane–water-mixture 2 : 1 (4.0 ml) (NPOE-Matrix) m/z = 683.22 [Fe(LOH)(Cl)]+, 701.24 [Fe(LOH)-
was added drop wise. The solution was allowed to warm up to (Cl)]+ + H2O, 715.28 [Fe(LOH)(Cl)]+ + MeOH.
0 °C and was stirred overnight. The solution was acidified with
[Fe(L)(OMe)](ClO4)2: L (50.0 mg, 0.08 mmol, 1 eq.) was sus-
concentrated sulfuric acid until the solution remained clear. pended in methanol (4.0 ml), Fe(ClO4)2 (41 mg, 0.17 mmol,
After stirring for 3 hours at 0 °C, the solution was alkalized 2 eq.) was added and the yellow complex precipitated. The
with sodium hydroxide solution (20 wt% in water) and LOH mixture was stirred at room temperature over-night, the solid
was extracted with methylene chloride. After drying the was filtered of and dried under vacuum. The raw product was
organic extracts over sodium sulfate and evaporating the taken up in acetonitrile and subjected to diethylether
solvent, and recrystallizing from ethanol, the product was diffusion to obtain yellow-brown needles (36 mg, 49%), suit-
obtained as a white powder (0.30 g, 93% yield). ESI-MS (pos): able for X-ray diffraction. Evans-NMR: µeff = 5.1882 B.M., molar
m/z = 595.2 [LOH + H]+, 617.3 [LOH + Na]+, elemental analysis susceptibility 1.1415 × 10−2 cm3 mol−1
.
(C35H40N6O6, report no.: 29984) calc. C(66.11), H(6.03),
N(13.61), obs. C(66.01), H(5.77), N(13.83).
[Fe(L)(HOMe)](BF4)2: under argon atmosphere L (100 mg,
0.17 mmol, 1 eq.) was stirred with Fe(BF4)2·6H2O (57 mg,
[CuII(L)](BF4)2·3H2O. Solutions of L (100 mg, 168.73 µmol, 0.17 mmol, 1 eq.) in methanol (3.0 ml) at room temperature
1 eq.) in MeCN (4.0 ml) and dry Cu(BF4)2 (40 mg, 168.73 µmol, over-night. The yellow solution was subjected to diethylether
1 eq.) in MeCN (1.0 ml) were combined and the deep blue diffusion to obtain yellow needles (78 mg, 54%) suitable for
solution was refluxed for 1 hour. The solvent was evaporated X-ray diffraction. Elemental analysis calc. C(46.67), H(4.41),
to dryness and the residue was taken up in MeOH and sub- N(9.68), obs. C(45.76), H(4.52), N(9.72), UV/vis (MeCN): λ =
jected to diethyl ether diffusion to obtain blue needles 364 nm (27 472 cm−1), ε = 1245 M−1 cm−1, CV: 474 mV (H2O
(104 mg, 74% yield). UV/vis λ = 626 nm (15 974 cm−1), ε = 119 vs. K3[Fe(CN)6]), Evans-NMR: µeff = 4.9613 B.M., molar suscep-
M−1 cm−1; CV: −651 mV (MeCN vs. Fc/Fc+), −786 mV (H2O vs. tibility 1.0438 × 10−2 cm3 mol−1
.
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[MnCl(L)]2[MnCl4]. L (50.0 mg, 0.08 mmol, 1 eq.) was sus- 15 M. Atanasov, P. Comba and S. Helmle, Inorg. Chem., 2012,
pended in acetonitrile (2.0 ml) and heated to 50 °C until com- 51, 9357–9368.
plete solution of the ligand. MnCl2·4H2O (17.0 mg, 0.08 mmol, 16 M. Atanasov, P. Comba, S. Helmle, D. Müller and F. Neese,
1 eq.) in acetonitrile–methanol 1 : 1 (2.0 ml) was added, and Inorg. Chem., 2012, 51, 12324–12335.
the colorless solution was stirred at room temperature over- 17 D. S. C. Black, M. A. Horsham and M. Rose, Tetrahedron,
night. The solvent was evaporated the residue was redissolved 1995, 51(16), 4819–4828.
in methanol. The supernatant was separated and subjected to 18 P. Comba, S. Hunoldt, M. Morgen, J. Pietzsch, H. Stephan
diethyl ether diffusion, to obtain colorless needles (33 mg, and H. Wadepohl, Inorg. Chem., 2013, 52, 8131–8143.
56%), suitable for X-ray diffraction. Elemental analysis calc. 19 P. Comba, M. Kubeil, J. Pietzsch, H. Rudolf, H. Stephan
C(48.18), H(4.97), N(9.63), obs. C(48.13), H(4.55), N(9.63), mag- and K. Zarschler, Inorg. Chem., 2014, 53, 6698–6707.
netic susceptibility: 4.168 cm3 K mol−1, CV: (MeCN) 791 mV 20 S. Juran, M. Walther, H. Stephan, R. Bergmann,
(vs. Fc/Fc+).
J. Steinbach, W. Kraus, F. Emmerling and P. Comba, Bio-
conjugate Chem., 2009, 20, 347–359.
21 C. Busche, P. Comba, A. Mayboroda and H. Wadepohl,
Eur. J. Inorg. Chem., 2010, 1295–1302.
22 D. Brox, P. Comba, D.-P. Herten, E. Kimmle, M. Morgen,
C. Rühl, A. Rybina, H. Stephan, G. Storch and
H. Wadepohl, Dalton Trans., submitted.
Acknowledgements
Financial support by the German Science Foundation (DFG),
the University of Heidelberg and the Helmholtz Association
(funding through the Helmholtz Virtual Institute NanoTrack- 23 C. Nájera, J. Gil-Moltó and S. Karström, Adv. Synth. Catal.,
ing, Agreement Number VH-VI-421 is gratefully acknowledged.
2000, 346, 1798–1811.
24 G. Roelfes, V. Vrajmasu, K. Chen, R. Y. N. Ho, J. Rohde,
C. Zondervan, R. M. la Crois, E. P. Schudde, M. Lutz,
A. L. Spek, R. Hage, B. Feringa, E. Munck and L. Que Jr.,
Inorg. Chem., 2003, 42, 2639–2653.
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