5,5′-diamino-2,2′-bipyridine: A versatile building block for the synthesis of bipyridine/catechol ligands that form homo- and heteronuclear helicates

Article abstract of DOI:10.1002/chem.200401262

Herein we present an improved synthesis of 5,5′-diamino-2,2′- bipyridine (1) starting from the pyrrole-protected aminopyridine 4. By standard reactions 1 can easily be transformed into the imine- or amide-bridged dicatechol-bipyridine ligands L¹

Full text of DOI:10.1002/chem.200401262

DOI: 10.1002/chem.200401262
5,5’-Diamino-2,2’-bipyridine: A Versatile Building Block for the Synthesis of
Bipyridine/Catechol Ligands That Form Homo- and Heteronuclear Helicates
Markus Albrecht,*[a] Ingo Janser,[a] Arne Lützen,*[b] Marko Hapke,[b]
Roland Frçhlich,[c] and Patrick Weis[d]
Abstract: Herein we present an im-
proved synthesis of 5,5’-diamino-2,2’-bi-
pyridine (1) starting from the pyrrole-
protected aminopyridine 4. By stan-
dard reactions 1 can easily be trans-
formed into the imine- or amide-bridg-
ed dicatechol–bipyridine ligands L1-H4
and L2-H4. Whereas ligand L1 readily
forms
homodinuclear
helicates
dination compounds from this ligand
did not work. However, the amide-con-
nected ligand L2 affords mononuclear
([(L2-H4)PdCl2], [(L2-H4)3Zn]2+), dinu-
clear ([(L2)3Ti2]4À), and heterotrinu-
[(L1)3Ti2]4À, the attempted formation of
mono-, tri-, or even oligonuclear coor-
Keywords: coupling reactions
cryptands · helicates · N ligands ·
self-assembly
·
clear
coordination
compounds
([(L2)3Ti2Zn]2À).
Introduction
Many publications on the formation of helicates have ap-
peared during the last two decades, but only a few of them
describe the formation of heteronuclear metal complexes.
The chief problem is the incorporation of different metal
binding units that are specific for different metal ions. Ele-
gant approaches were described by Piguet and Lehn and
their co-workers, in which binding sites with ligand units dif-
fering in their denticity were used.[5] We introduced a cate-
chol/aminophenol ligand that can bind different metals
owing to the different electronic properties of the binding
sites.[6]
The present project developed as we first started to inves-
tigate bis(catecholimines) as ligands for helicate formation.[7]
5,5’-Diamino-2,2’-bipyridine (1) seemed to be the ideal
building block to obtain bipyridine-bridged di(catechol-
imine) ligands L1-H4L2-H4 and their corresponding metal
complexes.
During the last 15 years, helicates were investigated with the
aim to understand the mechanisms of their formation as
well as their structural features.[1] Helicates can be consid-
ered to be the “drosophila”of metallosupramolecular
chemistry: important mechanistic aspects can very easily be
studied and much knowledge can be gained by using them
as simple model systems for more complex multinuclear
supramolecular coordination compounds.[2] Although func-
tionality is an important aspect in supramolecular chemis-
try,[3] only a few attempts have been made to study helicates
owing to special reactivities or properties.[4]
[a] Prof. Dr. M. Albrecht, I. Janser
Institut für Organische Chemie der RWTH-Aachen
Landoltweg 1, 52074 Aachen (Germany)
Fax : (+49)241-80-92385
E-mail: markus.albrecht@oc.rwth-aachen.de
Results and Discussion
[b] Priv.-Doz. Dr. A. Lützen, Dr. M. Hapke
Institut für Reine und Angewandte Chemie
der Universität Oldenburg
An improved synthesis of 5,5’-diamino-2,2’-bipyridine (1):
The preparation of 5,5’-diamino-2,2’-bipyridine (1) was pre-
viously described by Zhang and Breslow[8] and Janiak and
co-workers;[9] both groups used nickel-mediated/catalyzed
coupling reactions for the synthesis. However, when we ap-
plied the described conditions, they only worked in a few ex-
periments and we were not able to reproduce the results on
a regular basis. In a new approach, we have now prepared
the diamine 1 using a dimethyl-substituted pyrrole as the
Postfach 2503, 26111 Oldenburg (Germany)
Fax : (+49)441-798-3329
E-mail: arne.luetzen@uni-oldenburg.de
[c] Dr. R. Frçhlich
Organisch-Chemisches Institut der Universität Münster
Corrensstrasse 40, 48149 Münster (Germany)
[d] Dr. P. Weis
Institut für Physikalische Chemie der Universität Karlsruhe
Fritz-Haber-Weg, 76128 Karlsruhe (Germany)
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FULL PAPER
protecting group for the amine.[10] This procedure provided
the desired bipyridine 1 reproducibly in good yields and
high purity.
red solutions which, after evaporation of the solvent, yielded
M4[(L1)3Ti2] as red-orange solids. Analysis of the NMR spec-
troscopic data of these complexes revealed significant but
expected differences to that of the free ligand L1-H4 (d=
9.05 (s), 8.72 (s), 8.46 (d, J=8.2 Hz), 8.00 (d, J=8.6 Hz),
7.14 (d, J=7.4 Hz), 6.97 (d, J=7.4 Hz), 6.80 ppm (t, J=
7.4 Hz)), but also indicated the high degree of symmetry of
dinuclear metal coordination compounds, since for example,
Compound 1 was synthesized starting from 2-chloro-5-
aminopyridine (2). The amine group in 2 was protected as a
pyrrole by reaction with 2,5-hexadione (3; Scheme 1). The
resulting compound 4 could be homocoupled with zinc as
reducing agent either in the presence of palladium(ii) ace-
tate and 2-biphenylbis(tert-butyl)phosphane ((2-biph)PtBu2)
or with [Ni(PPh3)2Br2] and tetraethylammonium iodide. The
latter procedure is superior to the palladium-catalyzed cou-
pling due to the much lower costs and the higher yield in
the reaction. The resulting coupling product 5 was obtained
in 85% yield. The amine groups of 5 were deprotected by
reaction with hydroxylamine in the presence of triethyl-
amine. For a complete transformation, additional hydroxyl-
amine had to be added after the reaction mixture had been
refluxed for 20 h; the mixture was then heated for another
24 h. This procedure gave 5,5’-diamino-2,2’-bipyridine (1) as
the bis-HCl adduct in 77% yield (Scheme 1).
1
the H NMR spectrum of Na4[(L1)3Ti2] in [D6]DMSO shows
only half a set of signals for the bipyridine unit at d=8.46
(d, J=2.4 Hz), 8.25 (d, J=8.3 Hz), and 7.67 ppm (dd, J=8.3,
2.4 Hz), and for the catecholates at d=7.08 (d, J=7.7 Hz,
6H), 6.41 (pseudo t, J=7.7 Hz, 6H), and 6.22 ppm (d, J=
7.7 Hz, 6H). The imine protons are shifted to d=8.82 ppm
(s, 6H).
In addition, we were also able to obtain crystals of
Na4[(L1)3Ti2] from DMF/diethyl ether which showed that its
solid-state structure is similar to the one which was observed
for the corresponding helicate having biphenyl as spacer in-
stead of the bipyridine.[13] Three ligands L1 and two titan-
ium(iv) ions form a cylinder of approximately 2.1 nm length
with the linear rigid ligands slightly twisting around the
metal–metal axis (Figure 1a,b). Surprisingly one of the bi-
pyridine units of the spacers possesses the nitrogen atoms
orientated s-trans to each other, while the others are s-cis
configured. The reason for this is presumably the packing of
the crystal and its symmetry in the solid. The distance be-
tween the two Ti centers is 16.980 Š.
Two sodium cations are encapsulated in the interior of the
helicate and are separated by 10.603 Š. Clearly, the alkali
metal cations do not interact with the bipyridine nitrogen or
imine nitrogen atoms but rather solely bind to the internal
oxygen atoms of the catecholates (shown for one of the cat-
ions in Figure 1c). Three molecules of DMF coordinate to
each of the sodium cations and lead to a sixfold coordina-
tion. Two further sodium cations bind to the termini of the
Synthesis of dicatechol/2,2’-bipyridine ligands L1-H4 and L2-
H4: The preparation of the ligands L1-H4 and L2-H4 is
straightforward. Condensation of 2,3-dimethoxybenzalde-
hyde (6) and 5,5’-diamino-2,2’-bipyridine (1) in methanol af-
forded the bisimine ligand L1-H4 in 69%. The corresponding
amide-connected ligand L2-H4 was also obtained in 69%
yield by initially generating an active ester of 2,3-dimethoxy-
benzoic acid 7 with hydroxybenztriazoluronium hexafluoro-
phosphate (HBTU)[11] followed by addition of 1. Finally, the
methyl ethers were cleaved by reaction with BBr3 to obtain
the ligand L2-H4 in quantitative yield.
Formation of helicates of the imine-bridged ligand L1-H4:[12]
Stirring of L1-H4 (3 equiv), [TiO(acac)2] (2 equiv), and
M2CO3 (M=Li, Na, K; 2 equiv) in DMF overnight led to
Scheme 1. Preparation of 5,5’-diamino-2,2’-bipyridine (1) and of bipyridine-bridged dicatechol ligands L1-H4 and L2-H4.
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5743

M. Albrecht and A. Lützen et al.
Figure 2. Preferred conformations at complexes of the ligands L1 and L2
and representation of the obtained internal space.
es the imines, which leads to hydrolysis by reaction with re-
sidual water in the solvent. Similar imine hydrolysis is ob-
served by direct reaction of K2PdCl4 with L1-H4.
Formation of helicates of the amide-bridged ligand L2-H4:
Following the concept shown in Figure 2, the complexes of
the amide-bridged ligand L2 should provide a cavity that is
better preorganized for the incorporation of a single metal
ion that can interact with all bipyridine moieties. Hydrogen
bonding of the amides forces the bipyridine units to be ori-
entated to the inside of the cavity. However, owing to the ri-
gidity of the ligands and their linear orientation, the incor-
porated metal ions have to adopt a coordination geometry
that is closer to trigonal prismatic than to octahedral. In ad-
dition, amides are more stable than the corresponding
imines and less prone to hydrolysis.
Figure 1. The structure of [(L1)3Ti2]4À in the solid state; a) side view, b)
top view, c) coordination geometry of encapsulated sodium cations, and
d) formation of a polymeric strand in the solid state.
helicate and through DMF-bridging lead to an infinite poly-
mer in the solid state (Figure 1d) with alternating helicity of
the helices in the polymer strand.
The bipyridine/catechol ligand L1-H4 was developed to
form heteronuclear coordination compounds. As is schemat-
ically depicted in Figure 2, dinuclear complexes of the
imine-bridged ligand L1 possess a conformation that pro-
vides a cavity, which is too large to bind a single metal ion
in the interior by coordination to more than one bipyridine
unit. Repulsion of the lone pair at the imines and the
“charge”at the catecholate oxygen atoms force the spacer
in an “outward”orientation.
Therefore, we tested ligand L2-H4 in a series of coordina-
tion studies (Scheme 3). In the reaction of L2-H4 with
K2PdCl4 we obtained the desired mononuclear complex
[(L2-H4)PdCl2] without hydrolysis of the spacer.[14] [(L2-
H4)PdCl2] was characterized by its 1H NMR spectrum,
which showed, for example, a low-field shift of the protons
in the 6- and 6’-position of the bipyridine unit to d=
9.55 ppm compared to the free ligand. Mass spectrometry
revealed the molecular peak at m/z 638. Unfortunately, we
were not able to use the complex [(L2-H4)PdCl2] as a ligand
for the formation of triple-stranded helicates.
Based on this assumption we attempted to bind three
metal complex units to the “outside”of the triple-stranded
helicate [(L1)3Ti2]4À. Three equivalents of K2PdCl4 were al-
lowed to react with [(L1)3Ti2]4À.
However, the clean reaction
(which was monitored by
NMR spectroscopy in wet
[D6]DMSO) that was observed,
unfortunately only resulted in
the hydrolysis products 1-PdCl2
and
[(3-formylcatecholate)3-
Ti]2À (8; Scheme 2). Evidently,
binding of dichloropalladium
to the bipyridine moiety labiliz-
Scheme 2.
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Homo- and Heteronuclear Helicates
FULL PAPER
plexes, for example, at m/z 1473
[Li2H(L2)3Ti2]À,
[Na3(L2)3Ti2]À,
1572
1575
and
[K3(L2)3Ti2] À, respectively.
In [(L2)3Ti2]4À
a cavity is
formed that provides a close to
trigonal prismatic coordination
site for cations. Metals with d0
or d10 configuration do not pos-
sess an electronic preference
for octahedral or trigonal-pris-
matic geometry.[16] Therefore,
zinc(ii) was used as a d10 metal
ion. A complexation study of
L2-H4 (3 equiv) was performed
with [TiO(acac)2] (2 equiv) and
ZnCl2 (1 equiv) in the presence
of
potassium
carbonate.
Hereby, K2[(L2)3Ti2Zn] was ob-
tained as a red solid in quanti-
tative yield. FT-ICR ESI MS
showed the presence of the het-
erotrinuclear complex by
a
strong signal at m/z 761 corre-
sponding
to
the
dianion
[(L2)3Ti2Zn]2À. As shown in Fig-
ure 3d, the 1H NMR spectrum
shows the signals of the amide
NH group at d=11.48 ppm (s),
the resonances of the bipyridine
at d=8.81 (d, J=8.6 Hz), 8.75
Scheme 3. Preparation of different complexes from ligand L2-H4.
(d, J=8.6 Hz), and 7.99 ppm
(s), and the ones of the catechol
Instead of the PdCl2 fragment, other metals can be bound
to the bipyridine unit to give tris(bipyridine) complexes.
Thus, coordination studies were performed with three equiv-
alents of L2-H4 and zinc(ii) chloride to obtain the complex
[(L2-H4)3Zn]2+ (Scheme 3). The peak of the dication can be
observed by positive-ion ESI MS in methanol at m/z 719
unit at d=7.00 (d, J=7.7 Hz), 6.49 (t, J=7.7 Hz), and
6.37 ppm (d, J=7.7 Hz), respectively. Especially remarkable
is the shift of the protons in the 6- and 6’-position of the bi-
pyridine to d=7.99 ppm, which is due to the fixation of this
proton in the interior of the cavity close to the metal center.
1
(correct isotopic pattern). In the H NMR spectrum of [(L2-
H4)3Zn]Cl2 in [D6]DMSO the catechol resonances are not
shifted significantly. However, the signals of the bipyridine
are now observed at d=9.03 (s), 8.42 (d, J=8.7 Hz), and
8.35 ppm (dd, J=8.7, 2.4 Hz) (see Figure 3, c). Owing to the
high polarity of the solvent, the NMR resonances could be
averaged signals over different complexes of zinc with L2-H4
and the free ligand, which exchange in a fast equilibrium.
In addition to the bipyridine units, the catecholates can
also be selectively addressed. Ligand L2 forms dinuclear
triple-stranded helicates M4[(L2)3Ti2] with titanium(iv) ions
in the presence of lithium, sodium, or potassium carbonate
(Scheme 3).[15] As is shown in Figure 3b for K4[(L2)3Ti2], the
1H NMR signal of the amide proton is shifted to low field
(d=12.44 (Li), 12.50 (Na), 12.54 ppm (K)). This is due to
the formation of a hydrogen bond from the amide to the
catecholate oxygen atom upon metal coordination (see
Figure 2). ESI MS showed the peaks of the dinuclear com-
Conclusion
Herein we presented a facile synthesis of 5,5’-diamino-2,2’-
bipyridine (1), which is an important building block for the
synthesis of multitopic ligands for the self-assembly of met-
allosupramolecular aggregates. For example, the dicatechol
imine ligand L1-H4 forms triple-stranded dinuclear helicates
with titanium(iv) ions; however, due to the lability of the
imine bonds it cannot bind additional metal ions at the bi-
pyridine moieties. Therefore, the corresponding amide-con-
nected ligand L2-H4 was prepared and also tested in coordi-
nation studies to show the higher stability of the connecting
units. During the course of this study we were able to
obtain, for example, mononuclear [(L2)3Zn]2+ and dinuclear
[(L2)3Ti2]4À in which the metal ions are bound either to the
bipyridine or to the catecholate binding site, and we were
also able to establish heterotrinuclear complexes
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M. Albrecht and A. Lützen et al.
reaction without further purification (1.47 mg, 91%). An analytically
pure sample was obtained after column chromatography on silica gel
with hexane/ethyl acetate/triethylamine (10/1/0.05 v/v) as eluent. m.p. 67–
688C; 1H NMR (CDCl3, 500.1 MHz): d=8.29 (d, J=2.7 Hz, 1H), 7.53
(dd, J=8.3, 2.7 Hz, 1H), 7.45 (d, J=8.3 Hz, 1H), 5.93 (s, 2H), 2.04 ppm
(s, 6H); 13C NMR (CDCl3, 125.8 MHz): d=150.3, 148.9, 138.1, 134.6,
128.8, 124.5, 107.0, 12.9 ppm; MS (CI, isobutane): m/z (%): 207.3 (100)
[MH+]; elemental analysis calcd (%) for C11H11N2Cl (206.67): C 63.93, H
5.36, N 13.55; found: C 64.07, H 5.41, N 13.56.
5,5’-Bis(2,5-dimethyl-1H-pyrrole)-2,2’-bipyridine (5): Bis(triphenylphos-
phane)nickel(ii) bromide (0.74 g, 1 mmol), zinc powder (556 mg,
8.5 mmol), and tetraethylammonium iodide (1.28 g, 5 mmol) were sus-
pended in absolute THF (20 mL). 1-(2-Chloropyridine)-5-yl-2,5-dimethyl-
1H-pyrrole (4; 1.04 g, 5 mmol) dissolved in absolute THF (10 mL) was
slowly added to this mixture by syringe. The resulting mixture was stirred
for 3 h at 608C until TLC monitoring revealed complete consumption of
the starting material. After that time concentrated ammonia (25%,
20 mL), water (15 mL), and dichloromethane (60 mL) were added. After
the mixture had been stirred for 15 min, the precipitate was filtered off
and the organic layer was separated. The aqueous phase was further ex-
tracted with small portions of dichloromethane several times. The com-
bined organic phases were washed with water and brine. After the organ-
ic phases had been dried over MgSO4, the solvent was removed in vacuo.
The residue was subjected to column chromatography on silica gel 60
using petroleum ether 40/60/ethyl acetate (9:1) containing 1% of triethyl-
amine as eluent to give the desired product (724 mg, 85%). If necessary
the product can be crystallized from 2-propanol. m.p. 215–2168C;
1H NMR (CDCl3, 500.1 MHz): d=8.59 (d, J=2.4 Hz, 2H), 8.58 (d, J=
8.2, 2H), 7.71 (dd, J=8.2, 2.4 Hz, 2H), 5.97 (s, 4H), 2.10 ppm (s, 12H);
13C NMR (CDCl3, 125.8 MHz): d=154.3, 148.5, 136.4, 135.8, 128.9, 121.3,
106.9, 13.0 ppm; MS (CI, i-butane): m/z (%): 342.2 (100) [MH+]; elemen-
tal analysis calcd (%) for C22H22N4 (342.22): C 77.16, H 6.48, N 16.36;
found: C 77.56, H 6.57, N 16.32.
5,5’-Diamino-2,2’-bipyridine dihydrochloride (1):[8] 5,5’-Bis(2,5-dimethyl-
1H-pyrrole)-2,2’-bipyridine (5; 1.19 g, 3.48 mmol), hydroxylamine hydro-
chloride (7.3 g, 105 mmol), triethylamine (4 mL), ethanol (25 mL), and
water (10 mL) were heated under reflux for 20 h. After that time another
portion of hydroxylamine hydrochloride (7.30 g, 105 mmol) and triethyla-
mine (2 mL) was added. The solution was further heated under reflux for
24 h until TLC monitoring revealed complete consumption of the starting
material. The reaction mixture was allowed to cool to room temperature
before it was quenched by pouring it into ice-cold 1n HCl (30 mL). Etha-
nol (50 mL) was added to the resulting suspension of a golden-yellow
precipitate and the mixture was cooled to 08C and stirred at this temper-
ature for 1 h. After that time the product was collected as a golden-
yellow precipitate, washed with cold ethanol, and dried in high vacuum
(690 mg, 77%). 1H NMR (D2O, 500.1 MHz): d=8.59 (m, 2H), 8.02 (d,
J=8.8, 2H), 7.75 ppm (d, J=8.8 Hz, 2H); 13C NMR (D2O, 125.8 MHz):
d=143.5, 137.8, 132.8, 129.6, 124.0 ppm; MS (ESI, DMSO/MeOH): m/z
(%): 187.3 (100) [MH+].
Figure 3. 1H NMR spectra of a) L2-H4
,
b) K4[(L2)3Ti2], c) [(L2-
H4)3Zn]Cl2, and d) K2[(L2)3Ti2Zn] in [D6]DMSO (*=DMF).
[(L2)3ZnTi2]2À in which both metal binding sites are involved
in the coordination of the different metal ions. Further stud-
ies focussed on the formation of heterometallic coordination
networks and the incorporation of metals into the cavity of
the helicate are currently going on in our laboratories.
ExperimentalSection
N,N’-Bis[(2,3-dihydroxyphenyl)methylen]-2,2’-bipyridine-5,5-diamine
(L1-H4): 5,5’-Diamino-2,2’-bipyridine dihydrochloride (1; 0.69 g,
2.68 mmol) was suspended in ethanol (50 mL), and triethylamine (ap-
proximately 5 mL) was added to form a clear solution. After addition of
2,3-dihydroxybenzaldehyde 6 (0.74 g, 5.36 mmol), the mixture was stirred
for 72 h at room temperature. The precipitate was filtered off and was
dried in vacuum (0.79 g, 69%). M. p. 2698C (decomp); 1H NMR
([D6]DMSO, 500.1 MHz): d=9.05 (s, 2H), 8.72 (s, 2H), 8.46 (d, J=
8.2 Hz, 2H), 8.00 (d, J=8.6 Hz, 2H), 7.14 (d, J=7.4 Hz, 2H), 6.97 (d, J=
7.4 Hz, 2H), 6.80 ppm (t, J=7.4 Hz, 2H); 13C NMR ([D6]DMSO,
125.8 MHz): d=165.9, 153.4, 149.8, 146.2, 144.9, 144.0, 129.3, 123.2, 121.3,
120.1, 119.4 ppm (one signal cannot be observed); MS (EI, 70 eV): m/z
(%): 426 (100) [M+]; elemental analysis calcd (%) for C24H18N4O4·1/
4H2O: C 66.89, H 4.33, N 13.00; found: C 66.80, H 4.58, N 12.70.
NMR spectra were recorded on a Bruker DRX 500, WM 400, a Varian
Inova 400, or a Unity 500 spectrometer. FT-IR spectra were recorded by
diffuse reflection (KBr) on a Bruker IFS spectrometer. Mass spectra (EI,
70 eV; FAB with 3-nitrobenzoic acid (3-NBA) as matrix) were taken on
a Finnigan MAT 90, 95, or 212 mass spectrometer. FT-ICR ESI mass
spectra were measured on a Bruker Bioapex II FTMS equipped with a
7 Tesla magnet. Elemental analyses were obtained with a Heraeus CHN-
O-Rapid analyzer. Melting points: Büchi B-540 (uncorrected).
1-(2-Chloropyridine)-5-yl-2,5-dimethyl-1H-pyrrole (4):[10] 5-Amino-2-
chloropyridine (2; 1.0 g, 7.8 mmol), 2,5-hexanedione (3; 1.1 mL,
9.4 mmol), and p-TsOH (15 mg, 0.08 mmol) were dissolved in toluene
(15 mL) and heated in a Dean–Stark apparatus for 2 h. After the dark
brown reaction mixture had been cooled, it was washed with saturated
aqueous NaHCO3 solution, five times with water, and with brine. After
solution was dried over MgSO4, the solvent was removed in vacuo. The
dark residue was dried under high vacuum and was used for the coupling
N,N’-Bis(2,3-dimethoxybenzoate)-2,2’-bipyridine-5,5-diamine (L2-Me4):
2,3-Dimethoxybenzoic acid 7 (118 mg, 0.65 mmol) was dissolved in aceto-
nitrile (25 mL), and HBTU (295 mg, 0.78 mmol) and diisopropylethyl-
amine (244.6 mL=184 mg, 1.43 mmol) were added. After 30 min at room
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Homo- and Heteronuclear Helicates
FULL PAPER
temperature, a slightly yellow solution was formed. Then, bipyridine 1
(84 mg, 0.33 mmol) dissolved in acetonitrile (20 mL) and diisopropyl-
ethylamine (222.3 mL, 167 mg, 1.30 mmol, 2 equiv) were added. The sol-
vent was removed after stirring overnight, to leave a yellow solid, which
was dissolved in ethyl acetate and washed with aqueous NH4Cl,
NaHCO3, H2O, and brine. The protected ligand L2-Me4 was obtained
after removal of the solvent (117 mg, 69%). M. p. 2478C (decomp);
1H NMR ([D6]DMSO, 400.0 MHz): d=10.61 (s, 2H), 8.95 (t, J=1.6 Hz,
2H), 8.34 (d, J=1.6 Hz, 4H), 7.24 (dd, J=7.7, 1.9 Hz, 2H), 7.20 (t, J=
7.7 Hz, 2H), 7.16 (dd, J=7.7, 1.9 Hz, 2H), 3.88 (s, 6H), 3.83 ppm (s, 6H);
13C NMR (CDCl3, 125.8 MHz): d=163.2, 152.4, 151.2, 147.1, 140.4, 134.9,
127.7, 125.9, 124.7, 122.8, 120.8, 116.0, 61.7, 56.1 ppm; MS (EI, 70 eV):
m/z (%): 514 (100) [M+]; elemental analysis calcd (%) for C28H26N4O6:
C 65.36, H 5.09, N 10.89; found: C 64.89, H 4.88, N 10.53.
N,N’-Bis(2,3-dihydroxybenzoate)-2,2’-bipyridine-5,5-diamine (L2-H4): L2-
Me4 (71 mg, 0.14 mmol) was dissolved in dichloromethane (20 mL) and
cooled to 08C. At this temperature BBr3 (0.13 mL, 285.6 mg, 1.40 mmol)
was added. The yellow mixture was stirred overnight at room tempera-
ture and then methanol was added. The solvent was removed in vacuo
and the residue was dissolved in ethyl acetate and washed with water.
Removal of the solvent afforded L2-H4 (64 mg, quantitative). M.p. 2618C
(decomp); 1H NMR ([D6]DMSO, 400.0 MHz): d=10.86 (s, 2H), 9.20 (d,
J=2.0 Hz, 2H), 8.55 (m, 4H), 7.40 (dd, J=8.0, 1.4 Hz, 2H), 7.04 (dd,
J=8.0, 1.4 Hz, 2H), 6.82 ppm (t, J=8.0 Hz, 2H); 13C NMR ([D6]DMSO,
125.8 MHz): d=167.5, 147.1, 145.9, 144.7, 138.8, 136.4, 130.8, 121.9, 118.9,
118.5, 117.6 ppm (one signal cannot be observed); MS (EI, 70 eV): m/z
(%): 458 (100) [M+]; elemental analysis calcd (%) C24H18N4O6: C 62.88,
H 3.96, N 12.22; found: C 62.57, H 4.27, N 11.79.
refinement SHELXL-97 (G. M. Sheldrick, Universität Gçttingen, 1997),
graphics SCHAKAL (E. Keller, Universität Freiburg, 1997).
CCDC-241101 contains the supplementary 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.
K4[(L1)3Ti2]: Yield: 76.0 mg (quantitative); 1H NMR ([D6]DMSO,
500.1 MHz): d=8.83 (s, 6H), 8.49 (d, J=2.0 Hz, 6H), 8.29 (d, J=8.4 Hz,
6H), 7.74 (dd, J=8.4, 2.0 Hz, 6H), 7.10 (d, J=7.7 Hz, 6H), 6.41 (pseudo
t, J=7.7 Hz, 6H), 6.22 ppm (d, J=7.7 Hz, 6H); ESI-MS (methanol):
m/z: 1479 [MÀK]À, 720 [MÀ2K]2À, 701 [MÀ3K+H]2À, 467 [MÀ3K]3À
;
elemental analysis calcd (%) for C72H42N12K4O12Ti2·2H2O·4DMF:
C 54.60, H 4.04, N 12.13; found: C 54.47, H 4.39, N 11.84.
Li4[(L2)3Ti2]: Yield: 16.2 mg (quantitative); 1H NMR ([D6]DMSO,
400 MHz): d=12.44 (s, 6H), 8.93 (s, 6H), 7.64 (br, 6H), 7.21–7.17 (m,
12H), 6.58 (t, J=7.6 Hz, 6H), 6.42 ppm (d, J=7.6 Hz, 6H); negative-ion
mode ESI MS: m/z: 1473 [MÀ2Li+H]À; IR (drift, KBr): n˜ =3409, 1661,
1590, 1535, 1467, 1441, 1389, 1246, 1210, 1059, 844, 748, 679, 524 cmÀ1
;
elemental analysis calcd (%) for C72H42Li4N12O18Ti2·DMF·4H2O: C 55.20,
H 3.52, N 11.16; found: C 55.21, H 3.28, N 11.04.
Na4[(L2)3Ti2]: Yield: 16.9 mg (quantitative); 1H NMR ([D6]DMSO,
400 MHz): d=12.50 (s, 6H), 8.90 (s, 6H), 7.77 (d, J=7.3 Hz, 6H), 7.32–
7.21 (m, 12H), 6.59 (t, J=7.6 Hz, 6H), 6.44 ppm (d, J=7.6 Hz, 6H); neg-
ative-ion mode ESI MS: m/z: 1527 [MÀNa]À, 741 [MÀ3Na+H]2À; IR
(drift, KBr): n˜ =3408, 1659, 1588, 1532, 1465, 1439, 1386, 1285, 1245,
1208, 1056, 842, 745, 677, 522 cmÀ1; elemental analysis calcd (%) for
C72H42N12Na4O18Ti2·DMF·12H2O: C 48.95, H 4.00, N 9.89; found: C
49.12, H 4.04, N 8.87.
K4[(L2)3Ti2]: Yield: 17.6 mg (quantitative); 1H NMR ([D6]DMSO,
400 MHz): d=12.54 (s, 6H), 8.86 (s, 6H), 7.83 (br, 6H), 7.33–7.26 (m,
6H), 7.21 (d, J=7.6 Hz, 6H), 6.58 (t, J=7.6 Hz, 6H), 6.44 ppm (d, J=
7.6 Hz, 6H); negative-ion mode ESI MS: m/z: 1575 [MÀK]À, 1537
[MÀ2K+H]À, 768 [MÀ2K]2À; IR (drift, KBr): n˜ =3427, 1660, 1587,
1531, 1464, 1439, 1386, 1283, 1244, 1208, 1055, 842, 744, 678, 522 cmÀ1; el-
emental analysis calcd (%) for C72H42N12K4O18Ti2·2DMF·6H2O: C 50.11,
H 3.67, N 10.49; found: C 49.98, H 3.89, N 10.01.
General procedure for the preparation of dinuclear complexes
M4[(L)3Ti2] (M=Li, Na, K): Ligand L1-H4 (3 equiv), [TiO(acac)2]
(2 equiv), and the alkali metal carbonate (2 equiv) were mixed in DMF
and stirred overnight. The solvent was removed in vacuo to obtain the
complexes as red-orange solids which were purified by filtration over Se-
phadex LH 20.
Li4[(L1)3Ti2]: Yield: 69.5 mg (quantitative); 1H NMR ([D6]DMSO,
500.1 MHz): d=8.72 (s, 6H), 8.38 (d, J=2.4 Hz, 6H), 8.24 (d, J=8.4 Hz,
6H), 7.65 (dd, J=8.4, 2.4 Hz, 6H), 7.03 (d, J=7.7 Hz, 6H), 6.40 (pseudo
t, J=7.7 Hz, 6H), 6.19 ppm (d, J=7.7 Hz, 6H); 13C NMR ([D6]DMSO,
125.7 MHz): d=165.3, 162.8, 161.6, 152.1, 149.6, 143.2, 128.8, 121.1, 120.9,
119.6, 118.5, 116.8 ppm; ESI-MS (methanol): m/z: 688 [MÀ2Li]2À, 685
[MÀ3Li+H]2À, 456 [MÀ3Li]3À, 454 [MÀ4Li+H]3À; elemental analysis
calcd (%) for C72H42N12Li4O12Ti2·9H2O·2DMF: C 55.14, H 4.39, N 11.54;
found: C 55.08, H 5.02, N 11.85.
(L2-H4)PdCl2: L2-H4 (15 mg, 0.033 mmol) and K2PdCl4 (10.7 mg,
0.033 mmol) were heated in DMF for 5 h to 708C. The solvent was re-
moved in vacuo and the residue was washed with water and then dried to
obtain 21 mg of
a
yellow solid in quantitative yield. 1H NMR
([D6]DMSO, 300 MHz): d=11.05 (s, 2H), 9.55 (d, J=2.5 Hz, 2H), 8.64
(dd, J=8.9, 2.5 Hz, 2H), 8.46 (d, J=8.9 Hz, 2H), 7.38 (dd, J=7.9, 1.4 Hz,
2H), 7.04 (dd, J=7.9, 1.4 Hz, 2H), 6.80 ppm (t, J=7.9 Hz, 2H); MS (EI,
70 eV): m/z (%): 638 (100) [M]+; IR (drift, KBr): n˜ =3434, 2921, 1657,
1582, 1540, 1497, 1471, 1384, 1323, 1273, 1222, 840, 801, 741 cmÀ1; ele-
mental analysis calcd (%) for C24H18N4O6PdCl2: C 45.34, H 2.85, N 8.81;
found: C 44.89, H 3.10, N 9.28.
Na4[(L1)3Ti2]: Yield: 72.7 mg (quantitative); 1H NMR ([D6]DMSO,
500.1 MHz): d=8.82 (s, 6H), 8.46 (d, J=2.4 Hz, 6H), 8.25 (d, J=8.3 Hz,
6H), 7.67 (dd, J=8.3, 2.4 Hz, 6H), 7.08 (d, J=7.7 Hz, 6H), 6.41 (pseudo
t, J=7.7 Hz, 6H), 6.22 ppm (d, J=7.7 Hz, 6H); 13C NMR ([D6]DMSO,
125.7 MHz): d=165.2, 162.8, 161.2, 152.1, 149.5, 143.2, 129.1, 121.1, 120.7,
119.6, 118.8, 116.8 ppm; ESI-MS (methanol): m/z: 1431 [MÀNa]À, 704
[(L2-H4)3Zn]Cl2: The ligand L2-H4 (15 mg, 0.033 mmol) and ZnCl2
(1.5 mg, 0.011 mmol) were stirred overnight in DMF. Removal of the sol-
vent afforded a yellow solid in quantitative yield (16.5 mg); 1H NMR
([D6]DMSO, 300 MHz): d=11.28 (br, 6H), 10.68 (s, 6H), 9.56 (br, 6H),
9.03 (s, 6H), 8.42 (d, J=8.7 Hz, 6H), 8.35 (dd, J=8.7, 2.4 Hz, 6H), 7.43
(dd, J=7.9, 1.5 Hz, 6H), 7.02 (dd, J=7.9 Hz, 1.5 Hz, 6H), 6.81 ppm (t,
J=7.9 Hz, 6H); IR (drift, KBr): n˜ =3424, 1656, 1532, 1477, 1388, 1261,
1219, 1058, 840, 739 cmÀ1; positive-ion mode ESI MS (methanol): m/z:
[MÀ2Na]2À, 693 [MÀ3Na+H]2À, 462 [MÀ3Na]3À, 455 [MÀ4Na+H]3À
;
elemental analysis calcd (%) for C72H42N12Na4O12Ti2·4H2O·4DMF: C
55.45, H 4.32, N 12.32; found: C 55.46, H 4.67, N 11.89.
X-ray crystal structure analysis for Na4[(L1)3Ti2]: formula C72H42N12O12Ti2-
Na4·12C3H7NO·H2O, Mr =2350.10, red crystal 0.30”0.20”0.10 mm, a=
15.586(1),
b=20.796(1),
c=38.513(1) Š,
b=100.72(1)8,
V=
[MÀ2Cl]2+
;
elemental
analysis
calcd
(%)
for
12265.2(10) Š3, 1calcd =1.273 gcmÀ3, m=2.21 cmÀ1, empirical absorption
correction (0.937ꢀTꢀ0.978), Z=4, monoclinic, space group C2/c (no.
15), l=0.71073 Š, T=198 K, w and f scans, 18878 reflections collected
(Æh, Æk, Æl), [(sinq)/l]=0.59 ŠÀ1, 10751 independent (Rint =0.042) and
6630 observed reflections [Iꢁ2s(I)], 710 refined parameters, R=0.103,
wR2 =0.295, max. residual electron density 1.83(À0.55) eŠÀ3, some of the
DMF molecules show severe disorder, refinement with split positions did
not improve the model, hydrogen atoms as part of water molecules could
not be located, others calculated and refined riding.
719
C72H54N12O18Cl2Zn·3DMF·2H2O: C 55.06, H 4.51, N 11.89; found: C
54.96, H 4.78, N 12.59.
K2[(L2)3Zn]Ti2: L2-H4 (15 mg, 0.033 mmol), [TiO(acac)2] (5.7 mg,
0.022 mmol), K2CO3 (3 mg, 0.022 mmol), and ZnCl2 (1.5 mg, 0.011 mmol)
were mixed in DMF and stirred overnight. The solvent was removed and
the residue washed with water and dried in vacuo to obtain a red solid in
quantitative yield (17.6 mg). 1H NMR ([D6]DMSO, 400 MHz): d=11.48
(s, 6H), 8.81 (d, J=8.6 Hz, 6H), 8.75 (d, J=8.6 Hz, 6H), 7.99 (s, 6H),
7.00 (d, J=7.7 Hz, 6H), 6.49 (t, J=7.7 Hz, 6H), 6.37 ppm (d, J=7.7 Hz,
6H); negative-ion mode ESI MS (methanol): m/z: 761 [MÀ2K]2À; IR
(drift, KBr): n˜ =3440, 1664, 1590, 1538, 1480, 1440, 1385, 1308, 1247,
1207, 1056, 848, 742, 679, 522 cmÀ1; elemental analysis calcd (%) for
The data set was collected with a Nonius KappaCCD diffractometer,
equipped with a rotating-anode generator. Programs used: data collection
COLLECT (Nonius B.V., 1998), data reduction Denzo-SMN,[17] absorp-
tion correction SORTAV,[18] structure solution SHELXS-97,[19] structure
Chem. Eur. J. 2005, 11, 5742 – 5748
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5747

M. Albrecht and A. Lützen et al.
C72H42K2N12O18Ti2Zn·3DMF·5H2O: C 50.89, H 3.85, N 10.99; found: C
50.76, H 4.01, N 11.02.
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Acknowledgements
Support by the Deutsche Forschungsgemeinschaft (SPP 1118), the COST
D31 programme (working group “Functional Helicates”), and the Uni-
versitätsgesellschaft Oldenburg e.V. is gratefully acknowledged. We
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Received: December 8, 2004
Published online: July 20, 2005
5748
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ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2005, 11, 5742 – 5748