Homobimetallic Nickel and Zinc Complexes
FULL PAPER
magnetic fields of 5000 Oe. Diamagnetic corrections were estimated ac-
cording to Pascalꢁs constants.
synthetic strategy towards unsymmetric ligand systems, that
has been recently developed by us.[21] The ligand molecule
provides two entirely different binding compartments, which
are both suitable for accommodating either zinc(II) or nick-
el(II) ions, as we have shown by way of the homodinuclear
complexes ZnZn and NiNi. In case of simultaneous pres-
ence of both metal ions the formation of the heterodinu-
clear complex NiZn is observed. This process is highly di-
rected by the different coordination requirements of the
metal ions and the distinct chemical environments of the
ligand compartments, resulting in a hydrazide-bound zinc,
whereas nickel is selectively placed in the amine compart-
ment of the H2bpampbh ligand.
An interesting feature of our system are two variable
binding positions at the hydrazide-bound metal center that
are accessible for external donor molecules. The strong
Lewis acidity of the hydrazide-bound metal site, quantified
for the homobimetallic nickel system by spectrophotometric
titrations, makes H2bpampbh-based complex compounds
suitable candidates for activity tests in catalytic reactions. In
this study we demonstrated that the homobimetallic com-
plex NiNi shows low but significant SOD-like activity in in-
hibiting the reduction of NBT by superoxide radicals. Con-
sidering the water solubility of the present complexes and
the importance of nickel and zinc in hydrolytically active en-
zymes, the examination of our system regarding urease and
phosphatase activity seems promising and is subject of our
ongoing work.
Syntheses: Proligand Hbpahmb was synthesized as previously report-
ed.[21] All other chemicals and solvents are commercially available and
were used without further purification.
Benzoic acid [1-(3-{[2-(bispyridin-2-ylmethylamino)ethylimino]methyl}-2-
hydroxy-5-methylphenyl)methylidene]hydrazide (H2bpampbh): A solu-
tion of Hbpahmb in methanol was treated with one equivalent benzoic
acid hydrazide dissolved in methanol, accompanied by a color change of
the solution from yellow to bright red. After two hours of stirring at
room temperature, the solvent was removed in vacuo. The crude product
was purified by size exclusion chromatography with Sephadex LH-20 to
remove small quantities of the symmetric side products, and H2bpampbh
was obtained as an analytically pure, highly viscous red oil. Yield: 82%.
1H NMR (DMSO, 400 MHz): d=2.29 (s, 3H; CH3), 2.81 (t, 3J=5.80 Hz,
3
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2H; N CH2), 3.76 (t, J=5.88 Hz, 2H; =N CH2), 3.83 (s, 4H; N CH2
py), 7.21 (m, 2H; CHpy), 7.26 (m, 1H; CHPh), 7.45–7.68 (m, 7H; 4CHpy
and 3CHPh), 7.77 (m, 1H; CHPh), 7.94 (m, 2H; CHPh), 8.46 (m, 2H;
ꢀ
CHpy), 8.50 (s, 1H; HC=N), 8.84 (s, 1H; HC=N N), 11.87 (s, 1H; NH),
14.29 ppm (s, 1H; OH); 13C NMR (DMSO, 100 MHz): d=20.4 (CH3),
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54.3 (N CH2), 55.1 (=N CH2), 60.1 (N CH2 py), 118.9 (CPh), 120.6
(CPh), 122.6 (Cpy), 123.0 (Cpy), 126.5, 128.1, 128.9, 129.8, 132.1, 133.9,
ꢀ
134.3 (all CPh), 136.9 (Cpy), 143.7 (C=N N), 149.2 (Cpy), 159.6 (Cpy), 160.9
ꢀ
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(C=N), 163.4 (C OH), 166.7 ppm (C=O); IR(KBr): n˜ =3215 (N H),
1636 cmꢀ1 (Amide I and C=N); MS (micro-ESI in methanol): m/z: 529
(100%, [H2bpampbh+Na]+); elemental analysis calcd (%) for
H2bpampbh·H2O, C30H32N6O3, (524.62): C 68.68, H 6.15, N 16.02; found:
C 68.44, H 6.29, N 16.77.
[Zn2(bpampbh)(m,h1-OAc)(h1-OAc)] (ZnZn): The ligand H2bpampbh
(200 mmol) and triethylamine (2 equiv) were dissolved in acetonitrile
(20 mL). Solid Zn(OAc)2·2H2O (2 equiv) was added, and the resulting
mixture was stirred for 2 h at room temperature. The metal salt dissolved
completely upon complexation and the color of the reaction mixture
turned from yellow-red to bright yellow. Single crystals suitable for X-ray
crystallography were obtained after a few days at ꢀ208C. After reduction
of the solution volume, a second crystalline sample could be obtained.
Furthermore, while the main goal of the present work was
to confirm the versatility and high potential of our synthetic
route towards unsymmetric ligand and complex systems, our
future efforts will be focused on the directed generation of
unsymmetric coordination compounds with closer relation
to biological systems, thus promising and interesting bioana-
log properties. As we could demonstrate in this paper, our
synthetic approach provides an appropriate tool for this pur-
pose.
Overall yield: 61%. 1H NMR (MeOD, 400 MHz): d=1.95 (s, 6H; CH3
3
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acetate), 2.27 (s, 3H; CH3), 2.86 (t, J=5.20 Hz, 2H; CH2 N=), 3.06 (t,
3
2
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J=5.18 Hz, 2H; CH2 N), 4.37 (d, J=16.01 Hz, 2H; 1H of each CH2
py), 4.67 (d, J=16.01 Hz, 2H; 1H of each CH2 py), 7.13 (m, 1H), 7.32–
7.40 (m, 6H), 7.47 (m, 2H), 7.90 (m, 2H), 8.01 (m, 2H) (all CHarom), 8.10
2
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(s, 1H; HC=N), 8.56 (m, 2H; CHarom), 8.69 ppm (s, 1H; HC=N N);
13C NMR (MeOD, 100 MHz): d=19.8 (CH3), 23.7 (CH3 acetate), 56.2
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(CH2 N), 59.8 (CH2 N=), 62.5 (CH2 py), 123.7, 124.3, 125.6, 126.5,
128.9, 129.0, 131.6, 136.9, 140.4, 140.9, 141.0, 149.0 (all Carom), 156.2 (C=
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N N), 157.0 (Carom), 167.1 (Ph O), 169.2 (C=N), 173.7 (N=C O),
179.6 ppm (C=O acetate); IR(KBr): n˜ =1647 and 1606 cmꢀ1 (C=N and
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C=N N=C); UV/Vis (MeCN): lmax (e)=292 (13400), 343 (12000), 402
Experimental Section
(16700), 415 nm (sh, 16400 mꢀ1 cmꢀ1) (see Figure S5 in the Supporting In-
formation); MS (micro-ESI in methanol/acetonitrile): m/z: 651
([Zn2(bpampbh)(OH)]+), 665 ([Zn2(bpampbh)(OMe)]+), 693 (100%,
Physical measurements: The NMR spectra were recorded on a Bruker
Avance 400 MHz spectrometer. IR spectra were measured on a Bruker
IFS55/Equinox spectrometer. For UV/Vis solution spectra a Varian Cary
5000 UV/Vis/NIR spectrophotometer equipped with a dual cell peltier
accessory was used. Mass spectra were recorded on a MAT95XL Finni-
gan instrument. Elemental analyses were acquired by use of a LECO
CHN/932 and a VARIO EL III elemental analyzer. Cyclic voltammetry
measurements have been performed by means of a three electrode tech-
nique by using a home built computer controlled instrument (for details
see[37]). The experiments were performed in solutions of tetra-n-butylam-
monium perchlorate (0.25m) in acetonitrile under a blanket of solvent sa-
turated with argon. Ag/AgCl was used as reference electrode in a solu-
tion of tetra-n-butylammonium chloride (0.25m) in acetonitrile. The re-
ported potentials are referenced with respect to the ferrocenium/ferro-
cene couple, which was recorded at the end of each experiment. The
working electrode was a hanging mercury drop (mHgꢀdrop ꢂ4 mg) generat-
[Zn2(bpampbh)(OAc)]+);
[Zn2(bpampbh)(OAc)2](H2O)3, C34H40N6O9Zn2 (807.5): C 50.57, H 4.99,
N 10.41; found: C 50.74, H 4.56, N 10.04.
elemental
analysis
calcd
(%)
for
[Ni2(bpampbh)(m-H2O)(h1-OAc)(H2O)](OAc) (NiNi): A solution of the
ligand H2bpampbh (200 mmol) and triethylamine (2 equiv) in acetonitrile
(15 mL) was added to a suspension of Ni(OAc)2·4H2O (2 equiv) in aceto-
nitrile (5 mL). After 2 h stirring at room temperature, the nickel salt was
completely dissolved. The volume of the mixture was reduced to 10 mL
and the resulting red-brown solution was left at ꢀ208C. Single crystals
suitable for X-ray crystallography were obtained after a few days. A
second crop of crystalline material could be isolated by slow evaporation
at room temperature after two days. Overall yield: 68%. IR(KBr): n˜ =
1650 and 1606 cmꢀ1 (C=N and C=N N=C); UV/Vis (MeCN): lmax(e)=
ꢀ
307 (15400), 349 (13400), 407 (14000), 570 (sh, 30), 802 (sh, 25), 937 nm
(47 mꢀ1 cmꢀ1) (see Figure S6 in the Supporting Information); MS (micro-
ESI in acetonitrile): m/z: 637 (100%, [Ni2(bpampbh)(OH)]+), 679
ed by
a CGME instrument (Bioanalytical Systems, West Lafayette,
USA). Magnetic susceptibilities were measured with a Quantum Design
MPMSR-5S-SQUID magnetometer in the range from T=2 to 300 K at
([Ni2(bpampbh)(OAc)]+);
elemental
analysis
calcd
(%)
for
Chem. Eur. J. 2008, 14, 1571 – 1583
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1581
Roth, Arne
