Joachim Strähle

Synthesis, characterization and antifungal activity of group 12 metal complexes of 2-acetylpyridine-4N-ethylthiosemicarbazone (H4EL) and 2-acetylpyridine-N-oxide-4N-ethylthiosemicarbazone (H4ELO)

Abstract Reaction of group 12 metal halides in ethanol with the thiosemicarbazones 2-acetylpyridine-4N-ethylthiosemicarbazone (H4EL) and 2-acetylpyridine-N-oxide-4N-ethylthiosemicarbazone (H4ELO) produced the compounds [M(H4EL)X2] and [M(H4ELO)X2] [M=Zn(II), Cd(II) or Hg(II), X=Cl, Br or I]. The ligands and complexes were characterized by elemental analysis and by IR and NMR (1H, 13C, 113Cd, 199Hg) spectroscopy, and the structures of H4ELO·H2O and the complexes [Cd(H4EL)I2]·2DMSO, [Hg(H4EL)Br2]–DMSO, [Zn(H4ELO)Cl2] and [Zn(H4ELO)Br2] were determined by X-ray diffraction. The metal centers in the complexes have coordination number five, H4EL and H4ELO behaving as neutral NNS- and ONS-tridentate ligands, respectively. The coordination polyhedra are close to tetragonal pyramids, the degree of distortion towards trigonal bipyramids was estimated by τ calculation. Against the pathogenic fungi Aspergillus niger and Paecilomyces variotii, the mercury complexes of H4ELO had activities that at some doses exceeded that of nystatin.

Structure of Cu2(indomethacin)4 and the reaction with superoxide in aprotic systems

The copper complex of indomethacin (1-(p-chlorobenzoyl)-5-methoxy-2-methyl-indole acetate), a common anti-inflammatory drug, was prepared and characterized. Crystal structure determination revealed the dimeric form of the 1 : 2 complex, namely Cu2(indomethacin)4 x L2, in the unit cell. Surprisingly, the copper-copper distance (263 pm) was very close to metallic copper (256 pm). The two coordination sites in the copper-copper axis can be readily replaced by superoxide. An intriguing similarity to Cu2(acetate)4 was seen. Due to the lipophilic nature of the indomethacin ligand, this copper complex reacted with superoxide in aprotic solvents. the superoxide dismutating activity was successfully demonstrated in Me2SO/water and acetonitrile/water mixtures using the nitro-blue tetrazolium assay and pulse radiolysis. The second-order rate constant of 6 x 10(9) M-1 x s-1 in strictly aqueous systems dropped only slightly to 1.1 x 10(9) M-1 x s-1 when aprotic solvents were used. This is the fastest rate constant ever observed for a copper-dependent dismutation of superoxide. The KO2-induced lipid peroxidation in both erythrocytes and liver microsomes was suppressed by 70% in the presence of 1 x 10(-10) mol x ml-1 of Cu2(indomethacin)4. The inhibitory action dropped to 25% when Cu2Zn2superoxide dismutase was employed. The formation of copper x indomethacin in rat serum after administration of indomethacin was shown in vitro and vivo.

Phenyl-substituted copper di-Schiff base, a potent Cu2Zn2 superoxide dismutase mimic surviving competitive biochelation

Abstract [ N , N ′-bis(2-pyridyl-phenyl)methylene-1,4-butanediamine]-( N , N ′, N ″, N ‴)-copper( II ), Cu(II)PuPhePy, a copper(II) di-Schiff base in both its chloride and perchlorate form, has been prepared and crystallized with a yield of 50 ± 10%. IR spectra confirmed the successful preparation. The electronic absorption ϵ 690 was 136 M −1 cm −1 . The EPR parameters g ⊥ = 2.048 and g ∥ = 2.217 were in close agreement with the respective values of intact Cu 2 Zn 2 SOD. Comparison of the crystal structures of this complex and the copper binding centre of Cu 2 Zn 2 SOD revealed a virtually identical coordination chemistry. The pulse-radiolytically-determined superoxide dismutation proceeded even in the presence of a fourfold molar excess of EDTA at a rate of 0.48 × 10 9 M −1 s −1 . In the indirect nitroblue tetrazolium assay 0.27 μM of Cu(II)PuPhePy(ClO 4 ) 2 were required to cause 50% inhibition. The thermodynamic stability constant log K = 18.33 ± 0.77 was calculated from CD data. The stability being two orders of magnitude higher than that of serum albumin, a competitive biological Cu(II) chelator and its ‘model’ EDTA was deduced. Of all the many superoxide dismutase mimics examined, the present Cu complex is in closest agreement in both structure and catalytic function with the active centre of intact Cu 2 Zn 2 SOD.

Synthesis of 3-trimethylsilylpyridine-2-thione (3-Me3SipytH) complexes of nickel, copper, zinc and cadmium: crystal and molecular structure of [Cd(3-Me3Sipyt)2]

Abstract A series of complexes of Ni, Cu, Zn and Cd with 3-trimethylsilylpyridine-2-thione (3-Me 3 SipytH) as ligand has been prepared. Complexes [M(3-Me 3 Sipyt) 2 ] (M=Ni(II), Zn(II) and Cd(II)) and [Cu(3-Me 3 Sipyt)] are obtained by electrochemical oxidation of the metal in an acetonitrile solution of the neutral ligand (3-Me 3 SipytH). Adducts [Ni(3-Me 3 Sipyt) 2 L] (L=2,2-bipyridine or 1,10-phenanthroline) were obtained by addition of the extra ligand to the electrolyte phase. Treatment of [Cu(3-Me 3 Sipyt)] with 1,2-bis(diphenylphosphino)ethane (dppe) in acetone gave [Cu 2 (3-Me 3 Sipyt) 2 (dppe) 3 ]. The X-ray structure of [Cd(3-Me 3 Sipyt) 2 ] has been determined: monoclinic, space group P2 1 / n , with a = 11.818(1), b = 13.649(1), c = 13.218(1) A, β = 92.00(1)° and Z = 4. The structure was determined by direct methods and refined to R = 0.030 and R w = 0.031. In the binuclear complex each cadmium(II) centre has a trigonal bipyramidal coordination sphere with an equatorial S 3 plane, involving two bridging sulfur and one terminal sulfur. The axial positions are occupied by the nitrogen atoms of two ligands. Vibrational, electronic and 1 H, 13 C and 31 P NMR spectral data are presented for all the compounds synthesized.

Nitrido bridges between transition metals and main group elementsillustrated by the series [M]NNa to [M]NCl

A survey is given of the structures and bonding modes of nitrido bridges between transition metals with MN multiple bonds and main group elements. Illustrated by the period row sodium (I) to chlorine (VII) (or a homologue) along with variable transition metals M, characteristic examples are compiled, their principles of synthesis are presented and the step-by-step alterations of the bonding conditions that occur in this period are discussed on the basis of structural parameters. These bonding conditions can be divided into three groups. (1)  Electrostatic bond between nitrido ligand and main group element (I, II) (2)  Covalent single bond (III, IV) (3)  Multiple bonds between both neighbouring elements (V–VII) One example each is designed to illustrate this aim: (i) Na6[MoN4]; (ii) [Mg(THF)4{NMoCl4(THF)}2 ]; (iii) [ReN–GaCl3(PMe2Ph)(Et 2dtc)2] (no example with Al is known up to now); (iv) Cl3VN–SiMe3; (v) O3ReNPMe3; (vi) [Cl5WNSCl]−; (vii) [F5WNCl]−.

Eight-coordinate chelate complexes of zirconium(IV) and niobium(IV): X-ray diffractometric and EPR investigations

Abstract The N,N -diethylcarbamato derivative of zirconium(IV), Zr(O 2 CNEt 2 ) 4 has been studied by X-ray crystallography. Crystal data: C 20 H 40 Na 4 O 8 Zr, monoclinic, space group C 2/ c , a = 14.057(1), b = 12.168(1), c = 16.746(2) A, β = 108.071(4)°, Z = 4, D c = 1.356, F(000) = 1168, T = 213 K. The compound is isotypic with the corresponding niobium(IV) derivative with a dodecahedral coordination at the zirconium atom. By reaction of NbCl 4 (THF) 2 with Tl(hfacac), the hexafluoroacetylacetonato derivative of niobium (IV), Nb(hfacac) 4 , has been prepared and structurally characterized. The compound crystallizes in the orthorhombic space group Pna 2 1 with the following cell constants: a = 10.399(4), b = 15.852(9), c = 119.073(1) A. It is not isotypic with the corresponding zirconium(IV) derivative, Zr(hfacac) 4 . Crystal data: C 20 H 4 F 24 O 8 Zr, monoclinic, space group P 2 1 / n , a = 11.974(4), b = 20.451(6), c = 13.140(3) A, β = 104.487(11)°, Z = 4, D c = 1.960, F(000) = 1776, T = 223 K. Although in both compounds the central metal atom shows a square antiprismatic coordination, the coordination mode of the ligands is different and slight deviations from the D 4 (llll) and C 2 (llss) ideal geometries have been observed in the case of niobium and zirconium, respectively. An EPR study has been performed on the Nb(IV) derivatives as diluted solid solutions in frozen organic solvents or in the diamagnetic matrix of the corresponding zirconium(IV) compound. The EPR spectra have confirmed the presence of non-interacting paramagnets in the solid solutions and, in the case of Nb(O 2 CNEt 2 ) 4 , the point symmetry of the paramagnetic centre has been found to be in agreement with the results of the X-ray investigation. An EPR spectrum of rhombic symmetry has been observed for the hexafluoroacetylacetonato derivative of Nb(IV) when diluted in frozen THF solution or in Zr(hfacac) 4 .

Reactions of Coordinated Azido Groups

Abstract Coordinated azido groups undergo a great variety of reactions and therefore exhibit an interesting synthetic potential. In most cases the azido group decomposes and transforms partially or completely to molecular nitrogen yielding new compounds with metal-nitrogen bonds or complexes with a reduced metal. The products can be nitrido, nitrene, or phosphoraniminato complexes with metal-nitrogen multiple bonds as well as nitrosyl, cyanato, chlorineamine and dinitrogen complexes. In other cases the complete azido group is involved in a cycloaddition reaction or a nitrene is inserted in a metal-metal or metal-ligand bond. Typical examples of the different types of reactions are discussed.

Synthesis and reactivity of η6-arene derivatives of niobium(II), niobium(I), and niobium(O)

Abstract The primary reduction products in the Al/AlX 3 /NbX 5 /arene system, namely Nb(η 6 -arene)(AlX 4 ) 2 , X = Cl, arene = benzene, hexamethylbenzene; X = Br, arene = hexamethylbenzene, have been isolated. Tetrahydrofuran at room temperature reacts with Nb(η 6 -hexamethylbenzene)(AlBr 4 ) 2 , to give the aluminium-free complex Nb 2 (η 6 -hexamethylbenzene) 2 Br 4 , whose crystal structure was determined by X-ray diffraction methods. In the presence of tetrahydrofuran or dimethoxyethane, the η 6 -mesitylene-tetrahaloaluminato complexes are further reduced by aluminium to bis-mesityleneniobium(0), Nb(mes) 2 , which undergoes: a) disproportionation with CO to [Nb(mes) 2 (CO)] + [Nb(CO) 6 ] − , b) oxidation by V(CO) 6 or (4,4′-dimethyl-2,2′-dipyridyl)(BPh 4 ) 2 under carbon monoxide to [Nb(mes) 2 (CO)]X, X = [V(CO) 6 ] − or BPh 4 − . The structure of [Nb(mes) 2 (CO)] BPh 4 has been determined by X-ray diffraction methods. In the presence of CO, Nb(mes) 2 is reduced by CoCp ☆ 2 [Cp ☆ = η 5 -C 5 (CH 3 ) 5 ] to [Nb(CO) 6 ] − , which was isolated as its CoCp ☆ 2 + derivative; it efficiently deoxygenates CO 2 to CO in the presence of carbon monoxide acceptors such as the [Nb(mes) 2 (THF)] + cation.

Direct electrochemical synthesis of pyridine-2-thionato complexes of nickel(II): the crystal structure of (2,2′-bipyridine)bis(pyridine-2-thionato)nickel(II)-2,2′-bipyridine(2/1)

The compound [Ni(pyt)2] has been prepared in good yield by electrochemical oxidation of the metal in a solution of pyridine-2-thione (Hpyt) in acetonitrile. When pyridine (py), 2,2′-bipyridine (bipy), or 1,10-phenanthroline (phen) is present in the electrochemical cell the corresponding adducts [Ni(pyt)2(py)2], [Ni(pyt)2(bipy)], or [Ni(pyt)2(phen)] is obtained. The crystal structure of [Ni(pyt)2(bipy)]·0.5 bipy is monoclinic, with a= 10.409(2), b= 12.013(3), c= 19.790(3)A, β= 103.95(3)°, space group P21/c, and R= 0.032 for 3 176 reflections with |Io| > 3σ|Io|. The molecule has a distorted octahedral NiN4S2 kernel, with average bond distances of 2.065 A for Ni–N and 2.485 A for Ni–S. The vibrational and electronic spectra of the compounds are discussed.

Synthesis, structure and catalase-like activity of a new dinuclear mixed valence Mn II Mn III complex containing an unsymmetric N 5 O 2 donor ligand

Abstract The new dinuclear mixed valence [MnIIMnIII(BPBPMP)(OAc)2]BF4 complex with the unsymmetrical polydentate ligand 2-bis[{(2-pyridylmethyl)-aminomethyl}-6-{(2-hydroxybenzyl)(2-pyridylmethyl)}-aminomethyl]-4-methylphenol (H2BPBPMP) was synthesized. The complex has an MnIIMnIII(μ-phenoxo)(μ-OAc)2 core and was structurally, IR and UV–Vis spectroscopically and by cyclic voltammetry characterized. The reactivity towards H2O2 shows a catalase-like activity.