Heinz Gornitzka

Preparation, characterization and crystal structures of manganese(II), iron(III) and copper(II) complexes of the bis[di-1,1-(2-pyridyl)ethyl]amine (BDPEA) ligand; evaluation of their DNA cleavage activities

Abstract. The synthesis of a new tetrapyridyl ligand, bis[di-1,1-(2-pyridyl)ethyl]amine (BDPEA), is described. Complexation of this ligand with manganese(II), iron(III) or copper(II) chlorides afforded mononuclear complexes: Mn(BDPEA)Cl2 (1) [Fe(BDPEA)Cl2]Cl (2) and [Cu(BDPEA)Cl]Cl (3). In all cases, BDPEA is coordinated to the metal center by three pyridine nitrogen atoms and the secondary amine. The geometrical environments around the metals in Mn(BDPEA)Cl2 and [Fe(BDPEA)Cl2]Cl are best described as distorted octahedrals and in [Cu(BDPEA)Cl]Cl as a slightly distorted square pyramid. The DNA cleavage activities of manganese(II), iron(III) or copper(II) complexes of both BDPEA and another tetrapyridyl ligand, bis[di(2-pyridyl)methyl]amine (BDPMA), in the presence of an oxidant (H2O2) or a reducing agent (ascorbate) with air, are reported. The iron(III) complexes exhibited significantly enhanced efficiencies, compared to copper(II) complexes. [Fe(BDPEA)Cl2]Cl is found to be the most active DNA cleaver, in agreement with a better stability of BDPEA in oxidizing conditions.

Three coordinate divalent Group 14 element compounds with a β-diketiminate as supporting ligand L2MX [L2=PhNC(Me)CHC(Me)NPh, X=Cl, I; M=Ge, Sn]

Abstract The new heteroleptic divalent germanium and tin compounds L2MX [L2=PhNC(Me)CHC(Me)NPh. X=Cl; M=Ge (1), Sn (2). X=I; M=Ge (3), Sn (4)] have been synthesized and physicochemically and structurally (2) characterized. The halide ligand of all compounds can either be removed by reaction with NaBPh4 leading to the cationic Ge(II) and Sn(II) species L2M+ or may be replaced by other groups after nucleophilic substitution giving L2MR compounds [R=N(SiMe3)2; M=Ge, Sn. M=Sn; R=OSO2CF3, N3]. Reactions of 1 and 2 with elemental S8, Se or transition metal complexes M′(CO)5·THF have resulted in the isolation of the new complexes L2(Cl)ME (E=S; M=Ge, Sn. E=Se, M=Ge) and L2(Cl)MM′(CO)5 (M′=Cr, W; M=Ge, Sn).

Combined Cation–π and Anion–π Interactions for Zwitterion Recognition

Brothers and enemies: Anion-π and cation-π interactions act in a synergistic way when gathered in the molecular cavity of a hemicryptophane host, affording an efficient contribution (-170 kJ mol(-1)) in zwitterion recognition. NMR titration experiments and calculations reveal the positioning of the guest in the cavity of the heteroditopic receptor. This study emphasizes the importance of anion-π bonds in host-guest chemistry.

1,2,4-Triazolium-5-ylidene and 1,2,4-triazol-3,5-diylidene as new ligands for transition metals

Ab initio calculations show the 1,2,4-triazolium-5-ylidene (3a) and 1,2,4-triazol-3,5-diylidene (4a) are true minima on the potential surface. As expected, 4a is much higher in energy than its triazole isomers 5a, 6a and 8a and the 1,2,4-triazol-3-ylidene (7a). Sodium methoxyde adds to the diquaternary salt of 1,2,4-triazoles (9b,c) to give the corresponding monocationic heterocycles 10b,c in 70 and 50% yield, respectively. One equivalent of silver(I) acetate reacts with 9b leading to the bis(1,2,4-triazolium-5-ylidene)silver(I) complex (11b) in 80% yield. Under the same experimental conditions, but using two equivalents of silver(I) acetate, solid-state one-dimensional polymers 12′b,c featuring the coplanar 1,2,4-triazol-3,5-diylidene ligands coordinated to silver(I) are obtained in 90% yield. 12′c has been fully characterized including a single-crystal X-ray diffraction study.

Phosphane- and phosphorane Janus Head ligands in metal coordination

Abstract Our principal strategy to include the substituent periphery of phosphanides and phosphoranates in metal coordination is outlined. Rather than providing merely bulk or stereo information like in classical phosphane ligands to d-block metal centres the 2-pyridyl substituted species supply a second coordination site. Additional to the found σ/π coordination site selectivity these Janus Head ligands might serve as anionic staples in mixed Group 13/d-block metal complexes in homogeneous catalysis. The classical NP(Ph2)N− chelating ligand is converted into a NP(Py2)N− tripodal ligand. The pyridyl substitution has not only considerable impact on the metal coordination but also on the reactivity, emphasising the fact that this heteroaromatic substituent cannot simply be regarded as eka-phenyl. It facilitates double PC bond cleavage and reduction of iminophosphoranes to phosphanamines in a one-pot reaction. Even PN bond cleavage is observed. Several new routes to multidentate ligands in metal side-arm coordination were established.

Neodym(III)komplexe mit stark raumerfüllenden Cyclopentadienyl- und Benzamidinat-Liganden: Ein Vergleich

Abstract [Cp** 2 Nd(μ-CI)] 2 ( 1 ) has been prepared by treatment of NdCI 3 (THF) 2 with two equivalents of KCp** (Cp** = 1,3-di-t-butylcyclopentadienyl). Similarly, Li[(CF) 3 ) 3 C 6 H 2 C(NSiMe 3 ) 2 ] reacts with NdCl 3 (THF) 2 to give [(CF 3 ) 3 C 6 H 2 C(NSiMe 3 ) 2 ] 2 Nd(μ-Cl) 2 Li(THF) 2 ( 2 ). Recrystallization of 2 from DME/hexane yields the binuclear derivative (μ-DME)[{(CF 3 ) 3 C 6 H 2 C(NSiMe 3 ) 2 } 2 Nd(μ-Cl) 2 Li(THF)] 2 ( 3 ). The molecular structures of 1 , 2 and 3 have been determined by X-ray diffraction. The 2,4,6-trisub- stituted benzamidinate anion [(CF 3 ) 3 C 6 H 2 C(NSiMe 3 ) 2 ] − can be regarded as a steric equivalent of bulky cyclopentadienyl ligands such as Cp* or Cp**.

Antimalarial Activity of Simalikalactone E, a New Quassinoid from Quassia amara L. (Simaroubaceae)

ABSTRACT We report the isolation and identification of a new quassinoid named simalikalactone E (SkE), extracted from a widely used Amazonian antimalarial remedy made out of Quassia amara L. (Simaroubaceae) leaves. This new molecule inhibited the growth of Plasmodium falciparum cultured in vitro by 50%, in the concentration range from 24 to 68 nM, independently of the strain sensitivity to chloroquine. We also showed that this compound was able to decrease gametocytemia with a 50% inhibitory concentration sevenfold lower than that of primaquine. SkE was found to be less toxic than simalikalactone D (SkD), another antimalarial quassinoid from Q. amara, and its cytotoxicity on mammalian cells was dependent on the cell line, displaying a good selectivity index when tested on nontumorogenic cells. In vivo, SkE inhibited murine malaria growth of Plasmodium vinckei petteri by 50% at 1 and 0.5 mg/kg of body weight/day, by the oral or intraperitoneal routes, respectively. The contribution of quassinoids as a source of antimalarial molecules needs therefore to be reconsidered.

Synthesis and structure of 1,2,4-triazol-2-ium-5-ylidene complexes of Hg(II), Pd(II), Ni(II), Ni(0), Rh(I) and Ir(I)

Abstract The reaction of M(OAc)2 [M=Hg(II), Pd(II), Ni(II)] or M(acac)(CO)2 [M=Rh(I), Ir(I)] with dicationic 1,2,4-triazolium salts 2 affords a series of water-soluble 1,2,4-triazol-2-ium-5-ylidene complexes 4–8, arising from deprotonation-complexation of the N-heterocyclic ligand. Reduction of [Ni(trz)2I2(TfO)2] (trz=1,2,4-triazol-2-ium-5-ylidene) (6a) with zinc powder in the presence of carbon monoxide results in the formation of the corresponding Ni(0)–carbene complexe 9. The latter has also been prepared by the reaction of Ni(CO)4 with the corresponding in situ generated triazoliumylidene. The solid state structure of [Hg(trz)2(dmso)(TfO)4] (4), [Pd(trz)2I4] (5a), [Ni(trz)2I2(TfO)2] (6a) and [Ni(trz)2(CO)2] (9) were determined by single-crystal X-ray diffraction studies.

Synthesis, structures, and antimalarial activities of some silver(I), gold(I) and gold(III) complexes involving N-heterocyclic carbene ligands.

A series of mono-and dinuclear silver(I) and mononuclear gold(I) complexes containing bis(N-heterocyclic carbene) (NHC) or N-functionalized NHC ligands were synthesized and fully characterized by spectroscopic methods and, in some cases, by single crystal X-ray diffraction. The in vitro antiplasmodial and antifungal activities of a previously described family of N-functionalized bis(imidazolium) proligands and their corresponding silver(I), gold(I) and gold(III) complexes but also the new here described compounds were investigated in a chloroquine-resistant strain of Plasmodium falciparum, and against two Candida strains, respectively. For the first family, interesting antiplasmodial and antifungal activities were found for the dinuclear silver(I) species but they also showed strong hemolytic properties. Pharmaco-modulations leading to the second series of complexes allowed notably increase in the antiplasmodial activity, in particular of the mononuclear gold(I) complexes with IC(50) values up to 330 nM, without any hemolysis.

Encaging the Verkade’s Superbases: Thermodynamic and Kinetic Consequences

Proazaphosphatranes, also known as Verkades superbases, are nonionic species, which exhibit catalytic properties for a wide range of reactions. The properly designed host molecule 3 and its protonated counterpart [3·H](+)Cl(-) were synthesized to study how confinement can modify the stability and the reactivity of a Verkades superbase. The results show that the encapsulation does not alter the strong basicity of the proazaphosphatrane, but dramatically decreases the rate of proton transfer.