Višnja Vrdoljak

Novel thiosemicarbazone derivatives as potential antitumor agents: Synthesis, physicochemical and structural properties, DNA interactions and antiproliferative activity

The paper describes synthesis of several novel thiosemicarbazone derivatives. Furthermore, crystal and molecular structure of 4-diethylamino-salicylaldehyde 4-phenylthiosemicarbazone revealed planarity of conjugated aromatic system, which suggested the possibility of DNA binding by intercalation, especially for here studied naphthalene derivatives. However, here presented DNA binding studies excluded this mode of action. Physicochemical and structural properties of novel derivatives were compared with previously studied analogues, taken as reference compounds, revealing distinctive differences. In addition, novel thiosemicarbazone derivatives (1, 2 and 5-8) clearly display stronger antiproliferative activity on five tumor cell lines than the reference compounds 3 and 4, which supports their further investigation as potential antitumor agents.

A Series of Molybdenum(VI) Complexes with Tridentate Schiff Base Ligands

Mononuclear and polynuclear dioxomolybdenum(VI) complexes with Schiff base ligands have been prepared by the reaction of [MoO2(acac)2] with salicylaldehyde (1 and 4), 2-hydroxy-1-naphthaldehyde (2 and 5) and 2-hydroxy-3-methoxybenzaldehyde (3 and 6) with addition of appropriate amine. All prepared complexes of the general formulae [MoO2LD] and [MoO2L]n consist of cis-MoO22+ core coordinated by Schiff-base ligand (L) in a tridentate manner through two deprotonated hydroxyl groups and one imino nitrogen. The usual octahedral coordination around molybdenum atom is completed by monodentate solvent molecules D (methanol, ethanol or dimethylsulphoxide). All compounds were characterized by means of chemical analysis, IR spectroscopy, thermogravimetric analysis and some of them by X-ray crystallography (1a, 2c, 3a, 4c and 6c). Eine Reihe von Molybdan(VI)-Komplexen mit dreizahnigen Schiff-Basen-Liganden Ein- und vielkernige Dioxomolybdan(VI)-Komplexe mit Schiff-Basen-Liganden wurden durch Reaktion von [MoO2(acac)2] mit Salicylaldehyd (1 und 4), 2-Hydroxy-1-naphthaldehyd (2 und 5) und 2-Hydroxy-3-methoxybenzaldehyd (3 und 6) durch Zugabe von Amin hergestellt. Alle Komplexe der allgemeinen Formeln [MoO2LD] und [MoO2L]n enthalten die cis-MoO22+-Einheit, die durch die Schiff-Basen-Liganden dreifach durch zwei deprotonierte Hydroxyl-Gruppen und durch ein Imino-Stickstoffatom koordiniert ist. Die ubliche oktaedrische Koordination am Molybdanatom wird durch einzahnige Solvens-Molekule D (Methanol, Ethanol oder Dimethylsulfoxid) erganzt. Alle Verbindungen werden durch Elementaranalysen, IR-Spektren, thermogravimetrische Analysen und einige von ihnen durch Kristallstrukturanalysen (1a, 2c, 3a, 4c und 6c) charakterisiert.

Dioxomolybdenum(VI) and dioxotungsten(VI) complexes chelated with the ONO tridentate hydrazone ligand: synthesis, structure and catalytic epoxidation activity

Synthesis of the dioxomolybdenum(VI) complexes [MoO2(L3OMe)(EtOH)] (1), [MoO2(L4OMe)(EtOH)] (2) and [MoO2(LH)(EtOH)] (3) and dioxotungsten(VI) complexes [WO2(L3OMe)(EtOH)] (4), [WO2(L4OMe)(EtOH)] (5) and [WO2(LH)]n (6a) was carried out using [MO2(C5H7O2)2] (M = Mo or W) and the corresponding aroylhydrazone ligand H2LR (3-methoxysalicylaldehyde 4-hydroxybenzhydrazone (H2L3OMe), 4-methoxysalicylaldehyde 4-hydroxybenzhydrazone (H2L4OMe), or salicylaldehyde 4-hydroxybenzhydrazone (H2LH) in ethanol. Compounds obtained upon heating of the mononuclear complexes in acetonitrile or dichloromethane, [MO2(LR)]n (1a–6a) or [MoO2(L3OMe)]2 (1b), respectively, were also investigated. Crystal and molecular structures of the mononuclear 1, 2 and 3, polynuclear 1a·MeCN and dinuclear 1b complexes were determined by the single crystal X-ray diffraction method. Powder X-ray diffraction showed isostructurality of 1 and 4, and 2 and 5. The complexes were further characterized by elemental analysis, IR spectroscopy, TG and DSC analyses, and one- and two-dimensional NMR spectroscopy. The catalytic performances of 1–5 and 6a were investigated for epoxidation of cyclooctene using aqueous tert-butyl hydroperoxide (TBHP) as the oxidant.

Synthesis, structure and properties of molybdenum(VI) oxalate complexes of the types M2[Mo2O5(C2O4)2(H2O)2] and M2[MoO3(C2O4)] (M=Na, K, Rb, Cs)

The reaction of molybdenum(VI) oxide with oxalic acid or alkali oxalate and alkali halides results in the formation of two series of molybdenum(VI) oxalate complexes: one of the general formula M-2[Mo2O5(C2O4)(2)(H2O)(2)] containing the Mo2O5 core and the other of the formula M-2[MoO3(C2O4)] with a MoO3 core (M = Na, K, Rb, Cs). Both series were characterized by chemical analysis, ESR, UV and IR spectroscopy, thermogravimetry, differential scanning calorimetry, X-ray powder method and some of them by single-crystal X-ray structure analysis. Complexes of the first series adopt dimeric structures, the second series infinite polymeric structures. In both types of structures molybdenum ions are six-coordinated being surrounded by terminal ore-oxygens, bridging oxygens and bidentate bonded oxalate ligands. When exposed to UV light all these complexes in the solid state exhibit photochromic behavior changing color from colorless to green-brown. These changes are remarkably more pronounced in the complexes with dimeric structures. There is definite correlation between their coloration and the UV induced ESR signal indicative for molybdenum(V). Such behavior is explained by the partial reduction of Mo(VI) to Mo(V) only at the crystal surfaces. This is also the explanation why K-2[Mo2O5(C2O4)(2)(H2O)(2)] was so far described as being red or pale reddish tan. All attempts to prepare the corresponding lithium complexes were unsuccessful. They are most probably very unstable because of the small radius of the lithium ion

Pyridoxal hydrazonato molybdenum(VI) complexes: assembly, structure and epoxidation (pre)catalyst testing under solvent-free conditions

Pyridoxal hydrazonato molybdenum(VI) complexes were prepared by the reaction of the corresponding hydrazone (H2L1 = pyridoxal isonicotinic acid hydrazone, H2L2 = pyridoxal benzhydrazone, H2L3 = pyridoxal 4-hydroxy benzhydrazone) and [MoO2(acac)2] under appropriate conditions. The complexes can be classified into three categories: mononuclear [MoO2(L1–3)(MeOH)], polynuclear [MoO2(L1–3)]n and hybrid organic–inorganic compounds with the Lindqvist polyoxomolybdate [MoO2(HL1–3)]2Mo6O19. A unique example of a cationic polymer assembly with Lindqvist anions is reported herein for the first time. The compounds were characterised by elemental, TG and DSC analyses and by spectroscopic (IR, UV-Vis, 1H, 13C NMR) techniques. The crystal and molecular structure of the pyridoxal benzhydrazone H2L2, three mononuclear complexes [MoO2(L1–3)(MeOH)], and the Lindqvist-containing compounds [MoO2(HL2)]2Mo6O19·2MeCN and (H4L1)Mo6O19 were determined by single crystal X-ray diffraction. All complexes were tested as (pre)catalysts for the epoxidation of cyclooctene under solvent-free conditions with the use of aqueous TBHP (TBHP = tert-butylhydroperoxyde) as an oxidant. Optimal results in terms of conversion, selectivity, TOF and TON were obtained at very low (pre)catalyst loadings (0.05% [Mo] vs. substrate). The influence of the Linqvist anion on catalytic performance is discussed.

New Dinuclear Molybdenum(V) Complexes With β′‐Hydroxy‐β‐enaminones Containing a 4‐Hydroxy‐2‐pyrone Ring

New dinuclear molybdenum(V) complexes of the general formula [Mo2O4L2D2], were prepared by the reaction of [Mo2O3(acac)4] (acac = acetylacetonate ion) with β′-hydroxy-β-enaminones (L). All prepared complexes consist of Mo2O42+ cores coordinated by two ligands L via two donor oxygen atoms as in the analogous β-diketonates. The usual octahedral coordination around the molybdenum atoms is completed by the monodentate solvent molecules D (methanol, ethanol, or 2-propanol). All compounds were characterized by elemental analyses, IR, one- and two-dimensional NMR spectra, and thermal analysis, and some of them by X-ray crystallography (1a, 4a, 8b, and 9a). (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Hybrid organic–inorganic compounds based on the Lindqvist polyoxomolybdate and dioxomolybdenum(VI) complexes

Organic–inorganic hybrids, based on the Lindqvist-type polyoxometalate (POM) and dioxomolybdenum(VI) complexes, have been synthesized by hydrolysis of [MoO2(acac)2] (acac = acetylacetonate) in the presence of aroylhydrazone ligands in weak donor solvents. This provides an efficient route to materials that contain open coordination sites or sites occupied by labile ligands. Removal upon grinding or heating of the labile acetonitrile and acetone molecules on the dioxomolybdenum centres and the reaction in the solid-state represent a way for designing structures with the Lindqvist Mo6O192− anion coordinated to the metal centres of two complex cations. The compounds were characterised by the single crystal and powder X-ray diffraction methods, elemental analysis, IR spectroscopy, TG and DSC analyses.

Hexanuclear complexes of molybdenum(V) containing [Mo6O12(OCH3)4(acac)3]− anion

Abstract The novel hexanuclear oxoclusters of the general formula R[Mo 6 O 12 (OCH 3 ) 4 (acac) 3 ] ( 1 – 7 ), where R=CH 3 NH 3 ( 1 ), C 5 H 5 NH ( 2 ), (CH 3 ) 2 CHNH 3 ( 3 ), (CH 3 ) 3 CNH 3 ( 4 ), C 5 H 11 NH ( 5 ), (C 2 H 5 ) 3 NH ( 6 ), and C 6 H 5 NC 11 H 13 O 2 ( 7 ) have been obtained by the reactions of the binuclear oxomolybdenum(V) complex [Mo 2 O 3 (acac) 4 ] (acac=acetylacetonate ion) with a variety of alkyl or aryl amines or corresponding alkyl or aryl ammonium chlorides in methanol. The formation of 3,5-diacyl-2,6-dimethyl-1-pheny-l-pyridinium cation in 7 is explained by the cyclization via Hantzsch condensation of acetylacetone, formaldehyde and aniline. The molecular structures of complexes 5 , 6 and 7 have been determined by a single-crystal X-ray diffraction study. In all salts the anion is of hexanuclear nature in which molybdenum atoms are bridged by oxo-oxygen and methoxo-oxygen atoms. Six Mo-octahedra are fused through edges, thus allowing the formation of localized metalmetal bonds between three pairs of molybdenum atoms.

Synthesis and characterization of some new acetato complexes of molybdenum(IV), (V) and (VI). Crystal structures of Na2[Mo2O4(OCOCH3)6]·NaOCOCH3·CH3COOH and K[MoO2(OCOCH3)3]·CH3COOH

Abstract The acetato complexes of molybdenum(VI), (V) and (IV): [MoO2(OCOCH3)2] (1), Na2[Mo2O4(OCOCH3)6]·NaOCOCH3·CH3COOH (2), K[MoO2(OCOCH3)3]·CH3COOH (3), [Mo2O3(OCOCH3)4] (4), [Mo3O2(OCOCH3)6(H2O)(OH)2]·16H2O (5) and [Mo3O2(OCOCH3)6(H2O)3]Cl2·14H2O (6) have been prepared and characterized by chemical analyses, ESR and IR spectroscopy. The crystal structures of 2 and 3 have been determined by single-crystal X-ray crystallography. Both complexes contain octahedrally coordinated molybdenum atoms with bonds formed to two terminal oxo-oxygen atoms and four oxygen atoms from the acetate ligands. In 2 two acetate ligands are monodentately bonded to each molybdenum atom while the third one together with its centrosymmetrical pair acts as a bridging ligand between two molybdenum atoms. In 3 two acetate ligands are monodentately and one bidentately bonded to molybdenum. In both structures the acetic acid molecules are not involved in bonding to molybdenum but act as bridges over both (in 2) or only one oxygen atom (in 3) connecting centrosymmetrically related sodium and potassium ions, respectively.

Dioxotungsten(VI) complexes with isoniazid-related hydrazones as (pre)catalysts for olefin epoxidation: solvent and ligand substituent effects

The mononuclear dioxotungsten(VI) complexes [WO2(L3OMe)(D)] (1a and 1b), [WO2(L4OMe)(D)] (2a and 2b) and [WO2(LH)(D)] (3a and 3b) (D = EtOH (1a–3a) or MeOH (1b–3b); L3OMe = 3-methoxy-2-oxybenzaldehyde isonicotinoyl hydrazonato, L4OMe = 4-methoxy-2-oxybenzaldehyde isonicotinoyl hydrazonato, LH = 2-oxybenzaldehyde isonicotinoyl hydrazonato) were synthesized by the reaction of [WO2(acac)2]·0.5C6H5Me with the respective isoniazid-related hydrazone. The compounds were characterized by microanalysis, FT-IR and NMR spectroscopy, thermogravimetric analysis, and powder X-ray diffraction method. The crystal and molecular structures of 1a, 1b, 3a and [WO2(acac)2]·0.5C6H5Me were determined by single crystal X-ray diffraction. The structures of 1a, 1b, 3a are mononuclear and form hydrogen bonded centrosymmetric dimers. In all three complexes, the dimers are also held together by π⋯π interactions between aromatic rings. The catalytic performances (activity and selectivity) of 1a–3a and 1b–3b towards alkene epoxidation by tert-butyl hydroperoxide (TBHP) were investigated under different conditions.