Biserka Prugovečki

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.

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.

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.

New dinuclear thiobenzoato complexes of molybdenum(V) containing Mo2O2S2 core. X-ray crystal structures of [Mo2O2S2(OSCC6H5)2(py)2] and [Mo2O2S2(OSCC6H5)2(γ-pic)2]·2H2O

Abstract The [Mo2O2S2(OSCC6H5)2] (1) has been prepared either by the reaction of [Mo2O3(C5H7O2)4] or of [Mo4Cl2O6(O2CCH3)6]·(CH3CO)2O with thiobenzoic acid. The product was then used to prepare two complexes of the general formula [Mo2O2S2(OSCC6H5)2L2] (where L = pyridine (2) or γ-picoline (3)). All complexes were characterized by elemental analyses, IR spectra and magnetic measurements. The structures of (2) and (3) were proved by X-ray structure analysis. Both complexes are dinuclear containing Mo2O2S2 core with two Mo atoms linked by a Mo–Mo single bond. The Mo atoms are octahedrally coordinated by oxo-oxygen, two bridging sulfido-sulfurs, one pyridine (or γ-picoline)-nitrogen and thiobenzoato-sulfur and thiobenzoato-oxygen atoms.

Dioxidomolybdenum( vi ) complexes with isoniazid-related hydrazones: solution-based, mechanochemical and UV-light assisted deprotonation

Synthesis of the dioxidomolybdenum(VI) complexes [MoO2(HLR)(MeOH)]Cl (1–3) was carried out by using MoO2Cl2 and the corresponding ONO aroylhydrazone ligand H2LR (ligand H2LR is salicylaldehyde isonicotinoylhydrazone (H2LSIH), 2-hydroxy-naphthaldehyde isonicotinoylhydrazone (H2LNIH), or p-(N,N′-diethylamino)salicylaldehyde isonicotinoylhydrazone (H2LEt2NSIH) in methanol. Compounds [MoO2(HLR)(H2O)]Cl (1a–3a) were obtained upon exposure of the corresponding mononuclear complexes 1–3 to moisture. Deprotonation of the mononuclear complexes 1–3 was performed by using Et3N as a base (by the conventional solution based-method and by the mechanochemical approach) as well as by UV-light assisted reactions yielding [MoO2(LSIH)(MeOH)] (4), [MoO2(LNIH)(MeOH)] (5) and [MoO2(LEt2NSIH)]n (6), respectively. Crystal and molecular structures of all complexes were determined by the single crystal X-ray diffraction method. The complexes were further characterized by elemental analysis, IR spectroscopy, TG analysis, one- and two-dimensional NMR spectroscopy and powder X-ray diffraction.

Synthesis of Acylated Methyl 2‐Acetamido‐2‐Deoxy‐α‐D‐Mannopyranosides

Abstract 2‐Acetamido‐2‐deoxy‐β‐D‐mannopyranose (1) was glycosylated by the Fischer method using an acidic ion‐exchange resin as the catalyst to give α‐methyl glycoside 2. Selective pivaloylations of methyl 2‐acetamido‐2‐deoxy‐α‐D‐mannopyranoside (2) have been studied under various reaction conditions. Two partially pivaloylated products were submitted to additional acetylations. All structures were established by NMR spectroscopy. Structure of the methyl 2‐acetamido‐2‐deoxy‐3,6‐di‐O‐pivaloyl‐α‐D‐mannopyranoside (4) was determined by X‐ray analysis.

Methyl 3,4-di-O-pivaloyl-β-d-xylo­pyran­oside

The crystal and molecular structure of the title compound, C16H28O7, has been determined by X-ray analysis at 100 K. The six-membered ring adopts the chair conformation. Molecules are connected in pairs around twofold rotation axes via two O—H⋯O hydrogen bonds with 2.852 (2) A.

Synthesis and structural studies of dioxomolybdenum(VI) complexes with isoniazid related hydrazones

The chemistry of hydrazones is continuing to be an interesting area of research because of their modularity, easiness of synthesis and stability towards hydrolysis.[1−3] Synthesis of the dioxomolybdenum(VI) complexes [MoO2(HLR) (MeOH)]Cl (1−3), was carried out using MoO2Cl2 and the corresponding aroylhydrazone ligand H2LR (salicylaldehyde isonicotinoylhydrazone (H2LSIH), 2-hydroxy-naphthaldehyde isonicotinoylhydrazone (H2LNIH), or p-(N, N’- diethylaminosalicylaldehyde isonicotinoylhydrazone (H2LEt2NSIH) in methanol. Compounds [MoO2(HLR)(H2O)]Cl (1a−3a) obtained upon exposure of the coresponding mononuclear complexes 1-3 to moisture were also investigated. Deprotonation of the mononuclear complexes [MoO2(HLR)(MeOH)]Cl (1−3), was performed using Et3N as a base (by conventional solution based-method and mechanochemical aproach) as well as by UV-light assisted reactions yielding [MoO2(LSIH)(MeOH)] (4) [4], [MoO2(LNIH)(MeOH)] (5) and [MoO2(LEt2NSIH)]n (6), respectively. Crystal and molecular structures of all complexes were solved by the single-crystal X-ray diffraction method. In all complexes the ligand coordinates the metal centre of the cis-MoO22+ core tridentately via phenolic-oxygen, azomethine-nitrogen and ketohydrazone oxygen forming five and six member chelate rings. The remaining sixth coordination site of the distorted octahedron is occupied by the oxygen atom of the solvent molecule (methanol in 1-3 and 5, water in 1a −3a) or nitrogen atom of the bridging izonicotinyl moiety of the neighboring complex (in 6). We were interested to investigate importance of nonbonding interactions in the structures, especially the ability of these complexes to form different hydrogen bonding motifs depending on the protonation state of the complexes. References: [1] S. Banerjee, A. Ray, S. Sen, S. Mitra, D. L. Hughes, R. J. Butcher, S. R. Batten and D. R. Turner, Inorg. Chim. Acta., 2008, 361, 2692. [2] J. G. Vos and M. T. Pryce, Coord. Chem. Rev., 2010, 254, 2519. [3] A. Kobayashi, D. Yamamoto, H. Horiki, K. Sawaguchi, T. Matsumoto, K. Nakajima, H.-C. Chang and M. Kato, Inorg. Chem., 2014, 53, 2573. [4] S. Gao, L.-H. Huo, H. Zhao and S. W. Ng, Acta Cryst. 2004, E60, m1757.

4-Acetamido-N-(λ5-triphenyl­phospho­ranyl­idene)benzene­sulfonamide

There are two independent molecules per asymmetric unit of the title compound, C26H23N2O3PS. Their superposition shows that they differ in the conformation of the CH3CO– group and the benzene rings from the triphenylphosphorane group. In the crystal structure, independent molecules are interconected by strong N—H⋯O hydrogen bonds, forming infinite chains along the a axis.

Crystallization and structure of two bovine insulin derivatives

Insulin is a polypeptide hormone, produced by the  -cells in the pancreas, that regulates carbohydrate metabolism and it also takes part in the metabolism of fat and proteins. Insulin is structured as two polypeptide chains, chain A consists of 21 and chain B of 30 amino acids. Bovine insulin differs in sequence from human insulin at residues A8, A10 and B30. There are three forms of insulin hexamers. These forms of insulin are used in therapeutc preparations for the control of diabetes. The crystal structure of T6 bovine insulin was described by Smith et al in 2005 [1]. It has been known for many years that native insulin is in the T3R3 form in the crystals grown in high chloride ion concentrations [2]. This work presents crystallization of two bovine insulin derivatives: in high iodine and bromine concentrations. Structural investigations on bovine bromo- and iodo-derivatives show that these halogen atoms are bound to the zinc ions. Crystals were grown by the hanging drop vapour diffusion crystallisation method. Single crystal diffraction data were collected on laboratory instrument at 100 K. The investigated insulin derivatives belong to the R3 rhombohedral space group with cell parameters a = 79.73 A ; , c = 36.34 A ; and a = 79.25 A ; , c = 36.97 A ; for the bromo- and iodo-derivative, respectively. Conformation of the insulin molecule and coordination of Zn- ions will be discussed.