Ruthenium complexes of 3-hydroxy-4-pyranones and of 3-hydroxy-4-pyridinones

Reactions of hydrated ruthenium chloride with 2-methyl-3-hydroxy-4-pyranone, ethylmaltol (etmaltH) and with 1,2-dimethyl-3-hydroxy-4-pyridinone (dmppH) are described. The former results in the formation of Ru(etmalt)₃, but the course of the latter depends on conditions, producing the earlier-characterised Ru(dmmp)₃Cl in ethanol–water solution, Ru(dmmp)₃ in aqueous solution under mild conditions, and Ru(dmpp)₂(H₂O)₂ after extended refluxing. EXAFS studies established ruthenium-oxygen distances in Ru(etmalt)₃ and in Ru(dmmp)₃ · 6H₂O. Solubilities of Ru(dmmp)₃ in methanol–water mixtures reveal greater solubility in methanol than in water, and indications of a modest solubility maximum, and thus synergic solvation, in methanol-rich mixtures.     

N,N-diethyldithiocarbamates of 3d metals as catalysts for decomposition of tertiary hydroperoxides

Decomposition kinetics of tertiary cumene hydroperoxides and tert-butyl in ethylbenzene in the presence N,N-diethyldithiocarbamates of 3d metals was studied at moderately low temperatures, 323–383 K. The kinetic parameters of the catalytic decomposition of the hydroperoxides were calculated and a decrease in the activation energy as compared with the thermal decomposition was noted.     

Cement-containing catalysts of ozone decomposition based on iron oxides

Cement-containing catalysts of ozone decomposition were synthesized on the basis of iron oxides obtained by ozonation of iron-containing aqueous solutions. X-ray diffraction analysis and Mössbauer spectroscopy showed that α-Fe₂O₃ occurs in the catalyst as highly dispersed nanoparticles. The catalysts obtained are efficient in the reaction of ozone decomposition and are as active as the best representatives of cement-containing catalysts of the GTT type.     

Resolution of racemic 4-hydroxy-2-cyclopentenone with immobilized penicillin G acylase

Enantiomerically pure 4-oxo-2-cyclopentenyl derivatives were prepared by kinetic resolution with penicillin G acylase (EC 3.5.1.11) immobilized on an epoxy activated polymer. The enzyme selectively hydrolyzes the phenylacetyl ester of the (S)-enantiomer to give the (S)-alcohol. The enantioselectivity E increases from 12.4 in 0.05 M phosphate buffer, to E = 100–110 in acetonitrile-buffer (20% v/v) and E >200 in diisopropyl ether. The immobilized enzyme is stable and retains >90% of its activity after 10 recycles over one week at room temperature.     

Oxide talum-containing catalysts of ozone decomposition and methane oxidation

The oxidation of manganese ions is shown to occur in ozone decomposition on manganese-containing catalyst, leading to the deactivation of a sample. The structure of the iron-containing catalyst does not change, ensuring its high stability during ozone decomposition in a dry gas flow at room temperature, conducted in the region of inner diffusion with an activation energy of 15.5 ± 0.7 kJ/mol. The presence of manganese cations in the intermediate stages of reduction is found to increase their activity in the reaction of deep methane oxidation.     

Platinum(II) complexes with 9,10-phenanthraquinone and 3-hydroxy-2-methyl-4-pyrone

Conclusions The Pt(II) complexes with 9,10-phenanthraquinone and 3-hydroxy-2-methyl-4-pyrone were obtained and characterized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 900–902, April, 1981.     

Studies of decomposition kinetics for ozone complexes with cumene and chlorobenzene

Kinetic regularities in decomposition of complexes of aromatic compounds with O₃ have been studied for ozone complexes with cumene and chlorobenzene. Oxidation effect of these complexes on both aromatic compounds and olefins has been established.

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O₃. .

     

Metal complexation with 2-hydroxy-6-methylpyridine-3-carboxylic acid

Metal complexation with 2-hydroxy-6-methylpyridine-3-carboxylic acid has been studied. The ligand finds use in detection and determination of iron (III). The order of stability constants of the bivalent transition metal complexes is Cu > Zn > Fe > Ni > Co > Mn. b]¦de¦Die Komplexbildung von Metallen mit 2-Hydroxy-6-methylpyridin-3-carbonsäure wurde untersucht. Der Ligand findet Verwendung beim Nachweis und bei der Bestimmung von Eisen(III). Die Reihenfolge der Stabilitätskonstanten der Komplexe mit zweiwertigen Überg angsmetallen ist Cu > Zn > Fe > Ni > Co > Mn.     

Use of immobilized transition metal complexes as recyclable catalysts for oxidation reactions with hydrogen peroxide as oxidant

A tetradentate Schiff base (teta), obtained from triethylenetetramine and salicylaldehyde, has been covalently bonded to divinylbenzene cross-linked chloromethylated polystyrene. This chelating ligand, abbreviated as PS-teta (PS = polymeric support), reacts with metal chlorides (Cu²⁺, Co²⁺, and Ni²⁺) in methanol to give polymer-bound transition metal complexes, PS-Cu(II)teta/(Cat-1), PS-Ni(II)teta/(Cat-2), and PS-Co(II)teta/(Cat-3), formation of which has been established by various physiochemical methods and spectroscopic techniques. The catalytic potential of these materials has been tested for the oxidation of various alkenes, alkanes, alcohols, and thioethers in the presence of 30% H₂O₂ as an oxidant. At the same time, these catalysts are very stable and could be reused in oxidation reactions for more than five times without noticeable loss of their catalytic activity.     

Promoted porous Co_3O_4-Al_2O_3 catalysts for ammonia decomposition

Transition metal catalysts have been considerably used for NH_3 decomposition because of the potential application in CO_x-free H_2 generation for fuel cells.However,most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components.Here,we adopted an efficient method,aerosol-assisted selfassembly approach(AASA),to prepare the optimized cobalt-alumina(Co_3O_4-Al_2O_3)catalysts.The Co_3O_4-Al_2O_3catalysts exhibited excellent catalytic performance in the NH_3 decomposition reaction,which can reach 100%conversion at 600°C and maintain stable for 72 h at a gaseous hourly space velocity(GHSV)of 18000 cm~3g~(-1)_(cat)h~(-1).The catalysts were characterized by various techniques including transmission electron microscope(TEM),scanning electron microscope(SEM),nitrogen sorption,temperature-programmed reduction by hydrogen(H_2-TPR),ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction(XRD)to obtain the information about the structure and property of the catalysts.H_2-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species,which influences the redox properties of the catalysts.It is found that even a low content of alumina(10 at%)is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components,which ensures the high activity and superior stability of the cobalt-alumina catalysts.     

Magnetically Active 3d Metal Complexes with 3-Amino-4-Ethoxycarbonylpyrazole

Russian Journal of Coordination Chemistry - Coordination compounds of iron(II) and nickel(II) with 3-amino-4-ethoxycarbonylpyrazole (L), FeL2A2 (A = Cl– (I),...     

Metal complexes as phase transfer catalysts in the synthesis of O-acetylmandelonitrile

The asymmetric synthesis of O-acetylated mandelonitrile derivative was accomplished from PhCHO, KCN, and Ac₂O in a toluene--water system in the presence of transition metal complexes of Schiff"s bases as phase transfer catalysts.     

Metal oxo complexes as catalysts for the isomerisation of allylic alcohols

The 1,3-allylic rearrangement of allylic alcohols is an important transformation in organic synthesis and various methods for effecting such a transposition have been reported. This short review will focus on the development of transition metal oxo complexes as catalysts for the isomerisation of allylic alcohols. Mechanistic investigations are also discussed.     

Novel vanadyl complexes with 2-hydroxy-3-methyl-2-cyclopenten-1-one

Two examples of novel vanadyl complexes of 2-hydroxy-3-methyl-2-cyclopenten-1-one, Hmcp, with 1:2 stoichiometry have been characterised by elemental analysis, i.r. and optical spectral studies. [VOCl₂(H₂O)(Hmcp)₂] (1) contains neutral Hmcp coordinated to vanadium through a carbonyl oxygen and both molecules are trans to each other. [VO(mcp)₂H₂O] (2) contains the mono-anionic form of Hmcp. Both complexes have distorted octahedral geometry.     

Solubilities of iron(III) complexes of 3-hydroxy-2-ethyl-4-pyranone and of 3-hydroxy-1,2-dimethyl-4-pyridinone in aqueous salt solutions

Solubilities are reported for the tris-ligand–iron(III) complexes of 3-hydroxy-2-ethyl-4-pyranone and of 3-hydroxy-1,2-dimethyl-4-pyridinone in aqueous solutions of alkali halides and of ammonium and tetraalkylammonium bromides. The Setchenow coefficients estimated from salt effects on solubilities for these complexes are compared with those for other inorganic complexes.     

Rhodium phosphine complexes immobilized on silica as active catalysts for 1-hexene hydroformylation and arene hydrogenation

In immobilizing the rhodium complexes [Rh(acac)(CO)(P)] (1) and [Rh(acac)(P)₂] (2) (P = Ph₂PCH₂CH₂Si(OMe)₃) onto SiO₂, acetylacetone is found to be released through protonation of the acac ligand by the acidic silica-OH groups. The resulting complexes [Rh(O-{SiO₂}(HO-{SiO₂})(CO)(P-{SiO₂})] (1a) and [Rh(O-{SiO₂})(HO-{SiO₂})(P-{SiO₂})₂] (2a) were successfully tested with respect to their catalytic action on 1-hexene hydroformylation as well as benzene and toluene hydrogenation. The reaction outcome, viz. the formation of aldehydes versus isomerization, depends strongly on the presence and concentration of a phosphine co-catalyst. Thus, while 1a gave only a 17% yield of aldehyde in the absence of phosphines, the yield is increased to 54% in the presence of phosphinated silica P-{SiO₂} or even 94% if PPh₃ is added to the solution. Without extra added phosphine, both 1a and 2a effect mainly the isomerization of 1-hexene to 2-hexene. Pre-catalyst 1a catalyzes also the hydrogenation of benzene at 10.5 atm H₂ and 90 °C to give cyclohexane with a TOF of 608 h⁻¹.     

A DFT quantum mechanical study of 3-hydroxy-4-pyrone and 3-hydroxy-4-pyridinone based oxidovanadium(IV) complexes

Oxidovanadium(IV) complexes have revealed interesting pharmacological properties which make them promising agents in the treatment of diabetes mellitus. A computational study of 17 complexes of oxidovanadium(IV) with 3-hydroxy-4-pyrone- and 3-hydroxy-4-pyridinone-based ligands was carried out at the density functional theory level. The geometry, electronic structure, and vibration modes at the metallic center were predicted, and their dependence on the nature of the ligand was evaluated. Slight distinctions between both classes of compounds were observed, namely the higher value of dipole moments and the smaller HOMO–LUMO energy gap for the 3-hydroxy-4-pyridinone-based complexes. The modes of vibration at the metallic coordination region do not vary significantly throughout the whole series, and a particular corrective scaling factor is proposed for the V=O stretching mode of this type of oxidovanadium(IV) complexes. The results presented here are of particular relevance since it was not yet possible to obtain X-ray diffraction data for the oxidovanadium(IV) complexes of 3-hydroxy-4-pyridinones, and also as the influence of the solvent, in particular the local interaction at the sixth coordination position, was considered.