Selective oxidation of ethylbenzene by dioxygen. The effect of chelate center on catalysis by bicyclic nickel complexes

The effect of the nature of the chelate center in Ni^II complexes on their catalytic activity in the selective oxidation of ethylbenzene by dioxygen to α-phenylethyl hydroperoxide in the presence of nickel bis(acetylacetonate) (chelate center Ni(O,O)₂) and nickel bis(enaminoacetonate) (chelate center Ni(O,NH)₂) was studied. The efficiency of selective oxidation of ethylbenzene increases substantially in the presence of the chelate with the Ni(O,NH)₂ active center as a catalyst, which is mainly due to the transformation of the catalyst into more active species during the oxidation process. The mechanism of transformation of nickel bis(enaminoacetonate) under the action of dioxygen was suggested. The sequence of formation of the reaction products at different stages of the catalytic process was determined. The activity of the nickel complex with the Ni(O,NH)₂ chelate center and the products of its transformation in the elementary stages of chain oxidation of ethylbenzene is discussed. Translated fromIzvestiya Akedemii Nauk. Seriya Khimicheskaya, No. 1, pp. 55–60, January, 1999.     

Thermal decomposition of nicotinate complexes of cobalt and nickel in dynamic nitrogen atmosphere

Thermal decomposition of cobalt and nickel nicotinate was studied by TG, DTG and DSC. The mechanism of decomposition has been established from TG and DSC data. The kinetic parameters namelyE, A together with ΔH were calculated from DSC curves using mechanistic and non-mechanistic integral equations.

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Zusammenfassung Mittels TG, DTG und DSC wurde die thermische Zersetzung von Cobaltund Nickelnikotinat untersucht. Der Zersetzungsmechanismus wurde anhand der TG-und DSC-Daten entwickelt. Die kinetischen ParameterE, A wurden zusammen mit ΔH anhand der DSC-Kurven mit Hilfe von mechanistischen und nichtmechanistischen Integrationsgleichungen berechnet.

     

Composition catalysts of ethylbenzene oxidation based on bis(acetylacetonato)nickel(ii) and phase transfer catalysts as ligands 2. Quaternary ammonium salts

New composition catalysts based on bis(acetylacetonato)nickel(II) and ammonium salts, R₄NBr (Me_4NBr,n-C₁₆H₃₃Me₃NBr) for selective oxidation of aromatic hydrocarbons to the appropriate hydroperoxides have been introduced. It is demonstrated that the rate, selectivity, and degree of conversion of ethylbenzene to -ethylphenylhydroperoxide in this case are significantly higher than those observed for monodentate and macrocyclic ligands used as activating additives. The data obtained are in good agreement with the suggestion that the selective catalyst is formed in the course of ethylbenzene oxidation as a result of regioselective interaction of dioxygen with the -carbon atom of the acetylacetonate ligand controlled by R₄NBr.For communication 1 see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1412–1417, August, 1994.     

Solid-phase thermal decomposition of polynuclear nickel(II) and cobalt(II) complexes

Solid-phase thermal decomposition of polynuclear Ni^II and Co^II pivalate complexes was studied by differential scanning calorimetry and thermogravimetry. The decomposition of the polynuclear (from bi-to hexanuclear) Co^II carboxylate complexes is accompanied by aggregation to form a volatile octanuclear complex. Thermolysis of the polynuclear NiII carboxylates results in their destructure, and the phase composition of the decomposition products is determined by the nature of coordinated ligands. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 250—260, February, 2006.     

Composition catalysts of ethylbenzene oxidation based on bis(acetylacetonato)nickel(ii) and phase transfer catalysts as ligands 1. Macrocyclic polyethers

The addition of the macrocyclic polyether 18-Crown-6 (18C6) increases the selectivity of oxidation of ethylbenzene to -phenylethylhydroperoxide (PEH) in the presence of Ni(acac)₂. The initial oxidation rate, selectivity and degree of conversion of ethylbenzene to PEH are greater than those catalyzed by Ni(acac)₂ only. The efficiency of the macrocyclic ligand as an activator of Ni(acac)₂ exceeds that of monodentate donor ligands. The high selectivity of the process is due to both the primary Ni(acac)₂ · 18C6 complexes and the products of their transformation in the course of oxidation. The mechanism of ethylbenzene oxidation catalyzed by Ni(acac)₂ · 18C6 complexes is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1406–1411, August, 1994.     

Chemical model of oxidases. CuI-catalyzed oxidation of secondary alcohols by dioxygen

Oxidation of secondary alcohols (2-propanol, 2-butanol, and cyclohexanol) by dioxygen, catalyzed by Cu^I ando-phenanthroline complexes, in the presence of alkali, was studied. The conditions under which oxidative dehydrogenation of secondary alcohols result in fast formation of ketones as the only primary oxidation products were found. Bis-phenanthrolinates [Cu(phen)₂]⁺ are the active forms of the catalyst. The catalytic turnover number for complexes between copper(i) ando-phenanthroline is 1 to 2 s^–1 at room temperature.Kinetic regularities of the reaction are similar to those of the oxidation of alcohols in the presence of oxidases. The mechanism of the process is proposed, suggesting that the oxidation of secondary alcohols occursvia a concerted two-electron mechanism involving a stage of formation of the ternary complex [O₂...Cu(phen)₂ ⁺...^–OCHR¹R²]. It is significant for the oxidation mechanism that a hydrogen atom is transferred from the anionic form of a substrate to oxygen, which is confirmed by the value of the kinetic isotope effectk _H/k _D = 2.1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1952–1958, October, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-08733a) and the International Science Foundation (Grant MN4 000).     

Flash photolysis studies of charge-transfer photochemistry of nickel(II) and cobalt(III) complexes

The photochemical behavior of cobalt(III) and nickel(II) complexes on excitation in the charge-transfer bands is reviewed in this article with particular reference to the study of intermediates. Investigations on the photoredox reactions of cobalt(III) and nickel(II) complexes using flash kinetic spectroscopic methods reveal details on the characteristics of the intermediates produced from the charge-transfer excited states of these metal complexes. The reactive species produced on photolysis of cobalt(III)-amine complexes activate molecular oxygen, producing mononuclear and dinuclear dioxygen species coordinated as superoxo and peroxo forms. Cobalt(III)-amino-acid complexes on photolysis lead to the formation of cobalt(III)-alkyl complexes which are identified as transients. The spectra and the decay kinetics are described with the view to elucidate mechanistic details. Nickel(II) macrocyclic complexes on excitation in the charge-transfer bands lead to oxidation of the metal centre. Scavenging experiments using dioxygen, alcohols and acids were carried out to understand the mechanistic details.     

Electrocatalytic reduction of organic halides with cobalt bipyridine complexes

The electrocatalytic reduction of organic halides by the [Nibpy]⁺complexes coordinationally unsaturated with bpy (at potentials of the first wave) and by the coordinationally saturated [Nibpy₂]^–complexes (at potentials of the second wave) was observed. The apparent rate constant of the process decreased with an increase in the difference of the reduction potentials of the substrate and catalyst in a large range of the driving force of the process.     

Efficient oxidation of ethylbenzene catalyzed by cobalt zeolitic imidazolate framework ZIF-67 and NHPI

Efficient catalytic oxidation of ethylbenzene to acetophenone was realized using the catalytic system of cobalt zeolitic imidazolate framework ZIF-67/N-hydroxyphthalimide （NHPI） under mild conditions. 95.2% conversion of ethylbenzene with 90.3% selectivity to acetophenone could be obtained at 373 K under 0.3 MPa 02 for 9 h. The results show that there exists synergetic effect between ZIF-67 and NHPI. 1-Phenylethyl hydroperoxide （PEHP） was generated via a radical process involving the hydrogen abstraction from ethylbenzene by phthalimide N-oxyl, and subsequently effectively decomposed to acetophenone by ZIF-67.     

Unsymmetrical dinuclear cobalt and nickel trimethylacetate complexes

The reaction of the dinuclear complex Co₂(-OOCCMe₃)₂(²-OOCCMe₃)₂bpy₂ (1) with the polymer [Co(OH) _n (OOCCMe₃)_2–n ] _x afforded the unsymmetrical dinuclear complex bpyCo₂(₂-O,²-OOCCMe₃)(₂-O,O"-OOCCMe₃)₂(²-OOCCMe₃) (2). The reaction of 2,2"-dipyridylamine with [Co(OH) _n (OOCCMe₃)_2–n ] _x gave rise to the analogous complex [(C₅H₄N)₂NH]Co₂(₂-O,²-OOCCMe₃)(-OOCCMe₃)₂(²-OOCCMe₃) (3). The reaction of complex 1 with Ni₄(₃-OH)₂(-OOCCMe₃)₄(OOCCMe₃)₂(MeCN)₂[²-o-C₆H₄(NH₂)(NHPh)]₂ (4) produced an isostructural heterometallic analog of complex 2 with composition bpyM₂(₂-O,²-OOCCMe₃)(₂-O,O"-OOCCMe₃)₂(²-OOCCMe₃) (5) (M = Co, Ni; Co : Ni = 1 : 1) and the dinuclear heterometallic complex bpy(HOOCCMe₃)M(-OH₂)(-OOCCMe₃)₂M(OOCCMe₃)₂[o-C₆H₄(NH₂)(NHPh)] (6) (M = Co, Ni; Co : Ni = 0.15 : 1.85). Compounds 2 and 5 exhibit ferromagnetic spin-spin exchange interactions.     

Reaction of substituted iron phthalocyanines with dioxygen in acidic medium

The reaction of acidic form of the substituted icon phthalocyanine complex (3-PhS- 5-Bu^t)⁴pcFe (pcFe) with dioxygen in o-dichlorobenzene in the presence of dichloroacetic acid (HX) was investigated. The oxidation of HpcFeX gives the corresponding radical cation, which was confirmed by the stoichiometry of reduction of the product formed in this reaction with a two-electron reducing agent. The kinetic equation obtained on the basis of dependences of the oxidation rate on the HpcFeX, HX, and O₂ concentrations are consistent with the reaction mechanism that implies the formation of a HpcFeX complex with O₂ and its transformation to give a radical cation under the action of HX.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1592–1597, August, 2004.     

Binuclear and polynuclear transition metal complexes with macrocyclic ligands 1. Synthesis and the structure of an antiferromagnetic binuclear nickel complex prepared by the reaction of o-phenylenediamine with pyrrole-2,5-dicarbaldehyde and nickel pivalate

The reaction of pyrrole-2,5-dicarbaldehyde (1) with o-phenylenediamine (2) in anhydrous EtOH afforded a [1+1]-condensation product, viz., Schiff"s base. The structure of the latter was established by NMR spectroscopy and X-ray diffraction analysis. The reaction of this product or a mixture of 1 and 2 with Ni₉(_n-OOCBu^t)₁₂(HOOCBu^t)₄(₄-OH)₃(₃-OH)₃ in MeCN in the presence of AcOH gave rise to an antiferromagnetic binuclear complex. According to the X-ray diffraction data, the macrocycle in the latter complex is a [2+2]-condensation product of compounds 1 and 2, _eff ranging from 0.569 to 2.614 B (2—301 K), –2J = 360 cm^–1. The Ni₂(OAc)₂ fragment is located in the central cavity of the macrocycle. The structures of the condensation products are discussed based on the results of DFT quantum-chemical calculations.     

Oxidation of ascorbic acid in the presence of phthalocyanine metal complexes. Chemical aspects of catalytic anticancer therapy. 1. Catalysis of oxidation by cobalt octacarboxyphthalocyanine

The kinetics of oxidation of ascorbic acid in the presence of cobalt octa-4,5-carboxyphthalocyanine sodium salt (Teraphthal) was studied. A kinetic equation was obtained and a scheme of the process was proposed. According to the scheme, the first stage is the formation of a complex of the catalyst with dioxygen, and the limiting stage is the reaction of dioxygen with the ascorbate monoanion. The influence of the pH of the medium and the presence of a transport protein (albumin) on the state and catalytic activity of Teraphthal was studied. The involvement of hydrogen peroxide and oxygen-centered radicals in the catalytic oxidation of ascorbic acid was proved.     

Partial oxidation of 4-tert-butyltoluene catalyzed by homogeneous cobalt and cerium acetate catalysts in the Br-/H2O2/acetic acid system: insights into selectivity and mechanism

The partial oxidation of 4-tert-butyltoluene to 4-tert-butylbenzaldehyde by hydrogen peroxide in glacial acetic acid, catalyzed by bromide ions in combination with cobalt(II) acetate or cerium(III) acetate, has been studied in detail. Based on the observed differences in reaction rates and product distributions for the different catalysts, a reaction mechanism involving two independent pathways is proposed. After the initial formation of a benzylic radical species, either oxidation of this intermediate by the metal catalyst or reaction with bromine generated in situ occurs, depending on which catalyst is used. The first pathway leads to the exclusive formation of 4-tert-butylbenzaldehyde, whereas reaction of the radical intermediate with bromine leads to formation of the observed side products 4-tert-butylbenzyl bromide and its hydrolysis and solvolysis products 4-tert-butylbenzyl alcohol and 4-tert-butylbenzyl acetate, respectively. The cobalt(II) catalysts Co(OAc)(2) and Co(acac)(2) are able to quickly oxidize the radical intermediate, thereby largely preventing the bromination reaction (i.e., side-product formation) from occurring, and yield the aldehyde product with 75-80 % selectivity. In contrast, the cerium catalyst studied here exhibits an aldehyde selectivity of around 50 % due to the competing bromination reaction. Addition of extra hydrogen peroxide leads to an increased product yield of 72 % (cerium(III) acetate) or 58 % (cobalt(II) acetate). Product inhibition and the presence of increasing amounts of water in the reaction mixture do not play a role in the observed low incremental yields.     

Reactions of pyrrole-2,5-dicarbaldehyde with 2-aminodiphenylamine in the presence of nickel and cobalt trimethylacetates

The reactions of pyrrole-2,5-dicarbaldehyde (1) with 2-aminodiphenylamine (3) taken in a ratio of 1 : 2 in the presence of polinuclear nickel(ii) and cobalt(ii) trimethylacetate complexes were studied in MeCN. The reaction with Ni₉(HOOCCMe₃)₄(₄-OH)₃(₃-OH)₃(OOCCMe₃)₁₂ (2) afforded the mononuclear complex Ni(OOCCMe₃)₂[(PhHN)C₆H₄NHCHC₄H₂NCHNC₆H₄(NHPh)] (4) with a new ligand, which is the product of condensation of one molecule 1 with two molecules 3 and contains two NHPh groups. By contrast, the reaction with the polymeric complex [Co(OH) _n (OOCCMe₃)_2–n ] _x (5, n = 0.05—0.1) gave rise to the tetranuclear complex Co₄(₄-O)(-OOCCMe₃)₄L₂ (6), where L is, apparently, the product of further oxidation of Schiff"s base to the benzimidazole derivative. The structures of compounds 4 and 6 were established by X-ray diffraction analysis.     

Henry reaction catalyzed by copper(I) complexes of a new pyridine‐containing macrocyclic ligand

The synthesis and characterization of copper(I) complexes of the novel pyridine‐containing macrocyclic ligand (PC‐L) and their use as catalysts in the Henry reaction are reported. The pyridine‐based 12‐membered tetraaza macrocyclic (PC‐L) ligand 1 can be obtained in good overall yield (85%) from commercially available starting materials. The Cu(I) complexes showed good catalytic activities in the Henry reaction of different aldehydes and nitroalkanes. Remarkable diastereoselectivity was observed when isatine was reacted with nitroethane under catalytic conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

PVC matrix membrane electrodes based on cobalt and nickel phenanthroline complexes for selective determination of cobalt(II) and nickel(II) ions

Potentiometric sensors for determining cobalt and nickel ions are described. They are based on the use of cobalt and nickel tris(1,10-phenanthroline)-TPB as electroactive compounds dispersed in plasticized poly(vinyl chloride) matrix. The sensors exhibit fast, near-Nernstian responses for cobalt and nickel-phenanthroline cations over the pH range 3–11 with a slope of 30.3 ± 0.3 mV/concentration decade. In the presence of excess 1,10-phenanthroline reagent, cobalt(II) and nickel(II) ions at concentration levels as low as 4 × 10^–6 M are accurately determined. The results show an average metal ion recovery of 98.5% with a mean standard deviation of 0.5%. Cobalt in organometallic compounds and nickel in silicate rocks are determined by these sensors and results agreeing fairly well with atomic absorption spectrometry are obtained.     

Magnetic d‐penicillamine‐functionalized cellulose as a new heterogeneous support for cobalt(II) in green oxidation of ethylbenzene to acetophenone

A new efficient heterogeneous catalyst is introduced for the oxidation of ethylbenzene. The catalyst was obtained in three steps: functionalization of cellulose with d ‐penicillamine, deposition of Fe₃O₄ nanoparticles on cellulose–d ‐penicillamine and then anchoring of Co(II) to the magnetic cellulose–d ‐penicillamine. High yield and excellent selectivity were achieved for the oxidation of ethylbenzene to acetophenone in ethanol under reflux conditions using H₂O₂ as a green oxidant. Also, the recovered catalyst could be applied six times without a decrease in activity.     

Preparation and catalysis of chloromethylated polystyrene‐supported macrocyclic Schiff base metal complexes for the oxidation of cumene

Chloromethylated polystyrene‐supported macrocyclic Schiff base metal complexes (PS‐L‐M, M = Cu²⁺, Co²⁺, Ni²⁺, and Mn²⁺) were synthesized and characterized by the methods of IR, ICP, and small area X‐ray photoelectron spectroscopy (XPS). The oxidation of cumene by molecular oxygen in the absence of solvent with the synthesized complexes employed as catalyst was carried out. In comparison with their catalytic activities, PS‐L‐Cu is a more effective catalyst for the oxidation of cumene. The main products are 2‐phenyl‐2‐propanol (PP) and cumene hydroperoxide, which were measured by GC/MS. The influences of reaction temperature, the amount of catalyst, as well as the reaction time on the oxidation of cumene were investigated. Copyright © 2008 John Wiley & Sons, Ltd.