Search

This research focuses to studying on the process of glycolysis of polycarbonate (PC) catalyzed by zinc chloride. The degradation of polyester into monomers (bisphenol A, or BPA, and ethylene carbonate, or EC), which may then interact with one another to generate the matching ethers, was discovered to be the process. As a result, the optimal conditions for the depolymerization of PC to obtain bisphenol A and ethylene carbonate with the highest yield were therefore identified as 180 °C, a molar ratio of 11 between EG and PC, and a mass concentration of 0.12% ZnCl2. A scheme of PC glycolysis has been proposed, and a mathematical model adequately describing the experimental data has been developed.

The crude glycerol is the main by-product of biodiesel production and contains large amounts of potassium (or sodium) soap. These alkaline compounds may be reacted with ester groups of polyethylene terephthalate (PET) to form the corresponding terephthalic acid salts. In this work, the process of PET depolymerization with crude glycerol with a high content of potassium salts was studied. Depolymerization is the multistage process and proceeds through the formation of oligomers of various molecular weights. Subsequently, the resulting intermediate compounds decompose to low molecular weight oligomers (dimers and trimers), up to dipotassium terephthalate (DPT). A general reaction scheme and a mathematical model of the process are represented, and rate constants of all reactions are estimated.

The patterns of epoxidation of linoleic acid methyl ester in a mixture of methyl esters of sunflower oil fatty acids with atmospheric oxygen in a bubble column reactor are analyzed at various feed rates of the gas phase. It was found that the oxidation process takes place in the transition region, under diffusion control conditions. The contributions of the diffusion and kinetic components to the rate of oxidative epoxidation of fatty acid methyl esters are determined. It was established that the selectivity of the epoxidation reaction decreases with the transition of the oxidation process from the diffusion region to the kinetic.

During the aerobic oxidation of esters of both mono- and diunsaturated fatty acids and their mixtures, epoxide compounds are first forming, as well as the peroxide compounds with different structures and reactivities depending on the number of double bonds in the original molecule. The mild aerobic oxidation conditions in the column-type apparatus led to a number of features of the process. It was shown that both types of esters are consumed in independent ways, despite the fact that the whole process is radical. Therefore, this means the absence of processes of transfer of oxidation chains, as well as the chains of radical reactions themselves. Thus, we can conclude that the process under study is radical without chain transfer from one type of ester to another. Peroxides forming from monounsaturated fatty acid esters are able to participate in catalytic epoxidation by hydroperoxides, which proceeds with high selectivity. From diunsaturated fatty acid esters, at least two types of peroxides with different reactivities are formed. One of them can enter into catalytic epoxidation reaction, the other forms secondary oxidation products, which are mainly represented by the products of the Baeyer–Villiger reaction. In this contribution upon using different mono- and diunsaturated fatty acid esters, the mechanism of products formation has been investigated and discussed.

During the last decades, palladium nanoparticles (Pd(0) NPs) and Pd(II) compounds were shown to be attractive catalysts for fine organic synthesis. Nanostructured Pd(0) or Pd(II) catalysts have a relatively low environmental impact, but, at the same time, they are indispensable for such processes as Suzuki cross-coupling. This paper describes the preparation of Pd(0) or Pd(II) supported/embedded in hyper-cross-linked polystyrene (HPS) and compares their activity in Suzuki cross-coupling between phenylboronic acid and 4-bromoanisole. Obviously, the palladium charge (Pd(0) ↔ Pd(II)) changes continuously during the reaction catalytic cycle. It would seem that the use of the starting palladium in the form of Pd(0) or Pd(II) should not affect the reaction’s kinetic laws for both catalysts, but their special individuality is manifested between them. Nanoparticulate Pd(0) catalysts are stable during the reaction. In contrast, catalysts based on Pd(II) are extremely active in the initial period of the reaction, but then the “hot form” of the catalyst is rapidly converted into the form of Pd(0), whose activity is identical to that of the preliminarily reduced catalyst. This work discusses the possible nature of this phenomenon. A mathematical model for Suzuki cross-coupling reaction was suggested that was able to adequately describe experimental data. The level of reliability (R2) of the correlation between the experimental and calculated data was R2 = 0.97–0.99.

A kinetic study of dry reforming of methane (DRM) on the traditional powder and membrane catalysts with the active component WC was performed. The paper presents the mass balance of DRM. A kinetic model in which the formation of carbon deposits is absent on both catalysts has been proposed. The model was established that DRM proceeds identically on the traditional and membrane catalysts, that made it possible to propose a kinetic model applicable to both catalysts over the entire range of temperatures, concentrations and flow rates. The rate constant of direct reaction of dry reforming of methane on a membrane catalyst at a temperature of 900 °C is 30 times higher than on a traditional catalyst at the same temperature. This is one more proof of the intensification of catalytic processes with using the membrane catalysts. It has been suggested that the intensification on the membrane catalyst is associated with the features of mass transfer under the conditions of Knudsen diffusion.

This work is addressed to the phenomenon of catalyst deactivation taking place during the repeated uses in the reaction of Suzuki-Miyaura (S-M) cross-coupling, which is widely applied in industry for C-C bond formation. Ligandless catalysts based on Pd(0) NPs supported on hyper-cross-linked polystyrene (HPS) of two types (non-functionalized and bearing tertiary amino groups) were studied in a model S-M reaction between 4-bromoanisole and phenylboronic acid. Synthesized catalysts were shown to be highly active under mild reaction conditions. HPS allows stabilization of Pd(0) NPs and prevents their agglomeration and detectable Pd leaching. However, the loss of catalytic activity was observed during recycling. The deactivation issue was assigned to the hydrophobic nature of non-functionalized HPS, which allowed a strong adsorption of cross-coupling product during the catalyst separation procedure. A thorough washing of Pd/HPS catalyst by hydrophobic solvent was found to improve to the big extent the observed catalytic activity, while the replacement of non-functionalized HPS by a one containing amino groups increased the catalyst stability at the expense of their activity.

A kinetic model of the isothermal initiated cracking of tar has been developed, and parameters of the reactions have been found. A computer model of isothermal thermo-oxidative cracking of tar is implemented to determine kinetic constants, and a criterion for mismatching the calculated and experimental data is minimized. The kinetic simulation of the process has been carried out in isothermal regime so that the parameters that allow for increase in yield of target products have been determined.

The article presents the results of processing heavy oil residues initiated by atmospheric oxygen. We found that the introduction of a small amount of atmospheric oxygen (2–6%) in the thermo cracking reactor (thermo-oxidative cracking) significantly increases the yields of light fractions. E.g. A thermo cracking of vacuum residue (visbreacking) with the air supply to the soaker camera gives twice more light fractions than traditional visbreacking process (36% of petrol and diesel fractions compared to 10–15% in conventional process). Thermo-oxidative cracking of atmospheric residue gives up to 60% of light fractions. In order to obtain a mathematical description of the process needed for its subsequent industrial implementation we conducted experiments on thermo-oxidative cracking of atmospheric and vacuum residues in a continuous flow reactor with a wide variation of the process parameters. Based on the analysis of the experimental data a common scheme for thermo-oxidative cracking, a mathematical model of the process and its parameters were established. The model adequately describes all the experimental data obtained in the temperature range 430–460 °C, pressure 2–8 atm, retention times 4–33 min and relations oxygen/raw material 0,9–2,5 % wt. Industrial implementation of thermo-oxidative cracking needed just minimal modification of the existing thermal installations through the organization of air supply in the soaker chamber. This modification will increase the output of light fractions in the thermal processing heavy oil residues in 2–3 times with minimal capital investments.

This paper discusses the results of investigations on the kinetics of cumene oxidation to cumene hydroperoxide by molecular oxygen in the presence of N-hydroxyphthalimide as a catalyst. A mathematical model has been developed on the basis of the regularities of hydroperoxide and by-products formation. The model adequately describes changes in all reaction components in the course of the reaction. It has also been established that the role of N-hydroxyphthalimide in the process consists in the creation of a steady-state concentration of N-phthalimide radicals initiating oxidation by interacting with the hydrocarbon.

Stearic acid hydrodeoxygenation into n-heptadecane on the catalyst containing Pd nanoparticles incorporated in the hypercrosslinked polystyrene matrix was studied. The used catalysts were characterized using TEM, CO chemisorption, low-temperature nitrogen physisorption and XPS. A clear hydrogen pressure dependent induction period was noticed. Kinetic regularities were studied for the indicated reaction in the presence of polymer based catalysts. A mathematical model for decarboxylation was suggested which was able to adequately describe experimental data at different temperatures, hydrogen pressures and initial concentrations of stearic acid. Kinetic constants were calculated and their statistical analysis was performed.

The paper discusses in detail the first stage of the catalytic oxidation of fatty acid methyl esters with atmospheric oxygen. According to the data obtained as a result of processing the kinetic data, it was concluded that the reactivity of the components of biodiesel. It is established that polyunsaturated and monounsaturated compounds have different reactivity from each other. The kinetic pattern of consumption of unsaturated components of biodiesel was set up and kinetic constants were calculated, which are equal to: oxidation of C18/1 k1 = 0.106 ± 0.008 h−1, and oxidation of C18/2 k2 = 0.269 ± 0.005 h−1, respectively

We studied the kinetics of glucose hydrogenation over a catalyst containing Ru nanoparticles in a super-cross-linked polystyrene matrix. Two hydrogenation pathways, whose rates differ by several orders of magnitude (“fast” and “slow” pathways), were found. The first pathway includes the reaction of glucose from its aqueous solution with hydrogen sorbed on the catalyst’s metal, and the second one includes the reaction of sorbed substrate with hydrogen occurring on the catalyst support due to spillover. A mathematical description of the reaction pathways was proposed, and the most probable scheme of the process was suggested. The role of hydrogen spillover in the kinetics of the occurring processes was considered.

The kinetics of D-glucose hydrogenation on the catalyst containing Ru nanoparticles in the matrix of hypercrosslinked polystyrene was studied. Two routes of the hydrogenation reaction were revealed; their rates differ by several digits. The first route includes the interaction of d-glucose with the spilled-over hydrogen supplied by the catalyst; the second one includes classical interaction of the sorbed substrate with incident hydrogen from the reaction medium. A mathematical description of D-glucose conversion and the change of the catalyst activity by the first method of D-glucose hydrogenation were obtained. The most probable scheme of the process flow was suggested. The main kinetic parameters were calculated. The role of hydrogen spillover phenomenon in the kinetics of the processes is discussed.

The kinetics of maleic acid hydroxylation by H 2 O 2 in the presence of a homogeneous catalyst have been studied. A rate equation for the consumption of H 2 O 2 has been obtained. The retardation of the reaction resulting from catalyst deactivation was observed. The fall in the activity of catalyst during the course of the reaction has been associated with the formation of a complex between the former and the reaction product

The general kinetic laws relating the changes in reactants and products ratios with changes in the operating conditions of the catalytic epoxidation and hydroxylation reaction of maleic acid by hydrogen peroxide have been analyzed. In the course of the hydroxylation reaction, the formation of epoxysuccinic and tartaric acids, and the decomposition of hydrogen peroxide to molecular oxygen have been observed to take place in parallel. The catalytic complex (Cat.2H 2 T) formed between sodium tungstate (catalyst) and tartaric acid in the course of the reaction is found to be inactive in the epoxidation reaction but active in the catalysis of the decomposition of hydrogen peroxide. This fact explains the non-formation of tartaric acid at high maleic acid conversion. The mathematical model for the overall process has been developed

The rate of anaerobic glucose fermentation by baker's yeast is found to be altered when tap water is replaced with “levitated” (i.e., hydrodynamically processed) water. To analyze the effect in more detail, we developed a fermentation kinetics model that differentiates between (i) nutrient transport into the cell, (ii) the “catabolic” and (iii) the “anabolic” reactions. As a result, the levitated water affects specifically the glucose uptake kinetics, whereas the other kinetic parameters remain unchanged. Remarkably, the sign of the effect changes with the water used to prepare the culture. When levitated water is used for both the culture preparation and the fermentation, the rate constant of glucose transport is increased by (67±25)%, relative to ordinary tap-water. When the culture is prepared in ordinary water and only the fermentation is performed in levitated water, the rate constant of glucose transport decreased by (50±12)%. Three-week old levitated water has no discernable effect any more.

The interaction between any fragments bonded to some central atom are increasingly recognized as an important factor in determining, e.g. the geometry and properties of metal complexes. Here we analyze the class of the two-legged piano stool complexes Cp′ML 2 (Cp′=cyclopentadienyl or a derivative, M=Fe(II) and Ru(II), L=phosphorus and nitrogen co-ligands) with the aid of the through-space coupling (TSC) concept. This is the molecular orbital representation of van der Waals-like repulsive–attractive forces between the ligands in addition to the interactions with the metal center. The combination of both, i.e. the interaction between the new collective ligands orbitals and the metal AO's is shown to be the main determinant for deciding whether a planar or pyramidal structure is adopted and further, whether the complex is diamagnetic or paramagnetic. In addition the TSC concepts aids in understanding the effect of intercomplex interactions on the nucleophilic and electrophilic behavior of the 16e-complexes towards an incoming ligand. In fact, interpretations hitherto solely in terms of electronic ligand effects appear to be inadequate. The present paper is a continuation of our former work in which we successfully applied the TSC concept to rationalize the diverse array of structural arrangements as well as reactivities of the main-group Cp metal complexes (Sapunov et al. Coord. Chem. Reviews 214 (2001) 143).

A number of 16e two-legged piano-stool complexes [Cp*Ru(PP)][BAr‘4] have been prepared by reaction of NaBAr‘4 with either [Cp*RuCl(PP)] (PP = (PEt3)2, iPr2PCH2CH2PiPr2 (dippe), (PPh3)2) or [Cp*RuCl...

Absolute single-ion thermodynamic quantities of hydration at 298.15 K are derivable from the conventional enthalpies and entropies if the values of S°(Haq+) and ΔhydH°(H+) are known. Here we suggest S°(Haq+) = −5.5 J K−1 mol-1 based on the thermodynamics of the dissociation of water. This assignment, in turn, corresponds to ΔhydH°(H+) = −1078 kJ mol-1 according to a self-consistent analysis of Krestov. Using these values, as a main result, the anions are more strongly hydrated than usually thought, in line with recent calculations. Only the group 1, 2, and 15 nobel gas ions are dealt with. For each series, the conventional enthalpies and entropies are linearly related to one another. From these linear free energy relationships (LFERs) a relationship between S°(Haq+) and ΔhydH°(H+) is derived. Further, a connection is detected between the Born radii rB, calculated from the free energies of hydration, and the distances d, corresponding to the upper limits of the experimental first peak position of the ionoxygen radial distribution curves, upon implication, in the case of a cation, the covalent radius rcov of oxygen, and in the case of an anion, the water radius rwater, Finally, from the differences between the enthalpies and free energies of hydration the temperature derivatives of the Born radii are determined.

The cationic 16e complexes [RuCp*(η 2 (N,N)-Me 2 NCH 2 CH 2 N(CH 2 CHMe 2 ) 2 )] + ( 1 ) and [RuCp*(η 2 (N,N)-Me 2 NCH 2 CH 2 H 2 ] + ( 2 ) as well as the 18e complex [RuCp*(η 6 -C 6 H 5 -N(Me)NCH 2 CH 2 NMe 2 )] + ( 3 ) have been synthesized as the BAr′ 4 (Ar′=3,5-C 6 H 3 (CF 3 ) 2 ) salts in one-pot reactions starting from [RuCp*(Cl)] 4 . For 1 , the X-ray crystal structure has also been determined showing the absence of any agostic interactions between ruthenium and the C–H bonds of the diamine ligand, and only minor deviations from the planar geometry despite the bulky diamine ligand. Based on EH model calculations, the extraordinary kinetic inertness of the planar 16e [Cp*Ru(NN)] + structure is traced to a high HOMO–LUMO gap deriving from through-bond coupling through the intervening σ skeleton of the chelating diamine (NN) ligand (in contrast to the P analogs) and further to the high π donor strength of Cp* (relative to parent Cp). Possible ligand rearrangements to increase the chemical reactivity are analyzed.

Complexes of the types [Ru(η5-C5H5)(η4-C5H4O)]2(CF3SO3)2 (1) and [Ru(η5-C5H5)(η4-C5H4O)(L)]CF3SO3 (L = CH3CN (2), pyridine (3), thiourea (4)) react with tertiary phosphines to give (i) 1,1‘- (12) or (ii) 1,2-disubstituted ruthenocenes (13) depending primarily on the basicity of the entering phosphine and the nature of L. Path i proceeds via the intermediacy of [Ru(η3-C5H5)(η4-C5H4O)(PR3)]22+ (5) and [Ru(η3-C5H5)(η4-C5H4O)(PR3)(L)]+ (6−8); i.e., the hapticity of the C5H5 ligand is changed from η5 to η3 while forming an additional Ru−P bond. The η3 bonding mode was established by 1H and 13C{1H} NMR spectroscopies. The kinetics of these reactions were studied in detail, providing enthalpies and entropies of both activation and reaction. The conversions to 6−8 are exothermic (ΔH° = −5.5 to −16.9 kcal mol-1) but entropically unfavorable (ΔS° = −44.8 to −19.0 cal K-1 mol-1). The activation parameters and rate constants vary little with the phosphine, suggesting a preequilibrium between η5 and η3 species of the ...

The three title cyanoruthenium complexes have been characterized by means of X-ray diffraction analysis, IR and NMR solution spectroscopies, as well as extended Huckel molecular orbital calculations examining the properties of the cyanide fragment changing with complexation and with the co-ligands Cp and PPh3. Explanations are given for crystallographic results of the C-N bond shortening upon complexation, the supershort (2.573 A) bond length of N(H) ⋯ N in the bridged complex, as well as the Ru-C-N and C-N-H-N-C bendings. Although the crystallographically found asymmetry of coordinated Cp is not significant, the MO calculations suggest a distorted endocyclic bond-length pattern indicative of the relative importance of σ and π bonding in the metalcyclopentadienyl interactions.

This paper reports on the synthesis and reactivity of Ru(IV) η4-diene complexes of the type Ru(η5-C5Me5)(η4-diene)Br2+ obtained by oxidative bromine additions to Ru(II) η4-diene complexes. Mechanistic details are derived from the reaction products varying with the oxidizing agent and the leaving ligand and are backed up by extended Huckel molecular orbital calculations. The diene fragment in Ru(IV) is prone to gauche deformation and is therefore extremely susceptible to nucleophilic attack of even weak anionic bases generating the corresponding Ru(IV) η3-allyl complexes. Accordingly, Ru(IV) η4-diene complexes are stabilized either by using 2,3-disubstituted diene ligands in which case gauche deformation is highly unfavorable or else by excluding nucleophilic agents. For the latter method, two convenient routes to affording Ru(IV) η4-diene complexes are (i) the reaction of Br+CF3SO3- with Ru(η5-C5Me5)(η4-diene)Br and (ii) the reaction of dibromine with labile Ru(η5-C5Me5)(η4-diene)(CF3SO3). The conversion ...

The neutral η3-cyclohexenone complexes [Mo(η3-C6H7O)(CO)2(MeCN)2Br] 1, [Mo(η3-C6H7O)(CO)2{HB(pz)3}] 2, [Mo(η3-C6H7O)(CO)2(bipy)Br] 3 (bipy = 2,2′-bipyridine) and [Mo(η3-C6H7O)(CO)2(dppm)Br] 4 (dppm = Ph2PCH2PPh2) have been synthesized. The structure of 2 has been determined by X-ray crystallography. All these complexes resist hydride abstraction using Ph3C+PF6–, in sharp contrast to the η3-cyclopentenone analogues where η3-allyl/η4-diene conversion is a facile process. A rationale for this different behaviour is provided by extended-Huckel calculations combined with a Walsh analysis of hydrogen abstraction. Thus, while in the η3-C5H5O → η4-C5H4O conversion a Mobius system is formed upon release of hydride via electrophilic attack, this is not possible in the hypothetical η3-C6H7O → η4-C6H6O process. Therefore, η3-C6H7O is a C–H acid. Also, the occurrence of different conformations, exo for allyl and endo for diene complexes, is rationalized.

The kinetics of catalytic and non-catalytic hydrolysis of cis-epoxysuccinic acid have been studied. The hydrolysis leading to tartaric acid has been found to proceed much faster in the presence of iron (III) catalyst than the reaction without a catalyst or with tungstate catalyst. A complex of the form {cat · H2E} between iron(III) salts (catalyst) and epoxysuccinic acid seems to be responsible for the main catalytic effect. On the other hand, the reaction has been found to be retarded by the product of hydrolysis, tartaric acid (H2T). The inhibiting effect was caused by the formation of a catalyst deactivating complex in the forms {cat · H2T} and {cat · 2H2T}. A mathematical model for the overall process has been developed and the mechanism of reaction discussed.

The kinetics of outer-sphere oxidation of Fe(Xphen) 3 2+ ions (X=H or several methyl substituents) in acetonitrile (MeCN) solution by iron(III), introduced as Fe(tmp)6(ClO4)3 (tmp=trimethylphosphate), have been investigated at 25°C. The reactions are very complex because of solvation equilibria betweentmp andMeCN coordinated at Fe3+, with a reduction potential difference of 0.20 V for the replacement of onetmp byMeCN. This makes the various solvate species highly different in driving force. The second essential feature is the high charge-type of +2/+3. This brings about strong acceleration by salt because of ion association reducing the work necessary to overcome the Coulombic repulsion in forming the precursor complex.

Studies of kinetic peculiarities in hydroxylation of phenols by H2O2 in the presence of ferric sulfate have revealed general regularities of this process. A scheme of this process is suggested accounting for the stepwise conversion of Fe3+ into various complex forms. The reaction is suggested to take place in the coordination sphere of Fe3+.

The structures and properties of metal complexes are traditionally treated in terms of hybridization and electronic ligand effects. What is notoriously neglected, however, is the fact that in such an aggregate the ligands approach so closely to one another — on the order of van der Waals (vdW) distances — that intramolecular packing effects come into play. Actually, non-bonded interactions between any atoms bonded to some central atom are increasingly recognized as an important factor in determining bond distances, bond angles and the like. The class of the main group cyclopentadienyl (Cp) metal complexes appears to be a case study in this respect, because of the large extension of the Cp group and its ring structure on the one hand, and on the other, the minimal d-orbital involvement, dissimilar to the transition-metal analogues. It is shown that the diverse array of structural arrangements, such as linear, ring-slipped, bent, and polymeric chain structures, as well as their reactivities, are brought under the umbrella of one treatment with the aid of the through-space coupling (TSC) concept. This is the molecular orbital representation of vdW repulsive–attractive forces. As a central feature, the individual ligands are at first combined to a united system of TSC orbitals and then allowed to interact with the metal AOs. The energy splitting of the TSC orbitals and the electron density shift from one of them to a vacant metal orbital determine the repulsive and attractive interligand forces and hence fine-tune the geometry of the complex. Along these lines a physical explanation for the interplay between vdW attraction and repulsion becomes available. More specifically we are dealing here with complexes of the type Cp′nMLm (n=1–3, m=0–3) via united {Cp′nLm} molecular orbitals. Bending and slipping of the Cp′ ligands are rooted in vdW attraction and repulsion, respectively, with geometry and hapticity of the Cp′-metal bonding adjusted so as to optimize TSC.

The [TpRu(pn)](+) fragment (Tp = tripyrazolyl, pn = Ph(2)PCH(2)CH(2)NMe(2)), featuring a strong sigma acceptor and a weak pi donor, forms reversible complexes with a variety of sigma donor ligands L including N(2) which appears to be more strongly bonded than even CH(3)CN. X-ray crystal structures of the complexes with L = H(2)O, acetone, CO, N(2), and vinylidene are included (adding to that for L = CH(3)CN from former work), as well as a comparative MO study on the bonding nature of L. The sequence of complex stabilities of [TpRu(pn)L](+) is CF(3)SO(3)(-) < acetone approximately H(2)O < CH(3)CN < N(2) < CO < vinylidene as suggested from EHMO calculations and crystallographic data as well as qualitative experimental results. Despite the notable stability of [TpRu(pn)(eta(1)-N(2))](+), the N-N bond length is 1.097(5) A, exactly that in free N(2). Our analysis suggests that the insensitivity of the N-N bond essentially originates from the counterbalance of pi bond weakening (through back-donation) and sigma bond strengthening (through reducing the antibonding character of the sigma (2sigma(u)) MO in molecular dinitrogen.

The oxidation of iron(II) solvates by Fe(phen)3+3 in acetonitrile (An) and propanediolcarbonate (PDC) proceeds via the same reaction scheme as the reduction of iron(III) solvates by Fe(tetramethylphen)2+3. Solutions of iron(II) solvates in these solvents contain not only FeL2+6, but also complexes of lower coordination number. The lower the coordination number the faster the oxidation of the iron(II) species. In An an intermediate is formed between the pentacoordinated solvate and Fe(phen)3+3 which is obviously stabilized by the solvent.

The reaction between tris(acetylacetonato)magnanese(III) and hexa(N,N-dimethylformamide)iron(III) perchlorate in acetonitrile proceeds in two stages. The first stage corresponds to the reaction of pentacoordinated Fe(DMF) with Mn(acac)3, and the rate-determining step of the second stage consists mainly in the elimination of a DMF ligand from Fe(DMF) to yield Fe(DMF) which reacts rapidly with the manganese complex. The formation of Fe(DMF) is catalyzed by Mn(acac)3, this catalytic effect being decreased by manganese products. The rate-determining step for the formation of Fe(acac)3 is the transfer of the first acetylacetonate to yield Fe(acac)2+. The final products of iron depend on the ratio of reactant concentrations. With Mn or Fe in excess, Fe(acac)3 or Fe(acac)2+ are mainly produced.

Losungen von Hexaquo-eisen(III) in schwach koordinierenden Losungsmitteln enthalten neben hexakoordiniertem (inaktivem) [Fe(OH2)6]3+ (Fei3+) auch eine pentakoordinierte (aktive) Spezies (Fea3+), bei der ein Molekul H2O outer-sphere-komplex gebunden ist. Fea3+ steht mit Fei3+ im Gleichgewicht und wird tausendmal schneller als dieses reduziert. Daneben tritt auch in kleiner Konzentration ein tetrakoordinierter Komplex auf, der noch aktiver als Fea3+ ist. Die Geschwindigkeitskonstanten der Reduktion sowie der Gleichgewichtseinstellung Fei3+ Fea3+ und die Gleichgewichtskonstante [Fea3+]/[Fei3+] zeigen eine starke Abhangigkeit vom Solvens, die den unterschiedlichen Outer-sphere-Effekten der Losungsmittel zugeschrieben wird. Solutions of hexaquo-iron(III) in weakly coordinating solvents contain in addition to hexacoordinated (inactive) [Fe(OH2)6]3+ (Fei3+) a pentacoordinated (active) species (Fea3+), in which one H2O molecule is in the outer-sphere and these two species are in equilibrium. Fea3+ is reduced a thousand times faster than Fei3+. Even a small concentration of a tetracoordinated complex is supposed which is more reactive than Fea3+. The rate constants of the reduction and of the formation of Fea3+ as well as the equilibrium constant [Fea3+]/[Fei3+] depend considerably on the solvent and this is regarded as due to different outer-sphere-effects.

The transfer of oxinate ions from thallium (III)oxinate to trivalent Fe(DMF)63+ in propylenecarbonate takes place via rearrangements within a rapidly formed binuclear thallium(III)—iron(III) complex. In a last rapid step this rearranged complex reacts with excess reactants to the final products whose composition accordingly depends on the ratio of the reactant concentrations.

Losungen von Eisen(III)-solvaten in Acetonitril enthalten neben [FeL6]3+ auch niedriger koordinierte Komplexe, die um so schneller reduziert werden, je kleiner die Koordinationszahl ist. Die Abhangigkeit des prozentualen Anteils des pentakoordinierten Komplexes von der Donizitat der Liganden beweist, das seine Bildung aus dem Hexasolvat uber zwei Reaktionsschritte erfolgt. Bei gegebener Koordinationszahl sinkt die Reduktionsgeschwindigkeit eines Komplexions mit steigender Donizitat seiner Liganden. Solutions of iron(III)-solvates in acetonitrile contain in addition to the species [FeL6]3+ complexes of lower coordination number. The lower the coordination number the faster is the reduction of the complex. The dependence of the percentage of the pentacoordinate complex on the donicity of the ligands proves that its formation from the hexa-solvate proceeds via two reaction steps. For given coordination number the rate of reduction of a complex ion decreases with increase of the donicity of its ligands.

The kinetics of the iron(II) reduction of thallium(III) oxinate does not differ essentially from that of the oxinate-transfer from thallium(III)-oxinate to iron(III), described before: formation of a binuclear intermediate, rearrangements within, and subsequent reaction with the excess reactant to the final products. As for the redox process, these intermediates are binuclear Tl(II)-Fe(III) complexes which, with initial reactants, form further complexes in which the second electron is transferred. In the cases of excess Tl(ox)3 and of equimolar reactants, disproportionations are likely involved.

The electron transfer step of the reduction of Mn(acac)3 and Co(acac)3 by Fe(II) in acetonitrile is preceded by the one-ended dissociation of an acac ligand and the formation of a binuclear bridged complex. After the electron transfer has taken place through the bridging ligand, the complex dissociates into the products M(acac)2 (M = Mn, Co) and Fe(acac)2+. These primary reaction products could not be identified, since the transfer of acac from M(acac)2 to Fe(acac)2+ is too rapid, producing ultimately Fe(acac)3 and M2+. The M(III)-oxygen cleavage is accelerated by M(acac)2. Furthermore, the dissociation of the binuclear intermediate is catalyzed by the M(acac)3 reactant. Mn(acac)3 is reduced more than a thousand times faster than Co(acac)3.

The mutual interrelations between common points of intersection in various temperature-dependent linear free-energy relationships (LFERs) are analysed and compared with experimental examples. With this approach isoparametric and isokinetic relationships are brought under the umbrella of one treatment. Both Hammett and Broensted reaction series are used for comparison with experiment.

Die Kinetik der Reduktion von Eisen(III)-Solvaten mit Tetramethylferroin ist in hohem Mase losungsmittelabhangig. Die Reduktionsgeschwindigkeit nimmt in der Reihenfolge AN > PDC > NM ab. Das in AN auftretende Zwischenprodukt eines pentakoordinierten Solvates mit Ferroin kann in NM und PDC nicht nachgewiesen werden. Dies deutet darauf hin, das AN an der Redoxreaktion beteiligt ist. Fur ein gegebenes Losungsmittel sinkt die Reduktionsgeschwindigkeit von [FeL6]3+ mit steigender Donizitat von L. The kinetics of the reduction of iron(III) solvates by tetramethylferroin is highly dependent on the solvent. The reduction rate decreases in the order AN > PDC > NM. The intermediate being formed between the pentacoordinated solvate and ferroin in AN cannot be detected in NM and PDC. This indicates the participation of AN in the redox reaction. In each of the solvents the reduction rate of [FeL6]3+ decreases with increasing ligand donicity of L.

The structures and properties of metal complexes are traditionally treated in terms of hybridization and electronic ligand effects. What is notoriously neglected, however, is the fact that in such an aggregate the ligands approach so closely to one another — on the order of van der Waals (vdW) distances — that intramolecular packing effects come into play. Actually, non-bonded interactions between any atoms bonded to some central atom are increasingly recognized as an important factor in determining bond distances, bond angles and the like. The class of the main group cyclopentadienyl (Cp) metal complexes appears to be a case study in this respect, because of the large extension of the Cp group and its ring structure on the one hand, and on the other, the minimal d-orbital involvement, dissimilar to the transition-metal analogues. It is shown that the diverse array of structural arrangements, such as linear, ring-slipped, bent, and polymeric chain structures, as well as their reactivities, are brought under the umbrella of one treatment with the aid of the through-space coupling (TSC) concept. This is the molecular orbital representation of vdW repulsive–attractive forces. As a central feature, the individual ligands are at first combined to a united system of TSC orbitals and then allowed to interact with the metal AOs. The energy splitting of the TSC orbitals and the electron density shift from one of them to a vacant metal orbital determine the repulsive and attractive interligand forces and hence fine-tune the geometry of the complex. Along these lines a physical explanation for the interplay between vdW attraction and repulsion becomes available. More specifically we are dealing here with complexes of the type Cp′nMLm (n=1–3, m=0–3) via united {Cp′nLm} molecular orbitals. Bending and slipping of the Cp′ ligands are rooted in vdW attraction and repulsion, respectively, with geometry and hapticity of the Cp′-metal bonding adjusted so as to optimize TSC.