Determination of Kinetic Order of Reaction for its Duration in the Study of Solvation Factor Effect on Cyclohexene Hydrocarbomethoxylation Catalyzed by Palladium-Phosphine Systems

2019 ◽  
pp. 103-116
Author(s):  
N.T. Sevostyanova ◽  
S.A. Batashev
Keyword(s):  
Elevated Temperatures ◽  
Catalyst Deactivation ◽  
Initial Rate ◽  
Palladium Complexes ◽  
Methanol Concentration ◽  
Exchange Reactions ◽  
Kinetic Order ◽  
Rate Region ◽  
Factor Effect ◽  
Solvation Factor

The purpose of the study was to investigate homogeneous catalytic reaction of cyclohexene hydrocarbomethoxylation leading to the methyl cyclohexanecarboxylate formation. Pd(PPh3)2Cl2 and Pd(OAc)2 which were promoted by free PPh3 and p-toluenesulfonic acid were used as catalytic precursors. In the temperature range 358--393 K, we studied the methanol concentration effect on the value of kinetic order of the reaction with respect to cyclohexene for the duration of the reaction. Findings of research show that the kinetic order increased from 1 to 10 with temperature increase and methanol concentration rise. We compared the kinetic order values for the duration of the reaction and the concentration order with respect to cyclohexene, which is equal to 1, set for the initial rate region. Based on this comparison, it was suggested that the formation of inactive palladium complexes is progressed by the action of excess methanol at elevated temperatures. We found that the regularities of methanol effect on the cyclohexene hydrocarbomethoxylation rate for the duration of the reaction were agreed with the regularities discovered for the initial rate region. With consideration of the data about enthalpy change in the ligand exchange reactions between the palladium complexes with participation of CH3OH, СО and PPh3, we draw the conclusion about the dominant contribution of specific solvation to the catalyst deactivation in the conditions of high methanol concentrations

scholarly journals Cross-Linker Control of Vitrimer Flow

2020 ◽  
Author(s):  
Bassil El-Zaatari ◽  
Jacob Ishibashi ◽  
Julia Kalow
Keyword(s):  
Stress Relaxation ◽  
Elevated Temperatures ◽  
Bulk Material ◽  
Relaxation Rates ◽  
Exchange Reactions ◽  
Activation Barriers ◽  
Flow Activation Energy ◽  
Wide Range ◽  
Cross Linker ◽  
Frequency Sweeps

<div><p>Vitrimers are a class of covalent adaptable networks (CANs) that undergo topology reconfiguration via associative exchange reactions, enabling reprocessing at elevated temperatures. Here, we show that cross-linker reactivity represents an additional design parameter to tune stress relaxation rates in vitrimers. Guided by calculated activation barriers, we prepared a series of cross-linkers with varying reactivity for the conjugate addition—elimination of thiols in a PDMS vitrimer. Surprisingly, despite a wide range of stress relaxation rates, we observe that the flow activation energy of the bulk material is independent of the cross-linker structure. Superposition of storage and loss moduli from frequency sweeps can be performed for different cross-linkers, indicating the same exchange mechanism. We show that we can mix different cross-linkers in a single material in order to further modulate the stress relaxation behavior.</p></div>

Pseudohalogenido complexes of iron-2,2′-bidipyrrins

2012 ◽  
Vol 16 (05n06) ◽  
pp. 641-650 ◽  
Author(s):  
Martin Bröring ◽  
Silke Köhler ◽  
Clemens Pietzonka
Keyword(s):  
High Spin ◽  
Spin State ◽  
Elevated Temperatures ◽  
High Spin State ◽  
Spectroscopic Studies ◽  
Axial Ligand ◽  
Ligand Field ◽  
Central Metal ◽  
Exchange Reactions ◽  
Dichloromethane Solution

The chlorido iron(III) complex of octaethyl-2,2′-bidipyrrin has been transformed to a series of pseudohalide complexes by ligand exchange reactions with azide, cyanate, thiocyanate and selenocyanate anions. All new complexes show the expected N-coordination of the axial ligand to the iron(III) center. In the solid state, all four species display an intermediate spin (S = 3/2) ground state, with a gradual increase of a high spin (S = 5/2) contribution at elevated temperatures for the members with the smallest ligand field strengths, i.e. the cyanato and the azido derivatives. In solution, proton NMR, and in particular IR spectroscopic studies support the interpretation of a high-spin state at ambient temperature throughout the series. The dependency of the spin state on the crystalline or dissolved state thus resembles that found for a similar series of halide derivatives before. In dichloromethane solution, the thiocyanato and selenocyanato complexes are very sensitive to aerial oxidation, forming oxacorrole and thiacorrole complexes as the only isolated products. These complexes show a S = 3/2 spin state in the solid as well as in solution, and their structural analyses prove the expected strong π-binding of the linear pseudohalide ion to the iron(III) central metal.

scholarly journals Cross-Linker Control of Vitrimer Flow

2020 ◽  
Author(s):  
Bassil El-Zaatari ◽  
Jacob Ishibashi ◽  
Julia Kalow
Keyword(s):  
Stress Relaxation ◽  
Elevated Temperatures ◽  
Bulk Material ◽  
Relaxation Rates ◽  
Exchange Reactions ◽  
Activation Barriers ◽  
Flow Activation Energy ◽  
Wide Range ◽  
Cross Linker ◽  
Frequency Sweeps

<div><p>Vitrimers are a class of covalent adaptable networks (CANs) that undergo topology reconfiguration via associative exchange reactions, enabling reprocessing at elevated temperatures. Here, we show that cross-linker reactivity represents an additional design parameter to tune stress relaxation rates in vitrimers. Guided by calculated activation barriers, we prepared a series of cross-linkers with varying reactivity for the conjugate addition—elimination of thiols in a PDMS vitrimer. Surprisingly, despite a wide range of stress relaxation rates, we observe that the flow activation energy of the bulk material is independent of the cross-linker structure. Superposition of storage and loss moduli from frequency sweeps can be performed for different cross-linkers, indicating the same exchange mechanism. We show that we can mix different cross-linkers in a single material in order to further modulate the stress relaxation behavior.</p></div>

Metathesis of methyl 10-undecenoate

1984 ◽  
Vol 49 (8) ◽  
pp. 1736-1745 ◽  
Author(s):  
Hynek Balcar ◽  
Alena Dosedlová ◽  
Vladimír Hanuš ◽  
Lidmila Petrusová ◽  
Bohumír Matyska
Keyword(s):  
Maximum Degree ◽  
Catalyst Deactivation ◽  
Initial Rate ◽  
Catalyst System ◽  
The Other ◽  
Metathesis Reaction ◽  
Tungsten Atom ◽  
Active Centre ◽  
Oxygen Ligand ◽  
Tungsten Hexachloride

The metathesis of methyl 10-undecenoate was studied using the WCl6 + (CH3)4Sn catalyst system. The rate of metathesis and the maximum degree of conversion are affected markedly by the reactions of the ester, and of the other oxygen compounds if present, with tungsten hexachloride. Introduction of an oxygen ligand to the central tungsten atom of the active centre increases the reactivity and stability of the latter, thus affecting positively the initial rate of the metathesis reaction. At the same time, however, the rate of the catalyst deactivation increasing concentration of the ester, whereupon the degree of the conversion decreases. As a result of competition of the two effects, a maximum appears in the dependence of the amount of the ester reacted on the ester-to-tungsten hexachloride ratio.

Mechanism of the HF Pulse in the Thermal Atomic Layer Etch of HfO2 and ZrO2: A First Principles Study

2019 ◽  
Author(s):  
Rita Mullins ◽  
Suresh Natarajan ◽  
Simon D. Elliott ◽  
Michael Nolan
Keyword(s):  
First Principles ◽  
Ligand Exchange ◽  
Elevated Temperatures ◽  
Atomic Layer ◽  
Level Control ◽  
Exchange Reactions ◽  
Nanoscale Device ◽  
High K ◽  
Reaction Models ◽  
High K Materials

<div>HfO2 and ZrO2 are two high-k materials that are important in the down-scaling of semiconductor devices. Atomic level control of material processing is required for fabrication of thin films of these materials at nanoscale device sizes. Thermal Atomic Layer Etch (ALE) of metal oxides, in which up to one monolayer of the material can be removed, can be achieved by sequential self-limiting fluorination and ligand-exchange reactions at elevated temperatures. However, to date a detailed atomistic understanding of the mechanism of thermal ALE of these technologically important oxides is lacking. In this paper, we investigate the hydrogen fluoride pulse in the first step in the thermal ALE process of HfO2 and ZrO2 using first principles simulations. We introduce Natarajan-Elliott analysis, a thermodynamic methodology, to compare reaction models representing the self-limiting (SL) and continuous spontaneous etch (SE) processes taking place during an ALE pulse. Applying this method to the first HF pulse on HfO2 and ZrO2 we found that thermodynamic barriers impeding continuous etch are present at ALE relevant temperatures. We performed explicit HF adsorption calculations on the oxide surfaces to understand the mechanistic details of the HF pulse. A HF molecule adsorbs dissociatively on both oxides by forming metal-F and O-H bonds. HF coverages ranging from 1.0 0.3 to 17.0 0.3 HF/nm2 are investigated and a mixture of molecularly and dissociatively adsorbed HF molecules is present at higher coverages. Theoretical etch rates of -0.61 0.02 Å /cycle for HfO2 and -0.57 0.02 Å /cycle ZrO2 were calculated using maximum coverages of 7.0 0.3 and 6.5 0.3 M-F bonds/nm2 respectively (M = Hf, Zr).</div>

Ultrafast and Reversible Multiblock Formation by the SET-Nitroxide Radical Coupling Reaction

2010 ◽  
Vol 63 (8) ◽  
pp. 1227 ◽  
Author(s):  
Jakov Kulis ◽  
Craig A. Bell ◽  
Aaron S. Micallef ◽  
Michael J. Monteiro
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Elevated Temperatures ◽  
Click Reaction ◽  
Coupling Reaction ◽  
Nitroxide Radical ◽  
Self Healing ◽  
Exchange Reactions ◽  
Radical Coupling ◽  
End Groups

The single electron transfer-nitroxide radical coupling (SET-NRC) reaction has been used to produce multiblock polymers with high molecular weights in under 3 min at 50°C by coupling a difunctional telechelic polystyrene (Br-PSTY-Br) with a dinitroxide. The well known combination of dimethyl sulfoxide as solvent and Me6TREN as ligand facilitated the in situ disproportionation of CuIBr to the highly active nascent Cu0 species. This SET reaction allowed polymeric radicals to be rapidly formed from their corresponding halide end-groups. Trapping of these carbon-centred radicals at close to diffusion controlled rates by dinitroxides resulted in high-molecular-weight multiblock polymers. Our results showed that the disproportionation of CuI was critical in obtaining these ultrafast reactions, and confirmed that activation was primarily through Cu0. We took advantage of the reversibility of the NRC reaction at elevated temperatures to decouple the multiblock back to the original PSTY building block through capping the chain-ends with mono-functional nitroxides. These alkoxyamine end-groups were further exchanged with an alkyne mono-functional nitroxide (TEMPO–≡) and ‘clicked’ by a CuI-catalyzed azide/alkyne cycloaddition (CuAAC) reaction with N3–PSTY–N3 to reform the multiblocks. This final ‘click’ reaction, even after the consecutive decoupling and nitroxide-exchange reactions, still produced high-molecular-weight multiblocks efficiently. These SET-NRC reactions would have ideal applications in re-usable plastics and possibly as self-healing materials.

scholarly journals Chloride Ion Catalysed Rearrangement, and Isotope Exchange of the Isomeric Methylallyl Chlorides in Acetonitrile

2021 ◽  
Author(s):  
◽  
Jacqueline Ann Hemmingson
Keyword(s):  
Kinetic Data ◽  
Isotope Exchange ◽  
Elevated Temperatures ◽  
Reaction Medium ◽  
Chloride Ion ◽  
Chloride Ions ◽  
Nucleophilic Attack ◽  
Elimination Reaction ◽  
Exchange Reactions ◽  
Rearrangement Reaction

<p><b>The bromide ion catalysed rearrangement reaction of ⍺-methylallyl bromide in acetone was studied by England and Hughes and assigned an S[n]2' mechanism, and this was the only isomeric rearrangement reaction proceeding by this mechanism which had been thoroughly investigated. 79,120 The kinetics and mechanism of the chloride ion catalysed isomeric rearrangement reactions of ⍺-and ɣ-methylallyl chloride in acetonitrile have now been investigated and an S[n]2' mechanism has been assigned to these reactions, various other possible mechanisms having been excluded. The kinetics and mechanics of the isotope exchange reactions of the two isomers in acetonitrile have also bean studied and these reactions have been assigned en S[n]2 mechanism. The isotope exchange reactions of both the methylallyl bromides and the methylallyl chlorides in acetone were studied by England and Hughes, the reaction medium being unfavourable for a study of the S[n]2' reactions of the latter substrates. A comparison of the kinetic data for the rearrangement end Isotope exchange reactions of the methylallyl chlorides in acetonitrile with that for the corresponding reactions of the methylallyl bromides in acetone la made. The two systems are similar in behaviour as may be seen from the data tabulated below.</b></p> <p>Substrate Mechanism K2 (25° C) Δ H°Δ S° (M⁻¹ sec.⁻¹) (kcal.mole⁻¹) (cal.deg.⁻¹ mole⁻¹)⍺-methylallyl chloride S[n]2 2.87X10⁻⁶ 20.8-13.9⍺-methylallyl chloride S[n]2'1.33X10⁻⁸ 24.2-13.4ɣ-methylallyl chlorideS[n]2 3.15X10⁻⁴ 18.8-11.6ɣ-methylallyl chloride S[n]2' 5.31X10⁻⁹ 24.3-14.9⍺-methylallyl bromide S[n]2 8.79X10⁻⁴ 15.9-19.1⍺-methylallyl bromide S[n]2' 1.49X10⁻⁵ 18.8-17.7ɣ-methylallyl bromide S[n]2 1.41X10⁻¹ 14.1-15.0⍺-methylallyl chloride S[n]2 2.30X10⁻⁷ 19.9-22.1ɣ-methylallyl chloride S[n]2 2.88X10⁻⁵ 15.8-26.2A comparison of the kinetic data for the isotope exchange reactions of the methylallyl chlorides in acetonitrile and acetone is also made. England and Hughes' data for the latter solvent is shown above. Relative rates of nucleophilic attack at saturated carbon, π-bonded carbon and hydrogen are discussed for these substrates, a minor concurrent elimination reaction accompanying the S[n]2' reaction of ⍺-methylallyl chloride in acetonitrile providing information on the latter. The nucleophilic reactivity of the halide ions is much greater for attack at a saturated carbon atom than for attack at a π-bonded carton atom, while toward hydrogen these ions are very weak nucleophiles as shown by the rate ratios given below for the chloride ion catalysed reactions of ⍺-methylallyl chloride in acetonitrile.</p> <p>[see thesis pdf for formula]In the absence of chloride ions a slow surface-catalysed elimination reaction takes place which promotes hydrogen chloride catalysed rearrangement. The addition of 0.05M Et4 NCl prevents the latter reaction from occurring and gives a rata ratio of 5.5 for the chloride ion catalysed and surface-catalysed elimination reactions. By comparison with other dipolar aprotic solvents, acetonitrile appears to be particularly suitable for slow reactions requiring prolonged reaction times at elevated temperatures. Acetone, as mentioned above, and both dimethyl sulphoxide and dimethylformamide were found to be unsuitable for S[n]2' studies, the latter two being: Investigated during the search for a suitable solvent in which to study the reactions of the methylallyl chlorides.</p>

CYCLOBUTADIENE–METAL COMPLEXES: PART VIII. SYNTHESIS OF TETRAPHENYLCYCLOBUTADIENE NICKEL HALIDES BY LIGAND-EXCHANGE REACTIONS

1966 ◽  
Vol 44 (22) ◽  
pp. 2673-2677 ◽  
Author(s):  
D. F. Pollock ◽  
P. M. Maitlis
Keyword(s):  
Metal Complex ◽  
Metal Complexes ◽  
Ligand Exchange ◽  
Palladium Complexes ◽  
Exchange Reactions ◽  
Reaction Proceeds ◽  
Halide Complexes

The preparation of cyclobutadiene nickel halide complexes (R4C4NiX2)2, where R is phenyl or substituted phenyl, by reaction of the palladium complexes, [R4C4PdX2]2, with a tert-phosphine metal complex, e.g. (n-Bu3P)2NiX2, is described. The reaction proceeds according to the equation[Formula: see text]Possible mechanisms are suggested.

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