Mechanism of the oxidative carbonylation of terminal alkynes at the ≡C-H bond in solutions of palladium complexes

The formation mechanism of the active catalyst in the oxidative carbonylation of terminal alkynes at the ≡C-H bond has been investigated for the catalytic system Pd(OAc)₂-PPh₃-p-benzoquinone (Q)-MeOH. It has been demonstrated by NMR spectroscopy, X-ray crystallography, and kinetic measurements that the catalytically active palladium is in the oxidation state 0 and is bound into complexes stabilized by p-benzoquinone (PdL₂Q, where L = PPh₃). A mechanism is suggested for the catalytic process, which includes the formation of the complex PdL₂Q, the oxidative addition of the alkyne to this complex at the ≡C-H bond, the insertion of CO into the Pd-C bond, and steps in which hydride hydrogen is intramolecularly transferred to the p-quinone.     

Ethylene and Cyclohexene Oxidation by p-Benzoquinone,Hydrogen Peroxide,and Oxygen in the Solutions of Cationic Pd(II) Complexes in Acetonitrile–Water and Ionic Liquid–Water Binary Solvents

Kinetics and Catalysis - Optimal conditions are selected for ethylene and cyclohexene oxidation reactions in the acetonitrile (AN)–water system in the presence of...     

New catalytic systems for oxidative carbonylation of acetylene to maleic anhydride

A classification of polyfunctional catalytic systems based on discrimination of the main component (the catalyst participating in all stages of the formation of the product of catalytic reaction) and elucidating the functions of additional components of a catalytic system is suggested. The role of additional components in a number of new palladium-based catalytic systems used in the synthesis of maleic anhydride by oxidative carbonylation of acetylene was studied. It was established that the functions of Co and Fe phthalocyanine complexes (PcCo and Pc^*Fe, respectively) in the mechanism of the process are different. Translated fromIzvestia Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1899–1905, October, 1999.     

Coupled processes in carbon monoxide oxidation: Kinetics and mechanism of CO oxidation by oxygen in PdX<Subscript>2</Subscript>-organic solvent-water systems

PdX₂-organic solvent-water solutions, where X = halide (preferably bromide or iodide) and the organic solvent is 1,4-dioxane or tetrahydrofuran, are suggested as catalytic systems for CO oxidation. A number of coupled processes take place in these systems. The kinetics and mechanism of CO oxidation by oxygen in the PdI₂-LiI-1,4-dioxane-water system are reported. Cyclohexene hydrocarboxylation into cyclohexanecarboxylic acid can be carried out as part of the coupled process occurring in the PdBr₂-tetrahydrofuran-water system.     

The state of palladium and copper bromides in the PdBr2-CuBr2-THF-H2O system used in the conjugated process of cyclohexanecarboxylic acid production

The state of bromide complexes of palladium and copper in model solutions and under conditions of the conjugated catalytic synthesis of cyclohexanecarboxylic acid by the hydrocarboxylation of cyclohexene is studied by electron and infrared spectroscopy. It is found that during the conjugated process, copper exists in the form of copper(I) compounds, and palladium is present in the form of palladium(II) carbonyl complex.     

Mechanisms of synthesis of maleic and succinic anhydrides by carbonylation of acetylene in solutions of palladium complexes

The mechanism of synthesis of maleic and succinic anhydrides from acetylene and CO in the PdBr₂−LiBr-organic solvent catalytic system was studied using the procedure of advancement and discrimination of hypotheses. The hypotheses were obtained using the data bank on elementary steps and the Combl combinatorial program. The discrimination of the hypotheses was based on the data of NMR and IR spectroscopy, studies of isotope exchange, the role of potential organic intermediates, the kinetic isotope effect, and one-factor kinetic experiments. The most probable mechanism of synthesis of maleic anhydride includes insertion of acetylene and CO into the Pd−Pd bond of the Pd^I complex, which is formed from Pd^II at the initial step of the process. Succinic anhydride results from the intramolecular transformation of the hydride complex of palladium and maleic anhydride. The palladium hydride complexes detected in the contact solution apparently play the crucial role in the conjugation of oxidation, reduction, and addition type reactions. Dedicated to the memory of Academician M. E. Vol'pin timed to his 75th birthday. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1104–1115, June, 1998.     

Synthesis and structure of a product of interaction of acetonitrile with hydrogen bromide, [H2N=C(Me)−NH−C(Me)Br2]Br

A mixture of solid products was obtained upon absorption of dry HBr by MeCN. One of the products, [H₂N=C(Me)−NH−C(Me)Br₂]Br, was isolated as white single crystals and characterized by X-ray diffraction analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2274–2277, November, 1998.     

Kinetics and mechanism of the low-temperature oxidation of carbon monoxide with oxygen on a PdCl<Subscript>2</Subscript>–CuCl<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

A systematic study of the kinetics of the low-temperature oxidation of carbon monoxide with oxygen on a PdCl₂–CuCl₂/γ-Al₂O₃ supported catalyst was carried out over a wide range of the partial pressures of oxygen, water, and CO in order to test hypotheses on the reaction mechanism. It was shown that, as the temperature was increased from 20 to 38°C, rate of formation of CO₂ decreased and the apparent activation energy was about–40 kJ/mol. The hypotheses of different degrees of complexity concerning the reaction mechanism were formulated based on physicochemical data and a Langmuir–Hinshelwood model. Mechanisms in which carbon dioxide is formed on the interaction of the surface Pd(I) and Pd(II) complexes that include carbon monoxide and water with the surface complex of Cu(I) that coordinates oxygen were recognized as the most probable.     

Kinetics and mechanism of carbon monoxide oxidation on the supported metal complex catalyst PdCl<Subscript>2</Subscript>-CuCl<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The kinetics of carbon monoxide oxidation with atmospheric oxygen on a PdCl₂-CuCl₂/γ-Al₂O₃ catalyst was studied at T = 27°C and an N₂-O₂-CO mixture pressure of 1 atm. The catalyst was prepared by cold impregnation. Three groups of mechanistic hypotheses are considered, and two of them are demonstrated to be consistent with kinetic data, although they differ in the roles of water and oxygen in carbon monoxide oxidation.     

State of active components on the surface of the PdCl<Subscript>2</Subscript>-CuCl<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for the low-temperature oxidation of carbon monoxide

The state of the active constituents of the freshly prepared PdCl₂-CuCl₂/γ-Al₂O₃ catalyst for the low-temperature oxidation of the carbon monoxide by molecular oxygen was studied by X-ray absorption spectroscopy (XAS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and diffuse reflectance IR Fourier transform spectroscopy (DRIFTS). It was shown that copper in the form of a crystalline phase of Cu₂Cl(OH)₃ with the structure of the mineral paratacamite and palladium chloride in an amorphous state occurred on the surface of γ-Al₂O₃. According to XAS data, the local environment of palladium consisted of four chlorine atoms, which formed a flat square with an increased distance between palladium and one of the chlorine atoms. The evolution of the local environments of copper and palladium upon a transition from the initial salts to the impregnating solutions and chlorides on the surface of γ-Al₂O₃ was considered. The role of γ-Al₂O₃ in the formation of the Cu₂Cl(OH)₃ phase was discussed. It was found by the DRIFTS method that linear (2114 cm⁻¹) and bridging (1990 and 1928 cm⁻¹) forms of coordinated carbon monoxide were formed upon the adsorption of CO on the catalyst surface. The formation of CO₂ upon the interaction of coordinated CO with atmospheric oxygen was detected. Active sites including copper and palladium were absent from the surface of the freshly prepared catalyst.