The mechanism of the hydroalkoxycarbonylation of ethene and alkene-CO copolymerization catalyzed by Pd(II)-diphosphine cations

All the intermediates in the "carboalkoxy" pathway, and their interconversions giving complete catalytic cycles, for palladium-diphosphine-catalyzed hydroalkoxycarbonylation of alkenes, and for alkene-CO copolymerization, have been demonstrated using (31)P{(1)H} and (13)C{(1)H} NMR spectroscopy. The propagation and termination steps of the "hydride" cycles and the crossover between the hydride and carboalkoxy cycles have also been demonstrated, providing the first examples of both cycles, and of chain crossover, being delineated for the same catalyst. Comparison of the propagation and termination steps in the pathways affords new insight into the selectivity-determining steps. Thus, reaction of [Pd(dibpp)(CH(3)CN)(2)](OTf)(2) (dibpp = 1,3-(iBu(2)P)(2)C(3)H(6)) with Et(3)N and CH(3)OH affords [Pd(dibpp)(OCH(3))(CH(3)CN)]OTf, which, on exposure to CO, gives [Pd(dibpp){C(O)OCH(3)}(CH(3)CN)]OTf immediately. Labeling studies show the reaction to be readily reversible. However, the back reaction is strongly inhibited by PPh(3), indicating an insertion/deinsertion pathway. Ethene reacts with [Pd(dibpp){C(O)OCH(3)}(CH(3)CN)]OTf at 243 K to give [Pd(dibpp){CH(2)CH(2)C(O)OCH(3)}]OTf, that is, there is no intrinsic barrier to alkene insertion into the Pd--C(O)OMe bond, as had been proposed. Instead, termination is proposed to be selectivity determining. Methanolysis of the acyl intermediate [Pd(dibpp){C(O)CH(3)}L]X (L = CO, CH(3)OH; X = CF(3)SO(3) (-) (OTf(-)), CH(3)C(6)H(4)SO(3) (-) (OTs(-))) is required in the hydride cycle to give an ester and occurs at 243 K on the timescale of minutes, whereas methanolysis of the beta chelate, required to give an ester from the carbomethoxy cycle, is slow on a timescale of days, at 298 K. These results suggest that slow methanolysis of the beta chelate, rather than slow insertion of an alkene into the Pd--carboalkoxy bond, as had previously been proposed, is responsible for the dominance of the hydride mechanism in hydroalkoxycarbonylation.     

Mechanism of aziridination of styrene catalyzed by copper(I) bis(oxazoline)

Experimental studies show that copper complexes can be effectively anchored onto the pores of mesoporous solids, having a good catalytic performance in several reactions, among them the aziridination of olefins and in particular, styrene. In this work, the mechanism of the aziridination of styrene catalyzed by a bis(oxazoline) copper(I) complex was studied in detail by means of density functional theory (DFT) calculations. For such reactions in the homogeneous phase, our calculations revealed a wide diversity of reaction‐pathways, which have not been considered in previous studies, and should be taken into account due to the small energy differences between them. What is more, our results show that there is a strong dependence on the chosen DFT functional. This has profound implications on the way the heterogeneous reaction is studied. © 2013 Wiley Periodicals, Inc.     

Kinetics and mechanism of grafting of undecylenic acid onto acrylonitrile–butadiene–styrene terpolymer

The graft copolymerization of undecylenic acid onto acrylonitrile–butadiene–styrene terpolymer (ABS) was initiated with benzoyl peroxide (BPO) in a 1,2‐dichloroethane solution. IR spectra confirmed that undecylenic acid was successfully grafted onto the ABS backbone. The influence of the concentrations of undecylenic acid, BPO, and ABS on the graft copolymerization was studied. A reaction mechanism was proposed: the grafting most likely took place through the addition of poly(undecylenic acid) radicals to the double bond of the butadiene region of ABS. A monomer cage effect on the graft reaction was observed to depend on the 1.5 power of the monomer concentration from the experimental results of the initial rate of graft copolymerization. The initial rate of graft copolymerization was written as R_p = 1.77 × 10⁻³[P][I₂][M]^2.5/([P]+2.75[M]^2.5)². © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 486–494, 2001     

Elucidating the mechanism of the asymmetric aza-Michael reaction

The mechanism of the palladium-catalysed asymmetric aza-Michael addition of aniline to alpha,beta-unsaturated N-imide was examined from several aspects using a combination of techniques, including X-ray crystallography, mass spectrometry, NMR, UV/Vis spectroscopy, and kinetic studies. The binding of aniline to the dicationic palladium(II) metal centre was found to occur in two consecutive steps: The binding of the first aniline is fast and reversible, whereas the binding of the second aniline is slower and irreversible. This occurs in competition with the binding of the N-imide, which forms a planar six-membered chelate ring with the metal centre; coordinating through the 1,3-dicarbonyl moiety. Isotopic labelling revealed that the addition of N-H occurs in a highly stereoselective manner, allowing the synthesis of optically active beta(2)- and beta(2,3)-amino acid derivatives. The stereochemistry of the addition is postulated to be syn. In situ kinetic studies provided evidence for product inhibition. The binding of the N-imide to the catalyst was found to be the rate-limiting step. Aniline was found to be an inhibitor of the pre-catalyst. The study culminated in the design of a new reaction protocol. By maintaining a low concentration of the aniline substrate during the course of the reaction, significant enhancement of yield and enantioselectivity can be achieved.     

Kinetics and mechanism of electroreduction of Pd(II) complexes

The kinetics and mechanism of processes of reduction of Pd(II) complexes with a number of inorganic (NH₃ , Cl^– , etc.) and organic (ethylenediamine, glycine, -alanine, etc.) ligands on a dropping-mercury electrode and a Pd electrode in solutions with various concentrations of ligands, hydrogen ions, and supporting electrolytes are reviewed. The nature of electrochemical and chemical steps of processes of reduction of various complexes of Pd(II) is discussed.Translated from Elektrokhimiya, Vol. 40, No. 12, 2004, pp. 1494–1502.Original Russian Text Copyright © 2004 by Kravtsov.     

Kinetics and mechanism of phosphorylation of monoethanolamine in reversed micelles of a cationic surfactant

The reactions of monoethanolamine with 4-nitrophenyl esters of tetracoordinated phosphorus acids in chloroform in the presence of 2-hydroxyethyldimethylpentadecylammonium bromide were studied. The effective rate constants of the reactions are increased by more than two orders of magnitude in the presence of the micelle-forming cationic surfactant. The latter also favors the formation of the product ofO-phosphorylation of monoethanolamine and leads to the appearance of a new ionic form of the 4-nitrophenol-monoethanolamine complex. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 280–283, February, 1998.     

Kinetics of alkaline hydrolysis of esters of phosphorus acids in micellar and hexagonal phases in the cetyldimethylethylammonium bromide—NaOH—water system

The influence of micellar (Mi) and hexagonal (E) mesophases of the cetyldimethylethylammonium bromide—NaOH—water system (I) on the rates on alkaline hydrolysis ofO-p-nitrophenyl-O,O-diethyl phosphate (2),O-p-nitrophenyl-O-ethylethyl phosphonate (3), andO,O-di(p-nitrophenyl)methyl phosphonate (4) was studied by UV spectrophotometry. The binding constants of the substrates, critical micelle concentrations, and rate constants of reactions in the micellar phase were determined. In micellar solutions of systemI, a tenfold increase in the rates of alkaline hydrolysis of2–4 was observed. An increase in the degree of medium ordering during the formation of the E-phase results in a twofold acceleration of alkaline hydrolysis of2 and3 and in the inhibition of this process in the case of4. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1499–1504, August, 1998.     

Kinetics and reaction mechanism of phenol hydroxylation catalyzed by La-Cu_4FeAlCO_3

Phenol hydroxylation is an industrially important reaction, whose main products are catechol and hy-droquinone being diverse applications which are im-portant intermediates for perfumes, drugs, and phar-maceuticals and so on[1]. The processes using H2O2 a…     

A convenient synthesis of fluoroalkylated γ-butyrolactones from polyfluoroalkyl iodides and 4-pentenoic acid catalyzed by Pd(PPh3)4

A convenient synthesis of fluoroalkylated γ-butyrolactones was realized through the reaction of fluoroalkyl iodides with 4-pentenoic acid in the presence of catalytic amounts of tetrakis(triphenylphosphine)palladium and sequential treatment with triethylamine in 79-85% yields.     

聚醚桥连二异羟肟酸配合物催化羧酸酯水解的动力学研究

研究羧酸酯和磷酸酯的水解在环境和生物应用等方面具有越来越重要的意义。为实现对环境友好、高经济效益的生产过程,许多研究者致力于研发反应条件温和、催化效率高和高度专一性的催化剂。因而,仿酶研究倍受人们的关注,其中,水解金属酶是被研究得较为广泛的一类。我们曾报道过异羟肟酸过渡金属配合物仿生催化氧化性能和二氧亲合性能。本文我们将4种聚醚桥连二异羟肟酸过渡金属铜（Ⅱ）、锌（Ⅱ）、钴（Ⅱ）和锰（Ⅱ）配合物（见图1）作为仿水解酶模型,在底物浓度高于催化剂浓度10倍以上的条件下,研究了配合物在缓冲溶液中催化α-吡啶甲酸对硝基苯酯（PNPP）的水解反应的机理,并建立了相应的动力学数学模型;考查了配合物中心金属离子、溶液酸度和反应温度等对催化PNPP水解反应性能的影响。     

Synthesis of 3,4-bis(2,5-dimethyl-3-thienyl)furan-2,5-dione from mucobromic acid

Palladium-catalyzed cross-coupling between 2,5-dimethyl-3-thienylboronic and mucobromic acids under phase transfer catalysis (PTC) conditions gave the expected 3,4-bis(2,5-dimethyl-3-thienyl)-5-hydroxyfuran-2-one in 32% yield. The by-product was 2,2’,5,5’-tetramethyl-3,3’-bithiophene. The oxidation of the obtained hemiacylal with potassium permanganate under PTC conditions afforded 3,4-bis(2,5-dimethyl-3-thienyl)furan-2,5-dione in high yield.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2238–2240, October, 2004.     

Synthesis and transformations of metallacycles. 27. Quantum-chemical study of the mechanism of styrene catalytic cyclometallation with triethylaluminum in the presence of Cp2ZrCl2

Cyclometallation of olefins with AlEt₃ in the presence of Cp₂ZrCl₂ affording five-membered monosubstituted cyclic organoaluminum compounds, was studied by the semiempirical quantum-chemical PM3 method. The proposed model of catalytic cycloalumination of styrene catalyzed by Cp₂ZrCl₂ is in a good accordance with experimental data obtained by dynamic NMR spectroscopy.     

Allylation of prochiral C-nucleophiles catalyzed by the Pd(0)—(<Emphasis Type="Italic">S</Emphasis>)-(—)-BINAP complex

The allylation of prochiral C-nucleophiles catalyzed by the Pd(0)—(S)-(—)-BINAP complex (BINAP is 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) was studied. The enantioselectivity of the allylation was found to be low. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1753—1755, August, 2008.     

Kinetics and mechanism of styrene hydroalkoxycarbonylation catalyzed by the complex PdCl2(Ph3P)2 in the presence of butanol

The single-factor experiment method was used to study the kinetics of styrene hydrobutoxycarbonylation catalyzed by the complex PdG₂(Ph₃P)₂ in dioxane (383 K, [BuOH] = 1–8 mol/1). The rates of accumulation of the regioisomeric reaction products as empirical functions of CO pressure and concentrations of styrene, triphenylphosphine, and the catalyst were found. The acyl complex (PhC₂H₄CO)PdCl(Ph₃P)₂ was isolated from the reaction mixture. The assumed intermediate of an alcoholate mechanism, the (BuOOC)PdCl(Ph₃P)₂ complex, is not formed by the reaction of PdCl₂(Ph₃P)₂ with CO and butanol. The set of data generally corresponds to a hydride mechanism of styrene hydrocarboxylation, which includes three key intermediates HPdCIL_2-n(CO)_n (n= 0–2). A change in the solvation properties of the reaction medium due to the replacement of water by butanol affects the kinetic scheme of the process.     

Codimerization of quadricyclane withendo,exo-hexacyclo[9.2.1.02,10.03,8.04,6.05,9]tetradec-12-ene catalyzed by the Pd(PPh3)4 complex

endo,exo-Hexacyclo[9.2.0^2,10.0^3,8.0^4,6.0^5,9]tetradec-12-ene (1) undergoes cyclocodimerization with quadricyclane (Q) in the presence of the Pd(PPh₃)₄ complex to giveexo,exo,endo,exo-decacyclo[9.9.1.0^2,10.0^3,8.0^4,6.0^5,9.0^12,20.0^13,18.0^14,16.0^15,19]heneicosane (2) andendo,exo,endo,exo-decacyclo[9.9.1.0^2,10.0^3,8.0^4,6.0^5,9.0^12,20.0^13,18.0^14,16.0^15,19]heneicosane (3) in a ratio of 10 7 (yield up to 26 %). Simultaneously, homocyclotrimerization of Q occurs to give three known C₂₁ hydrocarbons (4–6). The yields of compounds2 and3 and the selectivity of the process depend considerably on the reaction conditions and the molar ratio of1 and Q. Compounds2 and3 that were obtained were characterized by¹³C NMR spectra.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1983–1985, November, 1994.     

Mechanism of hydrolysis of azalactones catalyzed by a complex of Cu(II) with (S)-2-[(N-benzylpropyl)amino]benzaldoxime

The hydrolysis of 2-methyl-4-benzyl-5(4H)oxazolone (MBA) in a mixture of water and MeCN has been studied — both the spontaneous reaction and that catalyzed by a complex of Cu(II) with (S)-2-[(N-benzylpropyl)amino]benzaldoxime (1). It has been shown that the complex 1 is an effective catalyst for the hydrolysis of MBA (chymotrypsin does not catalyze MBA hydrolysis). The mechanism of MBA hydrolysis catalyzed by this complex includes the formation of a mixed catalyst—substrate complex in which the MBA is coordinated with the metal ion through the N ³ atom. It is suggested that the oxygen atom of the ionized oxime group in such a complex attacks the imine C ² atom of the MBA intramolecularly; this is the rate-determining stage. The change in the order of hydrolysis with respect to the catalyst from 1 to 1/2 when the concentration of 1 is increased indicates that the complex catalyst exists in aqueous solution in two forms, dimeric and monomeric, which are in equilibrium, and only the monomeric form of the complex is responsible for the catalysis. With an excess of the substrate we observe inhibition of the MBA hydrolysis — possibly an indirect indication of participation in the transition state by a water molecule coordinated in an apical position of the complex, which is displaced by excess substrate.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, Moscow 117813. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 536–546, March, 1992.     

Atom transfer radical polymerization of styrene and methyl methacrylate catalyzed by FeCl2/iminodiacetic acid

The atom transfer radical polymerization of styrene and methyl methacrylate with FeCl₂/iminodiacetic acid as the catalyst system in bulk was successfully implemented at 70 and 110 °C, respectively. The polymerization was controlled: the molecular weight of the resultant polymer was close to the calculated value, and the molecular weight distribution was relatively narrow (weight‐average molecular weight/number‐average molecular weight ∼ 1.5). Block copolymers of polystyrene‐b‐poly(methyl methacrylate) and poly(methyl methacrylate)‐b‐poly(methyl acrylate) were successfully synthesized, confirming the living nature of the polymerization. A small amount of water added to the reaction system increased the reaction rate and did not affect the living nature of the polymerization system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4308–4314, 2000