Influence of the reaction parameters on the Pd—HCl catalysed synthesis of phenylacetic acid derivatives via reduction of mandelic acid derivatives with carbon monoxide

The catalytic system Pd/C—HCl is highly active in the reduction of mandelic acid derivatives to phenylacetic acid derivatives with carbon monoxide when the aromatic ring is para-substituted with a hydroxy group. Typical reaction conditions are: 70–110 °C, 20–100 atm of carbon monoxide, benzene—ethanol as reaction medium, substrate/Pd=10²–10⁴/1, HCl/substrate=0.3–0.8/1. [Pd] = 10⁻² −10⁻⁴ M. When the catalytic system is used in combination with PPh₃ a slightly higher activity is observed. Comparable results are observed when using a Pd(II) catalyst precursor such as PdX₂, in combination with PPh₃, or PdX₂(PPh₃)₂ (XCl, AcO). When operating at 110 °C, decomposition to metallic palladium occurs. Pd(II) complexes with diphosphine ligands, such as diphenylphosphinemethane, -ethane, -propane or -butane, do not show any catalytic activity and are recovered unchanged. These observations suggest that Pd(0) complexes play a key role in the catalytic cycle. The proposed catalytic cycle proceeds as follows: the chloride ArCHClCOOR, formed in situ upon reaction of ArCHOHCOOR with hydrochloric acid, oxidatively adds to a Pd(0) species with formation of a catalytic intermediate having a Pd—[CH(Ar)COOR] moiety, which inserts a CO molecule, yielding an acyl intermediate of the type Pd—[COCH(Ar)COOR]. The nucleophilic attack of H₂O on the carbon atom of the carbonyl ligand gives back the Pd(0) complex to the catalytic cycle and yields a phenylmalonic acid derivative, which produces the final product, ArCH₂COOR, upon CO₂ evolution. Alternatively, protonolysis of the intermediate having a Pd—[CH(Ar)COOR] moiety yields directly the final product and a Pd(II) species, which is then reduced by CO to Pd(0). Moreover, no catalytic activity is observed when the Pd/C—HCl system is used in combination with any one of the above diphosphine ligands, probably because these ligands block the sites on the catalyst able to promote the catalytic cycle or because they prevent the reduction of Pd(II) to Pd(0). The influence of the following reaction parameters has been studied: concentration of HCl, PPh₃, palladium and substrate, pressure of carbon monoxide, the temperature, reaction time and solvent. The results are compared with those obtained in the carbonylation of aromatic aldehydes to phenylacetic acid derivatives catalyzed by the same system, for which it has been proposed that the catalysis occurs via carbonylation of the aldehyde to a mandelic acid derivative as an intermediate, which is further reduced with CO to yield the final product.     

Catalytic activity of Pd(II) and Pd(II)/DAB-R systems for the Heck arylation of olefins

Palladium-catalyzed reactions of aryl bromides with various olefins involving Pd(II)/diazabutadiene (DAB-R) systems have been investigated. The scope of a coupling process using Pd(II) sources and an α-diimine as ligand in the presence of Cs₂CO₃ as base was tested using various substrates. The Pd(OAc)₂/DAB-Cy (1, DAB-Cy=1,4-dicyclohexyl-diazabutadiene) system presents the highest activity with respect to electron-neutral and electron-deficient aryl bromides in coupling with electron rich olefins. The synthesis and X-ray characterization of a Pd(II)-diazabutadiene ligand is reported. Extensive optimization experiments showed that another Pd(II) source, Pd(acac)₂ (acac=acetylacetonate), proved to activate aryl bromides at high temperatures, low catalyst loadings when the appropriate concentration of ⁿBu₄NBr additive was employed. The effect of the DAB-Cy ligand is important at very low catalyst loadings and high temperatures. Pd(acac)₂ and Pd(acac)₂/DAB-Cy precatalysts were very effective for the arylation of various olefins with aryl bromides with respect to reaction rate, catalyst loadings, and functional group tolerance.     

A Direct Amination of Isoprene by Aniline – Catalyzed by Palladium Complexes

The reaction of isoprene with aniline, catalyzed by Pd (acac)₂–(RO)₃P‐CF₃COOH, (1:4:4) (R = Me, Et, acac = (CH₃CO)₂CH‐) in MeCN solution, results in high (up to 89 mol.%) selectivity of N–(3‐methyl‐2‐buten‐1‐yl) aniline. The presence of telomeric products in the reaction mixture is observed at a P/Pd ratio of 1:2 and 1:1. The use of (1,1,1‐trifluoro, 4‐perfluorocyclo hexyl ‐2,4‐butanedionato) palladium as the catalyst gives rise to 92 mol% mol.selectivity of telomers by the favored tail‐to‐head and head to head coupling.     

Allyl stannanes as electrophiles or nucleophiles in the palladium-catalyzed reactions with alkynes

The reactivity of the allyl stannanes can be inverted by changing the oxidation state of the catalyst from Pd(II) to Pd(0). Whereas with Pd(II) an anti nucleophilic attack of the allyl stannane on the alkyne takes place, the reaction with Pd(0) proceeds by oxidative addition to form (η³-allyl)palladium complexes leading to a formal syn addition to the alkyne. This mechanistic proposal is supported by DFT calculations.     

One-pot,solvent-free Pd(II)-catalyzed direct β-C-H arylation of carboxamides involving anhydrides as substrates via in situ installation of directing group

A one-pot, multicomponent-type, solvent-free Pd(II)-catalyzed direct β-C-H activation/arylation of carboxamides involving anhydrides as substrates via in situ installation of directing group (DG) is reported. Typically, the DG-assisted β-C-H activation/arylation of carboxamides is a two-step process comprising the installation of DG and Pd(II)-catalyzed CH arylation. We attempted a multicomponent-type reaction comprising an anhydride, a DG (e.g. 8-aminoquinoline), an aryl iodide in the presence of the Pd(II) catalyst and an appropriate additive. Different anhydrides, DGs, aryl iodides, catalysts and additives were screened to reveal the scope of this multicomponent-type CH arylation reaction process and various β-C-H arylated carboxamides were obtained in satisfactory to good yields.     

Synthesis and reactivity of new methylallylpalladium(II) complexes with bidentate 2-(methylthio-N-benzylidene)anilines

This work describes the synthesis, characterisation and reactivity of new methylallyl Pd(II) complexes that contain bidentate 2-(methylthio-N-benzylidene)anilines as ligands. The reaction of the binuclear complex [(η³-Me-allyl)Pd(μ-Cl)₂] with AgBF₄ causes the total abstraction of the chloride bridges, with the subsequent formation of an intermediary fragment of Pd(II). This fragment in turn reacts with neutral bidentate 2-(methylthio-N-benzylidene)anilines to give cationic complexes of Pd(II) of general formula [(η³-Me-allyl)Pd(η²-S,N-MeSC₆H₄NCHC₆H₄(X)Y)]BF₄ [X=H, Y=H (1); X=F, Y=H (2); X=Me, Y=H (3); X=H, Y=Cl (4); X=H, Y=Me₂N (5); X=H, Y=NO₂ (6)]. The new complexes were characterised by means of elemental analysis, IR, NMR [¹H, ¹⁹F{¹H}, ¹³C{¹H}, ³¹P{¹H}, Dept, ¹H-¹H-COSY, HSQC, HMBC] and mass spectroscopies. The reaction of the Pd(II) complexes with nucleophiles such as NaI, (EtO)₂PS₂K, KCN, KSCN or NaH lead to the deco-ordination of the bidentate ligands to give dimeric or polymeric complexes of Pd(II). The reactivity pattern observed is discussed by a theoretical analysis based on Fukui functions.     

Hydroesterification of styrene using an in situ formed Pd(OTs)2(PPh3)2 complex catalyst

Hydroesterification of styrene to 3-phenyl propionate 1, and 2-phenyl propionate 2, has been studied using a Pd(OTs)₂(PPh₃)₂ catalyst formed in situ from Pd(OAc)₂, PPh₃ and p-toluenesulfonic acid (p-tsa). Because of the weakly coordinating properties of the TsO⁻ ligand, the catalyst has vacant coordination sites capable of easy activation of reactants. The presence of water is found to be necessary for the reaction and hydrogen enhances the catalytic activity under certain conditions (with Pd:p-tsa=1). The beneficial effect of hydrogen, p-tsa and water is discussed in terms of favoring the formation of a Pd–H species, which initiates the catalytic cycle through the insertion of styrene into this bond with formation of a Pd-alkyl intermediate, which inserts CO to give a Pd-acyl intermediate, which, upon nucleophilic attack of the alkanol on the carbon atom of the acyl ligand, yields the final product and the starting hydride back to the catalytic cycle. p-tsa would favor the formation of a Pd–H species by reactivating any Pd(0) species that may form during the course of catalysis. Water would favor the formation of a Pd–H species through a reaction closely related to the water–gas shift reaction. The effect of various ligands, promoters, solvents and alcohols on catalytic activity as well as selectivity pattern has been studied. Regioselectivity to the branched product, 2, increases with decrease in basicity of the phosphorous ligands as well as steric bulk around the palladium center and polarity of the medium.     

Encapsulation of Pd(II) into superparamagnetic nanoparticles grafted with EDTA and their catalytic activity towards reduction of nitroarenes and Suzuki–Miyaura coupling

A robust, safe and magnetically recoverable palladium catalyst was synthesized by anchoring Pd(II) onto ethylenediaminetetraacetic acid‐coated Fe₃O₄ (Fe₃O₄@EDTA) magnetic nanoparticles. The Fe₃O₄ magnetic nanoparticle‐supported Pd(II)–EDTA complex catalyst thus obtained was characterized using scanning and transmission electron microscopies, thermogravimetric analysis, vibrating sample magnetometry, X‐ray diffraction, and inductively coupled plasma atomic emission and Fourier transform infrared spectroscopies. Fe₃O₄@EDTA–Pd(II) was screened for the Suzuki reaction and reduction of nitro compounds in water. The Pd content of the catalyst was measured to be 0.28 mmol Pd g^?1. In addition, the Fe₃O₄@EDTA–Pd catalyst can be easily separated and recovered with an external permanent magnet. The anchored solid catalyst can be recycled efficiently and reused five times with only a very slight loss of catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Nd（OprI）2Cl－AlEt_3均相二元催化剂异戊二烯聚合动力学Ⅰ．一般动力学研究

用膨胀计研究了Ｎｄ（ＯＰｒ＾ｉ）２Ｃｌ－ＡｌＥｔ３均相稀土催化剂异戊二烯聚合动力学。在实验条件下，本体系显示稳态聚合特征；聚合速度对单体浓度和催化剂浓度均为一级关系，即聚合速度方程为Ｒｐ－Ｋｐ［Ｎｄ］［Ｍ］；本体系总的活化能Ｅａ为５７．４ｋＪ／ｍｏｌ。     

Rapid Suzuki‐Miyaura cross‐coupling reaction catalyzed by zirconium carboxyphosphonate supported mixed valent Pd(0)/Pd(II) catalyst

Mixed valent Pd(0)/Pd(II) nano‐sized aggregates supported onto a chemically robust layered zirconium carboxyphosphonate framework is prepared and its catalytic activity in Suzuki‐Miyaura cross coupling reaction is explored. The exceptionally high catalytic efficacy of the heterogeneous catalyst in Suzuki‐Miyaura cross coupling reaction is signified by remarkably short reaction time 2 minutes and high turnover frequency of 1.3 x 10⁴ hr^?1. The catalyst can be recycled several times without significant loss of catalytic efficacy, while spectroscopic, structural and microscopic investigations suggest the integrity of the catalyst even after fifth catalytic cycle. The unique ability of the zirconium carboxyphosphonate framework to interact strongly with palladium in dual Pd(0)/Pd(II) oxidation states has been attributed to this remarkable augmentation of catalytic efficacy.     

Highly Selective Pd–Cu/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts for Liquid-Phase Hydrogenation: The Influence of the Pd: Cu Ratio on the Structure and Catalytic Characteristics

The structure and catalytic characteristics of a series of Pd–Cu/α-Al₂O₃ catalysts with Pd: Cu ratio varied from Pd₁–Cu_0.5 to Pd₁–Cu₄ were studied. The use of α-Al₂O₃ with a small surface area (S_sp = 8 m²/g) as a support made it possible to minimize the effect of diffusion on the catalytic characteristics and to study the structure of Pd–Cu nanoparticles by X-ray diffraction (XRD) analysis. The XRD analysis and transmission electron microscopy (TEM) data indicated the formation of uniform bimetallic Pd–Cu nanoparticles (d = 20–60 nm), whose composition corresponded to a ratio between the metals in the catalyst, and also the absence of monometallic Pd⁰ and Cu⁰ nanoparticles. The study of catalytic properties in the liquid-phase hydrogenation of diphenylacetylene (DPA) showed that the activity of the catalysts rapidly decreased with the Cu content increase; however, in this case, the yield of a desired alkene compound significantly increased. The selectivity of alkene formation on the catalysts with the ratios Pd: Cu = 1: 3 and 1: 4 was superior to the commercial Lindlar catalyst.     

Synthesis of γ-keto carboxylic acids from γ-keto-α-chloro carboxylic acids via carbonylation—decarboxylation reactions catalysed by a palladium system

A palladium-based catalytic system is highly active in the synthesis of γ-keto acids of type ArCOCH₂CH₂COOH via carbonylation-decarboxylation of the corresponding α-chloride. Typical reaction conditions are: P(CO) = 20–30 atm; substrate/H₂O/Pd = 100–400/800–1000/1 (mol); temperature: 100–110 °C; [Pd]=0.25 × 10⁻²−1 × 1O⁻² M; solvent: acetone; reaction time: 1–2 h. A palladium(II) complex can be used as catalyst precursor. Under the reaction conditions above, reduction of the precursor to palladium metal occurs to a variable extent. High catalytic activity is observed when the precursor undergoes extensive decomposition to the metal. Pd/C is also highly active. Slightly higher yields are obtainable when the catalytic system is used in combination with a ligand such as PPh₃. A mechanism for the catalytic cycle is proposed: (i) The starting keto chloride undergoes oxidative addition to reduced palladium with formation of a catalytic intermediate having a Pd-[CH(COOH)CH₂COPh] moiety. The reduced palladium may be the metal coordinated by other atoms of palladium and/or by carbon monoxide and/or by a PPh₃ ligand when catalysis is carried out in the presence of this ligand. It is also proposed that the keto group in the β-position with respect to the carbon atom bonded to chlorine weakens the CCl bond, easing the oxidative addition step and enhancing the activity of the catalyst. (ii) Carbon monoxide ‘inserts’ into the PdC bond of the above intermediate to give an acyl catalytic intermediate having a Pd-[COCH(COOH)CH₂COPh] moiety. (iii) Nucleophilic attack of H₂O to the carbon atom of the carbonyl group bonded to the metal of the acyl intermediate yields a malonic acid derivative as product intermediate. This, upon decarboxylation, gives the final product. Alternatively, the desired product may form without the malonic acid derivative intermediate, through the following reaction pathway: the acyl intermediate undergoes decarboxylation with formation of a different acyl intermediate, having a Pd-[CO-CH₂CH₂COPh] moiety, which, upon nucleophilic attack of H₂O on the carbon atom of the carbonyl group bonded to the metal, yields the final product.     

Polymer-supported Ziegler–Natta catalyst for the polymerization of isoprene

A polymer-supported Ziegler–Natta catalyst, polystyrene-TiCl₄AlEt₂Cl (PS–TiCl₄AlEt₂Cl), was synthesized by reaction of polystyrene–TiCl₄ complex (PS–TiCl₄) with AlEt₂Cl. This catalyst showed the same, or lightly greater catalytic activity to the unsupported Ziegler–Natta catalyst for polymerization of isoprene. It also has much greater storability, and can be reused and regenerated. Its overall catalytic yield for isoprene polymerization is ca. 20 kg polyisoprene/gTi. The polymerization rate depends on catalyst titanium concentration, mole ratio of Al/Ti, monomer concentration, and temperature. The kinetic equation of this polymerization is: R_p = k[M]^0.30[Ti]^0.41[Al]^1.28, and the apparent activation energy ΔE_act = 14.5 kJ/Mol, and the frequency factor A_p = 33 L/(mol s). The mechanism of the isoprene polymerization catalyzed by the polymer-supported catalyst is also described. © 1993 John Wiley & Sons, Inc.     

A highly selective and sensitive colorimetric chemosensor based on polyurethane foam impregnated with 3-methyl-2, 6-dimercapto-1,4-thiopyrone for on-site preconcentration and determination of palladium(II)

ABSTRACT

A new sorbent and chemosensor for highly selective and sensitive on-site preconcentration and colorimetric determination of Pd(II) was developed based on its reaction with 3-methyl-2,6-dimercapto-1,4-thiopyrone (MDT) immobilised onto polyurethane foam (PUF). Complexation of Pd(II) with MDT sorbed on PUF tablets leads to a contrast change in the sorbent colour from pale yellow to reddish-brown. The developed chemosensor is highly selective with respect to the transition and platinum group metals. It has a maximum sorption capacity of 17 µmol g^?1 for Pd(II). Reaction is possible in a strongly acidic medium (up to10 M HCl), and the properties of the chemosensor do not change during storage for a long time. The colorimetric response of the chemosensor was measured using red–green–blue (RGB) colour model. The dependence of the luminosity of the G channel on the Pd(II) concentration was linear in the concentration range from 0.3 to 64 µg L^?1 with a detection limit of 0.1 µg L^?1 (R² = 0.997). The colour scale for visual detection of Pd(II) was constructed in the concentration range of 0.02–0.64 mg L^?1 for the sorption from 20 mL of an aqueous sample. The accuracy of the developed methods was assessed by the analysis of a certified reference material (platinum–palladium alloy) and by comparison with the results of gravimetric or graphite furnace atomic absorption spectrometry (GFAAS) determination of Pd. The developed method was successfully applied to determine Pd in samples of mine water and road dust, in the electrolyte bath and in the sewage sludge of a palladium electroplating bath.     

The first enantioselective intramolecular aminocarbonylation of alkenes promoted by Pd(II)-spiro bis(isoxazoline) catalyst

The highly ligand acceleration effect of spiro bis(isoxazoline) ligand (SPRIX) on the Pd(II)-catalyzed intramolecular aminocarbonylation of alkenyl amine derivatives was realized. Furthermore, the chiral Pd(II)-SPRIX catalyst accomplished the first enantioselective intramolecular aminocarbonylation. The reaction of N-(2,2-dimethyl-pent-4-enyl)-p-toluenesulfonamide in the presence of Pd(II)-SPRIX catalyst and p-benzoquinone in methanol under a carbon monoxide atmosphere afforded [4,4-dimethyl-1-(p-toluene-sulfonyl)-pyrrolidin-2-yl]-acetic acid methyl ester in good yield with moderate enantioselectivity.     

Crystal structure and magnetic properties of a new heterometallic complex of Pd(II)-Cu(II) with 1-aminoethylidene-1,1-diphosphonic acid

A heterometallic complex of Pd(II)-Cu(II) with 1-aminoethylidene-1,1-diphosphonic (AEDP) acid (C₄H₂₂CuN₂O₁₆P₄Pd) _n (I) is synthesized. Single crystals of compound I are obtained; its crystal structure is determined by X-ray crystallography. The crystals are orthorhombic, space group Pbcn, a = 18.366(3) Å, b = 9.7661(17) Å, c = 20.198(4) Å, V = 3622.8(11) ų, Z = 8, d _x = 2.376 g/cm³. The compound crystallizes as a coordination polymer; the square environment of Pd(II) is formed by nitrogen atoms of amino groups and oxygen atoms of phosphonic groups, while at two non-equivalent copper atoms the octahedral environment is formed by oxygen atoms of phosphonic groups and water molecules. The crystal structure of compound I is characterized by the formation of a branched network of hydrogen bonds. Based on the analysis of the temperature dependence of the magnetic susceptibility it is found that for the heterometallic complex of Pd(II)-Cu(II) with AEDP antiferromagnetic interactions between the paramagnetic centers are dominant.     

高效组合型 Pd/C 催化剂用于 Suzuki 偶联反应

 采用有机金属 Pd2(dba)3 (dba 为二亚苄基丙酮) 还原分解法制得均匀分布的 Pd 纳米颗粒 (粒径为 3~6 nm) 混合液, 并用活性炭直接吸附得到了组合型 Pd/C 纳米催化剂. 采用透射电子显微镜、X 射线光电子能谱和 X 射线衍射等手段测定了催化剂表面 Pd 颗粒大小分布、晶型和化学态等. 将该催化剂用于 Suzuki 碳-碳偶联反应, 其催化活性比浸渍法制备的 Pd/C 催化剂高 2 倍以上. 以溴代芳烃为底物时, 在 80 oC 下 0.5 h 后偶联产物收率可达 98% 以上. 以邻氯硝基苯为底物时, 在 110 oC 下 1 h 后偶联产物收率可达 64%; 延长反应时间, 产物收率可达 90% 以上.     

Liquid-phase hydrogenation of alkenes and aromatic compounds with Pd-loaded oxidized diamond catalyst

Hydrogenation reactions of alkenes (cyclohexene, ethyl acrylate, styrene and 1,5-cyclooctadiene) and aromatic compounds (o-, m- and p-xylene) were carried out in order to examine the activity of palladium-loaded surface-oxidized diamond (Pd/O-Dia) catalyst in liquid-phase hydrogenation. The catalytic performance was compared to commercial palladium-loaded activated carbon (Pd/C) catalyst. The catalyst activities were evaluated by conversions of reactants and H₂ uptake rates in the early stage of the reaction. In all the hydrogenation reactions of alkenes and aromatic compounds, the activity of Pd/O-Dia was almost the same as or slightly higher than that of Pd/C. Dispersion of Pd metal was measured by a CO-pulsed adsorption technique and TEM observations of the catalysts. Pd dispersions were on the same order of magnitude according to the CO-pulsed adsorption technique, although the Pd/C catalyst had a higher surface area (718 m²/g) than that of Pd/O-Dia (23 m²/g). The Pd particle sizes on O-Dia measured by TEM observation were slightly smaller than those on the activated carbon. Such highly dispersed Pd particles on O-Dia would contribute to higher activity for the hydrogenation reaction of alkenes and aromatic compounds.     

Structure and thermal properties of heterometallic complexes for chemical vapor deposition of Cu–Pd films

Novel volatile heterocomplex compounds based on copper(II) and palladium(II) fluorinated β-diketonates are studied. The crystals of the synthesized compounds are shown to be composed of 1D coordination polymers in the form of chains of alternating molecules of monometallic complexes. The crystallographic data for [Cu(hfa)₂?Pd(zif)₂] are as follows: C₂₆H₂₂F₁₈O₁₀CuPd, P2₁/c, a = 7.9947(18) Å, b = 19.277(4) Å, c = 13.609(3) Å, β = 118.298(15)°, V = 1846.7(7) ų, Z = 2, d = 1.810 g/cm³. The thermal properties of the compounds are examined by TG-DTA and vacuum sublimation. The complexes are studied as the precursors for producing copper-palladium alloy films by chemical vapor deposition. It is demonstrated that bimetallic alloy coatings with a ratio Cu/Pd = 1:1 can be prepared from [Cu(hfa)₂?Pd(zif)₂].     

Rate coefficients for the gas‐phase reaction of isoprene with NO3 and NO2

Rate coefficients for the gas‐phase reaction of isoprene with nitrate radicals and with nitrogen dioxide were determined. A Teflon collapsible chamber with solid phase micro extraction (SPME) for sampling and gas chromatography with flame ionization detection (GC/FID) and a glass reactor with long‐path FTIR spectroscopy were used to study the NO₃ radical reaction using the relative rate technique with trans‐2‐butene and 2‐buten‐1‐ol (crotyl alcohol) as reference compounds. The rate coefficients obtained are k(isoprene + NO₃) = (5.3 ± 0.2) × 10^?13 and k(isoprene + NO₃) = (7.3 ± 0.9) × 10^?13 for the reference compounds trans‐2‐butene and 2‐buten‐1‐ol, respectively. The NO₂ reaction was studied using the glass reactor and FTIR spectroscopy under pseudo‐first‐order reaction conditions with both isoprene and NO₂ in excess over the other reactant. The obtained rate coefficient was k(isoprene + NO₂) = (1.15 ± 0.08) × 10^?19. The apparent rate coefficient for the isoprene and NO₂ reaction in air when NO₂ decay was followed was (1.5 ± 0.2) × 10^?19. The discrepancy is explained by the fast formation of peroxy nitrates. Nitro‐ and nitrito‐substituted isoprene and isoprene‐peroxynitrate were tentatively identified products from this reaction. All experiments were conducted at room temperature and at atmospheric pressure in nitrogen or synthetic air. All rate coefficients are in units of cm³ molecule^?1 s^?1, and the errors are three standard deviations from a linear least square analyses of the experimental data. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 57–65, 2005