Rate Coefficient for Self-Association Reaction of CF2 Radicals Determined in the Afterglowof Low-Pressure C4F8 Plasmas

We have analyzed decay kinetics of CF₂ radicals in the afterglow of low-pressure, high-density C₄F₈ plasmas. The decay curve of CF₂ density has been approximated by the combination of first- and second-order kinetics. The surface loss probability evaluated from the frequency of the first-order decay process has been on the order of 10^–4. This small surface loss probability has enabled us to observe the second-order decay process. The mechanism of the second-order decay is self-association reaction between CF₂ radicals (CF₂+CF₂C₂F₄). The rate coefficient for this reaction has been evaluated as (2.6–5.3)×10^–14 cm³/s under gas pressures of 2 to 100 mTorr. The rate coefficient was found to be almost independent of the gas pressure and has been in close agreement with known values, which are determined in high gas pressures above 1 Torr.     

A kinetic and mechanistic study of oxidation of arsenic(III) by hexacyanoferrate(III) in aqueous ethanoic acid

The kinetics of oxidation of As^IIIby Fe(CN)₆ ^3– has been studied spectrophotometrically in 60% AcOH–H₂O containing 4.0moldm^–3HCl. The oxidation is made possible by the difference in redox potentials. The reaction is first order each in [Fe(CN)₆ ^3–] and [As^III]. Amongst the initially added products, Fe(CN)₆ ^4– retards the reaction and As^Vdoes not. Increasing the acid concentration at constant chloride concentration accelerates the reaction. At constant acidity increasing chloride concentration increases the reaction rate, which reaches a maximum and then decreases. H₂Fe(CN)₆ ^–, is the active species of Fe(CN)₆ ^3–, while AsCl₅ ^2– in an ascending portion and AsCl₂ ⁺ in a descending portion are considered to be the active species of As^III. A suitable reaction mechanism is proposed and the reaction constants of the different steps involved have been evaluated.     

Synthesis and base hydrolysis kinetics of the nitrile complexes [Co(tetren)NCR]3+ (R=Me,Ph and p-MeOC6 H4) and the synthesis and kinetics of formation of the tetrazolato complexes [Co(tetren)N4R]2+ (R=Me and Ph; tetren=1,11-diamino-3,6,9-triazaundecane) by reaction with azide ion

The N-bonded nitrile complexes -[Co(tetren)NCR]³⁺ (R=Me, Ph, p-MeOC₆ H₄) have been prepared by the reaction of -[Co(tetren)OH₂]³⁺ with the corresponding nitrile. The kinetics of base hydrolysis have been studied by pH-stat methods. The reactions involve an SN₁CB displacement of the nitrile to give the hydroxopentamine; nucleophilic attack at the nitrile carbon to give the corresponding carboxamido complex does not occur. NaN₃ reacts with the nitrile complexes in slightly acidic solution (pH ca. 5.7) to give the tetrazolato complexes [Co(tetren)N₄ R]²⁺ (R=Me, Ph) which have been characterised. The reaction of azide ion with -[Co(tetren)NCMe]³⁺ has been studied kinetically. The reaction is biphasic involving the initial rapid formation of the N₁-bonded (5-methyltetrazolato) pentaminecobalt(III) complex with k=2×10^–2dm³ mol^–1s^–1 at 25°C followed by the slow isomerisation to the N₂-bonded complex with k=3.5×10^–5s^–1 at pH 5.7.     

Luminescence of salts and copolymers containing the (MoII6Cl8)4+ cluster

The photophysical properties (absorption, emission) of the (Bu₄N)₂[(Mo^II ₆Cl₈)L₆] (L = CF₃COO^–, CH₂=CHCOO^–) cluster salts and (Bu₄N)₂[(Mo^II ₆Cl₈)(CF₃COO)_6–n]—polyacrylic acid copolymers were studied. Both the cluster-containing monomers and corresponding copolymers phosphoresce intensely ( 0.2—0.4 ms at 77—300 K).     

An independent kinetic and mechanistic study of the secondary reactions in the substitution of [FeL(OH)](n−2)− (L= triethylenetetraaminehexaacetic acid) by cyanide ions

Summary The kinetics of reaction between [Fe(CN)₅OH]^3– and CN^– have been investigated spectrophotometrically at pH=11.00, I=0.25 M(NaClO₄) and temp.=25.0°C by disappearance of the absorption peak at 395 nm. The rate data for this reaction followed first order kinetics in both [Fe(CN)₅OH^3–] and [CN^–]. The second order rate constant (k_f) was found to be (3.44±0.08)×10^–3 M^–1 s^–1. The pH dependence of the reaction was also investigated in the range 9–12. The activation parameters were found to be H=36.4kJ mol^–1 and S=–168JK^–1 mol^–1.The reaction between [Fe(CN)₆]^3– and TTHA^6– (TTHA=triethylenetetraaminehexaacetic acid) has also been followed spectrophotometrically at 420 nm, pH=11.00, I=0.1M (NaClO₄) and temp.=25.0°C. This reaction also followed first order kinetics in both [Fe(CN) ₆ ^3– ] and [TTHA^6–]. The second order rate constant (k_f) was found to be (3.74±0.21)×10^–2 M^–1 s^–1. The rate of reaction was found to increase with pH in the range 9–11.5. The different reactive species of TTHA (L) are H₂L^4– HL^5– and L^6–. The rate constants for these species have been calculated and the pH profile is explained. The values of the activation parameters were found to be H= 30.9 kJmol^–1 and S=–167JK^–1 mol^–1. Electron transfer from [Fe(CN)₆]^3– to the substrate followed by decomposition of the latter is proposed. The oxidation products of TTHA have been investigated by g.l.c.     

Low-dimensional compounds containing cyano groups. IX. Preparation,structure and properties of the [Cu(bpy)<Subscript>2</Subscript>(dca)]CF<Subscript>3</Subscript>SO<Subscript>3</Subscript> complex

The ionic [Cu(C₂N₃)(C₁₀H₈N₂)₂](CF₃SO₃) compound, which contains two crystallographic independent formula units, is formed by [Cu(bpy)₂(dca)]⁺ complex cations (bpy=2,2-bipyridine, dca=dicyanamide) and uncoordinated CF₃SO ₃ ^– anions, which are in a staggered conformation. The shapes of coordination polyhedra around both copper atoms, which are fivefold coordinated by two bpy molecules and one dca ligand monodentately coordinated through a cyano N atom in the equatorial plane at a distance of 2.001(3)Å for the first and 1.988(4)Å for the second polyhedron, are distorted trigonal bipyramids. Besides the ionic forces the structure is stabilized by weak C–H...O hydrogen bonds and possible – interactions between pyridine rings of bpy molecules. Along with the structural-spectral correlation we discuss the thermal decomposition of the title complex.     

Oxidation of mesitylene by PtCl6 2− ions in trifluoroacetic acid

Conclusion The reaction of PtCl₆ ^2– ions with mesitylene in aqueous CF₃CO₂H leads to the formation of 2,4,6,3,5-pentamethyl)diphenylmethane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 935–937, April, 1987.     

Partial oxidation and oxidative condensation of methane with the participation of N2O on a V2O5/SiO2 catalyst

The catalytic reaction of CH₄, with N₂O at 773–823 K on a V₂O₅/SiO₂ catalyst affords products of the partial oxidation (HCHO and CH₃OH), exhaustive oxidation (CO), and oxidative condensation (C₂H₅OH and CH₃CHO) of methane. A mechanism is proposed for the complex reaction, including the intermediate compounds V⁵⁺O and V⁴⁺CH₃OH as common intermediates for all the routes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 5, pp. 641–646, September–October, 1987.     

Investigation of the structure and reactivity of the stable perfluorodiisopropylethylmethyl radical by ESR and molecular mechanics

The hyperfine coupling (HFC) constants of the unpaired electron with the fluorine nuclei in the stable radical [(CF₃)₂CF]₂CF₂CF₃ (II) were determined by ESR. The stable conformation and the barriers to rotation of the substituents in this radical were calculated by molecular mechanics. The results were consistent with the ESR data. The kinetics of the destruction of the radical (II) were investigated, and the kinetic parameters of the dissociation were determined (k₁₄₀=4.6·10^–4 sec^–1, E_act=30±5 kcal/mole). The disappearance of the radical (II) is accompanied by the accumulation of the new radical (CF₃)₂CF(CF₃)CF(CF₃)CF₂CF₃ (IV), which was studied by ESR. Heating of (II) in the presence of electron donors leads to the partly reversible reduction of the radical (II).Translated from Izvestiva Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1507–1512, July, 1991.     

Structure and Reactivity of the Radical Cations of Methyl tert-Butyl Ether in Condensed Phase: An ESR and Quantum Chemical Study

The structure of the methyl tert-butyl ether (MTBE) radical cation and mechanism of its thermal and photochemical reactions in irradiated freons (CFCl₃, CF₂ClCFCl₂, and CF₃CCl₃) were studied. Radical products of MTBE radiolysis in the liquid phase were investigated by the spin trapping technique. The quantum-chemical calculations of the structure of MTBE radical cations and products of their transformations were carried out by density functional theory (DFT) and ab initioMP2 methods. The primary MTBE radical cations are stabilized in dilute solutions in CFCl₃and CF₃CCl₃. The ion–molecule reaction (proton transfer from the radical cation) was found to occur in concentrated solutions in CFCl₃immediately during irradiation. The action of light ( = 436 to 546 nm) at 77 K on the MTBE radical cation in CFCl₃and CF₃CCl₃matrices results in intramolecular migration of the methyl group to yield the distonic radical cation (CH₃)₂ ^.CO⁺(CH₃)₂. The primary MTBE radical cations undergo an irreversible transformation with methane elimination resulting in formation of the 2-methoxypropene radical cation ^.CH₂=⁺(₃)₃in CFCl₃and CF₃CCl₃matrices in the temperature range 110–130 K. In the case of CF₂ClCFCl₂matrix, such a reaction occurs during irradiation at 77 K. Using the spin trapping technique, it was shown that the liquid-phase radiolysis of the neat ether resulted in the formation of fragmentation products (^.CH₃,CH₃^., and t-BuO^. radicals) from the primary radical cations, as well as the products of their rearrangements and ion–molecule reactions.     

Studies on transition-metal nitrido and oxo complexes. Part VII(1). Substituted nitrido complexes of osmium and ruthenium

Summary Addition reactions of [MNCl₄]^– (M = Os or Ru) with ligands L or L to give [MNCl₄ · L]^– or [(MNCl₄)₂L]^2– (L = pyridine, pyridine-N-oxide,iso-quinoline or DMSO; L = hexamethylenetetramine, pyrazine or dioxan) are described. With NCO^–, [OsNCl₅]^– gives [OsN(NCO)₅]^2– but NCS^– gives a thionitrosyl complex, [Os(NS)(NCS)₅]^2–. Reactions of OsNCl₃(AsPh₃)₂ with pyridine, 1,10-phenanthroline and tertiary phosphites and phosphinites have been studied, as have reactions of triphenylphosphine with OsOCl₄ andtrans- [MO₂Cl₄]^2– (M = Os or Ru). The nitrido-iodo complexes [OsNI₄]^– and OsNI₃, (SbPh₃)₂ are also reported.     

Novel Immobilized Hydrosilylation Catalysts Based on Rhodium 1,3-Bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidenes

Summary. The reactivity of a well defined Rh (I) complex, i.e. Rh(CF₃COO)(NHC)(COD) (1, NHC=1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene, COD=⁴-cycloocta-1,5-diene) in the hydrosilylation of 1-alkenes, alkynes, and ,-unsaturated carbonyl compounds, respectively, is described. With this complex, excellent reactivity was observed and turn-over numbers (TONs) up to 1000 were reached. A supported version of 1 was realized by reaction of RhCl(NHC)(COD) with PS-DVB–CH₂–O–CO–CF₂–CF₂–CF₂–COOAg (PS-DVB=poly(styrene-co-divinylbenzene) to yield PS-DVB–CH₂–O–CO–CF₂–CF₂–CF₂–COORh(NHC)(COD). This supported version of 1 exhibited at least comparable, in some cases increased reactivity compared to 1 and allowed the rapid removal of the catalyst from the reaction mixture. Due to reduced catalyst bleeding, the synthesis of target compounds with a Rh-content of less than 130ppm was accomplished.This revised version was published online in February 2005. In the previous version the issue was not marked as a special issue, and the issue title and the editor was missing     

Metal chelates of heterocyclic nitrogen containing ketones,XIII. Cobalt(II), nickel(II) and palladium(II) complexes of 2-picolyl- and 2-lutidyl-methyl ketones

Summary The preparation and characterization of a series of new coordination compounds of cobalt(II), nickel(II) and palladium(II) containing 2-picolyl- or 2-lutidyl-methyl ketone (HPMK or HLMK) and various anions, Cl^–, Br^–, NO ₃ ^– , NCS^– or BF ₄ ^– , are reported. Complexes of square planar, tetrahedral and octahedral stereochemistry as well as five-coordinate species were isolated. The reaction products were found to be dependent on the molar ratios, pH and the temperature at which the reaction takes place. Cobalt(II) thiocyanate was found to form a complex of the type [CoL₃][Co(NCS)₄] (L = HPMK or HLMK). Also complexes containing coordinated BF₄ were isolated. The ligand field parameters (Dq, B and ) for the cobalt(II) and nickel(II) complexes were calculated using the averaged-ligand-field approximation. The influence of the substituents of theses parameters and on the stereochemistry are discussed.     

Novel Immobilized Hydrosilylation Catalysts Based on Rhodium 1,3-Bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidenes

The reactivity of a well defined Rh (I) complex, i.e. Rh(CF₃COO)(NHC)(COD) (1, NHC=1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene, COD=⁴-cycloocta-1,5-diene) in the hydrosilylation of 1-alkenes, alkynes, and ,-unsaturated carbonyl compounds, respectively, is described. With this complex, excellent reactivity was observed and turn-over numbers (TONs) up to 1000 were reached. A supported version of 1 was realized by reaction of RhCl(NHC)(COD) with PS-DVB–CH₂–O–CO–CF₂–CF₂–CF₂–COOAg (PS-DVB=poly(styrene-co-divinylbenzene) to yield PS-DVB–CH₂–O–CO–CF₂–CF₂–CF₂–COORh(NHC)(COD). This supported version of 1 exhibited at least comparable, in some cases increased reactivity compared to 1 and allowed the rapid removal of the catalyst from the reaction mixture. Due to reduced catalyst bleeding, the synthesis of target compounds with a Rh-content of less than 130ppm was accomplished.     

Synthesis of Boron–Nitrogen–Phosphorus Compounds from N-Silylphosphoranimines

Two modes of reactivity of N-silylphosphoranimines have been utilized to prepare the title compounds containing either B–N=P or Si–N=P–N–B linkages. First, silicon-nitrogen bond cleavage reactions of the N-silylphosphoranimines, Me₃SiN=PMe(R)OCH₂CF₃ (1: R=Me, 2: R=Ph), with various chloroboranes gave the new N-borylphosphoranimines, Ph(Me₂N)B–N=PMe₂OCH₂CF₃ (2) and [(Me₃Si)₂N](Cl)B–N=PMe₂OCH₂CF₃ (10). In other cases, however, the expected B–N=P products were unstable and cyclic phosphazenes [Me(R)P=N]_3,4 were obtained. Second, deprotonation-substitution reactions of the aminophosphoranimines, Me₃SiN=P(R)Me–N(R)H, were used to prepare a series of novel (borylamino)-phosphoranimines, Me₃SiN=P(R)(Me)–N(R)–B(NMe₂)₂ (18: R=Me, R=t-Bu; 19: R=R=Me; 20: R=Ph, R=t-Bu; 21: R=Ph, R=Me) and Me₃SiN=PMe₂–N(t-Bu)–B(Ph)X (22: X=NMe₂, 23: X=OCH₂CF₃). All of the new boron–nitrogen–phosphorus products were fully characterized by multinuclear NMR (¹H, ¹³C, and ³¹P) spectroscopy and elemental analysis.     

Complex formation effects during the oxidation of cyclohexene with lead tetraacetate

The effect of complex formation between lead(IV) and trifluoroacetic or methanesulfonic acid and chloride ion in acetic acid and Freon 113 on the oxidation of cyclohexene by lead tetraacetate was investigated. As a result of the reaction the -chlorocyclohexyl esters of the corresponding acids are formed with high yields. The formation of the complexes Pb(OAc)_4–nL_n and Pb(OAc)_4–(n+1)L_nCl, where L = CF₃CO₂- or CH₃SO₃- with n=1 or 2, was demonstrated by potentiometric titration. A scheme is proposed for the oxidation of cyclohexene with the participation of unlike-ligand complexes of Pb(IV).Translated from Teoreticheskaya Eksperimental'naya Khimiya, Vol. 21, No. 5, pp. 567–572, September–October, 1985.     

The kinetics of base hydrolysis of [Co(trien)(amine)Cl]2+ complexes (amine=imidazole,pyridine,n-butylamine and 2,2-dimethoxyethylamine)

Summary The complexescis--[Co(trien)(ImH)Cl]²⁺ (ImH=imidazole, trien=1,8-diamino-3,6-diazaoctane),cis--[Co(trien)(Buⁿ-NH₂)Cl^–]²⁺,cis--[Co(trien)(NH₂CH₂-CH(OMe)₂)Cl^–]²⁺ andcis-₂-[Co(trien)(py)Cl]²⁺ (py=pyridine) have been characterised and their kinetics of base hydrolysis studied. Thecis--isomers which have afac-fac arrangement of the trien ligand have values of k _OH ²⁵ in the 73 to 253 dm³ mol^–1 s^–1 range at I=0.1 mol dm^–3. Extremely rapid base hydrolysis is observed withcis-₂-[Co(trien)(py)Cl]²⁺ where k _OH ²⁵ is 6.65×10⁶ mol³ mol^–1 s^–1 at I=0.1 mol dm^–3. This complex has amer-fac arrangement of the trien ligand with flatsec-NH donor leading to rapid base hydrolysis due to good -overlap between the conjugate base and cobalt(III). The pyridine ligand causes aca. 30 fold rate increase compared with the hydrolysis ofcis-₂-[Co(trien)(NH₃)Cl]²⁺.     

Nature of transient species formed during pulse radiolysis of 4-mercaptopyridine in aqueous solutions: Formation of a dimer radical species by one-electron reduction reaction

Reactions of one-electron reducing as well as oxidizing radicals with 4-mercaptopyridine (4-MPy) were studied in aqueous solutions at different pH values. One-electron oxidizing radicals such as N₃ and Br₂ ^–, react with 4-MPy by electron transfer reaction at pH 11 to give 4-pyridylthiyl radical. The reduction potential for the couple 4-PyS /4-PyS^– was estimated to be 0.93V vs. NHE by equilibrium reaction with I₂ ^– /2I^– couple. At pH 6.8, where the compound is predominantly present in the thione form, the transient species formed is a cation radical. OH radicals react with 4-MPy by addition to the pyridine ring at pH 6.8 and 11. At pH 0, OH radicals as well as one-electron oxidants like Cl₂ ^– and Br₂ ^– radicals react with 4-MPy to produce the protonated form of 4-pyridylthiyl radical. At pH 6.8 and 11, e_aq ^– reaction with 4-MPy gave an initial adducts which reacted with the parent molecule to give dimer radicals. Acetone ketyl radicals were unable to reduce 4-MPy at neutral pH. Reducing radicals like H-atoms and acetone ketyl radicals reacted with 4-MPy at acidic pH by H-abstraction reaction to give the same species as produced by oxidizing radicals.     

Chemistry of μ-hydridobis[pentacarbonylchromium(0)] species. Part III. Redox reactions with mercury(II) compounds and iodine

Summary [Cr₂(CO)₁₀(-H)]^– undergoes ready hydride substitution on reaction with HgX₂ (X = Cl, Br, I or SCN) or with iodine in acetone, yielding [Cr₂(CO)₁₀(-X)]^– complex species which can be converted quantitatively into [Cr(CO)₅X]^– anions by reactions conducted in the presence of an excess of X^–.LCr(CO)₅ and (L-L)Cr(CO)₄ complexes (L = pyridine; L-L = 1,10-phenanthroline or 2,2-bipyridine) are easily prepared by reactions performed in the presence of the L or L-L ligand, respectively.     

Transformations of the chiral diphosphine rhodium catalyst [(1,5-COD)Rh(—)R,R-DIOP]+CF3SO3– under conditions of hydrogenation

Transformation products of the cationic rhodium complex [(1,5-COD)Rh(—)R,R-DIOP]⁺CF₃SO₃ ^– (1) (COD is cycloocta-1,5-diene and DIOP is (±)-2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane), which were obtained in its reactions with molecular hydrogen, base (NEt₃), and solvents in the absence of a substrate, were investigated by ¹H and ³¹P NMR spectroscopy. The solvate complexes [(Solv)₂Rh(—)R,R-DIOP]⁺CF₃SO₃ ^–, which were generated from complex 1 in its reaction with molecular hydrogen, underwent destruction of the diphosphine ligand with elimination of benzene and were subjected to oxidation by traces of moisture and oxygen to form the DIOP dioxide complex with Rh^I. In the absence of hydrogen, complex 1 in solutions produced the diphosphine dioxide rhodium(i) complex and mono- and binuclear rhodium(i) solvate complexes. The scheme of deactivation of the complex in the absence of the substrate was proposed. The catalytic activity of the solvate complexes [(ArH)Rh(—)R,R-DIOP]⁺CF₃SO₃ ^–, which contain benzene, p-xylene, and mesitylene in the coordination sphere, was studied in hydrogenation of Z--acetamidocinnamic acid.