Formation of WF−6 and its dissociative products by collisional ionization

The formation of negative ions in electron transfer reactions between hyperthermal alkali atoms (Na, K) and WF₆ has been studied in the energy range 0–30 eV c.m. Relative cross sections and translational energy thresholds for ion pair formation have been measured, from which the following electron affinities (EA) and bond dissociation energies (D) have been derived: EA(WF₆) = 3.7 eV, EA(WF₅) = 1.25 eV, D(WF₅—F) = 5.1 eV, D)WF₅—F^?) = 5.4 eV, D(WF^?₅—F) = 7.6 eV. Several ion molecule reactions are discussed which result in formation of secondary fragmentation ions and WF^?₇.     

Palladium complexes with biological ligands—I. Equilibrium and reaction mechanism of Pd(II) complexes with ethionine

An equilibrium study has been carried out on the interaction of ethionine(eth) with Pd(II) in aqueous solution at I = 0.16 M (Cl⁻ and 25°C using potentiometic methods. It has been concluded that five complex species exist in the pH range 2.8–4.8. these species are: PdCl₃(Eth0H⁰₂, PdCl₂(Eth)⁻, PdClOH(Eth)⁻, Pd(Eth)₂(H)²⁺₂ and Pd(Eth)⁰₂. In addition, the stopped-flow method has been used to study the reaction kinetics of Pd(II) with Eth. Three kinetic steps were observed in the pH range 1–5.5. These steps are dependent on the total concentration of Eth (T_Eth) as well as the pH of the medium. The observed pseudo-first order rate constants for the three reaction kinetic steps at constant pH are expressed empirically by kⁱ_obs = m_i + m′_iT_Eth. The parameters m_i and m′_i are pH-dependent. It has been concluded that PdCl²⁻₄ and PdCl₂OH²⁻ species play an important role in the complex formation reactions with Eth. The data were interpreted in terms of the complex species obtained from the equilibrium study. cis-trans substitution reactions have been suggested to account for some kinetic steps.     

H-Ge bond activation by tungsten carbonyls: An experimental and theoretical study

The activation of the Ge-H bond and the formation of several hydride complexes, characterized by high-field resonances, have been detected during the ¹H NMR spectroscopy monitoring of the photochemical reaction of Et₃GeH and Et₂GeH₂ with W(CO)₆ and the norbornadiene complex [W(CO)₄(η⁴-nbd)]. The activation of the Ge-H bond of triethylgermane in the photochemical reactions of tungsten(0) complexes has been applied in the hydrogermylation of norbornadiene (nbd), which leads to the formation of endo-triethylgermylnorbornene as the major product. The complex [{W(μ-η²-H-GeEt₂)(CO)₄}₂] has been fully characterized by NMR spectroscopy and by a single-crystal X-ray diffraction study. Evidence for the hydride ligand of the W(μ-η²-H-GeEt₂) group has been provided by ¹H NMR spectroscopy (δ = −9.02, ¹J_H-W = 31 Hz) and by DFT calculations. A DFT study of the structural properties and ¹H NMR chemical shifts of several possible intermediate σ and hydride complexes formed during the photochemical reaction of W(CO)₆ and Et₂GeH₂ has been performed.     

Methyl-and tert-butyl-substituted hydroquinones and semiquinone radicals: Bond strength estimates, enthalpy of formation, and the rate constants of their reactions with peroxy radicals

The strength of the O-H bonds (D) in hydroquinone (HQH) and its alkyl derivatives has been estimated by the intersecting parabolas method using rate constants known for the reactions of these compounds with the styrene peroxy radical. For unsubstituted HQH, D = 352.6 kJ/mol; for substituted HQH derivatives, D = 349.9 (Me), 346.9 (2,5-Me₂), 343.0 (Me₃), 347.6 (CMe₃), and 340.2 (2,5-(CMe₃)₂) kJ/mol. The enthalpies of formation of these HQH derivatives have been calculated. The O-H bond strengths in the semiquinone radicals (HQ^.) resulting from the above HQH derivatives have been calculated using a thermochemical equation to be $D_{HQ^. } $ = 236.7, 237.4, 239.8, 244.7, 240.1, and 247.5 kJ/mol, respectively. Rate constants have been determined for the reactions of the hydroquinones with tertiary and secondary peroxy radicals and HOO^. at 323 K. The rate constants of the reactions between HOO^. and benzoquinones and the relative reactivities of the HQ^. radicals in their reactions with ROO^. have been estimated.     

Reactions of 2-arsa- and 2-stiba-1,3-dionato lithium complexes with group 4-7 metal halides

The reactions of a range of 2-arsa- and 2-stiba-1,3-dionato lithium complexes with group 4-7 metals have been investigated. These have given rise to several complexes in which an arsadionate acts as a chelating ligand; [V{η²-O,O-OC(Bu^t)AsC(Bu^t)O}₃], [M{η²-O,O-OC(Bu^t)AsC(Bu^t)O}₂(DME)], M=Cr or Mn; or as an η¹-As-diacylarsenide, [MnBr(CO)₄{As[C(O)Bu^t]₂Li(DME)}]₂. In addition, reactions of lithium arsadionates with TaCl₅ have led to metal mediated arsadionate decomposition reactions and arsadionate oxidative coupling reactions to give the known arsaalkyne tetramer, As₄C₄Bu^t₄, and the new tetraacyldiarsane, [{As[C(O)Mes]₂}₂] Mes=mesityl, respectively. The treatment of several lithium arsadionates with [MoBr₂(CO)₂(PPh₃)₂] has also initiated arsadionate decomposition reactions and the formation of the metal carboxylate complexes, [MoBr(CO)₂{η²-O₂C(R)}(PPh₃)₂] R=Bu^t, Ph, Mes. The X-ray crystal structures of six of the prepared complexes are discussed.     

Spectra and structure of iron(III) complexes with carbamide derivatives containing an acetyl group

Equilibria of complex formation reactions of Fe^III in aqueous solutions with CH₃CONHCONH₂ and CH₃CONHCONHCH₃ were investigated by the UV spectral method. The formation of complexes of [Fe(H₂O)_6-nL_n]⁺³ (where n = 1, 2) has been established and their stability constants determined. The following crystalline complexes have been obtained: [Fe(CH₃CONHCONH₂ )₃ ]Cl₃ and [Fe(CH₃CONHCONHCH₃)₃]Cl₃, and their structures investigated using IR and NMR spectra. Results suggest that they are six-membered ring structures. The influence of the polar effects of substituents on the stability of iron(III) complexes with acetylcarbamides has been discussed and mesomeric effects have been shown to dominate inductive effects and work in opposite directions.     

Kinetic and mechanistic investigations on the oxidation of N’-heteroaryl unsymmetrical formamidines by permanganate in aqueous alkaline medium

Kinetic studies on the oxidation of two substituted azinyl formamidines (Azn-Fs), namely N,N-dimethyl-N’-(pyrimidin-2-yl) formamidine (Pym-F) and N,N-dimethyl-N’-(pyridin-2-yl) formamidine (Py-F), by alkaline permanganate have been performed by spectrophotometry. The spectroscopic and kinetic evidence reveals the formation of 1:1 intermediate complexes between the oxidant and substrates. The influence of pH on the oxidation rates indicated that the reactions are base-catalyzed. The reactions show identical kinetics, being first order each in [MnO₄ ^?]₀ and [Azn-F]₀, but with a fractional first-order dependence on [OH^?]. The effect of temperature on the reaction rate has been studied. Increasing ionic strength has no significant effect on the rate. The final oxidation products of Pym-F and Py-F were identified as 2-aminopyrimidine and 2-aminopyridine, respectively, in addition to dimethyl amine and carbon dioxide. Under comparable experimental conditions, the oxidation rate of Py-F is higher than that of Pym-F. A reaction mechanism adequately describing the observed kinetic behavior is proposed, and the reaction constants involved in the different steps of the mechanism have been evaluated. The activation parameters with respect to the rate-limiting step of the reactions, along with thermodynamic quantities, are presented and discussed.     

Ion—molecule reactions in GeH4/SiH4 systems studied by ion trap mass spectrometry

Gas phase ion—molecule reactions occurring in GeH₄/SiH₄ systems under different partial pressures and their mechanisms have been investigated by ion trap mass spectrometry (ITMS). SiH⁺_n (n=0–3) and GeH⁺_n (n = 0–3) are the main ionic species at zero reaction time when the GeH₄: SiH₄ ratio is in the range 1:1 to 1:12. Self-condensation sequences are observed at increasing reaction times. Moreover, formation of ions containing GeSi bonds, such as GeSiH⁺_n (in = 2–5) and GeSi₂H⁺_n (n = 4, 5), occurs by reactions of Si₂H⁺_n (n = 2–5) and Si₃H⁺_n (n = 4, 5) with GeH₄. At longer reaction times, further substitution of silicon with germanium in GeSiH⁺_n (n = 2–5) ions has been observed, to give Ge₂H⁺_n (n = 2–5).     

Mechanism of the formation of complexes of trimethylchlorosilane with some nitrogen donors in nitrobenzene

Reactions of trimethylchlorosilane (Me ₃SiCl) with some nitrogen donors viz. pyridine, 2-, 3- and 4-picolines, quinoline and isoquinoline in nitrobenzene have been studied conductometrically. The conductivities of the solutions during these reactions have been interpreted in terms of the formation of (Me ₃Si.D)⁺, (Me ₃SiCl₂)^? andMe ₃SiCl.D (D=N-donor molecule) species.     

Dissociative double electron capture,dynamics of fragmentation of the water and hydrogen sulfide negative ions

The technique of ion kinetic energy spectrometry has been used to observe the unimolecular decompositions of H₂O^?? and H₂S^?? generated by charge exchange of the corresponding high velocity positive ions. The method involves dissociative double electron capture by a high velocity ion and allows the study of unstable negative ions that may be directly observable by conventional electron capture techniques. Information on the energetics of the reaction is obtained from the kinetic energy of the product ion. The reactions under consideration are shown in (1) and (2) where X = O or S.

The kinetic energy releases accompanying the reactions given in (1) and (2) have been measured and compared to those for the collision-induced reactions which produce the corresponding positive ions. The results have been used to deduce that the sequence of steps in the formation of the fragment negative ions is that given in (1) and (2). The cross section of OH^? formation is observed to be somewhat greater than for O^? production. This result is in contrast with dissociative electron capture cross sections from the neutral species and is interpreted on the basis of the energetic requirements for the reactions under consideration. H₂O^? reacts from different electronic states in yielding OH^? on the one hand and O^? on the other. The energy partitioning associated with reaction (2) suggests that the neutral productions 2H' rather than H₂. The kinetic energy losses accompanying excitation and kinetic energy releases upon fragmentation were similar for the corresponding reactions of the sulfur and oxygen-containing ions indicating related mechanisms in the two sets of reactions.     

Synthesis and properties of isocyanate and isothiocyanate d1- and d2-complexes of vanadocene

The reactions of vanadocene and its halides Cp₂VCl and Cp₂VCl₂ with R₃MNCX (M  Sn, Si, X  O, S) and R₂M(NCX)₂ in various molar ratios have been studied. The reactions proceed either by an exchange of groups, with no change in the oxidation state of vanadium, or by an oxidative addition of pseudohalide ligand: V^II → V^III; V^III → V^IV. Oxidative addition results in the formation of (R₃M)₂ or gaseous hydrogen (in the reaction with HCl) in the reaction products.We have prepared the first ever monomeric and readily oxidisable d²-complexes of V^III of Cp₂VNCX-type and asymmetric d¹-complexes of Cp₂V(Cl)NCX type, which, although rather stable in air, undergo disproportionation into symmetric d¹-complexes on heating. In transmetallation reactions the ligand activity is found to increase in the order C1 < NCO < NCS. The complexes were characterised by GLC analysis, IR and ESR spectroscopy. A general scheme for the disproportionation reaction of asymmetric complexes of vanadocene is supported by differential thermal analysis data.     

The state of 5,10,15,20-tetraphenyl-21H,23H-porphine rhenium(V) complexes in solutions of acids

The spectral properties (UV/Vis, IR, ¹H NMR) and stability of diverse forms of 5,10,15,20-tetraphenyl-21H,23H-porphine rhenium(V) complexes in neutral and protolytic solvents have been studied. Quantitative characteristics have been obtained for the reactions of formation and interconversion of the μ-oxo dimeric and monomeric rhenium(V) complex species in the benzene-AcOH system and dissociation at the coordination center of the H⁺-associated form of the monomeric rhenium(V) complex in mixed H₂O-H₂SO₄ solvents in a wide range of component concentrations. It has been shown that the stability of the coordination center of the rhenium(V) complexes sharply depends on the nature of a second acido ligand, in addition to the coordinated porphyrin.     

Thermochemistry of adducts of some bivalent transition metal bromides with pyridine

The compounds [MBr₂(py)₂] (where M is Mn(II), Co(II), Ni(II), Cu(II) or Zn(II); py = pyridine) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, metal(II) bromides and pyridine in 25% (v/v) 1.2 M aqueous HCl in methanol were measured and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_rH^θ), the standard enthalpies of formation (Δ_fH^θ), the standard enthalpies of decomposition (Δ_DH^θ), the lattice standard enthalpies (Δ_MH^θ) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH^θ(g)). The mean bond dissociation enthalpies of the M(II)-nitrogen bonds have been estimated as well as the enthalpies of the adducts formation in the gaseous phase.     

AIB induced chemical reactions at surfaces detected by SIMS

Secondary ion mass spectrometry (SIMS) has been used to detect the reactions induced by active ion bombardment (AIB) of N⁺₂ on surfaces of pyrolytic graphite and a (100) Si crystal. The SIMS spectra exhibit ions of CN^?, HCN^?, H_nC₂N^?(n = 2, 3, 4), HN^?, and SiN^?, indicating that reactions take place with the graphite and silicon as well as adsorbed hydrogen on the surfaces.     

Reactions of a phosphavinyl Grignard reagent with main group mono-halide compounds

The reactions of a phosphavinyl Grignard reagent, [CyPC(Bu^t)MgCl(OEt₂)] Cy=cyclohexyl, with a variety of main group 13, 14 and 16 mono-halide compounds have been investigated. When the Grignard reagent is reacted with bromocatecholborane the terminal phosphavinyl complex, [(C₆H₄O₂)B{C(Bu^t)PCy}], is formed. Related terminal phosphavinyl tin and gallium complexes, [R₃Sn{C(Bu^t)PCy}], R=Me or Buⁿ and [IGa{C(Bu^t)PCy}₂], have been prepared by similar routes. The reaction of the Grignard reagent with PhSeCl has afforded a new λ⁵,λ⁵-diphosphete, [{(Bu^t)CP(Cy)(SePh)}₂], the mechanism of formation of which is discussed. The preparation of a phosphavinyl selenium compound, [(C₈H₄O₂N)PC(Bu^t)(SePh)], is also described. All compounds have been spectroscopically characterised and several have been crystallographically authenticated.     

Synthesis and spectral studies of β-diketone and β-ketoester derivatives of aluminium zirconium isopropoxide

The reactions of aluminium zirconium heptaisopropoxide [AlZr(OPrⁱ)₇] with some β-diketones and β-ketoesters, resulting in the formation of derivatives of type ZrAl(OPrⁱ)_(7−x)L_x (where L = acetylacetone, benzoylacetone, methylacetoacetate or ethylacetoacetate; x = 1 or 2) have been carried out. These newly synthesized compounds have been characterized by elemental analyses, and IR and NMR (²⁷Al, ¹H and ¹³C) spectral studies.     

Rate constant for the reaction of nh2 with ozone in relation to atmospheric processes

The absolute rate constant of the reaction between NH₂ and ozone has been measured using a flash photolysis-laser resonance technique and found to be k₄ = 6.3 (=1.0) × 10^?14 cm³ molecule^? s^?1 at room temperature. The Arrhenius expression, determined from measurements in the temperature range 298–380 K is k₄ = 4.2 × 10^?12 exp(?2.5 = 0.5/RT) (E in kcal mole ^?1. The possibility of formation or elimination of nitrogen oxides from the reactions of NH₂ in the atmosphere is examined.     

Synthesis of (η-arene)(η-cyclopentadienyl) iron (II) complexes with heteroatom and carbonyl substituents. Part I: Oxygen and carbonyl substituents

A series of reactions have been used to introduce oxygen substituents into (η-arene)(η-cyclopentadienyl) iron (II) complexes. Photochemical ligand exchange led to the formation of the first recorded trioxygenated complex as well as mono- and di-oxygenated species. Using microwave techniques, reaction times for S_NAr displacement reactions of halobenzene complexes by phenols were reduced from several hours to a few minutes. Phenols protected by either t-butylation or trimethylsilylation were found to give modest yields of the corresponding phenol complexes, using conventional thermal ligand exchange reactions. Without such protection, yields were extremely low. The above method led to the synthesis of the first example of a dihydroxybenzene complex. Some miscellaneous syntheses are also reported.The Nef reaction has been adapted to convert (η⁶-α-nitroalkylarene)(η⁵-Cp) iron (II) salts to corresponding aldehyde and ketone complexes. The α-nitroalkyl arene complexes were synthesised in good yields from (η⁶-halobenzene)(η⁵-Cp) iron (II) complexes using NaOtBu in DMSO. H/D exchange reactions with ²[H]₆-DMSO in the presence of K₂CO₃ showed partial D incorporation in the methyl group for the unreacted α-nitroethylbenzene complex and complete exchange for the carbanion generated by deprotonation. Conversion of the α-nitroalkylarene complexes to the corresponding aldehyde and ketone complexes was accomplished in moderate yields using three methods:

(A)

H₂O₂ and NaOtBu in DMSO followed by reaction with CF₃CO₂H.

(B)

SnCl₂/aq. HCl.

(C)

K₂CO₃ in DMF using microwave-mediated reactions.

In addition, two one-pot syntheses are reported using methods B and C.     

Gas-Phase reactions of NO2− with nitrobenzenes and quinones. Electron transfer,clusters and formation of phenoxide and quinoxide negative ions. Use of NO2 as a negative ion chemical ionization reagent

Negative-ion/molecule reactions in systems containing methane as the major gas (∼ 4 torr), with NO₂ and compounds A at mtorr pressures were studied in a pulsed electron, high pressure mass spectrometer. The compounds A were substituted nitrobenzenes and quinones. All these A compounds have positive electron affinities. Three types of reactions were observed and examined. (1) Electron transfer: A⁻ + NO₂ = A + NO₂⁻. The exothermic electron transfer reactions proceeded with ADO collision rates for exothermicities from 30 to ∼ 10 kcal mol⁻¹. Lower exothermicities led to low collision yields. (2) Adduct formation: NO₂⁻ + A = NO₂⁻·A. The equilibria for adduct formation were determined. Stable adducts are formed when A has hydrogens with partial protic character. The stability of the adducts NO₂⁻·A increased with increase in the electron affinity of A, when A was a substituted nitrobenzene. Substituents that increase the electron affinity of nitrobenzene are electron-withdrawing groups which also increase the protic character of the hydrogens involved in bonding in NO₂⁻·A. (3) Some of the compounds A were converted to phenoxy negative ions on reaction with NO₂⁻. For example, para-dinitrobenzene leads to formation of the para-nitrophenoxide negative ion. The oxy-negative-ion-forming reaction can be isomer specific. The utility of reaction types (1)–(3) is examined from the standpoint of negative ion chemical ionization where the reagent gas is NO₂ in methane and the reagent ion is NO₂⁻.     

Spin-orbit coupling effects in the gas-phase reaction Se + O2

The potential energy surface sections of the ground and excited states of the SeOO (C _s ) superoxo complex have been constructed on the basis of spin-orbit coupling calculations. The activation barriers to the forward and reverse reactions??superoxide SeOO ? peroxide Se(O₂) ? dioxide SeO₂??have been calculated. Changes in the spectral and spin properties of oxygen (zero-field splitting) and possible channels of formation of active forms of ¹O₂ oxygen (¹?? _g , ¹?? _g ⁺ ) upon dissociation of excited states of selenium oxo complexes have been scrutinized.