Reactions of lead cluster ions with acetone

Reactions of lead cluster cations and anions with acetone have been studied using a homemade reflectron time-of-flight mass spectrometer. Association with acetone to form Pb(k)(CH(3)COCH(3))(n)(+), high-energy pathway reactions forming Pb(k)CH(3)(+), and intraheterocluster reaction of Pb(k)(CH(3)COCH(3))(n+1)(+) to give Pb(k)CH(3)(CH(3)COCH(3))(n)(+) were the main reaction pathways for lead cluster cations with acetone. Decomposition of acetone by Pb(k)(-) to give Pb(k)C(m)(-) ions and their further association with acetone, Pb(k)C(m)(CH(3)COCH(3))(-), were the dominant reactions of lead cluster anions with acetone. Pb(7)(-), Pb(10)(-), and Pb(k)C(5)(-) were 'magic numbers' with special structural stabilityin Pb(k)(-) and Pb(k)C(m)(-), respectively. In addition, Pb(k)H(-), CH(2)COCH(3)(CH(3)COCH(3))(n)(-) and Pb(k)CH(2)COCH(3)(CH(3)COCH(3))(n)(-) were also observed in the reaction of lead cluster anions. Some reaction mechanisms are proposed for these reactions. To investigate the isotope effect for the reaction of lead cluster cations and anions with acetone and to verify the structural assignments of the observed ions, reactions of lead cluster cations and anions with deuterated acetone-d(6) were also performed.     

Reactions of bare aluminum cluster ions

Absolute cross sections for reaction of aluminum atomic, dimer and trimer ions with oxygen, water and ethylene are reported. For all three reactions the dimer ion is by far the most reactive at low collision energies. The atomic ion is four to ten times less reactive and the trimer is non-reactive within our sensitivity. At higher collision energies the dimer reactivity drops and in some cases the atomic and trimer ion reactivities increase. Extensive fragmentation of the cluster ions is observed at collision energies above 3.0 eV.     

Reactions of small carbon cluster ions with HCN: a structural probe

The results of a detailed study of the primary and secondary reactions of carbon cluster ions, C _n ⁺ (3≤n≤20), with HCN are presented and discussed. The experiments were performed in a Fourier transform (ICR) mass spectrometer, using direct laser vaporization of graphite to form the carbon cluster ions. Evidence for two structural forms of then=7, 8 and 9 cluster ions is obtained from their differing reactivity with HCN. The C ₇ ⁺ ion is anomalous in its behavior in many respects, which is interpreted by an isomerization mechanism. The HCN reactions offer a contrast to the reactions with nonpolar neutrals studied previously. All HCN reactions produced ions of the type C_nX⁺ (primary product) or C_nXY⁺ (secondary product) where X, Y=H, CN or HCN. Fragmentation of the original carbon cluster was not observed, while radiative association is an important reaction channel. Low-energy collision-induced dissociation studies of the product ions support the mechanism of insertion into the H-CN bond and formation of covalent bonds at the carbene site for the primary reactions. In most secondary reactions however, the HCN associates weakly with the ion, rather than binding covalently.     

Reactions of carbon cluster ions stored in an RF trap

Reactions of carbon clusterions with O₂ were studied by using an RF ion trap in which cluster ions of specific size produced by laser ablation could be stored selectively. Reaction rate constants for positive and negative carbon cluster ions were estimated. In the case of the positive cluster ions, these were consistent with the previous experimental results using FTMS. Negative carbon cluster ions C _n ^– (n=4–8) were much less reactive than positive cluster ions. The C_nO^– products were seen only in n=4 and 6.     

Reactions of silylium ions with nucleophiles

Transformation of the diethylsilylium cation Et₂Si⁺H into ethyl-and dimethylsilylium ions EtSi⁺H₂ and Me₂Si⁺H in reactions with nucleophiles is induced by electron-donor compounds. Their activity increases in the order Bu₂O < BuOH < (Me₃Si)₂O < C₆H₆ and is determined by the structure of the intermediate adduct and electron density distribution in it. Qualitative estimation shows that the affinity of the tritiated diethylsilylium cation Et₂Si⁺T for a nucleophile increases in the order C₆H₆ < BuOH < Bu₂O < (Me₃Si)₂O. The higher affinity of the Et₂Si⁺H cation for hexamethyldisiloxane compared to dibutyl ether, at similar basicity of the nucleophiles, is attributable to the higher charge of the oxygen atom in (Me₂Si)₂O.     

Reactions of zero-valent platinum complexes with some diacetylenes

The complexes[Pt(C₂H₄)L₂] (L = PPh₃ or PMePh₂) react with 1,4-diphenyl-buta-1,3-diyne to give, successively, mono- and di-platinum compounds [Pt-(PhC₄Ph)L₂] and [Pt₂(PhC₄Ph)L₄]. Hexa-2,4-diyne and [Pt(C₂H₄)(PPh₃)₂] react similarly. In the di-platinum compounds both acetylenic linkages are η²-bonded to platinum atoms, as also occurs in the complex [Pt₂{HC₂(CH₂)₂C₂H}(PPh₃)₄] obtained from hexa-1,5-diyne. Reaction of [Pt₃(CN-t-Bu)₆ with 1,4-diphenylbuta-1,3-diyne and hexa-2,4-diyne affords di-platinum complexes, shown by spectroscopic studies to have structures containing diplatinacyclobutene rings.     

Reactions of actinide ions with ethylene oxide

Naked and oxo-ligated actinide (An) monopositive ions were reacted with ethylene oxide, cyclo-C(2)H(4)O (EtO). Along with An = U, Np, Pu and Am, ions of two lanthanide (Ln) elements, Ln = Tb and Tm, were studied for comparison. Metal and metal oxide ions, M(+), MO(+) and MO(2)(+), were generated by laser ablation and immediately reacted with EtO. Unreacted and product ions were detected by time-of-flight mass spectrometry. It was apparent that the overall reaction cross-sections decreased in the order U(+) > or = Np(+) > Pu(+) > Am(+). A primary reaction channel for each studied metal was the formation of MO(+) from M(+), in accord with the expected exothermicity of oxygen abstraction from EtO. For U, Np and Pu, the dioxides were also major products, indicating OAn(+)--O dissociation energies of at least 350 kJ mol(-1), the energy required for O-atom abstraction from EtO. For Am, Tb and Tm, the dioxides were only very minor products, reflecting the stabilities of the trivalent states and resistance to oxidation to higher valence states; the structures/bonding in these MO(2)(+) are intriguing given that the formal pentavalent bonding state is effectively unattainable. It was demonstrated that EtO, unlike more thermochemically favorable but kinetically restricted O-donors, is effective at achieving facile oxidation of actinide metal ions to the monoxide, and to the dioxide if the second O-abstraction reaction is exothermic. Several intriguing minor products were also identified, most of which incorporate metal--oxygen bonding and are attributed to the oxophilicity of the f-block elements; the contrast to the behavior of first-row d-block transition elements is striking in this regard. Particularly noteworthy was the formation of MH(4)(+) (and MOH(4)(+)), evidently via abstraction of all four H atoms from a single C(2)H(4)O molecule; the structures/bonding in these novel 'hydride' species are indeterminate and warrant further attention.     

Reactions of (chlorodifluoromethyl)benzene and (chlorodifluoromethoxy)benzene with nucleophilic reagents

Condensation reactions of (chlorodifluoromethyl)benzene and (chlorodifluoromethoxy)benzene with phenoxide and thiophenoxide ions have been performed in DMF or NMP with heating. In these conditions, the reaction between phenylselenide ion and (chlorodifluoromethyl)benzene did not occur. This latter reaction requires an additional visible light irradiation to proceed, as reported by Yoshida et al.     

Reactions of nitrogen monoxide on cobalt cluster ions: reaction enhancement by introduction of hydrogen

Absolute cross sections for NO chemisorption, NO decomposition, and cluster dissociation in the collision of a nitrogen monoxide molecule, NO, with cluster ions Con+ and ConH+ (n=2-5) were measured as a function of the cluster size, n, in a beam-gas geometry in a tandem mass spectrometer. Size dependency of the cross sections and the change of the cross sections by introduction of H to Con+ (effect of H-introduction) are explained by a statistical model based on the RRK theory, with the aid of the energetics obtained by a DFT calculation. It was found that the reactions are governed by the energetics rather than dynamics. For instance, Co3+ does not react appreciably with NO because the reactions are endothermic, while Co3H+ does because the reaction becomes exothermic by the H-introduction.     

Reactivity of niobium-carbon cluster ions with hydrogen molecules in relation to formation mechanism of Met-Car cluster ions

It is known that a niobium-carbon Met-Car cluster ion (Nb 8C 12 (+)) and its intermediates (Nb 4C 4 (+), Nb 6C 7 (+), etc.) are selectively formed by the aggregation of the Nb atoms in the presence of hydrocarbons. To elucidate the formation mechanism, we prepared Nb n C m (+) with every combination of n and m in the gas phase by the laser vaporization technique. The reactivity of Nb n C m (+) with H 2 was examined under the multiple collision condition, finding that Nb n C m (+) between Nb 2C 3 (+) and Nb 8C 12 (+) are not reactive with H 2. On the basis of the H 2 affinity of Nb n C m (+) experimentally obtained, we propose a dehydrogenation-controlled formation mechanism of niobium-carbon Met-Car cluster ions.     

Reactions of hydridosilacyclobutanes with low-valent complexes of iron or platinum

Unstable transition metal compounds formed from hydridosilacyclobutanes are described: 1-methyl-1-silacyclobutane reacts with nonacarbonyldiiron to give the complexes [Fe(CO)₄(H){$\text{Si(Me)CH}{}_2\text{CH}{}_2\text{C}$H₂}] and [$\text{Fe{CH}{}_2\text{CH}{}_2\text{CH}{}_2\text{Si}$(H)Me}(CO)₄], and with bis(triphenylphosphine)(ethylene)platinum(0) to give [Pt(H)(PPh₃)₂{$\text{Si(Me)CH}{}_2\text{CH}{}_2\text{C}$H₂}].     

Reactions of 2,5-pyrroledicarboxaldehyde with some metal ions

The coordination chemistry of the recently synthesized 2,5-pyrroledicarboxaldehyde has been investigated. The ligand reacts with metal ions only in basic media in which the pyrrole nitrogen is deprotonated. In the ionic form the ligand is bidentate using the pyrrolate nitrogen and an oxygen of one of the two aldehyde groups. The results of the reactions of the dialdehyde with Ni(II), Cu(II), Co(II), CO(III), Fe(III), Pd(II) and Pt(II) are reported.     

Charge neutralization of ions from benzene

Cross-sections have been measured for the charge neutrilization if ions from benzene in kiloelectron-volt collisions with benezene target molecules. Measured values range from 65 Ų for the symmetric [C₆H₆]⁺? C₆H₆ resonant reactions to 8 Ų for [C₃H₃]⁺? C₆H₆ reactions. Cross-sections computed using a simple resonance charge transfer model compare favourably with experimental data for the symmetric reactions. The cross-sections for asymmetric reactions are smaller that those for they symmetric system and magnitudes of the asymmetric cross-sections are correlated with recombination energies of the respective ions.     

Reactions of atomic transition-metal ions with long-chain alkanes

Understanding metal ion interactions with long-chain alkanes not only is of fundamental importance in the areas of organometallic chemistry, surface chemistry, and catalysis, but also has significant implication in mass spectrometry method development for the analysis of polyethylene. Polyethylene represents one of the most challenging classes of polymers to be analyzed by mass spectrometry. In this work, reactions of several transition-metal ions including Cr+, Mn+, Fe+, Co+, Ni+, Cu+, and Ag+ with long-chain alkanes, C28H58 and C36H74, are reported. A metal powder and the nonvolatile alkane are co-deposited onto a sample target of a laser desorption/ionization (LDI) time-of-flight mass spectrometer. The metal ions generated by LDI react with the vaporized alkane during desorption. It is found that all these metal ions can form adduct ions with the long-chain alkanes. Fe+, Co+, and Ni+ produce in-source fragment ions resulting from dehydrogenation and dealkylation of the adduct ions. The post-source decay (PSD) spectra of the metal-alkane adduct ions are recorded. It is shown that PSD of Ag+ alkane adduct ions produces bare metal ions only, suggesting weak binding between this metal ion and alkane. The PSD spectra of the Fe+, Co+, and Ni+ alkane adduct ions display extensive fragmentation. Fragment ions are also observed in the PSD spectra of Cr+, Mn+, and Cu+ alkane adduct ions. The high reactivity of Fe+, Co+, and Ni+ is consistent with that observed in small alkane systems. The unusually high reactivity of Cr+, Mn+, and Cu+ is rationalized by a reaction scheme where a long-chain alkane first forms a complex with a metal ion via ion/induced dipole interactions. If sufficient internal energy is gained during the complex formation, metal ions can be inserted into C-H and C-C bonds of the alkane, followed by fragmentation. The thermal energy of the neutral alkane is believed to be the main source of the internal energy acquired in the complex. Finally, the implication of this work on mass spectrometry method development for polyethylene analysis is discussed.     

Partial hydrogenation of benzene over platinum supported catalysts

Partial hydrogenation of benzene to cyclohexene has been studied on Pt/Nylon 66, Pt/MgO and Pt/TiO₂. An effect of the support on the selectivity to cyclohexene was observed, Pt/Nylon showing the highest selectivity, followed by Pt/MgO and Pt/TiO₂. An interaction of platinum with the more basic supports (Nylon, MgO) and a pretreatment under oxidizing conditions, results in a higher selectivity to cyclohexene.

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Pt/ 66, Pt/MgO PtTiO₂. , Pt/, Pt/MgO Pt/T,O₂. (, MgO) .