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Copper(II) acetate is frequently used as a catalyst for bond-forming reactions in organic synthesis. Unlike aqueous solutions, in which complete heterolysis to CuOAc+(aq) and AcO–(aq) prevails at low concentrations, it is clear that copper(II) acetate shows a large degree of aggregation in typical organic solvents. Here, the speciation behavior of Cu(OAc)2 in organic solvents is probed by electrospray ionization mass spectrometry (ESI-MS), which reveals an extensive clustering of copper acetate species to form ions of the general composition [Cun(X)2n–1]+ and [Cun(X)2n+1]– (X = OAc and OCH3), along with (solvated) monomeric species such as [Cu(OAc)(CH3OH)n]+. The ESI-MS measurements are complemented by solution-phase studies of Cu(OAc)2 by electron paramagnetic resonance spectroscopy, which support an extensive aggregation of Cu(OAc)2 in organic solvents. Collisional experiments reveal that either simple degradation or redox processes can be observed, depending on the coordinative saturation of the copper clusters. The formation of the copper clusters can be efficiently suppressed by contamination of the organic solvents by a small amount of water.

Electrospray ionization/mass spectrometry (ESI-MS) is used to monitor a Cu-catalyzed aerobic cross-coupling reaction between thiol esters and arylboronic acids. The ESI spectra show the formation of Cu-complexes with the starting thiol ester 1 and the coupling product. The formation of an ionic complex at m/z 305 is observed, most likely occurring upon the elimination of a mixed anhydride from [(1)CuOAc]+. An online monitoring of the reaction using ESI-MS was carried out allowing calculation of rate constants and thermodynamic parameters (ΔH‡, ΔS‡, and ∆G‡) for the title reaction.

Tebuconazole ( 1 ) belongs to a class of widely utilized plant fungicides, mostly in vineyards. Consequently, traces of this compound are present in plant tissues, wine as well as in soil. The aim of this study was in situ generation of Cu cations and creation of very stable Cu complexes with 1 . The proposed method involves a hyphenation of electrochemistry with electrospray ionization mass spectrometry (ESI-MS), based on the high affinity of 1 for dissolved copper cations. We demonstrate that at appropriate potentials (above 500 mV vs. silver reference electrode) Cu cations can be generated in an electrochemical cell, which subsequently form complexes with 1 present in the sample. The resulting complex [Cu( 1 )] + as well as its fragment [Cu( 1 -C 4 H 10 )] + are then detected with online-coupled ESI-MS. This finding is useful for a creation of an analytical method based on the detection of trace amounts of 1 in complex matrices (e.g., soil solution), in which the analyte may be spread among various species.

The reaction mechanism of the intermolecular oxidative formation of pyrazole 2 via a C–C/N–N bond-formation cascade of the enaminone 1 is investigated by means of ESI-MS. No direct reaction intermediates are observed; however, the formation of an unexpected imidazolid-3-one derivative X is observed that involves an oxidative dimerization of 1 in the presence of dioxygen. The derivative X is isolated and characterized by means of multidimensional 1H and 13C NMR spectroscopy.

The properties of neutral and monocationic complexes of iron with one and two water or carbonyl ligands (i.e. FeCO0/+, Fe(OH2)0/+, (OC)Fe(OH2)0/+, and (H2O)Fe(OH2)0/+) are studied by means of wave-function based ab initio theory. Not surprisingly, the addition of ligands to the metal center drastically changes the energetics of the cationic species, whereas the ligation of neutral iron has much smaller effects and the interaction is even repulsive for some neutral quintet states. As a consequence, the associated adiabatic and vertical transitions between the manifold of the neutral and monocationic species experience substantial changes with differences exceeding 1 eV in the ionization energies. The results are used to explain the results of earlier studies of (OC)Fe(OH2)0/+ and (H2O)Fe(OH2)0/+ by means of neutralization–reionization mass spectrometry.

Electrospray ionization of dilute solutions of phenylpyridines (phpy) in the presence of nickel(II) chloride leads to gaseous ions of the type [Ni(phpy)(m)](2+) with m = 3-5 and [NiCl(phpy)(n)](+) with n = 1-3, which are characterized by various gas-phase experiments in combination with calculations using density functional theory. Of the regioisomeric phpy's, 2-phpy behaves drastically different compared to 3- and 4-phpy. Ion mobility mass spectrometry allows a differentiation of the gaseous ions and an elucidation of characteristic properties of the metal complexes. For 2-phpy, C-H bond activation in the [NiCl(phpy)(2)](+) complex is significant, whereas this route is almost suppressed for the corresponding complexes of 3- and 4-phpy and only occurs at elevated energies.

RATIONALE Heavy metals are both a problem for the environment and an important resource for industry. Their selective extraction by means of organic ligands therefore is an attractive topic. The coordination of three thiacrown ethers to late 3d-metal ions was investigated by a combination of electrospray ionization mass spectrometry (ESI-MS) and electron paramagnetic resonance (EPR). METHODS The mass spectrometric experiments were carried out in an ion trap mass spectrometer with an ESI source. Absolute binding constants were estimated by comparison with data for 18-crown-6/Na(+). EPR spectroscopy was used as a complementary method for investigating the Cu(I) /Cu(II) redox couple. RESULTS The study found that thiacrown ethers preferentially bind traces of copper even at an excess of other metal ions (Co(II), Ni(II), and Zn(II)). The absolute association constants of the Cu(I) complexes were about 10(8) M(-1), and about two orders of magnitude lower for the other 3d-metal cations. The EPR spectra demonstrated that the reduction from Cu(II) to Cu(I) upon formation of the [(thiacrown)Cu](+) species takes place in solution. CONCLUSIONS ESI-MS demonstrated that the three thiacrown ligands examined had high binding constants as well as good selectivities for copper(I) at low concentrations, and in the presence of other metal ions. By a combination of ESI-MS and EPR spectrometry it was shown that the reduction from Cu(II) to Cu(I) occurred in solution.

Even in the highly diluted gas phase, rather than electron transfer the benzene dication C(6)H(6)(2+) undergoes association with dinitrogen to form a transient C(6)H(6)N(2)(2+) dication which is best described as a ring-protonated phenyl diazonium ion. Isotopic labeling studies, photoionization experiments using synchrotron radiation, and quantum chemical computations fully support the formation of protonated diazonium, which is in turn a prototype species of superacidic chemistry in solution. Additionally, reactions of C(6)H(6)(2+) with background water involve the transient formation of diprotonated phenol and, among other things, afford a long-lived C(6)H(6)OH(2)(2+) dication, which is attributed to the hydration product of Hogeveen's elusive pyramidal structure of C(6)H(6)(2+), as the global minimum of doubly ionized benzene. Nitrogen is essential for the formation of the C(6)H(6)OH(2)(2+) dication in that it mediates the formation of the water adduct, while the bimolecular encounter of the C(6)H(6)(2+) dication with water only leads to (dissociative) electron transfer.

Experimental data on the reactions of argon with BF n + monocations ( n = 0–3) and BF n 2+ dications ( n = 1, 2) and dications reveal the formation of the new argon species ArBF 2+ and ArBF 2 + . Theoretical calculations on the stability of these ions using density functional theory confirm the formation of the rare-gas compounds, but their formation is only exothermic for the reaction Ar + BF 2 2+ → ArBF 2+ + F. According to theory, the corresponding neon compounds all involve endothermic pathways and could hence only be formed via involvement of excited states.

We report efficient methods for the synthesis of both symmetrically and non-symmetrically substituted bis(imidazol-2-yliden)ammonium ions and a new family of bis(imidazol-2-ylidene)formamidines. The fragmentation pathways of these cations were studied in detail by electrospray ionization combined with tandem mass spectrometry. Interestingly, in these cations direct C–N bond cleavage leading to loss of alkyl radicals can compete with rearrangement reactions leading to closed-shell fragments. The experimental results for the major fragmentation channels are compared with those derived from DFT calculations. Inter alia, a novel rearrangement of the cationic species involving specific alkyl migrations between the two imidazole subunits has been found.

Dissociative double ionization of toluene using synchrotron radiation in conjunction with theoretical studies leads to a determination of the thermochemistry of the dication c - C 7 H 6 2 + . Further, photon-energy dependent reactivity studies reveal that the asymmetric energy deposition upon single-electron transfer in the C 7 H 8 2 + / C 7 D 8 collision system is not influenced by the internal energy content of the dication precursors. This finding agrees with the previous assignment of the asymmetric energy deposition as a consequence of the electronic states accessible upon recombination of a dication with an electron compared to the removal of an electron from a neutral compound, respectively.

Helquats are a recently introduced class of compounds, which can be perceived as a combination of helicenes with the skeleton of bispyridinium ions such as paraquat. In addition to their helical shape, some of these compounds can also adopt saddle-like conformations. The focus here is on a specific [5]helquat dication HQ2+, which is investigated by various experimental techniques in condensed media as well as in the gas phase in combination with parallel computational studies. For this compound, the helical form is strongly favored in the free dication HQ2+ in the gas phase as well as in the condensed-phase salts [HQ2+ ⋅ 2X−], whereas in the singly charged ion pairs in the gas phase, the saddle conformer [SQ2+ ⋅ X−] is significantly more stable than the helical form [HQ2+ ⋅ X−] for a number of anions X−. The reason for this inversion of stability in the binary ion pairs is that the saddle conformer has a central binding pocket, in which the anion can interact with both pyridinium centers, whereas the more compact helix conformer permits the anion to approach only a single cationic center efficiently.

Metal-oxide cations are models of catalyst mediating the C–H bond activation of organic substrates. One of the most powerful reagents suggested in the gas phase is based on CuO+. Here, we describe the activation of the aromatic C–H bonds of phenanthroline in its complex with CuO+. The reaction sequence starts with a hydrogen atom abstraction by the oxygen atom from the 2-position of the phenanthroline ring, followed by OH migration to the ring. Using infrared multiphoton spectroscopy, it is shown that the reaction can be energetically facilitated by additional coordination of a water ligand to the copper ion. As the reaction is intramolecular, a spectroscopic characterization of the product is mandatory in order to unambiguously address the reaction mechanism. Copyright © 2012 John Wiley & Sons, Ltd.

The gas-phase proton affinities of 2-iminoimidazolines with bulky substituents on the ring-nitrogen atoms are investigated by the kinetic method. The experimental results are complemented by calculations using density functional theory. It turns out that the title compounds can be termed as superbases with the largest proton affinities ranging up to 260 kcal mol −1 .

Electrospray ionization was used as a technique for the characterization of the interactions between cadmium(II) ions and malic acid (1) in aqueous solution. Particular attention was paid to the nature of the species formed, which generally correspond to complexes of CdX(+) cations with neutral malic acid, where X either is the counterion of the metal salt used as a precursor (i.e. X=Cl, I) or corresponds to singly deprotonated malic acid. In pure water solutions, also highly coordinated complexes [Cd(1-H)(1)(2)](+) and [CdCl(1)(2)](+) were detected, whereas the most abundant complexes detected in a sample of soil solution were: [Cd(1-H)(1)](+) and [CdCl(1)](+). With respect to possible application in environmental analysis, the effects of (i) metal salts present in solution, (ii) modest mineralization, and (iii) the matrices of real soil solutions were probed. While the presence of other metals leads to additional complexes, the characteristic species containing both cadmium(II) and malic acid can still be detected with good sensitivity.

The microhydrated cations [Co(NO 3 )(H 2 O) n ] + ( n = 2, 3) generated via electrospray ionization of aqueous cobalt(II) nitrate are studied by means of infrared-multiphoton dissociation (IRMPD) spectroscopy in an ion-trap mass spectrometer (IT-MS) at the free electron laser CLIO. While [Co(NO 3 )(H 2 O) 3 ] + shows a simple photo-induced fragmentation upon IRMPD, the situation is more complex for [Co(NO 3 )(H 2 O) 2 ] + because during storage in the IT-MS the ion associates with background water to afford [Co(NO 3 )(H 2 O) 3 ] + , and both species adsorb IR photons in the same range. By means of kinetic modeling, it is demonstrated that also in such a more complicated situation useful insights can be achieved. For all [Co(NO 3 )(H 2 O) n ] + cations studied ( n = 0–3) in parallel theoretical studies, a bidentate coordination of the nitrato ligand is preferred, and this conclusion finds support by a comparison of the computed and experimental IR spectra. In addition, the binuclear cluster [Co 2 (NO 3 ) 3 (H 2 O) 3 ] + is probed by means of IRMPD.

The formation of complexes between tebuconazole (Teb) and cadmium in simplified model solutions as well as soil solutions was studied using electrospray ionization mass spectrometry. Teb and cadmium form two types of complexes with the general formulas [Cd(Teb)n]2+ (n = 1–4) and [CdI(Teb)m]+ (m = 1–3), where iodine corresponds to the counterion used. The most intense Teb/cadmium complex is [CdI(Teb)2]+, and the most stable one is [Cd(Teb)(Teb − H)]+. Another detected complex, the dication [Cd(Teb)4]2+, was considered as the origin complex for the iodine-free complexes and was found in a sample prepared from forest soil solution naturally contaminated with cadmium ions.

The second ionization energy of β-picoline was determined from photoionization experiments as 2IEβ = (24.05 ± 0.1) eV and the threshold for the dehydrogenation of the dication generated by photoionization as AE(–H2)β = (25.0 ± 0.2) eV. The second ionization energy is about 0.5 eV lower than values recently determined for α- and γ-picoline, whereas the energies required for dehydrogenation are similar. In order to rationalize the different behavior of dications generated from these isomeric picolines, we have performed a mass spectrometric investigation of the fragmentation patterns of the individual picoline dications and an extensive series of DFT calculations to explain the observed spectra.

The mechanism of the copper-mediated disproportionation of aromatic imine disulfides to benzothiazoles in the gas phase is investigated by experimental and theoretical methods. Application of infrared multiphoton dissociation and hydrogen/deuterium exchange experiments combined with density functional theory (DFT) calculations of the relevant molecular structures and the associated infrared spectra allows the identification of the observed ionic intermediates. The theoretical investigation of the possible reaction pathways supported by collision-induced dissociation experiments provides a consistent mechanistic picture of the reaction catalyzed by a single copper(I) ion. Activation of the substrate proceeds via homolytic sulfur-sulfur bond cleavage, yielding metal complexes in the formal +3 oxidation state; carbon-sulfur coupling and hydrogen-atom transfer complete the transformation to the products. Exploratory studies demonstrate that in the gas phase, the disproportionation of the imine disulfide can also be mediated by other metal ions via different either homo- or heterolytic mechanisms without involving high-valent intermediates.

Electrospray ionization mass spectrometry (ESI-MS) is used to probe the binding of small anions to the macrocycle of bambus[6]uril. For the halide ions, the experimental patterns suggest F– < Cl– < Br– < I–, which is consistent with the order of anion binding found in the condensed phase. Parallel equilibrium studies in the condensed phase establish the association constants of halide anions and bambus[6]uril in mixed solvents. A detailed analysis of the mass spectrometric data is used to shed light on the correlations between the binding constants in the condensed phase and the ion abundances observed using ESI-MS. From the analysis it becomes apparent that ESI-MS can indeed represent the situation in solution to some extent, but the sampling in the gas-phase experiment is not 1:1 compared to that in solution.

Electrospray ionization mass spectrometry (ESI-MS) is used for monitoring the progress of the Suzuki–Miyaura cross-coupling reaction between bromobenzene and arylboronic acids using a palladium dichloro-bis(aminophosphine) complex as a precatalyst. The ESI-MS studies demonstrate that initiation of the catalytic reaction requires the presence of a base and that the selectivity for cross-coupling is favorable at elevated temperatures. Interestingly, after completion of the coupling reaction, the palladium is present as a dinuclear Pd0/PdII cluster, which still acts as an active catalyst when a new aliquot of reactants is added to the reaction mixture.

Solutions of palladium chloride in acetonitrile are investigated by means of electrospray ionization mass spectrometry (ESI-MS). In contrast to several other metal salts previously investigated using ESI-MS, PdCl2 has a pronounced tendency for aggregation to yield [PdmCl2m−1(CH3CN)n]+ clusters in the positive ion mode and [PdmCl2m+1]− clusters when the negative ions are sampled, respectively. The observation of these oligomers parallels polymeric structures of PdCl2 in the solid phase. The positive ions are most abundant for m = 2 and generally associated with several molecules of the solvent, whereas many different cluster sizes occur for the anions which generally do not appear as solvent associates. Parallel conductivity measurements in the condensed phase lend support to a pronounced tendency for aggregation of PdCl2 in acetonitrile solution.

Electrospray ionization mass spectrometry (ESI-MS) is used to probe the complex formation between tebuconazole (1) and copper(II) salts, which both are commonly used fungicides in agriculture. Experiments with model solutions containing 1 and CuCl2 reveal the initial formation of the copper(II) species [(1)CuCl]+ and [(1)2CuCl]+ which undergo reduction to the corresponding copper(I) ions [(1)Cu]+ and [(1)2Cu]+ under more drastic ionization conditions in the ESI source. In additional experiments, copper/tebuconazole complexes were also detected in samples made from soil solutions of various origin and different amount of mineralization. The direct sampling of such solutions via ESI-MS is thus potentially useful for understanding of the interactions between copper(II) salts and tebuconazole in environmental samples. Copyright © 2011 John Wiley & Sons, Ltd.

Electrospray ionization of methanolic solutions of p-hydroxyphenacyl derivatives HO-C(6)H(4)-C(O)-CH(2)-X (X = leaving group) provides abundant signals for the deprotonated species which are assigned to the corresponding phenolate anions (-)O-C(6)H(4)-C(O)-CH(2)-X. Upon collisional activation in the gas phase, these anions inter alia undergo loss of a neutral "C(8)H(6)O(2)" species concomitant with formation of the corresponding anions X(-). The energies required for the loss of the neutral roughly correlate with the gas phase acidities of the conjugate acids (HX). Extensive theoretical studies performed for X = CF(3)COO in order to reveal the energetically most favorable pathway for the formation of neutral "C(8)H(6)O(2)" suggest three different routes of similar energy demands, involving a spirocyclopropanone, epoxide formation, and a diradical, respectively.

The bimolecular reactivity of xenon with C(7)H(n)(2+) dications (n=6-8), generated by double ionization of toluene using both electrons and synchrotron radiation, is studied by means of a triple-quadrupole mass spectrometer. Under these experimental conditions, the formation of the organoxenon dications C(7)H(6)Xe(2+) and C(7)H(7)Xe(2+) is observed to occur by termolecular collisional stabilization. Detailed experimental and theoretical studies show that the formation of C(7)H(6)Xe(2+)+H(2) from doubly ionized toluene (C(7)H(8)(2+)) and xenon occurs as a slightly endothermic, direct substitution of dihydrogen by the rare gas with an expansion to a seven-membered ring structure as the crucial step. For the most stable isomer of C(7)H(6)Xe(2+), an adduct between the cycloheptatrienyldiene dication and xenon, the computed binding energy of 1.36 eV reaches the strength of (weak) covalent bonds. Accordingly, electrophiles derived from carbenes might be particularly promising candidates in the search for new rare-gas compounds.

The charge-reversal (CR) and neutralization–reionization (NR) mass spectra of the mass-selected allyloxide anion CH 2 CHCH 2 O − are reported. Similar to other alkoxide ions, the allyloxide anion shows only small abundances of the survivor cation in the CR and NR spectra. In combination with theoretical studies, the differences between the CR and NR experiments allow to explain why loss of atomic hydrogen corresponds to the major unimolecular decomposition channel of the neutral allyloxy radical. In addition, indirect evidence for an intramolecular rearrangement of the allyloxy radical to a carbon-centered oxiranyl methyl radical is provided. Interestingly, the patterns of the C 3 H n O + ions in the NR spectra show similarities to those of a recently reported photoionization study of oxygenated products formed upon interaction of V 4 O 11 − ions with propene. By extrapolation of our findings, we suggest that the reactions of the vanadium-oxide cluster anion V 4 O 11 − are initiated by allylic C–H bond activation of propene followed by oxygenation of the hydrocarbon fragment.

Electrospray ionization of an aqueous solution of nickel(II) sulfate provides direct experimental evidence for the formation of triple ions of the type [Ni(2)(SO(4))(H(2)O)(n)](2+) and [Ni(SO(4))(2)](2-), whose existence in aqueous solution has previously been proposed based on relaxation spectroscopy [Chen et al. J. Sol. Chem. 2005, 34, 1045]. Formally, these triple ions are formed by aggregation of the solvated ions Ni(2+) and SO(4)(2-), respectively, with the neutral ion pair NiSO(4). In addition, also higher adducts are observed, e.g. the "pentuple ions" [Ni(3)(SO(4))(2)(H(2)O)(n)](2+) (n = 7-9) and [Ni(2)(SO(4))(3)](2-), of which the dicationic is extensively hydrated, whereas the anionic is not. The structures of the dinuclear nickel clusters are derived from ab initio calculations and their infrared spectra are compared with experimental data obtained for the gaseous ions [Ni(2)SO(4)(H(2)O)(5)](2+) and [Ni(2)(SO(4))(3)](2-), respectively. The calculations show that the structures are crucially controlled by the degree of solvation of nickel ion. Explicit consideration of solvating water molecules within the first coordination sphere suggest that the dicationic triple ion [Ni(2)SO(4)](aq)(2+) is bent and thus bears a permanent dipole moment, whereas the [Ni(SO(4))(2)](aq)(2-) dianion tends to be quasi-linear. The experimental and theoretical data for the gaseous ions thus support the elegant, but indirect, deductions previously made based on solution-phase studies.

Mono- and dications of microsolvated nickel complexes of acetonitrile are probed by means of ion-mobility mass spectrometry. Specifically, the complexes [(CH3CN)nNi]+, [(CH3CN)nNi]2+, [(CH3CN)nNiOH]+, and [(CH3CN)nNiCl]+ (n = 0–6) are compared to each other and their reactions with background water are probed. In general, the arrival times of the ions in the ion-mobility experiment linearly increase with the mass-to-charge ratio, but for the smaller, more reactive complexes, the arrival times are notably larger than expected from their mass. This effect is attributed to the markedly larger reactivity of these particular ions, as reflected in both charge-separation processes as well as adduct formation upon interaction with background water.

The gas-phase reactivity of dications generated by dissociative electron ionization of several aromatic CmHnNo precursors with 4 ≤ m ≤ 13, 4 ≤ n ≤ 21, and 0 ≤ o ≤ 2 with rare gases is investigated. Whereas most of these reactions lead to monocations via simple electron transfer, proton transfer, or Coulomb explosion, the formation of organo rare-gas dications is observed in a few cases. Specifically, dications generated from 2,4,6-trimethylpyridine react with krypton and xenon to form organo rare-gas species as major products and under maintenance of the two-fold positive charge. Such a reactivity is not observed in the presence of lighter rare gases. The formation of organo rare-gas dications are also observed for dications generated from 3-vinylpyridine, N,N-dimethylaniline, isopropylbenzene, and 4-ethyltoluene as neutral precursors. In some cases, isomeric dications are characterized by very different reactivity toward rare gases, suggesting that the structure of the precursors is crucial and that electron ionization does not lead to a total scrambling of the structures of the doubly charged ions obtained.

Mono- and binuclear complexes of N,N-dimethylformamide (DMF) with chlorides of the divalent, late 3d metals M = Co, Ni, Cu, and Zn are investigated by means of electrospray ionization (ESI). Specifically, ESI leads to monocations of the type [(DMF)(n)MCl](+) and [(DMF)(n)M(2)Cl(3)](+), of which the species with n = 2 and 3 were selected for in-depth studies. The latter include collision-induced dissociation experiments, gas-phase infrared spectroscopy, and calculations using density functional theory. The mononuclear complexes [(DMF)(n)MCl](+) almost exclusively lose neutral DMF upon collisional activation with the notable exception of the copper complex, for which also a reduction from Cu(II) to Cu(I) concomitant with the release of atomic chlorine is observed. For the dinuclear clusters, there exists a competition between loss of a DMF ligand and cluster degradation via loss of neutral MCl(2) with decreasing cluster stability from cobalt to zinc. For the specific case of [(DMF)(n)ZnCl](+) and [(DMF)(n)Zn(2)Cl(3)](+), ion-mobility mass spectrometry indicates the existence of two isomeric cluster ions in the case of [(DMF)(2)Zn(2)Cl(3)](+) which corroborates parallel theoretical predictions.

Electrochemical studies of the newly synthesized bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl2(L)(PPh3)2] (1, with L = 2-(2′-pyridyl)quinoxaline, C13N3H9), were performed in acetonitrile (ACN). For this purpose, cyclic voltammograms (CVs) as well as electrochemical impedance spectra (EIS) were recorded on either glassy carbon (GC), platinum (Pt), gold (Au), or multi-walled carbon nanotube (MWCNT) electrodes. Qualitative examination of solutions of 1 in ACN was performed on the basis of conductivity measurements and electrospray ionization mass spectrometry (ESI–MS). The conductivity data suggest that 1 is a 1 : 1 type electrolyte in ACN. The ESI spectra further demonstrate that upon dissolution of 1 in ACN progressive replacement of chloro- and PPh3-ligands by ACN occurs, leading to formation of [RuCl(L)(PPh3)(CH3CN)2]+Cl−, [2 + Cl − ]. The CVs recorded for [2 + Cl − ] on various working electrodes demonstrate that the reversibility of the redox couple 22 +/+ enhances with the order: Au < Pt ...

The reactivity of molecular dications C(m)H(n)N(2+), generated by (dissociative) double ionization of different heteroaromatic compounds, with methane, ethane, and nitrogen is investigated using a triple-quadrupole mass spectrometer. About a quarter of the set of dications studied undergo carbon-carbon coupling reactions with methane, whereas only nonspecific reactions leading to the formation of monocations (such as proton-, electron- and hydride transfer as well as Coulomb explosions) occur in the presence of either ethane or nitrogen. Here, we report the reactivity observed for 42 different C(m)H(n)N(2+) dications formed via electron ionization of eleven different heteroaromatic precursors. The potential relevance of these results is discussed in the context of the growth of hydrocarbon species and their nitrogen-containing homologues at extremely low temperatures and pressures, such as in interstellar environments or the ionospheres of planets and moons, Saturn's moon Titan in particular.

The triple ion [ ( CH 3 ) 4 N + · PF 6 - · ( CH 3 ) 4 N + ], generated by electrospray ionization of tetramethylammonium hexafluorophosphate, is characterized by collision-induced dissociation and infrared spectroscopy of the mass-selected gaseous ion in the range from 1000 to 2000 cm−1. Quantum chemical calculations are used to elucidate the structures and energetics of the triple ion and its subunits and for the assignment of the infrared frequencies. The infrared bands observed in the gas-phase match quite closely with those of the bulk substance, suggesting that for this particular kind of ion associate the structural differences between the gas-phase and the condensed state are almost negligible.

The C-H bond activation of small alkanes by the gaseous MgO(+*) cation is probed by mass spectrometric means. In addition to H-atom abstraction from methane, the MgO(+*) cation reacts with ethane, propane, n- and iso-butane through several pathways, which can all be assigned to the occurrence of initial C-H bond activations. Specifically, the formal C-C bond cleavages observed are assigned to C-H bond activation as the first step, followed by cleavage of a beta-C-C bond concomitant with release of the corresponding alkyl radical. Kinetic modeling of the observed product distributions reveals a high preference of MgO(+*) for the attack of primary C-H bonds. This feature represents a notable distinction of the main-group metal oxide MgO(+*) from various transition-metal oxide cations, which show a clear preference for the attack of secondary C-H bonds. The results of complementary theoretical calculations indicate that the C-H bond activation of larger alkanes by the MgO(+*) cation is subject to pronounced kinetic control.

The ion–molecule reactions of C7H7+ ions with neutral toluene are investigated in an ion-trap mass spectrometer, which is shown to be suitable instrumentation for kinetic studies, although the absolute rate constant can only be derived with difficulties. The benzylium ions C6H5CH2+ undergo a formal CH2+ transfer with toluene to afford the corresponding xylenium ions, CH3–C6H4–CH2+, whereas the tropylium ions c-C7H7+ do not react. The results for the parent compound C7H7+ are complemented with data for the tert-butyl derivative generated by collision-induced dissociation of the corresponding p-(tert-butyl)benzyl pyridinium ion. For the tert-butyl substituted ion, the benzylium/tropylium dichotomy exists in a similar manner in that reactive and non-reactive fractions are observed, of which the former is assigned to the benzylium structure on the basis of infrared-multiphoton dissociation spectra.

Thermal reactions of the CF32+ dication with argon lead to the formation of an ArCF22+ dication, a new type of metastable species with an argon−carbon bond. None of the other rare gases undergo a similar reaction with CF32+. For the lighter rare gases (He and Ne), no reactions with CF32+ other than those due to electronically excited reactant ions are observed, whereas for the heavier rare gases (Kr and Xe), the prevailing reactive pathways involve single-electron transfer. At elevated collision energies, single-electron transfer predominates for collisions with all rare gases (He−Xe).

Dinuclear gold(III) clusters with a rhombic Au(2)O(2) core and 2,2'-bipyridyl ligands substituted in the 6-position (bipy(R)) are examined by tandem mass spectrometry. Electrospray ionization of the hexafluorophosphate salts affords the complexes [(bipy(R))Au(mu-O)(2)Au(bipy(R))](2+) as free dications in the gas phase. The fragmentation behavior of the mass-selected dications is probed by means of collision-induced dissociation experiments which reveal an exceptionally pronounced effect of substitution. Thus, for the parent compound with R = H, i.e., [(bipy)Au(mu-O)(2)Au(bipy)](2+), fragmentation at the dicationic stage prevails to result in a loss of neutral H(2)O concomitant with an assumed rollover cyclometalation of the bipyridine ligands. In marked contrast, all complexes with alkyl substituents in the 6-position of the ligands (bipy(R) with R = CH(3), CH(CH(3))(2), CH(2)C(CH(3))(3), and 2,6-C(6)H(3)(CH(3))(2)) as well as the corresponding complex with 6,6'-dimethyl-2,2'-dipyridyl as a ligand exclusively undergo Coulomb explosion to produce two monocationic fragments. It is proposed that the additional steric strain introduced to the central Au(2)O(2) core by the substituents on the bipyridine ligand, in conjunction with the presence of oxidizable C-H bonds in the substituents, crucially affects the subtle balance between dication dissociation under maintenance of the 2-fold charge and Coulomb explosion into two singly charged fragments.

The collision-induced fragmentation behavior of cationic [Pt(CX3)(L)]+ complexes (X = H, D; L = 1,10-phenanthroline (phen), 2,2′-bipyrimidine (bipyrm), 2,2′-bipyridine (bipy), and (o,o′-Cl2C6H3)N═C...

The ion/molecule reaction (IMR) of “roll-over” cyclometalated [Pt(bipy−H)] + ( 1 ) (bipy = 2,2′-bipyridine) with dimethyl sulfide ( 2 ) leads to the loss of ethene in the main reaction channel (55%); this corresponds to a formal dehydrosulfurization accompanied by the dehydrogenative (“oxidative”) C–C coupling of the two methyl groups in dimethyl sulfide to form ethene. In order to obtain deeper insight into this rare reaction, the IMRs of 1 with several symmetric, asymmetric as well as cyclic thioethers and some thiols are probed. Common to many substrates is the formal transfer of H 2 S from the organic sulfur compound to the [Pt(bipy−H)] + core accompanied by the expulsion of one or more alkene units. In contrast to the behavior of [Pt(bipy−H)] + ( 1 ), bare Pt + , diatomic PtH + , and also the complex [Pt(phpy−H)] + (phpy = 2-phenyl pyridine) are not able to bring about dehydrosulfurization. It is accordingly suggested that the (bipy−H)-ligand does not only affect the electronic structure of the platinum(II) core but, moreover, plays an active role as an acceptor in the initial hydrogen transfer from the thioether ligand to the LPt + core (L = heterocyclic ligand).

Electrospray ionization of uranyl nitrate dissolved in water generates gaseous species containing either hydroxo-uranyl [UO(2)(OH)](+) or nitrato-uranyl [UO(2)(NO(3))](+) contact ion pairs solvated by up to four water molecules. Furthermore, uranyl clusters of the general type [U(m)O(2m)(X,Y)(2m-1)(H(2)O)(n)](+) (X,Y = OH, NO(3)) with m = 1-5 and n = 2-4 are formed. Collision-induced dissociation experiments are used to probe the structures and the stoichiometries of the uranyl ions generated. A detailed investigation of the concentration-dependent behavior of the formed gaseous uranyl complexes reveals a preference for nitrate- over hydroxide-containing species with increasing concentration of the sprayed solution. This behavior reflects changes in the pH value of the bulk solutions that can be attributed to solvolysis of UO(2)(2+) in water. Further, the tendency for generation of polynuclear cluster ions is amplified with increasing concentration and can be explained by a mechanism which involves the association of cations present in solution with neutral species such as UO(2)(OH)(2), UO(2)(OH)(NO(3)), and UO(2)(NO(3))(2). The observed dependences of the cluster-ion intensities in the mass spectra from the concentration of the solutions fed to the electrospray source are used to suggest a scheme for a quantitative correlation between the gas-phase and solution-phase data. The results inter alia indicate that the effective concentrations of the spraying solution can be several orders of magnitude larger than those of the feed solutions entering the electrospray ionization source.

Electrospray ionization (ESI) of aqueous cobalt(II) and nickel(II) nitrate solutions inter alia affords the solvated, mono- and oligonuclear nitrato complexes [Mm(NO3)2m-1(H2O)n]+ (M = Co, Ni; m = 1-5; n = 1-4). The collision-induced dissociation spectra of the mass-selected ions imply that these ions correspond to genuine hydrated metal(II) nitrato complexes in that either cluster degradation through expulsion of neutral M(NO3)2 or sequential loss of water ligands take place. In the case of the lowest member of the series (m, n = 1), however, loss of water competes with homolytic cleavage of the N-O bond, which leads to the formation of [M,O2,H2]+ cations containing formal MIII. For m > 1, similar activation of the nitrato ligand was observed under harsher ionization conditions in ESI and provides access to cationic transition-metal oxide clusters in the gas phase. In addition to the collision experiments, thermal reactions of the solvated nitrato complexes with nitrogen monoxide reveal bond-activation pathways, which shed some light on the NO-assisted pyrolysis of solid metal nitrates for the preparation of metal oxide catalysts.