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Electrochemical reactions are better understood by gaining insight into the molecular transformations at the electrodes. This paper introduces a straightforward experimental arrangement in which the voltammetry experiment in a standard electrochemical cell integrates with online electrospray‐ionization mass‐spectrometry. The procedure allows for monitoring of the ions produced at the working electrode. The ionic species sampling is facilitated by a silica capillary embedded in the working electrode and connected directly to the electrospray ionization source. This integration configures real‐time monitoring of the ions produced at the working electrode, enhancing our knowledge of the electrochemical process. The methodology is thoroughly described and exemplified by monitoring the reactive intermediates and products that arise during the electrochemical oxidation of carbazole. This design provides an opportunity to study intermediates in electrochemical reactions with advanced mass spectrometry methods such as ion mobility separation or ion spectroscopy. [ABSTRACT FROM AUTHOR]

Copper(II) complexes with N‐oxyl reactants such as TEMPO can selectively oxidize alcohols to aldehydes or ketones. The proposed copper intermediates of the oxidation reaction were extensively theoretically studied, but they were never experimentally detected. Here, we present an analysis of "frozen" intermediates that contain alcohols without α‐hydrogen atoms, thus preventing oxidation. The copper(II)‐TEMPO complexes with a bipyridine‐type ancillary ligand were isolated by electrospray ionization mass spectrometry and investigated spectroscopically by cryogenic photodissociation spectroscopy. The vibrational characteristics of the complexes suggest that TEMPO retains its unpaired electron even upon coordination with copper(II). In agreement, the electronic photodissociation spectra of the TEMPO‐copper(II) complexes show a characteristic band for gaseous copper(II) complexes. These results contradict interpretations of some previous density functional theory (DFT) analyses of possible reaction intermediates. The experimental data were confronted with theoretical results obtained by pure DFT (OPBE, TPSS) and hybrid DFT (TPSSH, B3LYP) calculations. The methods favor different ground states and capture various aspects of the experimental results demonstrating a multiconfigurational character of the copper(II)‐TEMPO complexes. [ABSTRACT FROM AUTHOR]

ArIO (ArI = 2-(tBuSO2)-C6H4I) is an oxidant used to oxidize FeII species to their FeIV-oxo state, enabling hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions at low energy barriers. ArIO, as a ligand, generates masked FenO species of the type Fe(n‑2)-OIAr. Herein, we used gas-phase ion–molecule reactions and DFT calculations to explore the properties of masked iron–oxo species and to understand their unmasking mechanisms. The theory shows that the I–O bond cleavage in [(TPA)-FeIVO-(ArIO)]2+ (12+, TPA = tris-(2-pyridylmethyl)-amine)) is highly endothermic; therefore, it can be achieved only in collision-induced dissociation of 12+ leading to the unmasked iron-(VI) dioxo complex. The reduction of 12+ by HAT leads to [(TPA)-FeIIIOH-(ArIO)]2+ with a reduced energy demand for the I–O bond cleavage but is, however, still endothermic. The exothermic unmasking of the FeO bond is predicted after one-electron reduction of 12+ or after OAT reactivity. The latter leads to the 4e– oxidation of unsaturated hydrocarbons: The initial OAT from [(TPA)-FeIVO-(ArIO)]2+ leads to the epoxidation of an alkene and triggers the unmasking of the second FeO bond still within one collisional complex. The second oxidation step starts with HAT from a C–H bond and follows with the rebound of the C-radical and the OH group. The process starting with the one-electron reduction could be studied with [(TQA)-FeIVO-(ArIO)]2+ (22+, TQA = tris-(2-quinolylmethyl)-amine)) because it has a sufficient electron affinity for electron transfer with alkenes. Accordingly, the reaction of 22+ with 2-carene leads to [(TQA)-FeIIIO-(ArIO)]2+ that exothermically eliminates ArI and unmasks the reactive FeV–dioxo species. [ABSTRACT FROM AUTHOR]

This review is devoted to ion spectroscopy studies of complexes relevant for the understanding of methane activation with metal ions and clusters. Methane activation starts with the formation of a complex with a metal ion. The degree of the interaction between an intact methane molecule and the ion can be monitored by the perturbations of C–H stretch vibrations in the methane molecule. Binding mediated by the electrostatic interaction results in a η3 type coordination of methane. In contrast, binding governed by orbital interactions results in a η2 type coordination of methane. We further review the spectroscopic characterization of activation products of metal–methane reactions, such as the metal–carbene and carbyne products resulting from the interaction of selected 5d metals with methane. The focus of recent research in the field has shifted towards the investigation of interactions between methane and metal clusters. We show examples highlighting that metal clusters can be more reactive in methane activation reactions. [ABSTRACT FROM AUTHOR]

This perspective gives an overview of the action spectroscopy methods for measurements of electronic, vibrational, and rotational spectra of mass‐selected ions in the gas phase. We classify and give a short overview of the existing experimental approaches in this field. There is currently a plethora of names used for, essentially, the same techniques. Hence within this overview, we scrutinized the notations and suggested terms to be generally used. The selection was either driven by making the name unique and straightforward or the term being the most broadly used one. We believe that a simplification and a unification of the notation in ion spectroscopy can make this field better accessible for experts outside the mass spectrometry community where the applications of gas‐phase action ion spectroscopy can make a large impact. [ABSTRACT FROM AUTHOR]

The mechanism of oxidation of arylamines by copper enzymes is not clarified yet. Here, we explored a reaction between a possible high-valent copper(II)-oxyl intermediate and arylamine. We have employed a TPA ligand (TPA = tris(2-pyridylmethyl)amine) with the NH2 group in position 2 of one of the pyridine rings (TPANH2). This model system allows generation of [(TPANH2)Cu(O)]+ in the gas phase, which immediately undergoes a reaction between the arylamino group and the copper oxyl moiety. The reaction leads to elimination of H2O and formation of a copper–nitrene complex. The structure of the resulting copper–nitrene complex was confirmed by infrared spectroscopy in the gas phase. We show that the copper–nitrene complex reacts by hydrogen atom transfer with 1,4-cyclohexadiene and by an order of magnitude faster by a double hydrogen atom transfer with ethanethiol and methanol. DFT calculations explain the formation of the copper nitrene as well as its reactivity in agreement with the experimental findings. [ABSTRACT FROM AUTHOR]

Copper nitrenoids are key intermediates in copper‐catalyzed direct C−H amination reactions. Further development of this important reaction relies on knowing the properties and reactivity of the nitrenoid intermediates. This work utilizes antenna ligands to form copper nitrenoid complexes and monitor the consecutive C−H amination reactions under well‐defined single‐molecule conditions in the gas phase. The [Cu(Lphoto)(Lazide)]+ precursors (Lphoto is a bidentate antenna ligand, and Lazide is an organic azide) were stored in an ion trap at 3.5 K and irradiated by visible light, which resulted in denitrogenation of the complex. Further irradiation of the copper nitrenoid led to the consecutive C−H amination of the antenna ligand. The nitrenoid complexes, as well as the products of the C−H amination, were characterized by helium tagging IRPD spectroscopy, and the mechanism was described by DFT calculations. This research demonstrates that the antenna ligands can be used to promote the denitrogenation of metal azides in the gas phase and also channel the internal energy to promote further reactivity, which opens a new way to study the reactivity of highly reactive species under well‐defined conditions. [ABSTRACT FROM AUTHOR]

Copper nitrenoids are key intermediates in copper‐catalyzed direct C−H amination reactions. Further development of this important reaction relies on knowing the properties and reactivity of the nitrenoid intermediates. This work utilizes antenna ligands to form copper nitrenoid complexes and monitor the consecutive C−H amination reactions under well‐defined single‐molecule conditions in the gas phase. The [Cu(Lphoto)(Lazide)]+ precursors (Lphoto is a bidentate antenna ligand, and Lazide is an organic azide) were stored in an ion trap at 3.5 K and irradiated by visible light, which resulted in denitrogenation of the complex. Further irradiation of the copper nitrenoid led to the consecutive C−H amination of the antenna ligand. The nitrenoid complexes, as well as the products of the C−H amination, were characterized by helium tagging IRPD spectroscopy, and the mechanism was described by DFT calculations. This research demonstrates that the antenna ligands can be used to promote the denitrogenation of metal azides in the gas phase and also channel the internal energy to promote further reactivity, which opens a new way to study the reactivity of highly reactive species under well‐defined conditions. [ABSTRACT FROM AUTHOR]

Charge stripping (CS) of the molecular ion of toluene, C7H8+→C7H82++e, is often used as a reference for the determination of second ionization energies in energy-resolved CS experiments. For calibration of the kinetic energy scale, a value of IE(C7H8+)=(15.7±0.2) eV derived from the appearance energy of the toluene dication upon electron ionization has been accepted generally. Triggered by some recent discrepancies between CS measurements on the one hand and different experimental methods as well as theoretical predictions on the other, we have reinvestigated the photon-induced double ionization of toluene using synchrotron radiation. These photoionization measurements yield phenomenological appearance energies of AE(C7H8+)=(8.81±0.03) eV for the monocation and AE(C7H82+)=(23.81±0.06) eV for the dication. The former is in good agreement with a much more precise spectroscopic value, IE(C7H8)=(8.8276±0.0006) eV. Explicit consideration of the Franck–Condon envelopes associated with photoionization to the dication in conjunction with the application of the Wannier law leads to an adiabatic ionization energy IEa(C7H8+)=(14.8±0.1) eV, which is as much as 0.9 eV lower than the previous value derived from electron ionization. Because in many previous CS measurements the transition C7H8+→C7H82++e was used as a reference, the energetics of several gaseous dications might need some readjustment. [ABSTRACT FROM AUTHOR]

The search for the chemical structures that account for diffuse interstellar bands remains the main challenge in astrochemistry. It relies on experimental verification of structures obtained from stable isomers in laboratory conditions. The actual interstellar medium, however, is exposed to much harsher conditions. Herein we demonstrate the isomerisation of small, doubly charged polyaromatic hydrocarbon phenanthrene obtained by electron ionisation at relatively high electron energies. We performed electronic and vibrational tagging photodissociation spectroscopy measurements. Our results show that phenanthrene dication has a broad visible spectrum, making it unsuitable for DIB search. We also detected another C14H102+ isomer, originating from the isomerisation of phenanthrene dication during the ionisation process. Hole-burning spectroscopy experiments provided the IR spectrum of an isomer which could be assigned based on DFT calculations as a fully conjugated system representing the global minimum on the C14H102+ potential energy surface. [ABSTRACT FROM AUTHOR]

Helmut Schwarz - there is hardly a name found more often than this in the mass spectrometry and gas-phase chemistry literature. With this Special Issue, we celebrate the richly deserved election in 2018 of Helmut as a Foreign Associate of the US National Academy of Sciences, USA. [Extracted from the article]

Abstract: Infrared multiphoton dissociation (IRMPD) spectroscopy is commonly used to determine the structure of isolated, mass‐selected ions in the gas phase. This method has been widely used since it became available at free‐electron laser (FEL) user facilities. Thus, in this Minireview, we examine the use of IRMPD/FEL spectroscopy for investigating ions derived from small molecules, metal complexes, organometallic compounds and biorelevant ions. Furthermore, we outline new applications of IRMPD spectroscopy to study biomolecules. [ABSTRACT FROM AUTHOR]

A large number of cationic Au(I) π-complexes have been reported in the literature. However, a single X-ray structure of genuine [Au(PPh 3 )(hydrocarbon)] + π-complex without any additional stabilization has not been published so far. We present herein isolation and X-ray characterization of several complexes of this type. Also, we show that these π-complexes are more stable than previously reported and we investigate different modes of activation of the [Au(PPh 3 )]Cl precatalyst on their stability in solution. [ABSTRACT FROM AUTHOR]

The interrogation of reaction intermediates is key for understanding chemical reactions; however their direct observation and study remains a considerable challenge. Mass spectrometry is one of the most sensitive analytical techniques, and its use to study reaction mixtures is now an established practice. However, the information that can be obtained is limited to elemental analysis and possibly to fragmentation behavior, which is often challenging to analyze. In order to extend the available experimental information, different types of spectroscopy in the infrared and visible region have been combined with mass spectrometry. Spectroscopy of mass selected ions usually utilizes the powerful sensitivity of mass spectrometers, and the absorption of photons is not detected as such but rather translated to mass changes. One approach to accomplish such spectroscopy involves loosely binding a tag to an ion that will be removed by absorption of one photon. We have constructed an ion trapping instrument capable of reaching temperatures that are sufficiently low to enable tagging by helium atoms in situ, thus permitting infrared photodissociation spectroscopy (IRPD) to be carried out. While tagging by larger rare gas atoms, such as neon or argon is also possible, these may cause significant structural changes to small and reactive species, making the use of helium highly beneficial. We discuss the "innocence" of helium as a tag in ion spectroscopy using several case studies. It is shown that helium tagging is effectively innocent when used with benzene dications, not interfering with their structure or IRPD spectrum. We have also provided a case study where we can see that despite its minimal size there are systems where He has a huge effect. A strong influence of the He tagging was shown in the IRPD spectra of HCCl2+ where large spectral shifts were observed. While the presented systems are rather small, they involve the formation of mixtures of isomers. We have therefore implemented two-color experiments where one laser is employed to selectively deplete a mixture by one (or more) isomer allowing helium tagging IRPD spectra of the remaining isomer(s) to be recorded via the second laser. Our experimental setup, based on a linear wire quadrupole ion trap, allows us to deplete almost 100% of all helium tagged ions in the trap. Using this special feature, we have developed attenuation experiments for determination of absolute photofragmentation cross sections. At the same time, this approach can be used to estimate the representation of isomers in a mixture. The ultimate aim is the routine use of this instrument and technique to study a wide range of reaction intermediates in catalysis. To this end, we present a study of hypervalent iron(IV)-oxo complexes ([(L)Fe(O)(NO3)]+). We show that we can spectroscopically differentiate iron complexes with S = 1 and S = 2 according to the stretching vibrations of a nitrate counterion. [ABSTRACT FROM AUTHOR]

The interrogation of reaction intermediates is key for understanding chemical reactions; however their direct observation and study remains a considerable challenge. Mass spectrometry is one of the most sensitive analytical techniques, and its use to study reaction mixtures is now an established practice. However, the information that can be obtained is limited to elemental analysis and possibly to fragmentation behavior, which is often challenging to analyze. In order to extend the available experimental information, different types of spectroscopy in the infrared and visible region have been combined with mass spectrometry. Spectroscopy of mass selected ions usually utilizes the powerful sensitivity of mass spectrometers, and the absorption of photons is not detected as such but rather translated to mass changes. One approach to accomplish such spectroscopy involves loosely binding a tag to an ion that will be removed by absorption of one photon. We have constructed an ion trapping instrument capable of reaching temperatures that are sufficiently low to enable tagging by helium atoms in situ, thus permitting infrared photodissociation spectroscopy (IRPD) to be carried out. While tagging by larger rare gas atoms, such as neon or argon is also possible, these may cause significant structural changes to small and reactive species, making the use of helium highly beneficial. We discuss the "innocence" of helium as a tag in ion spectroscopy using several case studies. It is shown that helium tagging is effectively innocent when used with benzene dications, not interfering with their structure or IRPD spectrum. We have also provided a case study where we can see that despite its minimal size there are systems where He has a huge effect. A strong influence of the He tagging was shown in the IRPD spectra of HCCl2+ where large spectral shifts were observed. While the presented systems are rather small, they involve the formation of mixtures of isomers. We have therefore implemented two-color experiments where one laser is employed to selectively deplete a mixture by one (or more) isomer allowing helium tagging IRPD spectra of the remaining isomer(s) to be recorded via the second laser. Our experimental setup, based on a linear wire quadrupole ion trap, allows us to deplete almost 100% of all helium tagged ions in the trap. Using this special feature, we have developed attenuation experiments for determination of absolute photofragmentation cross sections. At the same time, this approach can be used to estimate the representation of isomers in a mixture. The ultimate aim is the routine use of this instrument and technique to study a wide range of reaction intermediates in catalysis. To this end, we present a study of hypervalent iron(IV)-oxo complexes ([(L)Fe(O)(NO3)]+). We show that we can spectroscopically differentiate iron complexes with S = 1 and S = 2 according to the stretching vibrations of a nitrate counterion. [ABSTRACT FROM AUTHOR]

Electrospray ionization mass spectrometry (ESI-MS) is becoming an important tool for mechanistic studies in organic and organometallic chemistry. It allows investigation of reaction mixtures including monitoring of reactants, products, and intermediates, studying properties of the intermediates and their reactivity. Studying the reactive species in the gas phase can be advantageously combined with theoretical calculations. This review is focused on ESI-MS studies of copper-catalyzed reactions. Possible effects of the electrospray process on the transfer of the copper complexes to the gas phase are discussed. The plethora of mass spectrometric approaches is demonstrated on copper mediated C-H activations, cross coupling reactions, rearrangements, organocuprate chemistry, and other examples. [ABSTRACT FROM AUTHOR]

Iron‐nitrenoid complexes can activate C−H bonds and, thus, potentially directly transform C−H into C−N bonds. Low‐coordination complexes are the main reported systems; however, octahedral iron complexes can be air‐stable alternatives forming the iron‐nitrenoid species. Here, a novel octahedral non‐heme iron‐acyl‐nitrenoid complex is presented. Its reactivity was studied using a flow chemistry setup with online mass spectrometry detection, which allows qualitative reaction kinetics evaluation and the detection of the intermediates. The iron‐nitrenoid complex reacts with thiophenol by H‐Atom transfer, followed by a rebound to form a new N−S bond. The rebound intermediate could be detected and distinguished from the product complex. The reaction of the iron‐acyl‐nitrenoid complex with hydrocarbons results in the activation of the C−H bond via hydrogen‐atom transfer with no subsequent rebound process. [ABSTRACT FROM AUTHOR]

Experimental techniques and terminology in gas-phase ion spectroscopy By Aleksandr Y. Pereverzev and Jana Roithová. [Extracted from the article]

Different isomers of the CHCl 2+ dications were studied using infrared predissociation spectroscopy with helium and neon tagging in a low-temperature trapping experiment. It is shown that H–C–Cl 2+ isomers form the dominant portion of the trapped dications that were detected by IRPD spectroscopy. Other possible isomers, such as H–Cl–C 2+ , are depleted by a proton transfer reaction with the helium buffer gas but by using neon tagging it was possible to stabilize the neon complexes of H–Cl–C 2+ and detect them in the IRPD experiment. [ABSTRACT FROM AUTHOR]

Proton affinities of several efficient organocatalysts METHOX, QUINOX, ANETOX, KOTOX, FUREOX, and FUROOX bearing a pyridine N-oxide or 2,2'-bipyridyl N,N'-dioxide moiety were determined by using extended kinetic method and density functional theory calculations. Proton affinities are in the range of 1030-1060 kJ mol-1. Using isodesmic reactions, the effect of combining two pyridine N-oxide units in the neutral and the protonated molecule was studied: The combination of an unfavorable interaction in the former case and a favorable interaction in the latter accounts for the superbasic properties of 2,2'-bipyridyl N,N'-dioxides. Last but not least, the theoretically predicted pKa in ethanol are 0.1, -2.7, 0.9, 1.8, 1.9, and 2.3 for the METHOX, QUINOX, ANETOX, FUROOX, FUREOX, and KOTOX, respectively. [ABSTRACT FROM AUTHOR]

Pyranoanthocyanins are formed during food treatment and maturation (e.g. wine, juices), and they can be considered a natural alternative to artificial food colorants. Tandem mass spectrometry (MS/MS) is perhaps the most important technique in analysis of anthocyanin dyes. Knowledge of fragmentation pattern is a key aspect of their successful structural characterization. Polyphenolic compounds are known to lose small molecules during collision-induced dissociation (CID) in MS/MS experiments. However, the specific positions where such losses occur preferentially are unknown. The aim of this communication is to investigate the energetically most preferred places for H2O and CO losses during the fragmentation of 5-methylpyranopelargonidin molecule by the means of computational chemistry (employing density functional theory) combined with CID MS/MS experiments and infrared multiphoton dissociation spectroscopy. Mechanisms responsible for the fragmentations were investigated, and optimal geometries and transition states were obtained. Cleavage of water as well as carbon monoxide occurs preferentially from the C-ring of flavonoid skeleton. In the most stable structure of 5-methylpyranopelargonidin, B-ring was found to be tilted with respect to the rest of the molecule. Planarization effort of the parent molecule contributes both to its decarbonylation and dehydration. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Reductive eliminationof ethane from the palladium(IV) complex[PdMe3(bpy)I] (bpy = 2,2′-bipyridine) is studiedby electrospray ionization mass spectrometry. Palladium(IV) complexescan be detected as binuclear clusters [Pd2Me6I(bpy)2]+or as complexes [PdMe3(bpy)(L)]+stabilized by an electron-donating ligand L.Fragmentation of all palladium(IV) complexes is dominated by eliminationof ethane which corresponds to the reductive elimination couplingof the methyl groups. The associated energy demands for differentcomplexes reveal that the mononuclear complexes with poorly electron-donatingligands provide the fastest reaction. [ABSTRACT FROM AUTHOR]

Preferential of differently N-substituted amides of 3-hydroxy-2-naphthoic acids 1 and 2 catalyzed by Cu(OH)Cl•TMEDA was observed. The reaction mechanism was investigated using mass spectrometry tools. It was shown that the properties of the N-substituent significantly influence the properties of the corresponding copper complexes of the deprotonated compounds ([(1-H)Cu(TMEDA)]+ and [(2-H)Cu(TMEDA)]+). Analysis of the patterns of the copper complexes revealed that while the former is prone to the one electron oxidation of (1-H)ˉ, the latter has a larger binding energy between (2-H)ˉ and copper(II). Interplay between the abundance of the copper complexes and their reactivities explains the preferential . The results are further supported by exploratory density functional theory calculations. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The reactivities of C9H x 2+ dications (x =6–8) generated by electron ionization (EI) of indene, 1-phenylpropyne, and 3-phenylpropyne, respectively, were studied in thermal collisions with methane. The most reactive dications correspond to dehydrogenated C9H6 2+, which show about 65% yield of C–C coupling products. The yield of coupling products in the reactions of radical dications C9H7 2+ drop to about 15% and the reactivity is dominated by electron transfer and charge-separation processes. The reaction between C9H8 2+ and methane leads mostly to proton transfer. There are differences between reactivities of analogous dications generated from different neutral precursors and therefore it can be stated that even dications generated by EI retain a partial memory of the structure of the neutral precursor. [Copyright &y& Elsevier]

Superelectrophilic chemistry in the gas phase is driven by the high intrinsic reactivity of dications. The formation of new doubly charged products proceeds via highly internally excited intermediates. Conditions for the formation of the doubly charged intermediates and a "cooling principle" in the reactivity of dications are explained. The reactivity is demonstrated with several examples. [ABSTRACT FROM AUTHOR]

Electrospray ionization of methanolic solutions of p-hydroxyphenacyl derivatives HO-C6H4-C(O)-CH2-X (X = leaving group) provides abundant signals for the deprotonated species which are assigned to the corresponding phenolate anions -O-C6H4-C(O)-CH2-X. Upon collisional activation in the gas phase, these anions inter alia undergo loss of a neutral "C8H6O2" 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 = CF3COO in order to reveal the energetically most favorable pathway for the formation of neutral "C8H6O2" suggest three different routes of similar energy demands, involving a spirocyclopropanone, epoxide formation, and a diradical, respectively. [ABSTRACT FROM AUTHOR]

The article discusses the experimental and theoretical methods in investigating the model reactions of alkane activation in the gas phase. It mentions that two general aspects of gas-phase ion chemistry and applied sciences need to be addressed for the gas-phase experiments which are measures for reactivity and selectivity in ion reactions. It examines the principles for the said experiments in which it cites the major methods to be used in the experiments which include guided-ion beam methods.

With the use of the model Complexes [(PQ)FeCl(CH3O)]+, [(phen)FeCl(CH3O)]+, and [(PQ)(phen)FeCl(CH3O)], where PQ is 9,10-phenanthraquinone and phen is 1,10-phenanthroline, the reactivity of phenanlhraquinone in complexes with iron(lll) is investigated. It is shown that 9,10-phenanthraquinone takes part in .redox processes occurring at iron and thereby allows the oxidation of methanolate to formaldehyde. The oxidation is driven by the reduction of iron(lll) to iron(ll) and 9,10-phenanthraquinone to Ihe semihydroquinone radical or semiquinolate, if the hydrogen atom is transferred from methanolate to chlorine rather than PQ. 1,10-Pher,anthroline, on the other hand, acts as an innocent ligand, and the [(phen)FeCl(CH3O)+ complex shows a typical two-state reactivity. The reactivity of [(PQ)(phen)FeCl(CH3O)+ reveals that the hexacoordination of iron energetically facilitates the oxidation of methanolate, and therefore it is proposed that, in the presence of suitable reductants, the mixture of iron(lll) and 9,10-phenanthraquinone can lead to the generation of the semihydroquinone radicals, species responsible for the toxicity of PQ. The fragmentation of ((PQ)(phen)FeCI(CH3O)]+ also demonstrates a strong binding of phen toward iron(lll), which is a reason for using phen as an iron chelator in biochemistry. The structures and reactivilies of the complexes are investigated by means of mass spectrometry, infrared multiphoton dissociation spectra, and density functional theory calculations. [ABSTRACT FROM AUTHOR]

Electrospray ionization of uranyl nitrate dissolved in water generates gaseous species containing either hydroxo-uranyl [UO[sub2](OH)][sup+] or nitrato-uranyl [UO[sub2](NO[sub3])][sup+] contract ion pairs solvated by up to four water molecules. Furthermore, uranyl clusters of the general type [U[subm]O[sub2m](X,Y)[sub2m-1](H[sub2]O)[subn]][sup+] (X,Y = OH, NO[sub3]) with m = 1-5 and n = 2-4 are formed. Collision-induced dissociation experiment 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[sub2][sup2+] 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[sub2](OH)[sub2], UO[sub2](OH)(NO[sub3]), and UO[sub2](NO[sub3])[sub2]. 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. [ABSTRACT FROM AUTHOR]

Abstract: The close interaction between experiment and theory is a key motif in contemporary transition-metal chemistry with mechanistic orientation. As an illustration of this aspect, we present selected examples from the gas-phase chemistry of the coinage metals (Cu, Ag, Au). The topics range from seemingly simple systems, such as hydrated metal ions, via the role of formal and real charge states in gaseous species to several case studies which demonstrate that modern mass spectrometry can contribute to the understanding of important processes in applied chemistry, such as Crmations using organocuprates, the epoxidation of ethylene on silver contacts, and the recent achievements in catalysis with gold compounds. [Copyright &y& Elsevier]

Abstract: The reactions of methane with the dications C7H6 2+, C7H7 2+, and C7H8 2+ generated by electron ionization of toluene are studied using mass-spectrometry tools. It is shown that the reactivity is dominated by the formation of doubly charged intermediates, which can either eliminate molecular hydrogen to yield doubly charged products or undergo charge-separation reactions leading to the formation of a methyl cation and the corresponding C7H n+1 + monocation. Typical processes observed for dications, like electron transfer or proton transfer, are largely suppressed. The theoretically derived mechanism of the reaction between C7H6 2+ and CH4 indicates that the formation of the doubly charged intermediate is kinetically preferred at low internal energies of the reactants. In agreement, the experimental results show a pronounced hydrogen scrambling and dominant formation of the doubly charged products at low collision energies, whereas direct hydride transfer prevails at larger collision energies. [Copyright &y& Elsevier]

Electrospray ionization (ESI) of dilute solutions of 1,1′-bi-2-naphthol (BINOL) and iron(II) or iron(III) sulfate in methanol/water allows the generation of monocationic complexes of iron and deprotonated BINOL ligands with additional methanol molecules in the coordination sphere, and the types of complexes formed can be controlled by the valence of the iron precursors used in ESI. Thus, iron(II) sulfate leads to [(BINOLate)Fe(CH3OH) n ]+ complexes (n = 0–3), whereas usage of iron(III) sulfate allows the generation of [(BINOLdiate)-Fe(CH3OH) n ]+ cations (n = 0–2); here, BINOLate and BINOLdiate stand for singly and doubly deprotonated BINOL, respectively. Upon collision-induced dissociation, the mass-selected ions with n > 0 first lose the methanol ligands and then undergo characteristic fragmentations. Bare [(BINOLdiate)Fe]+, a formal iron(III) species, undergoes decarbonylation, which is known as a typical fragmentation of ionized phenols and phenolates either as free species or as the corresponding metal complexes. The bare [(BINOLate)Fe]+ cation, on the other hand, preferentially loses neutral FeOH to afford an organic C20H12O+• cation radical, which most likely corresponds to ionized 1,1′-dinaphthofurane. [Copyright &y& Elsevier]

Abstract: The second ionization energies of phenol and the isomeric dihydroxybenzenes as well as their methyl ethers are determined by means of charge-stripping mass spectrometry. Compared to the parent molecule benzene, introduction of a hydroxy substituent lowers the second ionization energy by ca. 0.6eV, whereas a methoxy substituent exerts a much more pronounced effect of about 1.6eV. With regard to disubstitution, the effects behave almost completely additive for the para-derivatives, whereas the ortho-compounds are stabilized only about half that much by the second substituent, and for the meta-derivatives the influence of a second donor substituent is even smaller. The trends observed highlight the role of quinoid resonance structures for the stabilization of the dicationic compounds. [Copyright &y& Elsevier]

Abstract: Structures and fragmentation patterns of C7H7 2+, C8H9 2+, and C9H11 2+ dications generated from various precursors are studied by means of mass spectrometry in combination with density functional theory calculations. It is shown that double protonation of the prototype hydrocarbon triradical 1,3,5-trimethylenebenzene (C9H9), similar to single protonation, leads to relative stabilization of the doublet state so that it becomes the ground state of the radical dication. The preferred structures of the C9H11 2+ manifold are best described as primary, secondary, or tertiary alkyl cations attached to a benzene radical-cation core. The most abundant fragmentation corresponds to dehydrogenation. The also observed charge-separation fragmentations of the dications can be rationalized on the basis of the preferred molecular structures. In addition, a brief comparison of the dicationic systems C7H7 2+, C8H9 2+, and C9H11 2+ reveals that while the larger aromatic dications do indeed bear a structural memory, the lower homologues C7H7 2+ and C8H9 2+ completely lose the structural identity of their neutral precursors. [Copyright &y& Elsevier]

Electrospray ionization from methanolic solution can be used for the generation of the free cyclophane tetracations 14+-34+ from the corresponding hexafluorophosphates. In the idealized gas phase, these tetracations are long-lived and can easily be handled for further spectroscopic studies. Collision-induced dissociation of the free tetracations brings about charge separation via cleavage of the pyridinium bonds, leading to a pair of dications. Subsequently, these dications undergo another charge separation reaction to finally afford singly charged cations. In addition to the free tetracations, also the corresponding trications having one PF6- counterion are examined. Collision-induced dissociation of the trications leads to a formal substitution reaction concomitant with C-F bond formation. Further, the catenanes of the tetracations 14+-34+ with bis-p-phenylene-34-crown-10 (4) are investigated. For the parent compound 1, also the gas-phase infrared spectrum is reported for the first time. [ABSTRACT FROM AUTHOR]

Abstract: Reactions of the hydrocarbon dication C4H3 2+ with a series of atomic and molecular targets (Kr, Xe, N2, NO, NH3, C2H2, and CH4) were investigated in crossed-beam scattering and guided-beam (quadrupole–octopole–quadrupole, QOQ) experiments. Non-dissociative charge transfer (NDCT), leading to the product ion C4H3 +, and proton transfer (PT), leading to the product ion C4H2 +, were observed. In several systems, however, dissociative charge transfer (DCT) contributed significantly to the formation of the product ion C4H2 +. Full scattering diagrams of the products C4H3 and C4H2 + were obtained for the reaction with acetylene. For the other systems, energy profiles of the products close to the angular maximum were obtained. The hydrocarbon products C4H2 + and C4H3 + were scattered mostly forward, suggesting an impulsive mechanism of their formation at the collision energies investigated; the only exception was proton transfer with H2, where the energy profile of C4H2 + indicated substantial backward scattering and formation of an intermediate. From relative translational energy distributions of the products, conclusions could be made about electronic states of the hydrocarbon cations formed in these reactions. [Copyright &y& Elsevier]

Abstract: Electrospray ionization (ESI) of aqueous iron(III) nitrate solutions can be used as an easy route for the generation of bare iron-oxide and hydroxide cations such as FeO+, FeOH+, and Fe(OH)2 + in the gas phase. Analysis of the ESI mass spectra obtained under variable conditions in combination with complementary collision experiments suggest that the iron-oxo species are formed by collision-energy driven replacements of nitrato-ligands by water stemming from the sprayed solution. It is demonstrated that the gas-phase reactivity of methane with the iron-oxide cation FeO+ generated via ESI is in good agreement with the well-documented literature data for this reaction. [Copyright &y& Elsevier]

Abstract: The formation and fragmentation of the indene dication is studied using synchrotron radiation. The double-ionization energy of indene amounts to 21.8±0.1eV. The appearance energies of the fragments and are 25.8±0.1eV and 25.7±0.2eV, respectively. Although the appearance energies are almost the same, the dicationic fragment is formed in a higher yield than . It is suggested that the elimination of atomic hydrogen is associated with a considerable energy barrier, whereas the H2 elimination proceeds via very small barrier or is barrier-less process with respect to the reaction endothermicity. [Copyright &y& Elsevier]

The structure of the C7H82+ dication generated upon electron ionization of toluene is investigated by experimental and theoretical means. For the long-lived C7H82+ dication, the experimental findings obtained with a novel SIFT/GIB instrument suggest complete loss of structural integrity corresponding to the toluene structure. Instead, the manifold of C7H82+ dications most likely to be formed is assigned to a mixture of the cycloheptatriene dication and ring-protonated benzylium ions. [ABSTRACT FROM AUTHOR]

Abstract: Mass spectrometric methods are used for an investigation of the C–O bond formation between alkynes and alcohols mediated by cationic gold(I) complexes. In the condensed-phase catalysis, an efficient coupling to the corresponding enol ethers has been observed. In the gas phase, however, kinetic and entropic restrictions are too large for both bare Au+ as well as (CH3)3PAu+ to permit bond formation in strictly bimolecular collisions occurring at thermal energies. The experimental findings are complemented by a theoretical study of the Au+/C2H2/CH3OH system using density functional theory. [Copyright &y& Elsevier]

Ground and excited states of the dication CHCl2+ and the corresponding cation CHCl+ were investigated using the CASSCF-AQCC method with moderate ANO basis sets. Both isomers of the dication and cation were investigated: HCCl2+ and HCCl+ (with H bonded to C), and CClH2+ and CClH+ (with H bonded to Cl). The energetics and geometries of stable configurations were characterized and energies of both adiabatic and vertical transitions between the dication and the cation were determined. The data were found essential to interpret correctly experimental results on charge transfer collision of the dication with noble gases and to assess the role of the CClH+ isomer in them. [Copyright &y& Elsevier]

Collision energy dependence of integral cross-sections of charge transfer processes and chemical reactions in the system CHCl2++Ar and CHCl2++D2 was investigated in guided beam experiments. Both singly charged reaction products resulting from non-dissociative charge transfer and chemical reactions in these systems could be identified, in the former system CHCl+, Ar+; CCl+, ArH+, in the latter CHCl+, D2+; CHDCl+; CCl+, HD2+. The identification of ArH+ and HD2+ helps to specify the reaction of CCl+ formation as a proton transfer process from the dication CHCl2+. The integral cross-section for the charge transfer process with Ar was almost independent of collision energy and its value was close to 2 A˚2; the cross-sections for the chemical reaction of CCl+ formation with Ar was about 6 A˚2 and showed an increase at low collision energy. The integral cross-section of the reactions with D2 were of the same order of magnitude as those with Ar. [Copyright &y& Elsevier]

Photokatalytische Reaktionen, die einen reduktiven radikal‐polaren Übergang (RRPCO) beinhalten, erzeugen Intermediate mit carbanionischer Reaktivität. Viele dieser postulierten Intermediate entsprechen hochreaktiven metallorganischen Verbindungen. Die Bedingungen für ihre Bildung werden im Allgemeinen jedoch von ihren isolierten metallorganischen Analoga nicht toleriert und häufig wird eine andere Reaktivität beobachtet. Unsere Untersuchungen zu ihrer Natur und Reaktivität unter den üblichen photokatalytischen Bedingungen zeigen auf, dass diese Intermediate in der Tat als freie, superbasische Carbanionen beschrieben werden können, die in der Lage sind, gängige polare Lösungsmittel wie Acetonitril und Dimethylsulfoxid zu deprotonieren, die normalerweise als inert gelten. Ihre Basizität, nicht nur gegenüber Lösungsmitteln, sondern auch gegenüber Elektrophilen wie Aldehyden, Ketonen und Estern, ist vergleichbar mit der Reaktivität von isolierten Carbanionen in der Gasphase. Zuvor erfolglose Reaktionen, von denen man annahm, dass sie aus mangelnder Reaktivität resultieren, lassen sich durch ihre hohe Reaktivität gegenüber dem Lösungsmittel und schwach aciden Protonen der Reaktionspartner erklären. Dies liefert eine intuitive Erklärung für das Verhalten von photokatalytisch erzeugten Carbanionen, die es ermöglicht, Reaktionsmechanismen zu verifizieren, bei denen ein RRPCO‐Schritt vermutet wird, und erlaubt eine Abschätzung des synthetischen Anwendungsbereiches. [ABSTRACT FROM AUTHOR]

Photocatalytic reactions involving a reductive radical‐polar crossover (RRPCO) generate intermediates with carbanionic reactivity. Many of these proposed intermediates resemble highly reactive organometallic compounds. However, conditions of their formation are generally not tolerated by their isolated organometallic versions and often a different reactivity is observed. Our investigations on their nature and reactivity under commonly used photocatalytic conditions demonstrate that these intermediates are indeed best described as free, superbasic carbanions capable of deprotonating common polar solvents usually assumed to be inert such as acetonitrile, dimethylformamide, and dimethylsulfoxide. Their basicity not only towards solvents but also towards electrophiles, such as aldehydes, ketones, and esters, is comparable to the reactivity of isolated carbanions in the gas‐phase. Previously unsuccessful transformations thought to result from a lack of reactivity are explained by their high reactivity towards the solvent and weakly acidic protons of reaction partners. An intuitive explanation for the mode of action of photocatalytically generated carbanions is provided, which enables methods to verify reaction mechanisms proposed to involve an RRPCO step and to identify the reasons for the limitations of current methods. [ABSTRACT FROM AUTHOR]

The Eschenmoser coupling reaction (ECR) of thioamides with electrophiles is believed to proceed via thiirane intermediates. However, little is known about converting the intermediates into ECR products. Previous mechanistic studies involved external thiophiles to remove the sulfur atom from the intermediates. In this work, an ECR proceeding without any thiophilic agent or base is studied by electrospray ionization‐mass spectrometry. ESI‐MS enables the detection of the so‐far elusive polysulfide species Sn, with n ranging from 2 to 16 sulfur atoms, proposed to be the key species leading to product formation. Integrating observations from ion mobility spectrometry, ion spectroscopy, and reaction monitoring via flow chemistry coupled with mass spectrometry provides a comprehensive understanding of the reaction mechanism and uncovers the autocatalytic nature of the ECR reaction. [ABSTRACT FROM AUTHOR]

Complex reaction mixtures, like those postulated on early Earth, present an analytical challenge because of the number of components, their similarity, and vastly different concentrations. Interpreting the reaction networks is typically based on simplified or partial data, limiting our insight. We present a new approach based on online monitoring of reaction mixtures formed by the formose reaction by ion‐mobility‐separation mass‐spectrometry. Monitoring the reaction mixtures led to large data sets that we analyzed by non‐negative matrix factorization, thereby identifying ion‐signal groups capturing the time evolution of the network. The groups comprised ≈300 major ion signals corresponding to sugar‐calcium complexes formed during the formose reaction. Multivariate analysis of the kinetic profiles of these complexes provided an overview of the interconnected kinetic processes in the solution, highlighting different pathways for sugar growth and the effects of different initiators on the initial kinetics. Reconstructing the network's topology further, we revealed so far unnoticed fast retro‐aldol reaction of ketoses, which significantly affects the initial reaction dynamics. We also detected the onset of sugar‐backbone branching for C6 sugars and cyclization reactions starting for C5 sugars. This top‐down analytical approach opens a new way to analyze complex dynamic mixtures online with unprecedented coverage and time resolution. [ABSTRACT FROM AUTHOR]

Complex reaction mixtures, like those postulated on early Earth, present an analytical challenge because of the number of components, their similarity, and vastly different concentrations. Interpreting the reaction networks is typically based on simplified or partial data, limiting our insight. We present a new approach based on online monitoring of reaction mixtures formed by the formose reaction by ion‐mobility‐separation mass‐spectrometry. Monitoring the reaction mixtures led to large data sets that we analyzed by non‐negative matrix factorization, thereby identifying ion‐signal groups capturing the time evolution of the network. The groups comprised ≈300 major ion signals corresponding to sugar‐calcium complexes formed during the formose reaction. Multivariate analysis of the kinetic profiles of these complexes provided an overview of the interconnected kinetic processes in the solution, highlighting different pathways for sugar growth and the effects of different initiators on the initial kinetics. Reconstructing the network's topology further, we revealed so far unnoticed fast retro‐aldol reaction of ketoses, which significantly affects the initial reaction dynamics. We also detected the onset of sugar‐backbone branching for C6 sugars and cyclization reactions starting for C5 sugars. This top‐down analytical approach opens a new way to analyze complex dynamic mixtures online with unprecedented coverage and time resolution. [ABSTRACT FROM AUTHOR]