Jana Roithová

Bio: Jana Roithová is an academic researcher from Radboud University Nijmegen. The author has contributed to research in topics: Dication & Ion. The author has an hindex of 40, co-authored 219 publications receiving 5377 citations. Previous affiliations of Jana Roithová include Technical University of Berlin & Academy of Sciences of the Czech Republic.

Selective activation of alkanes by gas-phase metal ions.

Abstract: The importance of the selective activation of alkanes for science and technology in the forthcoming decades does not need to be explicitly pointed out in this thematic issue of Chemical ReViews. Instead, we would like to summarize the development and the state-of-art of experimental and theoretical methods for the investigation of model reactions for alkane activation in the gas phase.1 However, before doing so let us address the question, how other scientists, both in academia as well as industry, can profit from such model studies in the gas phase, usually involving very small, charged species under conditions in a mass spectrometer which are very far from real catalysis. To this end, we refer to the synthesis of HCN as a reasonably simple example of how large-scale technical processes can be investigated in microscopic models. † In memoriam of Dr. Andreas Fiedler. * To whom correspondence should be addressed. E-mail: detlef.schroeder@ uochb.cas.cz, E-mail: roithova@natur.cuni.cz. ‡ Charles University in Prague. § Academy of Sciences of the Czech Republic. Jana Roithová (right), Ph.D., leads a group on the topic of reaction mechanisms at the Faculty of Science at the Charles University in Prague. Her research is based on the synergy of gas-phase experiments and theoretical calculations. She received her Ph.D. degree in the group of Prof. Zdenek Herman (J. Heyrovsky Institute of Physical Chemistry, Prague) on the topic of reactivity of small molecular dications in 2003. Since then she has made key contributions to superelectrophilic chemistry in the gas phase, with particular attention toward the activation of nonreactive substrates such as rare gases, nitrogen, and methane. Recently, she concentrates her research on the properties of redox-active molecules, their interactions with transition metals, and mechanisms of organometallic reactions. She is author of more than 80 papers and received, among others, a “L’Oréal for Women in Science” stipend and the Hlavka prize.

Characterization of reaction intermediates by ion spectroscopy.

Abstract: In the last decade, we have experienced massive progress in spectroscopic methods for mass-selected ions. The aim of this tutorial review is to present action spectroscopy as a powerful tool for the investigation of ionic reaction intermediates. Examples span from ultraviolet and infrared photodissociation spectroscopy of model reaction intermediates to applications of infrared multiphoton dissociation spectroscopy (IRMPD) to intermediates directly sampled from reaction mixtures. The first example of double resonance IR-UV spectroscopy of model intermediates in an organometallic reaction is also mentioned.

Helium Tagging Infrared Photodissociation Spectroscopy of Reactive Ions

Abstract: 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 HCCl(2+) 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.

Gold-Catalyzed Organic Reactions

Abstract: Although homogeneous gold catalysis was known previously, an exponential growth was only induced 12 years ago. The key findings which induce that rise of the field are discussed. This includes early reactions of allenes and furanynes and intermediates of these conversions as well as hydroarylation reactions. Other substrate types addressed are alkynyl epoxides and N-propargyl carboxamides. Important vinylgold intermediates, the transmetalation from gold to other transition metals, the development of new ligands for gold catalysis, and significant contributions from computational chemistry are other crucial points for the field highlighted here.

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Aerobic Copper-Catalyzed Organic Reactions

Abstract: The chemistry of copper is extremely rich because it can easily access Cu0, CuI, CuII, and CuIII oxidation states allowing it to act through one-electron or two-electron processes. As a result, both radical pathways and powerful two-electron bond forming pathways via organmetallic intermediates, similar to those of palladium, can occur. In addition, the different oxidation states of copper associate well with a large number of different functional groups via Lewis acid interactions or π-coordination. In total, these feature confer a remarkably broad range of activities allowing copper to catalyze the oxidation and oxidative union of many substrates. Oxygen is a highly atom economical, environmentally benign, and abundant oxidant, which makes it ideal in many ways.1 The high activation energies in the reactions of oxygen require that catalysts be employed.2 In combination with molecular oxygen, the chemistry of copper catalysis increases exponentially since oxygen can act as either a sink for electrons (oxidase activity) and/or as a source of oxygen atoms that are incorporated into the product (oxygenase activity). The oxidation of copper with oxygen is a facile process allowing catalytic turnover in net oxidative processes and ready access to the higher CuIII oxidation state, which enables a range of powerful transformations including two-electron reductive elimination to CuI. Molecular oxygen is also not hampered by toxic byproducts, being either reduced to water, occasionally via H2O2 (oxidase activity) or incorporated into the target structure with high atom economy (oxygenase activity). Such oxidations using oxygen or air (21% oxygen) have been employed safely in numerous commodity chemical continuous and batch processes.3 However, batch reactors employing volatile hydrocarbon solvents require that oxygen concentrations be kept low in the head space (typically <5–11%) to avoid flammable mixtures, which can limit the oxygen concentration in the reaction mixture.4,5,6 A number of alternate approaches have been developed allowing oxidation chemistry to be used safely across a broader array of conditions. For example, use of carbon dioxide instead of nitrogen as a diluent leads to reduced flammability.5 Alternately, water can be added to moderate the flammability allowing even pure oxygen to be employed.6 New reactor designs also allow pure oxygen to be used instead of diluted oxygen by maintaining gas bubbles in the solvent, which greatly improves reaction rates and prevents the build up of higher concentrations of oxygen in the head space.4a,7 Supercritical carbon dioxide has been found to be advantageous as a solvent due its chemical inertness towards oxidizing agents and its complete miscibility with oxygen or air over a wide range of temperatures.8 An number of flow technologies9 including flow reactors,10 capillary flow reactors,11 microchannel/microstructure structure reactors,12 and membrane reactors13 limit the amount of or afford separation of hydrocarbon/oxygen vapor phase thereby reducing the potential for explosions. Enzymatic oxidizing systems based upon copper that exploit the many advantages and unique aspects of copper as a catalyst and oxygen as an oxidant as described in the preceding paragraphs are well known. They represent a powerful set of catalysts able to direct beautiful redox chemistry in a highly site-selective and stereoselective manner on simple as well as highly functionalized molecules. This ability has inspired organic chemists to discover small molecule catalysts that can emulate such processes. In addition, copper has been recognized as a powerful catalyst in several industrial processes (e.g. phenol polymerization, Glaser-Hay alkyne coupling) stimulating the study of the fundamental reaction steps and the organometallic copper intermediates. These studies have inspiried the development of nonenzymatic copper catalysts. For these reasons, the study of copper catalysis using molecular oxygen has undergone explosive growth, from 30 citations per year in the 1980s to over 300 citations per year in the 2000s. A number of elegant reviews on the subject of catalytic copper oxidation chemistry have appeared. Most recently, reviews provide selected coverage of copper catalysts14 or a discussion of their use in the aerobic functionalization of C–H bonds.15 Other recent reviews cover copper and other metal catalysts with a range of oxidants, including oxygen, but several reaction types are not covered.16 Several other works provide a valuable overview of earlier efforts in the field.17 This review comprehensively covers copper catalyzed oxidation chemistry using oxygen as the oxidant up through 2011. Stoichiometric reactions with copper are discussed, as necessary, to put the development of the catalytic processes in context. Mixed metal systems utilizing copper, such as palladium catalyzed Wacker processes, are not included here. Decomposition reactions involving copper/oxygen and model systems of copper enzymes are not discussed exhaustively. To facilitate analysis of the reactions under discussion, the current mechanistic hypothesis is provided for each reaction. As our understanding of the basic chemical steps involving copper improve, it is expected that many of these mechanisms will evolve accordingly.

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

Abstract: The review covers the knowledge on photoremovable protecting groups and includes all relevant chromophores studied in the time period of 2000–2012; the most relevant earlier works are also discussed.

Gold(I)-Catalyzed Activation of Alkynes for the Construction of Molecular Complexity

Abstract: 1.1. General Reactivity of Alkyne-Gold(I) Complexes For centuries, gold had been considered a precious, purely decorative inert metal. It was not until 1986 that Ito and Hayashi described the first application of gold(I) in homogeneous catalysis.1 More than one decade later, the first examples of gold(I) activation of alkynes were reported by Teles2 and Tanaka,3 revealing the potential of gold(I) in organic synthesis. Now, gold(I) complexes are the most effective catalysts for the electrophilic activation of alkynes under homogeneous conditions, and a broad range of versatile synthetic tools have been developed for the construction of carbon–carbon or carbon–heteroatom bonds. Gold(I) complexes selectively activate π-bonds of alkynes in complex molecular settings,4−10 which has been attributed to relativistic effects.11−13 In general, no other electrophilic late transition metal shows the breadth of synthetic applications of homogeneous gold(I) catalysts, although in occasions less Lewis acidic Pt(II) or Ag(I) complexes can be used as an alternative,9,10,14,15 particularly in the context of the activation of alkenes.16,17 Highly electrophilic Ga(III)18−22 and In(III)23,24 salts can also be used as catalysts, although often higher catalyst loadings are required. In general, the nucleophilic Markovnikov attack to η2-[AuL]+-activated alkynes 1 forms trans-alkenyl-gold complexes 2 as intermediates (Scheme 1).4,5a,9,10,12,25−29 This activation mode also occurs in gold-catalyzed cycloisomerizations of 1,n-enynes and in hydroarylation reactions, in which the alkene or the arene act as the nucleophile. Scheme 1 Anti-Nucleophilic Attack to η2-[AuL]+-Activated Alkynes