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Reaction intermediates in homogeneous gold catalysis
Shcherbachenko, Elena ; Roithová, Jana (advisor) ; Matoušová, Eliška (referee)
The presented master thesis is devoted to the investigation of reaction intermediates in homogeneous gold catalysis. Electrospray ionization mass spectrometry (ESI-MS) was used as the primary research technique in this study. Delayed reactant labeling was used as the main method. I have focused mainly on the hydration of 1-phenyl-1-propyne catalyzed by the gold complex [Au(IPr)(MeCN)]BF4 (IPr = 1,3-bis(2,6-di-iso-propylphenyl)imidazol-2- ylidene). I have detected two main intermediates containing one or two gold atoms, respectively (monoaurated and diaurated intermediate). I have obtained rate constants for the degradation of the reaction intermediates and their half-lives. I have derived kinetic isotope effects for the formation and the decomposition of the detected intermediates. I have shown that the kinetics of the degradation of both intermediates is identical, therefore I conclude that hydration of alkynes catalyzed by gold complex [Au(IPr)(MeCN)]BF4 proceeds most probably via neutral monoaurated intermediates. These neutral intermediates are detected by ESI-MS as protonated (monoaurated intermediate) or tagged by a second gold cation (diaurated intermediate). Key words: gold catalysis, reaction intermediates, electrospray ionization, mass spectrometry.
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Investigation of Non-Heme Iron-Oxo Intermediates in the Gas Phase
Andris, Erik ; Roithová, Jana (advisor) ; Nachtigall, Petr (referee) ; Klán, Petr (referee)
I used helium-tagging infrared photodissociation spectroscopy of ions in the IR (IRPD) and vis (visPD) range in conjunction with gas-phase reactivity studies to study biomimetic terminal iron-oxo complexes. In first part of the work, I measured IRPD spectra of iron(IV)- oxo complexes of TMC, N4Py and PyTACN amine ligands in different charge states. Results show that the gas-phase Fe=O stretching frequencies are, on average, blue-shifted by 9 cm-1 with respect to the condensed phase. I prepared stereoisomers of [(PyTACN)FeIV (O)(X)]+ complexes (X = CF3COO, NO3) that were in quintet and triplet state using nitrate cleavage method and showed that the Fe=O frequency of these iron(IV)-oxo complexes is not affected by the spin state. Gas-phase reactivity shows that dicationic complexes react with 1,4- cyclohexadiene by hydride transfer and monocationic complexes engage in hydrogen atom transfer (HAT) from the methylene group and oxygen atom transfer to the C=C bond. Variation of the ligand trans to the Fe=O unit has the greatest influence on reactivity, whereas the spin state has a modest effect. In the second part of the work, I prepared and studied gas- phase iron(III)-oxo complexes with N4Py, TPA, TQA and TMC ligands. IRPD and visPD spectra in conjunction with DFT calculations allowed me to assign the...
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Effect of silver in homogeneous gold catalysis
Motloch, Petr ; Roithová, Jana (advisor) ; Hocek, Michal (referee)
Gold catalysis has recently experienced a sustained upswing in interest from scientific community. The amount of new reactions catalysed by gold is so significant that little is known about mechanisms of most of these reactions. Research into mechanisms of (not only) gold catalysed reactions is therefore very significant area of interest and important to the continued improvement of gold catalysed reactions. Formation of cationic π-complexes is considered a first mechanistic step in reactions catalysed by gold(I). The bond dissociation energies of gas phase cationic π-complexes were investigated by mass spectrometry and theory calculations in this thesis. These complexes consisted of differently substituted unsaturated hydrocarbons (alkenes, alkynes, alkadienes and allenes) and complex cations of silver and gold containing second ligand (triphenylphosphine, acetonitrile). On the basis of the results obtained from this study, a possible origin of the "silver effect" in gold(I) catalysis is discussed. Key words catalysis, gold, silver, mass spectrometry, DFT calculations, reaction intermediates
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Study of C-C coupling of dienes catalyzed by ruthenium(II) complexes
Hanikýřová, Eva ; Roithová, Jana (advisor) ; Jaklová Dytrtová, Jana (referee)
Title: Study of C-C coupling of dienes catalyzed by ruthenium (II) complexes. Author: Bc. Eva Hanikýřová Department: Department of Organic Chemistry Supervisor: Mgr. Jana Roithová, Ph.D. Abstract Transition metal catalyzed cycloadditions have contributed extensively to organic synthesis. The use of ruthenium complexes in those reactions gain importance due to their demonstrated ability in the catalytic carbon-carbon bond formations via ruthenacycle intermediates. In our studies, we have concentrated on the interaction between ruthenium (II) and alkenes using mass spectrometry with electrospray ionization. This technique allows to investigate ruthenium complexes in the ionized states, and allows to investigate these structures by using MS/MS analyse. Our experimental research was complemented by quantum chemical calculations using Density functional theory. The research leads to a more detailed understanding to Ruthenium complexes with unsaturated hydrocarbons reaction mechanism. Key words Gas-phase chemistry, Reaction mechanisms, Electrospray Ionization, Catalyst, [CpRu(CH3CN)3]PF6, Mass Spectrometry
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Reversible interactions of pyrazines and photoluminescent dihydropyrazines
Coufal, Radek ; Drahoňovský, Dušan (advisor) ; Roithová, Jana (referee)
This thesis deals with two independent topics. The first is focused on the study of reversible covalent interactions of a carbonyl group with alcohols and water forming hemiacetals (respectively hydrate) derived from pyrazine trifluormethylketone. The main research method in this part is the NMR spectroscopy and experimental results are also supported by quantum chemical calculations. The second topic aims to the preparation and the study of photochemical properties of three dihydropyrazines which exhibit fluorescence both in solution and solid phase. The fluorescence can be influenced by means of complexation by various metal ions. Prepared dihydropyrazines also show interesting values of the Stokes shift. The structure of these new compounds was confirmed by X-ray analysis.
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Synthesis and aplication of Dewar benzenes
Janková, Štěpánka ; Kotora, Martin (advisor) ; Roithová, Jana (referee) ; Svoboda, Jiří (referee)
Dewar benzenes are valence isomers of benzenes, which can be prepared by their thermic or photochemical rearrangement.1,2,3 They posses interesting physical and chemical properties due to the presence of the strained bicyclic framework. I studied synthesis of para-substituted phenyl Dewar benzenes and consequently kinetics of their thermal rearrangement for new information about mechanism of this unclear reaction. I also showed synthesis of new substituted aromatic and polyaromatic compounds, in which the key intermediates were Dewar benzenes (Scheme 1). Their chemical and physical properties are also going to be discussed. Scheme 1 R R R Cl3Al R + Ar COOMe RR R R COOMe Ar DMSO Me Me Me Me C6H4-X COOMe Fe n CO2MeMe Me Me Me Me Me Me R R R R S Me MeO2C EtO2C R R R R 1. van Tamelen, E. E.;Pappas, S. P. J. Am. Chem. Soc. 1962, 84, 3789. 2. Koster, J. B.; Timmermans, G. J.; van Bekkum, H. Synthesis, 1971, 139. 3. Schäfer, W.; Hellmann, H. Angew. Chem. Int. Ed. 1967, 6, 518.
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Characterization of organogold compounds
Shcherbachenko, Elena ; Roithová, Jana (advisor) ; Míšek, Jiří (referee)
Geminally diaurated complexes are important intermediates involved in some of the gold catalyzed reactions and therefore they have become a subject of the current research. The aim of this thesis was to assess the influence of electronic structure of an aryl ligand on the stability of gold complexes with three-center-two-electron interaction Au2C. A series of geminally diaurated complexes was obtained by a reaction of gold complex [(IPr)Au(NCMe)]BF4 (IPr = 1,3-bis(2,6-di-iso-propylphenyl)imidazol-2-ylidene) with arylboronic acids ArB(OH)2 bearing different substituents at the aryl group (Ar = para- O2NC6H4, para-NCC6H4, para-ClC6H4, C6H5, para-H3CC6H4, para-H3COC6H4, meta- O2NC6H4, meta-NCC6H4, meta-H3CC6H4, ortho-O2NC6H4, ortho-NCC6H4, ortho-H3CC6H4). Mass spectrometry (MS) was used as the main experimental method in this study. Appearance energies (AE) for the fragmentation of geminally diaurated complexes were estimated by the methods MS/MS. The obtained energies were plotted against the corresponding Hammett σ-constants to assess the correlation between the electronic structure of a given aryl ligand and the stability of the Au2C bond. It was found that structures of gold complexes derived from the cyanophenylboronic acids do not correspond to the geminally diaurated complexes but to the...
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Ion spectroscopy of reaction intermediates
Škríba, Anton ; Roithová, Jana (advisor) ; Stará, Irena (referee) ; Martinů, Tomáš (referee)
The combination of mass spectrometry, infrared action spectroscopy and quantum-chemical calculations provides a great tool for the study of the structures, properties and reactivities of molecules in the gas phase. This thesis is divided into two main parts. The first part reviews some of the experimental (ESI-MS, ion spectroscopy) and theoretical (DFT) methods used in this thesis and gives a brief description on instrumentation. Second part is presenting four practical applications of gas phase studies in organic and organometallic chemistry: (1) Describing the influence of two functional groups of para-aminophenol on the protonation site. (2) Presenting how the structure and conformation of diethylmalonate is affected by the coordination with silver and gold. (3) Showing the possibility to distinguish between the isobaric complexes and identifying the key intermediates of ruthenium catalyzed C-C coupling. (4) Discussing the possible use of He-tagging infrared spectra not only for structure determination but also for the benchmarking of DFT methods.
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