|
|
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...
|
|
|
Investigation of copper complexes using mass spectrometry
Yassaghi, Ghazaleh ; Roithová, Jana (advisor) ; Jaklová Dytrtová, Jana (referee) ; Polášek, Miroslav (referee)
This dissertation thesis reports the study of several copper complexes and their reactivity in the gas phase. The complexes were analyzed using different methods, namely, electrospray ionization-mass spectrometry (ESI-MS), infrared multiphoton dissociation (IRMPD) spectroscopy and theoretical calculations. In the first part, the complexes of redox-active ligands (catechol, maltol, and phenanthraquinone) with copper were studied under electrospray ionization conditions. [Cu(PQ)2]+ (PQ = 9,10-phenanthraquinone), [Cu(maltol)(maltol-H)]+ and [Cu(maltol)(maltol-H2)]+ were produced by electrospray ionization. The copper complexes were compared with complexes of other metals (Zn, Ag, and Na), and the structures were studied by collision induced dissociation (CID) and IRMPD spectroscopy. The redox process of copper complexes was studied using the C-O stretching mode as a redox marker and using fragmentation experiments. Both the phenanthraquinone and maltol ligands showed redox activity of the studied copper complexes in the gas phase. In the second part, negatively charged complexes of copper with pincer ligand L (L = N,N'-bis[2,6-diisopropylphenyl]-2,6-pyridinedicarboxamide) were investigated to show the effects of different counter-ions. The results showed that electrospray ionization of copper chlorate...
|
|
|
Direct monitoring of metal-catalyzed reactions using electrospray ionization mass spectrometry
Tsybizova, Alexandra ; Roithová, Jana (advisor) ; Jahn, Ullrich (referee) ; Kvíčala, Jaroslav (referee)
The current dissertation thesis is focused on the investigation of metal-catalyzed reactions using electrospray ionization mass spectrometry as the primary research technique. However, other gas- phase methods such as tandem mass spectrometry, infrared multiphoton dissociation spectroscopy and quantum chemical calculations have also been involved to unravel and support the findings and proposals. As organometallic chemistry is a very broad and complicated topic, this thesis is only focused on a few projects. The fist of them is dedicated to copper acetate speciation in organic solvents, the second - to the mechanistic investigation of copper catalyzed aerobic cross coupling of thiol esters and arylboronic acids, the third studied coordination and bond activation of nickel(II) - phenylpyridine complexes and the last investigated carboxylate assisted C-H activation reactions.
|
|
|
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.
|
|
|
Research of gold catalyzed reactions
Jašíková, Lucie ; Roithová, Jana (advisor) ; Polášek, Miroslav (referee) ; Starý, Ivo (referee)
The main focus of the current dissertation thesis is research of gold catalyzed reactions. I was using mass spectrometry as the primary research technique. I complemented the results with infrared multiphoton dissociation spectroscopy, nuclear magnetic resonance spectroscopy and quantum chemical calculations. I have investigated the interaction of the gold(I) cation with unsaturated hydrocarbons in the first part of my thesis. Secondly, I have studied gold(I) or silver(I) affinity to gold acetylides. In the last part, I have investigated the reaction mechanism of a gold mediated addition of methanol to alkynes. I found out that the gold(I) cation interacts stronger with gold acetylides than with nonactivated triple CC bonds. I showed that the complexes containing two gold atoms represent the key intermediates in the mechanism of addition of methanol to alkynes and that the ligand on the gold catalyst plays a fundamental role in the determination of the mechanism. Powered by TCPDF (www.tcpdf.org)
|
|
|
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.
|
|
|
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...
|
|
|
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.
|
|
|
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
|
|
|
Mechanism of copper mediated oxidative coupling of naphthols
Schröpferová, Tereza ; Roithová, Jana (advisor) ; Polášek, Miroslav (referee)
The 2,2'-disubstituated 1,1'-binaphthyls (BINOLs) are important ligands in enantioselective synthesis . The major approach for their preparation is based on transition-metal-mediated oxidative C-C coupling of 2-substituted naphtalenes. This diploma thesis examined the mechanism of the coupling reaction in the gas phase using mass spectrometry with electrospray ionization. The aim of this thesis was to compare the selectivity of the copper(II)- catalyzed coupling reaction of 2-naphthol and its derivative with an electron-withdrawing group, to detect possible reaction intermediates, and to determine the origin of the preference of the cross-coupling. The electron-withdrawing group of naphthol slows down the coupling reaction which enabled us to detect the reaction intermediates. The intermediates in the reaction of 2-naphthol were not observed, because the coupling reaction proceeds too quickly. Hence, we have observed only complexes of the coupling products. The preferential cross coupling was explaned on the basis of an interplay between the probability of the formation of binuclear copper complexes and the reactivity of such complexes.
|
guest ::
