A series of (oligo)phenthiazines, thiazolium salts and sulfonic acid functionalized organic/inorganic hybrid materials were synthesized. The organic groups were covalently bound on the inorganic surface through reactions of organosilane precursors with TEOS or with the silanol groups of material surface. These synthetic methods are called the co-condensation process and the post grafting. The structures and the textural parameters of the generated hybrid materials were characterized by XRD, N2 adsorption-desorption measurements, SEM and TEM. The incorporations of the organic groups were verified by elemental analysis, thermogravimetric analysis, FT-IR, UV-Vis, EPR, CV, as well as by 13C CP-MAS NMR and 29Si CP-MAS NMR spectroscopy. Introduction of various organic groups endow different phsysical, chemical properties to these hybrid materials. The (oligo)phenothiazines provide a group of novel redox acitive hybrid materials with special electronic and optic properties. The thiazolium salts modified materials were applied as heterogenized organo catalysts for the benzoin condensation and the cross-coupling of aldehydes with acylimines to yield a-amido ketones. The sulfonic acid containing materials can not only be used as Broensted acid catalysts, but also can serve as ion exchangable supports for further modifications and applications.
C-H activations(C-H bond weakening effects) under impact of transition metal atoms
are theoretically investigated,
two model systems are used, one is CH3MX, the other is
n-ButMX, (X=F,Cl,Br,I,H,CN, M include all transition metal
atoms from group 4 to group 10).
C-H activations(C-H bond weakening effects) under impact of transition metal atoms are theoretically investigated, two model systems are used, one is CH3MX, the other is n-ButMX, (X=F,Cl,Br,I,H,CN, M include all transition metal atoms from group 4 to group 10).
This work introduces a promising concept for the preparation of new nano-sized receptors. Mixed monolayer protected gold nanoparticles (AuNPs) for low molecular weight compounds were prepared featuring functional groups on their surfaces. It has been shown that these AuNPs can engage in interactions with peptides in aqueous media. Quantitative binding information was obtained from DOSY-NMR titrations indicating that nanoparticles containing a combination of three orthogonal functional groups are more efficient in binding to dipeptides than mono or difunctionalised analogues. The strategy is highly modular and easily allows adapting the receptor selectivity to a
given substrate by varying the type, number, and ratio of binding sites on the nanoparticle
The present PhD thesis is mainly focused on synthesis, characterization and catalytic application of functionalized triphenylphosphine (TPP) ligands and their complexes. We developed a simple and effective strategy to immobilize TPP: A methylester group attached to one of the phenyl rings of TPP allowes the derivatization of the ligand with 3-trimethoxysilylpropylamine, a typical silane coupling agent used for the covalent immobilization of organic compounds on silica surfaces. The resulting functionalized TPP was further coordinated to Pd, Rh and Ru precursors to achieve homogeneous complexes which can be tethered on silica by the post synthetic grafting method and co-condensation method. The obtained heterogeneous catalysts exhibited excellent activity, selectivity and reusability in Suzuki, hydrogenation and transfer hydrogenation reactions. In order to investigate the stability of the catalysts, different types of characterizations such as TEM, solid state NMR of the used catalysts as well as AAS of filtrate and leaching tests were carried out. The results prove the practicability and efficiency of our method. This strategy was further modified to generate an anionic side chain linked to the TPP core by simply replacing the trimethoxysilylpropylamine group by sodium(3-amino- 1-propanesulfonate), which allowes the immobilization on imidazolium modified SBA-15 through electrostatic interaction. The obtained material was further reacted with PdCl2(CNPh)2 and the resulting hybrid material was used for the hydrogenation of olefins allowing mild reaction conditions. The catalyst shows excellent activity, selectivity and stability and it can furthermore be reused for at least ten times without any loss of activity. TEM images of the used catalyst clearly show the absence of palladium nanoparticles, proving the high stability of the palladium compound. By AAS no palladium could be detected in the products and further leaching tests very- fied the reaction to be truly heterogeneous. This concept of non-covalent immobili- zation guarantees a tight bonding of the catalytically active species to the surface in combination with a high mobility, which should be favorable for other catalyses.
Sterisch anspruchsvolle Cyclopentadienyl-Liganden wurden zur Stabilisierung neuer Mono(cyclopentadienyl) Verbindungen der schweren Erdalkalimetalle eingesetzt und deren Funktionalisierbarkeit dieser Spezies wurde exemplarisch durch die Synthese neutraler Tripeldecker-Sandwichkomplexe demonstriert. Die dabei ausgebildeten Molekülstrukturen lassen sich mittels DFT-Rechnungen zuverlässig vorhersagen. In diesem Zusammenhang wurde ebenfalls der Cyclononatetraenyl-Ligand, dessen Komplexeigenschaften bisher nur unzureichend untersucht wurden, eingesetzt. Im Rahmen dieser Arbeit gelang die Synthese des Bis(cyclononatetraenyl)bariums, Ba(C9H9)2, und dessen spektroskopische Charakterisierung. DFT-Rechnungen sagen für diesen Komplex eine Metallocenstruktur mit nahezu parallelen Ringen und einem Ba-Ring Abstand von 2.37 Å voraus. Durch den Einsatz des Tetraisopropylcyclopentadienyl (4Cp) und Tri(tert.-butyl)cyclopentadienyl (Cp’)-Liganden gelang die Synthese von Bis- und Monocyclopentadienyl-Verbindungen der frühen und späten Lanthanoide. Besonders interessant in diesem Zusammenhang ist die erfolgreiche Darstellung des Azido-Clusters, [Na(dme)3]2[4Cp6Yb6(N3)14] (4Cp= (Me2CH)4C5H), der die unterschiedlichen Koordinationsmöglichkeiten des Azido-Liganden in einem einzigen Komplex vereint. Vergleichbare Komplexe waren in der Organolanthanoidchemie bisher unbekannt. Durch Substitution am Cyclopentadienyl-System lassen sich dessen elektronische und sterische Eigenschaften signifikant verändern. Die Auswirkungen dieser Effekte können sehr eindrucksvoll an Manganocen-Komplexen demonstriert werden, in denen sich der low- und high-spin Zustand energetisch nur sehr wenig unterscheiden. Der elektronische Grundzustand einer Reihe unterschiedlich substituierter Manganocen-Komplexe wurde mittels Festkörpermagnetismus, ESR, Röntgenstrukturanalyse, EXAFS und variabler Temperatur UV-Vis Spektroskopie bestimmt, und mit dem Substitutionsmuster am Cyclopentadienyl-System korreliert. Spin-Gleichgewichte ließen sich für [(Me3C)C5H4]2Mn, [(Me3C)2C5H3]2Mn und [(Me3C)(Me3Si)C5H3]2Mn nachweisen. Theoretische Rechnungen postulieren, dass Cerocen, Ce(C8H8)2, ein Beispiel für Moleküle mit gemischt-konfiguriertem Grundzustand sei, der durch 80 % [(Ce)f1e2u(cot)e2u3] und 20 % [(Ce)f0e2u(cot)e2u4] beschreiben werden könne. Obwohl dieses Molekül bereits seit 1976 bekannt ist, ist dessen elektronische Struktur bis heute sehr umstritten. Im Rahmen dieser Arbeit wurden neue Synthesekonzepte für diese Verbindung entwickelt und die elektronische Struktur mittels magnetischer Messungen im Festkörper, EXAFS und XANES Studien untersucht. Die dabei erhaltenen Daten sind in sehr guter Übereinstimmung mit den theoretischen Rechnungen und belegen die Bedeutung eines gemischt-konfigurierten Grundzustandes bei der Bindung in Organometallkomplexen der f-Block Metalle. Während in Cerocen nur ein temperaturunabhängiger Paramagnetismus (TIP) beobachtet werden kann, findet man eine starke Temperaturabhängigkeit der magnetischen Suszeptibilität in Ytterbium Systemen des Typs Cp’2Yb(bipy’) [Cp´ und bipy´ sind substituierte Cyclopentadienyl- oder 4,4’-substituierter 2,2’-Bipyridyl-Liganden]. Temperaturabhängige XANES-Experimenten belegen, dass auch in diesen Systemen ein gemischt-konfigurierter Grundzustand vorliegt, der durch [(Yb)f14(bipy)b1()0] und [(Yb)f13(bipy)b1()1] beschreiben werden kann. Der relative Anteil beider Wellenfunktionen zum Grundzustand wird durch Substitution am 2,2’-Bipyridyl- oder Cyclopentadienyl-System signifikant beeinflusst. Modelle, mit denen sich dieses Verhalten qualitativ beschreiben lässt, wurden im Rahmen dieser Arbeit entwickelt. Ein kinetisch stabilisiertes, adduktfreies Titanocen wurde unter Verwendung des Di(tert.-butyl)cyclopentadienyl Liganden hergestellt und dessen Reaktivität gegenüber kleinen Molekülen, z.B. CO, N2 und H2 untersucht. Im Rahmen der Reaktivitätsstudien wurden ebenfalls 2,2’-Bipyridyl Addukte an das Cp’2Ti Fragment synthetisiert und deren magnetische Eigenschaften erforscht. Durch Variationen am 2,2’-Bipyridyl System lässt sich das Singlet-Triplet Splitting in diesem System gezielt steuern.
The main focus of this dissertation is the synthesis and characterization of more recent zeolites with different pore architectures. The unique shape-selective properties of the zeolites are important in various chemical processes and the new zeolites containing novel internal pore architectures are of high interest, since they could lead to further improvement of existing processes or open the way to new applications. This dissertation is organized in the following way: The first part is focused on the synthesis of selected recent zeolites with different pore architectures and their modification to the acidic and bifunctional forms. The second part comprises the characterization of the physicochemical properties of the prepared zeolites by selected physicochemical methods, viz. powder X-ray diffractometry (XRD), N2 adsorption, thermogravimetric analysis (TGA/DTA/MS), ultraviolet-visible (UV-Vis) spectroscopy, atomic absorption spectroscopy (AAS), infrared (IR) spectroscopy, scanning electron microscopy (SEM), 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, temperature-programmed reduction (TPR), temperature-programmed desorption of pyridine (pyridine TPD) and adsorption experiments with hydrocarbon adsorptives. The third part of this work is devoted to the application of test reactions, i.e., the acid catalyzed disproportionation of ethylbenzene and the bifunctional hydroconversion of n-decane, to characterize the pore size and architecture of the prepared zeolites. They are known to be valuable tools for exploring the pore structure of zeolites. Finally, an additional test, viz. the competitive hydrogenation of 1-hexene and 2,4,4-trimethyl-1-pentene, has been applied to probe the location of noble metals in medium pore zeolite. The synthesis of the following zeolite molecular sieves was successfully performed in the frame of this thesis (they are ranked according to the largest window size in the respective structure): • 14-MR pores: UTD-1, CIT-5, SSZ-53 and IM-12 • 12-MR pores: ITQ-21 and MCM-68 • 10-MR pores: SSZ-35 and MCM-71 All of them were obtained as pure phase (except zeolite MCM-71 with a minor impurity phase that is hardly to avoid and also present in samples shown in the patent literature). The synthesis conditions are very critical with respect to the formation of the zeolite with a given structure. In this work, the recommended synthesis recipes are included. Among the 14-MR zeolites, the aluminosilicates UTD-1 (nSi/nAl = 28), CIT-5 (nSi/nAl = 116) and SSZ-53 (nSi/nAl = 55) with unidimensional extra-large pore opening formed from 14-MR rings exhibit promising catalytic properties with high thermal stability and they possess strong Brønsted-acid sites. By contrast, the germanosilicate IM-12 with a structure containing 14-MR channels intersecting with 12-MR channels is unstable toward moisture. It was found that UTD-1 and SSZ-53 zeolites are highly active catalysts for the acid catalyzed disproportionation of ethylbenzene and n-decane hydroconversion due to their high Brønsted acidity. To explore their pore structures, the applied two test reactions suggest that UTD-1, CIT-5 and SSZ-53 zeolites contain a very open pore system (12-MR or larger pore systems) because the product distributions are not hampered by too small pores. ITQ-21, a germanoaluminosilicate zeolite with a three-dimensional pore system and large spherical cages accessible through six 12-MR windows, can be synthesized with nSi/nAl ratios between 27 and >200. It possesses a large amount of Brønsted-acid sites. The aluminosilicate zeolite MCM-68 (nSi/nAl = 9) is an extremely active catalyst in the disproportionation of ethylbenzene and in the n-decane hydroconversion. This is due to the presence of a high density of strong Brønsted-acid sites in its structure. The disproportionation of ethylbenzene suggests that MCM-68 is a large pore (i.e., at least 12-MR) zeolite, in agreement with its crystallographic structure. In the hydroconversion of n-decane, the presence of tribranched and ethylbranched isomers and a high isopentane yield of 58 % in the hydrocracked products suggest the presence of large (12-MR) pores in its structure. By contrast, a relatively high value for CI* (modified constraint index) of 2.9 suggests the presence of medium (10-MR) pores in its structure. As a whole, the results are in-line with the crystallographic structure of MCM-68. SSZ-35, a 10-MR zeolite, can be synthesized in a broad range of nSi/nAl ratios between 11 and >500. This zeolite is interesting in terms of shape selectivity resulting from its unusual pore system having unidimensional channels alternating between 10-MR windows and large 18-MR cages. This thermally very stable zeolite contains both, strong Brønsted- and strong Lewis-acid sites. The disproportionation of ethylbenzene classifies SSZ-35 as a large pore zeolite. In the hydroconversion of n-decane, the suppression of bulky ethyloctanes and propylheptane clearly suggests the presence of 10-MR sections in the pore system. By contrast, the low CI* values of 1.2-2.3 and the high isopentane yields of 56-60 % in the hydrocracked products suggest that SSZ-35 also possesses larger intracystalline voids, i.e., the 18-MR cages. The results from the catalytic characterization are in good agreement with the crystallographic structure of zeolite SSZ-35. It was also found that the nSi/nAl ratio influences the crystallite size and therefore the external surface area. As a consequence, product selectivities are also influenced: The lowest nSi/nAl ratio or the smallest crystallite size sample produces larger amounts of the relatively bulky products. The formation of these products probably results from the higher conversion or they are preferentially formed on the external surface area of the catalyst. Zeolite MCM-71 (nSi/nAl = 8) possesses an extremely thermally stable structure and contains a high concentration of Brønsted-acid sites. Its structure allows for the separation of n-alkanes from branched alkanes by selective adsorption. MCM-71 exhibits unique shape-selective properties towards the product distribution in ethylbenzene disproportionation, which is different to those obtained in the medium pore SSZ-35 zeolite. All reaction parameters are fulfilled to classify MCM-71 as medium pore zeolite and this is in good agreement with its reported structure consisting of two-dimensional network of elliptical 10-MR channels and an orthogonal sinusoidal 8-MR channels. The competitive hydrogenation of 1-hexene and 2,4,4-trimethyl-1-pentene was exploited to probe that the major part of the noble metal is located inside the intracrystalline void volume of the medium pore zeolite SSZ-35.
In the present work, magnetic moments of isolated Single Molecule Magnets (SMMs) and transition
metal clusters were investigated. Gas phase X‐ray Magnetic Circular Dichroism (XMCD) in
combination with sum rule analysis served to separate the total magnetic moments of the
investigated species into their spin and orbital contributions. Two different mass spectrometry based
setups were used for the presented investigations on transition metal clusters (GAMBIT‐setup) and
on single molecule magnets (NanoClusterTrap). Both experiments were coupled to the UE52‐PGM
beamline at the BESSY II synchrotron facility (Helmholtz Zentrum Berlin) which provided the
necessary polarized X‐ray photons. The investigation of the given compounds as isolated molecules
in the gas phase enabled a determination of their intrinsic magnetic properties void of any influences
of e.g. a surrounding bulk or supporting surface
Redox-neutral decarboxylative coupling reactions have emerged as a powerful strategy for C-C bond formation. However, the existing reaction conditions possess limitations, such as the coupling of aryl halides restricted to ortho-substituted benzoic acids; alkenyl halides were not applicable in decarboxylative coupling reaction. Within this thesis, the developments of Pd/Cu bimetallic catalyst systems are presented to overcome the limitations.
In the first part of the PhD work, a customized bimetallic PdII/CuI catalyst system was successfully developed to facilitate the decarboxylative cross-coupling of non-ortho-substituted aromatic carboxylates with aryl chlorides. The restriction of decarboxylative cross-coupling reactions to ortho-substituted or heterocyclic carboxylate substrates was overcome by holistic optimization of this bimetallic Cu/Pd catalyst system. All kinds of benzoic acids regardless of their substitution pattern now can be applied in decarboxylative cross-coupling reaction. This confirms prediction by DFT studies that the previously observed limitation to certain activated carboxylates is not intrinsic. The catalyst system also presents higher performance in the coupling of ortho-substituted benzoates, giving much higher yields than those previously reported. ortho-Methyl benzoate and ortho-phenyl benzoate which have never before been converted in decarboxylative coupling reactions, gave reasonable yields. These together further confirm the superiority of the new protocol.
In the second part of the PhD work, arylalkenes syntheses via two different Pd/Cu bimetallic-catalyzed decarboxylative couplings have been developed. This part consists of two projects: 2a) decarboxylative coupling of alkenyl halides; 2b) decarboxylative Mizoroki-Heck coupling of aryl halides with α,β-unsaturated carboxylic acids.
In project 2a, widely available, inexpensive, bench-stable aromatic carboxylic acids are used as nucleophile precursors instead of expensive and sensitive organometallic reagents that are commonly used in previously reported transition-metal catalyzed cross-couplings of alkenyl halides. With this protocol, alkenyl halides for the first time are used in decarboxylative coupling reaction, allowing regiospecific synthesis of a broad range of (hetero)arylalkenes in high yields. Unwanted double bond isomerization, a common side reaction in the alternative Heck reactions especially in the coupling of cycloalkenes or aliphatic alkenes, did not take place in this decarboxylative coupling reaction. Polysubstituted alkenes that hard to access with Heck reaction are also produced in good yields. The reaction can easily be scaled up to gram scale. The synthetic utility of this reaction was also demonstrated by synthesizing an important intermediate of fungicidal compound in high yield within 2 steps.
In project 2b, a Cu/Pd bimetallic catalyzed decarboxylative Mizoroki-Heck coupling of aryl halides with α, β-unsaturated carboxylic acids was successfully developed in which the carboxylate group directs the arylation into its β-position before being tracelessly removed via protodecarboxylation. It opens up a convenient synthesis of unsymmetrical 1,1-disubstituted alkenes from widely available precursors. This reaction features good regioselectivity, which is complementary to that of traditional Heck reactions, and also presents excellent functional group tolerance. Moreover, a one-pot 3-step 1,1-diarylethylene synthesis from methyl acrylate was achieved, where solvent changes or isolation of intermediates are not required. This subproject presents an example of carboxylic acids utility in synthesizing valuable compounds which are hard to access via conventional methodologies.
The scientific intention of this work was to synthesize and characterize new bidentate, tridentate and multidentate ligands and to apply them in heterogenous catalysis. For each type of the ligands, new methods of synthesis were developed. Starting from 1,1'-(pyridine-2,6-diyl)diethanone and dimethylpyridine-2,6-dicarboxylate different bispyrazolpyridines were
synthesized and novel ruthenium complexes of the type (L)(NNN)RuCl2 could be obtained. The complexes with L = triphenylphosphine turned out to be highly efficient
catalyst precursors for the transfer hydrogenation of aromatic ketones. Introduction of a butyl group in the 5-positions of the pyrazoles leads to a pronounced increase of catalytic activity.
To find a method for the synthesis of bispyrimidinepyridines, different reactants and condition were applied and it was found that these tridentate ligands can be obtained by mixing and grinding the tetraketone with guanidinium carbonate and silica, which plays the role of a catalyst in this ring closing reaction.
The bidentate 2-amino-4-(2-pyridinyl)pyrimidines were synthesized from different substrates according to the desired substituent on the pyrimidine ring.
Reacting these bidentate ligands with the ruthenium(II) precursor [(η6-cymene)Ru(Cl)(μ
2-Cl)]2 gave cationic ruthenium(II) complexes of the type [(η6-cymene)Ru(Cl)(adpm)]Cl (adpm = chelating 2-amino-4-(2-yridinyl)pyrimidine ligand). Stirring the freshly prepared complexes with either NaBPh4, NaBF4 or KPF6, the chloride anion was exchanged against other coordinating anions (BF4-, PF6-, BPh4-).Some of these ruthenium complexes have shown very special activities in the transfer hydrogenation of ketones by reacting them in the absence of the base. This led to detailed investigations on the mechanism of this reaction. According to the activities and with the help
of ESI-MS experiments and DFT calculations, a mechanism was proposed for the transfer hydrogenation of acetophenone in the absence of the base. It shows that in the absence of the base, a C-H bond activation at the pyrimidine ring should occur to activate the catalyst.
The palladium complexes of bidentate N,N ligands were examined in coupling reactions. As expected, they did not show very special activities.
Multidentate ligands, having pyrimidine groups as relatively soft donors for late transition metals and simultaneously possessing a binding position for a hard Lewis-acid, could be obtained using the new synthesized bidentate and tridentate ligands.