Krause, Melanie Tatiana Stefanie: Mechanistic Investigation of a HAuCl4 catalyzed oxidative C-C coupling reaction and Synthesis of new supramolecular Silver(I) and Gold(I) NHC compounds : or handling of a Mass Spectrometric Challenge and catching Counterions on Supramolecular Playgrounds. - Bonn, 2021. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5-61431
@phdthesis{handle:20.500.11811/9049,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5-61431,
author = {{Melanie Tatiana Stefanie Krause}},
title = {Mechanistic Investigation of a HAuCl4 catalyzed oxidative C-C coupling reaction and Synthesis of new supramolecular Silver(I) and Gold(I) NHC compounds : or handling of a Mass Spectrometric Challenge and catching Counterions on Supramolecular Playgrounds},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2021,
month = apr,

note = {Reaction monitoring by electrospray (ESI) mass spectrometry is a valuable technique to investigate reaction mechanisms. It allows a glimpse into the reacting solution and the characterization of transient intermediates bReaction monitoring by electrospray (ESI) mass spectrometry is a valuable technique to investigate reaction mechanisms. It allows a glimpse into the reacting solution and the characterization of transient intermediates by tandem mass spectrometry. Herein we studied a captivating gold(III)-catalyzed synthesis of dicoumarin derivatives which consists of a combination of hydroarylation and homo coupling steps. A special challenge lies in the corrosivity of the catalyst HAuCl4, which requires the use of inert material for every step. The application of a fused-silica capillary eliminated almost all side reactions of the catalyst during the mass spectrometric experiments. Another problem is the necessary switching of the measurement modus while investigating the reacting solutions. Whereas the reactants and products could be detected in positive mode, the negatively charged species, correlating with all proposed transient intermediates, could only be detected in negative mode. Fast reaction rates hampered the monitoring of the interesting species additionally. Therefore the reaction conditions had to be adjusted and improved. The interesting ions were characterized by accurate mass determinations and supporting gas phase fragmentation experiments. The following species could be detected and characterized: [AuCl2]-; [AuCl4]-; [A+AuCl4]- = B/ C+Cl-; [A-H+AuCl3]- = D; [2A-H+AuCl3]- = D+A; [2A-2H+AuCl3]- = E, F = coumarin, G = dicoumarin (The nomenclature of the species A, B, C, D, E, F and G originated from the postulated mechanism and is listed consecutively with the reaction steps). Thus, the nature and ligand sphere of all reaction intermediates, formerly proposed in the catalytic cycle, were clarified and their evolution over different periods of time were followed. A strong influence of the substrate and catalyst concentrations on the reaction time could be demonstrated.
Furthermore the synthesis and characterization of three consistent series of dinuclear gold(I) N-heterocyclic carbene (NHC) complexes in comparison with a previously reported series is presented. Herein the differences of the four compelling series consist in the imidazole or benzimidazole moieties, the lengths of the alkylene linkers (C1-C3), the methyl or ethyl side chains and the counterion Br- or PF6-. Single crystals suitable for x-ray diffraction were obtained as [M2L2]2+ macrocycles from all complexes and from additional two new PO2F2- salts and a NO3- salt.
Furthermore the crystal structure of a dinuclear gold(I) NHC BF4- complex with a notably short intramolecular Au•••Au distance of 2.999 Å was obtained. Significant influences of intra- and intermolecular π•••π- and Au•••Au interactions as well as hydrogen bonding, depending on the varying functionalization, have been found. Gold(I) NHC complexes are known for their intriguing luminescence behaviour. Therefore detailed UV/Vis- and fluorescence spectroscopic experiments were performed, which confirmed the impact of the counterions on the supramolecular interaction. The most outstanding examples are all propylene complexes. They have all shown an intense emission band at ~350-400 nm (λex (imidazolium) = 255 nm, λex (benzimidazolium) = 289 nm). The assumed aurophilic interactions could be altered via the addition of an excess of bromide, which leads to the quenching of the emission and the concurrent increase of a new lower energy maximum (~450-500 nm) and an additional emission band at shorter wavelengths (~350nm). Those are attributed to association complexes and/or changes of the Au•••Au bond lengths. The exceptional aggregation behaviour between the cationic complexes and other ions in solution was also investigated by additional NMR spectroscopic measurements. The imidazolium compounds have shown a strong interaction with bromide via hydrogen bonding with the aromatic protons, whereas the interactions with the benzimidazolium complexes have changed the chemical shift of the alkylene bridge protons. The strongest downfield shifts could be found for the methylene compounds. The results are all highly depending on the analytical technique, but all experiments have shown a strong interaction of the complexes with the counterions. The combined investigations illustrate the highly tuneable behaviour of the complexes and provide more information for a better understanding of it.
The last chapter of this thesis deals with larger astounding cage like trinuclear silver(I) and gold(I) NHC complexes. The enlargement of the system from two to three metal centres and a bigger cavity allows the insertion of larger substrates. The backbone of the new host molecules is based on tribenzotriquinacene. Three additional amine substituents were inserted to provide binding sites. Thereby a chiral C3 symmetry was obtained. The aromatic scaffold could be linked to the imidazolium units by an amidation reaction with DMAP and EDC. The key to an effective reaction was the use of the highly nucleophilic but steric hindered base DIPEA. Unfortunately the reaction was incomplete and lead to a mixture of three different imidazolium compounds, containing one, two or three successful coupled imidazolium units. Nevertheless the obtained main compound is the intended tripodal compound. Tested reactions of the ligand precursor mixture with a gold source did not yielded the trinuclear complexes, but different side products. Thus, the silver base route was used prior to create Ag cage templates. Silver(I) NHC compounds usually contain weaker M-C bonds than Au(I) NHC complexes and are known as dynamic and reversible in solution. This behaviour allows self driven ligand exchange processes, to sustain different products and correct mismatching. The syntheses of the corresponding gold compounds were realized via transmetallation of the silver cage molecules. The products were investigated by mass spectrometric means. Almost all possible silver and gold complexes could be detected and confirmed trough their accurate masses and isotopic pattern. This lead to a new library of a variety of fascinating silver and gold TBTQ cage compounds. In the future, possible supramolecular host-guest aggregations could get enabled via hydrogen bonding or π•••π- and Au•••Au interactions. Additional binding sites for specific guest molecules are available through the amide substituents. The chiral symmetry could potentially support the separation or differentiation of isomers. tandem mass spectrometry. Herein we studied a captivating gold(III)-catalyzed synthesis of dicoumarin derivatives which consists of a combination of hydroarylation and homo coupling steps. A special challenge lies in the corrosivity of the catalyst HAuCl4, which requires the use of inert material for every step. The application of a fused-silica capillary eliminated almost all side reactions of the catalyst during the mass spectrometric experiments. Another problem is the necessary switching of the measurement modus while investigating the reacting solutions. Whereas the reactants and products could be detected in positive mode, the negatively charged species, correlating with all proposed transient intermediates, could only be detected in negative mode. Fast reaction rates hampered the monitoring of the interesting species additionally. Therefore the reaction conditions had to be adjusted and improved. The interesting ions were characterized by accurate mass determinations and supporting gas phase fragmentation experiments. The following species could be detected and characterized: [AuCl2]-; [AuCl4]-; [A+AuCl4]- = B/ C+Cl-; [A-H+AuCl3]- = D; [2A-H+AuCl3]- = D+A; [2A-2H+AuCl3]- = E, F = coumarin, G = dicoumarin (The nomenclature of the species A, B, C, D, E, F and G originated from the postulated mechanism and is listed consecutively with the reaction steps). Thus, the nature and ligand sphere of all reaction intermediates, formerly proposed in the catalytic cycle, were clarified and their evolution over different periods of time were followed. A strong influence of the substrate and catalyst concentrations on the reaction time could be demonstrated.
Furthermore the synthesis and characterization of three consistent series of dinuclear gold(I) N-heterocyclic carbene (NHC) complexes in comparison with a previously reported series is presented. Herein the differences of the four compelling series consist in the imidazole or benzimidazole moieties, the lengths of the alkylene linkers (C1-C3), the methyl or ethyl side chains and the counterion Br- or PF6-. Single crystals suitable for x-ray diffraction were obtained as [M2L2]2+ macrocycles from all complexes and from additional two new PO2F2- salts and a NO3- salt. Furthermore the crystal structure of a dinuclear gold(I) NHC BF4- complex with a notably short intramolecular Au•••Au distance of 2.999 Å was obtained. Significant influences of intra- and intermolecular π•••π- and Au•••Au interactions as well as hydrogen bonding, depending on the varying functionalization, have been found. Gold(I) NHC complexes are known for their intriguing luminescence behaviour. Therefore detailed UV/Vis- and fluorescence spectroscopic experiments were performed, which confirmed the impact of the counterions on the supramolecular interaction. The most outstanding examples are all propylene complexes. They have all shown an intense emission band at ~350-400 nm (λex (imidazolium) = 255 nm, λex (benzimidazolium) = 289 nm). The assumed aurophilic interactions could be altered via the addition of an excess of bromide, which leads to the quenching of the emission and the concurrent increase of a new lower energy maximum (~450-500 nm) and an additional emission band at shorter wavelengths (~350nm). Those are attributed to association complexes and/or changes of the Au•••Au bond lengths. The exceptional aggregation behaviour between the cationic complexes and other ions in solution was also investigated by additional NMR spectroscopic measurements. The imidazolium compounds have shown a strong interaction with bromide via hydrogen bonding with the aromatic protons, whereas the interactions with the benzimidazolium complexes have changed the chemical shift of the alkylene bridge protons. The strongest downfield shifts could be found for the methylene compounds. The results are all highly depending on the analytical technique, but all experiments have shown a strong interaction of the complexes with the counterions. The combined investigations illustrate the highly tuneable behaviour of the complexes and provide more information for a better understanding of it.
The last chapter of this thesis deals with larger astounding cage like trinuclear silver(I) and gold(I) NHC complexes. The enlargement of the system from two to three metal centres and a bigger cavity allows the insertion of larger substrates. The backbone of the new host molecules is based on tribenzotriquinacene. Three additional amine substituents were inserted to provide binding sites. Thereby a chiral C3 symmetry was obtained. The aromatic scaffold could be linked to the imidazolium units by an amidation reaction with DMAP and EDC. The key to an effective reaction was the use of the highly nucleophilic but steric hindered base DIPEA. Unfortunately the reaction was incomplete and lead to a mixture of three different imidazolium compounds, containing one, two or three successful coupled imidazolium units. Nevertheless the obtained main compound is the intended tripodal compound. Tested reactions of the ligand precursor mixture with a gold source did not yielded the trinuclear complexes, but different side products. Thus, the silver base route was used prior to create Ag cage templates. Silver(I) NHC compounds usually contain weaker M-C bonds than Au(I) NHC complexes and are known as dynamic and reversible in solution. This behaviour allows self driven ligand exchange processes, to sustain different products and correct mismatching. The syntheses of the corresponding gold compounds were realized via transmetallation of the silver cage molecules. The products were investigated by mass spectrometric means. Almost all possible silver and gold complexes could be detected and confirmed trough their accurate masses and isotopic pattern. This lead to a new library of a variety of fascinating silver and gold TBTQ cage compounds. In the future, possible supramolecular host-guest aggregations could get enabled via hydrogen bonding or Π•••Π- and Au•••Au interactions. Additional binding sites for specific guest molecules are available through the amide substituents. The chiral symmetry could potentially support the separation or differentiation of isomers.},

url = {https://hdl.handle.net/20.500.11811/9049}
}

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